Roberto Z Guzman

Interests

Teaching

Have developed seminar series, in biotechnology for undergraduate students from different disciplines relevant to engineering and its interaction with biotechnology. These students eventually get involved in research activities in laboratories throughout the university. Have developed new courses in Nanomedicine Engineering, Nanomaterials in Drug Delivery and have modify a Bioprocessing course to include novel biomaterials and bioprocessing fields of interest and broader impact.

Research

Research Contributions and InnovationsThe main Research Interest in my research group has been the development of novel biomedical nanoparticle platforms for drug delivery, imaging and therapy. Main topics include;1.Nano/biomolecular polymeric structures with encapsulated anticancer drugs and gold shells for dual cancer therapy that combines controlled and targeted drug delivery and infrared thermal ablation. 2.Nano/biomolecular multifunctional para-magnetic metal-hybrid nanoparticles for diagnostics and target NIR therapy. We are now developing novel Nanoparticle Bioconjugates for Combination Therapy of Lung, Pancreatic and Breast cancer. We are also developing novel multifunctional magnetic nanoparticles for biodiagnostics and novel therapeutic applications.3.Development of novel specific adsorbents for low molecular weight biomarkers isolation and identification. Technology could be used not only for cancer biomarkers but potentially for any other disease that produces extraneous biomolecules.

Courses

Scholarly Contributions

Journals/Publications

• Guzman, R. Z. (2019). Biosynthesis of gold and silver nanoparticles using Parkinsonia florida leaf extract and antimicrobial activity of silver nanoparticles. Materials Research Express, 6(9), 1-12. doi:doi.org/10.1088/2053-1591/ab2d8e
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  In this work, the biosynthesis of gold and silver nanoparticles from a leaf extract of Parkinsonia florida (P. florida) is reported. The P. florida leaf extract was analyzed by a phytochemical screening, by measuring the DPPH radical scavenging activity, and by Fourier-transform infrared spectroscopy (FT-IR). The phytochemical screening results indicated that biomolecules like carbohydrates, phenols, proteins, aminoacids, saponins, and flavonoids present in P. florida leaf extract might have participated in the chemical reduction of the metallic salts and further colloidal stabilization.
• Guzman, R. Z. (2019). Differential Response of BEAS-2B and H-441 Cells to Methylene Blue Photoactivation. ANTICANCER RESEARCH, 39(1), 3739-3744. doi:doi:10.21873/anticanres.13522
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  Cancer incidence andmortalities are growing worldwide, therefore research anddevelopment of more effective and less invasive treatments,such as photodynamic therapy, are needed. Herein, weinvestigated the methylene blue (MB) photoactivation effectsin lung epithelial cells (BEAS-2B) and lung adenocarcinomacells (H-441). Materials and Methods: The reactive oxygenspecies (ROS) produced by the laser photoactivation of MBin aqueous solutions and cell cultures were measured withprobes, and the cell viability was evaluated with acolorimetric assay.
• Guzman, R. Z. (2019). Mathematical modeling and parametrical analysis of the temperature dependency of control drug release from biodegradable nanoparticles. RSC Adv., 9(1), 8728. doi:DOI: 10.1039/c9ra00821g
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  Mathematical modeling and parametrical analysis of the temperature dependency of control drug release from biodegradable nanoparticles.
• Guzman, R. Z. (2019). Mathematical modeling and parametrical analysis of the temperature dependency of control drug release from biodegradable nanoparticles. Royal Society of Chemistry. doi:DOI: 10.1039/c9ra00821g
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  In this study we describe amathematical analysis that considers the temperature effects of the controlleddrug release process from biodegradable poly-D,L-lactide-co-glycolide (PLGA) nanoparticles.Temperature effects are incorporated and applied to two drug release models. The first one consistsof a two-stage release process that considers only simultaneous contributions of initial burst andnanoparticle degradation–relaxation (BR model). The second one is a three release stage model thatconsiders, additionally, a simultaneous drug diffusion (BRD model) step. In these models, thetemperature dependency of the release parameters, initial burst constant, kb, the rate of degradation–relaxation constant, kr, time to achieve 50% of release, tmax, and effective diffusion coefficient constant(De), are determined using mathematical expressions analogous to the Arrhenius equation. Thetemperature dependent models are used to analyze the release of previously encapsulated Rhodamine6G dye as a model drug in polyethylene glycol modified PLGA nanoparticles. The experimental dataused to develop the mathematical model was obtained from release studies carried out in phosphatebuffer pH 7.4 at 37 C, 47 C, and 57 C. Multiphasic release behaviors with an overall increase rateassociated with the incubation temperature were observed. The study incorporates a parametricalanalysis that can evaluate diverse temperature variation effects of the controlled release parametersfor the two models.
• Guzman, R. Z. (2019). Substrate-source flexibility of an exponential-fed perfusion process to produce plasmid DNA for use as leishmaniasis vaccine. Biotechnology & Biotechnological Equipment,, on line, 16. doi:https://doi.org/10.1080/13102818.2018.1560232
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  The use of plasmid DNA (pDNA) for human vaccines is a novel approach against leishmaniasis, a neglected tropical disease with severe clinical manifestations. The development of feasible bioprocesses to obtain such vaccines is a public-health priority. The aim of this work was to investigate the substrate-source flexibility of an exponential-fed perfusion (EFP) system to produce the plasmid pVAX1-NH36 for use as a leishmaniasis vaccine. Batch and EFP cultures were conducted using Escherichia coli DH5a as a host and glucose or glycerol as a carbon source. The culture kinetics of the cell, substrate and plasmid concentrations were measured. Mathematical kinetics models were fitted to experimental data and used to describe the system comportment (r2 > 0.95). Plasmid productivities of 13.3 mg/(L h) using glucose and 19.4 mg/(L h) using glycerol were obtained. These levels represent a 1–3-fold increase in performance index compared with previously reported cultures using E. coli DH5a. The novel aspect of this work is the demonstration of the flexibility of EFP cultures for production of pDNA vaccines. Our data suggest that E. coli engineering to increase pDNA production using glucose can be circum-vented with an EFP culture, reducing the host strain development costs. In addition, the greater productivity of EFP cultures entails a reduction in manufacturing costs.
• Guzman, R. Z. (2019). Substrate-source flexibility of an exponential-fed perfusion process to produce plasmid DNA for use as leishmaniasis vaccine. Biotechnology & Biotechnological Equipment, 33(1), 195-203. doi:DOI: 10.1080/13102818.2018.1560232
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  Substrate-source flexibility of an exponential-fed perfusion process to produce plasmid DNA for use as leishmaniasis vaccine.
• Guzman, R. Z. (2018). Enhancement of pDNA Uptake and Expression in H441 Cells by Using PLGA Nanocarriers.. Microscopy and Microanalysis, 24(S1), 1414-1415. doi:doi:10.1017/S1431927618007559.
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  The use of nanocarriers in medical applications is one of the most promising technologies for drug delivery and vaccination purposes of the last 50 years [1]. In gene therapy, nanocarriers such as polymeric nanoparticles can protect the integrity of plasmid DNA from undesirable systemic interactions. Also, nanocarriers could improve some treatments by controlling the release rate of the encapsulated compound [2–4]. Poly-dl-lactic-co-glycolic acid (PLGA) has been used in the encapsulation of plasmid DNA [5]. One of the advantages of PLGA is that it could contain uncapped carboxylic acids that can be easily functionalized with other molecules before or after nanoparticles preparation [2]. Coupling of fluorescent dyes such as rhodamine can be used to perform in vitro microscopic visualization. In this work, fluoresce labeled polymeric nanoparticles loaded with a plasmid containing the green fluorescent protein gene (pGFP) were prepared by using the double emulsification-solvent evaporation technique. Lung adenocarcinoma cells (H-441) were treated with naked and encapsulated pGFP. Protein expression was compared by observing fluorescence.
• Guzman, R. Z. (2018). Evaluation of a combined emulsion process to encapsulate methylene blue into PLGA nanoparticles. RSC Adv, 8, 414 - 422. doi:DOI: 10.1039/c7ra12296a
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  The delivery of photosensitizer compounds using biodegradable nanoparticles could improve dosage,controlled release and its bioavailability. In this study, methylene blue (MB) loaded PLGA nanoparticles(MB-PNP) are prepared by a new approach combining single and double emulsification techniques.Comparisons of MB-PNP obtained with the combined and the individual techniques are presented.Nanoparticles are characterized by dynamic light scattering, laser Doppler electrophoresis and scanningelectron microscopy. Particles prepared by the combined technique presented hydrodynamic diametersof 186 nm.
• Guzman, R. Z. (2018). Hollow Gold Nanoshells Encapsulated in PNIPAM Nanoparticles. Microscopy and Microanalysis, 24(S1), 1794-1795. doi:doi:10.1017/S1431927618009455
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  In recent decades, nanostructured materials have been of great interest for applications in several areasfor technological developments [1]. Research in medical applications have led to the potential use ofnanotechnology for the diagnosis, treatment and the monitoring of diseases, improving routes ofadministration, dosage, and reducing side effects. Nanoparticles of noble metals like gold or silver havebecome highly relevant due to the multiple possibilities of interactions with biological systems [2]. Also,these metallic nanoparticles present optical properties which depend on the size and shape of them.Metallic nanoparticles can be prepared with different structures, including solid nanoparticles, hollowcore nanoshells, and nanorods, among others. Hollow gold shells (HGS) can be prepared by a wellknownmethod involving a galvanic replacement of silver for gold. According to literature, it is a highlyscalable method that utilizes minimal amounts of toxic reagents; also, the HGS core can be adjusted insize and thickness depending on the silver/gold reagent ratios
• Guzman, R. Z. (2018). Mathematical modeling of the batch adsorption of proteins on new restricted access media with poly(ethylene glycol) as a semi-permeable barrier using compact finite differences. Brazilian Journal of Chemical Engineering., 35(1), 237–251. doi:dx.doi.org/10.1590/0104-6632.20180351s20160404.
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  Mathematical modeling of the batch adsorption of proteins on new restricted access media with poly(ethylene glycol) as a semi-permeable barrier using compact finite differences
• Guzman, R. Z. (2018). Plasmid-DNA lipid nanovaccines: An innovative approach for a better world health. In Lipid Nanocarriers for Drug Targeting. 2019 Elsevier Inc., 232-267. doi:http://dx.doi.org/10.1016/B978-0-12-813687-4.00006-2
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  One of the most important applications of immunology has been the productionof various types of vaccines, which have saved the lives of millions of people. However, according to World HealthOrganization (WHO) estimates, 18 million people die each year as a direct consequenceof infection, showing that these diseases still remain because of lack of avaccine, inefficient drug therapies, new pathogens, old pathogen reactivation, andan increased microbial resistance to antimicrobials and antibiotics treatments.This highlights the importance of developing new vaccines against infectiousagents.Conventional vaccine production is founded in egg and cell culture-basedapproaches. This technology is inefficient, labor intensive, time consuming, andsubject to contamination.The original empirical approach to vaccine research and development has changedgreatly to one more rational and supported by both basic and applied science. In order to modernize vaccine technology, rather than producinga virus or a protein to inject into an organism, a sequence of DNA can beproduced to create the immune response.
• Guzman, R. Z. (2018). Plasmid-DNA lipid nanovaccines: An innovative approach for a better world health. Lipid Nanocarriers for Drug Targeting-Book. doi:http://dx.doi.org/10.1016/B978-0-12-813687-4.00006-2
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  One of the most important applications of immunology has been the productionof various types of vaccines, which have saved the lives of millions of people. However, according to World HealthOrganization (WHO) estimates, 18 million people die each year as a direct consequenceof infection, showing that these diseases still remain because of lack of avaccine, inefficient drug therapies, new pathogens, old pathogen reactivation, andan increased microbial resistance to antimicrobials and antibiotics treatments.This highlights the importance of developing new vaccines against infectiousagents.
• Guzman, R. Z. (2017). Aqueous-Organic Phase Transfer of Gold and Silver Nanoparticles Using Thiol-Modified Oleic Acid. Applied Sciences. doi:10.3390/app7030273
• Guzman, R. Z. (2017). Evaluation of a combined emulsion process to encapsulate methylene blue into PLGA nanoparticles.. Royal Society of Chemistry.
• Guzman, R. Z. (2017). Performance analysis of exponential-fed perfusion cultures for pDNA vaccines production. Journal of Chemical Technology and Biotechnology, 92(2), 342–349.
• Guzman, R. Z. (2015). Nanoparticle encapsulation and controlled release of a hydrophobickinase inhibitor: Three stage mathematical modelingand parametric analysis. International Journal of Pharmaceutics, 404, 249–257. doi:http://dx.doi.org/10.1016/j.ijpharm.2015.07.049
• Guzman, R. Z. (2016). Folate Functionalized PLGA Nanoparticles Loaded with Plasmid pVAX1-NH36: Mathematical Analysis of Release. Applied Sciences, 6, 364-379.
• Guzman, R. Z. (2017). “Hollow Au–Ag bimetallic nanoparticles with high photothermal stability.”. Advances in the Royal Society of Chemistry (RSC Adv.), 6, 41304–41312.
• Guzman, R. Z. (2015). Batch Equilibrium and Kinetic Studies of Plasmid pCI Adsorption onto Perfusion Particles. Journal of Liquid Chromatography & Related Technologies, 38, 196–200. doi:DOI: 10.1080/10826076.2014.896818
• Guzman, R. Z. (2015). K88 Fimbrial Adhesin Targeting of Microspheres Containing Gentamicin Made with Albumin Glycated with Lactose. International Journal of Molecular Sciences, 16, 22425-22437. doi:doi:10.3390/ijms160922425
• Guzman, R. Z. (2015). Purification of Human Serum Immunoglobulins Using Immobilized Metal Affinity Chromatography with Ethylenediamine Triacetic Acid as Chelating Agent. Journal of Liquid Chromatography & Related Technologies, 38, 74–81. doi:DOI: 10.1080/10826076.2014.883534
• Guzman, R. Z., & Guzman, R. Z. (2015). Purification of Human Serum Immunoglobulins Using Immobilized Metal Affinity Chromatography with Ethylenediamine Triacetic Acid as Chelating Agent. Journal of Liquid Chromatography & Related Technologies, 38, 74-81. doi:DOI: 10.1080/10826076.2014.883534
• González-Ortega, O., Porath, J., & Guzmán, R. (2012). Adsorption of peptides and small proteins with control access polymer permeation to affinity binding sites. Part I: Polymer permeation-immobilized metal ion affinity chromatography separation adsorbents with polyethylene glycol and immobilized metal ions. Journal of Chromatography A, 1227, 115-125.
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  PMID: 22281505;Abstract: Despite the many efforts to develop efficient protein purification techniques, the isolation of peptides and small proteins on a larger than analytical scale remains a significant challenge. Recovery of small biomolecules from diluted complex biological mixtures, such as human serum, employing porous adsorbents is a difficult task mainly due to the presence of concentrated large biomolecules that can add undesired effects in the system such as blocking of adsorbent pores, impairing diffusion of small molecules, or competition for adsorption sites. Adsorption and size exclusion chromatography (AdSEC) controlled access media, using polyethylene glycol (PEG) as a semi-permeable barrier on a polysaccharide matrix, have been developed and explored in this work to overcome such effects and to preferentially adsorb small molecules while rejecting large ones. In the first part of this work, adsorption studies were performed with small peptides and proteins from synthetic mixtures using controlled access polymer permeation adsorption (CAPPA) media created by effectively grafting PEG on an immobilized metal affinity chromatography (IMAC) agarose resin, where chelating agents and immobilized metal ions were used as the primary affinity binding sites. Synthetic mixtures consisted of bovine serum albumin (BSA) with small proteins, peptides, amino acids (such as histidine or Val 4-Angiotensin III), and small molecules-spiked human serum. The synthesized hybrid adsorbent consisted of agarose beads modified with iminodiacetic (IDA) groups, loaded with immobilized Cu(II) ions, and PEG. These CAPPA media with grafted PEG on the interior and exterior surfaces of the agarose matrix were effective in rejecting high molecular weight proteins. Different PEG grafting densities and PEG of different molecular weight were tested to determine their effect in rejecting and controlling adsorbent permeation properties. Low grafting density of high molecular weight PEG was found to be as effective as high grafting density of low molecular weight PEG in the rejecting properties of the semi-permeable synthesized media. © 2012 Elsevier B.V.
• González-Ortega, O., Porath, J., & Guzmán, R. (2012). Adsorption of peptides and small proteins with control access polymer permeation to affinity binding sites. Part II: Polymer permeation-ion exchange separation adsorbents with polyethylene glycol and strong anion exchange groups. Journal of Chromatography A, 1227, 126-137.
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  PMID: 22265175;Abstract: In chromatographic separations, the most general problem in small biomolecule isolation and purification is that such biomolecules are usually found in extremely low concentrations together with high concentrations of large molecular weight proteins. In the first part of this work, adsorption and size exclusion chromatography (AdSEC) controlled access media, using polyethylene glycol (PEG) as a semi-permeable barrier on a polysaccharide Immobilized Metal Affinity Chromatography (IMAC) matrix was synthesized and used to develop chromatographic adsorbents that preferentially adsorb and separate low molecular weight biomolecules while rejecting large molecular weight proteins. In this second part, we expand the concept of controlled access polymer permeation adsorption (CAPPA) media by grafting polyethylene glycol (PEG) on a high capacity polysaccharide ion exchange (IEX) chromatographic resin where PEG acts as a semi-permeable barrier that preferentially allows the permeation of small molecules while rejecting large ones. The IEX resin bearing quaternary ammonium groups binds permeated biomolecules according to their ion exchange affinity while excluding large biomolecules by the PEG barrier and thus cannot compete for the binding sites. This new AdSEC media was used to study the retention of peptides and proteins covering a wide range of molecular weights from 1 to 150. kDa. The effect of protein molecular weight towards retention by ion exchange was performed using pure protein solutions. Recovery of insulin from insulin-spiked human serum and insulin-spiked human urine was evaluated under polymer controlled permeation conditions. The CAPPA media consisted of agarose beads modified with amino-PEG-methoxy and with trimethyl ammonium groups, having chloride capacities between 20 and 40. μeq/mL and were effective in rejecting high molecular weight proteins while allowing the preferential adsorption of small proteins and peptides. © 2012 Elsevier B.V.
• Guzman, R., González-Ortega, O., Porath, J., & Guzman, R. Z. (2012). Adsorption of peptides and small proteins with control access polymer permeation to affinity binding sites. Part I: Polymer permeation-immobilized metal ion affinity chromatography separation adsorbents with polyethylene glycol and immobilized metal ions. Journal of chromatography. A, 1227.
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  Despite the many efforts to develop efficient protein purification techniques, the isolation of peptides and small proteins on a larger than analytical scale remains a significant challenge. Recovery of small biomolecules from diluted complex biological mixtures, such as human serum, employing porous adsorbents is a difficult task mainly due to the presence of concentrated large biomolecules that can add undesired effects in the system such as blocking of adsorbent pores, impairing diffusion of small molecules, or competition for adsorption sites. Adsorption and size exclusion chromatography (AdSEC) controlled access media, using polyethylene glycol (PEG) as a semi-permeable barrier on a polysaccharide matrix, have been developed and explored in this work to overcome such effects and to preferentially adsorb small molecules while rejecting large ones. In the first part of this work, adsorption studies were performed with small peptides and proteins from synthetic mixtures using controlled access polymer permeation adsorption (CAPPA) media created by effectively grafting PEG on an immobilized metal affinity chromatography (IMAC) agarose resin, where chelating agents and immobilized metal ions were used as the primary affinity binding sites. Synthetic mixtures consisted of bovine serum albumin (BSA) with small proteins, peptides, amino acids (such as histidine or Val⁴-Angiotensin III), and small molecules-spiked human serum. The synthesized hybrid adsorbent consisted of agarose beads modified with iminodiacetic (IDA) groups, loaded with immobilized Cu(II) ions, and PEG. These CAPPA media with grafted PEG on the interior and exterior surfaces of the agarose matrix were effective in rejecting high molecular weight proteins. Different PEG grafting densities and PEG of different molecular weight were tested to determine their effect in rejecting and controlling adsorbent permeation properties. Low grafting density of high molecular weight PEG was found to be as effective as high grafting density of low molecular weight PEG in the rejecting properties of the semi-permeable synthesized media.
• Guzman, R., González-Ortega, O., Porath, J., & Guzman, R. Z. (2012). Adsorption of peptides and small proteins with control access polymer permeation to affinity binding sites. Part II: Polymer permeation-ion exchange separation adsorbents with polyethylene glycol and strong anion exchange groups. Journal of chromatography. A, 1227.
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  In chromatographic separations, the most general problem in small biomolecule isolation and purification is that such biomolecules are usually found in extremely low concentrations together with high concentrations of large molecular weight proteins. In the first part of this work, adsorption and size exclusion chromatography (AdSEC) controlled access media, using polyethylene glycol (PEG) as a semi-permeable barrier on a polysaccharide Immobilized Metal Affinity Chromatography (IMAC) matrix was synthesized and used to develop chromatographic adsorbents that preferentially adsorb and separate low molecular weight biomolecules while rejecting large molecular weight proteins. In this second part, we expand the concept of controlled access polymer permeation adsorption (CAPPA) media by grafting polyethylene glycol (PEG) on a high capacity polysaccharide ion exchange (IEX) chromatographic resin where PEG acts as a semi-permeable barrier that preferentially allows the permeation of small molecules while rejecting large ones. The IEX resin bearing quaternary ammonium groups binds permeated biomolecules according to their ion exchange affinity while excluding large biomolecules by the PEG barrier and thus cannot compete for the binding sites. This new AdSEC media was used to study the retention of peptides and proteins covering a wide range of molecular weights from 1 to 150 kDa. The effect of protein molecular weight towards retention by ion exchange was performed using pure protein solutions. Recovery of insulin from insulin-spiked human serum and insulin-spiked human urine was evaluated under polymer controlled permeation conditions. The CAPPA media consisted of agarose beads modified with amino-PEG-methoxy and with trimethyl ammonium groups, having chloride capacities between 20 and 40 μeq/mL and were effective in rejecting high molecular weight proteins while allowing the preferential adsorption of small proteins and peptides.
• Sarabia-Sainz, A., Ramos-Clamont, G. M., Lizardi-Mendoza, J., Del, M., Del, M., Guzman, R. Z., Lucero-Acuña, A., & Vazquez-Moreno, L. (2012). Formulation and characterization of gentamicin-loaded albumin microspheres as a potential drug carrier for the treatment of E. coli K88 infections. International Journal of Drug Delivery, 4(2).
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  Abstract: The aim of this study was to formulate and characterize gentamicin-loaded albumin microspheres for their potential therapeutic use in E. coli K88 infections. Based on in vitro assays, it is proposed that microspheres may serve as a carrier of gentamicin and may provide localized antibacterial activity in the treatment of porcine colibacillosis. Gentamicin-albumin microspheres (GAM) were obtained using a water/oil (W/O) emulsion followed by cross-linking with different concentrations of glutaraldehyde. Electron microscopy showed spherical particles with indentations. The average size of the GAM was 10.5-12.3 μm. At pH 7.2, the release kinetics of gentamicin from the GAM was successfully described as an initial burst defined by a first order equation. Gentamicin release was unaffected by the glutaraldehyde concentrations used but was affected by acidic conditions. The behavior of gentamicin release from the GAM was not altered by digestion with trypsin and chymotrypsin at pH 7.2. Additionally, the concentration of gentamicin released from GAM to reach antibacterial activity was similar to that of free gentamicin against E. coli K88. This work shows the potential use of GAM as therapeutic vehicles of gentamicin to counteract intestinal infections in pigs.
• Cortes, P., Zhu, T., Guzman, R., & Smith, G. B. (2011). Covalent coupling of polyacrylic acid coated magnetic-nanoparticles to multi-wall carbon nanotubes for manipulation targets. Journal of Experimental Nanoscience, 6(6), 665-678.
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  Abstract: This research effort investigated the chemical heterojunction between magnetic nanoparticles coated with polyacrylic acid and multi-wall carbon nanotubes (MWCNTs). Here, magnetic nanoparticles were covalently attached to open-ended nanotubes in the presence of diclohexylcarbodiiimide. Initial evidence demonstrated that short functionalised multi-wall nanotubes can be continuously connected at their terminals ends to build-up relatively large nanostructures. It has also been shown that magnetic-carbon nanotubes (CNTs) systems exhibited defined arrangements due to the influence of magnetic fields. Indeed, linear arrays of CNTs interconnected through magnetic nanoparticles were prone to be manipulated in the presence of a magnetic device. A potential application of these kind of magnetic nanostructures was shown here by successfully manipulating agarose beads in a buffer solution. These results suggest that the use of continuously connected magnetic nanostructures with non-modified sidewall surfaces will find potential applications in the area of bio-sensing, force transduction and cancer screening-manipulation among many others. © 2011 Taylor & Francis.
• Guerrero-Germán, P., Montesinos-Cisneros, R. M., Guzmán, R., & Tejeda-Mansir, A. (2011). Modelling and simulation of plasmid DNA adsorption on ion-exchange membrane columns. Canadian Journal of Chemical Engineering, 89(3), 536-544.
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  Abstract: A transport model that considers convection, diffusion, and finite kinetic rate on the membrane column as well as the influence of extra column dispersion and lag times, was used in this study to mathematically describe the frontal adsorption behaviour of plasmid DNA in an ion-exchange membrane chromatography system. The corresponding partial differential equations system was solved using the numerical method of lines (MOL) on a MATLAB platform. Experimental data from literature describing the frontal adsorption of pCI DNA in an ion-exchange membrane column was used as a model system for validation of MOL solution of the transport model. This approach results in a unique way to predict frontal performance and it is a valuable tool to assess the use of membrane adsorbers in large scale processes for plasmid purification. © 2010 Canadian Society for Chemical Engineering.
• Cheung, L. S., Zheng, X. J., Stopa, A., Schroeder, J., Heimark, R. L., Baygents, J. C., Guzman, R., & Zoharl, Y. (2009). Flow acceleration effect on canser cell deformation abd detachment. Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems (MEMS), 431-434.
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  Abstract: The effect of flow acceleration, rather than just the flow rate, on the response of an attached cancer cell is for the first time reported. Selective binding of prostate cancer cells to a surface functionalized with anti-N-cadherin antibodies utilizing a microfluidic system under flow conditions has been studied [1]. Here, the behavior of a captured cell under a time-dependent flow field is investigated experimentally and numerically. Under slowly increasing flow rate, the cell deformation is more pronounced resulting in lower drag force on attached cells. Furthermore, the contact area between the cell and the functionalized surface is larger, potentially enhancing the cell adhesion force. Consequently, a higher flow rate is required to detach cells exposed to such a flow field. Numerical simulations have been utilized in effort to quantify the required detachment force. The results confirm that to obtain a similar shear stress, a higher flow rate is needed for attached cells under lower flow acceleration. ©2009 IEEE.
• Guerrero-Germán, P., M., D., Guzmán, R., Montesinos-Cisneros, R. M., & Tejeda-Mansir, A. (2009). Purification of plasmid DNA using tangential flow filtration and tandem anion-exchange membrane chromatography. Bioprocess and Biosystems Engineering, 32(5), 615-623.
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  PMID: 19083017;Abstract: A new bioprocess using mainly membrane operations to obtain purified plasmid DNA from Escherechia coli ferments was developed. The intermediate recovery and purification of the plasmid DNA in cell lysate was conducted using hollow-fiber tangential filtration and tandem anion-exchange membrane chromatography. The purity of the solutions of plasmid DNA obtained during each process stage was investigated. The results show that more than 97% of RNA in the lysate was removed during the process operations and that the plasmid DNA solution purity increased 28-fold. One of the main characteristics of the developed process is to avoid the use of large quantities of precipitating agents such as salts or alcohols. A better understanding of membrane-based technology for the purification of plasmid DNA from clarified E. coli lysate was developed in this research. The convenience of anion-exchange membranes, configured in ready-to-use devices can further simplify large-scale plasmid purification strategies. © 2008 Springer-Verlag.
• Montesinos-Cisneros, R. M., De, J., Ortega, J., Guzmán, R., & Tejeda-Mansir, A. (2007). Breakthrough performance of plasmid DNA on ion-exchange membrane columns. Biotechnology Progress, 23(4), 881-887.
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  PMID: 17567039;Abstract: Breakthrough performance of plasmid DNA adsorption on ion-exchange membrane columns was theoretically and experimentally investigated using batch and fixed-bed systems. System dispersion curves showed the absence of flow non-idealities in the experimental arrangement. Breakthrough curves (BTC) were significantly affected by inlet flow rate and solute concentration. In the theoretical analysis, a model was integrated by the serial coupling of the membrane transport model and the system dispersion model. A transport model that considers finite kinetic rate and column dispersed flow was used in the study. A simplex optimization routine, coupled to the solution of the partial differential model equations, was employed to estimate the maximum adsorption capacity constant, the equilibrium desorption constant, and the forward interaction rate constant, which are the parameters of the membrane transport model. The analysis shows that as inlet concentration or flow rate increases, the deviation of the model from the experimental behavior decreases. The BTCs displacement as inlet concentration increases was explained in terms of a greater degree of column saturation reached and more efficient operation accomplished. The degree of column saturation was not influenced by inlet flow rate. It was necessary to consider in the column model the slight variation in the BTC produced by the axial dispersion, in order to accomplish the experimental curve dispersion. Consequently, the design criteria that for Pe > 40 the column axial dispersion can be neglected should be taken with precaution. © 2007 American Chemical Society and American Institute of Chemical Engineers.
• Montesinos-Cisneros, R. M., Lucero-Acuña, A., Ortega, J., Guzmán, R., & Tejeda-Mansir, A. (2007). Breakthrough performance of large proteins on ion-exchange membrane columns. Biotechnology and Applied Biochemistry, 48(2), 117-125.
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  PMID: 17868026;Abstract: Protein adsorption of large proteins on ion-exchange membrane columns was theoretically and experimentally investigated using batch and fixed-bed systems. Thyroglobulin was used as the model protein. The study strongly suggests that part of the protein is physically retained inside the column during frontal mode operation. These experimental results were used to obtain a filtration function of the chromatographic system. In the theoretical analysis of the frontal protein adsorption, a model was integrated by the serial coupling of the membrane-transport model, the filtration model and the system-dispersion model. Two different techniques were employed in the estimation of the maximum adsorption capacity, the equilibrium desorption constant and the forward interaction rate constant, which are the parameters of the membrane-transport model. The fit of the model to the experimental data was not possible using the equilibrium parameters obtained in the batch experiments. The parameter estimation using a simplex optimization routine coupled to the solution of the partial differential model equations yields full prediction of the adsorption phenomena. © 2007 Portland Press Ltd.
• Trzaskowski, B., Guzman, R., & Adamowicz, L. (2007). Cyclododecane and cyclotridecane complexes with cobalt as potent histidine chelators: A theoretical study. Polyhedron, 26(12), 2477-2481.
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  Abstract: Density functional theory calculations have been employed to study the interaction between cyclododecane and cyclotridecane derivatives complexing cobalt and interacting with histidine. The results suggest that some of these derivatives have high molecular affinities toward histidine, higher than in the commonly used iminodiacetate-cobalt system. Those derivatives may become new, potent chelators for use in the immobilized-metal-ion-affinity chromatography to immobilize and/or purify peptides and proteins. © 2006 Elsevier Ltd. All rights reserved.
• Montesinos-Cisneros, R. M., Ortega, J., Guzmán, R., & Tejeda-Mansir, A. (2006). Breakthrough performance of linear-DNA on ion-exchange membrane columns. Bioprocess and Biosystems Engineering, 29(2), 91-98.
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  PMID: 16770595;Abstract: Breakthrough performance of linear-DNA adsorption on ion-exchange membrane columns was theoretically and experimentally investigated using batch and fixed-bed systems. System dispersion curves showed the absence of flow non-idealities in the experimental arrangement. Breakthrough curves were not significantly affected by flow-rate or inlet solution concentration. In the theoretical analysis a model was integrated by the serial coupling of the membrane transport model and the system dispersion model. A transport model that considers finite kinetic rate and column dispersed flow was used in the study. A simplex optimization routine coupled to the solution of the partial differential model equations was employed to estimate the maximum adsorption capacity constant, the equilibrium desorption constant and the forward interaction rate-constant, which are the parameters of the membrane transport model. Through this approach a good prediction of the adsorption phenomena is obtained for inlet concentrations and flow rates greater than 0.2 mg/ml and 0.16 ml/min. © Springer-Verlag 2006.
• Ramos-Clamont, G., del, M., Zamudio, R. G., & Vazquez-Moreno, L. (2006). Novel hydrophobic interaction chromatography matrix for specific isolation and simple elution of immunoglobulins (A, G, and M) from porcine serum. Journal of Chromatography A, 1122(1-2), 28-34.
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  PMID: 16650852;Abstract: A new, highly acetylated agarose matrix (HA-Sepharose) was synthesized and used as a hydrophobic interaction chromatography (HIC) medium to specifically isolate immunoglobulins (Igs) from porcine serum. Recovery of Igs was in a single step and under mild conditions. HA-Sepharose adsorption was studied in terms of salt, gel acetylation time, flow rate, and protein concentration on the loading buffer. At 0.5 M Na2SO4, control with unmodified Sepharose retained a small fraction (0.70 mg/mL of matrix) of serum albumin. On the contrary HA-Sepharose retained primary Igs (IgA, IgG, and 53% of IgM) as revealed by sodium dodecyl sulphate 10% polyacrylamide gel electrophoresis (SDS-PAGE), quantitative radial immunodiffusion and immunodetection. At a flow rate of 1 mL/min, the HA-Sepharose column capacity (3.9 mg/mL of matrix) was similar to the reported capacity for the commercial thiophilic T-gel. However, HA-Sepharose showed higher recovery of IgA and IgM than the T-gel in the same salt conditions, clearly an advantage in terms of immunoglobulin recovery strategies. Acetylation changed the matrix adsorption from albumin to immunoglobulins; thus, the highly acetylated gel rendered recoveries of Igs from unprocessed porcine serum practically free of albumin. © 2006 Elsevier B.V. All rights reserved.
• Stepanian, S. G., Trzaskowski, B., Deymier, P. A., Guzman, R., & Adamowicz, L. (2006). Selectivity of the chelator-protein interactions: A high level quantum chemistry study. Journal of Computational and Theoretical Nanoscience, 3(1), 78-87.
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  Abstract: We have employed correlated ab-initio and density functional theory (DFT) calculations to elucidate the selectivity of the interactions between chelators, which include -N-(CH2-COO-)n fragments and which coordinate di- and trivalent transition metal atoms and amino acids, with electron donor residues (histidine, cystein, methionine). The aim of the study is to initiate compilation of a database for such interactions based on the results obtained from the calculations. We found that an optimal (reliable and yet not too computationally damaging) approach for obtaining accurate interaction energies between chelators and amino acid residues involves an equilibrium geometry calculation at the DFT/6-31G* (for C, N, O, S, H atoms)/VTZ (for metal atoms) level of theory followed by a MP2 energy calculation performed at the DFT equilibrium geometry with the aug-cc-pVDZ VTZ basis set. The most accurate interaction energies were obtained when the water molecules belonging to the first coordination sphere were included in the calculations. Also, accounting for the zero-point vibrational energy correction and the basis set superposition energy correction aided the accuracy of the calculations. The interaction energy calculations performed for the chosen set of chelators, metal ions (Zn2+, Co2+, Fe2+, Ni2+ Cu2+ Pd2+, Cd2+), and amino acid residues allowed us to elucidate the selectivity of the interactions. Copyright © 2006 American Scientific Publishers. All rights reserved.
• Trzaskowski, B., Stepanian, S. G., Leś, A., Deymier, P. A., Guzman, R., & Adamowicz, L. (2006). Iminodiacetate as a chelating agent for histidine: A theoretical study. Journal of Computational and Theoretical Nanoscience, 3(5), 775-784.
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  Abstract: Density functional theory and ab-initio MP2 theoretical calculations have been employed to study the interaction between the iminodiacetate chelator, divalent metal cations, and histidine. The results of the study allow us to quantify the affinities of all divalent cations towards the iminodiacetate chelator and to suggest systems that are the best candidates for the most effective chelators. We have found that the transition-metal cations of the sixth and tenth groups are the best chelating agents. Systems with the iminodiacetate molecule loaded with either Mo, Pd, or Pt cation are predicted to strongly bind histidine and facilitate immobilization of proteins with exposed histidine residues. Copyright © 2006 American Scientific Publishers All rights reserved.
• Yangg, Y., Deymier, P. A., Wang, L., Guzman, R., Hoying, J. B., McLaughlin, H. J., Smith, S. D., & Jongewaar, I. N. (2006). Nucleation and growth of microtubules from γ-tubulin-functionalized gold surfaces. Biotechnology Progress, 22(1), 303-312.
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  PMID: 16454524;Abstract: Microtubules are protein filaments that are emerging as potential building blocks in manufacturing nanoscale structures and systems such as interconnecting nanowires. Future development in using microtubules necessitates a control of their nucleation and growth. We report the controlled nucleation and growth of microtubules from functionalized gold on a hydrophilic oxidized silicon wafer. The gold substrate is functionalized with γ-tubulin, a natural nucleating agent for microtubule growth. We show that the attached γ-tubulin retains its biological functionality and leads to nucleation and assembly of microtubules from the functionalized gold surface. We also analyze the interplay between the geometry of the nucleating substrates and the morphology of microtubules arrays and networks grown from them. We consider two geometrical arrangements of the substrates: (a) a square lattice of small gold pads on a hydrophilic oxidized silicon wafer and (b) a large flat surface. Fluorescence microscopy and scanning electron microscopy are employed to provide a detailed characterization of the length and morphology of the nucleated and grown microtubules. The observed microtubule morphologies are modeled, analyzed and discussed within the context of reaction-diffusion and nucleation controlled processes. © 2006 American Chemical Society and American Institute of Chemical Engineers.
• del, M., García, J., Guzmán, R., Porath, J., & Vázquez-Moreno, L. (2006). Isolation of human serum immunoglobulins with a new salt-promoted adsorbent. Journal of Chromatography A, 1118(2), 211-217.
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  PMID: 16620854;Abstract: In this work a highly acetylated-ethylenediamine-Novarose (HA-EDA-Novarose) gel was synthesized and used as a new agarose-based salt-promoted adsorption chromatography (SPAC) matrix to effectively isolate serum immunoglobulins without the need of denaturing conditions. Samples of human serum in 0.5 M Na2SO4, 10 mM 3-(N-morpholino)-propane-sulfonic acid (MOPS), pH 7.6 were applied to a chromatographic column packed with the SPAC gel. Immunoglobulins (Igs) with affinity for the HA-EDA ligands were specifically adsorbed to the matrix, non-bound serum proteins were readily removed by washing the column with the same feed solution buffer. Bound Igs were effectively and very gently eluted by simply removing the salt from the feed solution buffer. The elution buffer consisted thus of only 10 mM MOPS, at pH 7.6 and no salt. The salt-dependent adsorption capacity of this system was estimated to be 7.3 mg/ml with protein recovery of about 93%. Sodium dodecyl sulfate-polyacrylamide gel (SDS-PAGE) electrophoresis analysis, radial immunodiffusion and enzyme-linked immunosorbent assays showed that immunoglobulins G, M and A (IgG, IgM and IgA) were the main components present in the elution fraction. The new SPAC adsorbent was used to purify Igs from human serum and IgG and IgA from non-pure commercially available Igs preparations in a very gentle single step. © 2006 Elsevier B.V. All rights reserved.
• Montesinos, R. M., Tejeda-Mansir, A., Guzmán, R., Ortega, J., & Schiesser, W. E. (2005). Analysis and simulation of frontal affinity chromatography of proteins. Separation and Purification Technology, 42(1), 75-84.
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  Abstract: A transport model that considers pore diffusion, external film resistance, finite kinetic rate and column dispersed flow, was used to mathematically describe a frontal affinity chromatography system. The corresponding differential equations system was solved in a simple and accurate form by using the numerical method of lines (MOL). The solution was compared with experimental data from literature and the analytic Thomas solution. The frontal affinity chromatography of lysozyme to Cibacron Blue Sepharose CL-6B was used as a model system. A good fit to the experimental data was made with the simulated runs of the transport model using the MOL solution. This approach was used to perform a parametric analysis of the experimental frontal affinity system. The influence of process and physical parameters on the frontal affinity chromatography process was investigated. The MOL solution of the transport model results in an unique and simple way to predict frontal affinity performance as well a better understanding of the fundamental mechanisms responsible for the separation. © 2004 Elsevier B.V. All rights reserved.
• Trzaskowski, B., Les, A., Adamowicz, L., Deymier, P. A., Guzman, R., & Stepanian, S. G. (2005). Multilevel quantum chemistry approach to the development of a database of the SAM-ligand-metal ion-protein interactions. Journal of Computational and Theoretical Nanoscience, 2(3), 456-468.
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  Abstract: An ab-initio approach towards building a database of immobilized ligands targeting proteins is presented. Iminodiacetic chelators, precursors of self-assembled monolayers, attached to the gold surface and complexing three divalent metal ions (Cu(ll), Zn(ll), Ni(ll)) is investigated. The strength of the protein-ligand interaction is estimated. Ten models of the iminodiacetic acid metal complex with different degree of complexity were constructed, each focusing on different structural features of the system. The calculations have been performed using the quantum mechanical density functional theory method. The results show that reduction of the complexity of the model by removing the gold surface, the neighboring alkyl chains and the presence of the solvent does not have much impact on the iminodiacetic acid - aminoacid affinity. The interaction between the chelator and the aminoacid represented by imidazole moiety of histidine are also almost unaffected by the length of the alkyl chain. The results indicate that advanced quantum mechanical methods and relatively small model systems can be used to adequately describe the self-assembled monolayer-ligand-metal ion-protein interactions and to create a comprehensive database of ligands for the monolayers. Copyright © 2005 American Scientific Publishers. All rights reserved.
• Tejeda-Mansir, A., Montesinos, R. M., Magaña-Plaza, I., & Guzmán, R. (2003). Breakthrough performance of stacks of dye-cellulosic fabric in affinity chromatography of lysozyme. Bioprocess and Biosystems Engineering, 25(4), 235-242.
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  PMID: 14505002;Abstract: The breakthrough performance of stacks of dye-cellulosic fabric in affinity chromatography of lysozyme was investigated in batch and flow experiments. Breakthrough curves were significantly affected by flow rate and were not dependent on the feed solution concentration. System dispersion curves could not explain the flow-rate dependence. Breakthrough curves were analyzed by coupling the kinetic model for pore mass transfer as the only controlling resistance and a system dispersion model. From the analysis, pore film mass transfer resistance was found to be the leading rate-limiting factor when the residence time in the column is greater than 5 min. The model was used to predict the operating and design parameters needed to obtain sharp breakthrough curves. Selectivity studies using lysozyme and bovine serum albumin mixtures showed a high system selectivity for lysozyme.
• Montesinos, R. M., Guzmán, R., & Tejeda-Mansir, A. (2001). Simulation of stirred tank affinity processes applied to separation of proteins. International Journal of Bio-Chromatography, 6(3), 231-243.
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  Abstract: A model, which includes pore diffusion, external film resistance, and finite kinetic rate, was used to mathematically describe a batch affinity adsorption system. The corresponding differential equations system was solved using two numerical methods: the numerical method of lines (NUMOL) and the global (implicit) finite difference method. In each case, simulation studies were conducted to determine the mass-transfer-controlled mechanism. Experimental data from literature describing batch affinity adsorption of immunoglobulin G to protein A-Sepharose was used as a model system. The best fit of the experimental data was obtained with the mass-transfer process controlled by pore diffusion and film resistance, in the simulation studies, using the NUMOL solution. The transport model was used to perform a parametric analysis of the experimental batch system. The influence of both process parameters as well as physical parameters on the affinity adsorption process was investigated.
• Tejeda-Mansir, A., Montesinos, R. M., & Guzmán, R. (2001). Mathematical analysis of frontal affinity chromatography in particle and membrane configurations. Journal of Biochemical and Biophysical Methods, 49(1-3), 1-28.
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  PMID: 11694270;Abstract: The scaleup and optimization of large-scale affinity-chromatographic operations in the recovery, separation and purification of biochemical components is of major industrial importance. The development of mathematical models to describe affinity-chromatographic processes, and the use of these models in computer programs to predict column performance is an engineering approach that can help to attain these bioprocess engineering tasks successfully. Most affinity-chromatographic separations are operated in the frontal mode, using fixed-bed columns. Purely diffusive and perfusion particles and membrane-based affinity chromatography are among the main commercially available technologies for these separations. For a particular application, a basic understanding of the main similarities and differences between particle and membrane frontal affinity chromatography and how these characteristics are reflected in the transport models is of fundamental relevance. This review presents the basic theoretical considerations used in the development of particle and membrane affinity chromatography models that can be applied in the design and operation of large-scale affinity separations in fixed-bed columns. A transport model for column affinity chromatography that considers column dispersion, particle internal convection, external film resistance, finite kinetic rate, plus macropore and micropore resistances is analyzed as a framework for exploring further the mathematical analysis. Such models provide a general realistic description of almost all practical systems. Specific mathematical models that take into account geometric considerations and transport effects have been developed for both particle and membrane affinity chromatography systems. Some of the most common simplified models, based on linear driving-force (LDF) and equilibrium assumptions, are emphasized. Analytical solutions of the corresponding simplified dimensionless affinity models are presented. Particular methods for estimating the parameters that characterize the mass-transfer and adsorption mechanisms in affinity systems are described. © 2001 Elsevier Science B.V. All rights reserved.
• Varady, R. G., Arnold, R. G., Carter, D. E., Guzmán, R., & Peña, C. E. (2000). Hazardous waste and the US-Mexico border region: Toward a Binational, University-Based Institution. Environmental Practice, 2(1), 38-45.
• Tejeda, A., Ortega, J., Magaña, I., & Guzmán, R. (1999). Optimal design of affinity membrane chromatographic columns. Journal of Chromatography A, 830(2), 293-300.
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  Abstract: A method for the optimal affinity membrane column design, based in the solution of the Thomas kinetic model for frontal analysis in membrane column adsorption, is presented. The method permits to choose suitable membrane operating conditions, column dimensions and processing time, to maximize the throughput when an operating capacity restriction in the range of 80-95% of the column capacity is used. Two basic design charts were obtained by computer simulation, for residence and processing time calculation, respectively. These charts can be used and manipulated in a wide range of operational conditions, provided that four design specifications related to column axial and radial Peclet numbers, length and pressure drop, are fulfilled. The application of the method was illustrated using experimental data and a simple analytical procedure. The implications of the method and results on the design and optimization of affinity membrane chromatographic columns are discussed. Copyright (C) 1999 Elsevier Science B.V.
• Nedonchelle, E., Leduc, C., Garcia, X., Guzman, R., & Vijayalakshmi, M. A. (1998). Production of 'neometalloenzymes' by de novo biosynthesis: New ELISA method for their characterization. Annals of the New York Academy of Sciences, 864, 106-117.
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  PMID: 9928085;Abstract: Several approaches known for producing 'neometalloenzymes' are classified into two categories: protein engineering using antibodies as starting materials and 'de novo' biosynthesis of metal-binding antibodies with potential catalytic metal-binding structure. This latter approach is chosen in this study. Polyclonal anti-zinc-iminodiacetate [IDA-Zn(II)] antibodies are produced in rabbits and mice. Because of the absolute need for the unequivocal screening of the hapten [IDA-Zn(II)] specific antibodies, a new ELISA method was developed using a biheaded polyethylene glycol with biotin on one end and the hapten on the other end. The parameters for optimizing the immunization and the ELISA technique are discussed and the method is validated with rabbit and mice sera.
• Ruiz-Manríquez, A., Magaña, P., López, V., & Guzmán, R. (1998). Biosorption of Cu by Thiobacillus ferrooxidans. Bioprocess Engineering, 18(2), 113-118.
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  Abstract: Current technologies for removal and recovery of both toxic and industrial interest metals usually produce wastes with high concentrations of those substances. They are an important source of environmental pollution, specially when they contain heavy metals. This is one of the most important environmental problems, and of the most difficult to solve. So far, there have been a number of studies considering the possibility of removing and recovering heavy metals from diluted solutions. These are due, principally, because of the commercial value of some metals as well as the environmental impact caused by them. The traditional methods for removing have several disadvantages when metals are present in concentrations lower than 100 mg/l. Biosorption, which uses biological materials as adsorbents, has been considered as an alternative method. In this work, several variables that affect the capacity for copper biosorption by T. ferrooxidans have been studied. Particularly, the effect of pH, chemical pretreatment, biomass concentration and temperature have been considered. Results indicate that a capacity as high as 119 mg of Cu/g of dry biomass can be obtained at a temperature of 25 °C.
• Tejeda, A., Noriega, J. A., Ortega, J., & Guzmán, R. (1998). Dye affinity adsorbent replacement optimization. Biotechnology Progress, 14(3), 493-495.
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  PMID: 9622532;Abstract: A method to determine the optimal replacement time for dye affinity adsorbents used in protein purification processes that are subjected to severe regeneration conditions has been developed. To demonstrate the utility of the method, an experimental fixedbed decay model was employed to determine the optimum number of cycles for the adsorbent replacement. This number is a function of the column regeneration frequency and of the capital and operation costs. The implications of the results on the design and operation of dye-ligand chromatographic processes are discussed.
• Tejeda-Mansir, A., Juvera, J. M., Magaña, I., & Guzmán, R. (1998). Design of affinity membrane chromatographic columns. Bioprocess Engineering, 19(2), 115-119.
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  Abstract: A method for affinity membrane column design, based on the analytical solution of the Thomas model for frontal analysis in membrane column adsorption, was developed. The method permits to find the operating conditions to reach a 93.5% of the column capacity as operating capacity, using a sharpness restriction for the system breakthrough curve. The solution of the model is presented in a graphic form and can be used in a wide range of operational conditions, provided that four design restrictions are fulfilled. The application of the method was illustrated using experimental data and a simple procedure. The implications of the results on the design and optimization of affinity membrane chromatographic columns are discussed.
• Téllez, C. M., Gaus, K. P., Graham, D. W., Arnold, R. G., & Guzman, R. Z. (1998). Isolation of copper biochelates from Methylosinus trichosporium OB3b and soluble methane monooxygenase mutants. Applied and Environmental Microbiology, 64(3), 1115-1122.
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  PMID: 9501450;PMCID: PMC106376;Abstract: Methylosinus trichosporium OB3b produces an extracellular copper- binding ligand (CBL) with high affinity for copper. Wild-type cells and mutants that express soluble methane monooxygenase (sMMO) in the presence and absence of copper (sMMO(c)) were used to obtain cell exudates that were separated and analyzed by size exclusion high-performance liquid chromatography. A single chromatographic peak, when present, contained most of the aqueous-phase Cu(II) present in the culture medium. In mutant cultures that were unable to acquire copper, extracellular CBL accumulated to high levels both in the presence and in the absence of copper. Conversely, in wild-type cultures containing 5 μM Cu(II), extracellular CBL was maintained at a low, steady level during exponential growth, after which the external ligand was rapidly consumed. When Cu(II) was omitted from the growth medium, the wild-type organism produced the CBL at a rate that was proportional to cell density. After copper was added to this previously Cu-deprived culture, the CBL and copper concentrations in the medium decreased at approximately the same rate. Apparently, the extracellular CBL was produced throughout the period of cell growth, in the presence and absence of Cu(II), by both the mutant and wild-type cultures and was reinternalized or otherwise utilized by the wild-type cultures when it was bound to copper. CBL produced by the mutant strain facilitated copper uptake by wild-type cells, indicating that the extracellular CBLs produced by the mutant and wild-type organisms are functionally indistinguishable. CBL from the wild-type strain did not promote copper uptake by the mutant. The molecular weight of the CBL was estimated to be 500, and its association constant with copper was 1.4 x 1016 M-1. CBL exhibited a preference for copper, even in the presence of 20-fold higher concentrations of nickel. External complexation may play a role in normal copper acquisition by M. trichosporium OB3b. The sMMO(c) phenotype is probably related to the mutant's inability to take up CBL-complexed copper, not to a defective CBL structure.
• Chaga, G. S., Guzman, R., & Porath, J. O. (1997). A new method of synthesizing biopolymeric affinity ligands. Biotechnology and Applied Biochemistry, 26(1), 7-13.
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  PMID: 9261997;Abstract: (1) A new concept for producing soluble polymeric affinity ligands is proposed and exemplified. By solid-phase synthesis, an insoluble hydrophilic polymer is converted into an affinity gel. The gel is hydrolytically degraded to water-soluble affinity polymeric ligands which are recovered and purified. (2) A water-soluble biopolymeric metal-affinity carrier based on an iminodiacetic acid (IDA) derivative of dextran has been synthesized through the modification of Sephadex G-200 by IDA, followed by hydrolysis with dextranase and size-exclusion chromatographic purification of the high-molecular-mass fragments. (3) The molecular size of the soluble products as a function of hydrolysis time with dextranase from Penicillium sp., was determined. The range of molecular size of the biopolymeric chelating ligand varies from around 200 Da to greater than 580 kDa. (4) The influence of three metal ions chelated with the Sephadex derivative on the hydrolysis rate and the molecular-size distribution of end products was studied. Eu3+ was found to improve the rate of solubilization. Ni2+ and Cu2+ decreased the hydrolysis rate, as compared with that of the metal-free IDA-Sephadex. (5) The method introduced here has the potential of being developed and applied as a general technology for synthesis of soluble multifunctional affinity ligands. Such ligands should be useful for liquid-phase extraction as well as for the synthesis of adsorbents with localized multiple binding sites. Other possible fields of applications are to be found in medicine, where they could be used for slow drug delivery or deterification, and in analytical chemistry, where they could be used in various assays.
• Ehteshami, G. R., Sharma, S. D., Porath, J., & Guzman, R. Z. (1997). Synthesis of monoprotected derivatives of homo-bifunctional molecules. Reactive and Functional Polymers, 35(3), 135-143.
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  Abstract: Selective derivatization of one of the two functional groups in a symmetrical homo-bifunctional molecule is always an uphill synthetic task. A novel method for synthesis of mono-protected homo-bifunctional poly(ethylene glycol) (PEG) is described in this work. The methodology utilizes a combination of two protecting groups that are orthogonal to each other for the introduction of one of these groups into symmetrical homo-bifunctional PEG polymers. Different well-known protecting groups, namely the carbobenzyloxy (Z) and the t-butyloxycarbonyl (Boc) groups, have been evaluated for this particular purpose. The approach appears to be straightforward in terms of separation of desired products from other non-desirable products or reactants. The methodology described here might be applicable to any symmetrical homo-bifunctional molecular substance and for synthesis of its corresponding monoprotected derivatives.
• López, Z. K., Tejeda, A., Montesinos, R. M., Magaña, I., & Guzmán, R. (1997). Modeling column regeneration effects on ion-exchange chromatography. Journal of Chromatography A, 791(1-2), 99-107.
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  PMID: 9463896;Abstract: The effect of in-place regeneration on equilibrium and kinetic characteristics of the adsorption of bovine serum albumin to a DEAE-cellulose anion exchanger has been determined. Regeneration with sodium hydroxide and time of exposure showed no effect on equilibrium behavior. Breakthrough curves were measured for protein adsorption on fixed-bed columns and analyzed by a simple model to determine the relevant rate constants for the adsorption process. It was found that forward adsorption rate constant decreased exponentially with the chemical treatment exposure time. The implications of the results on the design and optimization of ion-exchange chromatographic processes are discussed.
• Noriega, J. A., Tejeda, A., Magaña, I., Ortega, J., & Guzmán, R. (1997). Modeling column regeneration effects on dye-ligand affinity chromatography. Biotechnology Progress, 13(3), 296-300.
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  Abstract: The effect of in-place regeneration of dye-ligand adsorbents on protein adsorption characteristics is presented. Regeneration with chemical treatments and time of exposure determined the protein capacity of the adsorbent, but no effect was observed on its protein binding affinity. Fixed-bed adsorption of bovine serum albumin and its selectivity with respect to lysozyme was studied. Breakthrough curves were measured for protein adsorption on fixed-bed columns and analyzed by a simple model to determine the relevant rate constants for the adsorption process. It was found that forward adsorption rate constant increased exponentially with the chemical treatment exposure time. Column linear gradient elution studies showed that adsorbent selectivity decreased with the chemical treatment exposure time due mainly to column loss of adsorption capacity. The implications of the results on the design and optimization of dye-ligand chromatographic processes are discussed.
• Porath, J., Chaga, G., Louria, D., Kunz, S., & Guzman, R. (1997). Adsorptive size exclusion chromatography (concentration), AdSEC. International Journal of Bio-Chromatography, 3(1), 9-17.
• Tejeda, A., Noriega, J. A., Ruíz, A., Montesinos, R. M., Yeomans, H., & Guzmán, R. (1997). Introduction to bioseparations: Affinity adsorption. Chemical Engineering Education, 31(2), 124-129.
• Tejeda-Mansir, A., Espinoza, R., Montesinos, R. M., & Guzmán, R. (1997). Modelling regeneration effects on protein A affinity chromatography. Bioprocess Engineering, 17(1), 39-44.
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  Abstract: The effect of in-place regeneration of protein A adsorbents on protein adsorption characteristics is investigated. Regeneration with sodium hydroxide and time of exposure determined the protein capacity of the adsorbent, but no effect was observed on the adsorbent protein affinity. Fixed-bed adsorption of human immunoglobulin G was studied. Breakthrough curves were measured for protein adsorption on fixed-bed columns. These data were analyzed by a simple kinetic model to determine the rate constants for the adsorption process. It was found that forward adsorption rate constant remained constant along the chemical treatment exposure time. Protein A adsorbent selectivity was determined using mouse serum immunoglobulins G1 and G3. Column linear gradient elution showed that adsorbent selectivity decreased with the exposure time chemical treatment. The implications of these results on the design and optimization of protein A chromatographic process are discussed.
• Aguiñaga-Díaz, P., & Guzmán, R. (1996). Affinity partitioning of metal ions in aqueous polyethylene glycol/salt two-phase systems with PEG-modified chelators. Separation Science and Technology, 31(10), 1483-1499.
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  Abstract: The systematic partitioning of metal ions in the presence of polyethylene glycol (PEG) chelate derivatives in PEG/salt two-phase systems is described. Results show that the partitioning is enhanced significantly, and this effect is apparently based on the characteristics of binding of the chelate and the nature of the metal ion in addition to the effect of the attached PEG molecule. Previous work with PEG-iminodiacetic acid has been extended with the chelating derivatives PEG-TED [tris(carboxymethyl)ethylene diamme], PEG-TREN-Cm [carboxymethylated-tris(2-aminoethyl)amine], and PEG-ASP (aspartic acid). Their effectiveness to selectively partition the metal ions is demonstrated and discussed. The partition experiments were performed using two-phase systems of PEG (8000 MW), sodium sulfate, the PEG-chelating derivatives, and different concentrations of copper, nickel, and cobalt as model metal ions. Partition coefficients (ratio of top to bottom metal concentrations) greater than 1 were obtained for the metal ions with all the chelating derivatives tested. Selective enhancement of partitioning was observed in all cases. Based on the experimental results and theoretical principles, the method shows potential as an alternative mode to remove efficiently and selectively metal ions from solutions using aqueous two-phase systems and PEG - chelate derivatives.
• Ehteshami, G., Porath, J., & Guzmán, R. (1996). Interactions and Applications of Soluble Heterobifunctional Affinity Chelating Polymers in Immobilized Metal Affinity Chromatography. Journal of Molecular Recognition, 9(5-6), 733-737.
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  PMID: 9174965;Abstract: The interaction of immobilized metal-chelating adsorbents with a dual heterobifunctional soluble polyethylene glycol (PEG) of the form X-PEG-Y is described, where X represents an affinity ligand and Y a dictating agent. The bifunctional PEG derivative used in this study was biotin-PEG-iminodiacetic acid (EDA). Affinity and metal binding constants of this conjugate for copper and avidin were found to be in excellent agreement with the binding affinities of the corresponding unconjugated groups IDA and biotin, respectively. The characteristics of the interaction of this bifunctional derivative is described in terms of its adsorption in immobilized metal affinity chromatographic (IMAC) adsorbents. The results show that this derivative can be reversibly and selectively bound to specific IMAC adsorbents under certain experimental conditions. This immobilized scheme resembles a system where an IMAC adsorbent was transformed into an affinity adsorbent as a result of the interactions of both dictating derivatives, one in solution (biotin-PEG-IDA) and the other on the solid matrix (IMAC adsorbent). Apparently the modified IMAC adsorbents, once the affinity dictating ligands are attached, exhibit characteristics similar to those of covalently bound affinity ligands in affinity chromatographic systems.
• Guzman, R., Torres, J. L., Carbonell, R. G., & Kilpatrick, P. K. (1989). Water-soluble nonionic surfactants for affinity bioseparations. Biotechnology and Bioengineering, 33(10), 1267-1276.
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  PMID: 18587859;Abstract: Reversible competitive inhibitors of the three enzymes β-galactosidase, trypsin, and serum cholinesterase have been covalently attached to nonionic ethoxylated surfactants. The binding of the resulting affinity-derivatized surfactants to the respective enzymes has been quantified by measuring Michaelis-Menten inhibition constants with kinetic assays. The surfactant-inhibitor of serum cholinesterase, octaethylene glycol monohexadecyl ether pyridinium (C16E8-PYR), was adsorbed in aqueous solution to an octadecyl-bonded reverse-phase silica packing in a 2×0.2 cm stainless steel test column. The ability of the test column to function as a high-performance affinity chromatography (HPAC) column was determined by applying a mixture of bovine serum albumin and cholinesterase (4:1 w/w). Virtually all of the cholinesterase bound and was eluted by applying a gradient in ionic strength. The applied cholinesterase was covered with a yield of over 90% and an 11-fold purification.
• Torres, J. L., Guzman, R., Carbonell, R. G., & Kilpatrick, P. K. (1988). Affinity surfactants as reversibly bound ligands for high-performance affinity chromatography. Analytical Biochemistry, 171(2), 411-418.
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  PMID: 3407942;Abstract: Pyridine was coupled covalently to a nonionic ethoxylated alcohol: octaethylene glycol n-hexadecyl ether. This modified surfactant was found to be a reversible, competitive inhibitor of horse serum cholinesterase. The surfactant bound irreversibly, in aqueous media, to octadecylbonded reverse phase silica particles commonly used for high-performance liquid chromatography. The amount of ligand bound was found to be 550 μmol/ml of packing, a concentration that is over 100 times higher than what can be normally bound to agarose affinity chromatography supports. With this packing, a 280-fold purification of cholinesterase from horse serum and a 79-fold purification of human serum cholinesterase were accomplished, with yields greater than 80%, using a 2-cm-long column and a 7-min elution time. The affinity surfactant could be eluted from the column using a 6:4 (v/v) mixture of methanol and isopropanol. This technique should be generally applicable in the development of biospecific supports for high-performance affinity chromatography. © 1988.
• Guzman, R. Z., Carbonell, R. G., & Kilpatrick, P. K. (1986). The adsorption of proteins to gas-liquid interfaces. Journal of Colloid And Interface Science, 114(2), 536-547.
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  Abstract: A kinetic model of protein adsorption to gas-liquid interfaces is described. The model is based on a formalism similar to that used to describe adsorption at gas-solid interfaces, but with proteins we allow for both tight adsorption of a first layer and loose packing of a second layer of proteins. The model is fit to the adsorption isotherm data of Graham and Phillips for the three proteins: β-casein, bovine serum albumin, and lysozyme. We also fit the model to adsorption rate data for the two proteins lysozyme and β-casein. The experimental adsorption rates are considerably faster than those for molecular diffusion alone. The rate of mass transfer of protein to the interface was accordingly modeled by an effective mass-transfer coefficient. The ratio of the mass-transfer coefficients for two different proteins can be predicted by the free-convection correlation of Globe and Dropkin, suggesting that small temperature gradients may have existed in the vessel during the measurements. Finally, we have predicted desorption rates for exchange experiments in which fresh solution replaces bulk protein solution after equilibrium adsorption has been reached. Depending on the residence time of the bulk fluid in the reservoir, our results indicate desorption can be very difficult to measure, particularly at low surface concentrations and even if equilibrium is assumed between the interface and the solution just below the surface. Thus, there appears to be no need to postulate irreversible adsorption of protein to account for the available experimental data on protein adsorption and desorption. © 1986.

Presentations

• Guzman, R. Z. (2017, June). Affinity Adsorption Chromatography Modulated by Polymer Permeation Control. A strategy to purify peptides and small proteins. AFFINITY 2017. The 22th Meeting of the International Society for Molecular Recognition. Paris, France: International Society for Molecular Recognition.
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  Roberto Guzmán. Invited Conference Speaker.
• Guzman, R. Z. (2017, May). Nanotecnología y Nanopartículas en Aplicaciones Biomédicas. Terapias Especificas para el Tratamiento de Cáncer. 4rd International Biotechnology Congress at Universidad Popular Autónoma del Estado de Puebla (UPAEP). Puebla, Pue., México.: Universidad Popular Autónoma del Estado de Puebla (UPAEP).
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  Roberto Guzmán. Invited Colloquium speaker.
• Guzman, R. Z. (2017, October). Cancer Nanotechnology –Current Status and Future Opportunities–Perspectives from the NCI Alliance for Nanotechnology in Cancer. 2017 Annual Nanomaterials and Nanotechnology Symposium at the Universidad de Sonora. Hermosillo, Sonora Mexico: Departement of Physics, Universidad de Sonora.
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  Invited Colloquium Speaker
• Guzman, R. Z. (2017, October). Nanotechnology and Biomedical Applications. Nanoparticles in Diagnostics and Specific Therapies for Cancer Treatment. 2017 Annual Nanomaterials and Nanotechnology Symposium at the Universidad de Sonora. Hermosillo, Sonora, Mexico.: Departement of Physics, Universidad de Sonora.
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  Invited Colloquium Speaker
• Guzman, R. Z. (2017, September). Control Drug Delivery with Polymeric Nanoparticles”. 2do Simposio de Ingeniería de Procesos, Universidad Veracruzana. Xalapa, Veracruz, México: Universidad Veracruzana, Xalapa, Veracruz, México.
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  Invited Colloquium speaker
• Guzman, R. Z. (2017, September). La Ingenieria Quimica/Bioquimica y Nanobiotecnologia. Tendencias, Oportunidades y Aplicaciones in Biomedicina. 6to Simposio Nacional de Ingeniería Química y Bioquímica Aplicada (SNQBA 2017). Tlaxcala, Tlaxcala. México: Universidad Autónoma de Tlaxcala.
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  Invited Keynote Speaker

Poster Presentations

• Guzman, R. Z., & Garcia-Soto, M. (2017, June). Gold derivatized nanocomposites for the effective detection, contrast imaging and thermal ablation in cancer research. AFFINITY 2017. The 22th Meeting of the International Society for Molecular RecognitionInternational Society for Molecular Recognition.
• Guzman, R. Z., & Lucero, A. A. (2017, June). Polymeric nanoparticles for controlled drug delivery: Synthesis, modeling and application in vitro and in vivo to pancreatic cancer. AFFINITY 2017. The 22th Meeting of the International Society for Molecular Recognition. Paris, France: International Society for Molecular Recognition.
• Guzman, R. Z., Yan, S., & Wang, L. (2017, June). Affinity chelating liposomes for protein separations and effect of PEG on aggregation and binding interactions. AFFINITY 2017. The 22th Meeting of the International Society for Molecular Recognition. Paris, France: International Society for Molecular Recognition.
• Guzman, R. Z., Zheng, X. J., Cheung, L. S., Wang, L., Baygents, J. C., Schroeder, J. A., Heimark, R. L., & Zohar, Y. (2017, June). Antibody-functionalized microfluidic chamber arrays for specific binding of metastatic breast cancer cells. AFFINITY 2017. The 22th Meeting of the International Society for Molecular Recognition. Paris, France: International Society for Molecular Recognition.