carlos vera | Universidad Estatal De Cuenca (original) (raw)

Papers by carlos vera

Annals of Biomedical Engineering, 2003

It is a long-standing mystery why erythrocyte actin filaments in the junctional complex (JC) are ... more It is a long-standing mystery why erythrocyte actin filaments in the junctional complex (JC) are uniformly ∼37 nm and the membrane skeleton consists of hexagons. We have previously proposed that a “molecular ruler” formed by E-tropomodulin and tropomyosin 5 or 5b functions to generate protofilaments of 12 G actin under mechanical stress. Here, we illustrate that intrinsic properties of actin filaments, e.g., turns, chemical bonds, and dimensions of the helix, also favor fragmentation into protofilaments under mechanical stress. We further construct a mechanical model in that a pair of G actin is wrapped around by a split α and β spectrin, which may spin to two potential positions, and stabilize to one when the tail end is restricted. A reinforced protofilament may function as a mechanical axis to anchor three (top, middle, and bottom) pairs of Sp. Each Sp pair may wrap around the protofilament with a wide dihedral angle (∼166.2°) and a minimal axial distance (2.75 nm). Such three Sp pairs may spiral down (right handed) the protofilament from the pointed end with a dihedral angle of ∼55.4° in between the Sp pairs. This first three-dimensional model of JC may explain the hexagonal geometry of the erythrocyte membrane skeleton. © 2003 Biomedical Engineering Society. PAC2003: 8716Ka, 8716Dg, 8714Ee, 8716Ac

European Journal of Engineering Education, 2006

The paper focuses on educational projects developed in the ETSII (Escuela Técnica Superior de Ing... more The paper focuses on educational projects developed in the ETSII (Escuela Técnica Superior de Ingenieros Industriales) of the Polytechnic University of Madrid during the past few years. These projects were developed as new tools for enhancing the active role of students, for improving practical teaching, especially by means of virtual laboratories and different sets of problems and exercises, and for promoting self-learning. The paper analyses the use of ICT in teaching, with the case of a developed e-learning platform as a tracking system for subjects. The paper concludes by discussing the new educational trends in the Centre, devoted to develop an active role of students by activities such as peer mentoring and laboratory monitors programs, and competitions for achieving multidisciplinary engineering challenges.

Biotechnology Progress, 2014

Fed-batch synthesis of galacto-oligosaccharides (GOS) from lactose with β-galactosidase from Aspe... more Fed-batch synthesis of galacto-oligosaccharides (GOS) from lactose with β-galactosidase from Aspergillus oryzae was evaluated experimentally and reaction yield was maximized via optimal control technique. The optimal lactose and enzyme feed flow rate profiles were determined using a model for GOS synthesis previously reported by the authors. Experimentally it was found that fed-batch synthesis allowed an increase on the maximum total GOS concentration from 115 (batch synthesis) to 218 g L(-1) as consequence of the increase in total sugars concentration from 40 to 58% w/w. Such high concentration of total sugars was not attainable in batch operation because of the low solubility of lactose at the reaction temperature (40°C). Simulations predicted a GOS yield of 32.5 g g(-1) in fed-batch synthesis under optimal conditions, while experimentally the same yield as in batch synthesis was obtained (28 g g(-1) ). Besides, an enrichment of total oligosaccharides in GOS with a high polymerization degree (GOS-5 and GOS-6) was observed in the fed-batch synthesis. Experimental profiles for all sugars were similar to the ones predicted by simulation, which supports the use of this methodology for the optimization of GOS synthesis.

Biophysical Journal, 2007

To investigate the nanomechanics of the erythrocyte membrane we developed a hybrid model that cou... more To investigate the nanomechanics of the erythrocyte membrane we developed a hybrid model that couples the actin-spectrin network to the lipid bilayer. This model features a Fourier space Brownian dynamics model of the bilayer, a Brownian dynamics model of the actin protofilament, and a modified wormlike-chain model of the spectrin (including a cable-dynamics model to predict the oscillation in tension). This model enables us to predict the nanomechanics of single or multiple units of the protein network, the lipid bilayer, and the effect of their interactions. The present work is focused on the attitude of the actin protofilament at the equilibrium states coupled with the elevations of the lipid bilayer through their primary linkage at the suspension complex in deformations. Two different actin-spectrin junctions are considered at the junctional complex. With a point-attachment junction, large pitch angles and bifurcation of yaw angles are predicted. Thermal fluctuations at bifurcation may lead to mode-switching, which may affect the network and the physiological performance of the membrane. In contrast, with a wrap-around junction, pitch angles remain small, and the occurrence of bifurcation is greatly reduced. These simulations suggest the importance of threedimensional molecular junctions and the lipid bilayer/protein network coupling on cell membrane mechanics.

Annals of Biomedical Engineering, 2011

Our 3-D model for a junctional complex (JC) in the erythrocyte membrane skeleton proposed that th... more Our 3-D model for a junctional complex (JC) in the erythrocyte membrane skeleton proposed that the helical actin protofilament functions as a mechanical axis for three pairs of ab spectrin (Sp), and each pair wraps around the protofilament in a back-to-back fashion. The distal end of each Sp is further associated with the lipid bilayer by a suspension complex (SC). Here, we detail how splitting and rejoining of ab Sp around a protofilament may form a loop that sustains and equilibrates tension. Sequential association of b and a Sp solves the challenge of constructing multiple loops along the protofilament, and topological connection facilitates their re-association. The wrap-around model minimizes the strain of the actin binding site on b Sp due to tension, redirection, or sliding of intertwined Sp. Pairing Sp balances the opposing forces and provides a mechanism for elastic recovery. The wrap-around junction thus provides mechanical advantages over a point-attachment junction in maintaining the integrity and functionality of the network. Severing a or b Sp may convert a wrapping-around junction to a point-attachment junction. In that case, a ''bow up'' motion of JC during deformation may disturb or flip the overlaid lipid bilayer, and mark stressed erythrocytes for phagocytosis.

Annals of Biomedical Engineering, 2010

Erythrocytes undergo deformations when they transport O 2 and CO 2 across the membrane, yet the 3... more Erythrocytes undergo deformations when they transport O 2 and CO 2 across the membrane, yet the 3D nanomechanics of the skeletal network remains poorly understood. Expanding from our previous single isolated unit, we now simulate networks consisting of 1-10 concentric rings of repeating units in equibiaxial deformation. The networks are organized with (1) a 3D model for a single unit, (2) a wrap-around mode between Sp and actin protofilament in the intra-unit interaction, and (3) a random inter-unit connectivity. These assumptions permit efficient five-degreesof-freedom (5DOF) simulations when up to 30 pN of radial forces are applied to the boundary spectrin (Sp) and the center and other units are analyzed. As 6 Sp balance their tensions, hexagonal units become irregular. While actin protofilaments remain tangent to the network, their yaw (F) angles change drastically with addition of neighboring units or an Sp unfolding. It is anticipated that during deformation, transmembrane complexes associated with the network move laterally through the lipid bilayer and increase the diffusion of molecules across the membrane. When protofilament/Sp sweeps under the lipid bilayer, they mix up the submembrane concentration gradient. Thus, the nanomechanics of actin protofilaments and Sp may enhance the transport of molecules during erythrocyte deformation.

Biodiesel - Feedstocks and Processing Technologies, 2011

Applied Catalysis A-general, 1998

SO42−

Química Nova, 2012

ABSTRACT A study of the different hydrocarbon reactions over Ni doped WO 3-ZrO 2 catalysts was pe... more ABSTRACT A study of the different hydrocarbon reactions over Ni doped WO 3-ZrO 2 catalysts was performed. Ni was found as NiO at low Ni concentration while at high Ni concentrations a small fraction was present as a metal. For both cases, Ni strongly ...

Journal of Chemical Technology & Biotechnology, 2012

ABSTRACT BACKGROUND: Partial hydrogenation of alkynes have industrial and academic relevance on a... more ABSTRACT BACKGROUND: Partial hydrogenation of alkynes have industrial and academic relevance on a large scale; industries such as petrochemical, pharmacology and agrochemical use these compounds as raw material. Typical commercial catalysts contains palladium. Finding an economic, active and selective catalyst for the production of alkenes via partial hydrogenation of alkynes is thus an important challenge. On the other hand, the literature on kinetic studies of partial hydrogenation of heavy alkynes is scarce. So the main objectives of this work were to prepare a cheaper catalyst based on low W loading, and study the kinetic of the partial hydrogenation of 1-heptyne. A pseudo-homogeneous and six heterogeneous kinetic models were analyzed. The catalyst was characterized by ICP, XPS, DRX, TPR and hydrogen chemisorption techniques. RESULTS: The characterization results indicate that only WOx species are present on the alumina surface. The WOx/Al2O3 catalyst was active and selective for producing 1-heptene even at low reaction temperatures, the partial hydrogenation of 1-heptyne proceeds via two irreversible reactions in parallel. CONCLUSION: The best fit of the experimental data was achieved with a heterogeneous Langmuir-Hinshelwood-Hougen-Watson model in which the rate controlling step is the dissociative adsorption of hydrogen. The activation energy was estimated as EH2 = 34.8 kJ mol−1. Copyright © 2012 Society of Chemical Industry

Journal of Chemical Technology & Biotechnology, 2014

... 178-186, 1998 Research Paper Kinetics of Liquid Phase Selective Hydrogénation of Methylacetyl... more ... 178-186, 1998 Research Paper Kinetics of Liquid Phase Selective Hydrogénation of Methylacetylene and Propadiene in C3 Streams Hakan UYGUR1, Süheyda AT ALA Y2 ... Re^Re^Sc05 -L (7) 0.2 eL is the liquid hold-up in the bed and given by the correlation (Tarhan, ...

Journal of Catalysis, 1999

A study of the deactivation of SO 2− 4 -ZrO 2 catalysts during isomerization of n-butane showed t... more A study of the deactivation of SO 2− 4 -ZrO 2 catalysts during isomerization of n-butane showed that a small amount of a carbonaceous deposit (1-1.2%) is formed. A high proportion of this deposit is produced during the first minutes of the reaction and it seems to be responsible for the initial short-term catalyst deactivation but it is doubtful whether it is connected to the long-term loss of activity. Activity in isomerization of n-C 4 was very sensitive to activation conditions while coking was more consistent; in all cases, SZ catalysts had a limiting content of 1 to 1.2% coke when fully deactivated. In an oxygen flow, the coke deposit could be burned at 500 • C, but it could also easily be removed by stripping with an oxygen-free inert gas at higher temperatures. In the latter case, the coke was oxidized by the catalyst surface groups, most likely sulfate. The coke was soluble only in polar solvents (methanol, pyridine) and was highly insoluble in benzene and hexane. An FD-mass spectrum of the soluble fraction of the coke indicated the presence of compounds with m/z up to 2700, but the distribution was concentrated around m/z = 350 to 500. The latter value, when compared with the small amount of total carbon, indicates that only a small fraction of the surface sites was affected by the coke, or that deactivation proceeded by a mechanism other than site blocking. A surface reduction process by the reacting hydrocarbon may also be linked to the activity loss. ESR results indicated that the catalyst was also reduced during the reaction; the intensity of the Zr 3+ signal was higher on the coked catalysts. The probable concurrence of reduction could explain the long-term activity decline which seems not to be directly linked to the coking process.

Energy & Fuels, 2006

Biodiesel obtained by transesterification of soy oil with methanol was isomerized in the liquid p... more Biodiesel obtained by transesterification of soy oil with methanol was isomerized in the liquid phase at 125-275°C using solid acid catalysts. The purpose of this work was to improve the cold flow properties of biodiesel by inhibiting the formation of crystals. Crystallization was analyzed by means of the measurement of the cloud point of the fuel. Tested catalysts were SO 4 2--ZrO 2 and H-mordenite. At a temperature of reaction (T r ) lower than 125°C, the catalytic activity was negligible. At T r > 200°C, the reaction rate was greatly accelerated, but the cetane number was also decreased and the amount of coke deposits was greatly increased. While reacting biodiesel at 150-200°C, a small decrease (4-6.5°C) of the cloud point was obtained without a meaningful decrease of the cetane index. Best results were obtained with SO 4 2--ZrO 2 at 125°C. Isomerization had both positive and negative effects on fuel properties: it reduced the cloud point but also increased the viscosity and decreased the cetane index. Due to the different reactivity between the saturated fraction (estearates, palmitates) and the unsaturated one (linoleates, linolenoates, oleates), an adequate control of the degree of isomerization was only possible by performing a previous fractionation step. A good combination was obtained by reacting the saturates rich fraction at 200°C over H-mordenite and the unsaturated rich fraction at 150°C over SO 4 2--ZrO 2 . The fuel obtained by mixing both reacted fractions had a cetane index of 49.5 and a cloud point of -2°C. However, this combined approach yields only a little benefit compared to those obtained with the single reaction over SO 4 2--ZrO 2 at 125°C.

Enzyme and Microbial Technology, 2012

The effect of enzyme to substrate ratio, initial lactose concentration and temperature has been s... more The effect of enzyme to substrate ratio, initial lactose concentration and temperature has been studied for the kinetically controlled reaction of lactose transgalactosylation with Aspergillus oryzae ␤-galactosidase, to produce prebiotic galacto-oligosaccharides (GOS). Enzyme to substrate ratio had no significant effect on maximum yield and specific productivity. Galacto-oligosaccharide syntheses at very high lactose concentrations (40, 50 and 60%, w/w, lactose monohydrate) were evaluated at different temperatures (40, 47.5 and 55 • C). Within these ranges, lactose could be found as a supersaturated solution or a heterogeneous system with precipitated lactose, resulting in significant effect on GOS synthesis. An increase in initial lactose concentration produced a slight increase in maximum yield as long as lactose remained dissolved. Increase in temperature produced a slight decrease in maximum yield and an increase in specific productivity when supersaturation of lactose occurred during reaction. Highest yield of 29 g GOS/100 g lactose added was obtained at a lactose monohydrate initial concentration of 50% (w/w) and 47.5 • C. Highest specific productivity of 0.38 g GOS h −1 mg enzyme −1 was obtained at lactose monohydrate initial concentration of 40% (w/w) and 55 • C, where a maximum yield of 27 g GOS/100 g lactose added was reached. This reflects the complex interplay between temperature and initial lactose concentration on the reaction of synthesis. When lactose precipitation occurred, values of yields and specific productivities lower than 22 g GOS/100 g lactose added and 0.03 g GOS h −1 mg enzyme −1 were obtained, respectively.

Energy & Fuels, 2006

Biodiesel obtained by transesterification of soy oil with methanol was isomerized in the liquid p... more Biodiesel obtained by transesterification of soy oil with methanol was isomerized in the liquid phase at 125-275°C using solid acid catalysts. The purpose of this work was to improve the cold flow properties of biodiesel by inhibiting the formation of crystals. Crystallization was analyzed by means of the measurement of the cloud point of the fuel. Tested catalysts were SO 4 2--ZrO 2 and H-mordenite. At a temperature of reaction (T r ) lower than 125°C, the catalytic activity was negligible. At T r > 200°C, the reaction rate was greatly accelerated, but the cetane number was also decreased and the amount of coke deposits was greatly increased. While reacting biodiesel at 150-200°C, a small decrease (4-6.5°C) of the cloud point was obtained without a meaningful decrease of the cetane index. Best results were obtained with SO 4 2--ZrO 2 at 125°C. Isomerization had both positive and negative effects on fuel properties: it reduced the cloud point but also increased the viscosity and decreased the cetane index. Due to the different reactivity between the saturated fraction (estearates, palmitates) and the unsaturated one (linoleates, linolenoates, oleates), an adequate control of the degree of isomerization was only possible by performing a previous fractionation step. A good combination was obtained by reacting the saturates rich fraction at 200°C over H-mordenite and the unsaturated rich fraction at 150°C over SO 4 2--ZrO 2 . The fuel obtained by mixing both reacted fractions had a cetane index of 49.5 and a cloud point of -2°C. However, this combined approach yields only a little benefit compared to those obtained with the single reaction over SO 4 2--ZrO 2 at 125°C.

Energy & Fuels, 2006

This report studies the feasibility of carrying out the elimination of benzene contained in paraf... more This report studies the feasibility of carrying out the elimination of benzene contained in paraffinic feedstocks (3-15%) with economy of equipment and sparing of pretreatment steps by hydrogenating benzene to cyclohexane and isomerizing partly the latter to ...

Catalysis Today, 2008

Pt-Re-Ge/gAl 2 O 3 catalysts were prepared by the catalytic reduction method using different impr... more Pt-Re-Ge/gAl 2 O 3 catalysts were prepared by the catalytic reduction method using different impregnation media (H 2 O, HCl and NH 3 ) and different Ge contents (0.0, 0.1, 0.3, 1.0 and 2.0%). The influence of these preparation parameters on the activity for n-heptane conversion and the selectivity to toluene at atmospheric pressure was assessed. The catalysts were also characterized by ICP-AES, temperature programmed reduction, pyridine temperature programmed desorption and CO pulse chemisorption. The results show that as the pH is increased the Ge content increases and the catalysts present a lower hydrogenolytic activity and a lower toluene selectivity. Ge addition modifies both metal and acid functions. The catalyst with minimum Ge content prepared using water as impregnation medium has the best performance. #

Biotechnology and Bioengineering, 2011

A pseudo steady-state model for the kinetically controlled synthesis of galacto-oligosaccharides ... more A pseudo steady-state model for the kinetically controlled synthesis of galacto-oligosaccharides (GOS) with Aspergillus oryzae β-galactosidase is presented. The model accounts for the dynamics of lactose consumption and production of galactose, glucose, di, tri, tetra, and penta-oligosaccharides during the synthesis, being able to describe the total GOS content in the reaction medium at the experimental conditions evaluated. Experimental results show that the formation of GOS containing only galactose residues is significant at high conversions of substrate, which was taken into account in the model. The formation of enzyme transition complexes was considered and reasonable assumptions were made to reduce the number of parameters to be determined. The model developed has 8 parameters; 2 of them were experimentally determined and the other 6 were estimated by fitting to the experimental data using multiresponse regression. Temperature effect on kinetic and affinity constants was determined in the range from 40 to 55°C, and the data were fitted to Arrhenius type equation. Parameters of the proposed model are independent from the enzyme load in the reaction medium and, differently from previously reported models, they have a clear biochemical meaning. The magnitude of the kinetic and affinity constants of the enzyme suggests that the liberation of galactose from the galactosyl-enzyme complex is a very slow reaction and such complex is driven into GOS formation. It also suggests that the affinity for sugars of the galactosyl-enzyme complex is higher than that of the free enzyme.

Annals of Biomedical Engineering, 2003

It is a long-standing mystery why erythrocyte actin filaments in the junctional complex (JC) are ... more It is a long-standing mystery why erythrocyte actin filaments in the junctional complex (JC) are uniformly ∼37 nm and the membrane skeleton consists of hexagons. We have previously proposed that a “molecular ruler” formed by E-tropomodulin and tropomyosin 5 or 5b functions to generate protofilaments of 12 G actin under mechanical stress. Here, we illustrate that intrinsic properties of actin filaments, e.g., turns, chemical bonds, and dimensions of the helix, also favor fragmentation into protofilaments under mechanical stress. We further construct a mechanical model in that a pair of G actin is wrapped around by a split α and β spectrin, which may spin to two potential positions, and stabilize to one when the tail end is restricted. A reinforced protofilament may function as a mechanical axis to anchor three (top, middle, and bottom) pairs of Sp. Each Sp pair may wrap around the protofilament with a wide dihedral angle (∼166.2°) and a minimal axial distance (2.75 nm). Such three Sp pairs may spiral down (right handed) the protofilament from the pointed end with a dihedral angle of ∼55.4° in between the Sp pairs. This first three-dimensional model of JC may explain the hexagonal geometry of the erythrocyte membrane skeleton. © 2003 Biomedical Engineering Society. PAC2003: 8716Ka, 8716Dg, 8714Ee, 8716Ac

European Journal of Engineering Education, 2006

The paper focuses on educational projects developed in the ETSII (Escuela Técnica Superior de Ing... more The paper focuses on educational projects developed in the ETSII (Escuela Técnica Superior de Ingenieros Industriales) of the Polytechnic University of Madrid during the past few years. These projects were developed as new tools for enhancing the active role of students, for improving practical teaching, especially by means of virtual laboratories and different sets of problems and exercises, and for promoting self-learning. The paper analyses the use of ICT in teaching, with the case of a developed e-learning platform as a tracking system for subjects. The paper concludes by discussing the new educational trends in the Centre, devoted to develop an active role of students by activities such as peer mentoring and laboratory monitors programs, and competitions for achieving multidisciplinary engineering challenges.

Biotechnology Progress, 2014

Fed-batch synthesis of galacto-oligosaccharides (GOS) from lactose with β-galactosidase from Aspe... more Fed-batch synthesis of galacto-oligosaccharides (GOS) from lactose with β-galactosidase from Aspergillus oryzae was evaluated experimentally and reaction yield was maximized via optimal control technique. The optimal lactose and enzyme feed flow rate profiles were determined using a model for GOS synthesis previously reported by the authors. Experimentally it was found that fed-batch synthesis allowed an increase on the maximum total GOS concentration from 115 (batch synthesis) to 218 g L(-1) as consequence of the increase in total sugars concentration from 40 to 58% w/w. Such high concentration of total sugars was not attainable in batch operation because of the low solubility of lactose at the reaction temperature (40°C). Simulations predicted a GOS yield of 32.5 g g(-1) in fed-batch synthesis under optimal conditions, while experimentally the same yield as in batch synthesis was obtained (28 g g(-1) ). Besides, an enrichment of total oligosaccharides in GOS with a high polymerization degree (GOS-5 and GOS-6) was observed in the fed-batch synthesis. Experimental profiles for all sugars were similar to the ones predicted by simulation, which supports the use of this methodology for the optimization of GOS synthesis.

Biophysical Journal, 2007

To investigate the nanomechanics of the erythrocyte membrane we developed a hybrid model that cou... more To investigate the nanomechanics of the erythrocyte membrane we developed a hybrid model that couples the actin-spectrin network to the lipid bilayer. This model features a Fourier space Brownian dynamics model of the bilayer, a Brownian dynamics model of the actin protofilament, and a modified wormlike-chain model of the spectrin (including a cable-dynamics model to predict the oscillation in tension). This model enables us to predict the nanomechanics of single or multiple units of the protein network, the lipid bilayer, and the effect of their interactions. The present work is focused on the attitude of the actin protofilament at the equilibrium states coupled with the elevations of the lipid bilayer through their primary linkage at the suspension complex in deformations. Two different actin-spectrin junctions are considered at the junctional complex. With a point-attachment junction, large pitch angles and bifurcation of yaw angles are predicted. Thermal fluctuations at bifurcation may lead to mode-switching, which may affect the network and the physiological performance of the membrane. In contrast, with a wrap-around junction, pitch angles remain small, and the occurrence of bifurcation is greatly reduced. These simulations suggest the importance of threedimensional molecular junctions and the lipid bilayer/protein network coupling on cell membrane mechanics.

Annals of Biomedical Engineering, 2011

Our 3-D model for a junctional complex (JC) in the erythrocyte membrane skeleton proposed that th... more Our 3-D model for a junctional complex (JC) in the erythrocyte membrane skeleton proposed that the helical actin protofilament functions as a mechanical axis for three pairs of ab spectrin (Sp), and each pair wraps around the protofilament in a back-to-back fashion. The distal end of each Sp is further associated with the lipid bilayer by a suspension complex (SC). Here, we detail how splitting and rejoining of ab Sp around a protofilament may form a loop that sustains and equilibrates tension. Sequential association of b and a Sp solves the challenge of constructing multiple loops along the protofilament, and topological connection facilitates their re-association. The wrap-around model minimizes the strain of the actin binding site on b Sp due to tension, redirection, or sliding of intertwined Sp. Pairing Sp balances the opposing forces and provides a mechanism for elastic recovery. The wrap-around junction thus provides mechanical advantages over a point-attachment junction in maintaining the integrity and functionality of the network. Severing a or b Sp may convert a wrapping-around junction to a point-attachment junction. In that case, a ''bow up'' motion of JC during deformation may disturb or flip the overlaid lipid bilayer, and mark stressed erythrocytes for phagocytosis.

Annals of Biomedical Engineering, 2010

Erythrocytes undergo deformations when they transport O 2 and CO 2 across the membrane, yet the 3... more Erythrocytes undergo deformations when they transport O 2 and CO 2 across the membrane, yet the 3D nanomechanics of the skeletal network remains poorly understood. Expanding from our previous single isolated unit, we now simulate networks consisting of 1-10 concentric rings of repeating units in equibiaxial deformation. The networks are organized with (1) a 3D model for a single unit, (2) a wrap-around mode between Sp and actin protofilament in the intra-unit interaction, and (3) a random inter-unit connectivity. These assumptions permit efficient five-degreesof-freedom (5DOF) simulations when up to 30 pN of radial forces are applied to the boundary spectrin (Sp) and the center and other units are analyzed. As 6 Sp balance their tensions, hexagonal units become irregular. While actin protofilaments remain tangent to the network, their yaw (F) angles change drastically with addition of neighboring units or an Sp unfolding. It is anticipated that during deformation, transmembrane complexes associated with the network move laterally through the lipid bilayer and increase the diffusion of molecules across the membrane. When protofilament/Sp sweeps under the lipid bilayer, they mix up the submembrane concentration gradient. Thus, the nanomechanics of actin protofilaments and Sp may enhance the transport of molecules during erythrocyte deformation.

Biodiesel - Feedstocks and Processing Technologies, 2011

Applied Catalysis A-general, 1998

SO42−

Química Nova, 2012

ABSTRACT A study of the different hydrocarbon reactions over Ni doped WO 3-ZrO 2 catalysts was pe... more ABSTRACT A study of the different hydrocarbon reactions over Ni doped WO 3-ZrO 2 catalysts was performed. Ni was found as NiO at low Ni concentration while at high Ni concentrations a small fraction was present as a metal. For both cases, Ni strongly ...

Journal of Chemical Technology & Biotechnology, 2012

ABSTRACT BACKGROUND: Partial hydrogenation of alkynes have industrial and academic relevance on a... more ABSTRACT BACKGROUND: Partial hydrogenation of alkynes have industrial and academic relevance on a large scale; industries such as petrochemical, pharmacology and agrochemical use these compounds as raw material. Typical commercial catalysts contains palladium. Finding an economic, active and selective catalyst for the production of alkenes via partial hydrogenation of alkynes is thus an important challenge. On the other hand, the literature on kinetic studies of partial hydrogenation of heavy alkynes is scarce. So the main objectives of this work were to prepare a cheaper catalyst based on low W loading, and study the kinetic of the partial hydrogenation of 1-heptyne. A pseudo-homogeneous and six heterogeneous kinetic models were analyzed. The catalyst was characterized by ICP, XPS, DRX, TPR and hydrogen chemisorption techniques. RESULTS: The characterization results indicate that only WOx species are present on the alumina surface. The WOx/Al2O3 catalyst was active and selective for producing 1-heptene even at low reaction temperatures, the partial hydrogenation of 1-heptyne proceeds via two irreversible reactions in parallel. CONCLUSION: The best fit of the experimental data was achieved with a heterogeneous Langmuir-Hinshelwood-Hougen-Watson model in which the rate controlling step is the dissociative adsorption of hydrogen. The activation energy was estimated as EH2 = 34.8 kJ mol−1. Copyright © 2012 Society of Chemical Industry

Journal of Chemical Technology & Biotechnology, 2014

... 178-186, 1998 Research Paper Kinetics of Liquid Phase Selective Hydrogénation of Methylacetyl... more ... 178-186, 1998 Research Paper Kinetics of Liquid Phase Selective Hydrogénation of Methylacetylene and Propadiene in C3 Streams Hakan UYGUR1, Süheyda AT ALA Y2 ... Re^Re^Sc05 -L (7) 0.2 eL is the liquid hold-up in the bed and given by the correlation (Tarhan, ...

Journal of Catalysis, 1999

A study of the deactivation of SO 2− 4 -ZrO 2 catalysts during isomerization of n-butane showed t... more A study of the deactivation of SO 2− 4 -ZrO 2 catalysts during isomerization of n-butane showed that a small amount of a carbonaceous deposit (1-1.2%) is formed. A high proportion of this deposit is produced during the first minutes of the reaction and it seems to be responsible for the initial short-term catalyst deactivation but it is doubtful whether it is connected to the long-term loss of activity. Activity in isomerization of n-C 4 was very sensitive to activation conditions while coking was more consistent; in all cases, SZ catalysts had a limiting content of 1 to 1.2% coke when fully deactivated. In an oxygen flow, the coke deposit could be burned at 500 • C, but it could also easily be removed by stripping with an oxygen-free inert gas at higher temperatures. In the latter case, the coke was oxidized by the catalyst surface groups, most likely sulfate. The coke was soluble only in polar solvents (methanol, pyridine) and was highly insoluble in benzene and hexane. An FD-mass spectrum of the soluble fraction of the coke indicated the presence of compounds with m/z up to 2700, but the distribution was concentrated around m/z = 350 to 500. The latter value, when compared with the small amount of total carbon, indicates that only a small fraction of the surface sites was affected by the coke, or that deactivation proceeded by a mechanism other than site blocking. A surface reduction process by the reacting hydrocarbon may also be linked to the activity loss. ESR results indicated that the catalyst was also reduced during the reaction; the intensity of the Zr 3+ signal was higher on the coked catalysts. The probable concurrence of reduction could explain the long-term activity decline which seems not to be directly linked to the coking process.

Energy & Fuels, 2006

Biodiesel obtained by transesterification of soy oil with methanol was isomerized in the liquid p... more Biodiesel obtained by transesterification of soy oil with methanol was isomerized in the liquid phase at 125-275°C using solid acid catalysts. The purpose of this work was to improve the cold flow properties of biodiesel by inhibiting the formation of crystals. Crystallization was analyzed by means of the measurement of the cloud point of the fuel. Tested catalysts were SO 4 2--ZrO 2 and H-mordenite. At a temperature of reaction (T r ) lower than 125°C, the catalytic activity was negligible. At T r > 200°C, the reaction rate was greatly accelerated, but the cetane number was also decreased and the amount of coke deposits was greatly increased. While reacting biodiesel at 150-200°C, a small decrease (4-6.5°C) of the cloud point was obtained without a meaningful decrease of the cetane index. Best results were obtained with SO 4 2--ZrO 2 at 125°C. Isomerization had both positive and negative effects on fuel properties: it reduced the cloud point but also increased the viscosity and decreased the cetane index. Due to the different reactivity between the saturated fraction (estearates, palmitates) and the unsaturated one (linoleates, linolenoates, oleates), an adequate control of the degree of isomerization was only possible by performing a previous fractionation step. A good combination was obtained by reacting the saturates rich fraction at 200°C over H-mordenite and the unsaturated rich fraction at 150°C over SO 4 2--ZrO 2 . The fuel obtained by mixing both reacted fractions had a cetane index of 49.5 and a cloud point of -2°C. However, this combined approach yields only a little benefit compared to those obtained with the single reaction over SO 4 2--ZrO 2 at 125°C.

Enzyme and Microbial Technology, 2012

The effect of enzyme to substrate ratio, initial lactose concentration and temperature has been s... more The effect of enzyme to substrate ratio, initial lactose concentration and temperature has been studied for the kinetically controlled reaction of lactose transgalactosylation with Aspergillus oryzae ␤-galactosidase, to produce prebiotic galacto-oligosaccharides (GOS). Enzyme to substrate ratio had no significant effect on maximum yield and specific productivity. Galacto-oligosaccharide syntheses at very high lactose concentrations (40, 50 and 60%, w/w, lactose monohydrate) were evaluated at different temperatures (40, 47.5 and 55 • C). Within these ranges, lactose could be found as a supersaturated solution or a heterogeneous system with precipitated lactose, resulting in significant effect on GOS synthesis. An increase in initial lactose concentration produced a slight increase in maximum yield as long as lactose remained dissolved. Increase in temperature produced a slight decrease in maximum yield and an increase in specific productivity when supersaturation of lactose occurred during reaction. Highest yield of 29 g GOS/100 g lactose added was obtained at a lactose monohydrate initial concentration of 50% (w/w) and 47.5 • C. Highest specific productivity of 0.38 g GOS h −1 mg enzyme −1 was obtained at lactose monohydrate initial concentration of 40% (w/w) and 55 • C, where a maximum yield of 27 g GOS/100 g lactose added was reached. This reflects the complex interplay between temperature and initial lactose concentration on the reaction of synthesis. When lactose precipitation occurred, values of yields and specific productivities lower than 22 g GOS/100 g lactose added and 0.03 g GOS h −1 mg enzyme −1 were obtained, respectively.

Energy & Fuels, 2006

Biodiesel obtained by transesterification of soy oil with methanol was isomerized in the liquid p... more Biodiesel obtained by transesterification of soy oil with methanol was isomerized in the liquid phase at 125-275°C using solid acid catalysts. The purpose of this work was to improve the cold flow properties of biodiesel by inhibiting the formation of crystals. Crystallization was analyzed by means of the measurement of the cloud point of the fuel. Tested catalysts were SO 4 2--ZrO 2 and H-mordenite. At a temperature of reaction (T r ) lower than 125°C, the catalytic activity was negligible. At T r > 200°C, the reaction rate was greatly accelerated, but the cetane number was also decreased and the amount of coke deposits was greatly increased. While reacting biodiesel at 150-200°C, a small decrease (4-6.5°C) of the cloud point was obtained without a meaningful decrease of the cetane index. Best results were obtained with SO 4 2--ZrO 2 at 125°C. Isomerization had both positive and negative effects on fuel properties: it reduced the cloud point but also increased the viscosity and decreased the cetane index. Due to the different reactivity between the saturated fraction (estearates, palmitates) and the unsaturated one (linoleates, linolenoates, oleates), an adequate control of the degree of isomerization was only possible by performing a previous fractionation step. A good combination was obtained by reacting the saturates rich fraction at 200°C over H-mordenite and the unsaturated rich fraction at 150°C over SO 4 2--ZrO 2 . The fuel obtained by mixing both reacted fractions had a cetane index of 49.5 and a cloud point of -2°C. However, this combined approach yields only a little benefit compared to those obtained with the single reaction over SO 4 2--ZrO 2 at 125°C.

Energy & Fuels, 2006

This report studies the feasibility of carrying out the elimination of benzene contained in paraf... more This report studies the feasibility of carrying out the elimination of benzene contained in paraffinic feedstocks (3-15%) with economy of equipment and sparing of pretreatment steps by hydrogenating benzene to cyclohexane and isomerizing partly the latter to ...

Catalysis Today, 2008

Pt-Re-Ge/gAl 2 O 3 catalysts were prepared by the catalytic reduction method using different impr... more Pt-Re-Ge/gAl 2 O 3 catalysts were prepared by the catalytic reduction method using different impregnation media (H 2 O, HCl and NH 3 ) and different Ge contents (0.0, 0.1, 0.3, 1.0 and 2.0%). The influence of these preparation parameters on the activity for n-heptane conversion and the selectivity to toluene at atmospheric pressure was assessed. The catalysts were also characterized by ICP-AES, temperature programmed reduction, pyridine temperature programmed desorption and CO pulse chemisorption. The results show that as the pH is increased the Ge content increases and the catalysts present a lower hydrogenolytic activity and a lower toluene selectivity. Ge addition modifies both metal and acid functions. The catalyst with minimum Ge content prepared using water as impregnation medium has the best performance. #

Biotechnology and Bioengineering, 2011

A pseudo steady-state model for the kinetically controlled synthesis of galacto-oligosaccharides ... more A pseudo steady-state model for the kinetically controlled synthesis of galacto-oligosaccharides (GOS) with Aspergillus oryzae β-galactosidase is presented. The model accounts for the dynamics of lactose consumption and production of galactose, glucose, di, tri, tetra, and penta-oligosaccharides during the synthesis, being able to describe the total GOS content in the reaction medium at the experimental conditions evaluated. Experimental results show that the formation of GOS containing only galactose residues is significant at high conversions of substrate, which was taken into account in the model. The formation of enzyme transition complexes was considered and reasonable assumptions were made to reduce the number of parameters to be determined. The model developed has 8 parameters; 2 of them were experimentally determined and the other 6 were estimated by fitting to the experimental data using multiresponse regression. Temperature effect on kinetic and affinity constants was determined in the range from 40 to 55°C, and the data were fitted to Arrhenius type equation. Parameters of the proposed model are independent from the enzyme load in the reaction medium and, differently from previously reported models, they have a clear biochemical meaning. The magnitude of the kinetic and affinity constants of the enzyme suggests that the liberation of galactose from the galactosyl-enzyme complex is a very slow reaction and such complex is driven into GOS formation. It also suggests that the affinity for sugars of the galactosyl-enzyme complex is higher than that of the free enzyme.