Angel Garcia - Academia.edu (original) (raw)

Papers by Angel Garcia

Research paper thumbnail of A simple score normalisation technique for multimodal biometric authentication

International Journal of Biometrics, 2009

In multimodal biometric authentication, the unimodal scores are used to produce the final decisio... more In multimodal biometric authentication, the unimodal scores are used to produce the final decision, following the score fusion approach. Researchers have often decomposed the score fusion problem into two steps: a'score normalisation'and a'fusion'step. This paper ...

Research paper thumbnail of The Pressure Dependence of Hydrophobic Interactions is Consistent with the Observed Pressure Denaturation of Proteins

Proceedings of The National Academy of Sciences, 1998

Proteins can be denatured by pressures of a few hundred MPa. This finding apparently contradicts ... more Proteins can be denatured by pressures of a few hundred MPa. This finding apparently contradicts the most widely used model of protein stability, where the formation of a hydrophobic core drives protein folding. The pressure denaturation puzzle is resolved by focusing on the pressure-dependent transfer of water into the protein interior, in contrast to the transfer of nonpolar residues into water, the approach commonly taken in models of protein unfolding. Pressure denaturation of proteins can then be explained by the pressure destabilization of hydrophobic aggregates by using an information theory model of hydrophobic interactions. Pressure-denatured proteins, unlike heat-denatured proteins, retain a compact structure with water molecules penetrating their core. Activation volumes for hydrophobic contributions to protein folding and unfolding kinetics are positive. Clathrate hydrates are predicted to form by virtually the same mechanism that drives pressure denaturation of proteins.

Research paper thumbnail of Folding Funnels and Frustration in Off-Lattice Minimalist Protein Landscapes

Proceedings of The National Academy of Sciences, 1998

A full quantitative understanding of the protein folding problem is now becoming possible with th... more A full quantitative understanding of the protein folding problem is now becoming possible with the help of the energy landscape theory and the protein folding funnel concept. Good folding sequences have a landscape that resembles a rough funnel where the energy bias towards the native state is larger than its ruggedness. Such a landscape leads not only to fast folding and stable native conformations but, more importantly, to sequences that are robust to variations in the protein environment and to sequence mutations. In this paper, an off-lattice model of sequences that fold into a ␤-barrel native structure is used to describe a framework that can quantitatively distinguish good and bad folders. The two sequences analyzed have the same native structure, but one of them is minimally frustrated whereas the other one exhibits a high degree of frustration.

Research paper thumbnail of alpha Helical stabilization by side chain shielding of backbone hydrogen bonds

Proceedings of The National Academy of Sciences, 2002

We study atomic models of the thermodynamics of the structural transition of peptides that form a... more We study atomic models of the thermodynamics of the structural transition of peptides that form alpha-helices. The effect of sequence variation on alpha-helix formation for alanine-rich peptides, Ac-Ala21-methyl amide (A21) and Ac-A5 (AAARA)3A-methyl amide (Fs peptide), is investigated by atomic simulation studies of the thermodynamics of the helix-coil transition in explicit water. The simulations show that the guanidinium group in the Arg side chains in the Fs peptide interacts with the carbonyl group four amino acids upstream in the chain and desolvates backbone hydrogen bonds. This desolvation can be directly correlated with a higher probability of hydrogen bond formation. We find that Fs has higher helical content than A21 at all temperatures. A small modification in the amber force field reproduces the experimental helical content and helix-coil transition temperatures for the Fs peptide.

Research paper thumbnail of Structure and texture of AlPO4-cesium oxide (20 wt.%) catalysts obtained by impregnation with cesium chloride

Reaction Kinetics and Catalysis Letters, 1998

A1PO4-cesium oxide (20 wt.%) materials retain a low degree of crystallinity on calcination at 873... more A1PO4-cesium oxide (20 wt.%) materials retain a low degree of crystallinity on calcination at 873 K for 3 h. After DTA measurements (1423 K), AIPO4 crystallizes (tridymite form). Furthermore, DRIYF spectroscopy shows that the P-OH stretching vibration (at 3670 cm "1) of AIPO4 support disappears upon cesium oxide loading. Moreover, AI and P atoms remain in tetrahedral coordination as in unmodified AIPO4. Furthermore, the incorporation of cesium oxide leads, simultaneously, to a progressive decrease in surface area and pore volume as well as to an increase in the most frequently occurring pore radius.

Research paper thumbnail of Chemical transformations of glucose to value added products using Cu-based catalytic systems

Physical Chemistry Chemical Physics, 2013

Cu nanoparticles have been supported by two types of aluminosilicate materials with and without Z... more Cu nanoparticles have been supported by two types of aluminosilicate materials with and without Zn in their composition in view of their application in the microwave-assisted conversion of glucose to valuable products via tandem formic acid-promoted dehydration (to 5-hydroxymethylfurfural--HMF) and further selective hydrogenation to 5-methylfurfuryl alcohol (MFA). Results show that interesting selectivities (up to 60% to MFA or HMF) could be achieved after short times of reaction (typically 2-30 min) using Cu-containing nanomaterials. Zn was found to play an interesting role in the selectivity to reduced products, even if present in very small quantities (0.2 wt%).

Research paper thumbnail of Structure, Texture, Surface Acidity, and Catalytic Activity of AlPO4–ZrO2(5–50 wt% ZrO2) Catalysts Prepared by a Sol–Gel Procedure☆

Journal of Catalysis, 1998

A series of AlPO 4 -ZrO 2 (APZr) systems with various zirconia loadings (5-50 wt%) were prepared ... more A series of AlPO 4 -ZrO 2 (APZr) systems with various zirconia loadings (5-50 wt%) were prepared by sol-gel deposition of zirconia onto AlPO 4 and characterized by TGA /DTA, XRD, DRIFT, laser-Raman spectroscopy, SEM-EDX, XPS, 27 Al and 31 P MAS NMR, and nitrogen adsorption. Surface acid characterization was carried out through pyridine chemisorption and cyclohexene skeletal isomerization reaction. Addition of ZrO 2 onto AlPO 4 prevented the formation of monoclinic zirconia and increased the temperature of crystallization into the tetragonal form, so that APZr systems were still amorphous after calcination at 1073 K. This higher thermal stability was responsible for its large surface area as well as pore volume in relation to pure components. SEM showed nonhomogeneous distribution in morphology, texture, and particle size. Also, EDX and XPS indicated that the surface concentration ratios were practically the same as the expected values of stoichiometric composition. Moreover, 27 Al and 31 P MAS NMR showed that the local structure of the AlPO 4 support did not change with zirconia. Good correlations were obtained between catalytic activities in cyclohexene skeletal isomerization and surface acid densities of AlPO 4 -ZrO 2 systems (as determined by pyridine chemisorption at 373 and 573 K).

Research paper thumbnail of Spanish Sepiolite Clay as a New Heterogeneous Catalyst for the Tetrahydropyranylation of Alcohols and Phenols

Synthetic Communications, 1994

... Titre du document / Document title. SPANISH SEPIOLITE CLAY AS A NEW HETEROGENEOUS CATALYST FO... more ... Titre du document / Document title. SPANISH SEPIOLITE CLAY AS A NEW HETEROGENEOUS CATALYST FOR THE TETRAHYDROPYRANYLATION OF ALCOHOLS AND PHENOLS. Auteur(s) / Author(s). CAMPELO JM ; GARCIA A. ; LAFONT F. ; LUNA D. ; MARINAS JM ; ...

Research paper thumbnail of A simple score normalisation technique for multimodal biometric authentication

International Journal of Biometrics, 2009

In multimodal biometric authentication, the unimodal scores are used to produce the final decisio... more In multimodal biometric authentication, the unimodal scores are used to produce the final decision, following the score fusion approach. Researchers have often decomposed the score fusion problem into two steps: a'score normalisation'and a'fusion'step. This paper ...

Research paper thumbnail of The Pressure Dependence of Hydrophobic Interactions is Consistent with the Observed Pressure Denaturation of Proteins

Proceedings of The National Academy of Sciences, 1998

Proteins can be denatured by pressures of a few hundred MPa. This finding apparently contradicts ... more Proteins can be denatured by pressures of a few hundred MPa. This finding apparently contradicts the most widely used model of protein stability, where the formation of a hydrophobic core drives protein folding. The pressure denaturation puzzle is resolved by focusing on the pressure-dependent transfer of water into the protein interior, in contrast to the transfer of nonpolar residues into water, the approach commonly taken in models of protein unfolding. Pressure denaturation of proteins can then be explained by the pressure destabilization of hydrophobic aggregates by using an information theory model of hydrophobic interactions. Pressure-denatured proteins, unlike heat-denatured proteins, retain a compact structure with water molecules penetrating their core. Activation volumes for hydrophobic contributions to protein folding and unfolding kinetics are positive. Clathrate hydrates are predicted to form by virtually the same mechanism that drives pressure denaturation of proteins.

Research paper thumbnail of Folding Funnels and Frustration in Off-Lattice Minimalist Protein Landscapes

Proceedings of The National Academy of Sciences, 1998

A full quantitative understanding of the protein folding problem is now becoming possible with th... more A full quantitative understanding of the protein folding problem is now becoming possible with the help of the energy landscape theory and the protein folding funnel concept. Good folding sequences have a landscape that resembles a rough funnel where the energy bias towards the native state is larger than its ruggedness. Such a landscape leads not only to fast folding and stable native conformations but, more importantly, to sequences that are robust to variations in the protein environment and to sequence mutations. In this paper, an off-lattice model of sequences that fold into a ␤-barrel native structure is used to describe a framework that can quantitatively distinguish good and bad folders. The two sequences analyzed have the same native structure, but one of them is minimally frustrated whereas the other one exhibits a high degree of frustration.

Research paper thumbnail of alpha Helical stabilization by side chain shielding of backbone hydrogen bonds

Proceedings of The National Academy of Sciences, 2002

We study atomic models of the thermodynamics of the structural transition of peptides that form a... more We study atomic models of the thermodynamics of the structural transition of peptides that form alpha-helices. The effect of sequence variation on alpha-helix formation for alanine-rich peptides, Ac-Ala21-methyl amide (A21) and Ac-A5 (AAARA)3A-methyl amide (Fs peptide), is investigated by atomic simulation studies of the thermodynamics of the helix-coil transition in explicit water. The simulations show that the guanidinium group in the Arg side chains in the Fs peptide interacts with the carbonyl group four amino acids upstream in the chain and desolvates backbone hydrogen bonds. This desolvation can be directly correlated with a higher probability of hydrogen bond formation. We find that Fs has higher helical content than A21 at all temperatures. A small modification in the amber force field reproduces the experimental helical content and helix-coil transition temperatures for the Fs peptide.

Research paper thumbnail of Structure and texture of AlPO4-cesium oxide (20 wt.%) catalysts obtained by impregnation with cesium chloride

Reaction Kinetics and Catalysis Letters, 1998

A1PO4-cesium oxide (20 wt.%) materials retain a low degree of crystallinity on calcination at 873... more A1PO4-cesium oxide (20 wt.%) materials retain a low degree of crystallinity on calcination at 873 K for 3 h. After DTA measurements (1423 K), AIPO4 crystallizes (tridymite form). Furthermore, DRIYF spectroscopy shows that the P-OH stretching vibration (at 3670 cm "1) of AIPO4 support disappears upon cesium oxide loading. Moreover, AI and P atoms remain in tetrahedral coordination as in unmodified AIPO4. Furthermore, the incorporation of cesium oxide leads, simultaneously, to a progressive decrease in surface area and pore volume as well as to an increase in the most frequently occurring pore radius.

Research paper thumbnail of Chemical transformations of glucose to value added products using Cu-based catalytic systems

Physical Chemistry Chemical Physics, 2013

Cu nanoparticles have been supported by two types of aluminosilicate materials with and without Z... more Cu nanoparticles have been supported by two types of aluminosilicate materials with and without Zn in their composition in view of their application in the microwave-assisted conversion of glucose to valuable products via tandem formic acid-promoted dehydration (to 5-hydroxymethylfurfural--HMF) and further selective hydrogenation to 5-methylfurfuryl alcohol (MFA). Results show that interesting selectivities (up to 60% to MFA or HMF) could be achieved after short times of reaction (typically 2-30 min) using Cu-containing nanomaterials. Zn was found to play an interesting role in the selectivity to reduced products, even if present in very small quantities (0.2 wt%).

Research paper thumbnail of Structure, Texture, Surface Acidity, and Catalytic Activity of AlPO4–ZrO2(5–50 wt% ZrO2) Catalysts Prepared by a Sol–Gel Procedure☆

Journal of Catalysis, 1998

A series of AlPO 4 -ZrO 2 (APZr) systems with various zirconia loadings (5-50 wt%) were prepared ... more A series of AlPO 4 -ZrO 2 (APZr) systems with various zirconia loadings (5-50 wt%) were prepared by sol-gel deposition of zirconia onto AlPO 4 and characterized by TGA /DTA, XRD, DRIFT, laser-Raman spectroscopy, SEM-EDX, XPS, 27 Al and 31 P MAS NMR, and nitrogen adsorption. Surface acid characterization was carried out through pyridine chemisorption and cyclohexene skeletal isomerization reaction. Addition of ZrO 2 onto AlPO 4 prevented the formation of monoclinic zirconia and increased the temperature of crystallization into the tetragonal form, so that APZr systems were still amorphous after calcination at 1073 K. This higher thermal stability was responsible for its large surface area as well as pore volume in relation to pure components. SEM showed nonhomogeneous distribution in morphology, texture, and particle size. Also, EDX and XPS indicated that the surface concentration ratios were practically the same as the expected values of stoichiometric composition. Moreover, 27 Al and 31 P MAS NMR showed that the local structure of the AlPO 4 support did not change with zirconia. Good correlations were obtained between catalytic activities in cyclohexene skeletal isomerization and surface acid densities of AlPO 4 -ZrO 2 systems (as determined by pyridine chemisorption at 373 and 573 K).

Research paper thumbnail of Spanish Sepiolite Clay as a New Heterogeneous Catalyst for the Tetrahydropyranylation of Alcohols and Phenols

Synthetic Communications, 1994

... Titre du document / Document title. SPANISH SEPIOLITE CLAY AS A NEW HETEROGENEOUS CATALYST FO... more ... Titre du document / Document title. SPANISH SEPIOLITE CLAY AS A NEW HETEROGENEOUS CATALYST FOR THE TETRAHYDROPYRANYLATION OF ALCOHOLS AND PHENOLS. Auteur(s) / Author(s). CAMPELO JM ; GARCIA A. ; LAFONT F. ; LUNA D. ; MARINAS JM ; ...