Especificaciones alternativas de la estructura temporal de volatilidades

En este trabajo se describe y analiza la estructura temporal de volatilidades instantáneas de los tipos de interés forward correspondientes al mercado español durante el periodo 1999-2002. Este estudio se realiza en el contexto del Modelo de Mercado LIBOR proponiéndose, además, una nueva fórmula para describir la volatilidad instantánea de los tipos de interés forward con parámetros fácilmente interpretables. Junto a este modelo se calibran otros dos alternativos propuestos en la literatura que son utilizados como benchmark para contrastar su validez. Esta contrastación se lleva a cabo a partir de datos del mercado de caps proporcionando resultados satisfactorios para el modelo aquí presentado.In this paper we examine the term structure of instantaneous volatilities of forward rates for the Spanish market covering the period 1999-2002. This analysis is undertaken within the LIBOR Market Model framework. A new model with easily understandable parameters is proposed to describe the behaviour of the instantaneous volatility of forward rates. Two other alternatives are calibrated using data from the cap market and used as benchmarks to test the accuracy of the new [email protected]

Theoretical site-directed mutagenesis. The Asp168Ala mutant of L-Lactate Dehydrogenase

The reduction of pyruvate to lactate catalyzed by the L-Lactate dehydrogenase has been studied in this paper by means of hybrid Quantum Mechanical / Molecular Mechanical simulations. A very flexible molecular model consisting on the full tetramer of the enzyme, together with the cofactor NADH, the substrate and solvent water molecules has allowed to theoretically mimic site directed mutagenesis studies, most of them previously experimentally performed. The potential energy surfaces obtained for every single mutation, compared with the one corresponding to the native enzyme, have been used to trace the possible reaction pathways and to locate and characterize the structures corresponding to the stationary points. The analysis of the results has been a very powerful tool to conclude about the role of key residues on the vacuole formed in the active site of the enzyme. Our results are in very good agreement with the previous conclusions derived from site directed mutagenesis. This strategy can be extrapolated to other enzyme systems thus opening the door of a very promising methodology that, in combination with the appropriate experimental technique, will enable us to describe enzyme catalysis phenomenon and the particular role of the residues that form the protein. This knowledge placed us in a privileged position to modify the activity of enzymes and to propose efficient inhibitor

Computational design of biological catalysts

The purpose of this tutorial review is to illustrate the way to design new and powerful catalysts. The first possibility to get a biological catalyst for a given chemical process is to use existing enzymes that catalyze related reactions. The second possibility is the use of immune systems that recognize stable molecules resembling the transition structure of the target reaction. We finally show how computational techniques are able to provide an enormous quantity of information, providing clues to guide the development of new biological catalyst

A quantum mechanics-molecular mechanics study of dissociative electron transfer : The methylchloride radical anion in aqueous solution

The dissociative electron transfer reaction CH3Cl+e−→CH3•+Cl− in aqueous solution is studied by using a QM/MM method. In this work the quantum subsystem (a methylchloride molecule plus an electron) is described using density functional theory while the solvent (300 water molecules) is described using the TIP3P classical potential. By means of molecular dynamics simulations and the thermodynamic integration technique we obtained the potential of mean force (PMF) for the carbon–chlorine bond dissociation of the neutral and radical anion species. Combining these two free energy curves we found a quadratic dependence of the activation free energy on the reaction free energy in agreement with Marcus’ relationship, originally developed for electron transfer processes not involving bond breaking. We also investigated dynamical aspects by means of 60 dissociative trajectories started with the addition of an extra electron to different configurations of a methylchloride molecule in solution. The PMF shows the existence of a very flat region, in which the system is trapped during some finite time if the quantum subsystem quickly losses its excess kinetic energy transferring it to the solvent molecules. One of the most important factors determining the effectiveness of this energy transfer seems to be the existence of close contacts (hydrogen bonds) between the solute and the [email protected] [email protected]

Diseño computacional de catalizadores biológicos

Enzymes are a source of inspiration for the design of new and powerful industrial catalysts able to work, in principle, in mild conditions of pressure, temperature and solvents. The Transition State of the reaction is the keystone to understand how enzymes are able to speed up reactions. This information can be then employed to design protein structures or successful mutations in the active site of proteins leading to the synthesis of new biocatalysts. In this paper we show advances in this field, classified according to the starting material: catalytic antibodies, modified enzymes and enzymes designed de novo.Las enzimas son una fuente de inspiración para el diseño de nuevos catalizadores con usos industriales que puedan funcionar en condiciones suaves de presión, temperatura y disolventes. El estado de transición de la reacción que se pretende catalizar, es la pieza clave para comprender cómo las enzimas son capaces de acelerar las reacciones. A partir de esta información se pueden proponer estructuras proteicas, o posibles mutaciones en el centro activo de proteínas, conduciendo a la síntesis de nuevos biocatalizadores. En este artículo presentamos los avances en este campo, clasificados en función del material de partida: anticuerpos catalíticos, enzimas modificadas y enzimas diseñadas de novo

Aminoacid zwitterions in solution : Geometric, energetic, and vibrational analysis using density functional theory-continuum model calculations

Glycine and alanine aminoacids chemistry in solution is explored using a hybrid three parameters density functional (B3PW91) together with a continuum model. Geometries, energies, and vibrational spectra of glycine and alanine zwitterions are studied at the B3PW91/6-31+G∗∗ level and the results compared with those obtained at the HF and MP2/6-31+G∗∗ levels. Solvents effects are incorporated by means of an ellipsoidal cavity model with a multipolar expansion (up to sixth order) of the solute’s electrostatic potential. Our results confirm the validity of the B3PW91 functional for studying aminoacid chemistry in solution. Taking into account the more favorable scaling behavior of density functional techniques with respect to correlated ab initio methods these studies could be extended to larger [email protected] ; [email protected]

Dependence of enzyme reaction mechanism on protonation state of titratable residues and QM level description: lactate dehydrogenase

We have studied the dependence of the chemical reaction mechanism of L-lactate dehydrogenase (LDH) on the protonation state of titratable residues and on the level of the quantum mechanical (QM) description by means of hybrid quantum-mechanical/molecular-mechanical (QM/MM) methods; this methodology has allowed clarification of the timing of the hydride transfer and proton transfer components that hitherto had not been possible to state definitively.Ferrer Castillo, Silvia, [email protected], Silla Santos, Estanislao, [email protected] ; Tuñon Garcia de Vicuña, Ignacio Nilo, [email protected]