Coupling of complex aromatic ring vibrations to solvent through hydrogen bonds: effect of varied on-ring and off-ring hydrogen-bonding substitutions

In this study, we examine the coupling of a complex ring vibration to solvent through hydrogen-bonding interactions. We compare phenylalanine, tyrosine, l-dopa, dopamine, norepinephrine, epinephrine, and hydroxyl-dl-dopa, a group of physiologically important small molecules that vary by single differences in H-bonding substitution. By examination of the temperature dependence of infrared absorptions of these molecules, we show that complex, many-atom vibrations can be coupled to solvent through hydrogen bonds and that the extent of that coupling is dependent on the degree of both on- and off-ring H-bonding substitution. The coupling is seen as a temperature-dependent frequency shift in infrared spectra, but the determination of the physical origin of that shift is based on additional data from temperature-dependent optical experiments and ab initio calculations. The optical experiments show that these small molecules are most sensitive to their immediate H-bonding environment rather than to bulk solvent properties. Ab initio calculations demonstrate H-bond-mediated vibrational coupling for the system of interest and also show that the overall small molecule solvent dependence is determined by a complex interplay of specific interactions and bulk solvation characteristics. Our findings indicate that a full understanding of biomolecule vibrational properties must include consideration of explicit hydrogen-bonding interactions with the surrounding microenvironment.     

Clonazepam quantification in human plasma by high-performance liquid chromatography coupled with electrospray tandem mass spectrometry in a bioequivalence study

A rapid, sensitive and specific method for quantifying clonazepam in human plasma using diazepam as the internal standard (IS) is described. The analyte and the IS were extracted from plasma by liquid-liquid extraction using a hexane/diethylether (20 : 80, v/v) solution. The extracts were analysed by high-performance liquid chromatography coupled with electrospray tandem mass spectrometry (HPLC-MS-MS). Chromatography was performed on a Jones Genesis C8 4 microm analytical column (100 x 2.1 mm i.d.). The method had a chromatographic run time of 3.0 min and a linear calibration curve over the range 0.5-50 ng/ml (r2 > 0.9965). The limit of quantification was 0.5 ng/ml. This HPLC/MS/MS procedure was used to assess the bioequivalence of two clonazepam 2 mg tablet formulations (clonazepam test formulation from Ranbaxy Laboratories Ltd and Rivotril from Roche Laboratórios Ltda as standard reference formulation).     

Jacobi’s last multiplier,Lie symmetries,and hidden linearity: “Goldfishes” galore

In addition to the reduction method, we present a novel application of Jacobi’s last multiplier for finding Lie symmetries of ordinary differential equations algorithmically. These methods and Lie symmetries allow unveiling the hidden linearity of certain nonlinear equations that are relevant in physics. We consider the Einstein-Yang-Mills equations and Calogero’s many-body problem in the plane as examples. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 151, No. 3, pp. 495–509, June, 2007.     

Intramolecular dynamics and conformational transition in proteins studied by biophysical labelling methods. Common and specific features of proteins from thermophylic micro-organisms

A general survey is carried out on the theoretical grounds for methods of spin, luminescence and M?ssbauer labels, as well as their application in the study of protein intramolecular dynamics. When combined, these methods allow the protein dynamics to be investigated within a wide range of correlation times (tau c = 10(2) - 10(-10) s) and amplitudes. The purposeful application of the methods to various proteins at different temperatures (30-330 K), water content, substrate addition, etc., revealed a number of dynamical processes and conformational transitions in proteins. The experiments indicated correlations between the local segmental mobility of protein globules in a nanosecond temporal scale and biochemical reactions, such as long-distance electron transfer, hydrolysis and photoreactions. The biophysical labelling methods results were analysed together with the data on dynamics obtained using complementary physico-chemical methods and theoretical calculations. Special emphasis is given to recent results on proteins from thermophylic micro-organisms. The mechanisms of protein intramolecular dynamics and their role in the stability and functions of proteins and enzymes are discussed.     

An integrable SIS model

We provide a demonstration of the integrability of a classical model of an infectious disease which neither kills nor induces autoimmunity by means of the Painlevé analysis and use the Lie theory of transformation groups to present an explicit solution.     

On the propagation of one-dimensional acoustic waves in liquids

Within the framework of one-dimensional unsteady compressible flow in deformable pipes, the present work proposes expressions able to represent the stress state of a “fluid-pipe” continuous system. The coefficients needed to define the friction forces are calibrated against experimental results. The proposed expressions highlight the crucial role played by the fluid compressibility on the wave resistance.