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Small Modifications (small + modifications)

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Chemistry	50%

Selected Abstracts

Porphyrin derivatives as photosensitizers for the inactivation of Bacillus cereus endospores

JOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2009
A. Oliveira
Abstract Aims:, In this study, we propose (i) to study the photodynamic inactivation (PDI) efficiency of neutral and cationic porphyrin derivatives, (ii) to characterize the kinetics of the inactivation process using Bacillus cereus as a model endospore-producing bacterium and (iii) to conclude on the applicability of porphyrin derivatives in the inactivation of bacterial endospores. Methods and Results:, The study of PDI of Bacillus cereus endospores, taken as model-endospores, using porphyrin derivatives differing in the number of positive charges and in the meso-substituent groups, showed that neutral, monocationic and dicationic porphyrins are quite ineffective, in contrast with the tri- and tetra-cationic molecules. The most effective porphyrin is a tricationic porphyrin with a meso-pentafluorophenyl group. With this photosensitizer (PS), at 0·5 ,mol l,1, a reduction of 3·5 log units occurs after only 4 min of irradiation. None of the porphyrin derivatives showed toxicity in the absence of light. Conclusions:, Some porphyrin derivatives are efficient PSs for the inactivation of bacterial endospores and should be considered in further studies. Small modifications in the substituent groups, in addition to charge, significantly improve the effectiveness of the molecule as a PS for endospore inactivation. Significance and Impact of the Study:, Tetrapyrrolic macrocycles should be regarded as worthy to explore for the PDI of spore-producing gram-positive bacteria. The development of molecules, more selective and effective, emerges as a new objective. [source]

Analytical stiffness matrices with Green,Lagrange strain measure

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2005
Pauli Pedersen
Abstract Separating the dependence on material and stress/strain state from the dependence on initial geometry, we obtain analytical secant and tangent stiffness matrices. For the case of a linear displacement triangle with uniform thickness and uniform constitutive behaviour closed-form results are listed, directly suited for coding in a finite element program. The nodal positions of an element and the displacement assumption give three basic matrices of order three. These matrices do not depend on material and stress/strain state, and thus are unchanged during the necessary iterations for obtaining a solution based on Green,Lagrange strain measure. The approach is especially useful in design optimization, because analytical sensitivity analysis then can be performed. The case of a three node triangular ring element for axisymmetric analysis involves small modifications and extension to four node tetrahedron elements should be straight forward. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Evaluation of different protein sources for aquafeeds by an optimised pH-stat system

JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 7 2002
Francisco J Alarcón
Abstract This paper presents the results of some experiments oriented to optimise and standardise the measurement of protein hydrolysis by fish proteases using the pH-stat technique. Various factors affecting the degree of hydrolysis (DH) were considered (autohydrolysis of the protein sources, type of enzymes utilised, substrate/enzyme ratio and effect of inhibitors). The crude extracts obtained from fish digestive tissues showed their suitability for the determination of protein hydrolysis, rendering better results than those obtained using mixtures of commercial enzymes. DH values for a given protein were greatly affected by the substrate/enzyme ratio, since small modifications in protein concentration resulted in significant variations in DH. Protease inhibitors present in various plant protein sources produced a reduction in DH values. © 2002 Society of Chemical Industry [source]

A Density Functional Theory Study on the Electrocyclization of 1,2,4,6-Heptatetraene Analogues: Converting a Pericyclic to a Pseudopericyclic Reaction

CHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2005
Enrique M. Cabaleiro-Lago Prof. Dr.
Abstract A comprehensive B3LYP/6-31+G* study on the electrocyclization of 1,2,4,6-heptatetraene analogues was conducted. Starting from the cyclization of (2Z)-2,4,5-hexatrienal, a pericyclic disrotatory process favored by the assistance of a electron lone pair, we incorporated small modifications in its molecular structure to obtain a truly pseudopericyclic process. To this purpose electronegative atoms (fluorine and nitrogen) were added to give a more electrophilic character on the carbon atom which is attacked by the electron lone pair of the oxygen atom. The complete pathway for each reaction was determined, and changes in magnetic properties were monitored with a view to estimating the aromatization associated with each process. This information, together with the energetic and structural results, allowed us to classify the reactions as pseudopericyclic or pericyclic. Among all studied reactions only one was a truly pseudopericyclic process and another was a borderline case. The features of this unequivocally pseudopericyclic case were analyzed in depth. Se ha llevado a cabo un exhaustivo estudio B3LYP/6-31+G* de la electrociclación de análogos del 1,2,4,6-heptatetraeno. Partiendo de la ciclación del (2Z)-2,4,5-hexatrienal, un proceso pericíclico disrotatorio favorecido por la ayuda de un par electrónico solitario, hemos incorporado pequeñas modificaciones en su estructura molecular con el fin de obtener un proceso verdaderamente pseudopericíclico. Con este propósito se añadieron átomos electronegativos (flúor y oxígeno) para conseguir un mayor carácter electrofílico en el átomo de carbono que es atacado por el par electrónico solitario del átomo de oxígeno. Se han determinado los caminos de reacción completos y se ha observado la variación de las propiedades magnéticas con el fin de estimar la aromatización asociada a cada proceso. Esta información, junto con los resultados energéticos y estructurales, nos han permitido clasificar las reacciones como pseudopericíclicas o pericíclicas. De todas las reacciones estudiadas sólo una resultó ser realmente pseudopericíclica y otra resultó ser un caso límite. Las características de este caso inequívocamente pseudopericíclico han sido analizadas en profundidad. [source]