Publications

Abstract Trihydroxycinnamic derivatives were synthesized and evaluated for their antioxidant and cytotoxic activities. The ester derivatives exhibited a higher radical-scavenging activity, when liposomes were used as target systems, a fact which may be related to their lipophilicity and conformational preferences. These compounds were found to display significant growth inhibition and cytotoxic effects towards a human cervix adenocarcinoma cell line (Hel,a). The partition coefficients presently obtained for the trihydroxycinnamic derivatives correlate well both with their structural characteristics and with their antioxidant/cytotoxic activities. A positive structure-activity-property relationship between cytotoxic and antioxidant activities, which is intrinsically related with physico-chemical and conformational properties, is anticipated, as a noteworthy study that must be done for phenolic systems. As damage events are frequently correlated with oxidative stress, the prevalence of both properties in a single compound could be beneficial in terms of rationale preventive or therapeutic purposes.

Abstract A Raman study of hydroxycinnamic and hydroxybenzoic esters (caffeates, ferulates and gallates) displaying antioxidant and anticancer properties was undertaken, with particular emphasis on the analysis of the effect of the ring substituents and the nature of the ester alkyl chain on their spectroscopic features. A complete assignment of the spectra was carried out for all the compounds investigated, in the light of the corresponding calculated wavenumbers (at the density functional theory level). Distinct vibrational patterns were observed for each type of ester, thereby allowing their ready characterisation and identification by Raman spectroscopy. Evidence of the occurrence of intermolecular hydrogen bonds, leading to the formation of dimers in the condensed phase, was also obtained. Copyright (c) 2007 John Wiley & Sons, Ltd.

Abstract Adenosine A(2A) receptors are members of the G protein-coupled receptor family and mediate multiple physiological effects of adenosine, both at the central nervous system (CNS) and at peripheral tissues, by activating several pathways or interacting with other receptors or proteins. Increasing evidence relate A(2A) receptors with pharmacological stress testing, neurodegenerative disorders (such as Parkinson's disease) and inflammation, renewing the interest in these receptors, increasingly viewed as promising therapeutic targets. Series of agonists and antagonists have been developed by medicinal chemistry artwork either by structure activity relationship (SAR) or quantitative structure activity relationship (QSAR) studies. These studies have allowed identification of the structural and electrostatic requirements for high affinity A(2A) receptor binding and, therefore, contributing to the rational design of A(2A) receptor ligands. Additional rational chemical modifications of the existing A(2A) receptor ligands may further improve their affinity/selectivity. The purpose of this review is to analize and summarize aspects related to the medicinal chemistry of A(2A) receptor ligands, their present and potencial therapeutic applications by exploring the molecular structure and physiological and pathophysiological roles of A(2A) receptors.

Abstract A comparison of linear and non-linear regression method in selecting the optimum isotherm was made to the experimental equilibrium data of methylene blue sorption by activated carbon. The r(2) was used to select the best fill linear theoretical isotherm. In the case of non-linear regression method, six error functions, namely coefficient of determination (r(2)), hybrid fractional error function (HYBRID), Marquardt's percent standard deviation (MPSD), average relative error (ARE), sum of the errors squared (ERRSQ) and sum of the absolute errors (EABS) were used to predict the parameters involved in the two and three parameter isotherms and also to predict the optimum isotherm. For two parameter isotherm, MPSD was found to be the best error function in minimizing the error distribution between the experimental equilibrium data and predicted isotherms. In the case of three parameter isotherm, r2 was found to be the best error function to minimize the error distribution structure between experimental equilibrium data and theoretical isotherms. The present study showed that the size of the error function alone is not a deciding factor to choose the optimum isotherm. In addition to the size of error function, the theory behind the predicted isotherm should be verified with the help of experimental data while selecting the optimum isotherm. A coefficient of non-determination, K-2 was explained and was found to be very useful in identifying the best error function while selecting the optimum isotherm.

Abstract A three-layer feed-forward neural network was constructed and tested to analyze the kinetic dye uptake of a batch activated carbon adsorption process. The operating variables studied are the contact time, initial dye concentration, agitation speed, temperature, initial solution pH, activated carbon mass, and volume of the dye solution treated. The studied operating variables were used as the input to the constructed neural network to predict the dye uptake at any time as the output or the target. The constructed network was found to be precise in modeling the rate of dye uptake for the operating conditions studied. The constructed neural network was found to be highly precise in predicting the dye uptake rate for the new input data, which are kept unaware of the trained neural network showing its applicability to determine the reaction rate for any operating conditions.

Abstract The present work reports the values of the gaseous standard (p degrees = 0.1 MPa) molar enthalpy of formation of three pyridine derivatives substituted with one, two, and three tert-butyl groups, in positions para, ortho-ortho and ortho-para-ortho to the nitrogen, respectively. The standard molar energies of combustion of each compound, determined by static bomb calorimetry, yielded their standard molar enthalpies of formation in the condensed phase at T = 298.15 K, which together with the values of the standard molar enthalpies of vaporization or sublimation, measured by Calvet microcalorimetry, allowed the calculation of the standard gas phase molar enthalpy of formation of each compound studied. The enthalpies of combustion for 4-tert-butylpyridine (1), 2,6-di-tert-butylpyridine (1) and 2,4,6-tri-tert-butylpyridine (cr) were found to be, respectively, -(5 370.1 +/- 3.4) kJ mol(-1), -(7954.2 +/- 4.0) kJ mol(-1), and -(10 542.9 +/- 4.9) kJ mol(-1). The molar enthalpies of vaporization were measured as (54.4 +/- 1.3) kJ mol(-1) for 4-tert-butylpyridine, (56.6 +/- 1.2) kJ mol(-1) for 2,6-di-tert-butylpyridine, whereas the enthalpy of sublimation of 2,4,6-tri-tert-butylpyridine was found to be (78.3 +/- 1.7) kJ mol(-1).

Abstract A comparison of linear and non-linear regression method in selecting the optimum isotherm was made to the experimental equilibrium data of basic red 9 sorption by activated carbon. The r(2) was used to select the best fit linear theoretical isotherm. In the case of non-linear regression method, six error functions namely coefficient of determination (r(2)), hybrid fractional error function (HYBRID), Marquardt's percent standard deviation (MPSD), the average relative error (ARE), sum of the errors squared (ERRSQ) and sum of the absolute errors (EABS) were used to predict the parameters involved in the two and three parameter isotherms and also to predict the optimum isotherm. Non-linear regression was found to be a better way to obtain the parameters involved in the isotherms and also the optimum isotherm. For two parameter isotherm, MPSD was found to be the best error function in minimizing the error distribution between the experimental equilibrium data and predicted isotherms. In the case of three parameter isotherm, r2 was found to be the best error function to minimize the error distribution structure between experimental equilibrium data and theoretical isotherms. The present study showed that the size of the error function alone is not a deciding factor to choose the optimum isotherm. In addition to the size of error function, the theory behind the predicted isotherm should be verified with the help of experimental data while selecting the optimum isotherm. A coefficient of non-determination, K-2 was explained and was found to be very useful in identifying the best error function while selecting the optimum isotherm.

Abstract The present study reports that it is impossible and inappropriate to approximate the Langmuir-Hinshelwood kinetics to zero order kinetics.