Theoretical analysis of the electrostatic interactions between charged polarisable particles

Theoretical approaches to calculating electrostatic interactions between charged particles of dielectric materials are presented and applied to diverse examples of electrostatic behaviour. The accuracy of numerical predictions based on the multipole expansion used in calculations of the electrostatic force is discussed. Strict corresponding convergence criteria are established, particularly when addressing problems involving materials with high dielectric constants, large differences in particles size and short inter-particle separation distances. An extensive study of various types of electrostatic interactions is undertaken, with greater stress on the circumstances in which rather counterintuitive events might exist, namely the attraction between like-charged particles, generally dependant on certain degrees of asymmetry in charge density and charge distribution on the surface of the interacting particles, and the repulsion between oppositely charged particles, which involves magnitudes of charge that are below some critical limit and the presence of a sufficiently polarisable medium. Several examples addressing experimental problems, notably the growth mechanism of aerosols in the atmosphere of Saturn’s moon Titan, and electrostatic self-assembly processes, are included. Many-particle dynamics simulations of electrostatically driven systems are finally presented through some selected scenarios

Theoretical analysis of the electrostatic interactions between charged polarisable particles

Theoretical approaches to calculating electrostatic interactions between charged particles of dielectric materials are presented and applied to diverse examples of electrostatic behaviour. The accuracy of numerical predictions based on the multipole expansion used in calculations of the electrostatic force is discussed. Strict corresponding convergence criteria are established, particularly when addressing problems involving materials with high dielectric constants, large differences in particles size and short inter-particle separation distances. An extensive study of various types of electrostatic interactions is undertaken, with greater stress on the circumstances in which rather counterintuitive events might exist, namely the attraction between like-charged particles, generally dependant on certain degrees of asymmetry in charge density and charge distribution on the surface of the interacting particles, and the repulsion between oppositely charged particles, which involves magnitudes of charge that are below some critical limit and the presence of a sufficiently polarisable medium. Several examples addressing experimental problems, notably the growth mechanism of aerosols in the atmosphere of Saturn’s moon Titan, and electrostatic self-assembly processes, are included. Many-particle dynamics simulations of electrostatically driven systems are finally presented through some selected scenarios

Structural evaluation and SAR of E- (2) -benzothiazole hydrazones with antitumor activity

Cancer is still a major threat to global health, representing the leading cause of death in economically developed countries and the second leading cause of death in developing countries. Due to limited efficacy and high toxicity of the currently used cancer therapies, the development of new anticancer molecules is still a need. In this work, divided into two parts, the structural evaluation were conducted for determining the molecular structure of (E)-2 benzothiazole hydrazones with antitumor activity, as well as a SAR study, for the identification of molecular characteristics favorable for the desired pharmacological activity. The application of a methodology involving semi-empirical and quantummechanical methods proved adequate for the structural evaluation of the studied compounds, and through the SAR studies it was possible to identify some molecular characteristics, as the presence of hydroxyl groups in the substituent part of each compound, which is possibly favorable for the antitumor activity, in contrast to the presence of halogens, as the fluorine, chlorine and bromine atoms, which was found to be unfavorable to this activity. Finally, a new potential candidate to antitumor agent was proposed, based on the identified favorable characteristics to the antitumor activity.Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorO câncer ainda é uma das principais ameaças à saúde mundial, representando a principal causa de morte em países economicamente desenvolvidos e a segunda causa de morte em países em desenvolvimento. Devido à eficácia limitada ou elevada toxicidade das terapias empregadas atualmente no combate ao câncer, o desenvolvimento de novas moléculas antitumorais ainda é uma necessidade. Neste trabalho, dividido em duas partes, foram realizados a avaliação estrutural, para a determinação da estrutura molecular de derivados (E) 2- benzotiazolidrazônicos com atividade antitumoral, e um estudo de SAR, para a identificação de características moleculares favoráveis à atividade farmacológica desejada. O emprego de uma metodologia envolvendo métodos semi-empíricos e quanto-mecânicos mostrou-se adequada para a avaliação estrutural dos compostos estudados e através dos estudos de SAR foi possível identificar certas características moleculares, como a presença de hidroxilas na parte substituinte de cada composto, que são possivelmente favoráveis à atividade antitumoral, em contrapartida à presença de halogênios, como os átomos de flúor, cloro e bromo, que mostrou-se desfavorável a esta atividade. Ao final do trabalho foi proposta uma nova molécula, potencial candidata a agente antitumoral, com base nas características identificadas como favoráveis à atividade antitumoral

Synthesis and Biological Evaluation of Novel 6-Hydroxy-benzo[d][1,3]oxathiol-2-one Schiff Bases as Potential Anticancer Agents

With the aim of discovering new anticancer agents, we have designed and synthesized novel 6-hydroxy-benzo[d][1,3]oxathiol-2-one Schiff bases. The synthesis started with the selective nitration at 5-position of 6-hydroxybenzo[d][1,3]oxathiol-2-one (1) leading to the nitro derivative 2. The nitro group of 2 was reduced to give the amino intermediate 3. Schiff bases 4a–r were obtained from coupling reactions between 3 and various benzaldehydes and heteroaromatic aldehydes. All the new compounds were fully identified and characterized by NMR (1H and 13C) and specifically for 4q by X-ray crystallography. The in vitro cytotoxicity of the compounds was evaluated against cancer cell lines (ACP-03, SKMEL-19 and HCT-116) by using MTT assay. Schiff bases 4b and 4o exhibited promising cytotoxicity against ACP-03 and SKMEL-19, respectively, with IC50 values lower than 5 μM. This class of compounds can be considered as a good starting point for the development of new lead molecules in the fight against cancer