As pesquisas na área de Química Medicinal têm envolvido diversos aspectos focando o tratamento de doenças tais como câncer, em especial, a combinação de potenciais terapêuticos apresentados por moléculas distintas. Visando isso, realizou-se um estudo computacional combinando a pirazinamida (PZA), um imprescindível tuberculostático com a cisplatina, importante antitumoral, para obter as melhores características de ambas. Foi feita a busca por uma estrutura mais estável para o complexo de estequiometria PZA:platina(II) 2:1 cis-[PtCl2(PZA)2], ou cis-diclorobis(pirazinamido)-platina(II), utilizando para isso a teoria do funcional densidade (DFT) associada ao uso de um planejamento fatorial misto de dois fatores do tipo 5 × 3, para um total de 15 experimentos. Através da avaliação da superfície de resposta e da realização de sete experimentos para validação do modelo, inferiu-se que a estrutura de maior estabilidade refere-se àquela com o diedro 2Cl/1Pt/5O/7C sob um ângulo de 18,9°.

Research in Medicinal Chemistry has involved numerous aspects focusing on the treatment of several kinds of diseases, such as cancer, especially by the combination of therapeutic potentials by using different molecules. With this aim, a computational study combining pyrazinamide (PZA), an indispensable tuberculostatic drug, and cisplatin, an important antitumoral agent, was conducted to combine the best features of both compounds. A search for the most stable structure of the platinum(II)-PZA complex at a 2:1 stoichiometry: diclorodi(pyrazinamido)platinum(II), or cis-[PtCl2(PZA)2], was performed, using functional theory (DFT) associated to a mixed-level factorial design of two factors type 5 × 3, totaling 15 experiments. After evaluating the response surface and following the performance of seven experiments to validate the area identified as optimal, the most stable structure is that in which the dihedral 2Cl/1Pt/5O/7C is at an 18.9° angle.

As interações entre ciclodextrinas e seus agregados com cadeias poliméricas, têm atraído a atenção de pesquisadores em diferentes subáreas da química supramolecular. Esses compostos, conhecidos como "necklaces", podem ser empregados na formulação de fios e nanotubos moleculares. No presente artigo a formação de dímeros de α-CD foi estudada teoricamente considerando as três possíveis orientações relativas, denominadas "head-to-head" (HH), "tail-to-tail" (TT) e "head-to-tail" (HT). A influência da cadeia polimérica na estabilidade relativa das diferentes associações foi avaliada através do estudo dos compostos de inclusão de ( α-CD)2 com oligo(etilenoglicol) (OEG). Os resultados mostram que a orientação relativa das CDs é definida, primeiramente, pelas interações intermoleculares entre as unidades de α-CD, tendo a cadeia polimιrica um papel secundário no processo de agregação.

Cyclodextrins (CDs) and polymeric chains have attracted considerable attention, being addressed in the literature as novel molecular assembly. The so-called "Molecular Necklace" synthesized by the inclusion of a polymeric chain inside CDs cavity has been employed in the formulation of molecular wires and nanotubes. In this paper we applied our previous reported mixed basis set approach in order to investigate theoretically the α-CD inclusion complexes formed by two CD units and an oligo(ethylene glycol) (OEG). In attempt to analyze the role played by the OEG in the formation of pseudo-rotaxane in gas-phase, DFT calculations were performed for six possible dimer associations of CDs, named head-to-head (HH), tail-to-tail (TT) and head-to-tail (HT) with or without an OEG threadlike molecule included in the cavity formed by the α-CD dimer. The comparison between relative energies of empty (HH, TT and HT) and filled associations (HH-OEG, TT-OEG and HT-OEG) shows that the OEG chain does not interfere significantly in the relative stabilization energies of the supramolecular systems, therefore the relative arrangements of CDs in the necklace structures should be primarily driven by interactions between cyclodextrin units.

No presente artigo, métodos teóricos foram utilizados para o estudo da interação entre o complexo 5a,6-anidrotetraciclina-dicloro-platina(II) (AHTC-Pt) e os nucleófilos adenina (A), guanina (G), cisteína (Cys) e metionina (Met). A espécie [Pt(AHTC)Cl(H2O)]+ foi considerada como reagente em todos os processos investigados. Os valores calculados para ΔGa,aq no nível B3LYP/6-311+G(2d,p) foram 21,7 e 20,7 kcal mol-1 para as interações com A e G, respectivamente, os quais estão em acordo com o comportamento esperado, sendo a reação com G mais rápida (ΔGa expt = 18,5 kcal mol-1 para G). Para os processos envolvendo os aminoácidos, as barreiras de energia calculadas foram 17,6 (Cys) e 18,5 kcal mol-1 (Met), as quais são ligeiramente menores do que os valores experimentais para a cisplatina (20,5 e 20,2 kcal mol-1, respectivamente). Esses resultados mostram que a reatividade do complexo AHTC-Pt é comparável a da cisplatina e, portanto, o mesmo pode ser considerado um sistema relevante para o desenvolvimento de novos agentes antitumorais.

This paper describes a theoretical analysis of the interaction between 5a,6-anhydrotetracycline platinum(II) complex (AHTC-Pt) and some biological nucleophiles; adenine (A), guanine (G), cysteine (Cys) and methionine (Met). The aquated species [Pt(AHTC)Cl(H2O)]+ was taken as reagent for the processes studied here. For DNA bases (A and G), the calculated values for ΔGa,aq at the B3LYP/6-311+G(2d,p) level were 21.7 and 20.7 kcal mol-1 for interaction with A and G, respectively, which are in accordance with the expected behavior of faster process involving G. These values are higher than the experimental activation energy for the parent compound cisplatin (18.5 kcal mol-1 for interaction with G). For the process involving the amino-acids, the barriers were 17.6 (Cys) and 18.5 kcal mol-1 (Met), which are lower than the observed values for cisplatin (20.5 and 20.2 kcal mol-1, respectively). These outcomes show that AHTC-Pt hybrid complex may be considered a promising lead compound in the development of novel anticancer drugs based on platinum complex.

The conformational equilibrium for two 5,5' biphenyl lignin models have been analyzed using a quantum mechanical semiempirical method. The gas phase and solution structures are discussed based on the NMR and X-ray experimental data. The results obtained showed that the observed conformations are solvent-dependent, being the geometries and the thermodynamic properties correlated with the experimental information. This study shows how a systematic theoretical conformational analysis can help to understand chemical processes at a molecular level.