We reported experimental and theoretical investigation of conformers of 1,2,3-triazole derivatives, substances of exclusively synthetic origin, subject of extensive studies, because of several biological properties, such as antiviral, antimicrobial and antileishmaniasis. We reported molecular/supramolecular X-ray structures of antiophidian compounds I and II. For I and II there are two crystallographic different molecules in the unit cell (A and B). To explore the causes of the similarities in the compound’s crystal structures, intermolecular interactions were explored using the Hirshfeld surface as the fingerprint plots. In addition, density functional theory (DFT) calculations were carried out at the ωB97x-D/6-31G(d,p)-PCM-CHCl3 level aiming to contribute to the interpretation of the experimental data and complement the experimental findings. Two structures named 2A and 5B were found in good agreement with the respective X-ray solid state ones (A and B). Theoretical 1H nuclear magnetic resonance (NMR) spectra calculated for 5B rotated structure (torsion angles deviation around 40° to 90°) was in fine agreement with experimental results (in CDCl3) indicating that the solution molecular structure is considerably different from optimized equilibrium geometries and solid-state structure. Therefore, care is needed when using X-ray structures or DFT geometries to model interaction of drugs with biological targets since significant conformational changes may take place in solution.

S-states at oxygen evolving complex (OEC) are widely studied due to its large importance in photo-oxidation water process. The structural aspects involving S0, S1, S2, S3 and S4 states are still not solved theoretically. Particularly, spin states have been analyzed as an important aspect in S-state models. Seeking to obtain a relevant and simple model to cover high-spin (HS) S0-S4 states we develop a 55-57 atoms model. Through quantum chemical calculations we figured out that our interatomic distance parameters are in agreement with experimental and other theoretical reference values by ca. 10.0 and 3.5%, respectively, being also in good agreement with other theoretical models containing a large number of atoms. Our HS models presented expected oxidation states according to other data on literature for small theoretical models.

The effect of γ-Al2O3 support on the NO adsorption on Pd4 clusters was investigated by means of density functional theory (DFT) calculations. Pd4 adsorbed on γ-Al2O3 (represented by a Al14O24H6 cluster) changes its preferential geometry from tetrahedral to a distorted planar structure. The alumina support promotes a higher dispersion in the palladium catalyst and reduces the NO adsorption energy to -25.6 kcal mol-1 (computed at B3LYP/LANL2DZ/6-311+G(d)), in close agreement with the experimental value of -27.2 kcal mol-1. On the bare planar Pd4 cluster the NO molecule adsorbs in a bridge arrangement, with adsorption energy of -41.2 kcal mol-1. Adsorption on the tetrahedral Pd4 cluster occur preferentially in an atop mode, with adsorption energy of -30.6 kcal mol-1. Charge density analysis show that the electron flux between the NO molecule and Pd4 depends on the adsorption form, with back-donation being stronger in the bridge adsorption mode.

No presente artigo o efeito do pseudopotencial de caroço (ECP) para o átomo de platina no erro de sobreposição de base (BSSE) foi avaliado para as energias de interação entre o complexo cisplatina ([Pt(NH3)2Cl2]) e água. Oito orientações espaciais distintas para os monômeros cisplatina-água foram consideradas na determinação do BSSE utilizando o procedimento padrão "counterpoise". O BSSE foi também avaliado ao longo das curvas de energia potencial, as quais são importantes para a determinação dos parâmetros do potencial de Lennard-Jones. Os cálculos foram feitos em diferentes níveis de teoria, incluindo HF, DFT (funcionais: BLYP, B3LYP, BP86, PBE, PW91) e MP2 com conjunto de funções de base do tipo "split-valence" de Pople e "correlated consistent" de Dunning.

In this article the role played by the effective core potential (Pt atom) on the evaluation of basis set superposition error (BSSE) and interaction energies for the complex between cisplatin ([Pt(NH3)2Cl2]) and water was investigated. Eight distinct spatial monomer orientations in the cisplatin-water complex were considered with the counterpoise procedure being employed to calculate the BSSE. The BSSE effect on potential energy curves, required for the determination of Lennard-Jones parameters, is also discussed. The calculations were performed at the HF, DFT (BLYP, B3LYP, BP86, PBE, PW91 functional) and MP2 level with Pople's split valence and Dunning's correlated consistent basis sets.

No presente artigo, métodos teóricos foram utilizados na análise da estrutura e propriedades eletrônicas de oligômeros de alquiltiofenos considerando diferentes regiosseletividades. A lacuna de energia entre as bandas de valência e condução foi calculada nos níveis ab initio Hartree-Fock (HF) e teoria do funcional de densidade (DFT) e semi-empírico ZINDO/S-CI. Os resultados mostraram que o isômero Head-Head-Tail-Tail (HH-TT) apresenta menores valores para a lacuna de energia quando oligômeros com mais de três unidades monoméricas são considerados e que a substituição do anel tiofeno por grupos alquila não afeta significativamente a lacuna de energia. Esse resultado é importante no sentido que mostra que polímeros mais processáveis podem ser obtidos através da alquilação sem perda considerável de suas características condutoras.

In the present paper a theoretical analysis of alkylthiophenes with Head-Tail-Head-Tail (HT-HT) and Head-Head-Tail-Tail (HH-TT) regioselectivities up to 6 monomeric units was carried out. Structure and electronic properties for the syn and anti forms were calculated by ab initio Hartree-Fock (HF) and Density Functional Theory (DFT) approaches. The energy gap between the conduction and valence bands was obtained at HF and DFT levels and also calculated with the semiempirical ZINDO/S-CI method. The results showed that the isomer with HH-TT regioselectivity presents lower energy gap for longer oligomers and the substitution of thiophene by alkyl groups does not change significantly the energy gap. This is important in the sense that more processable polymers can be obtained through alkylation without decrease the energy gap that is a molecular properties related to the electronic conductivity. Regarding to the conformational equilibrium, the syn form was found to be stable only for the HT-HT isomer and in this case the energy gap was found to be lower than those calculated for the anti form.

A síntese de dois novos arsadifosfóis de fórmula (AsP2C2Bu t2 )CH(SiMe3)2, a partir dos anéis aniônicos 4-arsa-1,2-difosfaciclopentadienil e 2-arsa-1,4-difosfaciclopentadienil é reportada, junto com suas caracterizações utilizando RMN de 31P. Cálculos ab initio no nível MP2/6-31G(d) de teoria foram realizados para se investigar as barreiras de inversão piramidal, estabilidade relativa e o caráter aromático de todos os possíveis isômeros dos arsadifosfóis, em fase gasosa. A distribuição termodinâmica dos isômeros está em completo acordo com os resultados experimentais. O caráter de aromaticidade obtido para os três isômeros contendo um fósforo sp³ é maior quando comparado com o 1,2,4-trifosfol, sintetizado previamente. Os efeitos dos grupos substituintes volumosos sobre a aromaticidade e as barreiras de inversão piramidal são também discutidos.

The synthesis of two new arsadiphospholes of formula (AsP2C2Bu t2 )CH(SiMe3)2, from 4-arsa-1,2-diphosphacyclopentadienyl and 2-arsa-1,4-diphosphacyclopentadienyl ring anions are reported together with their characterization by 31P NMR. Ab initio calculations at the MP2/6-31G(d) level of theory were carried out to investigate the energy barrier for pyramidal inversion about the pyramidal P and As atoms, relative stability and aromaticity character of all possible isomers in the gas phase. The thermodynamic isomers distribution is in agreement with the experimental results. The inversion barrier at the sp³ phosphorus compared to the inversion barrier found for the arsenic atom is low. This fact is directly related with the aromaticity of the rings and shows the preference of the side group for the phosphorus atom, which leads to a more aromatic ring structure. The aromaticity character found for three isomers containing a sp³-phosphorus is greater if compared with that of 1,2,4-triphosphole synthesized previously. The effects of bulky R substituents on the aromaticity and on the energy barrier for pyramidal inversion are also discussed.

A isomerização cis -> trans do composto quadrático plano d8 [Pt(Cl)(SnCl3)(PH3)2 ] foi investigada utilizando-se o nível ab initio de cálculo MP4(SDQ)//MP2. As estruturas otimizadas, localizadas na superfície de energia potencial em fase gasosa, indicam que esta reação se processa através de um estado de transição quase-tetraédrico. A influência dos efeitos eletrônicos dos ligantes no mecanismo da reação foi investigada utilizando-se o método de Análise de Decomposição de Carga (CDA), o qual forneceu suporte para a compreensão do forte efeito trans do ligante SnCl3. O efeito devido ao solvente na energia de reação em fase gasosa foi avaliado utilizando-se os modelos contínuos SCRF e IPCM. Em ambos os casos um aumento na barreira de energia para o processo foi observado, sendo que a estabilidade termodinâmica dos isômeros cis e trans foi alterada pela solvatação.

The cis -> trans isomerization of the d8 square planar [Pt(Cl)(SnCl3)(PH3)2 ] compound was investigated at the MP4(SDQ)//MP2 level of theory. The optimized structures located on the gas-phase potential energy surface indicate that this reaction proceeds through a quasi-tetrahedral transition state. The influence of electronic effects of the ligands on the reaction mechanism was investigated with the Charge Decomposition Analysis (CDA) method, which gave support to understand the strong trans effect of the SnCl3 ligand. The solvent effect on the gas phase energy reaction was evaluated using the SCRF and IPCM continuum models. In both cases, an increase on the energy barrier for the process was observed and, the thermodynamical stability of the cis and trans isomers was changed upon solvation.

The infrared (IR) spectra of the four distict conformers located on the multidimensional potential energy surface (PES) for the 3-phenyl-1,2,3-oxathiazolidine 2-oxide compound have been calculated using the semiempirical quantum-mechanical method PM3. The band spectra are reported and compared directly with the experimental spectrum. The IR intensities are shown to be much more sensitive to conformational changes than the vibrational frequencies and so, the theoretical analysis of the IR spectrum can be used as a tool for helping in the elucidation of the structure of heterocyclic compounds.

Results of high level ab initio calculations of the intermolecular potentials and theoretical dispersion coefficients for the Ne2 and Ar2 dimers were utilized to build analytical potentials for these species. The obtained potentials were used in the calculation of the dimers rovibrationals levels, and their respective spectroscopic constants determined. A comparison of high level experimental data with our theoretical results shows a very good agreement for Ne2, and also a good agreement for the Ar2 dimer.

Energias de estabilização para complexos moleculares fracamente ligados, relativas aos monomeros isolados, tem sido determinadas experimentalmente através do modelo pseudo-diatômico (PD) o qual faz uso de um potencial do tipo Lennard-Jones 6-12 (LJ), aqui denominado modelo PD-LJ. Este método utiliza dados espectroscópicos para avaliar a profundidade do poço de potencial para sistemas fracamente ligados. Neste trabalho é mostrada uma comparação sistemática entre valores experimentais de energias de estabilização disponíveis na literatura e calculados à nível ab initio para uma série de complexos binários, objetivando avaliar a eficácia do modelo PD-LJ.

Stabilization energies of weakly bound molecular complexes, relative to the isolated monomers constituents, have been evaluated experimentally using the pseudo-diatomic (PD) model employing a Lennard-Jones 6-12 potential (LJ), here denominated the PD-LJ model. This method uses spectroscopic data to estimate the potential depth of weakly bound species. In this work we report a systematic comparison between high level ab initio stabilization energy values and the respective experimental data available for a series of binary complexes, aiming to assess the efficaciousness of the PD-LJ model.

Os movimentos de grande amplitude no complexo HF...ClF foram estudados teoricamente. Na solução das equações dinâmicas foi utilizada uma superfície de energia potencial ab initio calculada a nível MP2/DZ+(2d1f/2p1d)//HF/DZP, incluindo a correção para o erro de superposição do conjunto de bases (BSSE). A freqüência para o estiramento da ligação de van der Waals e a freqüência e a intensidade da deformação HF...Cl foram calculadas e comparadas com valores experimentais harmônicos teóricos e experimentais disponíveis. A freqüência de estiramento calculada é 97,60 cm-1, a qual está em excelente acordo com o valor experimental harmônico de 100 ± 2 cm-1. O valor para esta freqüência incluindo a anarmonicidade é 89,38 cm-1. A freqüência fundamental calculada para a deformação HF...Cl é 13,12 cm-1, enquanto cálculos ab initio considerando a aproximação harmônica prevêem um valor de 72 cm-1. Esta diferença significativa é devida ao movimento de tunelamento através do ângulo HF...Cl, o qual tem uma barreira para esta rotação interna de 151 cm-1. As intensidades destas transições foram calculadas em duas temperaturas. Em 10 K, apenas a transição fundamental é significativa, enquanto que a 300 K uma banda quente em 81,30 cm-1, resultante de uma transição entre o terceiro e o quarto nível, domina o espectro.

The intermolecular large amplitude motions of the HF...ClF complex were studied theoretically. The ab initio intermolecular potential energy surface, calculated at the MP2/DZ+(2d1f/2p1d)//HF/ DZP level of theory including BSSE correction, was used in the solution of the dynamical equations. The frequency for the van der Waals stretching and the frequency and the intensity of the HF...Cl bending were calculated. The frequency results were compared with reported theoretical and the experimental harmonic values. The harmonic stretching frequency calculated is 97.60 cm-1, which is in excellent agreement with the experimental harmonic value of 100 ± 2 cm-1. The frequency value calculated including anharmonicity is 89.38 cm-1. The calculated fundamental frequency of the HF...Cl bending vibration is 13.12 cm-1, while harmonic ab initio calculations predicted a value of 72 cm-1. This significant difference is due to tunneling motion through the HF...Cl angle, which has a barrier to internal rotation of 151 cm-1. The intensities of these transitions at two temperatures have also been calculated. At 10 K, only the fundamental transition is significant, whereas the hot band transition of 81.30 cm-1 between the third and fourth levels dominates the spectrum at 300 K.