The dependence on ammonia pretreatment of N-O activation by Co(II) sites in zeolites: a DFT and ab initio molecular dynamics study.

This work is focused on the donor properties of cobalt-exchanged cationic sites in zeolites. It is based on cluster and periodic density functional theory modeling for relevant {[Co(II)(NH3)n]-NO} adducts, where Co(II) means a cobalt cation embedded either in a periodic model of chabasite (CHA) zeolite or in model clusters. NO stretching frequencies were derived from MD trajectories and compared to harmonic values from cluster calculations. By relating calculated NO frequencies to experimental FTIR spectra, it was shown that the forms of {Co(II)-NO} adducts comprising three or four ammonia co-ligands dominate the spectrum taken in ammonia-saturation conditions while forms with two NH3 ligands prevail under intermediate ammonia saturation. Finally, this work confirms the critical dependence of Co(II) activation ability towards NO upon the center donor properties, reinforced by ligation of strong donor ammonia ligands. However, strongly bound ligands appear also to compete with interaction of the center with the electron-rich framework, and a balance must be observed to maintain optimal activation ability. Graphical abstract A snapshot from MD trajectory showing a fragment of periodic framework with twoCo(II)-NO centers, bound to one framework oxygen and strongly coordinating three ammonia ligands with four others forming the second coordination sphere.

Quantum chemical modeling of electrochromism of tungsten oxide films.

A cluster model is proposed to describe the excitations in solid tungsten oxide. The density-functional theory approach is used to calculate the ground-state electronic structure of the model cluster and its optimum geometry; subsequently, time-dependent density-functional theory calculations are performed to obtain the oscillator strengths and energies of the excited states. The results are reported both for the electrically neutral cluster and for the cluster with an extra electron (mimicking the effect of electron injection from the cathode). They correctly locate the electrochemically active transition. The corresponding wave functions are delocalized, suggesting that electron localization at one tungsten center is rather unlikely, thereby shedding doubt as to the validity of the polaron model. Local lattice distortions presumably created at the stage of sample preparation are found to affect the excitation energies to a considerable extent, which explains the experimentally observable large width of optical absorption responsible for electrochromism.

Application of similarity matrices and genetic neural networks in quantitative structure-activity relationships of 2- or 4-(4-Methylpiperazino)pyrimidines: 5-HT(2A) receptor antagonists.

Antagonists of the 5-HT(2A) receptor are being used to treat many psychiatric disorders. The present work focuses on a group of 27 antagonists possessing varying affinities toward the receptor. These are 26 title compounds and clozapine as a reference antagonist. The active conformers of the conformationally flexible ligands were proposed by using the active rigid analogue approach and performing similarity calculations. The calculations involved genetic neural network (GNN) computations deriving QSARs from similarity matrices (SM) with cross-validated correlation coefficients exceeding 0.92. The performance of neural networks with variety of architectures was studied. As the computations were performed for cations and neutral molecules separately, the relevance of the ligand charging is discussed.

Quantum chemical modeling (DFT) of active species on the V-W-O catalyst surface in various redox conditions

This study concerns quantum chemical modeling of water behaviour on V-W-O systems. It was undertaken in order to validate the hypothesis that the presence of W atoms on (001) surface of the crystalline vanadia-like species, facilitates low temperature water dissociation. Quantum chemical calculations were done with the use of modern electronic structure methodology, based on the density functional theory (DFT). The program package DMol of Molecular Simulations, was applied for the calculations. The calculations were performed for small clusters representing two adjacent metal sites, in pentacoordinated oxygen environment, analogous to bipiramidal clusters, introduced in description of the (001) layers of vanadium pentoxide.

Characteristics of the ligand-binding site interaction for a series of arecoline-derived muscarinic agonists: a quantum chemical study.

This work focuses on electronic and conformational structure of bicyclic analogues of arecoline and sulfoarecoline--muscarinic receptor agonists structurally related to 4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridin-3-ol (THPO) and its S-methylsulfonium derivative (DHTO). Conformational freedom of six-member rings containing sulphur and nitrogen has been investigated by means of semiempirical AM1 method. Interaction between 'cationic heads' of two representative compounds and HCO2- ion serving as a model of carboxyl group of Asp in the muscarinic receptor has been modelled using DFT method in local approximation (LDA with VWN exchange correlation functional). Electrostatic potential (ESP) around studied complexes and ligands with added electron (simulation of complex formation) are presented and analysed. Position and depth of ESP minima in a series of studied ligands correlate well with their activity as muscarinic agonists. On the basis of our results the mechanism of ligand-binding site interaction may be elucidated. The calculations allow also for the comparison of bicyclic analogues of arecoline with already existing model for muscarinic pharmacophore and for rationalization of model parameters.