Simple Model Description of Chemical Reactivity and Reaction Pathways

Simple model of preliminary selection of possible reaction pathways for the reaction between multiatomic molecules is proposed. Most probable directions of the attack are estimated from plots of the total energy gradient as a function of mutual orientation of reacting molecules for large intermolecular distances. The method is verified for the oxidation reactions of ethylene and amidogen and also for amidogen interaction with NO. The possibility of the application of the proposed method to catalytic reactions is discussed

Application of density functional theory in model ling of electron properties of oxodimolybdenum scorpionate complexes

W artykule, na przykładzie skorpionianowych kompleksów oksodimolibdenowych o mieszanej walencyjności, przedstawiono zastosowanie modelowania DFT do określenia i interpretacji fizycznej wpływu wzajemnej orientacji grup [MoII,INO]3+,2+ (par donorowo- akceptorowych, D-A) na przepływ gęstości elektronowej we fragmencie Mo-O-Mo. Zależność struktury elektronowej, tj. lokalizacji/ delokalizacji niesparowanego elektronu od wzajemnego położenia lokalnych układów współrzędnych D i A, może nadawać kompleksom właściwości molekularnych przełączników i reostatów.This paper presents the application of DFT modelling in the determination and physical interpretation of the effect of mutual orientation of [MoII, INO] 3+,2+ groups (donor-acceptor pairs, D-A) on the electron density flow in the Mo-O-Mo moiety, exemplified by oxodimolybdenum scorpionate complexes of mixed valence. The relationship between the electron structure, i.e. localization/ delocalization of unpaired electron and mutual position of D and A coordinate systems, may bestow the properties of molecular switches and rheostats on complexes

Spin and electron density redistribution upon binding of non-innocent ligand by iron in enzymatic environment: challenges for quantum chemistry

The quality of the description of a chemical bond between the metal (active site) and the ligand (substrate) critically depends on the electronic processes accompanying the bond formation. However, as far as transition metal centers (TM) in enzymes are considered, most of the properties related to their electronic structure are extremely challenging for quantum chemistry. Especially severe problems appear for the bonding of NO to ferrous sites, e.g. in myoglobin or non-heme enzymes. Therefore, special care has to be shown in the assessment of a quantum chemical method employed with respect to its power in describing the properties of interest. In this work we discuss spin-resolved Fe-NO charge transfers and their relation to the metal spin state, with special attention paid to the interpretation of the bonding between NO and the transition metal center in terms of dative or covalent contributions; furthermore, the impact of spin and the electron transfer on the reactivity of the center is discussed. The stress is put on the role of the coordinating environment in controlling the reaction mechanism via fine-tuning of the spin and the oxidation status of the metal core. This goes in line with the high significance of spin in enzymatic reaction mechanisms (cf. multi-state reactivity proposed for iron enzymes)