Theoretical investigation of the first-shell mechanism of acetylene hydration catalyzed by a biomimetic tungsten complex.

The reaction mechanism of the hydration of acetylene to acetaldehyde catalyzed by [W(IV)O(mnt)(2)](2-) (where mnt(2-) is 1,2-dicyanoethylenedithiolate) is studied using density functional theory. Both the uncatalyzed and the catalyzed reaction are considered to find out the origin of the catalysis. Three different models are investigated, in which an aquo, a hydroxo, or an oxo coordinates to the tungsten center.

Why iron? A spin-polarized conceptual density functional theory study on metal-binding specificity of porphyrin.

Heme is a key cofactor of hemoproteins in which porphyrin is often found to be preferentially metalated by the iron cation. In our previous work [Feng, X. T.

DFT study of the asymmetric nitroaldol (Henry) reaction catalyzed by a dinuclear Zn complex.

We report the mechanism of asymmetric nitroaldol (Henry) reaction catalyzed by a dinuclear Zn complex using density functional theory. The experimentally proposed catalytic cycle is validated, in which the first step is the deprotonation of nitromethane by the ethyl anion of the catalyst, subsequently a C-C bond formation step, and then the protonation of the resulting alkoxide. Three mechanistic scenarios (differing in binding modes) have been considered for the C-C bond formation step.

Dipeptide hydrolysis by the dinuclear zinc enzyme human renal dipeptidase: mechanistic insights from DFT calculations.

The reaction mechanism of the dinuclear zinc enzyme human renal dipeptidase is investigated using hybrid density functional theory. This enzyme catalyzes the hydrolysis of dipeptides and beta-lactam antibiotics. Two different protonation states in which the important active site residue Asp288 is either neutral or ionized were considered.

DFT study on the mechanism of Escherichia coli inorganic pyrophosphatase.

Escherichia coli inorganic pyrophosphatase (E-PPase) is a tetranuclear divalent metal dependent enzyme that catalyzes the reversible interconversion of pyrophosphate (PPi) and orthophosphate (Pi), with Mg(2+) conferring the highest activity. In the present work, the reaction mechanism of E-PPase is investigated using the hybrid density functional theory (DFT) method B3LYP with a large model of the active site. Our calculated results shed further light on the detailed reaction mechanism.

Theoretical studies on pyridoxal 5'-phosphate-dependent transamination of alpha-amino acids.

Density functional methods have been applied to investigate the irreversible transamination between glyoxylic acid and pyridoxamine analog and the catalytic mechanism for the critical [1,3] proton transfer step in aspartate aminotransferase (AATase). The results indicate that the catalytic effect of pyridoxal 5'-phosphate (PLP) may be attributed to its ability to stabilize related transition states through structural resonance. Additionally, the PLP hydroxyl group and the carboxylic group of the amino acid can shuttle proton, thereby lowering the barrier.

Water-assisted transamination of glycine and formaldehyde.

A computational study on the transamination reaction of molecular complexes that consist of NH2CH2COOH + CH2O + nH2O, where n = 0, 1, 2, is presented. This work has allowed the description of the geometries of all the intermediates and transition states of the reactions, which can be described by five steps: carbinolamine formation, dehydration, 1,3 proton transfer, hydrolysis, and carbinolamine elimination. Among the five steps of the reaction, hydrolysis and elimination occur with the existence of general acid catalysis related to the carboxylic group.

Insights into the photochemical processes of ClC(O)SCl from ab initio calculations.

All possible unimolecular processes upon photolysis of ClC(O)SCl in the UV-visible region have been characterized in the present paper through the optimized stationary structures and computed potential-energy profiles of the S0, S1, T2, and S2 states with the MP2, B3LYP, CASSCF, and MR-CI methods in conjugation with the cc-pVDZ basis set. Upon photoexcitation in the range of 300-400 nm, the ClC(O)SCl molecules are excited to the S1 state. From this state, the dissociation into ClC(O)S + Cl takes place immediately and subsequently Cl2 and SCO are formed.

Striving to understand the photophysics and photochemistry of thiophosgene: a combined CASSCF and MR-CI study.

The potential energy surfaces for Cl(2)CS dissociation into ClCS + Cl in the five lowest electronic states have been determined with the combined complete active space self-consistent field (CASSCF) and MR-CI method. The wavelength-dependent photodissociation dynamics of Cl(2)CS have been characterized through computed potential energy surfaces, surface crossing points, and CASSCF molecular dynamics calculations. Irradiation of the Cl(2)CS molecules at 360-450 nm does not provide sufficient internal energy to overcome the barrier on S(1) dissociation, and the S(1)/T(2) intersection region is energetically inaccessible at this wavelength region; therefore, S(1) --> T(1) intersystem crossing is the dominant process, which is the main reason S(1)-S(0) fluorescence breaks off at excess energies of 3484-9284 cm(-1).

Photodissociation of acetic acid in the gas phase: an ab initio study.

Photodissociation of acetic acid in the gas phase was investigated using ab initio molecular orbital methods. The stationary structures on the ground-state potential energy surfaces were mainly optimized at the MP2 level of theory, while those on the excited-state surfaces were determined by complete active space SCF calculations with a correlation-consistent basis set of cc-pVDZ. The reaction pathways leading to different photoproducts are characterized on the basis of the computed potential energy surfaces and surface crossing points.

Theoretical studies on cycloaddition reactions between 1-aza-2-azoniaallene cation and olefins.

Density functional (B3LYP) calculations using the 6-31++g basis set have been employed to study the title reaction between the cationic 1,3-dipolar 1-aza-2-azoniaallene ion (H2C=N(+)=NH) and ethene. Our calculations confirmed that [3 + 2] cycloaddition reaction takes place via a three-membered ring intermediate. In addition, solvent effects and substituent effects were also studied.