Chalcogen atom effect on the intersystem crossing kinetic constant of oxygen- and sulfur disubstituted heteroporphyrins.

The modulation of the photophysical properties of di-substituted porphyrin rings upon the oxygen and sulfur-for-nitrogen replacement has been investigated at density functional theory (DFT) and its time-dependent formulation (TDDFT). The considered properties range from structural behaviors and excitation energies to spin-orbit coupling (SOC) and nonradiative intersystem kinetic constants. Results show that the SOC strongly increase upon chalcogen substitution and, accordingly, the computed nonradiative kinetic constant also indicate an efficient singlet-triplet intersystem crossing in the sulfur containing macrocycle.

A DFT study on non-enzymatic degradations of anti-tuberculosis drug isoniazid.

Context: Isoniazid (INH) is one of the medications most used for tuberculosis (TB) treatment. However, long-term continuous therapy can cause hepatotoxicity and peripheral neuritis. The degradation of INH is an important aspect of the research in the field of drug stability as well as drug formulation for controlling release.

A DFT study on NO oxidation and methanol synthesis over BiO: single-site catalytic model of α-BiMoO.

Catalytic conversion of methane to methanol is one of the most promising processes for effective natural gas resource utilization. In this work, BiO-catalyzed oxidation of methane to methanol with NO as an oxidizing reactant has been investigated by DFT calculation. For the overall reaction mechanism of three NO molecules on BiO catalyst, two catalytic cycles were proposed.

Theoretical insight into joint photodynamic action of a gold(i) complex and a BODIPY chromophore for singlet oxygen generation.

Density functional theory is herein employed to provide theoretical insight into the mechanism involved in 1O2 photosensitization by a gold-BODIPY combined complex proposed as a promising photodynamic therapy agent. The protocol is thus used to compute the non-radiative rate constants for the S1 → Tj intersystem crossing transitions. Calculations show that while the incorporation of an iodine atom into the core skeleton of BODIPY enhances the singlet-triplet intersystem crossing (ISC) efficiency due to the occurrence of the singlet-triplet transition between states with different orbital characters (ππ* → πn*), the presence of a gold atom, even if not directly anchored to the chromophore core but through a triplet bond, equally entails an increase of the spin-orbit coupling constant due to the heavy atom effect.

Coumarins and alkaloids from the roots of Toddalia asiatica.

The EtOAc and MeOH extracts of the roots of Toddalia asiatica Lam. were investigated for the roots' chemical constituents. Two new compounds including 2'R-acetoxytoddanol (1) and 8S-10-O-demethylbocconoline (3) as well as 15 known compounds were isolated.

Tautomeric transformation of temozolomide, their proton affinities and chemical reactivities: A theoretical approach.

The gas-phase geometry optimizations of bare, mono- and dihydrated complexes of temozolomide isomers were carried out using density functional calculation at the M06-2X/6-31+G(d,p) level of the theory. The structures and protonation energies of protonated species of temozolomide are reported. Chemical indices of all isomers and protonated species are also reported.

A dye sensitized solar cell using natural counter electrode and natural dye derived from mangosteen peel waste.

Mangosteen peel is an inedible portion of a fruit. We are interested in using these residues as components of a dye sensitized solar cell (DSSC). Carbonized mangosteen peel was used with mangosteen peel dye as a natural counter electrode and a natural photosensitizer, respectively.

A density functional theory study on peptide bond cleavage at aspartic residues: direct vs cyclic intermediate hydrolysis.

In this work, peptide bond cleavages at carboxy- and amino-sides of the aspartic residue in a peptide model via direct (concerted and step-wise) and cyclic intermediate hydrolysis reaction pathways were explored computationally. The energetics, thermodynamic properties, rate constants, and equilibrium constants of all hydrolysis reactions, as well as their energy profiles were computed at the B3LYP/6-311++G(d,p) level of theory. The result indicated that peptide bond cleavage of the Asp residue occurred most preferentially via the cyclic intermediate hydrolysis pathway.

Theoretical study on isomerization and peptide bond cleavage at aspartic residue.

Isomerization and peptide bond cleavage at aspartic residue (Asp) in peptide models have been reported. In this study, the mechanisms and energies concerning the isomerization and peptide bond cleavage at Asp residue were investigated by the density functional theory (DFT) at B3LYP/6-311++G(d,p). The integral equation formalism-polarizable continuum model (IEF-PCM) was utilized to calculate solvation effect by single-point calculation of the gas-phase B3LYP/6-311++G(d,p)-optimized structure.

DFT and TDDFT study on the electronic structure and photoelectrochemical properties of dyes derived from cochineal and lac insects as photosensitizer for dye-sensitized solar cells.

Essential parameters related to the photoelectrochemical properties, such as ground state geometries, electronic structures, oxidation potential and electron driving force, of cochineal insect dyes were investigated by DFT and TDDFT at the B3LYP/6-31+G(d,p) level of the theory. The results show that the major charge flow dynamic for all dyes is the HOMO→LUMO transition. The bi-coordinated binding mode, in which the dye uses one carboxyl- and hydroxyl oxygen bound to Ti(IV), is found for all dye-TiO(2) systems.

Conformational analysis of alkali metal complexes of anionic species of aspartic acid, their interconversion and deprotonation: a DFT investigation.

Gas-phase geometry-optimized structures of aspartate complexes of anionic species (Hasp(-)) with lithium, sodium and potassium metal cations and transition-state structures for their interconversions were obtained using the density functional theory computations at the B3LYP/6-311++G(d,p) level of theory. The metal ion affinities of Hasp(-) species and deprotonation energies of [Hasp-M] complexes, M=Li+, Na+ and K+, and their conformers were obtained. Relative energies of the [Hasp-M] complex conformers, reaction energies, thermodynamic properties, rate and equilibrium constants of their complexation are reported.

Conformational analysis of alkali metal complexes of aspartate dianion and their interactions in gas phase.

The gas-phase geometry optimizations of mono and dinuclear complexes of dianionic species of aspartic acid, asp(2-) with lithium, sodium and potassium cations were carried out using density functional calculation at the B3LYP/6-311++G(d,p) level. The metal ion affinities (MIAs) of asp(2-) species and its complexes [asp-M](-), M=Li(+), Na(+) and K(+) were determined using the vibrational frequency calculations at the same level of theory. The most stable complex conformer for aspartate complexes with Li(+), Na(+) and K(+) alkali cations were found as a tri-coordinated form.