4-hydroxy-2,5-dimethylphenyl-benzophenone: conformational stability, FT-IR and Raman investigation

Reactivity, vibrational spectroscopy, internal rotation and thermochemical aspects of methylarsine

The aim of this investigation was to perform a characterization of the spectroscopic and thermodynamic properties of methylarsine (CH₃AsH₂). Post-Hartree-Fock, 29 DFT methods and eight different composite methodologies were employed in these analyses. A comparison between harmonic and anharmonic frequency accuracies in reproducing the observable frequencies was performed here. In addition, the CH₃AsH₂→CH₂AsH₃ isomerization barrier energy was estimated in 100kcalmol^-1, whereas the H₂-release routes barrier heights were in the 45-107kcalmol^-1 range. A rate constant of 10^-66s^-1 was predicted regarding the isomerization route, while the CH₂AsH₃ hydrogen elimination mechanism is faster than the methylarsine one. The transition state structure of the CH₃AsH₂ internal rotational barrier energy varied between 1.0 and 1.4kcalmol^-1. For the CH₂AsH₃ internal rotation the estimated barrier heights varied 0.6-2.5kcalmol^-1. The adiabatic ionization energy and the heat of formation each structure was also calculated here.

Intramolecular interactions, isomerization and vibrational frequencies of two paracetamol analogues: A spectroscopic and a computational approach

The aim of this investigation was to determine the molecular properties and provide an interpretation of the vibrational mode couplings of these two paracetamol analogues: 2-bromo-2-methyl-N-(4-nitrophenyl)-propanamide and 2-bromo-2-methyl-N-p-tolyl-propanamide. E/Z isomers, keto/enol unimolecular rearrangement and prediction of the transition state structures in each mechanism were also assessed using the Density Functional Theory (DFT). The DFT estimates a high energy gap between E and Z isomers (9-11 kcal·mol(-1)), with barrier heights ranging from 16 to 19 kcal·mol(-1). In contrast, the barrier energies on the keto/enol isomerization are almost 10 kcal·mol(-1) higher than those estimated for the E/Z rearrangement. The kinetic rate constant was also determined for each reaction mechanism. Natural bond orbital analysis and the quantum theory of atoms in molecules were used to interpret the intramolecular hydrogen bonds and to understand the most important interactions that govern the stabilization of each isomer. Furthermore, an analysis of the atomic charge distribution using different population methodologies was also performed.

Tailoring the electronic properties among oxoarsine, arsinoyl and arsine oxide isomers: the simplest molecular systems with an arsenic–oxygen bond

The main goal of this investigation is to understand the reaction pathways and the electronic and spectroscopy properties of AsOH_n radicals (n = 0–3), which are some of the simplest compound models with an arsenic–oxygen bond.

Computer modeling of the complexes of Chlorin e6 with amphiphilic polymers

Recently it has been shown that Chlorin e6 (Ce6) when complexed with Pluronics (hydrophilic ethylene and propylene oxide block copolymers) and poly(N-vinylpyrrolidone) (PVP) exhibits considerably higher phototoxicity towards tumor cells than free Ce6. The present work aimed to model Ce6 interactions with hydrophilic Pluronic F127 and PVP and find out the nature of intermolecular forces stabilizing these complexes. Modeling included 3 steps: (i) application of molecular dynamics to study polymer folding using AMBER 8 program, (ii) evaluation of partial charges in the Ce6 molecule using different quantum mechanical, semi-empirical and topological approaches and (iii) docking analysis of Ce6 interactions with polymer coils using AUTODOCK 4.2. It was found that the folding in regular polymers does not occur stochastically, but involves the formation of "primary" helical structures, which further combined to form hairpin-like "secondary" structures. The latter in turn associated to form coils with minimal solvent accessible hydrophobic area. The Ce6 ring lies flat on the surface of the polymer coil at the interface between hydrophobic and hydrophilic regions. Calculations showed higher affinity of Ce6 for PVP in comparison to Pluronic and revealed marginal contribution of Coulomb forces to the stabilization of both complexes, which are mainly stabilized by van der Waals and hydrogen interactions.