Substituent effects on the aromaticity of benzene-An approach based on interaction coordinates.

Benzene and 23 monosubstituted and 32 disubstituted derivatives of benzene were optimized for minimum energy structures using the B3LYP/cc-pVTZ method. The force fields of all the compounds were evaluated at their optimized geometries using the same method and basis set. In order to understand the effect of substitution(s) on the aromaticity of benzene, the aromaticity index based on interaction coordinates (AIBIC) values were computed for each and the change from the benzene value was obtained.

Making and breaking of small water clusters: A combined quantum chemical and molecular dynamics approach.

We present a combined quantum chemical and molecular dynamics study of cyclic and noncyclic water n-mers ([(H O] , n = 2-6) at four different temperatures and showcase that the dynamics of small water clusters can reproduce the known properties of bulk water reasonably well. We investigate the making and breaking of the water clusters by computing the hydrogen bond strengths, average lifetimes, and relative stabilities, which are important to understand the complex solution dynamics. We compare the behavior of water clusters in the gas phase and in the solution phase as well as the variation in the properties as a function of cluster size and highlight the notably more interesting cluster dynamics of the water trimer when compared to the other water clusters.

Quantification of Aromaticity of Heterocyclic Systems Using Interaction Coordinates.

Recently, we proposed an aromaticity index based on interaction coordinates (AIBIC) ( J. Phys. Chem.

Using porphyrin-amino acid pairs to model the electrochemistry of heme proteins: experimental and theoretical investigations.

Quasi reversibility in electrochemical cycling between different oxidation states of iron is an often seen characteristic of iron containing heme proteins that bind dioxygen. Surprisingly, the system becomes fully reversible in the bare iron-porphyrin complex: hemin. This leads to the speculation that the polypeptide bulk (globin) around the iron-porphyrin active site in these heme proteins is probably responsible for the electrochemical quasi reversibility.

Understanding Translational-Rotational Coupling in Liquid Water through Changes in Mass Distribution.

A molecular dynamics study of liquid water and models of water has been carried out to understand the effect of changes in the mass distribution on molecular translation and rotation. Calculations on the motion of HO and HO, where m and n vary over a range of values by varying the mass at the hydrogen and oxygen positions, show that these form two distinct series. The two series exhibit different translational and rotational properties.

Quantification of Hydrogen Bond Strength Based on Interaction Coordinates: A New Approach.

A new approach to quantify hydrogen bond strengths based on interaction coordinates (HBSBIC) is proposed and is very promising. In this research, it is assumed that the projected force field of the fictitious three atoms fragment (DHA) where D is the proton donor and A is the proton acceptor from the full molecular force field of the H-bonded complex characterizes the hydrogen bond. The "interaction coordinate (IC)" derived from the internal compliance matrix elements of this three-atom fragment measures how the DH covalent bond (its electron density) responds to constrained optimization when the HA hydrogen bond is stretched by a known amount (its electron density is perturbed by a specified amount).

Quantification of Aromaticity Based on Interaction Coordinates: A New Proposal.

Attempts to establish degrees of aromaticity in molecules are legion. In the present study, we begin with a fictitious fragment arising from only those atoms contributing to the aromatic ring and having a force field projected from the original system. For example, in benzene, we adopt a fictitious C6 fragment with a force field projected from the full benzene force field.

Reaction mechanisms of aqueous monoethanolamine with carbon dioxide: a combined quantum chemical and molecular dynamics study.

Aqueous monoethanolamine (MEA) has been extensively studied as a solvent for CO2 capture, yet the underlying reaction mechanisms are still not fully understood. Combined ab initio and classical molecular dynamics simulations were performed to revisit and identify key elementary reactions and intermediates in 25-30 wt% aqueous MEA with CO2, by explicitly taking into account the structural and dynamic effects. Using static quantum chemical calculations, we also analyzed in more detail the fundamental interactions involved in the MEA-CO2 reaction.

Communication: Enhanced oxygen reduction reaction and its underlying mechanism in Pd-Ir-Co trimetallic alloys.

Based on a combined density functional theory and experimental study, we present that the electrochemical activity of Pd3Co alloy catalysts toward oxygen reduction reaction (ORR) can be enhanced by adding a small amount of Ir. While Ir tends to favorably exist in the subsurface layers, the underlying Ir atoms are found to cause a substantial modification in the surface electronic structure. As a consequence, we find that the activation barriers of O/OH hydrogenation reactions are noticeably lowered, which would be mainly responsible for the enhanced ORR activity.

Role of the surface-subsurface interlayer interaction in enhancing oxygen hydrogenation to water in Pd3Co alloy catalysts.

Based on density functional theory calculations, we present mechanisms underlying the improvement in the catalytic performance of Pd-based alloys for oxygen hydrogenation to water. As a model case, we consider the Pd/Pd3Co system where one or two Pd overlayers are located on top of the bimetallic substrate. Our calculations clearly demonstrate that the subsurface Co atoms assist in facilitating the oxygen reduction reaction by lowering the activation barriers for O/OH hydrogenation with a slight increase in the O2 scission barrier; however, we also find that the Co atoms lying below the subsurface have no significant contribution in altering the surface reactivity towards oxygen hydrogenation.