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A series of Mn(I) complexes Mn(L1)(CO)3Br, Mn(L2)(CO)3Br, Mn(L1)(CO)3(OAc) and Mn(L3)(CO)3Br [L1=2‐(5‐tert‐butyl‐1H‐pyrazol‐3‐yl)‐1,8‐naphthyridine, L2=2‐(5‐tert‐butyl‐1H‐pyrazol‐3‐yl)pyridine, L3=2‐(5‐tert‐butyl‐1‐methyl‐1H‐pyrazol‐3‐yl)‐1,8‐naphthyridine] were synthesized and fully characterized. The acid‐base equilibrium between the pyrazole and the pyrazolato forms of Mn(L1)(CO)3Br was studied by 1H NMR and UV‐vis spectra. These complexes are screened as catalysts for acceptorless dehydrogenative coupling (ADC) of primary alcohols and aromatic diamines for the synthesis of benzimidazole and quinoline derivatives with the release of H2 and H2O as byproducts. The protic complex Mn(L1)(CO)3Br shows the highest catalytic activity for the synthesis of 2‐substituted benzimidazole derivatives with broad substrate scope, whereas a related complex [Mn(L3)(CO)3Br], which is devoid of the proton responsive β‐NH unit, shows significantly reduced catalytic efficiency validating the crucial role of the β‐NH functionality for the alcohol dehydrogenation reactions. Control experiments, kinetic and deuterated studies, and density functional theory (DFT) calculations reveal a synchronous hydride‐proton transfer by the metal‐ligand construct in the alcohol dehydrogenation step. [ABSTRACT FROM AUTHOR]

The molecular conformations of phospholipids comprising a lipid bilayer determine the physico-chemical properties of the latter. In this study, we attempt to understand the various possible conformations available for an anionic lipid molecule dimyristoylphosphatidylglycerol (DMPG) with Na as its charge-compensating cation. The various possible molecular orientations available for lipid molecule are analysed using a density functional theory-based method. Our study reveals a rich conformational space with two different types of glycerol body orientations, more commonly known as rotamers. Interestingly, this is in agreement with the molecular conformations proposed earlier by NMR studies on lipid monomer solutions. We demonstrate that these conformations are an outcome of delicate balance of electrostatic and van der Waals forces along with intra-molecular hydrogen bonds achieved by a critical combination of torsion angles. Na+ ions are seen to interact predominantly with the oxygen atoms of the glycerol groups in tail and head along with that of phosphate oxygen atoms leading to a cage-like orientation of lipid molecule around the Na+. Following the conformational analysis, we attempt to evaluate the electronic properties of few low-lying conformations. This study shows that though the water molecules screen the Na-Olipid interactions, they do not dramatically modify the Na-Olipid bond distances. The lipid conformation retains the cage-like structure around the Na+ in the presence of water molecules. Some amount of charge transfer from the water molecules to Na ion is noted. The water molecules modify the phosphate-tail glycerol group interactions leading to a more stable Na-DMPG-H2O and Na-DMPG-4H2O complexes. [ABSTRACT FROM AUTHOR]

Conceptual density functional theory is exploited to understand the reactivity in a medium of solvents with increasing dielectric constants. Aprotic as well as protic solvents are used for this study. It is found that the global parameters, such as chemical potential and hardness, decrease from gas phase to solvent phase with increasing dielectric constant. However, it is observed that the Fukui functions of the reactive atoms increase significantly with the dielectric constants of the aprotic solvents while for the protic solvents the variation of the reactivity indices is insignificant. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [ABSTRACT FROM AUTHOR]

Abstract: We consider a series of dipolar organic molecules where the donor groups and the acceptor groups are separated by π-conjugation like phenyl ring or alkene chains. We have performed extensive quantum chemical calculations based on density functional theory (DFT) to calculate their linear and non-linear optical coefficients. We show that though DFT is known to overestimate the polarizabilities of quasi-linear systems, the results with proper inclusion of exchange correlation compare well with the experimental studies. On increasing the π-conjugation length, the coefficients increase non-linearly. We also vary the donor and the acceptor groups and study the role of chemical modifications on the response properties. Herein we suggest experimental methods by which the molecules may be arranged in non-centrosymmetric fashion in the bulk for device integration. [Copyright &y& Elsevier]

Low temperature oxidation of CO to CO2 is an important process for the environment. Similarly adsorption of CO from the releasing sources is also of major concern today. Whereas the potential of gold and silver clusters is well proven for the catalysis of the above mentioned reaction, the potential of aluminum (Al) clusters remains unexplored. The present study proves that, similar to the transition metals, Al clusters can also be used for adsorption of gases. We first tested the potential of Al cluster as adsorbents for CO. The high binding energy (BE) values prove that Al clusters can be used for adsorbing both CO and O2. Since oxygen binding is more facile, we adsorbed oxygen on Al and then checked the effect of this O2 on the BE of CO. The results were obtained by DFT calculations at M062X/TZVP level of theory.Activation of carbon monoxide (CO) on oxygen-adsorbed aluminum (Al) cluster [ABSTRACT FROM AUTHOR]

Abstract: A profile of the number of electrons with distance along the M–X bond in gas-phase diatomic molecules has been obtained from electron density plots calculated using DFT B3LYP 6-311G∗∗ method for some representative molecules. This “number profile” is compared with that expected from the partitioning of the 1D bond-distance into atom-specific transferable “hub” or core atomic sizes of the M and X atoms and another “axle” size which is associated with a pair of (bonding) electrons. The “hub” size is proportional to a core atom-specific size, rnZ c with rnZ c (M)⩾ rnZ c (X). For “single bonds”, the “hub” size for M atom is CMrnZ c (M) and for X atom is CXrnZ c (X). The “axle” size, DMX , is usually the ordinary (∼4aH /3 where aH is the Bohr radius of the hydrogen atom) or elongated (∼2aH ) bond length of the hydrogen molecule. The “hub” and “axle” sizes could be characterized “charge-transfer” (CM =π2/3 =2.144; CX =π4/3/2=2.300 and DMX = 4aH /3) or “neutral” (CM or CX =1, 2, … and DMX =2aH ). We use a new “static” or “peripatetic” classification for the core sizes which is derived from a new condition for metallization in elements based on atomic size. The charge-transfer distance, dMX ±, is usually found for “static” conditions while the “neutral” description is usually found when X=F or for “peripatetic” conditions. Such a partitioning is seen to agree with that from the plot of the total number of electrons, N el, vs r along a bond axis. The N el vs r plots from each atom are described by a simple hydrogen-atom-like function which differ away (“out”) or towards (“in”) the M–X bond. Thus N in,out(M,X)=(ZM,X ±1)exp(−r/B in,out) where the minus sign is associated with M and plus sign with X and B in,out being related inversely to the Slater orbital exponent. [Copyright &y& Elsevier]