Abstract

Understanding synergistic effect by calculating electronic structure is essential to fine-tune the catalytic properties of bimetallic nanoalloy clusters which might be used for design of novel efficient catalysts. Density functional theory PBE0 calculations were performed to investigate the structure and energetics of various intermediates involved in the CO oxidation reaction catalyzed by Au3-xYx (x= 0–3 and Y denotes Ag or, Pt or, Pd) trimeric clusters through two possible pathways: Eley-Rideal (ER) and Langmuir-Hinshelwood (LH). The results of this investigation show that the catalytic behavior of the nanocluster highly depends on its composition and the reaction site taken into consideration. The most active reaction centres of goldsilver, gold-palladium, gold-platinum clusters are gold, palladium and platinum atoms respectively. The gold-silver clusters and AuPt2 prefer ER mechanism whereas, gold-palladium and Au2Pt selectively favour LH mechanism in comparison to the other. Bimetallic clusters, in general, are more efficient in comparison to their pristine mono-metallic counterparts, in activating the OO bond for the reaction and have relatively easy CO2 dissociation. Overall results indicate that the alloyed clusters could potentially have a better catalytic activity as compared to pure gold clusters for CO oxidation at low temperatures.

Abstract

We developed a set of conformationally locked molecules each of which makes a single CH⋯O H-bond/short contact and has different electron density at the acceptor oxygen atom. The downfield shift of the 1H NMR signals due to the hydrogen involved in the CH⋯O H-bond varied from 0.93–1.6 ppm, and the magnitude of Δδ is in correlation with the hybridization state of the acceptor oxygen and with the CH⋯O H-bond strengths quantified using a computational method.

Abstract

Urea-assisted denaturation of protein and RNA has been shown to be a valuable tool to study their stabilities and folding phenomena. It has been shown that stacking interactions between nucleobases and urea are one of the driving forces of denaturation. In this study, the ability of urea to form unconventional stacking interactions with RNA bases is investigated by performing high-level quantum calculations (RI-MP2/aug-ccpVDZ level) on a few thousands of model systems. Four systems were considered based on the RNA nucleobases (GUA, ADE, CYT, and URA) for the investigation. For each system, a set of models were designed to study the role of hetero-atoms/groups of the nucleobases on stacking interactions with urea moiety with respect to every possible pair. Several plane-parallel complexes were generated with urea on top of aromatic systems to exhaustively study all possible factors for urea-nucleobases stacking interactions. Energy decomposition analysis (EDA), atoms in molecules (AIM) and natural bond orbital (NBO) analysis were performed to gain better insights on non-covalent stacking interactions. Dispersion component was found to be heavily stabilizing, while the EHF was found to be repulsive for all the four systems indicating lack of hydrogen bonding (HB) type interactions and presence of dispersion type interactions. Amide and carbonyl groups of urea molecule were found to play a major role in favourable stacking interactions. We demonstrate that along with functional groups present on the nucleobases, the orientation of urea molecules plays a vital role in stabilizing the urea-nucleobase non-covalent interactions. The proposed study quantifies and provides a comprehensive theoretical description of urea nucleobase unconventional stacking interactions which helps to unravel urea driven RNA unfolding mechanism.

Abstract

An understanding of the determinants of the thermal stability of thermostable proteins is expected to enable design of enzymes that can be employed in industrial biocatalytic processes carried out at high temperatures. A major factor that has been proposed to stabilize thermostable proteins is the high occurrence of salt bridges. The current study employs free energy calculations to elucidate the thermodynamics of the formation of salt bridge interactions and the temperature dependence, using acetate and methylguanidium ions as model systems. Three different orientations of the methylguanidinium approaching the carboxylate group have been considered for obtaining the free energy profiles. The association of the two ions becomes more favorable with an increase in temperature. The desolvation penalty corresponding to the association of the ion pair is the lowest at high temperatures. The occurrence of …

Abstract

Gold clusters are currently regarded as new-generation catalysts owing to their exceptional efficiency in accelerating several classes of reactions. Density functional theory (DFT) is the method of choice for the investigation of energy pathways of reactions assisted by metal nanoparticles due to their computational efficiency. However, the reliability of such theoretical studies depends to a large extent on the choice of the DFT functional used. In the present work, the performance of a series of DFT-based functionals to accurately model the prototypical CO oxidation reaction catalyzed by a cluster has been examined by comparing the results with those obtained from high-level ab initio CCSD(T) method. This comparison study has been carried along the two possible pathways [Eley–Rideal (ER) and the Langmuir–Hinshelwood (LH)]. No significant differences among the DFT functionals were observed in …

Abstract

Multidrug resistance in Mycobacterium tuberculosis (M. Tb) and its coexistence with HIV are the biggest therapeutic challenges in anti-M. Tb drug discovery. The current study reports a Virtual Screening (VS) strategy to identify potential inhibitors of Mycobacterial cyclopropane synthase (CmaA1), an important M. Tb target considering the above challenges. Five ligand-based pharmacophore models were generated from 40 different conformations of the cofactors of CmaA1 taken from molecular dynamics (MD) simulations trajectories of CmaA1. The screening abilities of these models were validated by screening 23 inhibitors and 1398 non-inhibitors of CmaA1. A VS protocol was designed with four levels of screening i.e., ligand-based pharmacophore screening, structure-based pharmacophore screening, docking and absorption, distribution, metabolism, excretion and the toxicity (ADMET) filters. In an …

Abstract

Bimetallic nanoparticles (NPs) have been shown to exhibit certain advantages over pure NPs in catalysis due to a synergistic effect. It is common to disperse NPs in a polymer matrix such as polyvinylpyrrolidone (PVP) to prevent flocculation, which imparts considerable electronic effects on the NPs. In the present study, the interactions between aqueous solutions of N-ethylpyrrolidone (EP, system chosen to model the monomeric form of PVP) and Au/Pd bimetallic NPs, which are relevant in catalysis, have been investigated using molecular dynamics simulations and density functional theory (DFT) method. The adequacy of the force fields used was assessed based on their ability to reproduce the structures and adsorption energies obtained using DFT calculations. The interactions of NPs with the environment were studied at various concentrations of aqueous solutions of EP to examine the strength of NP–EP and NP …

Abstract

Urea transporters are membrane proteins that selectively allow urea molecules to pass through. It is not clear how these transporters allow rapid conduction of urea, a polar molecule, in spite of the presence of a hydrophobic constriction lined by aromatic rings. The current study elucidates the mechanism that is responsible for this rapid conduction by performing free energy calculations on the transporter dvUT with a cumulative sampling time of about 1.3 μs. A parallel arrangement of aromatic rings in the pore enables stacking of urea with these rings, which, in turn, lowers the energy barrier for urea transport. Such interaction of the rings with urea is proposed to be a conserved mechanism across all urea-conducting proteins. The free energy landscape for the permeation of multiple urea molecules reveals an interplay between interurea interaction and the solvation state of the urea molecules. This is for the first time …

Abstract

DNA molecules tagged to metal nanoparticles, especially gold nanoparticles (AuNPs), have been shown to exhibit potential applications in designing and fabrication of novel electronic nano-devices, but the binding mechanism between gold nanoparticles and DNA bases and its implications are not completely understood. In this work, a comprehensive study to examine the effect of structural perturbations offered to DNA base pairs in terms of size expansion and adsorption on a gold cluster (Au3) has been done using density functional theory. Geometric and electronic features of these complexes provide evidences for distortion of certain base pairs depending on the binding site of the cluster. This is further substantiated via normal mode, natural bond orbital (NBO) and atoms in molecules (AIM) analyses. The natural population analysis (NPA) and NBO analysis indicate that complexation greatly affects the charge distribution on the base pairs due to charge transfer between base pair and gold cluster. This charge redistribution may offer a possibility of higher order interactions. Upon complexation, a marked decrease in the HOMO-LUMO gap is observed, which is more profound in cases where size expanded bases are involved due to the extended π-conjugation of the fused benzine rings. This study demonstrates the possibility of combining structural modifications to DNA base pairs and subsequent binding to gold nano particles to modulate and achieve molecular systems with desired optico-electronic properties.

Abstract

Herein, the conventional and unconventional hydrogen bonding potential of adenine in APA for double zipper helical assembly of deoxyoligonucleotides is demonstrated under ambient conditions. The quantum mechanical calculations supported the formation of hybrid DNA ensembles.