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

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

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

Silent information regulator 2 (Sir2), the founding member of the conserved sirtuin family of NAD+-dependent histone deacetylase, regulates several physiological processes including genome stability, gene silencing, metabolism and life span in yeast. Within the nucleus, Sir2 is associated with telomere clusters in the nuclear periphery and rDNA in the nucleolus and regulates gene silencing at these genomic sites. How distribution of Sir2 between telomere and rDNA is regulated is not known. Here we show that Sir2 is sumoylated and this modification modulates the intra-nuclear distribution of Sir2. We identify Siz2 as the key SUMO ligase and show that multiple lysines in Sir2 are subject to this sumoylation activity. Mutating K215 alone counteracts the inhibitory effect of Siz2 on telomeric silencing. SUMO modification of Sir2 impairs interaction with Sir4 but not Net1 and, furthermore, SUMO modified Sir2 shows …

Abstract

3a is an accessory protein from SARS coronavirus that is known to play a significant role in the proliferation of the virus by forming tetrameric ion channels. Although the monomeric units are known to consist of three transmembrane (TM) domains, there are no solved structures available for the complete monomer. The present study proposes a structural model for the transmembrane region of the monomer by employing our previously tested approach, which predicts potential orientations of TM α-helices by minimizing the unfavorable contact surfaces between the different TM domains. The best model structure comprising all three α-helices has been subjected to MD simulations to examine its quality. The TM bundle was found to form a compact and stable structure with significant intermolecular interactions. The structural features of the proposed model of 3a account for observations from previous …

Abstract

A new class of dendrimers, the poly(propyl ether imine) (PETIM) dendrimer, has been shown to be a novel hyperbranched polymer having potential applications as a drug delivery vehicle. Structure and dynamics of the amine terminated PETIM dendrimer and their changes with respect to the dendrimer generation are poorly understood. Since most drugs are hydrophobic in nature, the extent of hydrophobicity of the dendrimer core is related to its drug encapsulation and retention efficacy. In this study, we carry out fully atomistic molecular dynamics (MD) simulations to characterize the structure of PETIM (G2–G6) dendrimers in salt solution as a function of dendrimer generation at different protonation levels. Structural properties such as radius of gyration (Rg), radial density distribution, aspect ratio, and asphericity are calculated. In order to assess the hydrophilicity of the dendrimer, we compute the number of bound …

Abstract

Bacillus halodurans (Bh) ribonuclease H (RNase H) belongs to the nucleotidyl-transferase (NT) superfamily and is a prototypical member of a large family of enzymes that use two-metal ion (Mg2+ or Mn2+) catalysis to cleave nucleic acids. Long timescale molecular dynamics simulations have been performed on the BhRNase H-DNA-RNA hybrid complex and the respective monomers to understand the recognition mechanism, conformational preorganization, active site dynamics and energetics involved in the complex formation. Several structural and energetic analyses were performed and significant structural changes are observed in enzyme and hybrid duplex during complex formation. Hybrid molecule binding to RNase H enzyme leads to conformational changes in the DNA strand. The ability of the DNA strand in the hybrid duplex to sample conformations corresponding to typical A- and …

Abstract

DNA molecules tagged to metal nanoparticles, especially gold nanoparticles (AuNPs), have been shown to have potential applications in the design 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 caused to DNA base pairs in terms of size expansion and adsorption on a gold cluster (Au3) has been carried out using density functional theory. The geometric and electronic features of these complexes provide evidence for the 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 …

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.

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.