Ponnambalam Venuvanalingam

Interaction of anthraquinone dyes with lysozyme: Evidences from spectroscopic and docking studies

The interaction between lysozyme and anthraquinone dyes such as Alizarin Red S, Acid blue 129 and Uniblue was studied using steady state, time resolved fluorescence measurements and docking studies. Addition of anthraquinone dyes effectively quenched the intrinsic fluorescence of lysozyme. Fluorescence quenching of lysozyme by dyes has revealed the formation of complex. The number of binding sites (n) and binding constant (K) for all the three dyes was calculated by relevant fluorescence quenching data. Based on Försters non-radiative energy transfer theory, distance (r(0)) between the donor (lysozyme) and acceptor (dyes) as well as the critical energy transfer distance (R(0)) has also been calculated. The interaction between dyes and lysozyme occurs through static quenching mechanism as confirmed by time resolved spectroscopy. The conformational change of lysozyme has been analyzed using synchronous fluorescence measurement. Finally, docking studies revealed that specific interactions were observed with the residue of Trp 62.

Tuning nonlinear optical and optoelectronic properties of vinyl coupled triazene chromophores: a density functional theory and time-dependent density functional theory investigation.

Triazenes are a unique class of polyazo compounds containing three consecutive nitrogen atoms in an acyclic arrangement and are promising NLO candidates. In the present work, a series of 15 donor-π-acceptor type vinyl coupled triazene derivatives (VCTDs) with different acceptors (-NO(2), -CN, and -COOH) have been designed, and their structure, nonlinear response, and optoelectronic properties have been studied using density functional theory and time-dependent density functional theory methods. B3LYP/6-311g(d,p) optimized geometries of the designed candidates show delocalization from the acceptor to donor through a π-bridge. Molecular orbital composition analysis reveals that HOMO is stabilized by the π-bridge, whereas acceptors play a major role in the stabilization of LUMO. Among the three acceptors, nitro derivatives are found to be efficient NLO candidates, and tri- and di-substituted cyano and carboxylic acid derivatives also show reasonably good NLO response. The effect of solvation on these properties has been studied using PCM calculations. From TDDFT calculations, the computed absorption spectra of these candidates lie in the range of 350-480 nm in the gas phase and have positive solvatochromism. The ground-state stabilization interactions are accounted from NBO calculations. In an effort to substantiate the thermal stability of the designed candidates, computations have been done to identify the weak interactions in the systems through NCI and AIM analysis. In summary, 10 out of 15 designed candidates are found to have excellent NLO and optoelectronic properties.

Topological resonance energy predictions of the stability of fullerene clusters

The topological resonance energies (TRE) for various fullerene clusters (C20 to C60) have been computed and based on this, stabilities of fullerenes are discussed. Trend in stability predicted by the TRE model is compared with predictions from the conjugated circuit model as well as the MNDO and ab initio methods. Reasonable agreement is found between the TRE model and rigorous quantum mechanical methods.

LITHIUM BONDING INTERACTION IN H2CY...LIF (Y=O,S) COMPLEXES : A THEORETICAL PROBE

Ab initio calculations at 6-31++G(d,p) level have been done on H2CY⋯LiF (Y=O,S) complexes choosing ten possible orientations in each complex. The effect of correlation on complex binding energies has been studied via single point MP2 (full) calculations done on 6-31++G(d,p) geometry. Binding energies have been corrected for basis set superposition error. Frequency calculations confirm that H2CO⋯LiF and H2CS⋯LiF complexes have three and two stable forms, respectively. The most stable form in each complex has been found to have a strong lithium bonding interaction and a secondary hydrogen bonding interaction. NBO analysis has revealed that in this form oxygen donates nσ lone pair while sulfur donates its nπ lone pair. In yet another stable form of these complexes, mixed donation of π and nσ electrons have been observed.

Highly Emissive Luminogens Based on Imidazo[1,2‐a]pyridine for Electroluminescent Applications

A search for novel organic luminogens led us to design and synthesize some N-fused imidazole derivatives based on imidazo[1,2-a]pyridine as the core and arylamine and imidazole as the peripheral groups. The fluorophores were synthesized through a multicomponent cascade reaction (A(3) coupling) of a heterocyclic azine with an aldehyde and alkyne, followed by Suzuki coupling and a multicomponent cyclization reaction. All of the compounds exhibited interesting photophysical responses, especially arylamine-containing derivatives, which displayed strong positive solvatochromism in the emission spectra that indicated a more polar excited state owing to an efficient charge migration from the donor arylamine to the imidazo[1,2-a]pyridine acceptor. The quantum yields ranged from 0.2 to 0.7 and depended on the substitution pattern, most notably that based on the donor group at the C2 position. Moreover, the influence of general and specific solvent effects on the photophysical properties of the fluorophores was discussed with four-parameter Catalán and Kamlet-Taft solvent scales. The excellent thermal, electrochemical, and morphological stability of the compounds was explored by cyclic voltammetry, thermogravimetric analysis, and AFM methods. Furthermore, to understand the structure, bonding, and band gap of the molecules, DFT calculations were performed. The performance of the electroluminescence behavior of the imidazo[1,2-a]pyridine derivative was investigated by fabricating a multilayer organic light-emitting diode with a configuration of ITO/NPB (60 nm)/EML (40 nm)/BCP (15 nm)/Alq3 (20 nm)/LiF (0.5 nm)/Al(100 nm) (ITO=indium tin oxide, EML=emissive layer, BCP=2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, Alq3 =tris(8-hydroxyquinolinato)aluminum), which exhibited white emission with a turn-on voltage of 8 V and a brightness of 22 cd m(-2).

Elucidating the structures and binding of halide ions bound to cucurbit[6]uril, hemi-cucurbit[6]uril and bambus[6]uril using DFT calculations

Understanding the binding and nature of the interactions present in host–guest complexes are central to supramolecular chemistry. In this paper, we tried to understand the nature of bonding between halides and three related host molecules using density functional theory. We have addressed a number of issues such as the role of solvation, the role of cations and the use of appropriate density functional calculations that are crucial for modeling host–guest complexes. Calculations show that the binding of halides in cucurbit-[6]-uril is assisted by a cation, whereas in hemi-cucurbit-[6]-uril, it is assisted by solvents. AIM calculations reveal the nature of non-bonded interactions present in these host–guest complexes and in particular brings out the two types of hydrogen bonding present in hm-CB-[6] and BU-[6] complexes.

Surfactant–copper(II) Schiff base complexes: synthesis, structural investigation, DNA interaction, docking studies, and cytotoxic activity

A series of surfactant–copper(II) Schiff base complexes (1–6) of the general formula, [Cu(sal-R2)2] and [Cu(5-OMe-sal-R2)2], {where, sal = salicylaldehyde, 5-OMe-sal = 5-methoxy- salicylaldehyde, and R2 = dodecylamine (DA), tetradecylamine (TA), or cetylamine (CA)} have been synthesized and characterized by spectroscopic, ESI-MS, and elemental analysis methods. For a special reason, the structure of one of the complexes (2) was resolved by single crystal X-ray diffraction analysis and it indicates the presence of a distorted square-planar geometry in the complex. Analysis of the binding of these complexes with DNA has been carried out adapting UV-visible-, fluorescence-, as well as circular dichroism spectroscopic methods and viscosity experiments. The results indicate that the complexes bind via minor groove mode involving the hydrophobic surfactant chain. Increase in the length of the aliphatic chain of the ligands facilitates the binding. Further, molecular docking calculations have been performed to understand the nature as well as order of binding of these complexes with DNA. This docking analysis also suggested that the complexes interact with DNA through the alkyl chain present in the Schiff base ligands via the minor groove. In addition, the cytotoxic property of the surfactant–copper(II) Schiff base complexes have been studied against a breast cancer cell line. All six complexes reduced the visibility of the cells but complexes 2, 3, 5, and 6 brought about this effect at fairly low concentrations. Analyzed further, but a small percentage of cells succumbed to necrosis. Of these complexes (6) proved to be the most efficient aptotoxic agent.

AM1 AND PM3 TRANSITION STRUCTURES FOR THE EPOXIDATION OF ALKENES AND ALLENE BY METHYLATED DIOXIRANES

Abstract AM1 and PM3 calculations reveal that epoxidations of ethylene (ET) by dimethyldioxirane (DMD) and methyl(trifluoro-methyl) dioxirane (MTMD), and 1,2-dichloroethylene (DCE) and allene by DMD pass through a spiro transition structure (TS) and in the reactions, peroxide bond σ ∗ level takes part at a very early stage. MTMD is found to be the most reactive dioxirane as the CF3 group in it stabilizes this σ ∗ level. Differential preference of cis- to trans-DCE in the reaction is explained as due to steric repulsion by the chlorine atom on the approaching dioxirane during the reaction and the calculated results are thus more favorable for Z-epoxide formation over E-epoxide. Compared to ethylene, allene is found to be less reactive in the epoxidation by DMD. Computed AM1 and PM3 barriers agree reasonably with the available experimental results. Deformation energy analysis provide new insight into the factors involving in the activation process. The bond order analysis clearly reveals the extent of bond make-break at TS, and through that, explains the reaction barrier.

Synthesis, DNA binding and docking studies of copper(II) complexes containing modified phenanthroline ligands

Copper(II) complexes, [Cu(Hsal)(L)(ClO4)] (where Hsal = salicylaldehyde, 1: L = dpqC = dipyrido[3,2-a:2′,3′-c](6,7,8,9-tetrahydro)phenazine and 2: L = dppz = dipyrido[3,2-a:2′,3′-c]phenazine), were synthesized and characterized using elemental analysis and spectroscopic methods. Single-crystal XRD on 1 confirms the presence of square pyramidal geometry around Cu(II). DNA interaction studies were performed for both the complexes using UV–visible, fluorescence and circular dichroism spectroscopic techniques, and viscosity. These complexes bind with DNA through partial intercalation. Molecular docking studies confirm our experimental findings of mode of binding of our complexes with DNA. Graphical Abstract

Harmonic analysis of vibrations of morpholine-4-ylmethylthiourea: A DFT, midinfrared and Raman spectral study

The FTIR and FT-Raman spectra of morpholine-4-ylmethylthiourea (MMTU) were recorded in the region of mid-IR (400-4,000 cm(-1)). Initial geometry generated from the standard geometrical parameters was relaxed without any constraint on the potential energy surface at MP2 and DFT levels adopting the standard 6-31++G and 6-311+G basis set. With the help of two specific scaling procedures the computed harmonic frequencies have been compared with the observed vibrational wave numbers of FTIR and FT-Raman spectra and assigned to different normal modes of the molecule. Most of the vibrational modes have wave numbers in the expected range. The appropriate theoretical spectrograms of the IR spectra of MMTU have been also constructed.