Collective excitations in liquid DMSO : FIR spectrum, Low frequency vibrational density of states and ultrafast dipolar solvation dynamics

Valuable dynamical and structural information about neat liquid DMSO at ambient conditions can be obtained through study of low frequency vibrations in the far infrared (FIR), that is, terahertz regime. For DMSO, collective excitations as well as single molecule stretches and bends have been measured by different kinds of experiments such as OHD-RIKES and terahertz spectroscopy. In the present work we investigate the intermolecular vibrational spectrum of DMSO through three different computational techniques namely (i) the far-infra red spectrum obtained through Fourier transform of total dipole moment auto time correlation function, (ii) from Fourier transform of the translational and angular velocity time autocorrelation functions and a (iii) quenched normal mode analysis of the parent liquid at 300K. The three spectrum, although exhibit differences among each other, reveal similar features which are in good, semi-quantitative, agreement with experimental results. Study of participation ratio of the density of states obtained from normal mode analysis shows that the broad spectrum around 100 cm-1 involves collective oscillations of 300-400 molecules. Dipolar solvation dynamics exhibit ultrafast energy relaxation (dipolar solvation dynamics) with initial time correlation function around 140 fs which can be attributed to the coupling to the collective excitations. We compare properties of DMSO with those of water vis-a-vis the existence of the low frequency collective modes. Lastly, we find that the collective excitation spectrum exhibits strong temperature dependence.Comment: 24 pages,8 figure

Hydrophobic hydration driven self-assembly of Curcumin in water: Similarities to nucleation and growth under large metastability, and an analysis of water dynamics at heterogeneous surfaces

As the beneficial effects of curcumin have often been reported to be limited to its small concentrations, we have undertaken a study to find the aggregation properties of curcumin in water by varying the number of monomers. Our molecular dynamics simulation results show that the equilibrated structure is always an aggregated state with remarkable structural rearrangements as we vary the number of curcumin monomers from 4 to 16 monomers. We find that curcumin monomers form clusters in a very definite pattern where they tend to aggregate both in parallel and anti-parallel orientation of the phenyl rings, often seen in the formation of beta-sheet in proteins. A considerable enhancement in the population of parallel alignments is observed with increasing the system size from 12 to 16 curcumin monomers. Due to the prevalence of such parallel alignment for large system size, a more closely packed cluster is formed with maximum number of hydrophobic contacts. We also follow the pathway of cluster growth, in particular the transition from the initial segregated to the final aggregated state. We find the existence of a metastable structural intermediate involving a number of intermediate-sized clusters dispersed in the solution. The course of aggregation bears similarity to nucleation and growth in highly metastable state. The final aggregated form remains stable with total exclusion of water from its sequestered hydrophobic core. We also investigate water structure near the cluster surface along with their orientation. We find that water molecules form a distorted tetrahedral geometry in the 1st solvation layer of the cluster, interacting strongly with hydrophilic groups at the surface of curcumin. The dynamics of such quasi-bound water molecules near the surface of curcumin cluster is considerably slower than the bulk signifying a restricted motion as often found in protein hydration layer.Comment: 31 pages, 9 figure

Sol-gel synthesis of mesoporous hollow titania microspheres for photodegradation of 4-chlorophenol

Mesoporous titania (TiO2) hollow microspheres have been prepared by sol-gel method and characterized by XRD, Raman, FTIR, N2 adsorption-desorption study, FESEM, TEM and UV-DRS. The FESEM images reveal hollow spherical shaped particles of size 2–4 µm. The BET surface area, total pore volume and average pore diameter of 400 °C-treated sample are found to be 74.52 m2 g-1, 0.23 cm3 g-1 and 12.37 nm, respectively. The band gap energy of the product is calculated as 3.06 eV. The prepared TiO2 hollow spheres show ~90% photodegradation of the water pollutant, 4-chlorophenol, within 1 h. The photocatalytic reaction shows pseudo-first order reaction with a rate constant of 0.027 min-1. The photocatalytic experiments repeated for another three cycles showed no significant changes in the k (min-1) values, indicating the potential reusability of the material

Nitrogen-Doped Nanoporous Carbon Nanospheroids for Selective Dye Adsorption and Pb(II) Ion Removal from Waste Water

In the presence of melamine and block copolymers, namely, F108, F127, and P123, nitrogen-doped nanoporous carbon nanospheroids (N@CNSs) were synthesized by the hydrothermal process. The F127-modified sample (CNF127) exhibits the maximum BrunauerEmmettTeller (BET) surface area of 773.4 m(2)/g with a pore volume of 0.877 cm(3)/g. The microstructural study reveals that nanospheroids of size 50200 nm were aggregated together to form a chainlike structure for all triblock copolymer-modified samples. The X-ray photoelectron spectroscopy study shows the binding energies of 398.33 and 400.7 eV attributed to sp(2) (CN-)- and sp(3) (CN)-hybridized nitrogen-bonded carbons, respectively. The synthesized N@CNS samples showed selective adsorption of organic dye methylene blue (MB) in the presence of methyl orange (MO) as well as Pb(II) ion removal from contaminated water. The adsorptions for MB and Pb(II) ions followed pseudo-first-order and pseudo-second-order kinetic models, respectively. The sample CNF127 showed the highest adsorption of 73 and 99.82 mg/g for MB and Pb(II) adsorptions, respectively. The adsorption capacity for MB of the copolymer-modified samples follows the order CNF127 > CNP123 > CNF108, which corroborated with the mesoporosity as well as nitrogen content of the corresponding samples. The maximum % adsorption of Pb(II) follows the order CNF127 (99.82%) > CNF108 (98.74%) > CNP123 (91.82%), and this trend is attributed to the BET surface area of the corresponding samples. This study demonstrates multicomponent removal of water pollutants, both organic dyes and inorganic toxic metal ions

Rapid template-free synthesis of an air-stable hierarchical copper nanoassembly and its use as a reusable catalyst for 4-nitrophenol reduction

A hierarchical copper nanoassembly was synthesized by one-pot solvothermal treatment at 150 degrees C for 2 h in the presence of copper nitrate, formamide and water. The product exhibited phase pure hierarchical Cu microspheroids (2-7 mu m) comprising a nanorod (50-100 nm) assembly. The Cu microspheroids showed excellent air-stability, antioxidative properties and catalytic reduction of p-nitrophenol

From collective relaxation phenomena to phase separation in binary mixtures and some contributions to the hydration dynamics in the vicinity of biologically active molecules

The thesis presents detailed results of theoretical analyses based on extensive computer simulation studies with an aim to explore, quantify whenever possible, and understand the collective excitations, relaxation processes and temperature dependent phase separation kinetics in several binary mixtures. We also investigate the structure and dynamics of water in the vicinity of several biologically active proteins and small hydrophobes. Based on the phenomena studied the thesis has been divided into four major parts I. Collective excitations and ultrafast solvation dynamics in binary mixtures II. Non-equilibrium solvation dynamics in binary mixture: Composition dependence of non-linear relaxation III.Nanoscale heterogeneous phase separation kinetics in binary mixtures: Multistage dynamics IV.Spatial dependence of dielectric constant in protein-water systems and hydrophobic hydration driven self-assembly of hydrophobic molecules in water: Role of nucleatio