Intra-molecular hydrogen bonding with organic fluorine in the solution state: Deriving evidence by a two dimensional NMR experiment

The direct evidence for the existence of intra-molecular C-F center dot center dot center dot H-N hydrogen bond in organofluorine molecules, in the liquid state, is derived using NMR spectroscopy by the detection of long range interactions among fluorine, nitrogen and hydrogen atoms. The present study reports the determination of the relative signs and magnitudes of through space and through bond couplings to draw unambiguous evidence on the existence of weak molecular interactions involving organic fluorine. It is a simple, easy to implement, N-15 natural abundant two dimensional heteronuclear N-15-H-1 double quantum-single quantum correlation experiment. The existence of intra-molecular hydrogen bond is conclusively established in the investigated molecules. (C) 2011 Elsevier B.V. All rights reserved.

Growth Kinetics of Nanoclusters in Solution

We study the growth kinetics of nanoclusters in solution. There are two generic factors that drive growth: (a) reactions that produce the nanomaterial; and (b) diffusion of the nanomaterial due to chemical-potential gradients. We model the growth kinetics of ZnO nanoparticles via coupled dynamical equations for the relevant order parameters, We study this model both analytically and numerically. We find that there is a crossover in thenanocluster growth law: from L(t) similar to t(1/2) in the reaction-controlled regime to L(t) t(1/3) in the diffusion-controlled regime.

Hydration dynamics of protein molecules in aqueous solution: Unity among diversity

Dielectric dispersion and NMRD experiments have revealed that a significant fraction of water molecules in the hydration shell of various proteins do not exhibit any slowing down of dynamics. This is usually attributed to the presence of the hydrophobic residues (HBR) on the surface, although HBRs alone cannot account for the large amplitude of the fast component. Solvation dynamics experiments and also computer simulation studies, on the other hand, repeatedly observed the presence of a non-negligible slow component. Here we show, by considering three well-known proteins (lysozyme, myoglobin and adelynate kinase), that the fast component arises partly from the response of those water molecules that are hydrogen bonded with the backbone oxygen (BBO) atoms. These are structurally and energetically less stable than those with the side chain oxygen (SCO) atoms. In addition, the electrostatic interaction energy distribution (EIED) of individual water molecules (hydrogen bonded to SCO) with side chain oxygen atoms shows a surprising two peak character with the lower energy peak almost coincident with the energy distribution of water hydrogen bonded to backbone oxygen atoms (BBO). This two peak contribution appears to be quite general as we find it for lysozyme, myoglobin and adenylate kinase (ADK). The sharp peak of EIED at small energy (at less than 2 k(B)T) for the BBO atoms, together with the first peak of EIED of SCO and the HBRs on the protein surface, explain why a large fraction (similar to 80%) of water in the protein hydration layer remains almost as mobile as bulk water Significant slowness arises only from the hydrogen bonds that populate the second peak of EIED at larger energy (at about 4 k(B)T). Thus, if we consider hydrogen bond interaction alone, only 15-20% of water molecules in the protein hydration layer can exhibit slow dynamics, resulting in an average relaxation time of about 5-10 ps. The latter estimate assumes a time constant of 20-100 ps for the slow component. Interestingly, relaxation of water molecules hydrogen bonded to back bone oxygen exhibit an initial component faster than the bulk, suggesting that hydrogen bonding of these water molecules remains frustrated. This explanation of the heterogeneous and non-exponential dynamics of water in the hydration layer is quantitatively consistent with all the available experimental results, and provides unification among diverse features.

Solution processable quinoxaline based molecular materials for organic field effect transistors

Three new solution processable quinoxaline based donor-acceptor-donor (D-A-D) type molecules have been synthesized for application in field effect transistors. These molecules were characterized by UV-visible spectroscopy, thermal gravimetric analysis, differential scanning calorimetry and cyclic voltammetry. DFT calculation gives deeper insight into the electronic structure of these molecules. The crystallinity and morphology features of thin film were investigated using X-ray diffraction. These molecules show liquid crystalline phase confirmed by DSC and optical polarizing microscopy. Investigation of their field effect transistor performance indicated that these molecules exhibited p-type mobility up to 9.7 x 10 (4) cm(2) V (1) s (1) and on/off ratio of 10(4). (C) 2012 Elsevier B.V. All rights reserved.

Cyclopentac]thiophene oligomers based solution processable D-A copolymers and their application as FET materials

Two new solution processable, low band gap donor-acceptor (D-A) copolymers (P1 and P2) comprising a cyclopentac] thiophene (CPT) based oligomers as donors and benzoc]1,2,5] selenadiazole (BDS) and 2-dodecyl1,2,3]-benzotriazole (BTAz) as acceptors were synthesized and characterized and their field effect transistor properties were studied. The internal charge transfer interaction between the electron-donating CPT based oligothiophene and the electron-accepting BDS or BTAz unit effectively reduces the band gap in polymers to 1.3 and 1.66 eV with low lying highest occupied molecular orbital (HOMO). The absorption spectrum of P1 was found to be more red shifted than that of P2 because of incorporation of the more electron-withdrawing BDS unit. The color of neutral P1 was found to be green in both solution and film states with two major bands in the absorption spectra; however, neutral P2 revealed one dominant absorption exhibiting red color in both solution and film state which could be attributed to the less electron-withdrawing effect of the BTAz unit. The polymers were further characterized by GPC, TGA, DSC and cyclic voltammetry. P1 and P2 exhibited charge carrier mobilities as high as 9 x 10(-3) cm(2) V-1 s(-1) and 2.56 x 10(-3) cm 2 V-1 s(-1), respectively with the current on/off ratio (I-on/I-off) in the order of 10(2).

On the solution of bivariate population balance equations for aggregation: Pivotwise expansion of solution domain

The solution of a bivariate population balance equation (PBE) for aggregation of particles necessitates a large 2-d domain to be covered. A correspondingly large number of discretized equations for particle populations on pivots (representative sizes for bins) are solved, although at the end only a relatively small number of pivots are found to participate in the evolution process. In the present work, we initiate solution of the governing PBE on a small set of pivots that can represent the initial size distribution. New pivots are added to expand the computational domain in directions in which the evolving size distribution advances. A self-sufficient set of rules is developed to automate the addition of pivots, taken from an underlying X-grid formed by intersection of the lines of constant composition and constant particle mass. In order to test the robustness of the rule-set, simulations carried out with pivotwise expansion of X-grid are compared with those obtained using sufficiently large fixed X-grids for a number of composition independent and composition dependent aggregation kernels and initial conditions. The two techniques lead to identical predictions, with the former requiring only a fraction of the computational effort. The rule-set automatically reduces aggregation of particles of same composition to a 1-d problem. A midway change in the direction of expansion of domain, effected by the addition of particles of different mean composition, is captured correctly by the rule-set. The evolving shape of a computational domain carries with it the signature of the aggregation process, which can be insightful in complex and time dependent aggregation conditions. (c) 2012 Elsevier Ltd. All rights reserved.

Robust solver based on modified particle swarm optimization for improved solution of diffusion transport through containment facilities

Accurate estimation of mass transport parameters is necessary for overall design and evaluation processes of the waste disposal facilities. The mass transport parameters, such as effective diffusion coefficient, retardation factor and diffusion accessible porosity, are estimated from observed diffusion data by inverse analysis. Recently, particle swarm optimization (PSO) algorithm has been used to develop inverse model for estimating these parameters that alleviated existing limitations in the inverse analysis. However, PSO solver yields different solutions in successive runs because of the stochastic nature of the algorithm and also because of the presence of multiple optimum solutions. Thus the estimated mean solution from independent runs is significantly different from the best solution. In this paper, two variants of the PSO algorithms are proposed to improve the performance of the inverse analysis. The proposed algorithms use perturbation equation for the gbest particle to gain information around gbest region on the search space and catfish particles in alternative iterations to improve exploration capabilities. Performance comparison of developed solvers on synthetic test data for two different diffusion problems reveals that one of the proposed solvers, CPPSO, significantly improves overall performance with improved best, worst and mean fitness values. The developed solver is further used to estimate transport parameters from 12 sets of experimentally observed diffusion data obtained from three diffusion problems and compared with published values from the literature. The proposed solver is quick, simple and robust on different diffusion problems. (C) 2012 Elsevier Ltd. All rights reserved.

Vacancy wind effect on interdiffusion in a dilute Cu(Sn) solid solution

A study has been conducted on a Cu(Sn) solid solution to examine the role of the vacancy wind effect on interdiffusion. First, the interdiffusion and the intrinsic diffusion coefficients are calculated. The trend of the interdiffusion coefficients is explained with the help of the driving force. Following this, the tracer diffusion coefficients of the species are calculated with and without consideration of the vacancy wind effect. We found that the role of the vacancy wind is negligible on the minor element in a dilute solid solution, which is the faster diffusing species in this system and controls the interdiffusion process. However, consideration of this effect is important to understand the diffusion rate of the major element, which is the slower diffusing species in this system.

Solution Combustion Synthesis of Nanosized Copper Chromite and Its Use as a Burn Rate Modifier in Solid Propellants

Nano sized copper chromite, which is used as a burn rate accelerator for solid propellants, was synthesized by the solution combustion process using citric acid and glycine as fuel. Pure spinel phase copper chromite (CuCr2O4) was synthesized, and the effect of different ratios of Cu-Cr ions in the initial reactant and various calcination temperatures on the final properties of the material were examined. The reaction time for the synthesis with glycine was lower compared to that with citric acid. The synthesized samples from both fuel cycles were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), BET surface area analysis, and scanning electron microscope (SEM). Commercial copper chromite that is currently used in solid propellant formulation was also characterized by the same techniques. XRD analysis shows that the pure spinel phase compound is formed by calcination at 700 degrees C for glycine fuel cycle and between 750 and 800 degrees C for citric acid cycle. XPS results indicate the variation of the oxidation state of copper in the final compound with a change in the Cu-Cr mole ratio. SEM images confirm the formation of nano size spherical shape particles. The variation of BET surface area with calcination temperature was studied for the solution combusted catalyst. Burn rate evaluation of synthesized catalyst was carried out and compared with the commercial catalyst. The comparison between BET surface area and the burn rate depicts that surface area difference caused the variation in burn rate between samples. The reason behind the reduction in surface area and the required modifications in the process are also described.

Synthesis, luminescence and EPR studies on CaSiO 3: Pb, Mn-nano phosphors synthesized by the solution combustion method

Nano-ceramic phosphor CaSiO 3 doped with Pb and Mn was synthesized by the low temperature solution combustion method. The materials were characterized by Powder X-Ray Diffraction (XRD), Thermo-gravimetric and Differential Thermal Analysis (TG-DTA), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The Electron Paramagnetic Resonance (EPR) spectrum of the investigated sample exhibits a broad resonance signal centered at g=1.994. The number of spins participating in resonance (N) and its paramagnetic susceptibility (�) have been evaluated. Photoluminescence of doped CaSiO 3 was investigated when excited by UV radiation of 256 nm. The phosphor exhibits an emission peak at 353 nm in the UV range due to Pb 2+. Further, a broad emission peak in the visible range 550-625 nm can be attributed to 4T 1� 6A 1 transition of Mn 2+ ions. The investigation reveals that doping perovskite nano-ceramics with transition metal ions leads to excellent phosphor materials for potential applications. © 2012 Elsevier Ltd and Techna Group S.r.l.

High resolution methyl selective C-13-NMR of proteins in solution and solid state

New C-13-detected NMR experiments have been devised for molecules in solution and solid state, which provide chemical shift correlations of methyl groups with high resolution, selectivity and sensitivity. The experiments achieve selective methyl detection by exploiting the one bond J-coupling between the C-13-methyl nucleus and its directly attached C-13 spin in a molecule. In proteins such correlations edit the C-13-resonances of different methyl containing residues into distinct spectral regions yielding a high resolution spectrum. This has a range of applications as exemplified for different systems such as large proteins, intrinsically disordered polypeptides and proteins with a paramagnetic centre.

Activation of TGF-beta Pathway by Areca Nut Constituents: A Possible Cause of Oral Submucous Fibrosis

Oral submucous fibrosis (OSF) is a chronic inflammatory disease characterized by the accumulation of excess collagen, and areca nut chewing has been proposed as an important etiological factor for disease manifestation. Activation of transforming growth factor-beta signaling has been postulated as the main causative event for increased collagen production in OSF. Oral epithelium plays important roles in OSF, and arecoline has been shown to induce TGF-beta in epithelial cells. In an attempt to understand the role of areca nut constituents in the manifestation of OSF, we studied the global gene expression profile in epithelial cells (HaCaT) following treatment with areca nut water extract or TGF-beta. Interestingly, 64% of the differentially regulated genes by areca nut water extract matches with the TGF-beta induced gene expression profile. Out of these, expression of 57% of genes was compromised in the presence of ALK5 (T beta RI) inhibitor and 7% were independently induced by areca nut, highlighting the importance of TGF-beta in areca nut actions. Areca nut water extract treatment induced p-SMAD2 and TGF-beta downstream targets in HaCaT cells but not in human gingival fibroblast cells (hGF), suggesting epithelial cells could be the source of TGF-beta in promoting OSF. Water extract of areca nut consists of polyphenols and alkaloids. Both polyphenol and alkaloid fractions of areca nut were able to induce TGF-beta signaling and its downstream targets. Also, SMAD-2 was phosphorylated following treatment of HaCaT cells by Catechin, Tannin and alkaloids namely Arecoline, Arecaidine and Guvacine. Moreover, both polyphenols and alkaloids induced TGF-beta 2 and THBS1 (activator of latent TGF-beta) in HaCaT cells suggesting areca nut mediated activation of p-SMAD2 involves up-regulation and activation of TGF-beta. These data suggest a major causative role for TGF-beta that is induced by areca nut in OSF progression.

Oncogenic MicroRNA-155 Down-regulates Tumor Suppressor CDC73 and Promotes Oral Squamous Cell Carcinoma Cell Proliferation IMPLICATIONS FOR CANCER THERAPEUTICS

The CDC73 gene is mutationally inactivated in hereditary and sporadic parathyroid tumors. It negatively regulates beta-catenin, cyclin D1, and c-MYC. Down-regulation of CDC73 has been reported in breast, renal, and gastric carcinomas. However, the reports regarding the role of CDC73 in oral squamous cell carcinoma (OSCC) are lacking. In this study we show that CDC73 is down-regulated in a majority of OSCC samples. We further show that oncogenic microRNA-155 (miR-155) negatively regulates CDC73 expression. Our experiments show that the dramatic up-regulation of miR-155 is an exclusive mechanism for down-regulation of CDC73 in a panel of human cell lines and a subset of OSCC patient samples in the absence of loss of heterozygosity, mutations, and promoter methylation. Ectopic expression of miR-155 in HEK293 cells dramatically reduced CDC73 levels, enhanced cell viability, and decreased apoptosis. Conversely, the delivery of a miR-155 antagonist (antagomir-155) to KB cells overexpressing miR-155 resulted in increased CDC73 levels, decreased cell viability, increased apoptosis, and marked regression of xenografts in nude mice. Cotransfection of miR-155 with CDC73 in HEK293 cells abrogated its pro-oncogenic effect. Reduced cell proliferation and increased apoptosis of KB cells were dependent on the presence or absence of the 3'-UTR in CDC73. In summary, knockdown of CDC73 expression due to overexpression of miR-155 not only adds a novelty to the list of mechanisms responsible for its down-regulation in different tumors, but the restoration of CDC73 levels by the use of antagomir-155 may also have an important role in therapeutic intervention of cancers, including OSCC.

Solid State and Solution Mediated Multistep Sequential Transformations in Metal-Organic Coordination Networks

Sequential transformation in a family of metal-organic framework compounds has been investigated employing both a solid-state as well as a solution mediated route. The compounds, cobalt oxy-bis(benzoate) and manganese oxybis(benzoate) having a two-dimensional structure, were reacted with bipyridine forming cobalt oxy-bis(benzoate)-4,4'-bipyridine and manganese oxy-bis(benzoate)-4,4'-bipyridine, respectively. The bipyridine containing compounds appear to form sequentially through stable intermediates. For the cobalt system, the transformation from a two-dimensional compound, Co(H2O)(2)(OBA)] (OBA = 4,4'-oxy-bis(benzoate)), I, to two different three-dimensional compounds, Co(bpy)(OBA)]center dot bpy, II, (bpy = 4,4'-bipyridine) and Co(bpy)(0.5)(OBA)], III, and reversibility between II and III have been investigated. In the manganese system, transformation from a two-dimensional compound, Mn(H2O)(2)(OBA)], Ia, to two different three-dimensional compounds, Mn (bpy)(OBA)]center dot bpy, Ha and Ha to Mn(bpy)(0.5)(OBA)], Ilia, has been investigated. It has also been possible to identify intermediate products during these transformation reactions. The possible pathways for the formation of the compounds were postulated.

Temperature dependent structural and dielectric investigations of PbZr0.5Ti0.5O3 solid solution at the morphotropic phase boundary

PbZr1-xTixO3 ceramics synthesised by low temperature calcination followed by sintering at 1280 degrees C show a Morphotropic Phase Boundary (MPB) for compositions of x=0.44-0.51. The morphotropic phase boundary is wider for samples with smaller grain sizes due to the synthesis route. A Rietveld analysis is performed on a composition of x=0.5 composition to quantify the phase fractions of the tetragonal and monoclinic phases present in the PZT system. Temperature dependent X-ray diffraction and dielectric studies of PbZr0.5Ti0.5O3 composition demonstrated a phase transformation from monoclinic to tetragonal at 270 degrees C followed by a ferroelectric tetragonal to a paraelectric cubic transition at 370 degrees C. Thus, the poling of these ceramics should be performed below 270 degrees C to benefit from the presence of a monoclinic phase. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.