Surface tension of some binary organic solutions of alkylbenzenes and 1-alkanols

The surface tensions of binary mixtures of 1-alkanols (Cl-Cd with benzene, toluene, or xylene were measured. The results were correlated with the activity coefficients calculated through the group contribution method such as UNIFAC, with the maximum deviation from the experimental results less that 5%. The coefficients of the correlation are correlated with the chain length.

A possible origin of viscosity in Keplerian accretion disks due to secondary perturbation: Turbulent transport without magnetic fields

The origin of hydrodynamic turbulence in rotating shear flow is a long standing puzzle. Resolving it is especially important in astrophysics when the flow's angular momentum profile is Keplerian which forms an accretion disk having negligible molecular viscosity. Hence, any viscosity in such systems must be due to turbulence, arguably governed by magnetorotational instability, especially when temperature T greater than or similar to 10(5). However, such disks around quiescent cataclysmic variables, protoplanetary and star-forming disks, and the outer regions of disks in active galactic nuclei are practically neutral in charge because of their low temperature, and thus are not expected to be coupled with magnetic fields enough to generate any transport due to the magnetorotational instability. This flow is similar to plane Couette flow including the Coriolis force, at least locally. What drives their turbulence and then transport, when such flows do not exhibit any unstable mode under linear hydrodynamic perturbation? We demonstrate that the three-dimensional secondary disturbance to the primarily perturbed flow that triggers elliptical instability may generate significant turbulent viscosity in the range 0.0001 less than or similar to nu(t) less than or similar to 0.1, which can explain transport in accretion flows.

Porous, catalytically active palladium nanostructures by tuning nanoparticle interactions in an organic medium

We present a simple template-free method for the synthesis of interconnected hierarchical porous palladium nanostructures by controlling the aggregation of nanoparticles in organic media. The interaction between the nanoparticles is tuned by varying the dielectric constant of the medium consistent with DLVO calculations. The reaction products range from discrete nanoparticles to compact porous clusters with large specific surface areas. The nanoclusters exhibit hierarchical porosity and are found to exhibit excellent activity towards the reduction of 4-nitrophenol into 4-aminophenol and hydrogen oxidation. The method opens up possibilities for synthesizing porous clusters of other functional inorganics in organic media.

Self-assembled composite nano-materials exploiting a thermo reversible n-acene fibrillar scaffold and organic-capped ZnO nanoparticles

An organic-inorganic composite material is obtained by self-assembly of 2,3-didecyloxy-anthracene (DDOA), an organogelator of butanol, and organic-capped ZnO nanoparticles (NPs). The ligand 3, 2,3-di(6-oxy-n-hexanoic acid)-anthracene, designed to cap ZnO and interact with the DDOA nanofibers by structural similarity, improves the dispersion of the NPs into the organogel. The composite material displays mechanical properties similar to those of the pristine DDOA organogel, but gelates at a lower critical concentration and emits significantly less, even in the presence of very small amounts of ZnO NPs. The ligand 3 could also act as a relay to promote the photo-induced quenching process.

Analysis of Hydrogen Bonding and Stability of Protein Secondary Structures in Molecular Dynamics Simulation

Molecular Dynamics (MD) simulations provide an atomic level account of the molecular motions and have proven to be immensely useful in the investigation of the dynamical structure of proteins. Once an MD trajectory is obtained, specific interactions at the molecular level can be directly studied by setting up appropriate combinations of distance and angle monitors. However, if a study of the dynamical behavior of secondary structures in proteins becomes important, this approach can become unwieldy. We present herein a method to study the dynamical stability of secondary structures in proteins, based on a relatively simple analysis of backbone hydrogen bonds. The method was developed for studying the thermal unfolding of beta-lactamases, but can be extended to other systems and adapted to study relevant properties.

Utility of microbes in organic-synthesis - selective transformations of acyclic isoprenoids by aspergillus-niger

Bioconversion of acyclic isoprenoids using a strain of Aspergillus niger results in hydroxylated metabolites with regio- and stereoselectivity. The organism carries out oxidation of the terminal allylic methyl group and the remote double bond in all the compounds tested (I-VII). However, these two activities seem to have preferential structural requirements. When an acyclic isoprenoid with a ketone functionality such as geranylacetone is used as the substrate, the organism also carries out the asymmetric reduction of the keto group. All the metabolites formed have been purified and characterized by conventional spectroscopic methods and quantification has been made by gas chromatographic analyses.

Oxygen-Exchange Reactions Accompanying Oxidation of Vanadyl Sulfate by Diperoxovanadate

The absorption spectrum in the visible range and the, ESR spectrum of vanadyl sulfate were lost on addition of diperoxovanadate. The V-51-NMR spectra revealed that diperoxovanadate was reduced to vanadate and its oligomers. With excess vanadyl, tetrameric vanadate was found to be the major product, During this reaction oxygen was released into the medium. The oxygen-release reaction was inhibited by a variety of organic ligands-imidazole, benzoate, formate, mannitol, ethanol, Tris, DMPO, malate, and asparagine. An oxygen-consuming reaction emerged at high concentrations of some of these compounds, e.g. benzoate and ethanol. Using DMPO as the spin-trap, an oxygen-radical species with a 1:2:2:1 type of ESR spectrum was detected in the reaction mixtures resulting from vanadyl oxidation by diperoxovanadate which was unaffected by addition of catalase or ethanol. The results showed that secondary oxygen-exchange reactions occur which depend on and utilize the intermediates in the primary reaction during diperoxovanadate-dependent oxidation of vanadyl sulfate.

Physical characterization of the organic nonlinear optical crystal � 3-methoxy 4-hydroxy benzaldehyde

We highlight our recent experimental work on an efficient molecular nonlinear optical crystal, 3-methoxy 4-hydroxy benzaldehyde (MHBA). Optical quality single crystals of MHBA were grown from mixtures of solvents and from melt. The overall absorption and transparency window were improved by growing them in a mixture of chloroform and acetone. The grown crystals were characterized for their optical transmission, mechanical hardness and laser damage. We have observed a strong correlation between mechanical properties and laser induced damage.

Role of organic fluorine in crystal engineering

The design of compounds with novel and improved physico-chemical properties as advanced functional materials with a specific application spectrum requires the knowledge about possible supramolecular packing motifs and their experimental control in crystalline lattice. Besides the structure of the individual molecule, non-covalent interactions play a significant role in the determination of molecular conformation, along with the formation of three-dimensional supramolecular architecture in a crystal as a requirement for molecular recognition processes, and the related bioactivity. Involvement of functional groups will contribute to the formation of a predefined packing motif due to their well-defined interactions. The strength and directionality of these interactions create characteristic packing motifs, which can be used for the design of supramolecular arrangements by the development of appropriate strategies for the precise control of their topology. Most relevant of these non-covalent interactions are stacking interactions and hydrogen bonds, which have been subjects of extensive study in the last two decades. In recent literature, substantial efforts have been put in by various researchers towards the understanding of interactions involving organic fluorine and the role they play in generating different packing motifs which guides assembling of molecules in the crystal lattice.

Characterization of aerosol black carbon over a tropical semi-arid region of Anantapur, India

Black carbon (BC) aerosol mass concentrations measured using an aethalometer at Anantapur, a semi-arid tropical station in the southern part of peninsular India, from August 2006 to July 2007 are analyzed. Seasonal and diurnal variations of BC in relation to changes in the regional meteorological conditions have been studied along with the mass fraction of BC to the total aerosol mass concentration (M-t) and fine particle mass (FPM) concentration in different months. The data collected during the study period shows that the annual average BC mass concentration at Anantapur is 1.97 +/- 0.12 mu g m(-3). Seasonal variations of BC aerosol mass concentration showed high during the dry (winter and summer) seasons and low during the post-monsoon followed by the monsoon seasons. Diurnal variations of BC aerosols attain a gradual build up in BC concentration from morning and a sharp peak occurs between 07:00 and 09:00 h almost an hour after local sunrise and a broad nocturnal peak from 19:00 to 21:00 h with a minimum in noon hours. The ratio of BC to the fine particle mass concentration was high during the dry season and low during the monsoon season. The regression analysis between BC mass concentration and wind speed indicates that, with increase in wind speeds the BC mass concentrations would decrease and vice-versa. Aerosol BC mass concentration shows a significant positive correlation with total mass concentration (M-t) and aerosol optical depth (ACID, tau(p)) at 500 nm. (C) 2010 Elsevier B.V. All rights reserved.

Stabilized alpha-Ni(OH)2 as electrode material for for alkaline secondary cells

Hydrotalcite-like compounds of formula Ni1-xAl(x)(OH)2(CO3)x/2 . nH2O (x = 0.1 to 0.25), having the same structure as that of alpha-Ni(OH)2, have been synthesized by substituting nickel hydroxide with aluminum. Of these, the compounds of compositions x greater-than-or-equal-to 0.2 are found to have prolonged stability in strong alkaline medium. The electrodes comprising stabilized alpha-Ni(OH)2 of x = 0.2 composition are rechargeable with discharge-capacity values of 240 (+/- 15) mAh-g-1 and are attractive for applications in various alkaline secondary cells employing nickel-positive electrodes.

The Reaction of a Nitro-Capped Cobalt(III) Cage Complex With Base: the Crystal Structure of a Contracted Cage Complex, and the Mechanism of Its Formation

The synthesis, properties and crystal structure of the cage complex (1-hydroxy-8-methyl-3,6,10,13,15,18-hexaazabicyclo[6.6.5]nonadecane)cobalt(III) chloride hydrate ([Co(Me,OH-absar)] C13.H2O) are reported. The mechanism of the formation of this contracted cavity cage from a nitro-capped hexaazabicycloicosane type cage has been investigated. Treatment of (1-methyl-8-nitro-3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane)cobalt(III) chloride ([Co(Me,NO2-sar)] 3+) with excess base in aqueous solution leads initially to rapid (t1/2 < 1 ms) and reversible deprotonation of one coordinated secondary amine. This species undergoes a retro-Mannich type reaction and imine hydrolysis (t1/2 almost-equal-to 90 s). Quenching the reaction with acid gives rise to a pair of isomeric intermediate species which have been isolated and characterized. They have a pendant arm macrocyclic structure, resulting from the loss of a methylene unit from one of the arms of the cap. Heating either isomer in aqueous solution gives the new cage compound with the contracted cap. It is postulated that this occurs through a Nef reaction, resulting in the formation of a ketone which then condenses with the coordinated primary amine. A comparison with the corresponding bicycloicosane analogue indicates a reduced chromophoric cavity size for the contracted cage. The reduction potential of the cobalt(III)/cobalt(II) couple is 170 mV more negative for the smaller cage, and, in the electronic spectrum of the cobalt(III) complex, the d-d transitions are both shifted to higher energy, corresponding to a stronger ligand field.