Water as green oxidant: a highly selective conversion of organosilanes to silanols with water

Selective hydrolytic oxidation of organohydrosilanes was achieved with water in the presence of Pt‐nanoparticle catalyst. The selectivity of the process was established by NMR analysis. In addition, various Pt‐based catalysts were screened to compare the activity and selectivity with Pt‐nanoparticles catalysis. The method was equally applicable to hydrosilanes bearing unsaturated functional groups, which led to corresponding silanols under mild reaction conditions without formation of any side products. Pt‐nanoparticle catalysis was studied in details using UV–vis, TEM and mercury poisoning experiments during the transformation. Copyright © 2009 John Wiley & Sons, Ltd.     

A composition dependent thermal behavior of GexSe35−xTe65 glasses

Alternating differential scanning calorimetric (ADSC) studies have been performed to understand the thermal behavior of bulk Ge_xSe_35?xTe₆₅ glasses (17 ? x ? 25); it is found that the glasses with x ? 20 exhibit two crystallization exotherms (T_c1 & T_c2). On the other hand, those with x ? 20.5, show a single crystallization reaction upon heating. The exothermic reaction at T_c1 has been found to correspond to the partial crystallization of the glass into hexagonal Te and the reaction at T_c2 is associated with the additional crystallization of rhombohedral GeTe phase. The glass transition temperature of Ge_xSe_35?xTe₆₅ glasses is found to show a linear but not-steep increase, indicating a progressive, but a gradual increase in network connectivity with Ge addition. It is also found that T_c1 of Ge_xSe_35?xTe₆₅ glasses with x ? 20, increases progressively with Ge content and eventually merges with T_c2 at x ≈ 20.5 (〈r〉 = 2.41); this behavior has been understood on the basis of the reduction in TeTe bonds of lower energy and increase in GeTe bonds of higher energy, with increasing Ge content. Apart from the interesting composition dependent crystallization, an anomalous melting behavior is also exhibited by the Ge_xSe_35?xTe₆₅ glasses.     

Simultaneous HPTLC-UV quantification of colchicine and gloriosine alkaloids in the natural population of Gloriosa superba L., collected from Eastern Ghats of India for the identification of elite chemotypes

Abstract

Intra-specific chemical variability in the natural population of Gloriosa superba from Eastern Ghats (India) was recorded through validated HPTLC method and in vitro antiarthritic activity of elite chemotypes was evaluated. In total, 36 population(s) of G. superba were mapped and, collected from the phytogeography and densitometric quantification through validated HPTLC-UV method revealed a significant (p?>?0.05) difference in the metabolite content of germplasm(s). Colchicine and gloriosine content varied from 0.005 to 0.275% and 0.003 to 0.119%, maximum was recorded in NBG-34 (Tirupati, Andhra Pradesh) and NBG-70 (Panchgani hill, Maharashtra) respectively. On cluster analysis, six chemotypes were selected for in vitro antiarthritic activity, although activity was not significantly different. The elite chemotype with highest metabolite(s) content did not exhibit the highest biological activity and thus suggests the synergistic action of extract toward the pharmacological activity. The study promotes the use of G. superba in herbal formulation development as an adjuvant therapy in gouty arthritis and will aid in site-specific exploration of elite chemotype(s) with validated pharmacological action to meet out the medicinal and commercial demands.     

Studies on the reaction of aziridines with nitriles and carbonyls: synthesis of imidazolines and oxazolidines

Reaction of N-tosylaziridines with nitriles and carbonyls to produce imidazolines and oxazolidines has been studied in the presence of a variety of Lewis acids. The reaction is efficient with 1 equiv of BF3.Et2O or Et3OBF4 in CH2Cl2. However, it is catalytic with metal triflates that give the best results for cycloaddition of N-tosylaziridine with nitriles under solvent free conditions. The same reaction with carbonyls proceeds best in CH2Cl2 in the presence of molecular sieves. Among various triflates, Zn(OTf)2 has been found to be the best. The cleavage of the N-Ts bond of the cyclized products has been studied in order to make it more versatile in synthesis. The mechanistic aspect of the reaction has been studied by using chiral aziridines as substrates. These formal [3+2] cycloaddition reactions of aziridines with nitriles and carbonyls proceed in a Ritter fashion.     

A convenient approach to the total synthesis of (±) 4-demethoxydaunomycinone

A convenient and most practical approach to the synthesis of (±) 4-demethoxydaunomycinone starting from 2-methylhydroquinone is described.     

A Comparative Evaluation of Nitrogen Compounds in Petroleum Distillates

Although the concentration of nitrogen compounds in crude oil is relatively low, they can become more concentrated in petroleum distillates and poison the catalysts used in refining processes. They cause undesirable deposits, color formation and odor in products; they also contribute to air pollution and some are highly carcinogenic. The poisoned catalyst becomes deactivated for hydrodesulfurization and unable to remove sulfur from middle distillates. In order to understand the effect on catalytic processes, it is desirable to identify the nitrogen compounds in various petroleum distillates. This paper compares the nitrogen species profiles in different petroleum distillates using a nitrogen chemiluminescence detector. In addition, four different petroleum distillate samples from different refineries were analyzed to find the variation in their nitrogen profiles. The nitrogen compounds in petroleum distillate samples were identified as anilines, quinolines, indoles, and carbazoles and their alkyl derivatives. Quantitation was carried out against known reference standards. The quantitative data were compared to the total nitrogen content determined by elemental analysis.     

Supramolecular assemblies of block copolymers as templates for fabrication of nanomaterials

Self-assembled polymeric systems have played an important role as templates for nanofabrication; they offer nanotemplates with different morphologies and tunable sizes, are easily removed after reactions, and could be further modified with different functional groups to enhance the interactions. Among the various self-assembled polymeric systems, block copolymer supramolecular assemblies have received considerable attention because of the inherent processing advantages. These supramolecular assemblies are formed by the non-covalent interactions of one of the blocks of the block copolymer with a low molar-mass additive. Selective extraction of the additive leads to porous membranes or nano-objects which could then be used as templates for nanofabrication leading to a variety of ordered organic/inorganic nanostructures. In this feature article, we present an over-view of the recent developments in this area with a special focus on some examples from our group.     

Diastereoselective synthesis of a core fragment of ritonavir and lopinavir

A novel approach to the synthesis of Boc-core, a key starting material for ritonavir and lopinavir involving an unprecedented diastereoselective nitroaldol reaction on β-amino aldehyde is disclosed.     

Thermodynamics and bulk viscosity of approximate black hole duals to finite temperature quantum chromodynamics

We consider classes of translationally invariant black hole solutions whose equations of state closely resemble that of QCD at zero chemical potential. We use these backgrounds to compute the ratio zeta/s of bulk viscosity to entropy density. For a class of black holes that exhibits a first-order transition, we observe a sharp rise in zeta/s near Tc. For constructions that exhibit a smooth crossover, like QCD does, the rise in zeta/s is more modest. We conjecture that divergences in zeta/s for black hole horizons are related to extrema of the entropy density as a function of temperature.