Stereoselective total synthesis of (+/-)-tochuinyl acetate and (+/-)-dihydrotochuinyl acetates

Details of the first total synthesis of the marine natural product dihydrotochuinyl acetate is described. Cyclopentenone annulation of p-methylacetophenone via a Claisen rearrangement-Wacker oxidation based sequence generated the cyclopentenone 3, a known precursor for the sesquiterpenes cuparene, laurene, alpha-cuparenone and beta-cuparenones. Conversion of the ketone moiety into a carboxylate followed by stereoselective alkylation and reduction transformed the cyclopentenone 3 into the primary alcohol 19. Birch reduction of the alcohol 19 followed by acetylation furnished (+/-)-dihydrotochuinyl acetate, whereas direct acetylation of 19 furnished (+/-)-tochuinyl acetate. (C) 1998 Elsevier Science Ltd. All rights reserved.

Synthetic studies directed towards the potent cytotoxic natural product ottelione A: stereoselective construction of the complete framework

A stereoselective strategy for the rapid acquisition of the complete framework (dideoxyottelione A) of the promising cytotoxic agent ottelione A, with four contiguous stereogenic centres on a hydrindane skeleton and a sensitive 4-methylenecyclohex-2-enone functionality, from the readily available Diels-Alder adduct of 1,2,3,4-tetrachloro-5,5-dimethoxycyclopentadiene and norbornadiene, is delineated.

Electrochemical co-deposition of bimetallic Pt-Ru nanoclusters dispersed on poly(3,4-ethylenedioxythiophene) and electrocatalytic behavior for methanol oxidation

Nanoclusters of bimetallic Pt-Ru are electrochemically deposited on conductive polymer, poly(3,4-ethylenedioxythiophene)(PEDOT), which is also electrochemically deposited on a carbon paper substrate. The bimetallic deposition is carried out in an acidic electrolyte consisting of chloroplatinic acid and ruthenium chloride at 0.0 V versus saturated calomel electrode (SCE) on PEDOT coated carbon paper. A thin layer PEDOT on a carbon paper substrate facilitates the formation of uniform, well-dispersed, nano clusters of Pt-Ru of mean diameter of 123 nm, which consist of nanosize particles. In the absence of PEDOT, the size of the clusters is about 251 nm, which are unevenly distributed on carbon paper substrate. Cyclic voltammetry studies suggest that peak currents of methanol oxidation are several times greater on PtRu-PEDOT electrode than on Pt-Ru electrode in the absence of PEDOT. (C) 2011 Elsevier B.V. All rights reserved.

Half-sandwich (eta(6)-arene)ruthenium(II) chiral Schiff base complexes: Analysis of the diastereomeric mixtures in solution by 2D-NMR spectroscopy

2D NMR spectroscopy has been used to determine the metal configuration in solution of three complexes, viz. [(eta(6)-p-cymene)Ru(L*)Cl] (1) and [(eta(6)-p-cymene)Ru(L*)(L')] (ClO4) (L' = H2O, 2; PPh3, 3), where L* is the anion of (S)-(1-phenylethyl)salicylaldimine. The complexes exist in two diastereomeric forms in solution. Both the (R-Ru,S-C)- and (S-Ru,S-C)-diastereomers display the presence of attractive, CH/pi interaction involving the phenyl group attached to the chiral carbon and the cymene ring hydrogens. This interaction restricts the rotation of the C*-N single bond and, as a result, two structural types with either the hydrogen atom attached to the chiral carbon (C*) or the methyl group attached to C* in close proximity of the cymene ring protons get stabilized. Using 2D NMR spectroscopy as a tool, the spatial interaction involving these protons are studied in order to obtain the metal configuration(s) of the diastereomeric complexes in solution. This technique has enabled us to determine the metal configuration as (R-Ru,S-C) for the major isomers of 1-3 in solution.

Hybrid systems through natural product leads: An approach towards new molecular entities

Hybrid systems are constructs of different molecular entities, natural or unnatural, to generate functional molecules in which the characteristics of various components are modulated, amplified or give rise to entirely new properties. These hybrids can be designed from carefully selected components either through domain intergration of key structural/functional features or via straightforward covalent linkages. Some of the recently reported hybrid systems based on steroid, carbohydrate, C-60-fullerene platforms, amongst others, mainly crafted with the object of enhancement of the therapeutical spectrum, will be discussed.

Orthometalation in calixarenes: Synthesis and structural characterization of a novel orthopalladated calix[4]arene bisphosphite

The treatment of a symmetrically bridged p-Bu-t-calix[4] arene bisphosphite with PdCl2(NCPh)(2) yields a novel orthopalladated derivative by a C-C bond scission of a t-butyl group attached to an aryl ring. The structure of this orthopalladated calix[4]arene derivative has been established by X-ray crystallography.

Oxidation and decomposition of NH3 over combustion synthesized Al2O3 and CeO2 supported Pt, Pd and Ag catalysts

The catalytic oxidation and decomposition of NH3 have been carried out over combustion synthesized Al2O3 and CeO2 supported Pt, Pd and Ag catalysts using temperature programmed reaction (TPR) technique in a packed bed tubular reactor. Metals are ionically dispersed over CeO2 and fine metal particles are found on Al2O3. NH3 oxidation occurs over 1% Pt/Al2O3, 1% Pd/Al2O3 and 1% Ag/Al2O3 at 175, 270 and 350 C respectively producing N-2, NO, N2O and H2O, whereas 1% Pt/CeO2, 1% Pd/CeO2 and 1% Ag/CeO2 give N-2 along with NO, N2O and H2O at 200, 225 and 250degreesC respectively. N-2 predominates over other nitrogen-containing products during the reaction on all catalysts. At less O-2 concentration, N-2 and H2O are the only products obtained during NH3 Oxidation. NH3 decomposition over all the catalysts occurs above 450degreesC.

Renewable surface electrodes based on dopamine functionalized exfoliated graphite: NADH oxidation and ethanol biosensing

Exfoliated graphite (EG) was modified by covalently attaching dopamine (DA) (3,4-dihydroxyphenethylamine) through amide linkages, using -COOH groups introduced on the EG surface. The modified material was characterized by FT-IR spectroscopy, Xray photoelectron spectroscopy and electrochemical techniques. Composites of DA modified EG dispersed in organically modified silicates were prepared by a sol-get process. Electrodes were fabricated by casting the composites in glass tubes. The sol-gel based electrodes were found to be active for the electrocatalytic oxidation of NADH and biosensing of ethanol in presence of NAD(+) and alcohol dehydrogenase enzyme. The modified composite electrodes were found to be stable for several months. The surface of the electrode could be renewed just by mechanically polishing the electrode using emery sheets. The modified EG was also pressed and restacked in the form of a pellet and the use of this material as a binderless bulk-modified electrode was also demonstrated. The performance of sol-gel derived composite EG electrodes with binderless bulk-modified EG electrodes was compared. (C) 2002 Elsevier Science B.V. All rights reserved.

An XPS study on oxidation states of Pt and its alloys with Co and Cr and its relevance to electroreduction of oxygen

Cathodic reduction of oxygen in fuel cells is known to be enhanced on platinum alloys in relation to the platinum metal. The higher performance of the platinum alloys is as a result of the improved oxygen-reduction kinetics on the alloys but there is hardly any increase in the electrode platinum-surface-areas for the platinum alloys as compared to the platinum metal, and thus the higher performance is solely due to the enhanced electrocatalytic activity of the alloys as compared to the platinum metal. The present X-ray photoelectron spectroscopic (XPS) study on carbon-supported Pt, Pt–Co and Pt–Co–Cr electrocatalysts suggests the presence of a relatively lower Pt-oxide content on the alloys. The X-ray powder diffraction patterns for these electrocatalysts show that while the carbon-supported platinum electrocatalyst has a face-centered cubic (fcc) phase, carbon-supported Pt–Co and Pt–Co–Cr electrocatalysts exhibit a face-centered tetragonal (fct) phase. But, Pt electrocatalyst has a lower particle-size and, hence, a higher dispersion. Previous studies have shown higher activities on the Pt-alloys than on Pt, and have attributed it to changes in the electronic and structural characteristics of Pt. These changes can be correlated with the lower oxidation-state of Pt sites, as found in this study.

A comparative study of Pt/CeO2 catalysts for catalytic partial oxidation of methane to syngas for application in fuel cell electric vehicles

In the framework of a project aimed at developing a reliable hydrogen generator for mobile polymer electrolyte fuel cells (PEFCs), particular emphasis has been addressed to the analysis of catalysts able to assure high activity and stability in transient operations (frequent start-up and shut-down cycles). In this paper, the catalytic performance of 1 at.% Pt/ceria samples prepared by coprecipitation, impregnation and combustion, has been evaluated in the partial oxidation of methane. Methane conversion and hydrogen selectivity of 96 and 99%, respectively, associated with high stability during 100h of reaction under operative conditions (start-up and shut-down cycles), have been obtained. (C) 2002 Elsevier Science B.V. All rights reserved.

Performance evaluation of nonthermal plasma reactors for NO oxidation in diesel engine exhaust gas treatment

The discharge plasma-chemical hybrid process for NOinfinity removal from the flue gas emissions is an extremely effective and economical approach in comparison with the conventional selective catalytic reduction system. In this paper we bring out a relative comparison of several discharge plasma reactors from the point of NO removal efficiency. The reactors were either energized by ac or by repetitive pulses. Ferroelectric pellets were used to study the effect of pellet assisted discharges on gas cleaning. Diesel engine exhaust, at different loads; is used to approximately simulate the flue gas composition. Investigations were carried out at room temperature with respect to the variation of reaction products against the discharge power. Main emphasis is laid on the oxidation of NO to NO2, without reducing NOx concentration (i.e., minimum reaction byproducts), with least power consumption. The produced NO2 will be totally converted to N-2 and Na-2 SO4 using Na-2 SO3. The ac packed-bed reactor and pelletless pulsed corona reactor showed better performance, with minimum reaction products for a given power, when the NO concentration was low (similar to 100 ppm). When the engine load exceeds 50% (NO > 300 ppm) there was not much decrease in NO reduction and more or less all the reactors performed equally. The total operating cost of the plasma-chemical hybrid system becomes $4010/ton of NO, which is 1/3-1/5 of the conventional selective catalytic process.

Cyclometalated complexes derived from calix[4] arene bisphosphites and their catalytic applications in cross-coupling reactions

Palladium and platinum dichloride complexes of a series of symmetrically and unsymmetrically substituted 25,26;27,28-dibridged p-tert-butyl-calix[4]arene bisphosphites in which two proximal phenolic oxygen atoms of p-tert-butyl-or p-H-calix[4]arene are connected to a P(OR) ( R = substituted phenyl) moiety have been synthesized. The palladium dichloride complexes of calix[4]arene bisphosphites bearing sterically bulky aryl substituents undergo cyclometalation by C-C or C-H bond scission. An example of cycloplatinated complex is also reported. The complexes have been characterized by NMR spectroscopic and single crystal X-ray diffraction studies. During crystallization of the palladium dichloride complex of a symmetrically substituted calix[4]arene bisphosphite in dichloromethane, insertion of oxygen occurs into the Pd-P bond to give a P,O-coordinated palladium dichloride complex. The calix[4]arene framework in these bisphosphites and their metal complexes adopt distorted cone conformation; the cone conformation is more flattened in the metal complexes than in the free calix[4]arene bisphosphites. Some of these cyclometalated complexes proved to be active catalysts for Heck and Suzuki C-C cross-coupling reactions but, on an average, the yields are only modest. (C) 2011 Elsevier B.V. All rights reserved.

A Method for Evaluation of Product Lifecycle Alternatives under Uncertainty

In each stage of product development, we need to take decisions, by evaluating multiple product alternatives based on multiple criteria. Classical evaluation methods like weighted objectives method assumes certainty about information available during product development. However, designers often must evaluate under uncertainty. Often the likely performance, cost or environmental impacts of a product proposal could be estimated only with certain confidence, which may vary from one proposal to another. In such situations, the classical approaches to evaluation can give misleading results. There is a need for a method that can aid in decision making by supporting quantitative comparison of alternatives to identify the most promising alternative, under uncertain information about the alternatives. A method called confidence weighted objectives method is developed to compare the whole life cycle of product proposals using multiple evaluation criteria under various levels of uncertainty with non crisp values. It estimates the overall worth of proposal and confidence on the estimate, enabling deferment of decision making when decisions cannot be made using current information available.