No abstract

Diphenylprolinol silyl ether was found to be an effective organocatalyst for promoting the asymmetric, catalytic, intramolecular [6 + 2] cycloaddition reactions of fulvenes substituted at the exocyclic 6-position with a δ-formylalkyl group to afford synthetically useful linear triquinane derivatives in good yields and excellent enantioselectivities. The cis-fused triquinane derivatives were obtained exclusively; the trans-fused isomers were not detected among the reaction products. The intramolecular [6 + 2] cycloaddition occurs between the fulvene functionality (6π) and the enamine double bond (2π) generated from the formyl group in the substrates and the diphenylprolinol silyl ether. The absolute configuration of the reaction products was determined by vibrational circular dichroism. The reaction mechanism was investigated using molecular orbital calculations, B3LYP and MP2 geometry optimizations, and subsequent single-point energy evaluations on model reaction sequences. These calculations revealed the following: (i) The intermolecular [6 + 2] cycloaddition of a fulvene and an enamine double bond proceeds in a stepwise mechanism via a zwitterionic intermediate. (ii) On the other hand, the intramolecular [6 + 2] cycloaddition leading to the cis-fused triquinane skeleton proceeds in a concerted mechanism via a highly asynchronous transition state. (iii) The fulvene functionality and the enamine double bond adopt the gauche-syn conformation during the C-C bond formation processes in the [6 + 2] cycloaddition. (iv) The energy profiles calculated for the intramolecular reaction explain the observed exclusive formation of the cis-fused triquinane derivatives in the [6 + 2] cycloaddition reactions. The reasons for the enantioselectivity seen in these [6 + 2] cycloaddition reactions are also discussed.

Tamarind fruit shell was used as a low cost biosorbent for the removal of malachite green from aqueous solution. The various factors affecting adsorption such as agitation, pH, initial dye concentration, contact time, and temperature were investigated. It was observed that the dye adsorption capacity was strongly dependent on solution pH as well as temperature. The equilibrium data were described by the Langmuir, Freundlich, and Temkin isotherm models. The Langmuir isotherm model showed good fit to the equilibrium adsorption data and the maximum adsorption capacity obtained was 1.951 mg/g at 303 K. The kinetics of adsorption followed the pseudo-second-order model and the rate constant decreased with increase in temperature indicating exothermic nature of adsorption. The Arrhenius equation was used to obtain the activation energy (E a ) for the adsorption system. The activation energy was estimated to be 63.56 kJ/mol. Thermodynamic parameters such as Gibbs free energy (DG 0 ), enthalpy (DH 0 ), and entropy (DS 0 ) were also investigated. Results suggested that adsorption of malachite green onto tamarind fruit shell was a spontaneous and exothermic process. Present investigation suggests that tamarind fruit shell may be utilized as a low cost adsorbent for removal of malachite green from aqueous solution. IntroductionBiosorption is the property of certain inactive, dead, microbial biomass to adsorb or bind solute particles (heavy metals or dye or contaminants mainly from industrial effluents) present in liquid phase [1]. These solute particles are removed by using various types of biosorbent. The biosorbents materials are highly porous in nature. This porous volume is associated with small pores and so as a result diffusional resistance will occur. The adsorption phenomenon in biosorbent occurs primarily on the pore walls or at specific sites inside the particles. Biosorbents consist of mainly lipids, polysaccharides, and proteins and provide different functional groups such as phenolic, imidazole, carboxyl, hydroxyl, and carbonyl groups that can make coordination complex with different dye. Biosorbents can be used live or dead cells but in practical applications, the use of non-living biomass is more convenient and practical because living biomass cells often require the addition of fermentation process which increases the biological oxygen demand or chemical oxygen demand in the effluent. In addition, non-living biomass is not affected by the toxicity of the metal ions, they can be subjected to different chemical and physical treatment techniques to enhance their performance, and adsorbed metals can be easily recovered from the biomass by many chemical and physical methods [2][3][4][5].Malachite green (N-methylated diaminotriphenylmethane dye) is cationic dye and readily soluble in water. It is used for dyeing silk, cotton, leather, and paper. It is also used as biological strain for microscopic analysis of cell and tissue samples as a fungicide and ectoparasiticide in aquaculture and in fisheries and as therape...

Amine catalysis, through HOMO-activating enamine and LUMO-activating iminium-ion formation, is receiving increasing attention among other organocatalytic strategies, for the activation of unmodified carbonyl compounds. Particularly, the HOMO-raising activation concept has been applied to the greatest number of asymmetric transformations through enamine, dienamine, and SOMO-activation strategies. Recently, trienamine catalysis, an extension of amine catalysis, has emerged as a powerful tool for synthetic chemists with a novel activation strategy for polyenals/polyenones. In this review article, we discuss the initial developments of trienamine catalysis for highly asymmetric Diels-Alder reactions with different dienophiles and emerging opportunities for other types of cycloadditions and cascade reactions.

Controlled functionalization of carbon nanotubes (CNTs) through the use of cycloaddition reactions is described. By employing various cycloaddition reactions, a wide range of molecules could be coupled onto CNTs without disruption of the structural integrity as well as with a statistical distribution of functional groups onto the surface of the CNTs. The cycloaddition reactions represent an effective and tailored approach for preparing CNT-based advanced hybrid materials that would be useful for a wide range of applications from nanobiotechnology to nanoelectronics.