Selective protecting group manipulations on the 1-deoxynojirimycin scaffold

Iminosugars are inhibitors of glycoprocessing and are of interest as scaffolds for medicinal chemistry, as their successful application as peptide mimetics has shown. The synthesis of novel peptidomimetics based on 1-deoxynojirimycin (DNJ) requires practical strategies that allow introduction of amino acid side chains or pharmacophore groups at each of its hydroxyl groups or to the nitrogen atom. This paper describes one approach towards achieving selective protection and deprotection at the hydroxyl and amino groups of DNJ and a novel synthesis of DNJ from l-sorbose is included.     

Numerical simulation and parametric analysis of latent heat thermal energy storage system

This paper presents the numerical analysis of the transient performance of the latent heat thermal energy storage unit established on finite difference method. The storage unit consists of a shell and tube arrangement with phase change material (PCM) filled in the shell space and the heat transfer fluid (HTF) flowing in the inner tube. The heat exchange between the HTF, wall and PCM has been investigated by developing a 2-D fully implicit numerical model for the storage module and solving the complete module as a conjugate problem using enthalpy transforming method. A comparative investigation of the total melting time of the PCM has been performed based on natural convection in liquid PCM during the charging process. The novelty of this paper lies in the fact it includes convection in PCM and this investigation includes a detailed parametric study which can be used as a reference to design latent heat storage. The results indicate that natural convection accelerates the melting process by a significant amount of time. In order to optimize the design of the thermal storage unit, parametric study has been accompanied to analyze the influence of various HTF working conditions and geometric dimensions on the total melting time of the PCM. Another important feature considered in this work is the influence of the inner wall of the tube carrying the HTF on the entire melting time of the PCM. An error of around 7.2% is reported when inner wall of the tube is ignored in the analysis.

     

Latent sulfur chelated ruthenium catalysts: Steric acceleration effects on olefin metathesis

A series of sulfur chelated dormant ruthenium olefin metathesis catalysts is presented. The catalysts prepared were shown to possess the uncommon cis-dichloro arrangement and were mostly inactive at room temperature. By systematically modifying the size of the substituent groups at the chelating sulfur atom, catalyst activity at different temperatures was significantly affected; more bulky substituents fomented activity at lower temperatures. The catalysts were also shown to be stable in solution and retained their catalytic activity even after being exposed to air for two weeks.     

Oriented immobilization of periodateoxidized monoclonal antibodies on amino and hydrazide derivatives of eupergit C

Amino and hydrazyno derivatives of Eupergit C were prepared by reaction of the beads with hexamethylene diamine (HMD) and adipic acid dihydrazide (ADH), respectively. Monoclonal antibodies (mAbs) against carboxypeptidase A (CPA) and horse radish peroxidase (HRP) were prepared, and those that did not inhibit the respective enzymatic activities were selected. The carbohydrate moieties of these antibodies were oxidized by reaction with sodium periodate and then coupled onto the modified beads. The oxidation and coupling reactions were optimized to achieve highly active matrix-conjugated antibodies. Thus, antibody-matrix conjugates that possessed antigen-binding activities close to the theoretical value of 2 mol antigen bound/mol immobilized antibody were obtained.     

Knoevenagel Condensation in Heterogeneous phase Catalyzed by IR Radiation and Tonsil Actisil FF

Infrared radiation promoted the synthesis of benzylidenemalononitriles, benzylidenecyanoacetamides and benzylidenecyanoacetic acids by condensation of aromatic aldehydes with the corresponding active methylene compound in the presence of Tonsil Actisil FF, without solvent. Mass of catalyst, solvent, and reaction time were assessed in order to improve the efficiency of this process.     

Can DFT methods correctly and efficiently predict the coordination number of copper(I) complexes? A case study

The coordination number of various experimentally known Cu(I) compounds is studied using density functional theory. Various basis sets are tested, aiming to establish a reliable level for prediction of the coordination number of these and other Cu(I) complexes. It is found that most levels exhibit correct trends, namely, the bulkier ligands demonstrate larger preference for coordination of two ligands. Proper absolute values are obtained when dispersion corrections are also included in the calculations. It is concluded that the fairly small modified 6‐31+G* basis set due to Pulay represents a good compromise between accuracy and efficiency, followed by Balabanov and Peterson's all‐electron aug‐cc‐pVDZ basis set. The overall energy is decomposed into various components whose relative contribution to the overall tendency of forming a complex with a particular coordination is examined. It is shown that two opposing contributions play a major role: the interaction energy of the ligand being added and the deformation energy of the copper's coordination sphere prior to the ligand addition. The former being a stabilizing contribution, leads to higher coordination numbers while the later, a destabilizing contribution, is shown to favor lower coordination numbers. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010     

Dissipative dynamics of laser induced nonadiabatic molecular alignment

Nonadiabatic alignment induced by short, moderately intense laser pulses in molecules coupled to dissipative environments is studied within a nonperturbative density matrix theory. We focus primarily on exploring and extending a recently proposed approach [Phys. Rev. Lett. 95, 113001 (2005)], wherein nonadiabatic laser alignment is used as a coherence spectroscopy that probes the dissipative properties of the solvent. To that end we apply the method to several molecular collision systems that exhibit sufficiently varied behavior to represent a broad variety of chemical environments. These include molecules in low temperature gas jets, in room temperature gas cells, and in dense liquids. We examine also the possibility of prolonging the duration of the field free (post-pulse) alignment in dissipative media by a proper choice of the system parameters.     

New organic noble gas molecules: energetics, stability and potential energy surfaces of HCCXeCCH and HCCKrCCH

The diacetylides of Xe and Kr, HCCXeCCH and HCCKrCCH, are predicted to exist as metastable, chemically-bound compounds. The electronic structure, properties of the potential energy surfaces and decomposition paths are computed and analyzed. MP2, MCSCF and CASPT2 ab initio methods are used, as appropriate for each of the properties studied. Using transition state theory and the computed barrier for decomposition, the lifetime of HCCXeCCH is calculated as a function of temperature. The molecule is predicted to be stable well above the cryogenic range, with a lifetime of 24 h at 200 K. The implications for organic chemistry of the noble gases are discussed.     

An efficient enantioselective approach to cyclic beta-amino acid derivatives via olefin metathesis reactions

The asymmetric synthesis of polyfunctionalized piperidine- and pyrrolidine-based scaffolds, specifically designed for the preparation of cyclic, conformationally constrained beta-amino acids, is realized combining a biocatalytic access to a versatile chiral building block with a wide range of transformations based on olefin metathesis.