LUMO Energies (lumo + energy)

Distribution by Scientific Domains

Terms modified by LUMO Energies

  • lumo energy level

  • Selected Abstracts

    The Use of Atomic Charges and Orbital Energies as Hydrogen-bonding-donor Parameters for QSAR Studies: Comparison of MNDO, AM1 and PM3 Methods

    Hydrogen-bonding, important in drug-receptor interactions, also determines the solubility and partitioning of drugs between phases. It is, therefore, important to incorporate the effects of hydrogen-bonding in studies of quantitative structure-activity relationships (QSAR). In this study the atomic charge on the most positively charged hydrogen atom in a molecule and the energy of the lowest unoccupied molecular orbital (LUMO) have been used as a measure of hydrogen-bond-donor capacity. For several hydrogen-bonding acids the Mulliken atomic charges and the energy of the LUMO produced by use of three semi-empirical methods, AM1, PM3 and MNDO, and MNDO electrostatic-potential-derived atomic charges, have been compared in correlations with solvatochromic hydrogen-bonding acidity (,,2H). Atomic charges and LUMO energies, particularly those calculated by use of the AM1 and MNDO methods, were found to correlate well with ,,2H. They were also found to be good models of hydrogen-bonding in QSAR correlations. [source]

    Structure-stability correlations for imine formation in aqueous solution

    C. Godoy-Alcántar
    Abstract Imine formation between 25 aldehydes and 13 amines in aqueous solution in the pH range 7,11 was studied by 1H NMR spectroscopy. A three-parameter linear equation correlating logarithms of imine formation constants with pKa and HOMO energies of amines and LUMO energies of aldehydes is proposed. In view of the widespread occurrence of imine-forming processes in both chemistry and biology, the data presented are of significance for physical organic chemistry and of particular interest for dynamic combinatorial chemistry. Copyright © 2005 John Wiley & Sons, Ltd. [source]

    Insight into the Bioactivity and Metabolism of Human Glucagon Receptor Antagonists from 3D-QSAR Analyses

    HaiFeng Chen
    Abstract Descriptors, such as logP, the number of hydrogen bond donors, the number of hydrogen bond acceptors, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) combined with fields of CoMFA and CoMSIA to construct models for hyperglycemia decrease activity and metabolism of human glucagon receptor antagonists. The results reveal that including logP, HOMO and LUMO energies is meaningful for QSAR/QSMR model. The models were validated by using a test set of structural diverse compounds that had not been included in the CoMFA and CoMSIA models. Support Vector Machines (SVM) have been used to select the suitable additional descriptors to construct 3D-QSAR/QSMR models. A key factor to mention is that activity and metabolism models simultaneously. These in silico ADME models are helpful in making quantitative prediction of inhibitory activities and rates of metabolism before resorting in vitro and in vivo experimentation. [source]

    In Situ Spectroelectrochemical Studies on Ladder-Type Oligomers in Solution and the Solid State

    Peter Rapta Dr.
    Abstract A series of thermally stable fluoranthenopyracylene oligomers with extended , conjugation were studied by in situ ESR-UV/Vis/NIR spectroelectrochemistry with respect to their application in devices such as organic light-emitting diodes and field-effect transistors. The oligomers are both soluble in o -dichlorobenzene and form thin films by evaporation in the temperature range of 300,500,°C in vacuum. Their electrochemical behavior was studied in reduction (n doping) and oxidation (p doping) under standard voltammetric and thin-layer conditions. The HOMO and LUMO energies and the band gaps of all compounds under study were estimated from both electrochemical and UV/Vis/NIR spectroscopic data. The fluorene-type oligomers A2,A6 and B2 bearing flexible alkyl chains exhibit both reversible multistep reductions and oxidations. The spectroelectrochemistry indicates substantial differences in delocalization of the positive and negative charges in these ladder-type oligomers. The formation of doubly charged , dimers was observed for the first time for both the radical anion and radical cation of the same molecule (B1). The redox behavior of the oligomers was studied in the solid state and in solution. [source]

    Development of Pharmaceutical Drugs, Drug Intermediates and Ingredients by Using Direct Organo-Click Reactions

    Dhevalapally B. Ramachary
    Abstract Here we report on our studies of the use of combinations of amino acids, amines, K2CO3 or Cs2CO3 and CuSO4/Cu for catalysing green cascade reactions. We aimed to prepare the highly reactive and substituted olefin species 7 and 8, under very mild and environmentally friendly conditions, thus giving the hydrogenated products 10 and 12 through the action of Hantzsch ester (4) by self-catalysis through decreasing the HOMO,LUMO energy gaps between olefins 7/8 and Hantzsch ester (4) through biomimetic reductions. Highly useful compounds 10 to 14 were assembled from simple substrates such as aldehydes 1, ketones 2, CH acids 3, Hantzsch ester (4) and alkyl halides 5 by diversity-oriented green synthesis involving cascade olefination/hydrogenation (O/H), olefination/hydrogenation/alkylation (O/H/A) and hydrogenation/olefination/hydrogenation (H/O/H) reaction sequences in one-pot fashion with stereospecific organo- and organo-/metal-carbonate catalysis. Highly functionalized diverse compounds such as 10 to 14 are biologically active products and have found wide applications as pharmaceutical drugs, drug intermediates and drug ingredients. For the first time in organocatalysis, we report the O/H/A/TE reaction to furnish high yields of transesterification products 11 by simply mixing the reactants under proline/K2CO3 catalysis conditions. Additionally, a novel organocatalytic H/O/H reaction sequence for the synthesis of alkyl-substituted aromatics has been developed. Furthermore, for the first time we have developed organocatalysed cascade olefination/hydrogenation/hydrolysis (O/H/H) reactions to furnish highly useful materials such as 2-oxochroman-3-carboxylic acid (14kc) and 2-amino-4H -chromene-3-carbonitrile (14kj) in good yields. Experimentally simple and environmentally friendly organocatalytic two-carbon homologation through cascade O/H/H reactions of aldehydes 1, Meldrum's acid (3c), Hantzsch ester (4) and acetic acid/triethylamine in ethanol has been demonstrated. Additionally, we have developed a green synthesis of the highly substituted 1,2,3-triazole 17 from simple substrates through a two-step combination of olefination/hydrogenation/alkylation and Huisgen cycloaddition reaction sequences under stereospecific organocopper catalysis conditions. In this paper we have found strong support for our hypothesis that, "decreasing the HOMO,LUMO energy gap between olefins 7/8 and Hantzsch ester (4) will drive the biomimetic hydrogenation reaction by self-catalysis". This self-catalysis was further confirmed with many varieties of examples.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Structural, Electronic, and Bonding Properties of Zeolite Sn-Beta: A Periodic Density Functional Theory Study

    Sharan Shetty
    Abstract The structural, electronic, and the bonding properties of the zeolite Sn-beta (Sn-BEA) have been investigated by using the periodic density functional theory. Each of the nine different T-sites in BEA were substituted by Sn atoms and all the nine geometries were completely optimized by using the plane-wave basis set in conjunction with the ultra-soft pseudopotential. On the basis of the structural and the electronic properties, it has been demonstrated that the substitution of Sn atoms in the BEA framework is an endothermic process and hence the incorporation of Sn in the BEA is limited. The lowest unoccupied molecular orbitals (LUMO) energies have been used to characterize the Lewis acidity of each T-site. On the basis of the relative cohesive energy and the LUMO energy, the T2 site is shown to be the most favorable site for the substitution Sn atoms in the BEA framework. [source]