| | 2 | Author
| Sophie Creuzet, TeresaM. Iranda, Jean-M Arc Ducruet | Requires cookie* | | | Title
| Comparison of Experimental and Calculated Hydrogen Bonding Properties of Some Urea and Triazine Inhibitors of Photosystem II  | | | | Abstract
| Previous studies o f structure/activity relationships o f photosystem II inhibitors, including com parisons o f their inhibitory power in herbicide-resistant and susceptible chloroplasts, have led to predict the role o f hydrogen bonding, associated to hydrophobicity, in the binding onto the Qb site. The crystallographic structures o f bacterial reaction centers now allow these bonds to be identified. In order to be able to understand the binding o f various herbicides and the effects o f resistance mutations within the Q B site, a reliable estimation o f hydrogen bonding strengths is needed. We show here, by calculating interactions with model com pounds, con trolled by physicochemical measurements, that the hydrogen bonding properties o f the C = X nucleophilic moiety present in most PS II inhibitors are different for triazines as compared to urea or amide derivatives. Semiempirical methods (AM 1) fail to reproduce the energies o f hy drogen bonds between a triazine ring nitrogen and a phenolic proton. An empirical method (SI BFA), designed to reproduce interaction energies, has been adapted with the aim o f calculat ing the binding energies o f various herbicides with models o f the Q B site. | | | |
Reference
| Z. Naturforsch. 48c, 179 (1993); received November 12 1992 | | | |
Published
| 1993 | | | |
Keywords
| Herbicide, Herbicide Resistance, Hydrogen Bonding, M olecular Calculation, Photosystem II | | | |
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| | | | | TEI-XML for
| default:Reihe_C/48/ZNC-1993-48c-0179.pdf | | | | Identifier
| ZNC-1993-48c-0179 | | | | Volume
| 48 | |
| 3 | Author
| Wanda Wagner, Maria Zaborowska, Wlodzimierz Puzyna, David Shugar | Requires cookie* | | | Title
| Studies on Purine-Pyrimidine Hydrogen Bonded Base Pairing by Means of Absorption and Emission Spectroscopy | | | | Abstract
| Procedures are described for measurement of association constants between potentially com plementary purine and pyrimidine bases by hydrogen bonding in non-aqueous medium by means of absorption and emission spectroscopy. The methods require that one of the two constituents be fluorescent and exhibit a long wavelength absorption band not, or only partially, overlapped by the second constituent. The foregoing has been applied to measurements of the association constants, and other parameters, of hydrogen-bonded complexes of 2-aminopurine with 1-substituted uracil, thymine and barbital in chloroform solution, both in the ground and excited states. It was estab lished that the 1:1 hydrogen-bonded base pairs 2-aminopurine : 1-cyclohexyluracil and 2-amino purine: 1-octylthymine maintain the ground-state equilibrium during the life time of the excited state, whereas for the corresponding pair 2-aminopurine: 1-methylbarbital this equilibrium is per turbed on excitation. The influence of N-alkylation of the 2-aminopurine residue on base-pairing with the pyrimidines has also been examined. The results are compared with those obtained by other methods. The specific advantages of the procedures employed, and their possible applications to studies on the behaviour of fluorescent residues in polynucleotides, are discussed. | | | |
Reference
| (Z. Naturforsch. 29c, 672 [1974]; received August 1 1974) | | | |
Published
| 1974 | | | |
Keywords
| Purines and Pyrimidines, Hydrogen Bonding, Base-pairing, Excited States, Fluorescence | | | |
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| default:Reihe_C/29/ZNC-1974-29c-0672.pdf | | | | Identifier
| ZNC-1974-29c-0672 | | | | Volume
| 29 | |
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