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  • 1
    Digitale Medien
    Digitale Medien
    On the out-of-plane deformation of aromatic rings, and its representation by molecular mechanics (1987)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 8 (1987), S. 1051-1056 
    Details
    ISSN: 0192-8651
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Biochemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Informatik
    Notizen: It has been found that the previous MM2 (or MMP2) description of out-of-plane deformation of aromatic rings sometimes yields distortions which are much too large. As a result, rotational barriers involving distortions of such rings may be calculated to have values which are too low. Examples are collected and discussed. An alternative formulation, which appears to significantly reduce the calculational error, is presented.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jcc.540080713
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  • 2
    Digitale Medien
    Digitale Medien
    Molecular mechanics simulation studies of dienoic hydrocarbons: From alkenes to 1-Palmitoyl-2-linoleoyl-phosphatidylcholines (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 17 (1996), S. 1013-1024 
    Details
    ISSN: 0192-8651
    Schlagwort(e): Chemistry ; Theoretical, Physical and Computational Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Informatik
    Notizen: Although no crystal structures of mixed-chain phosphatidylcholines with unsaturated sn-2 acyl chains exist, the force field method in conjunction with the experimentally determined structure of saturated identical-chain phosphatidylcholine can be applied to simulate molecular structure for mixed-chain phosphatidylcholines. In this study, the packing models of mixed-chain 1-palmitoyl-2-linoleoyl-phosphatidylcholines in bilayers at temperatures below the gel-liquid crystalline phase transition temperature or T 〈 Tm are simulated by using Allinger's MM3(92) force field. Our results indicate that the unsaturated sn-2 acyl chains of the mixed-chain lipid can fold into two energy-minimized topologies: the crankshaftlike and the U-shaped motifs. The folded region in the crankshiftlike sn-2 acyl chain is characterized by a sequence s- Δs+s+Δs-, and the U-shaped chain arises from the characteristic sequence s-Δs+s-Δs+, where s± denotes the ± skew conformation and Δ the cis carbon-carbon double bond. These modeled structures of 1-palmitoyl-2-linoleoyl-phosphatidylcholines in the bilayer at T 〈 Tm should not be regarded as highly rigid structures, since torsion angles of carbon-carbon bonds associated with sequences s Δs+s+Δs and s Δs+s-Δ s+ can fluctuate somewhat without appreciably affecting the steric energy of the corresponding lipid bilayer. © 1996 by John Wiley & Sons, Inc.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Studies on organophosphorus compounds. XXXVI.For Part XXXV, see S. S. Li, Z. Y. Chen and C. Y. Yuan Scientia Sinica (Series B) 136, (1989).. Substituent effects of alkylphosphonates and -phosphinates in alkaline hydrolysis (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 48-54 
    Details
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Alkaline hydrolysis of diethyl alkylphosphonates and alkyl diethylphosphinates was studied in aqueous dimethyl sulphoxide. The behaviour of these acyclic phosphorus esters is very similar to that of some cyclic phosphorus esters. Rate constants were measured at three temperatures over a 30°C range, and the activation functions of the reaction were estimated. The basic hydrolytic process was proved to be a bimolecular AE reaction. Multiple regression analyses involving rate constants and substituent parameters gave, as a rule, poor results using steric constants derived from carbon compounds. However, the substituent steric effect on the rate of hydrolysis of phosphonates and phosphinates studied correlated very well with ΔΔE, representing the difference in steric energy calculated by molecular mechanics. It is attributed to the various degrees of susceptibility of carbon and phosphorus atoms to the steric hindrance of the substituents. Moreover, Newman's rule of six for the hydrolytic reaction of carboxylates was completely eliminated in phosphorus ester hydrolysis.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/poc.610030110
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  • 4
    Digitale Medien
    Digitale Medien
    Studies on organophosphorus compounds XXXII. A molecular mechanics study of the hydrolytic reaction of alkylphosphonates and alkylphosphonyl chlorides (1989)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989), S. 146-160 
    Details
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The alkaline hydrolysis of several alkylphosphonates and alkylphosphonyl chlorides has been investigated by molecular mechanics calculations (MM2, 1985 version). The difference of the steric energies (ΔE) between tetracoordinate substrate and pentacoordinate transition state of phosphorus compounds represents the activation energy (ΔE≠) in hydrolysis. The change of ΔE for various alkyl groups relative to methyl group (ΔΔER) is suggested as a measure of the steric effect of substituents. Thus the correlation analysis involving log k and ΔΔER of the branched alkyl group gives good results and it is reasonable to anticipate that analogous treatment using ΔΔER for the straight chain alkyl group is not satisfactory owing to the minor contribution of steric effect of the latter. However, the multiple regression analysis of log k with ΔΔER and Taft's σ* provides very good results. As shown by us, for the hydrolytic reactions studied, the proposed ΔΔER is much better than Taft's Es and Charton's ν, the commonly used well-known steric parameters in the chemistry of carbon compounds.
    Zusätzliches Material: 7 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/poc.610020207
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  • 5
    Digitale Medien
    Digitale Medien
    Treatment of electrostatic effects within the molecular mechanics method. 3. Double bonds and conjugated systems (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 467-478 
    Details
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The previously developed general method (IDME), which includes calculation of electrostatic and solvation effects on conformational equilibria, has been extended to molecules containing double bonds and conjugated systems. It was applied in connection with MM2 studies to the calculation of the charge distributions and dipole moments, and to the conformational energies of some β-substituted cyclohexenes, exo-methylenecyclohexanes and benzocycloheptenes. Conformational equilibria and dipole moments were well calculated. It was concluded that electrostatic interactions do not play a major role in determining conformational preferences in these compounds. On the other hand, the energies of the preferred conformations of the ten-membered ring in (E)-3β-acetoxy-5,10-seco-1(10)-cholesten-5-one are poorly calculated without the IDME procedure, and fairly well with it.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/poc.610040802
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  • 6
    Digitale Medien
    Digitale Medien
    Quantum mechanical and molecular mechanical studies of the hydrolysis of methyl nitrate and the solvent effect (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 361-366 
    Details
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The alkaline hydrolysis reaction of methyl nitrate was simulated by quantum mechanical and molecular mechanical methods. The gas-phase reaction was calculated to proceed with no barrier when ab initio calculations at the STO-3G level were utilized, and with a very small barrier (5.70 kJ mol-1) when the MINDO/3 method was applied. In solution, the solvation energy was estimated to be 70.33 kJ mol-1 by molecular mechanical calculations. Thus the activation energy (76.03 kJ mol-1) of alkaline hydrolysis of methyl nitrate was found to be in good agreement with the available experimental value (82.42 kJ mol-1). The results indicated that the substantial activation barrier in alkaline hydrolysis was essentially solvent-induced.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/poc.610050613
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  • 7
    Digitale Medien
    Digitale Medien
    New strategy for the synthesis of functionalized phosphonic acidsThis article was presented as an invited lecture at 4th International Conference on Heteroatom Chemistry, Seoul, Korea, August 1995. The abstract was published in Pure and Applied Chemistry, 68, 1996, 907. (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Heteroatom Chemistry 8 (1997), S. 103-122 
    Details
    ISSN: 1042-7163
    Schlagwort(e): Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Various approaches leading to mono-, di-, and polyfunctionalized phosphonates as well as phosphoryl heterocycles are reported for the systematic study of relationships between chemical structure and biological activity of this most important class of organophosphorus compounds. © 1997 John Wiley & Sons, Inc.
    Zusätzliches Material: 30 Ill.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Studies on organophosphorus compounds 61 substituent effects in organophosphorus estersDedicated to Professor Dr. L. Horner on the occasion of his seventieth birthday. (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Heteroatom Chemistry 4 (1993), S. 23-31 
    Details
    ISSN: 1042-7163
    Schlagwort(e): Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Examination of several model organophosphorus compounds, bicyclic phosphates (1), p-substituted phenylphosphonates (2), and acidic alkylphosphonates (3) reveals that the polar substituent effect in organophosphorus esters parallels that of carbon compounds. No significant variation in polar effects of different alkyl groups with up to 10 carbon atoms is observed. As demonstrated by us, the commonly used Kabachnik polar constant σΦ for alkyl groups of organophosphorus compounds reflects the steric effect associated with steric hindrance to solvation of acidic anions. Therefore, a set of solvation steric parameters Eps has been calculated from pKa values of organophosphorus acids. This parameter can be applied to describe the structural effect on dissociation of organic acids and, after suitable modification, may reflect the steric effect of alkyl groups in hydrolytic reactions of organophosphorus esters.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hc.520040105
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