摘要:

AbstractThe mechanism of biologically important (net) hydride transfer from NADH or NADPH to a substrate has been discussed from the viewpoint of physical organic chemistry. It is emphasized that the (net) hydride transfer involves an electron‐transfer complex as an intermediate of the reaction. The intermediate plays a crucial role in determining the stereochemistry of the reaction. Orientation of a dipolar functional group such as carbonyl or sulphinyl determines the molecular face for complexation, and consequently defines the face of reaction. Steric bulkiness is of secondary importance in defining the face of reaction. The mechanism observed is called non‐steric stereochemistry. Molecular interactions observed in organic reactions and discussed herein are found to be closely related to those observed in biological reacti

ISSN:0894-3230    

DOI:10.1002/poc.610080902

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

Abstract1H,13C,15N and17O NMR spectra ofN‐phenylacetamide (acetanilide) and 21ortho‐substituted acetanilides were measured and assigned. The observed NMR parameters are related to the Hammett substituent parameters and conformational characteristics of the acetamido moiety estimated by molecular mechanics calculations. Significant relationships were found for the13C NMR chemical shifts of C‐5 (parato substituent) and the direct spin–spin coupling constant,1J(C, H), of C‐3 (orthoto substituent) with Hammett substituent parameters. For15N NMR chemical shifts of the amido nitrogen, no general correlation with the Hammett substituent parameters was found. The interactions between functionalities contiguous to the carbonyl group and the amino nitrogen in acetanilides are effectively hampered owing to the increased twist angle between the planes containing the phenyl ring and the H–N–C fragment in derivatives bearing bulkyorthosubstituents. Especially inortho‐halogen‐substituted derivatives the15N NMR chemical shift of the amino nitrogen is very clearly related to the twist angle between the phenyl ring and H–N–C fragment. For17O NMR chemical shifts of the acetamido carbonyl, the observed variations can be related to the steric inhibition of resonance between the benzene ring an

ISSN:0894-3230    

DOI:10.1002/poc.610080903

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe reductive cyclization of several 2‐nitroarylamides was studied by radiolytic reduction, examining the effects of substituents on the nitrophenyl ring and on the leaving aniline and variations in the nature of the link between the nitrophenyl ring and the leaving aniline. The stoichiometry of the reduction and the identification ofN‐hydroxylactam and aniline products suggest that the major initial products of such a reduction of the nitroamides are the corresponding hydroxylamines. Under anaerobic conditions, cyclization via the hydroxylamines was considerably faster (up to 160‐fold) than via the corresponding amines under comparable conditions, but was similarly influenced by changes in geometry. Unlike cyclization via the amines, rates of cyclization via the hydroxylamines were sensitive to substitution on the leaving aniline, being accelerated by electron‐withdrawing groups. The rate‐determining step in the cyclization of the hydroxylamines is proposed to be breakdown of the tetrahedral int

ISSN:0894-3230    

DOI:10.1002/poc.610080904

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractA series of mono‐, bis‐ and tetra‐acridine ligands were prepared and their effects on the higher order structure of DNA were studied by dynamic fluorescence microscopy. The single‐crystal structure of the bis‐acridine derivativeN‐[2‐(dimethylamino) ethyl]‐4‐[2‐(9‐acridinylamino)benzamido]‐2‐(9‐acridinylamino)benzamide trihydrochloride (4) was determined, and shows that the molecule is sufficiently flexible to fold into an intramolecular stacking interaction in the crystal, supporting earlier hydrodynamic evidence that this compound can bis‐intercalate into DNA forming a single base pair (bp) sandwich complex. The corresponding tetra‐acridine analogue 1,11‐bis[4‐[2‐(9‐acridinylamino)benzamido]‐2‐(9‐acridinylamino)phenyl]‐1,11‐dioxo‐6‐methyl‐2,6,10‐triazaundecane pentahydrochloride (6) was synthesized, and dynamic fluorescence microscopy was used to study the effects of 4 and 6 on the higher order structure of large T4 DNA molecules (166 kbp), by measuring the average long‐axis legth (persistence length,l) of the complexes. The mono‐intercalating ligand acridine orange (5) increasel, whereas the bisintercalating diacridine 4 has no apparent effect and the putative multi‐intercalating tetracridine derivative 6 decreaseslby compacting the higher order DNA structure. These results demonstrate the usefulness of the technique for directly observing ligand–DNA complexes, and show that ligands with suitably positioned multiple binding sites can influence the

ISSN:0894-3230    

DOI:10.1002/poc.610080905

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractInteractions between compounds containing phosphoryl, carbonyl, or hydroxyl groups (or combinations of these groups) with metal ions (Na+, Mg2+) were probed in CD3CN solutions by17O NMR spectroscopy. For all phosphoryl and carbonyl substrates a strong high—field shift of the PO and CO signals was observed on the addition of a salt; no shift was observed, however, for the OH group signal, indicating that no chelation takes place in the hydroxyphosphoryl (or hydroxycarbonyl) derivatives. For 2‐hydroxy‐3‐benzoylpropylphosphonic diester the17O NMR studies, together with conformational analysis based on the1H spectroscopy, demonstrated the chelation of a metal ion by the PO and CO functions (fermation of an eight–membered cyclic structure) with the OH group involved in the intramolecular hydrogen bonding, but not in the complexation

ISSN:0894-3230    

DOI:10.1002/poc.610080906

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe aminolysis and hydrolysis of several sulphamate esters, RNHSO2ONp (R = PhCH2, Ph, 4‐MeC6H44, 3‐MeC6H4, 4‐FC6H4, 4‐ClC6H4, 3‐ClC6H4, H; Np = 4‐NO2C6H4) were been studied in 50% (v/v) aqueous acetonitrile at various temperatures. Reaction of the esters with an amine (R1NH2) gives−ONp and both sulphamide, (RNHSO2NHR1) and sulphamate (RNHSO2O−R1NH3+) products. First‐order rates were determined by the appearance of−ONp and sometimes also by the disapperance of ester. The reaction was found to be independent of amine type and concentration and at the high pHs that obtain the substrate esters are fully ionized. A Hammett ρacylof −;1·8 was obtained for the decomposition of the sulphamate anions and this is consistent with substantial NS bonding in the transition state leading to N‐sulphonylamine, RNSO2. This intermediate then partitions very rapidly, reacting with R1NH2and H2O respectively. ΔH‡, ΔS‡ and a deuterium solvent isotope effect were determined and were also interpreted in favour of the proposed mechanism. The dimethyl sulphamate ester (Me2NSO2ONp) does

ISSN:0894-3230    

DOI:10.1002/poc.610080907

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractEmpirical solvent polarity parametersET(30) were determined by UV–visible spectrophotometry using Dimroth– Reichardt's betaine dye, as a function of composition, for (aprotic + aprotic) and (aprotic + protic) binary solvent mixtures. For (aprotic + aprotic) solvent systems the cosolvent was toluene, and the other solvents used were selected with different structural characteristics and an extensive range of polarity: chloroform, 1,4‐dioxane, ethyl acetate, tetrahydrofuran, acetone, nitromethane andN,N‐dimethylformamide. For (aprotic + protic) solvent systems, the protic cosolvent used was methanol, and the aprotic solvents selected were toluene, chloroform, 1,1,1‐trichloroethane, tetrahydrofuran, acetone,N,N‐dimethylformamide, and dimethyl sulphoxide. Each system was analysed according to its deviations from additivity due to selective solvation of the betaine. A preliminary application of these empirical solvent polarity parameters was related to the solvent effects in a simple example of a nucleophilic aromatic substituti

ISSN:0894-3230    

DOI:10.1002/poc.610080908

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractAn IR spectroscopic study of the hydrogen bonding of Bu3N+N−C≡N with 4‐fluorophenol showed that the site of complexation is the nitrogen of the nitrile function. THe formation constant of the 1:1 complex in CCl4indicates that this cyanamidate is a stronger hydrogen‐bond base than is any nitrile, amine or pyridine. The Bu3N+–N−group increases the basicity of the nitrile group very efficiently because of the conjugation of two lone pairs on the anionic nitrogen with the π systems of the cyano group. This conjugation is also exemplified by the very low ν(C≡N) wavenum

ISSN:0894-3230    

DOI:10.1002/poc.610080909

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

ISSN:0894-3230    

DOI:10.1002/poc.610080901

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY