摘要:

The standard free energies of transferof the 2-carbomethoxypropionate ion (R−) have been determined from the solubilities of the silver salt (AgR) in water and six aqueous mixtures of ethylene glycol (1–60%) at 25 °C, using the literature values ofof Ag+. Utilizing these values of the R−ion as well as the literature values ofof the OH−ion, combined with the experimental values of ΔG≠for the alkaline hydrolysis of R−ion, the corresponding transfer parameters of the transition statesfor the hydrolysis reaction in aquo-glycolic media at 25 °C have been calculated. Attempts have been made to correlate the rates and activation parameters with the transfer quantities and solvent properties.

ISSN:0008-4042    

DOI:10.1139/v87-038

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The fluorescence characteristics of the polyene antibiotic Nystatin have been studied by measurements of quantum yields, lifetimes, and anisotropies in a model bilayer membrane. These measurements have been performed as a function of temperature and fluorophore-to-phospholipid molar ratio. Comparisons with data available for the parinaric acids demonstrate that the photophysics of the two polyene chromophores is similar. The quantum yield decreases at increasing Nystatin densities while the lifetimes are constant. These observations combined with quantitative comparisons with calculations of the density dependence of dynamic quenching in two-dimensional systems show that Nystatin fluorescence is quenched in bilayer membranes by a static process. This is likely due to the formation of complexes within the bilayer. The quenching is equally efficient in both the gel and liquid crystalline phases of the bilayer which suggests that the formation of the complexes occurs at all temperatures. At high Nystatin densities, there is also a quenching of the polarization, but the mechanism whereby this occurs is not clear. The limiting anisotropy at low concentrations is between 0.33 and 0.35 at all temperatures, suggesting that the Nystatin monomer is highly restricted in its reorientational motion in both gel and liquid crystalline phases.

ISSN:0008-4042    

DOI:10.1139/v87-039

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The fluorescence properties of variousN-carbonyl-substituted indoles (compounds1–7) are examined. TheN-benzoyl-indole derivatives1and3–5are shown to fluoresce weakly and the effect of solvent polarity upon the energy of the emitting state and upon the quantum yield of fluorescence is described. It is concluded that the initially formed singlet excited state is non-emissive and can relax to an intramolecular charge transfer state which is weakly fluorescent. The solvent effects are consistent with a general type of solvent interaction, and the solvent-induced shifts in the wavelength of the fluorescence emission correlate well with the Lippert equation relating the stabilisation of the excited state to a function of solvent dielectric and refractive index. A poor correlation with the empiricalET(30) solvent polarity parameter is observed.

ISSN:0008-4042    

DOI:10.1139/v87-040

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Kinetic studies of the reaction ofp-dinitrobenzene with H2O2and NaOH in 10%, 30%, and 50% aqueous dioxane have been carried out at 30.0 °C. The reaction involves the formation of a reasonably stable intermediate which absorbs strongly in the visible region, with the rate of formation being about 18 times faster than the rate of conversion to final product which isp-nitrophenol. Proton and13C nmr spectra of the kinetic solution provide strong evidence that the intermediate isp-nitrophenyl hydroperoxide, apparently the first time that a true aryl peroxide species has been identified.

ISSN:0008-4042    

DOI:10.1139/v87-041

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The crystal and molecular structures of the dopaminergic ergoline derivative pergolide have been determined both as the free base and as the mesylate salt. Despite differences in protonation at the nitrogen atom, the two structures are extremely similar in all aspects. Stereochemical comparisons are made with bromocriptine, and possible dopaminergic pharmacophores in ergolines are discussed.

ISSN:0008-4042    

DOI:10.1139/v87-042

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

1,1,3,3-Tetracyanopropane,1, was prepared in low yields by a literature method with 2,2,4,4,6-pentacyanocyclohexenamine,2, as a major by-product. The products were examined by X-ray crystallography.1has an orthorhombic space group,Pbcn(No. 60) with cell dimensions,a = 7.158(2),b = 10.510(3),c = 9.733(2) Å and has four formula units in the unit cell.2has a monoclinic cell,P21/c(No. 14) with cell dimensionsa = 14.368(3),b = 6.626(1),c = 12.300(2) Å, β = 115.60(1)° and has 4 formula units in the unit cell. Data were collected with use of MoKα radiation and a Nicolet P3 diffractometer. The crystal structures were determined by standard methods and refined toRw = 0.037 (1) andRw = 0.040 (2) on the basis of 782 and 2108 unique reflections. Bond lengths and angles in the two compounds are normal.2has what has been considered to be the less likely tautomeric structure. Both compounds were examined by1H,13C nmr, vibrational spectroscopy, and mass spectroscopy. For2there was no evidence of the alternative tautomeric structure. New methods were developed for the preparation of both compounds and the mechanism of the original reaction rationalized.

ISSN:0008-4042    

DOI:10.1139/v87-043

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Crystals of 2′,5′-anhydroarabinosylcytosine hemihydrate belong to the monoclinic space groupP21. The cell dimensions area = 9.643(2),b = 10.328(1),c = 10.544(2) Å, β = 94.55(1)°. X-ray intensity data were measured on a diffractometer and the structure was determined by direct methods. Least-squares refinement, which included all nucleoside hydrogen atoms, converged atR = 0.041 for 2298 observed reflections. The asymmetric unit contains two molecules of the nucleoside and one molecule of water. In both nucleoside molecules, the conformation about the glycosyl bond isand, with XCNvalues of 15.5(3) and 26.3(3)°, respectively. In the bicyclic sugar moiety, the arabinofuranose rings adopt aC(3′)exo/C(2′)endoconformation and are highly puckered (τm = 57°). The solution conformation was studied by1H and13C nmr spectroscopy. A difference nOe proton nmr spectrum and3J(C,H) coupling constants reveal ananticonformation in solution, with torsion angles very similar to those obtained from X-ray analysis. A comparison of observed3J(H,H) coupling constants with those calculated on the basis of a modified Karplus equation shows significant differences, probably due to the presence of the bicyclic system.

ISSN:0008-4042    

DOI:10.1139/v87-044

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The oxidation ofn-propanol by aquomanganese(III) ions in perchlorate medium of constant ionic strength (4 mol dm−3, NaClO4) is described by the rate law [i] which is based on the consideration of the reactions [ii]–[ix].A further analysis of the rate law in terms of the results indicated that MnOH2+(aq) is the major oxidant. The values of the equilibrium constant (β1) and rate determining constant (k1) are reported together with the associated thermodynamic parameters. The values of the other constants,k,Ka, and β, could not be determined though an assumption was made that β ≈ β

ISSN:0008-4042    

DOI:10.1139/v87-045

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The conversion of aldehydes into α-aminonitriles and thence into imidazolidin-4-thiones has been studied. Hydrolysis of the appropriate imidazolidin-4-thiones gave thioamides of nine naturally occurring α-amino acids. The possible pre-biotic significance of these compounds is discussed.

ISSN:0008-4042    

DOI:10.1139/v87-046

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The flash vacuum pyrolysis of Diels–Alder adducts of anthracene constitutes a rapid and selective route to methanethial1and methanethialS-oxide2, as analyzed in the gas phase by photoelectron spectroscopy. Low temperature infrared and nuclear magnetic resonance (1H,13C) spectra are also reported for sulfine2.

ISSN:0008-4042    

DOI:10.1139/v87-047

出版商:NRC Research Press    

年代:1987

数据来源: NRC