摘要:

Pyridine-2-azo-p-phenyltetramethylguanidine (PAPT) was synthesized and the properties of this compound examined. The dissociation constants of the conjugate acids in H2O areandat 25 °C atI = 0.1, and in acetonitrile areand. The properties of metal–ligand chelates in acetonitrile have been examined and the stability constants for Ni2+, Co2+, and Zn2+complexes measured. The rates of reaction of PAPT with Ni2+, Co2+, and Zn2+in acetonitrile have been determined and the activation parameters measured for the complex formation of LNi2+. The stability constants for both complexing centres of PAPT have been calculated. The13C NMR spectra for PAPT and LNi2+are quoted. The expected enhancement of the metal ion complexing ability of PAPT due to the strongly electron-releasing nature of the tetramethylguanidinyl group was not found.Keywords: metal ion complexes, pyridine-2-azo-p-phenyltetramethylguanidine, stability constants, pKa.

ISSN:0008-4042    

DOI:10.1139/v91-185

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

We have studied the 184.9 and 147.0 nm photochemistry of gaseous cw-1,3-pentadiene: the main products observed at 184.9 nm aretrans-1,3-pentadiene and 1,3-cyclopentadiene. The formation of radicals also occurs as shown through the use of DI as a radical scavenger. Cyclopentadiene is the likely product of successive eliminations of two hydrogen atoms from the photoexcited molecule after rearrangement of the pentadienyl radical to the cyclopentenyl structure: Ф0(cyclo-C5H6) ≈ 0.25. Elimination of a methyl radical (Ф0 ≈ 0.50) also occurs, with formation of CH2=CHCH=ĊH* and, in a lower yield, CH2=C=CHĊH2*. However, it is not possible to identify properly the mechanism of the formation of the latter radical. It may be the result of the isomerization of either the first photoexcited molecule or the excited 1,3-butadienyl radicals. A small amount of 1,4-pentadiene formation is also observed (Ф0 ≈ 0.035 ± 0.015). At 147.0 nm, the same characteristics are observed, together with higher fragmentation due to the higher energy content of the photoexcited molecules. It appears that the photofragmentation at both wavelengths is more in line with that of acyclic alkenes than with that of 1,3-butadiene, which tends to undergo isomerization of the photoexcited molecules to the 1,2-butadiene structure.Keywords: 1,3-pentadiene, far UV, vacuum UV, photolysis, monomolecular, fragmentation, sta

ISSN:0008-4042    

DOI:10.1139/v91-186

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Rate constants are reported for the reaction of muonium atoms in water with some 36 organic compounds, many of interest in biology. ThesekMvalues range from < l05to 7 × 1010 M−1s−1, according to thetypeof reaction involved, with the sugar–phosphate backbones of nucleic acids being at the low end and their bases at the high end. They are compared with corresponding published H-atom data (kH), where possible, and show kinetic-isotope-effects ranging over five orders of magnitude. Since all kHdata were obtained at pH = 1, whilekMvalues refer to pH ~ 7 of the natural state, the pH-dependence ofkMwas examined in representative cases. The changes found result from protonation of the solute rather than a changed reactivity of Mu on being converted to MuH+. On localizing the solutes in the hydrophobic phase of dilute micelles, the reactivity of Mu was again measured (kM(mic)). The resulting "enhancement" factor was considered in terms of: the reaction mechanism, its dependence on microenvironment (solvation), and the concentrating effect of mutual confinement to small sections of a biphasal system.Keywords: kinetic isotope effects, muonium, biochemicals, micelles.

ISSN:0008-4042    

DOI:10.1139/v91-187

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

In this work we report the excess molar volumes,for the miscible mixtures {xc-C5H10 + (1 − x)CH3OH} and {xc-CkH2k + (1 − x)ClH2l+1OH} wherek = 5, 6, 7, 8, or 10 andl = 2 or 3. Theresults are discussed in terms of the size of the cycloalkane ring and the type of alcohol.Keywords: Excess volumes, cycloalkane + alkanol.

ISSN:0008-4042    

DOI:10.1139/v91-188

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

In acetonitrile and methanol, methyl 1- and methyl 2-naphthoate (1- and 2-NpCO2CH3) underwent [2 + 2] photocycloaddition with acetylacetone (acacH) from a reactive species derived from the lowest spectroscopic singlet excited state to give cyclobutane derivatives such as9that ring-opened to afford addition products of acetyl and acetonyl moieties at the 7,8-position for 1-NpCO2CH3(2and3) and the 1,2-position for 2-NpCO2CH3(7). Further irradiation of3and7caused a deep-seated rearrangement of3to give4and an intramolecular addition of7to give the caged product8. The photocycloaddition quantum yields were increased remarkably in the presence of a trace amount (< 0.001 M) of protic acids. For example, the limiting quantum yield of2and3with Фadducts = 0.033 (in the absence) increased to Фadducts> 0.5 under comparable conditions in the presence of [H2SO4] = 0.001 M, approaching the maximum asymptotically at about this concentration; the increases of the quantum yield could not be correlated with H2SO4concentrations. The acid promotion of the product formation elevated the photocycloaddition to a significantly useful preparative reaction. The photocycloaddition of 2-NpCO2CH3was quenched by tributylamine, dimethylaniline, and methyl iodide, and could not be initiated by typical triplet sensitization. Strong fluorescence of 2-NpCO2CH3at 358 nm in CH3CN was quenched by acetylacetone, tributylamine, dimethylaniline, and methyl iodide, the last of which concurrently enhanced the phosphorescence intensity of 2-NpCO2CH3. In the presence of [H2SO4] > 0.005 M the fluorescence intensity at 358 nm was quenched and a new fluorescence at 470 nm corresponding to protonated12-NpCO2CH3appeared. However, in the [H2SO4] < 0.002 M region, the new fluorescence was not observed, indicating that the protonation scarcely occurred. The Stern–Volmer constant, obtained by the quantum yield monitor, of the 2-NpCO2CH3photocycloaddition with acacH was more than an order of magnitude smaller than that obtained by the quenching of 2-NpCO2CH3fluorescence by acacH. The discrepancies outlined above clearly demonstrate that the reactive intermediate of the photocycloaddition is not the exciplex of the spectroscopic singlet excited species of12-NpCO2CH3and acacH, but one that is derived from the exciplex. It is speculated that this unknown reactive intermediate interacts with a proton to promote the photocycloaddition.Keywords: photocycloaddition of naphthoates, photorearrangement of styryl ketones, acid catalysis of quantum yields, fluorescence of protonated naphthoates, acid enhancement of singlet quenchin

ISSN:0008-4042    

DOI:10.1139/v91-189

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

AK1401 is a mutant ofPseudomonasaeruginosastrain PAO1 (serotype 05) that does not express O-antigen, but does express "A-band" lipopolysaccharide (LPS). The polysaccharide portion of the A-band LPS (A-PS) from AK1401 was found to consist mainly ofD-rhamnose, with smaller amounts of 3-O-methylrhamnose, ribose, mannose, glucose, and a 3-O-methylhexose.1H nuclear magnetic resonance spectra of the intact A-PS indicated that the main structural feature was a repeating trisaccharide of α-D-rhamnose having the following structure:The1H NMR spectrum of the repeating unit was completely assigned through the use of 2D shift-correlated and relayed coherence transfer NMR spectroscopy. The linkage positions and sequence of residues were found by nuclear Overhauser enhancement difference spectroscopy.Keywords:Pseudomonasaeruginosa, lipopolysaccharide,1H NMR.

ISSN:0008-4042    

DOI:10.1139/v91-190

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Phosphate derivatives of glucose and fructose are well-known intermediates in sugar fermentation. Proton and deuterium NMR spectroscopy studies of the fermentation process provide information about proton (deuteron) transfers that are likely to occur in such biotransformations. In this paper we describe the influence of complexation of those metabolites with praseodymium trichloride and of pH on their proton NMR chemical shifts. We determine the conditions under which all the protons of both the α. and β forms of these cyclic sugars are separated. Glucose-1 phosphate was found to be the most suitable derivative for this type of study. Furthermore, comparing the behaviour of these compounds with 2-phosphoglyceric acid allows us to specify the exact conformation of the latter.Keywords: phosphate sugar derivatives, NMR, LIS effects.

ISSN:0008-4042    

DOI:10.1139/v91-191

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Peptide nitriles are reversible inhibitors of papain that form thioimidates with the cysteine thiol in the enzyme's active site. These thioimidates undergo reactions with thiols and amines to form acids and amidines, respectively. These reactions were also found to be stereospecific. Only a thioimidate derived from anL-amino acid nitrile will react with exogenous nucleophiles. These reactions were followed by13C and15N NMR techniques.Keywords: papain, nitrile,l3C NMR,15N NMR, thioimidate.

ISSN:0008-4042    

DOI:10.1139/v91-192

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The crystal structure of 3′,3″,5′,5″-tetrabromophenolphthalein ethyl ester (TBPE) has been determined by X-ray diffraction at room temperature. This compound crystallizes in space group, witha = 12.361(4),b = 12.533(4),c = 9.986(2) Å, α = 99.57(3), β = 112.76(2), γ = 100.73(3) °, andZ = 2. The structure was solved by direct methods and refined by full-matrix least-squares calculations to a residual of 0.034 for 1862 observed reflections. TBPE is propeller shaped about the central carbon and crstallizes with one molecule of benzene solvent per asymmetric unit. In 1:1 CD2Cl2:CDCl3solution complete1H and13C NMR signal assignments have been made via1H1H COSY and1H13C HETCOR experiments. The quinoidal and phenolic integrities are retained on the NMR timescale. By contrast for an acetone-d6solution only 1413C resonances are found and the colour of the solution changed from green to dark blue. These changes in acetone solution are attributed to the presence of a trace of base which induces the loss of the phenolic proton of TBPE and the existence of resonance forms which render the phenolic and quinoidal rings equivalent.Keywords: crystal structure, NMR, 3′3″5′5″-tetrabromophenolphthalein ethyl ester.

ISSN:0008-4042    

DOI:10.1139/v91-193

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Two polymorphic crystal forms (yellow and orange) of 2,2-di(p-nitrophenyl)-1-picrylhydrazine were crystallized from the same dichloromethane solution, and their crystal structures determined. The yellow form is triclinic,P1,a = 9.055(3),b = 10.396(4),c = 13.3187(3) Å, α = 89.83(2), β = 79.89(3), γ = 70.83(3)° at 228 K;R = 0.060, andRw = 0.057 for 3511 reflections withI > 2σI. The orange form is monoclinic,P21/c,a = 8.999(3),b = 25.041(11),c = 12.207(5) Å, β = 121.66(2)° at 223 K;R = 0.053, andRw = 0.058 for 3651 reflections withI > 2σI. The molecular structures in the two crystal forms are very similar. Both forms contain one solvent molecule per molecule of 2,2-di(p-nitrophenyl)-1-picrylhydrazine. In each, the two hydrazine nitrogen atoms have strong resonance interactions with the vicinal aromatic groups and both aresp2hybridized. The molecular structure around the N—N linkage shows a staggered conformation. Thus the resonance interaction between the picryl group and the other twop-nitrophenyl groups is negligible. The difference in color between the two crystal forms is attributed to a difference in molecular packing.Keywords: crystal structure, polymorphism, picrylhydrazine, conformation.

ISSN:0008-4042    

DOI:10.1139/v91-194

出版商:NRC Research Press    

年代:1991

数据来源: NRC