Showing papers in "Canadian Journal of Chemistry in 1991"
TL;DR: In this paper, the frequency of the so-calledamide I band (amide C=O stretching vibration, vC=O) of proteins is discussed in terms of the dihedral angles of the various secondary structures present within proteins.
Abstract: The frequency of the so-called "amide I" band (amide C=O stretching vibration, vC=O) of proteins is discussed in terms of the dihedral angles of the various secondary structures present within prot...
108 citations
TL;DR: 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:The 1H NMR spectrum of the repeating unit was completely assigned through the use of 2D shift-correlated and relayed coherence transfer NMR spectroscopy.
Abstract: AK1401 is a mutant of Pseudomonas aeruginosa strain PAO1 (serotype 05) that does not express O-antigen, but does express "A-band" lipopolysaccharide (LPS). The polysaccharide portion of the A-band ...
108 citations
TL;DR: A kinetic and ultraviolet-visible study of a series of thermo- and photochromic dyes is reported in this paper, showing that ultraviolet irradiation of the indolino-benzospiropyran derivatives 1′-4′ leads to their transforma...
Abstract: A kinetic and ultraviolet–visible study of a series of thermo- and photochromic dyes is reported. Ultraviolet irradiation of the indolino-benzospiropyran derivatives 1′–4′ leads to their transforma...
97 citations
TL;DR: The crystal and molecular structures of Sn(O-t-Bu)4 and [Sn(O -i-Pr)4•HO-I-Pr]2 have been determined by single-crystal X-ray diffraction as discussed by the authors.
Abstract: The crystal and molecular structures of Sn(O—t-Bu)4• and [Sn(O—i-Pr)4•HO—i-Pr]2 have been determined by single-crystal X-ray diffraction. Sn(O—t-Bu)4 crystallizes in the monoclinic crystal system with space group C2/c, where a = 17.382(6) A, b = 8.742(2) A, c = 15.518(5) A, β = 116.44(1)°, Z = 4, and R = 2.5%. Sn(O—t-Bu)4 is monomeric in the solid state, with a distorted tetrahedral tin coordination environment. [Sn(O—i-Pr)4•HO—i-Pr]2 crystallizes in the monoclinic crystal system with space group P21/n, where a = 11.808(3) A, b = 14.356(3) A, c = 12.380(2) A, β = 95.27(2)°, Z = 2, and R = 4.9%. [Sn(O—i-Pr)4•HO—i-Pr]2 exhibits an edge-shared, bi-octahedral structure in the solid state that is distorted due to the presence of asymmetric hydrogen bonding between axially coordinated alcohol ligands and an isopropoxide ligand.13C NMR and IR spectroscopic data have been recorded for Sn(O—t-Bu)4 and Sn(O—t-Bu-d9)4 to establish criteria for unambiguous identification of solution structures of tin(IV) alkoxides. I...
84 citations
TL;DR: The equilibrium reactions between rutin, 3-[6-O-(6-deoxy-α-L-mannopyranosyl)-(β-D-glucopyranoyl)oxy]-2-(3,4-dihydroxyphenyl)-5,7-Dihydroxy-4H-1-benzopyran-4-one, and quercetin (rutin aglycone) wit...
Abstract: The equilibrium reactions between rutin, 3-[6-O-(6-deoxy-α-L-mannopyranosyl)-(β-D-glucopyranosyl)oxy]-2-(3,4-dihydroxyphenyl)-5,7-dihydroxy-4H-1-benzopyran-4-one, and quercetin (rutin aglycone) wit...
78 citations
TL;DR: In this paper, the Taylor dispersion (peak-broadening) technique was used to measure the mutual diffusion coefficients of the mixed salt solutions MgCl2+MgSO4+H2O.
Abstract: The Taylor dispersion (peak-broadening) technique is used to measure the ternary mutual diffusion coefficients of the mixed salt solutions MgCl2 + MgSO4 + H2O and Na2SO4 + MgSO4 + H2O at 25 °C. The...
71 citations
TL;DR: In this paper, the results of a controlled alkaline degradation of the Dawson-type anion α-[As2W18O62]6− were obtained for di-, tri-, and hexavacant lacunary tungstoarsenates.
Abstract: The di-, tri-, and hexavacant lacunary tungstoarsenates α-[HAs2W16O59]11−, α-[As2W15O56]12−, and α-[H2As2W12O48]12− were prepared by controlled alkaline degradation of the Dawson-type anion α-[As2W18O62]6−. The relationships between all these anions and the two α-[As2W17O61]10− isomers were established. The mixed saturated derivatives α-[As2VxW18−xO62](6+x)− (x = 1,2,3) and α-[As2MoxW18−xO62]6− (x = 1, 3) were obtained by refilling the lacunas with vanadium and molybdenum respectively. The new mixed anion α2-[As2Mo2W15O61]10− was used concurrently with α-[HAs2WI6O59]11− to obtain α-[As2Mo2W16O62]6−; in both cases minor parts of α-[As2MoxW18−xO62]6− (x = 1 and 3) were obtained simultaneously. All species have been characterized by polarography and by IR spectrometry. Proposed structures, based on the similarity of the redox properties and syntheses processes to those of the corresponding Dawson-type lacunary and mixed tungstophosphates, were given for all these species. The structures of the "saturated" tu...
65 citations
TL;DR: The structure of the solvated lithium cation in methyl acetate (MA) solutions has been investigated using Raman spectroscopy Two bands at 844 and 864 cm−1 have been assigned to two different types as mentioned in this paper.
Abstract: The structure of the solvated lithium cation in methyl acetate (MA) solutions has been investigated using Raman spectroscopy Two bands at 844 and 864 cm−1 have been assigned to two different types
63 citations
TL;DR: Both amino-oxo and amino-hydroxy tautomeric forms of 9-methylguanine have been identified in approximately equal abundance in infrared studies of these molecules isolated in the hydrophobic enviro...
Abstract: Both amino-oxo and amino-hydroxy tautomeric forms of 9-methylguanine have been identified in approximately equal abundance in. infrared studies of these molecules isolated in the hydrophobic enviro...
63 citations
TL;DR: In this paper, the authors find the most effective catalyst of stoichiomagnetic ferrospinels for the decomposition of H2O2, their effectiveness is dependent on the composition of the catalyst.
Abstract: Some ferrospinels act as catalysts for the decomposition of H2O2, their effectiveness is dependent on the composition of the catalyst. This study is to find the most effective catalyst of stoichiom...
56 citations
TL;DR: In this paper, the authors show that the FT-IR transmission spectra of liquids in well-made and firmly held cells with KBr or NaCl windows are usually very reproducible except that their baselines often show unexpected variations.
Abstract: FT-IR transmission spectra of liquids in well-made and firmly held cells with KBr or NaCl windows are usually very reproducible except that their baselines often show unexpected variations. To obta...
TL;DR: In this article, the non-degenerate, symmetric stretch (A1,SO3) and (A 1,ClO4) Raman mod were compared by studying the nonsmooth stretch of LiCF3SO3 in polypropylene glycol (PPG 400 and PPG 4000).
Abstract: Solutions of LiCF3SO3 and LiClO4 in acetone and in poly(propylene glycol) (PPG 400 and PPG 4000) have been compared by studying the nondegenerate, symmetric stretch (A1,SO3) and (A1,ClO4) Raman mod
TL;DR: Treatment of ribonucleosides with thionyl chloride/pyridine/acetonitrile (0 °C to ambient temperature) resulted in essentially quantitative formation of 5′-chloro-5′-deoxy-2′,3′-Osulfinylnucleosid.
Abstract: Treatment of ribonucleosides with thionyl chloride/pyridine/acetonitrile (0 °C to ambient temperature) resulted in essentially quantitative formation of 5′-chloro-5′-deoxy-2′,3′-O-sulfinylnucleosid...
TL;DR: In this paper, the rotational motion of deuterated hydrocarbons, which is related to the micellar microviscosity at the location of the hydrocarbs, was probed by 'H NMR relaxation.
Abstract: Information concerning the solubilization of hydrocarbons in ionic surfactant micelles was obtained from 'H NMR relaxation, 'H NMR chemical shifts, and 'H NMR paramagnetic relaxation measurements. The rotational motion of deuterated hydrocarbons, which is related to the micellar microviscosity at the location of the hydrocarbons, was probed by 'H NMR relaxation. The relaxation data are interpreted using both the two-step and the single-step models, and the results are discussed in terms of the micellar microviscosity and the location of the hydrocarbons in micelles. The location of the hydrocarbons in micelles was further investigated by determining the aromatic ring current-induced 'H chemical shifts along the surfactant alkyl chain and by comparing the 'H spin-lattice relaxation enhancement of the hydrocarbons and the surfactant alkyl chain, induced by ~n'' on the micellar surface. The hydrocarbons used include benzene, naphthalene, acenaphthalene, triphenylene, cyclohexane, cyclododecane, and tert-butylcyclohexane and the surfactants studied are hexadecyl-, tetradecyl-, and dodecyltrimethylammonium bromide; hexadecyl-, tetradccyl-, and dodecylpyridinium halide; and sodium dodecyl sulfate. The results indicate that the micellar microviscosity at the location of saturated hydrocarbons is approximately 5 cP for both the cationic and anionic micelles, whereas the micellar microviscosity at the location of unsaturated hydrocarbons is much higher. The unsaturated hydrocarbons are found to reside primarily near the surfactant headgroup in the cationic micelles, but are distributed evenly throughout the anionic SDS micelles. The saturated hydrocarbons appear to be located in the interior of the micelles.
TL;DR: The fractionation by solvents of the contents of the seeds of Annona muricata (Annonaceae), guided by the toxic activity towards the brine shrimp larva and the KB cancer cells, has enabled us to isolate two new cytotoxic mono-tetrahydrofuran γ-lactones: corossolone 1 and corossolin 2.
Abstract: The fractionation by solvents of the contents of the seeds of Annona muricata (Annonaceae), guided by the toxic activity towards the brine shrimp larva and the KB cancer cells, has enabled us to is...
TL;DR: In this article, the structure of N-phenylmaleimide and dimethyl acetylenedicarboxylate with benzene oxide was determined unequivocally by nuclear Overhauser enhancements in their 1H nuclear magnetic resonance spectra and by X-ray crystallographic methods.
Abstract: The Diels–Alder reactions of N-phenylmaleimide and dimethyl acetylenedicarboxylate with benzene oxide (1,3,5-cyclohexatriene 1,2-oxide, 3) and its more substituted derivatives 1,2-dimethyl-1,3,5-cyclohexatriene 1,2-oxide (7) and 10-oxatricyclo[4.3.1.0]deca-2,4-diene (11) in a kinetic manner gave exclusively products of addition anti to the plane-nonsymmetrical oxygen. The structures of the adducts were determined unequivocally by nuclear Overhauser enhancements in their 1H nuclear magnetic resonance spectra and by X-ray crystallographic methods. The π-facial stereoselectivity was rationalized in terms of unfavorable orbital interactions, steric hindrance between the dienophile and the syn face of benzene oxide, and σ-donation by the oxygen. Key words: cycloaddition, Diels–Alder, syn-anti, π-facial stereoselectivity, benzene oxide.
TL;DR: In this article, the kinetics of permanganate oxidation of DL-α-alanine in aqueous perchloric acid solution at a constant ionic strength of 2.0
Abstract: The kinetics of permanganate oxidation of DL-α-alanine in aqueous perchloric acid solution at a constant ionic strength of 2.0 mol dm−3 has been investigated spectrophotometrically. The reaction wa...
TL;DR: In this paper, a thermodynamic study of the three isomers of dihydroxybenzene was performed by combustion calorimetry of small amounts of substance, sublimation calorimation, differential the...
Abstract: The present work is concerned with a thermodynamic study of the three isomers of dihydroxybenzene. By combustion calorimetry of small amounts of substance, sublimation calorimetry, differential the...
TL;DR: In this paper, a series of para-substituted aryl 2-acetamido-2-deoxy-β-D-glucopyranosides were prepared using phase transfer catalysis conditions with tetrabutylammonium hydrogen sulfate.
Abstract: Starting from chloride 1, a series of para-substituted aryl 2-acetamido-2-deoxy-β-D-glucopyranosides were prepared using phase transfer catalysis conditions with tetrabutylammonium hydrogen sulfate...
TL;DR: In this article, a novel and reliable method for the synthesis of the polymers [Cu(4-Xpz)2]x (where X = H, Cl, Br, and Me; pz = pyrazolate) is presented.
Abstract: Novel and reliable methods for the synthesis of the polymers [Cu(4-Xpz)2]x (where X = H, Cl, Br, and Me; pz = pyrazolate) are presented. The X = Cl compound was obtained as green and brown forms. S...
TL;DR: Two novel diterpenoids, chromodorolides A (1) and B (2), have been isolated from skin extracts of the tropical dorid nudibranch Chromodoris cavae.
Abstract: Two novel diterpenoids, chromodorolides A (1) and B (2), have been isolated from skin extracts of the tropical dorid nudibranch Chromodoris cavae. Complete NMR assignments are presented for chromod...
TL;DR: In this article, the complexation constants of β-cyclodextrine with 13 ammonium surfactants were determined by a potentiometric method using electrodes selective to amphiphilic ions.
Abstract: The complexation constants K of β-cyclodextrine with 13 ammonium surfactants were determined by a potentiometric method using electrodes selective to amphiphilic ions. Especially for C12, C14, and ...
TL;DR: In this paper, a comparison between DMZ and DMT catalyzed dehydrocoupling of organosilanes is reported, and the polymerization rates of primary silanes are ab...
Abstract: A systematic comparison between the dimethylzirconocene (DMZ) and dimethyltitanocene (DMT) catalyzed dehydrocoupling of organosilanes is reported. The polymerization rates of primary silanes are ab...
TL;DR: The condensation reactions occurring between vanadate and a number of amino acids and simple peptides have been studied by 51V nuclear magnetic resonance (NMR) signals as discussed by the authors.
Abstract: The condensation reactions occurring between vanadate and a number of amino acids and simple peptides have been studied by 51V nuclear magnetic resonance. Vanadate and ligand stoichiometry has been established for the complexes formed and their formation constants determined. The amino acids were all found to undergo rather weak interactions with vanadate and in general provided two products with 51V chemical shifts near −545 and −555 ppm. The peptides also gave minor products with NMR signals occurring with that of vanadate itself. However, in this case, the major products occur at approximately −510 ppm. These latter complexes are monovanadate, monoligand complexes which require the terminal amino, the carboxylate groups and an unsubstituted nitrogen in the peptide linkage in order for product formation to occur. Sidechains promote product formation, apparently by favouring a more readily complexed peptide conformation. Formation constants vary from about 20 to 50 M−1 depending on the sidechain. The car...
TL;DR: An improved route for the synthesis of cyclodextrin (CD)-based enzyme models having catalytic groups on the secondary face is presented in this paper, where an epoxide derived from heptakis(6-O-tert-butyldimethylsilyl)-β-CD was prepared via intermediates that can be purified by conventional flash chromatography on a preparative scale.
Abstract: An improved route for the synthesis of cyclodextrin (CD)-based enzyme models having catalytic groups on the secondary face is presented. An epoxide derived from heptakis(6-O-tert-butyldimethylsilyl)-β-CD was prepared via intermediates that can be purified by conventional flash chromatography on a preparative scale. Reaction of β-cyclodextrin with; tert-butyldimethylsilyl chloride in pyridine gave heptakis(6-O-tert-butyldimethylsilyl)-β-CD (1). Treatment of 1 with N-tosylimidazole and NaOMe in chloroform gave mono(2-O-tosyl) heptakis(6-O-tert-butyldimethylsilyl)-β-CD (2) in 22% yield. The latter was converted smoothly to mono(2A, 3A-anhydro) heptakis(6-O-tert-butyldimethylsilyl)-β-CD (3), in which one glucose subunit has been converted to a manno-epoxide, by treatment with KOEt in refluxing ethanol (87% yield). Compounds 1, 2, and 3 were characterized by a variety of one- and two-dimensional NMR techniques. These results open the door to attachment of catalytic groups to the cyclodextrin in a well-defined ...
TL;DR: In this paper, the molecular structure, interaction energy, and infrared spectrum of the linearly hydrogen bonded 1:1 molecular complex of water and ammonia have been predicted by means of a series of ab initio molecular orbital calculations, at the level of second order Moller-Plesset perturbation theory, using the 6-31G** basis set.
Abstract: The molecular structure, interaction energy, and infrared spectrum of the linearly hydrogen bonded 1:1 molecular complex of water and ammonia have been predicted by means of a series of ab initio molecular orbital calculations, at the level of second order Moller–Plesset perturbation theory, using the 6-31G** basis set. The calculated wavenumbers and intensities have been compared with those calculated earlier for the respective monomers, and the wavenumber shifts and intensity changes rationalized in terms of the hydrogen bond interaction responsible for the stability of the complex.The calculated hydrogen bond energy of the complex has been compared with those of the linear water and ammonia dimers, reported in a previous publication, and the relative strengths of interaction of the three aggregates have been rationalized on the basis of the electron donor/acceptor capacities of the respective monomer units. Key words: ab initio, infrared spectrum, water, ammonia.
TL;DR: The complexes (C5Me4H)2MR1R2 (M ǫ=Ti, Zr) and (C4H5)1MR 1R2(M � = Zr, ZR) have been prepared as discussed by the authors and the NMR and IR spectra of the complexes have been analyzed.
Abstract: The complexes (C5Me4H)2MR1R2 (M = Ti, Zr) and (C5Me4H)(C5H5)MR1R2 (M = Ti) have been prepared (R1 = R2 = Cl, CH3, C6H5, p-C6H4CH3, CO; R1 = Cl, R2 = CH3, C6H5, p-C6H4CH3). The NMR and IR spectra of...
TL;DR: Semihydrogenation of 1,2-bis(3,4-dicyanophenyl)ethyne gave cis-1, 2-bis (3, 4-dimethyl)ethene and binuclear phthalocyanines were produced from these precursors as mentioned in this paper.
Abstract: Semihydrogenation of 1,2-bis(3,4-dicyanophenyl)ethyne gave cis-1,2-bis(3,4-dicyanophenyl)ethene. From these precursors, binuclear phthalocyanines were produced containing linear binuclear phthalocy...
TL;DR: The biotransformation of 1,2-diphenylethane by the fungus Mortierella isabellina ATCC 42613 and that of a series of alkyl benzyl sulfides by the fungi M. isabelina and Helminthosporium species NR...
Abstract: The biotransformation of 1,2-diphenylethane by the fungus Mortierella isabellina ATCC 42613, and that of a series of alkyl benzyl sulfides by the fungi M. isabellina and Helminthosporium species NR...
TL;DR: In this paper, the ground and excited state dipole moments suggest that twisting of either the donor (D) with respect to the acceptor (A) or vice versa can have a large impact on the resultant charge distribution, particularly on the excited state charge distribution.
Abstract: Planar and conformationally twisted p-nitroaniline (PNA) and N,N-dimethyl-p-nitroaniline (DMPNA) systems have been subjected to electric field study (electrochromism) to understand their charge transfer characteristics in the ground and excited states. The observed values of ground and excited state dipole moments suggest that twisting of either the donor (D) with respect to the acceptor (A) or vice versa can have a large impact on the resultant charge distribution, particularly on the excited state charge distribution. These observations remarkably support the TICT hypothesis and minimum overlap rule, as proposed by Grabowski et al. Simple molecular orbital calculations provide adequate explanation for the observed changes in the dipole moment and reasonable agreement has been found in each case studied. Key words: electrochromism, dipole moments, charge transfer.