Showing papers in "Canadian Journal of Chemistry in 1997"
TL;DR: Using the rotating ring disk technique (RRDPt(hkl)E), the ORR was studied in sulfuric acid solution over the temperature range 298 −333 K at the same temperature, the exc...
Abstract: Using the rotating ring-disk technique (RRDPt(hkl)E), the oxygen-reduction reaction (ORR) was studied in sulfuric acid solution over the temperature range 298–333 K At the same temperature, the exc...
793 citations
TL;DR: Hartree and Fock as discussed by the authors performed calculations on the benzenoid hydrocarbons benzene, naphthalene, phenanthrene, anthracene, pyrene, tetracene and coronene.
Abstract: Hartree–Fock/6-31G** calculations on the benzenoid hydrocarbons benzene, naphthalene, phenanthrene, anthracene, pyrene, tetracene, triphenylene, chrysene, perylene, and coronene are used to investi...
153 citations
TL;DR: Oligo-tridentate ligands based on alternating pyridines and pyrimidines were synthesized by Stille-type carbon-carbon bond-forming reactions as discussed by the authors.
Abstract: Oligo-tridentate ligands based on alternating pyridines and pyrimidines were synthesised by Stille-type carbon–carbon bond-forming reactions. The terpyridine-like sites are designed to coalign upon...
96 citations
TL;DR: In this paper, the condensation of methyl 3,5-dihydroxybenzoate with tetra(ethylene glycol) dichloride has been studied.
Abstract: Optimization studies of the condensation of methyl 3,5-dihydroxybenzoate (1) with tetra(ethylene glycol) dichloride (3) resulted in improvement of the yield of the 1 + 1 cyclization product, 5-carb...
72 citations
TL;DR: In this paper, Humic substances (HS) were extracted from the sediments of four Sudbury area lakes, namely, Tilton, Clearwater, Silver, and Ramsey Lakes, with the aid of 0.1 M Na4P2O7 and 0.5
Abstract: Humic substances (HS) were extracted from the sediments of four Sudbury area lakes, namely, Tilton, Clearwater, Silver, and Ramsey Lakes, with the aid of 0.1 M Na4P2O7 and 0.5 M NaOH solutions. The...
69 citations
TL;DR: In this paper, high-level ab initio molecular orbital and density functional theory calculations predict the existence of a very short-strong hydrogen bond in the monoanion of maleic acid (hydrogen maleate).
Abstract: High-level ab initio molecular orbital and density functional theory calculations predict the existence of a very short-strong hydrogen bond in the monoanion of maleic acid (hydrogen maleate). At all levels of theory (HF, MP2, BLYP, and B3LYP) except B3PW91 the potential energy surface is predicted to contain two minima, and hence resembles a double well. The barrier to proton transfer via a symmetrical transition state is calculated to be very small at all levels of theory. In all cases the calculated zero point vibrational energy available to the system is larger than the calculated barrier for proton transfer, thus the resulting hydrogen bond formed in hydrogen maleate is predicted to be symmetrical. Using the B3PW91 functional and the 6-31 + G(d,p) basis set results in a single-well potential and a symmetrically positioned hydrogen. All correlated methods predict the gas phase hydrogen bond energy to be approximately 27 kcal/mol. Effects due to solvents were estimated using solvent cavity methods. App...
67 citations
TL;DR: Several compounds of the type PhCR1R2-TEMPO (where TEMPO = 2,2,6,6-tetramethylpiperidine-Noxide) have been prepared and examined as potential photosensitized initiators for "living" free radical p...
Abstract: Several compounds of the type PhCR1R2-TEMPO (where TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxide) have been prepared and examined as potential photosensitized initiators for "living" free radical p...
62 citations
TL;DR: The role of quinones and hydroxyquinones as sensitizers and quenchers in Type II photooxygenations has been examined in this paper, for the first time in the open literature.
Abstract: The role of quinones and hydroxyquinones as sensitizers and as quenchers in Type II photooxygenations has been examined. The second aspect is discussed here, through a systematic study, for the first time in the open literature. Quinonic compounds are excellent generators of O2(1Δg) in aprotic solvents (excluding those quinones possessing substituents in positions adjacent to the carbonyl groups, in the case of anthraquinone derivatives). Benzoquinones, anthraquinones, and hydroxy derivatives are good O2(1Δg) quenchers upon dye-sensitized photoirradiation. The excited oxygen species is deactivated with rate constants in the range 106–107 M−1 s−1 depending on the solvent employed. The quenching process deactivates O2(1Δg) without further destruction of the quinone. The main interaction with O2(1Δg) is driven by the quinone moiety, in spite of the presence of potentially active nuclear substituents. The quenching mechanism could involve a reversible charge transfer intermediate, with the quinonic compound a...
61 citations
TL;DR: Bromation of 1,10-phenanthroline with Br2 proceeds smoothly in the presence of S2Cl2 and pyridine to give 3,8-dibromo-1,10phenanthusline in good yield.
Abstract: Bromation of 1,10-phenanthroline with Br2 proceeds smoothly in the presence of S2Cl2 and pyridine to give 3,8-dibromo-1,10-phenanthroline in good yield. Bromation of 2,9-dibutoxy-1,10-phenanthrolin...
60 citations
TL;DR: In this paper, the interlamellar surface of kaolinite has been modified with molecules possessing amino functionalities, either the dimethyl sulfoxide intercalate of Kao/DMSO or the N-methylformamide.
Abstract: The interlamellar surface of kaolinite has been modified with molecules possessing amino functionalities. Either the dimethyl sulfoxide intercalate of kaolinite (Kao/DMSO) or the N-methylformamide ...
57 citations
TL;DR: In this paper, a general composition IrxTi(1−x)O2 with 0.2 √ 2 √ 1.0 was obtained by calcination of the chlorides at 450 °C.
Abstract: Electrodes of general composition IrxTi(1−x)O2 with 0.2 ≤ x ≤ 1.0 were prepared on a Ti support by calcination of the chlorides at 450 °C. Ex situ and in situ characterization included the use of t...
TL;DR: The spectral displacement technique with phenolphthalein as the chromophore has been used to obtain 1:1 equilibrium binding constants for a homologous series of hydrocarbon series (hc) (CnH2n+1COONa,...
Abstract: The spectral displacement technique with phenolphthalein as the chromophore has been used to obtain 1:1 equilibrium binding constants (K2) for a homologous series of hydrocarbon (hc) (CnH2n+1COONa, n = 5–13) and fluorocarbon (fc) anionic surfactants (CnF2n+1COONa, n = 3–8) with β-cyclodextrin (β-CD). The magnitude of K2 increases as the alkyl chain length increases in each homologous series. K2 values in the ranges of 102–105 M−1 and 101–104 M−1 were obtained for the β-CD–fc and for the β-CD–hc surfactant complexes, respectively. The different binding affinity of β-CD with hc and fc surfactants is discussed in terms of such physicochemical properties of the guest species as hydrophobicity, geometrical size, conformational effects, molecular polarizability, and solvation of the head group. Keywords: spectral displacement, phenolphthalein, cyclodextrin, surfactant, binding constant.
TL;DR: In this article, toxicity-guided fractionation of extractives of the Irisgermanica rhizomes and I. japonica roots using killie-fish (Oryziaslatipes), 12 iridal-type triterpenoids including three new iridal...
Abstract: Upon toxicity-guided fractionation of the extractives of the Irisgermanica rhizomes and I. japonica roots using killie-fish (Oryziaslatipes), 12 iridal-type triterpenoids including three new iridal...
TL;DR: Preclinical studies with peryle... to address preclinical limitations of PhotofrinTM, a preparation of hematoporphyr in derivatives with the bulk of the porphyrin monomers removed.
Abstract: Photodynamic therapy relies on the selective accumulation of photosensitizers within neoplastic tissue, followed by light activation to generate cytotoxic singlet oxygen. At present, PhotofrinTM, a preparation of hematoporphyrin derivatives (HPD) with the bulk of the porphyrin monomers removed, is the only clinically approved photosensitizer. Intravesical administration of Photofrin or HPD has failed to photosensitize bladder tumors. Bladder cancer is the second most common genitourinary malignancy. In 1994 there were an estimated 51 200 cases of bladder cancer with 10 600 deaths in the United States. The predominant histopathology is transitional cell carcinoma, occurring in 90–95% of these cases. Most patients (85%) have superficial disease at the time of initial diagnosis. Superficial bladder cancer is defined as disease involving the mucosa with carcinoma in situ or papillary lesions and invasion limited to submucosa. To address these limitations we have been conducting preclinical studies with peryle...
TL;DR: Iodine and iodine supported on polyvinylpyrrolidone (betadine) have been used as catalysts for ring opening of epoxides and as reagent for ring-opening dimerization of thiiranes in alcohols, water, and soap bubbles as discussed by the authors.
Abstract: Iodine and iodine supported on polyvinylpyrrolidone (betadine) have been used as catalysts for ring opening of epoxides and as reagent for ring-opening dimerization of thiiranes in alcohols, water,...
TL;DR: In this article, chemical investigations of Cadlinaluteomarginata skin extracts, egg masses, and dietary sponges have led to the identification of the novel terpenoids cadlinaldehyde (30), spongian 32, seco-spongian 35, 20-acetoxy-12-marginatone (38), and lutenolide (39) from the nudibranch skin extracts.
Abstract: Chemical investigations of Cadlinaluteomarginata skin extracts, egg masses, and dietary sponges have led to the identification of the novel terpenoids cadlinaldehyde (30), spongian 32, seco-spongian 35, 20-acetoxy-12-marginatone (38), and lutenolide (39) from the nudibranch skin extracts, the new drimane sesquiterpenoid 1α,2α-diacetoxyalbicanyl acetate (40) from the nudibranch's egg mass, and the new sesquiterpenoids O-methyl-9-oxofurodysininlactone (47), 2-oxomicro-cionin-2-lactone (48), and O-methyl-2-oxomicrocionin-2-lactone (49), from the dietary sponge Pleraplysilla sp. The known terpenoids furodysinin (1), furodysin (16), marginatafuran (21), and 9,11-dihydrogracillin A (37), which have been frequently isolated from C. luteomarginata skin extracts, were found for the first time in extracts of the dietary sponges Pleraplysilla sp. and Aplysilla sp. One of the new terpenoids, cadlinaldehyde (30), has an unprecedented degraded sesterterpenoid skeleton. Keywords: nudibranch, sponge, terpenoids, structur...
TL;DR: Preparation of bisannulated salts of 2,2′-biimidazole, 2-(2′)-imidaxolyl)benzimidaze, 2, 2′-bibenzimidazyole, and annulated salt of 1,1′-dimethyl-2,2''-biIMidazoles, 1, 1''-dimethyldimethyl-1,1''-imidozolyl be...
Abstract: Preparation of bisannulated salts of 2,2′-biimidazole, 2-(2′-imidazolyl)benzimidazole, 2,2′-bibenzimidazole, and annulated salts of 1,1′-dimethyl-2,2′-biimidazole, 1,1′-dimethyl-2-(2′-imidazolyl)be...
TL;DR: In this paper, the initial stages of the anodic oxidation of Au(111) were investigated by means of cyclic voltammetry as well as in situ scanning tunneling microscopy (STM).
Abstract: The initial stages of the anodic oxidation of Au(111) were investigated by means of cyclic voltammetry as well as in situ scanning tunneling microscopy (STM). The results suggest that the place exc...
TL;DR: The kinetics of the oxidation of 2-propanol, 1,1,1-trifluoro-2-propagation, 1-phenyl-2, 2,2,2 trifluoromethane, 1-(4-methylphenyl)-2, 1.2,3, 3, 3-hexafluoro, 2.5-hexaphosphoric acid, and 1-(3-bromophe....
Abstract: The kinetics of the oxidation of 2-propanol, 1,1,1-trifluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 1-phenyl-2,2,2-trifluoroethanol, 1-(4-methylphenyl)-2,2,2-trifluoroethanol, 1-(3-bromophe...
TL;DR: In this paper, the electronic absorption spectra of 18 hydroxycoumarin derivatives and their ionized forms have been studied and close agreement between experimental and the PPP CI calculated electron absorption band en...
Abstract: Electronic absorption spectra of 18 hydroxycoumarin derivatives and their ionized forms have been studied. Close agreement between experimental and the PPP CI calculated electron absorption band en...
TL;DR: Preliminary results indicated that nonavalent α-sialodendrimer 29 had a greater affinity towards dimeric wheat germ agglutinin and the lectin from the slug Limaxflavus than the co...
Abstract: Hyperbranched glycodendrimers containing sialic acid residues were synthesized in order to further understand the multivalency effect and its role in carbohydrate–protein interactions. Gallic acid ...
TL;DR: In this article, an ab initio conformational analysis performed at the RHF/3-21G level on a phenylalanine-containing diamide model system (N-Formyl-L-Phe-NH2) revealed 19 different structures.
Abstract: Phenylalanine is the simplest among the four natural amino acid residues that have aromatic side chains. The ab initio conformational analysis performed at the RHF/3-21G level on a phenylalanine-containing diamide model system (N-Formyl-L-Phe-NH2) revealed 19 different structures. Single-point energy calculations were performed using RHF/6-31+G* and DFT(B3LYP)/6-311++G** levels for all conformers. The inverse (γL) and the normal (γD) gamma turn, the extended (βL), the left-handed helical , and the inverse polyproline II backbone conformers each have three (g+, a, and g−) side-chain (χ1,) rotamers. The and the type main-chain conformers have only two side-chain orientations, respectively. No minima have been found for the conformational building unit of the right-handed helical and for the polyproline II structures. The present ab initio conformational analysis for For-L-Phe-NH2 is a unique example in which a systematic and complete conformational set was established for a diamide system with an aromatic s...
TL;DR: A series of pyrazole derivatives with two and three alkylating sites were prepared and their cytotoxicity against cancer cells as well as antitumor activity against L1210 was investigated.
Abstract: A series of pyrazole derivatives with two and three alkylating sites were prepared and their cytotoxicity against cancer cells as well as antitumor activity against L1210 was investigated. The best result of cytotoxicity was obtained with the trichloride 5 and the best antitumor activity (ILS 33%) with the dibromide 3. These results can provide valuable information for further study of the more effective antitumor agent. Keywords: pyrazole, synthesis, cytotoxicity, antitumor activity, polyalkylator.
TL;DR: In this paper, Mobile Order theory was used to predict trans-stilbene solubilities in 28 organic nonelectrolyte solvents containing methyl, ether, hydroxy, and tert-butyl functional groups.
Abstract: Experimental solubilities are reported at 25.0 °C for trans-stilbene dissolved in 28 different organic nonelectrolyte solvents containing methyl, ether, hydroxy, and tert-butyl functional groups. Results of these measurements are used to test the applications and limitations of expressions derived from Mobile Order theory. For the 20 solvents for which predictions could be made, computations show that Mobile Order theory does provide fairly reasonable (although by no means perfect) estimates of the saturation mole fraction solubilities. Average absolute deviation between predicted and observed values is ca. 24%. In comparison, the average absolute deviation increases significantly to 935% when ideal solution behavior is assumed. KeyWords: trans-stilbene solubilities, organic nonelectrolyte solvents, solubility predictions.
TL;DR: In this article, the diastereoselective H2-hydrogenation of lignin degradation model compounds 4-propylphenol, 2-methoxy-4propyl phenol, and 2,6-dimethoxy -4-propylonphenol was investigated.
Abstract: Di-µ-chloro-bis(η4-1,5-hexadiene)dirhodium(I) in a two-phase hexane–aqueous medium catalyzes the diastereoselective H2-hydrogenation of lignin degradation model compounds 4-propylphenol, 2-methoxy-4-propylphenol, and 2,6-dimethoxy-4-propylphenol. The all-cis diastereomer is obtained selectively when the phenolic hydroxy group is protected as a methyl ether or when a model compound possessing two methoxy substituents adjacent to the phenolic hydroxy group is used. The relative stereochemistries of the hydrogenated products are established by X-ray crystal structure analysis and (or) 1H NMR. Keywords: catalytic hydrogenation, diastereomer, lignin degradation model compounds, stereoselective, X-ray crystal structure.
TL;DR: For example, 4-hydroxy-2-chromenone tautomeric forms are known to undergo H-D exchange at the C(3) atom of the lactone ring as mentioned in this paper.
Abstract: 4-Hydroxycoumarin 1, 4,5-dihydroxycoumarin 2, and 4,7-dihydroxycoumarin 3 undergo H–D exchange at the C(3) atom of the lactone ring. Although only the 4-hydroxy-2-chromenone tautomeric forms are se...
TL;DR: In this article, the reaction between the potassium salts of the hydrotris-pyrazolylborate ligands TpMe'Me and TptBu'Me, and the tris THF adduct of scandium trichloride lead to isolation of the Scandium complexes (TpMe...
Abstract: Reaction between the potassium salts of the hydro-tris-pyrazolylborate ligands TpMe'Me and TptBu'Me and the tris THF adduct of scandium trichloride lead to isolation of the scandium complexes (TpMe...
TL;DR: Alginic acid, obtained from Sargassum brown algae that drift from the Sargasso Sea to beaches in Cuba, has been examined as an aqueous solution by 1H and 13C NMR spectroscopy, and also in the solid...
Abstract: Alginic acid, obtained from Sargassum brown algae that drift from the Sargasso Sea to beaches in Cuba, has been examined as an aqueous solution by 1H and 13C NMR spectroscopy, and also in the solid...
TL;DR: In this paper, the synthesis of (S)-(−)-rosmarinic acid (30) in 9% overall yield was described by a convergent route in which 3-(3′,4′-dihydroxyphenyl)-(S)-lactic acid (23) and caffeic...
Abstract: The synthesis of (S)-(−)-rosmarinic acid (30) in 9% overall yield is described. The synthesis was achieved by a convergent route in which 3-(3′,4′-dihydroxyphenyl)-(S)-lactic acid (23) and caffeic ...
TL;DR: A number of methoxy-substituted phenoxyl radicals have been generated and characterized by laser flash photolysis techniques in solution and on paper as mentioned in this paper, and the radicals were produced by three routes in solution: hydrogen abstraction from phenols by tert-butoxyl radical, photolyisation of α-aryloxyacetophenones, and direct excitation of phenols.
Abstract: A number of methoxy-substituted phenoxyl radicals have been generated and characterized by laser flash photolysis techniques in solution and on paper. The radicals have been produced by three routes in solution: hydrogen abstraction from phenols by tert-butoxyl radical, photolysis of α-aryloxyacetophenones, and direct excitation of phenols. Most of the phenoxyl radicals studied have a characteristic absorption near 400 nm; the ortho-substituted radicals have an additional broad absorption in the visible in non-hydroxylic solvents (e.g., 650 nm for 2-methoxyphenoxyl radical). The relative intensities of the 400 nm and the long-wavelength bands vary with substitution pattern and solvent, with the long wavelength band being much weaker in hydroxylic solvents. Direct excitation of phenols provides an alternate source of phenoxyl radicals in some cases. However, for 4-methoxyphenol there are overlapping absorptions due to triplet phenol and phenol radical cation, both of which absorb in the 400–460 nm region. ...