Showing papers in "Canadian Journal of Chemistry in 1988"
TL;DR: In this article, it was shown that organic compounds can be synthesized up to 1240 times faster in sealed Teflon vessels in a microwave oven than by conventional (reflux) techniques.
Abstract: This work demonstrates that organic compounds can be synthesized up to 1240 times faster in sealed Teflon vessels in a microwave oven than by conventional (reflux) techniques. It is shown that all ...
277 citations
TL;DR: In this paper, the results of the application of multiple linear regression analysis are discussed, and the processes examined include examples of deterministic and stochastic processes, as well as deterministic linear regression.
Abstract: Solvent effects on a number of different processes have been surveyed, and results of the application of multiple linear regression analysis are discussed. The processes examined include examples o...
251 citations
TL;DR: In this article, conductance measurements were used to identify and to obtain association constants for the complexes formed between cyclodextrins (CD) with emphasis on β-cyclodextrin (βCD), and surfactants such as...
Abstract: Conductance measurements were used to identify and to obtain association constants for the complexes formed between cyclodextrins (CD) with emphasis on β-cyclodextrin (βCD), and surfactants such as...
138 citations
TL;DR: It is proposed that with the evolution of cholesterol and related sterols in an oxygen-rich atmosphere, the resulting modification of physical constraints on membrane properties made it possible for new evolutionary driving forces to manifest themselves leading to the peculiar properties of plasma membranes of eucaryotic cells.
Abstract: Consideration of the influence of cholesterol on the physical properties of biological membranes leads to the conclusion that cholesterol increases the thickness of fluid membrane bilayers without appreciably increasing the microviscosity component of membrane fluidity. At sufficiently high cholesterol concentrations, the gel–liquid crystalline phase transition is completely eliminated in phospholipids–cholesterol mixtures and the system has the properties of a two-dimensional liquid over a wide range of temperatures. It is proposed that with the evolution of cholesterol and related sterols in an oxygen-rich atmosphere, the resulting modification of physical constraints on membrane properties made it possible for new evolutionary driving forces to manifest themselves leading to the peculiar properties of plasma membranes of eucaryotic cells.
116 citations
TL;DR: Efficient syntheses of approximately 70 simple substituted representatives of pyrazolo[3,4,b]pyridine 1 are reported from the following: (a) suitably substituted pyridines onto which a pyrazole rin...
Abstract: Efficient syntheses of approximately 70 simple substituted representatives of pyrazolo[3,4-b]pyridine 1 are reported from the following: (a) suitably substituted pyridines onto which a pyrazole rin...
104 citations
TL;DR: The enthalpy of transformation to ice Ic of ice II, IX, V, VI, and VIII that have been recovered at 77 K and ambient pressure, and of the transformation of ice Ic to Ih, has been measured in a heat chamber as discussed by the authors.
Abstract: The enthalpy of transformation to ice Ic of ice II, IX, V, VI, and VIII that have been recovered at 77 K and ambient pressure, and of the transformation of ice Ic to Ih, has been measured in a heat...
77 citations
TL;DR: In this paper, Koga et al. measured the excess partial molar enthalpies of tert-butanol (TBA) in water and butanol mixtures at 20.00, 26.90, 45.17, and 59.49 °C in the water-rich region and at 30.00 °C for the entire range.
Abstract: Excess partial molar enthalpies of tert-butanol (TBA) in water–tert-butanol mixtures were measured at 20.00, 26.90, 45.17, and 59.49 °C in the water-rich region, and at 30.00 °C for the entire range. The results together with those of the previous work, (Y. Koga. Can. J. Chem. 64, 206 (1986)), appear to support the following views: At XTBA ≈ 0, TBA molecules form hydrogen bonds with H2O molecules, and they enhance the structure of the hydrogen bond network of H2O. The latter effect is of very long range; the enthalpic repulsion between solutes is already operative via enhancement of hydrogen bond network when two TBA molecules are separated by 12 H2O molecules. This enthalpic repulsion becomes stronger as the concentration of TBA increases. At a certain threshold, XTBA ≈ 0.03 at 30.00 °C for example, the new scheme in which solutes tend to associate sets in, and for XTBA > 0.06 this scheme becomes predominant. The effect of higher temperature is to shift this threshold to the lower values of XTBA. Therefo...
73 citations
TL;DR: In this paper, the entire composition range for dibutyl ether + n-hexadecane and n-heptane was measured at 298.15 Ã 0.15 K.
Abstract: Calorimetric measurements of excess enthalpies are reported over the entire composition range for dibutyl ether + n-heptane, + n-deeane, + n-dodecane, and + n-hexadecane at 298.15 K. The results ar...
70 citations
TL;DR: In this paper, the authors studied the anthracene-sensitized photolyses of diphenyliodonium and triphenylsulphonium salts in solution using both steady-state and laser flash photolysis techniques.
Abstract: We have studied the anthracene-sensitized photolyses of both diphenyliodonium and triphenylsulphonium salts in solution using both steady-state and laser flash photolysis techniques. Photoproducts,...
67 citations
TL;DR: In this article, the photochemical dehalogenation of α-haloacetophenones (Cl, Br) in benzene solution has been examined under conditions of continuous and pulsed laser irradiation.
Abstract: The photochemical dehalogenation of α-haloacetophenones (Cl, Br) in benzene solution has been examined under conditions of continuous and pulsed laser irradiation. Product and quantum yield studies indicate that carbon-halogen bond cleavage occurs with quantum yields of 0.88 and 0.41 for α-chloro- and α-bromoacetophenone, respectively. These values are based on trapping studies in which the PhC(O)ĊH2 radicals produced photochemically are scavenged by hydrogen donors such as benzenethiol. Laser flash photolysis studies lead to intense transient signals due to benzene–halogen complexes. Combination of transient data and quantum yields lead to extinction coefficients of 1 800 and 23 700 M−1 cm−1 for the chlorine (490 nm) and bromine (550 nm) complexes, respectively.
64 citations
TL;DR: A series of 3-hydroxy-2-methyl-4(1H)-pyridinones has been prepared with the substituents H, CH3, n-C6H11, and CH2CH2NH2 at the ring N as discussed by the authors.
Abstract: A series of 3-hydroxy-2-methyl-4(1H)-pyridinones has been prepared with the substituents H, CH3, n-C6H11, and CH2CH2NH2 at the ring N. The dipyridinone 1,6-bis(3-hydroxy-2-methyl-4(1H)-pyridinon-1-...
TL;DR: The radial charge distribution for the neutral atoms, hydrogen through uranium, and the singly positive ions, helium through barium and lutetium through radium, are computed from the non-relaxation as discussed by the authors.
Abstract: The radial charge distribution, D(r), for the neutral atoms, hydrogen through uranium, and the singly positive ions, helium through barium and lutetium through radium, are computed from the non-rel...
TL;DR: Two novel bicyclic diterpenoides, agelasimine-A and -B, have been isolated from the orange sponge Agelas mauritiana and exhibit a wide range of interesting biological activities such as cytotoxicity, inhibition of adenosine transfer into rabbit erythrocytes, Ca2+-channel antagonistic action, and α1 adrenergic blockade.
Abstract: Two novel bicyclic diterpenoides, agelasimine-A (9), and agelasimine-B (10), have been isolated from the orange sponge Agelas mauritiana. Also, a new bromine-containing alkaloid, 5-debromomidpacami...
TL;DR: In this paper, all possible regio-and stereoisomers of 1:1:1 (alcohol:olefin:aromatic) adducts were identified, including cyclohexene, cyclic olefins, norbornene, and 2-methylnorbornene.
Abstract: Direct irradiation of acetonitrile–methanol (3:1) solutions of 1,4-dicyanobenzene and the cyclic olefins, cyclohexene, 1-methylcyclohexene, norbornene, and 2-methylnorbornene, leads to formation of regio- and stereoisomers of the 1:1:1 (alcohol:olefin:aromatic) adducts. This reaction can be photosensitized by electron transfer; addition of electron donors, biphenyl or phenanthrene, to the irradiation mixture generally increases the efficiency and yield of adduct formation. The efficiency of the reaction and the ratio of isomeric adducts are also affected by the addition of salts, particularly magnesium perchlorate. All of the possible regio- and stereoisomers from cyclohexene and 1-methylcyclohexene have been identified, two from cyclohexene and four from 1-methylcyclohexene. Three of the four possible isomers from norbornene were characterized; the endo,endo isomer was not detected. There are eight possible isomers from 2-methylnorbornene; six were detected and five have been isolated and identified. The...
TL;DR: In this article, the absolute oscillator strength spectra of perfluoro-n-alkanes from C2 to C6 and perfluorocycloalkane from C 3 to C 6 were determined from inner-shell electron energy loss spectra recorded under electric-dipole scattering conditions.
Abstract: Absolute oscillator strength spectra in the C 1s (280–340 eV) and F 1s (680–740 eV) regions of the perfluoro-n-alkanes from C2 to C6 and perfluorocycloalkanes from C3 to C6 have been determined from inner-shell electron energy loss spectra recorded under electric-dipole scattering conditions. The spectral features are interpreted in terms of spatially localized transitions terminating at orbitals of predominantly σ*(C—F) and σ*(C—C) character. When compared to the spectra of the perfluoro-n-alkanes, both the C 1s and F 1s spectra of the perfluorocycloalkanes exhibit additional low-lying bands which are assigned to transitions terminating at σ*(C—C) orbitals which are shifted to low energy by the combination of the strain of cyclization and the inductive effect of the fluorination. The electron transmission spectra of selected perfluorocycloalkanes (which provide information on their anion states) show as well that the electron affinities of the cyclic systems are substantially lower than those of the corr...
TL;DR: In situ infrared spectroelectrochemistry has been used to observe electrolyte/solvent breakdown processes in TBAF/acetonitrile at a platinum electrode as discussed by the authors.
Abstract: In situ infrared spectroelectrochemistry has been used to observe electrolyte/solvent breakdown processes in TBAF/acetonitrile at a platinum electrode. Anodic breakdown gives the adduct CH3CNBF3 as...
TL;DR: Excess molar volumes, VE, and excess molar heat capacities at constant pressure were obtained for some n-alkanoate+n-alkane mixtures at 298.15 K from density and volumetric heat capacity as discussed by the authors.
Abstract: Excess molar volumes, VE, and excess molar heat capacities at constant pressure, , have been obtained for some n-alkanoate + n-alkane mixtures at 298.15 K from density and volumetric heat capacity ...
TL;DR: The infrared spectra over the range 4000-50 cm−1 of three copper basic sulfates, viz. Cu4(OH)6SO4, Cu4 (OH)4OSO4, and Cu3(OH)-4SO4 along with site group and factor group analysis for Cu4, 6SO4 and 3SO4 are available.
Abstract: The infrared spectra over the range 4000–50 cm−1 of three copper basic sulfates, viz. Cu4(OH)6SO4, Cu4(OH)4OSO4, Cu3(OH)4SO4 along with site group and factor group analysis for Cu4(OH)6SO4 are repo...
TL;DR: In this paper, the free energies and entropies of transfer of amino acids from water to aqueous mixtures of glycerol (GL) and urea (UH) have been determined from solubility measurements at different temperatures.
Abstract: Standard free energies and entropies of transfer of glycine (G), diglycine (DG), and triglycine (TG), from water to aqueous mixtures of glycerol (GL) and urea (UH) have been determined from solubility measurements at different temperatures. This was also extended to an ionic cosolvent system like aqueous sodium nitrate solutions for G and DG. The observed and –composition profiles, as well as those obtained after correcting for the "cavity effect" as estimated by scaled particle theory (SPT), were examined in the light of various interactions. The corrected and values show a regular function of the peptide chain length of the amino acids and impart useful information regarding the involved relative structural effects of these ionic and non-ionic cosolvents.
TL;DR: In this paper, the bisphosphine monochalcogenides, [Ph2PCH2P(Y)R2], were characterized by complete 13C, 31P, 77Se, and 195Pt NMR studies and by two crystal structure determinations.
Abstract: Reactions of the bisphosphine monochalcogenides, [Ph2PCH2P(Y)R2], Y = O, S, or Se, R = Ph, Pri, or But, with the chloro-bridged dimers [M2Cl4(PR′3)2], M = Pd or Pt, R′ = Et or Bun, in the presence of either NaClO4 or NaBF4 yield perchlorate and fluoroborate salts of the complex cations cis- and trans-[PtCl(PR′3){Ph2PCH2P(Y)R2}]+. In many cases both cis and trans isomers (defined by the relative orientation of the two M—P bonds) are obtained and the precise isomer distribution is a sensitive function of the substituents. Corresponding neutral complexes, cis- and trans-[PtCl(PR′3){Ph2PCHP(Y)R2}], can be synthesized either by deprotonation of the cations using NaH or by use of the salts Li[Ph2PCHP(Y)R2] in the initial bridge cleavage reactions. These and related complexes are characterized by complete 13C, 31P, 77Se, and 195Pt NMR studies and by two crystal structure determinations. The complexes I, trans-[PtCl(PEt3){But2PCH2P(O)Me2}][ClO4], and II, trans-[PtCl(PEt3){Ph2PCH2P(S)But2}][ClO4], crystallize in t...
TL;DR: In this article, the tandem type hydrogenated amorphous silicon (a-Si) electrode having an [n−p−n−i−p] structure and a similar tandem a-Si electrode having [n-p−N−i-p] layers deposited on p-type crystalline Si showed cathodic photocurrents accompanied by hydrogen evolution starting at potentials 1.67 and 2.08
Abstract: The tandem type hydrogenated amorphous silicon (a-Si) electrode having an [n–i–p–n–i–p] structure and a similar tandem a-Si electrode having [n–i–p–n–i–p–n] layers deposited on p-type crystalline Si showed cathodic photocurrents accompanied by hydrogen evolution starting at potentials 1.67 and 2.08 V, respectively, more positive than the thermodynamic hydrogen evolution potential in a sulfuric acid solution. These electrodes, when connected to an RuO2 counterelectrode, caused sustained water splitting without external bias, giving solar-to-chemical conversion efficiencies of 1.98% and 2.93%, respectively, under simulated AM 1, 100 mW cm−2 solar radiation. These efficiencies are critically compared with the efficiency of another type of solar photoelectrolysis of water, namely, the electrolysis of water by the electrical output from solid-state solar cells.
TL;DR: A series of ruthenium(II) complexes of formulation RuCl2(dmso)2Ln, where dmso = S-bonded dimethylsulfoxide, L is a 4-nitroimidazole derivative, and n = 1 or 2, have been synthesized and characterized by spectroscopic methods, particularly 1H nmr and X-ray photoelectron spectroscopy as discussed by the authors.
Abstract: A series of ruthenium(II) complexes of formulation RuCl2(dmso)2Ln, where dmso = S-bonded dimethylsulfoxide, L is a 4-nitroimidazole derivative, and n = 1 or 2, have been synthesized and characterized by spectroscopic methods, particularly 1H nmr and X-ray photoelectron spectroscopy. With L = 4-nitroimidazole itself (4-NO2Im), RSU-1170, -3083 or -3100, n = 2 and the six-coordinate complexes are considered to be of cis,cis,cis-geometry. The N-methyl-4-nitroimidazole (NMe-4-NO2Im) ligand (n = 1) chelates through the imidazole-N and the oxygen of NO2. The RSU-3159 ligand (n = 1) binds through the sulfur and may be chelated. The complexes are of interest because of their radiosensitizer properties toward hypoxic tumour cells; the RuCl2(dmso)2(NMe-4-NO2Im) complex has a higher sensitizing enhancement ratio than the free imidazole ligand, and shows no cytoxicity in vitro, and these data are compared to those reported previously for RuCl2(dmso)2(4-NO2Im)2. Some aspects of the aqueous solution chemistry of the com...
TL;DR: In this article, the rate of electron transfer between bisulfates in D2O/D2SO4 is represented by the activation parameters (at ionic strength I´0.046−0.4 Ã 0.
Abstract: Proton nmr line-broadening experiments at ambient and elevated (to 215 MPa) pressures show that the rate of electron transfer between Fe(phen)32+ and Fe(phen)33+ as bisulfates in D2O/D2SO4 is represented by the activation parameters (at ionic strength I ~ 0.4 mol kg−1) ΔH≠ = 1.6 ± 0.5 kJ mol−1, ΔS≠ = −102.2 ± 1.6 JK−1mol−1, k(276 K) = 1.31 × 107 kg mol−1s−1, and (at I ~ 0.3 mol kg−1 and a mean pressure of 100 MPa) ΔV≠ = −2.2 ± 0.1 cm3mol−1. For the same reaction of the perchlorate salts (total [Fe] 0.046–0.065 mol kg−1) in CD3CN, ΔH≠ = 11.0 ± 1.0 kJ mol−1, ΔS≠ = −72.5 ± 3.6 J K−1 mol−1, k(277 K) = 8.0 × 106 kgmol−1s−1, and ΔV≠ = −5.9 ± 0.5 cm3 mol−1. For water as solvent, ΔV≠ is satisfactorily accounted for by a classical theory of the Stranks–Hush–Marcus type. Volumes of activation for electron self-exchange are shown to provide criteria for non-adiabaticity and for dominance of (non-aqueous) solvent reorganization dynamics; on this basis, it is seen that neither of these factors is important in the titl...
TL;DR: In this paper, the 1.77Se and 1H nuclear magnetic resonance spectra have been measured for selenols, diselenides, and selenenyl sulfides.
Abstract: 77Se and 1H nuclear magnetic resonance spectra have been measured for selenols (RSeH), diselenides (RSeSeR), and selenenyl sulfides (RSeSR′), including selenenyl sulfides formed by reaction of glut...
TL;DR: The metal ion complexation behavior of four 18crown-6 ethers derived from (+)- and meso-tartaric acid was examined in this paper, and the preparation of a mesocrown ether diacid and of a crown ether hexacid from three different types of acid acid was performed.
Abstract: The metal ion complexation behavior of four 18-crown-6 ethers derived from (+)- and meso-tartaric acid is examined. Preparations of a meso-crown ether diacid and of a crown ether hexacid from three...
TL;DR: A detailed investigation of the electrochemical behavior of flavin adenine dinucleotide (FAD) in neutral solutions has been carried out at Hg and glassy carbon electrodes as discussed by the authors.
Abstract: A detailed investigation of the electrochemical behavior of flavin adenine dinucleotide (FAD) in neutral solutions has been carried out at Hg and glassy carbon electrodes. At FAD concentrations of about 10−4 M, cyclic voltammetry (CV) shows a pair of anodic and cathodic peaks having a peak separation at low sweep rates indicative of a two-electron transfer process and yielding a formal redox potential for FAD of −0.206 ± 0.003 V vs. NHE at pH 7. Evidence for FAD adsorption was obtained in experiments at high sweep rates, from the effect of time of exposure of the electrode surface to FAD in solution and from the effect of the potential limits on the cyclic voltammetric response. The process of FAD adsorption was studied in detail in dilute FAD solutions (ca 10−6 M) using a hanging mercury drop electrode and the techniques of CV and ac voltammetry. Three distinct stages of FAD adsorption were observed and a model of the orientation of FAD on the electrode surface as a function of time and potential is pres...
TL;DR: In this paper, the Schrodinger equation for the charge density is calculated for the neutral atoms from hydrogen to uranium, and the singly positive ions, from helium to barium and lutetium to radium.
Abstract: The one-electron potential, , appearing in the Schrodinger equation for the charge density is calculated for the neutral atoms from hydrogen to uranium, and the singly positive ions, from helium to barium and lutetium to radium. These computations, utilizing the nonrelativistic SCF wavefunctions of Clementi and Roetti and McLean and McLean, were performed in order to investigate the concept of shell structure as defined by this potential. exhibits a number of zeros and extrema corresponding to classically allowed and forbidden regions, with its topology being very similar in nature to that of . The significant difference is that displays all seven shells in the heavier elements of the periodic table, whereas displays only five shells; i.e. compared with , has additional zeros and extrema at large distances corresponding to the two outer shells. The positions of these additional zeros and extrema, when plotted against atomic number Z, exhibit large deviations from the Bohr model of the hydrogen atom. The o...
TL;DR: In this article, the authors measured the apparent heat capacities for fifteen branched and cyclic alcohols in dilute n-decane solution at 25 °C. The alcohols were 2-methyl-2-propanol, cyclohexanol, 3-ethyl-3-pentanol, cyclooctanol, 5-decanol, 4-propyl-4-heptanol and cyclododecanol.
Abstract: Apparent heat capacities have been measured for fifteen branched and cyclic alcohols in dilute n-decane solution at 25 °C. The alcohols were 2-methyl-2-propanol, cyclohexanol, 3-methyl-3-pentanol, trans-, cis-, and mixed isomer 2-methylcyclohexanol, 1-methylcyclohexanol, 3-ethyl-3-pentanol, cyclooctanol, 3,7-dimethyl-1-octanol, 5-decanol, 4-propyl-4-heptanol, cyclododecanol, 5-butyl-5-nonanol, and 8-hexadecanol (in n-hexane). Excess heat capacities CpE throughout the concentration range were measured at 25 °C for: 1-hexanol + n-hexadecane (n-C16) and + 2,2,4,4,6,8,8-heptamethylnonane (br-C16), 4-propyl-4-heptanol, and 1-decanol + n-decane, 3-methyl-3-pentanol + n-C16 and + br-C16 and at 27 °C for cyclohexanol + n-C16 and + br-C16. Also, for 3-methyl-3-pentanol + n-decane CpE was measured at 10, 25, 40, and 50 °C. For a series of isomeric alcohols, the apparent molar heat capacities show a maximum against concentration which decreases and moves to higher alcohol concentration as the hydroxyl group on the a...
TL;DR: The Raman and infrared spectra of DABCO have been measured as a function of the pH, and the vibrational bands of the two protonated forms have been tabulated and assigned.
Abstract: The Raman and infrared spectra of DABCO have been measured as a function of the pH, and the vibrational bands of the two protonated forms of DABCO have been tabulated and assigned. The frequencies of several of the Raman bands were found to exhibit substantial shifts upon protonation, and the appearance of the Raman spectrum in the region between 900 and 1100 cm−1 in particular shows differences which can be used to differentiate between the three forms of DABCO. The values of the two pKa's were determined from the intensity versus pH plots for the three species.
TL;DR: The oximes of 2-acylthioanisole derivatives may be conveniently converted into 1,2-benzisothiazoles by acetic anhydride in pyridine as discussed by the authors.
Abstract: The oximes of 2-acylthioanisole derivatives may be conveniently converted into 1,2-benzisothiazoles by acetic anhydride in pyridine. 3-(2-Methylthiophenyl)-1,2-benzisothiazole, prepared by this met...