摘要:

The quantitative efficacy of the Stranks–Marcus–Hush theory of volumes of activation ΔV‡for outer-sphere electron transfer between metal complexes in solution is assessed. The theory predicts ΔV‡accurately for several couples in aqueous solution, but is satisfactory for polar nonaqueous solvents only at pressures of ca. 100 MPa and above, and accuracy is not improved when the molecular nature of the solvent is allowed for through the Mean Spherical Approximation approach. At low pressures, the calculations become numerically unstable when the isothermal compressibility of the solvent is high and its relative permittivity is low, particularly for the more highly charged couples. For aqueous systems, departures from the predicted ΔV‡afford insights into the role of the counterions, the incursion of inner-sphere pathways, the enhanced reactivity of CoIII/IIcage complexes relative to conventional chelates, and the question of "spin forbiddenness" of electron transfer processes that involve a large change in spin multiplicity.Keywords: redox kinetics, inorganic reaction mechanisms, pressure effects, Marcus–Hush theory, activation volumes.

ISSN:0008-4042    

DOI:10.1139/v96-068

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Uses of heat capacities of solutions of electrolytes are reviewed, with a particular emphasis on the standard state partial molar heat capacities and their applications to calculations of the effects of temperature on equilibrium constants, electrode potentials, enthalpies, and entropies. Methods of obtaining these standard partial molar heat capacities are summarized, followed by comparisons of values obtained in different ways. Many of the "best" such heat capacities are collected and then used as the basis for establishing single-ion heat capacities based on the convention thatCpO(H+) = 0, followed by illustrations of the convenient use of these quantities. Finally, there is brief discussion of theoretical analysis of these standard partial molar heat capacities in relation to ion–solvent interactions.Keywords: heat capacities, electrolytes; aqueous solutions, heat capacities; thermodynamics, electrolytes.

ISSN:0008-4042    

DOI:10.1139/v96-069

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The electrochemical investigation of a number of polyarene–iron complexes ([3]2+–[9]5+) containing etheric, sulphide, and sulphone bridges indicated that there were various degrees of interaction based on the nature of the bridging heteroatoms. While the electrochemical investigation of all etheric complexes showed that the metallic moieties behaved as isolated redox centers, it was found that there was electronic communication (ca. 70–80 mV) for the isomeric sulphide complexes [4]2+and [6]2+. The rate constant of the following chemical reaction (kf) was calculated for some of these complexes and it was found that these rates were affected by the nature of the solvent, the bridging ligand, and the temperature. At various temperatures,kfindicated a higher degree of stability for complexes containing sulphide bridges than for those containing etheric bridges, especially at room temperature. The effect of a strong coordinating solvent, such as acetonitrile, on thekfof complex [3]2+indicated that the substitution of the arene ligand with acetonitrile molecules proceeded as a dissociative mechanism. Controlled potential coulometry was also used to verify the transfer of two electrons in the first reduction process of the di-iron complexes.Keywords: cyclopentadienyliron, cyclic voltammetry, arene complexes, isolated and interacting redox centers.

ISSN:0008-4042    

DOI:10.1139/v96-070

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The rates of oxidation of CoII(dmgBF2)2(OH2)2by CoIII(NH3)5X2+(X = Br−, Cl−, and N3−) have been studied at 25 °C in 0.10 M LiClO4. The rate constants are 50 ± 9, 2.6 ± 0.2, and 5.9 ± 1.0 M−1s−1for X = Br−, Cl−, and N3−, respectively, in 0.01 M acetate buffer at pH 4.7. The relative rates are consistent with the inner-sphere bridging mechanism established earlier by Adin and Espenson for the analogous reactions of CoII(dmgH)2(OH2)2. The rate constants with CoII(dmgBF2)2(OH2)2typically are ~103times smaller and this is attributed largely to the smaller driving force for the CoII(dmgBF2)2(OH2)2complex. The outer-sphere oxidations of cobalt(II) sepulchrate by CoIII(dmgH)2(OH2)2+(pH 4.76–7.35, acetate, MES, and PIPES buffers) and CoIII(dmgBF2)2(OH2)2+(pH 3.3–7.42, chloroacetate, acetate, MES, and PIPES buffers) have been studied. The pH dependence gives the following rate constants (M−1s−1) for the species indicated: (1.55 ± 0.09) × 105(CoIII(dmgBF2)2(OH2)2+); (5.5 ± 0.3) × 103(CoII(dmgH)2(OH2)2+); (3.1 ± 0.5) × 102(CoIII(dmgH)2(OH2)(OH)); (2.5 ± 0.3) × 102(CoIII(dmgBF2)2(OH2)(OH)). The known reduction potentials for cobalt(III) sepulchrate and the diaqua complexes, and the self-exchange rate for cobalt(II/III) sepulchrate, are used to estimate the self-exchange rate constants for the dioximate complexes. Comparisons to other reactions with cobalt sepulchrate indicates best estimates of the self-exchange rate constants are ~2.4 × 10−2 M−1s−1for CoII/III(dmgH)2(OH2)2and ~5.7 × 10−3 M−1s−1for CoII/III(dmgBF2)2(OH2)2.Keywords: electron transfer, cobaloxime, inner sphere, outer sphere, self-exchange.

ISSN:0008-4042    

DOI:10.1139/v96-071

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The monoterpene thujone (1) is ring expanded regioselectively to provide homothujone (4) in order to explore its potential as a chiral starting material. Stereoselective Robinson annulation of homothujone provides an enone intermediate (5), further derivatization of which was undertaken to furnish functionalized naphthalenones useful for synthesis of the antifeedant (−)-polygodial and the ambergris fragrance (−)-Ambrox®.Keywords: thujone, homothujone, synthesis, naphthalenones, polygodial, Ambrox.

ISSN:0008-4042    

DOI:10.1139/v96-072

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Gold surfaces coated with monolayers of alkyl thiols are significant in the field of biosensors and chromatography. There is a general concern about the quality of coatings in terms of surface density and voids. The self-assembly of the short-chain hexane (C6) thiol and long-chain dodecane (C12) and hexadecane (C16) thiols to polycrystalline gold surfaces has been investigated in situ and in real time using surface plasmon resonance (SPR) spectroscopy and surface plasmon microscopy (SPM). The self-assembly was followed based on observed changes in reflectivity at a fixed angle of incidence as a function of time. Our results indicate that the data for hexane, dodecane, and hexadecane thiol adsorption to gold surfaces were best fit by a two-step process rather than a one-step process. The mechanism may involve fast adsorption to the surface to give 80% (C12, C16) or 50% (C6) coverage followed by a slow (100-fold slower) "rearrangement" of the adsorbed thiol. SPM shows these surfaces to be smooth and homogenous at a 4 μm scale. An understanding of the process of rearrangement could lead to control of the quality of coatings for analytical applications.Keywords: surface plasmon, alkyl thiols, gold, monolayer, kinetics, ellipsometry, microscopy.

ISSN:0008-4042    

DOI:10.1139/v96-073

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Protonolyses of carbon–hydrogen bonds can occur under suitable conditions to produce carbocations and H2. In an effort to accelerate these fundamental reactions, we have attempted to make them intramolecular by devising compounds in which carbon–hydrogen bonds designed to be particularly good formal donors of hydride are held in close proximity to acidic sites. Dihydrobenzimidazoles4and11are compounds of this type, since the carbon–hydrogen bonds at C2 are activated as formal donors of hydride by adjacent lone pairs in a dihydroaromatic ring, and acidic anilinium and carboxylic acid groups are held nearby. Unfortunately, this proximity does not lead to the formation of H2by protonolysis; instead, other reactions intervene when compounds4and11are subjected to pyrolysis.Keywords: intramolecular protonolysis of carbon–hydrogen bonds, formal donors of hydride, generation of H2, dihydrobenzimidazoles.

ISSN:0008-4042    

DOI:10.1139/v96-074

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

A series of five, structurally related, substituted 2-phenyl-benzopyrylium (flavylium) salts were synthesized and characterized by NMR, absorption, and fluorescence techniques. Their hydration and deprotonation constants were obtained through thermodynamic and relaxation kinetic methods. Metallic complexation with the two compounds possessing a catechol group and its effect on the fluorescence intensity was also studied. The ground state properties of the five pigments are correlated with the theoretical data collected through AM1 molecular orbital calculations.Keywords: naphthoflavylium synthesis, hydration and deprotonation constants, fluorescence, metallic complexation, molecular orbital calculations.

ISSN:0008-4042    

DOI:10.1139/v96-075

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

A fibre-optic-based evanescent wave biosensor has been used for the detection of virus. Polyclonal antibody directed against the model analyte, Newcastle disease virus, was covalently immobilized on aminosilane-coated quartz fibres, which served as the capture and concentration element of the sensor system. Radiolabelling studies demonstrated a high degree of antibody attachment to the quartz solid support. Maximal coverage could be attained with antibody solution as low as 10 μg/mL and carbonyldiimidazole as the cross-linking agent. Fluorescein-labelled anti-NDV served as the detector antibody in a sandwich format. Assay times were approximately 15 min with a limit of detection of about 2 ng of purified virus in 0.2 mL sample volume. The biosensor detection system possesses several desirable characteristics such as a limited number of mechanical components, a multiple use active surface, and low baseline variation, which indicate that it has the potential to serve as an on-line continuous monitoring device of an automated or semi-automated detection system.Keywords: fibre optic, biosensor, fluorescence, evanescence, immunoassay, antibody, Newcastle disease virus.

ISSN:0008-4042    

DOI:10.1139/v96-076

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Excess partial molar enthalpies,HAE, of methanol, ethanol, and 1- and 2-propanols in aqueous solutions were measured directly, accurately, and in small increments in mole fraction at 25 °C. From these data, the solute–solute enthalpic interactions,HAAE≡N(∂HAE/∂nA), were evaluated for each alcohol. These data indicate that three distinctively different mixing schemes, I, II, and III exist, as was the case for aqueous 2-butoxyethanol previously studied in our laboratory. The transition from mixing scheme I to II appears to take place gradually within a small composition range. As the hydrophobic moiety becomes smaller from 2-butoxyethanol to methanol, the locus of the transition moves to a higher value in mole fraction of the alcohol. At the same time, the range of transition becomes wider and the solute–solute enthalpic interaction weaker.Keywords: excess partial molar enthalpies in aqueous solutions, methanol, ethanol, 1-propanol, 2-propanol, enthalpic interaction, transition of mixing scheme.

ISSN:0008-4042    

DOI:10.1139/v96-077

出版商:NRC Research Press    

年代:1996

数据来源: NRC