Biomedical subjects

Carol Creutz

Publications and source records attributed to Carol Creutz.

7 recordsLinked to original sources

PubMed2006

Interfacial charge-transfer absorption: 3. Application to semiconductor-molecule assemblies.

Interfacial charge-transfer absorption (IFCTA) provides information concerning the barriers to charge transfer between molecules and the energy levels of a metal/semiconductor and the magnitude of the electronic coupling and could thus provide a powerful tool for understanding interfacial charge-transfer kinetics. Here we utilize a previously published model (J. Phys. Chem. B 2005, 109, 10251) to predict the energetics of IFCTA spectra for semiconductors and compare literature observations to these predictions for n-type semiconductors (largely TiO2). In contrast to metals, where IFCTA has been only rarely observed, new absorption features due to IFCTA are common for semiconductors such as TiO2. At issue is whether the electron accepting states in the TiO2 are localized or delocalized over the conduction band.

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PubMed2006

Henry Taube: inorganic chemist extraordinaire.

The numerous innovative contributions of Henry Taube to modern inorganic chemistry are briefly reviewed. Highlights include the determination of solvation numbers and lability, elucidation of substitution mechanisms, discovery and documentation of inner-sphere electron transfer, and discovery of the remarkable coordination chemistry of ruthenium and osmium ammine complexes with unsaturated ligands and mixed-valence complexes and their fundamental relationship to intramolecular electron transfer.

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PubMed2006

Transition state characterization for the reversible binding of dihydrogen to bis(2,2'-bipyridine)rhodium(I) from temperature- and pressure-dependent experimental and theoretical studies.

Thermodynamic and kinetic parameters for the oxidative addition of H2 to [Rh(I)(bpy)2]+ (bpy = 2,2'-bipyridine) to form [Rh(III)(H)2(bpy)2]+ were determined from either the UV-vis spectrum of equilibrium mixtures of [Rh(I)(bpy)2]+ and [Rh(III)(H)2(bpy)2]+ or from the observed rates of dihydride formation following visible-light irradiation of solutions containing [Rh(III)(H)2(bpy)2]+ as a function of H2 concentration, temperature, and pressure in acetone and methanol. The activation enthalpy and entropy in methanol are 10.0 kcal mol(-1) and -18 cal mol(-1) K(-1), respectively. The reaction enthalpy and entropy are -10.3 kcal mol(-1) and -19 cal mol(-1) K(-1), respectively. Similar values were obtained in acetone. Surprisingly, the volumes of activation for dihydride formation (-15 and -16 cm(3) mol(-1) in methanol and acetone, respectively) are very close to the overall reaction volumes (-15 cm(3) mol(-1) in both solvents). Thus, the volumes of activation for the reverse reaction, elimination of dihydrogen from the dihydrido complex, are approximately zero. B3LYP hybrid DFT calculations of the transition-state complex in methanol and similar MP2 calculations in the gas phase suggest that the dihydrogen has a short H-H bond (0.823 and 0.810 Angstroms, respectively) and forms only a weak Rh-H bond (1.866 and 1.915 Angstroms, respectively). Equal partial molar volumes of the dihydrogenrhodium(I) transition state and dihydridorhodium(III) can account for the experimental volume profile found for the overall process.

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PubMed2005

Interfacial charge-transfer absorption: semiclassical treatment.

Optically induced charge transfer between adsorbed molecules and a metal electrode was predicted by Hush to lead to new electronic absorption features but has not been experimentally observed. However, Gerischer characterized photocurrents arising from such absorption between adsorbed metal atoms and semiconductor conduction bands. Interfacial charge-transfer absorption (IFCTA) provides information concerning the barriers to charge transfer between molecules and the metal/semiconductor and the magnitude of the electronic coupling and could thus provide a powerful tool for understanding interfacial charge-transfer kinetics. Here we provide a framework for modeling and predicting IFCTA spectra. The key feature of optical charge transfer to or from a band of electronic levels (taken to have a constant density of states and electronic coupling element) is that the absorption probability reaches half intensity at lambda + DeltaG(theta), where lambda and DeltaG(theta) are the reorganization energy and free-energy gap for the optical charge transfer, attains >90% intensity at lambda + DeltaG(theta) + 0.9 square root[4lambdak(B)T], and remains essentially constant until the top (bottom) level of the band is attained. However, when the electronic coupling and transition moment are assumed to be independent of photon energy (Mulliken-Hush model), a peaked, highly asymmetric absorption profile is predicted. We conclude that, in general, the electronic coupling between molecular adsorbates and the metal levels is so small that absorption is not detectable, whereas for semiconductors there may be intense features involving coupling to surface states.

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PubMed2004

Rapid phosphine exchange on 1.5-nm gold nanoparticles.

Triphenylphosphine-cappped, 1.5-nm gold nanoparticles "Au(101)(PPh(3))(21)Cl(5)" prepared following Hutchison's procedure (Weare, W. W.; Reed, S. M.; Warner, M. G.; Hutchison, J. E. J. Am. Chem. Soc. 2000, 122, 12890) undergo rapid exchange of capping ligand phosphine with dissociated and added phosphine in dichloromethane solvent at 298 K. Remarkably, while the (1)H NMR spectrum resonances of the attached phosphine are broad, characteristic of a range of incompletely averaged environments, the (31)P NMR spectrum (observable only at 213 K and below) exhibits a single, narrow resonance indicating that all of the phosphorus atoms are magnetically equivalent.

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PubMed2002

Optical transitions of symmetrical mixed-valence systems in the Class II-III transition regime.

In the Robin and Day classification, mixed-valence systems are characterized as Class I, II or III depending on the strength of the electronic interaction between the oxidized and reduced sites, ranging from essentially zero (Class I), to moderate (Class II), to very strong electronic coupling (Class III). The properties of Class I systems are essentially those of the separate sites. Class II systems possess new optical and electronic properties in addition to those of the separate sites. However, the interaction between the sites is sufficiently weak that Class II systems are valence trapped or charge localized and can the be described by a double-well potential. In Class III systems the interaction of the donor and acceptor sites is so great that two separate minima are no longer discernible and the energy surface features a single minimum. The electron is delocalized and the system has its own unique properties. The Robin and Day classification has enjoyed considerable success and most of the redox systems studied to date are readily assigned to Class II. However the situation becomes much more complicated when the system shows borderline Class II/III behavior. Such "almost delocalized" mixed-valence systems are difficult to characterize. In this article spectral band shapes and intensities are calculated utilizing increasingly complex models including two to four states. Free-energy surfaces are constructed for harmonic diabetic surfaces and characterized as a function of increasing electronic coupling to simulate the Class II to III transition. The properties of the charge-transfer absorption bands predicted for borderline mixed-valence systems are compared with experimental data. The treatment is restricted to symmetrical (delta G0 = 0) systems.

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PubMed1997

Electronic and Molecular Structures of Pentaammineruthenium Pyridine and Benzonitrile Complexes as a Function of Oxidation State.

The structural characterization of both Ru(II) and Ru(III) compounds containing Ru(NH(3))(5)(2+/3+) with pyridine or benzonitrile as the sixth ligand (L) is described. Crystal data for L = pyridine, [(NH(3))(5)Ru(NC(5)H(5))](SO(3)CF(3))(2) (1): orthorhombic space group Pbcn, Z = 4, a = 13.096(2) Å, b = 11.541(2) Å, c = 13.179(2) Å. For [(NH(3))(5)Ru(NC(5)H(5))]Cl(3).1.4H(2)O (2): orthorhombic space group Pnma, Z = 4, a = 22.667(12) Å, b = 7.095(2) Å, c = 10.097(8) Å. For L = benzonitrile, [(NH(3))(5)Ru(NCC(6)H(5))](SO(3)CF(3))(2) (3): monoclinic space group P2(1)/n, Z = 4, a = 9.561(1) Å, b = 18.424(4) Å, c = 12.181(1) Å, beta = 95.73(1) degrees. For [(NH(3))(5)Ru(NCC(6)H(5))](S(2)O(6))(3/2).2H(2)O (4): triclinic space group P&onemacr;, Z = 2, a = 7.8947(6) Å, b = 11.517(2) Å, c = 11.630(1) Å, alpha = 99.61(1) degrees, beta = 97.275(8) degrees, gamma = 102.25(1) degrees. The Ru(II)-N(L) and Ru(III)-N(L) distances are respectively 2.058(8) and 2.077(10) Å for L = pyridine and 1.945(5) and 2.025(4) Å for L = benzonitrile. The new data yield a comprehensive set of structural parameters for modeling and interpreting electron transfer barriers and for investigating the dependence of metal-ligand coupling on d(M)(-)(N), for which the results of INDO calculations are also reported here.

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