Biomedical subjects

Amanda S Harper

Publications and source records attributed to Amanda S Harper.

3 recordsLinked to original sources

PubMed2004

Hexanethiolate monolayer protected 38 gold atom cluster.

The nucleation-growth-passivation Brust reaction has been modified so as to enrich the product in useful quantities of a 38-atom gold nanoparticle coated with a hexanethiolate monolayer. Two modifications are described, using -78 degrees C reduction temperature and a hyperexcess of thiol. Compositional evidence is presented that establishes the product as a Au38(C6)24 hexanethiolate monolayer protected cluster (MPC), based on transmission electron microscopy, laser ionization-desorption mass spectrometry, thermogravimetric analysis, and elemental analysis. Reverse phase HPLC confirms the relatively good monodispersity of the MPC products, but high-resolution double-column HPLC reveals that the MPCs are a mixture of closely related but chromatographically distinct products. Voltammetry, low energy spectrophotometry, and spectroelectrochemistry reveal, respectively, a 1.6 eV electrochemical energy gap between the first oxidation and the first reduction, an optical HOMO-LUMO energy absorbance edge at 1.3 eV, and a bleaching of optical absorbance near the 1.3 eV band edge that accompanies electrochemical oxidation of the nanoparticle.

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PubMed2004

Electrochemistry and optical absorbance and luminescence of molecule-like Au38 nanoparticles.

This paper describes electrochemical and spectroscopic properties of a well-characterized, synthetically accessible, 1.1 nm diam Au nanoparticle, Au(38)(PhC(2)S)(24), where PhC(2)S is phenylethylthiolate. Properties of other Au(38) nanoparticles made by exchanging the monolayer ligands with different thiolate ligands are also described. Voltammetry of the Au(38) nanoparticles in CH(2)Cl(2) reveals a 1.62 V energy gap between the first one-electron oxidation and the first reduction. Based on a charging energy correction of ca. 0.29 V, the indicated HOMO-LUMO gap energy is ca. 1.33 eV. At low energies, the optical absorbance spectrum includes peaks at 675 nm (1.84 eV) and 770 nm (1.61 eV) and an absorbance edge at ca. 1.33 eV that gives an optical HOMO-LUMO gap energy that is consistent with the electrochemical estimate. The absorbance at lowest energy is bleached upon electrochemical depletion of the HOMO level. The complete voltammetry contains two separated doublets of oxidation waves, indicating two distinct molecular orbitals, and two reduction steps. The ligand-exchanged nanoparticle Au(38)(PEG(135)S)(13)(PhC(2)S)(11), where PEG(135)S is -SCH(2)CH(2)OCH(2)CH(2)OCH(3), exhibits a broad (1.77-0.89 eV) near-IR photoluminescence band resolvable into maxima at 902 nm (1.38 eV) and 1025 nm (1.2 eV). Much of the photoluminescence occurs at energies less than the HOMO-LUMO gap energy. A working model of the energy level structure of the Au(38) nanoparticle is presented.

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PubMed2003

Ion atmosphere relaxation control of electron transfer dynamics in a plasticized carbon dioxide redox polyether melt.

The sorption of CO(2) into the highly viscous, semisolid hybrid redox polyether melt, [Co(phenanthroline)(3)](MePEG-SO(3))(2), where MePEG-SO(3) is a MW 350 polyether-tailed sulfonate anion, remarkably accelerates charge transport in this molten salt material. Electrochemical measurements show that as CO(2) pressure is increased from 0 to 800 psi (54 atm) at 23 degrees C, the physical diffusion coefficient D(PHYS) of the Co(II) species, the rate constant k(EX) for Co(II/I) electron self-exchange, and the physical diffusion coefficient of the counterion D(COUNTERION) all increase, from 4.3 x 10(-10) to 6.4 x 10(-9) cm(2)/s, 4.1 x 10(6) to 1.6 x 10(7) M(-1) s(-1), and 3.3 x 10(-9) to 1.6 x 10(-8) cm(2)/s, respectively. Plots of log(k(EX)) versus log(D(PHYS)) and of log(k(EX)) versus log(D(COUNTERION)) are linear, showing that electron self-exchange rate constants are closely associated with processes that also govern D(PHYS) and D(COUNTERION). Slopes of the plots are 0.68 and 0.98, respectively, indicating a better linear correlation between k(EX) and D(COUNTERION). The evidence indicates that k(EX) can be controlled by relaxation of the counterion atmosphere about the Co complexes in the semisolid redox polyether melts. Because the counterion relaxation is in turn controlled by polyether "solvent" fluctuations, this is a new form of solvent dynamics control of electron transfer.

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