Laboratory for Analytical Chemistry: MolecularElectrochemistry, Electroanalytical Chemistry andInterfacial Chemistry

http://www.sci.osaka-cu.ac.jp/chem/analy/analy.html

Current Research and Principal Research Interests
Selected Publications

1. Current Research and Principal Research Interests
My research interests are primarily in the area of molecular electrochemistry including
electroanalytical chemistry. Many of the projects are interdisciplinary in nature and involve
collaboration with scientists in inorganic chemistry, physical chemistry, and the environmentalsciences. Some of our current projects are listed below.
Redox properties of multinuclear metal complexes. An electron is the simplest chemicalreagent. We have increasingly recognized the role of electron-transfer (ET) reactions in thelaboratory and in nature. Our research focuses sharply on the ET properties of multinuclear
metal complexes, with a primary aim of understanding how the structure and reactivity of thecomplex is changed by addition or removal of electrons. We use mainly voltammetry
experiments to realize the redox mechanism. Many of our electrochemical experiments areproperly interfaced with spectroscopic instruments that enable us to use optical spectroscopy
and magnetic resonance spectroscopies to characterize ET products and intermediates. We havebeen developing new and universally applicable in-situ spectroelectrochemical techniques in
uv.-vis.-near IR region to characterize stable mixed-valence states that are formed in eachone-electron redox process of multinuclear complexes having multi-redox metal centers as wellas to detect intermediates in the redox processes.

Three stepwise one-electron redox processes and two mixed-valence statesIn-situ spectroelectrochemical cell consisting of an optically transparent thin-layer electrode, amirror and a two-way optical fiber
Direct voltammetric measurements of excited state redox potentials. Excited state species are
more easily oxidized and reduced than the corresponding ground state species. There have been
many studies of photoinduced electron transfer reactions utilizing the strong reducing andoxidizing ability of the excited state species. We have so far estimated redox potentials of
excited state species using the ground state redox potentials and the energy gap between the 0th.
vibrational levels of the ground and excited states. The estimated values, however, contain
uncertainties of 100 mV or more. Now we fully recognize that direct measurements of theexcited state redox potentials by a precise voltammetric method are of great value for the studiesof photoinduced electron transfer reactions. We now choose porphyrins and metalloporphyrins
as the target compounds, which have been widely used for the construction of artificiallyphotosynthetic and photoenergy conversion systems.

Electroanalytical chemistry in nonaqueous solvents. Electrochemical use of nonaqueous
solvents has spread from laboratory experiments to the industrial field including lithium
secondary batteries. Many of the ET reactions in biological systems take place at a relativelyhydrophobic reaction field. We are studying nonaqueous electroanalytical chemistry to reveal
fundamentally important aspects of the redox reactions in nonaqueous and pseudo-nonaqueous
electrolyte solutions. Precise measurements of redox potentials by voltammetric techniques
provide us better understanding of solvation of redox active species. Furthermore, we aredeveloping a universal reference electrode independent of solvent properties and estimating its
absolute potential. Using this reference electrode, we can correctly compare redox potentials
which are measured under different nonaqueous solution conditions.
Chemical characterization of humic acid. Humic acid is a fascinating substance that can haveprofound environmental consequences. The ability to form complexes with toxic metal ions andorganic agricultural chemicals has been recognized by researchers interested in their migrationand mobilization. The micellar properties also show the ability to play important roles in thesolubilization and transport of hydrophobic substances. We are applying electroanalyticaltechniques involving ion-transfer voltammetry between immiscible aqueous and organic
solutions to chemical characterization of humic acid, in connection with redox reactivity,hydrophobicity, and ionic exchange ability. We are attempting to quantitatively interpret theinteraction of chemical substances of environmental interest with humic acid.

Electrostatic and hydrophobic interaction of methylviologen (used for a pesticide) and humic acid

2. Selected Publications
1. "Redox Chemistry of Dinuclear Molybdenum Dithiolene Complexes. Interconversion of theBridging Disulfide and Sulfides", Y. Miki, H.Takagi, A. Ichimura, H. Akashi and T. Shibahara,
Chem. Lett., 482-483 (2002).
2. "Unusual Oxidation of Oxo-Peroxomolybdenum(VI) Tetramesitylporphyrin GivingMolybdenum(V) Porphyrin and Dioxygen", T. Fujihara, K. Myougan, A. Ichimura, Y. Sasakiand T. Imamura, Chem. Lett., 178-179 (2001).
3. "Oxo- and Alkoxo-Bridged Dimeric Molybdenum(III) Ethylenediamine Complexes", S.
Kiyoda, H. Akashi, A. Ichimura and T. Shibahara, Chem. Lett., 1422-1423 (2000).
4. "Brominated Trihalomethane Formation in Halogenation of Humic Acid in the Coexistence ofHypochlorite and Hypobromite ions", K. Ichihashi, K. Teranishi and A. Ichimura, Water Res.,33, 477-483 (1999).
5. "Feasible Attachment of a Dinuclear Ruthenium Complex to Gold Electrode Surfaces. A
Screening Method to Find Functional Electrodes", H. Takagi, A. Ichimura, T. Yano, I. Kinoshita,
K. Isobe, M. Abe, Y. Sasaki, Y. Mikata, T. Tanase, N. Takeshita, C. Inoue, Y. Kimura, S. Endo,
K. Tamura and S. Yano, Electrochemistry, 67, 1192-1193 (1999).
6. "Perpendicularly Arranged Ruthenium Porphyrin Dimers and Trimers", K. Funatsu, A.
Kimura, T. Imamura, A. Ichimura and Y. Sasaki, Inorg. Chem., 36, 1625-1635 (1997).
7. "Syntheses and Electrochemistry of Incomplete Cubane-Type Clusters with M3S4 Cores(M=Mo,W). X-ray Structures of [W3S4(H2O)9](CH3C6H4SO3)4･9H2O, Na2[W3S4(Hnta)3]･
5H2O, and (bpyH)5[W3S4(NCS)9]･3H2O", T. Shibahara, M. Yamasaki, G. Sakane, K. Minami,
T. Yabuki and A. Ichimura, Inorg. Chem., 31, 640-647 (1992).

8. "The Dinuclear Palladium(II) Complex of Pyridine-2-thiol. Synthesis, Structure, andElectrochemistry", K. Umakoshi, A. Ichimura, I. Kinoshita, and S. Ooi, Inorg. Chem., 29,4005-4010 (1990).
9. "Technetium Electrochemistry. 2. Electrochemical and Spectroelectrochemical Studies of theBis(tertiary phosphine) (D) Complexes trans-[TcIIID2X2]+ (X = Cl, Br) and [TcID3]+", A.
Ichimura, W. R. Heineman, J.-L. Vanderheyden and E. Deutsch, Inorg. Chem., 23, 1272-1278(1984).
10. "Reactivity of Coordinated Disulfides. 1. Nucleophilic Cleavage of the Sulfur-Sulfur Bond",
A. Ichimura, D. L. Nasco and E. Deutsch, J. Am. Chem. Soc., 105, 844-850 (1983).