Highly Reactive Nonheme Iron(III) Iodosylarene Complexes in Alkane Hydroxylation and Sulfoxidation Reactions

High‐spin iron(III) iodosylarene complexes bearing an N‐methylated cyclam ligand are synthesized and characterized using various spectroscopic methods. The nonheme high‐spin iron(III) iodosylarene intermediates are highly reactive oxidants capable of activating strong C? H bonds of alkanes; the reactivity of the iron(III) iodosylarene intermediates is much greater than that of the corresponding iron(IV) oxo complex. The electrophilic character of the iron(III) iodosylarene complexes is demonstrated in sulfoxidation reactions.     

Studies on glycosylation of the mitomycins. Syntheses of 7-N-(4-O-glycosylphenyl)-9a-methoxymitosanes

Two new derivatives of glycosyl mitomycin C, 7-N-[4-O-(beta-D-glucopyranosyl and alpha-sialosyl)phenyl]-9a- methoxymitosanes, were synthesized, and their structures were elucidated by analysis of the nuclear magnetic resonance spectra. Field desorption mass spectrometry was successfully used for the confirmation of these structures. The cytotoxic, antibacterial, and antitumor activities of 7-N-(4-glycosylphenyl)-9a- methoxymitosanes were also examined.     

Measurement of LET distribution and dose equivalent on board the space shuttle STS-65

Space radiation dosimetry measurements have been made on board the Space Shuttle STS-65 in the Second International Microgravity Laboratory (IML-2). In these measurements, three kinds of detectors were used; one is a newly developed active detector telescope called “Real-time Radiation Monitoring Device (RRMD)” utilizing silicon semi-conductor detectors and others are conventional detectors of thermoluminescence dosimeters (TLDs) and CR-39 plastic track detectors. Using the RRMD detector, the first attempt of real-time monitoring of space radiation has been achieved successfully for a continuous period of 251.3 h, giving the temporal variations of LET distribution, particle count rates, and rates of absorbed dose and dose equivalent. The RRMD results indicate that a clear enhancement of the number of trapped particles is seen at the South Atlantic Anomaly (SAA) without clear enhancement of dose equivalent, while some daily periodic enhancements of dose equivalent due to high LET particles are seen at the lower geomagnetic cutoff regions for galactic cosmic ray particles (GCRs). Therefore, the main contribution to dose equivalent is seen to be due to GCRs in this low altitude mission (300 km). Also, the dose equivalent rates obtained by TLDs and CR-39 ranged from 146.9 to 165.2 μSv/day and the average quality factors from 1.45 to 1.57 depending on the locations and directions of detectors inside the Space-lab at this highly protected orbit for space radiation with a small inclination (28.5°) and a low altitude (300 km). The LET distributions obtained by two different detectors, RRMD and CR-39, are in good agreement in the region of 15–200 keV/mm and difference of these distributions in the regions of LET < 15 keV/mm and LET > 200 keV/mm can be explained by considering characteristics of CR-39 etched track formation especially for the low LET tracks.     

Catalytic mechanism of water oxidation with single-site ruthenium-heteropolytungstate complexes

Catalytic water oxidation to generate oxygen was achieved using all-inorganic mononuclear ruthenium complexes bearing Keggin-type lacunary heteropolytungstate, [Ru(III)(H(2)O)SiW(11)O(39)](5-) (1) and [Ru(III)(H(2)O)GeW(11)O(39)](5-) (2), as catalysts with (NH(4))(2)[Ce(IV)(NO(3))(6)] (CAN) as a one-electron oxidant in water. The oxygen atoms of evolved oxygen come from water as confirmed by isotope-labeled experiments. Cyclic voltammetric measurements of 1 and 2 at various pH's indicate that both complexes 1 and 2 exhibit three one-electron redox couples based on ruthenium center. The Pourbaix diagrams (plots of E(1/2) vs pH) support that the Ru(III) complexes are oxidized to the Ru(V)-oxo complexes with CAN. The Ru(V)-oxo complex derived from 1 was detected by UV-visible absorption, EPR, and resonance Raman measurements in situ as an active species during the water oxidation reaction. This indicates that the Ru(V)-oxo complex is involved in the rate-determining step of the catalytic cycle of water oxidation. The overall catalytic mechanism of water oxidation was revealed on the basis of the kinetic analysis and detection of the catalytic intermediates. Complex 2 exhibited a higher catalytic reactivity for the water oxidation with CAN than did complex 1.     

Preparation and photocatalytic activity under visible light irradiation of mesostructured titania particles modified with phthalocyanine in the pores

Mesostructured titania particles modified with phthalocyanine (Pc) were prepared by using molecular self-assemblies of cetyltrimethylammonium bromide (CTAB) with solubilized Pc as a template. Low-angle X-ray diffraction pattern and transmission electron microscopy (TEM) image clearly show the formation of Pc/titania particles with hexagonal mesopore structures. Diffuse reflectance UV–vis spectrum and fluorescence spectrum of Pc/titania indicate that Pc molecules in the pores are in a monomeric state. In addition, Pc/titania particles have photocatalytic activity under visible light irradiation (>610 nm) due to the reduction reaction by the electrons transferred from Pc to titania.     

Isothermal phase equilibria and structural phase transition in the carbon dioxide + cyclopropane mixed-gas hydrate system

The isothermal phase equilibria of the carbon dioxide + cyclopropane mixed-gas hydrate system were investigated by means of static temperature measurement and Raman spectroscopic analysis. Raman spectra indicated that the crystal structure of the carbon dioxide + cyclopropane mixed-gas hydrate changes from structure-I to structure-II and back to structure-I with an increase of the equilibrium carbon dioxide composition at 279.15 K, while each simple gas hydrate belongs to structure-I at the temperature. Whereas, unlike 279.15 K, no structural phase transition occurs along the isothermal stability boundary at 284.15 K.     

Electrocatalytic reduction of CO2 to methanol: Part VIII. Photoassisted electrolysis and electrochemical photocell with n-TiO2 anode

Carbon dioxide has been reduced to methanol with an electrochemical photocell composed of an n-TiO₂ photoanode and a metal complex-confined platinum cathode in the presence of homogeneous catalysts. The feasibility of the reduction of CO₂ with the photocell depended greatly on the pH value of the anolyte. Photocells containing an anolyte of pH 12 led to the formation of methanol in the cathode compartment, and oxygen gas evolved at the photoanode with a high current efficiency. In photocells in which the pH value of the anolyte was smaller than 11, however, CO₂ was reduced only when an external bias was present.     

Characterization of Mononuclear Non‐heme Iron(III)‐Superoxo Complex with a Five‐Azole Ligand Set

Reaction of O₂ with a high‐spin mononuclear iron(II) complex supported by a five‐azole donor set yields the corresponding mononuclear non‐heme iron(III)–superoxo species, which was characterized by UV/Vis spectroscopy and resonance Raman spectroscopy. ¹H NMR analysis reveals diamagnetic nature of the superoxo complex arising from antiferromagnetic coupling between the spins on the low‐spin iron(III) and superoxide. This superoxo species reacts with H‐atom donating reagents to give a low‐spin iron(III)–hydroperoxo species showing characteristic UV/Vis, resonance Raman, and EPR spectra.     

In situ infrared spectroscopic investigations on the electrochemical properties of prussian blue-polyaniline-modified electrodes with various anionic Fe(II) complexes working as a mediator for the electroreduction of CO2

Various Fe(II) complexes have been incorporated into Prussian blue (PB)|polyaniline (PAn)-modified electrodes, and their spectroelectrochemical properties been investigated using in situ and ex situ FTIR methods. It is shown that large anionic complexes once incorporated in the PAn matrix are not dedoped during the potential cycling and the charge balance is maintained by dedoping or incorporating electrolyte cations. This electrode system was applied to the electrocatalytic reduction of CO₂ in aqueous solution, and the reduction products were identified by taking in situ FTIR spectra during the anodic stripping. At potentials higher than 0 V, the IR bands associated with the loss of carboxylic acid at 1362 cm⁻¹ and the gain of CO₂ at 2343 cm⁻¹ were simultaneously observed, indicating that the CO₂ was derived from the reoxidation of carboxylic acid. It is therefore confirmed that CO₂ can be reduced to organic species including carboxylic acid on the PB|PAn-modified electrode with anionic Fe(II) complexes in aqueous solution, with an indication that the existence of the anionic metal complex is essential to such mediated reduction of CO₂.     

Threshold characteristics of microcavity semiconductor lasers

The influence of spontaneous emission coupling on the threshold characteristics of microcavity semiconductor lasers is studied using explicit algebraic expressions for the pump rate dependence of photon and carrier numbers. It is shown that fractional spontaneous emission coupling in practical microcavity laser structures imposes limitations on thresholdless lasing operation.