Yoshiharu Usui

Solute-solvent and solvent-solvent interactions evaluated through clusters isolated from solutions: Preferential solvation in water-alcohol mixtures

Abstract Mass spectrometric analysis of clusters in alcohol (methanol, ethanol, 1-propanol)-water binary mixtures provided information on the microscopic structures of these binary mixtures at the cluster level. Preferential solvation for the hydrophobic substrates by the alcohol molecules in the alcohol-water mixtures was found to be promoted by the alcohol self-aggregation in the solution.

Hydrolysis of phosphate esters catalyzed by copper(II)-triamine complexes. The effect of triamine ligands on the reactivity of the copper(II) catalysts

Abstract Hydrolyses of lithium 2,4-dinitrophenyl ethyl phosphate (7) and 2,4-dinitrophenyl diethyl phosphate (8) catalyzed by copper(II)—triamine complexes (triamine = cis,cis-triaminocyclohexane (1), 1,5,9-triazacyclododecane (2), 1,4,7-triazacyclononane (3), dipropylenetriamine (4), N-(2-aminoethyl)-1,3-propanediamine (5), diethylenetriamine (6)) were investigated at pH 7.0–9.5, and the reactivity of the catalysts was found to increase in the order 5 ∼ 6 ∼ 4

Photosensitized Reduction of Methyl Viologen Using Eosin-Y in Presence of a Sacrificial Electron Donor in Water–Alcohol Mixture

Abstract Photoreduction of methyl viologen (MV2+) by eosin-Y (EY2−) in the presence of triethanolamine (TEOA) has been investigated in water–methanol mixture by means of steady-state photolysis and laser-flash photolysis in the visible/near-infrared regions. The complete conversion to the persistent methyl viologen radical cation (MV·+) was observed in the presence of lower concentrations of EY2− and excess TEOA. By laser-flash photolysis measurements, electron transfer was confirmed to occur from the triplet state of EY2− [3(EY2−)*] to MV2+ in the rate constants of ca 2.0 × 1010 M−1 s−1. The rates and efficiencies of production of MV·+ were found to be dependent on solvent compositions and concentrations of MV2+ ionic salt and TEOA. The back electron transfer reaction from MV·+ to EY·− was retarded in the presence of TEOA, which supports that EY2− is reproduced by accepting an electron from TEOA. In the presence of excess TEOA, the indirect formation of MV·+ from EY·3− which was produced by accepting an electron from TEOA, was confirmed. The contributions of both the oxidative and reductive routes of 3(EY2−)* for the MV·+ formation have been confirmed.

The Electron Transfer Reaction between Triplet Methylene Blue and Aromatic Compounds

The electron transfer reaction from aromatic compounds to méthylène blue in the triplet state has been studied in acetonitrile by flash photolysis. The relationship between the rate constant of the reaction in the triplet state and the free enthalpy change involved was investigated. For a positive free enthalpy change, the electron transfer reaction does not occur, in contrast to what has been observed in the excited singlet state.

Hydrolytic cleavage of DNA by a novel copper(ii) complex with cis,cis-1,3,5-triaminocyclohexane

Copper(II) complex with cis,cis-1,3,5-triaminocyclohexane effectively promotes the hydrolytic cleavage of phage DNA with a rate constant of 4.34 ± 0.77 h - 1 at pH 8.1 and 35 °C.

MIGRATION OF SINGLET EXCITATION ENERGY FROM ACRIDINE ORANGE‐10‐DODECYL BROMIDE TO METHYLENE BLUE IN MICELLES

The efficient energy transfer occurred from photoexcited singlet stale of acridine orange‐10‐dodecyl bromide dissolved in SDS micelles to methylene blue absorbed on the micelle surface. The sensitized fluorescence of methylene blue was effectively quenched by the addition of a small amount of ethanol and with the increase in temperature.

Determination of the S*—T transition probabilities of some acridine dyes and of thiopyronine by the method of sensitized delayed fluorescence

Abstract Parkers method of delayed fluorescence as a means of determining the S * —T transition probability Φ ST was extended to systems in which reversible triplet energy transfer occurs between donor and acceptor. The Φ ST values of proflavine, acriflavine and acridine orange in ethanol were determined by this extended method using anthracene or 9-methylanthracene as an acceptor and eosine as a reference donor. The Φ ST values thus obtained are 0.45 ± 0.05 (proflavine), 0.53 ± 0.07 (acriflavine) and 0.30 ± 0.05 (acridine orange). The Φ ST values of eosine and thiopyronine were also determined by the method in Parkers original form using perylene as an acceptor and erythrosine as a reference donor. The Φ ST values obtained, 0.44 ± 0.01 (eosine) and 0.24 (thiopyronine), agree satisfactorily with those obtained by a chemical method, 0.43 ± 0.04 (eosine) and 0.28 ± 0.03 (thiopyronine).

Newly developed decontamination technology based on gaseous reactions converting to carbonyl and fluoric compounds

A new gas-phase decontamination technology is developed based on gaseous reactions utilizing the volatile properties of the carbonyl and fluoric compounds of radioactive transition elements and actinides (corrosion products, fission products, and transuranium) on a materials surface. The feasibility of this new technology is determined by removing nonradioactive (Co, Cr, Ni, Re, Mo, Mn, Ru, and Zn) and radioactive ( 60 Co, 63 Ni, and 103 Ru) nuclide transition elements as gaseous forms under high CO pressure (50 to 200 atm) and high temperature (∼350°C). Experiments involving U and using fluoric gases are also performed. For radioactive nuclides existing in an oxide layer of stainless steel, pretreatment with supercritical CO 2 + I 2 + H 2 O is used to remove the oxide layer completely, and by the subsequent gaseous reaction, 95 to 99% of 60 Co is removed from the layer by CO gas treatment at a pressure of 200 atm. The plasma treatment using fluorine gas results in U being removed with high efficiency (∼60%) after only 5 min, even at a reduced pressure of I Torr and at room temperature. When the carbonyl and fluoric species generated from a nontoxic gas mixture (1 Torr) of CF 4 and O 2 is used, U and 60 Co are removed simultaneously with high removal efficiencies of 80 and 100% for 60 Co and U, respectively. The data provide evidence that chemically reactive plasma treatment is available as a gas-phase decontamination method that can be conducted using nontoxic gases under safe and mild conditions such as reduced pressure, shorter time periods, and ambient temperature. Finally, a fluoric chemical reaction can be used to remove solid U deposits by converting them to gaseous U compounds at room temperature and without using plasma treatment. The pressure of ClF 3 gradually affects the higher removal efficiency of U, and the removal efficiency is >90% under the conditions of 30 min and >100 Torr. The results verify that chemical reactions involving carbonylation and fluorination reactions can be utilized for gas-phase decontamination, and the potential for this new idea for decontamination is affirmed. If gas-phase decontamination technology is further developed, it will be not only convenient but also economically advantageous because decontaminating and treating the large volume of nuclear wastes-especially nonincinerable radioactive wastes-are currently very difficult.

Solvent effects on the intrinsic enhancement factors of the triplet exciplex generated by photoinduced electron transfer reaction between eosin Y and duroquinone

The spin dynamics of the duroquinone anion radical (DQ•-) generated by photoinduced electron transfer reactions from triplet eosin Y (3EY2-) to DQ have been studied by using transient absorption and pulsed EPR spectroscopy. Unusual net-absorptive electron spin polarization plus net-emissive polarization were observed, suggesting the production of the triplet exciplex or contact radical pair as the reaction intermediate. The kinetic parameters and intrinsic enhancement factors of the electron spin polarization were determined in various alcoholic solvents. The net-absorptive electron spin polarization was also observed in ethanol-water mixed solvents. The solvent effects on the radical yield are analysed on the basis of a stochastic Liouville equation established for the magnetic field effects on the radical yield. The zero-field splitting constants of the triplet exciplex are estimated from the solvent viscosity dependence of the enhancement factors due to spin-orbit coupling induced depopulation of the reaction intermediate.

ACID-BASE INTERACTION FROM THE VIEWPOINT OF MOLECULAR CLUSTERING: EFFECTS OF SOLVENT, PKA AND SIZE OF ALKYL GROUP

Acid–base interactions were investigated by mass spectrometry of clusters isolated from solutions containing a carboxylic acid (propionic, butyric or hexanoic acid), an aromatic base (pyridine or pyrazine) and a solvent (water, acetonitrile or propionitrile). In water, self-aggregation of the carboxylic acid molecules due to hydrophobic interaction to form carboxylic acid clusters, such as (butyric acid)n, was prominent, and acid–base interaction proceeded between the carboxylic acid clusters and the basic molecules. In acetonitrile, the acid–base interaction was sensitive to the relative strength of the base. When pyridine (relatively strong base) was used as a base, clustering proceeded through the formation of a polarized acid–base complex, (acid)δ-(base)δ+. However, when pyrazine (relatively weak base) was used as a base, self-aggregation of the acid molecules became favorable. In propionitrile, such clusters were not observed because each molecule was separated by individual solvation. This solvent effect is related to the solvation structure, which determines the balance between the self-aggregation of the acid molecules and the formation of the polarized acid–base complex. It has also been demonstrated that the balance of the above intermolecular interactions is also dependent on the size of the alkyl group of the carboxylic acid. The results of the mass spectrometry partially show the microscopic view for the effect of solvent, pKa and the size of the alkyl group on the acid–base interaction in solution.