This account summarizes our recent work on measurements of the correlation function of the transition frequency fluctuations by a three-pulse photon echo method. The correlation function of the transition frequency fluctuations is a sensitive measure for the magnitudes and time scales of dynamical interactions between solute and solvent. We describe the results of the solvation dynamics of small ions in protic solvents such as methanol and water obtained by an infrared photon echo method.
This account is a review of the research on the characteristics of adsorbed water molecules and the photocatalytic reaction sites of incorporated organic molecules on various TiO2 photocatalysts in powder and film forms by means of 1H NMR spectroscopy. The adsorbed water can be categorized into four distinctively different water species: i) rigid water species with restricted mobility near the solid surface; ii) less mobile water molecules in the intermediate water layer; iii) relatively mobile water molecules in the outer water layer; iv) very loosely adsorbed water molecules which exchange slowly with gaseous water molecules in air. The temperature dependence of the NMR signal of a small quantity of ethanol molecules incorporated in TiO2 suggests that the actual photocatalytic reaction site can be these adsorbed water regions. The surface conversion of hydrophilic properties of TiO2 films induced by photoirradiation is well reflected in the NMR signal change. The enhancement of water molecularly adsorbed on TiO2 films is evidently detected on UV irradiation; this phenomenon has been difficult to elucidate so far with alternative spectroscopic techniques.
We fabricated organic light-emitting diodes (OLED) from horse-heart cytochrome c, and measured the electroluminescence (EL) spectra, current–voltage and EL intensity–voltage characteristics. The external quantum efficiency evaluated from those characteristics was 6–8 × 10−8 at an applied voltage of 13 V. The EL spectrum shows the Soret band around 400 nm, the Q band around 500 nm, and the 690 nm band. The three bands became obscure for a sample prepared in an acidic solution (pH = 1.68) and in a basic solution (pH = 10.01). Based on the energy diagram of the /ITO/cytochrome c/Al/ junction, we considered the difference in the EL spectrum from the photoluminescence or absorption spectrum.
By using the single molecule detection (SMD) technique based on laser scanning fluorescence microscopy, we have developed a method to count the number of labeled fluorophores in a single biomolecule. The number of labeled fluorophores in an individual molecule was measured by counting the number of discrete level jumps in the fluorescence-intensity transients, or Gaussian fitting of the fluorescence-intensity histogram. The instabilities of intensity transients due to humid environments of biomolecules were minimized by optimizing the matrix materials and sample-preparation condition and adding a strong triplet quencher, AET (2-aminoethanethiol). After validating the counting method and estimating the counting uncertainties through observations of a well-defined number of fluorophores, the distribution of the number of incorporated fluorophores in a DNA strand was observed. The advantages in biological analysis by using a single-molecule fluorescence technique have been considered.
The reaction between a cobalt porphycene complex, [CoII(TPrPc)] (TPrPc is a dianion of 2,7,12,17-tetrapropylporphycene), and dioxygen was investigated by means of UV–vis, ESR, and resonance Raman (RR) spectroscopies. These spectra indicate the formation of [CoIII–O2−•]. In the presence of pyridine as an axial ligand, the formation of a six-coordinated superoxide species was confirmed by its characteristic ESR spectrum. The six-coordinated dioxygen adduct exhibits an RR band at 1144 cm−1, which is characteristic of O–O stretching of superoxide. ν(Co–O2) stretching is also observed at 540 cm−1. The ν(O–O) and ν(Co–O2) wavenumbers in the complex were assigned by means of 18O2 substitution. ν(Co–O2) of the O2 adduct shows a higher frequency relative to those of cobalt porphyrin complexes. On standing for one day at room temperature, the compound was auto-oxidized to a CoIII complex, which was structurally determined by X-ray analysis. The complex crystallized in the monoclinic space group P21/n, a = 9.6266(4) Å, b = 12.6343(5) Å, c = 15.6566(6) Å, β = 99.1200(10)°, V = 1880.17(13) Å3, and Z = 2. The CoIII ion lies on the plane of the porphycenato core, and coordinates four porphycenato nitrogen atoms and two pyridine nitrogen atoms. The complex cation, [CoIII(TPrPc)(Py)2]+, exhibits a slightly distorted octahedral coordination geometry. The average Co–N (porphycenato pyrrole) distance and the Co–N (pyridine) distance are 1.929 and 1.952 Å, respectively.
Anion effects on the formation of a cross-linked Ag–Ag interaction in the molecular construction of a series of AgX complexes with bis(3-pyridyl)dimethylsilane (L) (X− = CF3SO3−, PF6−, and NO3−) have been carried out. The slow diffusion of an organic solution of L into an aqueous solution of AgX afforded [Ag(L)]X or [Ag(X)(L)]. Each L connected two Ag(I) ions (Ag–N = 2.110(5)–2.161(4) Å) to form a wave strand. For CF3SO3− and PF6− anions, each single strand cross-linked the adjacent single strands via an argentophilic interaction (Ag–Ag = 3.0551(7) Å for CF3SO3−, 3.279(1) Å for PF6−) to produce unique 2D sheets. In contrast, for the NO3− anion, the anion acts as a ligand (Ag–O3N = 2.61–2.79 Å) instead of the argentophilic interaction (Ag···Ag = 3.351(1) Å). That is, a small coordinating anion is an obstacle to form the argentophilic interaction, whereas a big noncoordinating anion favors the argentophilic interaction in the present molecular construction. For all complexes, the geometry around the Ag(I) ion is a typical T-shaped arrangement. The thermal stability can be explained in terms of the structural properties, including the argentophilic interaction.
A new complex of chloro[3-(2,3-diaminopropionylamino)propionic acid](dimethyl sulfoxide)platinum(II) ([PtCl(dmso)(Hdapap)]CF3CO2·2H2O) was synthesized and characterized. Among a series of nucleic acids, the selective and 1:1 binding between [PtCl(dapap)(dmso)] and a guanosine 5′-monophosphate ion (Hgmp−) in an aqueous solution at pH 4.0 (20 mmol dm−3, each) was achieved by conducting ESI-MS and NMR experiments. This reaction included the initial chloride ion displacement by H2O, followed by metal coordination to the N7-position of the guanine base. The latter step was not affected in the case of guanosine-3′,5′-cyclic monophosphate ion (cgmp−), indicating that the phosphate–Pt binding can be ruled out in this system. In order to monitor the binding reaction of [PtCl(dapap)(dmso)] with several nucleic acids, time-course 1H and 31P NMR experiments were performed at 25 °C. Changes in the NMR chemical shifts of H8, H1′, and phosphate signals in Hgmp− upon the addition of [PtCl(dapap)(dmso)] revealed that two products finally remained. Since the synthetic dapap ligand could regulate the reactivity of a ligand coordinated to the Pt-center in [PtCl(dapap)(dmso)], this may arise from the presence of cis- and trans-isomers of [PtCl(dapap)(dmso)] in solution.
Calixarene derivatives with four imine units at the upper rim and different spacers between two calixarenes were employed as highly promising lipophilic neutral carriers to prepare a series of silver-selective electrodes. These calixarenes possess a flexible conformation for rapid ion-exchange across the PVC membrane to provide good response for silver ions. The prepared silver ion-selective electrodes exhibited near-Nernstian responses for silver ions over a wide concentration range of 1.0 × 10−1–1.0 × 10−5 M with a very low detection limit of ∼10−6 M. The potentiometric responses were independent of the pH of the test solution over wide acidic pH range. The effect of various plasticizers on the electrode characteristics was also examined, and bis(2-ethylhexyl) sebacate proved to be the most suitable, since it provided the best slope and other electrode characteristics. High selectivity for Ag+ over Hg2+, Na+, and many other cations was found. The high selectivity for silver ions is mainly attributed to host–guest interactions that occur between the silver and appended groups of calixarene derivatives. The electrodes were used as indicator electrodes in potentiometric titration involving silver ion, and provided a simple method for the determination of Ag+ and Cl− in water samples.
Treatment of [Tp*Rh(coe)(MeCN)] (Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate; coe = cyclooctene) with S8 in MeCN afforded a complex with a chelating pentasulfido(2−) ligand [Tp*Rh(S5)(MeCN)], which was converted further to [Tp*Rh(S5)(CNXy)] (3; Xy = 2,6-Me2C6H3) by the reaction with XyNC. An X-ray analysis was carried out for 3, which disclosed a chair conformation for the RhS5 ring.
Unusual values of K1 and K2 for the formation of complexes CuL2 with L = 2,2′-bipyridyl (bpy) and substituted 1,10-phenanthrolines (phen) have been discussed in relation to the structural change from CuL to CuL2 and the hydrophobic interaction between the coordinated ligands. The free energy for the structural change from the distorted octahedral CuL2 to the trigonal bipyramidal CuL2 has been estimated to be 0.80 (−4.5 kJ mol−1) for L = bpy and 0.47 (−2.7 kJ mol−1) for L = phen.
A dinuclear copper(II) complex, [Cu2(L)](ClO4)2, of the macrocyclic ligand (H2L) derived from the [2:2] condensation of 2,6-diformyl-4-methylphenol and 1,3-diaminopropane, was reacted with [Cr(ox)3]3− and [Co(CN)6]3− to produce [Cu2(L)]3[Cr(ox)3]2·6MeOH (1) of a discrete octanuclear structure and [Cu2(L)]3[Co(CN)6]2·6MeOH·2DMF (2) of a 2-D grid structure, respectively.
Asymmetric PCR is generally used to produce ssDNA, which could function as probes for detecting various kinds of genes. An asymmetric PCR technique based on magnetic nanoparticles (MNPs) has been developed in this work. One of the two amplification primers was bound to the MNP surface by modifying its 5′-end and leaving the 3′-end available for DNA polymerase activity, while the other was unbound. The results obtained showed that PCR could proceed successfully when the concentration ratio of the unbound primer to the MNP-bound primer was from 1:100 to 1:10. Plenty of target ssDNA connected with MNPs (MNP–ssDNA complexes) along with some dsDNA with one strand connected to MNPs could be generated. In virtue of their immobilization on the MNP surface, asymmetric PCR products could be easily isolated by the external magnetic field. This new surface asymmetric amplification process can be used not only to produce MNP–ssDNA complexes, but also to provide an alternative route to isolate products of asymmetry PCR.
1,3-Diaryltriazenes, prepared from a 2-methoxy-4-nitrobenzenediazonium salt and primary arylamines, exist as “azo-transfer” tautomers in which the 2-methoxy-4-nitrophenyl group is present on the saturated nitrogen atom and forms a hydrogen bond between the 2-methoxy group and the N–H moiety. The synthetic utility of the diazonium salt as a practical diazonium-transfer agent for primary arylamines via tautomerism of the 1,3-diaryltriazenes has been demonstrated by the deaminative iodination and arylation of the arylamines without direct diazotization. The starting 2-methoxy-4-nitrophenylamine can be easily recovered after the reactions.
Radical cyclization of β-(3-indolyl) ketone O-pentafluorobenzoyloximes proceeds by the treatment with a catalytic amount of copper powder in 1,2-dichloroethane to generate 3,4-dihydro-α-carbolines, which are oxidized to α-carbolines with chloranil.
The use of alkenyl acylphosphonate and acylphosphine oxide derivatives as acceptors in radical cyclizations was studied under thermal and photochemical conditions, respectively. The cyclizations of alkenyl acylphosphonates under thermal conditions occurred smoothly in refluxing dioxane using benzoyl peroxide as an initiator; the addition of diethyl phosphite increased the chemical yield. Photochemically induced cyclizations of alkenyl acyldiphenylphosphine oxides at 300 nm gave similar results, although a notable difference was observed in one case. The intramolecular cyclization of S-but-3-enyl phosphinothiolformates occurred under thermal and photochemical conditions, providing thiolactones, whereas S-pent-4-enyl phosphinothiolformate afforded the tetrahydrothiophene derivative under similar conditions.
A remarkable addition effect of bases, like AcOK, was observed in the radical addition of cyanoacetates to alkenes catalyzed by a Mn(II)/Co(II)/O2 redox system. Thus, a carbon radical from ethyl cyanoacetate could be catalytically generated by adding AcOK to the Mn(II)/Co(II)/O2 redox system, even at room temperature, and the resulting carbon radical readily added to 1-octene to give an adduct, ethyl 2-cyanodecanoate, in good yield, while no reaction took place at all in the absence of AcOK. Ethyl cyanoacetate added smoothly to a variety of alkenes under mild conditions in the presence of a base to lead to the corresponding adducts in fair-to-good yields. It is reasonable to assume that the base added accelerated the deprotonation from a transient carbocation intermediate generated by the one-electron oxidation of ethyl cyanoacetate by the Mn(III) ion. This method provides an alternative route to alkylation of cyanoacetates under mild conditions.
The electrooxidation of alcohols in a disperse system with N-oxyl-immobilized polymer particles (PE-co-AA-N-Oxyl), prepared from poly(ethylene-co-acrylic acid) (PE-co-AA-CO2H), as a disperse phase and an aqueous saturated NaHCO3 containing 20 wt % NaBr as a disperse medium was successfully performed in a simple beaker-type undivided cell under constant-current conditions. The electrooxidation of alcohols proceeded in a similar manner by the use of PE-co-AA-CO2H as a disperse phase, though the current efficiency decreased in some extent. Protection of most of the carboxylic acid moieties on the surface of PE-co-AA-CO2H by esterification or amidation resulted in significant decrease of the product yields, suggesting that the carboxylic acid moieties on the surface of PE-co-AA-CO2H would also act as a mediator for the electrooxidation of alcohols. Both the recovered PE-co-AA-N-Oxyl and the aqueous solution were used repeatedly for the electrooxidation of alcohols, thereby offering a formally closed system for the electrooxidation of alcohols.
The decomposition behavior under electron-beam irradiation was examined for polychlorinated dibenzo-p-dioxin (PCDD, polychlorinated dibenzo[b,e][1,4]dioxin) and polychlorinated dibenzofuran (PCDF) isomers in incinerator gases at a temperature of 473 K. Significant decomposition was obtained for all PCDD isomers over the investigated absorbed doses, which resulted from oxidation reactions with OH radicals yielded by electron-beam irradiation. In the case of PCDFs, specific isomers having symmetrical structures, such as 1,2,8,9-, 2,3,7,8-, and 3,4,6,7-TeCDFs, were yielded through the dechlorination of PeCDF isomers. Thermal electrons probably played a role in the dechlorination of PeCDF isomers. Simultaneous formation and subsequent destruction were observed in the electron-beam treatment of TeCDFs in incinerator gases.
Chemical force microscopy (CFM) was applied for the lateral force microscopic imaging of micropatterned organosilane monolayer surfaces with oppositely charged phases using chemically modified cantilever tips. Chemically modified cantilever tips with oxidized mercaptosilane, aminosilane, and unmodified cantilever tip were employed as a tip for CFM. Lateral force imaging of the micropatterned surface with opposite charge was successfully achieved by controlling the pH of the aqueous solution in consideration of the electrostatic condition of functional groups on the cantilever tip and substrate surface.
The oxidative polymerization of sulfonatopropoxyphenols in alkaline water, along with the easy monomer preparation, provided a simple and atom economical way to prepare sulfoalkoxy-pendant poly(phenylene oxide)s. The polymerization in alkaline water reduced the oxidation potential of the sulfonated phenols, and produced water-soluble polymers. The polymers produced a transparent, tough, and flexible membrane, which showed high thermal stability and proton conductivity.
A hydrophobic solute, thymol, was separated from a hydrophilic solute, glucose, with a separation factor of over 230 across a hydrophobic FEP membrane. Hydrophobic solutes are highly partitioned to the membrane, diffused, and back-extracted to the alkaline receiving phase solution by their dissociation, while hydrophilic solutes are rejected by the membrane.