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The effect of MCM-41 on the ESR spectrum of an aqueous spin probe solution was observed. The sharp ESR spectrum turns into a rather broad characteristic one leaving a sharper signal as the minor component, immediately after the addition of MCM-41 powder to the system. This observation indicates that MCM-41 traps the solute molecule into the nanochannel by letting the solvent water form a rather stable molecular cage, since the ESR line shape indicates that the nitroxide radical undergoes anisotropic rotation without being adsorbed on the wall. Thermodynamic parameters for this process are estimated from the temperature dependencies of the trapping efficiency. This process is explained in terms of the surface enthalpy of the liquid specifically intensified in the nanospace.

A spin-probe ESR study has been made on the dynamics of 2-propanol and water molecules in the nanochannel of MCM-41 at various temperatures. In the former system, 2-propanol is separated into two phases: one with molecules immobilized in the ESR time scale and the other with mobile ones, even at temperatures more than 40 degrees higher than the bulk melting point. In the case of water, on the other hand, only the "immobilized" water was detected at a temperature as high as 313 K. At higher temperature, spin-probe molecule undergoes anisotropic rotational diffusion to reduce resistance from the solvent molecules in the nanochannel. These results are explained in relation to the intermolecular network intensified in the nanochannel. Static as well as dynamic structures of these solutions have been discussed.

The physical states of long-chain n-alkane molecules in the nanochannel of MCM-41, a mesoporous silica, were studied by observing the ESR spectra of alkyl radicals formed by radiolysis. The ESR spectra for the systems with n-decane, n-undecane, n-dodecane, or n-tridecane, which were confined in the MCM-41 nanochannel and irradiated with γ-rays at 77 K, were almost identical. Since the ESR spectra for the irradiated n-alkane crystals, which are due to the three types of radicals, R I (*CH 2 CH 2 R), R I I (CH 3 *CHCH 2 R'), and R I I I (RCH 2 *CHCH 2 R"), change alternatively as the carbon number changes consecutively, the above results suggest that these n-alkanes are solidified in a similar way and cannot form regular crystals in the nanochannel. A model is proposed for the molecular packing from the dynamics, the relative yields of these three radicals, which do not deviate largely from those for n-undecane and n-tridecane crystals, and their temperature dependencies.

13C NMR spectra were observed for the mixed solutions composed of 2-propanol and cyclohexane in contact with a mesoporous silica, MCM-41, to study the distribution and dynamics of these molecules in the nanochannel of MCM-41. From the analysis of the spectral and relaxation data, we deduced that a high concentration gradient exists in the radial distribution of these liquid molecules in the nanochannel: alcohol molecules prefer the region near the surface and cyclohexane molecules the central portion of the nanochannel. Further evidence for this new model have been obtained by the spin-probe ESR observations. In addition, we obtained a model for the movement of solution molecules in the nanochannel: molecules “flow or diffuse collectively” by slipping on the channel surface.

The photoreaction of xanthone in an alcoholic solution flowing through a column reactor filled with the mesoporous silica MCM-41 was performed. It was found that the product yields depend greatly on both the pore size of the filler and the nature of the solvent. The product yields of this reaction, which involves a pair of radicals as an intermediate, were dependent on the magnetic field as well. These results were interpreted with a model wherein the lifetime of the radical pair was elongated by several hundred times or more in the mesopore, or nanotube, compared with that in the bulk solution. This unusual phenomenon was attributed to the collective movement of the solvent molecules in the nanotube, which would thereby inhibit the translational diffusion of the solute molecules.

The fluorescence detected ESR (ODESR) spectrum of a squalane solution of p-terphenyl was observed at various temperatures, concentrations, and microwave powers. Analysis of the ODESR amplitude, the line shape, and the area under the spectrum which is normalized by the fluorescence intensity led us to conclude that two geminate pairs (one with a terphenyl anion and a hole of the solvent squalane and the other with a terphenyl anion and its cation) contribute to the ODESR spectrum. It was also concluded that the former pair has a much shorter recombination time than that of the latter. It is suggested that though the hole center hops among the solvent squalanes, the rate is much less than that for the hole in aromatic solvents.

Spin adduct yields in the photoreduction of menadione (2-methylnaphthoquinone) in isotope labeled micellar solutions were measured as functions of the external magnetic field. As surfactants, ordinary SDS, perdeuteriated SDS, and a mixture of the two were employed. In a mixed micellar solution, a normal isotope effect on the spin adduct yield was observed. On the other hand, in the pure micellar solutions with each of the former two surfactants, a reversed isotope effect was observed. These two apparent isotope effects depend on the external magnetic field and were separated into two independent isotope effects: one is the primary isotope effect on the hydrogen abstraction step and the other is the secondary magnetic isotope effect on the intersystem crossing step of the intermediate radical pair.

An apparatus for irradiation and subsequent ESR measurements at variable temperatures below 77°K was constracted by combining an ESR spectrometer, and an X-ray irradiator, and a laboratory scale low temperature refrigerator operating at the temperature region between 77 and 4.2°K. A device for rotating the single crystal specimen was made to measure the angular dependence of the ESR spectra. The lowest specimen temperature achieved was estimated to be 6°K and the precision of the temperature control was less than ±0.5°K for a period of several hours. The apparatus makes it possible to irradiate samples and to measure ESR spectra at any temperature in the range between 77 and 6°K. Some applications for irradiation and ESR measurements at low temperatures are also described. An unstable radical which disappears at about 60°K was found in an irradiated single crystal of L-cystine dihydrochloride. Experimental evidence for the quantum tunnelling of the methyl group in polymethylmethacrylate radical was also f...

Materials enabling intelligent humidity control were synthesized using fumed silica, tetraethylorthotitanate and quaternary alkylammonium surfactant (decyl-, dodecyl-, tetradecyl and hexadecyltrimethylammonium chlorides) as a liquid-crystal template under hydrothermal conditions. X-ray diffraction profiles and transmission electron micrographs indicated that a homogeneous hexagonal structure of SiO2-TiO2 was formed from those products. The mesostructured products had high BET surface areas from 540 to 863m2/g, with uniform pore diameters of 1.5-3nm. These physical quantities were controlled by varying the size of the organic template. Water vapor adsorption isotherms for these materials experienced a sharp increase in adsorption when the relative water vapor pressure (P/P0) was in the range of 0.4-0.6. Over this range of pressures, the maximum amount of adsorbed water was between 20 and 50mass%. The isotherms were classified as type V in the IUPAC notation, showed an unusually large hysteresis. The large hysteresis could be explained by the difference in contact angle between adsorption and desorption. For both the 2nd and 3rd. water vapor adsorption-desorption isotherms, any morphological change was not observed in the isotherms, meaning that these materials have high durability in their humidity control ability. A small shift of the broad Q4 29Si-MAS/NMR spectra indicated that a wider distribution of the Si-O-Si angles in the SiO4 tetrahedra when titanium was incorporated into the silica matrix.