Host-guest interaction between swelling clay minerals and poorly water-soluble drugs. 1: Complex formation between a swelling clay mineral and griseofulvin

The formation of a complex between a swelling clay mineral and griseofulvin (GF), a poorly water-soluble drug, was examined. A strong host-guest interaction between the neutral drug molecules and the clay mineral was observed not only in the solid state but also in aqueous dispersion. The powder X-ray diffraction patterns revealed the disappearance of a crystalline phase of GF through host-guest interaction for samples having low GF contents. The complex formation was confirmed to be due to monolayer adsorption on the basis of quantitative thermochemical analyses. The strong interaction between GF and the clay was also detected when the complex powder was dispersed in an aqueous medium on the basis of the intensity changes of from free GF solution in CD and fluorescence spectra as compared with those observed for the free GF solution.     

Intermolecular electron transfer from naphthalene derivatives in the higher triplet excited states

Intermolecular electron transfer (ELT) from a series of naphthalene derivatives (NpD) in the higher triplet excited states (T(n)) to carbon tetrachloride (CCl(4)) in Ar-saturated acetonitrile was observed using the two-color two-laser flash photolysis method. The ELT efficiency depended on the driving force of ELT. Since the ELT from the T(n) state occurred competitively with the internal conversion (IC, T(n) --> T(1)) and the triplet energy transfer (ENT), the ELT became apparent only when sufficient free energy change of ELT was attained. On the other hand, ELT from the T(1) state was not observed, although ELT from the T(1) state with sufficiently long lifetime has a slightly exothermic driving force. The fast ELT from the T(n) state and lack of the reactivity of the T(1) state were explained well by the "sticky" dissociative electron-transfer model based on one-electron reductive attachment to CCl(4) leading to the C-Cl bond cleavage.     

Importance of properties of the lowest and higher singlet excited states on the resonant two-photon ionization of stilbene and substituted stilbenes using two-color two-lasers

Radical cations of trans-stilbene and substituted trans-stilbenes (stilbenes and the radical cations denote Sand S(*+), respectively) were generated from the resonant two-photon ionization (TPI) in acetonitrile with irradiation of one-laser (266- or 355-nm laser) and with simultaneous irradiation of two-color two-lasers (266- and 532-nm or 355- and 532-nm lasers) with the pulse width of 5 ns each. The formation yields of S(*+), the TPI efficiency, depended on the properties of S in the lowest and higher singlet excited state (S(S(1)) and S(S(n))), generated from one-photon excitation with 266- or 355-nm laser and from two-photon excitation with simultaneous irradiation of 266- and 532-nm or 355- and 532-nm lasers, respectively. The TPI efficiency using two-color two-lasers increased compared with that using one-laser. It is confirmed that the TPI proceeds through two-step two-photon excitation with the S(0) --> S(1) --> S(n)() transition. In addition to the electronic character of S(S(0)) which depends on the substituent of S, oxidation potential, and molar absorption coefficient of the S(0) --> S(1) absorption as well-known important factors for the TPI efficiency, it is shown that properties of S(S(1)) and S(S(n)) such as lifetimes, electronic characters of S(S(1)) and S(S(n)), molar absorption coefficient of the S(1) --> S(n) absorption, and ionization rate from S(S(n)) are also important.     

Anomalous fluorescence from the azaxanthone ketyl radical in the excited state

The time-resolved absorption and fluorescence spectra of the azaxanthone (AX) ketyl radical (AXH.) in the excited state (AXH.(Dn) (n = 1 or 2)) were observed during the nanosecond-picosecond two-color two-laser flash photolysis. AXH. showed dual fluorescence peaks at 460 and 645 nm, which were assigned to the D2 --> D0 and D1 --> D0 transitions, respectively. It was found that the lifetime of the D2 --> D0 fluorescence (1.0 ns) was longer than that of the D1 --> D0 fluorescence (0.4 ns). The fluorescent quantum yields of the D1 --> D0 and D2 --> D0 fluorescence were estimated to be 0.0008 +/- 0.0002 and 0.05 +/- 0.02, respectively. These anomalous emitting properties can be attributed to the pyridine ring in AX. AXH. is a new example of a neutral radical which violates Kasha's rule.     

Hydrogen-bond-assisted control of H versus J aggregation mode of porphyrins stacks in an organogel system

To obtain insights into a correlation relationship between the structure and the aggregation mode in an organogel system, we synthesized gelators 2a-4a bearing a porphyrin moiety as a one-dimensional aggregation unit and amide groups as peripheral hydrogen-bonding sites. Gelators 3a and 3b bearing the amide groups at the 4-position of the meso-phenyl groups are classified as versatile gelators, gelating 10 and 14 solvents, respectively, among 23 solvents tested herein. In contrast, gelators 2a and 4a bearing the amide groups at the 3,5-positions and 3-position, respectively, are classified as poor gelators. Examination by spectroscopic methods (UV-vis, ATR-FTIR, XRD, etc.) revealed that in the organogel phase porphyrins in 3a adopt the H aggregation mode whereas those in 2a and 4a adopt the J aggregation mode. X-ray analysis of the single crystals established that in fact 3b features a columnar stack of porphyrin moieties that can be classified as the H-aggregate, whereas 2a results in a two-dimensional a-b plane, in which porphyrin moieties are arranged in the J-aggregate. Very interestingly, the difference in the H versus J aggregation mode is well-reflected by the difference in the macroscopic aggregate morphology observed by SEM: 3a + cyclohexane gel results in a one-dimensionally aggregated fibrillar structure, whereas 2a + cyclohexane gel results in a two-dimensional sheetlike structure. These findings indicate that the H versus J aggregation mode of porphyrin stacks can be controlled by the peripheral hydrogen-bonding interactions and the microscopic hydrogen-bonding network structure is well-reflected by the macroscopic SEM-observed structure.     

Background levels of238U and226Ra in atmospheric aerosols

The²³⁸U and²²⁶Ra contents of small-volume aerosols are determined by a chemical analysis technique. Mean activity concentrations of²³⁸U and²²⁶Ra in aerosols over approximately ten years are 0.29·10^–5 and 0.93·10^–5 Bq/m³, respectively. The yearly variation of²³⁸U and²²⁶Ra in aerosols is small. The concentrations of²²⁶Ra are always larger than those of²³⁸U in the same sampling time. The correlation of²³⁸U and²²⁶Ra cannot be recogonized (r=0.18). The concentrations of summer samples are greater than those of winter samples for²³⁸U. One of the causes of seasonal difference may be due to the fact that the components of aerosols are different according to soil size, soil components, weathering states, etc.     

Small-angle neutron-scattering study on a structure of microemulsion mixed with polymer networks

The structure of a microemulsion mixed with polymer networks was investigated by means of small-angle neutron scattering (SANS). The system consists of nonionic surfactant, polymer network, oil, and water. The microemulsion and the polymer network employed in this work are known to undergo temperature-induced structural transition and volume phase transition, respectively. Polymer solutions and gels were made by polymerizing monomer solutions in the presence of microemulsion droplets. In the case of a mixture of an N-isopropylacrylamide (NIPA) monomer solution and a microemulsion, the NIPA monomer was found to behave as a cosurfactant. However, polymerization resulted in a phase separation to polymer-rich and -poor phases. Interestingly, SANS results indicated that a well-developed ordered structure of oil domains was formed in polymer network and the structure was very different from its parent systems. Furthermore, the system underwent two different types of structural transitions with respect to temperature. One was originated from the structural transition of microemulsion due to the change of the spontaneous curvature and the other from the volume phase transition of the NIPA gel.     

Porphyrin-based organogels: control of the aggregation mode by a pyridine-carboxylic acid interaction

To find a new strategy for designing porphyrin-based organogelators, hydrogen-bond-donating (carboxylic acid)/accepting (pyridine) substituents or electron-donating (dialkylamino)/withdrawing (pyridine) substituents were introduced into peripheral positions of a porphyrin (1cp or 1ep, respectively), and the gelation properties were compared with those of symmetrical reference compounds bearing two pyridyl substituents or two ester groups (1pp or 1ee, respectively). It was found that the symmetrical molecules show a solubility that is quite inferior to that of 1cp and 1ep having a dipole moment and precipitate from most organic solvents. 1cp, 1ep, and 1ee formed gels with cyclohexane, methylcyclohexane, and several alcoholic solvents, but scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations revealed that their superstructures constructed in the organogels are very different. In cyclohexane, 1cp resulted in a sheetlike structure, whereas 1ep and 1ee resulted in a fiberlike structure. The difference is attributed to the two-dimensional interactive forces in 1cp consisting of the porphyrin-porphyrin pi-pi stacking and the carboxylic acid-pyridine hydrogen bonding. In fact, when the hydrogen-bonding interaction was weakened by alcoholic solvents or by adding pyridine or N,N-(dimethylamino)pyridine, the sheetlike structure was transfigured to the fiberlike structure. Further detailed analyses of their aggregation modes were conducted by spectroscopic methods such as ultraviolet-visible (UV-vis) absorption, Fourier transform infrared (FT-IR), and X-ray diffraction (XRD). On the basis of these findings, the influence of these peripheral substituents on the gel formation and the aggregation mode was discussed.     

Matrix‐free detection of intact ions from proteins in argon‐cluster secondary ion mass spectrometry

In the secondary ion mass spectrometry (SIMS) of organic substances, the molecular weight of the intact ions currently detectable is at best only as high as 1000 Da, which for all practical purposes prevents the technique from being applied to biomaterials of higher mass. We have developed SIMS instrumentation in which the primary ions were argon cluster ions having a kinetic energy per atom, controlled down to 1 eV. On applying this instrumentation to several peptides and proteins, the signal intensity of fragment ions was decreased by a factor of 10² when the kinetic energy per atom was decreased below 5 eV; moreover, intact ions of insulin (molecular weight (MW): 5808) and cytochrome C (MW: 12 327) were detected without using any matrix. These results indicate that fragmentation can be substantially suppressed without sacrificing the sputter yield of intact ions when the kinetic energy per atom is decreased to the level of the target's dissociation energy. This principle is fully applicable to other biomolecules, and it can thus be expected to contribute to applications of SIMS to biomaterials in the future. Copyright © 2009 John Wiley & Sons, Ltd.     

Functors on the category of quasi-fibrations

We consider the following questions: when can we extend a continuous endofunctor on Top the category of topological spaces to a fibrewise continuous endofunctor on Top(2) the category of continuous maps? If this is true, does such fibrewise continuous endofunctor preserve fibrations? In this paper, we define Fib the topological category of cell-wise trivial fibre spaces over polyhedra and show that any continuous endofunctor on Top induces a fibrewise continuous endofunctor on Fib preserving the class of quasi-fibrations.