Photochemical and electrochemical properties of zinc chlorin-C60 dyad as compared to corresponding free-base chlorin-C60, free-base porphyrin-C60, and zinc porphyrin-C60 dyads.

The photochemical and electrochemical properties of four chlorin-C60 or porphyrin-C60 dyads having the same short spacer between the macrocycle and the fullerene are examined. In contrast with all the previous results on porphyrin-fullerene dyads, the photoexcitation of a zinc chlorin-C60 dyad results in an unusually long-lived radical ion pair which decays via first-order kinetics with a decay rate constant of 9.1 x 10(3) x s(-1). This value is 2-6 orders of magnitude smaller than values reported for all other porphyrin or chlorin donor-acceptor of the molecule dyad systems. The formation of radical cations of the donor part and the radical anion of the acceptor part was also confirmed by ESR measurements under photoirradiation at low temperature. The photoexcitation of other dyads (free-base chlorin-C60, zinc porphyrin-C60, and free-base porphyrin-C60 dyads) results in formation of the ion pairs which decay quickly to the triplet excited states of the chlorin or porphyrin moiety via the higher lying radical ion pair states as is expected from the redox potentials.     

Probing the donor-acceptor proximity on the physicochemical properties of porphyrin-fullerene dyads: "tail-on" and "tail-off" binding approach.

A new approach of probing proximity effects in porphyrin-fullerene dyads by using an axial ligand coordination controlled "tail-on" and "tail-off" binding mechanism is reported. In the newly synthesized porphyrin-fullerene dyads for this purpose, the donor-acceptor proximity is controlled either by temperature variation or by an axial ligand replacement method. In o-dichlorobenzene, 0.1 M (TBA)ClO(4), the synthesized zincporphyrin-fullerene dyads exhibit seven one-electron reversible redox reactions within the accessible potential window of the solvent and the measured electrochemical redox potentials and UV-visible absorption spectra reveal little or no ground-state interactions between the C(60) spheroid and porphyrin pi-system. The proximity effects on the photoinduced charge separation and charge recombination are probed by both steady-state and time-resolved fluorescence techniques. It is observed that in the "tail-off" form the charge-separation efficiency changes to some extent in comparison with the results obtained for the "tail-on" form, suggesting the presence of some through-space interactions between the singlet excited zinc porphyrin and the C(60) moiety in the "tail-off" form. The charge separation rates and efficiencies are evaluated from the fluorescence lifetime studies. The charge separation via the singlet excited states of zinc porphyrin in the studied dyads is also confirmed by the quick rise-decay of the anion radical of the C(60) moiety within 20 ns. Furthermore, a long-lived ion pair with lifetime of about 1000 ns is also observed in the investigated zinc porphyrin-C(60) dyads.     

Evaluation of different tubing geometries for high-speed counter-current chromatography

Different tubing geometries were evaluated for use in high-speed counter-current chromatography. Standard round tubing was compared to rectangular and twisted rectangular tubing. The number of theoretical plates for a standard anthocyanin mixture from black currant was determined for each experiment. The results of twisted rectangular tubing were superior to a standard setup.     

Phlomisflavosides A and B, new flavonol bisglycosides from Phlomis spinidens

From the aerial parts of Phlomis spinidens, two new flavonol bisglycosides, phlomisflavosides A (1) and B (2), were isolated together with the known compounds, astragalin, isoquercitrin, lamiridoside, phlomoside A, shanzhiside methyl ester, 8-O-acetylshanzhiside methyl ester, phlorigidoside C, rodioloside (=salidroside), forsythoside B, citroside A and lariciresinol-4'-O-beta-D-glucoside. The structures of the new compounds were elucidated based on spectral and chemical evidence.     

Comproportionation reaction and hindered rotation of coordinated pyridine rings in an acetate-bridged tetraplatinum(II) cluster with pyridine-based ligands in the cluster plane

A series of pyridine-substituted derivatives of octaacetatotetraplatinum(II), [Pt4(CH3COO)8-n(L)2n]n+ (L= 4-dimethylaminopyridine (dmap), pyridine (py), 4-cyanopyridine (cpy); n = 1-4) were prepared, and the tetra- and octasubstituted forms (n = 2 and 4) were isolated. 1HNMR spectra showed that this type of cluster undergoes a comproportionation reaction. Reactions between clusters in which n = 0 and 2, n = 0 and 4, and n = 2 and 4 afforded Pt4 clusters with n = 1, 2, and 3, respectively, as a main product in acetonitrile. The dmap-substituted clusters, trans-[Pt4(CH3COO)6(dmap)4](ClO4)2 x 3CH3NO2 (3a(ClO4)2 x 3CH3NO2) and [Pt4(CH3COO)4(dmap)8](ClO4)4 x 4 H2O (5a(ClO4)4-4H2O), have been structurally characterized. Both 3a and 5a have a square-planar cluster core comprised of four PtII ions, and all eight out-of-plane coordination sites are occupied by acetate ligands in a bridging mode. In 5a, all of the in-plane sites are occupied by dmap ligands. In 3a, four dmap ligands occupy the coordination sites at the two mutually opposite edges of the square planar cluster skeleton, giving a trans tetrasubstituted form of [Pt4(CH3COO)8-] (1). In octasubstituted 5a, adjacent dmap ligands are so closely arranged that the Pt-N distances (2.20(3), 2.30(3) A) are longer than those in tetrasubstituted 3a (2.13(1), 2.15(1) A) and related Pt4 clusters. Furthermore, rotation of the dmap ligand about the Pt-N bond in 5a was restricted, and the rate constant of the rotation was 4.5s(-1) at 20 degrees C from dynamic NMR study. Cluster [Pt4(CH3COO)5(dmap)6]3+ (4a) also exhibited similar hindered rotation with the rate constants of 2.0s(-1), 12s(-1) and approximately 10(4)s(-1) at 20 degrees C depending on the coordination sites of the dmap ligands in 4a.     

Synthesis of benzimidazole derivatives as potential H1-antihistaminic agents

Several types of benzimidazole derivatives were prepared and were screened for H ₁-antihistaminic activity. Most of the compounds showed potent antihistaminic activity in vitro. Among them 2-[(1-piperazinyl)methyl]-benzimidazoles 14 and 2-[(1-homopiperazinyi)methyl]benzimidazoles 15 exhibited potent activity also in vivo.     

Effects of pressure and solvent on the diffusion of aromatic compounds through polymers

The diffusion of six azo and five anthraquinone derivatives through nylon 6, poly(ethylene terephthalate) and secondary cellulose acetate films were studied under high hydrostatic pressures of up to 3000 bar and at temperatures 80–130 °C, by analyzing the diffusion profiles yielded in a stacked multiple film, placed in the solution of the diffusant. It was found that the diffusion coefficient,D, of the diffusant decreased with increasing pressure, giving a linear relationship between InD and the pressure, the slope of which gave the activation volume for the diffusion,V . It was revealedV increased linearly with increasing intrinsic molecular volume of the diffusant,V _w , the slopes being different between the azo and the anthraquinone derivatives. The ratio ofV toV _w (V /V _w ) ranged from 0.13 to 0.93, depending in a sensitive manner on the degree of swelling of the polymer matrix which in turn was varied by the solvent. The overall results could be explained in accordance with the formulation,V _{f, local} +V =V _w , whereV _{f, local} represents the free volume contribution. It was proposed thatV _w is increased by solvation when the solvent is good for the diffusant.