A dramatic elongation of the lifetime of charge-separated state by complexation with yttrium triflate in ferrocene-anthraquinone linked dyad

Seven million times elongation of the lifetime of charge-separated state is attained in the presence of yttrium triflate [Y(OTf)3] in the photoinduced electron-transfer reaction of a ferrocene-anthraquinone dyad (Fc-AQ) with a rigid amide spacer in benzonitrile at 298 K as compared with the lifetime in its absence. Such remarkable elongation of the CS lifetime in the presence of Y(OTf)3 results from the strong binding of Y(OTf)3 with the AQ*- moiety of Fc+-AQ*-.     

Spectral, electrochemical, and photophysical studies of a magnesium porphyrin-fullerene dyad

A covalently linked magnesium porphyrin-fullerene (MgPo-C60) dyad was synthesized and its spectral, electrochemical, molecular orbital, and photophysical properties were investigated and the results were compared to the earlier reported zinc porphyrin-fullerene (ZnPo-C60) dyad. The ab initio B3LYP/3-21G(*) computed geometry and electronic structure of the dyad predicted that the HOMO and LUMO are mainly localized on the MgP and C60 units, respectively. In o-dichlorobenzene containing 0.1 M (n-Bu)4NClO4, the synthesized dyad exhibited six one-electron reversible redox reactions within the potential window of the solvent. The oxidation and reduction potentials of the MgP and C60 units indicate stabilization of the charge-separated state. The emission, monitored by both steady-state and time-resolved techniques, revealed efficient quenching of the singlet excited state of the MgP and C60 units. The quenching pathway of the singlet excited MgP moiety involved energy transfer to the appended C60 moiety, generating the singlet excited C60 moiety, from which subsequent charge-separation occurred. The charge recombination rates, k(CR), evaluated from nanosecond transient absorption studies, were found to be 2-3 orders of magnitude smaller than the charge separation rate, k(CS). In o-dichlorobenzene, the lifetime of the radical ion-pair, MgPo*+-C60*-, was found to be 520 ns which is longer than that of ZnPo*+-C60*- indicating better charge stabilization in MgPo-C60. Additional prolongation of the lifetime of MgPo*+-C60*- was achieved by coordinating nitrogenous axial ligands. The solvent effect in controlling the rates of forward and reverse electron transfer is also investigated.     

Efficient intracellular delivery of rifampicin to alveolar macrophages using rifampicin-loaded PLGA microspheres: effects of molecular weight and composition of PLGA on release of rifampicin

Monodispersed PLGA microspheres containing rifampicin (RFP) have been prepared by solvent evaporation method using a Shirasu porous glass (SPG) membrane. The microspheres were spherical and their average diameter was about 2 microm. The loading efficiency of rifampicin was dependent on the molecular weight of PLGA. The higher loading efficiency was obtained by the usage of PLGA with the lower molecular weight, which may be caused by the interaction of the amino groups of rifampicin with the terminal carboxyl groups of PLGA. PLGA with the monomer compositions of 50/50 and 75/25, of lactic acid/glycolic acid, were used in this study. From rifampicin-loaded PLGA microspheres formulated using PLGA with the molecular weight of 20,000, rifampicin was released with almost constant rate for 20 days after the lag phase was observed for the initial 7 days at pH 7.4. On the other hand, from rifampicin-loaded PLGA microspheres formulated using PLGA with the molecular weight of 5000 or 10,000, almost 90% of rifampicin-loaded in the microspheres was released in the initial 10 days. Highly effective delivery of rifampicin to alveolar macrophages was observed by the usage of rifampicin-loaded PLGA microspheres. Almost 19 times higher concentration of rifampicin was found to be incorporated in alveolar macrophages when rifampicin-loaded PLGA microspheres were added to the cell culture medium than when rifampicin solution was added.     

Ruthenium-catalyzed formal [4 + 2] cycloaddition of alkynes with alkenes: formation of cyclohexenedicarboxylates via isomerization of alkynes and successive Diels-Alder reaction

Formal [4 + 2] cycloaddition of alkynes with electron-deficient alkenes, which affords 3,6-dialkyl-4-cyclohexene-1,2-dicarboxylates, was achieved using Ru(η⁶-1,3,5-cyclooctatriene)(η²-dimethyl fumarate)₂ as a catalyst. The reaction mechanism consists of two steps, isomerization of an alkyne to conjugated dienes and successive Diels-Alder reaction of the generated dienes with an electron-deficient alkene.     

Separation of enantiomers on anion exchangers modified with heparin in liquid chromatography

Hepatitis B virus surface antigen (HBsAg) particles were efficiently adsorbed (retained) on a Sulfate-cellulose (S-C) bead column, and then desorbed with sodium chloride solutions (0.5-3.0 M). The HBsAg particles were not efficiently retained onto either sulfopropyl-agarose (SP-A) or quaternary amine-agarose (Q-A) at pH 4.5, 6 and 8. The size-exclusion curve showed that proteins of molecular mass higher than ca. 20,000 cannot penetrate into the pores of S-C beads. The dynamic binding capacity (DBC) values of lysozyme (ca. 7 mg/ml-gel) and of gamma-globulin (ca. 3 mg/ml gel) for S-C did not depend on the flow velocity while the DBC of gamma-globulin for SP-A decreased sharply with an increase in flow velocity. These results indicated that very large molecules are adsorbed only onto the surface of S-C, which resulted in fast adsorption-desorption rates although the equilibrium adsorption capacity is lower than conventional porous gel beads. Because of the rapid adsorption rate, the DBC values of gamma-globulin for S-C at high flow-rate regions are similar to those for SP-A. Bovine serum albumin was not adsorbed onto S-C. As this can not be explained by a simple electrostatic interaction mechanism, molecular recognition of S-C might be different from the agarose-based ion-exchange beads.     

Spectroelectrochemical studies on mixed-valence states in a cyanide-bridged molecular square, [Ru(II)(2)Fe(II)(2)(mu-CN)(4)(bpy)(8)](PF6)(4).CHCl(3).H(2)O

A cyanide-bridged molecular square of [Ru(II) (2)Fe(II) (2)(mu-CN)(4)(bpy)(8)](PF(6))(4).CHCl(3).H(2)O, abbreviated as [Ru(II) (2)Fe(II) (2)](PF(6))(4), has been synthesised and electrochemically generated mixed-valence states have been studied by spectroelectrochemical methods. The complex cation of [Ru(II) (2)Fe(II) (2)](4+) is nearly a square and is composed of alternate Ru(II) and Fe(II) ions bridged by four cyanide ions. The cyclic voltammogram (CV) of [Ru(II) (2)Fe(II) (2)](PF(6))(4) in acetonitrile showed four quasireversible waves at 0.69, 0.94, 1.42 and 1.70 V (vs. SSCE), which correspond to the four one-electron redox processes of [Ru(II) (2)Fe(II) (2)](4+) right arrow over left arrow [Ru(II) (2)Fe(II)Fe(III)] (5+) right arrow over left arrow [Ru(II) (2)Fe(III) (2)](6+) right arrow over left arrow [Ru(II)Ru(III)Fe(III) (2)](7+) right arrow over left arrow [Ru(III) (2)Fe(III) (2)](8+). Electrochemically generated [Ru(II) (2)Fe(II)Fe(III)](5+) and [Ru(II) (2)Fe(III) (2)](6+) showed new absorption bands at 2350 nm (epsilon =5500 M(-1) cm(-1)) and 1560 nm (epsilon =10 500 M(-1) cm(-1)), respectively, which were assigned to the intramolecular IT (intervalence transfer) bands from Fe(II) to Fe(III) and from Ru(II) to Fe(III) ions, respectively. The electronic interaction matrix elements (H(AB)) and the degrees of electronic delocalisation (alpha(2)) were estimated to be 1090 cm(-1) and 0.065 for the [Ru(II) (2)Fe(II)Fe(III) (2)](5+) state and 1990 cm(-1) and 0.065 for the [Ru(II) (2)Fe(III) (2)](6+) states.     

Hydration processes of electrolyte anions and cations on pt(111), Ir(111), Ru(001) and Au(111) surfaces: coadsorption of water molecules with electrolyte ions

Water adsorption on Pt( 111) and Ru(001) treated with oxygen, hydrogen chloride and sodium atom at 20 K has been studied by Fourier transform infrared spectroscopy, scanning tunneling microscopy and surface X-ray diffraction. Water molecules chemisorb predominantly on the sites of the electronegative additives, forming hydrogen bonds. Three types of hydration water molecules coordinate to an adsorbed Na atom through an oxygen lone pair. In contrast, water molecules adsorb on electrode surfaces in a simple way in solution. In 1 mM CuSO4 + 0.5 M H2SO4 solution on an Au(111) electrode surface, water molecules coadsorb not only with sulfuric acid anions through hydrogen bonding but also with copper, over wide potential ranges. In the first stage of underpotential deposition (UPD), each anion is accommodated by six copper hexagon (honeycomb) atoms on which water molecules dominate. At any UPD stage water molecules interact with both the copper atom and sulfuric acid anions on the Au(111) surface. Water molecules also coadsorb with CO molecules on the surface of 2 x 2-2CO-Ru(001). All of the hydration water molecules chemisorb weakly on the surfaces. There appears to be a correlation between the orientation of hydrogen bonding water molecules and the electrode potential.     

Cloud point extraction of iron(III) and vanadium(V) using 8-quinolinol derivatives and Triton X-100 and determination of 10(-7)moldm(-3) level iron(III) in riverine water reference by a graphite furnace atomic absorption spectroscopy

The cloud point extraction behavior of iron(III) and vanadium(V) using 8-quinolinol derivatives (HA) such as 8-quinolinol (HQ), 2-methyl-8-quinolinol (HMQ), 5-butyloxymethyl-8-quinolinol (HO₄Q), 5-hexyloxymethyl-8-quinolinol (HO₆Q), and 2-methyl-5-octyloxymethyl-8-quinolinol (HMO₈Q) and Triton X-100 solution was investigated. Iron(III) was extracted with HA and 4% (v/v) Triton X-100 in the pH range of 1.70-5.44. Above pH 4.0, more than 95% of iron(III) was extracted with HQ, HMQ, and HMO₈Q. Vanadium(V) was also extracted with HA and 4% (v/v) Triton X-100 in the pH range of 2.07-5.00, and the extractability increased in the following order of HMQ < HQ < HO₄Q < HO₆Q. The cloud point extraction was applied to the determination of iron(III) in the riverine water reference by a graphite furnace atomic absorption spectroscopy. When 1.25 × 10⁻³ M HMQ and 1% (v/v) Triton X-100 were used, the found values showed a good agreement with the certified ones within the 2% of the R.S.D. Moreover, the effect of an alkyl group on the solubility of 5-alkyloxymethyl-8-quinolinol and 2-methyl-5-alkyloxymethyl-8-quinolinol in 4% (v/v) Triton X-100 at 25 °C was also investigated.     

Structure of activated complex of CO2 formation in a CO + O2 reaction on Pd(110) and Pd(111)

Examinations of CO2 formed during steady-state CO oxidation reactions were performed using infrared (IR) chemiluminescence. The CO2 was formed using a molecular-beam method over Pd(110) and Pd(111). The CO2 formation rate is temperature dependent under various partial pressure conditions. The temperature of the maximum formation rate is denoted as TSmax. Analyses of IR emission spectra at surface temperatures higher than TSmax showed that the average vibrational temperature (TVAV) is higher for Pd(111) than for Pd(110). The antisymmetric vibrational temperature (TVAS) is almost equal on both surfaces. These results suggest that the activated CO2 complex is more bent on Pd(111) and straighter on Pd(110). Furthermore, the difference in the TVAV value was small for surface temperatures less than TSmax. The TVAS value was much higher than TVAV on both surfaces. These phenomena were observed only when the surface temperature was lower than TSmax: they became more pronounced at lower temperatures, suggesting that the activated complex of CO2 formation is much straighter on both Pd surfaces than that observed at higher surface temperatures. Combined with kinetic results, the higher CO coverage at the lower surface temperatures is inferred to be related to the linear activated complex of CO2 formation.     

Highly effective, easily accessible screw-sense-determining end group in the asymmetric polymerization of 1,2-diisocyanobenzenes

Enantiopure helical poly(quinoxaline-2,3-diyl) was formed stereoselectively in the polymerization of 1,2-diisocyanobenzene using a new organopalladium initiator bearing the (4S,5S)-N-acyl-4,5-dihydro-4,5-diphenyl-1H-imidazol-2-yl group as the polymer-end screw-sense-determinant.