Photostabilized chlorophyll a in mesoporous silica: adsorption properties and photoreduction activity of chlorophyll a

Chlorophyll a was adsorbed to mesoporous silica (FSM, folded-sheet mesoporous material) to form a chlorophyll-FSM conjugate, in which a nanometer-scale interaction between chlorophyll a molecules resembles a living plant leaf. The mesopores of FSM acted as nanoscale spaces not only for an interaction between chlorophyll molecules and the silica support but also for a nanoscale interaction between the absorbed chlorophyll molecules. These interactions contribute to photostability. An increase in the amount of chlorophyll adsorbed to the pores of FSM leads to an enhancement of the photostability accompanied by a shift in the absorbance maximum to a longer wavelength. The physiological function of the chlorophyll-FSM conjugate was explored as chlorophyll-FSM exhibited the photoinduced ability to catalyze the reduction of methyl viologen (an electron carrier). The evolution of hydrogen gas was observed for 14 h without deterioration when an aqueous suspension containing chlorophyll-FSM, methyl viologen, 2-mercaptoethanol (an electron donor), and platinum was illuminated with visible light.     

Water‐Exchange Mechanism for Zinc(II), Cadmium(II), and Mercury(II) Ions in Water as Studied by Umbrella‐Sampling Molecular‐Dynamics Simulations

Umbrella‐sampling molecular‐dynamics simulations were performed to investigate the water‐exchange reactions of zinc(II), cadmium(II), and mercury(II) ions in aqueous solution. The dissociation of a coordinating water molecule to the M? O distance at 3.34, 3.16, and 3.26 Å for Zn^II, Cd^II, and Hg^II, respectively, leads the system to a transition state. For Zn^II, the first hydration shell is occupied by five spectator water molecules in the transition state, indicating that the water‐exchange reaction proceeds via a dissociative mode of activation. In contrast, the number of spectator water molecules of 5.85 and 5.95 for Cd^II and Hg^II, respectively, suggests an associative exchange for these larger metal ions. The average M? O distance of the spectator molecules is shortened by 0.06 Å for the dissociative exchange of Zn^II, while it is elongated by 0.04 and 0.03 Å for Cd^II and Hg^II, respectively. The water‐exchange rate constants of 4.1×10⁸, 6.8×10⁸, and 1.8×10⁹ s^?1 are estimated for Zn^II, Cd^II, and Hg^II, respectively, at 298 K in terms of the transition‐state theory based on the assumption of a transmission coefficient of unity.     

Re-examination of the Reactivity of N-Carboxy Amino Acid Anhydrides 1. Polymerisation of Amino Acid NCAs in Acetonitrile and in the Solid State in Hexane

Ring-opening polymerisation of N-carboxy anhydrides of γ-benzyl-L- glutamate, L-alanine and L-leucine by a primary amine initiator in acetonitrile and in hexane was examined, with care taken to avoid contamination by moisture. The polymerisation of amino acid NCAs initiated by butylamine in hexane proceeded in the crystalline state (solid state) because the NCA crystals did not dissolve in hexane. Although amino acid NCAs were believed to polymerise completely in acetonitrile, polymerisation of the amino acid NCAs in acetonitrile was found to stop at around 20% conversion. As resulting polypeptides did not dissolve in acetonitrile, the polymer terminals were considered to be occluded in the polymer precipitate. On the other hand, each amino acid NCA was much more reactive in the solid state in hexane than in acetonitrile. Especially, L-leucine NCA showed remarkable reactivity in the solid state. The reactivity in the solid state was explained with reference to the crystal structure.     

Chlorophyllin coupled with polyethylene glycol: A potent photosensitizer

Chlorophyllin a prepared by the saponification of chlorophyll a was conjugated with α-(3-aminopropyl)-ω-methoxypoly(oxyethylene), PEG-NH₂, to form PEG-chlorophyllin through acid-amide bonds. PEG-chlorophyllin was readily soluble not only in aqueous solution but also in organic solvents. The absorption maxima of the conjugate were located at 657 nm and 418 nm in aqueous solution, and at 656 nm and 422 nm in benzene. The conjugate seems to be more stable toward light-illumination than uncoupled chlorophyllin. Furthermore, PEG-chlorophyllin possessed a potent photosensitizing activity to produce superoxide anion during the illumination, although chlorophyllin immediately lost its activity by light-illumination.     

Development of aromatic ethers as solvents for a calix[6]arene derivative and extraction of amino acids and proteins

Journal of Inclusion Phenomena and Macrocyclic Chemistry - Calixarene derivatives are excellent host compounds for ionic species in liquid–liquid extraction. However, many studies using...     

Structural characterization and formation kinetics of sitting-atop (SAT) complexes of some porphyrins with copper(II) ion in aqueous acetonitrile relevant to porphyrin metalation mechanism. Structures of aquacopper(II) and cu(II)-SAT complexes as determined by XAFS spectroscopy

The formation of the sitting-atop (SAT) complexes of 5,10,15,20-tetraphenylporphyrin (H(2)tpp), 5,10,15,20-tetrakis(4-chlorophenyl)porphyrin (H(2)t(4-Clp)p), 5,10,15,20-tetramesitylporphyrin (H(2)tmp), and 2,3,7,8,12,13,17,18-octaethylporphyrin (H(2)oep) with the Cu(II) ion was spectrophotometrically confirmed in aqueous acetonitrile (AN), and the formation rates were determined as a function of the water concentration (C(W)). The decrease in the conditional first-order rate constants with the increasing C(W) was reproduced by taking into consideration the contribution of [Cu(H(2)O)(an)(5)](2+) in addition to [Cu(an)(6)](2+) to form the Cu(II)-SAT complexes. The second-order rate constants for the reaction of [Cu(an)(6)](2+) and [Cu(H(2)O)(an)(5)](2+) at 298 K were respectively determined as follows: (4.1 +/- 0.2) x 10(5) and (3.6 +/- 0.2) x 10(4) M(-1) s(-1) for H(2)tpp, (1.15 +/- 0.06) x 10(5) M(-1) s(-1) and negligible for H(2)t(4-Clp)p, and (4.8 +/- 0.3) x 10(3) and (1.3 +/- 0.3) x 10(2) M(-1) s(-1) for H(2)tmp. Since the reaction of H(2)oep was too fast to observe the reaction trace due to the dead time of 2 ms for the present stopped-flow technique, the rate constant was estimated to be greater than 1.5 x 10(6) M(-1) s(-1). According to the structure of the Cu(II)-SAT complexes determined by the fluorescent XAFS measurements, two pyrrolenine nitrogens of the meso-substituted porphyrins (H(2)tpp and H(2)tmp) bind to the Cu(II) ion with a Cu-N(pyr) distance of ca. 2.04 A, while those of the beta-pyrrole-substituted porphyrin (H(2)oep) coordinate with the corresponding bond distance of 1.97 A. The shorter distance of H(2)oep is ascribed to the flexibility of the porphyrin ring, and the much greater rate for the formation of the Cu(II)-SAT complex of H(2)oep than those for the meso-substituted porphyrins is interpreted as due to a small energetic loss at the porphyrin deformation step during the formation of the Cu(II)-SAT complex. The overall formation constants, beta(n), of [Cu(H(2)O)(n)()(an)(6)(-)(n)](2+) for the water addition in aqueous AN were spectrophotometrically determined at 298 K as follows: log(beta(1)/M(-1)) = 1.19 +/- 0.18, log(beta(2)/M(-2)) = 1.86 +/- 0.35, and log(beta(3)/M(-3)) = 2.12 +/- 0.57. The structure parameters around the Cu(II) ion in [Cu(H(2)O)(n)(an)(6-n)](2+) were determined using XAFS spectroscopy.     

Potent estrogen agonists based on carborane as a hydrophobic skeletal structure. A new medicinal application of boron clusters

BACKGROUND: Carboranes (dicarba-closo-dodecaboranes) are a class of carbon-containing polyhedral boron-cluster compounds having remarkable thermal stability and exceptional hydrophobicity. Applications of the unique structural and chemical properties offered by icosahedral carboranes in boron neutron capture therapy have received increasing attention over the past 30 years. However, these features of carboranes may allow another application as a hydrophobic pharmacophore in biologically active molecules that interact hydrophobically with receptors. RESULTS: We have designed candidate estrogen-receptor-binding compounds having carborane as a hydrophobic skeletal structure and synthesized them. The most potent compound bearing a carborane cage exhibited activity at least 10-fold greater than that of 17beta-estradiol in the luciferase reporter gene assay. Estrogen receptor-alpha-binding data for the compound were consistent with the results of the luciferase reporter gene assay. The compound also showed potent in vivo effects on the recovery of uterine weight and bone loss in ovariectomized mice. CONCLUSION: Further development of the potent carborane-containing estrogenic agonists described here, having a new skeletal structure and unique characteristics, should yield novel therapeutic agents, especially selective estrogen receptor modulators. Furthermore, the suitability of the spherical carborane cage for binding to the cavity of the estrogen receptor-alpha ligand-binding domain should provide a basis for a similar approach to developing novel ligands for other steroid receptors.     

Ruthenium- and gold-catalysed sequential reactions: a straightforward synthesis of substituted oxazoles from propargylic alcohols and amides

A convenient and straightforward one-pot reaction of propargylic alcohols bearing a terminal alkyne moiety with amides by the sequential action of ruthenium and gold catalysts gives the corresponding substituted oxazoles in good yields with a complete regioselectivity.     

Studies of CO adsorption on Pt(100), Pt(410), and Pt(110) surfaces using density functional theory

Adsorption of CO on Pt(100), Pt(410), and Pt(110) surfaces has been investigated by density functional theory (DFT) method (periodic DMol(3)) with full geometry optimization and without symmetry restriction. Adsorption energies, structures, and vibrational frequencies of CO on these surfaces are studied by considering multiple possible adsorption sites and comparing them with the experimental data. The same site preference as inferred experiments is obtained for all the surfaces. For Pt(100), CO adsorbs at the bridge site at low coverage, but the atop site becomes most favorable for the c(2 x 2) structure at 1/2 monolayer. For Pt(410) (stepped surface with (100) terrace and (110) step), CO adsorbs preferentially at the atop site on the step edge at 1/4 monolayer, but CO populates also at other atop and bridge sites on the (100) terrace at 1/2 monolayer. The multiple possible adsorption sites probably correspond to the multiple states in the temperature-programmed desorption spectra for CO desorption. For Pt(110), CO adsorbs preferentially at the atop site on the edge for both the reconstructed (1 x 2) and the un-reconstructed (1 x 1) surfaces. When adjacent sites along the edge row begin to be occupied, the CO molecules tilt alternately by ca. 20 degrees from the surface normal in opposite directions for both the (1 x 2) and (1 x 1) surfaces.