Synthesis, properties, and crystal structure of a novel anthracene-bridged molybdenum-zinc porphyrin dimer

The synthesis and properties of novel anthracene-bridged porphyrin dimers having an oxomolybdenum(V) porphyrin unit, H(2)(DPA)[Mo(V)O(OMe)] (1) and (DPA)[Mo(V)O(OMe)][Zn(II)(MeOH)] (2), and the relevant monomer porphyrin complexes Mo(V)O(MPP)OMe (3) and Zn(II)(MPP) (4) are presented. An oxomolybdenum(V) unit was introduced into one of the two porphyrins in DPA to give 1, which has a free-base porphyrin unit. By introducing a zinc(II) ion to the free-base part, a mixed-metal complex of 2 was prepared and isolated. The structure of 2 was analyzed by X-ray crystallography (2.(7)/(6)CH(2)Cl(2), triclinic, P(-)1 (no. 2), a = 15.2854(12) A, b = 19.9640(15) A, c = 13.6915(12) A, alpha = 90.968(3), beta = 113.108(4), gamma = 96.501(4), Z = 2, R1 = 9.9, wR2 = 19.2). The structure of 2 demonstrated that a methanol is stably coordinated to the Zn(II) ion with the aid of a hydrogen bond to the methoxo ligand on the Mo(V) ion in the binding pocket of DPA. The electrochemical measurements of 2 suggested that the methanol was kept in the pocket of DPA in solution even at the reduced state of the molybdenum ion.     

Synthetic oligopeptides as isoelectric point markers for capillary isoelectric focusing with ultraviolet absorption detection

Sixteen peptides (trimers to hexamers) were designed for use as a set of pI markers for capillary isoelectric focusing (CIEF). Each peptide contains one tryptophan residue for detection by UV absorption and other amino acid residues having ionic side chains, which are responsible for focusing to its pI. The pIs of these peptides were determined by slab-gel IEF using commercial carrier ampholytes. The focused peptides in the gel were detected by absorption measurement at 280 nm using a scanning densitometer and the pH gradient was determined by measuring the pH of the gel using an oxidized metal membrane electrode. The pI values of the peptides ranged from 3.38 to 10.17. The obtained values agreed well with the predicted ones, which were calculated based on amino acid compositions, with root mean square differences of 0.15 pH unit. The peptides were detected at 280 nm as very sharp peaks when separated by CIEF. The pI values of some standard proteins were redetermined by CIEF by using this set of peptide pI markers and the values agreed closely with those reported previously. The sharp focusing, stability, high purity and high solubility of these synthetic pI markers should facilitate the profiling of a pH gradient in a capillary and the determination of the pI values of proteins.     

Photoelectrochemistry of p-type Cu2O semiconductor electrode in ionic liquid

We investigated the photoelectrochemical characteristics and photo-stability of Cu₂O layered on a copper plate using a hydrophobic ionic liquid. Our findings revealed that Cu₂O is stable under white light irradiation, provided water is removed from the electrolyte. Methyl viologen derivative, a well-established electron acceptor, was introduced to the ionic liquid electrolyte, allowing the photo-induced electron transfer reaction at the Cu₂O/electrolyte interface to be characterized. The methyl viologen derivative exhibited two distinct redox reactions at −0.56 V and −0.98 V vs. Ag/AgCl, clearly indicating that no dimer formation or co-proportionation reaction occurred. The excessive photocurrents being continuously generated resulted from a viable photo-induced electron transfer reaction from the Cu₂O to the acceptor. However, in contrast, the reduction of the Cu₂O by water in the aqueous solution causes this electron transfer to be inhibited. We further demonstrate that these findings are vital to understanding the role of the Cu₂O and its photoelectrochemical applications.     

The role of carbon dioxide in chemoselective hydrogenation of halonitroaromatics over supported noble metal catalysts in supercritical carbon dioxide

Chemoselective hydrogenation of halogenated nitrobenzenes over Pt/C catalysts proceeds effectively in supercritical carbon dioxide (scCO2) to produce halogenated anilines with excellent selectivity; the rate of the hydrogenation of nitro groups is markedly enhanced in scCO2 compared to the neat reaction, and the dehalogenation reaction is significantly suppressed.     

Simultaneous determination of radionuclides separable into natural decay series by use of time-interval analysis

A delayed coincidence method, time-interval analysis (TIA), has been applied to successive – decay events on the millisecond time-scale. Such decay events are part of the ²²⁰Rn²¹⁶Po (T_1/2 145 ms) (Th-series) and ²¹⁹Rn²¹⁵Po (T_1/2 1.78 ms) (Ac-series). By using TIA in addition to measurement of ²²⁶Ra (U-series) from -spectrometry by liquid scintillation counting (LSC), two natural decay series could be identified and separated. The TIA detection efficiency was improved by using the pulse-shape discrimination technique (PSD) to reject -pulses, by solvent extraction of Ra combined with simple chemical separation, and by purging the scintillation solution with dry N₂ gas. The U- and Th-series together with the Ac-series were determined, respectively, from alpha spectra and TIA carried out immediately after Ra-extraction. Using the ²²¹Fr²¹⁷At (T_1/2 32.3 ms) decay process as a tracer, overall yields were estimated from application of TIA to the ²²⁵Ra (Np-decay series) at the time of maximum growth. The present method has proven useful for simultaneous determination of three radioactive decay series in environmental samples.     

Chiral self-dimerization of vanadium complexes on a SiO2 surface: the first heterogeneous catalyst for asymmetric 2-naphthol coupling

The self-dimerized chiral assembly of vanadium-Schiff-base complexes was found to occur on a SiO2 surface and to be the first heterogeneous catalyst for the asymmetric oxidative coupling of 2-naphthol with 100% selectivity and 90% enantioselectivity.     

An improvement in the bending ability of a hinged trisaccharide with the assistance of a sugar-sugar interaction

Hinged di- and trisaccharides incorporating 2,4-diamino-beta-D-xylopyranoside as a hinge unit (Hin) were synthesized. Bridging of the diamino group of Hin by carbonylation or chelation to a metal ion results in a conformational change from (4)C1 to (1)C4, which in turn causes a bending of the oligosaccharides. In this study, the bending abilities of the hinged oligosaccharides were compared, in terms of the reactivities toward carbonylation and chelation. Di- or trisaccharides containing a 6-O-glycosylated mannopyranoside or galactopyranoside at their reducing ends had bending abilities similar to that of the Hin monosaccharide, probably because there were neither attractive nor repulsive interactions between the reducing and nonreducing ends. However, when Hin was attached at O2 of methyl mannopyranoside (Man alphaMe), the bending ability was dependent on the nonreducing sugar and the reaction conditions. Typically, a disaccharide--Hin beta(1,2)Man alphaMe--was difficult to bend under all the tested reaction conditions, and the bent population in the presence of Zn(II) was only 4%. On the other hand, a trisaccharide--Man alpha(1,3)Hin beta(1,2)Man alphaMe--was bent immediately after the addition of Zn(II) or Hg(II), and the bent population reached 75%, much larger than those of all the other hinged trisaccharides ever tested (<40%). This excellent bending ability suggests an attractive interaction between the reducing and nonreducing ends. The extended conformation was recovered by the addition of triethylenetetramine, a metal ion chelator. Reversible, quick, and efficient bending of the hinged trisaccharide was thus achieved.     

Absolute stereochemistry of citrinadins a and B from marine-derived fungus

[Structure: see text]. Citrinadin A (2) is a pentacyclic indolinone alkaloid isolated from the cultured broth of a fungus, Penicillium citrinum, which was separated from a marine red alga. The absolute stereochemistry of the pentacyclic core in 2 and its new congener, citrinadin B (1), was elucidated by analysis of the ROESY spectrum for the chlorohydrin derivative (3) of 1 as well as comparison of the electronic circular dichroism (ECD) spectra for 1 and 2 with those of known spirooxiindole alkaloids. On the other hand, the absolute configuration at C-21 bearing an epoxide ring was assigned as S by comparison of the vibrational circular dichroism (VCD) spectra of 1 with those of model compounds 2S- and 2R-2,3-epoxy-3,3-dimethyl-1-phenylpropan-1-one (4a and 4b, respectively).     

Water‐Soluble N‐(n‐Fatty acyl)chitosans

Chitosan was partially N‐acylated by treatment with n‐fatty acid anhydrides in a homogeneous solution in 2 vol.‐% aqueous acetic acid‐methanol (1:2 v/v). The degree of substitution (d.s.) for N‐acyl groups in the water‐soluble N‐acylchitosan derivatives was in the range of 0.42–0.82 for N‐acetyl, 0.37–0.76 for N‐propionyl, 0.52–0.71 for N‐butyryl and 0.54–0.64 for N‐pentanoyl and ca. 0.58 for N‐hexanoyl, respectively.

Water soluble N‐(n‐fatty acyl)chitosans.