Synthesis of poly(vinylene-arsine)s: alternating radical copolymerization of arsenic atomic biradical equivalent and phenylacetylene

Novel organoarsenic polymers, poly(vinylene-arsine)s, were synthesized by a free-radical alternating copolymerization of phenylacetylene with cyclooligoarsines as an atomic biradical equivalent. The polymerization between pentamethylpentacycloarsine (1a) or hexaphenylhexacycloarsine (1b) with phenylacetylene (2) in the presence of a catalytic amount of AIBN (in benzene; refluxing; for 12 h) gave the corresponding poly(vinylene-arsine)s. The obtained polymers were soluble in common organic solvents such as THF, chloroform, and benzene. From gel permeation chromatographic analysis (chloroform, PSt standards), the number-average molecular weights of the polymers from 1a and 1b were found to be 11500 and 3900, respectively. The structures of the polymers were supported by 1H and 13C NMR spectroscopies. The corresponding polymer was also obtained by irradiation of a benzene solution of 1a and 2 with xenon lamp at room temperature. After the polymer from 1a was stirred vigorously with 30% H2O2, the 1H NMR spectrum of the polymer showed the methyl proton that was assigned to As(III)-Me, suggesting the insensitivity of the trivalent state arsenic in the main chain to the oxidation. The structures and the molecular weights of the polymers were insensitive to the feed ratio of the monomers. This result indicates that the addition of the arsenic radical to phenylacetylene was a rate-determining step in the copolymerization.     

Host-guest interactions in the supramolecular incorporation of fullerenes into tailored holes on porphyrin-modified gold nanoparticles in molecular photovoltaics

Novel gold nanoparticles modified with a mixed self-assembled monolayer of porphyrin alkanethiol and short-chain alkanethiol were prepared (first step) to examine the size and shape effects of surface holes (host) on porphyrin-modified gold nanoparticles. The porphyrin-modified gold nanoparticles with a size of about 10 nm incorporated C60 molecules (guest) into the large, bucket-shaped holes, leading to the formation of a supramolecular complex of porphyrin-C60 composites (second step). Large composite clusters with a size of 200-400 nm were grown from the supramolecular complex of porphyrin-C60 composites in mixed solvents (third step) and deposited electrophoretically onto nanostructured SnO2 electrodes (fourth step). Differences in the porphyrin:C60 ratio were found to affect the structures and photoelectrochemical properties of the composite clusters in mixed solvents as well as on the SnO2 electrodes. The photoelectrochemical performance of a photoelectrochemical device consisting of SnO2 electrodes modified with the porphyrin-C60 composites was enhanced relative to a reference system with small, wedged-shaped surface holes on the gold nanoparticle. Time-resolved transient absorption spectroscopy with fluorescence lifetime measurements suggest the occurrence of ultrafast electron transfer from the porphyrin excited singlet states to C60 or the formation of a partial charge-transfer state in the composite clusters of supramolecular complexes formed between porphyrin and C60 leading to efficient photocurrent generation in the system. Elucidation of the relationship between host-guest interactions and photoelectrochemical function in the present system will provide valuable information on the design of molecular devices and machines including molecular photovoltaics.     

Constituents of Crinoidea, 4. Isolation and structure of ceramides and glucocerebrosides from the feather star Comanthus japonica

Five ceramides, JC-1-JC-5, and four glucocerebrosides, JCer-1-JCer-4, have been isolated from their parent ceramide and glucocerebroside molecular species JC and JCer obtained from the less polar lipid fraction of the chloroform/methanol extract of the feather star Comanthus japonica. The structures of these sphingolipids have been determined on the basis of chemical and spectroscopic evidence. Reversed-phase HPLC was effective at isolating these sphingolipids, revealing very close resemblance in their structures. JC-1, JC-3, JC-4, JC-5 and JCer-2, JCer-4 are newly found ceramides and glucocerebrosides, respectively.     

Evaluation of the adsorption affinity of proteins to calcium hydroxyapatites by desorption and pre-adsorption methods

The adsorption affinity of bovine serum albumin (BSA) and lysozyme (LSZ) to calcium hydroxyapatite (CaHAP) was evaluated by desorption and two step adsorption methods. These experiments were carried out at 15°C in a 1×10⁻⁴ mol dm⁻³ KCl solution of pH 6.0. BSA molecules were scarcely desorbed, exhibiting an irreversible adsorption of BSA, though LSZ slightly desorbed. This result supports our previous findings that LSZ adsorbs weakly onto phosphate ions exposed on ac or bc faces of CaHAP while BSA adsorbs strongly onto positively charged sites on ac or bc faces of CaHAP. The amount of adsorbed LSZ was markedly increased by the pre-adsorption of BSA, where LSZ was adsorbed onto BSA-covered CaHAP. On the other hand, the amount of adsorbed BSA was not changed by the pre-adsorption of LSZ. In both pre-adsorption systems it was confirmed by an HPLC method that no protein molecule pre-adsorbed was desorbed after the post-adsorption procedure. Therefore, it was interpreted that the enhancement of adsorption of positively charged LSZ is induced by an electrostatic attractive force through pre-adsorption of negatively charged BSA molecules with a high coverage. However, since the coverage of LSZ onto CaHAP is considerably low, no stimulation of BSA adsorption occurred on the LSZ-covered surface. The formation of double protein adsorbed layers consisting of pre- and post-adsorbed proteins was proposed.     

Analysis of phenothiazines in human body fluids using disk solid-phase extraction and liquid chromatography

Seven phenothiazine derivatives, perazine, perphenazine, prochlorperazine, propericiazine, thioproperazine, trifluoperazine, and flupentixol, have been found to be extractable from human plasma and urine samples using disk solid-phase extraction (SPE) with an Empore C18 cartridge. Human plasma and urine (1 mL each) containing the 7 phenothiazine derivatives were mixed with 2 mL of 0.1M NaOH and 7 mL distilled water and then poured into the disk SPE cartridges. The drugs were eluted with 1 mL chloroform- acetonitrile (8 + 2) and determined by liquid chromatography with ammonium formate/formic acid-acetonitrile gradient elution. The detection was performed by ultraviolet absorption at 250 nm. The separation of the 7 phenothiazine derivatives from each other and from impurities was generally satisfactory using a SymmetryShield RP8 column (150 x 2.1 mm id, 3.5 microm particle size). The recoveries of the 7 phenothiazine derivatives spiked into plasma and urine samples were 64.0-89.9% and 65.1-92.1%, respectively. Regression equations for the 7 phenothiazine derivatives showed excellent linearity, with detection limits of 0.021-0.30 microg/mL for plasma and 0.017-0.30 microg/mL for urine. The within-day and day-to-day coefficients of variation for both samples were commonly below 9.0 and 14.9%, respectively.     

Preparation and characterization of carbonated barium-calcium hydroxyapatite solid solutions

Particles of carbonated barium-calcium hydroxyapatite solid solutions (BaCaHap) with different Ba/(Ba+Ca) (X(Ba)) atomic ratios were prepared by a wet method at 100 degrees C and characterized by various means. The crystal phases and structures of the products strongly depended on the composition of the starting solution, that is, the Ba/(Ba+Ca) atomic ratio ([X(Ba)]) and H3PO4 concentration ([H3PO4]) in the solution. BaCaHap with X(Ba)0.43 could be prepared at [X(Ba)]0.7 by changing [H3PO4], but could never be obtained at [X(Ba)]=0.8-0.95 regardless of [H3PO4]. The carbonated calcium hydroxyapatite particles prepared at [X(Ba)]=0 were fine and short rod-shaped particles (ca. 14x84 nm). With increasing [X(Ba)] from 0 to 0.8, the particles obtained became large spherical agglomerates. The carbonated barium hydroxyapatite particles formed at [X(Ba)]=1 were long rod-shaped agglomerates (ca. 0.2x2 microm) of fine primary particles. The amount of CO2 adsorbed irreversibly on a series of BaCaHaps showed a minimum at (Ba+Ca)/(P+C) atomic ratio of around 1.56, which agreed well with the minimum cation/P ratio obtained for the other hydroxyapatites, as already reported.     

Synthesis of (S-(−)-wybutine,the fluorescent minor base from yeast phenylalanine transfer ribonucleic acids

The Wittig reaction of 1-benzyl-7-formylwye (12) with (R)-[2-carboxy-2-[(methoxycarbonyl)amino]ethyl]triphenylphosphonium chloride (8) followed by successive methylation and reduction gave (-)-wybutine [(S)-1a].     

Intermediate state during the crystal transition in aspartame, studied with thermal analysis, solid-state NMR, and molecular dynamics simulation

Aspartame (L-alpha-aspartyl-L-phenylalanine methyl ester) is a dipeptide sweetener about 200 times as sweet as sugar. It exists in crystal forms such as IA, IB, IIA, and IIB, which differ in crystal structure and in the degree of hydration. Among these, IIA is the most stable crystal form, and its crystal structure has been well determined (Hatada et al., J. Am. Chem. Soc., 107, 4279-4282 (1985)). To elucidate the structural factors of thermal stability in the IIA form of aspartame and to examine the physical process in the crystal transformation between the IIA and IIB forms, we performed a thermal analysis and solid-state NMR measurements. We found that a quasi-stable intermediate state exists in the transformation, and it has the same crystal lattice as the usual IIA form, despite the dehydration from 1/2 mol to 1/3 mol per 1 mol of aspartame. The results of the energy component analysis and the molecular dynamics simulation suggest that the entropic effect promotes the generation of the intermediate state, which is presumably caused by the evaporation of the water of crystallization and the increase of molecular motion in aspartame. Thus, the thermal stability of the IIA form is attributable to a structural property, i.e., the crystal lattice itself is retained during the above dehydration. Moreover, the molecular dynamics simulations suggest that the aspartame molecules have two kinds of conformational flexibility in the intermediate state.     

Synthesis of human renin inhibitory peptides, angiotensinogen transition-state analogs containing a retro-inverso amide bond

The experimental details for the synthesis of human renin inhibitors are described. In order to avoid metabolic degradation of the Phe-His (P3-P2) amide bond in transition-state analogs, structurally modified acyl residues (P4-P3) were incorporated into the inhibitors. Compound 1a, which contained 2-(1-naphthylmethyl)-3-(N-phenethylcarbamoyl)propionyl residue (P4-P3) with a retro-inverso amide bond, L-histidine, and norstatine isoamylamide residue (P1-P1) as a transition-state mimic, had potent human renin inhibitory activity, and it lowered blood pressure when administered orally to common marmosets.     

Synthesis and photophysical evaluations of β-fused uracil-porphyrin derivatives

New β-fused uracil-porphyrin conjugates were synthesized by the tetramerization of uracil-pyrroles under acidic conditions. Two different synthetic approaches were systematically studied in order to evaluate their efficiency, as well as the possibility to obtain a single regioisomer. Metallation effects were studied for aggregation in solution, and preliminary photophysical experiments were also performed in order to evaluate the potential of these new compounds.