Crystal structure and peroxidase activity of myoglobin reconstituted with iron porphycene

The incorporation of an artificially created metal complex into an apomyoglobin is one of the attractive methods in a series of hemoprotein modifications. Single crystals of sperm whale myoglobin reconstituted with 13,16-dicarboxyethyl-2,7-diethyl-3,6,12,17-tetramethylporphycenatoiron(III) were obtained in the imidazole buffer, and the 3D structure with a 2.25-A resolution indicates that the iron porphycene, a structural isomer of hemin, is located in the normal position of the heme pocket. Furthermore, it was found that the reconstituted myoglobin catalyzed the H2O2-dependent oxidations of substrates such as guaiacol, thioanisole, and styrene. At pH 7.0 and 20 degrees C, the initial rate of the guaiacol oxidation is 11-fold faster than that observed for the native myoglobin. Moreover, the stopped-flow analysis of the reaction of the reconstituted protein with H2O2 suggested the formation of two reaction intermediates, compounds II- and III-like species, in the absence of a substrate. It is a rare example that compound III is formed via compound II in myoglobin chemistry. The enhancement of the peroxidase activity and the formation of the stable compound III in myoglobin with iron porphycene mainly arise from the strong coordination of the Fe-His93 bond.     

Thickness-dependent photocatalytic performance of ZnO nanoplatelets

In this paper, we report the large-scale synthesis of ZnO nanoplatelets as thin as 10 nm. The nanoplatelets show higher efficiency in photodegrading organic dyes than ZnO nanorods do, and for the nanoplatelets, the thinner they are, the higher the performance. The photocatalytic decomposition of organic dyes (eosin B) by ZnO nanoplatelets compares favorably to the performances of ZnS porous nanoparticles and commercial Degussa P25 titania particles. This finding may have significant implications in the environment remediation and the fabrication of functional nanodevices.     

Ring transformation of pyrimidines to pyridines. Synthesis of 4-alkylaminopyridin-2-ones by alkaline hydrolysis of 6-(2-dimethylaminovinyl)uracils

Alkaline hydrolysis of 1,3-disubstituted 6-(2-dimethylaminovinyl)uracils 2 induced a novel ring transformation giving 4-alkylaminopyridin-2-ones 3 via ring-opening and ring-closure processes. The 4-methylamino-3-nitropyridin-2-one ( 3a ) thus obtained was employed for the synthesis of 3-deazahypoxanthine derivative 8. 4-Alkylamino-3-cyanopyridin-2-ones 11 , ricinine analogs, were also prepared by the reaction of 4-chloro-3-cyano-1-methylpyridin-2-one ( 10 ) with amines.     

Photoisomerization of 1,2-diphenylcyclopropane sensitized by polypeptides containing naphthalene groups in their side chain

Poly(γ-1-naphthylmethyl L - and DL -glutamate) (PNLG and PNDLG) and copolypeptides of γ-1-naphthylmethyl L -glutamate and γ-benzyl-L -glutamate were used as sensitizers for isomerization of trans-1,2-diphenylcyclopropane. Quantum yields relative to that of 1-methylnaphthalene were measured in dichloroethane (DCE) and dichloroacetic acid (DCA). The relative quantum yield in DCE was smaller than unity for PNLG, but greater than unity for PNDLG and copolypeptides. The result is discussed in terms of increased effective collisional radius and energy trapping by excimer formation. The relative quantum yields in DCA were close to unity except for the copolypeptides of higher γ-benzyl L -glutamate content. This suggests that the naphthalene groups act in the same manner as their monomeric counterparts in the random conformation and that the greater proportion of γ-benzyl L -glutamate in the copolypeptides lowers the quantum efficiency because trans-1,2-diphenylcyclopropane must penetrate through the polymeric medium in order to encounter the excited naphthalene.     

Synthetic studies on β-lactam antibiotics. 19. Synthesis of 3′-nor-type 1-oxacephems

Synthesis of optically active 3′-nor-type 1-oxacephems from 6-APA was described. $\text{p}$-Nitrobenzyl 7β-amino-3-chloro-7α-methoxy-1-oxa-3-cephem-4-carboxylate $\text{39}$ was also prepared.     

Asymmetric Induction at Remote Quaternary Centers of Cyclohexadienones by Rhodium‐Catalyzed Conjugate Hydrosilylation

The enantioselective desymmetrizing conjugate hydrosilylation of prochiral differently γ,γ‐disubstituted cyclohexadienone derivatives 2 to furnish the corresponding cyclohexenones 4 with a remote chiral all‐carbon quaternary center at the γ position is described. Chiral rhodium–bis(oxazolinyl)phenyl complexes 1 were effective catalysts for this transformation. This catalytic system was extended to the asymmetric transformation of spirocarbocyclic cyclohexadienones 5 to give the corresponding products 6 with high enantiomeric ratios.     

C2-substituted 8-aza-7-deaza-2′-deoxyadenosines as environmentally sensitive fluorescent nucleosides for discriminating apurinic/apyrimidinic sites in DNA duplex

We synthesized various C2-naphthylethynylated 8-aza-7-deaza-2′-deoxyadenosines 1a–1c as novel environmentally sensitive fluorescent (ESF) purine nucleosides. In particular, the N,N-dimethylamino-substituted derivative 1c exhibits a remarkably high solvatochromicity (Δ$\mathrm{\lambda }$ = 111 nm). 1c-containing oligodeoxynucleotide (ODN) probes clearly discriminated an apurinic/apyrimidinic site (AP site) in the complementary strand via a change in emission wavelength and intensity when hybridized with a target ODN.     

Water-soluble porphyrins appending platinum(II) complexes as binders for synthetic nucleic acid polymers

Water-soluble porphyrins containing four platinum(II) complexes per molecule, [5alpha,10beta,15alpha,20beta-tetrakis(2-trans-(alpha,beta,alpha,beta-trans-Pt) and cis-(alpha,beta,alpha,beta-cis-Pt) [PtCl(NH(3))(2)]N-2-aminophenylporphyrin)], were synthesized and characterized. The binding of synthetic nucleotide polymers (poly(dG)-poly(dC), poly(dA)-poly(dT)) to the porphyrins was examined spectrophotometrically in aqueous solution. UV-vis spectral data suggested that these porphyrins bind to the nucleic acids by coordinative and Coulomb interactions.     

γ-Radiolysis of 2′-deoxy-5-fluorouridine derivatives with sulfur-containing substituents

2′-Deoxy-5-fluorouridine (5-FUdR) derivatives having various types of sulfur-containing substituents at the 5′-O-position were synthesized and their γ-radiolyses were studied in aqueous solutions. The γ-radiolysis of compounds having 1,3-dithiol-2-yl and 1,3-dithian-2-yl substituents at the 5′-O-position efficiently gave 5-FUdR, specifically via the attack of hydroxyl radical. On the other hand, the γ-radiolysis of a compound having a sulfonylmethyl substituent at the 5′-O-position gave less efficiently 5-FUdR, specifically via the attack of the hydrated electron. The mechanistic features of these reactions are discussed.     

Preparation and properties of novel soluble aromatic polyimides from 4,4′-diaminotriphenylamine and aromatic tetracarboxylic dianhydrides

New aromatic polyimides containing triphenylamine unit were prepared by two different methods, i.e., a conventional two-step method starting from 4,4′-diaminotriphenylamine and aromatic tetracarboxylic dianhydrides and the one-step thioanhydride method starting from the aromatic diamine and aromatic tetracarboxylic dithioanhydrides. Both procedures yielded high-molecular-weight polyimides with inherent viscosities of 0.47–1.17 dL/g. Some of these polymers were soluble in organic solvents such as N,N-dimethylacetamide, N-methyl-2-pyrrolidone, m-cresol, and pyridine. All the polyimides afforded transparent, flexible, and tough films, and the color varied from pale yellow to dark red, depending markedly on the tetracarboxylic acid components. The glass transition temperatures (T_gs) of these polyimides were in the range of 287–331°C and the 10% weight loss temperatures were above 520°C in air. The polyimides prepared by the one-step method exhibited better solubility in organic solvents and had somewhat lower T_gs than the polymers prepared by a conventional two-step method.