Effect of enzyme concentration on the dynamic behavior of a membrane-bound enzyme system

The dynamic behavior of the reaction-diffusion system, composed of glucose oxidase (EC 1.1.3.4) immobilized at a uniform concentration in a membrane, used as a glucose electrode is represented by a diffusion equation with a nonlinear reaction-term in one-dimensional space. The mathematical model is analyzed by computer simulation, that is, numerical integration of the equation under various initial and boundary conditions, to examine the effect of enzyme concentration on the response characteristics (responsiveness and linearity in response) of the electrode. The analysis of the responses of the system to stepwise changes in the boundary value (glucose concentration in simple solution) infers that the enzyme concentration governs the patterns of the spatial distributions of the substrates (glucose and dissolved oxygen) in steady states and transient responses. It is also revealed that the response characteristics of the electrode are optimized with concentration of immobilized enzyme and that the system establishes the steady states at the same spatial distributions of the substrates, regardless of the boundary value. The diffusion of the substrates and the oxygen concentration also have significant effects on the response characteristics of the electrode.     

Magnetic structure of the europium fulleride ferromagnet Eu(6)C(60)

The powder neutron diffraction technique has been used for the direct observation of magnetic scattering below a Curie temperature of approximately 14 K in the fullerene-based molecular ferromagnet Eu6C60. Europium is in the divalent state with a magnetic moment of 7.1(3) muB per atom, and the configurational symmetry of the magnetic structure is body-centered cubic. Close contacts between Eu2+ and neighboring C60 units provide the signature of orbital hybridization, which can evidently account for the conducting and magnetic properties of the material.     

Synthesis, characterization and FET properties of novel dithiazolylbenzothiadiazole derivatives

Dithiazolylbenzothiadiazoles easily obtained have high electron affinity and the FET device of a trifluoromethylphenyl derivative exhibited a good n-type performance with high electron mobility.     

Synthesis of tricyclic compounds as steroid 5alpha-reductase inhibitors

A series of 4-phenoxybutyric acid derivatives attached to a tricyclic skeleton were prepared and evaluated as 5alpha-reductase inhibitors. Structure activity relationships for these compounds in terms of rat epididymis (type 2) 5alpha-reductase inhibitory activities reveal that 1) the substitution pattern at the 11-position of dibenz[b,e]oxepin influenced potency, 2) higher lipophilicity of the tricyclic skeleton improved potency, whereas the existence of a basic nitrogen atom in this skeleton was detrimental to potency, and 3) isobutyl substitution at the 8 positon of the azepine skeleton was tolerated. Among the tricyclic compounds studied, 4-[3-[5-benzyl-8-(2-methyl)propyl-10,11-dihydrodibenz[b,f]azepine- 2-carboxamido]phenoxy]butyric acid (26) was the most potent inhibitor of rat type 2 5alpha-reductase at 0.1 microM.     

Sulfur-bridged early-late heterobimetallics synthesized by incorporation of titanium,vanadium, and molybdenum into bis(hydrosulfido) templates of group 9 metals

Reactions of the bis(hydrosulfido) complexes [Cp*Rh(SH)(2)(PMe(3))] (1a; Cp* = eta(5)-C(5)Me(5)) with [CpTiCl(3)] (Cp = eta(5)-C(5)H(5)) and [TiCl(4)(thf)(2)] in the presence of triethylamine led to the formation of the sulfido-bridged titanium-rhodium complexes [Cp*Rh(PMe(3))(micro(2)-S)(2)TiClCp] (2a) and [Cp*Rh(PMe(3))(micro2-S)(2)TiCl(2)] (3a), respectively. Complex 3a and its iridium analogue 3b were further converted into the bis(acetylacetonato) complexes [Cp*M(PMe(3))(micro(2)-S)(2)Ti(acac)(2)] (4a, M = Rh; 4b, M = Ir) upon treatment with acetylacetone. The hydrosulfido complexes 1a and [Cp*Ir(SH)(2)(PMe(3))] (1b) also reacted with [VCl(3)(thf)(3)] and [Mo(CO)(4)(nbd)] (nbd = 2,5-norbornadiene) to afford the cationic sulfido-bridged VM2 complexes [(Cp*M(PMe(3))(micro2-S)(2))2V](+) (5a(+), M = Rh; 5b(+), M = Ir) and the hydrosulfido-bridged MoM complexes [Cp*M(PMe(3))(micro2-SH)(2)Mo(CO)(4)] (6a, M = Rh; 6b, M = Ir), respectively.     

2,6-Diphenylbenzo[1,2-b:4,5-b']dichalcogenophenes: a new class of high-performance semiconductors for organic field-effect transistors

2,6-Diphenylbenzo[1,2-b:4,5-b']dichalcogenophenes including thiophene, selenophene, and tellurophene analogues as organic semiconductors for field-effect transistors were effectively synthesized in three steps from commercially available 1,4-dibromobenzene. All three benzodichalcogenophenes acted as good p-type semiconductors, and particularly the selenophene analogue, 2,6-diphenylbenzo[1,2-b:4,5-b']diselenophene, showed high FET mobility of 0.17 cm2 V-1 s-1.     

A ruthenium-catalyzed reaction of aromatic ketones with arylboronates: a new method for the arylation of aromatic compounds via C-H bond cleavage

The ruthenium-catalyzed reaction of aromatic ketones with arylboronic acid esters (arylboronates) gave the ortho arylation product. For this coupling reaction, a RuH2(CO)(PPh3)3 complex exhibited the highest catalytic activity among the complexes screened. Several aromatic ketones, for example, acetophenones, acetonaphthone, alpha-tetralone, and benzosuberone, can be used in this coupling reaction. A variety of arylboronates containing electron-donating (OMe and NMe2) and -withdrawing (F and CF3) groups were found to react with aromatic ketones to give the corresponding aylation products. The corresponding arylboronic acids could be used in this coupling reaction, but the yields were slightly lower, as compared to those of the reaction using the corresponding arylboronates.     

Synthesis of TiRru2 heterobimetallic and TiRuM (M = Rh, Rr, Pd, Pt) heterotrimetallic sulfido clusters from a hydrosulfido-bridged titanium-ruthenium complex

Treatment of the hydrosulfido-bridged titanium-ruthenium heterobimetallic complex [Cp2Ti(mu2-SH)2RuCl(eta5-C5Me5)] (1; Cp = eta5-C5H5) with an excess of triethylamine followed by addition of [RuCl2(PPh3)3] and [[(cod)M]2(mu2-Cl)2] (M = Rh, Ir; cod = 1,5-cyclooctadiene) led to the formation of the TiRu2 and TiRuM mixed-metal sulfido clusters [(CpTi)[(eta5-C5Me5)Ru][Ru(PPh3)2](mu3-S)2(mu2-Cl)2] (3) and [(CpTi)[(eta5-C5Me5)Ru][M(cod)](mu3-S)2(mu2-Cl)] (M = Rh (4a), Ir (4b)), respectively. On the other hand, the reactions of 1 with [M(PPh3)4] (M = Pd, Pt) afforded the TiRuM trinuclear clusters [(CpTiCl)[(eta5-C5Me5)Ru][M(PPh3)2](mu3-S)(mu2-S)(mu2-H)] (M = Pd (5a), Pt (5b)) with an unprecedented M3(mu3-S)(mu2-S) core. The detailed structures of these triangular clusters 3-5 have been determined by X-ray crystallography. Crystal data: 3, triclinic, P1, a = 12.448(4) A, b = 12.773(4) A, c = 17.270(4) A, alpha = 100.16(2) degrees, beta = 99.93(2) degrees, gamma = 114.11(3) degrees, V = 2373(1) A(3), Z = 2; 4a, triclinic, P1, a = 7.714(2) A, b = 11.598(3) A, c = 14.802(4) A, alpha = 80.46(2) degrees, beta = 82.53(2) degrees, gamma = 71.47(2) degrees, V = 1234.0(6) A3, Z = 2; 4b, triclinic, P1, a = 7.729(1) A, b = 11.577(2) A, c = 14.766(3) A, alpha = 80.14(1) degrees, beta = 82.71(1) degrees, gamma = 71.55(1) degrees, V = 1231.1(4) A3, Z = 2; 5a, monoclinic, P2(1)/c, a = 11.259(4) A, b = 16.438(4) A, c = 26.092(5) A, beta = 102.23(3) degrees, V = 4719(2) A(3), Z = 4; 5b, monoclinic, P2(1)/n, a = 11.369(2) A, b = 16.207(3) A, c = 26.116(2) A, beta = 102.29(1) degrees, V = 4701(1) A3, Z = 4.     

Donor–acceptor–acceptor-type near-infrared fluorophores that contain dithienophosphole oxide and boryl groups: effect of the boryl group on the nonradiative decay

The use of donor–π–acceptor (D–π–A) skeletons is an effective strategy for the design of fluorophores with red-shifted emission. In particular, the use of amino and boryl moieties as the electron-donating and -accepting groups, respectively, can produce dyes that exhibit high fluorescence and solvatochromism. Herein, we introduce a dithienophosphole P-oxide scaffold as an acceptor–spacer to produce a boryl- and amino-substituted donor–acceptor–acceptor (D–A–A) π-system. The thus obtained fluorophores exhibit emission in the near-infrared (NIR) region, while maintaining high fluorescence quantum yields even in polar solvents (e.g. λ_em = 704 nm and Φ_F = 0.69 in CH₃CN). A comparison of these compounds with their formyl- or cyano-substituted counterparts demonstrated the importance of the boryl group for generating intense emission. The differences among these electron-accepting substituents were examined in detail using theoretical calculations, which revealed the crucial role of the boryl group in lowering the nonradiative decay rate constant by decreasing the non-adiabatic coupling in the internal conversion process. The D–A–A framework was further fine-tuned to improve the photostability. One of these D–A–A dyes was successfully used in bioimaging to visualize the blood vessels of Japanese medaka larvae and mouse brain.

Combination of electron-accepting diarylboryl terminal groups and dithienophosphole oxide spacers with electron-donating triarylamine moieties produces donor–acceptor–acceptor type π-systems, which exhibit emissions in the near-infrared region.     

Cyclization mechanism for the synthesis of macrocyclic antibiotic lankacidin in Streptomyces rochei

The lankacidin biosynthetic gene cluster in Streptomyces rochei strain 7434AN4 was found to span 31 kb of the giant linear plasmid pSLA2-L and contain a polyketide synthase (PKS)/nonribosomal peptide synthetase (NRPS) hybrid gene (lkcA), type I PKS genes, and pyrroloquinoline quinone (PQQ) biosynthetic genes (lkcK-lkcO). Feeding of PQQ to a pqq mutant restored the lankacidin production, suggesting its crucial role in an oxidation process. However, formation of the 17-membered macrocyclic ring was not catalyzed by PQQ-dependent dehydrogenase (Orf23), but was by flavin-dependent amine oxidase (LkcE). Compound LC-KA05 isolated from an lkcE disruptant was an acyclic intermediate lacking the C2-C18 linkage. These results suggested a cyclization mechanism for the synthesis of the lankacidin macrocyclic skeleton.