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Reactions of Et2NSiPh2B(pin) with [Pd(PCy3)(2)] and [Pt(PCy3)(2)] produce dinuclear Pd(0) and Pt(0) complexes bearing a bridging diphenylsilylene ligand, [{M-1(PCy3)}-{M-2(PCy3)(2)}(mu-SiPh2)] (1-Pd-2, M-1 = M-2 = Pd; 1-PdPt, M-1 ...
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Reactions of Et2NSiPh2B(pin) with [Pd(PCy3)(2)] and [Pt(PCy3)(2)] produce dinuclear Pd(0) and Pt(0) complexes bearing a bridging diphenylsilylene ligand, [{M-1(PCy3)}-{M-2(PCy3)(2)}(mu-SiPh2)] (1-Pd-2, M-1 = M-2 = Pd; 1-PdPt, M-1 = Pd, M-2 = Pt; 1-Pt-2, M-1 = M-2 = Pt), and a trinuclear Pd complex, [{Pd(PCy3)}(3)(mu-SiPh2)(mu(3)-SiPh2)] (2), depending on the con-ditions used. X-ray crystallographic studies of 1-Pd2, 1-PdPt, and 1-Pt-2 show that the molecules contain an almost linear P-M-M- P arrangement with P-M-M angles in the range of 157-168 degrees. The distance between two metal centers decreased in the order of 1-Pd-2 > 1-PdPt > 1-Pt-2. Complex 2 is composed of a bent Pd-3 backbone with a Pd-Pd-Pd angle of 110 degrees. All Pd atoms are bridged by a SiPh2 ligand, while two of them are bridged by another SiPh2 ligand. Complex 1-Pd-2 catalyzes the 1:2 cycloaddition of Et2NSiPh2B(pin) with HCCPh to form 2,4-and 3,4-disubstituted siloles. A similar reaction with HC (CBu)-Bu-t afforded a mixture of the corresponding siloles and alkynyl(alkenyl)diphenylsilane, ((BuC)-Bu-t C)((BuCH)-Bu-t CH)SiPh2 (5c). The yields and selectivities of the products are lower than those obtained in the previously reported reactions catalyzed by the Pd-PPh3 catalytic system. The stoichiometric reactions of HC (CBu)-Bu-t and HC CSiMe3 with 1-Pt-2 trigger a C-H(sp) bond activation process to occur to form complexes with the alkynyl ligand, [{PtH(PCy3)}{Pt(PCy3)}(mu-SiPh2)(mu-eta(1),eta(2)-C CR)] (6b, R = Bu-t; 6c, R = SiMe3) at room temperature. Complex 6c reacts with alkynes at 70 degrees C to form complexes bearing the bridging alkenylsilyl ligand, [{Pt(PCy3)}(2){mu-eta(1),eta(2)-SiPh2C(SiMe3)=CH2}(mu-eta(1),eta(2)-C CR)] (7b, R = Bu-t; 7c, R = SiMe3). Complex 7c undergoes reductive elimination of alkynyl(alkenyl)diphenylsilane upon the addition of a diphosphine ligand. The reaction of dimethyl acetylenedicarboxylate with 1-Pt2 gives a diplatinum complex with a silaplatinacyclohexadiene structure, [{(Cy3P)<(Pt(CZ=CZSiPh(2)CZ=CZ)Pt)over bar>(PCy3)}(mu-eta(1),eta(2)-CZ CZ)] (8, Z = CO2Me). The mechanisms of the stoichiometric and catalytic reactions are discussed based on our experimental results.
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Phosphoribulokinase (PRK), one of the enzymes in the Calvin-Benson cycle, is a well-known target of thioredoxin (Trx), which regulates various enzyme activities by the reduction of disulfide bonds in a light-dependent manner. PRK ...
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Phosphoribulokinase (PRK), one of the enzymes in the Calvin-Benson cycle, is a well-known target of thioredoxin (Trx), which regulates various enzyme activities by the reduction of disulfide bonds in a light-dependent manner. PRK has two Cys pairs conserved in the N-terminal and C-terminal regions, and the N-terminal one near the active site is thought to be responsible for the regulation. The flexible clamp loop located between the N-terminal two Cys residues has been deemed significant to Trx-mediated regulation. However, cyanobacterial PRK is also subject to Trx-dependent activation despite the lack of this clamp loop. We, therefore, compared Trx-mediated regulation of PRK from the cyanobacterium Anabaena sp. PCC 7120 (A.7120_PRK) and that from the land plant Arabidopsis thaliana (AtPRK). Interestingly, peptide mapping and site-directed mutagenesis analysis showed that Trx was more effective in changing the redox states of the C-terminal Cys pair in both A.7120_PRK and AtPRK. In addition, the effect of redox state change of the C-terminal Cys pair on PRK activity was different between A.7120_PRK and AtPRK. Trx-mediated redox regulation of the C-terminal Cys pair was also important for complex dissociation/formation with CP12 and glyceraldehyde 3-phosphate dehydrogenase. Furthermore, in vivo analysis of the redox states of PRK showed that only one disulfide bond is reduced in response to light. Based on the enzyme activity assay and the complex formation analysis, we concluded that Trx-mediated regulation of the C-terminal Cys pair of PRK is important for activity regulation in cyanobacteria and complex dissociation/formation in both organisms.
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(Bi, K)TiO3 is a lead-free ferroelectric material that has large tetragonality at room temperature. High-quality films of (Bi, K)TiO3 have been difficult to grow due to the high volatilities of the constituent Bi and K. Epitaxial ...
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(Bi, K)TiO3 is a lead-free ferroelectric material that has large tetragonality at room temperature. High-quality films of (Bi, K)TiO3 have been difficult to grow due to the high volatilities of the constituent Bi and K. Epitaxial tetragonal (Bi, K)TiO3 films with large remanent polarization of about 84 mu C/cm(2) were grown on (100)(c)SrRuO3//(100)SrTiO3 substrates by the hydrothermal method. In this study, we systematically investigated the effects of the input amounts of the starting materials on the compositions, crystal structures, and ferroelectric properties of films grown on (100)(c)SrRuO3//(100)SrTiO3 substrates. As a resultant, (001)-oriented (Bi, K)TiO3 single-phase films were obtained with input Bi/(Bi + Ti) ratios of 0.056-0.450 at a KOH concentration of 10.0 mol/L. This indicates an approximately one-order-wide process window of the input Bi/(Bi + Ti) source ratio for (001)-oriented (Bi, K)TiO3 single-phase films. On the other hand, these films were also obtained at KOH concentrations of 8.0 - 13.5 mol/L and with a fixed input Bi/(Bi + Ti) source ratio of 0.22. This suggests the high reproducibility of (001)-oriented (Bi, K)TiO3 films even with fluctuations in the input source amount. In addition, all films deposited within this KOH concentration range showed large remanent polarization of about 84 mu C/cm(2). Moreover, good insulation characteristics were achieved for the films deposited at higher KOH concentrations of 10.0 to 13.5 mol/L.
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We investigated a viscous protein layer formed on self-assembled monolayers (SAMs) in crowded biological environments. The results were obtained through force spectroscopic measurements using colloidal probes and substantiated by ...
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We investigated a viscous protein layer formed on self-assembled monolayers (SAMs) in crowded biological environments. The results were obtained through force spectroscopic measurements using colloidal probes and substantiated by exhaustive analysis using a quartz crystal microbalance with an energy dissipation technique. A hydrophobic SAM of n-octanethiol (C8 SAM) in bovine serum albumin (BSA) solution is buried under an adlayer of denatured BSA molecules and an additional viscous interphase layer that is five times more viscous than the bulk solution. C8 SAMs in fetal bovine serum induced a formation of a thicker adsorbed protein layer but with no observable viscous interphase layer. These findings show that a fouling surface is essentially inaccessible to any approaching molecules and thus has a new biological and physical identity arising from its surrounding protein layers. In contrast, the SAMs composed of sulfobetaine-terminated alkanethiol proved to be sufficiently protein-resistant and bio-inert even under crowded conditions due to a protective barrier of its interfacial water, which has implications in the accurate targeting of artificial particles for drug delivery and similar applications by screening any non-specific interactions. Finally, our strategies provide a platform for the straightforward yet effectual in vitro characterization of diverse types of surfaces in the context of targeted interactions in crowded biological environments.
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摘要 :
We investigated a viscous protein layer formed on self-assembled monolayers (SAMs) in crowded biological environments. The results were obtained through force spectroscopic measurements using colloidal probes and substantiated by ...
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We investigated a viscous protein layer formed on self-assembled monolayers (SAMs) in crowded biological environments. The results were obtained through force spectroscopic measurements using colloidal probes and substantiated by exhaustive analysis using a quartz crystal microbalance with an energy dissipation technique. A hydrophobic SAM of n-octanethiol (C8 SAM) in bovine serum albumin (BSA) solution is buried under an adlayer of denatured BSA molecules and an additional viscous interphase layer that is five times more viscous than the bulk solution. C8 SAMs in fetal bovine serum induced a formation of a thicker adsorbed protein layer but with no observable viscous interphase layer. These findings show that a fouling surface is essentially inaccessible to any approaching molecules and thus has a new biological and physical identity arising from its surrounding protein layers. In contrast, the SAMs composed of sulfobetaine-terminated alkanethiol proved to be sufficiently protein-resistant and bio-inert even under crowded conditions due to a protective barrier of its interfacial water, which has implications in the accurate targeting of artificial particles for drug delivery and similar applications by screening any non-specific interactions. Finally, our strategies provide a platform for the straightforward yet effectual in vitro characterization of diverse types of surfaces in the context of targeted interactions in crowded biological environments.
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Ketosynthase-like decarboxylase (KSQ) domains are widely distributed in the loading modules of modular polyketide synthases (PKSs) and are proposed to catalyze the decarboxylation of a malonyl or methylmalonyl unit for the constru...
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Ketosynthase-like decarboxylase (KSQ) domains are widely distributed in the loading modules of modular polyketide synthases (PKSs) and are proposed to catalyze the decarboxylation of a malonyl or methylmalonyl unit for the construction of the PKS starter unit. KSQ domains have high sequence similarity to ketosynthase (KS) domains, which catalyze transacylation and decarboxylative condensation in polyketide and fatty acid biosynthesis, except that the catalytic Cys residue of KS domains is replaced by Gln in KSQ domains. Here, we present biochemical analyses of GfsA KSQ and CmiP4 KSQ, which are involved in the biosynthesis of FD-891 and cremimycin, respectively. In vitro analysis showed that these KSQ domains catalyze the decarboxylation of malonyl and methylmalonyl units. Furthermore, we determined the crystal structure of GfsA KSQ in complex with a malonyl thioester substrate analogue, which enabled identification of key amino acid residues involved in the decarboxylation reaction. The importance of these residues was confirmed by mutational analysis. On the basis of these findings, we propose a mechanism of the decarboxylation reaction catalyzed by GfsA KSQ. GfsA KSQ initiates decarboxylation by fixing the substrate in a suitable conformation for decarboxylation. The formation of enolate upon decarboxylation is assisted by two conserved threonine residues. Comparison of the structure of GfsA KSQ with those of KS domains suggests that the Gln residue in the active site of the KSQ domain mimics the acylated Cys residue in the active site of KS domains.
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A setup and approach for simultaneous measurement of the inverse and direct transverse piezoelectric co-efficients of piezoelectric films was constructed. A longitudinal vibration mode resonator with a hydrothermally synthesized (...
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A setup and approach for simultaneous measurement of the inverse and direct transverse piezoelectric co-efficients of piezoelectric films was constructed. A longitudinal vibration mode resonator with a hydrothermally synthesized (K,Na)NbO3 film deposited on a SrRuO3/SrTiO3 substrate was investigated. The fabricated vibrator consists of two upper electrodes, one for actuation and the other for sensing. A driving voltage was applied to the actuator electrode to generate mechanical vibration at its resonance frequency. The vibration velocity was measured with a laser Doppler vibrometer, and the output current from the shorted sensing electrode was also measured to simultaneously evaluate the inverse and direct piezoelectric responses. The obtained inverse piezoelectric coefficient e31 was-3.60 C/m2, while the direct piezoelectric coefficient e31 was almost same at-3.69 C/m2. From these values, the inverse and direct piezoelectric coefficients e31,f were-4.93 and-5.05 C/ m2, respectively.
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pi-Conjugated poly(arylene ethynylene)s containing both thiophene-2,5-diyl and fused metallacycles such as titanafluorene-diyl and dithienotitanacyclopentadiene-diyl units in their alternating sequence were synthesized and their o...
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pi-Conjugated poly(arylene ethynylene)s containing both thiophene-2,5-diyl and fused metallacycles such as titanafluorene-diyl and dithienotitanacyclopentadiene-diyl units in their alternating sequence were synthesized and their optoelectronic features were studied by the UV-vis spectra and theoretical calculations. The polymerization of 2,5-diethynyl-3-dodecylthiophene and arylene dihalides possessing fused organometallic units such as a 2,7-dibromo-9-titanafluorene and a 5,5'-diiodo-dithienotitanacyclopentadiene was carried out at 70 degrees C for 48 h in tetrahydrofuran (THF) in the presence of palladium dichloride/4,5-bis (diphenylphosphino)-9,9-dimethylxanthene as a catalyst and diisopropylamine as a base to produce black purple-colored polymers in 51% and 49% yields, respectively. The polymers are soluble in organic solvents such as THF, chloroform, and dichloromethane and they are stable under air at ambient temperature. In the UV-vis absorption spectra of the polymers thus obtained, the absorption maxima (lambda(max)) were observed at 395 nm and 486 nm, respectively, which are bathochromically shifted compared to those of model compounds, 2,7-bis(2-thienylethynyl)titanafluorene and 5,5'-bis(2-thienylethynyl)dithienotitanacyclopentadiene derivatives (lambda(max) = 372 and 418 nm, respectively). The optical band gap (E-g(opt)) of the polymer containing the titanafluorene unit is estimated to be 2.28 eV on the basis of the absorption onset, which is narrower than that of the model compound, the bis(thienylethynyl)titanafluorene derivative (3.06 eV). In the case of the polymer containing the dithienotitanacyclopentadiene unit, E-g(opt) was estimated to be 2.12 eV, which is also narrower than that of the model compound, the 5,5'-bis(2-thienylethynyl)dithienotitanacyclopentadiene derivative (2.51 eV).
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2-Deoxy-scyllo-inosose (2DOI, [2S,3R,4S,5R]-2,3,4,5-tetrahydroxycyclohexan-1-one) is a biosynthetic intermediate of 2-deoxystreptamine-containing aminoglycoside antibiotics, including butirosin, kanamycin, and neomycin. In produce...
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2-Deoxy-scyllo-inosose (2DOI, [2S,3R,4S,5R]-2,3,4,5-tetrahydroxycyclohexan-1-one) is a biosynthetic intermediate of 2-deoxystreptamine-containing aminoglycoside antibiotics, including butirosin, kanamycin, and neomycin. In producer microorganisms, 2DOI is constructed from d-glucose 6-phosphate (G6P) by 2-deoxy-scyllo-inosose synthase (DOIS) with the oxidized form of nicotinamide adenine dinucleotide (NAD(+)). 2DOI is also known as a sustainable biomaterial for production of aromatic compounds and a chiral cyclohexane synthon. In this study, a one-pot enzymatic synthesis of 2DOI from d-glucose and polyphosphate was investigated. First, 3 polyphosphate glucokinases (PPGKs) were examined to produce G6P from d-glucose and polyphosphate. A PPGK derived from Corynebacterium glutamicum (cgPPGK) was found to be suitable for G6P production under ordinary enzymatic conditions. Next, 7 DOISs were examined for the one-pot enzymatic reaction. As a result, cgPPGK and BtrC, the latter of which is a DOIS derived from the butirosin producer Bacillus circulans, achieved nearly full conversion of d-glucose to 2DOI in the presence of polyphosphate.
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In electrochemical devices, it is important to control the ionic transport between the electrodes and solid electrolytes. However, it is difficult to tune the transport without applying an electric field. This paper presents a met...
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In electrochemical devices, it is important to control the ionic transport between the electrodes and solid electrolytes. However, it is difficult to tune the transport without applying an electric field. This paper presents a method to modulate the transport via tuning of the electrochemical potential difference by controlling the electronic states at the interfaces. We fabricated thin-film solid-state Li batteries using LiTi2O4 thin films as positive electrodes. The spontaneous Li-ion transport between the solid electrolyte and LiTi2O4 is controlled by tuning the electrochemical potential difference via use of an electrically conducting Nb-doped SrTiO3 substrate. This study establishes the foundation for rectifying the ionic transport via electronic energy band alignment.
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