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1.
Escherichiacoli RecBCD is a bipolar DNA helicase possessing two motor subunits (RecB, a 3′-to-5′ translocase, and RecD, a 5′-to-3′ translocase) that is involved in the major pathway of recombinational repair. Previous studies indicated that the minimal kinetic mechanism needed to describe the ATP-dependent unwinding of blunt-ended DNA by RecBCD in vitro is a sequential n-step mechanism with two to three additional kinetic steps prior to initiating DNA unwinding. Since RecBCD can “melt out” ∼ 6 bp upon binding to the end of a blunt-ended DNA duplex in a Mg2+-dependent but ATP-independent reaction, we investigated the effects of noncomplementary single-stranded (ss) DNA tails [3′-(dT)6 and 5′-(dT)6 or 5′-(dT)10] on the mechanism of RecBCD and RecBC unwinding of duplex DNA using rapid kinetic methods. As with blunt-ended DNA, RecBCD unwinding of DNA possessing 3′-(dT)6 and 5′-(dT)6 noncomplementary ssDNA tails is well described by a sequential n-step mechanism with the same unwinding rate (mkU = 774 ± 16 bp s− 1) and kinetic step size (m = 3.3 ± 1.3 bp), yet two to three additional kinetic steps are still required prior to initiation of DNA unwinding (kC = 45 ± 2 s− 1). However, when the noncomplementary 5′ ssDNA tail is extended to 10 nt [5′-(dT)10 and 3′-(dT)6], the DNA end structure for which RecBCD displays optimal binding affinity, the additional kinetic steps are no longer needed, although a slightly slower unwinding rate (mkU = 538 ± 24 bp s− 1) is observed with a similar kinetic step size (m = 3.9 ± 0.5 bp). The RecBC DNA helicase (without the RecD subunit) does not initiate unwinding efficiently from a blunt DNA end. However, RecBC does initiate well from a DNA end possessing noncomplementary twin 5′-(dT)6 and 3′-(dT)6 tails, and unwinding can be described by a simple uniform n-step sequential scheme, without the need for the additional kC initiation steps, with a similar kinetic step size (m = 4.4 ± 1.7 bp) and unwinding rate (mkobs = 396 ± 15 bp s− 1). These results suggest that the additional kinetic steps with rate constant kC required for RecBCD to initiate unwinding of blunt-ended and twin (dT)6-tailed DNA reflect processes needed to engage the RecD motor with the 5′ ssDNA.  相似文献   

2.
Expression in Escherichia coli of his-tagged human mevalonate diphosphate decarboxylase (hMDD) has expedited enzyme isolation, characterization, functional investigation of the mevalonate diphosphate binding site, and crystal structure determination (2.4 Å resolution). hMDD exhibits Vmax = 6.1 ± 0.5 U/mg; Km for ATP is 0.69 ± 0.07 mM and Km for (R,S) mevalonate diphosphate is 28.9 ± 3.3 μM. Conserved polar residues predicted to be in the hMDD active site were mutated to test functional importance. R161Q exhibits a ∼1000-fold diminution in specific activity, while binding the fluorescent substrate analog, TNP-ATP, comparably to wild-type enzyme. Diphosphoglycolyl proline (Ki = 2.3 ± 0.3 uM) and 6-fluoromevalonate 5-diphosphate (Ki = 62 ± 5 nM) are competitive inhibitors with respect to mevalonate diphosphate. N17A exhibits a Vmax = 0.25 ± 0.02 U/mg and a 15-fold inflation in Km for mevalonate diphosphate. N17A’s Ki values for diphosphoglycolyl proline and fluoromevalonate diphosphate are inflated (>70-fold and 40-fold, respectively) in comparison with wild-type enzyme. hMDD structure indicates the proximity (2.8 Å) between R161 and N17, which are located in an interior pocket of the active site cleft. The data suggest the functional importance of R161 and N17 in the binding and orientation of mevalonate diphosphate.  相似文献   

3.
Trypanosoma cruzi dihydroorotate dehydrogenase (TcDHODH) catalyzes the oxidation of l-dihydroorotate to orotate with concomitant reduction of fumarate to succinate in the de novo pyrimidine biosynthetic pathway. Based on the important need to characterize catalytic mechanism of TcDHODH, we have tailored a protocol to measure TcDHODH kinetic parameters based on isothermal titration calorimetry. Enzymatic assays lead to Michaelis-Menten curves that enable the Michaelis constant (KM) and maximum velocity (Vmax) for both of the TcDHODH substrates: dihydroorotate (KM = 8.6 ± 2.6 μM and Vmax = 4.1 ± 0.7 μM s-1) and fumarate (KM = 120 ± 9 μM and Vmax = 6.71 ± 0.15 μM s-1). TcDHODH activity was investigated using dimethyl sulfoxide (10%, v/v) and Triton X-100 (0.5%, v/v), which seem to facilitate the substrate binding process with a small decrease in KM. Arrhenius plot analysis allowed the determination of thermodynamic parameters of activation for substrates and gave some insights into the enzyme mechanism. Activation entropy was the main contributor to the Gibbs free energy in the formation of the transition state. A factor that might contribute to the unfavorable entropy is the hindered access of substrates to the TcDHODH active site where a loop at its entrance regulates the open-close channel for substrate access.  相似文献   

4.
By combining single-molecule magnetic tweezers and osmotic stress on DNA assemblies, we separate attractive and repulsive components of the total intermolecular interaction between multivalent cation condensed DNA. Based on measurements of several different cations, we identify two invariant properties of multivalent cation-mediated DNA interactions: repulsive forces decay exponentially with a 2.3 ± 0.1 Å characteristic decay length and the attractive component of the free energy is always 2.3 ± 0.2 times larger than the repulsive component of the free energy at force-balance equilibrium. These empirical constraints are not consistent with current theories that attribute DNA-DNA attractions to a correlated lattice of counterions. The empirical constraints are consistent with theories for Debye-Hückel interactions between helical line charges and with the order-parameter formalism for hydration forces. Each of these theories posits exponentially decaying attractions and, if we assume this form, our measurements indicate a cation-independent, 4.8 ± 0.5 Å characteristic decay length for intermolecular attractions between condensed DNA molecules.  相似文献   

5.
X-ray diffuse scattering was measured from oriented stacks and unilamellar vesicles of dioleoylphosphatidylcholine lipid bilayers to obtain the temperature dependence of the structure and of the material properties. The area/molecule, A, was 75.5 Å2 at 45°C, 72.4 Å2 at 30°C, and 69.1 Å2 at 15°C, which gives the area expansivity αA = 0.0029/deg at 30°C, and we show that this value is in excellent agreement with the polymer brush theory. The bilayer becomes thinner with increasing temperature; the contractivity of the hydrocarbon portion was αDc = 0.0019/deg; the difference between αA and αDc is consistent with the previously measured volume expansivity αVc = 0.0010/deg. The bending modulus KC decreased as exp(455/T) with increasing T (K). Our area compressibility modulus KA decreased with increasing temperature by 5%, the same as the surface tension of dodecane/water, in agreement again with the polymer brush theory. Regarding interactions between bilayers, the compression modulus B as a function of interbilayer water spacing DW was found to be nearly independent of temperature. The repulsive fluctuation pressure calculated from B and KC increased with temperature, and the Hamaker parameter for the van der Waals interaction was nearly independent of temperature; this explains why the fully hydrated water spacing, DW, that we obtain from our structural results increases with temperature.  相似文献   

6.
A highly sensitive HPLC–ESI-MS method has been developed and validated for the quantification of ginkgolic acid (15:1) in a small quantity of rat plasma (50 μL) using its homologous compound ginkgolic acid (17:1) as an internal standard. GA (15:1) and GA (17:1) were extracted from biological matrix by direct protein precipitation with 5-fold volume of methanol and separated on an Elite hypersil BDS C18 column (2.1 × 100 mm, 3 μm), eluted with acetonitrile:water (92:8, v/v, containing 0.3% glacial acetic acid). Linear range was 8–1000 ng/mL with the square regression coefficient (r2) of 0.996. The lowest concentration (8 ng/mL) in the calibration curve was estimated as LLOQ with both deviation of accuracy and RSD of precision <20% (n = 6). The intra- and inter-day precision ranged from 3.6% to 9.9%, and the intra- and inter-day accuracy was between 89.9% and 101.3%. This method was successfully applied to study pharmacokinetics of GA (15:1) in rats after oral administration at a dose of 10 mg/kg. GA (15:1) pharmacokinetic parameters Cmax, Tmax, t1/2, AUC0–12h are 1552.9 ± 241.0 ng/mL, 0.9 ± 0.7 h, 5.5 ± 2.6 h, 3356.0 ± 795.3 ng h/mL, respectively.  相似文献   

7.
8.
An increasing attention has been dedicated to the characterization of complex networks within the protein world. Before now most investigations about protein structures were only considered where the interactive cutoff distance Rc=5 or 7 Å. It is noteworthy that the length of peptide bond is about 1.5 Å, the length of hydrogen bond is about 3 Å, the range of London-van der Waals force is about 5 Å and the range of hydrophobic effect can reach to 12 Å in protein molecule. Present work reports a study on the topological properties of the amino acid network constructed by different interactions above. The results indicate that the small-world property of amino acid network constructed by the peptide and hydrogen bond, London-van der Waals force and the hydrophobic effect is strong, very strong and relatively weak, respectively. Besides, there exists a precise exponential relation Ck−0.5 at Rc=12 Å. It means that the amino acid network constructed by the hydrophobic effect tend to be hierarchical. Functional modules could be the cause for hierarchical modularity architecture in protein structures. This study on amino acid interactive network for different interactions facilitates the identification of binding sites which is strongly linked with protein function, and furthermore provides reasonable understanding of the underlying laws of evolution in genomics and proteomics.  相似文献   

9.
Two crystal complexes of copper(I) chloride with tetravinylsilane (TVS) dimethyltetravinyldisiloxane (DMTVDS) were prepared and examined by IR spectroscopy and X-ray diffraction: sp. gr. P2/a, Z = 4, a = 13.428(1) Å, b = 7.9584(7) Å, c = 14.694(1) Å for [Cu4Cl4(TVS)]; sp. gr. P21/c, a = 10.505(1) Å, b = 13.487(1) Å, c = 13.870(1) Å for [Cu4Cl4(DMTVDS)]. The influence of the vinylsilicon ligands on the efficiency of the Cu?CC interaction is discussed. Thus, the consideration of dSi ← π∗CC ← dCu conjugate system may help to understand how the silicon π-acceptor properties influence on the degree of trigonal distortion of the Cu(I) coordination tetrahedron as well as on the inorganic part organization. The present studies are aimed at the use of the structure controlled nanoparticles supported on vinyl modified silicon (or silicone) substrate.  相似文献   

10.
Nudaurelia capensis ω virus is a T = 4, icosahedral virus with a bipartite, positive-sense RNA genome. Expression of the coat protein gene in a baculovirus system was previously shown to result in the formation of procapsids when purified at pH 7.6. Procapsids are round, porous particles (480 Å diameter) and have T = 4 quasi-symmetry. Reduction of pH from 7.6 to 5.0 resulted in virus-like particles (VLP5.0) that are morphologically identical with authentic virions, with an icosahedral-shaped capsid and a maximum dimension of 410 Å. VLP5.0 undergoes a maturation cleavage between residues N570 and F571, creating the covalently independent γ peptide (residues 571-641) that remains associated with the particle. This cleavage also occurs in authentic virions, and in each case, it renders the morphological change irreversible (i.e., capsids do not expand when the pH is raised back to 7.6). However, a non-cleavable mutant, N570T, undergoes the transition reversibly (NT7.6 ↔ NT5.0). We used electron cryo-microscopy and three-dimensional image reconstruction to study the icosahedral structures of NT7.6, NT5.0, and VLP5.0 at about 8, 6, and 6 Å resolution, respectively. We employed the 2. 8-Å X-ray model of the mature virus, determined at pH 7.0 (XR7.0), to establish (1) how and why procapsid and capsid structures differ, (2) why lowering pH drives the transition, and (3) why the non-cleaving NT5.0 is reversible. We show that procapsid assembly minimizes the differences in quaternary interactions in the particle. The two classes of 2-fold contacts in the T = 4 surface lattice are virtually identical, both mediated by similarly positioned but dynamic γ peptides. Furthermore, quasi and icosahedral 3-fold interactions are indistinguishable. Maturation results from neutralizing the repulsive negative charge at subunit interfaces with significant differentiation of quaternary interactions (one 2-fold becomes flat, mediated by a γ peptide, while the other is bent with the γ peptide disordered) and dramatic stabilization of the particle. The γ peptide at the flat contact remains dynamic when cleavage cannot occur (NT5.0) but becomes totally immobilized by noncovalent interactions after cleavage (VLP5.0).  相似文献   

11.
A hydrothermal reaction of a mixture of Gd(NO3)3, 1,2-benzenedicarboxylic acid (1,2-BDC), piperazine, NaOH and water at 180 °C for three days under autogeneous pressure gave rise to a new compound of the formula [C4N2H12][Gd2(H2O)2(C6H4(COO)2)2] (I). The connectivity between GdO8 distorted dodecahedra and 1,2-BDC units gives rise to a two-dimensional structure with large apertures. The fully protonated piperazine molecule occupies the middle of these apertures. The compound has favorable CH?π interactions between the benzene rings of adjacent layers and shows photoluminescence at room temperature. Crystal data: monoclinic, space group = P21/c (No. 14), a = 13.1671(3) Å, b = 13.7336(3) Å, c = 11.3100(1) Å, β = 115.411(1)°, v = 1847.34(6) Å3, Z = 4, R1 = 0.0238 for 2658 reflections [I > 2σ(I)].  相似文献   

12.
In present study, an HPLC method coupled with photodiode array detector (HPLC-PDA) was established for determination and pharmacokinetics of gastrodin (GAS) in human plasma after an oral administration of GAS capsule. In the method, ethanol and dichloromethane were respectively used for deproteinization and purification during the sample preparation procedure. Separation of GAS was achieved on an AichromBond-AQ C18 column (5 μm, 150 mm × 4.6 mm) with the mobile phase of methanol–0.1% phosphoric acid solution (2:98, v/v) at a flow rate of 0.8 ml/min. The wavelength was set at 220 nm and the injection volume was 20 μl. Under the conditions, the calibration curve was linear within the concentration range of 50–4000 ng/ml with the correlation coefficient (r) of 0.99554 (weight = 1/X2) and the lower limit of quantification (LLOQ) was 50 ng/ml. The inter- and intra-day precisions were less than 11% and the accuracies (%) were within the range of 95.55–103.78%. The extraction recoveries were over 65% with RSDs less than 5.50%. The GAS was proved to be stable under tested conditions. Thus, the method was valid enough to be applied for pharmacokinetic study of GAS in human plasma. The pharmacokinetic parameters of GAS in human plasma after an oral administration of 200 mg GAS capsule were described as: Cmax, 1484.55 ± 285.05 ng/ml; Tmax, 0.81 ± 0.16 h; t1/2α, 3.78 ± 2.33 h; t1/2β, 6.06 ± 3.20 h; t1/2Ka, 0.18 ± 0.53 h; K12, 0.18 ± 0.41/h; K21, 0.20 ± 0.16/h; K10, 4.11 ± 15.81/h; V1/F, 180.35 ± 89.44 L; CL/F, 62.50 ± 140.03 l/h; AUC0→t, 5619.41 ± 1972.88 (ng/ml) h; and AUC0→∞, 7210.26 ± 3472.74 (ng/ml) h, respectively. These will be useful for the clinical application of GAS.  相似文献   

13.
A series of tridentate ligands consisting of mixed aromatic and aliphatic amine derivatives of single amino acid chelates and phenylpiperazine have been developed, and their reactions with [NEt4]2[ReBr3(CO)3] have been investigated. The compounds [Re(CO)3{(NC5H4CH2)NCH3(C2H4)NHCH3}]Br (4), [Re(CO)3{(NC5H4CH2)NCH3(C2H4)NCH3(CH2)xCOOC2H5}]Br (x = 1, 5; x = 4, 6) [Re(CO)3{(NC5H4CH2)NH(C2H4)N(CH3)2}]Br (7), [Re(CO)3{(NC5H4CH2)N(CH 2COOC2H5)(C2H4)N(CH3)2}]Br (8) and [Re(CO)3(NC5H4CH2)(C2H4NH2)N(CH2)3-CH3Ophenpip]Br (9) (phenpip: phenylpiperazine, -C6H4-(CH2CH2)2N-) were prepared and characterized by elemental analysis, NMR, IR, HSMS and X-ray crystallography. All complexes exhibit fac-{Re(CO)3N3} coordination geometry in the cationic molecular unit. Crystal data for C13H17BrN3O3Re (4): orthorhombic, Pbca, a = 13.4510(8) Å, b = 10.5728(6) Å, c = 22.5378(13) Å, V = 3205.2(3) Å3, Z = 8; C17H23BrN3O5Re (5): orthorhombic, Pcca, a = 16.5907(7) Å,b = 14.8387(6) Å, c = 16.7075(7) Å, V = 4113.1(3) Å3, Z = 8; C13H25BrN3O7Re (7 · 4H2O): monoclinic, P21/n, a = 14.0698(17) Å, b = 9.6760(12) Å, c = 15.6099 (19) Å, β = 114.930(2)°, V = 1927.1(4) Å3, Z = 4; C17H23BrN3O5Re (8): monoclinic, P21/n, a = 7.5312(5) Å, b = 16.0366(10) Å, c = 16.8741(10) Å, β = 98.9990(10)°, V = 2012.9(2) Å3, Z = 4.  相似文献   

14.
A novel chain-like luminescent samarium coordination polymer {Sm3(C8H4O4)4(C12N2H8)2(NO3)}n (C8H4O4 = phthalate, C12N2H8 = 1,10-phenanthroline) has been assembled by hydrothermal process. The title complex crystallizes in the monoclinic system, space group P2(1)/c, with lattice parameters a = 22.56(3) Å, b = 11.155(15) Å, c = 20.32(3) Å, β = 96.70(2)°, V = 5078(12) Å3, F(000) = 2964, GOF = 0.857, R1 = 0.0358, wR2 = 0.0597, Z = 4. Samarium ions exhibit different coordination modes from each other and lead to the unexpected high asymmetrical structure. To our knowledge, it is the first example of lanthanide coordination polymers comprising the three asymmetrical central Sm3+ fragments. The photophysical properties have been studied with excitation and emission spectra.  相似文献   

15.
Structural changes of barnase during folding were investigated using time-resolved small-angle X-ray scattering (SAXS). The folding of barnase involves a burst-phase intermediate, sometimes designated as the denatured state under physiological conditions, Dphys, and a second hidden intermediate. Equilibrium SAXS measurements showed that the radius of gyration (Rg) of the guanidine unfolded state (U) is 26.9 ± 0.7 Å, which remains largely constant over a wide denaturant concentration range. Time-resolved SAXS measurements showed that the Rg value extrapolated from kinetic Rg data to time zero, Rg,0, is 24.3 ± 0.1 Å, which is smaller than that of U but which is expanded from that of folding intermediates of other proteins with similar chain lengths (19 Å). After the burst-phase change, a single-exponential reduction in Rg2 was observed, which corresponds to the formation of the native state for the major component containing the native trans proline isomer. We estimated Rg of the minor component of Dphys containing the non-native cis proline isomer (Dphys,cis) to be 25.7 ± 0.6 Å. Moreover, Rg of the major component of Dphys containing the native proline isomer (Dphys,tra) was estimated as 23.9 ± 0.2 Å based on Rg,0. Consequently, both components of the burst-phase intermediate of barnase (Dphys,tra and Dphys,cis) are still largely expanded. It was inferred that Dphys possesses the N-terminal helix and the center of the β-sheet formed independently and that the formation of the remainder of the protein occurs in the slower phase.  相似文献   

16.
To characterize driving forces and driven processes in formation of a large-interface, wrapped protein-DNA complex analogous to the nucleosome, we have investigated the thermodynamics of binding the 34-base pair (bp) H′ DNA sequence to the Escherichia coli DNA-remodeling protein integration host factor (IHF). Isothermal titration calorimetry and fluorescence resonance energy transfer are applied to determine effects of salt concentration [KCl, KF, K glutamate (KGlu)] and of the excluded solute glycine betaine (GB) on the binding thermodynamics at 20 °C. Both the binding constant Kobs and enthalpy ΔH°obs depend strongly on [salt] and anion identity. Formation of the wrapped complex is enthalpy driven, especially at low [salt] (e.g., ΔHoobs = − 20.2 kcal·mol− 1 in 0.04 M KCl). ΔH°obs increases linearly with [salt] with a slope (dΔH°obs/d[salt]), which is much larger in KCl (38 ± 3 kcal·mol− 1 M− 1) than in KF or KGlu (11 ± 2 kcal·mol− 1 M− 1). At 0.33 M [salt], Kobs is approximately 30-fold larger in KGlu or KF than in KCl, and the [salt] derivative SKobs = dlnKobs/dln[salt] is almost twice as large in magnitude in KCl (− 8.8 ± 0.7) as in KF or KGlu (− 4.7 ± 0.6).A novel analysis of the large effects of anion identity on Kobs, SKobs and on ΔH°obs dissects coulombic, Hofmeister, and osmotic contributions to these quantities. This analysis attributes anion-specific differences in Kobs, SKobs, and ΔH°obs to (i) displacement of a large number of water molecules of hydration [estimated to be 1.0(± 0.2) × 103] from the 5340 Å2 of IHF and H′ DNA surface buried in complex formation, and (ii) significant local exclusion of F and Glu from this hydration water, relative to the situation with Cl, which we propose is randomly distributed. To quantify net water release from anionic surface (22% of the surface buried in complexation, mostly from DNA phosphates), we determined the stabilizing effect of GB on Kobs: dlnKobs/d[GB]  = 2.7 ± 0.4 at constant KCl activity, indicating the net release of ca. 150 H2O molecules from anionic surface.  相似文献   

17.
A case study on Centaurea gymnocarpa Moris & De Not., a narrow endemic species, was carried out by analyzing its morphological, anatomical, and physiological traits in response to natural habitat stress factors under Mediterranean climate conditions. The results underline that the species is particularly adapted to the environment where it naturally grows. At the plant level, the above-ground/below-ground dry mass (1.73 ± 0.60) shows its investment predominately in the above-ground structure with a resulting total leaf area per plant of 1399 ± 94 cm2. The senescent attached leaves at the base of the plant contribute to limit leaf transpiration by shading soil around the plant. Moreover, the dense C. gymnocarpa leaf pubescence, leaf rolling, the relatively high leaf mass area (LMA = 12.3 ± 1.3 mg cm−2) and leaf tissue density (LTD = 427 ± 44 mg cm−3) contribute to limit leaf transpiration, also postponing leaf death under dry conditions. At the physiological level, a relatively low respiration/photosynthesis ratio (R/PN) in spring results from high R [2.26 ± 0.59 μmol (CO2) m−2 s−1] and PN [12.3 ± 1.5 μmol (CO2) m−2 s−1]. The high photosynthetic nitrogen use efficiency [PNUE = 15.5 ± 0.4 μmol (CO2) g−1 (N) s−1] shows the large amount of nitrogen (N) invested in the photosynthetic machinery of new leaves, associated to a high chlorophyll content (Chl = 35 ± 5 SPAD units). On the contrary, the highest R/PN ratio (1.75 ± 0.19) in summer is due to a significant PN decrease and increase of R in response to drought. The low PNUE [1.5 ± 0.2 μmol (CO2) g−1 (N) s−1] in this season is indicative of a greater N investment in leaf cell walls which may contribute to limit transpiration. On the contrary, the low R/PN ratio (0.05 ± 0.02) in winter is resulting from the limited enzyme activity of the respiratory apparatus [R = 0.23 ± 0.08 μmol (CO2) m−2 s−1] while the low PNUE [3.5 ± 0.2 μmol (CO2) g−1 (N) s−1] suggests that low temperatures additionally limit plant production. The experiment of the imposed water stress confirms that the C. gymnocarpa growth capability is in conformity with the severe conditions of its natural habitat, likewise as it may be the case with others narrow endemic species that have occupied niches with similar extreme conditions.  相似文献   

18.
The first organically templated molybdenum iodates (C5H6N)2Mo2O5(IO3)4(H2O)2 (1), (C10H8N2)[MoO2(IO3)3] · H3O (2), and uranium iodate (C5H5N)2[(UO2)(IO3)3](IO3) (3), have been successfully synthesized under mild hydrothermal conditions. Compound 1 is simple zero-dimensional units consisting of [(Mo2O5(IO3)4)]2− anions, which can be described as a tetranuclear unit hanged on either side by two [IO3] groups. The [Mo2O5(IO3)4]2− anions are in a close connection through the water molecules and protonated pyridine cations, via hydrogen bonds and intermolecular actions. Compound 2 is built up from [MoO6] octahedra and [IO3] pyramids to two-dimensional layers, in which 4,4′-bipy molecules and water cations are located, forming strong hydrogen bonds with the inorganic framework, leading to pseudo three-dimensional structure. Compound 3 is one-dimensional ribbons containing {[(UO2)(IO3)3](IO3)}2− anions and charge neutrality is achieved by the protonated 4,4′-bipy cations, which reside between two ribbons, forming hydrogen bonds with the inorganic framework and resulting in pseudo two-dimensional structure. Crystal data are as follows: (C5H6N)2Mo2O5(IO3)4(H2O)2 (1), orthorhombic, Pnma, a = 24.097(5) Å, b = 13.532(3) Å, c = 7.836(16) Å, Z = 4, V = 2555.2(9) Å3; (C10H8N2)[MoO2(IO3)3] · H3O (2), monoclinic, C2/c, a = 24.176(5) Å, b = 10.751(2) Å, c = 7.5074(15) Å, β = 107.44(3)°, Z = 8, V = 1861.6(6) Å3; (C5H5N)2[(UO2)(IO3)3](IO3) (3), monoclinic, P21/n, a = 14.430(3) Å, b = 7.3459(15) Å, c = 19.811(4) Å, β = 106.70(3)°, Z = 4, V = 2011.3(7) Å3.  相似文献   

19.
The binding affinity of the two substrate–water molecules to the water-oxidizing Mn4CaO5 catalyst in photosystem II core complexes of the extremophilic red alga Cyanidioschyzon merolae was studied in the S2 and S3 states by the exchange of bound 16O-substrate against 18O-labeled water. The rate of this exchange was detected via the membrane-inlet mass spectrometric analysis of flash-induced oxygen evolution. For both redox states a fast and slow phase of water-exchange was resolved at the mixed labeled m/z 34 mass peak: kf = 52 ± 8 s− 1 and ks = 1.9 ± 0.3 s− 1 in the S2 state, and kf = 42 ± 2 s− 1 and kslow = 1.2 ± 0.3 s− 1 in S3, respectively. Overall these exchange rates are similar to those observed previously with preparations of other organisms. The most remarkable finding is a significantly slower exchange at the fast substrate–water site in the S2 state, which confirms beyond doubt that both substrate–water molecules are already bound in the S2 state. This leads to a very small change of the affinity for both the fast and the slowly exchanging substrates during the S2 → S3 transition. Implications for recent models for water-oxidation are briefly discussed.  相似文献   

20.
The synthesis of triethylphosphine gold(I) 4-nitrobenzenethiolate, Et3PAu(SC6H4NO2-4), is reported. Et3PAu(SC6H4NO2-4) displays a low energy visible electronic absorption band which is solvent dependent: EtOH (λmax = 385 nm), acetonitrile (λmax = 391 nm), THF (λmax = 395 nm), and DMSO (λmax = 402 nm). The corresponding low energy visible electronic absorption band of 4-nitrobenzenethiolate, 4-NO2C6H4S also shows solvent dependency: acetonitrile, (λmax = 484 nm), DMSO (λmax = 502 nm), dimethylformamide (λmax = 505 nm). The positive solvatochromic shifts for Et3PAu(SC6H4NO2-4) and 4-NO2C6H4S are consistent with an intraligand (IL) charge transfer transition, i.e. π(S) → ∗π (C6H4NO2-4) or n(S) → ∗π (C6H4NO2-4). Assignment of 4-NO2C6H4S was aided by a DFT calculation.  相似文献   

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