共查询到20条相似文献,搜索用时 31 毫秒
1.
Rudakov YO Shumyantseva VV Bulko TV Suprun EV Kuznetsova GP Samenkova NF Archakov AI 《Journal of inorganic biochemistry》2008,102(11):2020-2025
Stoichiometry of the electrocatalytical cycle of cytochrome P450 2B4 was studied in kinetic mode according to bielectrode scheme. Graphite screen-printed electrodes with immobilized cytochrome P450 2B4 were used as the operating electrode (at the potential E0′ = −450 mV) and electrodes, modified with cytochrome c (E0′ = −50 mV) or Prussian Blue (E0′ = 0), as measuring electrodes (for H2O2) and Clark-type electrode (for O2). Benzphetamine N-demethylation rate was 17 ± 3 nmol/nmol of enzyme/min, peroxide production was 4.8 ± 0.7 nmol/nmol of enzyme/min (substrate-free system), 3.3 ± 0.6 nmol/nmol of enzyme/min (0.5 mM benzphetamine), the oxygen consumption rate by Р450 2В4 was 19.4 ± 0.6 nmol/nmol of enzyme/min (in the presence of benzphetamine), 4.8 ± 0.4 nmol/nmol of enzyme/min (without substrate). Based on stoichiometry of P450 electrocatalysis adequacy of electrochemical reduction and P450-monooxygenase system was revealed. 相似文献
2.
Sensitive amperometric immunosensor for α-fetoprotein based on carbon nanotube/gold nanoparticle doped chitosan film 总被引:2,自引:0,他引:2
Jiehua Lin 《Analytical biochemistry》2009,384(1):130-57
A novel strategy for the fabrication of sensitive immunosensor to detect α-fetoprotein (AFP) in human serum has been proposed. The immunosensor was prepared by immobilizing AFP antigen onto the glassy carbon electrode (GC) modified by gold nanoparticles and carbon nanotubes doped chitosan (GNP/CNT/Ch) film. GNP/CNT hybrids were produced by one-step synthesis based on the direct redox reaction. The electrochemical properties of GNP/CNT/Ch films were characterized by impedance spectroscopy and cyclic voltammetry. It was indicated that GNP/CNT nanohybrid acted as an electron promoter and accelerated the electron transfer. Sample AFP, immobilized AFP, and alkaline phosphatase (ALP)-labeled antibody were incubated together for the determination based on a competitive immunoassay format. After the immunoassay reaction, the bound ALP label on the modified GC led to an amperometric response of 1-naphthyl phosphate (1-NP), which was changed with the different antigen concentrations in solution. Under the optimized experimental conditions, the resulting immunosensor could detect AFP in a linear range from 1 to 55 ng ml−1 with a detection limit of 0.6 ng ml−1. The proposed immunosensor, by using GNP/CNT/Ch as the immobilization matrix of AFP, offers an excellent amperometric response of ALP-anti-AFP to 1-NP. The immunosensor provided a new alternative to the application of other antigens or other bioactive molecules. 相似文献
3.
Xianghong Wu 《Inorganica chimica acta》2009,362(6):1847-1960
The reaction of uranyl acetate with (2,2′-(1E,1′E)-(2-benzyl-3-hydroxyquinoxaline-6,7-diyl)bis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene) diphenol) (H2L1) at room temperature in methanol and chloroform yields the UO2L1 complex. Crystals were grown through solvent diffusion of the ligand-metal complex in dimethyl formamide with diethyl ether to prepare: UO2L1 · DMF (1). Complexes with 2,2′-(1E,1′E)-(2-benzyl-3-hydroxyquinoxaline-6,7-diyl)bis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)dibenzene-1,4-diol (H2L2) and 2,2′-(1E,1′E)-(2-hydroxy-3-isopropylquinoxaline-6,7-diyl)bis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)diphenol (H2L3) were also prepared, and crystals of the uranyl complexes (UO2L2 · DMF (2) and (3)) grown from DMF/ether. A fourth complex UO2L4 · H2O (4) was prepared through layering a solution of the tetra-tert-butyl substituted 2-quinoxalinol salen ligand H2L4 in acetone with an aqueous solution containing uranyl acetate. The complexes exhibit a symmetric core featuring a slightly distorted bicapped pentagonal geometry around the uranium center with two oxo-groups and two imine groups from the ligand chelating the ligand and the fifth site in the coordination plane of the ligand occupied by a solvent molecule. These compounds have been characterized using solution (NMR and UV-Vis) and solid-state (IR, X-ray crystallography) techniques. Complexes of H2L4 with early transition metals; Mn2+, Co2+, Ni2+, and Cu2+ are also prepared and characterized for comparison of solution and spectroscopic characteristics. 相似文献
4.
Large catalase based bioelectrode for biosensor application 总被引:1,自引:0,他引:1
A large catalase (CAT) (Mr ~ 90 kDa), immobilized on multiwalled carbon nanotubes—Nafion® (MWCNT-NF) matrix and encapsulated with polyethylenimine (PEI) on glassy carbon electrode (GCE), showed a pair of nearly reversible cyclic voltammetric peaks for Fe(III)/Fe(II) couple with formal potential of about −0.45 V (vs. Ag/AgCl electrode at pH 7.5). PEI significantly reduced the charge transfer resistance and stabilized the bioelectrode through electrostatic interaction. The electron transfer rate constant and surface coverage of the immobilized CAT were 1.05 ± 0.2 s−1 and 2.1 × 10−10 mol cm−2, respectively. Studies on electrocatalytic activity and kinetics of GCE/MWCNT-NF/CAT/PEI for hydrogen peroxide (H2O2) showed the apparent Michaelis-Menten constant of 3 mM, linear response in the range of 10 μM to 5 mM, response time of ~ 2 s for steady state current, and detection limit of ~ 1 μM. A high operational and storage stability was also demonstrated for the bioelectrode. Hence, the direct electrochemistry of the large catalase and its potential biosensor application have been established through this investigation. 相似文献
5.
Effendy Corrado di Nicola Adriano Pizzabiocca Neil Somers 《Inorganica chimica acta》2006,359(1):64-80
Single crystal X-ray structural characterizations are recorded for a number of adducts of MX:dpex (2:3) stoichiometry (MX = simple univalent copper or silver salt; dpex = Ph2E(CH2)xEPh2 (E = P, As)). CuX:dppe (2:3) (X = Cl, Br, I, CN) are binuclear [(dppe-P,P′)CuX(P-dppe-P′)CuX(P,P′-dppe)], all centrosymmetric. AgX:dpex (2:3) (dpex = ‘dpae’ (Ph2As(CH2)2AsPh2), X = Br, F3CCO2 (= ‘tfa’), F3CSO3 (≡ ‘tfs’); dpex = ‘dpape’ (Ph2As(CH2)2PPh2), X = CN, SCN, OClO3) are one-dimensional polymers ?-E′)1AgX(E-dpex-E′)2-AgX(E-dpex-E′)1AgX?, P, As sites scrambled in the latter. AgNO3:dpam (2:3) is also a one-dimensional polymer, ?AgO·NO·OAg(As-dpam-As)AgO·NO·OAg? (‘dpam’ ≡ Ph2As(CH2)2AsPh2). AgX:dpae (2:3) (X = I, CN, ClO4, NO3) and AgX:dpape (2:3) (X = Br, I, NO3) are two-dimensional polymers with large 30-membered macrocyclic rings; similar webs are found for dppx ligands in AgOH:dppb (2:3) and AgNCO, Agtfa:dpph (2:3) with 42- and 54-membered rings. Complexes AgX:dpape (1:3) (X = Cl, Br) are defined as mono-nuclear [XAg(Ph2P(CH2)2AsPh2)3] arrays, the unidentate ligands predominantly P-bound. Synthetic procedures for the adducts are reported, selected compounds being characterized both in solution (1H, 31P NMR, ESI MS) and in the solid state (IR). 相似文献
6.
Michael W. Cooke 《Inorganica chimica acta》2008,361(8):2259-2269
We herein describe the synthesis and characterization of a series of homoleptic, Ru(II) complexes bearing peripheral carboxylic acid functionality based upon the novel ligand 4′-(4-carboxyphenyl)-4,4″-di-(tert-butyl)tpy (L1), as well as 4′-(4-carboxyphenyl)tpy (L2) and 4′-(carboxy)tpy (L3) (where tpy = 2,2′: 6′,2″-terpyridine). Inspection of the metal-based oxidations (E1/2 = 1.22-1.42 V) indicates an anodic shift (∼0.2 V) for (L3)2Ru2+ (3b) (E1/2 = 1.40 V) relative to (L2)2Ru2+ (2b) (E1/2 = 1.22 V). The metal-based oxidation (E1/2 = 1.22 V) and ligand-based reductions (E1/2 = −1.25 to −1.52 V) of (L1)2Ru2+ (1) are essentially invariant relative to those of the structural analogue 2b (PF6)2, which suggests no significant electronic effect caused by the tert-butyl groups. This is supported by invariance in the metal-to-ligand charge transfer bands in both the electronic absorption (494-489 nm) and emission spectra (654-652 nm). However, contrary to 2b, complex 1 is both very soluble and exhibits a highly porous solid-state structure with internal cavity dimensions of 15 Å × 14 Å due to the preclusion of inter-annular interactions by the bulky tert-butyl substituents. 相似文献
7.
Ali Canlier 《Inorganica chimica acta》2010,363(1):1-4850
Crystal structure of [ReO2(4-MeOpy)4][PF6] (4-MeOpy = 4-methoxypyridine) complex has been examined by the single crystal X-ray analytical method. This complex shows a trans-dioxo geometry (average Re-O bond length = 1.766(2) Å) and its equatorial plane is occupied by four 4-MeOpy molecules (average Re-N bond length = 2.156(4) Å). Electrochemical reaction of [ReO2(4-MeOpy)4]+ in CH3CN solution containing tetra-n-butylammonium perchlorate as a supporting electrolyte has been studied using cyclic voltammetry at 24 °C. Cyclic voltammograms show one redox couple around 0.65 V (Epa) and 0.58 V (Epc) [versus ferrocene/ferrocenium ion redox couple, (Fc/Fc+)]. Potential differences between two peaks (ΔEp) at scan rates in the range from 0.01 to 0.10 V s−1 are 65 mV, which is almost consistent with the theoretical ΔEp value (59 mV) for the reversible one electron transfer reaction at 24 °C. The ratio of anodic peak currents to cathodic ones is 1.04 ± 0.03 and the (Epa + Epc)/2 value is constant, 0.613 ± 0.001 V versus Fc/Fc+, regardless of the scan rate. Spectroelectrochemical experiments have also been carried out by applying potentials from 0.40 to 0.77 V versus Fc/Fc+ with an optically transparent thin layer electrode. It was found that the UV-visible absorption spectra show clear isosbestic points at 228, 276, and 384 nm, and that the electron stoichiometry is evaluated as 1.03 from the Nernstian plot. These results indicate that the [ReO2(4-MeOpy)4]+ complex is oxidized reversibly to the [ReO2(4-MeOpy)4]2+ complex. Furthermore, it was clarified that the [ReO2(4-MeOpy)4]2+ in CH3CN has the characteristic absorption bands at 236, 278, 330, 478, and 543 nm and their molar absorption coefficients are 4.3 × 104, 4.5 × 103, 1.0 × 104, and 6.1 × 103 M−1 cm−1 (M = mol dm−3), respectively. 相似文献
8.
Three mono oxovanadium(V) complexes of tridentate Schiff base ligands [VO(OMe)L1] (1), [VO(OMe)L2] (2) and [VO(OMe)L3] (3) obtained by monocondensation of 3-hydroxy-2-naphthohydrazide and aromatic o-hydroxyaldehydes have been synthesized (H2L1 = (E)-3-hydroxy-N′-(2-hydroxy-3-methoxybenzylidene)-2-naphthohydrazide, H2L2 = (E)-3-hydroxy-N′-(2-hydroxybenzylidene)-2-naphthohydrazide and H2L3 = (E)-N′-(5-bromo-2-hydroxybenzylidene)-3-hydroxy-2-naphthohydrazide). The complexes were characterized by spectroscopic methods in the solid state (IR) and in solution (UV-Vis, 1H NMR). Single crystal X-ray analyses were performed with 1 and 2. The catalytic potential of these complexes has been tested for the oxidation of cyclooctene using H2O2 as the terminal oxidant. The effects of various parameters including the molar ratio of oxidant to substrate, the temperature, and the solvent have been studied. The catalyst 2 showed the most powerful catalytic activity in oxidation of various terminal, cyclic and phenyl substituted olefins. Excellent conversions have been obtained for the oxidation of cyclic and bicyclic olefins. 相似文献
9.
Photoinduced electron transfer between [Ru(bpy)2mbpy-pyr]2+ complex, where mbpy = 4-methyl-4′-carbonyl-2,2′-bipyridine and pyr = 1-aminopyrene, and N,N-dimethylaniline (DMA) gives rise to an irreversible process which ultimately leads to the cleavage of the amide bond that links the pyrene to the ruthenium diimine complex. The photochemical reaction under stationary irradiation was monitored by emission and IR spectroscopic techniques as well as by HPLC chromatographic methods. The results suggest that the amide bond fragmentation occurs after the initial electron transfer process, involving the 3MLCT state of the Ru complex and DMA moiety that results in the formation of [Ru(bpy)2mbpy]2+ complex and pyrene-1-isocyanate primary photoproducts. This last photoproduct suffers hydrolysis in aqueous medium regenerating the 1-aminopyrene ligand and carbon dioxide. 相似文献
10.
Damien M. Murphy Patricia Richardson Richard E.P. Winpenny 《Inorganica chimica acta》2011,374(1):435-441
Electrochemical and spectroelectrochemical (UV-Vis, IR, EPR) of pd (pd = 1,10-phenanthroline-5,6-dione), Pt(N,N′-pd)Cl2, Pd(N,N′-pd)Cl2, [Ru(bpy)2(N,N′-pd)]Cl2 (bpy = 2,2′-bipyridine) and Pt(O,O′-pd)(PPh3)2, where N,N′ and O,O′ refers to coordination of pd to the metal centre via N and O atoms, respectively, reveals that the electron transfer processes between +0.5 and −1.25 V all occur at the pd ligand in agreement with DFT calculations. The two CO groups carry a significant amount of the negative charge in mono-reduced pd1−. The mode of coordination of pd has a greater influence on its redox chemistry than the metal centre or the ancillary ligands. 相似文献
11.
An amperometric lactate biosensor was developed based on a conducting polymer, poly-5,2′-5′,2′′-terthiophene-3′-carboxylic acid (pTTCA), and multiwall carbon nanotube (MWNT) composite on a gold electrode. Lactate dehydrogenase (LDH) and the oxidized form of nicotinamide adenine dinucleotide (NAD+) were subsequently immobilized onto the pTTCA/MWNT composite film. The modified electrode was characterized by quartz crystal microbalance (QCM), scanning electron microscopy (SEM), and electrochemical experiments. The detection signal was amplified by the pTTCA/MWNT assembly onto which a sufficient amount of enzyme was immobilized and stabilized by the covalent bond formation between the amine groups of enzyme and the carboxylic acid groups of the pTTCA/MWNT film. Experimental parameters affecting the sensor responses, such as applied potential, pH, and temperature, were assessed and optimized. Analytical performances and dynamic ranges of the sensor were determined, and the results showed that the sensitivity, stability, and reproducibility of the sensor improved significantly using pTTCA/MWNT composite film. The calibration plot was linear (r2 = 0.9995) over the range of 5 to 90 μM. The sensitivity was approximately 0.0106 μA/μM, with a detection limit of 1 μM, based on a signal/noise ratio of 3. The applicability of the sensor for the analysis of l-lactate concentration in commercial milk and human serum samples was demonstrated successfully. 相似文献
12.
Joshua Telser Kun-Yuan Chen Dmitry Smirnov J. Krzystek 《Journal of inorganic biochemistry》2009,103(4):487-495
Aminocarboxylate complexes of vanadium(III) are of interest as models for biologically and medicinally relevant forms of this interesting and somewhat neglected ion. The V(III) ion is paramagnetic, but not readily suited to conventional EPR, due to its integer-spin ground state (S = 1) and associated large zero-field splitting (zfs). High-frequency and -field EPR (HFEPR), however, has the ability to study such systems effectively. Three complexes, all previously structurally characterized: Na[V(trdta)] · 3H2O, Na[V(edta)(H2O)] · 3H2O, and [V(nta)(H2O)3] · 4H2O (where trdta stands for trimethylenediamine-N,N,N′,N′-tetraacetate and nta stands for nitrilotriacetate) were studied by HFEPR. All the investigated complexes produced HFEPR responses both in the solid state, and in aqueous solution, but those of [V(nta)(H2O)3] · 4H2O were poorly interpretable. Analysis of multi-frequency HFEPR spectra yielded a set of spin Hamiltonian parameters (including axial and rhombic zfs parameters: D and E, respectively) for these first two complexes as solids: Na[V(trdta)] · 3H2O: D = 5.60 cm−1, E = 0.85 cm−1, g = 1.95; Na[V(edta)(H2O)] · 3H2O: D = 1.4 cm−1, E = 0.14 cm−1, g = 1.97. Spectra in frozen solution yielded similar parameters and showed multiple species in the case of the trdta complex, which are the consequence of the flexibility of this ligand. The EPR spectra obtained in frozen aqueous solution are the first, to our knowledge, of V(III) in solution in general and show the applicability of HFEPR to these systems. In combination with very insightful previous studies of the electronic absorption of these complexes which provided ligand-field parameters, it has been possible to describe the electronic structure of V(III) in [V(trdta)]− and [V(edta)(H2O)]−; the quality of data for [V(nta)(H2O)3] does not permit analysis. Qualitatively, six-coordinate V(III) complexes with O,N donor atoms show no electronic absorption band in the NIR region, and exhibit relatively large magnitude zfs (D ? 5 cm−1), while analogous seven-coordinate complexes do have a NIR absorption band and show relatively small magnitude zfs (D < 2 cm−1). 相似文献
13.
Sophie Romain Marius Retegan Allan G. Blackman Marie-Noëlle Collomb 《Inorganica chimica acta》2011,374(1):187-196
To complete the elucidation of the electrochemical properties of MnII-bis(terpyridine) complexes in CH3CN and evaluate the influence of the bulkiness of the terpy substituents, the oxidation processes of [MnII(L)2]2+ (L = terpy for 2,2′:6′,2″-terpyridine, pTol-terpy for 4′-(4-methylphenyl)-2,2′:6′,2″-terpyridine and tBu3-terpy for 4,4′,4″-tri-tert-butyl-2,2′:6′,2″-terpyridine) have been investigated in aqueous (1 M) CH3CN solution. In this medium, exhaustive oxidations at 1.10-1.20 V versus Ag/Ag+ release two electrons per molecule of initial complex and lead to clean dimerization processes with the quantitative formation of the oxo-bridged binuclear [Mn2IVO2(L)2(H2O)2]4+ complex for L = tBu3-terpy and of the tetranuclear [Mn4IVO5(L)4(H2O)2]6+ complexes for L = terpy and pTol-terpy. The formation of the tetranuclear complex with the tBu3-terpy derivative is prevented by the steric hindrance induced by the bulkiness of the tert-butyl groups, as confirmed by molecular mechanics calculations, as well as by their strong electron-donating properties. All these electrogenerated multinuclear complexes have been fully characterized in solution by UV-vis and electron paramagnetic resonance (EPR) spectroscopy. A markedly improved chemical synthesis of [Mn4IVO5(terpy)4(H2O)2]6+ is also reported. 相似文献
14.
Paul Hamon Jean-François Meunier Loïc Toupet Michel Etienne Jean-René Hamon 《Inorganica chimica acta》2009,362(12):4389-11551
The white homoleptic high-spin iron(II) complexes Fe[TpMe2,4Cl]2 (1) was isolated in quantitative yield from reaction mixtures containing 1 equiv of FeCl2(THF)1.5 and 2 equiv of K[TpMe2,4Cl] (TpMe2,4Cl = hydrotris[(4-chloro-3,5-dimethyl-pyrazolyl)]borate). Its purple low-spin iron(III) counterparts 1[O3SCF3] and 1[PF6] were synthesized and isolated in 85% yields upon treatment of 1 with 1 equiv of silver triflate and silver hexafluorophosphate, respectively. The three paramagnetic compounds are air and thermally stable as solids and in solution; they were characterized by elemental analyses, IR, magnetic susceptibility measurements, 1H NMR, and Mössbauer spectroscopy. In addition, 1[PF6] was authenticated by a single-crystal X-ray diffraction. The two scorpionate ligands are κ3-N,N′,N′′ ligated to the central FeIII ion, forming an almost perfect FeN6 octahedron with an average Fe-N bond distance of 1.9551(18) Å. In addition, complex 1 which oxidizes reversibly at E1/2 = 0.483 V/SCE (ΔEp = 94 mV), remains high-spin (S = 2) when the temperature is lowered to 2 K. 相似文献
15.
Andreia N. de Carvalho Weverson R. Gomes Antonio E.H. Machado 《Inorganica chimica acta》2011,370(1):444-448
This work reports on the bimolecular sensitization of nitric oxide release from cis-[Ru(bpy)2(iso)NO](PF6)3 (1) (iso = isoquinoline and bpy = 2,2′-bipyridine) by irradiating the MLCT transition of the chloro analog cis-[Ru(bpy)2(iso)Cl]PF6 (2). The compounds displayed peaks in the ESI-MS spectra at m/z 749.1 and m/z 578.1 ascribed, respectively, to ([1(NO0)−2PF6·CH3OH]2+) and ([2−PF6]+). In the cyclic voltammograms, the nitrosyl complex presented two redox waves related to the NO ligand at 0.48 and −0.37 V (versus Ag/AgCl, NO+/0/−1 processes), while the sensitizer showed two reversible waves at 0.79 and −1.46 V (versus Ag/AgCl, Ru2+/3+ and bpy 0/−1, respectively). The most important feature of this system is that the nitrosyl compound does not have significant absorption in the visible region, while the sensitizer has an intense band centered at 496 nm. The irradiation of an equimolar mixture of the two compounds in an ethanol:water solution (v:v) with light of λ > 500 nm leads to NO release, as probed by amperometric measurements. The variational method was applied, showing that the two compounds self-assembly in solution with a 1:1 stoichiometry. Fluorescence spectra acquired at 77 K provided the E0-0 for the system and, from the thermodynamic cycle it was estimated that the photoinduced electron transfer between the species has a ΔG value of −1.59 eV. 相似文献
16.
The coordination behavior of Cp2Mo2+ towards the ribonucleosides and ribonucleoside monophosphates uridine, adenosine, cytidine, guanosine, 5′-UMP, 5′-AMP, 5′-CMP and 5′-GMP has been studied in solution in the range 4 ? pD ? 9 using NMR spectroscopy. The ribonucleosides were found to bind Cp2Mo2+ exclusively through the ribose moiety giving rise to the chelate complexes [Cp2Mo(urd-O2′,O3′)], [Cp2Mo(ade-O2′,O3′)], [Cp2Mo(cyd-O2′,O3′)], and [Cp2Mo(gua-O2′,O3′)]. The ribonucleotides form three types of complex with Cp2Mo2+ in neutral solution, namely N,PO-macrochelates, PO,O3′-coordinated species as well as O2′,O3′-chelates, while at pD 9 only sugar coordination is observed. 相似文献
17.
Heteroleptic complexes [Ru(bpy)2(R2bpm)]2+, where bpy = 2,2′-bipyridine and R2bpm = 6,6′-diaryl-4,4′-bipyrimidine, have been synthesized and characterized, together with the homoleptic complex [Ru(R2bpm)3]2+, in which R2bpm = 6,6′-diphenyl-4,4′-bipyrimidine. The substituent aryl on the bipyrimidine has significant effects on the properties of these complexes as compared to the parent [Ru(bpy)2(bpm)]2+ complex. The complexes exhibit Ru-to-bpm charge transfer (CT) absorptions centered at about 540 nm and Ru-to-bpy CT absorptions centered at about 435 nm. The assignment of the low energy absorptions is supported by the relative ease of the reduction of the new complexes as compared to [Ru(bpy)3]2+. The new complexes exhibit a relatively intense emission at room temperature, with lifetimes in the 10-50 ns range, with the homoleptic species exhibiting the higher-energy (maximum at 724 nm) and the longest-lived (τ = 48 ns) emission among the complexes. Luminescence lifetimes and quantum yields are governed by the energy gap law, indicating that direct deactivation to the ground state is the dominant relaxation pathway for 1-6, while thermally activated processes are inefficient. 相似文献
18.
Divalent metal ions are necessary in the self splicing reaction of group I introns, and we report that metal interaction to the 2′ position of guanosine for the Azoarcus ribozyme is required for catalysis. Moreover, this metal coordination promotes the guanosine-substrate coupled binding to the ribozyme, which is another conserved feature seen across phylogenetic boundaries. Typically there is a 4-9-fold difference in binding of G to Efree versus E · S. In the Tetrahymena ribozyme’s case this substrate-guanosine communication was attributed to conformational change(s) that lead to cooperative binding of the two cofactors which is almost nonexistent at low temperatures (4 °C). In the prokaryotic Azoarcus ribozyme we also see a 4-5-fold difference in binding of the guanosine/substrate to Efree versus E · G or E · S at 10 °C that is attributed to guanosine-substrate coupling. This coupling is diminished when the metal (Mg2+) coordination to the 2′ is disrupted with use of 2′-amino-2′-deoxyguanosine. The coupling is restored when softer Mn2+ ions are added to the buffer. This evidence generalizes a model for group I ribozyme catalysis that involves metal coordination to the 2′ position of guanosine. However, we see one striking difference in that the guanosine-substrate coupling is reversed. In the Azoarcus system (10 °C) the guanosine/substrate binds 5-fold more tightly to Efree than to E · S or E · G, which is the opposite for Tetrahymena even when the later is run at 4 °C. One implication for this difference in coupling is that the Azoarcus is in a folded state well accommodated for guanosine or substrate binding. This initial binding actually causes a conformational change that retards the subsequent binding of the second cofactor, which contrasts what was found for the Tetrahymena ribozyme. These results indicate that while the role for the metal ions in the chemical catalysis is conserved across phylogenetic boundaries, there is variability in the folding pattern of the ribozyme that leads to phosphoryl transfer. 相似文献
19.
Ronald R. Ruminski Kristin D.K. Zimmer Kelliann A. Rita Mackenzie A. Knobbe Carrie Dean 《Inorganica chimica acta》2009,362(6):1772-165
New Os(II) complexes including [Os(dpop′)2](PF6)2 (dpop′= dipyrido(2,3-a;3′,2′-j)phenazine) and a series of mixed ligand [Os(dpop′)(N-N)Cl]PF6 (N-N = 2,2′-bipyridine(bpy); 2,2′-bipyrimidine(bpm) and 2,3-bis(2-pyridyl)pyrazine(dpp)) were synthesized. The Os dπ → dpop′ π∗ MLCT transitions for [Os(dpop′)2]2+ are observed at lower energy than for Os dπ → tpy π∗ (tpy = 2,2′:6′,2″-terpyridine) and Os dπ → tppz π∗ (tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine) (The ligand abbreviations tpd, tpp and tpypz have also appeared in the literature for 2,3,5,6- tetrakis(2-pyridyl)pyrazine in addition to tppz.) MLCT transitions in the comparative [Os(tpy)2]2+ and [Os(tppz)2]2+ complexes. The Os dπ → dpop′ π∗ MLCT transitions are observed at lower energy in mixed bidentate ligand N-N systems compared with [Os(dpop′)2]2+. Cyclic voltammetry shows more positive osmium oxidation, and less negative ligand reduction potentials for [Os(dpop′)2]2+ as compared to [Os(tpy)2]2+ and [Os(tppz)2]2+ complexes. The osmium oxidation potentials in mixed ligand [Os(dpop′)(N-N)Cl]+ complexes are at less positive potential than for the [Os(dpop′)2]2+ ion. NMR results show different chemical shifts for ring protons either trans or cis to dpop′ in mixed ligand systems, and also show two geometrical isomers for the [Os(dpop′)(dpp)Cl]+ complex. The [Os(dpop′)(dpp)Cl]+ geometric isomer with the pyrazine ring of dpp trans to dpop′ is found more predominate by 1.0/0.7 over the isomer with the pyrazine ring of dpp cis to dpop′ and that inter-conversion of geometric isomers does not occur in room temperature solution on the NMR timescale. 相似文献
20.
Treatment of [Rh(β-diketonato)(cod)] with CO resulted in better yields of [Rh(FcCOCHCOR)(CO)2] than by treating [Rh(Cl)(CO)2]2 with FcCOCH2COR, R = CF3 (Hfctfa), CH3 (Hfca), Ph (Hbfcm, Ph = phenyl) and Fc (Hdfcm, Fc = ferrocenyl). The single crystal structure of the fctfa rhodium(I) complex [C16H10F3FeO4Rh], monoclinic, C 2/c(15), a = 13.266(3) Å, b = 19.553(3) Å, c = 13.278(3) Å, β = 100.92(2)°, Z = 8 showed both rotational and translational displacement disorders for the CF3 group. An electrochemical study revealed that the formal reduction potential, E0′, for the electrochemically reversible one electron oxidation of the ferrocenyl group varied between 0.304 (for the fctfa complex) and 0.172 V (for the dfcm complex) versus Fc/Fc+ in a manner that could be directly traced to the group electronegativities, χR, of the R groups on the β-diketonato ligands, as well as to the values of the free β-diketones. Anodic peak potentials, Epa,Rh, for the dominant cyclic voltammetry peak associated with rhodium(I) oxidation were between 0.718 (bfcm complex) and 1.022 V (dfcm complex) versus Fc/Fc+. Coulometric experiments implicated a second, much less pronounced anodic wave for the apparent two-electron RhI oxidation that overlaps with the ferrocenyl anodic wave and that the redox processes associated with these two RhI oxidation waves are in slow equilibrium with each other. 相似文献