Probing the electronic factors responsible for the cyclic electron-transfer induced isomerism fac ? mer: Synthesis, electrochemical and spectroscopic studies of fac-[Mn(CO)3(L′-L′)L] complexes

Spectroscopic (IR, ³¹P NMR and UV-Vis) and electrochemical studies on fac-[Mn(CO)₃(L′-L′)(L)]^0/+,where L′-L′ = 1,2-bis(diphenylphosphino)ethane (dppe) or 1,10-phenanthroline (phen) and L = bromide, triflate, imidazole (im), isonicotinamide (isn) or N-(2-hydroxyethyl)isonicotinamide (heisn), were undertaken to understand the effect of various ligands on the CO-Mn-L and CO-Mn-(L′-L′) bonding characteristics of these complexes. Crystal structures for L = triflate/L′-L′ = dppe, L = triflate/L′-L′ = phen and L = isn/L′-L′ = phen are reported and they show that the two Mn-O(OSO₂CF₃) and Mn-N(isn) distances are similar. The tricarbonyl complexes exhibit two major bands in the 250-300 and 350-450 nm region of the UV-Vis spectrum. The lowest energy bands have been assigned as a contribution from both the metal-centered (MC) and metal to ligand (d_π → L′-L′) charge transfer (MLCT) transitions. The energy of this maximum absorption decreases in the order Br⁻ ∼ triflate > im > isn ∼ heisn. The cyclic four-component mechanism was observed at room temperature by voltammetric techniques for all the cases. On the basis of d metal orbital splitting, an electronic molecular orbital diagram is proposed. In this model, the ligands along the z-axis play a relevant role in the reverse of the HOMO energies of the fac/mer isomers by stabilizing the metal d_z² orbital relative to d_xy in mer-Mn(II).     

Synthesis, structure and properties of unsymmetrical μ-alkoxo-dicopper(II) complexes: biological relevance to phosphodiester and DNA cleavage and cytotoxic activity

The unsymmetric dinucleating ligand N-(2-hydroxybenzyl)-N,N′,N′-tris(2-pyridylmethyl)-1,3-diaminopropan-2-ol (L = H₂btppnol) and the corresponding copper(II) complex [Cu₂(Hbtppnol)(μ-CH₃COO)](ClO₄)₂ (1) have been recently reported in part in a short communication [Inorg. Chem. Commum. 8 (1999) 334]. In this study, we investigated the ability of complex 1 to promote the hydrolysis of P-O phosphate diester bonds in bis(2,4-dinitrophenyl) phosphate (2,4-BDNPP) and the cleavage of genomic and plasmid DNA molecules. Reaction of 1 with excess of the diester 2,4-BDNPP, at pH 7.0, results in the formation of the monoester phosphate coordinated [Cu₂(Hbtppnol)(μ-((NO₂)₂-C₆H₃)PO₄)]ClO₄ (3) complex, which was also characterized by X-ray crystallography. In addition, the stable μ-phosphate complex [Cu₂(Hbtppnol)(μ-(NO₂-C₆H₄)PO₄)](ClO₄) (2) obtained from the reaction of 4-nitrophenyl phosphate with complex 1 was also characterized by X-ray crystallography, indicating that 1 is unable to cleave monoester-phosphate bonds. The kinetics for the promotion of bis(2,4-dinitrophenyl) phosphate (2,4-BDNPP) hydrolysis by complex 1 was investigated as a function of pH, catalyst concentration and substrate concentration. On the basis of kinetic and potentiometric studies, the deuterium isotope effect (k^H/k^D ∼ 1) and the X-ray structure of the monoester phosphate coordinated [Cu₂(Hbtppnol)(μ-((NO₂)₂-C₆H₃)PO₄)]ClO₄ (3) complex as the product of the reaction, we demonstrated that the aquo/hydroxo complex is the active species and the reaction occurs through the formation of a ternary complex in which one Cu^II binds the substrate and the second copper center has a terminal bound hydroxide to attack the phosphorus atom, at physiological pH. A rate enhancement factor of ∼100 was calculated relative to that measured for the uncatalyzed reaction under identical conditions. Complex 1 effectively promotes the cleavage of double-stranded genomic and plasmid DNA, at physiological pH, probably through a hydrolytic mechanism in agreement with that proposed for the reaction of 1 with 2,4-BDNPP. Finally, cytotoxic activity of 1 in a human small cell lung carcinoma cell line (GLC4) and its cisplatin resistant subline (GLC4/CDDP) was studied and the IC₅₀ values were determined.     

Synthesis and characterization of three new Cu(II)-dipeptide complexes

Three new copper(II) complexes of stoichiometry [Cu(L-dipeptide)].nH(2)O, containing as ligands the dipeptides L-alanine-L-isoleucine, L-alanine-L-threonine and L-alanine-L-tyrosine were prepared. They were characterized by single crystal X-ray diffractometry, and electronic and infrared spectroscopy. In all cases, the Cu(II) cation has essentially the same elongated square pyramidal coordination, being equatorially cis coordinated by a N(2)O(2) arrangement of ligand atoms and axially by a carbonyl oxygen atom. The compounds show rather similar polymeric structures which resemble those recently reported for the [Cu(ala-val)] and [Cu(ala-phe)] complexes. The electronic and infrared spectra are briefly discussed on the basis of the structural peculiarities of the complexes. Superoxide dismutase (SOD)-like activity was also tested for the compounds.     

Characterisation of the ACC oxidase activity in transgenic auxin overproducing tomato during ripening

As part of our studies on the role of auxin in regulating the ethylenebiosynthesis during fruit ripening, in this paper we describe the functionalproperties of the ACC oxidase activity extracted from transgenic tomato(Lycopersicum esculentum Mill. cv. Ailsa craig)overexpressing the tryptophan monooxygenase or iaaM protein fromAgrobacterium tumefaciens that increases the auxin levels.Maximal activity was recovered by extracting the enzyme at pH 8.0 from fruitspicked three days after the onset of the colour change. The enzyme exhibits ahalf-life of 85 min, two relative maxima at 30 and 38°C, an optimum pH of 7.9 and an apparent Km forACC of 118 M. Our results also show the first evidence of anallosteric type kinetic of the ACC oxidase activity with respect to itscosubstrate ascorbate, with an apparent Km of 12.5mM,estimated as the concentration which gave 50% Vmax.     

Heterotropic effectors exert more significant strain on monoligated than on unligated hemoglobin

The effect of allosteric effectors, such as inositol hexakisphosphate and/or bezafibrate, has been investigated on the unliganded human adult hemoglobin both spectroscopically (employing electronic absorption, circular dichroism, resonance Raman, and x-ray absorption near-edge spectroscopies) and functionally (following the kinetics of the first CO binding step up to a final 4% ligand saturation degree). All data indicate that the unliganded T-state is not perturbed by the interaction with either one or both effectors, suggesting that their functional influence is only exerted when a ligand molecule is bound to the heme. This is confirmed by the observation that CO dissociation from partially liganded hemoglobin ( 相似文献   

Light induced states in MbCO denatured with Guanidine hydrochloride

We present the results of a comparative study of the binding of carbon monoxide to myoglobin in glycerol/buffer solution with different concentrations of guanidine hydrochloride, under extended illumination over the temperature range 30 – 80 K. The changes in the Soret band indicate that the folding state of the protein is a key parameter in determining the photodissociation process and the relaxation rate of the protein. Received: 30 January 1997 / Accepted: 14 August 1997     

An x-ray absorption near edge structure spectroscopy study of metal coordination in Co(II)-substituted Carcinus maenas hemocyanin.

High-resolution x-ray absorption near edge structure spectroscopy was used to characterize the metal sites in three different cobalt-substituted derivatives of Carcinus maenas hemocyanin (Hc), including a mononuclear cobalt, a dinuclear cobalt and a copper-cobalt hybrid derivative. Co(II) model complexes with structures exemplifying octahedral, trigonal bipyramidal, pseudo-tetrahedral, and square planar geometries were also studied. The results provide structural information about the metal binding site(s) in the Co-Hcs that extend earlier results from EPR and optical spectroscopy (Bubacco et al. 1992. Biochemistry. 31: 9294-9303). Experimental spectra were compared to those calculated for atomic clusters of idealized geometry, generated using a multiple scattering approach. The energy of the dipole forbidden 1s-->3d transition and of the absorption edge in the spectra for all cobalt Hc derivatives confirmed the cobaltous oxidation state which rules out the presence of an oxygenated site. Comparisons between data and simulations showed that the mononuclear and dinuclear Co(II) derivatives, as well as the hybrid derivative, contain four-coordinate Co(II) in distorted tetrahedral sites. Although the spectra for Co(II) in dinuclear metal sites more closely resemble the simulated spectrum for a tetrahedral complex than do spectra for the mononuclear derivative, the Co(II) sites in all derivatives are very similar. The Cu K-edge high resolution x-ray absorption near edge structure spectrum of the hybrid Cu-Co-Hc resembles that of deoxy-Hc demonstrating the presence of three-coordinate Cu(I).     

Excitatory signaling in bacterial probed by caged chemoeffectors.

Chemotactic excitation responses to caged ligand photorelease of rapidly swimming bacteria that reverse (Vibrio alginolyticus) or tumble (Escherichia coli and Salmonella typhimurium) have been measured by computer. Mutants were used to assess the effects of abnormal motility behavior upon signal processing times and test feasibility of kinetic analyses of the signaling pathway in intact bacteria. N-1-(2-Nitrophenyl)ethoxycarbonyl-L-serine and 2-hydroxyphenyl 1-(2-nitrophenyl) ethyl phosphate were synthesized. These compounds are a 'caged' serine and a 'caged' proton and on flash photolysis release serine and protons and attractant and repellent ligands, respectively, for Tsr, the serine receptor. The product quantum yield for serine was 0.65 (+/- 0.05) and the rate of serine release was proportional to [H+] near-neutrality with a rate constant of 17 s-1 at pH 7.0 and 21 degrees C. The product quantum yield for protons was calculated to be 0.095 on 308-nm irradiation but 0.29 (+/- 0.02) on 300-350-nm irradiation, with proton release occurring at > 10(5) s-1. The pH jumps produced were estimated using pH indicators, the pH-dependent decay of the chromophoric aci-nitro intermediate and bioassays. Receptor deletion mutants did not respond to photorelease of the caged ligands. Population responses occurred without measurable latency. Response times increased with decreased stimulus strength. Physiological or genetic perturbation of motor rotation bias leading to increased tumbling reduced response sensitivity but did not affect response times. Exceptions were found. A CheR-CheB mutant strain had normal motility, but reduced response. A CheZ mutant had tumbly motility, reduced sensitivity, and increased response time to attractant, but a normal repellent response. These observations are consistent with current ideas that motor interactions with a single parameter, namely phosphorylated CheY protein, dictate motor response to both attractant and repellent stimuli. Inverse motility motor mutants with extreme rotation bias exhibited the greatest reduction in response sensitivity but, nevertheless, had normal attractant response times. This implies that control of CheY phosphate concentration rather than motor reactions limits responses to attractants.