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1.
《Inorganica chimica acta》1986,118(2):157-164
Copper(II) complexes with 2-methylamino-3-picoline N-oxide (3MMH) and 2-ethylamino-3-picoline N- oxide (3MEH) have been prepared from the following salts: tetrafluoroborate, nitrate, chloride, bromide and acetate. Solids of the general formula [Cu(LH)4]- (X2) (where LH = either ligand when X = BF4tau; and LH = 3MMH when X = NO3tau; ); [Cu(3MEH)2- (ONO2)2]; [Cu(LH)X2] (where LH = either ligand and X = Cltau; , Brtau; ) and CuL2 (where L = either ligand's conjugate base) were characterized using spectral methods (i.e., IR, UV-Vis and ESR). Both coordinate as monodentate ligands via their N-oxide oxygen in their complexes with salts having polyatomic anions. They bond as neutral bidentate ligands in their halide complexes, but as anionic bidentate ligands in the complexes formed from copper(II) acetate. The bonding to Cu(II) ccnters via the N-oxide oxygen is the strongest tor these two ligands based on spectral data than any of the 2-aminopyridine N-oxides or 2- aminopicoline N-oxides studied to date. 相似文献
2.
Rathinasabapathi Prabhakaran Ramasamy Karvembu Karuppannan Natarajan 《Inorganica chimica acta》2007,360(2):691-694
An unusual coordination mode of salicylaldehyde-N-phenylthiosemicarbazone (H2-Sal-Ptsc) ligand was observed in unusual ruthenium(III) carbonyl complex for the first time when it was reacted with [RuHCl(CO)(PPh3)3]. The EPR and electrochemical analysis conformed the formation of Ru(III) species. 相似文献
3.
《Inorganica chimica acta》1986,115(2):141-146
A series of new aromatic N-oxide ligands have been prepared by converting the 2-amino group of 2-aminopyridine N-oxide, 2-aminopicoline N-oxides and 2-amino-4,6-lutidine N-oxide into a urethane. Two series of copper(II) complexes have been prepared and characterized by their infrared, electronic and ESR spectra along with other physicochemical methods. One series has the stoichiometry [Cu(UOH)4](ClO4)2 and involves monodentate coordination via the N-oxide oxygen and the other series is prepared from copper(II) acetate and has the stoichiometry [Cu(UO)2]. In this latter series coordination occurs via the N-oxide oxygen and the deprotonated amino function. 相似文献
4.
T. Wu A. M. Griffin C. A. Gorski E. S. Shelobolina H. Xu R. K. Kukkadapu 《Geomicrobiology journal》2017,34(3):231-241
Dissimilatory microbial reduction of solid-phase Fe(III)-oxides and Fe(III)-bearing phyllosilicates (Fe(III)-phyllosilicates) is an important process in anoxic soils, sediments and subsurface materials. Although various studies have documented the relative extent of microbial reduction of single-phase Fe(III)-oxides and Fe(III)-phyllosilicates, detailed information is not available on interaction between these two processes in situations where both phases are available for microbial reduction. The goal of this research was to use the model dissimilatory iron-reducing bacterium (DIRB) Geobacter sulfurreducens to study Fe(III)-oxide vs. Fe(III)-phyllosilicate reduction in a range of subsurface materials and Fe(III)-oxide stripped versions of the materials. Low-temperature (12 K) Mossbauer spectroscopy was used to infer changes in the relative abundances of Fe(III)-oxide, Fe(III)-phyllosilicate, and phyllosilicate-associated Fe(II) (Fe(II) phyllosilicate). A Fe partitioning model was employed to analyze the fate of Fe(II) and assess the potential for abiotic Fe(II)-catalyzed reduction of Fe(III)-phyllosilicates. The results showed that in most cases Fe(III)-oxide utilization dominated (70–100%) bulk Fe(III) reduction activity, and that electron transfer from oxide-derived Fe(II) played only a minor role (ca. 10–20%) in Fe partitioning. In addition, the extent of Fe(III)-oxide reduction was positively correlated to surface area-normalized cation exchange capacity and the Fe(III)-phyllosilicate/total Fe(III) ratio. This finding suggests that the phyllosilicates in the natural sediments promoted Fe(III)-oxide reduction by binding of oxide-derived Fe(II), thereby enhancing Fe(III)-oxide reduction by reducing or delaying the inhibitory effect that Fe(II) accumulation on oxide and DIRB cell surfaces has on Fe(III)-oxide reduction. In general our results suggest that although Fe(III)-oxide reduction is likely to dominate bulk Fe(III) reduction in most subsurface sediments, Fe(II) binding by phyllosilicates is likely to play a key role in controlling the long-term kinetics of Fe(III) oxide reduction 相似文献
5.
Raji Raveendran 《Inorganica chimica acta》2006,359(10):3212-3220
The reactions of [Ru(PPh3)3Cl2], N-(benzoyl)-N′-(5-R-salicylidene)hydrazines (H2bhsR, R = H, OCH3, Cl, Br and NO2) and triethylamine (1:1:2 mole ratio) in methanol afford mononuclear ruthenium(III) complexes having the general formula trans-[Ru(bhsR)(PPh3)2Cl]. In the case of R = H, a dinuclear ruthenium(III) complex of formula [Ru2(μ-OCH3)2(bhsH)2(PPh3)2] has been isolated as a minor product. The complexes are characterized by elemental analysis, magnetic, spectroscopic and electrochemical measurements. The crystal structures of the dinuclear complex and two mononuclear complexes have been determined. In the dinuclear complex, each metal centre is in distorted octahedral NO4P coordination sphere constituted by the two bridging methoxide groups, one PPh3 molecule and the meridionally spanning phenolate-O, imine-N and amide-O donor bhsH2−. The terminal PPh3 ligands are trans to each other. In the mononuclear complexes, bhsR2− and the chlorine atom form an NO2Cl square-plane around the metal centre and the P-atoms of the two PPh3 molecules occupy the remaining two axial sites to complete a distorted octahedral NO2ClP2 coordination sphere. All the complexes display ligand-to-metal charge transfer bands in the visible region of the electronic spectra. The cryomagnetic measurements reveal the antiferromagnetic character of the diruthenium(III) complex. The low-spin mononuclear ruthenium(III) complexes as well as the diruthenium(III) complex display rhombic EPR spectra in frozen solutions. All the complexes are redox active in CH2Cl2 solutions. Two successive metal centred oxidations at 0.69 and 1.20 V (versus Ag/AgCl) are observed for the dinuclear complex. The mononuclear complexes display a metal centred reduction in the potential range −0.53 to −0.27 V. The trend in these potential values reflects the polar effect of the substituents on the salicylidene moiety of the tridentate ligand. 相似文献
6.
Galina T. Babkina Jiří Jonák Ivan Rychlík 《Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression》1982,698(2):116-127
New types of azidoaryl analogs of GTP: γ-(4-azido)anilide of GTP (I), γ-(N-(4-azidobenzyl)-N-methyl)amide of GTP (II) and of GDP: β-(4-azido)anilide of GDP (III), β-(N-(4-azidobenzyl)-N-methyl)amide of GDP (IV) have been synthesized by treatment of the nucleotide in aqueous solution with N-cyclohexyl-N′-β-(4-methylmorpholinium)- ethylcarbodiimidep-toluene sulfonate and the respective amine. The analog of GTP bearing at the γ-phosphate an alkylating 2-chloroethylamino group: γ-(4-N-(2-chloroethyl)-N-methylaminobenzyl)amide of GTP (V) was prepared by the method described previously for the preparation of the analog of ATP (Knorre, D.G., Kurbatov, V.A. and Samukov, V.V. (1976) FEBS Lett. 70, 105–108). Azidoaryl analogs of GTP and GDP as well as the chloroethylaminoaryl analog of GTP compete with GDP in the formation of the binary complex EF-Tu·GDP with the respective Ki values 3.9·10?7 M (I), 2.9·10?8 M (II), 6.9·10?7 M (III), 5.0·10?7 M (IV) and 3.8·10?8 M (V) relative to GDP. constants of the complexes of the radioactively-labeled GTP analogs I, II and V with elongation factor Tu were calculated to be 8.5·10?6 M, 3.4·10?7 M and 4.6·10?8 M, respectively, or approx. 1740-, 70- and 9-times greater than that of GDP. GTP analogs I, II and V were found to substitute GTP in the stimulation of EF-Tu-dependent binding of aminoacyl-tRNA to the ribosome-mRNA complex. 相似文献
7.
Debabrata Chatterjee Susan Basak Ayon Sengupta Jacques Muzart 《Inorganica chimica acta》2006,359(4):1325-1328
A mixed-ligand ruthenium(III) catalyst complex, [RuIII(TDL*)(bipy)(H2O)]Cl (1) (TDL* = N-3,5-di-(t-butyl)salicylidine-d-glucosamine; bipy = 2,2′-bipyridine) exhibited catalytic activity toward enantioselective alkene epoxidation using tert-butyl hydroperoxide as terminal oxidant. Styrene, 4-chlorostyrene, 4-methylstyrene, 4-methoxystyrene, 1-methylcyclohexene and 1,2-dihydronaphthalene were effectively converted to their organic epoxides with moderate enantioselectivity (37-47% ee) at ambient temperature. A mechanism involving the formation of a high-valent Ru(V)-oxo species, and the subsequent oxo-transfer to the alkene through a metallaoxetane intermediate is proposed. 相似文献
8.
Isamu Murakoshi Eiji Kidoguchi Minako Nakamura Joju Haginiwa Shigeru Ohmiya Kimio Higashiyama Hirotaka Otomasu 《Phytochemistry》1981,20(7):1725-1730
From the fresh leaves of Sophora tomentosa, three new lupin alkaloids, (?)-epilamprolobine, (+)-epilamprolobine N-oxide and 5-(3′-methoxycarbonylbutyroyl)aminomethyl-trans-quinolizidine N-oxide, have further been isolated along with (+)-matrine, (+)-matrine N-oxide, (+)-sophocarpine N-oxide, (?)-anagyrine, (?)- baptifoline, (?)-cytisine, (?)-N-methylcytisine, (?)-N-formylcytisine, (?)-N-acetylcytisine and (±)-ammodendrine. The absolute configurations of (+)-epilamprolobine N-oxide (1R:5R:6S) and (?)-epilamprolobine (5R:6S) have also been established by spectroscopic data and by comparison with synthetic (+)-epilamprolobine (5S:6R)derived from (?)-lupinine (5R:6R). (?)-Epilamprolobine is a diastereomer of (+)-lamprolobine (5R:6R) in Lamprolobium fruticosum and 5-(3′-methoxycarbonylbutyroyl) aminomethyl-trans-quinolizidine N-oxide is presumed to be an artefact. A biosynthetic pathway for the formation of (?)-epilamprolobine is also proposed. 相似文献
9.
The copper(II) complex of the acyclic EBTA ligand (H4EBTA = 1,2-bis(2-aminoethoxy)benzene-N,N,N′,N′-tetraacetic acid) has been prepared and characterized by X-ray analysis. The two copper ions of the dinuclear unit present the same distorted octahedral coordination polyhedra. The EBTA ligand is shared between two copper coordination centres, with the formation of centrosymmetric dimers, which are linked in a supramolecular tridimensional structure via additional interactions through the coordinated waters molecules with adjacent carboxylic oxygen atoms. The stability and protonation constants of EBTA with Cu(II) and Zn(II) ions indicate a higher stability of these complexes with respect to the corresponding complexes with the more flexible EGTA ligand (H4EGTA = ethyleneglycol-bis(2-aminoethylether)-N,N,N′,N′-tetraacetic acid). On the other hand, the lower stability of [Gd(EBTA)]− than [Gd(EGTA)]− results in a decreased overall selectivity (lower Ksel) of EBTA towards Gd(III) and suggests that this complex may undergoes transmetallation reactions under physiological conditions. 相似文献
10.
Hanif M Meier SM Kandioller W Bytzek A Hejl M Hartinger CG Nazarov AA Arion VB Jakupec MA Dyson PJ Keppler BK 《Journal of inorganic biochemistry》2011,105(2):224-231
The synthesis, characterization, reactivity and in vitro anticancer activity of a series of RuII-arene complexes with carbohydrate-derived phosphite and biscarboxylato co-ligands are reported. The compounds were characterized by NMR spectroscopy and electrospray ionization (ESI) mass spectrometry, and the molecular structures of oxalato(η6-p-cymene)(3,5,6-bicyclophosphite-1,2-O-isopropylidene-α-D-glucofuranoside)ruthenium(II) and oxalato(η6-p-cymene)(3,5,6-bicyclophosphite-1,2-O-cyclohexylidene-α-D-glucofuranoside)ruthenium(II) were determined by X-ray diffraction analysis. In contrast to their dichlorido counterparts, the biscarboxylato complexes did not exhibit significant reactivity towards biomolecules, such as cysteine, methionine, ubiquitin or the DNA model 5′-GMP, and resist hydrolysis; no hydrolytic species were detected by 1H and 31P{1H} NMR spectroscopy over several days. These structural alterations led to a decrease in the tumor-inhibiting potency of the compounds in human cancer cell lines. 相似文献
11.
Direct Identification of a Bacterial Manganese(II) Oxidase, the Multicopper Oxidase MnxG, from Spores of Several Different Marine Bacillus Species
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Gregory J. Dick Justin W. Torpey Terry J. Beveridge Bradley M. Tebo 《Applied microbiology》2008,74(5):1527-1534
Microorganisms catalyze the formation of naturally occurring Mn oxides, but little is known about the biochemical mechanisms of this important biogeochemical process. We used tandem mass spectrometry to directly analyze the Mn(II)-oxidizing enzyme from marine Bacillus spores, identified as an Mn oxide band with an in-gel activity assay. Nine distinct peptides recovered from the Mn oxide band of two Bacillus species were unique to the multicopper oxidase MnxG, and one peptide was from the small hydrophobic protein MnxF. No other proteins were detected in the Mn oxide band, indicating that MnxG (or a MnxF/G complex) directly catalyzes biogenic Mn oxide formation. The Mn(II) oxidase was partially purified and found to be resistant to many proteases and active even at high concentrations of sodium dodecyl sulfate. Comparative analysis of the genes involved in Mn(II) oxidation from three diverse Bacillus species revealed a complement of conserved Cu-binding regions not present in well-characterized multicopper oxidases. Our results provide the first direct identification of a bacterial enzyme that catalyzes Mn(II) oxidation and suggest that MnxG catalyzes two sequential one-electron oxidations from Mn(II) to Mn(III) and from Mn(III) to Mn(IV), a novel type of reaction for a multicopper oxidase. 相似文献
12.
Yan Z. Voloshin Oleg A. Varzatskii Zoya A. Starikova Valentin V. Novikov 《Inorganica chimica acta》2011,370(1):322-332
The triribbed-functionalized cobalt(II,III) and ruthenium(II) clathrochelate derivatives of the vic-dioximes with two nitrogen or sulfur atoms in α-positions to π-conjugated diazomethine chelate fragments of a macrobicyclic framework were obtained in moderate yields under mild and high dilution conditions by nucleophilic substitution of six reactive chlorine atoms of the boron-capped macrobicyclic cobalt and ruthenium(II) precursors with N2- and S2-dinucleophiles (ethylenediamine and the corresponding α-dithiols in the presence of triethylamine, respectively). The complexes obtained were characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV-Vis, 1H and 13C{1H} NMR and EPR spectroscopies, magnetochemistry and X-ray crystallography. The MN6-coordination polyhedra of all the X-ray studied clathrochelates possess a slightly distorted trigonal prismatic geometry. The encapsulated cobalt(II) ions are shifted from the centers of the cavities formed by the macrobicyclic ligand due to the Jahn-Teller distortion, while the ruthenium and iron(II) ions in their clathrochelate analogs do occupy these centers. The main geometrical parameters of the macrobicyclic frameworks vary with Shannon radius of an encapsulated metal ion. In the case of the tris-ethylenediamine cobalt(III) clathrochelate, the field strength of the macrobicyclic amine ligand is essentially lower than those for their aromatic and aliphatic analogs because of the negative σpara-effect of the ribbed alkylamine substituents. The magnetometry and EPR data confirmed the low-spin character of the cobalt(II) complexes synthesized. The electrochemically generated oxidized cobalt clathrochelates are stable in the CVA time scale, whereas their ruthenium- and iron-containing analogs as well as the reduced forms of all the cobalt, ruthenium and iron complexes obtained are unstable. 相似文献
13.
Tao Wu Ravi K. Kukkadapu Aron M. Griffin Christopher A. Gorski Hiromi Konishi Huifang Xu 《Geomicrobiology journal》2016,33(9):793-806
Fe(III)-oxides and Fe(III)-bearing phyllosilicates are the two major iron sources utilized as electron acceptors by dissimilatory iron-reducing bacteria (DIRB) in anoxic soils and sediments. Although there have been many studies on microbial Fe(III)-oxide and Fe(III)-phyllosilicate reduction with both natural and specimen materials, no controlled experimental information is available on the interaction between these two phases when both are available for microbial reduction. In this study, the model DIRB Geobacter sulfurreducens was used to examine the pathways of Fe(III) reduction in Fe(III)-oxide stripped subsurface sediment that was coated with different amounts of synthetic high surface area (HSA) goethite. Cryogenic (12K) 57Fe Mössbauer spectroscopy was used to determine changes in the relative abundances of Fe(III)-oxide, Fe(III)-phyllosilicate, and phyllosilicate-associated Fe(II) [Fe(II)-phyllosilicate] in bioreduced samples. Analogous Mössbauer analyses were performed on samples from abiotic Fe(II) sorption experiments in which sediments were exposed to a quantity of exogenous soluble Fe(II) (FeCl2?2H2O) comparable to the amount of Fe(II) produced during microbial reduction. A Fe partitioning model was developed to analyze the fate of Fe(II) and assess the potential for abiotic Fe(II)-catalyzed reduction of Fe(III)-phyllosilicates. The microbial reduction experiments indicated that although reduction of Fe(III)-oxide accounted for virtually all of the observed bulk Fe(III) reduction activity, there was no significant abiotic electron transfer between oxide-derived Fe(II) and Fe(III)-phyllosilicatesilicates, with 26–87% of biogenic Fe(II) appearing as sorbed Fe(II) in the Fe(II)-phyllosilicate pool. In contrast, the abiotic Fe(II) sorption experiments showed that 41 and 24% of the added Fe(II) engaged in electron transfer to Fe(III)-phyllosilicate surfaces in synthetic goethite-coated and uncoated sediment. Differences in the rate of Fe(II) addition and system redox potential may account for the microbial and abiotic reaction systems. Our experiments provide new insight into pathways for Fe(III) reduction in mixed Fe(III)-oxide/Fe(III)-phyllosilicate assemblages, and provide key mechanistic insight for interpreting microbial reduction experiments and field data from complex natural soils and sediments. 相似文献
14.
Ternary oxovanadium(IV) complexes [VO(salmdtc)(B)] (1-3), where salmdtc is dianionic N-salicylidene-S-methyldithiocarbazate and B is N,N-donor phenanthroline bases like 1,10-phenanthroline (phen, 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq, 2) and dipyrido[3,2-a:2′,3′-c]phenazine (dppz, 3), are prepared, characterized and their DNA binding and DNA cleavage activity studied. Complex 3 is structurally characterized by single-crystal X-ray crystallography. The molecular structure shows the presence of a vanadyl group in six-coordinate VN3O2S coordination geometry. The S-methyldithiocarbazate Schiff base acts as a tridentate NSO-donor ligand in a meridional binding mode. The N,N-donor heterocyclic base displays a chelating mode of binding with an N-donor site trans to the vanadyl oxo-group. The complexes show a d-d band in the range of 675-707 nm in DMF. They exhibit an irreversible oxidative cyclic voltammetric response near 0.9 V due to the V(V)/V(IV) couple and a quasi-reversible reductive V(IV)/V(III) redox couple near −1.0 V vs. SCE in DMF-0.1 M TBAP. The complexes show good binding propensity to calf thymus DNA giving binding constant values in the range of 7.4 × 104-2.3 × 105 M−1. The thermal denaturation and viscosity binding data suggest DNA surface and/or groove binding nature of the complexes. The complexes show poor chemical nuclease activity in dark in the presence of 3-mercaptopropionic acid (MPA) or hydrogen peroxide. The dpq and dppz complexes show efficient DNA cleavage activity in UV-A light of 365 nm via a type-II mechanistic pathway involving formation of singlet oxygen (1O2) as the reactive species. 相似文献
15.
《Inorganica chimica acta》1987,135(1):33-35
Reactions of cis-[Ru(en)2(OH2)2]2+ (or cis-[Ru (NH3)4(OH2)2]2+) with Pseudomonas aeruginosa azurin (Az), horse heart myoglobin (Mbh), and horse heart cytochrome c (cyt c) give Ru-labelled proteins. The ruthenium binding sites in the singly modified derivatives are His-83 (Az), His-81 (Mbh), and His-33 (cyt c). Spectroscopic and electrochemical measurements indicate that the structures of the proteins are not perturbed by the surface-bound ruthenium complexes. The E°f values of the Ru(III)/(II) couple in these Ru-modified proteins fall between −0.07 and −0.13 V vs. NHE. 相似文献
16.
《Free radical biology & medicine》2006,40(12):1581-1590
Iron(II)–dithiocarbamate complexes are used to trap nitrogen monoxide in biological samples, and the resulting nitrosyliron(II)–dithiocarbamate is detected and quantified by ESR. As the chemical properties of these compounds have been little studied, we investigated whether iron dithiocarbamate complexes can redox cycle. The electrode potentials of iron complexes of N-(dithiocarboxy)sarcosine (dtcs) and N-methyl-d-glucamine dithiocarbamate (mgd) are 56 and −25 mV at pH 7.4, respectively, as measured by cyclic voltammetry. The autoxidation and Fenton reaction of iron(II)–dtcs and iron(II)–mgd were studied by stopped-flow spectrophotometry with both iron(II) complexes and dioxygen or hydrogen peroxide in excess. In the case of excess iron(II)–dtcs and –mgd complexes, the rate constants of the autoxidation and the Fenton reaction are (1.6–3.2) × 104 and (0.7–1.1) × 105 M−1 s−1, respectively. In the presence of nitrogen monoxide, the oxidation of iron(II)–dtcs and iron(II)–mgd by hydrogen peroxide is significantly slower (ca. 10–15 M−1 s−1). The physiological reductants ascorbate, cysteine, and glutathione efficiently reduce iron(III)–dtcs and iron(III)–mgd. Therefore, iron bound to dtcs and mgd can redox cycle between iron(II) and iron(III). The ligands dtcs and mgd are slowly oxidized by hydrogen peroxide with rate constants of 5.0 and 3.8 M−1 s−1, respectively. 相似文献
17.
Samuel G. Gattis Marcy Hernick Carol A. Fierke 《The Journal of biological chemistry》2010,285(44):33788-33796
UDP-3-O-((R)-3-hydroxymyristoyl)-N-acetylglucosamine deacetylase (LpxC) catalyzes the deacetylation of UDP-3-O-((R)-3-hydroxymyristoyl)-N-acetylglucosamine to form UDP-3-O-myristoylglucosamine and acetate in Gram-negative bacteria. This second, and committed, step in lipid A biosynthesis is a target for antibiotic development. LpxC was previously identified as a mononuclear Zn(II) metalloenzyme; however, LpxC is 6–8-fold more active with the oxygen-sensitive Fe(II) cofactor (Hernick, M., Gattis, S. G., Penner-Hahn, J. E., and Fierke, C. A. (2010) Biochemistry 49, 2246–2255). To analyze the native metal cofactor bound to LpxC, we developed a pulldown method to rapidly purify tagged LpxC under anaerobic conditions. The metal bound to LpxC purified from Escherichia coli grown in minimal medium is mainly Fe(II). However, the ratio of iron/zinc bound to LpxC varies with the metal content of the medium. Furthermore, the iron/zinc ratio bound to native LpxC, determined by activity assays, has a similar dependence on the growth conditions. LpxC has significantly higher affinity for Zn(II) compared with Fe(II) with KD values of 60 ± 20 pm and 110 ± 40 nm, respectively. However, in vivo concentrations of readily exchangeable iron are significantly higher than zinc, suggesting that Fe(II) is the thermodynamically favored metal cofactor for LpxC under cellular conditions. These data indicate that LpxC expressed in E. coli grown in standard medium predominantly exists as the Fe(II)-enzyme. However, the metal cofactor in LpxC can switch between iron and zinc in response to perturbations in available metal ions. This alteration may be important for regulating the LpxC activity upon changes in environmental conditions and may be a general mechanism of regulating the activity of metalloenzymes. 相似文献
18.
《Inorganica chimica acta》1986,124(4):187-198
The redox behavior of the head-to-head bis(μ- (1-methyluracilato-N3,O2)-bis(cis-diammine platinum(II)) dinitrate, PtMeU, and platinum 1-methyluracil blue, PtMeUB, was studied by cyclic voltammetry (CV), rotating disk voltammetry (RDV), and controlled-potential coulometry (CPC). Redox titrimetry, electrochemistry/electron paramagnetic resonance spectroscopy (EPR), and liquid chromatography (LC) served as complementary techniques. The former reactant exhibits two-step electro-oxidation, consistent with the formation of a mixed-valence Pt(II, III) state en route to Pt(III, III). The latter also appears to oxidize to a uniform Pt(III) state. Although the oxidative-reductive electrochemistry of both reactants exhibits chemical reversibility, the heterogeneous electron-transfer kinetics are notably sluggish. The latter appears to be associated with the formation of an inhibiting film on the electrode surface. A slow conversion of PtMeU to a PtMeUB-like state was revealed by CV and LC. The complex, oligomeric nature of PtMeUB was revealed by means of gradient LC examination. Comparing oxidative and reductive electrolysis curves for PtMeUB yielded an average platinum oxidation state of 2.08. All observed behavior for PtMeUB, as well as for PtMeU, is accounted for by invoking +2 and +3 oxidation states for platinum; redox titrimetry using Ce(IV) revealed inconsequential oxidation of both of these systems beyond the III state. An estimate of molecular weight for the platinum blue was made by employing RDV in conjunction with the Einstein-Stokes equation. 相似文献
19.
Orsolya Szabó 《Inorganica chimica acta》2011,376(1):500-508
Complexes formed between Mn(II) ion and acetohydroxamic acid (HAha), benzohydroxamic acid (HBha), N-methyl-acetohydroxamic acid (HMeAha), DFB model dihydroxamic acids (H2(3,4-DIHA), H2(3,3-DIHA), H2(2,5-DIHA), H2(2,5-H,H-DIHA), H2(2,4-DIHA), H2(2,3-DIHA)) and two trihydroxamate based natural siderophores, desferrioxamine B (H4DFB) and desferricoprogen (H3DFC) have been investigated under anaerobic condition (and some of them also under aerobic condition). The pH-potentiometric results showed the formation of well-defined complexes with moderate stability. Monohydroxamic acids not, but all of the dihydroxamic acids and trihydroxamic acids were able to hinder the hydrolysis of the metal ion up to pH ca. 11. Maximum three hydroxamates were found to coordinate to the Mn(II) ion, but presence of water molecule in the inner-sphere was also indicated by the corresponding relaxivity values even in the tris-chelated complexes. Moreover, prototropic exchange processes were found to increase the relaxation rate of the solvent water proton over the value of [Mnaqua]2+ in the protonated Mn(II)-siderophore complexes at physiological pH. The much higher stability of Mn(III)-hydroxamate (especially tris-chelated) complexes compared to the corresponding Mn(II)-containing species results in a significantly decreased formal potential compared to the Mn(III)aqua/Mn(II)aqua system. As a result, air oxygen becomes an oxidizing agent for these manganese(II)-hydroxamate complexes above pH 7.5. The oxidation processes, followed by UV-Vis spectrophotometry, were found to be stoichiometric only in the case of the tris-chelated complexes of siderophores, which predominate above pH 9. ESI-MS provided support about the stoichiometry and cyclic-voltammetry was used to determine the stability constants for the tris-chelated complexes, [Mn(HDFB)]+ and [MnDFC]. 相似文献
20.
Nicotine-1-N-oxide, trans and cis isomers of nicotine-1′-N-oxide and of nicotine-1,1′-di-N-oxide have been prepared and characterised by NMR, MS and reduction to nicotine. The trans and cis isomers of nicotine-1′-N-oxide have been identified in leaves, stems and roots of Nicotiana tabacum, N. affinis and N. sylvestris. 相似文献