共查询到20条相似文献,搜索用时 15 毫秒
1.
Cristina M. Coates 《Inorganica chimica acta》2009,362(13):4797-9373
In order to assess the changes in the redox activity of a metal ion that result from inductive effects, three electronically modified derivatives of the ligand, N-benzyl-N,N′-bis(2-pyridylmethyl)-1,2-ethanediamine (LH), have been prepared: N-(4-nitro)benzyl-N,N′-bis(2-pyridylmethyl)-1,2-ethanediamine (LNO2), N-(4-chloro)benzyl-N,N′-bis(2-pyridylmethyl)-1,2-ethanediamine (LCl), and N-(4-methoxy)benzyl-N,N′-bis(2-pyridylmethyl)-1,2-ethanediamine (LOMe). Due to the lack of a fully conjugated π-system between the 4-benzyl substituent and the N-donors, the electronic perturbation should influence a bound metal ion’s redox properties through primarily inductive pathways. The organic ligands react with MnCl2 to form mononuclear complexes with the general formula [Mn(LR)Cl2]. The parent ligand, LH, and its three derivatives each coordinate Mn(II) ions in a cis-α conformation, with the amine N-donors installed trans to the Mn-Cl bonds. Despite its distance from the metal ion, the electron-donating or - withdrawing group has a notable impact on both the metrical parameters of the Mn(II) compounds and the Mn(III/II) reduction potential. A single inductive perturbation can vary the reduction potential by as much as 50 mV. 相似文献
2.
Manganese(II) complexes, Mn2L13(ClO4)4, MnL1(H2O)2(ClO4)2, MnL2(H2O)2(ClO4)2, and {(μ-Cl)MnL2(PF6)}2 based on N,N′-bis(2-pyridinylmethylene) ethanediamine (L1) and N,N′-bis(2-pyridinylmethylene) propanediamine (L2) ligands have been prepared and characterized. The single crystal X-ray diffraction analysis of Mn2L23(ClO4)4 shows that each of the two Mn(II) ion centers with a Mn-Mn distance of 7.15 Å are coordinated by one ligand while a common third ligand bridges the metal centers. Solid-state magnetic susceptibility measurements as well as DFT calculations confirm that each of the manganese centers is high-spin S = 5/2. The electronic structure obtained shows no orbital overlap between the Mn(II) centers indicating that the observed weak antiferromagentism is a result of through space interactions between the two Mn(II) centers. Under different reaction conditions, L1 and Mn(II) yielded a one-dimensional polymer, MnL1(H2O)2(ClO4)2. Ligand L2 when reacted with manganese(II) perchlorate gives contrarily to L1 mononuclear MnL2(H2O)2(ClO4)2 complex. The analysis of the structural properties of the MnL2(H2O)2(ClO4)2 lead to the design of dinuclear complex {(μ-Cl)MnL2(PF6)} where two chlorine atoms were utilized as bridging moieties. This complex has a rhomboidal Mn2Cl2 core with a Mn-Mn distance of 3.726 Å. At room temperature {(μ-Cl)MnL2(PF6)} is ferromagnetic with observed μeff = 4.04 μB per Mn(II) ion. With cooling, μeff grows reaching 4.81 μB per Mn(II) ion at 8 K, and then undergoes ferromagnetic-to-antiferromagnetic phase transition. 相似文献
3.
Mohamad Jaber Al-Jeboori Husam H. Al-Tawel Reyadh Mahmood Ahmad 《Inorganica chimica acta》2010,363(6):1301-170
New tetradentate ligands 2-(2-mercaptoethylthio)-N-(pyridin-2-ylmethyl)acetamide H2L1 and 2-chloro-2-(2-mercaptoethylthio)-N-(pyridin-2-ylmethyl)acetamide H2L2 were synthesised from the reaction of 2-aminomethanepyridine with 1,4-dithian-2-one and 3-chloro-1,4-dithian-2-one, respectively. Monomeric complexes of these ligands, of general formulae K[CrIII(Ln)Cl2], K2[MnII(Ln)Cl2] and [M(Ln)] (M = Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) or Hg(II); n = 1, 2) are reported. The mode of bonding and overall geometry of the complexes were determined through IR, UV-Vis, NMR and mass spectral studies, magnetic moment measurements, elemental analysis, metal content and conductance. These studies revealed octahedral geometries for the Cr(III), Mn(II) complexes, square planar for Ni(II) and Cu(II) complexes and tetrahedral for the Fe(II), Co(II), Zn(II), Cd(II) and Hg(II) complexes. The study of complex formation via molar ratio in DMF solution has been investigated and results were consistent to those found in the solid complexes with a ratio of (M:L) as (1:1). 相似文献
4.
Giulio Lupidi Norberto Masciocchi Sartaj Tabassum Elisabetta Damiani 《Journal of inorganic biochemistry》2010,104(8):820-1608
A series of Cu(II), Zn(II) and Mn(II) coordination compounds has been synthesized by reaction of the corresponding metal salts and pyrazolyl-based ligands, i.e. the neutral 1-(2-(4-((2,2,2-tri(1H-pyrazol-1-yl)ethoxy)methyl)benzyloxy)-1,1-di(1H-pyrazol-1-yl)ethyl)-1H-pyrazole {p-C6H4[CH2OCH2C(pz)3]2, (L1), and the anionic hydridotris(3-phenyl-5-methylpyrazolyl)borate (L2)−, bis(pyrazolyl)acetate (L3) and bis(3,5-dimethylpyrazolyl)acetate (L4)−: the species [L1(CuCl2)2] (1), [L1(Cu(OAc)2)2] (2), [L1(Zn(OAc)2)2] (3), [(CuCl(L2)(HpzPh,Me)] (4), [Mn(L3)2]·2H2O, (5), [ZnCl(L3)(imH)]·MeOH [CuCl(L4)(imH)]·2H2O (7) have been obtained (HpzPh,Me = 3-phenyl-5-methylpyrazole, imH = imidazole). Complexes 1 and 4 have been structurally characterized, also using less conventional powder diffraction methods. The superoxide scavenging activity has been characterized by indirect assays including EPR analysis. All complexes exhibit superoxide scavenging activity with IC50 in the µM range and they protect against the oxidative action of peroxynitrite in different ways. 1, 4 and 7 exert both an anti- and pro-oxidant effect depending on their concentration as evaluated by EPR and fluorescence methods. The pro-oxidative effects are absent in Zn(II) and Mn(II) complexes. 相似文献
5.
《Inorganica chimica acta》1986,112(1):17-21
The reaction of Cu(ClO4)2·6H2O with the Schiff base derived from 1,1′-(2,6-pyridyl)-bis-1,3-butanedione and 3-amino-1-propanol, (H4L2), yields the complex Cu(H4L2)(ClO4)2·H2O. The crystal structure of this complex is triclinic, R = 0.0521, 5602 reflections. The species is dimeric leading to a binuclear copper(II) complex in which the well- separated (8.93 Å intramolecular and 5.46 Å inter- molecular) copper(II) atoms are in distorted square pyramidal geometries. 相似文献
6.
The preparations are reported of the ‘extended reach’ ligand N,N′-o-phenylene-dimethylenebis(pyridin-4-one) (o-XBP4) and of a range of its metal complexes with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II), two of which have been shown by X-ray studies to have polymeric structures. In the compound [Mn(o-XBP4)(H2O)2(NO3)](NO3) the o-XBP4 ligands link ‘Mn(H2O)2(NO3)’ units into chains which are then cross-linked into sheets by the bridging action of the coordinated nitrate. In [Cu(o-XBP4)(NO3)2] chains are also formed by the bridging action of the o-XBP4 ligands but here they simply pack trough-in-trough with no nitrate cross-linking. X-band EPR spectra are reported for these and the other Mn and Cu compounds as are relevant spectroscopic results for the other complexes. 相似文献
7.
Bovine brain hexokinase enhances the effect of Mn(II) on the longitudinal relaxation rate of water protons. Direct interaction of Mn(II) with the enzyme has been studied using electron spin resonance and proton relaxation rate enhancement methods. The results indicate that brain hexokinase has 1.05 ± 0.13 tight binding sites and 7 ± 2 weak binding sites with a dissociation constant, KD = 25 ± 4 μM and K′D = 1050 ± 290 μM, respectively, at pH 8.0, 23 °C. The characteristic enhancement ?b) for hexokinase-Mn(II) complex evaluated from proton relaxation rate enhancement studies, gave ?b = 3.5 ± 0.4 for tight binding sites and an average ?b = 2.3 ± 0.5 per site for weak binding sites at 9 MHZ. The dissociation constant of Mn(II) for tight binding sites on the enzyme exhibits strong temperature dependence. In the low-temperature region (5–12 °C) brain hexokinase probably undergoes a conformational change. Frequency dependence of the normalized relaxation rate for bound water at various temperatures has shown that the number of exchangeable water molecules left in the first coordination sphere of bound Mn(II) is about one at 30 °C and about two at 18 °C. Binding of glucose 6-phosphate to hexokinase results in large-line broadening of the resonances of anomeric protons of the sugar. However, no such effect was observed in the case of glucose binding. These results suggest different modes of interaction of these two sugars to hexokinase. Line broadening of the C-(1) hydrogen resonances of glucose caused by Mn(II) in the presence of hexokinase suggests the proximity of the Mn(II) binding site to that of glucose. A lower limit of 1330 ± 170 s?1 for the rate of dissociation of glucose from enzyme-Mn(II)-glucose complex has been obtained from these studies. 相似文献
8.
Shadrick I.M. Paris Shengwen Liang Steffen Tschirschwitz Mark C. McMills Jeffrey L. Petersen Michael P. Jensen 《Inorganica chimica acta》2010,363(13):3390-1715
Manganese(II) complexes [Mn(L)X2] were prepared and characterized, where L is a neutral di-Schiff base ligand incorporating pyridylimine donor arms, including (1R,2R)-N,N′-bis(2-pyridylmethylidene)-1,2-diphenylethylenediimine (L1), (1R,2R)-N,N′-bis(6-methyl-2-pyridylmethylidene)-1,2-cyclohexyldiimine (L2), or (1R,2R)-, (1S,2S)- or racemic N,N′-bis(2-pyridylmethylidene)-1,2-cyclohexyldiimine (L3), and X− = or Cl−. Product complexes were structurally characterized, specifically including [Mn(R,R-L1)(NCCH3)3](ClO4)2, [Mn(R,R-L2)(OH2)2](ClO4)2 and racemic [Mn(L3)Cl2]. The first of these complexes features a heptacoordinate ligand field in a distorted pentagonal bipyramid, and the latter two are hexacoordinate, but retain equatorially monovacant pentagonal bipyramidal structures. Complexes [Mn(L3)X2] (X− = Cl−, ) were reacted with the primary phosphine FcCH2PH2 (Fc = -C5H4FeC5H5), H2O and ethyldiazoacetate (EDA). The first two substrates prompted reactivity at a single ligand imine bond, resulting in hydrophosphination and hydrolysis, respectively. Complexes of the derivative ligands were also structurally characterized. Evidence for EDA activation was obtained by electrospray ionization mass spectrometry, but catalytic carbene transfer was not obtained. 相似文献
9.
The use of 13C spin lattice relaxation times to study the interaction of alpha-methyl-D-glucopyranoside with concanavalin A 总被引:2,自引:0,他引:2
The spin lattice relaxation rates () of the natural abundance 13C of all seven carbons of α-methyl-d-glucopyranoside were measured in the presence of Mn(II)-concanavalin A. The paramagnetic contribution to the relaxation rates was used to calculate the distance between the Mn(II) site and the saccharide. The results are consistent with the binding of the saccharide in a unique configuration on the surface of the protein with the ?CH2OH (6 carbon) ~9Å, the ?CH3 (7 carbon) 14Å, and carbons 1–5 about 10Å from the Mn(II). Notwithstanding the fact that these distances may be 10% or less in error, these data are in disagreement with a value of greater than 10Å between the saccharide and Mn(II) binding sites determined from X-ray diffraction studies by Edelman et al. ((1972) Proc. Nat. Acad. Sci. USA69, 2580–2584) and Hardman and Ainsworth ((1972) Biochemistry11, 4910–4919). 相似文献
10.
Rupam Sarma 《Inorganica chimica acta》2011,377(1):50-55
A 1D-coordination polymer [{Mn3(C6H5COO)6(BPNO)2(MeOH)2}(MeOH)2]n (1) having benzoate as the anionic ligand and 4,4′-bipyridyl-N,N′-dioxide (BPNO) as bridging ligand is synthesized by reacting benzoic acid with manganese(II) acetate tetrahydrate followed by reaction with 4,4′-bipyridyl-N N′-dioxide. The bridging bidentate BPNO ligands in this coordination polymer along with the benzoate bridges hold the repeated units. The chain like structure in one dimension by benzoate bridges are connected to each other through the μ3-η2:η1 bridges of BPNO ligands. This coordination polymer can be transformed to a molecular complex [Mn(H2O)6](C6H5COO)2.4BPNO (2). In this complex the BPNO remains outside the coordination sphere but they are hydrogen bonded to water molecules to form self assembled structure. The reaction of 3,5-pyrazoledicarboxylic acid (L1H2) and BPNO with manganese(II) acetate or zinc(II) acetate led to molecular complexes with composition [M2(L1)2(H2O)6].BPNO·xH2O {where M = Mn(II) (3), Zn(II)(4)}. These molecular complexes of BPNO are characterised by X-ray crystallography. The complexes 3-4 are binuclear carboxylate complexes having M2O2 core formed from carboxylate ligands with two metal ions. 相似文献
11.
A. A. Tufts M. Flores T. L. Olson J. C. Williams J. P. Allen 《Photosynthesis research》2014,120(1-2):207-220
The electronic structure of a Mn(II) ion bound to highly oxidizing reaction centers of Rhodobacter sphaeroides was studied in a mutant modified to possess a metal binding site at a location comparable to the Mn4Ca cluster of photosystem II. The Mn-binding site of the previously described mutant, M2, contains three carboxylates and one His at the binding site (Thielges et al., Biochemistry 44:389–7394, 2005). The redox-active Mn-cofactor was characterized using electron paramagnetic resonance (EPR) and electron spin echo envelope modulation (ESEEM) spectroscopies. In the light without bound metal, the Mn-binding mutants showed an EPR spectrum characteristic of the oxidized bacteriochlorophyll dimer and reduced quinone whose intensity was significantly reduced due to the diminished quantum yield of charge separation in the mutant compared to wild type. In the presence of the metal and in the dark, the EPR spectrum measured at the X-band frequency of 9.4 GHz showed a distinctive spin 5/2 Mn(II) signal consisting of 16 lines associated with both allowed and forbidden transitions. Upon illumination, the amplitude of the spectrum is decreased by over 80 % due to oxidation of the metal upon electron transfer to the oxidized bacteriochlorophyll dimer. The EPR spectrum of the Mn-cofactor was also measured at the Q-band frequency of 34 GHz and was better resolved as the signal was composed of the six allowed electronic transitions with only minor contributions from other transitions. A fit of the Q-band EPR spectrum shows that the Mn-cofactor is a high spin Mn(II) species (S = 5/2) that is six-coordinated with an isotropic g-value of 2.0006, a weak zero-field splitting and E/D ratio of approximately 1/3. The ESEEM experiments showed the presence of one 14N coordinating the Mn-cofactor. The nitrogen atom is assigned to a His by comparing our ESEEM results to those previously reported for Mn(II) ions bound to other proteins and on the basis of the X-ray structure of the M2 mutant that shows the presence of only one His, residue M193, that can coordinate the Mn-cofactor. Together, the data allow the electronic structure and coordination environment of the designed Mn-cofactor in the modified reaction centers to be characterized in detail and compared to those observed in other proteins with Mn-cofactors. 相似文献
12.
Mohamad J. Al-Jeboori Fahad A. Al-Jebouri Muayed A.R. Al-Azzawi 《Inorganica chimica acta》2011,379(1):163
A new class of polydentate Mannich bases featuring an N2S2 donor system, bis((2-mercapto-N-phenylacetamido)methyl)phosphinic acid H3L1 and bis((2-mercapto-N-propylacetamido)methyl)phosphinic acid H3L2, has been synthesised from condensation of phosphinic acid and paraformaldehyde with 2-mercaptophenylacetamide W1 and 2-mercaptopropylacetamide W2, respectively. Monomeric complexes of these ligands, of general formula K2[CrIII(Ln)Cl2], K3[M′II(Ln)Cl2] and K[M(Ln)] (M′ = Mn(II) or Fe(II); M = Co(II), Ni(II), Cu(II), Zn(II), Cd(II) or Hg(II); n = 1, 2) are reported. The structures of new ligands, mode of bonding and overall geometry of the complexes were determined through IR, UV–Vis, NMR, and mass spectral studies, magnetic moment measurements, elemental analysis, metal content, and conductance. These studies revealed octahedral geometries for the Cr(III), Mn(II) and Fe(II) complexes, square planar for Ni(II) and Cu(II) complexes and tetrahedral for the Co(II), Zn(II), Cd(II) and Hg(II) complexes. Complex formation studies via molar ratio in DMF solution were consistent to those found in the solid complexes with a ratio of (M:L) as (1:1). 相似文献
13.
Adrenal cytochrome b561 (cyt b561), a transmembrane protein that shuttles reducing equivalents derived from ascorbate, has two heme centers with distinct spectroscopic signals and reactivity towards ascorbate. The His54/His122 and His88/His161 pairs furnish axial ligands for the hemes, but additional amino acid residues contributing to the heme centers have not been identified. A computational model of human cyt b561 (Bashtovyy, D., Berczi, A., Asard, H., and Pali, T. (2003) Protoplasma 221, 31-40) predicts that His92 is near the His88/His161 heme and that His110 abuts the His54/His122 heme. We tested these predictions by analyzing the effects of mutations at His92 or His110 on the spectroscopic and functional properties. Wild type cytochrome and mutants with substitutions in other histidine residues or in Asn78 were used for comparison. The largest lineshape changes in the optical absorbance spectrum of the high-potential (bH) peak were seen with mutation of His92; the largest changes in the low-potential (bL) peak lineshape were observed with mutation of His110. In the EPR spectra, mutation of His92 shifted the position of the g = 3.1 signal (bH) but not the g = 3.7 signal (bL). In reductive titrations with ascorbate, mutations in His92 produced the largest increase in the midpoint for the bH transition; mutations in His110 produced the largest decreases in ΔA561 for the bL transition. These results indicate that His92 can be considered part of the bH heme center, and His110 part of the bL heme center, in adrenal cyt b561. 相似文献
14.
A di-N-functionalized 14-membered tetraaza macrocycle, [H4L3](ClO4)2 (L3 = 1,8-bis(2-carboxyethyl)-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane), has been synthesized by acid hydrolysis of 1,8-bis(2-cyanoethyl)-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L2). The copper(II) complexes [CuL2](ClO4)2 and [Cu(H2L3)](ClO4)2 were prepared and characterized. The complex [Cu(H2L3)]2+ readily reacts with methanol to yield [CuL4]2+ (L4 = 1,8-bis(2-carbomethoxyethyl)-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane). The N-CH2CH2COOH groups of [Cu(H2L3)](ClO4)2 are not coordinated to the metal ion in the solid state but are involved in coordination in various non-aqueous solvents or in aqueous solutions of pH ? 1.0. Interestingly, [CuL4](ClO4)2 exists as two stable structural isomers, 1 (the pendant ester groups are not involved in coordination) and 2 (one of the two ester groups is coordinated to the metal ion), in the solid state; the two isomers can be prepared selectively by controlling ionic strength of a methanol solution of the complex. Crystal structures and coordination behaviors of the two isomers are described. The di-N-cyanoethylated macrocyclic complex [CuL2](ClO4)2 is rapidly decomposed in 0.1 M NaOH solution even at room temperature. On the other hand, [Cu(H2L3)](ClO4)2 and [CuL4](ClO4)2 are quite inert against decomposition under similar basic conditions. In acidic or basic aqueous solutions, [CuL4]2+ is hydrolyzed to [Cu(H2L3)]2+ or [CuL3]. 相似文献
15.
Frederik Schleife 《Inorganica chimica acta》2011,374(1):521-527
The metal complexation properties of a functionalized N3O2 donor ligand H2L2, where H2L2 stands for 2,6-diacetyl-4-carboxymethyl-pyridine bis(benzoylhydrazone), are investigated by structural and spectroscopic (IR, ESI-MS and EPR) characterization of its Mn(II) and Co(II) complexes. The ligand H2L2 is observed to react essentially in the same fashion as its unmodified parent H2L1 producing mixed-ligand [M(H2L2)(Cl2)] complexes (M = MnII (1), CoII (3)) upon treatment with MCl2. Complexes [M(HL2)(H2O)(EtOH)]BPh4 (M = Mn 2, M = Co 4), incorporating the supporting ligand in the partially deprotonated form (HL2)−, are formed by salt elimination of the [M(H2L2)(Cl2)] compounds with NaBPh4. Compounds 2 and 4 are isostructural featuring distorted pentagonal-bipyramidal coordinated MnII and CoII ions, with the H2O and EtOH ligands bound in axial positions. Intermolecular hydrogen bonding interactions of the type M-OH2?O-M involving the H2O ligands and the carbonyl functions of the supporting ligand assembles the complexes into dimers. Temperature-dependent magnetic susceptibility measurements (2-300 K) show a substantially paramagnetic Curie behavior for the Mn2+ compound (2) influenced by zero-field splitting and significant orbital angular momentum contribution for 4 (high-spin CoII). The exchange coupling across the MnII-OH2?O-MnII bridges in 2 was found to be less than 0.1 cm−1, suggesting that no significant intradimer exchange coupling occurs via this path. 相似文献
16.
《Inorganica chimica acta》1986,119(1):75-82
Nickel(II) complexes with the compartmental Schiff bases derived from 2,6-diformyl-4-chlorophenol and 1,5-diamino-3-thiapentane (H2L1) or 3,3′-diamino-N-methyl-dipropylamine (H2L2) were synthesized, and the crystal structures of [Ni(L1)- (py)2] and [Ni(L2)(dmf)]·H20 were determined by X-ray crystallography.Ni(L1)(py)2 is monoclinic, space group C2/c, with a= 18.457(6), b = 11.116(7), c= 16.098(6) Å, and β = 115.79(5)°; Dc = 1.49 g cm−3 for Z = 4. The structure was refined to the final R of 6.9%. The molecule has C2 symmetry. The nickel atom is six-coordinated octahedral. Selected bond lengths are: NiO 2.04(1) Å, NiN (L1) 2.08(1) Å, NiN(py) 2.17(1) Å.[Ni(L2)(dmf)]·H2O is monoclinic, space group P21/n, with a = 17.329(6), b = 13.322(7), c = 12.476(7) Å and β = 95.43(5)°; Dc = 1.45 g cm−3 for Z = 4. The structure was refined to the final R of 5.1%. The nickel atom is bonded in the octahedral geometry to the bianionic pentadentate ligand L2 and to one molecule of dimethylformamide. Selected bond lengths are: NiO (charged) 2.063(3) Å (mean value), NiO (neutral) 2.120(3) Å, NiN (planar) 2.050(3) Å (mean value), NiN (tetrahedral) 2.177(3) Å. 相似文献
17.
Hassan Keypour Hamid Goudarziafshar Robin G. Pritchard 《Inorganica chimica acta》2008,361(5):1415-1420
A series of Mn(II) macrocyclic Schiff-base complexes [MnLn]2+ have been prepared via the Mn(II) templated [1+1] cyclocondensation of 2,9-dicarboxaldehyde-1,10-phenanthroline with appropriate linear and branched amines. In this way ligands the pentaaza macrocycle L1 which is 15-membered and L2 which is 16-membered possessing no pendant arm, L6 is 15-membered with one 2-aminoethyl pendant arm and L8 which is 18-membered hexaaza macrocycle with two 2-aminoethyl pendant arms are formed. All the complexes have been characterized using spectroscopic methods. The crystal structures of [MnL8](ClO4)2 · EtOH were determined and indicate that in the solid state the complex adopts a slightly distorted hexagonal bipyramid geometry with the Mn(II) ion located within a hexaaza macrocycle with the two pendant amines coordinating in the axial positions. 相似文献
18.
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
19.
Nikos Lekkas Achilleas Garoufis Joseph Kobe Edward R.T. Tiekink 《Inorganica chimica acta》2006,359(13):4297-4303
The Pd(II) and Pt(II) complexes with triazolopyrimidine C-nucleosides L1 (5,7-dimethyl-3-(2′,3′,5′-tri-O-benzoyl-β-d-ribofuranosyl-s-triazolo)[4,3-a]pyrimidine), L2 (5,7-dimethyl-3-β-d-ribofuranosyl-s-triazolo[4,3-a]pyrimidine) and L3 (5,7-dimethyl[1,5-a]-s-triazolopyrimidine), [Pd(en)(L1)](NO3)2, [Pd(bpy)(L1)](NO3)2, cis-Pd(L3)2Cl2, [Pd2(L3)2Cl4] · H2O, cis-Pd(L2)2Cl2 and [Pt3(L1)2Cl6] were synthesized and characterized by elemental analysis and NMR spectroscopy. The structure of the [Pd2(L3)2Cl4] · H2O complex was established by X-ray crystallography. The two L3 ligands are found in a head to tail orientation, with a Pd?Pd distance of 3.1254(17) Å. L1 coordinates to Pd(II) through N8 and N1 forming polymeric structures. L2 coordinates to Pd(II) through N8 in acidic solutions (0.1 M HCl) forming complexes of cis-geometry. The Pd(II) coordination to L2 does not affect the sugar conformation probably due to the high stability of the C-C glycoside bond. 相似文献
20.
A series of new binuclear copper (II) and nickel (II) complexes of the macrocyclic ligands bis(1,4,7-triazacyclononan-1-yl)butane (Lbut) and bis(1,4,7-triazacyclononan-1-yl)-m-xylene (Lmx) have been synthesized: [Cu2LbutBr4] (1), [Cu2Lbut(imidazole)2Br2](ClO4)2 (2), [Cu2Lmx(μ-OH)(imidazole)2](ClO4)3 (3), [Cu2Lbut(imidazole)4](ClO4)4 · H2O (4), [Cu2Lmx(imidazole)4](ClO4)4 (5), [Ni2 Lbut(H2O)6](ClO4)4 · 2H2O (6), [Ni2Lbut(imidazole)6](ClO4)4 · 2H2O (7) and [Ni2Lmx (imidazole)4(H2O)2](ClO4)4 · 3H2O (8). Complexes 1, 2, 7 and 8 have been characterized by single crystal X-ray studies. In each of the complexes, the two tridentate 1,4,7-triazacyclononane rings of the ligand facially coordinate to separate metal centres. The distorted square-pyramidal coordination sphere of the copper (II) centres is completed by bromide anions in the case of 1 and/or monodentate imidazole ligands in complexes 2, 4 and 5. Complex 3 has been formulated as a monohydroxo-bridged complex featuring two terminal imidazole ligands. Complexes 6-8 feature distorted octahedral nickel (II) centres with water and/or monodentate imidazole ligands occupying the remaining coordination sites. Within the crystal structures, the ligands adopt trans conformations, with the two metal binding compartments widely separated, perhaps as a consequence of electrostatic repulsion between the cationic metal centres. The imidazole-bearing complexes may be viewed as simple models for the coordinative interaction of the binuclear complexes of bis (tacn) ligands with protein molecules bearing multiple surface-exposed histidine residues. 相似文献