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PubMed2005

Pi-accepting-pincer rhodium complexes: an unusual coordination mode of PCP-type systems.

The novel pi-accepting, pincer-type ligand, dipyrrolylphoshinoxylene (DPyPX), is introduced. This ligand has the strongest pi-accepting phosphines used so far in the PCP family of ligands and this results in some unusual coordination chemistry. The rhodium(I) complex, [(DPyPX)Rh(CO)(PR3)] (4, R=Ph, Et, pyrrolyl) is prepared by treating the relevant [(DPyPX)Rh(PR3)] (3) complex with CO and is remarkably resistant to loss of either ligand. X-ray crystallographic analysis of complex 4 b (R=Et) reveals an unusual cisoid coordination of the PCP phosphine ligands. These observations are supported by density functional theory (DFT) calculations.

Journal Article↗
PubMed2004

Novel lanthanide(II) complexes supported by carbon-bridged biphenolate ligands: synthesis, structure and catalytic activity.

[Ln[N(SiMe3)2]2(THF)2](Ln = Sm, Yb) reacts with 1 equiv. of carbon-bridged biphenols, 2,2'-methylene-bis(6-tert-butyl-4-methylphenol)(L1H2) or 2,2'-ethylidene-bis(4,6-di-tert-butylphenol)(L2H2), in toluene to give the novel aryloxide lanthanide(II) complexes [[LnL1(THF)n]2](Ln = Sm, n = 3 (1); Ln = Yb, n = 2 (2)) and [[LnL2(THF)3]2](Ln = Sm (5); Ln = Yb (6)) in quantitative yield, respectively. Addition of 2 equiv. of hexamethylphosphoric triamide (HMPA) to a tetrahydrofuran (THF) solution of 1, 2 and 5 affords the corresponding HMPA-coordinated complexes, [[LnL1(THF)m(HMPA)n]2(THF)y](Ln = Sm, n = 2, m = 0, y = 2 (3); Ln = Yb, m = 1, n = 1, y = 6 (4)) and [[SmL2(HMPA)2]2](7) in excellent yields. The single-crystal structural analyses of 3, 4 and 7 revealed that these aryloxide lanthanide(II) complexes are dimeric with two Ln-O bridges. The coordination geometry of each lanthanide metal can be best described as a distorted trigonal bipyramid. Complexes 1-3, 5 and 7 can catalyze the ring-opening polymerization of epsilon-caprolactone (epsilon-CL), and 1-3, along with 5 show moderate activity for the ring-opening polymerization of 2,2-dimethyltrimethylene carbonate (DTC) and the copolymerization of epsilon-CL and DTC to give random copolymers with high molecular weights and relatively narrow molecular weight distributions..

Journal Article↗
PubMed2005

Development of an automated protein-tyrosine phosphatase 1B inhibition assay and the screening of putative insulin-enhancing vanadium(IV) and zinc(II) complexes.

The inhibition of protein-tyrosine phosphatase 1B (PTP1B) is a potential target for treatment of type 2 diabetes. Vanadium and zinc metal coordinated complexes have insulin-enhancing activities, and while vanadium compounds inhibit PTP1B, little is known on the mode of action of zinc compounds. In this study we developed an automated PTP1B inhibition assay that allows for a rapid assessment of the PTP1B inhibition strength of candidate compounds. Synthetic vanadium(IV) and zinc(II) complexes were evaluated: IC50 values for vanadium complexes ranged from 0.06 to 0.8 microM whereas for zinc compounds, values were above 10 microM. Vanadium sulfate, a non-conjugated inorganic salt, had stronger inhibition activity than any of the conjugated metal complexes.

Dose-Response Relationship, Drug↗
PubMed2001

Characterization of recombinant barley oxalate oxidase expressed by Pichia pastoris.

Oxalate oxidase catalyzes the oxidation of oxalate to carbon dioxide and hydrogen peroxide, making it useful for clinical analysis of oxalate in biological fluids. An artificial gene for barley oxalate oxidase has been used to produce functional recombinant enzyme in a Pichia pastoris heterologous expression system, yielding 250 mg of purified oxalate oxidase from 5 L of fermentation medium. The recombinant oxalate oxidase was expressed as a soluble, hexameric 140 kDa glycoprotein containing 0.2 g-atom Mn/monomer with a specific activity of 10 U/mg, similar to the properties reported for enzyme isolated from barley. No superoxide dismutase activity was detected in the recombinant oxalate oxidase. EPR spectra indicate that the majority of the manganese in the protein is present as Mn(II), and are consistent with the six-coordinate metal center reported in the recent X-ray crystal structure for barley oxalate oxidase. The EPR spectra change when bulky anions such as iodide bind, indicating conversion to a five-coordinate complex. Addition of oxalate perturbs the EPR spectrum of the Mn(II) sites, providing the first characterization of the substrate complex. The optical absorption spectrum of the concentrated protein contains features associated with a minor six-coordinate Mn(III) species, which disappears on addition of oxalate. EPR spin-trapping experiments indicate that carboxylate free radicals (CO2*-) are transiently produced by the enzyme in the presence of oxalate, most likely during reduction of the Mn(III) sites. These features are incorporated into a turnover mechanism for oxalate oxidase.

Carboxylic Acids↗
PubMed1990

Prothrombin activation on membranes with anionic lipids containing phosphate, sulfate, and/or carboxyl groups.

Factor Xa catalyzed prothrombin activation is strongly stimulated by the presence of negatively charged membranes plus calcium ions. Here we report experiments in which we determined the prothrombin-converting activity of phosphatidylcholine (PC) membranes that contain varying amounts of different anionic lipids, viz., phosphatidylserine (PS), phosphatidic acid (PA), phosphatidylmethanol (MePA), phosphatidylglycerol (PG), phosphatidylethanolamine (PE), phosphatidyl-beta-lactate (PLac), sulfatides (SF), sodium dodecyl sulfate (SDS), and oleic acid. All anionic lipids tested were able to accelerate factor Xa catalyzed prothrombin activation, in both the absence and presence of the protein cofactor Va. This shows that the prothrombin-converting activity of negatively charged membranes is not strictly dependent on the presence of a phosphate group but that lipids which contain a carboxyl or sulfate moiety are also able to promote the formation of a functionally active prothrombinase complex. In the absence of factor Va, the prothrombin-converting activity of membranes with MePA, PG, PE, PLac, SF, or SDS was strongly inhibited at high ionic strength, while the activity of PS- and PA-containing membranes was hardly affected by ionic strength variation. This suggests that in the case of the ionic strength sensitive lipids electrostatic forces play an important role in the formation of the membrane-bound prothrombinase complex. For PS and to a lesser extent for PA we propose that the formation of a coordinated complex (chelate complex) with Ca2+ as central ion and ligands provided by the gamma-carboxyglutamic acid residues of prothrombin and factor Xa and the polar head group of phospholipids is the major driving force in protein-membrane association. Our data indicate that the anionic lipids used in this study can be useful tools for further investigation of the molecular interactions that play a role in the assembly of a membrane-bound prothrombinase complex. Membranes that were solely composed of PC can also considerably enhance prothrombin activation in the presence of factor Va. This activity of PC is only observed on membranes which are composed of PC that contains unsaturated hydrocarbon side chains. Membranes prepared from phosphocholine-containing lipids with saturated hydrocarbon side chains such as dimyristoyl-PC, dipalmitoyl-PC, distearoyl-PC, and dioctadecylglycerophosphocholine hardly accelerated prothrombin activation.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium↗
PubMed2003

Ab initio molecular orbital study on the G-selectivity of GGG triplet in copper(I)-mediated one-electron oxidation.

The G-selectivity for Cu(I)-mediated one-electron oxidation of 5'-TG(1)G(2)G(3)-3' and 5'-CG(1)G(2)G(3)-3' has been examined by ab initio molecular orbital calculations. It was confirmed that G(1) is selectively damaged by Cu(I) ion for both 5'-TG(1)G(2)G(3)-3' and 5'-CG(1)G(2)G(3)-3', being good agreement with experimental results. The Cu(I)-mediated G(1)-selectivity is primarily due to the stability of the Cu(I)-coordinated complex, [-XG(1)G(2)G(3)-,-Cu(I)(H(2)O)(3)](+). The Cu(I) ion coordinates selectively to N7 of G(2) of 5'-G(1)G(2)G(3)-3' rather than N7 of G(1). The G(2)-selective coordination induces the G(1)-selective trap of a hole that is created by one-electron oxidation and migrates to GGG triplet. Therefore, the radical cation of G(1) is selectively created in both 5'-TG(1)G(2)G(3)-3' and 5'-CG(1)G(2)G(3)-3', giving the G(1)-selective damage of 5'-G(1)G(2)G(3)-3'.

Cations, Monovalent↗
PubMed1990

In vitro evidence for a relationship between magnesium and vitamin B-6.

Vitamin B-6 and magnesium appear to interact in vivo and it has been suggested that vitamin B-6 may enhance transport or accumulation of magnesium in cells. The purpose of this study was to evaluate the possibility of the formation of B-6 vitamer-Mg complexes in vitro using spectrophotometric analysis of ultraviolet or visible spectra or change in fluorescence intensity of B-6 vitamers. Pyridoxal phosphate but not pyridoxal appears to form a complex with Mg as evidenced by a change in the ultraviolet and visible spectra with an increase in absorption and spectral shift in the visible maxima from 389 to 388 nm and a decrease in the ultraviolet absorption maxima at 296 nm. Addition of Mg to pyridoxal phosphate but not the other B-6 vitamers enhanced the fluorescent intensity of pyridoxal phosphate at least threefold and evoked a spectral shift in both the fluorescence excitation and emission maximum. Electrochemical titration of pyridoxal phosphate in the presence of Mg affects the pKa- of the phenolic hydroxyl and the secondary phosphate ionization. These data collectively indicate that pyridoxal phosphate, but not pyridoxal, appears to form a coordinated complex with Mg and the coordination site is likely to be related to the primary phosphate and aldehyde moiety of pyridoxal phosphate.

Chelating Agents↗
PubMed1998

Characterization of the antimonial antileishmanial agent meglumine antimonate (glucantime).

Meglumine antimonate (Glucantime), a drug of choice for the treatment of leishmaniasis, is produced by the reaction of pentavalent antimony with N-methyl-D-glucamine, a carbohydrate derivative. We investigated the structure and composition of meglumine antimonate, which remain poorly understood, despite 50 years of use. Measurement of the antimony content of meglumine antimonate powder indicated a 1:1.37 molar ratio of antimony to N-methyl-D-glucamine. Osmolality measurements performed with meglumine antimonate solutions demonstrated an average of 1.43 antimony atoms per molecule of meglumine antimonate. The osmolality of a 1:10 dilution of stock meglumine antimonate increased by 45% over 8 days, suggesting hydrolysis to less complex species. A comparison of the proton nuclear magnetic resonance spectra of N-methyl-D-glucamine and meglumine antimonate revealed an increase in complexity in the latter but with all of the resonances of the former still being evident, consistent with the presence of coordination complexes between antimony and each of the N-methyl-D-glucamine hydroxyls. Fast atom bombardment and electrospray ionization mass spectrometry coupled with several derivatization procedures provided evidence that up to four N-methyl-D-glucamine hydroxyls are coordinated with each antimony. A series of oligomers were observed. The major moiety has a molecular mass of 507 atomic mass units and consists of NMG-Sb-NMG, where Sb represents antimony and NMG represents N-methyl-D-glucamine. Additional species containing up to four antimony atoms and five N-methyl-D-glucamine moieties and corresponding to the general form (NMG-Sb)n-NMG are also present. These results suggest that this agent is a complex mixture that exists in equilibrium in aqueous solution.

Antiprotozoal Agents↗
PubMed2000

Molecular and electronic structure of nitridocyanometalates of chromium(V) and manganese(V): a combined experimental and DFT study.

The six-coordinate complexes [M(N)(CN)5]3- (M = Cr, Mn) have been isolated as salts of robust rhodium amine complexes. [Rh(en)3][Mn(N)(CN)5].H2O (1) and [Rh(tn)3] [Cr(N)(CN)5].2H2O (2) have been characterized by single-crystal X-ray crystallography: 1 crystallizes in the hexagonal space group P6(3) with a = b = 15.810(2) A, c = 13.844(3) A, V = 2996.8(8) A3, and Z = 6; 2 crystallizes in the orthorhombic space group Pbcn with a = 9.723(1) A, b = 14.564(2) A, c = 31.498(4) A, V = 4460.3(8) A3, and Z = 8. In 1, all the anions are oriented with their Mn identical to N directions almost coparallel to the crystallographic 3-fold axis. Polarized single-crystal UV-vis spectroscopy of 1 confirms the validity of the Jørgensen-Ballhausen-Gray d-orbital splitting scheme with the lowest energy transition being dxy-->[dyz,dzx]. Single-crystal EPR spectroscopy of [Cr(N)(CN)5]3- diluted into 1 shows the hyperfine (53Cr) and super-hyperfine (14N) tensors to be quite anisotropic with different major axes. For the hyperfine interaction we observe A Parallel > A Perpendicular, whereas, for the super-hyperfine interaction to the terminal nitrido ligand, the reverse ordering is found: A Perpendicular > A Parallel. The complexes [M(N)(CN)5]3-, trans-[M(N)(CN)4(py)]2-, and [M(N)(CN)4]2- (M = Cr, Mn) were investigated by DFT methods. Good reproduction of the molecular structures, vibrational, and UV-vis spectra was obtained. However, pronounced differences between local density and gradient corrected functionals were observed in the description of the weak bonding to the ligands trans to the nitrido ligand. For the five-coordinate [M(N)(CN)4]2- complexes the LUMO is predicted to be a strongly admixed dz2(M)-pz(M) hybrid.

Journal Article↗
PubMed2004

Robust hydrogen-bonded self-assemblies from biimidazole complexes. Synthesis and structural characterization of [M(biimidazole)2(OH2)2]2+ (M = Co2+, Ni2+) complexes and carboxylate modules.

A robust heteromeric hydrogen-bonded synthon [R2(2) (9)-Id] is exploited to drive the modular self-assembly of four coordination complexes [M(H2biim)2(OH2)2]2+ (M = Co2+, Ni2+) and carboxylate counterions. This strategy allowed us to build molecular architectures of 0-, 1-, and 2-dimensions. A hydrogen-bonded 2D-network with cavities has been designed, which maintains its striking integrity after reversible water desorption-resorption processes.

Carboxylic Acids↗
PubMed2005

Formation of mono(dithiolene)-thiocarboxamido complexes in reactions of thio(dithiocarbamato)-Mo/W complexes and dimethyl acetylenedicarboxylate.

Reactions of TpMS(S(2)CNEt(2)) with dimethyl acetylenedicarboxylate in dichloromethane produce olive green/black TpM{S(2)C(2)(CO(2)Me)(2)}(SCNEt(2)-kappa(2)S,C) (M = Mo (1), W (2); Tp = hydrotris(3,5-dimethylpyrazol-1-yl)borate). The seven-coordinate complexes exhibit pseudo-octahedral (1) and distorted pentagonal bipyramidal (2) coordination spheres comprised of tridentate fac-Tp, bidentate dithiolene, and thiocarboxamido-kappa(2)S,C ligands. In the solid state, molecules of 1 exhibit pseudo-C(s)() symmetry, with the thiocarboxamide NEt(2) group in a cleft in the Tp ligand. Molecules of 2 have C(1) symmetry in the solid state; here, the thiocarboxamide unit is orientated along one of the W-S(dithiolene) bonds with its NEt(2) group projecting away from the Tp ligand. Both complexes possess effective C(s)() symmetry in solution. Reaction of TpMoI(CO)(3) with AgS(2)CNEt(2) affords olive green TpMo(S(2)CNEt(2))(CO)(2) (3), which reacts with propylene sulfide in a new synthesis for TpMoS(S(2)CNEt(2)), the starting material for 1. Complex 3 exhibits a distorted pentagonal bipyramidal structure, the axial sites being defined by a Tp nitrogen atom and a carbonyl ligand, the pentagonal plane by the remaining nitrogen and carbonyl donors and the two sulfur atoms of the bidentate dithiocarbamate ligand.

Journal Article↗
PubMedDate not supplied

Optimizing the targeted chemical nuclease activity of 1,10-phenanthroline-copper by ligand modification.

Our interest in improving the efficiency of targeted scission reagents has prompted us to study the influence of ring substituents on the nuclease activity of 1,10-phenanthroline-copper conjugated to oligonucleotides and DNA-binding proteins. Since methyl substitution at all but the 2 and 9 positions enhances the copper-dependent chemical nuclease activity of 1,10-phenanthroline, we have compared the activity of conjugates prepared from 5-(aminomethyl)-1,10-phenanthroline (MOP) to those of conjugates prepared from 5-amino-1,10-phenanthroline (amino-OP). Tethering MOP derivatives to the Escherichia coli Fis protein enhances DNA scission several-fold at the weaker cleavage sites initially observed with conjugates prepared from amino-OP. However, scission efficiency is not increased at the stronger cleavage sites, or when scission is targeted to single-stranded DNA by a complementary oligonucleotide. These results are consistent with a change in the rate-determining step for cleavage associated with the differential accessibility of the DNA-bound coordination complex to solvent and reductant. Although the free bis cuprous complex of 2,9-dimethyl-1,10-phenanthroline (neocuproine) is redox-inactive, an oligonucleotide tethered to neocuproine through C5 of the phenanthroline ring efficiently cleaves a complementary DNA sequence. These results establish that the nucleolytic species in targeted scission is the 1:1 cuprous complex and suggest that the oxidative reaction proceeds through a copper-oxo intermediate rather than a metal-coordinated peroxy species. However, substituents at the 2 and 9 positions of the ligand will often hinder close approach of the phenanthroline-copper moiety to the oxidatively sensitive ribose as shown by the preference of the oligonucleotide-targeted chimera for cleavage of single-stranded regions and the failure of neocuproine-DNA-binding protein chimeras and a C2-tethered chimera to cleave DNA.

Amino Acid Transport Systems, Neutral↗
PubMed2005

Azide addition to give a tetra-azazirconacycle complex.

Addition of the dilithium salt, ortho-(Me3SiNLi)2C6H4, to ZrCl4 affords a base-free, D2d-symmetric complex Zr(IV)[ortho-(Me3SiN)2C6H4]2 (2), with rigorously planar ortho-phenylenediamine ligands. Lewis acidic 2 readily coordinates donor ligands such as NHEt2 to give the five-coordinate complex, Zr(IV)(NHEt2)[ortho-(Me3SiN)2C6H4]2 (3), which is also accessible by the reaction of Zr(NEt2)4 with 2 equiv of ortho-(Me3SiNH)2C6H4. Aryl azides react with 2 and 3 to give an unusual tetra-azametallacycle complex, 4, via 1,2-addition of a ligand N-Si bond to the organic azide. An X-ray crystal structure of 4 reveals a planar, five-membered metallacycle comprising the zirconium atom, one nitrogen atom of the ortho-(Me3SiN)2C6H4 ligand, and all three nitrogen atoms of the aryl azide.

Journal Article↗
PubMed2005

Copper(II) interaction with unstructured prion domain outside the octarepeat region: speciation, stability, and binding details of copper(II) complexes with PrP106-126 peptides.

Copper(II) complexes of the neurotoxic peptide fragments of human and chicken prion proteins were studied by potentiometric, UV-vis, CD, and EPR spectroscopic and ESI-MS methods. The peptides included the terminally blocked native and scrambled sequences of HuPrP106-126 (HuPrPAc106-126NH2 and ScrHuPrPAc106-126NH2) and also the nona- and tetrapeptide fragments of both the human and chicken prion proteins (HuPrPAc106-114NH2, ChPrPAc119-127NH2, HuPrPAc109-112NH2, and ChPrPAc122-125NH2). The histidyl imidazole-N donor atoms were found to be the major copper(II) binding sites of all peptides; 3N and 4N complexes containing additional 2 and 3 deprotonated amide-N donors, respectively, are the major species in the physiological pH range. The complex formation processes for nona- and tetrapeptides are very similar, supporting the fact that successive deprotonation and metal ion coordination of amide functions go toward the N-termini in the form of joined six- and five-membered chelates. As a consequence, the peptide sequences investigated here, related to the neurotoxic region of the human PrP106-126 sequence, show a higher metal-binding affinity than the octarepeat fragments. In the case of the HuPrP peptide sequences, a weak pH-dependent binding of the Met109 residue was also detected in the 3N-coordinated complexes.

Amino Acid Sequence↗
PubMed2006

Heptametallic bowl-shaped complexes derived from conjugated Schiff-base macrocycles: synthesis, characterization, and X-ray crystal structures.

The reaction of chelating conjugated macrocycles 1a-c with Zn(OAc)2 gives bowl-shaped heptanuclear Zn complexes featuring Zn in tetrahedral, octahedral, and square-pyramidal geometries. Crystallographic and NMR results indicate that vacant Zn coordination sites within the bowl may be accessed, suggesting that these coordination complexes may be used as mimics for Zn fingers and carbonic anhydrase.

Journal Article↗
PubMed2006

[The IR spectra of complexes of 2-hydroxy-2-ferrocenylpropylamine with Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II)].

alpha-Cyano-alpha-ferrocenylethoxytrimethylsilame was prepared by the addition of trimethysilyl cyanide to acetylferrocene. 2-Hydroxy-2-ferrocenylpropylamine(FcA) was synthesized by the reduction of alpha-cyano-alpha-ferrocenylethoxytrimethylsilame with lithium aluminum hydride. A series of coordinate complexes--FcA-Ni(II), FcA-Cu(II), FcA-Zn(II), FcA-Cd(II) and FcA-Hg(II) were obtained through coordination of this ligand with MCl2 (M= Ni, Cu, Zn, Cd and Hg). The FTIR spectra of the complexes and ligand were obtained in the range of 4 000-400 cm(-1). Their major bands were assigned and compared. The results showed that in all complexes some bands(upsilonO-H, upsilonN-H sigmaO-H, sigmaN-H) were shifted to lower wave number, and some(upsilonC-N, upsilonO-N) were shifted to higher wave number. The aminoalcohol groups and metal ions were bound with coordinated bond.

English Abstract↗
PubMed2001

Effects of reduction and ligation of heme iron on the thermal stability of heme-hemopexin complexes.

Hemopexin has two homologous domains (N- and C-terminal domains), binds 1 mole of heme per mole with high affinity (Kd < 1 pM) in a low-spin bis-histidyl complex, and acts as a transporter for the heme. Transport is accomplished via endocytosis without degradation of the protein. Factors that affect stability of the heme coordination complex and potentially heme release in vivo were examined. The effects of temperature on hemopexin, its N-terminal domain, and their respective ferri-, ferro-, and CO-ferro-heme complexes were studied using absorbance and circular dichroism (CD) spectroscopy. As monitored with second-derivative absorbance spectra, the higher order structure of apo-hemopexin unfolds with a Tm of 52 degrees C in 50 mM sodium phosphate buffer and is stabilized by 150 mM NaCl (Tm 63 degrees C). Bis-histidyl heme coordination by hemopexin, observed by Soret absorbance, is substantially weakened by reduction of ferri-heme-hemopexin (Tm 55.5 degrees C) to the ferro-heme form (Tm 48 degrees C), and NaCl stabilizes both complexes by 10-15 degrees C. CO binding to ferroheme-hemopexin restores complex stability (Tm 67 degrees C). Upon cooling, unfolded apo- and ferriheme-hemopexin extensively refold and recover substantial heme-binding activity, but the characteristic ellipticity of the native protein (UV region) and heme complex (Soret region) are not regained, indicating that altered refolded forms are produced. Lowering the pH from 7.4 to 6.5 has little effect on the stability of the apo-protein but increases the Tm of heme complexes by 5-12 degrees C. The stability of the apo-N-terminal domain (Tm 53 degrees C) is similar to that of intact hemopexin, and the ferri-, ferro-, and CO-ferro-heme complexes of the N-terminal domain have Tm values of 53 degrees C, 33 degrees C, and 75 degrees C, respectively.

Animals↗