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At least 19 recordsLinked to original sources
PubMed2005

Coordination chemistry of the HNO ligand with hemes and synthetic coordination complexes.

The coordination chemistry of the one-electron reduced form of nitric oxide, termed a nitroxyl or nitrosyl hydride (NO- or HNO), is described with special focus on its interaction with hemes and heme model complexes. Nitroxyl intermediates have been proposed in the catalytic cycles of several heme-based nitrite and nitric oxide reductases; in fungal cytochrome P450nor, a short-lived nitroxyl-adduct has been observed during catalytic turnover. Ferrous-nitroxyl adducts were first identified in electrochemical reductions of nitrosyl porphyrins and heme proteins, but only recently have these species been characterized in solution. Small molecule HNO complexes of transition metals are rare, and the several reported species are presented with descriptions of their synthesis, and a comparison of available spectroscopic data. Special emphasis is given to the long-lived HNO adduct of myoglobin, including its synthesis by various routes and characterization by 1H NMR, resonance Raman and X-ray absorption spectroscopy. HNO is isoelectronic with 1O2, and as with oxymyoglobin, there are several possible descriptions for its bonding with a ferrous heme; an analogy to the pi-bonding interactions of a Fischer carbene is presented. A survey of the reactivity associated with the characterizable HNO complexes is made, including redox and protonation equilibrium, reactivity with small molecules, and dissociation or displacement reactions.

Electrochemistry↗
PubMed1975

Synthesis of a bifunctional coordination complex of osmium with curariform activity.

Based on the known curariform action of tris(bipyridyl)iron(II) sulfate and other complex ions, two series of bifunctional ligands designed to hold transition metal ions at approximately the same distance apart as the interquaternary ammonium distance in the potent neuromuscular block agents were synthesized. In the first series two 1,10-phenanthrolines (R1) were joined at the 2 position to form four compounds: R1CO-c-N(CH2CH2)2N-COR1, R1CONH-1,2-C6H10-NHCOR1, R1CONH-1,2-C6H4-NHCOR1, and R1CON(CH3)(CH2)2N(CH3)COR1. In the second series two terpyridines (R1) were joined by different chains to give R2(CH2)2CH=CH(CH2)2R2, R2CH2C(CH3)(OH)(CH2)2C(CH23)(OH)CH2R2, R2CH2C(CH3)(OH)C(CH3)(OH)CH2R2, and R2CH2(OH)-1,4-C6H10-(OH)CH2R2. Three other ligands in which the terpyridines were joined by 5-, 60, and 7-methylene groups were also made. The ligands were converted to nickel(II) complexes and the coordination of each nickel ion was completed by adding terpyridine. These were assayed by the intravenous mouse LD50 method. The most potent ligand, the di-hydroxy compound R2CH2(OH)-1,4-C6H10-(OH)CH2R2 was then converted to the bis(pyridinebipyridine)diosmium-(II) coordinated complex and assayed by the iv mouse LD50 method and by the ED50 isolated guinea-pig diaphragm method. By the iv mouse LD50 method, it was about twice as potent as d-tubocurarine and by the isolated diaphragm method, it was 16 times more potent. The compound has been called dihydroxyosmarine tetrachloride or DHO for short. The term "transarine" ions is proposed for transition metal coordination complexes having curariform action. The position of the transarine ions is discussed in the classification of cholinergic ligands, in structure-action relationships, and in relation to some current ideas on receptor mechanisms.

Animals↗
PubMed1986

Inter-strand cross-links and single-strand breaks produced by gold(I) and gold(III) coordination complexes.

The ability of gold coordination complexes to bind to DNA and produce inter-strand cross-links in DNA was assessed in an assay system based on the fluorescence properties of the DNA intercalative dye, ethidium bromide. Results from these studies using a variety of gold(I) and gold(III) complexes suggest that the ability of gold complexes to bind to and produce inter-strand cross-links in DNA is not dependent on the oxidation state of gold in the complex but is influenced by the nature of the coordinating ligands. Those complexes in which the gold was ligated through one or more weakly coordinating ligands showed evidence for DNA binding. However, only those complexes with two or more of these relatively weak coordinating ligands produced inter-strand cross-links. Both the amount of binding to and cross-linking of DNA by these compounds were decreased by treatment of the gold-DNA complex with 2-mercaptoethanol and other thiol containing agents. As shown by agarose gel electrophoresis, 2-mercaptoethanol caused a dissociation of the gold-DNA complexes and a regeneration of closed circular superhelical pBR322 DNA. DNA strand breakage also resulted from treatment of a number of gold-DNA complexes with 2-mercaptoethanol; this was observed with the gold compounds which were shown to produce inter-strand cross-links in DNA. The amount of DNA strand breakage produced by treatment of gold-DNA complexes with 2-mercaptoethanol was influenced by the initial conformation of the DNA; gold-DNA complexes which resulted from the binding of gold compounds to covalently closed superhelical DNA were more sensitive to the breakage induced by 2-mercaptoethanol treatment than those complexes in which closed circular, relaxed DNA was used as substrate. The DNA breakage was not reduced in partially anaerobic conditions or by free-radical scavengers, suggesting that it is not mediated by oxygen. The results are discussed with respect to the potential for the interaction of gold complexes with intracellular DNA and chromatin and their biological implications.

Anaerobiosis↗
PubMed1998

Enhancing the relaxivity of paramagnetic coordination complexes through the optimization of the molecular electrostatic potential.

The low relaxivity of paramagnetic coordination complexes limits their use as contrast agents in magnetic resonance imaging (MRI). To address this problem, we study the relationship between the molecular structure of these complexes and their relaxivity. While others have investigated the vibrational modes as molecular determinants of the electronic spin relaxation time, we focus on the analysis of the molecular electrostatic potential (MEP) of the paramagnetic coordination complex. Electrostatic forces dominate the interaction between the coordination complex and water. Hence, in addition to steric forces, the molecular electrostatic potential should be a determinant of the lifetime of the water-metal link (tm), the internuclear distance between the water hydrogens and the metal (R), and the number of water molecules attached to the metal in the inner and outer spheres of coordination. We compute the molecular electrostatic potential for a series of model metalloporphyrins because their physical and biologic properties are well known, and they are putative magnetic resonance imaging contrast agents with affinity to neoplastic tissue. Replacing the sulfonato groups in MnTPPS4 with carboxylate groups in the ortho position of the phenyl rings attached to the meso carbons results in an electrostatic focusing field that should reduce R and increase tm. Similar substitutions involving polar groups, including one modeled after a well-known picket-fence porphyrin, are not strong enough to generate a focusing field. Instead, these polar groups should modulate the water-metal interactions through steric interactions. Molecular dynamic simulations show a large outer sphere of coordination around the paramagnet that extends almost three times the distance of the inner sphere of coordination.

Contrast Media↗
PubMed1986

Correlation of the in vitro cytotoxic and in vivo antitumor activities of gold(I) coordination complexes.

A series of gold(I) coordination complexes including analogues of the antiarthritic agent auranofin 1 were evaluated for in vitro cytotoxic potency against both B16 melanoma cells and P388 leukemia cells and in vivo antitumor activity against P388 leukemia in mice. A number of the complexes showed potent cytotoxic activity in vitro and antitumor activity in vivo, with the phosphine-coordinated gold(I) thiosugar complexes demonstrating the greatest in vitro and in vivo activity. The data compiled for 63 complexes of the general structural formula LAuX provide the basis for the following observations: potent in vitro cytotoxic activity is observed for substituted (phosphine) gold complexes, lack of potency in vitro correlates well with lack of antitumor activity, potent cytotoxicity in vitro is not necessarily predictive of activity in vivo, in vivo antitumor activity is generally optimized by ligation of Au(I) with a substituted phosphine and a thiosugar.

Animals↗
PubMed1993

Sequential and coordinative complexity: age-based processing limitations in figural transformations.

Dimensions of cognitive complexity in figural transformations were examined in the context of adult age differences. Sequential complexity was manipulated through figural transformations of single objects in a multiple-object array. Coordinative complexity was induced through spatial or nonspatial transformations of the entire array. Results confirmed the prediction that age-related slowing is larger in coordinative complexity than in sequential complexity conditions. The effect was stable across 8 sessions (Experiment 1), was obtained when age groups were equated in accuracy with criterion-referenced testing (Experiment 2), and was corroborated by age-differential probabilities of error types (Experiments 1 and 2). A model is proposed attributing age effects under coordinative complexity to 2 factors: (a) basic-level slowing and (b) time-consuming reiterations through the processing sequence due to age-related working memory failures.

Adult↗
PubMed1983

Alteration in the nucleosome and chromatin structures upon interaction with platinum coordination complexes.

The interaction of various platinum coordination complexes with nucleosomes and chromatin has been investigated by ultraviolet absorption spectrophotometry, circular and electric linear dichroism, and thermal denaturation, at low binding ratios (r less than 0.1-0.2). The general trend of the changes in these physicochemical properties is similar to that observed for the DNA-platinum complexes, which indicates that the same binding sites are involved in the platinum interaction with DNA and with its nucleoprotein complex. The cis-bidentate ligands, cis-dichlorodiammine, diaminocyclohexane and ethylenediamine platinum(II), showed a distinct behavior, with a more important destabilization of the DNA structure in the nucleoprotein than the trans-bidentate ligand, trans-dichlorodiammine-Pt(II), and monodentate ligand, diethylenetriamine-Pt(II). The drastic decrease of the negative electric dichroism in the 260 nm absorption band of the bases, observed with the five ligands, indicates a profound alteration of the DNA arrangement in chromatin and nucleosomes, attributed to a condensation of its superhelical structure. Some differences with previous observations on DNA complexes with the same platinum compounds indicate the possible formation of protein-DNA crosslinks in chromatin and nucleosomes. These could have some importance for the biological effects.

Animals↗
PubMed2005

Mononuclear five-coordinate molybdenum(IV) and -(V) monosulfide complexes coordinated with dithiolene ligands: reversible redox of Mo(V)/Mo(IV) and irreversible dimerization of [MoVS]- cores to a dinuclear [MoV2(mu-S)2]2- Core.

A mononuclear five-coordinate molybdenum(IV) monosulfide complex, (Et4N)2[MoS(L)2] (L = cyclohexene-1,2-dithiolate) (1), was obtained and characterized by IR, UV-vis spectroscopic methods, and X-ray crystallography. 1 was oxidized by an equivalent ferrocenium cation to give the corresponding mononuclear molybdenum(V) complex, (Et4N)[MoS(L)2] (2), which was stable for a few minutes under a lower concentration than 0.3 mM and then further dimerized to (Et4N)2[Mo(L)2]2(mu-S)2 (3).

Journal Article↗
PubMed2001

Effect of platinum coordination complex (PtCx) on citrate uptake by rat renal brush border membrane vesicles (BBMV): direct effect of carboplatin.

Inhalation of platinum, as soluble salts, is known to cause respiratory distress and severe dermatitis in workers. Platinum coordination complexes are widely used in the treatment of a variety of solid tumors. However, the clinical use of cisplatin (CDDP) (the most useful agent) is limited by the development of nephrotoxicity. High dose accidental exposure to soluble platinum in platinum refineries and pharmaceutical factories could induce occupational nephrotoxicity. Carboplatin (CBDCA), a second-generation platinum coordination complex, is highly effective against a variety of malignancies at doses five- to ten-times higher than CDDP. At therapeutic doses, CBDCA is less nephrotoxic than CDDP. Additionally, urinary citrate is freely filtered at the glomerulus, and its reabsorption in the proximal tubule is the major determinant of the rate of renal excretion. In our previous study, the preincubation of rat renal brush border membrane vesicles (BBMV) with 5 mM cisplatin for 4 and 8 hours significantly inhibited the citrate uptake compared with that of the control BBMV. In this study, we exposed BBMV to 100 mM carboplatin (twenty-times higher concentration than cisplatin) and examined the citrate uptake characteristics to clarify the toxic mechanism of platinum coordination complexes. The preincubation of BBMV with 100 mM carboplatin for 8 hours also significantly inhibited the citrate uptake compared with that of the control BBMV, but the alterations were not as severe as those with 5 mM cisplatin.

Animals↗
PubMed1993

Constitutional, configurational and conformational analysis of transition metal coordination complexes.

A computational approach to conformational analysis is applied to the study of transition metal coordination complexes. The method provides a means of rapidly exploring conformational space without any inherent reliance on energy calculations and is therefore applicable to a wide variety of systems. It has been incorporated into an algorithm which explores the constitutional, configurational and conformational degrees of freedom for a metal ion and a number of potential ligands. The program determines which of the possible coordination complex products could form stable conformations and can therefore be used to rationalise the products obtained from the mixture. The method is illustrated using two cases: the cobalt(III)-triethylenetetramine-glycine system and complexes of diindolopyridine derivatives.

Algorithms↗
PubMed2004

Evaluation of in vitro antimicrobial and in vivo cytotoxic properties of some novel titanium-based coordination complexes.

The aim of the present study was to determine the antimicrobial and cytotoxic activities of eight novel titanium(III) based coordination complexes [Ti(Pht)(2)(DL-serine)(2), S(1)], [Ti(Pht)(2)(glycine)(2), S(2))], [Ti(Pht)(2)(cystine)(2), S(3)], [Ti(Pht)(2)(DL-leucine)(2), S(4)], [Ti(Suc)(2)(L-leucine)(2), S(5)], [Ti(Suc)(2)(cystine)(2), S(6)], [Ti(Suc)(2)(cystein)(2), S(7)] and [Ti(Suc)(2)(DL-serine)(2), S(8)] against several gram-positive and -negative bacteria, fungi and brine shrimp nauplii. The investigation showed that almost all of the complexes were moderately active against tested bacteria and fungi at high concentration (200 microg/disc) compared with the standard antibiotic, amoxicillin and the antifungal agent, nystatin. In vivo lethality bioassay experiment showed that only S(7) and S(8) among the complexes had better cytotoxic effect than standard gallic acid. The LC(50) values of these two complexes were found to be 1.00 and 1.21 microg/ml, respectively. Thus the results suggest that only two complexes (S(7), S(8)) among the titanium(III) based coordination complexes show the anticancer properties comparable to the standard cytotoxic agent, and further studies of these two complexes may be helpful for their clinical implication.

Animals↗
PubMed2005

Formation of Au(III)-DNA coordinate complex by laser ablation of Au nanoparticles in solution.

We discovered that an Au(III)-DNA coordinate complex, Au(III)(DNA-base)2(amine)L, are formed by laser ablation of Au nanoparticles in an aqueous solution containing DNA molecules in the presence of amines and multi-valent cations, where L represents an unknown ligand (either amine or water). Optical absorption spectrum of the solution after laser ablation exhibited a 360 nm absorption peak assined to ligand-->Au(III) charge transfer (LMCT) band of the coordinate complex. The complex is considered to be formed as follows: (1) the DNA molecules are neutralized by binding the multi-valent cations to their negatively charged phosphate groups, and adsorbed on the surface of the Au nanoparticles by a hydrophobic interaction, (2) Au(III) ions are liberated from the Au nanoparticles by laser ablation, and (3) an Au(III) ion reacts with amine and two DNA bases of a DNA molecule into an Au(III)(DNA-base)2(amine)L.

Amines↗
PubMed2004

Toward a general strategy for the synthesis of heterobimetallic coordination complexes for use as precursors to metal oxide materials: synthesis, characterization, and thermal decomposition of Bi(2)(Hsal)(6).M(acac)(3) (M = Al, Co, V, Fe, Cr).

Bismuth(III) salicylate, [Bi(Hsal)(3)](n), reacts readily with the trivalent metal beta-diketonate compounds M(acac)(3) (acac = acetylacetonate; M = Al, V, Cr, Fe, Co) to produce trinuclear coordination complexes of the general formula Bi(2)(Hsal)(6).M(acac)(3) (M = Al, V, Cr, Fe, Co) in 60-90% yields. Spectroscopic and single crystal X-ray diffraction experiments indicate that these complexes possess an unusual asymmetric nested structure in both solution and solid state. Upon standing in dichloromethane solution, Bi(2)(Hsal)(6).Co(acac)(3) eliminates Bi(Hsal)(3) to give the 1:1 adduct Bi(Hsal)(3).Co(acac)(3). The 2:1 heterobimetallic molecular compounds undergo facile thermal decomposition on heating in air to 475 degrees C to produce heterometallic oxide materials, which upon annealing for 2 h at 700 degrees C form crystalline oxide materials. The synthetic approach detailed here represents a unique, general approach to the formation of heterobimetallic bismuth-based coordination complexes via the coordination of M(acac)(3) complexes to bismuth(III) salicylate.

Journal Article↗
PubMed1989

Inositol hexaphosphate and its Cu(II) coordinate complex as inhibitors of intestinal alkaline phosphatase.

Myo-Inositol hexaphosphate (phytic acid), a naturally occurring plant constituent capable of forming coordinate complexes with polyvalent cations, reversibly inhibits the hydrolysis of p-nitrophenyl phosphate by alkaline phosphatase. Kinetics of the inhibition is of the strictly competitive type with Ki equal to 260 microM at pH 8.0 and 25 degrees. A similar result is also obtained in the presence of an inositol hexaphosphate-cupric ion coordinate complex. This inhibition of substrate hydrolysis by either inositol hexaphosphate or its Cu(II) complex is to be differentiated from the effect of the latter on alkaline phosphatase in the absence of substrate. In this case total inhibition of the enzyme is obtained in a time-dependent process which apparently involves a metal ion exchange reaction, i.e., substitution of the enzyme's zinc atoms for copper atoms. The effect of inositol hexaphosphate on alkaline phosphatase contrasts with that of inorganic phosphate which gives inhibition kinetics of the partially competitive type with Ki (for its effect on KM) 17.1 microM; a value close to that of KM for the substrate (15.2 microM). At a low phosphate concentration relative to that of inositol hexaphosphate in the assay solution the observed inhibition was partially additive. At a higher phosphate to inositol hexaphosphate ratio, the inhibition was essentially a phosphate effect. This provides additional support for the conclusion that Inositol hexaphosphate and, by extension, an inositol hexaphosphate-Cu(II) complex inhibits alkaline phosphatase by interaction at the active sites in competition with the substrate.

Alkaline Phosphatase↗
PubMed2005

Structural and functional characterization of novel G-quadruplexed DNA-heme coordination complex.

We analyzed the coordination structure of G-quadruplexed DNA-heme complex which exhibits remarkably similar spectroscopic characters to hemoprotein such as myoglobin. We found that some exogenous ligands can be accommodated at the 6th coordination site of heme in the G-quadruplexed DNA-heme complex with a DNA base coordinated to the 5th site. The G-quadruplexed DNA-hemin complex is expected to play a role as a novel DNAzyme. These findings provide novel insights into molecular design for creating artificial heme enzymes using spontaneous assembly between G-quadruplexed DNA and heme.

DNA↗
PubMed2003

Synthesis and activity of ruthenium alkylidene complexes coordinated with phosphine and N-heterocyclic carbene ligands.

This paper reports the synthesis and characterization of a variety of ruthenium complexes coordinated with phosphine and N-heterocyclic carbene (NHC) ligands. These complexes include several alkylidene derivatives of the general formula (NHC)(PR(3))(Cl)(2)Ru=CHR', which are highly active olefin metathesis catalysts. Although these catalysts can be prepared adequately by the reaction of bis(phosphine) ruthenium alkylidene precursors with free NHCs, we have developed an alternative route that employs NHC-alcohol or -chloroform adducts as "protected" forms of the NHC ligands. This route is advantageous because NHC adducts are easier to handle than their free carbene counterparts. We also demonstrate that sterically bulky bis(NHC) complexes can be made by reaction of the pyridine-coordinated precursor (NHC)(py)(2)(Cl)(2)Ru=CHPh with free NHCs or NHC adducts. Two crystal structures are presented, one of the mixed bis(NHC) derivative (H(2)IMes)(IMes)(Cl)(2)Ru=CHPh, and the other of (PCy(3))(Cl)(CO)Ru[eta(2)-(CH(2)-C(6)H(2)Me(2))(N(2)C(3)H(4))(C(6)H(2)Me(3))], the product of ortho methyl C-H bond activation. Other side reactions encountered during the synthesis of new ruthenium alkylidene complexes include the formation of hydrido-carbonyl-chloride derivatives in the presence of primary alcohols and the deprotonation of ruthenium vinylcarbene ligands by KOBu(t). We also evaluate the olefin metathesis activity of NHC-coordinated complexes in representative RCM and ROMP reactions.

Alkenes↗