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PubMed2005

The first beta-diketiminate-Ag(I) complexes. Macrocyclic dinuclear and tetranuclear Ag(I)-complexes and linear coordination polymer Ag(I)-complex.

Reactions of Ag(I) and a series of beta-diketiminate ligands have been investigated to demonstrate that unique macrocyclic dinuclear and tetranuclear Ag(I)-complexes and a linear coordination polymer Ag(I)-complex as well as oxidative C-C coupling dimer products of the ligands were obtained depending on the substituents on the carbon framework of beta-diketiminate ligands.

Journal Article↗
PubMed2005

Six-coordinate titanium complexes of a tripodal aminetris(phenoxide) ligand: synthesis, structure, and dynamics.

The five-coordinate titanium(IV) alkoxide LTi(O(t)Bu) (LH(3) = tris(2-hydroxy-3,5-di-tert-butylbenzyl)amine) is protonolyzed readily by the conjugate acids of monoanionic bidentate ligands, both symmetrical (tropolone, acetylacetone, di-p-toluoylmethane) and unsymmetrical (8-hydroxyquinoline, salicylaldehyde, 2,6-diformyl-p-cresol, anthrarufin). The geometry of these complexes, which is pseudo-octahedral with the tripodal ligand adopting a chiral, propeller-like conformation, has been confirmed in four cases by X-ray crystallography. Variable-temperature NMR spectroscopy indicates that the six-coordinate complexes undergo two dynamic processes. First, the ligands undergo a twisting motion that results in racemization, a process which is over 10(4) times faster than in five-coordinate complexes. The rate acceleration upon binding of an equatorial ligand is ascribed to steric repulsions with one of the cis phenoxides; the dynamics of a binuclear dibenzyl phosphate-bridged compound, which has a unique conformation of the tripodal ligand, indicates that flexing the cis phenoxide is the rate-limiting step in racemization. Second, the complexes undergo a process that interchanges the inequivalent arms of the tripodal ligand. This process involves a trigonal twist that shifts the bidentate ligand between clefts in the tripod. The intermediate geometry in the reaction appears to be a transition state and not a long-lived intermediate, as judged from the relative rates of interconversion of tripod arms and chelate ends in the ditoluoylmethane complex. Tripod arm interchange takes place without partial dissociation of the bidentate chelate, a reaction that has been observed on a slower time scale in one case.

Journal Article↗
PubMed1979

[Cis-diamminedichloroplatinum(II). A new antineoplastic agent derived from the group of heavy metal complexes (author's transl)].

Platinum coordination complexes represent a new class of antineoplastic agents among which only cis-diamminedichloroplatinum(II) (cis-DDP) has undergone extensive clinical trials. Cis-DDP and some of its congeners share the potential to form DNA-crosslinks with the group of bifunctional alkylating agents, yet cross-resistance is incomplete. The prominent dose-limiting nephrotoxicity can be effectively circumvented by forced diuresis. Cis-DDP not only displays outstanding activity against non-seminomatous testicular cancer but also has a broad spectrum of clinical activity. It ranks very high in activity against bladder cancer and head and neck tumors. Since myelosuppression by cis-DDP is mild, it combines well with other antineoplastic agents. Synergism has been experimentally shown for cyclophosphamide and several other antineoplastic agents. For testicular cancer combination chemotherapy including cis-DDP has become accepted treatment. The simple geometry of platinum coordination complexes allows substitutions of leaving and remaining ligands with anorganic or organic moieties thus altering pharmakokinetic, antineoplastic, and toxic properties in comparison to the parent compound. Mechanism of action, pharmacology, and clinical use of cis-DDP as well as of potentially useful congeners are discussed in this review, since cis-DDP is expected to be available for general use in medical oncology in the near future.

Animals↗
PubMed1998

Synergistic activation of soluble guanylate cyclase by YC-1 and carbon monoxide: implications for the role of cleavage of the iron-histidine bond during activation by nitric oxide.

BACKGROUND: Nitric oxide (.NO) is used in biology as both an intercellular signaling agent and a cytotoxic agent. In signaling, submicromolar quantities of .NO stimulate the soluble isoform of guanylate cyclase (sGC) in the receptor cell. .NO increases the Vmax of this heterodimeric hemoprotein up to 400-fold by interacting with the heme moiety of sGC to form a 5-coordinate complex. Carbon monoxide (CO) binds to the heme to form a 6-coordinate complex, but only activates the enzyme 5-fold, YC-1 is a recently discovered compound that relaxes vascular smooth muscle by stimulating sGC. RESULTS: In the presence of YC-1, CO activates sGC to the same specific activity as attained with .NO. YC-1 did not affect the NO-stimulated activity. The on-rate (kon) and off-rate (koff) of CO for binding to sGC in the presence of YC-1 were determined by stopped-flow spectrophotometry. Neither the kon nor the koff varied from values previously obtained in the absence of YC-1, indicating that YC-1 has no effect on the affinity of CO for the heme. In the presence of YC-1, the visible spectrum of the sGC-CO complex has a Soret peak at 423 nm, indicating the complex is 6-coordinate. CONCLUSIONS: YC-1 has no effect on the affinity of CO for the heme of sGC. In the presence of YC-1, maximal activation of sGC by CO is achieved by formation of a 6-coordinate complex between CO and the heme indicating that cleavage of the Fe-His bond is not required for maximal activation of sGC.

Carbon Monoxide↗
PubMed2004

Hydrated metal(II) complexes of N-(6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl) derivatives of glycine, glycylglycine, threonine, serine, valine and methionine: a monomeric complex and coordination polymers in one, two and three dimensions linked by hydrogen bonding.

Nine hydrated complexes of Group 2 (alkaline earth) cations with organic ligands which are N-substituted amino acids containing the 6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl group have been structurally characterized. The octahydrated calcium glycinate complex, where the six-coordinate Ca cation lies on an inversion centre in the space group P(-)1, forms a finite (zero-dimensional) complex. The hexahydrated barium glycinate complex contains eight-coordinate Ba and it is isostructural with the known Sr analogue, and its one-dimensional coordination polymer takes the form of a simple chain. The octahydrated calcium and strontium threonine complexes are isostructural, with eight-coordinate cations lying on twofold rotation axes in the space group C2: the one-dimensional coordination polymers take the form of a chain of spiro-fused rings and a similar chain of spiro-fused rings is found in the heptahydrated barium serine complex, although here the ten-coordinate cation lies in a general position. In the tetrahydrated strontium and barium glycylglycinate complexes, the eight-coordinate cations lie on twofold rotation axes in the space group C2/c, but in the Sr complex the coordination polymer is a chain of spiro-fused rings, while in the Ba complex the coordination polymer forms deeply puckered sheets. There are two types of Ca site in the hexahydrated calcium valine complex: one is eight coordinate and gives rise to a two-dimensional coordination polymer, while the other is seven coordinate forming a finite, zero-dimensional coordination complex. In the heptahydrated barium methionine complex, the coordination polymer is three dimensional. In all of the complexes, the coordination aggregates are further linked by an extensive series of hydrogen bonds.

Amino Acids↗
PubMed2004

Synthesis, structure, and reductive elimination chemistry of three-coordinate arylpalladium amido complexes.

Four three-coordinate arylpalladium amido complexes with a single hindered phosphine were isolated and structurally characterized. Each possessed a T-shaped geometry. Several of these complexes possessed true three-coordinate structures that lacked any additional coordination by ligand C-H bonds. All of the three-coordinate complexes underwent reductive elimination to form the corresponding triarylamine. A comparison of the rate of reaction of the three-coordinate compounds demonstrated that the rate of elimination from the pentaphenylferrocenyl di-tert-butylphosphine complex were the fastest. A comparison of the rates of reactions between three-coordinate and four-coordinate complexes showed that the rates were much faster from the three-coordinate complexes.

Amides↗
PubMedDate not supplied

[Cognitive deterioration in Parkinson's disease].

The purpose of this study is to contrast a sampling of 20 patients diagnosed as suffering from "Idiopathic Parkinson's Disease" (mean age, 54; schooling, 8.5 years; length of disease, 6.07 years) with a healthy control group, in order to detect possible correlation between intellectual impairment and depression in the individuals affected by Parkinsonism. An integrated battery of neuropsychological testing (PIEN-Test Barcelona. Peña, 1990) was used, in conjunction with "Beck's Depression Inventory". The results show significant differences in the following areas: expressive language, complex language comprehension, motor coordination, complex visuospatial factors, verbal memory and WAIS-type intelligence factors. Discriminant analysis was performed to select the most discriminating variables. The results were as follows, beginning with the most discriminating factor: motor coordination, complex comprehension, complex visuospatial factors, math skills and an overall slowing down. The patients with the highest depression levels were found to have the greatest impairment in mental control/attention and complex comprehension.

Aged↗
PubMed2006

Pi-bonded quinonoid transition-metal complexes.

Coordination of the carbocyclic ring of hydroquinones to electrophilic transition-metal fragments such as Mn(CO)3+ and Rh(COD)+ produces stable pi-bonded eta6-complexes that are activated to facile reversible deprotonation of the -OH groups. The deprotonations are accompanied by electron transfer to the transition metal, which acts as an internal oxidizing agent or electron sink. With manganese as the metal, the resulting eta5-semiquinone and eta4-quinone complexes have been used to synthesize one- two- and three-dimensional polymeric metal-organometallic coordination networks. With rhodium as the metal, the pi-quinonoid complexes have been demonstrated to play a unique role in multifunctional C-C coupling catalysis and in the synthesis of new organolithium reagents. Both classes of pi-quinonoid complexes appear to have significant applications in nanochemistry by providing an excellent vehicle for templating the directed self-assembly of nanoparticles into functional materials.

Catalysis↗
PubMed2002

Gas-phase ion-molecule reactions of transition metal complexes: the effect of different coordination spheres on complex reactivity.

Using a modified quadrupole ion trap mass spectrometer, a series of metal complex ions have been reacted with acetonitrile in the gas phase. Careful control of the coordination number and the type of coordinating functionality in diethylenetriamine-substituted ligands enable the effects of the coordination sphere on metal complex reactivity to be examined. The association reaction kinetics of acetonitrile with these pentacoordinate complexes are followed in order to obtain information about the starting complexes and the reaction dynamics. The kinetics and thermodynamics of acetonitrile addition to the metal complex ions are strongly affected by the chemical environment around the metal center such that significant differences in reactivity are observed for Co(II) and Cu(II) complexes with various coordination spheres. When thiophene, furan, or benzene moieties are present in the coordination sphere of the complex, addition of two acetonitrile molecules is readily observed. In contrast, ligands with better sigma donors react mainly to add one acetonitrile molecule. Among the ligands with good sigma donors, a clear trend in reactivity is observed in which complexes with nitrogen-containing ligands are the least reactive, sulfur-containing complexes are more reactive, and oxygen-containing complexes are the most reactive. In general, equilibrium and reaction rate constants seem to be consistent with the hard and soft acid and base (HSAB) principle. Interestingly, the presence of certain groups (e.g., pyridine and imidazole) in the coordination sphere clearly can change the acid character of the metal as seen by their effect on the binding properties of other functional groups in the same ligand. Finally, we conclude that because complexes with different coordination spheres react to noticeably different extents, ion-molecule (I-M) reactions may be potentially useful for obtaining coordination structure information for transition metal complexes.

Journal Article↗
PubMed2004

N,N-coordinated pi radical anions of S-methyl-1-phenyl-isothiosemicarbazide in two five-coordinate ferric complexes [Fe III(L Me*)(2)X] (X = CH3S-, Cl-).

The reaction between [Fe(III)(dmf)(6)](ClO(4))(3) and the ligand S-methyl-1-phenyl-isothiosemicarbazide, H(2)[L(Me)], and triethylamine (1:3:6) in methanol under an argon blanketing atmosphere at elevated temperatures (reflux) yields a purple solution from which upon cooling to 20 degrees C dark green crystals of [Fe(III)(L(Me)(*))(2)(SCH(3))] (1) were obtained in 15% yield. From a similar reaction mixture using FeCl(3) as starting material in the solvent acetone under anaerobic conditions at -80 degrees C, dark green crystals of [Fe(III)(L(Me)(*))(2)Cl] (2) were obtained in 21% yield. The structures of complexes 1 and 2 have been determined by single-crystal X-ray crystallography at 100 K. Both complexes are five-coordinate square base pyramidal ferric species containing two N,N-coordinated, monoanionic pi radicals, (L(Me)(*))(1)(-), of the parent S-methyl-1-phenyl-isothiosemicarbazide(2-) dianion in the basal positions whereas the axial position is occupied by methylthiolate in 1 and chloride in 2, respectively. The electronic structure of both species has been elucidated by their electronic spectra, magnetic properties, and X-band EPR and Mössbauer spectra. Both possess an S(t) = (1)/(2) ground state which is attained via an antiferromagnetic coupling between the spins of an intermediate spin ferric ion (S(Fe) = (3)/(2)) and two ligand pi radical anions (S(rad) = (1)/(2)).

Journal Article↗
PubMed2004

Supramolecular and coordination polymer complexes supported by a tripodal tripyridine ligand containing a 1,3,5-triethylbenzene spacer.

By By combining a tripodal tripyridine ligand containing a 1,3,5-triethylbenzene spacer (L) with several divalent transition-metal chlorides, we have selectively prepared a capsule-type supramolecular complex, [PdII3(L)2Cl6] x 2H2O, and one-dimensional (1D) coordination polymer complexes, ([CuII(L)Cl2] x C2H5OH)n, ([CoII3(L)2Cl6] x 2CH2Cl2)n, and ([ZnII3(L)2Cl6] x 2H2O)n, with a zigzag polymer chain, a linear polymer chain, and a ladder polymer chain structure, respectively. All the structures were established in detail by single-crystal X-ray diffraction analysis, and the factors inducing the structural differences among the complexes are discussed by taking account of the differences in coordination geometry (square planar vs tetrahedral) as well as metal-ligand binding strength in the complexes.

Journal Article↗
PubMed1996

Trans effects in nitric oxide binding to myoglobin cavity mutant H93G.

When nitric oxide (NO) binds to heme proteins, it exerts a repulsive trans effect on the proximal ligand, resulting in weakening or rupture of the proximal ligand-iron bond. The general question of whether NO binding generates a five-coordinate complex with proximal ligand release is important for the function of enzymes such as guanylate cyclase. This question can be addressed by studying NO binding to the myoglobin cavity mutant H93G, where the proximal histidine has been replaced by glycine. When this protein is expressed in the presence of imidazole (Im), an imidazole molecule occupies the proximal cavity and serves as a ligand to the iron [Barrick, D. (1994) Biochemistry 33, 6546-6554]. This proximal imidazole can be exchanged for a variety of exogenous ligands [DePillis, G.D., Decatur, S. M., Barrick, D., & Boxer, S.G. (1994) J. Am. Chem. Soc. 116, 6981-6982]. While CO binds to H93G(Im) to form a stable six-coordinate complex similar to that of the wild type and NO binds to wild-type myoglobin to form a six-coordinate complex, we find that the binding of NO to H93G(Im) under similar conditions results in the cleavage of the exogenous imidazole-iron bond at neutral pH, leaving a five-coordinate heme-NO complex, H93G-NO, inside the protein. When a large excess of imidazole is added to this five-coordinate NO complex, a six-coordinate complex can be formed; thus, the binding constant of a sixth ligand to the five-coordinate H93G-NO complex can be measured. This is found to be several orders of magnitude smaller than the binding constant of Im to the carbonmonoxy, deoxy, or the metcyano forms of protein. By replacement of Im with methyl-substituted imidazoles which have hindered or strained binding conformations, this binding constant can be reduced further and some of the factors responsible for favoring the five-coordinate form can be elucidated. Thus, the cavity mutant H93G provides a novel model system for studying the factors that control the coordination state of NO complexes of heme proteins and serves as a bridge between synthetic heme model complexes in simple solvents and site-directed mutants in the structured environment found in proteins.

Animals↗
PubMed2002

Characterization of the side-on coordinated bissuperoxo complexes of aluminum FAl(O(2))(2), ClAl(O(2))(2), and BrAl(O(2))(2) with triplet electronic ground states: a combined matrix IR and quantum chemical study.

Matrix isolation has been used to study the photolytically induced reaction of AlX (X = F, Cl, or Br) with O(2). The peroxo and bisperoxo compounds XAlO(2) and XAl(O(2))(2) are found to be the products of these reactions. While the peroxo species XAlO(2) were already addressed in a separate work, we concentrate herein on the bissuperoxo complexes XAl(O(2))(2), which are to our knowledge the first examples of such complexes with Al centers. Our IR spectroscopic results taking in the effect of isotopic substitution ((16)O/(18)O) allied with quantum chemical calculations show that the O(2) moieties in these complexes are side-on coordinated, leading to an overall C(2)(v)() symmetry of the complexes and a spin multiplicity of 3. The O-O distance of about 1.366 A argues for the presence of superoxide units. The force constants are, however, somewhat smaller than expected for a superoxide anion and indicate that the bonding in the complexes cannot be described simply on the basis of an ionic model. Interestingly a photoinduced intramolecular isotopic scrambling process is observed for the compounds resulting in partial conversion of the XAl((16)O(2))((18)O)(2) isotopomer into XAl((16)O(18)O)((16)O(18)O). The properties of the complexes will be compared to those of complexes to transition metal centers.

Journal Article↗
PubMed2003

Core-modified porphyrin incorporating a phenolate donor. Characterization of Pd(II), Ni(II), Zn(II), Cd(II), and Fe(III) complexes.

Coordinating properties of acetoxybenziporphyrin, (TPBPOAc)H, have been investigated for a number of metal ions. Insertion of Ni, Pd, and Fe results in the cleavage of the acetoxy group leading to complexes (TPBPO)Ni(II), (TPBPO)Pd(II), and (TPBPO)Fe(III)X containing a M-O bond. No cleavage is observed with Zn(II) and Cd(II), which form complexes (TPBPOAc)M(II)Cl, where M = Zn, Cd. (TPBPO)Ni(II) can also be obtained from the dication of hydroxybenziporphyrin, [(TPBPOH)H(3)]Cl(2), which is prepared by acid hydrolysis of the acetoxy compound. The diamagnetic (TPBPO)Ni(II) can be transformed into the paramagnetic (TPBPOAc)Ni(II)Cl in a reaction with acetyl chloride. X-ray structures have been determined for (TPBPO)Pd(II) and (TPBPOAc)Zn(II)Cl. In the palladium species, the phenolate moiety forms a strong bond to the Pd ion and an unusual interaction geometry is observed, enforced by the macrocyclic environment. Association of a TFA molecule to the phenolic oxygen does not cause significant structural changes in the (TPBPO)Pd(II) molecule. In (TPBPOAc)Zn(II)Cl, the metal ion weakly interacts with the phenolic fragment. The paramagnetic Fe(III) complexes, (TPBPO)Fe(III)X, have been investigated with (1)H NMR spectroscopy. The observed spectral patterns are consistent with the presence of a high-spin Fe(III) center and pi delocalization of spin density onto the phenoxide fragment. Each of the compounds (TPBPO)Fe(III)X exists in solution as a mixture of two isomers, which for X = I are shown to remain in a temperature-dependent equilibrium. The observed isomerism results from two nonequivalent orientations of the axial halide with respect to the puckered macrocyclic ring.

Journal Article↗
PubMed2006

Self-assembly of luminescent ternary complexes between seven-coordinate lanthanide(III) complexes and chromophore bearing carboxylates and phosphonates.

Luminescent lanthanide complexes have been prepared by exploiting the interaction between lanthanide DO3A complexes and chromophore bearing carboxylates or phosphonates. This interaction can be utilised to probe the choice of sensitising chromophore suited to a given lanthanide. Furthermore, ternary complexes obtained from chromophore appended carboxylates dissociate in the presence of phosphate, while those obtained from phosphonates do not.

Journal Article↗
PubMed1997

Syntheses, Structures, and Binding Constants of Cyclic Ether and Thioether Adducts of Soluble Cadmium(II) Carboxylates. Intermediates in the Homopolymerization of Oxiranes and Thiiranes and in Carbon Dioxide Coupling Processes.

A synthetic methodology for the preparation of a large variety of eta(3)-HB(3-Phpz)(3)Cd(acetate) adducts is presented which involves replacement of toluene in the eta(3)-HB(3-Phpz)(3)Cd(acetate) solvate complex by the appropriate cyclic ether or cyclic thioether. In this manner, adducts of THF, dioxane, propylene oxide, cyclohexene oxide, and propylene sulfide were isolated. The solid-state structures of several of these complexes were determined by X-ray crystallography, revealing a six-coordinate complex where the acetate ligand is shown to be fairly symmetrically bonded to the cadmium center. In methylene chloride solution, the cyclic ether or thioether readily dissociates to afford the five-coordinate complex, as demonstrated by (113)Cd NMR. A quantitative assessment of the binding of these base adducts of eta(3)-HB(3-Phpz)(3)Cd(acetate) was determined by measuring the temperature dependence of the equilibrium constants for the five- and six-coordinate derivatives. The presence of one sharp (113)Cd resonance in this equilibrium mixture is indicative of rapid intermolecular exchange between the five- and six-coordinate complexes when compared to the chemical shift differences in these two species ( approximately 6600 Hz at 89 MHz). The order established for ether binding is THF > dioxane > propylene sulfide > cyclohexene oxide >/= propylene oxide, with DeltaH degrees and DeltaS degrees spanning the ranges -27.7 to 24.3 kJ/mol and -89.7 to -94.1 J/(mol K). The epoxide and thioepoxide adducts were shown to serve as models for the initiation step in the copolymerization of epoxides with carbon dioxide catalyzed by metal carboxylates. That is, the carboxylate ligand was shown to ring-open the epoxide or thioepoxide, subsequently affording polyethers or polythioethers with ester end groups. By way of contrast, in the presence of CO(2) and epoxides, this system led to cyclic carbonate production.

Journal Article↗