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PubMed2003

Laser photolysis studies of the photochemical reactions of chromium(III) octaethylporphyrin and tetramesitylporphyrin complexes in toluene solution.

A nanosecond laser photolysis study was carried out for the Cr(III) porphyrin complexes of 2,3,7,8,12,13,17,18-octaethylporphyrin, [Cr(OEP)(Cl)(L)], and of 5,10,15,20-tetramesitylporphyrin, [Cr(TMP)(Cl)(L)], in toluene containing water and an excess amount of L (L = axial ligand). The laser photolysis generates the triplet excited state of the parent complex as well as a five-coordinate complex, [Cr(porphyrin)(Cl)], produced by the photodissociation of the axial ligand L. The yields for the formation of the triplet state and the photodissociation of L are found to markedly depend on the nature of both L and porphyrin ligand. The five-coordinate [Cr(porphyrin)(Cl)] readily reacts with both H(2)O and L in the bulk solution to give [Cr(porphyrin)(Cl)(H(2)O)] and [Cr(porphyrin)(Cl)(L)], respectively. The axial H(2)O ligand in [Cr(porphyrin)(Cl)(H(2)O)] is then substituted by the ligand L to regenerate the original complex [Cr(porphyrin)(Cl)(L)]. In principle, the substitution reaction takes place by the dissociative mechanism: the first step is the dissociation of H(2)O from [Cr(porphyrin)(Cl)(H(2)O)], followed by the reaction of the five-coordinate [Cr(porphyrin)(Cl)] with the ligand L to regenerate [Cr(porphyrin)(Cl)(L)]. The rate constants for this ligand substitution reaction are found to exhibit bell-shaped ligand concentration dependence. The detailed kinetic analysis revealed that both ligands L and H(2)O in toluene make a hydrogen bond with the axial H(2)O ligand in [Cr(porphyrin)(Cl)(H(2)O)] to yield dead-end complexes for the substitution reaction. The reaction mechanisms are discussed on the basis of the substituent effects of the porphyrin peripheral groups and the kinetic parameters determined from the temperature dependence of the rate constants.

Journal Article↗
PubMed2000

Novel Mn(II)Mn(III)Mn(II) trinuclear complexes with carbohydrate bridges derived from seven-coordinate manganese(II) complexes with N-glycoside.

Reactions of MnX2.nH2O with tris(N-(D-mannosyl)-2-aminoethyl)amine ((D-Man)3-tren), which was formed from D-mannose and tris(2-aminoethyl)amine (tren) in situ, afforded colorless crystals of [Mn((D-Man)3-tren)]X2 (3a, X = Cl; 3b, X = Br; 3c, X = NO3; 3d, X = 1/2SO4). The similar reaction of MnSO4.5H2O with tris(N-(L-rhamnosyl)-2-aminoethyl)amine ((L-Rha)3-tren) gave [Mn((L-Rha)3-tren)]SO4 (4d), where L-rhamnose is 6-deoxy-L-mannose. The structures of 3b and 4d were determined by X-ray crystallography to have a seven-coordinate Mn(II) center ligated by the N-glycoside ligand, (aldose)3-tren, with a C3 helical structure. Three D-mannosyl residues of 3b are arranged in a delta(ob3) configuration around the metal, leading to formation of a cage-type sugar domain in which a water molecule is trapped. In 4d, three L-rhamnosyl moieties are in a delta(lel3) configuration to form a facially opened sugar domain on which a sulfate anion is capping through hydrogen bonding. These structures demonstrated that a configurational switch around the seven-coordinate manganese(II) center occurs depending on its counteranion. Reactions of 3a, 3b, and 4d with 0.5 equiv of Mn(II) salt in the presence of triethylamine yielded reddish orange crystals formulated as [[Mn((aldose)3-tren)]2Mn(H2O)X3.nH2O (5a, aldose = D-Man, X = Cl; 5b, aldose = D-Man, X = Br; 6d, aldose = L-Rha, X = 1/2SO4). The analogous trinuclear complexes 6a (aldose = L-Rha, X = Cl), 6b (aldose = L-Rha, X = Br), and 6c (aldose = L-Rha, X = NO3) were prepared by the one-pot reaction of Mn(II) salts with (L-Rha)3-tren without isolation of the intermediate Mn(II) complexes. X-ray crystallographic studies revealed that 5a, 5b, 6c, and 6d have a linearly ordered trimanganese core, Mn(II)Mn(III)Mn(II), bridged by two carbohydrate residues with Mn-Mn separations of 3.845(2)-3.919(4) A and Mn-Mn-Mn angles of 170.7(1)-173.81(7) degrees. The terminal Mn(II) atoms are seven-coordinate with a distorted mono-face-capped octahedral geometry ligated by the (aldose)3-tren ligand through three oxygen atoms of C-2 hydroxyl groups, three N-glycosidic nitrogen atoms, and a tertiary amino group. The central Mn(III) atoms are five-coordinate ligated by four oxygen atoms of carbohydrate residues in the (aldose)3-tren ligands and one water molecule, resulting in a square-pyramidal geometry. In the bridging part, a beta-aldopyranosyl unit with a chair conformation bridges the two Mn(II)Mn(III) ions with the C-2 mu-alkoxo group and with the C-1 N-glycosidic amino and the C-3 alkoxo groups coordinating to each metal center. These structures could be very useful information in relation to xylose isomerases which promote aldose-ketose isomerization by using divalent dimetal centers such as Mn2+, Mg2+, and Co2+.

Carbohydrates↗
PubMed1998

Metal-Ligand Bonding in Coinage Metal-Phosphine Complexes: The Synthesis and Structure of Some Low-Coordinate Silver(I)-Phosphine Complexes.

Reaction of AgBF(4) with 2 equiv of Ph(3)P in acetonitrile followed by recrystallization from dichloromethane/hexane yields the mixed phosphine-nitrile complex [(Ph(3)P)(2)AgNCCH(3)]BF(4) (I) as its dichloromethane solvate, I.0.5CH(2)Cl(2). This solvate crystallizes in the monoclinic space group C2/c with a = 22.928(5), b = 12.700(3), c = 25.156(5) Å, beta = 97.53(3) degrees, and Z = 8. The acetonitrile ligand in I is loosely bound to the metal center and easily lost, even in the solid state, without decomposition. Hence, recrystallization of dried samples of I.0.5CH(2)Cl(2) from CH(2)Cl(2)/hexane results in isolation of the novel low-coordinate phosphine complex [(Ph(3)P)(2)Ag]BF(4) (II). II crystallizes in the monoclinic space group C2/c with a = 21.733(9), b = 12.272(4), c = 24.356(9) Å, beta = 95.01(3) degrees, and Z = 8. In both cases, a weak interaction is present between a fluorine atom of the BF(4)(-) anion and the silver cation. However, these interactions appear to be essentially electrostatic rather than dative in nature, implying that I is best considered a three-coordinate silver complex and that II is a rare, structurally characterized example of a two-coordinate silver-phosphine complex. These solid-state geometric assignments are supported by (31)P NMR studies, which reveal a Ag-P coupling constant of 550 Hz for II, consistent with the presence of a linear two-coordinate complex in solution. The NMR data also indicate that the phosphine ligands are involved in exchange processes, which are accelerated by the presence of a donor solvent such as acetonitrile. Comparison of II with its gold analogue supports the previously stated concept that gold atoms are smaller than silver atoms. An analysis of 13 other isostructural pairs of silver and gold complexes culled from the crystallographic database lends further support to this concept.

Journal Article↗
PubMed2002

Silver ion liquid-chromatographic mobility of plant diacylglycerols as a function of their composition and spatial arrangement.

Coordination complexes of unsaturated rac-1,2-diacylglycerols (DAGs) with silver ions were separated by adsorption and reversed-phase TLC (silver ion TLC and silver ion RP-TLC, respectively). During silver ion TLC, silver ion complexes are formed by an indeterminate number of coordination centers of various nature and only at the adsorbent surface; separation of the complexes proceeds according to an adsorption mechanism, and there is an inverse exponential relationship between DAG unsaturation and their mobility. With silver ion RP-TLC, the complexes are formed only with double bonds, only in solution, and at a 1:1 ratio; the complexes are fractionated by lipophilic partitioning between two liquid phases, and the relationship between the unsaturation of DAGs and their mobility is a direct linear one. Nevertheless, in spite of all these differences, the use of both methods demonstrated that DAG species characterized by a coiled acyl configuration always greatly exceeded in polarity those with the same unsaturation, but with the configuration close to an extended one; in the former group, this excess amounted to two- to three-fold and 30-40% for silver ion TLC and silver ion RP-TLC, respectively. In addition, for both versions of silver ion LC, these two groups of species differ from each other quantitatively, but not qualitatively, in the pattern of the relationship between the unsaturation and mobility of DAG complexes. Thus, under all conditions of silver ion LC studied here, the polarity of DAG complexes and, therefore, their mobility are conditional not only on the number of double bonds, but also on their configuration.

Chromatography, Liquid↗
PubMed2004

X-ray structure of physiological copper(II)-bis(L-histidinato) complex.

The isolation and the X-ray crystal structure of physiological copper(II)-L-histidine complex are reported. The neutral five-coordinate complex shows distorted square pyramidal geometry with bidentate and tridentate L-histidine ligands. The basic character of the pendent imidazole group and H-bonding interactions of bidentate L-histidine ligand are important for copper transport. The unique structural features help explain the origin of its thermodynamic stability and kinetic reactivity in human blood along with the ternary copper(II)-amino acid complexes. The role of L-histidine in interaction with copper(II)-albumin, in cellular uptake of copper, and in treatment of Menkes disease can be studied using these results.

Copper↗
PubMed2002

Rapid excited-state structural reorganization captured by pulsed X-rays.

Visible light excitation of [Cu(I)(dmp)(2)](BArF), where dmp is 2,9-dimethyl-1,10-phenanthroline and BArF is tetrakis(3,5-bis(trifluoromethylphenyl))borate, in toluene produces a photoluminescent, metal-to-ligand charge-transfer (MLCT) excited state with a lifetime of 98 +/- 5 ns. Probing this state within 14 ns after photoexcitation with pulsed X-rays establishes that a Cu(II) center, borne in a Cu(I) geometry, binds an additional ligand to form a five-coordinate complex with increased bond lengths and a coordination geometry of distorted trigonal bipyramid. The average Cu-N bond length increases in the excited state by 0.07 A. The transiently formed five-coordinate MLCT state is photoluminescent under the condition studied, indicating that the absorptive and emissive states have distinct geometries. The data represent the first X-ray characterization of a molecular excited state in fluid solution on a nanosecond time scale.

Journal Article↗
PubMed2005

Solid-phase synthesis, characterization and DNA binding properties of the first chloro(polypyridyl)ruthenium conjugated peptide complex.

A general method for the synthesis of chloro(polypyridyl)ruthenium conjugated peptide complexes via a solid-phase strategy is described. The method is applied to synthesize two positional isomers of the complex [Ru(terpy)(4-CO2H-4'-Mebpy-Gly-L-His-L-LysCONH2)Cl](PF6). Even though the separation of the isomers was only partially achieved chromatographically, the isomers were unambiguously assigned by NMR spectroscopy. The interactions of the complex [Ru(terpy)(4-CO2H-4'-Mebpy-Gly-L-His-L-LysCONH2)Cl](PF6) with CT-DNA and plasmid DNA, have been studied with various spectroscopic techniques, showing that (i) the complexes coordinatively bind to DNA preferring the bases guanine and cytosine over the bases thymine and adenine after hydrolysis of the coordinated chloride, (ii) electrostatic interactions between the complex cation and the polyanionic DNA chain assist this binding (iii) only in the case of one isomer the peptide does interact further with DNA as evidenced from 31P NMR spectroscopy, (iv) DNA unwinding occurs in all cases with high binding ratio (Ru/base) values (r > 0.3).

Animals↗
PubMed2006

Engineering emissive europium and terbium complexes for molecular imaging and sensing.

Emissive f-block coordination complexes constitute an important class of optical probes, with applications ranging from sensing of bioactive species, high throughput assays and screening protocols in vitro, to time-resolved imaging studies in cellulo or in vivo. The key chemistry issues to be addressed in complex design and characterisation are defined, with an emphasis on the use of emissive europium and terbium complexes and their conjugates in molecular imaging. Both luminescent 'tags' useful in energy transfer studies and 'responsive' systems for sensing are discussed.

Chemistry↗
PubMed2006

An unusual example of a linearly coordinated acetone ligand in a six-coordinate iron(II) complex.

The title compound, acetonediaqua[2,6-bis(3-tert-butylpyrazol-1-yl)pyridine]iron(II) bis(tetrafluoroborate) acetone disolvate, [Fe(C19H25N5)(C3H6O)(H2O)2](BF4)(2).2C3H6O, contains a C2-symmetric six-coordinate complex dication, with an acetone ligand in its equatorial plane that is linearly coordinated by symmetry (Fe-O=CMe2=180 degrees). This is a consequence of close steric contacts between the coordinated carbonyl group and the two distal tert-butyl substituents on the tridentate ligand.

Journal Article↗
PubMed2004

Alkyl-eta2-alkene niobocene and tantalocene complexes with the allyldimethylsilyl-eta5-cyclopentadienyl ligand: synthesis, NMR studies and DFT calculations.

Group 5 metal complexes [M(eta5-C5H5)[eta5-C5H4SiMe2(CH2-eta]2-CH=CH2)]X] (M = Nb, X = Me, CH2Ph, CH2SiMe3; M = Ta, X = Me, CH2Ph) and [Ta(eta5-C5Me5)[eta5-C5H4SiMe2(CH2-eta2-CH=CH2)]X] (X = Cl, Me, CH2Ph, CH2SiMe3) containing a chelating alkene ligand tethered to a cyclopentadienyl ring have been synthesized in high yields by reduction with Na/Hg (X = Cl) and alkylation with reductive elimination (X = alkyl) of the corresponding metal(iv) dichlorides [M(eta5-Cp)[eta5-C5H4SiMe2(CH2CH=CH2)]Cl2] (Cp = C5H5, M = Nb, Ta, Cp = C5Me5, M = Ta). These chloro- and alkyl-alkene coordinated complexes react with CO and isocyanides [CNtBu, CN(2,6-Me2C6H3)] to give the ligand-substituted metal(III) compounds [M(eta5-Cp)[eta5-C5H4SiMe2(CH2CH=CH2)]XL] (X = Cl, Me, CH2Ph, CH2SiMe3). Reaction of the chloro-alkene tantalum complex with LiNHtBu results in formation of the imido hydride derivative [Ta(eta5-C5Me5)[eta5-C5H4SiMe2(CH2CH=CH2)]H(NtBu)]. NMR studies for all of the new compounds and DFT calculations for the alkene-coordinated metal complexes are compared with those known for related group 4 metal cations.

Journal Article↗
PubMed2002

A bis-acetonitrile two-coordinate copper(I) complex: synthesis and characterization of highly soluble B(C(6)F(5))(4)(-) salts of [Cu(MeCN)(2)](+) and [Cu(MeCN)(4)](+).

Copper(I)-acetonitrile complexes are exceedingly useful starting materials for the synthesis of copper(I) complexes with polydentate ligands. To extend the utility of such chemistry to solution studies in relatively low-dielectric solvents (i.e., diethyl ether, toluene) and to aid in obtaining products amenable to X-ray diffraction studies, we have recently begun to employ counteranions such as B(C(6)F(5))(4)(-) for bioinorganic studies. Thus, the synthesis of [Cu(MeCN)(4)]B(C(6)F(5))(4) (1) is presented. Its recrystallization from CH(2)Cl(2)/pentane yields the linear, two-coordinate complex [Cu(MeCN)(2)]B(C(6)F(5))(4) (2), whose centrosymmetric X-ray structure shows that its Cu-N distance is significantly shorter than that in other two-coordinate Cu(I) complexes with nitrogen ligands or that in the tetrahedral complex [Cu(MeCN)(4)]ClO(4). Infrared spectroscopy indicates interesting and diagnostically useful differences between the nu(CN) of 1 and 2.

Acetonitriles↗
PubMed2002

Five-coordinate platinum(IV) complex as a precursor to a novel Pt(II) olefin hydride complex for alkane activation.

The five-coordinate platinum(IV) complex (nacnac)PtMe3 (nacnac- = [{(o-iPr2C6H3)NC(CH3)}2CH]-) thermally eliminates ethane and methane to produce a novel olefin(hydrido)platinum(II) complex, where the olefin is part of the nacnac-type ligand. This Pt(II) product activates hydrocarbons, including alkanes under mild conditions, as indicated by scrambling of hydrogen and deuterium between the hydrocarbon solvent and selected positions on the ligand of the platinum complex. A mechanism in which olefin insertion into the metal hydride bond opens a site to allow hydrocarbon coordination and C-H bond oxidative addition is proposed.

Journal Article↗
PubMed2003

Reversible anion exchanges between the layered organic-inorganic hybridized architectures: syntheses and structures of manganese(II) and copper(II) complexes containing novel tripodal ligands.

Six noninterpenetrating organic-inorganic hybridized coordination complexes, [Mn(3)(2)(H(2)O)(2)](ClO(4))(2).2 H(2)O (5), [Mn(3)(2)(H(2)O)(2)](NO(3))(2) (6), [Mn(3)(2)(N(3))(2)].2 H(2)O (7), [Cu(3)(2)(H(2)O)(2)](ClO(4))(2) (8), [Mn(4)(2)(H(2)O)(SO(4))].CH(3)OH.5 H(2)O (9) and [Mn(4)(2)](ClO(4))(2) (10) were obtained through self-assembly of novel tripodal ligands, 1,3,5-tris(1-imidazolyl)benzene (3) and 1,3-bis(1-imidazolyl)-5-(imidazol-1-ylmethyl)benzene (4) with the corresponding metal salts, respectively. Their structures were determined by X-ray crystallography. The results of structural analysis of complexes 5, 6, 7, and 8 with rigid ligand 3 indicate that their structures are mainly dependant on the nature of the organic ligand and geometric need of the metal ions, but not influenced greatly by the anions and metal ions. While in complexes 9 and 10, which contain the flexible ligand 4, the counteranion plays an important role in the formation of the frameworks. Entirely different structures of complexes 5 and 10 indicate that the organic ligands greatly affect the structures of assemblies. Furthermore, in complexes 5 and 6, the counteranions located between the cationic layers can be exchanged by other anions. Reversible anion exchanges between complexes 5 and 6 without destruction of the frameworks demonstrate that 5 and 6 can act as cationic layered materials for anion exchange, as determined by IR spectroscopy, elemental analyses, and X-ray powder diffraction.

Journal Article↗
PubMed2004

Kinetico-mechanistic studies of C-H bond activation on new Pd complexes containing N,N'-chelating ligands.

The hybrid imine/amine palladium(II) coordination complexes [PdX2(kappa2-N(imino),N(amino))](X = Cl, AcO; kappa2-N(imino),N(amino)= 4ClC6H4CHNCH2(CH2)nN(CH3)2, n= 1, 2) have been prepared in different isomeric forms which include E/Z arrangement around the C[double bond]N bond of the hybrid ligand and {Pd(kappa(2)-N(imino),N(amino))} ring conformation. The crystal structures of four of them, E-1AcO, Z-1AcO, E-2AcO and E-2Cl, have been determined and the solution behaviour in acetic acid, the common cyclometallating solvent, for all these systems studied. The complexes in acetic acid solution are shown to maintain the structure determined by X-ray crystallography, as they do in deuterated chloroform. Nevertheless, a partial opening equilibrium of the {Pd(kappa2-N(imino),N(amino))} ring is observed by NMR experiments. When the complexes are held in solution for longer periods the corresponding cyclometallated derivatives, 1AcO-CM, 2AcO-CM, 1Cl-CM and 2Cl-CM, containing the {Pd(kappa2-C,N(imino))} palladacycle are obtained, as characterized by 1H NMR spectroscopy. In these compounds the total opening of the N(amino) moiety of the ligand has occurred. The C-H bond activation process has been studied kinetico-mechanistically at different temperatures, pressures and acid concentrations; the results agree with the need of an opening of the chelate ring in [PdX2(kappa2-N(imino),N(amino))] prior to the proper cyclometallation reaction. The values of the enthalpies of activation are higher than those observed for known N-monodentated cyclometallating ligands, as should correspond to the contribution of a ligand dechelation pre-equilibrium. The entropies and volumes of activation are also indicative of this predissociation that include an important amount of contractive ordering. The presence of small amounts of triflic acid in the reaction medium accelerates the reaction to the value observed for N(imino)-monodentate systems, indicating that the full opening of the chelate ring has taken place. For the badly oriented isomeric forms of the ligand in the chelated complex (Z), the cyclometallation process is even more slow and corresponds directly to the reorganization of the ligand to its cyclopalladation-active (E) conformation.

Journal Article↗
PubMedDate not supplied

Organo-platinum complexes as antitumor agents (review).

Rosenberg et al discovered in the coordination complexes of platinum a new, novel type of potential antitumor agent. Cisplatin [cis-dichlorodiammine platinum (II)4 proved active against a variety of rodent tumors and acted synergistically when combined with other chemotherapeutic agents. Initial clinical tests by Hill et al in 1971, showed cisplatin to be active against malignant lymphoma, Hodgkin's disease, and certain other malignancies. Significant nephrotoxicity, nausea, and vomiting were noted. Since then, cisplatin has been tested alone and in combination chemotherapy and has proven an efficacious anticancer agent in squamous cell carcinoma of head and neck, ovarian carcinoma, disseminated testicular cancer, and others. Its therapeutic value was acknowledged when approved in 1978 by the U.S. FDA for treatment of the latter cancer. The current clinical literature indicates clearly that the full potential of this drug has not yet been realized. Hydration and diuresis have served to mitigate much of the nephrotoxicity, while significant strides toward amelioration of the nausea and vomiting have also been achieved. Literally, thousands of chemically-related congeners have been synthesized, and many have shown marked potency against rodent tumors. Very few, however, have been evaluated clinically, vis-a-vis malonato trans(-)-1,2-diaminocyclohexane platinum(II); this appears a most promising and fertile area of future investigation.

Animals↗
PubMed1976

Cr(III) complexes as active site probes of yeast inorganic pyrophosphatase.

The inert coordination complex of Cr(III) with PP1 (CrPP1) is not a substrate for yeast inorganic pyrophosphatase and does not inhibit the Mg2+-dependent activity of this enzyme. These results, when compared with the effects of CrPP1 on other enzymes and with the effects of other divalent metal ions on this enzyme, suggest that yeast inorganic pyrophosphatase binds substraather than the phosphate groups. Mg2+ partially protects against a slow inactivation of the enzyme by Cr(H2O)6(3)+; this exchange inert ion may provide a means of labeling the metal ion binding site of this enzyme.

Binding Sites↗
PubMed2003

Luminescent nido-carborane-diphosphine anions [(PR2)2C2B9H10](-) (R = Ph, (i)Pr). Modification of their luminescence properties upon formation of three-coordinate gold(I) complexes.

The free nido-diphosphine anions [(PR(2))(2)C(2)B(9)H(10)](-) (R = Ph, (i)Pr) show luminescence properties whereas the closo-diphosphines [(PR(2))(2)C(2)B(10)H(10)] do not. Four families of three-coordinate complexes of stoichiometry [Au[(PR(2))(2)C(2)B(10)H(10)]L]OTf (L = tertiary phosphine) and [Au[(PR(2))(2)C(2)B(9)H(10)]L] have been studied in order to analyze the influence of the closo- or nido-nature of the diphosphine, the monophosphine coordinated to gold and the substituent at the diphosphine on the luminescence of the complexes. Only the nido-derivatives show luminescence. The maxima of the emissions are shifted to lower energies than those of the corresponding free nido-diphosphines. When the substituent at the diphosphine is phenyl, a new emission appears, which has been assigned as arising from a metal to ligand charge transfer [Au-->pi(L)] excited state.

Journal Article↗