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PubMed1996

Induction of luminol chemiluminescence by the manganese cluster of the photosystem II water-oxidizing complex to the S0, S1, S2, and S3 states.

Luminol chemiluminescence (CL) (lambda(max) = 425 nm) induced by the manganese cluster of photosystem II (PSII) (t(max) = 1-5 min) along with CL induced by mono-, di-, or tetranuclear manganese coordination complexes (t(max) = 2-40 s) is observed when either 200 mM sodium phosphate or 1 M Tris-HCl + 200 microM EDTA are present in the reaction medium (pH 8.5) containing peroxidase. This light emission is not observed when Tris is used in the reaction medium without EDTA. The yield of a given CL without peroxidase is 5%-20% of that with peroxidase. The peroxidase-dependent CL is inhibited by catalase (I50 = 0.14-0.17 mu M), while the peroxidase-independent CL is not inhibited by 100 mM ethanol, 1 mM NaN3, 20 mu M Cyt c, or 0.6 mu M catalase. The CL induced by the Mn cluster of the water-oxidizing complex (WOC) in the S3 or S2 state exceeds that of lower S states by 15-20-fold. The magnitude of CL induced by Mn complexes is dependent on the ligand type of the complex. The ligand types of the Mn complexes and the WOC in different S states are ranked according to the magnitude of the induced CL: 1,10-phenanthroline > 2.2'-bipyridine > WOC (S3 or S2) > hydrotris(pirazolyl) borate > WOC (S0-2 or S0, S1) > 1,4,7-triazacyclononane. It is concluded that CL is caused by H2O2 formed as a result of the oxidation of luminol by triplet molecular oxygen. The Mn cluster of WOC and manganese coordination complexes, acting as catalysts of this reaction, show oxidase activity. Upon S2-S3 or S1-S2 transition, changes occur in the ligand environment of the Mn cluster of WOC influencing the induction of luminol CL.

Chlorophyll↗
PubMed1997

Parkinsonism reduces coordination of fingers, wrist, and arm in fine motor control.

This experiment investigates movement coordination in Parkinson's disease (PD) subjects. Seventeen PD patients and 12 elderly control subjects performed several handwriting-like tasks on a digitizing writing tablet resting on top of a table in front of the subject. The writing patterns, in increasing order of coordination complexity, were repetitive back-and-forth movements in various orientations, circles and loops in clockwise and counterclockwise directions, and a complex writing pattern. The patterns were analyzed in terms of jerk normalized for duration and size per stroke. In the PD subjects, back-and-forth strokes, involving coordination of fingers and wrist, showed larger normalized jerk than strokes performed using either the wrist or the fingers alone. In the PD patients, wrist flexion (plus radial deviation) showed greater normalized jerk in comparison to wrist extension (plus ulnar deviation). The elderly control subjects showed no such effects as a function of coordination complexity. For both PD and elderly control subjects, looping patterns consisting of circles with a left-to-right forearm movement, did not show a systematic increase of normalized jerk. The same handwriting patterns were then simulated using a biologically inspired neural network model of the basal ganglia thalamocortical relations for a control and a mild PD subject. The network simulation was consistent with the observed experimental results, providing additional support that a reduced capability to coordinate wrist and finger movements may be caused by suboptimal functioning of the basal ganglia in PD. The results suggest that in PD patients fine motor control problems may be caused by a reduced capability to coordinate the fingers and wrist and by reduced control of wrist flexion.

Adult↗
PubMed1993

Lysyl oxidase copper-talon complex: a model.

The translated primary amino-acid sequences from human genomic and human, rat and mouse lysyl oxidase cDNAs were subjected to computer comparison. This revealed a highly-conserved primary structure and similar computer-predicted secondary structures. A prototypical lysyl oxidase structural model was reconciled with the known physical, chemical and biological properties. Analysis of the post-translationally-modified and proteolytically-processed mature enzyme model revealed a copper coordination complex that may be contained as part of the active site. This integral copper coordination complex resembles a talon. The proposed model should facilitate the elucidation of these and other structural and functional relationships within the lysyl oxidase molecule.

4-Hydroxycoumarins↗
PubMed2004

Molecular and electronic structure of four- and five-coordinate cobalt complexes containing two o-phenylenediamine- or two o-aminophenol-type ligands at various oxidation levels: an experimental, density functional, and correlated ab initio study.

The bidentate ligands N-phenyl-o-phenylenediamine, H(2)((2)L(N)IP), or its analogue 2-(2-trifluoromethyl)anilino-4,6-di-tert-butylphenol, ((4)L(N)IP), react with [Co(II)(CH(3)CO(2))(2)]4H(2)O and triethylamine in acetonitrile in the presence of air yielding the square-planar, four-coordinate species [Co((2)L(N))(2)] (1) and [Co((4)L(O))(2)] (4) with an S=1/2 ground state. The corresponding nickel complexes [Ni((4)L(O))(2)] (8) and its cobaltocene reduced form [Co(III)(Cp)(2)][Ni((4)L(O))(2)] (9) have also been synthesized. The five-coordinate species [Co((2)L(N))(2)(tBu-py)] (2) (S=1/2) and its one-electron oxidized forms [Co((2)L(N))(2)(tBu-py)](O(2)CCH(3)) (2 a) or [Co((2)L(N))(2)I] (3) with diamagnetic ground states (S=0) have been prepared, as has the species [Co((4)L(O))(2)(CH(2)CN)] (7). The one-electron reduced form of 4, namely [Co(Cp)(2)][Co((4)L(O))(2)] (5) has been generated through the reduction of 4 with [Co(Cp)(2)]. Complexes 1, 2, 2 a, 3, 4, 5, 7, 8, and 9 have been characterized by X-ray crystallography (100 K). The ligands are non-innocent and may exist as catecholate-like dianions ((2)L(N)IP)(2-), ((4)L(N)IP)(2-) or pi-radical semiquinonate monoanions ((2)L(N)ISQ)(*) (-), ((4)L(N)ISQ)(*) (-) or as neutral benzoquinones ((2) L(N)IBQ)(0), ((4) L(N)IBQ)(0); the spectroscopic oxidation states of the central metal ions vary accordingly. Electronic absorption, magnetic circular dichroism, and EPR spectroscopy, as well as variable temperature magnetic susceptibility measurements have been used to experimentally determine the electronic structures of these complexes. Density functional theoretical (DFT) and correlated ab initio calculation have been performed on the neutral and monoanionic species [Co((1)L(N))(2)](0,-) in order to understand the structural and spectroscopic properties of complexes. It is shown that the corresponding nickel complexes 8 and 9 contain a low-spin nickel(II) ion regardless of the oxidation level of the ligand, whereas for the corresponding cobalt complexes the situation is more complicated. Spectroscopic oxidation states describing a d(6) (Co(III)) or d(7) (Co(II)) electron configuration cannot be unambiguously assigned.

Journal Article↗
PubMed1977

Noble metal complexes in cancer chemotherapy.

Platinum coordination complexes form a new class of active anticancer agents in animals and man. Cis-dichlorodiammineplatinum (II), the most widely investigated drug, is now in experimental clinical use against a wide variety of cancers in man. The dose-limiting toxicity in man is renal tubular damage. Hydration of the patient and the use of osmotic diuretics have minimized this effect and allowed higher doses with largely improved responses. Combination chemotherapy with the drug has also produced significant response rates in a variety of cancers. The mode of action of the drug is not yet clear, but most likely involves a primary lesion on nuclear DNA and the stimulation of a host reaction to the cancer. So far, only square planar and octahedral complexes of platinum, with a variety of inorganic and organic ligands, have shown marked activity in animal studies.

Alkylating Agents↗
PubMed1988

Rh(DIP)3(3+): a shape-selective metal complex which targets cruciforms.

The coordination complex tris(4,7-diphenylphenanthroline)rhodium(III), Rh(DIP)3(3+), binds to and, upon photoactivation, cleaves both DNA strands near the base of a DNA cruciform. Sites of photoinduced double-stranded DNA cleavage by the rhodium complex map to regions containing cruciforms on closed circular pBR322, pColE1 and phi X174 (replicative form) DNAs. Neither cleavage nor binding by the metal complex, assayed using S1 nuclease, is found on the linear plasmid which lacks the extruded cruciform. High resolution mapping experiments reveal that Rh(DIP)3(3+) cleaves at a specific AT-rich site neighboring the stem of the minor cruciform on pBR322. The primary site of cleavage is found at position 3238 on the 3'-strand and 3250 on the 5'-strand and is remarkably specific. The pattern of cleavage, to one side only of the cruciform stem, indicates an asymmetry in the cruciform structure recognized by the complex. These results suggest that Rh(DIP)3(3+) may provide a useful reagent to probe cruciform sites. In addition, the high degree of specificity found in targeting the cruciform structure with this simple metal complex underscores the utility of shape-selection for the recognition of specific sites on a DNA strand.

Base Sequence↗
PubMed1976

Rat liver pyruvate carboxylase. Inhibition by chromium nucleotide complexes.

The effect of inert coordination complexes of chromium (III) with various nucleotides on the catalytic activity of rat liver pyruvate carboxylase was determined. The chromium nucleotides are effective initial inhibitors of pyruvate carboxylase and the inhibition becomes more severe with time. The initial rate decreases for several minutes, reaching a new slower rate that is then maintained until considerable net reaction occurs. Incubation of the enzyme with chromium nucleotides in the presence of Mg2+ and HCO3- causes maximal inhibition of the reaction and linear initial rates are then observed. This effect is similar to that found with yeast hexokinase (Dannenberg, K.D., and Cleland, W.W. (1975) Biochemistry 14, 28-39). The specificity of the carboxylase toward the nucleotide complexes suggests that the alpha and beta nucleotide phosphates are as important as the gamma phosphate in binding to the enzyme. A stable pyruvate carboxylase chromium nucleotide complex was not observed. These results are quite different from those found with yeast hexokinase where a stable complex between CrATP, sugar, and enzyme is found and hexokinase appears to be specific toward the beta, gamma phosphates of its nucleotide substrates.

Adenosine Diphosphate↗
PubMed1998

19F NMR and Structural Evidence for Spin-State Modulation of Six-Coordinate Cobalt(II) in a Weak Field Porphyrin Ligand(1).

The syntheses and characterization of [2,3,7,8,12,13,17,18-octafluoro-5,10,15,20-tetraphenylporphinato]cobalt, Co(F(8)TPP), and [2,3,7,8,12,13,17,18-octafluoro-5,10,15,20-tetrakis(pentafluorophenyl)porphinato]cobalt, Co(F(28)TPP), are reported. Co(F(28)TPP).2tol (tol = toluene) crystallizes in the monoclinic space group C2/c-C(h)() (No. 15) with a = 22.1616(5) Å, b = 12.0274(3) Å, c = 19.9159(2) Å, beta = 110.645(1) degrees, V = 4967.6(2) Å(3), and Z = 4 {d(calcd) = 1.818 g/cm(3); &mgr;(a)(Mo Kalpha) = 0.50 mm(-)(1)}, and Co(F(28)TPP).2THF crystallizes in the triclinic space group P&onemacr; (No. 2) with a = 11.0691(1) Å, b = 12.0451(1) Å, c = 12.9558(2) Å, alpha = 62.531(1) degrees, beta = 69.544(1) degrees, gamma = 76.181(1) degrees, V = 1429.71(3) Å(3) and Z = 1 {d(calcd) = 1.700 g/cm(3); &mgr;(a)(Mo Kalpha) = 0.45 mm(-)(1)}. A comparison of the X-ray crystal structure data from Co(F(28)TPP).2tol and Co(F(28)TPP).2THF indicates that the porphyrin core expands dramatically (0.08 Å) in the six-coordinate complex. Optical and (19)F NMR spectroscopic studies of Co(F(28)TPP) in the presence of added ligand demonstrate that spin-state modulation of the six-coordinate Co(II) center is facile. Partial population of the (4)E(g) state is accessed upon coordination of the cobalt center with THF sigma-donor ligands, while six-coordinate complexes with 1-methylimidazole result in complete conversion to the high spin state, as evinced by 280 ppm downfield chemical shifts for the beta-fluorine resonances in the (19)F NMR spectrum. Co(F(28)TPP) is the first example of a porphyrin which supports a high-spin cobalt ion.

Journal Article↗
PubMed2003

Effect of the sixth axial ligand in CS-ligated iron(II)octaethylporphyrinates: structural and Mössbauer studies.

The effect of a sixth ligand in a series of low-spin thiocarbonyl-ligated iron(II)octaethylporphyrinates has been investigated. Six-coordinate complexes have been synthesized and characterized by Mössbauer and infrared spectroscopy and single-crystal X-ray structure determinations. The results are compared with the five-coordinate parent complex. The crystal structures of [Fe(OEP)(CS)(1-MeIm)] and [Fe(OEP)(CS)(Py)] are reported and discussed. The 1-methylimidazole and pyridine derivatives exhibit Fe-C(CS) bond distances of 1.703(4) and 1.706(2) A that are significantly longer than the 1.662(3) A reported for five-coordinate [Fe(OEP)(CS)] (Scheidt, W. R.; Geiger, D. K. Inorg. Chem. 1982, 21, 1208). The trans Fe-N(ligand) distances of 2.112(3) and 2.1550(15) A observed for the 1-methylimidazole and pyridine complex are approximately 0.13 A longer than those observed for analogous bis-ligated complexes and are consistent with a significant structural trans effect for the CS ligand. Mössbauer investigations carried out for five- and six-coordinate thiocarbonyl derivatives with several different sixth axial ligands reveal interesting features. All derivatives exhibit very small isomer shift values, consistent with a very strong interaction between iron and CS. The five-coordinate derivative has delta(Fe) = 0.08 mm/s, and the six-coordinate complexes exhibit delta(Fe) = 0.14 to 0.19 mm/s at 4.2 K. The five-coordinate complex shows a large quadrupole splitting (DeltaE(q) = 1.93 mm/s at 4.2 K) which is reduced on coordination of the sixth ligand (DeltaE(q) = 0.42-0.80 mm/s at 4.2 K). Addition of a sixth ligand also leads to a small decrease in the value of nu(CS). Correlations in structural, IR, and Mössbauer results suggest that the sixth ligand effect is primarily induced by changes in sigma-bonding. The structure of [Fe(OEP)(CS)(CH(3)OH)] is briefly reported. Crystal data: [Fe(OEP)(CS)(1-MeIm)] crystallizes in the monoclinic system, space group P2(1)/n, Z = 4, a = 9.5906(5) A, b = 16.704(4) A, c = 23.1417(6) A, beta = 100.453(7) degrees. [Fe(OEP)(CS)(Py)] crystallizes in the triclinic system, space group P1, Z = 5, a = 13.9073(6) A, b = 16.2624(7) A, c = 22.0709(9) A, alpha = 70.586(1) degrees, beta = 77.242(1) degrees, gamma = 77.959(1) degrees. [Fe(OEP)(CS)(CH(3)OH)] crystallizes in the triclinic system, space group P1, Z = 1, a = 9.0599(5) A, b = 9.4389(5) A, c = 11.0676(6) A, alpha = 90.261(1) degrees, beta = 100.362(1) degrees, gamma = 114.664(1) degrees.

Crystallography, X-Ray↗
PubMed2003

Structural analysis of nine-coordinate lanthanide complexes: steric control of the metal-water distance across the series.

The structures of 10 isomorphous lanthanide (Ln) complexes of a chiral DOTA tetra-amide ligand (L(1)), [LnL(1)(H(2)O)](CF(3)SO(3))(3).3H(2)O, crystallizing in space group P2(1), have been studied by single-crystal X-ray diffraction. The Ln coordination is a O(4)N(4) square antiprism, the O(4) base of which is capped by an aqua ligand. The sterically demanding position of the latter results in the lengthening of the Ln-OH(2) distance along the Pr to Lu series by 0.06 A (after allowing for the lanthanide contraction). In parallel, the distance between the bound water oxygen and the second-sphere water oxygen is reduced from 3.17 A (Pr) to 3.04 A (Lu), consistent with the enhanced hydrogen bond acceptor ability of the coordinated water oxygen across the series. A Cambridge Structural Database survey of [Ln(H(2)O)(9)](CF(3)SO(3))(3) salts (space group P6(3)/m) and of six reported isostructural complexes of DOTA [L(2)] revealed a similar trend. The implications of the resultant destabilization of the ground state structure for the water interchange process are discussed.

Journal Article↗
PubMed1981

Mutagenicity of a series of hexacoordinate rhodium(III) compounds.

19 rhodium(III) compounds have been tested for genetic damaging capabilities using an Escherichia coli differential repair assay and for mutagenicity in the strains of Salmonella typhimurium. 10 of these were active in both assays. Presence of the plasmid pKM101 was required for mutagenicity in Salmonella. Both the composition of the ligands and the free-dimensional structures of the coordination complexes profoundly affect genetic activity. In general, the structure--activity relationships appear to favor complexes with (1) a +1 charge, (2) 2-relatively labile leaving groups with 4 more strongly bonded amine ligands, and (3) a relatively slow rate of exchange of the ligands which is characteristic of substitutionally inert coordination complexes.

Escherichia coli↗
PubMed2006

Quantum chemical study on the coordination environment of the catalytic zinc ion in matrix metalloproteinases.

X-ray analyses of matrix metalloproteinases (MMPs) have shown that the catalytic zinc ion (Zn1) can bind to one to three water molecules in addition to three conserved histidine residues. To estimate the relative stability of the possible Zn1 coordination structures in the active site of the MMPs, we carry out computational analyses on the coordination environment of the Zn1 ion in the gelatinase A enzyme (or matrix metalloproteinase 2; MMP-2). Four-, five-, and six-coordinated complexes representative of the Zn1 site are fully characterized by means of quantum mechanical (QM) methodologies. On one hand, B3LYP/LACVP* minimizations of various cluster models of the MMP-2 active site show that the trigonal bipyramidal geometry is energetically favored in the gas phase and that continuum solvent effects stabilize preferentially the tetrahedral complexes. On the other hand, B3LYP/OPLS-AA hybrid QM/molecular mechanical calculations in the solvated catalytic domain of the MMP-2 enzyme complemented with electrostatic Poisson-Boltzmann calculations show that the mature enzyme presents most likely a Zn1 ion coordinated by three histidine residues and two water molecules, while the active site glutamic acid is negatively charged. In consonance with X-ray diffraction data, other possible Zn1 configurations, a six-coordinated structure with Zn1-water as well as four- and five-coordinated complexes with a Zn1-bound hydroxide, are predicted to be very close in energy.

Algorithms↗
PubMed2001

Strategies for the Construction of Supramolecular Compounds through Coordination Chemistry.

Synthetic organic chemists enjoy the luxury of having a large collection of reliable reactions at their disposal for preparing small molecules, mesoscopic structures, and polymers. Coordination chemists, on the other hand, are faced with the fact that transition metal chemistry, when normalized for the number of transition metals, has relatively few high-yielding reactions, when compared to the chemistry of carbon, for preparing even small molecule structures. This lack of control is manifested, in large part, in the weak metal-ligand interactions found in coordination complexes as compared with the strong covalent bonds in organic compounds. Weak bonding often translates into many reaction pathways that are not substantially different from an energetic point of view, and therefore, results in poor selectivity. As a result, many coordination chemists in recent years have come to the realization that it may be easier and more productive to develop straightforward and reliable routes to mesoscopic supramolecular structures by capitalizing on the modest collection of high-yielding reactions in coordination chemistry, the directional bonding afforded by metal centers, and strategies aimed at taking advantage of the weak metal bonds found in coordination complexes. Three emerging synthetic strategies, the symmetry-interaction, directional-bonding, and weak-link synthetic approaches, all use metal centers as structural building blocks to rationally assemble molecular components into supramolecular metallocyclophanes. These three approaches are discussed herein, and the fundamental principles underlying each as well as their capabilities are compared and contrasted.

Journal Article↗
PubMed2002

[(C5H5)Co(P(O)(OH)2)3H]: a novel organometallic tris-phosphonic acid that dissolves glass to form a six-coordinate silicon complex.

The sodium salt of the tripodal oxygen ligand Na[(C5H5)Co(P(O)(OMe)2)3] (1) reacts with gaseous hydrogen chloride in dichloromethane to give sodium chloride and [(C5H5)Co(P(O)(OMe)2)3H2]Cl (2). Addition of an equimolar amount of 1 leads to precipitation of sodium chloride again to yield the acid form of the ligand [(C5H5)Co(P(O)(OMe)2)3H] (3). Its solid-state structure contains a very short intramolecular OH.O hydrogen bond. The compound hydrolyses in boiling water to give methanol and the title complex [(C5H5)Co(P(O)(OH)2)3H] (4). This complex is a rather strong tris-phosphonic acid (pK(a1) 2.0, pK(a2) 4.0, pK(a3) 6.3, and pK(a4) 9.6). Attempts to grow single crystals of this highly water-soluble yellow crystalline compound lead to the silicon complex [((C5H5)Co[P(O)(OH)2]2[P(O)2(OH)])(2)Si].8 H2O (5). The crystal structure determination shows that it is a molecular complex of two tris-phosphonic acids that each act as a tris-chelating ligand. Additional water molecules form a complex net of hydrogen bonds between the complexes of 5. The SiO6 octahedron is only insignificantly distorted with Si-O bond lengths of 1.78 A. Complex 4 reacts with stoichiometric amounts of potassium carbonate to yield the potassium salt K[(C5H5)Co(P(O)(OH)2)3] (6). The crystal structure of 6 has also been determined. In the solid state it is a two-dimensional coordination polymer with each potassium ion being coordinated by twelve oxygen atoms of six tris-phosphonic acids.

Journal Article↗
PubMed2006

Silver(I) complexes in coordination supramolecular system with bulky acridine-based ligands: syntheses, crystal structures, and theoretical investigations on C-H...Ag close interaction.

In our efforts to investigate the coordination architectures of transition metals and organic ligands with tailored structures, we have prepared two structurally related rigid bulky acridine-based ligands, 9-[3-(2-pyridyl)pyrazol-1-yl]- acridine (L(1)) and 9-(1-imidazolyl)acridine (L2), and synthesized and characterized four of their Ag(I) complexes, {[AgL1](ClO4)}2 (1), {[AgL1](NO3)}2 (2), [AgL2(2)](ClO4) (3), and {[(Ag3L2(3))(NO3)](NO3)2(H2O)}(infinity) (4). The single-crystal X-ray diffraction analysis shows that the structures of 1 and 2 are similar to each other, with the two intramolecular Ag(I) centers of each complex being encircled by two L1 ligands; this forms a unique boxlike cyclic dimer, which is further linked to form one-dimensional (1D) chains of 1 and a two-dimensional (2D) network of 2 by intermolecular face-to-face pi...pi stacking and/or weak C-H...O hydrogen-bonding interactions, respectively. 3 has a mononuclear structure, which is further assembled into a 2D network via intermolecular Ag...O and pi...pi stacking weak interactions. 4 possesses two different 1D motifs that are further interlinked through interlayer face-to-face pi...pi stacking and Ag...O weak interactions, resulting in a 2D network. It is worth noting that one of the interesting structural features of 1, 2, and 4 is the presence of obvious C-H...M hydrogen-bonding interactions between the Ag centers and some acridine ring H atoms identified by X-ray diffraction on the basis of the van der Waals radii. Furthermore, as a representative example, full geometry optimization on the basis of the experimental structure, the natural bond orbital (NBO), and topological analysis of 1 were carried out by DFT and AIM (Atoms in Molecules) calculations. The total C-H...Ag interaction energy in 1 is estimated to be about 14 kJ/mol. Therefore, this work offers three new rare examples (1, 2, and 4) that exhibit C-H...Ag weak interactions, in which the N donors of the acridine rings coordinate to Ag(I) ions. Also, these results strongly support the existence of C-H...Ag close interactions and allow us to have a better understanding of the nature of such interactions in the coordination supramolecular systems.

Journal Article↗
PubMed2005

Catalytic alcohol oxidation by an unsymmetrical 5-coordinate copper complex: electronic structure and mechanism.

Density functional theory reveals the detailed mechanism of alcohol oxidation by a model copper complex, Cu(II)L, L = cis-1-(3',5'-dimethoxy-benzylideneamino)-3,5-[2-hydroxy-(3',5'-di-tert-butyl)benzylideneimino]cyclohexane. Despite the obvious structural and functional parallels between the title compound and the enzyme galactose oxidase, the details of the catalytic pathway are fundamentally different. In the enzyme, coordination of the substrate produces an active form containing a Cu(II) centre and a tyrosyl radical, the latter being responsible for the abstraction of hydrogen from the substrate. In the model system, in marked contrast, the active form contains a Cu(II) centre, but the ligand radical character is localised on the substrate (alcoholate) oxygen, rather than the phenolate ligand. The result is a significantly higher barrier to hydrogen-atom abstraction compared to the enzyme itself. The origin of these significant differences is traced to the rigid nature of the pentadentate ligand, which resists changes in coordination number during the catalytic cycle.

Journal Article↗
PubMed2002

Synthesis, crystal structures, and redox potentials of 2,3,12,13-tetrasubstituted 5,10,15,20-tetraphenylporphyrin zinc(II) complexes.

Zinc(II) complexes of antipodal beta-tetrasubstituted meso-tetraphenylporphyrin with trifluoromethyl (Zn(TPP(CF(3))(4)) (1a)), bromine (Zn(TPPBr(4)) (2a)), and methyl groups (Zn(TPP(CH(3))(4)) (3a)) were synthesized in order to examine the steric and the electronic effects of trifluoromethyl groups on the macrocycle. The analysis of X-ray crystal structures of the five-coordinate complexes Zn(TPP(CF(3))(4))(EtOH)(3) (1b), Zn(TPPBr(4))(MeOH)(DMF) (2b), and Zn(TPP(CH(3))(4))(THF)(1.6)(CHCl(3))(0.4) (3b) revealed distorted macrocyclic cores where significant differences in the Zn-N distance between the beta-substituted and the non-beta-substituted side were observed. The difference was significant in 1b due to the strong steric interactions among the peripheral substituents and the electronic effects of trifluoromethyl groups. The macrocycles of 1b-3b are saddle-distorted and slightly ruffled due to the five-coordination of zinc(II) and the peripheral substitution. Distortion of the macrocycles of 2b and 3b were modest. On the other hand, distortion in 1b was severe due to the peripheral strain. Cyclic voltammetric measurements of the four-coordinate complexes Zn(TPP) and 1a-3a were performed and their redox potentials were analyzed together with previously reported potentials of Zn(TPP(CN)(4)). The oxidation potential of 1a did not gain as much as expected from the electron-withdrawing effect of the four trifluoromethyl groups. The HOMO-LUMO gap of 1a was very small (1.5 V) and cannot just be explained by macrocyclic distortion. The magnitude of this gap is very similar to that of Zn(TPP(CN)(4)). Compound 2a also exhibited a modest gap contraction. Compound 3a was easier to oxidize and harder to reduce than Zn(TPP), even though the HOMO-LUMO gap of 3a was similar to that of Zn(TPP).

Journal Article↗
PubMed2003

The DNA and RNA specificity of eilatin Ru(II) complexes as compared to eilatin and ethidium bromide.

Eilatin-containing ruthenium complexes bind to a broad range of different nucleic acids including: calf thymus (CT) DNA, tRNA(Phe), polymeric RNAs and DNAs, and viral RNAs including the HIV-1 RRE and TAR. The nucleic acid specificity of Lambda- and Delta-[Ru(bpy)2eilatin]2+ have been compared to that of the 'free' eilatin ligand, and to the classic intercalating agent ethidium bromide. Interestingly, all four compounds appear to bind to nucleic acids by intercalation, but the trends in nucleic acid binding specificity are highly diverse. Unlike ethidium bromide, both eilatin and the eilatin-containing coordination complexes bind to certain single-stranded RNAs with high affinity (K(d) < or = 1 microM). Eilatin itself is selective for electron-poor polymeric purines, while the eilatin-coordination complexes exhibit preference for the polypyrimidine r(U). These results show how the binding specificity of an intercalating ligand can change upon its incorporation into an octahedral metal complex.

Base Sequence↗