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PubMed2001

Methanol addition to dihapto-coordinated rhenium complexes of furan.

The complexes [TpRe(CO)(L)(4,5-eta(2)-furan)], present as diastereomeric mixtures (L = (t)BuNC (1A, 1B), PMe(3) (2A, 2B), pyridine (3A, 3B), or 1-methylimidazole (4A, 4B)), undergo acid-catalyzed methanol addition in CH(2)Cl(2) at -40 degrees C, resulting in the syntheses of dihapto-coordinated 2-methoxy-2,3-dihydrofuran complexes. In all cases, two diastereomers resulted, one in which the oxygen of the dihydrofuran is oriented toward the L ligand (5A, 6A, 7A, and 8A), and one in which the oxygen is oriented away from the L ligand (5B, 6B, 7B, and 8B). In all cases, the methoxy group adds stereoselectively, anti to the metal fragment. In addition, the (t)BuNC complex 1 yields a dihapto-coordinated vinyl ether (5C) that results from ring opening of the protonated furan ligand. In no case does the diastereomeric ratio of products correlate with that of the starting material.

Furans↗
PubMed2006

Solution 1H NMR characterization of the axial bonding of the two His in oxidized human cytoglobin.

Solution 1H NMR spectroscopy has been used to determine the relative strengths (covalency) of the two axial His-Fe bonds in paramagnetic, S = 1/2, human met-cytoglobin. The sequence specific assignments of crucial portions of the proximal and distal helices, together with the magnitude of hyperfine shifts and paramagnetic relaxation, establish that His81 and His113, at the canonical positions E7 and F8 in the myoglobin fold, respectively, are ligated to the iron. The characterized complex (approximately 90%) in solution has protohemin oriented as in crystals, with the remaining approximately 10% exhibiting the hemin orientation rotated 180 degrees about the alpha-, gamma-meso axis. No evidence could be obtained for any five-coordinate complex (<1%) in equilibrium with the six-coordinate complexes. Extensive sequence-specific assignments on other dipolar shifted helical fragments and loops, together with available alternate crystal coordinates for the complex, allowed the robust determination of the orientation and anisotropies of the paramagnetic susceptibility tensor. The tilt of the major axis is controlled by the His-Fe-His vector, and the rhombic axes are controlled by the mean of the imidazole orientations for the two His. The anisotropy of the paramagnetic susceptibility tensor allowed the quantitative factoring of the hyperfine shifts for the two axial His to reveal an indistinguishable pattern and magnitudes of the contact shifts or pi spin densities, and hence, indistinguishable Fe-imidazole covalency for both Fe-His bonds.

Anisotropy↗
PubMed1996

113Cd Shielding Tensors of Monomeric Cadmium Compounds Containing Nitrogen Donor Atoms. 3. CP/MAS Studies on Five-Coordinate Cadmium Complexes Having N(3)X(2) (X = H, N, O, and S) Donor Atoms.

The principal elements of the (113)Cd shielding tensor for a set of five- coordinate compounds having mixed donor atoms coordinating to the cadmium were determined via CP/MAS NMR experiments. The first complex, [HB(3,5-Me(2)pz)(3)]CdBH(4) (where pz = pyrazolyl), has a CdN(3)H(2) inner coordination sphere. The isotropic chemical shift in the solid state is 355.1 ppm, and its chemical shift anisotropy (CSA, Deltasigma) is -596 ppm with an asymmetry parameter (eta) of 0.64. The second complex, [HB(3,5-Me(2)pz)(3)]Cd[H(2)B(pz)(2)], has five nitrogen donor atoms bonded to the cadmium. This N(5) or N(3)N(2) compound was the only material of this study to manifest dipolar splitting of the cadmium resonance from the quadrupolar (14)N. The isotropic chemical shift, CSA, and the value of eta for this material were therefore determined at higher field where the dipolar splitting was less than the linewidth, yielding values of 226.6 ppm, -247 ppm, and 0.32, respectively. A second N(5) material, [HB(3-Phpz)(3)]Cd[H(2)B(3,5-Me(2)pz)(2)], was also investigated and has an isotropic shift of 190.2 ppm, a CSA of 254 ppm, and an eta of 0.86. Also studied was [HB(3-Phpz)(3)]Cd[(Bu(t)CO)(2)CH], which has an CdN(3)O(2) inner core. The isotropic chemical shift of this complex is 173.6 ppm, and the values of Deltasigma and eta were determined to be -258 ppm and 0.38, respectively. The final compound, [HB(3,5-Me(2)pz)(3)]Cd[S(2)CNEt(2)], with N(3)S(2) donor atoms, has an isotropic shift of 275.8 ppm, an eta of 0.51, and a CSA of +375 ppm. Utilizing previous assignments, the most shielded tensor element was determined to be oriented normal to the plane of the tridentate ligand. The shielding tensor information is used to speculate on the coordination geometry of the CdN(3)O(2) inner core complex.

Journal Article↗
PubMed1996

Synthesis, X-ray Crystal Structure Determination, and NMR Spectroscopic Investigation of Two Homoleptic Four-Coordinate Lanthanide Complexes: Trivalent ((t)Bu(2)P)(2)La[(&mgr;-P(t)Bu(2))(2)Li(thf)] and Divalent Yb[(&mgr;-P(t)Bu(2))(2)Li(thf)](2)(,)(1).

La(OSO(2)CF(3))(3) reacts with 4 equiv of LiP(t)Bu(2) in tetrahydrofuran to give dark red ((t)Bu(2)P)(2)La[(&mgr;-P(t)Bu(2))(2)Li(thf)] (1). Yb(OSO(2)CF(3))(3) reacts with LiP(t)Bu(2) in tetrahydrofuran in a 1:5 ratio to produce Yb[(&mgr;-P(t)Bu(2))(2)Li(thf)](2) (2) and 1/2 an equiv of (t)Bu(2)P-P(t)Bu(2). Both 1 and 2 crystallize in the monoclinic space group P2(1)/c. Crystal data for 1 at 214 K: a = 11.562 (1) Å, b = 15.914 (1) Å, c = 25.373 (3) Å, beta = 92.40 (1) degrees; V = 4664.5 Å(3); Z = 4; D(calcd) = 1.137 g cm(-)(3); R(F)() = 2.61%. Crystal data for 2 at 217 K: a = 21.641 (2) Å, b = 12.189 (1) Å, c = 20.485 (2) Å, beta = 109.01 (1) degrees; V = 5108.9 Å(3); Z = 4; D(calcd) = 1.185 g cm(-)(3); R(F)() = 2.80%. The molecular structures of 1 and 2 show the four-coordinate lanthanide atoms in distorted tetrahedral environments. These complexes are the first representatives of the lanthanide elements surrounded by four only-phosphorus-containing substituents. The main features of the crystal structure of 1 are the shortest La-P distances (2.857(1) and 2.861(1) Å) reported so far and a three-coordinate lithium cation. The molecular structure of 2 represents a divalent bis "ate" complex with two three-coordinate lithium cations. Complex 2 shows photoluminescent properties. VT NMR spectra ((7)Li and (31)P) are reported for 1and 2.

Journal Article↗
PubMed2002

A spectrochemical walk: single-site perturbation within a series of six-coordinate ferrous complexes.

A series of ferrous complexes with the pentadentate ligand 2,6-(bis-(bis-2-pyridyl)methoxymethane)pyridine (PY5) was prepared and examined. PY5 binds ferrous iron in a square-pyramidal geometry, leaving a single coordination site accessible for complexation of a wide range of monodentate exogenous ligands: [Fe(II)(PY5)(X)](n+), X = MeOH, H(2)O, MeCN, pyridine, Cl-, OBz-, N(3)-, MeO-, PhO-, and CN-. The spin-states of these ferrous complexes are extremely sensitive to the nature of the single exogenous ligand; the spectroscopic and structural properties correlate with their high-spin (hs) or low-spin (ls) electronic ground state. Systematic metrical trends within six crystallographic structures clearly indicate a preferred conformational binding mode of the PY5 ligand. The relative binding affinities of the exogenous ligands in MeOH indicate that exogenous ligand charge is the primary determinant of the binding affinity; the [Fe(II)(PY5)](2+) unit preferentially binds anionic ligands over neutral ligands. At parity of charge, strong-field ligands are preferentially bound over weak-field ligands. In MeOH, the pK(a) of the exogenously ligated MeOH in [Fe(PY5)(MeOH)](2+) (9.1) limits the scope of exogenous ligands, as strongly basic ligands preferentially deprotonate [Fe(PY5)(MeOH)](2+) to yield [Fe(PY5)(OMe)](1+) rather than ligate to the ferrous center. Exogenous ligation by a strongly basic ligand, however, can be achieved in polar aprotic solvents.

Chemistry, Physical↗
PubMed2003

N=N bond cleavage by a low-coordinate ironII hydride complex.

Reaction of the three-coordinate complex LFeCl (L = bulky beta-diketiminate) with KBEt3H gives a dark red iron(II) hydride complex. The complex is a dimer in the solid state, but spectroscopy and kinetics suggest that an orange three-coordinate monomer is in equilibrium with the dimer in solution. The double bond of azobenzene is completely cleaved by heating with the hydride complex, and a hydrazido intermediate can be isolated.

Journal Article↗
PubMed2004

Octaethylporphyrin and expanded porphyrin complexes containing coordinated BF2 groups.

In contrast to octaethylporphyrin, which forms a very labile bis-BF(2) complex, treatment of the hexa- and octapyrrolic expanded porphyrins amethyrin and [32]octaphyrin with BF(3).Et(2) under standard reaction and work-up conditions gives rise to stable, non-labile mono- and bis-BF(2) complexes; these were readily characterised by, inter alia, X-ray diffraction analyses.

Boron Compounds↗
PubMed2004

Preparation and reactivity studies of synthetic microperoxidases containing b-type heme.

In order to create a heme environment that permits biomimicry of heme-containing peroxidases, a number of new hemin-peptide complexes--hemin-2(18)-glycyl-L-histidine methyl ester (HGH), hemin-2(18)-glycyl-glycyl-L-histidine methyl ester (HGGH), and hemin-2,18-bis(glycyl-glycyl-L-histidine methyl ester) (H2GGH)--have been prepared by condensation of glycyl-L-histidine methyl ester or glycyl-glycyl-L-histidine methyl ester with the propionic side chains of hemin. Characterization by means of UV/vis- and 1H NMR spectroscopy as well as cyclic- and differential pulse voltammetry indicates the formation of five-coordinate complexes in the case of HGH and HGGH, with histidine as an axial ligand. In the case of H2GGH, a six-coordinate complex with both imidazoles coordinated to the iron center appears to be formed. However, 1H NMR of H2GGH reveals the existence of an equilibrium between low-spin six-coordinate and high-spin five-coordinate species in solution. The catalytic activity of the hemin-peptide complexes towards several organic substrates, such as p-cresol, L-tyrosine methyl ester, and ABTS, has been investigated. It was found that not only the five-coordinate HGH and HGGH complexes, but also the six-coordinate H2GGH, catalyze the oxidation of substrates by H2O2. The longer and less strained peptide arm provides the HGGH complex with a slightly higher catalytic efficiency, as compared with HGH, due to formation of more stable intermediate complexes.

Catalysis↗
PubMed2003

Three- and four-coordinate gold(I) complexes of 3,6-bis(diphenylphosphino)pyridazine: monomers, polymers, and a metallocryptand cage.

The slightly yellow polymeric complexes [Au(2)Cl(2)(P(2)pz)(3)](n), 1 x 6CHCl(3), (P(2)pz is 3,6-bis(diphenylphosphino)pyridazine) and [[Au(2)(P(2)pz)(3)](PF(6))(2)](n), 2, are prepared by the stoichiometric reaction of AuCl(tht) (tht is tetrahydrothiophene) and P(2)pz in either dichloromethane or dichloromethane/methanol, respectively. Addition of 2 equiv of AuCl(tht) to a dichloromethane solution of 1 equiv of P(2)pz generates the simple (AuCl)(2)(P(2)pz) compound, 3. Compound 3 contains nearly linear P-Au-Cl units with intermolecular Au.Au separations of 3.570 A. Au(2)I(2)(P(2)pz)(3), 4, is prepared by reacting excess NaI with 2 in a dichloromethane/methanol mixture. Characterization of 1, 2, and 4 by X-ray crystallography confirms the 2:3 gold/ligand ratio of all three complexes. The coordination polymer 1 maintains a high degree of solvation in the solid-state with three chloroform adducts hydrogen-bonded to the chloride ligand on each gold atom. These chloroform molecules are sandwiched between the two-dimensional polymeric sheets of 1. The crystal structure of 4 reveals an empty, iodide-capped metallocryptand cage with the tetrahedrally distorted gold atoms and the nitrogen atoms on the pyridazine rings directed away from the center of the cavity. No metal ion encapsulation was observed for complex 4. Complex 2 forms one-dimensional arrays of [Au(2)(P(2)pz)(2)](2+) metallomacrocycles connected to each other by a third P(2)pz ligand. The electronic absorption spectra (CH(2)Cl(2)) of 1-4 show broad, nearly featureless absorption bands that tail into the visible with pi-pi bands at 296 nm and discernible shoulders at 314 nm for 2 and 334 nm for 3. Excitation into the low energy band of 2 produces only a modest emission in solution at 540 nm (lambda(ex) 468 nm) and 493 nm (lambda(ex) 403 nm). Under identical conditions, the P(2)pz ligand also emits at 540 and 493 nm.

Journal Article↗
PubMed2002

Control of manipulative forces during unimanual and bimanual tasks in patients with Huntington's disease.

The aim of the study was to investigate grip-load force regulation in Huntington's disease (HD) patients as compared to control subjects during the performance of a manipulative task that required rhythmical unimanual or bimanual isodirectional/non-isodirectional actions in the sagittal plane. Results showed that the profile of grip-load ratio force was characterized by maxima and minima that were attained at upward and downward hand positions, respectively. Minimum force ratio was higher in patients than in controls, which points to an elevated baseline that may be related to the inherent bradykinesia observed in HD. Maximum force ratio was also increased in patients, but this effect depended on the performance condition, with largest amplifications occurring during non-isodirectional movements. The latter rescaling may be associated with the complexity of the coordination mode and its asymmetrical load characteristics. In addition, the temporal delay between the grip and load force peaks was augmented in patients versus controls, indicating a disturbed coupled activation of both forces. Furthermore, the interval was largest during non-isodirectional movements followed by isodirectional and unimanual movements, which denotes that the grip-load force coupling deteriorated as a function of coordinative complexity. Together, these data indicate a deficit in the grip-load force constraint due to HD and illustrate the degrading effect of striatal dysfunction on (bi)manual manipulative function.

Adult↗
PubMed1983

Generation of hydroxyl radicals during the enzymatic reductions of the Fe3+-ADP-phosphate-adriamycin and Fe3+-ADP-EDTA systems. Less involvement of hydroxyl radical and a great importance of proposed perferryl ion complexes in lipid peroxidation.

A system which contains NADPH, purified cytochrome P-450 reductase (enzyme) and Fe3+-ADP-adriamycin complex in Tris-HCl buffer does not produce hydroxyl radical, but possesses a strong lipid peroxidation activity on exogenously added phospholipid micelles. Fe3+-ADP-adriamycin complex, a tightly coordinated complex in Tris-HCl buffer, could be dissociated to Fe3+-ADP-phosphate complex and adriamycin in phosphate buffer. Hydroxyl radical, which can be detected by a spin trapping method using N-tert-butyl-alpha-phenylnitrone, is produced during the enzymatic reduction of a mixture of Fe3+-ADP-phosphate complex and adriamycin or of Fe3+-ADP-EDTA complex while it is not involved in phospholipid peroxidation under the conditions used. With hydroxyl radical-generating systems, little or no quenching of hydroxyl radical in Tris-HCl buffer could be demonstrated. The oxidative cleavage of phospholipid is initiated by the proposed perferryl ion complex, which may be generated by the interaction of Fe2+-ADP-adriamycin complex with O2. A similar perferryl ion complex is also produced during the enzymatic reduction of Fe3+-ADP-EDTA complex with a molar ratio of 2 for [Fe3+]/[EDTA] in the presence of air. This is also able to catalyze lipid peroxidation.

Adenosine Diphosphate↗
PubMed2001

trans-bis(benzoato-O)tetrakis(methanol-O)iron(II): ligand bulk is not structure-determining.

The title compound, [Fe(C7H5O2)2(CH4O)4], is a centrosymmetric six-coordinate Fe(II) complex coordinated by two axial monodentate benzoate ligands and four methanol ligands in the equatorial plane [Fe-O(benzoate) 2.0935 (7) A, and Fe-O(methanol) 2.1310 (7) and 2.1290 (7) A]. The benzoate ligands adopt monodentate ligation, rather than a bridged polymeric structure, because of strong intra- and intermolecular hydrogen bonds to the methanol ligands. This structure is nearly identical to that obtained with a much bulkier carboxylate ligand [Chavez, Que & Tolman (2001). Chem. Commun. pp. 111-112].

Journal Article↗
PubMed1989

Psychomotor screening for USAF pilot candidates: selecting a valid criterion.

Subjects for this research were 153 prospective pilots who were tested on computerized versions of the Two Hand Coordination (2HC) and Complex Coordination (CC) psychomotor tests. Independent variables included five basic error scores associated with the two psychomotor tests. The criterion for pilot performance was conceptualized as a function of the number of flying hours required to graduate from Undergraduate Pilot Training (UPTFLY). Results of MANOVA and multiple regression analyses revealed that performance on the two psychomotor tests was significantly related to the criterion for pilot performance (UPTFLY). The multiple regression analysis resulted in 27.1% of the variability of UPTFLY being accounted for by psychomotor performance. When the data were reanalyzed using a pass/fail UPT criterion the variability accounted for remained high, suggesting an anomaly associated with sample selection. Undergraduate pilot training outcome (pass/fail) remains the most valid criterion for Undergraduate Pilot Training success.

Adult↗
PubMed1988

Utilization of psychomotor screening for USAF pilot candidates: enhancing predictive validity.

Subjects for this research were 320 prospective pilots who were tested on computerized versions of the Two Hand Coordination (2HC) and Complex Coordination (CC) psychomotor tests. Independent variables included five basic error measures associated with the two tests, as well as seven new variables that had not previously been utilized. Results of MANOVA and multiple regression analyses revealed that performance on the two psychomotor tests were significantly related to Undergraduate Pilot Training (UPT) outcome. A trend was observed for a prediction model based on early and total trial data to yield higher simple and multiple correlations than a model based on late trials. Regressing the basic five independent variables on UPT outcome yielded R values of 0.334, 0.271, and 0.310 for early, late, and total trial data, respectively. The predictive validity of the basic five error scores was not incrementally increased by stepping in independent variables associated with the hypotenuse of horizontal and vertical error or stick movement. A stepwise multiple regression analysis revealed that the best two-variable prediction equation included the hypotenuse of horizontal and vertical error for both psychomotor tests (R = 0.329).

Aerospace Medicine↗
PubMed2004

Production and collision-induced dissociation of gas-phase, water- and alcohol-coordinated uranyl complexes containing halide or perchlorate anions.

Electrospray ionization was used to generate mono-positive gas-phase complexes of the general formula [UO2A(S)n]+ where A = OH, Cl, Br, I or ClO4, S = H2O, CH3OH or CH3CH2OH, and n = 1-3. The multiple-stage dissociation pathways of the complexes were then studied using ion-trap mass spectrometry. For H2O-coordinated cations, the dissociation reactions observed included the elimination of H2O ligands and the loss of HA (where A = Cl, Br or I). Only for the Br and ClO4 versions did collision-induced dissociation (CID) of the hydrated species generate the bare, uranyl-anion complexes. CID of the chloride and iodide versions led instead to the production of uranyl hydroxide and hydrated UO2+. Replacement of H2O ligands by alcohol increased the tendency to eliminate HA, consistent with the higher intrinsic acidity of the alcohols compared to water and potentially stronger UO2-O interactions within the alkoxide complexes compared to the hydroxide version.

Journal Article↗
PubMed1998

Clinical development of platinum complexes in cancer therapy: an historical perspective and an update.

The vast amount of basic research on platinum coordination complexes has produced, over the past 25 years, several thousand new molecules for preclinical screening and 28 compounds which have entered clinical development. The goals of these research activities have been to identify compounds with superior efficacy, reduced toxicity, lack of cross-resistance or improved pharmacological characteristics as compared with the parent compound, cisplatin. After the remarkable therapeutic effects of cisplatin had been established, only a few other platinum compounds succeeded in reaching general availability. Whereas carboplatin is an analogue with an improved therapeutic index (mostly driven by reduced organ toxicity) over that of cisplatin, new compounds clearly more active than or non-cross-resistant with cisplatin have not yet been identified. The platinum analogues that remain under investigation are focusing on expanding the utilisation of platinum therapy to tumour types not usually treated with, or responsive to, cisplatin or carboplatin. In addition, novel routes of administration constitute another avenue of research. The clinical development of platinum coordination complexes, with emphasis on those compounds still under active development, is reviewed.

Antineoplastic Agents↗
PubMed2003

Synthesis, characterization, and dioxygen reactivity of tetracarboxylate-bridged Diiron(II) complexes with coordinated substrates.

The synthesis and characterization of [Fe(2)(micro-O(2)CAr(Tol))(4)L(2)] complexes, where L is benzylamine or 4-methoxybenzylamine (BA(p)()(-)(OMe)), are described. The reaction of the latter diiron(II) complex with dioxygen at -78 degrees C affords a metastable mixed-valent Fe(II)Fe(III) green intermediate. When O(2) is introduced at ambient temperature, N-dealkyation occurs to yield anisaldehyde, eliminating N-oxidation as a viable pathway for the reaction. Use of [Fe(2)(micro-O(2)CAr(T)(omicron)(l))(4)(alpha-d(1)-BA(p)()(-)(OMe))(2)] allowed a deuterium kinetic isotope of approximately 3 to be determined.

Benzylamines↗
PubMed2004

Novel supramolecular isomerism in coordination polymer synthesis from unsymmetrical bridging ligands: solvent influence on the ligand placement orientation and final network structure.

The assembly of Co(NCS)(2) with 1-methyl-1'-(3-pyridyl)-2-(4-pyridyl)ethene (L(1)) exhibits a novel supramolecular isomerism of [Co(L(1))(2)(NCS)(2)](infinity) caused by different placement orientation of L(1) around metal centers. The reaction in MeOH/H(2)O and EtOH/H(2)O resulted in a double chain structure of 1, and that in EtOH/CH(3)NO(2) led to an open framework structure of 2. The reaction in MeOH/CH(3)NO(2) solvent system concomitantly afforded 1 and 2. The assemblies of 1-(3-pyridyl)-2-(4-pyrimidyl)ethene (L(2)) with Co(NCS)(2) created the water-coordinated complexes of Co(L(2))(2)(H(2)O)(2)(NCS)(2) (3 and 4), an MeOH coordinated complex of Co(L(2))(2)(H(2)O)(2)(NCS)(2) (5), and an open framework coordination polymer of [Co(L(1))(2)(NCS)(2)](infinity) (6) depending on the reaction solvent system. From these observations, it is suggested that in the formation of 1, the solvent-coordinated intermediate species would be generated first and its trans coordination configuration should define the placement orientation of L(1) in the resulting polymer of 1. On the other hand, it is presumed that the solvent-coordinated intermediate would not be produced during the formation of 2 due to the weaker coordination ability of EtOH and CH(3)NO(2) molecules. The open framework coordination polymers of 2 and 6 are converted in the solid state into the isomeric coordination polymer of 1 and hydrogen bonded network structure of 3, respectively.

Journal Article↗