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PubMed2001

Characterization of inorganic coordination complexes by matrix-assisted laser desorption/ionization mass spectrometry.

We report the direct laser desorption/ionization (LDI) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometric (MALDI-TOFMS) analysis of four inorganic coordination complexes: monometallic [Ir(dpp)(2)Cl(2)](PF(6)), homonuclear trimetallic ([(bpy)(2)Ru(dpp)](2)RuCl(2))- (PF(6))(4), and heteronuclear [(tpy)Ru(tpp)Ru(tpp)RhCl(3)](PF(6))(4) and ([(bpy)(2)Ru(dpp)](2)IrCl(2))(PF(6))(5) (dpp = 2,3-bis-(2'-pyridyl)pyrazine, bpy = 2,2'-bipyridine, tpy = 2,2',6',2"-terpyradine, tpp = 2,3,5,6,-tetrakis-(2'-pyridyl)pyrazine). Spectral intensities and fragmentation patterns are compared and evaluated for instrument parameters, matrix selection, and matrix-to-analyte ratio. Direct LDI and MALDI mass spectra of the monometallic complex showed the same ion peaks and differed only in the relative peak intensities. Direct LDI of the trimetallic complexes produced only low-mass fragments containing one metal at most. MALDI spectra of the trimetallic complexes exhibited little fragmentation in the high-mass region (>1500 Da) and less fragmentation in the low-mass region compared to direct LDI. Significant fragments of the molecules were detected and identified, including ligand fragments, intermediate-mass fragments such as [Ru(tpy)](+), and molecular ions with varying degrees of PF(6)(-) loss ([M - n(PF(6))](+), where n = 1-3). A correlation exists between the solution-phase electrochemistry and the observed [M - n(PF(6))](+) series of peaks for the trimetallic complexes. Proper matrix selection for MALDI analysis was vital, as was an appropriate matrix-to-analyte ratio. The results demonstrate the applicability of MALDI-TOFMS for the structural characterization of labile inorganic coordination complexes.

Journal Article↗
PubMed2004

The electronic structure of Mn in oxides, coordination complexes, and the oxygen-evolving complex of photosystem II studied by resonant inelastic X-ray scattering.

Resonant inelastic X-ray scattering (RIXS) was used to collect Mn K pre-edge spectra and to study the electronic structure in oxides, molecular coordination complexes, as well as the S1 and S2 states of the oxygen-evolving complex (OEC) of photosystem II (PS II). The RIXS data yield two-dimensional plots that can be interpreted along the incident (absorption) energy or the energy transfer axis. The second energy dimension separates the pre-edge (predominantly 1s to 3d transitions) from the main K-edge, and a detailed analysis is thus possible. The 1s2p RIXS final-state electron configuration along the energy transfer axis is identical to conventional L-edge absorption spectroscopy, and the RIXS spectra are therefore sensitive to the Mn spin state. This new technique thus yields information on the electronic structure that is not accessible in conventional K-edge absorption spectroscopy. The line splittings can be understood within a ligand field multiplet model, i.e., (3d,3d) and (2p,3d) two-electron interactions are crucial to describe the spectral shapes in all systems. We propose to explain the shift of the K pre-edge absorption energy upon Mn oxidation in terms of the effective number of 3d electrons (fractional 3d orbital population). The spectral changes in the Mn 1s2p(3/2) RIXS spectra between the PS II S1 and S2 states are small compared to that of the oxides and two of the coordination complexes (Mn(III)(acac)3 and Mn(IV)(sal)2(bipy)). We conclude that the electron in the step from S1 to S2 is transferred from a strongly delocalized orbital.

Electrons↗
PubMed2001

Effect of platinum coordination complex (PtCx) on citrate uptake by rat renal brush border membrane vesicles (BBMV): cisplatin-intoxicated rats.

Platinosis with severe dermatitis and/or asthma is broadly defined as the effects of soluble platinum salts on people exposed to them occupationally. Platinum coordination complexes are widely used in the treatment of a variety of solid tumors. However, the clinical use of cisplatin, the most useful agent, is limited by the development of nephrotoxicity. Thus, an accidental exposure to soluble platinum at a high dose in platinum refineries and pharmaceutical factories could induce occupational nephrotoxicity. Urinary citrate is freely filtered at the glomerulus, and its reabsorption in the proximal tubule is the major determinant of the rate of renal excretion. In our previous studies, we found that the preincubation of rat renal brush border membrane vesicles (BBMV) with cisplatin and carboplatin, a second-generation platinum coordination complex, significantly inhibited the citrate uptake compared with that of the control BBMV. In this study, we performed in vivo experiments in cisplatin-intoxicated rats to elucidate the toxic mechanism of cisplatin. And our results showed that the citrate uptake was significantly inhibited in cisplatin-intoxicated rats at 1 min compared with that of control rats.

Animals↗
PubMed2006

Small molecule activation at uranium coordination complexes: control of reactivity via molecular architecture.

Electron-rich uranium coordination complexes display a pronounced reactivity toward small molecules. In this Feature article, the exciting chemistry of trivalent uranium ions coordinated to classic Werner-type ligand environments is reviewed. Three fundamentally important reactions of the [(((R)ArO)3tacn)U]-system are presented that result in alkane coordination, CO/CO2 activation, and nitrogen atom-transfer chemistry.

Alkanes↗
PubMed2002

Redox energetics and kinetics of uranyl coordination complexes in aqueous solution.

Detailed voltammetric results for five uranyl coordination complexes are presented and analyzed using digital simulations of the voltammetric data to extract thermodynamic (E(1/2)) and heterogeneous electron-transfer kinetic (k(0) and alpha) parameters for the one-electron reduction of UO(2)(2+) to UO(2)(+). The complexes and their corresponding electrochemical parameters are the following: [UO(2)(OH(2))(5)](2+) (E(1/2) = -0.169 V vs Ag/AgCl, k(0) = 9.0 x 10(-3) cm/s, and alpha = 0.50); [UO(2)(OH)(5)](3-) (-0.927 V, 2.8 x 10(-3) cm/s, 0.46); [UO(2)(C(2)H(3)O(2))(3)](-) (-0.396 V, approximately 0.1 cm/s, approximately 0.5); [UO(2)(CO(3))(3)](4-) (-0.820 V, 2.6 x 10(-5) cm/s, 0.41); [UO(2)Cl(4)](2-) (-0.065 V, 9.2 x 10(-3) cm/s, 0.30). Differences in the E(1/2) values are attributable principally to differences in the basicity of the equatorial ligands. Differences in rate constants are considered within the context of Marcus theory of electron transfer, but no specific structural change(s) in the complexes between the two oxidation states can be uniquely identified with the underlying variability in the heterogeneous rate constants and electron-transfer coefficients.

Journal Article↗
PubMed2005

Synthesis and structural characterization of a new heterobimetallic coordination complex of barium and cobalt for use as a precursor for chemical vapor deposition.

Ba(dmae)2 (dmaeH=N,N-dimethylaminoethanol, C4H11NO) reacts with Co(acac)2 (acac=2,4-pentanedionate) to produce the trinuclear coordination complex [Ba2Co(acac)4(dmae)3(dmaeH)] in an 85% yield. Spectroscopic and single-crystal X-ray diffraction experiments indicate that the complex possesses a structure in which two barium atoms and a cobalt atom are bridged by acac and dmae groups. The barium centers are eight and nine coordinate with BaO7N and BaO7N2 coordination spheres while the cobalt is a more regular CoO5N octahedron. This 2:1 heterobimetallic molecular complex was investigated as precursor for the deposition of thin film by AACVD. The film was characterized by SEM and XRD. TGA shows that the complex starts thermal decomposition upon heating in nitrogen atmosphere at 105 degrees C to produce barium cobalt oxide material of a Ba2CoO3 composition with an orthorhombic structure. The synthetic approach detailed here represents a unique route to the formation of a heterobimetallic barium cobalt coordination complex.

Journal Article↗
PubMed1997

Sequential and coordinative complexity in time-accuracy functions for mental arithmetic.

Time-accuracy functions for tasks involving single-digit mental addition and subtraction were derived in a sample of 18 younger (mean age = 21.7 years) and 16 older adults (mean age = 68.8 years). Sequential complexity was manipulated by varying the number of operations (5 vs. 10); coordinative complexity was induced by bracketing. Age differences were apparent in the coordinative conditions, even though no age difference was present in the sequential conditions. This indicates that the age difference under conditions of high coordinative demands could not be attributed solely to a decline in basic speed of processing. The Age x Complexity interaction was due to larger onset times and lower asymptotic performance by the older adults in the coordinative conditions but not due to to rate of approach to the asymptote. This implies that coordinative demands do not differentially hurt access from semantic memory in older adults; however, coordinative demands do have disproportionately negative consequences for computation speed and self-monitoring in older adults.

Adult↗
PubMed1976

SAM Complex Coordinator and Multidimensional Pursuit Test: annotated bibliographies.

A brief description of the SAM Complex Coordinator (Mashburn Apparatus) and the SAM Multidimensional Pursuit Test (MDP or MPT) and annotated bibliographies including 144 and 51 citations respectively are presented. All references are annotated as to subject matter within six categories; Factor Analytic-Task Taxonomy, Aircrew Selection-Classification, Learning Phenomena, Stress Effects, History and Development, General Reviews.

Aerospace Medicine↗
PubMedDate not supplied

Effect of copper coordination complexes on sister-chromatid exchanges in plant cells.

The effectiveness of several copper coordination complexes in the induction of sister-chromatid exchanges (SCE) in meristematic cells of Allium cepa roots was studied. A significant increase in the frequencies of SCE was observed when cells were exposed to different concentrations of copper complexes for 3 h. This effect, which is concentration dependent, seems to be related to the possibility of intercalative binding modes between the planar copper complexes and DNA.

Allium↗
PubMed1994

A novel trans-platinum coordination complex possessing in vitro and in vivo antitumor activity.

As part of a drug discovery program to discover more effective platinum-based anticancer drugs, a series of platinum complexes of trans coordination geometry centered on trans-ammine(cyclohexylaminedichlorodihydroxo)platinum(IV) (JM335) has been evaluated in vitro against a panel of cisplatin-sensitive and cisplatin-resistant human tumor cell lines (predominantly ovarian). In vitro, against 5 human ovarian carcinoma cell lines, JM335 was comparably cytotoxic to cisplatin itself and over 50-fold more potent than transplatin (mean 50% inhibitory concentrations: JM335, 3.1 microM; cisplatin, 4.1 microM; transplatin, 162 microM). With the use of seven pairs of human tumor cell lines (parent and subline with acquired resistance to cisplatin and encompassing all of the known major mechanisms of resistance to cisplatin) JM335 exhibited a different cross-resistance pattern to that of its cis isomer (JM149). JM335 showed non-cross-resistance in six of the seven resistant lines, cross-resistance in the A2780cisR line possibly being associated with high levels of glutathione. Preliminary intracellular DNA binding studies showed that in contrast to transplatin, JM335 was efficient at forming DNA-DNA interstrand cross-links. In vivo, JM335 produced growth delays in excess of 15 days against 4 of 6 human ovarian carcinoma xenografts and was unique among the complexes studied in retaining some efficacy against a cisplatin-resistant subline of the murine ADJ/PC6 plasmacytoma. JM335 is the first trans-platinum complex to demonstrate marked antitumor efficacy against both murine and human s.c. tumor models and represents a significant structural lead to complexes capable of circumventing cross-resistance to cisplatin.

Animals↗
PubMed2003

Elucidation of the collision induced dissociation pathways of water and alcohol coordinated complexes containing the uranyl cation.

Multiple-stage tandem mass spectrometry was used to characterize the dissociation pathways for complexes composed of (1) the uranyl ion, (2) nitrate or hydroxide, and (3) water or alcohol. The complex ions were derived from electrospray ionization (ESI) of solutions of uranyl nitrate in H2O or mixtures of H2O and alcohol. In general, collisional induced dissociation (CID) of the uranyl complexes resulted in elimination of coordinating water and alcohol ligands. For undercoordinated complexes containing nitrate and one or two coordinating alcohol molecules, the elimination of nitric acid was observed, leaving an ion pair composed of the uranyl cation and an alkoxide. For complexes with coordinating water molecules, MS(n) led to the generation of either [UO2(2+)OH-] or [UO2(2+)NO3(-)]. Subsequent CID of [UO2(2+)OH-] produced UO2(+). The base peak in the spectrum generated by the dissociation of [UO2(2+)NO3(-)], however, was an H2O adduct to UO2(+). The abundance of the species was greater than expected based on previous experimental measurements of the (slow) hydration rate for UO2(+) when stored in the ion trap. To account for the production of the hydrated product, a reductive elimination reaction involving reactive collisions with water in the ion trap is proposed.

Journal Article↗
PubMed2002

Five-coordinate complexes [FeX(depe)(2)]BPh(4), X = Cl, Br: electronic structure and spin-forbidden reaction with N(2).

The bonding of N(2) to the five-coordinate complexes [FeX(depe)(2)](+), X = Cl (1a) and Br (1b), has been investigated with the help of X-ray crystallography, spectroscopy, and quantum-chemical calculations. Complexes 1a and 1b are found to have an XP(4) coordination that is intermediate between square-pyramidal and trigonal-bipyramidal. Mössbauer and optical absorption spectroscopy coupled with angular overlap model (AOM) calculations reveal that 1a and 1b have (3)B(1) ground states deriving from a (xz)(1)(z(2))(1) configuration. The zero-field splitting for this state is found to be 30-35 cm(-1). In contrast, the analogous dinitrogen complexes [FeX(N(2))(depe)(2)](+), X = Cl (2a) and Br (2b), characterized earlier are low-spin (S = 0; Wiesler, B. E.; Lehnert, N.; Tuczek, F.; Neuhausen, J.; Tremel, W. Angew. Chem, Int. Ed. 1998, 37, 815-817). N(2) bonding and release in these systems are thus spin-forbidden. It is shown by density functional theory (DFT) calculations of the chloro complex that the crossing from the singlet state (ground state of 2a) to the triplet state (ground state of 1a) along the Fe-N coordinate occurs at r(C) = 2.4 A. Importantly, this intersystem crossing lowers the enthalpy calculated for N(2) release by 10-18 kcal/mol. The free reaction enthalpy Delta G degrees for this process is calculated to be 4.7 kcal/mol, which explains the thermal instability of N(2) complex 2a with respect to the loss of N(2). The differences in reactivity of analogous trans hydrido systems are discussed.

Journal Article↗
PubMed1998

Zero-length protein-nucleic acid crosslinking by radical-generating coordination complexes as a probe for analysis of protein-DNA interactions in vitro and in vivo.

Redox-active coordination complexes such as 1,10-phenanthroline-Cu(II) (OP-Cu) and bleomycin-Fe(III) are commonly used as "chemical nucleases" to introduce single-strand breaks in nucleic acids. Here we report that under certain conditions these complexes may crosslink proteins to nucleic acids. In vitro experiments suggest that proteins are crosslinked to DNA by a mechanism similar to dimethyl sulfate-induced crosslinking. Furthermore, we demonstrate that the OP-Cu complex can generate protein-DNA crosslinks in mammalian cells in vivo. By combining the OP-Cu crosslinking and a "protein shadow" hybridization assay we identify proteins interacting with DNA in isolated pea chloroplasts and show that this methodology can be applied to detect DNA-binding proteins on specific DNA sequences either in vitro or in vivo.

Animals↗
PubMed1986

An in vitro screening system for the nephrotoxicity of various platinum coordination complexes. A cytochemical study.

Isolated rat kidney tubules were cultured in Earle's medium with and without the platinum coordination complexes. Aliquots were taken at 0, 1, 2, 3, 4, 5, 6, and 8 h and analyzed for the amount of Na+/K+-ATPase, Ca2+-ATPase, alkaline phosphatase, and acid phosphatase. Culture medium was also analyzed biochemically for the amounts of alkaline phosphatase present. There is a decrease in the various enzymes levels of the tubules after incubation in nephrotoxic analogues with a corresponding increase in the culture medium. These results compare favorably with in vivo studies. The alkaline phosphatase monitored in the rat kidney cross sections from both the normal and the drug-treated animals at 0, 3, 5, 10, and 20 days showed a correlation in the decrease of enzyme levels in the kidney with a corresponding increase in the urinary levels in both the Wistar and the Long Evans rats. The baseline levels were higher in the Long Evans rats than in the Wistar rats. After cisplatin (nephrotoxic) treatment the Long Evans rats had twice as much alkaline phosphatase in the urine at day 5 as the Wistar rats. Rats treated with cyclobutanedicarboxylatoplatinum (II) did have some alkaline phosphatase output in the urine in excess of the normal levels, but this increase was not so highly significant as to justify classifying the drug as nephrotoxic.

Acid Phosphatase↗
PubMed2004

Solid-supported cross-coupling catalysts derived from homogeneous nickel and palladium coordination complexes.

Solid-supported catalysts derived from homogeneous nickel(II) and palladium(II) non-symmetrical salen-type coordination complexes have been prepared and shown to be effective in the heterogeneous catalysis of carbon-carbon cross-coupling reactions. The nickel catalyst has been used in room-temperature Tamao-Kumada-Corriu reactions and the palladium catalyst in the Heck reaction at elevated temperatures. The complexes were prepared by improved methods and characterised by spectroscopic techniques. Comparisons between the solid-supported catalysts and their homogeneous analogues are reported. The single-crystal structure determination of the nickel and palladium complexes [M(salenac-OH)][M = Ni, Pd; salenac-OH = 9-(2',4'-dihydroxyphenyl)-5,8-diaza-4-methylnona-2,4,8-trienato](2-)] is reported.

Journal Article↗
PubMed2001

Metallomicellar Catalysis Cleavage of p-Nitrophenyl Picolinate Catalyzed by Binuclear Metal Complexes Coordinating Tripeptide in CTAB Micellar Solution.

The catalytic hydrolysis of p-nitrophenyl picolinate (PNPP) by Cu(II) and Zn(II) complexes coordinating tripeptide were studied kinetically by observing the rates of release of p-nitrophenol in the buffered micellar solution at 25 degrees C and different pH values. The experimental results indicate that 1 : 2 ligand : metal ion complexes in CTAB micellar solution are the active species in the reaction, and the complexes, especially that with Cu(II), efficiently catalyze the hydrolysis of PNPP. As a result, a kinetic model of binuclear metal complex catalysis involving a ternary complex in CTAB micellar solution is proposed to analyze the kinetic behavior of catalysis, and thus, relative kinetic and thermodynamic parameters are obtained. The results predict that the catalytic reaction by metallomicelle with binuclear complex involves a bifunctional mechanism. Copyright 2001 Academic Press.

Journal Article↗