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PubMed2004

Molecular properties of adsorbates that affect the growth kinetics of archerite (KDP).

We explore the molecular properties of adsorbates that dramatically affect growth kinetics and morphology of the [100] face of archerite, also known as potassium dihydrogen phosphate (KH(2)PO(4) or KDP). Aqueous complexes of Al(III), Fe(III), and Cr(III) are known to affect KDP growth, albeit the actual step-pinning complex(es) is unknown. Using in situ atomic force microscopy (AFM), we measured changes in the growth rates of the [100] face of KDP with supersaturation in the presence of trace amounts of [Co(NH(3))(6)](3+), [Fe(CN)(6)](3-), eta(1)-[Co(NH(3))(5)HPO(4)](+), eta(2)-[Co(NH(3))(4)HPO(4)](+), eta(2)-[Co(NH(3))(4)P(2)O(7)H(2)](+), and [Rh(H(2)PO(4))(2)(H(2)O)(4)](+). Unlike in experiments using trivalent-metals, these complexes do not change stoichiometry or structure on the timescale of step motion, so that the actual molecular interactions that affect growth can be studied. Step velocity and morphology on the [100] face are unaffected by outer-sphere coordination complexes of either charge. Surprisingly, inner-sphere phosphatoammine complexes do not affect growth rates regardless of how the phosphate group is coordinated to the metal. However, doping the growth solution with [Rh(H(2)PO(4))(2)(H(2)O)(4)](+) results in profound step pinning, matching the behavior of KDP surfaces grown in the presence of Rh(III) after an equilibration period. Not only is an inner-sphere phosphate group needed to dock a trivalent metal to the step edge, but compatible hydrogen bonding of the remainder of the inner-sphere ligands with the bulk lattice is also essential.

Journal Article↗
PubMed2005

Interactions between metal ions and carbohydrates. The coordination behavior of neutral erythritol to neodymium ion.

A single crystal of a coordinated complex of neutral erythritol (C4H10O4,E) with a neodymium ion, NdE(II), was synthesized and studied using FT-IR and X-ray diffraction analysis. In NdE(II) (NdCl3.2.5C4H10O4.C2H5OH) the Nd3+ coordinates with one chloride ion and eight OH groups from three erythritol molecules. There are two neodymium centers linked by one erythritol molecule with same coordination structure in the molecule. Two erythritol molecules provide 1,3,4-hydroxyl groups to coordinate with a neodymium ion; another erythritol molecule coordinates to two Nd ions via its 1,2-hydroxyl groups and 3,4-hydroxyl groups, respectively. The OH groups of erythritol act as ligand to coordinate to neodymium ions, and OH groups of erythritol form hydrogen bond networks that link chain and layer together to build three-dimensional structures. The ratio of metal to ligand is 1:2.5. The structure of NdE(II) is more complicated than the previously reported NdE(I), which is NdCl3.C4H10O4.6H2O; in NdE(I), Nd3+ is coordinated to four hydroxyl groups from two erythritol molecules, four water molecules and one chloride ion. The results indicate the complexity of metal-sugar interaction.

Journal Article↗
PubMed2003

Trace element speciation by ICP-MS in large biomolecules and its potential for proteomics.

Latest studies on the chemical association of trace elements to large biomolecules and their importance on the bioinorganic and clinical fields are examined. The complexity of the speciation of metal-biomolecules associations in various biological fluids is stressed. Analytical strategies to tackle speciation analysis and the-state-of-the-art of the instrumentation employed for this purpose are critically reviewed. Hyphenated techniques based on coupling chromatographic separation techniques with ICP-MS detection are now established as the most realistic and potent analytical tools available for real-life speciation analysis. Therefore, the status and potential of metal and semimetals elemental speciation in large biocompounds using ICP-MS detection is mainly focused here by reviewing reported metallo-complexes separations using size-exclusion (SEC), ion-exchange (IE), reverse phase chromatography (RP) and capillary electrophoresis (CE). Species of interest include coordination complexes of metals with larger proteins (e.g. in serum, breat milk, etc.) and metallothioneins (e.g. in cytosols from animals and plants) as well as selenoproteins (e.g. in nutritional supplements), DNA-cisplatin adducts and metal/semimetal binding to carbohydrates. An effort is made to assess the potential of present trace elements speciation knowledge and techniques for "heteroatom-tagged" (via ICP-MS) proteomics.

Animals↗
PubMed1995

Correlation between cytotoxicity and DNA binding of polypyridyl ruthenium complexes.

The cytotoxicity of chloropolypyridyl ruthenium complexes of structural formulas [Ru(terpy)-(bpy)Cl]Cl, cis-[Ru(bpy)2Cl2], and mer-[Ru(terpy)Cl3] (terpy = 2,2':6'2"-terpyridine, bpy = 2,2'-bipyridyl) has been studied in murine and human tumor cell lines. The results show that mer-[Ru(terpy)Cl3] exhibits a remarkably higher cytotoxicity than the other complexes. Moreover, investigations of antitumor activity in a standard tumor screen have revealed the highest efficiency for mer-[Ru(terpy)Cl3]. In a cell-free medium, the ruthenium complexes coordinate to DNA preferentially at guanine residues. The resulting adducts can terminate DNA synthesis by thermostable VentR DNA polymerase. The reactivity of the complexes to DNA, their efficiency to unwind closed, negatively supercoiled DNA, and a sequence preference of their DNA adducts (studied by means of replication mapping) do not show a correlation with biological activity. On the other hand, the cytotoxic mer-[Ru(terpy)Cl3] exhibits a significant DNA interstrand cross-linking, in contrast to the inactive complexes which exhibit no such efficacy. The results point to a potential new class of metal-based antitumor compounds acting by a mechanism involving DNA interstrand cross-linking.

2,2'-Dipyridyl↗
PubMed2006

Precursor chemistry for TiO2: titanium complexes with a mixed nitrogen/oxygen ligand sphere.

Novel mixed amido-malonato complexes of titanium are reported. The complexes were synthesized by partially replacing the amido groups from the complexes [Ti(NMe2)4] and [Ti(NEt2)4] via Brønstedt acid/base reactions, using the malonate-ligands di-isopropylmalonate (Hdpml) and di-tert-butylmalonate (Hdbml). Four representative complexes were synthesized and fully characterised by 1H NMR, 13C NMR, CHN analysis and mass spectrometry. The crystal structures of the six-coordinated complexes [Ti(NMe2)2(dbml)2] (3) and [Ti(NEt2)2(dbml)2] (4) are presented and discussed. The complexes are solids and the chemical and thermal characteristics of the complexes strongly depend on the substitution at the malonate ligand. While dpml containing complexes show a promising behaviour for classical MOCVD, dbml containing complexes seem to be more suitable for liquid injection-metal-organic chemical vapour deposition (LI-MOCVD). Based on its thermal characteristics, the most promising complex for thermal CVD, [Ti(NEt2)2(dpml)2] (2) was selected for preliminary MOCVD experiments, which indicate a good suitability for the deposition of TiO2 thin films.

Journal Article↗
PubMed1984

Studying enzyme mechanism by 13C nuclear magnetic resonance.

High-resolution carbon-13 nuclear magnetic resonance (NMR) spectra of enzyme-inhibitor and enzyme-substrate complexes provide detailed structural and stereochemical information on the mechanism of enzyme action. The proteases trypsin and papain are shown to form tetrahedrally coordinated complexes and acyl derivatives with a variety of compounds artificially enriched at the site or sites of interest. These results are compared with the structural information derived from x-ray diffraction. Detailed NMR studies have provided a clearer picture of the ionization state of the residues participating in enzyme-catalyzed processes than other more classical techniques. The dynamics of enzymic catalysis can be observed at sub-zero temperatures by a combination of cryoenzymology and carbon-13 NMR spectroscopy. With these powerful techniques, transient, covalently bound intermediates in enzyme-catalyzed reactions can be detected and their structures rigorously assigned.

Binding Sites↗
PubMed2002

Electronic structure of Ni complexes by X-ray resonance Raman spectroscopy (resonant inelastic X-ray scattering).

The potential of 1s2p resonant inelastic (Raman) X-ray scattering (RIXS) is demonstrated for a series of Ni coordination complexes. In this technique, incident and scattered photon energies lie in the hard X-ray range (>5 keV). The 1s2p RIXS contour plots provide information that is complementary to K-edge and L-edge spectroscopy. RIXS spectroscopy promises to be a valuable probe of electronic structure

Nickel↗
PubMed2005

Substituted N-picolylethylenediamines of the type (ArNHCH2CH2){(2-C5H4N)CH2}NR [R = Me, 4-CH2=CH(C6H4)CH2, (2-C5H4N)CH2] and their transition metal(II) halide complexes.

Alkylation of (ArNHCH2CH2){(2-C5H4N)CH2}NH with RX [RX = MeI, 4-CH2=CH(C6H4)CH2Cl) and (2-C5H5N)CH2Cl] in the presence of base has allowed access to the sterically demanding multidentate nitrogen donor ligands, {(2,4,6-Me3C6H2)NHCH2CH2}{(2-C5H4N)CH2}NMe (L1), {(2,6-Me3C6H3)NHCH2CH2}{(2-C5H4N)CH2}NCH2(C6H4)-4-CH=CH2 (L2) and (ArNHCH2CH2){(2-C5H4N)CH2}2N (Ar = 2,4-Me2C6H3 L3a, 2,6-Me2C6H3 L3b) in moderate yield. L3 can also be prepared in higher yield by the reaction of (NH2CH2CH2){(2-C5H4N)CH2}2N with the corresponding aryl bromide in the presence of base and a palladium(0) catalyst. Treatment of L1 or L2 with MCl2 [MCl2 = CoCl2.6H2O or FeCl2(THF)1.5] in THF affords the high spin complexes [(L1)MCl2](M = Co 1a, Fe 1b) and [(L2)MCl2](M = Co 2a, Fe 2b) in good yield, respectively; the molecular structure of reveals a five-coordinate metal centre with bound in a facial fashion. The six-coordinate complexes, [(L3a)MCl2](M = Co 3a, Fe 3b, Mn 3c) are accessible on treatment of tripodal L3a with MCl2. In contrast, the reaction with the more sterically encumbered leads to the pseudo-five-coordinate species [(L3b)MCl2](M = Co 4a, Fe 4b) and, in the case of manganese, dimeric [(L3b)MnCl(mu-Cl)]2 (4c); in 4a and 4b the aryl-substituted amine arm forms a partial interaction with the metal centre while in 4c the arm is pendant. The single crystal X-ray structures of , 1a, 3b.MeCN, 3c.MeCN, 4b.MeCN and 4c are described as are the solution state properties of 3b and 4b.

Journal Article↗
PubMed1983

Metal-nucleotide structure at the active sites of the mammalian hexokinases.

The diastereomers of adenosine 5'-O-(2-thiotriphosphate) (ATP beta S) in the presence of Mg2+, Co2+ and Cd2+ have been used to determine the stereospecificity of the metal-nucleotide binding site of rat muscle hexokinase type II and rat liver glucokinase by the method developed by Jaffe and Cohn [J. Biol. Chem. 254, 10839-10845 (1979)]. The kinetic parameters, Km and V, for the mammalian hexokinase reaction have been determined for ATP beta S in the presence of the three divalent metal ions. In the presence of Mg2+, both enzymes exhibit a preference for the B diastereomer of ATP beta S (V ratio, B/A approximately equal to 20). With Cd+, the stereospecificity is reversed and the A diastereomer is the preferred substrate, suggesting direct coordination of S on the beta-P to this metal ion. Co2+ exhibits a decreased specificity for the B diastereomer over Mg2+. This decreasing order of stereo-specificity for the B isomer reflects primarily the decreasing ratios of nucleotide complexes coordinated to O rather than S on the beta-P as the metal ion is changed from Mg2+ to Co2+ to Cd2+. The kinetic parameters for the hexokinases have also been determined for adenosine 5'-O-(1-thiotriphosphate) (ATP alpha S) using the same three metal ions as activators. The A diastereomer is the preferred substrate regardless of the metal ion. This absence of reversal of stereospecificity for metal-ATP alpha S suggests that the alpha-P is not involved in coordinating the metal on the enzyme, unlike the beta-P. That is, the structural constraints of the ATP-binding site on the enzyme overcome the preferred coordination of Cd2+ to S. Given the greater stability of bidentate metal-ATP complexes over monodentate, these data are interpreted as indicating that MgATP binds to the mammalian hexokinases as the beta gamma-bidentate complex in the A screw sense geometry, as has been found for the yeast hexokinase (Jaffe and Cohn, reference cited above).

Animals↗
PubMed2004

Human medial intraparietal cortex subserves visuomotor coordinate transformation.

In the macaque, the posterior parietal cortex (PPC) integrates multimodal sensory information for planning and coordinating complex movements. In particular, the areas around the intraparietal sulcus (IPS) serve as an interface between the sensory and motor systems to allow for coordinated movements in space. Because recent imaging studies suggest a comparable functional and anatomical organization of human and monkey IPS, we hypothesized that in humans, as in macaques, the medial intraparietal cortex (area MIP) subserves visuomotor transformations. To test this hypothesis, changes of neural activity were measured using functional magnetic resonance imaging (fMRI) while healthy subjects performed a joystick paradigm similar to the ones previously employed in macaques for studying area MIP. As hypothesized, visuomotor coordinate transformation subserving goal-directed hand movements activated superior parietal cortex with the local maximum of increased neural activity lying in the medial wall of IPS. Compared to the respective visuomotor control conditions, goal-directed hand movements under predominantly proprioceptive control activated a more anterior part of medial IPS, whereas posterior medial IPS was more responsive to visually guided hand movements. Contrasting the two coordinate transformation conditions, changing the modality of movement guidance (visual/proprioceptive) did not significantly alter the BOLD signal within IPS but demonstrated differential recruitment of modality specific areas such as V5/MT and sensorimotor cortex/area 5, respectively. The data suggest that the human medial intraparietal cortex subserves visuomotor transformation processes to control goal-directed hand movements independently from the modality-specific processing of visual or proprioceptive information.

Adult↗
PubMed2005

Tantalum complexes with all nitrogen coordination sphere: mixed amido-, imido-, guanidinato complexes of tantalum and their thermal behaviour.

Novel mixed amido-/imido-/guanidinato-complexes of tantalum are reported. The complexes were synthesised by insertion reactions of carbodiimides of the type C(NR)2(R =iso-propyl (i-Pr)) into the M-N bonds of tantalum mixed amido/imido complexes. Three representative complexes were synthesised and fully characterised by 1H-NMR, 13C-NMR, CHN-analysis and mass spectroscopy. The crystal structure of the complex [Ta(NMe2){(i-Pr-N)2C(NMe2)}2(N-t-Bu)](1)(Me = methyl, t-Bu =tert-butyl) is presented and discussed. The complexes are solids that can be quantitatively sublimed at moderate temperatures (120-130 degrees C) without any sign of decomposition. The thermal properties of the new compounds were studied (TGA) and preliminary MOCVD-experiments were performed. TaN films were deposited and characterised by XRD and XPS.

Amides↗
PubMed2004

Perception-action coupling during bimanual coordination: the role of visual perception in the coalition of constraints that govern bimanual action.

Constraints pertaining to interlimb coordination have been studied extensively in the past decades. In this debate, F. Mechsner (2004) has taken a provocative position by putting primary emphasis on perceptual principles that mediate coordinative stability. Whereas the present authors agree that the role of perceptual principles is of critical importance during coordination, they take issue with Mechsner's extreme position and with the evidence forwarded to support a purely perceptual-cognitive approach to bimanual coordination. More specifically, the authors emphasize that current knowledge about brain function argues against a dualism between perception and action, criticize the presented evidence that posture manipulations during coordination provide decisive evidence against motoric and muscular constraints, and report on potential pitfalls associated with the use of visual transformation procedures to support complex coordination patterns.

Hand↗
PubMed1986

Recognition and transport of ferric enterobactin in Escherichia coli.

The specificity of the outer membrane protein receptor for ferric enterobactin transport in Escherichia coli and the mechanism of enterobactin-mediated transport of ferric ions across the outer membrane have been studied. Transport kinetic and inhibition studies with ferric enterobactin and synthetic structural analogs have mapped the parts of the molecule important for receptor binding. The ferric complex of the synthetic structural analog of enterobactin, 1,3,5-N,N',N''-tris-(2,3-dihydroxybenzoyl)triaminomethylbenzene (MECAM), was transported with the same maximum velocity as was ferric enterobactin. A double-label transport assay with [59Fe, 3H]MECAM showed that the ligand and the metal are transported across the outer membrane at an identical rate. Under the growth conditions used, large fractions of the transported complexes were available for exchange across the outer membrane when a large excess of extracellular complex was added to the cell suspension; at least 60% of the internalized [59Fe]enterobactin exchanged with extracellular [55Fe]enterobactin. Internalized [59Fe, 3H]MECAM was released from the cell as the intact complex when either unlabeled Fe-MECAM or Fe-enterobactin was added extracellularly. The results suggest a mechanism of active transport of unmodified coordination complex across the outer membrane with possible accumulation in the periplasm.

Bacterial Outer Membrane Proteins↗
PubMedDate not supplied

[Principles and methods of occupational psychophysiological selection of deep-water divers].

A complex of methods is suggested for professional psychophysiological selection of deep divers: the count of signals under time deficit conditions, simple and complex coordination of analyzers function, tepping test, the study of attention concentration using the Ivanov-Smolensky tables and finding of numbers with switching. This complex together with assessment of number range by deviation method allows making correct prediction during selection of specialists with high probability equal to 0.9. The efficiency of professional selection increases due to the reliable correlation between the results of psychophysiological research and predisposition to development of decompressive disease.

Adolescent↗
PubMed1998

Pyramidal Inversion at Phosphorus Facilitated by the Presence of Proximate Lewis Acids. Coordination Chemistry of Group 13 Elements with the Macrocyclic Bis(amidophosphine) Ligand [P(2)N(2)] ([P(2)N(2)] = [PhP(CH(2)SiMe(2)NSiMe(2)CH(2))(2)PPh]).

Investigations on the preparation of four- and five-coordinate aluminum and gallium bis(amidophosphine) derivatives are reported. The reaction of the macrocyclic ligand precursor anti-Li(2)(THF)(2)[P(2)N(2)] ([P(2)N(2)] = [PhP(CH(2)SiMe(2)NSiMe(2)CH(2))(2)PPh]) with AlCl(3) or GaCl(3) in toluene at 25 degrees C leads to the formation of the four-coordinate species anti-MCl[P(2)N(2)] (M = Al (1), Ga (2)). An X-ray diffraction study of anti-GaCl[P(2)N(2)] shows it to be monomeric with a distorted tetrahedral geometry at Ga; only one of the phosphine donors of the [P(2)N(2)] ligand binds to the gallium, resulting in the retention of the anti-configuration. The solution NMR spectra are consistent with C(s)() symmetry. The addition of AlCl(3) or GaCl(3) to the macrocyclic ligand precursor syn-Li(2)(dioxane)[P(2)N(2)] in toluene at 25 degrees C yields the five-coordinate complexes syn-MCl[P(2)N(2)] (M = Al (3), Ga (4)). The X-ray crystal structure of syn-GaCl[P(2)N(2)] reveals a trigonal bipyramidal geometry about the metal atom, necessitating the coordination of both phosphorus atoms. The solution NMR spectra are consistent with a C(2)(v)() symmetric complex. Heating the anti complexes results in the clean conversion to the syn complexes, with pyramidal inversion observed at phosphorus. The kinetics of this inversion were studied by (1)H NMR spectroscopy and found to be first-order. Barriers to pyramidal inversion (DeltaG()) were calculated to be 29.1 and 30.1 kcal mol(-)(1) for the aluminum and gallium complexes, respectively; these barriers are approximately 2-3 kcal mol(-)(1) lower than that determined for the metal-free, protonated compounds anti- and syn-H(2)[P(2)N(2)]. It is suggested that the role that the metals play in this inversion, based on the values of DeltaG(), involves the large negative entropies of activation and thus help organize the transition state.

Journal Article↗
PubMed2006

Urea coordinated titanium trichloride Ti(III)[OC(NH)2]6Cl3: a single molecular precursor yielding highly visible light responsive TiO2 nanocrystallites.

A coordination complex, Ti(III)[OC(NH2)2]6Cl3, was first synthesized via reacting hot alcoholic solutions of TiCl3 and urea, which was subsequently employed as a molecular precursor for nanocrystalline TiO2 via thermal decomposition. Fourier transform IR spectroscopy confirmed C=O-->Ti coordination bond formation, while Rietveld refinement revealed a hexagonal crystal structure (space group: Pc1) for the complex with a = b = 16.438(4) A, c = 15.423(3) A, alpha = beta = 90 degrees , gamma = 120 degrees , and V = 3608.9(13) A3. Thermal decomposition and phase evolution processes of the complex were investigated in air by combined means of elemental analysis, Fourier transform IR, differential thermal analysis/thermogravimetry, X-ray diffraction, and Raman spectroscopy. Characterizations of the resultant TiO2 powders were achieved by scanning electron microscopy, high-resolution transmission electron microscopy, the Brunauer-Emmett-Teller analysis, thermal desorption spectroscopy, and UV-vis spectroscopy. Simultaneous doping of C, N, and Cl was realized upon pyrolyzing the molecular precursor in air, leading to significantly lowered direct and indirect interband transition energies of the resultant TiO2. As a consequence, the anatase nanopowders obtained at 450 and 500 degrees C, with specific surface areas of 97.8 and 64.1 m2/g, respectively, exhibit significantly higher efficiency than Degussa P25 in the bleaching of methyl orange solution under visible light (mainly consisting two wavelengths of 405 and 436 nm at 81:100 intensity ratio) irradiation, either at a fixed weight of TiO2 loading or at a fixed surface area of the loaded TiO2 powder.

Journal Article↗