Marc A. Walters

A Raman and infrared spectroscopic investigation of biological hydroxyapatite

Raman spectra were acquired on ox femur samples treated with hydrazine to remove the organic components of bone. A large increase in the signal-noise ratio of the mineral spectrum resulted from the exposure of the mineral surface and the removal of fluorescent components of the organic matrix. The effect of hydrazine treatment of the mineral matrix has been reinvestigated and shown to be slight on the basis of second derivative FTIR data. This is the first time that this high resolution technique has been applied to biological minerals.

Crossover between thermally assisted and pure quantum tunneling in molecular magnet Mn12-acetate

The crossover between thermally assisted and pure quantum tunneling has been studied in single crystals of high spin (S = 10) uniaxial molecular magnet Mn12 using micro-Hall-effect magnetometry. Magnetic hysteresis and relaxation experiments have been used to investigate the energy levels that determine the magnetization reversal as a function of magnetic field and temperature. These experiments demonstrate that the crossover occurs in a narrow ( approximately 0. 1 K) or broad ( approximately 1 K) temperature interval depending on the magnitude of the field transverse to the anisotropy axis.

The effect of cadmium on the formation and properties of hydroxyapatite In vitro and its relation to cadmium toxicity in the skeletal system

In order to understand the biological action of cadmium (Cd) in inducing bone pathologies, the effect of Cd on the formation, structure, and properties of hydroxyapatite (HA) in vitro was investigated using three biologically relevant test systems: (1) direct precipitation of HA with no precursor phase; (2) transformation of amorphous calcium phosphate (ACP) to crystalline HA; and (3) growth of HA seed crystals. Cd-containing HA was prepared by transforming ACP to HA in the presence of Cd at a pH of 10; Cd/Ca ratios of 0.05, 0.10, and 0.20 were obtained. Infrared and x-ray diffraction analyses were performed on the Cd-HA samples, and measurements were made of Cd adsorption on HA and of the dissolution characteristics of Cd-containing HA. Cd incorporation in HA introduced little strain in the lattice but resulted in a decreasing C-axis spacing and a corresponding crystal size decrease in the C-axis direction. Cd incorporation had a nominal effect on HA dissolution. Cd had an inhibitory effect on HA formation kinetics in all three test systems. Infrared spectroscopy of Cd-HA showed a complex series of small changes in the spectra as a function of Cd concentration resulting from some distortion in the crystal perfection and symmetry. The interference of Cd with mineralization can be partially explained by its inhibitory effect on HA nucleation and growth in addition to any cellular involvement. Furthermore, Cd probably has little effect on bone mineral dissolution. Our results explain the Cd incorporation reported in bone.

Iron(III) nitrilotriacetate and iron(III) iminodiacetate, their X-ray crystallographic structures and chemical properties

Mononuclear iron(III) nitrilotriacetato dichloride, [Fe(nta)Cl2] 2 , and iron(III) bis-iminodiacetato, [Fe(ida)2] , complexes were formed in py, from which they were isolated and characterized by X-ray crystallography. The iron/nta complex is the structurally simplest of the reported solid state iron/nta complexes, and is catalytic for the air oxidation of hydrogen sulfide to sulfur. # 2003 Elsevier Science Ltd. All rights reserved.

Lanthanide complexes on Ag nanoparticles: designing contrast agents for magnetic resonance imaging.

This paper describes colloidal particles that are designed to induce hyper-intensity contrast (T(1) relaxation) in MRI. The contrast agents consist of discrete gadolinium complexes tethered to 10 nm diameter silver nanoparticles. The gadolinium complexes (1) [Gd(DTPA-bisamido cysteine)](2-) and (2) [Gd(cystine-NTA)(2)](3-), undergo chemisorption to particle surfaces through thiol or disulfide groups, respectively, to form two new contrast agents. The resulting nanoparticulate constructs are characterized on the basis of their syntheses, composition, spectra and contrast enhancing power. The average r(1) relaxivities of the of the surface bound complexes (obtained at 9.4 T and 25 degrees C) are 10.7 and 9.7 s(-1) mM(-1), respectively, as compared to 4.7 s(-1) mM(-1) for the clinical agent Magnevist. Correspondingly, the respective whole particle relaxivities are 27927 and 13153 s(-1) mM(-1).

Effect of N–H⋯S amide–thiolate hydrogen bonding on bond lengths in rubredoxin models [(CH3)3NCH2CONH2]2[M(S2-o-xyl)2]

Abstract The complexes [(CH 3 ) 3 NCH 2 CONH 2 ] 2 [M(S 2 - o -xyl) 2 ], M=Fe ( 1 ), Co ( 2 ), and [(CH 3 ) 4 N] 2 [Co(S 2 - o -xyl) 2 ]·1/2C 2 H 5 OH ( 3 ) have been characterized by X-ray crystallography and vibrational spectroscopy. Complexes 1 and 2 exhibit linear one-dimensional concatenated hydrogen bonded structures. In complex 2 there is an increase in the average metal–ligand bond length in the hydrogen-bonded form relative to 3 , which contains a non-hydrogen bonded congener.

Molecular structure at the bone-implant interface: A vibrational spectroscopic characterization

SummaryTest implant plates surgically retrieved from distal femurs of dogs were studied by Raman spectroscopy in order to characterize the bone-implant interface. The implant surface consisted of phosphate mineral, plasma sprayed on a titanium substrate. On the basis of its spectroscopic signature, the phosphate mineral of bone and the implant surface formed a mixed phase in the interface.

S K- and Mo L-edge X-ray absorption spectroscopy to determine metal-ligand charge distribution in molybdenum-sulfur compounds.

Mo L-edge and S K-edge X-ray absorption spectroscopy were applied to investigate the charge distribution between Mo and S in a series of Mo thiolate compounds, which serve as amide-sulfur H-bonding models and exhibit different redox potentials arising from polar group effects and ligand hydrogen bonds near the redox center. For all oxidized complexes, the S K-edge spectra exhibit a thiolate-based pre-edge feature centered at 2470.2 eV and the inflection point oCCurs at 2472.0 eV. No intense pre-edge feature is observed in the spectra for the reduced Mo model compounds and the energy shift of the S K-edge position depends on the S-ligand. Correlations between ligand charge density and the redox potential of the Mo-S cores are observed.

A neutral trizirconium cluster with chelating and exobidentate dialkoxide groups. The synthesis and crystal structure of Zr3(μ3-O)-(DMPD)4(DMPDH)2 (DMPDH2=2,4-dimethylpentane-1,4-diol)

Abstract Zr3(μ3-O){[CH2C(CH3)2O]2}4 {[HO(CH3)2CCH2C(CH3)2O]}2 was prepared by a transesterification reaction between Zr(O-n-Pr)4 and 2,4-dimethylpentane-2,4-diol, DMPDH2. The product was obtained as a white crystalline solid containing discrete molecules of a μ3-O bridged trizirconium cluster with one chelating DMPD, two chelating DMPDH groups and three exobidentate DMPD groups, with one end bonded to a single Zr atom and the other bridging adjacent Zr atoms. The two chelating DMPDH groups form strong hydrogen bonds to the oxygen atoms of the chelated DMPD group.

Micro-Hall magnetometry studies of thermally assisted and pure quantum tunneling in single molecule magnet Mn12-acetate

We have studied the crossover between thermally assisted and pure quantum tunneling in single crystals of high spin (S=10) uniaxial single molecule magnet Mn12 using micro-Hall effect magnetometry. Magnetic hysteresis experiments have been used to investigate the energy levels that determine the magnetization reversal as a function of magnetic field and temperature. These experiments demonstrate that the crossover occurs in a narrow ( 0.1 K) or broad ( 1 K) temperature interval depending on the magnitude and direction of the applied field. For low external fields applied parallel to the easy axis, the energy levels that dominate the tunneling shift abruptly with temperature. In the presence of a transverse field and/or large longitudinal field these energy levels change with temperature more gradually. A comparison of our experimental results with model calculations of this crossover suggests that there are additional mechanisms that enhance the tunneling rate of low-lying energy levels and broaden the crossover for small transverse fields.