Biomedical subjects

M A Walters

Publications and source records attributed to M A Walters.

17 recordsLinked to original sources

PubMed2001

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.

Ligands↗

PubMed2000

Titanium alkoxide complexes: condensed phase and gas phase comparisons.

The complex [Ti(2,4-dimethyl-2,4-pentanediolate)2]2 (1) has been synthesized from [Ti(OiPr)4] by transesterification with a stoichiometric amount of 2,4-dimethyl-2,4-pentanediol. We have characterized complex 1 in the solid state by single-crystal X-ray diffraction and in the gas phase by desorption chemical ionization mass spectrometry (DCI-MS). The structural and mass spectrometric data show complex 1 to be stable as a dimer in both the solid and gas phases. The retention of dimeric nuclearity in the gas phase sets complex 1 apart from other simple titanium alkoxide complexes [Ti(OiPr)4] and [Ti(OMe)4]4 that give rise to respective families of molecular ions in the DCI-MS experiment. The highest mass molecular ions for Ti alkoxide complexes in the gas phase may reveal the highest nuclearity that these complexes achieve in condensed phases. According to this interpretation the complex [Ti(OiPr)4] is principally dimeric in the gas phase and probably also in the pure liquid phase and should be represented by the formula [Ti(OiPr)4]2.

Journal Article↗

PubMed1995

Determination of the mineral phases and structure of the bone-implant interface using Raman spectroscopy.

The bone-implant interface formed in a canine distal femur was examined by means of a Raman microprobe using an implant model designed to test calcium phosphate surface coatings. By using the 960 cm-1 band of calcium phosphate to characterize the interface and adjacent mineral, we obtained spatial and compositional information about the attachment of bone to the synthetic calcium phosphate coating on a titanium support. The interface between bone and the synthetic calcium phosphate is approximately 30-40 microns in width.

Animals↗

PubMed1991

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

Test 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.

Animals↗

PubMed1990

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.

Animals↗

PubMed1982

Resonance raman spectroscopic studies of axial ligation in oxyhemoglobin, oxymyoglobin, and nitrosylmyoglobin.

Raman intensity measurements for the Fe-O2 stretching band of HbO2 (Hb = hemoglobin) have been used to construct an excitation profile, which shows that resonance enhancement occurs mainly via the B and Q transition; no contribution is detectable from an out-of-plane charge-transfer transition. Direct coupling of VFe-O2 to the porphyrin pi-pi* transitions is explained on the basis of competition between the pi* orbitals of porphyrin and O2 for Fe d pi electrons. The RR spectrum of MbNO (Mb = myoglobin) at pH 8.4 is due solely to six-coordinate heme--NO, but lowering the pH to 5.8 converts the RR spectrum to one characteristic of five-coordinate heme--NO, consistent with Fe-ImH (ImH = imidazole) dissociation via protonation. The Fe-NO stretching frequencies are at 553 and 596 cm-1 for the high- and low-pH forms, as expected, but the low-pH form shows an additional 15NO-sensitive band, at 573 cm-1, which is assigned to Fe-N-O bending in the five-coordinate complex. The RR spectrum of MbO2 shows a shoulder at approximately 270 cm-1, which shifts down by approximately 3 cm-1 upon 18O2 substitution, and is suggested to contain the Fe-ImH stretching mode. The weakness of VFe-ImH, relative to VFe-O2, is attributable to the lack of ImH involvement in the heme pi bonding.

Myoglobin↗

PubMed1980

Transcutaneous oxygen monitoring during exercise stress testing.

Transcutaneous oxygen tension (tcPO2) was compared with simultaneous arterial oxygen tension (PaO2) in 3 normal young adults and 4 pediatric lung disease patients at rest and during exercise to assess the usefulness of tcPO2 monitoring during exercise stress testing. At rest, the regression coefficient of tcPO2 on PaO2 was 0.78 +/- 0.03 (SEM) (r = 0.924; P < 0.0005). During exercise, the regression coefficient of tcPO2 on PaO2 was 0.88 +/- 0.02 (r = 0.958; P < 0.0005), indicating that tcPO2 approximates PaO2 equally well at rest and during exercise. After a step change in inspired oxygen concentration (FIO2) from 0.21 to 0.17, there was no significant difference in the tcPO2 time constant at rest (66.2 +/- 8.5 s) and during exercise (73.0 +/- 3.1 s). Neither PaO2 nor tcPO2 fell in normal subjects during graded exercise stress testing. However, in 3 of 4 pediatric lung disease patients, there were decreases in both PaO2 (40.7 +/- 11.6 Hg) and tcPO2 (28.7 +/- 10.0 mm Hg) during 7 exercise stress tests. These results indicate that tcPO2 approximates PaO2 equally well at rest and during exercise.

Adolescent↗

PubMed1968