Denis F. R. Gilson

FT-Raman and high-pressure infrared spectroscopic studies of dicalcium phosphate dihydrate (CaHPO4·2H2O) and anhydrous dicalcium phosphate (CaHPO4)

Abstract The FT-Raman spectra and the pressure dependence of the infrared spectra of the hydrated and anhydrous forms of dicalcium phosphate, CaHPO4 · 2H2O and CaHPO4, have been studied. The hydrated salt exhibits a phase transition at 21 kbar (1.0 kbar=0.1 Gpa) but no high pressure transition was observed for anhydrous dicalcium phosphate. The O–H stretching frequencies of the water molecules in CaHPO4 · 2H2O all showed negative pressure dependences and correlate with the O ⋯ O distances. The PO–H stretch increased with increasing pressure, indicating a strong hydrogen bond. The frequencies associated with the phosphate ion showed a normal pressure dependence.

An FT-Raman Spectroscopic Investigation of Dentin and Collagen Surfaces Modified by 2-Hydroxyethylmethacrylate

Although 2-hydroxyethylmethacrylate (HEMA) is commonly used for adhesive bonding to dentin, its role in promoting adhesion is not completely understood. Here, we use FT-Raman spectroscopy to elucidate further the nature of the interaction of HEMA with dentin. Ground dentin was exposed to 2.5% (w/w) nitric acid, washed, dried in air, and treated with HEMA. The samples were then sequentially washed with distilled water, with FT-Raman spectra being obtained after different wash times. Hydroxyapatite and bovine type I collagen were similarly treated with HEMA except for the acid exposure. The FT-Raman spectra of these samples were also recorded. The spectra of HEMA-treated, water-washed dentin and collagen revealed the following changes: (1) The band intensities of HEMA absorbed on dentin and collagen decreased with increasing wash times; (2) the v(C=O) and v(CCO) modes of HEMA at 1718 and 607 cm -1, respectively, either disappeared or decreased after extensive washing; (3) the v(C=C) (1640 cm-1) and δ(=CH2) (1403 cm -1) bands exhibited minor variations in band position and relative intensity. These results demonstrate that HEMA interacts with dentin both physically and chemically. The chemical interaction can be interpreted by either hydrogen bonding or the formation of a new bond to the ester group of HEMA.

FT-Raman and high-pressure FT-infrared spectroscopic investigation of monocalcium phosphate monohydrate, Ca(H2PO4)2·H2O

Abstract The FT-infrared spectra of monocalcium monohydrate, Ca(H 2 PO 4 ) 2 ·H 2 O, have been measured as a function of pressure up to 50 kbar. A phase transition occurs at 18 kbar. The Lippincott–Schroeder model for the hydrogen bond has been used to explain the pressure dependence of the vibrational frequencies.

Effect of high external pressures on the vibrational spectra of biomedical materials: Calcium hydroxyapatite and calcium fluoroapatite

Infrared and Raman spectra of the principal mineral component of human hard tissue, calcium hydroxyapatite, Ca10(PO4)6(OH)2, or HAP, and the analogous calcium fluoroapatite, Ca10(PO4)6F2, or FAP, have been recorded, using a diamond-anvil cell, at pressures ranging from ambient to 30 kbar. For FAP, the absence of any discontinuities in the slopes of the nu (cm-1) versus P (kbar) plots for the observed bands indicates that no pressure-induced structural transition occurs in this material throughout the pressure range investigated. For the internal vibrational modes of HAP, however, there are distinct breaks at approximately 20 kbar in the nu versus P plots, suggesting the occurrence of a structural change at this pressure. The OH stretching mode of HAP shifts to higher wave numbers with increasing pressure while the associated OH librational mode shifts in the opposite direction. The pressure-induced structural transition in HAP is reversible and occurs at approximately 22 kbar upon decompression. Further evidence for a structural change taking place at approximately 20 kbar was provided by a parallel pressure-tuning Raman study. Hydrogen bonding does not occur, or is very weak, in HAP.

Application of photoacoustic infrared spectroscopy in the forensic analysis of artists' inorganic pigments.

Fourier-transform photoacoustic infrared (PAIR) spectroscopy has been used in the analysis of 12 inorganic pigments commonly in use by artists today, viz., cobalt blue, ultramarine blue, Prussian blue, azurite, malachite, chromium oxide, viridian, cadmium yellow, chrome yellow, iron oxide, yellow ochre and Mars orange. The authenticity of these 12 commercial pigments was first established by recording their Raman spectra. The subsequent PAIR spectra were highly reproducible and matched well in the mid-IR region with previously published data for these pigments. A number of additional overtone and combination bands were also detected that will prove useful in the identification of the pigments in the future. The PAIR technique is a promising and reliable method for the analysis of inorganic pigments, especially since it involves much simpler preparation than is required for conventional IR measurements.

The molecular structures of ethylene and 1,1-dichloro-cyclopropane: a comparison of averaged structures

Abstract The cis to gem distance ratios of hydrogen atom positions for the vibrationally averaged (rα ) structures of ethylene and 1,1-dichlorocyclopropane have been derived from partially oriented nuclear magnetic resonance spectroscopic data. Good agreement with the results obtained from other methods is found for ethylene but for 1,1-dichlorocydopropane the agreement is poor and an alternative structure is proposed for this molecule.

Spin lattice relaxation time studies of ring rotation in cyclopentadienylmetal complexes

Abstract Proton spin lattice relaxation time measurements have been used to determine the barriers to rotation of the cyclopentadienyl ring in the complexes (η 5 -2.4-cyclopentadien- 1-yl)trichlorotitanium(IV). CpTiCl 3 (9.6 kJ mol −1 ): di-η 5 -cyclopentadien-1- ylhexacarbonyldimolybdenum(I). [CpMo(CO) 3 ] 2 (13.9 kJ mol −1 ): and di-η 5 -2.4- cyclopentadien-1-yltitanium(IV) pentasulphide. Cp 2 TiS 5 for which two T 1 processes were observed, with barriers of 8.9 and 7.7 kJ mol −1 assigned to the axial and equatorial rings, respectively.

Analysis of the vibrational spectra, force fields, and molecular structures of pentacarbonyl(methyl)manganese(I) and pentacarbonyl(methyl)rhenium(I)

Abstract Vibrational spectra of CH 3 Mn(CO) 5 and CH 3 Re(CO) 5 have been reinvestigated in particular in the far-IR (500–50 cm −1 ) region. Raman (3500–50 cm −1 ) solid phase (at ambient and liquid nitrogen temperature) and solution (in CH 2 Cl 2 ) polarization data for the Re compound are presented. Based on the available and the present experimental data and the results of the normal coordinate calculations, the assignment of the frequencies has been reviewed and some modifications in the low frequency region have been suggested. Force-field calculations have been performed on the basis of vibrational data of the –CH 3 , –CD 3 , and – 13 CH 3 species of gaseous, dissolved, and solid samples. Density functional theory calculations show that the rotational barrier of the methyl group is less than 0.5 kcal mol −1 . The study of pressure effect on CO and M–CH 3 stretching force constants proved that the stronger CO bonds have a relatively smaller pressure effect than the much weaker M–CH 3 bonds. As a characteristic of pressure sensitivity ‘bond compressibility’ has been introduced.

Raman, FTIR, photoacoustic-FTIR and inelastic neutron scattering spectra of alkaline earth and lanthanide salts of hexahydridoruthenate(II), A2RuH6, (A = Ca, Sr, Eu) and their deuterides.

The vibrational spectra (Raman, photoacoustic and Fourier transform infrared and inelastic neutron scattering) of the calcium, strontium and europium salts of hexahydrido- and hexadeuteridoruthenate(II) have been analyzed. All observed fundamental modes and overtone and combination bands are assigned. Density functional theory calculations of the vibrational frequencies assist in the analysis.

High-Pressure Diamond-Anvil-Cell Micro-Raman Spectra of Mercuric Cyanide, Hg(CN)2, and Cesium Dodecahydroborate, Cs2[B12H12]:

The development of the diamond-anvil cell (DAC) has had a major impact on the field of high-pressure Raman spectroscopy. Despite its success, the DAC still has one drawback, however, in that it requires care and precision in the optical alignment of the cell and other components in the scattering chamber of the Raman spectrometer. The use of the DAC together with a micro-Raman spectrometer should overcome this limitation. Additional advantages of the micro-Raman technique lie in the high collection efficiency of the microscope optics, so that very low laser powers can be used. Low laser powers are necessary to avoid local heating and decomposition of thermally sensitive compounds. Recently, Sharma et al. have used a DAC and microscope combination to examine the stress induced in the diamond anvils under pressure, but, to our knowledge, the method has not been used to study phase transitions in solids.