ABSTRACT
Synthetic alpha - and beta -Hopeite, two polymorphs of zinc phosphate tetrahydrates (ZPT) have been synthesized by hydrothermal crystallization from aqueous solution at 20 degrees C and 90 degrees C respectively. Aside from their sub-title crystallographic differences originating from a unique hydrogen bonding pattern, their thermodynamic interrelation has been thoroughfully investigated by means of X-Ray diffraction (XRD) and differential scanning calorimetry (DSC), combined with thermogravimetry (TGA-MS). Using a new heterogeneous step-reaction approach, the kinetics of dehydration of the two forms of ZPT was studied and their corresponding transition temperature determined. Low temperature DRIFT, FT-Raman and (1)H, (31)P MAS-NMR reveal an oriented distortion of the zinc phosphate tetrahedra, due to a characteristic hydrogen bonding pattern and in accordance with the molecular tetrahedral linkage scheme of the phosphate groups. Biogenic Hydroxyapatite (HAP) and one of its metastable precursors, a calcium dihydrogen phosphate dihydrate (DCPD) or Brushite were also obtained and used to underline the resulting variations of chemical reactivity in zinc phosphates.
Subject(s)
Biocompatible Materials/chemistry , Bone Substitutes/chemistry , Phosphates/chemistry , Zinc Compounds/chemistry , Calcium Phosphates/chemistry , Calorimetry, Differential Scanning , Crystallization , Crystallography, X-Ray , Durapatite/chemistry , Humans , Hydrogen Bonding , Kinetics , Magnetic Resonance Spectroscopy , Models, Molecular , Spectroscopy, Fourier Transform Infrared , Spectrum Analysis, Raman , Temperature , Thermodynamics , Thermogravimetry , Water/chemistry , X-Ray DiffractionABSTRACT
The microwave rotational spectrum of the p-fluorotoluene-argon van der Waals complex was analyzed with a molecular beam Fourier transform microwave spectrometer. In the frequency splitting of molecular transitions caused by the internal rotation of the methyl group with respect to the aromatic ring is contained the structure and barrier information. Elucidation is reduced by the analysis of internal rotors direction with respect to the principal axis system of the complex the number of possible solutions in the structure. An rs and r0 structure of the complex was calculated from these data. The argon is located 3.541(1) Å above the aromatic ring. By forming the complex, the barrier height of internal rotation is changed. An additional V3 term in the potential function occurs in the complex because the molecular symmetry of the p-fluorotoluene, containing a V6 but no V3 term, is reduced by the argon. For assumed V6 = 144.79(19) GHz or 57.777(76) J/mol, V3 is found to equal 552.0(10) GHz or 220.31(40) J/mol. Copyright 1999 Academic Press.
