Solid-state Phosphorus-31 Research Articles

Modifying cellulose with metaphosphoric acid and its efficiency in removing brilliant green dye

In this study, cellulose was chemically modified through the addition of the phosphorylating agent, metaphosphoric acid in order to obtain a new material (MPCel) with higher adsorptive properties than the starting material. Both materials were characterized by infrared spectroscopy, X-ray diffraction, solid-state phosphorus-31 nuclear magnetic resonance spectroscopy and thermogravimetric analysis. Maximal adsorption capacity, at 45°C for pure cellulose, was 90.5mgg−1, at pH=10 and contact time of 40min, with experimental isotherms better adjusted to the Langmuir model. MPCel at the same temperature conditions showed contact time of 10min, pH=10, and maximal adsorption capacity of 150.0mgg−1, being better adjusted to the Temkin model. The kinetic study of both materials followed the pseudo-second-order model. Modification successfully occurred and both adsorbents were shown able to be capable of removing the brilliant green dye, but MPCel was more efficient for purpose, when compared to the pure cellulose.

Interactions between silica nanoparticles and phospholipid membranes

Silica nanoparticles (SNPs) are widely used for biomedical applications. However, their parenteral administration may induce hemolysis. Molecular mechanisms leading to this effect are still controversially discussed. We therefore used a combination of biophysical techniques to investigate the interaction of hemolytic and non-hemolytic SNPs with model phospholipid membranes. MethodsInteraction of SNPs with membranes was studied using a dye-leakage assay, dynamic light scattering (DLS), isothermal titration calorimetry, and solid state nuclear magnetic resonance. Results and discussionThe dye leakage assay revealed that only hemolytic, negatively charged SNPs, but not non-hemolytic positively charged SNPs, destabilized POPC based phospholipid bilayers. Interaction of SNPs with lipid vesicles leading to particle agglomeration was demonstrated by DLS. Isothermal titration calorimetry confirmed the interaction between negatively charged SNPs and phospholipids, which is characterized by an exothermic reaction enthalpy ΔH0SNP of −0.04cal/g at 25°C. Calorimetric titrations at different temperatures revealed a molar heat capacity change of zero. This finding excluded a contribution of electrostatic interactions. Mechanistic insight was provided by solid state phosphorus-31 NMR and deuterium NMR measurements. ConclusionsOur results demonstrate that electrostatic interaction between hemolytic SNPs and model phospholipid membranes is negligible. SNPs induce membrane destabilization and adsorptive processes induced by agglomeration of phospholipid vesicles. The interaction is driven by van der Waals forces at the level of the hydration layer on the vesicles surface.

Structure–property relationship of new polyimide–organically modified silicate–phosphotungstic acid hybrid material system

A new hybrid material system was successfully developed from the combination of polyimide (PI), organically modified silicate (ORMOSIL), and phosphotungstic acid (HPW) from polycondensation reactions and sol–gel process. The materials were obtained in the form of flexible and free-standing films, with the formation of PI and ORMOSIL network confirmed by Fourier transform infrared. Solid-state phosphorus-31 nuclear magnetic resonance evaluated the HPW structure and confirmed its presence and also structural integrity in the materials after synthesis procedure. Thermogravimetric analysis revealed that the materials were thermally stable up to 773 K, and scanning electron microscopy images and X-ray micro-fluorescence mapping showed very good compatibility between the organic and inorganic phases with ORMOSIL improving the HPW dispersion. Furthermore, both ORMOSIL and HPW enhanced the permittivity of the materials from 2.5 to 4.3, compared to the neat PI, appointing them as potential candidates for electric and electronic applications.

Quantitative Evaluation of MDP-Ca Salt and DCPD after Application of an MDP-based One-step Self-etching Adhesive on Enamel and Dentin.

To investigate the effects of an experimental 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-based one-step self-etching adhesive (EX adhesive) applied to enamel and dentin on the production of calcium salt of MDP (MDP-Ca salt) and dicalcium phosphate dehydrate (DCPD) at various periods. The EX adhesive was prepared. Bovine enamel and dentin reactants were prepared by varying the application period of the EX adhesive: 0.5, 1, 5, 30, 60 and 1440 min. Enamel and dentin reactants were analyzed using x-ray diffraction and solid-state phosphorus-31 nuclear magnetic resonance (31P NMR). Curvefitting analyses of corresponding 31P NMR spectra were performed. Enamel and dentin developed several types of MDP-Ca salts and DCPDs with amorphous and crystalline phases throughout the application period. The predominant molecular species of MDP-Ca salt was determined as the monocalcium salt of the MDP monomer. Dentin showed a faster production rate and greater produced amounts of MDP-Ca salt than did enamel, since enamel showed a knee-point in the production rate of the MDP-Ca salt at the application period of 5 min. In contrast, enamel developed greater amounts of DCPD than did dentin and two types of DCPDs with different crystalline phases at application periods > 30 min. The amounts of MDP-Ca salt developed during the 30-s application of the EX adhesive on enamel and dentin were 7.3 times and 21.2 times greater than DCPD, respectively. The MDP-based one-step adhesive yielded several types of MDP-Ca salts and DCPD with an amorphous phase during the 30-s application period on enamel and dentin.

Solid-state phosphorus-31 NMR study of phosphine- and phosphite-substituted cobaloximes

Solid-state 31P NMR spectra of two phosphite- and 17 phosphine-substituted cobaloximes have been acquired under conditions of magic-angle spinning (MAS) and cross polarization (CP) at two applied magnetic fields. In the majority of cases, eight-peak multiplets are observed in the 31P CPMAS NMR spectra, arising from one-bond indirect spin-spin coupling to cobalt (spin S = 7/2). The spacings between adjacent peaks gradually increase or decrease from low to high frequency, due to the presence of residual dipolar coupling between the cobalt and phosphorus nuclei. Values of 1J(59Co,31P) were estimated from the spacing between the central peaks of the eight-peak multiplets. For the phosphine-substituted cobaloximes, values of 1J(59Co,31P) range from 225 to 372 Hz, while in the phosphite derivatives this coupling is considerably larger, from 420 to 615 Hz. From comparison with cobaloximes for which the cobalt nuclear quadrupole coupling interaction is fully characterized, the residual dipolar shift, d, and sense of the 31P NMR spectrum can be utilized to infer the electric field gradient (EFG) orientations at the cobalt nucleus in cobaloximes for which such data are unavailable. The magnitudes of 1J(59Co,31P) and d, as well as the sense of the spectra, are shown to be dependent upon the nature of the axially-substituted ligands. Phosphorus-31 CPMAS NMR spectra of several cobaloximes exhibit broad peak shapes at room temperature. Variable-temperature 31P NMR experiments reveal that the cobalt nucleus is effectively self-decoupled at room temperature; however, splittings due to 1J(59Co,31P) were observed in spectra acquired at low temperatures.Key words: solid-state 31P NMR, 59Co-31P spin-spin coupling constants, 59Co electric field gradient tensors, cobaloximes.

Quantitative solid-state NMR imaging of synthetic calcium phosphate implants.

It is shown that solid-state phosphorus-31 nuclear magnetic resonance imaging can be used to measure quantitatively the mass of hydroxyapatite (HA), a synthetic calcium phosphate used as an orthopedic implant material, in the presence of bone. A three-dimensional projection reconstruction technique was used to produce solid-state images from 998 free induction decays sampled in the presence of a fixed amplitude field gradient whose direction was varied uniformly over the unit sphere. Chemical selection is achieved using T1 contrast, as the synthetic calcium phosphate has a shorter T1 (1.8 sec at 4.7 T) compared with the bone (approximately 15 sec at 4.7 T in vivo, 42 sec ex vivo). Experimental results demonstrating the linear relationship between image intensity and HA density in phantoms containing HA and silicon (IV) oxide, and HA and bone are shown. Chemically pure images of bone mineral and synthetic HA have been computed from images of New Zealand White rabbits acquired in vivo at two different recycle times. The technique can be used to follow noninvasively the resorption and remodeling of calcium phosphate implants in vivo.

Solid-state phosphorus-31 NMR study of phosphine- and phosphite-substituted cobaloximes

Solid-state 31P NMR spectra of two phosphiteand 17 phosphine-substituted cobaloximes have been acquired under conditions of magic-angle spinning (MAS) and cross polarization (CP) at two applied magnetic fields. In the majority of cases, eight-peak multiplets are observed in the 31P CPMAS NMR spectra, arising from one-bond indirect spin–spin coupling to cobalt (spin S = 7/2). The spacings between adjacent peaks gradually increase or decrease from low to high frequency, due to the presence of residual dipolar coupling between the cobalt and phosphorus nuclei. Values of 1J(59Co,31P) were estimated from the spacing between the central peaks of the eight-peak multiplets. For the phosphine-substituted cobaloximes, values of 1J(59Co,31P) range from 225 to 372 Hz, while in the phosphite derivatives this coupling is considerably larger, from 420 to 615 Hz. From comparison with cobaloximes for which the cobalt nuclear quadrupole coupling interaction is fully characterized, the residual dipolar shift, d, and sense of the 31P NMR spectrum can be utilized to infer the electric field gradient (EFG) orientations at the cobalt nucleus in cobaloximes for which such data are unavailable. The magnitudes of 1J(59Co,31P) and d, as well as the sense of the spectra, are shown to be dependent upon the nature of the axially-substituted ligands. Phosphorus-31 CPMAS NMR spectra of several cobaloximes exhibit broad peak shapes at room temperature. Variable-temperature 31P NMR experiments reveal that the cobalt nucleus is effectively self-decoupled at room temperature; however, splittings due to 1J(59Co,31P) were observed in spectra acquired at low temperatures.

Proton induced vesicle fusion and the isothermal L α→H II phase transition of lipid bilayers: a 31P-NMR and titration calorimetry study

The proton-induced isothermal fusion of unilamellar lipid vesicles (Duzgunes et al., Biochemistry 24 (1985) 3091–3098) is compared with the lamellar (L α)→hexagonal (H II) phase transition of multilamellar lipid dispersions. Both lipid systems are composed of 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphoethanolamine (POPE) and oleic acid (OA) at a 7:3 molar ratio. Using solid-state phosphorus-31 nuclear magnetic resonance ( 31P-NMR) it is demonstrated that the multilamellar lipid dispersions are in the bilayer state at physiological pH and undergo a L α→H II phase transition between pH 6.3 and 5.7. This phase transition can also be induced at constant pH by increasing the temperature. The midpoint of the temperature-induced L α→H II transition is T h=56°C (at pH 7.4) and the corresponding transition enthalpy is Δ H=0.7±0.1 kcal/mol as determined with differential scanning calorimetry. Both the proton-induced and the temperature-induced phase transition can be completely inhibited by addition of 30 mol% of 1-palmitoyl-2-hydroxy- sn-glycero-3-phosphocholine (LPC). In a second set of experiments unilamellar vesicles are prepared either by sonication or by extrusion through polycarbonate filters at pH 7.4 and are titrated into buffer at pH 5.7. The proton-induced fusion of the lipid vesicles is monitored with isothermal titration calorimetry, light scattering and fluorescence spectroscopy. The fusion reaction is characterized by an endothermic enthalpy of Δ H=0.5±0.2 kcal/mol (at 28°C). The fusion enthalpy is independent of the vesicle diameter and is only slightly reduced by an increase in temperature to 50°C. Vesicle fusion is accompanied by an increase in light scattering, indicating the formation of larger lipid structures. The transition from unilamellar vesicles to fused lipid structures occurs in the same narrow pH range of 6.3–5.7 as observed for the L α→H II transition of multilamellar dispersions. Vesicle fusion can be inhibited with 30% LPC. The virtually identical set of parameters found for the L α→H II phase transition and the vesicle fusion reaction suggests that vesicle fusion also entails a L α→H II phase transition.

Evaluation of bone mineral density using three-dimensional solid state phosphorus-31 NMR projection imaging.

A solid state magnetic resonance imaging technique is used to measure true three-dimensional mineral density of synthetic hydroxyapatite phantoms and specimens of bone ex vivo. The phosphorus-31 free induction decay at 2.0 T magnetic field strength is sampled following application of a short, hard radiofrequency excitation pulse in the presence of a fixed amplitude magnetic field gradient. Multiple gradient directions covering the unit sphere are used in an efficient spherical polar to Cartesian interpolation and Fourier transform projection reconstruction scheme to image the three-dimensional distribution of phosphorus within the specimen. Using 3-6 Gauss/cm magnetic field gradients, a spatial resolution of 0.2 cm over a field of view of 10 cm is achieved in an imaging time of 20-35 minutes. Comparison of solid state magnetic resonance imaging with dual energy X-ray absorptiometry (DXA), gravimetric analysis, and chemical analysis of calcium and phosphorus demonstrates good quantitative accuracy. Direct measurement of bone mineral by solid state magnetic resonance opens up the possibility of imaging variations in mineral composition as well as density. Advantages of the solid state magnetic resonance technique include avoidance of ionizing radiation; direct measurement of a constituent of the mineral without reliance on assumptions about, or models of, tissue composition; the absence of shielding, beam hardening, or multiple scattering artifacts; and its three-dimensional character. Disadvantages include longer measurement times and lower spatial resolution than DXA and computed tomography, and the inability to scan large areas of the body in a single measurement, although spatial resolution is sufficient to resolve cortical from trabecular bone for the purpose of measuring bone mineral density.

Characterization of Phosphate Sites in Native Ovine, Caprine, and Bovine Casein Micelles and Their Caseinomacropeptides: A Solid-State Phosphorus-31 Nuclear Magnetic Resonance and Sequence and Mass Spectrometric Study

The phosphate sites in native ovine, caprine, and bovine casein micelles have been analyzed using sequence analysis, mass spectrometric analysis, and solid-state 31P nuclear magnetic resonance spectroscopy. Using a combination of S-ethylcysteine derivatization, sequence analysis, and mass spectrometric analysis, the phosphorylation sites of ovine (SerP151 and SerP168) caprine (SerP151 and SerP168), and bovine (SerP149) caseinomacropeptides have been localized. Various solid-state 31P methods using magic angle spinning have been applied to ascertain the local structure and dynamics of the phosphorylated serine residues and the inorganic calcium phosphates within the micelles. Contributions from the phosphorylated serine residues of κ-CN, located in the C-terminal portion of the molecule, to the mobile constituents of the micelles were assigned by comparison with 31P nuclear magnetic resonance spectra of purified caseinomacropeptides from the various species in the dissolved state. Comparison of the 31P magic angle spinning nuclear magnetic resonance spectra of ovine, caprine, and bovine casein micelles indicates that the micelles from these species are very similar but not identical.

Quadrupole−Dipole Effects in Solid-State Phosphorus-31, CP-MAS NMR Spectra of Tertiary Phosphine Substituted Alkyl- and Acyltetracarbonylmanganese(I) Complexes

A series of tertiary phosphine substituted alkyl- and acyltetracarbonylmanganese(I) complexes has been studied by cross-polarization and magic-angle-spinning (CP-MAS), 31P solid-state NMR spectrosc...

Vibrational and solid-state phosphorus-31 nuclear magnetic resonance spectroscopic studies of 1 : 1 complexes of PPh3 with gold(I) halides; crystal structure of [AuBr(PMe3)

The crystal structure of [AuBr(PMe3)], like that of the corresponding chloride, was found to consist of three crystallographically independent molecules linked through weak Au ⋯ Au contacts to form helical chains. The Au ⋯ Au distances [3.648(1), 3.980(2), 3.548(2)Å] are, however, significantly longer than in the chloro- and iodo-complexes, implying that the Au ⋯ Au interaction is weakest in the bromide. The far-IR and Raman spectra of [AuX(PMe3)](X = Cl, Br or I) have been measured, and assignments made for the bands observed. The spectra were analysed to see whether they show any effects of the weak Au ⋯ Au bonding evident in the crystal structures. In particular, the low-wavenumber limit of previously reported Raman spectra for these species has been extended in order to search for ν(Au2) bands. The X = Cl or I compounds show a strong Raman band which can be assigned to the δ(PAuX) deformation, but no ν(Au2) bands were found in the region predicted on the basis of recent assignments for such modes in other complexes which display Au ⋯ Au contacts of similar length. Possible reasons, including an interaction between ν(Au2) and δ(PAuX) modes, are discussed. The solid-state cross polarization magic angle spinning 31P NMR spectra of the chloride and iodide complexes consist of doublets due to the presence of 1J(197Au–31P) coupling. This is a rare observation of spin–spin coupling between the spin I=½31P nucleus and the strongly quadrupole coupled 197Au nucleus, and permits estimation of the 1J(197Au–31P) coupling constants for these complexes.

Action of melittin on the DPPC-cholesterol liquid-ordered phase: a solid state 2H-and 31P-NMR study

Solid-state deuterium and phosphorus-31 nuclear magnetic resonance studies of deuterium-labeled beta--[2,2',3,4,4',6-2H6]-cholesterol and 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine have been undertaken to monitor the action of melittin on model membranes containing 30 mol% cholesterol, both at the molecular and macroscopic level. Cholesterol totally inhibits the toxin-triggered formation of large unilamellar vesicles and strongly restricts the appearance of small discs. The latter remain stable over a wide temperature range (20-60 degrees C) because of an increase in their cholesterol content as the temperature increases. This process is related to a constant disc hydrophobic thickness of approximately 29 A. The system, when not in the form of discs, appears to be composed of very large vesicles on which melittin promotes magnetically induced ellipsoidal deformation. This deformation is the greatest when the maximum of discs is observed. A model to describe both the disc formation and stability is proposed.

Solid State Phosphorus‐31 Magnetic Resonance Imaging of Bone Mineral

Chemically selective solid state phosphorus-31 nuclear magnetic resonance (NMR) imaging of the mineral phase of bone and synthetic calcium phosphate models for bone mineral is demonstrated with microscopy-scale (about 5 mm field of view) apparatus at 6.0 T magnetic field strength. Pixel-by-pixel linear combination of image data from multiple radio frequency (RF) pulse sequences, chosen to develop contrast between chemical constituents of interest in the mineral, generates derived images showing the distribution of individual constituents. The technique combines the noninvasive character of magnetic resonance imaging (MRI) with the ability of solid state NMR spectroscopy to characterize subtle chemical variations in bone mineral, as well as to measure the amount of mineral. These methods are, in principle, extensible to larger dimensional scales suitable for live animal subjects or human limbs.

A Unique Protonated Phosphate Group in Bone Mineral Not Present in Synthetic Calcium Phosphates: Identification by Phosphorus-31 Solid State NMR Spectroscopy

The detailed chemical composition and microstructure of freshly deposited bone mineral, and how these properties change with maturation of the mineral, have been studied intensively and still remain controversial. For example, current analytical technology is inadequate for the unambiguous characterization of the monohydrogen phosphate ions in bone mineral. Using a differential cross polarization/magic angle spinning solid state nuclear magnetic resonance spectroscopy technique, we suppress the dominant orthophosphate (PO 4 -3) signal to reveal the spectra of the minor phosphate constituents. This method depends upon differences in the cross polarization time constants for phosphorus-31 nuclei in protonated and non-protonated phosphate ions. It is now possible for the first time to directly measure both the proportion of acid phosphate (HPO 4 -2) as well as the parameters which characterize its isotropic and anisotropic chemical shift. In bone from three species at several developmental stages, we have found a single type of acid phosphate species, identical in all of the specimens examined. The phosphorus-31 isotropic chemical shift of this acid phosphate group in bone mineral corresponds precisely with that of acid phosphate in octacalcium phosphate, and not with that of brushite. In contrast, the bone acid phosphate anisotropic chemical shift parameters are close to those of brushite, and differ significantly from those of octacalcium phosphate. The orthophosphate resonances of bone mineral, synthetic hydroxyapatite and synthetic octacalcium phosphate share identical chemical isotropic shifts, and similar chemical shift anisotropies. The implication of these results is that the intimate structure of the acid phosphate group in bone mineral is unique, and that none of the common synthetic calcium phosphates accounts well for all of the observed solid state phosphorus-31 NMR properties of bone mineral.

Resolution of individual lipids in mixed phospholipid membranes and specific lipid-cytochrome c interactions by magic-angle spinning solid-state phosphorus-31 NMR.

A model of the inner mitochondrial membrane was constructed with dioleoyphosphatidylcholine (PC), dioleoylphosphatidylethanolamine (PE), and cardiolipin (CL) at a PC:PE:CL molar ratio of 2:2:1, and the interaction of the peripheral membrane protein cytochrome c with this mixed membrane has been investigated by static and magic-angle spinning (MAS) solid-state 31P NMR. The static 31P NMR spectrum of the three-component membrane is a typical broad powder pattern for phospholipids in a bilayer structure, and is a result of three overlapping spectra of each individual phospholipid component in the mixed membrane, with an average effective chemical shift anisotropy of approximately 41 ppm. Using magic-angle spinning NMR methods, three resolved resonances are observed in the narrowed MAS 31P NMR spectrum, each of which has been assigned to each lipid component in the mixed membrane. This allows the investigation of individual phospholipid-protein interactions in multicomponent lipid bilayers. The interaction of cytochrome c with each lipid in a model mitochondrial membrane could now be evaluated. Phosphorus-31 spin-lattice (T1) relaxation times for each lipid phosphate were measured as a function of temperature, in the absence and presence of bound cytochrome c. T1 was not affected for any lipid upon binding of cytochrome c over the temperature range analyzed. However, averaging of the phosphorus-31 chemical shift anisotropy for the cardiolipin component in mixed PC/PE/CL bilayers at lower temperatures ceases to be axially symmetric on binding of cytochrome c, while for PC and PE components the axial symmetry is retained over the temperature interval studied here.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of cholesterol on the polymorphism of dipalmitoylphosphatidylcholine/melittin complexes: an NMR study

In order to get insights into the effects of cholesterol on protein activity, the lytic power of melittin on 1,2-dipalmitoyl- sn-glycero-3- phosphocholine (DPPC)/ cholesterol mixtures was studied using solid-state deuterium and phosphorus-31 nuclear magnetic resonance spectroscopy ( 2H and 31P-NMR). After incubation, melittin disrupts pure DPPC vesicles, leading to the formation of small lipid/peptide complexes below the phase transition temperature ( T m , whereas large bilayer assemblies are reformed above T m ; the transition between these two species is thermally reversible. This study reveals that cholesterol modifies this thermal behavior and that this modulation of the lytic power of melittin is indirect, since it is essentially related to the original effect of the sterol on the thermotropism of pure lipid bilayers. It is known that melittin does not lyse gel phase DPPC bilayers spontaneously. Our study shows that the addition of large amounts of sterol (30 mol%) does not promote the spontaneous lysis at 26°C, despite the increased fluidity of the lipid system. The lysis takes place around 32°C, regardless of the cholesterol concentration. This study also shows that high concentrations of cholesterol ( ≧ 30%) in DPPC bilayer inhibit the lysis. It is proposed that the tight lipid packing due to high cholesterol concentrations prevents the penetration of melittin into the bilayer. When melittin interacts with cholesterol-rich bilayers (30 mol%), the lysis is only partial, and leads to the formation of small cholesterol-depleted particles. Finally, DPPC which bears deuteriated acyl chains was used to determine the infuence of melittin on the orientational order of the lipid chains in the large assemblies. The quadrupolar splittings obtained in the presence of melittin are not considerably different than those obtained in the absence of melittin.

Solid-state phosphorus-31 NMR and structural studies on copper(I) complexes of tetradentate-N2P2 ligands

The new tetradentate-N 2 P 2 ligands 1,10-bis(dimethylphosphino)-4,7-dimethyl-4,7-diazadecane (1,10-mm-N 2 P 2 ), 1,10-bis(diphenylphosphino)-4,7-dimethyl-4,7-diazadecane (1,10-pp-N 2 P 2 ), and 1,10-bis(dicyclohexylphosphino)-4,7-dimethyl-4,7-diazadecane (1,10-cycy-N 2 P 2 ) have been synthesized and characterized in solution by 1 H and 31 P NMR spectroscopy.

Solid-State Phosphorus-31 Nuclear Magnetic Resonance Differentiation of Bone Mineral and Synthetic Apatite Used to Fill Bone Defects

Bioabsorption of synthetic apatite compounds used to promote bone healing and remodeling has been difficult to evaluate. In this study, solid-state phosphorus-31 nuclear magnetic resonance (NMR) has been used to characterize and quantitate bone mineral and a synthetic apatite in order to establish a model for bioabsorption studies. Pulverized solid samples of cortical rabbit bone and a synthetic fluoridated apatite were examined in vitro at variable degrees of hydration. A 9.4 T superconducting spectrometer was used to obtain 31P magic angle spinning NMR spectra and T1 relaxation times. Quantitation was attempted in mixed samples using T1 recovery data. Bone mineral and synthetic apatite could be distinguished by chemical shift and T1 relaxation time in variable hydration states, and were readily differentiated in mixtures by their T1 relaxation time. NMR estimates of relative proportions of components in mixed samples were accurate within 2% of evaluations based on weight. Solid-state 31P NMR therefore provides a suitable method for monitoring the bioabsorption of synthetic apatites.

Solid-state phosphorus-31 NMR and x-ray crystallographic studies of tertiary phosphines and their derivatives

High-resolution, solid-state {sup 31}P NMR spectra of PPh{sub 3} and its oxide, sulfide, and selenide and PCy{sub 3} and its oxide, sulfide, and selenide are presented and interpreted in terms of reported space group information from x-ray crystallographic studies. The spectra of Ph{sub 2}PCH{sub 2}CH{sub 2}PPh{sub 2} and Ph{sub 2}PCH{sub 2}PPh{sub 2} are similarly described. In order to fully interpret the NMR spectra, the x-ray crystal structures of PCy{sub 3} (1), OPCy{sub 3} (2), and SePCy{sub 3} (3) were determined, and the data are presented. 33 refs., 7 figs., 9 tabs.