P. Hartmann

The structure of CaO-Na2O-MgO-P2O5 invert glass

Abstract The short and intermediate range order of invert glasses of the system CaO–Na2O–MgO–P2O5 have been examined by using X-ray and neutron diffraction and 31P magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy. The depolymerization of the phosphate chains with decreasing P2O5 mol% content from 39.4 to 28.7 and simultaneous addition of MgO from 0 to 22.8 mol% are quantitatively described by the increase in the concentration of Q1 and Q0 groups. With progressive depolymerization the structure of the glasses becomes more compact indicated by the shortening of the distances between the MeOn (Me stands for the metal ion) polyhedra and between the decreasingly long PO4 chains, which correlates with the increase in packing density, w. These changes have as a consequence that the glass transition temperature, Tg, and the chemical durability continuously increase. Two effects could be a factor contributing to the glass-forming tendency of the high network modifier (>60 mol%) compositions of the invert glasses: (i) The Mg–O co-ordination number, which does not significantly change in dependence on composition, was found to be smaller in the glasses (NMgO∼5) than in the related crystal structures (NMgO=6). (ii) In the pyrophosphate region, a disproportionation of the Q1 species in the glass melt to Q0 and Q2 is indicated by the NMR results. In addition, the concentration of the Q0 and Q1 sites towards orthophosphate composition deviates from the chemical ordering model which can be explained by the occurrence of unreacted MgO. A small angle scattering effect indicating the presence of heterogeneities of electron density between 0.8 and 1.0 nm in diameter is observed for the samples, with the exception of the glass near the pyrophosphate stoichiometry. Additional information on their nature is gained from examinations of heat treated samples.

NMR study of phosphate glasses and glass ceramic structures

Abstract 31P and 27Al magic angle spinning (MAS)-nuclear magnetic resonance (NMR) measurements were used to investigate P2O5CaONa2O(Al2O3) and P2O5CaONa2OMgO(Al2O3) glasses and glass ceramics. The structures of these materials were analyzed as a function of MgO and Al2O3 content. The change of Q[2] group content during heat treatment is discussed. The structure of an unknown complex phosphate phase was investigated.

Measurements of chain length distributions in calcium phosphate glasses using 2D 31P double quantum NMR.

31P double quantum (DQ) NMR is used for improved studies of the structure of phosphate glasses. The common Qn notation of the network forming tetrahedral phosphate units with n bridging oxygen atoms is extended to Qn,jkl indicating the Q type of the bonded adjacent units by the additional superscripts j,k and l. It will be shown that: (i) Q1 units have different isotropic chemical shifts depending on whether they form diphosphate anions in the amorphous state (Q1,1) or end groups of chains (Q1,2) and (ii) that even Q2 units possess different isotropic chemical shifts such that in the DQ dimension Q2,11 can be distinguished from Q2,12 and middle groups of longer chains or rings (Q2,22). Based on this result the opportunity for measuring chain length distributions in the amorphous state is discussed and first results for binary calcium phosphate glasses are presented. The advantages and also the limitations of this novel approach will be discussed.

Structural study of magnesium polyphosphate glasses

Abstract Magnesium polyphosphate glasses with molar ratios, y=n(MgO)/n(P2O5), ranging from 1.0 to 1.9 have been examined by X-ray and neutron scattering and 31P magic angle spinning nuclear magnetic resonance spectroscopy to extract information on their short-range, intermediate-range and submicroscopic structure. The depolymerization of the PO4 chains with rising MgO content is quantitatively described by the increasing concentration of Q1 and Q0 groups determined by NMR. In the pyrophosphate region the Q1 sites disproportionate to Q0 and Q2 groups, whereas there is no disproportionation of the Q2 sites at metaphosphate composition. The shortening of the real-space distances, rm, indicates that the structure of the glasses becomes more compact with progressive depolymerization which is due to the increasing connection of the MgOn polyhedra by sharing the non-bridging oxygen atoms. The Mg–O co-ordination sphere was found to change not significantly in dependence on composition. Heterogeneities about 1 nm in diameter exist in the glasses with MgO content exceeding 46.6 mol% indicated by a weak small angle X-ray scattering.

31P MAS and 2D exchange NMR of crystalline silicon phosphates

Abstract 31P MAS NMR has been used to determine 31P chemical shift tensors of crystalline silicon phosphates. The chemical shift data of five polymorphs of SiP2O7 (hexagonal, tetragonal, cubic and two monoclinic forms) are presented besides those of Si3(PO4)4. Results of 31P 2D exchange NMR on a phase mixture of different silicon diphosphates are shown. This novel approach allows an unambiguous identification of the various phases even in multicomponent mixtures as occurring in ceramics.

New 2D NMR experiments for determining the structure of phosphate glasses: a review

Abstract Double quantum nuclear magnetic resonance measurements exploiting the dipole coupling between the phosphorus atoms as well as a novel two-dimensional exchange experiment using the scalar coupling are described for measuring the connectivities of phosphate tetrahedra in glasses. It is shown that bonding scenarios of up to four connected tetrahedra can be determined in phosphates and phosphate glasses and that estimations of the chain length distributions are possible in glasses having shorter chain fragments. Nuclear magnetic resonance (NMR) is also capable of measuring local order in extruded phosphate glasses using rotorsynchronized excitation in combination with magic angle sample spinning. Finally, we show that the relative orientations of chemical shift tensors can be determined by two-dimensional nuclear magnetic resonance. This determination provides an additional verification of connectivities and can possibly enable access to bonding angle data in the future.

Differentiation, proliferation and adhesion of human neuroblastoma cells after treatment with retinoic acid.

Because of the known property of spontaneous regression in stage IVS of neuroblastoma all attempts are made to elucidate whether differentiation inducers possibly could be applied for neuroblastoma therapy. Here we examined the influence of retinoic acid (RA) in vitro on differentiation, proliferation and adhesion of 10 permanent and 4 primary cell lines as well as of several SCID-mouse tumour transplants. In general, after RA treatment morphologically different cell types which are characteristic for neuroblastoma cells have changed. N (neuronal)-type cells prolonged their neuronal processes, whereas S (epithelial, substrate-adherent, Schwann cell-like)-type cells lost their adherence to substratum and became apoptotic. Additionally, the reactions of all neuroblastoma cell lines with monoclonal antibodies against β-tubulin (for neuronal cells) and glial fibrillary acidic protein (for epithelial cells) were determined. The anti-proliferative effect of all-trans-RA as well as 13-eis-RA was more profound in S-type cells (up to 40% in primary cell lines). To elucidate the role of adhesion molecules during neuronal cell differentiation, we have analysed the adhesion of neuroblastoma cells on poly-D-lysin-precoated plates under RA influence. While N-type cells displayed an increased adhesion, all S-type cell lines as well as all primary cell lines exhibited a reduced adhesion (IMR-5 and IMR-32: p < 0.001; JW, SR and PM: p < 0.05). RA treatment increased predominantly the tested antigens (HCAM, ICAM-1, NCAM, PECAM-1, VCAM-1, cadherin, FGF-R, IGF-R, NGF-R, TGF-β/1, NF200, NF160, NF68, NSE, HLA-ABC) in all cell lines independently of their phenotypes (TGFβ/1: p < 0.001; NF68: p < 0.01; PECAM-1 and NGF-R: p < 0.05). In recultured SCID-mouse-passaged tumour cells antigens were down-regulated (FGF-R: p < 0.01), but increased again after RA influence (TGF-β/1: p < 0.05). In summary, the RA differentiation model demonstrates the possibility to interfere in cell adhesion and to diminish growth potential both in N-type as well as S-type neuroblastoma cells.

Structure and ionic conductivity of sodium titanophosphate glasses

Abstract 50Na 2 O– x TiO 2 –(50− x )P 2 O 5 (with x =0, 5, 10, 15) glasses have been characterized by infrared spectroscopy, 31 P magic angle spinning nuclear magnetic resonance (MAS–NMR) and 31 P double-quantum (DQ) MAS–NMR. MAS–NMR spectra show that phosphate network depolymerization occurs when x increases. Infrared spectra indicate that titanium is incorporated as TiO 6/2 units. DQ MAS–NMR enables us to characterize the Q n , ij phosphate units. Their chemical shifts, measured on DQ MAS–NMR spectra, were used as constraints for the deconvolution of one-dimensional MAS–NMR spectra. It indicates the formation of diphosphate units bonded to sodium and titanium Q 1,1 (Na,Ti) , even at the lowest x value. A structural unit formed by the sequence –Q 2,22 (Na) –Q 2,21 (Na) –Q 1,2 (Na,Ti) –TiO 6/2 –Q 1,1 (Na,Ti) –Q 1,1 (Na,Ti) –TiO 6/2 can be proposed. The increase of conductivity and glass transition temperature with x is discussed from this structural model.

Off-angle correlation spectroscopy applied to spin-1/2 and quadrupolar nuclei.

A two-dimensional correlation experiment is described, in which homonuclear dipolar couplings are used to realize through-space magnetization exchange on spin-1/2 (31P) and on quadrupolar nuclei (23Na and 11B). In the detection period, Magic Angle Spinning is applied to enhance resolution, and the dipole couplings are re-introduced in the mixing period by spinning off the Magic Angle. The dependency of the exchange rates on the mixing time and the spinning angle is investigated. The influence of strong spin-locking during mixing is discussed, and shown in the spin-1/2 case to remove the dependence on chemical shift offset effects. For quadrupolar spins, the experiment yields information on the relative tensor orientations of the coupled quadrupoles. Applications to crystalline sodium aluminum diphosphate, sodium sulphite, and potassium borate glasses are shown.

Nuclear magnetic resonance investigations of aluminum containing phosphate glass-ceramics

Abstract Glasses and glass-ceramics of the system P 2 O 5 –CaO–Na 2 O–{Al 2 O 3 } have been studied by 31 P and 27 Al and two-dimensional correlation nuclear magnetic resonance. The basic glasses have a chain-like structure including amorphous diphosphate and longer chains having at least four units. The Q 1 /Q 2 group ratios depend on both the content of network-modifying oxides and aluminum oxide. Crystallization of the glasses involves the conversion of glassy metaphosphate sites into crystalline pyro- and orthophosphate sites. 27 Al correlation experiments do not detect the presence of Al–O–Al bonds in the glasses and in the glass-ceramics.