Solid-State27Al and 29Si Magic-Angle Spinning NMR of Aluminosilicate Gels

The environment of the Al and Si atoms of diphasic and single-phase aluminosilicate gels was determined by solid-state ²⁷Al and ²⁹Si magic-angle spinning nuclear magnetic resonance (MASNMR) spectroscopy, The tetrahedral coordination of Al increased with decreasing Al/Si ratio in single-phase gels but not in diphasic gels. The results showed that ultrahomogeneous mixing on a next-nearest-neighbor level is achieved in single-phase aluminosilicate gels, while in diphasic gels this has successfully been avoided .     

Growth of transition metal oxide crystals by halide vapour hydrolysis

Single crystals of NiO, CoO, FeO, Co₃O₄, and Fe₃O₄ have been epitaxially deposited on MgO single-crystal substrates by the hydrolysis of anhydrous metal bromides in the gaseous phase. All of the crystals were grown at temperatures below 700° C and at a total pressure of less than 25 torr. The deposition was usually complete after approximately 30 min, and the crystals were of uniform thickness with a glassy-clear, smooth surface. Depending on the number of depositions, these crystals can be formed in various thicknesses ranging from approximately 5 m to 1 mm. The crystals were found to deposit in parallel alignment with the (100) cleavage plane of MgO. A substantial increase in chemical purity is observed, and only 10³ to 10⁵ dislocations/cm² were observed in all NiO crystals. A reaction mechanism is proposed which involves: (i) the formation of a hydroxybromide transport phase with fluid properties; (ii) adsorption of the transport phase on the MgO substrate; followed by (iii), the chemical disproportionation-crystallisation of the intermediate phase to the oriented, solid oxide phase.Also associated with the Department of Geochemistry and Mineralogy.     

27Al and29Si magic angle spinning nuclear magnetic resonance spectroscopy of Al-substituted tobermorites

Solid-state²⁷Al and²⁹Si NMR spectroscopy with magic angle spinning (MAS) of samples was used to study several 1.13 nm tobermorites, most of which were deliberately substituted with aluminium.²⁷Al MASNMR clearly showed that aluminium is tetrahedrally co-ordinated in tobermorite structures. In addition two different aluminium environments resonating at 57 and 64 ppm from [Al(H₂O)₆]³⁺ were detected.²⁹Si MASNMR of pure, anomalous tobermorites showed resonances at –85.7 and –95.7 ppm from tetramethylsilane representing chain middle groups (Q²) and branching sites (Q₃), respectively. Anomalous Al-substituted tobermorites, on the other hand, showed two to four resonances representing different silicon environments. One Al-substituted tobermorite showed two resonances at –84.6 and –91.5 ppm which were assigned to Q²(0 Al) and Q³ (1 Al), respectively. In the above tobermorite aluminium appeared to have substituted into branching sites only. Two other Al-substituted tobermorites, however, showed four distinct resonances at –82.0, –85.2, –92.0 and –96.0 and these were assigned to Q² (1 Al), Q² (0 Al), Q³ (1 Al) and Q³ (0 Al), respectively. Thus these two tobermorites showed substitution of aluminium in the chain middle groups as well as branching sites. Another Al-substituted tobermorite which showed a normal thermal behaviour exhibited, as expected, only Q²(0 Al) and Q² (1 Al) sites resonating at –84.7 and –80.2 ppm, respectively. No Q³ sites were detected because few or no branching sites are present in this normal tobermorite. The results reported here clearly demonstrate the usefulness of solid-state²⁷Al and²⁹Si MASNMR spectroscopy for the investigation of short-range order in alumino-silicate materials.     

Diphasic xerogels: I. Ceramic-metal composites

The sol-gel process has been extended to the preparation of new diphasic xerogels leading to new hybrid ceramic-metal materials. The final component compositions were Al₂O₃, SiO₂, ZrO₂ as oxides and Cu, Pt, Sn, and Ni as metals.The xerogels as examined by XRD, SEM, TEM, consisted or a noncrystalline (in a few cases, microcrystalline) ceramic matrix with small metallic islands (5–50 nm) and micro and macro pores. The fine structure of these materials can be controlled by both preparation steps: the gelation parameters and subsequent thermal treatment.     

Folic acid-enhanced synergy for the combination of trimetrexate plus the glycinamide ribonucleotide formyltransferase inhibitor 4-[2-(2-amino-4-oxo-4,6,7,8-tetrahydro-3H-pyrimidino[5,4,6][1,4]thiazin -6-yl)-(S)-ethyl]-2,5-thienoylamino-L-glutamic acid (AG2034): comparison across sensitive and resistant human tumor cell lines

Folic acid (PteGlu)-enhanced intense synergy has been observed between nonpolyglutamylatable dihydrofolate reductase (DHFR) inhibitors and polyglutamylatable inhibitors of other folate-requiring enzymes, such as glycinamide ribonucleotide formyltransferase (GARFT) and thymidylate synthase. Since this phenomenon is potentially therapeutically useful, we explored its universality by examining the combined action of a DHFR inhibitor, trimetrexate (TMQ), with a GARFT inhibitor, 4-[2-(2-amino-4-oxo-4,6,7,8-tetrahydro-3H-pyrimidino[5,4,6][1,4]++ +thiazin-6-yl)-(S)-ethyl]-2,5-thienoylamino-L-glutamic acid (AG2034), in eight human cultured cell lines. Using a 96-well plate cell growth inhibition assay, four ileocecal adenocarcinoma cell lines [HCT-8, HCT-8/DW2 (Tomudex-resistant), HCT-8/DF2 (Tomudex-/FdUrd-resistant), and HCT-8/50 (adapted to 50 nM PteGlu)], three head and neck carcinoma cell lines [A253, FaDu, and Hep-2/500 (FdUrd-resistant)], and a non-small cell lung carcinoma cell line [H460] were treated for 96 hr with TMQ + AG2034 in the presence of 23 or 40 microM PteGlu. Cell growth was measured with the sulforhodamine B assay at the end of this period. Drug interactions were assessed by fitting a 7-parameter model including a synergism parameter, alpha, to data with weighted nonlinear regression. Isobologram analysis was also applied. At 23 microM PteGlu, cells exhibited similar intensities of Loewe synergy for the combination of TMQ + AG2034. Loewe synergy was abolished in HCT-8/50 cells cultured and studied in 50 nM PteGlu. At 40 microM PteGlu, the intensity of the combined action in all cell lines was increased However, the most intense Loewe synergy was seen with HCT-8, HCT-8/DF2, H460, FaDu, A253, and Hep-2/500 cells, whereas the HCT-8/50 subculture showed less of the phenomenon, and PteGlu enhancement was the least with HCT-8/DW2, a subline deficient in folylpolyglutamate synthetase (FPGS). The universality of the PteGlu-enhanced intense synergy phenomenon is suggested. Impaired FPGS activity and low-folate adaptation prior to treatment significantly lessen the degree of PteGlu enhancement.     

Crystal chemistry of the NaZr2(PO4)3, NZP or CTP,structure family

The NaZr₂(PO₄)₃ type structure (abbreviated as NZP or CTP, CaTi₄(PO₄)₆), has emerged as a new family, which has extraordinary technological utility in three fields: fast-ion conductors, radwaste solidification and zero expansion ceramics. NZP or CTP is formed by an extraordinary range of discrete compositions and crystalline solutions. In this paper these compositions are classified according to their crystal chemical substitution scheme, and some uncommon trends in the systematic variation of their lattice parameters are shown. Some of the major trends are explained by correlation with the rotation of polyhedra in the structure.     

ULTRALOW-EXPANSION CERAMICS IN THE SYSTEM NA2O-ZRO2P2O5-SIO2

Compositions in the series Na_1+xZr₂P3-_xSi_xO₁₂ and Na_1+4zZr₂-_zP₃O₁₂, where x = 0≤x≤1 and z=0≤z≤1/2, have thermal expansions that can be controlled (by selecting the composition) to values in the range <10×10_-7 in a temperature regime of a few hundred degrees. The lowest a values were obtained for x ∼0.33 and z∼0.125.     

Microwave-Assisted Synthesis and Sintering of NZP Compounds

We have identified the high microwave susceptibility of the sodium di-hydrogen phosphate monohydrate (NHPM), NH₂PO₄·H₂O. This acid phosphate of sodium can be heated to >900°C when exposed to 2.45 GHz microwave radiation. Using NHPM and microwave energy, a novel single-step synthesis of many important crystalline NZP compounds has been accomplished in a very short time. Interestingly, the combination of microwaves and nonstoichiometric oxide precursors for the preparation of NZP materials is found to reduce the reaction temperatures and enhance the reaction kinetics further. The microwave synthesis method is found to be simple and fast, minimizing the loss of volatile chemical species from the reaction. A microwave-assisted procedure for the rapid sintering of NZP compounds has also been demonstrated. Densification (>97%) has been achieved in <30 min at sintering temperature much lower than normally required in conventional processes. Finer microstructure and better densification are the main advantages of the microwave sintering in this study.