A . K . Kleppe
نویسندگان
چکیده
Raman spectra of a single-crystal fragment of hydrous c-Mg2SiO4, synthesized in a multianvil press, have been measured in a diamond-anvil cell with helium as pressure-transmitting medium to 56.5 GPa at room temperature. All five characteristic spinel Raman modes shift continuously up to the highest pressure, showing no evidence for a major change in the crystal structure despite compression well beyond the stability field of ringwoodite in terms of pressure. At pressures above 30 GPa a new mode on the low-frequency site of the two silicate-stretching modes is clearly identifiable, indicating a modification in the spinel structure which is reversible on pressure release. The frequency of the new mode (802 cm 1 extrapolated to 1 bar) suggests the presence of Si–O–Si linkages and/or a partial increase in the coordination of Si. Direct determination of the subtle structural change causing the new Raman mode would require high-pressure, single-crystal synchrotron X-ray diffraction experiments. The Raman modes of hydrous and anhydrous Mg-end-member ringwoodite are nearly identical up to 20 GPa, suggesting that protonation has only minor effect on the lattice dynamics over the entire pressure stability range for ringwoodite in the mantle.
منابع مشابه
Total synthesis of the structural gene for the precursor of a tyrosine suppressor transfer RNA from Escherichia coli. 11. Enzymatic joining to form the total DNA duplex.
The DNA duplex corresponding to the entire length (126 nucleotides) of the precursor for an Escherichia coli tyrosine tRNA has been synthesized. Duplex [I] (Sekiya, T., Besmer, P., Takeya, T., and Khorana, H. G.(1976) J. Biol. Chem. 251, 634-641), corresponding to the nucleotide sequence 1-26, containing single-stranded ends and carrying one appropriately labeled 5'-phosphate group, was joined ...
متن کاملPreparation and separation of d(pT)-10-n oligonucleotides.
A series of oligomers having the general formula d(pT)-10-n, n varying from 2 to 20, has been prepared by enzymatic joining of d(pT)-10, annealed on poly dA, employing T-4 polynucleotide ligase. The oligomers could be separated on 8 or 12% polyacrylamide gels. Such oligomers may prove useful as molecular weight markers and initiators for various polymerases.
متن کاملPreparations and properties of ribonucleic acid polymerase from Acinetobacter calcoaceticus.
Deoxyribonucleic acid (DNA)-dependent ribonucleic acid (RNA) polymerase (EC 2.7.7.6) from Acinetobacter calcoaceticus was purified to apparent homogeneity and its properties were compared with those of the Escherichia coli B enzyme. The molecular weights of the two native active enzymes as well as their alpha and beta subunits appeared to be similar. No subunit corresponding to that of sigma fr...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
دوره شماره
صفحات -
تاریخ انتشار 2002