PubMed · 422384
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
G H Zeman, G I Snyder. 1979. Neutron dose precision using LiF TLD.. https://pubmed.ncbi.nlm.nih.gov/422384/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
The synthetic analog of antamanide in which all four phenylalanyl residues are hydrogenated to cyclohexylalanyl (Cha) residues, cyclic(Val-Pro-Pro-Ala-Cha-Cha-Pro-Pro-Cha-Cha), has a complete loss of antitoxic potency despite its ability to form ion complexes in the same manner as antamanide. The conformation of Li+.perhydroantamanide has been established in the present paper by x-ray diffraction analysis of a single crystal. The backbone encapsulates a Li+ ion in an almost identical manner as in Li+ antamanide. However, in Li+ antamanide the four phenyl groups are folded against the globular backbone, thus providing a hydrophobic surface for the complex, whereas in Li+ X perhydroantamanide the four cyclohexyl moieties are extended away from the folded backbone, resulting in the exposure of large portions of the polar backbone to the environment. As a consequence, four NH groups form hydrogen bonds with Br- ions, three C--O groups form hydrogen bonds with water molecules, and one C--O group makes a ligand to an additional external Li+ ion. The internal Li+ ion is pentacoordinated, whereas the external Li+ ion is tetracoordinated. The large change of the hydrophobicity around the midsection of the perhydroantamanide complex may be related to the biological inactivity. The content per asymmetric unit of the crystal is C64H102N10O10 X 2Li+ X 4H2O X 2CH3CN.2Br- in space group P2(1)2(1)2(1) with a = 21.740(7), b = 21.566(4), and c = 17.361(4) A. The agreement factor is 8.2% for 5135 data.
The recoil tritium reactions were studied with lithium beta-phenylpropionate having both the aromatic and aliphatic C-H bonds in the molecule, mainly in terms of the moderator effect on the intramolecular tritium distribution. Recoil tritium atoms were produced by the 6Li(n,alpha)3H reaction. Water molecules were used as the moderator. The tritium activity of the ethylene group represented relative to that of the corresponding ring assumed as a standard (= 100) is 30 in the moderator-free system and is reduced to 13 in the moderated system in which the H2O/beta-PhC2H4CO2Li mole ratio is 328. In the ring, the tritium distribution shows a slight ortho- and para-orientation in the moderator-free system and the selectivity is pronounced when the H2O/beta-PhC2H4CO2Li mole ratio is large. The data show that the aromatic ring tritiation in the moderated system is given by increasing contribution of the reactions of tritium atoms having lower energy than the threshold energy of the ethylene group tritiation.
CNDO/2 calculations are reported for dilithium and disodium porphyrin. The total energy is calculated as a function of the metal-ring distance for symmetrical (D4h) structures. For dilithium porphyrin, the equilibrium metal-ring distance is 0.87 A and the metal-metal vibrational frequency is 123 cm-1. For disodium porphyrin, the distance is 1.64 A and the frequency is 77 cm -1. Little mixing of metal and porphyrin orbitals takes place; the two lowest unoccupied and the two highest occupied MOs hardly differ from those in porphyrin, but lower MOs are considerably rearranged.