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T F Koetzle

Publications and source records attributed to T F Koetzle.

10 recordsLinked to original sources
PubMed1989

Structure of cycloguanil hydrochloride by neutron diffraction.

4,6-Diamino-1-(p-chlorophenyl)-1,2-dihydro-2,2-dimethyl-s-triazine hydrochloride, C11H15-CIN5+.Cl-, Mr = 288.20, monoclinic, P21/c, a = 8.783 (2), b = 10.267 (2), c = 17.234 (3) A, beta = 115.72 (1) degrees, U = 1400.1 (5) A3, Z = 4, Dx = 1.337 Mg m-3, lambda = 1.15882 (7) A for unit-cell determination and 1.04702 (7) A for collection of intensity data, mu = 0.191 mm-1, T = 15.0 (5) K, final R(F2) = 0.050 and wR(F2) = 0.063 for 3099 independent reflections. Five atoms of the triazine ring are nearly coplanar. The sixth, the quaternary C(2), is displaced from this plane (P1) so that the bond to one of its methyl substituents is nearly perpendicular to P1 while the other methyl substituent lies almost in the plane. The chlorophenyl-ring plane is nearly perpendicular to P1. The heterocycles form cyclic dimers via hydrogen bonds from the 6-amino group to ring atom N(5) of an adjacent molecule. All other N-H units are hydrogen bonded to the Cl- counter ion. The ring is protonated at position N(3).

Chemical Phenomena↗
PubMed1988

Determination of the absolute configuration of (-)-(2R)-succinic-2-d acid by neutron diffraction study: unambiguous proof of the absolute stereochemistry of the NAD+/NADH interconversion.

The absolute configuration of the CHD group (D = deuterium) in (-)-(2R)-succinic-2-d acid, as prepared from (-)-(2S,3R)-malic-3-d acid, has been shown unambiguously to be R by the technique of single-crystal neutron diffraction. The optically active cation (+)-phenylethylammonium was used as the chiral reference. The structure of [C6H5CH3CHNH3]+[HOOCCH2CHDCOO]- has been studied with x-ray diffraction at room temperature and neutron diffraction at 100 K. Crystal data from the neutron diffraction analysis of the phenylethylammonium salt of the title compound at 100 K: space group P21; a = 8.407(2) A, b = 8.300(4) A, c = 8.614(2) A, beta = 91.20(3) degrees; unit cell volume = 600.9(3) A3, zeta = 2 (numbers in parentheses are the estimated standard deviations). Final agreement factors are R(F2) = 0.0355 and R(wF2) = 0.0457 for 1690 independent neutron reflections and 297 parameters varied. The result confirms the stereochemistry of the malate/succinate transformation, as well as the NAD+/NADH interconversion, and demonstrates the usefulness of the single-crystal neutron diffraction method for determining the absolute configuration of molecules having a chiral monodeuteriomethylene group.

Chemical Phenomena↗
PubMed1977

The Protein Data Bank. A computer-based archival file for macromolecular structures.

The Protein Data Bank is a computer-based archival file for macromolecular structures. The Bank stores in a uniform format atomic co-ordinates and partial bond connectivities, as derived from crystallographic studies. Text included in each data entry gives pertinent information for the structure at hand (e.g. species from which the molecule has been obtained, resolution of diffraction data, literature citations and specifications of secondary structure). In addition to atomic co-ordinates and connectivities, the Protein Data Bank stores structure factors and phases, although these latter data are not placed in any uniform format. Input of data to the Bank and general maintenance functions are carried out at Brookhaven National Laboratory. All data stored in the Bank are available on magnetic tape for public distribution, from Brookhaven (to laboratories in the Americas), Tokyo (Japan), and Cambridge (Europe and worldwide). A master file is maintained at Brookhaven and duplicate copies are stored in Cambridge and Tokyo. In the future, it is hoped to expand the scope of the Protein Data Bank to make available co-ordinates for standard structural types (e.g. alpha-helix, RNA double-stranded helix) and representative computer programs of utility in the study and interpretation of macromolecular structures.

Computers↗