Open AccessAnomalous dispersion of sulfur in quinidine sulfate, (C 20 H 25 N 2 O 2 ) 2 SO 4 ·2H 2 O: Implications for structure analysis
Author(s) -
Isabella L. Karle,
Jerome Karle
Publication year - 1981
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.78.10.5938
Subject(s) - crystallography , chemistry , quinuclidine , ion , absorption (acoustics) , molecule , sulfur , dispersion (optics) , stereochemistry , materials science , physics , organic chemistry , optics , composite material
A Patterson-type map computed with Bijvoet differences squared as coefficients, (ǀF h ǀ - ǀF -h ǀ)2 , as recommended by Rossmann, readily yielded the position of the S atom. The experiment was performed with Cu Kα radiation which is far from the absorption edge for sulfur. The coordinates of the remainder of the 54C, N, and O atoms were derived by means of partial structure development by use of the tangent formula. The latter was used only to effect phase extension, not phase refinement. A main purpose of this experiment was to reaffirm, as first shown in the investigation of the protein crambin by Hendrickson and Teeter, that, in the presence of a large number of lighter atoms, sulfur atoms can be located by use of anomalous dispersion at wave-lengths far from the absorption edge. The space group is P21 witha = 26.718(8) Å,b = 6.987(3) Å,c = 10.857(6) Å, and β = 99.51(4)° and contains two quinidyl ions, one sulfate ion, and two water molecules per asymmetric unit. The conformations of the two independent quinidyl ions differ mainly in the torsional angle of the bond between the vinyl side chain and the quinuclidine moiety. TheR factor is 4.9% for all 2869 data.