Dear All, Recently I collected a data set to about 3.1 angstrom. Using Xtriage program, I found a pseudo translational symmetry on the c-axis. I noticed that overall diffraction intensity is weak for this dataset. I wonder if there are flaws in the crystal and I have difficulty to solve the structure using phaser. Has anyone seen similar cases and any comments and suggestions? Thanks!
Below is some analysis results from the Xtriage. Cell 102.937, 102.937, 203.059, 90, 90, 90, P422 ----------------------------------------------------------------------------------------- Largest Patterson peak with length larger than 15 Angstrom Frac. coord. : 0.000 0.000 0.350 Distance to origin : 71.133 Height (origin=100) : 48.451 p_value(height) : 8.588e-05 ---------------------------------------------------------- Wilson ratio and moments Acentric reflections <I^2>/<I>^2 :2.568 (untwinned: 2.000; perfect twin 1.500) <F>^2/<F^2> :0.728 (untwinned: 0.785; perfect twin 0.885) <|E^2 - 1|> :0.850 (untwinned: 0.736; perfect twin 0.541) Centric reflections <I^2>/<I>^2 :3.953 (untwinned: 3.000; perfect twin 2.000) <F>^2/<F^2> :0.577 (untwinned: 0.637; perfect twin 0.785) <|E^2 - 1|> :1.111 (untwinned: 0.968; perfect twin 0.736) --------------------------------------------------------------------------------------------------- NZ test (0<=z<1) to detect twinning and possible translational NCS ----------------------------------------------- | Z | Nac_obs | Nac_theo | Nc_obs | Nc_theo | ----------------------------------------------- | 0.0 | 0.000 | 0.000 | 0.000 | 0.000 | | 0.1 | 0.126 | 0.095 | 0.293 | 0.248 | | 0.2 | 0.239 | 0.181 | 0.394 | 0.345 | | 0.3 | 0.327 | 0.259 | 0.471 | 0.419 | | 0.4 | 0.401 | 0.330 | 0.521 | 0.474 | | 0.5 | 0.464 | 0.394 | 0.557 | 0.520 | | 0.6 | 0.518 | 0.451 | 0.597 | 0.561 | | 0.7 | 0.569 | 0.503 | 0.635 | 0.597 | | 0.8 | 0.613 | 0.551 | 0.660 | 0.629 | | 0.9 | 0.648 | 0.593 | 0.683 | 0.657 | | 1.0 | 0.679 | 0.632 | 0.706 | 0.683 | ----------------------------------------------- | Maximum deviation acentric : 0.071 | | Maximum deviation centric : 0.052 | | | | <NZ(obs)-NZ(twinned)>_acentric : +0.054 | | <NZ(obs)-NZ(twinned)>_centric : +0.035 | -------------------------------------------------------------------------------------- L test for acentric data using difference vectors (dh,dk,dl) of the form: (2hp,2kp,3lp) where hp, kp, and lp are random signed integers such that 2 <= |dh| + |dk| + |dl| <= 8 Mean |L| :0.490 (untwinned: 0.500; perfect twin: 0.375) Mean L^2 :0.323 (untwinned: 0.333; perfect twin: 0.200) The distribution of |L| values indicates a twin fraction of 0.00. Note that this estimate is not as reliable as obtained via a Britton plot or H-test if twin laws are available. ------------------------------------------------------------------------------- Twinning and intensity statistics summary (acentric data): Statistics independent of twin laws <I^2>/<I>^2 : 2.568 <F>^2/<F^2> : 0.728 <|E^2-1|> : 0.850 <|L|>, <L^2>: 0.490, 0.323 Multivariate Z score L-test: 0.686 ------------------------------------------------------------------------------- Jiyuan Ke, Ph.D. Research Scientist Van Andel Research Institute 333 Bostwick Ave NE Grand Rapids, MI 49503
