Crystallographic R-factor

Brunger AT, Kuriyan J, Karpins M. Crystallographic r-factor refinement by molecular dynamics. Science 1987 235 458-60... 

The relationship to the conventional crystallographic R factor is obvious. A value for R aroimd 20-25% is a good indicator of phase consistency. 

A. T. Stringer, J. Kutiyan, and M. Karplus. Crystallographic R factor refinement by molecular dynamics. Science 235 458-462 (1987). 

Hamilton, W. C. Significance tests on the crystallographic R-factor. Acta Cryst. 18, 502-510 (1965). 

Briinger, A. T., Kuriyan, J. and Kamlus, M. (1987) Crystallographic R Factor Refinement by Molecular Dynamics, Science 235, 458-460. 

Only structures of high precision were included on the basis that either (a) the crystallographic R factor was < 0.07 and the reported mean estimated standard deviation (e.s.d.) of the C - C bond lengths was < 0.030 A (corresponds to AS flag = 1, 2 or 3 in CSD), or (b) the crystallographic R factor was < 0.05 and the mean e.s.d. for C - C bonds was not available in the data base (AS = 0 in CSD). Where the structure of a given compound had been determined more than once within the limits of (i)-(v), then only the most precise determination was used. For Table A.l, additional restrictions were imposed such that structures with disorder were rejected, as were structures with reported mean e.s.d. of the C-C bond lengths >0.010 A. 

Brunger A T, J Kuriyan and M Karplus 1987. Crystallographic R-factor Refinement by Molecular D5mamics. Science 235 458-460. ... 

Crystals of the asparagine 166 and lysine 166 variants that are isomorphous with the crystal of the native enzyme have been grown. Diffraction data were collected to 2.25 and 2.0 A resolution and three-dimensional models have been determined and refined to a crystallographic R-factor of 0.16 and 0.17 for the lysine and asparagine 166 variants, respectively. 

All of these factors tend to lead to more accurate structure factors, better internal agreement, and ultimately to lower crystallographic R factors and somewhat more precise atomic parameters, hence the best accuracy for neutron single-crystal structure determination. Constant wavelength single-crystal diffraction is the method of choice if ultimate precision is required in an individual structure determination. The high-flux reactor sources are currently favored for larger unit cells or smaller crystals. 

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