Index

Protein Data Bank exchange dictionary (pdbx) version 1.0521

_pdbx_soln_scatter.mean_guiner_radius

Definition:

   The mean radius of structural elongation of the sample.
     In a given solute-solvent contrast, the radius of gyration
     R_G is a measure of structural elongation if the internal
     inhomogeneity of scattering densities has no effect. Guiner 
     analysis at low Q gives the R_G and the forward scattering at 
     zero angle I(0).

         lnl(Q) = lnl(0) - R_G^2Q^2/3

     where 
   Q = 4(pi)sin(theta/lamda)
   2theta = scattering angle
   lamda = wavelength

     The above expression is valid in a QR_G range for extended 
     rod-like particles. The relative I(0)/c values ( where
      c = sample concentration) for sample measurements in a
     constant buffer for a single sample data session, gives the
     relative masses of the protein(s) studied when referenced
     against a standard.

     see: O.Glatter & O.Kratky, (1982). Editors of "Small angle
          X-ray Scattering, Academic Press, New York.
          O.Kratky. (1963). X-ray small angle scattering with
          substances of biological interest in diluted solutions.
          Prog. Biophys. Chem., 13, 105-173.

          G.D.Wignall & F.S.Bates, (1987). The small-angle approximation
          of X-ray and neutron scatter from rigid rods of non-uniform
          cross section and finite length. J.Appl. Crystallog., 18, 452-460.

     If the structure is elongated, the mean radius of gyration
     of the cross-sectional structure R_XS  and the mean cross sectional
     intensity at zero angle [I(Q).Q]_Q->0 is obtained from

        ln[I(Q).Q] = ln[l(Q).(Q)]_Q->0 - ((R_XS)^2Q^2)/2

Type: float

Mandatory item: no

Related item: _pdbx_soln_scatter.mean_guiner_radius_esd (associated_esd)

Category: pdbx_soln_scatter