FIGURE 2.

Canonical SAXS scattering equations. A) Guinier approximation describing the linear relationship between the observed scattering intensities, I(q), and scattering angle, q. The approximation determines the radius-of-gyration, R_g, and scattering at q=0, I(0). I(0) is directly related to the particle’s volume, V, and electron density contrast, Δρ. B) Kratky plot of scattering data illustrating changes in the behavior of the curve for folded (sphere), partially folded (sphere-random coil) and completely unfolded particles (random coil). For a folded particle, the integrated area under the curve determines the Porod invariant, Q, and is scaled by concentration, c. C) SAXS derived structural parameters. The ratio of I(0) to Q determines the volume of the scattering particle sometimes known as the Porod volume, V_P. Application of the Porod-Debye law determines the surface area, S, of the scattering particle that is scaled by concentration and Δρ that can be normalized using Q.