Three-isotopic-substitutions method in small-angle neutron scattering

Abstract

A new method is proposed for the study of the structure and arrangement of components in multi‐component particles. In this method the difference between the scattering curve of a solution containing two types of structurally identical particles differing only in degree of deuteration and the scattering curve of a solution containing particles of a third type deuterated to an intermediate degree is considered. This difference scattering curve is distinguished only by a numerical multiplier from the `vacuum' scattering curve of the particle in which the scattering density is equal to the difference between the scattering densities of particles of the first and second types. This means that components protonated (deuterated) to the same degree within particles of the three types considered do not contribute to the difference scattering curve and, consequently, are `invisible' to neutrons. The difference scattering curve depends neither on the solvent isotopic content nor on interparticle interference and particle association. Possible applications of the method to a study of the structure of macromolecules in solution are discussed.

Experimental verification of the triple isotopic substitution method in small-angle neutron scattering

“…The principal equations of the method were derived by Pavlov & Serdyuk (1987) and can be written as follows:…”

“…The principal equations were analysed in detail in previous papers (Pavlov & Serdyuk, 1987;Serdyuk & Pavlov, 1988). The following can be predicted.…”

“…Recently, we proposed a new approach which could be considered as a fourth experimental approach in SANS (Pavlov & Serdyuk, 1987;Serdyuk & Pavlov, 1988). In this method, particles of three different types are used and the scattering is measured from two solutions: one contains a mixture of protonated and deuterated particles and one is a solution containing intermediately deuterated particles in the same concentration.…”

“…The theory predicts that at the defined fraction of deuterated particles in the first solution the difference scattering curve (solution I minus solution II) would differ only by a numerical multiplier from the scattering curve of a particle whose scattering density is equal to the difference of scattering densities between the deuterated and protonated particles (Pavlov & Serdyuk, 1987). It follows that a particle component of constant scattering density in the particles of the three different types will not contribute to the difference scattering curve and thus will be 'invisible'.…”

Neutron diffraction intensities from arrays of isotopically substituted particles in an invisible matrix

“…For complexes (or aggregates of complexes) containing two smaller isotopically substituted particles, Hoppe (1973) pointed out that the correct intrapair distance can be determined by making the measurements on the appropriate mixtures of unsubstituted, singly substituted and doubly substituted proteins. In order to obtain undistorted in situ solution scattering curves for single particles embedded in a matrix, a novel triple isotopic substitution method has recently been devised for eliminating both interparticle interference effects and fluctuation effects (Pavlov & Serdyuk, 1987;Serdyuk & Paviov, 1988;Pavlov et al, 1991). This method utilizes scattering measurements from a mixture of complexes bearing both protonated and deuterated type-B particles and from a solution of substituted complexes bearing only particles having intermediate deuteration.…”