Proton magnetic relaxation in concentrated aqueous solutions of dextran

Abstract

A study was made of proton magnetic relaxation in aqueous solutions of dextran of concentration c = 1–25% and molecular weight (17–500) × 10 3 at frequencies of 20 and 90 Mc/s. Relationships of W(c, M), τ cb ∗ (c, M) and β(c) were obtained, where W is the degree of hydration, τ cb ∗ , the most likely correlation time of “combined” water molecules and β characterizes their width of distribution, according to correlation times. W decreases with all MW values on increasing c> c θ = 1/[ η] θ , where [η] θ is the intrinsic viscosity of dextran under θ conditions. The higher the MW, the higher the W value and this regularity is maintained in the entire concentration range. Dependences of W( c) with different MW values are extrapolated to point W = 0, c = 55±2%; this value of c satisfies the condition cv 0 = 1, where v 0 is the volume of a dextran macromolecular unit. Dependences of τ cb ∗ (c) with different MW may be presented by a generalized curve in coordinates τ cb ∗ = τ cb ∗W and ∼ c = c/ c 0. It has a minimumwith ∼c ≌ 2. It was shown that the motion of “combined” water molecules and macromolecular units of dextran shows a correlation, therefore τ cb ∗ values enable dynamics of the molecular motion of dextran to be evaluated.