Initial Phases of DNA Rehydration by NMR and Sorption Isotherm

Abstract

The initial stages of rehydration of salmon sperm deoxyribonucleic acid (DNA) lyophilizates were observed using hydration kinetics, sorption isotherm, and high power proton relaxometry (at 30 MHz). The hydration kinetics reveals (i) a very tightly bound water not removed by incubation over silica gel (A0 = 0.057±0.010), (ii) a tightly bound water [saturating at A1 = 0.149± 0.007, hydration time t1 = (0.27± 0.08) h], a tightly bound water (iii) [saturating at A2 = 0.694± 0.039, with the hydration time t2 = (9.8± 3.2) h], and (iv) a loosely bound water fraction for the samples hydrated at p/p0 ≥ 76% [with the hydration time t3 = (44± 14) h, and the contribution progressively increasing with the air humidity]. For the hydration at p/p0 = 100%, after t0 = (244 ± 22) h of incubation the swelling process begins. The amount of additional water uptake at swelling depended on the macrostructure of the sample. Sorption isotherm is sigmoidal in form and is fitted well by the Dent model with the mass of water saturating primary binding sites ∆M/m0 = 0.114. Proton free induction decay is a superposition of the immobilized proton signal (Gaussian, with T ∗ 2S ≈ 20 μs) and two liquid signal components coming from tightly bound (T ∗ 2L1 ≈ 100 μs, with the mass saturating at ∆m/m0 = 0.111 ± 0.044) and loosely bound water fraction (with the amplitude proportional to the mass of water added).