Rehydration of CTMA modified DNA powders observed by NMR

Abstract

The rehydration of salmon sperm deoxyribonucleic acid (DNA) and cetyltrimethylammonium chloride (C19H42ClN) complexes was observed using hydration kinetics, sorption isotherm, and high power proton relaxometry (at 30 MHz). The hydration kinetics shows (i) a very tightly bound water not removed by incubation over silica gel (Ah0 = 0.061 ± 0.004), (ii) a tightly bound water saturating at A h1 = 0.039 ± 0.011, with the hydration time t h1 = (1.04 ±0.21) h, a loosely bound water fraction (iii) with the hydration time th2 = (19.1 ±3.2) h and the contribution progressively increasing with the air humidity. For the hydration at p/p0 = 100%, after t0 = (152.6 ± 2.5) h of incubation the swelling process begins. The swelling time was t h3 = (12.5 ± 5.4) h, and the swelling amplitude Ah3 = 0.140 ±0.016. The sorption isotherm is sigmoidal in form and is fitted by the Dent model with the mass of water saturating primary binding sites ΔM/m0 = 0.102 ± 0.021. Proton free induction decay is a superposition of the immobilized proton signal (Gaussian, with T2S* ≈ 30 μs) and two liquid signal components coming from tightly bound (T2L1* ≈ 100 μs) and loosely bound water fraction with the amplitude proportional to the mass of water added (T2L2* ≈ 1000 μs).