Rehydration of CTMA Modified DNA Powders Observed by NMR

The rehydration of salmon sperm deoxyribonucleic acid (DNA) and cetyltrimethylammonium chloride ${\displaystyle \left(C_{19}{H}_{42}ClN\right)}$ 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 (${\displaystyle A_0^h}$ = 0.061 ± 0.004), (ii) a tightly bound water saturating at ${\displaystyle A_1^h}$ = 0.039 ± 0.011, with the hydration time ${\displaystyle t_1^h}$ = (1.04 ± 0.21) h, a loosely bound water fraction (iii) with the hydration time ${\displaystyle t_2^h}$ = (19.1 ± 3.2) h and the contribution progressively increasing with the air humidity. For the hydration at ${\displaystyle p/p_0}$ = 100%, after ${\displaystyle t_0}$ = (152.6 ± 2.5) h of incubation the swelling process begins. The swelling time was ${\displaystyle t_3^h}$ = (12.5 ± 5.4) h, and the swelling amplitude ${\displaystyle A_3^h}$ = 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 Δ M/${\displaystyle m_0}$ = 0.102 ± 0.021. Proton free induction decay is a superposition of the immobilized proton signal (Gaussian, with ${\displaystyle T_{2S}}$* ≈ 30 μs) and two liquid signal components coming from tightly bound (${\displaystyle T_{2L_1}}$* ≈ 100 μs) and loosely bound water fraction with the amplitude proportional to the mass of water added (${\displaystyle T_{2L_2}}$* ≈ 1000 μs).