Solid-state NMR studies of CRYSMEB-based polymers molecular dynamics

Cyclodextrins-based three dimensional polymers recently received great attention because of their peculiar properties of swelling, absorption/inclusion of chemicals, and release of small drug molecules[1]. These materials find applications in pharmaceutical industry, analytical chemistry and food industry. In particular, soluble polymers of a partially secondary rim methylated beta-CD, commonly referred to as CRYSMEB, have been synthesized with imprinting technique using toluene as guest molecule. We present a phisico-chemical investigation of these materials using solid state 13C{1H} cross-polarization/magic angle spinning NMR spectroscopy (CP/MAS) techniques. Three CRYSMEB-based polymers, synthesized with different amount of toluene, have been studied performing variable contact time (CP/MAS) experiments. The growth of the spin magnetization, in the "fast CP regime" is governed by the cross-relaxation time, TCH related to the size of the C-H dipolar couplings, while its decay is governed by the rate of T1rho (1H) relaxation. The relaxation parameters TCH and T1rho have been determined by fitting the experimental curves for the three polymers. Most of the 13C species revealed short TCH values indicating highly efficient magnetization transfer. A comparison between the three samples show that changing the amount of toluene, the TCH values change for all the carbon atoms implying that the dynamic of the system can be modulated by the amount of the guest molecule. On the other hand, the T1rho values are similar for the three samples, suggesting that the chemical environment experienced by each carbon atom is similar for all the samples.