Development of DNP enhanced solid-state NMR techniques for the characterization of functionalized cellulose-based materials

• Applicant: Professor Dr. Torsten Gutmann
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Analytical Chemistry
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 429632542

Functionalized cellulose-based materials have a wide range of applications in the field of microfluidics and sensor technology. Their optimization for special applications requires detailed knowledge of the local structures as well as the surface functionalization and their interaction with fluids. This requires analytic techniques that allow characterization at the molecular level. The objectives of this application are therefore the further development and application of analytic techniques for investigation of functionalized cellulose-based materials. Dynamic nuclear polarization (DNP) combined with solid-state NMR is used as an important analytical tool. DNP enables the selective amplification of signals through suitable sample preparation. Employing selective amplification allows targeting, and possibly identification and characterization of structures in different pore spaces in functionalized cellulose-based materials. Based on the findings of the first funding period of the project, the development of methods in the field of selective amplification of signals in DNP experiments will be continued. For this purpose, defined model systems based on porous silica or polymer membranes with different surface functionalization (hydrophobic, hydrophilic, ionic) are first examined for achievable signal amplification in 1D DNP NMR experiments (13C, 29Si, 15N). Here, the sample preparation is varied employing different solvents/solvent mixtures and radicals, and the resulting signal amplifications are compared. The selective signal amplifications are then correlated with the macroscopic wetting behavior of the samples to obtain insights into structure-property relationships. These are then applied to the characterization of complex functionalized cellulose materials. In a second step, the interaction of solvents or solvent mixtures with the surface functionalization on different substrates is systematically investigated to gain a deeper understanding of the mechanism of polarization transfer in the systems. For this purpose, DNP enhanced 1H-X HETCOR (X=13C, 29Si, 15N) experiments are used, and build-up times Tb as well as relaxation times in the rotating frame T1rho are determined. Finally, the use of 19F-containing molecules as molecular probes for DNP studies of local environments in functionalized materials will be investigated. For this purpose, novel matrices of fluorine-containing ionic liquids as polarization sources for DNP-enhanced 19F solid-state NMR experiments are systematically investigated with respect to their efficiency and their potential for polarization transfer experiments to X nuclei (X=13C, 29Si, 15N). Finally, the findings are applied to the characterization of complex cellulose-based materials at the molecular level.

• DFG Programme: Research Grants