Kinetics of H-C multiple-contact cross-polarization as a powerful tool to determine the structure and dynamics of complex materials: application to graphene oxide.

Date publication

juin 2020

Journal

Physical chemistry chemical physics : PCCP

Auteurs

Membres identifiés du Cancéropôle Est :
Dr BIANCO Alberto

Tous les auteurs :
Raya J, Bianco A, Hirschinger J

Lien Pubmed

https://www.ncbi.nlm.nih.gov/pubmed/32432267

Résumé

Hartmann-Hahn cross-polarization (HHCP) is the most widely used solid-state NMR technique to enhance the magnetization of dilute spins from abundant spins. Furthermore, as the kinetics of CP depends on dipolar interactions, it contains valuable information on molecular structure and dynamics. In this work, analytical solutions are derived for the kinetics of HHCP and multiple-contact CP (MC-CP) using both classical and non-classical spin-coupling models including the effects of molecular dynamics and several H, C relaxation and H-C CP experiments are performed in graphene oxide (GO). HHCP is found to be inefficient in our GO sample due to very fast H T relaxation. By contrast, the MC-CP technique which alleviates most of the magnetization loss by H T relaxation leads to a much larger polarization transfer efficiency reducing the measuring time by an order of magnitude. A detailed analysis of the HHCP and MC-CP kinetics indicates the existence of at least two different kinds of hydroxyl (C-OH) functional groups in GO, the major fraction (∼90%) of these groups being in the unusual "slow CP regime" in which the rate of H T relaxation is fast compared to the rate of cross-polarization. This C signal component is attributed to mobile C-OH groups interacting preferentially with fast-relaxing water molecules while the remaining carbons (∼10%) in the usual "fast CP regime" are assigned to C-OH groups involved in hydrogen bonding with neighboring hydroxyl and/or epoxy groups.

Référence

Phys Chem Chem Phys. 2020 Jun 7;22(21):12209-12227