INVESTIGATION OF STRUCTURE AND MOBILITY OF SILICA BONDED STATIONARY ACRIDINE PHASES BY MEANS OF FLUORESCENCE AND NMR-SPECTROSCOPY

Ligand mobility of silica-based HPLC stationary phases modified by var ious surface coverages of acridine-9-carboxy(N-aminoethylaminopropyl)a mide ligands was investigated by fluorescence spectroscopy, time-resol ved fluorescence anisotropy measurements, as well as solid-state C-13- CP/MAS- and H-1-MAS-NMR spectroscopy, Rotational correlation times, ta u(R), of the bound acridine fluorophore obtained from fluorescence ani sotropy measurements are significantly longer in the hound phase, than in solution, Also, in time-resolved experiments anisotropies do not d ecay to zero. These results are interpreted in terms of wobble-in-cone ligand motion, The mobility of the fluorophore in the presence of liq uid phase correlates strongly with the solubility of the model compoun d acridine-9-carboxy-n-butylamide in the same solvent, In the good sol vent acetonitrile tau(R) = 3.2 ns is found, whereas in methanol, tau(R ) > 80 ns is obtained, NMR measurements of the dry phase yield large l inewidths, cross polarization constants, T-CH, and spin-lattice relaxa tion times, T-1 rho H, shifting around the minimum in the correlation time curve. Both fluorescence and NMR data indicate medium to low liga nd mobility, No difference in the mobilities of alkyl spacer and aroma tic group is observed, probably due to the rigidity of the amide group .