C-13-H-1 HSQC experiment of probe molecules aligned in thermotropic liquid crystals: Sensitivity and resolution enhancement in the indirect dimension

摘要

The spectra of molecules oriented in liquid crystalline media are dominated by partially averaged dipolar couplings. In the C-13-H-1 HSQC, due to the inefficient hetero-nuclear dipolar decoupling in the indirect dimension, normally carried out by using a pi pulse, there is a considerable loss of resolution. Furthermore, in such strongly orienting media the H-1-H-1 and C-13-H-1 dipolar couplings leads to fast dephasing of transverse magnetization causing inefficient polarization transfer and hence the loss of sensitivity in the indirect dimension. In this study we have carried out C-13-H-1 HSQC experiment with efficient polarization transfer from H-1 to C-13 for molecules aligned in liquid crystalline media. The homonuclear dipolar decoupling using FFLG during the INEPT transfer delays and also during evolution period combined with the pi pulse heteronuclear decoupling in the ti period has been applied. The studies showed a significant reduction in partially averaged dipolar couplings and thereby enhancement in the resolution and sensitivity in the indirect dimension. This has been demonstrated on pyridazine and pyrimidine oriented in the liquid crystal. The two closely resonating carbons in pyrimidine are better resolved in the present study compared to the earlier work [H.S. Vinay Deepak, Ann Joy, N. Suryaprakash, Determination of natural abundance N-15-H-1 and C-13-H-1 dipolar couplings of molecules in a strongly orienting media using two-dimensional inverse experiments, Magn. Reson. Chem. 44 (2006) 553-565]. (C) 2007 Elsevier Inc. All rights reserved.