EFFICIENT NMR PULSE SEQUENCES TO TRANSFER THE PARAHYDROGEN-INDUCED POLARIZATION TO HETERO NUCLEI

The PASADENA or PHIP effect originates from the breakdown of the parah ydrogen symmetry when the two protons are found in magnetically inequi valent positions after hydrogenation. As a result, a signal enhancemen t of up to 10(4) in the proton NMR spectra can be observed. We introdu ce three polarization transfer techniques, namely PH-INEPT, PH-INEPT+, and INEPT(+pi/4), that are highly effective to record in situ hetero NMR spectra of parahydrogen-labeled compounds. A complete product oper ator treatment as well as experimental results for C-13 and Si-29 have been given. With these sequences we obtained a signal enhancement of 500 which allows in situ NMR investigations of hetero nuclear systems at natural abundance.