A NOESY-HSQC SIMULATION PROGRAM, SPIRIT

A program SPIRIT (Simulation Program considering Incomplete Recovery o f z magnetization and INEPT Transfer efficiency) has been developed to simulate three-dimensional NOESY-HSQC spectra. This program takes int o account (1) different transfer efficiency during INEPT and reverse I NEPT durations due to differential relaxation rates and (1)J coupling constants; (2) the different effect of the sensitivity-enhancement sch eme on CH. CH2 and CH3 systems; and (3) incomplete recovery of longitu dinal magnetization between scans. The simulation program incorporates anisotropic tumbling mode for symmetric tops, and allows for differen tial external relaxation rates for protons. Some well-defined internal motions, such as the fast rotation of methyl groups. are taken into a ccount. The simulation program also allows for input of multiple confo rmations and their relative populations to calculate the average relax ation matrix to account for slow internal motions. With the SPIRIT pro gram, the sensitivity-enhanced NOESY-HSQC experiment can be used direc tly in the evaluation of the accuracy of structures, which can potenti ally be improved by direct refinement against the primary data.