Wh. Gmeiner et al., USE OF SHAPED PULSES FOR SEMI-SELECTIVE EXCITATION OF IMINO H-1 RESONANCES IN DUPLEX DNA AND RNA, Magnetic resonance in chemistry, 33(6), 1995, pp. 449-452
The application of shaped pulses, e.g. TOPHAT and hyperbolic secant, f
or the semi-selective excitation of the imino H-1 resonances of duplex
DNA and RNA in aqueous solution is explored. The excitation profiles
for the shaped poises are calibrated on a sample containing a mixture
of A:U base pairs in deuteriochloroform solution. The data obtained by
performing a semi-selective inversion-recovery pulse sequence using a
TOPHAT waveform for the 90 degrees pulse and a hyperbolic secant wave
form for the 180 degrees pulse are fitted well by a single exponential
function, are independent of transmitter offset over a 1 kHz bandwidt
h and are in good agreement with the value obtained with hard rectangu
lar pulses. This approach for measuring T-1 values was applied to a 2
mM sample of a self-complementary oligoribonucleotide containing the n
ucleoside analogue 5-fluorouridine in 90% H2O. The T-1 values were cal
culated as a function of Tris concentration, a catalyst added to promo
te imino hydrogen exchange. The T-1 values were obtained by good fits
of single exponential functions to the inversion-recovery data. The T-
1 values depend on the concentration of added Tris. Shaped pulses prov
ide a convenient alternative to long rectangular pulses and hard pulse
trains for the semi-selective excitation of imino H-1 resonances.