Improvements for Measuring ¹H–¹H Coupling Constants in DNA via New Stripe-COSY and Superstripe-COSY Pulse Sequences Combined with a Novel Strategy of Selective Deuteration

Journal Article · Mon Dec 01 00:00:00 EST 1997 · Journal of Magnetic Resonance

DOI:https://doi.org/10.1006/jmre.1997.1261· OSTI ID:1491741

Yang, Jiping; Silks, Louis; Wu, Ruilian; Isern, Nancy; Unkefer, Cliff; Kennedy, Michael A.

Three bond proton-proton vicinal coupling constants are of potential value for analyzing sugar conformations in DNA. However, self-cancellation in antiphase cross peaks and modulation of peak splittings by transverse cross relaxation can alter the apparent coupling constants such that they do not accurately reflect the sugar conformations. Transverse cross relaxation is most effective between strongly coupled geminal proton pairs. Here we report the use of stereospecific deuteration at the H2" position in the A5 and A6 residues in the 12 base pair DNA sequence [d(CGCGAATTCGCG)2] as a means of investigating the effect of transverse cross relaxation on P.E.COSY type cross peaks. Deuteration of the H2" proton is expected to reduce the transverse cross relaxation rate by the square of ratio of the proton to deuteron gyromagnetic ratios, i.e., by a factor of 42. Additionally, a striking eight- to ninefold increase in the signal intensity was observed for cross peaks involving the remaining H2' proton resulting from diminished dipolar relaxation. Further improvements in signal-to-noise ratio were realized by collecting P.E.COSY spectra in strips, using an experiment referred to as stripe-COSY, employing selective excitation pulses which reduced the number of required t1 increments by a factor of four. A final improvement was achieved by employing selective time-shared homonuclear decoupling during the acquisition period, in an experiment referred to as superstripe-COSY, to collapse splittings due to passive couplings. Collectively, these approaches provide P.E. COSY-type spectra with two to three orders of magnitude increased sensitivity per unit time and that are relatively free from artifacts.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1491741
• Report Number(s): PNNL-SA-38875
• Journal Information: Journal of Magnetic Resonance, Vol. 129, Issue 2; ISSN 1090-7807
• Publisher: Elsevier
• Country of Publication: United States
• Language: English