Double-helical DNA 1H chemical shifts:: an accurate and balanced predictive empirical scheme

Chemical shifts of exchangeable and non-exchangeable protons in double-helical B DNA fragments were collected from the literature (1982-97), subjected to statistical analysis and tabulated. The tables are arranged according to the central residue involved (A, G, C and T) and to the 5'- and 3'-flanking residues (triplet model). The standard deviations in the mean (90% confidence limits) are of the order of 0.02-0.04ppm for most protons. In addition, data on terminal residues were collected (terminal doublets) and it is shown that these shifts play a key role in the empirical determination of physically meaningful shielding/deshielding increments induced by the 5'- and 3'-flanking bases in triplets. The r.m.s. error of the shifts predicted with the aid of our new incremental scheme is 0.01-0.03 ppm. The analysis throws new light on the mechanism involved in the fraying process. Copyright (C) 2000 John Wiley & Sons, Ltd.