title: IP-COSY, a totally in-phase and sensitive COSY experiment.
abstract: The IP-COSY experiment presented in this paper gives an in-phase spectral presentation in both the F(1) and F(2) dimensions by a combined use of a constant evolution time (CT) in t(1) and a symmetrical refocusing period before t(2). Compared with DQF-COSY and CT-COSY, IP-COSY further alleviates the effect of signal reduction due to a small ratio p (= J/linewidth), showing (1) improved lineshape and cross-peak definition and (2) especially enhancement in signals of the peaks of small active J coupling constant and the peaks of broader linewidth. A new strategy was adopted to eliminate or reduce effectively artifactual peaks by adding a 0.1-0.2 ms variation to the time delays of the CT period used for each scan of the FID in IP-COSY and CT-COSY. (3)J(H,H) coupling constants of larger than 4 Hz in the fingerprint region of peptides can be directly derived from the separation of doublets. IP-COSY cross peaks are stronger than those in DQF-COSY by 4-20-fold for tested peptides and oligonucleotides (MW < 8 kDa) with acquisition and processing parameters used in the work, and they are easier to identify than those in CT-COSY. The overall improvement in IP-COSY should make the detection/autodetection of the COSY cross peaks and the measurements of the various coupling constants more easily achieved, providing valuable information for the structure elucidation of peptides/small proteins and oligonucleotides.
authors.affiliation: Department of Chemistry, University of Houston, Houston, Texas 77004-5003, USA.
authors.forename: Youlin
authors.initials: Y
authors.lastname: Xia
authors.forename: Glen
authors.initials: G
authors.lastname: Legge
authors.forename: Kyu-Yeon
authors.initials: KY
authors.lastname: Jun
authors.forename: Yulan
authors.initials: Y
authors.lastname: Qi
authors.forename: Hunjoong
authors.initials: H
authors.lastname: Lee
authors.forename: Xiaolian
authors.initials: X
authors.lastname: Gao
mesh_terms: D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D009690:Nucleic Acid Conformation; D009841:Oligonucleotides / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D011487:Protein Conformation; D011506:Proteins / Q000737:chemistry*; D013997:Time Factors
chemical_list: D009841:Oligonucleotides; D010455:Peptides; D011506:Proteins