Conformational analysis

Carbon13 NMR in conformational analysis of nucleic acid fragments. 2. A reparametrization of the Karplus equation for vicinal NMR coupling constants in CCOP and HCOP fragments.Lankhorst PP, Haasnoot CA, Erkelens C, Altona C; J Biomol Struct Dyn 1 (1984) 13871405 PubMed 6400827 Abstract13C31P coupling constants of 10 oligoribonucleoside phosphates, measured at a number of temperatures, are presented. The combination of these data with 1H31P couplings of the same compounds leads to the derivation of two new and mutually consistent sets of Karplus parameters: J(CCOP) = 6.9cos2 phi3.4cos phi + 0.7 J(HCOP) = 15.3cos2 phi6.1cos phi + 1.6 At the same time new values for the base sequence dependent magnitude of the trans conformer of the backbone angle epsilon (C4'C3'O3'P) are calculated. The present results show that the magnitude of epsilon(t) in righthanded ribo helices is confined to the range 214 degrees226 degrees (average 219 degrees), which is in much better agreement with single crystal Xray studies (average 218 degrees) than were previous deductions from NMR spectroscopic results (average 208 degrees). Equation^{3}J=15.3*cos^{2}(θ)6.1*cos(θ)+1.6
