title: The effect of monovalent cations on the self-association of cytidylyl-(3-5')-guanosine and guanylyl-(3'5')-cytidine in aqueous solution.
abstract: The hydrogen-bonding, base stacking, and formation of extended aggregates has been investigated for salts of guanylyl-3'-5')-cytidine, GpC, and cytidylyl-(3'-5')- guanosine, CpG, in which the cation was Na+, K+, or tetramethylammonium (TMA+). Variable temperature studies were done at 2-70 degrees C on aqueous solutions at pD4 and 8 using 1H NMR and FTIR. At low temperatures it has been found that at pD 8 both GpC and CpG form Watson-Crick dimers which stack upon each other to form larger species. A slight cation effect is observed below 35 degrees C which has the order: TMA+ > Na+ > K+. This order suggests that the cations are interacting with the phosphate and interactions with the bases are unlikely. The 1H NMR spectrum for TMACpG at pD 4 has been assigned and exhibits chemical shift differences from those at pD 8 which are consistent with protonation of the N3 of the cytidine residue. Based on NMR line broadening, CpG at pD 4 has a greater degree of self-association at low temperature than it or GpC have at pD 8. A different type of hydrogen bonding and self-association occur in CpG at pD 4 compared to pD 8, but the structures are uncertain. Due to hemi-protonation of the cytidine N3, parallel G-G/C-C+ base paired dimers or G-tetrads may be forming.
authors.affiliation: Division of Earth and Physical Sciences, University of Texas at San Antonio 78249, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Walmsley
authors.forename: R M
authors.initials: RM
authors.lastname: Wilson
authors.forename: L A
authors.initials: LA
authors.lastname: Garza
authors.forename: R T
authors.initials: RT
authors.lastname: West
authors.forename: T E
authors.initials: TE
authors.lastname: Lytle
authors.forename: R C
authors.initials: RC
authors.lastname: Heldt
authors.forename: M J
authors.initials: MJ
authors.lastname: Maguire
mesh_terms: D002414:Cations, Monovalent / Q000737:chemistry*; D015226:Dinucleoside Phosphates / Q000737:chemistry*; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D011522:Protons; D012996:Solutions; D013055:Spectrophotometry, Infrared; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D002414:Cations, Monovalent; D015226:Dinucleoside Phosphates; D011522:Protons; D012996:Solutions; D014867:Water; C015772:CpG dinucleotide; C004804:guanylyl-(3',5')-cytidine