title: An ab initio study of the guanidinium groups in saxitoxin.
abstract: Quantum chemical (Hartree-Fock) calculations were performed on neutral and protonated saxitoxin in order to obtain optimum geometries, rotational energy barriers for the guanidinium ions and proton affinities. For comparison purposes, as model compounds, guanidinium systems in five and six membered rings were also investigated. In addition, DFT (B3LYP) calculations with the 6-31G** basis set were performed and the sodium affinities of the guanidinium groups in saxitoxin were obtained. It was concluded that the inhibition of the sodium channels by the saxitoxin is due to the interaction of the guanidinium group with carboxylate groups from the wall of the channel and not to the binding of the sodium ions.
authors.affiliation: John Jay College and Graduate Center of the City, University of New York, 445 W 59th St, New York, NY 10019, USA. acransg6@aol.com
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Sapse
authors.forename: Robert
authors.initials: R
authors.lastname: Rothchild
authors.forename: Kyu
authors.initials: K
authors.lastname: Rhee
mesh_terms: D019791:Guanidine / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D011789:Quantum Theory; D012399:Rotation; D012530:Saxitoxin / Q000737:chemistry*
chemical_list: D012530:Saxitoxin; D019791:Guanidine