title: Intercluster reactions show that (CH3)2S(+)CH2CO2H is a better methyl cation donor than (CH3)3N(+)CH2CO2H.
abstract: The intrinsic methylating abilities of the known biological methylating zwitterionic agents, dimethylsulfonioacetate (DMSA), (CH(3))(2)S⁺CH(2)CO(2)(-) (1) and glycine betaine (GB), (CH(3))(3)N⁺CH(2)CO(2)(-) (2), have been examined via a range of gas phase experiments involving collision-induced dissociation (CID) of their proton-bound homo- and heterodimers, including those containing the amino acid arginine. The relative yields of the products of methyl cation transfer are consistent in all cases and show that protonated DMSA is a more potent methylating agent than protonated GB. Since methylation can occur at more than one site in arginine, the [M+CH(3)](+) ion of arginine, formed from the heterocluster [DMSA+Arg+H](+), was subject to an additional stage of CID. The resultant CID spectrum is virtually identical to that of an authentic sample of protonated arginine-O-methyl ester but is significantly different to that of an authentic sample of protonated N(G)-methyl arginine. This suggests that methylation has occurred within a salt bridge complex of [DMSA+Arg+H](+), in which the arginine exists in the zwitterionic form. Finally, density functional theory calculations on the model salts, (CH(3)CO(2)(-))[(CH(3))(3)S(+)] and (CH(3)CO(2)(-))[(CH(3))(4)N(+)], show that methylation of CH(3)CO(2)(-) by (CH(3))(3)S(+) is both kinetically and thermodynamically preferred over methylation by (CH(3))(4)N(+).
authors: School of Chemistry, University of Melbourne, Victoria 3010, Australia.
authors: Ellie Jung Hwa
authors: EJ
authors: Yoo
authors: Linda
authors: L
authors: Feketeová
authors: George N
authors: GN
authors: Khairallah
authors: Richard A J
authors: RA
authors: O'Hair
mesh_terms: D001120:Arginine; D001622:Betaine / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D008745:Methylation; D021241:Spectrometry, Mass, Electrospray Ionization; D013452:Sulfonium Compounds / Q000737:chemistry*; D053719:Tandem Mass Spectrometry
chemical_list: D002412:Cations; D013452:Sulfonium Compounds; D001622:Betaine; C121105:dimethylsulfonioacetate; D001120:Arginine