title: A new chiral probe for sulfate anion: UV, CD, fluorescence, and NMR spectral studies of 1:1 and 2:1 complex formation and structure of chiral guanidinium-p-dimethylaminobenzoate conjugate with sulfate anion.
abstract: A new chiral chromophoric host 1, possessing a 4-(N,N-dimethylamino)benzoate (DMAB) group tethered to a chiral bicyclic guanidinium subunit, was synthesized and applied to the probe for sulfate anion. Host 1 showed typical successive 1:1 and 2:1 host:guest complexation behavior toward the divalent sulfate anion, as revealed by UV-vis, CD, fluorescence, and 1H NMR spectroscopic studies. The DMAB chromophore was shown to be a sensitive CD spectral probe for assessing not only the complexation behavior but also complex stoichiometry and structure. The stepwise 1:1 and 2:1 complexation constants (K1 and K2) were determined as 1.53 x 10(6) and 4.84 x 10(4) M(-1), respectively, by NMR titration in CD3CN. The CD exciton chirality method allowed us to determine the chiral sense (spatial arrangement) of the two DMAB moieties in the 2:1 complex as negative (counterclockwise). The dual fluorescence behavior of DMAB was employed for elucidating the role of the countercation upon complexation of host 1 with sulfates possessing lipophilic countercation(s) such as tetrabutylammonium.
authors.affiliation: Department of Environmental Systems Engineering, Kochi University of Technology, Tosayamada, Japan. kobiro.kazuya@kochi-tech.ac.jp
authors.forename: Kazuya
authors.initials: K
authors.lastname: Kobiro
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Inoue
mesh_terms: D010129:4-Aminobenzoic Acid / Q000737:chemistry; D000838:Anions; D002942:Circular Dichroism; D019791:Guanidine / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D013237:Stereoisomerism; D013431:Sulfates / Q000032:analysis* / Q000737:chemistry; D017186:Titrimetry; D062366:para-Aminobenzoates
chemical_list: D000838:Anions; D013431:Sulfates; D062366:para-Aminobenzoates; D019791:Guanidine; D010129:4-Aminobenzoic Acid