title: Simultaneous nucleophilic-substituted and electrostatic interactions for thermal switching of spiropyran: a new approach for rapid and selective colorimetric detection of thiol-containing amino acids.
abstract: Complementary electrostatic interaction between the zwitterionic merocyanine and dipolar molecules has emerged as a common strategy for reversibly structural conversion of spiropyrans. Herein, we report a concept-new approach for thermal switching of a spiropyran that is based on simultaneous nucleophilic-substitution reaction and electrostatic interaction. The nucleophilic-substitution at spiro-carbon atom of a spiropyran is promoted due to electron-deficient interaction induced by 6- and 8-nitro groups, which is responsible for the isomerization of the spiropyran by interacting with thiol-containing amino acids. Further, the electrostatic interaction between the zwitterionic merocyanine and the amino acids would accelerate the structural conversion. As proof-of-principle, we outline the route to glutathione (GSH)-induced ring-opening of 6,8-dinitro-1',3',3'-trimethylspiro [2H-1-benzopyran-2,2'-indoline] (1) and its application for rapid and sensitive colorimetric detection of GSH. In ethanol-water (1:99, v/v) solution at pH 8.0, the free 1 exhibited slight-yellow color, but the color changed clearly from slight-yellow to orange-yellow when GSH was introduced into the solution. Ring-opening rate of 1 upon accession of GSH in the dark is 0.45 s(-1), which is 4 orders of magnitude faster in comparison with the rate of the spontaneous thermal isomerization. The absorbance enhancement of 1 at 480 nm was in proportion to the GSH concentration of 2.5 × 10(-8)-5.0 × 10(-6) M with a detection limit of 1.0 × 10(-8) M. Furthermore, due to the specific chemical reaction between the probe and target, color change of 1 is highly selective for thiol-containing amino acids; interferences from other biologically active amino acids or anions are minimal.
authors.affiliation: State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha, 410082, China.
authors.forename: Yinhui
authors.initials: Y
authors.lastname: Li
authors.forename: Yu
authors.initials: Y
authors.lastname: Duan
authors.forename: Jishan
authors.initials: J
authors.lastname: Li
authors.forename: Jing
authors.initials: J
authors.lastname: Zheng
authors.forename: Huan
authors.initials: H
authors.lastname: Yu
authors.forename: Ronghua
authors.initials: R
authors.lastname: Yang
mesh_terms: D000596:Amino Acids / Q000032:analysis*; D001578:Benzopyrans / Q000737:chemistry*; D003116:Color; D003124:Colorimetry; D000431:Ethanol / Q000737:chemistry; D005978:Glutathione / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D007211:Indoles / Q000737:chemistry*; D009574:Nitro Compounds / Q000737:chemistry*; D055672:Static Electricity; D013237:Stereoisomerism; D013438:Sulfhydryl Compounds / Q000032:analysis*; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D000596:Amino Acids; D001578:Benzopyrans; D007211:Indoles; D009574:Nitro Compounds; D013438:Sulfhydryl Compounds; C548873:merocyanine; C088184:spiropyran; D014867:Water; D000431:Ethanol; D005978:Glutathione