title: Pd2+fluorescent sensors based on amino and imino derivatives of rhodamine and improvement of water solubility by the formation of inclusion complexes with β-cyclodextrin.
abstract: Mono- and bis-rhodamine derivatives appended with amino (RhB1) and imino (BRI) groups, respectively, have been designed as colorimetric and fluorescent sensors for the selective detection of Pd2+. In addition, an attempt has been made to improve the water solubility of the probe by synthesizing inclusion complexes of RhB1 with β-cyclodextrin as the host molecule. The resulting probe, RhB1-CD, exhibited exactly the same physicochemical phenomena as the guest molecule RhB1, indicating that complexation with β-CD improved the water solubility of RhB1 without affecting its sensing ability. With increasing concentrations of Pd2+, the absorption (556 nm) and emission (591 nm) intensities of BRI as well as the absorption intensities of RhB1/RhB1-CD (563 nm) increase, whereas the emission intensities of RhB1/RhB1-CD decrease due to fluorescence quenching. Therefore, BRI can act as an "OFF-ON" fluorescent probe switch in CH3CN/H2O (3 : 2 v/v) with a detection limit of 1 μM in solution, whereas RhB1 and RhB1-CD act as "ON-OFF" fluorescent probes in EtOH/H2O (1 : 1 v/v) and water, respectively, with a detection limit of 10 μM. All these probes exhibited high selectivity for Pd2+and reversibility by treatment with Na2S. In the presence of commonly coexisting metal ions, such as Hg2+, Fe3+, Cu2+and Al3+, BRI undergoes either catalytic Schiff base hydrolysis or it is unaffected by its affinity to the metal ions. However, Pd2+can be effectively distinguished by a 12-15 nm bathochromic shift in its emission spectrum when compared with that of other metal ions. A Job's plot revealed that BRI forms 1 : 2 complexes by a spirolactam ring opening mechanism, whereas RhB1/RhB1-CD form 2 : 1 complexes by a ring opening mechanism followed by Pd2+-induced dimerization; the proposed binding mechanisms are presented.
authors.affiliation: Department of Chemical Engineering, National Cheng Kung University, Tainan 70101, Taiwan, Republic of China. jhliu@mail.ncku.edu.tw.
authors.forename: Yan-Song
authors.initials: YS
authors.lastname: Zhang
authors.forename: Rathinam
authors.initials: R
authors.lastname: Balamurugan
authors.forename: Jian-Chin
authors.initials: JC
authors.lastname: Lin
authors.forename: Sri
authors.initials: S
authors.lastname: Fitriyani
authors.forename: Jui-Hsiang
authors.initials: JH
authors.lastname: Liu
authors.forename: Alexander
authors.initials: A
authors.lastname: Emelyanenko
mesh_terms: D005456:Fluorescent Dyes / Q000737:chemistry*; D012235:Rhodamines / Q000737:chemistry*; D012995:Solubility; D013050:Spectrometry, Fluorescence; D047392:beta-Cyclodextrins / Q000737:chemistry*
chemical_list: D005456:Fluorescent Dyes; D012235:Rhodamines; D047392:beta-Cyclodextrins