Xiangfeng Guo

Substituent-dependent fluorescent sensors for zinc ions based on carboxamidoquinoline

A series of carboxamidoquinoline-based fluorescent sensors (the AQZ family) were synthesized and characterized. The AQZ family members were highly soluble in water and showed good selectivity for Zn(2+)via enhanced fluorescence in aqueous buffer solution. Fluorescence signals could be tuned from dual-wavelength ratiometric changes to changes in the intensity of a single wavelength upon binding Zn(2+) through the introduction of different substituents onto the quinoline ring. Concentrations of free Zn(2+) of 10(-5)-10(-6) M could be detected using the sensors. Changes of substituents and their positions on the quinoline ring influenced the sensitivity for Zn(2+), but had little effect on Zn(2+) affinities.

Bi-8-carboxamidoquinoline derivatives for the fluorescent recognition of Zn2+.

Three fluorescent sensors which were composed of a phendiol (o-, m-, p-isomers) and two carboxamidoquinolines have been synthesized and characterized. Research on the Zn2+-sensing properties of the three sensors was carried out, and the results showed a significant difference in the recognition performance for Zn2+. The fluorescence intensity (I510 nm) of ortho isomeric sensor binding to Zn2+ was enhanced 23-fold, the meta 15-fold, the para 8-fold. As the distance between two carboxamidoquinolines became longer, the fluorescence enhancement decreased. In addition, the selectivity of sensors got poor and the detection limit became higher with rising the distance between two receptors.

Surface activities and thermodynamic properties of novel cationic surfactants with hydroxymethyl group

ABSTRACT A new series of cationic surfactants, N–alkyl–N,N–dimethyl–N–(p–(hydroxymethyl) benzyl) ammonium chlorides (p-DHBA-m), were synthesized and the structures were characterized by 1HNMR, 13CNMR, FT–IR and ESI–MS. The surface activities, thermodynamic properties and aggregation behaviors of p-DHBA-m in aqueous solutions were respectively studied by means of surface tension, isothermal titration calorimetry and steady-state fluorescence methods. Thermodynamic parameters show that the micellization is an entropy-driven process. According to the fluorescence quenching method, the micelle aggregation numbers (Nagg) of p-DHBA-m were calculated and found that the increase of temperature or the elongation of alkyl chain length could lead to the reduction of the Nagg, respectively. GRAPHICAL ABSTRACT

A novel sensing membrane for the determination of ferric ions in aqueous solutions

A new fluorescent sensing membrane, in which a naphthalimide derivative containing two long hydrophobic hydrocarbon chains, amphiphilic molecule castor oil polyoxyethylene ether and PVC were respectively used as the fluorescent indicator, plasticizer and matrix, for specific recognition of Fe3+ was prepared based on the physical entrapment method. The results show that the fluorescence of the sensing membrane is selectively quenched by Fe3+ ions over other common metal ions in aqueous solutions. A good linear response range of the sensing membrane is achieved from 5.0 × 10−5 to 1.5 × 10−3 M (R2 = 0.9906), with a detection limit of 4.0 × 10−7 M. The sensing membrane shows good reversibility, a fast response of less than 20 s and satisfactory stability with a relative standard deviation of ±1.5%. Moreover, it was successfully applied in the detection of Fe3+ in tap water with recovery in the range of 97.6–101.2%.

A novel method for cetylpyridinium bromide determination in aqueous solution based on fluorescence quenching of dye

A new, highly selective and sensitive fluorescent detection method was developed for determining quaternary pyridinium salts cationic surfactant in an aqueous solution of polyoxyethylene-23-lauryl ether (Brij 35). The method was based on the emission of a fluorescent dye, disodium-4,4′-bis-(4-anilino-6-morpholino-s-triazin-2-ylamino)-2,2′-stilbenedisulfonate (CXT), was quenched by cetylpyridinium bromide (CPB). The fluorescence intensity of CXT showed distinct changes towards CPB with excellent selectivity and sensitivity among a series of common surfactants at the optimum pH 8.0. Furthermore, the fluorescence of the CXT/CPB complex is not affected by other common surfactants and most anions commonly associated with the quaternary pyridinium salt cationic surfactant in environmental samples. Also, the fluorescent intensity of CXT (5.0 μM) shows a linear response toward the concentration of CPB from 0 to 20 μM (R2 = 0.9956) and the detection limit was calculated to be 65 nM. The method is found to be precisely applicable to the analysis of CPB in real environmental samples.