Abstract

A new glassy carbon electrode modified with novel calix[4]-arene derivative was prepared and then applied to the selective recognition of lead ion in aqueous media by cyclic and square wave voltammetry. A new anodic stripping peak at − 0.92 V (vs. Ag/Ag⁺) in square wave voltammogram can be obtained by scanning the potential from − 1.5 to − 0.6 V, of which the peak current is proportional to the concentration of Pb²⁺. The modified electrode in 0.1 mol/L HNO₃ solution showed a linear voltammetric response in the range of 2.0 × 10–⁸–1.0 × 10–⁶ mol/L and a detection limit of 6.1 × 10–⁹ mol/L. In the modified glassy carbon electrode no significant interference occurred from alkali, alkaline and transition metal ions except Hg²⁺, Ag⁺ and Cu²⁺ ions, which can be eliminated by the addition of KSCN. The proposed method was successfully applied to determine lead in aqueous samples.

The noncovalent interactions of night blue (NB) with several nucleic acids in buffer medium of Britton-Robinson at pH 4.1 have been studied by spectroscopic methods. It is shown that the binding of NB with nucleic acids involves the J-aggregation of NB molecules on the surface of nucleic acids. The aggregation was encouraged by polyanions nucleic acids, in which nucleic acids served for acting templates. In this connection, a new method of nucleic acids with sensitivity at nanogram level is proposed based on the measurement of enhanced resonance light scattering (RLS). The linear range of ctDNA, fsDNA and yRNA is 0.01—2.5, 0.03—2.5 and 0.04—1.0 μg/mL, respectively, and the corresponding detection limits (3s̀) are 9.4, 7.3 and 5.7 ng/mL at 2.5 × 10–⁵mol/L of NB. Synthetic and real samples were analyzed with satisfactory results.

The interaction of pinacyanol chloride (PC) with nucleic acids has been investigated by a series of experiments. Extensive hypochromism, appreciable peak shifts, isosbestic points and new peaks of the product of binding to nucleic acids in the spectra were observed. They showed that the interaction between PC and nucleic adds occurred. The results from absorption spectra of DNA, DNA melting, electrophoresis and fluorescence polarization studies have indicated that PC binds to DNA in nonintercalative way. Consistent with the nonintercalation, the studies of fluorescence titration and absorption titration specified that the binding of PC to nucleic acids occurred by an outside stacking binding, in which nucleic acids served for acting templates. The fact that the new absorption peaks of bound PC at ca. 485 nm are just close to the absorption bands of H-aggregate of PC at high concentrations without DNA further supports the outside stacking binding mode. In addition, other evidence indicated that the interaction between PC and nucleic acids is not purely electrostatic.

Molecularly imprinted microspheres (MIMs) were prepared using 4-aminopyridine (4-AP) as template molecule by aqueous microsuspension polymerization. The MIMs were packed into stainless steel column (250 × 4.6 mm I. D.) for selective separation of 4-aminopyridine (4-AP) and 2-aminopyridine (2-AP). The influences of pH, kinds and concentration (c) of buffer on capacity factors were investigated in detail. The relationships of capacity factor (k′) with pH and concentration of buffer are quantitatively described firstly. The effects of pH of phosphate and acetate buffer on capacity factors are very different. The relationship between k′ and pH can be described by the following equation: k′ = −8.23 + 9.23 pH–0.99 pH² (in phosphate buffer) with R² = 0.9775 and k′ = 6.79–3.76 pH + 0.68 pH² (in acetate buffer) with R² = 0.9866. Furthermore, the capacity factors were also greatly affected by the concentration of acetate buffer in mobile phase while non-imprinted molecule is poorly changed. It increases with decreasing the concentration of buffer—especially in low concentration buffer (c_acetate < 0.02 mol/L, final concentration in mobile phase). The fit curve of log k′ to log c is described by equation: log k′ = −0.571–1.256 × log c −0.186 × (log c)² with R² = 0.9979. The ratio of acetate buffer to methanol was investigated and the optimal ratio for separation of 4-AP and 2-AP is below 1:7.5 (V/V).