Ke An Li

Molecular spectroscopic study of DNA binding with neutral red and application to assay of nucleic acids

Abstract Under acidic conditions, neutral red (NR) binds with DNA. The Scatchard plots for the reaction were constructed from the fluorescence spectral data which are best fitted by the neighbour exclusion model with an intrinsic binding constant of 4.5xa0×xa010 5 xa0M −1 and an exclusion parameter of about 1 base pair. Upon binding to DNA, broadening was observed; in addition there is a hypochromic effect and small blue shift at low concentrations of DNA. In contrast, there is a hyperchromic effect and red shifts in the absorption spectrum for high concentrations of DNA. Fluorescence of NR is efficiently quenched by DNA at low concentrations and is greatly enhanced by DNA at high concentrations. The Stern–Volmer quenching constant was obtained from the linear quenching plots. Resonance light scattering (RLS), using a common spectrofluorometer, was applied for determination of nucleic acids with NR. At pH 2.3, the weak light scattering of NR is enhanced greatly at 330xa0nm and 590xa0nm. The enhanced light scattering is proportional to the concentration of nucleic acids in the range 0.048–5.25xa0μgxa0ml −1 for calf thymus DNA, 0.035–4.30xa0μgxa0ml −1 for fish sperm DNA and 0.205–5.80xa0μgxa0ml −1 for yeast DNA. The detection limits were 48.2xa0ngxa0ml −1 for calf thymus DNA, 35.2xa0ngxa0ml −1 for sperm fish DNA and 205xa0ngxa0ml −1 for yeast RNA. The relative standard deviations (8 replicates) were within 4.3% in the middle of the linear response range.

Preconcentration, separation and determination of trace Hg(II) in environmental samples with aminopropylbenzoylazo-2-mercaptobenzothiazole bonded to silica gel

Abstract This paper reports a simple and highly selective method for the preconcentration and separation of trace Hg(II) with aminopropylbenzoylazo-2-mercaptobenzothiazole bonded to silica gel (ABMBT·SG). ABMBT·SG was tested for the selective extraction of Hg(II) and it showed an exchange capacity of 41.4xa0μmolxa0g −1 . After preconcentration and separation using an ABMBT·SG column, trace Hg(II) in environmental samples can be determined by UV–VIS spectrophotometry. The chromatographic column packed with ABMBT·SG can be reused. The method is simple and efficient, and is applied to polluted soil (2xa0μgxa0g −1 ), incinerated biological material (9 or 18xa0ngxa0g −1 ) and spiked natural water (5xa0μgxa0l −1 ).

Microdetermination of proteins by Rayleigh light scattering technique with acid green 25

Abstract Based on the enhancement of Rayleigh light scattering (RLS) of acid green 25 (Ag25) by proteins, a new quantitative determination method for proteins in aqueous solutions has been developed. This assay is very sensitive (0.136-10.20 μg/ml), rapid (

Determination of proteins by fluorescence quenching of erythrosin B

Abstract Erythrosin B (EB) binding to proteins causes a decrease in the fluorescence maximum of EB at 550 nm. Based on this, a new, fast and simple fluorescence quenching method for the determination of proteins is developed. The linear range of this assay is 1.36–20.4 μg ml −1 . The method has very few interferences, most of which can be minimized by dilution. In the detection of proteins in human serum, this method gave values close to that of the Coomassie brilliant blue method.

Determination of proteins with Alizarin Red S by Rayleigh light scattering technique.

A new protein determination method by enhanced Rayleigh light scattering (RLS) technique has been developed. In acid condition (pH=3.60), RLS of 1,2-dihydroxyanthraquinone-3-sulfonate (Alizarin Red S) can be greatly enhanced by addition of proteins, resulting in two characteristic peaks, 360 and 505nm, respectively. The new protein assay is based on the RLS enhancement and spectrum change. The optimum condition for the reaction was investigated. The linear range is 0.20-24.9mugml(-1) for BSA and 0.20-15.5mugml(-1) for HSA. The detection limits (S/N=3) are 9.59ngml(-1) for BSA and 9.51ngml(-1) for HSA. The results of determination for human serum samples were comparable to those obtained by Bradford method. The binding stoichiometry was determined.

Study on the interaction of protein with Sulfonazo III by Rayleigh light scattering technique and its application

Abstract This is the first report on the determination of proteins with Sulfonazo III by Rayleigh light scattering (RLS). At pH 4.23, the weak RLS of Sulfonazo III can be enhanced greatly by the addition of proteins, resulting in three characteristic peaks. Based on this, the reaction of Sulfonazo III and proteins was studied and a new method for quantation of proteins has been developed. This method is very sensitive (0.30–30.5xa0μgxa0ml –1 for bovine serum albumen), rapid ( Mechanistic studies show that the RLS peaks correspond to the absorption valleys of the protein-Sulfonazo III complex.

Simple and sensitive assay for nucleic acids by use of Rayleigh light scattering technique with rhodamine B

Abstract Based on the enhancement of Rayleigh light scattering of rhodamine B by nucleic acids under acidic condition at 378xa0nm, a new method for determination of nucleic acids in aqueous solutions has been developed. This assay has a wide linear range for calf thymus DNA (0.10–16.0xa0μgxa0ml−1). Besides its high sensitivity, it has some other advantages: rapidity of reaction (

Enhancement of Rayleigh light scattering of acid chrome blue K by proteins and protein assay by the scattering technique.

Rayleigh light scattering of Acid Chrome Blue K (ACBK) is enhanced greatly by proteins. Based on this, a method for protein assay in aqueous solution was developed. This assay matches the sensitivity of the colorimetric dye-binding method with a linear range of 0.136-10.88 micrograms ml-1. The measurements can be made easily on a common fluorimeter. The reaction between ACBK and proteins is completed in 2 min and the scattered light signal is stable for at lest 3 h. Protein-to-protein variability is encountered in this method as in many other protein assays. There is little or no interference from amino acids, most metal ions and complexing agents (e.g., EDTA). Interferences from salts, urea and detergents can be minimized by dilution.

Spectrophotometry of nucleic acids by their effect on the complex of cobalt(II) with 4-[(5-chloro-2-pyridyl)azo]-1,3-diaminobenzene

Abstract A new ternary azo-dye complex reaction involving nucleic acids has been studied to provide a sensitive spectrophotometric method for nucleic acids. In alkaline conditions, single-stranded nucleic acids react with the complex of Co(II) with 4-[(5-chloro-2-pyridyl)azo]-1,3-diaminobenzene (5-Cl-PADAB), resulting in purple ternary compounds with maximum absorbance at 545.0 nm against the binary complex blank. The mole ratio of Co(II) to 5-Cl-PADAB in the ternary compounds is 1:2, and each nucleotide residue can bind two binary complex molecules. There are linear relationships between the absorbance and the concentrations of the tested nucleic acids, such as calf thymus DNA, fish sperm DNA and yeast RNA in the range 0–4.0 μg ml −1 . The 3σ limit of detection for calf thymus DNA is 40 ng ml −1 , the relative standard deviation at 3.0 μg ml −1 is 0.79% ( n = 10) and the Sandells sensitivity is 5.3 ng cm −2 . The same parameters for fish sperm DNA are 41 ng ml −1 , 0.84% and 5.4 ng cm −2 , and for yeast RNA are 49 ng ml −1 , 0.58% and 6.2 ng cm −2 . Synthetic samples were analyzed satisfactorily.

Fast determination of flavonoids in Glycyrrhizae radix by capillary zone electrophoresis

Abstract A fast capillary zone electrophoresis (CZE) method has been developed for the determination of four flavonoids (liquiritin, licoisoflavone A, licochalconel A and calycosin) in Glycyrrhizae radix . After a series of optimization experiments, 100xa0mM borate buffer (pH 10.5), 30xa0kV applied voltage and 35xa0°C temperature were selected. The contents of four flavonoids in cultivated and wild crude drugs of Glycyrrhizae radix with different growth periods from one to four years, collected from different areas were successfully determined within 8xa0min, with satisfactory repeatability and recovery.