Cai Ruxiu

Organic solvent enhanced spectrofluorimetric method for determination of laccase activity

A novel fluorimetric method for determination of laccase activity in organic solvents is proposed, based on the oxidation ofo-phenylenediamine (1,2-diaminobenzene, OPDA) catalyzed by laccase yielding 2,3-diaminophenazine. The optimal conditions for laccase in organic media areT=55°C, pH=6.5, 1.0×10−2mol/L OPDA, 1.25 mL ethanol, 1.25 mL 1,4-dioxane and 1.25 mL acetone. The linear range of the method proposed in ethanol, 1,4-dioxane and acetone media were 0.44–19.33, 0.11–20.85, 0.38–21.05 U with the detection limit of 0.088, 0.022, 0.076 U, respectively. The proposed method has been applied to the analysis of laccase activity of real samples with more accurate and sensitive than that of the previous method reported.

Determination of hexacyanoferrates based on the diacetone–BrO3––Mn(II)–H2SO4 chemical oscillatory reaction

A new method for the determination of hexacyanoferrates in an oscillating chemical system involving the Mn(II)-catalysed reaction between diacetone and potassium bromate in an acidic medium is proposed. The best reaction conditions and reactant concentrations are reported. The method relies on the linear relationship between the changes in the oscillation period of the chemical system and the concentration of hexacyanoferrates in the range 1.0 × 10–7–3.3 × 10–5 mol dm–3. The relative standard deviation for 4 × 10–6 mol dm–3 Fe(CN)63– is 2.0% (n = 6). The possible mechanism of this reaction is discussed.

Highly sensitive spectrofluorimetric determination of L-cysteine based on inhibition of hemoglobin.

A highly sensitive spectrofluorimetric method for the determination of L-cysteine based on its inhibitory action on hemoglobin (Hb) activity was developed. The optimal conditions were studied. A linear calibration graph was obtained over the range 2.00 x 10(-7)-1.50 x 10(-6) mol l(-1) for L-cysteine. The relative standard derivation was 1.30% at L-cysteine concentration of 8.00 x 10(-7) mol l(-1) (n=11). Further experimental results revealed that the inhibition of L-cysteine on this system was of the competitive type. The method was applied to determine L-cysteine in protein hydrolysate and cystine electrolyte samples with satisfactory results.

Study and analytical application of rare earth inhibition of laccase

The effect of metal ions on the laccase-catalyzed redox reaction of 5,6-dibromo-2,3-dicyanohydroquinone to 5,6-dibromo-2,3-dicyanosemiquinone was studied. The results show that rare earth ions strongly inhibited the reaction, while most of the common elements such as Ca(2+), Mg(2+), Cu(2+), Zn(2+), Al(3+) and Fe(3+), etc. had no inhibition on the reaction. Further experimental results reveal that the inhibition of lanthanum (III) on laccase activity was of the comparative type and the degree of inhibition of La(3+) on laccase activity was proportional to the concentration of La(3+). Based on this, a simple, rapid and new stopped-flow enzyme-catalyzed analytical kinetic method for determination of rare earth was proposed and applied to the determination of trace amounts of rare earth in water.

Myoglobin as mimetic enzyme and its analytical application in determination of H2O2

The characteristic of Myoglobin as mimetic enzyme was studied and applied in the determination of H2O2 witho-phenylenediamine as substrate. The absorbance obtained at 40°C was found to be proportional to the concentration of H2O2 in the range of 2.0×10−5–2.0×10−7 mol/L, with a correlation coefficient of 0.999 1. The proposed method is simple and highly sensitive to a detection limit of 2.7×10−8 mol/L. The relative standard deviations were within 5% for the determination of different concentrations of H2O2. Satisfied results were obtained in the determination of H2O2 in rainwater by this method, and the recoveries were at the range of 97.2%–105.4%.

Highly sensitive spectrofluorimetric determination of riboflavin based on the generation of active oxygen coupled with enzymatic reaction

A spectrofluorimetric method for the determining riboflavin (VB2) based on its enhancement on the fluorescence of hemoglobin-catalyzed enzymatic reaction was proposed. The proposed method consisted of two reactions. One was the photochemical reaction of VB2, the other was a hemoglobin-catalyzed enzymatic reaction. The optimal experimental conditions for the determinations were established. The linear range of the method was 5.0×10−9−1.0×10−7 mol/L of VB2. The detection limit was calculated to be 3.65×10−9 mol/L. The relative standard deviation of this method was 2.3% at 7.0×10−2 mol/L for 11 determinations.

Organic media enhanced spectrofluorimetric determination of L-ascorbic acid

A novel spectrofluorimetric method for the determination of L-ascorbic acid is proposed. It is based on the inhibition of L-ascorbic acid on the formation of 2,3-diaminophenazine, which is an oxidation product ofo-phenylenediamine catalyzed by laccase. The fluorescence (at λcx/λcm=464 nm /530 nnm) was enhanced strongly in the presence of organic media. The mechanism ofo-phenylenediamine oxidation reaction catalyzed by laccase in the presence of L-ascorbic acid is discussed. L-ascorbic acid is determined in the ethanol, 1,4-dioxane and acetone over the linear range of 4.0×10−7≈1.2×10−4 mol/L, 4.0×10−7≈8.0×10−5 mol/L and 4.0×10−7≈1.0×10−4 mol/L with a detection limit of 1.20×10−5 mol/L, 1.19×10−5 mol/L and 1.24×10−8 mol/L, respectively. The method has been successfully applied to the simple and rapid determination of L-ascorbic acid in pharmaceuticals and milk powder.

Cell Toxicity Effect of Cadmium on Yeast Cells by Detecting NADH Autofluorescence

The cytotoxic effect of cadmium is studied by detecing intracellular nicotinamide adenine dinucleotidea(NADH) autofluorescence in this work. NADH autofluorescence in processes of cadmium-induced apoptosis, necrosis and reversible injury are recorded timely. The relativity between time course of NADH autofluorescence and cadmium toxicity is established. The cell toxicity effect of Cadmium on yeast cells is studied by detecting the time courses of intracellular reduced NADH autofluorescence in this work. The relativity between time courses of NADH autofluorescence and Cadmium toxicity is established.

Resonance Light-Scattering Spectroscopy Study on Interaction between Gold Colloid and Thiol Containing Pharmaceutical

In this paper, we used resonance light-scattering (RLS) spectroscopy to study the interaction between thiol-containing pharmaceutical and gold colloid. And for the first time, we proposed that this highly sensitive, gold colloid-based assay using RLS technique may have potential application in detecting thiol-containing substances.

Study on Mimetic Peroxidase and Molecular Recognition of Phenols With Inclusion Complex of Ironporphyrin Immobilized by β-CD Polymer

Abstractβ-Cyclodextrin (β-CD) and its cross-linked polymer (β-CDP) were known as the mimetic models. Metalloporphyrin had been widely used in the enzymatic method of analysis and molecular recognition. In present work, it was investigation that supramolecular recognition for halogenated phenols, three crosols, three nitrophenols and three aminophenols, served respectively as the substrate of the mimetic receptor, iron-5, 10, 15, 20-tetrakis (sulforphenyl)-21H, 23H-porphine (FeTPPS) or FeTPPS-β-CDP. Supramolecular complex, FeTPPS-β-CDP with function of mult i-recognition and induced-fit, was a advanced kind of mimetic peroxidase; Methyl phenol or polyphenol was the substitute of chlorophenic acid, while aminophenols and other phenols were suggested not to be utilized to enzymatic assay of H2O2. Being a mimetic enzyme mimicking the space structure of overall proteinase, beaimed by immobilized mimetic enzyme with a large number of β-CD interior cavities, chlorophenol was identified optimal substrate in the system tested.