title: A stable water-soluble tetramethylbenzidine-2-hydroxypropyl-beta-cyclodextrin inclusion complex and its applications in enzyme assays.
abstract: 3,3',5,5'-Tetramethylbenzidine (TMB), a hydrophobic and noncarcinogenic chromogen with a high absorption coefficient widely used in solid-phase assays involving labeled horseradish peroxidase was rendered soluble (up to 40 mM) and more stable for at least 2 months at 22-24 degrees C by forming a water-soluble inclusion complex with 2-hydroxypropyl-beta-cyclodextrin (hp-beta-CyD). Cyclic voltammetry and absorbency measurement were employed to characterize the TMB-hp-beta-CyD complex. Well-defined cyclic voltammograms of TMB exhibited two oxidation waves which merged into a single wave with increasing hp-beta-CyD concentrations. Cyclic voltammetry was then used to examine the effect of complexation with hp-beta-CyD on the oxidation potential of TMB and provided evidence of a 1:1 complex between TMB and the cyclodextrin molecule with a formation constant of 1.6 M-1. Enzyme assays for D-glucose, lactate, and glutamate were performed by coupling the TMB-hp-beta-CyD/horseradish peroxidase system to the respective oxidase enzymes with the formation of either a blue (absorption coefficient of 35,800 M-1 cm-1 at 650 nm) or a yellow color (absorption coefficient of 67,300 M-1 cm-1 at 450 nm) as an indication of the metabolite concentration. These assays possessed a sensitivity limit below 10 microM and the results obtained were in excellent agreement with standard enzymatic assays when tested in various food and clinical samples.
authors.affiliation: Biotechnology Research Institute, National Research Council Canada, Montreal, Quebec.
authors.forename: M V
authors.initials: MV
authors.lastname: Cattaneo
authors.forename: J H
authors.initials: JH
authors.lastname: Luong
mesh_terms: D000073738:2-Hydroxypropyl-beta-cyclodextrin; D001560:Benzidines; D002863:Chromogenic Compounds; D003505:Cyclodextrins; D004355:Drug Stability; D004563:Electrochemistry; D005947:Glucose / Q000032:analysis; D018698:Glutamic Acid / Q000032:analysis; D006735:Horseradish Peroxidase; D006861:Hydrogen Peroxide / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D007773:Lactates / Q000032:analysis; D019344:Lactic Acid; D012995:Solubility; D013053:Spectrophotometry; D014867:Water; D047392:beta-Cyclodextrins
chemical_list: D001560:Benzidines; D002863:Chromogenic Compounds; D003505:Cyclodextrins; D007773:Lactates; D047392:beta-Cyclodextrins; D014867:Water; D000073738:2-Hydroxypropyl-beta-cyclodextrin; D019344:Lactic Acid; C021758:3,3',5,5'-tetramethylbenzidine; D018698:Glutamic Acid; D006861:Hydrogen Peroxide; D006735:Horseradish Peroxidase; D005947:Glucose