Study On The Determination And Mechanism Of Aloe Polysacchride By Fluorescence Quenching And Electrochemical Method

With many biological functions of aloe polysaccharide (APS) being constantly revealed and understood, the content of APS representing the quality of aloe has been accepted, so the method for the determination of APS becomes the focus of attention. In this paper, we used fluorometric and electrochemical analyses to establish new methods for the determination of APS on the basis of the fluorescence nature and electrical activity of Alizarin red (AR) under optimal conditions. The results show that the proposed method is sensitive, simple, selective and consistent with the traditional spectrophotometric one. The main contents are shown as follows:(1) A novel method for the analysis of APS was developed by fluorescence quenching method based on the fact that AR (the fluorescent agent) and APS (the quencher) could form purple non-fluorescent complex in deionized water at room temperature. In doubly deionized water, the quenched fluorescence intensity of AR was positively proportional to the concentration of APS in the range of 0.444-16.65μg?mL^-1 and the linear regression equation isΔF=0.8807C+1.8132, R²=0.9999 with the detection limit (3σ) of 0.1425 mg?L^-1. The relative standard deviation is RSD≤3%. The method has been successfully applied to the determination of APS in the aloe products.(2) The linear sweep voltammetric method for the determination of APS has been proposed based on the forming of a non-electrical activity AR-APS complex between AR and APS in the acid medium with a glassy carbon (GC) electrode modified with multi-wall carbon nanotubes (MWNTs). Moreover, APS-AR complex can greatly reduce current intensity signal of AR and the reduced current intensity (ΔI"p) was proportional to the concentration of APS. Under the optimum conditions, a sensitive cathodic peak of AR on the MWNTs modified GC electrode was obtained at around -0.36V (vs. SCE). The reduction peak current was linearly proportional with the concentration of APS over the range of 5.0×10^-9 to 10.0×10^-8 mol·L^-1 with a detection limit of 9.33×10^-10 mol·L^-1. The relative standard deviation was RSD≤0.8%. The mole ratio and the binding constant are 1:1 and 2.75×10⁴, respectively. The proposed method is sensitive and accurate, and can be applied to determine APS in simulated samples and real samples with satisfactory results.(3)The interaction between AR and APS in weakly acidic media was investigated by fluorescence spectrophotometric (FS) and UV spectroscopic (UV) methods. The experimental results indicate that the quenching mechanism of APS by AR was a static quenching procedure. Various parameters have been evaluated, such as K_q, K_sv (K_q is the quenching rate constant of the biomolecule, K_sv is the dynamic quenching constant),ΔHΘ,ΔGΘandΔSΘ. The AR-APS purplish red complex is formed by hydrophobic interaction on the foundation of electrostatic interaction between AR and APS. Based on the F?rster's theory of non-radiation energy transfer, the binding distance, r, between the donor (APS) and acceptor (AR) was evaluated by synchronous fluorescence. The results show that the binding of AR to APS can induce conformational changes in APS.