Study Of Ions Recognition By Chlorophyll-porphyrin Compounds

Fluorescence analysis is a method obtained by monitoring fluorescence. It is an important component of the molecules spectrum . There are various advantages in using fluorescence. Firstly, it is a powerful visual phenomenon. Secondly, its sensitivity is several orders of magnitude higher than that of absorption spectroscopy. Thirdly, a spectrofluorimeter is a piece of equipment commonly available in many scientific laboratories. Fluorescence analysis has been rapid development and been widely used in industrial analysis, food, medicine, biology and other fields in recent decades .Porphyrins are aromatic compounds comprising a large 20-membered aromatic ring and they can act as ligands, coordinating to a wide variety of metal ions via four nitrogen atoms. In analytical chemistry,porphyrins are often used for molecular recognition and ion identification for its special structure.In this paper, pheophytins were obtained from chlorophylls and were used to detect Cu2+,Mn2+.The main work of the research as follows:1. The chlorophyll-a and chlorophyll-b are separated from fresh spinach leaves by the column chromatography with the sucrose as immobile phase and ether-petroleum (1:9v/v)as mobile phase. The pheophytin-a and pheophytin-b were obained by mixing chlorophyll-a and chlorophyll-b with HClO4 solution. By the absorption spectra, we can see that the purity of purified chlorophyll was up to 87% and the the conversion rate of chlorophyll-a to pheophytin-a was about 95%.TheUV-vis spectra and fluorescence emission spectra of chlorophyll-a,chlorophyll-b,pheophytin-a and pheophytin-b were studied.2. Pheophytin-a was mixed with a Cu2+ ion aqueous solution. A fluorescence quenching phenomenon was thus observed when the acetone solution of Pheophytin-a was mixed with an aqueous solution of Cu2+ ions. However, other physiologically relevant cations rarely caused any quenching fluorescence of Pheoa under the same experimental conditions. Kinetics of the fluorescence fading process was investigated by measuring the effects of Cu2+ ion concentration, reaction time and reaction temperature on the fluorescence intensity of the Pheoa acetone solution. An activation energy of 10±1 kJ mol-1 was estimated from Arrhenius empirical relation assuming that the interaction between the Pheoa and the Cu(II) ions was the first order reaction. The calibration graph obtained with the fluorescence was linear over the Cu2+ concentration range of 8.0×10-5—8.0×10-7 mol dm-3 with a detection limit of 8.0×10-7 mol dm-3 for Cu2+ i o n .3. Pheophytin-a mixed with a Mn2+ ion acetic acid solution. A fluorescence quenching phenomenon was thus observed when the ethanol solution of Pheoa was mixed with an acetic acid solution of Mn2+ ions at 60℃for 4 hours. A new method of detection of Mn2 +was provided .