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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-22 2:22 |
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Conference: Bucharest University Faculty of Physics 2001 Meeting
Section: Biophysics; Medical Physics
Title:
Studies of Colloidal Chlorophyll a in Dioxane-Water Mixtures
Authors:
Elena Puchianu, Doina M. Gazdaru
Affiliation:
University of Bucharest, Physics Department, POB MG-11, Romania
E-mail
Keywords:
Abstract:
The preparation and spectroscopic properties of the aggregated forms of
chlorophyll a in dioxane and water were studied. Chlorophyll a (Chl a) has
extracted from fresh spinach leaves and has purified by using column
chromatography on sugar, according to a standard procedure with a slight
modification. Chl a was stored as a stock solution in n-hexane at –7 °C.
Purity of Chl a in diethyl ether solution was ascertained before use by
measuring the ratios of the absorption at 429.6 nm to that at 661.6 nm and
also at 661.6 nm to 505.0 nm; the values of 1.29 and 58, respectively,
fulfil purity criteria of Chl a. Chl a dissolved in a small volume of
dioxan was mixed with a large volume of buffer (pH = 7.0) containing
dioxane.
In dioxane-water solutions, Chl a formed aggregates absorbing at 688 nm and
672 nm. Kinetics of conversion of 672 species in 688 species were
investigated for the samples containing dioxane concentrations below 0.08 M.
The relative amount of the 688 nm colloid incresed with increasing dioxane
concentration. Kinetics of the conversion reaction were also investigated
for samples containing different Chl a concentrations and the same dioxane
concentration.
A mechanism which is believed to be compatible with these results, is based
on the ability of dioxane to lower the dielectric constant of aqueous
solutions. In the present case the lowering of the solvent dielectric
constant, leading to increased electrostatic repulsion between charged
particles, is believed to be responsible for the formation of a new
colloidal state with a distinct absorption spectrum.
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