Hydration of Chlorophyll a
The sorption isothermes and infrared spectra (4000–1000 cm-1) of Chlorophyll a (chl a) are compared.
Between 90 and 10 % relative humidity r.h. 1–2 H2O/chl a is present during desorption. The H2O spectra indicate the presence of two spectroscopically different H2O molecules containing free OH groups and H- bonds of intermediate strength. At low H2O contents (below 1 H2O chl a) H2O interactions are very different and strong H-bonds are formed. This H2O is desorbed only at elevated temperatures (80–100°C). During the subsequent H2O adsorption process water molecules form 2 moderately strong H-bonds with chl a. The changes in H2O interaction are reflected by the spectra of chl a in the C=O streching region as well.
The results are interpreted with respect to a cooperative influence of the magnesium-ion of chl a on the hydration.
KeywordsAcid Ethyl Ester Intermediate Strength Acetic Acid Ethyl Photochemical Energy Conversion Cooperativity Factor
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