Recently, much attention is focused on a study of bioactive compounds of
plant origin with antibacterial and antioxidant properties. Such a kind of the
compounds in a relatively novel preparation (Enoxil) was obtained by the
oxidation of tannins extracted from grape seeds and it was found to possess high
antibacterial and antioxidant activity. The Enoxil is a mixture of monomeric
derivatives of catehine and epicatehine in the free form and esterified with gallic
acid as well as with peroxidic compounds. Due to high content of hydrophilic
groups, Enoxil is characterized by enhanced hygroscopicity, which, in turn,
requires special conditions for its storage or inclusion in formulation preventing
excess water uptake.
It is known that highly dispersed silica may be used in the drug
composition as a carrier of biologically active substance, which also decreases
the hygroscopicity of the latter. In the previous study we did reveal a decrease in
Enoxil hygroscopicity when this preparation was dispersed at silica surface. The
aim of this work was to prepare the Enoxil-silica composites with various
Enoxil-to-silica ratios and to examine the effect of silica content on water
absorption by these composites.
Fumed silica with Ssp of 300 m2g (A-300, Kalush, Ukraine) was mechanically
mixed with Enoxil powder (produced at the Institute of Chemistry, Academy of
Sciences of Moldova). The Enoxil-to-silica ratio was varied within 0.1’1.0
range. The capability of Enoxil, silica and Enoxil-silica composites to absorb
water from the gas phase was determined gravimetrically by the sample mass
change before and after holding in an exsiccator. The data on water absorption
by each composite was compared to the theoretically calculated amount of water
which would be absorbed by the composite in the case when individual
components do not affect the water absorption by each other.
For all the composites studied, the water absorption was found to be less than
that for the Enoxil powder. The largest decrease in hygroscopicity was observed
for the composites with Enoxil-to-silica ratio of 0.1’0.2, corresponding to the
approximate Enoxil monolayer formed at silica surfаce. Thus, the approach to
prepare Enoxil-silica composites was found to be suitable for decreasing the
Enoxil hygroscopicity and for improvement its storage stability.
Acknowledgements. The research leading to these results has received funding from the People Programme
(Marie Curie Actions) of the European Union's Seventh Framework Programme FP7/2007-2013/ under REA
grant agreement n° PIRSES-GA-2013-612484.