Antibacterial activity of thymol/carvacrol and clinoptilolite composites prepared by supercritical solvent impregnation

Novel composites based on natural zeolite-clinoptilolite and monoterpene phenols-thymol and carvacrol were prepared by supercritical solvent impregnation (SSI) in supercritical carbon dioxide (scCO(2)) at 30 MPa and 35 degrees C during 18 h. The content of phenols in composites (thymol-23.0 and carvacrol-19.1 wt%) was determined using both C,H,N and thermal analysis (TGA); interactions of the phenols with the zeolite lattice studied by Fourier transform infrared spectroscopy (FTIR) and powder X-ray diffraction (PXRD) showed that the zeolite lattice was preserved in the composites. The composites exhibited antibacterial activity toward Gram-negative bacteria Escherichia coli DSM 498 and Gram-positive bacteria Staphylococcus aureus ATCC 25923 in different water media (phosphate buffer solution, spring water and lake water). After 1 h carvacrol-containing clinoptilolite showed better antibacterial activity than composite with thymol. Both composites expressed bactericidal effect after 24 h of contact. Leaching of the phenols from composite in water was more pronounced from thymol (22.7-32.1%) than for carvacrol (6.2-8.9%) suggesting influence of steric effect on the desorption process.