Study of antibacterial effects of Transcarpathian clinoptilolite compositions modified in different chemical ways

Abstract

Background. Natural clinoptilolite (CL) meets most of the requirements for the multifunctional mineral nanomaterials. It is considered biologically neutral and non-toxic. CL is the only representative of natural zeolites that has been approved for use in medical practice and food industry. Antibacterial activity of Transcarpathian clinoptilolite was shown to be enhanced via its modification using thermal, chemical and mechanochemical treatments. The natural form of this mineral contains a significant concentration of surface silanol (-OH) groups. An increase in the efficiency of zeolite-based materials in terms of biological activity can be achieved by means of thermal and chemical treatments, replacement of cations in the exchange complex, doping with heavy metal cations, or mechanochemical treatment. Materials and Methods. FTIR spectroscopy, Electronic spectroscopy, Particle size distribution, IR spectroscopy, Crystal structure and morphology, Measurement of antibacterial activity. Results. Intact and thermally modified CL was shown to exhibit weak antibacterial effect, while its mechanical modification led to an enhanced activity. It was established that H-form of clinoptilolite demonstrated higher efficiency in inhibiting the growth of Gram-positive bacteria, compared to the Na-form of the clinoptilolite, but their effect on growth of Gram-negative bacteria was insignificant. Such an activity was accompanied by an increase in the specific surface area and porosity that promoted better contact with bacteria. Conclusions: Different samples of CL had dissimilar effect on specific types of bacteria. Intact CL has a weak antibacterial activity of inhibiting growth of microorganisms, while thermal, chemical, and mechanical modifications of the CL structure differentially increased such an activity. The H-form of CL inhibited the growth of Gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis) more effectively compared to the Na-form of CL. However, H-form of CL has a weak effect on growth of the Gram-negative bacteria (Pseudomonas aeruginosa, Pseudomonas fluorescens).