Kinetic and thermodynamic parameters of sorption of steroid saponin Tribulus Terrestris on a natural biopolymer – chitosan

Abstract

In the modern pharmaceutical market, herbal medicines occupy a significant share, in particular, preparations based on steroid saponins isolated from the well-known medicinal plant Tribulus Terrestris (creeping anchors). These biologically active compounds are widely used in various fields, including medicine for the treatment and prevention of a wide range of diseases, the pharmaceutical industry as components of biologically active food additives (dietary supplements), as well as in the cosmetology industry. One of the promising areas in modern drug development technology is the method of immobilization of biologically active molecules in the structure of a carrier matrix in order to form so-called nanomicelles containing an encapsulated active ingredient. Chitosan, a natural biopolymer, can be used as a basis for creating such innovative compounds. Chitosan, due to its high biocompatibility with body tissues, its ability to biodegrade (biodegradability), its non-toxicity, and its cationic properties, has significant potential as a carrier material for targeted drug delivery in the body. Numerous scientific studies have shown that incorporating a drug into a carrier structure protects the active ingredient from degradation under in vivo (within the body) and in vitro (outside the body) conditions, enhancing its therapeutic efficacy and preserving its biological activity for an extended period. The work carried out a study of the kinetics of sorption of steroid saponins on chitosan. The total fraction of steroid saponins extracted from the medicinal plant Tribulus Terrestris was chosen as the object of research. Chitosan produced by the company LLC Bioprogress was used as a sorbent. Kinetic curves of sorption of saponin on chitosan were obtained by the limited volume method. Selected aliquots were analyzed for the content of saponin by UV spectrophotometry. It was found that the time of equilibrium is on average about 30 minutes. During the sorption process, there is no significant change in the acidity (pH) of the solution, which suggests that there is no significant ionic interaction with the protonated amino groups in the chitosan structure. Various mathematical models were used to analyze the kinetic parameters of the sorption process, including the Boyd-Adams diffusion model, pseudo-first-order and pseudo-second-order kinetic equation models, and the Weber-Moris equation, which takes into account the influence of the internal diffusion stage on the absorption rate of the target substance. A comparison of the results obtained using these models showed that the kinetics of saponin sorption on chitosan is most adequately described by a pseudo-second-order equation, which is confirmed by sufficiently high values of the determination coefficients (R²). In addition, the influence of temperature on the nature of the sorption isotherms was studied. Some equilibrium characteristics of the studied process (the energy of the sorption process, its enthalpy, and entropy) were calculated. It was found that the absorption of saponin from a solution is accompanied by an endothermic effect.