Synthesis of Carbonate beta-cyclodextrin nanosponges utilizing choline Chloride-ZnCl2 deep eutectic solvent

Abstract

Carbonate cyclodextrins are a form of nanosponges widely used in several areas, including the pharmaceutical field, because they are non-toxic, stable at high temperatures (up to 300 °C), and exhibit a strong affinity for biological compounds. However, their preparation into petroleum solvents (DMF or DMSO), as well as the time and heating required were the main drawbacks of carbonate cyclodextrin nanosponges (CD-NS). Therefore, it is crucial to prepare CS-NS in an environmental condition and cost-effective method. Thus, CD-NS were obtained by crosslinking beta-cyclodextrin (βCD) and diphenyl carbonate (DPC), for the first time, into deep eutectic solvents (DES) based on choline chloride (ChCl) and zinc chloride (ZnCl₂) under microwave irradiations. As an experimental procedure, the preparation of DES was performed under different molar ratios (ChCl:ZnCl₂, 1:1, 1:2, 1:4, 2:1). Then, βCD was cross-linked to DPC (1:4 as a molar ratio) under irradiation (80 W) into DES. The four CS-NS obtained were weighted, and particle characteristics of the formulations, crystalline and morphology properties, molecular structure and thermal behavior were thoroughly examined. As a result, yields were comprised between 65.2 % and 13.7 % for the CD-NS formulations 1:2 and 1:4, respectively. Furthermore, the dynamic light scattering studies showed a particle size ranging from 666.9 to 730.4 nm with a narrow size distribution. In addition, powder X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscopy, and thermogravimetry analysis demonstrated the successful formation of CD-NS. Therefore, preparing carbonate cyclodextrin nanosponges into a deep eutectic solvent under microwave irradiation proved an efficient method with a green solvent and a low-cost process.