Crystal engineering of ionic cocrystals comprising Na/K salts of hesperetin with hesperetin molecules and solubility modulation

Abstract

Hesperetin (HES) is a weakly acidic flavonoid of topical interest owing to its antiviral properties. Despite the presence of HES in many dietary supplements, its bioavailability is hindered by poor aqueous solubility (1.35 µg ml−1) and rapid first-pass metabolism. Cocrystallization has evolved as a promising approach to generate novel crystal forms of biologically active compounds and enhance the physicochemical properties without covalent modification. In this work, crystal engineering principles were employed to prepare and characterize various crystal forms of HES. Specifically, two salts and six new ionic cocrystals (ICCs) of HES involving sodium or potassium salts of HES were studied using single-crystal X-ray diffraction (SCXRD) or powder X-ray diffraction and thermal measurements. Structures of seven of the new crystalline forms were elucidated by SCXRD, which revealed two families of isostructural ICCs in terms of their crystal packing and confirmed the presence of phenol...phenolate (PhOH...PhO−) supramolecular heterosynthons. Diverse HES conformations were observed amongst these structures, including unfolded and folded (previously unreported) conformations. One ICC, HES with the sodium salt of HES (NESNAH), was scalable to the gram scale and found to be stable after accelerated stability testing (exposure to elevated heat and humidity). HESNAH reached Cmax after 10 min in PBS buffer 6.8 compared with 240 min in pure HES. In addition, relative solubility was observed to be 5.5 times greater, offering the possibility of improved HES bioavailability.

Keywords

• crystal engineering
• ionic cocrystals
• phenol–phenolate synthons
• nutraceuticals
• molecular crystals