Amorphous solid dispersion (ASD) technology is popularly used for enhancing the solubility of poorly water-soluble drugs. Drug molecules in ASDs can be dispersed in the form of either amorphous (AASD) or molecular (MASD) forms. The boundary between AASDs and MASDs (A–M boundary) is defined as the drug concentration at which the existence of MASDs obviously influences the physicochemical properties of ASDs. In this work, fluorescence spectroscopy based on the aggregation-caused quenching (ACQ) phenomenon was used to determine the A–M boundary of curcumin (CUR) ASDs prepared via neat ball milling. The relationship between the fluorescence intensity and the loading of CUR in the sample is consistent with the Stern–Volmer equation. For the CUR ASDs with PVP, the samples with CUR loading below 10% show significantly increased fluorescence and have a higher solubility (~178 μg·mL−1), suggesting the A–M boundary is around 10%. Similar A–M boundaries around 10% were also observed for CUR ASDs with PVPVA, Soluplus, HPMC, and HPMCAS. It is of great significance to define the A–M boundary of ASDs for guiding pharmaceutical ASD formulas by balancing drug loading, stability, and solubility.
Yi Qin,Cheng-Hao Chuang,Xiaojing Liu,Xian Liang,Linfeng Xie,Kuan Wang,Chih-Wen Pao,Ying-Rui Lu,Yang Liu,Yawei Chen,Zhanwu Lei,Pengfei Yan,Liang Wu,Shuhong Jiao,Qing Li,Ruiguo Cao
Molecular catalysts have attracted significant attention because of their high activity, selectivity, and tunability. However, in heterogeneous catalysis, the uniform dispersion and immobilization of molecular catalysts on the supporting substrate remain a significant challenge due to their aggregation tendency. Here, we present a facile strategy to molecularly disperse and immobilize a series of macrocyclic metal complexes onto reduced graphene oxide (rGO) by using DNA as a mediator. The electroactive amounts of molecularly dispersed iron phthalocyanine (FePc) molecules are increased by ∼50 times greater than that of pristine FePc catalyst. As a result, the single-molecule catalyst demonstrates a notable power density (∼290 mW cm–2) in an H2/O2 alkaline polymer electrolyte fuel cell. Operando X-ray absorption spectroscopy experiments combined with density functional theory calculations reveal that the coordination interaction between FePc and DNA enables the molecular dispersion and immobilization of FePc on the surface of rGO, and consequently improves the activity by regulating the electronic structure of active centers. This study points out a facile strategy to tackle the fundamental challenges facing molecular catalysts in long-lasting energy conversion technologies.
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