ABSTRACT
The hydrogen evolution reaction (HER) plays a crucial role in hydrogen gas production. Layers of transition-metal dichalcogenides (TMDs) possess adjustable electronic structures, and TMDs with H-phase structures have been proposed as substitute HER catalysts. Nonetheless, there are few systematic theoretical analyses of the HER catalytic properties of TMDs with T'-phase structures. Using a DFT calculation, we investigated the electrocatalytic properties of W-based dichalcogenides (WS2, WSe2, and WTe2) through defect engineering. It was found that the interaction of H atoms with the basal plane can be tuned using non-metallic atomic doping, especially with P, thereby enhancing catalytic activity. Furthermore, the computation results demonstrated that high P-doping concentrations can enhance the number of active sites and exhibit a suitable ΔGH*.
Subject(s)
Hydrogen , Transition Elements , Catalysis , Hydrogen/chemistry , TungstenABSTRACT
Formulating drugs into amorphous solid dispersions (ASDs) represents an attractive means to enhance the aqueous solubility of drugs. Furthermore, water-soluble polymers have proven highly advantageous for stabilizing supersaturated solutions of ASDs. However, the performance and mechanism of various polymers in stabilizing supersaturated drug solutions have not been well-studied. The aim of this study was to investigate the effects of different commercial polymers on the dissolution behaviors and supersaturation stabilization of the ASDs and to further explore the mechanism of polymer mediated supersaturation maintenance by studying the crystallization behaviors of the ASDs. In this study, nimodipine (NMD) was used as a model drug because of its poor water-solubility and fast crystallization rate in aqueous solution, and three polymers polyvinylpyrrolidone (PVP), vinylpyrrolidone-vinyl acetate copolymer (PVP VA), and polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft co-polymer (Soluplus) was selected as the drug carriers to form the ASDs with NMD. Solid-state characterizations of the ASDs confirmed the amorphous state of the ASD systems. ASDPVP VA demonstrated superior supersaturation maintenance in dissolution experiments compared to the other two ASD systems. Among the polymers tested, PVP VA most efficiently maintained dissolution of NMD and prevented its crystallization from the supersaturated solution. The ability of PVP VA to most-effectively maintain supersaturation of the drug was manifested by inhibition of crystal nucleation rather than inhibition of crystal growth following nucleation. These results suggest that nucleation inhibition was instrumental in enabling the polymer-mediated supersaturation maintenance, at least with NMD.
Subject(s)
Nimodipine , Polymers , Crystallization , Humans , Polymers/chemistry , Povidone/chemistry , SolubilityABSTRACT
Objective: Conventional chloramphenicol (CHL) eye drops are widely used anti-infection formulations for acute bacterial conjunctivitis. However, the therapeutic effects are limited by insufficient concentration in the conjunctival sac. Hence, the objective of this study is to formulate and develop novel CHL eye drops with improved topical concentrations by increasing the solubility and decreasing the transcorneal penetration. Research design and methods: CHL was included in the sulfobutyl ether-ß-cyclodextrin (SBE-ß-CD) using the freeze-drying method. Eye drops containing CHL/SBE-ß-CD complexes were prepared and evaluated for in vitro and in vivo studies. Results: The formation of CHL/SBE-ß-CD inclusion was confirmed by DSC, XRD, NMR, and SEM. The aqueous solubility of CHL was significantly enhanced, and the drug transcorneal penetration was inhibited after inclusion. The CHL/SBE-ß-CD displayed sustained release profiles. The tear fluid elimination kinetic study showed that the CHL/SBE-ß-CD eye drops had better ability to prolong the residence time, and significantly increase CHL concentration in the conjunctival sac. Besides, it was shown that CHL/SBE-ß-CD eye drops were nonirritating to rabbits' eyes. Conclusions: The SBE-ß-CD inclusions offer a potential alternative strategy for ocular administration of poorly water-soluble drugs in the conjunctival sac.
