Normal- and reversed-phase high-performance thin-layer chromatography methods for the simultaneous determination of remogliflozin etabonate and metformin hydrochloride antidiabetic drugs in bulk and tablet formulation

JPC – Journal of Planar Chromatography – Modern TLC - Two new, simple, fast, and sensitive methods, normal- and reversed-phase high-performance thin-layer chromatography (NP-HPTLC and...     

Antioxidant Polymers with Enhanced Neuroprotection Against Insulin Fibrillation

Lipoic acid (LA) and dihydrolipoic acid (DHLA) are well established antioxidants to scavenge reactive oxygen species (ROS). However, they are carboxylates with ≈4.7 pKa making them negatively charged at physiological pH (7.4) reducing their passive diffusion through cell membranes. LA is known to be capable of reducing protein fibrillation. Incorporation of LA and especially DHLA in polymer side chains are scarce. Herein, the first examples of the anti-amyloidogenic effect of LA and DHLA incorporated into the side-chain of a block copolymer with a water-soluble poly(polyethylene glycol methyl ether methacrylate) (PPEGMA) segment are presented. The resultant polymers show improved ROS scavenging activity and improved ability to reduce insulin fibrillation compared to free LA and DHLA. Furthermore, the resultant polymers are also capable of disintegrating preformed insulin firbrils. Interestingly, polymers with dihydro-lipoate moieties showed 93% free radical scavenging activity with 91% anti-fibrillating efficacies for insulin protein confirmed by 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay and Thioflavin T (ThT) dye binding study, respectively. Further, the antioxidant polymers increase the cell viability against fibrillar insulin aggregates that may be involved in the etiology of several diseases. Overall, this work reveals that antioxidant polymer-based therapeutic agents can serve as a powerful modulation strategy for developing novel drugs in future against amyloid-related disorders.     

Catalytic Deactivation and Regeneration of Nickel Microparticles in a Home-Built Microchannel-Coupled Millireactor: Substrate Specificity and Multiphase Flow Dependency

Substrate-assisted product desorption often proposed in heterogeneous catalysis (nanozymes) denounces the catalytic deactivation of these catalysts. On the contrary, the catalytic deactivation of rigid heterogeneous catalyst becomes noticeable in a continuous flow reactor. Surprisingly, it has been addressed inadequately and in an isolated manner. In this study, we have developed a cost-effective non-lithographic method for the fabrication of a PDMS-based microchannel-coupled-millreactor. Immobilized nickel particles are resistant to leaching in the flow process. During continuous operation, millireactors show a strong catalytic activity for reduction of resazurin and p-nitrophenol with a conversion rate of almost 100 %. Catalytic poisoning is ubiquitous and gets gradually prominent whereas complete catalytic deactivation of magnetic Ni-microparticles is found to be an instantaneous process. Relatively large-sized resorufin binds predominantly to the surface and thereby blocks the access of the substrate to the Ni-particles. The dissociations of product molecules - resorufin and p-aminophenol are the rate-limiting steps that caused the abrupt deactivation of Ni-microparticle. The kinetic mechanism of heterogeneous derived from the Langmuir-Hinshelwood mechanism satisfactorily explains the catalytic poisoning and deactivation of nickel microparticles. This study sheds light on the intricacies of catalytic activity and poisoning of magnetic nickel microparticles.