The exo-hydroxyl group (exo-OH) on isosorbide (ISB) has long been asserted as a highly reactive moiety compared with the endo-hydroxyl group (endo-OH). In this study, calculations based on density functional theory and experiments without adding catalysts reveal that endo-OH has strong nucleophilic ability, and in the case of transesterification with diphenyl carbonate, the nucleophilic attack surmounts steric hindrance in rendering endo-OH more reactive than exo-OH. The kinetics of transesterification with different catalysts is investigated to determine the catalytic reactivity and molecular structure evolution. The results show that preferential activation of exo-OH moieties can be achieved either by reducing the coordination ability of catalytic cations (lg β1) or by enhancing the alkalinity of catalytic anions. Despite the low reactivity of exo-OH on ISB monomers, terminal exo-OH on carbonate oligomers exhibits higher reactivity than terminal endo-OH, justifying the experimental fact that ISB-based polycarbonates (ISB-PCs) are mostly terminated by endo-OH. Balancing the reactivity between endo-OH and exo-OH can be promoted by increasing the reaction temperature, thus accelerating transesterification to a high equilibrium constant. These findings help to clarify the mechanism of ISB transesterification and provide new strategies for the synthesis of high-molecular-weight ISB-PCs.
Rongmu Lv,Keke Du,Qianqian Liu,Xiangyu Meng,Lizhu Chen,Zhifei Wang
Efficiently, enhancing intracellular oxidative stress via increasing intracellular hydroxyl radicals (˙OH), which is based on the Fenton reaction and lowering glutathione (GSH) is a promising approach for cancer treatment. Herein, we synthesized a new alloy nanomaterial, Fe5Cu3O@BSA (FCB) with good dispersity aimed at introducing copper ions to improve the Fenton reaction efficiency and reduce GSH. Under the weak acid microenvironment at the tumor, FCB can release Fe2+ and Cu2+ and the released free electrons are expected to combine with oxygen to further generate H2O2, leading to an excessive production of H2O2 in the cells. Meanwhile, the released Fe2+ and Cu2+ can not only perform a higher reaction efficiency on producing ˙OH but also consume GSH, which dramatically increases the intracellular oxidative stress in both directions. In vitro experiments showed that the incubation of human breast cancer cells (MCF-7 cells) with 100 μg mL−1 FCB nanoparticles resulted in a 65.9% mortality rate after 24 h. The in vivo experiments showed that FCB could effectively inhibit tumor growth. In this study, a therapeutic strategy based on metal biomaterials with good biocompatibility was established to effectively enhance oxidative stress and has great potential in tumor treatment.
In this study, a series of high-activity imidazole-based dicationic ionic liquids (DILs) were designed and prepared as efficient catalysts for balancing the reactivity between the endo-hydroxyl group (endo-OH) and the exo-hydroxyl group (exo-OH) of isosorbide (ISO) to synthesize high molecular weight poly(isosorbide carbonate) (PIC). Meanwhile, the thermal performance of PIC was precisely optimized by regulating the chain configuration. The results showed that when the trace amounts (4.5 × 10−5 based on the ISO molar amount) of bis-(3-methyl-1-imidazole)-ethylene dibromide ([C2(Min)2][Br]2) were used, the weight average molecular weight (Mw) of PIC reached 98 700 g mol−1. It could be concluded from the results of the experiment and the stimulation that the high catalytic activity of DILs was attributed to the strong electrostatic interaction between the cation and the substrate and the effective balance of the reactivity of the endo-OH and the exo-OH. Furthermore, we found that the reduction of hydroxyl groups in the terminal groups and the increase of endo–endo (a1) structure in the repeating unit improved the thermal properties of PIC. Finally, 1H NMR, Fourier infrared spectroscopy, and density functional theory (DFT) calculations were used to verify the reaction process through anion and cation multi-site synergistic effect and a possible electrophilic–nucleophilic reaction mechanism was successfully obtained.
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