Production of Hydroxyl Radical via the Activation of Hydrogen Peroxide by Hydroxylamine

The production of the hydroxyl radical (HO·) is important in environmental chemistry. This study reports a new source of HO· generated solely from hydrogen peroxide (H₂O₂) activated by hydroxylamine (HA). Electron paramagnetic resonance analysis and the oxidation of a HO· probe, benzoic acid, were used to confirm the production of HO·. The production of HO· increased with increasing concentrations of either HA or H₂O₂ as well as decreasing pH. The second-order rate constant for the reaction was (2.2 ± 0.2) × 10^–4 M^–1 s^–1. HO· was probably produced in two steps: the activation of H₂O₂ by protonated HA and then reaction between the H₂O₂ and the intermediate protonated aminoxyl radical generated in the first step. Such a two-step oxidation can possibly be ascribed to the ionizable hydroxyl moiety in the molecular structure of HA, as is suggested by comparing the reactivity of a series of HA derivatives in HO· production. The results shed light on a previously unknown source of HO· formation, which broadens the understanding of its role in environmental processes

Effective Synergistic Effect of Dipeptide-Polyoxometalate-Graphene Oxide Ternary Hybrid Materials on Peroxidase-like Mimics with Enhanced Performance

Dipeptide-polyoxometalates (POMs)-graphene oxide (GO) ternary hybrid is an excellent peroxidase-like mimic, exhibiting enhanced peroxidase-like activity compared to POMs alone. The hybrid was readily prepared through a reprecipitation method involving electrostatic encapsulation of H₃PW₁₂O₄₀ (PW₁₂) by cationic diphenylalanine (FF) peptide and coassembly of FF@PW₁₂ spheres with graphene oxide (GO). Using 3,3′,5,5′-tetramethylbenzidine (TMB) as the chromogenic substrate, the peroxidase-like activity of FF@PW₁₂ was evaluated in the heterogeneous phase, and it is 13 times higher than that of pristine PW₁₂ in the homogeneous phase. Furthermore, ternary hybrids of FF@PW₁₂@GO containing 5 wt % GO could enhance the activity 1.7 times higher than that of FF@PW₁₂. The noncovalent interactions of hydrogen bonding and ionic interaction between GO and POMs are speculated to result in the synergistic effect for the enhancement of peroxidase-like performance. The strong interactions between rGO and PW₁₂ are evaluated by a four-probe Hall measurement via the van der Pauw method, and rGO is significantly p-doped by the doping effect of PW₁₂ with lower LUMO energy than that of the energy level of rGO and also due to the electron reservoir feature of PW₁₂. Cyclic voltammogram measurements also suggest that GO causes significant influence on the electronic structure of the reduced forms of the redox couples of PW₁₂. The nature of the TMB catalytic reaction may originate from the generation of the hydroxyl radical (^•OH) from the decomposition of H₂O₂ by ternary hybrids and the formation of peroxo species of POM. Taking advantage of the UV–vis signals of TMB being correlated to the concentration of H₂O₂, FF@PW₁₂@GO can be used to detect H₂O₂ within the limit of detection of 0.11 μM, and the detection range is 1–75 μM. The present method indeed opens up a promising route in constructing heterogeneous peroxidase-like mimics through the use of POMs via the introduction of GO for building H₂O₂ sensors

Synthesis, characterization, and biological evaluations of some steryl 2-methoxybenzoates as anticancer agents

<p>Using cholesterol, stigmasterol and sitosterol as starting materials, a series of 7-subsitituted-ster-3-yl 2-methoxybenzoate analogs were prepared through reacting with 2-methoxybenzoyl chloride and introducing some function groups, such as carbonyl, hydroxyl and various thiosemicarbazones, at 7-position of steroidal nucleus. The structures of these new compounds were characterized by IR, NMR and HRMS. Their antiproliferative activities were evaluated by using several types of cancer cells. Interestingly, the compounds displayed potent antiproliferative activity against CNE-2 (nasopharyngeal carcinoma cell lines), BEL-7402 (human liver cancer cell lines) and HepG2 (human liver cancer cell lines), suggesting that they have potential to be drug candidates for cancer treatment.</p