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Electrochemical Generation of Superoxide Ion and Other Oxy Radicals
Published in Robert A. Greenwald, CRC Handbook of Methods for Oxygen Radical Research, 2018
Donald T. Sawyer, Kenneth Yamaguchi, Thomas S. Calderwood
Electrogeneration — Solutions of superoxide are prepared by use of an oxygen-saturated (1 atm O2) aprotic solvent. At 1 atm, the saturation concentration of O2 in Me2SO is 2.1 mM, in DMF is 4.8 mM, in Py is 4.9 mM, and in MeCN is 8.1 mM.2b A cyclic voltammogram is obtained by scanning negatively from the rest potential (see Figure 1). The peak potential for the reduction of dioxygen plus −0.14 V is used to set the control voltage for the potentiostat. During the electrolysis, dioxygen is continuously bubbled through a stirred solution. Upon completion of the electrolysis, argon is passed through the solution to purge the dissolved dioxygen. Argon is continuously passed over the solution during the cyclic voltammetry experiment. The potential is scanned positively from the rest potential of the deaerated O2− solution. The anodic peak current from a positive-sweep voltammogram (initiated at the rest potential of the argon-purged solution) provides a measure of the O2− concentration in the product solution. This value, along with the integrated coulometric current, is used to calculate the efficiency of the electrosynthesis of O2−. Typical generation efficiencies at platinum and graphite electrodes in several aprotic solvents are given in Table 1. The efficiency of an electrosynthesis is limited by the presence of protic sources and Lewis acids in the solvent, on the surfaces of the electrodes, and on the interior walls of the electrolysis cells. Both H2O and trace levels of transition metals are the major cause of decomposition of O2− solutions via disproportionation.8
Emerging theranostics to combat cancer: a perspective on metal-based nanomaterials
Published in Drug Development and Industrial Pharmacy, 2022
Tejas Girish Agnihotri, Shyam Sudhakar Gomte, Aakanchha Jain
Metal-organic frameworks (MOFs) are porous coordination polymers, which have been self-assembled from ligand molecules. They have been the subject of attraction due to their high porosity, large surface area, thermostability, and ability to functionalize with different drugs or moieties. They are quite useful in the treatment of cancer because of their remarkable properties including the high binding ability to cancer cells eliciting targeted therapy, drug delivery in terms of pH stimuli, and photosensitization. There have been several methods of synthesis of MOFs such as microwave-based synthesis, solvothermal synthesis, vapor deposition synthesis, solvent-free synthesis, and electrosynthesis. The characterization methods comprise of morphological evaluation by scanning electron microscopy and atomic force microscopy, X-ray diffraction technique, and X-ray absorption spectroscopy to characterize the crystalline structure of MOFs [120]. MOFs have been widely employed in detecting biomarkers for cancer because of their distinctive features. Lanthanides are suitable candidates for functionalization with MOFs by virtue of their luminescence emission in the visible region [121]. Photodynamic therapy (PDT), one of the treatment modalities in cancer makes use of photosensitizers that are dependent on oxygen, however; on the contrary, the tumor microenvironment is in hypoxic condition making PDT ineffective. To overcome this challenge, scientists have come up with hypoxia-activated prodrugs in combination with PDT. Liu et al. [122] formulated Hf-TCPP nanoscale MOFs by solvothermal method with porphyrin being a photosensitizer agent. Tirapazamine, a prodrug was attached to Hf-TCPP MOF and further functionalized with polymer, DOPA-PIMA-PEG to make stable and controlled release delivery. Due to the higher content of porphyrin in NPs, the formulated system was able to produce a higher level of ROS, which enabled it to cytotoxic to tumor cells upon administration. MOFs have also been utilized in PTT. Indocyanine green, a photoactive dye that has been approved by US-FDA suffers from some limitations like low solubility profile, low responsiveness to theranostics, and low targeting ability to cancerous cells. To overcome these problems, Cai et al. [123] designed MOF based on hyaluronic acid–iron NPs with the incorporation of indocyanine green. The research findings showed that more than 40% of dye was loaded in MOF with high uptake into MCF-7 cells. The targeting ability of developed MOF-based NPs was also proved based on tumor xenograft models establishing a good platform for cancer imaging and therapeutic applications in cancer.