Nitrosyl complexes of iron are formed in living species in the presence of nitric oxide. They are considered a form in which NO can be stored and stabilized within a living cell. Upon entering a topic in bioinorganic chemistry the researcher faces a wide spectrum of issues concerning synthetic methods, the structure and chemical properties of the complex on the one hand, and its biological implications on the other. The aim of this review is to present the newest knowledge on nitrosyl iron complexes, summarizing the issues that are important for understanding the nature of nitrosyl iron complexes, their possible interactions, behavior in vitro and in vivo, handling of the preparations etc. in response to the growing interest in these compounds. Herein we focus mostly on the dinitrosyl iron complexes (DNICs) due to their prevailing occurrence in NO-treated biological samples. This article reviews recent knowledge on the structure, chemical properties and biological action of DNICs and some mononitrosyls of heme proteins. Synthetic methods are also briefly reviewed.

The modification of cyclodextrins (CDs) with side chains containing aromatic groups was found to lead to an increase of the stability of the complex with the anticancer drug doxorubicin (Dox). The formation constants evaluated by voltammetry were several orders of magnitude larger than that of the unmodified β-CD ligand. For the CDs with aromatic moieties connected by linkers containing a triazole group, the formation constants of the complexes at pH 5.5 and 7.4 were very different. At lower pH, binding was much weaker as a result of protonation of the triazole moiety in the linker. The drug was then released from the complex. Molecular modeling of the Dox-β-CD system revealed different possible interactions between Dox and β-CD. The observed pH dependence of the complex formation constant can be exploited for drug delivery to the targeted cells. The toxicities of the synthesized complexes and each of the complex components were tested by the MTT assay on two cell lines, the human lung carcinoma and human cervical cancer cell lines.

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Nanomaterials with enzyme-like activity (nanozymes) have found applications in various fields of medicine, industry, and environmental protection. This review discusses the use of nanozymes in the regulation of cellular homeostasis. We also review the latest biomedical applications of nanozymes related to their use in cellular redox status modification and detection. We present how nanozymes enable biomedical advances and demonstrate basic design strategies to improve diagnostic and therapeutic efficacy in various diseases. Finally, we discuss the current challenges and future directions for developing nanozymes for applications in the regulation of the redox-dependent cellular processes and detection in the cellular redox state changes.