Since the discovery in 1922 of 2,2-diphenyl-1-(2,4,6-trinitrophenyl) hydrazyl stable free radical (DPPH^·), the chemistry of such open-shell compounds has developed continuously, allowing for both theoretical and practical advances in the free radical chemistry area. This review presents the important, general and modern aspects of the chemistry of hydrazyl free radicals and the science behind it.

A series of Au nanoparticles functionalised with nitroxide spin labels has been prepared and studied by EPR spectroscopy. Samples with low coverage of the spin label were used to investigate the dynamics of the surface-attached labels at different distances from the Au surface. The rotational correlation times of spin labels vary from 10⁻¹⁰ s to more than 3 × 10⁻⁹ s, depending on the chain length of the label and the surrounding ligand. The samples with higher coverage of the spin label show an increasing contribution of the exchange interaction between nitroxides adsorbed in a close proximity to each other on the same nanoparticle. Quantitative analysis of the EPR spectra of these samples suggests the presence of non-equivalent binding sites on the surface of Au nanoparticles. Additionally, EPR signals of isolated radical pairs were observed at intermediate coverage.

The increasing clinical use of artificial medical devices raises the issue of microbial contamination, which is a risk factor for the occurrence of biofilm-associated infections. A huge amount of scientific data highlights the promising potential of essential oils (EOs) to be used for the development of novel antibiofilm strategies. We aimed to review the relevant literature indexed in PubMed and Embase and to identify the recent directions in the field of EOs, as a new modality to eradicate microbial biofilms. We paid special attention to studies that explain the mechanisms of the microbicidal and antibiofilm activity of EOs, as well as their synergism with other antimicrobials. The EOs are difficult to test for their antimicrobial activity due to lipophilicity and volatility, so we have presented recent methods that facilitate these tests. There are presented the applications of EOs in chronic wounds and biofilm-mediated infection treatment, in the food industry and as air disinfectants. This analysis concludes that EOs are a source of antimicrobial agents that should not be neglected and that will probably provide new anti-infective therapeutic agents.