Dear Colleagues,

In 2021, the 90th anniversary of the birth of Prof. Leonid B. Volodarsky, a remarkable organic chemist, a recognized expert in the chemistry of nitrogenous heterocyclic compounds and stable nitroxide radicals, an excellent teacher, an erudite scientist in many fields and an organizer of science. Leonid Volodarsky was born in Moscow on 18 July 1931, in 1949 he entered the Moscow Mendeleev Institute of Chemical Technology, and in 1952 he continued his studies at the Leningrad Institute of Technology. In 1963 he defended his PhD thesis "Transformations of N-(1-oximino-1,2,3,4-tetrahydronaphyl-2)hydroxylamine" in Novosibirsk Institute of Organic Chemistry, and in 1972 he got Habilitation degree (Doctor of Sciences in Russia) "Study of the chemistry of  a-hydroxylaminoximes". Leonid Volodarsky laid the foundations of the scientific direction in the chemistry of nitrogenous bases of a number of hydroxylamines by synthesizing various hydroxylaminoximes and showing that these compounds are very promising precursors of a wide range of heterocyclic compounds. A new class of stable heterocyclic nitroxyl radicals (HP), derivatives of 3-imidazoline, was synthesized on the basis of hydroxylaminoximes and their derivatives. Later these radicals were called Volodarsky radicals, similar to the nitroxyl radicals of the 2-imidazoline series, named Ullman's radicals, in honor of their discoverer, Professor Edvin F. Ullman. Under the leadership of Volodarsky, original methods for the synthesis of mono- and di-N-oxides of imidazole, pyrazine, and pyrimidine derivatives were developed. He was the author of more than 300 scientific papers, 70 copyright certificates and 6 international patents and was the organizer and participant of many international scientific conferences. Lev Volodarsky was awarded by the State Prize of the Russian Federation in 1994 and in 2002, he was awarded the honorary V. V. Voevodsky Prize for the development of research in the field of nitroxyl radicals. In 2018 book by Volodarsky L.B., Reznikov V.A., Ovcharenko V.I Synthetic chemistry of stable nitroxides”, CRCPress, Boca Raton, Fla., 1994, was awarded by Elsevier as the most highly cited publication for last three years in Europe, Asia, Latin America and Russia. The calculation was carried out using the Scopus scientific publications database.The main scientific interest of Leonid Borisovich was stable nitroxyl radicals. Stable radicals are molecules with one or several unpaired electron spins on their outer shell. Nitroxide and triarylmethyl radicals are the most important classes of stable radicals. The discovery and development of electron paramagnetic spectroscopy has stimulated great interest in the chemistry of stable radicals. During recent decades, the application of stable radicals has expanded significantly, encompassing many scientific fields. For example, stable radicals have been used as building blocks in molecular magnetics, as mediators in controlled radical polymerization, as spin labels in structural biology, as spin probes in EPR tomography, as contrast agents in MRI, and as polarizing agents in dynamic nuclear polarization, to name but a few. Great progress has been made in the synthesis of different stable radicals with very fancy functional properties, such as high stability, narrow EPR lines, etc.

During the last years a huge library of new spin tags and spin probes for molecular biology, biochemistry, and biophysics was obtained by Volodarsky former PhD students, successors and colleagues. In recent years new possibilities of using nitroxyl radicals in biophysics arose, for example, the method of pH-sensitive spin probe, spin labels for biological substrates. The contribution of Volodarsky and his school to the development of the chemistry of coordination compounds with HP as paramagnetic ligands is undeniable and very significant. The first work in this area was related to the use of HP series of imidazoline, capable of forming chelate complexes with metal ions, to create a new analytical method for the quantitative determination of various metals using EPR spectroscopy. Since the complexes with paramagnetic metals themselves were of great theoretical interest as multi-spin systems consisting of several paramagnetic centers of different nature, a huge number of complex compounds with various metals were synthesized and characterized using Volodarsky radicals. For some of these complexes, the phenomenon of a low-temperature phase transition to the magnetic state was detected. It is not surprising that from these, in fact, pioneering works, a new scientific direction–the synthesis and study of molecular magnets-has emerged and is actively developing at the present time.

It is with this in mind that we honor Leonid Volodarsky  on the occasion of his 90-th years of birth and  for his outstanding achievements in the areas of organic synthesis, as well as his critical role in creating pH-sensitive nitroxide radicals.

The Special Issue on “Stable Radicals: Synthesis, Structure, and Applications” will provide an open forum where researchers may share their investigations and findings in this promising field and, thanks to the open access platform, increase their visibility. Contributions to this issue, in the form of both original research and review articles, may cover all aspects of the synthesis of stable radicals, the study of their chemical and physical properties, and different applications; studies with multidisciplinary input that offer new methodologies or insights are particularly welcome.

Prof. Dr. Elena Bagryanskaya

Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

• nitroxide radicals
• triarylmethyl radicals
• spin labels
• spin probes
• pulse dipole EPR spectroscopy
• EPR tomography
• synthesis of stable radicals
• nitroxide-mediated polymerization