{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,9]],"date-time":"2026-09-09T13:08:31Z","timestamp":1788959311648,"version":"build-2803163510"},"reference-count":92,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2026,9,9]],"date-time":"2026-09-09T00:00:00Z","timestamp":1788912000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Pharmaceuticals"],"abstract":"<jats:p>Background\/Objectives: Electron paramagnetic resonance (EPR) spectroscopy is a direct and highly specific method for detecting paramagnetic species, including free radicals, transition-metal centers, spin labels and spin probes. In pharmaceutical research, it is particularly valuable in systems involving radical chemistry, oxidative degradation, drug\u2013membrane interactions, drug delivery carriers, metallodrugs and oxygen-sensitive microenvironments. This review aims to summarize current applications of and emerging opportunities for EPR spectroscopy in pharmaceutical research, with primary emphasis on continuous-wave (CW) EPR, the mode most widely used for routine pharmaceutical measurements. Methods: This review is organized around the main CW-EPR approaches relevant to pharmaceutical research, including direct detection of paramagnetic species, spin trapping, spin labeling and spin-probe analysis. The discussion emphasizes how spectral parameters such as the g-value, hyperfine splitting, signal intensity and linewidth can provide structural, kinetic and microenvironmental information. Results: CW-EPR supports the study of radical-mediated drug activity and toxicity, antioxidant properties, formulation stability, membrane interactions, carrier structure, metallodrug behavior and oxygenation. Its main strength is the ability to connect molecular-level radicals and paramagnetic processes with broader pharmaceutical questions related to drug efficacy, safety, stability and delivery. Conclusions: CW-EPR is a specialized but versatile analytical tool at the interface of radical chemistry, pharmaceutical technology and biomedical research. Recent developments in compact instrumentation, selective probes and spectral simulation may further expand its use in pharmaceutical development, stability assessment and drug delivery research.<\/jats:p>","DOI":"10.3390\/ph19091424","type":"journal-article","created":{"date-parts":[[2026,9,9]],"date-time":"2026-09-09T12:26:11Z","timestamp":1788956771000},"page":"1424","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Continuous-Wave Electron Paramagnetic Resonance Spectroscopy in Pharmaceutical Research: Current Applications and Emerging Opportunities"],"prefix":"10.3390","volume":"19","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-1116-4655","authenticated-orcid":false,"given":"Erim","family":"Be\u0161i\u0107","sequence":"first","affiliation":[{"name":"Department of Biophysics, Faculty of Pharmacy and Biochemistry, University of Zagreb, 10000 Zagreb, Croatia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8871-6622","authenticated-orcid":false,"given":"Davor","family":"\u0160aki\u0107","sequence":"additional","affiliation":[{"name":"Department of Analytical Chemistry, Faculty of Pharmacy and Biochemistry, University of Zagreb, 10000 Zagreb, Croatia"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,9,9]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Sies, H. (2020). Oxidative eustress and oxidative distress: Introductory remarks. Oxidative Stress: Eustress and Distress, Academic Press.","DOI":"10.1016\/B978-0-12-818606-0.00001-8"},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Juan, C.A., P\u00e9rez de la Lastra, J.M., Plou, F.J., and P\u00e9rez-Lebe\u00f1a, E. (2021). The chemistry of reactive oxygen species (ROS) revisited: Outlining their role in biological macromolecules (DNA, lipids and proteins) and induced pathologies. Int. J. Mol. Sci., 22.","DOI":"10.3390\/ijms22094642"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"2499","DOI":"10.1007\/s00204-023-03562-9","article-title":"Reactive oxygen species, toxicity, oxidative stress, and antioxidants: Chronic diseases and aging","volume":"97","author":"Jomova","year":"2023","journal-title":"Arch. Toxicol."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"165","DOI":"10.3233\/BSI-200206","article-title":"Electron paramagnetic resonance (EPR) spectroscopy: Food, biomedical and pharmaceutical analysis","volume":"9","author":"Iravani","year":"2020","journal-title":"Biomed. Spectrosc. Imaging"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"21","DOI":"10.1016\/j.ymeth.2016.05.013","article-title":"Detection and characterisation of radicals using electron paramagnetic resonance (EPR) spin trapping and related methods","volume":"109","author":"Davies","year":"2016","journal-title":"Methods"},{"key":"ref_6","first-page":"557","article-title":"Advancements in electron paramagnetic resonance (EPR) spectroscopy: A comprehensive tool for pharmaceutical research","volume":"74","year":"2024","journal-title":"Acta Pharm."},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Sch\u00f6neich, C. (2023). Primary processes of free radical formation in pharmaceutical formulations of therapeutic proteins. Biomolecules, 13.","DOI":"10.3390\/biom13071142"},{"key":"ref_8","first-page":"e56624","article-title":"In vivo EPR assessment of pH, pO2, redox status, and concentrations of phosphate and glutathione in the tumor microenvironment","volume":"79","author":"Bobko","year":"2018","journal-title":"J. Vis. Exp."},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Chumakova, N.A., Golubeva, E.N., Kuzin, S.V., Ivanova, T.A., Grigoriev, I.A., Kostjuk, S.V., and Melnikov, M.Y. (2020). New insight into the mechanism of drug release from poly(lactic-co-glycolic acid) microparticles using electron paramagnetic resonance spectroscopy. Polymers, 12.","DOI":"10.3390\/polym12123046"},{"key":"ref_10","first-page":"254","article-title":"Molecular imaging biomarkers of the tumor microenvironment: Advances in early cancer detection and treatment monitoring","volume":"8","author":"Rajendran","year":"2026","journal-title":"Adv. Biomark. Sci. Technol."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"11","DOI":"10.1016\/j.freeradbiomed.2024.01.012","article-title":"Sensitive simultaneous measurements of oxygenation and extracellular pH by EPR using a stable monophosphonated trityl radical and lithium phthalocyanine","volume":"213","author":"Buyse","year":"2024","journal-title":"Free Radic. Biol. Med."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"100009","DOI":"10.1016\/j.rbc.2023.100009","article-title":"Electron paramagnetic resonance (EPR) for investigating relevant players of redox reactions: Radicals, metalloproteins and transition metal ions","volume":"5\u20136","author":"Augusto","year":"2023","journal-title":"Redox Biochem. Chem."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"114","DOI":"10.3109\/10408363.2011.591772","article-title":"Free radicals and antioxidants at a glance using EPR spectroscopy","volume":"48","year":"2011","journal-title":"Crit. Rev. Clin. Lab. Sci."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"708","DOI":"10.1016\/j.bbagen.2013.03.034","article-title":"Detection and characterisation of radicals in biological materials using EPR methodology","volume":"1840","author":"Hawkins","year":"2014","journal-title":"Biochim. Biophys. Acta"},{"key":"ref_15","unstructured":"Gordy, W. (1980). Theory and Applications of Electron Spin Resonance, Wiley-Interscience. Techniques of Chemistry."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"2574","DOI":"10.1021\/acs.jpca.3c07892","article-title":"Regioselective rearrangement of nitrogen- and carbon-centered radical intermediates in the Hofmann\u2013L\u00f6ffler\u2013Freytag reaction","volume":"128","author":"You","year":"2024","journal-title":"J. Phys. Chem. A"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"4873","DOI":"10.1021\/acs.joc.4c02997","article-title":"Mechanistic insights into the propagation cycle of the Hofmann\u2013L\u00f6ffler\u2013Freytag reaction: Halogen vs hydrogen atom transfer","volume":"90","author":"You","year":"2025","journal-title":"J. Org. Chem."},{"key":"ref_18","first-page":"725","article-title":"Light-induced rearrangement from macrocyclic to bicyclic lactam: A case study of N-chlorinated laurolactam","volume":"74","author":"You","year":"2025","journal-title":"Acta Pharm."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"1924","DOI":"10.1002\/pol.20200039","article-title":"Recent progress in EPR study of spin labeled polymers and spin probed polymer systems","volume":"58","author":"Uddin","year":"2020","journal-title":"J. Polym. Sci."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"140653","DOI":"10.1016\/j.bbapap.2021.140653","article-title":"Nitroxide spin labels and EPR spectroscopy: A powerful association for protein dynamics studies","volume":"1869","author":"Torricella","year":"2021","journal-title":"Biochim. Biophys. Acta Proteins Proteom."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"4930","DOI":"10.1021\/jp8093947","article-title":"EPR line shifts and line shape changes due to spin exchange and dipole\u2013dipole interactions of nitroxide free radicals in liquids: 5. Further experimental and theoretical efforts to separate the effects of the two interactions","volume":"113","author":"Bales","year":"2009","journal-title":"J. Phys. Chem. A"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"65","DOI":"10.1006\/jmra.1995.1057","article-title":"Rapid quantitation from inhomogeneously broadened EPR spectra by a fast convolution algorithm","volume":"113","author":"Smirnov","year":"1995","journal-title":"J. Magn. Reson. A"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"42","DOI":"10.1016\/j.jmr.2005.08.013","article-title":"EasySpin, a comprehensive software package for spectral simulation and analysis in EPR","volume":"178","author":"Stoll","year":"2006","journal-title":"J. Magn. Reson."},{"key":"ref_24","unstructured":"\u0160aki\u0107, D., Be\u0161i\u0107, E., and Zub\u010di\u0107, G. (2026, September 03). VisualEPR, Online EPR Spectra Visualization and Simulation Tool. Available online: https:\/\/github.com\/DSakicLab\/visualEPR."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"31","DOI":"10.1016\/j.ymeth.2016.05.001","article-title":"Use of spin traps to detect superoxide production in living cells by electron paramagnetic resonance (EPR) spectroscopy","volume":"109","author":"Abbas","year":"2016","journal-title":"Methods"},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"619","DOI":"10.1089\/152308604773934387","article-title":"Detection of reactive oxygen and nitrogen species by EPR spin trapping","volume":"6","author":"Villamena","year":"2004","journal-title":"Antioxid. Redox Signal."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"24","DOI":"10.1016\/j.watres.2016.04.053","article-title":"Stability of 5,5-dimethyl-1-pyrroline-N-oxide as a spin-trap for quantification of hydroxyl radicals in processes based on Fenton reaction","volume":"99","author":"Fontmorin","year":"2016","journal-title":"Water Res."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"21","DOI":"10.1021\/acsmeasuresciau.2c00049","article-title":"Electron paramagnetic resonance for the detection of electrochemically generated hydroxyl radicals: Issues associated with electrochemical oxidation of the spin trap","volume":"3","author":"Braxton","year":"2022","journal-title":"ACS Meas. Sci. Au"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"143","DOI":"10.1021\/envhealth.4c00142","article-title":"Hydroperoxide-independent generation of spin trapping artifacts by quinones and DMPO: Implication for radical identification in quinone-related reactions","volume":"3","author":"Wang","year":"2024","journal-title":"Environ. Health"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"404","DOI":"10.1006\/abio.1997.2067","article-title":"Quantitative measurement of superoxide generation using the spin trap 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide","volume":"247","author":"Roubaud","year":"1997","journal-title":"Anal. Biochem."},{"key":"ref_31","first-page":"100123","article-title":"Characterization of radicals in polysorbate 80 using electron paramagnetic resonance (EPR) spectroscopy and spin trapping","volume":"4","author":"Mittag","year":"2022","journal-title":"Int. J. Pharm. X"},{"key":"ref_32","doi-asserted-by":"crossref","unstructured":"Rahmani-Manglano, N.E., Fallahasghari, E.Z., Mendes, A.C., Andersen, M.L., Guadix, E.M., Chronakis, I.S., and Garc\u00eda-Moreno, P.J. (2024). Oxidative stability of fish oil-loaded nanocapsules produced by electrospraying using kafirin or zein proteins as wall materials. Antioxidants, 13.","DOI":"10.3390\/antiox13091145"},{"key":"ref_33","doi-asserted-by":"crossref","unstructured":"Di Prima, G., De Caro, V., Cardamone, C., Oliveri, G., and D\u2019Oca, M.C. (2024). EPR spectroscopy coupled with spin trapping as an alternative tool to assess and compare the oxidative stability of vegetable oils for cosmetics. Appl. Sci., 14.","DOI":"10.3390\/app142210766"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"143","DOI":"10.1016\/j.freeradbiomed.2021.12.303","article-title":"Detection of singlet oxygen by EPR: The instability of the nitroxyl radicals","volume":"180","author":"Ferreira","year":"2022","journal-title":"Free Radic. Biol. Med."},{"key":"ref_35","doi-asserted-by":"crossref","unstructured":"Moghadam, M.S., Wiens, E., Gauvrit, S., Sammynaiken, R., and Collins, M.M. (2025). Electron paramagnetic resonance spectroscopy for analysis of free radicals in zebrafish. PLoS ONE, 20.","DOI":"10.1371\/journal.pone.0318212"},{"key":"ref_36","doi-asserted-by":"crossref","unstructured":"Berliner, L.J., and Reuben, J. (1989). Spin Labeling: Theory and Applications, Plenum Press. Biological Magnetic Resonance.","DOI":"10.1007\/978-1-4613-0743-3"},{"key":"ref_37","doi-asserted-by":"crossref","unstructured":"Sahu, I.D., and Lorigan, G.A. (2020). Electron paramagnetic resonance as a tool for studying membrane proteins. Biomolecules, 10.","DOI":"10.3390\/biom10050763"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"106","DOI":"10.3390\/biophysica1020009","article-title":"Probing structural dynamics of membrane proteins using electron paramagnetic resonance spectroscopic techniques","volume":"1","author":"Sahu","year":"2021","journal-title":"Biophysica"},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"102936","DOI":"10.1016\/j.sbi.2024.102936","article-title":"Non-canonical amino acids for site-directed spin labeling of membrane proteins","volume":"89","author":"Ledwitch","year":"2024","journal-title":"Curr. Opin. Struct. Biol."},{"key":"ref_40","doi-asserted-by":"crossref","unstructured":"Gallez, B. (2026). Electron paramagnetic resonance (EPR) meets drug delivery and biomaterials: A magnetic love story. Drug Deliv. Transl. Res., Advance online publication.","DOI":"10.1007\/s13346-025-01992-9"},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"715","DOI":"10.1146\/annurev-biochem-061516-045037","article-title":"Oxidative Stress","volume":"86","author":"Sies","year":"2017","journal-title":"Annu. Rev. Biochem."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"604","DOI":"10.1021\/ac051697f","article-title":"Electron paramagnetic resonance spectroscopy studies of oxidative degradation of an active pharmaceutical ingredient and quantitative analysis of the organic radical intermediates using partial least-squares regression","volume":"78","author":"Williams","year":"2006","journal-title":"Anal. Chem."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"453","DOI":"10.1016\/j.cub.2014.03.034","article-title":"ROS function in redox signaling and oxidative stress","volume":"24","author":"Schieber","year":"2014","journal-title":"Curr. Biol."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"3042","DOI":"10.1016\/j.foodchem.2013.05.133","article-title":"A study of the antioxidant properties of beers using electron paramagnetic resonance","volume":"141","author":"Polak","year":"2013","journal-title":"Food Chem."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"129566","DOI":"10.1016\/j.foodchem.2021.129566","article-title":"Exploring the chemical space of white wine antioxidant capacity: A combined DPPH, EPR and FT-ICR-MS study","volume":"355","author":"Romanet","year":"2021","journal-title":"Food Chem."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"512","DOI":"10.1016\/j.foodchem.2008.02.015","article-title":"Antioxidant and radical-scavenging activities of Slovak honeys\u2014An electron paramagnetic resonance study","volume":"110","author":"Zalibera","year":"2008","journal-title":"Food Chem."},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"351","DOI":"10.1038\/s41598-023-51099-9","article-title":"The amount of antioxidants in honey has a strong relationship with the plants selected by honey bees","volume":"14","author":"Shakoori","year":"2024","journal-title":"Sci. Rep."},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"127578","DOI":"10.1016\/j.foodchem.2020.127578","article-title":"Evaluation of PBN spin-trapped radicals as early markers of lipid oxidation in mayonnaise","volume":"334","author":"Merkx","year":"2021","journal-title":"Food Chem."},{"key":"ref_49","first-page":"950","article-title":"Evaluation of oxidative stability of vegetable oils enriched with herb extracts by EPR spectroscopy","volume":"69","author":"Zawada","year":"2015","journal-title":"Chem. Pap."},{"key":"ref_50","doi-asserted-by":"crossref","first-page":"11924","DOI":"10.1021\/bi0346087","article-title":"Antitumor agents 4. Characterization of free radicals produced during reduction of the antitumor drug 5H-pyridophenoxazin-5-one: An EPR study","volume":"42","author":"Alberti","year":"2003","journal-title":"Biochemistry"},{"key":"ref_51","doi-asserted-by":"crossref","first-page":"471","DOI":"10.3109\/10715769809066884","article-title":"EPR evidence for the involvement of free radicals in the iron-catalysed decomposition of qinghaosu (artemisinin) and some derivatives; antimalarial action of some polycyclic endoperoxides","volume":"28","author":"Butler","year":"1998","journal-title":"Free Radic. Res."},{"key":"ref_52","doi-asserted-by":"crossref","first-page":"740","DOI":"10.1016\/j.ejmech.2016.10.053","article-title":"Determination of the structures of radicals formed in the reaction of antimalarial drug artemisinin with ferrous ions","volume":"127","author":"Asano","year":"2017","journal-title":"Eur. J. Med. Chem."},{"key":"ref_53","doi-asserted-by":"crossref","first-page":"595","DOI":"10.2478\/acph-2024-0033","article-title":"Unveiling the antiglioblastoma potential of harmicens, harmine and ferrocene hybrids","volume":"74","author":"Poje","year":"2024","journal-title":"Acta Pharm."},{"key":"ref_54","doi-asserted-by":"crossref","unstructured":"Suzen, S., Gurer-Orhan, H., and Saso, L. (2017). Detection of reactive oxygen and nitrogen species by electron paramagnetic resonance (EPR) technique. Molecules, 22.","DOI":"10.3390\/molecules22010181"},{"key":"ref_55","doi-asserted-by":"crossref","first-page":"39879","DOI":"10.1074\/jbc.M104012200","article-title":"EPR detection of glutathionyl and protein-tyrosyl radicals during the interaction of peroxynitrite with macrophages","volume":"276","author":"Augusto","year":"2001","journal-title":"J. Biol. Chem."},{"key":"ref_56","unstructured":"Bruker (2026, September 03). Seeing the Unseen: Degradation Measured by EPR Spectroscopy. Application Note. Available online: https:\/\/www.syntechinnovation.com\/images\/Knowledge\/mat_epr\/Degradation_measured_by_EPR_spectroscopy.pdf."},{"key":"ref_57","unstructured":"Bruker (2026, September 03). Pharmaceutical Applications of EPR Spectroscopy. Webinar, 2018. Available online: https:\/\/www.bruker.com\/de\/news-and-events\/webinars\/2018\/pharmaceutical-applications-of-epr-spectroscopy.html."},{"key":"ref_58","doi-asserted-by":"crossref","first-page":"707","DOI":"10.1016\/j.freeradbiomed.2008.11.024","article-title":"Physical properties of lipid bilayers from EPR spin labeling and their influence on chemical reactions in a membrane environment","volume":"46","author":"Subczynski","year":"2009","journal-title":"Free Radic. Biol. Med."},{"key":"ref_59","doi-asserted-by":"crossref","first-page":"25","DOI":"10.1016\/0005-2736(95)00155-6","article-title":"Use of a novel method for determination of partition coefficients to compare the effect of local anesthetics on membrane structure","volume":"1240","author":"Schreier","year":"1995","journal-title":"Biochim. Biophys. Acta"},{"key":"ref_60","doi-asserted-by":"crossref","first-page":"107187","DOI":"10.1016\/j.polymertesting.2021.107187","article-title":"A novel methodology for hydrogel water content determination by EPR: The basis for real-time monitoring of controlled drug release and hydrogel swelling and degradation","volume":"98","author":"Nakarada","year":"2021","journal-title":"Polym. Test."},{"key":"ref_61","doi-asserted-by":"crossref","first-page":"26","DOI":"10.1016\/j.ejpb.2007.05.020","article-title":"Characterization of thermosensitive chitosan-based hydrogels by rheology and electron paramagnetic resonance spectroscopy","volume":"68","author":"Kempe","year":"2008","journal-title":"Eur. J. Pharm. Biopharm."},{"key":"ref_62","doi-asserted-by":"crossref","unstructured":"Sanaeifar, N., M\u00e4der, K., and Hinderberger, D. (2022). Macro- and nanoscale effect of ethanol on bovine serum albumin gelation and naproxen release. Int. J. Mol. Sci., 23.","DOI":"10.3390\/ijms23137352"},{"key":"ref_63","doi-asserted-by":"crossref","unstructured":"Veskovi\u0107, A., Nakarada, \u0110., Vasiljevi\u0107, O., Dobrov, A., Spengler, G., Enyedy, \u00c9.A., Arion, V.B., and Popovi\u0107 Bijeli\u0107, A. (2022). The release of a highly cytotoxic paullone bearing a TEMPO free radical from the HSA hydrogel: An EPR spectroscopic characterization. Pharmaceutics, 14.","DOI":"10.3390\/pharmaceutics14061174"},{"key":"ref_64","doi-asserted-by":"crossref","first-page":"94","DOI":"10.1016\/j.ejpb.2016.10.001","article-title":"Localization of dexamethasone within dendritic core\u2013multishell (CMS) nanoparticles and skin penetration properties studied by multi-frequency electron paramagnetic resonance (EPR) spectroscopy","volume":"116","author":"Saeidpour","year":"2017","journal-title":"Eur. J. Pharm. Biopharm."},{"key":"ref_65","doi-asserted-by":"crossref","first-page":"PL503","DOI":"10.1016\/0024-3205(94)00724-1","article-title":"Pharmacokinetic properties of nitroxide-labeled albumin in mice","volume":"54","author":"Liebmann","year":"1994","journal-title":"Life Sci."},{"key":"ref_66","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/S0010-8545(01)00437-4","article-title":"Paramagnetic spectroscopy of vanadyl complexes and its applications to biological systems","volume":"228","author":"Smith","year":"2002","journal-title":"Coord. Chem. Rev."},{"key":"ref_67","doi-asserted-by":"crossref","unstructured":"Alessio, E., and Messori, L. (2019). NAMI-A and KP1019\/1339, two iconic ruthenium anticancer drug candidates face-to-face: A case story in medicinal inorganic chemistry. Molecules, 24.","DOI":"10.3390\/molecules24101995"},{"key":"ref_68","doi-asserted-by":"crossref","unstructured":"Sharfalddin, A.A., Al-Younis, I.M., Mohammed, H.A., Dhahri, M., Mouffouk, F., Abu Ali, H., Anwar, M.J., Qureshi, K.A., Hussien, M.A., and Alghrably, M. (2022). Therapeutic properties of vanadium complexes. Inorganics, 10.","DOI":"10.3390\/inorganics10120244"},{"key":"ref_69","doi-asserted-by":"crossref","first-page":"1758835918780140","DOI":"10.1177\/1758835918780140","article-title":"5-fluorouracil and cardiotoxicity: A review","volume":"10","author":"Sara","year":"2018","journal-title":"Ther. Adv. Med. Oncol."},{"key":"ref_70","doi-asserted-by":"crossref","first-page":"99","DOI":"10.1016\/j.ijms.2003.11.010","article-title":"Electron impact ionization of 5- and 6-chlorouracil: Appearance energies","volume":"232","author":"Denifl","year":"2004","journal-title":"Int. J. Mass Spectrom."},{"key":"ref_71","doi-asserted-by":"crossref","first-page":"140080","DOI":"10.1016\/j.molstruc.2024.140080","article-title":"EPR study of a copper impurity center in a single crystal of 6-chlorouracil","volume":"1321","year":"2025","journal-title":"J. Mol. Struct."},{"key":"ref_72","doi-asserted-by":"crossref","unstructured":"Lagostina, V., Regueiro-Figueroa, M., Rousselin, Y., Esteban-G\u00f3mez, D., Platas-Iglesias, C., and Tripier, R. (2023). Magnetic and relaxation properties of vanadium(IV) complexes: An integrated 1H relaxometric, EPR and computational study. Inorg. Chem. Front., 10.","DOI":"10.1039\/D2QI02635J"},{"key":"ref_73","doi-asserted-by":"crossref","first-page":"1606","DOI":"10.1016\/j.jinorgbio.2006.05.008","article-title":"Oxidation of hydroxyurea with oxovanadium(V) ions in acidic aqueous solution","volume":"100","author":"Zahl","year":"2006","journal-title":"J. Inorg. Biochem."},{"key":"ref_74","doi-asserted-by":"crossref","first-page":"9021","DOI":"10.1016\/j.tetlet.2007.10.085","article-title":"Formation of free radicals during the oxidation of N-methylhydroxyurea with dioxovanadium(V) ion","volume":"48","author":"Weitner","year":"2007","journal-title":"Tetrahedron Lett."},{"key":"ref_75","first-page":"807","article-title":"Kinetics and mechanism of oxidation of hydroxyurea with hexacyanoferrate(III) ions in aqueous solution","volume":"82","author":"Budimir","year":"2009","journal-title":"Croat. Chem. Acta"},{"key":"ref_76","doi-asserted-by":"crossref","first-page":"133","DOI":"10.5562\/cca1799","article-title":"Kinetics and mechanism of oxidation of hydroxyurea derivatives with hexacyanoferrate(III) in aqueous solution","volume":"84","author":"Budimir","year":"2011","journal-title":"Croat. Chem. Acta"},{"key":"ref_77","first-page":"226","article-title":"Electron paramagnetic resonance: A powerful tool to support magnetic resonance imaging research","volume":"10","author":"Danhier","year":"2014","journal-title":"Contrast Media Mol. Imaging"},{"key":"ref_78","doi-asserted-by":"crossref","first-page":"197","DOI":"10.1007\/978-1-4939-8864-8_13","article-title":"Electron paramagnetic resonance spectroscopy of metalloproteins","volume":"1876","author":"Jasniewski","year":"2019","journal-title":"Methods Mol. Biol."},{"key":"ref_79","first-page":"e934116","article-title":"A review of the role of hypoxia in radioresistance in cancer therapy","volume":"27","author":"Boulefour","year":"2021","journal-title":"Med. Sci. Monit."},{"key":"ref_80","doi-asserted-by":"crossref","first-page":"120057","DOI":"10.1016\/j.lfs.2021.120057","article-title":"The impact of hypoxia on immune state in cancer","volume":"286","author":"Mortezaee","year":"2021","journal-title":"Life Sci."},{"key":"ref_81","doi-asserted-by":"crossref","unstructured":"Bigos, K.J., Quiles, C.G., Lunj, S., Smith, D.J., Krause, M., Troost, E.G., West, C.M., Hoskin, P., and Choudhury, A. (2024). Tumour response to hypoxia: Understanding the hypoxic tumour microenvironment to improve treatment outcome in solid tomours. Front. Oncol., 14.","DOI":"10.3389\/fonc.2024.1331355"},{"key":"ref_82","doi-asserted-by":"crossref","first-page":"149","DOI":"10.1016\/j.jmr.2017.04.017","article-title":"In vivo preclinical cancer and tissue engineering applications of absolute oxygen imaging using pulse EPR","volume":"280","author":"Epel","year":"2017","journal-title":"J. Magn. Reson."},{"key":"ref_83","doi-asserted-by":"crossref","unstructured":"Matsumoto, K., Mitchell, J.B., and Krishna, M.C. (2021). Multimodal functional imaging for cancer\/tumor microenvironments based on MRI, EPR, and PET. Molecules, 26.","DOI":"10.3390\/molecules26061614"},{"key":"ref_84","doi-asserted-by":"crossref","unstructured":"Schaner, P.E., Williams, B.B., Chen, E.Y., Pettus, J.R., Schreiber, W.A., Kmiec, M.M., Jarvis, L.A., Pastel, D.A., Zuurbier, R.A., and DiFlorio-Alexander, R.M. (2021). First-in-human study in cancer patients establishing the feasibility of oxygen measurements in tumors using electron paramagnetic resonance with the OxyChip. Front. Oncol., 11.","DOI":"10.3389\/fonc.2021.743256"},{"key":"ref_85","doi-asserted-by":"crossref","first-page":"312","DOI":"10.1016\/j.freeradbiomed.2008.04.019","article-title":"In vivo EPR measurement of glutathione in tumor-bearing mice using improved disulfide biradical probe","volume":"45","author":"Roshchupkina","year":"2008","journal-title":"Free Radic. Biol. Med."},{"key":"ref_86","doi-asserted-by":"crossref","unstructured":"Babi\u0107, N., and Peyrot, F. (2019). Molecular probes for evaluation of oxidative stress by in vivo EPR spectroscopy and imaging: State-of-the-art and limitations. Magnetochemistry, 5.","DOI":"10.3390\/magnetochemistry5010013"},{"key":"ref_87","first-page":"125","article-title":"Simulation of ESR spectra of oxygen-sensitive spin-label probe CTPO","volume":"56","author":"Hyde","year":"1984","journal-title":"J. Magn. Reson."},{"key":"ref_88","doi-asserted-by":"crossref","first-page":"247","DOI":"10.1007\/s00723-021-01446-8","article-title":"EPR oximetry with nitroxides: Effects of molecular structure, pH, and electrolyte concentration","volume":"53","author":"Voinov","year":"2021","journal-title":"Appl. Magn. Reson."},{"key":"ref_89","doi-asserted-by":"crossref","first-page":"31","DOI":"10.1016\/j.canlet.2020.05.032","article-title":"Hypoxia-responsive nanoparticles for tumor-targeted drug delivery","volume":"490","author":"Li","year":"2020","journal-title":"Cancer Lett."},{"key":"ref_90","doi-asserted-by":"crossref","first-page":"105660","DOI":"10.1016\/j.jddst.2024.105660","article-title":"Targeting hypoxic and acidic tumor microenvironment by nanoparticles: A review","volume":"96","author":"Saadh","year":"2024","journal-title":"J. Drug Deliv. Sci. Techn."},{"key":"ref_91","doi-asserted-by":"crossref","first-page":"1379","DOI":"10.1016\/j.saa.2003.10.036","article-title":"EPR oximetry of tumors in vivo in cancer therapy","volume":"60","year":"2004","journal-title":"Spectrochim. Acta A Mol. Biomol. Spectrosc."},{"key":"ref_92","doi-asserted-by":"crossref","first-page":"126","DOI":"10.1016\/j.radonc.2008.10.015","article-title":"Repeated tumor pO2 measurements by multi-site EPR oximetry as a prognostic marker for enhanced therapeutic efficacy of fractionated radiotherapy","volume":"91","author":"Hou","year":"2009","journal-title":"Radiother. Oncol."}],"container-title":["Pharmaceuticals"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8247\/19\/9\/1424\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,9,9]],"date-time":"2026-09-09T12:44:10Z","timestamp":1788957850000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8247\/19\/9\/1424"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,9,9]]},"references-count":92,"journal-issue":{"issue":"9","published-online":{"date-parts":[[2026,9]]}},"alternative-id":["ph19091424"],"URL":"https:\/\/doi.org\/10.3390\/ph19091424","relation":{},"ISSN":["1424-8247"],"issn-type":[{"value":"1424-8247","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,9,9]]}}}