{ "id": "epjbqgm3xe", "slug": "spin-labeling", "title": "Spin labeling", "updated": "2026-10-25", "topic_path": [ { "id": "life", "label": "Life and health", "api_url": "https://www.edgepedia.org/api/v1/topics/life" }, { "id": "life.biology", "label": "Biological foundations", "api_url": "https://www.edgepedia.org/api/v1/topics/life.biology" }, { "id": "life.biology.biochemistry", "label": "Biochemistry and metabolism", "api_url": "https://www.edgepedia.org/api/v1/topics/life.biology.biochemistry" }, { "id": "life.biology.biochemistry.practice", "label": "Biochemistry field and methods", "api_url": "https://www.edgepedia.org/api/v1/topics/life.biology.biochemistry.practice" }, { "id": "life.biology.biochemistry.practice.methods", "label": "Biochemical methods and techniques", "api_url": "https://www.edgepedia.org/api/v1/topics/life.biology.biochemistry.practice.methods" }, { "id": "life.biology.biochemistry.practice.methods.detect", "label": "Detection methods and analytical reactions", "api_url": "https://www.edgepedia.org/api/v1/topics/life.biology.biochemistry.practice.methods.detect" } ], "geo": [ { "id": "geo.nongeo.t1946.life.biology.biochemistry.practice.methods.detect", "label": "Non-geographic · 1946 to 2000: Detection methods and analytical reactions", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life.biology.biochemistry.practice.methods.detect", "path": [ { "id": "geo.nongeo", "label": "Non-geographic", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo" }, { "id": "geo.nongeo.t1946", "label": "Non-geographic · 1946 to 2000", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946" }, { "id": "geo.nongeo.t1946.life", "label": "Life and health", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life" }, { "id": "geo.nongeo.t1946.life.biology", "label": "Biological foundations", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life.biology" }, { "id": "geo.nongeo.t1946.life.biology.biochemistry", "label": "Biochemistry and metabolism", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life.biology.biochemistry" }, { "id": "geo.nongeo.t1946.life.biology.biochemistry.practice", "label": "Biochemistry field and methods", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life.biology.biochemistry.practice" }, { "id": "geo.nongeo.t1946.life.biology.biochemistry.practice.methods", "label": "Biochemical methods and techniques", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life.biology.biochemistry.practice.methods" }, { "id": "geo.nongeo.t1946.life.biology.biochemistry.practice.methods.detect", "label": "Detection methods and analytical reactions", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.life.biology.biochemistry.practice.methods.detect" } ] } ], "excerpt": "Spin labeling is a biochemical technique that attaches a stable paramagnetic group, usually a nitroxide radical, to a biomolecule so EPR spectroscopy can report its structure and dynamics.", "snippet": "Spin labeling is a biochemical technique that attaches a stable paramagnetic group, usually a nitroxide radical, to a biomolecule so EPR spectroscopy can report its structure and dynamics.", "node": "life.biology.biochemistry.practice.methods.detect", "markdown": "# Spin labeling\n\nSpin labeling covalently attaches a stable paramagnetic group, most often a nitroxide radical, to a selected site on a biomolecule so that electron paramagnetic resonance (EPR) spectroscopy can report on that molecule's structure, dynamics, and interactions.[1](https://www.sciencedirect.com/science/article/abs/pii/S1570963921000595) A spin label is a synthetic paramagnetic species, either an organic free radical such as a nitroxide or trityl, or a metal-chelate label bearing paramagnetic metal ions, whose structure or reactivity directs it to a particular target site in a biological macromolecule.[2](https://www.cambridge.org/core/journals/quarterly-reviews-of-biophysics/article/abs/physics-and-chemistry-of-spin-labels/7ECCF29E493FC2FFF86B259ECC2A8A84) [Site-directed spin labeling](https://www.edgepedia.org/site-directed-spin-labeling) (SDSL) places such centers at user-defined positions, letting continuous-wave (cw) EPR report side-chain motion, solvent accessibility, and conformational changes at room temperature, and pulsed dipolar EPR deliver nanometer-scale distance distributions.[1](https://www.sciencedirect.com/science/article/abs/pii/S1570963921000595) • [3](https://pubs.rsc.org/en/content/articlehtml/2016/ob/c6ob00473c)\n\n| Key fact | Detail |\n|---|---|\n| What it measures | Distance distributions, side-chain motion (ps–ns regime), solvent accessibility, and conformational changes, at residue-level resolution by choice of labeling site[1](https://www.sciencedirect.com/science/article/abs/pii/S1570963921000595) |\n| DEER distance range | 1.5–8 nm routinely; up to 16 nm in fully deuterated samples[1](https://www.sciencedirect.com/science/article/abs/pii/S1570963921000595) |\n| Work-horse label | MTSL, a sulfhydryl-reactive methanethiosulfonate nitroxide, forming the R1 side chain on cysteine[3](https://pubs.rsc.org/en/content/articlehtml/2016/ob/c6ob00473c) |\n| Standard DEER temperatures | 40–60 K for nitroxides, 10–20 K for metal centers, 80–110 K for trityl labels[4](https://pmc.ncbi.nlm.nih.gov/articles/PMC9890500/) |\n| Sensitivity and sample | EPR is up to three orders of magnitude more sensitive than NMR; samples from ~70 nL to several mL[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC5828257/) |\n| Origin | Stone, Buckman, Nordio, and McConnell, \"Spin-labeled biomolecules\", PNAS, 1965[6](https://doi.org/10.1073/pnas.54.4.1010) |\n| SDSL | Altenbach, Marti, Khorana, and Hubbell, spin labeling of bacteriorhodopsin mutants, Science, 1990[7](https://doi.org/10.1126/science.2160734) |\n\n## How it works\n\nThe classic nitroxide is TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl), a heterocyclic free radical carrying an unpaired electron (S = ½) in the N–O moiety, sterically protected by four bulky methyl groups at the carbons alpha to the nitrogen.[1](https://www.sciencedirect.com/science/article/abs/pii/S1570963921000595) • [8](https://www.st-andrews.ac.uk/~jel20/9781782629436-00001.pdf) Five-membered-ring nitroxides (pyrrolidinyl) tend to be more stable than six-membered ones, and larger alpha-alkyl substituents add steric shielding, though bulkier labels raise the risk of perturbing the protein.[3](https://pubs.rsc.org/en/content/articlehtml/2016/ob/c6ob00473c)\n\nTwo unpaired electrons interact through the magnetic dipole–dipole coupling, whose energy scales as \\( 1/r^{3} \\) with interspin distance \\( r \\). Below about 20 Å this coupling significantly broadens the cw-EPR lineshape, so cw dipolar broadening covers an intermediate range of 8–20 Å; pulsed [DEER](https://www.edgepedia.org/double-electron-electron-resonance) extends the range to 20–80 Å.[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC5828257/) In cw spectra, the inverse linewidth of the central line measures relative mobility, and plotting it against sequence gives a periodic profile that predicts local secondary structure. Power saturation with paramagnetic reagents reports the topology of a labeled site with respect to the membrane and can identify functional domains in membrane proteins.[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC5828257/)\n\n## How it is done\n\nIn the standard SDSL workflow, all native nondisulfide-bonded cysteines are first replaced with alanine or serine; a unique cysteine is then introduced by site-directed mutagenesis and reacted with a sulfhydryl-specific nitroxide reagent such as MTSL.[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC5828257/) The methanethiosulfonate (MTS) label is a widely used protein labeling chemistry, being cysteine-specific and installable by site-specific mutagenesis.[9](https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/16602/ChemSocRev_accepted.pdf?isAllowed=y&sequence=1) Alternatives include iodoacetamide and maleimide nitroxides, click chemistry, and genetic encoding: the nitroxide amino acid SLK-1 has been incorporated co-translationally in E. coli via an evolved [Methanosarcina](https://www.edgepedia.org/methanosarcina) mazei pyrrolysyl-tRNA-synthetase.[3](https://pubs.rsc.org/en/content/articlehtml/2016/ob/c6ob00473c) • [10](https://doi.org/10.1021/ja411535q)\n\nAfter labeling, cw spectra are recorded at room temperature for motion and accessibility, and pulsed experiments (DEER/PELDOR, [ESEEM](https://www.edgepedia.org/electron-spin-echo-envelope-modulation)) are run on a cryogenically cooled spectrometer.[11](https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/26012/Lane_2022_STAR_protocols_HDX_guided_EPR_spectroscopy_CC.pdf;jsessionid=087A5308A7DED7CAA10441452B203090?sequence=1)\n\n## Origin\n\nSpin labeling of biomolecules was reported by T. J. Stone, T. Buckman, P. L. Nordio, and H. M. McConnell in \"Spin-labeled biomolecules\" (PNAS, 1965)[6](https://doi.org/10.1073/pnas.54.4.1010); the McConnell group followed with spin-labeled hemoglobin crystals by S. Ohnishi, J. C. Boeyens, and H. M. McConnell (PNAS, 1966).[12](https://doi.org/10.1073/pnas.56.3.809) An early authoritative review came from O. Hayes Griffith and A. S. Waggoner (Accounts of Chemical Research, 1969).[13](https://doi.org/10.1021/ar50013a003) The reversible thiol-specific MTSL label was synthesized by Lawrence J. Berliner, Jacob Grunwald, H. Olga Hankovszky, and Kalman Hideg (Analytical [Biochemistry](https://www.edgepedia.org/biochemistry), 1982).[14](https://doi.org/10.1016/0003-2697%2882%2990612-1)\n\nSDSL as practiced today was pioneered by Wayne Hubbell, starting with spin labeling of bacteriorhodopsin mutants in collaboration with [H. Gobind Khorana](https://www.edgepedia.org/h-gobind-khorana) (Science, 1990)[7](https://doi.org/10.1126/science.2160734) • [15](https://www.intechopen.com/chapters/39010), and has been the method of choice since the 1990s.[15](https://www.intechopen.com/chapters/39010) Hubbell, David S. Cafiso, and Christian Altenbach later codified its use for identifying conformational changes (Nature Structural Biology, 2000).[16](https://doi.org/10.1038/78956)\n\n## Variants\n\nMTSL/R1 is the most popular label, highly selective for thiols with minimal impact on protein secondary and tertiary structure; its disulfide linkage and N–O moiety are both susceptible to reducing conditions inside live cells.[3](https://pubs.rsc.org/en/content/articlehtml/2016/ob/c6ob00473c) • [17](https://www.mdpi.com/1420-3049/19/10/16998) Cysteine-reactive alternatives compared head-to-head include IPSL (iodoacetamide), MPSL (maleimide), and the biradical IDSL, whose shortest tether gives the highest precision, with distributions similar to Cu(II) labeling of double-histidine sites.[18](https://pubmed.ncbi.nlm.nih.gov/34946616/) The two-point \"double MTS\" label, known as Rx once attached to a pair of proximal cysteines, reduces the distance distribution width through its rigidity.[8](https://www.st-andrews.ac.uk/~jel20/9781782629436-00001.pdf)\n\nMetal and trityl labels form the other main families: nitroxides, metal chelates (Gd(III), Cu(II), Mn(II)), and trityl radicals, plus a newer family of photoexcitable triplet-state labels based on porphyrins or fullerenes used in LaserIMD/LiDEER experiments.[4](https://pmc.ncbi.nlm.nih.gov/articles/PMC9890500/) • [19](https://www.sciencedirect.com/science/article/abs/pii/S0076687915003511) Gd(III) ions offer high-field sensitivity and isotropic excitation, but free Gd³⁺ degrades DEER data, so bulky high-affinity chelates are required, and labeled protein must be microinjected or transfected for in-cell work.[3](https://pubs.rsc.org/en/content/articlehtml/2016/ob/c6ob00473c) Tetrathiatriarylmethyl (trityl, TAM) radicals show a 90 mG linewidth and microsecond transverse relaxation at room temperature, with in-cell survival in the range of hours.[17](https://www.mdpi.com/1420-3049/19/10/16998) • [20](https://doi.org/10.1021/ja505122n) The constrained amino acid TOAC has allowed determination of orientation as well as distance for nucleotides.[17](https://www.mdpi.com/1420-3049/19/10/16998)\n\nThe four-pulse DEER/PELDOR sequence, applied at two microwave frequencies to chemically identical labels, yields a distance distribution between 1.5 and 8.0 nm, with the modulation frequency depending on \\( r^{-3} \\)[4](https://pmc.ncbi.nlm.nih.gov/articles/PMC9890500/); up to 16 nm is reachable in fully deuterated samples.[1](https://www.sciencedirect.com/science/article/abs/pii/S1570963921000595) Below roughly 2.5 nm dipole–dipole coupling directly broadens the cw spectrum, and below about 1.2 nm exchange contributions set a lower limit.[3](https://pubs.rsc.org/en/content/articlehtml/2016/ob/c6ob00473c) An early \"spectroscopic ruler\" on doubly labeled helical polypeptides estimated 8–25 Å distances with a 0.9 Å standard deviation.[21](https://doi.org/10.1073/pnas.92.18.8239) For Cu(II) labels, dHis-Cu(II) distributions are up to 5 times narrower than common nitroxides, though Cu(II) measurements typically need 2–5 times higher concentrations.[22](https://pubs.acs.org/jpclcd/article/16/39/10256/3742975/Rational-Design-of-a-Cu-II-Spin-Label-Improves-the) [Performance](https://www.edgepedia.org/performance) depends strongly on label choice, attachment chemistry, and experimental conditions.[23](https://link.springer.com/rwe/10.1007/978-3-319-28275-6_109-1) Newer labels target stability and precision: the NOAI label, attached via a thioester bond to protein thiols, gives shorter label-to-protein connections than MTSL, narrower DEER distributions, and resistance to reducing reagents.[24](https://pubmed.ncbi.nlm.nih.gov/41613978/)\n\n## Applications\n\nSDSL DEER has been applied to membrane proteins including KcsA, KCNE1, bacteriorhodopsin, NhaA, and proteorhodopsin[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC5828257/), and HDX-MS-guided labeling has covered 26 residues spanning all domains of the pentameric MscL channel.[11](https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/26012/Lane_2022_STAR_protocols_HDX_guided_EPR_spectroscopy_CC.pdf;jsessionid=087A5308A7DED7CAA10441452B203090?sequence=1) For RNA, a hammerhead ribozyme double-labeled with TEMPO-isocyanate showed a magnesium-induced conformational change by DEER consistent with its X-ray structure, and alkyne labels introduced via 5-iodouridine [Sonogashira coupling](https://www.edgepedia.org/sonogashira-coupling) supported pioneering in-cell EPR in Xenopus oocytes.[9](https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/16602/ChemSocRev_accepted.pdf?isAllowed=y&sequence=1) In-cell work spans Gd(III)-labeled proteins in cells[25](https://doi.org/10.1021/ja5079392), in-cell SDSL-EPR of the intrinsically disordered bacterial GTPase UreG in intact bacteria[1](https://www.sciencedirect.com/science/article/abs/pii/S1570963921000595), and bacterial in-cell labeling, where nitroxides and trityl labels such as FTAM and OX063 have been used for in situ labeling and PELDOR/DEER of membrane proteins inside E. coli.[4](https://pmc.ncbi.nlm.nih.gov/articles/PMC9890500/)\n\n## Limitations and alternatives\n\nReduction in cells is the major drawback of nitroxides: they are rapidly converted to EPR-silent hydroxylamines, with further reactions producing other diamagnetic species.[4](https://pmc.ncbi.nlm.nih.gov/articles/PMC9890500/) [Ubiquitin](https://www.edgepedia.org/ubiquitin) double-labeled with 3-maleimido-PROXYL showed an approximate radical half-life of 50 minutes in oocytes[8](https://www.st-andrews.ac.uk/~jel20/9781782629436-00001.pdf), whereas five-membered-ring nitroxides such as TPA resist reduction better and tolerated up to seventy minutes.[17](https://www.mdpi.com/1420-3049/19/10/16998) Label flexibility is a second limit: DEER distance distributions must be interpreted accounting for the conformational distribution of the label itself, addressed with rotamer libraries and simulations.[26](https://www.annualreviews.org/content/journals/10.1146/annurev-physchem-032511-143716) • [17](https://www.mdpi.com/1420-3049/19/10/16998) Incomplete labeling also matters: IDSL required a 20:1 label excess to exceed 90% efficiency and avoid disulfide-bridged dimers, while IPSL labeled quantitatively overnight at low excess.[18](https://pubmed.ncbi.nlm.nih.gov/34946616/) Membrane-protein DEER faces shorter phase-memory times, local high spin concentration in membranes, and poor modulation depth in liposomes.[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC5828257/)\n\nCompared with alternatives, spin labels are significantly smaller than fluorophores and have not perturbed protein structure in various tested cases; DEER can use two identical labels where FRET needs a donor–acceptor pair, and while FRET allows single-molecule detection it usually does not yield precise distances or distributions.[3](https://pubs.rsc.org/en/content/articlehtml/2016/ob/c6ob00473c) • [9](https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/16602/ChemSocRev_accepted.pdf?isAllowed=y&sequence=1) DEER requires no crystallization and no size limit, and SDSL-EPR detects minor population states difficult to see by [X-ray crystallography](https://www.edgepedia.org/x-ray-crystallography) or cryo-EM.[26](https://www.annualreviews.org/content/journals/10.1146/annurev-physchem-032511-143716) • [1](https://www.sciencedirect.com/science/article/abs/pii/S1570963921000595)\n\n## References\n\n1. [Nitroxide spin labels and EPR spectroscopy: A powerful association for protein dynamics studies](https://www.sciencedirect.com/science/article/abs/pii/S1570963921000595)\n2. [Physics and chemistry of spin labels (McConnell & McFarland, Q. Rev. Biophys. 1970)](https://www.cambridge.org/core/journals/quarterly-reviews-of-biophysics/article/abs/physics-and-chemistry-of-spin-labels/7ECCF29E493FC2FFF86B259ECC2A8A84)\n3. [Site-directed spin labeling of proteins for distance measurements in vitro and in cells (Org. Biomol. Chem., 2016)](https://pubs.rsc.org/en/content/articlehtml/2016/ob/c6ob00473c)\n4. [Dance with spins: site-directed spin labeling coupled to electron paramagnetic resonance spectroscopy directly inside cells](https://pmc.ncbi.nlm.nih.gov/articles/PMC9890500/)\n5. [Site-Directed Spin Labeling EPR for Studying Membrane Proteins](https://pmc.ncbi.nlm.nih.gov/articles/PMC5828257/)\n6. [T J Stone and colleagues (1965). Spin-labeled biomolecules.. Proceedings of the National Academy of Sciences.](https://doi.org/10.1073/pnas.54.4.1010)\n7. [Christian Altenbach and colleagues (1990). Transmembrane Protein Structure: Spin Labeling of Bacteriorhodopsin Mutants. Science.](https://doi.org/10.1126/science.2160734)\n8. [Tuning the properties of nitroxide spin labels... (RSC book chapter PDF)](https://www.st-andrews.ac.uk/~jel20/9781782629436-00001.pdf)\n9. [Nitroxide radicals for biomolecule spin labelling (Tutorial Review, Chemical Society Reviews)](https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/16602/ChemSocRev_accepted.pdf?isAllowed=y&sequence=1)\n10. [Moritz J. Schmidt and colleagues (2014). A Genetically Encoded Spin Label for Electron Paramagnetic Resonance Distance Measurements. Journal of the American Chemical Society.](https://doi.org/10.1021/ja411535q)\n11. [HDX-guided EPR spectroscopy to interrogate membrane protein dynamics (STAR Protocols)](https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/26012/Lane_2022_STAR_protocols_HDX_guided_EPR_spectroscopy_CC.pdf;jsessionid=087A5308A7DED7CAA10441452B203090?sequence=1)\n12. [S Ohnishi, J C Boeyens, H M McConnell (1966). Spin-labeled hemoglobin crystals.. Proceedings of the National Academy of Sciences.](https://doi.org/10.1073/pnas.56.3.809)\n13. [O. Hayes Griffith, A. S. Waggoner (1969). Nitroxide free radicals: spin labels for probing biomolecular structure. Accounts of Chemical Research.](https://doi.org/10.1021/ar50013a003)\n14. [A novel reversible thiol-specific spin label: Papain active site labeling and inhibition (Analytical Biochemistry, 1982)](https://doi.org/10.1016/0003-2697%2882%2990612-1)\n15. [History of the Use of Nitroxides (Aminoxyl Radicals) in Biochemistry (Berliner, IntechOpen)](https://www.intechopen.com/chapters/39010)\n16. [Wayne L. Hubbell, David S. Cafiso, Christian Altenbach (2000). Identifying conformational changes with site-directed spin labeling.. Nature Structural Biology.](https://doi.org/10.1038/78956)\n17. [New Developments in Spin Labels for Pulsed Dipolar EPR (Molecules, MDPI)](https://www.mdpi.com/1420-3049/19/10/16998)\n18. [A Comparison of Cysteine-Conjugated Nitroxide Spin Labels for Pulse Dipolar EPR Spectroscopy](https://pubmed.ncbi.nlm.nih.gov/34946616/)\n19. [Development and Application of Spin Traps, Spin Probes, and Spin Labels (Methods in Enzymology)](https://www.sciencedirect.com/science/article/abs/pii/S0076687915003511)\n20. [Georgiy Yu. Shevelev and colleagues (2014). Physiological-Temperature Distance Measurement in Nucleic Acid using Triarylmethyl-Based Spin Labels and Pulsed Dipolar EPR Spectroscopy. Journal of the American Chemical Society.](https://doi.org/10.1021/ja505122n)\n21. [M D Rabenstein, Y K Shin (1995). Determination of the distance between two spin labels attached to a macromolecule.. Proceedings of the National Academy of Sciences.](https://doi.org/10.1073/pnas.92.18.8239)\n22. [Rational Design of a Cu(II) Spin Label Improves the Sensitivity of Distance Measurements (J. Phys. Chem. Lett.)](https://pubs.acs.org/jpclcd/article/16/39/10256/3742975/Rational-Design-of-a-Cu-II-Spin-Label-Improves-the)\n23. [Long-Range Distance Constraints in Biomacromolecules by SDSL and DEER Spectroscopy (Springer reference work)](https://link.springer.com/rwe/10.1007/978-3-319-28275-6_109-1)\n24. [Rigid and stable nitroxide spin label for high-resolution distance measurements on proteins by DEER experiments (Magn Reson Lett, 2025)](https://pubmed.ncbi.nlm.nih.gov/41613978/)\n25. [Andrea Martorana and colleagues (2014). Probing Protein Conformation in Cells by EPR Distance Measurements using Gd3+ Spin Labeling. Journal of the American Chemical Society.](https://doi.org/10.1021/ja5079392)\n26. [DEER Distance Measurements on Proteins (Annual Review of Physical Chemistry)](https://www.annualreviews.org/content/journals/10.1146/annurev-physchem-032511-143716)\n\n---\n*Topic: Encyclopedia › Life and health › Biological foundations › Biochemistry and metabolism › Biochemistry field and methods › Biochemical methods and techniques › Detection methods and analytical reactions*\n\n*Initially written Sep 29, 2026 · Edited: Oct 15, 2026; Oct 25, 2026*\n\n*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*\n\nLicense: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license\n", "same_as": [], "url": "https://www.edgepedia.org/spin-labeling", "markdown_url": "https://www.edgepedia.org/spin-labeling.md", "license": { "name": "Edgepedia Community License 1.0", "url": "https://www.edgepedia.org/edgepedia/license", "summary": "Free with credit, commercial use included. AI training is open to everyone. For other uses, organizations over USD 100M in revenue or 100M monthly users license separately.", "spdx": "LicenseRef-Edgepedia-Community-1.0" }, "credit": "\"Spin labeling\", Edgepedia (EdgeChat), https://www.edgepedia.org/spin-labeling. Edgepedia Community License 1.0.", "credit_md": "\"[Spin labeling](https://www.edgepedia.org/spin-labeling)\", Edgepedia (EdgeChat), [https://www.edgepedia.org/spin-labeling](https://www.edgepedia.org/spin-labeling). [Edgepedia Community License 1.0](https://www.edgepedia.org/edgepedia/license).", "credit_html": "\"Spin labeling\", Edgepedia (EdgeChat), https://www.edgepedia.org/spin-labeling. Edgepedia Community License 1.0.", "speakable": "Spin labeling is a biochemical technique that attaches a stable paramagnetic group, usually a nitroxide radical, to a biomolecule so EPR spectroscopy can report its structure and dynamics." }