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Lockyer SJ, Nawaz S, Brookfield A, Fielding AJ, Vitorica-Yrezabal IJ, Timco GA, Burton NA, Bowen AM, Winpenny REP, McInnes EJL. Conformational Flexibility of Hybrid [3]- and [4]-Rotaxanes. J Am Chem Soc 2020; 142:15941-15949. [PMID: 32820906 PMCID: PMC7605720 DOI: 10.1021/jacs.0c06547] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The synthesis, structures, and properties of [4]- and [3]-rotaxane complexes are reported where [2]-rotaxanes, formed from heterometallic {Cr7Ni} rings, are bound to a fluoride-centered {CrNi2} triangle. The compounds have been characterized by single-crystal X-ray diffraction and have the formulas [CrNi2(F)(O2CtBu)6]{(BH)[Cr7NiF8(O2CtBu)16]}3 (3) and [CrNi2(F)(O2CtBu)6(THF)]{(BH)[Cr7NiF8(O2CtBu)16]}2 (4), where B = py-CH2CH2NHCH2C6H4SCH3. The [4]-rotaxane 3 is an isosceles triangle of three [2]-rotaxanes bound to the central triangle while the [3]-rotaxane 4 contains only two [2]-rotaxanes bound to the central triangle. Studies of the behavior of 3 and 4 in solution by small-angle X-ray scattering and atomistic molecular dynamic simulations show that the structure of 3 is similar to that found in the crystal but that 4 has a different conformation to the crystal. Continuous wave and pulsed electron paramagnetic resonance spectroscopy was used to study the structures present and demonstrate that in frozen solutions (at 5 K) 4 forms more extended molecules than 3 and with a wider range of conformations.
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Affiliation(s)
- Selena J Lockyer
- Department of Chemistry and Photon Science Institute, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K
| | - Selina Nawaz
- Department of Chemistry and Photon Science Institute, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K
| | - Adam Brookfield
- Department of Chemistry and Photon Science Institute, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K
| | - Alistair J Fielding
- School of Pharmacy and Biomolecular Sciences, Liverpool John Moores University, Liverpool L3 3AF, U.K
| | - Inigo J Vitorica-Yrezabal
- Department of Chemistry and Photon Science Institute, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K
| | - Grigore A Timco
- Department of Chemistry and Photon Science Institute, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K
| | - Neil A Burton
- Department of Chemistry and Photon Science Institute, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K
| | - Alice M Bowen
- Department of Chemistry and Photon Science Institute, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K
| | - Richard E P Winpenny
- Department of Chemistry and Photon Science Institute, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K
| | - Eric J L McInnes
- Department of Chemistry and Photon Science Institute, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K
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2
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Lockyer S, Fielding AJ, Whitehead GFS, Timco GA, Winpenny REP, McInnes EJL. Close Encounters of the Weak Kind: Investigations of Electron-Electron Interactions between Dissimilar Spins in Hybrid Rotaxanes. J Am Chem Soc 2019; 141:14633-14642. [PMID: 31411874 PMCID: PMC6814243 DOI: 10.1021/jacs.9b05590] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Indexed: 01/14/2023]
Abstract
We report a family of hybrid [2]rotaxanes based on inorganic [Cr7NiF8(O2CtBu)16]- ("{Cr7Ni}") rings templated about organic threads that are terminated at one end with pyridyl groups. These rotaxanes can be coordinated to [Cu(hfac)2] (where Hhfac = 1,1,1,5,5,5-hexafluoroacetylacetone), to give 1:1 or 1:2 Cu:{Cr7Ni} adducts: {[Cu(hfac)2](py-CH2NH2CH2CH2Ph)[Cr7NiF8(O2CtBu)16]}, {[Cu(hfac)2][py-CH2NH2CH2CH3][Cr7NiF8(O2CtBu)16]}, {[Cu(hfac)2]([py-CH2CH2NH2CH2C6H4SCH3][Cr7NiF8(O2CtBu)16])2}, {[Cu(hfac)2]([py-C6H4-CH2NH2(CH2)4Ph][Cr7NiF8(O2CtBu)16])2}, and {[Cu(hfac)2]([3-py-CH2CH2NH2(CH2)3SCH3][Cr7NiF8(O2CtBu)16])2}, the structures of which have been determined by X-ray diffraction. The {Cr7Ni} rings and CuII ions both have electronic spin S = 1/2, but with very different g-values. Continuous-wave EPR spectroscopy reveals the exchange interactions between these dissimilar spins, and hence the communication between the different molecular components that comprise these supramolecular systems. The interactions are weak such that we observe AX or AX2 type spectra. The connectivity between the {Cr7Ni} ring and thread terminus is varied such that the magnitude of the exchange interaction J can be tuned. The coupling is shown to be dominated by through-bond rather than through-space mechanisms.
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Affiliation(s)
- Selena
J. Lockyer
- School
of Chemistry and Photon Science Institute, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
| | - Alistair J. Fielding
- School
of Pharmacy and Biomolecular Sciences, Liverpool
John Moores University, Liverpool L3 5UX, U.K.
| | - George F. S. Whitehead
- School
of Chemistry and Photon Science Institute, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
| | - Grigore A. Timco
- School
of Chemistry and Photon Science Institute, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
| | - Richard E. P. Winpenny
- School
of Chemistry and Photon Science Institute, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
| | - Eric J. L. McInnes
- School
of Chemistry and Photon Science Institute, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
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3
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Fernandez A, Moreno Pineda E, Muryn CA, Sproules S, Moro F, Timco GA, McInnes EJL, Winpenny REP. g-Engineering in Hybrid Rotaxanes To Create AB and AB2 Electron Spin Systems: EPR Spectroscopic Studies of Weak Interactions between Dissimilar Electron Spin Qubits. Angew Chem Int Ed Engl 2015. [PMID: 26224489 DOI: 10.1002/anie.201504487] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Hybrid [2]rotaxanes and pseudorotaxanes are reported where the magnetic interaction between dissimilar spins is controlled to create AB and AB2 electron spin systems, allowing independent control of weakly interacting S=${{ 1/2 }}$ centers.
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Affiliation(s)
- Antonio Fernandez
- School of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL (UK)
| | - Eufemio Moreno Pineda
- School of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL (UK).,Current address: Institute of Nanotechnology, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen (Germany)
| | - Christopher A Muryn
- School of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL (UK)
| | - Stephen Sproules
- School of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL (UK).,Current address: WestCHEM, School of Chemistry, University of Glasgow, Glasgow G12 8QQ (UK)
| | - Fabrizio Moro
- School of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL (UK).,Current address: School of Physics and Astronomy, The University of Nottingham, University Park, NG7 2RD, Nottingham (UK)
| | - Grigore A Timco
- School of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL (UK)
| | - Eric J L McInnes
- School of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL (UK)
| | - Richard E P Winpenny
- School of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL (UK).
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4
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Fernandez A, Moreno Pineda E, Muryn CA, Sproules S, Moro F, Timco GA, McInnes EJL, Winpenny REP. g-Engineering in Hybrid Rotaxanes To Create AB and AB2Electron Spin Systems: EPR Spectroscopic Studies of Weak Interactions between Dissimilar Electron Spin Qubits. Angew Chem Int Ed Engl 2015. [DOI: 10.1002/ange.201504487] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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5
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Lueders P, Jäger H, Hemminga MA, Jeschke G, Yulikov M. Multiple Pathway Relaxation Enhancement in the System Composed of Three Paramagnetic Species: Nitroxide Radical-Ln(3+)-O2. J Phys Chem Lett 2012; 3:1336-1340. [PMID: 26286779 DOI: 10.1021/jz300316q] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Longitudinal relaxation of nitroxide spin-labels has been measured for a membrane-incorporated α-helical polypeptide in the presence and absence of residual amounts of membrane-dissolved O2 and paramagnetic Dy(3+) ions. Such a model system, containing three different types of paramagnetic species, provides an important example of nonadditivity of two different relaxation channels for the nitroxide spins.
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Affiliation(s)
- Petra Lueders
- †Laboratory of Physical Chemistry, ETH, Zurich, Switzerland
| | - Heidrun Jäger
- ‡Laboratory of Biophysics,Wageningen University, Wageningen, The Netherlands
| | - Marcus A Hemminga
- ‡Laboratory of Biophysics,Wageningen University, Wageningen, The Netherlands
| | - Gunnar Jeschke
- †Laboratory of Physical Chemistry, ETH, Zurich, Switzerland
| | - Maxim Yulikov
- †Laboratory of Physical Chemistry, ETH, Zurich, Switzerland
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6
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Liu G, Khlobystov AN, Charalambidis G, Coutsolelos AG, Briggs GAD, Porfyrakis K. N@C60–Porphyrin: A Dyad of Two Radical Centers. J Am Chem Soc 2012; 134:1938-41. [PMID: 22239715 DOI: 10.1021/ja209763u] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Guoquan Liu
- Department of Materials, Oxford University, Oxford OX1 3PH, United Kingdom
| | - Andrei N. Khlobystov
- School of Chemistry, University of Nottingham, Nottingham NG7 2RD, United
Kingdom
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7
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TOYAMA NAMIKI, ASANO-SOMEDA MOTOKO, KAIZU YOUKOH. EPR spectra of gable-type copper(II) porphyrin dimers in fluid solution: extraction of exchange interaction in weakly coupled doublet pairs. Mol Phys 2009. [DOI: 10.1080/0026897021000054808] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
- NAMIKI TOYAMA
- a Department of Chemistry , Tokyo Institute of Technology , O-okayama, Meguro-ku , Tokyo , 152-8551 , Japan
| | - MOTOKO ASANO-SOMEDA
- a Department of Chemistry , Tokyo Institute of Technology , O-okayama, Meguro-ku , Tokyo , 152-8551 , Japan
| | - YOUKOH KAIZU
- a Department of Chemistry , Tokyo Institute of Technology , O-okayama, Meguro-ku , Tokyo , 152-8551 , Japan
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8
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Biczo R, Hirsh DJ. Structure and dynamics of a DNA-based model system for the study of electron spin-spin interactions. J Inorg Biochem 2008; 103:362-72. [PMID: 19114287 DOI: 10.1016/j.jinorgbio.2008.11.013] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2008] [Revised: 10/26/2008] [Accepted: 11/20/2008] [Indexed: 11/18/2022]
Abstract
We report on the structure and dynamics of a model system for measuring long-range distances in biological macromolecules by saturation-recovery EPR. Four DNA duplexes that incorporate a paramagnetic dysprosium ion (Dy(III)) and a nitroxide spin-label were examined by electron paramagnetic resonance (EPR), circular dichroism (CD), and ultra-violet absorbance (UV) spectroscopy. Dy(III) is chelated by the modified base deoxythymidine-EDTA, (dT-EDTA). Electron spin-spin interactions between the Dy(III) ion and the nitroxide radical are observed at distances as great as approximately 5.3 nm. A slight change in the conformation of those nucleotides lying between the EDTA(Dy(III)) complex and the nitroxide spin-label results in a "stiffening" of the DNA helix on the EPR time scale. Changes in conformation and helix dynamics are due to the binding of the EDTA(Dy(III)) complex to the phosphodiester backbone of the complementary strand. Molecular mechanics calculations indicate that binding occurs in the 5' direction on the complementary strand, at a position 3 or 4 phosphates distant from the dT-EDTA(Dy(III))*dA base pair.
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Affiliation(s)
- Ryan Biczo
- Department of Chemistry, The College of New Jersey, PO Box 7718, Ewing, NJ 08628, United States
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9
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Chen XJ, Schramm J, Tuohy C, Skiff H, Hummel K, Szklarski AR, Vacirca N, Wolf BA, Hirsh DJ. Progress towards a DNA-based model system for the study of electron spin-spin interactions. Biophys Chem 2007; 129:148-62. [PMID: 17574723 DOI: 10.1016/j.bpc.2007.05.014] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2007] [Revised: 05/22/2007] [Accepted: 05/23/2007] [Indexed: 10/23/2022]
Abstract
A DNA-based model system is described for studying electron spin-spin interactions between a paramagnetic metal ion and a nitroxide spin label. The modified base deoxythymidine-EDTA (dT-EDTA) chelates the divalent or trivalent metal ion and produces a new feature in the circular dichroism (CD) spectra that makes it possible to monitor local DNA melting. Based on the results of optical and electron paramagnetic resonance (EPR) experiments, we find that the terminus of the DNA duplex that incorporates dT-EDTA and the spin-label melts at a higher temperature than the rest of the DNA duplex. EPR microwave progressive power saturation experiments performed at 77 K are consistent with the specific binding of Dy(III) at the EDTA site and an intramolecular dipole-dipole interaction between the nitroxide spin-label and the chelated Dy(III). This model system should be suitable for studying the relaxation properties of metal ions by saturation-recovery EPR.
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Affiliation(s)
- Xi Jun Chen
- Department of Chemistry, The College of New Jersey, PO Box 7718, Ewing, NJ 08628, USA
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10
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Öztürk R, Güner S, Aktaş B, Gül A. Synthesis, Characterization and EPR Studies of Supramolecular Porphyrazines. Supramol Chem 2006. [DOI: 10.1080/10610270412331337295] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- Ramazan Öztürk
- b Department of Chemistry , Fatih University , 34500, Buyukcekmece, Istanbul, Turkey
| | - Sadik Güner
- c Department of Physics , Fatih University , 34500, Buyukcekmece, Istanbul, Turkey
| | - Bekir Aktaş
- d Department of Physics , Gebze Institute of Technology , 41400, Gebze, Kocaeli, Turkey
| | - Ahmet Gül
- a Department of Chemistry , Technical University of Istanbul , 34469, Maslak, Turkey
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11
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Fielding AJ, Fox S, Millhauser GL, Chattopadhyay M, Kroneck PM, Fritz G, Eaton GR, Eaton SS. Electron spin relaxation of copper(II) complexes in glassy solution between 10 and 120 K. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2006; 179:92-104. [PMID: 16343958 PMCID: PMC2919208 DOI: 10.1016/j.jmr.2005.11.011] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2005] [Revised: 11/17/2005] [Accepted: 11/18/2005] [Indexed: 05/05/2023]
Abstract
The temperature dependence, between 10 and 120 K, of electron spin-lattice relaxation at X-band was analyzed for a series of eight pyrrolate-imine complexes and for ten other copper(II) complexes with varying ligands and geometry including copper-containing prion octarepeat domain and S100 type proteins. The geometry of the CuN4 coordination sphere for pyrrolate-imine complexes with R=H, methyl, n-butyl, diphenylmethyl, benzyl, 2-adamantyl, 1-adamantyl, and tert-butyl has been shown to range from planar to pseudo-tetrahedral. The fit to the recovery curves was better for a distribution of values of T1 than for a single time constant. Distributions of relaxation times may be characteristic of Cu(II) in glassy solution. Long-pulse saturation recovery and inversion recovery measurements were performed. The temperature dependence of spin-lattice relaxation rates was analyzed in terms of contributions from the direct process, the Raman process, and local modes. It was necessary to include more than one process to fit the experimental data. There was a small contribution from the direct process at low temperature. The Raman process was the dominant contribution to relaxation between about 20 and 60 K. Debye temperatures were between 80 and 120 K. For samples with similar Debye temperatures the coefficient of the Raman process tended to increase as gz increased, as expected if modulation of spin-orbit coupling is a major factor in relaxation rates. Above about 60 K local modes with energies in the range of 260-360 K (180-250 cm-1) dominated the relaxation. For molecules with similar geometry, relaxation rates were faster for more flexible molecules than for more rigid ones. Relaxation rates for the copper protein samples were similar to rates for small molecules with comparable coordination spheres. At each temperature studied the range of relaxation rates was less than an order of magnitude. The spread was smaller between 20 and 60 K where the Raman process dominates, than at higher temperatures where local modes dominate the relaxation. Spin echo dephasing time constants, Tm, were calculated from two-pulse spin echo decays. Near 10 K Tm was dominated by proton spins in the surroundings. As temperature was increased motion and spin-lattice relaxation made increasing contributions to Tm. Near 100 K spin-lattice relaxation dominated Tm.
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Affiliation(s)
- Alistair J. Fielding
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, USA
| | - Stephen Fox
- Department of Chemistry, University of Louisiana at Monroe, Monroe, LA 71219-0530, USA
| | - Glenn L. Millhauser
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA 95064, USA
| | - Madhuri Chattopadhyay
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA 95064, USA
| | | | - Günter Fritz
- Fachbereich Biologie, Universitat Konstanz, 78457 Konstanz, Germany
| | - Gareth R. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, USA
| | - Sandra S. Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, USA
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12
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Eaton SS, Eaton GR. Relaxation Times of Organic Radicals and Transition Metal Ions. DISTANCE MEASUREMENTS IN BIOLOGICAL SYSTEMS BY EPR 2002. [DOI: 10.1007/0-306-47109-4_2] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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13
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Zhou Y, Bowler BE, Eaton GR, Eaton SS. Electron spin-lattice relaxation rates for high-spin Fe(III) complexes in glassy solvents at temperatures between 6 and 298 K. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2000; 144:115-122. [PMID: 10783280 DOI: 10.1006/jmre.2000.2047] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The temperature dependence of spin-lattice relaxation rates was analyzed for four high-spin nonheme iron proteins between 5 and 20 K, for three high-spin iron porphyrins between 5 and 118 K, and for four high-spin heme proteins between 5 and 150 to 298 K. For the nonheme proteins the zero-field splittings, D, are less than 0.7 cm(-1), and the relaxation is dominated by the Orbach and Raman processes. For the iron porphyrins and heme proteins D is between 4 and 12 cm(-1) and the relaxation is dominated by the Orbach process between about 5 and 100 K and by a local mode at higher temperatures. The relaxation rates for the heme proteins in glassy matrices extrapolated to values at room temperature that are similar to values obtained by NMR relaxivity in fluid solution. This similarity suggests that for high-spin Fe(III) heme proteins with effective intramolecular spin-lattice relaxation processes, the additional motional freedom gained when a relatively large protein goes from glassy solid to liquid solution at room temperature has little impact on spin-lattice relaxation.
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Affiliation(s)
- Y Zhou
- Department of Chemistry and Biochemistry, University of Denver, Colorado 80208, USA
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14
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Zhou Y, Bowler BE, Eaton GR, Eaton SS. Electron spin lattice relaxation rates for S = 12 molecular species in glassy matrices or magnetically dilute solids at temperatures between 10 and 300 K. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 1999; 139:165-174. [PMID: 10388595 DOI: 10.1006/jmre.1999.1763] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The temperature dependence of X-band electron spin-lattice relaxation between about 10 and 300 K in magnetically dilute solids and up to the softening temperature in glassy solvents was analyzed for three organic radicals and 14 S = 12 transition metal complexes. Contributions from the direct, Raman, local vibrational mode, thermally activated, and Orbach processes were considered. For most samples it was necessary to include more than one process to fit the experimental data. Debye temperatures were between 50 and 135 K. For small molecules the Debye temperature required to fit the relaxation data was higher in 1:1 water:glycerol than in organic solvents. For larger molecules the Debye temperature was less dependent upon solvent and more dependent upon the characteristics of the molecule. The coefficients of the Raman process increased with increasing g anisotropy and decreasing rigidity of the molecule. For the transition metal complexes the data are consistent with major contributions from local modes with energies in the range of 185 to 350 K (130 to 240 cm-1). The coefficient for this contribution increases in the order 3d < 4d transition metal. For C-60 anions there is a major contribution from a thermally activated process with an activation energy of about 240 cm-1. For low-spin hemes the dominant contribution at higher temperatures is from a local mode or thermally activated process with a characteristic energy of about 175 cm-1.
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Affiliation(s)
- Y Zhou
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado 80208, USA
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