1
|
Vallotto C, Williams HE, Murphy DM, Ayres ZJ, Edge R, Newton ME, Wedge CJ. An Electron Paramagnetic Resonance (EPR) spectroscopy study on the γ-irradiation sterilization of the pharmaceutical excipient l-histidine: Regeneration of the radicals in solution. Int J Pharm 2017; 533:315-319. [PMID: 28964903 DOI: 10.1016/j.ijpharm.2017.09.068] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2017] [Revised: 09/25/2017] [Accepted: 09/26/2017] [Indexed: 11/17/2022]
Abstract
The effects of γ-radiation sterilization on the parenteral excipient l-histidine were analysed by means of EPR spectroscopy. The irradiation process was found to induce the formation of a deamination radical which was persistent in the solid state. The nature and reactivity of the radicals following dissolution in water was evaluated using spin-trapping EPR experiments. The deamination radical was found to regenerate in solution in the presence of trace metals, potentially leading to radical induced degradation reactions occurring up to an hour after the dissolution process. Understanding this process is significant for the improved design of parental pharmaceutical formulations in which unwanted radical reactions after γ-radiation sterilization could lead to degradation of active ingredients.
Collapse
Affiliation(s)
- C Vallotto
- Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
| | - H E Williams
- Product Development, AstraZeneca, Silk Road Business Park, Macclesfield, SK10 2NA, UK
| | - D M Murphy
- School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff, CF10 3AT, UK
| | - Z J Ayres
- Department of Chemistry, University of Warwick, Coventry, CV4 7AL, UK
| | - R Edge
- Dalton Cumbrian Facility, The University of Manchester, Westlakes Science & Technology Park, Moor Row, Cumbria CA24 3HA, UK
| | - M E Newton
- Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
| | - C J Wedge
- Department of Physics, University of Warwick, Coventry, CV4 7AL, UK; Department of Chemical Sciences, University of Huddersfield, Queensgate, Huddersfield, HD1 3DH, UK.
| |
Collapse
|
2
|
Dodson CA, Wedge CJ, Murakami M, Maeda K, Wallace MI, Hore PJ. Fluorescence-detected magnetic field effects on radical pair reactions from femtolitre volumes. Chem Commun (Camb) 2015; 51:8023-6. [PMID: 25865161 DOI: 10.1039/c5cc01099c] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
We show that the effects of applied magnetic fields on radical pair reactions can be sensitively measured from sample volumes as low as ∼100 femtolitres using total internal reflection fluorescence microscopy. Development of a fluorescence-based microscope method is likely to be a key step in further miniaturisation that will allow detection of magnetic field effects on single molecules.
Collapse
Affiliation(s)
- C A Dodson
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford OX1 3TA, UK
| | | | | | | | | | | |
Collapse
|
3
|
Maeda K, Storey JG, Liddell PA, Gust D, Hore PJ, Wedge CJ, Timmel CR. Probing a chemical compass: novel variants of low-frequency reaction yield detected magnetic resonance. Phys Chem Chem Phys 2014; 17:3550-9. [PMID: 25537133 DOI: 10.1039/c4cp04095c] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We present a study of a carotenoid-porphyrin-fullerene triad previously shown to function as a chemical compass: the photogenerated carotenoid-fullerene radical pair recombines at a rate sensitive to the orientation of an applied magnetic field. To characterize the system we develop a time-resolved Low-Frequency Reaction Yield Detected Magnetic Resonance (tr-LF-RYDMR) technique; the effect of varying the relative orientation of applied static and 36 MHz oscillating magnetic fields is shown to be strongly dependent on the strength of the oscillating magnetic field. RYDMR is a diagnostic test for involvement of the radical pair mechanism in the magnetic field sensitivity of reaction rates or yields, and has previously been applied in animal behavioural experiments to verify the involvement of radical-pair-based intermediates in the magnetic compass sense of migratory birds. The spectroscopic selection rules governing RYDMR are well understood at microwave frequencies for which the so-called 'high-field approximation' is valid, but at lower frequencies different models are required. For example, the breakdown of the rotating frame approximation has recently been investigated, but less attention has so far been given to orientation effects. Here we gain physical insights into the interplay of the different magnetic interactions affecting low-frequency RYDMR experiments performed in the challenging regime in which static and oscillating applied magnetic fields as well as internal electron-nuclear hyperfine interactions are of comparable magnitude. Our observations aid the interpretation of existing RYDMR-based animal behavioural studies and will inform future applications of the technique to verify and characterize further the biological receptors involved in avian magnetoreception.
Collapse
Affiliation(s)
- Kiminori Maeda
- Department of Chemistry, University of Oxford, Centre for Advanced Electron Spin Resonance, Inorganic Chemistry Laboratory, Oxford, OX1 3QR, UK.
| | | | | | | | | | | | | |
Collapse
|
4
|
Abstract
Within the framework of the radical pair mechanism, magnetic fields may alter the rate and yields of chemical reactions involving spin-correlated radical pairs as intermediates. Such effects have been studied in detail in a variety of chemical systems both experimentally and theoretically. In recent years, there has been growing interest in whether such magnetic field effects (MFEs) also occur in biological systems, a question driven most notably by the increasing body of evidence for the involvement of such effects in the magnetic compass sense of animals. The blue-light photoreceptor cryptochrome is placed at the centre of this debate and photoexcitation of its bound flavin cofactor has indeed been shown to result in the formation of radical pairs. Here, we review studies of MFEs on free flavins in model systems as well as in blue-light photoreceptor proteins and discuss the properties that are crucial in determining the magnetosensitivity of these systems.
Collapse
Affiliation(s)
- Emrys W. Evans
- Centre for Advanced Electron Spin Resonance, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, UK
| | - Charlotte A. Dodson
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford OX1 3TA, UK
| | - Kiminori Maeda
- Centre for Advanced Electron Spin Resonance, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, UK
| | - Till Biskup
- Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstraße 21, 79104 Freiburg, Germany
| | - C. J. Wedge
- Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, UK
| | - Christiane R. Timmel
- Centre for Advanced Electron Spin Resonance, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, UK
| |
Collapse
|
5
|
Wedge CJ, Lau JCS, Ferguson KA, Norman SA, Hore PJ, Timmel CR. Spin-locking in low-frequency reaction yield detected magnetic resonance. Phys Chem Chem Phys 2013; 15:16043-53. [PMID: 23963374 DOI: 10.1039/c3cp52019f] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The purported effects of weak magnetic fields on various biological systems from animal magnetoreception to human health have generated widespread interest and sparked much controversy in the past decade. To date the only well established mechanism by which the rates and yields of chemical reactions are known to be influenced by magnetic fields is the radical pair mechanism, based on the spin-dependent reactivity of radical pairs. A diagnostic test for the operation of the radical pair mechanism was proposed by Henbest et al. [J. Am. Chem. Soc., 2004, 126, 8102] based on the combined effects of weak static magnetic fields and radiofrequency oscillating fields in a reaction yield detected magnetic resonance experiment. Here we investigate the effects on radical pair reactions of applying relatively strong oscillating fields, both parallel and perpendicular to the static field. We demonstrate the importance of understanding the effect of the strength of the radiofrequency oscillating field; our experiments demonstrate that there is an optimal oscillating field strength above which the observed signal decreases in intensity and eventually inverts. We establish the correlation between the onset of this effect and the hyperfine structure of the radicals involved, and identify the existence of 'overtone' type features appearing at multiples of the expected resonance field position.
Collapse
Affiliation(s)
- C J Wedge
- Department of Chemistry, University of Oxford, Centre for Advanced Electron Spin Resonance, South Parks Road, Oxford, OX1 3QR, UK.
| | | | | | | | | | | |
Collapse
|
6
|
Wedge CJ, Timco GA, Spielberg ET, George RE, Tuna F, Rigby S, McInnes EJL, Winpenny REP, Blundell SJ, Ardavan A. Chemical engineering of molecular qubits. Phys Rev Lett 2012; 108:107204. [PMID: 22463450 DOI: 10.1103/physrevlett.108.107204] [Citation(s) in RCA: 153] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2011] [Indexed: 05/05/2023]
Abstract
We show that the electron spin phase memory time, the most important property of a molecular nanomagnet from the perspective of quantum information processing, can be improved dramatically by chemically engineering the molecular structure to optimize the environment of the spin. We vary systematically each structural component of the class of antiferromagnetic Cr(7)Ni rings to identify the sources of decoherence. The optimal structure exhibits a phase memory time exceeding 15 μs.
Collapse
Affiliation(s)
- C J Wedge
- Centre for Advanced Electron Spin Resonance, Clarendon Laboratory, Department of Physics, University of Oxford, OX1 3PU, United Kingdom
| | | | | | | | | | | | | | | | | | | |
Collapse
|
7
|
Wedge CJ, Rodgers CT, Norman SA, Baker N, Maeda K, Henbest KB, Timmel CR, Hore PJ. Radiofrequency polarization effects in low-field electron paramagnetic resonance. Phys Chem Chem Phys 2009; 11:6573-9. [DOI: 10.1039/b907915g] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
8
|
Rodgers CT, Wedge CJ, Norman SA, Kukura P, Nelson K, Baker N, Maeda K, Henbest KB, Hore PJ, Timmel CR. Radiofrequency polarization effects in zero-field electron paramagnetic resonance. Phys Chem Chem Phys 2009; 11:6569-72. [DOI: 10.1039/b906102a] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|