scholarly journals Spin-Labelled Mechanically Interlocked Molecules as Models for the Interpretation of Biradical EPR Spectra

2021 ◽  
Author(s):  
Lorenzo Gualandi ◽  
Paola Franchi ◽  
Elisabetta Mezzina ◽  
Stephen Goldup ◽  
Marco Lucarini
Keyword(s):  
Epr Spectra ◽  
Spin Probes ◽  
Interlocked Molecules

Biradical spin probes can provide detailed information about the distances between molecules/regions of molecules because the through-space coupling of radical centres, characterised by J, is strongly distance dependent. However, if...

scholarly journals Spin-Labelled Mechanically Interlocked Molecules as Models for the Interpretation of Biradical EPR Spectra

2021 ◽  
Author(s):  
Lorenzo Gualandi ◽  
Paola Franchi ◽  
Elisabetta Mezzina ◽  
Stephen Goldup ◽  
marco lucarini
Keyword(s):  
Detailed Analysis ◽  
Epr Spectra ◽  
Supramolecular Complexes ◽  
Spin Probes ◽  
Nitronyl Nitroxide ◽  
Epr Spectrum ◽  
Interlocked Molecules ◽  
Conformational Interconversion ◽  
Multiple Configurations ◽  
Spectral Shapes

<div> <p>Biradical spin probes can provide detailed information about the distances between molecules/regions of molecules because the through-space coupling of radical centres, characterised by <i>J</i>, is strongly distance dependent. However, if the system can adopt multiple configurations, as is common in supramolecular complexes, the shape of the EPR spectrum is influenced not only by <i>J</i> but also the rate of exchange between different states. In practice, it is often hard to separate these variables and as a result, the effect of the latter is sometimes overlooked. To demonstrate this challenge unequivocally we synthesised rotaxane biradicals containing nitronyl nitroxide units at the termini of their axles. The rotaxanes exchange between the available biradical conformations more slowly than the corresponding non-interlocked axles but, despite this, in some cases, the EPR spectra of the axle and rotaxane remain remarkably similar.<i> </i>Detailed analysis allowed us to demonstrate that the similar EPR spectral shapes result from different combinations of <i>J</i> and rates of conformational interconversion, a phenomenon suggested theoretically more than 50 years ago. This work reinforces the idea that thorough analysis must be performed when interpreting the spectra of biradicals employed as spin probes in solution.</p></div>

scholarly journals Spin-Labelled Mechanically Interlocked Molecules as Models for the Interpretation of Biradical EPR Spectra

2021 ◽  
Author(s):  
Lorenzo Gualandi ◽  
Paola Franchi ◽  
Elisabetta Mezzina ◽  
Stephen Goldup ◽  
marco lucarini
Keyword(s):  
Detailed Analysis ◽  
Epr Spectra ◽  
Supramolecular Complexes ◽  
Spin Probes ◽  
Nitronyl Nitroxide ◽  
Epr Spectrum ◽  
Interlocked Molecules ◽  
Conformational Interconversion ◽  
Multiple Configurations ◽  
Spectral Shapes

<div> <p>Biradical spin probes can provide detailed information about the distances between molecules/regions of molecules because the through-space coupling of radical centres, characterised by <i>J</i>, is strongly distance dependent. However, if the system can adopt multiple configurations, as is common in supramolecular complexes, the shape of the EPR spectrum is influenced not only by <i>J</i> but also the rate of exchange between different states. In practice, it is often hard to separate these variables and as a result, the effect of the latter is sometimes overlooked. To demonstrate this challenge unequivocally we synthesised rotaxane biradicals containing nitronyl nitroxide units at the termini of their axles. The rotaxanes exchange between the available biradical conformations more slowly than the corresponding non-interlocked axles but, despite this, in some cases, the EPR spectra of the axle and rotaxane remain remarkably similar.<i> </i>Detailed analysis allowed us to demonstrate that the similar EPR spectral shapes result from different combinations of <i>J</i> and rates of conformational interconversion, a phenomenon suggested theoretically more than 50 years ago. This work reinforces the idea that thorough analysis must be performed when interpreting the spectra of biradicals employed as spin probes in solution.</p></div>

The polyliquid crystalline EPR spectra of nitroxide spin probes and their interpretation

1981 ◽  
Vol 43 (1) ◽  
pp. 141-153 ◽  
Author(s):  
Claudio Zannoni ◽  
Gian Franco Pedulli ◽  
Lanfranco Masotti ◽  
Alberto Spisni
Keyword(s):  
Epr Spectra ◽  
Spin Probes ◽  
Nitroxide Spin Probes

scholarly journals EPR spectra of spin labels in lipid bilayers. II. Rotation of steroid spin probes

1974 ◽  
Vol 61 (7) ◽  
pp. 2946-2949 ◽  
Author(s):  
Hansgeorg Schindler ◽  
Joachim Seelig
Keyword(s):  
Lipid Bilayers ◽  
Epr Spectra ◽  
Spin Labels ◽  
Spin Probes

Analysis of the factors determining the EPR spectra of spin probes that partition between aqueous and lipid phases

1978 ◽  
Vol 100 (26) ◽  
pp. 8223-8232 ◽  
Author(s):  
Carl F. Polnaszek ◽  
Shirley Schreier ◽  
Keith W. Butler ◽  
Ian C. P. Smith
Keyword(s):  
Epr Spectra ◽  
Spin Probes

Properties of electrochemically generated primary cationradicals of phenyl- and 2-(4-tolyl)-1,3,4,7-tetramethylisoindoles

1980 ◽  
Vol 45 (6) ◽  
pp. 1669-1676 ◽  
Author(s):  
Pavel Kubáček
Keyword(s):  
Electrochemical Oxidation ◽  
Spin Polarization ◽  
High Spin ◽  
Epr Spectroscopy ◽  
Half Life ◽  
Electrochemical Behaviour ◽  
Epr Spectra ◽  
Electrochemical Generation ◽  
Splitting Constant ◽  
Reduced Temperature

The first step of electrochemical oxidation of 2-phenyl- and 2-(4-tolyl)-1,3,4,7-tetramethylisoindoles in anhydrous acetonitrile produces relatively stable cationradicals which have been studied by means of EPR spectroscopy using the method of internal electrochemical generation of radicals under reduced temperature. The same electrochemical behaviour of the both studied derivatives and identical EPR spectra of their cationradicals can be explained within the Huckel MO method. The largest contribution to the magnitude of splitting constant of nitrogen nucleus is due to π-σ-spin polarization of C-N bonds caused by high spin abundance of pz-AO of carbon atoms. Half-life of decomposition of the studied cationradicals is 4 min at -30°C.

Complexes of copper(II) and nickel(II) with a Schiff base bonded to a polymeric support

1983 ◽  
Vol 48 (7) ◽  
pp. 2021-2027 ◽  
Author(s):  
Eliška Kálalová ◽  
Olga Populová ◽  
Štěpánka Štokrová ◽  
Pavel Stopka
Keyword(s):  
Magnetic Properties ◽  
Schiff Base ◽  
Coordination Sphere ◽  
Polymer Matrix ◽  
Glycidyl Methacrylate ◽  
Epr Spectra ◽  
Polymeric Support ◽  
Tetrahedral Configuration ◽  
Paramagnetic Complexes

Copper(II) and nickel(II) ions were bonded in complexes of salicylideneimine type on a glycidyl methacrylate-ethylenedimethacrylate copolymer. The geometry of the complexes on the polymer was studied by measuring their magnetic properties, EPR spectra, and ultraviolet-visible spectra.Only paramagnetic complexes possessing a pseudo-tetrahedral configuration were found. The effect of the polymer matrix and of the immobility of the bonded Schiff base on the distortion of the coordination sphere of the central ion is discussed.

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