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Nitroxides: Versatile Reporters and Reactants

Posted on 14. June, 2011.

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First synthesised in the early 1960s, nitroxides have become probably the most popular persistent radicals. Their long half lives and the sensitivity of their spectromagnetic properties to local environment (polarity, hydrogen bonding power, pH and viscosity of the surrounding medium and proximity to other paramagnetic or charged species) and intramolecular effects (conformation and vibrational behaviour) make them attractive tools in various areas of application, particularly in the fields of biochemistry, biophysics and materials science.

In the May issue of Journal of Chemical Research, Evelyn Zottler and Georg Gescheidt (both pictured below) from the Institute of Physical and Theoretical Chemistry, Graz University of Technology, Austria review the developments in the field of nitroxide spin probes and their various applications, with the main focus on the pH-sensitive imidazoline nitroxide family. 

Evelyn Zottler and Georg Gescheidt

Evelyn Zottler received her MSc degree in chemistry from the University of Technology in Graz.
She participated in a student exchange project with Syracuse University, USA, where she did a
research internship in the group of Prof. M. B. Sponsler. She also worked as an IAESTE trainee at
the University of Edinburgh, UK, in Dr D. Uhrin’s group. She spent a year as an ERASMUS student
at the University of Liverpool, UK. For her diploma thesis, she has been working on interactions
between metal ions and pH-sensitive imidazoline nitroxides together with Prof. G. Gescheidt at the
Institute of Physical and Theoretical Chemistry in Graz.

Georg Gescheidt obtained his diploma in chemistry at the Albert-Ludwigs-University in Freiburg
(Germany). Then he joined the group of Prof. Fabian Gerson where he obtained his PhD in the field
of radical ions and their investigation by EPR spectroscopy. After two years of editorial work at
Helvetica Chimica Acta (1988–90), he returned to university life. Since 2003 he has held a chair in
Physical Chemistry at the University of Technology in Graz. His research interests are the molecular
basis of radical and radical ion reactions in chemistry, catalysis, biomimetic systems and material
science (polymer chemistry). Short-lived species are established by magnetic-resonance methods
(EPR, ENDOR, time-resolved EPR (ns time scale), CIDNP), theoretical approaches, cyclovoltammetry,
and, partly, by optical spectroscopy.

CONTENTS

1 Introduction
2 Nitroxide EPR spectra
3 Basic research

3.1 Hydrogen bonds
3.2 Macromolecular ions
3.3 Interactions with metal ions
3.4 Distance measurements
3.5 pH-sensitive nitroxides
4 Life sciences
4.1 Proteins
4.2 Redox probes
4.3 RNA
4.4 Membranes and micelles
4.5 Macromolecular pH-probes
4.6 Medicinal and pharmaceutical applications
5 Technology
5.1 Polymers
5.2 Spin trapping
5.3 Ionic liquids
5.4 Organic glasses
5.5 Porous systems
5.6 Nanoparticles
6 Concluding remarks
7 References

Over the last 50 years or so, nitroxides have evolved into one of most extensively researched group of radicals. This review charts numerous examples of their widespread applications, and expands on the popular pH-sensitive imidazoline nitroxide series and the related proton exchange. It is, therefore, not astonishing that new and better nitroxide spin probes are continually synthesised and characterised. The number of current publications in the field shows that developments and scientific interest are not on the wane.

doi: 10.3184/174751911X13040218227310