I believe that electron paramagnetic resonance (EPR) has the potentiality of becoming one of the most powerful experimental methods of investigation on the electron distribution in molecules, and on the properties of their environments. The need for fast, effective and non-biased interpretative computational techniques is evident. Thus, the attempt to describe sophisticated quantum mechanical approaches in terms of their interest also for non-specialists has been appreciated by the scientific community.

  Does it describe a new discovery, methodology, or synthesis of knowledge?

“The introduction of methods rooted into the Density Functional Theory (DFT) represents a turning point for the calculations of spin-dependent properties.”

It describes the building blocks of an integrated methodological and computational approach to the analysis of complex phenomena in the specific field of spectroscopy, but with a view to more general applications requiring integration of different methodologies and points of view.

  Would you summarize the significance of your paper in layman’s terms?

Spectroscopic techniques are capable of sensing the chemical environment surrounding probe molecules. In particular, the last several years have seen the increasing impact of EPR for characterizing molecular systems in the life sciences, materials sciences, and applied chemistry. Unfortunately, interpretation of experimental results is not without ambiguities, since the relationship between spectroscopic parameters and the underlying structural/dynamical features is only indirect, and, moreover, different environmental factors can also exert a complex influence.

Here theoretical approaches come into play, provided that they are able to couple reliability and feasibility for large systems. After considerable success for small isolated systems, computational tools developed by theoretical chemists are becoming capable of taking those effects into the proper account, as well as for large flexible molecules in condensed phases. We have tried to sketch, in our paper, the status and perspectives of such an integrated approach.

  How did you become involved in this research and were any particular problems encountered along the way?

I completed a postdoctoral fellowship in a laboratory devoted to the study of free radicals issuing from radiation damage, and the leader of the laboratory was one of the first to convince himself that collaboration between experimentalists and theoreticians was mandatory for the development of the field. Thus, I started to study small model systems with very refined quantum mechanical approaches.

The introduction of methods rooted into the Density Functional Theory (DFT) represents a turning point for the calculations of spin-dependent properties. Before DFT, quantum mechanical (QM) calculations of magnetic tensors were either prohibitively expensive, even for medium-size radicals, or not sufficiently reliable for predictive and interpretative purposes.

Today, last-generation functionals coupled to purposely tailored basis sets allow one to compute magnetic tensors in remarkable agreement with their experimental counterparts. Computations can take into proper account both average environmental effects and short-time dynamical contributions, e.g., vibrational averaging from intramolecular vibrations and/or solvent librations, thus providing a set of parameters that can be confidently used for further calculations.

For instance, different boundary conditions can be enforced to properly describe solutions (Figure 1) and solids (Figure 2). The present situation is the result of considerable work, imagination, and collaboration between scientists with quite different competencies.

  Where do you see your research leading in the future?

In order to make further progress, it is necessary to integrate refined theoretical tools, from the world of quantum mechanics calculations and also from the world of statistical thermodynamics. It is quite a challenge, for a theoretical chemist, to combine them in an integrated working approach and I am trying to define a possible route to accomplish this task (see Figure 3).

A likely development is the production of user-friendly black-box software able to predict, from the structure of the molecular probe and appropriate information on the chemical environment, the full EPR spectrum. We believe that such a tool would be very valuable in many contexts, and can be extended to other spectroscopies, like, e.g., nuclear magnetic resonance (NMR).

  Are there any social or political implications for your research?

Since a number of phenomena (e.g., aging, or some cancers) are related to the formation and reaction of organic free radicals, a better understanding of their characteristics is a mandatory starting point for the development of new control strategies of significant social impact.