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HIMS researcher Dr Aurora J. Cruz-Cabeza, postdoc with the group for Computational Chemistry, recently published a review article in Chemical Reviews, the highest impact factor chemistry journal. Together with Joel Bernstein of New York University (Abu Dhabi), she shines a new light on the phenomenon of Conformational Polymorphism in Molecular Materials.

Aurora Cruz-Cabeza
Dr Aurora J. Cruz-Cabeza

Both researchers refine definitions, help identify the phenomenon and quantify its occurrence through a combination of database analysis, theoretical calculations and literature review. The result is an in-depth and comprehensive view of Conformational Polymorphism.  Aurora: "With our article we expect to change the way the phenomenon is recognised and appreciated. We think it will serve as a key reference for future scientists working in the field".

Crystal structures and conformations

Molecular crystals are perfectly ordered symmetric materials. They are encountered in day-to-day products such as food, pigments, drugs or cosmetics.

Conformations of 1,3-bis(m-nitrophenyl)urea as found in three different polymorphs.
Conformations of 1,3-bis(m-nitrophenyl)urea as found in three different polymorphs.

To form a crystal a huge number of molecules (in the order of 10 to the power of 23) have to come together. 

In many cases the same molecules can crystallise in more than one crystal structure. These different crystal structures are referred to as polymorphs. Polymorphs can differ considerably in their properties. 

From time to time molecules also change their shape (referred to as conformation) when they crystallise in different polymorphs. This phenomenon, called Conformational Polymorphism, is the subject of Aurora's article in Chemical Reviews.

Celebrating crystallography

The publication is well-timed since this year has been declared by UNESCO as the International Year of Crystallography. Elucidating the structure of crystals has propelled advances in many areas of science, from biology through chemistry to metallurgy and geology. Just over a century ago the British researchers William Henry Bragg and William Lawrence Bragg (father and son) performed their ground-breaking research on the determination of crystal structures by means of X-ray crystallography.

Aurora feels particularly inspired by the work of crystallographer Carolina MacGillavry, an  alumnus of the University of Amsterdam. "I feel that she would have liked our contribution which, of course, would have not been possible without her work."

Aurora's research was funded by the Netherlands Organisation for Scientific Research by means of a VENI grant (2011). The cooperation with Joel Bernstein originated in 2005 in a conference in Finland. "Back then, I was starting my Ph.D. at Cambridge University. With the years we became very close in research interests and good friends. Thanks to my VENI grant, we have now been able to work together. I consider our article the perfect combination of Joel's experience and enthusiasm with my new way of thinking and contemporary skills."

Aurora Cruz-Cabeza and Joel Bernstein
Aurora Cruz-Cabeza and Joel Bernstein

Article 

Conformational Polymorphism 
A.J. Cruz-Cabeza and J. Bernstein  
Chem. Rev. , 2014, doi:10.1021/cr400249d