Understanding geometric isotope effect

Published in Chemistry
Understanding geometric isotope effect

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The paper in Nature Communications is here: http://rdcu.be/F7jL

Hydrogen (H) bond refers to the attractive interaction between the H atom and a more electronegative atom with a typical form of X−H···Y where X and Y represent the H bond donor and acceptor, respectively. It plays a vital role in biological systems and various ion- and molecule-based aggregates, e.g., to maintain the structures and functions of DNA and proteins, to control the anomalous melting/freezing process of H2O and to trigger the structural phase transitions in H-bonded ferroelectrics.

Deuteration is a powerful tool to probe and tune the H bonds by replacing the protium (H) with the deuterium (D). One effect of the substitution, known as geometric isotope effect (GIE), is the generation of noticeable H bond geometry changes which would exert internal pressure on the global H-bonded networks and cause new phases in crystals and, therefore, regulate their properties and functions.

These constitute the background of our work on the GIE in a simple host-guest hydrogen-bonded crystal. In this model system, the GIE is well identified by X-ray diffraction method. Upon deuteration, the donor–acceptor distance in the O—H···O hydrogen bonds in the host structure is found to increase, resulting in the changes of the global hydrogen-bonded supramolecular structure and the dynamics of the confined guest.

At the beginning of the study, however, we lacked a comprehensive understanding of the GIE. For example, the primary GIE was not taken into consideration. The effect was only regarded as an addition property of the crystal in the field of ferroelectric/dielectric phase transitions. Its significance has been gradually recognized during literature searching and data analyzing. Thanks for the reviewers' valuable comments and suggestions, we finally completed the story that is now self-contained.

The work has important implications for materials science, biomolecular systems and crystal engineering. As an H/D isotope doping approach, the GIE can be used to probe and tune H-bonded structures and associated physical/chemical/biological properties and functions, such as substrate binding, enzyme catalysis, protein folding and stabilization, and phase transition and related properties. The study also sets a strict limit on the use of deuterated samples as proxies in structural studies of biological systems. 

The paper in Nature Communications is here: http://go.nature.com/2E0tiaB

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