Hydrogen bonding may safeguard biomolecules against the damaging effects of UV light.
Researchers from the University of Southampton, Center for Free-Electron Laser Science in Hamburg and the CLF have used the Artemis facility to study the role of hydrogen bonding by comparing the effects of light absorption in a hydrogen-bonded molecular complex with those in isolated molecules.
The team examined whether hydrogen bonds within DNA may protect biomolecules against damaging ultra-violet light which can be carcinogenic. They used the ammonia dimer as a model chromophore, the parts of the molecule responsible for its colour, to mimic the hydrogen bonding interactions in DNA for these experiments. The dimer is an important model for larger biological systems because it contains the same hydrogen bond that ties DNA nucleobases together, linking an NH group and a nitrogen atom.
“Usually in spectroscopy we focus on individual molecules but it is also important to understand how molecules interact and are connected with each other,” explains PI Russell Minns. “This is early stage research but has potential to help us understand the stability of DNA as well as the initial stages of cell damage.”
Hydrogen bonding is important throughout photobiology. In almost all photobiological processes, light is initially absorbed by a central chromophore. It is connected to the surrounding protein and solvent environment by a network of hydrogen bonds and these play a vital, but not yet understood role, in cell dynamics and help control the way the protein works.
The team excited the dimer with UV laser pulses and, using visible-light pulses, measured the dimer’s photoelectron spectrum at a series of times after absorption. From these, they could infer the molecule's changing structure with femtosecond resolution. They found striking differences between the dynamics of the complex and that of the isolated molecule. Whereas isolated ammonia exhibited a high probability for dissociation through hydrogen abstraction, the ammonia dimer showed an efficient pathway back to the electronic ground state, enabled by a single hydrogen bonding interaction Further information:
Hydrogen Bonds in ExcitedState Proton Transfer
D. A. Horke, H. M. Watts, A. D. Smith, E. Jager, E. Springate, O.Alexander, C. Cacho, R. T. Chapman, and R. S. Minns
Physical Review Letters;117, 163002 (2016). doi:10.1103/PhysRevLett.117.163002 (link opens in a new window).
Synopsis in Physics: http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.117.163002 (link opens in a new window)
Ultrafast Dynamics Group (link opens in a new window), University of Southampton
More information on Artemis
CLF Contact: Richard Chapman