Identifying Energy Dispersal Pathways in Bare and Hydrated Nuclear Bases: A New Dimension in Nanosecond Electronic Spectroscopy

Molecules involved in biology, such as in our bodies, are affected by the absorption of energy, particularly from light. We see this via sunburn, skin aging and via skin cancer, mainly caused by ultraviolet radiation. These effects occur as the energy absorbed is not spread out quickly enough, and so can damage molecules locally. In fact, DNA and other biological molecules are very good at losing energy so it is only when we expose ourselves to large amounts of sunlight that damage occurs. One way to protect ourselves is to use sun creams that contain special organic molecules that can spread out the Sun's energy efficiently so that it does not reach the skin. Hence knowledge of how energy spreads through molecules is very important: both to understand how our molecules get damaged, but also in designing new molecules that can protect us from sunlight.

In this work we will look at the energy levels in molecules and identify the pathways by which energy spreads through molecules, both in isolation, but also in the presence of water molecules, since molecules in our bodies are typically surrounded by water. However, it is expected that the strongest effect will come from the first few water molecules interacting with the molecule, since these will attach to the most active sites (it is the first few children who get a good view of the ice cream van, the rest only catch glimpses through the crowd!).

Our experiments will be carried out under carefully-controlled conditions, allowing us to understand in detail what is happening, and to have the ability of seeing the effect of adding water molecules one at a time. We shall be able to see how the energy can move through the molecule, and how this is affected by the addition of the water.

To understand the experiments we need to be able to model the systems, but such models are currently not reliable. Hence we shall develop new modelling tools, and test them against our experiments. Since the experiments are well-defined, it means that the models can be tested in a fair manner. Once the models are established, then they can be used to gain insight into the attributes of the molecules which make them stable in sunlight, and this will help with understanding skin damage (aging, skin cancer) and allow new chemicals for sun protection to be designed by industry.

Although the work is quite "academic" or "pure" in nature, there is the potential for longer-term benefits in a range of arenas. The central issue is what happens when ultraviolet energy is absorbed by a molecule, and how this energy is either lost or dissipated. Such processes affect whether a molecule might be damaged (for example, fall apart), how quickly it might react (electronically excited states generally react faster than ground states) and whether stored energy can be kept localized in a molecule, for example to allow selective photochemistry to occur. It may thus be seen that there are positive and negative effects. As mentioned in the proposal and elsewhere on this form, damage of biomolecules is a particular concern, as it leads to cancers, particularly skin cancer, and aging. Protection from these can come from sun creams, which themselves partially rely on added organic molecules which can disperse the Sun's energy so it does not reach the skin in a damaging form.

One active area of modern chemistry is controlling reactions with light, with the outcome of many reactions being found to be controllable when irradiated with particular wavelengths of light. Photodissociation of molecules is also wavelength dependent, and so photochemists can control which nascent radicals they can produce by changing the radiation employed. Such methods rely, to some extent, on the energy remaining in the correct vibrational coordinate long enough to allow the photodissociation event to occur - if the energy quickly disperses then there will not be enough in the correct coordinate for photodissociation to occur; or, the selectivity of a photochemical reaction will be lost. It is therefore important, depending on the desired outcome, to be able to design molecules that lose energy efficiently, or alternatively that do not. Understanding the attributes of molecules that lead to vibrational coupling will allow us to design a molecule with the appropriate properties.

Longer term, understanding photodamage to sensitive biomolecules could lead to breakthroughs into understanding cancer formation, and ameliorating the risks of this occurring.