Robertson - Optical spectroscopy of atmospheric and biological molecules
There is more to light than meets the eye. Light with wavelengths invisible to human sight but detected by sophisticated instruments called spectrometers provide us with a detailed view of the "nanoscopic" molecular world that underpins daily life.
We exploit powerful light sources such as infrared, visible and ultraviolet lasers, or the Australian Synchrotron's infrared beamline, to study molecules relevant to pharmaceutics, atmospheric and aerosol chemistry and even the interstellar medium. This type of molecular sensing can reveal the shape of neurotransmitter molecules that act as the 'key' in receptor 'locks' involved with signaling in the brain; the details of how much radiant heat is absorbed by greenhouse gases; the size and temperature of ice nanoparticles like those in high altitude clouds; or the spectral fingerprint patterns that allow molecules in space to be identified through radioastronomy. Research is supported by ARC grants, the Australian Synchrotron and National Computing Infrastructure.
The conformational shape of biomolecules
The conformational shape of biomolecules and their interactions with the surrounding environment including water are critical to their functioning. Laser-based gas phase spectroscopy, combined with ab initio calculations, generates precise molecular structural information on molecules such as neurotransmitters that provide a rigorous platform for understanding their behaviour and, ultimately, rationalising drug design.
Many neurotransmitter molecules are comprised of an aromatic ring linked to a flexible alkylamine side chain. Comparison of theoretical simulations with experimental IR-UV spectra reveals the preferred arrangements of those chains, which is governed in turn by non-covalent, intramolecular interactions such as NH…pi type hydrogen bonds.
We are exploring how this class of neurotransmitters differs to those with constrained side chains. We are also measuring hydrogen bonding interactions between water molecules and various functional groups such as nitriles, halogens, and thiols by making and studying size specific clusters.
Cold aerosol nanoparticles
Aerosols impact earth's climate both directly through absorption and reflection of light, and indirectly by hosting chemical reactions and influencing cloud formation. Recently, a new generation of collisional cooling cell designed by one of our collaborators (Sigurd Bauerecker) has created possibilities for studying aerosols generated by pulsed sequences of injections.
With recent development work on the cooling cell at the Australian Synchrotron it is now possible to extend these measurements to the crucial but unexplored far IR region. Aerosol spectra can reveal diagnostic information about particle size, temperature and the physical phase as well as provide fundamental optical constants needed to quantify scattering and absorption of radiation. We are studying cold aerosols comprised of water and other hydrocarbons relevant to astrochemical environments.
Atmospheric molecules and high resolution infrared spectroscopy
Experiments conducted at the High resolution and Far IR beamline of the Australian Synchrotron provide IR spectra that are analysed to obtain rovibrational properties of atmospheric molecules such as dichlorodifluoromethane. Commonly known as CFC-12 or refrigerant R12, it persists in the atmosphere for 100 years and a global warming potential (GWP) 8100 times larger than CO2 makes it one of the more important anthropogenic greenhouse gases.
IR spectra can be measured for samples at room temperature or cooled to as low as 100K to facilitate the assignment of several thousand individual rovibrational lines. Constants obtained from such analyses may be used to efficiently model the complex pattern of IR absorption within the atmospheric greenhouse window. Interstellar molecules are also studied to aid in the identification of spectral lines found in radioastronomy.
Meet the team