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Molecular simulations of the disintegration of charged droplets in the presence of macromolecules. 4490 project, 2009

Highly charged liquid droplets that contain solvent and excess of ions of the same sign are ubiquitous in aerosol and atmospheric chemistry, electrospray methods, as well as in technologies such as inkjet-printing and air-purification processes. In analytical chemistry techniques, electrospray methods are coupled to mass spectrometry (ESMS). Electrospray mass spectrometry is often used for the detection of macromolecules such as polypeptides or proteins in solution. The operation of electrospray methods is based on cascades of fragmentation events of charged droplets where charged droplets shrink due to solvent evaporation and then fragment due to high ratio of charge versus volume of droplet. Finally the charged analytes emerge from the droplet and are detected by the mass spectrometer from their charge to mass ratio. For a macromolecule, a charge distribution is detected instead of a single peak that corresponds to a single charge to mass ratio. In this project we will study the effect of conformation in the charge state of a macromolecule. The droplet will be composed of water molecules, ions and a polypeptide. The interactions in the system will be modelled by molecular mechanics force fields. The behavior of the system will be simulated by molecular dynamics and Monte Carlo methods.
The students involved in the the project will become familiar with computer programming, methods of molecular dynamics and Monte Carlo and concepts of statistical mechanics. The project itself will help the students to obtain a better understanding of microscopic details of physical and chemical mechanisms that are involved in experiments.