Adam Willard

Graduate Student Chandler Group Department of Chemistry University of California at Berkeley Berkeley, CA 94720 Phone: 510-643-7128 Fax: 510-643-1566 Email: awillard"AT"berkeley"DOT"edu

Research Interests

The Hydrophobic Effect

• An interesting thing happens as you increase the size of a hydrophobic solute in water. Hydrophobic solutes with radius less than about one nano meter have a solvation free energy that scales with solute volume while hydrophobic solutes with radius larger than about one nano meter have a solvation free energy that scales with solute surface area. The physical picture associated with this crossover is that small solutes can be accommodated within the solvent's network of hydrogen bonds. The presence of the solute restricts the accessible configurations available to the solvent and its hydrogen bonding network, the restriction imposed by the solute depends on the volume of physical space the solute occupies. Larger solutes cannot be accommodated in the hydrogen bonding network which means that water molecules adjacent to the solute surface can only form hydrogen bonds back into the bulk. The unbalanced bonding forces adjacent to the hydrophobic solute induce a liquid/vapor interface to form, which surrounds the solute particle (for a more detailed description of hydrophobic effect click here . The liquid/vapor interface around a large hydrophobic solute exhibits the same type of equilibrium fluctuations as a liquid/vapor interface associated with ordinary phase coexistence.
  
  These fluctuations in the interface surrounding a large hydrophobic solute become very significant when another large hydrophobic solute is nearby. I study the role of these solvent fluctuations in the assembly of two large hydrophobic solutes. Below is a short movie which shows the aggregation of two hydrophobic particles which are about 2.5 nano meters in diameter in water that has been coarse grained in space and time. The translucent white cubes represent regions of solvent with low density (vapor).
  
  The rapid collapse of the solute particles is typically preceded by the formation of a vapor tunnel connecting the solvent cavities the solute particles occupy
  For a movie showing an example of hydrophobic collapse click here
  
  It turns out that in order to properly describe the aggregation of two large hydrophobic particles, one must say something about the solvent. By choosing an appropriate solvent coordinate, it is possible to construct the free energy surface associated with the aggregation of the solutes.
  
  

Teaching

• Chemistry 220A - Fall 2006
• Chemistry 120B - Spring 2006
• Chemistry 1A - Fall 2004 - Sec.120

History

B.S., Chemistry and Mathematics, 2003, University of Puget Sound, Tacoma WA

Past Research
Time-resolved and Steady-state phosphorescence of 3-Fluoro-Tyrosine in a Polypeptide Chain
Advisor:Prof. Kenneth Rousslang, Univeristy of Puget Sound, 2003

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Last updated: 1/29/2007