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SUMMARY:Aromatic interactions in simple and complex liquids - Neal Skipper
 \, UCL
DTSTART:20150430T110000Z
DTEND:20150430T120000Z
UID:TALK58674@talks.cam.ac.uk
CONTACT:Catherine Pearson
DESCRIPTION:Aromatic π-π interactions are now known to play a key role i
 n a wide range of important problems\, including the stereochemistry\nof o
 rganic reactions\, organic host-guest chemistry and crystal packing\, prot
 ein folding and structure\, DNA and RNA base stacking\, protein-nucleic ac
 id recognition\, drug design\, and asphaltene (heavy crude oil) aggregatio
 n and fouling. However\, detailed knowledge of the structures adopted by s
 imple model aromatic liquids is currently lacking and essential to our fun
 damental understanding of π-π interactions in condensed\nmatter. We have
  high-resolution neutron diffraction in conjunction with hydrogen/deuteriu
 m isotopic labeling to determine the structure of simple aromatic liquids\
 , and more complex solutions of fullerene\, graphene and carbon nanotubes.
  From our studies of benzene and toluene we have discovered the nature of 
 aromatic π-π interactions in the liquid state by constructing six-dimens
 ional spatial and orientational pictures of these systems. We find that in
  each case the nearest neighbour coordination shell contains approximately
  12 molecules. At small molecular separations (<5 A) there is a preference
  for parallel π-π contacts in which the molecules are offset to mimic th
 e interlayer structure of graphite. At larger separations (>5 A) the neigh
 bouring aromatic rings are predominantly perpendicular\, with two H atoms 
 per molecule directed toward the acceptor's π orbitals. The so-called "an
 ti-hydrogen-bond" configuration\, proposed as the global minimum for the b
 enzene dimer\, occurs only as a saddle point in our data. In the case of g
 raphitic carbon nanostructures such as fullerene and graphene\, charging i
 n metal-ammonia solutions allows us to dissolve high concentrations of the
 se solute molecules. We have then used neutron diffraction to obtain a det
 ailed picture of the solvation of these particles\, and to elucidate for e
 xample the nature of hydrogen bonding to the π-orbitals.\n
LOCATION:Open Plan Area\, BP Institute\, Madingley Rise CB3 0EZ
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