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SUMMARY:Completing the library of amino-acid neutron structures
DTSTART;VALUE=DATE-TIME:20211125T080000Z
DTEND;VALUE=DATE-TIME:20211125T080100Z
DTSTAMP;VALUE=DATE-TIME:20260718T053348Z
UID:indico-contribution-4350@events01.synchrotron.org.au
DESCRIPTION:Speakers: Garry McIntyre (Australian Nuclear Science and Techn
 ology Organisation)\nAccurate neutron structures of the 20 naturally occur
 ring amino acids that are the building blocks of proteins are key to inves
 tigations of polymorphism\, condensed-phase NMR analysis\, periodic densit
 y-functional-theory calculations\, as restraints in X-ray protein refineme
 nts\, and as initial structures in the computer modelling of proteins.  Th
 e first 16 members of the family were determined in the 1970s by groups at
  Brookhaven National Laboratory and the Indian Atomic Energy Laboratory\, 
 but the last four proved to be elusive due to the lack of single crystals 
 large enough for the monochromatic neutron diffractometers of the time.  S
 tate-of-the-art reactor-based neutron Laue diffractometers\, such as Koala
  on OPAL\, allow high-precision structural investigations of single crysta
 ls with volumes around 0.1 mm3. This opens the door to completing the libr
 ary of high-precision amino-acid neutron structures.\n\nHere we describe v
 ariable-temperature studies of three naturally-occurring amino acids using
  Koala\, L-leucine [1] which is one of the four missing members and the tw
 o polymorphs of L-histidine.  The data on the orthorhombic form of L-histi
 dine greatly improve on the precision of a previous monochromatic neutron 
 study.  The second\, monoclinic\, form has been studied with neutrons for 
 the first time [2].  Both studies were complemented by interaction-energy 
 calculations using the Pixel method\, and\, for L-histidine\, Hirshfeld At
 om Refinement against X-ray data at the same temperatures. The resulting n
 eutron structures yield geometric parameters with sufficient precision and
  accuracy for inclusion in restraint libraries of macromolecular structure
  refinements.\n\nThe search continues for neutron-quality crystals of L-is
 oleucine\, L-methionine and L-tryptophan.\n\n[1] J. Binns et al. Acta Crys
 t. B72 (2016) 885.\n[2] G. Novelli et al. Acta Cryst B. In press.\n\nhttps
 ://events01.synchrotron.org.au/event/146/contributions/4350/
LOCATION:Online
URL:https://events01.synchrotron.org.au/event/146/contributions/4350/
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