title: Crystal structure of neotame anhydrate polymorph G.
abstract: OBJECTIVE
  To determine the crystal structure of the neotame anhydrate polymorph G and to evaluate X-ray powder diffractometry (XRPD) with molecular modeling as an alternative method for determining the crystal structure of this conformationally flexible dipeptide.
  
  
  METHODS
  The crystal structure of polymorph G was determined by single crystal X-ray crystallography (SCXRD) and also from the X-ray powder diffraction (XRPD) pattern using molecular modeling (Cerius2, Powder Solve module).
  
  
  RESULTS
  From SCXRD, polymorph G crystals are orthorhombic with space group of P2(1)2(1)2(1) with Z = 4, unit cell constants: a = 5.5999(4), b = 11.8921(8), c = 30.917(2) A, and one neotame molecule per asymmetric unit. The XRPD pattern of polymorph G, analyzed by Cerius2 software, led to the same P2(1)2(1)2(1) space group and almost identical unit cell dimensions. However, with 13 rigid bodies defined, Cerius2 gives a conformation of the neotame molecule, which is different from that determined by SCXRD.
  
  
  CONCLUSIONS
  For neotame anhydrate polymorph G, the unit cell dimensions calculated from XRPD were almost identical to those determined by SCXRD. However, the crystal structure determined by XRPD closely resembled that determined by SCXRD, only when the correct conformation of the neotame molecule had been chosen before detailed analysis of the XRPD pattern.
authors.affiliation: Department of Pharmaceutics, College of Pharmacy, University of Minnesota, Minneapolis 55455-0343, USA.
authors.forename: Zedong
authors.initials: Z
authors.lastname: Dong
authors.forename: Victor G
authors.initials: VG
authors.lastname: Young
authors.forename: Agam
authors.initials: A
authors.lastname: Sheth
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Munson
authors.forename: Steve A
authors.initials: SA
authors.lastname: Schroeder
authors.forename: Indra
authors.initials: I
authors.lastname: Prakash
authors.forename: David J W
authors.initials: DJ
authors.lastname: Grant
mesh_terms: D003460:Crystallization; D004151:Dipeptides / Q000032:analysis / Q000737:chemistry*
chemical_list: D004151:Dipeptides; C404525:neotame