title: Methyl dynamics in crystalline amino acids: MD and NMR.
abstract: Correlation times for rotation of deuterated methyls in crystalline leucine, valine, and cyclo-L-alanyl-L-alanine are calculated with molecular dynamics and compared with NMR data. The simulations distinguish between methyls having different steric environments in the crystal, yielding correlation times differing by a factor of up to 30 for methyls within a given crystal. MD and NMR correlation times agree to within a factor of 2. However, averaging over nonequivalent methyls can yield correlation functions that, although actually multiexponential, are well fit by single exponentials. This may have significance for interpreting NMR data; previous NMR data did not distinguish between the methyls in these crystals. Adiabatic rotational barriers calculated with the X-ray structure differ from effective barriers during simulation by up to +/-1 kcal/mol; the difference indicates that dynamical effects have a significant role in determining rotational correlation times.
authors.affiliation: Chemistry Department, Florida International University, Miami, Florida 33199, USA. chatfield@flu.edu
authors.forename: David C
authors.initials: DC
authors.lastname: Chatfield
authors.forename: Alberto
authors.initials: A
authors.lastname: Augsten
authors.forename: Cassian
authors.initials: C
authors.lastname: D'Cunha
authors.forename: Sergio E
authors.initials: SE
authors.lastname: Wong
mesh_terms: D000465:Algorithms; D000596:Amino Acids / Q000737:chemistry*; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D007930:Leucine / Q000737:chemistry; D008697:Methane / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular; D010456:Peptides, Cyclic / Q000737:chemistry; D011487:Protein Conformation; D013816:Thermodynamics; D014633:Valine / Q000737:chemistry
chemical_list: D000596:Amino Acids; D010456:Peptides, Cyclic; C053149:cyclo(alanylalanyl); D007930:Leucine; D014633:Valine; D008697:Methane