Methyl dynamics in crystalline amino acids: MD and NMR.
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.
Chatfield
David C
DC
Chemistry Department, Florida International University, Miami, Florida 33199, USA. chatfield@flu.edu
Augsten
Alberto
A
D'Cunha
Cassian
C
Wong
Sergio E
SE
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
D000596:Amino Acids; D010456:Peptides, Cyclic; C053149:cyclo(alanylalanyl); D007930:Leucine; D014633:Valine; D008697:Methane