Entropy drives an attached water molecule from the C- to N-terminus on protonated proline.
Results from infrared photodissociation (IRPD) spectroscopy and kinetics of singly hydrated, protonated proline indicate that the water molecule hydrogen bonds preferentially to the formally neutral carboxylic acid at low temperatures and at higher temperatures to the protonated N-terminus, which bears the formal charge. Hydration isomer populations obtained from IRPD kinetic data as a function of temperature are used to generate a van't Hoff plot that reveals that C-terminal binding is enthalpically favored by 4.2-6.4 kJ/mol, whereas N-terminal binding is entropically favored by 31-43 J/(mol K), consistent with a higher calculated barrier for water molecule rotation at the C-terminus.
Prell
James S
JS
Department of Chemistry, University of California, Berkeley, California 94720-1460, USA.
Correra
Thiago C
TC
Chang
Terrence M
TM
Biles
Jeffrey A
JA
Williams
Evan R
ER
D019277:Entropy; D006860:Hydrogen Bonding; D011392:Proline / Q000737:chemistry*; D011522:Protons; D013057:Spectrum Analysis / Q000379:methods
D011522:Protons; D011392:Proline