Mass spectrometer study of evaporation of. cap alpha. -amino acids
The NH/sub 4//sup +/ proton transfer mass spectra of 19 ..cap alpha..-amino acids have been obtained by evaporation of 5--8-nmol samples from a rapidly heated Teflon surface. The protonated amino acid parents are observed in all samples and serve as the base peaks in all spectra but two. Time evolutions of fragment ions are coincident with those of the protonated parent in nearly all cases, indicating that deamination, dehydration, and loss of formic acid occur predominantly in the gas phase. Analyses of the rates of sublimation yield activation energies for sublimation ranging from 12 to 34 kcal/mole. Vapor pressures for the amino acids at the experimentally observed threshold temperatures for sublimation were estimated from the time evolutions of protonated parent ions. Enthalpies of sublimation derived from activation energies for rates of sublimation are used with liteature values of heats of solution to calculate heats of aqueous solvation of the ..cap alpha..-amino acids.
- Research Organization:
- Brookhaven National Lab., Upton, NY
- OSTI ID:
- 7303484
- Journal Information:
- J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 99:13; ISSN JACSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
AMINO ACIDS
CARBOXYLIC ACIDS
ENTHALPY
EVAPORATION
MASS SPECTROSCOPY
ORGANIC ACIDS
ORGANIC COMPOUNDS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
SOLUTION HEAT
SOLVATION
SPECTROSCOPY
SUBLIMATION HEAT
THERMODYNAMIC PROPERTIES
TRANSITION HEAT