Improved proton affinity measurements for proline and modified prolines using triple quadrupole and ion trap mass spectrometers.
Proton affinity (PA) of compounds such as proline, cis-3-methylproline, cis-3-ethylproline, cis-3-isopropylproline and cis-3-isopentanylproline was determined by kinetic method with amines as the reference bases. The effective temperatures determined using ion trap and triple quadrupole mass spectrometers were found to be significantly different. In the case of the triple quadrupole instruments, the effective temperature depends significantly on the collision energy. The influence of the apparent basicity (GBapp) on the effective temperature may be used to estimate the difference in protonation entropy (DeltaDeltaS degrees) between the sample and reference compounds. In case of the ion trap mass spectrometer, the variation of the effective temperature as a function of the excitation amplitude is small, so it is difficult to account for the contribution of the entropy effects to the proton affinity value. A better estimation of the PA and DeltaDeltaS degrees values for the investigated molecules is obtained by combining the GBapp and Teff data pairs that are obtained from both the mass spectrometers.
Mezzache
S
S
Synthèse, Structure et Fonction de Molécules Bioactives, CNRS, UMR 7613, Université Pierre et Marie Curie, 4 place Jussieu, 75252 Paris cedex 05, France.
Bruneleau
N
N
Vekey
K
K
Afonso
C
C
Karoyan
P
P
Fournier
F
F
Tabet
J-C
JC
D007700:Kinetics; D008968:Molecular Conformation; D011392:Proline / Q000031:analogs & derivatives* / Q000737:chemistry*; D011522:Protons; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D013816:Thermodynamics
D011522:Protons; D011392:Proline