Improved proton affinity measurements for proline and modified prolines using triple quadrupole and ion trap mass spectrometers

• Published in: Journal of mass spectrometry. 2005-10, Vol.40 (10), p.1300-1308
• Main Authors: Mezzache, S., Bruneleau, N., Vekey, K., Afonso, C., Karoyan, P., Fournier, F., Tabet, J.-C.
• Format: Article
• Language: English
• Subjects: amino acids; Atomic and molecular physics; Bond strengths, dissociation energies; effective temperature; entropy; Exact sciences and technology; kinetic method; Kinetics; Molecular Conformation; Molecular properties and interactions with photons; Physics; Proline - analogs & derivatives; Proline - chemistry; Properties of molecules and molecular ions; proton affinity; Protons; Spectrometry, Mass, Electrospray Ionization - methods; Thermodynamics
• ISSN: 1076-5174; 1096-9888
• DOI: 10.1002/jms.905

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 (ΔΔS°) 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 ΔΔS° values for the investigated molecules is obtained by combining the GBapp and Teff data pairs that are obtained from both the mass spectrometers. Copyright © 2005 John Wiley & Sons, Ltd.