title: Gas-phase lithium cation affinity of glycine.
abstract: The gas-phase lithium cation binding thermochemistry of glycine has been determined theoretically by quantum chemical calculations at the G4 level and experimentally by the extended kinetic method using electrospray ionization quadrupole time-of-flight tandem mass spectrometry. The lithium cation affinity of glycine, ∆(Li)H°(298)(GLY), i.e. the∆(Li)H°(298) of the reaction GlyLi(+)→ Gly + Li(+)) given by the G4 method is equal to 241.4 kJ.mol(-1) if only the most stable conformer of glycine is considered or to 242.3 kJ.mol(-1) if the 298K equilibrium mixture of neutral conformers is included in the calculation. The ∆(Li)H°(298)(GLY) deduced from the extended kinetic method is obviously dependent on the choice of the Li(+) affinity scale, thus∆(Li)H°(298)(GLY) is equal to 228.7±0.9(2.0) kJ.mol(- 1) if anchored to the recently re-evaluated lithium cation affinity scale but shifted to 235.4±1.0 kJ.mol(-1) if G4 computed lithium cation affinities of the reference molecules is used. This difference of 6.3 kJ.mol(-1) may originate from a compression of the experimental lithium affinity scale in the high ∆(Li)H°(298) region. The entropy change associated with the reaction GlyLi(+)→Gly + Li(+) reveals a gain of approximately 15 J.mol(-) 1.K(-1) with respect to monodentate Li(+) acceptors. The origin of this excess entropy is attributed to the bidentate interaction between the Li(+) cation and both the carbonyl oxygen and the nitrogen atoms of glycine. The computed G4 Gibbs free energy,∆(Li)G°(298)(GLY) is equal to 205.3 kJ.mol(-1), a similar result, 201.0±3.4 kJ.mol(-1), is obtained from the experiment if the∆(Li)G°(298) of the reference molecules is anchored on the G4 results.
authors: Laboratoire de Chimie Moléculaire. Ecole Polytechnique. UMR 9168 CNRS 91128 Palaiseau, France. sophie.bourcier@polytechnique.edu.
authors: Sophie
authors: S
authors: Bourcier
authors: N anyang Technological University. 21 Nanyang Link. 637371 Singapore.
authors: Ru Xuan
authors: RX
authors: Chiaa
authors: Université de Tours. Département de Chimie. Parc Grandmont. 37200 Tours, France.
authors: Rosa Ngo Biboum
authors: RN
authors: Mimbong
authors: Laboratoire de Chimie Moléculaire. Ecole Polytechnique. UMR 9168 CNRS. 91128 Palaiseau, France. Université Paris-Sud XI. 91400 Orsay, France. guy.bouchoux@polytechnique.edu.
authors: Guy
authors: G
authors: Bouchoux
mesh_terms: D001665:Binding Sites; D002412:Cations; D003198:Computer Simulation; D005740:Gases / Q000737:chemistry*; D005998:Glycine / Q000737:chemistry*; D007700:Kinetics; D008094:Lithium / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D044367:Phase Transition; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D013816:Thermodynamics
chemical_list: D002412:Cations; D005740:Gases; D008094:Lithium; D005998:Glycine