Proton and sodium ion affinities of glycine and its sodium salt in the gas phase. Ab initio calculations

✍ Scribed by S. Bouchonnet; Y. Hoppilliard

• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: English
• Weight: 594 KB
• Volume: 27
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/oms.1210270202

✦ Synopsis

The energies of protonation and Na' cationization of glycine (GLY) and its (GLY -H + Na) salt in the gas phase were calculated using ab initio calculations. The proton affinity of GLY, valued at the MP2/6-31G*//3-21G level, is 937 kJ mol-'. The amino function is confirmed to be the most favourable site of protonation: 'proton affinities' of the carbonyl and hydroxyl functions are calculated to be 75 and 180 kJ mol-', respectively, lower than that of NH, at the MP2/6-31G*//3-21G level. Calculations performed up to the MP2/6-31G*//3-21G level give the Na' affinity of GLY as 189 kJ mol-' and the H+ and Na+ affinities of (GLY -H + Na) as 1079 and 298 kJ mol-I, respectively. The geometries of all neutral and protonated species optimized with the 3-21G basis set are described. Both H+ and Na' cations complex preferably between the nitrogen atom and the carbonyl oxygen atom, leading to pseudo-five-membered ring structures in which N a -0 and Na-N bonds lengths are greater than 2 A.