Cation−π Interactions and the Gas-Phase Thermochemistry of the Na+/Phenylalanine Complex
| Autor: | Alexei Gapeev, Robert C. Dunbar |
|---|---|
| Rok vydání: | 2001 |
| Předmět: |
Alanine
Chemistry Stereochemistry Phenylalanine Sodium Kinetics Molecular Conformation Proteins General Chemistry Cations Monovalent Ligand (biochemistry) Mass spectrometry Biochemistry Catalysis Fourier transform ion cyclotron resonance chemistry.chemical_compound Crystallography Colloid and Surface Chemistry Pyridine Thermochemistry Thermodynamics |
| Zdroj: | Journal of the American Chemical Society. 123:8360-8365 |
| ISSN: | 1520-5126 0002-7863 |
| Popis: | The complex of Na(+) with phenylalanine (Phe) is a prototype for the participation of cation-pi interactions in metal-ion binding to biological molecules. A recent comparison of this complex with the Na(+)/alanine (Na(+)/Ala) counterpart suggested only a small contribution of the phenyl ring interaction to binding, casting doubt on the extent of the cation-pi effect. The present work reexamines this thermochemistry using ligand-exchange equilibrium measurements in the Fourier transform ion cyclotron resonance (FT-ICR) ion trapping mass spectrometer. An increment of 7 +/- 2 kcal mol(-1) was found in the Ala/Phe comparison of binding enthalpies, confirming the importance of cation-pi binding enhancement in the Phe case. Absolute Na(+) binding enthalpies of 38 +/- 2 and 45 +/- 2 kcal mol(-1) were assigned for Ala and Phe, respectively, using pyridine as the thermochemical reference ligand. All of these results were supported by quantum calculations using both density functional and Hartree-Fock/MP2 methods, improved in several respects over previous calculations. Alanine methyl ester (AlaMe) was also observed, and found to have an Na(+) ion affinity larger by 2.3 kcal mol(-1) than Ala. New, lower energy conformations of neutral Phe were discovered in the computations. |
| Databáze: | OpenAIRE |
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