Amino Acid Anions in Organic Ionic Compounds. An ab Initio Study of Selected Ion Pairs

The combination of amino acids in their deprotonated and thus anionic form with a choline cation gives origin to a new and potentially important class of organic ionic compounds. A series of such neutral ion pairs has been investigated by first principle methods. The results reveal intriguing struct...

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Bibliographic Details
Published in:The journal of physical chemistry. B 2014-03, Vol.118 (9), p.2471-2486
Main Authors: Benedetto, A, Bodo, E, Gontrani, L, Ballone, P, Caminiti, R
Format: Article
Language:English
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Amino acids
Amino Acids - chemistry
Analogies
Anions
Anions - chemistry
Cations
Cations - chemistry
Choline
Choline - chemistry
Gases - chemistry
Ion pairs
Ionic Liquids - chemistry
Molecular Dynamics Simulation
Optical properties
Phosphorylcholine - chemistry
Protons
Thermodynamics
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Summary:The combination of amino acids in their deprotonated and thus anionic form with a choline cation gives origin to a new and potentially important class of organic ionic compounds. A series of such neutral ion pairs has been investigated by first principle methods. The results reveal intriguing structural motives as well as regular patterns in the charge distribution and predict a number of vibrational and optical properties that could guide the experimental investigation of these compounds. The replacement of choline with its phosphocholine analogue causes the spontaneous reciprocal neutralization of cations and anions, taking place through the transfer of a proton between the two ions. Systems of this kind, therefore, provide a wide and easily accessible playground to probe the ionic/polar transition in organic systems, while the easy transfer of H+ among neutral and ionic species points to their potential application as proton conductors. The analysis of the ab initio data highlights similarities as well as discrepancies from the rigid-ions force-field picture and suggests directions for the improvement of empirical models.
ISSN:1520-6106
1520-5207
DOI:10.1021/jp412281n