Specific anion effects on the optical rotation of alpha-amino acids.
Changes in optical rotation of some alpha-amino acids are induced by electrolytes. Such effects on l- and d-enantiomers of a range of amino acids are explored for sodium salts with varying anion. The amino acids studied were alanine, aspartic acid, glutamic acid, glutamine, proline, threonine, and tryptophan. The anion's polarizability in solution accounts for the change in [alpha] only for the halides. Self-association of amino acids in solution and pH changes due to the presence of the electrolytes do not account for the observed variations in optical activity. Specific interactions of anions with the chiral amino acids (Hofmeister effects) and salt-induced perturbations of the amino acid hydration shell appear to be responsible for the effects, and conformational changes in the chiral solutes due to the presence of ionic species are discussed.
Rossi
Simona
S
Department of Chemistry and CSGI, University of Florence, via della Lastruccia 3, 50019 Sesto Fiorentino (Firenze), Italy.
Lo Nostro
Pierandrea
P
Lagi
Marco
M
Ninham
Barry W
BW
Baglioni
Piero
P
D000596:Amino Acids / Q000737:chemistry*; D000838:Anions / Q000737:chemistry; D003198:Computer Simulation; D004151:Dipeptides / Q000737:chemistry; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D055095:Optics and Photonics; D013237:Stereoisomerism; D013816:Thermodynamics; D013912:Threonine / Q000737:chemistry
D000596:Amino Acids; D000838:Anions; D004151:Dipeptides; D013912:Threonine