Side chain interactions in aromatic dipeptides

✍ Scribed by Charles M. Deber; Henry Joshua

• Book ID: 102760251
• Publisher: Wiley (John Wiley & Sons)
• Year: 1972
• Tongue: English
• Weight: 659 KB
• Volume: 11
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1972.360111209

✦ Synopsis

Abstract

A study of the 100‐MHZ nuclear magnetic resonace spectra in D~2~O solution was made of a series of linear dipeptides of the types L‐phenylalanine‐L‐and‐D‐X, and L‐phenylalanine‐L‐and‐D‐Y, where X comprised a group of amino acid residues with polar side chains (X = glutamine, glutamic acid, arginine, and N^ε^‐acetyllysine) and Y comprised amino acid residues with purely aliphatic side chains (Y = α‐aminobutyric acid and norvaline). It was found that regardless of the side chain length, resonances due to the α‐methylene protons in the X and Y side chains of the L‐Phe‐D‐Y series consistently exhibited upfield shifts greater than any other protons in these side chains, when compared to the corresponding side chain resonances of the nonaromatic dipeptide series L‐Ala‐L‐X and L‐Ala‐L‐Y. The magnitudes of these shielding effects were consistently and considerably greater for the L‐Phe‐D‐X series than for the L‐Phe‐D‐Y series. An intramolecular complex–formed by association of armatic π‐electrons with the positive end of the dipole in the polar side chains—was proposed as one plausible interpretation of the enhanced shielding effects. An increase in temperature from 32 to 70–80° was sufficient to overcome the enhanced shielding attributable to the suggested complex.