Dipeptide Structure Determination by Vibrational Circular Dichroism Combined with Quantum Chemistry Calculations

✍ Scribed by Kyung-Koo Lee; Kwang-Im Oh; Hochan Lee; Cheonik Joo; Hogyu Han; Minhaeng Cho

• Book ID: 102809818
• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 665 KB
• Volume: 8
• Category: Article
• ISSN: 1439-4235
• DOI: 10.1002/cphc.200700352

✦ Synopsis

Abstract

The solution structure and the local solvation environments of alanine dipeptide (AD, 1 a) and its isotopomer (AD*, 1 b, ^13^C on the acetyl end CO) are studied by using infrared (IR) spectroscopy and vibrational circular dichroism (VCD). From the amide I IR spectra of AD* in various protic solvents, it is found that each of the two carbonyl groups is fully H‐bonded to two water molecules. However, the number of alcohol molecules H‐bonded to each CO varies from one to two, and the local solvation environments are asymmetric around the two peptides of AD* in alcohol solutions. The amide I VCD spectra of AD and AD* in D~2~O are also measured, and a series of density functional theory (DFT, B3LYP/6‐311++G**) calculations are performed to obtain the amide I normal‐mode rotational strengths of AD and the intrinsic rotational strengths of its two peptide fragments. By combining the VCD‐measurement and DFT‐calculation results and employing a coupled oscillator theory, we show that the aqueous‐solution structure of the dipeptide can be determined. We believe that the present method will be of use in building up a library of dipeptide solution structures in water.