An exploration of conformational search of leucine molecule and their vibrational spectra in gas phase using ab initio methods

作者：Rai Amareshwar Kumar; Song Ce; Lin Zijing^*

来源：Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy , 2009, 73(5): 865-870.

DOI：10.1016/j.saa.2009.04.023

• Leucine conformers
• Conformational distribution
• Infrared spectrum
• DFT/B3LYP methods
• Proton affinity

An extensive exploration of the conformational space has been carried out to characterize all possible gas phase structures of leucine. A total of 324 unique trial structures for canonical leucine were generated by considering all possible combinations of single bond rotamers. All trial structures were optimized at the B3LYP/6-311G* level of the DFT method. A total of 77 unique and stationary canonical conformers were found. Further, 15 most stable conformers were reoptimized at B3LYP/6-311 G** level and their respective relative energies, vertical ionization energies, hydrogen bonding patterns, rotational constants and dipole moments were calculated. A single point energy calculations for leucine conformers have also been done at both B3LYP/6-311 G(2df, p) and MP2/6-311 G(2df,p) levels. The good agreement between our estimates of rotational constants for two most stable conformers and available experimental measurements supports the reliability of the B3LYP/6-311 G** level of theory for describing the conformational behavior of leucine molecule. The proton affinity and gas phase basicity were also determined. Using the statistical approach, conformational distributions at various temperatures have also been performed and analyzed. Vibrational spectra were also calculated. It is also observed that zwitterions of leucine are not stable in gas phase.

• 出版日期2009-9-1
• 单位中国科学技术大学