Download and D-Amino Acids by Permethylated β

Chiral Differentiation of Protonated L- and D-Amino Acids by Permethylated
β-cyclodextrin: Experiments and Theory
(Department of Applied Chemistry, Kyung Hee Univ., Gyeonggi 446-701, Republic of Koreaa,
Department of Chemistry, Sogang Univ., Seoul 121-742, Republic of Korea b,
State Key Lab. of Elemento-Organic Chemistry, Nankai Univ., Tianjin 300071, Chinac,
Collaborative Innovation Center of Chemical Science and Engineering, Nankai Univ.,
Tianjin 300071, Chinad.)
Sung-Sik Leea, Soojin Parkb, Xianglei Kongc,d*([email protected]), Sungyul Leea*
([email protected]), Han Bin Ohb([email protected])
Structures of gaseous permethylated β-cyclodextrin/H+/H2O and /H+/Ala are studied
using electrospray, IRMPD spectroscopy and density functional theory calculations. The
protonated non-covalent complexes of permethylated β-cyclodextrin and the D- or
L-alanine were mass-selected and investigated by IR laser pulses in the wavelength
region of 2650-3800 cm-1. The remarkably different features of the IRMPD spectra for
D- and L-alanine are described, and their origin is elucidated by quantum chemical
calculations. We show that the differentiation of the experimentally observed spectral
features is the result of different local interactions of D- and L-alanine with
permethylated β-cyclodextrin. The very high Gibbs free energies of the gaseous
permethylated β-cyclodextrin/H+/H2O and permethylated β-cyclodextrin/H+/Ala
complexes are noted. We focus on the extremely high frequency bands at > 3700 cm-1,
assigning them to completely isolated carboxyl group. We also find that the high Gibbs
free energy of gas phase permethylated β-cyclodextrin/H+/H2O system is due to the
presence of separate H+ and H2O rather than H3O+. These findings are discussed in relation
to solution phase host-guest-solvent configurations.