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Download and D-Amino Acids by Permethylated β
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Transcript
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.