To confirm this, we measured the mass spectrum of β-MCD with phenylalanine (PheH +), in which the phenol OH of tyrosine is replaced by hydrogen (Fig. If this is the case, the chiral selectivity should be decreased without phenol OH. 3 Mass spectrum of complexes of b-MCD with L- and D-TyrH +įrom these results, we conclude that the high chiral selectivity of β-MCD for D-TyrH+ is due to the fact that only the D-TyrH + complex can take the phenolic bonded form. These results are in agreement with the theoretical infrared spectra obtained by quantum chemical calculations.įig. On the other hand, in the D-TyrH + complex, a band of hydrogen-bonded phenol OH was observed at 3430 cm ‑1, suggesting that the "phenol-bonded" type, in which β-MCD and phenol OH are hydrogen-bonded, also coexists in addition to "amino-bonded" complex. 4, the "amino-bonded" form, in which the carboxylic acid OH and amino group NH of tyrosine form hydrogen-bonds with b-MCD, was observed in both complexes.
TYROSINE ION BONDING FREE
4(a) and (b)), bands at 3640 cm -1, 3430 cm -1, 3300~3400 cm -1, 3020~3300 cm -~2800 cm -1 are assigned to free phenol OH stretching without hydrogen-bonding, hydrogen-bonded phenol OH stretching, free NH stretching, hydrogen-bonded NH stretching and hydrogen-bonded carboxylic acid OH stretching vibration, respectively. From comparison with the spectra of tyrosine and β-MCD alone (Fig. The IRPD spectra of the complexes of protonated tyrosine and β-MCD are shown in Fig. The IRPD spectra of each of the TyrH + complexes were then measured in order to determine the structural basis for this difference in chiral selectivity. The D-TyrH + complex is three times stronger than the L-TyrH + complex, indicating that β-MCD has a chiral selectivity for D-TyrH +. 3 shows the mass spectrum of the complexes of protonated tyrosines and β-MCD, where the molecular weight of L-tyrosine is 10 times larger than that of D-tyrosine due to the isotope substitution ( 13C, 15N). By scanning the wavelength of the IR light while monitoring the amount of fragment ions, the IR photodissociation (IRPD) spectrum corresponding to the IR absorption spectrum was measured.įirst, to investigate whether β-MCD is more selective for L- or D- tyrosine, we electrosprayed a solution containing equal amounts of L-tyrosine and D-tyrosine with β-MCD and measured the mass spectrum. The fragment ions (complex ions) generated by this dissociation were detected by a time-of-flight mass spectrometer (TOF-MS). When the complex ion was irradiated with a tunable infrared (IR) laser light, the molecular hydrogen dissociated by vibrational excitation due to IR absorption. Hydrogen gas was introduced to the complex ion, and molecular hydrogen was attached to the complex ion.
The complexes of tyrosine and β-MCD, protonated using electrospray (ESI) method, were extracted into the gas phase, selected for specific masses using a quadrupole mass spectrometer, and trapped in a cooled ion trap (~10 K). β-MCD eliminates the complex OH stretching vibrational bands derived from CD, and the vibrational bands derived from protonated tyrosine can be clearly observed. We attempted to elucidate the mechanism of chiral discrimination of CD from the difference of the host-guest interaction. In this study, we investigated the interaction between two enantiomers of protonated tyrosine and methyl β-CD (β-MCD), in which all OH groups of β-CD are methoxylated, by using cryogenic ion-trap infrared spectroscopy. However, the pore size of β-CD is 6 Å, which is much larger than the size of amino acids (2~3 Å), and it is not clear why such a large host can recognize the chirality of small guests. Although β-CD, which is composed of seven D-glucose moieties, is widely adapted to small guest molecules such as amino acids, the pore size of β-CD is 6 Å, which is smaller than that of amino acids (2~3 Å). CD has been used as a stationary phase in liquid chromatography and has been put to practical use as a chiral column for splitting optical isomers. Since CD has chirality, when a guest molecule has chirality, each enantiomer has a different affinity for CD. Paris-Saclay, Profs Keisuke Hirata and Shun-ichi Ishiuchi in School of Science.Ĭyclodextrins (CDs) are cyclic oligosaccharides composed of D-glucose linked by a-1,4 glycosidic linkages, which form vacancies in the molecule (Fig. In this article, I would like to introduce our joint research with Prof. Keisuke Hirata a, c，Shun-ichi Ishiuchi a, c，Anne Zehnacker-Rentien b, c and Masaaki Fujii cĪ) Dep.
0 kommentar(er)
