Measurement of Chiral Recognition Properties of Crown Ethers Using Matrix Assisted Laser Desorption Ionization Mass Spectrometry

Hydrogen bonding host-guest complex ions between chiral crown ethers and chiral amino acid ester salts, detected by matrix assisted laser desorption ionization (MALDI) mass spectrometry (MS) with a DHBA or MSA matrix, were studied on the view point of chiral recognition properties of the chiral crown hosts. The chiral recognition property (IR/IS-dn value≅1.0) obtained by the present MALDI-MS is sharply different from the IR/IS-dn value obtained by FAB-MS or ESI-MS (≠1.0) in the same host-guest combinations. The direct comparison on the basis of the IR/IS-dn values suggests that MALDI-MS is not a suitable measurement tool for chiral host-guest interactions probably because of the particular way of sample preparation involving a crystallization process

Chiral Recognition of 18-Crown-6-tetracarboxylic Acid toward Amino Acids and Organic Amines by Fast Atom Bombardment Mass Spectrometry.A Comparison with Capillary Electrophoresis

Chiral recognition of the host-guest complexations between the (RRRR)-18-crown-6-tetracarboxylic acid (18 C6TCA) host (H) and α-amino acid or their ester derivative guests (G) has been systematically determined using both FAB mass spectrometry (MS) and capillary zone electrophoresis (CE). A comparison of these two techniques for the same series of guests was then done for the first lime. In the case of 18C6TCA，we found that there is no correlation between the chiral recognition obtained from FABMS (i.e.，the IRIS value)and from CE(i.e.，the α value in an aqueous buffer solution) covering three sets of guests including amino acids，amino acid esters，and primary aromatic amines. On the other hand. the former showed a good agreement with that from NMR (i.e.，the KR/Ks value: the ratio of the corresponding equilibrium constants)， supporting our earlier conclusion that FABMS is a good measurement tool for predicting differences (44G°values) in the respective chiral H-G interactions in solution. We also found that when a given guest changes from an amino acid to its corresponding amino acid　ester，the α value by CE dramatically changes from α>1.0 toα<1.0，though the IRIS value by FABMS does not show any such changes. These findings，were considered to be due to the characteristic contributions of the dissociable host\u27s COOH functions under the experimental pH conditions in CE