title: Fluorometric and theoretical studies on inclusion complexes of β-cyclodextrin and D-, L-phenylalanine.
abstract: Inclusion complexes of β-cyclodextrin (β-CD) with L- and D-phenylalanine (Phe) have been characterized in solution by fluorometry and in gas phase by semiempirical PM3 calculations. The unimolar stoichiometric ratio of both β-CD-L-Phe and β-CD-D-Phe complexes and the stability constants (K) were deduced from fluorometric titrations. The β-CD-L-Phe complex is more stable than the β-CD-D-Phe complex as indicated by the larger K values, 21.1 vs. 6.86 M(-1). This is consistent with the stabilization energies (ΔE(stb)) and inclusion geometries obtained from PM3 calculations. The β-CD-L-Phe complex with L-Phe residing in the central β-CD cavity and pointing its COOH group downwards to the O6 end has ΔE(stb)=-62.7 kJ mol(-1), whereas the β-CD-D-Phe complex with D-Phe placing at 3Å beneath the β-CD O4-plane and pointing its COOH group upwards to the O2/O3 end has ΔE(stb)=-53.3 kJ mol(-1). The unison of host-guest intermolecular hydrogen bonds, hydrophobic interactions and molecular deformations plays an essential role in forming and stabilizing the inclusion complexes. Our results show that the β-CD-L-Phe and β-CD-D-Phe inclusion complexes are relatively stable and differentiable, suggesting the applications of CDs in foods and drugs.
authors.affiliation: Department of Chemistry, Faculty of Science, Chulalongkorn University, Pathumwan, Bangkok 10330, Thailand. thammarat.aree@gmail.com
authors.forename: Thammarat
authors.initials: T
authors.lastname: Aree
authors.forename: Rungthiwa
authors.initials: R
authors.lastname: Arunchai
authors.forename: Narongsak
authors.initials: N
authors.lastname: Koonrugsa
authors.forename: Amarawan
authors.initials: A
authors.lastname: Intasiri
mesh_terms: D005470:Fluorometry / Q000379:methods*; D007700:Kinetics; D008958:Models, Molecular; D008968:Molecular Conformation; D010649:Phenylalanine / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013237:Stereoisomerism; D013816:Thermodynamics; D047392:beta-Cyclodextrins / Q000737:chemistry*
chemical_list: D047392:beta-Cyclodextrins; D010649:Phenylalanine; C031215:betadex