Complexation and chiral recognition thermodynamics of gamma-cyclodextrin with N-acetyl- and N-carbobenzyloxy-dipeptides possessing two aromatic rings.
The stability constants (K) and the standard free energy (deltaG degrees ), enthalpy (deltaH degrees ), and entropy changes (deltaS degrees ) for the complexation of gamma-cyclodextrin with 34 enantiomeric and diastereomeric N-acetyl- and N-carbobenzyloxy-d/l-dipeptides with two aromatic moieties were determined in aqueous buffer solution at 298.15 K by titration microcalorimetry. Chiral recognition of the enantiomeric dipeptide pairs by gamma-cyclodextrin was found to be fairly poor, exhibiting only small percentage differences in K, while the diastereomeric dipeptides were discriminated to much greater extent with affinity differences of up to 6-7 times. The complex structures of several selected pairs were elucidated by NMR techniques. Combining the microcalorimetric and NMR data, the complexation and chiral recognition behavior of gamma-cyclodextrin is discussed in particular in terms of the length, bulkiness, and flexibility of the tether connecting the two aromatic moieties in a guest.
Rekharsky
Mikhail V
MV
Entropy Control Project, ICORP, JST, 4-6-3 Kamishinden, Toyonaka 560-0085, Japan.
Yamamura
Hatsuo
H
Kawai
Masao
M
Inoue
Yoshihisa
Y
D002942:Circular Dichroism; D003505:Cyclodextrins / Q000737:chemistry*; D004151:Dipeptides / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D013237:Stereoisomerism; D013816:Thermodynamics
D003505:Cyclodextrins; D004151:Dipeptides