Fluorometric studies on inclusion complexation of L/D-tryptophan by beta-cyclodextrin 6-O-pyridinecarboxylates.
Novel beta-cyclodextrin (beta-CD) derivatives, bearing a nicotinic or isonicotinic moiety, have been synthesized by a convenient method in 21 and 25% yields, respectively. The stability constants (K) and Gibbs free energy changes (-DeltaG degrees ) for the inclusion complexation of beta-cyclodextrin 6-O-mono(3-pyridinecarboxylate) (1), 6-O-mono(4-pyridinecarboxylate) (2), and 6-O-monobenzoate (3) with L- and D-tryptophan have been determined by spectrofluorome try in aqueous buffer solution (pH = 7.20) at 25.0 degrees C. All of the modifications dramatically enhanced the original K for beta-CD by a factor of 30-280 and interestingly switched the original enantiomer preference for L- to D-tryptophan, thus affording the inverted enantio-selectivities of K(L)/K(D) = 2.5 for beta-CD and K(D)/K(L) = 1.2-2.1 for the modified CDs 1-3. These results are discussed from the viewpoints of the size-fit and geometrical complementary relationship between the host and guest.
Liu
Y
Y
Department of Chemistry, Nankai University, Tianjin, 300071, China. yuliu@public.tpt.tj.cn
Li
B
B
Wada
T
T
Inoue
Y
Y
D002264:Carboxylic Acids / Q000737:chemistry; D002942:Circular Dichroism; D003505:Cyclodextrins / Q000737:chemistry*; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy; D011725:Pyridines / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared; D014364:Tryptophan / Q000737:chemistry*; D047392:beta-Cyclodextrins
D002264:Carboxylic Acids; D003505:Cyclodextrins; D007202:Indicators and Reagents; D011725:Pyridines; D047392:beta-Cyclodextrins; D014364:Tryptophan; C031215:betadex