The inclusion complexes of cyclomaltoheptaose (/3-CD) and /~-CD's 50% hydroxyethyl-substituted derivative (HE-/3-CD) with chlorogenic acid (CA) were studied with regard to temperature and water activity (all2 o = mole fraction = XH2 o = 0.8--0.99; 0.1 M Na phosphate buffer) utilizing first-derivative spectrophotometric analyses of bathochromic shifts (AA) in CA's UV absorbance as a function of variable [CD]. From the dependence of the apparent stability constant, K, on XH: o (K = K*X~o) we estimated that the fl-CD • CA complex's apparent stoichiometric coefficient, z, for water was ca. 7 + 1 (K ~ = 1032_ 54 M-l); this value agrees with recently published literature concerning the minimum number of waters needed to stabilize a similar fl-CD adduct. However, we determined that z was significantly lower (4 + 0.3; K ~: = 809 + 31 M-1) for the HE-/3-CD-CA complex. These results argue that a unique species of bound water is involved in fl-CD • CA stability since a 50% substitution resulted in an equivalent loss in z as well as a substantial decrease in K ~;. This hypothesis was supported by NMR inversion recovery experiments whereupon the most significant perturbation to spin-lattice relaxation (AT 1 = Tl~_c ° -Tl~_co CA) was associated with fl-CD's 1H at position 3 (H-3; AT t = 585 ms). Small ATlS were also observed for H-2 (160 ms) and H-6,6' (83 ms). fl-CD's H-3 ATls were dependent not only upon the adduct's concentration but also diminished at a high ionic strength. These data indicate that AT 1 was related to changes in [D20] at or near/3-CD's hydroxyl groups and that these D20 molecules were bound with a relatively long residence time. Thermochemical measurements of