The association of 4-(N,N-dimethylamino)benzonitrile and β-cyclodextrin in dimethyl sulfoxide and N,N-dimethylformamide

Fluorescence and absorption studies indicate the association between beta-cyclodextrin (CD) and 4-(N,N-dimethylamino)benzonitrile (DMABN) in dimethyl sulfoxide (DMSO) and in N,N-dimethylformamide (DMF). In DMSO, the fluorescence emission maximum of the host-guest (HG) complex is at 335 nm, and the values of the equilibrium constant and the Delta G(0) at 298 K are 6.0 +/- 0.6 M-1 and -4.4 +/- 0.2 kJ mol(-1), respectively. The process shows a weak favorable enthalpy change, although a reliable entropy measurement was not possible. The DMABN excimer is formed in DMSO at concentrations above 5 x 10(-7) M, which presents a broad fluorescence band with maximum around 510 nm. A large increase in the molar absorptivity of DMABN in DMF is observed upon addition of CD. The equilibrium constant in DMF at 298 K equals 10.2 +/- 0.7 M-1 and conforms with a 1 : 1 model for complexation. (C) 1999 Elsevier Science S.A. All rights reserved.