The enthalpies of solution of ethanol, n-butanol, n-pentanol and n-octanol into aqueous acetonitrile mixtures at T = (288.2 and 283.2) K are reported. These data are combined with literature values for the n-alcohols at T = 298.2 K and for a range of tetraalkylammonium bromides at several temperatures to allow determination of the enthalpy of transfer of CH2 moieties, Delta(t)Hdegrees(CH2), from acetonitrile to the aqueous mixed solvents. It is found that the Delta(t)Hdegrees(CH2) values pass through minima at intermediate solvent compositions, with the minimum becoming deeper with decreasing temperature and with increasing chain length. It is proposed that these minima originate from microphase formation of the aqueous acetonitrile mixtures. (C) 2004 Elsevier Ltd. All rights reserved.