Impact of Host Structure on Guest−Host Recognition at Self-Assembled Surfaces of Tetrathiol and Tetrasulfide Derivatives of Calix[4]resorcinarene

Guest−host recognition at self-assembled surfaces of two different synthetic calix[4]resorcinarene receptors, a tetrasulfide (R4SC7) and a tetrathiol (R4SH) host, was performed. The host structure was found to impact the molecular organization within the monolayers as well as the interfacial properties. Comparison of structural characterization of the SAMs formed from R4SC7 and R4SH on gold substrates revealed a larger area per molecule for the tetrasulfide host, which indicated that the dialkyl sulfide chains do not pack commensurately below the calix[4]resorcinarene headgroup and can lead to interstitial cavities. As a consequence, the self-assembled surfaces formed from R4SC7 are slightly more hydrophobic and thinner than the SAMs formed from R4SH. Guest−host recognition of a small neutral molecule, α-hydroxy-γ-butyrolactone (HBL), occurred from aqueous solutions on both surfaces on a time scale of several hundred seconds. Adsorption isotherms for the two surfaces revealed that the difference in the fr...