Ion recognition at the interface of self-assembled monolayers (SAMs) of bis-thioctic ester derivatives of oligo(ethyleneglycols)

Self-assembled monolayers (SAMs) of bis-thioctic ester derivatives of oligo ethylene glycols were prepared. When the number of (-CH2-CH2-O-)(n) units i n these podands was either five or six, the corresponding SAMs showed ion b inding properties and selectivities similar to those exhibited by 15-crown- 5 or 18-crown-6 in aqueous solution, respectively. Impedance data for the S AMs as a function of metal ion concentrations were fitted by using a Langmu ir isotherm to determine the association constants (K-a) with the different ions. The SAM derived from the n=5 compound is selective for Na+ while tha t with n=6 is selective for K+. Results presented here confirm the formatio n of ion recognition domains during self-assembly of acyclic polyethylene g lycol derivatives on gold surfaces; this suggests that surface-confined pse udocrown ether structures are formed.