TY - JOUR
T1 - Electrostatistically-induced inclusion of anions in cyclodextrin monolayers on electrodes
AU - Chamberlain, Richard V.
AU - Slowinska, Katarzyna
AU - Majda, Marcin
AU - Bühlmann, Philippe
AU - Aoki, Hiroshi
AU - Umezawa, Yoshio
PY - 2000/2/8
Y1 - 2000/2/8
N2 - Oxidative mercury-thiolate bond formation accounts for the assembly of densely packed monolayers of per-2,3-methylated per-6-thiolated α-, β-, and γ-cyclodextrins on the hanging mercury drop electrode. Inclusion of inorganic ions and uncharged hydrophobic guests into these monolayers was investigated by capacitance measurements. In the range of potentials where the electrode is positively charged, the interfacial capacitance depends on the type of electrolyte anions and on the applied potential. This can be explained with electrostatic double-layer forces. Whereas the smaller and less well solvated anions CL-, NO3-, and ClO4- are included in the cyclodextrin cavities of these monolayers, the larger and more strongly solvated anions F-, SO42-, and H2PO4- are excluded. Anion inclusion constants can be obtained from the dependence of the interfacial capacitance on the anion concentration. The potential dependence of these inclusion constants shows that the nonelectrostatic contribution to the driving force for NO3(-) inclusion is negligibly small. Competitive binding of hydrophobic guest molecules decreases the interfacial capacitance. Fitting Langmuir isotherms to the plots of the interfacial as a function of adamantanol concentration yielded the binding constants 1.0 × 104 and 2.6 × 104 M-1 for the β- and γ-cyclodextrin monolayers, respectively. Binding of adamantanol to α-cyclodextrin monolayers could not be observed, apparently because this guest is too large for the internal cavity of the α-cyclodextrin receptor. In contrast, 1-hexanol binds to α-cyclodextrin monolayers with the binding constant 8.9 × 104 M-1. This shows that changes in the capacitance can serve as a general signal transduction mode to monitor interactions between cyclodextrin monolayers and charged or neutral guests. Also, the extension of these types of measurements into solid electrodes and the application to other guest-selective host monolayers open the possibility of designing a novel type of electrochemical sensors for electroinactive analytes.
AB - Oxidative mercury-thiolate bond formation accounts for the assembly of densely packed monolayers of per-2,3-methylated per-6-thiolated α-, β-, and γ-cyclodextrins on the hanging mercury drop electrode. Inclusion of inorganic ions and uncharged hydrophobic guests into these monolayers was investigated by capacitance measurements. In the range of potentials where the electrode is positively charged, the interfacial capacitance depends on the type of electrolyte anions and on the applied potential. This can be explained with electrostatic double-layer forces. Whereas the smaller and less well solvated anions CL-, NO3-, and ClO4- are included in the cyclodextrin cavities of these monolayers, the larger and more strongly solvated anions F-, SO42-, and H2PO4- are excluded. Anion inclusion constants can be obtained from the dependence of the interfacial capacitance on the anion concentration. The potential dependence of these inclusion constants shows that the nonelectrostatic contribution to the driving force for NO3(-) inclusion is negligibly small. Competitive binding of hydrophobic guest molecules decreases the interfacial capacitance. Fitting Langmuir isotherms to the plots of the interfacial as a function of adamantanol concentration yielded the binding constants 1.0 × 104 and 2.6 × 104 M-1 for the β- and γ-cyclodextrin monolayers, respectively. Binding of adamantanol to α-cyclodextrin monolayers could not be observed, apparently because this guest is too large for the internal cavity of the α-cyclodextrin receptor. In contrast, 1-hexanol binds to α-cyclodextrin monolayers with the binding constant 8.9 × 104 M-1. This shows that changes in the capacitance can serve as a general signal transduction mode to monitor interactions between cyclodextrin monolayers and charged or neutral guests. Also, the extension of these types of measurements into solid electrodes and the application to other guest-selective host monolayers open the possibility of designing a novel type of electrochemical sensors for electroinactive analytes.
UR - http://www.scopus.com/inward/record.url?scp=0034620353&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0034620353&partnerID=8YFLogxK
U2 - 10.1021/la990826i
DO - 10.1021/la990826i
M3 - Article
AN - SCOPUS:0034620353
SN - 0743-7463
VL - 16
SP - 1388
EP - 1396
JO - Langmuir
JF - Langmuir
IS - 3
ER -