Cyclodextrin monolayer

Figure 18. Cyclic voltammograms of 1,4-benzoquinone (p-quinone) as permeability marker. Curve A in the absence of a cyclodextrin monolayer on a buffer solution containing no guest (p.1 M CH3C02Na-CH3C00H, pH 6.0). Curve B in the presence of the condensed monolayer of p-cyclodextrin derivative 41 on a buffer solution containing no guest. Curve C-E in the presence of the condensed monolayer of 41 on a buffer solution containing guest 59 at concentrations of 5.0 x 10", 1.0 x 10 , and 2.0 x 10 M, respectively (reprinted with permission from Anal. Chem. 1993, 65, 930. Copyright 1993 American Chemical Society).

X alculated as a percentage of the voltammogram peak area relative to that measured in the absence of the cyclodextrin monolayer (bate electrode). 

Different cyclodextrin monolayers have been synthesized and their surface properties have been characterized. Kaifer et al. prepared per-6-thiol-cyclodextrins, and described the interfacial monovalent ferrocene complexation at the monolayer.55 Mittler-Neher et al. studied the kinetics of the adsorption of mono- and multithiolate-functionalized CD SAMs.56,57 Beulen et al.,58 Huskens et al.,59 Auletta et al.,60 and Nijhuis et al.61 reported on the concept of molecular printboards, that is, (3-cyclodextrin ((3-CD) SAMs on gold or silicon oxide substrates, onto which complementary multivalent guest-functionalized dendrimer molecules were adsorbed, resulting in the formation of kinetically stable supramolecular assemblies. With the... 

Interesting systems have been reported in which a (3-cyclodextrin monolayer has been immobilized on gold electrodes to act as an active interface for the... 

Figure 5.41 Optoelectronic functions of the cyclodextrin-monolayer-modified electrode and bipyridinium-azobenzene diad, as reported by Willner and co-workers [73]. Photoisomerization of the diad alters its ability to include in the cyclodextrin cavity and consequently write to the electrode...

Lahav, M., Ranjit, K. T, Katz, E., and Willner, I. A p-amino-cyclodextrin monolayer-modified Au electrode A command surface for the amperometric and microgravimetric transduction of optical signals recorded by a photoisomerizable bipyridinium-azobenzene diad. Chem. Commun. 1997, 259-260. 

Yasuda, S. Futaba, D.N. Takeuchi, O. Suzuki, L Yase. K. Sumaoka. J. Komiyama. M. Shigeliawa, H. Mono-layer formation of 6-deoxy-6-thiol-P-cyclodextrin on a Au(lll) surface studied by scanning tunneling microscopy. J. Vac. Sci. Technol.. A 2001. 19. 1266-1269. Yasuda. S. Shigekawa, H. Suzuki, L Nakamura. T. Matsumoto. M. Komiyama, M. Scanning tunneling microscopy on the formation of lipoamide-cyclodextrin monolayer on Audi 1). Appl. Phys. Lett. 2000. 76, 643-645. 

Dependence of Marker Permeability on Surface Pressure The dependence of the cyclic voltammogram area on the surface pressure applied to the cyclodextrin monolayer was examined. By increasing the surfece pressure from 10 to 50 mN m or, in other words, by decreasing the molecular area from 260 to 210 molecule the voltammogram areas for all three markers decreased almost linearly. However, an important point to be emphasized here is that the magnitudes of the decrease were different the decrease for p-quinone was much smaller than that for [Co(phen)3]2+ and [Mo(CN)g]. This is also consistent with the capability of p-quinone and incapability of the other two bulky markers to sterically pass tiirough the P-cyclodextrin cavity. 

Another point to be noted is the fact that a dramatic increase in the voltammogram area upon a decrease in the surface pressure was observed for both of the two bulky markers, regardless of whether the marker is hydrophilic ([Mo(CN)g] ) or hydrophobic ([Co(phen)3]2+). These results indicate that the main factor controlling the permeability through e intramolecular channel is the steric bulkiness rather than the hydrophobicity of the marker. Such an aspect seems to be characteristic of the cyclodextrin monolayer and contrasts to the properties of monolayers of simple alkane derivatives, in which the permeability (through intermolecular voids) is controlled mainly by the hydrophobicity and not the steric bulkiness of the marker (30). 

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