Alkylsilanated electrode surface

Figure 7. Model of a single surface-bound membrane formed by detergent dialysis on an alkylsilanated electrode surface.

To assemble the surface-bound membrane structure, we first form a hydrophobic monolayer by using alkylsilanization to covalently attach long-chained hydrocarbon chains to hydroxyl groups in the oxide layer on the electrode surface. Such a hydrophobic surface can be thought of as one leaflet of a membrane bilayer. Alkylsilane-modified surfaces have been widely used as substrates for lipid monolayers deposited by Langmuir-Blodgett techniques. The lipids in these monolayers have mobilities like those of lipids... 

We simultaneously incorporate both lipid and protein by using dialysis to remove detergent from a solubilized lipid-protein mixture in the presence of the alkylsilanated substrate. Under our conditions, from the evidence in this paper and elsewhere (9), the surface structures appear to be single bilayer membranes. Our hypothesis is that the hydrocarbon chains attached to the surface serve as initiation sites for a lipid bilayer membrane to form as the detergent is slowly removed. The model is of a membrane that is anchored to the surface by hydrophobic interactions with the surface-bound hydrocarbon layer. Integral membrane proteins are retained in these structures by their interaction with the hydrophobic core of the membrane without being directly attached to the electrode surface. 

Alkylsilanization. Alkylsilanization of electrode surfaces was carried out by a modification of the procedure of Sagiv (22). The anhydrous solvent was prepared with 80 12 8 hexadecane-chloroform-carbon tetrachloride under dried nitrogen in a glove bag (relative humidity < 4%). The dried electrodes were silanized by reaction in stirred 3% (v/v) OTS solution for 3 h or 6% (v/v) DMOCS solution for 6 h. The silanized electrode surface was rinsed with dry solvent and then with chloroform and cured in a vacuum oven at 100 °C for 12 h. 

Electrochemical impedance spectroscopy provides a sensitive means for characterizing the structure and electrical properties of the surface-bound membranes. The results from impedance analysis are consistent with a single biomembrane-mimetic structure being assembled on metal and semiconductor electrode surfaces. The structures formed by detergent dialysis may consist of a hydrophobic alkyl layer as one leaflet of a bilayer and the lipid deposited by dialysis as the other. Proteins surrounded by a bound lipid layer may simultaneously incorporate into pores in the alkylsilane layer by hydrophobic interactions during deposition of the lipid layer. This model is further supported by the composition of the surface-bound membranes and by Fourier transform infrared analyses (9). 

An equivalent circuit can be derived for the surface-bound membrane formed in this work similar in a manner to the approach taken for porous anodic films and porous electrodes (41-46). An equivalent circuit network, proposed in Figure 8a, corresponds to the model in Figure 7. This network has three RC subnetworks that represent the oxide layer, the surface-bound membrane layer, and the double layer. Cox and Rox are the capacitance and resistance of oxide. and Rdl are the double-layer capacitance and the polarization resistance, known as the charge transfer resistance at the membrane-water interface. For the subnetwork of the surface-bound membrane layer, one branch represents a tightly packed alkylsilane and lipid bilayer in series, and the other branch represents the pores and defects through the bilayer. Calk, Clip and Ralk, Rhp are the capacitances and resistances of... 

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