Sulphur, The Synthesis And Characterization Of Calixarenes And Their Modified Electrodes For The Detection Of Dopamine

1. Preparation and characterization of Thiolated Calix[4、6、8]areneCalixarene is characteristic of flexible structures (especially conformation) which are easy to modify. Variety of acceptors with hydrophobic/hydropholic properties, which are able to bond with ions as well as other guest molecules with different properties and sizes, can be obtained by introducing various functional groups to the calixarene upper or lower edge.In this paper, calix[n]arenes (n=4,6,8) were firstly obtained from tert-butyl phenol and formaldehyde. And then thiolated calix[n]arenes (n=4,6,8) were synthesized through a five-stepped procedure including chemical modification and functional group derivativation at the lower edge of the tert-butyl calix[n]arene phenolic hydroxyl. Lastly, the products of all steps were characterized by IR and H NMR, proving that the thiolated calix[n]arene has been successfully synthesized.2. Modification and characterization of Thiolated Calix[4、6、8]arene SAMs electrodesIn the second part of this theme, the immobilization of the Thiolated Calix[n]arene (n=4,6,8) on the gold electrode was performed by the irreversible adsorption. We found from cyclic voltammetry that the AEp increased and the peak current gradually reduced when the modification time is increased. And both the AEP and the peak current would be basically stable for12h. The thiolated calix[8]arene modified electrode is greatly different from the other two. The heterogeneous rate constants of Fe(CN)63-/4-on the modified electrodes were calculated. Also, the coverages of Thiolated Calix[n]arene(n=4,6,8) on gold electrodes were estimated to be84.85%,88.8%,90.64%respectively. Characterization of AC impedance reveals that the electron transfer of Fe(CN)63-/4-on the gold electrode surface is more difficult with the growth of modification time. The thiolated calix[8]/Au electrode hinder the electron transfer larger than thiolated calix[6]/Au electrode, the smallest thiolated calix[4]/Au electrode. We can observe to the morphology of the modified electrode surfaces from AFM images, The thiolated Calix[n]arcne (n=4,6,8) on gold electrode surfaces modified with granular and aggregate size were approximately250-550nm,150-350nm,100-250nm. Finally, the contact angle of the small droplets modified electrode surfaces were104.3°,107.4°,108.8°by the contact angle measurements. With cyclic voltammetry, AC impedance, AFM characterization and contact angle measurements show that:the thiolated Calix[n]arene(n=4,6,8) have been successfully modified to gold electrode surfaces.3. Detection of dopamine by Thiolated Calix[4、6、8]arene modified gold electrodesThis chapter explored the detection of dopamine using the thiolated Calix[n]arene(n=4,6,8) modified electrodes. It is found that the thiolated Calix[4,6,8]arene modified electrodes exhibit electrocatalytic activity toward the oxidation of dopamine. Compared with the bare electrode, the redox peak currents are significantly enhanced. This is mainly resulted from that the calixarene molecules modified on the electrode surface have a strong recognition of dopamine. When detecting the dopamine at different pH, the dopamine oxidation peak potential Epa and pH showed a good linear relationship, and the slopes were very close to the theoretical value of the proton transfer and other electronic-58pH/mV, indicating that the reaction process of DA on the modified electrodes were processes with the two-electron two proton transformation. When thiolated Calix[4]/Au electrode detect the dopamine controlling pH=6.6, and thiolated Calix[6,8]/Au electrode at pH=5.7. The thiolated Calix[n]arene(n=4,6,8) modified electrodes detect different concentrations of dopamine by DPV method, the oxidation peak current and dopamine concentration showed a good linear relationship, wide linear range and low detection limit. Meanwhile, the effects of Na+, K+and glucose were also investigated. The results reveal that ascorbic acid and L-cysteine showed greater interference to the measurement of dopamine than other factors. These modified electrodes to measure dopamine showed good stability and reproducibility.