Electrochemistry of Cyclodextrins

Cydodextrins (CyDs) with their largely hydrophobic cavities of variable size and numerous ways of chemical modification are the subject of intensive electrochemical research induding both their behavior in homogeneous solutions and in thin films attached to the electrode surfaces [1-8]. Electroanalytical methods measuring the current response to the potential applied, linear scan, staircase, and pulse voltammetries, and potential-step techniques such as chronoamperometry and 

If the concentrations of the redox compounds in the solution or at the electrode surface are low, and better sensitivities are needed than those optimal for LSV and SCV, differential pulse (DPV), normal pulse (NPV) and Osteryoung square-wave voltammetries (OSWV) are more suitable [9a, 9b]. They allow better elimination of the capacitive/background currents and, therefore, the measurement of smaller faradic signals becomes easier. This is achieved either by sampling the current at the end of each pulse (OSWV, NPV) (Fig. 10.5.IE and F) or twice at the end and before pulse application (DPV) (Fig. 10.5.ID). 

Normal and reverse pulse voltammetries are often employed for the studies of stepwise or chemically complicated processes where the direct product of electrode reaction is unstable and undergoes transformations into other species - either elec-troinactive or active in a different potential range. Reverse pulse voltammetry allows a direct examination of the product generated between pulse applications thus it is simply a short electrolysis (seconds) followed by recording the produa of electrooxidation or reduction on the time-scale of milliseconds. 

The relationship between electrode potential and current is determined by the electrochemical reaction taking place at the working electrode. Measurements are done usually in a three-electrode arrangement with a reference electrode to control the potential of the working electrode (typically no current is in practice allowed to flow through the reference electrode and its potential is constant) and a counter (auxiliary) electrode where a counterbalancing but not rate-deterrnmirig electrode process takes place. In cyclic voltammetry for a reversible electrode reaction, the cathodic, pc and anodic, pa peak potentials depend on the formal potential, E  

This equation is often used to determine the formal potential of a given redox system with the help of cyclic voltammetry. However, the assumption that mid-peak potential is equal to formal potential holds only for a reversible electrode reaction. The diagnostic criteria and characteristics of cyclic voltammetric responses for solution systems undergoing reversible, quasi-reversible, or irreversible heterogeneous electron-transfer process are discussed, for example in Ref [9c]. An electro-chemically reversible process implies that the anodic to cathodic peak current ratio, lpa/- pc equal to 1 and fipc — pa is 2.218RT/nF, which at 298 K is equal to 57/n mV and is independent of the scan rate. For a diffusion-controlled reduction process, Ip should be proportional to the square root of the scan rate v, according to the Randles-Sevcik equation [10]  

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Radi, AE and S Eissa (2010). Electrochemistry of cyclodextrin inclusion complexes of pharmaceutical compounds. The Open Chemical and Biomedical Methods Journal, 3, 74-85. 

Gonzalez B, Casado CM, Alonso B, Cuadrado I, Moran M, Wang Y, Kaifer AE (1998) Synthesis, electrochemistry and cyclodextrin binding of novel cobaltocenium-functionalized dendrimers. Chem Commun 2569-2570... 

Gonzalez, B. Casado. C.M. Alonso, B. Cuadrado. I. Moran. M. Wang, Y. Kaifer. A.E. Synthesis, electrochemistry and cyclodextrin binding of novel cobaltoce-nium-functionalized dendrimers. Chem. Commun. 1998, 2569-2570. 

A. Kitajima, T. Teranishi, and M. Miyake, Detection of nitric oxide on carbon electrode modified with ionic polymers and alpha-cyclodextrin. Electrochemistry 69, 16-20 (2001). 

Cardona CM, McCarley TD, Kaifer AE (2000) Synthesis, electrochemistry, and interactions with P-cyclodextrin of dendrimers containing a single ferrocene subunit located off-center . J Org Chem 65 1857-1864... 

Usually the functional moiety is covalently linked to the conjugated backbone, but it can be sometimes added to ECP as a dopant when it is under an ionic form e.g., sulfonated P-cyclodextrins have been successfiilly incorporated in one step as anionic dopants in PPy by electropolymerization [230]. In some cases, electrochemistry can be combined to chemical reactions to derive functional ECPs functional PANI materials can be obtained from the reduction of the emeraldine form by alkylthiols [255] and the functionality degree on the PANI backbone can be monitored by successive oxidation-reduction cycles various functionalized PANIs can also be synthesized through electrophilic substitution or nucleophilic addition reactions [256]. For example. Figure 18.10 shows the similar electrochemical behaviors of sulfonated PANI made from reduction of emeraldine by sulfite salt followed by reoxidation, compared to thin films deposited from solution of highly sulfonated PANIs. 

ELECTROCHEMISTRY AND SUPRAMOLECULAR INTERACTIONS OF FERROCIFEN ANTICANCER DRUGS WITH CYCLODEXTRINS AND LIPID BILAYERS AN ELECTROCHEMICAL OVERVIEW... 

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