Electrochemical behavior model compound

It should also be recalled that a full electrochemical, as well as spectroscopic and photophysical, characterization of complex systems such as rotaxanes and catenanes requires the comparison with the behavior of the separated molecular components (ring and thread for rotaxanes and constituting rings in the case of catenanes), or suitable model compounds. As it will appear clearly from the examples reported in the following, this comparison is of fundamental importance to evidence how and to which extent the molecular and supramolecular architecture influences the electronic properties of the component units. An appropriate experimental and theoretical approach comprises the use of several techniques that, as far as electrochemistry is concerned, include cyclic voltammetry, steady-state voltammetry, chronoampero-metry, coulometry, impedance spectroscopy, and spectra- and photoelectrochemistry. 

Because of the presence of several redox-active units, the cyclic voltammogram of this rotaxane shows a complex redox pattern. However, the comparison to the electrochemical behavior of its molecular components and suitable model compounds (Fig. 13.29) enables to obtain useful information not only on its coconforma-tional features, but also, and most importantly, on its machine-like operation. 

As an extension of our previous studies[4,8], we report here the syntheses, the photophysical properties, and the electrochemical chracterization of the shape-persistent macrocyclic ligand 1, containing one bpy unit, and its [Ru(bpy)2(l)]2+ and [Os(bpy)2(l)]2+ complexes (Scheme 1). We also report the syntheses of simpler Ru(II) and Os(II) complexes that together with other previously synthesized species (Scheme 2) have been used as model compounds for interpreting the behavior of the new macrocyclic ligand and its complexes. 

Coates and Johnson255 measured the kinetic acidity of 5-methyl-5,6-dihydrodibenz[h,/]azocine (185), and found that, when compared to carbocyclic models, 185 evinced very small rate enhancement. Compound 162 exhibited electrochemical behavior similar to that of the 2-benzazocine (i.e., two-electron reduction), but electron addition was more difficult, consistent with the benzannelation effect.260 Interestingly, 162, when chemically reduced, undergoes an atypical transannular reaction to give... 

In a previous section, we have already seen two good examples of experimental results that are consistent with the chemiosmotic theory the difference in electron-transfer behavior between TMPD and DAD, two compounds with identical chemical composition but with different electrochemical behavior and the photophosphorylation coupled to a proton gradient formed in a minimum PS-I/membrane model system. In this section we present additional examples that render evidence that even more directly supports the chemiosmotic theory. 

Costa-type model compounds, however, have been shown to be a closer mimic of the Bi2 electrochemical behavior than the cobaloximes, or any other model compounds . Hence, they are used more widely as models in kinetic studies relevant to the mechanisms of catalysis mediated by B,2, which involve electron transfer processes . The nonplanarity of the equatorial ligand of (DO) (DOH)pn, caused by propylene group pucker , also appears to mimic the distortion in the corrin ring. 

The materials were of low to medium molecular weight = 4,000-13,500) and showed very interesting electrochemical behavior. Studies of model compounds show that on reduction or oxidation the Fe-Fe bond is cleaved. The polymers, on the other hand, show reversible two-electron oxidation processes in THF/[ Bu4N][BF4] at fast scan rates, as the Fe-Fe bonds reform after cleavage due to the fact that Fe atoms are held in close proximity by the bridging organosiloxane units. 

The first reports dealing with the electrochemical behavior of vitamin E-type compounds are those of Smith and co-workers who studied the polarographic oxidation waves of a-tocopherol and a number of tocopherol model compounds in methanol-water (1 1, v/v). These workers concluded that the electrooxidation of tocopherols consisted of an initial, reversible le-lYi reaction of the tocopherol [(I, Eq. (7)] to give an unstable quinonoid intermediate [(II, Eq. (7)] which was rapidly transformed into the corresponding tocopherylquinone [(III, Eq. (7)]. These first reports pointed out the possibility of an unstable species intermediate between tocopherol and tocopherylquinone in the oxidation reaction. Controversy still remains regarding the nature of this putative intermediate species. Among the proposed alternative structures for this intermediate are a-tocopheroxide (12a or and... 

The electrochemical behavior of a-tocopherylquinone and related model compounds points out a number of interesting facts. For example, in aprotic media in the absence of protons or proton donors essentially all biological quinones, including a-tocopherylquinone, are electrochemically reduced in stepwise e processes giving first an anion radical and then a dianion. Both these processes are electrochemically reversible. However, addition of protons or a proton donor to the a-tocopherylquinone or other bioquinones in an... 

Abstract Recent advances in molecular modeling provide significant insight into electrolyte electrochemical and transport properties. The first part of the chapter discusses applications of quantum chemistry methods to determine electrolyte oxidative stability and oxidation-induced decomposition reactions. A link between the oxidation stability of model electrolyte clusters and the kinetics of oxidation reactions is established and compared with the results of linear sweep voltammetry measurements. The second part of the chapter focuses on applying molecular dynamics (MD) simulations and density functional theory to predict the structural and transport properties of liquid electrolytes and solid elecfiolyte interphase (SEI) model compounds the free energy profiles for Uthium desolvation from electrolytes and the behavior of electrolytes at charged electrodes and the electrolyte-SEl interface. 

As it turns out, similar EC behavior has been observed in oligomeric polyaniline, and thus some effort has been directed toward preparing such systems as both model compounds to enhance the understanding of the behavior of PANI and as EC materials (23,30-33). Although these oligomers do not produce stable films and are subject to similar poor solubility, such structures hold promise since they can be incorporated into a well behaved polymer system In this way, it may be possible to construct uniform, electrochemically stable, and behaviorally predictable films containing this electrochromic fi agment. 

In this paper, recent results of studies performed on the imide derivatives of the trimeric aniline are presented. Films of TANI-polyimide were also prepared and their electrochemical and electrochromic properties were probed. It is shown from this work that well behaved polymeric materials incorporating aniline trimers can be prepared, these trimers can be addressed electrochemically within such polymeric systems and the behavior of the trimer within the polymer does not differ significantly from that within the model compounds. 

Efficient photoelectrochemical decomposition of ZnSe electrodes has been observed in aqueous (indifferent) electrolytes of various pHs, despite the wide band gap of the semiconductor [119, 120]. On the other hand, ZnSe has been found to exhibit better dark electrochemical stability compared to the GdX compounds. Large dark potential ranges of stability (at least 3 V) were determined for I-doped ZnSe electrodes in aqueous media of pH 0, 6.3, and 14, by Gautron et al. [121], who presented also a detailed discussion of the flat band potential behavior on the basis of the Gartner model. Interestingly, a Nernstian pH dependence was found for... 

Porphyrin complexes are particularly suitable cores to construct dendrimers and to investigate how the behavior of an electroactive species is modified when surrounded by dendritic branches. In particular, dendritic porphyrins can be regarded as models for electron-transfer proteins like cytochrome c [42, 43]. Electrochemical investigation on Zn-porphyrins bearing polyether-amide branches has shown that the first reduction and oxidation processes are affected by the electron-rich microenvironment created by the dendritic branches [42]. Furthermore, for the third generation compound all the observed processes become irreversible. 

The solution electrochemical redox behavior of systems 34, 35, and model multi-TTFs has been studied. For compound 34 two redox couples typical of the TTF system were observed at and = 0.43 and 0.81 V, respectively (vs. 

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