Redox properties conformations

Tricyclic dithiine derivatives of tetrathiafulvalene (TTF) 32 have been prepared for their increased electropolymerization potential <2000CC1005>. The effect of different tricyclic heterocycles upon the redox properties of TTF analogues was explored, and showed that the furan derivative 33 had an unusual nonplanar conformation that allowed for the attainment of higher oxidation states at relatively low oxidation potentials <2004JMC2822>. 

For the cytochrome c-plastocyanin complex, the kinetic effects of cross-linking are much more drastic while the rate of the intracomplex transfer is equal to 1000 s in the noncovalent complex where the iron-to-copper distance is expected to be about 18 A, it is estimated to be lower than 0.2 s in the corresponding covalent complex [155]. This result is all the more remarkable in that the spectroscopic and thermodynamic properties of the two redox centers appear weakly affected by the cross-linking process, and suggests that an essential segment of the electron transfer path has been lost in the covalent complex. Another system in which such conformational effects could be studied is the physiological complex between tetraheme cytochrome and ferredoxin I from Desulfovibrio desulfuricans Norway the spectral and redox properties of the hemes and of the iron-sulfur cluster are found essentially identical in the covalent and noncovalent complexes and an intracomplex transfer, whose rate has not yet been measured, takes place in the covalent species [156]. 

Ring Conformation, Solution, and Redox Properties of Nickel(II) Derivatives of [14]aneN4... 

Fig. 10. Hypothetical reaction cycle for D. gigas hydrogenase, based on the EPR and redox properties of the nickel (Table II). Only the nickel center and one [4Fe-4S] cluster are shown. Step 1 enzyme, in the activated conformation and Ni(II) oxidation state, causes heterolytic cleavage of H2 to produce a Ni(II) hydride and a proton which might be associated with a ligand to the nickel or another base in the vicinity of the metal site. Step 2 intramolecular electron transfer to the iron-sulfur cluster produces a protonated Ni(I) site (giving the Ni-C signal). An alternative formulation of this species would be Ni(III) - H2. Step 3 reoxidation of the iron-sulfur cluster and release of a proton. Step 4 reoxidation of Ni and release of the other proton.

Further studies are required to unravel this mystery of how the methoxy substitutions and the a, p-unsaturated p-diketone moiety actually influence conformational changes, lipophillicity, electron density distribution, and redox properties of curcuminoids. Correlating these physicochemical properties with the unique pleiotropic effects of curcuminoids is a rewarding exercise. Such studies would definitely provide proper reasoning in understanding these markedly different antioxidant, antitumor, and anti-inflammatory activities of natural curcuminoids from turmeric. 

The extended set of locally excited conformations will produce the charge-separated (CS) set of states, whereas the folded set will generate the exciplex state. Finally, Coulombic-induced molecular folding (harpooning [57]) in the extended set of CS states will lead to increased production of the exciplex state. The dynamic competition between the various processes outlined in Figure 15 depends not only on the chain length and the redox properties of the donor and acceptor groups, but also on solvent polarity. 

Beer, P.D. Chen. Z. Grieve. A. Haggitt. J. A new bipyridinium bis benzo crown-ether ligand whose redox properties are dependent upon complexed cation-induced conformational switching effects. J. Chem. Soc., Chern. Commun. 1994, 2413-2414. 

These calculations and previous results for model porphyrins and photosynthetic reaction centers suggest that conformational variations play a significant role in determining optical and redox properties of porphyrin derivatives and thus may offer attractively simple rationales, in conjunction with additional modulations imposed by protein residues or solvents, for their properties in vivo and vitro. 

The combination of theoretical and experimental results strongly suggests that conformational variations observed for porphyrin derivatives can provide a mechanism for altering optical and redox properties. Such effects, in combination with additional modulations induced by protein residues (or solvents), thus provide an attractive mechanism for fine-tuning the electronic properties of the chromophores in vitro and in vivo. 

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