OXIDATION–REDUCTION POLYMERS: II. STANDARD OXIDATION POTENTIALS OF REDOX HOMOPOLYMERS AND THEIR MONOMERIC MODELS

1963 ◽  
Vol 41 (2) ◽  
pp. 483-494 ◽  
Author(s):  
I. H. Spinner ◽  
W. D. Raper ◽  
W. Metanomski

A new monomer, 2,5-bis-(2-tetrahydropyranyloxy)-4-methyl-4′-vinyldiphenyl sulphone, has been prepared. The standard oxidation potentials of two linear redox homopolymers, derived from this monomer and the one previously reported (1), and of their intermediate and model compounds, have been measured using continuous and discontinuous titration techniques.

1970 ◽  
Vol 25 (3) ◽  
pp. 255-265 ◽  
Author(s):  
Jürgen-Hinrich Fuhrhop

Many metallochlorins can be reversibly oxidized in a one electron step. The midpoint oxidation potentials of magnesium-octaethyl-chlorin (MgOÄC), ZnOÄC, CuOÄC, NiOÁC and PdOÄC were found to be approximately 107, 197, 331, 356, and 422 mV vs. a saturated calomel electrode in chloroformmethanol. As with analogous metalloporphyrins the order of the oxidations potentials increases approximately linearly with the electronegativity values of the metal ions. The midpoint potentials of the one-electron oxidation of metallochlorins were found to be about 300 mV lower than those of analogous metallporphyrins. Sn (IV) -OÄC-dihydroxide and the monocation of OÄC could not be reversibly oxidized. A simple electrostatic argument can explain the oxidation behavior of these and other porphyrin derivatives. The more negative the ligand ring, the easier it is to remove an electron and vice versa. Thus experimental results point to a more ionic character of the metal-ligand bonds in metallochlorins as compared to metalloporphyrins. The unusual behavior of chlorophyll a and the optical and ESR-spectra of the resulting radicals are discussed.Some general properties of the chlorin- and porphyrin macrocycles are compared. Characteristic differences between the two ligand-systems are explained by the low basicity of the pyrrolin-nitrogen and the decreased symmetry of the ligand field in the chlorins.


2022 ◽  
Author(s):  
Jesús Lucia-Tamudo ◽  
Gustavo Cárdenas ◽  
Nuria Anguita-Ortiz ◽  
Sergio Díaz-Tendero ◽  
Juan J. Nogueira

The determination of the redox properties of nucleobases is of paramount importance to get insight into the charge-transfer processes in which they are involved, as those occurring in DNA-inspired biosensors. Although many theoretical and experimental studies have been conducted, the value of the one-electron oxidation potentials of nucleobases is not well defined. Moreover, the most appropriate theoretical protocol to model the redox properties has not been established yet. In this work, we have implemented and evaluated different static and dynamic approaches to compute the one-electron oxidation potentials of solvated nucleobases. In the static framework, two thermodynamic cycles have been tested to assess their accuracy against the direct determination of oxidation potentials from the adiabatic ionization energies. Then, the introduction of vibrational sampling, the effect of implicit and explicit solvation models, and the application of the Marcus theory have been analyzed through dynamic methods. The results revealed that the static direct determination provides more accurate results than thermodynamic cycles. Moreover, the effect of sampling has not shown to be relevant, and the results are improved within the dynamic framework when the Marcus theory is applied, especially in explicit solvent, with respect to the direct approach. Finally, the presence of different tautomers in water does not affect significantly the one-electron oxidation potentials.


1987 ◽  
Vol 52 (8) ◽  
pp. 1985-1991 ◽  
Author(s):  
Jan Schraml ◽  
Jaan Past ◽  
Jüri Puskar ◽  
Tõnis Pehk ◽  
Endel Lippmaa ◽  
...  

Selective heteronuclear (Si-C) INADEQUATE method has been successfully used to assign all 29Si chemical shifts in six pertrimethylsilylated lignin model compounds. Empirical assignment of the lines in the region δ = 23-25 to trimethylsilyl esters of carboxylic compounds has been confirmed. Selectivity of the method permits unambiguous assignment to trimethylsiloxy groups which differ by their position on the benzene ring only. The assignment is possible despite that 29Si-13C two-bond coupling constants (2·1-3·0 Hz) are of comparable magnitude with the three-bond coupling constants (1-2·3 Hz). The chemical shifts of trimethylsiloxy groups on the benzene ring are sensitive to substituent effect to such an extent that their assignment cannot rely on an empirical rule but requires experimental method such as the one used here.


2003 ◽  
Vol 58 (9) ◽  
pp. 877-884 ◽  
Author(s):  
Michael Schmittel ◽  
Mukul Lal ◽  
Wolfdieter A. Schenk ◽  
Michael Hagel ◽  
Nicolai Burzlaff ◽  
...  

Four novel stable enols (one characterized by X-ray crystal structure analysis) were synthesized and investigated under oxidative conditions to yield benzofurans. Depending on the donor qualities of the heteroaryl substituent the reaction following the one-electron oxidation could be stopped on the stage of the cyclohexadienyl cation whose lifetime was measured. Oxidation potentials were determined for the enols, the enolates and the α-carbonyl radicals. Oxidation of benzofurans yielded dimeric species or intramolecular cyclization products.


In the light of experimental observations of parts I and II various kinetic schemes for the operation of the Pasteur effect in Bact. lactis aerogenes are considered and some simple models investigated. The essential assumptions upon which these schemes are based are: (1) that anaerobic growth requires the development of a new mechanism for the re-oxidation of reduced hydrogen carriers (which in aerobic growth are dealt with ultimately by molecular oxygen); (2) that there are competitive reactions in which a reduced system is re-oxidized on the one hand by molecular oxygen and on the other in processes which lead to consumption of the primary substrate. By lowering the ratio XH 2 /X in the reducing system, oxygen will automatically cut down the competing alternatives. This may result in a diminution of the total rate of attack upon the substrate, and give rise to the other characteristic features of the Pasteur effect.


1992 ◽  
Vol 247 ◽  
Author(s):  
Chizuko Tanaka ◽  
Jiro Tanaka

ABSTRACTThe optimized molecular structures of doped polyacetylene model compounds are studied by the ab initio SCF MO method. The calculated structures are assigned to polaron, charged soliton and poison unit. The one dimensional energy band structures of the charged soliton-antisoliton and the polson-antipolson lattices are investigated. The latter one gives a quasi-metallic energy band. The results of the energy band calculation are consistent with the electrical properties and ultraviolet photoemission spectra of the doped polyacetylene.


1964 ◽  
Vol 42 (3) ◽  
pp. 554-559 ◽  
Author(s):  
I. H. Spinner ◽  
H. P. Kasserra ◽  
W. Metanomski

The preparation of two new sulphonyl derivatives of methoxy- and naphtha-hydroquinone as possible intermediate compounds in the synthesis of redox monomers is described. The standard oxidation potentials of these and other sulphonyl derivatives of hydroquinones were determined and compared with the values for similar compounds, reported previously (1).


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