Intercalator electron affinity

DNA, laced with an intercalator characterized by a high electron affinity, is y-ir-radiated and observed by EPR. The one-electron reduced intercalator presents an EPR spectrum that is readily distinguishable from that of the DNA-trapped radicals. A key example is mitoxantrone (MX), with an electron affinity of 6.25 eV and a radical anion spectrum that is a sharp singlet. Charges are injected into the DNA by y-irradiation at a preselected temperature (4 130 K). Holding the temperature constant, the EPR spectrum changes as a function of time (0.5-30 h). Thereby, a direct measure of the rate of electron transfer from one-electron reduced pyrimidines (Pryre) to the intercalator, e.g., MX, is measured. The turmeling rate is observed to depend on the electron affinity (EA) of the... 

Drug-receptor interactions often involve CT complex formation. Examples include the reactions of antimalarials with their receptors and of some antibiotics that intercalate with DNA. The CT energy is proportional to the ionization potential of the donor and the electron affinity of the receptor, but is usually no higher than about 30 kJ/mol. 

At loadings lower than 1 MX per 20 DNA bps, the fraction of the electrons captured by the intercalator was found to follow Eq. 7 and increase with ln(f) as expected for a single-step tunneling process. The distances of electron transfer and the values of the tunneling constant for all the studied in-tercalators are compiled in Table 1, along with gas-phase estimates of the electron affinities (EA) of intercalators calculated by density functional theo-... 

Theoretically calculated electron affinities were computed with the DFT method at the pBP86/DN //DN level by subtraction of the total energy of the parent molecule from that of the electron adduct in the geometry of the parent molecule. The electrostatic attraction of the positively charged intercalators increases the gas- phase EA artificially. The relative values should be considered... 

Anderson RF, Wright GA (1999) Energetics and rate of electron transfer in DNA from base radial anions to electron-affinic intercalators in aqueous solution. Phys Chem Chem Phys 1 4827-4831 Anderson RF, Patel KB, Wilson WR (1991) Pulse radiolysis studies of electron migration in DNA from DNA base-radical anions to nitroacridine intercalators in aqueous solution. J Chem Soc Faraday Trans 87 3739-3746... 

In the relevant experiment to determine electron transfer, the DNA intercalator mitoxantrone (MX) is used. MX binds well to DNA and has a high electron affinity. MX appears to intercalate randomly if used at an intercalator base-pair ratio of 1/20 or less. In a 7-M LiBr glass at 77 K, /-irradiation produces electrons that attach randomly onto the DNA and MX, and the holes are... 

Electron affinities and intercalation. The molecule S2O6F2 is in equilibrium with the S03F radical (19) at... 

Because the late transition series hexafluorides (MF, M = Ru, Rh, Ir, and Pt) and the group 5 pentafluorides, in combination with F2, have electron affinities (24) higher than that of SO3F, it appeared probable that these oxidizers would also bring about fi-BN intercalation. The metal hexafluorides, however, simply acted as potent fluorinating agents and no evidence of intercalation was observed, even when low reaction temperatures were employed. 

The discovery of what appears to be a thermodynamic threshold governing the intercalation of graphite by fluoro anions, MF,, has required the evaluation of the thermodynamic stability of a number of such species. Since germanium tetrafluoride and fluorine are intercalated, in combination, by graphite to form both GeFj" and GeFs ", the first and second fluoride ion affinities of that molecule are each of interest. Evaluation of the fluoride ion affinity of boron trifluoride by Altshuller yielded a value of-71 kcal moF. This has been accepted by several authors as the basis for other fluoride ion affinities and electron affinities. Sharpe, however, has preferred a value of -91 kcal moF, based upon the data of Bills and Cotton. Although this latter value is in harmony with other fluoride ion affinities and electron affinities, its confirmation was clearly desirable to provide a firm basis for correction of affinities based upon the lower value. This paper describes the studies that have provided these fluoride ion affinities. 

Whether oxidative intercalation of graphite byfluoroanions can occur may be estimated from the electron affinity, E (-AHm in kcal mol ), of the oxidizing half reaction. For first-stage salts with MFe guests, E must exceed 120 kcal moF . The values of E(e + % MFs MFe + V2 MF3) for AsFs and PFs (125 and 87 kcal mol respectively) account for the spontaneous intercalation of graphite by AsFs and the failure of PFe to do so. Spontaneous intercalation by PFs + Fs occurs because E(e + PFs + V2 F2 PFe ) = 165 kcal... 

This chapter provides further evidence for the importance of the electron affinity of the oxidizing half reaction in the intercalation of graphite by fluo-rospecies. Moreover, the simple thermodynamic model that accounts for the oxidative intercalation of graphite by fluoroanions is confirmed by reversal of the intercalation in reactions of known enthalpy change. Threshold values of electron affinity (E) for the onset of intercalation and for first-stage intercalation by MFg have also been assessed. 

Figure 2. Intercalation of graphite hy perfluoroanions as a function of the electron affinity of the oxidizing half reaction.

The pattern of graphite intercalation by hexafluorides of the third transition series [1] had indicated that the intercalation of such molecules, to form Cx MFs salts, requires a minimum electron affinity of approximately 120 kcal mor. Such a threshold electron affinity also accounts [2, 3] for the spontaneous intercalation of graphite by arsenic pentafluoride and for the failure of the physically similar pentafluoride of phosphorus to do likewise. For the half reaction... 

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