Hydroxyl ionization potential

Aromatic hydroxylation of this type is a highly specific test for hydroxyl radicals, provided the ionization potential of the aromatic compound is not too low. 

S. Ma, S. K. Chowdhury, and K. B. Alton, Thermally induced N-to-O rearrangement of ferf-V-oxides in atmospheric pressure chemical ionization and atmospheric pressure photoionization mass spectrometry Differentiation of V-oxidation from hydroxylation and potential determination of V-oxidation site. Anal. Chem. 77 (2005), 3676-3682. 

Figure 2. Dependencies of shift of valence vibration band of silica surface hydroxyl groups at adsorption of small organic bases (a) and organosilicon compounds (b) on the maximum negative charge of the bases (a) and on the ionization potential of organosilicon compounds (b).

The conversion of carboxylic acids into alcohols with one less carbon atom is an important synthetic transformation. Such decarboxylative hydroxylations have proven to be difficult to accomplish by classical ionic methods. Electrochemical decarboxylation (Hofer-Moest reaction) [23] has been applied successfully to different types of carboxylic acids such as amino acids (Scheme 11, Eq. 11.1) [24]. This reaction proceeds through an intermediate radical that is further oxidized to a car-benium ion and trapped by the solvent. The efficiency of the second oxidation step (the formation of the carbenium ion) depends on the ionization potential of the in-... 

To understand the correlation between sulfoxidation barrier height and ionization potential of the substrate, also here a VB curve-crossing diagram was set up (106), which is shown in Fig. 13. In contrast to aliphatic hydroxylation and epoxidation discussed above, the sulfoxidation reaction is concerted without a reaction intermediate. Therefore, the reactants connect with products directly and the promotion gap as a result reflects the excitation energy from the reactant wave function to the product wave fimc-tion in the reactant geometry. The excited wave fimction Fp essentially refers to the one-electron transfer from substrate to oxidant hence it is proportional to the IE of the substrate and the electron affinity of the oxidant. Consequently, the correlation... 

In this chapter, we review recent theoretical results of studies of radiation damage to DNA obtained in gas phase and in solution with the use of ab initio molecular orbital theory which has the advantage of being free of any empirical parameters. In the first part, we discuss results from works performed on species that are predominant in the direct effect, that is the natural DNA bases and their radical ions in various environments (i.e. base pairs, stacked systems, solvent), focusing on electron affinities and ionization potentials. We then review theoretical data obtained for species which result from OH and H attack in the indirect effect (sugar radicals, hydroxyl and hydrogen base adducts). In a third part, we discuss the fate of the hydroxyl base adducts, which upon H atom addition and subsequent dehydration lead to the regeneration of the natural DNA bases. Finally, we focus on the radioprotective roles of selected thiols and the possible mechanisms by which they act. Since an excellent and comprehensive review of the tools and methods currently used in molecular orbital theory has recently appeared, [15] it will not be further discussed here. 

In the investigation of species resulting from the indirect effect, calculations of the electron affinities and ionization potentials of the hydrogen and hydroxyl adduct DNA base radicals allow for further understanding of possible electron transfer processes. In conjunction with experimental observations, our ab initio results provide us with a complete list of redox properties for the DNA radical intermediates and predict that only a fraction of the base adduct radicals can be reduced via electron transfer from thiols, while DNA sugar radicals will be reduced. 

Internal and External Phases. When dyeing hydrated fibers, for example, hydrophUic fibers in aqueous dyebaths, two distinct solvent phases exist, the external and the internal. The external solvent phase consists of the mobile molecules that are in the external dyebath so far away from the fiber that they are not influenced by it. The internal phase comprises the water that is within the fiber infrastmcture in a bound or static state and is an integral part of the internal stmcture in terms of defining the physical chemistry and thermodynamics of the system. Thus dye molecules have different chemical potentials when in the internal solvent phase than when in the external phase. Further, the effects of hydrogen ions (H" ) or hydroxyl ions (OH ) have a different impact. In the external phase acids or bases are completely dissociated and give an external or dyebath pH. In the internal phase these ions can interact with the fiber polymer chain and cause ionization of functional groups. This results in the pH of the internal phase being different from the external phase and the theoretical concept of internal pH (6). 

Fiber-reactive dye is also hydrolyzed by reaction with free OH ions in the aqueous phase. This is a nonreversible reaction and so active dye is lost from the system. Hydrolysis of active dye can take place both in the dyebath and on the fiber, although in the latter case there is a competition between the reactions with free hydroxyl ions and those with ionized ceUulose sites. The hydrolyzed dye estabHshes its own equUibrium between dyebath and fiber which could be different from the active dye because the hydrolyzed dye has different chemical potentials in the two phases. The various reactions taking place can be summarized as in Figure 2. 

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