Transient absorption spectroscopy reduction

Kimura Y, Alfano JC, Walhout PK, Barbara PF (1994) Ultrafast transient absorption spectroscopy of the solvated electron in water. J Phys Chem 98 3450-3458 Li X, Sevilla MD, Sanche L (2003) Density functional theory studies of electron interaction with DNA can zero eV electrons induce strand breaks J Am Chem Soc 125 13668-13699 Lind J, Shen X, Eriksen TE, Merenyi G, Eberson L (1991) One-electron reduction of N-bromosuccin-imide. Rapid expulsion of a bromine atom. J Am Chem Soc 113 4629-4633 Marasas RA, lyoda T, Miller JR (2003) Benzene radical ion in equilibrium with solvated electrons. J Phys Chem A 107 2033-2038... 

The mechanism for the generation of quinone methide 58 by reductive elimination of 55 has been investigated.106 Single-electron reduction by 55 by pulse radiolysis in water gives the semiquinone radical anion 56, whose decay was monitored by transient absorption spectroscopy. This radical anion partitions between disproportionation to 60 and elimination to form the radical 58. Disproportionation dominates at pH 7, but as the pH is lowered to 3 the competing elimination reaction to form the quinone methide radical 58 is observed for X = -OMe and -OPh. It was proposed that the product yields are controlled by the position of the equilibrium for protonation of 56 and that 56 undergoes mainly disproportionation, while the semiquinone radical 57 - undergoes mainly elimination of HX (Scheme 28). The quinone methide 59 is then formed by the one-electron reduction of 58. 

CO absorbed on Cu nanoparticles is detected, and based on this observation, it is proposed that the photocatalytic CO2 reduction takes place on copper atoms of the nanoalloy. Furthermore, transient absorption spectroscopy has provided an useful spectroscopic evidence showing that CO2 only quenches the charge separation state of the photocatalyst when Cu is present on titania [27]. Figure 1.1 presents selected temporal profiles of the transient signal monitored at long wavelengths in the absence and in the presence of CO2 for a sample of Cu/P25 and Au/P25. 

Baldovi HG, Neatu , Khan A, Asiri AM, Kosa S A, Garcia H (2015) Understanding the origin of the photocatalytic C02 reduction by An- and Cu-loaded Ti02 a microsecond transient absorption spectroscopy study. J Phy Chem C 119 6819-6827... 

Electronic absorption spectroscopy is also a useful technique for the characterization of Cr intermediates. When coupled with global kinetic analysis, ligand stoichiometries, and spectra of transient species in the redox chemistry of Cr can be determined. The first applications of this global analysis to biologically relevant systems involved studies of the Cr(Vl) reactions with the main biological reductants Cys, GSH, and ascorbate (70, 97). The distinct electronic absorption features of the Cr(VI), Cr(V), Cr(lV), and Cr(lll) oxidation states... 

Common techniques usually employed to monitor electron transfer processes on QD sensitizing oxides are photoluminescence (PL) and transient absorption (TA) spectroscopy (both probing carrier populations within the QDs). The reduction of QD luminescenceor increase in absorptionsignals after their attachment to the oxide film is an indirect signature of efficient electron transfer between the species. However, the disappearance of electrons from the QD can also be explained by alternative recombination pathways (caused by changes in the QD surface chemistry after attachment) that are not present for dispersed QDs in a solvent. Indeed, TA and PL measurements on, for example. 

The presence of permanent [Fe2S2] clusters in holo-NifU impeded spectroscopic characterization of transient clusters assembled in a NifS-mediated process. However, unambiguous evidence for NifS-directed assembly of oxidatively and reductively labile [Fe2S2] " clusters on NifU-1 was obtained using the combination of UV-visible absorption and resonance Raman spectroscopies (Yuvaniyama et al. 2000). The anaerobic reaction mixture involved NifU ferric ammonium citrate P-mercaptoethanol l-cysteine NifS in a 50 100 5000 1000 1 ratio. The presence of catalytic amounts of NifS facilitated meaningful UV-visible absorption results and monitoring the time course of cluster assembly. Although ferric ammonium citrate was used for these cluster assembly studies, control experiments... 

More definite evidence for the transient existence of the un-cyclized l-(jS-aminoethyl)-3,4-benzoquinones has been obtained recently by Kodja and Bouchilloux,77 78 who noted that a transient yellow color (Amax ca. 385 mp) was occasionally observed during the enzymic oxidations of catecholamines (particularly in unbuffered systems at low temperatures). This phenomenon was probably due to the formation of the transient o-quinones. (The absorption maximum of o-benzoquinone, the effective chromophore of the open-chain quinones, is known to occur at ca. 390 mp.79) An absorption maximum at 390 mp is characteristic of the formation of the dopa-quinone chromophore during oxidation of small C -terminal tyrosine peptides in the presence of tyrosinase.37 48 Similar spectroscopic features were observed when the oxidations were carried out with lead dioxide in sulfuric acid solutions (pH> 1). If the initial oxidation was carried out for a short period of time, it was possible to regenerate the original catecholamines by reduction (e.g. with sodium bisulfite, potassium iodide, and zinc powder) and to show that the 385 mp peak disappeared.77,78 Kodja and Bouchilloux were also able to identify 2,4-dinitrophenylhydrazones of several of the intermediate non-cyclized quinones by paper chromatography and spectroscopy (Amax n weakly acid solution ca. 350 mp with a shoulder at ca. 410 mp).77,78... 

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