Electrons hydration dynamics

Keszei, E., Murphrey, T. H. and Rossky, P. J. Electron hydration dynamics simulation results compared to pump and probe experiments, J.Phys.Chem., 99 (1995), 22-28... 

H. Tachikawa,/. Chem. Phys., 125, 144307, 1-8 (2006). Electron Hydration Dynamics in Water Clusters A Direct ab Initio Molecular Dynamics Approach. 

With site-directed mutation and femtosecond-resolved fluorescence methods, we have used tryptophan as an excellent local molecular reporter for studies of a series of ultrafast protein dynamics, which include intraprotein electron transfer [64-68] and energy transfer [61, 69], as well as protein hydration dynamics [70-74]. As an optical probe, all these ultrafast measurements require no potential quenching of excited-state tryptophan by neighboring protein residues or peptide bonds on the picosecond time scale. However, it is known that tryptophan fluorescence is readily quenched by various amino acid residues [75] and peptide bonds [76-78]. Intraprotein electron transfer from excited indole moiety to nearby electrophilic residue(s) was proposed to be the quenching... 

Fig. 15.5 The first observation of hydration dynamics of electron. Absorption profiles of the electron during its hydration are shown at 0, 0.08, 0.2, 0.4, 0.7,1, and 2 ps. The absorption changes its character in a way that suggests that two species are involved, the one that absorbs in the infrared is generated immediately and converted in time to the fully solvated electron that absorbs near 700 nm. (From A. Migus, Y. Gauduel, J. L. Martin, and A. Antonetti, Phys. Rev Lett. 58, 1559 (1987).) For later developments in this subject see, for example, K. Yokoyama, C. Silva, D. Hee Son, P. K. Walhout, and P. F. Barbara, J. Phys. Chem. A, 102, 6957 (1998).)...

Paik, D. H., I.-R. Lee, D.-S. Yang, J. S. Baskin and A. H. Zewail (2004)Electrons in finitesized water cavities Hydration dynamics observed in real time. Science 306, 672-675 Pakkanen, T. A. (1996) Study of formation of coarse particle nitrate aerosol. Atmospheric Environment 30, 2475-2482... 

Electron hydration is quite an interesting and important issne and many experimental and theoretical studies have already been devoted to the issue. [93, 123, 154, 166, 167, 199, 209, 341, 374, 382] It is a prototjqie of solution-phase chemistry in polar solvent. Also, the dynamics are expected to provide an important insight into charge-transfer chemistry. 

Rossky, P.J., Schnitker, J. The hydrated electron quantum simulation of structure, spectroscopy and dynamics. J. Phys. Chem. 92 (1988) 4277-4285. 

Schwartz, B. J. and Rossky, P. J. Aqueous solvation dynamics with a quantum mechanical solute computer simulation studies of the photoexcited hydrated electron, J.Chem.Phys., 101 (1994), 6902-6916... 

Other transient radicals such as (SCN)2 [78], carbonate radical (COj ) [79], Ag and Ag " [80], and benzophenone ketyl and anion radicals [81] have been observed from room temperature to 400°C in supercritical water. The (SCN)2 radical formation in aqueous solution has been widely taken as a standard and useful dosimeter in pulse radiolysis study [82,83], The lifetime of the (SCN)2 radical is longer than 10 psec at room temperature and becomes shorter with increasing temperature. This dosimeter is not useful anymore at elevated temperatures. The absorption spectrum of the (SCN)2 radical again shows a red shift with increasing temperature, but the degree of the shift is not significant as compared with the case of the hydrated electron. It is known that the (SCN) radical is equilibrated with SCN , and precise dynamic equilibration as a function of temperature has been analyzed to reproduce the observation [78],... 

When an electron is injected into a polar solvent such as water or alcohols, the electron is solvated and forms so-called the solvated electron. This solvated electron is considered the most basic anionic species in solutions and it has been extensively studied by variety of experimental and theoretical methods. Especially, the solvated electron in water (the hydrated electron) has been attracting much interest in wide fields because of its fundamental importance. It is well-known that the solvated electron in water exhibits a very broad absorption band peaked around 720 nm. This broad absorption is mainly attributed to the s- p transition of the electron in a solvent cavity. Recently, we measured picosecond time-resolved Raman scattering from water under the resonance condition with the s- p transition of the solvated electron, and found that strong transient Raman bands appeared in accordance with the generation of the solvated electron [1]. It was concluded that the observed transient Raman scattering was due to the water molecules that directly interact with the electron in the first solvation shell. Similar results were also obtained by a nanosecond Raman study [2]. This finding implies that we are now able to study the solvated electron by using vibrational spectroscopy. In this paper, we describe new information about the ultrafast dynamics of the solvated electron in water, which are obtained by time-resolved resonance Raman spectroscopy. 

In order to study the influence of electron concentration on the observed dynamics, we performed experiments with different laser power densities. As an illustration, the transient absorption signals recorded at 715 nm in ethylene glycol upon photoionisation of the solvent at 263 nm with three different laser power densities are presented in Fig.3. As expected for a two-photon ionization process, the signal intensity increases roughly with the square of the power density. However, the recorded decay kinetics does not depend on the 263 nm laser power density since the normalised transient signals are identical (Cf. Fig.3 inset). That result indicates that the same phenomena occur whatever the power density and consequently that the solvation dynamics are independent of the electron concentration in our experimental conditions i.e. we are still within the independent pair approximation as opposed to our previous work on hydrated electron [8]. 

The hydrated electron is characterized by its strong absorption at 720 nm (e = 1.9 x 104 dm3 mol-1 cm-1 (Hug 1981) the majority of the oscillator strength is derived from optical transitions from the equilibrated s state to the p-like excited state (cf. Kimura et al. 1994 Assel et al. 2000). The 720-nm absorption is used for the determination of its reaction rate constants by pulse radiolysis (for the dynamics of solvation see, e.g Silva et al. 1998 for its energetics see, e.g Zhan et al. 2003). IP only absorbs in the UV (Hug 1981), and rate constants have largely been determined by EPR (Neta et al. 1971 Neta and Schuler 1972 Mezyk and Bartels 1995) and competition techniques (for a compilation, see Buxton et al. 1988). In many aspects, H and eaq behave very similarly, which made their distinction and the identification of eaq" difficult (for early reviews, see Hart 1964 Eiben 1970 Hart and Anbar 1970), and final proof of the existence of the... 

Sherman WV (1967b) Light-induced and radiation-induced reactions in methanol. I. y-Radiolysis of solutions containing nitrous oxide. J Phys Chem 71 4245-4255 Sherman WV (1967c) The y-radiolysis of liquid 2-propanol. III. Chain reactions in alkaline solutions containing nitrous oxide. J Phys Chem 71 1695-1702 Silva C, Walhout PK, Yokoyama K, Barbara PF (1998) Femtosecond solvation dynamics of the hydrated electron. Phys Rev Lett 80 1086-1089... 

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