Proton ultrafast

Chudoba C, Riedle E, Pfeiffer M and Elsaesser T 1996 Vibrational coherence in ultrafast excited-state proton transfer Cham. Phys. Lett. 263 622-8... 

We have seen that 10" M s is about the fastest second-order rate constant that we might expect to measure this corresponds to a lifetime of about 10 " s at unit reactant concentration. Yet there is evidence, discussed by Grunwald, that certain proton transfers have lifetimes of the order 10 s. These ultrafast reactions are believed to take place via quantum mechanical tunneling through the energy barrier. This phenomenon will only be significant for very small particles, such as protons and electrons. 

It has been shown that photoexcitation of the guanine-cytosine (G-C) base pair leads to proton transfer [231], Watson-Crick (WC) base pairs have excited state lifetimes much shorter than other non-WC base pairs indicating once again that the natural occurring WC base pairs are more photostable than other alternative configurations [115, 118, 232-235], Much work has been done in the gas phase where many different base pair isomers exist. The ultrafast relaxation of the WC base pair has also been confirmed in solution using fluorescence up-conversion measurements [117]. 

Nielsen SB, Soiling TI (2005) Are conical intersections responsible for the ultrafast processes of adenine, protonated adenine, and the corresponding nucleosides . Chem Phys Chem 6 1276... 

Elsaesser TH, Bakker HJ (2002) Ultrafast hydrogen bonding dynamics and proton transfer processes in the condensed phase. Springer, Heidelberg... 

Ameer-Beg S, Ormson SM, Brown RG et al (2001) Ultrafast measurements of excited state intramolecular proton transfer (ESIPT) in room temperature solutions of 3-hydroxyflavone and derivatives. J Phys Chem A 105 3709-3718... 

Takeuchi T, Tahara T (2005) Coherent nuclear wavepacket motions in ultrafast excited-state intramolecular proton transfer sub-30-fs resolved pump-probe absorption spectroscopy of 10-hydroxybenzo[h]quinoline in solution. J Phys Chem A 109 10199-10207... 

Stoner-Ma D, Melief EH, Nappa J et al (2006) Proton relay reaction in green fluorescent protein (GFP) polarization-resolved ultrafast vibrational spectroscopy of isotopically edited GFP. J Phys Chem B 110 22009-22018... 

Ultrafast ESPT from the neutral form readily explains why excitation into the A and B bands of AvGFP leads to a similar green anionic fluorescence emission [84], Simplistic thermodynamic analysis, by way of the Forster cycle, indicates that the excited state protonation pK.J of the chromophore is lowered by about 9 units as compared to its ground state. However, because the green anionic emission is slightly different when it arises from excitation into band A or band B (Fig. 5) and because these differences are even more pronounced at low temperatures [81, 118], fluorescence after excitation of the neutral A state must occur from an intermediate anionic form I not exactly equivalent to B. State I is usually viewed as an excited anionic chromophore surrounded by an unrelaxed, neutral-like protein conformation. The kinetic and thermodynamic system formed by the respective ground and excited states of A, B, and I is sometimes called the three state model (Fig. 7). 

Stoner-Ma D, laye AA, Matousek P, Towrie M, Meech SR, Tonge PJ (2005) Observation of excited-state proton transfer in green fluorescent protein using ultrafast vibrational spectroscopy. I Am Chem Soc 127 2864—2865... 

Hosoi H, Mizuno H, Miyawaki A, Tahara T (2006) Competition between energy and proton transfer in ultrafast excited-state dynamics of an oligomeric fluorescent protein red Kaede. J PhysChemB 110 22853-22860... 

Chattoraj, M., King, B. A., Bublitz, G. U. and Boxer, S. G. (1996). Ultrafast excited state dynamics in green fluorescent protein Multiple states and proton transfer. Proc. Natl. Acad. Sci. USA 93, 8362-7. 

The several theoretical and/or simulation methods developed for modelling the solvation phenomena can be applied to the treatment of solvent effects on chemical reactivity. A variety of systems - ranging from small molecules to very large ones, such as biomolecules [236-238], biological membranes [239] and polymers [240] -and problems - mechanism of organic reactions [25, 79, 223, 241-247], chemical reactions in supercritical fluids [216, 248-250], ultrafast spectroscopy [251-255], electrochemical processes [256, 257], proton transfer [74, 75, 231], electron transfer [76, 77, 104, 258-261], charge transfer reactions and complexes [262-264], molecular and ionic spectra and excited states [24, 265-268], solvent-induced polarizability [221, 269], reaction dynamics [28, 78, 270-276], isomerization [110, 277-279], tautomeric equilibrium [280-282], conformational changes [283], dissociation reactions [199, 200, 227], stability [284] - have been treated by these techniques. Some of these... 

S. Bratos, J.-C. Leicknam, G. Gallot, and H. Ratajczak, Ultrafast Hydrogen Bond Dynamics and Proton Transfer Processes in the Condensed Phase, T. Elsaesser and H.J. Bakker (eds.), Kluwer Academic, Dordrecht, 2002, p. 5. 

Bimodal intermolecular proton transfer in water photoacid-base pairs studied with ultrafast infrared spectroscopy... 

Symmetry breaking wavepacket motion and absence of deuterium isotope effect in ultrafast excited state proton transfer... 

The 196 cm"1 mode is antisymmetric and thereby optically inactive and does not appear in the Raman spectrum. Since a direct optical excitation of the mode is excluded by symmetry selection rules we conclude that it is solely excited by the single proton transfer which breaks the symmetry. This demonstrates for the first time that the coherent excitation of a vibrational mode results exclusively from an ultrafast reactive process. 

Ultrafast inter molecular proton transfer from 10-hydroxy-... 

Unlike the case of simple diatomic molecules, the reaction coordinate in polyatomic molecules does not simply correspond to the change of a particular chemical bond. Therefore, it is not yet clear for polyatomic molecules how the observed wavepacket motion is related to the reaction coordinate. Study of such a coherent vibration in ultrafast reacting system is expected to give us a clue to reveal its significance in chemical reactions. In this study, we employed two-color pump-probe spectroscopy with ultrashort pulses in the 10-fs regime, and investigated the coherent nuclear motion of solution-phase molecules that undergo photodissociation and intramolecular proton transfer in the excited state. 

Ultrafast photophysics of the protonated Schiff base of retinal in alcohols studied by femtosecond fluorescence up-conversion... 

Transient absorption experiments have shown that all of the major DNA and RNA nucleosides have fluorescence lifetimes of less than one picosecond [2—4], and that covalently modified bases [5], and even individual tautomers [6], differ dramatically in their excited-state dynamics. Femtosecond fluorescence up-conversion studies have also shown that the lowest singlet excited states of monomeric bases, nucleosides, and nucleotides decay by ultrafast internal conversion [7-9]. As discussed elsewhere [2], solvent effects on the fluorescence lifetimes are quite modest, and no evidence has been found to date to support excited-state proton transfer as a decay mechanism. These observations have focused attention on the possibility of internal conversion via one or more conical intersections. Recently, computational studies have succeeded in locating conical intersections on the excited state potential energy surfaces of several isolated nucleobases [10-12]. 

The above CT systems represent the case for intermolecular electron transfer. There is some analogy to proton transfer in acid-base reactions [5]. We have also examined intramolecular electron transfer systems and studied the influence of IVR and geometric changes this work is detailed elsewhere [5]. Other reactions involving ultrafast electron transfer are those of harpooning in Xe + I2) Nal, and more recently Xe/Ch (see Ref. 1). 

Ultrafast proton transfer. The diffusion-controlled limit for second-order rate constants (Section A3) is 1010 M 1 s 1. In 1956, Eigen, who had developed new methods for studying very fast reactions, discovered that protons and hydroxide ions react much more rapidly when present in a lattice of ice than when in solution.138 He observed second-order rate constants of 1013 to 1014 M 1 s These represent rates almost as great as those of molecular vibration. For example, the frequency of vibration of the OH bond in water is about 1014 s . The latter can be deduced directly from the frequency of infrared light absorbed in exciting this vibration Frequency v equals wave number (3710 cm-1 for -OH stretching) times c, the velocity of light (3 x 1010 cm s ). 

This ultrafast transfer of protons can be explained as follows The OH ion and the proton, which is combined with a water molecule to form HsO+, are both hydrogen-bonded to adjacent water molecules. 

The preassociation mechanism is more efficient than the trapping mechanism because it generates an intermediate which immediately reacts by an ultrafast proton transfer (in the pre-association complex, Int) and thus avoids the diffusion-controlled step bringing the catalyst and intermediate together. This mechanism is sometimes called a spectator mechanism because, although the catalyst is present in the transition structure, it is not undergoing any transformation [10]. 

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