Picosecond time-resolved Raman spectra of water were measured under the resonance condition with the s f p electronic transition of the solvated electron for the first time. We found that a strong transient Raman band appears in the frequency region 30 cm -1 lower than the OH-bend band of bulk water in accordance with the formation of solvated electrons. The observed transient Raman band was assigned to the vibration of the solvating water molecules that strongly interact with the solvated electron in the first solvation shell. The mechanism of this novel resonance enhancement is discussed on the basis of the vibronic theory.

Heliorhodopsins (HeRs) are a new category of retinal-bound proteins recently discovered through functional metagenomics analysis that exhibit obvious differences from type-1 microbial rhodopsins. We conducted the first detailed structural characterization of the retinal chromophore in HeRs using resonance Raman spectroscopy. The observed spectra clearly show that the Schiff base of the chromophore is protonated and forms a strong hydrogen bond to a species other than a water molecule, highly likely a counterion residue. The vibrational mode of the Schiff base of HeRs exhibits similarities with that of photosensory microbial rhodopsins, that is consistent with the previous proposal that HeRs function as photosensors. We also revealed unusual spectral features of the in-plane chain vibrations of the chromophore, suggesting an unprecedented geometry of the Schiff base caused by a difference in the retinal pocket structure of HeRs. These data demonstrate structural characteristics of the photoreceptive site in this novel type of rhodopsin family.

Transient resonance Raman and absorption spectra of the anion radical CM•- and lowest excited triplet state 3CM* of coumarin were measured. Vibrational assignments of the ground state S0, CM•-, and 3CM* were performed based on both the frequency shifts on isotopic (18O, 13C, and deuterium) substitutions and normal-coordinate calculations using the force constants obtained by ab initio molecular orbital computations. The vibrational assignments and ab initio MO calculations provided much information on the structures of S0, CM•-, and 3CM*. It is concluded that the C(3)C(4) bond of the pyrone ring is lengthened markedly in CM•- and drastically in 3CM*. This suggests that the C(3)C(4) bond is one of the reactive sites of coumarin and furocoumarins in their photochemical reactions, which is in good accord with the formation of cyclobutane-type adducts with pyrimidine bases, particularly with thymine, through the C(3)C(4) bond of furocoumarins and the C(5)C(6) bond of pyrimidine bases. The CO bond was found to be moderately lengthened both in CM•- and 3CM*. The moderate lengthening of the CO bond of 3CM* is consistent with the π−π* character of 3CM*.

Third-order optical nonlinearity around the exciton resonance in (C6H13NH3)2PbI4 was measured using time-integrated and spectrally-resolved four-wave-mixing (FWM) techniques. For excitation below the exciton resonance, biexciton contribution to the FWM signals was observed. The dephasing energy of the biexcitons was estimated to be larger than 10 meV.

Active ion transport across membranes is vital to maintaining the electrochemical gradients of ions in cells and is mediated by transmembrane proteins. Halorhodopsin (HR) functions as a light-driven inward pump for chloride ions. The protein contains all-trans-retinal bound to a specific lysine residue through a protonated Schiff base. Interaction between the bound chloride ion and the protonated Schiff base is crucial for ion transport because chloride ion movement is driven by the flipping of the protonated Schiff base upon photoisomerization. However, it remains unknown how this interaction evolves in the HR photocycle. Here, we addressed the effect of the bound anion on the structure and dynamics of HR from Natronomonas pharaonis in the early stage of the photocycle. Comparison of the chloride-bound, formate-bound, and anion-depleted forms provided insights into the interaction between the bound anion and the chromophore/protein moiety. In the unphotolyzed state, the bound anion affects the π-conjugation of the polyene chain and the hydrogen bond of the protonated Schiff base of the retinal chromophore. Picosecond time scale measurements showed that the band intensities of the W16 and W18 modes of the tryptophan residues decreased instantaneously upon photoexcitation of the formate-bound form. In contrast, these intensity decreases were delayed for the chloride-bound and anion-depleted forms. These observations suggest the stronger interactions of the bound formate ion with the retinal chromophore and the chromophore pocket. On the nanosecond to microsecond timescales, we found that the interaction between the protonated Schiff base and the bound ion is broken upon formation of the K intermediate and is recovered following translocation of the bound anion toward the protonated Schiff base in the L intermediate. Our results demonstrate that the hydrogen-bonding ability of the bound anion plays an essential role in the ion transport of light-driven anion pumps.

No abstract

No abstract

No abstract