The change has strengthened InsP6 binding to the allosteric modulator by fold 5. Moreover, hydrogen bond can modulate the metabolism process, such as the hydrogen bond can facilitate the ubiquitous ultra-weak photon emission mode 9 , In addition, the fluorescent phenomena originated from de-excitation process are very widespread in all sorts of scale of biological systems Therefore, the dynamic mechanism of hydrogen bond will be extensively studied in the photo-excitation process by contemporary investigators 12 , 13 , Especially, the excited state hydrogen bond strengthening mechanism has been put forward for the first time by Han et al.
Hydrogen bond strength depends on its bond length, the bond angle, the local dielectric constant, the electronegativity of the donor and acceptor groups, temperature, and pressure, etc. The hydrogen bonding interaction and corresponding dynamical behaviour have been interpreted via a variety of photophysical and photochemical phenomena 16 , 29 , 30 , 31 , 32 , The electron density of proton donor group and acceptor group will reduce and increase, respectively Therefore, the proton transfer process will be facilitated in the S 1 state 11 , However, the ESIPT process can be understood as a four-level circular loop model and it is a great important process in the photochemistry, biochemistry and so on refs 38 , As discussed by Toshiki Mutai et al.
They have drawn a conclusion that the fluorescence yield can be widely enhanced by changing the surroundings from the polar liquid state to the solid state Actually, the non-radiative decay process plays a prominent role in the biological systems 41 , Subsequently, the radiationless decay will jump from the T 1 state to the S 0 state.
However, the torsion of HPIP isomer can be prohibited in the solid state surroundings, the nearly co-planar form will emit a drastic fluorescence In this study, we will carefully investigate the fluorescence quenching mechanism of deactivation process. As Zhao and Liu et al. In the present work, we utilize a mixed solvent model 44 to investigate the reaction where a THF molecule bounds to imino group of HPIP, the other solvent can be substituted by polarizable continuum model PCM.
The complex can be established by hydrogen bond interaction. As Fileti et al. Especially, Fileti et al. Therefore, in this study HPIP complexs have been certified as most stable structures when considering different spatial configurations of complex. As Wang et al.
Otherwise it cannot be primely explained in the conventional PCM model. In this study, we primarily investigate the photophysics and photochemistry properties of HPIP. Chu et al. However, in this study a new competitive mechanism of intramolecular and intermolecular hydrogen bond will be investigated in the torsional process. It should be noted that the k-HPIP has not occurred torsion. For illustrating the reliability of our computation, the absorption and emission spectra have been calculated in the mixed liquid model.
The above those peak values have coincided with the computational results of Toshiki Mutai et al. Herein, we have proved the availability of the computing method. However, the stable structures have not been investigated exclusively in the mixed liquid model. In the Fig.
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As shown in Fig. The reaction mechanism has been exhibited in the Fig. Subsequently, for above structures we have dissected carefully the changes of crucial bond parameters in the S 0 and S 1 state. We find that the o-HPIP form has the torsion of about The corresponding bond lengths are 4. The intermolecular hydrogen bonding interaction can compete with the intramolecular hydrogen bonding interaction of the ik-HPIP form in the mixed liquid model.
Yan et al. Non-coplanar ik-HPIP form results in the intramolecular hydrogen bond is extremely weak. The reduced density gradient RDG isosurfaces have been shown in the Fig. Some crucial bond parameters have been shown. Theoretically simulating the absorption and fluorescence spectra of the HPIP in the PCM solvation, the violet vertical lines stand for the corresponding peak values in the theoretical calculation discussed by Toshiki Mutai et al. The detail explanations of curves can be given by the legend on the top right corner.
Theoretically simulating the absorption and fluorescence spectra of the HPIP in the mixed liquid model. For guaranteeing these structures are the true most stable, the corresponding IR vibrational frequency has been calculated. The IR vibrational spectra of hydrogen bond have been shown in the Fig. The stretching bands of these bonds in the S 0 and S 1 state have been shown. The legend can give reader the detail explanations. We guess the rotation is connected with relative displacement of the electron clouds and the nucleus in molecule under the photo-induced.
The centre of gravity of positive and negative charges is tipped, which results in the drastic change of dipole moment. The corresponding maxima and minima have been exhibited on the figure, we can clearly found that the negative and positive electrostatic potential exist a drastic polarization distribution on the surface. Moreover, in the Fig. Their fluorescence compared with the fluorescence of cis-HPIP has been quenched.
Therefore, we draw a conclusion that factitious torsion of molecule structure cannot result in the drastic electron redistribution on the np-HPIP. The electron redistribution of these isomeric forms is great different from that of cis-HPIP. These isomeric forms are zwitterions that the imino group carries positive electric charges and the ketonic oxygen atom carries negative electric charges. ICT character of these zwitterions can lead to the increasing of the dipole moments in the S 1 state, so the corresponding electron population will be unbalanced in the molecule.
Moreover, the unbalanced electron population can further result in the torsion of isomeric forms. The corresponding maxima and minima have been labelled in the surface.
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For further studying the non-radiative decay process, comprehending the optical properties and pathways of electronic transition, the potential energy curves of the HPIP in the S 0 and S 1 state have been carefully investigated. The potential energy curves will be drawn with the bond length and dihedral angle increased by the fixed step sizes, respectively. The reactive potential barriers and stable structures have been obtained in the potential curves. Firstly, we study the potential energy curves in the S 0 state.
As shown in the Fig. In the Figure the k-HPIP form is a stable structure and it has been used as the original structure in dihedral angle scan. Proton transfer cannot spontaneously occur in the S 0 state, because the process needs to cross a potential barrier 7. Similarly, the dihedral angle torsion cannot also spontaneously occur, and the process needs to cross an energy barrier 9.
However, the energy instantly reduces about 3. Secondly, we study the potential energy curves in the S 1 state. In the mixed liquid model the keto form will directly be optimized into the v-HPIP form, so the v-HPIP form has been used as the initial structure in dihedral angle scan. The reversed torsion process needs to get over a small energy barrier 0. The corresponding potential barrier is the critical point of cis- and trans-isomer.
Hydrogen Bonding. New Insights
The numerical values in the graphs stand for the energy barriers of the reactions. To sum up, we have fully explained the reactive pathways for the HPIP complexes via analyzing the corresponding potential energy curves in the S 0 and S 1 state. However, the non-radiative transition process is still ambiguous, so we have further calculated the potential energy curves of the T 1 state. Because the oscillator strength of v-HPIP we have calculated is 0. Therefore, herein searching the MECP has become mainly work for us. As Harvey et al. It should be noted that the point sobMECP has sought out is about 0.
The numerical value in the graph stands for the energy barrier of the reaction.
The MECP and the corresponding structure have been shown. The negligible energy barrier of o-HPIP is 0. On the contrary, in the Fig. The stable np-HPIP form locates in about Therefore, the intramolecular hydrogen bond can preclude the torsion of HPIP structure. The numerical values in the graph stand for the energy barriers of the torsion and reversed torsion process. For illustrating the reliability of our computation, we have compared the electronic spectra with that of Toshiki Mutai et al. Both of the computed results are tremendous coincidental. The hydrogen bonding strengthening mechanism has been proved via analyzing the bond parameters of hydrogen bond in the S 0 and S 1 state.
In addition, the analysis of IR vibrational spectra can further illustrate the above strengthening mechanism. MOs analysis has indicated that the unbalanced electron population of the keto forms can give rise to the torsion of structures. For further studying the model of non-radiative decay process, comprehending the optical properties and pathways of electronic transition, the potential energy curves have been studied.