Theoretical Studies for the Rates and Kinetic Isotope Effects of the Excited-State Double Proton Transfer in the 1:1 7-Azaindole:H2O Complex Using Variational Transition State Theory Including Multidimensional Tunneling

Halogen substituent effect on the water-assisted excited-state tautomerization of 2, 7-diazaindole-H2O complex in aqueous solution: A theoretical study

We studied the ESPT process in the 2-DAI-H₂O complex theoretically for the first time, and compared the kinetics of 2-DAI-H₂O with those features of 7-DAI-H₂O. The substituted effect on the dynamics of excited-state double proton transfer in 2-DAI-H₂O and 7-DAI-H₂O clusters in water were also investigated at the TD-M06-2X/6-311+G(d, p) level. In this work, 2,7-DAI-H₂O is also expressed as 2-DAI-H₂O and 7-DAI-H₂O, in which correspond to different ESPT reactions and generate two tautomers (N₂H form and N₇H form). In both the 2-DAI-H₂O and 7-DAI-H₂O complexes, ESPT processes happened in a concertedly but asynchronously protolysis pathway. The ESPT process preferred to occur in the 7-DAI-H₂O complex due to its lower barrier height. For the 3-X-2-DAI-H₂O and 3-X-7-DAI-H₂O (X = H, F, Cl, Br) complexes, the replacement of halogen atom did not influence the ESPT mechanism. However, the replacement of halogen atom changed the structural parameters evidently, reduced the barrier height up to 4-5 kcal/mol, and enlarged the asynchronicity of ESPT apparently. ∆(R₁+R₂) values in the 3X-2-DAI-H₂O and 3X-7-DAI-H₂O complexes have linear correlation to the ZPE-corrected ESPT barrier height linearly.

Effect of different alkyl groups on excited-state tautomerization of 7AI-azaindole-H2O: A theoretical study

The effect of substituted alkyl groups at different substituted position on the first excited-state proton transfer of nR7AI-H₂O (n = 2-6; R = CH₃, C₂H₅, CF₃) complexes were theoretically investigated at the TD-M06-2X/6-31 + G(d, p) level. Here n value denoted the substituted position C_n of R group. The replacement of alkyl R group had no effect on the features of HOMO and LUMO, but influenced the S₀ → S₁ adiabatic transition energies of the nR7AI-H₂O complex. Through computation, we found that the double proton transfer took place in a concerted but asynchronous protolysis pattern regardless of substituted group R and substituted position in the nR7AI-H₂O complex. The vibrational-mode specific nature of ESPT was verified. The alkyl group R changed the geometrical parameters of TS, and resulted in enlarging/narrowing the asynchronousity of ESPT. The ESPT barrier height was also affected by the substituted group and position.

Variational transition state theory: theoretical framework and recent developments

This article reviews the fundamentals of variational transition state theory (VTST), its recent theoretical development, and some modern applications.

Effective Thermal Conductivity of Spherical Particulate Nanocomposites: Comparison with Theoretical Models, Monte Carlo Simulations and Experiments

The purpose of this work is to study heat conduction in systems that are composed out of spherical micro-and nanoparticles dispersed in a bulk matrix. Special emphasis will be put on the dependence of the effective heat conductivity on various selected parameters as dimension and density of particles, interface interaction with the matrix. This is achieved by combining the effective medium approximation and extended irreversible thermodynamics, whose main feature is to elevate the heat flux vector to the status of independent variable. The model is illustrated by three examples: Silicium-Germanium, Silica-epoxy-resin and Copper-Silicium systems. Predictions of our model are in good agreement with other theoretical models, Monte-Carlo simulations and experimental data.

Solvent effects in the excited-state tautomerization of 7-azaindole: a theoretical study

The solvent effect often changes the mechanism of a chemical reaction. Experimental studies of the excited-state tautomerization of 7-azaindole (7AI) suggested that the intrinsic reactions occur via the concerted triple and double proton transfer mechanisms in the gas and liquid phases, respectively. Theoretical study is required to understand how the solvent effect changes the mechanism; however, such studies have rarely been performed in the excited-state. In this study, systematic quantum mechanical calculations were performed to study the excited-state tautomerization of 7AI in methanol. Electronic structures and energies for the reactant, transition state, and product were computed at the complete active space self-consistent field levels with the second-order multireference perturbation theory (MRPT2) to consider the dynamic electron correlation. The IEFPCM and SM8 methods were used to include solvent effect in the excited and ground-state calculations, respectively. The excited-state double proton transfer (ESDPT) in 7AI-CH(3)OH and the triple proton transfer (ESTPT) in 7AI-(CH(3)OH)(2) both occur via a concerted but asynchronous mechanism. The ESTPT barrier was smaller than the activation energy of solvent reorganization; however, the amount of 7AI-(CH(3)OH)(2) in methanol is very small because the complex formation is entropically very unfavorable. Therefore, the ESTPT is not an important path. The MRPT2 barrier of ESDPT was 2.8 kcal/mol, which agrees very well with the experimental value. The MRPT2 barrier of deuterium (D) transfer is larger than the activation energy of solvent reorganization; therefore, the intrinsic D transfer is rate-limiting, while the proton transfer must compete with solvent reorganization. The time-dependent density functional theory (TDDFT) was also used for comparison. Most TDDFT methods used in this study failed to predict transition state structures or barriers of the excited-state tautomerization. Additionally, the TDDFT levels failed to predict correct dipole moments in the excited-state, which produced an unreliable solvent effect on barrier heights.