One-dimensional description of multidimensional electron transfer reactions in condensed phase

We derive a one-dimensional energy diffusion equation for describing the dynamics of multidimensional electron transfer reactions in condensed phase, which is conceptually simpler and computationally more economic than the conventional approaches. We also obtain an analytical expression for the rate of electron transfer reactions for a general one-dimensional effective potential as well as an energy dependent diffusitivity. As an illustrative example, we consider application to electron transfer in a contact ion pair system modeled through harmonic potentials consisting of two slow classical modes and a high frequency vibrational mode for which the numerical results calculated using the proposed one-dimensional approach are shown to be in good agreement with experimental results. The energy diffusion equation and the rate expression for electron transfer obtained from the present theory, therefore, open up the possibility of describing the dynamics of electron transfer in complex systems, through a simpler approach.     

Wittig and Wittig-Horner reactions under phase transfer catalysis conditions

Wittig and Wittig-Horner reactions are favorite tools in preparative organic chemistry. These olefination methods enjoy widespread and recognition because of their simplicity, convenience, and effciency. Phase transfer catalysis (PTC) is a very important method in synthetic organic chemistry having many advantages over conventional, homogenous reaction procedures. In this paper, we attempt to summarize the aspects concerning Wittig and Wittig-Horner reactions that take place under phase transfer catalysis conditions.     

相转移催化反应中界面性能的研究

过去在研究相转移催化反应机理时仅考虑在相转移催化剂作用下反应物、中间体(离子)、产物在两相间的转移,并导致两相间反应进行。我们以研究结果证明水相的表面能和两相的界面能与相转移催化反应的结果有密切关系。     

Nucleophilic reactions in the indole series: displacement of bromine under phase transfer catalysis

A novel synthetic approach for the synthesis of 3-substituted indoles by nucleophilic substitution of 3-bromo derivatives under phase transfer catalysis (PTC) was reported.     

Radical-olefin addition reactions in condensed phase

A study has been made of the rate constant for the reaction The states of the product have quasilevels E_n — i_n, which, depending on the heat of reaction, may be in resonance with the state of the reactants after surmounting the activation barrier. Because of this, there is no monotonic variation of the propagation rate constant, even as a function of the heat of reaction; the behavior of the rate constant has a resonance character. The results obtained in this investigation are in good agreement with experimental data.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 1, pp. 25–32, January–February, 1990.     

Linking the historical and chemical definitions of diabatic states for charge and excitation energy transfer reactions in condensed phase

Marcus theory of electron transfer (ET) and Fo?rster theory of excitation energy transfer (EET) rely on the Condon approximation and the theoretical availability of initial and final states of ET and EET reactions, often called diabatic states. Recently [Subotnik et al., J. Chem. Phys. 130, 234102 (2009)], diabatic states for practical calculations of ET and EET reactions were defined in terms of their interactions with the surrounding environment. However, from a purely theoretical standpoint, the definition of diabatic states must arise from the minimization of the dynamic couplings between the trial diabatic states. In this work, we show that if the Condon approximation is valid, then a minimization of the derived dynamic couplings leads to corresponding diabatic states for ET reactions taking place in solution by diagonalization of the dipole moment matrix, which is equivalent to a Boys localization algorithm; while for EET reactions in solution, diabatic states are found through the Edmiston-Ruedenberg localization algorithm. In the derivation, we find interesting expressions for the environmental contribution to the dynamic coupling of the adiabatic states in condensed-phase processes. In one of the cases considered, we find that such a contribution is trivially evaluable as a scalar product of the transition dipole moment with a quantity directly derivable from the geometry arrangement of the nuclei in the molecular environment. Possibly, this has applications in the evaluation of dynamic couplings for large scale simulations.     

Kinetics of energy transfer in the condensed phase

The decay kinetics of the donor state is studied; this decay is determined by the resonance energy transfer to the surrounding donor molecules of the medium. A new element is the consideration of the strong interaction of the donor with the acceptor over short distances, thanks to which the onset of decomposition assumes an exponential character. It was shown that this circumstance does not affect the fluorescence quenching, but it can exert a considerable effect on phenomena related to radiation shielding.     

Ionic transformations in extremely nonpolar fluorous media: phase transfer catalysis of halide substitution reactions

Fluorous solutions of alkyl halides Rf8(CH2)mX (m = 2, 3; X = Cl, Br, I) are inert toward solid or aqueous NaCl, NaBr, and KI, but halide substitution occurs in the presence of fluorous phosphonium salts (10 mol %, 76-100 degrees C).     

Nonperturbative quantum simulation of time-resolved nonlinear spectra: Methodology and application to electron transfer reactions in the condensed phase

A quantum dynamical method is presented to accurately simulate time-resolved nonlinear spectra for complex molecular systems. The method combines the nonpertubative approach to describe nonlinear optical signals with the multilayer multiconfiguration time-dependent Hartree theory to calculate the laser-induced polarization for the overall field–matter system. A specific nonlinear optical signal is obtained by Fourier decomposition of the overall polarization. The performance of the method is demonstrated by applications to photoinduced ultrafast electron transfer reactions in mixed-valence compounds and at dye–semiconductor interfaces.     

Synergism and antagonism in phase transfer catalysis

Synergism and antagonism phenomena in phase transfer catalytic reactions have been considered. The factors responsible for the Synergism in the catalysis by an onium salt-crown ether mixture have been determined. Special attention have been paid to quantitative estimation of synergism and antagonism. The influence of addition of water on the rates of the reactions in solid-liquid systems have been discussed.In memory of the 75th anniversary of Member of the Academy of Sciences of Ukrainian SSR L. M. Litvinenko.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2108–2114, November, 1995.     

A convenient route to alkynes via phase transfer catalysis: Applications of phase transfer catalysis,part 19

High yield, rapid formations of alkynes from vicdibromides are possible using powered potassium hydroxide and catalytic amounts of lipophilic phase transfer catalysts. Reasons are given why molar amounts of expensive catalysts were necessary in earlier procedures.     

Low temperature electron transfer in strongly condensed phase

Electron transfer coupled to a collective vibronic degree of freedom is studied in strongly condensed phase and at lower temperatures where quantum fluctuations are essential. Based on an exact representation of the reduced density matrix of the electronic + reaction coordinate compound in terms of path integrals, recent findings on the overdamped limit in quantum dissipative systems are employed. This allows us to give a consistent generalization of the well-known Zusman equations to the quantum domain. Detailed conditions for the range of validity are specified. Using the Wigner transform these results are also extended to the quantum dynamics in full phase space. As an important application electronic transfer rates are derived that comprise adiabatic and nonadiabatic processes in the low temperature regime including nuclear tunneling. Accurate agreement with precise quantum Monte Carlo data is observed.     

Simple quantum-mechanical model of the elementary event of organic nucleophilic substitution reactions in the condensed phase

A semiempirical model is proposed for the elementary event of nucleophilic S_N2 substitution in alkyl halides. An analysis was made of the factors which determine the activation energies of the processes, i.e., the energy of approach of the reagents, the energy of extension of the chemical bonds, the energy of reorganization of the medium, and the equilibrium energy of the elementary event. The contributions from the first three energy parameters are commensurable, and the energy of approach has a predominant role. The role of the equilibrium energy, determined by the solvation energy of the reacting ions and the energy of the formed and broken chemical bonds, involves the creation of thermally neutral conditions for the reactions. The effective potential surfaces of the repulsive interaction between the halide ions and the methyl halides were constructed in terms of the model. The tunneling factor and the kinetic isotope effect for the lightest reacting particle in the reaction series (the fluoride ion) were also determined.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 4, pp. 417–424, July–August, 1985.     

Ab initio model study on acetylcholinesterase catalysis: potential energy surfaces of the proton transfer reactions

Ab initio molecular orbital (MO) and hybrid density functional theory (DFT) calculations have been applied to the initial step of the acylation reaction catalyzed by acetylcholinesterase (AChE), which is the nucleophiric addition of Ser200 in catalytic triads to a neurotransmitter acetylcholine (ACh). We focus our attention mainly on the effects of oxyanion hole and Glu327 on the potential energy surfaces (PESs) for the proton transfer reactions in the catalytic triad Ser200-His440-Glu327. The activation barrier for the addition reaction of Ser200 to ACh was calculated to be 23.4 kcal/mol at the B3LYP/6-31G(d)//HF/3-21G(d) level of theory. The barrier height under the existence of oxyanion hole, namely, Ser200-His440-Glu327-ACh-(oxyanion hole) system, decreased significantly to 14.2 kcal/mol, which is in reasonable agreement with recent experimental value (12.0 kcal/mol). Removal of Glu327 from the catalytic triad caused destabilization of both energy of transition state for the reaction and tetrahedral intermediate (product). PESs calculated for the proton transfer reactions showed that the first proton transfer process is the most important in the stabilization of tetrahedral intermediate complex. The mechanism of addition reaction of ACh was discussed on the basis of theoretical results.     

Hydroxide ion initiated reactions under phase transfer catalysis conditions—IV : Effect of catalyst structure

The nature of the quat-anion interactions in a PTC/OH^? system was probed by examining the reactivity and selectivity of a CA/O-ambident anion towards an alkylating agent in the presence of various quats. It is suggested that the accessibility of the positive N center of the qual for association with the anion is the major factor in determining the behavior of PTC/OH^? reactions proceeding through the Makosza mechanism.     

Hydroxide ion initiated reactions in phase transfer catalysis. I. Isomerization of allylbenzene.

Allylbenzene (pK_a ≈ 34) was isomerized to trans and cis β-methylstyrene under phase transfer catalysis conditions. Several half lives of this reaction were measured under various conditions.     

Extended spin-boson model for nonadiabatic hydrogen tunneling in the condensed phase

A nonadiabatic rate expression for hydrogen tunneling reactions in the condensed phase is derived for a model system described by a modified spin-boson Hamiltonian with a tunneling matrix element exponentially dependent on the hydrogen donor-acceptor distance. In this model, the two-level system representing the localized hydrogen vibrational states is linearly coupled to the donor-acceptor vibrational mode and the harmonic bath. The Hamiltonian also includes bilinear coupling between the donor-acceptor mode and the bath oscillators. This coupling provides a mechanism for energy exchange between the two-level system and the bath through the donor-acceptor mode, thereby facilitating convergence of the time integral of the probability flux correlation function for the case of weak coupling between the two-level system and the bath. The dependence of the rate constant on the model parameters and the temperature is analyzed in various regimes. Anomalous behavior of the rate constant is observed in the weak solvation regime for model systems that lack an effective mechanism for energy exchange between the two-level system and the bath. This theoretical formulation is applicable to a wide range of chemical and biological processes, including neutral hydrogen transfer reactions with small solvent reorganization energies.     

Coupled chemoenzymatic transfer hydrogenation catalysis for enantioselective reduction and oxidation reactions

Stereoselective reductions of prochiral ketones were performed using a new thermophilic, NAD-dependent alcohol dehydrogenase from Thermus sp. (TADH). The enzyme was produced on 2L-scale from recombinant Escherichia coli and purified by a simple, one-step heat treatment procedure yielding 220 mg of pure enzyme. Regeneration of NADH was catalyzed by the organometallic complex [Cp*Rh(bpy)(H₂O)]²⁺ using formate as a reducing agent. The catalytic performance of [Cp*Rh(bpy)(H₂O)]²⁺ in terms of total number of catalytic cycles and number of catalytic cycles per hour achieved herein (up to 1500 and more than 400 h⁻¹, respectively), are the highest reported for a non-enzymatic nicotinamide regeneration system so far. Chemoenzymatic reduction reactions in a two liquid phase setup were performed on a gramme-scale, for example, 1.3 g of enantiopure (1S,3S)-3-methylcyclohexanol was obtained after purification. The volumetric productivity reached up to 3.9 mM h⁻¹ with an average of 2.6 mM h⁻¹ (5.3 g L⁻¹ d⁻¹) over 10 h. In addition, chemoenzymatic oxidations utilizing the same catalyst set and molecular oxygen as a terminal electron acceptor were performed. Thus, the preparative value of chemoenzymatic transfer hydrogenations with [Cp*Rh(bpy)(H₂O)]²⁺ as a regeneration catalyst coupled especially to thermophilic ADHs was demonstrated.