Lagrangian of extended multiconfigurational self-consistent field second-order quasidegenerate perturbation theory combined with reference interaction site model self-consistent field constraint spatial electron density.

Lagrangians of the state-averaged multiconfigurational self-consistent field (SA-MCSCF) and multistate extended second-order quasidegenerate perturbation theory (MS-XMCQDPT2) coupled with the reference interaction site model self-consistent field constraint spatial electron density are defined. In addition, variational equations were derived to calculate the excitation energies of the target molecules dissolved in various solvents. The theory was applied to a phenol molecule in various solutions, and the gradients and Hessian matrices were calculated to evaluate the absorption spectral lines, including the broadening bandwidth. Numerical calculations revealed fine structures in any solvent surroundings. The main intramolecular vibrational modes related to such fine structures were stretching vibrations of the aromatic ring and the oxygen atom of the phenol molecule. The present theory plays an important role in predicting the structure of potential energy surfaces, such as Hessian matrices for various solvent types, during the photoexcitation process.

Recent developments and applications of reference interaction site model self-consistent field with constrained spatial electron density (RISM-SCF-cSED): A hybrid model of quantum chemistry and integral equation theory of molecular liquids.

The significance of solvent effects in electronic structure calculations has long been noted, and various methods have been developed to consider this effect. The reference interaction site model self-consistent field with constrained spatial electron density (RISM-SCF-cSED) is a hybrid model that combines the integral equation theory of molecular liquids with quantum chemistry. This method can consider the statistically convergent solvent distribution at a significantly lower cost than molecular dynamics simulations. Because the RISM theory explicitly considers the solvent structure, it performs well for systems where hydrogen bonds are formed between the solute and solvent molecules, which is a challenge for continuum solvent models. Taking advantage of being founded on the variational principle, theoretical developments have been made in calculating various properties and incorporating electron correlation effects. In this review, we organize the theoretical aspects of RISM-SCF-cSED and its distinctions from other hybrid methods involving integral equation theories. Furthermore, we carefully present its progress in terms of theoretical developments and recent applications.

Unimolecular Chemiexcited Oxygenation of Pathogenic Amyloids.

Pathogenic protein aggregates, called amyloids, are etiologically relevant to various diseases, including neurodegenerative Alzheimer disease. Catalytic photooxygenation of amyloids, such as amyloid-ß (Aß), reduces their toxicity; however, the requirement for light irradiation may limit its utility in large animals, including humans, due to the low tissue permeability of light. Here, we report that Cypridina luciferin analogs, dmCLA-Cl and dmCLA-Br, promoted selective oxygenation of amyloids through chemiexcitation without external light irradiation. Further structural optimization of dmCLA-Cl led to the identification of a derivative with a polar carboxylate functional group and low cellular toxicity: dmCLA-Cl-acid. dmCLA-Cl-acid promoted oxygenation of Aß amyloid and reduced its cellular toxicity without photoirradiation. The chemiexcited oxygenation developed in this study may be an effective approach to neutralizing the toxicity of amyloids, which can accumulate deep inside the body, and treating amyloidosis.

Investigation of the metastable structures of polyiodide in acetonitrile studied using global reaction route mapping and the reference interaction site model self-consistent field explicitly including constrained spatial electron density distribution.

In this study, we theoretically analyzed the metastable structures of polyiodide (I7-) in the gas and acetonitrile phases using global reaction route mapping and the reference interaction site model self-consistent field explicitly including constrained spatial electron density distribution. From the chemical reaction pathways of I7- in acetonitrile, it was found that there would be 2 types of isomerization pathways. One proceeds with constant stoichiometry and the other takes place by breaking and forming I-I bonds. In addition, we discovered that I7- had various metastable structures within ∼10 kcal mol-1. Comparing the most stable structure in the gas and acetonitrile phases, the tetrapot type is found to be the most stable structure in the gas phase; however, it is the zigzag type in acetonitrile. In order to understand this difference, we performed the decomposition analysis of the thermal correlation term in the gas and acetonitrile phases. It was found that thermal correction plays a key role in the stability and we could explain the difference in the population of the EQ states of I7- in each phase. Overall, we revealed that the solvation effect must be one of the crucial factors to stabilize the isomers of I7- and determine the chemical reaction pathways.

Hyper-Raman spectroscopy of benzene and pyridine revisited.

Hyper-Raman (HR) spectra of benzene-h6, benzene-d6, and pyridine in the liquid phase excited at 1064 nm were measured by a picosecond laser with a high repetition rate. Although benzene and pyridine are important aromatic molecules, the qualities of the HR spectra previously reported were not high enough to be compared with those of IR and Raman spectroscopy. Our HR spectroscopic system significantly improves sensitivity that enables the detection of HR bands of benzene and pyridine not observed before. In addition to band assignments, we interpret HR bands of benzene based on the vibronic coupling theory of (pre-) resonance hyper-Raman scattering. Depolarization ratios of HR bands of benzene and pyridine, obtained from polarized-HR measurements, are first examined from a theoretical point of view of HR spectroscopy. Moreover, we evaluate quantum chemical calculations for HR spectra by comparing experimental and computational spectra. We show that the frequency-dependent polarizability and hyperpolarizability calculations using time-dependent density functional theory well reproduce the HR experiments for bulk aromatic compounds.

Reference interaction site model self-consistent field with constrained spatial electron density approach for nuclear magnetic shielding in solution.

We propose a new hybrid approach combining quantum chemistry and statistical mechanics of liquids for calculating the nuclear magnetic resonance (NMR) chemical shifts of solvated molecules. Based on the reference interaction site model self-consistent field with constrained spatial electron density distribution (RISM-SCF-cSED) method, the electronic structure of molecules in solution is obtained, and the expression for the nuclear magnetic shielding tensor is derived as the second-order derivative of the Helmholtz energy of the solution system. We implemented a method for calculating chemical shifts and applied it to an adenine molecule in water, where hydrogen bonding plays a crucial role in electronic and solvation structures. We also performed the calculations of 17O chemical shifts, which showed remarkable solvent dependence. While converged results could not be sometimes obtained using the conventional method, in the present framework with RISM-SCF-cSED, an adequate representation of electron density is guaranteed, making it possible to obtain an NMR shielding constant stably. This introduction of cSED is key to extending the method's applicability to obtain the chemical shift of various chemical species. The present demonstration illustrates our approach's superiority in terms of numerical robustness and accuracy.

Investigating the Nonradiative Decay Pathway in the Excited State of Silepin Derivatives: A Study with Second-Order Multireference Perturbation Wavefunction Theory.

The fluorescence quantum yield for fluorescent organic molecules is an important molecular property, and tuning it up is desired for various applications. For the computational estimation of the fluorescence quantum yield, the theoretical prediction of the nonradiative decay rate constant has become an attractive subject of study. The rate constant of thermally activated nonradiative decay is related to the activation energy in the photoreaction; thus, the accuracy and reliability of the excited-state potential energies in the quantum chemical computation are critical. In this study, we employed a second-order multireference perturbation wavefunction theory for studying the thermally activated decay via conical intersection (CI) of 1,1-dimethyldibenzo[b,f]silepin derivatives. The correlation between the computed activation energy to reach the CI geometry in the S1 state and the experimentally determined fluorescence quantum yield implied that silepins nonradiatively decay via the CI triggered by the twisting of the central C-C bond. Geometry optimization of the transition state using multireference perturbation theory drastically reduced the estimated activation energy. Our computation gave reasonable predictions of the activation free energies of photoexcited 1,1-dimethyldibenzo[b,f]silepin. The energy profiles and geometry optimizations using proper quantum chemical methods played a critical role in reliable estimation of the rate constant and fluorescence quantum yield.

Multireference Perturbation Theory Combined with PCM and RISM Solvation Models: A Benchmark Study for Chemical Energetics.

The polarizable continuum model (PCM) has been one of the most widely used approaches to take into account the solvation effect in quantum chemical calculations. In this paper, we performed a series of benchmark calculations to assess the accuracy of the PCM scheme combined with the second-order complete-active-space perturbation theory (CASPT2) for molecular systems in polar solvents. For solute molecules with extensive conjugated π orbitals, exemplified by elongated conjugated arylcarbenes, we have incorporated the ab initio density matrix renormalization group algorithm into the PCM-CASPT2 method. In the previous work, we presented a combination of the DMRG-CASPT2 method with the reference interaction site model (RISM) theory for describing the solvation effect using the radial distribution function and compared its performance to the widely used density-functional approaches (PCM-TD-DFT). The work here allows us to further show a more thorough assessment of the RISM model compared to the PCM with an equal level of the wave function treatment, the (DMRG-)CASPT2 theory, toward a high-accuracy electronic structure calculations for solvated chemical systems. With the exception that the PCM models are not capable of properly describing the hydrogen bondings, accuracy of the PCM-CASPT2 model is in most cases quite comparable to the RISM counterpart.

Analytical second derivatives of the free energy in solution by the reference interaction site model self-consistent field explicitly including constrained spatial electron density distribution.

The application of analytical derivative methods to solution systems is important because several chemical reactions occur in solution. The reference interaction site model (RISM) is one of the solvation theories used to study solution systems and has shown good performance, especially in the polar solvent systems. Although the analytical first derivative based on the RISM coupled with quantum methods (RISM-SCF) has already been derived, the analytical second derivative has not been proposed yet. Therefore, in this study, the analytical second derivative was derived using RISM-SCF explicitly including constrained spatial electron density distribution (RISM-SCF-cSED). The performance of this method was validated with the Hessian calculations of formaldehyde and para-nitroaniline in solution, and the results demonstrated that the method accurately calculated frequency values at a small computational cost.

Analytical energy gradient for the second-order Møller-Plesset perturbation theory coupled with the reference interaction site model self-consistent field explicitly including spatial electron density distribution.

Solvatochromic shifts of the activation free energies are important aspects to consider for reaction control. To predict the energies, the stationary points in a solution must be accurately determined along the reaction pathway. In this study, the second-order Møller-Plesset perturbation (MP2) theory combined with the reference interaction site model was applied using our fitting approach, and the MP2 analytical energy gradient was determined. The coupled-cluster energy and thermal correction were calculated using the MP2 optimized geometry with solvent effect, and the activation free energies of the Diels-Alder reaction between cyclopentadiene and methyl vinyl ketone are within an error of 2 kcal/mol compared with the experimental data.

A Molecular Hybrid of an Atomically Precise Silver Nanocluster and Polyoxometalates for H2 Cleavage into Protons and Electrons.

Atomically precise silver (Ag) nanoclusters are promising materials as catalysts, photocatalysts, and sensors because of their unique structures and mixed-valence states (Ag+ /Ag0 ). However, their low stability hinders the in-depth study of their intrinsic reactivity and catalytic property accompanying their redox processes. Herein, we demonstrate that a molecular hybrid of an atomically precise {Ag27 }17+ nanocluster and polyoxometalates (POMs) can efficiently cleave H2 into protons and electrons. The Ag nanocluster accommodates electrons through the redox reaction from {Ag27 }17+ to {Ag27 }13+ , and the POM ligands play the following important roles: (i) a significant stabilization of the typically unstable Ag nanocluster to preserve its structure during the redox reaction with H2 , (ii) formation of a unique interface between the Ag nanocluster and metal oxides for efficient H2 cleavage, and (iii) storage of the generated protons on the negatively charged basic surface.

Alkyltriflones in the Ramberg-Bäcklund Reaction: An Efficient and Modular Synthesis of gem-Difluoroalkenes.

The unprecedented synthesis of gem-difluoroalkenes through the Ramberg-Bäcklund reaction of alkyl triflones is described herein. Structurally diverse, fully substituted gem-difluoroalkenes that are difficult to prepare by other methods can be easily prepared from readily available triflones by treatment with specific Grignard reagents. Experimental and computational studies provide insight into the unique and critical role of the Grignard reagent, which serves both as a base to remove the α-proton and as a Lewis acid to assist C-F bond activation.

σ-Bond Hydroboration of Cyclopropanes.

Hydroboration of alkenes is a classical reaction in organic synthesis in which alkenes react with boranes to give alkylboranes with subsequent oxidation resulting in alcohols. The double bond (π-bond) of alkenes can be readily reacted with boranes owing to its high reactivity. However, the single bond (σ-bond) of alkanes has never been reacted. To pursue the development of σ-bond cleavage, we selected cyclopropanes as model substrates since they present a relatively weak σ-bond. Herein, we describe an iridium-catalyzed hydroboration of cyclopropanes, resulting in ß-methyl alkylboronates. These unusually branched boronates can be derivatized by oxidation or cross-coupling chemistry, accessing "designer" products that are desired by practitioners of natural product synthesis and medicinal chemistry. Furthermore, mechanistic investigations and theoretical studies revealed the enabling role of the catalyst.

Chemical potentials of electric double layers at metal-electrolyte interfaces: dependence on electrolyte concentration and electrode materials, and application to field-effect transistors.

When a metal is soaked in an electrolyte solution, the metal and solution affect each other through the formation of electric double layers (EDLs) at their interfaces. The EDLs at metal-electrolyte interfaces can realize high-density charge-carrier injections and accumulations, and thus have recently attracted attention for their potential application to energy storage, and electronic and electrochemical devices. In such EDL-based devices, including field-effect transistors (FETs), the potential energy of surface electrons in the metal electrodes (EM) governs the transistor device performance. This is in clear contrast to redox-driven electrochemical devices such as dye-sensitized solar cells and electrochromic devices, whose performance is primarily governed by the potentials of the redox-active species. However, there has been no systematic research to bridge the distance between metal electrons and electrolyte ions. In the present study, we carefully examined the dependence of EM of ITO, Au and Pt electrodes on the concentration of the PEG solutions of LiCl and MgCl2, because it has been well established that the chemical potential of electrolyte solutions is dependent on the solution concentrations. Our results showed that, at the same electrolyte concentration, the values of EM increased in the order of ITO, Au and Pt; moreover, on the same electrode, EM showed linear decreases as a function of the logarithm of the electrolyte concentrations. To understand these behaviors, we developed a theoretical treatment of the EDLs based on the simple Gouy-Chapman model, and obtained the theoretical expressions of EM in terms of the concentration of electrolyte and the work function of the metal electrode (ΦM), which were found to successfully explain the dependences of EM on the electrolyte concentration and the electrode materials. We also examined the EDL-FETs of platinum phthalocyanine (PtPc), with various LiCl-PEG solutions of different concentrations as gate electrolytes. The threshold voltage eVT and EM exhibited a linear relation, which was well explained by the relation between EM and the valence band energy EVB of PtPc. The transfer characteristics at various gate voltage VG were found to be well normalized by a function of eVG + EM.

Electrostatic Potential Fitting Method Using Constrained Spatial Electron Density Expanded with Preorthogonal Natural Atomic Orbitals.

In this study, an electrostatic potential (ESP) fitting method using constrained spatial electron density (cSED) expanded with preorthogonal natural atomic orbitals (pNAOs) was proposed. In this method, the electron density of a molecule is divided into spherical atom-centered electron densities and the expansion coefficient is determined to reproduce the ESP around the molecule. Our method was then applied to two systems: (i) a hydration reaction of cis-platin and (ii) a variety of organic/inorganic molecules. By evaluating the atomic charges along the hydration reaction, our method showed good conformational transferability, which cannot be obtained using conventional ESP fitting methods. Moreover, we successfully obtained the hydration structure along the reaction by coupling our method with a reference interaction site model (RISM). Reasonable data were obtained not only for organic molecules but also for inorganic molecules. This success came from the introduction of pNAOs as auxiliary basis sets in the charge fitting.

Nuclear magnetic shielding of molecule in solution based on reference interaction site model self-consistent field with spatial electron density distribution.

A new method for calculating nuclear magnetic shielding in solutions is developed based on the reference interaction site model self-consistent field (RISM-SCF) with spatial electron density distribution (SEDD). In RISM-SCF-SEDD, the electrostatic interaction between the solute and the solvent is described by considering the spread of electron to obtain more realistic electronic structure in solutions. It is thus expected to allow us to predict more quantitative chemical shifts of a wide variety of chemical species in solutions. In this study, the method is applied to a water molecule in water and is validated by examining the dependence of the solvent temperature and density on chemical shifts. The dependence of solvent species is also investigated, and more accurate results are obtained for polar solvents compared to the previous RISM-SCF study. Another application example of this method is the 15N chemical shifts of two azines in water, which is difficult to predict with the polarizable continuum model (PCM). Our results are in good agreement with the previous quantum mechanical/molecular mechanics study and experimental results. It is also shown that our method gives more realistic results for methanol and acetone than the PCM.

An Ultrastable, Small {Ag7 }5+ Nanocluster within a Triangular Hollow Polyoxometalate Framework.

Small Agn nanoclusters (n<10) have been emerging as promising materials as sensing, biolabeling, and catalysis because of their unique electronic states and optical properties. However, studying synthesis, structure determination, and exploration of their properties remain major challenges as a result of the low stability of small Ag nanoclusters. Herein, we synthesized an atomically precise face-centered-cubic-type small {Ag7 }5+ nanocluster supported by a novel triangular hollow polyoxometalate (POM) framework [Si3 W27 O96 ]18- . The cluster showed unique {Ag7 }5+ -to-POM charge transfer bands in both visible and UV light regions. Furthermore, this small {Ag7 }5+ nanocluster exhibited an unprecedented ultrastability in solution, despite having exposed Ag sites that can be accessed by small molecules, such as O2 , water, and solvents.

Unveiling Latent Photoreactivity of Imines.

Unlike carbonyl compounds, it has long been common understanding that excited imines show virtually no photoreactivity, and hence their properties and potential utility in chemical science remain largely unexplored. Now, a strategy is presented for eliciting latent photoreactivity of imines based on the introduction of a donor-acceptor (D-A) structure to extend the lifetime of their photoexcited states. A series of spectroscopic analyses and density functional theory calculations reveal unique photophysical properties of the D-A-type imines. Furthermore, the reactivity of the D-A-type imines is demonstrated by using them as a photoredox catalyst for atom-transfer radical addition. These findings illuminate a previously neglected chemical space in the field of photochemistry, which will be exploited by taking advantage of the inherent structural modularity of imines.

Controlled Assembly Synthesis of Atomically Precise Ultrastable Silver Nanoclusters with Polyoxometalates.

Silver nanoclusters have attracted scientific interest due to their properties and applications. However, practical synthetic methods to access these materials are still limited mainly due to the low stability. Here, we report a controlled assembly strategy for fabricating atomically precise silver nanoclusters using polyoxometalates (POMs) as structure-directing as well as functionalizing units. A trefoil-propeller-shaped {Ag27}17+ nanocluster was synthesized by assembling reactive nanoclusters supported by open-Dawson-type POMs [Si2W18O66]16-. The {Ag27}17+ nanocluster possessed 10 delocalized valence electrons and showed unprecedented ultrastability in solutions. The cluster showed unique {Ag27}-to-POM charge transfer bands in the visible light region.

Theoretical Elucidation of Potential Enantioselectivity in a Pd-Catalyzed Aromatic C-H Coupling Reaction.

The mechanism of an aromatic C-H coupling reaction between heteroarenes and arylboronic acids using a Pd catalyst was theoretically and experimentally investigated. We identified the C-B transmetalation as the rate-determining step. The (S)-catalyst-reactant complex was found to be stabilized by hyperconjugation between π-orbitals on the tolyl group and the S-O σ* antibonding orbital in the catalyst ligand. Our findings suggest routes for the design of new, improved Pd catalysts with higher stereoselectivity.