Vibrational Self-Consistent Field (VSCF) and Post-VSCF Method Calculations Combined with the Reference Interaction Site Model Self-Consistent Field Method Coupled with the Constrained Spatial Electron Density Distribution: Applications to NaHCOO in Aqueous Phase.

Investigating vibrational behavior in solution is crucial for understanding molecular dynamics within a solvent environment. Notably, the analysis of Raman spectra for molecules in solution is important owing to its ability to unveil intricate solute-solvent interactions. Previous studies have effectively employed frequency calculations utilizing the reference interaction site model self-consistent field method in conjunction with constrained spatial electron density distribution (RISM-SCF-cSED) to understand molecular vibrations in solution, primarily focusing on fundamental vibrational modes. However, the oversight of overtones and combination tones in these studies prompted us to combine the vibrational self-consistent field (VSCF) and vibrational second-order MoÌ·ller-Plesset perturbation (VMP2) methods with RISM-SCF-cSED to address these aspects theoretically. Illustrating the efficacy of this integrated approach, we computed the Raman spectra of sodium formate (NaHCOO) in water, revealing the necessity of accounting for molecular anharmonicity in solution vibrational analysis. Our findings underscore the potency of VSCF and VMP2 in conjunction with RISM-SCF-cSED as a robust theoretical framework for such calculations.

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.

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.

Theoretical Study of Raman Intensities of p-Nitroaniline in Different Solvent Conditions by Using a Reference Interaction Site Model Self-Consistent Field Explicitly Including Constrained Spatial Electron Density Distribution.

Raman spectroscopy is one of the most powerful tools to understand and characterize the states and structures of systems in several environments. To obtain highly accurate changes in Raman intensities of systems in solution, theoretical treatment, which can deal with not only the states and structures of systems but also the environment around molecules, proves to be significant. Hence, in this study, we developed the calculation of changes in Raman intensities of systems in different solvent conditions by using the reference interaction site model self-consistent field study explicitly including constrained spatial electron density distribution; this model is designed based on elements from both quantum mechanics and statistical mechanics. We showed that our calculation method could reproduce the changes in Raman intensities of p-nitroaniline (pNA) under different solvent conditions, including supercritical water, which has been observed in previous experimental studies. Based on the analysis of the calculation results, we observed that the ratio of the Raman intensity change of pNA in different solvent conditions is strongly correlated with the charge-transfer character of pNA.

Description of Solvatochromism of Peak Broadening in Absorption Spectra in Solution Using the Reference Interaction Site Model Self-Consistent Fields Spatial Electron Density Distribution.

We quantified and subsequently analyzed bandwidth of ultraviolet and visible photoabsorption spectral lines in solution by applying time-dependent first-order perturbation theory using the Born-Oppenheimer adiabatic potential calculated using the multistate extended-multi-configurational quasi-degenerated second-order perturbation theory (MS-XMCQDPT2) coupled with the reference interaction site model self-consistent field spatial electron density distribution (RISM-SCF-cSED). The proposed method was implemented for 2-thiocytosine in solution, and solvatochromism of the bandwidth of the πSπ* transition was clearly observed. The standard deviation of a characteristic electronic excitation was decomposed into the contributions of the characteristic vibrational mode of 2-thiocytosine. The main vibrational modes contributing to peak broadening were found to be for acetonitrile, methanol, and the aqueous phase. We concluded that the mechanism for peak broadening is qualitatively different for phases of protic and aprotic solvents because of the structural variation in 2-thiocytosine driven by the breakage of the resonance structures.

Interpretable Attribution Assignment for Octanol-Water Partition Coefficient.

With the increasing development of machine learning models, their credibility has become an important issue. In chemistry, attribution assignment is gaining relevance when it comes to designing molecules and debugging models. However, attention has only been paid to which atoms are important in the prediction and not to whether the attribution is reasonable. In this study, we developed a graph neural network model, a highly interpretable attribution model in chemistry, and modified the integrated gradients method. The credibility of our approach was confirmed by predicting the octanol-water partition coefficient (logP) and evaluating the three metrics (accuracy, consistency, and stability) in the attribution assignment.

Surface-exposed silver nanoclusters inside molecular metal oxide cavities.

The surfaces of metal nanoclusters, including their interface with metal oxides, exhibit a high reactivity that is attractive for practical purposes. This high reactivity, however, has also hindered the synthesis of structurally well-defined hybrids of metal nanoclusters and metal oxides with exposed surfaces and/or interfaces. Here we report the sequential synthesis of structurally well-defined {Ag30} nanoclusters in the cavity of ring-shaped molecular metal oxides known as polyoxometalates. The {Ag30} nanoclusters possess exposed silver surfaces yet are stabilized both in solution and the solid state by the surrounding ring-shaped polyoxometalate species. The clusters underwent a redox-induced structural transformation without undesirable agglomeration or decomposition. Furthermore, {Ag30} nanoclusters showed high catalytic activity for the selective reduction of several organic functional groups using H2 under mild reaction conditions. We believe that these findings will serve for the discrete synthesis of surface-exposed metal nanoclusters stabilized by molecular metal oxides, which may in turn find applications in, for example, the fields of catalysis and energy conversion.

Theoretical Understanding of the Nonlinear Raman Shift of C≡N Stretching Vibration of p-Aminobenzonitrile in Supercritical Water.

Subcritical and supercritical fluids (SCF) have attracted significant attention in the past few decades because of their unique properties. In a previous study, a nonlinear Raman shift of the C≡N stretching vibration of p-aminobenzonitrile (p-ABN) with respect to the supercritical water (SCW) density was observed [K. Osawa et al., J. Phys. Chem. A 2009, 113, 3143-3154]. Although a plausible mechanism of the nonlinear Raman shift was proposed in the study, the discussion at the atomistic level was inadequate. To elucidate the nonlinear Raman shift mechanism of the C≡N stretching vibration of p-ABN in SCW from a theoretical viewpoint, we employed RISM-SCF-cSED, which is the hybrid method between quantum mechanics and statistical mechanics. We discovered that the hydrogen-bonding effect is dominant at low- and middle-density regions, while the packing effect is dominant at the high-density region. The balances of these effects determine the Raman shift of p-ABN in SCF.

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.

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.

Spin-Orbit Coupling Calculation Combined with the Reference Interaction Site Model Self-Consistent Field Explicitly Including Constrained Spatial Electron Density Distribution.

Studying the radiative and non-radiative decay processes of molecules in a solution is an important issue in the design of organic and functional molecules. Theoretical approaches have great potential for revealing this decay process through computation of various parameters, such as the energy surfaces at the excited state and spin-orbit coupling (SOC). The development of quantum chemical programs has enabled the calculation of SOC values to become popular for the gas phase. However, SOC calculations in solution have some difficulties that need to be overcome. In the present study, the authors combined the SOC calculations with the reference interaction site model self-consistent field explicitly including constrained spatial electron density distribution. To validate the reliability of our method, the decay process of dimethylaminobenzonitrile in cyclohexane and acetonitrile was studied. By computing the SOC values in both solution systems, the authors were able to investigate the decay process at the atomistic level. Furthermore, a natural transition orbital analysis and the measurement of the decomposed SOC values were found to provide a clear understanding of intersystem crossing.

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.

Variable control of the electronic states of a silver nanocluster via protonation/deprotonation of polyoxometalate ligands.

The properties of metal nanoclusters depend on both their structures and electronic states. However, in contrast to the significant advances achieved in the synthesis of structurally well-defined metal nanoclusters, systematic control of their electronic states is still challenging. In particular, stimuli-responsive and reversible control of the electronic states of metal nanoclusters is attractive from the viewpoint of their practical applications. Recently, we developed a synthesis method for atomically precise Ag nanoclusters using polyoxometalates (POMs) as inorganic ligands. Herein, we exploited the acid/base nature of POMs to reversibly change the electronic states of an atomically precise {Ag27} nanocluster via protonation/deprotonation of the surrounding POM ligands. We succeeded in systematically controlling the electronic states of the {Ag27} nanocluster by adding an acid or a base (0-6 equivalents), which was accompanied by drastic changes in the ultraviolet-visible absorption spectra of the nanocluster solutions. These results demonstrate the great potential of Ag nanoclusters for unprecedented applications in various fields such as sensing, biolabeling, electronics, and catalysis.

Basicity of isostructural porous ionic crystals composed of Nb/Ta-substituted Keggin-type polyoxotungstates.

Three isostructural porous ionic crystals (PICs) based on Keggin-type POMs with different compositions but equal negative charge ([BW12O40]5- (BW12), [SiW11NbO40]5- (SiW11Nb), and [SiW11TaO40]5- (SiW11Ta)) are synthesized. Experimental and theoretical characterizations of the three PICs (1_BW12, 1_SiW11Nb, and 1_SiW11Ta) show that the substitution of Nb/Ta for W in the POMs enhances the basicity of PICs, which increases in the order of 1_BW12 < 1_SiW11Nb < 1_SiW11Ta. These findings clearly show that the increase in basicity is due not only to the increase in negative charge of the POM molecule as is often explained, but also to the character of the substituted element itself.

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.

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.

Synthesis of quaternary centres by single electron reduction and alkylation of alkylsulfones.

A new method for the generation of tertiary radicals through single electron reduction of alkylsulfones promoted by Zn and 1,10-phenanthroline has been developed. These radicals could be employed in the Giese reaction, affording structurally diverse quaternary products in good yields. With the high modularity and functional group compatibility of sulfones, the utility of this method was demonstrated by intramolecular and iterative reactions to give complex structures. The radical generation process was investigated by control experiments and theoretical calculations.

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.

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.