2-Aryl-3H-1,3-Benzazaphosphole Oxides: Synthesis, Optical Properties, and Excited State Intramolecular Proton Transfer.

Inclusion of a heteroatom to the phosphole ring is a promising strategy to intrinsically modulate the optical properties of phosphole derivatives. We report on a series of 2-aryl-3H-1,3-benzazaphosphole oxides that were efficiently prepared via sequential C-P cross-coupling, dehydrative [3+2] cycloaddition, and ring-oxidation reactions. The inclusion of one nitrogen atom into the benzophosphole framework caused red shifting of the absorption and emission maxima, reflecting the greater stabilization of the LUMO level. 2-(2-Hydroxyphenyl)benzazaphosphole oxide underwent excited state intramolecular proton transfer and emitted a weak fluorescence from the excited state of the N-H tautomer.

Generalized Foldy-Wouthuysen transformation for relativistic two-component methods: Systematic analysis of two-component Hamiltonians.

The generalized Foldy-Wouthuysen (GFW) transformation was proposed as a generic form that unifies four types of transformations in relativistic two-component methods: unnormalized GFW(UN), and normalized form 1, form 2, and form 3 (GFW(N1), GFW(N2), and GFW(N3)). The GFW transformation covers a wide range of transformations beyond the simple unitary transformation of the Dirac Hamiltonian, allowing for the systematic classification of all existing two-component methods. New two-component methods were also systematically derived based on the GFW transformation. These various two-component methods were applied to hydrogen-like and helium-like ions. Numerical errors in energy were evaluated and classified into four types: the one-electron Hamiltonian approximation, the two-electron operator approximation, the newly defined "picture difference error (PDE)," and the error in determining the transformation, and errors in multi-electron systems were discussed based on this classification.

Theoretical examination of QED Hamiltonian in relativistic molecular orbital theory.

Theoretical discussions are given on issues in relativistic molecular orbital theory to which the quantum electrodynamics (QED) Hamiltonian is applied. First, several QED Hamiltonians previously proposed are sifted by the orbital rotation invariance, the charge conjugation and time reversal invariance, and the nonrelativistic limit. The discussion on orbital rotation invariance shows that orbitals giving a stationary point of total energy should be adopted for QED Hamiltonians that are not orbital rotation invariant. A new total energy expression is then proposed, in which a counter term corresponding to the energy of the polarized vacuum is subtracted from the total energy. This expression prevents the possibility of total energy divergence due to electron correlations, stemming from the fact that the QED Hamiltonian does not conserve the number of particles. Finally, based on the Hamiltonian and energy expression, the Dirac-Hartree-Fock (DHF) and electron correlation methods are reintroduced. The QED-based DHF equation is shown to give information on positrons from negative-energy orbitals while having the same form as the conventional DHF equation. Three electron correlation methods are derived: the QED-based configuration interactions and single- and multireference perturbation methods. Numerical calculations show that the total energy of the QED Hamiltonian indeed diverged and that the counter term is effective in avoiding the divergence. The relativistic molecular orbital theory presented in this article also provides a methodology for dealing with systems containing positrons based on the QED Hamiltonian.

Synthesis, Structure, and Redox and Optical Properties of 5,10,15,20-Tetraaryl-5-azaporphyrinium Salts.

The fundamental properties of azaporphyrins can be modulated over a wide range by changing the number of meso-nitrogen atoms. Reported herein are the first examples of 5,10,15,20-tetraaryl-5-azaporphyrinium (MTAMAP) salts, which were prepared via metal-templated cyclization of the corresponding zinc(II) and copper(II) complexes of 10-aryl-1-chloro-19-benzoyl-5,15-dimesityl-10-azabiladiene-ac. The inclusion of one meso-nitrogen atom in the 5,10,15,20-tetraarylporphyrin skeleton considerably changes the redox and optical properties as well as the degree of aromaticity of the porphyrin ring. The present findings suggest that MTAMAP salts would be promising scaffolds for the development of new azaporphyrin-based ionic fluorophores and photosensitizers.

Theoretical Analysis of the Role of Water in Ligand Binding to Cucurbit[n]uril of Different Sizes.

The role of water in host-ligand binding was investigated using a combination of molecular dynamics simulation and three-dimensional reference interaction site model theory. Three different hosts were selected (CB6, CB7, and CB8). Six organic molecules were used as representative ligands: dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), acetone, 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO), cyclopentanone (CPN), and pyrrole. From the binding free energy and its components, we divided the ligands into two groups: those with relatively small molecular size (DMSO, DMF, acetone, and pyrrole) and those with relatively large molecular size (DBO and CPN). We established that the solvent water in the CB6 cavity can be completely displaced by small ligands, resulting in a greater binding affinity compared with larger CBs, except in the case of the small pyrrole ligand, due to outstanding intrinsic properties such as the relatively high hydrophobicity and low dipole moment. In the case of the large ligands, the solvent water can be displaced by DBO and CPN in both CB6 and CB7; there were similar tendencies in their binding affinities, with the greatest affinity in the CB7 complexes. However, the tendencies of the binding affinity components are completely different due to the difference between the complex structure and the solvation structure when a ligand binds with a CB structure. The binding affinities suggest that the size fit between the ligand and CB cannot guarantee the greatest binding affinity gain because the binding structure and intrinsic properties of CB and ligand equally play a crucial role.

Solvent effects in four-component relativistic electronic structure theory based on the reference interaction-site model.

A combined method of the Dirac-Hartree-Fock (DHF) method and the reference interaction-site model (RISM) theory is reported; this is the initial implementation of the coupling of the four-component relativistic electronic structure theory and an integral equation theory of molecular liquids. In the method, the DHF and RISM equations are solved self-consistently, and therefore the electronic structure of the solute, including relativistic effects, and the solvation structure are determined simultaneously. The formulation is constructed based on the variational principle with respect to the Helmholtz energy, and analytic free energy gradients are also derived using the variational property. The method is applied to the iodine ion (I- ), methyl iodide (CH3 I), and hydrogen chalcogenide (H2 X, where X = O-Po) in aqueous solutions, and the electronic structures of the solutes, as well as the solvation free energies and their component analysis, solvent distributions, and solute-solvent interactions, are discussed.

Computational Analysis of the SARS-CoV-2 RBD-ACE2-Binding Process Based on MD and the 3D-RISM Theory.

The binding process of angiotensin-converting enzyme 2 (ACE2) to the receptor-binding domain (RBD) of the severe acute respiratory syndrome-like coronavirus 2 spike protein was investigated using molecular dynamics simulation and the three-dimensional reference interaction-site model theory. The results suggested that the protein-binding process consists of a protein-protein approaching step, followed by a local structural rearrangement step. In the approaching step, the interprotein interaction energy decreased as the proteins approached each other, whereas the solvation free energy increased. As the proteins approached, the glycan of ACE2 first established a hydrogen bond with the RBD. Thereafter, the number of interprotein hydrogen bonds increased rapidly. The solvation free energy increased because of the desolvation of the protein as it approached its partner. The spatial distribution function of the solvent revealed the presence of hydrogen bonds bridged by water molecules on the RBD-ACE2 interface. Finally, principal component analysis revealed that ACE2 showed a pronounced conformational change, whereas there was no significant change in RBD.

Synthesis, Optical Properties, and Electrochemical Behavior of 5,10,15,20-Tetraaryl-5,15-diazaporphyrin-Amine Hybrids.

This work reports a series of covalently linked hybrids comprising 5,10,15,20-tetraaryl-5,15-diazaporphyrinoids (M-TADAP; M = Ni, Zn, Cu) and amines. M-TADAP-amine hybrids were prepared via the metal-templated cyclization of the corresponding metal(II)-dipyrrin complexes and redox reactions on the DAP unit. In the UV/vis/near-IR absorption spectra of the hybrids containing an 18π-electron DAP ring, broad charge-transfer bands were observed, reflecting the electron-donating property of the para-aminophenyl groups and the electron-accepting property of the 18π TADAP dication. The electrochemical behavior of the M-TADAP-amine hybrids was strongly dependent on the structure of the peripheral amine units. Further electrochemical oxidation of the hybrids bearing N-Ph groups conceivably generated amine-centered radicals, which sequentially underwent irreversible coupling to form benzidine-linked M-TADAP polymer films. The Ni-TADAP-benzidine polymer exhibited the electric conductivity of 1×10-3  S m-1 .

Doubly Strapped Redox-Switchable 5,10,15,20-Tetraaryl-5,15-diazaporphyrinoids: Promising Platforms for the Evaluation of Paratropic and Diatropic Ring-Current Effects.

This paper presents a novel series of chemically stable and redox-switchable 20π, 19π, and 18π 5,10,15,20-tetraaryl-5,15-diazaporphyrinoids (TADAPs) that have two alkyl-chain straps above and below the diazaporphyrin ring. Three types of doubly strapped TADAPs were prepared as nickel(II) complexes using meso-N-(2,6-dihydroxyphenyl)-substituted TADAP and the corresponding aliphatic diacids as precursors. Theoretical calculations revealed that regardless of their oxidation states, all strapped TADAPs had essentially flat π-planes. It was found that the alkyl-chain straps slightly affected the optical and electrochemical properties of the DAP rings, particularly in the oxidized forms. 1H NMR spectroscopy was used to evaluate the antiaromatic character of the 20π TADAPs and the aromatic character of the 18π TADAP dications, and it was observed that they displayed paratropic and diatropic ring-current effects, respectively, on the chemical shifts of methylene protons in the spatially separated alkyl chains. The degree of shielding and deshielding depended on the position of the methylene units; it decreased with increase in separation from the π-plane and central axis of the porphyrin ring. The NMR experiments also revealed that the degree of the diatropic ring currents was clearly related to the π-electron density of the porphyrin ring; the ring-current effects decreased as the charge increased from 0 to +2. These findings are also qualitatively supported by the nucleus-independent chemical shifts.

A computational method to simulate global conformational changes of proteins induced by cosolvent.

A computational method to investigate the global conformational change of a protein is proposed by combining the linear response path following (LRPF) method and three-dimensional reference interaction site model (3D-RISM) theory, which is referred to as the LRPF/3D-RISM method. The proposed method makes it possible to efficiently simulate protein conformational changes caused by either solutions of varying concentrations or the presence of cosolvent species by taking advantage of the LRPF and 3D-RISM. The proposed method is applied to the urea-induced denaturation of ubiquitin. The LRPF/3D-RISM trajectories successfully simulate the early stage of the denaturation process within the simulation time of 300 ns, whereas no significant structural change is observed even in the 1 µs standard MD simulation. The obtained LRPF/3D-RISM trajectories reproduce the mechanism of the urea denaturation of ubiquitin reported in previous studies, and demonstrate the high efficiency of the method.

Distinct ionic adsorption sites in defective Prussian blue: a 3D-RISM study.

Ferric hexacyanoferrate (FeHCF) or Prussian blue (PB) exhibits selective alkali ion adsorption and has great potential for use in various applications. In the present work, alkali ion (Li+, Na+, K+, and Cs+) and water configurations in defective PB (d-PB) were studied by using the statistical mechanics of molecular liquids. The three-dimensional (3D) distribution functions of the ions and water were determined by solving the 3D-reference interaction site model (RISM) equation of systems of a unit lattice of d-PB in electrolyte solutions, i.e., LiCl, NaCl, KCl, and CsCl. The results show the difference in the ion-water configurations and distributions between small (Li+ and Na+) and large ions (K+ and Cs+). The adsorption sites of Li+ and Na+ are located off-center and lie on the diagonal axis. By contrast, the larger ions, K+ and Cs+, are adsorbed at the center of the unit cell. The degree of dehydration due to the adsorption of alkali ions indicates that there was no water exchange during Li+ and Na+ adsorption, whereas two and three water molecules were removed after adsorption of K+ or Cs+ in the unit cell.

Effect of Molecular Orientational Correlations on Solvation Free Energy Computed by Reference Interaction Site Model Theory.

The effect of molecular orientational correlations on the solvation free energy (SFE) of one-dimensional and three-dimensional reference interaction site models (1D- and 3D-RISM) is investigated. The repulsive bridge correction (RBC) and the partial wave (PW) expansion are representative approaches for accounting for the orientational correlation partially lacking in original 1D- and 3D-RISM. The SFEs of 1D- and 3D-RISM for a set of small organic molecules are compared with the simulation results. Accordingly, the SFE expressions, based on RBC and PW, provide more accurate results than those of the uncorrected HNC or KH SFE expressions, which indicates that accounting for molecular orientational dependencies significantly contributes to the improvement of the SFE. The SFE component analysis indicates that the nonpolar component mainly contributes to the correction. The dependence of the error in the RISM SFE on the number of solute sites is examined. In addition, we discuss the differences between 1D- and 3D-RISM through the effect of these corrections.

Three-Dimensional Reference Interaction Site Model Self-Consistent Field Study on the Coordination Structure and Excitation Spectra of Cu(II)-Water Complexes in Aqueous Solution.

The molecular and solvation structures of the hydrated Cu2+ ions and their excitation spectra were investigated using the Kohn-Sham density functional theory (DFT) and the three-dimensional reference interaction site model (3D-RISM) self-consistent field method. Five stable geometrical structures were found to exist in aqueous solution: the distorted octahedral [Cu(H2O)6]2+ in C i and D2 h symmetries, the square pyramidal and trigonal bipyramidal [Cu(H2O)5]2+, and the square planar [Cu(H2O)4]2+. The distorted octahedral structure in the C i symmetry is preferred in [Cu(H2O)6]2+, and the square pyramidal and trigonal bipyramidal [Cu(H2O)5]2+ show almost the same stability. Among these geometries, the six-coordinate complex [Cu(H2O)6]2+ in the C i symmetry had the lowest Helmholtz energy. [Cu(H2O)6]2+ had a distorted octahedral structure, that is, two long axial bonds and four short equatorial bonds. The spatial and radial distribution function analyses for [Cu(H2O)5]2+ and [Cu(H2O)4]2+ showed that [Cu(H2O)5]2+ and [Cu(H2O)4]2+ had one and two solvent water molecules that constituted a distorted octahedron with ligand water distribution. The coordination numbers (CNs) derived from the distribution functions were 5.2-5.4 for [Cu(H2O)5]2+ and 5.3 for [Cu(H2O)4]2+. These results indicated that the Cu2+ ion in an aqueous solution had 5-6 coordination water molecules in the first hydration shell and some structures with different CNs may interchange in the solution. The excitation energies and electronic configurations of low-lying d-d excited states were calculated using the time-dependent DFT with the electric field generated by 3D-RISM. The orbital energies and electronic configurations were in a similar picture to those of the classical crystal field theory because of the highly symmetrical features of all structures. In [Cu(H2O)6]2+, the degeneracies of orbitals were resolved, whereas in [Cu(H2O)5]2+ and [Cu(H2O)4]2+, weak and strong quasi-degeneracies remained. As a result, only the four-coordinate complex generated third and fourth excited states, whereas in other complexes, there were no obvious characters of degeneracies. The resulting excitation energies were in good agreement with the absorption spectra.

A computational scheme of pKa values based on the three-dimensional reference interaction site model self-consistent field theory coupled with the linear fitting correction scheme.

A scheme for quantitatively computing the acid dissociation constant, pKa, of hydrated molecules is proposed. It is based on the three-dimensional reference interaction site model self-consistent field (3D-RISM-SCF) theory coupled with the linear fitting correction (LFC) scheme. In LFC/3D-RISM-SCF, pKa values of target molecules are evaluated using the Gibbs energy difference between the protonated and unprotonated states calculated by 3D-RISM-SCF and the parameters fitted by the LFC scheme to the experimental values of training set systems. The pKa values computed by LFC/3D-RISM-SCF show quantitative agreement with the experimental data.

Direct and Regioselective Amination of ß-Unsubstituted 5,15-Diazaporphyrins with Amines: A Convenient Route to Near-Infrared-Responsive Diazaporphyrin Sensitizers.

We have established a convenient method for the base-promoted direct amination of ß-unsubstituted 5,15-diazaporphyrins (DAPs) with secondary and primary amines to produce 3,7,13,17-tetraamino- and 3-amino-DAPs, respectively, regioselectively. The amino groups attached at the periphery cause significant red shifts of the absorption bands as a result of their perturbation of the HOMO and/or LUMO in the DAP π-system. The palladium complex of a 3,7,13,17-tetrakis(diphenylamino)-DAP generated singlet oxygen in high yield under irradiation with near-infrared light.

Syntheses, Properties, and Catalytic Activities of Metal(II) Complexes and Free Bases of Redox-Switchable 20π, 19π, and 18π 5,10,15,20-Tetraaryl-5,15-diazaporphyrinoids.

In spite of significant advances in redox-active porphyrin-based materials and catalysts, little attention has been paid to 20π and 19π porphyrins because of their instability in air. Here we report the meso-modification of 5,10,15,20-tetraarylporphyrin with two nitrogen atoms, which led to redox-switchable 20π, 19π, and 18π 5,10,15,20-tetraaryl-5,15-diazaporphyrinoids (TADAPs). Three kinds of metal(II) complexes and free bases of TADAP were prepared by the metal-templated annulation of the corresponding metal-bis(dipyrrin) complexes. The inductive and resonance effects of the meso-nitrogen atoms on the aromatic, optical, electrochemical, and magnetic properties of the entire TADAP π-systems were assessed by using various spectroscopic measurements and density functional theory calculations. The aromaticity and π-π* electronic transition energies of the TADAPs varied considerably, and were shown to be dependent on the oxidation states of the π-systems. In contrast to the isoelectronic 5,10,15,20-tetraarylporphyrin derivatives, the 20π and 19π TADAPs were chemically stable under air. In particular, the 19π TADAP radical cations were extremely stable towards dioxygen, moisture, and silica gel. This reflected the low-lying singly occupied molecular orbitals of their π-systems and the efficient delocalization of their unshared electron spin. The capability of MgTADAP to catalyze aerobic biaryl formation from aryl Grignard reagents was demonstrated, which presumably involved a 19π/20π redox cycle.

Solvatochromism and preferential solvation of Brooker's merocyanine in water-methanol mixtures.

The excitation energy of Brooker's merocyanine in water-methanol mixtures shows nonlinear behavior with respect to the mole fraction of methanol, and it was suggested that this behavior is related to preferential solvation by methanol. We investigated the origin of this behavior and its relation to preferential solvation using the three-dimensional reference interaction site model self-consistent field method and time-dependent density functional theory. The calculated excitation energies were in good agreement with the experimental behavior. Analysis of the coordination numbers revealed preferential solvation by methanol. The free energy component analysis implied that solvent reorganization and solvation entropy drive the preferential solvation by methanol, while the direct solute-solvent interaction promotes solvation by water. The difference in the preferential solvation effect on the ground and excited states causes the nonlinear excitation energy shift. © 2017 Wiley Periodicals, Inc.

Nitrogen-Bridged Metallodiazaporphyrin Dimers: Synergistic Effects of Nitrogen Bridges and meso-Nitrogen Atoms on Structure and Properties.

NH-bridged and pyrazine-fused metallodiazaporphyrin dimers have been prepared from nickel(II) and copper(II) complexes of 3-amino-5,15-diazaporphyrin by Pd-catalyzed C-N cross-coupling and oxidative dimerization reactions, respectively. The synergistic effects of the nitrogen bridges and meso-nitrogen atoms play major roles in enhancing the light-harvesting properties and delocalization of an electron spin over the entire π-skeletons of the metallodiazaporphyrin dimers.

Unsymmetrically Substituted Donor-π-Acceptor-Type 5,15-Diazaporphyrin Sensitizers: Synthesis, Optical and Photovoltaic Properties.

The first examples of unsymmetrical ß-substituted donor-π-acceptor (D-π-A)-type 5,15-diazaporphyrin (DAP) sensitizers with both p-aminophenyl and p-carboxyphenyl groups at their peripheral 3-, 7-, 13-, and/or 17-positions have been synthesized for use in dye-sensitized solar cells (DSSCs). UV/Vis absorption and emission spectroscopy, electrochemical measurements, and DFT calculations revealed that these D-π-A dyes exhibit high light-harvesting properties over the whole visible range because of the intrinsic charge-transfer character of their electronic transitions. The cell performances of TiO2 -based DSSCs fabricated with the newly prepared DAP derivatives were evaluated under standard AM1.5 conditions. Among the four dyes examined, 13,17-bis(p-carboxyphenyl)-3,7-bis[p-(N,N-dimethylamino)phenyl]-DAP showed the highest power conversion efficiency (2.0 %), which was 20 times larger than that obtained with 3-(p-carboxyphenyl)-DAP. These results show that the DAP chromophore could be used as the electron-accepting π unit in various types of functional dyes.