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The impact of the electronic effect of the carbazole group on the radiative decay process based on the intramolecular charge transfer (ICT) transition of closo-o-carborane was examined herein. Four...

Molecular dynamics (MD) simulations with the umbrella sampling (US) method were used to investigate the properties of micelles formed by sodium lauryl ether sulfate with two ether groups (SLE2S) and behaviors of corresponding surfactants transferring from micelles to ceramide and DMPC bilayer surfaces. Average micelle radii based on the Einstein-Smoluchowski and Stokes-Einstein relations showed excellent agreement with those measured by dynamic light scattering, while those obtained by evaluating the gyration radius or calculating the distance between the micelle sulfur atoms and center of mass overestimate the radii. As an SLE2S micelle was pulled down to the ceramide bilayer surface in a 400 ns constant-force steered MD (cf-SMD) simulation, the micelle was partially deformed on the bilayer surface, and several SLE2S surfactants easily were partitioned from the micelle into the ceramide bilayer. In contrast, a micelle was not deformed on the DMPC bilayer surface, and SLE2S surfactants were not transferred from the micelle to the DMPC bilayer. Potential of mean force (PMF) calculations revealed that the Gibbs free energy required for an SLE2S surfactant monomer to transfer from a micelle to bulk water can be compensated by decreased Gibbs free energy when an SLE2S monomer transfers into the ceramide bilayer from bulk water. In addition, micelle deformation on the ceramide bilayer surface can reduce the Gibbs free energy barrier required for a surfactant to escape the micelle and help the surfactant partition from the micelle into the ceramide bilayer. An SLE2S surfactant partitioning into the ceramide bilayer is attributed to hydrogen bonding and favorable interactions between the hydrophilic surfactant head and ceramide molecules, which are more dominant than the dehydration penalty during bilayer insertion. Such interactions between surfactant and lipid molecule heads are considerably reduced in DMPC bilayers owing to dielectric screening by water molecules deep inside the head/tail boundary between the DMPC bilayer. This computational work demonstrates the distinct behavior of SLE2S surfactant micelles on ceramide and DMPC bilayer surfaces in terms of variation in Gibbs free energy, which offers insight into designing surfactants used in transdermal drug delivery systems and cosmetics.

An efficient transition-metal-free protocol for the hydroboration of aldehydes and ketones (reduction) was developed. The hydroboration of a wide range of aldehydes and ketones with pinacolborane (HBpin) under the K2CO3 catalyst has been studied. The reaction system is practical and reliable and proceeds under extremely mild and operationally simple conditions. No prior preparation of the complex metal catalyst was required, and hydroboration occurred stoichiometrically. Further, the chemoselective reduction of aldehydes over ketones was carried out. Moreover, we demonstrated the use of K2CO3 as an efficient catalyst for the hydroboration of alkenes. The operational simplicity, inexpensive and transition-metal-free catalyst, and the applicability to gram-scale synthesis strengthen its potential applications for hydroboration (reduction) at an industrial scale.

An approach to the design of a series of quinolinol-based indium complexes that can exhibit different optical properties is proposed. Mono-incorporated (Inq1 and InMeq1), bis-incorporated (InMeq2), and tris-incorporated (Inq3 and InMeq3) indium quinolinate complexes have been prepared. These complexes have also been characterized by X-ray crystallography. The photophysical properties of these complexes have also been examined by a combination of experimental and theoretical techniques. The indium complexes with a single quinolinol ligand (Inq1 and InMeq1) showed higher quantum efficiency than those with two or three quinolinate ligands; in particular, InMeq1 exhibited the highest quantum yield [ΦPL = 59% in poly(methyl methacrylate) film]. The insights into the nature of these findings were obtained by the sequential synthesis of the quinolinol-based indium luminophores and a detailed investigation of their structural stability.

A series of triphenylamine (TPA)-containing salen-Al assembly dyads, [salen(3- tBu-5-R)2Al(OC6H4- p-N(C6H5)2)] [salen = N, N'-bis(salicylidene)ethylenediamine; R = H (D1), tBu (D2), Ph (D3), OMe (D4), and NMe2 (D5)], were prepared in good yield (50-80%) and fully characterized by NMR spectroscopy and elemental analysis. Both the UV/vis absorption and photoluminescence (PL) spectra of D1-D4, except for D5, in a tetrahydrofuran solution exhibited dual patterns, which are assignable to the salen-Al-centered π-π* transition (low-energy region) and the TPA-centered π-π* transition (high-energy region). In particular, the emission spectra of the dyads displayed interesting dual-emissive patterns via a significant intramolecular energy transfer (IET) process between the salen-Al moiety and TPA group. Notably, this IET process was systematically tuned by varying the substituents and dominantly observed in the rigid state. More interestingly, compared to the salen-Al complexes (A1-A4) without the TPA group, D1-D4 exhibited enhanced quantum efficiencies. Time-dependent density functional theory calculations on the S1-optimized structures of D1-D5 further supported these experimental results by indicating the existence of independent transition states between the salen-Al moiety and TPA group in the assembly dyads. The present study reports the first example of salen-Al complexes bearing electron-rich TPA moieties.

Pyrazinoindole-based Lewis-acid/base assemblies are prepared through the use of regioselective formal [3 + 3] cycloaddition reactions, and their intriguing photophysical properties are described. The assemblies exhibit strong emissions in THF solution, which are attributed to through-space intramolecular charge-transfer (ICT) transitions between the branched Lewis-acid/base moieties. Furthermore, these show ratiometric color-change responses in PL titration experiments, which give rise to new colors through turn-on emissions ascribable to ICT transitions that alternate between the pyrazinoindole units and each triarylboryl or amino moiety, a consequence of the binding of the fluoride or acid. Pieces of filter paper covered by these assemblies exhibited blue-shifted color changes when immersed in aqueous acidic solutions, suggesting that these are promising candidate indicators that detect acid through emissive color. Computational data for these assemblies and their corresponding adducts verify the existence of ICT transitions that alternate through fluoride or acid binding.

Four biphenyl- and fluorene-based o-carboranyl compounds, 4-[2-(p-n-butylphenyl)-1-o-carboran-1-yl]biphenyl (1B), 4,4″-bis[2-(p-n-butylphenyl)-1-o-carboran-1-yl]biphenyl (2B), 2-[2-(p-n-butylphenyl)-1-o-carboran-1-yl]fluorene (1F), and 2,7-bis[2-(p-n-butylphenyl)-1-o-carboran-1-yl]fluorene (2F), were prepared and fully characterized by multinuclear NMR spectroscopy and elemental analysis. The crystal structures of 1B and 2B, analyzed by single-crystal X-ray diffraction, exhibited distinct distortions of the central biphenyl rings with dihedral angles of 44.2 and 33.1°. In photoluminescence measurements, fluorene-based carboranyl compounds in the rigid state (e.g., in solution at 77 K and as films) exhibited a noticeable emission in the low-energy region below 400 nm. 1F displayed a low-energy emissive trace in solution at ambient temperature, whereas biphenyl-based carboranes mainly exhibited high-energy emissions above 400 nm. TD-DFT calculations on the first excited singlet (S1) state of each compound s...

The series of novel salen-based indium complexes (3-tBu-5-R-salen)In-Me (3-tBu-5-R-salen = N,N'-bis(2-oxy-3-tert-butyl-5-R-salicylidene)-1,2-diaminoethane, R = H (1), tBu (2), Br (3), Ph (4), OMe (5), NMe2 (6)) and [(3-tBu-5-NMe3-salen)In-Me](OTf)2 (7; OTf = CF3SO3-) have been synthesized and fully characterized by NMR spectroscopy and elemental analysis. All indium complexes 1-7 are highly stable in air and even aqueous solutions. The solid-state structures for 3-5, which were confirmed by single-crystal X-ray analysis, exhibit square-pyramidal geometries around the indium center. Both the UV/vis absorption and PL spectra of 1-7 exhibit significant intramolecular charge transfer (ICT) transitions based on the salen moieties with systematically bathochromic shifts, which depend on the introduction of various kinds of substituents. Consequently, the emission spectra of these complexes cover almost the entire visible region (λem = 455-622 nm).

Potential of mean force (PMF) profiles and position-dependent diffusion coefficients of Na+ and K+ are calculated to elucidate the translocation of ions through a cyclic peptide nanotube, composed of 8 × cyclo[-(d-Leu-Trp)4-] rings, in water and in hydrated DMPC bilayers. The PMF profiles and PMF decomposition analysis for the monovalent cations show that favorable interactions of the cations with the CPN as well as the lipid bilayer and dehydration free energy penalties are two major competing factors which determine the free energy surface for ion transport through CPNs both in water and in lipid bilayers, and that the selectivity of CPNs to cations mainly arises from favorable interaction energies of cations with CPNs and lipid bilayers that are more dominant than the dehydration penalties. Calculations of the position-dependent diffusion coefficients and dynamic friction kernels of the cations indicate that the dehydration process along with the molecular rearrangements occurring outside the channel a...

A dimeric o-carboranyl triarylborane compound (2) with a biphenylene bridge group was prepared and characterized. Also, its solid-state structure was determined via X-ray diffraction. Treatment of 2 with an excess amount of KF in the presence of 18-crown-6 formed a dimer-type potassium salt, [2·F2][K·18-crown-6]2; its structure was fully confirmed by multinuclear NMR spectroscopy. UV–vis titration experiments carried out in THF showed that 2 binds fluoride ions with a binding constant (K) of 8.5 × 105 M–1. The linear decline of the UV/vis absorption of 2 upon titration with fluoride suggested that the triarylborane moieties acted as independent binding sites, which were not affected by each other. Contrary to a single emission (λem = 376 nm) of 2 assignable to an intramolecular charge transfer (ICT) transition at 298 K in THF, a broad low-energy emission band was additionally observed at 77 K, which is dominant in the film state. The TD-DFT calculation on the first excited singlet state (S1) of 2 shows th...

Three dithienosilole (DTS) derivatives bearing naphthyl segments, 5,5′-dinaphthyl-1,1-dimethyldithienosilol (1), 5,5′-dinaphthyl-1-methyl-1-phenyldithienosilole (2), and 5,5′-dinaphthyl-1,1-diphenyldithienosilol (3), are prepared through Pd(II)-catalyzed cross-coupling using an organoindium reagent as a nucleophile. The molecular structure of 3 is confirmed by single-crystal X-ray analysis. In addition, thermal, photophysical, and electrochemical properties for all three compounds are systematically investigated. The introduction of naphthyl segments into the DTS framework leads to an excellent enhancement of thermal stability with relatively high glass transition (Tg: 87 °C) and decomposition temperatures (Td: 320−380 °C). A red shift in both absorption and emission is observed in the DTS series as the 1,1-substituents on the ring silicon atom become more electronegative. On the basis of absorption spectra and DFT/TDDFT calculations, intense green photoluminescence observed for all compounds can be attri...

Photodissociation dynamics of propargyl alcohol (HC identical withC-CH(2)OH) at 212 nm in the gas phase was investigated by measuring rotationally resolved laser-induced fluorescence spectra of OH ((2)Pi) radicals exclusively produced in the ground electronic state. From the spectra, internal energies of OH and translational energy releases to products were determined. The electronic transition at 212 nm responsible for the OH dissociation was assigned as the pi(C[triple bond]C) --> pi*(C[triple bond]C) transition by time-dependent density functional theory calculations. In addition, an energy barrier at the exit channel along the reaction coordinate on the excited electronic potential energy surface was identified by ab initio calculations. The observed energy partitioning among the fragments was successfully modeled by the so-called "barrier-impulsive model".

Mixed quantum-classical atomistic simulations have been carried out to investigate the mechanistic details of excited state intramolecular electron transfer in a betaine-30 molecule in acetonitrile. The key electronic degrees of freedom of the solute molecule are treated quantum mechanically using the semiempirical Pariser-Parr-Pople Hamiltonian, including the solvent influence on electronic structure. The intramolecular vibrational modes are also treated explicitly at a quantum level, with the remaining elements treated classically using empirical potentials. The electron-transfer rate, corresponding to S1 --S0 relaxation, is evaluated via time-dependent perturbation theory with the explicit inclusion of the dynamics of solvation and intramolecular conformation. The calculations reveal that, while solvation dynamics is critical to the rate, the intramolecular torsional dynamics also plays an important role. The importance of the use of multiple high-frequency quantum modes is also discussed.

Electronic decoherence induced only by intramolecular vibrational motions is investigated in a betaine molecule, pyridinium N-phenoxide betaine [4-(1-pyridinio)phenolate], having 60 vibrational modes. The analysis is based on the nuclear overlap/phase function (NOPF) that appears in the electronic reduced density matrix. To do so, geometry optimizations and vibrational normal-mode analysis in the ground state and the first excited state are performed. Coherence dissipation times according to alternative approximations are obtained, including analysis of the role of frequency shifts and Duschinsky rotation. Geometry optimization reveals a large difference between the central torsional angles of the ground and the first excited state, with a tilted geometry of the pyridinium ring also observed in the first excited state. Nevertheless, the Duschinsky rotation matrix appears nearly diagonal with only a few considerable off-diagonal elements. We find that the low frequency torsional motion does not make any si...

Franck−Condon (FC) factors and the FC density associated with an electron transfer reaction are calculated for a betaine molecule, pyridinium-N-phenoxide betaine (4-(1-pyridinio)phenolate) in its S1 excited state. FC factors and density functions for harmonic vibrational modes are computed first by modifying the three level-fixed binary tree algorithm (Ruhoff, P. T.; Ratner, M. A. Int. J. Quant. Chem. 2000, 1, 383), a sum-over-states method based on recursion relations. This modified method allows the calculation of FC factors for 60 vibrational modes and avoids memory problems due to the large number of modes. The effects on the FC density of frequency shifts and mode mixing (Duschinky rotation) are included. For comparison, the more efficient time-dependent alternative is also employed for the calculation of the FC density function for the harmonic motion. In all cases, for a torsional motion which cannot be described by a harmonic potential, the FC density function is computed through the time-dependen...

One of the most fundamental challenges in biochemistry and biophysics is describing the function of ion channels, proteins that control ion transport across cell membranes. One approach to this problem is the application of Poisson�Nernst�Planck (PNP) theory. In practice, applying PNP theory involves creating a computational model of the ion channel and generating a numerical solution of differential equations that describes ion transport and electrostatic interactions. The PNP Cyclic Peptide Ion Channel Model is a simulation tool designed to offer an integrated approach to this important problem in bionanotechnology by demonstrating and explaining the application of PNP theory in a way that is accessible to students at an upper undergraduate level. The program interface was made using the free Rapid Application Infrastructure (Rappture) software made available by the Network for Computational Nanotechnology (NCN). Rappture is designed specifically for Web-based applications. Here we introduce a free version of the PNP Cyclic Peptide Ion Channel Model for use in the simulation of ion transport properties for a model ion channel structure that has been the subject of recent experiments.