Modulating Electronic Properties of Dinitrosoarene Polymers

We present a comprehensive analysis on how the electronic structure and the optical properties of an organic polymer can be modulated, based on the example of the dinitrosobenzene polymer (1). Using a combination of computational and experimental tools, we explore the effects of solid-state packing, backbone torsion, surface adsorption, the conjugation in the aromatic core, and substituents. The band gap (Eg) and optical spectrum of 1 are calculated using both GW-BSE with zero-gap renormalization (ZGR) and hybrid TD-DFT, with the former method predicting a value (2.41 eV) in excellent agreement with our diffuse reflectance spectroscopy measurements (2.39 eV). Using GW-BSE-ZGR, changes occurring upon solidstate packing are separated into a contribution arising from (i) the change in the torsional angle and (ii) the change in the screened Coulombic interaction, which strongly effects the exciton binding energies. Comprehensive hybrid TD-DFT calculations find that the effects of substituents on Eg and on transport properties can mostly be explained through changes in the torsional angle, and predict a linear dependence between it and Eg. Extending the conjugation in the aromatic core is found to enhance transport properties and narrow Eg, identifying future synthetic targets. Atomic force microscopy and spectroscopic ellipsometry are used to study 1 adsorbed to a (111) gold surface (1@Au), with the latter method showing a significant narrowing of the band gap to 0.68 eV, in good agreement with TD-DFT predictions.

Momentum Removal to Obtain the Position-Dependent Diffusion Constant in Constrained Molecular Dynamics Simulation

<div>The position-dependent diffusion coefficient along with free energy profile are important parameters needed to study mass transport in heterogeneous systems such as biological and polymer membranes, and molecular dynamics (MD) calculation is a popular tool to obtain them. Among many methodologies, the Marrink-Berendsen (MB) method is often employed to calculate the position-dependent diffusion coefficient, in which the autocorrelation function of the force on a fixed molecule is related to the friction on the molecule. However, the diffusion coefficient is shown to be affected by the period of the removal of the center-of-mass velocity, which is necessary when performing MD calculations using the Ewald method for Coulombic interaction. We have clarified theoretically in this study how this operation affects the diffusion coefficient calculated by the MB method, and the theoretical predictions are proven by MD calculations. Therefore, we succeeded in providing guidance on how to select an appropriate the period of the removal of the center-of-mass velocity in estimating the position-dependent diffusion coefficient by the MB method. This guideline is applicable also to the Woolf-Roux method.</div>

Momentum Removal to Obtain the Position-Dependent Diffusion Constant in Constrained Molecular Dynamics Simulation

<div>The position-dependent diffusion coefficient along with free energy profile are important parameters needed to study mass transport in heterogeneous systems such as biological and polymer membranes, and molecular dynamics (MD) calculation is a popular tool to obtain them. Among many methodologies, the Marrink-Berendsen (MB) method is often employed to calculate the position-dependent diffusion coefficient, in which the autocorrelation function of the force on a fixed molecule is related to the friction on the molecule. However, the diffusion coefficient is shown to be affected by the period of the removal of the center-of-mass velocity, which is necessary when performing MD calculations using the Ewald method for Coulombic interaction. We have clarified theoretically in this study how this operation affects the diffusion coefficient calculated by the MB method, and the theoretical predictions are proven by MD calculations. Therefore, we succeeded in providing guidance on how to select an appropriate the period of the removal of the center-of-mass velocity in estimating the position-dependent diffusion coefficient by the MB method. This guideline is applicable also to the Woolf-Roux method.</div>

Hydropower generation by transpiration from microporous alumina

Traditional hydropower generation is one of the most sustainable energy sources; however, the local environmental impact of hydroelectric dams and reservoirs is serious, and hydroelectric power requires high-cost turbines and generators. Because these installations utilize gravitational potential energy of massive volumes of falling water, this sort of hydropower generation is unsuitable for ubiquitous, small-scale energy production. Here, we report that wetting and evaporation of pure water from a tiny block of porous alumina generates electrical current in the direction of water transpiration. The current induced in microporous alumina is associated with mass transport of water accompanying ions that accumulate near the negatively charged surface of alumina pores. Without any pre-treatment or additives, once evaporation commences, a 3 × 3 cm2 piece of alumina can generate an open-circuit voltage as large as 0.27 V. The power generation scheme we propose here is simple, clean, and versatile, and it can be employed anywhere, as it utilizes only spontaneous capillary action of water and Coulombic interaction at the alumina-water interface, without requiring any input of heat or light.

Molecular Basis for Reduced Cleavage Activity and Drug Resistance in D30N HIV-1 protease

Nelfinavir is one of the FDA approved HIV-1 protease inhibitors and is a part of HAART therapy for the treatment of HIV-AIDS. Nelfinavir was the first HIV-1 protease inhibitor to be approved as a Paediatric formulation. The application of HAART had resulted into significant improvement in the life of AIDS patients. However, emergence of drug resistance in HIV-1 protease limited the use of many of these drugs including nelfinavir. A unique mutation observed frequently in patients treated with nelfinavir is D30N as it is selected exclusively by nelfinavir. It imparts very high resistance to nelfinavir but unlike other primary mutations does not give cross resistance to the majority of other drugs. D30N mutation also significantly reduces cleavage activity of HIV-1 protease and affects the viral fitness. Here, we have determined structures of D30N HIV-1 protease in unliganded form and in complex with the drug nelfinavir. These structures provide rationale for rduced cleavage activity and molecular basis of resistance induced by D30N mutation. The loss of coulombic interaction part of a crucial hydrogen bond between the drug and the enzyme, is a likely explanation for reduced affinity and drug resistance towards nelfinavir. The decreased catalytic activity of D30N HIV protease, due to altered interaction with substrates and reduced stability of folding core may be the reasons for reduced replicative capacity of the HIV harboring D30N HIV-1 protease.

Hydropower Generation by Transpiration from Microporous Alumina

Traditional hydropower generation is one of the most sustainable energy sources; however, the local environmental impact of hydroelectric dams and reservoirs is serious, and hydroelectric power requires high-cost turbines and generators. Because these installations utilize gravitational potential energy of massive volumes of falling water, this sort of hydropower generation is unsuitable for ubiquitous, small-scale energy production. Here, we report that wetting and evaporation of pure water from a tiny block of porous alumina generates electrical current in the direction of water transpiration. The current induced in microporous alumina is associated with mass transport of water accompanying ions that accumulate near the negatively charged surface of alumina pores. Without any pre-treatment or additives, once evaporation commences, a 3×3 cm2 piece of alumina can generate an open-circuit voltage as large as 0.27 V. The power generation scheme we propose here is simple, clean, and versatile, and it can be employed anywhere, as it utilizes only spontaneous capillary action of water and Coulombic interaction at the alumina-water interface, without requiring any input of heat or light.

The significance of long-range correction to the hydroperoxyl radical-scavenging reaction of trans-resveratrol and gnetin C

Density functional theory has been gaining popularity for studying the radical scavenging activity of antioxidants. However, only a few studies investigate the importance of calculation methods on the radical-scavenging reactions. In this study, we examined the significance of (i) the long-range correction on the coulombic interaction and (ii) the London dispersion correction to the hydroperoxyl radical-scavenging reaction of trans-resveratrol and gnetin C. We employed B3LYP, CAM-B3LYP, M06-2X exchange-correlation functionals and B3LYP with the D3 version of Grimme’s dispersion in the calculations. The results showed that long-range correction on the coulombic interaction had a significant effect on the increase of reaction and activation energies. The increase was in line with the change of hydroperoxyl radical’s orientation in the transition state structure. Meanwhile, the London dispersion correction only had a minor effect on the transition state structure, reaction energy and activation energy. Overall, long-range correction on the coulombic interaction had a significant impact on the radical-scavenging reaction.

Thermal and Transport Properties of Molten Chloride Salts with Polarization Effect on Microstructure

Molten chloride salt is recognized as a promising heat transfer and storage medium in concentrating solar power in recent years, but there is a serious lack for thermal property data of molten chloride salts. In this work, local structures and thermal properties for molten chloride salt—including NaCl, MgCl2, and ZnCl2—were precisely simulated by Born–Mayer–Huggins (BMH) potential in a rigid ion model (RIM) and a polarizable ion model (PIM). Compared with experimental data, distances between cations, densities, and heat capacities of molten chloride slats calculated from PIM agree remarkably better than those from RIM. The polarization effect brings an extra contribution to screen large repulsive Coulombic interaction of cation–cation, and then it makes shorter distance between cations, larger density and lower heat capacity. For NaCl, MgCl2, and ZnCl2, PIM simulation deviations of distances between cations are respectively 3.8%, 3.7%, and 0.3%. The deviations of density and heat capacity for NaCl between PIM simulation and experiments are only 0.6% and 2.2%, and those for MgCl2 and ZnCl2 are 0.7–10.7%. As the temperature rises, the distance between cations increases and the structure turns into loose state, so the density and thermal conductivity decrease, while the ionic self-diffusion coefficient increases, which also agree well with the experimental results.

Consistent Inclusion of Continuum Solvation in Energy Decomposition Analysis: Theory and Application to Molecular CO2 Reduction Catalysts

<p>To facilitate computational investigation of intermolecular interactions in the solution phase, we report the development of ALMO-EDA(solv), a scheme that allows the application of continuum solvent models within the framework of energy decomposition analysis (EDA) based on absolutely localized molecular orbitals (ALMOs). In this scheme, all the quantum mechanical states involved in the variational EDA procedure are computed with the presence of solvent environment so that solvation effects are incorporated in the evaluation of all its energy components. After validation on several model complexes, we employ ALMO-EDA(solv) to investigate substituent effects on two classes of complexes that are related to electrochemical CO₂ reduction catalysis. For [FeTPP(CO₂−κC)]²⁻ (TPP = tetraphenylporphyrin), we reveal that two ortho substituents which yield most favorable CO2 binding, −N(CH₃)₃⁺ (TMA) and −OH, stabilize the complex via through-structure and through-space mechanisms, respectively. The Coulombic interaction between the positively charged TMA group and activated CO₂ is found to be largely attenuated by the polar solvent. Furthermore, we also provide computational support for the design strategy of utilizing bulky, flexible ligands to stabilize activated CO₂ via long-range Coulomb interactions, which creates biomimetic solvent-inaccessible “pockets” in that electrostatics is unscreened. For the reactant and product complexes associated with the electron transfer from the <i>p</i>-terphenyl radical anion to CO₂ , we demonstrate that the double terminal substitution of <i>p</i>-terphenyl by electron-withdrawing groups considerably strengthens the binding in the product state while moderately weakens that in the reactant state, which are both dominated by the substituent tuning of the electrostatics component. These applications illustrate that this new extension of ALMO-EDA provides a valuable means to unravel the nature of intermolecular interactions and quantify their impacts on chemical reactivity in solution.<br></p>