Coconut fibers contain many lignocellulosic components; therefore, they have the potential to be used as cellulose-based materials. This study aims to synthesize carboxymethyl cellulose (CMC) for bioplastic applications from coconut fiber cellulose obtained from South Tangerang, Indonesia. The isolation of cellulose was conducted in two key stages: alkaline treatment using a delignification reactor and bleaching with hydrogen peroxide (H2O2). The facile synthesis of CMC involved two important steps: alkaline treatment and carboxymethylation of isolated cellulose. The yield of cellulose isolated from coconut fiber was 16.39% for biomass and 64.84% for delignification products. The cellulose produced exhibited a crystallinity index (C.I.) of 89%. The yield of CMC was 14.67%, with a C.I. was 56.66%. The CMC obtained was categorized as having a medium molecular weight of 249,048 Da with a polymerization degree of 1046. Cellulose starts to decompose at a temperature interval of 292.05–381.45°C, whereas CMC decomposes at a lower temperature interval of 245.42–299.73°C. Thermochemical calculations were conducted by using the density functional theory (DFT), confirming a spontaneous reaction with a Gibbs free energy of −5.25 kJ mol−1. Bioplastics were fabricated in two stages: blending with carboxymethyl chitosan (CMChi) and plasticizing with glycerol. The addition of CMCh increased the C.I. and tensile strength, while the addition of glycerol to CMC/CMChi (80/20) blend-based bioplastic reduced the C.I. and tensile strength, but enhanced the relative contact angle. Highlights: Cellulose was isolated from coconut fibers through a two-stage process involving delignification and bleaching; Carboxymethyl cellulose was synthesized by monochloroacetic acid in isopropanol with NaOH as the catalyst; The optimum condition for achieving the highest elongation at break among the blending compositions was found in the CMC/CMChi (80/20) blend bioplastic; Adding up to 30 wt% glycerol decreased the tensile strength and increased the elongation at break; The addition of glycerol enhanced the hydrophobic properties of CMC/CMCh blend-based bioplastics.

As optical properties, the ultraviolet-visible (UV-Vis) absorption spectra of capsanthin-based red natural dye are a decisive parameter for their usage in various applications. Thus, accurately predicting the maximum UV-Vis wavelength ( λ max ) values is critical in designing dye-conjugated material. Extensive metadynamics simulations were carried out to generate capsanthin conformers at various levels of the extended tight-binding method. Benchmarking the time-dependent density-functional theory (TD-DFT) methods help understand the results of a particular functional and allows a comparison between results obtained with different functional. The long-range correction (LC) scheme in LC-TD-DFT-D4/ωB97X/def2-SVP has been found to reproduce the experimental λ max , and exhibited the effect of conformational changes to the calculated wavelengths. On the other hand, an inexpensive yet efficient LC-TD-DFTB method reproduced the experimental λ max insensitive to conformational changes.

This paper discusses the process of determining the energy density and electronic properties of sodium-ion batteries with nickel doping and the manganese-oxygen combination (Na2Mn3-zNizO7) using the density-functional theory calculation in Quantum Espresso software. These materials were chosen due to their abundance in nature as an alternative to overcome the limitations of lithium materials. Moreover, Na2Mn3-zNizO7has a similar structure to lithium-based batteries that have been widely used. The Na transfer process and activation energy were simulated, and the voltage and the electronic properties of the material were analyzed using first-principles calculation. This research shows that the material (Na2Mn3-zNizO7) has the potential to be implemented as a cathode material in secondary batteries.

Acetonitrile has been widely viewed as a weakly coordinating solvent in metal-catalyzed reactions. Evidence is presented herein that it worked as an actor ligand in nickel-catalyzed stereoselective isomerizations of eugenol, methyl eugenol, estragole, and allylphenol, with trans-isomerized products of ≥95%. Nickel(0)(nitrile)phosphines were generated in situ from Ni(II) salt in the presence of phosphines, Zn, and nitrile with Ni/phosphines/Zn/nitrile mole ratio as low as 1:2:1:1. The isomerization of eugenol gave trans-isoeugenol of >97% in 30 min at r.t. with Ni turnover frequency (TOF) up to 1,116 h−1 and the activation energy of 61 kJ·mol−1. High selectivity of trans-isoeugenol was retained in continuous and multi-gram trials. Density functional theory (DFT)/PBE0-D3 calculations rationalized the possible formation of nickel hydride (i.e., Ni(H)(η1-CH2CN)(phosphine) complex) from η1-N(end-on)-Ni complex. This nitrile modulated-Ni(0) complex indicated the complex followed an alkyl-type isomerization, instead of a conventional allylic-type one.

The aqueous sodium-ion battery is a promising alternative to the well-known lithium-ion battery owing to the large abundance of sodium ion resources. Although it is safer than the lithium-ion battery, the voltage window of the sodium-ion battery is narrower than that of the lithium-ion battery, thus limiting its practical implementation. Therefore, a highly concentrated electrolyte is required to address this issue. In the present work, the effect of the salt concentration on the transport properties of water molecules is investigated via theoretical analyses at the quantum mechanical level. A molecular dynamics simulation at the quantum mechanical level revealed that as the salt concentration increases, the ion-water interactions became stronger, leading to a lower diffusivity and a lower electronic band gap. These imply that the superconcentrated aqueous-based electrolytes have high potentials for the sodium-ion battery applications.

Thioesterase, cloning, expression, extreme thermostable, natural sample

Ceria (CeO2) is a promising metal-oxide support that is used in three-way catalysis (TWC). The activity of ceria-supported TWC depends on the location and concentration of oxygen vacancies. Oxygen diffusion can occur once the oxygen vacancy is created, and it leads to enhanced catalytic activity. In this study, the density-functional tight-binding method was used to estimate the free-energy barriers of oxygen diffusion in bulk CeO2 and on a (111)-CeO2 surface. The reconstructed freeenergy surfaces from metadynamics sampling show that the diffusion in the bulk CeO2 is faster than that on the (111)-CeO2 surface, with activation barriers of 7.4 and 31.6 kcal/mol, respectively.

Carbonaceous or oxy-carbon species are intermediates formed during CxHy combustion on a Ptn/Al2O3 catalyst, which contain carbon, hydrogen, and oxygen atoms. The accumulation of the carbonaceous species, arguably, leads to catalytic deactivation; therefore, their removal is of importance. As the diffusion process is occasionally the rate-determining step in the growth of carbonaceous species, the present study aims to reveal the diffusion mechanisms. The free energy barriers of acetate, formate, and methoxy diffusion on the (100)-γ-Al2O3 surface were evaluated through extensive metadynamics simulations at the density-functional tight-binding level. The present work deduces that each adopted carbonaceous species exhibits different diffusion mechanisms and supports experimental evidence that the acetate species exhibits the slowest diffusivity among the adopted carbonaceous species.

Water confined within one-dimensional (1D) hydrophobic nanochannels has attracted significant interest due to its unusual structure and dynamic properties. As a representative system, water-filled carbon nanotubes (CNTs) are generally studied, but direct observation of the crystal structure and proton transport is difficult for CNTs due to their poor crystallinity and high electron conduction. Here, we report the direct observation of a unique water-cluster structure and high proton conduction realized in a metal-organic nanotube, [Pt(dach)(bpy)Br]4(SO4)4·32H2O (dach: (1R, 2R)-(-)-1,2-diaminocyclohexane; bpy: 4,4'-bipyridine). In the crystalline state, a hydrogen-bonded ice nanotube composed of water tetramers and octamers is found within the hydrophobic nanochannel. Single-crystal impedance measurements along the channel direction reveal a high proton conduction of 10-2 Scm-1. Moreover, fast proton diffusion and continuous liquid-to-solid transition are confirmed using solid-state 1H-NMR measurements. Our study provides valuable insight into the structural and dynamical properties of confined water within 1D hydrophobic nanochannels.

Proton transfer in water-based environments occurs because of hydrogen-bond interaction. There are many interesting physicochemical phenomena in this field, causing fast structural diffusion of hydronium and hydroxide ions. During the last few decades, to support experimental observations and measurements, quantum-mechanical molecular dynamics (QMMD) simulations with reasonable accuracy and efficiency have significantly unraveled structural, energetic, and dynamical properties of excess proton in aqueous environments. This review summarizes the state-of-the-art QMMD studies of proton transfer processes in aqueous solutions and complex systems including bulk liquid water, ice phases, and confined water in nanochannel/nanoporous materials as well as reports on CO2 scrubbing by amine-based chemical absorption. This article is categorized under: Structure and Mechanism > Reaction Mechanisms and Catalysis Molecular and Statistical Mechanics > Molecular Dynamics and Monte-Carlo Methods Electronic Structure Theory > Semiempirical Electronic Structure Methods Theoretical and Physical Chemistry > Reaction Dynamics and Kinetics.

The density-functional tight-binding (DFTB) method is one of the useful quantum chemical methods, which provides a good balance between accuracy and computational efficiency. In this account, we reviewed the basis of the DFTB method, the linear-scaling divide-and-conquer (DC) technique, as well as the parameterization process. We also provide some refinement, modifications, and extension of the existing parameters that can be applicable for lithium-ion battery systems. The diffusion constants of common electrolyte molecules and LiTFSA salt in solution have been estimated using DC-DFTB molecular dynamics simulation with our new parameters. The resulting diffusion constants have good agreement to the experimental diffusion constants.

The structural, dynamical, and energetic properties of the excess proton in ice were studied using density-functional tight-binding molecular dynamics simulations. The ice systems investigated herein consisted of low-density hexagonal and cubic crystalline variants (ice Ih and Ic) and high-density structures (ice III and melted ice VI). Analysis of the temperature dependence of radial distribution function and bond order parameters served to characterize the distribution and configuration of hundreds of water molecules in a unit cell. We confirmed that ice Ih and Ic possess higher hexagonal symmetries than ice III and melted ice VI. The estimated Grotthuss shuttling diffusion coefficients in ice were larger than that of liquid water, indicating a slower proton diffusion process in high-density structures than in low-density systems. The energy barriers calculated on the basis of the Arrhenius plot of diffusion coefficients were in reasonable agreement with experimental measurement for ice Ih. Furthermore, the energy barriers for high-density structures were several times larger than those of low-density systems. The simulation results were likely related to the suppression of proton transfer in disordered water configurations, in particular, ice with low hexagonal symmetry.

Predicting pKa values for different types of amine species with high accuracy and efficiency is of critical importance for the design of high performance and economical solvents in carbon capture and storage with aqueous amine solutions. In this study, we demonstrate that density-functional tight-binding-based metadynamics simulations are a promising approach to calculate the free energy difference between the protonated and neutral states of amines in aqueous solution with inexpensive computational cost. The calculated pKa values were in satisfactory agreement with the experimental values, the mean absolute deviation being only 0.09 pKa units for 34 amines commonly used in CO2 scrubbing. Such superior reproducibility and correlation compared to estimations by static quantum mechanical calculations highlight the significant effect of dynamical proton transfer processes in explicit solvent molecules for the improvement of the estimation accuracy.

Abstract

Divide-and-conquer-type density-functional tight-binding molecular dynamics simulations of the CO2 absorption process in monoethanolamine (MEA) solution have been performed for systems containing thousands of atoms. The formation of carbamate anions has been widely investigated for neutral systems via ab initio molecular dynamics simulations, yet the present study is aimed at identifying the role of hydroxide ions in acid-base equilibrium. The structural and electronic analyses reveal that the hydroxide ion approaches, via Grotthuss-type shuttling, the zwitterionic intermediates and abstracts a proton from the nitrogen atom of MEA. We also estimated the fraction of reacted CO2 and carbamate formed at different initial CO2 concentrations that confirm a high absorbed CO2 concentration decreases the fraction of MEA(C) formed due to the abundance of MEA(Z) in the solution.

The diffusion of the hydroxide ion in bulk water was examined by linear-scaling divide-and-conquer density-functional tight-binding molecular dynamics (DC-DFTB-MD) simulations using three different-sized unit cells that contained 522, 1050, and 4999 water molecules as well as one hydroxide ion. The repulsive potential for the oxygen-oxygen pair was improved by iterative Boltzmann inversion, which adjusted the radial distribution function of DFTB-MD simulations to that of the reference density functional theory-MD one. The calculated diffusion coefficients and the Arrhenius diffusion barrier were in good agreement with experimental results. The results of the hydroxide ion coordination number distribution and potential of mean force analyses supported a dynamical hypercoordination diffusion mechanism.

The process of proton diffusion in liquid water was investigated using molecular dynamics (MD) simulations, and the total energy and atomic forces were evaluated by the divide-and-conquer-type density-functional tight-binding (DC-DFTB) method. The effectiveness of this approach was confirmed by comparing the computational time of water clusters with conventional treatments. The unit cell employed herein, which contained 523 water molecules and 1 excess proton, was moderately large in comparison with those used in previous studies. The reasonable accuracy obtained by using this unit cell was confirmed by examining the temperature fluctuation. The diffusion coefficients for the vehicular and Grotthuss processes were accurately reproduced by the DC-DFTB-MD simulations with the unit cell containing 523 water molecules. Furthermore, the energy barriers were evaluated from the temperature dependence of the diffusion coefficient for each process. The calculated barrier for Grotthuss diffusion was in good agreement with the experimental value.