Preparation of a Water-Based Lubricant from Lignocellulosic Biomass and Its Tribological Properties

Lignocellulosic biomass is considered as a major feedstock to produce value-added renewable chemicals. In this study, a new water-based lubricant was prepared using biomass-derived levulinic acid (LA) and polyols such as ethylene glycol and glycerol. The products were separated by rotary film molecular distillation and characterized by ¹H NMR and mass spectrometry. Lubricant properties such as kinematic viscosity, pour, cloud, and flash points, copper strip corrosion, and volatility at 120 °C were evaluated according to standard ASTM methods. Furthermore, the hydrolytic stability and tribological properties of the products were tested for water-based lubricants. The results indicated that glycerol ester of levulinic acid (LAGLE) exhibited superior lubricant properties, strong resistance to hydrolytic degradation, and excellent antiwear performance, implying that the biomass-derived LAGLE was a potential water-based lubricant

Rational Design of Methodology-Independent Metal Parameters Using a Nonbonded Dummy Model

A nonbonded dummy model for metal ions is highly imperative for the computation of complex biological systems with for instance multiple metal centers. Here we present nonbonded dummy parameters of 11 divalent metallic cations, namely, Mg²⁺, V²⁺, Cr²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Sn²⁺, and Hg²⁺, that are optimized to be compatible with three widely used water models (TIP3P, SPC/E, and TIP4P-EW). The three sets of metal parameters reproduce simultaneously the solvation free energies (Δ<i>G</i>_sol), the ion–oxygen distance in the first solvation shell (IOD), and coordination numbers (CN) in explicit water with a relative error less than 1%. The main sources of errors to Δ<i>G</i>_sol that arise from the boundary conditions and treatment of electrostatic interactions are corrected rationally, which ensures the independence of the proposed parameters on the methodology used in the calculation. This work will be of great value for the computational study of metal-containing biological systems

Conversion of Ethanol and Acetaldehyde to Butadiene over MgO–SiO₂ Catalysts: Effect of Reaction Parameters and Interaction between MgO and SiO₂ on Catalytic Performance

For the effect of structural features on the catalytic performance of the conversion of ethanol and acetaldehyde to butadiene to be investigated, a series of MgO–SiO₂ catalysts with different structural properties were synthesized by tuning the calcination temperature, investigated, and characterized. The best butadiene selectivity of 80.7% appears for the MgO–SiO₂ catalyst calcined at 500 °C using a mixture of acetaldehyde/ethanol/water (22.5:67.5:10 wt %) as feed. Addition of the appropriate amount of water (10 wt %) improved butadiene selectivity by inhibiting the formation of 1-butanol and C₆ compounds. Results from XRD, FT-IR, and ²⁹Si MAS NMR indicate the generation of a significant amount of amorphous magnesium silicates along with few crystalline magnesium silicates for the catalyst calcined at 500 °C. XPS results indicate that it contains the lowest binding energies of both Si–O and Mg–O from Si–O–Mg bonds. For the catalysts calcined at low temperature (350 and 400 °C), more 1-butanol and C₆ compounds formed, which are considered to be related to residual Mg­(NO₃)₂. Additionally, more ethylene, diethyl ether, and butylene isomers were produced over the MgO–SiO₂ catalyst calcined at 700 °C with the formation of forsterite Mg₂SiO₄. Further results from Fourier transform infrared spectroscopy after pyridine adsorption and CO₂ temperature-programmed desorption show that the high catalytic performance is related to the presence of Lewis acidic sites and an intermediate number of basic sites

Generalized Born and Explicit Solvent Models for Free Energy Calculations in Organic Solvents: Cyclodextrin Dimerization

Evaluation of solvation (binding) free energies with implicit solvent models in different dielectric environments for biological simulations as well as high throughput ligand screening remain challenging endeavors. In order to address how well implicit solvent models approximate explicit ones we examined four generalized Born models (<i>GB</i>^Still, <i>GB</i>^HCT, <i>GB</i>^OBC<i>I</i>, and <i>GB</i>^OBC<i>II</i>) for determining the dimerization free energy (Δ<i>G</i>⁰) of β-cyclodextrin monomers in 17 implicit solvents with dielectric constants (<i>D</i>) ranging from 5 to 80 and compared the results to previous free energy calculations with explicit solvents (Zhang et al. J. Phys. Chem. B 2012, 116, 12684−12693). The comparison indicates that neglecting the environmental dependence of Born radii appears acceptable for such calculations involving cyclodextrin and that the <i>GB</i>^Still and <i>GB</i>^OBC<i>I</i> models yield a reasonable estimation of Δ<i>G</i>⁰, although the details of binding are quite different from explicit solvents. Large discrepancies between implicit and explicit solvent models occur in high-dielectric media with strong hydrogen bond (HB) interruption properties. Δ<i>G</i>⁰ with the GB models is shown to correlate strongly to 2­(<i>D</i>–1)/(2<i>D</i>+1) (<i>R</i>² ∼ 0.90) in line with the Onsager reaction field (Onsager J. Am. Chem. Soc. 1936, 58, 1486−1493) but to be very sensitive to <i>D</i> (<i>D</i> < 10) as well. Both high-dielectric environments where hydrogen bonds are of interest and low-dielectric media such as protein binding pockets and membrane interiors therefore need to be considered with caution in GB-based calculations. Finally, a literature analysis of Gibbs energy of solvation of small molecules in organic liquids shows that the Onsager relation does not hold for real molecules since the correlation between Δ<i>G</i>⁰ and 2­(<i>D</i>–1)/(2<i>D</i>+1) is low for most solutes. Interestingly, explicit solvent calculations of the solvation free energy (Zhang et al. J. Chem. Inf. Model. 2015, 55, 1192−1201) reproduce the weak experimental correlations with 2­(<i>D</i>–1)/(2<i>D</i>+1) very well

Modeling Coordination-Directed Self-Assembly of M₂L₄ Nanocapsule Featuring Competitive Guest Encapsulation

Exploring the mechanism of self-assembly and guest encapsulation of nanocapsules is highly imperative for the design of sophisticated molecular containers and multistimuli-responsive functional materials. Here we present a molecular dynamics simulation protocol with implicit solvent and simulated annealing techniques to investigate the self-assembly and competitive guest (C₆₀ and C₇₀ fullerenes) encapsulation of a M₂L₄ nanocapsule that is self-assembled by the coordination of mercury cations and bent bidentate ligands. Stepwise formation of the nanocapsule and competitive fullerene encapsulation during dynamic structural changes in the self-assembly were detected successfully. Such processes were driven by coordination bonding and π–π stacking and obey the minimum total potential energy principle. Potential of mean force calculations for guest binding to the M₂L₄ nanocapsule explained the mechanism underlying the competitive encapsulations of C₆₀ and C₇₀. This work helps design new functional nanomaterials capable of guest encapsulation and release

Mixed Matrix Membrane Based on Cross-Linked Poly[(ethylene glycol) methacrylate] and Metal–Organic Framework for Efficient Separation of Carbon Dioxide and Methane

The key in preparing mixed matrix membranes for the desired gas separation is to rationally select a suitable combination of inorganic fillers and polymers and to develop fabrication techniques enabling formation of a continuous inorganic phase with dual transport pathway. Herein, we report the facile design of flexible poly­[poly­(ethylene glycol) methacrylate-<i>co</i>-poly­(ethylene glycol) dimethacrylate] membranes containing metal organic frameworks UiO-66 prepared from zirconium chloride and 2-aminoterephthalic and terephthalic acid varying in contents, shapes, and sizes. The surface chemistry effects of both polymer matrix and MOFs on permeability and selectivity were investigated. The bare polymer membrane exhibited a permeability for CO₂ of around 117 barrer and a selectivity of up to 15. Addition of glycidyl methacrylate in the polymerization mixture led to membranes that were modified with hexamethylene­diamine to provide for basicity. However, this modification did not improve performance of the membranes. In contrast, addition 35 wt % UiO-66 octahedron enhanced both permeability and selectivity for CO₂ to about 205 barrer and 19, respectively. By adjusting the size and shape of UiO-66, the best hybrid membrane containing 35 wt % clusters of aggregated UiO-66 formed a close to continuous phase desirable for the dual transport mechanism and exhibited a 247% increase in CO₂ permeability up to 365 barrer

Quantification of Solvent Contribution to the Stability of Noncovalent Complexes

We introduce an indirect approach to estimate the solvation contributions to the thermodynamics of noncovalent complex formation through molecular dynamics simulation. This estimation is demonstrated by potential of mean force and entropy calculations on the binding process between β-cyclodextrin (host) and four drug molecules puerarin, daidzin, daidzein, and nabumetone (guest) in explicit water, followed by a stepwise extraction of individual enthalpy (Δ<i>H</i>) and entropy (Δ<i>S</i>) terms from the total free energy. Detailed analysis on the energetics of the host–guest complexation demonstrates that flexibility of the binding partners and solvation-related Δ<i>H</i> and Δ<i>S</i> need to be included explicitly for accurate estimation of the binding thermodynamics. From this, and our previous work on the solvent dependency of binding energies (Zhang et al. <i>J. Phys. Chem. B</i> <b>2012</b>, <i>116</i>, 12684–12693), it follows that calculations neglecting host or guest flexibility, or those employing implicit solvent, will not be able to systematically predict binding free energies. The approach presented here can be readily adopted for obtaining a deeper understanding of the mechanisms governing noncovalent associations in solution

High-Quality Jet Fuel Blend Production by Oxygen-Containing Terpenoids Hydroprocessing

Biojet fuel production has attracted a lot of research interest due to the double threats of fuel shortage and environmental concerns. This paper works on the high-quality jet fuel blend production by oxygen-containing terpenoids hydroprocessing. Hydroprocessing of three typical oxygen-containing terpenoids (geranyl acetone, nerolidol, and geraniol) over Pt/Al₂O₃ was first studied. The results indicate that the coexistence of branched carbon backbone, carbon–carbon double bond, and oxygen-containing functional group makes the terpenoids highly reactive during the hydroprocessing. The Pt/Al₂O₃ catalyst, which is considered to have a mild acidity, is still too active in terpenoids hydrogenation and results in large heat release and extensive side reactions. Hence, Pt supported on a support with a milder acidity and better diffusion property was proposed to build a suitable terpenoids hydroprocessing catalyst. Pt/Al-MCFs (MCF: mesocellular silica foam) were then successfully prepared, characterized, and tested in this reaction. Acidic sites could be introduced into MCFs by Al grafting of the pure silica MCF. The acidities of MCF supports, and consequently Pt/MCFs, could be fine-tuned by the Si/Al ratio in the resulting supports. Pt/Al-MCF-20 with a milder acidity than Pt/Al₂O₃ shows an excellent performance in geranyl acetone hydroprocessing with complete deoxygenation, limited side reaction, and high stability. Characterization results of Pt/Al-MCFs and Pt/MCF indicate that Al introduction is critical for the stable performance. The products obtained from geranyl acetone hydroprocessing over Pt/Al-MCF-20 are highly promising as jet fuel or jet fuel blend due to their multibranched alkane and alkyl-cycloalkane nature, which meets all the specifications of ASTM 7566 in the desired freezing point (−72 °C), density (0.80 g/mL), flash point (51 °C), heat of combustion (45 MJ/kg), and aromatics content (<1%)

Atomistic Simulation of Protein Encapsulation in Metal–Organic Frameworks

Fabrication of metal–organic frameworks (MOFs) with large apertures triggers a brand-new research area for selective encapsulation of biomolecules within MOF nanopores. The underlying inclusion mechanism is yet to be clarified however. Here we report a molecular dynamics study on the mechanism of protein encapsulation in MOFs. Evaluation for the binding of amino acid side chain analogues reveals that van der Waals interaction is the main driving force for the binding and that guest size acts as a key factor predicting protein binding with MOFs. Analysis on the conformation and thermodynamic stability of the miniprotein Trp-cage encapsulated in a series of MOFs with varying pore apertures and surface chemistries indicates that protein encapsulation can be achieved via maintaining a polar/nonpolar balance in the MOF surface through tunable modification of organic linkers and Mg–O chelating moieties. Such modifications endow MOFs with a more biocompatible confinement. This work provides guidelines for selective inclusion of biomolecules within MOFs and facilitates MOF functions as a new class of host materials and molecular chaperones

Molecular Recognition in Different Environments: β‑Cyclodextrin Dimer Formation in Organic Solvents

Electrostatic and van der Waals interactions as well as entropy contribute to the energetics governing macromolecular complexation in biomolecules. Hydrogen bonds play a particularly important role in such interactions. Here we use molecular dynamics (MD) simulations to investigate the hydrogen bond (HB) orientations of free beta-cyclodextrin (β-CD) and head-to-head dimerization of β-CD monomers with and without guest molecules in different environments, namely, in 10 different solvents covering a wide range of polarity. Potentials of mean force for the dimer dissociation are derived from umbrella sampling simulations, allowing determination of the binding affinity between monomers. The HB orientations are in good agreement with available experimental data in water and dimethyl sulfoxide, yielding confidence in the force field used. HB exchanges at the secondary rim of β-CD are observed with a fast rate in water and with a low rate or even no exchange in other solvents. Orientational preferences of interglucopyranose HBs and their effects on the β-CD structure in these solvents are discussed in detail. Polar solvents with stronger HB accepting abilities can interrupt intermolecular HBs more easily, resulting in a less stable dimer. Guest molecules included in the channel-type cavity strengthen the binding affinity between two monomers to some extent, particularly in polar solvents. Formation of the head-to-head dimer is therefore solvent-dependent and guest-modulated. There is only limited correlation between the dimer binding energies and solvent properties like the dielectric constant. This implies that implicit solvent models will not be capable of predicting important properties like binding energy for other solvents than water without a complete reparameterization. This work provides a deeper comprehension on the properties of β-CD, and implications for the application of cyclodextrins in aqueous and nonaqueous media are discussed