Improved Estimates of the Critical Point Constants for Large <i>n</i>‑Alkanes Using Gibbs Ensemble Monte Carlo Simulations

In this work, we present improved estimates of the critical temperature (<i>T</i>_c), critical density (ρ_c), critical pressure (<i>P</i>_c), and critical compressibility factor (<i>Z</i>_c) for <i>n</i>-alkanes with chain lengths as large as C₄₈. These are obtained for several different force field models with Gibbs ensemble Monte Carlo simulations. We implement a recently proposed data analysis method designed to reduce the uncertainty in <i>T</i>_c, ρ_c, <i>P</i>_c, and <i>Z</i>_c when predicted with molecular simulation. The results show a large reduction in the uncertainties compared to the simulation literature with the greatest reduction found for ρ_c, <i>P</i>_c, and <i>Z</i>_c. Previously, even the most computationally intensive molecular simulation studies have not been able to elucidate the <i>n</i>-alkane <i>P</i>_c trend with respect to larger carbon numbers. The results of this study are significant because the uncertainty in <i>P</i>_c is small enough to discern between conflicting experimental data sets and prediction models for large <i>n</i>-alkanes. Furthermore, the results for <i>T</i>_c resolve a discrepancy in the simulation literature with respect to the correct <i>T</i>_c trend for large <i>n</i>-alkanes. In addition, the <i>Z</i>_c results are reliable enough to determine the most accurate prediction trend for <i>Z</i>_c. Finally, finite-size effects are shown to not be significant even for the relatively small system sizes required for efficient simulation of longer chain lengths

New Vapor-Pressure Prediction with Improved Thermodynamic Consistency using the Riedel Equation

Vapor pressure, heat of vaporization, liquid heat capacity, and ideal-gas heat capacity for pure compounds between the triple point and critical point are important properties for process design and optimization. These thermophysical properties are related to each other through temperature derivatives of thermodynamic relationships stemming from a temperature-dependent vapor-pressure correlation. The Riedel equation has been considered to be an excellent and simple choice among vapor-pressure correlating equations [Velasco et al. J. Chem. Thermodyn. 2008, 40 (5), 789−797] but requires modification of the final coefficient to provide thermodynamic consistency with thermal data [Hogge et al. Fluid Phase Equilib. 2016, 429, 149−165]. New predictive correlations with final coefficients in integer steps from 1 to 6 have been created for compounds with limited or no vapor-pressure data, based on the methodology used originally by Riedel [Chem. Ing. Tech. 1954, 26 (2), 83−89]. Liquid heat capacity was predicted using these vapor-pressure correlations, and the best final coefficient values were chosen based on the ability to simultaneously represent vapor pressure and liquid heat capacity. This procedure improves the fit to liquid heat-capacity data by 5–10% (average absolute deviation), while maintaining the fit of vapor-pressure data similar to those of other prediction methods. Additionally, low-temperature vapor-pressure predictions were improved by relying on liquid heat-capacity data

The Locational Impact of Site-Specific PEGylation: Streamlined Screening with Cell-Free Protein Expression and Coarse-Grain Simulation

Although polyethylene glycol (PEG) is commonly used to improve protein stability and therapeutic efficacy, the optimal location for attaching PEG onto proteins is not well understood. Here, we present a cell-free protein synthesis-based screening platform that facilitates site-specific PEGylation and efficient evaluation of PEG attachment efficiency, thermal stability, and activity for different variants of PEGylated T4 lysozyme, including a di-PEGylated variant. We also report developing a computationally efficient coarse-grain simulation model as a potential tool to narrow experimental screening candidates. We use this simulation method as a novel tool to evaluate the locational impact of PEGylation. Using this screen, we also evaluated the predictive impact of PEGylation site solvent accessibility, conjugation site structure, PEG size, and double PEGylation. Our findings indicate that PEGylation efficiency, protein stability, and protein activity varied considerably with PEGylation site, variations that were not well predicted by common PEGylation guidelines. Overall our results suggest current guidelines are insufficiently predictive, highlighting the need for experimental and simulation screening systems such as the one presented here

Melting Point, Enthalpy of Fusion, and Heat Capacity Measurements of Several Polyfunctional, Industrially Important Compounds by Differential Scanning Calorimetry

The present paper reports a differential scanning calorimetry (DSC) study of 19 industrially important compounds that lacked key experimental data in their respective two-phase vapor liquid regions. The compounds are <i>o</i>-tolualdehyde (CAS 529-20-4), <i>m</i>-tolualdehyde (CAS 620-23-5), <i>p</i>-tolualdehyde (CAS 104-87-0), 3-methylbenzyl alcohol (CAS 587-03-1), <i>p</i>-toluic acid (CAS 99-94-5), 1-phenyl-1-propanol (CAS 93-54-9), 1-phenyl-2-propanol (CAS 698-87-3), 2-phenyl-1-propanol (CAS 1123-85-9), 2-isopropylphenol (CAS 88-69-7), 2,5-dimethylfuran (CAS 625-86-5), 5-methylfurfural (CAS 620-02-0), phenyl acetate (CAS 122-79-2), ethyl 2-phenylacetate (CAS 101-97-3), <i>n</i>-hexylcyclohexane (CAS 4292-75-5), 6-undecanone (CAS 927-49-1), 1<i>H</i>-perfluorooctane (CAS 335-65-9), 2,6-dimethoxyphenol (CAS 91-10-1), <i>trans</i>-isoeugenol (CAS 5932-68-3), and 1-propoxy-2-propanol (CAS 1569-01-3). New experimental melting temperatures, enthalpies of fusion, glass transition temperatures, and heat capacities of the liquid compounds as a function of temperature are reported with a comparison to similar compounds