Formation Enthalpies of C3 and C4 Brominated Hydrocarbons: Bringing Together Classical Thermodynamics, Modern Mass Spectrometry, and High-Level Ab Initio Calculations.

The enthalpies of formation of brominated C3-C4 hydrocarbons were critically evaluated using experimental data sources ranging from classical thermodynamics methods to modern high-precision mass spectrometry and reported in a time span of a century. The experimental data were used in conjunction with the results of modern high-level ab initio calculations. To facilitate quantitative analysis, a recently developed local coupled cluster-based computational protocol was extended to organic compounds containing univalent Br. Several erroneous data sources were identified in a course of the study. Possible reasons for the inconsistency between the ΔfHm° values recommended by the Committee on Data of the International Science Council (CODATA) and Active Thermochemical Tables for HBr in the gas and aqueous solution were discussed. The most up-to-date recommendations based on the comprehensive analysis of collected information are provided for 23 brominated hydrocarbons. For several compounds under consideration, the recommended values were previously lacking, while improved values and uncertainties were obtained for those with existing recommendations.

Towards improved FAIRness of the ThermoML Archive.

The ThermoML Archive is a subset of Thermodynamics Research Center (TRC) data holdings corresponding to cooperation between NIST TRC and five journals: Journal of Chemical Engineering and Data (ISSN: 1520-5134), The Journal of Chemical Thermodynamics (ISSN: 1096-3626), Fluid Phase Equilibria (ISSN: 0378-3812), Thermochimica Acta (ISSN: 0040-6031), and International Journal of Thermophysics (ISSN: 1572-9567). Data from initial cooperation (around 2003) through the 2019 calendar year are included. The archive has undergone a major update with the goal of improving the FAIRness and user experience of the data provided by the service. The web application provides comprehensive property browsing and searching capabilities; searching relies on a RESTful API provided by the Cordra software for managing digital objects. JSON files with a schema derived from ThermoML are provided as an additional serialization to lower the barrier to programmatic consumption of the information, for stakeholders who may have a preference of JSON over XML. The ThermoML and JSON files for all available entries can be downloaded from data.nist.gov (https://data.nist.gov/od/id/mds2-2422).

Efficient Ab Initio Estimation of Formation Enthalpies for Organic Compounds: Extension to Sulfur and Critical Evaluation of Experimental Data.

The efficient protocol for the estimation of gas-phase enthalpies of formation developed previously for C, H, O, N, and F elements was extended to sulfur. The protocol is based on a local coupled cluster with single, double, and perturbative triple excitation [CCSD(T)] approximation and allows rapid evaluation of compounds with sizes computationally prohibitive to canonical CCSD(T) using quadruple zeta basis sets. As a part of model development, a comprehensive review and critical evaluation of experimental data were performed for 87 sulfur-containing organic and inorganic compounds. A compact model with only three empirical parameters for sulfur introduced to address the effects beyond frozen core CCSD(T) was developed. The model exhibits approximately 2 kJ·mol-1 standard deviation over a set of experimental values for a diverse collection of sulfur-containing compounds. The complete basis set version of the model demonstrates a similar performance and requires only one empirical parameter. Multiple problems with the existing experimental data were identified and discussed. In addition, a lack of reliable data for certain important classes of sulfur compounds was found to impede the model generalization and confident performance assessment.

Heat capacity and decomposition of rimantadine hydrochloride.

Heat capacities of the antiviral drug rimantadine hydrochloride in the crystalline state were measured by adiabatic calorimetry and differential scanning calorimetry in the temperature range from (7 to 453) K. A broad low-enthalpy solid-state phase anomaly was detected between (170 and 250) K. Thermodynamic functions for crystalline rimantadine hydrochloride were derived. Decomposition of the studied compound was probed by the Knudsen effusion method and thermogravimetry with the support of quantum chemical calculations. The enthalpy of decomposition of rimantadine hydrochloride into the corresponding amine and hydrogen chloride was estimated from those data. The thermodynamic functions of the corresponding amine in the ideal gaseous state, including enthalpy of formation, were obtained using statistical thermodynamics with the necessary molecular parameters computed using quantum chemical methods. The enthalpy of formation of crystalline rimantadine hydrochloride was estimated.

Critical evaluation of the enthalpies of formation for fluorinated compounds using experimental data and high-level ab initio calculations.

The ab initio method for prediction of the enthalpies of formation for CHON-containing organic compounds proposed earlier (J. Chem. Theory Comput. 2018, 14, 5920-5932) has been extended to their fluorinated derivatives. A single experimental Δf H o m is typically available for compounds in this scope. Thus, a priori evaluation of the data quality was found to be inefficient despite all available experimental data for C1─C3 hydrofluorocarbons and 34 data points for medium-size organofluorine compounds being considered. The training set was derived by analyzing consistency of the experimental and predicted values and removal of outliers. Significant issues in the experimental data, including inconsistency across different laboratories, were identified and potential causes for these problems were discussed. A conservative estimate of uncertainty for the experimental Δf H o m of organofluorine compounds was proposed.

Efficient implementation of periodic boundary conditions in Monte Carlo simulation.

Determination of the shortest distances between particles is one of the most time-consuming parts of molecular simulation by the Monte Carlo method. In this work, we demonstrate that the use of signed-integer storage of coordinates in a scaled box allows one to skip multiple conditional statements in realization of periodic boundary conditions in cubic and rectangular boxes, which, in turn, increases the performance. Performance of the improved procedure was tested in NVT Monte Carlo simulations for liquid krypton and water. © 2018 Wiley Periodicals, Inc.

Candidates to Replace R-12 as a Radiator Gas in Cherenkov Detectors.

Dichlorodifluoromethane (R-12) has been widely used as a radiator gas in pressure threshold Cherenkov detectors for high-energy particle physics. However, that compound is becoming unavailable due to the Montreal Protocol. To find a replacement with suitably high refractive index, we use a combination of theory and experiment to examine the polarizability and refractivity of several non-ozone-depleting compounds. Our measurements show that the fourth-generation refrigerants R-1234yf (2,3,3,3-tetrafluoropropene) and R-1234ze(E) (trans-1,3,3,3-tetrafluoropropene) have sufficient refractivity to replace R-12 in this application. If the slight flammability of these compounds is a problem, two nonflammable alternatives are R-218 (octafluoropropane), which has a high Global Warming Potential, and R-13I1 (trifluoroiodomethane), which has low Ozone Depletion Potential and Global Warming Potential but may not be sufficiently inert.

Efficient DLPNO-CCSD(T)-Based Estimation of Formation Enthalpies for C-, H-, O-, and N-Containing Closed-Shell Compounds Validated Against Critically Evaluated Experimental Data.

An accurate and cost-efficient methodology for the estimation of the enthalpies of formation for closed-shell compounds composed of C, H, O, and N atoms is presented and validated against critically evaluated experimental data. The computational efficiency is achieved through the use of the resolution-of-identity (RI) and domain-based local pair-natural orbital coupled cluster (DLPNO-CCSD(T)) approximations, which results in a drastic reduction in both the computational cost and the number of necessary steps for a composite quantum chemical method. The expanded uncertainty for the proposed methodology evaluated using a data set of 45 thoroughly vetted experimental values for molecules containing up to 12 heavy atoms is about 3 kJ·mol-1, competitive with those of typical calorimetric measurements. For the compounds within the stated scope, the methodology is shown to be superior to a representative, more general, and widely used composite quantum chemical method, G4.

Corrections to standard state in combustion calorimetry: an update and a web-based tool.

Combustion calorimetry is the predominant method for determination of enthalpies of formation for organic compounds. Both initial and final states of the calorimeter deviate significantly from the standard conditions. Correction of the obtained results to the standard state must be applied as accurately as possible to determine the combustion energy with an acceptable uncertainty, which is typically a few hundredths of a percent. The correction procedures in their current form were introduced in 1956 with simplifications to allow application in a pre-computer era. In this work, the procedures have been updated with respect to both the equations and reference values. The most reliable data sources are identified, and the updated algorithm is presented in the form of a Web-based tool available through the NIST TRC Web site.

ENTHALPY OF FORMATION OF AQUEOUS HYDROFLUORIC ACID: REVISION NEEDED?

Accurate enthalpies of formation of hydrofluoric acid in the gas and liquid states as well as in aqueous solutions are critical for reduction and interpretation of combustion calorimetry data for fluorinated compounds. Analysis of current recommendations reveals inconsistencies with the existing literature that can significantly affect experimental values derived using these recommendations. Through thorough and comprehensive analysis of available experimental data, including the sources not considered before, we provide recommendations that substantially improve consistency with these results. However, the scatter in the existing data also prevents further improvements and uncertainty reduction. New experimental data, particularly for aqueous HF solutions, are needed to advance.

Thermodynamic behavior and polymorphism of 1-butyl-3-methylimidazolium hexafluorophosphate composites with multiwalled carbon nanotubes.

Based on room-temperature densities measured in this research for ionic nanofluids (INFs) with four ionic liquids (ILs), we conclude that evacuation is a necessary step to maximize the IL penetration into multiwalled carbon nanotubes (MWCNT). An improved procedure for reproducible preparation of INFs is proposed. Thermal behavior of five (1-butyl-3-methylimidazolium hexafluorophosphate + MWCNT) samples was studied by adiabatic calorimetry over the temperature range (78 to 370) K. The samples contained from 0.11 to 0.92 mass fraction of the nanophase. Their appearance changed from the fluid to the powder with increasing the MWCNT content. For the fluid samples, the specific heat capacity was found be an additive quantity of the specific heat capacities of the components for the crystal and liquid phases, and the temperatures of phase transitions did not change relative to the bulk values. For the powder-like sample with the highest IL content, a sigmoidal heat capacity curve was observed. Thus, the internal diameter of the studied MWCNT was small enough to switch from the isothermal melting process to the gradual transition from the crystal-like structures to the liquid-like ones.

Validation of thermophysical data for scientific and engineering applications.

High quality thermophysical property data are essential to many scientific and engineering applications. These data are produced at a high rate and are affected by a range of experimental and reporting error sources that often exceed stated uncertainties. As a result, critical evaluation is required to establish the limits of reliability in a quantified way. The present work describes reporting recommendations and property data validation methods developed and applied at the Thermodynamics Research Center at NIST through the use of the ThermoData Engine (TDE; SRD 103a/b) software. Examples are provided with an emphasis on various consistency checks, which may include the use of equations of state (EOS).

Thermodynamic Properties of Organic Substances: Experiment, Modeling, and Technological Applications.

In this review, results of the studies of thermodynamic properties of organic substances conducted at the Chemistry Department of the Belarusian State University (Minsk, Belarus) over a period of more than 50 years are summarized. Emphasis is made on precise measurements (both calorimetry and equilibria) and prediction methods, including group-contribution, quantum chemical, and statistical mechanical, for a broad range of thermodynamic properties of various classes of chemical substances. The principal purposes of these studies were to establish relationships between thermodynamic properties of organic substances and their molecular structure, develop methods of extrapolation and prediction of the properties of substances lacking experimental data, and provide thermodynamic background for innovative energy- and resource-saving technologies.

Efficient Estimation of Formation Enthalpies for Closed-Shell Organic Compounds with Local Coupled-Cluster Methods.

Efficient estimation of the enthalpies of formation for closed-shell organic compounds via atom-equivalent-type computational schemes and with the use of different local coupled-cluster with single, double, and perturbative triple excitation (CCSD(T)) approximations was investigated. Detailed analysis of established sources of uncertainty, inclusive of contributions beyond frozen-core CCSD(T) and errors due to local CCSD(T) approximations and zero-point energy anharmonicity, suggests the lower limit of about 2 kJ·mol-1 for the expanded uncertainty of the proposed estimation framework. Among the tested computational schemes, the best-performing cases demonstrate expanded uncertainty of about 2.5 kJ·mol-1, based on the analysis against 44 critically evaluated experimental values. Computational efficiency, accuracy commensurable with that of a typical experiment, and absence of the need for auxiliary reactions and additional experimental data offer unprecedented advantages for practical use, such as prompt validation of existing measurements and estimation of missing values, as well as resolution of experimental conflicts. The utility of the proposed methodology was demonstrated using a representative sample of the most recent experimental measurements.

Aqueous Ion Trapping and Transport in Graphene-Embedded 18-Crown-6 Ether Pores.

Using extensive room-temperature molecular dynamics simulations, we investigate selective aqueous cation trapping and permeation in graphene-embedded 18-crown-6 ether pores. We show that in the presence of suspended water-immersed crown-porous graphene, K+ ions rapidly organize and trap stably within the pores, in contrast with Na+ ions. As a result, significant qualitative differences in permeation between ionic species arise. The trapped ion occupancy and permeation behaviors are shown to be highly voltage-tunable. Interestingly, we demonstrate the possibility of performing conceptually straightforward ion-based logical operations resulting from controllable membrane charging by the trapped ions. In addition, we show that ionic transistors based on crown-porous graphene are possible, suggesting utility in cascaded ion-based logic circuitry. Our results indicate that in addition to numerous possible applications of graphene-embedded crown ether nanopores, including deionization, ion sensing/sieving, and energy storage, simple ion-based logical elements may prove promising as building blocks for reliable nanofluidic computational devices.

Nucleobase-functionalized graphene nanoribbons for accurate high-speed DNA sequencing.

We propose a water-immersed nucleobase-functionalized suspended graphene nanoribbon as an intrinsically selective device for nucleotide detection. The proposed sensing method combines Watson-Crick selective base pairing with graphene's capacity for converting anisotropic lattice strain to changes in an electrical current at the nanoscale. Using detailed atomistic molecular dynamics (MD) simulations, we study sensor operation at ambient conditions. We combine simulated data with theoretical arguments to estimate the levels of measurable electrical signal variation in response to strains and determine that the proposed sensing mechanism shows significant promise for realistic DNA sensing devices without the need for advanced data processing, or highly restrictive operational conditions.

A MoS2-Based Capacitive Displacement Sensor for DNA Sequencing.

We propose an aqueous functionalized molybdenum disulfide nanoribbon suspended over a solid electrode as a capacitive displacement sensor aimed at determining the DNA sequence. The detectable sequencing events arise from the combination of Watson-Crick base-pairing, one of nature's most basic lock-and-key binding mechanisms, with the ability of appropriately sized atomically thin membranes to flex substantially in response to subnanonewton forces. We employ carefully designed numerical simulations and theoretical estimates to demonstrate excellent (79% to 86%) raw target detection accuracy at ∼70 million bases per second and electrical measurability of the detected events. In addition, we demonstrate reliable detection of repeated DNA motifs. Finally, we argue that the use of a nanoscale opening (nanopore) is not requisite for the operation of the proposed sensor and present a simplified sensor geometry without the nanopore as part of the sensing element. Our results, therefore, potentially suggest a realistic, inherently base-specific, high-throughput electronic DNA sequencing device as a cost-effective de novo alternative to the existing methods.