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Obtaining deuterated microgels is essential to characterize their architecture and determine their response to crowding using neutron scattering. Here, we explain the effect of deuteration on the phase transition temperature.

Bio-hybrid fuels are a promising solution to accomplish a carbon-neutral and low-emission future for the transportation sector. Two potential candidates are the heterocyclic acetals 1,3-dioxane (C

Vibrational spectroscopy in supersonic jet expansions is a powerful tool to assess molecular aggregates in close to ideal conditions for the benchmarking of quantum chemical approaches. The low temperatures achieved as well as the absence of environment effects allow for a direct comparison between computed and experimental spectra. This provides potential benchmarking data which can be revisited to hone different computational techniques, and it allows for the critical analysis of procedures under the setting of a blind challenge. In the latter case, the final result is unknown to modellers, providing an unbiased testing opportunity for quantum chemical models. In this work, we present the spectroscopic and computational results for the first HyDRA blind challenge. The latter deals with the prediction of water donor stretching vibrations in monohydrates of organic molecules. This edition features a test set of 10 systems. Experimental water donor OH vibrational wavenumbers for the vacuum-isolated monohydrates of formaldehyde, tetrahydrofuran, pyridine, tetrahydrothiophene, trifluoroethanol, methyl lactate, dimethylimidazolidinone, cyclooctanone, trifluoroacetophenone and 1-phenylcyclohexane-cis-1,2-diol are provided. The results of the challenge show promising predictive properties in both purely quantum mechanical approaches as well as regression and other machine learning strategies.

ChemPhysChem e202200783 (2023). doi:10.1002/cphc.202200783, Published by Wiley-VCH Verl., Weinheim

This work presents a novel parametrization for the ReaxFF formalism as a means to investigate reaction processes of chlorinated organic compounds. Force field parameters cover the chemical elements C, H, O, Cl and were obtained using a novel optimization approach involving relaxed potential energy surface scans as training targets. The resulting ReaxFF parametrization shows good transferability, as demonstrated on two independent ab initio validation sets. While this first part of our two-paper series focuses on force field parametrization, we apply our parameters to the simulation of chlorinated dibenzofuran formation and decomposition processes in Part II.

Di-tert butyl peroxide is a commonly used cetane booster. It is a potential methyl radical source and therefore suited as a precursor for the investigation of elementary reactions including methyl radicals. In the present study, an independent approach of theory and pyrolysis experiments was used to determine the reaction rate constants for the most important DTBP-dissociation reactions which are the DTBP dissociation into two tert-butoxy (R1) and the subsequential β-scission (R2) to acetone and methyl. In the experimental part a Rapid Compression Machine (RCM) and a Shock Tube (ST) were used to measure pyrolysis times (PTs) and ignition delay times (IDTs) over a temperature range from 540 K to 650 K at pressures of 10 bar, 20 bar and 30 bar with different bath gases in airlike diluted atmospheres. The theoretical investigations considered the O–O dissociation of DTBP and the subsequent β-scission of tert-butoxy to acetone and methyl, treated via Transition State Theory (TST) and Phase Space Theory (PST) and at the DLPNO-CCSD(T)//DSDPBEP86 level of theory. The O–O dissociation rate constants were determined by experiments to k R1 = 2.941 · 10 15 · exp ( − 36672 cal · mol − 1 / ( R · T ) ) · s − 1 and the subsequent β-scission reaction rates can be expressed by k R2 = 5.077 · 10 13 · T 0.223 · exp ( − 11383 cal · mol − 1 / ( R · T ) ) · s − 1 . The experimentally determined rate coefficients of R1 are within the assumed uncertainty of the theoretically obtained reaction constants, which was estimated to be ± 1 kcal mol − 1 in the calculated energy barrier. In this work, a comparison of TST and PST-based rate coefficient showed the limits of TST for this kind of dissociation reactions and the predictivity of PST was proven. Additional, a comprehensive study of the oxidation of the DTBP products was carried out to outline the need for more research for key reactions of the methyl and acetone sub mechanisms.

Resonance-stabilized cyclopentadienyl radicals are important intermediate species in the combustion of transportation fuels. It not only serves as precursors for polycyclic aromatic hydrocarbon (PAH) formation, but also involves in the formation of fundamental PAH precursors such as propargyl and acetylene. In this work, the unimolecular reactions of the cyclopentadienyl radicals are theoretically studied based on high-level quantum chemistry and RRKM/master equation calculations. Stationary points on the potential energy surface (PES) are calculated at the CCSD(T)/CBS//M06–2X/6–311++(d,p) level of theory. The branching ratios of unimolecular reactions of the cyclopentadienyl radicals are analyzed for a broad temperature range from 500 to 2500 K and pressures from 0.01 to 100 atm. It is found that the isomerization reaction of the cyclopentadienyl radical via 1,2-hydrogen transfer dominates at low temperatures and high pressures, while the well-skipping decomposition reaction which forms propargyl and acetylene is important at high temperatures and low pressures. Both the decomposition reaction of the cyclopentadienyl radicals and its reverse reaction show pronounced pressure dependence, and their reaction rate constants are compared against available low-pressure experimental measurements and theoretical studies. The temperature- and pressure-dependent rate coefficients for important reactions involved on the C5H5 PES are calculated and updated in a chemical kinetic model. Impacts of the unimolecular reactions of the cyclopentadienyl radicals on the PAH formation are explored by the numerical modeling of a low-pressure cyclopentene counterflow diffusion flame.

The use of equations of state (EOS) requires the knowledge of model parameters for each molecule, but experimental data for parameter regression might not always be available. The physical soundnes...

The spectroscopic quantification of mixture compositions usually requires pure compounds and mixtures of known composition for calibration. Since they are not always available, methods to fill such gaps have evolved, which are, however, not generally applicable. Therefore, calibration can be extremely challenging, especially when multiple instable species, e.g. intermediates, exist in a system. This study presents a new calibration approach that uses ab initio Molecular Dynamics (AIMD)-simulated spectra as to set up and calibrate models for the physics-based spectral analysis method Indirect Hard Modeling (IHM). To demonstrate our approach called AIMD-IHM, we analyze Raman spectra of ternary hydrogen-bonding mixtures of acetone, methanol, and ethanol. The derived AIMD-IHM pure-component models and calibration coefficients are in good agreement with conventionally generated experimental results. The method yields compositions with prediction errors of less than 5% without any experimental calibration input. Our approach can be extended, in principle, to IR and NMR spectroscopy and allows for the analysis of systems that were hitherto inaccessible to quantitative spectroscopic analysis.

The recently discovered, membrane-active peptide LBF14 contains several non-proteinogenic amino acids and is able to transform vesicles into tubule networks. The exact membrane interaction mechanism and detailed secondary structure are yet to be determined. We performed molecular dynamics simulations of LBF14 and let it fold de novo into its ensemble of native secondary structures. Histidine protonation state effects on secondary structure were investigated. An MD simulation of the peptide with a lipid bilayer was performed. Simulation results were compared to circular dichroism and electron paramagnetic resonance data of previous studies. LBF14 contains a conserved helical section in an otherwise random structure. Helical stability is influenced by histidine protonation. The peptide localized to the polar layer of the membrane, consistent with experimental results. While the overall secondary structure is unaffected by membrane interaction, Ramachandran plot analysis yielded two distinct peptide conformations during membrane interaction. This conformational change was accompanied by residue repositioning within the membrane. LBF14 only affected the local order in the membrane, and had no measurable effect on pressure. The simulation results are consistent with the previously proposed membrane interaction mechanism of LBF14 and can additionally explain the local interaction mechanism. Communicated by Ramaswamy H. Sarma.

Anharmonicity can greatly affect rate constants. One or even several orders of magnitude of deviation are found for obtaining rate constants using the standard rigid-rotor harmonic-oscillator model. In turn, reactive molecular dynamics (MD) simulations are a powerful way to explore chemical reaction networks and calculate rate constants from the fully anharmonic potential energy surface. However, the classical nature of the dynamics and the required numerical efficiency of the force field limit the accuracy of the resulting kinetics. We combine the best of both worlds by presenting an approximation that pairs anharmonic information intrinsic to classical MD with high-accuracy energies and frequencies from quantum-mechanical electronic structure calculations. The proposed scheme is applied to hydrogen abstractions in the methane system, which allows for the benchmarking of rate constants corrected by our approach against experimental rate constants. This comparison reveals a standard deviation of factor 2.6. Two archetypes of possible failure are identified in the course of a detailed investigation of the CH3• + H• → CH22• + H2 reaction. From this follows the application range of the method, within which the method shows a standard deviation of factor 2.1. The computational efficiency and beneficial scaling of the method allow for application to larger systems, as shown for hydrogen abstraction from 2-butanone by HO2•.

In part I of this paper, the reaction kinetics and thermochemistry of cyclopentanol have been studied numerically. In this part, the ignition and combustion behavior of cyclopentanol are studied experimentally in a shock tube, a rapid compression machine, a combustion vessel, and a counterflow burner. Fundamental combustion properties, such as ignition delay times, laminar flame speeds, and extinction strain rates, are reported. All measurements probe a variety of initial conditions and provide an initial evaluation of the performance of cyclopentanol under different combustion modes. The experimental results are compared with those computed using the chemical mechanism presented in Part I. Reasonable agreement is observed. The controlling kinetics of cyclopentanol oxidation is explored considering various combustion modes. Moreover, cyclopentanol is compared to a variety of C5 fuels including cyclopentane, n-pentanol, and n-pentane with respect to their combustion characteristics in order to evaluate the impact of functional groups. The auto-ignition propensity of cyclopentanol is found to be lower than that of its paraffinic and linear counterparts, while the premixed flames of all these fuels propagate with approximately identical velocities at the investigated conditions.

Biomass derived chemicals may offer sustainable alternatives to petroleum derived hydrocarbons, while also enhancing engine combustion performance with co-optimization of fuels and engines. This paper presents a numerical study on the oxidation and combustion of a novel biofuel compound, cyclopentanol. Its reaction kinetics and thermochemistry are first explored using ab initio quantum chemistry methods. Thermochemical properties are calculated for cyclopentanol and a set of its key oxidation intermediates. C-H bond dissociation energies of cyclopentanol are computed for different carbon sites. For the fuel radicals, the energy barriers of their ring-opening reactions and the potential energy surfaces of their oxidation reactions are determined. Based on the theoretical results, a chemical kinetic mechanism is proposed to describe the oxidation of cyclopentanol at low and high temperatures. The model is compared against data obtained from shock tube, rapid compression machine, combustion vessel, and counterflow burner experiments over a range of initial conditions. Furthermore, reaction pathway analysis is performed using the present mechanism to give insights into the underlying oxidation chemistry of cyclopentanol. It is found that the α-radical of cyclopentanol undergoes preferably an alcohol-specific HO2 elimination reaction to form stable cyclopentanone and this reaction can strongly retard reactivity. The major reaction pathways of β- and γ-radicals are similar to those of cyclopentyl radicals that are the sequential and formally direct reactions of fuel radicals with O2 to form cyclopentenols and HO2 radicals. The existence of the hydroxy moiety affects the bond dissociation energies and reaction barriers, slightly favoring the chain-branching channel for γ-radicals at low temperatures.

The kinetics of chemical reactions in the liquid phase are often strongly determined by the reaction solvent. Consequently, the choice of the optimal solvent is an important task in chemical proces...

We measure and model the effect of CO2 addition on equilibrium composition and volume expansion for solvent system 2-methyltetrahydrofuran (2-MTHF)/water. Our experimental data cover pressures from...

In this study (Part II), the oxidation of dimethoxymethane (DMM) is investigated and a detailed chemical reaction model developed for a comprehensive description of both high- and low-temperature oxidation processes. The sub-mechanism of DMM is implemented using AramcoMech2.0 as the base mechanism. Rate coefficients are based on analogies with those for dimethyl ether, diethyl ether, and n-pentane oxidation. Furthermore, theoretical studies from recent works are also included in the present model and new calculations for the dissociation kinetics of Q ˙ OOH radicals have been carried out at the CCSD(T)/CBS(aug-cc-pVXZ; X = D, T) // B2PLYP-D3/6-311 + + G(d,p) level of theory. For validation, new ignition delay time experiments have been performed in a shock tube (ST), a rapid compression machine (RCM), and in a laminar flow reactor covering a wide range of conditions (p = 1–40 bar, T = 590–1215 K, φ = 1). In addition, the kinetic model is validated against laminar burning velocities, jet-stirred reactor, plug flow reactor and further ST and RCM experimental datasets from the literature. Pathway and sensitivity analyses were used to identify critical reaction pathways in the DMM oxidation mechanism. These show that the reactivity of DMM at intermediate temperatures is controlled by the branching between pathways initiated on the primary or secondary fuel radical. While primary fuel radicals eventually lead to chain branching, secondary fuel radical consumption is controlled by fast β-scission over a wide range of temperatures, which inhibits reactivity.

This work focuses on the ionic liquid (IL) synthesis starting from dimethyl carbonate and 1-ethylimidazole in methanol. In-situ IR-spectroscopy is used to gain time-dependent concentrations for kinetic analysis. The reaction is found to be self-accelerating, since the solvent polarity increases with the formation of the ionic product. This corresponds to a salting-out effect. Since the reaction rate is increasing in the beginning, pre-dosing of the product is proposed to enhance the overall productivity. Therefore, the space-time-yield is calculated as the arithmetic mean of the reaction rate with a varying starting point. It turns out that pre-dosing does not enhance the productivity here, since the space-time-yield of the complete reaction progress is below the initial reaction rate. Beyond that, two sharp bends can be observed in the progress of the reaction rate coefficient that point towards sudden changes in the reaction environment. The first bend can be assigned to a phase separation of the ionic liquid on a microscopical scale. The second bend takes place when the IL concentration surpasses roughly one sixth of the methanol concentration. Above that threshold, the whole amount of methanol is captured in the solvation shell of the anion monomethyl carbonate, as quantum chemical calculations suggest. Finally, the reaction rate coefficients were calculated using quantum chemical methods with respect to the solvent environment. The theoretical results show a good accordance with experimental values for the starting compositions. Thus, theoretical calculations help to estimate productive reaction mixtures.

Catalysts are of paramount importance as most chemical processes would be uneconomical without suitable catalysts. Consequently, the identification of appropriate catalysts is a key step in chemical process design. However, the number of potential catalysts is usually vast. To suggest promising candidates for experimental testing, in silico catalyst design methods are highly desirable. Still, such computational methods are in their infancy. Moreover, simple performance indicators are commonly employed as design objective instead of evaluating the actual process performance enabled by considered catalysts. Here, we present the CAT-COSMO-CAMPD method for integrated in silico design of homogeneous molecular catalysts and processes. CAT-COSMO-CAMPD integrates design of molecular catalysts with process optimization, enabling a process-based evaluation of every designed candidate catalyst. Reaction kinetics of catalytic reactions are predicted by advanced quantum chemical methods. We demonstrate for a catalytic carbamate-cleavage process that CAT-COSMO-CAMPD successfully identifies catalyst molecules maximizing the predicted process performance., Computers & Chemical Engineering, 153, ISSN:0098-1354, ISSN:1873-4375

The chemistry of urethanes plays a key role in important industrial processes. Although catalysts are often used, the study of the reactions without added catalysts provides the basis for a deeper understanding. For the non‐catalytic urethane formation and cleavage reactions, the dominating reaction mechanism has long been debated. To our knowledge, the reaction kinetics have not been predicted quantitatively so far. Therefore, we report a new computational study of urethane formation and cleavage reactions. To analyze various potential reaction mechanisms and to predict the reaction rate constants quantum chemistry and transition state theory were employed. For validation, experimental data from literature and from own experiments were used. Quantitative agreement of experiments and predictions could be demonstrated. The calculations confirm earlier assumptions that urethane formation reactions proceed via mechanisms where alcohol molecules act as auto‐catalysts. Our results show that it is essential to consider several transition states corresponding to different reaction orders to enable agreement with experimental observations. Urethane cleavage seems to be catalyzed by an isourethane, leading to an observed 2nd‐order dependence of the reaction rate on the urethane concentration. The results of our study support a deeper understanding of the reactions as well as a better description of reaction kinetics and will therefore help in catalyst development and process optimization., Reaction kinetics and mechanisms of urethane formation and cleavage reactions were investigated based on advanced quantum chemical methods. These reactions represent important model reactions in urethane chemistry. The results confirm that both urethane formation and cleavage proceed via autocatalytic mechanisms. Several mechanisms contribute to the observed reaction rate for urethane formation. A validation using own experimental data and literature data confirmed that the used quantum chemical methods yield quantitative predictions.

Ultra-low cross-linked (ULC) microgels are extremely soft polymers with advanced material properties exhibiting a colloid-to-polymer transition. Poly(N-isopropylacrylamide) (pNIPAM) microgels are commonly synthesized by radical precipitation polymerization of the fully protonated monomer N-isopropylacrylamide (NIPAM). Analogous deuterated monomers arouse interest regarding their varying scattering length densities in small-angle neutron scattering (SANS). An isotope substitution in the main monomer of a microgel changes its scattering length density, which enables the exploitation of the technique of contrast variation in SANS. Here, we demonstrate that the synthesis of the deuterated pNIPAM ULC microgels encounters challenges related to the self-cross-linking mechanism of the polymer chains. The location of the deuterium isotopes is crucial for the generation of deuterated pNIPAM ULC microgels: when the isopropyl group of NIPAM is deuterated, the cross-linking is strongly restrained and the formation of microgels is precluded. However, the deuteration of the vinyl group of NIPAM, ending as backbone in the pNIPAM chains, allows the self-cross-linking. Ab initio calculations of the bond dissociation enthalpies endorse that the cross-linking of the pNIPAM chains occurs via hydrogen atom abstraction at the tertiary carbon atom of the isopropyl group. Additionally, we show that the deuteration of the vinyl group barely shifts the transition temperature of the polymer compared to protonated pNIPAM, whereas deuteration of the isopropyl group results in a significant shift of the transition temperature toward higher temperatures. Finally, the deuterated ULC micro- and nanogels reveal a stronger cross-linked network with lower swelling ability compared to the protonated microgels.

Diethoxymethane (DEM) is a promising oxygenated fuel and fuel additive, which has similar positive combustion characteristics as dimethoxymethane. DEM contains C-C bonds and can form ethylene via beta-scission, which potentially increases its sooting tendency. Since DEM is rarely studied, however, kinetic modeling attempts are forced to rely on rate constant analogies. Therefore, we employ high level CCSD(T)/aug-cc-pV(T+D)Z//B2PLYPD3BJ/6-311++(d,p) theory along with transition state theory to predict reaction rate constants for H-abstraction by H and CH3 and the subsequent unimolecular reactions. We further prove that the DLPNO approximation to CCSD(T) leads to a deviation of less than 0.25 k/mol in barrier heights for the presently studied open-shell electronic structures and use it for the prediction of reaction rate constants for H-abstraction by C2H5 radicals. We find that H-abstraction by ethyl radicals might denote a significant pathway, which should not be neglected in kinetic modeling studies of DEM. It is also shown that reaction pathways leading to ethylene formation are of minor importance and give thereby a first insight into the fate of the C-C bonds. To the best of our knowledge, this study represents the first high-level ab-initio study of DEM, which makes the reaction kinetics and thermochemistry data provided by this study vital for future comprehensive kinetic modeling of DEM. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Functional microgels are novel materials, which can potentially be used for diverse applications such as drug delivery. Among other material properties, the radial cross-linker profile is of special importance to ensure desired product functionality. However, in the system under investigation, only a high cross-linker fraction in the center and a low cross-linker fraction in the shell is obtained in batch synthesis due to the fast reaction kinetics of the cross-linker. Other radial cross-linker fraction profiles can be synthesized in fed-batch, yet the determination of the required feeding profiles is not intuitively obvious. Based on recently developed quantitative nonlinear process models, a fed-batch synthesis can be dynamically optimized under constraints set by product quality and process limitations. Here, we apply dynamic optimization to microgel synthesis to obtain large microgels under constraints posed by the radial cross-linker profile and conversion. We present three different case studies to show in silico that a wide range of different cross-linker fraction profiles is feasible. The results show that the specified constraints are met and that various cross-linker profiles can be achieved while maintaining the microgel size.

The prediction of solvation free energies is essential for a variety of applications. Solvation free energies of neutral systems can be predicted quite accurately. The accuracy of predictions for solvation free energies of ionic solutes dissolved in neutral solvents, however, has been reported to be worse by at least 1 order of magnitude. In this study, the performance of three approaches for solvation free energy prediction of several hundred ions dissolved in neutral solvents is evaluated. The applied methods are COSMO-RS, cluster continuum model (CCM) together with COSMO-RS, and COSMO-RS-ES. It is emphasized that the reference data for model evaluation are subject to large uncertainties stemming from the impossibility to measure the so-called elusive absolute free energies of solvation of a single ion. Consequently, such uncertainty must be considered during the evaluation of prediction methods. Therefore, a straightforward approach to account for the underlying uncertainty is applied here. Hereby, it is revealed that the true performance of the method is better than what is often reported. The average absolute deviation (AAD) of COSMO-RS is calculated to be 2.3 kcal mol-1, while applying the CCM and COSMO-RS-ES each results in AADs of 2.0 kcal mol-1. This accuracy allows for qualitative assessment of solvation free energy-dependent quantities, such as reaction rate constants.

Combustion and flame 189, 433-442 (2018). doi:10.1016/j.combustflame.2017.07.037, Published by Elsevier Science, Amsterdam [u.a.]