Chemistry Interactions Research Articles

Multi-resolution analysis of partially-stirred reactor models for subgrid turbulence / chemistry interactions

A multi-resolution analysis (MRA) technique in which coupled sequences of LES simulations are solved on successively coarsened meshes is used to analyze the relative performance of several algebraic partially-stirred reactor (PaSR) subgrid models for turbulent combustion. The test case is a methane-hydrogen bluff-body flame, and the ‘truth solution’ is obtained from a fine-mesh LES that resolves the flow into the dissipative scales. The velocity field from this solution drives the solutions obtained on the underlying coarser meshes, enabling a tight correlation of eddy structures. Conditional distributions of chemical production rate norms and local heat release over a subgrid Reynolds-number / Damköhler sample space are extracted from each coarse-mesh level. The results show that none of the tested PaSR methods accurately predicts the combustion characteristics evidenced from the finest mesh; results improve when coupling with an ‘outer environment’ is included. Optimal forms for the characteristic PaSR time scale and fine-scale volume fraction are regressed from the data and can be modeled effectively using resolved scale information. The use of these forms provides improved results and yields a level of mesh-independence that is not found in the original algebraic PaSR models.

Non-Covalent Interactions in Coordination Chemistry

Non-covalent interactions [...]

Advanced numerical simulation of hydrogen/air turbulent non-premixed flame on model burner

A numerical investigation of hydrogen (H2)/air turbulent non-premixed flame on the model burner was conducted. A large eddy simulation of reacting flow with partial and detailed chemical kinetic mechanisms was employed to obtain a high-resolution and accurate prediction of thermochemical states inside the combustion chamber, including pollutant NO, which have not been adequately predicted until now. This study employed temperature and species mass fraction data from two combustion cases of fully developed turbulent and transition regimes with a fuel composition of 50 % H2 and 50 % N2, experimentally measured by the German Aerospace Center (DLR) and TU Darmstadt. A reactor-based partially-stirred reactor (PaSR) model was used to handle the turbulence chemistry interaction. The employed chemical mechanisms included GRI-Mech 3.0 and partial Mevel mechanism. The effects of chemical mechanism and inlet jet velocity on simulation accuracy were discussed. The more elaborative nitrogen reactions in GRI-Mech 3.0 result in a better NO prediction compared to the partial Mevel mechanism. The implementation of finite rate chemistry in a PaSR model yields a significantly improved prediction of NO from the flamelet probability density function approach with less than 1 % root mean square deviation from experimental data. The performed simulation successfully captured the thermochemical profile of a fully developed turbulent flame; however, further improvement on boundary condition modeling is still required for a flame undergoing a transition from laminar to turbulent regimes. Finally, using the partial Mevel mechanism leads to a computational cost reduction of 32.66 % compared to the GRI-Mech 3.0 mechanism, which confirms the proportional relation between the size of the mechanism and computational cost.

Towards the definition of a solar forcing dataset for CMIP7

Abstract. The solar forcing prepared for Phase 6 of the Coupled Model Intercomparison Project (CMIP6) has been used extensively in climate model experiments and has been tested in various intercomparison studies. Recently, an International Space Science Institute (ISSI) working group has been established to revisit the solar forcing recommendations, based on the lessons learned from CMIP6, and to assess new datasets that have become available, in order to define a road map for building a revised and extended historical solar forcing dataset for the upcoming Phase 7 of CMIP. This paper identifies the possible improvements required and outlines a strategy to address them in the planned new solar forcing dataset. Proposed major changes include the adoption of the new Total and Spectral Solar Irradiance Sensor (TSIS-1) solar reference spectrum for solar spectral irradiance and an improved description of top-of-the-atmosphere energetic electron fluxes, as well as their reconstruction back to 1850 by means of geomagnetic proxy data. In addition, there is an urgent need to consider the proposed updates in the ozone forcing dataset in order to ensure a self-consistent solar forcing in coupled models without interactive chemistry. Regarding future solar forcing, we propose consideration of stochastic ensemble forcing scenarios, ideally in concert with other natural forcings, in order to allow for realistic projections of natural forcing uncertainties.

Development and Validation of a Compressible Reacting Gas-Dynamic Flow Solver for Supersonic Combustion

An approach based on the OpenFOAM library has been developed to solve a high-speed, multicomponent mixture of a reacting, compressible flow. This work presents comprehensive validation of the newly developed solver, called compressibleCentralReactingFoam, with different supersonic flows, including shocks, expansion waves, and turbulence–combustion interaction. The comparisons of the simulation results with experimental and computational data confirm the fidelity of this solver for problems involving multicomponent high-speed reactive flows. The gas dynamics of turbulence–chemistry interaction are modeled using a partially stirred reactor formulation and provide promising results to better understand the complex physics involved in supersonic combustors. A time-scale analysis based on local Damköhler numbers reveals different regimes of turbulent combustion. In the core of the jet flow, the Damköhler number is relatively high, indicating that the reaction time scale is smaller than the turbulent mixing time scale. This means that the combustion is controlled by turbulent mixing. In the shear layer, where the heat release rate and the scalar dissipation rate have the highest value, the flame is stabilized due to finite rate chemistry with small Damköhler numbers and a limited fraction of fine structure. This solver allows three-dimensional gas dynamic simulation of high-speed multicomponent reactive flows relevant to practical combustion applications.

Characterization and Improvement Dissolution Profile of the Hydrochlorothiazide-β-Cyclodextrin Inclusion Complex using Kneading Method

Hydrochlorothiazide is a drug antihypertensives are classified into Biopharmaceutics Classification System (BCS) class IV, so required technique formulation to improve solubility, one of them with complex inclusion. The inclusion complex was prepared with a kneading method with a comparison amount of hydrochlorothiazide - β- cyclodextrin 1:1 (F1) mol, 2:1 (F2) mol, and a physical mixture prepared in a ratio of 1:1 mol. This research aims to see the effect of complex formation inclusion on dissolution rate and characteristics of physicochemical properties of hydrochlorothiazide. Complex inclusions formed are characterized by scanning electron microscopy (SEM), and infrared spectrophotometer (FT-IR). X-ray diffraction, differential scanning calorimetry (DSC), and dissolution profiles. Characterization of physicochemical results analysis diffraction X-rays show that powder complex inclusion hydrochlorothiazide with β-cyclodextrin experiences decline peak intensity approaches a more amorphous nature. Characterization results FT-IR analysis shows No interaction chemistry exists between hydrochlorothiazide β-cyclodextrin. SEM analysis shows morphology substance active Already coated with β- cyclodextrin. DSC analysis shows a decline in enthalpy of the complex inclusions that indicate physical interactions form a simple eutectic mixture. Research results show that complex inclusion hydrochlorothiazide - β-cyclodextrin can repair characteristic physicochemical and can increase hydrochlorothiazide dissolution profile in a way significant (p<0.05) compared with powder The physical mixture with the highest dissolution results was shown by the F1 inclusion complex (82.843 %).

Enhanced photocatalytic degradation of dyes using a novel waste toner-based TiO2/Fe2O3@nanographite nanohybrid: A sustainable approach

This study synthesized a ferric oxide–nanographite (NG) nanocomposite (Fe2O3@NG) from waste toner powder through carbonization. Subsequently, a TiO2/Fe2O3@NG nanohybrid was fabricated using the sol–gel technique to improve the photocatalytic degradation of dyes. TiO2/Fe2O3@NG nanocomposites were prepared at TiO2:Fe2O3@NG ratios of 2:1 (Ti:T-21), 1:1 (Ti:T-11), and 1:2 (Ti:T-12). The porosity, morphology, surface chemistry, and chemical interactions between TiO2, Fe2O3, and graphite in the prepared TiO2/Fe2O3@NG nanocomposites were characterized using the Brunauer–Emmett–Teller (BET) method and microscopic and spectroscopic analyses. The TiO2/Fe2O3@NG nanohybrid exhibited a reduced bandgap (2.4–2.9 eV) and enhanced charge carrier separation through charge transfer at the junction of the hetero-structured TiO2/Fe2O3@NG nanohybrid. Preliminary experiments revealed that Ti:T-21 was the most effective photocatalyst for degrading acid blue-25 (AB-25) compared to Ti:T-11, Ti:T-12, sole TiO2, and Fe2O3@NG. This study also investigated the impacts of catalyst dose and initial dye concentration on the AB-25 photocatalytic degradation. Notably, 97% of 5-mg/L AB-25 was removed using 1.25-g/L Ti:T-21 at an unmodified pH of 6.4 within 120 min. Furthermore, Ti:T-21 exhibited remarkable recyclability in its immobilized form, achieving degradation ratios of 74.7%–71.8% over five consecutive runs, compared to removal efficiencies of 85.0%–62.3% in the suspended mode. Trapping experiments identified hydroxyl radicals, holes, and superoxide as the principal reactive radicals. The TiO2/Fe2O3@NG/light system was effective in disintegrating and mineralizing other synthetic dyes such as Congo red, methylene blue, and methyl red, indicating its potential for industrial-scale degradation of authentic dye wastewater. The utilization of waste toner for water treatment is highlighted as a strategy to promote environmental sustainability, foster a circular economy, and contribute to pollution remediation.

ChemisTree: A Novel, Interactive Chemistry Game to Teach Students about Electron Configuration

ChemisTree: A Novel, Interactive Chemistry Game to Teach Students about Electron Configuration

Developing An Interactive Chemistry E-module Based on Problem-based Learning to Improve Critical Thinking Skills of High School Students

This study aims to develop an interactive chemistry E-module based on problem-based learning (PBL) to improve the critical thinking skills of high school students in class X and measure its feasibility. This research used the research and development method with the ADDIE model, which consists of 5 stages (Analysis, Design, Development, Implementation, and Evaluation). The tools used in this study were test tools and non-test tools, namely modified BSNP standard verification sheets and essay questions. The data analysis techniques used in this research were qualitative and quantitative. The results of the feasibility test from the materials specialist instructors, and chemistry teachers, as well as media specialists, an average result of 82.7% met the "very fair" criterion. An average result of 93.12% met the "highly feasible" criterion. Based on classroom learning experiments, the E-module can improve students' critical thinking skills by achieving an N gain value of 0.48 in the medium category. It was also evidence of a 55% increase in students' average critical thinking ability score using electronic modules and belonging to the critical category. When learning with the E module, a significant difference occurs at the significance level α=0.000.

Advances and Prospects in Understanding London Dispersion Interactions in Molecular Chemistry.

London dispersion (LD) interactions are the main contribution of the attractive part of the van der Waals potential. Even though LD effects are the driving force for molecular aggregation and recognition, the role of these omnipresent interactions in structure and reactivity had been largely underappreciated over decades. However, in the recent years considerable efforts have been made to thoroughly study LD interactions and their potential as a chemical design element for structures and catalysis. This was made possible through a fruitful interplay of theory and experiment. This review highlights recent results and advances in utilizing LD interactions as a structural motif to understand and utilize intra- and intermolecularly LD-stabilized systems. Additionally, we focus on the quantification of LD interactions and their fundamental role in chemical reactions.

Advances and Prospects in Understanding London Dispersion Interactions in Molecular Chemistry

AbstractLondon dispersion (LD) interactions are the main contribution of the attractive part of the van der Waals potential. Even though LD effects are the driving force for molecular aggregation and recognition, the role of these omnipresent interactions in structure and reactivity had been largely underappreciated over decades. However, in the recent years considerable efforts have been made to thoroughly study LD interactions and their potential as a chemical design element for structures and catalysis. This was made possible through a fruitful interplay of theory and experiment. This review highlights recent results and advances in utilizing LD interactions as a structural motif to understand and utilize intra‐ and intermolecularly LD‐stabilized systems. Additionally, we focus on the quantification of LD interactions and their fundamental role in chemical reactions.

Numerical Modeling of Swirl Stabilized Lean-Premixed H2–CH4 Flames With the Artificially Thickened Flame Model

Abstract The lean premixed technology is a very convenient combustion strategy to progressively move from natural gas to high hydrogen content fuels in gas turbines limiting the pollutants emissions at the same time. The enabling process that will allow the combustor to manage a full H2 operation requires relevant design modifications, and in this framework, the numerical modeling will be a pivotal tool that will support this transition. In this work, high-fidelity simulations of perfectly premixed swirl stabilized flames have been performed varying the H2 content in the fuel from 0 to 100% to investigate the effect of the hydrogen addition on the methane flame. The artificially thickened flame model (ATFM) has been used to treat the turbulent chemistry interaction. The numerical results have been compared with the detailed experimental data performed at Cardiff University's Gas Turbine Research Center. After the numerical model validation against experimental OH* chemiluminescence maps has been presented, a deep numerical investigation of the effect of the H2 addition on the flame has been performed. In this way, the work aims to highlight the good prediction capability of the ATFM, and, at the same time, highlight the change in the different contributions that govern the flame reactivity moving from 100% CH4 to 100% H2 in very lean conditions.

Stabilized four-electron aqueous zinc-iodine batteries by quaternary ammonium complexation.

Four-electron aqueous zinc-iodine batteries (4eZIBs) leveraging the I-/I0/I+ redox couple have garnered attention for their potential high voltage, capacity, and energy density. However, the electrophilic I+ species is highly susceptible to hydrolysis due to the nucleophilic attack by water. Previous endeavors to develop 4eZIBs primarily relied on highly concentrated aqueous electrolytes to mitigate the hydrolysis issue, nonetheless, it introduced challenges associated with dissolution, high electrolyte viscosity, and sluggish electrode kinetics. In this work, we present a novel complexation strategy that capitalizes on quaternary ammonium salts to form solidified compounds with I+ species, rendering them impervious to solubilization and hydrolysis in aqueous environments. The robust interaction in this complexation chemistry facilitates a highly reversible I-/I0/I+ redox process, significantly improving reaction kinetics within a conventional ZnSO4 aqueous electrolyte. The proposed 4eZIB exhibits a superior rate capability and an extended lifespan of up to 2000 cycles. This complexation chemistry offers a promising pathway for the development of advanced 4eZIBs.

Computationally aided design of defect-appended aliphatic amines for CO2 activation within UiO-66.

The introduction of aliphatic amine groups in metal-organic frameworks (MOFs) can improve their ability to capture CO2 at low pressures, driven by chemisorptive formation of C-N bonds. Understanding the chemistry of amine-CO2 interaction within the confined porous space in MOFs is key to design and develop effective CO2 adsorbents. Here, we report a computational study of CO2 adsorption and subsequent formation of carbamic acid within defective UiO-66 functionalised with a series of four amino acids of varying aliphatic chain length (glycine, beta-alanine, gamma-aminobutyric acid and 5-aminovaleric acid). Periodic density functional theory (DFT) calculations suggest that CO2 can be activated by the aliphatic amines only when they are sufficiently close to each other to form hydrogen bonds and stabilise the adduct with CO2, a condition met only by UiO-66 functionalised with gamma-aminobutyric acid and 5-aminovaleric acid. The proposed mechanism involves the formation of a carbamate zwitterionic intermediate, which evolves via a simultaneous double hydrogen transfer with a proximal amine group to a carbamic acid. For the 5-aminovaleric acid case, it is suggested that even the functionalisation of just 16% of the available defective sites can be sufficient to form the CO2-amine adduct. Finally, we also investigate the effect of a possible protonation of the amine groups by the hydroxyl groups in the clusters, finding that this could lead to even more favourable interaction with CO2.

Effect of NO2 addition on the oxidation kinetics of n-pentane and natural gas blends with C1–C5n-alkanes

This study presents new ignition delay time (IDT) data for NO2 blended multi-component natural gas mixtures with methane as the major component including C2–C5 primary n-alkanes in different concentrations. The data are measured using a high-pressure shock tube and a rapid compression machine at compression pressures of 20 and 30 bar in the temperature range of 715–1480 K for stoichiometric mixtures. This paper builds upon our previous work on the development of a C1–C3/NOx kinetic mechanism and focusses on understanding the interaction chemistry of heavier n-alkane/NOx mixtures by determining the IDT characteristics of various NO2 blended n-C5H12/air combinations with 200, 400 and 1000 ppm concentrations of NO2 present at compression pressures of 10, 20 and 30 bar. The newly measured IDT results and existing experimental data from the literature are used to improve model predictions for the oxidation of n-C4H10/NOx, n-C5H12/NOx, NG2/NOx, and NG3/NOx by updating NUIGMech1.2. The improvement in the performance of GalwayMech1.0 is attributed to updated rate constants for the n-C5H12 + NO2 ↔ Ċ5H11–1, -2, -3 + HONO reactions as well as the inclusion of Ṙ + NO2 ↔ RONO reaction channels. The IDT decreased slightly when 1000 ppm of NO2 is added to n-pentane, which contrasts with propane (C3H8), where there was a significant decrease in the mixture reactivity as reported previously (A. A. E. S. Mohamed, A. B. Sahu, S. Panigrahy, M. Baigmohammadi, G. Bourque, H.J. Curran, The effect of the addition of nitrogen oxides on the oxidation of propane: An experimental and modeling study. Combust. Flame 245 (2022) 112306). This is because the competition between NO2 and O2 for 1-propyl radicals formed by H-atom abstraction from C3H8 decreases mixture reactivity, while in the case of n-C5H12, although NO2 and O2 compete for 1-pentyl radicals, the increase in reactivity is facilitated by the availability of 2-pentyl radicals in the system which also leads to chain branching when they add to O2, unlike 2-propyl (iso-propyl) radicals which ultimately do not lead to chain branching in the oxidation of propane.

Microsecond Timescale Conformational Dynamics of a Small-Molecule Ligand within the Active Site of a Protein.

The possible internal dynamics of non-isotope-labeled small-molecule ligands inside a target protein is inherently difficult to capture. Whereas high crystallographic temperature factors can denote either static disorder or motion, even moieties with very low B-factors can be subject to vivid motion between symmetry-related sites. Here we report the experimental identification of internal μs timescale dynamics of a high-affinity, natural-abundance ligand tightly bound to the enzyme human carbonic anhydrase II (hCAII) even within a crystalline lattice. The rotamer jumps of the ligand's benzene group manifest themselves both, in solution and fast magic-angle spinning solid-state NMR 1 H R1ρ relaxation dispersion, for which we obtain further mechanistic insights from molecular-dynamics (MD) simulations. The experimental confirmation of rotameric jumps in bound ligands within proteins in solution or the crystalline state may improve understanding of host-guest interactions in biology and supra-molecular chemistry and may facilitate medicinal chemistry for future drug campaigns.

Embodied preparation for learning basic quantum chemistry: A mixed‐method study

AbstractBackgroundHaptic feedback has been shown to be an effective facilitator of the learning of scientific concepts in a series of studies. However, little is known about the underlying salient learning mechanisms, which are activated when learning from haptic feedback.ObjectivesWe investigate the learning mechanism in a higher chemistry education setting, in which the students learned about the abstract concept of potential energy in a quantum chemical context.MethodsIn this work, we present a mixed‐methods problem‐solving prior to instruction (PS‐I) study with chemistry bachelor students. In an interactive quantum chemistry learning environment, the students explored the energetic profiles of nucleophilic substitution reactions and the corresponding activation barriers experienced as repulsion and attraction. We measured cognitive and affective mechanisms which have been shown to be activated in PS‐I designs, such as knowledge gap awareness, state curiosity, and positive affect as well as the learning outcome quantitatively and the learning trajectories qualitatively.Results and ConclusionsPlanned contrasts revealed a small hindering effect of the haptic feedback on the learning outcome. Thematic analysis of the qualitative data lets us attribute this effect to the lack of scaffolding of the haptic feedback and the spontaneous atomic movements in the simulation, which may be interpreted as a visual representation of force in itself.This work highlights the importance of accurate mappings of the haptic feedback unto the target domain and further delivers insight into the prior conceptions of chemistry undergraduate students.

Contributions of London Dispersion Forces to Solution-Phase Association Processes.

ConspectusDespite their ubiquity and early discovery, London dispersion forces are often overlooked. This is due, in part, to the difficulty in assessing their contributions to molecular and polymeric structure, stability, properties, and reactivities. However, recent advances in modeling have revealed that dispersion interactions play an important role in many important chemical and biological processes. Experimental confirmation of their impact in solution has been challenging, leading to controversies about their relative importance.In the course of studying noncovalent interactions using molecular devices, our understanding and appreciation for the importance of dispersion interactions have evolved. This Account follows this intellectual journey by using examples from the literature. The goals are twofold: to describe recent advances in understanding the interaction and to provide guidance to researchers studying weak noncovalent interactions. However, first, the experimental methods for measuring the effects of dispersion interactions and the strategies for isolating their influence are described. These include the design of molecular devices to measure these weak noncovalent interactions and the strategies to disentangle the solvation, solvophobic, and dispersion components of the resulting equilibria.The literature examples are organized around five fundamental questions. (1) Do dispersion interactions have a measurable effect on solution equilibria? (2) To what extent do solvents attenuate or compensate for dispersion interactions? (3) To what extent do the solvation and solvophobic terms influence the dispersion equilibria? (4) Can we predict whether a system will form attractive dispersion or repulsive steric interactions? (5) Can the dispersion term be isolated and interrogated? We were often surprised by the answers to these questions. In each case, we describe how the systems were designed to address these questions and discuss possible interpretations of the results.While dispersion interactions in solution were weak (usually <1 kcal/mol), their influence on complexation and conformational equilibria can be observed and measured. This underscores the significance of these interactions in molecular recognition, coordination chemistry, reaction design, and catalysis. The solvent components of the dispersion equilibria can also be significant. Therefore, the isolation of the dispersion contributions from the solvation and solvophobic effects represents an ongoing challenge. The experimental studies also provide important benchmarks and offer valuable insights to help refine the next generation of computational solvent models.

Probing the effects of NO2 and N2O additions on the auto-ignition behaviors of gasoline at engine relevant conditions

It is important to investigate the effects of NO2 and N2O additions on the auto-ignition behaviors of gasoline, as these species can affect the combustion of gasoline engines via exhaust gas recirculation (EGR). In this study, both a rapid compression machine and a high-pressure shock tube were used to measure the ignition delay times (IDTs) of China Stage-VI gasoline (Research Octane Number 95) in ‘air’ mixtures with NO2 and N2O additions, at equivalence ratios of 0.5, 1.0 and 2.0, at 10 bar, and over a temperature range of 600 ‒ 1400 K. The effects of NO2/N2O additions up to 1000 ppm were studied. The results show that the NO2 additions can obviously promote the oxidation of gasoline and decrease the IDTs at the studied conditions, and the promoting effects increase with NO2 concentrations. Meanwhile, NO2 additions show larger effects on IDTs at low temperatures than that at high temperatures. However, the N2O additions show little effects on the IDTs of gasoline. To further understand the chemistry, a multi-component gasoline surrogate model (n-heptane/isooctane/toluene) including the interaction chemistry between NOx and surrogates was proposed and employed to simulate these experimental IDTs. In general, the proposed kinetic model can simulate well these new IDTs over a wide temperature range. The flux analysis results show that the interaction chemistry between NO2 and toluene presents the largest effects on IDTs among the surrogates.

Large Eddy Simulation of Soot Formation in a Real Aero-Engine Combustor Using Tabulated Chemistry and a Quadrature-Based Method of Moments

Abstract Considering the increasingly stringent targets for aircraft emissions, computational fluid dynamics (CFD) is becoming a viable tool for improving future aero-engine combustors. However, predicting pollutant formation remains challenging. In particular, directly solving the evolution of soot particles is numerically expensive. To reduce the computational cost but retain detailed physical modeling, quadrature-based moments methods can be efficiently employed to approximate the particle number density function (NDF). An example is the recently developed split-based extended quadrature method of moments (S-EQMOM), which enables a continuous description of the soot particles' NDF, essential to consider particle oxidation accurately. This model has shown promising results in laminar premixed flames up to turbulent laboratory scale configurations. However, the application to large-scale applications are still scarce. In this work, the S-EQMOM model is applied to the Rolls-Royce BR710 aero-engine combustor to investigate the soot evolution process in practically relevant configurations. For this, the soot model is embedded into a high-fidelity simulation framework, consisting of large eddy simulation for the turbulent flow and mixing and the flamelet-generated manifold method for chemistry reduction. An additional transport equation for polycyclic aromatic hydrocarbons is solved to model their slow chemistry and the transition from the gaseous phase to the solid phase. Simulations are performed for different operating conditions (idle, approach, climb, takeoff) to validate the model using experimental data. Subsequently, the results are analyzed to provide insights into the complex interactions of hydrodynamics, mixing, chemistry, and soot formation.