Chemistry Interactions Research Articles

Numerical and experimental analysis of fuel regression rate in a lab-scale hybrid rocket engine with swirl injection

In this work the regression rate performance and flow physics of a lab-scale hybrid rocket engine burning gaseous oxygen and paraffin-based fuels are experimentally and numerically investigated. Regression rates are obtained by thickness-over-time averaging procedures and through a non-intrusive optical method enabling fuel grain port diameter tracking. A numerical rebuilding of the experimental data is performed with axisymmetric Reynolds-averaged Navier-Stokes simulations, using sub-models accounting for the effects of turbulence, chemistry, radiation, and fluid-surface interaction. Simulations are performed with different computational setups, also considering the fuel grain shape variation over time, obtaining a fairly good agreement between the numerical and experimental data. A parametric analysis is also performed to assess the variation of the fuel regression rate with swirl intensity.

Physiology of intracellular calcium buffering.

Calcium signaling underlies much of physiology. Almost all the Ca2+ in the cytoplasm is bound to buffers, with typically only ∼1% being freely ionized at resting levels in most cells. Physiological Ca2+ buffers include small molecules and proteins, and experimentally Ca2+ indicators will also buffer calcium. The chemistry of interactions between Ca2+ and buffers determines the extent and speed of Ca2+ binding. The physiological effects of Ca2+ buffers are determined by the kinetics with which they bind Ca2+ and their mobility within the cell. The degree of buffering depends on factors such as the affinity for Ca2+, the Ca2+ concentration, and whether Ca2+ ions bind cooperatively. Buffering affects both the amplitude and time course of cytoplasmic Ca2+ signals as well as changes of Ca2+ concentration in organelles. It can also facilitate Ca2+ diffusion inside the cell. Ca2+ buffering affects synaptic transmission, muscle contraction, Ca2+ transport across epithelia, and the killing of bacteria. Saturation of buffers leads to synaptic facilitation and tetanic contraction in skeletal muscle and may play a role in inotropy in the heart. This review focuses on the link between buffer chemistry and function and how Ca2+ buffering affects normal physiology and the consequences of changes in disease. As well as summarizing what is known, we point out the many areas where further work is required.

Long-term studies of water chemistry and zooplankton interactions in a submontane dam reservoir in variable hydrological years (dry, wet, average)

The differences in environmental parameters and zooplankton community were studied in the epilimnion of the Carpathian Dobczyce Dam Reservoir on the Raba River (southern Poland) between hydrologically dry (HD), average (HA) and wet (HW) years distinguished on the basis of mean annual flow for 2000-2017. We found significant differences in water chemistry (conductivity, nutrients: P-tot, PO43−, NH4+) in the epilimnion between the studied hydrological years. The total density and dry weight of zooplankton and the density of Rotifera: Keratella quadrata (Müller, 1786), Copepoda: Copepoda n. det. (immature stages), Cyclops strenuus Fischer, 1851, Eudiaptomus gracilis (Sars G.O., 1863) and Cladocera: Bosmina longirostris (O.F.Müller, 1776), Daphnia cucullata G.O. Sars, 1862, and D. longispina (O.F.Müller, 1776) were significantly higher in HA and HW years than in HD years. The highest densities of many Rotifera, Cladocera and Copepoda species were found in HA and HW years with high flows or floods in the river in spring or early summer. At these times, the epilimnion was rich in P-tot (diffuse pollution), considered as a limiting factor for algal growth in Carpathian reservoirs. The best Generalized Linear Models (GLM) for zooplankton density included 4-6 factors, among which P-tot, NO3−, and pH were always present. We found that river flows prevailing in a given year determine water chemistry and eutrophication processes, which has a significant impact on densities and dry weight of zooplankton communities in HD, HA and HW years. The results obtained have important implications for proper management in mountain catchments.

Interstitial carbonates in pillowed metabasaltic rocks from the Pilbara Craton, Western Australia: A vestige of Archean seawater chemistry and seawater-rock interactions

Calcites hosted in the interpillow void spaces of extremely well preserved, 3.47–3.12 Ga pillow lavas of the Archean Pilbara Craton, Australia, provide new geochemical insights into the composition of Archean seawater and its interaction with basaltic crust. We present a comprehensive dataset of major and trace elements, radiogenic 147Sm-143Nd, 87Rb-87Sr, and stable C-O isotopes for these calcites.Based on their elemental composition and Post-Archean Australian Shale-normalized rare earth element and yttrium (REYPAAS) patterns, two types of calcites can be distinguished. Type I (n = 9) are coarse-grained calcites with elevated Mn concentrations (478–14,790 ppm) and high REY concentrations that match the basaltic host rock compositions. Petrographic textures in combination with geochemical data indicate precipitation from boiling seawater trapped between pillows during basalt eruption. Small light-REYPAAS depletions, only slightly super-chondritic Y/Ho (34.5–39.1), and low δ18O(VSMOW2) (9.25–16.66 ‰) suggest relatively high fluid-rock interactions of boiling seawater with the basaltic host rock. These characteristics are similar to those of interstitial carbonates found in modern mid-ocean ridge basalts. Type II carbonates (n = 6) are fine-grained, low-Mn (13.7–420 ppm) calcites that exhibit comparably high Sr concentrations (825–2,516 ppm) and anoxic modern seawater-like REYPAAS patterns, strong super-chondritic Y/Ho (39.1–55.8) and δ18O(VSMOW2) values of 9.10–13.18 ‰. These features hint to direct calcite precipitation from seawater within the degassing space with little fluid-rock interaction.Almost all (Type I and Type II) of the calcites investigated here, combined with their respective host rocks, yield well-defined Sm-Nd isochron ages for the Apex (3,466 ± 23 Ma), Euro (3,365 ± 43 Ma), Honeyeater (3,187 ± 33 Ma), and Bradley (3,131 ± 24 Ma) formations. Only calcites from the Mt. Ada Basalt and their associated host rocks show a ∼ 100 Ma younger Sm-Nd isochron age (3,361 ± 22 Ma) compared to the U-Pb zircon age of formation.Highly radiogenic initial Sr isotope compositions of the high-Mn calcites (Type I) and low Sr concentrations, suggest Sr remobilization for these calcites. In contrast, the low-Mn calcite (Type II) exhibit higher Sr concentrations and lower 87Sr/86Sr(i) of 0.7010–0.7011 at 3.34 Ga and 0.70137 at 3.12 Ga, suggesting increasing influence of crustal weathering on the composition of Paleoarchean seawater through time, and progressive decoupling from the Archean mantle (87Sr/86Sr(i) = 0.7003–0.7007).

Translating Kratom-Drug Interactions: From Bedside to Bench and Back.

Kratom is a botanical natural product belonging to the coffee family, with stimulant effects at low doses and opioid-like effects at higher doses. During the last two decades, kratom has been purported as a safer alternative to pharmaceutical and illicit drugs to self-manage pain and opioid withdrawal symptoms. Kratom alkaloids, typically mitragynine, have been detected in biologic samples from overdose deaths. These deaths are often observed in combination with other drugs and are suspected to result from polyintoxications. This review focuses on the potential for kratom to precipitate pharmacokinetic interactions with object drugs involved in these reported polyintoxications. The legal status, chemistry, pharmacology, and toxicology are also summarized. The aggregate in vitro and clinical data identified kratom and select kratom alkaloids as modulators of cytochrome P450 (P450) enzyme activity, notably as inhibitors of CYP2D6 and CYP3A, as well as P-glycoprotein-mediated efflux activity. These inhibitory effects could increase the systemic exposure to co-consumed object drugs, which may lead to adverse effects. Collectively, the evidence to date warrants further evaluation of potential kratom-drug interactions using an iterative approach involving additional mechanistic in vitro studies, well designed clinical studies, and physiologically based pharmacokinetic modeling and simulation. This critical information is needed to fill knowledge gaps regarding the safe and effective use of kratom, thereby addressing ongoing public health concerns. SIGNIFICANCE STATEMENT: The botanical kratom is increasingly used to self-manage pain and opioid withdrawal symptoms due to having opioid-like effects. The legal status, chemistry, pharmacology, toxicology, and drug interaction potential of kratom are reviewed. Kratom-associated polyintoxications and in vitro-in vivo extrapolations suggest that kratom can precipitate pharmacokinetic drug interactions by inhibiting CYP2D6, CYP3A, and P-glycoprotein. An iterative approach that includes clinical studies and physiologically based pharmacokinetic modeling and simulation is recommended for further evaluation of potential unwanted kratom-drug interactions.

An exploratory modelling study of chemiluminescence in ammonia-fuelled flames. Part 2

The detailed kinetic mechanism of the author was extended by reactions describing formation and consumption of excited species which are formed in NH3+CH4+air flames, complementing the modelling efforts presented in Part 1. Currently the model includes the following excited species: O(1D), OH*, O2*, CH*, CH2(1), NO2*, NO(A), NH*, N2(A), NH2*, C2*, CO2*, CH2O*, and CN*, among which many were observed in chemiluminescence signatures of ammonia-fuelled flames. The new model predictions were compared with the experimental data obtained in laminar premixed counterflow NH3+CH4+air flames (Combust. Flame 231 (2021) 111508). The overall agreement between the measurements and calculations was not as good as it was observed for NO(A), OH* and NH* in NH3+H2+air flames presented in Part 1. It was argued that both unquantified experimental uncertainties and remaining deficiencies of the model could contribute to the discrepancies found. Nevertheless, for OH*, NH*, CN*, CO2* and CH*, as well as for several ratios of chemiluminescence intensity of different excited species the predicted trends both in terms of their variation with equivalence ratio and the amounts of ammonia in the fuel are in qualitative agreement with the measurements. The most important inconsistency between the experiments and modelling is found for NO(A), which is the only species in NH3+CH4+air flames forming, according to the present mechanism, by the energy transfer from N2(A). This indicates that either formation of N2(A) precursors, namely NH and N, is not accurate due to missing interaction of nitrogen and hydrocarbon chemistry, or reactive quenching of N2(A) is incomplete and requires further development.

On the interactions involving serine proteases obtained from Monacrosporium thaumasium (Ascomycota: Orbiliomycetes) and deoxyribonucleic acid (DNA): biological macromolecules in action

The use of force spectroscopy approaches performed with optical tweezers can be very useful in determining the binding modes and the physical chemistry of DNA interactions with ligands, from small drugs to proteins. Helminthophagous fungi, on the other hand, have important enzyme secretion mechanisms for various purposes, and the interactions between such enzymes and nucleic acids are very poorly studied. Therefore, the main goal of the present work was to investigate, at the molecular level, the mechanisms of interaction between fungal serine proteases and the double-stranded (ds) DNA molecule. Experimental assays performed with this single molecule technique consist in exposing different concentrations of the protease of this fungus to dsDNA until saturation while monitoring the changes on the mechanical properties of the macromolecular complexes formed, from where the physical chemistry of the interaction can be deduced. It was found that the protease binds strongly to the double-helix, forming aggregates and changing the persistence length of the DNA molecule. The present work thus allowed us to infer information at the molecular level on the pathogenicity of these proteins, an important class of biological macromolecules, when applied to a target specimen.

Can Polar Stratospheric Clouds Explain Arctic Amplification?

Abstract Climate models underestimate the magnitude of Arctic warming in past warm climates, like the early Cretaceous and Paleogene periods, implying that certain physical processes might be missing or poorly represented. Previous studies suggest that a large increase in wintertime Arctic polar stratospheric clouds (PSCs) might have promoted Arctic amplification through additional greenhouse warming. High methane concentrations in warm climates might have increased stratospheric water vapor providing favorable conditions for PSCs. However, methane concentrations in past warm climates are extremely uncertain. Here, we revisit the PSC hypothesis by exploring PSC changes under very high methane levels, 4× preindustrial carbon dioxide, and strong polar-amplified surface warming, using a whole-atmosphere model with fully interactive chemistry. We find that with polar-amplified warming there is a large increase in Arctic outgoing longwave radiation (OLR) that reduces as the methane concentration is increased. PSCs increase monotonically with methane concentration. A large radiative cooling and an increase in water vapor in the stratosphere increases Arctic PSCs, which follow a power law with respect to relative humidity. Using a two-way partial radiative perturbation technique, we show that the OLR reduction due to PSCs is similar to the direct radiative forcing of methane for high methane levels. Thus, we find that PSCs could play an important role in Arctic warming in a warmer-than-present-day climate, but only if methane levels were higher than suggested by previous modeling studies for past warm climates.

19 F-Labeled Probes for Recognition-Enabled Chromatographic 19 F NMR.

The NMR technique is among the most powerful analytical methods for molecular structural elucidation, process monitoring, and mechanistic investigations; however, the direct analysis of complex real-world samples is often hampered by crowded NMR spectra that are difficult to interpret. The combination of fluorine chemistry and supramolecular interactions leads to a unique detection method named recognition-enabled chromatographic (REC) 19 F NMR, where interactions between analytes and 19 F-labeled probes are transduced into chromatogram-like 19 F NMR signals of discrete chemical shifts. In this account, we summarize our endeavor to develop novel 19 F-labeled probes tailored for separation-free multicomponent analysis. The strategies to achieve chiral discrimination, sensitivity enhancement, and automated analyte identification will be covered. The account will also provide a detailed discussion of the underlying principles for the design of molecular probes for REC 19 F NMR where appropriate.

Unsteady Combustion of the Heptane-in-Water Emulsion Foamed with Hydrogen–Oxygen Mixture

This research paper numerically studies how hydrocarbon additives affect hydrogen combustion in the process of complex fuel burning on the example of the combustible foam representing the heptane-in-water emulsion foamed with a hydrogen–oxygen mixture. It is demonstrated that the two-phase hydrodynamic model with an account of foam structure and chemical kinetics reproduces quite accurately, at least at the qualitative level, the experimentally observed features of foamed emulsion combustion. Due to this, it is concluded that a proposed model can be fruitfully used for the interpretation of the combustion features observed in such a complex combined fuel. Based on the obtained numerical data, it is found that there are two main possibilities related to the hydrogen–hydrocarbon chemistry interactions. In the case of near-stoichiometric, hydrocarbons act mainly as an inhibitor of hydrogen combustion; however, for lean hydrogen–oxygen mixtures, flame propagation is determined by the joint hydrocarbon and hydrogen oxidation kinetics. Herewith, the hydrocarbon burns together with the hydrogen inside the flame front in the case of slow combustion, while in the case of high-speed combustion, hydrogen oxidation kinetics becomes predominant, and hydrocarbons evaporate and burn behind the flame front, causing a lesser effect on the flame dynamics.

Comparison of the simulated outcomes of aerosol–cloud interaction by a meteorological model with and without an interactive chemistry module

With the general rise of computational capacities and the continued efforts to improve computational efficiencies, more and more studies have been utilizing state-of-the-art atmospheric models that enable cloud-resolving simulations over a global domain. Microphysical processes inside clouds, however, are on a scale much smaller than that of a cloud itself, and therefore resolving clouds in a model is not equivalent to resolving cloud microphysical processes. When aerosol–cloud interaction (ACI) is studied, chemistry models enable the prognostic calculations for chemical species, including aerosols, which can perturb cloud microphysics and eventually impact clouds and climate. The large drawback of these models is the high computational cost required for tracking chemical species in space and time that may not be affordable in some studies. As a result, some studies have used non-chemistry models with prescribed cloud droplet number concentrations n_c and compared multiple simulations with different n_c to assess the impacts of varying aerosol concentrations on clouds. In this study we assess whether the same or similar ACI can be simulated when the aerosol number is increased in a chemistry model and when n_c is raised in a non-chemistry model. A case study has been conducted over the Maritime Continent in September 2015 when an extremely large number of aerosols were observed due to fires under a dry condition brought by a strong El Niño. The comparison of the simulations by the chemistry and non-chemistry models shows that the aerosol-driven enhancement of rainfall in the chemistry simulations was not present in the non-chemistry simulations, even with prescribed n_c with certain spatial variation based on the chemistry runs. Therefore, simulated ACI may largely differ depending on the manner by which an increase or decrease of aerosols is represented in a model. The result suggests the further need for powerful computational capabilities and the pursuit of a rigorous means to incorporate aerosol species in a non-chemistry model.

Highly dispersed PtO over g-C3N4 by specific metal-support interactions and optimally distributed Pt species to enhance hydrogen evolution rate of Pt/g-C3N4 photocatalysts

Understanding the fundamental chemistry of metal-support interactions during catalyst preparation is essential to develop a highly efficient Pt/g-C3N4 photocatalyst for the H2 evolution reaction (HER). In this study, we prepared Pt/g-C3N4 photocatalysts via a loading process of different Pt contents onto solvothermally treated g-C3N4 (SCN) and a successive hydrogen reduction. The physicochemical interactions between Pt species and O-containing functional groups over SCN were tracked, and we investigated how the interactions influenced the photocatalytic properties and performance of Pt/SCN. During the reduction process, Pt(OH)22+ ions in liquid phase specifically interacted with neighboring C = O groups over SCN, resulting in highly dispersed PtO species via chemical bonding to SCN. Due to the limited number of the neighboring C = O groups over SCN, the chemically bonded PtO species were saturated at a certain amount, and 1Pt/SCN (1 wt% of Pt) showed the highest Pt dispersion in this study. In the reduction process, excess Pt was readily reduced to Pt metallic phase and then agglomerated in Pt clusters at high Pt loadings. Therefore, the highly active and stable Pt2+ sites were uniformly dispersed and immobilized over 1Pt/SCN by specific interactions with the O-containing functional groups, showing an outstanding HER activity per gram Pt (120.6 mmol∙gPt−1∙h−1). However, data for the optical and electrochemical properties demonstrated that 3Pt/SCN (3 wt% of Pt) had the best charge separation efficiency because of the optimal distribution of the Pt species over SCN. Correspondingly, the optimized 3Pt/SCN exhibited the highest HER rate of 1255.52 μmol∙gcat−1∙h−1, which was about 50 times higher than SCN photocatalyst (25.2 μmol∙gcat−1∙h−1).

Sway-Based Interactive Chemistry Learning Media: Feasibility for Improving Students’ Conceptual Understanding and Self-efficacy

Self-efficacy greatly determines the success of students in learning. However, most students have low self-efficacy. This study aims to develop sway-based interactive chemistry learning media to improve the students’ conceptual understanding of stoichiometry and self-efficacy. The research used a 4D development model which consists of the stages of define, design, develope, and disseminate. Sway-based media trials include individual trials involving 3 students, small group trials involving 8 students, and field trials involving 2 classes consisting of 70 students of class X MIPA SMA Negeri 4 Banjarmasin. The study indicated that the developed sway-based media: (1) very valid from the aspect of content, presentation, language, and media; (2) practical based on one to one and small group trials, students’ responses, and learning process management data; and (3) effective based on the N-gain score of the students’ conceptual understanding of stoichiometric concept and self-efficacy in the medium and high categories, respectively. It can be concluded that sway-based interactive learning media is feasible used in chemistry learning to improve students’ conceptual understanding of stoichiometric concepts and self-efficacy.

The development of interactive chemistry lessons on the topic: «Mineral fertilizers»

The main methodological innovations today are the use of interactive learning technologies, involving each student in the learning process, i.e. in the process of cognition. The introduction of modern interactive learning technologies creates conditions for improving the quality of the training session, as well as methods of teaching chemistry. Each teacher uses new learning technologies to ensure that classes are systematic, high-quality, interesting, and effective. It is known that students have different ways of thinking and when conducting lessons, performing tasks with the help of illustrations, video materials, animation, and games increases interest in the subject. In this paper, interactive apps identified and described that contribute to increasing the activity of students and the effectiveness of the learning process in lower secondary school, as well as interactive chemistry lessons on the topic "Mineral fertilizers" are developed. In implementing the developed interactive lessons, such teaching methods as interactive lectures, interactive exercises, and didactic games were used. A relatively small sample size limited this study, but the results obtained have essential data for the professional development of teachers and the development of modern interactive lessons using ICT. The results obtained after a survey of students, in which 100 students participated, indicate that interactive lessons support learning and increase students' motivation, and this has a positive effect on their attitude to the subject

Interaction and Redox Chemistry between Iron, Dopamine, and Alpha-Synuclein C-Terminal Peptides.

α-Synuclein (αS), dopamine (DA), and iron have a crucial role in the etiology of Parkinson's disease. The present study aims to investigate the interplay between these factors by analyzing the DA/iron interaction and how it is affected by the presence of the C-terminal fragment of αS (Ac-αS119-132) that represents the iron-binding domain. At high DA:Fe molar ratios, the formation of the [FeIII(DA)2]- complex prevents the interaction with αS peptides, whereas, at lower DA:Fe molar ratios, the peptide is able to compete with one of the two coordinated DA molecules. This interaction is also confirmed by HPLC-MS analysis of the post-translational modifications of the peptide, where oxidized αS is observed through an inner-sphere mechanism. Moreover, the presence of phosphate groups in Ser129 (Ac-αSpS119-132) and both Ser129 and Tyr125 (Ac-αSpYpS119-132) increases the affinity for iron(III) and decreases the DA oxidation rate, suggesting that this post-translational modification may assume a crucial role for the αS aggregation process. Finally, αS interaction with cellular membranes is another key aspect for αS physiology. Our data show that the presence of a membrane-like environment induced an enhanced peptide effect over both the DA oxidation and the [FeIII(DA)2]- complex formation and decomposition.

The combined effects of heterogeneous chemistry and aerosol-radiation interaction on severe haze simulation by atmospheric chemistry model in Middle-Eastern China

Heterogeneous chemistry and aerosol-radiation interaction (ARI) are considered two of the key mechanisms affecting haze formation and their reasonable parameterizations in atmospherically chemical models play an important role in accurate haze or air quality prediction. However, until the present, their relative contributions to severe haze have rarely been evaluated. Using the double-way atmospherically chemical model GRAPES_Meso5.1/CUACE CW, the relative contributions of heterogeneous chemistry and ARI to PM2.5 are investigated under different pollution levels in Middle-Eastern China (MEC) during December 2016. Study results show that the combined effects of heterogeneous chemistry and ARI generate 29.7% of total PM2.5 mass in MEC of December 2016, of which ARI contributes 19.7%, much higher than heterogeneous chemistry (6.1%). However, heterogeneous chemistry is important for reasonable reproduction of the proportion of secondary inorganic aerosols (SIA) of PM2.5, especially during heavy haze. Both the contributions of heterogeneous chemistry and ARI to PM2.5 increase with the haze pollution aggravation but to different degrees. The contribution of heterogeneous chemistry to modeled PM2.5 concentration rises from 4.0% on clean days to 6.6% under moderate pollution and 7.8% under heavy haze. And that of ARI increases rapidly from 9.1% on clean days to 21.0% under moderate pollution and 29.1% during heavy pollution. It is worth noticing that there is an additional contribution to PM2.5 caused by the combination of heterogeneous chemistry and ARI except for their respective contributions, which reaches up to 7.3% of PM2.5 mass and 18.5% of SIA generation under heavily polluted conditions. This is because ARI further promotes heterogeneous oxidation of SO2 and NOx by increasing the aerosol surface area concentration (SAC), causing additional SIA production via heterogeneous pathways. This work indicates the contribution of ARI to severe haze formation not only by altering meteorological conditions but also by reforming the chemical processes in the model.

A microscopy study of nickel-based superalloys performance in type I hot corrosion conditions

ABSTRACT Alloy material selection for sustainable, efficient, and cost-effective use in components is a key requirement for both power generation and aerospace sectors. Superalloys are manufactured using a combination of different elements, selected carefully to balance mechanical performance and environmental resistance to be used in a variety of different service conditions. Therefore, a fundamental understanding of each element is critical to alloy design. In this paper, the interaction of alloy chemistry, particularly chromium as a corrosion-resistant element along with titanium and molybdenum, and their effect on alloys performance for the relevant gas turbine industries were discussed. Based on the findings, the single-crystal alloy is found to be a better corrosion resistant alloy exhibited higher corrosion resistance in comparison to polycrystal alloys and proved that microstructure has a significant impact on alloy performance. This study also established that molybdenum level in chromia former alloys can significantly enhance the corrosion damage.

On the Importance of Model Selection for CFD Analysis of High Temperature Gas-Solid Reactive Flow; Case Study: Post Combustion Chamber of HIsarna Off-Gas System

In this paper a CFD analysis of HIsarna off-gas system for post combustion of CO-H2-carbon particle mixture is presented to evaluate the effect of different sub-models and parameters on the accuracy of predictions and simulation time. The effects of different mesh type, mesh grid size, radiation models, turbulent models, kinetic mechanism, turbulence chemistry interaction models, including and excluding gas-solid reactions, number of reactive solid particles are investigated in detail. Based on the accuracy of the predictions and agreement with counterpart measured values, the best combination is selected and conclusions are derived. It was found that radiation and turbulence chemistry interaction model have a major effect on the temperature and composition profile prediction along the studied off-gas system, compared to the variations in other models. The effect of these two models becomes even more evident when the temperature and fuel content of the flue gas are high.

Computational insights into the adsorption mechanisms of anionic dyes on the rutile TiO2 (1 1 0) surface: Combining SCC-DFT tight binding with quantum chemical and molecular dynamics simulations

Metal oxides are gaining momentum rapidly for application in water pollutant remediation. In this study, the adsorption proprieties of two anionic dyes, i.e., acid yellow 36 (AY36) and acid orange 6 (AO6) on the (110) surface of rutile titanium dioxide (TiO2) in an aqueous medium were investigated using computational methods. The density functional theory (DFT) was used to determine the reactivity of organic molecules by calculating the frontier molecular orbital energies, energy gap (ΔEgap), chemical hardness (η), chemical softness (σ), electronegativity (χ), chemical potential (μ), electrophilicity (ω), the fraction of electrons transferred (ΔN), back-donation energy (ΔEback-donation), Mulliken charge, and Fukui indices. The obtained results showed that the AY36 molecule is more reactive than the AO6 molecule and may have a good adsorption capability compared to the AO6 dye. The most favorable adsorption configurations of AY36 and AO6 molecules were investigated using molecular dynamics (MD) simulation. The calculated interaction energies by MD simulation showed that the TiO2 (110) surface has a high sensitivity to interact with the two anionic dyes, with more affinity toward the AY36 molecule. Furthermore, to get deep insights into the chemistry of interactions between the anionic dyes and the TiO2 (110) surface, the self-consistent charge density functional tight-binding (SCC-DFTB) method was carried out. Results showed that anionic dyes adsorbed on the TiO2 (110) surface by forming covalent bonds between oxygen atoms of the sulfonic group and Ti atoms. Theoretical insights from this work would serve as a guide for researchers to explore the application of oxides in water pollutant remediation.

How Chemistry Determines Separations: Influence of Selectivity on Resolution

Resolution in chromatography is influenced by retention, engineering, and selectivity. Retention relates to how long analytes are in the column; generally, longer retention leads to increased resolution. Engineering relates to the design and operation of the chromatographic system, as expressed by the number of theoretical plates. Generally, more theoretical plates lead to greater resolution. Finally, selectivity is generated by the chemistry of the intermolecular interactions between the stationary phase and the analytes. Larger differences in the strength of these interactions leads to greater selectivity. In this installment, we examine the relationship between selectivity and resolution.