Hydrogen Bond Acceptor Research Articles

Theoretical Study on Intramolecular Hydrogen Bonds of Flavonoid Cocrystals.

This study investigates the role of intramolecular hydrogen bonds in the formation of cocrystals involving flavonoid molecules, focusing on three active pharmaceutical ingredients (APIs): chrysin (CHR), isoliquiritigenin (ISO), and kaempferol (KAE). These APIs form cocrystals with different cocrystal formers (CCFs) through intramolecular hydrogen bonding. We found that disruption of these intramolecular hydrogen bonds leads to decreased stability compared to molecules with intact bonds. The extrema of molecular electrostatic potential surfaces (MEPS) show that flavonoid molecules with disrupted intramolecular hydrogen bonds have stronger hydrogen bond donors and acceptors than those with intact bonds. Using the artificial bee colony algorithm, dimeric structures of these flavonoid molecules were explored, representing early-stage structures in cocrystal formation, including API-API, API-CCF, and CCF-CCF dimers. It was observed that the number and strength of dimeric interactions significantly increased, and the types of interactions changed when intramolecular hydrogen bonds were disrupted. These findings suggest that disrupting intramolecular hydrogen bonds generally hinders the formation of cocrystals. This theoretical study provides deeper insight into the role of intramolecular hydrogen bonds in the cocrystal formation of flavonoids.

Liquid–liquid extraction of mandelic acid using deep eutectic solvent prepared by mixing choline chloride and ethylene glycol: an optimisation study

ABSTRACT In this study, deep eutectic solvent (DES) was prepared using choline chloride (a hydrogen bond acceptor) and ethylene glycol (a hydrogen bond donor) in different molar ratios for extracting mandelic acid from its aqueous matrix. At first, the experiments were performed with different molar ratios of DES with 0.1 and 1 M concentrations of mandelic acid to screen out the best combination of DES to be used in the optimisation study. A set of 20 runs was obtained using a central composite design method considering acid concentration, DES to aqueous solution volume ratio, ultrasonication time as input variables, and extraction efficiency as a response. The highest extraction efficiency was predicted to be 86.78% at acid concentration = 0.33 M, ultrasonication time = 12.15 min, and aqueous phase/DES volume ratio = 4.68. Further, solvent recovery and back-extraction of acid were performed using a sodium hydroxide solution.

Enhanced Coplanarity and Giant Birefringence in Hydroxypyridinium Nitrate via Hydrogen Bonding between Planar Donors and Planar Acceptors.

Birefringent crystals, which possess optical anisotropy, are important optical components. However, designing and synthesizing birefringent crystals faces the challenge of achieving anisotropic structures, especially coplanar geometries. Herein, we achieve a significant birefringence in an ionic compound (C5H6ON)+(NO3)-, (4-hydroxypyridinium nitrate, 4HPN) by hydrogen bonding between planar donors and planar acceptors. We demonstrate that the interactions between the planar hydrogen bond donor ((C5H6ON)+) and planar hydrogen bond acceptor ((NO3)-) ensure the coplanarity during the crystal packing, generating the desired giant optical anisotropy. On two manually cut crystal chips, we observe a = 0.494 (= 0.593), which is the largest among nitrates, or hydroxypyridinium derivatives. This value already surpasses those of the benchmark crystals, e.g., YVO4 and CaCO3, commonly used in the UV to visible and near IR spectral range. 4HPN also exhibits a strong second harmonic generation response (9.55 × KDP). This strategy offers a promising avenue for the design and development of birefringent crystals with potential applications in optical communication, sensing and signal processing devices.

Deep Eutectic Solvents for Next-generation Cyclodextrin Science

Abstract In cyclodextrin science, water has been almost exclusively employed as solvent, and this imposes non-negligible limitations to the scope of applications. Accordingly, deep eutectic solvents, constructed from hydrogen-bonding donors and acceptors, have been attracting much interest as important substitutes of water. This review comprehensively covers chemical and physicochemical features of cyclodextrins in these eco-friendly solvents. In one category, cyclodextrins or their derivatives are dissolved as solutes in conventional deep eutectic solvents. All of α-, β-, and γ-cyclodextrins efficiently form inclusion complexes with various guest molecules, exactly as observed in water. Notably, chemically modified cyclodextrins (e.g., 2-hydroxypropyl-cyclodextrins) form still more stable inclusion complexes than native cyclodextrins. Alternatively, deep eutectic solvents are prepared by combining cyclodextrins with other hydrogen-bonding components. The cyclodextrin units in these mixtures also form inclusion complexes with guest molecules. It has been proposed that enhanced flexibility of cylindrical structures of cyclodextrins allows effective induced-fit to stabilize inclusion complexes. The applications of these systems widely range from catalysis for organic synthesis to extraction, analysis, pharmaceutics, and many other fields. High solubilities of CDs and various chemicals in these solvents guarantee high productivity of target transformation, and unprecedentedly novel functions are promising for these unique systems.

Optimizing corncob pretreatment with eco-friendly deep eutectic solvents to enhance lignin extraction and cellulose-to-glucose conversion

Deep eutectic solvents (DES) are an eco-friendly, cost-effective alternative to traditional ionic liquids for biomass pretreatment, with unique characteristics encompassed by hydrogen bond donor (HBD), the molar ratio of hydrogen bond acceptor (HBA) to HBD, temperature, and time affecting efficiency. Despite its potential, a comprehensive study exploring the interplay of these factors is limited. This study explores the optimization of pretreatment variables using choline chloride/lactic acid (1:5) via the response surface method (RSM). It aims to evaluate the effects of time and temperature on lignin extraction, cellulose-to-glucose conversion, and hemicellulose removal. Employing a 22 central composite design with temperature (80–140 °C) and time (2–6 h) as variables, optimal conditions were 123 °C for 6 h. Results include 90.08±1.42 % lignin extraction, 68.77±6.9 % cellulose-to-glucose conversion, and 77.34±0.85 % hemicellulose removal, with 52.52±8.07 % lignin recovery. The fractions of pretreated CC and lignin recovered in the optimal condition found were characterized by X-ray diffraction (XDR), Fourier transform infrared spectroscopy (FTIR), 1H, 13C, 2D-HSQC NMR spectroscopy, Thermogravimetric analysis (TGA/DTG), Gel Permeation Chromatography (GPC) to elucidate chemical characteristics of the materials obtained and facilitate downstream valorization. High efficiency was achieved in lignin extraction and cellulose conversion, and addressing solvent viscosity and DES recycling will further enhance the potential for industrial scalability.

Dithiocarbamate fungicides suppress aromatase activity in human and rat aromatase activity depending on structures: 3D-QSAR analysis and molecular simulation

ABSTRACT Dithiocarbamate fungicides have been widely used in agricultural practices due to their effective control of fungal diseases, thereby contributing to global food security and agricultural productivity. In this study, the inhibitory potency of eight compounds on human and rat aromatase (CYP19A1) activity was evaluated. The results revealed that zineb exhibited the highest inhibitory potency on human CYP19A1 (IC50, 2.79 μM). Maneb (IC50, 3.09 μM), thiram (IC50, 4.76 μM), and ferbam (IC50, 6.04 μM) also demonstrated potent inhibition on human CYP19A1. For the rat CYP19A1, disulfiram (IC50, 1.90 μM) displayed the strongest inhibition followed by maneb (2.16 μM), zineb (2.54 μM), and thiram (6.99 μM). These dithiocarbamates acted as mixed/non-competitive inhibitors of human and rat CYP19A1. Dithiothreitol (DTT), a reducing agent, partially rescued thiram-mediated inhibition when incubated at the same. Moreover, positive correlations were observed between log P, topological polar surface area, molecular weight, and heavy atoms and IC50 values. 3D-QSAR analysis revealed the hydrogen bond acceptor and donor play critical roles in the binding of dithiocarbamates to human CYP19A1. In silico analysis showed that dithiocarbamates bind to the haem binding site, containing Cys437 residues. In conclusion, some dithiocarbamates potently inhibit human and rat CYP19A1 via interacting with haem-binding Cys437 residues.

Utilization of benzoic acid–based green deep eutectic solvents for the fractionation of lignocellulosic biomass

The fractionation of lignocellulose utilizing green solvents is essential for the effective operation of biorefineries. In this study, a deep eutectic solvent (DES) system composed of benzoic acid (BA, hydrogen bond donor) and choline chloride (ChCl, hydrogen bond acceptor) was fabricated and successfully applied to the lignocellulose fractionation. The DES has low toxicity and little pollution. In this system, 67.8 % of lignin and 91.2 % of hemicellulose in poplar were removed, leaving 95.8 % of cellulose intact as solid residue. Due to the removal of the amorphous components, crystallinity of cellulose-rich water-insoluble solid (CIS) substantially increased from 55.6 % to 68.6 %, and CIS was used as feedstock for nanocrystalline cellulose preparation with excellent properties. The results showed that the obtained lignin had similar properties to CEL by GPC, FT-IR, 2D-NMR and TGA. A high-purity lignin rich in G units was recovered with a well-preserved structure, which has β–O–4 linkage content up to 53.01 %, low molecular weight, low polydispersity (1.99). Finally, the hydrolyzate can be used for fermentation. This study demonstrated that BA is suitable for DES design with excellent properties on lignin extraction, and this promising DES enable efficient pretreatment for economically feasible biomass conversion. This ChCl-BA DES facilitates environmentally friendly production of functional materials derived from cellulose and lignin under mild conditions.

Beyond the Arbitrariness of Drug-Likeness Rules: Rough Set Theory and Decision Rules in the Service of Drug Design

Lipinski’s Rule of Five and Ghose filter are empirical guidelines for evaluating the drug-likeness of a compound, suggesting that orally active drugs typically fall within specific ranges for molecular descriptors such as hydrogen bond donors and acceptors, weight, and lipophilicity. We revisit these practices and offer a more analytical perspective using the Dominance-based Rough Set Approach (DRSA). By analyzing representative samples of drug and non-drug molecules and focusing on the same molecular descriptors, we derived decision rules capable of distinguishing between these two classes systematically and reproducibly. This way, we reduced human bias and enabled efficient knowledge extraction from available data. The performance of the DRSA model was rigorously validated against traditional rules and available machine learning (ML) approaches, showing a significant improvement over empirical rules while achieving comparable predictive accuracy to more complex ML methods. Our rules remain simple and interpretable while being characterized by high sensitivity and specificity.

Crystal structure of catena-poly[[diaquadiimidazolecobalt(II)]-μ2-2,3,5,6-tetrabromobenzene-1,4-dicarboxylato

The asymmetric unit of the title compound, [Co(C8Br4O4)(C3H4N2)2(H2O)2] n or [Co(Br4bdc)(im)2(H2O)2] n , comprises half of CoII ion, tetrabromobenzenedicarboxylate (Br4bdc2−), imidazole (im) and a water molecule. The CoII ion exhibits a six-coordinated octahedral geometry with two oxygen atoms of the Br4bdc2− ligand, two oxygen atoms of the water molecules, and two nitrogen atoms of the im ligands. The carboxylate group is nearly perpendicular to the benzene ring and shows monodentate coordination to the CoII ion. The CoII ions are bridged by the Br4bdc2− ligand, forming a one-dimensional chain. The carboxylate group acts as an intermolecular hydrogen-bond acceptor toward the im ligand and a coordinated water molecule. The chains are connected by interchain N—H...O(carboxylate) and O—H(water)...O(carboxylate) hydrogen-bonding interactions and are not arranged in parallel but cross each other via interchain hydrogen bonding and π–π interactions, yielding a three-dimensional network.

Screening deep eutectic solvents as green solvents for efficient extraction of carbazole from model crude anthracene oil

Carbazole is a high value-added component of crude anthracene. Highly efficient and sustainable extraction solvents are extremely significant for carbazole separation. Deep eutectic solvents (DESs), as a new class of green solvents, have gained extensive attention from researchers in the field of separation. However, a large number of DESs are generated due to the enormous combinations of hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs), which makes it challenging to identify the most suitable DES for specific separation process. Therefore, a reliable and effective method for DESs screening was highly desirable. In this work, a DESs screening method was proposed for the separation of carbazole. Initially, the COSMO-RS model was employed to calculate thermodynamic properties at infinite dilution. Subsequently, the liquid–liquid phase equilibrium behavior of prescreened DESs was further predicted by COSMO-RS to eliminate those that were miscible with toluene. Finally, the practical extraction performance of the top DES candidates was evaluated through experimental investigation. The results well validated the reliability of the screening method, identifying tetraethylammonium chloride/propionic acid (1:2) as the most promising DES for carbazole separation. Furthermore, the extraction mechanism was explored using FT-IR analysis and quantum chemical calculations.

Novel application of citric acid based natural deep eutectic solvent in drilling fluids for shale swelling prevention

Swelling of shale in clastic reservoirs poses a significant challenge, causing instability in wellbores. Utilizing water-based drilling mud with shale inhibitors is preferable for environmental reasons over oil-based mud. Ionic liquids (ILs) have garnered interest as shale inhibitors due to their customizable properties and strong electrostatic features. However, widely used imidazolium-based ILs in drilling fluids are found to be toxic, non-biodegradable, and expensive. Deep Eutectic Solvents (DES), considered a more economical and less toxic alternative to ILs, still fall short in terms of environmental sustainability. The latest advancement in this field introduces Natural Deep Eutectic Solvents (NADES), renowned for their genuine eco-friendliness. This study explores NADES formulated with citric acid (as a Hydrogen Bond Acceptor) and glycerine (as a Hydrogen Bond Donor) as additives in drilling fluids. The NADES based drilling mud was prepared according to API 13B-1 standards and their efficacy was compared with KCl, imidazolium based ionic liquid, and Choline Chloride: Urea-DES based mud. A thorough physicochemical characterization of the in-house prepared NADES is detailed. The research evaluates rheological, filtration and shale inhibition properties of the mud, demonstrating that NADES enhanced the yield point to plastic viscosity ratio (YP/PV), reduced mudcake thickness by 26%, and decreased filtrate volume by 30.1% at a 3% concentration. Notably, NADES achieved an impressive 49.14% inhibition of swelling and improved shale recovery by 86.36%. These outcomes are attributed to NADES’ ability to modify surface activity, zeta potential, and clay layer spacing which are discussed to understand the underlying mechanism. This sustainable drilling fluid promises to reshape the drilling industry by offering a non-toxic, cost-effective, and highly efficient alternative to conventional shale inhibitors, paving the way for environmentally conscious drilling practices.

Design of some phthalazine molecules as novel VEGFR-2 target inhibitors through 3D-QSAR modeling, molecular docking and dynamic simulation and pharmacokinetics profiling

AbstractBreast cancer is one of the dominant cause of cancer-related mortality in females, with an incidence of approximately 1.3 million cases annually, necessitating the development of effective therapeutic strategies. In this study, 3D-QSAR models were reported based on Phthalazine derivatives as VEGFR-2 inhibitors. The activities of these derivatives were correlated with the steric (S), electrostatic (E), hydrogen bond acceptor (A), and donor (D), and hydrophobic (H) fields, which served as critical parameters in model development. Statistical studies of these models showed that the best models are; CoMFA_S (Q2 = 0.623, R2 = 0.941), and CoMSIA_E + D (Q2 = 0.615, R2 = 0.977). Based on the insights from the model fields and docking simulation of the template (compound 17), twelve molecules were designed. These novel molecules exhibited stronger potency compared to the template and the standard, Sorafenib. Compound 17A emerged as the most potent, with pIC50 = 5.98, for CoMFA_S and 5.85, for CoMSIA_E + D, and a strong docking affinity of − 97.271 kcal/mol, therefore subjected to a 100-ns MD simulation. Results indicate better interaction and stabilizing potential over Sorafenib, due to the lower RMSD, RMSF, Rg, values and favorable hydrogen bond analyses. These conclusions were validated by Gibbs free energy analysis and MM-GBSA calculations, revealing a more favorable interaction free energy of − 18.48 kcal/mol related to Sorafenib. Furthermore, these designed compounds demonstrated promising pharmacokinetic profiles.

Synthesis of new 1,4-dihydropyridine derivative, anti-cancer, bacterial activity, molecular docking and adsorption, distribution, metabolism and excretion analysis.

Aim: The amination and cyclization method developed a new strategy for designing and assembling new 1,4-dihydropyridine derivatives of compounds 3a-g and 4a-g.Methods & materials: Newly prepared pyridine compounds are more economical, and reduce the reaction time. FT-IR, 1H-NMR, 13C-NMR, mass spectroscopy and elemental analyses elucidated the synthesized derivatives. All the derivatives are subjected to in vitro assay against MCF-7 (breast) and anti-bacterial activity.Results: In the anti-bacterial activity compound 3c is moderately active against Escherichia coli (6.0g/ml), and 4c is extremely active against Lactiplantibacillus plantarum (10.0g/ml) compared with standard Erythromycin. In cytotoxic activity, the compound 3g (lC50 24.5μM) is slightly active against standard doxorubicin. We also present the outcome of a molecular docking study connecting the methoxsalen (Protein Data Bank, PDB ID: 1Z11). Compound 3g shows a higher binding affinity (-7.7Kcal/mol) matching up with doxorubicin(-9.0Kcal/mol). The synthesized analogs were predicted for their adsorption, distribution, metabolism and excretion profiles and pharmacokinetics. The compound 3g has three rotatable bonds (NROB≤10), five hydrogen bond acceptors (HBA≤10) and four hydrogen bond donors (HBD≤5). All the compounds follow Lipinski's rule.Conclusion: Therefore, the compounds 3c and 3g are used as cytotoxic and anti-bacterial drugs in feature.

Ligand-based pharmacophore modeling targeting the fluoroquinolone antibiotics to identify potential antimicrobial compounds

Antibiotic resistance presents a serious challenge to global healthcare, making the discovery of new therapeutic agents crucial. In this study, we used pharmacophore modeling and virtual screening to identify potential lead compounds against drug-resistant bacteria. We developed a shared feature pharmacophore (SFP) map using four antibiotics—Ciprofloxacin, Delafloxacin, Levofloxacin, and Ofloxacin—and generated a drug library of 160,000 compounds from ZINCPharmer based on these features, which included hydrophobic areas, hydrogen bond acceptors (HBA), hydrogen bond donors (HBD), and aromatic moieties (Ar). Through virtual screening, we identified 25 potential drug compounds as hits, with fit scores ranging from 97.85 to 116 and RMSD values from 0.28 to 0.63. These hits were then subjected to molecular docking against the DNA gyrase subunit A protein (PDB ID: 4DDQ), with ciprofloxacin as a control. The top five compounds—ZINC09133461, ZINC03791737, ZINC21983587, ZINC26469742, and ZINC26740199—achieved the highest docking scores, ranging from − 7.3 to − 7.4 kcal/mol and ciprofloxacin − 7.3 kcal/mol. After evaluating the drug-likeness of these compounds using Lipinski’s rule and analyzing their physicochemical properties, ZINC26740199 emerged as the most promising lead, offering hope in the fight against antibiotic resistance. Furthermore, molecular scaffold analysis revealed key similarities between ZINC26740199 and Ciprofloxacin, particularly in aromatic rings, hydrophobic regions, and hydrogen bond acceptors. These features suggest its potential as an effective antimicrobial agent, though further laboratory studies are needed to confirm its efficacy.

Diethylene glycol-zinc chloride based deep eutectic solvent for green extraction of bixin compound

Deep eutectic solvents (DESs) are ionic liquid alternatives that replace volatile and flammable organic solvents. DESs are formed by hydrogen bond interaction between the hydrogen bond donor (HBD) and the hydrogen bond acceptor (HBA). We prepared DES using zinc chloride (ZnCl2) as HBA and diethylene glycol (DEG) as HBD. Formed DES was applied to extract the bixin contained in annatto seeds. The homogenous liquid mixtures were analysed for their pH, viscosity, density, conductivity, thermal properties, and solubility in various solvents. Bixin extracted using DES was identified by thin-layer chromatography (TLC), UV–Vis spectrophotometer, Fourier Transform Infra-Red (FTIR), and Proton Nuclear Magnetic Resonance (1HNMR). The mixtures with a mole fraction of ZnCl2 0.1 (DES1), 0.2 (DES2), and 0.3 (DES3) are liquid at room temperature. The analysis results prove that bixin has been successfully extracted using DES, where DES1 was better for bixin extraction than DES2 and DES3, with extracted bixin levels of 32.42, 28.84, and 0.46 mg g-1 by dry seeds mass, respectively. In this case, DES1, DES2, and DES3 could extract 62.17, 55.31, and 0.88 % of bixin from the entire total bixin contained in annatto seeds. The DES can be used for bixin extraction using a relatively simple method based on the results obtained.

Optimization of White Tea Flavanol Extraction Process by the Ultrasonic‐Assisted Deep Eutectic Solvent Method and Determination of the Antioxidant and Antibacterial Activity

ABSTRACTFlavanols have a variety of health benefits and biological activities and become the hotspot of the food development and research. In this research, flavanols were extracted from white tea by ultrasonic‐assisted deep eutectic solvent (DES) method. High‐performance liquid chromatography was used to determine the content of flavanols. The influence of four factors on the flavanol extraction yield was analyzed by single factor experiments, including deep eutectic solvent mole ratio (the mole of hydrogen bond acceptors: the mole of hydrogen bond donors), solid–liquid ratio (white tea sample weight/g: the volume of DES/mL), extraction time and extraction temperature. On the basis of single factor experiments, the factors which had significant effects on the flavanol extraction yield were further optimized by the response surface test. The results showed that the optimized extraction conditions were as follows: the mole ratio of DES 1: 4 (choline chloride: 1,2‐propanediol), the solid–liquid ratio 1:30, the extraction temperature 56°C, the extraction time 53 min, and the ultrasonic power 341 W. Under the above parameters, the extraction yield of white tea flavanols was 9.63 mg/g. After purification with macroporous resin, antioxidation and antibacterial experiments were carried out. The results showed that the antioxidant and antibacterial effects of white tea flavanols were remarkable. The antibacterial effects performed best on Escherichia coli, followed by Bacillus subtilis and Staphylococcus aureus. The maximum diameter of the antibacterial zone on Escherichia coli was 0.95 ± 0.11 mm. The best radical scavenging rates of OH, ABTS+ and DPPH were 97.1%, 97.5%, and 88.4%, respectively, when the flavanol concentration was 9.5 mg/mL. The conclusions of this research can provide theoretical foundation for the further study of white tea flavanols.

Structure Elucidation of Pharmaceutically Relevant Compounds Within Pyrene-Based Frameworks.

Single-crystal X-ray diffraction (SCXRD) is the preferred and most accurate technique for determining molecular structures. However, it can present challenges when dealing with specific small molecules and active pharmaceutical ingredients (APIs), as many do not form quality crystals without coformers or can be unstable. In this study, we introduce tetrakis(guanidinium) pyrenetetrasulfonate (G4PYR), a robust guanidinium-organosulfonate (GS) framework that efficiently encapsulates small molecules and APIs rich in functional groups. The hydrogen bonding frameworks formed by G4PYR display well-ordered structures with predictable pyrene-pyrene distances, making them ideally suited for targeting arene-based APIs with pendant groups. Successful encapsulation of various guests, including benzaldehyde, benzamide, and arenes containing multiple hydrogen bond donors and acceptors like uracil and thymine, was achieved. Furthermore, we successfully encapsulated important pharmaceutical and biologically relevant compounds, such as lidocaine, ropinirole, adenosine, thymidine, and others. Notably, we present a workflow for investigating host-guest complex formation using powder X-ray diffraction and high throughput experimentation.

Constructing Cyclic Hydrogen Bonding to Suppress Side Reactions and Dendrite Formation on Zinc Anodes.

The high electrochemical reactivity of H2O molecules and zinc metal results in severe side reactions and dendrite formation on zinc anodes. Here we demonstrate that these issues can be addressed by using N-hydroxymethylacetamide (NHA) as additives in 2 M ZnSO4 electrolytes. The addition of NHA molecules, acting as both a hydrogen bond donor and acceptor, enables the formation of cyclic hydrogen bonding with H2O molecules. This interaction disrupts the existing hydrogen bonding networks between H2O molecules, hindering proton transport, and containing H2O molecules within the cyclic hydrogen bonding structure to prevent deprotonation. Additionally, NHA molecules show a preference for adsorption on the (101) crystal surface of zinc metal. This preferential adsorption reduces the surface energy of the (101) plane, facilitating the homogeneous Zn deposition along the (101) direction. Thus, the NHA enables Zn||Zn symmetric cell with a cycle lifespan of 1100 hours at 5 mA cm-2 and Zn||Cu asymmetric cell with a high Coulombic efficiency over 99.5 %. Moreover, the NHA-modified Zn||AC zinc ion hybrid capacitor is capable of sustaining 15000 cycles at 2 A g-1. This electrolyte additive engineering presents a promising strategy to enhance the performance and broaden the application potential of zinc metal-based energy storage devices.

Kinetic and mechanistic studies on the synthesis of dimethyl carbonate reaction using deep eutectic solvents as catalysts

Dimethyl carbonate (DMC) is extensively utilized in various industries due to its exceptional physical and chemical properties, functioning as an additive in gasoline and an electrolyte solvent in lithium batteries. Among several production methods, the transesterification of propylene carbonate (PC) with methanol (MeOH) is the most efficient and environmentally friendly. This study synthesized various deep eutectic solvents (DESs) using choline chloride (ChCl) as the hydrogen bond acceptor (HBA) and monoethanolamine (MEA) as the hydrogen bond donor (HBD) in molar ratios of 1: n (n = 5, 6, 7, 8). The DESs’ structures were analyzed using Fourier Transform Infrared (FT-IR) spectroscopy, and their melting points were determined via differential scanning calorimetry (DSC). The density, viscosity, and surface tension of the DESs were measured over a temperature range from 318.15 K to 358.15 K. The catalytic effects of four different DESs on PC transesterification with MeOH were investigated, revealing that ChCl-6MEA was the most effective catalyst, prompting its selection for further experiments. Subsequent investigations examined the effects of temperature, MeOH quantity, and catalyst dosage on PC conversion and DMC yield. Additionally, this study explored chemical equilibrium and reaction kinetics through experimental and theoretical approaches. Activity-based chemical equilibrium constants, derived from experimental data, and the van’t Hoff equation elucidated their temperature dependency. A pseudo-homogeneous (PH) model characterized the non-ideal thermodynamic behavior of the liquid phase in reaction kinetics analysis. The Arrhenius equation was employed to delineate the impact of temperature variations on reaction rate constants. Finally, the proposed reaction mechanism for ChCl-6MEA catalyzed transesterification was elucidated and verified through quantum chemistry (QC) calculations.

Fast Collective Hydrogen-Bond Dynamics in HexafluoroisopropanolRelated to its Chemical Activity.

Using fluorinated mono-alcohols, in particular hexafluoro-isopropanol (HFIP), as a solvent can enhance chemical reaction rates in a spectacular manner. Previous work has shown evidence that this enhancement is related to the hydrogen-bond structure of these liquids. Here, we investigate the hydrogen-bond dynamics of HFIP and compare it to thatof its non-fluorinated analog, isopropanol. Ultrafast infrared spectroscopy show that the dynamics of individual hydrogen-bonds is about twice as slow in HFIP as in isopropanol. Surprisingly, from dielectric spectroscopy we find the opposite behavior for the dynamics of hydrogen-bonded clusters: collective rearrangements are3 times faster in HFIP than in isopropanol. This difference indicates that the hydrogen-bonded clusters in HFIP are smaller than in isopropanol. The differences in cluster size can be traced to changes in the hydrogen-bond donor and acceptor strengths upon fluorination. The smaller cluster size canboostreaction rates in HFIP by increasing the concentration of reactive, terminal OH-groups of the clusters, whereas the fast collective dynamics can increase the rate of formation of hydrogen bonds with the reactants. The longer lifetime of the individual hydrogen bonds in HFIP can enhance the stability of the hydrogen-bonded clusters, and so increase the probability of reactant-solvent hydrogen bonding.