Hydrogen Bond Donor Research Articles

Efficient selective leaching of ytterbium and lutetium oxides by new hydrophobic deep eutectic solvents

This research reports the first study of selective leaching of ytterbium-lutetium oxides mixture with hydrophobic deep eutectic solvents (DESs), and high-efficiency and simple-prepared were used to separate and beneficiate lutetium. With hydrophobic DESs, which were formed with hydrophobic salicylic acid (SA) or 3,5-dinitrosalicylic acid (DNS) as the hydrogen bond donor (HBD) and hydrophobic tri-n-octyl phosphine oxide (TOPO) as the hydrogen bond acceptor (HBA), powdered eutectic mixtures of ytterbium-lutetium oxides were leached. The separation factor of ytterbium-lutetium was concluded to reached 2.11 with a solid-liquid (S/L) ratio of 1/50 g/ml, a temperature of 90 °C and a 4 h leaching time, and the experimental conditions, such as the S/L ratio, temperature and reaction time, were explored. The formation of intermolecular hydrogen bonds between the HBD and HBA was revealed through multiple methods, such as IR (disappearance of OH characteristic peaks), 1H NMR (formation of sharp peaks not present for intramolecular hydrogen bonds) and 31P NMR (shift of P = O peaks to higher fields). The lattice energies of the intermolecular hydrogen bonds and the solid oxide lattice energies, which were calculated with Gaussian 16 software (0.87 eV for SA/TOPO = 1:1 and 0.94 eV for DNA/TOPO = 1:1) and the Born–Haber cycle (12957.56 kJ/Mol for Yb2O3 and 12993.59 kJ/Mol for Lu2O3), provided a theoretical illustration of preferential Yb/Lu dissolution leading to separation. The stripping, regeneration and recycling capabilities of the DESs were investigated with stripping and recirculation experiments. Based on these results, the new DES as the leaching agent to separation of ytterbium lutetium oxide is identified as a new efficient mothed with industrialization potential.

Rational Combination of π-Conjugated and Non-π-Conjugated Groups Achieving Strong Nonlinear Optical Response, Large Optical Anisotropy, and UV Light-Switchable Fluorescence.

Combining π-conjugated and non-π-conjugated groups is an important strategy for synthesizing new nonlinear optical (NLO) crystals. However, the second harmonic generation (SHG) response and optical anisotropy can be limited by improper spatial alignment of these functional groups in the crystal structure. In this work, it is revealed that non-π-conjugated [NH2SO3] group acts as both hydrogen bond donor and acceptor, effectively regulating the 2D planar structure formed by π-conjugated [C4N3H6] groups. The resulting organic-inorganic hybrid crystal C4N3H6SO3NH2 exhibits a strong SHG response (2.5 × KDP), large optical anisotropy (0.233@546nm), and blue-violet and green fluorescence near 360 and 520nm, respectively. This work expands the methodology for creating new NLO crystals through organic-inorganic hybridization, while also showcasing the potential of C4N3H6SO3NH2 as a multifunctional optical material.

Deep Eutectic Solvents as Agents for Improving the Solubility of Edaravone: Experimental and Theoretical Considerations.

In this study, both practical and theoretical aspects of the solubility of edaravone (EDA) in Deep Eutectic Solvents (DESs) were considered. The solubility of edaravone in some media, including water, can be limited, which creates the need for new efficient and environmentally safe solvents. The solubility of EDA was measured spectrophotometrically and the complex intermolecular interactions within the systems were studied with the COSMO-RS framework. Of the four studied DES systems, three outperformed the most efficient classical organic solvent, namely dichloromethane, with the DES comprising choline chloride and triethylene glycol, acting as hydrogen bond donor (HBD), in a 1:2 molar proportion yielding the highest solubility of EDA. Interestingly, the addition of a specific amount of water further increased EDA solubility. Theoretical analysis revealed that in pure water or solutions with high water content, EDA stacking is responsible for self-aggregation and lower solubility. On the other hand, the presence of HBDs leads to the formation of intermolecular clusters with EDA, reducing self-aggregation. However, in the presence of a stoichiometric amount of water, a three-molecular EDA-HBD-water complex is formed, which explains why water can also act as a co-solvent. The high probability of formation of this type of complexes is related to the high affinity of the components, which exceeds all other possible complexes.

Terpenes based hydrophobic deep eutectic solvents for dispersive liquid-liquid microextraction of aliphatic aldehydes in drinking water and alcoholic beverages

Aliphatic aldehydes are a class of organic compounds containing aldehyde groups, which are widespread, and closely related to people's daily life and health. In this work, a series of terpenes based hydrophobic deep eutectic solvents were designed and synthesized using hexafluoroisopropanol as hydrogen bond donor and menthol/thymol as hydrogen bond acceptor. Then they are used as extraction solvent in dispersive liquid-liquid microextraction for extracting and determining seven aliphatic aldehydes from drinking water and alcoholic beverage combined with high performance liquid chromatography-ultraviolet. Due to the fact that these hydrophobic deep eutectic solvents are liquid at the room temperature, a density greater than that of water, a lower viscosity (≤26.10 mPa s, 25 °C), after extraction and centrifugation, the microvolume DES-rich phase in the bottom is convenient for collection and direct analysis without further dissolution or dilution with organic solvents. Some factors affecting the extraction recovery were optimized by one-variable-at-a-time and response surface methodology. Under the optimal conditions, the enrichment factors for the seven aliphatic aldehydes were 48–56. The method had good performance: linear ranges of 1.0–200, 0.5–200, 0.2–200, 0.4–400, 1.0–400, 0.4–400 and 0.4–400 μg L−1 for seven aliphatic aldehydes (r2 ≥ 0.9949), limits of detection of 0.1–0.5 μg L−1, intra-day and inter-day precisions <4.9%. The recoveries of seven aliphatic aldehydes ranged from 76.0 to 119.0%. The proposed dispersive liquid-liquid microextraction method is simple, rapid, highly efficient, and green, which effectively reduces the amount of toxic chemical reagents used and their impact on the environment. Rapid and efficient detection of aliphatic aldehydes helps ensure a healthy diet and has great application prospects in food safety analysis.

Symmetry of Pyridine Derivatives Controlled Two-Dimensional Nanostructural Diversity by Co-Assembly with Aromatic Carboxylic Acids.

The self-assembly behaviors of aromatic carboxylic acids are commonly investigated at the liquid/solid interfaces because of their rigid skeletons and both hydrogen-bond donors and receptors. However, self-assemblies of aromatic carboxylic acids with low symmetry and interactions between carboxylic acid and pyridine derivatives are worth exploring. In this work, the self-assembled structural transitions of a kind of low-symmetric aromatic carboxylic acid (H4QDA) are regulated by the coadsorption of two pyridine derivatives (DPE and T4PT) with different symmetry, which are investigated by scanning tunneling microscopy under ambient conditions. For the H4QDA/DPE system, the grid structure appears. For the H4QDA/T4PT system, the coassembled morphologies display an obvious concentration dependence. With the increase of solution concentration of T4PT, three coassembled patterns (network structure, chiral linear structure, and brick-like structure) are observed. Corresponding structural models suggest that the O-H···N hydrogen bonds have great contributions to stabilizing these coassembled structures. Our studies will help to explore the complexity, diversity, and functionality of multiple component systems and are conducive to further understanding the underlying mechanisms in the assembly process.

Sodium Citrate Electrolyte Additive to Improve Zinc Anode Behavior in Aqueous Zinc-Ion Batteries

Despite features of cost-effectiveness, high safety, and superior capacity, aqueous zinc-ion batteries (ZIBs) have issues of uncontrolled dendritic cell failure and poor Zn utilization, resulting in inferior cycling reversibility. Herein, the environmentally friendly and naturally abundant sodium citrate (SC) was adopted as a dual-functional additive for ZnSO4-based (ZSO) electrolytes. Owing to the abundant hydrogen-bond donors and hydrogen-bond acceptors of SC, the Zn2+-solvation shell is interrupted to facilitate Zn desolvation, resulting in inhibited corrosion reactions. Additionally, sodium ions (Na+) from the SC additive with a lower effective reduction potential than that of zinc ions (Zn2+) form an electrostatic shield inhibiting the formation of initial surface protuberances and subsequent Zn dendrite growth. This assists in the Zn three-dimensional (3D) diffusion and deposition, thereby effectively enhancing cycling stability. Specifically, a long cycling lifespan (more than 760 h) of the Zn//Zn symmetric cell is achieved with a 2 M ZSO-1.0 SC electrolyte at a current density of 1 mA cm−2. When coupled with the NaV3O8·1.5 H2O (NVO) cathode, the full battery containing SC additive exhibited a capacity retention rate (40.0%) and a cycling life of 400 cycles at a current density of 1 A g−1 compared with that of pure ZnSO4 electrolyte (23.8%). This work provides a protocol for selecting an environmentally friendly and naturally abundant dual-functional electrolyte additive to achieve solvation shell regulation and Zn anode protection for the practical large-scale application of ZIBs.

Ce-UiO-66-F4-based composites decorated with green carbon dots for universal adsorption of organic pollutants containing hydrogen bond donors and its application exploration

Efficient and stable water purification is essential for the protection of water resources. Current adsorbents based on metal–organic frameworks face limitations of restricted active sites and single adsorption objects. In this study, we developed a cost-effective and environmentally friendly Tea-L-CDs@Ce-UiO-66-F4 composites by growing Tea and L-tryptophan carbon dots (Tea-L-CDs) over Ce-UiO-66-F4 MOF, and the interaction force was enhanced by hydrogen bonding (-F/O/N…H-O-, -F/O/N…H-N-, etc.) to achieve universal adsorption. In detail, the maximum adsorption capacity (qm) of the adsorbent for trypan blue (TB), congo red (CR), and CR (adjust pH) was 773.4, 1428.6, and 4761.9 mg/g. The universal experiment showed that the composites exhibited excellent qm for alizarin red S (ARS, 662.7 mg/g) and rhodamine B (RdB, 374.0 mg/g). Meanwhile, Tea-L-CDs@Ce-UiO-66-F4 composites maintained good anti-interference ability (salt solution, temperature, etc.). Remarkably, the adsorption capacity of the adsorbent for dyes exceeded 97 % of qm within 1 min of contact time. The adsorption performance of synthetic material for TB, CR, ARS, and RdB is better than most of the adsorbents, especially the qm for TB is higher than any adsorbent previously reported. Besides, this adsorbent had excellent storage stability in the air for 30 days. Based on this nanomaterial, we successfully developed an automated dye filtration and contamination assessment system for blocking dye-attached adsorbent and online detection of dye residues after water purification. Thus, the synthesized Tea-L-CDs@Ce-UiO-66-F4 composites, with universal adsorption, high efficiency, and good storage stability, hold great potential for wastewater purification.

Development of Silica‐Immobilized Material as Heterogeneous Hydrogen Bond Donor (HBD) Catalyst: Synthesis of Cyclic Carbonates from CO2 and Epoxides

AbstractComposite silica materials have been developed by hydrothermal method and utilized as heterogeneous Hydrogen Bond Donor (HBD) catalysts, where the functionalized ketimine derivatives have been immobilized on the solid support. Such functional materials have been found to be efficient catalysts for the synthesis of cyclic carbonates through the installation of CO2 with epoxides. Characterization of these materials was systematically done using various spectroscopic and imaging techniques to confirm the presence of organic compounds on the silica surface. These composite materials exhibited significantly higher catalytic activity as compared to the other homogeneous methods. Additionally, this synthetic process was extremely convenient in terms of all the external parameters such as, solvent free condition at ambient reaction temperature with normal pressure of CO2, very low catalyst loading with proper regeneration and reusability of the catalyst. These facets have definitely made this technique greener and more sustainable.

Molecular Deformation Is a Key Factor in Screening Aggregation Inhibitor for Intrinsically Disordered Protein Tau.

Direct inhibitor of tau aggregation has been extensively studied as potential therapeutic agents for Alzheimer's disease. However, the natively unfolded structure of tau complicates the structure-based ligand design, and the relatively large surface areas that mediate tau-tau interactions in aggregation limit the potential for identifying high-affinity ligand binding sites. Herein, a group of isatin-pyrrolidinylpyridine derivative isomers (IPP1-IPP4) were designed and synthesized. They are like different forms of molecular "transformers". These isatin isomers exhibit different inhibitory effects on tau self-aggregation or even possess a depolymerizing effect. Our results revealed for the first time that the direct inhibitor of tau protein aggregation is not only determined by the previously reported conjugated structure, substituent, hydrogen bond donor, etc. but also depends more importantly on the molecular shape. In combination with molecular docking and molecular dynamics simulations, a new inhibition mechanism was proposed: like a "molecular clip", IPP1 could noncovalently bind and fix a tau polypeptide chain at a multipoint to prevent the transition from the "natively unfolded conformation" to the "aggregation competent conformation" before nucleation. At the cellular and animal levels, the effectiveness of the inhibitor of the IPP1 has been confirmed, providing an innovative design strategy as well as a lead compound for Alzheimer's disease drug development.

Theoretical investigation of the nature of hydrogen bonds and cooperativity effect in methanol-water and ethanol-water clusters

ABSTRACT This study aims to cast light on the nature of hydrogen bonds and their cooperativity that exists in alcohol-water ( ROH ( H 2 O ) n ) ( R = − C H 3 ( − Me ) , − C H 2 C H 3 ( − Et ) ) (n = 1–10) clusters using atoms in molecules (AIM) theory and symmetry-adapted perturbation theory (SAPT). The investigation of optimum structures suggests that alcohol ( ROH ) forms two hydrogen bonds, one primary hydrogen bond ( O − H ⋅ ⋅ ⋅ O ) , and one secondary hydrogen bond ( C − H ⋅ ⋅ ⋅ O ) Two types of hydrogen bonds are addressed in these studies, where alcohol works as the hydrogen bond donor ( ROH ⋅ ⋅ ⋅ O H 2 ) and hydrogen bond acceptor ( RHO ⋅ ⋅ ⋅ HOH ) . The AIM results reveal that RHO ⋅ ⋅ ⋅ HOH and ROH ⋅ ⋅ ⋅ O H 2 hydrogen bonds are partially covalent. The SAPT study demonstrates that in all the clusters studied herein, the electrostatic interaction between alcohol and water is the main attractive force, and its contribution may be two times larger than the separate corresponding contributions from the dispersion and the induction terms. The electron density (ρ) at the bond critical point (BCP) is a suitable parameter to assess the strength of the interaction. The current study shows the strength and nature of ROH ⋅ ⋅ ⋅ O H 2 and RHO ⋅ ⋅ ⋅ HOH hydrogen bond, and cooperative effect in ( ROH ( H 2 O ) n ) ( R = − C H 3 ( − Me ) , − C H 2 C H 3 ( − Et ) .) (n = 1–10).

Stable supercooling formation of guanidine monohydrochloride-based deep eutectic solvent induced by monosubstitution of urea as hydrogen bond donor

ABSTRACT Two- and three-component mixtures were prepared using the monosubstituted urea of 1-methylurea (Um) and 1-hydroxyurea (Uh) as hydrogen bond donors, and guanidine monohydrochloride (GuHCl) as a hydrogen bond acceptor. Differential scanning calorimetry (DSC) thermograms and the solution-state nuclear magnetic resonance (NMR) spectra of the mixtures were compared with those of a deep eutectic solvent (DES) composed of urea (U) and GuHCl. At room temperature, 2Um-GuHCl was a DES in the supercooled state unlike solid state 2 U-GuHCl. Conversely, 2Uh-GuHCl did not form a DES. The methylation of urea resulted in the weakening of the hydrogen bonding of Cl− with others.

Per- and polyfluoroalkyl substances inhibit human and rat 17β-hydroxysteroid dehydrogenase 1: Quantitative structure-activity relationship and molecular docking analysis

Per- and polyfluoroalkyl (PFAS) substances are enduring industrial materials. 17β-Hydroxysteroid dehydrogenase isoform 1 (17β-HSD1) is an estrogen metabolizing enzyme, which transforms estrone into estradiol in human placenta and rat ovary. Whether PFAS inhibit 17β-HSD1 and what the structure-activity relationship (SAR) remains unexplored. We screened 18 PFAS for inhibiting human and rat 17β-HSD1 in microsomes and studied their SAR and mode of action(MOA). Of the 11 perfluorocarboxylic acids (PFCAs), C8-C14 PFCAs at a concentration of 100 μM substantially inhibited human 17β-HSD1, with order of C11 (half-maximal inhibition concentration, IC50, 8.94 μM) > C10 (10.52 μM) > C12 (14.90 μM) > C13 (30.97 μM) > C9 (43.20 μM) > C14 (44.83 μM) > C8 (73.38 μM) > others. Of the 7 per- and poly-fluorosulfonic acids (PFSAs), the potency was C8S (IC50, 14.93 μM) > C7S (80.70 μM) > C6S (177.80 μM) > others. Of the PFCAs, C8-C14 PFCAs at 100 μM markedly reduced rat 17β-HSD1 activity, with order of C11 (IC50, 9.11 μM) > C12 (14.30 μM) > C10 (18.24 μM) > C13 (25.61 μM) > C9 (67.96 μM) > C8 (204.39 μM) > others. Of the PFSAs, the potency was C8S (IC50, 37.19 μM) > C7S (49.38 μM) > others. In contrast to PFOS (C6S), the partially fluorinated compound 6:2 FTS with an equivalent number of carbon atoms demonstrated no inhibition of human and rat 17β-HSD1 activity at a concentration of 100 μM. The inhibition of human and rat enzymes by PFAS followed a V-shaped trend from C4 to C14, with a nadir at C11. Moreover, human 17β-HSD1 was more sensitive than rat enzyme. PFAS inhibited human and rat 17β-HSD1 in a mixed mode. Docking analysis revealed that they bind to the NADPH and steroid binding site of both 17β-HSD1 enzymes. The 3D quantitative SAR (3D-QSAR) showed that hydrophobic region, hydrogen bond acceptor and donor are key factors in binding to 17β-HSD1 active sites. In conclusion, PFAS exhibit inhibitory effects on human and rat 17β-HSD1 depending on factors such as carbon chain length, degree of fluorination, and the presence of carboxylic acid or sulfonic acid groups, with a notable V-shaped shift observed at C11.

Conducting 2D and 3D QSAR Analyses and Molecular Docking Studies of Analogues of 2-(1-(1,3,4-thiadiazol-2-yl)piperidin-4-yl)ethan-1-ol with the Aim of Identifying Promising Drug Candidates for Targeting Glioblastoma

Background: 2-(1-(1,3,4-thiadiazol-2-yl)piperidin-4-yl) ethan-1-ol analogues represent novel glutaminase 1 inhibitors. Their exemplary antineoplastic efficacy underscores their prospective utility in glioblastoma chemotherapy. Objectives: This study aimed to elucidate 2D and 3D-QSAR models that authenticate the antineoplastic efficacy of ethan-1-ol analogues and delineate optimal structural configurations conducive to new pharmaceutical design. Methods: The Heuristic Method (HM) was employed for the development of a 2D-linear QSAR paradigm, whilst the Gene Expression Programming (GEP) algorithm was employed for a 2D-nonlinear QSAR paradigm. Concurrently, the CoMSIA methodology was deployed to scrutinize the nexus between pharmaceutical structure and potency. An ensemble of 200 nascent anti-glioma ethan-1-ol compounds was conceptualized, and their potency levels were prognosticated via chemical descriptors and molecular field delineations. Pharmaceuticals epitomizing peak potency were earmarked for molecular docking validation. Results: The empirical modeling exhibited pronounced superiority with the 3D paradigm, succeeded by the GEP nonlinear paradigm and culminated with the HM linear model. The 3D paradigm was characterized by a robust Q2 (0.533), R2 (0.921), and F-values (132.338) complemented by a minimal SEE (0.110). The molecular descriptor MNO coupled with the hydrogen bond donor field facilitated novel pharmaceutical conceptualizations, leading to the identification of the quintessential active molecule, 24J.138, lauded for its superlative antineoplastic attributes and docking proficiency. Conclusion: The orchestration of bidimensional and tridimensional paradigms, synergized by innovative amalgamation of contour maps and molecular descriptors, provides novel insights and methodologies for the synthesis of glioblastoma chemotherapeutic agents.

Simultaneous adsorption of fulvic acid and organic contaminants by KOH activated mesoporous biochar with large surface area

Returning carbon materials from biomass to soil is a potential technology to retard organic contaminants or dissolved organic matter (DOM) in soil by adsorption, as well as to store carbon in soil for carbon sequestration. However, DOM was widely reported to inhibit adsorption of organic contaminants on carbon materials by competition and by enhancing contaminants' solubility. In this study, a KOH activated carbon material (KAC), pyrolyzed from bamboo chips, with high surface area (3108 m2/g), micropores volumes (0.964 cm3/g), mesopores volumes (1.284 cm3/g), was observed that it can adsorb fulvic acid (FA) and organic contaminants (e.g., nitrobenzene, phenols, and anilines) simultaneously with weak competition and high adsorption capacity. With 50 mg TOC/L FA, for example, the average competition suppressing rate (ΔKf/Kf-m) of organic contaminants on KAC was lower than 5%, the adsorption for organic contaminants and FA were higher than 1100 mg/g and 90 mg TOC/g, respectively. The weak competition on KAC could be attributed to the low micropore blockage (<35%) and the weak adsorption sites competition on mesopores of KAC, as well as the minimal solubility enhancement of organic contaminants by FA because most FA is adsorbed on KAC but is not dissolved in the solution. In addition, adsorption of organic contaminants with high hydrogen-bonding donor ability (αm) and adsorption affinity was less suppressed by FA because of the heterogeneous nature of hydrophilic sites on KAC's surface. Therefore, KAC could be a potential carbon material to be produced to implement to soil for carbon storage and simultaneous retarding organic contaminants and DOM.

Tertiary Amides as Directing Groups for Enantioselective C−H Amination using Ion‐Paired Rhodium Complexes

AbstractEnantioselective C−H amination at a benzylic methylene is a vital disconnection towards chiral benzylamines. Here we disclose that butyric and valeric acid‐derived tertiary amides can undergo highly enantioselective benzylic amination using an achiral anionic Rh complex that is ion‐paired with a Cinchona alkaloid‐derived chiral cation. A broad scope of compounds can be aminated encompassing numerous arene substitutions, amides, and two different chain lengths. Excellent tolerance of ortho substituents was observed, which has not been achieved before in asymmetric intermolecular C−H amination with Rh. We speculate that the tertiary amide group of the substrate engages in hydrogen bonding interactions directly with the chiral cation, enabling a high level of organisation at the transition state for C−H amination. This is in contrast with our previous work where a substrate bearing a hydrogen bond donor was required. Control experiments led to the discovery that methyl ethers also function as proficient directing groups under the optimised conditions, potentially also acting as hydrogen bond acceptors. This finding has the promise to dramatically expand the applicability of our ion‐paired chiral catalysts.

Crystal structure of indacaterol hydrogen maleate (C24H29N2O3)(HC4H2O4)

The crystal structure of indacaterol hydrogen maleate has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional techniques. Indacaterol hydrogen maleate crystallizes in space group P-1 (#24) with a = 8.86616(9), b = 9.75866(21), c = 16.67848(36) Å, α = 102.6301(10), β = 94.1736(6), γ = 113.2644(2)°, V = 1273.095(7) Å3, and Z = 2 at 295 K. The crystal structure consists of layers of cations and anions parallel to the ab-plane. Traditional N–H⋯O and O–H⋯O hydrogen bonds link the cations and anions into chains along the a-axis. There is a strong intramolecular charge-assisted O–H⋯O hydrogen bond in the non-planar hydrogen maleate anion. There are also two C–H⋯O hydrogen bonds between the anion and cation. The cation makes a strong N–H⋯O hydrogen bond to the anion, but also acts as a hydrogen bond donor to an aromatic C in another cation. The amino group makes bifurcated N–H⋯O hydrogen bonds, one intramolecular and the other intermolecular. The hydroxyl group acts as a donor to another cation. The powder pattern has been submitted to ICDD for inclusion in the Powder Diffraction File™ (PDF®).

Tertiary Amides as Directing Groups for Enantioselective C-H Amination using Ion-Paired Rhodium Complexes.

Enantioselective C-H amination at a benzylic methylene is a vital disconnection towards chiral benzylamines. Here we disclose that butyric and valeric acid-derived tertiary amides can undergo highly enantioselective benzylic amination using an achiral anionic Rh complex that is ion-paired with a Cinchona alkaloid-derived chiral cation. A broad scope of compounds can be aminated encompassing numerous arene substitutions, amides, and two different chain lengths. Excellent tolerance of ortho substituents was observed, which has not been achieved before in asymmetric intermolecular C-H amination with Rh. We speculate that the tertiary amide group of the substrate engages in hydrogen bonding interactions directly with the chiral cation, enabling a high level of organisation at the transition state for C-H amination. This is in contrast with our previous work where a substrate bearing a hydrogen bond donor was required. Control experiments led to the discovery that methyl ethers also function as proficient directing groups under the optimised conditions, potentially also acting as hydrogen bond acceptors. This finding has the promise to dramatically expand the applicability of our ion-paired chiral catalysts.

Asymmetric cyclization catalyzed by a chiral phosphoric acid–gold(I) hybrid complex as a multifunctional catalyst

Abstract We herein report the development of a novel hybrid complex containing gold(I) and a chiral phosphoric acid moiety to generate a multifunctional catalyst. While the use of chiral phosphoric acid as a bifunctional catalyst is a common strategy in asymmetric organic synthesis, chiral phosphoric acid–transition metal hybrid complexes as multifunctional catalysts have not been investigated. Thus, we designed and synthesized a novel gold(I) hybrid complex as a multifunctional catalyst that promotes asymmetric catalytic reactions through multipoint nonclassical noncovalent interactions in substrates that lack classical hydrogen-bond donors. In addition, we demonstrate its usefulness as a multifunctional catalyst by successfully developing the first catalytic asymmetric synthesis of dihydrocyclohepta[b]indoles. Experimental and theoretical studies revealed that this asymmetric catalytic reaction involves the kinetic resolution of the reaction intermediate, and that the favored diastereomeric transition state for yielding enantiomeric products is formed through multipoint nonclassical noncovalent interactions originating from the acid–base nature of the chiral phosphoric acid moiety.

Insight into the role of hydrogen bond donor in deep eutectic solvents

Deep eutectic solvent (DES) is considered as one of the green solvents with bright prospect in this century. Its excellent performance is closely related to the hydrogen bonds formed between hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD). Through changing the type of HBD and adjusting its molar fraction, it makes a difference to the intensity of the hydrogen bonds. In this work, tetrabutylammonium chloride (TBAC) was chosen as HBA, decanoic acid (DEC) and octanoic acid (OC) were chosen as HBD. With the molar ratios ranging from 3:1 to 1:3, seven TBAC-DEC-based DES and seven TBAC-OC-based DES were synthesized. Based on the study of the structural characteristics and the thermophysical properties, such as the eutectic point, the thermal stability, the density and the viscosity, the effect of HBD on DES was investigated. The increased HBD destroyed the orderly configuration of DES. Meanwhile, the elongation of the HBD’s alkyl chain enhanced the interaction between the components. Moreover, the mass-connectivity-based model and the hard sphere model were introduced to predict the density and viscosity, respectively. Both of the two models exhibited good predictivity, with the average absolute relative deviation less than 0.2 % and 5 %, respectively.

Experimental and computational studies on isolation of cardanol from cashew nut shell liquid using diethanolamine‐based deep eutectic solvent at different molar ratios

AbstractBACKGROUNDAmine‐based deep eutectic mixtures composed of choline chloride and a DEA‐based hydrogen‐bond donor (HBD) can be used in various molar ratios such as 1:2, 1:3, 1:4, 1:5, 1:6 and 1:7 for isolation of cardanol from cashew nut shell liquid (CNSL).RESULTSIn this study, green techniques were created to extract cardanol from CNSL by utilizing a deep eutectic solvent (DES) based on diethanolamine with various molar ratios [hydrogen‐bond acceptor (HBA): HBD] of 1:2, 1:3,1:4,1:5, 1:6 and 1:7. To enhance cardanol's solubility in DES, promote phase separation, and increase cardanol yield, ethyl acetate (EA) and isobutyl methyl ketone (IBMK) could be utilized as co‐solvents. At temperatures ranging from 293 to 343.15 K and 1 atm, the density of various molar ratios of DES was determined. Additionally, the prepared DES pH behaviour as well as the relationship between pH and temperature were investigated. All investigated DES temperature increases caused a decrease in pH value. By using thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC), similar molar ratios of amine‐based DESs were studied for their thermal stability in terms of decomposition temperature, mass loss and melting temperature. The melting temperature and thermal stability were both increased when the HBD increased. The thermal stability of DES, which mostly depends on intermolecular interactions, is greatly influenced by HBD. Finally, at T = 298.15 K and 1 atm, cardanol was extracted from 50 mL CNSL using different volumes of various molar ratios of DES (100 mL, 75 mL, 50 mL and 25 mL) together with 25 mL IBMK and 25 mL EA. The extracted cardanol was evaluated using Fourier transform infrared spectroscopy and gas chromatography–mass spectrometry.CONCLUSIONIt was observed that the yields of cardanol from each prepared molar ratios ratio of 100 mL DES were 96.57%, 95.38% and 92.87%, respectively. In this study, the sigma potential and sigma profile of chosen HBA and HBD were determined using conductor‐like screening model for real solvents (COSMO‐RS), and the interactions between the molecules during the extraction process were analyzed. The findings demonstrated the viability of using the chosen DESs for the polyphenol extraction process. © 2024 Society of Chemical Industry (SCI).