Potential Separation Research Articles

Cis-Trans and Length-Selective Molecular Discrimination of Halogenated Organic Compounds by a Crystalline Hybrid Macrocyclic Arene.

The development of adsorbents with robust molecular discrimination capabilities for halogenated organic compounds (HOCs) holds significant importance due to their potential in adsorptive separation and mitigation of associated health risks. In this study, we report a molecular discrimination behavior based on crystalline hybrid macrocyclic arene H, offering precise capture of cis-trans isomers and length-selective separation of HOCs. The activated H crystals (Hα) demonstrate exceptional discrimination and separation performance by selectively capturing trans-1,2-dichloroethylene (trans-DCE) from cis/trans-isomer mixtures with a high selectivity of 98.8%. Evidenced by single-crystal X-ray diffraction and density functional theory (DFT) calculations, this high adsorption selectivity arises from the formation of more stable complex crystals between H and the preferred guest trans-DCE. Moreover, Hα exhibits the ability to selectively trap size-matched 1,2-dibromoethane (DBE) from mixtures of alkylene dibromides with varying alkane-chain lengths, although their capture and separation are recognized to be difficult as a consequence of low-polarity bonds. The solid-state transformations between guest-free and guest-containing Hα crystals indicate their recyclability, showcasing promising prospects for potential applications.

Facilitating Water Permeation in Graphene Oxide Membranes via Incorporating Sulfonato Calix[n]arenes.

Graphene oxide (GO) with its atomic thickness and abundant functional groups holds great potential in molecular-scale membrane separation. However, constructing high-speed and highly selective water transport channels within GO membranes remains a key challenge. Herein, sulfonato calix[n]arenes (SCn) molecules with a cavity structure, hydrophilic entrance, and hydrophobic wall were incorporated into GO interlayer channels through a layer-by-layer assembly approach to facilitate water permeation in a water/ethanol separation process. The hydrophilic entrance enables preferential access of water molecules to the cavity over ethanol molecules, while the high hydrophobicity of the cavity wall confers low resistance for water diffusion. After incorporating SCn molecules, the membrane shows a remarkable increase in the water/ethanol separation factor from 732 to 1260, while the permeate flux also increases by about 50%. In addition, the strong electrostatic interactions between the building blocks endow the membrane with excellent swelling resistance even under a high water content. This work provides an effective strategy of constructing high-efficiency water transport channels in membrane.

Water-Resistant, Scalable, and Inexpensive Chiral Metal–Organic Framework Featuring Global Negative Electrostatic Potentials for Efficient Acetylene Separation

Water-Resistant, Scalable, and Inexpensive Chiral Metal–Organic Framework Featuring Global Negative Electrostatic Potentials for Efficient Acetylene Separation

Recent Progress in Janus Nano-Objects with Asymmetric Polymer Brushes.

Over the past few decades, Janus materials have drawn much interest owing to the combination of two different functionalities on the opposite sides. Janus nano-objects (JNOs) with asymmetric polymer brushes are one unique material of them, which consist of a polymeric or inorganic core and asymmetric polymer chains coated on the core. Combining the properties of nanomaterials, asymmetric structures and flexible polymer brushes, hairy JNOs have shown great potential in interfacial compatibilization, interfacial catalysis, oil-water separation and drug delivery. This review summarizes recent progress in the preparation strategies of JNOs with asymmetric polymer brushes via self-assembly or grafting strategies, as well as their applications in interfacial engineering, biomedicine and other aspects. Finally, the outlook and challenges of this direction are discussed.

Synthesis and evaluation of aromatic stationary phases based on linear solvation energy relationship model for expanded application in supercritical fluid chromatography

In the last decade, the separation application based on aromatic stationary phases has been demonstrated in supercritical fluid chromatography (SFC). In this paper, four aromatic stationary phases involving aniline (S-aniline), 1-aminonaphthalene (S-1-ami-naph), 1-aminoanthracene (S-1-ami-anth) and 1-aminopyrene (S-1-ami-py) were synthesized based on full porous particles (FPP) silica, which were not end-capped for providing extra electrostatic interaction. Retention mechanism of these phases in SFC was investigated using a linear solvation energy relationship (LSER) model. The aromatic stationary phases with five positive parameters (a, b, s, e and d+) can provide hydrogen bonding, π-π, dipole-dipole and cation exchange interactions, which belong to the moderate polar phases. The LSER results obtained using routine test solutes demonstrated that the aforementioned interactions of four aromatic stationary phases were influenced by the type and bonding density of the ligand, but to a certain extent. Furthermore, the LSER data verified that the S-1-ami-anth column based on full porous particles silica had higher cation exchange capacity (d+ value), compared to the commercialized 1-AA column (based on the ethylene-bridged hybrid particles). The relationship between the d+ value and SFC additive was quantitatively proved so as to regulate electrostatic interaction reasonably. This value was greatly increased by phosphoric acid, slightly increased by trifluoroacetic acid and formic acid, but significantly reduced by ammonium formate and diethylamine. Taking the S-1-ami-naph column as an example, better peek shape of the flavonoids was obtained after the addition of 0.1 % phosphoric acid in MeOH while isoquinoline alkaloids were eluted successfully within 11 min after adding 0.1 % diethylamine in MeOH. Combined with the unique π-π interaction and controllable electrostatic interaction, the aromatic stationary phases in this study have been proven to have expandable application potential in SFC separation.

Developing a Multiband Electronic Band Structure Model and Predictive Maps for Bismuth-Rich Mg3(Sb1-xBix)2 Thermoelectric Materials.

In recent years, bismuth-rich Mg3(Sb1-xBix)2 (x = 0.5-0.8) compositions have generated significant interest due to their excellent thermoelectric (TE) performance near room temperature, making them potential applicants for recovery of low-grade waste heat. The superior performance in these materials is due to its complex electronic band structure (EBS) with presence of multiple near degenerate bands close to the conduction band edge. The position and curvature of these bands strongly depend on the alloy composition, doping amount as well as temperature. Thus, identifying optimal material compositions to get the best TE performance depends on an understanding of the temperature dynamics of EBS and forms the objective of this work. Mg3Sb0.6Bi1.4 (x = 0.7) is chosen for this study due to its reported high near room temperature performance, and compositions with varying doping concentrations (Te used as dopant) have been synthesized. EBS parameters like effective mass and deformation potential of bands, interband separation and band gap values have been estimated using a recently developed refinement approach. Refinement results indicate that the interband separation between conduction bands to be a function of both temperature and doping concentration. Further, thermal conductivity (κ) was estimated for all of the compositions. Utilizing the EBS and κ information, predictive 3D maps indicating the variation in zT (TE figure of merit) with doping concentration and temperature have been generated. The 3D maps reveal an interesting surface topography with a broad peak zT region. This observation explains why these materials have high TE performance and are less sensitive to doping inhomogeneities. Our results provide detailed EBS information and fundamental insights on the TE properties of Mg3Sb0.6Bi1.4. Further, the proposed technique can be utilized to probe other Mg3(Sb1-xBix)2 compositions and TE materials.

Filter prepared from Janus-like graphene oxide nanosheets with heterogeneous nanochannels for highly efficient dye removal

A Janus graphene oxide filter with heterogeneous nanochannels exhibits a high interception rate and water flux towards dye removal.

Identifying Separation Potency and Relationship of Grade and Density of Copper Ore for Gravity-Based Early Coarse Gangue Rejection using Statistical Method

The mineral processing industry faces a pressing challenge of declining productivity, particularly in metal minerals production, driven by soaring operational costs, with crushing and grinding operations accounting for a substantial portion of the energy consumption. To mitigate these challenges, early gangue rejection or preconcentration is proposed as an effective solution. This approach involves the removal of non-valuable materials and the concentration of valuable minerals at the initial processing stages, leading to increased efficiency, higher ore feed grades, cost savings, and reduced environmental impact. Various methods for gangue rejection exist, with gravity-based separation and ore sorting being the predominant options. Gravity-based separation stands out for its simplicity and versatility, making it the preferred choice in many scenarios. This study introduces a novel approach for evaluating gangue rejection potential, optimizing data distribution, and generating theoretical separation potential curves that account for both grade and density criteria. These curves provide insights into material rejection, metal losses, and optimal separation points, offering valuable guidance for mineral processing operations. Additionally, the study investigates the correlation between raw ore grade and density data, highlighting a strong relationship across different size fractions. This finding suggests that gravity-based separation can effectively rely on both grade and density parameters, resolving previous disparities observed in distribution models. By shedding light on advanced gangue rejection strategies, this research contributes to improved productivity and informed decision-making in the mineral processing industry.

Facile room-temperature synthesis of a spherical mesoporous covalent organic framework for capillary electrochromatography

Herein, a spherical covalent organic framework COF TAPB-DMTP was facilely synthesized from 2,5-dimethoxyterephthalaldehyde (DMTP) and 1,3,5-tri-(4-aminophenyl)benzene (TAPB) as monomers. COF TAPB-DMTP with regular mesoporous and excellent mass transfer ability was first introduced into the capillary and immobilized on the inner wall of the capillary through a simple in situ growth method. Through various characterization results, COF TAPB-DMTP was successfully prepared and modified onto the capillary inner wall. The separation performance and potential of COF TAPB-DMTP modified capillary column was explored. The new developed COF modified column achieved a highly efficiency and selective separation between analytes with different properties, including halogeno benzenes, alkylbenzenes, phenols and sulfonamides. Satisfactory stability and reproducibility were observed on COF TAPB-DMTP modified columns. The intraday, interday and three batch columns relative standard deviations were all less than 1.85 % for the retention time. The separation performance of prepared column has no significant change after 90 continuous runs. Additionally, the COF TAPB-DMTP modified capillary column was successfully used for separation and detection of triazole antifungal drugs in human plasma, and the recoveries of three antifungal drugs (fluconazole, isavuconazole and posaconazole) in spiked samples were in the range of 98.6–100.8 %, 92.4–102.1 % and 99.9–107.5 %, respectively. This self-made column showed excellent application potential in chromatography separation science.

Pervaporation properties of silylated ionic liquid-derived organosilica membrane

We previously reported gas/vapor permselectivities, microstructures, and permeation mechanisms of silylated ionic liquid (IL)-derived organosilica membranes (IL organosilica membranes), which are a class of chemically stabilized IL membranes. In this study, an IL organosilica membrane was used for organic liquid separation using pervaporation (PV) for the first time. Unary PV tests were conducted using alcohols, ketones, aromatic hydrocarbons, and alkanes. We investigated the relationship between the permeances of the organic compounds and differences in the Hansen solubility parameters between the membrane and organic compounds to evaluate the selective permeability of the organic compounds through the membrane. Second, binary PV tests were conducted to separate (1) alcohols/alkanes and (2) aromatics/alkanes. In the toluene/n-hexane (toluene 48 mol%) separation tests, a toluene/n-hexane permeance ratio of 11 was obtained with a toluene permeance of 2.6 × 10−6 mol m−2s−1Pa−1. Further, the membrane exhibited high selectivity for 1-hexanol in a binary 1-hexanol/n-hexane mixture. The IL organosilica membrane exhibited excellent potential for affinity-based organic liquid separation.

Insights into the photocatalytic role of glycine-assisted sol-gel auto-combustion synthesized (Co, Mn)(Co, Mn)2O4 nanostructures for efficient visible light-driven degradation of methyl orange

Research on the use of new materials and the improvement of existing fast ways for removal of water pollutants is still challenging. This work documented rational fabrication of (Co, Mn)(Co, Mn)2O4 nanoparticles as nano-photocatalyst materials with improved charge carrier separation and strong redox potential for efficient degradation of methyl orange (MO) in wastewater. This investigation illustrated that the Co/Mn molar ratio can greatly affect the textural and structural properties. From the point of view of size and shape, the optimum product with 1:3 M ratio of Co to Mn precursors was selected as a catalyst in the photocatalysis process. The prepared highly crystallized phase of tetragonal (Co, Mn)(Co, Mn)2O4 describe an optical band gap of 1.7 eV, according to the DRS data, which make them as efficient visible driven photocatalysts. The photodegradation experiments of spinel mixed structures were assessed by investigation of photocatalyst dosages and initial MO concentrations to unravel how these operational parameters affect Co-Mn-O photocatalysis. A remarkable discoloration capability of 68.07 % could result from the catalyst dosage of 0.04 g and dye concentration of 15 mg/L after 120 min of visible light. The kinetics survey further unveiled the maximum rate constant of 0.0080 min−1 for the MO degradation. In the scavenger trials, singlet oxygen (1O2) and superoxide (●O2−) radicals were principal reactive oxygen species (ROS) responsible for pollutant photodegradation in the presence of pure (Co, Mn)(Co, Mn)2O4 structures. In addition, the cyclic performance of catalyst depicted a removal efficiency of 60.1 % over 5 runs.

Ligand Fishing Approach to Explore Amaryllidaceae Alkaloids as Potential Antiviral Candidates Targeting SARS-CoV-2 Nsp4

Ligand fishing, also described as affinity-based assay, represents a convenient and efficient approach to separate potential ligands from complex matrixes or chemical libraries. This approach contributes to the identification of lead compounds that can bind to a specific target. In the context of COVID-19, the search for novel therapeutic agents is crucial. Small molecule-based antiviral drugs, such as Amaryllidaceae alkaloids, have been described as potential candidates because they can inhibit RNA viruses. Among various SARS-CoV-2 proteins, Nsp3, Nsp4, and Nsp6 play a crucial role in the pathogenicity of the virus and are attractive targets for developing COVID-19 treatments. These proteins are responsible for the replication/transcription complex (RTC) within double-membrane vesicles (DMVs), and their inhibition disrupts the virus’s infectious cycle.Herein, we have successfully expressed and immobilized the SARS-CoV-2 Nsp4 protein on magnetic beads (Nsp4-MBs) and employed a ligand fishing assay to screen a collection of ten Amaryllidaceae-based alkaloids and applied to Hippeastrum aulicum extract. Remarkably, four out of ten alkaloids, namely 2-α-7-dimethoxyhomolycorine (6), hemanthamine (5), albomaculine (8), and tazettine (9), exhibited selective affinities for Nsp4. Albomaculine (8) and hemanthamine (5) were also identified from extract by the affinity assay. These findings highlight the potential of these alkaloids as model compounds for future drug discovery studies aimed at developing therapeutic interventions against SARS-CoV-2 infections.

Breaking the Permeability-Selectivity Trade-Off: Advanced carbon molecular sieve membranes derived from thermally rearranged Mixed-Matrix membrane precursors

A crucial problem in membrane-based gas separation is to fabricate membranes with excellent permeability, selectivity, and stability. Here, a high-performance carbon molecular sieves membrane of TR-CMS/SSZ-13 was successfully produced by pyrolyzing a thermally rearranged (TR) mixed matrix membrane (MMM) that obtained from a copolyimide precursor (6FDA/ODA/6FAP(3:2)) and SSZ-13 zeolite as filler at 450 °C. The effect of SSZ-13 zeolite content and structures of precursors on the transport behavior of derived CMS membranes was thoroughly studied. After TR process, the as formed polybenzoxazole (PBO) chain resulted in an enhanced rigidity, higher fractional free volume (0.15 vs 0.17), and a significantly increased (1898 times) BET surface area. Further enhancing the treatment temperature to 650 °C, the formed TR-CMS membranes exhibited a huge improved BET surface area from 228.2 to 639.3 m2/g, delivering a remarkable gas separation performance with H2 permeability of 7089 Barrer and H2/CH4 selectivity of 136. When doping with SSZ-13 till 15 wt%, the TR-CMS/SSZ-13–15 % showed an even higher H2 (9726 Barrer) and CO2 permeability (6932 Barrer), as well as H2/CH4 (150 vs 136) and CO2/CH4 (107 vs 57) selectivity than the pure TR-CMS, which surpassed the newest 2019 Robeson Upper bound. This can associate with the strong interaction between the modified SSZ-13 and the polymer matrix that prevent the collapse of the aromatic strand during the pyrolysis process, thereby create more ultra-micropore volume and concentration. Conclusively, pyrolyzing TR-MMM precursor is an effective way to form high-performance membranes with good potential for CO2 separation and H2 purification.

High-pH mobile phase in reversed-phase liquid chromatography-tandem mass spectrometry to improve the separation efficiency of aminoglycoside isomers.

In chromatography, the use of extreme conditions can often lead to unique separation selectivity. In this study, a highly basic mobile phase (pH > 11), which is not typically employed for reversed-phase liquid chromatography (RPLC), was utilized in RPLC-tandem mass spectrometry (MS/MS) to achieve effective separation between electrically neutral bases of aminoglycosides (AGs). A mixture of AGs was simultaneously analyzed using 500mmol L-1 ammonia aqueous solution (pH 11.8) as the mobile phase. A total of 11 AGs, including 2 stereoisomers of neomycin (B and C) and 5 structurally similar components of gentamicin (C1, C1a, C2, C2a, and C2b), were completely separated for the first time. The high separation performance for AGs was mainly due to two factors: First, slight differences in hydrophobicity among the AGs were significantly enhanced at a high pH by the complete acid dissociation of amines. Second, the high pH of the mobile phase minimized any electrostatic interactions between the AGs and residual silanol groups in the stationary phase, resulting in extremely sharp peaks for the AGs. The sensitivity of spectinomycin decreased by more than 20% when using the highly basic mobile phase (pH 11.8) due to its degradation, therefore, a mixture of 10 AGs was analyzed with 250mmol L-1 ammonia aqueous solution (pH 11.5) with less degradation as the optimum condition. The developed analytical method could be used to determine the concentrations of trace AGs in milk with high accuracy and precision. Thus, RPLC-MS/MS using a high-pH mobile phase has great potential for the efficient separation of basic compounds containing amino sugars such as AGs.

Cadmium sulfide composite reduced graphene oxide for selective oxidation of 5-hydroxymethylfurfural to 2.5-diformylfurans

In this study, the Cadmium sulfide composite reduced graphene oxide photocatalyst (CdS/xrGO) was successfully synthesized to enhance the conversion of photocatalytic oxidation of 5-hydroxymethylfurfural (HMF). The conversion of 5-hydroxymethylfurfural and the yield of 2.5-diformylfurans (DFF) were 71.18 % and 69.72 %, respectively under optimum conditions, and the selectivity of DFF was significantly higher of about 97.94 %. Compared with CdS as a catalyst, HMF conversion and the DFF yield were roughly double. The excellent photocatalytic performance can be found through various characterization results because specific surface area of rGO is larger which provides many numbers of reaction sites for the reaction, reducing the clustering of CdS and allowing better contact between the photocatalyst and the substrate. Meanwhile, photogenerated electrons were easily transferred to the surface of rGO, which results in improving the separation potential of photogenerated carriers inhibited its complexation and resulting in enhanced photocatalytic performance.

Composite membranes based on ether oxygen-rich polyimide with superior CO2/N2 separation properties prepared by interfacial polymerization

Ether oxygen-rich polymeric membranes emerge as promising membranes in CO2 separation due to the high affinity between CO2 molecules and ethylene oxide segments. However, there is a massive challenge in developing asymmetric membranes with high CO2 permeation performance and CO2/light gas separation performance. This work revealed composite membranes with ether oxygen-rich polyimide separation layers were developed by interfacial polymerization between 1,2,4,5-benzenetetracarbonyl tetrachloride and commercial diamines named o,o'-bis(2-aminopropyl) polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol followed by thermal imidization. The influences of the polymerization time and monomer concentrations on the gas transport and separation properties of the composite membranes were studied based on single-gas permeation. The optimum membrane possessed a superior high ideal CO2/N2 separation factor of 429 accompanied with a moderate permeance of 150 GPU for CO2 at 25oC and 0.2 MPa. The performance stability was studied by operating the membrane at various pressures and temperatures. The result showed the composite membrane possessed excellent plasticization resistivity at high pressures. The separation property of composite membranes for CO2/N2 binary mixture was also evaluated. The influences of the operation parameters, including stage-cut and pressure ratio on the product purity and recovery were investigated. The results showed great practical application potential in efficient separation of flue gas.

Membranes based on Covalent Organic Frameworks through Green and Scalable Interfacial Polymerization using Ionic Liquids for Antibiotic Desalination

AbstractCovalent organic framework (COF) membranes featuring uniform topological structures and devisable functions, show huge potential in water purification and molecular separation. Nevertheless, the inability of uniform COF membranes to be produced on an industrial scale and their nonenvironmentally friendly fabrication method are the bottleneck preventing their industrial applications. Herein, we report a new green and industrially adaptable scraping‐assisted interfacial polymerization (SAIP) technique to fabricate scalable and uniform TpPa COF membranes. The process used non‐toxic and low‐volatility ionic liquids (ILs) as organic phase instead of conventional organic solvents for interfacial synthesis of TpPa COF layer on a support membrane, which can simultaneously achieve the purposes of (i) improving the greenness of membrane‐forming process and (ii) fabricating a robust membrane that can function beyond the conventional membranes. This approach yields a large‐area, continuous COF membrane (19×25 cm2) with a thickness of 78 nm within a brief period of 2 minutes. The resulting membrane exhibited an unprecedented combination of high permeance (48.09 L m−2 h−1 bar−1) and antibiotic desalination efficiency (e.g., NaCl/adriamycin separation factor of 41.8), which is superior to the commercial benchmarking membranes.

Membranes based on Covalent Organic Frameworks through Green and Scalable Interfacial Polymerization using Ionic Liquids for Antibiotic Desalination.

Covalent organic framework (COF) membranes featuring uniform topological structures and devisable functions, show huge potential in water purification and molecular separation. Nevertheless, the inability of uniform COF membranes to be produced on an industrial scale and their nonenvironmentally friendly fabrication method are the bottleneck preventing their industrial applications. Herein, we report a new green and industrially adaptable scraping-assisted interfacial polymerization (SAIP) technique to fabricate scalable and uniform TpPa COF membranes. The process used non-toxic and low-volatility ionic liquids (ILs) as organic phase instead of conventional organic solvents for interfacial synthesis of TpPa COF layer on a support membrane, which can simultaneously achieve the purposes of (i) improving the greenness of membrane-forming process and (ii) fabricating a robust membrane that can function beyond the conventional membranes. This approach yields a large-area, continuous COF membrane (19×25 cm2 ) with a thickness of 78 nm within a brief period of 2 minutes. The resulting membrane exhibited an unprecedented combination of high permeance (48.09 L m-2 h-1 bar-1 ) and antibiotic desalination efficiency (e.g., NaCl/adriamycin separation factor of 41.8), which is superior to the commercial benchmarking membranes.

Oil/water separation by super-hydrophobic wastepaper cellulose-candelilla wax cryogel: a circular material-based alternative

Introduction: One of the most attractive fields for cellulose aerogels is water remediation, basically in the pollutant’s adsorption and oil/water separation. There are different sources to extract cellulose, but the extraction from paper waste is an excellent option for impulse circular materials applications.Methods: We obtained cellulose from office waste paper through a simple alkali method and used it to fabricate an aerogel by freeze-drying based on the materials’ circularity. To increase lipophilicity, the aerogel was modified using two different coatings: polycaprolactone (WOPP) and candelilla wax (WOPW), extracted from a Mexican plant. The aerogels were analyzed by several physicochemical techniques such as Scanning Electronic Microscopy, Infrared spectroscopy, and thermal analysis.Results and Discussion: To our knowledge, this is the first time that candelilla wax has been reported as aerogel modification. The highly porous aerogels showed a density of around 0.1 g/cm3 and a fibrous structure. Furthermore, the contact angle of the aerogels was measured to compare the hydrophobicity of the surfaces, showing values around 120° in the modified aerogels compared with the hydrophilic behavior of pristine cellulose aerogel. The achieved recycled mineral oil absorption capacity for WOPW was 6.1 g/g, while for WOPP was 4.88 g/g. Thus, we obtained a natural coating aerogel with a high water/oil separation potential.

Specific Propyne Trapping Sites within a Robust MOF for Efficient Propyne/Propadiene Separation with Record Propadiene Productivity.

Separating propyne/propadiene to produce pure propadiene is extremely challenging in industry due to their similar properties. Herein, a novel ZrF6 2- anion pillared cage-like metal-organic framework (termed as CuZrF6 -TPA) for highly efficient propyne/propadiene separation is reported. It exhibits high propyne capacity (177.4/188.6 cm3 /cm3 at 0.5/1.0 bar and 298 K), benchmark separation selectivity (6.0), and remarkable separation potential (5.7 mol L-1 ) simultaneously. Record propadiene productivity (≈4.7 mol L-1 ) is achieved through a single adsorption process in breakthrough experiments with excellent recycle stability even under humid conditions. Based on the structure of propyne-loaded single crystals, two binding sites are identified, including a major propyne trapping site at the windows and a minor binding site located in the large cages. Modelling studies further confirm that the contracted cage windows surrounded with rotating Lewis basic F atoms and aromatic rings are the optimal bonding sites to capture propyne with multiple hydrogen bonding and π···π interactions.