Charge-assisted Hydrogen Bonds Research Articles

Synthesis and Characterization of Two Sparfloxacin Crystalline Salts: Enhancing Solubility and In Vitro Antibacterial Activity of Sparfloxacin

Background: To improve the solubility and permeability of Sparfloxacin (SPX) and enhance its antimicrobial activity in vitro, two unreported pharmaceutical crystalline salts were synthesized and characterized in this paper. One is a hydrated crystal of Sparfloxacin with Pimelic acid (PIA), another is a hydrated crystal of Sparfloxacin with Azelaic acid (AZA), namely, SPX-PIA-H2O (2C19H23F2N4O3·C7H10O4·2H2O) and SPX-AZA-H2O (4C19H23F2N4O3·2C9H14O4·5H2O). Methods: The structure and purity of two crystalline salts were analyzed using solid-state characterization methods such as single-crystal X-ray diffraction, powder X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, and infrared spectroscopy. Additionally, the interaction characteristics between two crystal salt molecules were examined by constructing Hirshfeld surfaces and mapping specific real-space functions through Hirshfeld surface analysis. The solubility under physiological conditions, diffusivity across simulated biological membranes, and in vitro antibacterial activity against specific bacterial strains of two crystalline salts were evaluated using established assays, including minimum inhibitory concentration (MIC) tests. Results: Single-crystal X-ray diffraction and Hirshfeld surface analysis indicate that SPX forms stable crystal structures with PIA through charge-assisted hydrogen bonds N1-H1e···O10 (1.721 Å, 173.24°), N5-H5a···O11 (1.861 Å, 169.38°), and with AZA through charge-assisted hydrogen bonds N5-H5B···O8 (1.810 Å, 154.55°), N4-H4B···O6 (1.806 Å, 174.97°). The binding sites of two crystalline salts were at the nitrogen atoms on the piperazine ring of SPX. Compared with SPX, the equilibrium solubility of the two crystalline salts was improved by 1.17 and 0.33 times, respectively, and the permeability of the two crystalline salts was increased by 26.6% and 121.9%, respectively. In addition, SPX-AZA-H2O has much higher antibacterial activity on Pseudomonas aeruginosa and Bacillus subtilis than SPX. Conclusions: This research yielded the successful synthesis of two crystalline salts of Sparfloxacin (SPX), significantly improving its solubility and diffusivity, and bolstering its antibacterial efficacy against targeted bacterial species. These breakthroughs set the stage for innovative advancements in the realm of antimicrobial drug development.

Trimesic Acid as a Building Block for Ternary and Quaternary Salts and Salt Cocrystals.

In the field of cocrystals, the synthon-based design of two-component crystals is well established and the interest is now shifting toward higher order cocrystals as the next challenge. Carboxylic acids form a robust synthon with pyridyl coformers and interact with 2-aminopyrimidines through a pair of strong, charge-assisted hydrogen bonds. In this work we describe the formation of higher order salts and salt cocrystals of trimesic acid using 2,4-diaminopyrimidine (pyrimethamine, trimethoprim) and pyridyl (4,4'-bipyridine, 1,2-di(4-pyridyl)ethylene, 1,3-di(4-pyridyl)propane, 4-phenylpyridine) coformers. We report the single crystal structures of five binary, eight ternary and three quaternary systems with the compositions AB, A2B, A3B, A2BC, A3BC, A2BC1.5, ABC1.5, A1 2A2B, ABC1C,2 A2BC1C2 0.5, and A1A2BC where A is a 2,4-diaminopyrimidine cation, B is the mono-, di- or trianion of trimesic acid and C is a pyridine. We also show that the ternary and quaternary salts and salt cocrystals can be prepared in bulk quantities by liquid-assisted grinding.

Dual drug molecular salt of antibacterial: Formulation, physicochemical properties study, theoretical calculations and evaluation of antibacterial activity

A molecular salt combined with the fluoroquinolone antibacterial gatifloxacin (GAT) and the sulfonamides antibacterial sulfamerazine (SMZ) is designed and synthesized successfully, which is the first report of the dual-drug cocrystallization of gatifloxacin. The precise structure of the acquired molecule salt GAT-SMZ has been characterized via single crystal X-ray diffraction and other techniques. Single crystal diffraction analysis displays that due to the transfer of protons from SMZ to GAT, the molecular salt of GAT-SMZ is formed, and the supramolecular network is dominated by charge-assisted one-dimensional hydrogen bond chain and two-dimensional accumulation layer in the crystal. Such structural feature endows molecular salt with superior physicochemical properties, including enhanced solubility and permeability. More importantly, the superior pharmaceutical performances of the dual-drug salt resulted in enhanced antibacterial activity against the tested strains. These observations are strongly supported by theoretical studies based on Hirshfeld surface and molecular docking analyses. Thus, this contribution not only highlights the validity of combining theory with experiment to drive the problem of physicochemical properties of drugs through co-crystallization methods, but also fills in the previous studies gatifloxacin dual-drug salt synergistic antibacterial research blank.

Fluorescent Dye-Based Chiral Crystalline Organic Salt Networks for Circularly Polarized Luminescence.

A facile and general strategy is developed herein for the construction of circularly polarized luminescence (CPL) materials with simultaneously high fluorescence quantum efficiency (Φ) and large luminescence dissymmetry factor (glum). The self-assembly of fluorescent dye, disodium 4,4'-bis(2-sulfonatostyryl)biphenyl (CBS), with chiral diamines such as (R,R)/(S,S)-1,2-diaminocyclohexane (R/S-DACH) and R/S-1,2-diaminopropane (R/S-DAP), produces four chiral crystalline organic salt networks (COSNs). These as-synthesized organic salts emit strong blue-color CPL upon excitation, with both high Φ and glum values of up to 79% and 0.022. The well-defined molecular structures and arrangements of CBS are directly observed through single crystal X-ray analysis, offering crucial information regarding the origins of high-efficiency CPL performance. The chirality of amine is effectively transferred to CBS and further amplified to the supramolecular structure by multiple hydrogen bonding and π-π stacking interactions, giving rise to the large glum factors; meanwhile, the fixation and the ordered arrangement of CBS by these multiple interactions empower efficient suppression of molecular motions, facilitating strong fluorescence. This work can inspire the assembly of CPL organic materials with high Φ and glum via charge-assisted hydrogen bonds between fluorescent dyes and chiral inducers. It also offers important insight into the structural origins of supramolecular chirality and CPL performance.

The potential of supramolecular synthon to develop coamorphous systems with tailored physical stability: Mechanistic insights integrating kinetics and thermodynamics

Coamorphous drug delivery systems have received increasing interest owing to their potential to improve the solubility, dissolution and bioavailability of poorly water-soluble drugs. However, the crystallization risk is one of major limitations in their application. It has been widely recognized that the coformer plays a vital role in physical stability of coamorphous formulation. Unfortunately, the screen of optimal coformer still adopts a trial-and-error method, which is time-consuming and expensive. Herein, a supramolecular synthon approach based on the interaction between functional groups, was exploited to design coamorphous systems (CMs) consisting of lurasidone hydrochloride (LH) and three coformers, saccharin (SAC), L-tryptophan (TRP), and L-cysteine hydrochloride (CYS). X-ray powder diffraction suggested the order of physical stability of the coamorphous systems was ranked as LH-CYS CM > LH-TRP CM > LH-SAC CM. The charge-assisted hydrogen bond between LH and coformer was confirmed by infrared spectroscopy and solid-state 13C NMR. Moreover, structural, electronic, and molecular interaction information, especially hydrogen bonding interactions, were quantified by theoretical calculations, including miscibility calculations, molecular dynamics simulations and quantum chemical calculations. It was revealed that LH-CYS CM exhibited the best miscibility, strongest binding energy and strongest H-bond with partially covalent character, demonstrating the significant role of supramolecular synthon in stabilizing coamorphous formulations. Interestingly, LH-TRP CM, not LH-CYS CM, exhibited the lowest molecular mobility among three coamorphous systems, which was inconsistent with their physical stability. But from thermodynamic perspective, the order of configurational entropy and physical stability of coamorphous systems was completely consistent. We shed light on the comprehensive effects of molecular mobility and configurational entropy on physical stability of coamorphous systems. Importantly, the relationship between supramolecular synthon and kinetic/thermodynamic mechanisms was also discussed, and the positive correlation between configurational entropy and intermolecular interactions was proposed in this paper. Our findings demonstrated the great potential of supramolecular synthon in designing coamorphous systems with tailored physical stability, and further provided a deeper insight into the mechanisms of physical stability of coamorphous systems.

Where Fluoride Is Present, Hexafluorosilicate Might Be Encountered: Supramolecular Binding of the SiF6 2- Anion by Nanojars.

While the fact that HF etches glass is rather common chemical knowledge, the reaction of fluoride ions in an organic solvent with glassware under alkaline conditions has not yet been documented. It becomes apparent that, in general, whenever any fluorine-containing material is handled in silicon-based glassware, the possible presence of SiF6 2- should be considered regardless of the pH of the reaction medium. Subsequent to the initial, inadvertent synthesis by the reaction of CuF2 with laboratory glassware, hexafluorosilicate-entrapping supramolecular assemblies (nanojars) of the formula [SiF6⊂{cis-CuII(μ-OH)(μ-pz)} n ]2- (Cu n SiF 6 ; n = 28, 30, 32, 34) were rationally prepared by the reaction of Cu2+ with pyrazole (Hpz) in the presence of a base and SiF6 2- ions or by combining Cu n CO 3 with H2SiF6 or HF. This work demonstrates that nanojars are excellent anion-binding agents not only for trigonal planar/pyramidal or tetrahedral anions but also for larger, octahedral anions, which are bound exclusively by charge-assisted hydrogen bonds. The SiF6 2- anion guest is preferentially bound by a larger Cu32 host, whereas CO3 2- favors a smaller Cu27 nanojar. The Cu n SiF 6 mixture was characterized by electrospray ionization mass spectrometry as well as variable-temperature, paramagnetic 1H and 19F NMR spectroscopy in solution, complemented by single-crystal X-ray diffraction studies in the solid state, which reveal the unprecedented structure of a Cu8+14+10 nanojar (where Cu8, Cu10, and Cu14 are the component Cu x metallamacrocycles of the Cu32 nanojar).

Desorption hysteresis of antibiotics on biochar produced at high temperature: The role of amine groups and amidation reaction

Knowledge of antibiotic desorption from high-temperature biochar is essential for assessing their environmental risks, and for the successful application of biochar to remove antibiotics. In previous studies, irreversible pore deformation, formation of charge-assisted hydrogen bonds or amide bonds were individually proposed to explain the desorption hysteresis of antibiotics on biochars, leading to a debate on hysteresis mechanism. In this study, desorption of sulfamethoxazole (SMX), ciprofloxacin (CFX) and tetracycline (TET) on a wood chip biochar produced at 700 °C (WBC700) and its oxidized product (O-WBC700) was investigated to explore the underlying hysteresis mechanism. Significant desorption hysteresis was observed for SMX, CFX and TET on WBC700 and O-WBC700. Hysteresis index (HI) of each antibiotic was higher on O-WBC700 with more oxygen-containing groups than WBC700, and was higher at lower equilibrium concentration. HI of antibiotics on WBC700 (or O-WBC700) increased in the order of SMX < CFX < TET. The calculated adsorption enthalpy of each antibiotic on WBC700 was positive, indicating an endothermic process. These phenomena together with FTIR, XPS spectra confirmed that the desorption hysteresis mechanism of antibiotics on high-temperature biochar is the formation of amide bonds by amidation reaction, but not the pore deformation or the hydrogen bond. Moreover, antibiotic can form amide bonds with WBC700 only if the amine group with pKa > 4.0, and the HI values were positively correlated with their pKa values. Amine group of antibiotics with higher pKa value show more nucleophilicity and could form stronger amide bonds with carboxyl group of biochar. The obtained results could help to solve the debate on desorption hysteresis mechanism of antibiotics on high-temperature biochars, and provide a new insight into the role of amine groups and amidation reaction on the hysteresis.

Improved photostability, solubility, hygroscopic stability and antimicrobial activity of fleroxacin by synthesis of fleroxacin-D-tartaric acid pharmaceutical salt

To improve the solubility of the fluoroquinolone drug fleroxacin (FL), based on the previous experience of our research group in synthesizing co-crystals/salts of quinolone drugs to improve the physicochemical properties of drugs, Fleroxacin-D-tartaric acid dihydrate salt (FL-D-TT, C17H19F3N3O3·C4H5O6·2(H2O)), was synthesized for the first time using fleroxacin and D/L-tartaric acid (D/L-TT). Structural characterization of FL-D-TT was carried out using single-crystal X-ray diffraction, infrared spectral analysis (FT-IR) and powder X-ray diffraction (PXRD). Molecular electrostatic potential analysis showed that D-tartaric acid interacted more readily with FL than L-tartaric acid. The solubility of FL-D-TT (9.71 mg/mL, 1.82 mg/mL) was significantly higher compared to FL (0.39 mg/mL, 0.71 mg/mL) in water and buffer solution at pH 7.4. This may be attributed to the formation of charge-assisted hydrogen bonds (CAHBs) between FL and D-TT that facilitates the dissociation of FL cations in the dissolution medium, leading to an increase in FL solubility. This also led to some improvement in the in vitro antimicrobial activity of FL-D-TT against E. coli, S. typhi, and S. aureus. In addition, the hygroscopic stability of FL has been improved. Surprisingly, FL-D-TT had better photostability than FL, which could be attributed to the introduction of D-TT to make the photosensitizing moiety of FL more stable, which led to the improvement of the photostability of FL.

Evaluation of charge-assisted hydrogen bonds and weak intermolecular interaction in trimethoprim 2-aminobenzoate: A combined crystallographic and theoretical approach

A comprehensive investigation of the weak non-covalent interactions within the crystal structure of trimethoprim 2-aminobenzoate (2,6-diamino-5-(3,4,5-trimethoxybenzyl)pyrimidin-1-ium 2-aminobenzoate) is presented. The protonation of trimethoprim and the deprotonation of 2-aminobenzoate were confirmed by NMR spectroscopy and a single-crystal X-ray diffraction study. Qualitative Hirshfeld surface analysis identified intermolecular H···H, O···H, and C···H contacts as the three primary interactions within the title salt. Fourteen molecular pairs (M1AA−M14AB) were extracted from the crystal packing of the title salt using the PIXEL method. These molecular dimers were further characterized using the QTAIM and DFT approaches. Seven intermolecular pairs (M1AA−M7BB) formed between like-charged species (i.e. +1···+1 or -1···-1) resulted in destabilization, with total energies (Etot) ranging from 67.2 to 200.1 kJ mol-1. Conversely, molecular pairs formed between oppositely charged species (i.e. +1···-1) exhibited stabilizing behavior, with interaction energies ranging from -133.7 to -449.7 kJ mol-1. Topological analysis of charge density revealed that two N–H···O hydrogen bonds between cation and anion displayed an intermediate character between shared and closed-shell interactions. Additionally, comparison with previously reported similar TMP salts (CSD ref. code: CESRUN, HURMOW and PARWUB) demonstrated 3D-isostructural packing features in the crystal structure of the title salt.

Participation of strong charge-assisted hydrogen bonds in interactions of dissolved organic matter represented by Suwannee River Humic Acid

Terrestrial dissolved organic matter (DOM) plays critical roles in many biotic and abiotic environmental reactions as well as in water treatment. Its structure is therefore of great interest. We examined dissolved Suwannee River Humic Acid (HA) to probe the potential participation of exceptionally strong, negative charge-assisted hydrogen bonds, (−)CAHB, in DOM cohesion and interaction with small weak acids using high performance size exclusion chromatography (HPSEC), transmission electron microscopy, zeta-pH curves, and pH drift experiments. The results support a previously proposed two-tier state of aggregation, in which tightly-knit primary particles (≤ ∼10 kDa) form larger secondary aggregates (up to micrometer in size). Evidence for (−)CAHB is gained through zeta potential changes and pH drift experiments. The primary particles interact with (−)CAHB-capable solutes (simple carboxylic acids and phosphate) but not (−)CAHB-incapable solutes. We identified disruption of intra-segmental and inter-molecular (−)CAHB leading to swelling and disaggregation, as well as formation of nouveau (−)CAHB with free groups on HA. The effects were solute-concentration dependent and greater at pH 5 than pH 6, consistent with CAHB theory. Phosphate induced the greatest shifts in the HPSEC molecular size distribution curves. The shifts were unaffected by prior stripping of innate polyvalent metals. We conclude that the (−)CAHB contributes to the cohesion of DOM, affecting its size and charge, and provides a means by which weak acid pollutants, nutrients, and natural compounds can interact with DOM. Such interactions have implications for the behavior of DOM in the environment, the fate and transport of anthropogenic pollutants, and the roles DOM play in water treatment technologies.

Novel Conductive and Redox-Active Molecularly Imprinted Polymer for Direct Quantification of Perfluorooctanoic Acid.

This study developed a novel molecularly imprinted polymer (MIP) that is both conductive and redox-active for directly quantifying perfluorooctanoic acid (PFOA) electrochemically. We synthesized the monomer 3,4-ethylenedioxythiophene-2,2,6,6-tetramethylpiperidinyloxy (EDOT-TEMPO) for electropolymerization on a glassy carbon electrode using PFOA as a template, which was abbreviated as PEDOT-TEMPO-MIP. The redox-active MIP eliminated the need for external redox probes. When exposed to PFOA, both anodic and cathodic peaks of MIP showed a decreased current density. This observation can be explained by the formation of a charge-assisted hydrogen bond between the anionic PFOA and MIP's redox-active moieties (TEMPO) that hinder the conversion between the oxidized and reduced forms of TEMPO. The extent of the current density decrease showed excellent linearity with PFOA concentrations, with a method detection limit of 0.28 ng·L-1. PEDOT-TEMPO-MIP also exhibited high selectivity toward PFOA against other per- and polyfluoroalkyl substances (PFAS) at environmentally relevant concentrations. Our results suggest electropolymerization of MIPs was highly reproducible, with a relative standard deviation of 5.1% among three separate MIP electrodes. PEDOT-TEMPO-MIP can also be repeatedly used with good stability and reproducibility for PFOA detection. This study provides an innovative platform for rapid PFAS quantification using redox-active MIPs, laying the groundwork for developing compact PFAS sensors.

Comparison of the crystal structures of the JAK1/2 inhibitor ruxolitinib and its hydrate and phosphate.

Ruxolitinib {RUX; systematic name: (3R)-3-cyclopentyl-3-[4-(7H-pyrrolo[2,3-d]pyrimidin-4-yl)-1H-pyrazol-1-yl]propanenitrile, C17H18N6} is an orally bioavailable JAK1/2 inhibitor approved for treating intermediate- or high-risk myelofibrosis (MF) and high-risk polycythemia vera (PV). Recent patents claim that RUX can exist in many different forms, information for which is important for the clinical utilization of RUX, especially for the formulation and bioavailability of the drug. But there has been no detailed study on its forms so far. Herein crystals of RUX and its dihydrate (RUX-2H; C17H18N6·2H2O) and phosphate (RUX-P; systematic name: 4-{1-[(1R)-2-cyano-1-cyclopentylethyl]-1H-pyrazol-4-yl}-7H-pyrrolo[2,3-d]pyrimidin-3-ium dihydrogen phosphate, C17H19N6+·H2PO4-) were prepared successfully and their structures studied in detail for the first time. Our study shows that the three crystals of RUX differ in the orientation of the pyrimidine ring relative to the pyrazole ring of the RUX molecule, and in their hydrogen-bond interactions. The water molecules in RUX-2H and the dihydrogen phosphate anion in RUX-P enrich the hydrogen-bond networks in these forms. The expected proton transfer occurs in RUX phosphate and the protonated N atom is engaged in a charge-assisted hydrogen bond with the counter-anion. Hydrogen-bonding interactions dominate in the crystal packing of the three forms. The detailed conformations and packing of the three forms were compared through the calculation of both Hirshfeld surfaces and fingerprint plots.

Comparison of rhodamine B adsorption and desorption on the aged non-degradable and degradable microplastics: Effects of charge-assisted hydrogen bond and underline mechanism

The accumulation of microplastics (MPs) in the environment and their role as carriers for ionic organic pollutants are increasingly attracting attention. This study evaluated the adsorption-desorption characteristics of the cationic organic pollutant on virgin and UV-aged non-degradable polystyrene (PS) as well as degradable poly(butylene succinate) (PBS) and poly(butylene adipate-co-terephthalate) (PBAT) MPs. The results showed that aging treatment made the surface of MPs rougher and more porous, causing the adsorption to shift from monolayer to multilayer adsorption. Aging increased the oxygen-containing groups on MPs, significantly enhancing the H bond (HB) donor capabilities of degradable aged PBS and PBAT, thereby improving adsorption by more than 10 times. This significant increase in adsorption is mainly due to the combined effects of strong HB (including ordinary HB (OHB) and charge-assisted HB (CAHB)), electrostatic interactions, and π-π interactions. Notably, the stronger HB enabled aged PBS and PBAT to achieve efficient and stable adsorption of rhodamine B over a wide pH range, with significant desorption hysteresis (HI > 1.80). This indicates that degradable aged MPs can act as carriers for long-distance pollutant transport. The significant total desorption of cationic pollutants from aged PBS and PBAT in simulated animal gastrointestinal fluids confirmed the greater environmental hazards of degradable aged MPs. This work is the first to demonstrate that degradable aged MPs, as unique HB donors, can primarily adsorb ionic organic pollutants through strong HB (CAHB and OHB), which helps assess the environmental fate of biodegradable microplastics and pollutants in aquatic systems.

Microplastics and Antibiotics in Aquatic Environments: A Review of Their Interactions and Ecotoxicological Implications

Microplastics and antibiotics are two significant emerging pollutants found together in water bodies, raising concerns about their mutual effects. This review delves into how microplastics and antibiotics interact in aqueous environments and the ecotoxicological implications of such interactions, particularly the bioavailability of antibiotics and the prevalence of antibiotic-resistance genes. It outlines that antibiotics attach to microplastics primarily through hydrophobic, hydrogen-bonding, and electrostatic interactions. Other bonds, comprising halogen bonding, cation−π interaction, and negative charge-assisted hydrogen bonds, may also be involved to better explain antibiotic adsorption patterns. The adsorption of antibiotics to microplastics often follows the pseudo-second-order kinetic model and in some instances, the pseudo-first-order kinetic model. The common adsorption isotherms governing this interaction are the linear and Freundlich models. Microplastics may increase the biodegradation of adsorbed antibiotics due to the presence of antibiotic-degrading bacteria in the biofilms. They could also hamper direct photodegradation but facilitate indirect photodegradation of adsorbed antibiotics. However, their photodegradative effect remains inconclusive. Microplastics and antibiotics exhibit significant toxicity to algae, while their effects on fish and daphnia are less noticeable, suggesting that their combination does not pose an immediate threat to the well-being and proliferation of larger aquatic organisms. In some instances, microplastics reduce the deleterious effects of antibiotics on aquatic life. Microplastics serve as catalysts for gene transfer, enhancing the propagation of antibiotic-resistance genes in these ecosystems. This review underscores the importance of understanding the regulatory mechanisms of microplastics on antibiotic-resistance gene diversity, particularly at the gene expression level.

Adsorption dynamics of per- and polyfluoroalkyl substances (PFAS) on activated carbon: Interplay of surface chemistry and PFAS structural properties

Using activated carbon (AC) to adsorb per- and polyfluoroalkyl substances (PFAS) is highly practical for environmental remediation. However, examining the surface chemistry of carbonaceous material with regard to the removal of various PFAS has been limited, as the focus has often solely been on perfluorooctanoic acid and perfluorooctane sulfonic acid. Consequently, this study systematically explores the role of AC surface chemistry in the adsorption of PFAS with various structural properties using ACs that have been modified for different degrees of acidity, basicity, and hydrophobicity. Batch adsorption studies have demonstrated that the affinity of PFAS for the AC surface is negatively correlated with surface acidity. The removal performance at an adsorbent dose of 2 mg/L and an initial PFAS concentration of 600 ng/L is 27.4–91.4 %, 57.2–95.6 %, 92.4–99.2 %, and 89.1–99.6 % for an AC with an acidic surface, unmodified AC, defunctionalized AC, and AC with basic surface, respectively. Analyses of the adsorption isotherms, kinetics, and removal performance of the four types of ACs and 14 PFAS in water at different pH and ionic strengths reveal that hydrophobic, electron donor–acceptor, and electrostatic interactions, as well as negative charge-assisted hydrogen bond formation are necessary to describe the key adsorption characteristics observed in the experiments. The relative significance of the adsorption mechanisms depends on the PFAS structural properties, AC surface chemistry, and water composition. This extensive discourse contributes substantially to the design of an efficient carbonaceous adsorbent with specific surface moieties for removing PFAS from water.

Insights into the Roles of Surface Functional Groups and Micropores in the Sorption of Ofloxacin on Banana Pseudo-Stem Biochars

In the present study, banana pseudo-stem (BS) was pyrolyzed under anaerobic conditions without any physical or chemical modification. Their properties, as well as their sorption affinity to ofloxacin (OFL), were studied. As a result, oxalates and KCl formed at a relatively low temperature of 300 °C, while bicarbonates generally formed at a pyrolysis temperature above 400 °C. Surface functional groups of BS biochars facilitated OFL sorption mainly via specific interactions including electronic attraction (EA), π–π electron donor–acceptor (π–π EDA) interaction, the ordinary hydrogen bond (OHB), and the negative charge-assisted hydrogen bond ((−)CAHB). Except for (−)CAHB, these interactions all decreased with an elevated pH, resulting in overall decreased OFL sorption. Significant OFL sorption by BS biochars produced at 300 °C, observed even at an alkaline condition was attributed to (−)CAHB. Micropores formed in BS biochar prepared at 500 °C, with a specific surface area as high as 390 m2 g−1 after water washing treatment. However, most micropores could not be accessed by OFL molecules due to the size exclusion effect. Additionally, the inherent K-containing salts may hinder OFL sorption by covering the sorption sites or blocking the inner pores of biochars, as well as releasing OH− into the solution. Thus, BS biochar produced at 300 °C is an excellent sorbent for OFL removal due to its high sorption ability and low energy. Our findings indicate that biochar techniques have potential win–win effects in recycling banana waste with low energy and costs, and simultaneously converting them into promising sorbents for the removal of environmental contaminants.

Spirobifluorene-Based Porous Organic Salts: Their Porous Network Diversification and Construction of Chiral Helical Luminescent Structures.

Porous organic salts (POSs) are organic porous materials assembled via charge-assisted hydrogen bonds between strong acids and bases such as sulfonic acids and amines. To diversify the network topology of POSs and extend its functions, this study focused on using 4,4',4'',4'''-(9,9'-spirobi[fluorene]-2,2',7,7'-tetrayl)tetrabenzenesulfonic acid (spiroBPS), which is a tetrasulfonic acid comprising a square planar skeleton. The POS consisting of spiroBPS and triphenylmethylamine (TPMA) (spiroBPS/TPMA) was constructed from the two-fold interpenetration of an orthogonal network with pts topology, which has not been reported in conventional POSs, owing to the shape of the spirobifluorene backbone. Furthermore, combining tris(4-chlorophenyl)methylamine (TPMA-Cl) and tris(4-bromophenyl)methylamine (TPMA-Br), which are bulkier than TPMA owing to the introduction of halogens at the p-position of the phenyl groups with spiroBPS allows us to construct novel POSs (spiroBPS/TPMA-Cl and spiroBPS/TPMA-Br). These POSs were constructed from a chiral helical network with pth topology, which was induced by the steric hindrance between the halogens and the curved fluorene skeleton. Moreover, spiroBPS/TPMA-Cl with pth topology exhibited circularly polarized luminescence (CPL) in the solid state, which has not been reported in hydrogen-bonded organic frameworks (HOFs).

Biochar derivation at low temperature: A novel strategy for harmful resource usage of antibiotic mycelial dreg

Antibiotic mycelial dreg (AMD) has been categorized as hazardous waste due to the high residual hazardous contaminants. Inappropriate management and disposal of AMD can cause potential environmental and ecological risks. In this study, the potential of pleuromutilin mycelial dreg (PMD) as a novel feedstock for preparing tetracycline hydrochloride (TC) adsorbent was explored to achieve safe management of PMD. The results suggested that residual hazardous contaminants were completely eliminated after pyrolysis. With the increase of pyrolysis temperature, the yields, H/C, O/C, (O + N)/C, and pore size in PMD-derived biochars (PMD-BCs) decreased, while BET surface area and pore volume increased, resulting in the higher stability of the PMD-BCs prepared from higher temperatures. The TC adsorption of the PMD-BCs increased from 27.3 to 46.9 mg/g with the increase of the pyrolysis temperature. Surprisingly, pH value had a strong impact on the TC adsorption, the adsorption capacity of BC-450 increased from 6.5 to 71.1 mg/g when the solution pH value increased from 2 to 10. Lewis acid-base interaction, pore filling, π-π interaction, hydrophobic interaction, and charge-assisted hydrogen bond (CAHB) are considered to drive the adsorption. This work provides a novel pathway for the concurrent detoxification and reutilization of AMD.

Molecular rotators anchored on a rod-like anionic coordination polymer adhered by charge-assisted hydrogen bonds.

On the basis of variable-temperature single-crystal X-ray diffraction, variable-temperature/frequency dielectric analysis, variable-temperature solid-state nuclear magnetic resonance spectroscopy, and molecular dynamics simulations, here we present a new model of crystalline supramolecular rotor (i-PrNHMe2)[CdBr3], where a conformationally flexible near-spherical (i-PrNHMe2)+ cation functions as a rotator and a rod-like anionic coordination polymer {[CdBr3]-}∞ acts as the stator, and the adhesion of them is realized by charge-assisted hydrogen bonds.

Network topology diversification of porous organic salts.

Hydrogen-bonded organic frameworks (HOFs) are porous organic materials constructed via hydrogen bonds. HOFs have solubility in specific high-polar organic solvents. Therefore, HOFs can be returned to their components and can be reconstructed, which indicates their high recyclability. Network topologies, which are the frameworks of porous structures, control the pore sizes and shapes of HOFs. Therefore, they strongly affect the functions of porous materials. However, hydrogen bonds are usually weak interactions, and the design of the intended network topology in HOFs from their components has been challenging. Porous organic salts (POSs) are an important class of HOFs, are hierarchically constructed via strong charge-assisted hydrogen bonds between sulfonic acids and amines, and therefore are expected to have high designability of the porous structure. However, the network topology of POSs has been limited to only dia-topology. Here, we combined tetrasulfonic acid with the adamantane core (4,4',4'',4'''-(adamantane-1,3,5,7-tetrayl)tetrabenzenesulfonic acid; AdPS) and triphenylmethylamines with modified substituents in para-positions of benzene rings (TPMA-X, X = F, methyl (Me), Cl, Br, I). We changed the steric hindrance between the adamantane and substituents (X) in TPMA-X and obtained not only the common dia-topology for POSs but also rare sod-topology, and lon- and uni-topologies that are formed for the first time in HOFs. Changing template molecules under preparation helped in successfully isolating the porous structures of AdPS/TPMA-Me with dia-, lon-, and sod-topologies which exhibited different gas adsorption properties. Therefore, for the first time, we demonstrated that the steric design of HOF components facilitated the formation, diversification, and control of the network topologies and functions of HOFs.