Hydrogen-bonding Sites Research Articles

Construction of cyclodextrin microporous organic network based drug delivery platform for controllable release and targeting delivery of doxorubicin

Rational design and fabrication of effective drug delivery systems (DDS) are crucial for improving the therapeutic effectiveness and overcoming the shortcomings of chemotherapy. Herein, we report the construction of a novel cyclodextrin microporous organic network (CD-MON)-based DDS via a convenient thiol‑yne click reaction and dehydration condensation modification for the controllable release and targeted delivery of doxorubicin (DOX), a typical chemotherapy drug. The constructed DDS afforded multiple hydrophobic, hydrogen-bonding, and host-guest interaction sites, allowing for the efficient loading of DOX. The obtained DDS also exhibited good sustained and long-term release of DOX. Additionally, the proposed DDS offers good biocompatibility and exhibits an obvious aggregation-induced emission. Furthermore, the introduction of folic acid (FA) into the CD-MON-based DDS provided excellent targeting capacity for FA receptor-positive NCI-H226 cells. This study proved the universality of the design, synthesis, and application of CD-MON-based DDS, revealing the great potential of CD-MONs in drug delivery.

A {PMo12}-based 2D sandwich-like supramolecular network constructed from a new semi-rigid amide-derived ligand with enhanced capacitive activity and electrochemical sensing performances

To achieve high electrochemical performance of polyoxometalates (POMs)-based materials, introducing POMs to crystalline supramolecular structures via hydrogen bonding interactions represents a potential strategy. Herein, a new semi-rigid pyrazole-amide-derived bis(pyridyl) ligand N,N'-bis(3-pyridinamide)-1-hydropyrazole (3-Hdpyp) was designed due to the abundant hydrogen bond sites of amide group, as well as the multiple N-donor sites, which was used to assemble with the Keggin-type [PMo12O40]3− (PMo12) anion and cobalt under solvothermal condition. A new 2D sandwich-like supramolecular network [Co2(3-dpyp)2(H2O)2][HPMo12O40] (1) was synthesized and structurally characterized. The PMo12 anions are fixed between the 1D metal–organic chains [Co2(3-dpyp)2(H2O)2]n2n+via hydrogen bonding interaction. Complex 1 shows excellent specific capacitances 1062.5F g−1 at the current density of 1 A g−1. After 1000 cycles, it can maintain 90.0% of the capacitance retention. Meanwhile, complex 1 represents an excellent amperometric sensor for measurement of Cr(VI) with low detection limit of 0.22 µM. The excellent electrochemical performance can be attributed the discrete 2D sandwich-like structures, which can improve the active area of POMs and conductivity of the network.

Construction of Stable Magnetic Vinylene-Linked Covalent Organic Frameworks for Efficient Extraction of Benzimidazole Fungicides.

Covalent organic frameworks (COFs) have attracted impressive interest in separation on aqueous media. Herein, we integrated the stable vinylene-linked COFs with magnetic nanosphere via the monomer-mediated in situ growth strategy to construct a crystalline Fe3O4@v-COF composite for enrichment and determination of benzimidazole fungicides (BZDs) from complex sample matrices. The Fe3O4@v-COF has a crystalline assembly, high surface area, porous character together with a well-defined core-shell structure, and serves as progressive pretreatment materials for magnetic solid phase extraction (MSPE) of BZDs. Adsorption mechanism studies revealed that the extended conjugated system and numerous polar cyan groups on v-COF provides abundant π-π and multiple hydrogen bonding sites, which are conducive to interact with BZDs collaboratively. Fe3O4@v-COF also displayed enrichment effects to various polar pollutions with conjugated structures and hydrogen-bonding sites. Fe3O4@v-COF-based MSPE-high-performance liquid chromatography exhibited the low limit of detection, wide linearity, and good precision. Moreover, Fe3O4@v-COF showed better stability, enhanced extraction performance, and more sustainable reusability in comparison with its imine-linked counterpart. This work proposes a feasible strategy on constructing the crystalline stable magnetic vinylene-linked COF composite for the determination of trace contaminants in complex food matrices.

Polarity-Evolution Control and Luminescence Regulation in Multiple-Site Hydrogen-Bonded Organic Frameworks.

Hydrogen-bonded organic frameworks (HOFs) have shown great potential in separation, sensing and host-guest chemistry, however, the pre-design of HOFs remains challenging due to the uncertainty of solvents' participation in framework formation. Herein, the polarity-evolution-controlled framework/luminescence regulation is demonstrated based on multiple-site hydrogen-bonded organic frameworks. Several distinct HOFs were prepared by changing bonding modes of building units via the evolution of electrostatic forces induced by various solvent polarities. High-polar solvents with strong electrostatic attraction to surrounding units showed the tendency to form cage structures, while low-polar solvents with weak electrostatic attraction only occupy hydrogen-bond sites, conducive to the channel formation. Furthermore, the conformation of optical building unit can be adjusted by affecting the solvent polarity, generating different luminescence outputs. These results pave the way for the rational design of ideal HOFs with on-demand framework regulation and luminescence properties.

Two-Sided Impact of Water on the Relaxation of Inner-Valence Vacancies of Biologically Relevant Molecules.

After ionization of an inner-valence electron of molecules, the resulting cation-radicals store substantial internal energy which, if sufficient, can trigger ejection of an additional electron in an Auger decay usually followed by molecule fragmentation. In the environment, intermolecular Coulombic decay (ICD) and electron-transfer mediated decay (ETMD) are also operative, resulting in one or two electrons being ejected from a neighbor, thus preventing the fragmentation of the initially ionized molecule. These relaxation processes are investigated theoretically for prototypical heterocycle-water complexes of imidazole, pyrrole, and pyridine. It is found that the hydrogen-bonding site of the water molecule critically influences the nature and energetics of the electronic states involved, opening or closing certain relaxation processes of the inner-valence ionized system. Our results indicate that the relaxation mechanisms of biologically relevant systems with inner-valence vacancies on their carbon atoms can strongly depend on the presence of the electron-density donating or accepting neighbor, either water or another biomolecule.

Tritium separation from radioactive wastewater by hydrogen isotope-selective exchange of hydrogen-bonded fluorine

The separation of tritium (3H) from radioactive wastewater is a persistent challenging problem in the nuclear industry from an environmental perspective. This study provides new insight into the tritium separation by investigating hydrogen isotope-selective exchange reaction on hydrogen-bonded fluorine (F····H····O) site. In this study, fluorinated mesoporous silica, F-MCM-41_NCs were prepared as a novel tritium sorbent that showed a significantly enhanced tritium isotope separation factor (α) compared to the pristine MCM-41 (α = 1.2). The optimal α of 3.3 is achieved using 0.5F-MCM-41_NC prepared with 0.5 g of NH4F per gram of MCM-41. This optimal α is attributed to an excellent compromise between the amount and the stability of (NH4)2SiF6 on the pore channel with the integrity of the MCM-41 framework. Experimental, theoretical, and analytical characterization results consistently support chemical affinity quantum sieving effect at F····H····O hydrogen-bonding sites via the hydrogen isotope-selective exchange reaction as the dominant tritiumseparation mechanism.

Room temperature enhancement of flexural strength in silicon carbide green body via the addition of cellulose nanofiber

Silicon carbide (SiC) green bodies fabricated using robocasting were strengthened by incorporating cellulose nanofiber (CNF) into a SiC slurry and just drying at room temperature. The measured flexural strength of a SiC green body modified via the CNF with a liquid phase weight ratio (water-to-CNF slurry) of 80:20 was 813 ± 37 kPa, 1.5 times larger than the strength of an unmodified green body. The strength was improved due to the increased number of hydrogen-bonding sites between the raw particles and CNF. After annealing at 250 °C, the lowering of the flexural strength indicated the occurrence of the bonding sites via water that was trapped on the CNF. The addition of CNF increased the viscosity and yield stress of the SiC slurry, which remained in the Bingham pseudoplastic behavior regardless of the CNF used. Moreover, this addition showed no effect on the relative densities, microstructures, and crystalline phases of the sintered SiC body. Therefore, the addition of CNF to the SiC slurry aided in handling the green body during processing and showed no detrimental effects on robocasting.

Recent Advances in Pharmaceutical Cocrystals: A Focused Review of Flavonoid Cocrystals

Cocrystallization is currently an attractive technique for tailoring the physicochemical properties of active pharmaceutical ingredients (APIs). Flavonoids are a large class of natural products with a wide range of beneficial properties, including anticancer, anti-inflammatory, antiviral and antioxidant properties, which makes them extensively studied. In order to improve the properties of flavonoids, such as solubility and bioavailability, the formation of cocrystals may be a feasible strategy. This review discusses in detail the possible hydrogen bond sites in the structure of APIs and the hydrogen bonding networks in the cocrystal structures, which will be beneficial for the targeted synthesis of flavonoid cocrystals. In addition, some successful studies that favorably alter the physicochemical properties of APIs through cocrystallization with coformers are also highlighted here. In addition to improving the solubility and bioavailability of flavonoids in most cases, flavonoid cocrystals may also alter their other properties, such as anti-inflammatory activity and photoluminescence properties.

Effective ammonia separation by non-chloride deep eutectic solvents composed of dihydroxybenzoic acids and ethylene glycol through multiple-site interaction

The effective separation of ammonia (NH3) has important implication for the conversion improvement and pollution control during the synthesis of NH3. In the present work, a novel kind of non-chloride deep eutectic solvents (DESs) were constructed from dihydroxybenzoic acids (DHBAs) and ethylene glycol (EG). The DHBA + EG DESs exhibit several weak acidic sites and hydrogen-bond sites, thus were proposed for NH3 separation. We found that the amounts of NH3 absorbed by DHBA + EG DESs are quite impressive, particularly at reduced pressures. The capacities can reach 5.64 and 11.69 mol/kg at 0.1 and 1 bar respectively, when the temperature of 298.2 K is considered. Besides, after five absorption–desorption cycles, the DHBA + EG DESs can preserve the excellent NH3 absorption performance. The DHAB + EG DESs can also selectively absorb NH3 from N2 and H2 in the mixed gas. The NH3 absorption mechanism of DHBA + EG DESs was further deeply illustrated by spectroscopic techniques and theoretical calculations.

A novel role of various hydrogen bonds in adsorption, desorption and co-adsorption of PPCPs on corn straw-derived biochars

The effect of various hydrogen bonds with different strength on the environmental behaviors of PPCPs remains unclear. In this study, three pharmaceutical pollutants including clofibric acid (CA), sulfamerazine (SMZ), and acetaminophen (ACT) with different functional groups and pKa, were selected as representative of PPCPs to investigate the pivotal role of hydrogen bonds in adsorption/desorption and co-adsorption behaviors of PPCPs on two corn straw-derived biochars prepared at 300 °C (BCs-300) and 600 °C (BCs-600), respectively. The results indicated that charge-assisted hydrogen bond (CAHB) and ordinary hydrogen bond (OHB) with different intensities were the pivotal mechanisms responsible for the adsorption of three PPCPs on biochars, which was further confirmed by FTIR, but their immobilization effects of PPCPs on biochars were completely different. Compared with OHB formed between CA and BCs-600, the stronger CAHB (formed between CA and BCs-300, and SMZ/ACT and BCs-300/BCs-600) with covalent bond characteristics that derived from the smaller |ΔpKa| (<5.0), resulted in the greater adsorption capacity (Qs) and affinity (Kf) of the three PPCPs on BCs-300 (Qs ≥ 195 μmol·g−1, Kf ≥ 1.9956) than that on BCs-600 (Qs ≤ 92 μmol·g−1, Kf ≤ 0.5192), thereby making the better immobilization effect of PPCPs by biochar. In addition, in the coexisting systems, either SMZ coexisting with CA/ACT on BCs-300, or ACT coexisting with CA/SMZ on BCs-600, both implied that when the |ΔpKa| between the target PPCPs and biochar is smaller than that between the coexisting compound and biochar, the target PPCPs can preferentially occupy the shared hydrogen bond sites on the biochar surface, and hard to be replaced by the coexisting compound. This work not only expand the application of designed biochar as engineering adsorbents to control and removal of the specific PPCPs in the environment, but also facilitate accurate assessment of the environmental risk of co-existing PPCPs.

Molecular investigation of interplay mechanism between polydopamine and graphene oxide: The effect of oxidation degree on the adsorption behavior of polydopamine

The interfacial behaviors taking place between polydopamine (PDA) and graphene oxide (GO), two types of biocompatible functional nanomaterials popular in drug delivery and cancer therapy, were investigated by classical molecular dynamics (MD) simulations. The analysis of the self-assembly of PDA on the GO surface indicated that the rise in oxidation degree of PDA (signifying the increase of the carbon-to-hydrogen ratio and intramolecular cyclization) enhanced the adsorption capacity of GO to PDA, as a result of the impact of resonance effect of substituents on the polarity of functional groups. The inter-/intramolecular hydrogen bonds were proved to play a crucial role in mediating the adsorption of PDA. The non-amine-participating hydrogen bonds can promote the adsorption of PDA, whereas the amine-participating hydrogen bonds only have limited benefits to the adsorption, meanwhile, consume or preempt the hydrogen-bond sites on GO surface. Moreover, the hydrophobicity of functional groups in PDA was proved to be an important driving force to determine the adsorption affinity between PDA and GO, relying on the estimations of solvent accessible surface area and hydrogen bonding interaction with water molecules. The present computational study provides insights into the intrinsic mechanisms of the functional modification of carbon-based nanomaterials by the organic coatings.

Energy Transfer and Restructuring in Amorphous Solid Water upon Consecutive Irradiation.

Interstellar and cometary ices play an important role in the formation of planetary systems around young stars. Their main constituent is amorphous solid water (ASW). Although ASW is widely studied, vibrational energy dissipation and structural changes due to vibrational excitation are less well understood. The hydrogen-bonding network is likely a crucial component in this. Here, we present experimental results on hydrogen-bonding changes in ASW induced by the intense, nearly monochromatic mid-IR free-electron laser (FEL) radiation of the FELIX-2 beamline at the HFML-FELIX facility at the Radboud University in Nijmegen, The Netherlands. Structural changes in ASW are monitored by reflection-absorption infrared spectroscopy and depend on the irradiation history of the ice. The experiments show that FEL irradiation can induce changes in the local neighborhood of the excited molecules due to energy transfer. Molecular dynamics simulations confirm this picture: vibrationally excited molecules can reorient for a more optimal tetrahedral surrounding without breaking existing hydrogen bonds. The vibrational energy can transfer through the hydrogen-bonding network to water molecules that have the same vibrational frequency. We hence expect a reduced energy dissipation in amorphous material with respect to crystalline material due to the inhomogeneity in vibrational frequencies as well as the presence of specific hydrogen-bonding defect sites, which can also hamper the energy transfer.

Hydration-Facilitated Coordination Tuning of Metal-Organic Frameworks toward Water-Responsive Fluorescence and Proton Conduction.

Developing smart stimuli-responsive metal-organic frameworks (MOFs) with diversified induced readable signals is highly desirable; however, reported multimode responsive MOFs are always achieved under strong environmental stimulations, making it difficult to keep MOF structures stable for practical applications. Herein, we reported a hydration-facilitated coordination tuning strategy to achieve the dual-mode water response in fluorescence and proton conduction from a single MOF. The designed MOF permitted reversible single-crystal transformation via the controllable hydration effect on metal nodes. The change in coordination modes leads to the regulation on conformations of optical ligands, contributing to the switch of fluorescence emissions. Moreover, the hydration effect adds additional hydrogen-bond sites in channels and optimizes hydrogen-bond networks, abruptly enhancing the proton conductivity by ∼20 times. These results pave new avenues for the exploitation of smart MOFs with multimode responsive behavior for on-demand sensing/detection applications.

Identification of Novel Antifreeze Peptides from Takifugu obscurus Skin and Molecular Mechanism in Inhibiting Ice Crystal Growth.

Foodborne hydrolyzed antifreeze peptides have been widely used in the food industry and the biomedical field. However, the components of hydrolyzed peptides are complex and the molecular mechanism remains unclear. This study focused on identification and mechanism analysis of novel antifreeze peptides from Takifugu obscurus skin by traditional methods and computer-assisted techniques. Results showed that three peptides (EGPRAGGAPG, GDAGPSGPAGPTG, and GEAGPAGPAG) possessed cryoprotection via reducing the freezing point and inhibiting ice crystal growth. Molecular docking confirmed that the cryoprotective property was related to peptide structure, especially α-helix, and hydrogen bond sites. Moreover, the antifreeze peptides were double-faces, which controlled ice crystals while affecting the arrangement of surrounding water molecules, thus exhibiting a strong antifreeze activity. This investigation deepens the comprehension of the mechanism of antifreeze peptides at molecular scale, and the novel efficient antifreeze peptides can be developed in antifreeze materials design and applied in food industry.

Investigation of effective bonding between varied binders and Si anode with different particle sizes

The size of silicon (Si) particles and used binder directly affects the flow uniformity of the slurry, the mechanical properties, and the electrochemical performance of the electrode. In this study, we tried to clarify the adaptation law of Guar gum (GG) and sodium alginate (SA) with 200 nm-Si and 1 μm-Si from the above-mentioned aspects. The rheological properties of the slurry showed that the slurry with GG due to the gelatinization had a poorer dispersion than that with SA. The tests of zeta potentials, thermogravimetric analysis, peeling-off, and nano-indentation profiles explained the performance differences of the electrodes from the mechanical properties. Because of more hydrogen bond sites, the discharge specific capacity of the nm-Si/GG electrode (1116.05 mA h g−1) was higher than the nm-Si/SA electrode (657.74 mA h g−1) after 70 cycles. On the contrary, the μm-Si/SA electrode owing to a rigid skeleton in the SA molecule exhibited a discharge specific capacity of 1681.47 mA h g−1 after 50 cycles, while the μm-Si/GG electrode was 486.58 mA h g−1. In addition, the results inspire more reasonable optimization of the Si-based electrode design.

Three-center-four-electron halogen bond enables non-metallic complex catalysis for Mukaiyama-Mannich-type reaction

SummaryThe three-center-four-electron halogen bond (3c4e X-bond) presents a fundamental design concept for catalysis. By integrating halogen(I) (X+: I+ or Br+), the bis-pyridyl ligand NN, and a non-nucleophilic counteranion Y, we developed non-metallic complex catalysts, [N···X···N]Ys, that exhibited outstanding activity and facilitated the Mukaiyama-Mannich-type reaction of N-heteroaromatics with parts-per-million-level catalyst loading. The high activity of [N···X···N]SbF6 was clearly demonstrated. NMR titration experiments, CSI-MS, computations, and UV-vis spectroscopic studies suggest that the robust catalytic activity of [N···X···N]Y can be attributed to the unique ability of the 3c4e X-bond for binding chloride: i) the covalent nature transforms the [N···X···N]+ complexation to sp2 CH as a hydrogen-bonding donor site, and ii) the noncovalent property allows for the dissociation of [N···X···N]+ for the formation of [Cl···X···Cl]−. This study introduces the application of 3c4e X-bonds in catalysis via halogen(I) complexes.

Ethidium hepta-fluoro-butyrate.

In the title compound (systematic name: 3,8-diamino-5-ethyl-6-phenylphenanthridin-5-ium 2,2,3,3,4,4,4-heptafluorobutyrate), C21H20N3 +·C4F7O2 -, two ethidium ions, C21H20N3 + form a dimerized structure due to π-π inter-actions, even though they are positively charged. The hepta-fluoro-butyrate anions are connected to neighbouring cation dimers via hydrogen-bonding inter-actions, the hydrogen-bonding donor sites of the -NH2 groups of the ethidium ions connecting to the hydrogen-bonding acceptor sites of the -COO- groups of the hepta-fluoro-butyrate anions.

Rational Construction of Molecular Electron-Conducting Nanowires Encapsulated in a Proton-Conducting Matrix in a Charge Transfer Salt.

Insulated molecular wires have gained significant attention owing to their potential contribution in the fields of nanoelectronics and low-dimensional chemistry/physics. Based on molecular charge transfer salts, we demonstrate, for the first time, the rational construction of molecular electron-conducting wires encapsulated in a proton-conducting matrix, which possibly paves the way to ionoelectronics. As expected from the molecular structure of the newly designed complex anion (i.e., propeller-shaped structure with hydrogen-bonding sites at four edges), a three-dimensional hydrogen-bonded framework was constructed within the crystal, which contains a one-dimensional array of an electron donor, tetrathiafulvalene (TTF). From the single-crystal crystallographic and spectroscopic studies, it was clarified that the nonstoichiometric deprotonation of anions and partial oxidation of TTFs occur, whereas the anion is electronically inert. Moderate conductivities of electron and proton were confirmed by dc and ac conductivity measurements. In addition, the electronic isolation of TTF wires was confirmed by the magnetic susceptibility data.

Uncovering the Morphological Regulation Mechanism of Low Sensitivity and Highly Energetic Materials in Solvents: Changing Crystal Morphology Induced by Hydrogen Bonding

Low sensitivity and highly energetic materials (LSHEMs) are currently the most promising high-energy materials due to their structural stability. However, many problems exist due to their abundant hydrogen bonding (HB) in the structure, such as low solubility and difficulty controlling the crystallization process. In this paper, aiming at regulating the crystal morphology of LSHEMs, 4,4′,5,5′-tetranitro-1H,1′H-[2,2′-biimidazole]-1,1′-diamine is used as a model substance to explore the mechanism of controlling the crystal morphology in solvents. The molecular structure, crystal structure, and HB sites on crystal faces were investigated by molecular electrostatic potential surface, Hirshfeld surface, and HB analyses, and it was found that the HB density [δ(HB)] of faces is of the order (011) > (11–1) > (110) > (100) in crystal or solution, determining the tendency of interaction with polar solvents. Then, using molecular dynamics simulation and the modified attachment energy model, we found that the attachment energy of crystal faces and the predicted crystal morphologies in different solvents were determined by HB sites on faces and strongly correlated with the solvent polarity. The experimental morphologies were consistent with the trend predicted including the aspect ratio trend, which confirmed our theoretical speculation. This work provides an effective method of choosing solvents for morphology customization of LSHEMs, which will help guide the morphology control and realize the industry application of LSHEMs.

An Ultra-Stretchable Polyvinyl Alcohol Hydrogel Based on Tannic Acid Modified Aramid Nanofibers for Use as a Strain Sensor.

The mechanical performance is critical for hydrogels that are used as strain sensors. p-Aramid nanofiber (ANF) is preferable as an additive to the reinforce the mechanical performance of a poly(vinyl alcohol) (PVA). However, due to the limited hydrogen bond sites, the preparation of ultra-stretchable, ANF-based hydrogel strain sensor is still a challenge. Herein, we reported an ultra-stretchable PVA hydrogel sensor based on tea stain-inspired ANFs. Due to the presence of numerous phenol groups in the tannic acid (TA) layer, the interaction between PVA and the ANFs was significantly enhanced even though the mass ratio of TA@ANF in the hydrogel was 2.8 wt‰. The tensile breaking modulus of the PVA/TA@ANF/Ag hydrogel sensor was increased from 86 kPa to 326 kPa, and the tensile breaking elongation was increased from 356% to 602%. Meanwhile, the hydrogel became much softer, and no obvious deterioration of the flexibility was observed after repeated use. Moreover, Ag NPs were formed in situ on the surfaces of the ANFs, which imparted the sensor with electrical conductivity. The hydrogel-based strain sensor could be used to detect the joint movements of a finger, an elbow, a wrist, and a knee, respectively. This ultra-stretchable hydrogel described herein was a promising candidate for detecting large-scale motions.