Covalent Bonds Research Articles

Charge-solvated versus protonated salt forms of cyclodepsipeptide toxins in electrospray: Dissociation of alkali-cationized forms enables straightforward sequencing of cereulide.

Bacillus cereus is responsible for foodborne outbreaks worldwide. Among the produced toxins, cereulide induces nausea and vomiting after 30 min to 6h following the consumption of contaminated foods. Cereulide, a cyclodepsipeptide, is an ionophore selective to K+ in solution. In electrospray, the selectivity is reduced as [M + Li]+; [M + Na]+ and [M + NH4]+ can also be detected without adding corresponding salts. Two forms are possible for alkali-cationized ions: charge-solvated (CS) that exclusively dissociates by releasing a bare alkali ion and protonated salt (PS), yielding alkali product ions by covalent bond cleavages (CBC) promoted by mobile proton. Based on a modified peptide cleavage nomenclature, the PS product ion series (b, a, [b + H2O] and [b + CnH2nO] [n = 4, 5]) are produced by Na+/Li+/K+-cationized cereulide species that specifically open at ester linkages followed by proton mobilization promoting competitive ester CBC as evidenced under resonant collision activation. What is more, unlike the sodiated or lithiated cereulide, which regenerates little or no alkali cation, the potassiated forms lead to an abundant K+ regeneration. This occurs by splitting of (i) the potassiated CS forms with an appearance threshold close to that of the PS first fragment ion generation and (ii) eight to four potassiated residue product ions from the PS forms. Since from Na+/Li+-cationized cereulide, (i) the negligible Na+/Li+ regeneration results in a higher sensibility than that of potassiated forms that abundantly releasing K+, and (ii) a better sequence recovering, the use of Na+ (or Li+) should be more pertinent to sequence isocereulides and other cyclodepsipeptides.

Strengthening-Durable Trade-Off and Self-Healing, Recyclable Shape Memory Polyurethanes Enabled by Dynamic Boron-Urethane Bonds.

Addressing the demand for integrating strength and durability reinforcement in shape memory polyurethane (SMPU) for diverse applications remains a significant challenge. Here we synthesized a series of SMPUs with ultra-high strength, self-healing and recyclability, and excellent shape memory properties through introducing dynamic boron-urethane bonds. The introducing of boric acid (BA) to polyurethane leading to the formation of dynamic covalent bonds (DCB) boron-urethane, that confer a robust cross-linking structure on the SMPUs led to the formation of ordered stable hydrogen-bonding network within the SMPUs. The flexible crosslinking with DCB represents a novel strategy for balancing the trade-off between strength and durability, with their strengths reaching up to 82.2MPa while also addressing the issue of durability in prolonged usage through the provision of self-healing and recyclability. The self-healing and recyclability of SMPU were demonstrated through rapid dynamic exchange reaction of boron-urethane bonds, systematically investigated by dynamic mechanical analysis (DMA). This study sheds light on the essential role of such PU with self-healing and recyclability, contributing to the extension of the PU's service life. The findings of this work provide a general strategy for overcoming traditional trade-offs in preparing SMPUs with both high strength and good durability. This article is protected by copyright. All rights reserved.

Damage-Tolerant and Self-Repairing Web-Like Borate Type Binder Enable Stable Operation of Efficient Si-Based Anodes.

Novel binder designs are shown to be fruitful in improving the electrochemical performance of silicon (Si)-based anodes. However, issues with mechanical damage from dramatic volume change and poor lithium-ion (Li+) diffusion kinetics in Si-based materials still need to be addressed. Herein, an aqueous self-repairing borate-type binder (SBG) with a web-like architecture and high ionic conductivity is designed for Si and SiO electrodes. The 3D web-like architecture of the SBG binder enables uniform stress distribution, while its self-repairing ability promotes effective stress dissipation and mechanical damage repair, thereby enhancing the damage tolerance of the electrode. The tetracoordinate boron ions ( ) in the SBG binder boosts the Li transportation kinetics of Si-based electrodes. Based on dynamic covalent and ionic conductive boronic ester bonds, the diverse requirements of the binder, including uniform stress distribution, self-repairing ability, and high ionic conductivity, can be met by simple components. Consequently, the proposed straightforward multifunction design strategy for binders based on dynamic boron chemistry provides valuable insights into fabricating high-performance Si-based anodes.

Sulfur‐Rich Polymers Coatings

AbstractAdvancements in the synthesis of sulfur‐rich materials are driving progress across diverse fields owing to the rich and tunable functionalities of those materials. These materials are typically valued for their electrochemical behaviors, high refractive indices, heavy metal affinity, and ability to form dynamic covalent bonding. As a result, their applications span various industries including electronics, catalysis, lithium‐sulfur batteries, water reclamation, and optoelectronics. Moreover, elemental sulfur, a byproduct of the petroleum industry, is produced abundantly, necessitating the exploration of novel valorization routes for polymers made from this feedstock. The unique combination of properties of sulfur‐rich polymers also makes them an ideal platform for the development of high‐performance functional coatings, offering durability and tailored functionalities for protective coatings, thus enhancing materials lifespan and performances in a variety of environmental conditions. The presence of dynamic covalent bonds in many sulfur‐rich polymers enables the creation of self‐healing coatings, while sulfur itself or the comonomers can contribute to antimicrobial, antifouling, and corrosion‐resistant properties. Furthermore, sulfur‐rich polymers have the potential to be used in the design of icephobic and superhydrophobic coatings. This underscores the versatility of sulfur‐rich polymers as a platform for the creation of advanced coatings with superior properties.

Adsorption of Multiple NO Molecules on Anionic Gold Clusters: Electron Transfer and Disproportionation Enhanced by Molecular Aggregation.

The reactions of Aun- clusters with multiple nitric oxide (NO) molecules are explored at 150 K by utilizing a mini-flow-tube reactor and a time-of-flight mass spectrometer. Adsorption of multiple NO molecules is observed on most Aun-, while disproportionation reactions only occur on even-sized Aun- with n = 4, 6, 8, 20 and odd-sized ones with n = 5 and 7. Theoretical calculations reveal the geometric structures and electronic states of the products containing bimolecular and trimolecular NO units, where two NO molecules typically form dimers. Different from NO monomers that weakly interact with odd-sized Aun- and form electron-sharing covalent bonds with Au10-(D3h) and Au16-, NO dimers can extract significant charge from parent Aun-. Regarding the three NO molecules, a predilection toward condensation into trimers on even-sized Aun- is observed, while the tendency is more toward an adsorption pattern of a dimer plus a monomer on odd-sized Aun-. The NO trimers register even higher charge gain from Aun- as compared with the NO dimers, which leads to an elevated degree of activation and induces the progression of disproportionation reactions. Therefore, when considering the reaction between NO and Aun-, it appears that NO has a propensity to form dimers or trimers on Aun-. This behavior of aggregate formation substantially enhances the ability of NO to absorb negative charges from Aun- although the occurrence of disproportionate dissociation reactions is initiated only for specific sizes.

2D Exfoliation Chemistry Towards Covalent Pseudo‐Layered Phosphate Framework Derived by Radical/Strain‐Synergistical Process

2D compounds exfoliated from weakly bonded bulk materials with van der Waals (vdW) interaction are easily accessible. However, the strong internal ionic/covalent bonding of most inorganic crystal frameworks greatly hinders 2D material exfoliation. Herein, we first proposed a radical/strain‐synergistic strategy to exfoliate non‐vdW interacting pseudo‐layered phosphate framework. Specifically, hydroxyl radicals (•OH) distort the covalent bond irreversibly, meanwhile, H2O molecules as solvents, further accelerating interlayered ionic bond breakage but mechanical expansion. The innovative 2D laminar NASICON‐type Na3V2(PO4)2O2F crystal, exfoliated by •OH/H2O synergistic strategy, exhibits enhanced sodium‐ion storage capacity, high‐rate performance (85.7 mA h g‐1 at 20 C), cyclic life (2300 cycles), and ion migration rates, compared with the bulk framework. Importantly, this chemical/physical dual driving technique realized the effective exfoliation for strongly coupled pseudo‐layered frameworks, which accelerates 2D functional material development.

Dynamic Covalent BondsRegulate Zinc Plating/Stripping Behaviors for High-Performance Zinc Ion Batteries.

Artificial interfaces provide a comprehensive approach to controlling zinc dendrite and surface corrosion in zinc-based aqueous batteries (ZABs). However, due to consistent volume changes during zinc plating/stripping, traditional interfacial layers cannot consistently adapt to the dendrite surface, resulting in uncontrolled dendrite growth and hydrogen evolution. Herein, dynamic covalent bonds exhibit the Janus effect towards zinc deposition at different current densities, presenting a holistic strategy for stabilizing zinc anode. The PBSC intelligent artificial interface consisting of dynamic B-O covalent bonds is developed on zinc anode to mitigate hydrogen evolution and restrict dendrite expansion. Owing to the reversible dynamic bonds, PBSC exhibits shape self-adaptive characteristics at low current rates, which rearranges the network to accommodate volume changes during zinc plating/stripping, resisting hydrogen evolution. Moreover, the rapid association of B-O dynamic bonds enhances mechanical strength at dendrite tips, presenting a shear-thickening effect and suppressing further dendrite growth at high current rates. Therefore, the assembled symmetrical battery with PBSC maintains a stable cycle of 4500 hours without significant performance degradation and the PBSC@Zn||V2O5 pouch cell demonstrates a specific capacity exceeding 170 mAh g-1. Overall, the intelligent interface with dynamic covalent bonds provides innovative approaches for zinc anode interfacial engineering and enhances cycling performance.

Dynamic Covalent Bonds Regulate Zinc Plating/Stripping Behaviors for High‐Performance Zinc Ion Batteries

Artificial interfaces provide a comprehensive approach to controlling zinc dendrite and surface corrosion in zinc‐based aqueous batteries (ZABs). However, due to consistent volume changes during zinc plating/stripping, traditional interfacial layers cannot consistently adapt to the dendrite surface, resulting in uncontrolled dendrite growth and hydrogen evolution. Herein, dynamic covalent bonds exhibit the Janus effect towards zinc deposition at different current densities, presenting a holistic strategy for stabilizing zinc anode. The PBSC intelligent artificial interface consisting of dynamic B‐O covalent bonds is developed on zinc anode to mitigate hydrogen evolution and restrict dendrite expansion. Owing to the reversible dynamic bonds, PBSC exhibits shape self‐adaptive characteristics at low current rates, which rearranges the network to accommodate volume changes during zinc plating/stripping, resisting hydrogen evolution. Moreover, the rapid association of B‐O dynamic bonds enhances mechanical strength at dendrite tips, presenting a shear‐thickening effect and suppressing further dendrite growth at high current rates. Therefore, the assembled symmetrical battery with PBSC maintains a stable cycle of 4500 hours without significant performance degradation and the PBSC@Zn||V2O5 pouch cell demonstrates a specific capacity exceeding 170 mAh g‐1. Overall, the intelligent interface with dynamic covalent bonds provides innovative approaches for zinc anode interfacial engineering and enhances cycling performance.

In-Sb Covalent Bonds over Sb2Se3/In2Se3 Heterojunction for Enhanced Photoelectrochemical Water Splitting.

Antimony selenide is a promising P-type photocatalyst, but it has a large number of deep energy level defects, leading to severe carrier recombination. The construction of a heterojunction is a common way to resolve this problem. However, the conventional heterojunction system inevitably introduces interface defects. Herein, we employ in situ synthesis to epitaxially grow In2Se3 nanosheets on Sb2Se3 nanorods and form In-Sb covalent interfacial bonds. This petal-shaped heterostructure reduced interface defects and enhanced the efficiency of carrier separation and transport. In this work, the photocurrent density in the proposed Sb2Se3/In2Se3 photocathode is 0.485 mA cm-2 at 0 VRHE, which is 30 times higher than that of pristine Sb2Se3 and it has prominent long-term stability for 24 h without obvious decay. The results reveal that the synergy of the bidirectional built-in electric field constructed between In2Se3 and Sb2Se3 and the solid In-Sb interfacial bonds together build a high-efficiency transport channel for the photogenerated carriers that display enhanced photoelectrochemical (PEC) water-splitting performance. This work provides efficient guidance for reducing interface defects via the in situ synthesis and construction of interfacial bonds.

Multiple‐State Control over Supramolecular Chirality through Dynamic Chemistry Mediated Molecular Engineering

Dynamic chemistry utilizing both covalent and noncovalent bonds provides valid protocols in manipulating properties of self‐assemblies and functions. Here we employ dynamic chemistry to realize multiple‐route control over supramolecular chirality up to five states. N‐protected fluorinated phenylalanine in the carboxylate state self‐assembled into achiral nanoparticles ascribed to the amphiphilicity. Protonation promoted one‐dimensional growth into helices with shrunk hydrophilicity, which in the presence of disulfide pyridine undergo chirality inversion promoted by the hydrogen bonding‐directed coassembly. Further interacting with the water‐soluble reductant cleavages the disulfide bond to initiate the rearrangement of coassemblies with a chirality inversion as well. Finally, by tuning the pH environments, aromatic nucleophilic substitution reaction between reduced products and perfluorinated phenylalanine occurs, giving distinct chiral nanoarchitectures with emerged luminescence and circularly polarized luminescence. We thus realized a particular five‐state control by combining dynamic chemistry at one chiral compound, which greatly enriches the toolbox in fabricating responsive chiroptical materials.

Multiple-State Control over Supramolecular Chirality through Dynamic Chemistry Mediated Molecular Engineering.

Dynamic chemistry utilizing both covalent and noncovalent bonds provides valid protocols in manipulating properties of self-assemblies and functions. Here we employ dynamic chemistry to realize multiple-route control over supramolecular chirality up to five states. N-protected fluorinated phenylalanine in the carboxylate state self-assembled into achiral nanoparticles ascribed to the amphiphilicity. Protonation promoted one-dimensional growth into helices with shrunk hydrophilicity, which in the presence of disulfide pyridine undergo chirality inversion promoted by the hydrogen bonding-directed coassembly. Further interacting with the water-soluble reductant cleavages the disulfide bond to initiate the rearrangement of coassemblies with a chirality inversion as well. Finally, by tuning the pH environments, aromatic nucleophilic substitution reaction between reduced products and perfluorinated phenylalanine occurs, giving distinct chiral nanoarchitectures with emerged luminescence and circularly polarized luminescence. We thus realized a particular five-state control by combining dynamic chemistry at one chiral compound, which greatly enriches the toolbox in fabricating responsive chiroptical materials.

Glued-bamboo composite based on a highly cross-linked cellulose-based adhesive and an epoxy functionalized bamboo surface

Bamboo, as a renewable bioresource, exhibits advantages of fast growth cycle and high strength. Bamboo-based composite materials are a promising alternative to load-bearing structural materials. It is urgent to develop high-performance glued-bamboo composite materials. This study focused on the chemical bonding interface to achieve high bonding strength and water resistance between bamboo and dialdehyde cellulose–polyamine (DAC-PA4N) adhesive by activating the bamboo surface. The bamboo surface was initially modified in a directional manner to create an epoxy-bamboo interface using GPTES. The epoxy groups on the interface were then chemically crosslinked with the amino groups of the DAC-PA4N adhesive, forming covalent bonds within the adhesive layer. The results demonstrated that the hot water strength of the modified bamboo was improved by 75.8 % (from 5.17 to 9.09 MPa), and the boiling water strength was enhanced by 232 % (from 2.10 to 6.99 MPa). The bonding and flexural properties of this work are comparable to those of commercial phenolic resin. The activation modification of the bamboo surface offers a novel approach to the development of low-carbon, environmentally friendly, and sustainable bamboo engineering composites.

Structural diversity of decalin forming Diels-Alderase.

The Diels-Alder (DA) reaction, specifically referring to the [4+2] cycloaddition reaction in pericyclic reactions, is a process that forms two carbon-carbon covalent bonds in a single step via an electron ring transition state. Among the secondary metabolites produced by microorganisms, numerous compounds are biosynthesized through DA reactions, most of which are enzymatic. Our research group has discovered an enzyme named Diels-Alderase (DAase) that catalyzes the DA reaction in filamentous fungi, and we have been investigating its catalytic mechanism. This review describes the reported microbial DAase enzymes, with a particular focus on those involved in the construction of the decalin ring.

C5 Pentacle Structures: A Localization-Delocalization Matrices Approach.

This article explores the possible presence of a pentacle valence bond structure in C cyclic molecules. At this end, we have used quantum chemistry tools to elucidate the possible arrangement and the nature of chemical bonds within linear, cyclic, and three-dimensional structures only formed by five carbon atoms. While the linear structure is clearly the most stable one, local minima were obtained for both bi- and three-dimensional structures. Using the localization-delocalization matrices approach, we characterize both the minimum linear structure and the cyclic ones. Interestingly, the linear structure is a combination of ionic and covalent bonds, albeit the four distances are almost identical, when using Density Functional Theory. For cyclic C , the pentacle bonding arrangement emerges as a significant Lewis structure, indicative of an unusual formal configuration characterized by five intersecting C-C bonds. Our calculations show that this pentacle arrangement in cyclic C scheme is also present in the more known cyclo-pentadienyl molecule.

Maize (Zea mays L.) Plants Alter the Fate and Accumulate Nonextractable Residues of Sulfamethoxazole in Farmland Soil.

The fate of sulfonamide antibiotics in farmlands is crucial for food and ecological safety, yet it remains unclear. We used [phenyl-U-14C]-labeled sulfamethoxazole (14C-SMX) to quantitatively investigate the fate of SMX in a soil-maize system for 60 days, based on a six-pool fate model. Formation of nonextractable residues (NERs) was the predominant fate for SMX in unplanted soil, accompanied by minor mineralization. Notably, maize plants significantly increased SMX dissipation (kinetic constant kd = 0.30 day-1 vs 0.17 day-1), while substantially reducing the NER formation (92% vs 58% of initially applied SMX) and accumulating SMX (40%, mostly bound to roots). Significant NERs (maximal 29-42%) were formed via physicochemical entrapment (determined using silylation), which could partially be released and taken up by maize plants. The NERs consisted of a considerable amount of SMX formed via entrapment (1-8%) and alkali-hydrolyzable covalent bonds (2-12%, possibly amide linkage). Six and 10 transformation products were quantified in soil extracts and NERs, respectively, including products of hydroxyl substitution, deamination, and N-acylation, among which N-lactylated SMX was found for the first time. Our findings reveal the composition and instability of SMX-derived NERs in the soil-plant system and underscore the need to study the long-term impacts of reversible NERs.

Localized Ionic Reinforcement of Double Network Granular Hydrogels.

Nature produces soft materials with fascinating combinations of mechanical properties. For example, the mussel byssus embodies a combination of stiffness and toughness, a feature that is unmatched by synthetic hydrogels. Key to enabling these excellent mechanical properties are the well-defined structures of natural materials and their compositions controlled on lengths scales down to tens of nanometers. The composition of synthetic materials can be controlled on a micrometer length scale if processed into densely packed microgels. However, these microgels are typically soft. Microgels can be stiffened by enhancing interactions between particles, for example through the formation of covalent bonds between their surfaces or a second interpenetrating hydrogel network. Nonetheless, changes in the composition of these synthetic materials occur on a micrometer length scale. Here, 3D printable load-bearing granular hydrogels are introduced whose composition changes on the tens of nanometer length scale. The hydrogels are composed of jammed microgels encompassing tens of nm-sized ionically reinforced domains that increase the stiffness of double network granular hydrogels up to 18-fold. The printability of the ink and the local reinforcement of the resulting granular hydrogels are leveraged to 3D print a butterfly with composition and structural changes on a tens of nanometer length scale.

Phosphate Esters: New Coating Materials for a Sustainable Release Paper.

AbstractPaper manufacturers have long used silicone as the coating agent for release liners. However, silicone‐based release paper is very difficult to recycle due to covalent bonds between silicone and fibers. The most suitable solution to overcome this problem is to use alternative coating materials with adequate release properties, provided that they can be easily repulped in typical paper recycling facilities. We proposed a coating agent composed of phosphate esters and dimethylacetamide in order to manufacture a recyclable and efficient release paper. Analyses carried out on coated sheets showed that phosphate esters allowed the formation of a surface with adequate release properties (low peeling force and surface free energy). In addition, the residual adhesion values obtained with phosphate esters confirmed that they are well anchored on the backing paper surface, thus limiting the mass transfer to the adhesive tape.

Application of supramolecular hydrogel in supercapacitors: Opportunities and challenges

AbstractSupercapacitors (SCs) are studied and used in various fields due to their high power density, fast charging/discharging rate, as well as long cycle life. Compared to other traditional electrode and electrolyte materials, supramolecular hydrogels have great advantages in the application of SCs due to their excellent properties. Unlike covalent bonds, supramolecular systems are assembled through dynamic reversible bonds, including host–guest interactions, ion interactions, electrostatic interactions, hydrogen bonding, coordination interactions, etc. The resulting supramolecular hydrogels show some special functions, such as stretching, compression, adhesion, self‐healing, stimulus responsiveness, etc., making them strong candidates for the next generation of energy storage devices. This paper reviews the representative progress of electrodes, electrolytes, and SCs based on supramolecular hydrogels. Besides, the properties of supramolecular hydrogels, such as conductivity, extensibility, compressibility and elasticity, self‐healing, frost resistance, adhesion, and flexibility, are also reviewed to highlight the key role of excellent properties of hydrogel materials in SCs. In addition, this article also discusses the challenges faced by current technologies, hoping to continue promoting future research in this field.

Rigid covalent bond of α-sulfur investigated via temperature-dependent EXAFS

This study performs extended x-ray absorption fine structure (EXAFS) measurements for the S-K edge in the temperature range of 10 and 300 K in the transmission mode using a photodiode to detect the transmitted x-rays. It provides the first report of temperature variations in the structural parameters of α-S. As the temperature increases from 10 to 300 K in the Fourier transform of kχ(k) the first peak corresponding to the covalent bond of the eight-membered ring becomes slightly low anomalously despite thermal disturbances. However, as in normal materials, the second peak at 300 K decreases to approximately half of that at 10 K, which contains several intra- and inter-ring correlations. All structural parameters of the covalent bond obtained by nonlinear least squares fitting exhibit missing temperature variations. A value of zero for the asymmetric parameter in the EXAFS (C 3) implies that the potential of the covalent bond is symmetric, and the constant value of the mean square relative displacement (MSRD) with temperature implies that the potential is extremely high. The Einstein model fitting for the temperature variation in the MSRD yields an Einstein temperature of 942 K and force constant (K) of 405 N m−1. The value of K is the largest among those of chalcogen elements.

Microwave synthesis of magnesium phosphate-rGO as an effective electrode for supercapacitor application

Abstract Transition metal phosphate based materials is being used for energy storage because of P–O covalent bond which facilitates more storage compared to other transition metals and this covalent bond enhanced the electrochemical performance for supercapacitor applications. Pure magnesium phosphate (Mg3(PO4)2) were synthesized via microwave synthesis as the composite varies with rGO (MgPO-XrGO) X=25,50,75,100mg. The prepared composite materials were examined employing XRD, Raman, FT-IR, SEM and XPS studies. Electrochemical studies (CV, EIS, GCD) of three electrode system for the prepared electrodes were performed using Biologic SP-150 with 2M (H2SO4) as electrolyte. From the XRD results, triclinic structured MgPO was confirmed (JCPDS card #35–0329) and rGO has enhanced the crystallinity of MgPO composite. From Raman analyses, the well graphitization nature of rGO in composite MgPO was identified and from XPS analysis chemical composition of the elements was analyzed. The FT-IR fundamental modes of vibrations of PO 4 3 − ${\text{PO}}_{4}^{3-}$ (γ 1,γ 3,γ 4) were obtained. The electrochemical analysis of the prepared material such as pure and composite materials showed better performance. The high specific capacitance was obtained for MgPO-50rGO because MgPO has high coordination with rGO. As Mg2+ oxidation state has high chemical reactivity compared to other earth metals and other advantage is P–O covalent bond that enhanced the performance of the electrode. By facilitating these advantages, rGO is included as composite to develop the electrode to favor the practical applications. By using the optimum level rGO composite with MgPO4-50rGO a better new candidate was successfully developed for supercapacitor applications. The fabricated MgPO-50rGO//Activate carbon full cell set up exhibited the specific capacitance 61 Fg−1 at 1 Ag−1, 21.7 Wh kg−1 energy density and 790.0 W kg−1 power densities and explored outstanding capacitive retention in 2 electrode full cell setup cyclic stability of 99.1 % over the 5000 cycles.