Bond Linkage Research Articles

In Vitro Characterization of Kitasetaline Biosynthesis Reveals a Bifunctional P450 Decarboxylase and a Vinyl β-Carboline Intermediate Susceptible to Nonenzymatic Thiol Addition.

Kitasetaline is one of the very few β-carbolines isolated from bacteria. It features a unique N-acetylcysteine moiety linked to the β-carboline core through a thioether bond. While earlier in vivo experiments identified the gene cluster and reported several putative biosynthetic intermediates, how the C-S bond linkage is constructed has remained elusive. Herein, in vitro reconstitution of kitasetaline biosynthesis reveals the involvement of a Pictet-Spenglerase (KslB) and a promiscuous dehydrogenase (KslA) that generate the characteristic β-carboline ring system. In addition, the P450 enzyme KslC was found to catalyze oxidative decarboxylation of 1-(2-carboxyethyl)-9H-pyrido[3,4-b]indole-3-carboxylic acid to yield the biosynthetic intermediate 1-vinyl-9H-pyrido[3,4-b]indole-3-carboxylic acid. KslC is also capable of catalyzing further oxidation of its product to yield an N-hydroxylated side product. Importantly, the vinyl intermediate was found to undergo nonenzymatic nucleophilic addition by N-acetyl-l-cysteine to generate the C-S bond leading directly to kitasetaline without the involvement of a mycothiolated intermediate proposed in a previous biosynthetic model. Thus, this work not only demonstrates that biosynthesis of β-carboline compounds is rich in unexpected chemistry but also adds to the growing realization that biological thiolation reactions are often nonenzymatic in nature, relying instead on enzymatic formation of reactive electrophiles.

Regulating natural galactomannan into composite hydrogels for improved adhesion, anti-swelling capability and efficient dye pollution removal

Constructing bio-based composite hydrogel materials are receiving much interest, while regulating the interactions of the hydrogel components and integrating functions for multi-application meet various challenges. Herein, composite hydrogels were prepared by cross-linking of poly-acrylamide (PAM) and poly-N-[3-(Dimethylamino) propyl] acrylamide (PDMAPAA), assisted by natural galactomannan (GM) regulation. Even distribution and compatibility of GM in the three-dimensional materials were proved by a series of chemical and morphological characterizations, which favored the improvement of mechanical properties (~80 kPa) and flexibility. Besides, the hydrogels were well-connected with double networks of noncovalent intermolecular hydrogen bonding interactions and hydrophobic interactions, in addition to covalent-linked polymers. Due to great amount of inner hydrogen bond linkages, the hydrogels present satisfying anti-swelling capabilities (<15 %), exhibiting high potential for application in water treatment. Meanwhile, abundant surface functional groups provided possibilities to form interactive layer with the various substrates surface, exhibiting highly adhesive properties. Significant dyes adsorption capabilities were revealed on the hydrogels according to the electrostatic attraction with Congo red and hydrogen bond interactions with Brilliant green respectively. Thus, the proposed composite hydrogels integrated multi-functions due to the tuning the surface groups and cross-linking interactions, which provided deeper understanding on bio-based materials on fields of water treatment and environmental protection.

Suppressing non-radiative recombination and tuning morphology via central core asymmetric substitution for efficient organic solar cells

It is necessary and challenging to achieve high-efficiency organic solar cells (OSCs) by suppressing nonradiative energy loss (ΔEnr) and fine-tuning active layer morphology through the delicate active material design. In this study, we design two asymmetric acceptors, a-CH-ThCl and a-CH-Th2Cl, featuring asymmetric conjugated substitutions on central cores via single bond linkages. Single crystals analysis indicate that these two acceptors exhibit intense J-aggregation induced by the asymmetric substitution, which favours for their high photoluminescence quantum yields and contributes to reducing non-radiative recombination. Meanwhile, the two asymmetric acceptors demonstrate enhanced miscibility and optimized morphology with the donor D18. Consequently, the binary device based on D18: a-CH-Th2Cl demonstrates an impressive efficiency of up to 19.10 % with a high open-circuit voltage of 0.935 V, attributed to the remarkably low ΔEnr of 0.179 eV and optimized morphology. These results provide an effective strategy for material design to optimize molecular packing, reduce non-radiative recombination and tune active layer morphology to achieve high-efficiency OSCs.

Effects of alkali-soluble hemicellulose separation on the structure of bamboo lignin and lignin-carbohydrate complexes

In this study, alkali treatment was used to preferentially separate hemicellulose, and the structural changes of lignin and lignin-carbohydrate complexes (LCC) in the residual bamboo solids were investigated. The chemical composition and structural characteristics of lignin and LCC were analyzed. After alkali treatment, the monosaccharide content in bamboo lignin decreased from 7.62 % to 2.90 % compared to the raw material. The obtained lignin exhibited higher purity and larger molecular weight, with the macromolecular lignin linked by β-O-4′ bonds remaining almost undegraded. After alkali treatment, the linkage bonds in the Björkman LCC were composed of phenyl glycoside (PhGlc), and the bond in LCC-AcOH consisted of benzyl ether (BE). The results showed that the preferential extraction of hemicellulose preserved the biopolymer structure of lignin in bamboo, thereby providing an important basis for the comprehensive separation and utilization of bamboo components.

Biosynthesis and Assembly Logic of Fungal Hybrid Terpenoid Natural Products.

In recent decades, fungi have emerged as significant sources of diverse hybrid terpenoid natural products, and their biosynthetic pathways are increasingly unveiled. This review mainly focuses on elucidating the various strategies underlying the biosynthesis and assembly logic of these compounds. These pathways combine terpenoid moieties with diverse building blocks including polyketides, nonribosomal peptides, amino acids, p-hydroxybenzoic acid, saccharides, and adenine, resulting in the formation of plenty of hybrid terpenoid natural products via C-O, C-C, or C-N bond linkages. Subsequent tailoring steps, such as oxidation, cyclization, and rearrangement, further enhance the biological diversity and structural complexity of these hybrid terpenoid natural products. Understanding these biosynthetic mechanisms holds promise for the discovery of novel hybrid terpenoid natural products from fungi, which will promote the development of potential drug candidates in the future.

Spectral properties and photophysical processes of triphenylamine-porphyrin-pyrimidine triads

Porphyrins have attracted considerable attention as an important family of photosensitizers used for dye-sensitized solar cells (DSSCs). In this work, a novel triphenylamine-porphyrin-pyrimidine triad with a triple bond linkage was synthesized and characterized. The sensitizer presents broad absorption in solution and on TiO2 films across the UV-Vis region benefiting from the extended conjugation. The acetenyl [Formula: see text]-conjugated bridge stimulates the photoinduced electron transfer (PET) process and brings a charge-separated state lifetime of around 4 μs. DSSC devices based on the sensitizer achieve a power conversion efficiency (PCE) of 3.77% thanks to the prolonged charge-separated state lifetime and suppressed charge recombination. The understanding of the structural, optical, and electrochemical properties of triphenylamine-porphyrin-pyrimidine triads provides new insights into the rational design of porphyrin sensitizers for various applications.

Efficient removal of allicin from the stalk of Allium fistulosum for dietary fiber production

The stalk of Allium fistulosum contains dietary fibers with complicated monosaccharide composition and glycosidic bond linkages, which renders it a better dietary fiber supplement. However, the unfavorable odor, majorly contributed by allicin, limits its applications. Although many physical and chemical methods have been developed to remove allicin, there is currently no comparison between their efficiencies. Here, we comprehensively compare all these methods of eliminating allicin in the Allium stalk by starting with optimization of the allicin extraction method. Results indicate that incubation of the chopped Allium stalk with water for 20 min and extraction with 75% ethanol reached a maximal extraction yield. Different methods of allicin elimination are examined, and physical removal of allicin by blanching at 100 °C reaches a maximal clearance rate of 73.3%, rendering it the most efficient and effective method eliminating allicin from the stalk of Allium fistulosum for the preparation of a totally green dietary fiber.

Nanoporosity changes of graphene oxide colloids on linkage-treatment with molecular linker and heating after the linkage-treating

This study examined the nanoporosity of graphene oxide (GO) and graphene colloids bridge-treated with amino linkers using comparative nanoporosimetry with N2 and Ar adsorption. The spectroscopic measurements revealed the linkage via amino linkers in the linkage-treated GO and graphene colloids. The linkage-treatment expanded the d-spacing of GO by 0.21 nm and the d-spacing of the linkage-treated GO colloid decreased from 1.01 to 0.35 nm upon heating. The linkage-treated graphene colloids exhibited significant adsorption and an adsorption hysteresis, regardless of the reduction of d-spacing. Heating of linkage bonds induced the local structural deformation, providing open pores and the assembled mesoscale structure.

Industrial Two-Phase Olive Pomace Slurry-Derived Hydrochar Fuel for Energy Applications.

The present study aims to resolve the existing research gaps on olive pomace (OP) hydrochars application as a fuel by evaluating its molecular structures (FTIR and solid NMR analysis), identifying influential characteristics (Pearson correlation analysis), process optimization (response surface methodology), slagging-fouling risks (empirical indices), and combustion performance (TG-DSC analysis). The response surfaces plot for hydrothermal carbonization (HTC) of OP slurry performed in a pressure reactor under varied temperatures (180-250 °C) and residence times (2-30 min) revealed 250 °C for 30 min to be optimal conditions for producing hydrochar fuel with a higher heating value (32.20 MJ·Kg-1) and energy densification ratio (1.40). However, in terms of process efficiency and cost-effectiveness, the optimal HTC conditions for producing the hydrochar with the highest energy yield of 87.9% were 202.7 °C and 2.0 min. The molecular structure of hydrochar was mainly comprised of aromatic rings with methyl groups, alpha-C atoms of esters, and ether bond linkages of lignin fractions. The slagging and fouling risks of hydrochars were comparatively lower than those of raw OP, as indicated by low slagging and fouling indices. The Pearson correlation analysis emphasized that the enrichment of acid-insoluble lignin and extractive contents, carbon densification, and reduced ash content were the main pivotal factors for hydrochar to exhibit better biofuel characteristics for energy applications.

New Transferrin Receptor-Targeted Peptide-Doxorubicin Conjugates: Synthesis and In Vitro Antitumor Activity.

Poor selectivity to tumor cells is a major drawback in the clinical application of the antitumor drug doxorubicin (DOX). Peptide-drug conjugates (PDCs) constructed by modifying antitumor drugs with peptide ligands that have high affinity to certain overexpressed receptors in tumor cells are increasingly assessed for their possibility of tumor-selective drug delivery. However, peptide ligands composed of natural L-configuration amino acids have the defects of easy enzymatic degradation and insufficient biological stability. In this study, two new PDCs (LT7-SS-DOX and DT7-SS-DOX) were designed and synthesized by conjugating a transferrin receptor (TfR) peptide ligand LT7 (HAIYPRH) and its retro-inverso analog DT7 (hrpyiah), respectively, with DOX via a disulfide bond linker. Both conjugates exhibited targeted antiproliferative effects on TfR overexpressed tumor cells and little toxicity to TfR low-expressed normal cells compared with free DOX. Moreover, the DT7-SS-DOX conjugate possessed higher serum stability, more sustained reduction-triggered drug release characteristics, and stronger in vitro antiproliferative activity as compared to LT7-SS-DOX. In conclusion, the coupling of antitumor drugs with the DT7 peptide ligand can be used as a promising strategy for the further development of stable and efficient PDCs with the potential to facilitate TfR-targeted drug delivery.

Unveiling the structural properties and induced resistance activity in rice of Chitin/Chitosan-Glucan Complex of Rhizoctonia solani AG1 IA inner cell wall

Phytopathogen cell wall polysaccharides have important physiological functions. In this study, we isolated and characterized the alkali-insoluble residue on the inner layers of the Rhizoctonia solani AG1 IA cell wall (RsCW-AIR). Through chemical composition and structural analysis, RsCW-AIR was mainly identified as a complex of chitin/chitosan and glucan (ChCsGC), with glucose and glucosamine were present in a molar ratio of 2.7:1.0. The predominant glycosidic bond linkage of glucan in ChCsGC was β-1,3-linked Glcp, both the α and β-polymorphic forms of chitin were presented in it by IR, XRD, and solid-state NMR, and the ChCsGC exhibited a degree of deacetylation measuring 67.08 %. RsCW-AIR pretreatment effectively reduced the incidence of rice sheath blight, and its induced resistance activity in rice was evaluated, such as inducing a reactive oxygen species (ROS) burst, leading to the accumulation of salicylic acid (SA) and the up-regulation of SA-related gene expression. The recognition of RsCW-AIR in rice is partially dependent on CERK1.

Chemoinformatics and machine learning techniques to identify novel inhibitors of the lemur tyrosine kinase-3 receptor involved in breast cancer.

Breast cancer is still the largest cause of cancer death in women, and around 70% of primary breast cancer patients are estrogen receptor (ER)-positive, which is the most frequent kind of breast cancer. The lemur tyrosine kinase-3 (LMTK3) receptor has been linked to estrogen responsiveness in breast cancer. However, the function of LMTK3 in reaction to cytotoxic chemotherapy has yet to be studied. Breast cancer therapy research remains tricky due to a paucity of structural investigations on LMTK3. We performed structural investigations on LMTK3 using molecular docking and molecular dynamics (MD) simulations of the LMTK3 receptor in complex with the top three inhibitor molecules along with a control inhibitor. Analysis revealed the top three compounds show the best binding affinities during docking simulations. Interactive analysis of hydrogen bonds inferred hotspot residues Tyr163, Asn138, Asp133, Tyr56, Glu52, Ser132, Asp313, and Asp151. Some other residues in the 5-Å region determined strong alkyl bonds and conventional hydrogen bond linkages. Furthermore, protein dynamics analysis revealed significant modifications among the top complexes and the control system. There was a transition from a loop to a-helix conformation in the protein-top1 complex, and in contrast, in complexes top2 and top3, the formation of a stabilizing sheet in the C chain was observed, which limited significant mobility and increased complex stability. Significant structural alterations were observed in the protein-top complexes, including a shorter helix region and the creation of some loop regions in comparison to the control system. Interestingly, binding free energies, including MMGB/PBSA WaterSwap analysis estimation, reveals that the top1 complex system was more stable than other systems, especially in comparison to the control inhibitor complex system. These results suggest a the plausible mode of action for the novel inhibitors. Therefore, the current investigation contributes to understanding the mechanism of action, serving as a basis for future experimental studies.

Conjugating uncoupler compounds with hydrophobic hydrocarbon chains to achieve adipose tissue selective drug accumulation

One potential approach for treating obesity is to increase energy expenditure in brown and white adipose tissue. Here we aimed to achieve this outcome by targeting mitochondrial uncoupler compounds selectively to adipose tissue, thus avoiding side effects from uncoupling in other tissues. Selective drug accumulation in adipose tissue has been observed with many lipophilic compounds and dyes. Hence, we explored the feasibility of conjugating uncoupler compounds with a lipophilic C8-hydrocarbon chain via an ether bond. We found that substituting the trifluoromethoxy group in the uncoupler FCCP with a C8-hydrocarbon chain resulted in potent uncoupling activity. Nonetheless, the compound did not elicit therapeutic effects in mice, likely as a consequence of metabolic instability resulting from rapid ether bond cleavage. A lipophilic analog of the uncoupler compound 2,6-dinitrophenol, in which a C8-hydrocarbon chain was conjugated via an ether bond in the para-position (2,6-dinitro-4-(octyloxy)phenol), exhibited increased uncoupling activity compared to the parent compound. However, in vivo pharmacokinetics studies suggested that 2,6-dinitro-4-(octyloxy)phenol was also metabolically unstable. In conclusion, conjugation of a hydrophobic hydrocarbon chain to uncoupler compounds resulted in sustained or improved uncoupling activity. However, an ether bond linkage led to metabolic instability, indicating the need to conjugate lipophilic groups via other chemical bonds.

Hyaluronan-decorated copper-doxorubicin-anlotinib nanoconjugate for targeted synergistic chemo/chemodynamic/antiangiogenic tritherapy against hepatocellular carcinoma

Copper-based nanomaterials show considerable potential in the chemodynamic therapy of cancers. However, their clinical application is restricted by low catalytic activity in tumor microenvironment and copper-induced tumor angiogenesis. Herein, a novel copper-doxorubicin-anlotinib (CDA) nanoconjugate was constructed by the combination of copper-hydrazide coordination, hydrazone linkage and Schiff base bond. The CDA nanoconjugate consists of a copper-3,3′-dithiobis(propionohydrazide)-doxorubicin core and an anlotinib-hyaluronan shell. Benefiting from hyaluronan camouflage and abundant disulfide bonds and Cu2+, the CDA nanoconjugate possessed excellent tumor-targeting and glutathione-depleting abilities and enhanced chemodynamic efficacy. Released doxorubicin significantly improved copper-mediated chemodynamic therapy by upregulating nicotinamide adenine dinucleotide phosphate oxidase 4 expression to increase intracellular H2O2 level. Furthermore, the nanoconjugate produced excessive •OH to induce lipid peroxidation and mitochondrial dysfunction, thus greatly elevating doxorubicin-mediated chemotherapy. Importantly, anlotinib effectively inhibited the angiogenic potential of copper ions. In a word, the CDA nanoconjugate is successfully constructed by combined coordination and pH-responsive linkages, and displays the great potential of copper-drug conjugate for targeted synergistic chemo/chemodynamic/antiangiogenic triple therapy against cancers.

How do the main components influence the VOCs emission characteristics and formation pathways during moso bamboo heat treatment?

Bamboo heat treatment will cause plenty of release of volatile organic compounds (VOCs) into the atmosphere which are important precursors for ozone (O3) formation. In this study, dewaxed bamboo was heat-treated at 180 °C for 2 h to investigate the emission characteristics and the formation pathways of VOCs during heat treatment by removing different main components. The results showed that aldehydes (22.61%–57.54%) and esters (14.64%–38.88%) are the primary VOCs released during heat treatment. These compounds mainly originate from the degradation of hemicellulose, lignin, cellulose, and the linkage bonds between them in bamboo. During the bamboo heat treatment, the degradation of CO, CH, and CO bonds in hemicellulose results in the release of 5-hydroxymethylfurfural, 3-furfural, and 1-(+)-ascorbic acid 2,6-dihexadecanoate. The breakage of benzene ring group and the CO and CH bonds of lignin leading to the emission of VOCs including m-Formylphenol, Vanillin, and Syringaldehyde. The degradation of aliphatic CH, CC, and CO bonds in the amorphous region of cellulose contributes to an enhanced release of alcohols, olefins, and alkanes. It is calculated that acids (28.92%–59.47%), esters (10.10%–22.03%) and aldehydes (17.88%–39.91%) released during heat treatment contributed more to Ozone Formation Potential (OFP).

Recent advances in the transformation reactions of the Betti base derivatives.

Betti bases are the products resulting from the one-pot multicomponent reaction involving 1-naphthol/2-naphthol, aliphatic/aromatic aldehydes, and secondary amines. This chemical process is commonly referred to as the Betti reaction. The significance of Betti bases in medicinal chemistry has grown substantially due to their diverse array of pharmacological applications. Furthermore, their synthetic utility is considerable, given their use as catalysts and ligands in asymmetric synthesis. Moreover, Mannich products, incorporating diverse functional groups such as -OH and -NH, find application in a range of organic reactions. This utilization enables the synthesis of novel C-C bond linkages and diverse heterocycles, including biologically active naphthoxazines, which hold biological applications such as antibacterial, antifungal and anticancer. The focus of this review article is on the application of aminonaphthol derivatives in transformation reactions and the synthesis of organic compounds, with particular emphasis on heterocycles.

Targeted Delivery of Geraniol via Hyaluronic Acid-Conjugation Enhances Its Anti-Tumor Activity Against Prostate Cancer.

Targeted delivery systems have been developed to improve cancer treatment by reducing side effects and enhancing drug efficacy. Geraniol, a natural product, has demonstrated promising anti-cancer effects in various cancer types, including prostate cancer, which is the most commonly diagnosed cancer in men. Hyaluronic acid (HA), a natural carrier targeting CD44-positive prostate cancer cells, can be utilized in a targeted delivery system. This study investigated the efficacy of a conjugate of HA and geraniol linked via a disulfide bond linker (HA-SS-Geraniol) in prostate cancer. The cytotoxicity of HA-SS-Geraniol was evaluated on human PC-3 prostate cancer cells. Flow cytometry was used to assess its effects on mitochondrial membrane potential, apoptosis, and cell cycle arrest. Additionally, proteomic analysis was conducted to explore the underlying mechanism of action induced by HA-SS-Geraniol treatment. A subcutaneous xenograft tumor model was established in nude mice to evaluate the toxicity and efficacy of HA-SS-Geraniol in vivo. The results demonstrated that HA-SS-Geraniol exhibited potent cytotoxicity against PC-3 prostate cancer cells by inducing mitochondrial membrane potential loss and apoptosis in vitro. The proteomic analysis further supported the hypothesis that HA-SS-Geraniol induces cell death through mitochondria-mediated apoptosis, as evidenced by differential protein expression. The in vivo mouse model confirmed the safety of HA-SS-Geraniol and its ability to inhibit tumor growth. HA-SS-Geraniol holds promise as a biologically safe and potentially effective therapeutic agent for prostate cancer treatment. Its targeted delivery system utilizing HA as a carrier shows potential for improving the efficacy of geraniol in cancer therapy.

Hydrophilic carbon-carbon covalent linkage network structure for strong acid/alkali resistant and antifouling nanofiltration membrane

The nanofiltration (NF) membrane plays a crucial role in wastewater treatment by separating ions and molecules. However, traditional polyamide (PA) thin-film composite (TFC) NF membranes have limitations in durability under acidic or alkaline conditions and are prone to fouling, which limits their applications and increases costs. In this study, we have successfully developed a new nanofiltration membrane with an active layer composed of hydrophilic carbon-carbon covalent bond linkage network through UV irradiation-initiated polymerization of a kind of sulfobetaine - [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide (DMAPS) - or acrylic acid (AA) on the surface of poly (ether sulfone) (PES) substrate. The carbon-carbon covalent bond (C–C) chemistry used in the preparation of the NF membrane results in exceptional durability towards acid and base, enabling it to maintain its ion separation efficiency (up to 94.2 % and 90.3 % of the initial Na2SO4 rejections) under strong acidic (20 % (w/v) H2SO4) and strong alkaline (2 M NaOH) conditions. Additionally, the water-attracting nature of polyDMAPS and PAA effectively prevents the fouling of protein and bacteria on the NF membrane surface. This breakthrough in manufacturing NF membranes significantly improves their environmental durability, making them suitable for use in highly acidic or alkaline environments (e.g., pH < 0 and pH > 14), including heavily contaminated ones.

Synthesis and Characterization of Novel pH-Responsive Aminated Alginate Derivatives Hydrogels for Tissue Engineering and Drug Delivery.

The aims of this study are to synthesize new derivatives of sodium alginate that improve the inherent properties, such as hydrogel strengthening, and create environmental sensitivity, such as pH sensitivity, for use in drug delivery. Today, hydrogels, due to outstanding properties such as biodegradability, biocompatibility, mechanical properties, and response to stimuli properties, are widely used as harmless biomaterials in various fields in drug delivery, wound dressing, and tissue engineering. Stimulus-sensitive polymers significantly respond to slight changes in their environment. Different types of stimuli are used to influence the properties of polymers, the most important of which are temperature and pH because these are two vital factors in the human body; hence, temperature-sensitive and pHsensitive hydrogels have been extensively studied. The ability to absorb water and swell the hydrogel is due to hydrophilic chains in the hydrogel network, and water absorption by hydrogel can be controlled by response to the stimuli. Since hydrogels mimic human tissue, the ability to retain water in them is essential. As a result, it is considered in many biomedical drug delivery systems. Stimulusresponsive swelling can control diffusion out of and into the hydrogel network, which allows temporal and spatial control of drug release. When a drug is loaded onto a biodegradable and stimulisensitive hydrogel, the drug delivery system has the added advantage of sustained release of the drug, which reduces side effects. In this study, two different hydrocarbons, [1,3-diaminopropane (DAP)] as a short-chain hydrocarbon, and [1,7-diaminoheptane (DAH)] as a long-chain hydrocarbon were grafted onto three types ofsodium alginate (SA), through amide bond linkages. The hydrogel copolymer matrices were compared with sodium alginate (SA) beads. The graft copolymers were characterized using FTIR, 1HNMR, XRD spectroscopy, elemental analysis (CHNS) and thermal analysis (TGA, DTA and DSC). An environmental scanning electron microscope (ESEM) was used to investigate the surface morphology of hydrogels. Effects of variables such as the length of hydrocarbon chains cross-linked to alginate, temperature, pH, and cross-linkers on the properties of hydrogels investigated in the temperature range of 2-70 ˚C and two different pH values (4.4 and 7.4). The results showed that when the hydrocarbon chain length of diamines decreases, the extent of cross-linking and strength of the hydrogels are increased. Other results suggest that the hydrogels obtained from high-viscosity alginate derivatives had positive pH sensitivity. Hydrogels prepared in this study demonstrated good mechanical and swelling ratios that are necessary for wound dressing. DAP-g-SA and DAH-g-SA pH-sensitive hydrogels were successfully synthesized through amide bond linkages. The new synthesis derivatives showed lower swelling levels at low pH (4.4). In contrast, their swelling levels at higher pH (7.4) were significantly enhanced. Higher swelling degree could be obtained at high pH. pH-responsive hydrogels are especially useful for various biological applications due to their unique feature of controlled swelling, biodegradability, biocompatibility, and fluid retention in their network structures. pH-responsive hydrogels, as intelligent systems, can be used in controlled-release drug delivery systems such as insulin delivery.

Synergistic selective photocleavage of lignin C–C bonds by triazine-rich tubular carbon nitride and high-temperature oxidation treatment

The key issue in lignin conversion depends on cutting the β-O-4 linkage bonds between units while keeping the aromatic ring intact. Triazine-heptazine homopolymers of carbon nitride are more prone to break the Cβ-H bond in the β-O-4 bond and generate the critical Cβ radical compared to the triazine or heptazine structure. Triazine-rich g-C3N4 was successfully prepared by ball milling-thermal polycondensation of melamine and cyanuric acid, which has the advantage of low cost and no desalting compared to the conventional eutectic salt method. The triazine-rich g-C3N4 has higher photocurrent density, lower photogenerated electron-transfer resistance, and less electron-hole recombination. Combined with high-temperature oxidation treatment, g-C3N4-O-Q-A5 has an excellent selective photocleavage efficiency of lignin β-O-4 bonds, which is 340 % higher than that of untreated g-C3N4. This paper reveals that the localization of holes in the photocleavage β-O-4 bond reaction, and the amount of superoxide radical generation are the main factors limiting the photocleavage efficiency.