Schiff Base polymers: synthesis and characterization

Gastric-mucus penetrating and responsive microgels for alleviating Helicobacter pylori-induced gastritis

Helicobacter pylori (H. pylori) is a prevalent global pathogen responsible for gastritis and the potential development of gastric cancer. Sulforaphane (SFN), a foodborne compound, exhibits notable antibiotic properties against H. pylori. However, its utility is limited by poor stability and susceptibility to environmental degradation. Here, we developed a gastric-responsive-release microgel for delivering anti-H. pylori SFN. The microgels were prepared by cross-linking α-lactalbumin nanotubes then coated with chitosan (CTS-MGs). SFN was loaded into microgels with a loading rate of 10.73 ± 0.25 %. The CTS-MG showed a strong adhesion to the gastric mucosa, prolonging gastric retention for up to 24 h and responsively releasing SFN in the stomach. Furthermore, CTS-MG/SFN dissociated and released nanotubes/SFN, which could penetrate into the gastric mucus layer and arrive at the deepest mucus sites where most H. pylori were colonized. Our results revealed that CTS-MG/SFN displayed an obvious inhibitory effect against H. pylori. The oral administration of CTS-MG/SFN in H. pylori-infected mice effectively alleviated H. pylori-induced gastritis and modulated gastric microbiota homeostasis. This work demonstrated high potential of CTS-MG microgels for gastric-targeted and oral delivery of antibiotic natural compounds against H. pylori infection.

Schiff bases of cellulose: Synthesis, characterization, and anticancer potency against hepatocellular carcinoma

The development of innovative anticancer agents with minimal side effects is crucial. Polymeric Schiff bases have unique features that make them a promising option for therapeutic uses. They are well known for their biological properties, especially anticancer activity. Therefore, the current report describes the synthesis of Schiff bases derived from microcrystalline cellulose. Cellulose Schiff bases were synthesized through three steps. First, cellulose was periodate oxidized to produce dialdehyde cellulose (DAC). Afterwards, DAC was grafted with hyper-branched polyethylenimine (hPEI) to obtain aminated cellulose. Schiff bases were obtained by reacting hPEI-cellulose with various aldehydes. The final products were characterized by spectroscopic and thermal methods. The cellulose Schiff bases were evaluated for their anticancer activities, and it was observed that they were able to inhibit the growth of different types of cells. Importantly, one of the cellulose derivatives (SB4), which contains trimethoxy benzaldehyde moieties, was capable of inducing cell cycle arrest and apoptosis in hepatocellular carcinoma cells (Hep G2). Interestingly, SB4 could act as a pro-oxidant by inducing reactive oxygen species and oxidative stress with notable decline in the antioxidant system within Hep G2 cells. The results displayed that cellulose-based Schiff bases may offer a new strategy for liver cancer therapy.

A novel avenue in the successful synthesis of Schiff base macromolecules via innovative plasma and classical approaches

Schiff base macromolecules have been successfully synthesized, utilizing a classical chemistry route and a dielectric barrier discharge (DBD) plasma technique. The synthesis of monomeric units has been accomplished through typical reactions of aldehyde and amine functional molecules. The condensation polymerization of the Schiff base molecules has been instigated chemically, using p-toluene sulfonyl chloride in refluxed ethanol. The molecular weight of the obtained polymers was discovered to be 524, 664 and 1,503,228 for Schiff base polymers 4a and 4b, respectively. Additionally, the polymerization reactions were prompted, employing a Dielectric Barrier Discharge (DBD) atmospheric pressure air plasma technique. The DBD plasma demonstrated a very powerful routine to produce high molecular weights macromolecules with optimum condition at 5 min. duration time, which could be an ecofriendly strategy to acquire this class of materials. The new polymeric materials have been characterized utilizing FTIR and NMR spectroscopy. Moreover, the complexation of polymer 4b with various metal moieties, Ru (II), Co (II), Cu (II), and Ni (II), has been executed in order to have a comparative study of their antitumor activity against MCF-7, HCT-116, and HepG-2 cell lines. Furthermore, the density functional theory was exploited to optimize the polymers and their complexes, and their HOMO-LUMO and energy gap were calculated, which was utilized to examine the inter/intra molecular charge transfer. The molecular electrostatic potential map was similarly quantified to investigate the reactive sites that are present in the investigated molecules. The result for the docking study confirmed that these complexed polymers adopted numerous important interactions with the amino acid of the targeted enzyme.

Pyrene-attached new Schiff base polymer: ACQ to AIE conversion and its prospects

Schiff base polymer (SBP) is a new research field and an excellent candidate for real-life applications such as photoresistors, fluorescent chemical sensing kits, electrochromic devices, flame-retarders, and electrochemical substances. The dye-containing SBP (DSBP) advances the material further. Herein, the quality of pyrene dye has been improved through its chemical attachment to polyethyleneimine by a facile Schiff base reaction. The new Schiff base polymer (SBP) converts water-insoluble aggregation-causing quenched (ACQ) dye into a highly water-soluble aggregation-induced emissive (AIE) dye. The computational analysis (geometry optimization, FMO analysis, MEP, etc.) elucidates the nature of aggregation (H, J, X, etc.) and its impact on AIE properties. The AIE system is suitable for fabricating a pH sensor, a fluorescence logic gate, and a reusable chemical sensing kit.

Structural Distortion of g-C3N4 Induced by a Schiff Base Reaction for Efficient Photocatalytic H2 Evolution

Photocatalytic H2 evolution by water splitting is a promising approach to address the challenges of environmental pollution and energy scarcity. Graphitic carbon nitride (g-C3N4) has emerged as a star photocatalyst because of its numerous advantages. To address the limitations of traditional g-C3N4, namely its inadequate visible light response and rapid recombination of photogenerated carriers, we employed a schiff base reaction to synthesize -C=N- doped g-C3N4. The introduction of -C=N- groups at the bridging nitrogen sites induced structural distortion in g-C3N4, facilitating n-π* electronic transitions from the lone pair electrons of nitrogen atom and extending light absorption up to 600 nm. Moreover, the presence of heterogeneous π-conjugated electron distribution effectively traps photogenerated electrons and enhances charge carrier separation. Benefiting from its expanded spectral response range, unique electronic properties, increased specific surface area, the doped g-C3N4 exhibited outstanding photocatalytic H2 evolution performance of 1050.13 μmol/g/h. The value was 5.9 times greater than the pristine g-C3N4.

Revealing mechanism of phenol-amine reaction to form humus in compost based on high-resolution liquid chromatography mass spectrometry and spectroscopy

Humus is the stable form of carbon storage in straw compost. The phenol-amine reaction is a pathway for humus formation in straw compost. In this study, two reaction systems, GP group (pyrogallol and glycine) and GCP group (catechol, pyrogallol, and glycine), were constructed in a simulated composting environment and revealed the molecular binding mechanism of the phenol-amine reaction through spectroscopy and mass spectrometry. The results showed that phenolic self-polymerization was faster than phenol-amine reaction. Therefore, the aromatization degree of GP was 27.14 % higher than that of GCP. The phenol-amine reaction first produced fulvic acid, and then formed humus units rich in active functional group structures (i.e., phenolic hydroxyl and carboxyl groups). These units further captured small molecule compounds to form humic acid eventually. This study would provide theoretical support for exploring the humus formation process and the promotion of straw humification by adding phenol or amino acids to compost.

Recent Progress in Covalent Organic Frameworks for Cathode Materials

Covalent organic frameworks (COFs) are constructed from small organic molecules through reversible covalent bonds, and are therefore considered a special type of polymer. Small organic molecules are divided into nodes and connectors based on their roles in the COF's structure. The connector generally forms reversible covalent bonds with the node through two reactive end groups. The adjustment of the length of the connector facilitates the adjustment of pore size. Due to the diversity of organic small molecules and reversible covalent bonds, COFs have formed a large family since their synthesis in 2005. Among them, a type of COF containing redox active groups such as -C=O-, -C=N-, and -N=N- has received widespread attention in the field of energy storage. The ordered crystal structure of COFs ensures the ordered arrangement and consistent size of pores, which is conducive to the formation of unobstructed ion channels, giving these COFs a high-rate performance and a long cycle life. The voltage and specific capacity jointly determine the energy density of cathode materials. For the COFs' cathode materials, the voltage plateau of their active sites' VS metallic lithium is mostly between 2 and 3 V, which has great room for improvement. However, there is currently no feasible strategy for this. Therefore, previous studies mainly improved the theoretical specific capacity of the COFs' cathode materials by increasing the number of active sites. We have summarized the progress in the research on these types of COFs in recent years and found that the redox active functional groups of these COFs can be divided into six subcategories. According to the different active functional groups, these COFs are also divided into six subcategories. Here, we summarize the structure, synthesis unit, specific surface area, specific capacity, and voltage range of these cathode COFs.

Stimuli-Responsive Polymer-Based Nanosystems for Cancer Theranostics

Stimuli-responsive polymers can respond to internal stimuli, such as reactive oxygen species (ROS), glutathione (GSH), and pH, biological stimuli, such as enzymes, and external stimuli, such as lasers and ultrasound, etc., by changing their hydrophobicity/hydrophilicity, degradability, ionizability, etc., and thus have been widely used in biomedical applications. Due to the characteristics of the tumor microenvironment (TME), stimuli-responsive polymers that cater specifically to the TME have been extensively used to prepare smart nanovehicles for the targeted delivery of therapeutic and diagnostic agents to tumor tissues. Compared to conventional drug delivery nanosystems, TME-responsive nanosystems have many advantages, such as high sensitivity, broad applicability among different tumors, functional versatility, and improved biosafety. In recent years, a great deal of research has been devoted to engineering efficient stimuli-responsive polymeric nanosystems, and significant improvement has been made to both cancer diagnosis and therapy. In this review, we summarize some recent research advances involving the use of stimuli-responsive polymer nanocarriers in drug delivery, tumor imaging, therapy, and theranostics. Various chemical stimuli will be described in the context of stimuli-responsive nanosystems. Accordingly, the functional chemical groups responsible for the responsiveness and the strategies to incorporate these groups into the polymer will be discussed in detail. With the research on this topic expending at a fast pace, some innovative concepts, such as sequential and cascade drug release, NIR-II imaging, and multifunctional formulations, have emerged as popular strategies for enhanced performance, which will also be included here with up-to-date illustrations. We hope that this review will offer valuable insights for the selection and optimization of stimuli-responsive polymers to help accelerate their future applications in cancer diagnosis and treatment.

Polymerization, Stimuli-induced Depolymerization, and Precipitation-driven Macrocyclization in a Nitroaldol Reaction System

Dynamic covalent polymers of different topology have been synthesized from an aromatic dialdehyde and α,ω-dinitroalkanes via the nitroaldol reaction. All dinitroalkanes yielded dynamers with the dialdehyde, where the length of the dinitroalkane chain played a vital role in determining the structure of the final products. For longer dinitroalkanes, linear dynamers were produced, where the degree of polymerization reached a plateau at higher feed concentrations. In the reactions involving 1,4-dinitrobutane and 1,5-dinitropentane, specific macrocycles were formed through depolymerization of the linear chains, further driven by precipitation. At lower temperature, the same systemic self-sorting effect was also observed for the 1,6-dinitrohexane-based dynamers. Moreover, the dynamers showed a clear adaptive behavior, displaying depolymerization and rearrangement of the dynamer chains in response to alternative building blocks as external stimuli.

{2-(((2-aminoethyl)imino)methyl)-6-bromophenolato-κ3 N,N′,O}iron(III) nitrate, C18H20Br2FeN5O5

C18H20Br2FeN5O5, monoclinic, P21/c (no. 14), a = 12.4534(3) Å, b = 10.8106(3) Å, c = 16.0339(4) Å, β = 94.0450(10)°, V = 2153.25(10) Å3, Z = 4, R gt(F) = 0276, wR ref(F 2) = 0.0644, T = 170.0 K.

[2,2′-{Ethane-1,2-diylbis[(azanylylidene)-methanylylidene]}bis(3-bromo-2-hydroxyphenyl)]iron(III) nitrate, C20H12Br2CuN2O2

C20H12Br2CuN2O2, orthorhombic, Pbca (no. 61), a = 7.7117(2) Å, b = 18.7735(4) Å, c = 24.8518(4) Å, V = 3597.93(13) Å3, Z = 8, Rgt (F) = 0399, wRref (F 2) = 0.1125, T = 213 K.

Competition among Refined Hollow Structures in Schiff Base Polymer Derived Carbon Microspheres

Synthetic polymer-derived hollow carbon spheres have great utilitarian value in many fields for which the synthesis of proper polymer precursors is a key process. The exploration of new suitable polymer precursors and the construction of refined hollow structures in emerging polymers are both of great significance for synthetic methodology and novel carbon materials. Here, for the first time Schiff base polymer (SBP) colloid spheres with refined hollow structures were synthesized by tandem gradient growth and confined polymerization processes. The Hill equation was employed as a mathematical model to explain the gradient growth of SBP spheres. The size-dependent inner structure of SBP spheres can be adjusted from hollow to multichamber-surrounded hollow, and then to a multichamber structure. SBP-derived carbon spheres having similar surface area and chemical composition but different inner structures provide an effective way to investigate the relationship between inner structure and performance.

Copper nanoclusters with/without salicylaldehyde-modulation for multifunctional detection of mercury, cobalt, nitrite and cyanide ions in aqueous solution and bioimaging

The sensitive determination of multiple heavy metal ions and toxic anions is important in biological and environmental fields. Here we report a facile strategy to construct a multifunctional chemosensor for the detection of Hg²⁺, [Formula: see text]Co²⁺, and CN^- in aqueous solution based on the fluorescent copper nanoclusters (Cu NCs). It was interesting to find that salicylaldehyde (SA) could effectively modulate the fluorescence property and sensing behavior of Cu NCs. In the absence of SA, Cu NCs showed 'on-off' fluorescence responses at the addition of Hg²⁺ and [Formula: see text] under different quenching mechanisms. Upon the presence of SA, Cu NCs exhibited a strong intramolecular charge transfer emission at 500 nm, accompanied by the decrease of the initial fluorescence of Cu NCs at 430 nm. This fluorescence on-state of Cu NC-SA at 500 nm was found to be exclusively turned off by Co²⁺ and enhanced by CN^-. Spectroscopy results combined with thermodynamic analysis provided sufficient information to deduce the sensing mechanisms. Finally, the Cu NCs showed high biocompatibility and were able to be used for fluorescence bioimaging in living cells. This study provided a novel and simple strategy to construct the multifunctional chemosensors for bioanalytical applications.

Synthesis and structures of three isoxazole-containing Schiff bases

The synthesis and structures of three isoxazole-containing Schiff bases are reported, namely, (E)-2-{[(isoxazol-3-yl)imino]methyl}phenol, C10H8N2O2, (E)-2-{[(5-methylisoxazol-3-yl)imino]methyl}phenol, C11H10N2O2, and (E)-2,4-di-tert-butyl-6-{[(isoxazol-3-yl)imino]methyl}phenol, C18H24N2O2. All three structures contain an intramolecular O-H...N hydrogen bond, alongside weaker intermolecular C-H...N and C-H...O contacts. The C-O(H) and imine C=N bond lengths were consistent with structures existing in the enol rather than the keto form. Despite having dihedral angles <25°, none of the compounds were observed to be strongly thermochromic, unlike their anil counterparts; however, all three compounds showed a visible colour change upon irradiation with UV light.