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In this work, the assembly behavior and structure of a compound collector with different carboxyl group positions at the low-rank coal (LRC)-water interface were investigated through coarse-grained molecular dynamics simulation (CGMD) combined with sum-frequency vibration spectroscopy (SFG). The choice of compound collector was dodecane +decanoic acid (D-DA) and dodecane +2-butyl octanoic acid (D-BA). CGMD results showed that the carboxyl group at the carbon chain's middle can better control the assembly process between carboxylic acid and D molecules. SFG research found that the carboxyl group at the carbon chain's termination had a greater impact on the displacement of the methyl/methylene symmetric stretching vibration peak, while the carboxyl group at the carbon chain's middle had a greater impact on the displacement of the methyl/methylene asymmetric stretching vibration peak. The spatial angle calculation results revealed that the methyl group's orientation angle in the D-BA molecule was smaller and the carboxyl group's orientation angle in the BA molecule was bigger, indicating that D-BA spread more flatly on the LRC surface than D-DA. This meant that the assembled structure had a larger effective adsorption area on the LRC surface. The flotation studies also verified that the assembly behavior and structure of D-BA with the carboxyl group at the carbon chain's middle at the LRC-water interface were more conducive to the improvement of flotation efficiency. The study of interface assembly behavior and structure by CGMD combined with SFG is crucial for the creation of effective compound collectors.

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Heavy metals (e.g., Cu) in wastewater are attractive resources for diverse applications, and adsorption is a promising route to recovery of heavy metals from wastewater. However, high-performance adsorbents with high adsorption capacity, speed, and stability remain challenging. Herein, chelating fibers were prepared by chemically grafting amine and carboxyl groups onto the polyacrylonitrile fiber surface and used in the wastewater's adsorption of Cu2+. The adsorption behavior of Cu2+ on the fibers was systematically investigated, and the post-adsorption fibers were comprehensively characterized to uncover the adsorption mechanism. The results show that chelated fiber has a 136.3 mg/g maximum capacity for Cu2+ adsorption at pH = 5, and the whole adsorption process could reach equilibrium in about 60 min. The adsorption process corresponds to the quasi-secondary kinetic and Langmuir models. The results of adsorption, FTIR, and XPS tests indicate that the synergistic coordination of -COOH and -NH2 plays a leading role in the rapid capture of Cu2+. In addition, introducing hydrophilic groups facilitates the rapid contact and interaction of the fibers with Cu2+ in the solution. After being used five times, the fiber's adsorption capacity remains at over 90% of its original level.

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In the 1980s, the identification of specific pharmacological antagonists played a crucial role in enhancing our comprehension of the physiological mechanisms associated with α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors (AMPARs). The primary objective of this investigation was to identify specific AMPA receptor antagonists, namely 2,3-benzodiazepines, that function as negative allosteric modulators (NAMs) at distinct locations apart from the glutamate recognition site. These compounds have exhibited a diverse array of anticonvulsant properties. In order to conduct a more comprehensive investigation, the study utilized whole-cell patch-clamp electrophysiology to analyze the inhibitory effect and selectivity of benzodiazepine derivatives that incorporate coumarin rings in relation to AMPA receptors. The study's main objective was to acquire knowledge about the relationship between the structure and activity of the compound and comprehend the potential effects of altering the side chains on negative allosteric modulation. The investigation provided crucial insights into the interaction between eight CD compounds and AMPA receptor subunits. Although all compounds demonstrated effective blockade, CD8 demonstrated the greatest potency and selectivity towards AMPA receptor subunits. The deactivation and desensitization rates were significantly influenced by CD8, CD6, and CD5, distinguishing them from the remaining five chemicals. The differences in binding and inhibition of AMPA receptor subunits can be attributed to structural discrepancies among the compounds. The carboxyl group of CD8, situated at the para position of the phenyl ring, substantially influenced the augmentation of AMPA receptor affinity. The findings of this study highlight the potential of pharmaceutical compounds that specifically target AMPA receptors to facilitate negative allosteric modulation.

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Recently, polyetheretherketone (PEEK) has shown promising dental applications. Surface treatment is essential for dental applications owing to its poor surface energy and wettability; however, no consensus on an effective treatment method has been achieved. In this study, we attempted to carboxylate PEEK sample surfaces via Friedel-Crafts acylation using succinic anhydride and AlBr3. The possibility of further chemical modifications using carboxyl groups was examined. The samples were subjected to dehydration-condensation reactions with 1H,1H-pentadecafluorooctylamine and N,N'-dicyclohexylcarbodiimide. Furthermore, the sample's surface properties at each reaction stage were evaluated. An absorption band in the 3300-3500 cm-1 wavenumber region was observed. Additionally, peak suggestive of COOH was observed in the sample spectra. Secondary modification diminished the absorption band in 3300-3500 cm-1 and a clear F1s signal was observed. Thus, Friedel-Crafts acylation with succinic anhydride produced carboxyl groups on the PEEK sample surfaces. Further chemical modification of the carboxyl groups by dehydration-condensation reactions is also possible. Thus, a series of reactions can be employed to impart desired chemical structures to PEEK surfaces.

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A simple and efficient sample pretreatment technology is very important for the accurate determination of trace drug residues in foods to ensure food safety. Herein, we report a new carboxyl group-functionalized ionic liquid hybrid solid- phase adsorbent (PS-IL-COOH) for the highly efficient extraction and quantitative determination of diclofenac sodium (DS) residue in milk samples. It was found that the adsorption efficiency of PS-IL-COOH for the ppb level of DS was greater than 93.0%, the adsorption capacity was 934.1 mg/g, and the enrichment factor was 620.0, which surpass most of the previously reported values for DS adsorbents. The high concentration of salts did not interfere with the adsorption of DS. Importantly, the recovery of DS was above 90% after 16 adsorption--regeneration cycles. The synergistic effect of the multiple interactions was found to be the main factor for the high efficiency of DS adsorption. The proposed method was applied to the extraction and detection of DS in milk samples, with the relative recovery ranging from 88.2 to 103.0%.

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Carbon-driven persulfate (PDS)-based Fenton-like reactions have been widely viewed as prospective strategies to cope with the water pollution. However, high cost, harsh condition and complex modification processes are usually required to boost the catalytic activities of carbocatalysts. Herein, we proposed an ultrafast, energy-efficient, and convenient approach to convert various low-performance carbon materials into highly efficient catalysts by microwave treatment in just 1 min without any other tedious treatment. This process only requires 57 kJ/g energy input, 5 orders of magnitude lower than the traditional calcination process. The catalytic performance of microwave-treated materials could increase by more than 380 times, which is even better than those of the single-atom catalysts. Moreover, DFT calculations and QSARs analyses reveal that the negatively charged carboxyl group is not conducive to the adsorption of PDS (S2O82-) due to electrostatic repulsion, and also increases the work function of the carbocatalysts, which hinders the electron transfer process.

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To efficiently eliminate highly polar organic pollutants from water has always been a difficult issue, especially in the case of ultralow concentrations. Herein, we present the facile synthesis of quinolinecarboxylic acid-linked COF (QCA-COF) via the Doebner multicomponent reaction, possessing multifunction, high specific surface area, robust physicochemical stability, and excellent crystallinity. The marked feature lies in the quinolinyl and carboxyl functions incorporated simultaneously to QCA-COF in one step. The major cis-orientation of carboxyl arms in QCA-COF was speculated by powder X-ray diffraction and total energy analysis. QCA-COF demonstrates excellent adsorption capacity for water-soluble organic pollutants such as rhodamine B (255.7 mg/g), methylene blue (306.1 mg/g), gentamycin (338.1 mg/g), and 2,4-dichlorophenoxyacetic acid (294.1 mg/g) in water. The kinetic adsorptions fit the pseudo-second order model and their adsorption isotherms are Langmuir model. Remarkably, QCA-COF can capture the above four water-soluble organic pollutants from real water samples at ppb level with higher than 95% removal efficiencies and excellent recycling performance.

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Carbon dots (CDs) with good water solubility and biocompatibility have become a research hotspot in the nano-enzyme and biomedical field. However, the problems of low catalytic activity and ambiguous catalytic site of CDs as nanozymes still need to be addressed. In this work, CDs loaded with Cu single atoms are obtained through pyrolysis, and the coordination structure and surface functional groups are regulated by adjusting the pyrolysis temperature. CDs obtained at 300 °C (named Cu-CDs-300) have the most carboxyl content and Cu is coordinated in the form of CuN2 O2 , which can better decompose H2 O2 to produce free radical and is beneficial to catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). The vmax is 6.56*10-7  m s-1 , 6.56 times higher than that of horseradish peroxidase (HRP). Moreover, Cu-CDs-300 can effectively lead to CT26 apoptosis by generating much free radicals. This work demonstrates the synergistic effect of oxygen-containing functional groups and metal coordination structures on peroxide-like activity of CDs and provides new ideas for the design of clear active structure and high efficiency peroxide-like single atom CDs catalyst.

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The role of carboxyl group in uronic acid in enhancing the anti-inflammatory activity of fish myofibrillar protein (Mf) was investigated, when lyophilized Mf was reacted with various reducing sugars at 60 °C and 35% relative humidity through the Maillard reaction. After pepsin and trypsin digestion, the anti-inflammatory activity was evaluated by measuring the secretions of tumor necrosis factor-α, interleukin-6, interleukin-1ß, and nitric oxide in lipopolysaccharide-stimulated RAW 264.7 macrophage. The anti-inflammatory activity of Mf was not affected by glycation with glucose or galactose, whereas strongly enhanced by glycation with uronic acid-type reducing sugars: glucuronic acid, galacturonic acid, and alginate oligosaccharide. These results indicate that the presence of carboxyl group in reducing sugar is important for enhancing the anti-inflammatory activity of Mf. This study also shows that the enhanced effect could depend upon the number of carboxyl group in bound reducing sugar.

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Previous studies have shown that chemical modification may increase the activity of proteins or confer novel activity to proteins. Some studies have indicated that myoglobin (Mb) is cytotoxic; however, the underlying mechanisms remain unclear. In this study, we investigated whether chemical modification of the carboxyl group by semicarbazide could promote the Mb cytotoxicity in human leukemia U937 cells and the underlying mechanism of semicarbazide-modified myoglobin (SEM-Mb)-induced U937 cell death. The semicarbazide-modified Mb (SEM-Mb) induced U937 cell apoptosis via the production of cleaved caspase-8 and t-Bid, while silencing of FADD abolished this effect. These findings suggest that SEM-Mb can induce U937 cell death by activating the death receptor-mediated pathway. The SEM-Mb inhibited miR-99a expression, leading to increased NOX4 mRNA and protein expression, which promoted SIRT3 degradation, and, in turn, induced ROS-mediated p38 MAPK phosphorylation. Activated p38 MAPK stimulated miR-29a-dependent tristetraprolin (TTP) mRNA decay. Downregulation of TTP slowed TNF-α mRNA turnover, thereby increasing TNF-α protein expression. The SEM-Mb-induced decrease in cell viability and TNF-α upregulation were alleviated by abrogating the NOX4/SIRT3/ROS/p38 MAPK axis or ectopic expression of TTP. Taken together, our results demonstrated that the NOX4/SIRT3/p38 MAPK/TTP axis induces TNF-α-mediated apoptosis in U937 cells following SEM-Mb treatment. A pathway regulating p38 MAPK-mediated TNF-α expression also explains the cytotoxicity of SEM-Mb in the human leukemia cell lines HL-60, THP-1, K562, Jurkat, and ABT-199-resistant U937. Furthermore, these findings suggest that the carboxyl group-modified Mb is a potential structural template for the generation of tumoricidal proteins.

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In the past decades, extensive efforts have been devoted to the mechanistic understanding of various heterogeneous Fenton reactions. Nevertheless, controversy still remains on the oxidation mechanism/pathway toward different organic compounds in the classical iron oxide-based Fenton reaction, largely because the role of the interaction between the organic compounds and the catalyst has been scarcely considered. Here, we revisited the classic heterogeneous ferrihydrite (Fhy)/H2O2 system toward different organic compounds on the basis of a series of degradation experiments, alcohol quenching experiments, theoretical modeling, and intermediate analysis. The Fhy/H2O2 system exhibited highly selective oxidation toward the group of compounds that bear carboxyl groups, which tend to complex with the surface ≡Fe(III) sites of the Fhy catalyst. Such interaction results in a nonradical inner sphere electron transfer process, which seizes one electron from the target compound and features negligible inhibition by the radical quencher. In contrast, for the oxidation of organic compounds that could not complex with the catalyst, the traditional HO· process makes the main contribution, which proceeds via hydroxyl addition reaction and could be readily suppressed by the radical quencher. This study implies that the interaction between the organic compounds and the catalyst plays a decisive role in the oxidation pathway and mechanism of the target compounds and provides a holistic understanding on the iron oxide-based heterogeneous Fenton system.

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In this study, we investigated whether modification of the carboxyl group with semicarbazide-enabled myoglobin (Mb) exhibits membrane-perturbing activity in physiological solutions. Mass spectrometry analysis showed that semicarbazide molecules were coupled to 19 of the 22 carboxyl groups in semicarbazide-modified Mb (SEM-Mb). Measurements of the absorption and circular dichroism spectra indicated that SEM-Mb lost its heme group and reduced the content of the α-helix structure in Mb. The microenvironment surrounding Trp residues in Mb changes after blocking negatively charged residues, as shown by fluorescence quenching studies. The results of the trifluoroethanol-induced structural transition indicated that SEM-Mb had higher structural flexibility than that of Mb. SEM-Mb, but not Mb, induced the permeability of bilayer membranes. Both proteins showed similar lipid-binding affinities. The conformation of SEM-Mb and Mb changed upon binding to lipid vesicles or a membrane-mimicking environment composed of SDS micelles, suggesting that membrane interaction modes differ. Unlike lipid-bound Mb, Trp residues in lipid-bound SEM-Mb are located at the protein-lipid interface. Altogether, our data indicate that modifying negatively charged groups relieves the structural constraints in Mb, consequently switching Mb structure to an active conformation that exhibits membrane-permeabilizing activity.

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Defective functional-group-endowed polymer semiconductors, which have unique photoelectric properties and rapid carrier separation properties, are an emerging type of high-performance photocatalyst for various energy and environmental applications. However, traditional oxidation etching chemical methods struggle to introduce defects or produce special functional group structures gently and controllably, which limits the implementation and application of the defective functional group modification strategy. Here, with the surface carboxyl modification of graphitic carbon nitride (g-C3N4) photocatalyst as an example, we show for the first time the feasibility and precise modification potential of the non-thermal plasma method. In this method, the microwave plasma technique is employed to generate highly active plasma in a combined H2+CO2 gas environment. The plasma treatment allows for scalable production of high-quality defective carboxyl group-endowed g-C3N4 nanosheets with mesopores. The rapid H2+CO2 plasma immersion treatment can precisely tune the electronic and band structures of g-C3N4 nanosheets within 10 min. This conjoint approach also promotes charge-carrier separation and accelerates the photocatalyst-catalyzed H2 evolution rate from 1.68 mmol h-1g-1 (raw g-C3N4) to 8.53 mmol h-1g-1 (H2+CO2-pCN) under Xenon lamp irradiation. The apparent quantum yield (AQY) of the H2+CO2-pCN with the presence of 5 wt.% Pt cocatalyst is 4.14% at 450 nm. Combined with density functional theory calculations, we illustrate that the synergistic N vacancy generation and carboxyl species grafting modifies raw g-C3N4 materials by introducing ideal defective carboxyl groups into the framework of heptazine ring g-C3N4, leading to significantly optimized electronic structure and active sites for efficient photocatalytic H2 evolution. The 5.08-times enhancement in the photocatalytic H2 evolution over the as-developed catalysts reveal the potential and maneuverability of the non-thermal plasma method in positioning carboxyl defects and mesoporous morphology. This work presents new understanding about the defect engineering mechanism in g-C3N4 semiconductors, and thus paves the way for rational design of effective polymeric photocatalysts through advanced defective functional group engineering techniques evolving CO2 as the industrial carrier gas.

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In this study, we investigated the functional roles of Asp40, Asp57, and C-terminal Asn60 in Naja atra cardiotoxin 3 (CTX3) structure and function by modifying these three carboxyl groups with semicarbazide. The conjugation of the carboxyl groups with semicarbazide produced two conformational isomers whose gross and fine structures were different from those of CTX3. The blocking of the carboxyl groups increased the structural flexibility of CTX3 in response to trifluoroethanol-induced effect. Despite presenting modest to no effect on decreasing the induction of permeability in zwitterionic phospholipid vesicles, the carboxyl group-modified CTX3 showed a marked reduction in its permeabilizing effect on anionic phospholipid vesicles in comparison to that of the native protein. Compared with native CTX3, carboxyl group-modified CTX3 exhibited lower activity in inducing membrane leakage in U937 cells. The CD spectra of lipid-bound toxins and the color transition of polydiacetylene/lipid assay showed that the membrane interaction mode of CTX3 was distinctly changed by the modification in the carboxyl groups. Given that the selective modification of Asp40 does not cause the conformational isomerization of CTX3, our data indicate that the carboxyl groups in Asp57 and Asn60 are essential in maintaining the structural topology of CTX3. Furthermore, modification of carboxyl groups changes the interdependence between the infrastructure and the global conformation of CTX3 in modulating membrane permeabilizing activity.

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The poor dispersibility and re-dispersibility of cellulose nanofibrils (CNFs) in various solvents and polymers have been recognized as the key factors limiting their potential applications. TEMPO oxidation, as the most common surface modification, can greatly improve the dispersion and re-dispersion of CNFs. However, the diameter of TEMPO-oxidized cellulose nanofibers (TOCNFs) has not been regulated in most researches, which was an important factor determining the dispersion and re-dispersion of TOCNFs. Herein, this work explored the effect of carboxyl groups on dispersion and re-dispersion of TOCNFs with uniform diameter in various solvents. Notably, fractal dimension was innovatively introduced to characterize the distribution of TOCNFs diameter. The fractal dimension and statistic diameter of TCONFs with different carboxyl group contents are ~1.56 and ~22 nm, demonstrating that the diameter of TOCNFs has been regulated in the same range. When the carboxyl group content is up to 1.58 mmol/g, the dispersion and re-dispersion of TOCNFs suspension in water and different organic solvents are the most uniform and stable. In a word, this work explores the dispersion and re-dispersion of TOCNFs with the uniform diameter and different carboxyl group contents, which can provide the theoretical guidance for various potential applications of nanofibrils in polymer matrix composites.

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The adsorption and recovery of dysprosium ions (Dy3+) from industrial wastewater are necessary but still challenging. Herein, we constructed a series of defect-containing metal-organic frameworks (MOFs) [UiO-66-(COOH)2] using sodium benzoate (BCNa) as a modulator. Upon the formation of defects, the porosity and surface charge properties of the MOFs were improved, leading to a higher utilization ratio of active groups and higher adsorption capacities for Dy3+. The synthesized UiO-66-(COOH)2-B10 with an optimal addition of BCNa exhibited a superior adsorption capacity of 150.6 mg g-1. Fast adsorption occurred at ∼5 min, and equilibrium was reached at ∼60 min. Higher pH and temperature were found to be beneficial for boosting Dy3+ adsorption, and selective adsorption over other metal ions was achieved in a multicomponent solution. Further, FTIR spectroscopy and XPS investigations indicate that free carboxyl contributes to the capture of Dy3+. Thus, this work provides a promising strategy to enhance the utilization ratio of active groups and further adsorption performance.

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Based on the accurate characterization of the binding sites of humic substances (HS) and their binding coefficients with ferric ions (Fe(III)), a coupled interaction-sedimentation (CIS) technology was proposed for dealing with HS in the biologically treated wastewater effluent (BTWE) from a full-scale antibiotic production wastewater treatment plant. The infrared spectral and carbon-13 nuclear magnetic resonance characteristics showed that (i) protonated carboxyl groups in HS were the main binding sites for Fe(III) and HS, (ii) one carboxyl group of HS interacted with one ferric ion, (iii) the Fe(III)-binding ability of fulvic acids (FA) was 2.8 times as much as that of humic acids (HA) when FA and HA coexisted, and (iv) the presence of non-humic substances in the effluent organic matter (EfOM) amplified the Fe(III)-binding ability difference between FA and HA to 4.9 times. Afterwards CIS technology was successfully optimized and applied in engineering-scale and superior HS and EfOM removal efficiencies of 94.2% and 84.0% were reached, respectively. The CIS technology and its engineering application in this study not only fulfill the direct discharging standard for antibiotic production wastewater, but also have the potential for replication in broader advanced treatments for BTWE.

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Noncovalent interactions are among the main tools of molecular engineering. Rational molecular design requires knowledge about a result of interplay between given structural moieties within a given phase state. We herein report a study of intra- and intermolecular interactions of 3-nitrophthalic and 4-nitrophthalic acids in the gas, liquid, and solid phases. A combination of the Infrared, Raman, Nuclear Magnetic Resonance, and Incoherent Inelastic Neutron Scattering spectroscopies and the Car-Parrinello Molecular Dynamics and Density Functional Theory calculations was used. This integrated approach made it possible to assess the balance of repulsive and attractive intramolecular interactions between adjacent carboxyl groups as well as to study the dependence of this balance on steric confinement and the effect of this balance on intermolecular interactions of the carboxyl groups.

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We investigated whether the modification of the negatively charged carboxyl groups with semicarbazide could confer membrane-disrupting and cytotoxic properties to bovine α-lactalbumin (LA). MALDI-TOF analysis revealed that eighteen of the twenty-one carboxyl groups in LA were coupled with semicarbazide molecules. Measurement of circular dichroism spectra and Trp fluorescence quenching studies showed that semicarbazide-modified LA (SEM-LA) had a molten globule-like conformation that retained the α-helix secondary structure but lost the tertiary structure of LA. Compared to LA, SEM-LA had a higher structural flexibility in response to trifluoroethanol- and temperature-induced structural transitions. In sharp contrast to LA, SEM-LA exhibited membrane-damaging activity and cytotoxicity. Furthermore, SEM-LA-induced membrane permeability promoted the uptake of daunorubicin and thereby its cytotoxicity. The microenvironment surrounding the Trp residues of SEM-LA was enriched in positive charges, as revealed by iodide quenching studies. The binding of SEM-LA with lipid vesicles altered the positively charged cluster around Trp residues. Although LA and SEM-LA displayed similar lipid-binding affinities, the membrane interaction modes of SEM-LA and LA differed. Collectively, these results suggest that blocking of negatively charged residues enables the formation of a molten-globule conformation of LA with structural flexibility and increased positive charge, thereby generating functional LA with membrane-disrupting activity and cytotoxicity.

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Functional carbon nanodots (FCNs) with multiple chemical groups have great impact on the growth regulation of plants. To understand the role of the chemical groups, FCNs were reduced from the raw material by pyrolysis method and hydrolysis method. The chemical structure of these materials were characterized by using TGA, TEM, FT-IR, XPS, Raman and elementary analysis. The raw and reduced FCNs were used as plants growth regulators in culture medium of Arabidopsis thaliana. Our results indicate there is a strong correlation between the physiological responses of plants and the surface chemistries (especially carboxyl group and ester group) of the nanomaterials. The quantum-sized FCNs with multiple carboxyl groups and ester groups show better aqueous dispersity and can induce various positive physiological responses in Arabidopsis thaliana seedlings compared with the FCNs decorated without carboxyl and ester as well as aggregated FCNs. The raw FCNs present higher promotion capacity in plants biomass and roots length, and the quantum-sized FCNs are easier to be absorbed by plants and generate more positive effects on plants.

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