Determination of VEGF165 using impedimetric aptasensor based on cyclohexanehexone-melem covalent-organic framework.

A porous nanostructured covalent-organic framework (COF) has been prepared via condensation polymerization between the two building blocks of melem and hexaketocyclohexane octahydrate (represented as M-HO-COF). Basic characterizations revealed that the M-HO-COF network was composed of C=N and highly conjugated aromatic moieties, along with a high surface area, large pore size, remarkable electrochemical activity, and strong bioaffinity toward aptamer strands. Given that the vascular endothelial growth factor 165 (VEGF165)-targeted aptamer was stably anchored over M-HO-COF via weak intermolecular forces, the prepared M-HO-COF network exhibited great potential as a sensitive and selective platform for the impedimetric VEGF165 aptasensor. Consequently, the M-HO-COF-based aptasensor displayed an ultralow limit of detection of 0.18 fg mL-1 within a wide range of VEGF165 concentrations from 1 fg mL-1 to 10 ng mL-1. Considering its strong fluorescence performance, excellent biocompatibility, and small nanosheet-like structure, the obtained COF-based aptasensor showed a superior sensing performance and regeneration capability after 7 regeneration cycles for the detection of osteosarcoma cells (K7M2 cells), which overexpressed with VEGF165, with a low limit of detection of 49 cells mL-1. For real f human serum samples, the obtained COF-based aptasensor exhibits acceptable mean apparent recoveries of 97.41% with a relative standard deviation of 4.60%. Furthermore, the proposed bifunctional aptasensor for the detection VEGF165 and K7M2 cells exhibited good stability, appropriate selectivity toward other biomarkers or normal cells, acceptable reproducibility, and applicability. A bifunctional sensing system was constructed for detecting osteosarcoma cells (K7M2 cells) and VEGF165 based on the a porous nanostructured covalent-organic framework (M-HO-COF) via condensation polymerization between melem and hexaketocyclohexane octahydrate. The M-HO-COF-based aptasensor displayed ultralow detection limit of 0.18 fg mL-1 toward VEGF165 and 49 cell mL-1 for K7M2 cells with high selectivity, acceptable reproducibility, and good stability.

Cyanuric Acid-Assisted Synthesis of Hierarchical Amorphous Carbon Nitride Assembled by Ultrathin Oxygen-Doped Nanosheets for Excellent Photocatalytic Hydrogen Generation.

Amorphous carbon nitride with typical short-range order arrangement as an effective photocatalyst is worth exploring but remains a great challenge because its disordered structure induces severe recombination of photogenerated charge carriers. Herein, for the first time, we demonstrate that a hierarchical amorphous carbon nitride (HACN) with structural oxygen incorporation can be synthesized via a cyanuric acid-assisted melem hydrothermal process, accompanied by freeze-drying and pyrolysis. The complex composed of melem and cyanuric acid exhibiting a unique 3D self-supporting skeleton and significant phase transformation is responsible for the formation of an interconnected hierarchical framework and amorphous structure for HACN. These features are beneficial to enhance its visible light harvesting by the multiple-reflection effect within the architecture consisting of more exposed porous nanosheets and introducing a long band tail absorption. The well-designed morphology, band tail state, and oxygen doping effectively inhibit rapid band-to-band recombination of the photogenerated electrons and holes and facilitate subsequent separation. Accordingly, the HACN catalyst exhibits exceptional visible light (λ > 420 nm)-driven photoreduction for hydrogen production with a rate of 82.4 µmol h-1, which is 21.7 and 9.5 times higher than those of melem-derived carbon nitride and crystalline nanotube carbon nitride counterparts, respectively, and significantly surpasses those of most reported amorphous carbon nitrides. Our controlling of rearrangement of the in situ supramolecular self-assembly of melem oligomer using cyanuric acid directly instructs the development of highly efficient amorphous photocatalysts for converting solar energy into hydrogen fuel.

Vacancy-Engineered 1D Nanorods with Spatially Segregated Dual Redox Sites for Visible-Light-Driven Cooperative CO2 Reduction.

Cooperative CO2 photoreduction with tailored organic synthesis offers a potent avenue for harnessing concurrently generated electrons and holes, facilitating the creation of both solar fuels and specialized chemical compounds. However, controlling the crystallization and morphologies of metal-free molecular nanostructures with exceptional photocatalytic activities toward CO2 reduction remains a significant challenge. These hurdles encompass insufficient CO2 activation potential, sluggish multielectron processes, delayed charge-separation kinetics, inadequate storage of long-lived photoexcitons, unfavorable thermodynamic conditions, and the precise control of product selectivity. Here, melem oligomer 2D nanosheets (MNSs) synthesized through pyrolysis are transformed into 1D nanorods (MNRs) at room temperature with the simultaneous engineering of vacancies and morphology. Transient absorption spectral analysis reveals that vacancies in MNRs trap charges, extending charge carrier lifetimes. Additionally, carbon vacancies enhance CO2 adsorption by increasing amine functional centers. The photocatalytic performance of MNRs for CO2 reduction coupled with benzyl alcohol oxidation is approximately ten times higher (CH3OH and aromatic aldehyde production rate 27 ± 0.5 and 93 ± 0.5 mmol g-1 h-1, respectively) than for the MNSs (CH3OH and aromatic aldehyde production rate 2.9 ± 0.5 and 9 ± 0.5 mmol g-1 h-1, respectively). The CO2 reduction pathway involved the carbon-coordinated formyl pathway through the formation of *COOH and *CHO intermediates, as mapped by in situ Fourier-transform infrared spectroscopy. The superior performance of MNRs is attributed to favorable energy-level alignment, enriched amine surfaces, and unique morphology, enhancing solar-to-chemical conversion.

Weighted Mostar invariants of chemical compounds: An analysis of structural stability.

The concept of the weighted Mostar invariant is a mathematical tool used in chemical graph theory to study the stability of chemical compounds. Several recent studies have explored the weighted Mostar invariant of various chemical structures, including hydrocarbons, alcohols, and other organic compounds. One of the key advantages of the weighted Mostar invariant is that it can be easily computed for large and complex chemical structures, making it a valuable tool for studying the stability of a wide range of chemical compounds. This notion has been utilized to build novel approaches for forecasting chemical compound stability, such as machine learning algorithms. The focus of the paper is to demonstrate the weighted Mostar indices of three specific nanostructures: silicon dioxide (SIO2, poly-methyl methacrylate network (PMMA(s)), and melem chains (MC(h)). The authors seek to provide the findings of their investigation of these nanostructures using the weighted Mostar invariant.

A Study on Byproducts in the High-Pressure Melamine Production Process.

The industrial production of melamine is carried out by the thermal decomposition of urea in two technological processes, using high or low pressure. The reaction may be accompanied by the formation of undesirable byproducts, oxoaminotriazines, and so-called polycondensates, mainly melam, melem, and melon, as well as their hydrates and adducts. Their presence leads to the deterioration of the quality of the final product and may lead to the release of troublesome deposits inside the apparatus of the product's separation node. With the limited possibility of controlling the crystallization of the byproducts of the process, improving the technological process requires the precise determination of the composition of the separated insoluble reaction byproducts, which is the main objective of this work. This work presents the results of qualitative and quantitative analyses of the composition of deposits sampled in the technological process of melamine production. The full characterization of the deposits was performed using inductively coupled plasma optical emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) techniques. The elemental analysis (EA) of carbon, hydrogen, and nitrogen allowed us to obtain characteristic C/H, C/N, and H/N ratios. X-ray diffraction (XRD) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy were also performed to confirm the obtained data. In addition, the morphology of the solid byproducts of the reaction was investigated, and the characteristics of the structures were determined using a scanning electron microscope. The elemental composition was investigated using scanning electron microscopy and the energy-dispersive X-ray spectroscopy (SEM-EDS) technique. The key finding of this research is that about 95% of the deposits are a mixture of melem and melem hydrate. The soluble part of the deposits contains melamine, urea, and oxyaminotriazines, as well as trace inorganic impurities.

Mononuclear ruthenium (II) complex covalently anchored on melem and g-C3N4 as efficient heterogeneous catalysts for chemical water oxidation.

Ru-melem and Ru-C3N4 were synthesized by a simple and facile strategy to construct a novel covalently anchoring by introducing easily synthesized amide bond as a bridge connecting the Ru-terpy and melem or g-C3N4, respectively. The covalent anchoring of Ru complex on melem or C3N4 not only makes these materials exhibit water oxidation activity under CeIV-driven (CeIV = Ce(NH4)2(NO3)6) reaction condition, but also makes the obtained heterogeneous catalysts show higher catalytic activity than the corresponding homogeneous catalysts, which reveals that the covalent anchoring strategy of Ru complex is beneficial to improve the catalytic activity of homogeneous Ru catalysts. The synthetic method of hybrid catalysts offers an insightful strategy for enhancing water oxidation activity of molecular catalysts.

A rod-like melem with high fluorescence quantum yield for sensitive detection of reduced glutathione.

A rod-like melem with high fluorescence quantum yield of 71.3 % was prepared in this work to enhance the chemiluminescence (CL) intensity of Na2SO3-Ce (Ⅳ) system. The results showed that the CL intensity of Na2SO3-Ce (Ⅳ) system could be increased by 350 times based on chemiluminescence resonance energy transfer (CRET) mechanism. Furthermore, a CL sensor based on Na2SO3-Ce (Ⅳ)-melem system was designed to detect reduced glutathione (G-SH). It was indicated that the CL sensor exhibited excellent G-SH detection performance with a detection limit of 0.065 nM and a linear range from 0.32 to 650 µM. This study applied melem for CL detection and provided a new way for the detection of G-SH.

Effect of Tricarboxylic Acids on the Formation of Hydrogels with Melem or Melamine: Morphological, Structural and Rheological Investigations.

Herein, aggregation behaviors of melem or melamine in the presence of three symmetric carboxylic acids (1,3,5-tris(4-carboxyphenyl)benzene (TPCA), 1,3,5-benzene-tri-carboxylic acid (BTA) and 1,3,5-cyclohexane-tri-carboxylic acid (CHTA)) have been performed to check the influence of acid on the formation of aggregated structures which have been investigated by optical microscopy, FESEM, FTIR, XRD and viscoelastic properties have been explored with rheological studies. Interestingly, melem, that has limited solubility in aqueous medium, forms aggregation that leads to the formation of hydrogels with TPCA. More significantly, hydrogel is formed here by matching the size selectivity. Melem forms hydrogel with only large tricarboxylic acid, whereas melamine produces hydrogel with any kind of its counterpart from small to large tricarboxylic acid derivatives. Present investigations and results provide the strategy of design of organic self-assembled materials having two component systems.

From pure water to hydrogen peroxide on a novel 2,5,8-triamino-tri-s-triazine (melem)-derived photocatalyst with a high apparent quantum efficiency.

Photocatalytic hydrogen peroxide (H2O2) production is a green process but remains a great challenge. Herein, a novel photocatalyst with high activity for H2O2 production, is developed based on 2,5,8-triamino-tri-s-triazine (melem) by linking it with 2, 3-naphthalene dicarboxylic anhydride (NDA). The obtained melem/NDA hybrid not only exhibited narrowed band gap and obviously enhanced visible light absorption, but also showed reduced charge recombination originated from its spatial distribution in HOMO and LUMO induced by the introduction of NDA as verified by DFT calculations. More significantly, the sufficient LUMO and HOMO positions for the optimal sample, melem/NDA0.5, ensured efficient H2O2 production from pure water via both the oxygen reduction reactions mainly through the two-step one-electron path and the water oxidation reaction through the one-step two-electron path. Consequently, melem/NDA0.5 achieves an apparent quantum efficiency of as high as 6.9 % at 420 nm. This work sheds light on developing high-performance organic photocatalysts for boosting photocatalytic H2O2 production.

Degradation of mixed cationic dye pollutant by metal free melem derivatives and graphitic carbon nitride.

Graphitic carbon nitride (GCN), a polymeric metal free catalyst is widely used to degrade the toxic organic dye from the aqueous pollution. However, its catalytic efficiency and effective simultaneous reduction of mixed dye is still a challenge. Here, we have tuned the physiochemical properties of the GCN and melem derivatives by facilely tuning the degree of polycondensation and examined their catalytic activity towards the removal of cationic dye individually and together in solution. Catalysts were synthesized by thermal treatment of low-cost melamine and characterized by XRD, FTIR, RAMAN, FE-SEM, EDX, UV-DRS, and FL spectroscopy to confirm materials' structure, phase, morphology and optical properties. A suitable phase of the catalyst (M-450) exhibited superior removal capacity with a high-rate constant compared to others. The results demonstrate that M-450 has a maximum loading efficacy of 2.13 and 1.12 mg g-1 for methylene blue (MB) and Rhodamine B (RhB) dyes respectively in a single dye system. Attractively, when MB and RhB co-exist in the solution, the efficacy increased by 14% (2.44 mg g-1) and 27% (1.43 mg g-1) for MB and RhB respectively. The adsorption kinetics, stability, effect of pH and reusability of M-450 catalyst was testified. Further, radical scavenger experiments and terephthalic acid tests were carried out to explain the reaction mechanism involved in the degradation of textile dyes. Moreover, electron paramagnetic resonance (EPR) analysis validated the availability of hydroxyl radicals in the photocatalytic reaction. Excellent stability and reusability were attained even after five successive cycles, demonstrating a suitable photocatalyst for the efficient degradation of mixed dye.

Ab-Initio Spectroscopic Characterization of Melem-Based Graphitic Carbon Nitride Polymorphs.

Polymeric graphitic carbon nitride (gCN) compounds are promising materials in photoactivated electrocatalysis thanks to their peculiar structure of periodically spaced voids exposing reactive pyridinic N atoms. These are excellent sites for the adsorption of isolated transition metal atoms or small clusters that can highly enhance the catalytic properties. However, several polymorphs of gCN can be obtained during synthesis, differing for their structural and electronic properties that ultimately drive their potential as catalysts. The accurate characterization of the obtained material is critical for the correct rationalization of the catalytic results; however, an unambiguous experimental identification of the actual polymer is challenging, especially without any reference spectroscopic features for the assignment. In this work, we optimized several models of melem-based gCN, taking into account different degrees of polymerization and arrangement of the monomers, and we present a thorough computational characterization of their simulated XRD, XPS, and NEXAFS spectroscopic properties, based on state-of-the-art density functional theory calculations. Through this detailed study, we could identify the peculiar fingerprints of each model and correlate them with its structural and/or electronic properties. Theoretical predictions were compared with the experimental data whenever they were available.

Highly Efficient Metal-Free Two-Dimensional Luminescent Melem Nanosheets for Bioimaging.

Two-dimensional (2D) luminescent materials have received tremendous attention for their intrinsic properties and promising practical applications. Achieving 2D luminescent materials with high photoluminescence (PL) efficiency is still a great challenge. Here, ultrathin metal-free 2D luminescent nanosheets of 2,5,8-triamino-tri-s-triazine (melem) are synthesized through a facile liquid exfoliation process assisted by ultrasound. The as-obtained melem nanosheets distribute in the size range from a few nanometers to around 150 nm with a thickness of about 5 to 6 atomic layers. Melem nanosheets exhibit efficient blue emission with a PL efficiency as high as 77.09%, much higher than the heavily explored 2D luminescent g-C3N4 nanosheets. The high efficiency of melem nanosheets comes from the absence of atom vacancies and the low carrier mobility. Benefiting from the easy synthesis, good stability, low cell toxicity, and high efficiency, melem nanosheets are successfully applied as bioimaging materials on human breast cancer cells, requiring no extra treatments such as surface coating or functionalization. These metal-free 2D luminescent melem nanosheets hold great potential for various applications including bioimaging and other biorelated applications.

Effect of Aromatic Amines on the Properties of Formaldehyde-Based Xerogels.

This study investigates the synthesis of formaldehyde-based xerogels using alternative aromatic precursors, with comparison to traditional resorcinol-formaldehyde analogues, in order to alter the chemical composition of the resulting gels. By replacing resorcinol with aromatic amine molecules, i.e., ammeline, melamine and melem, each expected to undergo similar reactions with formaldehyde as the substituted species, we found that for all substituted gels, at low additive contents, the gel structure was compromised and non-porous materials were formed, as opposed to the most abundant monomers, and therefore, these additives seem to act as impurities at low levels. Working towards higher additive contents, melem monomers exhibited low solubility (~5%), even at elevated temperatures, thereby limiting the range to which melem could act as a substitute, while melamine could be incorporated up to ~40% under acidic conditions, with enhanced microporosity over this range. Pure gels were successfully synthesised from ammeline, but their performance was inferior to resorcinol-formaldehyde gels, while melamine-formaldehyde analogues required acidic reaction conditions but shrank considerably on sub-critical drying, adversely affecting the gel properties and demonstrating their lack of potential as sorbents. This demonstrates the potential for the inclusion of aminated aromatics within resorcinol-based gel systems, however, only as partial substitutes and not complete replacements.

Synergistic Activation of Palladium Nanoparticles by Polyoxometalate-Attached Melem for Boosting Formic Acid Dehydrogenation Efficiency.

Pd nanoparticles (NPs) anchored on a phosphotungstic acid attached melem porous hybrid (PW/melem) were prepared by hybridization of phosphotungstic acid Pd salt and melem, followed by chemical reduction. PW/melem was demonstrated to be an outstanding support that can stabilize and disperse small Pd NPs (2 nm), and significantly boost their efficiency for H2 generation from the dehydrogenation of formic acid (FA). Experimental results and mechanistic investigations indicate that a strong electronic interaction exists between Pd NPs and the PW anions; the PW anions accept electrons from Pd first and, during FA dehydrogenation, the reduced blue PW donates electrons to Pd. Moreover, melem plays an important role in hydrogen transfer and can accelerate H2 generation. The overall synergistic effect of PW and melem endows Pd NPs with extremely high activity and stability for complete FA conversion at 50 °C, achieving a high turnover frequency of 15 393 h-1 .

A competitive photoelectrochemical immunosensor for the detection of diethylstilbestrol based on an Au/UiO-66(NH2)/CdS matrix and a direct Z-scheme Melem/CdTe heterojunction as labels.

A novel photoelectrochemical (PEC) bioassay protocol for diethylstilbestrol (DES) was systematically proposed. The Au/UiO-66(NH2) hybrid with countless active sites was fabricated using an in situ reduction strategy and was subsequently decorated with CdS nanoparticles (NPs) by a sequential chemical bath deposition process. The resulting Au/UiO-66(NH2)/CdS composites were exploited as a sensing matrix for the first time. The excellent photocurrent response of the as-prepared hybrid under visible light is attributed to its improved photo-electric conversion efficiency due to the local surface plasma resonance (LSPR) effect of Au and the matching energy-level structure between UiO-66(NH2) and CdS. In addition, the competitive strategy for the detection of DES was devised by employing the direct Z-scheme Melem/CdTe heterojunction covalently conjugated with bovine serum albumin (BSA)-DES as signal tags. As a consequence, a cascade-like band-edge level was obtained, which could effectively promote the transfer of photogenerated charges and markedly improve the photocurrent. On the basis of the above strategy, the concentrations of DES could be detected through the competitive binding of DES antibodies (Anti-DES) with either Melem/CdTe/BSA-DES or free DES. Under optimal conditions, the linear range for the detection of DES was 0.1 pg mL-1 to 20 ng mL-1. The detection limit was as low as 0.06 pg mL-1 (S/N = 3). Furthermore, the designed PEC DES-sensing approach has acceptable selectivity, reproducibility, and stability and offers great promise for the detection of small molecules in biomedical, food and environmental samples.

Melem-based derivatives as metal-free photocatalysts for simultaneous reduction of Cr(VI) and degradation of 5-Sulfosalicylic acid.

Carbon nitride has been considered as promising metal-free polymers for low-cost photocatalysis. Most prevailing concern about this fantastic material focuses on g-C3N4, while the potential of other derivatives have been overlooked. Herein, in order to determine the desired derivatives for environmental pollutant treatment, the impact of degree of thermal polymerization on the microstructure of carbon nitride was investigated. Interestingly, melem-based derivatives exhibit 4- and 6-fold enhanced activities than g-C3N4, when used as synergetic photocatalysts for the simultaneous treatment of heavy metal ions and organic contaminants. According to the fundamental study of reactive species formation, a microstructure-dependent photocatalytic mechanism was established. Hydrogen bond-facilitated trapping of photogenerated holes and superior ability for oxygen molecular activation contributed to the high-performance of melem-based derivatives. In contrast, g-C3N4 shows inferior performance during superoxide radical-dominated photodegradation reactions, as its microstructure is favorable for the generation of . Our research not only sheds new insights into the microstructure design of metal-free carbon nitride photocatalysts, but also has immense scientific and technological values for high-efficiency and synergetic environmental applications.

Metal-free melem/g-C3N4 hybrid photocatalysts for water treatment.

In this study, graphitic carbon nitride was engineered to produce metal-free melem/g-C3N4 hybrid photocatalysts through a hydrothermal technique. It was revealed that the hydrothermal treatment of g-C3N4 could produce a hybrid structure of "thorn ball" liked melem on g-C3N4 layer at a high temperature, and was able to modify the photoelectronic properties of g-C3N4. The spectroscopic measurements implied that a melem/g-C3N4 hybrid has better light absorption and lower electron/hole recombination than pristine g-C3N4. Therefore, the melem/g-C3N4 photocatalysts can decompose methylene blue solution under artificial sunlight with a higher rate and also present good stability.