Covalent Bond Formation Research Articles

Advanced prediction of organic–metal interactions through DFT study and electrochemical displacement approach

• 8-AN, 8-MQ, and 8-QSA chimisorbed on Mg(0001) surface via covalent bonds formation. • Upon the formation of coordination complexes between 8-AN and Mg 2+ , energy gap underwent change about ∆ E = 5.7 eV. • 8-AN, 8-MQ, and 8-QSA in their parallel configurations are found to interact strongly with the Mg atoms. • Electron donor effect of 8-AN compound strongly increases its coordination to Mg(0001) surface. • Interaction energies of all geometries follow the electrochemical performance trends. Heterocyclic compounds are the promising biological compounds as nature-friendly for the corrosion protection of metallic surface. In this work, three heterocyclic compounds such as 1-azanaphthalene-8-ol (8-AN), 2-methylquinoline-8-ol (8-MQ), and 8-quinolinol-5-sulfonic acid (8-QSA) were used as green compounds, and their anti-corrosion performance for AZ31 Mg in saline water was discussed on the basis of impedance interpretation and surface analysis. Findings found that the electrochemical performance was improved in the order of 8-AN > 8-MQ > 8-QSA, demonstrating the electron donor effect of N-heterocycles to form coordination complexes on the magnesium surface. From the electrochemical performance, the protective layer constructed at the optimal concentration reinforces the barrier against aggressive environments, with potential inhibition efficiency of 87.4%, 99.0%, and 99.9% for 8-QSA, 8-MQ, and 8-AN, respectively. Quantum chemical parameters and electron density distribution for free organic species in the absence and presence of Mg 2+ cation were evaluated using density functional theory (DFT). Upon the formation of coordination complexes between organic compound and Mg 2+ , energy gap underwent change about ∆ E = 5.7 eV in the 8-AN/Mg 2+ system. Furthermore, the adsorption of heterocyclic compounds on Mg surface reveals the formation of strong covalent bonds with Mg atoms, which further confirmed by the electron density difference and projected density of states analyses. Based on theoretical calculations, three inhibitors can adsorb on the metal surface in both parallel and perpendicular orientations via C, O and N atoms. In the parallel configuration, the C-Mg, N-Mg and O-Mg bond distances are between 2.11 and 2.25 Å, whereas the distances in the case of perpendicular adsorption are between 2.20 and 2.40 Å (covalent bonds via O and N atoms). The results indicated that parallel configurations are energetically more stable, in which the adsorption energies are -4.48 eV (8-AN), -4.28 eV (8-MQ) and -3.82 eV (8-QSA) compared to that of perpendicular adsorption (-3.65, -3.40, and -2.63 eV). As a result, experimental and theoretical studies were in well agreement and confirm that the nitrogen and oxygen atoms will be the main adsorption sites.

An in vivo and in silico evaluation of the hepatoprotective potential of Gynura procumbens: A promising agent for combating hepatotoxicity.

The liver, the most important metabolic organ of the body, performs a wide variety of vital functions. Hepatic cell injury occurs by the activation of reactive oxygen species (ROS) that are generated by carbon tetrachloride (CCl4), xenobiotics, and other toxic substances through cytochrome P450-dependent steps resulting from the covalent bond formation with lipoproteins and nucleic acids. Observing the urgent state of hepatotoxic patients worldwide, different medicinal plants and their properties can be explored to combat such free radical damage to the liver. In vivo and in silico studies were designed and conducted to evaluate the antioxidant and hepatoprotective properties of Gynura procumbens in rats. Gynura procumbens leaves were collected and extracted using 70% ethanol. The required chemicals CCl4, standard drug (silymarin), and blood serum analysis kits were stocked. The in vivo tests were performed in 140 healthy Wister albino rats of either sex under well-controlled parameters divided into 14 groups, strictly maintaining Institutional Animal Ethics Committee (IEAC) protocols. For the histopathology study, 10% buffered neutral formalin was used for organ preservation. Later the specimens were studied under a fluorescence microscope. In silico molecular docking and absorption, distribution, metabolism, excretion, and toxicity (ADMET) studies were performed, and the results were analyzed statistically. Gynura procumbens partially negate the deleterious effect of carbon tetrachloride on normal weight gain in rats. The elevated level of serum glutamate pyruvate transaminase (SGPT), serum glutamate oxaloacetate transaminase (SGOT), alkaline phosphatase (ALP), creatinine, LDH, total cholesterol (TC), low-density lipoprotein (LDL), triglycerides (TG), malondialdehyde (MDA), deoxyribonucleic acid (DNA) fragmentation ranges, gamma-glutamyl transferase (γ-GT) in CCl4 treated groups were decreased by both standard drug silymarin and G. procumbens leaf extract. We have found significant & highly significant changes statistically for different doses, here p<0.05 & p<0.01, respectively. On the other hand, G. procumbens and silymarin displayed Statistically significant (p<0.05) and high significant(p<0.01) increased levels of HDL, CAT SOD (here p<0.05 & p<0.01 for different doses) when the treatment groups were compared with the disease control group. Because the therapeutic activity imparted by plants and drugs accelerates the movement of the disturbed pathophysiological state toward the healthy state. In the molecular docking analysis, G. procumbens phytoconstituents performed poorly against transforming growth factor-beta 1 (TGF-β1) compared to the control drug silymarin. In contrast, 26 phytoconstituents scored better than the control bezafibrate against peroxisome proliferator-activated receptor alpha (PPAR-α). The top scoring compounds for both macromolecules were observed to form stable complexes in the molecular dynamics simulations. Flavonoids and phenolic compounds performed better than other constituents in providing hepatoprotective activity. It can, thus, be inferred that the extract of G. procumbens showed good hepatoprotective properties in rats.

Dual reactivity based dynamic covalent chemistry: mechanisms and applications.

Dynamic covalent chemistry (DCC) focuses on the reversible formation, breakage, and exchange of covalent bonds and assemblies, setting a bridge between irreversible organic synthesis and supramolecular chemistry and finding wide utility. In order to enhance structural and functional diversity and complexity, different types of dynamic covalent reactions (DCRs) are placed in one vessel, encompassing orthogonal DCC without crosstalk and communicating DCC with a shared reactive functional group. As a means of adding tautomers, widespread in chemistry, to interconnected DCRs and combining the features of orthogonal and communicating DCRs, a concept of dual reactivity based DCC and underlying structural and mechanistic insights are summarized. The manipulation of the distinct reactivity of structurally diverse ring-chain tautomers allows selective activation and switching of reaction pathways and corresponding DCRs (C-N, C-O, and C-S) and assemblies. The coupling with photoswitches further enables light-mediated formation and scission of multiple types of reversible covalent bonds. To showcase the capability of dual reactivity based DCC, the versatile applications in dynamic polymers and luminescent materials are presented, paving the way for future functionalization studies.

Ionizing radiation induces cross-linking of two noncovalently bound collagen mimetic peptide triple helices in the absence of a molecular environment.

Cross-linking is a fundamental molecular process that is highly important for many applications, in particular, to tune the properties of collagen-based biomaterials. Chemical reagents, the action of enzymes or physical factors such as heat or radiation can facilitate collagen cross-linking. Ionizing radiation has the advantages of being fast, efficient and free from potentially toxic reagents. Collagen cross-linking by ionizing radiation is thought to occur via a water-mediated pathway. In the past, synthesized collagen mimetic peptides have proven to be of great value for understanding the influence of the amino acid sequence on the stability of tertiary (fibrous) as well as secondary (triple helical) structures of collagen. Cross-linking of synthetic collagen mimetic peptides is often used for modifying the properties of biomaterials. In this work, for the first time, we apply radiation-induced cross-linking to synthetic collagen mimetic peptides and present an experimental and theoretical study of peptide hexamers consisting of two noncovalently bound triple helices in the absence of a molecular environment, i.e. in the gas phase. Our results show that X-ray photoabsorption of the hydroxylated hexamer leads to ionization and cross-linking of the two triple helices: thus, we found evidence that cross-linking can be achieved by ionizing radiation, without the presence of any reagent or water. We propose a cross-linking mechanism involving the creation of two radicals on hydroxyproline side-chains and their recombination, ultimately leading to covalent bond formation between the triple helices.

Formation and fragmentation of 2-hydroxyethylhydrazinium nitrate (HEHN) cluster ions: a combined electrospray ionization mass spectrometry, molecular dynamics and reaction potential surface study.

The 2-hydroxyethylhydrazinium nitrate ([HOCH2CH2NH2NH2]+NO3-, HEHN) ionic liquid has the potential to power both electric and chemical thrusters and provide a wider range of specific impulse needs. To characterize its capabilities as an electrospray propellant, we report the formation of HEHN cluster ions in positive electrospray ionization (ESI) and their collision-induced dissociation. The experiment was carried out using ESI guided-ion beam mass spectrometry which mimics an electrospray thruster in terms of ion emission, injection into a vacuum and fragmentation in space. Measurements include compositions of primary ions in the electrospray plume and their individual dissociation product ion cross sections and threshold energies. The results were interpreted in light of theoretical modeling. To determine cluster structures that are comprised of [HE + H]+ and NO3- constituents, classical mechanics simulations were used to create initial guesses; and for clusters that are formed by reactions between ionic constituents, quasi-classical direct dynamics trajectory simulations were used to mimic covalent bond formation and structures. All candidate structures were subject to density functional theory optimization, from which global minimum structures were identified and used for construction of reaction potential energy surface. The comparison between experimental values and calculated dissociation thermodynamics was used to verify the structures for the emitted species [(HEHN)nHE + H]+, [(HEHN)n(HE)2 + H]+, [(HE)n+1 + H]+ and [(HE)nC2H4OH]+ (n = 0-2), of which [(HE)1-2 + H]+ dominates. Due to the protic nature of HEHN, cluster fragmentation can be rationalized by proton transfer-mediated elimination of HNO3, HE and HE·HNO3, and the latter two become dominant in larger clusters. [(HE)2 + H]+ and [(HE)nC2H4OH]+ contain H-bonded water and consequently are featured by water elimination in fragmentation. These findings help to evaluate ion formation and fragmentation efficiencies and their impacts on electrospray propulsion.

Effect of TNF-Gold Nanoparticles Combination on Kidney and Liver Parameters of Female Mice

Background: Nanomedicine has emerged as a powerful platform for applying nanotechnology in the prevention and treating many diseases. Objective: To investigate the toxicity of designated anti-cancer drugs composed of gold nanoparticles (GNPs), tumor necrosis factor-alpha (TNF-α), and cysteine-Alanine-Leucine-Asparagine-Asparagine (CALNN) peptide on kidney and liver parameters, using animals’ model. Methods: A Combination of TNF-α and CALNN peptide on the surface of GNPs were achieved depending on formation of dative covalent bond between molecules and pH of solutions, which leads to react with active groups of different molecules of nanoparticles, which characterized using ultraviolet visible spectroscopy. Moreover, their effects on kidney and liver blood variables had been examined. These blood values included measurement of the glutamic oxaloacetic transaminase, glutamic pyruvic transaminase and alkaline phosphatase, creatinine, and urea levels after intraperitoneal injection of an anti-cancer drug in female albino mice. Results: Overall, the results indicated that there was no significant change in the concentration of different biochemical values between treated and control groups. Conclusion: The results suggest that GNPs-TNF-α-CALNN combination have no harmful impact on kidney and liver organs of tested mice. Keywords: Nanomedicine, GNPs, TNF-α, CALNN peptide, drug delivery, cytotoxicity Citation: Abood NA, Kadhim HS, Jabir MS. Effect of TNF-gold nanoparticles combination on kidney and liver parameters of female mice. Iraqi JMS. 2022; 20(2): 245-251. doi: 10.22578/IJMS.20.2.12

Enhanced strength without sacrificing ductility in FeCrMnVSix high entropy alloys via controlling the ratio of metallic to covalent bonding

It has been the pursuit of materials science to enhance strength without sacrificing the ductility of a material. By introducing the semi-metallic Si into the FeCrMnV high-entropy alloy (HEA) to control the ratio of metallic and covalent bonding, we obtained a FeCrMnVSix HEAs with high strength and favorable ductility from the perspective of interatomic bonding. First-principles calculation was employed to calculate the structural model, electronic environment, and mechanical properties. The theoretical calculations demonstrated that the covalent bonding had been obtained in the FeCrMnV HEA consisting of metallic bonding due to the addition of Si. Under the guidance of theoretical calculation, FeCrMnVSix HEAs were successfully prepared by laser cladding on 1Cr13 steel substrate. The nanoindentation, Vickers microhardness, and tensile tests were performed, and the results indicated that the strength of HEA was enhanced without sacrificing ductility. In addition, the as-prepared Si-containing HEA coatings exhibited excellent tribological properties. The mechanism of simultaneous formation of metallic and covalent bonds on the mechanical properties was analyzed. The enhanced strength without sacrificing ductility in FeCrMnVSix HEAs is attributed to the proper combination of metallic and covalent bonding, the metallic bonding facilitates favorable ductility while the covalent bonding contributes to excellent strength.

The role of organoclay in the diffusion of epoxy‐amine oligomers and in the cross‐linking density of the resulting network

AbstractEpoxy nanocomposites are promising for adhesive applications due to their high performance. In this work, an organoclay (PO), prepared by cationic exchanging using a quaternary phosphonium salt or a silylated PO (SPO) was added to an epoxy‐amine resin‐based adhesive to reduce its dripping. PO and SPO were dispersed in the epoxy network on a nanometric scale, mainly in an intercalated structure. A liquid‐to‐gel transition occurs at 4–6 wt% PO due to forming a continuous organoclay network throughout the epoxy volume, eliminating its dripping. The PO addition accelerates the curing reaction initially, and cured nanocomposites with over 3 wt% PO show a drastic reduction in the glass transition temperature (Tg). Moreover, a broadening of the secondary relaxation observed by DMA indicates an interaction between the epoxide‐amine oligomers with the silicate surface. This interaction, associated with forming a continuous organoclay network at 4–6 wt% PO, reduces the epoxy‐amine oligomers diffusion, resulting in their partial curing and consequent Tg decreasing. EPOXY_SPO nanocomposites show Tg values similar to or higher than that observed for the epoxy‐amine network attributed to the forming of covalent bonds between the glycidyloxypropyl end groups in the SPO surface and the hardener amine.

Effect of graphene on tribology, mechanical, and thermal properties of flax/E‐glass/epoxy hybrid nanocomposites

AbstractPolymer nanocomposites have received significant attention in the tribology and mechanical application due to their exceptional wear resistance, which cannot be expected in polymers. This study, involves preparation and fabrication of graphene hybrid (flax/E‐glass/epoxy) fiber‐reinforced polymer (HFRP) composites using compression molding. A study of the effect of graphene on the microhardness and wear behavior of HFRP composites was made using pin‐on‐disk tests at three different loads of 5, 10, and 15 N as per ASTM standards. Compared to HFRP composites, graphene in HFRP composites exhibits a distinguished enhancement in thermal stability, microhardness and tribological performance due to the formation of strong covalent bonds between graphene and epoxy matrix. Surface features were observed using a scanning electron microscope (SEM). The addition of graphene (0.0–1.2 wt%) to the matrix, especially 0.6 wt% of graphene in HFRP composites revealed extraordinary tribological properties, with a 35% decrease in the friction coefficient and wear rate under abrasive wear conditions. The result of the graphene in HFRP composites looks promising in wear‐resistant materials and other high‐performance areas in the automobile and aerospace industry.

A model study on the site-specificity of (−)-epicatechin-induced reactions in β-lactoglobulin by high-resolution mass spectrometry in combination with bioinformatics

Polyphenol–protein reactions in model solutions of β-lactoglobulin (β-LG) incubated with (−)-epicatechin at 37 °C and 60 °C were monitored by microLC–timsTOF Pro-MS/MS combined with bioinformatics strategies. The addition of (−)-epicatechin to the model solutions resulted in changes in tryptic peptide profiles. Covalent bond formation between (−)-epicatechin o-quinones and β-LG was identified for the residues S27, S30, K60, C66, K69, and C160, with C160 being the predominant binding site. Furthermore, the incubation of β-LG with (−)-epicatechin significantly promoted oxidation, especially for the residues M7 and M24. The reaction of monomeric (−)-epicatechino-quinone at C160 was also identified in the milk chocolate sample. The adaptation of this study by extending the scope of the reaction products offers significant potential for comprehensive food profiling strategies.

Semiconductor-metal transition in vulcanized NiCo2O4 film

The effects of vulcanization on the electrical transport properties and magnetic structure of NiCo2O4 were studied in this work. NiCo2O4 films were epitaxially grown on Al2O3 substrate, and then vulcanized. The NiCo2O4 structures with O replaced by S atoms were calculated based on the density functional theory. As O were replaced by S atoms, the orbital overlap between S and cations increases, the localized electrons around cations are transformed into collective electrons, and the conductive behavior of the film changes from semiconductor to metal. The formation of covalent bonds caused by S substitution leads to the weakening of the interaction between tetrahedral Co and octahedral Ni ions. Meanwhile, the d-orbital energy level of cations shifts. The spin direction of Ni ions and half tetrahedral Co ions is flipped in the vulcanized NiCo2O4 structure, and the electrons at Ni3+eg level enter the conduction band, which makes the carrier type of the vulcanized NiCo2O4 film change from p to n-type. These results indicate that S atoms play an active role in improving the conductivity of NiCo2O4.

Advanced Biomimetic Soybean Meal-Based Adhesive with High Strength and Toughness

Phenol–amine synergy and mineral reinforcement collectively provide excellent mechanical properties to insect exoskeletons. An advanced soybean meal (SM)-based adhesive, inspired by the insect sclerotization, was developed by integrating tannic acid-functionalized graphene (TA@G), amino-terminated hyperbranched aromatic polyether (HBAP) and SM. TA@G was simultaneously produced and functionalized in a green manner (tannic acid-assisted ball milling), and the active surface of TA@G led to excellent dispersion in the adhesive matrix. HBAP provided numerous reaction sites for the construction of phenol–amine cross-linking network. The dry/wet shear strengths and adhesion work of SM/HBAP/TA@G reached up to 2.59 MPa, 1.29 MPa, and 0.262 J, which were 65.0%, 95.5%, and 66.9% higher than the pure SM (PSM) adhesive, respectively. Compared with PSM, the residual rate of SM/HBAP/TA@G increased to 72.8% from 61.4%, demonstrating enhanced water resistance. The results indicated that more covalent bonds were generated in the adhesive system, which was attributed to the Schiff base reaction and Michael addition between TA@G and HBAP. The formation of massive covalent bonds and the natural waterproof barrier of graphene resulted in a remarkable improvement in SM-based adhesives. Therefore, this simple bionic design strategy provided a novel approach to developing super bioadhesives for the wood industry and could advance the development of tough and strong composites.

Design and synthesis of ether derivatives of spliceostatin A and their biological evaluation towards prostate cancer treatment

To confirm the hypothesis that the terminal epoxide structure of spliceostatin A may be active through hydrogen bond formation, we designed and synthesized novel ether derivatives of spliceostatin A, whose terminal epoxide is replaced with an ether-based moiety capable of hydrogen bond formation. The results of biological evaluation against AR-V7 and the conformational analysis of each derivative suggest that the terminal epoxide moiety of spliceostatin A expresses its activity through covalent bond formation rather than hydrogen bond formation.

Quantitative Analysis and Optimization of Site-Specific Protein Bioconjugation in Mammalian Cells.

Despite a range of covalent protein modifications, few techniques exist for quantification of protein bioconjugation in cells. Here, we describe a novel method for quantifying in cellulo protein bioconjugation through covalent bond formation with HaloTag. This approach utilizes unnatural amino acid (UAA) mutagenesis to selectively install a small and bioorthogonally reactive handle onto the surface of a protein. We utilized the fast kinetics and high selectivity of inverse electron-demand Diels-Alder cycloadditions to evaluate reactions of tetrazine phenylalanine (TetF) with strained trans-cyclooctene-chloroalkane (sTCO-CA) and trans-cyclooctene lysine (TCOK) with tetrazine-chloroalkane (Tet-CA). Following bioconjugation, the chloroalkane ligand is exposed for labeling by the HaloTag enzyme, allowing for straightforward quantification of bioconjugation via simple western blot analysis. We demonstrate the versatility of this tool for quickly and accurately determining the bioconjugation efficiency of different UAA/chloroalkane pairs and for different sites on different proteins of interest, including EGFP and the estrogen-related receptor ERRα.

Crosslinked poly (vinyl alcohol) composite reinforced with tunicate, wood, and hybrid cellulose nanocrystals: Comparative physicochemical, thermal, and mechanical properties

The development of sustainable and biodegradable composites has gained increasing attention in recent years. Effective interaction and adhesion between polymers and fillers are crucial. In this study, the effect of different aspect ratios of cellulose nanocrystals (CNCs) and their hybrid within a crosslinked poly (vinyl alcohol) (PVA) nanocomposite has been investigated to develop biodegradable materials. The physicochemical, thermal, and mechanical properties of the specimens have been studied. SEM images indicate that the addition of CNC reduced the porosity of the films. The XPS results confirmed the significant formation of covalent bonds for all composites except those reinforced with wood-CNC, which showed a lower amount of crosslinking and CC formation. EDS maps reveals that the dispersity of the CNCs could be different depending on the aspect ratio of the CNCs. Results from the solubility in water (SW) tests indicated that the use of hybrid-CNC in a crosslinked system decreased the SW significantly. The crosslinking and addition of CNC to the PVA composite led to improved mechanical properties. Elongation at break (EB) decreased significantly for the crosslinked hybrid-CNC nanocomposite. Overall, the results of this study indicate that the aspect ratio of CNCs as fillers in nanocomposites may contribute to their physicochemical, mechanical, and thermal properties for the development of biodegradable materials.

Antifouling zwitterionic peptide hydrogel based electrochemical biosensor for reliable detection of prostate specific antigen in human serum

An electrochemical biosensor based on the antifouling zwitterionic peptide hydrogel (CFEFKFC) and the poly(3,4-ethylenedioxythiophene) (PEDOT) was fabricated to accurately detect prostate specific antigen (PSA) in complex human serum. The electrode was modified with the conducting polymer PEDOT and gold nanoparticles (AuNPs) in sequence through electrodeposition, and then the designed zwitterionic peptide hydrogel prepared through self-assembly was immobilized onto the modified electrode surface via the Au–S bond. The zwitterionic peptide hydrogel with cysteine terminal is easy for immobilization onto the gold surface, and it is also suitable for the immobilization of biomolecules such as PSA antibody in this work, through the formation of covalent amide bonds. The peptide hydrogel possessed excellent antifouling property, and it was able to effectively prevent the adsorption of nonspecific proteins, cells and other biomolecules. The developed antifouling biosensor showed a linear response range from 0.1 ng mL−1 to 100 ng mL−1, with a low limit of detection down to 5.6 pg mL−1. These results encourage the wide use of zwitterionic peptide hydrogels as antifouling materials in various sensing and bio-sensing devices.

Hyaluronic Acid in Biomedical Fields: New Trends from Chemistry to Biomaterial Applications.

The aim of this review is to give an updated perspective about the methods for chemical modifications of hyaluronic acid (HA) toward the development of new applications in medical devices and material engineering. After a brief introduction on chemical, structural and biological features of this important natural polysaccharide, the most important methods for chemical and physical modifications are disclosed, discussing both on the formation of new covalent bonds and the interaction with other natural polysaccharides. These strategies are of paramount importance in the production of new medical devices and materials with improved properties. In particular, the use of HA in the development of new materials by means of additive manufacturing techniques as electro fluid dynamics, i.e., electrospinning for micro to nanofibres, and three-dimensional bioprinting is also discussed.

Mitotic Perturbation Is a Key Mechanism of Action of Decitabine in Myeloid Tumor Treatment

Background: Decitabine (DAC) is one of the first generation of epigenetic drugs used clinically to treat myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). Historically, DAC was considered as a cytotoxic agent when it was first developed in the 1960s. Subsequent studies in 1980s showed that DAC can induce DNMT1 degradation and DNA hypomethylation at non-cytotoxic concentration. Since then, DNA demethylation has been considered as the main mechanism of action of DAC. The DAC-induced DNA hypomethylation was shown to induce upregulation of tumor suppressor genes or endogenous retroviruses, which could contribute to the antitumor effect of DAC. Recently, DAC was also shown to be effective even in MDS and AML with TP53 mutations. However, it remains unclear why myeloid tumors, especially those with TP53 mutations, are particularly susceptible to DAC treatment. Methods: Cancer Dependency Map (DepMap) database was used to evaluate in vitro sensitivity of human cancer cell lines to DAC. To identify essential genes that regulate sensitivity of myeloid tumors to DAC, we performed a genome-wide CRISPR-dCas9 activation screen using murine MDS/AML cells expressing ASXL1 and SETBP1 mutants (cSAM cells). After transduction of mouse genome-wide CRISPRa-v2 library, cSAM cells were cultured with DMSO or DAC for 1 week. We extracted genomic DNA from the cells at the start and end of our screen and quantified the relative representation of each sgRNA. To assess the effect of DAC on mitosis, we established the time-lapse system optimized for non-adherent MDS-L-2007 cells (a human secondary AML (sAML) cell line derived from an MDS cell line, MDS-92). Results: We first explored DepMap database and found that myeloid tumors are susceptible to DAC at clinically achievable concentration, while most solid tumor cell lines are not. The CRISPR/dCas9-activation screen revealed that genes involved in chromosome segregation, including Cdk1, Cdc20, Cdca8 and Dsn1, were significantly enriched in DAC-resistant cells, indicating that overexpression of mitotic regulators conferred resistance to DAC in cSAM cells. We also found that DAC strongly induced aneuploidy and polyploidy (>4n) in myeloid tumors, especially in those with TP53 mutations and sAML cells. Furthermore, the time-lapse imaging revealed that DAC treatment prolonged the duration of metaphase and increased multipolar mitosis and abscission failure in MDS-L-2007 cells (Figure). Thus, DAC perturbs mitosis and has cytotoxic effects at low concentrations in myeloid tumors. Next, we assessed the role of DNMT1 in the DAC-induced mitotic defects in myeloid tumors. To our surprise, the DAC-induced aneuploidy and apoptosis were markedly attenuated in DNMT1-depleted myeloid tumors. In contrast, overexpression of Dnmt1 increased sensitivity of myeloid tumors to DAC. These results indicate that DAC perturbs mitosis not through DNMT1 degradation and subsequent DNA demethylation, but through DNMT1 itself in myeloid tumors. In line with this, chromatin-bound DNMT1 protein was retained even with DAC, whereas DAC induced rapid degradation of DNMT1 in the nucleoplasm fraction. Importantly, the Dnmt1-C1229A mutant, which loses the ability to induce DNMT1-DNA covalent bond formation, did not enhance the DAC-driven mitotic defects. In addition, DAC treatment increased frequency of cohesion loss between sister chromatids in MDS-L-2007 cells, as evidenced by the absence of centromere connection of sister chromatids at metaphase. Moreover, the in vitroXenopus cell-free system which reproduces replication-dependent DNA methylation maintenance revealed that addition of 5-aza-dCTP strongly promoted chromatin binding of DNMT1, while it inhibited that of cohesion complex members (SMC3 and SCC1). Taken together, these results strongly indicate that the aberrant DNMT1 retention on chromatin induced by DAC leads to cohesion loss and mitotic defects in myeloid tumors. Conclusion: These findings challenge the current assumption that DAC inhibits leukemogenesis by inducing DNA hypomethylation. Rather, the anti-leukemia effect of DAC is likely mediated mainly by the non-epigenetic mechanism: mitotic perturbation through aberrant DNMT1-DNA covalent bonds and cohesion loss of sister chromatids. Our study also suggests that DAC will be most effective on tumors with impaired mitotic fidelity, such as AML and MDS with TP53 mutations. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Opto-electronic properties of carbon doped NiO

Hybrid functional first principles calculations reveal the effects of substitutional carbon on electronic and optical properties in the anti-ferromagnetic configuration of NiO. Spin polarized projected density of states and unfolded band structures show electronic band edge modification and magnetic anisotropy due to carbon substituting both at nickel and oxygen sites; only carbon substituted at an oxygen site, however results in the emergence of inter-band gap impurity states. This is due in part to the steric differences between carbon substituting nickel vs oxygen as well as the difference in valence between carbon and oxygen. Carbon substituting nickel is more stable than substituting oxygen, with a lower formation energy both in O-rich and O-poor conditions. Charge density isosurface plots reveal that carbon substituting nickel does not result in any appreciable modification to the bonding profile around the substitution, while oxygen substitution results in the formation of covalent bonds between the carbon and the nearest nickel atoms. Substitutional carbon at either the nickel or oxygen site causes a red shift in all optical properties towards the visible light region. The anisotropy in the optical and electronic properties for both carbon substitution at nickel and oxygen sites implies that these properties may be tuned through carbon doping and oxygen growth control for transparent conducting oxide and optoelectronic device applications.

Imine and imine-derived linkages in two-dimensional covalent organic frameworks.

Covalent organic frameworks (COFs) are porous crystalline polymers that result from the formation of covalent bonds between precisely assembled organic units. Linkage chemistry is a crucial factor in the controllable synthesis andresulting physicochemical properties of COFs. Imine linkages are popular in the formation of polyfunctional two-dimensional (2D) COFs because they are formed easily with structural and functional diversity. There has beenmuch recent interest in expanding beyond this to COFs with imine-derived linkages. This review highlights the development of chemistry to modify and prepare derivatives of imines within 2D COFs. We discuss the derivation of imine bonds via covalent and noncovalent bonding and the properties and potential applications of the resulting materials in order to provide a better understanding of the relationship between covalent linkages and overall performance for 2D COF materials.