Heterocyclic Nitrogen Atom Research Articles

Synthesis, characterization and anticancer activity of zinc sulfide nanoparticle using heterocyclic Zn (II) thiosemicarbazone complex as a single source

The green synthesis of zinc sulphide nanoparticles (Zn S NPs) using Zn(II) complex as a single molecular precursor is gaining importance due to its simplicity, cost – effectiveness and pharmacologically active nature. Now – a- day’s nanobiotechnolgy is increasing at a fast rate due to its many possible applications in the biomedical and, pharmaceuticals fields. In this paper, we have reported the synthesis of Chalcogenide nanostructured pharmacologically active Zn S nanoparticles using Zn (II) Heterocyclic thiosemicarbazone Complex as a Single Source. Zn (II) complex was synthesized by the reaction between Schiff base ligand and Zinc acetate salt in 2:1 molar ratio. Thiosemicarbazone have a wide clinical antitumor spectrum with efficacy in various tumor types such as leukemia, pancreatic cancer, breast cancer, non- small cell lung cancer, cervical cancer, prostate cancer and bladder cancer. These compounds possessed significant antineoplastic activity when the carbonyl group attachment of the side chain was located at a position alpha to the heterocyclic nitrogen atom, whereas attachment of the side chain ꞵ or gamma to the heterocyclic nitrogen atom, resulted in inactive antitumor agents. In addition, replacement of the heterocyclic ring N with carbon also resulted in a biologically inactive compound suggesting that a conjugated N, N, S -tridentate donor set is essential for the biological activities of thiosemicarbazone ligands. In our study, for synthesis of Zn S nanoparticles, the synthesized Zn(II) complex of thiosemicarbazone ligand was treated with aqueous extract of Parmotrema perlatum flowers. The use of aqueous extract of Parmotrema perlatum flowers in the synthesis of ZnS particles plays a very important role in reducing reaction time, reducing minimum possibility of side reactions and conversion of metal complexes into its nanoparticles in a very less time. All synthesized compounds were characterized by various structural, morphological, electronic and vibrational spectroscopic techniques and also evaluate the pharmacological activities of compounds like antioxidant, anti-inflammatory and anticancer activities. The peaks at 3414.82 cm-1 in FT-IR spectra confirms the presence of –OH groups and other bioactive agents in the aqueous extract of Parmotrema perlatum flowers, which acts as a capping and stabilizing agents in the synthesis of Zn S nano particles. The effective results of anti-cancer activity of compounds showed that the ZnS nanoparticles shows good cytotoxic activity against human breast cancer cell lines (MCF-7) using MTT assay. In this study, normal human cell lines used as standard for comparison purpose. The CTC50 values of ZnS nanoparticles was found to be 49.375µg/ml respectively. Therefore, it could be concluded that this biogenic method is effective for synthesis of Zn S nanoparticles from Zn(II) complex with desirable properties for potential biomedical applications which can be consider as a good drug candidate for anti-cancer therapy

5-Diazo Dihydrouracils: Preparation and Some Transformations.

An approach to a new type of diazo reagents─diazo dihydrouracils─has been developed, and various transformations of the obtained diazo heterocycles have been studied, demonstrating their high synthetic potential for obtaining structurally diverse derivatives based on the privileged dihydrouracil scaffold. The X-H insertion reactions provide high yields of a variety of 5-substituted dihydrouracils. Cyclopropanation and 1,3-dipolar cycloaddition reactions involving a carbonyl ylide intermediate have been carried out to give spiro-annulated derivatives. The limitations of the modification methods with respect to the nature of substituents on the nitrogen atoms of the diazo heterocycle have been outlined.

Synthesis, Structure, and Properties of a Copper(II) Binuclear Complex Based on Trifluoromethyl Containing Bis(pyrazolyl)hydrazone.

A new complex of copper(II) with methyl-5-(trifluoromethyl)pyrazol-3-yl-ketazine (H2L) was synthesized with the composition [Cu2L2]∙C2H5OH (1). Recrystallization of the sample from DMSO yielded a single crystal of the composition [Cu2L2((CH3)2SO)] (2). The coordination compounds were studied by single-crystal X-ray diffraction analysis, IR spectroscopy, and static magnetic susceptibility method. The data obtained indicate that the polydentate ligand is coordinated by both acyclic nitrogen and heterocyclic nitrogen atoms. The cytotoxic activity of the ligand and complex 1 was investigated on human cell lines MCF7 (breast adenocarcinoma), Hep2 (laryngeal carcinoma), A549 (lung carcinoma), HepG2 (hepatocellular carcinoma), and MRC5 (non-tumor lung fibroblasts). The complex was shown to have a pronounced dose-dependent cytotoxicity towards these cell lines with LC50 values in the range of 0.18-4.03 μM.

Synthesis and characterization of novel quinaldic acid based Ni, Fe, and Cr Complexes: A computational and experimental study

Complexes ([Ni(quin-2-c)2(H2O)2]•2H2O, [Fe(quin-2-c)2(H2O)2], [Cr(quin-2-c)2(H2O)2] were synthesized from aqueous solutions of metal salts, quinaldic acid, and semicarbazide. In the crystal structure of the first complex, the nickel atom is chelated by the deprotonated quinaldic acid molecule through the oxygen atom of the carboxyl group, and the heterocyclic nitrogen atom, as well as two water molecules, are coordinated. The other two water molecules are located in the outer sphere. In the structure of the iron and chromium complexes, the metal atoms have a similar complex formation but do not have water molecules in the outer sphere. In all compounds, quinaldic acid acts as a bidentate ligand to form five-membered metallocycles. The electronic structure properties were investigated through theoretical modeling using the B3LYP method at the 6–31 + G(d,p) computational level. Density functional theory (DFT) was employed in quantum chemistry simulations to refine proposed structures and explore the characteristics of frontier orbitals via analysis of frontier molecular orbitals (FMOs). These computations facilitated the identification of specific sites on the surface of molecules by generating molecular electrostatic potential maps and provided insights into the structural and reactive properties. Hirshfeld surface analysis was conducted to examine intermolecular interactions, revealing a prevalence of H⋅⋅⋅H interactions.

Control over rotary motion and multicolour switching in 3-hydroxyphthalimide fluorophores: An interplay between AIE and ESIPT

In this paper, we demonstrate the ability of N-substituted 3-hydroxyphthalimides with pyridine and isoquinoline rings to perform multicolour switching by different stimuli. Restriction of the C–N rotary motion of the heterocycles allows control over their photoluminescence performance (PLQY = 54–65%) in water-induced aggregation by an additive interplay of excited-state proton-mediated processes in the aggregates. Restriction of the rotations by the affinity of the heterocyclic nitrogen atoms to Zn2+ and switching to new emission bands (PLQY = 8–29%) in solution and solid state were also achieved. Protonation of the pyridine/isoquinoline rings allows the formation of intramolecular hydrogen bonds with the imide carbonyl groups, resulting in restricted rotations. The protonated forms switch to strong blue emission due to local excitation of the protonated heterocycles, which are unable to undergo proton transfer. Understanding the interplay between both photophysical processes would allow the switching of emissions by multistimuli.

Excitation wavelength dependent S1-state decay dynamics of 2-aminopyridine and 3-aminopyridine.

The decay dynamics of 2-aminopyridine and 3-aminopyridine excited to the S1 state is investigated using femtosecond time-resolved photoelectron imaging. The lifetime of the S1 state for both molecules shows a rapid decrease with the increase of the vibrational energy. It is shown that, besides intersystem crossing to the lower-lying triplet state of T1, the decay to the ground state (S0) via internal conversion through a conical intersection plays an increasingly important role and becomes dominant for vibrational states well above the S1 state origin. The comparison between 2-aminopyridine and 3-aminopyridine suggests that the intramolecular hydrogen bonding between a hydrogen atom of the NH2 group and the heterocyclic nitrogen atom in 2-aminopyridine effectively hinders the ring deformation at lower vibrational states which is required for the wavepacket to reach the S1/S0 conical intersection, and therefore slows down the S1 to S0 internal conversion.

Pyridine‐2(1H)‐thione as a Bifunctional Nucleophile in Reaction with PdII and PtII Aryl Isocyanide Complexes

AbstractA method for obtaining C,S‐cyclometalated deprotonated diaminocarbene complexes via the addition of a bifunctional N,S‐nucleophile's endocyclic nitrogen atom to a coordinated isocyanide has been extended to the reactions with pyridine‐2(1H)‐thione. The coupling of PdII‐ and PtII‐bis(arylisocyanide) complexes with pyridine‐2(1H)‐thione leads to the formation of mononuclear C,S‐cyclometalated deprotonated diaminocarbene complexes in 90–96 % yield. The reaction proceeds via the initial coordination of the thione sulfur atom to the metal center followed by the intramolecular nucleophilic addition of the heterocyclic nitrogen atom to the metal‐ligated isocyanide carbon. Using an excess of pyridine‐2(1H)‐thione in this reaction leads to the formation of a mono‐C,S‐cyclometalated complex with a pendant mercaptopyridine ligand which is involved in the reversible intramolecular nucleophilic addition of the pyridine nitrogen to the isocyano carbon. The obtained complexes were characterized by elemental analysis, mass spectrometry, IR and NMR spectroscopies, and single‐crystal X‐ray diffraction.

Synthesis, Molecular and Supramolecular Structure Aspects, and Antimicrobial Activity of the Centrosymmetric [Ag(5-Nitroquinoline)2]ClO4 Complex

The new homoleptic [Ag(5-nitroquinoline)2]ClO4 centrosymmetric complex was synthesized and its structure aspects were investigated. It crystallized in the monoclinic space group C2/c with a = 10.0279(2) Å, b = 13.2295(3) Å, c = 14.7552(3) Å and β = 102.1050(10)° while V = 1913.96(7) Å3 and half molecule as asymmetric formula. The Ag(I) is coordinated with two symmetrically related 5-nitroquinoline ligand units via the heterocyclic nitrogen atom with Ag-N distance of 2.146(6) Å and N1-Ag-N1 angle of 173.0(3)°. The two coordinated 5-nitroquinoline have anti configuration to one another and the perchlorate anion is set freely uncoordinated. The only Ag…O interactions are Ag1…O2 (3.110 Å) and Ag1…O1 (3.189 Å) which occur between the Ag(I) in one complex unit and the O-atoms from the NO2 groups in the neighbouring complex units. Hence, Ag(I) has coordination number 2 and its coordination geometry is slightly bent. Hirshfeld analysis indicated that the O…H (51.1%), C…H (11.8%), H…H (10.8%) and C…C (8.9%) contacts are the most common. Exclusively, the O…H, C…O, N…O, O…O and Ag…O contacts are the only shorter contacts than the vdWs radii sum of the interacting atoms. The studied Ag(I) complex showed good antimicrobial activity. It has comparable antibacterial activity against P. vulgaris (MIC = 9.7 μg/mL) and S. aureus (39.1 μg/mL) to Gentamycin (4.8 and 9.7 μg/mL, respectively) while better antifungal activity against A. fumigatus (MIC = 39.1 μg/mL) than Ketoconazole (156.2 μg/mL).

Highly selective and sensitive detection of mercury (II) and dopamine based on the efficient electrochemiluminescence of Ru(bpy)32+ with acridine orange as a coreactant

Developing highly specific, rapid, and cost-effective electrochemiluminescence (ECL) methods capable of detecting multiple analytes remains a compelling research goal but it is still a substantial challenge due to narrow choice of ECL systems. In this study, efficient ECL detections were achieved by using anodic Ru(bpy)32+-acridine orange (AO) ECL system. In present system, dimethylamino substituent on acridine ring acts as active sites for strong ECL generation, while heterocyclic nitrogen atom (–N–) contributes to specific complex formation with metal ion. Accordingly, this anodic ECL method was exploited for highly sensitive detection of both mercury (II) (Hg2+) and dopamine (DA), with detection limits as low as 0.36 nM (linear range 0.01–50 μM) and 1.0 nM (linear range 0.01–10 μM), respectively. The mechanism of Hg2+ detection was supported by density functional theory (DFT) calculations. Notably, the ECL method exhibit superior selectivity over numerous competing interfering agents. Moreover, the method achieved the detection of both targets in practical media with excellent recoveries (96.0–103.8%). Importantly, the method demonstrates potential advantages in terms of selectivity, sensitivity, rapidity, simplicity, and low cost. This work realizes a successful attempt to further expand the analytical applications of ECL systems and may initiate new thoughts in utilizing acridines in diverse ECL-based sensing and imaging applications.

SYNTHESIS AND STRUCTURE OF HETEROMETALLIC – MIXED-LIGAND Ge(IV) – 3d-METAL COMPLEXES WITH GALLIC ACID AND 1,10-PHENANTHROLINE

Authors have developed optimal conditions and synthetic methods in water-organic solutions for ten heterometallic – mixed-ligand complexes of germanium(IV) and 3d-metals with gallic acid (Н2Gal) and 1,10-phenanthroline (phen), their composition and structure [M(phen)3][Ge(H2O)(HGal)2]∙nH2O (M = Mn (1), Co (2), Ni (3), Zn(5)); [CuCl(phen)2]2[Ge(H2O)(HGal)2]∙2H2O (4). Comparative analysis of their IR-spectra and spectra gallic acid and 1,10-phenanthroline with involvement diffuse reflection spectra allowed to establish coordination sphere of germanium and 3-metals. IR-spectra of complexes 1-5 are similar, therefore coordination of ligands in them is the same. Comparatively to the IR-spectrum of gallic acid, there are absent valence absorption bands of free carboxylic groups while two bands of asymmetric and symmetric oscillation of C-O groups in carboxylate ions CОО- appear in the spectra of complexes. Deformation bands d(Сarom-О-Н) are shifted to the low-frequency region for 50-40 cm-1, which indicates deprotonation and binding to the complexing agent of OH-groups from gallic acid. Appearance of deformation bands d(H2О) at 1625 сm-1 is characteristic for the coordination water in composition of complexes. Presence of coordination and crystalline water as well as unbonded OH-group are confirmed with the band n(Ge-О) at 620 сm-1. Thermal decomposition of mixed-metal complexes starts with an endothermic effect in the temperature range 80-160°С where elimination of certain number of water molecules takes place: two – for 1 and 4, three – for 2 and 5, four – for 3. On the thermogravigrams of all compounds one more endoeffect in the temperature range 160-220°С is presented, where removal of one coordination water molecule happens. It was established, that coordination polyhedron of germanium was formed by five oxygen atoms of deprotonated hydroxyl groups from two molecules of gallic acid and one water molecule in all compounds. Second ligand – 1,10-phenanthroline is coordinated to 3d-metal through heterocyclic nitrogen atoms with formation of cations with different composition [M(phen)3]2+ (M = Mn, Co, Ni, Zn) та [CuCl(phen)2]+.

Energy and reactivity profile and proton affinity analysis of rimegepant with special reference to its potential activity against SARS-CoV-2 virus proteins using molecular dynamics

Rimegepant is a new medicine developed for the management of chronic headache due to migraine. This manuscript is an attempt to study the various structural, physical, and chemical properties of the molecules. The molecule was optimized using B3LYP functional with 6-311G + (2d,p) basis set. Excited state properties of the compound were studied using CAM-B3LYP functional with same basis sets using IEFPCM model in methanol for the implicit solvent atmosphere. The various electronic descriptors helped to identify the reactivity behavior and stability. The compound is found to possess good nonlinear optical properties in the gas phase. The various intramolecular electronic delocalizations and non-covalent interactions were analyzed and explained. As the compound contain several heterocyclic nitrogen atoms, they have potential proton abstraction features, which was analyzed energetically. The most important result from this study is from the molecular docking analysis which indicates that rimegepant binds irreversibly with three established SARS-CoV-2 proteins with ID 6LU7, 6M03, and 6W63 with docking scores − 9.2988, − 8.3629, and − 9.5421 kcal/mol respectively. Further assessment of docked complexes with molecular dynamics simulations revealed that hydrophobic interactions, water bridges, and π–π interactions play a significant role in stabilizing the ligand within the binding region of respective proteins. MMGBSA-free energies further demonstrated that rimegepant is more stable when complexed with 6LU7 among the selected PDB models. As the pharmacology and pharmacokinetics of this molecule are already established, rimegepant can be considered as an ideal candidate with potential for use in the treatment of COVID patients after clinical studies.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00894-021-04885-z.

Heterocyclic Bridgehead Nitrogen Atom System: Review on [1,2,4] Triazolo[3,4-b] [1,3,4] thiadiazole and Its Pharmacological Screening.

There has been considerable interest in the development of novel anticonvulsant compounds, , analgesic, anti-inflammatory, antimicrobial, antimycobacterial, antitumour, and antitubercular activities. 1,3,4-thiadiazole constitute Significant class of compounds for new drugs development. They Have an interesting pharmacophore displaying a wide range of pharmacological activity. The 1,3,4-thiadiazole compound is an interesting heterocycle. A group that was used to synthesise a variety of useful bioactive compounds. The stability of the thiadiazole nucleus has inspired the medicinal chemist to perform various structural variations in the ring. Marketed drugs such as acetazolamide and methazolamide have shown their therapeutic potential Therefore, many researchers have identified these compounds as target structures and evaluated their biological activities. This review highlights the different pharmacological activities associated with the 1,3,4-thiadiazole ring system.

Tunable Covalent Organic Frameworks with Different Heterocyclic Nitrogen Locations for Efficient Cr(VI) Reduction, Escherichia coli Disinfection, and Paracetamol Degradation under Visible-Light Irradiation.

Covalent organic frameworks (COFs) have great application potentials in photocatalytic water treatment. By using p-phenylenediamine with different numbers and locations of heterocyclic nitrogen atoms as a precursor, five types of COFs with different nitrogen positions were synthesized. We found that Cr(VI) photoreduction,Escherichia coli inactivation, and paracetamol degradation by COFs were heterocyclic nitrogen location-dependent. Particularly, the photocatalytic performance for all three tested pollutants by five types of COFs followed the order of the best performance for COF-PDZ with two ortho position heterocyclic N atoms, medium for COF-PMD with two meta position heterocyclic N atoms, and COF-PZ with two para position heterocyclic N atoms, and COF-PD with a single heterocyclic N atom, the worst performance for COF-1 without a heterocyclic N atom. Compared to the other COFs, COF-PDZ contained improved quantum efficiency and thus enhanced generation of electrons. The lower energy barriers and larger energy gaps of COF-PDZ contributed to its improved quantum efficiencies. The stronger affinity to Cr(VI) with lower adsorption energy of COF-PDZ also contributed to its excellent Cr(VI) reduction performance. By transferring into a more stable keto form, COF-PDZ showed great stability through five regeneration and reuse cycles. Overall, this study provided an insight into the synthesis of high-performance structure-dependent COF-based photocatalysts.

Structural and thermal analysis of some imipramine complexes

imipramine interacts with transition metals to give different molar ratios (M:L), (1:1) with Mn(II), Zn(II), Cd(II) and Hg(II) and (1:2) with Cr(III), Fe(III), Co(II), Ni(II) and Cu(II) .All were characterized by elemental analysis, IR, electronic spectra and magnetic susceptibility. IR spectra indicated that imipramine behaves as a bidentate ligand through its heterocyclic nitrogen atom and the tertiary nitrogen atom of the side chain. The geometry around the metal atoms is octahedral in all complexes except for Zn has tetrahedral structure. It was indicated by TGA and DTA analysis that the thermal decomposition of most complexes ended with the formation of metal oxides and carbon residue as a final product. For this reaction, the kinetic parameters and the orders were estimated. The decomposition course and steps were also analyzed. Consequently, decomposition mechanisms were suggested.

Discovery of HIV entry inhibitors via a hybrid CXCR4 and CCR5 receptor pharmacophore‐based virtual screening approach

Chemokine receptors are key regulators of cell migration in terms of immunity and inflammation. Among these, CCR5 and CXCR4 play pivotal roles in cancer metastasis and HIV-1 transmission and infection. They act as essential co-receptors for HIV and furnish a route to the cell entry. In particular, inhibition of either CCR5 or CXCR4 leads very often the virus to shift to a more virulent dual-tropic strain. Therefore, dual receptor inhibition might improve the therapeutic strategies against HIV. In this study, we aimed to discover selective CCR5, CXCR4, and dual CCR5/CXCR4 antagonists using both receptor- and ligand-based computational methods. We employed this approach to fully incorporate the interaction attributes of the binding pocket together with molecular dynamics (MD) simulations and binding free energy calculations. The best hits were evaluated for their anti-HIV-1 activity against CXCR4- and CCR5-specific NL4.3 and BaL strains. Moreover, the Ca2+ mobilization assay was used to evaluate their antagonistic activity. From the 27 tested compounds, three were identified as inhibitors: compounds 27 (CCR5), 6 (CXCR4) and 3 (dual) with IC50 values ranging from 10.64 to 64.56 μM. The binding mode analysis suggests that the active compounds form a salt bridge with the glutamates and π-stacking interactions with the aromatic side chains binding site residues of the respective co-receptor. The presented hierarchical virtual screening approach provides essential aspects in identifying potential antagonists in terms of selectivity against a specific co-receptor. The compounds having multiple heterocyclic nitrogen atoms proved to be relatively more specific towards CXCR4 inhibition as compared to CCR5. The identified compounds serve as a starting point for further development of HIV entry inhibitors through synthesis and quantitative structure-activity relationship studies.

Cadmium(II) Chloride Complex Containing 1-Vinylimidazole Ligand: Structural, Spectroscopic and Thermal Properties

In this work dichlorotetrakis(1-vinylimidazole)cadmium(II), [CdCl2(vim)4] complex was synthesized using 1-vinylimidazole (vim) ligand and CdCl2. The structure of the complex was characterized by FT-IR spectroscopy, thermal analysis (TG, DTG, DTA) and X-ray single crystal studies. In the FT-IR spectrum of the complex, the characteristic peaks (C−H stretch, C=C and C=N vibration bands) of vim were observed. X-ray crystallographic data of the titled complex revealed that vim ligand coordinated to the metal atom via the heterocyclic ring nitrogen atom. The coordination geometry of the Cd(II) central atom is elongated octahedral. Compound crystallized in P21/n space group, and the mononuclear units were weakly linked to each other by C-H⋯Cl hydrogen bonds. It was determined by thermal analysis data that the complex degraded in four steps and total mass loss was 99%.

N-ethyl substituted 2-benzimidazolyl-3-hydroxychromone: Atypical to highly fluorescent dyes of flavonol series excited state intramolecular proton transfer to nitrogen

New derivative of 3-hydroxychromone possessing N-ethyl substituted benzimidazole moiety was specially synthesized with the aim to switch the excited state intramolecular proton transfer (ESIPT) to heterocyclic nitrogen atom, this ESIPT direction is generally less typical to fluorescent compounds of flavonol series. Bulky ethyl group makes conformation with intramolecular hydrogen bond to carbonyl group oxygen atom unfavorable in the ground state. We expected the same situation remaining in the excited state. Photophysics of the title compound was studied both experimentally and theoretically. Unlike weakly fluorescent 3-hydroxychromones with 2′-pyridyl or 2′-quinolyl heterocycles in position 2, the title compound demonstrates unexpectedly high fluorescence quantum yields in solvents of low-to-intermediate polarity. We consider the higher rate of intramolecular proton transfer reaction, in comparison with concurring radiationless intersystem crossing (ISC) process with participation of singlet and triplet nπ* levels of carbonyl group, as the main reason of bright fluorescence of title compound.

Enhanced adsorption of bisphenol A, tylosin, and tetracycline from aqueous solution to nitrogen-doped multiwall carbon nanotubes via cation-π and π-π electron-donor-acceptor (EDA) interactions

Doping heteroatoms in carbon nanotubes can substantially enhance the electronic polarizability of the carbon surface and thus may facilitate adsorptive interactions of organic contaminants. Here, the adsorption isotherms of three polar/ionizable emerging organic contaminants, bisphenol A, tylosin, and tetracycline from aqueous solutions to synthesized heteroatom nitrogen-doped multiwall carbon nanotubes (N-MCNT) were compared with those to commercial non-doped multiwall carbon nanotubes (MCNT) at pH ~ 6. N-MCNT exhibited much stronger adsorption (3–4 folds higher sorption distribution coefficients, Kd) towards the three adsorbates than MCNT. The hydroxyl group-substituted bisphenol A molecule is rich in π-electrons and thus interacts with the polarized π-electron-depleted N-heterocyclic aromatic ring on N-MCNT via π-π electron-donor-acceptor (EDA) interaction, whereas the protonated amino group and enone groups in the tylosin molecule are deficient in electrons and interact with the neighboring π-electron-rich aromatic ring on N-MCNT via cation-π and π-π EDA interactions, respectively. The tetracycline molecule contains both electron-rich moiety (phenol ring) and electron-depleted moieties (protonated amino group and enone groups), which interact with the corresponding π-electron-acceptor/donor sites on N-MCNT. The proposed adsorption mechanisms were tested by the effects of ionic strength (NaCl or CaCl2), co-present Cu2+ ion, and changing pH on adsorption, and further by the adsorption behavior of a model organic cation (tetraethylamine). These results indicate that enhanced adsorption of emerging organic contaminants to carbon nanotubes can be achieved by doping with heterocyclic nitrogen atoms to facilitate specific EDA interactions.Capsule: Nitrogen-doped multiwall carbon nanotubes exhibit enhanced adsorptive removal of bisphenol A, tylosin, and tetracycline from aqueous solutions.

Locally Sourced, Ecofriendly Hydrate Inhibitor Effective in Simulated Offshore Environment

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 193439, “Gas-Hydrate Inhibition in a Simulated Offshore Environment Using a Local Inhibitor,” by E.V. Urunwo, SPE, S.S. Ikiensikimama, J.A. Ajienka, SPE, O. Akaranta, M.O. Onyekonwu, SPE, T.O. Odutola, SPE, and E.O. Okon, University of Port Harcourt, prepared for the 2018 Nigeria Annual International Conference and Exhibition, Lagos, 6–8 August. The paper has not been peer reviewed. Gas hydrates pose a serious flow-assurance problem in offshore environments where accessibility is restricted. The complete paper investigates gas-hydrate inhibition in a simulated offshore environment using a plant extract (PE) as a local inhibitor. The work aims to identify an effective biodegradable gas-hydrate inhibitor from locally sourced materials and ascertain its effectiveness compared with the conventional hydrate inhibitor monoethylene glycol (MEG). Experiments were conducted using a mini-flow loop, and involved mitigating hydrate formation using varying weight percentages of the inhibitor (1, 2, and 3 wt%) and evaluating their effect on hydrate inhibition in the mini-flow loop. Sensitivity charts for pressure, temperature, and time for both the PE and MEG were made. In 1 and 2 wt% of the PE, better inhibitory capacity than MEG was demonstrated, while 3 wt% of the PE and MEG had a close match. Because of its ecofriendly and biodegradable nature, the PE is therefore recommended for field trial. Introduction Kinetic hydrate inhibitors (KHIs) are water-soluble polymeric compounds that prevent or delay hydrate formation. Antiagglomerants (AAs) function as surfactants and prevent hydrates from sticking together and clumping. The hydrate still forms, but the crystals do not plug and can be transported through pipelines. Unlike thermodynamic hydrate inhibitors (THIs) such as methanol or glycols, low-dosage hydrate inhibitors (LDHIs) do not stop hydrate from forming completely because they do not cause a hydrate-curve shift. Once hydrate forms, it cannot be eliminated by LDHIs because the operating conditions cannot be changed (lowering pressures or raising temperatures); thus, a well is still at risk when LDHIs are used. THIs must still be available on site, especially when shutting in or starting a well. The local inhibitor is a water-soluble PE containing flavonoids, tannins, alkaloids, and saponins. Flavonoids act against inflammation and are anticoagulants. They are polyphenolic compounds found in vegetables, fruits, and beverages, acting as powerful oxidants that protect against reactive oxygen. Tannins are a heterogeneous group of high-molecular-weight polyphenolic compounds with the capacity to form reversible and irreversible complexes. They are also found in fruits, legumes, and grasses. Polyphenolics are a class of chemical compounds consisting of a hydroxyl group bonded directly to an aromatic hydrocarbon group. They are otherwise called polyhydroxylphenols and are phytochemicals. They are a structural class of mainly natural products. Condensed tannins are the most-abundant polyphenols and are found in virtually all families of plants. Alkaloids are natural products that contain heterocyclic nitrogen atoms and are basic in character. They are synthesized naturally by a large number of organisms including animals, plants, bacteria, and fungi. Saponins are a group of secondary metabolites found widely distributed in plant life. They form a stable foam in aqueous solutions such as soap. Chemically, saponins as a group include compounds that are glycosylated steroids, hypernoids, and steroid alkaloids. Saponins also prevent agglomeration and are surface-acting agents with bubbles and foams acting as barriers that provide good stability.

The acid-base properties of 2-(benzoylamino)(1-R-2-oxoindolin-3-ylidene)acetic acids

Aim. To study the acid-base properties of derivatives of 2-(benzoylamino)(1-R-2-oxoindolin-3-ylidene)acetic acid substituted by the location 1 of oxoindolin fragment.Results and discussion. The compounds studied are weak acids, their strength decreases with the elongation of the alkyl fragment in a heterocyclic nitrogen atom due to the extinction of the inductive effect. The reaction center (carboxyl group) has low sensitivity to the influence of substituents, and it may be due to the location distance of the substituents, as well as disturbance of coplanarity between the reaction center and the bicyclic fragment of the molecule. The ionization constants of a series of 2-(benzoylamino)(1-R-2-oxoindolin-3-ylidene)acetic acids have been set; the compounds studied are weak acids, their strength regularly decreases with replacement of the hydrogen atom at the heterocyclic nitrogen atom with methyl fragment, while the elongation of the alkyl fragment has little effect on their dissociation. The dependence of the ionization process on the nature of the substituents according to the Hammeth equation is quantified and it is shown that the reaction center (carboxyl group) has a small sensitivity to the influence of the substituents, which can be related both to the distance of the substituents location and to the violation of the coplanarity between the reaction center and the bicyclic fragment of the molecule. The small value of the ionization constant is consistent with the data of the (2Z)-(benzoylamino)(1-methyl-2-oxoindolin-3-ylidene)acetic acid stereostructure.Experimental part. The acid-base properties of 2-(benzoylamino)(2-oxoindolin-3-ylidene)acetic acid derivatives was studied by the method of potentiometric titration on an EV-74 ionomer with a glass indicator electrode (ESP 43-074) and a saturated silver chloride (EVP-1) reference electrode at 298 К within three analytical runs. A mixture of 1,4-dioxane–water (60:40, v/v) was used as a solvent. The structure of the molecule of (2Z)-(benzoylamino)(1-methyl-2-oxoindolin-3-ylidene)acetic acid was determined by X-ray diffraction analysis.Conclusions. The reactivity of the series of 2-(benzoylamino)(1-R-2-oxoindolin-3-ylidene)acetic acid has been investigated by studying the acid-base equilibria. Their ionization constants have been determined and the influence of alkyl radicals at the heterocycle nitrogen atom on the acid-base properties has been analyzed; the low sensitivity of the reaction center to the influence of substituents has been proved. The correlation equation pKa – f(σ) obtained has reliable statistical characteristics and can be used for QSAR analysis of active pharmacophores of this isostructural series.