Nitrogen Ligands Research Articles

PEG-cored phosphorus dendrimers: Synthesis and functionalization

Dendrimers are macromolecular hyperbranched nano-structures, which properties are mainly driven by the type of their terminal functions. This paper reports the synthesis of dendritic structures built from difunctional polyethylene glycols (PEGs) used as core. Three different PEG lengths have been used: PEG300 (ca 6 CH2CH2-O units), PEG1000 (ca 22 CH2CH2-O units), and PEG2000 (ca 45 CH2CH2-O units). The first level of branching units is based on a dialdehyde of a dipiperazine triazine derivative. The second and third level of branching units are constituted of phosphorhydrazone linkages. The growing of the dendritic branches was found extremely slow with both PEG1000 and PEG2000 used as core, and was stopped early, whereas this problem was not observed with PEG300 used as core. These PEG-cored dendritic structures were finally functionalized on the surface with two types of nitrogen ligands.

Synthesis, Characterization of Ruthenium Compounds and Studies of Biological Effects in MCF-7 Tumors Cell Lines

This work presents the synthesis and characterization of compounds derived from the ruthenium transition metal with the nitrogenous ligand 4-aminopy- ridine (4-ampy). The synthesized compounds were characterized by FTIRmed spectroscopy and TG-DTA thermal analysis. For the cytotoxic evaluation of ruthenium compounds, a 66.0 μM aqueous solution containing the complex and the study of data observed in the biological assessment was performed using variance (ANOVA) analysis, followed by Tukey’s multiple comparisons test. Differences between treatments were considered significant when the p-value was less than 0.05 (p complex suggests a stoichiometry of [Ru(Cl)3(4-ampy)(H2O)2]·1/2H2O, which, due to the low solubility in an aqueous medium, was modified to increase its solubility for biological tests. The analysis of the spectra in the medium infrared region (FTIR) for the complex [Ru(Cl)3(4-ampy)(H2O)2]·1/2H2O, shows displacements of the bands observed at 1625 - 1566 cm﹣1 ν(C=C) e (C=N), indicating that coordination to the metallic center occurred by this group. Band displacements were observed in the modified Ru (III) complex, which suggests the presence of the 4-ampy ligand and the coordination by the groups ν(C=C) and (C=N) after the modification. In recent years, researchers worldwide have concentrated on obtaining, developing, and modifying drugs used as chemotherapeutic agents. The evaluation of the cell viability of the modified Ru (III) compound demonstrated cytotoxic effects in the MCF-7 cell line (15.33% ± DP 2.7) but did not affect normal cells (PBMC), which reflects the potential for possible applications.

Efficient photoluminescence from 1-(2-Naphthoyl)-3,3,3-trifluroacetonate complex of Eu3+ with bidentate neutral donors

Two new europium complexes, Eu(NTA)3(bath) and Eu(NTA)3(DPEPO), were synthesized and characterized by elemental analysis, Fourier transform infrared, mass spectrometry, thermogravimetric analysis and photoluminescence spectroscopy. The room-temperature photoluminescence spectra of the Eu3+ complexes are composed of the typical Eu3+ red emission, assigned to transitions between the first excited state (5Δ0) and the multiplet (7F0-4). The results demonstrate that the substitution of water molecules by bidentate oxygen or nitrogen ligands in Eu(NTA)3(H2O)2 richly enhances the overall quantum yield (Φoverall = 12% vs. 87%) and life time values (τobs = 339 vs. 521 μs).

Hybrid Supercapacitor Electrode Materials via Molecular Imprinting of Nitrogenous Ligands and Iron Complexes into Carbon Support

Novel hybrid supercapacitor materials were made by the covalent immobilization of nitrogenous ligands onto the surface of commercial carbon support (Vulcan XC-72), then coordinated to iron. The covalent attachment of the nitrogenous ligands allows for the controlled deposition of nitrogen functionalities on the surface of the carbon. The supercapacitor tests in acidic media showed significant growth of the capacitance as a result of the nitrogenous ligands on the support. Notably, the increase of the capacitance values directly correlates with the molecular loading on the surface. Following coordination of iron to the ligands on the surface further elevated the capacitance via Faradaic reactions of the metal center. Remarkably, the overall capacitance of materials significantly increased after the course of long-term cycling tests (ca. 110% or higher). At the beginning of durability studies, a small decline in capacitance was observed, due to some extent of molecular decomposition on the surface of the electrode. However, the intense cycling further propagates a steady growth of the overall capacitance of the materials. This could be attributed to the process of polymerization of physisorbed molecules/ radicals that result in the formation of a 3D network structure that eventually boosts the overall capacitance and the charge storage of the electrode.

Selectivity adjustment of Fe3O4 MNPs based silver catalyst in oxidation of sulfides with classical and ultrasonic methods and synthesis of 5-substituted 1H-tetrazoles from aryl nitriles in water

The surface of the Fe3O4 has been functionalized with 3-chloropropyltrimethoxysilane, which undergoes an SN2 substitution reaction of the chloro group with the nitrogen of ligand (creatinine), offering the Fe3O4@Creatinine. A new recyclable Ag attached Fe3O4 MNPs (Fe3O4 @Creatinine@Ag) has been produced through a post-synthetic method. FT-IR (Fourier Transforms Infrared), TGA (Thermogravimetric Analysis), XRD (X-ray Diffraction), EDS (Energy-Dispersive X-ray Spectroscopy) and VSM (Vibrating Sample Magnetometer) confirm the effectiveness of the performed chemical modification to synthesize the catalyst. This catalyst displays high catalytic performance in the synthesis of 5-substituted 1H-tetrazoles in water and the selective oxidation of sulfides. In the presence of nano- Fe3O4 @Creatinine@Ag as an efficient heterogeneous nano-catalyst, the corresponding 5-substituted 1H-tetrazoles and sulfoxide were afforded under the mild condition in good to excellent yields. A wide variety of sulfides furnished the corresponding sulfoxide with classical and ultrasonic methods. The results show that ultrasonic is an appropriate method for the oxidation of sulfides to the related sulfoxide. The catalyst can be separated by simple recovery and reused for several periods without any remarkable decrease in the catalysis activity and selectivity.In the synthesis of this catalyst, the environmentally friendly ligand is used to stabilize the eco-friendly active site on the desired support. What distinguishes this catalyst and this research is its high eco-friendliness in several respects. The structure of this catalyst and also, the reaction are based on green chemistry. At a relatively low temperature compared to the reported work, tetrazole derivatives are prepared in water solvent with good efficiency.

Solvent free synthesis of hydrazine carbothioamide derivatives as a precursor in the preparation of new mononuclear Mn(II), Cu(II), and Zn(II) complexes: Spectroscopic characterizations

ABSTRACT. Over the last few years considerable attention has been devoted to the study of Schiff base complexes of metal(II) containing nitrogen, oxygen and sulfur donor ligands due to their diverse biological activities. Therefore, the Schiff base thiosemicarbazone derivatives of 2-(2-hydroxy-3-methoxybenzylidene) hydrazine carbothioamide (HL1) and 2-(4-bromo-2-hydroxy-3-methoxybenzylidene) hydrazine carbothioamide (HL2) were synthesized with solvent free technique using silica gel as material support for the reaction. The structures of the precursor’s organic products confirmed with their 1H, 13C NMR, IR and microanalysis data. Six new manganese(II), copper(II), and zinc(II) complexes of HL1 and HL2 2-(2-hydroxy-3-methoxybenzylidene) hydrazinecarbothioamide derivatives with the general formulation [ML1Cl] and [ML2Cl], where M = Mn2+, Cu2+, and Zn2+ were prepared and well discussed by using elemental analyses, magnetic moments, molar conductance, infrared and electronic spectral techniques. The assignments data of spectroscopic analysis confirm that the synthesized thiosemicarbazone Schiff bases of acts as a tridentate ligand as sulfur-oxygen-nitrogen donating atoms. The values of magnetic moments agreed with the data of electronic spectra which both suggested a four-coordination geometry of the synthesized complexes.
 
 KEY WORDS: Schiff base, Thiosemicarbazone, Manganese(II) complex, Copper(II) complex, Zinc(II) complex
 
 Bull. Chem. Soc. Ethiop. 2021, 35(2), 413-424.
 DOI: https://dx.doi.org/10.4314/bcse.v35i2.14

Photocatalytic Properties and Electronic Effects of Incorporation Bis(acetylacetonato) Ruthenium(II/III) Complexes with Bidentate Nitrogen and Sulfur Ancillaries

AbstractTreatment of cis‐[Ru(acac)2(CH3CN)2] (acac−=acetylacetonate) with 1.5 equiv. of corresponding bidentate nitrogen and sulfur ligands in ethanol gave a series of bis(acetylacetonato) ruthenium(II/III) complexes [(acac)2Ru(dimbpy)](PF6) (dimbpy=4,4′‐dimethyl‐2,2′‐bipyridine) (1), [(acac)2Ru(phen)] (phen=o‐phenanthroline) (2), [(acac)2Ru(opd)] (opd=o‐phenylenediamine) (3), [(acac)2Ru(4‐Bropd)] (4‐Bropd=4‐bromo‐o‐phenylenediamine) (4) and [(acac)2Ru(S2CNMe2)] (5), respectively. Complexes 1–5 were characterized by FT‐IR, NMR and UV‐Vis spectroscopies along with their electrochemical properties. The structures of complexes 1–5 have been unambiguously established by single crystal X‐ray crystallography. The photocatalytic properties for hydrogen production by water splitting of complexes 1–5 under visible light (λ>420 nm) were also investigated in the paper.

Neuroglobin Provides a Convenient Scaffold to Investigate the Triplet-State Properties of Porphyrins by Time-Resolved EPR Spectroscopy and Magnetophotoselection

The photo-excited triplet state of Zn-protoporphyrin IX located in the heme pocket of human neuroglobin has been investigated by time-resolved EPR coupled to magnetophotoselection. The triplet state in the protein matrix has been compared with the model complex in organic glass, considering both non-coordinating and coordinating solvent mixtures. The protein matrix plays an important role in stabilizing the coordination of the embedded chromophore, resulting in a more homogeneous environment relative to that of the chromophore in a glassy solvent, even in the presence of an axial nitrogenous ligand like pyridine. The EPR spectral parameters point out a slow Jahn–Teller interconversion between slightly different triplet states, both in organic solvent and in the protein matrix. The EPR-magnetophotoselection allows us to propose a reinterpretation of the assignment of the Q bands in the electronic absorption spectrum.

Computational study of copper binding to DAHK peptide

Ligand Field Molecular Mechanics (LFMM), Density Functional Theory (DFT) and Semi-Empirical methods are used to study Cu(II) binding to the tetrapeptide Asp-Ala-His-Lys (DAHK). Two conformational searching tools, LFMM/AMBER and CREST/xTB, are used to predict the energy and geometry of Cu-DAHK, using DFT as a benchmark. In addition, DFT-predicted electronic spectra are used to evaluate the binding modes found. LFMM and DFT reproduce the experimentally determined coordination, a distorted square planar arrangement of 4 nitrogen ligands with axial coordination to a fifth, oxygen ligand. However, CREST conformational search was unsuccessful in predicting the coordination mode of Cu-DAHK, changing the bonding equatorial ligands from 4 N to 3N1O.

A novel method for generating p-type wide- and ultrawide-bandgap III-nitride by doping with magnetic elements

We propose a novel method to generate p-type conduction and low resistivity in wide- and ultrawide-bandgap III-nitride semiconductors via doping of a magnetic element. This method is based on the energetic competition between the covalency of the magnetic element and the ligand nitrogen atoms and the exchange-correlation energy of the magnetic impurity. Using magnetic elements with large exchange-correlation energy, we can obtain p-type wide- and ultrawide-bandgap semiconductors, which are basically difficult to synthesize due to the unipolarity.

How determinant is the iron precursor ligand in Fe-N-C single-site formation and activity for oxygen reduction reaction?

Metal-Nitrogen-Carbon (M-N-C) materials have emerged as one of the best non-PGM alternatives to Pt/C catalysts for the electrochemical reduction of O2 in fuel cells. In this work, we explore how decisive is the iron precursor ligand in the Fe-Nx site formation when a commercial carbon black (Vulcan XC72) is pyrolyzed in the presence of an iron complex. Iron complexes coordinating different nitrogen ligands such as phthalocyanine, 1,10-Phenanthroline, 2,2’-Bipyridyl, imidazole, EDTA, etc., were tested. Different Fe-N-C catalysts were synthetized by using twelve different complexes to achieve a better understanding on the role of ligands on site formation and activity, i.e. the site density (SD) and the turn-over frequency (TOF), respectively. It was found that Fe-Nx active site can be effectively formed only when ligands containing aromatic nitrogen rings are used and that the ligand decomposition leads to a substantial change in the carbon morphology developing an increased micropore volume, while mesopore surface area is reduced. The activity was checked in both acidic and alkaline electrolyte by RRDE technique showing that the catalytic activity deeply depends on the type of iron complex, even if such difference is much less important when KOH was used as electrolyte. Site density was determined according to nitrite stripping method, and it was found that the activity (E1/2) in sulphuric acid electrolyte well correlate with the SD, which reaches its maximum when Fe(phen)3Cl2 was used as precursor (SD = 4.24 × 1018 sites g−1; TOF = 6.66 e− sites−1 s−1). Indeed, Fe(phen)3Cl2 involves on one hand a higher mesopore occlusion (from 93 to 34 m2 g−1), but on the other hand the etching due to the small molecules developed by the pyrolysis of the ligand leads to higher micropore surface (from 132 to 246 m2 g−1), which is an important aspect for the formation of Fe-Nx active sites. This clearly places a limit on the ability to increase catalytic activity simply by playing on the initial content of complex, since while we try to increase the SD by increasing the complex loading at the same time the textural properties worsen.Stability test and post-stress test site density analysis on the best catalysts show a higher stability in alkaline electrolyte. In acid electrolyte, the kinetic current decreases by 60% after 7000 cycles and this was proven to depends by the decreasing of the SD, attesting the labile nature of Fe-Nx sites when used in demanding conditions.

Fixation of Dinitrogen at an Asymmetric Binuclear Titanium Complex.

A new type of dititanium dinitrogen complex supported by a triphenolamine (TPA) ligand is reported. Analysis by single-crystal X-ray diffraction and Raman and NMR spectroscopy reveals different coordination geometries for the two titanium centers. Hence, coordination of TPA and a nitrogen ligand results in trigonal-bipyramidal geometry, while an octahedral titanium center is obtained upon additional coordination of an ethoxide generated upon C-O bond cleavage in a diethyl ether solvent molecule. The titanium complex successfully generates ammonia in the presence of an excess amount of PCy3HI and KC8 in 154% yield (per titanium atom). A titanium complex with a bulkier TPA does not form a dinitrogen complex, and mononuclear titanium dinitrogen complexes were not accessible, presumably because of the high tendency of early transition metals to form binuclear dinitrogen complexes.

Syndiospecific Polymerization of Styrene Catalyzed by Half‐titanocenes Containing Monodentate Anionic Nitrogen Ligands

Main observation and conclusionStyrene polymerization catalyzed by the half‐titanocenes CpTiCl2[1,3‐R2(CH2N)2C=N] (6b: R= 2,6‐Me2C6H3, T4: R = 2,4,6‐Me3C6H2; T5: R = 2,6‐iPr2C6H3) was carried out in the presence of methylaluminoxane (MAO). Compared to the styrene conversion (31%) and syndiospecific index (45%) using reported 6b as precatalyst, T5 bearing ligand with isopropyl substitutes on the N‐aryl‐rings exhibits much higher styrene conversion (61%) and syndiospecific index (99%), indicating that the catalytic behavior could be improved obviously by the introduction of electronic donating and steric bulky substituents. One N atom in imidazolin‐2‐iminato ligand was replaced by O atom, affording half‐titanocenes CpTiCl2[3‐C6H5(CH2N)(CH2O)C=N (T1) and CpTiCl2[2,6‐Me2(C6H3O)(NiPr2)C=N] (T2). Compared to 6b, both higher styrene conversion and syndiospecific index are afforded by using half‐titanocene T1 containing 2‐imino‐3‐phenyloxazolidine ligand. All the results illustrate that both the chemical structure and the nature of substituents of the ligand have obvious influence on the styrene conversion and syndiospecific index in the polymerization of styrene. All the resulting syndiotactic polystyrenes (sPSs) are highly syndiospecific (rrr > 99%). Correspondingly, the sPS prepared using T5/MAO catalytic system exhibits high melting point and narrow molecular weight distribution. The results might show new light on designing more efficient half‐titanocenes for styrene polymerization with both high styrene conversion and high syndiospecific selectivity.

A theoretical investigation on the intermolecular potential curve between ruthenium tetroxide and NOX (X = 1, 2)

AbstractRuthenium tetroxide (RuO4) is one of chemical species of fission products assumed to be released to the environment during a severe accident of nuclear facilities and a target compound to assess the amount produced, reactivity, mobility and release timing. In this article, the NOX (X = 1, 2) adduct formation of RuO4 has been investigated, based on the potential energy curve (PEC) evaluated by UM06, UTPSSh, CASSCF, and CASPT2 methods. At several stationary points, CCSD and LR‐CCSD(T) energies are also computed for a comparison. The PEC shows that there is an activation barrier to form the NOX adduct and that the process is endothermic in terms of free energy. In the system, the electron transfer occurs from NOX to RuO4 when the bond between the nitrogen and oxo ligand is formed. It has been discussed in detail using active orbitals, weight of electron configurations and spin population obtained by CASSCF.

Selective hydrogenation of furfural to furfuryl alcohol catalysed by ruthenium complexes containing phosphorus‐nitrogen ligands

AbstractTwo ruthenium (II) complexes containing heterobidentated phosphorous–nitrogen ligands were studied as homogeneous catalysts in the hydrogenation of furfural, a key step in the transformation of biomass to biofuels or renewable chemicals. The catalysts exhibited high percentages of conversion towards the formation of furfuryl alcohol. The studied ruthenium (II) complexes are able to maintain their catalytic activities in substrate/catalyst ratios ranging from 1000/1 to 6000/1. The reaction is sensitive to hydrogen pressure and the substrate concentration. The maximum conversion is achieved at a pressure of 40 bar and a substrate/catalyst ratio of 3000/1 (TOF 3000 h−1). In situ 1H‐NMR (proton nuclear magnetic resonance) analysis suggests that the presence of a phosphorous–nitrogen ligand improves the catalytic activity of the complex by stabilizing the intermediate ruthenium‐dihydride, which is considered the active species in the hydrogenation reactions.

Nickel-Catalyzed C(sp3)-H Functionalization of Benzyl Nitriles: Direct Michael Addition to Terminal Vinyl Ketones.

An efficient nickel(0)-catalyzed addition of benzyl nitriles to terminal vinyl ketones via C(sp3)-H functionalization has been developed. The reaction provides a novel and efficient protocol for the synthesis of α-functionalized benzyl nitriles with a wide range of structural diversity under mild reaction conditions while obviating the use of a strong base. The work might be potentially useful toward the development of an enantioselective variant using chiral nitrogen ligands.

Metal ion fluxes controlling amphibian fertilization.

Mammalian oocytes undergo major changes in zinc content and localization in order to be fertilized, the most striking being the rapid exocytosis of over ten billion zinc ions, known as zinc sparks. Here we report that fertilization of amphibian Xenopus laevis eggs also initiates a zinc spark that progresses across the cell surface in coordination with dynamic calcium waves. This zinc exocytosis is accompanied by a newly recognized loss of intracellular manganese: synchrotron-based X-ray fluorescence and analytical electron microscopy reveal that zinc and manganese are sequestered in a system of cortical granules that are abundant at the animal pole. Through Electron-Nuclear Double-Resonance (ENDOR) studies, we rule out Mn2+ complexation with phosphate or nitrogenous ligands in intact eggs but the data are consistent with a carboxylate coordination environment. Our observations suggest that zinc and manganese fluxes are a conserved feature of fertilization in vertebrates and that they function as part of a physiological block to polyspermy.

New Nitrogen, Sulfur-, and Selenium-Donating Ligands Derived from Chiral Pyridine Amino Alcohols. Synthesis and Catalytic Activity in Asymmetric Allylic Alkylation

Although many chiral ligands for asymmetric catalysis have been developed, there is still a need for new structures allowing the modular approach. Recently, easy synthesis of chiral pyridine-containing β-amino alcohols has been elaborated by opening respective epoxides with enantiomeric 1-phenylethylamine. This paper reports the synthetic transformation of β-amino alcohols into the new complexing pyridine-containing seleno- and thioethers. The amino alcohols were effectively converted to cyclic sulfonamidates, which were reacted with thiolates or phenyl selenide nucleophile. The reaction was diastereoselective, and its outcome depended on the configuration at the substitution center. The problem was discussed considering DFT optimized structures of both diastereomeric sulfonamidates. New amino-aldimine ligands were also synthesized from chiral pyridine-containing diamines. Nine new chiral ligands were tested in the Tsuji-Trost allylic alkylation resulting in the enantiomerically enriched product in up to 75% ee. The observed stereochemical induction agrees with the prevailing nucleophilic attack at the allylic carbon laying opposite to the complexing nitrogen of pyridine in η3-allylic intermediate complexes.

Solid State Kinetics and Antimicrobial Studies for Copper (II) Sesame and Copper (II) Groundnut Complexes with Substituted Benzothiazole Ligand

The aim of this manuscript is to give an overview of new findings in the field of thermal degradation and antimicrobial studies for copper (II) sesame and copper (II) groundnut complexes with substituted benzothiazole ligand. Solid state kinetics and thermal degradation have gained the attention of the scientific community not only due to their numerous applications in environment, energy, wastewater treatment, pollution control and green chemistry but also due to their wide range of biological activities. This work aims to explore the study of chemical steps of the investigated degradation and the evaluation of the kinetic and thermodynamic parameters of the newly synthesized biologically active complexes (CSBe and CGBe) derived from two different edible oils, i.e., sesame and groundnut and ligand containing nitrogen, oxygen and sulphur atoms, i.e., 2-amino-6-ethoxy benzothiazole. The studies include Coats-Redfern equation (CRE), Horowitz-Metzger equation (HME), Broido equation (BE) and Piloyan-Novikova equation (PNE) for the analysis of the degradation and energetics for each step using kinetic data. The observation suggests that CGBe takes a longer time and higher temperature to decompose completely than CSBe. Antimicrobial activities against Staphylococcus aureus of these compounds have also been analysed which may provide an important account of information about their industrial utilization. The TGA study reveals that CSBe and CGBe complexes undergo stepwise thermal degradation of the ligand-soap bond of complex and saturated and unsaturated fatty acid components of edible oils, i.e., sesame and groundnut. The order of antimicrobial activities of the two complexes studied is – CSBe > CGBe. These results reveal that the nature of different nitrogen, oxygen and sulphur containing ligands coordinated with copper ion plays a significant role in the inhibition activity.

Quantifying Reversible Nitrogenous Ligand Binding to Co(II) Porphyrin Receptors at the Solution/Solid Interface and in Solution

We present a quantitative study comparing the binding of 4-methoxypyridine, MeOPy, ligand to Co(II)octaethylporphyrin, CoOEP, at the phenyloctane/HOPG interface and in toluene solution. Scanning tunneling microscopy (STM) was used to monitor ligand binding to the porphyrin receptors adsorbed on graphite with single-molecule resolution. Electronic spectroscopy was employed for examining this process in fluid solution. The on-surface coordination reaction was completely reversible and followed a simple Langmuir adsorption isotherm. Ligand affinities (or ΔG) for the binding processes in the two different chemical environments were determined from the respective equilibrium constants. The free energy value of -13.0±0.3 kJ/mol for the ligation reaction of MeOPy to CoOEP at the solution/HOPG interface is less negative than the ΔG for cobalt porphyrin complexed to the ligand in solution, -16.8±0.2 kJ/mole. This result indicates that the MeOPy-CoOEP complex is more stable in solution than on the surface. Additional thermodynamic values for the formation of the surface ligated species (ΔHc = -50 kJ/mol and ΔSc = -120 J/mol) were extracted from temperature dependent STM measurements. Density functional computational methods were also employed to explore the energetics of both the solution and surface reactions. At high concentrations of MeOPy the monolayer was observed to be stripped from the surface. Computational results indicate that this is not because of a reduction in adsorption energy of the MeOPy-CoOEP complex. Nearest neighbor analysis of the MeOPy-CoOEP in the STM images revealed positive cooperative ligand binding behavior. Our studies bring new insights to the general principles of affinity and cooperativity in the ligand-receptor interactions at the solution/solid interface. Future applications of STM will pave the way for new strategies designing highly functional multisite receptor systems for sensing, catalysis, and pharmacological applications.