Nitrogen Ligands Research Articles

Homodimerization Counteracts the Detrimental Effect of Nitrogenous Heme Ligands on the Enzymatic Activity of Acanthamoeba castellanii CYP51.

Acanthamoeba castellanii is a free-living amoeba that can cause severe eye and brain infections in humans. At present, there is no uniformly effective treatment for any of these infections. However, sterol 14α-demethylases (CYP51s), heme-containing cytochrome P450 enzymes, are known to be validated drug targets in pathogenic fungi and protozoa. The catalytically active P450 form of CYP51 from A. castellanii (AcCYP51) is stabilized against conversion to the inactive P420 form by dimerization. In contrast, Naegleria fowleri CYP51 (NfCYP51) is monomeric in its active P450 and inactive P420 forms. For these two CYP51 enzymes, we have investigated the interplay between the enzyme activity and oligomerization state using steady-state and time-resolved UV-visible absorption spectroscopy. In both enzymes, the P450 → P420 transition is favored under reducing conditions. The transition is accelerated at higher pH, which excludes a protonated thiol as the proximal ligand in P420. Displacement of the proximal thiolate ligand is also promoted by adding exogenous nitrogenous ligands (N-ligands) such as imidazole, isavuconazole, and clotrimazole that bind at the opposite, distal heme side. In AcCYP51, the P450 → P420 transition is faster in the monomer than in the dimer, indicating that the dimeric assembly is critical for stabilizing thiolate coordination to the heme and thus for sustaining AcCYP51 activity. The spectroscopic experiments were complemented with size-exclusion chromatography and X-ray crystallography studies. Collectively, our results indicate that effective inactivation of the AcCYP51 function by azole drugs is due to synergistic interference with AcCYP51 dimerization and promoting irreversible displacement of the proximal heme-thiolate ligand.

Synthesis and characterization of nonlinear optical metal organic frame work – Cadmium di glycinate monohydrate

The new non-linear optical single crystal of Cadmium di glycinate monohydrate have been synthesized by the slow evaporation solution growth technique and it was characterized by SXRD,powderXRD,SEM, FTIR, UV-Vis-NIR, TG/DTA and SHG measurements. In the polymeric structure the metal ion Cd (II) has coordinated with carboxylate oxygen atom and glycine ligand nitrogen atom. The crystalline nature of the material was proved by PXRD pattern. The lattice strain produced by the bimetallic cadmium is found to be 0.0042. The functional groups are confirmed by FTIR analysis, again the force constant of C-C bond was enhanced to 316 Nm−1. The UV-Visible spectrum reveals the optical qualities such as band gap, transmittance and refractive index of the grown crystal. The lower cut off wavelength was found to be 213 nm. The TG-DTA analyses were carried out to determine the thermal stability as well as the decomposition temperature. The Cadmium-Glycine frame work shows void morphology. The title compound shows superior SHG efficiency compared to standard KDP.

Synthesis, Catalysis and Antimicrobial activity of 5d- metal chelate complex of Schiff base ligands

The metal chelates of Iridium, platinum and gold with schiff base were synthesized using metal perchlorates of the respective metal ions, and schiff base formation was done by reaction of anthranilic acid and ortho hydroxybenzaldehyde in ethanolic environment. Various analytical techniques, like, UV–Visible, FT-IR, elemental analysis, molar conductance and magnetic susceptibility have been used for crystal structural analysis. A general formula of the type [M (HL) OH] of the metal complexes have been proposed by elemental and spectral analysis. The ligand to metal ratio was found to be 1:1 in all the metal chelate complexes. As per the Infrared spectral data study the interaction of oxygen (phenolic OH and acidic COOH) and an azomethine nitrogen of ligand have been found to coordinate tridentately with central metal ion. For the synthesis of metal chelate complexes the utilized activation energy was evaluated by the broido method. The synthesized metal chelate complexes and the parent ligands were analyzed also for the antibacterial activity determination against gram positive (B. subtilis, Bacillus anthracis) and gram negative (Yersinia pestis, Escherichia coli) bacterial species.

Preparation, spectroscopic and thermal investigation of fluorinated Sm(III) β-diketonates with bidentate N donor ligands

A series of samarium β-diketonates comprising nitrogen-heterocyclic auxiliary moiety were synthesized and characterized spectroscopically. A comprehensive analysis of complexes suggests the octacoordinated environment about samarium ion and similar structural behavior of complexes. The samarium ion is coordinated via carbonyl oxygen of diketone unit and nitrogen of neutral ligand. Energy band gap values of complexes lie in range of semiconducting materials. The photophysical properties of complexes were evaluated from photoluminescence spectra of complexes. By examining the energy transfer pathway and emission spectra, the sensitizing nature of chromophoric ligands is revealed. These synthesized complexes have shown peak around 649 nm (4G5/2→6H9/2) due to electric dipole transition. Results of luminescence spectra and colorimetric analysis have demonstrated the emission of synthesized samarium complexes in reddish orange region. The optical and photophysical properties of complexes claim the usefulness of prepared samarium complexes in designing display devices.

Assembly of a 3D Cobalt(II) Supramolecular Framework and Its Applications in Hydrofunctionalization of Ketones and Aldehydes

A ditopic nitrogen ligand (E)-N′-(pyridin-4-ylmethylene)isonicotinohydrazide (L) containing both divergent pyridyl coordination sites and a hydrogen-bonding hydrazide–hydrazone moiety was synthesized. The Co(NCS)2-mediated self-assembly of L has resulted in the synthesis of a novel 3-dimensional (3D) supramolecular framework (1) that features both coordination and hydrogen bonding interactions. X-ray structural analysis reveals the formation and coordination mode of 1 in the solid state. The rational utilization of coordination bonds and hydrogen bonding interactions is confirmed and responsible for constructing the 3D materials. Catalytic studies using 1 in the presence of an activator are performed for the hydroboration and hydrosilylation reactions of ketones and aldehydes, and the results are compared with previously reported cobalt-based polymeric catalysts.

Electrochemical ammonium-cation-assisted pyridylation of inert N-heterocycles via dual-proton-coupled electron transfer

SummaryA straightforward and practical strategy for pyridylation of inert N-heterocycles, enabled by ammonium cation and electrochemical, has been described. This protocol gives access to various N-fused heterocycles and bidentate nitrogen ligand compounds, through dual-proton-coupled electron transfer (PCET) and radical cross-coupling in the absence of exogenous metal and redox reagent. It features broad substrate scope, wide functional group tolerance, and easy gram-scale synthesis. Various experiments and density functional theory (DFT) calculation results show the mechanism of dual PCET followed by radical cross-coupling is the preferred pathway. Moreover, ammonium salt plays the dual role of protonation reagent and electrolyte in this conversion, and the resulting product 9-(pyridin-4-yl)acridine compound can be used for fluorescence recognition of Fe2+ and Pd2+ with high sensitivity.

Carbon materials functionalized by nitrogenous ligands for dual application in energy storage and production: Fuel cells and supercapacitors

Dual-purpose fuel cell/supercapacitor materials were made by covalent embedding of phenazin-iron adducts into various commercial carbon supports (Vulcan XC-72, Black Pearls 2000, Ketjen Black 600). The diazonium coupling reaction allows for controlled deposition of nitrogen functionalities to the carbon supports via the formation of the strong carbon-carbon bond between the nitrogenous ligand and carbon surface. The novel phenazin-functionalized carbon supports were prepared and fully characterized using thermogravimetric analysis, Raman spectroscopy, and BET pore size determination. Notably, the micro-and macrostructure and the porosity of the carbon support drastically affected the catalytic activity of the system in oxygen reduction reaction (ORR). The KB-phenazin-Fe-700 showed the highest activity for the ORR in both basic and acidic media. Interestingly, the heat treatment of the phenazin-based materials resulted in a significant increase in the ORR activity that is different from the trend we previously observed for terpyridine-based catalysts on Vulcan carbon that were demonstrating a significant decrease in the activity after heat treatment. Furthermore, the potential of the same materials to be used for energy storage was explored and their performance as supercapacitors was studied. The modification of the carbon surfaces by phenazin ligand shows significant improvement of the specific capacitance when examined in acidic media. Coordination of iron to the surface results in a further increase of the specific capacitance due to the additional Faradaic contributions. Drastic increases were seen in the capacitance when Fe was added to the BP-phenazin system. Interestingly, the heat treatment process was found to decrease the energy storage ability of the materials with a significant decrease of the specific capacitance. Thus, for phenazin-based materials, the heat treatment is a necessary step for the production of effective ORR catalysts but is undesirable for materials targeting mainly energy storage applications.

New Complexes of organotin(IV) and organosilicon(IV) with 2-{(3,4-dimethoxybenzylidene)amino}-benzenethiol: Synthesis, spectral, theoretical, antibacterial, docking studies

New series of dimethyl-, dibutyltin(IV), trimethylsilicon(IV), and phenylsilicon(IV) compounds with bidentate nitrogen and sulphur donor ligands have been synthesized with the 2-{(3,4-dimethoxybenzylidene)amino}-benzenethiol (LH), in molar ratios of 1:1 and 1:2. For structure elucidation, all produced compounds were characterized using IR, UV–vis, elemental analysis, conductance measurements, NMR (1H, 13C, 29Si, 119Sn) spectroscopy techniques. The 2-{(3,4-dimethoxybenzylidene)amino}-benzenethiol behaves as monofunctional bidentates, interacting with the tin and silicon atom via the thiolic-sulphur and azomethine-nitrogen atoms. Compound 1, 3, and 5 have a five-coordinated trigonal bipyramidal geometry surrounding the metal atoms, whereas Compound 2, 4, and 6 have deformed octahedral structures. The optimum geometrical parameters, including bond length, bond angles, HOMO, LUMO, electrophilicity index, chemical hardness, global softness, and mulliken atomic charges, were determined using density functional theory-based methods (DFT). The studied compounds and their ligands were simultaneously evaluated for antibacterial activity in-vitro and compared to streptomycin. The binding affinity of compound with bulky group and hydrogen bond acceptor groups is more in comparision of other compounds. The structure activity relationship revealed that compounds with bulky and hydrogen bond acceptor group will enhance the antibacterial activity agaisnt Staphylococcus aureus.

An Alternate [2×2] Grid Constructed Around TiO4 N2 Units.

The formation of a tetranuclear self-assembled species constructed around a TiO4 N2 motif is reported. This aggregate is generated from Ti(Oi Pr)4 , 2,2'-bipyrimidine (bpym) and a bis-biphenol strand (L2 H4 ) where two 2,2'-biphenol units are connected with a biphenyl spacer. The solid-state structure of the [Ti4 (L2 )4 (bpym)4 ] architecture reveals the formation of an unprecedented chiral alternate [2×2] grid. In addition to the structural characterization of the [Ti4 (L2 )4 (bpym)4 ] architecture, geometry optimisation on various possible isomeric tetrameric assemblies ([2×2] grid, alternate [2×2] grid, circular helicate or cyclic hemihelicate) is performed using DFT calculations. These results confirm the higher stability of the alternate [2×2] grid over the other possible tetranuclear isomers and allow examining the replacement of the bpym ligands by two novel diimine chelates within the tetranuclear assembly (2,2'-bipyridine=bipy and 2,2'-bipyrazine=bipyraz). From this initial theoretical investigation, the competition between these three nitrogen ligands in the course of the self-assembly process is next evaluated. Overall, this investigation shows that the exclusive formation of the alternate [2×2] grid is driven by CH⋅⋅⋅N interactions.

Studies on the binding of nitrogenous bases to protoporphyrin IX iron(II) in aqueous solution at high pH values

Studies are reported on the formation of low-spin six-coordinate [Fe(PPIX)L2] complexes from iron(II) protoporphyrin where L is one of a series of nitrogenous ligands (aliphatic, aromatic or heterocyclic). The bonding constants have been determined by titration of the metal complex with these ligands and are compared in relation to previous studies. The adduct formation was monitored utilising optical spectroscopy. In addition, Mӧssbauer spectroscopic experiments were conducted to monitor the electronic environment around the central iron atom in these complexes. The two complementary spectroscopic methods indicated that all nitrogen ligands formed low-spin octahedral complexes. The magnitude of the overall binding constants (β2 values) are discussed and related to (a) the pKa values of the free ligands and (b) the Mössbauer parameter ΔEQ, which represents the quadrupole splitting of the haem iron. The β2 and ΔEQ values are also discussed in terms of the structure of the ligand. Cooperative binding was observed for nearly all the ligands with Hill coefficients close to 2 for iron(II) protoporphyrin; one of these ligands displayed a much greater affinity than any we previously studied, and this was a direct consequence of the structure of the ligand. Overall conclusions on these and previous studies are drawn in terms of aliphatic ligands versus aromatic ring structures and the absence or presence of sterically hindered nitrogen atoms. The implications of the work for the greater understanding of haem proteins in general and in particular how the nitrogenous ligand binding results are relevant to and aid the understanding of the binding of inhibitor molecules to the cytochrome P450 mono-oxygenases (for therapeutic purposes) are also discussed.Graphical abstractChanges in the electronic absorption spectra of five-coordinate [Fe(II)(PPIX)(2-MeIm)] that occurred as the temperature was lowered from room temperature to 78° K

Synthesis, electronic structures, and reactivity of mononuclear and dinuclear low-valent molybdenum complexes in iminopyridine and bis(imino)pyridine ligand environments

Molybdenum in redox non-innocent ligand environments features prominently in biological inorganic systems. While Holm and coworkers, along with many other researchers, have thoroughly investigated formally high-oxidation-state molybdenum (Mo(IV)-Mo(VI)) ligated by dithiolenes, less is known about molybdenum in other formal oxidation states and/or different redox-active ligand environments. This work focuses on the investigation of low-valent molybdenum in four different redox non-innocent nitrogen ligand type environments (mononucleating and dinucleating iminopyridine, mononucleating and dinucleating bis(imino)pyridine). The reaction of iminopyridine N-(2,6-diisopropylphenyl)-1-(pyridin-2-yl)methanimine (L1) with Mo(CO)3(NCMe)3 produced Mo(L1)(CO)3(NCMe). Mo(L1)(CO)3(NCMe) undergoes transformation to Mo(L1)(CO)4 upon treatment with CS2 or prolonged stirring in dichloromethane. The reaction of the open-chain dinucleating bis(iminopyridine) ligand N,N′-(2,7-di-tert-butyl-9,9-dimethyl-9H-xanthene-4,5-diyl)bis(1-(pyridin-2-yl)methanimine) (L2) similarly produced an hexacarbonyl complex Mo2(L2)(CO)6(NCMe)2 which also underwent transformation to the octacarbonyl Mo2(L2)(CO)8. Both complexes featured anti-parallel geometry of the chelating units. The oxidation of Mo(L1)(CO)3(NCMe) with I2 resulted in Mo(L1)(CO)3I2. The reaction of mononucleating potentially tridentate bis(imino)pyridine ligand (L3) (N-mesityl-1-(6-((E)-(mesitylimino)methyl)pyridin-2-yl)methanimine) with both Mo(CO)3(NCMe)3 and Mo(CO)4(NCMe)2 produced complexes Mo(L3)(CO)3(NCMe) and Mo(L3)(CO)4 in which L3 was coordinated in a bidentate fashion, with one imino sidearm unbound. The reaction of dinucleating macrocyclic di(bis(imino)pyridine) analogue (L4) led to the similar chemistry of Mo2(L4)(CO)6(NCMe)2 and Mo2(L4)(CO)8 complexes. Treatment of Mo(L3)(CO)3(NCMe) with I2 formed a mono(carbonyl) complex Mo(L3)(CO)I2 in which molybdenum was formally oxidized and L3 underwent coordination mode change to tridentate. The electronic structures of formally Mo(0) complexes in iminopyridine and bis(imino)pyridine ligand environments were investigated by density functional theory calculations.

Recent Progress in Luminescent Cu(I) Halide Complexes: A Mini-Review.

Copper(I) halide complexes are well sought-after materials due to their rich structural diversities and photophysical properties. Profoundly, there is a direct relationship between each structural variation and luminescence of these complexes, for a purported use. In this review, recent publications within the last 2 years about copper(I) halide complexes, centering on their structural dimensionalities with derivatives of nitrogen, phosphorus, and sulfur ligands, have been considered alongside their effects on luminescence.

Nitrogen Atom Transfer Catalysis by Metallonitrene C−H Insertion: Photocatalytic Amidation of Aldehydes

AbstractC−H amination and amidation by catalytic nitrene transfer are well‐established and typically proceed via electrophilic attack of nitrenoid intermediates. In contrast, the insertion of (formal) terminal nitride ligands into C−H bonds is much less developed and catalytic nitrogen atom transfer remains unknown. We here report the synthesis of a formal terminal nitride complex of palladium. Photocrystallographic, magnetic, and computational characterization support the assignment as an authentic metallonitrene (Pd−N) with a diradical nitrogen ligand that is singly bonded to PdII. Despite the subvalent nitrene character, selective C−H insertion with aldehydes follows nucleophilic selectivity. Transamidation of the benzamide product is enabled by reaction with N3SiMe3. Based on these results, a photocatalytic protocol for aldehyde C−H trimethylsilylamidation was developed that exhibits inverted, nucleophilic selectivity as compared to typical nitrene transfer catalysis. This first example of catalytic C−H nitrogen atom transfer offers facile access to primary amides after deprotection.

Nitrogen Atom Transfer Catalysis by Metallonitrene C-H Insertion: Photocatalytic Amidation of Aldehydes.

C−H amination and amidation by catalytic nitrene transfer are well‐established and typically proceed via electrophilic attack of nitrenoid intermediates. In contrast, the insertion of (formal) terminal nitride ligands into C−H bonds is much less developed and catalytic nitrogen atom transfer remains unknown. We here report the synthesis of a formal terminal nitride complex of palladium. Photocrystallographic, magnetic, and computational characterization support the assignment as an authentic metallonitrene (Pd−N) with a diradical nitrogen ligand that is singly bonded to PdII. Despite the subvalent nitrene character, selective C−H insertion with aldehydes follows nucleophilic selectivity. Transamidation of the benzamide product is enabled by reaction with N3SiMe3. Based on these results, a photocatalytic protocol for aldehyde C−H trimethylsilylamidation was developed that exhibits inverted, nucleophilic selectivity as compared to typical nitrene transfer catalysis. This first example of catalytic C−H nitrogen atom transfer offers facile access to primary amides after deprotection.

Synthesis, characterization and crystal structure of a novel tetranuclear oxidovanadium(V) complex derived from N’-(2-hydroxy-3-methoxybenzylidene)isonicotinohydrazide with catalytic property

A novel tetranuclear oxidovanadium(V) complex, [V4O4(OEt)4L4], where L is the dianionic form of N’-(2-hydroxy-3-methoxybenzylidene)isonicotinohydrazide (H2L), has been prepared and characterized by physico-chemical methods and single crystal X-ray diffraction. The V atom in the complex is coordinated by the phenolate oxygen, imino nitrogen and enolate oxygen of one aroylhydrazone ligand, one pyridine nitrogen of another aroylhydrazone ligand, one deprotonated ethanol oxygen, and one oxo group, forming an octahedral coordination. The oxidation of olefins with the complex as the catalyst was evaluated, which indicated that the complex has effective catalytic efficiency in the oxidation of several aliphatic and aromatic substrates by using tert-butyl hydrogen peroxide as oxidant.

Synthesis, Supramolecular Structure, Thermal Analysis, and Luminescence Properties of Lanthanide Complexes Based on Different Aromatic Carboxylic Acids and Nitrogenous Ligands

Synthesis, Supramolecular Structure, Thermal Analysis, and Luminescence Properties of Lanthanide Complexes Based on Different Aromatic Carboxylic Acids and Nitrogenous Ligands

Reusable Co-nanoparticles for general and selective N-alkylation of amines and ammonia with alcohols.

A general cobalt-catalyzed N-alkylation of amines with alcohols by borrowing hydrogen methodology to prepare different kinds of amines is reported. The optimal catalyst for this transformation is prepared by pyrolysis of a specific templated material, which is generated in situ by mixing cobalt salts, nitrogen ligands and colloidal silica, and subsequent removal of silica. Applying this novel Co-nanoparticle-based material, >100 primary, secondary, and tertiary amines including N-methylamines and selected drug molecules were conveniently prepared starting from inexpensive and easily accessible alcohols and amines or ammonia.

Two Co(II)/Ni(II) complexes based on nitrogenous heterocyclic ligands as high-performance electrocatalysts for the hydrogen evolution reaction.

Two transition metal complexes {[Co2(bpda)4(H2O)2]·4H2O}n(Co-1) and {[Ni(bpda)2(H2O)2]·2H2O}(Ni-2) (H2bpda = 2,2'-bipyridine-4,4'-dicarboxylic acid) have been synthesized by a hydrothermal method and characterized. These two compounds can be explored as stable electrocatalysts in the hydrogen evolution reaction (HER) using two important parameters: the overpotential and Tafel slope (TS). Electrochemical studies suggest that the reaction kinetics of a Co-1 catalyst is more favorable than that of a Ni-2 catalyst. Co-1 exhibits better HER performance with an overpotential of 182 mV at a current density of 10 mA cm-2, a small TS of 87.21 mV dec-1 and superior long-term durability (of up to 3000 cycles). Structural analysis shows that its catalytic activity is improved due to the two mixed valence cobalt ions and the pore structure formed by hydrogen bonds in Co-1, which is different from that of Ni-2. In addition, the mechanism of the HER is also explained theoretically by DFT molecular orbital and free energy calculations in this article.

Study of Hydrazine Carboxamide, Characterization Method and Biological Activities with Transition Metal Using Cu (II) and Mn (II) as Central Metal

The co-ordination chemistry of transition metals and their derivatives has received much attention in the recent years, primarily because of their biological importance1-3, Nitrogen, Oxygen and Sulphur donor ligands possess a range of biological applications like antitomour4, antiviral5, antimaterial7 and antifungal activities. The legends of Hydrazine with their metal complexes with Cu (II) and Mn (II). Fungicidal activity of the ligand and their metal complexes were also done to establish any relation with the metal and ligands.

Biological importance of copper (II) sesame soap-urea complex

The study of transition metal complexes containing macrocyclic nitrogen and sulphur donor ligands has been an attractive and fascinating area of modern research activity during last few decades, because of their synthetic investigations and for their usefulness. These ligands and their metal complexes are good complexing agents. The present research work reports fundamental chemical properties and new investigations of coordination compounds of some transition metal ions with an overview of medicinal applications. Transition metals appear in almost every facet of our day-to-day life, from industrial uses such as the manufacture of construction and building materials, tools, vehicles, up to cosmetics, paints and fertilizers. The present work deals with the study of synthesis and characterization of biological properties of novel copper (II) soap urea complex.