Nitrogen Donor Atoms Research Articles

Theoretical study of bifurcated hydrogen bonding effects on the 1J(N,H), 1hJ(N,H), 2hJ(N,N) couplings and 1H, 15N shieldings in model pyrroles

According to the density functional theory calculations, the X...H...N (X=N, O) intramolecular bifurcated (three-centered) hydrogen bond with one hydrogen donor and two hydrogen acceptors causes a significant decrease of the (1h)J(N,H) and (2h)J(N,N) coupling constants across the N-H...N hydrogen bond and an increase of the (1)J(N,H) coupling constant across the N-H covalent bond in the 2,5-disubstituted pyrroles. This occurs due to a weakening of the N-H...N hydrogen bridge resulting in a lengthening of the N...H distance and a decrease of the hydrogen bond angle at the bifurcated hydrogen bond formation. The gauge-independent atomic orbital calculations of the shielding constants suggest that a weakening of the N-H...N hydrogen bridge in case of the three-centered hydrogen bond yields a shielding of the bridge proton and deshielding of the acceptor nitrogen atom. The atoms-in-molecules analysis shows that an attenuation of the (1h)J(N,H) and (2h)J(N,N) couplings in the compounds with bifurcated hydrogen bond is connected with a decrease of the electron density rho(H...N) at the hydrogen bond critical point and Laplacian of this electron density nabla(2)rho(H...N). The natural bond orbital analysis suggests that the additional N-H...X interaction partly inhibits the charge transfer from the nitrogen lone pair to the sigma*(N-H) antibonding orbital across hydrogen bond weakening of the (1h)J(N,H) and (2h)J(N,N) trans-hydrogen bond couplings through Fermi-contact mechanism. An increase of the nitrogen s-character percentage of the N-H bond in consequence of the bifurcated hydrogen bonding leads to an increase of the (1)J(N,H) coupling constant across the N-H covalent bond and deshielding of the hydrogen donor nitrogen atom.

Synthesis and characterization of a new class of polymeric ligand exchangers for selective removal of arsenate from drinking water

Six new chelating resins were prepared by functionalizing three commercially available XAD resins of various matrix properties, including XAD1180, XAD16 and XAD7HP. Two types of pyridinyl functional groups were loaded on these sorbents, one with two nitrogen donor atoms (2N) per functional group and the other with three N-donor (3N) atoms per functional group. Consequently, six polymeric ligand exchangers (PLE’s) were prepared by immobilizing Cu(II) ions onto these chelating resins, where Cu(II) serves as the surface central metal. The highest Cu(II) loading was determined to be 44 mg/g. Unlike standard strong base anion (SBA) exchangers, the PLE’s displayed greater affinity toward arsenate than for sulfate. The binary arsenate–sulfate separation factor ( α As/S) ranged from 5.1 to 10. Bench-scale column breakthrough tests confirmed the greater selectivity for arsenate over other common anions (sulfate, bicarbonate and chloride). The breakthrough of arsenate occurred last at ∼920 BV for XAD1180-3N–Cu. From batch kinetic tests, the PLE’s intraparticle diffusivity ( D) was determined to be more than one order of magnitude greater than standard SBA resins. The PLE’s can be effectively regenerated using 8% NaCl at pH 10. The arsenate capacity can be completely recovered using the brine. Despite the high surface area, the PLE’s sorption capacity was limited by the hyper-crosslinkage and the degree of methylation/amination of the template XAD resins.

Synthesis and Spectroscopic Characterization of New Ligand and Its Pd(II), Cu(II) Metal Complexes

A novel Schiff base ligand containing nitrogen and sulfur donor atoms was synthesized by condensing thioamide (TA) with imidothioic acid (IT) to form 1, 4 dithiane-2, 3-diamine (TAIT). Metal complexes of this ligand were prepared using Cu (II) chloride dihydrates and Pd (III) chloride. These complexes have been characterized using various physico-chemical and spectroscopic techniques. Based on physico-chemical and spectroscopic analyses, the structure of Cu (II) complex is expected to be octahedral, while Pd (II) complex is proposed to be square planner geometry. Schiff base and its metal complexes were expected to show strong bioactivity against microbes and cancer cells.

Chiral palladium complexes based on derivatives of benzylamine and 2α-hydroxypinan-3-one

Synthesized and characterized new chiral palladium complexes, some of which contain asymmetric donor nitrogen atom. Nitrogen-containing derivatives (+) - and (-)-2α-hydroxypinan-3-one- (1R,2R,5R)-3-(benzylimino)-2,6,6-trimethylbicy- clo[3.1.1]heptane-2-ol (HL1), (1S,2S,3S,5S)-3- (benzylamino)-2,6, 6-trimethylbicyclo[3.1.1]- heptane-2-ol (HL2), (1R,2R,5R)-3-((S)-α-methyl- benzylimino)-2,6,6-trimethylbicyclo[3.1.1]- heptane-2-ol (HL3), (1R,2R,3R,5R)-3-((S)-α-methyl- benzylamino)-2,6,6-trimethylbicyclo[3.1.1]- heptane-2-ol (HL4) -were studied as optically active ligands.

Nitritereduction by copper complexes

A series of copper complexes have been synthesised as potential agents for the catalytic reduction of nitrite anions. The ligands and corresponding copper complexes have been characterised by using a range of techniques including X-ray crystallography, NMR, microanalysis, mass spectrometry, infra-red spectroscopy, electrochemical studies and density functional theory calculations. For complexes with simple aliphatic substituents bonded to the equatorial donor nitrogen atoms, catalytic studies on the conversion of NO(2)(-) anions into NO and N(2)O gases revealed an excellent correlation between the initial rate of conversion and the experimental reduction potential as measured by cyclic voltammetry. Initial catalytic investigations reveal that these simple model complexes display a wide range of catalytic turnover rates, conversion yields and product gas compositions. Overall the results suggest that further investigations into the design and use of copper complexes as nitrite reduction catalysts are warranted.

Blue Luminescent Zn(II) and Hg(II) Complexes with 2-[4-(Dimethylamino)styryl]pyridine; Structural and Luminescent Properties

Luminescent organic and metal coordination compounds have attracted considerable attention for their potential applications in electroluminescent displays. Among coordination compounds, chelate d metal complexes are of great interest due to their high thermal stability and low cost as well as their good photoluminescent and electroluminescent properties. For example, Zn(II) complexes with nitrogen and oxygen donor atoms exhibit blue and white emissions. Meanwhile, less luminescent Hg(II) complexes have been reported. Recently some coordination polymeric Hg(II) complexes have shown blue fluorescence originating from intraligand charge transfer (ILCT) transitions. Herein, two novel d metal (M = Znand Hg) complexes with 2-[4-(dimethylamino)styryl] pyridine (dmasp) were prepared and their structural and luminescent properties were investigated. The dmasp ligand was of interest as it had an electron push-pull system, thereby stabilizing the π* levels and, in them, ILCT transitions could arise readily through a conjugated π system, which is also important to ILCT photoluminescent materials as well as the second-order nonlinear optical (NLO) materials.

Synthesis and characterization of Co(II), Ni(II), Zn(II) and Cu(II) complexes with a new tetraazamacrocyclic Schiff base ligand containing a piperazine moiety: X-ray crystal structure determination of the Co(II) complex

Two macrocyclic Schiff base ligands, L 1 [1+1] and L 2 [2+2], have been obtained in a one-pot cyclocondensation of 1,4-bis(2-formylphenyl)piperazine and 1,3-diaminopropane. Unfortunately, because of the low solubility of both ligands, their separation was unsuccessful. In the direct reaction of these mixed ligands (L 1 and L 2) and the appropriate metal ions only [CoL 1(NO 3)]ClO 4, [NiL 1](ClO 4) 2, [CuL 1](ClO 4) 2 and [ZnL 1(NO 3)]ClO 4 complexes have been isolated. All the complexes were characterized by elemental analyses, IR, FAB-MS, conductivity measurements and in the case of the [ZnL 1(NO 3)]ClO 4 complex with NMR spectroscopy. The crystal structure of the Co(II) complex has also been determined and the [CoL(NO 3)] + cation contains the Co(II) ion sited in the middle of the macrocyclic cavity endo-macrocyclicly coordinated in a distorted octahedral geometry with a N 4O 2 core, arising from coordination by the four donor nitrogen atoms from the macrocyclic framework and by two oxygen atoms from a bidentate nitrate ion. Neither positive-ion FAB mass spectrometry nor the X-ray crystal structure shows an indication relevant to the [2+2] macrocyclic products.

Theoretical Investigation on the Effect of Different Nitrogen Donors on Intramolecular Se⋅⋅⋅N Interactions

The effect of different donor nitrogen atoms on the strength and nature of intramolecular Se...N interactions is evaluated for organoselenium compounds having N,N-dimethylaminomethyl (dime), oxazoline (oxa) and pyridyl (py) substituents. Quantum chemical calculations on three series of compounds [2-(dime)C(6)H(4)SeX (1 a-g), 2-(oxa)C(6)H(4)SeX (2 a-g), 2-(py)C(6)H(4)SeX (3 a-g); X=Cl, Br, OH, CN, SPh, SePh, CH(3)] at the B3LYP/6-31G(d) level show that the stability of different conformers depends on the strength of intramolecular nonbonded Se...N interactions. Natural bond orbital (NBO), NBO deletion and atoms in molecules (AIM) analyses suggest that the nature of the Se...N interaction is predominantly covalent and involves nN-->sigma*(Se--X) orbital interaction. In the three series of compounds, the strength of the Se...N interaction decreases in the order 3>2>1 for a particular X, and it decreases in the order Cl>Br>OH>SPh approximately CN approximately SePh>CH(3) for all the three series 1-3. However, further analyses suggest that the differences in strength of Se...N interaction in 1-3 is predominantly determined by the distance between the Se and N atoms, which in turn is an outcome of specific structures of 1, 2 and 3, and the nature of the donor nitrogen atoms involved has very little effect on the strength of Se...N interaction. It is also observed that Se...N interaction becomes stronger in polar solvents such as CHCl(3), as indicated by the shorter r(Se...N) and higher E(Se...N) values in CHCl(3) compared to those observed in the gas phase.

Effect of pendant arm length and nitrogen donor disposition on the topology of luminescent cadmium phenylenedicarboxylate coordination polymers with bis(pyridylmethyl)piperazine co-ligands

Hydrothermal synthesis has afforded divalent cadmium coordination polymers containing bis(pyridylmethyl)piperazine (bpmp) tethers and either phenylenediacetate (phda) or phenylenedipropionate (phdp) ligands. {[Cd(1,4-phda)(4-bpmp)]·1.5H2O}n (1) displays a (4,4)-grid layered structure based on 4-connected {Cd2O2} dimeric units. Extension of the pendant arms generated {[Cd(1,4-phdp)(H4-bpmp)](ClO4)·3.5H2O}n (2, phdp = phenylenedipropionate), which possesses a rare (3,6) 2D trigonal lattice based on 6-connected {Cd2O2} dimers. Changing the nitrogen donor atom disposition by using 3-bpmp as the nitrogen co-ligand yielded [Cd(1,4-phdp)(3-bpmp)(H2O)]n (3), which crystallizes in a 3-fold interpenetrated achiral diamondoid lattice. [Cd(1,3-phda)(4-bpmp)]n (4) adopts a very similar structure to that of 1. Complexes 1–4 undergo blue-violet luminescence upon exposure to ultraviolet radiation.

Density functional theory analyses of bis(bipyridine)ruthenium noninnocent quinonoid and thiolosulfinato complexes containing ligands formally in the semiquinone oxidation state

Density functional theory and the polarized continuum model are used to derive the electronic structures of some open-shell, bis(bipyridine)ruthenium complexes bound to noninnocent quinonoid or thiolosulfinato ligands formally in the semiquinone oxidation state. The noninnocent properties of the o-thiolosulfinato ligand are explored and compared with those of the more conventional o-semiquinones with nitrogen, oxygen, and sulfur donor atoms. Spin densities are shown to be fairly localized in the metallocycle ring. It is demonstrated that oxidation of the parent [RuII(bpy)2 (1,2-(S,SO2)–C6H4] species occurs primarily in the metallocycle ring and is localized in the Ru–S0 bond.

Structural Variations and Molecular Dynamics of Rare-Earth Metal Complexes with theN,N-Bis(2-{pyrid-2-yl}ethyl)hydroxylaminato Ligand

The reaction of the donor-functionalised N,N-bis(2-{pyrid-2-yl}ethyl)hydroxylamine and [LnCp3] (Cp=cyclopentadiene) resulted in the formation of bis(cyclopentadienyl) hydroxylaminato rare-earth metal complexes of the general constitution [Ln(C5H5)2{ON(C2H4-o-Py)2}] (Py=pyridyl) with Ln=Lu (1), Y (2), Ho (3), Sm (4), Nd (5), Pr (6), La (7). These compounds were characterised by elemental analysis, mass spectrometry, NMR spectroscopy (for compounds 1, 2, 4 and 7) and single-crystal X-ray diffraction experiments. The complexes exhibit three different aggregation modes and binding motifs in the solid state. The late rare-earth metal atoms (Lu, Y, Ho and Sm) form monomeric complexes of the formula [Ln(C5H5)2{eta2-ON(C2H4-eta1-o-Py)(C2H4-o-Py)}] (1-4, respectively), in which one of the pyridyl nitrogen donor atoms is bonded to the metal atom in addition to the side-on coordinating hydroxylaminato unit. The larger Nd3+ and Pr3+ ions in 5 and 6 make the hydroxylaminato unit capable of dimerising through the oxygen atoms. This leads to the dimeric complexes [(Ln(C5H5)2{mu-eta1:eta2-ON(C2H4-o-Py)2})2] without metal-pyridine bonds. Compound 7 exhibits a dimeric coordination mode similar to the complexes 5 and 6, but, in addition, two pyridyl functions coordinate to the lanthanum atoms leading to the [(La(C5H5)2{ON(C2H4-o-Py)}{mu-eta1:eta2-ON(C2H4-eta1-o-Py)})2] complex. The aggregation trend is directly related to the size of the metal ions. The complexes with coordinative pyridine-metal bonds show highly dynamic behaviour in solution. The two pyridine nitrogen atoms rapidly change their coordination to the metal atom at ambient temperature. Variable-temperature (VT) NMR experiments showed that this dynamic exchange can be frozen on the NMR timescale.

Titanocene(IV) and vanadocene(IV) complexes of dicyanomethanidobenzoate

The new titanocene and vanadocene complexes of the non-linear pseudohalides Cp 2Ti(dcmb) 2, Cp 2VCl(dcmb), (η 5-C 5H 4Me) 2VCl(dcmb) and Cp 2V(dcmb) 2 were prepared by reaction of titanocene dichloride (Cp 2TiCl 2) and vanadocene dichlorides (Cp 2VCl 2, (η 5-C 5H 4Me) 2VCl 2) with dicyanomethanidobenzoic acid (dcmbH, PhC(OH)C(CN) 2). These reactions have proven that the dcmb ligand could be coordinated to the central metal by oxygen or nitrogen donor atoms. The bonding mode of the dcmb ligand reflects properties of the central metal. The strongly oxophilic titanium(IV) shows the bonding through oxygen atom while bonding through nitrogen atom was observed for less oxophilic vanadium(IV). The bonding fashion of the dcmb ligands was determined by spectroscopic methods. X-ray diffraction analysis was used for the structure determination of the compounds dcmbH·H 2O, Cp 2Ti(dcmb) 2·CH 2Cl 2, (η 5-C 5H 4Me) 2VCl(dcmb) and [Cp 2V(OC(Ph)C(CN)C(OMe)NH)][dcmb].

Synthesis and characterization of some new Co(II) and Cd(II) macroacyclic Schiff-base complexes containing piperazine moiety

Three Cd(II) or Co(II) macroacyclic Schiff-base complexes [CoL 1Br]ClO 4 ( 1), [CdL 2Cl]ClO 4 ( 2) and [CdL 3(NO 3)]ClO 4 ( 3) were prepared by template condensation of 2-pyridinecarboxaldehyde and three different amines containing piperazine moiety, N, N′-bis(2-aminoethyl)piperazine, N, N′(2-aminoethyl)(3-aminopropyl)piperazine and N, N′-bis(3-aminopropyl)piperazine, in the presence of Co(II) or Cd(II) metal ions, respectively. All complexes have been studied with IR, FAB mass and microanalysis and for complex ( 3) by 1H and 13C NMR spectra. One of these complexes, [CdL 3(NO 3)]ClO 4 ( 3) has been characterized through X-ray crystallography. In complex ( 3), the Cd(II) ion is coordinated by the six nitrogen donor atoms from the ligand and by one oxygen atom from a monodentate nitrate ion in a N 6O environment.

Rigid, Sterically Diverse N-Heterocyclic Carbene-Pyridine Chelates: Synthesis, Mild Palladation, and Palladium-Catalyzed Allylic Substitution

A series of four 1-(pyridin-2-yl)benzimidazolium salts was synthesized as precursors to rigid, bidentate N-heterocyclic carbene-pyridine ligands. With the goal of exploring the interplay between steric and electronic asymmetry in catalysis, the ligands are constructed with very small (H, Me) or very bulky (2,6-diisopropylphenyl, 2,4,6-triisopropylphenyl) groups adjacent to the nitrogen and carbon donor atoms. Cationic palladium-allyl complexes were synthesized under mild conditions, using triethylamine as base and potassium or silver hexafluorophosphate as counterion source. The structures of three complexes were verified using X-ray crystallography. All four palladium complexes were active catalysts for the allylic substitution reaction between allylic carbonates and either sodium diethyl-2-methylmalonate or N-methylbenzylamine, although significant ligand-controlled effects on regioselectivity were not observed under the conditions studied.

New three- and four-armed flexible bridging ligands for use in metallosupramolecular chemistry: syntheses and X-ray structures

Preparations are described of twelve new tritopic and tetratopic ligands by coupling of two phenolic precursors with a range of heterocyclic units. X-ray crystal structures of four representative examples revealed the conformations in the solid state with the nitrogen donor atoms separated by distances ranging from 10.9 to 18.2 Å.

A novel vanadyl complex with a polypyridyl DNA intercalator as ligand: A potential anti-protozoa and anti-tumor agent

In the search for new metal-based drugs for the treatment of tumoral and parasitic diseases a vanadyl complex, [V(IV)O(SO(4))(H2O)(2)(dppz)].2H(2)O, that includes the bidentate polypyridyl DNA intercalator dipyrido[3,2-a:2',3'-c]phenazine (dppz), was synthesized, characterized by a combination of techniques, and in vitro evaluated on the human acute promyelocytic leukemia cell line HL-60 and against Dm28c strain epimastigotes of the parasite Trypanosoma cruzi, causative agent of Chagas' disease. EPR spectroscopy suggests a distorted octahedral geometry for the complex with the dppz ligand acting as bidentate, binding through both nitrogen donor atoms in an axial-equatorial mode. An oxo group, two water molecules and a sulphate donor occupy the remainder coordination positions. The complex, as well as the anti-trypanosomal reference drug Nifurtimox, showed IC(50) values in the muM range against T. cruzi Dm28c strain. In addition the complex exhibited excellent in vitro anti-tumor activity against leukemia (HL-60 cell line) comparable to that of cisplatin, inducing cell death by apoptosis with IC(50) values in the micromolar range. Data from gel electrophoresis and atomic force microscopy indicate that the complex interacts with DNA, suggesting that its mechanism of action may include DNA as a target. EPR and (51)V NMR experiments were also carried out with aged aerated solutions of the complex to get insight into the stability of the complex in solution and the species responsible for the in vitro activities observed.

The joint inhibiting effect of cobalt(III) complexes and amines in ethylbenzene oxidation

Effective inhibitor pairs have been obtained by targeted selection of the nature of ligands in Co(III) complexes and compounds containing nitrogen and sulfur donor atoms. Under the initiated ethylbenzene oxidation conditions (75°C), the joint antioxidant activity of four Co(III) complexes, five amines, and a disulfide used in pairs has been studied. Plausible modes of oxidation chain termination by the newly formed Co(III) complexes [Co(dtcR1R2)3-amine] and [(Co(ac,ac)3-amine] have been established. The specific features of the structure of the Co(III) complexes and amines responsible for the enhancement of the inhibiting activity in their application in pairs have been studied, a development that is important for designing other antioxidant systems.

Molecular orbital studies of the mast cell zinc-histamine storage complex

A zinc-histamine-heparin complex is proposed as a storage form of histamine in rat mast cells. A ring nitrogen and the ethylamine nitrogen of two histamine molecules in a square planar arrangement about one divalent zinc ion may intercalate with a portion of the heparin molecule such that two sulfonic acid or carboxylate residues provide the fifth and sixth coordinating ligands above and below the plane of the zinc histamine complex. Semiempirical molecular orbital calculations employing an iterative extended Huckel method, Cusach's modification, indicate that there is little or no covalent bonding between the Zn atom and the donor nitrogen atoms. Thus the stability of the complex would appear to be owing to electrostatic interactions. These data correlate well with the demonstrated case of liberation of histamine from mast cell granules.

Ni(II) complexes of stereo-isomeric hexazamacrocyclic ligands derived from 2,6-diacetylpyridine

The nitrate and perchlorate Ni(II) complexes of the stereo-isomeric hexazamacrocyclic ligands L 1 (3,6,14,17,23,24-hexaazatricyclo[17.3.1.18,12]tetracosa-1(23),8,10,12(24),19,21-hexaene,2,7,13,18-tetramethyl) and L 2 (3,7,15,19,25,26-hexaazatricyclo[19.3.1.19,13]hexacosa-1(25),9,11,13(26),21,23-hexaene,2,8,14,20-tetramethyl) derived from 2,6-diacetylpyridine have been synthesized and characterized by microanalysis, LSI-MS, conductivity measurements, IR, UV–Vis spectroscopy and magnetic studies. Crystal structures of L 1·2H 2O as well as of the complexes [ NiL 1 ] ( ClO 4 ) 2 and [ NiL 2 ] ( NO 3 ) 2 have been determined. The X-ray studies show the presence of mononuclear endomacrocyclic complexes with the metal ion coordinated to all the nitrogen donor atoms from the macrocyclic framework in a N6 core. The geometry around the metal ions can be described as distorted octahedral. The nitrate and perchlorate anions do not coordinate to the metal ions, but they are involved in intermolecular interactions through hydrogen bonds to the amine groups of the macrocyclic ligands.

Interaction of Copper(II) with the Prion Peptide Fragment HuPrP(76−114) Encompassing Four Histidyl Residues within and outside the Octarepeat Domain

Complex formation processes between the 39-mer residue peptide fragment of human prion protein, HuPrP(76-114), and copper(II) ions have been studied by potentiometric, UV-vis, circular dichroism (CD), electron paramagnetic resonance, and electrospray ionization mass spectrometry methods. This peptide consists of 39 amino acid residues and contains two histidines (His77 and His85) belonging to the octarepeat domain and two histidines (His96 and His111) outside this domain. It was found that HuPrP(76-114) is able to bind 4 equiv of metal ions and all histidyl residues are independent, except nonequivalent metal binding sites in the oligonuclear species. Imidazole nitrogen donor atoms are the primary and exclusive metal binding sites below pH 5.5 in the form of various macrochelates. The macrochelation slightly suppresses, but cannot prevent, the deprotonation and metal ion coordination of amide functions, resulting in the formation of (N(im),N(-)), (N(im),N(-),N(-)), and (N(im),N(-),N(-),N(-))-coordinated copper(II) complexes in the pH range from 5.5 to 9. CD spectroscopy results gave clear evidence for the differences in the metal binding affinity of the histidyl sites according to the following order: His111 > His96 >> His77 approximately His85. Among the oligonuclear complexes, the formation of di- and tetranuclear species seems to be favored over the trinuclear ones, at pH values beyond the physiological ones. This phenomenon was not observed in the complex formation reactions of HuPrP(84-114), a peptide fragment containing only one histidyl residue from the octarepeat. As a consequence, the data support the existence of cooperativity in the metal binding ability of this peptide probably due to the presence of two octarepeat sequences of the dimeric octarepeat domain of HuPrP(76-114) at basic pH values.