Heterocyclic Nitrogen Bases Research Articles

Mixed Ligand Complexes of Cobalt(II): Synthesis, Reactivity, Physico-Chemical and Spectroscopic Studies

The mixed ligand complexes of Co(II) metal ions with some heterocyclic nitrogen bases along with 1-cyano-1-carboethoxyethylene-2,2-dithiolate ion (CED2−) of the compositions, Co(N-N)(CED)·2H2O [N-N = o-phen/2,2′-bipy] and Co(N-N)(CED)L2 [N-N = o-phen/2,2′-bipy, CED2– = 1-cyano-1- carboethoxyethylene-2,2-dithiolate, L = γ-picoline (γ-pic), β-picoline (β-pic), α-picoline (α-pic), pyridine (py)] were characterized and isolated by analytical data as well as physico-chemical methods for example infrared spectroscopy, electronic, magnetic susceptibility, molar conductance. The complexes are soluble in coordinating solvents like DMSO and DMF and decompose below 250 ºC. The synthesized complexes in DMF solution are non-electrolytic as shown by their molar conductance data. The calculated magnetic moments suggest that the synthesixed cobalt(II) compounds are paramagnetic and produce a low-spin environment for the Co(II) ion. Thermal studies reveal that Co(N-N) contains two coordinated water molecules (CED)·2H2O. Electronic spectra of cobalt(II) complexes with mixed ligands in DMF solution are consistent with distorted octahedral stereochemistry. The IR studies indicates that the CED2- ion exhibits bidentate chelating behaviour and that heterocyclic nitrogen donors coordinate to Co atoms (II). Reaction with heterocyclic nitrogen donors (γ-picoline, β-picoline, α-picoline, pyridine) signifying the ligand exchange reaction.

DFT Investigations on the Ring-Opening Polymerization of Trimethylene Carbonate Catalysed by Heterocyclic Nitrogen Bases

Organocatalysts for polymerization have known a huge interest over the last two decades. Among them, heterocyclic nitrogen bases are widely used to catalyse the ring-opening polymerization (ROP) of heterocycles such as cyclic carbonates. We have investigated the ring-opening polymerization of trimethylene carbonate (TMC) catalysed by DMAP (4-dimethylaminopyridine) and TBD (1,5,7-triazabicyclo[4.4.0]dec-5-ene) as case studies in the presence of methanol as co-initiator by Density Functional Theory (DFT). A dual mechanism based on H-bond activation of the carbonyl moieties of the monomer and a basic activation of the alcohol co-initiator has been shown to occur more preferentially than a direct nucleophilic attack of the carbonate monomer by the heterocyclic nitrogen catalyst. The rate-determining step of the mechanism is the ring opening of the TMC molecule, which is slightly higher than the nucleophilic attack of the TMC carbonyl by the activated alcohol. The calculations also indicate TBD as a more efficient catalyst than DMAP. The higher energy barrier found for DMAP vs. TBD, 23.7 vs. 11.3 kcal·mol−1, is corroborated experimentally showing a higher reactivity for the latter.

Highly conjugative heterocyclic nitrogen base derivative and its metal complexes towards optoelectronic materials: Chemical architecture, synthesis, structural elucidation, catalytic, optoelectronic and pharmacological studies

The pharmacologically active structural architecture of highly conjugative heterocyclic structure core comprised of 1, 10-Phenanthroline derivatives with different metal acetates to arrive different complexes with molecular formulae of [M II L] where L = 1,10-Phenanthroline derivative. The structural features of synthesized compounds using elemental compositions, molar conductivity, magnetic properties as well spectral (UV–Vis., IR, NMR, ESR), thermal analysis and cyclic voltammetry protocols. On the basis of analytical and spectroscopic approaches demonstrated that an octahedral geometry for the Co(II), Zn(II), Cu(II) and Ni(II) chelates. The voltage–current output was utilized to conclude the threshold voltage (V on ) of synthesized metal complexes as emerging materials. The catalytic conversion of benzyl alcohol into benzaldehyde and to optimize the reaction situations were performed to attain enhanced turn over number. The prepared title chelates were accessed for antibacterial efficiency with B. subtilis, E. coli, S. aureus,) and fungi strains (A. flavus, C. albicans and A. niger ). The observed outcomes has indicated that the complexes showed greater antimicrobial efficiencies than ligand. Additionally, the SOD biomimetic activity of prepared metal complexes was measured and discussed. Antituberculosis efficiencies of 1,10-Phenanthroline derivative and its chelates was assessed against strain , M. tuberculosis H 37 Rv with the help of MABA assay protocol.

Synthesis, characterization and antimicrobial activities of mixed ligand transition metal complexes with isatin monohydrazone Schiff base ligands and heterocyclic nitrogen base

Mixed ligand complexes of Co(II), Ni(II), Cu(II) and Zn(II) with various uninegative tridentate ligands derived from isatin monohydrazone with 2-hydroxynapthaldehyde/substituted salicylaldehyde and heterocyclic nitrogen base 8-hydroxyquinoline have been synthesized and characterized by elemental analysis, conductometric studies, magnetic susceptibility and spectroscopic techniques (IR, UV–VIS, NMR, mass and ESR). On the basis of these characterizations, it was revealed that Schiff base ligands existed as monobasic tridentate ONO bonded to metal ion through oxygen of carbonyl group, azomethine nitrogen and deprotonated hydroxyl oxygen and heterocyclic nitrogen base 8-hydroxyquinoline existed as monobasic bidentate ON bonded through oxygen of hydroxyl group and nitrogen of quinoline ring with octahedral or distorted octahedral geometry around metal ion. All the compounds have been tested in vitro against various pathogenic Gram positive bacteria, Gram negative bacteria and fungi using different concentrations (25, 50, 100, 200μg/mL) of ligands and their complexes. Comparative study of antimicrobial activity of ligands, and their mixed complexes indicated that complexes exhibit enhanced activity as compared to free ligands and copper(II) Cu(LIV)(Q)⋅H2O complex was found to be most potent antimicrobial agent.

Efficient Cobalt-Catalyzed Oxidative Conversion of Lignin Models to Benzoquinones

Phenolic lignin model monomers and dimers representing the primary substructural units of lignin were successfully oxidized to benzoquinones in high yield with molecular oxygen using new Co-Schiff base catalysts bearing a bulky heterocyclic nitrogen base as a substituent. This is the first example of a catalytic system able to convert both S and G lignin model phenols in high yield, a process necessary for effective use of lignin as a chemical feedstock.

Heteroleptic tri-tert-butoxysilanethiolate complexes of manganese(II)

The thermal behavior of Mn(II) silanethiolate series [Mn(SR)2L(MeOH)n], where R=SSi(OBut)3, L=heterocyclic nitrogen base and n=0, 1 or 2 has been comparatively investigated using differential scanning calorimetry (DSC), thermogravimetry (TG) and TG-infrared spectoscopy (IR) techniques. The TG curves indicate the differences in the thermal decomposition due to presence of distinct N-donor ligands and labile MeOH molecules coordinated to the central atom. The first step on the TG curves (60–110°C) corresponds to the elimination of alcohol from respective complexes. The main step (150–350°C) can be assigned to the decomposition of the complexes yielding Mn3O4 and silica as the main final products, identified by X-ray diffraction patterns.

Synthesis and spectroscopic studies of mononuclear mixed ligand Schiff base complexes of Cu(II) involving conjugated heterocyclic nitrogen base and N-phOHA or N-phDHA

Mononuclear complexes of Cu(II) have been prepared by reacting a 1:1:1 molar ratio of N- phOHA or N-phDHA, dipy or phen and cupric chloride where, N-phOHA = N-phenyl-O-hydroxyacetophenonimine, N-phDHA = N-phenyl-2,4-dihydroxy acetophenonimine, dipy = 2,2′-bipyridil, phen = 1,10-phenanthroline. All complexes were characterized on the basis of their microanalysis data, molar conductance, magnetic moment at room temperature, UV-Vis, IR, 1H NMR, and ESR spectra. The monomeric and ionic nature of complexes was confirmed by their magnetic moment data and molar conductance values. The ESR spectra of metal chelates in polycrystalline and solution state at 300 K and 77 K were recorded and their silent features are reported. The ESR spectra of the metal chelates provided information about their structure on the basis of Hamiltonian parameters of the complexes and also degree of covalency.

Spectroscopic characterization and electrochemical studies of ruthenium(II) carbonyl complexes containing bidentate Schiff bases and triphenylphosphine or a nitrogen heterocycle

Reactions of ruthenium(II) carbonyl complexes of the type [RuHCl(CO)(PPh3)2(B)] [B = PPh3, pyridine (py), piperidine (pip) or morpholine (mor)] with bidentate Schiff base ligands derived from the condensation of 2-hydroxy-1-naphthaldehyde with aniline, o-, m- or p-toluidine in a 1 : 1 mol ratio in benzene resulted in the formation of complexes formulated as [RuCl(CO)(L)(PPh3)(B)] [L = bidentate Schiff base anion, B = PPh3, py, pip, mor]. The complexes were characterized by analyses, IR, electronic and 1H NMR spectroscopy, and cyclic voltammetric studies. In all cases, the Schiff bases replace one molecule of phosphine and a hydride ion from the starting complexes, indicating that Ru–N bonds in the complexes containing heterocyclic nitrogenous bases are stronger than the Ru–P bond to PPh3. Octahedral geometry is proposed for the complexes.

Synthesis, characterization, redox property and biological activity of Ru(II) carbonyl complexes containing O,N-donor ligands and heterocyclic bases

Stable ruthenium(II) carbonyl complexes having the general composition [RuCl(CO)(PPh 3)(B)(L)] (where B=PPh 3, pyridine, piperidine or morpholine; L = anion of bidentate Schiff bases (Vanmet, Vanampy, Vanchx)) were synthesized from the reaction of [RuHCl(CO)(PPh 3) 2(B)] with bidentate Schiff base ligands derived from condensation of o-vanillin with primary amines such as methylamine, 2-aminopyridine and cyclohexylamine. The new complexes were characterized by elemental analysis, IR, UV-Vis and 1 H NMR spectral data. The redox property of the complexes were studied by cyclic voltammetric technique and the stability of the complexes towards oxidation were related to the electron releasing or electron withdrawing ability of the substituent in the phenyl ring of o-vanillin. An octahedral geometry has been assigned for all the complexes. In all the above reactions, the Schiff bases replace one molecule of PPh 3 and hydride ion from the starting complexes, which indicate that the Ru–N bonds present in the complexes containing heterocyclic nitrogen bases are stronger than the Ru–P. The Schiff bases and their ruthenium(II) complexes have been tested in vitro to evaluate their activity against bacteria, viz., Staphylococus aureus (209p) and E. coli (ESS 2231).

Synthesis, ESR and TGA Studies of Mononuclear and Single‐Bridged Binuclear Complexes of Copper(II) Involving Heterocyclic Nitrogen Bases and Heterocyclic β‐Diketones

Binuclear complexes of copper(II) have been synthesised by the reaction of aromatic diamines with mixed‐ligand (mononuclear) complexes. The mixed‐ligand complexes consist of the ligands 2,2′‐dipyridyl or 1,10‐phenanthroline and 1‐phenyl‐3‐methyl‐4‐benzoyl‐2‐pyrazolin‐5‐one (HPmBzP) or 1‐phenyl‐3‐methyl‐4‐acetyl‐2‐pyrazolin‐5‐one (HpmAcP). On reaction with 2,6‐diaminopyridine (DIPy) or m‐phenylenediamine (m‐PhDA) condensation occurs with the R–C=O groups of two complexed molecules, thus bridging the two united ligand copper(II) complexes. Electronic, infrared and ESR spectra, the magnetochemistry, thermogravimetric and conductometric studies of these complexes are described. Since having one bridge between two paramagnetic centres, these complexes are expected to be better for a comparative study of long‐range antiferromagnetic interactions. ESR spectral data in solution indicate weak antiferromagnetic interaction resulting from the electron delocalization to the ligand system. The energy of the activation of each step of the thermal decomposition of the complexes has been calculated and the thermal stability of these complexes are presented.

Preparation of Coordination Compounds of Cp*2Yb with Heterocyclic Nitrogen Bases: Examples of Antiferromagnetic Exchange Coupling across Bridging Ligands

Several adducts are isolated between heterocyclic nitrogen bases and Cp*2Yb. The adducts fall into several general classes. The membership within the class is related to the reduction potential of the given heterocyclic base relative to that of Cp*2Yb. Analytically pure 1:1 adducts of the type Cp*2Yb(L) are formed with pyrazine, quinoxaline, 1,5- and 1,8-naphthyridine, and 4,4‘-bipyridine as toluene-insoluble solids. The 1:1 adducts with phthalazine and azobenzene and the 1:2 adduct with pyridazine are soluble in toluene, from which they may be isolated by crystallization. All of the adducts in this class are paramagnetic, and their effective magnetic moments are consistent with the formulation Cp*2YbIII(L•-) (L•- = radical anion), in which spins on the individual units are uncoupled to 5 K. Adducts between Cp*2Yb and phenazine, 2,2‘-azopyridine, 2,2‘-bipyrimidine, 2,2‘-azobenzene, and 2,3-bis(2-pyridino)quinoxaline are of 2:1 stoichiometry: (Cp*2Yb)2(μ-L). The crystal structure of (Cp*2Yb)2(μ-bipyrimidi...

Synthesis and photophysics in organic solvents of mesosubstituted pentamethine and related metal complexes cyanine dyes

The reaction of a ratio of 1 mol of diacetylchloromethane with the heterocyclic nitrogen base afforded N-substituted heheterocyclidinium ylide halide 1a–1f. Reaction of a ratio of 1 mol of 1a–1f with 2 and 3 mol of 2(4)-methylheterocyclic quaternary salts in basic catalyst afforded meso-substituted pentamethine 2a–2f and monomethine meso-substituted pentamethine 3a-3c cyanine dyes respectively. Reaction of equimolar ratios of 6a–6e with equi-(bi)- molar ratios of 2(4)-methylheterocyclic quaternary salts in basic medium afforded asymmetrical (symmetrical) meso-substituted mono-(bis) monomethine metal complex cyanine dyes 7 and 8a–8e. Elemental analyses, IR and 1H NMR spectral data confirmed the structures of newly synthesized compounds. The electronic absorption spectra of these dyes in ethanol and photophysics in different organic solvents are discussed.

Electronic spectral determination of the heterocyclic nitrogen base adducts of nickel(II)-di(2,6-dichlorophenyl)carbazonate

The ligand di(2,6-dichlorophenyl)carbazone (hereafter named as D2,6DClPC) and its nickel(II) complex have been synthesised and characterised by elemental analyses, magnetic moment and spectral measurements. The adduct formation constants of various heterocyclic nitrogen bases with nickel(II) chelates of D2,6DClPC have been determined in a monophase chloroform by electronic spectral study. Bathochromic and hypsochromic shifts were observed in the optical spectra in the visible range, due to adduct formation. The saturated monodentate bases such as pyrrolidine, piperidine, etc., form pentacoordinate adducts of 1:1 stoichiometry, whereas bidentate and unsaturated monodentate bases form hexacoordinated adducts with 1:1 metal–ligand stoichiometry. The experimental results are discussed in terms of steric properties, basicity and ring structures of the various heterocyclic bases.

The synthesis of cationic glycerolipid acetals containing aliphatic and heterocyclic bases

1,3-Dioxolane series cationic lipids containing residues of aliphatic or heterocyclic nitrogenous bases were synthesized. The bases were attached to the glycerol backbone either directly (piperazine) or via a spacer group through a thioether bond.

Heterocyclic nitrogen base adducts of nickel(II)–di(2,4-dibromophenyl)carbazonate

The title complex was prepared and characterized by elemental and spectral analyses. The formation constants of various heterocyclic nitrogen base adducts with the NiII–di(2,4-dibromophenyl)carbazonate have been determined in a monophase by spectrophotometry at 25 ± 0.1 °C. The monodenatate and bidentate bases form penta- and hexa-coordinated adducts respectively with 1:1 stoichiometry for the metal chelate-base, whereas the unsaturated monodentate bases form hexa-coordinated adducts with 1:2 stoichiometry. The behaviour of saturated heterocyclic bases such as pyrrolidine, piperidine, hexamethyleneimine and morpholine towards the metal chelate has been studied, and the results are discussed in terms of steric hindrance, basicity and ring structure.

Spectrophotometric study on the adduct formation of nickel (II)-di(2,4-dimethylphenyl)carbazonate with heterocyclic nitrogen bases

The study of the adduct formation of Ni(II)di(2,4-dimethylphenyl)cabazonate has been undertaken by synthesising and characterising it by magnetic susceptibility, IR and 1H-NMR spectral measurements. The Ni(II) chelate forms adducts with heterocyclic nitrogen bases, spectrophotometeric method has been employed for the study of the adduct formation in a monophase chloroform. Both bidentate and unsaturated monodenate heteronuclear nitrogen bases form hexa-coordinated adducts with 1:1 stoichiomety (metal chelate, base). However, the saturated nitrogen bases form penta-coordinated adducts with 1:1 stoichiometry. The results are discussed in terms of basicity and steric factors of the bases.

Chloride-Sensitive Fluorescent Indicators

Three fluorescent halide-sensitive quinolinium dyes have been produced by the reaction of the 6-methylquinoline heterocyclic nitrogen base with methyl bromide, methyl iodide, and 3-bromo-1-propanol. The quaternary salts, unlike the precursor molecule, are readily water soluble and the fluorescence intensity of these salts is reduced in the presence of aqueous chloride, bromide, and iodide ions, allowing halide solution concentrations to be determined using well-known Stern–Volmer kinetics. One of the dyes, dye 1, has a chloride Stern–Volmer constant of 255 mol−1 dm3 which is more than twice that of SPQ [6-methoxy-N-(3-sulfopropyl)quinolinium] used in recent physiological measurements to measure intracellular chloride levels. The dyes have been characterized using steady-state fluorescence spectroscopy and are compared to three similar dyes based on the 6-methoxyquinoline nucleus, reported earlier by the authors, and also to dyes reported by Krapf et al. (Anal. Biochem. 169, 142–150, 1988). The interference of aqueous anions and the potential for using these dyes in biological halide-sensing applications are discussed.

Synthesis of nickel(II)-di(2,3-dichlorophenyl)carbazonate and its adduct formation with heterocyclic nitrogen bases

The nickel(II)-di(2,3-dichlorophenyl)carbazonate [Ni(D2,3DClPC)2] complex has been prepared and characterized by elemental and spectral studies. The NiII chelate forms adducts with heterocyclic nitrogen bases, which were studied spectrophotometrically in monophase CHCl3 media. Saturated monodentate bases such as pyrrolidine, piperidine, etc., form pentacoordinate adducts of 1:1 stoichiometry, whereas bidentate and unsaturated monodentate bases form hexacoordinated adducts with 1:1 and 1:2 metal–ligand stoichiometries respectively. The results are discussed interms of steric properties, basicity and ring structures of the heterocyclic bases.

New fluorescent quinolinium dyes — applications in nanometre particle sizing

Bromide, iodide and tetraphenylborate quaternary salts of four new highly fluorescent dyes have been produced by the reaction of the 6-methoxyquinoline heterocyclic nitrogen base with 3-bromo-1-propanol, methyl iodide and methyl bromide with one of the dyes having its counter-ion exchanged for the tetraphenylborate ion. Three of the dyes, unlike the base, are readily water soluble, the tetraphenylborate salt only slightly water soluble and all are fluorescent over a broad pH range. The dyes have been characterised in terms of their water solubility, their steady-state fluorescence spectra and their bi-exponential fluorescence lifetimes, which are all found to be in the range ≈ 10–30 ns. We have found that the cationic dyes readily bind to negatively charged colloidal silica particles and because of the suitably long fluorescence lifetimes we have been able to determine the particle size of Du Pont's SM30 colloidal silica using time-resolved fluorescence anisotropy. The average particle diameter, determined using three of the dyes, was 6.8 ± 0.6 nm, which compares well with Du Pont's mean value of 7 nm.

New fluorescent indolium and quinolinium dyes for applications in aqueous halide sensing

Bromide and teraphenylborate salts of six new highly fluorescent dyes, produced by the reaction of two heterocyclic nitrogen bases with 8-bromo-octanoic acid, 11-bromo-undecanoic acid and 15-bromo-pentadecanoic acid have been prepared. Unlike the bases themselves, the quaternary salts are water soluble and have fluorescence characteristics independent of pH in the pH range 7–11. Both the fluorescence intensity and fluorescence lifetime of these dyes are reduced in the presence of aqueous halide ions, allowing halide concentrations to be determined accurately at concentrations of importance to both medicine and industry. All the dyes have been characterised in terms of steady state fluorescence spectra and steady-state Stern-Volmer analysis. The Stern–Volmer constants, ( K SV), for the dyes are compared to those obtained for some commercially available dyes. The prospects for using these dyes in halide sensor devices are discussed.