Bipy Complexes Research Articles

Structure-bioactivity relationship study on anticancer Pd and Pt complexes with aliphatic glycine derivative ligands

To investigate the structure and bioactivity relationship, six Pd(II)/Pt(II) complexes with N-isobutylglycine (L1) and cyclohexylglycine (L2) as N^O amino acid bidentate ligands, 1,10′-phenanthroline (phen) and 2,2′-bipyridine (bipy) as N^N donor ligands, and [Pd(L1)(bipy)]NO3 (1), [Pd(L2)(bipy)]NO3 (2), [Pd(L1)(phen)]NO3 (3), [Pd(L2)(phen)]NO3·2H2O (4), [Pt(L1)(phen)]NO3 (5), along with [Pt(L2)(phen)]NO3 (6) were prepared and then characterized. The geometry of each compound was validated by doing a DFT calculation. Furthermore, tests were conducted on the complexes’ water solubilities and lipophilicity. All bipy complexes had superior aqueous solubility and less lipophilicity in comparison with phen complexes, as well as complexes containing cyclohexyl-glycine compared to isobutyl-glycine complexes, probably because of the steric effects and polarity of cyclohexylglycine. The in-vitro anticancer activities of these compounds were examined against HCT116, A549, and MCF7 cancerous cell lines. Data revealed that all Pd/Pt complexes demonstrate higher anticancer activity than carboplatin, and complexes 3 and 4 are more cytotoxic than cisplatin against the HCT116 cell line, particularly against MCF7 cancerous cells. In addition, among all compounds, complex 4 has more anticancer ability than oxaliplatin. Due to different solubility and lipophilicity behavior, the accumulation of Pt complexes and clinical Pt drugs in each cancerous cell was investigated. The binding capabilities of these complexes to DNA, as the main target in chemotherapy, occur through minor grooves and intercalate into DNA, which was done using absorption, fluorescence, and circular dichroism spectroscopy. Finally, the docking simulation study showed the mode of DNA bindings is in good agreement with the spectral binding data.

Cytotoxicity evaluation and DNA interaction of RuII-bipy complexes containing coumarin-based ligands.

Although there are various treatment options for cancer, this disease still has caused an increasing number of deaths, demanding more efficient, selective and less harmful drugs. Several classes of ruthenium compounds have been investigated as metallodrugs for cancer, mainly after the entry of imidazolH [trans-RuCl4-(DMSO-S)(imidazole)] (NAMI-A) and indazolH [trans-RuCl4-(Indazol)2] (KP1019) in clinical trials. In this sense, RuII complexes with general formula [Ru(L1-3)(bipy)2]PF6 (1-3) (L1 = ethyl 3-(6-methyl-2-oxo-2H-chromen-3-yl)-3-oxopropanoate, L2 = ethyl 3-(7-(diethylamino)-2-oxo-2H-chromen-3-yl)-3-oxopropanoate, L3 = ethyl 3-(8-methoxy-2-oxo-2H-chromen-3-yl)-3-oxopropanoate and bipy = bipyridine) have been synthesized. The crystal structure of 2 revealed that the RuII atom lies on a distorted octahedral geometry with the deprotonated ligand (L2-) coordinated through β-ketoester group oxygen atoms. In vitro cytotoxic activity of the compounds was evaluated against 4T1 (murine mammary carcinoma) and B16-F10 (murine metastatic melanoma) tumor cells, and the non-tumor cell line BHK-21 (baby hamster kidney). Coordination with RuII resulted in expressive enhancement of cytotoxic activity. The precursors were inactive below 100 μM and the final RuII complexes (1-3) showed IC50 ranging from 2.0 to 12.8 μM; 2 being the most potent compound. DNA interaction studies revealed a greater capacity of the complexes to interact with DNA than the ligands, where, 2 exhibited the highest Kb constant of 2.2 × 104 M-1. Fluorescence investigation demonstrated that 1-3 are capable of quenching the fluorescence emission of the EtdBr-DNA complex up to 40%. Molecular docking showed that the interaction of 1-3 between the DNA base pairs from the coumarin portion was with scores of 67.28, 68.62 and 64.88, respectively, and 75.45 for ellipticine, suggesting an intercalative mode of binding. Our findings show that the RuII complexes are eligible for continuing to be investigated as potential antitumor compounds.

Insights into the Chemistry and Structural Features of the Copper(II) 2,2′-Bipyridyl–Thiosulfate System

In this paper, we present our findings on a series of copper(ii) 2,2′-bipyridyl (bipy) complexes that inhibit the oxidation of thiosulfate, a current problem in the gold leaching process. The formation of six complexes, five of which have been structurally characterized by X-ray crystallography, illustrate a thermally induced, controllable switching between oxidation states, which in turn inhibits the oxidation of thiosulfate. These findings give further insight and understanding into the rich chemistry of the coinage metals and the hydrolytic processes involved with gold leaching.

Synthesis and characterization of Ru(III) complexes with 2-((E)-((4-((4-bromophenyl)ethynyl)phenyl)imino)methyl-4-((E)-phenyldiazenyl)phenol and their use as a precursor for RuO2 nanoparticles

Some Ru(III) complexes of the type [Ru(L)(phen)X] (1a, 2a) and [Ru(L)(bipy)X] (1b, 2b) (where L = 2-((E)-((4-((4-bromophenyl)ethynyl)phenyl)imino)methyl-4-((E)-phenyldiazenyl)phenol, phen = 1,10-phenanthroline, bipy = 2,2′- bipyridine, X = N3 and NCS) have been prepared and characterized on the basis of elemental analysis, FTIR, 1H NMR and mass spectral studies. Room temperature luminescence is observed for all complexes not only due to π→π* intra-ligand transition but also due to metal to ligand charge transfer character and varies considerably with π–acidic character of the coligands. Thermal stability of phen and bipy complexes was studied by TG analysis. The representative complexes 1a and 2b were calcinated at 600 °C for 5 h and RuO2 obtained were characterized by FTIR, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) techniques. PXRD analysis showed that the obtained oxides are crystalline and corresponded to RuO2 phases. Crystal size, shape and morphology were determined by SEM and TEM studies.

Synthesis and Characterization of Heteroleptic Ni(II) Bipyridine Complexes Bearing Bis(N-heterocyclic carbene) Ligands

The synthesis and characterization of four new Ni(II) bis(NHC) bipy complexes (bipy = 4, 4′-bipyridine, NHC = N-heterocyclic carbene) are reported. These represent the first examples of the NiII(NHC2) L2 class of compounds, where L is a two-electron-donor ligand. The introduction of a double propyl bridged bis-NHC ligand (CProp2C) imparts reversibility to the electrochemistry of these complexes. The electrochemical response includes two reductions, the first believed to be bipy ligand based, bipy0/–, and the second metal based. The unusual ligand arrangements in these complexes result in electronic structures in which both the HOMOs and LUMOs are ligand-based, as determined by DFT analysis of all four compounds.

Iron Pincer Complexes Incorporating Bipyridine: A Strategy for Stabilization of Reactive Species

Treatment of FeCl2(thf)1.5 with the pincer ligand bis(dicyclohexylphosphinomethyl)pyrrolide (CyPNP) in the presence of 2,2′-bipyridine (bipy) affords the six-coordinate complex [FeCl(bipy)(CyPNP)]. The chloride complex exhibits spin-crossover behavior and serves as a starting point for a series of bipy-coordinated iron(II) pincer compounds, including the hydride species [FeH(bipy)(CyPNP)]. Chemical reduction of [FeCl(bipy)(CyPNP)] generates the new complex [Fe(bipy)(CyPNP)], which is found to be consistent with a structure featuring iron(I) as opposed to a bipy radical anion. Reactivity studies with the bipy complexes demonstrate that they are more prone to migratory insertion and β-hydrogen elimination reactions than the corresponding dicarbonyl analogues and that in certain instances the bipy ligand can be sequestered by treatment with a Lewis acid. These observations demonstrate that coordination of bipyridine to pincer-ligated iron(II) species provides a means of stabilizing otherwise unstable compoun...

Heterobimetallic Cu(I)/Ru(II) Acetylide Bridged Hybrid Complexes Containing Coordination and Organometallic Sites

AbstractThe heterobimetallic complexes [Cu(phen)(NC5H4HC=NC6H4C≡CC6H4C≡CRu(dppe)2Cl)]X (1 a‐4 a) and [Cu(bipy)(NC5H4H C=NC6H4C≡CC6H4C≡CRu(dppe)2Cl)]X (1 b‐4 b) (where X= I, ClO4, BF4, PF6; phen= 1, 10 phenanthroline, bipy= 2, 2′ bipyridine) have been prepared by the reaction of (NC5H4HC=NC6H4C≡CC6H4C≡CRu(dppe)2Cl) with copper salts in presence of phen or bipy as a coligand. Our synthetic attempts and successes are discussed in combination with spectroscopic and electronic characterization of the compounds. Comparison between phen and bipy complexes were studied by thermal and electrochemical analysis where, thermally robust complexes demonstrate quasireversible redox behaviour analogous to CuI/II/RuII/III couple. SEM of representative complexes 2 a and 2 b clarify the average size and morphology of the complexes. Room temperature luminescence influenced by varying coordinating ability of counter anions along with π‐acidic character in green‐yellow region was observed. Solvent dependant emission displays positive solvatochromism at ambient temperature. The second harmonic generation (SHG) efficiency of the complexes was measured by Kurtz‐powder technique indicating that all complexes display the second harmonic generation (SHG) property.

Syntheses, structures, thermal stabilities and bacteriostatic activities of four lanthanide complexes

Four lanthanide complexes, [La2(2,4-DClBA)6(5,5′-DM-2,2′-bipy)2(H2O)2]·2C2H5OH (1) and [Ln(2,4-DClBA)3(5,5′-DM-2,2′-bipy)(C2H5OH)]2 (Ln = Pr(2), Sm(3), Gd(4); 2,4-DClBA = 2,4-dichlorobenzoate; 5,5′-DM-2,2′-bipy = 5,5′-dimethyl-2,2′-bipyridine), were synthesized and characterized via elemental analysis, infrared spectra and thermogravimetric analysis (TG). The crystal structures of 1 and 2–4 are different; Each La3+ is nine-coordinate adopting a distorted mono-capped square antiprism, while the Ln3+ ions of 2–4 are all eight-coordinate with a distorted square antiprismatic molecular geometry. There are subtle changes in the local coordination geometry of the lanthanide–5,5′-DM-2,2′-bipy complexes. Binuclear 1 complexes are stitched together via two kinds of hydrogen bonding interactions (OH⋯O and CH⋯O) to form 1-D chains along the y axis, while the units of 2–4 are stitched together via CH⋯O to form 1-D chains along the x axis. TG analysis revealed thermal decomposition processes and thermal stabilities of the complexes. The bacteriostatic activities of the complexes were evaluated against Candida albicans, Escherichia coli, and Staphylococcus aureus.

Ni(II) and Zn(II) Complexes Containing Alkynyl Functionalized Salicylaldimine Ligand and Heterocyclic Coligand: Synthesis, Characterization and Luminescence Properties.

Some nickel(II) and zinc(II) complexes of the type [Ni(L)(phen/bipy)]X (1a-6a) and [Zn(L) (phen/bipy)]X (1b-6b) (where L=2-{(E)-[(4-trimethylsilylethynylphenyl)imino]methyl}-4-(4-nitro phenylethynyl)phenol; phen=1, 10-phenanthroline, bipy=2, 2´-bipyridine; X=ClO4-, BF4-, PF6-) have been prepared and characterized on the basis of elemental analyses, FTIR, 1H NMR and mass spectral studies. The molecular structure of L was determined by single crystal X-ray diffraction studies. The electrochemical behaviour of the Ni(II) complexes indicate that the phen complexes appears at more positive potential as compared to those for bipy complexes, as a consequence of its strong π-acidic character. TGA was carried out to study the thermal behavior of the complexes. Room temperature luminescence is observed for all complexes corresponds to π→π* ILCT transition. The size of the counter anion and heterocyclic coligands phen and bipy shows marked effect on emission properties of the complexes.

Bipyridinium Polymers That Dock Tetrathiafulvalene Guests in Water Driven by Donor-Acceptor and Ion Pair Interactions.

Two water-soluble para-xylylene-connected 4,4'-bipyridinium (BIPY(2+) ) polymers have been prepared. UV-Vis absorption, (1) H NMR spectroscopy, and cyclic voltammetry experiments support that in water the BIPY(2+) units in the polymers form stable 1:1 charge-transfer complexes with tetrathiafulvalene (TTF) guests that bear two or four carboxylate groups. These charge-transfer complexes are stabilized by the donor-acceptor interaction between electron-rich TTF and electron-deficient BIPY(2+) units and electrostatic attraction between the dicationic BIPY(2+) units and the anionic carboxylate groups attached to the TTF core. On the basis of UV-Vis experiments, a lower limit to the apparent association constant of the TTF⋅BIPY(2+) complexes of the mixtures, 1.8×10(6) m(-1) , has been estimated in water. Control experiments reveal substantially reduced binding ability of the neutral TTF di- and tetracarboxylic acids to the BIPY(2+) molecules and polymers. Moreover, the stability of the charge-transfer complexes formed by the BIPY(2+) units of the polymers are considerably higher than that of the complexes formed between two monomeric BIPY(2+) controls and the dicarboxylate-TTF donor; this has been attributed to the mutually strengthened electron-deficient nature of the BIPY(2+) units of the polymers due to the electron-withdrawing effect of the BIPY(2+) units.

The stacking interactions of bipyridine complexes: the influence of the metal ion type on the strength of interactions.

The strength of the stacking interactions in the bipy complexes of nickel, palladium, and platinum, [M(CN)2 bipy]2 (M = Ni, Pd, Pt), was calculated using the ωB97xD/def2-TZVP method. The results show that for all considered geometries, interactions are the strongest for platinum, and weakest for nickel complexes, as a result of higher dispersion contributions of platinum over the palladium and nickel complexes. It was also shown that strength of interactions considerably rises with an increase of the stacking overlap area. As a consequence of the favorable electrostatic term, the strength of interactions also rises when metal atom and cyano ligands are involved in the overlap with bipy ligand. The strongest interaction was calculated in the platinum complex, for the geometry that has overlap of metal and cyano ligands with bipy ligand with an energy of -39.80 kcal mol(-1). The energies for similar geometries of palladium and nickel complexes are -34.60 and -32.45 kcal mol(-1). These energies, remarkably, exceed the strength of the stacking interactions between organic aromatic molecules. These results can be of importance in all systems with stacking interactions, from materials to biomolecules.

Stacking Interactions between Square-Planar Metal Complexes with 2,2′-Bipyridine Ligands. Analysis of Crystal Structures and Quantum Chemical Calculations

Stacking interactions between square-planar metal complexes containing bipyridine ligands (bipy) were studied by analyzing data in the Cambridge Structural Database (CSD) and by density functional theory (DFT) calculations. In most of the crystal structures, two bipy complexes were head-to-tail oriented. On the basis of the data from CSD, we classified the overlaps of bipy complexes into six types. The types were defined by values of geometrical parameters, and the interactions of the same type have very similar overlap geometries. The most frequent are the structures with quite large overlap area including chelate rings and pyridine fragments. The overlap is often influenced by ligands coordinated at the third and fourth coordinating positions or by molecules (ions) from the environment in the crystal structure. The interaction energies of all types of overlap were calculated on model systems using the DFT (TPSS-D3) method. The strongest calculated interaction has an energy of −31.66 kcal/mol and large area of overlap. By decreasing the overlap area, the strength of interactions decreases. The weakest calculated interaction has an energy of −7.26 kcal/mol and the small overlap area of pyridine fragments. These results presenting the geometries and energies of stacking interactions can be very important for various molecular systems.

How Do Proximal Hydroxy or Methoxy Groups on the Bidentate Ligand Affect [(2,2′;6′,2"‐Terpyridine)Ru(N,N)X] Water‐Oxidation Catalysts? Synthesis, Characterization, and Reactivity at Acidic and Near‐Neutral pH

AbstractWater‐oxidation catalysts (WOCs) can potentially be improved by installing pendant electron‐donor groups that may also be proton donors or acceptors. We have modified one of the most well‐studied WOCs with alkoxy or hydroxy substituents on the bidentate bipyridine ligand (N,N), thereby forming [(terpy)RuII(N,N)X] (X = Cl, H2O; terpy = 2,2′;6′,2"‐terpyridine). A combination of NMR spectroscopy (particularly 15N chemical‐shift data), UV/Vis spectroscopy, X‐ray diffraction, and oxygen evolution data point to interesting and beneficial effects of an oxygenated group proximal to X. A methoxy group on the 2,2′‐bipyridyl (bipy) ring cis to X = Cl is shown to facilitate ionization of the chloride ligand in aqueous acetone, perhaps by acceptance of a hydrogen bond from the aquo ligand. Hydrogen‐bond donation of a proximal hydroxy group to a bound aquo ligand is shown by X‐ray diffraction. Distinct differences in pKa values for the 4,4′‐ and 6,6′‐dihydroxy bipy complexes are seen. In water oxidation driven by ceric ammonium nitrate, the 6,6′‐dimethoxy species is somewhat faster and longer‐lived than the analogue that lacks the oxygenated groups [a turnover number (TON) of 215 instead of 138 in 10 h, and a turnover frequency (TOF) of 0.36 min–1 instead of 0.23 over the same time period]. Taken together, oxygenated groups near the WOC active site are promising electron or proton donors and/or hydrogen‐bond acceptors, and are the subject of further scrutiny.

Copper(II) complexes of N-(2-{[(2E)-2-(2-Hydroxy-(5-substituted)-benzylidene)-hydrazino]carbonyl}phenyl)benzamide ligands and heterocyclic coligands

Some copper(II) complexes of the type [Cu(L1–3)(phen]⋅CH2Cl2 (1a–3a) and [Cu(L1–3) (bipy)]⋅CH2Cl2 (1b–3b) (where L1=N-(2-{[(2E)-2-(2-Hydroxy-benzylidene)-hydrazino]carbonyl}phenyl)benzamide, L2=N-(2-{[(2E)-2-(2-Hydroxy-(5-bromo)-benzylidene)-hydrazino]carbonyl}phenyl)benzamide, L3=N-(2-{[(2E)-2-(2-Hydroxy-(5-methoxy)-benzylidene)-hydrazino]carbonyl}phenyl)benzamide; phen=1,10-phenanthroline, bipy=2,2′-bipyridine) have been prepared and characterized on the basis of elemental analyses, IR, UV–Vis and EPR spectral studies. IR spectra indicate that the ligand L1–3 exists in the keto form in the solid state, while at the time of complexation, it tautomerises into enol form. The single crystal X-ray diffraction study of the representative complex [Cu(L1) (phen)]⋅CH2Cl2 (1a) reveals the distorted square pyramidal geometry around copper(II). Crystal data of (1a): space group=P21/n, a=11.5691(16)Å, b=11.0885(15)Å, c=24.890(4)Å, V=3166.2(8)Å3, Z=4. The electrochemical behavior of all the complexes indicate that the phen complexes appears at more positive potential as compared to those for bipy complexes, as a consequence of its stronger π acidic character. All the complexes exhibit blue–green emission as a result of the fluorescence from the intra-ligand (π→π∗) emission excited state.

Slow Self‐Assembly Favors Hysteresis above Room Temperature for an Iron(II) 1D‐Chain Spin‐Crossover Complex

AbstractThe X‐ray structures and magnetic properties of three new iron(II) coordination polymers with the general formula [FeL1(Lax)]n are presented. L1 is the tetradentate N2O22– Schiff‐base‐like ligand (E,E)‐{dimethyl‐2,2′‐[1,2‐phenylenebis(iminomethylidyne)]bis(3‐oxobutanato)(2–)‐N,N′,O3,O3′}. For the axial coordination, 4,4′‐bipyridine (bipy), 1,2‐bis(4‐pyridyl)ethane (bpea), and 1,2‐bis(4‐pyridyl)ethene (bpee) were used. Spin‐transition behavior was observed for the bpea and the bipy complexes. In both cases, two different polymorphs were isolated, showing different magnetic properties. In the case of the bipy complex 1, different preparation methods were tested to elucidate which conditions favor one polymorph over another. It appears that a slow precipitation of the coordination polymer favors a cooperative spin transition above room temperature, whereas a fast precipitation results in a gradual spin transition at lower temperatures. In the case of the bpea complex, an incomplete spin transition is observed, which can be explained by the crystal packing.

Selective oxidation of benzyl alcohol with tert-butylhydroperoxide catalysed via Mn (II) 2, 2-bipyridine complexes immobilized over the mesoporous hexagonal molecular sieves (HMS)

A series of Mn(II)bipy complexes with different loading of Mn2 + supported on HMS was prepared. These samples were characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), Thermogravimetric and Differential Scanning Calorimetry (TG-DSC), Ultraviolet and Visible spectra (UV-Vis) and Fourier transforms Infrared (FT-IR). The catalytic activity of the supported Mn(II)bipy complexes, [Mn(bipy)2]2 + /HMS was evaluated in the oxidation of benzyl alcohol in the liquid phase using tert-butylhydroperoxide (TBHP) as an oxidant. The effects of Mn2 + loading and various solvents on the conversion and selectivity were studied. A second order function for the variation in catalytic activity with respect to the loading of Mn2 + ions in different catalyst samples was observed. The activity of the [Mn(bipy)2]2 + /HMS catalyst differs with the type of the solvent and in this case, acetonitrile gives the best conversion results. The kinetic of benzyl alcohol oxidation was investigated at temperatures of 27, 46, 60, 75 and 90°C using [Mn(bipy)2]2 + /HMS and excess TBHP. The order of reaction with respect to benzyl alcohol was determined to be pseudo-first order. The value of the apparent activation energy was also determined.

Discriminating octahedral transition metal ions: highly selective tripodal tris-(2,2′-bipyridine) functionalized piperazine cyclophane receptor for Cu2+ ions

New tripodal transition metal ion receptors, tris(5-ethoxycarbonyl-2,2'-bipyridine) and tris(5-carboxylate-2,2'-bipyridine) substituted 27-membered trimeric piperazine cyclophanes 5 and 7 as well as tetra(5-ethoxycarbonyl-2,2'-bipyridine) substituted 36-membered tetrameric piperazine cyclophane 6, have been prepared and their transition metal ion complexing properties studied in solution by UV-vis spectroscopy and in the solid state by single-crystal X-ray diffraction. The crystal structures of [H(3)5(3+)·Fe(2+)]·4(ClO(4)(-))·CF(3)COO(-) (V), [H(3)7(2+)·Fe(2+)]·2(SO(4)(2-)) (VII) and the reference complex [tris(5,5'-bis(ethoxycarbonyl)-2,2'-bipyridine)Fe(II) perchlorate] (I) showed that the robust piperazine cyclophane is an optimal platform in preorganizing the 2,2'-bipy moieties to form a very fixed octahedral coordination site. In an acidic water solution, the highly preorganized structure of 5 gives a [5·Fe(2+)] complex, the stability of which is comparable with the classical tris(2,2'-bipy) Fe(2+)-complex but it is a significant 3.7 logK units more stable than the non-preorganized tetrameric analog [6·Fe(2+)]. Detailed studies with other similar divalent octahedral transition metal cations showed that the restricted octahedral coordination in complexes of 5 results in an unusual selectivity. The selectivity order [Zn(2+)<Co(2+)<Ni(2+)≈Fe(2+)<Cu(2+)] deviates significantly from that of typical tris(2,2'-bipy) complexes [Zn(2+)<Co(2+)<Cu(2+)≈Fe(2+)<Ni(2+)]. As a highlight, cyclophane 5 exhibits exceptionally high selectivity towards Cu(2+) ions but very weak binding for Co(2+).

Lewis Base Sequestered Chalcogen Dihalides: Synthetic Sources of ChX2 (Ch=Se, Te; X=Cl, Br)

The synthesis and comprehensive characterization of a series of base-stabilized ChX(2) (Ch = Se, Te; X = Cl, Br) is reported using aryl-substituted diazabutadiene and 2,2'-bipyridine (bipy) as the ligands. In stark contrast to free ChX(2) the complexes display excellent thermal stability. Their use as viable ChX(2) reagents that may be stored for later use is demonstrated in principle. The syntheses are simple and high-yielding from commercially available or easily synthesized reagents. The bipy complexes are exceedingly rare examples of this ubiquitous ligand being utilized within Group 16 chemistry; the Se examples are the first to be characterized by X-ray crystallography, and the Te species are only the second.

Synthesis, characterization and potent superoxide dismutase-like activity of novel bis(pyrazole)-2,2'-bipyridyl mixed ligand copper(II) complexes.

Eleven new complexes of Cu(II) chloride and nitrate with bis(pyrazol-1-yl)propane and bis[2-(pyrazol-1-yl)ethyl]ether ligands were prepared and characterized by spectral and electrochemical methods. X-Ray crystal structure determination of bis[2-(3,5-dimethylpyrazol-1-yl)ethyl]etherdinitratocopper revealed a hepta-coordinated structure with the bis(pyrazole) ligand coordinated in a tridentate NNO-fashion and both of the nitrate ions in a bidentate fashion. Reaction of Cu(II) nitrate complexes with 2,2'-bipyridyl led to the displacement of one of the nitrate ions into the outer sphere and the formation of mixed-ligand complexes. Mixed-ligand bipyridyl Cu(II) complexes demonstrated the highest superoxide dismutase (SOD)-like activity in a chemical superoxide anion-generating system, with IC(50) values in the low micromolar range. Density functional theory calculations showed that introduction of a bipypidyl ligand into the complexes dramatically lowered the lowest unoccupied molecular orbital (LUMO) energy level, which explains the increased SOD-like activity of these complexes compared to non-bipy species. These bipy complexes were also effective scavengers of reactive oxygen species generated by phagocytes (human neutrophils and murine bone marrow leukocytes) ex vivo. Thus, these bipy mixed-ligand complexes represent a promising class of SOD mimetics for future development.

Heteroaromatic N-base ligands in 1,10-phenanthroline- and 2,2′-bipyridyl-assisted chromic acid oxidation of (−)- l-sorbose in aqueous micellar acid media: a kinetic study

In aqueous sulfuric acid media, Cr(VI) oxidation of (−)- l-sorbose in the presence and absence of catalysts like 1,10-phenanthroline (phen), 2,2′-bipyridyl (bipy) have been carried out under the conditions, [(−)- l-sorbose] T ≫ [Cr(VI)] T at different temperatures. Under the experimental conditions, the monomeric species of Cr(VI) has been found kinetically active in the absence of phen and bipy catalysts, while in the heteroaromatic N-base catalysed path, the Cr(VI)–phen and Cr(VI)–bipy complexes have been suggested as the active oxidants. In the catalysed path, Cr(VI)–L complex (L = phen, bipy) receives a nucleophilic attack by the substrate to form a ternary complex which subsequently experiences a redox decomposition through two-electron transfer leading to the organic products and a Cr(IV)–L complex. Both the uncatalysed and catalysed paths show first-order dependence on [(−)- l-sorbose] T and [Cr(VI)] T . The uncatalysed path shows second-order in [H +], while the catalysed path shows a first-order dependence on [H +]. The heteroaromatic N-base catalysed path is first-order in [phen] T or [bipy] T . These findings remain unchanged in the presence of externally added surfactants. The cationic surfactant (i.e., N-cetylpyridinium chloride (CPC)) inhibits the rate in both the catalysed and uncatalysed paths, whereas the anionic surfactant (i.e., sodium dodecyl sulfate (SDS)) shows the rate accelerating effect for both the uncatalysed and catalysed paths. The observed micellar effects have been rationalised by considering the distribution of the reactants between the micellar and aqueous phases in terms of the proposed reaction mechanism.