Syntheses, crystal structures and antimicrobial activities of 6-coordinate antimony(III) complexes with tridentate 2-acetylpyridine thiosemicarbazone, bis(thiosemicarbazone) and semicarbazone ligands

Five novel antimony(III) complexes with the mono- and bis(thiosemicarbazone) ligands of 2N1S or 4N2S donor atoms, N'-[1-(2-pyridyl)ethylidene]morpholine-4-carbothiohydrazide (Hmtsc, L1) and bis[N'-[1-(2-pyridyl)ethylidene]]-1,4-piperazinedicarbothiohydrazide (H(2)ptsc, L7), and the tridentate semicarbazone ligand of 2N1O donor atoms, 2-acetylpyridine semicarbazone (Hasc, L2b), were prepared by reactions of SbCl(3) or SbBr(3), and characterized by elemental analysis, TG/DTA, FT-IR and (1)H NMR spectroscopy. The crystal and molecular structures of five antimony(III) complexes were determined by single-crystal X-ray structure analysis. The neutral, 6-coordinate antimony(III) complexes ([Sb(mtsc)Cl(2)] 1, [Sb(mtsc)Br(2)] 2, [Sb(asc)Cl(2)] 3 and [Sb(asc)Br(2)] 4) are depicted with one electron pair (5s(2)) of the antimony(III) atom, deprotonated forms of multidentate thiosemicarbazone or semicarbazone ligands, and two monodentate halogen ligands, respectively. In the dimer complex 5 ([Sb(2)(ptsc)Cl(4)]) with the ligand in which two tridentate thiosemicarbazone moieties are connected by the piperazine moiety, each antimony(III) was also described as a neutral 6-coordinate structure. These antimony(III) complexes were thermally stable around 200 degrees C. Water-soluble antimony(III) complexes 1 and 2 showed moderate antimicrobial activities against Gram-positive (Bacillus subtilis and Staphylococcus aureus) and -negative bacteria (Escherichia coli and Pseudomonas aeruginosa), yeasts (Candida albicans and Saccharomyces cerevisiae) and molds (Aspergillus niger and Penicillium citrinum). Complex 5 showed moderate antimicrobial activities against four bacteria, and two molds, while the ligand itself showed only modest antimicrobial activities against selected bacteria (B. subtilis, E. coli and S. aureus). The molecular structures and antimicrobial activities of antimony(III) complexes were compared with those of bismuth(III) complexes in the same 15 group in the periodic table.     

N-2-(azol-1(2)-yl)ethyliminodiacetic acids: a novel series of Gd(III) chelators as T2 relaxation agents for magnetic resonance imaging

The synthesis, physicochemical properties, and toxicological implications of a novel series of N-2-(azol-1(2)-yl)ethyliminodiacetic acids, useful as contrast agents for magnetic resonance imaging are reported. Compounds were prepared by alkylation of methyl iminodiacetate with N-2-bromoethylazoles and subsequent hydrolysis. Stability constants of the corresponding Gd(III) complexes and T1 and T2 relaxivities were determined and interpreted in terms of optimized geometries obtained by semiempirical PM3 calculations. Compounds show increased T2 relaxivity and decreased toxicity in vitro as compared to EDTA-Gd(III) complexes.     

Some complexes of cobalt(III) and iron(III) are radiosensitizers of hypoxic EMT6 cells

The radiosensitizing potential in hypoxic EMT6 cells of several complexes of Co(III) and Fe(III) has been examined. The cytotoxicity of each of the agents toward oxygenated and hypoxic EMT6 cells was tested over the concentration range of 1 to 500 micron for 1-h drug exposure. There was no statistically significant difference between the cytotoxicity of these complexes toward oxygenated and hypoxic cells. Based on these findings, 100 micron was selected as the drug concentration for the initial assessment of radiosensitizing potential. The radiation survival of EMT6 cells in the presence of 100 microM drug for a series of Co(III) complexes in which the number of nitro ligands was varied showed that the hexanitro and the triamine-trinitro complexes are very effective radiosensitizers. The trans-tetrammine dinitro complex was a more effective radiosensitizer than the corresponding cis-dinitro complex. The diethylenetriamine and 1,10-phenanthroline complexes were very effective radiosensitizers, producing dose-modifying factors of 2.4. The trans-tetrammine dichloro complex was moderately effective, giving a dose-modifying factor of 1.9. On the other hand, the hexammine and triammine tricyano complexes and the trans-dinitro complex with negatively charged acetylacetonate ligands were ineffective as radiosensitizers in this system. Finally, three complexes with cyclopentadienyl ligands were examined. The ferricenium salt itself was a moderately effective radiosensitizer, giving a dose-modifying factor of 2.0. However, both the dimethylferricenium salt and the analogous cobalt complex were ineffective. The FSaIIC fibrosarcoma was used to study radiosensitizing potential in vivo. The trans-tetramminedinitro complex was administered at doses of 100, 200, or 300 mg/kg as a single ip injection 1 h prior to irradiation or as three daily ip injections. There was increasing dose modification with increasing drug dosage. With a fractionated radiation protocol in which five daily fractions of 2, 3, or 4 Gy were administered to the tumor-bearing limb with ip drug injections of 100 or 200 mg/kg given 1 h prior to irradiation, a dose-modifying effect of 1.6 was observed with 5 X 200 mg/kg of the drug.     

Identification of complexes containing glutathione with As(III), Sb(III), Cd(II), Hg(II), Tl(I), Pb(II) or Bi(III) by electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry (ESI-MS) of mixtures containing glutathione (GSH) and nitrates, oxides or chlorides of the heavy metals, arsenic, antimony, cadmium, mercury, thallium, lead or bismuth allows for definitive identification of complexes in the gas phase. In the positive ion mode, spectra show prominent m/z peaks that are assigned to monocations of general formulae [E(GSH)-xH]+ (E = Cd, Hg, Tl, Pb, As, Sb or Bi; x = 0, 1 or 2), [E(GSH)2-xH]+ (E = Hg, As, Sb, or Bi; x = 1 or 2), [E(GSH)3-xH]+ (E = As, Sb or Bi; x = 2), [E2(GSH)-xH]+ (E = Tl or Pb; x = 1 or 3), [E2(GSH)2-xH]+ (E = Bi; x = 5), [E2(GSH)3-xH]+ (E = Bi; x = 5), and/or [E3(GSH)-xH]+ (E = Tl; x = 2). Spectra obtained in the negative ion mode give m/z peaks observed in assigned to monoanionic species that correspond to some of the monocationic species listed above with two protons removed. The results demonstrate the potential application of ESI-MS as a versatile and efficient approach to study toxic heavy metals in biological systems. In addition, the observations provide a foundation database to understand the chemistry of these heavy metals with bio-molecules.     

Effect of organic Cr(III) complexes on chromium speciation

Abstract

Chromium speciation in the presence of organic chromium(III) complexes was investigated using solid-phase extraction. The adsorptions of Cr(VI) and Cr(III) on alumina and pumice powder were studied. Maximum sorption of Cr(VI) was obtained by alumina (90.22%), while Cr(III) was highly adsorbed onto pumice powder (86.65%). This result shows that pumice may be a new and promising adsorbent for Cr(III). The experimental equilibrium data for Cr(VI) adsorption onto alumina and Cr(III) sorption onto pumice were analysed using Langmuir and Freundlich isotherms. The separation and adsorption of Cr(VI), Cr(III) and five organic chromium(III) complexes onto pumice and alumina at different pH values were evaluated. Ethylenediaminetetraacetate (EDTA), oxalate, citrate, glycine, alanine and 8-hydroxyqinoline were used as ligands. Sorption of alanine and ethylenediaminetetraacetate complexes was higher onto alumina than pumice at pH>3. The enhancement of adsorption of chromium(III) complexes onto pumice was achieved by surface modification of pumice using a surfactant, namely hexadecyltrimethylammoniumbromür (HDTMA). The presence of surfactant enhanced the adsorption of Cr(III) citrate, oxalate, glycine and 8-hydroxyquinoline complexes onto pumice. However, the adsorption of EDTA and alanine complexes decreased, with ratio of 13.40% and 4.00% respectively. Here we demonstrate that chromium speciation methods depending on adsorption onto various adsorbents including alumina may lead erroneous results. Analytical measurements were performed by flame AAS, data were obtained by standard addition method.     

Interactions of bismuth with human lactoferrin and recognition of the Bi(III)-lactoferrin complex by intestinal cells.

Several bismuth compounds are currently used as antiulcer drugs, but the mechanism of action still remains unclear. The antimicrobial activity of Bi(III) complexes toward Gram-negative bacteria is reported to be dependent on the iron uptake system [Domenico, P., et al. (1996) J. Antimicrob. Chemother. 38, 1031-1040]. Electronic absorption and 13C NMR spectroscopic data show that Bi(III) binds to human lactoferrin at the specific Fe(III) sites along with either carbonate or oxalate as the synergistic anion. The uptake of Bi(III) by apo-hLF was rapid [minutes in 10 mM Hepes buffer and 5 mM bicarbonate (pH 7.4)], and almost equal in both lobes. The presence of ATP facilitates the release of Bi(III) from the Bi2-hLF complex when the pH is lowered. The Bi2-hLF complex blocked the uptake of the radiolabeled 59Fe-hLF complex into rat IEC-6 cells. Surprisingly, apo-hLF (but not apotransferrin) was almost as effective in blocking 59Fe uptake as bismuth-loaded lactoferrin. These results suggest that Bi(III)-loaded hLF might be recognized by the lactoferrin receptor and be taken up into cells.     

Optimization of parameters for semiempirical methods IV: extension of MNDO,AM1, and PM3 to more main group elements

The NDDO semiempirical methods MNDO, AM1, and PM3 have been extended to all the remaining non-radioactive elements of the main group, excluding the noble gases. Most of the new elements are of Groups I and II. 44 sets of parameters are presented for the following methods and elements. MNDO: Na, Mg, K, Ca, Ga, As, Se, Rb, Sr, In, Sb, Te, Cs, Ba, Tl, and Bi; AM1: Li, Be, Na, Mg, K, Ca, Ga, As, Se, Rb, Sr, In, Sn, Sb, Te, Cs, Ba, Tl, Pb, and Bi; PM3: B, Na, K, Ca, Rb, Sr, Cs, and Ba. Average errors are presented for heats of formation, molecular geometries, etc.     

Oxygen radical-mediated DNA damage by redox-active Cr(III) complexes.

The mechanism of DNA damage induced by Cr(III) complexes is currently unknown even though it is considered to be the ultimate biologically active oxidation state of chromium. In this study, we have employed the Salmonella reversion assay to identify mutagenic Cr(III) complexes. Cyclic voltammetry was used to differentiate the redox kinetics between mutagenic and selected nonmutagenic Cr(III) species. Plasmid relaxation of supercoiled DNA was employed to show in vitro interactions with plasmid DNA and correlate the interactions with the electrochemical behavior and biological activity. The results of this study demonstrate that the mutagenic Cr(III) complexes identified in the Salmonella reversion assay display characteristics of reversibility and positive shifts of the Cr(III)/Cr(II) redox couple consistent with the ability of these Cr(III) complexes to serve as cyclical electron donors in a Fenton-like reaction. These same mutagenic complexes display an ability to relax supercoiled DNA in vitro, presumably by the induction of single-strand breaks. Nonmutagenic complexes were selected to test different ligands to determine how the ligand directs the activity of Cr(III) complexes. All nonmutagenic complexes tested thus far have shown classical irreversibility, more negative reduction potentials, and an inability to relax supercoiled plasmid DNA. These results suggest that the mechanism by which chromium complexes potentiate mutagenesis involves an oxygen radical as an active intermediate. These data also demonstrate the effect of associated ligands with regard to the ability of a metal to generate an active redox center.     

Syntheses, crystal structures and antimicrobial activities of monomeric 8-coordinate, and dimeric and monomeric 7-coordinate bismuth(III) complexes with tridentate and pentadentate thiosemicarbazones and pentadentate semicarbazone ligands

Novel bismuth(III) complexes 1-4 with the tridentate thiosemicarbazone ligand of 2N1S donor atoms [Hmtsc (L1); 2-acetylpyridine (4N-morpholyl thiosemicarbazone)], the pentadentate double-armed thiosemicarbazone ligand of 3N2S donor atoms [H2dmtsc (L3); 2,6-diacetylpyridine bis(4N-morpholyl thiosemicarbazone)] and the pentadentate double-armed semicarbazone ligand of 3N2O donor atoms [H2dasc (L4b); 2,6-diacetylpyridine bis(semicarbazone)], were prepared by reactions of bismuth(III) nitrate or bismuth(III) chloride and characterized by elemental analysis, thermogravimetric and differential thermal analysis (TG/DTA), FTIR and NMR (1H and 13C) spectroscopy. The crystal and molecular structures of complexes 1, 2a, 2b and 4b, and the "free" ligand L1 were determined by single-crystal X-ray structure analysis. The dimeric 7-coordinate bismuth(III) complex [Bi(dmtsc)(NO3)]2, 1, and the monomeric 7-coordinate complexes [Bi(Hdasc)(H2O)](NO3)2.H2O (major product), 2a, and [Bi(dasc)(H2O)]NO3.H2O (minor product), 2b, all with pentagonal bipyramidal bismuth(III) centers, are depicted with one electron pair (6s2) of the bismuth(III) atom, deprotonated forms of multidentate thiosemicarbazone or semicarbazone ligands, and monodentate NO3 or H2O ligands, respectively. These complexes are related to the positional isomers of one electron pair of the bismuth(III) atom; 1 has an electron pair positioned in the pentagonal plane (basal position), while 2a and 2b have an electron pair in the apical position. The monomeric 8-coordinate complex [Bi(mtsc)2(NO3)], 4b, which was obtained by slow evaporation in MeOH of the 1.5 hydrates 4a, was depicted with one electron pair of the bismuth(III) atom, two deprotonated mtsc- ligand and one nitrate ion. On the other hand, crystals of the complex "[Bi(mtsc)Cl2]", 3, prepared by a reaction of BiCl3 with L1 showed several polymorphs (3a, 3b, 3c and 3d) due to coordination and/or solvation of dimethyl sulfoxide (DMSO) used in the crystallization. Bismuth(III) complexes 1 and 4a showed selective and effective antibacterial activities against Gram-positive bacteria. The structure-activity relationship was discussed.     

Unusual Cu(III)—Schiff's base complexes

A new series of CU(III) complexes of the type [Cu(SB)]ClO₄, where SB is a dibasic tetradentate Schiff's base, were synthesized and characterized by elemental analysis, IR and electronic spectra. The prepared complexes are compared with Cu(II) complexes of the same ligands. The room temperature magnetic susceptibility and the x-band EPR spectra of the two types of complexes showed different behaviour. Cu(II) complexes were non conducting whereas Cu(III) complexes gave a conductance corresponding to 1:1 electrolyte. In fact this is the first report on the Cu(III) complexes with the tetradentate Schiff base ligands.     

Some iron(III) complexes with polydentate Schiff base ligands

The iron(III) complexes of three Schiff base ligands are studied as their chloride or perchlorate salts and their electronic spectra, EPR spectra, and electrochemical behavior reported. Two of these ligands are formed from reaction between salicylaldehyde and 9 or 12-membered tri- or tetraazalkanes. EPR evidence indicates that one of the complexes, [1,12-bis(2-hydroxybenzylidene)-(1,4,9,12-tetraazadodec- 6-ene)iron(III)]perchlorate-1,5-water, is a spin-crossover species containing both high-spin and low-spin iron(III) in equilibrium. The third ligand comes from pyrrole-2-carboxaldehyde and a tetraazadodecane.     

The schiff base of gossypol with 3,6,9,12,15,18,21,24-octaoxa-pentacosylamine complexes and monovalent cations studied by electrospray ionization-mass spectrometry, (1)H nuclear magnetic resonance, Fourier transform infrared, as well as PM5 semiempirical methods

A Schiff base of gossypol with 3,6,9,12,15,18,21,24-octaoxa-pentacosylamine (GSOB) forms stable complexes with monovalent cations. This process of complex formation was studied by electrospray ionization-mass spectrometry, (1)H-NMR and Fourier transform infrared spectroscopy as well as by the PM5 semiempirical method. It was found that GSOB forms 1:6 complexes with Li(+) and Na(+), and 1:4 complexes with K(+) as well as 1:2 complexes with Rb(+) or Cs(+) cations and exists in all these complexes in the enamine-enamine tautomeric form. Moreover, within these complexes only Li(+) cations can fluctuate between the oxygen atoms of the octaoxaalkyl chains. The interactions of Li(+) cations with hydroxyl groups of the gossypol part is also possible. All other cations are much more localized. In the complex of GSOB with protons, a 1:2 stoichiometry is realized. The two protons are localized on the N atoms of the Schiff base, and the complex exists in the imine-imine tautomeric form. The structures of the complexes are calculated by PM5 semiempirical methods and discussed.     

Structure and electronic properties of heme complexes with various ligands

The electronic and atomic structures, and the molecular dynamics of the atomic structure at 310 K of a set of heme complexes with His and Gly amino acids in the 5th coordination position and some ligands (O2, NO) in the 6th position were studied by ab initio (3-21G basis set) and semiempirical (PM3) quantum chemistry methods and the method of molecular dynamics. It was shown that the type of coordination of the imidazole ring influences the constant of chemical bonding of molecular oxygen of the complexes. On the other hand, NO and O2 molecules have different transinfluence on the ligand in the 5th coordination position. It was shown that temperature affects profoundly the atomic and electronic structures of the complexes, the tightness of chemical bonding and their reactivity.     

Probing Aspergillus niger glucose oxidase with pentacyanoferrate(III) aza- and thia-complexes

Complexes of pentacyanoferrate(III) and biologically relevant ligands, such as pyridine, pyrazole, imidazole, histidine, and other aza- and thia-heterocycles, were synthesized. Their spectral, electrochemical properties, electron exchange constants, electronic structure parameters, and reactivity with glucose oxidase from Aspergillus niger were determined. The formation of the complexes following ammonia replacement by the ligands was associated with the appearance of a new band of absorbance in the visible spectrum. The constants of the complexes formation calculated at a ligand-pentacyanoferrate(III) concentrations ratio of 10:1, were 7.5 x 10(-5), 7.7 x 10(-5), and 1.8 x 10(-3) s(-1) for benzotriazole, benzimidazole, and aminothiazole ligands, respectively. The complexes showed quasi-reversible redox conversion at a glassy carbon electrode. The redox potential of the complexes spanned the potential range from 70 to 240 mV vs. saturated calomel electrode (SCE) at pH7.2. For most of the complexes self-exchange constants (k(11)) were similar to or larger than that of hexacyanoferrate(III) (ferricyanide). The complexes containing pyridine derivatives and thia-heterocyclic ligands held a lower value of k(11) than that of ferricyanide. All complexes reacted with reduced glucose oxidase at pH7.2. The reactivity of the complex containing pyrazole was the largest in comparison to the rest of the complexes. Correlations between the complexes' reactivity and both the free energy of reaction and k(11) shows that the reactivity of pentacyanoferrates obeys the principles of Marcus's electron transfer theory. The obtained data suggest that large negative charges of the complexes decrease their reactivity.     

Adsorption of Antimony on Sediments from Typical Water Systems in China: A Comparison of Sb(III) and Sb(V) Pattern

The present work investigated the adsorption of Sb(III) and Sb(V) on five sediment samples (Pearl River, Yangtze River, Yellow River, Yongding River, and Liao River) from typical water systems in China and the adsorption of Sb(V) on Pearl River sediment with different organic carbon (OC) fractions using batch experiments. In order to assess the contributions of sedimentary organic components to the overall adsorption of pentavalent Sb on sediments, one sediment sample was treated by commonly used chemical and physical methods to remove different organic components. Experimental data of Sb(III) and Sb(V) adsorption on five sediments were successfully modeled using the Freundlich (r² > 0.96) isotherm. In general, the sediments with high Fe and Al oxide contents and total organic carbon (TOC) had higher Sb(III) and Sb(V) adsorption than the sediments containing small amounts of Fe and Al oxides and TOC. Dissolved organic carbon (DOC) in sediment promoted the adsorption of Sb(V), and humin fractions and black carbon-like material in sediment had a high affinity for Sb(V).     

微生物氧化As(III)和Sb(III)的研究进展

砷(Arsenic,As)和锑(Antimony,Sb)属于同族元素,具有相似的化学性质,是公认的有毒类金属(metalloid),广泛存在于自然界中。随着人类的发展,环境中砷和锑的污染日益严重,类金属污染环境的修复已经刻不容缓。现已表明,自然界中的微生物在砷和锑的生物地球化学循环中发挥着重要的作用,尤其是微生物的氧化作用,可以将毒性较强的亚砷酸盐[Arsenite,As(III)]和亚锑酸盐[Antimonite,Sb(III)]氧化为毒性较低的砷酸盐[Arsenate,As(V)]和锑酸盐[Antimonate,Sb(V)],被认为是一种潜在的类金属污染环境修复方法。本文就国内外对As(III)氧化菌和Sb(III)氧化菌的多样性、As(III)和Sb(III)微生物氧化调控机制和应用的研究进展进行总结,旨在为深入了解和探索微生物介导的砷和锑生物地球化学循环及污染环境的微生物修复提供参考。     

Role of residual Sb(III) in meglumine antimoniate cytotoxicity and MRP1-mediated resistance

Despite the clinical use of pentavalent antimonials for more than half a century, their metabolism in mammals and mechanisms of action and toxicity remain poorly understood. It has been proposed that the more active and toxic trivalent antimony form Sb(III) plays a critical role in their antileishmanial activity and toxicity. The aim of this work was to investigate the role of residual Sb(III) both in the antileishmanial/antitumoral activities of the pentavalent meglumine antimoniate and in the MRP1 (multidrug resistance-associated protein 1)-mediated resistance to this drug. Samples of meglumine antimoniate differing in their amount of residual Sb(III) (meglumine antimoniate synthesized either from SbCl₅ or from KSb(OH)₆ as well as commercially-available meglumine antimoniate) were evaluated in vitro and in vivo on Leishmania amazonensis infections, as well as for their cytotoxicity to normal and MRP1-overexpressing GLC4 cell lines. Although in vitro the two most effective drugs contained the highest levels of Sb(III), no correlation was found in vivo between the antileishmanial activity of meglumine antimoniate and its residual Sb(III) content, suggesting that residual Sb(III) contributes only marginally to the drug antileishmanial activity. On the other hand, the GLC4 cells growth inhibition data strongly suggests a marked contribution of residual Sb(III). Additionally, the potassium salt of antimoniate (non-complexed form of Sb(V)) was found to be more cytotoxic than meglumine antimoniate. Although MRP1-overexpressing GLC4 cells showed a marked resistance to trivalent antimonials, cross-resistance to meglumine antimoniate was observed only for the products that contained relatively high levels of Sb(III) (at least 0.03% by weight), suggesting that MRP1 mediates resistance to Sb(III) but not to Sb(V). In conclusion, our data strongly suggest that residual Sb(III) in pentavalent antimonial drugs does not contribute significantly to their antileishmanial activity, but is responsible for their cytotoxic activity against mammalian cells and the MRP1-mediated resistance to these drugs.     

The influence of chelating agents upon the dissimilatory reduction of Fe(III) by Shewanella putrefaciens

The ability of S. putrefaciens to reduce Fe(III) complexed by a variety of ligands has been investigated. All of the ligands tested caused the cation to be more susceptible to reduction by harvested whole cells than when uncomplexed, although some complexes were more readily reduced than others. Monitoring rates of reduction by a ferrozine assay for Fe(II) formation proved inadequate using Fe(III) ligands giving Fe(II) complexes of low kinetic lability (e.g. EDTA). A more suitable assay for Fe(III) reduction in the presence of such ligands proved to be the observation of associated cytochrome oxidation and re-reduction. Where possible, an assay for Fe(III) reduction based upon the disappearance of Fe(III) complex was also employed. Reduction of all Fe(III) complexes tested was totally inhibited by the presence of O₂, partially inhibited by HQNO and slower in the absence of a physiological electron donor. Upon cell fractionation, Fe(III) reductase activity was detected exclusively in the membranes. Using different physiological electron donors in assays on membranes, relative reduction rates of Fe(III) complexes complemented the data from whole cells. The differences in susceptibility to reduction of the various complexes are discussed, as is evidence for the respiratory nature of the reduction.     

A comparison of the gas, solution, and solid state coordination environments for the Ni(II) complexes of a series of linear penta- and hexadentate aminopyridine ligands with accessible Ni(III) oxidation states

The synthesis and characterization of the nickel(II) complexes of a series of pentadentate and hexadentate aminopyridine ligands that contain ethylenediamine and/or propylenediamine groups are described. The ligands include: 1,12-bis(2-pyridyl)-2,5,8,11-tetraazadodecane, TRIEN-pyr; 1,13-bis(2-pyridyl)-2,5,9,12-tetraazatridecane, DIEN-PN-pyr; 1,14-bis(2-pyridyl)-2,6,9,13-tetraazatetradecane, DIPN-EN-pyr; 1,15-bis(2-pyridyl)-2,6,10,14-tetraazapentadecane, TRIPN-pyr; 1,9-bis(2-pyridyl)-2,5,8-triazanonane, DIEN-pyr; and 1,11-bis(2-pyridyl)-2,6,10-triazaundecane, DIPN-pyr. The following methods were used to determine the binding geometries of the nickel(II) complexes in the solid, solution, and gas phases: magnetic susceptibility measurements, absorption spectroscopy, EPR spectroscopy, electrochemistry, and electrospray ionization mass spectrometry. All of the ligands form 6-coordinate compounds in the solid, liquid, and gas states, with the exception of the TRIEN-pyr, DIEN-PN-pyr(partially), DIPN-pyr, and DIEN-pyr ligands which form 5-coordinate species in the gas state. All of the complexes could be oxidized to Ni(III) species electrochemically, although the Ni(III) complexes of TRIPN-pyr and DIPN-pyr were much less stable than the other four ligands. EPR spectra of the frozen solutions showed the low spin d⁷ Ni(III) complexes of TRIEN-pyr and DIPN-EN-pyr to be similar to those that have been found for poly-aza macrocyclic compounds.     

Enantioselective epoxidation of non-functionalized alkenes using carbohydrate based salen-Mn(III) complexes

Three new salen ligands with carbohydrate moieties were prepared from a salicylaldehyde derivative obtained by reaction of 1,2:5,6-di-O-isopropylidene-alpha-D-glucofuranose with 3-tert-butyl-5-(chloro-methyl)-2-hydroxybenzaldehyde. These ligands were coordinated with Mn(III) to give three chiral salen-Mn(III) complexes. The complexes were characterized and employed in the asymmetric epoxidation of unfunctionalized alkenes. Catalytic results showed that although there are no chiral groups on the diimine bridge, these complexes had some enantioselectivity, which indicates the carbohydrate moiety has an asymmetric inducing effect in the epoxidation reaction.