1,10-Phenanthroline-5,6-dione as a building block for the synthesis of homo- and heterometallic complexes

1,10-Phenanthroline-5,6-dione (C₁₂H₆N₂O₂ (1)) reacts with V(η⁶-mesitylene)₂ and Ti(η⁶-toluene)₂ affording coordination compounds of general formula M(O,O′---C₁₂H₆N₂O₂)₃ (M=Ti (2); M=V (3)) which further react with TiCl₄ or TiCp₂(CO)₂ yielding the tetrametallic species M(O,O′---C₁₂H₆N₂O₂---N,N′)₃(M′L_n)₃ (M=V, M′L_n=TiCl₄ (4); M=Ti, M′L_n=TiCp₂ (5); M=V, M′L_n=TiCp₂ (6)). The complex salt [Fe(N,N′---C₁₂H₆N₂O₂)₃][PF₆]₂ (7) has been obtained from iron(II) chloride tetrahydrate and 1 in the presence of NH₄PF₆. The reaction of 7 with TiCp₂(CO)₂ affords the tetrametallic derivative [Fe(N,N′---C₁₂H₆N₂O₂---O,O′)₃(TiCp₂)₃][PF₆]₂ (8). TiCl₂(THF)₂ reacts with MCp₂(O,O′---C₁₂H₆N₂O₂) to give MCp₂(O,O′---C₁₂H₆N₂O₂---N,N′)TiCl₂ (M=Ti (9); M=V (10)). By reaction of TiCp₂(O,O′---C₁₂H₆N₂O₂---N,N′)TiCl₂ (9) with C₁₂H₆N₂O₂, the bimetallic derivative TiCp₂(O,O′---C₁₂H₆N₂O₂---N,N′)TiCl₂(O,O′---C₁₂H₆N₂O₂) (11) has been prepared, which readily adds to TiCl₄, to give the trimetallic titanium derivative TiCp₂(O,O′---C₁₂H₆N₂O₂---N,N′)TiCl₂(O,O′---C₁₂H₆N₂O₂---N,N′)TiCl₄ (12). VCp₂(O,O′---C₁₂H₆N₂O₂---N,N′)TiCl₂ (10) reacts with the tris-chelate iron(II) cation 7 affording the heptametallic cationic complex [Fe(N,N′---C₁₂H₆N₂O₂---O,O′)TiCl₂(N,N′---C₁₂H₆N₂O₂---O,O′)VCp₂]₃ ⁺² isolated as the hexafluorophosphate 13.     

H NMR study of the interaction of N,N′,N″-triacetyl chitotriose with Ac-AMP2, a sugar binding antimicrobial protein isolated from Amaranthus caudatus

The interaction between Ac-AMP2, a lectin-like small protein with antimicrobial and antifungal activity isolated from Amaranthus caudatus, and N,N′,N″-triacetyl chitotriose was studied using ¹H NMR spectroscopy. Changes in chemical shift and line width upon increasing concentration of N,N′,N″-triacetyl chitotriose to Ac-AMP2 solutions at pH 6.9 and 2.4 were used to determine the interaction site and the association constant K_a. The most pronounced shifts occur mainly in the C-terminal half of the sequence. They involve the aromatic residues Phe¹⁸, Tyr²⁰ and Tyr²⁷ together with their surrounding residues, as well as the N-terminal Val-Gly-Glu segment. Several NOEs between Ac-AMP2 and the N,N′,N″-triacetyl chitotriose resonances are reported.     

Stereognostic coordination chemistry 4 the design and synthesis of a selective uranyl ion complexant

A new approach to ligand design for the sequestration of metal-oxo cations has been called stereognostic coordination chemistry, in that the ligand incorporates a traditional Lewis base coordination to the metal center and a hydrogen bond donor to interact with the oxo group. This paper reports the synthesis of ligands that are more rigid and sterically predisposed to bind the targeted UO₂²⁺ cation. These are the tripod ligands tris-N,N′,N′′-[2-(2-carboxy-phenoxy)ethyl]-1,4,7-triazacyclononane bis-hydrochloride (ETAC · 2HCl) and tris-N,N′,N′′-[2-(2-carboxy-4-decyl-phenoxy)ethyl]-1,4,7-triazacyclononane tris-hydrochloride (DETAC · 3HCl), which chelate uranyl with a tris-carboxylate coordination sphere and provide a hydrogen bond donor through a protonated amine on the triazacyclononane macrocycle to interact with one uranyl oxo atom. Structural models predict that upon uranyl binding the hydrogen bond donor must point directly towards the oxo atom, enforcing a stereognostic interaction. Both ETAC and DETAC chelate the uranyl ion; DETAC is a powerful extractant and will quantitatively extract uranyl into an organic phase at pH 1.9 and above. The extraction coefficient is estimated to be 10¹⁴ in neutral aqueous conditions. Vibrational spectra of ¹⁸O labeled UO₂²⁺ have been used to probe the stereognostic coordination to uranyl utilizing hydrogen bonding.     

Studies of the cation complexing ability of crowns Part I. Synthesis, characterization and crystal structure of diazacrowns and their barium complexes

A number of N,N′-bis(4-substituted phenyl)-1,7-diaza-12-crown-4 and N,N′-bis(4-substituted phenyl)-1, 10-diaza-18-crown-6 (where the substituents are OCH₃, CH₃, H, Cl, respectively) have been prepared by cyclization reaction of a ditosylate with the appropriately substituted diol. These new macrocyclic ligands have been characterized by means of elemental analysis, IR, ¹H NMR and MS spectra. The crystal structures of N,N′-bis(4-chlorophenyl)-1,10-diaza-18-crown-6 (21) and its complex with barium thiocyanate Ba(SCN)₂ (22) have been determined by single crystal X-ray diffraction. The crystallographic data are as follows: 21: C₂₄H₃₂Cl₂N₂O₄, orthorhombic, P2₁2₁2₁, A=4.852(1), B=11.989(2), C=41.231(8) Å, V=2398.7(8) ų, Z=4; 22: C₂₆H₃₂Cl₂N₄O₄S₂Ba, monoclinic, P2₁/c, A=8.801(2), B=11.653(9), C=15.756(6) Å, ß=105.96(3)°, V=1553.7(14) ų, Z=2. In the complex, the Ba atom is eight-coordinate (O(1), O(2), O(1)′, O(2)′, N(1), N(1)′, N(21), N(21)′) to form a distorted D_6h geometry with the Ba atom at the center of crystallographic symmetry.     

Redox state of the partially reduced cytochrome aa3-cyanide complex

The low-spin ferric cyanide complex of beef heart cytochrome aa₃ can be partially reduced by stoichiometric additions of ferrous cytochrome c or by similar additions of N,N,N′,N′-tetramethyl-p-phenylene diamine. In both cases the initial ratio of cytochrome c oxidized: cytochrome a reduced or Wurster's Blue: cytochrome a reduced approximates the value 2. It is concluded that the binding of a single HCN prevents the reduction of both cytochrome a₃ and its associated EPR-invisible Cu atom.     

Selective addressing of heteroditopic ligands by iron(II) and platinum(II)

The heteroditopic ligand 4′-(4,7,10-trioxadec-1-yn-10-yl)-2,2′:6′,2″-terpyridine, 2, contains an N,N′,N″-donor metal-binding domain that recognizes iron(II), and a terminal alkyne site that selectively couples to platinum(II). This selectivity has been used to investigate routes to the formation of heterometallic systems. The single crystal structures of ligand 2 and the complex [Fe(2)₂][PF₆]₂ are reported.     

Menadiol as an electron donor for reversed oxidative phosphorylation in submitochondrial particles

Dithiothreitol in the presence of menadione or N,N,N′,N′-tetramethyl-p-phenylenediamine provides the reducing equivalents for oxidative phosphorylation and the ATP-dependent reduction of NAD⁺ in submitochondrial particles. With menadione the reaction is nearly as fast as with succinate and it is insensitive to antimycin, indicating electron entry between the first and second sites of oxidative phosphorylation. The phenylenediamine-mediated reduction of NAD⁺ is nearly as fast as succinate-linked reduction and is antimycin sensitive.     

Synthesis of glycoconjugate polymer carrying globotriaose as artificial multivalent ligand for Shiga toxin-producing Escherichia coli O157: H7

As an artificial ligand, a glycoconjugate polymer carrying carbohydrate moiety of lactosyl ceramide or globotriaosyl ceramide (Gb₃) was synthesized. Gb₃ is known as the receptor of Shiga toxin-producing Escherichia coli O157: H7. The preparation of the glycoconjugate polymer initially involves the construction of the carbohydrate moiety of Gb₃ derivative which has n-pentenyl group as polymerizable group. In addition, the n-pentenyl group of the Gb₃ derivative was modified and different polymerizable groups such as acrylamide group were introduced at ω-position of the aglycon. Radical polymerization of the synthesized glycosyl monomers with or without acrylamide proceeded smoothly in water using ammonium persulfate and N, N, N′, N′-tetramethylethylenediamine as usual initiator system and gave water-soluble glycoconjugate polymers having various polymer compositions. These polymers have the potential to neutralize Shiga toxin by reason of cluster effect and multivalency.     

Calcium is required for the increase of dark respiration during diurnal nitrogen fixation by Synechococcus RF-1

Under 12/12 h light/dark cycles, 1 mM ethyleneglycol-bis-(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA, pH 8.0) added at the start of the dark period, inhibited the increase of dark respiration which was associated with nitrogen fixation in Synechococcus RF-1. Twenty-five millimolar NaNO₃ added 30 min before the start of dark period suppressed this respiratory increase. If 1.25 mM CaCl₂ was added to the EGTA-treated sample from 3 to at least 10 h later in the dark period, a quick rise in respiratory rate was observed. This rise was also reduced by 25 mM NaNO₃. Extracellular Ca²⁺ appears to be required for the increase in dark respiration associated with the rhythmic appearance of nitrogenase activity in the dark cycle.     

Synthetic routes to mono-N-functionalized P2N2-ligands

Three different synthetic routes have been explored for the synthesis of the mono-N-substituted phosphinoamine N-ethyl,N′bis[2(diphenylphosphino)phenyl]propane-1,3-diamine: (a) selective alkylation of N,N′bis[2(diphenylphosphino)phenyl]propane-1,3-diamine; (b) linkage of the different fragments of N-ethyl,N′bis[2(diphenylphosphino)phenyl]propane-1,3-diamine; (c) selective acylation of N,N′bis[2(diphenylphosphino)phenyl]propane-1,3-diamine followed by acetyl reduction. While approaches (a) and (b) were unsuccessful, N-ethyl,N′bis[2(diphenylphosphino)phenyl]propane-1,3-diamine was obtained by route (c) via separation of the mono- and di-alkylated P₂N₂-species obtained from reduction, through complexation of Ni(NO₃)₂6H₂O followed by demetallation reaction with KCN. Additional related phosphinoamine chelates and phosphonium adducts were synthesized and characterized by conventional physico–chemical techniques.     

N,N′-Ethylene-bis(3-methoxysalicylideneimine) mononuclear (4f) and heterodinuclear (3d–4f) metal complexes: Synthesis, crystal structure and luminescent properties

The stepwise synthesis of mononuclear (4f) and heterodinuclear (3d–4f) Salen-like complexes has been investigated through structural determination of the intermediate and final products occurring in the process. In the first step, reactions of ligand H₂L and Ln(NO₃)₃ · 6H₂O give rise to three mononuclear lanthanide complexes Ln(H₂L)(NO₃)₃ [H₂L = N,N′-ethylene-bis(3-methoxysalicylideneimine), Ln = Nd (1), Eu (2) and Tb (3)], in which N,N′-ethylene-bis(3-methoxysalicylideneimine) acts as tetradentate ligands with the O₂O₂ set of donor atoms capable of effective coordination. These species are fairly stable and have been isolated. Then, addition of Cu(Ac)₂ · H₂O to the mononuclear lanthanide complex yields expected heterodinuclear (3d–4f) complexes Cu(L)Ln(NO₃)₃ · H₂O [Ln = Nd (4) and Eu (5)] where the Cu(II) ion is inserted to the inner N₂O₂ cavity. Luminescent analysis reveals that complex 3 exhibits characteristic metal-centered fluorescence of Tb(III) ion. However, the characteristic luminescence of both Sm(III) and Eu(III) ions is not observed both in solution and solid state of the complexes.     

Membrane potential generation by two reconstituted mitochondrial systems: Liposomes inlayed with cytochrome oxidase or with ATPase

Formation of a membrane potential in two types of liposomes, one inlayed with cytochrome c + cytochrome oxidase, and another, with oligomycin-sensitive ATPase, has been demonstrated. To detect a membrane potential, phenyl dicarbaundecaborane (PCB⁻), a penetrating anion probe, was used.

The first type of liposome was reconstituted from a solution of purified cytochrome oxidase, mitochondrial phospholipids and cytochrome c, the latter being enclosed inside liposomes. Cytochrome c bound to the outer surface of the liposome membrane was removed by washing with NaCl. Such liposomes catalyzed oxidation of ascorbate by oxygen in the presence of phenazine methosulfate or N,N,N′,N′-tetramethyl-p-phenylenediamine. The oxidation was found to support the PCB⁻ uptake by liposomes. The PCB⁻ response was prevented and reversed by cyanide, protonophorous uncouplers and external cytochrome c.

Liposomes of the second type were prepared from a solution of mitochondrial phospholipids, coupling factors F₁and F_c, and the hydrophobic proteins of the oligomycin-sensitive ATPase. These liposomes catalyzed ATP hydrolysis coupled with the PCB⁻ uptake. The latter effect was prevented and reversed by oligomycin and uncouplers.

The conclusion is made that membrane potential can be independently formed by enzymic reactions of two different kinds: (1) redox (e.g. cytochrome c oxidase) and (2) hydrolytic (ATPase).     

X-ray crystal structure of Cu2(medpco-2H)Cl2, (medpco = N,N′-bis(2-N,N-dimethylaminoethyl)pyridine-2,6-dicarboxamide 1-oxide. Copper(II) complexes of a deprotonated binucleating pyridine N-oxide ligand

The X-ray structure is reported for the complex Cu₂(medpco-2H)Cl₂, (medpco = N,N′-bis-N,N-dimethylaminoethyl)pyridine-2,6-dicarboxamide 1-oxide. The complex is triclinic, , a=8.313(4), B=11.403(5), C=11.611(3) Å, =91.66(3), β=108.99(4), γ=109.60(3)° and Z=2. The deprotonated ligand (medpco-2H)²⁻ acts as a binulceating ligand, producing an N-oxide-bridged complex. Each copper in Cu₂(medpco-2H)Cl₂ is five-coordinate, being coordinated by a bridging N-oxide oxygen, a deprotonated amide nitrogen, a tertiary amine nitrogen and two bridging chlorides. The complex does not exhibit significant magnetic interaction, and this may be the result of distortion of the bridging geometry from planarity. A range of other, apparently N-oxide-bridged, complexes of the type Cu₂(medpco-2H)X₂ is reported. The complex Cu₂(medpco-2H)Br₂·H₂O is strongly antiferromagnetic, with magnetic data closely fitting the expected binuclear structure.     

A novel one-pot three-component reaction: synthesis of triheterocyclic 4H-pyrimido[2,1-b]benzazoles ring systems

A novel one-pot three-component condensation reaction of an aldehyde, β-ketoester and 2-aminobenzimidazole or 2-aminobenzothiazole in 1,1,3,3-N,N,N′,N′-tetramethylguanidinium trifluoroacetate as an ionic liquid is described. During the course of this reaction 4H-pyrimido[2,1-b]benzimidazoles or 4H-pyrimido[2,1-b]benzothiazoles are formed in high yields at 100 °C. The ionic liquid can be recovered conveniently and reused efficiently.     

Sulfide oxidation with H2O2 catalyzed by manganese complex of N,N′,N″-tris(2-hydroxypropyl)-1,4,7-triazacyclononane

[MnL](ClO₄)₂ (L = N,N′,N″-tris(2-hydroxypropyl)-1,4,7-triazacyclononane) has been tested for catalyzing sulfide oxidation. In the presence of this complex, ethyl phenyl sulfide, butyl sulfide and phenyl sulfide are completely oxidized to the corresponding sulfoxides and sulfones with H₂O₂ as the oxidant. 2-Chloroethyl phenyl sulfide oxidation yield 2-chloroethyl phenyl sulfone and phenyl vinyl sulfone. In ethyl phenyl sulfide oxidation, effects of complex and H₂O₂ concentration and temperature on the reaction rate have been discussed. Through controlling reaction conditions, ethyl phenyl sulfoxide and ethyl phenyl sulfone may be produced selectively. The UV–Vis and electron paramagnetic resonance (EPR) studies on catalyst solution indicate that metal centre of the complex is transformed from Mn(II) to Mn(IV) after the addition of H₂O₂. At 25 °C, rate constant for ethyl phenyl sulfide oxidation is 4.38 × 10⁻³ min⁻¹.     

Interaction of oxidized and reduced N-methylphenazonium methosulfate (PMS) with Photosystem II

In 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) poisoned chloroplasts, the restoration of the fluorescence induction is presumed to be due to a back reaction of the reduced primary acceptor (Q⁻) and the oxidized primary donor (Z⁺) of Photosystem II. Carbonylcyanide m-chlorophenylhydrazone (CCCP) is known to inhibit this back reaction. The influence of reduced N-methylphenazonium methosulfate (PMS) in the absence of CCCP and of oxidized PMS in the presence of CCCP on the back reaction was investigated and the following results were obtained:

1. (1) Reduced PMS at the concentration of 1 μM inhibits the back reaction as effectively as hydroxylamine, suggesting an electron donating function of reduced PMS for System II.

2. (2) The inhibition of the back reaction by CCCP is regenerated to a high degree by oxidized PMS which led to assume a cyclic System II electron flow catalysed by PMS.

3. (3) At concentrations of reduced PMS higher than 1 μM it is shown that both the fast initial emission and more significantly the variable emission are quenched.

One-dimensional polymeric chlorocadmate(II) systems of N-methylpiperazinium and N,N′-dimethylpiperazinium compounds: synthesis, structural and thermal properties

The chlorocadmate(II) systems of (H₂me₂pipz)[Cd₂Cl₆(H₂O)₂] (1) and (H₂mepipz)₂[Cd₃Cl₁₀(H₂O)] (2) (L = me₂pipz = N,N′-dimethylpiperazine; L′ = mepipz = N-methylpiperazine) were prepared and their structural and thermal properties investigated. Compound 1 is monoclinic, space group P2₁/c, A = 7.664(1), B = 7.472(4), C = 15.347(1) Å, β = 99.468(7)°, Z = 2, R = 0.024. The crystal structure consists of organic cations and infinite one-dimensional chains of [CdCl₃(H₂O)]_n³⁻ anions. Each Cd atom is octahedrally surrounded by bridged and terminal chlorine atoms and by a water molecule, which is in trans position with respect to the terminal chlorine atom. Inter- and intrachain hydrogen bond interactions between the terminal chlorine atoms and the water molecules contribute to the crystal packing. Compound 2 is orthorhombic, space group Cmc2₁, A = 15.286(3), B = 13.354(3), C = 13.154(3) Å, R = 0.023. The crystal structure consists of organic dications and infinite chains of [Cd₂Cl₆(CdCl₄H₂O]_n⁴⁻ units running along the [001] axis. Each unit is formed of regularly alternate six-coordinated Cd atoms, one of them linking one pentacoordinated Cd atom which completes its coordination througha water molecule. A strong hydrogen bond interaction involving the organic dication and the inorganic chain contributes to the crystal packing. Differential hydrogen bond interaction involving the organic dication and the inorganic chain contributes to the crystal packing. Differential scanning calorimetry measurements did not show the presence of any structural phase transitions. The structures are compared with those of (H₂pipz)[Cd₂Cl₆(H₂O)₂] (3), (H₂mepipz)[Cd₂Cl₆(H₂O)₂]·H₂O (4) and (H₂mepipz)[Cd₂Cl₆] (5) (L = pipz = piperazine, L′ = mepipz = N-ethylpiperazine).     

The influence of pH on the inhibition of oxidative phosphorylation and electron transport by triethyltin

The ability of triethyltin to inhibit oxidative phosphorylation and electron transport in tightly coupled rat liver mitochondria is very dependent on the pH and the ionic constitution of the assay medium.

1. 1. In an assay medium containing Cl⁻ at an alkaline pH, above 7.1, triethyltin inhibited both the ADP stimulated rate of oxygen uptake and the dinitrophenol-induced ATPase (EC 3.6.1.3) but had no effect on the dinitrophenol-stimulated rate of oxygen uptake. If the pH was reduced to below 6.9 the pattern of inhibition changed and both the ADP and dinitrophenol-stimulated rates of oxygen uptake were inhibited by triethyltin.

2. 2. In the absence of Cl⁻ in the medium triethyltin inhibited both the ADP-stimulated rate of oxygen uptake and dinitrophenol-induced ATPase and had no effect on the dinitrophenol-stimulated rate of oxygen uptake at either pH 7.4 or 6.6.

3. 3. In either the presence or absence of Cl⁻ the ability of triethyltin to inhibit ATP synthesis appears to markedly decrease as the pH is lowered from 7.4 to 6.6.

4. 4. The significance of these observations is discussed in relation to the operation of a Cl⁻/OH⁻ antiport in the coupling membrane.

Isolation and properties of plastocyanin from Anabaena variabilis

Plastocyanin is a copper protein found in photosynethetic tissue and it exhibits the properties of a physiological redox reagent. This protein has been purified from the blue-green alga Anabaena variabilis. Plastocyanin is required for a number of partial reactions of the photosynthetic electron transfer chain. These reactions include the transfer of electrons from reduced 2,3′,6-trichlorophenolindophenol,N,N,N′,N′- tetramethyl-p-phenylenediamine and 2,3,5,6-tetramethyl-p-phenylenediamine to low potential oxidants. Reduced cytochrome c photooxidation does not appear to be dependent on plastocyanin. Cytochrome f, isolated from this alga, will partially replace plastocyanin in many of these reations. Inhibition of photosynthetic reactions by copper chelators appears to occur at some site other than the site of plastocyanin function.     

Ruthenium complexes containing tertiary phosphines and imidazole or 2,2′-bipyridine ligands

Complexes RuCl₃(PPh₃)L₂ (L = MeIm (1a, Im (1b)) and [RuCl₂(PPh₃)₂(bipy)]Cl·4H₂O (2) have been synthesized via the ruthenium(III) precursor RuCl₃(PPh₃)₂ (DMA), and characterized, including an X-ray structural analysis for 1a (MeIm = N-methylimidazole, Im = imidazole, bipy = 2,2′-bipyridyl, and DMA = N, N′-dimethylacetamide). Crystals of 1a are monoclinic, space group P2₁/n, A = 10.5491(5), B = 20.4934(9), C = 12.8285(4) Å, β = 90.166(4)°, Z = 4. The structure, which reveals a mer configuration for the chlorides, and cis-methylimidazoles, was solved by conventional heavy atom methods and was refined by full-matrix least-square procedures to R = 0.041 and R_w = 0.042 for 3328 reflections with I 3σ(I). From the RuCl₂(PPh₃)₃ precursor, the ruthenium(II) complexes RuCl₂(PPh₃)₂L₂ and [RuCl(PPh₃)L₄]Cl have been made (L = Im or MeIm), while [RuCl(dppb)Im₃]Cl has been made from [RuCl₂(dppb)]₂(μ-dppb) (dppb = Ph₂P(CH₂)₄PPh₂).