Studies on groundnut proteins. V. Physico-chemical properties of arachin prepared by different methods.

ORD,¹ CD, and fluorescence spectra of arachin prepared by Tombs' (Biochem. J., 96, 119; 1965), Dawson's (Anal. Biochem., 41, 305; 1971) or Shetty and Rao's (Anal. Biochem., 62, 108; 1974) procedure were measured; the effect of denaturants such as SDS, GuHCl, and acid was also determined. ORD and CD spectra showed differences, whereas fluorescence spectra did not show any difference. The effect of the denaturants was the same on the three arachins. At low concentrations of GuHCl (<2 m), the denaturant was bound by the protein molecule without causing any conformational change. The binding affinity varied among the arachins.     

Polypeptide composition of acetylcholine receptor purified from teleost and elasmobranch electroplax membranes

Acetylcholine receptor (AcChR) was solubilized and purified from membranes derived from electric organs of the marine fish Torpedo marmorata, Torpedo nobiliana, Narcine brasliensis, and of the freshwater eel, Electrophorus electricus, using techniques originally developed for Torpedo californica (27., 28.Biochem. Biophys. Res. Commun.49, 572–578; 1973, Biochemistry12, 852–856. The conditions used were identical in each case and the goal was to determine the degree of similarity between receptors from each source since conflicting reports have appeared with regard to polypeptide composition. The Torpedo and Narcine preparations were of high specific activity and exhibited four polypeptide components of apparent molecular weights 64, 59, 50, and 40 × 10³ upon polyacrylamide gel electrophoresis in sodium dodecyl sulfate. Two components were observed upon gel electrophoresis in sodium cholate or upon sucrose density gradient centrifugation, representing monomeric and dimeric forms. Eel acetylcholine receptor exhibited three major subunits of apparent molecular weights 57, 49, and 40 × 10³. The amino acid and neutral sugar composition of the purified receptor preparations have been determined. The results support the contention that the receptor is composed of several types of polypeptide.     

Zinc(II) tweezers containing artificial peptides mimicking the active site of phosphotriesterase: The catalyzed hydrolysis of the toxic organophosphate parathion

Two new ligand-containing histidine based on N,N′,N″-tris(N-benzyl-l-histidinyl)tri(2-aminoethyl)amine, L¹, namely N,N′,N″-tris[(1S)-2-methoxy-2-oxy-1-(1-benzylimidazol-4-ylmethyl)]nitrilotriacetamide L² and N,N′,N″-tris{N-benzyl-N-[N-benzyl-N-(N-benzyl-l-histidinyl)-l-histidinyl]-l-histidinyl}tri(2-aminoethyl)amine L³ were prepared. Zinc(II) binding studies by these ligand systems were analyzed by means of potentiometric and ¹H NMR titrations in aqueous methanol (33 % v/v). Subsequently their zinc(II) complexes [L¹Zn(H₂O)](ClO₄)₂·HClO₄ (1), [L²Zn(OH₂)](ClO₄)₂·H₂O (2), and ([L³Zn₃(H₂O)₃](ClO₄)₆·3HClO₄·5H₂O (3), respectively were synthesized and characterized. The reactivity of the trinuclear complex (3) toward the hydrolysis of the toxic organophosphate parathion was investigated and compared with that of the mononuclear reference complex (1). From the pH dependence of the apparent rate constants, and the deprotonation constant (pK_a) of the coordinated water molecules in (1), the active species were confirmed to be {[HL¹Zn(OH)]²⁺/[L¹Zn(H₂O)]²⁺} at pH 8.5. The trizinc complex (3) effects hydrolysis of parathion, with three times rate enhancement over the mononuclear (1), indicating that cooperative action of the three zinc centers is limited.     

Racemic nickel(II) pyridine-2-aldoximate complexes capped by 2,2-bipyridine and 1,10-phenanthroline: syntheses, structures and magnetic properties

Two Ni(II) pyridine-2-aldoximate complexes, Ni(pao)₂(bpy) (1) and Ni(pao)₂(phen) (2) (pao⁻=pyridine-2-aldoximate, bpy=2,2^′-bipyridine, phen=1,10-phenanthroline), were synthesized via the deprotonation of NiCl₂(Hpao)₂ in methanol followed by the addition of bidentate ligands of 2,2^′-bipyridine and 1,10-phenanthroline. Crystallization in CHCl₃ gave block-type crystals of 1 and 2 in high yields. The mononuclear structure surrounded by three bidentate ligands, i.e., two pao⁻ and one bpy or phen, was revealed by X-ray crystallography: 1 crystallizes in monoclinic space group P2₁/c with cell dimensions of a=13.457(3) Å, b=14.493(3) Å, c=19.104(4) Å, β=108.681(3)°, Z=4, and 2 crystallizes in monoclinic space group P2₁/n with cell dimensions of a=14.235(5) Å, b=12.018(4) Å, c=20.696(7) Å, β=110.304(4)°, Z=4. 1 and 2 each have two oximate groups (pao⁻), with an NO-trans arrangement around the Ni^II ion. Complexes 1 and 2 are racemic, namely, each molecule has a chiral center of Δ or Λ, thereby forming NO-trans-Δ and -Λ geometries in the solid state. Magnetic measurements revealed a paramagnetic S=1 spin state with a positive zero-field splitting parameter.     

Mono- and dinuclear (o-thioetherphenolato)-copper(II) complexes. Structural models for galactose oxidase

Three new o-thioetherphenol ligands have been synthesized: 1,2-bis(3,5-di-tert-butyl-2-hydroxyphenylsulfanyl)ethane (H₂bse), 1,2-bis(3,5-di-tert-butyl-2-hydroxyphenylsulfanyl)benzene (H₂bsb), and 4,6-di-tert-butyl-2-phenylsulfanylphenol (Hpsp). Their complexes with copper(II) were prepared and investigated by UV-Vis-, EPR-spectroscopy; their electro- and magnetochemistry have also been studied: [Cu^II(psp)₂] (1), [Cu^II₂(bse)₂] (2), [Cu^II₂(bsb)₂] (3), [Cu^II(bsb)(py)₂] (4). The crystal structures of the ligands H₂bse, H₂bsb, Hpsp and of the complexes 1, 2, 3, 4 have been determined by X-ray crystallography.     

Nickel(II) complexes of terdentate or symmetrical tetradentate Schiff bases: Evidence of the influence of the counter anions in the hydrolysis of the imine bond in Schiff base complexes

Two sets of ligands, set-1 and set-2, have been prepared by mixing 1,3-diaminopentane and carbonyl compounds (2-acetylpyridine or pyridine-2-carboxaldehyde) in 1:1 and 1:2 ratios, respectively, and employed for the synthesis of complexes with Ni(II) perchlorate, Ni(II) thiocyanate and Ni(II) chloride. Ni(II) perchlorate yields the complexes having general formula [NiL₂](ClO₄)₂(L = L¹ [N³-(1-pyridin-2-yl-ethylidene)-pentane-1,3-diamine] for complex 1 or L²[N³-pyridin-2-ylmethylene-pentane-1,3-diamine] for complex 2) in which the Schiff bases are monocondensed terdentate, whereas Ni(II) thiocyanate results in the formation of tetradentate Schiff base complexes, [NiL(SCN)₂] (L = L³[N,N′-bis-(1-pyridin-2-yl-ethylidine)-pentane-1,3-diamine] for complex 3 or L⁴ [N,N′-bis(pyridin-2-ylmethyline)-pentane-1,3-diamine] for complex 4) irrespective of the sets of ligands used. Complexes 5 {[NiL³(N₃)₂]} and 6 {[NiL⁴(N₃)₂]} are prepared by adding sodium azide to the methanol solution of complexes 1 and 2. Addition of Ni(II) chloride to the set-1 or set-2 ligands produces [Ni(pn)₂]Cl₂, 7, as the major product, where pn = 1,3-diaminopentane. Formation of the complexes has been explained by the activation of the imine bond by the counter anion and thereby favouring the hydrolysis of the Schiff base. All the complexes have been characterized by elemental analyses and spectral data. Single crystal X-ray diffraction studies confirm the structures of three representative members, 1, 4 and 7; all of them have distorted octahedral geometry around Ni(II). The bis-complex of terdentate ligands, 1, is the mer isomer, and complexes 4 and 7 possess trans geometry.     

Four mononuclear platinum(II) complexes: synthesis,DNA/BSA binding,DNA cleavage and cytotoxicity

Four new platinum(II) complexes: Pt^II L1·H₂O (C1, H₂ L1 = C₂₀H₁₆N₂O₂), Pt^II L2Cl₂ (C2, L2 = C₂₂H₁₆N₂O₂), Pt^II L3Cl₂·H₂O (C3, L3 = C₂₀H₁₆N₂), Pt^II L4Cl₂·0.4H₂O (C4, L4 = C₁₈H₁₄N₄) have been synthesized and characterized by using various physico-chemical techniques. The binding interaction of the four platinum(II) complexes C1–C4 with calf thymus (CT)-DNA has been investigated by UV–Vis and fluorescence emission spectrometry. The apparent binding constant (K _app) values follow the order: C3 > C1 > C2 > C4. In addition, fluorescence spectrometry of bovine serum albumin (BSA) with the four platinum(II) complexes C1–C4 showed that the quenching mechanism might be a static quenching procedure. For C1–C4, the number of binding sites was about one for BSA and the binding constants follow the order: C3 (7.08 × 10⁵M^?1) > C1 (2.82 × 10⁵M^?1) > C2 (0.85 × 10⁵M^?1) > C4 (0.15 × 10⁵M^?1). With the single condition change such as absence of an external agent, the DNA cleavage abilities of C3 exhibit remarkable changes. In addition, the cytotoxicity of C3 in vitro on tumor cells lines (MCF-7, HepG2 and HT29) were examined by MTT and showed better antitumor effects on the tested cells.     

Mononuclear and polynuclear halide and nitrate Cu(II) compounds with 1,4,5-triazanaphthalene as a ligand: Characterization, magnetism and X-ray structures

Using the ligand 1,4,5-triazanaphthalene (abbreviated as tan) in combination with Cu(II) salts, three mononuclear compounds, Cu(tan)₂Cl₂ (1), Cu(tan)₂Br₂ (3), Cu(tan)₂(NO₃)₂ (5) and three polynuclear compounds, [Cu(tan)Cl₂]_n (2), [Cu(tan)Br₂]_n (4), [Cu(tan)(NO₃)₂]_n (6) have been synthesized and characterized by UV-Vis, EPR, FTIR and Far-FTIR spectroscopies. The crystal structures of compounds 1, 3, 5 and 6 are reported, as well as that of the dioxane adduct of compound 4, [Cu(tan)Br₂(C₄H₈O₂)](C₄H₈O₂) (4A).The structure of (2) was solved by X-ray powder diffraction. The coordination geometry around the Cu(II) atoms is tetrahedral for (1) and (3), square-pyramidal for (4A) and distorted octahedral for (5) and (6). Magnetic susceptibility measurements on the polynuclear compounds revealed weak antiferromagnetic interactions between the Cu(II) atoms with interaction constants (J) of J = −9.1 and −10.5 cm⁻¹, for 4 and 6, respectively. For compound 2 two options for possible interactions were considered, with interaction constants which vary for J_rung −22.0 to −13.5 cm⁻¹ and J_rail −19.6 to −17.0 cm⁻¹. These figures are discussed in the light of relevant structural parameters and literature.     

Stepwise syntheses, structure and spectroscopic studies of ruthenium complexes of 2,6-bis(benzimidazol-2-yl)pyridine with o-iminoquinone ancillary ligand

The ruthenium complexes [Ru^II(bbp)(L)(Cl)] (1), [Ru^II(bbp)(L)(H₂O)] (2) and [Ru^II(bbp)(L)(DMSO)] (3) {bbp = 2,6-bis(benzimidazol-2-yl)pyridine, L = o-iminoquinone} have been synthesized in a stepwise manner starting from [Ru^III(bbp)Cl₃]. The single crystal X-ray structures, except for the complex 2, have been determined. All the complexes were characterized by UV-Vis, FT-IR, ¹H NMR, Mass spectroscopic techniques and cyclic voltammetry. The Ru^III/Ru^II couple for complexes 1, 2, and 3 appears at 0.63, 0.49, 0.55 V, respectively versus SCE. It is observed that complex 2, on refluxing in acetonitrile, results into [Ru^II(bbp)(L)(CH₃CN)], 4 which has been prepared earlier in a different method. The structural, spectral and electrochemical properties of complexes 1, 2 and 3 were compared to those of earlier reported complex 4, [Ru^II(bbp)(L)(CH₃CN)].     

Hydrothermal synthesis, crystal structures and properties of new Fe, Co, Ni, and Zn complexes with 6-quinolinecarboxylate: Interplay of coordinative and noncovalent interactions

Reactions of Fe^II, Co^II, Ni^II, and Zn^II salts with 6-quinolinecarboxylic acid (HL) under the hydrothermal conditions afford three monomeric complexes [M(L)₂(H₂O)₄] (M = Fe^II for 1, Co^II for 2, and Ni^II for 3) and a 1-D polymeric species {[Zn(L)₂(H₂O)] · H₂O}_n (4). The crystal structures of the ligand HL and these four complexes have been determined by using the X-ray single-crystal diffraction technique. The results suggest that complexes 1-3 are isostructural, displaying novel 3-D pillar-layered networks through multiple intermolecular hydrogen bonds, whereas in coordination polymer 4, the 1-D comb-like coordination chains are extended to generate a hydrogen-bonded layer, which is further reinforced via aromatic stacking interactions. Solid-state properties such as thermal stability and fluorescence emission of the polymeric Zn^II complex 4 have also been investigated.     

Syntheses and characterization of titanium malonato and amino acid complexes: [Ti(cp)2(OOCCH2NMe2)] - The first structurally characterized α-amino acid titanium(III) complex

The reaction of [Ti(cp^∗)₂(BTMSA)] (1) (cp^∗ = η⁵-C₅Me₅, BTMSA = bis(trimethylsilyl)acetylene) with malonic acids ((HOOC)₂CR₂, R = H, Me) and N,N-dimethylglycine resulted in the formation of titanium(IV) dicarboxylato complexes [Ti(cp^∗)₂{(OOC)₂CR₂}] (R = H, 2; R = Me, 3) and an α-amino acid titanium(III) complex [Ti(cp^∗)₂(OOCCH₂NMe₂)] (4). The identities of complexes 2-4 were confirmed by microanalysis, ¹H and ¹³C NMR spectroscopy (2, 3), ESI-MS and CID experiments (2, 3) as well as by ESR and magnetic measurements (μ_eff = 1.81, 298 K) for 4. Single X-ray diffraction analyses of 2 and 4 exhibited monomolecular complexes in which the titanium atom is distorted tetrahedrally coordinated by two η⁵-C₅Me₅ rings and by the chelating bound malonato-κ²O,O′ (2) and N,N-dimethylglycinato-κ²O,O′ ligand (4).     

Synthesis and structure of dichloropalladium(II) complexes of heteroleptic N,S- and N,Se-donor ligands based on the 2-organochalcogenomethylpyridine motif, and Mizoroki-Heck catalysis mediated by complexes of N,S-donor ligands

Ligands containing the 2-organochalcogenomethylpyridine motif with substituents in the 4- or 6-position of the pyridyl ring, R⁴,R⁶-pyCH₂ER¹ [R⁴ = R⁶ = H, ER¹ = SMe (1), SeMe (2), SPh (6), SePh (7); R⁴ = Me, R⁶ = H, ER¹ = SMe (3), SPh (8), SePh (9); R⁴ = H, R⁶ = Me, ER¹ = SMe (4), SPh (10), SePh (11); R⁴ = H, R⁶ = Ph, ER¹ = SMe (5), SPh (12), SePh (13)] are obtained on the reaction of R⁴,R⁶-pyMe with LiBuⁿ followed by R¹EER¹. On reaction with PdCl₂(NCMe)₂, the ligands with a 6-phenyl substituent form cyclopalladated species PdCl{6-(o-C₆H₄)pyCH₂ER¹-C,N,E} (5a, 12a, 13a) with the structure of 13a (ER¹ = SePh) confirmed by X-ray crystallography; other ligands form complexes of stoichiometry PdCl₂(R⁴,R⁶-pyCH₂ER¹). Complexes with R⁶ = H are monomeric with N,E-bidentate configurations, confirmed by structural analysis for 3a (R⁴ = Me, ER¹ = SMe), 7a (R⁴ = H, ER¹ = SePh) and 9a (R⁴ = Me, ER¹ = SePh). Two of the 6-methyl substituted complexes examined by X-ray crystallography are oligomeric with trans-PdCl₂(N,E) motifs and bridging ligands, trimeric [PdCl₂(μ-6-MepyCH₂SPh-N,S)]₃ (10a) and dimeric [PdCl₂(μ-6-MepyCH₂SePh-N,Se)]₂ (11a). This behaviour is attributed to avoidance of the Me···Cl interaction that would occur in the cis-bidentate configuration if the pyridyl plane had the same orientation with respect to the coordination plane as observed for 3a, 7a and 9a [dihedral angles 8.0(2)-16.8(2)°]. When examined as precatalysts for the Mizoroki-Heck reaction of n-butyl acrylate with aryl halides in N,N-dimethylacetamide at 120 °C, the complexes exhibit the anticipated trends in yield (ArI > ArBr > ArCl, higher yield for electron withdrawing substituents in 4-RC₆H₄Br and 4-RC₆H₄Cl). The most active precatalysts are PdCl₂(R⁴-pyCH₂SMe-N,S) (R = H (1a), Me (3a)); complexes of the selenium containing ligands exhibit very low activity. For closely related ligands, the changes SMe to SPh, 6-H to 6-Me, and 6-H to 6-Ph lead to lower activity, consistent with involvement of both the pyridyl and chalcogen donors in reactions involving aryl bromides. The precatalyst PdCl₂(pyCH₂SMe-N,S) (1a) exhibits higher activity for the reaction of aryl chlorides in Buⁿ₄NCl at 120 °C as a solvent under non-aqueous ionic liquid (NAIL) conditions.     

A sensitive continuous and discontinuous photometric determination of oxygen, carbon dioxide, and carbon monoxide in gases and fluids.

The paper describes a sensitive, rapid, and precise photometric method for the continuous and discontinuous determination of O₂, CO₂, and CO. The method is based on highly specific color reactions: O₂ is determined by its reaction with alkaline catechol + Fe²⁺ yielding intensively colored products, CO₂ is determined by its color reaction with a solution of fuchsin + hydrazine; and CO is determined by its reaction with hemoglobin. The basic experimental equipment is that of the AutoAnalyzer (cf.Wolf, Zander, and Lang, 1976, Anal. Biochem.74, 585), with an additional chamber for the injection of small gas samples in the case of the discontinuous analysis. Continuously analyzing in a standardized gas flow of 1 ml · min^?1 (STPD), the lower limits of the sensitivities are 50 ppm for O₂, 100 ppm for CO₂, and 50 ppm for CO. The discontinuous analysis of the three gases requires the basic experimental equipment plus an airtight chamber. The lower limits of the amounts are 0.1 μl (STPD) for O₂, 0.2 μl for CO₂, and 0.1 μl for CO.     

Does copper-d-penicillamine catalyze the dismutation of O2−?

It has been reported (M. Younes and U. Weser, 1977, Biochem. Biophys. Res. Commun.78, 1247–1253; E. Lengfelder and E. F. Elstner, 1978, Hoppe-Seyler's Z. Physiol. Chem.359, 751–757) that the complex [Cu(I)₈Cu(II)₆(D-penicillamine)₁₂Cl]^5?-efficiently catalyzes the dismutation of O₂^? and that this activity is resistant to both EDTA and CN^?. However, careful study has demonstrated that this complex is unable to catalyze the dismutation of O₂^?, but that it slowly decomposes to simpler copper complexes which are active. Moreover, the activity which is observed is suppressed by EDTA or by Chelex 100 treatment.     

Pd(II) complexes containing N-alkyl-3-pyridine-5-trifluoromethyl pyrazole ligands: Synthesis, NMR studies and X-ray crystal structures

Palladium [PdCl₂(L)] complexes with N-alkylpyridylpyrazole derived ligands [2-(5-trifluoromethyl-1H-pyrazol-3-yl)pyridine (L¹), 2-(1-ethyl-5-trifluoromethyl-1H-pyrazol-3-yl)pyridine (L²), 2-(1-octyl-5-trifluoromethyl-1H-pyrazol-3-yl)pyridine (L³), and 2-(3-pyridin-2-yl-5-trifluoromethyl-pyrazol-1-yl)ethanol (L⁴) were synthesised. The crystal and molecular structures of [PdCl₂(L)] (L = L², L³, L⁴) were resolved by X-ray diffraction, and consist of monomeric cis-[PdCl₂(L)] molecules. The palladium centre has a typical square-planar geometry, with a slight tetrahedral distortion. The tetra-coordinate metal atom is bonded to one pyridinic nitrogen, one pyrazolic nitrogen and two chlorine ligands in cis disposition. Reaction of L (L², L⁴) with [Pd(CH₃CN)₄](BF₄)₂, in the ratio 1M:2L, gave complexes [Pd(L)]₂(BF₄)₂. Treatment of [PdCl₂(L)] (L = L², L⁴) with NaBF₄ and pyridine (py) and treatment of the same complexes with AgBF₄ and triphenylphosphine (PPh₃) yielded [Pd(L)(py)₂](BF₄)₂ and [Pd(L)(PPh₃)₂](BF₄)₂ complexes, respectively. Finally, reaction of [PdCl₂(L⁴)] with 1 equiv of AgBF₄ yields [PdCl(L⁴)](BF₄).     

Syntheses and molecular structures of Co-Na and Co-K coordination polymers constructed using mono- and bis-chelated cobalt(III) complexes of bis(2-pyridylcarbonyl)amide ion

Four new hetero-bimetallic Co³⁺-Na⁺ and Co³⁺-K⁺ coordination polymers having the molecular formulae [Na(H₂O)Co(L)(N₃)₃]_n (1), [Na₂Co(L)(N₃)₃(H₂O)₅][Co(L)(N₃)₃] (2), K[Co(L)(NCS)₃]·H₂O (3) and K[Co(L)₂][Co(NCS)₄]·0.5H₂O (4), were synthesized. Compounds 1-4 were characterized by single crystal X-ray diffraction, IR, UV-Vis, and thermogravimetric methods. These bimetallic systems have EE, EO azide bridge (1, 2) as well as bent (1, 2, 3) and linear (1, 4) aquo bridges. Important features observed among them were: a Z-shaped and diamond-shaped Co₂Na₂ clusters in 1, a centrosymmetric double ladder like polymer based on Na₄ cluster in 2, and a linear KOK core having paddle-wheel structure in 4.