Ruthenium(II) dipyridoquinoxaline-norbornene: synthesis, properties, crystal structure, and use as a ROMP monomer

The synthesis, X-ray structure, and electrochemical and photophysical characterization of [Ru(phen)(2)dpq-n][PF(6)](2) (phen = phenanthroline, dpq-n = dipyridoquinoxaline-norbornene) are described. This complex contains a Ru(phen)(3)(2+) moiety in close conjugation with a norbornene unit and is the first example of a Ru(II) diimine complex capable of undergoing ring-opening metathesis polymerization. Luminescence studies of this complex showed an increase in quantum efficiency in polar solvents and in water. Preliminary ring-opening metathesis polymerization studies, carried out at low monomer-to-initiator ratio, showed the formation of an oligomeric mixture composed mainly of the dimer of this complex. This dimer exhibits photophysical and redox properties similar to those of the monomer, indicating that the Ru(phen)(3)(2+) moiety remains intact during the polymerization.     

Ternary complexes of nickel(II) withAMP,ADP andATP as primary ligands and some biologically important polybasic oxygen acids as secondary ligands

Summary Potentiometric equilibrium measurements have been made at 25±0.1 °C (=0.1 mol dm^–3 KNO₃) for the interaction of adenosine-5-mono-, -di-, and-triphosphate (AMP,ADP, andATP) and Ni(II) with biologically important secondary ligand acids (malic, maleic, succinic, tartaric, citric and oxalic acids) in a 1:1:1 ratio and the formation of various 1:1:1 mixed ligand complex species inferred from the potentiometricpH titration curves. Initial estimates of the formation constants of the resulting species and the acid dissociation constants ofAMP,ADP,ATP and secondary ligand acid, have been refined with SUPERQUAD computer program. In some systems logK values are positive, i.e. the ternary complexes are found to be more stable than the corresponding binary complexes. H-bond formation seems to be most effective in deciding the stability of the ternary complexes formed in solution. Stabilities of mixed ligand complexes increases in the orderAMP<ADP<ATP. With respect to the secondary ligands, the formation constants of the mixed lignads complexes decrease in the order succinic>maleic>tartaric>malic>citric>oxalic acid.

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Ternäre Komplexe von Nickel(II) mitAMP,ADP undATP als Primärliganden und einigen biologisch wichtigen polyfunktionellen Carbonsäuren als Sekundärliganden

Zusammenfassung Es wurde die Wechselwirkung von Adenosin-5-mono-, -di- und -triphosphat (AMP,ADP undATP) und Ni(II) mit biologisch relevanten Säuren als Sekundärliganden (Äpfel-, Malein-, Bernstein-, Wein-, Zitronen- und Oxalsäure) im Verhältnis 1:1:1 mittels potentiometrischer Gleichgewichtsmessungen bei 25±0.1 °C und =0.1 mol dm^–3 KNO₃ untersucht. Aus den potentiometrischepH-Titrationen ergaben sich verschiedene 1:1:1-Komplexe mit gemischten Liganden. Zunächst abgeschätzte Komplexbildungskonstanten und Säuredissoziations-konstanten vonAMP,ADP,ATP mit den als Sekundärliganden eingesetzten Säuren wurden über das SUPERQUAD-Rechenprogramm verfeinert. In einigen Systemen sind die Werte von logK positiv, was bedeutet, daß die ternären Komplexe stabiler sind als die entsprechenden binären Komplexe. In einige ternären Komplexen scheinen die Wasserstoffbrücken zwischen den Liganden entscheidend zu sein. Die Stabilitäten der gemischten Liganden steigen in der ReiheAMP<ADP<ATP an. Bezüglich der Sekundärliganden ergibt sich die absteigende Stabilitätsreihung Bernsteinsäure>Maleinsäure>Weinsäure>Äpfelsäure>Zitronensäure>Oxalsäure.

     

Polarographic Determination of the Formation Constants of the Mixed Ligand Complexes of Cd(II) and Pb(II) with Thiosulphate and Halide Ions

The mixed ligand complexes of Cd(II) and Pb(II) with thiosulphate as a primary ligand and chloride, bromide of iodide (individually) as a secondary ligand have been polarographically, investigated at 30°C and at a constant ionic strength of μ = 1.0 M (NaClO₄). Two mixed ligand complexes were formed with the Cd(II) ion: log β₁₂ = 4.77, 5.30 and 6.78 for the chloride, bromide and iodide ions, respectively; and log β₂₁ = 5.36, 5.04 and 6.22 for the same ions. For the Pb(II)-Ts-Cl system, only one mixed ligand complex was formed with a log stability constant log β₂₁ =4.35. For the Pb(II)-Ts-Br system, three mixed ligand complexes are obtained with log β₁₁ = 3.63, log β₁₂ = 4.51 and log β₂₁ = 4.85.     

A Computational Study of 3‐D Helium Clusters

Physical and thermodynamic properties have been calculated and analyzed for the best and optimized geometries of the 3‐D clusters with N = 3 to N = 10 atoms and unit cells of three types of crystalline systems using ab initio RHF/6–31G^** method. Dependence of the lattice binding energy on the cluster parameter, R, has been studied. Similar behavior observed for the binding energies for all clusters shows that probabilities of their existence in the condensed phase are more or less the same. In the next step, thermodynamic properties have been calculated and analyzed for He₂₇ 3‐D helium clusters with simple cubic, body centered cubic (bcc), trigonal and hexagonal (hcp) configurations. The results show that the hexagonal cluster is more favored over other clusters. It is found that these clusters are electronically stable over a limited range of the values for the lattice parameter. Δ_fH is constant in this stability region and thus the Δ_fG exactly follows the variations of TΔ_fS. Surface effects have been investigated by comparing the square and hexagonal He₉ 2‐D lattices with the cubic and hexagonal He₂₇ 3‐D lattices, respectively. The lattice parameters, densities and molar volumes calculated for the clusters with hcp and bcc configurations have satisfactory agreement with the available experimental values. Properties of the He₁₃, He₃₄ and He₁₀₄ hcp clusters have also been calculated and analyzed.     

Metal–metal bonded alkaline-earth distannyls

The first families of alkaline-earth stannylides [Ae(SnPh₃)₂·(thf)_x] (Ae = Ca, x = 3, 1; Sr, x = 3, 2; Ba, x = 4, 3) and [Ae{Sn(SiMe₃)₃}₂·(thf)_x] (Ae = Ca, x = 4, 4; Sr, x = 4, 5; Ba, x = 4, 6), where Ae is a large alkaline earth with direct Ae–Sn bonds, are presented. All complexes have been characterised by high-resolution solution NMR spectroscopy, including ¹¹⁹Sn NMR, and by X-ray diffraction crystallography. The molecular structures of [Ca(SnPh₃)₂·(thf)₄] (1′), [Sr(SnPh₃)₂·(thf)₄] (2′), [Ba(SnPh₃)₂·(thf)₅] (3′), 4, 5 and [Ba{Sn(SiMe₃)₃}₂·(thf)₅] (6′), most of which crystallised as higher thf solvates than their parents 1–6, were established by XRD analysis; the experimentally determined Sn–Ae–Sn′ angles lie in the range 158.10(3)–179.33(4)°. In a given series, the ¹¹⁹Sn NMR chemical shifts are slightly deshielded upon descending group 2 from Ca to Ba, while the silyl-substituted stannyls are much more shielded than the phenyl ones (δ¹¹⁹Sn/ppm: 1′, −133.4; 2′, −123.6; 3′, −95.5; 4, −856.8; 5, −848.2; 6′, −792.7). The bonding and electronic properties of these complexes were also analysed by DFT calculations. The combined spectroscopic, crystallographic and computational analysis of these complexes provide some insight into the main features of these unique families of homoleptic complexes. A comprehensive DFT study (Wiberg bond index, QTAIM and energy decomposition analysis) points at a primarily ionic Ae–Sn bonding, with a small covalent contribution, in these series of complexes; the Sn–Ae–Sn′ angle is associated with a flat energy potential surface around its minimum, consistent with the broad range of values determined by experimental and computational methods.

The complete series of heterobimetallic alkaline-earth distannyls [Ae{SnR₃}₂·(thf)_x] (Ae = Ca, Sr, Ba) have been prepared for R = Ph and SiMe₃, and their bonding and electronic properties have been comprehensively investigated.     

Synthesis of the bryostatin 1 northern hemisphere (C1-C16) via desymmetrization by ketalization/ring-closing metathesis

[reaction: see text] Synthesis of the northern hemisphere (C1-C16) of bryostatin 1, a potent anticancer agent, has been accomplished in 14 steps and 11% overall yield via desymmetrization by ketalization/ring-closing metathesis. A 2,9-dioxabicyclo[3.3.1]nonane template facilitated stereoselective A-ring functionalization, while an efficient hetero-Diels-Alder reaction was used to elaborate the B-ring.     

Mass spectral characterization of tetracyclines by electrospray ionization,H/D exchange,and multiple stage mass spectrometry

Electrospray ionization (ESI) and collisionally induced dissociation (CID) mass spectra were obtained for five tetracyclines and the corresponding compounds in which the labile hydrogens were replaced by deuterium by either gas phase or liquid phase exchange. The number of labile hydrogens, x, could easily be determined from a comparison of ESI spectra obtained with N2 and with ND3 as the nebulizer gas. CID mass spectra were obtained for [M + H]+ and [M - H]- ions and the exchanged analogs, [M(Dx) + D]+ and [M(Dx) - D]- , and produced by ESI using a Sciex API-III(plus) and a Finnigan LCQ ion trap mass spectrometer. Compositions of product ions and mechanisms of decomposition were determined by comparison of the MS(N) spectra of the un-deuterated and deuterated species. Protonated tetracyclines dissociate initially by loss of H2O (D2O) and NH3 (ND3) if there is a tertiary OH at C-6. The loss of H2O (D2O) is the lower energy process. Tetracyclines without the tertiary OH at C-6 lose only NH3 (ND3) initially. MSN experiments showed easily understandable losses of HDO, HN(CH3)2, CH3 - N=CH2, and CO from fragment ions. The major fragment ions do not come from cleavage reactions of the species protonated at the most basic site. Deprotonated tetracyclines had similar CID spectra, with less fragmentation than those observed for the protonated tetracyclines. The lowest energy decomposition paths for the deprotonated tetracyclines are the competitive loss of NH3 (ND3) or HNCO (DNCO). Product ions appear to be formed by charge remote decompositions of species de-protonated at the C-10 phenol.     

The co-crystal of iron(II) complex hydrate with hydroxybenzoic acid: [Fe(Phen)<Subscript>3</Subscript>]Cl(p-hydroxybenzoate).2(p-hydroxybenzoic acid).7H<Subscript>2</Subscript>O

Crystal of [Fe(Phen)₃]Cl(PHB).2(PHBH).7H₂O (1) is triclinic, space group P-1 with a = 12.0388(11) ?, b = 15.5286(14) ?, c = 15.7794(14) ?, α = 89.759(2)°, β = 75.818(2)°, γ = 71.900(2)° and Z = 2, (phen = phenanthroline, PHBH = p-hydroxybenzoic acid, PHB = p-hydroxybenzoate anion). The phen in adjacent Fe(phen)₃ ²⁺ cations are π–π interacted forming offset face to face (OFF) motifs. Juxtaposition of four phen ligands from two cations encapsulate an R₂ ²(8) dimeric unit of H-bonded PHBH molecules within a centrosymmetric box froming a filled aryl box motif (FAB). Alternation of OFF and FAB motifs form {OFF⋯FAB}∞ strands. The Fe(phen)₃ ²⁺ cation engages its phen ligands in π–π and/or CH–π interactions with two crystalographically different PHBH molecules and one PHB anion. Seven water molecules and a chloride anion per iron(II) trisphenanthroline cation fill empty spaces in the structure forming a hydrophilic cluster. Extensive intermolecular H-bond interactions occur between water molecules, chloride anions, PHBH molecules, and PHB anions. Thermal analysis of (1) was done under N_2(g). The TG, and dTG curves revealed the expected mass losses. All associated processes are endothermic as shown in the DSC curve.     

Supramolecular structure of tetrakis-μ-(4-chloro-3-nitrobenzoato)-bis(methanol)dicopper(II)

The title compound, [Cu₂(II)(4-Cl-3-NO₂–C₆H₃CO₂)₄(CH₃OH)₂] or [Cu₂(4-chloro-3-nitrobenzoate)₄(MeOH)₂] has been prepared and its structure determined using X-ray crystallography. The complex crystallizes in the triclinic space group P-1 with a = 9.6887(9)Å, b = 10.6448(9)Å, c = 11.4194(10)Å, = 108.094(2), = 110.682(2), = 105.055(2), V = 952.691(15)ų, and Z = 1. The structure consists of centrosymmetric dimers in which the Cu(II) atoms display a square pyramidal CuO₅ coordination, with four carboxylate O atoms in the basal plane [CuO 1.951(2)–1.968(2)Å] and the methanol O atoms in the apical position [CuO 2.170(2)Å]. The Cu atoms are 2.614(1)Å apart and are bridged by four benzoate groups. The discrete dimers are extended into 1D chains that result from hydrogen bonding between the coordinated methanol on one Cu(II) dimer and the nitro substituent on an adjacent Cu(II) dimer. The chains are interdigited and held by – stacking interactions forming 3D supramolecular array.     

Exploring Amantadine Derivatives as Urease Inhibitors: Molecular Docking and Structure–Activity Relationship (SAR) Studies

This article describes the design and synthesis of a series of novel amantadine-thiourea conjugates (3a–j) as Jack bean urease inhibitors. The synthesized hybrids were assayed for their in vitro urease inhibition. Accordingly, N-(adamantan-1-ylcarbamothioyl)octanamide (3j) possessing a 7-carbon alkyl chain showed excellent activity with IC₅₀ value 0.0085 ± 0.0011 µM indicating that the long alkyl chain plays a vital role in enzyme inhibition. Whilst N-(adamantan-1-ylcarbamothioyl)-2-chlorobenzamide (3g) possessing a 2-chlorophenyl substitution was the next most efficient compound belonging to the aryl series with IC₅₀ value of 0.0087 ± 0.001 µM. The kinetic mechanism analyzed by Lineweaver–Burk plots revealed the non-competitive mode of inhibition for compound 3j. Moreover, in silico molecular docking against target protein (PDBID 4H9M) indicated that most of the synthesized compounds exhibit good binding affinity with protein. The compound 3j forms two hydrogen bonds with amino acid residue VAL391 having a binding distance of 1.858 Å and 2.240 Å. The interaction of 3j with amino acid residue located outside the catalytic site showed its non-competitive mode of inhibition. Based upon these results, it is anticipated that compound 3j may serve as a lead structure for the design of more potent urease inhibitors.