Spectroscopic and electrochemical properties of iron(II) complexes of polydentate Schiff bases containing pyrazine, pyridine and imidazole groups

We report the synthesis and spectroscopic/electrochemical properties of iron(II) complexes of polydentate Schiff bases generated from 2-acetylpyridine and 1,3-diaminopropane, acetylpyrazine and 1,3-diaminopropane, and from 2-acetylpyridine and L-histidine. The complexes exhibit bis(diimine)iron(II) chromophores in association with pyrazine, pyridine or imidazole groups displaying contrasting pi-acceptor properties. In spite of their open geometry, their properties are much closer to those of macrocyclic tetraimineiron(II) complexes. An electrochemical/spectroscopic correlation between E degrees(Fe(III/II)) and the energies of the lowest MLCT band has been observed, reflecting the stabilization of the HOMO levels as a consequence of the increasing backbonding effects in the series of compounds. Mossbauer data have also confirmed the similarities in their electronic structure, as deduced from the spectroscopic and theoretical data. (C) 2008 Elsevier B.V. All rights reserved.

Synthesis and application of chiral beta-amino disulfides as ligands for the enantioselective addition of diethylzinc to aldehydes

A new class of chiral beta-amino disulfides was synthesized from readily available and inexpensive starting materials by a straightforward method and their abilities as ligands were examined in the enantioselective addition of diethylzinc to aldehydes. Enantiomeric excesses of up to 99% have been obtained using 0.5 mol % of the chiral catalysts.

Insights into the Molecular Requirements for the Anti-obesity Activity of a Series of CB1 Ligands

Two-dimensional and 3D quantitative structure-activity relationships studies were performed on a series of diarylpyridines that acts as cannabinoid receptor ligands by means of hologram quantitative structure-activity relationships and comparative molecular field analysis methods. The quantitative structure-activity relationships models were built using a data set of 52 CB1 ligands that can be used as anti-obesity agents. Significant correlation coefficients (hologram quantitative structure-activity relationships: r 2 = 0.91, q 2 = 0.78; comparative molecular field analysis: r 2 = 0.98, q 2 = 0.77) were obtained, indicating the potential of these 2D and 3D models for untested compounds. The models were then used to predict the potency of an external test set, and the predicted (calculated) values are in good agreement with the experimental results. The final quantitative structure-activity relationships models, along with the information obtained from 2D contribution maps and 3D contour maps, obtained in this study are useful tools for the design of novel CB1 ligands with improved anti-obesity potency.

Synthesis, spectroscopic characterization and X-ray structures of five-coordinate diorganotin(IV) complexes containing 5-hydroxypyrazoline derivatives as ligands

Four new diorganotin(IV) complexes have been prepared from R(2)SnCl(2) (R = Me, Ph) with the ligands 5-hydroxy-3-metyl-5-phenyl-1-(S-benzildithiocarbazate)-pyrazoline (H(2)L(1)) and 5-hydroxy-3-methyl-5-phenyl-1-(2-thiophenecarboxylic)-pyrazoline (H(2)L(2)). The complexes were characterized by elemental analysis, IR. (1)H (13)C, (119)Sn NMR and Mossbauer spectroscopes The complexes [Me(2)SnL(1)], [Ph(2)SnL(1)] and [Me(2)SnL(2)] were also studied by single crystal X-ray diffraction and the results showed that the Sn(IV) central atom of the complexes adopts a distorted trigonal bipyramidal (TBP) geometry with the N atom of the ONX-tridentate (X = O and S) ligand and two organic groups occupying equatorial sites. The C-Sn-C angles for [Me(2)Sn(L(1))] and [Ph(2)Sn(L(1))] were calculated using a correlation between (119)Sn Mossbauer and X-ray crystallographic data based on the point-charge model Theoretical calculations were performed with the B3LYP density functional employing 3-21G(*) and DZVP all electron basis sets showing good agreement with experimental findings General and Sn(IV) specific IR harmonic frequency scale factors for both basis sets were obtained from comparison with selected experimental frequencies (C) 2010 Elsevier B V All rights reserved

The influence of perhydroazepine and piperidine as further ancillary ligands on Ru-PPh(3)-based catalysts for ROMP of norbornene and norbornadiene

Polynorbornadiene and polynorbornene were synthesized via ring opening metathesis polymerization (ROMP) with [RuCl(2)(PPh(3))(2)(amine)] as catalyst precursors, amine = piperidine (1) or perhydroazepine (2) in the presence of 5 mu L of ethyl diazoacetate (EDA) ([monomer]/[Ru] = 5000; 40 degrees C with 1; 25 degrees C with 2). The effects of the solvent volume (2-8 mL of CHCl(3)) reaction time (5-120 min) and atmosphere type (argon and air) on the yields were investigated to observe the behavior of the two different precursors. Quantitative yields were obtained for 60 or 120 min regardless of the starting volumes, either in argon or air, with both Ru species. However, low yields were obtained for short times (5-30 min) when the reactions are performed with large volumes (6-8 mL). In argon, the yields were larger with 2, associated to a faster propagation reaction controlled by the Ru active species. In air, the yields were larger with 1, associated to a higher resistance to O(2) of the starting and propagating Ru species. The different activities between 1 and 2 are discussed considering the steric hindrance and electronic characteristics of the amines such as ancillary ligands and their arrangements with PPh(3) and Cl(-) ions in the metal centers. (c) 2009 Elsevier B.V. All rights reserved.

Cationic and neutral phenylmercury(II) complexes with heterocyclic thione ligands. X-ray structures of [HgPh(dmpymtH)][BF(4)] center dot H(2)O and [{HgPh}(2)(mu-dtu)]

The neutral complex [HgPh(dmpymt)] 1 (dmpymtH = 4,6-dimethylpyrimidine-2(1H)-thione) reacts with HBF(4) to give the cationic complex [HgPh(dmpymtH)][BF(4)] 2. The X-ray molecular structure of the later revealed a [2+1] coordination sphere about the mercury(II) atom (C-Hg-S and Hg center dot center dot center dot N). In the dinuclear complex [(HgPh)(2)(mu-dtu)] 3 [dtuH(2) = 2,4(1H,3H)-pyrimidinedithione or dithiouracil] the coordination spheres are also [2+1] although dissimilar regarding the Hg center dot center dot center dot N secondary bonds. NMR spectroscopy ((1)H, (13)C and (199)Hg) studies were undertaken in solution and the results discussed in the light of the X-ray structures. (C) 2008 Elsevier B. V. All rights reserved.

Oxotechnetium(V) Complexes with a Novel Class of Tridentate Thiosemicarbazide Ligands

A novel tridentate thiosemicarbazide-type ligand class with an SNS donor set, H(2)L(1), was prepared by reactions of N-[N`,N`-dialkylamino(thiocarbonyl)]benzimidoyl chlorides with thiosemicarbazides. H(2)L(1) ligands readily react with (NBu(4))[TcOCl(4)] in MeOH under the formation of red oxotechnetium(V) complexes of composition [TcOCl(L(1))]. The monomeric, five-coordinate compounds are air-stable and bind (L(1))(2-) tridentate in the equatorial coordination sphere. The compounds represent the first examples of oxotechnetium(V) complexes with NS chelate-bonded thiosemicarbazones.

A novel nanostructured composite formed by interaction of copper octa(3-aminopropyl)octasilsesquioxane with azide ligands: Preparation, characterization and a voltammetric application

This study presents the preparation, characterization and application of copper octa(3-aminopropyl)octasilsesquioxane following its subsequent reaction with azide ions (ASCA). The precursor (AC) and the novel compound (ASCA) were characterized by Fourier transform infrared spectra (FTIR), nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), scanning electronic microscopy (SEM), X-ray diffraction (XRD), Thermogravimetric analyses and voltammetric technique. The cyclic voltammogram of the modified graphite paste electrode with ASCA (GPE-ASCA), showed one redox couple with formal potential (E(1/2)(ox)) = 0.30 V and an irreversible process at 1.1 V (vs. Ag/AgCl; NaCl 1.0 M; v = 20 mV s(-1)). The material is very sensitive to nitrite concentrations. The modified graphite paste electrode (GPE-ASCA) gives a linear range from 1.0 x 10(-4) to 4.0 x 10(-3) mol L(-1) for the determination of nitrite, with a detection limit of 2.1 x 10(-4) mol L(-1) and the amperometric sensitivity of 8.04 mA/mol L(-1). (C) 2010 Elsevier Ltd. All rights reserved.

Diorganotin dications stabilized by neutral ligands in the solid state: [R2Sn(H2O)2(OPPh3)2](O3SCF3)2 (R = Me, Bu)

The synthesis of [R₂Sn(H₂O)₂(OPPh₃)₂](O₃SCF₃)₂ (R = Me (1), Bu (2)) by the consecutive reaction of R₂SnO (R = Me, Bu) with triflic acid and Ph₃PO is described. Compounds 1 and 2 feature dialkyltin(IV) dications [R₂Sn(H₂O)₂(OPPh₃)₂]^₂+ apparently stabilized by the neutral ligands in the solid state. Compounds 1 and 2 readily dehydrate upon heating at 105 and 86 °C, respectively. The preparative dehydration of 1 afforded [Me₂Sn(OPPh₃)₂(O₃SCF₃)](O₃SCF₃) (1a), which features both bidentate and non-coordinating triflate anions. In compounds 1 and 2 the ligands Ph₃PO and H₂O are kinetically labile in solution and undergo reversible ligand exchange reactions. Compounds 1, 1a and 2 were characterized by multinuclear solution and solid-state NMR spectroscopy, IR spectroscopy, electrospray mass spectrometry, conductivity measurements, thermogravimetry and X-ray crystallography.

1-Naphthyl- and mesityltellurium(IV,II) derivatives of small bite chelating organic ligands: effect of steric bulk and intramolecular secondary bonding interaction on molecular geometry and supramolecular association

The synthesis and characterization of unsymmetric diorganotellurium compounds containing a sterically demanding I-naphthyl or
mesitylligand and a small bite chelating organic ligand capable of 1,4-Te···N(O) intramolecular interaction is described. The reaction
of ArTeCl₃ (Ar = I-C_lOH₇, Np; 2,4,6-Me₃C₆H_2' Mes) with (SB)HgCI [SB = the Schiff base, 2-(4,4'-N0₂C₆H₄CH=NC₆H₃-Me)] or a methyl ketone (RCOCH₃) afforded the corresponding dichlorides (SB)ArTeCI₂ (Ar = Np, 1Aa; Mes, 1Ba) or (RCOCH₂)ArTeCl₂ (Ar = Np; R = Ph (2Aa), Me (3Aa), Np (4Aa); Ar = Mes, R = Ph (2Ba)). Reduction of 1Aa and 1Ba by Na₂S₂0₅ readily gave the tellurides (SB)ArTe (Ar = Np (1A), Mes, (1B) but that of dichlorides derived from methylketones was complicated due to partial decomposition to tellurium powder and diarylditelluride (Ar₂Te₂), resulting in poor yields of the corresponding tellurides 2A, 2B and 3A. Oxidation of the isolated tellurides with S0₂Cl₂, Br₂ and I₂ yielded the corresponding dihalides. All the synthesized compounds have been characterized with the help of IR, ¹H, ^l3C, and ¹²⁵Te NMR and in the case of 2Aa, and 2Ba by X-ray crystallography. Appearance of only one ¹²⁵Te signal indicated that the unsymmetric derivatives were stable to disproportionation to symmetric species. Intramolecular 1,4-Te· . ·0 secondary bonding interactions (SBIs) are exhibited in the crystal structures of both the tellurium(IV) dichlorides, 2Aa, and 2Ba. Steric repulsion of the mesityl group in the latter dominates over lone pair-bond pair repulsion, resulting in significant widening of the equatorial C-Te-C angle. This appears to be responsible for the lack of Te· . ·CI involved supramolecular associations in the crystal structure of 2Ba.

Irreversible and bivalent ligands for selected G-protein coupled receptors

Derivatives of pharmaceutical compounds that could potentially bind irreversibly to a hypertension controlling receptor were synthesised to provide tools for studying this receptor. Also compounds that simultaneously activate two cardiovascular receptors with opposing cellular mechanisms were synthesised. This resulted in a desired partial reduction in the activity of one receptor.

Systemic activation of dendritic cells by toll-like receptor ligands or malaria infection impairs cross-presentation and antiviral immunity

The mechanisms responsible for the immunosuppression associated with sepsis or some chronic blood infections remain poorly understood. Here we show that infection with a malaria parasite (Plasmodium berghei) or simple systemic exposure to bacterial or viral Toll-like receptor ligands inhibited cross-priming. Reduced cross-priming was a consequence of downregulation of cross-presentation by activated dendritic cells due to systemic activation that did not otherwise globally inhibit T cell proliferation. Although activated dendritic cells retained their capacity to present viral antigens via the endogenous major histocompatibility complex class I processing pathway, antiviral responses were greatly impaired in mice exposed to Toll-like receptor ligands. This is consistent with a key function for cross-presentation in antiviral immunity and helps explain the immunosuppressive effects of systemic infection. Moreover, inhibition of cross-presentation was overcome by injection of dendritic cells bearing antigen, which provides a new strategy for generating immunity during immunosuppressive blood infections.

Synthesis and characterisation of rare earth complexes supported by para-substituted Cinnamate Ligands

The preparations and characterisations of a range of lanthanoid 4-(R)-substituted (4-Rcinn, R = OH, OMe, NO2, Cl), known to have good anticorrosion properties, are reported. The crystal structure of [Ce(4-OHcinn)3(MeOH)2(H2O)]·MeOH is a polymer, in which the cerium atoms are nonacoordinate, and adjacent cerium atoms are bridged by either two bridging bidentate or two bridging tridentate carboxylate ligands. Each cerium atom also has one monodentate 4-hydroxycinnamate ligand, one aqua ligand, and two methanol ligands.