Derivatives of the 21-tungsto-9-antimonate heteropolyanion. Part 2. Addition of transition metal cations

Ammonium salts of five new heteropolytungstates, [NaSb₉W₂₁O₈₆M₃]^12,9− (M=Mn^II, Fe^III, Co^II, Ni^II, Cu^II) have been prepared and characterized by elemental analysis, visible and i.r. spectroscopy, magnetic susceptibility measurements, and cyclic voltammetry. Evidence for ligand substitution at the M cation centres is presented, and possible binding sites for M on the polyanion surface are discussed.     

Norbornanes. Part 21. Bridging strain in norbornyl and oxanorbornyl cations

Further evidence is presented that the 2-norbornyl cation is stabilized primarily by C(2)–C(6) bridging, and that C(2)–C(7) bridging leads to prohibitive strain. Thus, a comparison of the heats of hydrogenation of nortricyclene 17 and bicyclo[3. 2. 0. 0.^2,7]heptane 18 indicates that the strain energy of the latter is ca. 21.5 kcal/mol higher that that of 17 . Furthermore, 6-exo-2-oxabicyclo[2. 2. 1]heptyl sulfonates 8 ionize with strong O(2) participation to the bridged oxonium ion 12. In contrast, 2-endo-7-oxabicyclo[2.2.1]heptyl sulfonates 11 ionize without O(7) participation to form the unbridged carbenium ion 15 .     

Complexation of lanthanide cations with ampicillin

The complexation of Ln³⁺ ions with ampicillin anions (Amp^?) in an aqueous solution at 25°C has been studied by pH titration on the background of 0.1 M KNO₃. Ln(OH)Amp⁺ complexes are formed in neutral and weakly alkaline media. The logarithm of β increases nonlinearly along the lanthanide series from 9.02 ± 0.06 for Ce(OH)Amp⁺ to 10.25 ± 0.09 for Lu(OH)Amp⁺. The structure of the Lu(OH)Amp⁺ complex was simulated by the PM6 semiempirical quantum-chemical method and the MOPAC 2009 software; the results of which impliy the formation of a chelate complex via bidentate coordination of Amp^? through the oxygen atoms of the carboxylate and β-lactam groups and the inclusion of up to five water molecules into the coordination sphere of Lu(III).     

Design and synthesis of phosphorylated pyridine-based ligands for lanthanide complexation. Part 1

Several new ligands constructed from a pyridine-ethynylnaphthalene platform have been engineered with a chelating pocket comprising bisdimethylaminocarboxylate/phosphonate or bisdimethylaminophosphonate units. Selective hydrolysis provides pockets with four to six anionic carboxylate or phosphate functions suitable for lanthanide complexation. Linkage at the opposite side of a flexible hanging arm either via a triple bond or through an amide tether offers the possibility of further use of these ligands for bioconjugation. Protocols to link the dedicated pockets via hydrophilic flexible chain to Biotin are also detailed.     

Tandem reactions catalyzed by lanthanide iodides. Part 1: Tandem Mukaiyama-Michael iminoaldol reactions

Samarium diiodide, as well as lanthanide triiodides catalyze a one-pot procedure allowing to perform sequentially the Mukaiyama-Michael addition of a ketene silyl acetal on a cyclic α,β-unsaturated ketone, followed by the addition of a glyoxylic, aromatic or heteroaromatic imine. According to the nature of the silyl group the adducts resulting from this tandem process are isolated as ketones or as enoxysilanes. The presence of a coordinating group on the imine increases the rate of the reaction.     

Inclusion of Bisphenols by Cyclodextrin Derivatives

Complexation of various kinds of bisphenols (BPs) with cycloheptaamylose(β-cyclodextrin, β-CD) derivatives (β-CD, hydroxyethyl-β-CD (HE-β-CD), 2,6-di-O-methyl-β-CD (DM-β-CD) and polymerised β-CD (L-Poly-β-CD)) was examined fluorimetrically using2-anilinonaphthalene-6-sulfonic acid (2,6-ANS) as a probe. From the inhibitory effectof BPs on the inclusion of 2,6-ANS by the β-CD derivatives, the associationconstants (K_ass) of BPs with the β-CD derivatives were determined.The K_ass values for bisphenol B (BPB) with β-cyclodextrin derivatives except for L-Poly-β-CD were always larger than those for other BPs including bisphenol A (BPA), due to the interaction between the non-polar cavity and hydrophobic BPB. Thermodynamic parameters indicated that the entropy change was always largely negative (-90～ -120 J/mol...K in the β-CD system, for example), and the inclusion of bisphenols into the CD cavity was completely enthalpy-driven. The very largely negative entropy change might be mainly due to the tight fixation of guest molecules in the CD cavity, resulting in the loss of freedom of both CD and guest molecules. The effect of the structure of guest and host molecules on the association was also examined.     

Novel antennae for the sensitization of near infrared luminescent lanthanide cations

Near Infrared (NIR) luminescence is useful for many applications ranging from lasers, telecommunication to biological imaging. We have a special interest for applications in biological media since NIR photons have less interference with such samples. NIR photons can penetrate relatively deeply in tissues and cause less damage to biological samples. The use of NIR luminescence also results in improved detection sensitivity due to low background emission. The lower scattering of NIR photons results in improved image resolution. NIR emitting lanthanide compounds are promising for imaging because of their unique properties such as sharp emission bands, long luminescence lifetimes and photostability. Here, we review our efforts to develop novel sensitizers for NIR emitting lanthanides. We have employed two global strategies: (1) monometallic lanthanide complexes based on derivatives of salophen, tropolonate, azulene and pyridine; and (2) polymetallic lanthanide compounds based on nanocrystals, metal-organic frameworks and dendrimers complexes.     

Structural correlations of the lanthanide halides and related compounds. Derivatives of the anti-nickel-arsenide structure

An examination of structural data for lanthanide halides and related compounds has shown that a substantial number of different structure types are conveniently described as layered structures derived from anti-NiAs by removal or shear of cation layers and distortion of the residual layers. The structural correlations of various MX, MX_1.5, MX₂, MXY, MX₃, and MX₂Y compositions (M = cation, X and Y = anions) are described by the presentation of a subgroup-supergroup diagram relating their space groups and by comparison of their structural projections. A close relationship between the CsCl- and NiAs-type structures is observed. The occurrence of displacive and order-disorder phase transitions, the formation ternary derivatives by ion accommodation processes and the possible formation of intermediate halides, M₂X_2n+1, by coherent intergrowth of MX₂ and MX₃ structures are discussed. The effects of radius ratio and cation coordination number on the stabilities of halide structures and on the formation of complex MX₂ layers derived from hexagonal-closest-packed metal arrays are examined.     

Comparison of covalency in the complexes of trivalent actinide and lanthanide cations

The complexes of trivalent actinide (Am(III) and Cm(III)) and lanthanide (Nd(III) and Sm(III)) cations with bis(2,4,4-trimethylpentyl)phosphinic acid, bis(2,4,4-trimethylpentyl)monothiophosphinic acid, and bis(2,4,4-trimethylpentyl)dithiophosphinic acid in n-dodecane have been studied by visible absorption spectroscopy and X-ray absorption fine structure (XAFS) measurements in order to understand the chemical interactions responsible for the great selectivity the dithiophosphinate ligand exhibits for trivalent actinide cations in liquid-liquid extraction. Under the conditions studied, each type of ligand displays a different coordination mode with trivalent f-element cations. The phosphinate ligand coordinates as hydrogen-bonded dimers, forming M(HL2)3. Both the oxygen and the sulfur donor of the monothiophosphinate ligand can bind the cations, affording both bidentate and monodentate ligands. The dithiophosphinate ligand forms neutral bidentate complexes, ML3, with no discernible nitrate or water molecules in the inner coordination sphere. Comparison of the Cm(III), Nd(III), and Sm(III) XAFS shows that the structure and metal-donor atom bond distances are indistinguishable within experimental error for similarly sized trivalent lanthanide and actinide cations, despite the selectivity of bis(2,4,4-trimethylpentyl)dithiophosphinic acid for trivalent actinide cations over trivalent lanthanide cations.     

Solvolysis of α-Bromo-p-aminostyrene. Mesomeric vinyl cations,Part IV

The preparation of α-bromo-p-aminostyrene ( 1b ) and its solvolysis rates and products have been reexamined in detail. In buffered 50 vol % aqueous dioxane between p_H* 13 and 3 the reaction rate is independent of hydrogen ion concentration. The ratio of the solvolysis products, viz. p-aminoacetophenone ( 3b ) and p-aminophenylacetylene ( 5a ), however, varies with the p_H* and with the buffer concentration. These findings confirm the unimolecular (S_N1-E1) mechanism involving an intermediate vinyl cation. The acid-catalysed hydration mechanism proposed by Schubert & Barfknecht is thereby excluded.     

Aromatic Nucleophilic Substitution. Part 1. Regiospecific Substitution of the Nitro Groups in 3,5-Dinitrophthalic-Acid Derivatives

The regioselectivity of nucleophilic substitution of the nitro groups in 3,5-dinitrophthalic anhydrides and 3,5-dinitrophthalimides (Scheme) with a variety of nucleophiles (Nu^?) was studied. In all cases, the 3-nitro group was selectively substituted. With excess of the same nucleophilic reagent or with other nucleophiles, the 5-nitro group could subsequently be replaced.     

Malonylation/Decarbalkoxylation of Furan Derivatives as Key Steps for the Preparation of Nonactic Acid Derivatives. Part II [1]

A malonylation/decarbalkoxylation sequence from 2-substituted furans was investigated in view of developing a scalable synthesis of hydrophobic nonactic acid analogues.     

Malonylation/Decarbalkoxylation of Furan Derivatives as Key Steps for the Preparation of Nonactic Acid Derivatives. Part II [1]

Summary. A malonylation/decarbalkoxylation sequence from 2-substituted furans was investigated in view of developing a scalable synthesis of hydrophobic nonactic acid analogues.     

Malonylation/Decarbalkoxylation of Furan Derivatives as Key Steps for the Preparation of Nonactic Acid Derivatives. Part I [1]

Summary. A malonylation/decarbalkoxylation sequence from 2-substituted furans was investigated in view of developing a scalable synthesis of hydrophobic nonactic acid analogues.     

Synthesis of Coumarins and Derivatives. Part 1. Biomimetic synthesis of esculetin and halogenated derivatives

Esculetin ( 1 ) and the novel compounds 5-chloroesculetin ( 5 ) and 5-bromoesculetin ( 6 ) were obtained from a light-induced cyclization of trans-caffeic acid ( 3 ) catalyzed by [FeNa(edta)] and/or H₂SO₄, HCI, or HBr (Scheme 1). The experimental conditions for trans-cis-isomerization of the cinnamic-acid derivative 3 and subsequent non-enzymatic cyclization were described. The photoperiod and the presence of air and iron-chelate catalyst are shown to be important parameters that markedly affect yields. The reactions probably occur by a free-radical mechanism involving a photo-initiated one-electron redox process (Scheme 2).