Search results for "MR"
showing 10 items of 3001 documents
Solid–liquid extraction of ω-amino acids using ditopic receptors
2008
Abstract Five heteroditopic ligands have been prepared to be used in solid–liquid extraction of ω-amino acids into DMSO solutions. The prepared ligands contain crown ethers as cation binding sites and thiourea or amide groups for anion recognition. The aliphatic zone of the 1H NMR spectra suggests that two different species related to the amino acid are present in solution. One of these species is the complexed zwitterionic form and the other seems to be free non-zwitterionic amino acid. The presence of these two species allows extraction efficiencies higher than 100%.
Alkyl- and aryl-substituted corroles. 5. Synthesis, physicochemical properties, and X-ray structural characterization of copper biscorroles and porph…
2004
The synthesis and characterization of cofacial copper biscorroles and porphyrin-corroles linked by a biphenylenyl or anthracenyl spacer are described. The investigated compounds are represented as (BCA)Cu(2) and (BCB)Cu(2) in the case of the biscorrole (BC) derivatives and (PCA)Cu(2) and (PCB)Cu(2) in the case of porphyrin (P)-corrole (C) dyads, where A and B represent the anthracenyl and biphenylenyl bridges, respectively. A related monomeric corrole (Me(4)Ph(5)Cor)Cu and monomeric porphyrin (Me(2)Et(6)PhP)Cu that comprise the two halves of the porphyrin-corrole dyads were also studied. Electron spin resonance (ESR), (1)H NMR, and magnetic measurements data demonstrate that the copper corr…
Complexation of planar, organic, five-membered cations with crown ethers
2000
Complexation of six aromatic, nitrogen-containing cations with various crown ethers has been studied using 1H NMR, mass spectrometric and crystallographic methods. Hydrogen bonding appears to be the most important interaction in complexation, but minor effects such as π-stacking or cation–π interactions have also been observed. The stability constants of five different imidazolium perchlorate ·crown ether complexes and five other similar cation·DB18C6 complexes were determined by 1H NMR titration in acetonitrile solution. The stability of these complexes in solution and in the gas phase is discussed. The crystal structures of seven complexes were determined in order to study complexation in…
Solid-state NMR characterization of the structure and thermal stability of hybrid organic-inorganic compounds based on a HLaNb2O7 Dion-Jacobson layer…
2016
Dion-Jacobson phases, like MLaNb2O7, are an interesting class of ion-exchangeable layered perovskites possessing electronic and photocatalytic properties. Their protonated and organo-modified homologues, in particular, have already been indicated as promising catalysts. However, the structural analysis of these highly tailorable materials is still incomplete, and both the intercalation process and thermal stability of the included organic moieties are far from being completely understood. In this study, we present a thorough solid-state NMR characterization of HLaNb2O7·xH2O intercalated with different amounts of octylamine, or with decylamine. Samples were analyzed as prepared, and after th…
Synthesis, structure and physical characterization of the dimer {[(bpy)2Co]2(TPOA)}4+ (bpy=2,2′-dipyridyl; H2TPOA=N,N′,N′′,N′′′-tetraphenyl oxalamidi…
2008
Abstract The reaction between CoCl 2 , 2,2′-dipyridyl (bpy) and N , N ′, N ′′, N ′′′-tetraphenyl oxalamidine (H 2 TPOA) in a water/ethanol mixture yields the {[(bpy) 2 Co] 2 (TPOA)} 2+ dimer, that is immediately oxidized in aerobic conditions leading to the Co III species {[(bpy) 2 Co] 2 (TPOA)} 4+ . This cation was isolated as the {[(bpy) 2 Co] 2 (TPOA)}(PF6) 4 ( 1 ) salt, that was characterized by X-ray diffraction on single crystals. The dimer is formed by two Co III ions in octahedral coordination bridged by a deprotonated μ 2 -TPOA ligand. The Co III ions appear in its low spin configuration. Thus, the dimers are essentially diamagnetic, as shown by 1 H NMR and magnetic measurements.
Alkali metal complexation properties of resorcinarene bis-crown ethers: effect of the crown ether functionality and preorganization on complexation
2008
Abstract The synthesis and characterization of tetramethoxy resorcinarene tribenzo-bis-crown ethers, m - and p -TBBC6 , are described. The effect of the added aromatic functionality in the crown ether bridge on the alkali metal complexation properties was investigated and compared to the properties of tetramethoxy resorcinarene bis-crown-5 ( BC5 ) by means of 1 H NMR spectroscopy and X-ray crystallography. It was found that BC5 and m -TBBC6 were capable of binding alkali metal cations (K + , Rb + , and Cs + ), with the highest affinity toward Cs + cation, while no binding was observed in the case of p -TBBC6 , which confirms the significance of the complementarity and preorganization for co…
Isolation of enantiomerically pure organometallic palladium compounds: synthesis of the triangles prepared from enantiopure [cis-Pd2(C6H4PPh2)2(NCCH3…
2009
Reaction of the racemic [Pd(C(6)H(4)PPh(2))Br](4) () with the silver salt of 1R-(1alpha,2beta,3alpha)]-3-methyl-2-(nitromethyl)-5-oxocyclopentaneacetate, (R)-AgO(2)CR*, results in the formation of a mixture of diastereoisomers (RRR)- and (SRR)- of the formula Pd(2)(C(6)H(4)PPh(2))(2)(O(2)CR*)(2) that were separated by standard chromatographic methods. Each diastereoisomer was readily converted into the tetrametallic stereoisomers (SS)- and (RR)-, of the formula [Pd(C(6)H(4)PPh(2))Br](4) that were isolated and characterized by X-ray crystallography. The R enantiomer of the solvated cationic species [cis-Pd(2)(C(6)H(4)PPh(2))(2)(NCCH(3))(4)](2+), obtained from (RR)-, was reacted with ammonium…
Bis(triorganometal) and diorganometal 1,3-dithiolates (R3M)2(C6H3XS2) and R2M(C6H3XS2) (M = Sn, Pb; X= H, Cl)
1984
Abstract Bis(triorganometal) and diorganometal 1,3-dithiolates (R3M)2(C6H3XS2) (C6H5XS2 1,3-dithiobenzene (for X = H) or 1,3-dithio-4-chlorobenzene (for X = Cl); M = Sn, X = Cl, R = CH3, C6H5; M = Pb, X = H, Cl, R = CH3, C2H5) and R2M(C6H3XS2) (R = CH3, C2H5, C6H5; M = Sn, X = Cl; M = Pb, X = H, Cl) have been prepared as the first organometal IVB derivatives of 1,3-dithiols, and investigated by vibrational, 1H NMR, and (in the case of organotin compounds) Mossbauer spectroscopy. The triorganometal derivatives are monomeric and the diorganometal derivatives dimeric in solution (37° C). For the latter a twelve-membered ring structure is proposed for both solution and the solid state.
Water-induced local ordering of chitosan polymer chains in thin layer films
2015
International audience; Carbon-13 NMR (CP-MAS and FSLG 1H–13C HETCOR) have been applied to chitosan salt films synthesized in acetic acid and exposed to different relative humidity environments (32% or 75%) at 20 °C for 1 month. It gives insight in the relationship between structure and functional properties according to the hydration level of this biomaterial as a film. The acetate ions trapped in the chitosan act as structuring agents between chitosan chains for the low hydration state. But, increasing the moisture content induces spontaneous removal of acetic acid and a subsequent modification in the film structure, with an increase in local ordering. HETCOR experiments also showed a mul…
On what terms and why the thermodynamic properties of polymer solutions depend on chain length up to the melt
2003
Theoretical considerations based on chain connectivity and conformational variability of polymers have lead to an uncomplicated relation for the dependence of the Flory-Huggins interaction parameter, chi, on the volume fraction of the polymer, phi, and on its number of segments, N. The validity of this expression is being tested extensively by means of vapor pressure measurements and inverse gas chromatography (complemented by osmotic and light scattering data from literature) for solutions of poly(dimethylsiloxane) in the thermodynamically vastly different solvents n-octane (n-C8), toluene (TL), and methylethylketone (MEK) over the entire range of composition for at least six different mol…