Fioretta Asaro

Complex Formation between Poly(vinylpyrrolidone) and Sodium Decyl Sulfate Studied through NMR

Recent experimental studies have shown a preferential interaction of poly(vinylpyrrolidone) (PVP) toward the alkyl sulfate surfactants rather than toward those belonging to the alkyl sulfonate series. To gain information on the complex formation between PVP and the alkyl sulfate surfactants, we have performed 1H and 13C NMR and NOESY measurements on aqueous solutions of sodium decyl sulfate (C10OS) in the presence and absence of PVP at 1wt %. The results show that C10OS interacts with PVP, forming micelle-like clusters bound onto the polymer, and furthermore suggest that the PVP−C10OS complex formation implies the synergic effects of the electrostatic attractions between the surfactant headgroup and the nitrogen and oxygen atoms in the pyrrolidone ring of PVP and of the hydrophobic interaction between the surfactant alkyl moiety and the ring carbons of PVP.

Experimental evidence of counterion affinity in alginates: the case of nongelling ion Mg2+.

The present contribution aims at testing experimentally the theoretical model previously devised (Donati, I.; Cesaro, A.; Paoletti, S.; Biomacromolecules 2006, 7, 281-287) for the description of the interaction between alginate and nongelling Mg(2+) ions. The model, based on an extension of the counterion condensation theory, introduces a contribution of free energy of affinity, DeltaG(aff,0), which depends on the monomer composition of the polyuronate. In the present work, three different alginates separately mimicking the mannuronan (polyM), the guluronan (polyG), and the polyalternating (polyMG) components of alginate, together with a natural alginate isolated from Laminaria hyperborea ( L. hyperborea ), were examined. They were treated with Mg(2+) ions, and relative variations in scattered light intensity, isothermal calorimetry (DeltaH(mix)), specific viscosity, and (23)Na NMR longitudinal relaxation rates were monitored with respect to samples at the same ionic strength but containing only Na(+) ions. The fraction of condensed magnesium counterions was found to be strongly dependent on alginate composition, increasing along the series mannuronan < polyalternating approximately L. hyperborea < guluronan, thus in good agreement with the theoretical predictions.

Comparison between alkylrhodoximes and alkylcobaloximes. Solution studies of some alkylrhodoximes, pyRh(DH)2R, and crystal structure of the complexes with RCH2CF3, CH2Cl, n-Pr

Syntheses, kinetics and NMR measurements of pyRh(DH) 2 R complexes, where py=pyridine and DH=monoanion of dimethylglyoxime, with various R alkyl groups are described. X-ray crystal structures of the compounds with RCH 2 CF 3 ( I ), CH 2 Cl ( II ), n-Pr ( III ) are reported. Comparison of the geometry of the Rh(DH) 2 and Co(DH) 2 moieties shows significant differences in the MN, NO and O···O distances, with a decrease of the approximate symmetry from D 2h in cobaloximes to C 2h in rhodoximes. The axial Rh-C and Rh-N distances lengthen with increasing bulk and the σ-donating ability of R, respectively; the Rh-C distances are 2.059(5) A in I and 2.069(5) A in II , and the Rh-N(axial) distances are 2.145(3) ( I ), 2.178(3) ( II ) and 2.188(5) ( III ) A. The chemical shifts of the pyridine meta and para carbons decrease with the increase of the alkyl group σ-donating power; the linear relationship found between the δ values of the pyridine para carbon in rhodoximes and the EP values, derived from NMR data of cobaloximes, shows that the transmission of electronic charge from R to the neutral ligand through rhodium occurs in a way similar to that through cobalt. The rate constants for the pyridine dissociation increase with the σ-donating ability of the alkyl group, as measured by EP parameters. These results show that, as already reported for cobaloximes, trans -influence and trans -effect have the same trend in rhodoximes too.

Polysaccharide-based networks from homogeneous chitosan-tripolyphosphate hydrogels: synthesis and characterization.

Polysaccharide networks, in the form of hydrogels and dried membranes based on chitosan and on the cross-linker tripolyphosphate (TPP), were developed using a novel approach. TPP was incorporated into chitosan by slow diffusion to favor a controlled gelation. By varying chitosan, TPP, and NaCl concentration, transition from inhomogeneous to homogeneous systems was achieved. Rheology and uniaxial compression tests enabled to identify the best performing hydrogel composition with respect to mechanical properties. FTIR, (31)P NMR, and spectrophotometric methods were used to investigate the interaction chitosan-TPP, the kinetics of phosphates diffusion during the dialysis and the amount of TPP in the hydrogel. A freeze-drying procedure enabled the preparation of soft pliable membranes. The lactate dehydrogenase assay demonstrated the biocompatibility of the membranes toward fibroblasts. Overall, we devised a novel approach to prepare homogeneous macroscopic chitosan/TPP-based biomaterials with tunable mechanical properties and good biocompatibility that show good potential as novel polysaccharide derivatives.

Diphenylborylated derivatives of organocobaloximes and organorhodoximes: Synthesis, spectroscopic and structural characterisation

Abstract A series of organometallic complexes derived by organocobaloximes and organorhodoximes in which either one or both the hydrogen bridges have been replaced by BPh 2 groups, RM(DH)(DBPh 2 ) N -MeIm and RM((DBPh 2 ) 2 N -MeIm, respectively, have been synthesised and characterised, both in solution and in solid state. 1 H NMR spectra show that they assume different interconverting conformations in solution. With increasing steric bulk of R, the axial phenyls of the BPh 2 group tend to face N -MeIm, forcing the latter in an orientation which is quite unusual in organocobaloximes and causing a lengthening of the Co-N bond. Some possible implications on the strength of the trans Co-C bond are discussed.

New organo-cobalt complexes derived from cobaloximes with one or two diphenylboron moieties in the oxime bridges

Abstract The reaction between methylcobaloxime [CH 3 Co(DH) 2 L] and diphenylborinic anhydride affords derivatives containing either one or two diphenylboron bridges, depending on the ratio of complex: diphenylborinic anhydride. The crystal structures of [CH 3 Co(DH)(DBPh 2 )( N -MeIm)] ( Ib ) and [CH 3 Co(DBPh 2 ) 2 CH 3 OH] ( IId ) show that in Ib the axial phenyl of the BPh 2 moiety faces the axial Me, while in IId the axial phenyls are “trans”. The preferred conformations of these complexes in solution, as inferred from NMR spectra, are analogous to those found in the solid state.

Synthesis and characterization of a novel tetranuclear bimetallic complex containing rhodium(II) and zinc(II) as metal centres

Rh(Hdmg)2(PPh3)Cl (Hdmg=monoanion of dimethylglyoxime) undergoes reduction with zinc amalgam to give the tetranuclear bimetallic compound [Rh(Hdmg)(ClZndmg)(PPh3)]2, characterized by elemental analysis, electronic, IR and NMR spectroscopy and X-ray crystallography. It crystallizes in the triclinic space group P1 with: a=14.262(4), b=14.675(4), c=14.698(4) A, α=82.15(4), β=87.57(4), γ=65.89(3)°, Z=2. The structure was refined up to R=0.13 for 4704 reflections. The molecule consists of two [Rh(dmg)(Hdmg)(PPh3)] subunits linked by an [Rh(II)(II)] bond of length equal to 2.852(3) A and by two Zn ions bridging the oxygens of the equatorial ligands. The binding with zinc relieves the equivalence among the atoms of each subunit.

Two- and four-coordinated gold(I) complexes with aryldithiocarboxylates and triphenylphosphine. X-ray diffraction crystal structure of the [Au(S2CPh)PPh3], [Au(S2CPh)(PPh3)2] and [Au0.56Cu0.44(S2C-p-tolyl)(PPh3)2] complexes; NMR investigations of [Au(S2CAr)(PPh3) n] (n=1, 2) compounds in solution

Abstract The synthesis of some Au(I) aryldithiocarboxylates (ArPh, o-tolyl, p-tolyl) and their 1:1 and 1:2 complexes with triphenylphosphine are reported and their properties are compared with those of the corresponding Cu(I) and Ag(I) derivatives. Variable temperature 1H and 13C NMR solution spectra of the phosphino complexes are discussed and show a particularly strong metal-phosphine interaction in the [Au(S2CAr)PPh3] molecules, which are fairly stable in solution. [Au(S2CAr)(PPh3)2] are stable in solution only below −30 °C. Approximate constants for the equilibria [Au(S2CAr)(PPh3)2]⇌[Au(S2CAr)PPh3]+PPh3 are reported. The intermolecular exchange of the phosphine between the mono and the bisphosphino complexes is fast and that between the latter and free phosphine even faster. Crystal and molecular structures have been determined by standard X-ray methods for the [Au(S2CPh)PPh3] (I), [Au(S2CPh)(PPh3)2] (II) and [(Au,Cu)S2C-p-tolyl(PPh3)2] (III) complexes. In I there are two independent monomeric units in both of which the dithiobenzoate is monodentate, the metal atoms being coordinated by the ligands in a linear geometry. The gold atom in II and the cocrystallized copper/gold atoms in III are pseudo-tetrahedrally coordinated by the two PPh3 and the chelating aryldithiocarboxylate anion. The four-membered chelate ring in II shows a remarkably long AuS bond (2.859(4) A). The coordination number of gold(I) and the strain involved in the formation of chelate rings with gold are discussed. Crystallographic data are as follows: C25H20AuPS2 (I), monoclinic, space group P21/n, with a=19.952(4), b=12.733(4), c=19.894(4) A, β=117.74(2)° and Z=8; C43H35AuP2S2 (II), monoclinic, space group P21/n, with a=20.712(3), b=19.552(2), c=9.180(2) A, β=98.54(1)° and Z=4; C44H37Au0.56Cu0.44P2S2 (III), orthorhombic, space group P212121, with a=20.492(2), b=15.823(2), c=11.980(2) A and Z=4. The structures, solved by Patterson and Fourier methods, were refined by blocked full matrix least-squares to R=0.068 (I), 0.044 (II) and 0.034 (III) for 3503 (I), 3242 (II) and 3273 (III) symmetry independent reflections.

Para-substituted diphenylborylated organocobaloximes: effects of substituents on conformation and redox properties.

Abstract Some new derivatives of organocobaloximes containing para -substituted diphenylboryl groups, RCo(DH) 2− n (DB( p- XPh) 2 ) n L (R=alkyl or aryl group, L= N -MeIm, Py or H 2 O, X=OCH 3 , CH 3 or Cl, n =1 or 2) have been synthesized. The X-ray structures and the 1 H-NMR spectra are compared with those of the corresponding RCo(DH) 2− n (DBPh 2 ) n L and RCo(DBF 2 ) 2 L complexes. The insertion of X groups in the phenyl rings does not significantly affect the equatorial CoN distances, whereas the CoPy distances increase slightly in the order (DB( p- OCH 3 Ph) 2 ) 2 p- ClPh) 2 ) 2 2 ) 2 . 1 H-NMR spectra suggest that the conformational distribution in solution is similar to that observed in the corresponding BPh 2 derivatives. Electrochemical studies on the corresponding MeCo(DB( p- XPh) 2 ) 2 H 2 O compounds show a mono-electron Co(III)/Co(II) transfer reaction followed by two parallel reactions: (a) mono-electron Co(II)/Co(I) transfer; (b) homolytic dissociation of the CoC bond with the formation of Co(I) species, the relative rates of the two processes being dependent on X. As the electron-withdrawing power of the equatorial ligand increases, the reduction potentials associated with both Co(III)/Co(II) and Co(II)/Co(I) processes shift towards more positive values, indicating a decrease of electron density on the Co atom. The effects are comparable with those observed by changing the axial ligands.

63Cu-31P coupling constants and 63Cu quadrupole couplings from 31P CP/MAS spectra of copper (I)—phosphine complexes with aryldithiocarboxylates or benzoate

Magic-angle spinning 31P NMR spectra of solid [CuS2C-Ph(PPh3)2] 1, [{CuS2C-pT}4(PPh3)2] 2, [{CuS2C-Ph}4(PPh3)2] 3. [CuS2C-Ph(dppm)]2 4 and [CuO2C-Ph(dppm)]2 5, (T = tolyl, dppm = bis(diphenylphosphino)methane) were obtained at 109.6 MH2. They consist of distorted quartets from non-equivalent phosphorus atoms and provide approximate values of the indirect spin-spin coupling constant J[63Cu,31P], that are indicative of the covalency of the dithiocarboxylate-copper bonding. The spacing distortions are related to a number of molecular and structural parameters and thereby allow an estimation of the copper quadrupole coupling constant e2qQ/h which, as expected, is smaller for tetra-coordinated (1, 2, 3 and 4) than for tri-coordinated (5) copper sites. The spectrum of 2 has been successfully simulated (including the isotope effects from the less abundant 65Cu isotope) using the full theory for calculation of the spin eigenfunctions of the quadrupolar nucleus.