13 research outputs found
Gel-type polyacrylic resins cross-linked with trimethylolpropanetrimethacrylate: the issue of their nanostructure unveiled with a combination of Inverse Steric Exclusion Chromatography (ISEC), ESR and CP MAS 13C NMR spectrometries
No full textAbstract: Six gel-type functional resins,
that is, three poly-DMAA-co-TMPTP
(DMAA=N,N-dimethylacrylamide,
TMPTP=trimethylolpropyltrimethacrylate)
samples with different degrees
of cross-linking (0.6, 1.2, 1.7% mol)
and three poly-DMAA-co-MA-co-
TMPTP (MA=methacrylic acid, ca.
5.5% mol) samples with 1.7, 3.5, and
7% mol cross-linking were investigated
with ISEC (inverse steric exclusion
chromatography), and ESR and CPMAS
(cross polarization magic angle
spinning) 13C NMR spectroscopy after
swelling in water and other solvents.
This unprecedented combination of
conceptually independent physicochemical
techniques provides a thorough
overall consistent picture of the
morphology of the resins on the nanometer
scale and of the molecular accessibility
of the swollen polymer framework
to the paramagnetic probe TEMPONE
(2,2,6,6-tetramethyl-4-oxo-1-
oxypiperidine) and to selected solvents
Cross-linked poly-4-vinylpiridines as useful supports in metal catalysis: micro- and nanometer scale morphology
No full textMETAL PALLADIUM DISPERSED INSIDE MACROPOROUS ION-EXCHANGE RESINS: ROTATIONAL AND TRANSLATIONAL MOBILITY INSIDE THE POLYMER NETWORK
No full textCommercial macroporous strongly acidic ion-exchange resin (Bayer UCP 118) in its acidic and Na+ forms and a resin/Pd composite were investigated by means of electron spin resonance (ESR) and pulse field gradient spin echo-nuclear magnetic resonance (PGSE-NMR) techniques, to determine their molecular accessibility to 2,2,6,6-tetramethyl-4-oxo-1-oxypiperidine (TEMPONE) dissolved in water and the molecular mobility of both TEMPONE and water inside their accessible domains. The paramagnetic probe and water itself occupy both the micro- and macroporous domains of the resin particles, among which a rapid exchange is observed. (C) 2000 Elsevier Science B.V. All rights reserved
Metal ions implantation onto acidic resins upon reaction of metal acetates and carbamates. Part I. Synthetic results
No full textModerately cross-linked gel-type resins bearing -SO3H, -COOH and -OH groups undergo facile metallation with Pd-II, Cu-II and Ni-II acetates with concomitant release of acetic acid. Successful and facile metallation is also observed upon reaction with Pd-II, Cu-II and Ni-II carbamates
Catalytic activity of bovine lactoperoxidase supported on macroporous poly(2-hydroxyethyl methacrylate-co-glycidyl methacrylate)
No full text2-Hydroxyethyl methacrylate (HEMA) and glycidyl methacrylate (GMA) (molar ratio 85/15) are copolymerised
upon c-ray exposure at 78 C in the presence of water to give a hydrophilic resin with a porosity that favours the
anchoring of bovine-lactoperoxidase (LPO). The resin, after mincing and sieving, is obtained as irregular microparticles
with size ranging from 80 to 1000 lm. The morphology of the resin in the swollen state is investigated with Inverse
Steric Exclusion Chromatography and ESR. The catalytic activity of immobilised and soluble LPO is monitored
and compared for 14 days at 4 C as well as enzyme stability toward thermal inactivation and resistance to denaturing
agents (acidity, urea, organic solvents). The results reveal a higher stability of supported LPO both in aqueous and
organic media as compared with the free enzyme. Evaluation of kinetic parameters of immobilised LPO suggests that
the enzyme turns out to be mainly linked to the external surface of the supporting particles
On the Growth and Shape of Sodium Taurodeoxycholate Micellar Aggregates: A Spin Label and Quasi – Elastic Light Scattering Investigation
No full textElectron spin resonance (ESR) and quasielastic laser scattering (QELS) measurements have been carried out on sodium taurodeoxycholate (NaTDC) micellar aqueous solutions. Computer simulation of the ESR line shape has been used to quantitatively analyze the rotational dynamics of the cholestan-spin label (CSL) dissolved by the NaTDC micellar aggregates as a function of temperature and NaCl concentration. The local reorientation of CSL has been accounted for motionally-averaged g- and A-tensors assuming fast oscillation around the spin-probe long molecular axis. The overall Brownian tumbling of CSL-micelle complexes has been modeled by an axially symmetric rotational tensor. Good agreement with experimental spectra is obtained. Best-fit rotational parameters and QELS data suggest that, in the circumstance of large aggregation, NaTDC micelles have cylindrical shape and micellar growth occurs along the cylinder axis. (C) 2004 American Institute of Physics
Conformational Changes at the Active Site of Pantetheine Hydrolase During Denaturation by Guanidine Hydrocloride
No full textNanostructure and molecular accessibility of gel-type resins for supported bio-catalysis. Part I. Poly-hydroxyethylmethacrylatehydroxypropylmethacrylate-trimethylolpropanetrimethacrylate
No full textMetal palladium supported on amphiphilic microporous synthetic organic supports. Part II. Catalytic investigations.
No full textTwo sets of resin-supported Pd(0) catalysts were compared in the hydrogenation of cyclohexene in methanol, under ambient conditions. Two lightly crosslinked poly-{styrene/2-methacryloxyethylsulfonic acid/methylenebisacrylamide} with different degrees of crosslinking (1 and 3 mol%), have been used as catalyst supports. Two catalysts with different palladium loadings (0.22 and 2.2 wt%) have been prepared from each support. When the size of the particles was relatively small, the catalysts with 2.2% and 0.22% Pd were almost equally active with respect to the amount of palladium in the reaction mixture. In contrast, when larger catalyst particles were used, catalysts with 2.2% metal produced conversion profiles typical of diffusion-controlled regimes (productivity decreased with increasing crosslinking). These catalysts were characterised by combined ESR and static gradient spin echo NMR spectrometries, which have provided information about molecular motion inside the polymer networks
Study on Intermicellar Interactions and Micellar Size in Aqueous Solution of Sodium Taurocholate by Measurements of Collective Diffusion and Self-Diffusion Coefficient
No full textAqueous micellar solutions of sodium taurocholate (NaTC) have been studied by using quasi-elastic lightscattering (QELS) and H-1 pulse-gradient-stimulated-echo NMR (PGSTE-NMR). The collective and selfdiffusion coefficients have been obtained as a function of NaTC concentration (0.05-0.20 M) and the ionic strength of the solution (0-0.8 M NaCl added). The comparison of the two techniques' data in each solution has been performed in the context of micellar growth and intermicellar interactions. The model of monodisperse Brownian particles with hydrodynamic interaction and hard core repulsion gives rise to a satisfactory agreement with the experimental data. The translational diffusion coefficient of the single micellar aggregate has been calculated for each solution. The size of the micellar aggregates depends on the ionic strength and bile salt concentration
