Self-aggregation and supramolecular structure investigations of Triton X-100 and SDP2S by NOESY and diffusion ordered NMR spectroscopy.

The self-aggregation and supramolecular micellar structure of two surfactants in aqueous solution, the anionic surfactant SDP2S (sodium dodecyl dioxyethylene-2 sulfate) and the nonionic surfactant Triton X-100 (octylphenol-polyoxyethylene ether with 9.5 ethoxy groups), were investigated by NMR spectroscopy. The critical micellar concentration (CMC), the size, and shape of the aggregates were determined by diffusion ordered NMR spectroscopy (DOSY), while 2D NOESY NMR spectra were used to study the mutual spatial arrangement of surfactant molecules in the aggregated state. A nonlinear increase of the micellar hydrodynamic radius, indicating possible sphere-to-rod shape transition, was found for SDP2S at higher surfactant concentrations. Triton X-100 micelles were found to be almost spherical at low surfactant concentrations, but formation of ellipsoid shaped particles and/or micellar aggregation was observed at higher concentrations. The NOESY data show that at low concentration Triton X-100 forms a two-layer spherical structure in the micelles, with partially overlapping internal and external layers of Triton X-100 molecules and no distinct hydrophilic-hydrophobic boundary.

In situ evaluation of interfacial affinity in CeO2 based hybrid nanoparticles by pulsed field gradient NMR.

Complexation affinity of laurate ligands (C(12)H(23)O(2)) grafted onto the surface of cerium(IV) oxide nanoparticles can be probed and quantified in situ, by pulsed field gradient (1)H NMR through the dependence of the diffusion coefficient on the size of a species.

Delayed interconversion of D-glucose anomers in D2O.

The anomeric specificity of D-glucose metabolism and functional effects is currently assessed either over about 5 min at 37 degrees C or longer periods at much lower temperatures. In the present study, the half-life for the interconversion of D-glucose anomers at 30 degrees C was found to be increased (P<0.005) from 17.2+/-0.9 min in a mixture of H2O/D2O (9/1, v/v) to 58.6+/-1.9 min in pure D2O. It is proposed that advantage can be taken from this delayed interconversion in D2O in experiments dealing with the anomeric specificity of D-glucose metabolic fate and functional effects. Thus, even over 60-min incubation at 30 degrees C, the integrated mean abundance of alpha- and beta-D-glucose would remain close to 82 and 89%, respectively, of the corresponding initial value (100%).

Metabolism of 13C-enriched D-fructose in hepatocytes from Goto-Kakizaki rats.

This study aims at assessing the conversion of exogenous D-[1-13C]fructose, D-[2-13C]fructose or D-[6-13C]-fructose (10 mM) to 13C-enriched and either hydrogenated or deuterated D-glucose, L-lactate and L-alanine released by rat liver cells prepared from Goto-Kakizaki rats and incubated for 120 min in the presence of unlabelled D-glucose (also 10 mM) and D2O. The results of this study are relevant to the relative contribution of fructokinase and hexokinase isoenzyme to the phosphorylation of D-fructose, the capacity of D-glucose to confer to glucokinase positive cooperativity towards D-fructose, the circulation of D-fructose 6-phosphate in the pentose phosphate pathway, the regulation of the cytosolic NADD/NADH ratio, the respective fate of D-fructose-derived D-glyceraldehyde and dihydroxyacetone phosphate, the deuteration of fructose-derived glycolytic intermediates at the phosphoglucoisomerase, phosphomannoisomerase, enolase, pyruvate kinase and glutamate-alanine transaminase levels, and the unequal generation of L-[1-13C]lactate by cells exposed to D-[1-13C]fructose or D-[6-13C]fructose versus D-[2-13C]-fructose.

Silica-anchored organotin trichloride: a recyclable and clean organotin catalyst for transesterification reactions.

A new synthetic scheme towards silica-supported organotrichlorotin derivatives has been developed. It involves the synthesis of (11-triethoxysilyl)undecyltricyclohexyltin, followed by sol-gel processing and, subsequently in the formation of the resulting hybrid silica, by electrophilic substitution of the tricyclohexyltin function by the target grafted trichlorotin using tin tetrachloride. HR-MAS (119)Sn and CP-MAS (29)Si NMR combined with N2-sorption and TEM measurements evidenced the formation of a mesoporous organic-inorganic hybrid silica including a functionally pure supported-organotrichlorotin species. This silica-grafted organotrichlorotin displays a satisfactory catalytic activity in the transesterification of ethyl acetate by 1-octanol. The catalyst could be recycled four times without significant loss of activity. Furthermore, tin leaching below 10 ppm evidences the benefits of the proposed strategy to limit tin contamination of the final products.

Characterization of titanium dioxide nanoparticles dispersed in organic ligand solutions by using a diffusion-ordered spectroscopy-based strategy.

Diffusion-ordered NMR spectroscopy (DOSY NMR) is presented as a tool for the determination of the diffusion coefficients of organic ligands in suspensions of titanium dioxide nanoparticles. The nanoparticles were prepared by a sol-gel process by hydrolysis and condensation reactions of titanium tetra-n-butoxide in the presence of pentane-2,4-dione (acacH: acetylacetone), as well as para-toluenesulfonic acid (pTsA) and n-butanol (nBuOH). NMR spectroscopic studies were performed in various deuterated solvents, on both dispersed xerosols and diluted sols. The bipolar-pulsed field gradient longitudinal eddy-current delay (LED) pulse sequence was used for data acquisition. The data were processed by inverse Laplace transformation (ILT), by using a maximum entropy algorithm, to afford 2D DOSY spectra. Different diffusion regimes for organic ligands in the bound and unbound states were successfully discriminated, more particularly in [D3]acetonitrile, thus allowing assessment of their interactions with the nanoparticles.

Polystyrene-supported organotin dichloride as a recyclable catalyst in lactone ring-opening polymerization: assessment and catalysis monitoring by high-resolution magic-angle-spinning NMR spectroscopy.

Dialkyltin dichloride grafted to a cross-linked polystyrene, with the formula [P-H]((1-t))[P-(CH2)nSnBuCl2]t (P=[CH2CH(pC6H4)], t=the degree of functionalization, and n=6 or 11), is investigated as a recyclable catalyst in the ring-opening polymerization (ROP) of epsilon-caprolactone (CL). It is demonstrated that high-resolution magic-angle-spinning (HR-MAS) NMR spectroscopy is an invaluable tool to characterize completely the supported catalyst. The 2D 1H-13C HSQC HR-MAS spectrum, in particular, allowed extensive assignment of the 1H and 13C resonances, as well as accurate measurement of the (n)J((1)H-(117/119)Sn) and (n)J((13)C-(117/119)Sn) coupling constants. 1H and 119Sn HR-MAS NMR spectroscopy is presented as a monitoring tool for catalytic processes based on organotin compounds, particularly for the investigation of the extent to which polymerization residues are observable in situ in the material pores and for the assessment of the chemical integrity and recycling conditions of the grafted catalyst. From polymerization experiments with CL, initiated by n-propanol and with [P-H]((1-t))[P-(CH2)nSnBuCl2]t of various compositions as the supported catalyst, it appears that a partial 'burst' of the polystyrene support occurs when the length of the alkyl spacer is limited to n=6, as a result of polymer chains growing within the pores of the support. However, extension of the length of the aliphatic polymethylene spacer from 6 to 11 carbon atoms preserves the support integrity and allows the production of catalyst-deprived poly(epsilon-caprolactone) (PCL) oligomers. A preliminary attempt to recycle the heterogeneous catalyst has shown that very good reproducibility can be obtained, in terms of both catalyst activity and molecular-weight parameters of the as-recovered PCL polyester chains.

Metabolism of D-[1-(13)C]fructose, D-[2-(13)C]fructose, and D-[6-(13)C]fructose in rat hepatocytes incubated in the presence of H(2)O or D(2)O.

Isolated hepatocytes from fed rats were exposed for 120 min to D-[1-(13)C]fructose, D-[2-(13)C]fructose, or D-[6-(13)C]fructose in the presence of H(2)O or D(2)O. The identification and quantification of (13)C-enriched metabolites (D-glucose, L-lactate) in the incubation medium and the measurement of their deuterated isotopomers indicated that the ketohexose was phosphorylated predominantly at the intervention of fructokinase and that the majority of the D-glyceraldehyde molecules generated from d-fructose 1-phosphate were further metabolized, e.g., after phosphorylation to D-glyceraldehyde 3-phosphate. It is proposed that the present procedure may help to further characterize the regulation of D-fructose metabolism in both hepatocytes and other cell types.

Probing ionic association on metal oxide clusters by pulsed field gradient NMR spectroscopy: the example of Sn12-oxo clusters.

Pulsed field gradient (1)H NMR spectroscopy has been applied to investigate the association behavior of the Sn(12)-oxo cluster macrocation [(BuSn)(12)O(14)(OH)(6)](2+) with two different and smaller anions, p-toluenesulfonate (PTS(-)) and diphenylphosphinate (Ph(2)PO(2) (-)). By monitoring the translational diffusion coefficients of the various species involved, it is shown that the association depends on the anion involved and on the solvent used. Moreover, the possibility to individually monitor the diffusion characteristics of multiple anionic and cationic species in mixtures, by virtue of resolved (1)H resonances available from each species, allows us to evidence the occurrence of ion exchange in such systems. Thus when [(BuSn)(12)O(14)(OH)(6)](PTS)(2) is mixed with two equivalents of Ph(2)PO(2)NMe(4), PTS(-) is displaced by Ph(2)PO(2) (-), highlighting the greater affinity of the organotin macrocation for the diphenylphosphinate. This example clearly illustrates the potential of pulsed field gradient (1)H NMR spectroscopy in inorganic/organometallic chemistry, to follow preferential ion pairing in multi-ion systems at the level of each individually charged species.

Mechanistic study of Bu2SnCl2-mediated ring-opening polymerization of epsilon-caprolactone by multinuclear NMR spectroscopy.

The ring-opening polymerization (ROP) of epsilon-caprolactone (CL) was carried out in toluene at 100 degrees C with n-propanol (nPrOH) in the presence of Bu(2)SnCl(2). It comes out that the molar mass of the polyester chains can be predicted from the initial monomer-to-alcohol molar ratio in accordance with a controlled ROP mechanism involving an O-acyl cleavage of the monomer to selectively form (alpha-propyloxy)(omega-hydroxy)poly(epsilon-caprolactone) chains. In order to gain fundamental understanding of the mechanistic factors governing the polyester chain growth, advanced (1)H, (13)C, and (119)Sn NMR investigations were performed in situ in [D(8)]toluene, as well as with model solutions that contained Bu(2)SnCl(2) and binary mixtures of the components at various concentrations and temperatures. This has enabled us to propose a mechanism in which Bu(2)SnCl(2) behaves as a catalyst, while nPrOH is the actual initiator. It involves non-aggregated, six-coordinate Bu(2)SnCl(2) complexes in which ligands exchange fast on the (119)Sn NMR observational timescale, and the simultaneous interactions of CL and alcohol function in such a way that it favors insertion/propagation reactions over transesterification ones, up to high monomer conversion.