Mehdi Yemloul

Solvent Dynamical Behavior in an Organogel Phase As Studied by NMR Relaxation and Diffusion Experiments

An organogelation process depends on the gelator-solvent pair. This study deals with the solvent dynamics once the gelation process is completed. The first approach used is relaxometry, i.e., the measurement of toluene proton longitudinal relaxation time T(1) as a function of the proton NMR resonance frequency (here in the 5 kHz to 400 MHz range). Pure toluene exhibits an unexpected T(1) variation, which has been identified as paramagnetic relaxation resulting from an interaction of toluene with dissolved oxygen. In the gel phase, this contribution is retrieved with, in addition, a strong decay at low frequencies assigned to toluene molecules within the gel fibers. Comparison of dispersion curves of pure toluene and toluene in the gel phase leads to an estimate of the proportion of toluene embedded within the organogel (found around 40%). The second approach is based on carbon-13 T(1) and nuclear Overhauser effect measurements, the combination of these two parameters providing direct information about the reorientation of C-H bonds. It appears clearly that reorientation of toluene is the same in pure liquid and in the gel phase. The only noticeable changes in carbon-13 longitudinal relaxation times are due to the so-called chemical shift anisotropy (csa) mechanism and reflect slight modifications of the toluene electronic distribution in the gel phase. NMR diffusion measurements by the pulse gradient spin-echo (PGSE) method allow us to determine the diffusion coefficient of toluene inside the organogel. It is roughly two-thirds of the one in pure toluene, thus indicating that self-diffusion is the only dynamical parameter to be slightly affected when the solvent is inside the gel structure. The whole set of experimental observations leads to the conclusion that, once the gel is formed, the solvent becomes essentially passive, although an important fraction is located within the gel structure.

New Application of Proton Nuclear Spin Relaxation Unraveling the Intermolecular Structural Features of Low-Molecular-Weight Organogel Fibers

Proton nuclear spin relaxation has been for the first time extensively used for a structural and dynamical study of low-molecular-weight organogels. The gelator in the present study is a modified phenylalanine amino acid bearing a naphthalimide moiety. From T(1) (spin-lattice relaxation time in the laboratory frame) and T(1ρ) (spin-lattice relaxation time in the rotating frame) measurements, it is shown that the visible gelator NMR spectrum below the liquid-gel transition temperature corresponds to a so-called isotropic compartment, where gelator molecules behave as in a liquid phase but exchange rapidly with the molecules constituting the gel structure. This feature allows one to derive, from accessible parameters, information about the gel itself. Nuclear Overhauser effect spectroscopy (NOESY) experiments have been exploited in view of determining not only cross-relaxation rates but also specific longitudinal rates. The whole set of relaxation parameters (at 25 °C) leads to a correlation time of 5 ns for gelator molecules within the gel structure and 150 ps for gelator molecules in the isotropic phase. This confirms, on one hand, the flexibility of the organogel fibers and, on the other hand, the likely presence of clusters in the isotropic phase. Concerning cross-relaxation rates, a thorough theoretical investigation in multispin systems of direct and relayed correlations in a NOESY spectrum allows one to make conclusions about contacts (around 2-3 Å) not only between naphtalimide moieties of different gelator molecules but also between the phenyl ring and the naphtalimide moiety again of different gelator molecules. As a result, not only is the head-to-tail structure of amino acid columns confirmed but also the entangling of nearby columns by the naphthalimide moieties is demonstrated.

Physicochemical of microcrystalline cellulose from oil palm fronds as potential methylene blue adsorbents

The present study sheds light on the physical and chemical characteristics of microcrystalline cellulose (MCC) isolated from oil palm fronds (OPF) pulps. It was found that the OPF MCC was identified as cellulose II polymorph, with higher crystallinity index than OPF α-cellulose (CrIOPFMCC: 71%>CrIOPFα-cellulose: 47%). This indicates that the acid hydrolysis allows the production of cellulose that is highly crystalline. BET surface area of OPF MCC was found to be higher than OPF α-cellulose (SBETOPFMCC: 5.64m2g-1>SBETOPFα-cellulose:Qa0 2.04m2g-1), which corroborates their potential as an adsorbent. In batch adsorption studies, it was observed that the experimental data fit well with Langmuir adsorption isotherm in comparison to Freundlich isotherm. The monolayer adsorption capacity (Qa0) of OPF MCC was found to be around 51.811mgg-1 and the experimental data fitted well to pseudo-second-order kinetic model.

The antitumor effects of an arsthinol–cyclodextrin complex in a heterotopic mouse model of glioma

In this paper, we examined arsthinol-cyclodextrin complexes, which display an anticancer activity. The association constants were 17,502±522 M(-1) for hydroxypropyl-β-cyclodextrin and 12,038±10,168 M(-1) for randomized methylated β-cyclodextrin. (1)H NMR experiments in solution also confirmed the formation of these complexes and demonstrated an insertion of the arsthinol (STB) with its dithiarsolane extremity into the wide rim of the hydroxypropyl-β-cyclodextrin cavity. Complexed arsthinol was more effective than arsenic trioxide (As2O3) and melarsoprol on the U87 MG cell line. Importantly, in the in vivo study, we observed significant antitumor activity against heterotopic xenografts after i.p. administration and did not see any signs of toxicity. This remains to be verified using an orthotopic model.

Combined maximum-quantum and DOSY 3D experiments provide enhanced resolution for small molecules in mixtures.

We illustrate here as the combination of high‐order maximum‐quantum (MaxQ) and Diffusion‐Ordered SpectroscopY (DOSY) NMR experiments in a 3D layout allows superior resolution for crowded NMR spectra. Non‐uniform sampling (NUS) allows compressing the experimental time effectively to reasonable durations. Because diffusion effects were encoded within multiple‐quantum coherences, increased sensitivity to magnetic field gradients is observed, requiring compensation for convection effects. The experiment was demonstrated on the spectra of a mix of small polyaromatic molecules. Specifically, in the case analyzed, the experiment provided an extreme simplification through the MaxQDOSY‐MaxQ projection plane that presents one peak per molecule. Copyright

Hepatic metabolic effects of Curcuma longa extract supplement in high-fructose and saturated fat fed rats

The metabolic effects of an oral supplementation with a Curcuma longa extract, at a dose nutritionally relevant with common human use, on hepatic metabolism in rats fed a high fructose and saturated fatty acid (HFS) diet was evaluated. High-resolution magic-angle spinning NMR and GC/MS in combination with multivariate analysis have been employed to characterize the NMR metabolite profiles and fatty acid composition of liver tissue respectively. The results showed a clear discrimination between HFS groups and controls involving metabolites such as glucose, glycogen, amino acids, acetate, choline, lysophosphatidylcholine, phosphatidylethanolamine, and β-hydroxybutyrate as well as an increase of MUFAs and a decrease of n-6 and n-3 PUFAs. Although the administration of CL did not counteract deleterious effects of the HFS diet, some metabolites, namely some n-6 PUFA and n-3 PUFA, and betaine were found to increase significantly in liver samples from rats having received extract of curcuma compared to those fed the HFS diet alone. This result suggests that curcuminoids may affect the transmethylation pathway and/or osmotic regulation. CL extract supplementation in rats appears to increase some of the natural defences preventing the development of fatty liver by acting on the choline metabolism to increase fat export from the liver.

Carbon-13 Heteronuclear Longitudinal Spin Relaxation for Geometrical (and Stereochemical) Determinations in Small or Medium Size Molecules

Owing to an extremely abundant literature making use of spin relaxation for structural studies, this review is limited to carbon-13 spectroscopy, to small or medium size molecules, to stereochemical and preferably geometrical determinations. The parameter of choice is evidently the Nuclear Overhauser effect (NOE) because it depends exclusively on the dipolar interaction mechanism, thus on 1/r6, where r is the distance between the two interacting spins. However, it depends also on the dynamical features of the system under investigation which must be characterized prior to any attempt for obtaining geometrical or stereochemical information. Therefore, this review is devoted not only to 1H–13C NOE but, more generally, to 13C longitudinal relaxation. After comprehensive theoretical developments, experimental methods presently available will be presented. The latter include the usual gated decoupling experiment and pulse experiments of the HOESY (Heteronuclear Overhauser Effect SpectroscopY) family. These pulse experiments, which imply carbon-13 observation, can be one-dimensional, selective one-dimensional or two-dimensional. The emphasis will be put on the interpretation which is different according to the occurrence or not of extreme narrowing conditions. Along with a literature survey, some selected examples will be presented in detail in order to illustrate the potentiality of the method.

Controlling the polymerization of coniferyl alcohol with cyclodextrins

The mono-electronic oxidation of coniferyl alcohol leads to phenoxy radicals and ultimately to the synthesis of dimeric lignans. Coniferyl alcohol and lignans are all potential guests for cyclodextrins (CDs) to form noncovalent host-guest inclusion complexes. Here, the influence of CDs with different cavity volumes (i.e. α, β or γCD) on the laccase-driven oxidation of coniferyl alcohol is studied. We are clearly showing that βCD interacts with the lignan products and selectively prevent their further oxidation by the enzyme. Moreover, amongst the three lignans generated the system made of a laccase and βCD allows a selective enrichment of pinoresinol, a behaviour somehow mimicking that of plant dirigent proteins.