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The transesterification reaction used to produce biodiesel was monitored with 1H high-resolution nuclear magnetic resonance (HRNMR), conventional low-resolution NMR (LRNMR), and unilateral NMR (UNMR) spectroscopy. HRNMR was used as a standard method to compare with the methods of LRNMR and UNMR. A Carr–Purcell–Meiboom–Gill (CPMG) pulse sequence was used in both LRNMR and UNMR experiments. In LRNMR, the CPMG signal was used to measure the transverse relaxation time (T 2), which depended on sample viscosity; it showed a good correlation (R = 0.994) for the concentration of biodiesel in the oil/biodiesel mixture. These measurements could only be used when the samples contained less than 1% of methanol. In UNMR, the CPMG decay of the biodiesel/oil mixture strongly depended on molecular diffusion because of the intrinsic high magnet field gradient (G) associated with the magnetic. The T 2eff had a good and negative correlation (R = −0.997) with the biodiesel concentration in the biodiesel/oil mixture. The UNMR measurements were insensitive to the methanol contamination up to 50%, which was contrary to the LRNMR method. As methanol diffused rapidly, its magnetization lost coherency quickly in the presence of strong G and it was not fully refocused by the CPMG sequence. Therefore, the use of the fast, portable, and low cost UNMR sensor to monitor transesterification reactions was demonstrated ex situ. Now, the UNMR sensor has been adapted to monitor the transesterification reaction in situ, in a biodiesel pilot plant.

The topologies of proparacaine (PPC) in beta-cyclodextrin (beta-CD), PPC in egg phosphatidylcholine (EPC) liposomes and PPC in beta-CD in EPC were investigated using NMR experiments (1D ROESY and saturation transfer difference (STD)). This is the first description of the STD technique applied to PPC-EPC-beta-CD system, revealing that not only PPC was imbedded in EPC bilayer, but beta-CD was also interacting with liposome vesicles. These results are novel and were rationalized as the spontaneous formation of a ternary complex with some beta-CD molecules bound to external liposome vesicles surfaces.

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We have examined the interaction of the neutral and protonated species of the local anesthetic prilocaine (PLC) with phosphatidylcholine (PC) bilayers combining experimental ((1)H NMR) and theoretical (molecular dynamics simulations) approaches. DOSY experiments allowed the determination of the association constants of protonated (Ka = 9 L/mol) and neutral (Ka = 21 L/mol) PLC to egg PC liposomes. Saturation transfer difference (STD) experiments showed a different trend depending on pH: At high pH the PLC hydrogen saturation was essentially uniform and at pH 5.5 the experiments show an enhancement of the aromatic moiety hydrogen saturation, with respect to the tail. Molecular dynamics simulations, performed with PLC molecules on planar bilayers of palmitoyloleyl-PC, revealed a preferential orientation for the protonated PLC species at the polar interface of the bilayer, and a nonoriented and deeper insertion for neutral PLC. Such preferential location of protonated and neutral PLC inside the bilayer can be described as different transient sites which could modulate the access of these molecules to their binding site(s) in the voltage-gated sodium channel, justifying differences in the anesthetic's potency upon ionization.

Although the effect of magnetic field (B) on electrochemical reactions (magnetoelectrolysis phenomenon) has been long known, it has not been considered in electrochemical reactions analyzed in situ by magnetic resonance methods, such as nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), and magnetic resonance imaging (MRI), which are intrinsically performed in the presence of B. In this report, the effect of B on the copper electrodeposition reaction, measured by a low-field (0.23 T) NMR spectrometer, was demonstrated. As expected, an enhancement in the reaction rate in comparison to the ex situ electrodeposition reaction was observed. Such enhancement was not dependent on electrodes/magnetic field orientations. Parallel and perpendicular orientations showed similar electrodeposition rates, which is explained by the cyclotron flows generated by distortions in electric and magnetic field lines near the electrode and the electrode edge. Therefore, NMR spectroscopy is not a passive analytical method, as assumed in preceding in situ spectroelectrochemical studies. Although the magnetoelectrolysis phenomenon demonstrated in this report used a paramagnetic ion, it can also be observed for diamagnetic species, since the magnetoelectrolysis phenomenon is independent of the nature of the species. Consequently, similar convection effects may occur in other electrochemical nuclear magnetic resonance (EC-NMR) experiments, such as the electrochemical reaction of organic molecules, as well as in electrocatalysis/fuel cells, lithium-ion batteries, and experiments that use electrochemical electron paramagnetic resonance (EC-EPR) and electrochemical magnetic resonance imaging (EC-MRI).

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