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2H NMR quadrupole splittings and longitudal relaxation times from the aromatics ring of benzyl alcohol-d5(Co), a commonly used anesthetic, and a series of linear alkyl benzyl-d5 ethers with chain lengths from 1 to 12 carbon atoms were measured. Both experiment and theory suggest that an aliphatic chain of about eight or nine carbon is sufficiently hydrophobic to completely align the guest molecule inside the aggregate.

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Most drugs have to cross cell membranes to reach their final target. A better understanding of the distribution, interactions, and dynamics of biologically active molecules in model bilayers is of fundamental importance in understanding drug functioning and design. 2H NMR quadrupole splittings (ΔνQ) and longitudinal relaxation times (T1) from the aromatic ring of benzyl alcohol-d5 (C0), a commonly used anesthetic, and a series of linear alkyl benzyl-d5 ethers with chain lengths from 1 to 12 carbon atoms (C1−C12), were measured. The molecules were dissolved in a nematic discotic lyotropic liquid crystal solution made of tetradecyltrimethylammonium chloride (TTAC)/decanol (DeOH)/NaCl/H2O. Values of ΔνQ and T1 from 1,1-dideuteriodecanol (15% enriched) and DHO (H2O with 0.2% D2O) were also measured. ΔνQ of DeOH and DHO remained constant throughout the series. The value of ΔνQ of the para position of the ring (Δνp) in C1 is 30% smaller than the Δνp of C0. This is attributed to the existence of an H-bond between the alcohol hydroxyl proton and the solvent, which influences the average orientation of the ring. The relaxation data show that T1o,m is always longer than T1p and both decrease with the increase in alkyl chain length. Molecular dynamics simulations of the experimentally studied systems were performed. The aggregate was represented as a bilayer. The distribution, average orientation, and order parameters of the aromatic ring of the guest molecules in the bilayer were examined. Rotational correlation functions of all the C−D bonds and the OH bond from H2O were evaluated, allowing an estimate of the correlation times and T1. According to these results all spins relax in extreme narrowing conditions, except DeOH. Experimental and calculated T1 values differ at most by a factor of 3. However, the order of magnitude and the observed trends are well reproduced by the calculations. The aromatic ring of C0 possesses a unique average orientation in the bilayer. For the ether series, the orientation is modified and the C2 symmetry axis of the aromatic ring is exchanging between two orientations averaging the quadrupole splittings from the ortho and meta positions. The simulation supports the existence of an H-bond between C0 and the solvent not found in the ethers, which should be responsible for the observed differences. [ABSTRACT FROM AUTHOR]

Understanding the molecular interactions that rule the physicochemical properties of molecular assemblies is of particular interest when trying to explain the behavior of much more complicated systems, such as the cell membranes. This work was devoted to study a discotic nematic lyotropic liquid crystal, formed by sodium dodecylsulphate (3% SDS-d25) and decanol (20% DeOH-α-d2), dissolved in aqueous solutions (0.1% D2O) of Na2SO4 or Li2SO4. The average size of the aggregates was estimated using fluorescence quenching experiments, and their dynamics were studied by measuring the 2H-NMR quadrupole splitting (ΔνQ) and the longitudinal relaxation times (T1) of the deuterated species. To provide an atomic insight into these assemblies, molecular dynamics simulations of the systems were carried out with atomic detail. As a previous step in this study, a reparameterization of the standard GROMOS 87 force field was required to perform the equilibrated simulations and to prevent instabilities emerging during the simulations. Finally, an excellent agreement between simulation and experimental data was obtained. In addition, variations in the long range electrostatic interactions at the aggregate/solution interface, the orientation and the reorientational relaxation time of the water dipole, the translational diffusion coefficient of sodium ions, and the amphiphile-counterion coordination associated with the presence of Li+ in the solution were other key aspects investigated to explain the variation in the quadrupole splittings (ΔνQ) in the presence of lithium in solution. [ABSTRACT FROM AUTHOR]