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We report translational diffusion coefficients in a columnar phase of a discotic liquid crystal formed by a triphenylene-based compound. The experiments were performed using 2H stimulated-echo-type pulsed-field-gradient spin-echo NMR applied to a chain-deuterated sample. The diffusion coefficients were found in the range of 1x10(-14)-4x10(-14) m2/s, three orders of magnitude lower than in the isotopic phase of the same compound. This, together with the high activation energy obtained in columnar phase, indicates that the diffusion is dominated by solidlike jump processes.

It is well documented that disaccharides in general and trehalose (TRH) in particular strongly affect physical properties and functionality of lipid bilayers. We investigate interactions between lipid membranes formed by 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and TRH by means of molecular dynamics (MD) computer simulations. Ten different TRH concentrations were studied in the range wTRH = 0-0.20 (w/w). The potential of mean force (PMF) for DMPC bilayer-TRH interactions was determined using two different force fields, and was subsequently used in a simple analytical model for description of sugar binding at the membrane interface. The MD results were in good agreement with the predictions of the model. The net affinities of TRH for the DMPC bilayer derived from the model and MD simulations were compared with experimental results. The area per lipid increases and the membrane becomes thinner with increased TRH concentration, which is interpreted as an intercalation effect of the TRH molecules into the polar part of the lipids, resulting in conformational changes in the chains. These results are consistent with recent experimental observations. The compressibility modulus related to the fluctuations of the membrane increases dramatically with increased TRH concentration, which indicates higher order and rigidity of the bilayer. This is also reflected in a decrease (by a factor of 15) of the lateral diffusion of the lipids. We interpret these observations as a formation of a glassy state at the interface of the membrane, which has been suggested in the literature as a hypothesis for the membrane-sugar interactions.

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The determination of the three-dimensional structure of organic and biomolecular compounds by NMR spectroscopy usually involves the measurement of 3 J coupling constants, [1] NOEs, [2] and cross-correlated relaxation [3] to obtain information about dihedral angles, distances, and projection angles, respectively. If interconversion of conformers takes place and is fast on the NMR time scale, NMR spectroscopic parameters for flexible parts of the molecule are motionally averaged. This effect is one of the main complications in the structure determination of nonrigid molecules and often prohibits the determination of the relative configuration of organic compounds.It has been shown that residual dipolar couplings (RDCs) can yield information complementary to that obtained from 3 J coupling constants and NOE parameters also for organic compounds [4][5][6][7][8][9][10] and enable the assignment of relative configurations even in the presence of a limited degree of motion. [11][12][13][14][15] The problem of the joint treatment of an unknown configuration and conformational averaging when residual dipolar couplings are used in structure determination has scarcely been tackled. Herein two approaches are discussed, and it is shown that even conformer populations can be obtained from experimentally determined RDCs.The example chosen for illustration is a five-memberedring compound investigated recently by some of us. The amethylene-g-butyrolactone had been synthesized as single diastereoisomer, [16] the relative configuration of which (trans, denoted 1, or cis, denoted 2) was unknown and could not be determined by using conventional NMR spectroscopic parameters.[11] By using RDCs, however, it was possible to assign the relative configuration as trans (Scheme 1).[11]The number of ring conformers of 1 is restricted to two, denoted A and B in the following. These conformers are envelope conformations, one with C2 below (A) and one with C2 above (B) the almost planar arrangement of the remaining ring atoms (see also Figure SI1 in the Supporting Information).[17] In the previous study, [11] we used the transition structure between A and B as a crude approximation of the average ring conformation of 1. Additionally, we fitted the structures of the two rigid conformers to the RDC data by using one order tensor [18,19] each. By using this method we were able to assign the relative configuration as trans.[20]However, we did not attempt to extract information concerning the populations of the two conformers (p A and p B ), which was therefore one subject of the current investigation.The direct (residual) dipolar coupling D IS between spins I and S, with magnetogyric ratios g I and g S , is given by Equation (1): [9,21] ISis the dipole-dipole coupling constant (in Hz), V IS is the angle between the interspin vector and the external magnetic field, and r IS is the interspin distance (which corresponds to the bond length for directly bound nuclei). The angular brackets indicate that the RDCs are averaged over both molecular tumbling ...

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Cardiolipin is a key lipid component in the inner mitochondrial membrane, where the lipid is involved in energy production, cristae structure, and mechanisms in the apoptotic pathway. In this article we used molecular dynamics computer simulations to investigate cardiolipin and its effect on the structure of lipid bilayers. Three cardiolipin/POPC bilayers with different lipid compositions were simulated: 100, 9.2, and 0% cardiolipin. We found strong association of sodium counterions to the carbonyl groups of both lipid types, leaving in the case of 9.2% cardiolipin virtually no ions in the aqueous compartment. Although binding occurred primarily at the carbonyl position, there was a preference to bind to the carbonyl groups of cardiolipin. Ion binding and the small headgroup of cardiolipin gave a strong ordering of the hydrocarbon chains. We found significant effects in the water dipole orientation and water dipole potential which can compensate for the electrostatic repulsion that otherwise should force charged lipids apart. Several parameters relevant for the molecular structure of cardiolipin were calculated and compared with results from analyses of coarse-grained simulations and available X-ray structural data.