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The effect of general anaesthetics alkan-1-ols (CnOH, where n = 10, 12, 14, 16 and 18 is the number of carbon atoms in the molecule) on the structure of dioleoylphosphatidylcholine (DOPC) model membrane was studied by small-angle neutron scattering (SANS) and small-angle neutron diffraction (SAND). Fluid bilayers were prepared at CnOH:DOPC = 0.3 molar ratio. The results of both the experiments show that bilayer thickness - a thickness parameter dg in the case of SANS and lamellar repeat distance D in the case of SAND - increases with increasing n. A coexistence of two lamellar phases with different D was detected by measuring the C18OH+DOPC oriented sample.

The amyloid-beta peptide (Aβ) is considered a key factor in Alzheimer's disease (AD) ever since the discovery of the disease. The understanding of its damaging influence has however shifted recently from large fibrils observed in the inter-cellular environment to the small oligomers interacting with a cell membrane. We studied the effect of temperature on the latter interactions by evaluating the structural characteristics of zwitterionic phosphatidylcholine (PC) membranes with incorporated Aβ 25-35 peptide. By means of small angle neutron scattering (SANS), we have observed for the first time a spontaneous reformation of extruded unilamellar vesicles (EULVs) to discoidal bicelle-like structures (BLSs) and small unilamellar vesicles (SULVs). These changes in the membrane self-organization happen during the thermodynamic phase transitions of lipids and only in the presence of the peptide. We interpret the dramatic changes in the membrane's overall shape with parallel changes in its thickness as the Aβ 25-35 triggered membrane damage and a consequent reorganization of its structure. The suggested process is consistent with an action of separate peptides or small size peptide oligomers rather than the result of large Aβ fibrils., (© 2021. The Author(s).)

We have studied the impact of cholesterol and/or melatonin on the static and dynamical properties of bilayers made of DPPC or DOPC utilizing neutron scattering techniques, Raman spectroscopy and molecular dynamics simulations. While differing in the amplitude of the effect due to cholesterol or melatonin when comparing their interactions with the two lipids, their addition ensued recognizable changes to both types of bilayers. As expected, based on the two-component systems of lipid/cholesterol or lipid/melatonin studied previously, we show the impact of cholesterol and melatonin being opposite and competitive in the case of three-component systems of lipid/cholesterol/melatonin. The effect of cholesterol appears to prevail over that of melatonin in the case of structural properties of DPPC-based bilayers, which can be explained by its interactions targeting primarily the saturated lipid chains. The dynamics of hydrocarbon chains represented by the ratio of trans/gauche conformers reveals the competitive effect of cholesterol and melatonin being somewhat more balanced. The additive yet opposing effects of cholesterol and melatonin have been observed also in the case of structural properties of DOPC-based bilayers. We report that cholesterol induced an increase in bilayer thickness, while melatonin induced a decrease in bilayer thickness in the three-component systems of DOPC/cholesterol/melatonin. Commensurately, by evaluating the projected area of DOPC, we demonstrate a lipid area decrease with an increasing concentration of cholesterol, and a lipid area increase with an increasing concentration of melatonin. The demonstrated condensing effect of cholesterol and the fluidizing effect of melatonin appear in an additive manner upon their mutual presence., (Copyright © 2021 Elsevier B.V. All rights reserved.)

We investigate the structural changes to lipid membrane that ensue from the addition of aliphatic alcohols with various alkyl tail lengths. Small angle neutron diffraction from flat lipid bilayers that are hydrated through water vapor has been employed to eliminate possible artefacts of the membrane curvature and the alcohol's membrane-water partitioning. We have observed clear changes to membrane structure in both transversal and lateral directions. Most importantly, our results suggest the alteration of the membrane-water interface. The water encroachment has shifted in the way that alcohol loaded bilayers absorbed more water molecules when compared to the neat lipid bilayers. The experimental results have been corroborated by molecular dynamics simulations to reveal further details. Namely, the order parameter profiles have been fruitful in correlating the mechanical model of structural changes to the effect of anesthesia., Competing Interests: The authors declare no conflict of interest.