Structure and phase behavior of O-stearoylethanolamine: A combined calorimetric, spectroscopic and X-ray diffraction study

ATP-Assisted Protocellular Membrane Formation with Ethanolamine-Based Amphiphiles

Prebiotic membranes are one of the essential elements of the origin of life because they build compartments to keep genetic materials and metabolic machinery safe. Since modern cell membranes are made up of ethanolamine-based phospholipids, prebiotic membrane formation with ethanolamine-based amphiphiles and phosphates might act as a bridge between the prebiotic and contemporary eras. Here, we report the prebiotic synthesis of O-lauroyl ethanolamine (OLEA), O-lauroyl methyl ethanolamine (OLMEA), and O-lauroyl dimethylethanolamine (OLDMEA) under wet-dry cycles. Turbidimetric, NMR, DLS, fluorescence, microscopy, and glucose encapsulation studies highlighted that OLEA-ATP and OLMEA-ATP form protocellular membranes in a 3:1 ratio, where ATP acts as a template. OLDMEA with a dimethyl group did not form any membrane in the presence of ATP. ADP can also template OLEA to form vesicles in a 2:1 ratio, but the ADP-templated vesicles were smaller. This suggests the critical role of the phosphate backbone in controlling the curvature of supramolecular assembly. The mechanisms of hierarchical assembly and transient dissipative assembly are discussed based on templated-complex formation via electrostatic, hydrophobic, and H-bonding interactions. Our results suggest that N-methylethanolamine-based amphiphiles could be used to form prebiotic vesicles, but the superior H-bonding ability of the ethanolamine moiety likely provides an evolutionary advantage for stable protocell formation during the fluctuating environments of early earth.

Base-triggerable lauryl sarcosinate-dodecyl sulfate catanionic liposomes: structure, biophysical characterization, and drug entrapment/release studies

Equimolar mixtures of oppositely charged single-chain amphiphiles form a variety of phases, including vesicles. Such catanionic mixed lipid systems show high stability and exhibit versatile physicochemical properties. In the present study we have investigated the aggregation behaviour of lauryl sarcosinate hydrochloride (LS·HCl) in aqueous dispersion as well as its interaction with the anionic surfactant sodium dodecyl sulfate (SDS). The CMC of LS·HCl was estimated to be ∼5 mM by isothermal titration calorimetry (ITC) and fluorescence spectroscopy using pyrene as the fluorescent probe. Turbidimetric and ITC studies on the interaction of LS·HCl with SDS demonstrated that the two surfactants form an equimolar catanionic complex. The crystal structure of the lauryl sarcosinate-dodecyl sulfate (LS-DS) complex revealed that the complex is stabilized by classical N-H⋯O as well as C-H⋯O hydrogen bonds, besides the electrostatic attraction between LS (cation) and DS (anion) and dispersion interactions between the hydrocarbon chains. Differential scanning calorimetry studies revealed that the phase transition of the equimolar LS-DS complex is significantly reduced compared to the analogous LG-DS and LA-DS complexes in the fully hydrated state. Dynamic light scattering, atomic force microscopy and transmission electron microscopy studies demonstrated that the LS-DS catanionic complex forms stable medium-sized vesicles (diameter of ∼300-500 nm). In vitro studies with 5-fluorouracil and rhodamine 6G showed efficient entrapment and release of these two anti-cancer drugs in the physiologically relevant pH range of 6.0-8.0, but with contrasting pH dependences. These observations indicate that LS-DS catanionic vesicles may find application in designing drug delivery systems.

Structure, thermotropic phase behavior and membrane interaction of N-acyl-β-alaninols. Homologs of stress-combating N-acylethanolamines

β-Alaninol and its derivatives were reported to exhibit interesting biological and pharmacological activities and showed potential application in formulating drug delivery vehicles. In the present study, we report the synthesis and characterization of N-acyl-β-alaninols (NABAOHs) bearing saturated acyl chains (n = 8-20) with respect to thermotropic phase behavior, supramolecular organization and interaction with diacylphosphatidylcholine, a major membrane lipid. Results obtained from DSC and powder XRD studies revealed that the transition temperatures (T_t), transition enthalpies (ΔH_t), transition entropies (ΔS_t) and d-spacings of NABAOHs show odd-even alteration. A linear dependence was observed in the values of ΔH_t and ΔS_t on the acyl chain length, independently for even and odd acyl chains in both dry and hydrated states; further, the even chainlength molecules exhibited higher values than the odd chainlength series. The crystals structures of N-lauroyl-β-alaninol and N-palmitoyl-β-alaninol, solved in monoclinic system in the P21/c space group, show that the NABAOHs adopt a tilted bilayer structure. A number of NH⋯O, O-H⋯O, and C-H⋯O hydrogen bonds between the hydroxyl and amide moieties of the head groups of NABAOH molecules belonging to adjacent and opposite layers stabilize the overall supramolecular organization of the self-assembled bilayer system. DSC studies on the interaction of N-myristoyl-β-alaninol (NMBAOH) with dimyristoylphosphatidylcholine (DMPC) indicate that these two lipids mix well up to 45 mol% NMBAOH, whereas phase separation was observed at higher contents of NMBAOH. Transmission electron microscopic studies reveal that mixtures containing 20-50 mol% NMBAOH form stable ULVs of 90-150 nm diameter, suitable for use in drug delivery applications.

A headgroup linker perturbs pKavia acyl chain migration: designing base-labile supramolecular assemblies

Acyl chain transfer, which perturbs the protonation equilibrium of amine and reduces the apparent pKa by 2.0-2.5 units, is used to develop a liposome-based drug delivery system.

Cardiolipin, a key component to mimic the E. coli bacterial membrane in model systems revealed by dynamic light scattering and steady-state fluorescence anisotropy

The phase transition temperatures of several lipidic systems were determined using two different techniques: dynamic light scattering (DLS) and steady-state fluorescence anisotropy, using two fluorescent probes that report different membrane regions (TMA-DPH and DPH). Atomic force microscopy (AFM) was used as a complementary technique to characterize different lipid model systems under study. The systems were chosen due to the increased interest in bacterial membrane studies due to the problem of antibiotic drug resistance. The simpler models studied comprised of mixtures of POPE and POPG lipids, which form a commonly used model system for Escherichia coli membranes. Given the important role of cardiolipin (CL) in natural membranes, a ternary model system, POPE/POPG/CL, was then considered. The results obtained in these mimetic systems were compared with those obtained for the natural systems E. coli polar and total lipid extract. DLS and fluorescence anisotropy are not commonly used to study lipid phase transitions, but it was shown that they can give useful information about the thermotropic behaviors of model systems for bacterial membranes. These two techniques provided very similar results, validating their use as methods to measure phase transitions in lipid model systems. The temperature transitions obtained from these two very different techniques and the AFM results clearly show that cardiolipin is a fundamental component to mimic bacteria membranes. The results suggest that the less commonly used ternary system is a considerably better mimic for natural E. coli membranes than binary lipid mixture.