The role of X-ray diffraction in studies of the crystallography of monoacid saturated triglycerides

Triglycerides as Novel Phase-Change Materials: A Review and Assessment of Their Thermal Properties

Latent Heat Storage (LHS) with Phase-Change Materials (PCMs) represents a high energy density storage technology which could be applied in a variety of applications such as waste heat recovery and integration of renewable energy technologies in energy systems. To increase the sustainability of these storage solutions, PCMs have to be developed with particular regard to bio-origin and biodegradability. Triglycerides represent an interesting class of esters as the main constituents of animal and vegetable fats, with attractive thermal properties. In order to be used as PCMs, the thermal behaviour of triglycerides has to be fully understood, as in some cases they have been reported to show polymorphism and supercooling. This study assesses the suitability of triglycerides as PCMs by reviewing the literature published so far on their behaviour and properties. In particular, melting points, enthalpies of fusion, polymorphism, thermal conductivities, heat capacities and thermal cycling stabilities are considered, with a focus on LHS and thermal energy storage applications. In addition, the efforts conducted regarding modelling and the prediction of melting points and enthalpies based on chemical structures are summarized and assessed.

Analysis of the structure of nanocomposites of triglyceride platelets and DNA

DNA-complexes with platelet-like, cationically modified lipid nanoparticles (cLNPs) are studied with regard to the formation of nanocomposite structures with a sandwich-like arrangement of the DNA and platelets.

Structure and functional properties of diacylglycerols in membranes

1. 1,2-Diacyl-sn-glycerols (DAG) are minor components of cell membranes (about 1 mole% of the lipids) and yet they are potent regulators of both the physical properties of the lipid bilayer and the catalytic behaviour of several membrane-related enzymes. 2. In the pure state DAG's present a considerable polymorphism, with several crystalline phases in addition to the neat fluid phase. The most stable crystalline phase is the so-called beta' phase, a monoclinic crystalline form with orthorhombic perpendicular subcell chain packing, in which both acyl chains lie parallel to each other in a hairpinlike configuration about the sn-1 and sn-2 glycerol carbon atoms. The molecules are organized in a bilayer, with the glycerol backbone roughly parallel to the plane of the bilayer, and the acyl chains tilted at approximately 60 degrees with respect to that plane. Acyl chain unsaturation, and particularly a single cis unsaturation, impairs chain packing in mixed-chain DAG's, and this results in an increased number of metastable crystalline phases. 3. DAG's mix with phospholipids in fluid bilayers when their melting temperature is below or close enough to the melting temperature of the bilayer system. When incorporated in phospholipid bilayers, the conformation of DAG is such that the glycerol backbone is nearly perpendicular to the bilayer, with the sn-1 chain extending from the glycerol Cl carbon into the hydrophobic matrix of the bilayer and the sn-2 chain first extending parallel to the bilayer surface, then making a 90 degrees bend at the position of the sn-1 carbonyl to become parallel to the sn-1 chain. DAG's are located in phospholipid bilayers about two CH2 units deeper than the adjacent phospholipids. DAG's mix nonideally with phospholipids, giving rise to in-plane separations of DAG-rich and -poor domains, even in the fluid state. DAG molecules also increase the separation between phospholipid headgroups, and decrease the hydration of the bilayer surface. Also, because the transversal section of the DAG headgroup is small when compared to that of the acyl chains, DAG favours the (negative) curvature of the lipid monolayers, and DAG-phospholipid mixtures tend to convert into inverted nonlamellar hexagonal or cubic phases. 4. A number of membrane enzyme activities are modulated (activated) by DAG, most notably protein kinase C, phospholipases and other enzymes of lipid metabolism. Protein kinase C activation (and perhaps that of other enzymes as well) occurs as the combined result of a number of DAG-induced modifications of lipid bilayers that include: changes in lipid headgroup conformation, interspacing and hydration, changes in the bilayer propensity to form inverted nonlamellar phases, and lateral phase separations of DAG-rich and -poor domains. Among the DAG-activated enzymes, phospholipases C show the peculiarity of yielding the activator DAG as their reaction product, and this allows the self-induced transition from a low- to a high-activity status. 5. DAG's induce or enhance membrane fusion in a number of ways, mainly through partial dehydration of the bilayer surface, increase in lipid monolayer curvature and perhaps lateral phase separation. DAG-increased fusion rates have been demonstrated in several instances of cation-induced fusion of model membranes, as well as in Ca(2+)-induced fusion of chromaffin granules with plasma membrane vesicles. Also phospholipase C has been shown to induce vesicle aggregation and fusion through the catalytic generation of DAG in the bilayers. A rather general property of DAG is that it promotes vesicular or interparticle aggregation. 6. In the living cell, DAG is often generated through phospholipid degradation in response to an extracellular agonist binding a specific receptor in the cell surface. DAG is said to act as an intracellular second messenger. (ABSTRACT TRUNCATED)

X-ray diffraction evidence for fully interdigitated bilayers of 1-stearoyllysophosphatidylcholine

X-ray diffraction experiments have been performed on 1-stearoyllysophosphatidylcholine or C(18):C(0)PC as a function of hydration at temperatures below the order/disorder transition (Tm = 26.2 degrees C). At these temperatures, hydrated C(18):C(0)PC forms lamellae. The bilayer thickness, as determined by the saturation hydration method and electron-density profile, is 35-36 A, and the average area per C(18):C(0)PC molecule at the lipid/water interface is 45.5 A2. The packing geometry of C(18):C(0)PC in the lamella is proposed to adopt a fully interdigitated model in which the long C(18) acyl chain extends across the entire hydrocarbon width of the bilayer. Thus far, three different types of interdigitated bilayers are known for phosphatidylcholines. These various types of chain interdigitation are discussed in terms of the chain length difference between the sn-1 and sn-2 acyl chains.