Phospholipid differential scanning calorimetry

Hydration of phospholipid head groups is essential properties not only for stabilizing bilayer structures in an aqueous environment, but also for fusion or endocytosis of biological membranes including protein transfers [33-35]. Hydration or swelling behavior has only been studied by indirect methods such as X-ray diffraction [36], differential scanning calorimetry (DSC) [37], and H-NMR [38,39]. 

Besides differential scanning calorimetry, electron microscopy can also serve for characterizing the mixing behavior of multicomponent vesicular systems. The ripple structure of phospholipids with saturated alkyl chains (also referred to as smectic Bca phase, Fig. 35) is taken to indicate patch formation (immiscibility) in mixed phos-close enough (1-2 nm) lipid molecules are able to diffuse from one membrane to the between the pre- and main-transition of the corresponding phospholipid, electron... 

PHOSPHOLIPID SYNTHESIS. Phospholipids were synthesized (H.Schuster, S.S. Hall, and R.Mendelsohn, in preparation) according to the procedures of Tulloch (26), modified with more modern and efficient coupling steps, and scaled up to produce 2-3 grams of specifically deuterated material. Derivatives were fully characterized with NMR, MS, FT-IR, and Differential Scanning Calorimetry (DSC). Purity is estimated from NMR data at > 98X. The extent of deuteration, as estimated from the residual intensity of the CHD rocking modes at... 

Ortiz, A. and Gomez-Femandez, J. C. A Differential scanning calorimetry study of the interaction of free fatty acids with phospholipid membranes. Chemistry and Physics of Lipids 45 75-9, 1987. 

The DHA-containing phospholipids exhibit very low phase transition temperatures. For example, 18 0,22 6 PC has its at about-9°C (Stillwell etal., 2000), whereas 22 6,22 6 PC s transition is at -68.4°C (Kariel et al., 1991) and the transition enthalpy H for homo acid is extremely low ( H = 0.5 kcal/mol) (Kariel et al., 1991). The low T, s are the result of packing restrictions resulting from steric effects caused by DHA s multiple rigid double bonds. The restrictions result in reductions in intermolecular and intramolecular van der Waal s interactions. The broad, low H transitions are consistent with the notion that interaction between saturated sn-1 chains stabilize the gel state in hetero acids (Kariel et al., 1991). Furthermore, differential scanning calorimetry (DSC) isothenns are often multi-component, suggesting microclustering and domain formation (Niebylski Salem, 1994). 

The influence of plant sterols on the phase properties of phospholipid bilayers has been studied by differential scanning calorimetry and X-ray diffraction [206]. It is interesting that the phase transition of dipalmitoylglycerophosphocholine was eliminated by plant sterols at a concentration of about 33 mole%, as found for cholesterol in animal cell membranes. However, less effective modulation of lipid bilayer permeability by plant sterols as compared with cholesterol has been reported. The molecular evolution of biomembranes has received some consideration [207-209]. In his speculation on the evolution of sterols, Bloch [207] has suggested that in the prebiotic atmosphere chemical evolution of the sterol pathway if it did indeed occur, must have stopped at the stage of squalene because of lack of molecular oxygen, an obligatory electron acceptor in the biosynthetic pathway of sterols . Thus, cholesterol is absent from anaerobic bacteria (procaryotes). 

Equally well, one can demonstrate this effect by differential scanning calorimetry (Fig. 7). The phospholipid shows an endothermic transition at a certain temperature. The enthalpy of transition Is lowered by adding a hopanold to the phospholipid. Furthermore, one can observe a broadening of the peak, meaning a lower coopera-tlvlty of the acyl chains at the phase transition [47]. 

The bouquet (91), incorporated into a phospholipid membrane of liposomes, increases the permeability of the membrane to Na" and Li. The ion transfer proceeds via a cation-cation antiport mechanism which has been established by Na and Li NMR spectroscopy <92AG(E)1637>. The incorporation of the bouquet molecule into several vesicular systems has been monitored by numerous techniques (UV, NMR, and CD spectroscopies, differential scanning calorimetry). It was concluded that different modes of incorporation take place and that several orientations of the bouquet coexist in the membranes <93JCS(P2)ioii>. 

Differential scanning calorimetry of the phospholipid mixmres was accomplished using a Perldn-Eliner DSC 7 system. 4 mg of the phospholipid... 

HIGH-SENSITMTY DIFFERENTIAL SCANNING CALORIMETRY OF POLYMER-PHOSPHOLIPID MIXTURES... 

Differential scanning calorimetry was performed to measure the chain melting temperature for non-cross-linked phospholipids (NCP) 1-3. Non-cross-linked vesicle dispersions (NCVD) and cross-linked vesicle dispersions (CVD) of 1 and 2 were also measured along with the chain melting transition of CVD-1 with a hydrophobic dye entrapped. Parent phospholipids DPPE and DLPE were used as references for NCP 1 and 2. Parent phospholipid EGGPE was used as reference for phospholipid 3. NCPs were weighed directly into the DSC pans. Vesicle dispersions were used for the non-cross-linked vesicle samples and freeze-dried powder was used for the cross-linked vesicle dispersion samples. 

The interesting property of the MPC copolymer is its affinity for phospholipids (5,72-74). The amount of a phospholipid, dipalmitoylphosphatidylcholine (DPPC), adsorbed on MPC copolymers was larger than that on polystyrene, poly(BMA) and poly(HEMA) and increased with increasing MPC moiety when the MPC copolymers were contacted with a liposomal solution of DPPC (5). This tendency was the same as that of the adsorption of phospholipid from human plasma which is indicated in Fig. 3. Thus, the affinity of poly(MPC-co-BMA) for the phospholipids could be observed even in the plasma. The DPPC molecules adsorbed on the poly(MPC-co-BMA) surface assumed an organized structure like that for a bilayer membrane, which was confirmed by differential scanning calorimetry(DSC) and X-ray photoelectron spectroscopy(XPS) when the poly(MPC-c -BMA) membrane was immersed in the solution containing DPPC (72,74) It is therefore concluded that the MPC copolymers stabilized the adsorption layer of phospholipids on the surface. Stabilization of the liposomal structure in water by a water-soluble MPC copolymer was also found (75). 

Differential scanning calorimetry is a basic method to study the phospholipid bilayer phase transitions since these are accompanied by a positive enthalpy of fusion. The excess heat capacity,... 

Yet, physicochemical studies using differential scanning calorimetry, infrared spectroscopy and small-angle X-ray diffraction have shown that B[a]P incorporates into phospholipid bilayers and localizes in the most apolar region of the phospholipid matrix. This phenomenon may account for the observation of an expanded and swollen membrane [11]. We have therefore, proposed that distortion of the physiochemical properties of the adipocyte plasma membrane by B[a]P decreases the signalling capacity of G-coupled receptors intimately linked to the phospholipid bilayer, via their seven transmembrane domains. 

The amount of phospholipids adsorbed from plasma on the MPC polymers increased with increasing amounts of MPC. In the case of hydrophobic poly( -butyl methacrylate (BMA)) and hydrophilic poly(2-hydroxyethyl methacrylate (HEMA)), the amount of adsorbed phospholipids was the same level (about 0.5 pg/cm ). This means that the MPC moiety in the poly(MPC-co-BMA) played an important role to increase adsorption. To clarify the state of phospholipids adsorbed on the polymer surface, the phospholipid liposomal suspension was put in contact with these polymers. Phospholipids were adsorbed on every polymer surface, however, the adsorption state of the phospholipids was different on each polymer. On the surface of the MPC polymer, the adsorbed phospholipids maintained a liposomal structure, like a biomembrane this was confirmed by a differential scanning calorimetry. X-ray photoelectron spectroscopy (XPS), quarts crystal microbalance, and atomic force microscope. The phospholipids adsorbed on the poly(BMA) and poly(HEMA) did have any organized form. It was concluded that the MPC polymers stabilized the adsorption layer of phospholipids on the surface. Small amounts of plasma proteins were adsorbed on the MPC polymer surface pretreated with phospholipid... 

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