Non-bilayer formation in the DPPE-DPPG vesicle system induced by deep rough mutant of Salmonella minnesota R595 lipopolysaccharide

The vesicle system consisting of 80 mol% dipalmitoylphosphatidylethanolamine (DPPE) and 20 mol% dipalmitoylphosphatidylglycerol (DPPG) undergoes to structural changes caused by various concentrations of Salmonella minnesota R595 lipopolysaccharide (LPS). The phenomenon was investigated by methods applying small- and wide-angle X-ray scattering (SAXS and WAXS), calorimetry (DSC) and freeze-fracture. In the low LPS concentration regime (investigated at 0.02 LPS/DPPE–DPPG molar ratio) a phase separation was observed. Two kind of domains are formed which are rich and poor in DPPE and in these domains cubic and lamellar structures are present, respectively. Increasing the LPS concentration up to 0.1 LPS/DPPE–DPPG molar ratio the phase separation is more expressed and the temperature domains of the phase transitions are more different. Increasing the temperature chain melting of the lamellar phase occurs first and destruction of the cubic phase is observed later. At high LPS concentration (equimolar ratio of LPS/DPPE–DPPG), where this amphiphilic molecule cannot be considered any more a guest molecule, the cubic structure dominates the phase behaviour of the LPS molecules.     

Interactions of cationic surfactantswith DPPC

The effects of different cationic surfactants (n-undecylammonum chloride, UDACl and dodecyldimethyl (dodecyloxymethyl) ammonium chloride, DDMDDACl) on fully hydrated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) vesicles have been studied. In the studied systems the molar ratio (x) of DPPC/surfactant ranged between x=0.0164–0.82 and from x=0.0352–1.76 for DPPC/DDMDDACl and DPPC/UDACl, respectively. For both systems, the enthalpy associated with the phase transition significantly decreases even at the lowest surfactant concentration. Also the main phase transition temperature is shifted towards lower temperatures. The structural parameters of the phases have been characterised by small angle X-ray scattering (SAXS). The SAXS results have proved that UDACl at x=0.0352 molar ratio significantly influences the DPPC lamellar structure, while its total disappearance was observed for x=0.176. The presence of DDMDDACl causes a total disappearance of the DPPC lamellar structure already at the lowest molar ratio (x=0.0352). Each surfactant in the system with DDPPC leads to a mixed micellar phase formation.     

Audio to microwave frequency dielectric study of the pretransition region in DPL-water systems

Abstract

The phospholipid–water mixtures are used as model systems to investigate the structure and function of biological membranes. The dielectric behaviour of DPPC–water and DPPE–water systems was explored at audio (≥ 2kHz) and microwave (10 GHz) frequencies versus temperature. Particular care was devoted to the pretransition below the main gel-liquid-crystalline phase transition. A possible interpretation of the pretransition mechanism is given in terms of capillary waves.     

髓鞘碱性蛋白对细胞膜脂质分子DPPC、DPPE单层膜影响机理研究

本文通过Langmuir单层膜的表面压力-平均分子面积(π-A)曲线的测定与分析,分别对髓鞘碱性蛋白(MBP)与细胞膜中不同头部基团脂质分子二棕榈酰基磷脂胆碱(DPPC)和二棕榈酰基磷脂酰乙醇胺(DPPE)在空气/液体界面上的相互作用过程进行了系统研究.实验结果表明:(1)当界面上脂质含量一定时,亚相中随着MBP浓度的增大,DPPC、DPPE单层膜的等温线向平均分子面积较大的方向移动;(2)在单层膜表面压力为10 mN/m时,一个MBP分子分别结合140±3个DPPC分子和100±3个DPPE分子,随着表面压力增大,当MBP分子分别与两种磷脂分子相互作用时,MBP插入到磷脂单层界面的个数逐渐减少;(3)随着蛋白质浓度的增加,脂分子形成的单层膜变得较为疏松,且MBP分子易于插入到分子头部较小的DPPE单层膜中;(4)蛋白质的存在使DPPC单层膜的表面压力逐渐减小,且蛋白质浓度越大表面压力降低越多,DPPC被MBP带入到亚相中越多;(5)对于DPPE单层膜,蛋白质通过与DPPE相互作用插入到界面膜中,引起表面压力增大,且蛋白质浓度越高,压力变化量越大.     

Molecular packing in sphingomyelin bilayers and sphingomyelin/phospholid mixtures

The molecular packing properties of sphingomyelin (SM) from egg yolk were studied. The influence of the spontaneous curvature of SM on the phase behaviour of SM/dodecane/water systems was investigated. A comparison was made to a previous study by Lindblom et al. (Liq. Cryst. 3 (1988) 783), of the phase behaviour of dipalmitoylphosphatidylcholine (DPPC)/dodecane/water systems, where a reversed hexagonal liquid crystalline was shown to form at high water contents (60-80%, w/w). In contrast, SM/dodecane/water systems mainly maintained a lamellar liquid crystalline phase at all compositions and temperatures >35 degrees C. This suggests that the spontaneous curvature of SM is larger than for DPPC. To further examine the packing properties of SM and DPPC, the phase behaviour of SM/dioleoylphosphatidylethanolamine (DOPE)/water and DPPC/DOPE/water systems were investigated. Aqueous dispersions of DOPE normally form a reversed hexagonal liquid crystalline phase, while an isotropic phase was formed at small additions (20 mol.%) of SM or DPPC and a lamellar liquid crystalline phase was maintained at higher fractions (>35 mol.%) of SM or DPPC.     

Cratylia mollis lectin at the air–aqueous solution interface: adsorption and lectin–lipid interactions

The interfacial behaviour of Cratylia mollis (Cra) at the air/water interface and its penetrant ability into spread phospholipid monolayers (Lipoid E80 and Epicuron 200) has been monitored by surface tension measurements. The first-order rate constants defining adsorption and rearrangement obtained from surface tension kinetics data reveal that Cra is a rather stable protein which exhibits characteristic protein adsorption patterns in which the breaking points separating diffusion–penetration and rearrangement profiles could have been easily distinguished. The penetration of Cra into Lipoid E80 and Epicuron 200 phospholipid monolayers has been inferred in terms of penetration pressure increments (ΔΠ) versus time relationships. The data clearly showed that penetrant ability of the lectin was, to a large extent, dependent on monolayer compressibilities. Thus, for Lipoid E80, which contained a rather high percentage of phosphatidylethanolamine (DPPE) in the mixture with phosphatidylcholine (DPPC), penetration of Cra at the high monolayer compression (20 mN m⁻¹) was lower than that observed for Epicuron 200, which did not contain DPPE. Indeed, in the middle of the Π-A isotherm, DPPE was markedly less compressible than DPPC. However, at the low monolayer surface coverage (3 mN m⁻¹), the rates of Cra penetration into both Lipoid E80 and Epicuron 200, although much higher for the latter at the beginning of adsorption, yielded similar limiting values of ΔΠ. This has been attributed to the occurrence of a hydrophobic interaction between the lectin and hydrophobic phospholipid chains that have the same length for both Lipoid E80 and Epicuron 200.     

Cerebroside Langmuir monolayers originated from the echinoderms I. Binary systems of cerebrosides and phospholipids

The surface pressure (pi)-area (A), the surface potential (DeltaV)-A and the dipole moment (mu( perpendicular))-A isotherms were obtained for two-component monolayers of two different cerebrosides (LMC-1 and LMC-2) with phospholipids of dipalmitoylphosphatidylcholine (DPPC) and with dipalmitoylphosphatidylethanolamine (DPPE) on a subphase of 0.5 M sodium chloride solution as a function of phospholipid compositions by employing the Langmuir method, the ionizing electrode method, and the fluorescence microscopy. Surface potentials (DeltaV) of pure components were analyzed using the three-layer model proposed by Demchak and Fort. The contributions of the hydrophilic saccharide group and the head group to the vertical component of the dipole moment (mu( perpendicular)) were estimated. The miscibility of cerebroside and phospholipid in the two-component monolayers was examined by plotting the variation of the molecular area and the surface potential as a function of the phospholipid molar fraction (X(phospholipid)), using the additivity rule. From the A-X(phospholipid) and DeltaV(m)-X(phospholipid) plots, partial molecular surface area (PMA) and apparent partial molecular surface potential (APSP) were determined at the discrete surface pressure. The PMA and APSP with the mole fraction were extensively discussed for the miscible system. Judging from the two-dimensional phase diagrams, these can be classified into two types. The first is a positive azeotropic type; the combinations of cerebrosides with DPPC are miscible with each other. The second is a completely immiscible type: the combination of cerebrosides with DPPE. Furthermore, a regular surface mixture, for which the Joos equation was used for the analysis of the collapse pressure of two-component monolayers, allowed calculation of the interaction parameter (xi) and the interaction energy (-Delta epsilon) between the cerebrosides and DPPC component. The miscibility of cerebroside and phospholipid components in the monolayer state was also supported by fluorescence microscopy.     

Segregation and phase transition in mixed lipid films

Energy dispersion X-ray diffraction (EDXD) was applied to investigate the structure of partly dehydrated mixed films formed by the phospholipid dimyristoyl phosphatidylcoline (DMPC) and any of the three diastereomers of the dicationic gemini surfactant (2S,3S)-2,3-dimethoxy-1,4-bis(N-hexadecyl-N,N-dimethylammonium) butane dibromide. As the surfactant to lipid molar ratio (R(S/L)) increases, the gemini monotonically solubilizes the lipid bilayer promoting the formation of a cubic phase of space group Pmn segregating from the residual lamellar phase of the lipid. Finally, at R(S/)(L) = 1, the phase transition is complete. The mixed film at the highest surfactant to lipid molar ratio (R(S/L) = 2.3) was hydrated by a vapor saturated atmosphere. At full hydration, a cubic to lamellar phase transition occurs. Coarse grain dynamic investigations, carried out as a function of both the surfactant to lipid molar ratio and the number of water molecules for amphiphile unit, allowed us to elucidate the structure of the emerging cubic phase and the hydration-induced structural pathway of the cubic to lamellar phase transition observed by EDXD.     

Phase behavior of mixed solution of a glycerin-modified cationic surfactant and an anionic surfactant

The phase behavior of mixed solution of newly synthesized monoglycerylcetyldimethylammonium chloride (MGCA) and sodium octyl sulfate (SOS) in water was investigated by cryo-transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), differential scanning calorimetry (DSC), and fluorescence polarizing for evaluation of the microviscosity of bilayers. No precipitate was observed in the mixed solution except at concentrations below 20 mM over all mixing ratios, and stable vesicles were formed in a considerably wide range of mixing ratio, even at the equimolar ratio. Vesicles formed in aqueous 1/1 MGCA/SOS mixture were found to exhibit no phase transition, and fluorescence polarizing measurements showed that the vesicle bilayers have a high fluidity. This flexibility allows the bilayers to have a spontaneous curvature, and thus vesicles rather than flat lamellae can be stabilized in the mixture even at the equimolar ratio. In addition, because the glycerin group of MGCA interacts strongly with water, the hydration repulsion contributes to prevent the bilayers consisting of MGCA and SOS from adhering and flocculating even though the charge neutralization between MGCA and SOS occurs at the equimolar ratio.     

Polymorphism of natural fatty acid liquid crystalline phases

We study the phase behavior in water of a mixture of natural long chain fatty acids (FAM) in association with ethylenediamine (EDA) and report a rich polymorphism depending on the composition. At a fixed EDA/FAM molar ratio, we observe upon dilution a succession of organized phases going from a lamellar phase to a hexagonal phase and, finally, to cylindrical micelles. The phase structure is established using polarizing microscopy, SAXS, and SANS. Interestingly, in the lamellar phase domain, we observe the presence of defects upon dilution, which SAXS shows to correspond to intrabilayer correlations. NMR and FF-TEM techniques suggest that these defects are related to an increase in the spontaneous curvature of the molecule monolayers in the lamellae. ATR-FTIR spectroscopy was also used to investigate the degree of ionization within these assemblies. The successive morphological transitions are discussed with regards to possible molecular mechanisms, in which the interaction between the acid surfactant and the amine counterion plays the leading role.     

Effects of lipid chain unsaturation and headgroup type on molecular interactions between paclitaxel and phospholipid within model biomembrane

Molecular interactions between paclitaxel, an anticancer drug, and phospholipids of various chain unsaturations and headgroup types were investigated in the present study by Langmuir film balance and differential scanning calorimetry. Both the lipid monolayer at the air-water interface and the lipid bilayer vesicles (liposomes) were employed as model cell membranes. It was found that, regardless of the difference in molecular structure of the lipid chains and headgroup, the drug can form nonideal, miscible systems with the lipids at the air-water interface over a wide range of paclitaxel mole fractions. The interaction between paclitaxel and phospholipid within the monolayer was dependent on the molecular area of the lipids at the interface and can be explained by intermolecular forces or geometric accommodation. Paclitaxel is more likely to form thermodynamically stable systems with 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) and 1,2-dielaidoyl-sn-glycero-3-phosphocholine (DEPC) than with 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC). Investigation of the drug penetration into the lipid monolayer showed that DPPC and DEPC have higher incorporation abilities for the drug than DPPE and DSPC. A similar trend was also evidenced by DSC investigation with liposomes. While little change of DSC profiles was observed for the DPPE/paclitaxel and DSPC/paclitaxel liposomes, paclitaxel caused noticeable changes in the thermographs of DPPC and DEPC liposomes. Paclitaxel was found to cause broadening of the main phase transition without significant change in the peak melting temperature of the DPPC bilayers, which demonstrates that paclitaxel was localized in the outer hydrophobic cooperative zone of the bilayer, i.e., in the region of the C1-C8 carbon atoms of the acyl chain or binding at the polar headgroup site of the lipids. However, it may penetrate into the deeper hydrophobic zone of the DEPC bilayers. These findings provide useful information for liposomal formulation of anticancer drugs as well as for understanding drug-cell membrane interactions.     

Phase structures of a hydrated anionic phospholipid composition containing cationic dendrimers and pegylated lipids

The effect of 4th generation poly(amidoamine) dendrimer (4G PAMAM) present in an anionic phospholipid composition, consisting of hydrogenated soyphosphatidylcholine (HSPC), cholesterol (CH), dicetyl phosphate (DCP), and poly(ethylene glycol) (Mw approximately 2000) derivatized phosphatidylethanolamine (PEG2000-PE), on the hydration and liquid crystalline structure formation was investigated. The optical and polarized light microscopies of the liposomal dispersion obtained from the hydrated lipid composition show two types of birefringent structures (mesophases): plastic, wormlike microstructures and conventional, over-elongated lamellae. Differential scanning calorimetry (DSC) shows an increase in the liquid crystalline phase transition (Tg) of the lipid composition from 60 to 94 degrees C with increasing 4G PAMAM concentrations from 0 to 0.011 mM, respectively. The Tg values of the two microstructures were 68 and 84 degrees C, respectively, indicating that the plastic microstructures were 4G PAMAM/DCP-complexes-rich (alpha mesophases) and the conventional and elongated lamellae were dendrimer-doped HSPC/CH-rich microstructures (beta mesophases). Optical microscopy shows that the alpha mesophases convert into various other types of vesicular structures such as giant unilamellar vesicles and biliquid foams, upon heating above the phase transition temperature of the lipid composition (approximately 60-65 degrees C). The microstructure transformation is a result of an osmotic influx of water and the detergent action of PEG2000-PE present in the lipid composition. The transmission electron microscopy (TEM) images of the liposomal dispersion show particles embedding circular transparent domains that exactly correlate to the theoretical 4G PAMAM/DCP complex sizes, thus, providing evidence of 4G PAMAM interspersed within the two mesophases. Small-angle X-ray scattering (SAXS) measurements indicate that the alpha mesophases are a dendrimer-interlinked, symmetrically undulated lamellar phase and the beta mesophases are dendrimer-doped, occasionally kinked lamellae. An increase in dendrimer concentration in the lipid composition was found to decrease interlamellar spacing. On the basis of optical microscopy, DSC, TEM, and SAXS data, a model of dendrimer-doped mesophase structure and lamellae fusion is proposed. This investigation provides new self-assembled materials for drug/gene delivery and supplements the understanding of mechanisms involved in various biological processes such as membrane fusion, transmembrane permeation, and endocytosis.     

Morphological Changes of Linear,Branched Polyethylenes and their Blends during Crystallization and Subsequent Melting by Synchrotron SAXS and DSC

Summary: The crystalline structure and phase morphology of linear, branched polyethylenes and their blends during crystallization and subsequent melting were investigated, using a combination of differential scanning calorimetry (DSC), and synchrotron small angle X-ray scattering (SAXS). A linear polyethylene (PE1) with weight-average molecular weight (M_w) of 114 000 g/mol, and two branched polyethylene copolymers, containing 4.8 mol% (PE4) and 15.3 mol% (PE10) hexane, with molecular weights of 93 000 g/mol and 46 000 g/mol were used as pure samples. Two blends, PE1-4 and PE1-10, each with a weight ratio of 50/50, were prepared by solution blending. Our results indicate that in PE4 a phase separation within the branched component itself occurred, forming a broad distribution of lamellar thicknesses during the crystallization process. PE10 on the other hand did hardly crystallize because of the high degree of branching. Co-crystallization of both components took place in blend PE1-4 and liquid-liquid phase separation occurred in the melt of PE1-10. Morphological parameters were determined by using Bragg's law and the correlation function, respectively. The detected semicrystalline morphology can be well described by the lamellar insertion mode where thin lamellae develop between thicker primary lamellae. During subsequent heating, lamellae melted in the reversed sequence of their formation. The evolution of the structural parameters as a function of temperature revealed that surface melting began at first, and then the complete melting of stacks occurred until the final melting temperature was reached.     

Role of dipolar interaction in the mesoscopic domains of phospholipid monolayers: dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylethanolamine

The role of dipolar interactions in determining the lipid domain shapes at the air-water interface with a change in the chemical structure of the head groups of lipids is theoretically studied. The phospholipids considered are dipalmitoylphosphatidylcholine (D,L-DPPC) and dipalmitoylphosphatidylethanolamine (DPPE). Despite closely similar chemical structures, the domains of the two lipids are strikingly different. The DPPC domains exhibit elongated arms, while the DPPE domains are nearly round-shaped. To compare the dipolar repulsions in the domains of the two phospholipids, different energy-minimized conformers of DPPC and DPPE are studied using the semiempirical quantum chemical method (PM3). It is found that the dipole moment of DPPC is significantly larger than that of DPPE. The in-plane and out-of-plane components of the dipole moments are calculated using grazing incidence X-ray diffraction data at different surface pressure values, as used in the experiment. The result indicates that the magnitude of the dipolar interaction is significantly larger in DPPC than that in DPPE over the surface pressure range considered. The enhanced dipolar repulsion corroborates well with the difference in the domain shapes in the two phospholipid monolayers. The larger dipolar repulsion in DPPC leads to development of elongated domain arms, while relatively less dipolar repulsion allows a closed shape of the condensed-phase DPPE domains.     

Equilibrium Crystallization Temperature of Syndiotactic Polystyrene <Emphasis Type="Italic">γ</Emphasis> Form

The crystallization behavior of syndiotactic polystyrene (sPS) γ form undergoing annealing at various temperatures was investigated using the thermodynamic phase diagram based on Strobl's crystallization theory.On the basis of the differential scanning calorimetric results,it was observed that γ form melt-recrystallization occurred at a higher temperature with the increasing lamellar thickness,which resulted from the pre-annealing at the elevating temperature after acetone induced crystallization.Further temperature dependent small-angle X-ray scattering (SAXS) measurement revealed the evolution of the γ form lamellae upon heating until phase transition,involving three different regimes:lamellae stable region (25-90 ℃),melt-recrystallization region (90-185 ℃) and pre-phase transition region (185-195 ℃).As a result,recrystallization line,equilibrium recrystallization line and melting line were developed for the sPS γform crystallization process.Since the melt of γform involved a γto-α/β form phase transition,the melting line was also denoted as the phase transition line in this special case.Therefore,the equilibrium crystallization temperature and melting (phase transition)temperatures were determined at around 390 and 220 ℃ on the basis of the thermodynamic phase diagram of the sPS γform.     

Salt‐induced microphase separation of amorphous dendritic poly(ethylene oxide)‐block‐linear polystyrene copolymers

We prepared two block copolymers 1 and 2 consisting of a third‐generation dendron with poly(ethylene oxide) (PEO) peripheries and a linear polystyrene (PS) coil. The PS molecular weights were 2000 g/mol and 8000 g/mol for 1 and 2 , respectively. The differential scanning calorimetry (DSC) data indicated that neither of the block copolymers showed glass transition, implying that there was no microphase separation between the PEO and PS blocks. However, upon doping the block copolymers with lithium triflate (lithium concentration per ethylene oxide unit = 0.2), two distinct glass transitions were seen, corresponding to the salt‐doped PEO and PS blocks, respectively. The morphological analysis using small angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM) demonstrated that a hexagonal columnar morphology was induced in salt‐doped sample 1‐Li⁺ , whereas the other sample ( 2‐Li⁺ ) with a longer PS coil revealed a lamellar structure. In particular, in the SAXS data of 2‐Li⁺ , an abrupt reduction in the lamellar thickness was observed near the PS glass transition temperature (T_g), in contrast to the SAXS data for 1‐Li⁺ . This reduction implies that there is a lateral expansion of the molecular section in the lamellar structure, which can be interpreted by the conformational energy stabilization of the long PS coil above T_g. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2372–2376, 2010     

Incorporation of substituted acrylamides to the lamellar mesophase of Aerosol OT

The structure and stability of the lamellar liquid crystal formed by the surfactant sodium bis-2ethylhexyl sulfosuccinate (AOT) in water is perturbed by small amounts of the substituted acrylamides N-isopropyl, N,N-diethyl, N-acryloylmorpholine, and N,N-dimethyl methacrylamide, as revealed by small angle X-ray scattering (SAXS), deuterium NMR, and microscopy. These molecules are water soluble and stay mostly in the water layers between lamellae, but a small fraction of them (5-19%) are incorporated into the AOT bilayers, thereby producing dramatic changes. Both, the degree of anisotropy in the water molecules hydrating AOT (quadrupolar splitting in (2)H NMR) and the long period spacing between lamellae (SAXS), decrease with addition of this molecules at low concentrations, which is attributed to the lower average headgroup density at the AOT/water interface when the acrylamide is incorporated. The strength of these perturbations depends on the acrylamide, and goes in parallel with the hydrophobic character of the alkyl side groups in its molecule, which suggests that the acrylamides incorporated to the bilayer enter into contact with the lipophilic tails of the AOT molecule. An interaction with the hydrated heads of AOT is also suggested in the particular case of N-isopropylacrylamide. On increasing the molecule concentration an incipient melting of the lamellar phase towards an isotropic solution takes place, first at the microscopic level, then macroscopic. Near this phase transition, the ordered domains lose the random orientation prevailing at lower acrylamide concentrations, and adopt a preferred orientation, perpendicular to the magnetic field.     

Interaction of propyl paraben with dipalmitoyl phosphatidylcholine bilayer: a differential scanning calorimetry and nuclear magnetic resonance study

The influence of the preservative, propyl paraben (PPB) on the biophysical properties of dipalmitoyl phosphatidyl choline (DPPC) vesicles, both in multilamellar vesicle (MLV) and unilamellar vesicle (ULV) forms, has been studied using DSC and (¹H and ³¹P) NMR. The mechanism by which PPB interacts with DPPC bilayers was found to be independent of the morphological organization of the lipid bilayer. Incorporation of PPB in DPPC vesicles causes a significant depression in the transition temperature and enthalpy of both the pre-transition (PT) and the gel to liquid crystalline transition. The presence of the PPB also reduces the co-operativity of these transitions. However, at high PPB concentration the PT disappears. DSC and NMR findings indicate that: (i) PPB is bound strongly to the lipid bilayer leading to increased headgroup fluidity due to reduced headgroup–headgroup interaction and (ii) the PPB molecules are intercalated between the DPPC polar headgroups with its alkyl chain penetrate into the co-operative region. MLV incorporated with high PPB concentration shows additional transitions whose intensity increases with increasing PPB concentration. This phase segregation observed could probably be due to co-existence of PPB-rich and PPB-poor phospholipid domains within the bilayers. The effect of inclusion of cholesterol in the PPB-free and PPB-doped DPPC dispersion was also studied. Equilibration studies suggest that PPB molecules are very strongly bound and remain intercalated between the polar headgroup for prolonged time.     

Crystal structure and thermal behavior of cold-crystallized poly(trimethylene terephthalate)

The structure and thermal behavior of cold-crystallized poly(trimethylene terephthalate) (PTT) are revealed in detail by DSC, AFM, TEM, and WAXD as well as in situ FTIR and SAXS techniques. There is no effect of crystallization temperature and initial state on the crystal modification, yet the morphology is strongly affected by these two factors. First, the small rod-like lamellae for PTT are obtained during the cold crystallization instead of the spherulites formed in the melt crystallization. Second, the edge-on lamellar orientation in thin films is identified during the cold crystallization. The thickness and the lateral width of rod-like lamellae get larger and larger with increasing crystallization temperature. Thin lamellar crystals assemble randomly when the cold-crystallization temperature is lower, while lamellar stacks composed of thicker lamellae are observed when the PTT was annealed at elevated temperature. Moreover, for the cold-crystallized PTT, the final melting temperature does not vary with the crystallization temperature. This phenomenon is explained by the structural improvement during the heating process. For the cold-crystallized PTT sample at lower temperature, three transitions occur when it is heated again: the relaxation of the rigid amorphous phase, the reorganization of molecules in the intermediate phase, and then the melt–recrystallization behavior. Those transitions finally lead to thicker lamellae besides a higher crystallinity before the final fusion. Therefore, the final melting peak of these lamellae is at the same temperature.     

Salicylic acid-induced effects in the mixed-lipid (dipalmitoyl phosphatidylcholine-dipalmitoyl phosphatidylethanolamine) model membrane

The effect of the keratolytic drug salicylic acid (SA) on the thermotropic properties and fluidity of the mixed lipid membrane dipalmitoyl phosphatidylcholine (DPPC)-dipalmitoyl phosphatidylethanolamine (DPPE) had been studied using DSC, (1H and 31P) NMR, SAXS, and dynamic light scattering. The membrane was in multilamellar vesicular (MLV) and unilamellar vesicular (ULV) form with SA/(DPPC+DPPE) molar ratios, R(m), in the range from 0 to 0.5. It was found that the mechanism of interaction of SA with the lipid mixture exhibited similar patterns in both ULV and MLV. Both the NMR and DSC studies indicated that the drug molecules were probably localized in the lipid-water interfacial region neighboring the lipid headgroups or the glycerol moiety. The presence of the drug increased the fluidity of the membrane and the acyl chain order. However, studies on MLV showed that the presence of the drug in high concentration (R(m)0.2), caused destabilization of the DPPC-DPPE mixture, as indicated by the appearance of two endothermic transitions. DSC studies indicated that prolonged equilibration of the membrane led to reduced interaction between the lipid headgroups and the SA molecules. This reduced interaction could be due to the sequestering of the drug molecules into the lipid-water interfacial region, out of proximity to the polar headgroup or glycerol moiety. Effect of inclusion of cholesterol in the membrane systems was also studied.