Phospholipid Profiles of Neoplastic Human Breast Tissues

Abstract

Membrane phospholipids from malignant, benign and non-involved human breast tissues were extracted by chloroform-methanol (2:l) and analyzed by ³¹P MR spectroscopy at 202.4 MHz. Fourteen phospholipids were identified as constituents of the profiles obtained among the 52 specimens of the three groups: PC, PC plas LPC, LPC plas, PE, PE plas, LPE, PS, SPH, PI, CL, PG, PA and one uncharacterized resonance at 0.13 6. The relative P-lipid profile mole percentages of phosphorus and indices representing sums and ratios of individual or grouped P-lipids were computed and analyzed by one-way analysis of variance and were compared as simple and complex statistical contrasts. The analysis permitted differentiation among the three groups with the most poignant simple contrast being the relative absence of PA in normal tissues, followed by the significant mean mole percentage differences in PC plas between noninvolved (3.09 ± 0.41) and malignant (4.49 ± 0.23) tissues and between these same tissues in the value, of the PC plas/PC index with mean values of 0.07 ± 0.01 and 0.10 ± 0.006, respectively. Significant complex contrasts were seen between the combined neoplastic tissues and noninvolved tissue in PE plas, LPC plas, PC plas and the (PA/Total Phosphatides-PA) index. Differences were also seen between malignant and non-malignant tissues in LPC, the LPC/PC, LPE/PE and PC plas/PC indices. Differentiation among histologically classified human breast tissues is possible with phospholipid profile analysis and metabolic insight.     

Phospholipids Analysis by 31P NMR

Abstract

Cell membrane phospholipids can be identified and quantitated using ³¹P NMR spectroscopy in conjunction with an analytical reagent composed of chloroform-benzene(d6)/methanol-CsEDTA 2:l ml/ml. 3 ml of this reagent dissolves between 0.01–100 mg crude tissue lipids obtained by the Folch procedure. When the source phospholipids are strongly contaminated with cations, it is necessary to modify the extraction method, backwashing with K-EDTA, 0.6 M, pH 6, instead of KC1. Also if source tissues must be stored for long periods of time, acetone desication is recommended. Using a 500 MHz ³¹PNMR spectrophotometer (magnetic field ?11.75 T), the extracted phospholipids yield narrow Lorenzian signals (1.8–3.2 Hz at half-height), with these widths at half-height corresponding to their 1/πT₂ values. Chemical shifts (δ) at 24 °C, following the IUPAC shift convention and relative to 85% phosphoric acid, were determined as follows:CAEP,21.09;LPG,l,O9;LPA,0.83;LPE plas,0.53;PG,0.50;LPE,0.43; PA,0.25;CL,0.18;LPI,0.10;PE plas,0.07;PE,0.03;PS,?0.O5;SPH,?0.O9; DiMePE,?b.18;LPC plas,?0.20;LPC,?0.28;PI,?0.37; PAF, ?0.70;PC plas,?0.77; PC, ?0.84. This reagent permits assays of high precision and accuracy that use little spectrometer time and that are suitable for automated procedures.     

Development of a polar lipid profiling method by supercritical fluid chromatography/mass spectrometry

We established a high-throughput and high-resolution analytical method based on supercritical fluid chromatography (SFC) coupled with mass spectrometry (MS) for the simultaneous profiling of diverse polar lipids in a mixture. Trimethylsilyl (TMS) derivatization was used for the analysis of ten polar lipids: phosphatidylglycerol (PG), phosphatidic acid (PA), phosphatidylinositol (PI), lysophosphatidylcholine (LPC), lysophosphatidylethanolamine (LPE), lysophosphatidylglycerol (LPG), lysophosphatidic acid (LPA), lysophosphatidylinositol (LPI), sphingomyeline (SM), and sphingosine-1-phosphate (S1P). Using the developed method, the peak tailings of PA, PI, LPA, LPI, and S1P improved, and the limit of detection of PG, PI, LPA, LPI, and S1P was enhanced by 12-, 40-, 510-, 39-, and 1490-fold, respectively. Next, in the analysis of sheep plasma, 20 minor species of PI, LPC, LPE, and SM, and 7 molecular species of LPA, LPI, and S1P were additionally analyzed. The relative ratio of the molecular species in each polar lipid was also found by quantification. Finally, the simultaneous and detail profiling of ten polar lipids was successfully performed by SFC/MS applying TMS derivatization. This developed method is particularly applicable to metabolomics, especially for targeting polar lipids.     

Measurement of phospholipids by hydrophilic interaction liquid chromatography coupled to tandem mass spectrometry: the determination of choline containing compounds in foods

A hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC LC-MS/MS) method using multiple scan modes was developed to separate and quantify 11 compounds and lipid classes including acetylcholine (AcCho), betaine (Bet), choline (Cho), glycerophosphocholine (GPC), lysophosphatidylcholine (LPC), lysophosphatidylethanolamine (LPE), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphocholine (PCho) and sphingomyelin (SM). This includes all of the major choline-containing compounds found in foods. The method offers advantages over other LC methods since HILIC chromatography is readily compatible with electrospray ionization and results in higher sensitivity and improved peak shapes. The LC-MS/MS method allows quantification of all choline-containing compounds in a single run. Tests of method suitability indicated linear ranges of approximately 0.25-25 μg/ml for PI and PE, 0.5-50 μg/ml for PC, 0.05-5 μg/ml for SM and LPC, 0.5-25 μg/ml for LPE, 0.02-5 μg/ml for Cho, and 0.08-8 μg/ml for Bet, respectively. Accuracies of 83-105% with precisions of 1.6-13.2% RSD were achieved for standards over a wide range of concentrations, demonstrating that this method will be suitable for food analysis. 8 polar lipid classes were found in a lipid extract of egg yolk and different species of the same class were differentiated based on their molecular weights and fragment ion information. PC and PE were found to be the most abundant lipid classes consisting of 71% and 18% of the total phospholipids in egg yolk.     

基于超高效液相色谱-四极杆-静电场轨道离子阱串联质谱的冷链贮藏过程中滩羊肉的脂质组学研究

该文建立了超高效液相色谱一四极杆一静电场轨道离子阱串联质谱(UHPLC-Q-Orbitrap MS/MS)结合脂质组学分析滩羊肉在冷链贮藏过程中脂质变化规律和脂质分子碎裂机理的方法.样品经异丙醇提取后,采用质谱全扫描模式和二级扫描模式对目标物质进行定性.共鉴定出48个变化显著性脂质,包括8个脂肪酰基肉碱、23个磷脂酰胆...     

Simultaneous Quantitative Analysis for Phospholipids in Human HDL and LDL Using Two Internal Standards by Liquid Chromatography/Mass Spectrometry

Abstract

A liquid chromatography/mass spectrometry method using two internal standards was developed for the simultaneous quantitative determination of phosphatidylglycerol (PG), phosphatidylinositol (PI), phosphatidylethanolamine (PE), phosphatidylcholine (PC), sphingomyelin (SM), and lysophosphatidylcholine (LPC) in human high‐density lipoprotein (HDL) and low‐density lipoprotein (LDL). We evaluated this method by examining precision, accuracy, and recovery of phospholipid concentrations in several matrixes. We obtained the time course of phospholipid content in human HDL and LDL treated with sPLA₂‐X and quantitatively observed the decrease of PC, PI, PE, and the increase of LPC. This method should be useful for examination of simultaneous change of endogenous phospholipids in various enzymatic assays.     

Phenylmethanesulfonyl fluoride pretreatment stabilizes plasma lipidome in lipidomic and metabolomic analysis

Though it is standard practice to test the stability of analytes in the matrix for routine bioanalytical method, stability evaluation is always impractical and skipped in untargeted lipidomic and metabolomic analysis because analytes in these studies are enormous, diverse and sometimes unknown. Lipidome represents a major class of plasma metabolome and shows great potential to be diagnostic and prognostic biomarkers. However, lipidome also faces stability problems because plasma contains kinds of lipid degradation enzyme. Here, using liquid chromatography time of flight mass spectrometry based lipidomic methodology, plasma levels of various lipids including triglyceride (TG), diglyceride (DG), free fatty acid (FFA), phosphatidylethanolamine (PE) phosphatidylcholine (PC), lyso-phosphatidylcholine (LPC), lyso-phosphatidylethanolamine (LPE), and sphingomyelin (SM) were dynamically determined within 4 h at ambient temperature. In mouse and rat plasma, the levels of most TG, DG, PC and PE species significantly decreased with respect to time, whereas those of LPC, LPE and FFA significantly increased with respect to time. However, such changes did not occur in human plasma, thus indicating hepatic lipase and esterase might involve in the species-specified degradation of lipid classes in plasma. Phenylmethanesulfonyl fluoride (PMSF) pretreatment prevented such lipidome instability in mouse plasma. The results suggested the instability of plasma lipidome should be highly concerned, and the enhancement of ex vivo stability of plasma lipidome could enable more reliable clinical translation of lipidomic data for biomarker discovery.     

Identification of glycerophospholipid fatty acid remodeling by using mass spectrometry imaging in bisphenol S induced mouse liver

Exposure to BPS induced glycerophospholipid fatty acid remodeling, which might be useful in toxicity evaluation for bisphenols-induced hepatic diseases.     

High performance liquid chromatography-tandem mass spectrometry of phospholipid molecular species in eggs from hens fed diets enriched in seal blubber oil

The total lipid fraction of eggs from hens fed diets enriched in seal blubber oil (1.25-5.0% SBO) was directly analysed with normal-phase high performance liquid chromatography coupled on-line with electrospray ionization ion-trap tandem mass spectrometry (HPLC-ESI-MS-MS) for the identification of the molecular species of phospholipids (PLs). The species of phosphatidylethanolamine (PE) and phosphatidylinositol (PI) were all detected as the [M-H](-) ions. The phosphatidylcholine (PC), sphingomyelin (Sph) and lysophosphatidylcholine (LPC) classes, were detected as formate adducts [M+HCOO](-). Tandem MS of PE and PI showed the loss of the carboxylate anions, and, for PI, also the loss of water and inositol. Product ion spectrum of PC, LPC and Sph contained only the [M-CH(3)](-) ion fragment. Feeding different levels of SBO for 5 weeks resulted in a significant increase of PE, PC and PI molecular species carrying eicosapentaenoic acid (C(20:5 omega3), EPA), docosapentaenoic acid (C(22:5 omega3), DPA) and docosahexaenoic acid (C(22:6 omega3), DHA), but not Sph nor LPC. The highest increase of the omega3/omega6 ratio occurred for PE and PC. On the contrary, PI was less affected by the increase of SBO in the diet.     

等度反相高效液相色谱法测定熊胆中磷脂类化合物

 摘要：建立了一种分离、测定磷脂酰胆碱（PC）、磷脂酸（PA）、心磷脂（CL）和磷脂酰甘油（PG）的等度RP-HPLC法。色谱条件为：在P-EC18柱上,用V（甲醇）：V（乙腈）：V（水）＝79:8:13的溶液作流动相,以2.0mL/min的流速进行等度洗脱,紫外检测波长205nm,谱带宽5nm。以熊胆为样品,经预处理后用所建立的方法进行分析,结果表明：6个熊胆样品中PC的质量比差别较大;PA的质量比除2号样品较低外,其余相近;PG除2号样品外都能检出,其中6号样品中PG的质量比稍大。PC的平均回收率为89     

Separation of phospholipid classes by hydrophilic interaction chromatography detected by electrospray ionization mass spectrometry

A new isocratic separation method was developed for separation of phospholipid (PL) classes based on a silica hydrophilic interaction liquid chromatography (HILIC) column with electrospray ionization (ESI) mass spectrometric detection. Although HILIC is typically used for polar compounds, also amphiphilic molecules like phospholipids can be separated very well. Compared to normal-phase (NP) chromatography, which is usually used for PL class separation, HILIC has the advantage to use on-line ESI-MS detection because its eluents are ESI compatible. Furthermore, this HILIC method is isocratic and hence less time consuming than most (gradient) NP HPLC methods. A chromatographic baseline separation of a standard mixture containing phosphatidylglycerol (PG), phosphatidylethanolamine (PE), phosphatidylcholine (PC), sphingomyelin (SM) and lysophosphatidylcholine (LPC) was achieved within a total run time of 17 min using a mobile phase consisting of acetonitrile, methanol and ammonium acetate 10 mM. The new method was subsequently tested on phospholipid fractions of a body fluid (human blood plasma) and a tissue extract (swine brain) whereby it achieved nearly the same baseline separation of the PL classes. The detected classes in both cases were PE, PC, SM and LPC.     

Thin Layer Chromatography of Phospholipid Composition in Mouse and Rabbit Spermatozoa

Abstract

The time course of the loss of different components of the phospholipids of rabbit and mouse epididymal spermatozoa during spontaneous lipid peroxidation was determined, using thin layer chromatography with a specific situ hydrolysis method to differentiate the acyl and alkenyl (plasmalogen) moieties. The components followed were phosphatidylethanolamine (PE), phosphatidylcholine (PC), the PE and PC phasmalogens, sphingomyelin (SP), cardiolipin (CL), and phosphatidyl-glycerol (PG). In both mouse and rabbit sperm, the PE component was found to be more than 90% diplasmalogen: 1,2-di(0-1′-alkenyl) glycerophosphoethanolamine. This component was lost rapidly during peroxidation. All PE has disappeared from rabbit sperm after 4 h aerobic incubation, at which point the other phospholipids had been little affected. In both mouse and rabbit sperm, the PC component was found to be 50% monoplasmalogen. The decrease in PC plasmalogen of rabbit sperm amounted to 74% after 20 h, compared to 42% loss of total PC. Similar observations were made with mouse sperm, except that rates of loss of all components were approximately twice those in rabbit. Distribution of the phospholipid components between sperm heads and tails was also determined: PE diplasmalogen was almost entirely found in the tail fraction, in both mouse and rabbit sperm. This mode of analysis allows the differentiation of sensitivities towards spontaneous peroxidation of the different types of phospholipid present in sperm membranes.     

Lipidomics of the Edible Brown Alga Wakame (Undaria pinnatifida) by Liquid Chromatography Coupled to Electrospray Ionization and Tandem Mass Spectrometry

The lipidome of a brown seaweed commonly known as wakame (Undaria pinnatifida), which is grown and consumed around the world, including Western countries, as a healthy nutraceutical food or supplement, was here extensively examined. The study was focused on the characterization of phospholipids (PL) and glycolipids (GL) by liquid chromatography (LC), either hydrophilic interaction LC (HILIC) or reversed-phase LC (RPLC), coupled to electrospray ionization (ESI) and mass spectrometry (MS), operated both in high and in low-resolution mode. Through the acquisition of single (MS) and tandem (MS/MS) mass spectra more than 200 PL and GL of U. pinnatifida extracts were characterized in terms of lipid class, fatty acyl (FA) chain composition (length and number of unsaturations), and regiochemistry, namely 16 SQDG, 6 SQMG, 12 DGDG, 5 DGMG, 29 PG, 8 LPG, 19 PI, 14 PA, 19 PE, 8 PE, 38 PC, and 27 LPC. The FA (C16:0) was the most abundant saturated acyl chain, whereas the monounsaturated C18:1 and the polyunsaturated C18:2 and C20:4 chains were the prevailing ones. Odd-numbered acyl chains, iJ., C15:0, C17:0, C19:0, and C19:1, were also recognized. While SQDG exhibited the longest and most unsaturated acyl chains, C18:1, C18:2, and C18:3, in the sn-1 position of glycerol, they were preferentially located in the sn-2 position in the case of PL. The developed analytical approach might pave the way to extend lipidomic investigations also for other edible marine algae, thus emphasizing their potential role as a source of bioactive lipids.     

Detection of related substances in polyene phosphatidyl choline extracted from soybean and in its commercial capsule by comprehensive supercritical fluid chromatography with mass spectrometry compared with HPLC with evaporative light scattering detection

Supercritical fluid chromatography with tandem mass spectrometry was used to comprehensively profile polyene phosphatidyl choline (PPC) extracted from soybean. We achieved an efficient chromatographic analysis using a BEH‐2EP column (3 × 100 mm², 1.7 μm) with a mobile phase consisting of CO₂ and a cosolvent in gradient combination at a flow rate of 1.0 mL/min. The cosolvent consisted of methanol, acetonitrile, and water (containing 10 mM ammonium acetate and 0.2% formic acid). The total single‐run time was 7 min. We used this method to accurately detect ten different phospholipids (PLs) during extraction. The limits of quantification for phosphatidyl choline, lyso‐phosphatidylcholine (LPC), phosphatidic acid (PA), sphingomyelin, phosphatidyl glycerol, phosphatidyl inositol (PI), cholesterol, cardiolipin, phosphatidyl serine, and phosphatidyl ethanolamine (PE) were 20.6, 19.52, 1.21, 2.38, 0.50, 2.28, 54.3, 0.60, 0.65, and 4.85 ng/mL, respectively. However, adopting the high‐performance liquid chromatography with evaporative light scattering detection method issued by the China Food and Drug Administration, only PA, LPC, PE, PI, and PPC could be analyzed accurately, and the limits of quantification were 33.89, 60.5, 30.3, 10.9, and 61.79 μg/mL, respectively. The total single‐run time was at the least 20 min. Consequently, the supercritical fluid chromatography with tandem mass spectrometry method was more suitable for the analysis of related PLs.     

Profiling of lipids in Leishmania donovani using hydrophilic interaction chromatography in combination with Fourier transform mass spectrometry

There is evidence from our current research on resistance to stibigluconate and from some previous observations that lipid composition may be altered in resistant Leishmania donovani and in order to explore this we required a comprehensive lipidomics method. Phospholipids can be analysed by direct infusion into a mass spectrometer and such methods can work very well. However, chromatographic methods can also be very effective and are extensively used. They potentially avoid ion suppression effects, associate lipid classes with a retention time range and deliver good quantitative accuracy. In the current study three chromatography columns were compared for their ability to separate different classes of lipid. Butylsilane (C‐4), Zic‐HILIC and a silica gel column were compared. The best results were obtained with a silica gel column used in hydrophilic interaction chromatography (HILIC) mode with a mobile phase gradient consisting of (A) 20% isopropyl alcohol (IPA) in acetonitrile (v/v) and (B) 20% IPA in 0.02 M ammonium formate. Using these conditions separate peaks were obtained for triglycerides (TG), phosphoinositols (PI), inositol phosphoceramides (IPC), phosphatidylethanolamines (PE), phosphatidylserines (PS), phosphatidylcholines (PC), sphingosines (SG), lysophosphatidyethanolamines (LPE) and lysophosphatidylcholines (LPC). The methodology was applied to the analysis of lipid extracts from Leishmania donovani and by coupling the chromatography with an LTQ Orbitrap mass spectrometer. It was possible to detect 188 lipid species in the extracts with the following breakdown: PC 59, PE 38, TG 35, PI 20, CPI 13, LPC 11, LPE 2 and SG 10. The fatty acid composition of the more abundant lipids was characterised by MS² and MS³ experiments carried out by using an LCQ Deca low‐resolution ion trap instrument coupled with the silica gel column. The separation of lipids into well‐defined groups gives extra confidence in their identification and minimises the risk of ion suppression effects. High‐resolution mass spectrometry was necessary in order to be able to differentiate between acyl‐ and acyl‐alkyl‐lipids. Copyright © 2010 John Wiley & Sons, Ltd.     

Quantification of plasma phospholipids by ultra performance liquid chromatography tandem mass spectrometry

We describe a fast and robust ultra performance liquid chromatography tandem mass spectrometry method for the quantification of phospholipid (PL) species in EDTA-plasma samples. We quantified total phosphatidylcholine (PC), phosphatidylethanolamine (PE), lysophosphatidylcholine (LPC), and sphingomyelin (SM) and several species within these classes using one or two external calibrators and one internal standard for each class. Inter-assay coefficients of variation were <10% for the most abundant species and <20% for all quantified PC, LPC, and SM species and the three most abundant PE species. Coefficients of linear regression were R ² > 0.98. Mean recoveries were between 83% and 123%. The limits of detection were 0.37 μmol/L for PC, 4.02 μmol/L for LPC, 3.75 μmol/L for PE, and 0.86 μmol/L for SM. Quantification was linear over the physiological ranges for PE, LPC, and SM and up to 500 μmol/L for PC. The concentrations of PLs in the plasma of healthy donors yielded results that were comparable with those of previous works.     

Effects of albumin and erythrocyte membranes on spread monolayers of lung surfactant lipids

Dipalmitoyl phosphatidylcholine (DPPC), one of the main constituents of lung surfactant is mainly responsible for reduction of surface tension to near 0 mN/m during expiration, resisting alveolar collapse. Other unsaturated phospholipids like palmitoyloleoyl phosphatidylglycerol (PG), palmitoyloleoyl phosphatidylcholine (POPC) and neutral lipids help in adsorption of lung surfactant to the air-aqueous interface. Lung surfactant lipids may interact with plasma proteins and hematological agents flooding the alveoli in diseased states. In this study, we evaluated the effects of albumin and erythrocyte membranes on spread films of DPPC alone and mixtures of DPPC with each of PG, POPC, palmitoyloleoyl phosphatidylethanolamine (PE), cholesterol (CHOL) and palmitic acid (PA) in 9:1 molar ratios. Surface tension-area isotherms were recorded using a Langmuir-Blodgett (LB) trough at 37 degrees C with 0.9% saline as the sub-phase. In the presence of erythrocyte membranes, DPPC and DPPC+PA monolayers reached minimum surface tensions of 7.3+/-0.9 and 9.6+/-1.4 mN/m, respectively. Other lipid combinations reached significantly higher minimum surface tensions >18 mN/m in presence of membranes (Newman Keul's test, p<0.05). The relative susceptibility to membrane inhibition was [(DPPC+PG, 7:3)=(DPPC+PG, 9:1)=(DPPC+POPC)=(DPPC+PE)=(DPPC+CHOL)]>[(DPPC+PA)=(DPPC)]. The differential response was more pronounced in case of albumin with DPPC and DPPC+PA monolayers reaching minimum surface tensions less than 2.4 mN/m in presence of albumin, whereas DPPC+PG and DPPC+POPC reached minimum surface tensions of around 20 mN/m in presence of albumin. Descending order of susceptibility of the spread monolayers of lipid mixtures to albumin destabilization was as follows: [(DPPC+PG, 7:3)=(DPPC+PG, 9:1)=(DPPC+POPC)]>[(DPPC+PE)=(DPPC+CHOL)]>[(DPPC+PA)=(DPPC)] The increase in minimum surface tension in presence of albumin and erythrocyte membranes was accompanied by sudden increases in compressibility at surface tensions of 15-30 mN/m. This suggests a monolayer destabilization and could be indicative of phase transitions in the mixed lipid films due to the presence of the hydrophobic constituents of erythrocyte membranes.     

Fluorescent determination of cardiolipin using 10-<Emphasis Type="Italic">N</Emphasis>-nonyl acridine orange

Cardiolipin (CL) plays an essential role as a marker for cell apoptosis. Quantitative detection of phospholipids (PLs) by UV absorbance is problematic due to the presence of few double bonds in the structure. Although 10-N-nonyl acridine orange (NAO) has been utilized for fluorescent visualization of liposomes and mitochondria through its interaction with CL, in this work, we have developed a specific fluorescent method for CL in solution using NAO. The interaction of sodium n-dodecyl sulfate (SDS), used to treat cells prior to lipid extraction, and other PLs found in cell membranes such as phosphatidic acid (PA), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), phosphatidiylserine (PS), and sphingomyelin (SM) with NAO is investigated. The fluorescence intensity of the 0.5 μM NAO signal is strongly quenched by SDS below 25% methanol in water but with a methanol content above 50%, no quenching of NAO by SDS is observed. No fluorescence quenching of NAO with a 50% methanol/50% water solvent by the previously mentioned PLs or 4–20 μM cholesterol with the exception of PG at above 8 μM is noted. Using this 50% methanol/50% water solvent, the fluorescence signal due to the NAO–CL interaction is quite stable from 3 to at least 15 min. With excitation and emission wavelengths set at 518 and 530 nm, respectively, 20 μM NAO provides an inverse linear fluorescence response at 0.2–10 μM CL with a correlation coefficient of 0.9929. The detection limit is 0.2 μM and the limit of quantification is 0.6 μM. Structurally analogous acridine orange and phenosafranin dyes are less effective as fluorescent probes for CL. The CL in the whole cell and membrane samples is quantitatively determined by standard addition to range from 0.2 to 1.5 μM. The level of CL in cell membrane samples, previously subjected to staurosporine which initiates cell apoptosis, is increased but not significantly through use of the t-test.     

Relationships between equilibrium spreading pressure and phase equilibria of phospholipid bilayers and monolayers at the air-water interface

The intricate interplay between the bilayer and monolayer properties of phosphatidylcholine (PC), phosphatidylglycerol (PG), and phosphatidylethanolamine (PE) phospholipids, in relation to their polar headgroup properties, and the effects of chain permutations on those polar headgroup properties have been demonstrated for the first time with a set of time-independent bilayer-monolayer equilibria studies. Bilayer and monolayer phase behavior for PE is quite different than that observed for PC and PG. This difference is attributed to the characteristic biophysical PE polar headgroup property of favorable intermolecular hydrogen-bonding and electrostatic interactions in both the bilayer and monolayer states. This characteristic hydrogen-bonding ability of the PE polar headgroup is reflected in the condensed nature of PE monolayers and a decrease in equilibrium monolayer collapse pressure at temperatures below the monolayer critical temperature, T(c) (whether above or below the monolayer triple point temperature, T(t)). This interesting phenomena is compared to equilibrated PC and PG monolayers which collapse to form bilayers at 45 mN/m at temperatures both above and below monolayer T(c). Additionally, it has been demonstrated by measurements of the equilibrium spreading pressure, pie, that at temperatures above the bilayer main gel-to-liquid-crystalline phase-transition temperature, T(m), all liquid-crystalline phospholipid bilayers spread to form monolayers with pie around 45 mN/m, and spread liquid-expanded equilibrated monolayers collapse at 45 mN/m to form their respective thermodynamically stable liquid-crystalline bilayers. At temperatures below bilayer T(m), PC and PG gel bilayers exhibit a drop in bilayer pi(e) values < or =0.2 mN/m forming gaseous monolayers, whereas the value of pic of spread monolayers remains around 45 mN/m. This suggests that spread equilibrated PC and PG monolayers collapse to a metastable liquid-crystalline bilayer structure at temperatures below bilayer T(m) (where the thermodynamically stable bilayer liquid-crystalline phase does not exist) and with a surface pressure of 45 mN/m, a surface chemical property characteristically observed at temperatures above bilayer T(m) (monolayer T(c)). In contrast, PE gel bilayers, which exist at temperatures below bilayer T(m) but above bilayer T(s) (bilayer crystal-to-gel phase-transition temperature), exhibit gel bilayer spreading to form equilibrated monolayers with intermediate pie values in the range of 30-40 mN/m; however, bilayer pie and monolayer pic values remain equal in value to one another. Contrastingly, at temperatures below bilayer T(s), PE crystalline bilayers exhibit bilayer pie values < or =0.2 mN/m forming equilibrated gaseous monolayers, whereas spread monolayers collapse at a value of pic remaining around 30 mN/m, indicative of metastable gel bilayer formation.     

TRANSESTERIFICATION OF POLY（BISPHENOL A CARBONATE） WITH AROMATIC AND ALIPHATIC SEGMENTS IN BUTYLENE TEREPHTHALATE-CAPROLACTONE COPOLYESTER

In this article, the transesterification of poly(bisphenol A carbonate) (PC) with butylene terephthalate-caprolactone copolyester at a weight ratio 50/50 (BCL(21)) was thoroughly investigated by proton nuclear magnetic resonance spectroscopy (^1H-NMR), in conjunction with a model compound. The ^1H-NMR results of the annealed blend PC/BCL(21) show that the formation of bisphenol A-terephthalate ester units is the same as in the annealed blend of PC with PBT, and the transesterification actually occurs between PC and butylene terephthalate (BT) segments in BCL(21). By comparison with the model compound bisphenol A dibutyrate, the new signal appearing at δ=2.56 in the ^1H-NMR spectrum confirms the existence of bisphenol A caprolactone ester units resulting from the exchange reaction of PC with caprolactone (CL) segments. ^1H-NMR analysis of the transesterification rates reveals that the reaction of PC with aromatic and aliphatic segments in BCL(21) proceeds in a random manner. The miscibility of the blend PC/BCL(21) copolyester is favorable for the transesterification of PC with BT segments and CL segments.