Combined effects of headgroup charge and tail unsaturation of lipids on lateral organization and diffusion of lipids in model biomembranes

Lateral organization and dynamics of lipids in plasma membranes are crucial for several cellular processes such as signal transduction across the membrane and still remain elusive.In this paper,using coarse-grained molecular dynamics simulation,we theoretically study the combined effects of headgroup charge and tail unsaturation of lipids on the lateral organization and diffusion of lipids in ternary lipid bilayers.In neutral ternary lipid bilayers composed of saturated lipids,unsaturated lipids,and cholesterols,under the conditions of given temperature and components,the main factor for the phase separation is the unsaturation of unsaturated lipids and the bilayers can be separated into liquid-ordered domains enriched in saturated lipids and cholesterols and liquid-disordered domains enriched in unsaturated lipids.Once the headgroup charge is introduced,the electrostatic repulsion between the negatively charged lipid headgroups will increase the distance between the charged lipids.We find that the lateral organization and diffusion of the lipids in the(partially) charged ternary lipid bilayers are determined by the competition between the headgroup charge and the unsaturation of the unsaturated lipids.In the bilayers containing unsaturated lipids with lower unsaturation,the headgroup charge plays a crucial role in the lateral organization and diffusion of lipids.The headgroup charge may make the lipid domains unstable and even can suppress phase separation of the lipids in some systems.However,in the bilayers containing highly unsaturated lipids,the lateral organization and diffusion of lipids are mainly dominated by the unsaturation of the unsaturated lipids.This work may provide some theoretical insights into understanding the formation of nanosized domains and lateral diffusion of lipids in plasma membranes.     

How Phospholipid-Cholesterol Interactions Modulate Lipid Lateral Diffusion, as Revealed by Fluorescence Correlation Spectroscopy

Cholesterol is a key player in regulating physico-chemical properties of cellular membranes and, thereby, ensuring cell viability. In particular, lipid-cholesterol interactions may provide important information on the spatio-temporal organization of membrane components. Here, we apply confocal imaging and Fluorescence Correlation Spectroscopy (FCS) to Giant Unilamellar Vesicles (GUVs) composed of binary mixtures of lipids and cholesterol.The effect of cholesterol on lipid dynamics and molecular packing order of unsaturated, monounsaturated, fully saturated (with both low and high phase transition temperatures, T_m) glycero-phospholipids and sphingomyelin has been investigated. We show that, for unsaturated glycerophospholipids, the decrease of the lipid diffusion coefficient as a result of the interaction with cholesterol does not depend on the fatty acid chain length. However, the values of the diffusion coefficient change as a function of chain length. The monounsaturated phospholipid palmitoyl-oleoyl-phosphatidylcholine (POPC) exhibits a dynamic behavior very similar to the unsaturated dioleoyl-phosphatidylcholine (DOPC). By contrast, for saturated (low T_m) glycero-phospholipids, cholesterol causes a decrease of lipid mobility in a chain length-dependent manner.FCS can be employed as a valuable tool to study lipid-sterol interactions and their effect on lipid dynamics, molecular packing and degree of conformational order.     

Raman spectroscopy of lipids: a review

Raman spectra of 35 lipids are presented and analyzed in this work. Selected compounds, i.e. saturated/unsaturated fatty acids, triacylglycerols, cholesterol, cholesteryl esters and phospholipids, were chosen to review key lipids involved in cardiovascular disease development. Differences in Raman signatures both between diverse groups of lipids as well as various members of the same family are investigated in detail in order to elucidate marker features enabling detection and discrimination of lipids in complex samples, particularly of biological origin. This work complements our previous review on important biomolecules, i.e. proteins, and presents a comprehensive database of Raman spectra of naturally occurring lipids. Copyright © 2014 John Wiley & Sons, Ltd.     

Protein fragment imaging using ink jet printing digestion technique

We have developed a capable tool for visualizing protein distribution at the sub-cell level with TOF-SIMS. This new method of visualizing a protein includes: (1) printing a digestive enzyme with ink jet (IJ) printing technology onto a tissue section, (2) measuring the two-dimensional distributions of decomposed peptide ions derived from digested protein on the tissue section by TOF-SIMS with a bismuth cluster ion (Bi₃⁺) source and using the aqueous ion enhancement method, and (3) analyzing the two-dimensional distributions of proteins using the results of proteome analysis. We have not yet tried this method onto a real tissue section. To show the possibility of this method, TOF-SIMS results of visualizing dot-patterned digested fragment peptide ions using IJ printing digestion technique onto a protein film are presented.     

Saturation of sodium fluorescence in a flame irradiated with a pulsed tunable dye laser

Theoretical and experimental saturation curves and associated saturation parameters for the Na-D doublet in an H₂-O₂-Ar flame at 1 atm (T=1700 K) are compared. These parameters are found to agree within the experimental error of 25%. An explanation based on the spatial and temporal distribution of the laser intensity is given for the deviating saturation curves reported by various authors. The shape of the fluorescence pulse is shown to depend on the O₂ concentration in the flame. A lower limit for the rate constant of the doublet mixing transition is estimated from the ratio of the saturated fluorescence intensities of the Na-D components and found to be 3x10⁸s^-1. Conclusions are drawn which restrict the use of saturated atomic fluorescence intensities as a measure for the total atomic number density in the flame.     

Investigation of natural dyes and ancient textiles from korea using TOF-SIMS

The identification of the colorants used on ancient textiles provides a historical pathway to the understanding of the processes associated with one of the oldest of chemical technologies, namely textile dyeing. In this paper, time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to detect dyes on textiles avoiding the time-consuming and destructive extraction procedures necessary for the spectrophotometric and chromatographic methods previously used. The plant dyes investigated belong to a variety of chemical groups, which include curcumin, crocin, carthamin, purpurin, alizarin, brazilin, shikonin, and indigo. Reference textile samples were prepared with dye extracts of plants and were characterized by TOF-SIMS. TOF-SIMS spectra for the dyed textiles showed element ions from metallic mordants, specific fragment ions, and molecular ions from organic dyes. Remnant dyes on excavated textiles have also been identified using TOF-SIMS. The ancient textile sample showed the presence of indigo clearly, although the fiber itself had degraded badly. From the results, it was concluded that most of plant dyes can be identified with TOF-SIMS and it is a very promising technique for the archaeology field.     

Comparison of secondary ion intensity enhancement from polymers on silicon and silver substrates by using Au-TOF-SIMS

The usefulness of the usage of cluster primary ion source together with an Ag substrate and detection of Ag cationized molecular ions was studied from the standpoint to realize high sensitivity TOF-SIMS analysis of organic materials. Although secondary ions from polymer thin films on a Si substrate can be detected in a higher sensitivity with Au₃⁺ cluster primary ion compared with Ga⁺ ion bombardment, it was clearly observed that the secondary ion intensities from samples on an Ag substrate showed quite a different tendency from that on Si. When monoatomic primary ions, e.g., Au⁺ and Ga⁺, were used for the measurement of the sample on an Ag substrate, [M+Ag]⁺ ions (M corresponds to polyethylene glycol molecule) were detected in a high sensitivity. On the contrary, when Au₃⁺ was used, no intensity enhancement of [M+Ag]⁺ ions was observed. The acceleration energy dependence of the detected secondary ions implies the different ionization mechanisms on the different substrates.     

Analysis of lipids with desorption atmospheric pressure photoionization-mass spectrometry (DAPPI-MS) and desorption electrospray ionization-mass spectrometry (DESI-MS)

In this article, the effect of spray solvent on the analysis of selected lipids including fatty acids, fat-soluble vitamins, triacylglycerols, steroids, phospholipids, and sphingolipids has been studied by two different ambient mass spectrometry (MS) methods, desorption electrospray ionization-MS (DESI-MS) and desorption atmospheric pressure photoionization-MS (DAPPI-MS). The ionization of the lipids with DESI and DAPPI was strongly dependent on the spray solvent. In most cases, the lipids were detected as protonated or deprotonated molecules; however, other ions were also formed, such as adduct ions (in DESI), [M-H](+) ions (in DESI and DAPPI), radical ions (in DAPPI), and abundant oxidation products (in DESI and DAPPI). DAPPI provided efficient desorption and ionization for neutral and less polar as well as for ionic lipids but caused extensive fragmentation for larger and more labile compounds because of a thermal desorption process. DESI was more suitable for the analysis of the large and labile lipids, but the ionization efficiency for less polar lipids was poor. Both methods were successfully applied to the direct analysis of lipids from pharmaceutical and food products. Although DESI and DAPPI provide efficient analysis of lipids, the multiple and largely unpredictable ionization reactions may set challenges for routine lipid analysis with these methods.     

Changes in the Condition Index and Chemical Contents of Venerupis (decussata decussate L.) from the Egyptian Coastal Waters.

Changes in the condition index and chemical contents of adult and young aged exotic Manila Venerupis (decussata decussata L.) have been studied. Animals were collected monthly from El-Mex Bay during the period from April 1993 to April 1994. Monthly variations in total lipid, phospholipid, triglyceride, free fatty acids (FFA), phosphorus, potassium and magnesium were determined in animals of different sizes. Their average values being; 20.93%, 10.54%, 1.04%, 1.26%, 4.23 mg/g, 3.26 mg/g and 1.71 mg/g dry weight for the corresponding parameters respectively. Mostly, there was a fall in the condition index associated with considerable rise in total lipid and their constituents (Phospholipid, FFA and triglycerides). Venerupis tissues are of extremly high lipid and relatively high phospholipids, it constitutes about 49% of the roe lipid comparing to about 6% FFA and 5% triglycerides and consequently low cholestrol content. It has very low Iodine value, mostly within the average of 27.8 to 31.85, and is characterized by low density and low unsaturated lipids.

Fluctuations in the lipid content of the animals followed the relative change in food intake throughout the year and the state of maturation. A marked reduction in lipid and some of its constituents was associated with lowering temperature in winter, as the result of the reduction in feeding activity. The major period of spawning occurred from June through September, and is accompanied by lipid metabolism.

P and K were found to promote the growth rate and increased with increasing the condition index and showed high bioaccumulation rate, in contrast to Mg.     

Laser ablation of a silicon carbide target: a time-of-flight quadrupole mass spectrometric study

Laser ablation of a SiC target was attempted to investigate the formation mechanisms and expansion dynamics of ionic species including silicon carbide cluster ions in the plume. Time-of-arrival distributions of ions were analysed to obtain their mean velocities and spatial distributions. Laser-plume interaction was examined by illuminating the plume with a UV laser pulse. Si₂C was found to be the major photodissociation product of silicon carbide cluster ions. PACS 82.40.Ra; 79.20.Ds; 79.20.La     

Polyamines and fatty acids in sucrose precultured banana meristems and correlation with survival rate after cryopreservation

Polyamines and fatty acids were studied in proliferating meristem cultures of 3 banana cultivars with high (Cachaco), medium (Williams Bronze free) and low (Mbwazirume) survival rates after cryopreservation. A 2-week preculture on medium containing 0.4 M sucrose which is essential to obtain survival after cryopreservation resulted in increased polyamine levels, especially putrescine. This increase in putrescine content was positively correlated with the survival rate after simple freezing or after vitrification. The total fatty acid content also increased after a 0.4 M sucrose pretreatment. However, only the ratio of unsaturated/saturated fatty acids correlated positively with the survival rate after cryopreservation. This is the first report showing a correlation of both putrescine increase and level of unsaturation of membrane lipids after sucrose treatment with survival rate after cryopreservation.     

Mutual information theory for biomedical applications: Estimation of three protein-adsorbed dialysis membranes

Protein-adsorbed dialysis membranes are evaluated with time-of-flight secondary ion mass spectrometry (TOF-SIMS) chemical imaging technique. Protein adsorption causing permeability change is one of big issues in the development of dialysis membranes. Bovine serum albumin adsorption onto three kinds of dialysis membranes has been evaluated with TOF-SIMS. In the present study three kinds of proteins, bovine serum albumin, α-chymotripsinogen A, and cytochrome C adsorbed onto hollow-fiber dialysis membranes, were measured by means of TOF-SIMS and then TOF-SIMS spectra were analyzed using mutual information. Then specific peaks of fragment ions related to α-chymotripsinogen A and bovine serum albumin were found, respectively. In this condition, however, specific peaks to cytochrome C were not able to find compared with other samples. Finally, chemical images of α-chymotripsinogen A and bovine serum albumin, respectively, adsorbed onto the membranes with co-existing proteins were obtained. The results of TOF-SIMS images of the proteins on the membranes show different tendency of adsorption depending on co-existing proteins. Further study is needed to study more detailed protein adsorption onto the membranes with co-existing proteins.     

Influences of the Structure of Lipids on Thermal Stability of Lipid Membranes

The binding free energy (BFE) of lipid to lipid bilayer is a critical factor to determine the thermal or mechanical stability of the bilayer. Although the molecular structure of lipids has significant impacts on BFE of the lipid, there lacks a systematic study on this issue. In this paper we use coarse-grained molecular dynamics simulation to investigate this problem for several typical phospholipids. We find that both the tail length and tail unsaturation can significantly affect the BFE of lipids but in opposite way, namely, BFE decreases linearly with increasing length, but increases linearly with addition of unsaturated bonds. Inspired by the specific structure of cholesterol which is a crucial component of biomembrane, we also find that introduction of carbo-ring-like structures to the lipid tail or to the bilayer may greatly enhance the stability of the bilayer. Our simulation also shows that temperature can influence the bilayer stability and this effect can be significant when the bilayer undergoes phase transition. These results may be helpful to the design of liposome or other self-assembled lipid systems.     

Non-evidence for Z 1 oscillations of the nuclear ion-atom interaction in an amorphous target

Periodic variations in the Z ₁ dependence of the interatomic potential has recently bevlen revealed by a channeling technique. To search for oscillations of similar kind in a target of randomly arranged atoms we have made systematic measurements on the scattering distributions of energetic (32–56 keV) ions in amorphous carbon. Our technique was to transmit light mass ions through carbon foils with a thickness of 2–4 μg/cm². The atomic number of the ions, Z, ranged from 3 to 18. The scattering distribution of the transmitted particles was recorded. From these curves the angular halfwidth,ψ ^1/2, and the relative intensity at a scattering angle 2.5 times ψ ^1/2 was determined. The experimental values are in good agreement with theoretical calculations based on the Thomas-Fermi and Lenz- Jensen potentials. Furthermore, the saturation value of the mean nuclear stopping cross sections for ions scattered in the straight forward direction with a mean energy of 50 keV are given. No evidence for a Z ₁ oscillatory behaviour could be found in any of the three parameters investigated.     

Mass spectrometric characterization of DNA microarrays as a function of primary ion species

Recent studies have shown TOF-SIMS to be an appropriate method for the detailed examination of the immobilization process of PNA and its ability to hybridize to unlabeled complementary DNA fragments. Unlabeled single-stranded DNA was hybridized to Si wafer biosensor chips containing both complementary and non-complementary immobilized PNA sequences. The hybridization of complementary DNA could readily be identified by detecting phosphate-containing molecules from the DNA backbone. An unambiguous discrimination was achieved between complementary and non-complementary sequences.In order to optimize detection parameters, different primary ions were applied, including monoatomic ions (Bi⁺) as well as cluster ions (Bi₂⁺, Bi₃⁺, Bi₄⁺, Bi₃⁺⁺, Bi₅⁺⁺), and secondary ion yield behavior and formation efficiencies were studied. It was found that cluster primary ions resulted in a significantly increased yield of DNA-correlated fragments, enabling higher signal intensities and better secondary ion efficiencies.TOF-SIMS is undoubtedly a highly useful technique for identifying hybridized DNA on PNA biosensor chips. It is suitable for studying the complexity of the immobilization and hybridization processes and may provide a rapid method for DNA diagnostics. With the absence of the labeling procedure and the simultaneous increase of the phosphate signal as a result of increasing DNA sequence length, this technique comes to be especially useful for the direct analysis of genomic DNA.     

Post-annealing effects on EPR response of irradiated nano-structure hydroxyapatite

In this work, the nano-structure hydroxyapatite was synthesized via the hydrolysis method. The produced powders were thermally treatment at different temperatures from 400 to 1200°C. The morphological and chemical analyses were carried out using the Fourier transmission infrared spectroscopy, transmission electron microscopy, and X-ray diffraction system. Then, the samples were irradiated at different absorbed doses from 1 to 80 kGy using ⁶⁰Co γ -ray. Electron paramagnetic resonance (EPR) responses of the samples were measured at room temperature in air. Subsequently, the variations of EPR signal intensities were constructed as the peak-to-peak signal amplitude and results were compared with those of non-annealed samples. The results show that the EPR responses of non-annealed samples are higher rather than other samples and also are saturated at higher doses in comparison with the others.     

直肠组织的高分辨魔角旋转核磁共振波谱研究

文章对6例直肠癌变及正常组织进行高分辨魔角旋转核磁共振波谱研究,结果显示直肠癌变和正常组织的核磁共振氢谱存在明显差异。这可以通过特征峰面积与0.88处峰积分面积的比值上的差异看出：（1）在化学位移0.75～1.55之间,癌组织各种氨基酸[缬氨酸,异亮氨酸,亮氨酸]与脂肪酸甲基的比值（I₂/I₁）,癌组织乳酸盐与脂肪酸甲基的比值(I₄/I₁)都明显增大。（2）在化学位移1.55～2.90之间,癌变组织中亮氨酸、赖氨酸、异亮氨酸与脂肪酸甲基的比值（I₇/I₁）, 谷氨酸、谷氨酰胺、缬氨酸、琥珀酸与脂肪酸甲基的比值((I₉+I₁₁)/I₁)、天冬氨酸与脂肪酸甲基的比值((I₁₂+I₁₄)/I₁)都较正常组织明显增大。（3）在化学位移2.90～3.49之间,癌变组织氨基酸与脂肪酸甲基的比值（I₁₅/I₁）、胆碱类与脂肪酸甲基的比值((I₁₆+I₁₇)/I₁)、牛磺酸与脂肪酸甲基的比值((I₁₈+I₁₉)/I₁)都较正常组织明显增大。（4）在化学位移3.49～4.50之间,其他代谢物与脂肪酸甲基的比值（I₂₀/I₁）,以及甘油基与脂肪酸甲基的比值（I₂₂/I₁）在癌变组织中都有增大的趋势。（5）化学位移4.5～10之间,癌变组织的核苷酸发生了变化,癌变组织的不饱和脂肪酸与脂肪酸甲基的比值（I₂₄/I₁）明显减小。（6）在化学位移-8～0.75之间,癌变组织的谱峰有减少的趋势。通过上述分析可知,通过癌变与正常组织代谢物NMR谱峰的差异,可以区分癌变和正常组织。说明核磁共振波谱技术可能发展成为一种诊断直肠癌的新方法。     

Evaluation of immobilized-lysozyme by means of TOF-SIMS

Evaluation of immobilized-proteins on bio-devices is important for the development of sophisticated devices. Lysozyme molecules immobilized on substrates were evaluated by means of time-of-flight secondary ion mass spectrometry (TOF-SIMS). Two types of the lysozyme-immobilized samples were prepared by controlling the binding parts, i.e., the amino groups or carboxyl groups, of the protein. The TOF-SIMS spectra of each sample were analyzed with mutual information to select fragment ions specific to each sample. According to the results, differences between the samples being immobilized in the different ways are suggested, and the surface structure of the lysozyme molecule immobilized at amino groups is determined based on three-dimensional structure of lysozyme in the Protein Data Bank.     

The characteristic bands of the stretching vibrations of the nitro group in infrared absorption

Correlations have been established between the values of the frequencies and intensities of the bands due to the two stretching vibrations of the nitro group and the structure of molecules. The use of band intensities extends considerably the possibilities in structural analysis, and makes it possible to distinguish reliably saturated, unsaturated, and aromatic nitro compounds and to make a more detailed differentiation between compounds within classes. It has been shown that the intensities are additive and that the intensity of one of the vibrations is highly characteristic; quantitative determination of nitro groups in molecules of unknown structure is possible.     

Effects of high pressure on unsaturated fatty acids

The objective of this study is to investigate the effects of high pressure processing on the molecular structure of some unsaturated fatty acids. Samples of elaidic acid, linoleic acid, ZE and EE conjugated linoleic acid are treated at 293 or 333?K at pressures up to 700?MPa. It is observed that the adiabatic heat generated from compression is able to bring the sample temperature above 373?K after 700?MPa. These relatively extreme conditions are of great interest for food sterilization, but they may induce undesirable change in fatty acid quality characteristics. To check for structural changes, Raman spectra of the samples are analysed after treatments. The comparison with Raman spectra of samples kept at atmospheric pressure shows that pressure induces some conformational changes at the hydrocarbon skeleton in solid samples, while the liquid ones remain unchanged. No cis/trans isomerization occurs, but gauche conformers are likely to be present.