Ion channel behavior of amphotericin B in sterol-free and cholesterol- or ergosterol-containing supported phosphatidylcholine bilayer model membranes investigated by electrochemistry and spectroscopy

Amphotericin B (AmB) is a popular drug frequently applied in the treatment of systemic fungal infections. In the presence of ruthenium (II) as the maker ion, the behavior of AmB to form ion channels in sterol-free and cholesterol- or ergosterol-containing supported phosphatidylcholine bilayer model membranes were studied by cyclic votammetry, AC impedance spectroscopy, and UV/visible absorbance spectroscopy. Different concentrations of AmB ranging from a molecularly dispersed to a highly aggregated state of the drug were investigated. In a fixed cholesterol or ergosterol content (5 mol %) in glassy carbon electrode-supported model membranes, our results showed that no matter what form of AmB, monomeric or aggregated, AmB could form ion channels in supported ergosterol-containing phosphatidylcholine bilayer model membranes. However, AmB could not form ion channels in its monomeric form in sterol-free and cholesterol-containing supported model membranes. On the one hand, when AmB is present as an aggregated state, it can form ion channels in cholesterol-containing supported model membranes; on the other hand, only when AmB is present as a relatively highly aggregated state can it form ion channels in sterol-free supported phosphatidylcholine bilayer model membranes. The results showed that the state of AmB played an important role in forming ion channels in sterol-free and cholesterol-containing supported phosphatidylcholine bilayer model membranes.

Direct electrochemistry of hemoglobin in egg-phosphatidylcholine films and its catalysis to H2O2

Direct electrochemistry of hemoglobin was observed in stable thin film composed of a natural lipid (egg-phosphatidylcholine) and hemoglobin on pyrolytic graphite (PG) electrode. Hemoglobin in lipid films shows thin layer electrochemistry behavior. The formal potential Edegrees' of hemoglobin in the lipid film was linearly varied with pH in the range from 3.5 to 7.0 with a slope of -46.4 mV pH(-1) Hemoglobin in the lipid film exhibited elegant catalytic activity for electrochemical reduction of H202, based which a unmediated biosensor for H2O2 was developed.

Effect of Eu3+ on the domain structures in phosphatidylcholine LB monolayer film observed by atomic force microscopy

Ordered domain structures were observed by atomic force microscope in dipalmitoylphosphatidycholine monolayer film, which was spread on the subphase of Eu3+ solution.

海洋小球藻Chlorella sp.甘油脂及脂肪酸、光合色素特征的研究

海洋微藻是海洋生态系统中最主要的初级生产者，也是海洋生物资源的重要来源。许多海洋微藻富含对人体具有重要的生理作用与保健功能的长链多不饱和脂肪酸，因此，筛选富含EPA、DHA等长链多不饱和脂肪酸的微藻和利用人工培养方法提高这些脂肪酸的产量是当前海洋生物学研究领域的热点之一。在本研究中，我们对被中科院海洋所定名为“Chlorella sp”（编号为1061）的一种海洋微藻的化学分类、甘油脂及其脂肪酸组成和外源葡萄糖和抗氧化剂（硫代硫酸钠）对这种微藻的脂肪酸含量的影响进行了研究，取得了以下主要结果。 海洋微藻是我固海水养殖中广泛使用的优良饵料藻。脂类物质是微藻最重要的营养指标之一，在本研究中，我们首先分析了被中科院海洋所定名为“Chlorellasp”的海洋微藻中的甘油脂及其脂肪酸种类和组成特点。结果表明，Chlorella sp.中的非极性脂主要为三脂酰甘油，极性甘油脂有10种。其中，一般培养条件下（温度23℃：光照，周期L/D14:10，强度60umolm-2-S-l）三脂酰甘油约占总脂的31 mol%，极性甘油脂约占总脂的69 rriol%。10种极性甘油脂是单半乳糖甘油二脂( monogalactosyldiacylglycerol． MGDG)、 双半乳糖甘油二脂( diagalactosyldiacylglycerol ， DGDG)、 硫代异鼠李糖甘油二脂( sulfoquinovosyldiacylglycerol，SQDG)、磷脂酰甘油(phosphatatidylglycerol，PG)、磷脂酰乙醇胺(phosphatidylethanolamine，PE)、磷脂酰胆碱( phosphatidylcholine，PC)、磷脂酰肌醇(phosphatidylinositol，PI)、磷脂酰丝氨醴(phosphatidylserine，Ps)、l，2-二酰基甘油-0-4，．（ⅣMⅣ-三甲基）高丝氨酸（diacylglyceryltrimethylhomoserine，DGTS）以及一种未能完全肯定，但可能是一中氯硫脂( chlorosulfolipid，CSL)。其中MGDG、DGDG、SQDG和PG是构成光合膜的主要成分，也是Chlorella sp中的主要极性脂。甜菜碱脂DGTS和磷脂PC是构成非光合膜的主要组分。Chlorella sp.中的主要脂肪酸为C16:0、C16:1耜C20：5（EPA)，后者主要存在于MGDG、DGDG和DGTS中，而三脂酰甘油也含有接近7%的EPA。 海洋微藻Chlorella sp.1061虽然被归属到绿藻纲绿藻目小球藻属，但是我们的研究表明，其色素、极性脂皮其脂肪酸组成与其它小球藻属藻类存在这很大差异Chl b是绿藻纲藻类中最主要的光合色素之一，1 6：4(n-3)和l 8：3(n-3)是绿藻微藻的主要脂肪酸，然而所有这些绿藻的特征化合物均未在Chlorella sp. 1061中检测到。DGTS和20:5(n-3)存在于很多的海洋微藻中，我们从Chlorella sp. 1061 中分离到占总极性甘油脂8 mo1%的DGTS，并从MGDG、DGDG和DGTS等极性甘油脂中检测到大量的20:5(n-3)。但是一般认为，小球藻属藻类中不舍这两种化合物。根据Chlorella sp. 1061的以上特点，这种藻不应该被归到小球藻属中。另外，由于Chlorella sp. 1061在色素、膜脂和脂肪酸组成特征方面大眼藻纲( Eustigmatophyceae)中的微绿球藻（Nannochloropsis）非常相似，因此，我们认为ChloreHa sp. 1061可能是Nannochloropsis中的一个种。但是未得到更进一步的证明和权威的认可之前，本文中我们仍然沿用ChloreHa sp,这一名称。 许多藻类中DGTS和PC -般不会同时存在，或者说一个存在时另外的一个的含量非常低。由此有人认为DGTS和PC之间存在着相互替代的关系。然而本研究中发现正常培养条件下Chlorella sp.中的DGTS和PC含量均较高（约10%）。磷处理实验结果表明，磷缺乏时Chlore Ha sp,中DGTS舍量大幅升高，而同时PC含量相应下降许多：但高浓度的磷并不能提高PC含量和降低DGTS含量，说明Chlorella sp,中DGTS仍可起替代PC的作用，然而PC可能并不能替代DGTS。Chlorella sp.中MGDG和DGTS脂肪酸组成及其位置分布结果显示，它们的组成和分布相似;在老化培养过程中MGDG和DGTS表现出周期性的相反的含量升高、降低的趋势，这进一步说明MGDG和DGTS之间存在着特殊的关系，MGDG可能合成自DGTS。 海洋微藻富含有利于人体健康的长链不饱和脂肪酸，如何提高微藻脂肪酸特别是多不饱和脂肪酸产量是目前研究的热点之一。本文首次报道了同时加入葡萄糖和硫代硫酸钠对Chlorelta sp,的生长、脂类组成和脂肪酸总产量的影响，结果显示葡萄糖和硫代硫酸钠存在明显而且强烈的互作，二者在培养液中的同时存在显著刺激了脂肪酸总产量的积累，在培养液中分别加入2.5 mM的葡萄糖和5mM的硫代硫酸钠，脂肪酸的产量可以比对照提高78%。而低浓度的葡萄糖和硫代硫酸钠对Chlorella sp.脂肪酸组成影响变化不明显，甚至在硫代硫酸钠存在下令人感兴趣的EPA含量还略有升高。显然，在Chlorella sp.培养中同时加入低浓度的葡萄糖和硫代硫酸钠是极具潜力的提高脂产量的方法，也可作为提高培养微藻其它活性物质产量借鉴的方法。在不久的将来，这种培养方法很可能发展成为生产实践中提高Chlore sp．乃至其它微藻脂肪酸、EPA和其它活性物质产量的经济有效的新途径。

Effects of molecular structures on the olfactory responses of phospholipid membranes to four alcohols

In order to understand the relationship between phospholipid molecular structures and their olfactory responses to odorants, we designed and synthesized four phosphatidylcholine analogues with different long hydrocarbon (CH) chains and selected three natural phospholipids with different head-groups. By using interdigital electrodes (IEs) as olfactory sensors (OSs), we measured the responses of the Ifs coated with these seven different lipid membranes to four alcohol vapors in a gas flow system. The Ifs voltage changes were recorded and the voltage-relative saturate vapor pressure (V-P/P degrees) curves were also plotted. It was found that with a methyl (-CH3) placed at the C-8 position in the 18-carbon chain, the olfactory responses could be improved about ten times and with conjugated double bonds (C=C) in the long chains, the sensitivity could be increased by 3 similar to 4 orders of magnitude. As to head-groups, choline is preferred over ethanolamine and serine in phospholipid structures in terms of high olfactory sensitivity: These results are expected to be useful in further designing and manufacturing lipid-mimicking OSs. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.

LIPID MICRORESISTOR AS MIMICKING OLFACTORY SENSOR - THE RULE OF THE RESPONSE OF LIPIDS TO C-1-C-4 ALCOHOLS

Phosphatidylcholine (PC) and six other PC-similar lipids are coated on interdigital electrodes, IEs, as sensitive membranes. Eight alcohols (C-1-C-4) are tested in a flow system at room temperature. It is found that all responses are log(response)-log(concentration) linear relations. These results agree with Steven's law in psychophysics. Moreover, the thresholds of the sensors are coincident with human olfactory thresholds. The authors have analysed the data of the lipid hypothesis suggested by Kurihara et al. We have found that this hypothesis is also in agreement with Steven's law. Lipid microresistors are real mimicking olfactory sensors. A definition of an olfactory sensor is suggested.

Characterization and property of DNA incorporated bilayer lipid membranes

Calf-thymus DNA-incorporated bilayer lipid membranes supported on a glassy carbon (GC) electrode was prepared by making layers of phosphatidylcholine dimyristoyl (DMPC) on GC electrode. DNA in the BLM was characterized by cyclic voltammetry, IR and AFM, and lipid layers formed on the GC electrode were demonstrated to be a bilayer lipid membrane by electrochemical impedance experiment. In IR and AFM experiments the findings indicated that DNA was incorporated into BLM. The ion channel of bilayer lipid membranes incorporated was studied. The result showed that the ion channel was opened in the presence of the stimulus quinacrine. In the absence of quinacrine the channel was switched. The process can repeat itself many times. The impedance spectroscopy measurements demonstrate that the stimulus quinacrine opens the channel for permeation of marker ion. The mechanism of forming an ion channel was investigated.

Interaction of K7Fe3+P2W17O62H2 with supported bilayer lipid membranes on platinum electrode

The influence of K7Fe3+P2W17O62H2 on l-alpha-phosphatidylcholine/cholesterol bilayer lipid membrane on Pt electrode was studied by voltammetry and AC impedance spectroscopy. The interaction of the polyoxometalates with the BLM can promote the access of Ru(NH3)(6)(3+) and [Fe(CN)(6)](3-/4-) to the electrode surface. It was found that some kind of pores had been formed on the BLM by AFM. The phenomenon is attributed to the interaction of K7Fe3+P2W17O62H2 with phosphatidylcholine phosphate groups located in its outer leaflet. Experimental results are helpful to understand the biological activity of the polyoxometalates in vivo.

Conformation change of horseradish peroxidase in lipid membrane

The electrochemical behavior of horseradish peroxidase (HRP) in the dimyristoyl phosphatidylcholine (DMPC) bilayer on the glassy carbon (GC) electrode was studied by cyclic voltammetry. The direct electron transfer of HRP was observed in the DMPC bilayer. Only a small cathodic peak was observed for HRP on the bare GC electrode. The electron transfer of HRP in the DMPC membrane is facilitated by DMPC membrane. UV-Vis and circular dichroism (CD) spectroscopy were used to study the interaction between HRP and DMPC membrane. On binding to the DMPC membrane the secondary structure of HRP remains unchanged while there is a substantial change in the conformation of the heme active site. Tapping mode atomic force microscopy (AFM) was first applied for the investigation on the structure of HRP adsorbed on supported phospholipid bilayer on the mica and on the bare mica. HRP molecules adsorb and aggregate on the mica without DMPC bilayer. The aggregation indicates an attractive interaction among the adsorbed molecules. The molecules are randomly distributed in the DMPC bilayer. The adsorption of HRP in the DMPC bilayer changes drastically the domains and defects in the DMPC bilayer due to a strong interaction between HRP and DMPC films.

Study of the interaction between lanthanide ions and a supported bilayer lipid membrane by cyclic voltammetry and ac impedance

The interaction of lanthanide ions with a supported bilayer lipid (1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine) membrane (sBLM) was investigated by cyclic voltammetry and ac impedance spectroscopy in this paper, Lanthanide can affect the conformation of the supported bilayer lipid membrane and cause pore formation. Through the pores, Fe(CN)(6)(3) (4) can reach the electrode surface and show its redox behaviour. Furthermore the redox currents or Fe(CN)(6)(3) (4) increased with increasing concentration of lanthanides and leveled off at 1.2 muM for Eu3+. The interaction ability of three lanthanides with sBLM follows the sequence: Eu3+ > Tb3+ > La3+.

Formation of a supported hybrid bilayer membrane on gold: A sterically enhanced hydrophobic effect

Adsorption of a monolayer of didecanoyl-L-alpha-phosphatidylcholine (DDPC) from dispersions of small unilamellar vesicles onto hydrophobic surfaces was investigated by mean of cyclic voltammetry and impedance spectroscopy. The hydrophobic surfaces were self-assembled monolayers of 2-mereapto-3-n-octylthiophene (MOT) on gold. One characteristic of the MOT monolayer is its permeability to organic molecules in aqueous solution, thus providing a more energetically favorable hydrophobic surface for the addition of phospholipid vesicles. The kinetics of the lipid monolayer formation were followed by measuring the time-dependent interfacial capacitance. Unusual values of thickness and capacitance of the MOT/ DDPC bilayers were observed. An interdigitating conformation of the bilayer structure was proposed to interpret the experimental results, The horseradish peroxidase reconstituted into the bilayer demonstrated the expected protein activity, showing practical use in research and in biosensor application.

Self-assembled monolayer growth of phospholipids on hydrophobic surface toward mimetic biomembranes: Scanning probe microscopy study

Atomic force microscopy (AFM) and lateral force microscopy (LFM) were used simultaneously to analyze a model membrane bilayer structure consisting of a phospholipid outer monolayer deposited onto organosilane-derivatized mica surfaces, which were constructed by using painting and self-assembly methods. The phospholipid used as outer monolayer was dimyristoylphosphatidylcholine (DMPC). The hydrocarbon-covered substrate that formed the inner half bilayer was composed of a self-assembly monolayer (SAM) of octadecyltrichloroorganosilane (OTS) on mica. SAMs of DMPC were formed by exposing hydrophobic mica to a solution of DMPC in decane/isobutanol and subsequently immersing into pure water. AFM images of samples immersed in solution for varying exposure times showed that before forming a complete monolayer the molecules aggregated into dense islands (2.2-2.6 nm high) on the surface. The islands had a compact and rounded morphology. LFM, coupled with topographic data obtained with the atomic force mode, had made possible the distinction between DMPC and OTS. The rate constant of DMPC growth was calculated. This is the first systematic study of the SAM formation of DMPC by AFM and LFM imaging. It reveals more direct information about the film morphology than previous studies with conventional surface analytical techniques such as infrared spectroscopy, X-ray, or fluorescence microscopy.

Electrocatalytic oxidation of ascorbic acid by ferrocene in lipid film cast on a glassy carbon electrode

A ferrocene-dimyristoyl phosphatidylcholine (DMPC) film electrode was prepared by casting the solution of ferrocene and DMPC in chloroform onto a glassy carbon electrode surface. Ferrocene retained in the biological membrane gave a couple of irreversible peaks of cyclic voltammogram. The electrode exhibited good electrocatalytic activity for the oxidation of ascorbic acid (H(2)A) in phosphate buffer (pH 6.64) with an anodic peak potential of +340 mV (vs. Ag/AgCl). The anodic current was directly proportional to the square root of the scan rate below 150 mV s(-1). The influence of the pH value was investigated and it was observed that pH 6.64 was the suitable value to the anodic peak potential and current. The thickness of the film and the interference of uric acid were also studied. The electrode can be used to determine H(2)A in the presence of equimolar uric acid. The catalytic peak current increased linearly with the concentration of H(2)A in the range of 1 X 10(-4)-5 X 10(-3) mol L-1.

NMR and FT-Raman studies on the interaction of lanthanide ions with sphingomyelin bilayers

The interactions of lanthanide ions with sphingomyelin bilayers have been studied by using 2D NOESY spectroscopy and FT-Raman spectroscopy methods. The results indicate that lanthanide ions, as well as divalent calcium, combine mainly to the phosphate group in the polar headgroup and do not change the conformation of O-C-C-N+ backbone in the choline group of sphingomyelin bilayers. The polar headgroup is still extending parallel to the bilayer surface and O-C-C-N+ group is still in its gauche conformer.