On the wettability of lipid DPPC films

By employing temperature-programmed desorption and time-of-flight secondary ion mass spectroscopy, the adsorption of water on the hydrophilic and hydrophobic surfaces of a lipid (DPPC) film has been investigated. It could be shown that it is possible to prepare lipid films ex situ with a preferential orientation of the lipid molecules on a solid support and to retain their specific properties under ultrahigh vacuum conditions. The water adsorption and desorption kinetics on the hydrophilic and hydrophobic surfaces provided by a lipid film are discussed in terms of their structural and chemical properties.     

Improvement on Hydrophilic and Hydrophobic Properties of Glass Surface Treated by Nonthermal Plasma Induced by Silent Corona Discharge

A fundamental study was conducted to investigate the improvement of the hydrophilic and hydrophobic properties of the glass surface using the atmospheric-pressure nonthermal plasma. The plasma was induced between the two parallel electrodes with a dielectric barrier using an AC 60Hz high voltage power supply. The objective is to demonstrate the possibility of the elimination of the windshield wiper from automobiles. Two approaches were undertaken for modifying the glass surface: one is hydrophilic approach using plasma alone and the other is hydrophobic approach using the combination of hydrophobic chemical and nonthermal plasma. The plasma application provided excellent hydrophilic properties (less than 4° of contact angle). However, the durability did not last for more than one day. The combination of hydrophobic Tri Alkoxy Silane (TAS) chemical coating and nonthermal plasma showed an excellent hydrophobic property and extended durability, more than five times more durable compared with TAS alone.     

Influence of water on the surface of hydrophilic and hydrophobic room-temperature ionic liquids

Vibrational spectroscopy, sum frequency generation, has been used to study the gas-liquid interface of imidazolium-based, room-temperature ionic liquids. The ionic liquids are divided into two categories on the basis of their miscibility with water, as hydrophobic (immiscible) and hydrophilic (miscible). The spectroscopy results indicate that water will reorient the cations of the hydrophobic ionic liquid, while in the hydrophilic ones they remain unaffected. Thus, under low water conditions the plane of the imidazolium ring remains parallel to the surface for both types of ionic liquid. However, at high water content the ring will reorient to along the surface normal for the hydrophobic ionic liquid but remain parallel to the surface for the hydrophilic one. This is a reversible process.     

Rheological properties of polyurethane adhesives containing silica as filler: influence of the nature and surface chemistry of silica

Four silicas, two fumed silicas (one hydrophilic and one hydrophobic) and two precipitated silicas (one hydrophilic and one hydrophobic), were added as filler to solvent‐based polyurethane (PU) adhesive formulations. In general, the addition of silica increased the viscosity, the storage and loss moduli of the PU adhesives but only the hydrophilic fumed silica exhibited pseudoplasticity and thixotropy. The rheological properties imparted by adding filmed silicas to PU adhesive solutions were more noticeable than that of precipitated silicas. Interactions between the hydrophilic fumed silica, the polyurethane and/or the solvent seemed to be responsible for the improved rheological properties of filled PU adhesives.     

The Natural Compound Hydrophobic Usnic Acid and Hydrophilic Potassium Usnate Derivative: Applications and Comparisons

Usnic acid is the best-studied lichen metabolite, presenting several biological activities, such as antibacterial, immunostimulating, antiviral, antifungal, anti-inflammatory, and antiparasitic agents; despite these relevant properties, it is a hydrophobic and toxic molecule. In this context, scientific research has driven the development of innovative alternatives, considering usnic acid as a source of raw material in obtaining new molecules, allowing structural modifications (syntheses) from it. The purpose is to optimize biological activities and toxicity, with less concentration and/or response time. This work presents a literature review with an analogy of the hydrophobic molecule of usnic acid with its hydrophilic derivative of potassium usnate, emphasizing the elucidation and structural characteristics, biological activities, and toxicological aspects of both molecules, and the advantages of using the promising derivative hydrophilic in different in vitro and in vivo assays when compared to usnic acid.     

The theory of metal electronucleation applied to the study of fundamental properties of liposomes

This short review describes how the theory of electrochemical metal nucleation considering non-stationary effects due to the activation of latent nucleation sites has been successfully translated and applied to describe phenomena observed on lipid membranes. This rather unexpected connection is merely formal, but has resulted in a completely new approach in liposome research. It has been proposed that hydrophobic active sites spontaneously and constantly appear and disappear on lipid membranes. These sites control the affinity of liposomes for hydrophobic surfaces and determine the permeability of the lipid membrane to small hydrophilic molecules. Thus, the kinetic models for liposome adhesion on hydrophobic substrates and for the spontaneous leakage of liposomal content are identical to that of non-stationary nucleation mentioned above. Therefore, the broad scope of the available work on metal nucleation has facilitated the interpretation of the data obtained in liposome research. Future applications of the nucleation model in the realm of liposomes are also discussed.     

How can azobenzene block copolymer vesicles be dissociated and reformed by light?

The underlying mechanism of UV light-induced dissociation and visible light-induced reformation of vesicles formed by an azobenzene diblock copolymer was investigated. These processes were studied in situ by monitoring changes in optical transmittance of the vesicular solution while being exposed to UV or visible light irradiation. The results indicate that the UV-induced dissociation of the vesicles results from their thermodynamic instability due to a shift of the hydrophilic/hydrophobic balance arising from the trans-cis isomerization, while their reaggregation takes place upon visible light irradiation that shifts the hydrophilic/hydrophobic balance in the opposite direction after the reverse cis-trans isomerization. The study suggests a specific design principle for obtaining UV light-dissociable and visible light-recoverable vesicles based on azobenzene block copolymers. On one hand, the structure of azobenzene moiety used in the hydrophobic block should have a small (near zero) dipole moment in the trans form and a significantly higher dipole moment in the cis form, which ensures a significant increase in polarity of the hydrophobic block under UV light irradiation. On the other hand, the hydrophilic block should be weakly hydrophilic. The conjunction of the two conditions can make the light-induced shift of the hydrophilic/hydrophobic balance important enough to lead to the reversible change in vesicular aggregation.     

SARS病毒E蛋白的计算机模拟的初步研究

以粗粒化的多肽链模型进行了SARS病毒包膜中E蛋白的计算机模拟,描述了该蛋白质空间构象的概貌.首先扩展了多肽链的HP模型,使之能够用于研究在水或脂环境下蛋白质折叠的行为,并且考虑了全部氨基酸残基疏水相互作用能的差异.相关格子链的MonteCarlo模拟显示了很高的计算效率.模拟再现了蛋白质的coil-globule转变,验证了蛋白质序列分布的重要性.结果表明,在水环境中,E蛋白质空间结构由紧致的疏水内核和部分向外延伸的亲水片段组成;在脂环境中,中部疏水片段会成为向外延伸的环,而当两侧紧致的亲水片段分开时,则形成桥.     

Water-templated transmembrane nanopores from shape-persistent oligocholate macrocycles

Hydrophobic interactions normally are not considered a major driving force for self-assembling in a hydrophobic environment. When macrocyclic oligocholates were placed within lipid membranes, however, the macrocycles pulled water molecules from the aqueous phase into their hydrophilic internal cavities. These water molecules had strong tendencies to aggregate in a hydrophobic environment and templated the macrocycles to self-assemble into transmembrane nanopores. This counterintuitive hydrophobic effect resulted in some highly unusual transport behavior. Cholesterol normally increases the hydrophobicity of lipid membranes and makes them less permeable to hydrophilic molecules. The permeability of glucose across the oligocholate-containing membranes, however, increased significantly upon the inclusion of cholesterol. Large hydrophilic molecules tend to have difficulty traversing a hydrophobic barrier. The cyclic cholate tetramer, however, was more effective at permeating maltotriose than glucose.     

Design and synthesis of cluster neoglycoconjugates based on D-glucose

Synthetic approaches have been developed to tetravalent neoglycoconjugates with different structures of the hydrophobic fragment and D-glucose fragment as branching core. The syntheses have been accomplished by preparation of blocks with terminal C≡C triple bonds and hydrophobic fragment and hydrophilic component (lactose derivative), followed by their conjugation.     

Lectin recognition of liposomes containing neoglycolipids. Influence of their lipidic anchor and spacer length

Eleven neoglycolipids were synthesized with a membrane anchor (cholesterol or Guerbet alcohols) attached, via a hydrophilic spacer, to a potential lectin-recognized sugar moiety (N-acetylglucosamine: GlcNAc). Neoglycolipids G24-0, G28-0 and G32-0, with a C₂₄, C₂₈ and C₃₂ Guerbet alcohol residue, had no spacer, while neoglycolipids G24-3, G28-3, G32-3 contained a triethoxy spacer. Cholesteryl neoglycolipids chol-1 to chol-4 and chol-7 contained one to four and seven ethoxy units. All the cholesteryl neoglycolipids were incorporated into liposomes, while, for the Guerbet derivatives, the presence (or not) of a spacer and the length of their alkyl chains played an important role for obtaining mixed liposomes. The abilities of liposomes to be recognized by wheat germ agglutinin (WGA) were measured as an increase of the absorbance at 450 nm. Significant WGA-induced aggregations were obtained with liposomes containing neoglycolipids chol-3, chol-4, chol-7, G28-3 and G32-3. As neoglycolipid G24-3 was not recognized, the accessibility of its GlcNAc moiety for WGA depended not only on the spacer length but on the nature of the anchor. The WGA-induced aggregations increased with increasing lectin concentrations until a maximum value, which depended on the nature of the neoglycolipid. The highest aggregation obtained with G28-3 and G32-3 occurred for a WGA–neoglycolipid mole ratio superior to the ratio observed with chol-3, chol-4 and chol-7. A preincubation of WGA with free GlcNAc did not inhibit the aggregation between WGA and mixed liposomes, demonstrating a greater affinity of WGA for the neoglycolipid GlcNAc than for free GlcNAc.     

An Efficient Method for the Conjugation of Hydrophilic and Hydrophobic Components by Solid‐Phase‐Assisted Disulfide Ligation

Chemical conjugation between hydrophilic and hydrophobic components is difficult because of their extremely different solubility. Herein, we report a new versatile method with a solid‐phase‐assisted disulfide ligation to overcome the difficulty of conjugation attributed to solubility. The method involves two steps in a one‐pot process: 1) loading of a hydrophobic molecule onto a resin in an organic solvent, and 2) release of the solid‐supported hydrophobic molecule as a conjugate with a hydrophilic molecule into an aqueous solvent. This strategy allows the use of a suitable solvent system for the substrates in each step. Conjugates of a water‐insoluble drug, plinabulin, with hydrophilic carriers that could not be prepared by solution‐phase reactions were obtained in moderate yields (29–45 %). This strategy is widely applicable to the conjugation of compounds with solubility problems.     

Bridging across length scales: multi-scale ordering of supported lipid bilayers via lipoprotein self-assembly and surface patterning

We show that a two-step process, involving spontaneous self-assembly of lipids and apolipoproteins and surface patterning, produces single, supported lipid bilayers over two discrete and independently adjustable length scales. Specifically, an aqueous phase incubation of DMPC vesicles with purified apolipoprotein A-I results in the reconstitution of high density lipoprotein (rHDL), wherein nanoscale clusters of single lipid bilayers are corralled by the protein. Adsorption of these discoidal particles to clean hydrophilic glass (or silicon) followed by direct exposure to a spatial pattern of short-wavelength UV radiation directly produces microscopic patterns of nanostructured bilayers. Alternatively, simple incubation of aqueous phase rHDL with a chemically patterned hydrophilic/hydrophobic surface produces a novel compositional pattern, caused by an increased affinity for adsorption onto hydrophilic regions relative to the surrounding hydrophobic regions. Further, by simple chemical denaturation of the boundary protein, nanoscale compartmentalization can be selectively erased, thus producing patterns of laterally fluid, lipid bilayers structured solely at the mesoscopic length scale. Since these aqueous phase microarrays of nanostructured lipid bilayers allow for membrane proteins to be embedded within single nanoscale bilayer compartments, they present a viable means of generating high-density membrane protein arrays. Such a system would permit in-depth elucidation of membrane protein structure-function relationships and the consequences of membrane compartmentalization on lipid dynamics.     

Effect of chlorogenic acid on the phase transition in phospholipid and phospholipid/cholesterol membranes

Chlorogenic acid (CGA) is present in many plants, especially in green coffee, dry plums, and bilberries. It is an important bioactive polyphenol. Studies showed that CGA has an antioxidative, bacteriostatic, anticancer, antiviral, and anti-inflammatory activity. Despite great interest in this compound, its interaction with the lipid model membrane has not yet been investigated. To better understand the relationship between the biological activity of CGA and its interaction with biological membranes, the thermotropic behavior of model lipid membranes was investigated. The effect of CGA on the model lipid membrane, specifically on the lipid bilayer phase transitions, was examined by the combined methods: differential scanning calorimetry and fluorescence spectroscopy. In particular, the degree of packing order of the hydrophilic phase of the lipid bilayer was determined using the fluorimetric method with Laurdan and Prodan probes, while the fluorescence anisotropy of the hydrophobic phase with the DPH and TMA-DPH probes. The results of the study show that CGA incorporates mainly into the hydrophilic part of membrane, changing the packing order of the polar heads of lipids. No significant changes were recorded in membrane fluidity of the hydrophobic membrane region, for the fluorescence anisotropy practically did not change. One can thus infer that CGA does not penetrate deep into the hydrophobic area of the membrane.     

The interaction of a peptide with a scrambled hydrophobic/hydrophilic sequence (Pro-Asp-Ala-Asp-Ala-His-Ala-His-Ala-His-Ala-Ala-Ala-His-Gly) (PADH) with DPPC model membranes: a DSC study

Depending on their hydrophobicity, peptides can interact differently with lipid membranes inducing dramatic modifications into their host systems. In the present paper, the interaction of a synthetic peptide with a scrambled hydrophobic/hydrophilic sequence (Pro-Asp-Ala-Asp-Ala-His-Ala-His-Ala-His-Ala-Ala-Ala-His-Gly) (PADH) with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) model membranes has been investigated by differential scanning calorimetry (DSC), adopting three different experimental approaches. In the first, the peptide is forced to be included into the hydrocarbon region of the lipid bilayer, by codissolving it with the lipid giving rise to mixed multilamellar vesicles–peptide systems; in the second, this system is passed through an extruder, thus producing large unilamellar vesicles–peptide systems; in the third, it is allowed to interact with the external surface of the membrane.

The whole of the DSC results obtained have shown that the incorporation of the peptide into the lipid bilayer by means of the first method induces a decrease in the enthalpy of the gel–liquid crystal transition of the membrane and a shift of the transition to the lower temperatures, thus resembling, in spite of its prevalently hydrophilic nature, the behavior of transbilayer hydrophobic peptides. The extrusion of these systems creates unilamellar vesicles free of peptides but of smaller size as evidenced by the decreased cooperativity of the transition. The peptide, added externally to the DPPC model membrane, has no effect on the phase behavior of the bilayer.

These findings suggest that the effect of the interaction of scrambled hydrophobic/hydrophilic peptides into lipid bilayers strongly affects the thermotropic behavior of the host membrane depending on the preparation method of the lipid/peptide systems. The whole of the results obtained in the present paper can be useful in approaching studies of bioactive peptides/lipids systems.     

Cyclic voltammetry of highly hydrophilic ions at a supported liquid membrane

Cyclic voltammetry has been used to study the coupling of ion transfer reactions at a liquid membrane. The liquids are either supported by a porous hydrophobic membrane (polyvinylidene difluoride, PVDF) when the organic solvent is non-volatile (o-nitrophenyloctylether) or are merely a free standing organic solvent layer such as 1,2-dichloroethane comprised between two hydrophilic dialysis membranes supporting the adjacent aqueous phases. The passage of current across the liquid membrane is associated with two ion transfer reactions across the two polarised liquid liquid interfaces in series. It is shown that it is possible to study the transfer of highly hydrophilic ions at one interface by limiting the mass transfer of the other ion transfer reaction at the other interface. Indeed, for systems comprising an ion M in one aqueous phase and a reference ion R partitioned between the membrane and the other aqueous phase, the observed and simulated cyclic voltammograms have a half-wave potential determined by the Gibbs energy of transfer of M transferring at one interface and by the limiting mass transfer of R at the other interface. This new methodology opens a way to measure the Gibbs energy of transfer of highly hydrophilic or hydrophobic ions, which usually limits the potential window at single liquid liquid interfaces (ITIES).     

Hydrophobic forces and hydrogen bonds in the adhesion between retinoid-coated surfaces

Interactions between hydrophobic chains of lipid monolayers and interactions between hydrophilic headgroups of lipid bilayers (with or without a molecular recognition step) are now well documented, especially for commonly used lipids. Here, we report force measurements between a new class of fluorinated lipid layers whose headgroups (synthetic ligands of retinoid receptors) display a very unusual polar/apolar character and can interact via a combination of hydrophobic forces and hydrogen bonds. Although these two interactions produce adhesion and are therefore not easily distinguishable, we show that it is possible to extract both contributions unambiguously. Experiments are performed both in pure water, where the adhesion is a combination of hydrophobic forces and hydrogen bonds, and in Tris buffer, where the hydrophobic effect is the dominant short-range attractive force. The contribution of hydrophobic forces scaled down to molecular interactions is deduced from force versus distance profiles, and the same value is found independently in pure water and Tris buffer, about 1 kBT. We also show that retinoid lipid layers attract each other through a very long-range (100 nm) exponential force, which is insensitive to the pH and the salinity. The origin of this long-range attraction is discussed on the basis of previously proposed mechanisms.     

3D-QSAR study on heterocyclic topoisomerase II inhibitors using CoMSIA

Selective topoisomerase II (Topo II) inhibitors have interested to a great extent for the design of new antitumoral compounds in recent years. Comparative molecular similarity indices analysis (CoMSIA) was performed on a series of previously synthesized benzoxazole, benzimidazole, and oxazolo(4,5-b)pyridine derivatives as eukaryotic Topo II inhibitors. A training set of 16 heterocyclic compounds was used to establish the CoMSIA model. They were constructed and geometrically optimized using SYBYL v7.0. The predictive ability of the model was assessed using a test set of 7 compounds. The best model has demonstrated a good fit having r2 value of 0.968 and cross-validated coefficient q2 value as 0.562 including steric and hydrophobic fields. The hydrophobic interactions showed a dominant role for increasing Topo II inhibitor activity and hydrophilic substituent was found more important than hydrophobic one on the 5 or 6 position of benzazole moiety. The model obtained from the present study can be useful for the modification and/or evaluation of the development of new Topo II inhibitors as potential antitumor compounds.     

Permeability of the outer membrane of bacteria.

The outer membrane of Gram-negative bacteria is an attractive system for the study of the structure-function relationships in biological membranes. This membrane has, inter alia, the task of regulating the inflow of nutrients and outflow of waste products. Investigations with the aid of mutants showed that there are at least two general pathways for the diffusion of small molecules across the outer membrane: one for hydrophobic and one for hydrophilic compounds. In the case of the “hydrophobic pathway” the hydrophobic compound dissolves in the interior of the membrane and then crosses the membrane in accordance with the partition coefficient. In wild-type forms of enteric bacteria this pathway cannot be used—presumably owing to the absence of regions with phospholipid bilayers. Small hydrophilic molecules, on the other hand, penetrate the membrane through water-filled pores.