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A Gliozzi

Publications and source records attributed to A Gliozzi.

At least 19 recordsLinked to original sources
PubMed2005

Bipolar tetraether lipids: chain flexibility and membrane polarity gradients from spin-label electron spin resonance.

Membranes of thermophilic Archaea are composed of unique tetraether lipids in which C40, saturated, methyl-branched biphytanyl chains are linked at both ends to polar groups. In this paper, membranes composed of bipolar lipids P2 extracted from the acidothermophile archaeon Sulfolobus solfataricus are studied. The biophysical basis for the membrane formation and thermal stability is investigated by using electron spin resonance (ESR) of spin-labeled lipids. Spectral anisotropy and isotropic hyperfine couplings are used to determine the chain flexibility and polarity gradients, respectively. For comparison, similar measurements have been carried out on aqueous dispersions of diacyl reference lipid dipalmitoyl phosphatidylcholine and also of diphytanoyl phosphatidylcholine, which has methyl-branched chains. At a given temperature, the bolaform lipid chains are more ordered and less flexible than in normal bilayer membranes. Only at elevated temperatures (80 degrees C) does the flexibility of the chain environment in tetraether lipid assemblies approach that of fluid bilayer membranes. The height of the hydrophobic barrier formed by a monolayer of archaebacterial lipids is similar to that in conventional fluid bilayer membranes, and the permeability barrier width is comparable to that formed by a bilayer of C16 lipid chains. At a mole ratio of 1:2, the tetraether P2 lipids mix well with dipalmitoyl phosphatidylcholine lipids and stabilize conventional bilayer membranes. The biological as well as the biotechnological relevance of the results is discussed.

Electron Spin Resonance Spectroscopy↗
PubMed2004

Self-assembled monolayers of organosulphur molecules bearing calix[4]arene moieties.

We investigate the self-assembly of modified calix[4]arene on gold surfaces. Calix[4]arene was modified through a reaction sequence which led to assembling of the crown-5 moiety and to the insertion of two thioether groups into the starting molecule. The so-obtained calix[4]arene-crown-5 bis(7-thiatridecyloxy) (hereafter called calix[4]arene) was in the stable 1,3-alternate conformation. The calix[4]arene/gold interface was investigated by means of spectroscopic ellipsometry (SE), scanning tunneling microscopy (STM) and cyclic voltammetry (CV). SE data indicate a layer thickness compatible with the formation of a monomolecular layer. This result is confirmed by STM imaging which shows the formation of a high density of small pits, one gold layer deep, a typical feature of self-assembled organosulphur monolayers on gold. CV measurements performed in presence of the [Ru(NH(3))(6)(2+/3+)] redox couple indicate a passivation of the metal electrode, resulting in a reduction of the redox current, after the layer deposition. CV has also been used to investigate the selectivity properties of calix[4]arene-covered gold electrodes by measuring the redox current decrease in the presence of different salt solutions. It is found that calix[4]arene-covered electrodes are able to complex K(+) and Ba(2+), while no complexation is observed in the case of Li(+), Na(+), Cs(+), Mg(2+) and Ca(2+).

Adsorption↗
PubMed2003

Encapsulated yeast cells inside Paramecium primaurelia: a model system for protection capability of polyelectrolyte shells.

One of the most promising applications of encapsulated living cells is their use as protected transplanted tissue into the human body. A suitable system for the protection of living cells is the use of nano- or microcapsules of polyelectrolytes. These shells can be deposited easily on top of the cells by means of a layer-by-layer technique. An interesting feature of the capsules is the possibility to control their properties on a nanometre level, tuning their wall texture via the preparation conditions. Here we introduce a model system to test the protection ability of polyelectrolyte capsules. Common bakery yeast cells were encapsulated. They were coated with a fluorescently labelled shell at conditions known to guarantee cell survival, and the cell interior was stained with DAPI. The protozoan Paramecium primaurelia was incubated with this double-stained living yeast and visualized by means of two-photon excitation fluorescence microscopy. Cross-sections of the dye-stained material as well as autofluorescence of the fixed protozoan allowed us to follow the digestion of the coated yeast with time. Our investigation reveals that capsules prepared under these deposition conditions are permeable to lysosomal enzymes, leading to degradation of the yeast inside the intact capsules. Our preliminary results indicate the suitability of the introduced model as a test system of this permeability.

Animals↗
PubMed2002

Confocal laser scanning microscopy to study formation and properties of polyelectrolyte nanocapsules derived from CdCO3 templates.

Three-dimensional confocal laser scanning microscopy (CLSM) was used as an essential investigation method to obtain information about the formation and morphological characteristics of nanocapsules. Nanocapsules are built by layer-by-layer deposition of alternatively charged polyelectrolytes on templates forming nanostructured hollow shells. CLSM is unique in allowing for monitoring of the core dissolution process in real time and for studying nanocapsule functioning in hydrated conditions within a three-dimensional and temporal framework. Since we are also interested in the identification of other possible templates, we briefly report on the use of yeast cells as biocolloidal cores monitored by means of two-photon microscopy. Here we focus our attention on the use of CdCO(3) crystals as template candidates for the preparation of stable capsules. Both cubic and spherical CdCO(3) cores have been produced. Cubic cores exhibit higher monodispersity and smaller size compared to spherical ones. Capsules templated on these cores have a higher surface-to-volume ratio that is valuable for applications related to drug delivery, functional properties of the shells and adsorption of proteins, and other biologically relevant molecules. Microsc. Res. Tech. 59:536-541, 2002.

Journal Article↗
PubMed2002

Impedance measurements of self-assembled lipid bilayer membranes on the tip of an electrode.

Supported lipid membranes were self-assembled on the tip of a freshly cleaved silver wire, in the presence of an appropriate polarization voltage, to facilitate, during the membrane formation, the organization of the lipids into an ordered structure. Radiowave impedance spectroscopy measurements have been carried out to provide information on the relaxation properties of the system. We have measured the conductometric and dielectric properties of bilayers built up of different lipids [dipalmitoylphosphatidic acid (DPPA), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), linoleic acid (LIN)] in a wide frequency range (from 10(3) to 10(6) Hz) and in electrolyte solutions of different ionic strengths, in the presence of uni-univalent (KCl) and di-univalent (CaCl(2), MgCl(2), ZnCl(2)) electrolytes. This made it possible to measure the influence of different cations and different lipid compositions on the membrane properties. In particular, we have found a different capacitive behaviour of the supported lipid bilayer membrane (s-BLM) structure in the presence of different counterions in the electrolyte solution. This peculiarity offers the opportunity for the preparation of a variety of biosensors with diverse applications in membrane biophysics, biochemistry and biotechnology.

Biosensing Techniques↗
PubMed2001

An atomic force microscopy investigation of protein crystal surface topography.

Tapping mode atomic force microscopy was employed to study the surface structure of different protein crystals in a liquid environment. The (101) face of hen egg-white lysozyme crystals and the (111) face of horse spleen ferritin crystals were studied. On the (101) face of lysozyme crystals we observed islands delimitated by micro-steps and elongated in the [010] direction. The elongation direction coincides with the preferential growth direction predicted by a growth model reported in the literature. The islands observed on the ferritin (111) face are also delimitated by micro-steps but have circular symmetry. Sectioning of the images allowed us to measure the step heights. The surface free energy was estimated from the growth step morphology. Molecular resolution was achieved for ferritin crystals, showing a hexagonal surface packing, as expected for the molecular lattice of a (111) face in a fcc crystal.

Animals↗
PubMed2001

Improvement of the quality of self assembled bilayer lipid membranes by using a negative potential.

Self-assembled lipid bilayer membranes (s-BLMs) on the tip of Teflon-coated silver electrodes were formed according to the T. Tien method. Their formation process and properties were investigated by capacitance and voltage current cycle measurements. The stability of the membranes was improved and defects were eliminated through the application of a negative dc potential during formation. Cyclic current-voltage measurements were applied to probe membrane integrity, by using an electrolyte interacting with the silver electrode. Oxidation and reduction peaks were observed for non defect-free membranes. These peaks were caused by oxidation of the silver electrode tip and their occurrence was a very sensitive means of measuring membrane integrity. The membrane was a barrier for the ion transport from the electrolyte solution to the electrode surface, and thus defect-free membranes inhibited the appearance of the peaks. With the s-BLMs produced by the described method, binding of ions and proteins to the membrane could be measured repetitively and reproducibly through changes in the system capacitance and the shape of the cyclovoltammogram. The presence of divalent ions lead to a specific increase in total system capacitance of membranes from charged lipids. Protein binding was measured as a decrease of the capacitance, in accordance with the thickness increase of the total membrane after binding. The facility of production and the sensitivity of the aforementioned substances could make the s-BLMs, produced by the described method, a valuable system to be developed in the field of biosensing.

Electrochemistry↗
PubMed1996

Interfacial air/water proton conduction from long distances by sulfolobus solfataricus archaeal bolaform lipids.

The stability, structural organization, and the ability to transfer protons long distances have been investigated in monolayers formed from archael bolaform lipids at the air/water interface. The lipids employed were the fractions GroR2Gro (R represents an acyl group with variable chain length typically consisting of 0-4 cyclopentane rings and 40 isoprenoid residues) and GroR2GroNon-Ol (Non-ol represents nonitol) extracted from Sulfolobus solfataricus by hydrolysis of the cytoplasmic membrane. GroR2-GroNon-ol films exhibit a very peculiar behaviour: the monolayer surface pressure increases with time, regardless of its low or high initial value. This finding is related to the possibility of GroR2GroNon-ol molecules to assume an upright (a metastable) or a U-shaped (stable) configuration. In the gaseous state and in the collapsed state of the film, no lateral proton conduction was observed. However, in the pressure range 0 < pi < 25 mN/m for GroR2Gro and 0 < pi < 30 mN/m for GroR2GroNon-ol monolayers, a lateral proton conduction at the air/water interface was observed. The structural organization of these bipolar lipids at the air/water interface can be related to the lateral proton conduction; it is possible to conclude that whatever configuration these lipids may adopt, they are able to structure the air/water interface in a hydrogen bond network that supports lateral proton conduction. This process may be ascribed to a percolation phenomenon occurring when the polar lipid head groups form a structured lattice of hydrogen bonds.

Air↗
PubMed1996

Valinomycin acts as a channel in ultrathin lipid membranes.

When the thickness of monolayer membranes formed by bolaform archaeal lipids is reduced to the approximate length of two valinomycin molecules, the zero-current conductance does not show any more a linear dependence on valinomycin concentration; instead, a quadratic behaviour is observed. This suggests that a dimer permeation pore is formed and therefore the conduction mechanism changes from carrier to channel.

Alkanes↗
PubMed1996

Effect of physical constraints on the mechanisms of membrane fusion: bolaform lipid vesicles as model systems.

Bolaform lipid vesicles were used to study the effect of physical constraints on membrane fusion. In these vesicles the membrane is organized in a single monolayer, because of the presence of covalent bonds in its middle plane. Therefore, the formation of fusion intermediates is subject to higher energy barriers and greater geometrical constraints than is usual in bilayer membranes. Bolaform lipids were extracted from the thermophilic archaeon Sulfolobus solfataricus. These lipids can be divided into two classes, the monosubstituted molecules, in which one of the polar heads is glycerol, and the bisubstituted molecules, endowed with two complex polar heads. The fusion process in vesicles composed of different mixtures of monosubstituted/bisubstituted molecules was studied by means of fluorescence techniques. Ca2+ or poly(ethylene glycol) was employed as a fusogenic agent. We found that fusion of such constrained membranes is still possible, provided that molecules able to mediate a structural rearrangement of the membrane are present. This condition is fulfilled by monosubstituted molecules, which are able to partition the glycerol headgroup in the apolar moiety. In addition, the presence of traces (approximately 5%) of the monopolar compound diphytanylglycerol is an important factor for fusion to occur. On the contrary, vesicles formed by bisubstituted molecules are unable to fuse, irrespective of the fusogen employed.

Cell Membrane↗
PubMed1995

Stability against temperature and external agents of vesicles composed of archael bolaform lipids and egg PC.

The bolaform lipid PLE extracted from the thermophilic archaeon Sulfolobus solfataricus and its mixtures with egg phosphatidyl-choline (egg PC) have been used to prepare sonicated vesicles. The leakage of entrapped calcein was continuously monitored by fluorescence dequenching. The half times of leakage have been used to compare vesicle stability under different conditions of temperature, lipid composition and presence of destabilizing agents like Ca2+ ions and poly(ethylene glycol) (PEG). It has been found that leakage is primarily modulated by the monopolar/bipolar lipid ratio. In particular, the half time of leakage for vesicles formed from a mixture of the polar lipid extract (PLE) and egg PC is characterized by a maximum at about 1:2 molar ratio. The free energy of mixing has been evaluated from pressure-area isotherms on monolayers at the air/water interface. The results indicate a non monotonous behaviour of the excess free energy of mixing as a function of the molar ratio and the occurrence of a minimum at a fixed molar ratio. The possible formation of a complex is discussed and compared with previous calorimetric measurements on similar compounds.

Calcium↗
PubMed1994

Calcium-induced interaction and fusion of archaeobacterial lipid vesicles: a fluorescence study.

The lipids extracted from the membrane of the thermophilic archaeobacterium Sulfolobus solfataricus have an unusual bipolar structure. Each molecule is formed by two isoprenoid chains (with up to four cyclopentane groups per chain) ether-linked at both ends to glycerol or nonitol groups. These groups can be variably substituted, mainly with complex sugars. Fluorescence resonance energy transfer, aqueous contents mixing and calcein release assays were employed to assess whether bipolar lipid vesicles were able to undergo a calcium-induced fusion process. The possibility of getting fusion depends strongly on the phase behaviour of the lipids. With vesicles formed by the natural polar lipid extract (PLE), a mixture showing a complex polymorphic behaviour, the fusion process was observed above the temperature T congruent to 60 degrees C at 15 mM Ca2+. By contrast, no fusion was observed in vesicles of P2, a fraction displaying only the lamellar phase. A dramatic change of the fusion process was observed when egg PC or P2 was added to PLE. In this case only lipid mixing, but not a real fusion process occurred at T > or = 60 degrees C. The dependence of such a process on ionic conditions has also been studied. Additional experiments involving surface tension measurements on monolayers have been performed to assess the importance of a surface tension increase to get fusion. In contrast to other monopolar lipid systems, no detectable change in surface tension has been observed in our bipolar lipids even in cases in which the fusion process is present.

Calcium↗
PubMed1994

Asymmetric black membranes formed by one monolayer of bipolar lipids at the air/water interface.

In this work a new technique is presented for the formation of black lipid membranes from a single monolayer of bipolar lipids at the air/water interface. The lipid, extracted from the thermophilic archaeobacterium Sulfolobus solfataricus, is characterized by two different polar heads. The membrane is formed with a technique similar to that introduced by Montal and Mueller; however, the lipid is spread only on one side of the teflon partition. Conductance in the presence of valinomycin, voltage-dependent capacitance, current-voltage measurements and electroporation indicate that, as expected, the membrane is asymmetric.

Air↗
PubMed1993

Electroporation in symmetric and asymmetric membranes.

We present results of electrical measurements performed both on symmetric and asymmetric membranes in current-clamp conditions. The current-voltage characteristic curve of the membranes shows a reversible conductance transition to a higher level above a critical potential Vc. The experimental results are interpreted in the light of the electroporation theory, which allows estimates of the line tension to be made. These estimates are compared to previous experimental findings or theoretical calculations. The behaviour of symmetric membranes of different chain lengths or consisting of mixtures of short and long chains indicates a strong dependence of Vc on the chain composition and on the presence of charges on the polar head. The electroporation process is also analyzed in asymmetric bilayers consisting of a charged and an uncharged monolayer, a condition which mimics that of natural membranes. Therefore it is possible to analyze the electrical forces acting on the uncharged monolayer due to the presence of charges on the other one, under several ionic-strength conditions. It is shown that the instability arises in the uncharged monolayer, while the coupling between the two monolayers triggers the electroporation process.

Electricity↗
PubMed1992

Molecular packing parameters of bipolar lipids.

The bipolar lipid fractions extracted from the thermophilic archaeobacterium Sulfolobus solfataricus have different chemical structures and geometrical shapes. The conditions which lead to the formation of vesicles were investigated in order to study the self-assembly of these molecules. Such conditions are fulfilled when an appropriate mixture of two different molecular species (both bipolar or bipolar and monopolar) is used. According to the theory introduced by Israelachvili and co-workers, lipid self-assembly results from the balance of interaction free energy, entropy and molecular geometry. We have shown that this theory can be extended to bipolar lipids, in spite of their more complex nature, and the experimental results obtained combining 1H-NMR, light scattering and entrapped volume techniques closely match theoretical expectations. To carry out calculations, it was necessary to introduce hypotheses about the disposition of bipolar molecules in the vesicle membrane. These hypotheses have been tested indirectly by measuring the transport properties mediated by carriers or channels, whose transport mechanism can be considered to be a probe of the membrane structure.

Hot Temperature↗
PubMed1990

Monopolar-bipolar lipid interactions in model membrane systems.

1H-NMR, dynamic light scattering and negative staining electron microscopy have been used to study the formation and physico-chemical properties of aqueous dispersions of mixtures of monopolar lipids extracted from Sulfolobus solfataricus. This microorganism is a thermophilic archaeobacterium growing optimally at about 85 degrees C and pH 3. The two hydrolytic fractions of the membrane complex lipids that have been studied are: the symmetric lipid glycerol dialkyl glycerol tetraether (GDGT) and the asymmetric lipid glycerol dialkyl nonitol tetraether (GDNT). Electron micrographs of pure and mixed GDNT and GDGT dispersions show the formation of complex structures. Only above a critical monopolar/bipolar lipid ratio, typical of the bipolar lipid, could closed structures be formed and good agreement was obtained in sizing with NMR, electron microscopy and dynamic light scattering. NMR spectra have been carried out at several temperatures from 25 degrees to 85 degrees C, to obtain information on the temperature-dependent structural, dynamic and permeability properties of the co-dispersed vesicles. The results are discussed in terms of the steric constraints and the chemico-physical interactions occurring among the different parts of the molecules and compared with previous studies performed with different physical techniques.

Glyceryl Ethers↗
PubMed1989

Conductance transition induced by an electric field in lipid bilayers.

A cooperative phenomenon showing a structural change in the organization of bilayer lipid membranes at a critical value of the applied electric field is presented. The transition is characterized by a sharp increase in conductance. The phenomenon can be observed under current-clamp conditions (rather than the usual voltage-clamp conditions) to avoid rupturing the membrane. At a critical potential value the conductance increases and therefore the potential decreases to keep the current constant. Results refer to membranes made of egg phosphatidylcholine (PC), diphytanoylphosphatidylcholine and cholesterol/egg PC. It is found that the critical potential at which the transition occurs depends dramatically on pH and ionic concentration, indicating that the electrical properties of the external surface determine the major characteristics of such a transition.

Cholesterol↗