Influence of cholesterol on tetraphenylborate transport through rat brain lipid artificial membranes

Summary The influence of cholesterol on TΦB⁻ transport through rat brain lipid model membranes has been studied by performing conductance studies. As a model system was used a rat brain lipid filter supported membrane. The weight percent of cholesterol as referred to total lipids was varied in a wide range. Cholesterol produced an increase of the conductance of membranes induced by the lipophilic anion tetraphenylborate. Moroever, an increase in the cholesterol mole fraction had a strong influence on steady-state I–V characteristics of rat brain lipid model membranes. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Undulations,steric interaction and cohesion of fluid membranes

Summary The theory of undulations of fluid membranes is reviewed and in some parts extended. The functional dependences of the steric interaction of undulating membranes are derived in a new way from simple physical arguments. Discussing the competition between steric repulsion and van der Waals attraction, one finds that membranes which usually separate (e.g. giant egg lecithin vesicles) should cohere if under lateral tension. The contours of two cohering vesicles observed when egg lecithin was swelling are analysed to show that the net energy of cohesion can be extremely small (≲10⁻⁵ erg cm⁻²). Paper presented at the ?Meeting on Lyotropics and Related Fields?, held in Rende, Cosenza, September 13–18, 1982.     

A proton NMR study of the interactions of catecholamines with phospholipids from chicken erythrocyte membranes

Summary High-resolution NMR spectroscopy has been applied to the study of the interaction of catecholamines, norepinephrine, epinephrine, isoproterenol and their antagonists propranolol and alprenolol with sonicated phospholipids extracted from chicken erythrocyte membranes (CEM). The catecholamine molecules are immobilized by the phospholipids of CEM and the magnitude of the effect seems to depend on the alkyl substitution of their amino group. Upon introduction of alprenolol and propranolol into phospholipid vesicles a broadening of the resonances of theN-methyl alkyl chain and the terminal methyl protons was observed. The results present evidence about the specificity of the interactions of catecholamines with phospholipids from CEM.

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Riassunto La spettrografia NMR ad alta risoluzione è stata applicata allo studio dell'interazione di catecolamine, norepinefrine, epinefria, isoproterenolo e i loro antagonisti propranololo e alprenolo con fosfolipidi estratti dalle membrane di eritrocina di pollo (CEM). Le molecole di catecolamina sono immobilizzate dai fosfolipidi di CEM e la grandezza dell'effetto sembra dipendere dalla sostituzione dell'alchile nel gruppo aminico. Con l _i introduzione di alprenolo e propranololo nelle vescicole fosfolipidiche si osserva un allargamento delle risonanze della catenaN-metil alchilica e dei protoni del metil terminale. I risultati offrono prove della specificità delle interazioni delle catecolamine coi fosfolipidi del CEM.

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Резюме ЯМР спектроскопия высокого разрешения применяется для исследования взаимодействия катеколаминов с фосфолипидами, извлеченными из мембраны эритроцитов цыпленка. Молекулы катеколаминов закрепляются фосфолипидами из мембраны эритроцитов цыпленка и величина эффекта, по-видимому, зависит от замещения алкилом их аминогруппы. При введении алпренола и пропранолола в пузырьки фосфолипидов наблюдается уширение резонансов. Полученные результаты подтверждают специфичность взаимодействия катеколаминов с фосфолипидами из мембран эритроцитов цыпленка.

     

Binding of Mn(II) ions to lecithin bilayers as determined by ESR and NMR investigations

Summary The Mn(II)-lecithin system was investigated by means of paramagnetic relaxation studies. Unsonicated and sonicated aqueous dispersions were considered at various temperatures andpH values. Information was derived from both the frequency dependence of the ESR line shape and the paramagnetic contributions to the water proton relaxation rates. A dynamic equilibrium was suggested, by taking into account the role of the through-water cation binding in the metal-lipid interaction.

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Riassunto Il sistema Mn(II)-lecitina è stato studiato per mezzo di misure di rilassamento paramagnetico. Sono state considerate dispersioni acquose sonicate e non a vari valori di temperature epH. Da misure EPR in funzione della frequenza e dallo studio di contributi paramagnetici alle velocità di rilassamento dei protoni dell’acqua sono state ottenute informazioni sul sistema Mn(II)-lecitina. Prendendo in considerazione il ruolo del legame acqua-catione, nell’interazione metallo lipide, è stato suggerito un equilibrio dinamico.

     

Elastic model of protein-protein interaction

Summary The elastic distortions of a model membrane are discussed, by taking into account those due to incorporated proteins. Two types of distortions exist: i) membrane compression and ii) displacement at constant thickness. The first mode decays on a very-short-length scale (≈nm). The second one is important since the characteristic lengh is of the order of the μm. This last distortion is characterized by a multipole expansion, in a way similar to electrostatics. The interaction of different elastic distortions is described in the context of their multipole expansion: for example, i) the monopole-monopole interaction is attractive (repulsive) in the case of opposite (equal) signs of the monopoles. The interaction energy behaves asW _AB≈Inr _AB (r _AB distance between the monopoles A and B) and may be even at large distance much higher thankT. ii) The dipole-dipole interaction is always attractive if the elastic dipole can rotate (fluid membrane). iii) The interaction energy varies asW _AB≈r _AB ⁻² (r _AB distance between the dipoles) and so on. This multipole concept may be used for the understanding of the recognition of different proteins. In addition, the particles which creaste the distortion may be polarizable. This means that shape changes of the particle could be induced by an external elastic field. We expect for a large particle a large polarizability. As a consequence, two static monopoles which reped each other may attract if they become polarizable. This feature is reminiscent of the Van der Waals interaction in electrostatics. Paper presented at the “Meeting on Lyotropics and Related Fields?, held in Rende, Cosenza, September 13–18, 1982.     

The role of ionic hydration in the conformations of DNA in electrolytic solutions

Summary The circular dichroism (CD) spectra of calf thymus deoxyribonucleic acid have been examined at 25°C over the wavelength range (215÷300) nm in aqueus solutions of LiCl, NaCl, KCl, and CsCl. The CD changes observed as the electrolyte concentration is varied have been correlated quantitatively with the magnitude of the hydration of the ions in these solutions (see a preceding paper). It is shown that specific cation effects present in this process correspond consistently to simple hydration properties of these same cations. To speed up publication, the author of this paper has agreed to not receive the proofs for correction.     

A study of tetraphenylborate transport through rat brain lipids impregnated filter-membranes

Summary The electrical properties of rat brain lipids impregnated filtermembranes exposed to the lipophilic ion tetraphenylborate (TPhB⁻) have been studied, using electrical relaxation techniques. The state of TPhB⁻ transport system depends on the applied voltage. It was also found that the initial membrane conductance depends on the applied voltage and changes with the concentration of TPhB⁻. Our results are presented in comparison with the electrical properties of BLM exposed to TPhB⁻. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

A comparison of DMPC membranes mixed with melittin or C12E5

Summary The effect of adding the defect-forming molecules melittin and C₁₂E₅ to DMPC membranes has been studied and the corresponding phase diagrams established. Light, X-ray and neutron small-angle scattering have been used to characterize the mixed membranes. Both systems show a melting of the lamellar L_α into an isotropic phase upon addition of the second membrane constituent. The molar ratio, where the melting occurs is the same in concentrated and dilute samples. For the DMPC/C₁₂E₅ system not only membrane composition, but also temperature can be used to induce a transition from an isotropic to a lamellar phase. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

NMR studies of carrier-mediated transport across lipid bilayer membranes

Two theoretical models are presented which show how the various kinetic steps involved in transport across lipid bilayer membranes affect NMR spectral lineshapes and relaxation times. The first model applies whenever the transported material moves across the membrane by restricted diffusion. The second model applies when the motion can be described as a jump between membrane interfaces. Both carrier-mediated and carrier-independent cases are treated. Special attention is given to the effects of relaxation in the membrane and to morphology. Exact analytical solutions for the simplest one-dimensional geometry are presented. More complicated morphologies are best treated numerically.     

Ion and water transport through permselective membranes

Electroosmotic transport of water accompanying ion transport across an anion-selective membrane has been measured at 25°C using 0.01 N NaC1 solution. Also electrical conductance, self-diffusion coefficient of counterion, and hydrodynamic permeability of the membrane have been measured. These data and others, such as water content and exchange capacity, have been used in the relations derived by Scattergood and Lightfoot employing the generalized Stefan-Maxwell equations to obtain values for the diffusivity coefficients D _1*1, D ₁₃, D ₁₄, and D_34. The isotope interaction term D _1*1 was the lowest.

Assuming the applicability of the Nernst-Einstein relation to the membrane system, the number of moles of water transported by electroconvection has been evaluated. The difference between the moles of total water transport and the moles of water moved electro-convectively has been assigned as the moles of water firmly associated with a mole of the moving ion. This way a value of 0.58 mole has been derived for the hydration of the Cl^? ion.     

Pink noise of ionic conductance through single artificial nanopores revisited

We report voltage-clamp measurements through single conical nanopore obtained by chemical etching of a single ion track in polyimide film. Special attention is paid to the pink noise of the ionic current (i.e., 1/f noise) measured with different filling liquids. The relative pink-noise amplitude is almost independent of concentration and pH for KCl solutions, but varies strongly using ionic liquids. In particular, we show that depending on the ionic liquid, the transport of charge carriers is strongly facilitated (low noise and higher conductivity than in the bulk) or jammed. These results show that the origin of the pink noise can be ascribed neither to fluctuations of the pore geometry nor to the pore wall charges, but rather to a cooperative effect on ions motion in confined geometry.     

Electronic transport properties of bismuth nanobridges through silicon-nitride membranes

The electronic transport through nanostructured bismuth nanobridges has been investigated at low temperatures (T<2 K) and in magnetic fields B up to 8.5 T. The samples show reproducible resistance fluctuations as a function of B, superimposed on a large magnetoresistance of up to 50%. In addition, time-dependent resistance fluctuations in zero magnetic field demonstrate the presence of bistable scatterers in the constriction region of our samples, which are described by two-level systems. Their dynamics are shown to be sensitive to subtle modifications of the static scatterer configuration in their vicinity, which cannot be detected in the sample magnetofingerprint.     

Surface-mediated liquid transport through molecularly thin liquid films on nanotubes

We studied surface-mediated liquid transport through molecularly thin films on individual nanotubes in ambient conditions. The surface fluid with molecular thickness (approximately 10 A) flowed at a constant speed (approximately 10 microm/s) and volume flow rate (approximately 10 al/s) along the nanotubes. The volume flow rate Q follows the power law dependence Q approximately d2.4 on the nanotube diameter d, which is explained with a generic microscopic model.     

液体在单根纳米管表面上的输运

文章研究了在单根纳米管表面上形成的分子级液膜的传输现象.实验发现,厚度在 ~ 10量级的表面流体在表面力的驱动下沿纳米管以恒定的速度（~ 10 μm/s）和容量流速（~ 10 al/s）流动.容量流速Q与纳米管直径d之间成幂函数关系,Q ~ d 2.4.此结果对实现用纳米管作为液体输运器件具有指导意义.     

液体在单根纳米管表面上的输运

文章研究了在单根纳米管表而上形成的分子级液膜的传输现象。实验发现，厚度在-10A量级的表面流体在表而力的驱动下沿纳米管以恒定的速度（-10μm/s）和容量流速（-10al／s）流动。容量流速Q与纳米管直径d之间成幂函数关系，Q—d^2．4。此结果对实现用纳米管作为液体输运器件具有指导意义。     

Kondo effect for electron transport through an artificial quantum dot

We have calculated the transport properties of electron through an artificial quantum dot by using the numerical renormalization group technique in this paper. We obtain the conductance for the system of a quantum dot which is embedded in a one-dimensional chain in zero and finite temperature cases. The external magnetic field gives rise to a negative magnetoconductance in the zero temperature case. It increases as the external magnetic field increases. We obtain the relation between the coupling coefficient and conductance. If the interaction is big enough to prevent conduction electrons from tunnelling through the dot, the dispersion effect is dominant in this case. In the Kondo temperature regime, we obtain the conductivity of a quantum dot system with Kondo correlation.     

Probing lateral diffusion in lipid membranes on nanoscale by PFG NMR with high gradient strength

This work demonstrates the feasibility of noninvasive studies of diffusion on a submicrometer length scale in aligned model lipid membranes using pulsed field gradient nuclear magnetic resonance with ultrahigh (up to 35 T/m) gradient strength. Application of such gradients allows the use of sufficiently small diffusion times under conditions of narrow-pulse approximation. As a result, monitoring anomalous or restricted diffusion in lipid membranes on a length scale in the range of 100 nm becomes possible. The ability to study diffusion in lipid membranes on this length scale is very important because it is comparable with the size of biologically relevant domains (i.e., rafts), which are believed to exist in biomembranes.     

Trehalose-protected lipid membranes for determining membrane protein structure and insertion

Trehalose preserves lipid bilayers during dehydration and rehydration by replacing water to form hydrogen bonds between its own OH groups and lipid headgroups. We compare the lipid conformation and dynamics between trehalose-protected lyophilized membranes and hydrated membranes, to assess the suitability of the trehalose-containing membrane as a matrix for membrane protein structure determination. (31)P spectra indicate that the lipid headgroup of trehalose-protected dry POPC membrane (TRE-POPC) have an effective phase transition temperature that is approximately 50K higher than that of the hydrated POPC membrane. In contrast, the acyl chains have similar transition temperatures in the two membranes. Intramolecular lipid (13)C'-(31)P distances are the same in TRE-POPC and crystalline POPC, indicating that the lipid headgroup and glycerol backbone conformation is unaffected by trehalose incorporation. Intermolecular (13)C-(31)P distances between a membrane peptide and the lipid headgroups are 10% longer in the hydrated membrane at 226 K than in the trehalose-protected dry membrane at 253 K. This is attributed to residual motions in the hydrated membrane, manifested by the reduced (31)P chemical shift anisotropy, even at the low temperature of 226 K. Thus, trehalose lyoprotection facilitates the study of membrane protein structure by allowing experiments to be conducted at higher temperatures than possible with the hydrated membranes.     

Magnetic-field-induced deformation of lipid membranes

The substantial effects of relatively low, steady magnetic fields less than 0.5 T up to high magnetic fields up to 30 T on the membrane potential and resistance of black lipid membranes of didodecyl phosphite and dipalmitoylphosphatidylcholine (DPPC) are presented. Also, the magnetic-field-induced fusion and division of DPPC liposomes are demonstrated. Such significant magnetoresponses should result in the magnetic orientation of the lipid molecules and associated undulation of the membranes. Thus, the addition to membranes of diamagnetic aromatics having a large magnetic anisotropy enhanced the magnetoresponses: larger changes in membrane potential and resistance and a lower shift of the onset magnetic-field, with abrupt changes in liposome sizes and membrane potential.