147 research outputs found
Probing membrane permeabilization by the antibiotic lipopeptaibol trichogin GA IV in a tethered bilayer lipid membrane
No full textAbstractThe lipopeptaibol trichogin GA IV (TCG) can be incorporated in the lipid bilayer moiety of a mercury-supported tethered bilayer lipid membrane (tBLM) at a non-physiological transmembrane potential of about −240mV, negative on the trans side of the bilayer. Once incorporated in the tBLM, TCG is stable over the range of physiological transmembrane potentials and permeabilizes the membrane at transmembrane potentials negative of −80÷−90mV. The chronocoulometric behavior is consistent with a kinetics of nucleation and growth of bundles of TCG building blocks with ion-channel properties. The TCG building blocks also permeabilize the lipid bilayer, albeit at more negative transmembrane potentials, and can be tentatively regarded as dimers of aligned TCG helical monomers. The cyclic voltammograms of tBLMs incorporating TCG point to a voltage-gated behavior of the TCG channel, similar to that exhibited by the peptaibol alamethicin
Au25(SCnH2 n+1)18 Clusters in Biomimetic Membranes: Role of Size, Charge, and Transmembrane Potential in Direct Membrane Permeation
No full textGold nanoclusters and nanoparticles are promising materials for applications in nanomedicine, and therefore, understanding their interaction with cell membranes is of particular importance. A series of neutral and anionic Au25(SCnH2n+1)18 monolayer protected clusters (MPCs) (briefly, Cn0 and Cn- clusters), was embedded into two types of biomimetic membranes supported by mercury electrodes. The first was a dioleoylphosphatidylcholine (DOPC) self-assembled monolayer (SAM), whereas the second was a tethered bilayer lipid membrane (tBLM) obtained by first anchoring a thiolipid monolayer to the mercury surface and then self-assembling a DOPC monolayer on top of it. The diameter of these clusters, from 1.7 to 2.7 nm depending on the thiolate ligand, is smaller than the thickness of biomembranes and biomimetic membranes. Both neutral and anionic Au25(SCnH2n+1)18 MPCs can penetrate the lipid bilayer moiety of the tBLM, without disrupting it; in particular, anionic Au25 clusters require positive transmembrane potentials to do so. Neutral Au25 clusters exchange one electron with mercury in a DOPC SAM, where they can come in contact with the mercury surface, whereas they are prevented from doing so at the tBLM because of their inability to cross the hydrophilic chain separating the lipid bilayer moiety from the mercury surface. The potential of these Au25 clusters to penetrate directly the plasma membrane is particularly convenient for targeted drug delivery. They are highly stable, biocompatible, and catalytic, and their uniform size is of importance in nanomedicine. Moreover, they may induce an efficient energy transfer to 3O2, allowing applications in radiotherapy and antimicrobial activity.
Effect of a Strong Interfacial Electric Field on the Orientationof the Dipole Moment of Thiolated Aib-Oligopeptides Tetheredto Mercury on Either the N- or C-Terminus
No full textFour oligopeptides consisting of a sequence of R-aminoisobutyric acid (Aib) residues, thiolated
at either the N- or C-terminus by means of a -(CH2)2-SH anchor, were self-assembled on mercury, which
is a substrate known to impart a high fluidity to self-assembled monolayers (SAMs). The surface dipole
potential of these peptide SAMs was estimated in 0.1 M KCl aqueous solution at a negatively charged
electrode, where the interfacial electric field is directed toward the metal. To the best of our knowledge,
this is the first estimate of the surface dipole potential of peptide SAMs in aqueous solution. The procedure
adopted consisted in measuring the charge involved in the gradual expansion of a peptide-coated mercury
drop and then combining the resulting information with an estimate of the charge density experienced by
diffuse layer ions. The dipole moment of the tethered thiolated peptides was found to be directed toward
the metal, independent of whether they were thiolated at the C- or N-terminus. This result was confirmed
by the effect of these SAMs on the kinetics and thermodynamics of the Eu(III)/Eu(II) redox couple. The
combined outcome of these studies indicates that a strong interfacial electric field orients the dipole moment
of peptide SAMs tethered to mercury, even against their “natural” dipole moment
A procedure for estimating the surface dipole potential of monolayers adsorbed on electrodes
No full textIncorporation of channel-forming peptides in a Hg-supported lipid bilayer
No full textThe channel-forming peptides gramicidin and alamethicin were incorporated in a mercury-supported lipid bilayer composed of a tethered thiolipid monolayer with a self-assembled dioleoylphosphatidylcholine monolayer on top of it. The thiolipid consists of a hexapeptide chain with a high tendency to form a 310-helical structure, which terminates at the N-terminus end with a sulfydryl group for anchoring to the metal while the C-terminus end is covalently linked to the polar head of dimyristolylphosphatidylethanolamine. The hexapeptide moiety has two triethyleneoxy side chains that impart a satisfactory hydrophilicity and are intended to keep the anchored thiolpeptide chains sufficiently apart, so as to accommodate water molecules and inorganic ions and to create a suitable environment for the incorporation of integral proteins. Changes in the conductance of this biomimetic membrane following the incorporation of gramicidin and alamethicin were detected by impedance spectroscopy. The surface dipole potential of the hexapeptide chain and the transmembrane potential of the lipid bilayer were estimated by using a simple electrostatic model of the mercury|solution interphase
Photoinduced electroreduction of chlorophyllide on alkanethiol-coated mercury
No full textMonolayers of n-alkanethiols of chain length from C-12 to C-18 were self-assembled on a hanging mercury drop electrode, and a film of chlorophyllide (Chlide) was adsorbed on top of them. The reduction photocurrents following illumination of the Chlide film were measured over the potential range in which the Chlide is electroinactive in the dark, and their action spectra were determined. Plotting the derivative of the photocurrents with respect to the applied potential against potential yields bell-shaped curves that can be fitted to a Gaussian. The potential of the Gaussian maximum was used to determine the reorganization energy for the Chlide electroreduction process. An increase in the thiol chain length causes A to decrease regularly and the photocurrent to decay exponentially with the monolayer thickness, with a decay constant beta of about 0. 17 Angstrom(-1)
Pulmonologist-Administered Balanced Propofol Analgosedation during Interventional Procedures: An Italian Real-Life Study on Comfort and Safety
No full textPropofol-based sedation provides faster recovery than midazolam-based regimens with similar safety and comfort during video flexible bronchoscope (VFB) procedures. Pulmonologist-administered propofol "balanced"analgosedation (PAP-BAS) is still debated in Italy. In this real-life study, PAP-BAS safety and comfort during VFB procedures were investigated. We analysed prospectively the subjects undergoing elective VFB procedures in the Pulmonology and RICU of Arezzo Hospital between February and July 2019. PAP-BAS combined low propofol and meperidine doses titrated to achieve an RASS score between 0 and -3. The primary end-point was the complications' rate. Secondary end-points were as follows: the relation between propofol's dose and a subject's comfort assessed with a VAS, recovery time according to a modified Aldrete score ≥9, RASS, and subjects' will of undergoing the procedure again. We collected postprocedure symptoms' intensity too. Our 158 study patients (67 years; SD ± 14; 64% males) incurred in 25% of complication, fully resolved with medical therapy. Neither recourse to ventilator support nor death was reported. Intraprocedural comfort was good (94% of VAS score ≤2). Among postprocedural symptoms, cough was the most frequently reported, in 36% of the cases. Although half of subjects remembered the procedure, 90% of them would have repeated it, if necessary. 85% of them recovered from procedures within 10 minutes. Complications, VAS, and recovery time were not correlated with propofol dose. To our knowledge, this is the first Italian study showing that PAP-BAS to perform a VFB procedure is safe, well tolerated with a quick recovery. Randomised controlled trials are warranted to confirm these preliminary results
Tehered bilayer lipid micromembranes for single-channel recording: the role of adsorbed and partially fused vesicles
No full textA mercury-supported bilayer lipid micromembrane was prepared by anchoring a thiolipid monolayer to a mercury cap electrodeposited on a platinum microdisc about 20 mu m in diameter; a lipid monolayer was then self-assembled on top of the thiolipid monolayer either by vesicle fusion or by spilling a few drops of a lipid solution in chloroform on the cap and allowing the solvent to evaporate. Single-channel recording following incorporation of the alamethicin channel-forming peptide exhibits quite different features, depending on the procedure followed to form the distal lipid monolayer. The "spilling" procedure, which avoids the formation of adsorbed or partially fused vesicles, yields very sharp single-channel currents lasting only one or two milliseconds. These are ascribed to ionic flux into the hydrophilic spacer moiety of the thiolipid. Conversely, the vesicle-fusion procedure yields much longer single-channel openings analogous to those obtained with conventional bilayer lipid membranes, albeit smaller. This difference in behavior is explained by ascribing the latter single-channel currents to ionic flux into vesicles adsorbed and/or partially fused onto the tethered lipid bilayer, via capacitive coupling
Electrochemical and photoelectrochemical behavior of chlorophyll a films adsorbed on mercury
No full textSafety and Diagnostic Yield of Medical Pleuroscopy (MP) Performed under Balanced Analgosedation by a Pneumological Team Compared to Video-Assisted Thoracic Surgery (VATS): A Retrospective Controlled Real-Life Study (TORAPO)
No full textIntroduction: Medical pleuroscopy (MP) is an invasive technique that provides access to the pleural space with a rigid or semi-rigid work instrument, allowing for visualization and the obtaining of bioptic pleural samples. Using pulmonologist-based analgosedation to perform pleuroscopy is still debated for safety reasons. The aim of this real-life study is to demonstrate the safety and diagnostic yield of MP performed under balanced analgosedation by a pulmonologist team with expertise in the management of critically ill patients in the respiratory intensive care unit (RICU) and interventional pulmonology unit as compared to video-assisted thoracic surgery (VATS) performed by a thoracic surgeon team under anesthesiologist-based analgosedation. Methods: In this multicentric retrospective controlled study, the inclusion criteria were patients older than 18 years old with pleural effusion of unknown diagnosis consecutively admitted in the years 2017–2022 to the pulmonology unit and RICU of San Donato Hospital in Arezzo (Italy, Tuscany) and to the thoracic surgery unit of Santa Maria Le Scotte in Siena (Italy, Tuscany) to undergo, respectively, MP under balanced propofol-based analgosedation on spontaneous breathing with local anesthesia provided by a pulmonologist team (Group A), and VATS provided by a surgeon team under propofol-based analgosedation managed by an anesthesiologist using invasive mechanical ventilation (IMV) via endotracheal intubation (ETI) (Group B). The primary endpoints were (1) a comparison between the two groups in terms of the diagnostic yield of pleural effusion, and (2) major and minor complications of pleuroscopic procedures. The secondary endpoints were (1) the length of the pleuroscopic procedure; (2) the duration of hospitalization; (3) propofol doses; and (4) the patient’s comfort after the procedure assessed using the Visual Analogue Scale (VAS). Results: We enrolled 91 patients in Group A and 116 patients in Group B. A conclusive diagnosis was obtained in 97.8% of Group A vs. 100% of Group B (p = 0.374). Malignant effusion was diagnosed in 59.3% of Group A and in 55.1% of Group B; p = 0.547. No intraoperative or postoperative mortality events or major complications were observed in Group A. The major complications observed in Group B were three major bleeding events (p = 0.079) and one exitus (p = 0.315) not related to the interventional procedure. No significant difference emerged between the two groups in terms of minor complications. The duration of the intervention was significantly lower in Group A (40.0 min ± 12.6 versus 51.5 ± 31.0; p = 0.001). Pain control and, therefore, patient comfort were better in Group A, with an average VAS of 0.34 ± 0.65 versus 2.58 ± 1.26, p < 0.001. The duration of hospitalization was lower in Group B (5.1 ± 2.6 vs. 15.5 ± 8.0, p < 0.001). The average overall dose of propofol administered was significantly lower in Group A (65.6 ± 35.8 mg versus 280 ± 20.0 mg; p < 0.001). Conclusions: This real-life study shows that the MP performed under propofol-based analgosedation by an independent pneumologist team is a safe and well-tolerated procedure with a diagnostic yield and complication rates similar to those obtained with VATS
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