Solid-state molecular tunnel junctions are often assumed to operate in the Landauer regime, which describes essentially activationless coherent tunnelling processes. In solution, on the other hand, charge transfer is described by Marcus theory, which accounts for thermally activated processes. In practice, however, thermally activated transport phenomena are frequently observed also in solid-state molecular junctions but remain poorly understood.
View Article and Find Full Text PDFRecent experiments demonstrate a temperature control of the electric conduction through a ferrocene-based molecular junction. Here we examine the results in view of determining means to distinguish between transport through single-particle molecular levels or via transport channels split by Coulomb repulsion. Both transport mechanisms are similar in molecular junctions given the similarities between molecular intralevel energies and the charging energy.
View Article and Find Full Text PDFPurpose: To compare microstructural changes along the optical radiations and brain structure volumes between glaucoma and control subjects using in vivo magnetic resonance imaging and to analyze their association with severity of the disease.
Methods: A total of 50 open-angle glaucoma subjects and 50 healthy age- and sex-matched controls underwent detailed ophthalmologic examinations (including visual field testing [VF], funduscopy, and spectral-domain optical coherence tomography) as well as diffusion tensor imaging (DTI) using 3.0-Tesla magnetic resonance imaging.
In this work we present a comparative study of the temperature behavior of charge current in both single-molecule transistors and self-assembled monolayer-based tunnel junctions with symmetrical molecules of alkanethiolates functionalized with a ferrocene (Fc) unit. The Fc unit is separated from the electrodes with two equal alkyl chains of enough length to ensure weak coupling of the Fc unit with the electrodes. These junctions do not rectify charge current and display exponential dependence with temperature with moderate slopes, which can be directly associated to the thermal broadening of the electronic occupation Fermi distribution in the electrodes.
View Article and Find Full Text PDFWe present a theoretical analysis aimed at understanding electrical conduction in molecular tunnel junctions. We focus on discussing the validity of coherent versus incoherent theoretical formulations for single-level tunneling to explain experimental results obtained under a wide range of experimental conditions, including measurements in individual molecules connecting the leads of electromigrated single-electron transistors and junctions of self-assembled monolayers (SAM) of molecules sandwiched between two macroscopic contacts. We show that the restriction of transport through a single level in solid state junctions (no solvent) makes coherent and incoherent tunneling formalisms indistinguishable when only one level participates in transport.
View Article and Find Full Text PDFUnderstanding how the mechanism of charge transport through molecular tunnel junctions depends on temperature is crucial to control electronic function in molecular electronic devices. With just a few systems investigated as a function of bias and temperature so far, thermal effects in molecular tunnel junctions remain poorly understood. Here we report a detailed charge transport study of an individual redox-active ferrocene-based molecule over a wide range of temperatures and applied potentials.
View Article and Find Full Text PDFJ Eur Acad Dermatol Venereol
April 2014
Background: LR2412, a synthetic derivative of jasmonic acid, improved the reconstruction and homeostasis of our organotypic skin models.
Objectives: The need for efficient 'anti-ageing' treatments, in particular for the management of photoaged skin, prompted us to investigate this new ingredient for its potential to correct signs of skin ageing in vitro and in vivo and to identify its mode of action.
Results: In vitro, penetration of LR2412 was evaluated using a Franz diffusion cell on excised human skin.
ATP-sensitive K(+) (K(ATP)) channels are the target of a number of pharmacological agents, blockers like hypoglycemic sulfonylureas and openers like the hypotensive cromakalim and diazoxide. These agents act on the channel regulatory subunit, the sulfonylurea receptor (SUR), which is an ABC protein with homologies to P-glycoprotein (P-gp). P-gp is a multidrug transporter expressed in tumor cells and in some healthy tissues.
View Article and Find Full Text PDFWe investigated the biotransformation of the oxidative arylamine (AA) hair dye ingredients [14C]-para-aminophenol (PAP) and [14C]-para-phenylenediamine (PPD) in reconstructed human epidermis and human hepatocytes. Human epidermis quantitatively transformed PAP to its N-acetylated derivative (APAP), whereas hepatocytes transformed PAP to sulfate or glucuronic acid conjugates of APAP or PAP as well as free APAP. Epidermis and hepatocytes converted PPD to N-mono- (MAPPD) and N,N'-di-acetylated (DAPPD) derivatives.
View Article and Find Full Text PDFObjectives: To investigate whether P-glycoprotein (P-gp) and multidrug resistance proteins (MRPs), which limit the bioavailability of HIV protease inhibitors (PIs) and nucleoside reverse transcriptase inhibitors (NRTIs), modulate the anti-HIV activity of NRTIs, non-NRTIs and PIs in vitro.
Design: We used primary cultures of major HIV target cells: human monocyte-derived macrophages (MDMs) and lymphocytes.
Methods: P-gp and MRP expression in response to long-term zidovudine (3'-azido-3'-deoxythymidine; AZT) or indinavir treatment was quantified by RT-PCR.
The multidrug transporter P-glycoprotein is a plasma membrane protein involved in cell and tissue detoxification and the multidrug resistance (MDR) phenotype. It actively expels from cells a number of cytotoxic molecules, all amphiphilic but chemically unrelated. We investigated the molecular characteristics involved in the binding selectivity of P-glycoprotein by means of a molecular modeling approach using various substrates combined with an enzymological study using these substrates and native membrane vesicles prepared from MDR cells.
View Article and Find Full Text PDFP-glycoprotein (P-gp) is a plasma membrane ATP-binding cassette transporter, responsible for multidrug resistance in tumor cells. P-gp catalyzes the ATP hydrolysis-dependent efflux of numerous amphiphilic compounds of unrelated chemical structures. In the absence of any identified substrate, P-gp exhibits an apparently futile, basal ATPase activity.
View Article and Find Full Text PDFP-glycoprotein (P-gp) is a multidrug transporter responsible for resistance to anticancer chemotherapy and physiologically involved in absorption, distribution, and excretion of a large number of hydrophobic xenobiotics. P-gp exhibits both an ATPase activity correlated with its drug transport function and a basal ATPase activity in the absence of any drug. We have developed a high-throughput screening test to detect specific interactions between drugs and P-gp.
View Article and Find Full Text PDFThe growing array of in vitro models of the blood-brain barrier (BBB) which have been used makes it difficult to draw firm conclusions concerning the BBB penetration of HIV-1 protease inhibitors. What is needed is a combined in vivo and in vitro study on biological models that mimic as closely as possible the normal human BBB, to establish whether and how indinavir crosses the BBB. We developed a new human BBB model using primary endothelial cells and astrocytes.
View Article and Find Full Text PDFCytogenet Cell Genet
December 2001
A comparative map of human chromosome 12 (HSA 12) and pig chromosome 5 (SSC 5) was constructed using ten pig expressed sequence tags (ESTs). These ESTs were isolated from primary granulosa cell cultures by differential display (EST b10b), or from a granulosa cDNA library (VIIIE1, DRIM, N*9, RIIID2 and RVIC1) or from a small intestine cDNA library (ATPSB, ITGB7, MYH9, and STAT2). Also used were two Traced Orthologous Amplified Sequence Tags (TOASTs) (LALBA, TRA1), one microsatellite-associated gene (IGF1) and finally five human YACs selected for their cytogenetic position, with a view to increasing the number of informative markers for the comparison.
View Article and Find Full Text PDFUpon osmotic downshock, a few cytoplasmic proteins, including thioredoxin, elongation factor Tu (EF-Tu), and DnaK, are released from Tris-EDTA-treated Escherichia coli cells by an unknown mechanism. We have shown previously that deletion of mscL, the gene coding for the mechanosensitive channel of the plasma membrane with the highest conductance, prevents the release of thioredoxin. We confirm and extend the implication of MscL in this process by showing that the release of EF-Tu and DnaK is severely impaired in MscL-deficient strains.
View Article and Find Full Text PDFEscherichia coli cells possess several mechanosensitive ion channels but only MscL, the channel with the highest conductance, which is activated at the highest membrane tension, has been cloned. We investigated the putative involvement of MscL in the effluxes caused by osmotic downshock. Osmotic shock caused the release of potassium glutamate, trehalose, and glycine betaine from wild type cells and cells lacking MscL.
View Article and Find Full Text PDFWe have produced human cyclin A in Escherichia coli and investigated how it generates H1 kistone kinase activity when added to cyclin-free extracts prepared from parthenogenetically activated Xenopus eggs. Cyclin A was found to form a major complex with cdc2, and to bind cdk2/Eg1 only poorly. No lag phase was detected between the time when cyclin A was added and the time when H1 histone kinase activity was produced in frog extracts, even in the presence of 2 mM vanadate, which blocks cdc25 activity.
View Article and Find Full Text PDFThe properties of kainate receptor/channels were studied in Xenopus oocytes injected with mRNA that was isolated from adult rat striatum and cerebellum and partially purified by sucrose gradient fractionation. Kainate (3-1000 microM) induced a smooth inward current that was competitively inhibited by gamma-D-glutamyl-aminomethanesulfonate (GAMS, 300 microM). In striatal mRNA-injected oocytes, the kainate current displayed nearly linear voltage-dependence and mean reversal potential (Er) of -6.
View Article and Find Full Text PDFA novel radioiodinated ligand of the butyrophenone type has been synthesized for the quantification and characterization of dopamine D2 receptors. This haloperidol-derived ligand, haloperidol-succinylglycyl[125I]iodotyrosine ([125I]HSGTI), binds rapidly (equilibrium is reached within 30 min, at 10 pM and 37 degrees C) and with high affinity (Kd = 0.3 nM) to bovine striatal membranes.
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