Search results for "Monolayer"

Invasive Observation by Atomic Force Microscope of a Langmuir-Blodgett Monolayer of Gramicidin

2002

The properties of gramicidin, a linear antibiotic polypeptide of 15 amino acids, have been studied at the air-water interface. Analysis of the pressure-area isotherm is not able to conclude about the conformational behavior of gramicidin in the monolayer. Langmuir-Blodgett deposition of gramicidin layers onto a mica substrate has been developed for atomic force microscopy (AFM) observations. At high pressure of deposition, the gramicidin monolayer is composed of dimers perpendicular to the surface. The possibility of removing the half upper part of this dimer monolayer with the AFM tip is more in favor of a structure of single-stranded helical dimers.

Discotic Twin and Triple Molecules with Charge-Transfer Interactions in Langmuir−Blodgett Films

1996

X-ray and atomic force microscopy observations reveal features of the surface morphology of Langmuir-Blodgett (LB) films from discotic donor-acceptor molecules with strong core-to-core interactions caused by a charge-transfer (CT) complexation. The compounds are designed to be twin and triple molecules composed of chemically connected donor (triphenylene) and acceptor (trinitrofluorenone) fragments which display liquid crystalline structure in the bulk state. The LB films from these compounds possess edge-on orientation of molecules within monolayers with a smooth surface on a submicron scale but with substantial macroscopic imperfections. These imperfections are represented by the micron s…

Effect of the surface stoichiometry on the interaction of Mo with TiO2 (110)

2000

Abstract Molydenum has been deposited at room temperature on (110) TiO2 surfaces with different stoichiometries, roughnesses and crystallinities. Whatever the substrate preparation is, in-situ Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) studies as well as ex-situ atomic force microscopy (AFM) and reflexion high-energy electron diffraction (RHEED) studies reveal a Stranski–Krastanov growth mode: the completion of three monolayers followed by islands growth is observed in every case. The three monolayers are always composed of amorphous molybdenum oxide with an oxidation state of molybdenum less than IV. The oxidation of the molybdenum layers generates Ti3+ an…

1994

Liquid crystalline side chain polymers containing photoreactive azobenzene chromophores in the dark-adapted trans form and phenylbenzoate groups as co-mesogens have been prepared and investigated as monomolecular layers at the water/air interface and as multilayer assemblies deposited onto solid supports by the Langmuir–Blodgett–Kuhn (LBK) technique. Pressure area isotherms at variable temperatures together with reflection absorption spectra and Brewster angle microscopic pictures have been taken and analyzed (i) to derive information about the structural order and the packing properties of the mesogenic side groups within the monolayers of different homo- and co-polymeric systems and ii) t…

Spontaneous growth of 2D coordination polymers on functionalized ferromagnetic surfaces

2018

2D coordination polymers grow spontaneously on reactive surfaces due to surface oxidation. The growth process is observed in real time.

Controlled iontophoretic release of glucocorticoids through epithelial cell monolayers

1998

In the present study the iontophoretic transdermal delivery of three different glucocorticoids through a confluent monolayer of MDCK cells, mimicking biological barriers, was studied. For this experiment an in vitro model with platinum electrodes for iontophoresis and MDCK cells was developed. With this model investigations concerning the biocompatibility of the cells depending on different current densities and the iontophoretic permeation of the three glucocorticoids through the cell monolayer were carried out. The permeation behavior of this living biological barrier should be very similar to the non-living barrier, human stratum corneum. Different current densities (12.74-38.22 microA/c…

Self-Assembled Monolayers: Bioinspired Catechol-Terminated Self-Assembled Monolayers with Enhanced Adhesion Properties (Small 8/2014)

2014

Low-fouling, mixed-charge poly-L-lysine polymers with anionic oligopeptide side-chains

2018

Biosensors and biomedical devices require antifouling surfaces to prevent the non-specific adhesion of proteins or cells, for example, when aiming to detect circulating cancer biomarkers in complex natural media (e.g., in blood plasma or serum). A mixed-charge polymer was prepared by the coupling of a cationic polyelectrolyte and an anionic oligopeptide through a modified "grafting-to" method. The poly-l-lysine (PLL) backbone was modified with different percentages (y%) of maleimide-NHS ester chains (PLL-mal(y%), from 13% to 26%), to produce cationic polymers with specific grafting densities, obtaining a mixed-charge polymer. The anionic oligopeptide structure (CEEEEE) included one cysteine…

An enzyme caught in action: Direct imaging of hydrolytic function and domain formation of phospholipase A2 in phosphatidylcholine monolayers

1989

AbstractPhospholipase A2, a ubiquitous lipolytic enzyme that actively catalyses hydrolysis of phospholipids, has been studied as a model for enzyme-substrate reactions, as a membrane structural probe, and as a model for lipid-protein interactions. Its mechanism of action remains largely controversial. We report here for the first time direct microscopic observation of the lipolytic action of fluorescently marked phospholipase A2 (Naja naja naja) against phosphatidylcholine monolayers in the lipid phase transition region. Under these conditions, phospholipase A2 is shown to target and hydrolyse solid-phase lipid domains of L-α-dipalmitoylphosphatidylcholine. In addition, after a critical ext…

Small unilamellar liposomes from mixed natural and polymeric phospholipids: stability and susceptibility to phospholipase A2.

1991

The concept of the uncorkable liposome composed of phase-separated mixtures of a polymerized phospholipid and an enzymically digestible phospholipid has been investigated, using small unilamellar vesicles composed of mixtures of (polymerized) dienoylphosphatidylcholine (DENPC) and dimyristoylphosphatidylcholine (DMPC). Mixed liposomes, even those containing only 10% DENPC, were much more stable than DMPC liposomes, as indicated by the release of entrapped [3H]inulin or [14C]glucose. DMPC liposomes released entrapped solute on exposure to phospholipase A2, whereas mixed vesicles were resistant. The results are compared with those of an earlier study on monolayers of similar compositions. It …