Atomic force microscopy observations of acyl chains in phospholipids

The potential use of atomic force microscopy (AFM) to image the mode of assembly and to measure the corresponding lattice parameters of model systems consisting of ordered aggregates of cardiolipin molecules has been investigated. An unprecedented resolution of about 0.2 nm has been achieved on suitably prepared specimens. This enables the orientational order and the positional correlations of the individual molecules in the lattice to be defined, and submolecular details, such as the acyl chains and the polar groups, to be imaged. The structural parameters derived from AFM have been compared with those obtained by transmission electron diffraction of the same specimen and found to be in excellent agreement. AFM turns out to be a powerful, and probably a unique tool to reveal local phase variations in systems, such as biological membranes, that have non-homogeneous composition and organization

Application of an Analytical Philips EM 400T TEM-FEG to Some Materials Problems

Abstract not availableNA-NOT AVAILABL

Atomic Force Microscopy: a modern technique in Membrane Science

Atomic force microscopy: a modern versatile technique in membrane scienc

Defects in ordered aggregates of cardiolipin visualized by atomic force microscopy

The formation and the nature of defects in ordered aggregates of cardiolipin (tetra acyl di phosphatidyl glycerol) supported on solid substrates have been investigated by atomic force microscopy (AFM). The experiments were performed on two model systems, i.e. three-dimensional liquid crystals dispersed in water and partially de-hydrated on a hydrophilic surface, and two-dimensional films of molecules self-assembled onto an isotropic hydrophobic surface. Defects were induced both by varying the preparation temperature and by treatment with specific chemicals known to modify the order parameters in natural and artificial membranes, specifically: 2,4-dinitro-phenol (DNP) and pentachloro-phenol (PCP). The effect of lipid oxidation on the nanocrystalline order was also investigated. The images obtained by AFM allow to characterize the type of defects and their local density at nanoscale level. They also provide additional information to differentiate the specific role of acyl chains and polar heads in the process of lipid self-organization. (c) 2007 Elsevier Ireland Ltd. All rights reserved

The cylindrical envelope projection model applied to SE images of curved surfaces and comparison with AFM evaluations

The Cylindrical Envelope Projection Model (CEPM) has been extended to images of curved objects (e.g., spheres), obtained in a SEM by means of SEs, in order to improve the accuracy of measurements (down to a few %). The test objects have been calibrated by means of an AFM equipped with home-made nanotips. A simple rule for measuring the diameter of spheres and cylinders from SE y-modulated traces is given. The rule is applicable to specimens of medium $(Z\geq 25)$ and high atomic number

Work function dependence on the thickness and substrate of carbon contamination layers by Kelvin probe force microscopy

The contact potential difference (CPD) between carbon contamination (CC) layers and the several substrates on which they were deposited has been measured as a function of the film thickness by means of Kelvin probe force microscopy (KPFM). The observed CPD trends may be divided into three categories: (i) an increase, or decrease, in CPD with thickness up to a saturation value with sign inversion with respect to the substrates (Al and Si); (ii) an oscillation with no sign inversion (substrates, gold and platinum); (iii) an oscillation through sign inversion (palladium substrate). Effects (ii) and (iii) seem to be typical of CC, since they have not been observed for other materials, including evaporated carbon. Several possible causes of the above two effects are examined, but a satisfactory interpretation has not been found yet. The sensitivity of KPFM is such that CC layers 10 nm thick are easily visible, whereas they are hardly detectable by topography

Lipid oxidation deletes the nanodomain organization of artificial membranes

Nanoscopic domains with different crystal structures have been induced in closed artificial membranes and have been directly imaged by atomic force microscopy at a spatial resolution better than 0.3 nm. These observations provide experimental evidence to the hydrophobic mismatching theory of lateral phase separation phenomena. Under oxidant conditions, the lipid-lipid assembly reorganises into a new steady-state structure with disappearance of specific nanodomains. This finding may contribute to understanding the mechanism of peroxidative damage to membrane properties. In fact, alterations of specific anodes of molecular conformation and packing may lead to perturbation of specific properties