Volume 25 Issue 3 April 2011

Nagib A. Elmarzugi ^1,2 and Clive J. Roberts ³ 1. Faculty of Pharmacy, Alfateh University, and 2. Biotechnology Research Center, Tripoli, Libya. 3. Laboratory of Biophysics and Surface Analysis, School of Pharmacy, University of Nottingham, UK.
The elucidation of the structure of biocomplexes of polymers and DNA is expected to shorten the way toward real implementation of multiple clinical applications, particularly gene therapy. It is possible to study biocomplex compounds by using conventional tools such as TEM. However, a potential application of using AFM for the study will give extra chance to elucidate the functional structure; similarly the gathering of comparative data as a result of using different techniques can support and confirm the structure of biocomplexes. Here, we studied complexes formed between dimethylaminoethylmethacrylate and DNA. Many morphological structures were seen at open circular, toroids, plectonemic, rod like, flower-like structure, and also represent end-like condensate structures such as globular structures. The different structures have revealed new insights in terms of study and expected applications.

Arpita Roychoudhury and Filipp Oesterhelt, Institute for Physical Biology, Heinrich Heine University, Düsseldorf, Germany
Atomic force microscope-based single-molecule force spectroscopy has made it possible to probe the mechanical stability and unfolding pathways of membrane proteins as well as the free-energy landscape of inter- and intramolecular interactions. Single-molecule force spectroscopy probes the mechanical properties of individual molecules by exerting mechanical forces and measures the induced conformational changes. Forces applied to a single protein acts as a denaturant leading to unfolding of its three dimensional structure thereby revealing its unfolding pathways. This technique is of great interest especially in the field of membrane proteins, which can be investigated under physiological conditions and in their native membrane environment. Examples illustrated here are those of bacteriorhodopsin and sensoryrhodopsin II.

Dalia G. Yablon and Andy H. Tsou, ExxonMobil Research and Engineering, Clinton, New Jersey, USA
The morphology and interfacial adhesion of a polypropylene-based impact copolymer were studied using atomic force microscopy with a tensile stage. Effects of deformation as a function of tensile stress were observed within both polypropylene (PP) and ethylene proplyene (EP) components as well as at the interface between the two materials. Most importantly, EP-PP interfacial strength can be measured by the corresponding local interfacial stretching extent or void length between EP and PP as the EP domains separate from the PP matrix upon delamination. Presently, there are no direct measurement methods available to determine interfacial adhesive strength of nano- and microscale domains within polymer blends, especially blends generated in situ in polymerization reactors where individual materials cannot be accessed directly. This approach could be used for direct determination of interfacial adhesion in complex polymer-containing materials such as blends and nanocomposites.

Antoine D. Touboul,¹ Richard Arinero¹ and Michel Ramonda² 1. Institut d’Electronique du Sud, UMR-CNRS, Montpellier II University, France. 2. Laboratoire de Microscopie en Champ Proche, Montpellier II University, France
A charged particle entering matter interacts with both the surrounding atoms and electrons. A part or all of its energy is then transferred to the electrons or converted into displacement damage, depending on the kinetic energy of the particle. We report here observations of individual ion tracks on silica using atomic force microscopy. Swift heavy ion irradiation may create defects in SiO2 and bumps at the oxide/silicon interface. The appearance of the silicon bumps can be explained by the thermal spike model and corresponds to a drastic decrease of the effective oxide thickness. We also observed elongated and intermittent surface tracks after swift heavy-ion irradiation under grazing incidence. This result leads to the assumption that energy transfer itself along the incoming ion trajectory is discontinuous, in disagreement with the usual simplifying assumptions. Such AFM measurements have allowed an improvement in our understanding of the physics of interaction at the atomic scale.