Macroporous poly(methyl methacrylate) produced by phase separation during polymerisation in solution

Polymethyl methacrylate (PMMA) sponges were obtained by polymerization in a solution with monomer/ethanol ratios up to 20:80. The material obtained after the elimination of the solvent present a homogeneous distribution of dispersed pores up to a monomer/ethanol ratio lower than 40:60. For higher ethanol contents in the reacting mixture, the morphology of the sponge corresponds to a network of PMMA microparticles, leaving large empty spaces leading to highly porous structure. The monomer/ethanol ratio during polymerization has a large influence on the porosity, thermal, and mechanical properties of the material and, for large solvent contents, on the size of the polymer microparticles.     

Age related changes in the thermal transition of Turkey leg flexor tendon collagen

A differential scanning calorimetric, thermogravimetric and electron microscopic investigation has been carried out on the uncalcified areas of turkey leg flexor tendon as a function of age. Rehydrated samples exhibit an increase of thermal stability with age. The H_D values drop from about 11 cal·g^–1 in the first weeks of life down to 7 cal·g^–1 after the 11th week.At about 11 weeks, the collagen fibril diameter distribution passes from unimodal to multimodal. The DSC curves as well as the TG-DTG curves recorded from dried samples do not show any appreciable difference with ageing. The variations in thermal behaviour of rehydrated samples and fibril diameter distribution could be related to modifications in water binding with ageing.The Authors are grateful to Dr. G. Fabris for discussion and help in the selection of the samples. They also wish to thank Mr. G. Pizzuto for excellent technical assistance. The financial support by Consiglio Nazionale delle Ricerche is gratefully acknowledged.     

LIGHT-SCATTERING STUDY OF POLYELECTROLYTE HOLLOW CAPSULES

Silver halide (AgX) microcrystal was used as template to synthesize hollow polyelectrolyte capsules. These hollow capsules were characterized by laser light scattering (LLS) used to measure the size of the capsules in solution. The ratio of hydrodynamic radius (Rh) from dynamic LLS to the radius of gyration (Rg) from static LLS is almost unity, revealing that the entities are hollow in solution. The results suggest that the LLS method can be regarded as a good complement to the confocal laser scanning microscopy (CLSM) method for the characterization of small hollow capsules, and it possesses the advantage of not needing fluorescence labeling.     

Voltage-Height Spectroscopy in the <Emphasis Type="Italic">Ex Situ</Emphasis> Configuration of a Scanning Tunneling Microscope

Basic regularities of electrochemical processes in the gap of an ex situ scanning tunneling microscope in conditions of condensation of air moisture at the sample surface are considered on a qualitative level. A layer of condensed moisture is viewed as an electrolyte in a two-electrode cell. The depolarizers present in this layer may experience electrochemical conversions on the tip and in an area of the sample surface near the tip. As a result, the recorded “tunneling” current includes electrochemical constituents. Depending on the electrochemical processes in the gap, various dependences of the tip-sample distance on the current and applied voltage can be expected. For preliminary diagnostics of processes in the gap it is suggested to use voltage-height spectra, whose shape and characteristic heights are sensitive to the nature and location of redox active species. Experimental data for various films on conducting supports (quasi-two-dimensional adsorbed layers of hemin and peroxidase, electrodeposited nonstoichiometric tungsten oxides, doped tin dioxide, solid electrolyte with ionic conduction) are presented as an examples.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 583–595.Original Russian Text Copyright © 2005 by Yusipovich, Vassiliev.     

Dynamic imaging of single DNA-protein interactions using atomic force microscopy

Atomic force microscopy (AFM) imaging of static DNA-protein complexes, in air and in liquid, can be used to directly obtain quantitative and qualitative information on the structure of different complexes. For example, DNA length, the location of preferential binding sites for proteins and bending of DNA as a result of the complexation can all be measured. Recording consecutive AFM images of DNA and protein molecules under conditions that they are still able to move and interact, or dynamic AFM imaging, however, can reveal information on the dynamic aspects of the interactions between these molecules. Here, an overview is given of the technical challenges that need to be considered for successful dynamic AFM imaging studies of individual DNA-protein interactions. Necessary technical improvements to the AFM set-up and the development of new sample preparation methods are described in this paper.     

Supramolecular structures of macromolecules containing bipyridine–copper(I) complexes as revealed from transmission electron microscopy studies

Transmission electron microscopy (TEM) studies on bipyridine (bpy) containing block copolymer systems showed the formation of nanoscopic polymer–ion complexes through complexation with copper(I) ions which segregated to highly ordered columnar domains of mesoscopic dimensions. The domains, i.e. stacks of [(bpy)₂Cu(I)] complex moieties could be visualized by complementary TEM techniques. First, electron energy loss spectra (EELS) showed the absorption edges of copper and nitrogen, which are specific for the bipyridine copper complexes. The element spectroscopic imaging (ESI) technique allowed the imaging of the net copper and net nitrogen distribution, and the coinciding pictures exhibited a microphase separated system in the case of a 3-block copolymer with complexed end segments. High resolution elastic bright field images showed interference lines with a line to line distance of about 8 A which could be related to the Cu–Cu distance in staggered Cu(I)–bipyridine complexes. Received: 6 August 1997 Accepted: 28 April 1998     

Deposition and characterization of Langmuir‐Blodgett films of cadmium arachidate/SWCNTs composites

The incorporation of single‐wall carbon nanotubes (SWCNTs) in cadmium arachidate film by means of the Langmuir‐Blodgett (LB) technique was investigated as a function of arachidic acid/SWCNT mass ratio at the air/water interface and in Langmuir‐Blodgett films. The behaviour at the air/water interface shows that SWCNTs act as an independent phase with respect to the cadmium arachidate. Deposition conditions are optimized when the weight ratio between the arachidic acid (AA) and SWCNTs is in the range 0.018:1 to 1:1. The general order of the LB multilayered structure was destroyed by the progressive density increase in SWCNT quantity as evidenced by X‐ray reflectivity (XRR) analysis. Scanning electron microscopy images indicated that when a multilayered structure was formed its layers consisted of SWCNT bundles stacked one over the other. Copyright © 2006 John Wiley & Sons, Ltd.