Angular- and temperature-dependent RSMR on myoglobin using 183W and 57Fe

Myoglobin crystals are investigated by Rayleigh scattering of Mössbauer radiation at T = 87 K and T = 300 K and angles up to sin(?)/λ = 0.44 Å^?1. The results are analysed in terms of normal modes.     

Biological applications of magnetic nanoparticles

In this review an overview about biological applications of magnetic colloidal nanoparticles will be given, which comprises their synthesis, characterization, and in vitro and in vivo applications. The potential future role of magnetic nanoparticles compared to other functional nanoparticles will be discussed by highlighting the possibility of integration with other nanostructures and with existing biotechnology as well as by pointing out the specific properties of magnetic colloids. Current limitations in the fabrication process and issues related with the outcome of the particles in the body will be also pointed out in order to address the remaining challenges for an extended application of magnetic nanoparticles in medicine.     

Antimicrobial Hydantoin‐Containing Polyesters

A new N‐hydantoin‐containing biocompatible and enzymatically degradable polyester with antibacterial properties is presented. Different polyesters of dimethyl succinate, 1,4‐butanediol, and 3‐[N,N‐di(β‐hydroxyethyl)aminoethyl]‐5,5‐dimethylhydantoin in varying molar ratios are prepared via two‐step melt polycondensation. The antibacterially active N‐halamine form is obtained by subsequent chlorination of the polyesters with sodium hypochlorite. Chemical structures, thermal properties, and spherulitic morphologies of the copolymers are studied adopting FT‐IR, NMR, TGA, DSC, WAXD, and POM. The polyesters exhibit antibacterial activity against Escherichia coli. The adopted synthetic approach can be transferred to other polyesters in a straightforward manner.

     

Cooperative Iron(II) spin crossover complexes with N4O2 coordination sphere

Two new spin crossover complexes [FeL(py)(2)] (1) and [FeL(DMAP)(2)] (2) with L being a tetradentate N(2)O(2)(2-) coordinating Schiff-base-like ligand [([3,3']-[1,2-phenylenebis(iminomethylidyne)]bis(2,4-pentanedionato)(2-)-N,N',O(2),O(2)'], py = pyridine and DMAP = p-dimethylaminopyridine have been investigated using temperature-dependent susceptibility and thermogravimetric and photomagnetic measurements as well as M?ssbauer spectroscopy and X-ray structure analysis. Both complexes show a cooperative spin transition with an approximately 9 K wide thermal hysteresis loop in the case of 2 (T(1/2) upward arrow = 183 K and T(1/2) downward arrow = 174 K) and an approximately 2 K wide thermal hysteresis loop in the case of the pyridine diadduct 1 (T(1/2) upward arrow = 191 K and T(1/2) downward arrow = 189 K). The spin transition was additionally followed by different temperature-scanning calorimetry and M?ssbauer spectroscopy for 2, and a good agreement for the transition temperatures obtained with the different methods was found. Results from X-ray structure analysis indicate that the cooperative interactions are due to elastic interactions in both compounds. They are more pronounced in the case of 2 with very short intermolecular iron-iron distances of 7.2 A and several intense C-C contacts. The change of the spin state at the iron center is accompanied by a change of the O-Fe-O angle, the so-called bit of the equatorial ligand, from 108 degrees in the high-spin state to 90 degrees in the low-spin state. The reflectivity measurements of both compounds give at low temperature indication that at the sample surface the light-induced excited spin state trapping (LIESST) effect occurs. In bulk condition using a SQUID magnetometer the complex 2 displays some photomagnetic properties with an photoexcitation level of 60% and a T(LIESST) value of 53 K.     

Dielectrophoretic trapping of DNA-coated gold nanoparticles on silicon based vertical nanogap devices

We report on the successful dielectrophoretic trapping and electrical characterization of DNA-coated gold nanoparticles on vertical nanogap devices (VNDs). The nanogap devices with an electrode distance of 13 nm were fabricated from Silicon-on-Insulator (SOI) material using a combination of anisotropic reactive ion etching (RIE), selective wet chemical etching and metal thin-film deposition. Au nanoparticles (diameter 40 nm) coated with a monolayer of dithiolated 8 base pairs double stranded DNA were dielectrophoretically trapped into the nanogap from electrolyte buffer solution at MHz frequencies as verified by scanning and transmission electron microscopy (SEM/TEM) analysis. First electrical transport measurements through the formed DNA-Au-DNA junctions partially revealed an approximately linear current-voltage characteristic with resistance in the range of 2-4 G? when measured in solution. Our findings point to the importance of strong covalent bonding to the electrodes in order to observe DNA conductance, both in solution and in the dry state. We propose our setup for novel applications in biosensing, addressing the direct interaction of biomolecular species with DNA in aqueous electrolyte media.     

Substrate dependent differences in morphology and elasticity of living osteoblasts investigated by atomic force microscopy

We have used the atomic force microscope (AFM) as a tool for testing the biocompatibility of implant materials by investigating the adhesion behavior of osteoblast cells in vitro. This technique allowed the investigation of cytomorphology and cytomechanical properties of living cells on a submicrometer scale. Cell adhesion was investigated on Cobalt–Chromium (CoCr), Titanium (Ti) and Titanium–Vanadium (TiV) substrates, which are of great interest in the field of implant research. The elastic properties and the morphology of living osteoblasts on the metallic substrates were compared with those of osteoblasts cultured on glass and tissue culture polystyrene (PS). Furthermore, a characterization of the surface roughness of the substrates was performed and the surface coverage of proteins after incubation with cell culture medium on the substrates was observed with the AFM.     

Magnetic targeting and cellular uptake of polymer microcapsules simultaneously functionalized with magnetic and luminescent nanocrystals

By using a flow channel system for modeling the bloodstream in the circulatory system and by locally creating a magnetic field gradient caused by a permanent magnet, we demonstrate specific trapping of polymer capsules simultaneously functionalized with two types of nanoparticles--magnetic and luminescent nanocrystals. In the regions where the capsules were trapped by the magnetic field, drastically increased uptake of capsules by cells has been observed. The uptake of capsules by cells could be conveniently monitored with a fluorescence microscope by the luminescence of CdTe nanocrystals that had been embedded into the shells of the capsules. Our experiments envisage the feasibility of magnetic targeting of polymer capsules loaded by pharmaceutical agents to pathogenic parts of a tissue.     

Quantitative Particle Uptake by Cells as Analyzed by Different Methods

There is a large number of two‐dimensional static in vitro studies about the uptake of colloidal nano‐ and microparticles, which has been published in the last decade. In this Minireview, different methods used for such studies are summarized and critically discussed. Supplementary experimental data allow for a direct comparison of the different techniques. Emphasis is given on how quantitative parameters can be extracted from studies in which different experimental techniques have been used, with the goal of allowing better comparison.     

Ion Transport Through Polyelectrolyte Multilayers

Polyelectrolyte multilayer (PEM) films and capsules loaded with ion‐sensitive fluorophores can be used as ion‐sensors for many applications including measurements of intracellular ion concentration. Previous studies have shown the influence of the PEM films/shells on the specific response of encapsulated ion‐sensitive fluorophores. PEM shells are considered as semipermeable barriers between the environment and the encapsulated fluorophores. Parameters such as the time response of the encapsulated sensor can be affected by the porosity and charge of the PEM shell. In this study, the time response of an encapsulated pH‐sensitive fluorophore towards pH changes in the surrounding environment is investigated. Furthermore, the conductance of PEM films for potassium ions is determined.

     

Synthesis and characterization of a dinuclear iron(II) spin crossover complex with wide hysteresis

The magnetic properties and results from X-ray structure analysis for a new pair of iron(II) spin-crossover complexes [FeL1(meim) 2](meim) ( 1(meim)) and [Fe 2L2(meim) 4](meim) 4 ( 2(meim) 4), with L1 being a tetradentate N 2O 2 (2-) coordinating Schiff-base-like ligand [([3,3']-[1,2-phenylenebis(iminomethylidyne)]bis(2,4-pentane-dionato)(2-)N,N',O (2),O (2)'], L2 being an octadentate, dinucleating N 2O 2 (2-) coordinating Schiff-base-like ligand [3,3',3',3']-[1,2,4,5-phenylenetetra(iminomethylidyne)]tetra(2,4-pentanedionato)(2-) N, N', N', N', O (2), O (2) ', O (2) ', O (2) '], and meim being N-methylimidazole, are discussed in this work. Crystalline samples of both complexes show a cooperative spin transition with an approximately 2-K-wide thermal hysteresis loop in the case of 1(meim) ( T 1/2 increase = 179 K and T 1/2 decrease = 177 K) and an approximately 21-K-wide thermal hysteresis loop in the case of dinuclear complex 2(meim) 4 ( T 1/2 increase= 199 K and T 1/2 decrease= 178 K). For a separately prepared powder sample of 2, a gradual spin transition with T 1/2 = 229 K is observed that was additionally followed by Mossbauer spectroscopy. The results from X-ray structure analysis give a deeper insight into the molecule packing in the crystal and, by this, help to explain the increase of cooperative interactions during the spin transition when going from the mononuclear to the dinuclear complex. Both compounds crystallize in the triclinic space group P1, and the X-ray structure was analyzed before and after the spin transition. The change of the spin state at the iron center is accompanied by a change of the O-Fe-O angle, the so-called bite of the equatorial ligand, from about 109 degrees in the high-spin state to 89 degrees in the low-spin state. The cooperative interactions responsible for the thermal hysteresis loop are due to elastic interactions between the complex molecules in both cases. However, due to the higher symmetry of the dinucleating ligand in 2(meim) 4, a 3D network of short contacts is formed, while for mononuclear complex 1(meim), a 2D layer of linked molecules is observed. The spin transition was additionally followed in solution using (1)H NMR spectroscopy for both complexes. In both cases, a gradual spin transition is observed, and the increase of cooperative interactions when going from the mononuclear to the dinuclear system is solely attributed to the extended network of intermolecular contacts.