Phantom Ring‐Closing Condensation Polymerization: Towards Antibacterial Oligoguanidines

The first example of phantom ring‐closing condensation polymerization for the synthesis of oligoguanidines is presented. A new oligoguanidine with a ring structure was achieved in one step by the condensation reaction of a triamine, like diethylenetriamine, with guanidine hydrochloride. The condensation reaction proceeded by selective ring‐closure towards the formation of five‐membered rings in the oligomer backbone. The resulting polymer repeat unit structure was different from the starting monomers (phantom polymer) and was formed by elimination of three molecules of ammonia per repeat unit. The inter‐, intra‐, and inter‐molecular reaction sequences led to the new structure as proved by different spectroscopic techniques (atmospheric pressure chemical‐ionization mass spectrometry, and one‐dimensional and two‐dimensional homo‐ and heteronuclear correlation NMR experiments) as well as supported by quantum chemical investigations. Preliminary results regarding antibacterial use of the resulting oligoguanidine were also promising and showed its effect within 15–30 min as an antibacterial material.

     

Thermo‐Switchable Antibacterial Activity

A copolymer system of 2‐aminoethyl methacrylate and N‐isopropylacrylamide comprises novel properties: changes in conformation and hydrophilicity upon heating influence the antibacterial activity and result in a switchable biocidal effect. The copolymers are characterized via NMR, MALDI‐ToF MS, phase transition behavior, and antibacterial tests with E. coli or B. subtilis. MIC and MBC are determined using standard dilution methods, temperature‐dependence via incubation at different temperatures and cytotoxicity by MTT tests. The copolymers exhibit lower MIC in globule than coil conformation, crosslinking on cotton results in non‐leaching materials with better antibacterial activity above than below the phase‐transition point.

     

Ion irradiation of exchange bias systems for magnetic sensor applications

It has been demonstrated that He⁺ ion irradiation is an excellent tool for modifying magnetic properties, like the magnetic anisotropy, the interlayer exchange coupling strength and the exchange bias field of ultra-thin magnetic layered systems. This paper summarizes the effects of ion irradiation on exchange bias systems. As a first example, for possible applications of the ion induced magnetic effects, the realization of an angle sensing device is described. Received: 11 November 2002 / Accepted: 12 November 2002 / Published online: 4 April 2003 RID="*" ID="*"Corresponding author. Fax: +49-631-205-4095, E-mail: fassbend@physik.uni-kl.de RID="**" ID="**"Present address: Université de Rouen, Rouen, France     

Antimicrobial Hydantoin‐grafted Poly(ε‐caprolactone) by Ring‐opening Polymerization and Click Chemistry

Novel degradable and antibacterial polycaprolactone‐based polymers are reported in this work. The polyesters with pendent propargyl groups are successfully prepared by ring‐opening polymerization and subsequently used to graft antibacterial hydantoin moieties via click chemistry by a copper(I)‐catalyzed azide‐alkyne cycloaddition reaction. The well‐controlled chemical structures of the grafted copolymers and its precursors are verified by FT‐IR spectroscopy, NMR spectroscopy, and GPC characterizations. According to the DSC and XRD results, the polymorphisms of these grafted copolymers are mostly changed from semicrystalline to amorphous depending on the amount of grafted hydantoin. Antibacterial assays are carried out with Bacillus subtilis and two strains of Escherichia coli and show fast antibacterial action.

     

Magnetization reversal in magnetic nanostripes via Bloch wall formation

We present results of micromagnetic simulations of the magnetization reversal in permalloy nanostripes with 5-10 nm thickness and 200-500 nm width under a longitudinal field of 0.4-16 kA m(-1). The data show four distinct field regions: the well-known regions of uniform and oscillating domain wall movement as well as a process with multiple vortices, and finally a new process including Bloch walls and the generation of vortex-antivortex pairs in the inner part of the stripe rather than at the edges. We investigate this process in detail and derive a criterion for the formation of Bloch walls.     

Relationship between nonadiabaticity and damping in permalloy studied by current induced spin structure transformations

By direct imaging we determine spin structure changes in Permalloy wires and disks due to spin transfer torque as well as the critical current densities for different domain wall types. Periodic domain wall transformations from transverse to vortex walls and vice versa are observed, and the transformation mechanism occurs by vortex core displacement perpendicular to the wire. The results imply that the nonadiabaticity parameter beta does not equal the damping alpha, in agreement with recent theoretical predictions. The vortex core motion perpendicular to the current is further studied in disks revealing that the displacement in opposite directions can be attributed to different polarities of the vortex core.