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Organisationseinheit der BAM
Solution Self-Assembly of Synthetic Copolymers bearing Complementary Nucleic Acid Funtionalities
(2005)
The radical polymerization of three monomers bearing nucleobases 1-(4-vinylbenzyl)thymine (VBT), 1-(4-vinylbenzyl)uracil (VBU) and 9-(4-vinylbenzyl)adenine (VBA) was investigated. The corresponding homopolymers could be prepared in high yields via conventional radical polymerization. However, the resulting polymers were found to be only soluble in a few polar solvents. On the other hand, copolymers of dodecyl methacrylate (DMA) with either VBT or VBA could be prepared via both free radical polymerization and atom transfer radical polymerization and could be dissolved in a large variety of organic solvents. Moreover, the formed complementary copolymers P(VBT-co-DMA) and P(VBA-co-DMA) were found to self-assemble in dilute solutions in dioxane or chloroform via base recognition, as evidenced by a significant hypochromicity effect in UV spectroscopy. Nevertheless, at higher concentrations in chloroform, both dynamic light scattering and optical microscopy indicate that P(VBT-co-DMA), P(VBA-co-DMA), or P(VBT-co-DMA)/P(VBA-co-DMA) mixtures spontaneously self-assemble into micron size spherical aggregates. 1H NMR and FTIR studies confirmed that the self-assembly process is driven in all cases via H-bond formation. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4805-4818, 2005
Metallosupramolecular coordination polyelectrolytes (MEPEs) based on rigid and flexible ditopic bis-terpyridine ligands and Fe(II) ions are investigated by Mössbauer spectroscopy. We demonstrate the influence of mechanical stress induced by grinding on the structure of MEPE as well as the ability of MEPE to self-repair through recrystallisation.
The self-organization of random copolymers composed of a nucleobase monomer (either 1-(4-vinylbenzyl)thymine or 9-(4-vinylbenzyl)adenine) and dodecyl methacrylate (DMA) was studied in dilute chloroform solutions. The balance between the molar fractions of the nucleobase monomer (leading to intermolecular H-bonding) and DMA (soluble moiety in chloroform) in the polymer chains was found to be the parameter that principally influences the self-organization. DMA-rich copolymers are molecularly soluble in chloroform, whereas nucleobase-rich copolymers are insoluble in this solvent. Copolymers possessing an equimolar comonomer composition self-assemble into micrometer-sized particles physically cross-linked by intermolecular H-bonds (either thymine-thymine or adenine-adenine interactions, depending on the studied copolymer). Nevertheless, when mixed together, thymine- and adenine-based colloids fuse into thermodynamically stable microspheres cross linked by adenine-thymine interactions.
The precursor [FeIII(L)Cl] (LH<sub2 = N,N'-bis(2'-hydroxy-benzyliden)-1,6-diamino-3-N-hexane is a high-spin (S = 5/2) complex. This precursor is combined with the bridging units [SnIV(X)4] (X = CN-, NCS-) to yield star-shaped pentanuclear clusters, [(LFeIII-X)4Sn]Cl4. For X = CN- the 57Fe-Mössbauer data show a multiple spin transition between iron(III) in the high-spin and low-spin state, while the 119mSn-Mössbauer data indicate a valence tautomerism between Sn(IV) and Sn(II). Changing the bridging unit from X = CN- to X = NCS- turns the switchability off.
Hydrophobically end-modified (HM) poly(2-ethyl-2-oxazolines) (PEtOx) and poly(2-isopropyl-2-oxazolines) (PiPrOx) bearing an n-octadecyl chain on both termini or on one chain end only were prepared by cationic ring-opening polymerization of 2-ethyl-2-oxazoline and 2-isopropyl-2-oxazoline, respectively, and subsequent end-group modification. The polymers had a molar mass (Mn) ranging from 7000 to 13000 g mol-1, a size distribution Mw/Mn < 1.20, and end-group functionality > 0.97. All polymers, except the semitelechelic sample C18-PiPrOx-OH 13K (Mn = 13000 g mol-1), formed core-shell micelles in cold water with a hydrodynamic radius (RH), measured by dynamic light scattering, between 7 and 12 nm and a core of radius (Rc), determined by analysis of small-angle X-ray scattering (SAXS) data, of ~1.3 nm. Aqueous solutions of all polymers underwent a heat-induced phase transition detected by an increase in solution turbidity at a temperature (Tcp, cloud point) ranging from 32 to 62 °C, depending on polymer structure and size. Temperature-dependent light scattering (LS) measurements and fluorescence depolarization studies with the probe diphenylhexatriene (DPH) revealed that extensive intermicellar bridging takes place in solutions heated in the vicinity of Tcp leading to large assemblies (RH ≥ 1 µm). Further heating caused these assemblies to shrink into objects with RH ~ 300-700 nm, depending on the size and structure of the polymer. The formation of H-bonds between water molecules and the main-chain amide nitrogen atoms imparts distinct features to the flower/star micelles formed by telechelic/semitelechelic PiPrOx and PEtOx, compared to the micelles formed by other hydrophobically end-modified water-soluble polymers, such as poly(ethylene oxide) or poly(N-isopropylacrylamide).
Silver nanoparticles (SNP) are among the most commercialized nanoparticles worldwide. They can be found in many diverse products, mostly because of their antibacterial properties. Despite its widespread use only little data on possible adverse health effects exist. It is difficult to compare biological data from different studies due to the great variety in sizes, coatings or shapes of the particles. Here, we applied a novel synthesis approach to obtain SNP, which are covalently stabilized by a small peptide. This enables a tight control of both size and shape. We applied these SNP in two different sizes of 20 or 40 nm (Ag20Pep and Ag40Pep) and analyzed responses of THP-1-derived human macrophages. Similar gold nanoparticles with the same coating (Au20Pep) were used for comparison and found to be non-toxic. We assessed the cytotoxicity of particles and confirmed their cellular uptake via transmission electron microscopy and confocal Raman microscopy. Importantly a majority of the SNP could be detected as individual particles spread throughout the cells. Furthermore we studied several types of oxidative stress related responses such as induction of heme oxygenase I or formation of protein carbonyls. In summary, our data demonstrate that even low doses of SNP exerted adverse effects in human macrophages.