Interactions between metals and biomacromolecules including proteins, polysaccharides, and nucleic acids are important since they can be essential for a number of natural and industrial phenomena. These range from interactions of highly specific metal cofactors with particular proteins [1] to biosorption of heavy metals by polysaccharide hydrogels.[2]The unique features of DNA have been exploited in the development of novel materials, especially in the areas of medicine and nanotechnology. Classical research concerning antitumor drugs has focussed on the interactions of platinumor ruthenium-containing compounds with the major or minor grooves of polynucleotides. [3][4][5][6] There is a tremendous interest in the use of DNA in nanotechnology as a positioning template for the immobilization of metal nanoclusters with view to future applications in the construction of nanoelectronic devices. [7][8][9][10][11] Herein we report the interaction of Au 55 nanoclusters with the major grooves of B-DNA. The Au 55 clusters are degraded to Au 13 clusters by the transition of B-DNA into A-DNA in ultrahigh vacuum, and the resulting shrinkage of the major grooves. We have performed molecular-dynamics simulations and provided further information on the mechanism by which wires of Au 13 clusters form, and attempt to explain the interwire separation of 0.5 nm.

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Electrochemical anodic oxidation of aluminium metal sheets leads to the formation of compact and dense, but highly porous alumina surfaces on top of the anode. The alumina surfaces obtained by anodic oxidation can be detached from the bare metal by using a voltage detachment procedure, without employing chemical etching techniques. This procedure leads to large area porous alumina membranes with closed backsides. Prestructuring of the aluminium base metal leads to ordered pore regions at anodisation voltages of 25, 40 and 50 V, resulting in porous alumina membranes with pore dia-

We report about the surface modification of polystyrene (PSt) with photoreactive alpha-4-azidobenzoyl-omega-methoxy poly(ethylene glycol)s (ABMPEG) of three different molecular weights (MWs of approximately 2, approximately 5, and approximately 10 kg/mol) and with two poly(ethylene glycol)/poly(propylene glycol) triblock copolymers (PEG-PPG-PEG) of about identical PEG/PPG ratio (80/20, w/w) and MW(PEG) of approximately 3 and approximately 6 kg/mol, all via adsorption from aqueous solutions. For ABMPEGs, an additional UV irradiation was used for photografting to the PSt. Contact angle (CA) and atomic force microscopy data revealed pronounced differences of the hydrophilicity/hydrophobicity and topography of the surfaces as a function of PEG type and concentration used for the modification. In all cases, an incomplete coverage of the PSt was observed even after modification at the highest solution concentrations (10 g/L). However, clear differences were seen between PEG-PPG-PEGs and ABMPEGs; only for the latter was a nanoscale-ordered interphase structure with an influence of MW(PEG) on the PEG density observed; after modification at the same solution concentrations, the density was significantly higher for lower MW(PEG). The adsorption of three proteins, myoglobin (Mgb), bovine serum albumin (BSA), and fibrinogen to the various surfaces was analyzed by surface plasmon resonance. Pronounced differences between the two PEG types with respect to the reduction of protein adsorption were found. At high, but still incomplete, surface coverage and similar CA, the shielding of ABMPEG layers toward the adsorption of Mgb and BSA was much more efficient; e.g., the adsorbed Mgb mass relative to that of unmodified PSt was reduced to 10% for ABMPEG 2 kg/mol while for both PEG-PPG-PEGs the Mgb mass was still around 100%. In addition, for the ABMPEG layers an effect of MW(PEG) on adsorbed protein mass-decrease with decreasing MW-could be confirmed; and the highest Mgb/BSA selectivities were also observed. A "two-dimensional molecular sieving", based on PEG molecules having a nanoscale order at the hydrophobic substrate polymer surface has been proposed, and the main prerequisites were the use of PEG conjugates which are suitable for an "end-on" grafting (e.g., ABMPEGs), the use of suitable (not too high) concentrations for the surface modification via adsorption/self-assembly, optionally the photografting on the substrate (possible only for ABMPEG), and presumably, a washing step to remove the excess of unbound PEGs. The results of this study also strongly support the hypothesis that the biocompatibility of hydrophobic materials can be very much improved by PEG modifications at surface coverages that are incomplete but have an ordered layer structure controlled by the size and steric interactions of surface-bound PEGs.

A laser temperature-jump technique is used to probe the impact of sodium halides on the temperature-dependent switching kinetics and thermodynamics of poly(N-isopropylacrylamide) brushes. An analysis on the basis of a two-state model reveals van't Hoff enthalpy and entropy changes. Sodium halides increase the endothermicity and the entropic gain of the switching process below and above Tc following the Hofmeister series: NaCl > NaBr > NaI. In contrast, enthalpic and entropic changes at Tc remain virtually unaffected. This provides an unprecedented insight into the underlying switching energetics of this classic stimuli-responsive polymer. Because of its model character, these results represent an essential reference on the way to unpuzzle the molecular driving forces of the Hofmeister effect.