Buried, covalently attached RGD peptide motifs in poly(methacrylic acid) brush layers: the effect of brush structure on cell adhesion

Iniferter-mediated surface-initiated photopolymerization was used to graft poly(methacrylic acid) (PMAA) brush layers obtained from surface-attached iniferters in self-assembled monolayers to a gold surface. The tethered chains were subsequently functionalized with the cell-adhesive arginine-glycine-aspartic acid (RGD) motif. The modified brushes were extended by reinitiating the polymerization to obtain an additional layer of PMAA, thereby burying the peptide-functionalized segments inside the brush structure. Contact angle measurements and Fourier transform infrared (FTIR) spectroscopy were employed to characterize the wettability and the chemical properties of these platforms. Time of flight secondary ion mass spectroscopy (TOF-SIMS) measurements were performed to monitor the chemical composition of the polymer layer as a function of the distance to the gold surface and obtain information concerning the depth of the RGD motifs inside the brush structure. The brush thickness was evaluated as a function of the polymerization (i.e., UV-irradiation) time with atomic force microscopy (AFM) and ellipsometry. Cell adhesion tests employing human osteoblasts were performed on substrates with the RGD peptides exposed at the surface as well as covered by a PMAA top brush layer. Immunofluorescence studies demonstrated a variation of the cell morphology as a function of the position of the peptide units along the grafted chains.     

Recent advances in hydrogen-bonded hexameric encapsulation complexes

Basic research in the chemistry of hexameric resorcin[4]arenes and pyrogallol[4]arenes during the last decade is reviewed. Applications of NMR methods to determine solution structures, host guest properties and exchange dynamics are discussed. The scientific issue is the behavior of molecules in small spaces; the challenge is to translate this information to practical applications in, say, catalysis or transport.     

Reversible pH-controlled switching of poly(methacrylic acid) grafts for functional biointerfaces

Responsive polymeric brushes of poly(methacrylic acid) (PMAA) were grafted from silicon surfaces using controlled surface-initiated atom-transfer radical polymerization (SI-ATRP). The growth kinetics of PMAA was investigated with respect to the composition of the ATRP medium by grafting the polymer in mixtures of water and methanol with different ratios. The dissociation behavior of the polymer layers was characterized by FTIR titration after incubating the polymer-grafted substrates in PBS buffer solutions with different pH values. PMAA layers show a strong pH-dependent behavior with an effective pK(a) of the bulk polymer brush of 6.5 ± 0.2, which is independent of the polymer brush thickness and methanol content of the ATRP grafting medium. The pH-induced swelling and collapse of the grafted polymer layers were quantified in real time by in situ ellipsometry in liquid environment. Switching between polymer conformations at pH values of 4 and 8 is rapid and reversible, and it is characterized by swelling factors (maximum thickness/minimum thickness) that increase with decreasing the methanol content of the SI-ATRP medium.     

Grafting of single, stimuli-responsive poly(ferrocenylsilane) polymer chains to gold surfaces

Redox-responsive poly(ferrocenylsilane) (PFS) polymer molecules were attached individually to gold surfaces for force spectroscopy experiments on the single molecule level. By grafting ethylenesulfide-functionalized PFS into the defects of preformed self-assembled monolayers (SAMs) of different omega-mercaptoalkanols on Au(111), the surface coverage of PFS macromolecules could be conveniently controlled. Atomic force microscopy (AFM), contact angle, as well as cyclic and differential pulse voltammetry measurements were carried out to characterize the morphology, wettability, and surface coverage of the grafted layers. The values of the PFS surface coverage were found to depend on the chain length of the omega-mercaptoalkanol molecules and on the concentration of the PFS solution but not on the insertion time or on the molar mass of PFS. The equilibrium surface coverages were successfully described by Langmuir adsorption isotherms. For low-surface coverage values (< 6.2 x 10(-4) chain/nm2), achieved by PFS insertion from very dilute solutions (8 x 10(-6) M) into long-chain SAMs, AFM and differential pulse voltammetry showed that surfaces exposing isolated individual polymer chains were obtained. The isolated PFS macromolecules were subjected to in situ AFM-based single molecule force spectroscopy (SMFS) measurements. The single chain elasticity of PFS in isopropanol (and ethanol) was fitted with the modified freely jointed chain (m-FJC) model. This procedure yielded a Kuhn segment length of 0.33 +/- 0.05 nm and a segment elasticity of 32 +/- 5 nN/nm.     

Probing Reversible Chemistry in Coenzyme B12‐Dependent Ethanolamine Ammonia Lyase with Kinetic Isotope Effects

Coenzyme B₁₂‐dependent enzymes such as ethanolamine ammonia lyase have remarkable catalytic power and some unique properties that enable detailed analysis of the reaction chemistry and associated dynamics. By selectively deuterating the substrate (ethanolamine) and/or the β‐carbon of the 5′‐deoxyadenosyl moiety of the intrinsic coenzyme B₁₂, it was possible to experimentally probe both the forward and reverse hydrogen atom transfers between the 5′‐deoxyadenosyl radical and substrate during single‐turnover stopped‐flow measurements. These data are interpreted within the context of a kinetic model where the 5′‐deoxyadenosyl radical intermediate may be quasi‐stable and rearrangement of the substrate radical is essentially irreversible. Global fitting of these data allows estimation of the intrinsic rate constants associated with Co?C homolysis and initial H‐abstraction steps. In contrast to previous stopped‐flow studies, the apparent kinetic isotope effects are found to be relatively small.     

Structure,properties and interfacial interactions in poly(lactic acid)/polyurethane blends prepared by reactive processing

Polyurethane elastomers are promising candidates for the impact modification of PLA producing blends for example for biomedicine. Poly(lactic acid) (PLA)/polyurethane elastomer (PU) blends were prepared by reactive processing and physical blending as comparison. The blends were characterized by a number of techniques including microscopy (scanning electron microscopy, SEM, and atomic force microscopy, AFM), rotational viscometry, thermal (dynamic mechanical analysis, DMA), and mechanical (tensile) measurements. The analysis and comparison of the structure and properties of physical and reactor blends proved the successful coupling of the phases. Coupling resulted in more advantageous structure and superior mechanical properties compared to those of physical blends as confirmed by morphology, macroscopic properties and the quantitative estimation of interfacial interactions. Structural studies and the composition dependence of properties indicated the formation of a submicron, phase-in-phase structure which positively influenced properties at large PU contents. The results strongly support that reactive processing is a convenient, cost-effective and environmentally friendly technique to obtain blends with superior properties.     

Probing a Hydrogen-π Interaction Involving a Trapped Water Molecule in the Solid State

The detection and characterization of trapped water molecules in chemical entities and biomacromolecules remains a challenging task for solid materials. We herein present proton-detected solid-state Nuclear Magnetic Resonance (NMR) experiments at 100 kHz magic-angle spinning and at high static magnetic-field strengths (28.2 T) enabling the detection of a single water molecule fixed in the calix[4]arene cavity of a lanthanide complex by a combination of three types of non-covalent interactions. The water proton resonances are detected at a chemical-shift value close to zero ppm, which we further confirm by quantum-chemical calculations. Density Functional Theory calculations pinpoint to the sensitivity of the proton chemical-shift value for hydrogen-π interactions. Our study highlights how proton-detected solid-state NMR is turning into the method-of-choice in probing weak non-covalent interactions driving a whole branch of molecular-recognition events in chemistry and biology.     

Efficient and robust coatings using poly(2-methyl-2-oxazoline) and its copolymers for marine and bacterial fouling prevention

Molecular design, fabrication, and properties of thin-film coatings based on poly(2-methyl-2-oxazoline) (PMOX) and its copolymers were investigated to tackle problem of marine and bacterial fouling prevention. The ultraviolet crosslinkable macromonomer poly(2-methyl-2-oxazoline) dimethylacrylate was synthesized by cationic ring-opening polymerization in a microwave reactor initiated by 1,4-dibromobutane. In order to study the charge effect of the PMOX coatings on the adhesion of fouling organisms, PMOX surfaces with negative, neutral, and positive ζ-potential values were prepared by copolymerization with the positively charged monomer [2-(methacryloyloxy)-ethyl]trimethylammonium chloride. The coatings were stable in sea water for at least 1 month without significant reduction in the film thickness. The marine antifouling activity was evaluated against barnacle cyprids Amphibalanus amphitrite and algae Amphora coffeaeformis. Results showed that PMOX coatings provide effective reduction of the settlement regardless of the molar mass and surface charge of the polymer. Bacterial adhesion test showed that PMOX coatings effectively reduce Staphylococcus aureus and Escherichia coli adhesion. Owing to its good stability and antifouling activity PMOX has a great potential as antifouling coating for marine antifouling applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 275–283     

Organometallic Polyelectrolytes: Synthesis,Characterization and Layer‐By‐Layer Deposition of Cationic Poly(ferrocenyl(3‐ammoniumpropyl)‐methylsilane)

The water soluble poly(ferrocenylsilane) polycation, poly(ferrocenyl(3‐ammoniumpropyl)methylsilane), was synthesized by transition metal‐catalyzed ring‐opening polymerization of the novel [1]ferrocenophane Fe(η‐C₅H₄)₂SiCH₃(CH₂)₃Cl and by subsequent side group modification. Amination of the chloropropyl moieties using potassium 1,1,3,3‐tetramethyldisilazide followed by acidic hydrolysis produced the polycation. The polycation was employed together with poly(sodium vinylsulfonate) in the electrostatic layer‐by‐layer self‐assembly process to form organometallic multilayers on quartz. The multilayer fabrication process was monitored using UV/Vis absorption spectroscopy and XPS.