Ultrathin Monomolecular Films and Robust Assemblies Based on Cyclic Catechols.

We introduce a newly designed catechol-based compound and its application for the preparation of homogeneous monomolecular layers as well as for robust assemblies on various substrates. The precisely defined cyclic catechol material (CyCat) was prepared from ortho-dimethoxybenzene in a phenolic resin-like synthesis and subsequent deprotection, featuring molecules with up to 32 catechol units. The CyCat's chemical structure was carefully assessed via matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF), proton nuclear magnetic resonance (1H NMR), diffusion ordered spectroscopy (2D DOSY) and high resolution electrospray ionization mass spectrometry (ESI MS) experiments. The formation of colloidal aggregates of the CyCat material in alkaline solution was followed by dynamic light scattering (DLS) and further verified by dropcasting CyCat from solution on highly oriented pyrolytic graphite (HOPG), which was examined by Kelvin probe force microscopy (KPFM). The adsorption behavior of the CyCat to form monomolecular layers was investigated in real time by surface plasmon resonance (SPR). Formation of these thin CyCat layers (1.6-2.1 nm) on Au, SiO2 and TiO2 substrates was corroborated by spectroscopic ellipsometry (SE) and X-ray photoelectron spectroscopy (XPS). The prepared coating perfectly reflects the surface structure of the underlying substrate and does not exhibit CyCat colloidal aggregates as verified by atomic force microscopy (AFM). The functional nature of the prepared catechol monolayers was evidenced by reaction with 4-bromophenethylamine and bis(3-aminopropyl)-terminated poly(ethylene oxide) (PEO). Multilayer assemblies were prepared by a simple procedure of iterative immersion in solutions of CyCat and a multifunctional amine on Au, SiO2 and TiO2 substrates forming thicker coatings (up to 12 nm). Postmodification with small organic molecules was performed to covalently attach trifluoroacetyl, tetrazole and 2-bromo-2-methylpropanoyl moieties to the amine groups of the multilayer assembly coating. Furthermore, the versatility of the novel multilayer coating was underpinned by "grafting-to" of phenacyl sulfide-terminated PEO and "grafting-from" of poly(methyl methacrylate) via surface-initiated atom transfer radical polymerization (ATRP).

Hetero diels-alder chemistry for the functionalization of single-walled carbon nanotubes with cyclopentadienyl end-capped polymer strands.

Single-walled carbon nanotubes (SWCNTs) are pre-functionalized with a pyridinyl-based dithioester to undergo a hetero Diels-Alder (HDA) reaction with cyclopentadienyl end-capped poly(methyl)methacrylate (Mn = 2700 g mol(-1) , PDI = 1.14). Fourier transform infrared spectroscopy, thermogravimetric analysis, elemental analysis (EA), and X-ray photoelectron spectroscopy (XPS) evidence the success of the grafting process. The estimated resulting grafting density (from XPS and EA) via the HDA reaction increases by a factor of more than two (0.0774 chains·nm(-2) via XPS) compared with typical values obtained via a direct cyclopentadiene driven Diels-Alder conjugation onto non-functional SWCNTs under similar conditions.

Biomimetic dopamine-diels-alder switches.

Mussel adhesives function as tools for surface modifications of a wide variety of materials due to their remarkable adhesion properties. Herein, a combination of bioinspired mussel adhesives based on a dopamine derivative, polymer chemistry, and well-established Diels-Alder (DA) chemistry leads to a bioinspired switchable surface system that possesses the capability of attaching and detaching specific polymers on demand. A dopaminemaleimide compound, which has been attached to a gold surface under maritime conditions undergoes DA- and retro-DA-click-conjugations with cyclopentadiene-carrying PEG chains. The surface attachment and the subsequent DA/rDA cycles are evidenced via XPS analysis.

Chiral benzamidinate ligands in rare-earth-metal coordination chemistry.

The treatment of the recently reported potassium salt (S)-N,N'-bis-(1-phenylethyl)benzamidinate ((S)-KPEBA) and its racemic isomer (rac-KPEBA) with anhydrous lanthanide trichlorides (Ln = Sm, Er, Yb, Lu) afforded mostly chiral complexes. The tris(amidinate) complex [{(S)-PEBA}(3)Sm], bis(amidinate) complexes [{Ln(PEBA)(2)(µ-Cl)}(2)] (Ln = Sm, Er, Yb, Lu), and mono(amidinate) compounds [Ln(PEBA)(Cl)(2)(thf)(n)] (Ln = Sm, Yb, Lu) were isolated and structurally characterized. As a result of steric effects, the homoleptic 3:1 complexes of the smaller lanthanide atoms Yb and Lu were not accessible. Furthermore, chiral bis(amidinate)-amido complexes [{(S)-PEBA}(2)Ln{N(SiMe(3))(2)}] (Ln = Y, Lu) were synthesized by an amine-elimination reaction and salt metathesis. All of these chiral bis- and tris(amidinate) complexes had additional axial chirality and they all crystallized as diastereomerically pure compounds. By using rac-PEBA as a ligand, an achiral meso arrangement of the ligands was observed. The catalytic activities and enantioselectivities of [{(S)-PEBA}(2)Ln{N(SiMe(3))(2)}] (Ln = Y, Lu) were investigated in hydroamination/cyclization reactions. A clear dependence of the rate of reaction and enantioselectivity on the ionic radius was observed, which showed higher reaction rates but poorer enantioselectivities for the yttrium compound.

Fusing Catechol-Driven Surface Anchoring with Rapid Hetero Diels-Alder Ligation.

We fuse the surface anchoring abilities of catechols with the rapid ligating nature of thiocarbonyl thio-based hetero-Diels-Alder (HDA) reactions via the synthesis of a new small molecule (HDA-DOPA-Cp) combining a HDA moiety with a catechol. Inspired by the mechanism of strong adhesion of marine mussels, we employed catechols as anchors to attach HDA ligation points to silicon wafers. The latter was exploited to generate a base for the HDA reactions on the surface employing α-cyclopentadiene (Cp) functional polymers such as poly(ethylene glycol)-Cp (PEG-Cp) and poly(trifluoro ethyl methacrylate)-Cp (PTFEMA-Cp) as dienes. By utilizing the fast and efficient HDA chemistry in combination with catechol anchoring groups, a new method for creating functional surfaces was developed.

A bioinspired light induced avenue for the design of patterned functional interfaces.

An avenue for the development of spatially resolved functional interfaces is presented. By introducing a novel, photo-reactive molecule - carrying a DOPA functionality and a photo-reactive group - we merge the ability of mussels to adhere to any surface with the spatial and temporal control of photo-click reactions, opening a plethora of applications in the biomedical and materials fields.

A facile avenue to conductive polymer brushes via cyclopentadiene-maleimide Diels-Alder ligation.

Cyclopentadienyl end-capped poly(3-hexylthiophene) was employed to fabricate conductive surface tethered polymer brushes via a facile route based on cyclopentadiene-maleimide Diels-Alder ligation. The efficient nature of the Diels-Alder ligation was further combined with a biomimetic polydopamine-assisted functionalization of surfaces, making it an access route of choice for P3HT surface immobilization.

A facile one-pot route to poly(carboxybetaine acrylamide) functionalized SWCNTs.

An unprecedented one-pot procedure employing a cyclopentadienyl functionalized RAFT agent allowed the grafting of poly(carboxybetaine acrylamide) - a highly functional and biocompatible polymer - from the surface of pristine SWCNTs. The pendant carboxylic acid groups of the surface grafted polymer were further conjugated with single-stranded (ss)-DNA, which was successfully hybridized with a Cy5 labelled complementary DNA strand.

Controlled cell adhesion on poly(dopamine) interfaces photopatterned with non-fouling brushes.

Bioinspired poly(dopamine) (PDA) films are merged with antifouling poly(MeOEGMA) brushes utilizing a nitrile imine-mediated tetrazole-ene cycloaddition (NITEC)-based phototriggered surface encoding protocol. The antifouling brushes were photopatterned on PDA surfaces, leading cells to form confluent layers in the non-irradiated sections, while no adhesion occurred on the brushes resulting in a remarkably precise cell pattern. The presented strategy paves the way for the design of tailor-made patterned cell interfaces.