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Mechanical responsiveness is essential to all biological systems down to the level of tissues and cells. The intra- and extracellular mechanics of such systems are governed by a series of proteins, such as microtubules, actin, intermediate filaments and collagen. As a general design motif, these proteins self-assemble into helical structures and superstructures that differ in diameter and persistence length to cover the full mechanical spectrum. Gels of cytoskeletal proteins display particular mechanical responses (stress stiffening) that until now have been absent in synthetic polymeric and low-molar-mass gels. Here we present synthetic gels that mimic in nearly all aspects gels prepared from intermediate filaments. They are prepared from polyisocyanopeptides grafted with oligo(ethylene glycol) side chains. These responsive polymers possess a stiff and helical architecture, and show a tunable thermal transition where the chains bundle together to generate transparent gels at extremely low concentrations. Using characterization techniques operating at different length scales (for example, macroscopic rheology, atomic force microscopy and molecular force spectroscopy) combined with an appropriate theoretical network model, we establish the hierarchical relationship between the bulk mechanical properties and the single-molecule parameters. Our results show that to develop artificial cytoskeletal or extracellular matrix mimics, the essential design parameters are not only the molecular stiffness, but also the extent of bundling. In contrast to the peptidic materials, our polyisocyanide polymers are readily modified, giving a starting point for functional biomimetic hydrogels with potentially a wide variety of applications, in particular in the biomedical field.

Helical structures play a vital role in nature, offering mechanical rigidity, chirality and structural definition to biological systems. Little is known about the influence of the helical architecture on the intrinsic properties of polymers. Here, we offer an insight into the nano architecture of helical polymers by measuring helical polyisocyanopeptides with single molecule force spectroscopy. An unprecedented large heterogeneity in the stiffness of the polymers was found. The heterogeneity persisted when the stiffness of these polymers was steered by: (1) enhancing the formation of the hydrogen bonding network along the polymer, (2) via pi-pi stacking interactions of aromatic perylenes, and (3) by changing the stereochemistry of the side chain. However, the heterogeneity was lost after completely disrupting the secondary structure by the addition of trifluoroacetic acid. Molecular dynamics simulations revealed three possible structural conformations which can account for the observed heterogeneity and their corresponding energy landscape is proposed.

We report on an ultra-compact co-integrated transmitter and receiver in SiGe BiCMOS technology for short reach optical interconnects. A fully integrated EPIC transceiver chip on silicon photonics technology is described. The chip integrates all photonic and electronic devices for an electro-optic transceiver and has been designed to be testable on wafer-scale. A node-matched diode modulator based on carrier injection is a key building block in the chip design. Its operation performance is presented with respect to insertion loss, signal-to-noise-ratio and power consumption at a 25.78125 Gbit/s in NRZ operation. A novel SiGe based photodetector exhibits a -3 dB bandwidth of up to 70 GHz and a responsivity of >1 A/W. Details are given about the process technology of co-integration of photonic and electronic integrated circuits using both silicon-on-insulator and bulk silicon. The implemented co-integration process requires only few additional process steps, leading to only a slight increase in complexity compared to conventional CMOS and BiCMOS baselines.

Click 'n' chips: Azide and alkyne-bearing sialic acids (purple diamond; see picture) were subjected to high-throughput click chemistry to generate a library of sialic acid analogues. Microarray printing of the library and screening with the siglec family of sialic-acid-binding proteins, led to the identification of high-affinity ligands for siglec-9 and siglec-10.

Carbazole functionalized polyisocyanides are known to exhibit excellent electronic properties (E. Schwartz, et al., Chemistry of Materials, 2010, 22, 2597). The functionalities and properties of such materials crucially depend on the organization and stability of the polymer structure. We combine solid-state Nuclear Magnetic Resonance (NMR) experiments with first-principles calculations of isotropic chemical shifts, within the recently developed converse approach, to rationalize the origin of isotropic chemical shifts in the crystalline monomer l-isocyanoalanine 2-(9H-carbazol-9-yl) ethyl amide (monomer 1) and thereby gain insight into the structural organization of its polymer (polymer 2). The use of state-of-the-art solid-state NMR experiments combined with Density Functional Theory (DFT) based calculations allows an unambiguous assignment of all proton and carbon resonances of the monomer. We were able to identify the structure stabilising interactions in the crystal and understand the influence of the molecular packing in the crystal structure on the chemical shift data observed in the NMR spectra. Here the Nuclear Independent Chemical Shift (NICS) approach allows discriminating between 'physical' interactions amongst neighboring molecules such as ring-current effects and 'chemical' interactions such as hydrogen bonding. This analysis reveals that the isocyanide monomer is stabilized by multiple hydrogen bonds such as a bifurcated hydrogen bond involving -N-H, -C-H and O=C- moieties and Ar-H···C≡N- hydrogen bonding (Ar = aromatic group). Based on the geometrical arrangement it is postulated that the carbazole units are involved in the weak σ-π interactions giving rise to a Herringbone packing of the molecules. The chemical shift analysis of the polymer spectra readily establishes the existence of N-H···O=C hydrogen bonds despite the limited resolution exhibited by the polymer spectra. It is also elucidated that the relative arrangement of the carbazole units in the polymer differs significantly from that of the monomer.

Stable helical polymers with a preferred handedness are compounds that offer intriguing characteristics. This review describes the progress in the synthesis of helical polyisocyanides and the investigations to determine their structural properties, such as helical pitch and handedness, by spectroscopic measurements and high resolution AFM. This review is not intended to be comprehensive; its purpose is to highlight recent studies that allow a better understanding of the main aspects of helical polyisocyanides.

The straightforward syntheses of polyisocyanides containing the alanine-cysteine motif in their side chains have been achieved. Detailed characterization of the polymers revealed a well-defined and highly stable helical conformation of the polyimine backbone responsible for the formation of rodlike structures of over one hundred nanometers. The 4(1) helix is further stabilized by beta-sheet-like interactions between the peptide arms. As a result, the cysteine sulfur atoms are regularly aligned along the polymer axis, which provides a unique platform for the scaffolding of various entities by using versatile click-chemistry postmodification approaches. For instance, pyrene derivatives were introduced through thio-specific reactions involving either maleimide, iodoacetamide, or thioester groups, leading to arrays of stacked chromophores with excimer-like emission. A water-soluble cysteine-rich polyisocyanide was successfully biotinylated and coupled to streptavidin.

The design and synthesis of functional biomimetic water soluble polymers with a defined secondary structure has been developed using β-sheet polyisocyanopeptide scaffolds. Water soluble isocyanopolymers were prepared by random copolymerisation of the azido functionalized isocyanopeptides with nonfunctionalised methyl ester isocyanides derived from alanine. Upon saponification of the latter function a rigid rod water soluble polymer was obtained with an accessible azide for postfunctionalization. The potential of these biomimetic polymers was successfully demonstrated by using the click chemistry reaction of these polymers with an acetylene functionalised rhodamine dye.

Photovoltaic devices incorporating perylene-substituted polyisocyanide materials have been demonstrated, using blend systems with polythiophene- and polyfluorene-based conjugated polymers. Prototypical structures with nominal (1:1) blend weight ratios of the polyisocyanide with poly(3-hexylthiophene) (P3HT) and poly(9,9'-dioctylfluorene-co-bis(N,N'-(4-butylphenyl))-bis(N,N'- phenyl)-1,4-phenyldiamine) (PFB) readily showed an order of magnitude improvement in power conversion efficiency, as compared to analogous blend architectures using a perylene (PDI) monomer, whereas the performance of strongly phase-separated F8BT (poly(9,9- dioctylfluorene-co-benzothidiazole) blend devices showed no such improvement. We propose that the use of polyisocyanide chains as a molecular template offers a method by which the morphology and connectivity of photovoltaic blends can be modified and enhanced. © 2009 American Chemical Society.

The electronic transport properties of stacks of perylene-bis(dicarboximide) (PDI) chromophores, covalently fixed to the side arms of rigid, helical polyisocyanopeptides, are studied using thin-film transistors. In device architectures where the transistor channel lengths are somewhat greater than the average polymer chain length, carrier mobilities of order 10−3 cm2 V−1 s−1 at 350 K are found, which are limited by inter-chain transport processes. The influence of π–π interactions on the material properties is studied by using PDIs with and without bulky substituents in the bay area. In order to attain a deeper understanding of both the electronic and the electronic-transport properties of these systems, studies of self-assembly on surfaces are combined with electronic characterization using Kelvin probe force microscopy, and also a theoretical study of electronic coupling. The use of a rigid polymer backbone as a scaffold to achieve a full control over the position and orientation of functional groups is of general applicability and interest in the design of building blocks for technologically important functional materials, as well as in more fundamental studies of chromophoric interactions.

The physicochemical properties of organic (multi)component films for optoelectronic applications depend on both the mesoscopic and nanoscale architectures within the semiconducting material. Two main classes of semiconducting materials are commonly used: polymers and (liquid) crystals of small aromatic molecules. Whereas polymers (e.g., polyphenylenevinylenes and polythiophenes) are easy to process in solution in thin and uniform layers, small molecules can form highly defined (liquid) crystals featuring high charge mobilities. Herein, we combine the two material types by employing structurally well-defined polyisocyanopeptide polymers as scaffolds to precisely arrange thousands of electron-accepting molecules, namely, perylenebis(dicarboximides) (PDIs), in defined chromophoric wires with lengths of hundreds of nanometers. The polymer backbone enforces high control over the spatial location of PDI dyes, favoring both enhanced exciton and charge transfer. When blended with an electron-donor system such as regioregular poly(3-hexylthiophene), this polymeric PDI shows a relative improvement in charge generation and diffusion with respect to monomeric, aggregated PDI. In order to correlate this enhanced behavior with respect to the architecture, atomic force microscopy investigations on the mixtures were carried out. These studies revealed that the two polymers form interpenetrated bundles having a nanophase-segregated character and featuring a high density of contact points between the two different phases. In order to visualize the relationship between the architecture and the photovoltaic efficiency, Kelvin probe force microscopy measurements were carried out on submonolayer-thick films. This technique allowed for the first time the direct visualization of the photovoltaic activity occurring in such a nanoscale phase-segregated ultrathin film with true nanoscale spatial resolution, thus making possible a study of the correlation between function and architecture with nanoscale resolution.

Contains fulltext : 36533.pdf (Publisher’s version ) (Closed access) Rigid rod polyisocyanopeptides have been synthesised containing acetylene groups on the side arms as scaffolds for multifunctional derivatisation by the copper-catalysed click reaction between an acetylene and an azide. All materials were characterised in detail by spectroscopic procedures and for the processable polymers, atomic force microscopy was used to determine the molecular weight parameters. The solubility properties of the synthesised macromolecules are very dependent on the stereochemistry and/or the presence of solubilising trimethylsilyl groups on the acetylene function. The potential for derivatisation of the acetylene-containing materials using click chemistry was successfully demonstrated by the reaction of these polymers with aliphatic tails functionalised with azide moieties.

The thermal motion of polymer chains in a crowded environment is anisotropic and highly confined. Whereas theoretical and experimental progress has been made, typically only indirect evidence of polymer dynamics is obtained either from scattering or mechanical response. Toward a complete understanding of the complicated polymer dynamics in crowded media such as biological cells, it is of great importance to unravel the role of heterogeneity and molecular individualism. In the present work, we investigate the dynamics of synthetic polymers and the tube-like motion of individual chains using time-resolved fluorescence microscopy. A single fluorescently labeled polymer molecule is observed in a sea of unlabeled polymers, giving access to not only the dynamics of the probe chain itself but also to that of the surrounding network. We demonstrate that it is possible to extract the characteristic time constants and length scales in one experiment, providing a detailed understanding of polymer dynamics at the single chain level. The quantitative agreement with bulk rheology measurements is promising for using local probes to study heterogeneity in complex, crowded systems.

Item does not contain fulltext The formation and reactivity of pyridine diimine rhodium(l) alkyl complexes without beta-hydrogens (Me, Bz, CH2SiMe3) is described. In contrast to the corresponding cobalt complexes, the rhodium complexes could not be activated to polymerise ethene. Rh ethyl complexes could not be prepared. Examples of hydrogen transfer to and from the ligand were observed, illustrating the active role the pyridine diimine ligand can play in the reactions of its complexes. Decomposition via loss of free ligand was observed in many cases, indicating that the pyridine diimine ligand is not a very suitable one for Rh-I. (C) 2004 Elsevier B.V. All rights reserved.

The siglec family of sialic acid-binding proteins are endocytic immune cell receptors that are recognized as potential targets for cell directed therapies. CD33 and CD22 are prototypical members and are validated candidates for targeting acute myeloid leukaemia and non-Hodgkin's lymphomas due to their restricted expression on myeloid cells and B-cells, respectively. While nanoparticles decorated with high affinity siglec ligands represent an attractive platform for delivery of therapeutic agents to these cells, a lack of ligands with suitable affinity and/or selectivity has hampered progress. Herein we describe selective ligands for both of these siglecs, which when displayed on liposomal nanoparticles, can efficiently target the cells expressing them in peripheral human blood. Key to their identification was the development of a facile method for chemo-enzymatic synthesis of disubstituted sialic acid analogues, combined with iterative rounds of synthesis and rapid functional analysis using glycan microarrays.

An optical filter based on all-polymer grating-assisted directional coupler is demonstrated. The wavelength tuning is differentially driven. The heater-electrodes created on the sidewalls of the polymer ridge can either blue- or red-shift the central wavelength. A total tuning range of 301 nm is achieved experimentally. The maximal local temperature gradient introduced across the coupler region is only 55°C-68°C. The filter is also insensitive to uniform ambient temperature change. Central wavelength jitter of ±3 nm is observed when the chip holder temperature cycles between 20°C and 80°C.

Multicore, compact, and low-crosstalk polymer waveguides have been designed, fabricated, and characterized. These single-mode waveguides are arranged in five layers following a hexagonal lattice with 20-\(\mu \) m pitch. The waveguides exhibit similar propagation loss of

This contribution describes the synthesis and full characterization of oligo(ethylene glycol) functionalized polyisocyanopeptides. The thermal behavior of the resulting semi-flexible polymers was investigated in diluted aqueous conditions and features a tunable Lower Critical Solution Temperature (LCST). In line with previously described oligo(ethylene glycol) decorated polymers, the LCST of the materials shows a very small hysteresis effect and directly correlates with the oligo(ethylene glycol) side-chains length; short oligo(ethylene glycol) substituents are associated with lower LCST. In contrast with poly[oligo(ethylene glycol) methacrylate], a significant effect of the degree of polymerization (DP) of the poly(isocyanopeptide) core on the LSCT of the materials was observed. Most remarkably, poly(isocyanopeptide)-graft-oligo(ethylene glycol) chains of high DP lead to the reversible formation of strong hydrogels above the transition temperature, even at very low polymer concentration (0.1 wt.%). AFM studies point towards the formation of a highly organized fibrillar network in the gel-state, reminiscent of structures observed for low molecular weight gelators, polysaccharides, and protein-based (hydro)gels. It is proposed that the stiff and well-defined helical poly(isocyanopeptide) backbone avoids the collapse of the chains into globules at the transition temperature as usually observed for more flexible systems. Thus, above a critical DP the semi-flexible non-linear PEGs chains are getting kinetically trapped in an extended fibrillar network, when the oligo(ethylene glycol) corona hydrophilicity is lowered at higher temperature. As a result these polymers exhibit a strong ability to gel water at extremely low polymer concentrations.

The Siglec family of sialic acid-binding proteins are differentially expressed on white blood cells of the immune system and represent an attractive class of targets for cell-directed therapy. Nanoparticles decorated with high-affinity Siglec ligands show promise for delivering cargo to Siglec-bearing cells, but this approach has been limited by a lack of ligands with suitable affinity and selectivity. Building on previous work employing solution-phase sialoside library synthesis and subsequent microarray screening, we herein report a more streamlined 'on-chip' synthetic approach. By printing a small library of alkyne sialosides and subjecting these to 'on-chip' click reactions, the largest sialoside analogue library to date was generated. Siglec-screening identified a selective Siglec-7 ligand, which when displayed on liposomal nanoparticles, allows for targeting of Siglec-7(+) cells in peripheral human blood. In silico docking to the crystal structure of Siglec-7 provides a rationale for the affinity gains observed for this novel sialic acid analogue.

Rigid rod polyisocyanopeptides bearing phthalocyanines as pendant groups have been synthesised through CuAAC of polyisocyanopeptides containing acetylene groups with zinc(II) phthalocyanine azide. As confirmed by UV/Vis, fluorescence, and circular dichroism spectroscopies, the phthalocyanines are arranged in a helical fashion along the polymer backbone, forming the longest reported well-defined phthalocyanine assembly described to date.

We report on the synthesis and detailed photo-physical investigation of four model chromophore side chain polyisocyanopeptides: two homopolymers of platinum-porphyrin functionalized polyisocyanopeptides (Pt-porphyrin-PIC) and perylene-bis(dicarboximide) functionalized polyisocyanopeptides (PDI-PIC), and two statistical copolymers with different ratios of Pt-porphyrin and PDI molecules attached to a rigid, helical polyisocyanopeptide backbone. (1)H NMR and circular dichroism measurements confirm that our model compounds retain a chiral architecture in the presence of the chromophores. The combination of Pt-porphyrin and PDI chromophores allows charge- and/or energy transfer to happen. We observe the excitation and relaxation pathways for selective excitation of the Pt-porphyrin and PDI chromophores. Studies of photoluminescence and transient absorption on nanosecond and picosecond scales upon excitation of Pt-porphyrin chromophores in our multichromophoric assemblies show similar photophysical features to those of the Pt-porphyrin monomers. In contrast, excitation of perylene chromophores results in a series of energy and charge transfer processes with the Pt-porphyrin group and forms additional charge-transfer states, which behave as an intermediate state that facilitates electronic coupling in these multichromophoric systems.

This critical review describes recent efforts in the field of chromophoric scaffolding. The advances in this research area, with an emphasis on rigid scaffolds, for example, synthetic polymers, carbon nanotubes (CNTs), nucleic acids, and viruses, are presented (166 references).

The optimization of the electronic properties of molecular materials based on optically or electrically active organic building blocks requires a fine-tuning of their self-assembly properties at surfaces. Such a fine-tuning can be obtained on a scale up to 10 nm by mastering principles of supra molecular chemistry, i.e., by using suitably designed molecules interacting via pre-programmed noncovalent forces. The control and fine-tuning on a greater length scale is more difficult and challenging. This Research News highlights recent results we obtained on a new class of macromolecules that possess a very rigid backbone and side chains that point away from this backbone. Each side chain contains an organic semiconducting moiety, whose position and electronic interaction with neighboring moieties are dictated by the central macromolecular scaffold. A combined experimental and theoretical approach has made it possible to unravel the physical and chemical properties of this system across multiple length scales. The (opto)electronic properties of the new functional architectures have been explored by constructing prototypes of field-effect transistors and solar cells, thereby providing direct insight into the relationship between architecture and function.

We report on the self-assembly and the electrical characterization of bicomponent films consisting of an organic semiconducting small molecule blended with a rigid polymeric scaffold functionalized in the side chains with monomeric units of the same molecule. The molecule and polymer are a perylene-bis(dicarboximide) monomer (M-PDI) and a perylene-bis(dicarboximide)-functionalized poly(isocyanopeptide) (P-PDI), which have been codeposited on SiO(x) and mica substrates from solution. These bicomponent films have been characterized by atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM), revealing the relationship between architecture and function for various supramolecular nanocrystalline arrangements at a nanometer spatial resolution. Monomer-polymer interactions can be controlled by varying solvent and/or substrate polarity, so that either the monomer packing dictates the polymer morphology or vice versa, leading to a morphology exhibiting M-PDI nanocrystals connected with each other by P-PDI polymer wires. Compared to pure M-PDI or P-PDI films, those bicomponent films that possess polymer interconnections between crystallites of the monomer display a significant improvement in electrical connectivity and a 2 orders of magnitude increase in charge carrier mobility within the film, as measured in thin film transistor (TFT) devices. Of a more fundamental interest, our technique allows the bridging of semiconducting crystals, without the formation of injection barriers at the connection points.

Self-trapping of NH-stretch vibrational excitations in synthetic beta-sheet helices is observed using femtosecond infrared pump-probe spectroscopy. In a dialanine-based beta-sheet helix, the transient-absorption change upon exciting the NH-stretch mode exhibits a negative absorption change at the fundamental frequency and two positive peaks at lower frequencies. These two induced-absorption peaks are characteristic for a state in which the vibrational excitation is self-trapped on essentially a single NH-group in the hydrogen-bonded NH center dot center dot center dot OC chain, forming a small (Holstein) vibrational polaron. By engineering the structure of the polymer we can disrupt the hydrogen-bonded NH center dot center dot center dot OC chain, allowing us to eliminate the self-trapping, as is confirmed from the NH-stretch pump-probe response. We also investigate a trialanine-based beta-sheet helix, where each side chain participates in two NH center dot center dot center dot OC chains with different hydrogen-bond lengths. The chain with short hydrogen bonds shows the same self-trapping behavior as the dialanine-based beta-sheet helix, whereas in the chain with long hydrogen bonds the self-trapping is too weak to be observable.

This article describes the first surface-initiated polymerization of isocyanide monomers onto various surfaces in a controlled manner. Brushes up to 200 nm could be easily obtained within 3 h of polymerization, and the polymer growth was studied as a function of reaction time, monomer concentration, and growth conditions, using atomic force microscopy (AFM) and ellipsometry. The monomers used in this study contain dipeptide (L,L-Ala-Ala) side groups; circular dichroism (CD) measurements, Fourier transform infrared spectroscopy (FTIR), and AFM confirmed that the well-defined helical conformation was retained in the polyisocyanide brushes with hydrogen bonds along the polymer chains.

Polyisocyanopeptides have been synthesised containing acetylene groups on the side arms as scaffolds for multifunctional derivatisation by the copper-catalysed click reaction with a variety of azides. By using ethylene glycol azide and perylene azide chromophoric water-soluble polymeric nanowires (Mw 1–2 million Daltons) were formed. The potential to incorporate multiple chromophores was also demonstrated by the reaction of the acetylene-containing polymers with perylene azide and azidocoumarin dyes. In the latter case a blue-shifted emission of the coumarin was observed due to the interaction with the coupled perylene molecules. In particular the ability to form water-soluble dye-containing polymers, which can be modified by the addition of biomolecules, such as antibodies, proteins and peptides, give materials that are very promising as novel biomarker materials.

Contains fulltext : 36705.pdf (Author’s version postprint ) (Open Access) The structure of the active complex in the Ni-cotolyzed polymerization of isocyonides to give polyisocyanides is investigated. It is shown by X-ray absorption spectroscopy (XAS), including EXAFS (extended X-ray absorption fine structure) and XANES (X-ray absorption near edge structure), and single-crystal X-ray diffraction, to contain a carbene-like ligand. This is the first structural characterization of a crucial intermediate in the so-coiled merry-go-round mechanism for Ni-catolyzed isocyanide polymerization.

The assembly behavior at surfaces of very stiff polyisocyanopeptides (PICs) functionalized with semiconducting perylenebis(dicarboximide) (PDI) side chains has been investigated by atomic force microscopy. These multi-chromophoric arrays are unique as they combine an ultra-stiff central polymer main-chain scaffold upon which the PDI chromophores can self-organize through π–π stacking, making them interesting and versatile building blocks for nanoelectronics. In this paper we compare three PIC derivatives featuring different side groups: M1—no chromophores, M2—chromophores capable of π–π stacking, and M3—chromophores where the stacking is hindered by the presence of bulky substituents in the bay area of the PDI. The effect of the different side functionalizations on the macromolecule assembly at surfaces was compared by studying the morphology and aggregation tendency of all three polymers when adsorbed on silicon, mica and graphite substrates. Making use of nano-manipulation of these functional rods with the AFM tip gave insight into the polymer structure and its coiling behaviour.

Solidification controlled by vacancy diffusion is studied by Monte Carlo simulations of a two-dimensional Ising model defined by a Hamiltonian which models a thermally driven fluid-solid phase transition. The nonequilibrium morphology of the growing solid is studied as a function of time as the system relaxes into equilibrium described by a temperature. At low temperatures the model exhibits fractal growth at early times and crossover to compact solidification as equilibrium is approached.

A simple two-dimensional microscopic model is proposed to describe solidifcation processes in systems with impurities which are miscible only in the fluid phase. Computer simulation of the model shows that the resulting solids are fractal over a wide range of impurity concentrations and impurity diffusional constants. A fractal-forming mechanism is suggested for impurity-controlled solidification which is consistent with recent experimental observations of fractal growth of solid phospholipid domains in monolayers. The Journal of Chemical Physics is copyrighted by The American Institute of Physics.