Alan E. Rowan

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Organization: Raboud University of Nijmegen , Belgium

Department: Department of Organic Chemistry

Title: (PhD)

TOPICS

Material Chemistry

Polymer

Inorganic Chemistry

Chemicals
References

Controlling T-Cell Activation with Synthetic Dendritic Cells Using the Multivalency Effect

Co-reporter:Roel Hammink, Subhra Mandal, Loek J. Eggermont, Marco Nooteboom, Peter H. G. M. Willems, Jurjen Tel, Alan E. Rowan, Carl G. Figdor, and Kerstin G. Blank

ACS Omega March 2017? Volume 2(Issue 3) pp:937-937

Publication Date(Web):March 16, 2017

DOI:10.1021/acsomega.6b00436

Artificial antigen-presenting cells (aAPCs) have recently gained a lot of attention. They efficiently activate T cells and serve as powerful replacements for dendritic cells in cancer immunotherapy. Focusing on a specific class of polymer-based aAPCs, so-called synthetic dendritic cells (sDCs), we have investigated the importance of multivalent binding on T-cell activation. Using antibody-functionalized sDCs, we have tested the influence of polymer length and antibody density. Increasing the multivalent character of the antibody-functionalized polymer lowered the effective concentration required for T-cell activation. This was evidenced for both early and late stages of activation. The most important effect observed was the significantly prolonged activation of the stimulated T cells, indicating that multivalent sDCs sustain T-cell signaling. Our results highlight the importance of multivalency for the design of aAPCs and will ultimately allow for better mimics of natural dendritic cells that can be used as vaccines in cancer treatment.Topics: Antibodies and Immunoglobulins; Biochemistry; Cell and Molecular biology; Organic compounds and Functional groups; Peptides and Proteins; Polymers; Proteins;

Metal ion-exchange on the muscovite mica surface

Co-reporter:Wester de Poel, Sarah L. Vaessen, Jakub Drnec, Anthonius H.J. Engwerda, Eleanor R. Townsend, Stelian Pintea, Aryan E.F. de Jong, Maciej Jankowski, Francesco Carlà, Roberto Felici, Johannes A.A.W. Elemans, Willem J.P. van Enckevort, Alan E. Rowan, Elias Vlieg

Surface Science 2017 Volume 665(Volume 665) pp:

Publication Date(Web):1 November 2017

DOI:10.1016/j.susc.2017.08.013

•Mica surface ions were exchanged for Ag, Ca, Mn, Fe, Ni, Cu, Zn, Co, and Cd.•The metal ions remain at the surface after washing with water.•No counter ions are present after metal ion exchange.The surface potassium ions of muscovite mica were exchanged for several different metal ions from aqueous solution (Ag, Ca, V, Mn, Fe, Ni, Cu, Zn, Co, and Cd). The surfaces were rinsed in water, dried under nitrogen atmosphere, and subsequently analysed using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and, for half the systems, surface X-ray diffraction (SXRD). XPS and SXRD confirmed the presence of the different metal ions at the muscovite mica surface, with a partial monolayer of the monovalent and divalent ions present on the surface. No counter ions from the used salts were detected. AFM revealed that Ni-, and Fe-terminated muscovite mica surfaces were partially covered by nanoparticles, most likely consisting of metal (hydr)oxide. The exchanged ions remained on the surface after rinsing with ultra pure water three times. SXRD showed that Cd and Ag have a lower affinity for the muscovite mica surface than Cu, Ca, and Mn.Download high-res image (118KB)Download full-size image

Carbenoid transfer reactions catalyzed by a ruthenium porphyrin macrocycle

Co-reporter:Onno I. van den Boomen, Ruud G.E. Coumans, Niels Akeroyd, Theo P.J. Peters, Paul P.J. Schlebos, Jan Smits, René de Gelder, Johannes A.A.W. Elemans, Roeland J.M. Nolte, Alan E. Rowan

Tetrahedron 2017 Volume 73, Issue 33(Issue 33) pp:

Publication Date(Web):17 August 2017

DOI:10.1016/j.tet.2017.05.035

A ruthenium porphyrin functionalized with a cavity based on diphenylglycoluril is applied as a catalyst in carbenoid transfer reactions using α-diazoesters as substrates. The latter compounds contain a blocking group connected via an α,ω-dioxyalkyl spacer of 3 or 6 carbon atoms. The reaction of an excess of the α-diazoester with the short spacer with the ruthenium porphyrin macrocycle leads to two products, a [2]rotaxane and a maleate ester, which are the result of dimerization reactions at the inside and the outside of the cavity, respectively. A similar reaction using the α-diazoester with the long spacer also yields high molecular weight species. Mass spectrometric and NMR studies suggest that CH and/or CC insertion reactions take place on the thread of the initially formed rotaxane. It is proposed that these reactions are favoured by effective molarity effects because of the close proximity of reactive species in the interlocked geometry.Download high-res image (267KB)Download full-size image

Bundle Formation in Biomimetic Hydrogels

Co-reporter:Maarten Jaspers, A. C. H. Pape, Ilja K. Voets, Alan E. Rowan, Giuseppe Portale, and Paul H. J. Kouwer

Biomacromolecules 2016 Volume 17(Issue 8) pp:

Publication Date(Web):July 13, 2016

DOI:10.1021/acs.biomac.6b00703

Bundling of single polymer chains is a crucial process in the formation of biopolymer network gels that make up the extracellular matrix and the cytoskeleton. This bundled architecture leads to gels with distinctive properties, including a large-pore-size gel formation at very low concentrations and mechanical responsiveness through nonlinear mechanics, properties that are rarely observed in synthetic hydrogels. Using small-angle X-ray scattering (SAXS), we study the bundle formation and hydrogelation process of polyisocyanide gels, a synthetic material that uniquely mimics the structure and mechanics of biogels. We show how the structure of the material changes at the (thermally induced) gelation point and how factors such as concentration and polymer length determine the architecture, and with that, the mechanical properties. The correlation of the gel mechanics and the structural parameters obtained from SAXS experiments is essential in the design of future (synthetic) mimics of biopolymer networks.

Nanoscale Study of Polymer Dynamics

Co-reporter:Masoumeh Keshavarz, Hans Engelkamp, Jialiang Xu, Els Braeken, Matthijs B. J. Otten, Hiroshi Uji-i, Erik Schwartz, Matthieu Koepf, Anja Vananroye, Jan Vermant, Roeland J. M. Nolte, Frans De Schryver, Jan C. Maan, Johan Hofkens, Peter C. M. Christianen, and Alan E. Rowan

ACS Nano 2016 Volume 10(Issue 1) pp:1434

Publication Date(Web):December 20, 2015

DOI:10.1021/acsnano.5b06931

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.Keywords: reptation; single molecule studies; time-resolved fluorescence microscopy;

Tuning Hydrogel Mechanics Using the Hofmeister Effect

Co-reporter:Maarten Jaspers;Paul H. J. Kouwer

Advanced Functional Materials 2015 Volume 25( Issue 41) pp:6503-6510

Publication Date(Web):

DOI:10.1002/adfm.201502241

The mechanical properties of hydrogels are commonly modified by changing the concentration of the molecular components. This approach, however, does not only change hydrogel mechanics, but also the microstructure, which in turn alters the macroscopic properties of the gel. Here, the Hofmeister effect is used to change the thermoresponsiveness of polyisocyanide hydrogels. In contrast to previous Hofmeister studies, the effect is used to change the phase transition temperatures and to tailor the mechanics of the thermoresponsive (semiflexible) polymer gels. It is demonstrated that the gel stiffness can be manipulated over more than two orders of magnitude by the addition of salts. Surprisingly, the microstructure of the gels does not change upon salt addition, demonstrating that the Hofmeister effect provides an excellent route to change the mechanical properties without distorting other influential parameters of the gel.

Polymer-Based Synthetic Dendritic Cells for Tailoring Robust and Multifunctional T Cell Responses

Co-reporter:Subhra Mandal, Roel Hammink, Jurjen Tel, Zaskia H. Eksteen-Akeroyd, Alan E. Rowan, Kerstin Blank, and Carl G. Figdor

ACS Chemical Biology 2015 Volume 10(Issue 2) pp:485

Publication Date(Web):November 5, 2014

DOI:10.1021/cb500455g

Dendritic cells (DCs) are antigen-presenting cells that play an essential role in T cell activation. Recent efforts in cancer immunotherapy have been directed at the development of artificial antigen presenting cells (aAPCs) loaded with tumor antigens. These aAPCs are designed to mimic DCs with the goal of triggering an efficient and specific T cell response directed against the tumor. We have designed a novel synthetic dendritic cell (sDC) that possesses the essential features of natural DCs. Our sDC is based on a semiflexible poly(isocyano peptide) polymer and carries anti-CD3 antibodies (αCD3) for triggering the T cell receptor/CD3 complex as well as anti-CD28 antibodies (αCD28) as a co-stimulatory signal. Multiple copies of both antibodies facilitate multivalent binding similar to natural DCs. The high mobility of these polymer-bound antibodies, reminiscent of protein motility in a natural plasma membrane, enables receptor rearrangements to occur during T cell activation. We show that our bifunctional αCD3/αCD28-sDC triggers T cell activation at significantly lower antibody concentrations than freely soluble antibodies. This superior performance is further demonstrated in comparison to a mixture of monofunctional αCD3-sDC and αCD28-sDC. The presence of both antibodies on the same polymer not only reduces the threshold for T cell activation but, more importantly, critically shapes the specificity of the T cell response. αCD3/αCD28-sDC is a far more efficient activator of multifunctional killer cells. These findings demonstrate the potential of multifunctional polymers for mimicking natural DCs, paving the way for their exploitation in immunotherapeutic strategies.

Interfacial Activation of Candida antarctica Lipase B: Combined Evidence from Experiment and Simulation

Co-reporter:Themistoklis Zisis, Peter L. Freddolino, Petri Turunen, Muriel C. F. van Teeseling, Alan E. Rowan, and Kerstin G. Blank

Biochemistry 2015 Volume 54(Issue 38) pp:

Publication Date(Web):September 8, 2015

DOI:10.1021/acs.biochem.5b00586

Lipase immobilization is frequently used for altering the catalytic properties of these industrially used enzymes. Many lipases bind strongly to hydrophobic surfaces where they undergo interfacial activation. Candida antarctica lipase B (CalB), one of the most commonly used biocatalysts, is frequently discussed as an atypical lipase lacking interfacial activation. Here we show that CalB displays an enhanced catalytic rate for large, bulky substrates when adsorbed to a hydrophobic interface composed of densely packed alkyl chains. We attribute this increased activity of more than 7-fold to a conformational change that yields a more open active site. This hypothesis is supported by molecular dynamics simulations that show a high mobility for a small “lid” (helix α5) close to the active site. Molecular docking calculations confirm that a highly open conformation of this helix is required for binding large, bulky substrates and that this conformation is favored in a hydrophobic environment. Taken together, our combined approach provides clear evidence for the interfacial activation of CalB on highly hydrophobic surfaces. In contrast to other lipases, however, the conformational change only affects large, bulky substrates, leading to the conclusion that CalB acts like an esterase for small substrates and as a lipase for substrates with large alcohol substituents.

Slippage of a Porphyrin Macrocycle over Threads of Varying Bulkiness: Implications for the Mechanism of Threading Polymers through a Macrocyclic Ring

Co-reporter:Dr. Alexer B. C. Deutman;Dr. Shaji Varghese;Mohamed Moalin;Dr. Johannes A. A. W. Elemans; Alan E. Rowan; Roel J. M. Nolte

Chemistry - A European Journal 2015 Volume 21( Issue 1) pp:360-370

Publication Date(Web):

DOI:10.1002/chem.201403740

Abstract

Threading of a polymer through a macrocyclic ring may occur directly, that is, by finding the end of the polymer chain, or by a process in which the polymer chain first folds and then threads through the macrocyclic ring in a hairpin-like conformation. We present kinetic and thermodynamic studies on the threading of a macrocyclic porphyrin receptor (H₂1) onto molecular threads that are blocked on one side and are open on the other side. The open side is modified by groups that vary in ease of folding and in bulkiness. Additionally, the threads contain a viologen binding site for the macrocyclic receptor, which is located close to the blocking group. The rates of threading of H₂1 were measured under various conditions, by recording as a function of time the quenching of the fluorescence of the porphyrin, which occurs when receptor H₂1 reaches the viologen binding site. The kinetic data suggest that threading is impossible if the receptor encounters an open side that is sterically encumbered in a similar way as a folded polymer chain. This indicates that threading of polymers through macrocyclic compounds through a folded chain mechanism is unlikely.

Designing Processive Catalytic Systems. Threading Polymers through a Flexible Macrocycle Ring

Co-reporter:Alexander B. C. Deutman ; Seda Cantekin ; Johannes A. A. W. Elemans ; Alan E. Rowan ;Roeland J. M. Nolte

Journal of the American Chemical Society 2014 Volume 136(Issue 25) pp:9165-9172

Publication Date(Web):May 22, 2014

DOI:10.1021/ja5032997

The translocation of polymers through pores is widely observed in nature and studying their mechanism may help understand the fundamental features of these processes. We describe here the mechanism of threading of a series of polymers through a flexible macrocyclic ring. Detailed kinetic studies show that the translocation speed is slower than the translocation speed through previously described more rigid macrocycles, most likely as a result of the wrapping of the macrocycle around the polymer chain. Temperature-dependent studies reveal that the threading rate increases on decreasing the temperature, resulting in a negative activation enthalpy of threading. The latter is related to the opening of the cavity of the macrocycle at lower temperatures, which facilitates binding. The translocation process along the polymer chain, on the other hand, is enthalpically unfavorable, which can be ascribed to the release of the tight binding of the macrocycle to the chain upon translocation. The combined kinetic and thermodynamic data are analyzed with our previously proposed consecutive-hopping model of threading. Our findings provide valuable insight into the translocation mechanism of macrocycles on polymers, which is of interest for the development of processive catalysts, i.e., catalysts that thread onto polymers and move along it while performing a catalytic action.

Muscovite mica: Flatter than a pancake

Co-reporter:Wester de Poel, Stelian Pintea, Jakub Drnec, Francesco Carla, Roberto Felici, Peter Mulder, Johannes A.A.W. Elemans, Willem J.P. van Enckevort, Alan E. Rowan, Elias Vlieg

Surface Science 2014 Volume 619() pp:19-24

Publication Date(Web):January 2014

DOI:10.1016/j.susc.2013.10.008

•One out of 2500 AFM measurements detected a step on muscovite surfaces.•Phase contrast microscopy detected a step-free area of 1 mm2 on muscovite.•Phase sensitive interferometry also did not find steps on this square millimetre.•Surface X-ray diffraction showed that 13 × 10 mm of muscovite is atomically flat.•The flatness of the muscovite is quality dependent.Muscovite mica is a widely used material because of its transparency, heat resistance and especially its flatness. This study investigates how flat muscovite mica really is. The surface of cleaved muscovite mica was studied with the help of several optical techniques, surface X-ray diffraction and with atomic force microscopy. The results show that for high-quality muscovite mica, large (> 1 cm2) step-free surface areas exist, which makes it one of the flattest materials around. Several reasons are given to explain why this crystal is so incredibly flat. The flatness of muscovite mica can be exploited in applications such as the surface force apparatus and creating a flat interface for organic solar cells.

Strong Induced-Fit Binding of Viologen and Pyridine Derivatives in Adjustable Porphyrin Cavities

Co-reporter:Dr. Alexer B. C. Deutman;Jan M. M. Smits;Dr. René deGelder;Dr. Johannes A. A. W. Elemans; Roel J. M. Nolte; Alan E. Rowan

Chemistry - A European Journal 2014 Volume 20( Issue 36) pp:11574-11583

Publication Date(Web):

DOI:10.1002/chem.201402919

Abstract

The synthesis and binding properties of new porphyrin cage compounds consisting of a rigid diphenylglycoluril part, which is connected via flexible bis(ethyleneoxy) spacers to a (metallo)porphyrin “roof”, are reported. Binding of viologen guests and pyridine ligands in these porphyrin cages are accompanied by significant conformational reorganizations of the hosts. Despite these structural changes, association constants are still very high, revealing that not only receptors that bind guests according to a lock-and-key mechanism but also those that bind guests by an induced-fit mechanism can exhibit strong binding.

Therapeutic nanoworms: towards novel synthetic dendritic cells for immunotherapy

Co-reporter:Subhra Mandal, Zaskia H. Eksteen-Akeroyd, Monique J. Jacobs, Roel Hammink, Matthieu Koepf, Annechien J. A. Lambeck, Jan C. M. van Hest, Christopher J. Wilson, Kerstin Blank, Carl G. Figdor and Alan E. Rowan

Chemical Science 2013 vol. 4(Issue 11) pp:4168-4174

Publication Date(Web):02 Aug 2013

DOI:10.1039/C3SC51399H

A new class of antibody-functionalized, semi-flexible and filamentous polymers (diameter 5–10 nm, length ∼200 nm) with a controlled persistence length, a high degree of stereoregularity and the potential for multiple simultaneous receptor interactions has been developed. We have decorated these highly controlled, semi-stiff polymers with T cell activating anti-CD3 antibodies and analyzed their application potential as simple synthetic mimics of dendritic cells (sDCs). Our sDCs do not only activate T cells at significantly lower concentrations than free antibodies or rigid sphere-like counterparts (PLGA particles) but also induce a more robust T cell response. Our novel design further yields sDCs that are biocompatible and non-toxic. The observed increased efficacy highlights the importance of architectural flexibility and multivalency for modulating T cell response and cellular function in general.

Stiffness versus architecture of single helical polyisocyanopeptides

Co-reporter:Arend M. van Buul, Erik Schwartz, Patrick Brocorens, Matthieu Koepf, David Beljonne, Jan C. Maan, Peter C. M. Christianen, Paul H. J. Kouwer, Roeland J. M. Nolte, Hans Engelkamp, Kerstin Blank and Alan E. Rowan

Chemical Science 2013 vol. 4(Issue 6) pp:2357-2363

Publication Date(Web):19 Mar 2013

DOI:10.1039/C3SC50552A

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 π–π 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.

Co-reporter:Femke F. B. J. Janssen ; Laurens C. J. M. Peters ; Paul P. J. Schlebos ; Jan M. M. Smits ; René de Gelder

Inorganic Chemistry 2013 Volume 52(Issue 22) pp:13004-13013

Publication Date(Web):October 31, 2013

DOI:10.1021/ic401522v

Tetranuclear carboxylate clusters with the general structural formula [M4(L)2(O2CR)4] (M = Cd, Zn; LH2 = 2,6-bis(1-(2-hydroxyphenyl)-iminoethyl)pyridine; R = CH3, C6H5) were studied by variable-temperature (VT) 1H NMR spectroscopy. The dynamics of these clusters in solution can be described by two uncorrelated dynamical processes. The first dynamical process is the interconversion, both inter- as well as intramolecular, between syn–syn bridging and chelating carboxylate ligands. It is shown that this carboxylate interconversion mechanism is predominantly intramolecular for [Cd4(L)2(O2CCH3)4] (1a), whereas for [Zn4(L)2(O2CCH3)4] (2a) it is predominantly intermolecular. Two models for the second dynamic process, which involves the diiminepyridine ligand, are described. The first model comprises a nondissociative rotation around an internal axis, which changes the chirality of the cluster. The second model is based on the dissociation of the tetranuclear cluster into two dimeric species, which recombine again. This last model is supported by scrambling experiments between [Zn4(L)2(O2CCH3)4] (2a) and [Zn4(L3)2(O2CCH3)4] (5) (L3H2 = 2,6-bis(1-(2-hydroxyphenyl)-iminoethyl)4-chloropyridine).

Preparation and characterization of non-linear poly(ethylene glycol) analogs from oligo(ethylene glycol) functionalized polyisocyanopeptides

Co-reporter:Matthieu Koepf, Heather J. Kitto, Erik Schwartz, Paul H.J. Kouwer, Roeland J.M. Nolte, Alan E. Rowan

European Polymer Journal 2013 Volume 49(Issue 6) pp:1510-1522

Publication Date(Web):June 2013

DOI:10.1016/j.eurpolymj.2013.01.009

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.

Templated Hierarchical Self-Assembly of Poly(p-aryltriazole) Foldamers

Co-reporter:Dr. Rueben Pfukwa;Dr. Paul H. J. Kouwer; Alan E. Rowan; Bert Klumperman

Angewandte Chemie 2013 Volume 125( Issue 42) pp:11246-11250

Publication Date(Web):

DOI:10.1002/ange.201303135

Templated Hierarchical Self-Assembly of Poly(p-aryltriazole) Foldamers

Co-reporter:Dr. Rueben Pfukwa;Dr. Paul H. J. Kouwer; Alan E. Rowan; Bert Klumperman

Angewandte Chemie International Edition 2013 Volume 52( Issue 42) pp:11040-11044

Publication Date(Web):

DOI:10.1002/anie.201303135

Beta Sheets with a Twist: The Conformation of Helical Polyisocyanopeptides Determined by Using Vibrational Circular Dichroism

Co-reporter:Dr. Erik Schwartz;Dr. Vincent Liégeois;Dr. Matthieu Koepf;Dr. Pavol Bodis;Dr. Jeroen J. L. M. Cornelissen;Dr. Patrick Brocorens;Dr. David Beljonne;Dr. Roel J. M. Nolte;Dr. Alan E. Rowan;Dr. Ser Woutersen;Dr. Benoît Champagne

Chemistry - A European Journal 2013 Volume 19( Issue 39) pp:13168-13174

Publication Date(Web):

DOI:10.1002/chem.201300073

Abstract

Detailed information on the architecture of polyisocyanopeptides based on vibrational circular dichroism (VCD) spectroscopy in combination with DFT calculations is presented. It is demonstrated that the screw sense of the helical polyisocyanides can be determined directly from the CN-stretch vibrational region of the VCD spectrum. Analysis of the VCD signals associated with the amide I and amide II modes provides detailed information on the peptide side-chain arrangement in the polymer and indicates the presence of a helical β-sheet architecture, in which the dihedral angles are slightly different to those of natural β-sheet helices.

Interlocked Porphyrin Switches

Co-reporter:Dr. Ruud G. E. Coumans;Dr. Johannes A. A. W. Elemans; Alan E. Rowan; Roel J. M. Nolte

Chemistry - A European Journal 2013 Volume 19( Issue 24) pp:7758-7770

Publication Date(Web):

DOI:10.1002/chem.201203983

Abstract

We describe the synthesis of a series of interlocked structures from porphyrin–glycoluril cage compounds and bis(olefin)-terminated viologens by an olefin-metathesis protocol. The length of the chain connecting the olefin substituents with the viologen has a marked effect on the products of the ring-closure reaction. Long chains give [2]- and [3]catenane structures, whereas short chains give a mixture of [3]-, [4]-, and [5]catenanes. For comparison several [2]rotaxane compounds were prepared. The interlocked catenane and rotaxane structures display switching behavior, which can be controlled by the addition of acid and base. The kinetic and thermodynamic parameters of the switching processes have been determined by NMR spectroscopy.

Postfunctionalization of Helical Polyisocyanopeptides with Phthalocyanine Chromophores by Click Chemistry

Co-reporter:Dr. Ismael López-Duarte;Dr. M. Victoria Martínez-Díaz;Dr. Erik Schwartz;Dr. Matthieu Koepf;Dr. Paul H. J. Kouwer; Alan E. Rowan; Roel J. M. Nolte; Tomás Torres

ChemPlusChem 2012 Volume 77( Issue 8) pp:700-706

Publication Date(Web):

DOI:10.1002/cplu.201200087

Abstract

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.

Triazole–pyridine ligands: a novel approach to chromophoric iridium arrays

Co-reporter:Michal Juríček, Marco Felici, Pablo Contreras-Carballada, Ján Lauko, Sandra Rodríguez Bou, Paul H. J. Kouwer, Albert M. Brouwer and Alan E. Rowan

Journal of Materials Chemistry A 2011 vol. 21(Issue 7) pp:2104-2111

Publication Date(Web):13 Dec 2010

DOI:10.1039/C0JM03117H

We describe a novel modular approach to a series of luminescent iridium complexes bearing triazole–pyridine-derived ligands that were conveniently prepared by using “click” chemistry. One, two or three triazole–pyridine units were effectively built into the heteroaromatic macromolecule using versatile acetylene- and azide-functionalised precursors. Using this approach, a series of iridium-derived molecules, that differ in the number of iridium centres, the structural characteristics of the cyclometalating ligand and the backbone, were synthesised. The preliminary photophysical properties of the prepared complexes indicate that there is only limited interaction (through space or through the backbone) between the iridium centres within one molecule and that each iridium centre retains its individual properties. The results show that our approach can be generally applied towards covalently linked multichromophoric systems with potential application, for instance, in the design and preparation of tunable light emitters. As a demonstration of this concept, a single molecule white-light emitter, constructed from two iridium centres (yellow emission) and a fluorene unit (blue emission), is presented.

Fusing Triazoles: Toward Extending Aromaticity

Co-reporter:Michal Juríček, Kathleen Stout, Paul H. J. Kouwer, and Alan E. Rowan

Organic Letters 2011 Volume 13(Issue 13) pp:3494-3497

Publication Date(Web):June 7, 2011

DOI:10.1021/ol201290q

A novel method to extend aromaticity by one benzene and two triazole rings was developed and optimized. This two-step route employs the copper-catalyzed azide–haloalkyne cycloaddition reaction of an ortho-bis(iodoacetylene) system and the subsequent intramolecular homocoupling fusion of the neighboring iodotriazoles, a process in which an additional benzene ring is formed. This versatile methodology allows one to extend the core size of chromophores and, consequently, to tune the material’s properties.

Triazole: a unique building block for the construction of functional materials

Co-reporter:Michal Juríček, Paul H. J. Kouwer and Alan E. Rowan

Chemical Communications 2011 vol. 47(Issue 31) pp:8740-8749

Publication Date(Web):09 May 2011

DOI:10.1039/C1CC10685F

Over the past 50 years, numerous roads towards carbon-based materials have been explored, all of them being paved using mainly one functional group as the brick: acetylene. The acetylene group, or the carbon–carbon triple bond, is one of the oldest and simplest functional groups in chemistry, and although not present in any of the naturally occurring carbon allotropes, it is an essential tool to access their synthetic carbon-rich family. In general, two strategies towards the synthesis of π-conjugated carbon-rich structures can be employed: (a) either the acetylene group serves as a building block to access acetylene-derived structures or (b) it serves as a synthetic tool to provide other, usually benzenoid, structures. The recently discovered copper-catalysed azide–alkyne cycloaddition (CuAAC) reaction, however, represents a new powerful alternative: it transforms the acetylene group into a five-membered heteroaromatic 1H-1,2,3-triazole (triazole) ring and this gives rise to new opportunities. Compared with all-carbon aromatic non-functional rings, the triazole ring possesses three nitrogen atoms and, thus, can serve as a ligand to coordinate metals, or as a hydrogen bond acceptor and donor. This Feature Article summarises examples of using the triazole ring to construct conjugation- and/or function-related heteroaromatic materials, such as tuneable multichromophoric covalent ensembles, macrocyclic receptors or responsive foldamers. These recent examples, which open a new sub-field within organic materials, started to appear only few years ago and represent “a few more bricks” on the road to carbon-rich functional materials.

Assemblies of perylene diimide derivatives with melamine into luminescent hydrogels

Co-reporter:Pradip K. Sukul, Deepak Asthana, Pritam Mukhopadhyay, Domenico Summa, Luca Muccioli, Claudio Zannoni, David Beljonne, Alan E. Rowan and Sudip Malik

Chemical Communications 2011 vol. 47(Issue 43) pp:11858-11860

Publication Date(Web):04 Oct 2011

DOI:10.1039/C1CC14189A

We report unique and spontaneous formation of hydrogels of perylene derivatives with melamine. The luminescent gel network is formed by H-type aggregation of the perylene core, supramolecularly cross-linked by melamine units. As a result of controlled aggregation in the extended nanofibers, strong exciton fluorescence emission is observed.

Helical poly(isocyanides): past, present and future

Co-reporter:Erik Schwartz, Matthieu Koepf, Heather J. Kitto, Roeland J. M. Nolte and Alan E. Rowan

Polymer Chemistry 2011 vol. 2(Issue 1) pp:33-47

Publication Date(Web):21 Sep 2010

DOI:10.1039/C0PY00246A

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.

1. Solvent, Linker, and Anion Effects on the Formation, Connectivity, and Topology of Cu(I)/PPh3/N-Donor Ligand Coordination Polymers

Co-reporter:Femke F. B. J. Janssen, Laurens P. J. Veraart, Jan M. M. Smits, René de Gelder, and Alan E. Rowan

Crystal Growth & Design 2011 Volume 11(Issue 10) pp:4313-4325

Publication Date(Web):September 13, 2011

DOI:10.1021/cg2006502

The effect of linker, anion, and solvent on the formation, topology, and connectivity of coordination polymers was investigated for polymers resulting from reactions between [Cu(MeCN)2(PPh3)2][X] (X = BF4–, ClO4–, and PF6–) and nitrogen donor ligands (pyrazine, 4,4′-bipyridine, and 3,4′-bipyridine) in three solvents (CH2Cl2, CHCl3, tetrahydrofuran (THF)). The 18 crystallization experiments with linear N-donor ligands yielded seven crystal structures of one-dimensional (1D) and five crystal structures of two-dimensional (2D) coordination polymers. The nine crystallization experiments with the nonlinear N-donor ligand yielded four crystal structures showing 1D coordination polymers. The isolated compounds with linear N-donor ligands were characterized by X-ray diffraction techniques, elemental analysis, and 1H NMR. The compounds with 3,4′-bipyridine were analyzed with single-crystal diffraction. The thermal properties of several coordination polymers were investigated by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) in order to determine the stability of the polymers. These techniques show that the decomposition pathway of these coordination polymers is not only determined by the topology of the polymers but also by the interchain interactions. These studies highlight that for a rational design and understanding of new coordination polymer systems one should first systematically analyze the effect of all parameters in order to filter out those ones that really determine the desired network properties.

2. The Multiple Phenyl Embrace as a Synthon in Cu(I)/PPh3/N-Donor Ligand Coordination Polymers

Co-reporter:Femke F. B. J. Janssen, René de Gelder, and Alan E. Rowan

Crystal Growth & Design 2011 Volume 11(Issue 10) pp:4326-4333

Publication Date(Web):September 13, 2011

DOI:10.1021/cg200651h

The multiple phenyl embrace is a supramolecular motif comprised of phenyl–phenyl interactions, which can, like hydrogen bonds, form extended networks between molecules in the solid state. The analysis of 23 crystal structures of coordination polymers based on the M/PPh3/N-donor ligand system (M = Cu(I) or Ag(I)) showed that 71% of the independent M–PPh3 groups are involved in a 6-fold phenyl embrace (6PE). Strong 6PE interactions are obtained when the geometry of the PPh3 group can be described as a rotor. The analysis of these groups showed that 83% of the PPh3 groups have their phenyl groups in the rotor conformation. It is shown, however, that these good rotors are not necessarily involved in the 6PE and that the 6PE can also be formed by nonrotors. In the Cu(I)/PPh3/N-donor ligand system, the 6PE interactions form an independent connection (often) perpendicular to the backbone of the coordination polymer. In many cases, the 6PE increases the dimensionality of the network formed between Cu(I) and N-donor ligands. Therefore, the multiple phenyl embrace seems to be a useful synthon in crystal engineering of stable networks.

Sequential Energy and Electron Transfer in Polyisocyanopeptide-Based Multichromophoric Arrays

Co-reporter:Ya-Shih Huang, Xudong Yang, Erik Schwartz, Li Ping Lu, Sebastian Albert-Seifried, Chris E. Finlayson, Matthieu Koepf, Heather J. Kitto, Burak Ulgut, Matthijs B. J. Otten, Jeroen J. L. M. Cornelissen, Roeland J. M. Nolte, Alan E. Rowan, and Richard H. Friend

The Journal of Physical Chemistry B 2011 Volume 115(Issue 7) pp:1590-1600

Publication Date(Web):January 31, 2011

DOI:10.1021/jp1071605

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. 1H 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.

Macromolecular multi-chromophoric scaffolding

Co-reporter:Erik Schwartz, Stéphane Le Gac, Jeroen J. L. M. Cornelissen, Roeland J. M. Nolte and Alan E. Rowan

Chemical Society Reviews 2010 vol. 39(Issue 5) pp:1576-1599

Publication Date(Web):02 Mar 2010

DOI:10.1039/B922160C

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).

Porphyrin Macrocyclic Catalysts for the Processive Oxidation of Polymer Substrates

Co-reporter:Cyrille Monnereau ; Pilar Hidalgo Ramos ; Alexander B. C. Deutman ; Johannes A. A. W. Elemans ; Roeland J. M. Nolte

Journal of the American Chemical Society 2010 Volume 132(Issue 5) pp:1529-1531

Publication Date(Web):January 14, 2010

DOI:10.1021/ja908524x

A novel cavity-containing porphyrin catalyst based on a previously reported clip architecture, substituted on the outer face with urea terminated tails, has been synthesized, and its properties toward the epoxidation of polybutadiene have been studied. It is shown that the presence of the urea tails provides efficient shielding of the manganese porphyrin against destruction and selectively directs the oxidation process to the inside of the catalyst cage, allowing for processive oxidation of a polymer substrate without the need of an additional axial ligand.

Synthesis, Characterization, and Surface Initiated Polymerization of Carbazole Functionalized Isocyanides

Co-reporter:Erik Schwartz, Eunhee Lim, Chandrakala M. Gowda, Andrea Liscio, Oliver Fenwick, Guoli Tu, Vincenzo Palermo, Rene de Gelder, Jeroen J. L. M. Cornelissen, Ernst R. H. Van Eck, Arno P. M. Kentgens, Franco Cacialli, Roeland J. M. Nolte, Paolo Samorì, Wilhelm T. S. Huck and Alan E. Rowan

Chemistry of Materials 2010 Volume 22(Issue 8) pp:2597

Publication Date(Web):March 15, 2010

DOI:10.1021/cm903664g

We describe the design and synthesis of carbazole functionalized isocyanides and the detailed investigation of their properties. Characterization by solid state NMR, CD, and IR spectroscopic techniques reveals that the polymer has a well-defined helical architecture. Surface-initiated polymerization of the isocyanide monomers onto various surfaces was carried out to give polymer brushes up to 150 nm thick. Insights into the electronic properties of the materials were obtained by Kelvin probe force microscopy (KPFM) and electroabsorption studies.

Direct Access to Polyisocyanide Screw Sense Using Vibrational Circular Dichroism

Co-reporter:Erik Schwartz, Sérgio R. Domingos, Alexander Vdovin, Matthieu Koepf, Wybren Jan Buma, Jeroen J. L. M. Cornelissen, Alan E. Rowan, Roeland J. M. Nolte, and Sander Woutersen

Macromolecules 2010 Volume 43(Issue 19) pp:7931-7935

Publication Date(Web):September 13, 2010

DOI:10.1021/ma101601e

We show that the screw sense of polyisocyanide helices can be determined in a simple manner from the vibrational circular dichroism (VCD) of their CN-stretching mode. The relation between VCD and molecular structure is obtained using the coupled-oscillator approximation. It is shown that since the C═N groups point approximately radially outward from the helical axis, the CN-stretch region of the VCD spectrum of a polyisocyanide helix consists of a single couplet, the sign of which is directly related to the screw sense of the helix. We use this method to determine the screw sense of poly(R)-2-isocyanooctane and poly(S)-2-isocyanooctane from their VCD spectrum.

Cysteine-Containing Polyisocyanides as Versatile Nanoplatforms for Chromophoric and Bioscaffolding

Co-reporter:Stéphane LeGac Dr.;Erik Schwartz Dr.;Matthieu Koepf Dr.;JeroenJ.L.M. Cornelissen Dr.;AlanE. Rowan Dr.;RoelJ.M. Nolte Dr.

Chemistry - A European Journal 2010 Volume 16( Issue 21) pp:6176-6186

Publication Date(Web):

DOI:10.1002/chem.200903502

Abstract

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 4₁ helix is further stabilized by β-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 Relationship between Nanoscale Architecture and Charge Transport in Conjugated Nanocrystals Bridged by Multichromophoric Polymers

Co-reporter:Reza Dabirian ; Vincenzo Palermo ; Andrea Liscio ; Erik Schwartz ; Matthijs B. J. Otten ; Chris E. Finlayson ; Emanuele Treossi ; Richard H. Friend ; Gianluca Calestani ; Klaus Müllen ; Roeland J. M. Nolte ; Alan E. Rowan ;Paolo Samorì ◼

Journal of the American Chemical Society 2009 Volume 131(Issue 20) pp:7055-7063

Publication Date(Web):April 30, 2009

DOI:10.1021/ja809731e

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 SiOx 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-trapped vibrational states in synthetic β-sheet helices

Co-reporter:Erik Schwartz, Pavol Bodis, Matthieu Koepf, Jeroen J. L. M. Cornelissen, Alan E. Rowan, Sander Woutersen and Roeland J. M. Nolte

Chemical Communications 2009 (Issue 31) pp:4675-4677

Publication Date(Web):23 Jun 2009

DOI:10.1039/B907830D

Femtosecond vibrational pump–probe spectroscopy on β-helical polyisocyanopeptides reveals vibrational self-trapping in the well-defined hydrogen-bonded side groups that is absent when non-hydrogen bonded monomers are mixed in.

Ligand-Controlled Magnetic Interactions in Mn4 Clusters

Co-reporter:Erik Kampert, Femke F. B. J. Janssen, Danil W. Boukhvalov, Jaap C. Russcher, Jan M. M. Smits, René de Gelder, Bas de Bruin, Peter C. M. Christianen, Uli Zeitler, Mikhail I. Katsnelson, Jan C. Maan and Alan E. Rowan

Inorganic Chemistry 2009 Volume 48(Issue 24) pp:11903-11908

Publication Date(Web):November 16, 2009

DOI:10.1021/ic901930w

A method is presented to design magnetic molecules in which the exchange interaction between adjacent metal ions is controlled by electron density withdrawal through their bridging ligands. We synthesized a novel Mn4 cluster in which the choice of the bridging carboxylate ligands (acetate, benzoate, or trifluoroacetate) determines the type and strength of the three magnetic exchange couplings (J1, J2, and J3) present between the metal ions. Experimentally measured magnetic moments in high magnetic fields show that, upon electron density withdrawal, the main antiferromagnetic exchange constant J1 decreases from −2.2 K for the [Mn4(OAc)4] cluster to −1.9 K for the [Mn4(H5C6COO)4] cluster and −0.6 K for the [Mn4(F3CCOO)4] cluster, while J2 decreases from −1.1 K to nearly 0 K and J3 changes to a small ferromagnetic coupling. These experimental results are further supported with density-functional theory calculations based on the obtained crystallographic structures of the [Mn4(OAc)4] and [Mn4(F3CCOO)4] clusters.

Helter-Skelter-Like Perylene Polyisocyanopeptides

Co-reporter:Erik Schwartz;Vincenzo Palermo Dr.;ChrisE. Finlayson Dr.;Ya-Shih Huang;MatthijsB.J. Otten;Andrea Liscio Dr.;Sara Trapani;Irene González-Valls;Patrick Brocorens Dr.;JeroenJ.L.M. Cornelissen Dr.;Kalina Peneva Dr.;Klaus Müllen Dr.;FrankC. Spano Dr.;Arkady Yartsev ;Sebastian Westenhoff Dr.;RichardH. Friend Dr.;David Beljonne Dr.;RoelJ.M. Nolte Dr.;Paolo Samorì Dr.;AlanE. Rowan Dr.

Chemistry - A European Journal 2009 Volume 15( Issue 11) pp:2536-2547

Publication Date(Web):

DOI:10.1002/chem.200801746

Squaring cooperative binding circles

Co-reporter:Alexander B. C. Deutman;Cyrille Monnereau;Mohamed Moalin;Ruud G. E. Coumans;Nico Veling;Michiel Coenen;Roeland J. M. Nolte;Gianfranco Ercolani;René de Gelder;Johannes A. A. W. Elemans;Jan M. M. Smits

PNAS 2009 Volume 106 (Issue 26 ) pp:10471-10476

Publication Date(Web):2009-06-30

DOI:10.1073/pnas.0810145106

The cooperative binding effects of viologens and pyridines to a synthetic bivalent porphyrin receptor are used as a model system to study how the magnitudes of these effects relate to the experimentally obtained values. The full thermodynamic and kinetic circles concerning both activation and inhibition of the cage of the receptor for the binding of viologens were measured and evaluated. The results strongly emphasize the apparent character of measured binding and rate constants, in which the fractional saturation of receptors with other guests is linearly expressed in these constants. The presented method can be used as a simple tool to better analyze and comprehend the experimentally observed kinetics and thermodynamics of natural and artificial cooperative systems.

Mechanism of Threading a Polymer Through a Macrocyclic Ring

Co-reporter:Alan E. Rowan;Roeland J. M. Nolte;Johannes A. A. W. Elemans;Cyrille Monnereau;Gianfranco Ercolani;Alexander B. C. Deutman

Science 2008 Volume 322(Issue 5908) pp:1668-1671

Publication Date(Web):12 Dec 2008

DOI:10.1126/science.1164647

Abstract

The translocation of biopolymers through pores and channels plays a fundamental role in numerous biological processes. We describe here the mechanism of the threading of a series of polymer chains through a synthetic macrocycle, which mimics these natural processes. The threading of polymers involves a kinetically favorable “entron” effect, which is associated with the initial filling of the cavity by the end of the polymer. A preassociation between the outside of the macrocycle and the polymer induces a process in which the polymer end loops back into the cavity of the macrocycle. This looping mechanism results in accelerated threading rates and unidirectional motion and is reminiscent of the protein translocation through membrane pores.

Manganese Porphyrin Hosts as Epoxidation Catalysts – Activity and Stability Control by Axial Ligand Effects

Co-reporter:Johannes A. A. W. Elemans;Edward J. A. Bijsterveld;Roel J. M. Nolte

European Journal of Organic Chemistry 2007 Volume 2007(Issue 5) pp:751-757

Publication Date(Web):5 DEC 2006

DOI:10.1002/ejoc.200600648

The catalytic performance of a cavity-containing [(porphyrin)Mn] in the epoxidation of alkenes is described. Inside the catalyst cavity, nitrogen-containing axial ligands can be bound to the porphyrin metal with high association constants, resulting in strong activation of the catalyst in the presence of only one equivalent of the ligand. Complexation of a sterically demanding ligand to the outside of the cavity-containing catalyst can prevent catalyst decomposition through the formation of μ-oxo dimers.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Giant Porphyrin Disks: Control of Their Self-Assembly at Liquid–Solid Interfaces through Metal–Ligand Interactions

Co-reporter:Marga C. Lensen Dr.;Johannes A. A. W. Elemans Dr.;Sra J. T. van Dingenen;Jan W. Gerritsen;Sylvia Speller ;Alan E. Rowan ;Roel J. M. Nolte

Chemistry - A European Journal 2007 Volume 13(Issue 28) pp:

Publication Date(Web):4 JUL 2007

DOI:10.1002/chem.200700131

The synthesis and self-assembly behaviour of porphyrin dodecamers 1H₂ and Zn–1, which consist of twelve porphyrins that are covalently attached to a central aromatic core, is described. According to STM, 1D and 2D NMR studies, and molecular modelling calculations, the porphyrin dodecamers have a yo-yo-shaped structure. Their large π surface, in combination with their disk-like shape, allows them to form self-assembled structures, which in the case of Zn–1 can be tuned by adding bidentate ligands. The self-assembly of the molecules at the liquid–solid interface of 1-phenyloctane with highly oriented pyrolytic graphite or Au(111) was imaged by using STM. The porphyrin disks in the self-assembled arrays have an edge-on orientation on the surface. The addition of bidentate axial ligands to the Zn–1 molecules in the arrays allows their intermolecular distance to be precisely controlled.

Positional Assembly of Enzymes in Polymersome Nanoreactors for Cascade Reactions

Co-reporter:Dennis M. Vriezema Dr.;Paula M. L. Garcia Dr.;Núria Sancho Oltra;Nikos S. Hatzakis Dr.;Suzanne M. Kuiper;Roel J. M. Nolte ;Alan E. Rowan ;Jan C. M. van Hest

Angewandte Chemie International Edition 2007 Volume 46(Issue 39) pp:

Publication Date(Web):17 AUG 2007

DOI:10.1002/anie.200701125

In a good position: Nanoreactors can be constructed by the controlled positioning of glucose oxidase (GOX) and horseradish peroxidase (HRP) within the central water pool and block-copolymer membrane of polymersomes. A one-pot multistep reaction sequence is performed with the nanoreactor in combination with free Candida antarctica lipase B (CALB) in the bulk solution (see picture; ABTS: 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)).

Positional Assembly of Enzymes in Polymersome Nanoreactors for Cascade Reactions

Co-reporter:Dennis M. Vriezema Dr.;Paula M. L. Garcia Dr.;Núria Sancho Oltra;Nikos S. Hatzakis Dr.;Suzanne M. Kuiper;Roel J. M. Nolte ;Alan E. Rowan ;Jan C. M. van Hest

Angewandte Chemie 2007 Volume 119(Issue 39) pp:

Publication Date(Web):17 AUG 2007

DOI:10.1002/ange.200701125

Gut positioniert: Durch gezielte Positionierung von Glucoseoxidase (GOX) und Meerrettichperoxidase (HRP) im zentralen Wasserreservoir bzw. in der Blockcopolymermembran von Polymersomen lassen sich Nanoreaktoren konstruieren. Mit ihnen kann in Kombination mit Candida-antarctica-Lipase B (CALB) in der Lösung eine mehrstufige Eintopfreaktionssequenz durchgeführt werden (siehe Bild; ABTS: 2,2′-Azinobis(3-ethylbenzothiazolin-6-sulfonsäure)).

Lyotropic liquid-crystalline behavior of polyisocyanodipeptides

Co-reporter:Gerald A. Metselaar;Ser J. Wezenberg;Jeroen J. L. M. Cornelissen;Roel J. M. Nolte and

Journal of Polymer Science Part A: Polymer Chemistry 2007 Volume 45(Issue 6) pp:981-988

Publication Date(Web):1 FEB 2007

DOI:10.1002/pola.21891

Rigid, helical polyisocyanodipeptides derived from alanine (PIAAs) that form lyotropic liquid-crystalline (LC) phases in tetrachloroethane are presented. An investigation by optical microscopy between crossed polarizers demonstrated that PIAAs prepared by the polymerization of isocyanodipeptide monomers with an activated tetrakis isocyanide nickel(II) catalyst could form cholesteric LC phases in tetrachloroethane in concentrations between 18 and 30 wt %. Cholesteric LC phases that were formed in solutions of greater than 25 wt % displayed a reversal of the cholesteric helix upon annealing at 50 °C. Diastereomeric PIAA mixtures displayed cholesteric LC behavior only when the PIAAs had the same helix screw sense. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 981–988, 2007

Polyisocyanides Derived from Tripeptides of Alanine

Co-reporter:Gerald A. Metselaar Dr.;P. J. Hans M. Adams;Roel J. M. Nolte ;Jeroen J. L. M. Cornelissen Dr.;Alan E. Rowan

Chemistry - A European Journal 2007 Volume 13(Issue 3) pp:

Publication Date(Web):18 OCT 2006

DOI:10.1002/chem.200600928

Helical polymers of isocyanotripeptides derived from alanine have been synthesized and their architectures studied in detail. The helical conformation of the polyisocyanotripeptides is stabilized by internal hydrogen-bonding arrays between the tripeptide side chains. The possibility of extending the well-defined hydrogen-bonded array, from dipeptide to tripeptide side chains, depends strongly on the stereochemistry of the constituent alanine amino acids, as has been shown by circular dichroism and IR studies. In polymers containing a weaker hydrogen-bonding array adjacent to the polymer backbone, due to steric interactions between the alanine methyl groups, a stronger second hydrogen-bonding array was present between the peptide bonds furthest away from the main chain, which is probably a result of stretching/compression of the helical-polymer conformation.

Molecular Materials by Self-Assembly of Porphyrins, Phthalocyanines, and Perylenes

Co-reporter:J. A. A. W. Elemans;R. van Hameren;R. J. M. Nolte;A. E. Rowan

Advanced Materials 2006 Volume 18(Issue 10) pp:1251-1266

Publication Date(Web):10 APR 2006

DOI:10.1002/adma.200502498

Porphyrins, phthalocyanines, and perylenes are compounds with great potential for serving as components of molecular materials that possess unique electronic, magnetic and photophysical properties. In general, a highly specific communication between a large number of these chromophores is required in order to express their function to a maximal level, and for this reason it is of importance to construct arrays in which the molecules are organized in well-defined geometries with respect to their neighbors. This review is an account of some recent efforts to construct highly ordered assemblies of porphyrins, phthalocyanines, and perylenes by means of self-assembly in solution and on surfaces, and by attaching them to polymeric scaffolds.

Synthesis and single enzyme activity of a clicked lipase–BSA hetero-dimer

Co-reporter:Nikos S. Hatzakis, Hans Engelkamp, Kelly Velonia, Johan Hofkens, Peter C. M. Christianen, Allan Svendsen, Shamkantr A. Patkar, Jesper Vind, Jan C. Maan, Alan E. Rowan and Roeland J. M. Nolte

Chemical Communications 2006 (Issue 19) pp:2012-2014

Publication Date(Web):09 Feb 2006

DOI:10.1039/B516551B

Click chemistry is used to construct a novel lipase–BSA hetero-dimer, in which the latter protein acts as a foot enabling the anchoring of the enzyme onto the surface for single enzyme studies.

Self-assembly studies of allosteric photosynthetic antenna model systems

Co-reporter:Paul J. Thomassen, Jantien Foekema, Ribera Jordana i Lluch, Pall Thordarson, Johannes A. A. W. Elemans, Roeland J. M. Nolte and Alan E. Rowan

New Journal of Chemistry 2006 vol. 30(Issue 2) pp:148-155

Publication Date(Web):20 Dec 2005

DOI:10.1039/B510968J

In this paper allosteric interactions are employed to enhance electron transfer in a pseudo-rotaxane system. Binding of an axial ligand (tbpy) to an electron donating mono-cavity appended zinc porphyrin (ZnP) increases the complexation strength to an electron accepting mono-substituted bipyridine, resulting in a more pronounced electron transfer process after excitation of the zinc porphyrin. Binding constants are presented for this host and different mono-substituted bipyridine guests.

Correctly validating results from single molecule data: The case of stretched exponential decay in the catalytic activity of single lipase B molecules

Co-reporter:Ophir Flomenbom, Johan Hofkens, Kelly Velonia, Frans C. de Schryver, Alan E. Rowan, Roeland J.M. Nolte, Joseph Klafter, Robert J. Silbey

Chemical Physics Letters 2006 Volume 432(1–3) pp:371-374

Publication Date(Web):4 December 2006

DOI:10.1016/j.cplett.2006.10.060

The question of how to validate and interpret correctly the waiting time probability density functions (WT-PDFs) from single molecule data is addressed. It is shown by simulation that when a stretched exponential WT-PDF, ϕoff(t)=ϕ0e-(t/τ)αϕoff(t)=ϕ0e-(t/τ)α, generates the off periods of a two-state trajectory, a reliable recovery of the input ϕoff(t) from the trajectory is obtained even when the bin size used to define the trajectory, dt, is much larger than the parameter τ. This holds true as long as the first moment of the WT-PDF is much larger than dt. Our results validate the results in an earlier study of the activity of single lipase B molecules and disprove recent related critique.How to correctly validate results from single molecule data? This issue is addressed by using numerical and analytical tools. The results of this Letter validate the results in an earlier study of the activity of single lipase B molecules and disprove recent related critique.

Processive enzyme mimic: Kinetics and thermodynamics of the threading and sliding process

Co-reporter:Johannes A. A. W. Elemans;Ruud G. E. Coumans;Roeland J. M. Nolte

PNAS 2006 Volume 103 (Issue 52 ) pp:19647-19651

Publication Date(Web):2006-12-26

DOI:10.1073/pnas.0603036103

The kinetics and thermodynamics of the treading and dethreading process of polymers through the cavity of a synthetic toroidal host is investigated by studying its complexation with a series of end-functionalized polymers of different lengths containing an end group that is selectively recognized by the host. The system is designed in such a way that complexation is only observed if the host has traveled all of the way across the complete polymer. Detailed kinetic investigations using fluorescence spectroscopy have revealed that the barrier for this process is length dependent and most likely related to the stretching of the polymer. Moreover, the results indicate that our previously reported processive enzyme mimic most likely operates by randomly sliding along its macromolecular substrate.

Chiral molecular tapes from novel tetra(thiafulvalene-crown-ether)-substituted phthalocyanine building blocks

Co-reporter:Joseph Sly, Peter Kasák, Elba Gomar-Nadal, Concepció Rovira, Lucía Górriz, Pall Thordarson, David B. Amabilino, Alan E. Rowan and Roeland J. M. Nolte

Chemical Communications 2005 (Issue 10) pp:1255-1257

Publication Date(Web):15 Dec 2004

DOI:10.1039/B416034G

A tetra(thiafulvalene-crown-ether) phthalocyanine self-assembles into helical tapes nanometers wide and micrometers long. Formation of these scrolled molecular architectures is a first for phthalocyanine fibres and shows potential as a novel conducting material.

Dynamic combinatorial olefin metathesis: templated synthesis of porphyrin boxes

Co-reporter:Paul C. M. van Gerven, Johannes A. A. W. Elemans, Jan W. Gerritsen, Sylvia Speller, Roeland J. M. Nolte and Alan E. Rowan

Chemical Communications 2005 (Issue 28) pp:3535-3537

Publication Date(Web):09 Jun 2005

DOI:10.1039/B503619D

A porphyrin macrocyclic square is efficiently prepared by a dynamic combinatorial approach to olefin metathesis and shown by scanning tunneling microscopy (STM) to self-assemble into highly ordered arrays on a graphite surface.

Construction of functional porphyrin polystyrene nano-architectures by ATRP

Co-reporter:Femke de Loos, Irene C. Reynhout, Jeroen J. L. M. Cornelissen, Alan E. Rowan and Roeland J. M. Nolte

Chemical Communications 2005 (Issue 1) pp:60-62

Publication Date(Web):01 Dec 2004

DOI:10.1039/B412067A

A series of mono-functionalized metallo-porphyrin polystyrenes have been synthesized using atom transfer radical polymerization and their self-assembling behavior was studied by electron microscopy showing that the polystyrene tail-length influences the aggregate architecture.

Acid-Initiated Stereospecific Polymerization of Isocyanopeptides

Co-reporter:Gerald A. Metselaar;Jeroen J. L. M. Cornelissen Dr. Dr.;Roel J. M. Nolte Dr.

Angewandte Chemie 2005 Volume 117(Issue 13) pp:

Publication Date(Web):23 FEB 2005

DOI:10.1002/ange.200462417

Die Krux mit der Helix: Die säurevermittelte Polymerisation von Dipeptid-Isocyaniden (siehe Schema) verläuft außerordentlich stereospezifisch, wenn ein helicales Templat vorliegt. Hohe Säurekonzentrationen ändern den Reaktionsverlauf: Das Templat wird zerstört, und die konkurrierende Cyclisierung überwiegt.

Titelbild: Single-Enzyme Kinetics of CALB-Catalyzed Hydrolysis (Angew. Chem. 4/2005)

Co-reporter:Kelly Velonia Dr.;Ophir Flomenbom;Davey Loos;Sadahiro Masuo;Mircea Cotlet Dr.;Yves Engelborghs Dr.;Johan Hofkens Dr. Dr.;Joseph Klafter Dr.;Roel J. M. Nolte Dr. and;Frans C. de Schryver Dr.

Angewandte Chemie 2005 Volume 117(Issue 4) pp:

Publication Date(Web):11 JAN 2005

DOI:10.1002/ange.200590009

Single-Enzyme Kinetics of CALB-Catalyzed Hydrolysis

Angewandte Chemie 2005 Volume 117(Issue 4) pp:

Publication Date(Web):23 DEC 2004

DOI:10.1002/ange.200460625

Echtzeitmessungen zur Katalyse- und Substratkinetik einer Hydrolyse durch ein einzelnes Enzymmolekül werden mithilfe von konfokaler Fluoreszenzmikroskopie (CFM) möglich (siehe Bild, CFM-Strahl=grün). Eine einzige Lipase kann eine Vielzahl von Konformationen einnehmen, die alle zur Gesamtaktivität des Enzyms beitragen. Dieser Sachverhalt wird bei Messungen an Ensembles häufig übersehen.

Acid-Initiated Stereospecific Polymerization of Isocyanopeptides

Co-reporter:Gerald A. Metselaar;Jeroen J. L. M. Cornelissen Dr. Dr.;Roel J. M. Nolte Dr.

Angewandte Chemie International Edition 2005 Volume 44(Issue 13) pp:

Publication Date(Web):23 FEB 2005

DOI:10.1002/anie.200462417

Recognition with a twist: The acid-initiated polymerization of dipeptide-derived isocyanides (see scheme) is found to be an exceptionally stereospecific process that requires a helical template. The reaction is very sensitive to the acid concentration. At high acid concentrations, the template is destroyed and a competing cyclization reaction becomes predominant.

Cover Picture: Single-Enzyme Kinetics of CALB-Catalyzed Hydrolysis (Angew. Chem. Int. Ed. 4/2005)

Angewandte Chemie International Edition 2005 Volume 44(Issue 4) pp:

Publication Date(Web):11 JAN 2005

DOI:10.1002/anie.200590009

Single-Enzyme Kinetics of CALB-Catalyzed Hydrolysis

Angewandte Chemie International Edition 2005 Volume 44(Issue 4) pp:

Publication Date(Web):23 DEC 2004

DOI:10.1002/anie.200460625

Real-time measurement of the catalysis and substrate kinetics of a single-enzyme hydrolysis reaction is demonstrated with confocal fluorescence microscopy (CFM; see picture, green=CFM beam). A single lipase is shown to have a broad range of conformations; each conformation contributes to the overall enzymatic activity, an observation that is often masked by ensemble measurements.

The mechanical microenvironment in cancer: How physics affects tumours

Co-reporter:Anika Nagelkerke, Johan Bussink, Alan E. Rowan, Paul N. Span

Seminars in Cancer Biology (December 2015) Volume 35() pp:62-70

Publication Date(Web):1 December 2015

DOI:10.1016/j.semcancer.2015.09.001

The tumour microenvironment contributes greatly to the response of tumour cells. It consists of chemical gradients, for example of oxygen and nutrients. However, a physical environment is also present. Apart from chemical input, cells also receive physical signals. Tumours display unique mechanical properties: they are a lot stiffer than normal tissue. This may be either a cause or a consequence of cancer, but literature suggests it has a major impact on tumour cells as will be described in this review. The mechanical microenvironment may cause malignant transformation, possibly through activation of oncogenic pathways and inhibition of tumour suppressor genes. In addition, the mechanical microenvironment may promote tumour progression by influencing processes such as epithelial-to-mesenchymal transition, enhancing cell survival through autophagy, but also affects sensitivity of tumour cells to therapeutics. Furthermore, multiple intracellular signalling pathways prove sensitive to the mechanical properties of the microenvironment.It appears the increased stiffness is unlikely to be caused by increased stiffness of the tumour cells themselves. However, there are indications that tumours display a higher cell density, making them more rigid. In addition, increased matrix deposition in the tumour, as well as increased interstitial fluid pressure may account for the increased stiffness of tumours.Overall, tumour mechanics are significantly different from normal tissue. Therefore, this feature should be further explored for use in cancer prevention, detection and treatment.

Single-enzyme kinetics with fluorogenic substrates: lessons learnt and future directions

Co-reporter:Petri Turunen, Alan E. Rowan, Kerstin Blank

FEBS Letters (1 October 2014) Volume 588(Issue 19) pp:3553-3563

Publication Date(Web):1 October 2014

DOI:10.1016/j.febslet.2014.06.021

Single-molecule fluorescence techniques have developed into powerful tools for studying the kinetics of biological reactions at the single-molecule level. Using fluorogenic substrates, enzymatic reactions can be observed in real-time with single-turnover resolution. The turnover sequence contains all kinetic information, giving access to reaction substeps and dynamic processes such as fluctuations in the reaction rate. Despite their clearly proven potential, the accuracy of current measurements is limited by the availability of substrates with 1:1 stoichiometry and the signal-to-noise ratio of the measurement. In this review we summarize the state-of-the-art and discuss these limitations using experiments performed with α-chymotrypsin as an example. We are further providing an overview of recent efforts aimed at the improvement of fluorogenic substrates and the development of new detection schemes. These detection schemes utilize nanophotonic structures such as zero mode waveguides or nanoantennas. Nanophotonic approaches reduce the size of the effective detection volume and are a powerful strategy to increase the signal-to-noise ratio. We believe that a combination of improved substrates and novel detection schemes will pave the way for performing accurate single-enzyme experiments in biologically relevant conditions.

Self-trapped vibrational states in synthetic β-sheet helices

Co-reporter:Erik Schwartz, Pavol Bodis, Matthieu Koepf, Jeroen J. L. M. Cornelissen, Alan E. Rowan, Sander Woutersen and Roeland J. M. Nolte

Chemical Communications 2009(Issue 31) pp:NaN4677-4677

Publication Date(Web):2009/06/23

DOI:10.1039/B907830D

Triazole: a unique building block for the construction of functional materials

Co-reporter:Michal Juríček, Paul H. J. Kouwer and Alan E. Rowan

Chemical Communications 2011 - vol. 47(Issue 31) pp:NaN8749-8749

Publication Date(Web):2011/05/09

DOI:10.1039/C1CC10685F

Assemblies of perylene diimide derivatives with melamine into luminescent hydrogels

Co-reporter:Pradip K. Sukul, Deepak Asthana, Pritam Mukhopadhyay, Domenico Summa, Luca Muccioli, Claudio Zannoni, David Beljonne, Alan E. Rowan and Sudip Malik

Chemical Communications 2011 - vol. 47(Issue 43) pp:NaN11860-11860

Publication Date(Web):2011/10/04

DOI:10.1039/C1CC14189A

Stiffness versus architecture of single helical polyisocyanopeptides

Chemical Science (2010-Present) 2013 - vol. 4(Issue 6) pp:NaN2363-2363

Publication Date(Web):2013/03/19

DOI:10.1039/C3SC50552A

Therapeutic nanoworms: towards novel synthetic dendritic cells for immunotherapy

Chemical Science (2010-Present) 2013 - vol. 4(Issue 11) pp:NaN4174-4174

Publication Date(Web):2013/08/02

DOI:10.1039/C3SC51399H

Triazole–pyridine ligands: a novel approach to chromophoric iridium arrays

Co-reporter:Michal Juríček, Marco Felici, Pablo Contreras-Carballada, Ján Lauko, Sandra Rodríguez Bou, Paul H. J. Kouwer, Albert M. Brouwer and Alan E. Rowan

Journal of Materials Chemistry A 2011 - vol. 21(Issue 7) pp:NaN2111-2111

Publication Date(Web):2010/12/13

DOI:10.1039/C0JM03117H

Macromolecular multi-chromophoric scaffolding

Co-reporter:Erik Schwartz, Stéphane Le Gac, Jeroen J. L. M. Cornelissen, Roeland J. M. Nolte and Alan E. Rowan

Chemical Society Reviews 2010 - vol. 39(Issue 5) pp:NaN1599-1599

Publication Date(Web):2010/03/02

DOI:10.1039/B922160C