Jun.-Prof. Dr. Michael Giese
University of Duisburg-Essen
- Naturally occurring polyphenols as building blocks for supramolecular liquid crystals-substitution pattern dominates mesomorphism
Balszuweit, J. and Blanke, M. and Saccone, M. and Mezger, M. and Daniliuc, C.G. and Wölper, C. and Giese, M. and Voskuhl, J.
Molecular Systems Design and Engineering 6 (2021)A modular supramolecular approach towards hydrogen-bonded liquid crystalline assemblies based on naturally occurring polyphenols is reported. The combination of experimental observations, crystallographic studies and semi-empirical analyses of the assemblies provides insight into the structure-property relationships of these materials. Here a direct correlation of the number of donor OH-groups as well as their orientation with the mesomorphic behavior is reported. We discovered that the number and orientation of the OH-groups have a stronger influence on the mesomorphic behavior of the supramolecular assemblies than the connectivity (e.g. stilbenoid or chalconoid) of the hydrogen bond donors. Furthermore, the photo-switching behavior of selected complexes containing azopyridine ligands was investigated. This study will help future scientists to gain a deeper understanding of the underlying mechanisms and structure-property relationships of supramolecular assemblies with mesomorphic behavior, which is still one of the major challenges in current science. This journal is © The Royal Society of Chemistry.
view abstract 10.1039/d0me00171f
- Photonic NO2 Gas Sensing with Binaphthyl-Based Dopants
Spengler, M. and Pschyklenk, L. and Niemeyer, J. and Kaul, P. and Giese, M.
Advanced Optical Materials (2021)A series of reactive binaphthyl-diimine-based dopants is prepared and investigated with respect to their potential for the chiral induction of structural coloration in nematic liquid crystal mixture E7 and the selective photonic sensing of nitrogen dioxide (NO2). Studies of the helical twisting power (HTP) in 4-cyano-4′-pentylbiphenyl (5CB) reveal HTP values as high as 375 µm-1 and the tremendous impact of structural compatibility and changes of the dihedral binaphthyl angle on the efficiency of the chiral transfer. Detailed investigation of the sensing capabilities of the systems reveals an extraordinarily high selectivity for NO2 and a response to concentrations as low as 100 ppm. The systems show a direct response to the analyte gas leading to a concentration-dependent shift of the reflectance wavelength of up to several hundred nanometers. Incorporation of copper ions remarkably improves the sensor's properties in terms of sensitivity and selectivity, enabling the tailored tweaking of the system's properties. © 2021 The Authors. Advanced Optical Materials published by Wiley-VCH GmbH
view abstract 10.1002/adom.202001828
- Prospects of ultraviolet resonance Raman spectroscopy in supramolecular chemistry on proteins
Kumar, V. and Holtum, T. and Voskuhl, J. and Giese, M. and Schrader, T. and Schlücker, S.
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy 254 (2021)Ultraviolet resonance Raman scattering (UVRR) has been frequently used for studying peptide and protein structure and dynamics, while applications in supramolecular chemistry are quite rare. Since UVRR offers the additional advantages of chromophore selectivity and high sensitivity compared with conventional non-resonant Raman scattering, it is ideally suited for label-free probing of relatively small artificial/supramolecular ligands exhibiting electronic resonances in the UV. In this perspective article, we first summarize results of UVRR spectroscopy in supramolecular chemistry in the context of peptide/protein recognition. We focus on selected artificial ligands which were rationally designed as selective carboxylate binders (guanidiniocarbonyl pyrrole, GCP, and guanidiniocarbonyl indole, GCI) and selective lysine binder (molecular tweezer, CLR01), respectively, via a combination of non-covalent interactions involving electrostatics, hydrogen bonding, and hydrophobic effects/van der Waals forces. Current limitations of applying UVRR as a universally applicable method for label-free and site-specific probing of molecular recognition between supramolecular ligands and proteins are highlighted. We then propose solutions to overcome these limitations for transforming UVRR spectroscopy into a generic tool in supramolecular chemistry on proteins, with an emphasis on mono- and multivalent GCP- and GCI-based ligands. Finally, we outline specific cases of supramolecular ligands such as molecular tweezers where alternative approaches such as laser-based mid-IR spectroscopy are required since UVRR can intrinsically not provide the required molecular information. © 2021 The Authors
view abstract 10.1016/j.saa.2021.119622
- Tuning the solid-state emission of liquid crystalline nitro-cyanostilbene by halogen bonding
Nath, S. and Kappelt, A. and Spengler, M. and Roy, B. and Voskuhl, J. and Giese, M.
Beilstein Journal of Organic Chemistry 17 (2021)The first example of halogen-bonded fluorescent liquid crystals based on the interaction of iodofluorobenzene derivatives with nitro-cyanostilbenes is reported. The systematic variation of the fluorination degree and pattern indicates the relevance of the halogen bond strength for the induction of liquid crystalline properties. The modular self-assembly approach enables the efficient tuning of the fluorescence behaviour and mesomorphic properties of the assemblies. © 2021 Nath et al.
view abstract 10.3762/BJOC.17.13
- Ultraviolet resonance Raman spectroscopy with a continuously tunable picosecond laser: Application to the supramolecular ligand guanidiniocarbonyl pyrrole (GCP)
Kumar, V. and Holtum, T. and Sebena, D. and Giese, M. and Voskuhl, J. and Schlücker, S.
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy 250 (2021)We present a UVRR spectroscopy setup which is equipped with a picosecond pulsed laser excitation source continuously tunable in the 210–2600 nm wavelength range. This laser source is based on a three-stage optical parametric amplifier (OPA) pumped by a bandwidth-compressed second harmonic output of an amplified Yb:KGW laser. It provides <15 cm−1 linewidth pulses below 270 nm, which is sufficient for resolving Raman lines of samples in condensed phase studies. For demonstrating the capability of this tunable setup for UVRR spectroscopy we present its application to the artificial ligand guanidiniocarbonyl pyrrole (GCP), a carboxylate binder used in peptide and protein recognition. A UVRR excitation study in the range 244–310 nm was performed for identifying the optimum laser excitation wavelength for UVRR spectroscopy of this ligand (λmax = 298 nm) at submillimolar concentrations (400 µM) in aqueous solution. The optimum UVRR spectrum is observed for laser excitation with λexc = 266 nm. Only in the relatively narrow range of λexc = 266–275 nm UVRR spectra with a sufficiently high signal-to-noise ratio and without severe interference from autofluorescence (AF) were detectable. At longer excitation wavelengths the UVRR signal is masked by AF. At shorter excitation wavelengths the UVRR spectrum is sufficiently separated from the AF, but the resonance enhancement is not sufficient. The presented tunable UVRR setup provides the flexibility to also identify optimum conditions for other supramolecular ligands for peptide/protein recognition. © 2020
view abstract 10.1016/j.saa.2020.119359
- Alkyl-Alkyl Interactions in the Periphery of Supramolecular Entities: From the Evaluation of Weak Forces to Applications
Giese, M. and Albrecht, M.
ChemPlusChem 85 (2020)Supramolecular chemistry is based on weak intermolecular forces which nevertheless are of importance for chemical processes. In this report the relevance of alkyl-alkyl interactions in supramolecular assemblies is discussed. We show how hierarchically formed helicates can be used to evaluate weak interactions of alkyl groups based on solvent-supported London dispersion. In addition, the role of nano-segregation of alkyl groups in the periphery of supramolecular assemblies is described, as well as how this can be used to improve the properties of liquid-crystalline materials by controlling the alkyl-chain-mediated aggregation process. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
view abstract 10.1002/cplu.202000077
- Chiral mesophases of hydrogen-bonded liquid crystals
Malotke, F. and Saccone, M. and Wölper, C. and Dong, R.Y. and Michal, C.A. and Giese, M.
Molecular Systems Design and Engineering 5 (2020)The chiral induction in hydrogen-bonded liquid crystals is investigated. The experimental study was accompanied by detailed density functional theory calculations and variable-temperature solid-state deuteron NMR measurements indicating that interactions between the linking groups of the hydrogen-bond accepting unit play a key role in the chiral induction. © The Royal Society of Chemistry.
view abstract 10.1039/d0me00070a
- Control of secondary structure and morphology of peptide–guanidiniocarbonylpyrrole conjugates by variation of the chain length
Liu, X. and Wang, K. and Externbrink, M. and Niemeyer, J. and Giese, M. and Hu, X.-Y.
Chinese Chemical Letters 31 (2020)Peptide amphiphiles with well-organized secondary structure are an important family of molecules that are known to assemble into a variety of nanostructures. In this work, we present three guanidiniocarbonylpyrrole (GCP) containing peptide amphiphiles, which show versatile morphology and secondary structure changes as a result of different chain lengths and in different concentration regimes. The random coil conformation, α-helix, and β-sheet are obtained for peptide 1, peptide 2, and peptide 3, respectively under neutral aqueous conditions. Furthermore, all peptide amphiphiles can aggregate to form nanoparticles at low concentrations. However, at high concentrations, peptide 1 self-assembles into left-handed twisted helical fibers, while longer bamboo-like morphology can be observed exclusively for peptide 2. For peptide 3, freshly prepared samples show uniform spherical morphology, whereas an obvious morphological transition from original nanoparticles to disordered fibers was realized after incubating for one week. These fascinating morphology changes were determined by the combination of circular dichroism, dynamic light scattering, transmission electron microscopy, atomic force microscopy, and theoretical calculations. © 2020 The Author
view abstract 10.1016/j.cclet.2019.10.036
- Functional Disruption of the Cancer-Relevant Interaction between Survivin and Histone H3 with a Guanidiniocarbonyl Pyrrole Ligand
Vallet, C. and Aschmann, D. and Beuck, C. and Killa, M. and Meiners, A. and Mertel, M. and Ehlers, M. and Bayer, P. and Schmuck, C. and Giese, M. and Knauer, S.K.
Angewandte Chemie - International Edition 59 (2020)The protein Survivin is highly upregulated in most cancers and considered to be a key player in carcinogenesis. We explored a supramolecular approach to address Survivin as a drug target by inhibiting the protein–protein interaction of Survivin and its functionally relevant binding partner Histone H3. Ligand L1 is based on the guanidiniocarbonyl pyrrole cation and serves as a highly specific anion binder in order to target the interaction between Survivin and Histone H3. NMR titration confirmed binding of L1 to Survivin's Histone H3 binding site. The inhibition of the Survivin–Histone H3 interaction and consequently a reduction of cancer cell proliferation were demonstrated by microscopic and cellular assays. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
view abstract 10.1002/anie.201915400
- Guanidiniocarbonyl-Pyrroles (GCP) – 20 Years of the Schmuck Binding Motif
Giese, M. and Niemeyer, J. and Voskuhl, J.
ChemPlusChem 85 (2020)In this Minireview, an overview about the past 20 years of the guanidiniocarbonyl-pyrrole (GCP) binding motif, which was designed, investigated and applied by Prof. Dr. Carsten Schmuck, is presented. Here we highlight the first steps from design and discovery, initial binding studies, applications in material science to advanced biomedical use in protein modulation and delivery of genetic material. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
view abstract 10.1002/cplu.202000142
- Photo-switchable Fluorescence in Hydrogen-Bonded Liquid Crystals
Kappelt, A. and Giese, M.
Chemistry - A European Journal 26 (2020)A series of hydrogen-bonded liquid crystals showing switchable fluorescence is reported. The fluorescence behavior results from the unique combination of hydrogen bonding, liquid crystallinity, and photobasicity. Thus, the molecular mobility in the mesophase is essential for the reversible photo-initiated proton transfer switching on the fluorescence of the assemblies. The application potential of the materials for photo-patterning was demonstrated. © 2020 The Authors. Published by Wiley-VCH GmbH
view abstract 10.1002/chem.202001696
- Photo-switching and -cyclisation of hydrogen bonded liquid crystals based on resveratrol
Blanke, M. and Balszuweit, J. and Saccone, M. and Wölper, C. and Doblas Jiménez, D. and Mezger, M. and Voskuhl, J. and Giese, M.
Chemical Communications 56 (2020)A series of hydrogen-bonded liquid crystals based on resveratrol and resveratrone is reported and investigated with respect to their photo-switchability (at 405 nm) and photo-cyclisation (at 300 nm). © 2020 The Royal Society of Chemistry.
view abstract 10.1039/c9cc07721a
- Plasmonic Seasoning: Giving Color to Desktop Laser 3D Printed Polymers by Highly Dispersed Nanoparticles
Hupfeld, T. and Wegner, A. and Blanke, M. and Doñate-Buendía, C. and Sharov, V. and Nieskens, S. and Piechotta, M. and Giese, M. and Barcikowski, S. and Gökce, B.
Advanced Optical Materials 8 (2020)Material development is key for continuing the exponential growth in the field of 3D printing. However, 3D printing of polymers by laser powder bed fusion (PBF-LB) still is limited to a few polymer powder materials, which restricts the range of applications. Tailoring the chemical, rheological, mechanical, or optical properties of the feedstock powder to the requirements of the laser printing process poses a significant challenge. In order to meet global trends in the commercialization of desktop 3D printers, the use of inexpensive and compact diode lasers for PBF-LB in the visible or near-infrared range is highly desired. However, at present, only black objects can be printed by desktop laser printers since only commercial carbon black-based composite powders meet their laser absorption requirements. In this study, a route for tuning the absorption properties of thermoplastic polyurethane polymers and incorporating color into printed objects by using minute amounts (i.e., 0.01 vol%) of highly dispersed plasmonic silver nanoparticles is reported, presenting a new way for colored parts to be produced through laser 3D printing. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/adom.202000473
- Smart Glycopolymeric Nanoparticles for Multivalent Lectin Binding and Stimuli-Controlled Guest Release
Saha, S. and Klein-Hitpaß, M. and Vallet, C. and Knauer, S.K. and Schmuck, C. and Voskuhl, J. and Giese, M.
Biomacromolecules 21 (2020)The synthesis and self-assembly of a polymer featuring a self-complementary supramolecular binding motif guanidiniocarbonyl pyrrole carboxylate zwitterion (GCP-zwitterion) bearing lactose moieties are reported. The GCP-zwitterion acts as a cross-linker to facilitate self-assembly of the polymeric chain into nanoparticles (NPs) at neutral pH in an aqueous medium. The formation of polymeric NPs can be controlled by addition of external stimuli (acid or base), which disfavors self-assembly of the GCP-zwitterion because of protonation or deprotonation of the GCP units in the polymer chain. The small-sized (<40 nm) NPs have a hydrophobic cavity and accessible lactose units on the outer shell for multivalent lectin binding. The multivalent interaction between NPs and the lectin peanut agglutinin was confirmed by agglutination experiments. In addition, the stimuli-responsive property of NPs was exploited for the uptake and release of a hydrophobic guest Nile red. Furthermore, the selectivity toward different cell lines (HEK 296T, HeLa, and Hep2G) was tested, and a cellular uptake of cargo-loaded NPs was found for Hep2G cells bearing the lactose-specific asialogylcoprotein receptor, whereas all other cells showed no NP interaction. Copyright © 2020 American Chemical Society.
view abstract 10.1021/acs.biomac.0c00292
- Alkylated Aromatic Thioethers with Aggregation-Induced Emission Properties—Assembly and Photophysics
Riebe, S. and Saccone, M. and Stelzer, J. and Sowa, A. and Wölper, C. and Soloviova, K. and Strassert, C.A. and Giese, M. and Voskuhl, J.
Chemistry - An Asian Journal 14 (2019)In this contribution, we present the synthesis and self-assembly of alkylated thioethers with interesting photophysical properties. To this end, the emission, absorption and excitation spectra in organic solvents and as aggregates in water were measured as well as the corresponding photoluminescence quantum yields and lifetimes. The aggregates in aqueous media were visualized and measured using transmission electron microscopy. Besides that, crystal structures of selected compounds allowed a detailed discussion of the structure–property relationship. Furthermore, the mesomorphic behavior was investigated using polarized optical microscopy (POM) as well as differential scanning calorimetry (DSC). © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/asia.201801564
- Alkyloxy modified pyrene fluorophores with tunable photophysical and crystalline properties
Kapf, A. and Eslahi, H. and Blanke, M. and Saccone, M. and Giese, M. and Albrecht, M.
New Journal of Chemistry 43 (2019)Novel alkyloxy modified 2,7-di-tert-butyl-4,5,9,10-tetra(arylethynyl)pyrenes were prepared through a straightforward Sonogashira coupling approach. Optical properties such as quantum yields and absorption/emission spectra of the fluorophores were investigated by UV/Vis and fluorescence measurements. Aggregation induced excimer formation of the chromophores in polar solvents and in the solid state was proved by the presence of a characteristic bathochromically shifted emission band and a decrease of the emission capability. These results strongly indicate the unexpected observation that the excimer formation of adjacent pyrene rings is not prevented by the introduction of bulky tert-butyl substituents. Single-crystal X-ray and computational analyses reveal the co-planar alignment of adjacent molecules and the presence of π-π-stacking in the molecular packing of the pyrene polyaromatics. Furthermore, fluorescence, DSC and POM measurements indicate that the aggregation behaviour, the thermal characteristics and the crystalline properties are significantly influenced by changing structural features of the attached functional groups at the periphery of the pyrene core. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
view abstract 10.1039/c9nj00652d
- Cellulose nanocrystals in nanoarchitectonics-towards photonic functional materials
Giese, M. and Spengler, M.
Molecular Systems Design and Engineering 4 (2019)The physical and chemical properties of nanomaterials do not only rely on the composition of the building blocks, but also on the nano-scaled structure itself. Therefore, a deep understanding of these materials calls for a close cooperation between various research fields such as physics, chemistry, materials science, engineering and biology. Nanoarchitectonics aims to unify the efforts towards the design and development of novel functional nanomaterials by combining methods of all these disciplines. The present review summarizes the recent achievements in the development of photonic functional materials based on cellulose nanocrystals (CNCs) or CNC templating. The unique self-assembly of CNCs to chiral nematic structures allows for the development of a variety of functional materials with application potential in photonic sensing, tunable reflectors or optoelectronics. © 2019 The Royal Society of Chemistry.
view abstract 10.1039/c8me00065d
- Hydrogen-bonded liquid crystals with broad-range blue phases
Saccone, M. and Pfletscher, M. and Dautzenberg, E. and Dong, R.Y. and Michal, C.A. and Giese, M.
Journal of Materials Chemistry C 7 (2019)We report a modular supramolecular approach for the investigation of chirality induction in hydrogen-bonded liquid crystals. An exceptionally broad blue phase with a temperature range of 25 °C was found, which enabled its structural investigation by solid state 19F-NMR studies and allowed us to report order parameters of the blue phase I for the first time. © The Royal Society of Chemistry 2019.
view abstract 10.1039/c8tc06428h
- Improving the mesomorphic behaviour of supramolecular liquid crystals by resonance-assisted hydrogen bonding
Saccone, M. and Pfletscher, M. and Kather, S. and Wölper, C. and Daniliuc, C. and Mezger, M. and Giese, M.
Journal of Materials Chemistry C 7 (2019)A systematic structure-property relationship study on hydrogen-bonded liquid crystals was performed, revealing the impact of resonance-assisted hydrogen bonds (RAHBs) on the self-assembling behavior of the supramolecular architecture. The creation of a six-membered intramolecular hydrogen-bonded ring acts as a counterpart to the self-organization between hydrogen bond donators and acceptors and determines thus the suprastructure. Variation of the hydrogen-bonding pattern allowed us to significantly improve the temperature range of the reported liquid crystalline assemblies. © 2019 The Royal Society of Chemistry.
view abstract 10.1039/c9tc02787d
- Photoresponsive Halogen-Bonded Liquid Crystals: The Role of Aromatic Fluorine Substitution
Saccone, M. and Spengler, M. and Pfletscher, M. and Kuntze, K. and Virkki, M. and Wölper, C. and Gehrke, R. and Jansen, G. and Metrangolo, P. and Priimagi, A. and Giese, M.
Chemistry of Materials 31 (2019)A new strategy for controlling the liquid crystalline and photophysical properties of supramolecular mesogens assembled via halogen bonding is reported. Changing the degree of fluorination at the halogen-bond donor of the supramolecular liquid crystal allows for the fine-tuning of the halogen bond strength and thereby provides control over the temperature range of the mesophase. At least three fluorine atoms have to be present to ensure efficient polarization of the halogen-bond donor and the formation of a mesophase. In addition, it was found that stilbazole acceptors are superior to their azopyridine counterparts in promoting stable liquid crystalline phases. The halogen-bond-driven supramolecular liquid crystals between fluorinated azobenzenes and stilbazole/azopyridine acceptors show a rich variety of photoinduced processes driven by azobenzene photoisomerization, dictated not only by the photochemical properties of the molecular components but also by the difference between the operation temperature and the clearing point. © 2019 American Chemical Society.
view abstract 10.1021/acs.chemmater.8b04197
- Polymorphism of hydrogen-bonded star mesogens-a combinatorial DFT-D and FT-IR spectroscopy study
Pfletscher, M. and Wysoglad, J. and Gutmann, J.S. and Giese, M.
RSC Advances 9 (2019)A comprehensive study combining detailed computational analyses with temperature-variable FT-IR experiments was performed in order to elucidate the structure of the hydrogen-bonded liquid crystals based on phloroglucinol and azopyridine in their mesophase. Conformational analysis revealed three relevant conformers: star, λ- and E-shape. The results demonstrate an entropy-driven unfolding mechanism of the assembly. The stability of the conformers is given by intermolecular π-π and dispersion interactions of the azopyridine side chains. Correlating the calculated vibrational frequency with experimental FT-IR spectra suggests a λ-folded conformation of the assemblies as the predominant species in the mesophase. © 2019 The Royal Society of Chemistry.
view abstract 10.1039/c8ra09458f
- Structure-property relationships in aromatic thioethers featuring aggregation-induced emission: Solid-state structures and theoretical analysis
Saccone, M. and Riebe, S. and Stelzer, J. and Wölper, C. and Daniliuc, C.G. and Voskuhl, J. and Giese, M.
CrystEngComm 21 (2019)We describe in this paper a structure-property relationship study of aromatic thioethers with aggregation-induced emission (AIE) properties. We combine a structural analysis based on geometrical consideration with an in-depth analysis of the crystalline packing supported by quantum mechanical calculations. Our results allow us to correlate the enhanced fluorescence quantum yields with the significant increase of C-H⋯π and the decrease of π⋯π interactions in the solid state-a result which supports the well-accepted AIE mechanism quantitatively. © 2019 The Royal Society of Chemistry.
view abstract 10.1039/c9ce00444k
- Hydrogen-Bonded Liquid Crystals in Confined Spaces—Toward Photonic Hybrid Materials
Spengler, M. and Dong, R.Y. and Michal, C.A. and Hamad, W.Y. and MacLachlan, M.J. and Giese, M.
Advanced Functional Materials 28 (2018)A series of hybrid materials based on chiral nematic mesoporous organosilica (CNMO) films infiltrated with liquid crystalline hydrogen-bonded assemblies is prepared and characterized with respect to the mutual manipulation of the photonic properties of the host and the liquid-crystalline behavior of the guest. Detailed differential scanning calorimetry studies reveal the impact of confinement on the mesomorphic behavior of the liquid crystalline assemblies in the pores of the CNMO films. The photonic properties of the chiral nematic mesoporous host can be controlled by changing the temperature or irradiating the films with UV light. These stimuli-induced phase transitions are accompanied by changes in the orientational order of the mesogens as revealed by 19F NMR spectroscopy. The combination of confinement and changes in the molecular orientation in a unique hybrid material based on hydrogen-bonded liquid crystals and a porous host with a chiral nematic mesostructure is an interesting concept for the design of optical sensors, reflectors, or filters. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/adfm.201800207
- On the blue phase structure of hydrogen-bonded liquid crystals via 19F NMR
Dong, R.Y. and Michal, C.A. and Saccone, M. and Spengler, M. and Wölper, C. and Giese, M.
Chemical Physics Letters 710 (2018)19F NMR spectra are simulated for blue phase I of FPHG(St1.5 ∗Ap1.5) based on a model of a double-twisted substructure inside cylinders that form a body-centred cubic lattice. A kinetic matrix is included to describe jump processes over quarter pitch lengths. Though the lines in the NMR spectra are broad and featureless, changes in the widths and positions with temperature are well described by the blue phase model structure. The spectra in the chiral nematic N∗ phase are also simulated. Dynamics in the BP I are found to be slower than in the N∗ phase. © 2018 Elsevier B.V.
view abstract 10.1016/j.cplett.2018.08.056
- On the impact of linking groups in hydrogen-bonded liquid crystals-a case study
Pfletscher, M. and Mezger, M. and Giese, M.
Soft Matter 14 (2018)The impact of the linking group in hydrogen-bonded liquid crystals is systematically studied by a modular approach. POM and DSC results exhibited tremendous differences in the mesomorphic behaviour of the assemblies, due to the versatile linkages of the side chains, which were correlated with structural features and the elctronical nature of the side chains. © The Royal Society of Chemistry.
view abstract 10.1039/c8sm00802g
- Ortho-Fluorination of azophenols increases the mesophase stability of photoresponsive hydrogen-bonded liquid crystals
Saccone, M. and Kuntze, K. and Ahmed, Z. and Siiskonen, A. and Giese, M. and Priimagi, A.
Journal of Materials Chemistry C 6 (2018)Photoresponsive liquid crystals (LCs) whose alignment can be controlled with UV-Visible light are appealing for a range of photonic applications. From the perspective of exploring the interplay between the light response and the self-assembly of the molecular components, supramolecular liquid crystals are of particular interest. They allow elaborating the structure-property relationships that govern the optical performance of LC materials by subtle variation of the chemical structures of the building blocks. Herein we present a supramolecular system comprising azophenols and stilbazoles as hydrogen-bond donors and acceptors, respectively, and show that ortho-fluorination of the azophenol dramatically increases the thermal stability of the LC phases, an important characteristics in their further utilization in photonics. The systems exhibit fast photoinduced order-disorder transitions, and rapid recovery of the liquid-crystalline state once the light irradiation is ceased, due to the photochemical properties of azophenols. © 2018 The Royal Society of Chemistry.
view abstract 10.1039/c8tc02611d
- Fluorination of supramolecular liquid crystals-tuning tool and analytical probe
Spengler, M. and Dong, R.Y. and Michal, C.A. and Pfletscher, M. and Giese, M.
Journal of Materials Chemistry C 5 (2017)A study on the impact of fluorination on the properties of photo-responsive hydrogen-bonded liquid crystals is reported. The chosen modular approach allows for efficient screening of a variety of hydrogen-bonded assemblies. Tremendous effects on the mesophase stabilization and morphology are described. In addition, the fluorine substituents are used as analytical probes for 19F solid-state NMR studies, providing insight into the molecular alignment of the assemblies. © The Royal Society of Chemistry.
view abstract 10.1039/c6tc05472b
- Molecular mechanisms of Slo2 K+ channel closure
Giese, M.H. and Gardner, A. and Hansen, A. and Sanguinetti, M.C.
Journal of Physiology 595 (2017)Key points: Intracellular Na+-activated Slo2 potassium channels are in a closed state under normal physiological conditions, although their mechanisms of ion permeation gating are not well understood. A cryo-electron microscopy structure of Slo2.2 suggests that the ion permeation pathway of these channels is closed by a single constriction of the inner pore formed by the criss-crossing of the cytoplasmic ends of the S6 segments (the S6 bundle crossing) at a conserved Met residue. Functional characterization of mutant Slo2 channels suggests that hydrophobic interactions between Leu residues in the upper region of the S6 segments contribute to stabilizing the inner pore in a non-conducting state. Mutation of the conserved Met residues in the S6 segments to the negatively-charged Glu did not induce constitutive opening of Slo2.1 or Slo2.2, suggesting that ion permeation of Slo2 channels is not predominantly gated by the S6 bundle crossing. Abstract: Large conductance K+-selective Slo2 channels are in a closed state unless activated by elevated [Na+]i. Our previous studies suggested that the pore helix/selectivity filter serves as the activation gate in Slo2 channels. In the present study, we evaluated two other potential mechanisms for stabilization of Slo2 channels in a closed state: (1) dewetting and collapse of the inner pore (hydrophobic gating) and (2) constriction of the inner pore by tight criss-crossing of the cytoplasmic ends of the S6 α-helical segments. Slo2 channels contain two conserved Leu residues in each of the four S6 segments that line the inner pore region nearest the bottom of the selectivity filter. To evaluate the potential role of these residues in hydrophobic gating, Leu267 and Leu270 in human Slo2.1 were each replaced by 15 different residues. The relative conductance of mutant channels was highly dependent on hydrophilicity and volume of the amino acid substituted for Leu267 and was maximal with L267H. Consistent with their combined role in hydrophobic gating, replacement of both Leu residues with the isosteric but polar residue Asn (L267N/L270N) stabilized channels in a fully open state. In a recent cryo-electron microscopy structure of chicken Slo2.2, the ion permeation pathway of the channel is closed by a constriction of the inner pore formed by criss-crossing of the S6 segments at a conserved Met. Inconsistent with the S6 segment crossing forming the activation gate, replacement of the homologous Met residues in human Slo2.1 or Slo2.2 with the negatively-charged Glu did not induce constitutive channel opening. © 2016 The Authors. The Journal of Physiology © 2016 The Physiological Society
view abstract 10.1113/JP273225
- Structure-property relationships in hydrogen-bonded liquid crystals
Pfletscher, M. and Hölscher, S. and Wölper, C. and Mezger, M. and Giese, M.
Chemistry of Materials 29 (2017)The structural impact of hydrogen-donating moieties on the liquid crystalline behavior of hydrogen-bonded assemblies (HBAs) is comprehensively investigated. Therefore, a series of phenol derivatives such as phenol, catechol (CA), resorcinol (RE), hydroquinone (HQ), pyrogallol, hydroxyhydroquinone, and phloroglucinol (PHG) were combined with alkoxyazopyridines (Ap-N) yielding 49 new HBAs, which were studied with respect to their mesomorphic properties. The present study revealed significant differences in the liquid crystalline behavior of the structurally diverse assemblies, ranging from the absence of a mesophase to smectic or nematic phases. In contrast to previous studies a comprehensive crystallographic analysis provides insight into the structure-property relationships of the assemblies and proves a correlation between the supramolecular architecture and the macroscopic properties (=liquid crystallinity). More specifically, comparison of the single crystal data with the 2D X-ray diffraction patterns indicates that linear assemblies tend to form crystalline or smectic phases (for the HQ and RE, respectively), while a bent-shaped assembly yields nematic phases (for CA and PHG). Furthermore, our results suggest that segregation of aliphatic and aromatic segments, as observed in the solid state structures, supports the formation of stable mesophases. © 2017 American Chemical Society.
view abstract 10.1021/acs.chemmater.7b03182
- A modular approach towards functional supramolecular aggregates-subtle structural differences inducing liquid crystallinity
Pfletscher, M. and Wölper, C. and Gutmann, J.S. and Mezger, M. and Giese, M.
Chemical Communications 52 (2016)Herein we report an efficient modular approach to supramolecular functional materials. Hierarchical self-assembly of azopyridine derivatives and hydrogen-bond donors yielded discotic assemblies. Subtle differences in the core units introduced mesomorphic behaviour and fast photo-response of the liquid crystals based on phloroglucinol. The presented results prove the benefits of a modular methodology towards highly responsive materials with tailor-made properties. © 2016 The Royal Society of Chemistry.
view abstract 10.1039/c6cc03966a
- Experimental investigation of anion-π interactions - Applications and biochemical relevance
Giese, M. and Albrecht, M. and Rissanen, K.
Chemical Communications 52 (2016)Anion-π interactions, intuitively repulsive forces, turned from controversial to a well-established non-covalent interaction over the past quarter of a century. Within this time frame the question "Anion-π interactions. Do they exist?" could be answered and even more importantly its functional relevance was proven. The present feature article summarizes the experimental findings of anion-π studies in the gas phase, solution and in the solid state and highlights the application of anion-π interactions in anion recognition, sensing and transport as well as in catalysis. Moreover, the biochemical relevance of this weak intermolecular force is comprehensively reviewed. © The Royal Society of Chemistry 2016.
view abstract 10.1039/c5cc09072e
- Magnetic Mesoporous Photonic Cellulose Films
Giese, M. and Blusch, L.K. and Schlesinger, M. and Meseck, G.R. and Hamad, W.Y. and Arjmand, M. and Sundararaj, U. and MacLachlan, M.J.
Langmuir 32 (2016)Novel hybrid materials of cellulose and magnetic nanoparticles (NPs) were synthesized and characterized. The materials combine the chiral nematic structural features of mesoporous photonic cellulose (MPC) with the magnetic properties of cobalt ferrite (CoFe2O4). The photonic, magnetic, and dielectric properties of the hybrid materials were investigated during the dynamic swelling and deswelling of the MPC films. It was observed that the dielectric properties of the generated MPC films increased tremendously following swelling in water, endorsing efficient swelling ability of the generated mesoporous films. The high magnetic permeability of the developed MPC films in conjunction with their superior dielectric properties, predominantly in the swollen state, makes them interesting for electromagnetic interference shielding applications. © 2016 American Chemical Society.
view abstract 10.1021/acs.langmuir.6b02974
- Anion-π interactions with fluoroarenes
Giese, M. and Albrecht, M. and Rissanen, K.
Chemical Reviews 115 (2015)Recent findings in anion-π interactions of fluoroarenes were studied. The study clearly demonstrates that there is still a gap between theoretical studies and experimental evidence for those weak intermolecular interactions. Although computational studies, gas-phase experiments, and crystallographic results support the attractive nature of anion-π interactions, numerous investigations suggest that anion-π bonding very often is too weak to compete against other noncovalent interactions such as hydrogen bonding, electrostatic attraction, solvent effects, or dipole interactions in solution. Even halogen bonding seems to overrule the interaction between anions and the π-system of electron-deficient arenes. Nevertheless anion-π interactions gained considerable attention in anion-recognition and host-guest chemistry, and due to recent findings their participation in ion transport, stabilization of reactive anionic species, catalysis, templation, and sensing of fluoride ions motivates further detailed studies on the nature and relevance of this intriguing intermolecular interaction.
view abstract 10.1021/acs.chemrev.5b00156
- Chiral nematic cellulose-gold nanoparticle composites from mesoporous photonic cellulose
Schlesinger, M. and Giese, M. and Blusch, L.K. and Hamad, W.Y. and Maclachlan, M.J.
Chemical Communications 51 (2015)Gold nanoparticles (NPs) have been loaded into mesoporous photonic cellulose (MPC) films. The NPs show a low polydispersity and a nanoparticle-based plasmonic chiroptical activity with potential for novel sensing materials. This journal is © The Royal Society of Chemistry.
view abstract 10.1039/c4cc07596j
- Functional materials from cellulose-derived liquid-crystal templates
Giese, M. and Blusch, L.K. and Khan, M.K. and MacLachlan, M.J.
Angewandte Chemie - International Edition 54 (2015)Cellulose nanocrystals (CNCs), known for more than 50 years, have attracted attention because of their unique properties such as high specific strength and modulus, high surface area, and fascinating optical properties. Just recently, however, their potential in supramolecular templating was identified by making use of their self-assembly behavior in aqueous dispersions in the presence of compatible precursors. The combination of the mesoporosity, photonic properties, and chiral nematic order of the materials, which are available as freestanding films, has led to a significant number of interesting and promising discoveries towards new functional materials. This Review summarizes the use of cellulose derivatives, especially CNCs, as novel templates and gives an overview of the recent developments toward new functional materials. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA.
view abstract 10.1002/anie.201407141
- The pentafluorophenyl group as π-acceptor for anions: A case study
Giese, M. and Albrecht, M. and Valkonen, A. and Rissanen, K.
Chemical Science 6 (2015)The present study gives a comprehensive insight into anion-π interactions in the solid state, focusing on purely organic and charge-neutral fluorophenyl groups bearing a positive charge located at a side chain. The detailed statistical analysis of a series of structural data sets shows the geometrical variability of anion-π bonding in the solid state. It reveals the directing substituents at the arene as key elements for the positional preferences of anions above π-systems. The structural variety of the interaction between anions and electron-deficient arenes is considered by use of the hapticity concept. Together with new evaluation criteria, two helpful tools to understand and describe anion-π interactions in the solid are used. This journal is © The Royal Society of Chemistry.
view abstract 10.1039/c4sc02762k
- Tuning the photonic properties of chiral nematic mesoporous organosilica with hydrogen-bonded liquid-crystalline assemblies
Giese, M. and Krappitz, T. and Dong, R.Y. and Michal, C.A. and Hamad, W.Y. and Patrick, B.O. and MacLachlan, M.J.
Journal of Materials Chemistry C 3 (2015)A series of novel hydrogen-bonded assemblies was synthesized and characterized with respect to their liquid-crystalline behaviour. Solid-state NMR spectroscopy gave insight into the columnar nematic mesophase and the corresponding ordering and alignment. Infiltrating the pores of chiral nematic mesoporous organosilica films with the liquid-crystalline compounds gives composite samples that undergo reversible phase changes with temperature, leading to tuneable photonic properties. The unique combination of liquid crystallinity arising from supramolecular interactions (hydrogen bonding) and chiral nematic organisation in a solid-state host is a promising new concept for developing optical sensors. © The Royal Society of Chemistry 2015.
view abstract 10.1039/c4tc02602k
- NMR of guest-host systems: 8CB in chiral nematic porous glasses
Manning, A.P. and Giese, M. and Terpstra, A.S. and MacLachlan, M.J. and Hamad, W.Y. and Dong, R.Y. and Michal, C.A.
Magnetic Resonance in Chemistry 52 (2014)Liquid crystals confined to porous materials often have different critical phenomena and ordering than in the bulk. Through the selection of pore size, structure and guest liquid crystal, these systems could enable a variety of functional materials for applications such as sensors and displays. A recent example of such a system is chiral nematic mesoporous films infiltrated with liquid crystal 4-cyano-4'-n-octylbiphenyl (8CB), which has reversible thermal switching of its optical bandgap. The optical bandgap is lost when the ordered 8CB guests are heated above ∼50 °C, where the 8CB becomes isotropic. In this study, we have used NMR cryoporometry and pulsed-field gradient diffusion measurements to determine the pore sizes and structures of various chiral nematic mesoporous silica and organosilica films. Temperature and orientation-dependent wideline 15N NMR spectra of films infiltrated with 15N-labelled 8CB guests show that the ordering of the 8CB mesogens is consistent with an average orientation parallel to the chiral nematic pore axes. Inclusion of a large, orientation-dependent shift was necessary to fit the spectra, probably due to susceptibility differences between the 8CB guests and the organosilica host. Copyright © 2014 John Wiley & Sons, Ltd.
view abstract 10.1002/mrc.4101
- Quantum-chemical investigations on the structural variability of anion-π interactions
Moha, V. and Giese, M. and Moha, R. and Albrecht, M. and Raabe, G.
Zeitschrift fur Naturforschung - Section A Journal of Physical Sciences 69 (2014)The structural versatility of anion-π interactions was investigated computationally. Employing quantum-chemically optimized structures of a series of C6H6-nFn/Br- complexes and the Coulomb law together with the London formula to calculate the electrostatic and the dispersion energy of the interaction between the anion and the p-system led to the result that up to the number of n = 2 due to a significantly repulsive electrostatic energy of interaction the dispersion energy is not sufficient to stabilize such structures in the gas phase where the anion is located above the plane defined by the aromatic ring. The energy surfaces resulting from the interaction of bromide anions with isolated arenes bearing varying numbers of fluorine atoms in different positions of the aromatic ring also show a pronounced dependency on the subsitution pattern of the aromatic system. Depending on the nature of the electron withdrawing group and its position, the energy surface can have a sharply defined energetically low minimum, in which the anion is 'fixed'. Other substitution patterns result in very flat energy surfaces, and even a surface with more than two local minima within the scanned area was found. Thus, our study reveals the reason for the experimentally observed structural versatility depending on the substitution pattern in the solid state. © 2014 Verlag der Zeitschrift für Naturforschung, Tübingen.
view abstract 10.5560/ZNA.2014-0031
- Responsive mesoporous photonic cellulose films by supramolecular cotemplating
Giese, M. and Blusch, L.K. and Khan, M.K. and Hamad, W.Y. and Maclachlan, M.J.
Angewandte Chemie - International Edition 53 (2014)Cellulose-based materials have been and continue to be exceptionally important for humankind. Considering the bioavailability and societal relevance of cellulose, turning this renewable resource into an active material is a vital step towards sustainability. Herein we report a new form of cellulose-derived material that combines tunable photonic properties with a unique mesoporous structure resulting from a new supramolecular cotemplating method. A composite of cellulose nanocrystals and a urea-formaldehyde resin organizes into a chiral nematic assembly, which yields a chiral nematic mesoporous continuum of desulfated cellulose nanocrystals after alkaline treatment. The mesoporous photonic cellulose (MPC) films undergo rapid and reversible changes in color upon swelling, and can be used for pressure sensing. These new active mesoporous cellulosic materials have potential applications in biosensing, optics, functional membranes, chiral separation, and tissue engineering. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/anie.201402214
- Single-crystal X-ray diffraction and solution studies of anion-π interactions in N-(pentafluorobenzyl)pyridinium salts
Giese, M. and Albrecht, M. and Repenko, T. and Sackmann, J. and Valkonen, A. and Rissanen, K.
European Journal of Organic Chemistry 2014 (2014)A solid-state structural study on anion-π interaction in various N-(pentafluorobenzyl)pyridinium salts accompanied by NMR spectroscopic investigations is presented. The crystal structures of 1a-1d reveal different kinds of contacts with anions, including anion-π interactions. In particular, the solid-state structure of 1b-I3 shows distinct evidence of anion-π interactions. Attempts to study anion-π interactions in solution were not successful, but their presence in solution could not be ruled out. The interactions of N-(pentafluorobenzyl)pyridinium salts are investigated in the solid state as well as in solution. The triiodide salt shows distinct evidence of anion-π interactions with both the pyridinium and the pentafluorophenyl unit. Solution investigations to prove the attractive nature of the noncovalent force failed, but they did not rule out the presence of the interaction. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/ejoc.201301336
- Solid state anion-π interactions involving polyhalides
Giese, M. and Albrecht, M. and Bohnen, C. and Repenko, T. and Valkonen, A. and Rissanen, K.
Dalton Transactions 43 (2014)The stabilization of polyhalides in the solid state with the support of electron-deficient pentafluorophenyl groups is described. Furthermore, a synthetic approach towards the sensitive tetraiodide dianion is described and ESI mass spectrometric evidence for its presence in solution is reported. © The Royal Society of Chemistry.
view abstract 10.1039/c3dt52960f
- Synthesis of 7-pentafluorophenyl-1 H -indole: An anion receptor for anion-π interactions
Sun, Z.-H. and Albrecht, M. and Giese, M. and Pan, F. and Rissanen, K.
Synlett 25 (2014)7-Pentafluorophenyl-1H-indole has the potential to be a key compound for the investigation of anion-π interactions in solution. Unfortunately, it was not possible to obtain it by aryl-aryl coupling reaction. Finally, it has been prepared by Bartoli indole synthesis. The key compound as well as analogues were submitted to preliminary studies of anion binding. Single crystals of two key receptors were obtained. © Georg Thieme Verlag Stuttgart New York.
view abstract 10.1055/s-0034-1378449
- The development of chiral nematic mesoporous materials
Kelly, J.A. and Giese, M. and Shopsowitz, K.E. and Hamad, W.Y. and MacLachlan, M.J.
Accounts of Chemical Research 47 (2014)ConspectusCellulose nanocrystals (CNCs) are obtained from the sulfuric acid-catalyzed hydrolysis of bulk cellulose. The nanocrystals have diameters of ∼5-15 nm and lengths of ∼100-300 nm (depending on the cellulose source and hydrolysis conditions). This lightweight material has mostly been investigated to reinforce composites and polymers because it has remarkable strength that rivals carbon nanotubes. But CNCs have an additional, less explored property: they organize into a chiral nematic (historically referred to as cholesteric) liquid crystal in water. When dried into a thin solid film, the CNCs retain the helicoidal chiral nematic order and assemble into a layered structure where the CNCs have aligned orientation within each layer, and their orientation rotates through the stack with a characteristic pitch (repeating distance). The cholesteric ordering can act as a 1-D photonic structure, selectively reflecting circularly polarized light that has a wavelength nearly matching the pitch.During CNC self-assembly, it is possible to add sol-gel precursors, such as Si(OMe)4, that undergo hydrolysis and condensation as the solvent evaporates, leading to a chiral nematic silica/CNC composite material. Calcination of the material in air destroys the cellulose template, leaving a high surface area mesoporous silica film that has pore diameters of ∼3-10 nm. Importantly, the silica is brilliantly iridescent because the pores in its interior replicate the chiral nematic structure. These films may be useful as optical filters, reflectors, and membranes.In this Account, we describe our recent research into mesoporous films with chiral nematic order. Taking advantage of the chiral nematic order and nanoscale of the CNC templates, new functional materials can be prepared. For example, heating the silica/CNC composites under an inert atmosphere followed by removal of the silica leaves highly ordered, mesoporous carbon films that can be used as supercapacitor electrodes. The composition of the mesoporous films can be varied by using assorted organosilica precursors. After removal of the cellulose by acid-catalyzed hydrolysis, highly porous, iridescent organosilica films are obtained. These materials are flexible and offer the ability to tune the chemical and mechanical properties through variation of the organic spacer.Chiral nematic mesoporous silica and organosilica materials, obtainable as centimeter-scale freestanding films, are interesting hosts for nanomaterials. When noble metal nanoparticles are incorporated into the pores, they show strong circular dichroism signals associated with their surface plasmon resonances that arise from dipolar coupling of the particles within the chiral nematic host. Fluorescent conjugated polymers show induced circular dichroism spectra when encapsulated in the chiral nematic host. The porosity, film structure, and optical properties of these materials could enable their use in sensors.We describe the development of chiral nematic mesoporous silica and organosilica, demonstrate different avenues of host-guest chemistry, and identify future directions that exploit the unique combination of properties present in these materials. The examples covered in this Account demonstrate that there is a rich diversity of composite materials accessible using CNC templating. © 2014 American Chemical Society.
view abstract 10.1021/ar400243m
- Anion-π interaction: An influential force in solid state molecular microstructures
Giese, M. and Albrecht, M. and Valkonen, A. and Rissanen, K.
European Journal of Organic Chemistry (2013)The crystal structures of simple triphenyl(pentafluorobenzyl)phosphonium salts provide crucial data on the influence of anion size on the molecular structure of bis(pentafluorobenzyl)phosphonium cations containing two adjacent electron-deficient moieties. Whereas the bromide anions interact by anion-π interaction in a 1:1 mode with the pentafluorobenzene unit Z-configured, the bulkier anions iodide, tetrafluoroborate, and hexafluorophosphate result in a 1:2 tweezer-like anti-configuration in which one anion interacts simultaneously with two pentafluorobenzene units. When spatial separation of the two electron-deficient rings match the size of the anion, anion-π interactions induce a conformational change from the anti-form observed for the smaller anion to the tweezer-like syn-form. The solid-state structures of a series of bis(pentafluorobenzyl)phosphonium salts reveal the crucial relevance of anion size in anion-π interactions, leading to conformational control. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/ejoc.201201704
- Di-, tri-, and tetra(pentafluorophenyl) derivatives for oligotopic anion-π interactions
Giese, M. and Albrecht, M. and Steike, S. and Ackermann, A. and Valkonen, A. and Rissanen, K.
Inorganic Chemistry 52 (2013)The present study describes a series of pentafluorobenzyl ammonium salts with two, three, or four C6F5 units in order to investigate simultaneous interactions of several perfluorinated arenes with anions in the crystalline state. Most of the structures show multiple anion-π contacts. However, only 6·2HI reveals an effective encapsulation of the iodide ion by the aromatic units. For comparison, the structure of 4b is investigated because it offers two π-systems with inverse charge distribution to a bromide anion. Only the electron-deficient π-system of the pentafluorophenyl group interacts with the anion. © 2013 American Chemical Society.
view abstract 10.1021/ic4008087
- Flexible mesoporous photonic resins with tunable chiral nematic structures
Khan, M.K. and Giese, M. and Yu, M. and Kelly, J.A. and Hamad, W.Y. and Maclachlan, M.J.
Angewandte Chemie - International Edition 52 (2013)Colors of nature: Mimicking of the structural colors of nature was achieved by the preparation of easily accessible chiral nematic polymer composites based on phenol-formaldehyde resins templated by cellulose nanocrystals. Removal of the template led to mesoporous polymer films with unique optical and physical properties. The potential application of these materials in optical sensors was also demonstrated. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/anie.201303829
- Imprinting of photonic patterns with thermosetting amino-formaldehyde- cellulose composites
Giese, M. and Khan, M.K. and Hamad, W.Y. and MacLachlan, M.J.
ACS Macro Letters 2 (2013)A family of new amino resin-cellulose nanocrystal composites is reported. Owing to the chiral nematic order of the cellulose nanocrystals (CNCs) embedded in the amino resin polymer, the materials appear highly iridescent and their color can be controlled by the addition of salt. The freshly prepared samples are highly flexible and their color can be manipulated by applying pressure to the films. Colored chiral nematic patterns can be permanently recorded in the composite films, suggesting their application for security features, pressure sensors, and decoration. © 2013 American Chemical Society.
view abstract 10.1021/mz4003722
- Iridescent chiral nematic cellulose nanocrystal/polymer composites assembled in organic solvents
Cheung, C.C.Y. and Giese, M. and Kelly, J.A. and Hamad, W.Y. and Maclachlan, M.J.
ACS Macro Letters 2 (2013)We describe an approach to prepare polymer composites with chiral nematic photonic structures through the self-assembly of cellulose nanocrystal (CNC) dispersions in organic solvents. Contrary to previous reports, we demonstrate that dispersions of neutralized sulfated CNCs in polar organic media readily form lyotropic chiral nematic liquid crystalline phases. We have investigated the effect of the neutralizing base on the CNC self-assembly, observing chiral nematic ordering for all counterions studied. The self-assembly of the organic CNC dispersions can be exploited to prepare iridescent polymeric composites simply by casting the CNC dispersion with a suitable polymer soluble in the organic solvent. Photonic properties of the composite films can be easily controlled by either varying the ratio of CNCs to polymer or adding salts. © 2013 American Chemical Society.
view abstract 10.1021/mz400464d
- Novel PPV/mesoporous organosilica composites: Influence of the host chirality on a conjugated polymer guest
Mehr, S.H.M. and Giese, M. and Qi, H. and Shopsowitz, K.E. and Hamad, W.Y. and Maclachlan, M.J.
Langmuir 29 (2013)The conjugated polymer poly(p-phenylenevinylene) (PPV) was polymerized in the pores of chiral nematic mesoporous organosilica to give a composite film showing the strong characteristic fluorescence of PPV as well as the iridescence due to the photonic band gap of the host material. Detailed circular dichroism (CD) studies reveal a chiral structure of the polymer within the pores. These new fluorescent materials undergo fluorescence quenching upon exposure to electron deficient aromatics such as 2,4,6-trinitrotoluene (TNT), indicating that they may be useful for developing chemical sensors. © 2013 American Chemical Society.
view abstract 10.1021/la4024597
- Thermal switching of the reflection in chiral nematic mesoporous organosilica films infiltrated with liquid crystals
Giese, M. and De Witt, J.C. and Shopsowitz, K.E. and Manning, A.P. and Dong, R.Y. and Michal, C.A. and Hamad, W.Y. and MacLachlan, M.J.
ACS Applied Materials and Interfaces 5 (2013)Materials that undergo stimulus-induced optical changes are important for many new technologies. In this paper, we describe a new free-standing silica-based composite film that exhibits reversible thermochromic reflection, induced by a liquid crystalline guest in the pores of iridescent mesoporous films. We demonstrate that selective reflection from the novel mesoporous organosilica material with chiral nematic organization can be reversibly switched by thermal cycling of the 8CB guest between its isotropic and liquid crystalline states, which was proven by solid-state NMR experiments. The switching of the optical properties of the chiral solid-state host by stimulus-induced transitions of the guest opens the possibility of applications for these novel materials in sensors and displays. © 2013 American Chemical Society.
view abstract 10.1021/am402266z
- Controlling the position of anions relative to a pentafluorophenyl group
Giese, M. and Albrecht, M. and Wiemer, K. and Valkonen, A. and Rissanen, K.
New Journal of Chemistry 36 (2012)The position of an anion above an electron-deficient arene can be controlled by the geometry of appended directing groups. Here a series of ammonium substituted pentafluorophenyl derivatives is investigated. The presented results are one step on the way to find the ideal structural features for an effective and superior receptor for anion-π studies. © 2012 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
view abstract 10.1039/c2nj40089h
- Cooperativity of H-bonding and anion-π interaction in the binding of anions with neutral π-acceptors
Giese, M. and Albrecht, M. and Krappitz, T. and Peters, M. and Gossen, V. and Raabe, G. and Valkonen, A. and Rissanen, K.
Chemical Communications 48 (2012)A rare anion-π complex between bromide and a neutral receptor is reported and related receptor systems are studied with a series of anions. The interaction is observed in the solid state and in solution, and further evidence for it is obtained by a computational study. © The Royal Society of Chemistry 2012.
view abstract 10.1039/c2cc34748b
- Geometrically diverse anions in anion-π interactions
Giese, M. and Albrecht, M. and Ivanova, G. and Valkonen, A. and Rissanen, K.
Supramolecular Chemistry 24 (2012)The role of different anion geometries in anion-π interactions is discussed. The chemistry described herein is different to the interaction of spherical cations with aromatics. The influence of different geometries makes selective anion recognition more complicated than respective cation sensing. The present structural study reveals attractive interactions between pentafluorophenyl units and geometrically diverse anions (linear, trigonal planar, tetrahedral and octahedral). Due to the electrostatic nature of anion-π interactions, the anion geometry seems to be irrelevant. The size of the anion controls the relative orientation of the anion and the π system (e.g. in compounds 1-3). The dimeric solid-state structure of ammonium tetrafluorophenolate betaine 4 shows π-π as well as anion-π interactions. In the solid-state structure of 5, the linear BrIBr anion is panelled by three pentafluorophenyl units. © 2012 Copyright Taylor and Francis Group, LLC.
view abstract 10.1080/10610278.2011.622384
- Lanthanide(III) complexes of bis-semicarbazone and bis-imine-substituted phenanthroline ligands: Solid-state structures, photophysical properties, and anion sensing
Nadella, S. and Selvakumar, P.M. and Suresh, E. and Subramanian, P.S. and Albrecht, M. and Giese, M. and Fröhlich, R.
Chemistry - A European Journal 18 (2012)Phenanthroline-based hexadentate ligands L1 and L2 bearing two achiral semicarbazone or two chiral imine moieties as well as the respective mononuclear complexes incorporating various lanthanide ions, such as LaIII, EuIII, TbIII, LuIII, and YIII metal ions, were synthesized, and the crystal structures of [ML1Cl3] (M=LaIII, EuIII, Tb III, LuIII, or YIII) complexes were determined. Solvent or water molecules act as coligands for the rare-earth metals in addition to halide anions. The big LnIII ion exhibits a coordination number (CN) of 10, whereas the corresponding EuIII, TbIII, LuIII, and YIII centers with smaller ionic radii show CN=9. Complexes of L2, namely [ML2Cl3] (M=EuIII, TbIII, LuIII, or YIII) ions could also be prepared. Only the complex of EuIII showed red luminescence, whereas all the others were nonluminescent. The emission properties of the Eu derivative can be applied as a photophysical signal for sensing various anions. The addition of phosphate anions leads to a unique change in the luminescence behavior. As a case study, the quenching behavior of adenosine-5′-triphosphate (ATP) was investigated at physiological pH value in an aqueous solvent. A specificity of the sensor for ATP relative to adenosine-5′-diphosphate (ADP) and adenosine-5′-monophosphate (AMP) was found. 31P NMR spectroscopic studies revealed the formation of a [EuL2(ATP)] coordination species. Illuminating the ion: Hexadentate bis-semicarbazone-based achiral and bis-imine chiral ligands of phenathroline together with their respective lanthanide complexes were synthesized. The crystal structures obtained for bis- semicarbazone-based LnIII complexes reveal coordination numbers of 9 and 10. Among the bis-imine chiral complexes, a luminescent EuIII complex was investigated for sensing various anions, and selectivity towards adenosine-5′-triphosphate (ATP) was achieved in an aqueous medium (see picture). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/chem.201201705
- Pentafluorophenyl salicylamine receptors in anion-π interaction studies
Giese, M. and Albrecht, M. and Plum, C. and Hintzen, D. and Valkonen, A. and Rissanen, K.
Supramolecular Chemistry 24 (2012)A crystal structure analysis confirms the appropriateness of pentafluorophenyl salicylamine (1a) as a-acceptor for anion-interactions. Crystals of 1aHCl show that the OH-group fixes the anion in a η 2-type binding motif above the electron-deficient arene. Attempts to find some relevance for this weak intermolecular force in solution failed. Stronger CH-, NH-and OH-anion interactions are dominant over the weak anion-interactions. Due to the hydrogen bonding, the non-fluorinated receptor exhibits the highest binding constants within this series. © 2012 Taylor and Francis Group, LLC.
view abstract 10.1080/10610278.2012.715648
- Weak intermolecular anion-π interactions in pentafluorobenzyl- substituted ammonium betaines
Giese, M. and Albrecht, M. and Wiemer, K. and Kubik, G. and Valkonen, A. and Rissanen, K.
European Journal of Inorganic Chemistry (2012)A series of ammonium-carboxylate and ammonium-sulfonate betaines was synthesized and studied by single-crystal X-ray diffraction analysis to investigate the weak intermolecular interactions as well as the intramolecular interactions in the solid state. None of the expected intramolecular anion-π interactions could be observed, probably because of the steric demands and the reduced nucleophilicity of the anionic part of the betaines. Nevertheless, a weak intermolecular anion-π interaction between the anionic part of the betaine and the pentafluorophenyl unit is present in the structure of 5a. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/ejic.201200184
- From attraction to repulsion: Anion-π interactions between bromide and fluorinated phenyl groups
Giese, M. and Albrecht, M. and Bannwarth, C. and Raabe, G. and Valkonen, A. and Rissanen, K.
Chemical Communications 47 (2011)Anion-π interactions in crystals of fluorobenzyl ammonium salts depend on the degree of fluorination at the aromatics. © The Royal Society of Chemistry 2011.
view abstract 10.1039/c1cc12667a