Ihmels, Heiko
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Publication Access status: Metadata only , Bis‐ and Tris‐norbornadienes with High Energy Densities for Efficient Molecular Solar Thermal Energy StorageMolecular solar thermal energy storage (MOST) systems can convert, store and release solar energy in chemical bonds, i.e., as chemical energy. In this work, phenyl‐ and naphthyl‐linked bis‐ and tris‐norbornadienes are presented as promising MOST systems with very high energy densities. The substrates were synthesized by Suzuki–Miyaura coupling reactions and their absorption properties and characteristic parameters for MOST applications were investigated. The norbornadiene derivatives showed absorption onsets of up to 386 nm and photoisomerization quantum yields of 56 % per photoisomerization event. The resulting quadricyclane products have half‐lifes up to 14 d and very high energy densities of up to 734 kJ/kg. Overall, these norbornadienes fulfill necessary criteria for an optimal MOST system and are, therefore, a highly promising basis for the development of materials for efficient solar energy conversion and storage.Source Type:Article3 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Extension of the π-system of monoaryl-substituted norbornadienes with acetylene bridges: influence on the photochemical conversion and storage of light energyThe photochromic norbornadiene/quadricyclane pair is a promising system for molecular solar thermal (MOST) energy storage, with which solar energy may be converted, stored, and released as heat in one integral molecular system. Herein, we present the synthesis of mono-, bis-, and tris-norbornadiene derivatives with alkynylbenzene and alkynylnaphthalene core units, along with studies of their photochemical properties. The target compounds were synthesized by Sonogashira–Hagihara coupling reactions of 2-bromonorbornadiene and the corresponding arylacetylenes. The norbornadienes showed absorption maxima in the range of 310–345 nm and long-wavelength zero onsets of up to 420 nm. The photoisomerization quantum yields were as high as 59% per photoisomerization event and the resulting quadricyclanes showed half-lives of up to 8 h at room temperature. Furthermore, the norbornadienes were transformed quantitatively into their quadricyclane photoproducts by irradiation with green light (520 nm) in the presence of a photosensitizer.Source Type:Article1 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Fluorimetric Cell Analysis with 9‐Aryl‐Substituted Berberine Derivatives as DNA‐Targeting Fluorescent ProbesDNA‐sensitive fluorescent light‐up probes based on berberine are presented. This biogenic fluorophore was chosen as central unit to use its potential biocompatibility and its DNA‐binding properties. To provide predictable fluorescence quenching in aqueous solution and a fluorescence light‐up effect upon DNA binding, aryl substituents were attached at the 9‐position by Suzuki‐Miyaura coupling reactions. The 9‐arylberberine derivatives have a very low fluorescence quantum yield ( Φ fl =<0.02), which is caused by the radiationless deactivation of the excited state by torsional relaxation about the biaryl axis. In addition, these berberine derivatives intercalate into DNA with high affinity ( K b =2.0−22×10 4 M −1 ). Except for the nitrophenyl‐ and hydroxyphenyl‐substituted derivatives, all tested compounds exhibited a pronounced fluorescence light‐up effect upon association with DNA, because the deactivation of the excited‐state by torsional relaxation is suppressed in the DNA binding site. Most notably, it was shown exemplarily with the 9‐(4‐methoxyphenyl)‐ and the 9‐(6‐methoxynaphthyl)‐substituted derivatives that these properties are suited for fluorimetric cell analysis. In particular, these probes generated distinct staining patterns in eukaryotic cells (NIH 3T3 mouse fibroblasts), which enabled the identification of nuclear substructures, most likely heterochromatin or nucleoli, respectively.Source Type:Article2 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Monoaryl‐Substituted Norbornadiene Photoswitches as Molecular Solar Thermal Energy Storage Compounds: Synthesis and InvestigationIn the search for improved photochromic systems that may be used for the efficient reversible conversion of light into chemical energy, eight monoaryl‐substituted norbornadienes are presented, which carry naphthyl, anthracenyl, or donor‐acceptor‐phenyl substituents to establish an extended π system. The substrates were synthesized by Suzuki‐Miyaura coupling reactions, and their absorption properties, the key parameters of the photochromic equilibrium, and the energy storage density of the quadricyclane products were examined. It was observed that these compounds have favorable properties for chemical energy storage. Specifically, 2‐(1‐naphthyl)norbornadiene showed a pronounced red shift of the absorption, a long half‐life (35 d) and a relatively high energy storage density (361 KJ/Kg) of the respective quadricyclane. Therefore, the so far neglected monoaryl‐norbornadienes represent a useful and complementary class of compounds that should be considered in the development of efficient molecular solar thermal energy storage (MOST) compounds, which can reversibly convert sunlight into chemical energy.Source Type:Article2 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Photocontrolled Binding of Styrylnaphthyridine Ligands to Abasic Site‐Containing DNA by Reversible [2+2] Cycloaddition and Cycloreversion(2024); Five novel styrylnaphthyridine derivatives were synthesized and shown to operate as photoswitchable, selective ligands for abasic site‐containing DNA (AP‐DNA), which is an important therapeutic and diagnostic target. These compounds associate with AP‐DNA with binding constants of 0.5–8.4×10 4 M −1 as shown by photometric and fluorimetric titrations. Specifically, these ligands bind preferentially to AP‐DNA relative to regularly paired duplex DNA. As a special feature, the association of these ligands with DNA can be controlled by means of a reversible [2+2] photocycloaddition. Upon irradiation at 420 nm the photodimer is formed, which does not bind to AP‐DNA. In turn, the naphthyridine is regained with excitation at 315 nm. Most notably, this photoinduced deactivation and release of the DNA ligand can be performed in situ in the presence of AP‐DNA, thus providing a tool for on‐demand delivery of a DNA binder. Overall, these results provide a promising starting point for the development of functional AP‐DNA ligands whose bioactivity can be modulated by light with local and temporal control.Source Type:Article3 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Photoinduced [2+2] and [4+4] Cycloaddition and Cycloreversion Reactions for the Development of Photocontrollable DNA Binders(2024); In the current field of photopharmacology, molecular photoswitches are applied whose interactions with DNA can be triggered or controlled by light. And although several photochromic reactions have been shown to serve this purpose well, the reversible photocycloaddition and photocycloreversion reactions have been largely neglected. This absence of research is surprising because especially the photodimerization of a DNA ligand leads to products with significant change of the size and shape which, in turn, leads to strongly diminished or even suppressed DNA association. Therefore, photocycloaddition–cycloreversion sequences have a huge potential for the photoinduced, reversible deactivation and activation of ligand–DNA interactions, as will be shown with selected examples in this Concept Article . Specifically, heterostyryl and ‐stilbene derivatives are presented whose DNA–binding properties are efficiently switched in reversible [2+2] photocycloaddition reactions. In addition, the photocontrolled DNA–binding of anthracene derivatives and their heterocyclic benzo[ b ]quinolizinium analogues in a [4+4] photocycloaddition, as well as the use of this reaction as part of dual–mode switches in combination with redox‐active functionalities, are highlighted. Furthermore, examples of conjugates are provided, in which the photochromic unit is bound covalently to nucleic acids or proteins, such that the photocycloaddition reaction can be used for reversible photoinduced crosslinking, ligation, or inhibition of gene expression.Source Type:Article3 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Photoinduced in situ generation of DNA-targeting ligands: DNA-binding and DNA-photodamaging properties of benzo[<i>c</i>]quinolizinium ionsThe photoreactions of selected styrylpyridine derivatives to the corresponding benzo[ c ]quinolizinium ions are described. It is shown that these reactions are more efficient in aqueous solution (97–44%) than in organic solvents (78–20% in MeCN). The quinolizinium derivatives bind to DNA by intercalation with binding constants of 6–11 × 10 4 M −1 , as shown by photometric and fluorimetric titrations as well as by CD- and LD-spectroscopic analyses. These ligand–DNA complexes can also be established in situ upon irradiation of the styrylpyridines and formation of the intercalator directly in the presence of DNA. In addition to the DNA-binding properties, the tested benzo[ c ]quinolizinium derivatives also operate as photosensitizers, which induce DNA damage at relative low concentrations and short irradiation times, even under anaerobic conditions. Investigations of the mechanism of the DNA damage revealed the involvement of intermediate hydroxyl radicals and C-centered radicals. Under aerobic conditions, singlet oxygen only contributes to marginal extent to the DNA damage.Source Type:Article4 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Photoinduced Reactions of Styrylpyridine Derivatives for the In Situ Formation of Selective Ligands for Apyrimidinic DNAThe photocyclization reaction of sterically demanding styrylpyridine derivatives was investigated and shown to depend on the type of substituent. With this method, a 2,2‐diphenyl‐1,3‐benzodioxolo‐annelated benzo[ c ]quinolizinium was synthesized, and its association with regular and abasic site‐containing DNA (AP‐DNA) was investigated by absorption, fluorescence, circular and linear dichroism spectroscopy. Specifically, this ligand binds preferentially to AP‐DNA relative to regular duplex DNA, and the AP‐DNA/ligand complex is formed in situ upon irradiation of the styrylpyridine substrate in the presence of the DNA.Source Type:Article2 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Reversible Restrain and Release of the Dynamic Valence Isomerization in a Shape‐shifting Bullvalene by Complex FormationIn search for structural features that enable the control of the valence isomerization of the fluxional bullvalene, a bullvalene‐bis(harmane) conjugate is identified that acts as chelating ligand in complexes with metal ions. Spectrometric titrations show that this ligand forms 1 : 1 complexes with Ag + , Cu + , Cu 2+ , and Zn 2+ . Most importantly, detailed NMR‐spectroscopic analysis at different temperatures reveals that the complexation with Ag + strongly affects the dynamic isomerization of the bullvalene unit of the ligand such that only one predominant valence isomer is formed, even at 5 °C. Detailed 1 H‐NMR‐spectroscopic studies disclose an increased barrier (~11 kJ mol −1 ) of the Cope rearrangement. Furthermore, the addition of hexacyclene displaces the Ag + from the complex, so that the valence isomerization is accelerated and an equilibrium with two predominant isomers is formed. In turn, repeated addition of Ag + regains the complex with the restrained isomerization of the bullvalene unit. This method to control the valence isomerism by straightforward chemical stimuli may be used to simplify structural analysis at elevated temperatures, i. e. a feature not available so far with bullvalenes, and it may be employed as functional element in dynamic supramolecular assemblies.Source Type:Article1 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Spectroscopic Investigation of the Quadruplex DNA‐Binding Properties of 9‐Aryl‐Substituted Isoquinolinium DerivativesThe spectroscopic investigation of the binding properties of berberine‐type 9‐aryl‐substituted isoquinolinium derivatives with G‐quadruplex DNA (G4‐DNA) are presented. Photometric titrations show that these ligands bind with high affinity to the telomeric G4‐DNA form 22AG ( K =1.0–44×10 5 M −2 ). Furthermore, fluorimetric analysis of thermal DNA denaturation (FRET melting) reveals a significant thermal stabilization of G4‐DNA 22AG upon association with the methoxy‐substituted derivatives. As an analytically useful property, the derivatives with a phenyl substituent or with additional electron‐donating groups show a very weak fluorescence intensity, which increased significantly upon G4‐DNA complexation (fluorescence light‐up effect). Additional time‐resolved fluorescence spectroscopy indicated increased fluorescence lifetimes of the DNA‐bound 9‐(4‐methoxyphenyl)‐substituted derivative, when interacting with the quadruplex‐forming strand 22AG . Notably, the changes of the steady‐state and time‐resolved emission properties of the ligand are more pronounced with G4‐DNA than with duplex DNA so that the combination of these complementary methods may be used for the selective G4‐DNA detection.Source Type:Article2
