Extension of the π-system of monoaryl-substituted norbornadienes with acetylene bridges: influence on the photochemical conversion and storage of light energy.

The 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.

Studies About the Effect of Halogenated Solvents on the Fluorescence Properties of 9-Aryl-Substituted Isoquinolinium Derivatives - A Case Study.

It was demonstrated that 9-aryl-substituted isoquinolinium derivatives have significantly increased fluorescence quantum yields in halogenated solvents, mostly pronounced in chloroalkanes, which appears to be specific for this type of solvents. Further analysis with selected halogenated solvents revealed that the type and number of halogen substituents and the dielectric constant of the solvent have a distinct impact on the emission quantum yield. The solvent effect is explained by a solvation of the charge shift (CS) state by attractive halogen-π interactions (halogen bond), which impedes the torsional relaxation of the excited state.

Reversible Restrain and Release of the Dynamic Valence Isomerization in a Shape-shifting Bullvalene by Complex Formation.

In 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, and Zn. 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.

Bis- and Tris-norbornadienes with High Energy Densities for Efficient Molecular Solar Thermal Energy Storage.

Molecular solar thermal energy storage (MOST) systems can convert, store and release solar energy in chemical bonds, i.e., as chemical energy.

Switching between DNA binding modes with a photo- and redox-active DNA-targeting ligand.

A disulfide-functionalized bis-benzo[]quinolizinium is presented that is transformed quantitatively into its cyclomers in a fast intramolecular [4 + 4] photocycloaddition. Both the bis-quinolizinium and the photocyclomers react with glutathione (GSH) or dithiothreitol (DTT) to give 9-(sulfanylmethyl)benzo[]quinolizinium as the only product. As all components of this reaction sequence have different DNA-binding properties, it enables the external control and switching of DNA association.

Pushing Photochemistry into Water: Acceleration of the Di-π-Methane Rearrangement and the Paternó-Büchi Reaction "On-Water".

Two representative organic photoreactions, namely a bimolecular photocycloaddition and a monomolecular photorearrangement, are presented that are accelerated when the reaction is performed "on-water", that is, at the water-substrate interface with no solvation of the reaction components. According to the established models of ground-state reactions "on-water", the enhanced efficiency of the photoreactions is explained by hydrophobic effects (Paternó-Büchi reaction) or specific hydrogen bonding (di-π-methane rearrangement) at the water-substrate interface that decrease the energy of the respective transition state. These results point to the potential of this approach to conduct photoreactions more efficiently in an ecologically favorable medium.

The Stereoselective Total Synthesis of Axially Chiral Naphthylisoquinoline Alkaloids.

The naphthylisoquinoline (NIQ) alkaloids are a thrilling class of natural biaryls─structurally, biosynthetically, and pharmacologically. A common feature of these metabolites is the biaryl bond between their naphthalene and isoquinoline moieties, which in most cases is rotationally hindered, leading to the phenomenon of axial chirality. Depending on their individual structures, including the respective axial configurations, NIQs show promising bioactivities.

Berberrubine Phosphate: A Selective Fluorescent Probe for Quadruplex DNA.

A phosphate-substituted, zwitterionic berberine derivative was synthesized and its binding properties with duplex DNA and G4-DNA were studied using photometric, fluorimetric and polarimetric titrations and thermal DNA denaturation experiments. The ligand binds with high affinity toward both DNA forms ( = 2-7 × 10 M) and induces a slight stabilization of G4-DNA toward thermally induced unfolding, mostly pronounced for the telomeric quadruplex . The ligand likely binds by aggregation and intercalation with ct DNA and by terminal stacking with G4-DNA.

Selective, pH-Dependent Colorimetric and Fluorimetric Detection of Quadruplex DNA with 4-Dimethylamino(phenyl)-Substituted Berberine Derivatives.

The 9- and 12-dimethylaminophenyl-substituted berberine derivatives 3 a and 3 b were readily synthesized by Suzuki-Miyaura reactions and shown to be useful fluorescent probes for the optical detection of quadruplex DNA (G4-DNA). Their association with the nucleic acids was investigated by spectrometric titrations, CD and LD spectroscopy, and with DNA-melting analysis. Both ligands bind to duplex DNA by intercalation and to G4-DNA by terminal π stacking.

Synthesis, DNA-binding and antiproliferative properties of diarylquinolizinium derivatives.

A series of ten 2,7- and 2,8-diarylquinolizinium derivatives was synthesized and their DNA-binding and cytotoxic properties were investigated. Except for one nitro-substituted derivative all tested diarylquinolizinium ions bind to DNA with sufficient affinity (2 × 10 M-2 × 10 M). It was shown with photometric, fluorimetric and polarimetric titrations as well as with flow-LD analysis that the ligands bind mainly by intercalation to duplex DNA, however, depending on the ligand-DNA ratio, groove binding and backbone association were also observed with some derivatives.

Fluorimetric Detection of Zn, Mg, and Fe with 3-Hydroxy-4-Pyridylisoquinoline as Fluorescent Probe.

The suitability of 3-hydroxy-4-pyridylisoquinoline to operate as fluorescent chemosensor for the detection of metal ions was investigated. For that purpose, the interactions of the title compound with selected metal ions were investigated by absorption and emission spectroscopy. The complexation of Zn, Fe, Mg with 1:1 and 2:1 stoichiometry leads to characteristic optical responses that depend significantly on the employed solvents, thus allowing for the fluorimetric identification and detection of particular metal cations in a matrix-based pattern analysis or by fluorimetric titrations.

Synthesis and investigation of quadruplex-DNA-binding, 9--substituted berberine derivatives.

A small series of five novel berberine derivatives was synthesized by the Cu-catalyzed click reaction of 9-propargyladenine with 9--(azidoalkyl)berberine derivatives. The association of the resulting berberine-adenine conjugates with representative quadruplex-forming oligonucleotides dA(GTTA)G and d(ACAGTGTG) was examined with photometric and fluorimetric titrations, thermal DNA denaturation analysis, and CD spectroscopy. The results from the spectrometric titrations indicated the formation of 2:1 or 1:1 complexes (ligand:G4-DNA) with log values of 10-11 (2:1) and 5-6 (1:1), which are typical for berberine derivatives.

Cation-induced ring-opening and oxidation reaction of photoreluctant spirooxazine-quinolizinium conjugates.

Two new spiroindolinonaphthoxazine derivatives with an electron-accepting styrylquinolizinium or styrylcoralyne unit, respectively, were synthesized, and the influence of such an arylvinyl substituent on the chemical and photochemical properties of the compounds was investigated. Specifically, these spirooxazines turned out to be resistant towards the photoinduced merocyanine formation, and the irradiation with light mainly led to photodegradation of the substrates. However, it was shown by colorimetric and fluorimetric screening assays as well as by detailed NMR spectroscopic and mass spectrometric studies that the addition of particular metal ions (Cu, Fe, and to a certain extent Hg) initially induced a ring-opening reaction that was irreversibly followed by a fast ring closure-deprotonation-oxidation sequence to give styryl-substituted naphthoxazole derivatives as the products quantitatively.

Reversible photoswitching of the DNA-binding properties of styrylquinolizinium derivatives through photochromic [2 + 2] cycloaddition and cycloreversion.

It was demonstrated that styrylquinolizinium derivatives may be applied as photoswitchable DNA ligands. At lower ligand:DNA ratios (≤1.5), these compounds bind to duplex DNA by intercalation, with binding constants ranging from = 4.