A photolabile protection strategy for terminal alkynes

We present a strategy for photolabile protection of terminal alkynes. Several photo-caged alcohols were synthesized via mild copper(II)-catalyzed substitution between tertiary propargylic alcohols and 2-nitrobenzyl alcohol to build up robust, base stable o-nitrobenzyl (NB) photo-cleavable compounds. We compare the new photolabile protecting group with the commonly used alkyne protecting group, 2-methyl-3-butyn-2-ol and the results show that NB ethers are stable under the cleaving conditions for the cleavage of methylbutynol protected alkynes. Additionally, we present the synthesis of photo-cleavable NB derivatives containing thiol groups that can serve as agents for photoinduced surface functionalization reactions.     

In Vitro and In Vivo Enzyme‐Mediated Biomineralization of Oligo(poly(ethylene glycol) Fumarate Hydrogels

The enzyme alkaline phosphatase (ALP) is added at different concentrations (i.e., 0, 2.5, and 10 mg · ml^?1) to oligo(poly(ethylene glycol)fumarate) (OPF) hydrogels. The scaffolds are either incubated in 10 mM calcium glycerophosphate (Ca–GP) solution for 2 weeks or implanted in a rat subcutaneous model for 4 weeks. Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and alizarin red staining show a strong ability to form minerals exclusively in ALP‐containing hydrogels in vitro. Additionally, the calcium content increases with increasing ALP concentration. Similarly, only ALP‐containing hydrogels induce mineralization in vivo. Specifically, small (≈5–20 µm) mineral deposits are observed at the periphery of the hydrogels near the dermis/scaffold interface using Von Kossa and alizarin red staining.

     

Anisotropy enhanced X‐ray scattering from solvated transition metal complexes

Time‐resolved X‐ray scattering patterns from photoexcited molecules in solution are in many cases anisotropic at the ultrafast time scales accessible at X‐ray free‐electron lasers (XFELs). This anisotropy arises from the interaction of a linearly polarized UV–Vis pump laser pulse with the sample, which induces anisotropic structural changes that can be captured by femtosecond X‐ray pulses. In this work, a method for quantitative analysis of the anisotropic scattering signal arising from an ensemble of molecules is described, and it is demonstrated how its use can enhance the structural sensitivity of the time‐resolved X‐ray scattering experiment. This method is applied on time‐resolved X‐ray scattering patterns measured upon photoexcitation of a solvated di‐platinum complex at an XFEL, and the key parameters involved are explored. It is shown that a combined analysis of the anisotropic and isotropic difference scattering signals in this experiment allows a more precise determination of the main photoinduced structural change in the solute, i.e. the change in Pt—Pt bond length, and yields more information on the excitation channels than the analysis of the isotropic scattering only. Finally, it is discussed how the anisotropic transient response of the solvent can enable the determination of key experimental parameters such as the instrument response function.     

Dihydroazulene-Boron Subphthalocyanine Conjugates with Oligo(phenyleneethynylene) Bridging Unit: Photoswitchable Fluorophores

In this work, we have linked the dihydroazulene (DHA)/vinylheptafulvene (VHF) photo-/thermoswitch and the boron subphthalocyanine (BsubPc) fluorophore via an axial oligo(phenyleneethynylene) bridging unit into new DHA-BsubPc conjugates. The objectives were to elucidate the influence of BsubPc on the DHA/VHF switching reactions and the influence of DHA/VHF on the BsubPc fluorescence in these conjugates for which the entire axial substituent connected to boron comprises one large, conjugated scaffold. We present the synthesis and properties of DHA-BsubPc conjugates with varying peripheral substituents on the BsubPc core, being either unsubstituted (H₁₂BsubPc) or partially fluorinated (F₆BsubPc). Fluorination of the BsubPc core provided a remarkable increase in the reversibility of the DHA-VHF interconversions promoted by light and heat, respectively, and accompanied by on/off switching of the BsubPc fluorescence. Synthetically, the units were connected using Sonogashira coupling reactions of suitable acetylenic building blocks.