A Benzophenone-Based Photocaging Strategy for the N7 Position of Guanosine.

Selective modification of nucleobases with photolabile caging groups enables the study and control of processes and interactions of nucleic acids. Numerous positions on nucleobases have been targeted, but all involve formal substitution of a hydrogen atom with a photocaging group. Nature, however, also uses ring-nitrogen methylation, such as m7 G and m1 A, to change the electronic structure and properties of RNA and control biomolecular interactions essential for translation and turnover. We report that aryl ketones such as benzophenone and α-hydroxyalkyl ketone are photolabile caging groups if installed at the N7 position of guanosine or the N1 position of adenosine. Common photocaging groups derived from the ortho-nitrobenzyl moiety were not suitable. Both chemical and enzymatic methods for site-specific modification of N7G in nucleosides, dinucleotides, and RNA were developed, thereby opening the door to studying the molecular interactions of m7 G and m1 A with spatiotemporal control.

New AdoMet Analogues as Tools for Enzymatic Transfer of Photo-Cross-Linkers and Capturing RNA-Protein Interactions.

Elucidation of biomolecular interactions is of utmost importance in biochemistry. Photo-cross-linking offers the possibility to precisely determine RNA-protein interactions. However, despite the inherent specificity of enzymes, approaches for site-specific introduction of photo-cross-linking moieties into nucleic acids are scarce. Methyltransferases in combination with synthetic analogues of their natural cosubstrate S-adenosyl-l-methionine (AdoMet) allow for the post-synthetic site-specific modification of biomolecules. We report on three novel AdoMet analogues bearing the most widespread photo-cross-linking moieties (aryl azide, diazirine, and benzophenone). We show that these photo-cross-linkers can be enzymatically transferred to the methyltransferase target, that is, the mRNA cap, with high efficiency. Photo-cross-linking of the resulting modified mRNAs with the cap interacting protein eIF4E was successful with aryl azide and diazirine but not benzophenone, reflecting the affinity of the modified 5' caps.

Facile Light-Mediated Preparation of Small Polymer-Coated Palladium-Nanoparticles and Their Application as Catalysts for Alkyne Semi-Hydrogenation.

A facile light-mediated preparation of small palladium nanoparticles (PdNPs) with a diameter of 1.3 nm and low dispersity by using low-priced and readily prepared photoactive polymers is presented. These polymers act as reagents for the photochemical reduction of Pd ions and they are also stabilizers for the PdNPs generated in situ. The PdNP-polymer hybrid materials prepared by this reliable approach are efficient hydrogenation catalysts that show high activity and Z-selectivity in the semi-hydrogenation of alkynes. These PdNP-catalyst hybrid materials can be readily recycled and reused up to five times.

Controlled Light-Mediated Preparation of Gold Nanoparticles by a Norrish Type†I Reaction of Photoactive Polymers.

Gold nanoparticles (AuNPs) are subjects of broad interest in scientific community due to their promising physicochemical properties. Herein we report the facile and controlled light-mediated preparation of gold nanoparticles through a Norrish type I reaction of photoactive polymers. These carefully designed polymers act as reagents for the photochemical reduction of gold ions, as well as stabilizers for the in situ generated AuNPs. Manipulating the length and composition of the photoactive polymers allows for control of AuNP size. Nanoparticle diameter can be controlled from 1.5 nm to 9.6 nm.

Photochemical preparation of gold nanoparticle decorated cyclodextrin vesicles with tailored plasmonic properties.

We report a photochemical strategy for the preparation of plasmonic vesicles by the in situ formation of gold nanoparticles at the surface of cyclodextrin host vesicle templates decorated with photoactive guest polymers. Upon irradiation with UV light, these carefully designed polymer shells undergo a Norrish type I reaction to generate reducing radicals for the in situ reduction of gold salts and simultaneously provide a stabilizing matrix allowing for a dense decoration with discrete gold seeds. In a highly controlled growth procedure the gold particle size can be adjusted between 3 and 28 nm resulting in an increasing interparticle plasmonic coupling as revealed by a pronounced redshift of the surface plasmon resonance (SPR) band and an enhanced absorption at wavelengths above 600 nm. This unique combination of cyclodextrin vesicles capable of specifically recognizing guest molecules with a plasmonic particle shell displaying multiple interparticle gaps acting as electromagnetic hotspots shows great potential for surface-enhanced Raman scattering (SERS) applications.

Visible-Light-Enabled Preparation of Palladium Nanoparticles and Application as Catalysts for Suzuki-Miyaura Coupling.

Silyl ketones were used for the preparation of palladium nanoparticles (PdNPs) starting with Pd(OAc)2 in dimethylformamide under irradiation with a visible light-emitting diode (LED). Variation of the silyl ketone structure allowed adjustment of the PdNP diameter (1.9 or 5.2 nm). The in situ-formed PdNPs were further stabilized with polyvinylpyrrolidone and then applied as recyclable catalysts in the Suzuki-Miyaura coupling of arylboronic acids with aryl iodides to obtain substituted biphenyls in excellent yields.

Light Mediated Preparation of Palladium Nanoparticles as Catalysts for Alkyne cis-Semihydrogenation.

A bisacylphosphine oxide photoinitiator was used for the light mediated preparation of palladium nanoparticles (PdNPs) with a small diameter of 2.8 nm. All starting materials are commercially available, and PdNP synthesis is experimentally very easy to conduct. The PdNP-hybrid material was applied as catalyst for the semihydrogenation of various internal alkynes to provide the corresponding alkenes in excellent yields (up to 99%) and Z-selectivities (Z/E ratios up to 99/1).