‘Clickable’ cyclopentadienyl iron carbonyl complexes for bioorthogonal conjugation of mid‐infrared labels to a model protein and PAMAM dendrimer

Owing to the intrinsic limitations of the conventional bioconjugation methods involving native nucleophilic functions of proteins, we sought to develop alternative approaches to introduce metallocarbonyl infrared labels onto proteins on the basis of the [3 + 2] dipolar azide‐alkyne cycloaddition (AAC). To this end, two cyclopentadienyl iron dicarbonyl (Fp) complexes carrying a terminal or a strained alkyne handle were synthesized. Their reactivity was examined towards a model protein and poly (amidoamine) (PAMAM) dendrimer, both carrying azido groups. While the copper (I)‐catalysed azide‐alkyne cycloaddition (CuAAC) proceeded smoothly with the terminal alkyne metallocarbonyl derivative, labelling by strain‐promoted azide‐alkyne cycloaddition (SPAAC) was less successful in terms of final coupling ratios. Infrared spectral characterization of the bioconjugates showed the presence of two bands in the 2000 cm^?1 region, owing to the stretching vibration modes of the carbonyl ligands of the Fp entities.     

The First Photochemical In Situ Production of Ti‐Based Nanoparticles: A SH2 Strategy Using Bis(cyclopentadienyl)titanium Dichloride (Cp2TiCl2)

Bis(cyclopentadienyl)titanium dichloride (Cp₂TiCl₂) is a high performance additive under UV light activation for both i) radical photopolymerization reactions (when added to a Type I photo­initiator such as 2,2‐dimethoxy‐2‐phenylacetophenone, the oxygen inhibition is reduced) and ii) a concomitant in situ photoinduced and oxygen mediated formation of Ti‐based nanoparticles (diameters ranging from 45 to 220 nm). The photochemical properties of Cp₂TiCl₂ are investigated by steady state photolysis and electron spin resonance, and its photoinitiation ability checked. The nanoparticles (NPs) are well characterized by transmission electron microscopy. The high reactivity of Cp₂TiCl₂ under air is ascribed to a bimolecular homolytic substitution (the S_H2 process is clearly demonstrated by density functional theory calculations and ESR experiments), which converts the peroxyls into new efficient initiating radicals. The photochemical in situ incorporation of Ti NPs has never previously been reported. The synthesis of metal nanoparticles by a S_H2 approach instead of the reduction of a metal salt appears to be a promising original method.