Photoaffinity labeling coupled to MS to identify peptide biological partners: Secondary reactions, for better or for worse?

Affinity photolabeling is a smart method to study noncovalent and transient interactions and provide a submolecular picture of the contacts between interacting partners. In this review, we will focus on the identification of peptide partners using photoaffinity labeling coupled to mass spectrometry in different contexts such as in vitro with a purified potential partner, in model systems such as model membranes, and with live cells using both targeted and nontargeted proteomics studies. Different biological partners will be described, among which glycoconjugates, oligonucleotides, peptides, proteins, and lipids, with the photoreactive label inserted either on the peptide of interest or on the potential partner. Particular attention will be paid to the observation and characterization of specific rearrangements following the photolabeling reaction, which can help characterize photoadducts and provide a better understanding of the interacting systems and environment.

Chemical Vapor Deposition of Azidoalkylsilane Monolayer Films

N₃-functionalized monolayers on silicon wafer substrates are prepared via the controlled vapor-phase deposition of 11-azidoundecyltrimethoxysilanes at reduced pressure and elevated temperature. The quality of the layer is assessed using contact angle, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and ellipsometry measurements. At 60 °C, longer deposition times are needed to achieve monolayers with similar N₃ density compared to depositions at 145 °C. The monolayers formed via the vapor phase are denser compared to those formed via a solvent-based deposition process. ATR-FTIR measurements confirm the incorporation of azido-alkyl chains in the monolayer and the formation of siloxane bridges with the underlying oxide at both deposition temperatures. X-ray photon spectroscopy shows that the N₃ group is oriented upward in the grafted layer. Finally, the density was determined using total reflection X-ray fluorescence after a click reaction with chlorohexyne and amounts to 2.5 × 10¹⁴ N₃ groups/cm². In summary, our results demonstrate the formation of a uniform and reproducible N₃-containing monolayer on silicon wafers, hereby providing a functional coating that enables click reactions at the substrate.

An unexpected route to aldehyde-decorated single-chain nanoparticles from azides

A new route towards the straightforward synthesis of aldehyde-decorated ultrafine single-chain nanoparticles from azides is described.

Chemical transformations supported by the [Re6(μ3-Se)8]2+ cluster core

This Perspective article discusses three interesting chemical transformations promoted by the octahedral [Re(6)(μ(3)-Se)(8)](2+) cluster core. These include (1) nucleophilic addition of alcohols to cluster-bound nitrile(s) to produce imino ester complexes; (2) synthesis of cluster-imine complexes with geometric specificity by reacting cluster nitrile solvates with organic azides; and (3) preparation and reactivity studies of carbonyl complexes of the cluster. We found that cluster-bound nitrile ligands were activated toward nucleophilic attack by methanol or ethanol, affording predominantly the Z-configured cluster-imino ester complexes, for which a mechanism evoking bifurcated hydrogen bonding interactions involving both the alcohol OH group and two nearest Se atoms of the cluster core was proposed. When reacted with organic azides, cluster-bound nitrile ligands were displaced and cluster-imine complexes were obtained, presumably through the formation of the corresponding cluster-azide complexes, followed by their photodecomposition. Lastly, cluster complexes featuring all-terminal carbonyl ligands were synthesized. Back-bonding interactions were verified, both experimentally and by computational studies. Their thermal and photo-stabilities were also evaluated, so was their reactivity toward methyl lithium for the eventual making of cluster-carbene catalysts. These findings, together with those by others, portend an exciting, new direction in the chemistry of solid-state type transition metal clusters.

Synthesis and biological evaluation of reversible inhibitors of IdeS, a bacterial cysteine protease and virulence determinant

Analogues of the irreversible protease inhibitors TPCK and TLCK have been synthesized and tested as inhibitors of the bacterial cysteine protease IdeS excreted by Streptococcuspyogenes. Eight compounds were identified as inhibitors of IdeS in an in vitro assay. The most potent compounds contained an aldehyde function, thus acting as efficient reversible inhibitors, nitrile and azide derivatives showed moderate activity.