Laboratoire P.A.S.T.E.U.R

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Remarkable Pressure Responses of Metal–Organic Frameworks: Proton Transfer and Linker Coiling in Zinc Alkyl Gates

Metal–organic frameworks demonstrate a wide variety of behavior in their response to pressure, which can be classified in a rather limited list of categories, including anomalous elastic behavior (e.g., negative linear compressibility, NLC), transitions between crystalline phases, and amorphization. Very few of these mechanisms involve bond rearrangement. Here, we report two novel piezo-mechanical responses of metal–organic frameworks, observed under moderate pressure in two materials of the zinc alkyl gate (ZAG) family. Both materials exhibit NLC at high pressure, due to a structural transition involving a reversible proton transfer between an included water molecule and the linker’s phosphonate group. In addition, the 6-carbon alkyl chain of ZAG-6 exhibits a coiling transition under pressure. These phenomena are revealed by combining high-pressure single-crystal X-ray crystallography and quantum mechanical calculations. They represent novel pressure responses for metal–organic frameworks, and pressure-induced proton transfer is a very rare phenomenon in materials in general.

 

 

Photoswitching kinetics and phase sensitive detection add discriminative dimensions for selective fluorescence imaging

Non-invasive separation-free protocols are attractive to analyze complex mixtures. To increase selectivity, we propose to perform analysis under kinetic control upon exploiting the photochemical reactivity of labeling contrast agents. Our simple protocol is applied in optical fluorescence microscopy, where autofluorescence, light scattering as well as spectral crowding presently bring limitations. We introduce OPIOM (Out-of-Phase Imaging after Optical Modulation), which exploits the rich kinetic signature of a photoswitching fluorescent probe to increase selectively and quantitatively its contrast. Filtering the specific contribution of the probe only requires phase-sensitive detection upon matching the photoswitching dynamics of the probe and the intensity and frequency of a modulated monochromatic light excitation. After in vitro validation, we applied OPIOM for selective imaging in mammalian cells and zebrafish, opening attractive perspectives for multiplexed observations in biological samples.

 

Real-Time Monitoring of Chromophore Isomerization and Deprotonation during the Photoactivation of the Fluorescent Protein Dronpa

 

Dronpa is a GFP-related photochromic fluorescent protein. It is known that the photochromic reaction involves cis/trans isomerization and protonation/deprotonation of the chromophore, but the sequence in time of the two steps and their characteristic timescales are much debated. We followed the entire photoactivation process of Dronpa in real time, by transient absorption spectroscopy from 100 fs to milliseconds.

 

Repair of the (6–4) Photoproduct by DNA Photolyase Requires Two Photons

It takes two (photons) to tango: Single-turnover flash experiments showed that the flavoenzyme (6–4) photolyase uses a successive two-photon mechanism to repair the UV-induced T(6–4)T lesion in DNA (see picture). The intermediate (X) formed by the first photoreaction is likely to be the oxetane-bridged dimer T(ox)T. The enzyme could stabilize the normally short-lived T(ox)T, allowing repair to be completed by the second photoreaction.

Ultraviolet-Induced Fluorescence of Polydopamine-Coated Emulsion Droplets

Polydopamine (PDA), a multifunctional biomaterial with strong adhesion and coating properties, exhibits melanin-like optoelectronic properties but is virtually devoid of intrinsic fluorescence. Herein we disclose the first PDA-based system that can develop fluorescence without chemical manipulation.