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Dramatic Decrease in CEST Measurement Times Using Multi-Site Excitation

ChemPhysChem 2018, 19, 1707-1710

 

Chemical exchange saturation transfer (CEST) has recently evolved into a powerful approach for studying sparsely populated, “invisible” protein states in slow exchange with a major, visible conformer. Central to the technique is the use of a weak, highly selective radio‐frequency field that is applied at different frequency offsets in successive experiments, “searching” for minor state resonances. The recording of CEST profiles with enough points to ensure coverage of the entire spectrum at sufficient resolution can be time‐consuming, especially for applications that require high static magnetic fields or when small chemical shift differences between exchanging states must be quantified. Here, we show – with applications involving 15N CEST – that the process can be significantly accelerated by using a multi‐frequency irradiation scheme, leading in some applications to an order of magnitude savings in measurement time.

 

Sample Ripening through Nanophase Separation Influences the Performance of Dynamic Nuclear Polarization

Angew. Chem. Int. Ed. 2018, 57, 5171 –5175

 

Mixtures of water and glycerol provide popular matrices for low-temperature spectroscopy of vitrified samples. However, they involve counterintuitive physicochemical properties, such as spontaneous nanoscopic phase separations (NPS) in solutions that appear macroscopically homogeneous. We demonstrate that such phenomena can substantially influence the efficiency of dynamic nuclear polarization (DNP) by factors up to 20% by causing fluctuations in local concentrations of polarization agents (radicals). Thus, a spontaneous NPS of water/glycerol mixtures that takes place on time scales on the order of 30–60 min results in a confinement of polarization agents in nanoscopic water-rich vesicles, which in return affects the DNP. Such effects were found for three common polarization agents, TEMPOL, AMUPol and Trityl.

Graftable SCoMPIs enable the labeling and X-ray fluorescence imaging of proteins

Chem. Sci.2018, 9, 4483-4487

 

Bio-imaging techniques alternative to fluorescence microscopy are gaining increasing interest as complementary tools to visualize and analyze biological systems. Among them, X-ray fluorescence microspectroscopy provides information on the local content and distribution of heavy elements (Z > 14) in cells or biological samples. In this context, similar tools to those developed for fluorescence microscopy are desired, including chemical probes or tags. In this work, we study rhenium complexes as a convenient and sensitive probe for X-ray fluorescence microspectroscopy. We demonstrate their ability to label and sense exogenously incubated or endogenous proteins inside cells.

Labeling of hyaluronic acids with a Re-tricarbonyl tag and percutaneous penetration studied by multimodal imaging

Bioconjugate Chem., 2018

 

Hyaluronic acids were labeled with a Re-tricarbonyl used as Single Core Multimodal Probe for Imaging and their penetration into human skin biopsies was studied using IR microscopy and fluorescence imaging. The penetration was shown to be dependent on the molecular weight of the molecule and limited to the upper layer of the skin.

Membrane Crossing and Membranotropic Activity of Cell- Penetrating Peptides: Dangerous Liaisons?

Acc. Chem. Research2017

 

In this Account, we focus on cationic cell-penetrating peptides (CPPs) and the way they cross cell membranes. We summarize the history of this fi eld that emerged around 20 years ago. CPPs were indeed fi rst identifi ed as protein-transduction domains from the human immunodefi ciency virus (HIV) TAT protein and the Antennapedia homeoprotein, a transcription factor from Drosophila. We highlight our contribution to the elucidation of CPP internalization pathways, in particular translocation, which implies perturbation and reorganization of the lipid bilayer, and endocytosis depending on sulfated glycosaminoglycans. We show a particular role of Trp (indole side chain) and Arg (guanidinium side chain), which are essential amino acids for CPP internalization. Interactions with the cell-surface are not only Coulombic; H-bonds and hydrophobic interactions contribute also significantly to CPP entry. The capacity of CPPs to cross cell membrane is not related to their strength of membrane binding. Finally, we present optimized methods based on mass spectrometry and fluorescence spectroscopy that allow unequivocal quantification of CPPs inside cells or bound to the outer leafl et of the membrane, and discuss some limitations of the technique of flow cytometry that we have recently highlighted.