Prix et distinctions
Séminaire à venir
UPMC, salle 22-23-401
UFR de chimie, couloir 32-42, salle 101
ChemPhysChem 2016, 17, 2066 – 2078
High-spin gadolinium(III) and manganese(II) complexes have emerged as alternatives to standard nitroxide radical spin labels for measuring nanometric distances by using pulsed electron–electron double resonance (PELDOR or DEER) at high fields/frequencies. For certain complexes, particularly those with relatively small zero-field splitting (ZFS) and short distances between the two metal centers, the pseudosecular term of the dipolar coupling Hamiltonian is non-negligible. However, in general, the contribution from this term during conventional data analysis is masked by the flexibility of the molecule of interest and/or the long tethers connecting them to the spin labels. The efficient synthesis of a model system consisting of two [Mn(dota)]2- (MnDOTA; DOTA4-=1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate) directly connected to the ends of a central rodlike oligo(phenylene–ethynylene) (OPE) spacer is reported. The rigidity of the OPE is confirmed by Q-band PELDOR measurements on a bis-nitroxide analogue. The MnII-MnII distance distribution profile determined by W-band PELDOR is in reasonable agreement with one simulated by using a simple rotamer analysis. The small degree of flexibility arising from the linking MnDOTA arm appears to outweigh the contribution from the pseudosecular term at this interspin distance. This study illustrates the potential of MnDOTA-based spin labels for measuring fairly short nanometer distances, and also presents an interesting candidate for in-depth studies of pulsed dipolar spectroscopy methods on MnII-MnII systems.
Angew.Chem.Int. Ed., 2016, 55, 9886-9889
Nuclear Magnetic Resonance has benefited tremendously from the steady increase of magnetic fields. Spectacular improvements in both sensitivity and resolution have allowed the investigation of molecular systems of rising complexity. At very high fields, this progress may be jeopardized by line broadening due to chemical exchange or relaxation by chemical shift anisotropy. Here, we introduce a two-field NMR spectrometer designed for both excitation and observation of nuclear spins at two distinct magnetic fields in a single experiment. NMR spectra were obtained, with two dimensions acquired at vastly different magnetic fields. We show that signals of exchanging groups broadened beyond recognition at high field can be sharpened up to narrow peaks in a low-field dimension. Two-field NMR makes it possible to measure chemical shifts at optimal fields, allows the observation of molecular systems that suffer from internal dynamics, and opens new avenues for NMR at very high magnetic fields.
ChemBioChem 2016, 17, 1-5
An organometallic derivative of praziquantel was studied directly in worms by using inductively coupled plasma-mass spectrometry (ICP-MS) for quantification and synchrotronbased imaging. X-ray fluorescence (XRF) and IR absorption spectromicroscopy were used for the first time in combination to directly locate this organometallic drug candidate in schistosomes. The detection of both CO (IR) and Cr (XRF) signatures proved that the Cr(CO)3 core remained intact in the worms. Images showed a preferential accumulation at the worm’s tegument, consistent with a possible targeting of the calcium channel but not excluding other biological targets inside the worm.
Phys. Chem. Chem. Phys., 2016,18, 10144-10151
By monitoring the effect of deuterium decoupling on the decay of transverse 15N magnetization in D–15N spin pairs during multiple-refocusing echo sequences, we have determined fast D–D exchange rates kD and compared them with fast H–H exchange rates kH in tryptophan to determine the kinetic isotope effect as a function of pH and temperature.