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Investigation of Intrinsically Disordered Proteins through Exchange with Hyperpolarized Water

Angew. Chem. Int. Ed2017, 56, 389 –392

 

Hyperpolarized water can selectively enhance NMR signals of rapidly exchanging protons in osteopontin (OPN), a metastasis-associated intrinsically disordered protein (IDP), at near-physiological pH and temperature. The transfer of magnetization from hyperpolarized water is limited to solventexposed residues and therefore selectively enhances signals in 1H-15N correlation spectra. Binding to the polysaccharide heparin was found to induce the unfolding of preformed structural elements in OPN.

Dissolution dynamic nuclear polarization of deuterated molecules enhanced by cross-polarization

J. Chem. Phys., 2016, 145, 194203

 

We present novel means to hyperpolarize deuterium nuclei in 13CD2  groups at cryogenic temperatures. The method is based on cross-polarization from 1 H to 13 C and does not require any radio-frequency fields applied to the deuterium nuclei. After rapid dissolution, a new class of longlived spin states can be detected indirectly by 13C NMR in solution. These long-lived states result from a sextet-triplet imbalance (STI) that involves the two equivalent deuterons with spin I  = 1. An STI has similar properties as a triplet-singlet imbalance that can occur in systems with two equivalent I  = 1/2  spins. Although the lifetimes TSTI  are shorter than T1(Cz), they can exceed the life-time T1(Dz) of deuterium Zeeman magnetization by a factor of more than 20.

 

A Bis-Manganese(II)–DOTA Complex for Pulsed Dipolar Spectroscopy

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.

Recovering Invisible Signals by Two-Field Nuclear Magnetic Resonance Spectroscopy

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.

 

Bimodal X-ray and Infrared Imaging of an Organometallic Derivative of Praziquantel in Schistosoma mansoni

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.