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Magic-angle spinning dynamic nuclear polarization (MAS-DNP) has been proven to be a powerful technique to enhance the sensitivity of solid-state NMR (SSNMR) in a wide range of systems. Here, we show that DNP can be used to polarize lipids using a lipid-anchored polarizing agent. More specifically, we introduce a C16-functionalized biradical, which allows localization of the polarizing agents in the lipid bilayer and DNP experiments to be performed in the absence of excess cryo-protectant molecules (glycerol, dimethyl sulfoxide, etc.). This constitutes another original example of the matrix-free DNP approach that we recently introduced. [ABSTRACT FROM AUTHOR]

Wild-type bacteriophage T4 lysozyme contains a hydrophobic cavity with binding properties that have been extensively studied by X-ray crystallography and NMR. In the present study, the monitoring of ¹H chemical shift variations under xenon pressure enables the determination of the noble gas binding constant (K = 60.2 M1-). Although the interaction site is highly localized, dipolar cross-relaxation effects between laser-polarized xenon and nearby protons (SPINOE) are rather poor. This is explained by the high value of the xenon-proton dipolar correlation time (0.8 ns), much longer than the previously reported values for xenon in medium-size proteins. This indicates that xenon is highly localized within the protein cavity, as confirmed by the large chemical shift difference between free and bound xenon. The exploitation of the xenon line width variation vs xenon pressure and protein concentration allows the extraction of the exchange correlation time between free and bound xenon. Comparison to the exchange experienced by protein protons indicates that the exchange between the open and closed conformations of T4 lysozyme is not required for xenon binding. [ABSTRACT FROM AUTHOR]

The hydrophobic cavity of Lipid Transfer Protein 1 from Nicotiana tabacum is investigated in detail by NMR using xenon as a spy. The analysis of the 129Xe chemical shifts and self-relaxation times gives evidence of protein-xenon interaction. Thermodynamics of the binding is characterized through the study of aliphatic ¹H and 13C chemical shift variation as a function of xenon pressure. The binding constant is evaluated to 75.5 ± 1.0 M-1 at 293 K. The location of xenon inside the cavity is deduced from SPINOE experiments. The noble gas appears to occupy four sites, and xenon self-relaxation experiments indicate that it quickly jumps between different sites. The chemical shifts of amide protons and nitrogens also depend on the xenon concentration, either specifically or nonspecifically for atoms at the external surface of the protein. Yet, contrary to aliphatic atoms, they do not correspond to short-range interactions as confirmed by magnetization transfer experiments between laser-polarized xenon and protons in H2O. These 15N chemical shift variations, used in combination with 15N transverse self-retaxation rates to determine the lower limit of the binding rate, consequently reveal subtle changes in the structure of the protein upon binding. [ABSTRACT FROM AUTHOR]

Matrix ‐ Free DNP on Lipid Membranes Dynamic nuclear polarization (DNP) has been proven to be a powerful technique to enhance the sensitivity of solid ‐ state NMR. However, until now, there has been limited success in its application to synthetic membrane ‐ type systems. In their Communication on page 4512 ff., G. De Paëpe et al. present an innovative approach based on system ‐ driven radical design in order to insert the polarizing agent inside a lipid bilayer. Combined with matrix ‐ free DNP, this strategy solves additive ‐ induced problems by releasing the need for a DNP ‐ compatible solvent. [ABSTRACT FROM AUTHOR]

Cryptophanes bearing OCH2COOH groups in place of the methoxy groups represent a new class of xenon-carrier molecules soluble in water at biological pH. By using ¹H and 129Xe NMR (thermally- and laser-polarized dissolved gas), the structural and dynamical behaviors of these host molecules as well as their interaction with xenon are studied. They are shown to exist in aqueous solution under different conformations in very slow exchange. A saddle form present for one of these conformations could explain the ¹H NMR spectra. Whereas the cryptophanes in such a conformation are unable to complex xenon, unprecedented high binding constants are found for cryptophanes in the other canonical crown-crown conformation. These host molecules could therefore be valuable candidates for biosensing using 129Xe MRI. [ABSTRACT FROM AUTHOR]

The heterodinuclear complexes [FeIII,MnII,(L-Bn)(μ-OAc)2](ClO4)2 (1) and [FeIIMnII(L-Bn)(μ<-OAc)2](ClO4) (2) with the unsymmetrical dinucleating ligand HL-Bn {[2-bis[(2-pyridylmethyl)aminomethyl]]-6-[benzyl-2-(pyridylmethyl)-aminomethyl]-4-methylphenol} were synthesized and character-ized as biologically relevant models of the new Fe/Mn class of nonheme enzymes. Crystallographic studies have been completed on compound 1 and reveal an FeIIIMnIIμ-phenoxobis(μ-carbox- ylato) core. A single location of the FeIII ion in 1 and of the FeII ion in 2 was demonstrated by Mossbauer and ¹H NMR spectroscopies, respectively. An investigation of the temperature dependence of the magnetic susceptibility of 1 revealed a moderate antiferromagnetic interaction (J = 20 cm-1) between the high-spin FeIII and MnII ions in 1, which was confirmed by Mossbauer and electron paramagnetic resonance (EPR) studies. The electrochemical properties of complex 1 are described. A quasireversible electron transfer at --40 mV versus Ag/AgCl corresponding to the FeIIIMnII/FeIIMnII couple appears in the cyclic voltammogram. Thorough investigations of the Mossbauer and EPR signatures of complex 2 were performed. The analysis allowed evidencing of a weak antiferromagnetic interaction (J = 5.72 cm-1) within the FeuMn" pair consistent with that deduced from magnetic susceptibility measurements (j = 6.8 cm-1). Owing to the similar value of the Fe11 zero-field splitting (DFe = 3.55 cm-1), the usual treatment within the strong exchange limit was precluded and a full analysis of the electronic structure of the ground state of complex 2 was developed. This situation is reminiscent of that found in many diiron and iron--manganese enzyme active sites. [ABSTRACT FROM AUTHOR]