Dynamics of a Globular Protein Adsorbed to Liposomal Nanoparticles

A solution-state NMR method is proposed to investigate the dynamics of proteins that undergo reversible association with nanoparticles (NPs). We applied the recently developed dark-state exchange saturation transfer experiment to obtain residue-level dynamic information on a NP-adsorbed protein in the form of transverse spin relaxation rates, <i>R</i>₂^bound. Based on dynamic light scattering, fluorescence, circular dichroism, and NMR spectroscopy data, we show that the test protein, human liver fatty acid binding protein, interacts reversibly and peripherally with liposomal NPs without experiencing significant structural changes. The significant but modest saturation transfer from the bound state observed at 14.1 and 23.5 T static magnetic fields, and the small determined <i>R</i>₂^bound values were consistent with a largely unrestricted global motion at the lipid surface. Amino acid residues displaying faster spin relaxation mapped to a region that could represent the epitope of interaction with an extended phospholipid chain constituting the protein anchor. These results prove that atomic-resolution protein dynamics is accessible even after association with NPs, supporting the use of saturation transfer methods as powerful tools in bionanoscience

Soft Photopolymerizations Initiated by Dye-Sensitized Formation of NHC-Boryl Radicals under Visible Light

A procedure for the production of N-heterocyclic carbene–boryl radicals (NHC-BH₂^•) upon visible light irradiation under soft conditions is presented. New acridine orange (dye)/diphenyl disulfide/NHC–BH₃ and dye/sulfonium salt/NHC–BH₃ three-component initiating systems are introduced for the efficient visible light photopolymerization of trimethylolpropane triacrylate. The new systems could be extendend to polymerization reactions in water (hydroxyethyl acrylate and hydroxyethyl methyl acrylate), which proceeded with strongly improved polydispersity. The chemical mechanisms are investigated through EPR and photolysis experiments

Solid-Phase Polarization Matrixes for Dynamic Nuclear Polarization from Homogeneously Distributed Radicals in Mesostructured Hybrid Silica Materials

Mesoporous hybrid silica–organic materials containing homogeneously distributed stable mono- or dinitroxide radicals covalently bound to the silica surface were developed as polarization matrixes for solid-state dynamic nuclear polarization (DNP) NMR experiments. For TEMPO-containing materials impregnated with water or 1,1,2,2-tetrachloroethane, enhancement factors of up to 36 were obtained at ∼100 K and 9.4 T without the need for a glass-forming additive. We show that the homogeneous radical distribution and the subtle balance between the concentration of radical in the material and the fraction of radicals at a sufficient inter-radical distance to promote the cross-effect are the main determinants for the DNP enhancements we obtain. The material, as well as an analogue containing the poorly soluble biradical bTUrea, is used as a polarizing matrix for DNP NMR experiments of solutions containing alanine and pyruvic acid. The analyte is separated from the polarization matrix by simple filtration