On the move: High intracrystalline mobilities and fast exchange between the crystal and the surrounding gas phase were found in NMR studies on the diffusion of methane, ethane, n‐hexane, and benzene in large crystals of the metal‐organic framework MOF‐5 (see SEM image). The results support future use of metal‐organic framework materials as tailorable sorbents for fast gas processing and gas‐storage materials in industry.

Supramolecular polyisobutylenes (PIB) bearing mono- and bifunctional chain ends with hydrogen-bonding units were prepared, and their association behavior in the melt state was investigated by dynamic rheology and compared to aggregation in solution, aiming at determining association dynamics in the solid state. A preparation combining living cationic polymerization with either azide/alkyne “click” reactions or nucleophilic substitution reactions enabled a full end group transformation to the final PIB polymers, modified with either thymine or 2,6-diaminotriazine end groups as proven by NMR and MALDI methods with molecular weights of ∼3500 and ∼10 000 g/mol. Stoichiometric mixtures of these polymers bearing specifically interacting thymine/triazine moieties were prepared by solution blending and the temperature-dependent dynamics investigated by rheological measurements. At temperatures of 20−60 °C all samples display strongly thermoreversible aggregation with sheet-type or partially cross-linked structures, which deaggregate at temperatures of ∼80 °C. More complex aggregates with bridged micellar structure were formed from the respective bifunctional PIB’s bearing thymine and 2,6-diaminotriazine moieties. Thus, in addition to specific linear aggregates, the formation of clusters and aggregates of different architecture has to be taken into account to understand and control structure and mechanical properties of supramolecular chains in the melt.

The effect of high concentration, also referred to as crowding conditions, on Brownian motion is of central relevance for the understanding of the physical, chemical and biological properties of proteins in their native environment. Specifically, the simple inverse relationship between the translational diffusion coefficient and the macroscopic solution viscosity as predicted by the generalized Stokes-Einstein (GSE) relation has been the subject of many studies, yet a consensus on its applicability has not been reached. Here, we use isotope-filtered pulsed-field gradient NMR to separately assess the μm-scale diffusivity of two proteins, BSA and an SH3 domain, in mixtures as well as single-protein solutions, and demonstrate that transient binding can account for an apparent violation of the GSE relation. Whereas GSE behavior applies for the single-protein solutions, it does not hold for the protein mixtures. Transient binding behavior in the concentrated mixtures is evidenced by calorimetric experiments and by a significantly increased apparent activation energy of diffusion. In contrast, the temperature dependence of the viscosity, as well as of the diffusivity in single-component solutions, is always dominated by the flow activation energy of pure water. As a practically relevant second result, we further show that, for high protein concentrations, the diffusion of small molecules such as dioxane or water is not generally a suitable probe for the viscosity experienced by the diffusing proteins.

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Slow protein folding processes during which kinetic folding intermediates occur for an extended time can lead to aggregation and dysfunction in living cells. Therefore, protein folding helpers have evolved, which prevent proteins from aggregation and/or speed up folding processes. In this study, we present the structural characterization of a long-living transient folding intermediate of RNase T1 (S54G/P55N) by time-resolved NMR spectroscopy. NMR resonances of this kinetic folding intermediate could be assigned mainly by a real-time 3D BEST-HNCA. These assignments were the basis to investigate the interaction sites between the protein folding helper enzyme SlyD(1-165) (SlyD*) from Escherichia coli (E. coli) and this kinetic intermediate at a residue resolution. Thus, we investigated the Michaelis-Menten complex of this enzyme reaction, because the NMR data acquisition was performed during the actual catalysis. The interaction surface of the transient folding intermediate is restricted to a region around the peptidyl-prolyl bond (Y38-P39), whose isomerization is catalyzed by SlyD*. The interaction surface regarding SlyD* extends from specific amino acids of the FKBP domain forming the peptidyl-prolyl cis/trans-isomerase active site to almost the entire IF domain. This illustrates an effective interplay between the two functional domains of SlyD* to facilitate protein folding catalysis.