The three‐dimensional structure of the holo form of recombinant cellular bovine heart fatty‐acid‐binding protein (H‐FABPc), a polypeptide of 133 amino acid residues with a molecular mass of 15 kDa, has been determined by multidimensional homonuclear and heteronuclear NMR spectroscopy applied to uniformly 15N‐labeled and unlabeled protein. A nearly complete set of 1H and 15N chemical shift assignments was obtained. A total of 2329 intramolecular distance constraints and 42 side‐chain χi dihedral‐angle constraints were derived from cross‐relaxation and J coupling information. 3D nuclear Overhauser enhancement and exchange spectroscopy combined with heteronuclear multiple‐quantum coherence (NOESY‐HMQC) experiments, performed on a sample of uniformly 13C‐labeled palmitic acid bound to unlabeled cellular heart fatty‐acid‐binding protein revealed 10 intermolecular contacts that determine the orientation of the bound fatty acid. An ensemble of protein conformations was calculated with the distance‐geometry algorithm for NMR applications (DIANA) using the redundant dihedral‐angle constraint (REDAC) strategy. After docking the fatty acid into the protein, the protein‐ligand arrangement was subject to distance‐restrained energy minimization. The overall conformation of the protein is a β‐barrel consisting of 10 antiparallel β‐strands which form two nearly orthogonal β‐sheets of five strands each. Two short helices form a helix‐turn‐helix motif in the N‐terminal region of the polypeptide chain. The palmitic acid is bound within the protein in a U‐shaped conformation close to the two helices. The obtained solution structure of the protein is consistent with a number of fatty‐acid‐binding‐protein crystal structures.

The NMR relaxation times T'2, T2, and T1 were measured in isolated rat lungs as functions of external magnetic field B0, temperature, and lung inflation. The observed linear dependence on B0 of the tissue-induced free induction decay rate (T'2)-1 provides independent confirmation of the air/water interface model of the lung. Furthermore, measurements of the Larmor frequency dependence of T1 are consistent with a spin-lattice relaxation rate of the form 1/T1 = A omega -1/2 + B as expected for the case in which the relaxation arises from water-biopolymer cross-relaxation, which should be proportional to the surface area of the lung. This prediction was verified by observations of an approximately linear dependence of 1/T1 on transpulmonary pressure and thus on the lung surface area.

We present a generalized nuclear spin bath model for embedded electron spin decoherence in organic solids at low temperatures, which takes the crucial influence from hindered methyl group rotation tunneling into account. This new, quantum many body model, after resolved using the cluster correlation expansion method, predicts the decoherence profiles directly from the proton relative position and methyl group tunneling splitting inputs. Decoherence profiles from this model explain adequately the influence from both strongly and weakly hindered methyl groups to embedded electron spin decoherence: The former accelerates decoherence by increasing the nearest neighbor nuclear spin coupling, while the latter enhances coherence through a novel confinement like’ mechanism, in which the very strong nuclear spin coupling from the tunneling splitting term suppresses those protons on the methyl rotors from participating in the bath dynamics. Both types of influences are successfully proven experimentally in representative organic polycrystalline matrices: methyl malonic acid for strongly hindered and acetamide for weakly hindered methyl groups, respectively.

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