We report the observation of undetected (until now) residues of the prion protein fragment HET-s(218-289) which give rise to well-resolved (13)C, (15)N, and (1)H NMR resonances under high-resolution magic-angle spinning (HRMAS) conditions. The observed signals belong to large polymeric units as shown by measuring the lateral diffusion constants. The amino acids identified in the spectra are compatible with their localization in the segments of the protein which could not be detected in earlier solid-state NMR experiments. The observed chemical shifts indicate that these residues are in a random-coil conformation. Complementary experiments which detect only dynamic or static residues, respectively, strongly suggest that they belong to different parts of the same molecule.

The DREAM scheme is an efficient adiabatic homonuclear polarization-transfer method suitable for multi-dimensional experiments in biomolecular solid-state NMR. The bandwidth and dynamics of the polarization transfer in the DREAM experiment depend on a number of experimental and spin-system parameters. In order to obtain optimal results, the dependence of the cross-peak intensity on these parameters needs to be understood and carefully controlled. We introduce a simplified model to semi-quantitatively describe the polarization-transfer patterns for the relevant spin systems. Numerical simulations for all natural amino acids (except tryptophane) show the dependence of the cross-peak intensities as a function of the radio-frequency-carrier position. This dependency can be used as a guide to select the desired conditions in protein spectroscopy. Practical guidelines are given on how to set up a DREAM experiment for optimized Cα/Cβ transfer, which is important in sequential assignment experiments.

Macrophomate synthase (MPS) catalyzes the reaction of oxaloacetate and 2-pyrones to give, over multiple steps, substituted benzoates. We detected a transient intermediate in the course of this transformation by monitoring the total time course either spectroscopically at 305 nm or by 1H NMR. This species was trapped by quenching the reaction with acetonitrile and cooling the sample to 270 K; its structure was determined to be an allylic cyclohexadienol by a complete 2D NMR spectroscopic analysis. It is formed according to Michaelis−Menten kinetics at a rate that is as fast or faster than the decarboxylation of oxaloacetate, the first step in the reaction sequence. Dehydration of this compound to give macrophomate, which limits the rate of the overall process, is not catalyzed by MPS. Although these results clarify the final stages of MPS catalysis, they shed no light on the early C−C bond-forming step(s). As a consequence, other methods will be needed to resolve the controversy as to whether this enzyme functions as a natural Diels−Alderase.

We report herein the synthesis of the N-methyl-NЈNЈЈ-diorganoiminodiacetic acid diamides MeN[CH 2 C(O)N(R)H] 2 [3: R = Me 2 N(CH 2 ) 2 ; 4: R = PhCH 2 ; 5: R = Me 3 CCH 2 ] and the novel tin(II) derivatives MeN[CH 2 C(O)N(R)] 2 Sn [6: R = Me 2 N(CH 2 ) 2 ; 7: R = PhCH 2 ; 8: R = Me 3 CCH 2 ]. The compounds were characterized by elemental analyses, 1 H NMR spectroscopy (3-5), solid-state 13 C and 119 Sn NMR spectroscopy (8), and single-crystal X-ray diffraction analysis (5,[a] 5836 8). Compound 8 shows intramolecular NǞSn and intermolecular OǞSn interactions with distances of 2.370(2) and 2.406(2) Å, respectively, the latter indicating that 8 is a coordination polymer. DFT calculations revealed covalent Sn-NC(O) and coordinative NǞSn and C=OǞSn bonds. The wB97Xd functional, which takes into account dispersive interactions, was employed for a correct theoretical description of, in particular, the latter bond. molecular coordination of a built-in donor function that fills the vacant p z orbital at the tin atom with electron density. [6][7][8][9] Sometimes this is achieved in combination with steric protection. In the case of tin(II) amides, this has been demonstrated for the intramolecularly coordinated compounds A, [10] B, [11] C, [12a] and D [12b] (Scheme 1). Scheme 1.