We
introduce two-dimensional NMR spectroscopy detected by recording and
processing the noise originating from nuclei that have not been subjected
to any radio frequency excitation. The method relies on cross-correlation
of two noise blocks that bracket the evolution and mixing periods.
While the sensitivity of the experiment is low in conventional NMR
setups, spin-noise-detected NMR spectroscopy has great potential for
use with extremely small numbers of spins, thereby opening a way to
nanoscale multidimensional NMR spectroscopy.
A training set of eleven X-ray structures determined for biomimetic complexes between cucurbit[n]uril (CB[7 or 8]) hosts and adamantane-/diamantane ammonium/aminium guests were studied with DFT-D3 quantum mechanical computational methods to afford ΔG binding energies. A novel feature of this work is that the fidelity of the BLYP-D3/def2-TZVPP choice of DFT functional was proven by comparison with more accurate methods. For the first time, the CB[n]⋅guest complex binding energy subcomponents [for example, ΔE , ΔE , ΔG , binding entropy (-TΔS), and induced fit E , E ] were calculated. Only a few weeks of computation time per complex were required by using this protocol. The deformation (stiffness) and solvation properties (with emphasis on cavity desolvation) of cucurbit[n]uril (n=5, 6, 7, 8) isolated host molecules were also explored by means of the DFT-D3 method. A high ρ =0.84 correlation coefficient between ΔG and ΔG was achieved without any scaling of the calculated terms (at 298 K). This linear dependence was utilized for ΔG predictions of new complexes. The nature of binding, including the role of high energy water molecules, was also studied. The utility of introduction of tethered [-(CH ) NH ] amino loops attached to N,N-dimethyl-adamantane-1-amine and N,N,N',N'-tetramethyl diamantane-4,9-diamine skeletons (both from an experimental and a theoretical perspective) is presented here as a promising tool for the achievement of new ultra-high binding guests to CB[7] hosts. Predictions of not yet measured equilibrium constants are presented herein.
PsbQ is one of the extrinsic proteins situated on the lumenal surface of photosystem II (PSII) in the higher plants and green algae. Its three-dimensional structure was determined by X-ray crystallography with exception of the residues 14-33. To obtain further details about its structure and potentially its dynamics, we approached the problem by NMR. In this paper we report (1)H, (15)N, and (13)C NMR assignments for the PsbQ protein. The very challenging oligo-proline stretches could be assigned using (13)C-detected NMR experiments that enabled the assignments of twelve out of the thirteen proline residues of PsbQ. The identification of PsbQ secondary structure elements on the basis of our NMR data was accomplished with the programs TALOS+, web server CS23D and CS-Rosetta. To obtain additional secondary structure information, three-bond H(N)-H(α) J-coupling constants and deviation of experimental (13)C(α) and (13)C(β) chemical shifts from random coil values were determined. The resulting "consensus" secondary structure of PsbQ compares very well with the resolved regions of the published X-ray crystallographic structure and gives a first estimate of the structure of the "missing link" (i.e. residues 14-33), which will serve as the basis for the further investigation of the structure, dynamics and interactions.
The importance of electrostatic and dispersion attractive interactions play a central role in promoting very high binding energies between cucurbit[n]uril (CB[n]) and diamondoid amine guest complexes, as shown by DFT‐BLYP‐D3/def2TZVPP calculations. This is illustrated by the “loop‐type” adamantane‐1‐NH2ethanoNH3 guest complexed with CB[7]. The spherical hydrocarbon skeleton provides auspicious space filling (dispersion) within the host cavity (depicted as a Connolly surface), and the two amino groups, separated by −CH2CH2−, each hydrogen bond to different uriedyl sites on the same portal face. More information can be found in the Full Paper by K. Mlinarić‐Majerski, L. Isaacs, R. Glaser, P. Hobza et al. on page 17226 ff.
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