Although the discussed 1D and 2D NMR spectra were in favour of the desired products, they were hardly sufficient for an unambiguous characterisation. As mentioned in Section 2, highly symmetric and big molecules (like the described rotaxane dendrimers and dendrons) are difficult to distinguish with NMR since the chemical environments of the signals are often similar and can overlap. 8 However in this case, ultimate proof was obtained from ESI-MS. Different charge state peaks of the formula [M − z PF 6] z+ ( z = 2, 3, 6, 13, depending on the molecule) were found for all dendrimers and dendrons confirming the correct synthetic products. D. Dai, X. Wang, Y. Liu, X. L. Yang, C. Glaubitz, V. Denysenkov, X. He, T. Prisner and J. Mao, Nat. Commun., 2021, 12, 6880 CrossRef CAS PubMed . When comparing the 1H-NMR spectra of resorcin[4]arene 1 with and without glutaric acid 2, different guest signals of 2 are found upfield-shifted. Additionally, integration yielded a host–guest stoichiometry of around 1 : 1, indicating six enclosed guest molecules. The extend of the encapsulation process was shown to increase with higher concentrations of glutaric acid and longer reaction times, which was readily observable due to the high sensitivity of the host aryl peak at 6.1 ppm. This supported the proposed encapsulation mechanism and additionally indicated a slowly occurring exchange mechanism at the expense of solvent molecules, in this case chloroform. C. Lhoste, B. Lorandel, C. Praud, A. Marchand, R. Mishra, A. Dey, A. Bernard, J.-N. Dumez and P. Giraudeau, Prog. Nucl. Magn. Reson. Spectrosc., 2022, 130–131, 1 CrossRef CAS PubMed .

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Diffusion-Ordered NMR Spectroscopy

Left) array of 1H PFGSTE spectra measured with linearly increasing field gradient, for a mixture containing TSP, choline and acetone in D 2O, and (right) the resultant DOSY spectrum, showing TSP signals in blue, choline in green and acetone in red. J. Kim, Y. Kim, Q. S. Luu, J. Kim, C. Qi, C. Hilty and Y. Lee, Chem. Commun., 2020, 56, 15000 RSC . G. Hornung, C. A. Schalley, M. Dieterle, D. Schroder and S. Derek, Chem. – Eur. J., 1997, 3, 1866–1883 CrossRef CAS. Homonuclear broadband decoupling methods can give excellent resolution for 1D 1H spectra. For this reason, they can help to distinguish peaks that overlap in an undecoupled 1D 1H spectrum. 17 The BIRD, ZS and PSYCHE broadband decoupling methods all come with a sensitivity penalty. For BIRD, since only 13C-bound protons contribute to the signal, the penalty is almost 100-fold. For the ZS methods, there exists a compromise between sensitivity losses and the minimum frequency difference between decoupled spins, and it results in a sensitivity loss of 10 to 50-fold. For PSYCHE, there is a trade-off between sensitivity and the size of decoupling artefacts, which is controlled through the flip angle of the frequency-swept pulses. A sensitivity loss of about a factor of 5 to 10-fold is typically reported.

Fig. 5 13C NMR spectra (quaternary region) of mature green tomato fruit pericarp extracts. (a) Conventional (non-hyperpolarised) spectrum of 20 mg extract (prepared from 20 mg lyophilized grounded tissue) dissolved in 700 μL D 2O, recorded with 1024 scans (11 h 45 min) at 700 MHz with a cryogenic probe. (b) Spectrum of an identical extract recorded with D-DNP combined with CP. The extract was first dissolved in a 200 μL mixture of H 2O/D 2O/glycerol-d 8 (2 : 3 : 5) doped with 25 mM TEMPOL, then polarized for 30 min at 1.2 K and 6.7 T, and finally dissolved with 5 mL of hot D 2O and transferred in about 10 seconds to a 500 MHz spectrometer equipped with a cryogenic probe. (c) Same as (b), but the tomato extract was replaced by a control sample prepared under strictly identical conditions without any biological material. The hyperpolarized spectra result from the sum of six consecutive acquisitions using 30° pulses spaced by 7.7 s. *Indicates the signal of a 13C-labeled pyruvate impurity from the D-DNP setting. Cit: citrate; GABA: γ-aminobutyrate; Gln: glutamine; Mal: malate. Reproduced from ref. 102 with permission from the Royal Society of Chemistry. G. Dal Poggetto, L. Castanar, M. Foroozandeh, P. Kiraly, R. W. Adams, G. A. Morris and M. Nilsson, Anal. Chem., 2018, 90, 13695 CrossRef CAS PubMed . N. V. Gramosa, N. Ricardo, R. W. Adams, G. A. Morris and M. Nilsson, Magn. Reson. Chem., 2016, 54, 815 CrossRef PubMed .

S. Katsikis, I. Marin-Montesinos, M. Pons, C. Ludwig and U. L. Günther, Appl. Magn. Reson., 2015, 46, 723 CrossRef CAS . A. Herrera, E. Fernandez-Valle, E. M. Gutierrez, R. Martinez-Alvarez, D. Molero, Z. D. Pardo and E. Saez, Org. Lett., 2010, 12, 144 CrossRef CAS PubMed . A. P. Deshmukh, D. Koppel, C. Chuang, D. M. Cadena, J. Cao and J. R. Caram, J. Phys. Chem. C, 2019, 123, 18702–18710 CrossRef CAS. In conclusion, Ustinov et al. present the first example of supramolecular polymers that are based on pairwise hydrophobic interactions between unprotected π-surfaces. With this study, the authors implemented the starting point for a new direction in the design process of hydrophobic polymers. Determining the polymeric structures of 18 and 19 in solution was achieved by a powerful combination of UV-vis and fluorescence spectroscopy, cryo-TEM, DLS, molecular modelling, EPR as well as SAXS. The discussed in-depth characterisation of both assemblies would hardly have been possible with fewer methods, again emphasising the relevance of multi-technique approaches for supramolecular structures. 9 Type III-B rotaxane dendrimers The word dendrimer, which is derived from the greek word dendron (engl.: tree), describes a class of hyperbranched molecules with repetitive units (similar to fractals). These molecules are known as established compounds and potential candidates for a wide range of applications, among others drug delivery, catalysis and chemical sensing. 88 Combining these compounds with rotaxanes leads to a new class of supramolecular molecules called rotaxane dendrimers, which can be divided into three different types (I, II and III) and subtypes (A, B and C). 89–91 A. Le Guennec, J. N. Dumez, P. Giraudeau and S. Caldarelli, Magn. Reson. Chem., 2015, 53, 913 CrossRef CAS PubMed .