Resonance and structural assignment in (car)borane clusters using <sup>11</sup>B residual quadrupolar couplings

Rüttger, Franziska; Stalke, Dietmar; John, Michael

doi:10.1039/d3cc05054h

Cited by 4 publications

(3 citation statements)

References 39 publications

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“…Nuclear magnetic resonance (NMR) plays a pivotal role in elucidating molecular structures. In this regard, anisotropic NMR parameters such as residual dipolar couplings (RDCs), − residual chemical shift anisotropies (RCSAs), , and residual quadrupolar couplings (RQCs), − contain significant information about molecular configuration and dominant conformation, which effectively accelerate the progress of NMR technique. In general, RDCs report on three-dimensional structures from the relative orientation of interatomic vectors, such as the common C–H and N–H bonds.…”

Section: Introductionmentioning

confidence: 99%

Weak Alignment Liquid Crystal Media from Colloidal Dispersion and Self-assembled Oligopeptide for Anisotropic NMR

Qin,

Zhao,

et al. 2024

Acc. Mater. Res.

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Metrics & MoreArticle Recommendations * sı Supporting Information CONSPECTUS: Acquiring anisotropic NMR parameters such as residual dipolar couplings (RDCs) and residual chemical shift anisotropies (RCSAs) has been demonstrated as a powerful route to elucidate the three-dimensional structure of organic molecules in organic and medicinal chemistry. However, this methodology is somewhat compromised by the limited availability of alignment media, which are indispensable to induce the partial orientation of analytes for anisotropic data acquisition. Given the feature of inherent anisotropy, lyotropic liquid crystals (LLCs) have been documented as excellent candidates to act as alignment media. This Account aims to review the research progress of developing LLCs to obtain anisotropic NMR data. We mainly focus on two complementary LC media, i.e., two-dimensional (2D) colloidal dispersions and self-assembled peptides, that are generated by a "top-down" approach and "bottom-up" approach, respectively. Our laboratory has been at the forefront of developing 2D colloidal dispersions as alignment media. We first demonstrated the applicability of graphene oxide (GO) LLCs in the RDC-based structural elucidation of small molecules. When used as alignment media, GO LLCs showed a striking feature of no background signals. Clean NMR spectra enable accurate data assignment without disturbances and even effective RDC measurements of rare natural products. To circumvent the limitation that preparing GO LLC media needs tedious solvent exchange to remove nondeuterated solvents for NMR experiments, we subsequently developed MXene LLCs. Different from GO media whose anisotropy would be destroyed after direct freeze-drying, MXene can self-align in the redispersed solution to recover LC behavior. This feature provides great convenience for sample preservation and rapid medium preparation. Another advantage of MXene LLCs over GO media is the applicability to directly measure RDCs of aromatic solutes with no need for chemical modification on MXenes.To complement the 2D colloidal media that are only compatible with strong polar solvents, we further develop supramolecular LLCs. Oligopeptides, due to their mature synthesis strategy, structural designability, and robust self-assembly ability, have been exploited to create supramolecular alignment media in different solvents. We first reported CH 3 OH-, DMSO-, and multiple solventcompatible peptide media, which show the broad applicability of their corresponding analytes. Meanwhile, the chiral amino acids confer oligopeptide LLCs with potential chirality, and we have demonstrated their relative application of enantiodiscrimination.Arising from the structural diversity of oligopeptides, several distinct LLC media are constructed and applied to measure independent sets of RDCs. This offers an opportunity for de novo structural determination of organic molecules.In light of the good fluidity of these media, analytes can rapidly penetrate the LLC phases for self-alignment, facilitating simple and fas...

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Section: Introductionmentioning

confidence: 99%

Weak Alignment Liquid Crystal Media from Colloidal Dispersion and Self-assembled Oligopeptide for Anisotropic NMR

Qin,

Zhao,

et al. 2024

Acc. Mater. Res.

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“…Using crosslinked PS swollen in tetrahydrofuran-d 8 , 11 B RQCs (0-640 Hz) were measured from a single 11 B NMR spectrum for all (yet unassigned) boron resonances of the targeted (car)borane. [98] Due to structural rigidity, the boron EFGs expressed in a common molecular coordinate system are precisely known, and the set of (4-6) 11 B RQCs can be fit to a single A (2-3 parameters) to yield the Cornilescu quality factor for every possible assignment. The sign problem was addressed by (i) fitting multiple sign combinations (ii) comparison to 1 H, 11 B RDCs and (iii) a modified 1 H, 11 BÀ HMQC experiment with short 11 B flip angle that reliably gave the sign from the tilt of correlationseven in the case of overlap or very small splittings (Figure 7b).…”

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confidence: 99%

“…[97] We recently started a project to use 11 B RQCs to assign the 11 B resonances of (car)borane clusters including ortho-carborane, its isomer meta-carborane, decaborane B 10 H 14 (4 resonances each) and a derivative of ortho-carborane with 6 resonances. [98] The icosahedral carboranes are highly stable compounds that even in the solid state show narrow resonances due to rapid tumbling. [99] Experimental 11 B quadrupole coupling constants have been derived from spin relaxation [100] and nuclear quadrupole resonance.…”

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confidence: 99%

Multinuclear Residual Quadrupolar Couplings for Structure and Assignment

John,

Rüttger

2024

ChemPhysChem

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Most stable isotopes have a nuclear spin > 1/2, but the quadrupole interaction poses challenge on their detection by nuclear magnetic resonance (NMR). On the other hand, the quadrupole interaction is a rich source of structural information that may be exploited for solution NMR in the form of residual quadrupolar couplings (RQCs) of weakly oriented samples. While 2H RQCs are now well established for structure verification and enantiomeric discrimination of organic molecules, we will in this article highlight some recent work on RQCs of other nuclei (especially 7Li and 11B).

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Cross‐Correlation Between ¹¹B Quadrupole and ¹¹B‐¹⁹F Dipole–Dipole Coupling in BF₂ Groups

Rüttger,

Franke,

Probst

et al. 2024

Magnetic Reson in Chemistry

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Resonance and structural assignment in (car)borane clusters using ¹¹B residual quadrupolar couplings

Abstract: 11B RQCs from stretched polystyrene gels provide the correct 11B resonance assignment in (car)borane clusters in a single step.

Cited by 4 publications

References 39 publications

Weak Alignment Liquid Crystal Media from Colloidal Dispersion and Self-assembled Oligopeptide for Anisotropic NMR

Weak Alignment Liquid Crystal Media from Colloidal Dispersion and Self-assembled Oligopeptide for Anisotropic NMR

Multinuclear Residual Quadrupolar Couplings for Structure and Assignment

Cross‐Correlation Between ¹¹B Quadrupole and ¹¹B‐¹⁹F Dipole–Dipole Coupling in BF₂ Groups

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Resonance and structural assignment in (car)borane clusters using 11B residual quadrupolar couplings

Abstract: 11B RQCs from stretched polystyrene gels provide the correct 11B resonance assignment in (car)borane clusters in a single step.

Cited by 4 publications

References 39 publications

Weak Alignment Liquid Crystal Media from Colloidal Dispersion and Self-assembled Oligopeptide for Anisotropic NMR

Weak Alignment Liquid Crystal Media from Colloidal Dispersion and Self-assembled Oligopeptide for Anisotropic NMR

Multinuclear Residual Quadrupolar Couplings for Structure and Assignment

Cross‐Correlation Between 11B Quadrupole and 11B‐19F Dipole–Dipole Coupling in BF2 Groups

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Resonance and structural assignment in (car)borane clusters using ¹¹B residual quadrupolar couplings

Cross‐Correlation Between ¹¹B Quadrupole and ¹¹B‐¹⁹F Dipole–Dipole Coupling in BF₂ Groups