NMR internal standard signal shifts due to cyclodextrin inclusion complexes

Abstract

Nuclear magnetic resonance (NMR)-based screening of materials is a powerful tool for quality control, authenticity testing, and purity testing of compounds.However, reliance on 3-(trimethylsilyl)-propane-1-sulfonate (DSS) and 3-(trimethylsilyl)propanoic acid (TMSP) for referencing the spectra of aqueous samples is not without hazard, particularly with automated analyses. The assumption that these reference signals always represent 0 ppm is ubiquitous in NMR spectroscopy and is routinely used for spectral alignment. However, it has been found that cyclodextrins readily generate inclusion complexes with DSS and TMSP with the effect of rendering this assumption incorrect. These inclusion complexes alter the electronic shielding of the trimethylsilane functional groups on DSS and TMSP yielding a small, but significant, shift to a higher frequency in the signal relied upon for spectral referencing. As a result, samples containing traces of these compounds may be incorrectly declared fraudulent, inconsistent with standards, or adulterated. In order to maintain the viability of this screening method, vigilance and/or improved referencing of spectra is needed.

Modulation of Gold Nanoparticle Ligand Structure–Dynamic Relationships Probed Using Solution NMR

“…Quantitative NMR was employed to determine the number of observable protons. Deuterated trimethylsilyl propanoic acid (TMSP) was utilized as an internal ref . The concentration ratio between TMSP and AuNP was maintained at 7:1.…”

Highly efficient catalytic performance on CuAAC reaction by polymer‐like supramolecular self‐assemblies‐Cu(I) in aqueous solution

“…The water solubility of CD‐SP 4 is 74.1 g/L, whereas the water solubility of free G2 is at approximately 0.018 g/L (see Figure S30). Besides, the 1 H NMR spectrum shows that once adamantane has entered the CD cavity, owing to shielding effect [ 44 ] and solvent effect, [ 45 ] the chemical shift of protons could be clearly observed (Figure 1b): The ax and eq bonds of H c in adamantane shifted from 2.45 to 1.8 ppm and 2.1 to 1.9 ppm, respectively, and H b of adamantine shifted from 3.1 to 2.1 ppm. The protons of β‐CD attached to C‐3 and C‐5 are placed in the interior of the cavity, and those attached to C‐2 and C‐4 are outside of the cavity.…”