Molecular Characterization

Creative Biostructure utilizes NMR spectroscopy, combined with other analytic approaches such as mass spectrometry and Fourier transformation infrared spectroscopy to characterize molecular properties of natural organic matter, polymers, unknowns, and contaminant residues.

Using simple ¹H mono-dimensional spectroscopy, aliphatic, carbohydrate, aromatic, and carboxyl-rich alicyclic molecules (CRAM) can be identified by chemical shift analysis. Furthermore, ¹³C investigation by multi-dimensional heteronuclear approaches, for example, heteronuclear multiple quantum coherence (HMQC) and heteronuclear multiple bonding coherence (HMBC), allow characterization of specific regions assignable to well-known organic species, such as anomeric carbons of carbohydrates, conjugated double bonds of aliphatic acids, CRAM, N-acetyls, etc. ¹H- ¹³C heteronuclear single quantum coherence (HSQC) spectrum provides correlation between the aliphatic carbon and its attached protons (Figure. 1).

Figure 1. Two-dimensional ¹H- ¹³C HSQC NMR spectra of pyridine.

Solid-state NMR is nowadays a well-established technique for structure elucidation. It allows investigation on short-range ordering (local environment) and structure. Several techniques have been developed for handling heteronuclear dipolar, homonuclear dipolar, and quadrupolar interactions (Table 1).

Table 1. Techniques used in high-resolution solid-state NMR.

One example of MAS is cross-polarization magic-angle spinning ¹³C NMR (CPMAS ¹³C NMR). Analysis performed with variable contact-time pulse sequences showed that the fractions contained aromatic, alkyl, and carbohydrate-like components. CPMAS ¹³C NMR has been increasingly used to identify the chemical composition of complex mixtures, natural organic matter for instance, and to quantify the distribution of different carbon nuclei by application of specific pulse sequences. CPMAS ¹³C NMR spectroscopy has also been recognized for its potential in providing conformational information about organic matter by usage of special pulse sequences designed to measure relaxation times.

Our NMR team at Creative Biostructure has extensive experience with molecular characterization and structure elucidation of both small organic molecules and biomacromolecules. Our specialists collaborate with customers to accelerate the research progress. Please contact us for detailed inquiry!

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References

1. Nebbioso A. and Piccolo A., (2013). Molecular characterization of dissolved organic matter (DOM): a critical review. Anal Bioanal Chem. 405: 109-124.
2. Salmon E., Behar F., and Hatcher P., (2011). Molecular characterization of type 1kerogen from the green river formation using advanced NMR techniques in combination with electrospray ionization/ultrahigh resolution mass spectrometry. Organic Geochemistry. 42: 301-315.
3. Stocker M., (2001). Product characterization by NMR. Verified Syntheses of Zeolitic materials. 57-61.