Solution-state 1H Nuclear Magnetic Resonance Research Articles

Chemical characterization of microbial-dominated soil organic matter in the Garwood Valley, Antarctica

Despite its harsh environmental conditions, terrestrial Antarctica contains a relatively large microbial biomass. Natural abundance carbon and nitrogen stable isotope signatures of organic materials in the dry valleys indicate mixed provenance of the soil organic matter (SOM) with varying proportions of contributions from lichens, mosses, lake-derived algae and cyanobacteria. Here we employed two complementary analytical techniques, biomarker measurements by gas chromatography/mass spectrometry and solution-state 1H nuclear magnetic resonance spectroscopy, to provide further information at a molecular-level about the composition and possible source of SOM in the Garwood Valley, Antarctica. The predominance of branched alkanes and short-chain lipids in the solvent extracts indicates that the primary contribution to the SOM was microbial-derived. Chemical structures in the NaOH extracts from soils were also dominated by amide, peptides, and a CH 3-dominating aliphatic region that were characteristic of microbial signatures. Furthermore, the SOM in the Garwood Valley contained compounds that were different from those in the cyanobacteria-dominated mat from a nearby lake (including monoethyl alkanes and enriched side-chain protons). This observation suggests that easily degradable carbon sources from the nearby lake did not dominate the SOM, which is consistent with a fast turnover of the mat-derived organic matter found in the valley. This study highlights the important role of native soil microbes in the carbon transformation and biogeochemistry in terrestrial Antarctica.

Chemometric prediction of alginate monomer composition: A comparative spectroscopic study using IR, Raman, NIR and NMR

The potential of using infrared (IR), Raman and near infrared (NIR) spectroscopy combined with chemometrics for reliable and rapid determination of the ratio of mannuronic and guluronic acid (M/G ratio) in commercial sodium alginate powders has been investigated. The reference method for quantification of the M/G ratio was solution-state 1H nuclear magnetic resonance (NMR) spectroscopy. For a set of 100 commercial alginate powders with a M/G ratio range of 0.5–2.1 quantitative calibrations using partial least squares regression (PLSR) were developed and compared for the three spectroscopic methods. All three spectroscopic methods yielded models with prediction errors (RMSEP) of 0.08 and correlation coefficients between 0.96 and 0.97. However, the model based on extended inverted signal corrected (EISC) Raman spectra stood out by only using one PLS component for the prediction. The results are comparable to that of the experimental error of the reference method estimated to be between 0.01 and 0.08.