Insight into the functionality of microbial exopolysaccharides by NMR spectroscopy and molecular modeling

Microbial polysaccharides represent an important class of microbial polymers with diverse functions such as biofilm formation, thickening and gelling properties as well as health-promoting properties.The broad range of exopolysaccharide functionalities has sparked a renewed interest in this class of molecules. Chemical, enzymatic as well as genetic modifications by metabolic engineering can be used to create large numbers of analogous exopolysaccharide variants with respect to exopolysaccharide functionality. While this top-down approach is effective in finding new candidates for desired functionality, there seems to be a lack of the corresponding bottom-up approach. The molecular mechanisms of the desired functionalities can be established from NMR and molecular models and it is proposed that these models can be fed back into the biotechnology by using a quantitative structure-property approach. In this way it will be possible to tailor specific functionality within a given design space.This perspective will include two well-known commercial microbial exopolysaccharide examples namely gellan and diutan and show how even a limited use of multiphase NMR and molecular modelling can increase the insight into their different properties, which are based on only minor structural differences

Characterization of free radicals by electron spin resonance spectroscopy in biochars from pyrolysis at high heating rates and at high temperatures

peer-reviewedThe concentration and type of free radicals from the decay (termination stage) of pyrolysis at slow and fast heating rates and at high temperatures (above 1000°C) in biomass char have been studied. A room-temperature electron spin resonance spectroscopy study was conducted on original wood, herbaceous biomass, holocelluloses, lignin and their chars, prepared at high temperatures in a wire mesh reactor, an entrained flow reactor, and a tubular reactor. The radical concentrations in the chars from the decay stage range up between 7·1016 and 1.5·1018 spins g−1. The results indicated that the biomass major constituents (cellulose, hemicellulose, lignin) had a minor effect on remaining radical concentrations compared to potassium and silica contents. The higher radical concentrations in the wheat straw chars from the decay stage of pyrolysis in the entrained flow reactor compared to the wood chars were related to the decreased mobility of potassium in the char matrix, leading to the less efficient catalytic effects of potassium on the bond-breaking and radical re-attachments. The high Si levels in the rice husk caused an increase in the char radical concentration compared to the wheat straw because the free radicals were trapped in a char consisting of a molten amorphous silica at heating rates of 103–104 K s−1. The experimental electron spin resonance spectroscopy spectra were analyzed by fitting to simulated data in order to identify radical types, based on g-values and line widths. The results show that at high temperatures, mostly aliphatic radicals (g = 2.0026–2.0028) and PAH radicals (g = 2.0027–2.0031) were formed

Comparison of high temperature chars of wheat straw and rice husk with respect to chemistry, morphology and reactivity

peer-reviewedFast pyrolysis of wheat straw and rice husk was carried out in an entrained flow reactor at high-temperatures (1000–1500) °C. The collected char was analyzed using X-ray diffractometry, N2-adsorption, scanning electron microscopy, particle size analysis with CAMSIZER XT, 29Si and 13C solid-state nuclear magnetic resonance spectroscopy and thermogravimetric analysis to investigate the effect of inorganic matter on the char morphology and oxygen reactivity. The silicon compounds were dispersed throughout the turbostratic structure of rice husk char in an amorphous phase with a low melting temperature (≈730 °C), which led to the formation of a glassy char shell, resulting in a preserved particle size and shape of chars. The high alkali content in the wheat straw resulted in higher char reactivity, whereas the lower silicon content caused variations in the char shape from cylindrical to near-spherical char particles. The reactivities of pinewood and rice husk chars were similar with respect to oxidation, indicating less influence of silicon oxides on the char reactivity

¹H NMR spectra dataset and solid-state NMR data of cowpea (Vigna unguiculata)

In this article the NMR data from chemical shifts, coupling constants, and structures of all the characterized compounds were provided, beyond a complementary PCA evaluation for the corresponding manuscript (E.G. Alves Filho, L.M.A. Silva, E.M. Teofilo, F.H. Larsen, E.S. de Brito, 2017) [3]. In addition, a complementary assessment from solid-state NMR data was provided. For further chemometric analysis, numerical matrices from the raw 1H NMR data were made available in Microsoft Excel workbook format (.xls)