Cellulose Regeneration in Imidazolium-Based Ionic Liquids and Antisolvent Mixtures: A Density Functional Theory Study.

Cellulose can be dissolved in ionic liquids (ILs), and it can be recovered by adding antisolvent such as water or alcohol. In addition, the regenerated cellulose can be used for textiles, degradable membranes, hydrogels/aerogels, etc. However, the regenerated mechanism of cellulose remains ambiguous. In this work, density functional theory (DFT) calculation is reported for the cellulose regeneration from a cellulose/1-n-butyl-3-methylimidazolium acetate (BmimOAc)/water mixture. To investigate the microscopic effects of the antisolvents, we analyzed the structures and H-bonds of BmimOAc-nH2O and cellobiose-ILs-nH2O (n = 0-6) clusters. It can be found that when n ≥ 5 in the BmimOAc-nH2O clusters, the solvent-separated ion pairs (SIPs) play a dominant position in the system. With the increasing numbers of water molecules, the cation-anion interaction can be separated by water to reduce the effects of ILs on cellulose dissolution. Furthermore, the BmimOAc-nH2O and cellobiose-ILs (n = 0-6) clusters tend to be a more stable structure with high hydration in an aqueous solution. When the water molecules were added to the system, H-bonds can be formed among H2O, the hydroxyl of cellulose, and the oxygen of OAc. Therefore, the interactions between cellulose and ILs will be decreased to promote cellulose regeneration. This work would provide some help to understand the mechanism of cellulose regeneration from the view of theoretical calculation.

Fischer-Helferich glycosidation mechanism of glucose to methyl glycosides over Al-based catalysts in alcoholic media.

The Fischer-Helferich glycosidation reaction is generally the initial step in the conversion of glucose to levulinate in alcohol media. However, the relevant molecular mechanism catalyzed by Al-based catalysts is still not well understood. In this work, the reaction mechanism of the glycosidation from glucose to methyl glycosides catalyzed by Al3+ coordinated with methanol/methoxyl was investigated through density functional theory (DFT) calculations. The whole reaction process includes ring-opening, addition, and ring-closure events. The addition of methanol to the ring-opening structure of glucose makes the electronegativity of C1 site stronger to proceed with the following ring-closure reaction. Among the 28 kinds of ways of ring-closure reaction, the most preferred way is to close the loop through the six-membered ring (O5-C1) to generate methyl glucoside (MDGP). The rate-determining step is the ring-closure and the Al3+ shows a great catalytic effect which is mainly reflected in coordinating with the solvents to transfer protons. The results would be helpful to understanding the Fischer-Helferich glycosidation mechanism catalyzed by Al-based catalysts and comprehend the conversion of glucose to high value-added chemicals.

Response of activity and community composition of nitrite-oxidizing bacteria to partial substitution of chemical fertilizer by organic fertilizer.

Nitrite oxidation as the second step of nitrification can become the determining step in disturbed soil systems. As a beneficial fertilization practice to maintain high crop yield and soil fertility, partial substitution of chemical fertilizer (CF) by organic fertilizer (OF) may exert a notable disturbance to soil systems. However, how nitrite oxidation responds to different proportions of CF to OF is still unclear. We sampled soils from a 4-year field experiment subject to a gradient of increasing proportions of OF to CF application. Activity, size, and structure of Nitrospira-like and Nitrobacter-like nitrite-oxidizing bacteria (NOB) community were measured. The results revealed that with increasing proportion of OF to CF application, potential nitrite oxidation activity (PNO) showed a marked decreasing trend. PNO was significantly correlated with the abundance of Nitrobacter-like but not Nitrospira-like NOB. The abundance of Nitrobacter-like was significantly influenced by soil organic matter, organic nitrogen (N), and available N. In addition, PNO was also affected by the structure of Nitrobacter-like NOB. The relative abundance of Nitrobacter hamburgensis, alkalicus, winogradskyi, and vulgaris responded differently to the proportions of OF to CF application. Organic N, organic matter, and available N were the main factor shaping their community structure. Overall, Nitrobacter-like NOB is more sensitive and plays a more important role than Nitrospira-like NOB in responding to different proportions of OF to CF application.