A small aggregate is composed of several or tens of molecules or ions, with at least one dimension in the range from a few to dozens of angstroms. Here, we named such aggregate system as Angstrom Aggregates(AA). AA with the specific size in angstrom meter might possess unique structure activity relationship. Unlike molecular level, nano system and the bulk, AA, an aggregate in angstrom scale is firstly proposed,its arrangement in order, electronic effect, surface interaction, confinement effect, is still unclear. However, recently, the structure and activity relationship of such aggregate in angstrom scale has attracted increasing interest in many areas, such as in ionic liquids, aqueous solution,catalytic system, and bio-system. As the physical and chemical propeties of AA strongly depends on its structure, the in situ characterizzation technique combined with theoretical methods should be developed to understand the exact interaction between the component of the clusters, the assembly formations, the special features, and the reaction activities. It has great scientific meaning to detect, represent and regulate the structure and function of AA precisely, facilitating in its application. A systematic and thorough research on AA in angstrom scale will promote the development of fundamental science and the progress of technology significantly.
Ionic liquids （ILs） have attracted many attentions in the dissolution of cellulose due to their unique physicochemical properties as green solvents. However, the mechanism of dissolution is still under debate. In this work, computational investigation for the mechanisms of dissolution of cellulose in [Bmim]Cl, [Emim]C1 and [Emim]OAc ILs was performed, and it was focused on the process of breakage of cellulose chain and ring opening using cellobiose as a model molecule. The detailed mechanism and reaction energy barriers were computed for various possible pathways by density functional theoretical method. The key finding was that 1Ls catalyze the dissolution process by synergistic effect of anion and cation, which led to the cleavage of cellulose chain and formation of derivatives of cellulose. The investigation on ring opening process ofcellobiose suggested that carbene formed in ILs played an important role in the side reaction of cellulose, and it facilitated the formation of a covalent bond between cellulose and imidazolium core. These computation results may provide new perspective to understand and apply ILs for pretreatment of cellulose.
