# Diversity of Potential (Bio)Technological Applications of Amino Acid-Based Ionic Liquids
## 2 Bioapplications of AA ILs: An Overview
### AA-ILs with Application in the Processing of Biomaterials  
#### 2.6.1 Cellulose Treatment and Processing  
Structural polysaccharides, which have a complex composition and include cellulose, hemicellulose, lignin, and pectin, comprise the cell walls of crops, woods, and various plant materials [87]. Lignocellulose, the most abundant natural material, is classified as a second-generation renewable resource. For example, lignocellulosic from wood residues, straws, and other plant wastes is a feedstock for bioethanol production [98]. Lignin, a highly cross-linked aromatic polymer, consists of three main phenylpropane units: p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol [99]. Due to its rigid and complex structure, lignin is highly resistant to enzymatic degradation. Therefore, an essential step in the processing of lignocellulosic biomass is delignification, which facilitates the subsequent extraction of valuable chemicals. Numerous studies have shown that some ILs are excellent solvents for biomass or media for biocatalysts for cellulosic processing. The [Ch][AAs] have been extensively studied for cellulose pretreatment with the goal of increasing biomass porosity, partially removing lignin, and disrupting crystalline cellulose. Mixtures of glycerol with [Ch][Phe], [Ch][Ser], or [Ch][Ala] can partially remove lignin, inhibit xylan loss, and increase polysaccharide conversion from pretreated wheat straw [100]. Using 50% [Ch][Ala]-glycerol, 67.6% lignin removal, 95.1% cellulose retention, 89.7% cellulose conversion, and 70.9% xylan conversion were achieved, demonstrating a pretreatment efficiency comparable to that of other solvents [100]. Interestingly, pretreatment of rice straw or sugar bagasse with 50% [Ch][AA]-water mixtures resulted in approximately 60% lignin removal for ILs containing Lys, Gly, Ala, Ser, Phe, and Pro anions [101; 102]. However, for the IL with the Glu anion, the efficiency was only 13%. After the IL-water pretreatment, the enzymatic digestion of the lignocellulosic biomass showed significantly improved efficiency in the samples with the most effective lignin removal. Except for the [Ch][Glu]-pretreated samples, the sugar yields were greater than 80% for glucose and about 50% for xylose [101; 102]. Similarly, [PERSON] et al. observed a strong dependence of the solubility of rice straw lignin on the type of AA anion in a series of choline-based ILs [24]. A lower concentration of [Ch][Lys] (20%) and a short pretreatment period (90 \({}^{\circ}\)C for 1 h) of rice straw also resulted in high sugar yields, reaching 81% for glucose and 48% for xylose during subsequent enzymatic hydrolysis [103]. It was also shown that even in the presence of 5 mM [Ch][AA] under the conditions tested, the lignin yield remained high, ranging between 140 and 220 mg/g IL in most media [24]. At the same time, xylan yield varied between 1 and 85 mg/g IL, while glucose was less than 5 mg/g IL in all ILs, indicating selectivity. In agreement with other reports, ILs containing negatively charged AA anions such as Glu, Asp, Gln, and Asn were the poorest solvents for lignin (yielding 10-26 mg/g IL), which is attributed to the lower pH and higher viscosity of these solutions [24]. In addition, facilitated enzymatic hydrolysis was observed, with up to a 7-fold increase in glucose yield from all [Ch][AA]-pretreated rice straw and microcrystalline cellulose samples [24]. The efficiency of delignification also depends on the source of lignocellulosic. For example, when [Ch][Arg] is used as the pretreatment solvent, the lignin extraction capacity decreases in the following order: rice straw (80%) \(\approx\) wheat straw (78%) > sugarcane bagasse (73%) > corncob (68%) > eucalyptus hardwood (55%) > pine (33%) [104]. Notably, IL was recovered after eight cycles of reuse, with the efficiency of the last cycle reported to be 75% [104].