(240h) On the Effects of Chaotropic Promoters on Enzyme Hydrolysis

Lignocellulosic biomass, being an abundant source of non-edible carbon is an ideal feedstock replacement for petroleum, originating in the form of biomass such as grasses, wood, and agricultural waste. This type of biomass is mainly composed of cellulose, hemicellulose, and lignin while the general method for the conversion of biomass to biofuel precursors consists of a pretreatment step followed by enzymatic hydrolysis into simple sugars, that can later be fermented into bioethanol. The pretreatment leading up to the conversion step removes lignin from the feedstock, leaving cellulose and hemicellulose, following up with preparation of the cellulose to be in a more reactive amorphous structure to later be used to create biofuel precursors.

Electrolytes such as chaotropes from the Hofmeister series salts have been shown to increase the solubility of organic molecules in water solutions. These substances can disrupt the hydrogen bond network in liquid water, thereby increasing entropy. Previous attempts to utilize the benefits of hydrolyzing amorphous cellulose have been unconcluded by the spontaneous recrystallization of cellulose to a less reactive form, by inhibiting the recrystallization using a chaotropic promoter, the process can take advantage of the benefits from the enhanced cellulose reactivity. Recent studies have shown that implementing Hofmeister series salt promoted cellulose hydrolysis reactions resulted in an increase in glucose yields by 80%, making the bioethanol production more economically favorable.

In this study, the focus is on understanding the effects of the Hofmeister series salt by exploring the chaotropic salt guanidinium chloride’s interaction with the enzyme used during hydrolysis with the use of cellobiose as the model reaction. Cellobiose is a water-soluble carbohydrate consisting of two glucose molecules that reproduces the glycosidic bonding of cellulose. As a water-soluble molecule, cellobioses reactivity is not affected by crystallinity or the effects of a water-solid interface.

The glucose yields at the different salt concentrations of guanidinium chloride for a reaction time span of 0 to 12 hours were studied and compared in which it was found that the glucose yields varied slightly (~10%) between the control enzyme hydrolysis sample with no salt added and the optimal sample promoted with 0.2 molar guanidinium chloride as shown in Fig. 1.

Figure 1. Glucose Yields from Cellobiose Enzymatic Hydrolysis

This study aims to shed light on the effects of Hofmeister series salts on the reaction by looking at cellobiose to see how the salt interacts with the enzyme reactivity. These results imply that other parameters like crystallinity may have an impact and more work is needed to be done to understand how the Hofmeister series salts are affecting the reactions. In doing so this process has the potential to unlock cost-effective biofuels at an industrial scale.