Factors determining the reaction temperature of the solvent-free enzymatic synthesis of trehalose esters

Abstract

Solvent-free synthesis encourages the design of processes and products that reduce the use and generation of hazardous chemicals. Given the importance of developing greener methodologies, we sought to determine the factors influencing the reaction temperature required for solvent-free, enzymatic synthesis of sugar esters such as trehalose (TRE) esters, using Novozyme 435 as the enzyme catalyst. The use of lauric acid (La) and ethyl laurate (LaEt) as acyl donors did not affect the activation temperature for the generation of trehalose diesters (TDEs), despite the differences in corresponding by-products (water and ethanol). However, when glucose (GLU) and La were employed as reaction substrates as a comparison, glucose monoester (GME) generation readily occurred at much lower temperatures than with the TRE esters, even without a water collection device. Moreover, when the glass transition temperature (T_g) of the sugar substrates increased, a higher reaction temperature was required. These results suggest that while the activation temperature of the reaction did not correlate with the boiling point of the by-product, it did correlate with the glass transition temperature (T_g) of the trehalose substrates. Thus, our work demonstrates the importance of the physical state of amorphous matrices in determining the optimal reaction temperature of a solvent-free sugar synthesis.

Keywords: Enzymatic synthesis; Glass transition temperature; Novozyme 435; Solvent-free; Sugar esters.