Grafting of glycine, alanine, serine, and threonine on cellulose membranes and their role in regulating the uniport, symport, and antiport permeation of glucose

Abstract

Four cellulose membranes were grafted with glycine, L-alanine, L-serine, and L-threonine amino acids. The grafted membranes were characterized by different physicochemical techniques (ATR-IR, gravimetry, thermal degradation and ninhydrin test). The degree of substitution was found to range from 0.29 to 0.85 per glycoside unit, mainly occurring at C6. This structural modification was further examined and found to modestly alter the thickness, hydrophilicity, pore size, porosity, tortuosity, and flux behavior of the native Cell-OH membranes. Accordingly, the performance of the modified membranes toward the permeation of D-glucose (D-Glu) was investigated in the presence of NaCl, KCl, and NaHCO3 salts under uniport, symport, and antiport conditions. Data analysis allows the inspection of the role played by [Na]+/[K]+ cations and [Cl]-/[HCO3]- in the permeation process of D-Glu. All data were examined in comparison with those obtained for the native Cell-OH membrane. The introduced functionalities are found to hinder the passage D-Glu under uniport conditions, while dramatically affect the symport and antiport migrations. The modified membranes facilitate the passage of D-Glu in symport mode where the anions (Cl- and HCO3 _) play a key role in comparison with the cations (Na+, K+). However, the role of both cations and anions is seen in the antiport mode.