Density Functional Theory Study of Intermolecular Interactions between Amylum and Cellulose

Abstract

Amylum is one of the polysaccharides developed into biodegradable plastic bags. However, amylum-based plastics are easily damaged due to their low mechanical strength and hydrophilic properties. Cellulose is used as a support material in amylum-based plastics to increase strength and reduce water damage. This study investigated the molecular interactions between amylum and cellulose computationally. The minimum interaction energy of amylum and cellulose was calculated using in silico modeling using the Density Functional Theory (DFT) method. The B3LYP function and the basis set 6-31++g** were used in the calculations. Simultaneously, D3 Grimme dispersion correction was used as the effect of water solvent in the measures. The results obtained from this study were the interaction energy of amylum and cellulose of –29.8 kcal/mol. The HOMO-LUMO energy gap of the cellulose-amylum complex was lower than cellulose, indicating that the cellulose-amylum complex was more reactive and bonded to each other. Analysis of Natural Bond Orbital (NBO), Quantum Theory Atom in Molecule (QTAIM), Reduced Density Gradient (RDG), Non-covalent Interaction Index (NCI), and Intrinsic Bond Strength Index (IBSI) showed that the cellulose-amylum complex had weak to medium intermolecular bonds. The hydrogen bond at O61···H48 was the strongest in the complex. All data show that cellulose and amylum could interact through non-covalent bonds.

Quantum Chemical Calculation for Intermolecular Interactions of Alginate Dimer-Water Molecules

“…Usually, the bonding interaction of hydrogen also consists of natural orbital to assure the strength of the interaction bond, which is investigated by NBO analysis. The result could also support the strength of the hydrogen bonding interaction that was predicted by the energy interaction [ 26 , 27 ]. NBO analysis is also used not only for investigating the intramolecular and intermolecular bonding interaction but also the charge transfer or conjugative interactions that happen in a molecular system.…”

“…The optimized structures of alginic acid (Alg) and sodium alginate (SA) are presented in Figure 1 . Dimer Alg and SA structure were chosen to represent the polymer due to the fact that the interaction energy and enthalpies between dimers, trimers, and oligomers with water are almost similar [ 24 , 25 , 26 , 27 ]. Researchers also used dimer structures to evaluate the polymer [ 24 , 26 , 28 , 29 ].…”

“…Dimer Alg and SA structure were chosen to represent the polymer due to the fact that the interaction energy and enthalpies between dimers, trimers, and oligomers with water are almost similar [ 24 , 25 , 26 , 27 ]. Researchers also used dimer structures to evaluate the polymer [ 24 , 26 , 28 , 29 ]. G blocks (GG) of the alginate structure are stiffer compared to alternate blocks (GM) and M blocks (MM) due to their diaxial connection, and hence, they are more soluble at lower pH [ 16 , 30 ].…”

“…On the other hand, a decreasing LUMO energy value signifies that the molecule tends to take up more electrons. The energy difference between HOMO energy and LUMO energy is well known as the HOMO-LUMO energy gap The can be deployed to predict the chemical species’ strength and stability [ 26 , 47 , 48 ]. A small corresponds to a molecule that is likely to transfer electrons and be more reactive.…”

“…All calculations in this study were fulfilled by the density functional theory (DFT-D3) method using the hybrid of Becke’s three-parameter Lee, Yang, and Parr (B3LYP) functional and the basis set 6-31++G** [ 24 , 26 ]. A solvation model based on density (SMD) was used to calculate the effect of the water as a solvent [ 26 , 50 ]. The MM-alginate dimer structure was collected from PubChem (CID: 45048803).…”