J. L. Willett

DFTMD studies of glucose and epimers: anomeric ratios, rotamer populations, and hydration energies

Results are presented from density functional molecular dynamics (DFTMD) simulations, based on constant energy dynamics, of glucose and its cyclic form of 6-carbon epimers. Both in vacuo and an implicit solvent method (COSMO) were examined, including simulations of low-energy conformations of each molecule. Analysis of the DFTMD results includes the following: energies averaged over the simulation time, calculated anomeric ratios, hydroxyl and hydroxymethyl rotamer populations, and hydration energies. Hydrogen-bonding networks persistence times were examined, and the effects of solvation on rotamer populations were described. Anomeric ratios calculated from energy optimization of an ensemble of low-energy conformers are compared to those obtained from ensemble averages from molecular dynamics, with dynamics simulations giving populations in best agreement with experimental anomeric ratios. Ensemble results in vacuo were not in agreement with experimental anomeric ratios or hydroxymethyl populations, producing in some cases reversal of the alpha:beta ratios. The difficulty in obtaining correct alpha:beta ratios increases with the number of axial groups; the mono-axial epimers being best represented, epimers with two axial groups being more difficult, and the epimers with three axial hydroxyl groups being most difficult to analyze, the result of a large number of very strong hydrogen-bonding networks that form the ensemble of low-energy conformations in the multi-axial structures.

Corrosion protection of low-carbon steel using exopolysaccharide coatings from Leuconostoc mesenteroides

Corrosion of metals is a serious and challenging problem faced worldwide by industry. Purified Leuconostoc mesenteroides exopolysaccharide (EPS) coatings, cast from aqueous solution, inhibited the corrosion of low-carbon steel as determined by electrochemical impedance spectroscopy (EIS). There were two different corrosion behaviors exhibited when EPS films from different strains were cast onto the steel. One EPS coating reacted immediately with the steel substrate to form an iron (III) oxide layer (“rust”) during the drying process while another did not. The samples that did not flash corrode had higher corrosion inhibition and formed an iron (II) passivation layer during EIS testing that persisted after the cells were disassembled. Corrosion inhibition was strain-specific as polysaccharides with similar structure did not have the same corrosion potential.

Microwave-Assisted Rapid Modification of Zein by Octenyl Succinic Anhydride

ABSTRACT Corn is one of the most important food and industrial crops in the United States. Zein constitutes about half of the endosperm proteins in corn. Potential applications of zein include use in fibers, adhesives, inks, cosmetics, textiles, and chewing gum. Recently, attempts have been made to utilize zein for food coatings and biodegradable materials. The new applications of zein require it to be resistant to water. Thus, we are interested in new routes for chemical modification of zein (Biswas et al, unpublished). 2-Octenyl succinic anhydride (OSA) is extensively used in modifying food starches. Our objective was to take advantage of OSA hydophobicity, flexibility, and compatibility with nonpolar groups and incorporate OSA onto zein. This OSA-modified zein would possess the best of both OSA and zein. A zein solution in dimethyl formamide (DMF) was reacted with various levels of OSA to give modified zein. In a microwave reactor, the reactions proceeded tremendously fast and they were over in 5 min. ...

Corn Gluten Meal as a Thermoplastic Resin: Effect of Plasticizers and Water Content

ABSTRACT Corn gluten meal (CGM) was studied to investigate the effect plasticizers and water have on its melt processing, and how this melting affects its mechanical properties. GCM containing varying amounts of water were mixed with 23% (w/w) plasticizers; (glycerol, triethylene glycol (TEG), dibutyl tartrate, and octanoic acid in a Haake bowl mixer at 80°C. The amount of water in the CGM affected the amount of torque produced in the Haake mixer. This increase in torque was correlated with how well the CGM melted in the mixer. SEM images of CGM melted in the mixer showed a more uniform homogenous structure when processed at its optimum moisture content. Glycerol, TEG, and dibutyl tartrate produced the greatest torque when the CGM contained <1% water. Octanoic acid produced the greatest torque when the CGM was processed at 8% moisture. CGM plasticized with TEG and octanoic acid were mixed at either their optimum moisture or at 9.6% moisture and then compression molded into tensile bars. The tensile streng...