Synthesis,Antimicrobial Activity Of Cinnamaldehyde-amino Acid Schiff Base And Research On Quantitative Structure Activity Relationship

Cinnamaldehyde is the main ingredient of cinnamon oil,which is extracted from the bark and leaves of cinnamon trees.Cinnamaldehyde is a natural antimicrobial agent.Cinnamaldehyde was approved as food preservative and antimicrobial agents,due to its high safety.However,the application of cinanamaldehyde is limited due to its unacceptable pungen odor,water-insoluility and high volatility.One alternative is chemical modification for exploring the new cinnamaldehyde derivatives with acceptable odor,good bioactivity,water-solubility.In this paper,cinnamaldehyde,p-chloro cinnamaldehyde,p-methoxy cinnamaldehyde and 7 amino acids were used to synthesis the new compounds with expected excellent bioactivity.The structures of 21 compounds were confirmed by FTIR,1H-NMR,MS and melting point.A paper disc method was applied to determine the antimicrobial activity of the designed compounds.The tested microorganism included two fungi(Aspergillus niger and Penicillium citrinum)and two bacteria(Escherichia coli and Staphylococcus aureus).The tested concentration were 0.25mol/L,0.125 mol/L,0.0625 mol/L and 0.03125 mol/L.The ciprofloxacin and fluconazole were used as comparators.The results shown that all compounds exhibited good antimicrobial activity against tested microorganism,and most of compounds exhibited better antimicrobial activity than control compounds.Furthermore,the broad spectrum antimcrobial properties of cinnamaldehyde-amino acid schiff base compounds were tested at the concentration of 0.125 mol/L,the tested microorganis included Saccharomycetes,Trametes versicolor,Gloeophyllum trabeum,Aspergillus terreus,and Bacillus subtilis.The results shown that cinnamaldehyde-amino acid schiff base compounds have broad spectrum antimicrobal property.According to the inhibition zone diameter results,the antimicrobial activity against four test microorganism depended on chemical structure.Different structure of compounds exhibited varied bioactivity.In order to make the relationship beween structures and activity of cinnamaldehyde compounds more explicit,Quantitative Structure-Activity Relationship(QSAR)is used to mathematically analyze information of cinnamaldehyde compounds.3D molecular structures of compounds were prepared and performed using Chembio 3D software,and all the structures were further optimized using Agui 9.2.1 software.The structure-data files were inputted into CODESSA 2.7.16 software to calculate the molecule structure descriptor.Next,the 'best multi-linear regression' was determined to calculate the relationship between antimicrobial activity and structure descriptors.Finally,the best QSAR mode was determined by the 'breaking point' rule.The internal verification and leave one out verification results shown that the best model is reliable and stable.The obtained models were used to design new compounds with good antimicrobial activity.According the structure molecule descriptors of the best QSAR model,there of the 3 cinnamaldehyde-amino acid Schiff base with the best predicted antimicrobial activity were screened,synthesized,and antimicrobial activity tested.Those three screened compounds exhibited excellent antimicrobial activity and very closed to the predicted antimicrobial actibity value from QSAR models.This new kind of cinnamaldehyde-amino acid Schiff base compounds not only eliminate the drawbacks of cinnamaldehyde applied in food and medical field,also has some advantages like high efficient antimicrobial activity,water solubility,the safety of raw materials,and simple synthesis method.Two cinnamaldehyde amino Schiff base compounds were selected as the active agents to prepare PVA antimicrobial film for food packaging.The film has good transparency can reach 90%in the visible light area.The microorganism growth curve was used to test the antibacterial activity properties of the film,and the growth of Staphylococcus aureus and Escherichia coli was inhibited.Banana protection result shown that the antimicrobial film can inhibit the growth of microorganisms on food surface and increase the shelf life.The physical properties of antimicrobal film shown that low content of Schiff base in film formed the hydrogen bond to enhance the mechanical property.The WVP increased because the cinnamaldehyde-amino acid Schiff base is water solubility.