title: Ultrasonic degradation of N-di and trihydroxy benzoyl chitosans and its effects on antioxidant activity.
abstract: Modified chitosans with 3,4-dihydroxy benzoyl groups (CS-DHBA) and 3,4,5-trihydroxy benzoyl groups (CS-THBA) were synthesized and their chemical structures were determined by Fourier transform infrared (FT-IR) and (1)H nuclear magnetic resonance ((1)H NMR) spectroscopy. Then, ultrasonic degradation of CS, CS-DHBA and CS-THBA in 1% acetic acid solution was investigated. The kinetics studies of degradation were followed by gel permeation chromatography (GPC). The results indicated that the weight-average molecular weight of chitosan decreased obviously after ultrasound treatment, but molecular weights of CS-DHBA and CS-THBA decreased slowly with increasing sonication time. Degradation kinetics model based on 1/Mt-1/M0=kt was used to estimate the degradation rate constant. It was found that the rates of degradation of CS-DHBA and CS-THBA are lower than CS, and follow the order: CS4>CS8>CS12>CS-THBA4>CS-THBA8 ≈ CS-DHBA4>CS-THBA12>CS-DHBA8>CS-DHBA12. The antioxidant activity of the CS, CS-DHBA and CS-THBA before and after sonication was investigated by the radical scavenging activity method using 1,1-diphenyl-2-picrylhydrazyl (DPPH). The DPPH scavenging free radical capacity of CS-THBA and CS-DHBA increased up to 89% and 74% respectively, when the concentration reached 6 μg/ml. The ultrasonic treatment of CS-DHBA and CS-THBA after 30 min decreased the DPPH free radical scavenging activity but ultrasonic treatment of CS increased the DPPH free radical scavenging activity.
authors.affiliation: Department of Physical Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz, Iran. Electronic address: mttaghizadeh@tabrizu.ac.ir.
authors.forename: Mohamad Taghi
authors.initials: MT
authors.lastname: Taghizadeh
authors.affiliation: Department of Physical Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz, Iran. Electronic address: a.bahadori@yahoo.com.
authors.forename: Ali
authors.initials: A
authors.lastname: Bahadori
mesh_terms: D001713:Biphenyl Compounds / Q000737:chemistry; D048271:Chitosan / Q000737:chemistry*; D016166:Free Radical Scavengers / Q000737:chemistry*; D007700:Kinetics; D008970:Molecular Weight; D010851:Picrates / Q000737:chemistry; D013010:Sonication
chemical_list: D001713:Biphenyl Compounds; D016166:Free Radical Scavengers; D010851:Picrates; D048271:Chitosan; C004931:1,1-diphenyl-2-picrylhydrazyl
keywords: Antioxidant activity; Degradation; Di- and tri-hydroxy benzoyl chitosans; Kinetics; Ultrasonic