The synthesis of polyelectrolyte complexes (PEC) based on chitosan and determination of their antibacterial properties had been conducted. The microstructure of PECs obtained were described by SEM analysis, while inhibition activity of PECs against S. aureus and E. coli was determined by measuring inhibitory zone diameter. Characteristics of chitosan, alginate and κ-carrageenan as natural polymers which non-toxic, biodagradable and safe to eat meet the edible film criteria. Chitosan as a polycationic interacts with alginate and κ-carrageenan as polyanionic under the appropriate conditions to form PEC film. Based on FTIR spectra, it was found that interaction of chitosan and alginate as well as chitosan and κ-carrageenan was an electrostatic interaction. Microstructure study using SEM found that PECs have irregular and fibrous surface structure. Based on their inhibitory activity against S. aureus and E. coli, PECs have the strongest antibacterial activity compared to their original polymer. Therefore, PECs film could be excellent edible film for food coating that protect product from bacterial contamination.
The preparation of polyelectrolyte complex (PEC) based on bio-composite materials often requires crosslinking agents to achieve the desired stability and properties of the material formed. PEC with opposite charges has the advantage in self-crosslinking through electrostatic interactions. Chitosan is a positively charged polysaccharide with -NH3
+ group while κappa-carrageenan is a negatively charged polysaccharide with -OSO3
− group. This work focused on synthesizing chitosan-carrageenan membrane and determining its characteristics. The membrane was prepared by interacting chitosan and carrageenan hydrosols at a pH of 5. The obtained chitosan-carrageenan membrane had better physical-mechanical properties, including tensile strength (load), elongation (strain), and elasticity (modulus young), adsorption, and resistance of water, than the constituent polymers. The FTIR spectra indicated the presence of self interaction in membrane between protonated amine groups of chitosan and sulfate groups of carrageenan. The difference in surface morphology among chitosan-carrageenan membrane and its constituent membranes was confirmed by SEM analysis.
Alginate-chitosan based biopolymer for possible application as edible film coating has been studied. Alginate hydrosol and chitosan hydrosol with mass ratio of 1:1 were mixed to form a thin membrane and then dried. The obtained alginate-chitosan membrane was confirmed using FTIR spectrophotometers. Characterization of the membrane, which includes thickness, tensile strength, water vapor sorption, resistance to pH change and antimicrobials properties, were conducted. It was showed that the interaction of alginate and chitosan in the membrane occurred through the electrostatic interaction of the carboxylic group of alginate and ammonium groups of chitosan. At the same thickness, the alginate-chitosan membrane tensile strength was higher and more resistant to pH changes than both native alginate and chitosan membranes. Furthermore, the alginate-chitosan membrane has good antibacterial potential against gram-positive bacteria (Staphylococcus aureus) and gram-negative bacteria (Escherichia coli). It is expected that the alginate-chitosan membrane has the potential application for safe and efficient fruit coating.
A screen-printed three-electrode system is fabricated to prepare a novel screen-printed biosensor for rapid determination of Hg(II) in aqueous solution. The amperometric biosensor is prepared by entrapping urease in alginate–chitosan membrane to modify the screen-printed carbon electrode. The urease/alginate–chitosan membrane for Hg(II) had optimum measurement conditions at work potential of -0.15 V, pH of 7, urea concentration of 75 mM, response time of 8 seconds, inhibition time of 7 minutes and temperature of 25 °C. The resulted biosensor characteristic were found to have the range concentration of Hg(II) ion between 40-90 ppb with the detection limit I10% was 66.45 ppb, the coefficient of variance (Cv) was 0.8%, and reactivation was 5 times reuse.
Determination of glucose concentration in urine and blood that anyone can use at any time is Benedict reagent based chemical sensor. This optical sensor was developed by immobilizing Benedict reagent into nata cellulose as supporting material via entrapment. The nata cellulose/Benedict membrane for glucose determination has optimum condition at maximum wavelenght of 541.57 nm, Benedict concentration of 0.4470 M, and ratio of nata cellulse mass to Benedict volume was 1:3. Characterization of optical sensor for glucose was in working range of 0-5000 ppm, limit of detection was 911,11 ppm, sensitivity was 0.0009 and reproducibility was 0.2295%.
CHEMICAL DEGRADATION OF NAFION MEMBRANES UNDER PEMFC AS INVESTIGATED BY DFT METHOD. An exsitu method has been developed to performance of Nafion's membrane in PEMFC (Proton Electrolyt Membrane Fuel Cells), caused by the chemical degradation of ·OH and ∙H radicals. The change of the chemical structure occurring during the degradation were primarily calculated of the relative energy of reactions by DFT (Density Functional Theory) method approach in the Gaussian software. This study aims to determine whether DFT method with functional B3LYP, PBEPBE, and B3PW91 and base sets 6-311++G can be used in determining the relative energy of a reaction and knowing the difference in role between ·OH and ∙H in the degradation process of the main chain Nafion with the final group are -CF2H, -CF=CF2 and -COOH. The three functionalities applied showed that the ·OH radical has more role than the ∙H radical in the degradation process of the Nafion main chain. In the -CF2H group was shown the relative energy value of reaction 2 is lower than reaction 5, in the -CF=CF2 group was shown the relative energy value of reaction 8* is lower than reaction 11 and in the -COOH group the relative energ value of reaction 14 is lower than reaction 16. By knowing the relative energy of the Nafion main chain degradation reaction with a certain final group and the role of certain radical compounds in the degradation process, the DFT method with functional B3LYP, PBEPBE and B3PW91 and base sets 6-311++G can recommend various modifications of the Nafion as a fuel cell membrane, particularly in increasing of membrane performance.
An optical chemical sensor based on a transparent membrane of polyelectrolyte complex (PEC), composed of alginate-chitosan membrane and 2,6-dichlorophenol-indophenol (2,6-DCPIP), coated on transparent mica was coupled with UV-Vis spectrophotometry and used for colorimetric measurements of ascorbic acid (AA). The transparent membranes of PEC were characterized using scanning electron microscopy (SEM) technique. The experimental parameters of the biosensor were optimized. Here, the optical chemical sensor showed maximum response at wavelength of 545 nm, with the optimum pH at 3. The calibration curve had a dynamic working range at 0.0 to 5.0 mM of AA with a limit of detection (LOD) of 0.13 mM AA. The membrane sensor has a long life time in the defined condition (4 o C). The developed optical chemical sensor correlated well with the standard method, HPLC for the determination of Ascorbic acid concentration in real samples.
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