Biocatalytic Synthesis of a Novel Polyaniline Derivative and Its Usage

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Biocatalytic synthesis of a novel polyaniline derivate and its usage for polypropylene stabilization Ali Bilici, #brahim Halil Gecibesler, Yunus Cogal, and Ismet Kaya Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b00555 • Publication Date (Web): 25 Jul 2017 Downloaded from http://pubs.acs.org on July 27, 2017

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Industrial & Engineering Chemistry Research

Biocatalytic synthesis of a novel polyaniline derivate and its usage for polypropylene stabilization Ali Bilicia*, Ibrahim Halil Geçibesler b, Yunus Çogalc, Ismet Kayaa a

Çanakkale Onsekiz Mart University, Faculty of Sciences and Arts, Department of Chemistry, Polymer Synthesis and Analysis Lab. 17020 Çanakkale, Turkey b Bingol University, Faculty of Health Sciences, Laboratory of Natural Product Research, 12000 Bingol, Turkey c Republic of Turkey, Ministry of Food Agriculture and Livestock, Çanakkale Food Control Laboratory Directorate, Atatürk Street No:33, 17100, Çanakkale, Turkey

ABSTRACT The synthesis, characterization and some physical properties of a new polyaniline derivate (PHCA), produced by Horseradish peroxidase (HRP)-initiated oxidative polymerization of 2hydroxy 5-chloro aniline (HCA), are presented. The spectroscopic measurements indicate that PHCA is consisted of a mixture of branched and linear aniline chain units. Data from antioxidant potential assays show that PHCA exhibits moderate DPPH radical scavenging activity but excellent metal ion chelating ability. The metal chelating ability of PHCA (82.14±2.39%) is higher about two times than that of EDTA (30.08±0.81%) at a concentration of 100 µg/mL. In addition, as a potent antioxidant stabilizer, the influence of PHCA on the thermooxidative degradation of polypropylene (PP) is also investigated. The insertion of PHCA to PP matrix improves significantly the both oxidation induction time (OIT) and onset oxidation temperature (OOT) of virgin PP. Keywords: Enzymatic polymerization, HRP, polyaniline, 2-hydroxy 5-chloro aniline, antioxidant activity, DPPH, ferric reducing ability, total phenolic To whom all correspondence should be addressed. Phone: +90 286 218 00 18 Fax: +90 286 218 05 33. e-mail: [email protected], [email protected] 1

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1. Introduction Amongst of conducting polymers, polyaniline and its derivates have gained considerable attention because of their fascinating optical and electrical properties1. They are used in a wide range of application areas including as in organic-field-effect transistors2, organic-light-emitting diodes3 and photovoltaic cells4 and lightweight batteries5,6. The practical applications of polyaniline and derivatives have not been limited with their optical and electrical properties. They are also gaining recognition for biomedical applications

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such

as artificial muscles13, controlled drug release14, nerve regeneration15. Aromatic amines are commercially avaible radical scavengers and they are often used for stabilization of polymer matrixes including polypropylene, polyethylene16-18. However, the use of stabilizers having small molecular weights could be cause their migration and evaporation from polymer matrixes19. It makes polymer surface oily and affects the physical and mechanical characteristics of industrial polymers, adversely19. Therefore, the polymeric antioxidants are used as the additives to minimize these defects17-18. Additives such as polypyrogallic acid19 and polyguaiacol20 were effectively used for these purposes. Phenol formaldehyde resins are also known as effective antioxidants for protection of plastics and rubber. However, health concern of formaldehyde limits its usage20. Polyaniline is another effective DPPH scavenger18. The potential role of polyaniline as an antioxidant is considered to slow down the rate of oxidation in polymer matrix21. Therefore, the polyanilines and their derivates are often incorporated into different polymers as additives10,18. Polymeric antioxidants are prepared by different methodologies. The chemical oxidation is one of the common used methods for the polymerization19. This method allows to gram scale polymer synthesis. However, major drawback of this method is its harsh synthetic conditions22: The 2


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experiments are often conducted in presence of stronger oxidants. The use of large amount of oxidizing agents in reactions is another undesirable situation22. The use of enzymes, especially in polymer synthesis, has become the focus of attention22-25 because the selective reactions are conducted under milder conditions with a high catalyst efficiency and producing minimal byproducts22. Further, it is a clean and eco-friendly process2629

. Therefore, it is used to obtain the polymeric antioxidants.

In this study, a novel polyaniline derivate, the poly(2-hydroxy 5-chloro aniline) (PHCA) is synthesized for the first time by (HRP)/H2O2-catalyzed oxidative coupling reaction and the spectroscopic characterization and some physical properties of oxidation product are presented. The antioxidant potential of PHCA is evaluated. Besides, the potent stabilizing effect of PHCA against the thermo-oxidative degradation of PP is investigated. 2. Experimental 2.1. Materials HRP (specific activity =259 purpurogallin units/mg and Rz= 3.0) was supplied from Sigma Chemical Company and it was used as received. The unstabilized PP (MH418 8080622) pellets were supplied from, Đzmir Aliağa, Petroleum Chemical Co. Ltd. HCA (97%), Ferrous chloride tetrahydrate (FeCl2.4H2O; 99.9%), potassium ferricyanide (K3Fe(CN)6; (≥99%), potassium persulfate (K2S2O8; %99.9) 2,2′- azinobis-(3-ethylbenzothiazoline-6-sulphonic acid)

(ABTS

>98%), and ferrozine (97%) were purchased from Sigma-Aldrich Inc. Ammonium thiocyanate (CH4N2S; ≥99%), trichloroacetic acid (TCA; ≥99.5%), 2,2-diphenyl-1-picrylhydrazyl (DPPH; ≥90%), gallic acid (≥98%), butylated hydroxyanisole (BHA; 98.5%), butylated hydroxytoluene (BHT; 99.5%), ethylenediaminetetraacetic acid (EDTA; 99.8%), trolox (≥98%), and iron (III)

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chloride (FeCl3; ≥98%) were purchased from Merck Chemicals Co. The standard solutions were prepared by using analytical grade solvents. 2.2. Characterization Techniques Ultraviolet–visible (UV–vis) measurements were conducted by Analytikjena Specord 210. Perkin Elmer FT-IR Spectrum One instrument (having ATR attachment) was used for FT-IR characterization of samples.1H-NMR spectrum of PHCA was recorded in Bruker Avance DPX400 instrument(solvent; deuterated DMSO and internal standard; tetramethylsilane). The molecular weight of product was revealed by Gel Permeation Chromatography-Light Scattering (GPC-LS) device of Malvern Viscotek GPC Dual 270 max. For GPC investigations a medium 300 x 8.00 mm dual column was used; as mobile phase (flow rate of 1 mL min- 1), 1% LiBr/dimethylformamide (DMF) was used. The measurements were performed using Light Scattering (LS) and refractive index detector (RID) and polystyrene standards. A Perkin Elmer Diamond Thermal Analysis was used for thermal characterization (between 15 and 1000 °C, in N2, 10°Cmin−1). DSC measurements were carried out using Perkin Elmer Pyris Sapphire DSC instrument (between 25 and 420°C; in N2, 10°C min−1). Oxidation Temperature (OOT) and Oxidation Induction Time (OIT) values for PP blends were determined by differential scanning calorimeter as reported in previous work19. A CH instruments 660C electrochemical workstation was used for cyclic voltammetry (CV) measurements. The measurements were performed using pseudo-reference electrode (Ag wire), counter electrode (Pt wire) and working electrode (platinum). The electrode system was immersed immersed in supporting electrolyte (1 M HCI). The scan rate was 100 mV/s. The measurements were conducted in room temperature (25°C). 2.3. Enzymatic polymerization of HCA 4


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Typical polymerization procedure is as follows29: 5 mmol of HCA and 5 mg HRP were dissolved in 0.01 M phosphate buffer (15 mL) and dioxane (35 mL) mixture. The initiation of polymerization was carried out by 5% aqueous hydrogen peroxide solution addition. After oxidant addition was completed (230 µL; for 1 h), the stirring was continued for 12 h. The volatiles were evaporated and the elution of product was conducted with distilled water and then ethanol. It was dried at 50°C (yield: 77%). 2.4. Determination of total phenolic content For these assays, the methods reported in the literature were used30,31. An aliquot of PHCA was prepared by dissolving 10 mg PHCA in the 10 mL ethanol:DMSO solvent system (ratio1:1; v:v) Then, the aliquots (100 µL) were taken into test tubes. The procedure was continued with the addition of distilled water (4.5 mL) and following 100 µL of reagent ( Folin–Ciocalteu). The each mixture was vortexed. After incubation (10 min.), the addition of Na2CO3 (3 mL; 20%;w:v) solution, stirring and heating processes ( in water bath, 40ºC, for 20 min.) were performed.. After stirring again, they were cooled to 25°C and finally, the measurements were taken at 760 nm. The each test was studied three times.The results were given as mg of gallic acid equivalent (GAE ) for g PHCA product. 2.5. Determination of antioxidant capacity 2.5.1. DPPH free radical-scavenging activity The method reported in the literature (Zovko Koncic et al.) was used for these tests32. The samples were prepared at different concentration ranges of 1-100 µg/mL. 2mM DPPH solution (in ethanol) was prepared in an erlenmayer flask and stirred for 3 hours. The outer surface of the erlenmeyer flask was covered with aluminum foil. The DPPH solutions (2.5 mL) were mixed

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with the sample solutions (0.5 mL) in the test tubes. After incubation of test tubes (30 min.), the absorbance measurements (517 nm) were obtained. The results were collected using the formula A (%) = (CA-NA/CA) x 100). In the formula, A is activity percentage, CA and NA are the absorbance values of the control and sample, respectively. For the calculation of the effective concentration (EC50) values of the samples, the activities of each sample were calculated by extrapolating graphic obtained. 2.5.2. Metal-ion chelating power The assays were conducted by measuring ferrozine-Fe2+ complex formation33. The samples were prepared at the various (1-100 µg/mL) concentrations. 2 mL of samples obtained were added to the iron (II) chloride (50 µL; 2 mM) solutions in the test tubes and they were vortexed. The test tubes were incubated for 50 minutes. They were additionally incubated for 10 min. after addition of ferrozine (100 µL; 5mM) solutions. Then, the absorbance measurements (562 nm) were performed. The results were calculated using the formula given for the DPPH assay. 2.5.3. Assay of reducing power The assays were performed by appliying a slightly modified Oyaizu method34. The experiments were conducted with the samples prepared at various (1-500 µg/mL) concentrations. The sample solutions (2.5 mL) were taken to test tubes and mixed with the phosphate buffer (2.5 mL, pH: 6,6) and following potassium ferrocyanide solutions (2.5 mL, 1% in water) and stirred, again. Then, the incubation (20 min., 50°C), the trichloroacetic acid addition (2.5 mL, 10% in water) and the centrifuging (1000 rpm, 8 min.) processes were conducted. The upper portion of the resulting mixture (5 mL), the distilled water (5 mL), the iron (III) chloride solutions (1 mL; 0.1% in water) were pipetted to tubes and mixed. The absorbance at 700 nm was obtained. 2.5.4. ABTS cation radical scavenging activity 6


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These tests were performed by using a slightly modified Re et al. method35. The phosphate buffer (pH: 7.4; 0,1 M) was used to dissolve the test reagents. The ABTS solution (7 mM in phosphate buffer) and potassium persulfate solution (2.45 M in phosphate buffer) were mixed in an erlenmeyer flask for 24 hours to produce the ABTS cation radicals. The outer surface of the erlenmeyer flask was covered with aluminum foil. The absorbance of the mixture containing the ABTS cation radicals was adjusted to 0.700 ± 0.02 at 734 nm. At various (1-600 µg/mL) concentrations of samples (0.1 mL) were transferred into test tubes and mixed with the ABTS cation radical solutions produced (1.9 mL). After incubation (10 min.), the absorbance values of samples at 734 nm were recorded using UV-VIS spectrophotometer. ABTS radical removing activity was calculated as DPPH assay tests. 2.5.5. Statistical analysis The each antioxidant test was conducted three times and the results are presented as mean ± SD (standard deviation). The differences between the samples were compared by using in a one-way analysis of variance (One-Way ANOVA) with a multiple-comparison (Post Hoc) Tukey HSD test. The difference was thought to be significant as p < 0.05. 2.6. Preparation of PP/PHCA blends The powdery PHCA and PP are blended with a co-rotating twin-screw extruder (DSM explore micro compounder). The screw speed is 150 rpm. The terminal temperature of extruder is 200°C. The quantity of PHCA in PP is 0.5 and 1%.

3. Results and Discussion 3.1. The characterization of PHCA HCA is a difunctional monomer (-OH and -NH2 groups) and it is derivate of 2-amino phenol. The chemical, electrochemical and enzymatic polymerization of 2-amino phenol were studied, 7



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extensively. Ladder like polymeric structures having intermediate phenoxazine units were suggested in these studies29,36,37. In this study, HCA is subjected to oxidative polymerization for the first time to best of our knowledge. HRP-catalyzed oxidative polymerization of HCA produce a purple colored polymer which was soluble DMF, NMP and DMSO, partially soluble methanol, ethanol, chloroform and insoluble in hexane, water. GPC analysis was conducted to determine of molecular mass of PHCA. DMF containing 1% LiBr (w/v) was used as eluent to reduce a possible aggregation38. The molecular mass values of PHCA, Mn, Mw,PDI, were estimated to be 5300 Da (about 37 repeating unit), 5400 Da and 1.01, respectively. The absorption spectra of HCA, PHCA are presented in Figure 1. HCA and PHCA exhibited absorption maxima at 303 nm and 447 nm, respectively. Insert Figure 1 Here Liu W. et al. reported that the HRP-triggered enzymatic oxidation of aniline produced different types of PANI structures39 (a mixture of branched and linear polyaniline structures). The band observed at 447 nm was assigned to branched polyaniline formation and harmony with the literature39. The optical band gaps (Eg) of compounds were measured from absorption spectra using Eg = 1242/λon equation, as described previously40 and Eg values of HCA and PHCA were 3.76 and 2.34 eV, respectively. Because of the increasing conjugation, PHCA had the lower band gap than that of HCA as expected. Figure 2 shows FTIR spectra of HCA and PHCA. Insert Figure 2 Here

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The peaks at 1494 and 1569, 1603 cm−1 belong to characteristic ring stretching of benzenoid (Nbenzene-N-) and quinoid (N=benzene=N) forms, respectively and harmony with the literature41. The intensive band appeared at 809 cm−1 was attributed to vibrations of out-of-plane C-H bendings for 1,4-disubstituted benzene skeleton42-44. The absorptions belong to ether (~1070 cm1

) and phenoxazine units (~575 cm-1) did not observed45.The peaks appeared at 851 and 809 cm-1

may be due to the existence of branched aniline units46. The peaks at 1190 and 1245 cm-1 are characteristics of the protonated form of PANI46. For further structural assignments, 1H NMR analysis was conducted (Figure 3). Insert Figure 3 Here The proton signals belong to phenyl ring were appeared between 6.2–8.4 ppm. The quinoid protons of PHCA were observed between 7.4 and 8.4 ppm whereas benzenoid protons of PHCA were observed high field area of spectrum between 6.2 and 7.2 ppm. The broad signals centered at 5.2 ppm can be attributed to -NH-protons. From these spectral observations, the possible structure for oxidation product should be a mixture of PANI derivate consisting of Unit A and Unit B as suggested by Liu W. et al. 39 (as shown in Figure 4). Insert Figure 4 Here It should be also noted that the enzymatic polymerization of aromatic monomer often yields undesired branching polymer structure. To minimize branching and obtain a more linear polymer, polymerization is often conducted in the presence of a polyelectrolyte templates39,47-49. Using an appropriate template, a linear polyaniline derivate can be obtained. TG and DSC analysis were conducted for thermal characterization of PHCA. The thermograms (TG-DTG-DTA) of PHCA recorded in nitrogen atmosphere are shown in Figure 5. Insert Figure 5 Here 9



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The thermograms indicate a three-main-step decomposition pattern. Thermal degradation of PHCA begins with an evolution of water (3.5% mass loss at temperatures up to 140°C), followed by exclusion of hydroxyl groups and chlorine atoms (20% mass loss at temperatures between 220-320°C). The mass losses in these range are also due to evaporation of dopant molecules in polymer and gradually mass losses at higher temperatures (400-1000°C) are attributed to decomposition of polymer main chain)50. The high char residue at 1000°C was observed as 53%. The similar type of thermal behaviour was also reported for other polyaniline derivates, such as poly(o-hydroxy aniline)51, poly(o-chloroaniline)52 and poly(N-ethylaniline)53. For comparison, TG analysis of HCA (not presented here) was also recorded in the same experimental conditions. HCA decomposes at 153°C. However, ~2.5% of PHCA is decomposed at 180°C. This assigns that PHCA is reasonably stable between 165 and 180°C ( processing temperature of PP)20. In other word, PHCA could be a possible candidate as additive for PP stabilization20. The cyclic voltammogram of the PHCA is recorded in 1 M HCl and given in Figure 6. Insert Figure 6 Here The oxidation peak of the PHCA is observed at 0.23 V and its reduction peak is observed at 0.2 V, which assigns to be a reversible process. The chemically and electrochemically prepared polyanilines are often characterized by two anodic and two cathodic peaks49,54. However, it was reported that the enzymatically synthesized polyaniline exhibited one oxidation peak49. The second peak was not observed possibly due to oxidation of PHCA to the pernigraniline state49. 3.2. Antioxidant assays for PHCA The antioxidant activities of polyphenols can be given through two basic mechanisms: The first is the removal of the free radicals with the transfer of hydrogen atom (THA) or single electron 10


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(TSE); the second is the inhibition of free radicals by chelation of the transition metals in the reaction medium55,56. For example, DPPH is a free radical with purple colored and can be transformed into to a colorless neutral molecule by taking up hydrogen atoms from suitable hydrogen donor. In the similar way, the polymeric substances can act in the chelating behavior of ferrous ions in the reaction medium56. The transition metals are the powerful pro-oxidant sources which initiate oxidative changes (for example: the formation of free radicals) in cellular elements57. The metal chelating capacity of polymeric materials is very important as they can deactivate the catalysis of transition metals. Therefore, polymeric substances can act as both radical scavengers and chelating agents56. Further, in many studies, a positive relationship was observed between the degree of polymerization and antioxidant activity of polymeric products. For example, Spranger et al.58 reported that the antioxidant activities of catechins varied in following order: polymer> oligomer >monomer. A similar effect was explained by Yamaguchi et al.59. They reported that the phenolic compound having the highest degree of polymerization exhibited the highest antioxidant activity59. Polyaniline derivates are known as efficient antioxidant stabilizers as stated above. Therefore, the antioxidant assays for PHCA were performed in this study. The antioxidant activities of the samples were evaluated by examining four different antioxidant activity parameters; DPPH free radical scavenging, ABTS cation radical scavenging, metal-ion chelating power (MCP) and reducing power activity (RPA). Figure 7a shows the DPPH free radical scavenging activity of HCA and its oxidation product as well as BHA and BHT. As can be seen figure 7a, all tested compounds and PHCA exhibited a remarkable concentrationdependent activity. Insert Figure 7 Here 11



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The antioxidant activities of HCA and PHCA against the DPPH radicals were 82.55 ± 0.58 and 47.22 ± 2.15%, respectively, for a concentration of 100 µg/mL. (Figure 7a). However, DPPH free radicals scavenging abilities of BHA and BHT were 73.72± 0.78 and 67.49 ± 1.02%, respectively at the corresponding concentrations. It seemed that DPPH radical scavenging potencies of polymeric product and synthetic reference antioxidants were comparable. At concentration of 100 µg/mL, both HCA and PHCA were chelated the ferrous ions by 74.42 ± 0.55 and 82.14 ± 2.39%, respectively, whereas chelating ability of EDTA, fabulous chelating agents, was 30.08 ± 0.81% at the same concentration (Fig.7d). The high absorbance value in the reducing power activity assays indicates a high reducing power. The reducing power activities of HCA, BHA and BHT showed a rapid increase with increasing concentration while the PHCA showed a slower increase (Fig.7c). At concentration of 500 µg/mL, HCA, BHA and BHT showed reducing power activities with absorbance values of 0.901 ± 0.016, 0.701 ± 0.001 and 0.653 ± 0.005, respectively, whereas reducing power activity of PHCA was 0.091 ± 0.007 at the same concentration. Figure 7b shows the plot of the scavenging activity of ABTS cation radicals. While a marginal activity of only 4.83 ± 0.96% was appeared at a concentration of 1 µg/mL in PHCA, this activity increased up to 36.86 ± 1.76% at concentrations of 600 µg/mL PHCA (Fig.7b). This antioxidant potency can be comparable with BHT, reference antioxidant agent, which exhibiting an antioxidant activity with value of 56.21 ± 0.81% at the concentration of 600 µg/mL. The effective concentration (EC50) values of the samples were given in Table 1 to compare antioxidant activity test results. Insert Table 1 Here

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To obtain EC50 values, the activity values of the samples were plotted at different concentrations and then, EC50 values were determined by extrapolating of the graphics. The inverse correlation is observed between EC50 value and the effectiveness in antioxidant properties60. Accordingly, the different antioxidant activity test parameters performed suggests that the PHCA may be a moderate antioxidant product capable of scavenging free radicals. As known, o-hydroxy azomethine monomer and polymers have high chelating capacities due to their ability to form stable ring formation with metal ions. Therefore, the excellent chelating ability of PHCA is attributed to formation of o-hydroxy azomethine moieties in its structure (Figure 4, Unit B). The DPPH radical scavenging activities are related to the hydrogen donating abilities of studied molecules. Therefore, the relatively low DPPH radical scavenging potencies of PHCA compared to HCA are attributed to high hydrogen binding ability of azomethine group in the polymer structure (formation of stable intramolecular hydrogen binding). This stable structure may be hinder to combine of hydrogen atoms of PHCA with the DPPH radicals and resultantly, may reduce to scavenging ability of DPPH radicals. In this study, the standard graph of gallic acid was used to find the total amount of phenolic compounds in the polymeric product (PHCA). The equation was obtained from graph as y = 44.9x + 0.0307 and R2= 0.9956. Using the obtained graphical equation, the total phenol content in 1 g PHCA was given as mg gallic acid equivalent (mg GAE /g PHCA). PHCA had total phenol content with a value of 1.97 ± 0.03 mg GAE/g PHCA. 3.3. Thermal behaviours of PHCA stabilized PP blends Figure 8 indicates the TG curves of PHCA stabilized PP blends. Insert Figure 8 Here 13



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The TG data are also given in Table 2. Insert Table 2 Here As seen figure 8 and Table 2, the decomposition temperatures of PHCA stabilized PP blends were higher than those of neat PP. The insertion of PHCA into PP matrix improved the thermal stability of PP. Cui Y. and coworkers studied thermal stability of pyrogallic acid stabilized PP19 and polyguaiacol stabilized PP20. Onset Oxidation Temperature (OOT) and Oxidation Induction Time (OIT), are two important parameters for evaluating of PP stability under oxidative conditions19,61. OIT is given as the passing duration before the sample oxidation begins19 and it is accepted that higher OOT and OIT values indicate more efficient PP stabilization19,61. Therefore, these parameters are often used for comparison of stabilizer performances. The DSC curves of PP/PHCA blends are shown in Fig. 9. Insert Figure 9 Here As seen from Figure 9, OIT of PP increases as PHCA content in PP increases. OIT value for 1% PHCA stabilized PP blend was found to be 3.53 minutes. OIT values of pyrogallic acid stabilized PP19 and polyguaiacol stabilized PP20 were found to be 17.2 and 4.28 minutes under oxidative atmosphere. OIT values of PHCA stabilized PP were lower than those of pyrogallic acid stabilized PP and comparable with polyguaiacol stabilized PP. The lower OIT values of PHCA may be explained by co-existence of different factors: phenol content, molecular weight or geometric structure of studied molecule. It is noted that the synthesized polymer in here had low phenol content. Therefore, the lower phenol content of PHCA may be responsible for its lower OIT values.

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It should be noted that the melting peaks of PP blends observed at 168°C did not change, importantly. It was also observed that the OOT values of PHCA stabilized PP blends were higher (about 50°C) than those of neat PP. The possible explanation for this was suggested Ke Zheng et al. and the others19,61. According to them, these additives are functional structures carrying active –OH and -NH2 groups and they are known as effective hydrogen donors to quench free radicals and thus prevent the of PP chains from oxidation reactions19,61. 4. Conclusion A novel polyaniline derivate, poly(2-hydroxy 5-chloro-aniline), was synthesized via enzymatic protocol for the first time. A polymer structure (PHCA) composed of a mixture of linear and branched aniline chains was suggested. From absorption spectrum, it was found that PHCA had an optical band gap of 2.34 eV. The antioxidant assays showed that PHCA had excellent metal ion chelating ability. The potential antistabilizer effect of PHCA against the thermooxidative decomposition of PP was investigated. It was understood that the both OIT and OOT values of PP/PHCA blends were higher than those of neat PP. In addition, only 2.5% of PHCA was decomposed in the processing temperature range of polypropylene although HCA was almost decomposed in this temperature range and this made PHCA a potential candidate for PP stabilization. Acknowledgement: Authors thank to The Scientific and Technical Research Council of Turkey (TUBĐTAK) for their support (Project No: 215M074).

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CAPTIONS OF FIGURES AND TABLES Figure 1. Normalized UV-vis spectra of HCA (a), and PHCA (b) in DMSO (0.3mg sample/1mL solvent) Figure 2. FTIR spectra of HCA (a) and PHCA (b) (Around 5 mg sample was used). Figure 3. 1H-NMR spectrum of PHCA in d6-DMSO. Figure 4. Possible polymer structure suggested. (A: Random-branched chain structure (C-C and C-N linkages at the different positions) and B: Linear polyaniline structure) Figure 5. TG-DTG-DTA curves of PHCA. Figure 6. The cyclic voltammogram of PHCA . Figure 7 Anti-oxidant activity scores at different concentrations of HCA and PHCA (a) DPPH radical scavenging activity; (b) ABTS cation radical scavenging activity; (c) Reducing power activity (RPA); (d) Metal-ion chelating power (MCP). Butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), Ethylenediaminetetraaceticacid (EDTA) and Trolox used as reference antioxidant agents. Figure 8. TG curves of virgin PP (a) and 0,5% (b) and1% (c) PHCA stabilized PP blends Figure 9. DSC curves of virgin PP (a) and 0,5% (b) and1% (c) PHCA stabilized PP blends Table 1. Antioxidant activity of HCA, PHCA and reference antioxidant substances. Table 2. The decomposition parameters for samples at heating rate of 10 °C/min.

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Figure 1.

Figure 2.

24


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Figure 3.

Figure 4.

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Figure 5.

Figure 6.

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(a)

(b)

(c)

(d)

Figure 7

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Figure 8.

Figure 9.

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Table 1. EC50 (µg/mL)

mg GAE/g PHCA

DPPH

ABTS

RPA

MCP

HCA

17.16 ± 0.10a

205.06 ± 0.85a

247.61 ± 0.75a

29.21 ± 0.10b

PHCA

85.85 ± 4.96d

>600d

>500d

200c

Trolox

-

261.22 ± 1.28b

-

-

TPC

1.97 ± 0.03

Values are given as the mean± standard deviation of three independent studies. The different numbers in the same column are statistically different (p

Biocatalytic Synthesis of a Novel Polyaniline Derivative and Its Usage

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