pH-Triggered Release of Boron and Thiamethoxam from Boric Acid Crosslinked Carboxymethyl Cellulose Hydrogel Based Formulations PDF

Polymer-Plastics Technology and Materials ISSN: 2574-0881 (Print) 2574-089X (Online) Journal homepage: www.tandfonline.com/journals/lpte21 pH-triggered Release of Boron and Thiamethoxam from Boric Acid Crosslinked Carboxymethyl Cellulose Hydrogel Based Formulations Dhruba Jyoti Sarkar & Anu...

Polymer-Plastics Technology and Materials ISSN: 2574-0881 (Print) 2574-089X (Online) Journal homepage: www.tandfonline.com/journals/lpte21 pH-triggered Release of Boron and Thiamethoxam from Boric Acid Crosslinked Carboxymethyl Cellulose Hydrogel Based Formulations Dhruba Jyoti Sarkar & Anupama Singh To cite this article: Dhruba Jyoti Sarkar & Anupama Singh (2019) pH-triggered Release of Boron and Thiamethoxam from Boric Acid Crosslinked Carboxymethyl Cellulose Hydrogel Based Formulations, Polymer-Plastics Technology and Materials, 58:1, 83-96, DOI: 10.1080/03602559.2018.1466165 To link to this article: https://doi.org/10.1080/03602559.2018.1466165 View supplementary material Published online: 29 May 2018. Submit your article to this journal Article views: 864 View related articles View Crossmark data Citing articles: 6 View citing articles Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=lpte21 POLYMER-PLASTICS TECHNOLOGY AND MATERIALS 2019, VOL. 58, NO. 1, 83–96 https://doi.org/10.1080/03602559.2018.1466165 pH-triggered Release of Boron and Thiamethoxam from Boric Acid Crosslinked Carboxymethyl Cellulose Hydrogel Based Formulations Dhruba Jyoti Sarkar and Anupama Singh Division of Agricultural Chemicals, Indian Agricultural Research Institute, New Delhi, India ABSTRACT KEYWORDS Boric acid crosslinked carboxymethyl cellulose hydrogels were synthesized to develop pH-trig- Boric acid; carboxymethyl gered release formulations (pH-TRFs) of boron and thiamethoxam. The developed hydrogels cellulose; hydrogel; showed pH sensitive water absorption capacity (16.75 to 110.80 g/g xerogel). Entrapment of thiamethoxam; triggered release formulations thiamethoxam was done through an ex-situ loading technique. The boron and thiamethoxam release was studied in pH buffer solutions (4.0, 7.0 and 9.2). Release kinetics analysis using mathematical models showed fast release in high pH solution as compared to acidic pH. These pH-TRFs may find usefulness in selective release of nutrients and pesticides in plant rhizospheric zone of problem soils viz. acidic soils and alkaline soils. GRAPHICAL ABSTRACT CONTACT Dhruba Jyoti Sarkar [email protected] Division of Agricultural Chemicals, Indian Agricultural Research Institute, New Delhi 110012, India Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lpte. Supplemental data for this article can be accessed here. © 2018 Taylor & Francis 84 D. J. SARKAR AND A. SINGH 1. Introduction of B is required. To address this pH controlled B avail- Delivery of pesticide along with plant nutrients through ability in soil, the present formulation approach was single carrier approach is not a new concept. Several conceptualized which will selectively accelerate the previous reports are available where pesticides and plant release of B under alkaline pH condition to maintain nutrients are combined together and reported to have the optimum plant availability. In addition to that a higher efficacy as compared to their separate applications systemic insecticide, thiamethoxam, was loaded in the [1, 2]. In the present manuscript, it is conceptualized to hydrogel matrix to integrate nutrient and insect pest develop a smart hydrogel carrier system, using plant control strategies. nutrient as one of the structural components of hydrogel and ex-situ loading of crop protection chemical, for com- bined delivery of crop nutrients and protection chemicals 2. Experimental along with advanced triggered release phenomena. The 2.1. Chemicals advantage of triggered release phenomena includes on Boric acid (BA) (H3BO3) and Sodium carboxymethyl demand delivery of biologically active ingredient (a.i.) to cellulose (CMC) (1100-1900cps) were procured from the target site. Ionic hydrogels have been recognised as Merck Specialties Pvt. Ltd., Mumbai, India and used smart responsive materials for developing triggered as received without further purification.Thiamethoxam release formulations (TRFs) due to their 3-D network technical grade, 96.5%,m/m was obtained through the properties and stimuli (pH, temperature, enzyme, etc.) courtesy of United Phosphorous Ltd., India. For rou- sensitive water swelling and release properties [3–5]. In tine work, analytical grade and for HPLC analysis, our previous work, use of citric acid crosslinked carbox- HPLC chemicals and solvents were used, respectively. ymethyl cellulose (CMC) hydrogels were reported as a carrier for TRFs of thiamethoxam intended to release selectively in the alkaline gut of lepidopteran pest. 2.2. Synthesis of boric acid crosslinked CMC The CMC based hydrogels showed responsive behavior hydrogels (BA-CMCs) towards external stimulus, like pH, due to the presence of anionic functional groups (-COO− and -OH) in the poly- The hydrogels (BA-CMCs) were synthesized by cross- mer chain. These anionic groups caused rapid swelling linking CMC with BA using a method reported earlier of hydrogels under alkaline pH condition due to the. Briefly, a solution of CMC (500 mg/mL) was production of large ion swelling pressure. Similarly, in prepared in distilled water (20 mL) and weighed quan- acidic pH, these hydrogels showed lower swelling due to tities of BA was added to it to achieve different con- reduction in the ion swelling pressure. This differential centrations of BA in the final reaction mass (Table 1). swelling response under varied pH conditions makes The reaction mass was stirred mechanically (Remi CMC hydrogels as a smart tool for triggered delivery of Motor, 1000 rpm) for 1 hr till a homogenous mixture bioactive agents. is formed followed by partial dehydration using vigor- Boric acid was reported extensively as a crosslinking ous stirring (3000 rpm) for 2 hr in acetone (100 mL). agent for PVA based hydrogel matrix [9, 10]. Borate The dehydrated feed mass was filtered and heated to ion (BO3−3) was reported to enhance the barrier prop- 110°C for 4 hr till constant weight (Supplementary erties of poly(vinyl alcohol)-graphene oxide composite Material Figure S1).The percent yield of dried gel film. Our previous work reported that in-situ load- mass (xerogel) was calculated by the following ing of borax in CMC-g-cl-Poly(Am) hydrogels led to equation: significant enhancement of viscoelastic properties due Wx Yield ð%Þ ¼  100 (1) to BO3−3 crosslinking of hydroxyl moieties of CMC WT. This finding led us to envisage boric acid cross- linked CMC hydrogels and its possible use in smart delivery of crop nutrients and protection chemicals. Here, Wx and WT are the weight of obtained xerogel Among the crop nutrients, deficiency of boron (B) is and combined dry weight of CMC and BA, respectively. widespread throughout the world [13, 14] and to miti- gate that boric acid is applied as fertilizer [15, 16]. In 2.3. Swelling investigation acidic soil the availability of B is high [17, 18] and application of a high dose of Boric acid may lead to B Accurately weighed powdered BA-CMCs (0.1 g, particle toxicity in crops.Contrarily in alkaline soil coupled size: 63–74 µm) was taken in a nylon bag and immersed in with low soil moisture and calcareous nature, availabil- an excess of buffer solution (100mL) of pH 4.0, 7.0 and 9.2 ity of B to plant is very low [17, 18] and higher supply in triplicate at 30 ± 2°C until equilibration was attained.  POLYMER-PLASTICS TECHNOLOGY AND MATERIALS 85 Table 1. Effect of BA on yield and swelling parameters of BA-CMCs. Mt ¼ 1  e τ 1 QH2O M1 BA-CMC Yield Hydrogels BA (µmol/mL) (%) pH 4.0 pH 7.0 pH 9.2 τ R2 SSR AB A A AB BA-CMC-1 0.484 94.50 15703.67 16922.50 19680.67 4.13 0.99 0.0005 BA-CMC-2 0.645 94.67AB 15668.11A 17082.00A 20825.22A 4.42 0.99 0.0005 BA-CMC-3 0.806 97.05A 10733.22B 12500.00B 16497.11B 4.97 0.99 0.0008 BA-CMC-4 4.032 97.27A 4459.67C 6487.67C 8532.67C 5.36 0.99 0.0010 BA-CMC-5 40.322 98.04A 3193.33CD 5633.00C 8030.33CD 5.98 0.99 0.0009 BA-CMC-6 80.645 96.12AB 2778.67D 5473.33C 6946.33CD 6.59 0.99 0.0008 BA-CMC-7 241.935 87.70B 1675.00D 3820.33C 4849.67D 7.19 0.99 0.0003 p-value 0.0029 BA-CMC-6 (28.91%) > BA-CMC-7 (17.90%). p-Value BA- CMC-6 (91.52%) > BA-CMC-7 (87.09%). The ability of 3.5. In vitro B release behavior of BA-CMCs Mt BA-CMC-7 to resist fractional B release ( M 0 ) as com- To cater the objective of present study i.e. to develop pared to others at highly alkaline pH can be explained formulations with an ability to release B triggered by by the presence of high crosslinking density, imparted basic pH, the release profile of the developed BA-CMCs by the high loading of BA, in the hydrogel matrix [44, was studied in water with different pH (4.0, 7.0 and 45]. The role of borate ion in increasing crosslinking 9.2). Soil is a very heterogeneous system with inherent density of hydrogel matrix was documented extensively buffering capacity and to simulate acidic soil (pH 2.5– in previous reports [10, 12]. 5.5), normal soil (pH 6.5–7.5) and alkaline soil (pH 8.0–10.0) pH buffer 4.0, 7.0 and 9.2 was selected, 3.6. In vitro thiamethoxam release behavior of BA- respectively. The cumulative release of B (µg B/g of CMC-Ts CA-CMCs) from the BA-CMCs at all the pH condi- tions followed the trend: BA-CMC-7> BA-CMC-6> Thiamethoxam is a neonicotinoid group of insecticide BA-CMC-5> BA-CMC-4> BA-CMC-3 with broad spectrum systemic activity. Controlled (Supplementary Material Figure S3). This reducing release formulations of thiamethoxam were reported trend of cumulative release from BA-CMC-7 to BA- extensively in view of highly toxic nature of same CMC-3 was due to differential loading of B in the towards nontarget organisms, especially to honey bees hydrogel matrix (Table 2). BA-CMCs with higher B [21, 46]. Amphiphilic block copolymers were reported content showed maximum cumulative release (µg B/g to encapsulate thiamethoxam in nanomicelle with con- of BA-CMCs) as compared to lower B loaded BA- trolled release properties. Some hydrogel based CMCs. Figure 3 depicts the influence of BA crosslink- formulations of thiamethoxam were also reported Mt ing on the release kinetics (fractional, M 0 ) of B from with differential release properties [6, 41]. In the pre- BA-CMCs in water of different pH (4.0, 7.0 and 9.2). It sent study kinetics of thiamethoxam release from the was observed that increase in BA content led to corre- developed BA-CMC-Ts was studied in different pH sponding slower release of B from BA-CMCs and the conditions (pH, 4.0, 7.0 and 9.2). The cumulative (µg Mt effect was more pronounced particularly at pH 4.0 and thiamethoxam/g of BA-CMC-Ts) and fractional ( M 0 ) 7.0. Similar phenomenon was reported previously, release trend of thiamethoxam from the BA-CMC-Ts at where higher loading of borax (Na2B4O7. 10H2O) in all the pH conditions were similar, as the amount of CMC-g-cl-PAam hydrogel matrix led to slower release loaded thiamethoxams in all the BA-CMC-Ts was of B. At pH 4.0 on 13th day, BA-CMC-3 released nearly same (Table 2). The periodic release of thia- maximum (82.68%) of loaded B followed by BA-CMC- methoxam in water from the prepared BA-CMC-Ts 4 (76.92%) > BA-CMC-5 (30.82%) > BA-CMC-6 formulations is shown in Supplementary Material 92 D. J. SARKAR AND A. SINGH Figure S4. The amount of thiamethoxam released at the kinetic release data were fitted to Korsmeyer- Peppas time interval was measured by HPLC. It was observed model (Eq. (7)), First order model (Eq. (8)) and Gallagher– that similar to the B release profile, the rate of release of Corrigan model (Eq. (9)). Table 3 shows kinetic para- thiamethoxam from the BA-CMC-Ts was lower in meters, R2 and SSR values of all batches of B release data. acidic pH (4.0), medium at neutral pH 7.0 and much The values of R2 of Korsmeyer-Peppas model (Eq. (7)) higher at basic pH condition (9.2). At pH 4.0 on 3rd fitted to B release data were low in all the formulations day, maximum thiamethoxam was released by BA- under all pH conditions. Depending on the release expo- CMC-5 (62.03%) followed by BA-CMC-6 (52.49%) > nent value (n) which is less or near the value of 0.5, it can be BA-CMC-7 (41.68%). At pH 7.0, BA-CMC-Ts released postulated that release was driven by Fickian diffusion. more amount of thiamethoxam and on 3rd day max- However, since this model did not fit sufficiently to the imum was released by BA-CMC-5 (79.69%) followed release data, it is inappropriate to elucidate the mechanism by BA-CMC-6 (72.91%) > BA-CMC-7 (51.61%). At pH of B release from the BA-CMCs on the basis of this model. 9.2 due to high ion swelling pressure and may be of fast Similar to Eq. (7), release data of B from BA-CMCs did erosion effect of the hydrogel matrix, the rate of thia- not fit well to the first order kinetic model (Eq. (8)). As the methoxam release is high and on 3rd day maximum first order kinetic equation describes the dissolution of an release was achieved by BA-CMC-5 (86.45%) followed bioactive compound not effectively enclosed in a poly- by BA-CMC-6 (78.26%) > BA-CMC-7 (63.97%). The meric matrix , it can be inferred that B was encapsu- role of BA in increasing the crosslinking density of BA- lated tightly in the hydrogel matrix which is evident from CMCs was evident by observing the reduced release the crosslinking of CMC with B source i.e. BA. The best fit rate of thiamethoxam with the increase in concentra- model which describes the kinetic profile of B release tion of BA in BA-CMCs matrix. In contrast to the from BA-CMCs was Gallagher-Corrigan equation (Eq. (9)) with high R2 value and low SSR as compared to observations recorded in previously reported citric other models (Eq. (7) and Eq. (8)) (Figure 4). This acid crosslinked CMC-bentonite hydrogel composite model describes an initial ‘burst release’ of an entrapped formulations where entire load of thiamethoxam was compound non-bound to the polymeric matrix and fol- released within 24hr , the present work reports much lowed by slow release determined by the matrix erosion or slower release of thiamethoxam from the developed Fickian diffusion. The rate constant (k1) of the initial stage BA-CMC-Ts from 7 to 14 day depending upon the of B release increases with an increase in pH of release pH of release medium and BA content. This effect medium. k1 for pH 4.0 and 7.0 is very less as compared to might also because of the presence of different salts pH 9.2 which might be due to the fast release of B at the and other buffer constituents in the release medium initial stage from the BA-CMCs due to higher ion swelling which was absent in the previous report. However, pressure and erosion effect of the hydrogel matrix. It was in the present study, the presence of buffer salts and also observed that at pH 4.0 and 7.0 though k1 is low for other constituents in release medium simulate the soil all the composition, the fraction MM1t of B released at solution more precisely than pure water. This slow B stage I is much higher than stage II. release trend of thiamethoxam from the BA-CMC-Ts Table 4 shows kinetic parameters, R2 and SSR values fit them into the traditionally controlled release pesti- of all batches of thiamethoxam release data. Among the cide formulations where the release of loaded pesticides three models, the best fit model for describing the was extended to several days [21, 47]. Similar to pre- release of thiamethoxam from BA-CMC-Ts is also Eq. sently reported hydrogel based thiamethoxam formula- (9) with high R2 value and low SSR (Supplementary tions, amphiphilic polymer based thiamethoxam Material Figure S5). Nearly in all cases, the rate con- formulations were reported with extended slow release stant (k1) for the initial stage (Stage I) increases with properties for around 10 to 15 days. Synthetic hydrogel the increase in pH from 4.0 to 9.2 which conclude (polyacrylamide) based bait formulation of thia- faster release rate of thiamethoxam from BA-CMC-Ts methoxam (0.007%) was reported with enhanced insec- under basic pH condition. Compliance of thia- ticidal activity due its slow water diffusion properties methoxam release data with Eq. (9) under acidic and over extended time period. neutral pH conditions conclude that under these con- ditions there are mainly two steps in release mechan- 3.7. Mechanism and mathematical modeling of ism, firstly burst release of loosely trapped boron and thiamethoxam release thiamethoxam from the surface layers upon imbibition To investigate the mechanism of B and thiamethoxam of swelling medium and secondly swelling controlled release from the BA-CMCs and BA-CMC-Ts respectively, diffusional release of dissolved thiamethoxam. Table 3. Effect of pH on release kinetic parameters of boron from BA-CMCs. Korsmeyer–Peppas First Order Gallagher-Corrigan k Mt kf Mt k1 t2max k2 Formulations pH (Day−n) n R2 SSR M1 max (Day−1) R2 SSR M1 B (Day−1) (Day) (Day−1) R2 SSR BA-CMC-3 4.0 0.15 0.65 0.94 0.048 1.07 0.12 0.99 0.015 1.25 0.15 0.001 0.18 0.99 0.005 7.0 0.52 0.27 0.59 0.536 0.99 0.95 0.83 0.231 3.09 0.53 2.07 0.93 0.87 0.172 9.2 0.97 0.01 0.57 0.001 0.99 9.18 0.98 8.0 x 10−5 0.97 27.08 0.00 0.02 0.98 8.65 x 10−5 BA-CMC-4 4.0 0.35 0.34 0.82 0.086 0.84 0.45 0.89 0.089 0.55 0.09 0.63 23.49 0.98 0.009 7.0 0.51 0.28 0.63 0.482 1.01 0.87 0.85 0.196 2.31 0.69 1.69 1.23 0.89 0.145 9.2 0.99 0.003 0.93 1.65 x 10−5 0.99 10.58 0.91 12.0 x 10−5 0.97 54.45 0.00 0.09 0.92 1.47 x 10−5 BA-CMC-5 4.0 0.18 0.28 0.87 0.008 0.34 0.78 0.77 0.027 0.65 0.02 0.99 0.04 0.92 0.004 7.0 0.24 0.41 0.97 0.012 0.74 0.24 0.93 0.033 0.75 0.06 0.47 10.51 0.99 0.001 9.2 0.93 0.02 0.91 6.7 x 10−4 0.97 5.70 0.29 5.5 x 10−3 0.84 47.61 0.45 0.25 0.94 4.60 x 10−4 BA-CMC-6 4.0 0.08 0.35 0.89 0.002 0.21 0.59 0.98 0.001 0.82 0.002 1.00 1.13 0.99 1.7 x 10−4 7.0 0.13 0.30 0.93 0.004 0.27 0.79 0.85 0.010 0.79 0.007 1.00 1.09 0.98 0.008 9.2 0.91 0.03 0.99 1.3 x 10−4 0.96 4.95 0.55 7.8 x 10−3 0.78 29.10 0.00 0.30 0.99 1.80 x 10−4 BA-CMC-7 4.0 0.06 0.17 0.73 0.0006 0.08 1.30 0.95 0.0003 0.92 0.0003 0.35 0.83 0.78 0.0005 7.0 0.09 0.26 0.82 0.004 0.16 1.13 0.94 0.0015 0.87 0.003 0.49 8.22 0.97 6.3 x 10−4 9.2 0.86 0.04 0.94 0.001 0.91 5.17 0.59 9.4 x 10−3 0.71 22.19 0.00 0.10 0.98 3.50 x 10−4 Mt Mt n, Release exponent and k, rate constant in Eq. (1); M1 max , Maximum fraction released and kf, first order rate constant; k 1 and k2 are the kinetic constants, M1 B , fraction released in stage I andt2max, the 2, time of maximal rate of release during stage II in Eq. (3); R Coefficient of determination; SSR, Sum of square residual. POLYMER-PLASTICS TECHNOLOGY AND MATERIALS 93  94 D. J. SARKAR AND A. SINGH Table 4. Effect of pH on release kinetic parametersof thiamethoxam from BA-CMC-Ts. Korsmeyer–Peppas First Order Gallagher-Corrigan k Mt kf Mt k1 t2max k2 Formulations pH (Day−n) n R2 SSR M1 max (Day−1) R2 SSR M1 B (Day−1) (Day) (Day−1) R2 SSR BA-CMC-5-T 4.0 0.42 0.25 0.91 0.033 0.66 1.98 0.91 0.032 0.516 0.07 0.19 15.38 0.99 0.003 7.0 0.63 0.20 0.76 0.145 0.88 4.20 0.94 0.360 0.822 4.85 8.09 0.70 0.98 0.014 9.2 0.62 0.22 0.83 0.106 0.89 3.89 0.83 0.112 0.075 0.00 0.48 1.96 0.78 0.142 BA-CMC-6-T 4.0 0.37 0.26 0.90 0.028 0.61 1.51 0.93 0.019 0.562 0.05 0.22 16.01 0.97 0.007 7.0 0.46 0.26 0.89 0.053 0.78 1.42 0.97 0.015 0.449 0.09 0.23 16.56 0.98 0.008 9.2 0.51 0.29 0.94 0.042 0.93 1.17 0.93 0.053 0.738 2.10 6.62 0.70 0.99 0.010 BA-CMC-7-T 4.0 0.28 0.29 0.92 0.016 0.52 0.88 0.96 0.008 0.582 0.02 0.61 2.49 0.95 0.011 7.0 0.38 0.31 0.96 0.019 0.74 0.72 0.96 0.016 0.466 0.06 0.66 1.91 0.96 0.015 9.2 0.49 0.23 0.99 0.003 0.79 1.31 0.86 0.047 0.562 0.14 0.00 3.93 0.99 0.002 Mt Mt n, Release exponent and k, rate constant in Eq. (1); M1 max , Maximum fraction released and kf, first order rate constant; k1 and k2 are the kinetic constants, M1 B , fraction released in stage I andt2max, the time of 2, maximal rate of release during stage II in Eq. (3); R Coefficient of determination; SSR, Sum of square residual.  POLYMER-PLASTICS TECHNOLOGY AND MATERIALS 95 Compliance of Eq. (9) with the release data of pH 9.2 Film as a Cross-Linking Agent: Melting Behaviors of can be explained by the addition of erosion controlled the Films with Boric Acid. Polymer. 2010, 51(23), release of thiamethoxam as a third step. 5539–5549. DOI:10.1016/j.polymer.2010.09.048. Miyazaki, T.; Takeda, Y.; Hoshiko, A.; Shimokita, K.; 4. Conclusions Ogomi, D. 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