Preparation of Antibacterial Softwood via Chemical

Feb 9, 2016 - ... attachment of QACs to the cell walls by providing easy access of QACs. .... mass spectroscopy facility manager, the department of Ch...
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Research Article pubs.acs.org/journal/ascecg

Preparation of Antibacterial Softwood via Chemical Attachment of Quaternary Ammonium Compounds Using Supercritical CO2 William Z. Xu, Lijuan Yang, and Paul A. Charpentier* Department of Chemical and Biochemical Engineering, University of Western Ontario, 1151 Richmond Street, London, Ontario N6A 5B9, Canada S Supporting Information *

ABSTRACT: Conversion of inexpensive and abundant softwood into useful construction materials is of significant economic and environmental importance. The currently available methods for wood treatment are not sufficiently effective to overcome the drawbacks of softwood including warping and biodeterioration. In the present research, a novel process was developed to address these challenges by chemically attaching antibacterial quaternary ammonium compounds (QACs) to hemlock using supercritical carbon dioxide (scCO2). Nine QACs containing at least one hydroxyl group were synthesized and characterized by 1D and 2D nuclear magnetic resonance spectroscopy (NMR), attenuated total reflectance Fourier transform infrared spectroscopy (ATRFTIR), and high resolution mass spectroscopy (HRMS). The antibacterial activity of these QACs were screened against the representative bacteria Escherichia coli, revealing that the antibacterial activity is dependent on the QAC molecular structure. Two QACs that demonstrated strong antibacterial activity were selected and chemically attached to hemlock by using hexamethylene diisocyanate (HDI) as a linker via a carbamate/urethane linkage in scCO2. The chemically modified hemlock demonstrated exceptional antibacterial activity and improved dimensional stability, suggesting potential application of this route in the conversion of softwood into advanced durable decking and fencing materials. KEYWORDS: Hemlock, Wood, Quaternary ammonium compound, Urethane, Antibacterial, Supercritical CO2

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The first-generation wood preservatives include oil-based creosote, pentachlorophenol and water-based arsenicals, primarily chromated copper arsenate (CCA).4 Although CCA has been the dominant preservative for wood treatment for several decades due to its effectiveness and low cost, it has been prohibited for residential applications in many countries due to the release of toxic arsenic into the environment.2 By removing arsenic, the second-generation preservatives are water-borne copper-rich systems including alkaline copper quat (ACQ) and copper azole (CA) containing noncomplexed copper(II) and an organic cobiocide.5 The major shortcomings of these systems include the release of copper into aquatic systems, significant corrosion of metal fasteners, mold growth on freshly treated wet lumber, and concerns about the ultimate disposal of the treated wood.5,6 These problems facilitated the development of the third-generation preservatives, i.e., totally organic ones.7 Because most organic biocides are not soluble in water, it is extremely challenging to achieve uniform distribution of the biocides within the wood products by employing the traditional pressure treatment method. Moreover, use of organic solvents would lead to VOC production, which must be eliminated for commercial wood products.8

INTRODUCTION

Recent years have seen growing interest in utilization of materials from sustainable resources.1 Of particular interest is the application of softwood, which accounts for 80% of the world’s production of timber, as a structural material including flooring, decking, and fencing, etc. Although softwood has many advantages including abundance, inexpensiveness, nontoxicity, and biodegradability, there are several inherent drawbacks limiting its applications.2 First, as a hygroscopic material, softwood swells when exposed to moisture from rain and humidity and shrinks as it dries. This behavior results in poor dimensional stability such as warping, bowing, and cupping particularly in outdoor applications. Second, softwood is subject to photodegradation when exposed to sunlight, losing its initial attractive appearance. Third, in comparison with both engineering materials and hardwood, softwood has much weaker mechanical properties, particularly hardness and flexural strength. In addition, under suitably mild temperatures, moisture and air, softwood tends to be adhesive to microorganisms such as fungi, insects and bacteria, which degrade it by biodeterioration, leading to permanent failure.3 Hence, to use softwood more effectively, we need to overcome these drawbacks, particularly with a focus on protection against attacks by fungi and insects using new benign wood preservatives. © XXXX American Chemical Society

Received: November 16, 2015 Revised: February 8, 2016

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DOI: 10.1021/acssuschemeng.5b01488 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

Research Article

ACS Sustainable Chemistry & Engineering Supercritical fluids are potentially advantageous in delivering chemicals into porous materials owing to their gas-like diffusivity and near zero-surface tension. Carbon dioxide is the most commonly used supercritical fluid due to its moderate critical constants (Tc = 31.1 °C, Pc = 7.4 MPa),9 and nonflammable and nontoxic nature. Supercritical carbon dioxide (scCO2) has been employed in many applications including extraction, dry cleaning, nano- and microparticle formation, and chemical reactions including polymerizations as a reaction medium.10 Indeed, Hampen Træforarbejdning A/S in Jutland, Denmark, has recently commissioned a plant for impregnating spruce wood using scCO2, i.e., Superimpregnation/Superwood where the active wood preservatives including propikonazol, tebukonazol, and 3-iodo-2-propynyl-butyl-carbamate (IPBC), are delivered into the fine pores.11,12 ScCO2treated wood demonstrated better properties than the pressuretreated counterpart in terms of distribution of the preservatives and antileaching performance.13 However, leaching of impregnated chemicals is still significant, inevitably resulting in both weakening of the antimicrobial performance with time and a continuous release of chemicals to the environment. Hence, to overcome the deteriorating performance resulting from leaching after physical treatment, chemical modification is desired to achieve permanent performance. Chemical modification of wood has been studied for several decades14 with acetylation15 and furfurylation16,17 receiving various degrees of success. There are three major components in wood, i.e., cellulose, hemicellulose, and lignin. All of these components are comprised of reactive hydroxyl groups. It is believed that digestion of wood by enzymes begins at the free hydroxyl sites.15 Conversion of the hydroxyl groups results in structural changes to the carbohydrate polymers in the cell wall, inhibiting substrate recognition while reducing cell wall water content that is postulated to be the most likely mechanism of fungal decay.18 Acetic anhydride and vinyl acetate19 were employed in acetylation of wood in combination with catalysts such as potassium acetate.20 Indeed, acetylation of wood has been commercialized by Accsys Technologies (Accoya Wood) and Eastman Chemical (Perennial Wood). However, the residual acetic acid in the acetylated wood can result in a vinegar-like smell and corrode regular steel fasteners. Moreover, acetylation of wood has been found to facilitate photobleaching.21 On the other hand, furfurylation of wood was commercialized by Kebony ASA (Visor Wood) where furfuryl alcohol was polymerized and linked to lignin units. Both acetylation and furfurylation can improve the antiweathering properties over untreated wood. However, they lack the ability to enhance the treated wood with satisfactory antibacterial and light-stability properties. There are many kinds of natural and synthetic antibacterial agents.22 Among the various antibacterial agents, quaternary ammonium compounds (QACs) are the most widely used due to their excellent antibacterial properties, low toxicity, low corrosivity, and excellent environmental stability.23,24 In addition, many antibacterial materials work by a “release” principle, i.e., gradually leaching biocides into the surroundings. Such antibiotics will sooner or later be exhausted, becoming ineffective, and those based on toxic heavy metal ions, will eventually pollute the environment.25 Hence, a nonreleasing strategy is desired in the development of antibacterial materials. Such permanent antibacterial materials can be prepared by grafting antibacterial agents onto substrates.26−28

In the present study, several novel QACs containing hydroxyl groups were synthesized and then chemically bonded to the softwood hemlock via a carbamate/urethane linkage, which will prevent release of biocides. Supercritical CO2 was employed as the reaction medium to facilitate penetration of the reactants into the softwood cell walls.

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EXPERIMENTAL SECTION

Materials. Hexamethylene diisocyanate (HDI, ≥98%), triethanolamine (TEOA, ≥99.0%), 2-dimethylaminoethanol (DMEA, 99.5%), 2[2-(dimethylamino)ethoxy]ethanol (DMAEE, 98%), iodomethane (99%), N,N-dimethyloctylamine (DMOA, 95%), N,N-dimethyltetradecylamine (≥95%), 11-bromo-1-undecanol (≥99%), 3-dimethylamino-1-propanol (99%), 1-bromoundecane (98%), N-methyldiethanolamine (MDEA, ≥99%), 4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-heptadecafluoroundecyl iodide (3-(perfluorooctyl) propyl iodide, ≥99%), diethyl ether, 1-propanol, methanol, and dibutyltin dilaurate (95%) were purchased from Sigma-Aldrich and used as received. Tetrahydrofuran (THF, HPLC grade) was purchased from Caledon Laboratories Ltd. and dried prior to use. Instrument grade carbon dioxide (CO2, 99.99%, with dip-tube) was supplied by Praxair Inc., Canada. Coastal hemlock was generously provided by Florcan Inc., Canada. Characterization. 1D (1H, 13C, and 19F) and 2D (gCOSY and gHSQC) nuclear magnetic resonance spectroscopy (NMR) spectra were recorded using either a Varian INOVA 600 or a Varian INOVA 400 spectrometer at 25 °C. 1D 13C{1H, 19F} and 2D 19F 13C HSQC NMR spectra were recorded using a Bruker AVIII600 spectrometer equipped with a 1H-13C-19F TXO probe at 25 °C. DMSO-d6 was used as the solvent and 1H and 13C chemical shifts were referenced to tetramethylsilane (TMS; 0.0 ppm) whereas 19F chemical shifts were referenced to trichloro-fluoro-methane (CFCl3; 0.0 ppm). Contact angles were measured using a PGX measuring head pocket goniometer (FIBRO System AB, Sweden). Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra were recorded using a smart iTR (diamond ATR) on a Nicolet 6700 FTIR spectrometer (Thermo Scientific) with a resolution of 4 cm−1 and a total of 64 scans for each sample. High resolution mass spectroscopy (HRMS) spectra were measured on a micrOTOF mass spectrometer (Bruker) by electrospray ionization (ESI) and run in the positive ion mode. Samples were dissolved in methanol. Methods. Synthesis of 2-Hydroxy-N,N,N-trimethylethanaminium Iodide (TMEAI; 1). TMEAI (1) was synthesized from 2dimethylaminoethanol (DMEA) and iodomethane. 4.0 mL (64.0 mmol) of iodomethane was added dropwise to a precooled solution of 5.1 mL (50 mmol) of DMEA in 50 mL of THF in an ice bath. Precipitation of 1 took place immediately. The reaction mixture was stirred in an ice bath for 1 h before the formed 1 was isolated by centrifugation. A white powder was obtained after washing three times with diethyl ether followed by drying under vacuum at room temperature. Yield: 99.1%. 1H NMR (DMSO-d6, 400 MHz) δ (ppm): 3.14 (CH3, 9H), 3.43 (CH2-CH2-OH, 2H), 3.81 (CH2-CH2OH, 2H), 5.14 (OH, 1H). 13C NMR (DMSO-d6, 100 MHz) δ (ppm): 53.1 (CH3), 55.0 (CH2-CH2-OH), 66.7 (CH2-CH2-OH). FTIR (cm −1): 3323 (υOH), 3005 (υasCH3 ), 2881 (υsCH3), 1472 (δasCH3), 1408, 1355, 1130, 1078, 1054 (υC-O), 1010, 954, 943, 894, 860. Synthesis of 2-(2-Hydroxyethoxy)-N,N,N-trimethylethanaminium Iodide (TMEEAI; 2). TMEEAI (2) was synthesized from 2-[2(dimethylamino)ethoxy]ethanol (DMAEE) and iodomethane. 2.4 mL (38.4 mmol) of iodomethane was added dropwise to a precooled solution of 4.3 mL (30 mmol) of DMAEE in 30 mL of THF in an ice bath. Precipitation of 2 took place immediately. The reaction mixture was stirred in the ice bath for 1 h before the formed 2 was isolated by centrifugation. A white powder was obtained after washing three times with diethyl ether followed by drying under vacuum at room temperature. Yield: 98.1%. 1H NMR (DMSO-d6, 400 MHz) δ (ppm): 3.13 (CH3, 9H), 3.48 (CH2-CH2-OH, 2H), 3.51 (CH2-CH2OH, 2H), 3.54 (N-CH2-CH2, 2H), 3.84 (N-CH2-CH2, 2H), 4.63 (br. B

DOI: 10.1021/acssuschemeng.5b01488 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

Research Article

ACS Sustainable Chemistry & Engineering s, OH, 1H). 13C NMR (DMSO-d6, 100 MHz) δ (ppm): 53.2 (CH3), 59.9 (CH2-CH2-OH), 64.0 (N-CH2-CH2), 64.4 (N-CH2-CH2), 72.0 (CH2-CH2-OH). FTIR (cm−1): 3414 (υOH), 3011 (υasCH3), 2877 (υsCH3), 1466 (δasCH3), 1404, 1361, 1141, 1125, 1078, 1058 (υC-O), 954, 890, 872, 832. HRMS(ESI) Calcd. for the cation [C7H18NO2]+: 148.22277. Found: 148.13278. Synthesis of 2-Hydroxy-N,N-bis(2-hydroxyethyl)-N-methylethanaminium Iodide (MTEAI; 3). MTEAI (3) was synthesized from triethanolamine and iodomethane. 4.00 mL (64.0 mmol) of iodomethane was added dropwise to a solution of 6.70 mL (50 mmol) of triethanolamine in 50 mL of THF. The reaction mixture was stirred at room temperature for 24 h. Phase separation took place with the formed 3 staying at the bottom phase, which was then isolated using a separation funnel. A colorless viscous liquid was obtained after washingthree times with diethyl ether followed by rotary evaporation at 50 °C. Yield: 100%. 1H NMR (DMSO-d6, 400 MHz) δ (ppm): 3.14 (CH3, 3H), 3.52 (CH2-CH2-OH, 6H), 3.82 (CH2-CH2-OH, 6H), 5.14 (OH, 3H). 13C NMR (DMSO-d6, 100 MHz) δ (ppm): 49.7 (CH3), 54.8 (CH2-CH2-OH), 64.1 (CH2-CH2-OH). FTIR (cm−1): 3328 (υOH), 2952 (υasCH3), 2885 (υsCH3), 1457 (δasCH3), 1354, 1040 (υC-O), 943. HRMS(ESI) Calcd. for the cation [C7H18NO3]+: 164.22217. Found: 164.12736. Synthesis of N-(2-Hydroxyethyl)-N,N-dimethylundecan-1-aminium Bromide (HEdMUABr; 4). HEdMUABr (4) was synthesized from 2-dimethylaminoethanol and 1-bromoundecane according to the reported method.29 12.0 mmol (1.08 g) of 2-dimethylaminoethanol was mixed with 13.2 mmol (3.17 g) of 1-bromoundecane and then refluxed at 80 °C for 30 min where the reaction mixture was solidified. The reaction mixture was subsequently cooled to room temperature followed by addition of 6 mL of 1:3(v/v) propanol:methanol to dissolve completely the reaction mixture. After that, the reaction mixture was refluxed at 80 °C for 20 h at which point the reaction mixture was cooled down to room temperature. A white powder was obtained after removing solvents by rotary evaporation, washed three times with diethyl ether, and dried in vacuo. Yield: 57.7%. 1H NMR (DMSO-d6, 600 MHz) δ (ppm): 0.86 (CH3-CH2, 3H), 1.18−1.33 (CH3-(CH2)8, 16H), 1.66 (CH2-CH2-CH2-N, 2H), 3.05 (CH3-N, 6H), 3.32 (CH2-CH2-CH2-N, 2H), 3.37 (N-CH2-CH2-OH, 2H), 3.81 (N-CH2-CH2-OH, 2H), 5.25 (OH, 1H). 13C NMR (DMSO-d6, 100 MHz) δ (ppm): 13.9 (CH3-CH2), 21.7 (CH2-CH2-CH2-N), 22.0 (CH3-CH2), 25.7 (CH2-CH2-CH2-N), 28.5 (CH2-CH2-CH2-CH2-N), 28.7 (CH3-CH2-CH2-CH2), 28.8 (CH2-CH2-CH2-CH2-CH2-N), 28.9 (CH3-CH2-CH2-CH2-CH2-CH2), 31.2 (CH3-CH2-CH2), 50.7 (CH3N), 54.8(N-CH2-CH2-OH), 64.0 (CH2-CH2-CH2-N), 64.4 (N-CH2CH2-OH). FTIR (cm−1): 3223 (υOH), 3006, 2955 (υasCH3), 2917 (υasCH2), 2850 (υsCH2), 1469 (δasCH3), 1077, 1051 (υC-O), 964, 915, 719 (ρCH2). HRMS(ESI) Calcd. for the cation [C15H34NO]+: 244.43601. Found: 244.26460. Synthesis of N-(3-Hydroxypropyl)-N,N-dimethylundecan-1-aminium Bromide (HPdMUABr; 5). HPdMUABr (5) was synthesized from 3-dimethylamino-1-propanol and 1-bromoundecane. 12.0 mmol (1.25 g) of 3-dimethylamino-1-propanol was mixed with 13.2 mmol (3.17 g) of 1-bromoundecane and then refluxed at 80 °C for 30 min where the reaction mixture was solidified. The reaction mixture was subsequently cooled to room temperature followed by addition of 6 mL of 1:3(v/v) propanol:methanol to dissolve completely the reaction mixture. After that, the reaction mixture was refluxed at 80 °C for 20 h at which point the reaction mixture was cooled down to room temperature. A white powder was obtained after removing solvents by rotary evaporation, washed three times with diethyl ether, and then dried in vacuo. Yield: 94.0%. 1H NMR (DMSO-d6, 600 MHz) δ (ppm): 0.86 (CH3-CH2, 3H), 1.20−1.34 (CH3-(CH2)8, 16H), 1.64 (CH2-CH2-CH2-CH2-N, 2H), 1.80 (N-CH2-CH2-CH2-OH, 2H), 3.01 (CH3-N, 6H), 3.24 (CH2-CH2-CH2-CH2-N, 2H), 3.31 (N-CH2-CH2CH2-OH, 2H), 3.47 (N-CH2-CH2-CH2-OH, 2H), 4.77 (OH, 1H). 13C NMR (DMSO-d6, 100 MHz) δ (ppm): 13.9 (CH3-CH2), 21.6 (CH2CH2-CH2-CH2-N), 22.0 (CH3-CH2), 25.3 (N-CH2-CH2-CH2-OH), 25.7 (CH2-CH2-CH2-CH2-N), 28.5 (CH2-CH2-CH2-CH2-N), 28.7 (CH3-CH2-CH2-CH2), 28.8 (CH2-CH2-CH2-CH2-CH2-N), 28.9 (CH3-CH2-CH2-CH2-CH2-CH2), 31.2 (CH3-CH2-CH2), 50.0 (CH3-

N), 57.5 (N-CH2-CH2-CH2-OH), 61.0 (N-CH2-CH2-CH2-OH), 62.8 (CH2-CH2-CH2-CH2-N). FTIR (cm−1): 3311 (υOH), 3009, 2955 (υasCH3), 2918 (υasCH2), 2850 (υsCH2), 1467 (δasCH3), 1323, 1069 (υC-O), 907, 721 (ρCH2). HRMS(ESI) Calcd. for the cation [C16H36NO]+: 258.46259. Found: 258.27912. Synthesis of 11-Hydroxy-N-(3-hydroxypropyl)-N,N-dimethylundecan-1-aminium Bromide (HHPdMUABr; 6). HHPdMUABr (6) was synthesized from 3-dimethylamino-1-propanol and 11-bromo-1undecanol. 3.9 mmol (0.47 mL) of 3-dimethylamino-1-propanol was mixed with 4.2 mmol (1.07 g) of 11-bromo-1-undecanol and then refluxed at 80 °C for 30 min where the reaction mixture was solidified. The reaction mixture was subsequently cooled down to room temperature followed by addition of 4 mL of 1:3(v/v) propanol:methanol. After that, the reaction mixture was refluxed at 80 °C for 20 h. at which point the reaction mixture was cooled down to room temperature. A white powder was obtained after removing solvents by rotary evaporation, washed three times with diethyl ether, and dried in vacuo. Yield: 96.4%. 1H NMR (DMSO-d6, 600 MHz) δ (ppm): 1.22− 1.34 (N-CH2-CH2-(CH2)7-CH2-CH2-OH, 14H), 1.39 (N-(CH2)9CH2-CH2OH, 2H), 1.64 (N-CH2-CH2-(CH2)9-OH, 2H), 1.80 (HOCH2-CH2-CH2-N, 2H), 3.00 (CH3-N, 6H), 3.24 (N-CH2-(CH2)10OH, 2H), 3.30 (HO-CH2-CH2-CH2-N, 2H), 3.37 (N-(CH2)10CH2OH, 2H) 3.47 (HO-CH2-CH2-CH2-N, 2H), 4.31 (N-(CH2)10CH2OH, 1H), 4.77 (HO-CH2-CH2-CH2-N, 1H). 13C NMR (DMSOd6, 100 MHz) δ (ppm): 21.7 (N-CH2-CH2-(CH2)9-OH), 25.3 (HOCH2-CH2-CH2-N), 25.5 (N-(CH2)8-CH2-CH2-CH2OH), 25.7 (NCH2-CH2-CH2(CH2)8OH), 28.5 (N-CH2-CH2-CH2CH2(CH2)7OH), 28.8 (N-(CH2)7-CH2-CH2-CH2-CH2OH), 28.9 (N-(CH 2 ) 4 -CH 2 -CH 2 -CH 2 -(CH 2 ) 4 OH), 29.0 (N-(CH 2 ) 5 -CH 2 (CH2)5OH), 32.5 (N-(CH2)9-CH2-CH2OH,), 50.0 (CH3-N), 57.6 (HO-CH2-CH2-CH2-N), 60.6 (N-(CH2)10-CH2OH), 61.0 (HO-CH2CH2-CH2-N), 62.8 (N-CH2-(CH2)10-OH). FTIR (cm−1): 3311 (υOH), 2917 (υasCH2), 2849 (υsCH2), 1482, 1464 (δasCH3), 1328, 1055 (υC-O), 913, 720 (ρCH2). HRMS(ESI) Calcd. for the cation [C16H36NO2]+: 274.46199. Found: 274.27506. Synthesis of N-(11-Hydroxyundecanyl-N,N-dimethyloctan-1-aminium Bromide (HUdMOABr; 7). HUdMOABr (7) was synthesized from N,N-dimethyloctylamine and 11-bromo-1-undecanol. 12.0 mmol (3.04 g) of 11-bromo-1-undecanol was mixed with 13.2 mmol (2.19 g) of N,N-dimethyloctylamine and then refluxed at 80 °C for 30 min. The reaction mixture was subsequently cooled down to room temperature followed by addition of 6 mL of 1:3(v/v) propanol:methanol. After that, the reaction mixture was refluxed at 80 °C for 20 h at which point the reaction mixture was cooled down to room temperature. A white powder was obtained after removing solvents by rotary evaporation, washed three times with diethyl ether, and dried in vacuo. Yield: 98.7%. 1H NMR (DMSO-d6, 600 MHz) δ (ppm): 0.87 (CH3-CH2, 3H), 1.22−1.33 (CH3-(CH2)5-CH2-CH2, N-(CH2)2-(CH2)7-CH2CH2-OH, 24H), 1.39 (N-(CH2)9-CH2-CH2-OH, 2H), 1.63 (CH2CH2-N-CH2-CH2, 4H), 2.98 (CH3-N, 6H), 3.22 (CH2-N-CH2, 4H), 3.37 (CH2-OH, 2H), 4.31 (OH, 1H). 13C NMR (DMSO-d6, 100 MHz) δ (ppm): 13.9 (CH3-CH2), 21.6 (CH2-CH2-N-CH2-CH2), 22.0 (CH3-CH2), 25.5 (CH2-CH2-CH2-OH), 25.7 (CH2-CH2-CH2-NCH2-CH2-CH2), 28.4 (CH2-CH2-CH2-CH2-CH2-N-CH2-CH2-CH2CH2), 28.7 (CH2-CH2-CH2-CH2-OH), 28.9 (CH2-CH2-CH2-CH2CH2-CH2-CH2-OH), 29.0 (CH2-CH2-CH2-CH2-CH2-CH2-OH), 31.1 (CH3-CH2-CH2), 32.5 (CH2-CH2-OH), 49.9 (CH3-N), 60.6 (CH2OH), 62.8 (CH2-N-CH2). FTIR (cm−1): 3287 (υOH), 2918 (υasCH2), 2854 (υsCH2), 1469 (δasCH3), 1331, 1057 (υC-O), 899, 717 (ρCH2). HRMS(ESI) Calcd. for the cation [C21H46NO]+: 328.59549. Found: 328.35810. Synthesis of N-(11-Hydroxyundecanyl-N,N-dimethyltetradecan1-aminium Bromide (HUdMTABr; 8). HUdMTABr (8) was synthesized from N,N-dimethyltetradecylamine and 11-bromo-1undecanol. 12.0 mmol (3.04 g) of 11-bromo-1-undecanol was mixed with 13.2 mmol (3.35 g) of N,N-dimethyltetradecylamine and then refluxed at 80 °C for 30 min. The reaction mixture was subsequently cooled down to room temperature followed by addition of 6 mL of 1:3(v/v) propanol:methanol. After that, the reaction mixture was refluxed at 80 °C for 20 h at which point the reaction mixture was C

DOI: 10.1021/acssuschemeng.5b01488 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

Research Article

ACS Sustainable Chemistry & Engineering Scheme 1. Chemical Structures of the Synthesized QACs

cooled down to room temperature. A white powder was obtained after removing solvents by rotary evaporation, washed three times with diethyl ether, and dried in vacuo. Yield: 95.0%. 1H NMR (DMSO-d6, 600 MHz) δ (ppm): 0.85 (CH3-CH2, 3H), 1.20−1.33 (CH3-(CH2)11CH2-CH2, N-(CH2)2-(CH2)7-CH2-CH2-OH, 36H), 1.39 (N-(CH2)9CH2-CH2-OH, 2H), 1.62 (CH2-CH2-N-CH2-CH2, 4H), 2.98 (CH3-N, 6H), 3.22 (CH2-N-CH2, 4H), 3.37 (CH2-OH, 2H), 4.31 (OH, 1H). 13 C NMR (DMSO-d6, 100 MHz) δ (ppm): 13.9 (CH3-CH2), 21.6 (CH2-CH2-N-CH2-CH2), 22.1 (CH3-CH2), 25.5 (CH2-CH2-CH2OH), 25.7 (CH2-CH2-CH2-N-CH2-CH2-CH2), 28.4 (CH2-CH2-CH2CH2-N-CH2-CH2-CH2-CH2), 28.7 (CH2-CH2-CH2-CH2-OH), 28.8 (CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2), 28.9 (CH3-CH2-CH2CH2-CH2-CH2-CH2-CH2-CH2-CH2), 29.0 (CH3-CH2-CH2-CH2CH 2 -CH 2 -CH2 -CH 2 -CH 2 , (CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 OH), 31.3 (CH3-CH2-CH2), 32.5 (CH2-CH2-OH), 49.9 (CH3-N), 60.6 (CH2-OH), 62.7 (CH2-N-CH2). FTIR (cm−1): 3300 (υOH), 2915 (υasCH2), 2848 (υsCH2), 1463 (δasCH3), 1054 (υC-O), 868, 719 (ρCH2). HRMS(ESI) Calcd. for the cation [C27H58NO]+: 412.75497. Found: 412.45232. Synthesis of 4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-Heptadecafluoro-N-(3-hydroxypropyl)-N,N-dimethylundecan-1-aminium Iodide (F17HPdMUAI; 9). F17HPdMUAI (9) was synthesized from 3dimethylamino-1-propanol and 4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11heptadecafluoroundecyl iodide. 0.3 mmol (31.3 mg) of 3-dimethylamino-1-propanol was mixed with 0.3 mmol (178.2 mg) of 4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-heptadecafluoroundecyl iodide and then refluxed at 80 °C for 90 min where the reaction mixture was solidified. The reaction mixture was subsequently cooled down to room temperature followed by addition of 4 mL of 1:3(v/v) propanol:methanol to dissolve completely the reaction mixture. After that, the reaction mixture was refluxed at 80 °C for 24 h, at which point the reaction mixture was cooled down to room temperature. A white powder was obtained after removing solvents by rotary evaporation, washed three times with diethyl ether, and dried in vacuo. Yield: 71.8%. 1H NMR (DMSO-d6, 600 MHz) δ (ppm): 1.83 (CH2-CH2-OH, 2H), 1.97 (CF2-CH2-CH2-CH2-N, 2H), 2.34 (CF2CH2-CH2-CH2-N, 2H), 3.06 (CH3-N, 6H), 3.38 (CH2-N-CH2, 4H), 3.49 (CH2-CH2-OH, 2H), 4.78 (OH, 1H). 13C(1H, 19F) NMR (DMSO-d6, 150 MHz) δ (ppm): 13.8 (CF2-CH2-CH2-CH2-N), 25.2 (N-CH2-CH2-CH2-OH), 26.7 (CF2-CH2-CH2-CH2-N), 50.3 (N-

CH3), 57.5 (N-CH2-CH2-CH2-OH), 61.4 (N-CH2-CH2-CH2-OH), 61.6 (CF2-CH2-CH2-CH2-N), 107.7 (CF3-CF2), 109.7 (CF3-CF2CF2), 110.2 (CF3-CF2-CF2-CF2), 110.3 (CF3-CF2-CF2-CF2-CF2), 110.5 (CF3-CF2-CF2-CF2-CF2-CF2-CF2), 110.7 (CF3-CF2-CF2-CF2CF2-CF2), 116.6 (CF3), 118.3 (CF2-CH2). 19F NMR (DMSO-d6, 376 MHz) δ (ppm): −126.0 (CF3-CF2), −123.3 (CF3-CF2-CF2-CF2-CF2CF2-CF2), −122.7 (CF3-CF2-CF2), −121.9 (CF3-CF2-CF2-CF2-CF2), −121.7 (CF3-CF2-CF2-CF2-CF2-CF2), −113.4 (CF2-CH2), −80.5 (CF3). FTIR (cm−1): 3364 (υOH), 1483, 1196, 1146, 1030 (υC-O), 703, 654. HRMS(ESI) Calcd. for the cation [C16H19F17NO]+: 564.30046. Found: 564.12045. Attachment of Isocyanate Linker to Coastal Hemlock. A 15 mL stainless-steel view cell was connected to a syringe pump (Isco 260D) for pumping CO2 as described previously.30 Temperature of the reaction mixture in the view cell was measured and controlled by means of a temperature controller (J-KEM Gemini-2) whereas the system pressure was measured using a pressure transducer (Omega). In a typical experiment, to the 15 mL view cell were added 1.40 g of dried coastal hemlock (dimensions of each piece of samples: longitudinal × tangential × radial = 17 mm × 17 mm × 3 mm, approximately), 2 mL of HDI, and 0.2 mL of dibutyltin diaurate followed by sealing the view cell. A small amount of CO2 was then pumped into the view cell reactor up to 2.8 MPa at room temperature. After that, the view cell was heated to 100 °C, at which point the pressure in the view cell was increased to 41.4 MPa by pumping CO2 into the reactor. After 20 h of reaction at 100 °C, the view cell was slowly depressurized after turning off the heater. The wood sample was subsequently washed with dry THF and then dried in vacuo for characterization and further attachment of QACs. Product weight was increased by ca. 30%. Link of QACs to Coastal Hemlock. The above view cell system was also used for linking QACs to wood. In a typical experiment, to the 15 mL view cell was added 0.85 g of the above HDI-functionalized wood and 0.24 g of the above synthesized 5 followed by sealing the view cell. A small amount of CO2 was then pumped into the reactor to 2.8 MPa at room temperature. Then, the view cell was heated to 100 °C, at which point the pressure in the view cell was increased to 41.4 MPa by pumping CO2 into the reactor. After 20 h of reaction at 100 °C, the view cell was slowly depressurized after turning off the heater. QACD

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Figure 1. (a) 1H and (b) 19F NMR spectra of the synthesized QAC 9 (in DMSO-d6). attached wood was obtained after washing with dry THF and then dried in vacuo. Product weight: 0.84 g. To explore how the QACs were distributed inside the timber, coastal hemlock (dimensions of each piece of samples: longitudinal × tangential × radial = 20 mm × 6 mm × 5 mm, approximately) were treated in the same way as the thinner samples described above. The obtained samples were then sliced for examining the cross sections by a digital microscope (ZEISS Smartzoom 5 equipped with an objective of PlanApo D 5× /0.3 FWD 30 mm). Testing of Antibacterial Activity of the Synthesized QACs. The antibacterial effect of the QAC materials was tested against Escherichia coli. In a typical experiment a specific amount (2 mg) of the synthesized QACs was added to a suspension (1 mL) of E. coli B (strain ATCC 29425) in 0.05 M aqueous PBS buffer (PH 7.3) containing approximately 105 CFU/mL. The mixture was then shaken at 250 rpm and 37 °C for 1 h, followed by a serial dilution using the aqueous PBS buffer solution. Subsequently, aliquots (100 μL) of diluted samples were mixed with 4 mL of Tryptic Soy Broth Agarose and then spread onto plates of nutrient Tryptic Soy Agar. After incubation for 24 h at 37 °C, the plates were examined. The number of colony forming units (CFU) was counted, and the results were expressed as mean colony forming units per 1 mL (CFU/mL). The test for each sample was run in triplicate. Testing of Antibacterial Activity of the QAC-Attached Wood. The antibacterial effect of the QAC-attached hemlock was tested against E. coli. In a typical experiment, a specific amount (500−600 mg) of the wood samples was added to a suspension (3 mL) of E. coli B (strain ATCC 29425) in 0.05 M aqueous PBS buffer (PH 7.3) containing approximately 103 CFU/mL. The mixture was then shaken at 250 rpm and 37 °C for 24 h. Subsequently, aliquots (100 μL) of liquid samples were mixed with 4 mL of Tryptic Soy Broth Agarose and then spread onto plates of nutrient Tryptic Soy Agar. After incubation for 24 h at 37 °C, the plates were examined. The number of colony forming units (CFU) was counted, and the results were expressed as mean CFU. The test for each sample was run in triplicate. Testing of Dimensional Stability of the QAC-Attached Wood after Immersion in Water. To determine the dimensional stability of

wood, the cubic wood samples were immersed in distilled water for 24 h at room temperature. The volume of the sample was determined by measuring the external dimensions of the sample including longitudinal, tangential, and radial lengths using a digital caliper. The sample was then dried in vacuum oven followed by measuring the external dimensions of the dried samples. The swelling ratio (S) was calculated by the following equation:

SX (%) =

X wet − Xdry Xdry

× 100 (1)

where X is either the longitudinal, tangential, and radial lengths or the volume that was calculated by multiplying the longitudinal, tangential, and radial lengths. Each measurement was repeated in quadruplicate.

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RESULTS AND DISCUSSION Synthesis of QACs. Nine QACs containing at least one hydroxyl group were synthesized via quaternization of a tertiary amine with an alkyl halide, as listed in Scheme 1. The synthesis of QACs 1−3 have been reported in the literature, with several different methods being employed to synthesize QAC 1. Among these, the simplest method ran the reaction in toluene for over 15 h.31 In comparison, our approach using a relatively more polar solvent THF resulted in completion of the reaction within 1 h. QAC 2 was previously synthesized in a different way by reacting 2-[2-(dimethylamino) ethoxy]ethanol with trimethylchlorosilane, followed by methylation with methyl iodide.32 QAC 3 was previously synthesized by reacting the same reactants for 10 h at 40 °C in dichloromethane resulting in a yield of 98%33 or in acetonitrile resulting in a yield of 92%.34 Our reaction was conducted in THF at room temperature for 24 h with a stoichiometric yield. The synthesized QACs 1, 2, and 3 were characterized by NMR (see Supporting Information), FTIR, and HRMS. However, the E

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Figure 2. (a) 13C{1H, 19F} and (b) 19F 13C HSQC NMR spectra of the synthesized QAC 9 (in DMSO-d6).

1H,1H,2H,2H-perfluorohexyl iodide, respectively. However, this approach was not successful when we attempted to synthesize 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-N-(3-hydroxypropyl)-N-dimethyloctan-1-aminium iodide by reacting 1H,1H,2H,2H-perfluorooctyl iodide with 3-dimethylamino-1propanol. We attribute this to the competitive elimination reaction of fluoroalkyl iodides containing a short -CH2CH2spacer.37 By employing a fluoroalkyl iodide with a longer -CH2CH2CH2- spacer37 using a modified method at a lower temperature, perfluorinated QAC 9 was synthesized and characterized by 1D (1H, 13C, and 19F) and 2D (gCOSY and 19 F 13C HSQC) NMR. As shown in Figure 1a, 7 peaks represent 8 different protons (H9−H16) as the peaks of H11 and H13 overlap. Figure 1b shows 7 peaks, representing 8 different fluorines (F1−F8) as the peaks of F4 and F5 overlap. Because of the significant splitting effect of fluorine on 13C NMR, the 13C NMR spectrum was measured by decoupling both 19F and 1H and is displayed in Figure 2a. All the carbon peaks are evident and assigned except the carbon in position 1 (C1), to which there are 3 fluorine atoms attached. The absence of peak C1 in the 13C{1H, 19F} spectrum is due to inefficient 19F decoupling. To determine the chemical shift of C1, the 19F 13C HSQC NMR spectrum of the synthesized QAC 9 was collected. As shown in Figure 2b, the chemical shift of C1 was identified at 116.6 ppm in addition to the other 7 carbons (C2−C8) to which fluorine atoms are attached. Hence, the NMR results confirmed the successful synthesis of QAC 9.

expected peak of the cation of QAC 1 was not observed in the MS spectrum. Instead, two significant peaks appeared at m/z = 90.1 and 143.1, which can be assigned to the proton absorbed 2-dimethylaminoethanol and proton absorbed iodomethane, respectively. These MS results confirm poor stability of QAC 1, which decomposed into 2-dimethylaminoethanol and iodomethane under the MS experimental conditions. To the best of our knowledge, there have been no literature reports on the synthesis of QACs 4, 6, and 8. QAC 5 was previously synthesized by Yagci et al.29 with a reported yield of 82%.35 We employed a different ratio of reactants and a longer reaction time to obtain a yield of 94.0%. In addition, QAC 7 was synthesized in acetonitrile with a reported yield of 91%.36 In the present study, we conducted the reaction in a mixture of methanol and 1-propanol to achieve a yield of 98.7%. The synthesized QACs 4−8 were characterized by NMR (see Supporting Information), FTIR, and HRMS. Perfluorinated QAC 9 was synthesized by reacting 4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-heptadecafluoroundecyl iodide with 3-dimethylamino-1-propanol. To the best of our knowledge, there has not been any literature report on the synthesis of QAC 9. Yagci et al.29 reported the preparation of 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluoro-N-(3-hydroxypropyl)-N,N-dimethyldecan-1-aminium iodide and 3,3,4,4,5,5,6,6,6-nonafluoro-N-(3-hydroxypropyl)-N,N-dimethylhexan-1-aminium iodide by reacting 3-dimethylamino-1propanol with 1H,1H,2H,2H-perfluorodecyl iodide and F

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ACS Sustainable Chemistry & Engineering Antibacterial Activity of the Synthesized QACs. The test of antibacterial activity of the synthesized QACs was conducted by mixing the materials with a suspension (1 mL, ca. 105 CFU/mL) of Escherichia coli in aqueous PBS buffer solution. After the mixture had been shaken at 37 °C for 1 h, the number of live bacteria was then measured via a serial dilution and incubation as described in the Experimental Section. As shown in Figure 3, three QACs (1, 2, and 3) did

hydrophilic hydroxyl group at the end of the hydrophobic alkyl chain. Attachment of QACs to Wood. Wood contains three major components, i.e., cellulose, hemicellulose, and lignin. The hydroxyl groups in these components enable chemical attachment of the QACs to wood structure. Scheme 2 displays the attachment of QACs to wood by using hexamethylene diisocyanate (HDI) via a urethane/carbamate bond. HDI was selected as a model compound due to its simple molecular structure in spite of its lower reactivity in comparison to other commercially used diisocyanates such as methylene diphenyl diisocyanate (MDI) and toluene diisocyanate (TDI). The reaction of HDI with wood (hemlock) and the further reaction of HDI-functionalized wood with the synthesized QACs were conducted in scCO2. There are many advantages of scCO2 in these reactions including: (1) scCO2 is an inexpensive green solvent in which both HDI and the synthesized QACs have good solubility; (2) there is no need to dry after the reactions; (3) much less moisture is brought to the reactions in comparison to high-boiling point hydrophilic organic solvents such as DMSO and DMF; and (4) much better penetration of HDI and QACs into the wood is possible due to the higher diffusivity of scCO2 than organic solvents. In addition, with impregnation of wood using scCO2 being successfully commercialized by Hampen Træforarbejdning A/S,40 it will no longer be a barrier to the design and manufacture of large pressure vessels for chemical modification of timber in scCO2. The synthesized HDI-functionalized coastal hemlock (CHHDI), the QAC 5-attached (CH-HDI-w-QAC 5) and QAC 9attached hemlock (CH-HDI-w-QAC 9) were characterized by both ATR-FTIR and contact angle analysis, then compared with the starting coastal hemlock. Figure 4 displays the FTIR spectra of the virgin hemlock and the chemically treated hemlock samples. After hemlock was reacted with HDI, the obtained HDI-functionalized coastal hemlock exhibits a typical isocyanate functional group as evidenced by the peak at 2262 cm−1 along with other functional groups including amide group (3315, 1684, 1513, and 1252 cm−1) and methylene group (2931 and 2856 cm−1) (Figure 4b). Further reaction of the HDI-functionalized coastal hemlock with QACs 5 and 9 afforded QAC 5-attached (Figure 4c) and QAC 9-attached hemlock (Figure 4d), respectively, with the remaining isocyanate group being consumed completely. The attachment of QAC 9 to hemlock was confirmed by the enhanced peaks at 1252 and 1154 cm−1 (asymmetric and symmetric C-F stretching modes, respectively), although these peaks are overlapped with other existing peaks such as C-O stretching and C-N deformation modes.

Figure 3. Antibacterial efficiency of the synthesized QACs (2 mg of sample in 1 mL of E. coli solution containing 105 CFU of live cells).

not demonstrate significant antibacterial activity whereas excellent antibacterial efficiency (100%) was obtained for five QACs including 4 and 5, and 7−9. The other QAC 6 showed a low antibacterial efficiency of 50.8%. These results indicate that antibacterial activity is not an inherent property of QACs but is significantly dependent on their molecular structure. QACs bind by ionic and hydrophobic interactions to microbial membrane surfaces, with the cationic headgroup facing outward and the hydrophobic tails inserted into the lipid bilayer, causing rearrangement of the membrane and subsequent leakage of intracellular constituents.38 The short methyl group in the first three QACs may not be long enough to penetrate into the lipid bilayer, resulting in no antibacterial activity. As also reported by Ahlstrom et al.,39 the bactericidal effects of 1-decyl, 1-dodecyl, and 1-tetradecyl betaine esters on Salmonella typhimurium 395 MS decreased with decreasing hydrocarbon chain lengths. This is in good agreement with our results, as the five QACs (4 and 5, 7−9) containing long hydrophobic chains demonstrated significantly enhanced antibacterial activity from the three QACs (1−3) containing short hydrophobic chains. QAC 6 has an additional hydroxyl group compared to QAC 5, leading to much lower antibacterial efficiency. This may be due to the decreased hydrophobicity by introduction of an additional Scheme 2. Synthetic Scheme for Attachment of QACs to Wood

G

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Figure 4. ATR-FTIR spectra of (a) coastal hemlock, (b) CH-HDI washed, (c) CH-HDI-w-QAC 5, and (d) CH-HDI-w-QAC 9.

Figure 5. Contact angle results of coastal hemlock, CH-HDI washed, CH-HDI-w-QAC 5, and CH-HDI-w-QAC 9.

Contact angle analysis can be used to examine the surface properties of these samples, as displayed in Figure 5. The water

droplet was gradually absorbed by the virgin coastal hemlock sample with the volume decreasing with time. After reaction H

DOI: 10.1021/acssuschemeng.5b01488 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

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ACS Sustainable Chemistry & Engineering with HDI, the surface of the HDI-functionalized coastal hemlock became highly hydrophobic with the contact angle remaining steadily at ca. 110°. Further reaction of the HDIfunctionalized coastal hemlock with QAC 5 resulted in a superhydrophilic surface of the QAC 5-attached hemlock with the water droplet being absorbed immediately. Further reaction of the HDI-functionalized coastal hemlock with QAC 9 resulted in a slightly hydrophobic surface of the QAC 9attached hemlock with the contact angle remaining at ca. 85°. These changes of contact angles confirmed the surface change during the treatments in addition to the chemical reactions occurring. The microstructures of the cross sections of the treated and untreated hemlock samples are compared in Figure 6. The pore size of the untreated hemlock sample is between 10 and 25 μm (Figure 6a). After reaction with HDI, the cell walls were coated with a layer of resin rather than being blocked (Figure 6b). These open pores are advantageous for the subsequent attachment of QACs to the cell walls by providing easy access of QACs. After reaction with QAC 5, these open pores were still visible (Figure 6c). The complete reaction of attached isocyanate groups with QAC 5 was also confirmed by ATRFTIR, as the isocyanate group peak was absent in the spectrum of the sliced sample of CH-HDI-w-QAC 5. Stability of the QAC-Modified Wood. Dimensional stability was estimated by measuring the swelling ratio of the wood samples after being immersed in water for 24 h. These swelling ratios were calculated in three different directions, i.e., longitudinal, tangential, and radial directions, and in volume. The swelling ratios of the modified and virgin hemlock samples are listed in Table 1. Compared to the 16% of volume swelling ratio of the virgin hemlock, the hemlock samples modified with QACs 5 and 9 swelled by 10% and 8% only, respectively. Interestingly, the virgin hemlock sample swelled mainly in the radial and tangential directions while there was nearly no swelling in the longitudinal direction. In contrast, the QAC modified samples swelled mainly in the longitudinal direction whereas there was no swelling in the radial direction. This phenomenon is attributed to the enhanced bonding of the cell walls by the chemical modification where cross-linking took place in the matrix of lignin and hemicellulose. Once these modified samples absorbed water, the cell wall containing primarily cellulose fibers stretched, resulting in swelling in the weakest longitudinal direction. On the contrary, when the virgin hemlock sample absorbed water, the matrix surrounding the cell wall swelled and pushed the cell walls to move in both radial and tangential directions. Hence, the QAC modified hemlock increased dimensional stability upon absorbing moisture and particularly minimized warping and bowing, which are mainly associated with the deformation in the radial and tangential directions. As for chemical stability, the immersed samples were characterized with ATR-FTIR after drying. In comparison to the spectra of the samples prior to moisture exposure, those of the immersed samples did not show additional peaks or significant changes in peaks attributed to the functional groups labeled in Figure 4. Hence, no significant loss in chemical stability was observed after immersion in water based on the FTIR analysis. Antibacterial Activity of the QAC-Modified Wood. To verify the antibacterial activity of the QAC-modified wood, two QAC-attached hemlock samples, i.e., QAC 5-attached (CHHDI-w-QAC 5) and QAC 9-attached hemlock (CH-HDI-w-

Figure 6. Structures of (a) coastal hemlock, (b) CH-HDI, and (c) CH-HDI-w-QAC 5. Scale bar: 200 μm.

QAC 9), were tested and compared with virgin hemlock and HDI-functionalized coastal hemlock (CH-HDI). A test was also conducted without adding any wood sample (blank) to estimate the concentration of the applied bacterial solution. As shown in Table 2, when costal hemlock was added to the E. coli solution, the number of viable bacteria increased from 232 to 552 CFU, suggesting additional bacteria were cultured with virgin hemlock added. This explains why hemlock tends to biodeterioration as a result of its affiliation with bacteria. In contrast, the two QAC-attached hemlock samples demonstrated excellent antibacterial activity with 0 and 1 CFU of viable bacteria when treating with QAC 5-attached and QAC 9attached hemlock, respectively. In addition, the HDI-functionalized coastal hemlock also exhibited a certain level of I

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ACS Sustainable Chemistry & Engineering Table 1. Swelling Ratios (%) of Hemlock Samples with and without Modification with QACs sample

longitudinal direction

tangential direction

radial direction

overall volume

coastal hemlock CH-HDI-w-QAC 5 CH-HDI-w-QAC 9

0.5 ± 0.6 6.4 ± 0.1 4.8 ± 0.1

8.6 ± 0.3 4.1 ± 0.5 3.2 ± 0.2

6.0 ± 4.8 −0.4 ± 1.9 −0.4 ± 1.9

16 ± 5 10 ± 2 8±2

Table 2. Viable Bacteria (CFU) after Testing with Different Wood Samples blank

hemlock

CH-HDI

CH-HDI-w-QAC 5

CH-HDI-w-QAC 9

232 ± 62

552 ± 15

81 ± 5

0±0

1±1

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ACKNOWLEDGMENTS The authors thank Prof. Jun Yang, the department of Mechanical and Material Engineering, UWO, and Mr. Yixing Tang, the department of Chemical and Biochemical Engineering (CBE), UWO, for assistance in the test of antibacterial properties, Mr. Doug Hairsine, mass spectroscopy facility manager, the department of Chemistry, UWO, for assistance in the high resolution MS measurements, Ms. Karen Nygard, Microscopy Specialist, Biotron, UWO, for assistance in imaging wood samples, and Ms. Valerie Robertson, NMR manager, the department of Physics, University of Guelph, for assistance in 1D 13C{1H, 19F} and 2D 19F 13C HSQC NMR measurements. Special thanks go to Eric C. Halls, president of Florcan Inc., Canada for providing wood samples, consistent support, and fruitful discussions.

antibacterial efficiency (65%). This may be due to its hydrophobic surface inhibiting the growth of bacteria, as revealed by the contact angle results. Hence, antibacterial hemlock was prepared by chemical attachment of functional QACs to coastal hemlock. This approach provides a feasible route toward the design and development of a new generation of green and sustainable wood materials as a replacement of the currently used pressuretreated woods. For outdoor applications such as decking and fencing, fungi are more responsible for wood decay than bacteria. However, this strategy can be potentially applied in chemical modifications of wood materials to achieve various functionalities including but not limited to antifungi and antiUV degradation by attaching the corresponding functional materials. Our future work includes examination of the antifungal and antibacterial efficiency after repeated exposure to bacterial solutions and the improvement of mechanical properties.

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(1) Titirici, M.-M.; White, R. J.; Brun, N.; Budarin, V. L.; Su, D. S.; del Monte, F.; Clark, J. H.; MacLachlan, M. J. Sustainable carbon materials. Chem. Soc. Rev. 2015, 44, 250−290. (2) Jeffrey, J. M. Chromated Copper Arsenate as a Wood Preservative. In Environmental Impacts of Treated Wood; CRC Press: Boca Raton, FL, 2006; pp 5−18. (3) Highley, T. L. Biodeterioration of wood. In Wood handbook: wood as an engineering material; USDA Forest Service: Madison, WI, 1999; pp 13.1−13.16. (4) Schultz, T. P.; Nicholas, D. D.; Preston, A. F. A brief review of the past, present and future of wood preservation. Pest Manage. Sci. 2007, 63, 784−788. (5) Freeman, M. H.; Nicholas, D. D.; Schultz, T. P. Nonarsenical wood protection: alternatives for CCA, creosote, and pentachlorophenol. In Environmental Impacts of Treated Wood; Townsend, T. G.; Solo-Gabriele, H., Eds.; CRC Taylor & Francis: Boca Raton, FL, 2006; pp 19−36. (6) Pankras, S.; Cooper, P. A.; Wylie, S. Relationship between copper species in solution and leaching from alkaline copper quat (ACQ) treated wood. Holzforschung 2012, 66, 505−514. (7) Barnes, H. M.; Lindsey, G. B. Bending properties of wood treated with a new organic wood preservative system. Bioresour. Technol. 2009, 100, 778−781. (8) Avery, R. J. Reactivity-Based VOC Control for Solvent Products: More Efficient Ozone Reduction Strategies. Environ. Sci. Technol. 2006, 40, 4845−4850. (9) Kemmere, M. Supercritical Carbon Dioxide for Sustainable Polymer Processes. In Supercritical Carbon Dioxide in Polymer Reaction Engineering; Kemmere, M. F.; Meyer, T., Eds.; Wiley-VCH: Weinheim, 2005; pp 1−14. (10) Woods, H. M.; Silva, M. M. C. G.; Nouvel, C.; Shakesheff, K. M.; Howdle, S. M. Materials processing in supercritical carbon dioxide: surfactants, polymers and biomaterials. J. Mater. Chem. 2004, 14, 1663−1678. (11) Kjellow, A. W.; Henriksen, O.; Sørensen, J. C.; Johannsen, M.; Felby, C. Partitioning of organic biocides between wood and supercritical carbon dioxide. J. Supercrit. Fluids 2010, 52, 1−5.

CONCLUSIONS Nine quaternary ammonium compounds (QACs) containing at least one hydroxyl group were successfully synthesized and well characterized with 1D and 2D NMR, ATR-FTIR, and high resolution MS. Antibacterial tests showed excellent antibacterial activity against E. coli of those QACs consisting of a long hydrophobic tail, in contrast to the poor activity of those QACs with a short hydrophobic tail. Two QACs with proven antibacterial activity were chemically attached to hemlock by using hexamethylene diisocyanate (HDI) as a linker in supercritical carbon dioxide, as confirmed by FTIR. With the QACs being coated on the cell walls, the chemically modified wood demonstrated outstanding antibacterial activity, dimensional stability, and improved surface properties.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.5b01488. NMR spectra of the synthesized QACs (PDF).

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*P. A. Charpentier. E-mail: [email protected]. Phone: (519) 661-3466. Fax: (519) 661-3498. Notes

The authors declare no competing financial interest. J

DOI: 10.1021/acssuschemeng.5b01488 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

Research Article

ACS Sustainable Chemistry & Engineering (12) Fernandes, J.; Kjellow, A. W.; Henriksen, O. Modeling and optimization of the supercritical wood impregnation process - Focus on pressure and temperature. J. Supercrit. Fluids 2012, 66, 307−314. (13) Kjellow, A. W.; Henriksen, O. Supercritical wood impregnation. J. Supercrit. Fluids 2009, 50, 297−304. (14) Rowell, R. M.; Tillman, A.-M.; Simonson, R. A Simplified Procedure for the Acetylation of Hardwood and Softwood Flaxes for Flakeboard Production. J. Wood Chem. Technol. 1986, 6, 427−448. (15) Rowell, R. M. Acetylation of Wood. Forest Prod. J. 2006, 56, 4− 12. (16) Lande, S.; Westin, M.; Schneider, M. Development of Modified Wood Products Based on Furan Chemistry. Mol. Cryst. Liq. Cryst. 2008, 484, 1/[367]−12/[378]. (17) De Vetter, L.; Pilgård, A.; Treu, A.; Westin, M.; Van Acker, J. Combined evaluation of durability and ecotoxicity: A case study on furfurylated wood. Wood Mater. Sci. Eng. 2009, 4, 30−36. (18) Hill, C. A. S. Why does acetylation protect wood from microbiological attack? Wood Mater. Sci. Eng. 2009, 4, 37−45. (19) Jebrane, M.; Pichavant, F.; Sèbe, G. A comparative study on the acetylation of wood by reaction with vinyl acetate and acetic anhydride. Carbohydr. Polym. 2011, 83, 339−345. (20) Obataya, E.; Minato, K. Potassium acetate-catalyzed acetylation of wood: extraordinarily rapid acetylation at 120°C. Wood Sci. Technol. 2008, 42, 567−577. (21) Mitsui, K. Acetylation of wood causes photobleaching. J. Photochem. Photobiol., B 2010, 101, 210−214. (22) von Nussbaum, F.; Brands, M.; Hinzen, B.; Weigand, S.; Häbich, D. Antibacterial Natural Products in Medicinal ChemistryExodus or Revival? Angew. Chem., Int. Ed. 2006, 45, 5072−5129. (23) Jampala, S. N.; Sarmadi, M.; Somers, E. B.; Wong, A. C. L.; Denes, F. S. Plasma-Enhanced Synthesis of Bactericidal Quaternary Ammonium Thin Layers on Stainless Steel and Cellulose Surfaces. Langmuir 2008, 24, 8583−8591. (24) Roy, D.; Knapp, J. S.; Guthrie, J. T.; Perrier, S. Antibacterial Cellulose Fiber via RAFT Surface Graft Polymerization. Biomacromolecules 2008, 9, 91−99. (25) Klibanov, A. M. Permanently microbicidal materials coatings. J. Mater. Chem. 2007, 17, 2479−2482. (26) Andresen, M.; Stenstad, P.; Moretro, T.; Langsrud, S.; Syverud, K.; Johansson, L.-S.; Stenius, P. Nonleaching Antimicrobial Films Prepared from Surface-Modified Microfibrillated Cellulose. Biomacromolecules 2007, 8, 2149−2155. (27) Hou, A.; Zhou, M.; Wang, X. Preparation and characterization of durable antibacterial cellulose biomaterials modified with triazine derivatives. Carbohydr. Polym. 2009, 75, 328−332. (28) Xu, W.; Gao, G.; Kadla, J. Synthesis of antibacterial cellulose materials using a “clickable” quaternary ammonium compound. Cellulose 2013, 20, 1187−1199. (29) Yagci, M. B.; Bolca, S.; Heuts, J. P. A.; Ming, W.; de With, G. Self-stratifying antimicrobial polyurethane coatings. Prog. Org. Coat. 2011, 72, 305−314. (30) Sui, R.; Rizkalla, A. S.; Charpentier, P. A. Formation of Titania Nanofibers: A Direct Sol-Gel Route in Supercritical CO2. Langmuir 2005, 21, 6150−6153. (31) Fukaya, Y.; Iizuka, Y.; Sekikawa, K.; Ohno, H. Bio ionic liquids: room temperature ionic liquids composed wholly of biomaterials. Green Chem. 2007, 9, 1155−1157. (32) Zhang, L.; Bikzhanova, G. A.; West, R. [2-(Hydroxyethoxy)ethyl]trimethylammonium iodide. Acta Crystallogr., Sect. E: Struct. Rep. Online 2007, 63, o2284−o2285. (33) Alam, T. M.; Dreyer, D. R.; Bielwaski, C. W.; Ruoff, R. S. Measuring Molecular Dynamics and Activation Energies for Quaternary Acyclic Ammonium and Cyclic Pyrrolidinium Ionic Liquids Using 14N NMR Spectroscopy. J. Phys. Chem. A 2011, 115, 4307−4316. (34) Acik, M.; Dreyer, D. R.; Bielawski, C. W.; Chabal, Y. J. Impact of Ionic Liquids on the Exfoliation of Graphite Oxide. J. Phys. Chem. C 2012, 116, 7867−7873.

(35) Amela-Cortes, M.; Paofai, S.; Cordier, S.; Folliot, H.; Molard, Y. Tuned red NIR phosphorescence of polyurethane hybrid composites embedding metallic nanoclusters for oxygen sensing. Chem. Commun. 2015, 51, 8177−8180. (36) Kim, W.; Chung, D.-w.; Kim, J. H. Effect of length of hydroxyalkyl groups in the clay modifier on the properties of thermoplastic polyurethane/clay nanocomposites. J. Appl. Polym. Sci. 2008, 110, 3209−3216. (37) Alhanash, H. B.; Brisdon, A. K. Quaternary ammonium ionic liquids containing fluorous ponytails: Competitive alkylation and elimination reactions of I(CH2)nRf (n = 2, 3) with tertiary amines. J. Fluorine Chem. 2013, 156, 152−157. (38) Ioannou, C. J.; Hanlon, G. W.; Denyer, S. P. Action of Disinfectant Quaternary Ammonium Compounds against Staphylococcus aureus. Antimicrob. Agents Chemother. 2007, 51, 296−306. (39) AhlstrÖ M, B.; Thompson, R. A.; Edebo, L. The effect of hydrocarbon chain length, pH, and temperature on the binding and bactericidal effect of amphiphilic betaine esters on Salmonella tvphimurium. APMIS 1999, 107, 318−324. (40) Iversen, S. B.; Larsen, T.; Henriksen, O.; Felsvang, K. The World’s First Commercial Supercritical Wood Treatement Plant. In The International Society for the Advancement of Supercritical Fluids - 6th International Symposium on Supercritical Fluids, Versailles, France, April 28−30, 2003.

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DOI: 10.1021/acssuschemeng.5b01488 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX