A.
Chiloeches
ab,
A.
Funes
c,
R.
Cuervo-Rodríguez
c,
F.
López-Fabal
de,
M.
Fernández-García
af,
C.
Echeverría
*af and
A.
Muñoz-Bonilla
*af
aInstituto de Ciencia y Tecnología de Polímeros (ICTP-CSIC), C/Juan de la Cierva 3, 28006 Madrid, Spain. E-mail: sbonilla@ictp.csic.es; cecheverria@ictp.csic.es
bUniversidad Nacional de Educación a Distancia (UNED), C/Bravo Murillo, 38, 28015 Madrid, Spain
cFacultad de Ciencias Químicas, Universidad Complutense de Madrid, Avenida Complutense s/n, Ciudad Universitaria, 28040 Madrid, Spain
dHospital Universitario de Móstoles C/Dr. Luis Montes, s/n, 28935 Móstoles, Madrid, Spain
eFacultad de Ciencias Experimentales, Universidad Francisco de Vitoria, Carretera Pozuelo a Majadahonda, Km 1.800, 28223, Madrid, Spain
fInterdisciplinary Platform for Sustainable Plastics towards a Circular Economy-Spanish National Research Council (SusPlast-CSIC), Madrid, Spain
First published on 5th May 2021
Herein, we report, for the first time, the synthesis of clickable polymers derived from biobased itaconic acid, which was then used for the preparation of novel cationic polymers with antibacterial properties and low hemotoxicity via click chemistry. Itaconic acid (IA) was subjected to chemical modification by incorporating clickable alkyne groups on the carboxylic acids. The resulting monomer with pendant alkyne groups was easily polymerized and copolymerized with dimethyl itaconate (DMI) by radical polymerization. The feed molar ratio of comonomers was varied to precisely tune the content of alkyne groups in the copolymers and the amphiphilic balance. Subsequently, an azide with a thiazole group, which is a component of the vitamin thiamine (B1), was attached onto the polymers by copper-catalyzed azide-alkyne cycloaddition (CuAAC) click chemistry leading to triazole linkages. N-Alkylation reactions of the thiazole and triazole groups with methyl and butyl iodides provide the corresponding itaconate derivatives with pendant azolium groups. The copolymers with variable cationic charge densities and hydrophobic/hydrophilic balances, depending on the comonomer feed ratio, display potent antibacterial activity against Gram-positive bacteria, whereas the activity was almost null against Gram-negative bacteria. Hemotoxicity assays demonstrated that the copolymers exhibited negligible hemolysis and excellent selectivity, more than 1000-fold, for Gram-positive bacteria over human red blood cells.
Here, we proposed a new versatile method to modify the carboxylic acids of the itaconic acid monomer by incorporating pendant alkyne groups leading to clickable itaconic acid derivatives that can be polymerized via radical polymerization. This new approach can be used to further functionalize the IA-biobased polymers by copper-catalyzed azide–alkyne cycloaddition (CuAAC) click chemistry via triazole linkages. The facile and efficient reaction will allow the synthesis of new functional polymers. Specifically, we focused on incorporating antimicrobial azolium functionalities derived from vitamin thiamine (B1) to render biobased antimicrobial polymers.
For the antibacterial assay, the following were obtained: sodium chloride solution (NaCl suitable for cell culture, BioXtra) and phosphate buffered saline powder (pH 7.4) were obtained from Sigma-Aldrich. BBL Mueller–Hinton broth used as a microbial growth medium was purchased from Becton, Dickinson and Company and 96 well microplates were purchased from BD Biosciences. Columbia agar (5% sheep blood) plates were obtained from BioMérieux. American Type Culture Collection (ATCC): Pseudomonas aeruginosa (P. aeruginosa, ATCC 27853), Escherichia coli (E. coli, ATCC 25922), Staphylococcus epidermidis (S. epidermidis, ATCC 12228) and Staphylococcus aureus (S. aureus, ATCC 29213), used as bacterial strains, were purchased from Oxoid.
Briefly, itaconic acid (15.0 g, 115 mmol), propargyl alcohol (32.3 g, 576 mmol) and hydroquinone (1.26 g, 11.5 mmol) were placed in a three neck flask equipped with a Dean–Stark trap and the mixture was dissolved in THF (50 mL) at 60 °C. Then, toluene (250 mL) and H2SO4 (300 μL, 5.75 mmol) were added and the reaction mixture was heated under reflux for 24 h, during which period 4 mL of water was collected. After that, the solvents were partially removed under reduced pressure using a rotary evaporator, and the mixture was washed repeatedly with saturated NaHCO3 aqueous solution. The organic extract was dried over anhydrous MgSO4 and then filtered. The residual reaction mixture was finally purified by passing through a neutral alumina column using hexane:EtOAc (1:1) as a solvent. After solvent evaporation under reduced pressure, a yellow oil was obtained (22.998 g, 97% yield). HR-MS (ESI): m/z required for C11H10O4, 206.05863; found, 206.05791.
1 H-NMR (400MHz, CDCl 3 ), δ(ppm): 6.40 (d, 1H, CH2), 5.80 (d, 1H, CH2), 4.76 (d, 2H, –CH2CCH), 4.70 (d, J = 2.45, 2H, –CH2CCH), 3.40 (s, 2H, –CH2), 2.48 (m, J = 2.45, 2H, –CH2CCH).
13 C-NMR (100MHz, CDCl 3 ), δ(ppm): 169.80 (CO), 165.75 (CO), 132.78 (–CCH2), 130.03 (–CCH2), 75.22 (2C, –CH2CCH), 52.72 (–CH2CCH), 52.56 (–CH2CCH), 37.38 (–CH2).
1 H-NMR (400 MHz, CDCl 3 ), δ(ppm): 8.57 (s, 1H, H-thiazole), 8.56 (s, 1H, H-thiazole), 7.42 (s, 1H, H-triazole), 7.40 (s, 1H, H-triazole), 6.32 (s, 1H, CH2), 5.70 (s, 1H, CH2), 5.22 (s, 2H, O–CH2-triazole), 5.15 (s, 2H, O–CH2-triazole), 4.55 (t, J = 6.8, 4H, CH2–N), 3.39 (t, J = 6.8, 4H, CH2-thiazole), 3.32 (s, 2H, –CH2–), 2.21 (s, 6H, CH3-thiazole).
13 C-NMR (100 MHz, CDCl 3 ), δ(ppm): 170.50 (CO), 165.90 (CO), 150.85 (2C, thiazole C–CH3), 150.50 (2C, thiazole C–H), 142.77 (2C, triazole Cquat), 133.23 (–CCH2), 129.77 (–CCH2), 125.85 (2C, thiazole Cquat), 124.5 (triazole C–H), 124.4 (triazole C–H), 58.26 (O–CH2–), 58.14 (O–CH2–), 51.18 (2C, CH2–N), 37.94 (–CH2–), 27.45 (2C, –CH2 thiazole), 14.71 (2C, CH3-thiazole).
Copolymer P50: 1 H-NMR (400 MHz, CDCl 3 ), δ(ppm): 4.67 (4H, –CH2CCH), 3.58 (6H, O–CH3), 2.49 (2H, –CH2CCH), 1.99–1.00 (8H, CH2–CO and –CH2-chain).
Copolymer P50: 1 H-NMR (400 MHz, DMSO-d 6 ), δ(ppm): 4.67 (4H, –CH2CCH), 3.58 (6H, O–CH3 and 2H, –CH2CCH), 3.00–1.50 (8H, –CH2CO and CH2-chain–).
Copolymer P50T: 1 H-NMR (400 MHz, CDCl 3 ), δ(ppm): 8.61 (2H, H-thiazole), 7.71 (2H, H-triazole), 5.15 (4H, O–CH2-triazole), 4.62 (4H, CH2–N), 3.64 (6H, O–CH3) 3.45 (4H, CH2-thiazole), 2.21 (6H, CH3-thiazole), 2.00–1.00 (8H, CH2–CO and –CH2-chain).
Copolymer P50T: 1 H-NMR (400 MHz, DMSO-d 6 ), δ(ppm): 8.74 (2H, H-thiazole), 8.00 (2H, H-triazole), 5.01 (4H, O–CH2-triazole), 4.52 (4H, CH2–N), 3.50 (6H, O–CH3) 3.26 (4H, CH2-thiazole), 2.10 (6H, CH3-thiazole), 3.00–1.50 (8H, CH2CO and CH2-chain–).
Homopolymer P100T-Me: 1 H-NMR (400 MHz, D 2 O), δ(ppm): 8.89 (2H, H-thiazole), 7.96 (2H, H-triazole), 5.44 (4H, O–CH2-triazole), 5.02 (4H, CH2–N), 4.37 (6H, N+CH3 triazole), 4.10 (6H, N+CH3 thiazole), 3.77 (4H, CH2thiazole), 2.51 (6H, CH3-thiazole).
Homopolymer P100T-Bu: 1 H-NMR (400 MHz, D 2 O), δ(ppm): 8.93 (2H, H-thiazole), 8.20 (2H, H-triazole), 5.46 (4H, O–CH2-triazole), 5.05 (4H, CH2–N), 4.65 (4H, N+CH2 triazole), 3.45 (4H, N+CH2 thiazole), 3.9–3.50 (4H, CH2-thiazole), 2.54 (6H, CH3-thiazole), 1.90 (8H, CH2–CH2–CH3), 1.37 (8H, CH2–CH2–CH3), 0.96 (12H, CH2–CH2–CH3).
Copolymer P50T-Me: 1 H-NMR (400 MHz, D 2 O), δ(ppm): 8.92 (2H, H-thiazole), 8.07 (2H, H-triazole), 5.48 (4H, O–CH2-triazole), 5.05 (4H, CH2–N), 4.41 (6H, N+CH3 triazole), 4.13 (6H, N+CH3 thiazole), 3.80 (4H, CH2-thiazole), 3.68 (6H, –O–CH3), 2.53 (6H, CH3-thiazole).
Copolymer P150T-Bu: 1 H-NMR (400 MHz, D 2 O), δ(ppm): 8.96 (2H, H-thiazole), 8.26 (2H, H-triazole), 5.47 (4H, O–CH2-triazole), 5.10 (4H, CH2–N), 4.68 (4H, N+CH2 triazole), 4.47 (4H, N+CH2 thiazole), 3.82 (4H, CH2-thiazole), 3.68 (6H, –O–CH3), 2.54 (6H, CH3-thiazole), 1.93 (8H, CH2–CH2–CH3), 1.40 (8H, CH2–CH2–CH3), 0.95 (12H, CH2–CH2–CH3).
An absolutely achromatic supernatant solution indicates no hemolysis (Anegative control) while a red solution indicates hemolysis (Apositive control). All experiments were performed in triplicate, and the data were expressed as mean ± SD (n = 3).
In the first approach, presented in Scheme S1A,† we attempted the radical polymerization of IA through the α,β-unsaturated double bond using an APS initiator in aqueous media at 70 °C for 24 h. Subsequently, the obtained poly(itaconic acid) (PIA) was subjected to post-modification of the two carboxylic acid functionalities by the condensation reaction with propargyl alcohol, using EDC/NHS chemistry in aqueous media. However, this approach was discarded because, in addition to the problems associated with the polymerization of PIA such as low conversion and slow rate, the poly(itaconic acid) was insoluble in most organic solvents. Then, the incorporation of propargyl alcohol into the PIA led to a polymer insoluble in an aqueous reaction medium, which hindered the complete modification of PIA.
The second approach that we considered was the synthesis of a clickable monomer derived from IA, di(prop-2-yn-1-yl)itaconate (PrI) (see the Experimental section and Scheme S1B†). In this approach, the solubility issues were solved as the IA monomer has a higher solubility than PIA. The PrI monomer was successfully synthesized by the reaction between IA and propargyl alcohol in a mixture of toluene/THF and H2SO4, reaching a yield of 97%. Fig. 1A shows the 1H-NMR spectrum of the obtained PrI monomer, which confirms the complete functionalization of the carboxylic acid groups and the presence of the vinyl signals at 6.40 and 5.80 ppm. The 13C-NMR spectrum displayed in Fig. S1A in the ESI† also corroborated the chemical structure of the PrI monomer. The second step of this approach consisted in the incorporation of thiazole groups by Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) click chemistry between the alkyne groups of PrI and 2-(4-methylthiazol-5-yl)ethanol azide forming a 1,2,3-triazole group, which is also susceptible to quaternization. Likewise, 1H-NMR (Fig. 1B) and 13C-NMR spectra show typical peaks of the introduced functional groups, confirming the success of the reaction and the formation of the monomer derivative with thiazole and triazole groups in its structure (TTI). See the ESI, Fig. S1B,† for the 13C NMR spectrum of this monomer.
Fig. 1 1H-NMR spectra of (A) clickable monomer PrI and (B) monomer derivative TTI with thiazole and triazole groups in deuterated chloroform. |
In spite of the satisfactory synthesis of the biobased monomer TTI, this monomer did not easily polymerize or copolymerize with a comonomer such as dimethyl itaconate (DMI). We tried different polymerization conditions, both in bulk and in DMF solution. However, after 48 h of reaction, we were not able to obtain any polymer under all conditions tested, probably due to high steric hindrance among other reasons.
Then, a third approach was proposed (Scheme 2), the development of a clickable polymer derived from itaconic acid instead of using a clickable monomer. In this strategy, the clickable monomer PrI was successfully radical homopolymerized and copolymerized with dimethyl itaconate in DMF solution, at a total monomer concentration of 2 M, at 70 °C, with AIBN as a radical initiator. Therefore, homopolymers and a series of copolymers with different chemical compositions were obtained using different feed molar ratios (PrI/DMI = 100/0, 75/25, 50/50, 25/75 and 0/100).
Fig. 2 and 3 show the FTIR and 1H-NMR spectra, respectively, of the clickable copolymer P(PrI-co-DMI) for a feed chemical composition of PrI/DMI = 50/50 (named P50). In the FTIR spectrum, the characteristic peak of the alkyne C–H stretching band at 3283 cm−1 and the bands assigned to the CC bond at 2128 cm−1 and the CC–H bond at 642 cm−1 clearly demonstrate the successful synthesis of the alkyne-functionalized polymers. Likewise, in the 1H-NMR spectrum (Fig. 3A), the terminal methyne proton of the alkyne groups appears at 3.58 ppm and the rest of the signals are consistent with the chemical structure of the copolymer. The chemical compositions of the obtained polymers, thus the molar content of PrI in the copolymer, were calculated by integration of the 1H NMR spectral signals at 3.50 ppm (6H, O–CH3 from DMI) compared to the signal at 4.67 ppm (4H) from PrI. Table 1 summarizes the molecular characteristics of the synthesized copolymers and homopolymers including the obtained chemical compositions. The molar ratios of the comonomers in the copolymers were found to be very similar to the feed molar ratios, and therefore, polymers will be referred to by their feed compositions to maintain uniformity. This fact is important because the copolymer composition can be easily modulated by varying the comonomer feed ratios.
Sample P(PrI-co-DMI) | Feed ratio [PrI]/[DMI] | Polymer ratio [PrI]/[DMI]a | n (g mol−1) | Đ | Sample P(TTI-co-DMI) | nb (g mol−1) | Đ | |
---|---|---|---|---|---|---|---|---|
a Polymer ratio [PrI]/[DMI] was determined by 1H-NMR. b n and Đ values of the polymers after click reactions leading to P(TTI-co-DMI) polymers. | ||||||||
P100 | 100.0/0 | 100.0/0 | 6700 | 1.58 | P100T | 7100 | 1.59 | |
P75 | 75.0/25.0 | 72.5/27.5 | 8100 | 1.35 | P75T | 11100 | 1.27 | |
P50 | 50.0/50.0 | 50.1/49.9 | 7500 | 1.31 | P50T | 11700 | 1.25 | |
P25 | 25.0/75.0 | 23.1/76.9 | 6300 | 1.36 | P25T | 6800 | 1.49 | |
P0 | 0/100.0 | 0/100.0 | 4800 | 1.27 | P0 | — | — |
The molecular weights of the polymers were determined using SEC (Table 1) and were found to be low for all polymers, with values in the range of n = 4800–8100 g mol−1, presenting low molecular weight dispersity (Đ) (1.58–1.27).
Once clickable polymers were synthesized with different contents of alkyne groups, the next step consists in the CuAAC click chemistry with 2-(4-methylthiazol-5-yl)ethanol azide, which led to polymers with thiazole and 1,2,3-triazole groups, P(TTI-co-DMI). The post-polymerization reaction was carried out under mild conditions and the degree of modification was almost quantitative. After the click reaction, the molecular weights of the polymers detected by SEC increased as a result of the incorporation of the azide molecules (Table 1), while the polydispersity indexes practically did not change. Equally, the new thiazole and triazole groups attached to the polymer structures were detected by FTIR. Fig. 2 shows the FTIR spectrum of P50T. The signals at 3132 and 3075 cm−1 corresponding to the C–H stretching vibrations of the triazole and thiazole groups, the signal at 1543 cm−1 attributed to the CN bond of thiazole, and the absence of the band associated with the CN bond clearly indicate the successful coupling. The NMR spectra also confirm the completion of the click reaction and the formation of the P(TTI-co-DMI) copolymers. All the signals of the 1H NMR spectra were consistent with the expected structures. The 1H NMR spectrum of P50T displayed in Fig. 3B, as an example, shows the characteristic peaks at 8.74 ppm and 8.00, corresponding to the thiazole and triazole protons, respectively, concomitant with the disappearance of propargyl methylene signal at 4.67 ppm.
The last step of the synthesis procedure consists in the incorporation of permanent positive charges into the polymers to provide them with antibacterial activities. Both the pendant nucleophilic azole groups, triazole and thiazole, can be modified using very reactive alkylating reagents such as alkyl iodides. In this study, two alkylating agents with different chain lengths were used, methyl and butyl iodide, to tune the final hydrophobic/hydrophilic balance of the copolymer. This hydrophobic/hydrophilic balance is well known to have a strong influence on the antimicrobial activity and toxicity of the resulting polymers,2,26–28 and, in this work, it was also controlled by the content of the hydrophobic comonomer DMI. The synthesized P(TTI-co-DMI) (P100T, P75T, P50T and P25T) copolymers were reacted with a large excess of either methyl iodide or butyl iodide in DMF at 70 °C under an argon atmosphere. The reaction was performed for one week to ensure quantitative modification, which was confirmed by NMR and FTIR spectroscopy. Fig. 2 shows the comparison of the FTIR spectra of the quaternized copolymers with either methyl or butyl iodide of the samples with a molar ratio [PrI]/[DMI] = 50 (P50T-Me and P50T-Bu, respectively) with their unquaternized copolymer precursor (P50T). In both cases, the band at 1543 cm−1 assigned to the ν(CN) disappears and a new band corresponding to the ν(CN)+ clearly emerges due to the formed thiazolium and triazolium groups, after the quaternization reactions. Similarly, the 1H NMR spectrum demonstrates the success of the quaternization reaction and almost quantitative modifications of the thiazole and triazole groups (Fig. 4). The two peaks assigned to the aromatic protons of the 1,2,3-thiazole (∼8.6 ppm) and 1,3-triazole (8.0–7.6 ppm) rings shift to lower field regions (∼8.90 and ∼8.3–8.0 ppm, respectively) as a result of the quaternization reaction due to the higher polarity resulting from the formation of azolium groups. Fig. S2, ESI†, displays the 1H-NMR spectrum of P50T-Me in DMSO-d6, which supports the signal assignments. Likewise, Figs. S3 and S4 in the ESI† display the COSY-NMR spectra of the P50T-Me and P50T-Bu copolymers, which were also obtained to support the signal assignments in the 1H-NMR spectra of the Hf and Hg protons at 3.80 ppm (4H, CH2-thiazole) and 3.68 ppm (6H, –O–CH3), respectively. These assignments were verified through the analysis of the COSY-NMR spectra based on the correlation of the Hf protons with the Hd protons.
For the estimation of the positive charge density of the synthesized copolymers, zeta potential measurements were performed in distilled water. Table 2 shows the zeta potential values (ζ) obtained for all the synthesized copolymers. As confirmed by NMR and FTIR studies, the quaternization reactions result in cationic copolymers with high positive ζ values, around +50 mV for both methylated and butylated copolymers. Only the copolymers with a low content of cationic units, P50T-Me and P25T-Me, present reduced charge density.
ζ (mV) | ζ (mV) | ||||||
---|---|---|---|---|---|---|---|
P100T-Me | P75T-Me | P50T-Me | P25T-Me | P100T-Bu | P75T-Bu | P50T-Bu | P25T-Bu |
56 ± 1 | 49 ± 3 | 38 ± 2 | 40 ± 3 | 48 ± 1 | 48 ± 2 | 49 ± 2 | 51 ± 2 |
Copolymer | MIC (μg mL−1) | HC50 (μg mL−1) | HC50/MICa | |||
---|---|---|---|---|---|---|
E. coli | P. aeruginosa | S. epidermidis | S. aureus | |||
a Calculated based on the MIC values of S. aureus. | ||||||
P100T-Me | >10000 | 10000 | 31 | 10 | >10000 | >1000 |
P75T-Me | 10000 | 10000 | 31 | 10 | >10000 | >1000 |
P50T-Me | >10000 | 10000 | 312 | 312 | >10000 | >32 |
P25T-Me | >10000 | 10000 | 312 | 312 | >10000 | >32 |
P100T-Bu | >10000 | 5000 | 8 | 10 | >10000 | >1000 |
P75T-Bu | 5000 | 5000 | 8 | 10 | >10000 | >1000 |
P50T-Bu | 5000 | 10000 | 16 | 10 | >10000 | >1000 |
P25T-Bu | >10000 | 10000 | 31 | 10 | >10000 | >1000 |
Remarkably, huge differences in the activities of the polymers against Gram-positive and Gram-negative bacteria are clearly appreciated. Whereas the biobased cationic polymers present excellent activity against Gram-positive bacteria, they are totally inefficient against Gram-negative bacteria. Typically, Gram-negative bacteria are found to be less susceptible to cationic polymers than Gram-positive due to the additional outer membrane that provides a tough barrier to be overcome.29 The nature of the membrane also varies; in Gram-negative bacteria, the membranes are made of two negative phospholipidic membranes and lipopolysaccharides within the outer bilayer, while Gram-positive bacteria have thick cell walls, which consist of a large multilayer region of peptidoglycan with wall teichoic acid and lipoteichoic acid. Although this better behavior against Gram-positive bacteria was also revealed in our previous investigations with cationic methacrylic polymers bearing thiazole and triazole groups, such polymers also presented significant activity against Gram-negative bacteria.22,25,30 In the current work, the polymers derived from IA present four positive charges per monomeric unit, thus, a very high positive charge. In this case, with a high charge density, even when high content of the hydrophobic monomer DMI is used, the activity is almost nullified against Gram-negative bacteria. It seems that an excessive positive charge is detrimental to the disruptive action of polymers on Gram-negative bacterial membranes. On the other hand, against Gram-positive cells, the polymers were able to completely inhibit the bacterial growth at a low concentration, with MIC values that depend on the chemical composition, [TTI]/[DMI] ratio, and the length of the alkyl group. The activity was increased as the content of the active TTI units augments in the copolymers. The butylated polymers with the highest contents of TTI, P100T-Bu and P75T-Bu, have a MIC value as low as 8 μg mL−1. When the influence of the length of the alkyl group on activity is compared, the copolymers quaternized with butyl iodide exhibit the lowest MIC values, which indicates that longer hydrophobic alkyl chains impart stronger antibacterial activity, as previously discussed in the literature.4,6 Then, it appears that increasing the hydrophobicity of the alkylating chains in the antimicrobial polymers enhances their activity, whereas the incorporation of the hydrophobic comonomer DMI into the copolymer structure not only did not improve the antibacterial potential, but also decrease the activity. Apparently the activity against Gram-positive bacteria strongly depends on the cationic charge in the polymers, which is diluted by incorporating the DMI units. In fact, the copolymers with higher content of DMI units exhibited lower charge density as determined by zeta potential measurements. Then, modifying the hydrophobic/hydrophilic balance by varying the length of the alkylating agent seems to be an effective way to improve the activity, as the density of cationic charge is maintained by increasing the hydrophobicity.
Fig. 5 Hemolytic activity of the copolymers quaternized with either (A) methyl iodide or (B) butyl iodide. |
As shown in Fig. 5, all the copolymers exhibit very low hemolysis, with hemolysis percentages well below 50% for the highest concentration tested, 10000 μg mL−1. In fact, most of them present values even below 5%, in particular copolymers quaternized with butyl iodide. With regard to selectivity against bacteria over red blood cells, calculated by the ratio of HC50 and MIC values (Table 3; herein, the MIC values against S. aureus were used), all the itaconic acid derivatives demonstrate excellent selectivity values, with most copolymers showing more than 1000-fold selectivity toward bacteria over RBCs. This series of copolymers derived from biobased itaconic acid are promising antibacterial polymers as they exhibit excellent activity against Gram-positive bacteria and negligible hemolysis. It is well established that the hydrophobic/hydrophilic balance of polymers plays a crucial role in the selective attachment to a bacterial cell membrane.33–35 Typically, polymers with high hydrophobicity show high hemolysis activity due to the strong interaction with the mammalian cell membrane.36 The polymers developed in the current work are very hydrophilic with high charge density, demonstrating null toxicity while maintaining the antibacterial activity.
Footnote |
† Electronic supplementary information (ESI) available. See DOI: 10.1039/d1py00098e |
This journal is © The Royal Society of Chemistry 2021 |