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Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Acknowledgements
  7. References

Previously we found that covalent attachment of long-chained, moderately hydrophobic polycations to surfaces of solid objects renders the latter permanently bactericidal. Herein we replaced such surface-specific, multistep immobilization techniques with a single-step, general procedure akin to common painting. Glass or polyethylene slides were briefly dipped into organic solutions of certain optimally hydrophobic N-alkyl-PEI (where PEI stands for branched 750-kDa polyethylenimine) polycations, followed by solvent evaporation. The resultant polycation-coated slides were able to kill on contact all of the encountered bacterial cells, whether the Gram-positive human pathogen Staphylococcus aureus or its Gram-negative brethren Escherichia coli. This biocidal effect was found not to be caused by N-alkyl-PEI molecules leached from the surface. Further examination of the mechanism of this bactericidal action suggested that the surface-deposited N-alkyl-PEI kills bacteria by rupturing their cellular membranes. This conclusion was further supported by studies in which the molecular weight of PEI and the hydrophobicity of the alkyl moiety were varied.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Acknowledgements
  7. References

There is an obvious and unmet need to render surfaces of common objects lethal to pathogenic bacteria while remaining nontoxic to people and animals. Thus over the past half decade, we have been designing and validating novel methods for derivatizing material surfaces to make them permanently microbicidal (see ref 1 for a review). In this quest, we have discovered that covalent attachment of various sufficiently long, moderately hydrophobic, synthetic polycations to diverse materials including glass, plastics, and textiles enables them to efficiently kill on contact a number of pathogenic bacteria and fungi, both airborne and waterborne (1–6). Importantly, these immobilized hydrophobic polycations kill bacteria by drastically damaging their membranes and/or cell walls and not by gradually leaching (detaching) from the derivatized surfaces (1, 2, 7). Consequently, bacteria seem unable to develop resistance to such immobilized polycations, which are not toxic to mammalian cells (7).

The foregoing studies, confirmed by others (e.g., 8, 9), have constituted a critical proof of principle for making self-sterilizing surfaces. However, the surface derivatization methods employed involve several synthetic steps, as well as harsh reagents and elevated temperatures (1). Therefore, while clearly effective and feasible, these methods are probably not practical for routine application by untrained personnel.

Common sense suggests that to overcome this practicality hurdle the coating procedure ideally should be like painting. No matter how complex a mixture of components and their nature are, as long as they are prepared in a factory, all the ultimate user has to do is spray or otherwise apply the resultant paint onto an object to be painted. In the present work, we have decided to emulate this straightforward painting rationale with bactericidal coatings. To this end, herein we have developed different hydrophobic polycationic systems that can serve as such a “bactericidal paint”. When a glass or polyethylene slide is dipped and the solvent evaporates, the resulting coated slide kills essentially 100% of Staphylococcus aureus and Escherichia coli bacteria reaching its surface. Furthermore, when optimized, such noncovalently deposited hydrophobic polycations, like their covalently immobilized counterparts, kill bacteria not as a result of gradual leaching but rather by rupturing bacterial membranes.

Materials and Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Acknowledgements
  7. References

Materials. The Live/Dead cell double staining kit was purchased from Fluka and 2,2′-azobis(isobutyronitrile) (AIBN) from Sigma-Aldrich. PEI (Mw values of 750, 25, and 2 kDa), 1-bromohexane, 1-bromododecane, 1-bromooctadecane, iodomethane, tert-amyl alcohol, allyl bromide, styrene, butyl methacrylate, methyl ethyl ketone, and all other chemicals and solvents were from Aldrich Chemical Co. and were used without further purification, except for styrene and butyl methacrylate, which were washed with 5% aqueous NaOH and deionized water and then dried with anhydrous CaCl2 prior to use.

Microorganisms. The strains employed in this work were the Gram-positive bacterium Staphylococcus aureus (ATCC 33807) and the Gram-negative bacterium Escherichia coli (E. coli genetic stock center, CGSC4401).

Solutions. Yeast-dextrose broth contained (per L of deionized water) 10 g of peptone, 8 g of beef extract, 5 g of NaCl, 5 g of glucose, and 3 g of yeast extract (10). Phosphate-buffered saline (PBS) contained (per L of deionized water) 8.2 g of NaCl and 1.2 g of NaH2PO4·H2O. The pH of the PBS solution was adjusted to 7.0 with a 1 N aqueous NaOH. Both solutions were autoclaved for 20 min prior to use.

Synthesis ofN-Alkyl,N-methyl-PEI (Scheme 1). A solution of 5.5 g of PEI and 21 g of K2CO3 in 70 mL of tert-amyl alcohol and 53, 90, and 120 mL of 1-bromohexane, 1-bromododecane, and 1-bromooctadecane, respectively, were mixed and stirred at 95 °C for 24, 96, and 108 h. After removing the solids by filtration under reduced pressure, 15 mL of iodomethane was added, followed by stirring at 60 °C for 24 h in a sealed bottle (11–14). The resultant solution was added to an excess of hexane for N-hexyl,N-methyl-PEI and acetone for the others, and the precipitate was recovered by filtration under reduced pressure, washed with an excess of hexane for N-hexyl,N-methyl-PEI and acetone for the others, and dried at room temperature under vacuum overnight. 1H NMR of N-hexyl,N-methyl-PEI in CDCl3 (δ, ppm):  0.85−1.0 [N-CH2-(CH2)4-CH3], 1.2−1.6 [N-CH2-(CH2)4-CH3], 3.2−3.8 [N-CH2-(CH2)4-CH3, N-CH3, alkylated PEI]. 1H NMR of N-dodecyl,N-methyl-PEI:  0.85−0.95 [N-CH2-(CH2)10-CH3], 1.1−1.5 [N-CH2-(CH2)10-CH3], 3.3−4.0 [N-CH2-(CH2)10-CH3, N-CH3, alkylated PEI]. 1H NMR of N-octadecyl,N-methyl-PEI:  0.8−0.9 [N-CH2-(CH2)16-CH3], 1.1−1.6 [N-CH2-(CH2)16-CH3], 3.2−4.5 [N-CH2-(CH2)16-CH3, N-CH3, alkylated PEI].

Preparation ofN-Copolymer,N-hexyl,N-methyl-PEI (Scheme 2). A solution of 5 g of styrene, 5 g of butyl methacrylate, and 10 g of allyl bromide in 50 mL of methyl ethyl ketone was placed in a three-necked glass flask, followed by purging with argon for 20 min. Then the reaction mixture was heated to 70 °C, and 0.2 g of the initiator AIBN was added (15, 16). After stirring for 24 h, the product (“copolymer-Br”) was precipitated with an excess of methanol, additionally washed with methanol, and dried at room temperature under vacuum.

Solutions of 1 g of PEI in 5 mL of tert-amyl alcohol and 2 g of the copolymer-Br in 20 mL of methyl ethyl ketone were mixed with 0.1 g of KOH and stirred at 60 °C for 5 h. After solvent evaporation, the PEI N-alkylated with the copolymer was washed with methanol, dried under vacuum, and placed in a solution of 10 mL of 1-bromohexane and 0.1 g of KOH in 20 mL of methyl ethyl ketone. After stirring at 70 °C for 12 h, the N-copolymer-N-hexyl-PEI formed was washed with methanol, dried under vacuum, and then N-methylated in a solution of 10 mL of iodomethane in 20 mL of methyl ethyl ketone at 60 °C for 12 h in a sealed bottle (11–14). The resultant N-copolymer,N-hexyl,N-methyl-PEI was washed with methanol and dried at room temperature under vacuum.

Polymer Analyses. The structure of the N-alkylated PEI polymers synthesized by us was confirmed by proton NMR in CDCl3 using a Brucker 400-MHz instrument. The molecular weight (Mw) of the polymeric alkylating agent prepared by us was determined by means of gel permeation chromatography using a Waters Styragel HT column with tetrahydrofuran as a mobile phase (0.1 mL/min flow rate) and a Waters 490 programmable multiwavelength detector.

Preparation of Coated Slides. Commercially available glass slides (25 mm × 75 mm, Sigma-Aldrich), as well as polyethylene ones (cut by us to a 25 mm × 75 mm size, Fiber Glast Development Corp.), were dipped for 1 min into a solution of 50 mg of N-alkyl,N-methyl-PEI per mL of methanol, butanol, or toluene, respectively, for alkyl = hexyl, dodecyl, or octadecyl, or into a solution of 100 mg of N-copolymer,N-hexyl,N-methyl-PEI per mL of methyl ethyl ketone, followed by air-drying.

Determination of Bactericidal (Killing) Efficiency. One hundred microliters of a suspension of S. aureus or E. coli in 0.1 M PBS (approximately 1011 cells/mL) was added to 20 mL of the yeast-dextrose broth in a 50-mL sterile centrifuge tube, followed by shaking at 200 rpm and 37 °C overnight (Innova 4200 Incubator Shaker, New Brunswick Scientific). The bacterial cells were harvested by centrifugation at 6,000 rpm for 10 min (Sorvall RC-5B, DuPont Instruments), washed twice with PBS, and diluted to 5 × 106 cells/mL for S. aureus and to 5 × 107 cells/mL for E. coli. The bacterial suspensions in PBS were sprayed onto slides at a rate of approximately 10 mL/min in a fume hood. After a 2-min drying under air, the resultant slide was placed in a Petri dish, and immediately covered with a layer of solid growth agar (1.5% agar in the yeast-dextrose broth, autoclaved, poured into a Petri dish, and allowed to gel at room temperature overnight). The Petri dish was sealed and incubated at 37 °C overnight, and the bacterial colonies grown on the slide surface were counted on a light box (2, 5).

Monitoring of Live/Dead Cells by Fluorescent Labeling. Fifty microliters of a bacterial suspension (approximately 109 cells/mL) in PBS was mixed with 50 μL of a Live/Dead cell staining solution consisting of 10 μL of the green fluorescent Calcein-AM stain {3′,6′-di(O-acetyl)-2′,7′-bis[N,N-bis(carboxylmethyl)aminomethyl]-fluorescein tetraacetoxymethyl ester}, 15 μL of the red fluorescent nucleic acid stain propidium iodide, and 25 μL of PBS. After incubation at room temperature for 15 min in the dark, a 5-μL aliquot of this mixture was placed on a glass surface, immediately covered with coverslip, and examined by fluorescence microscopy (Axioskop 2 MAT microscope, Carl Zeiss). Fluorescein and rhodamine band-pass filters were used for live and dead cells, respectively. Images of live/dead cells were recorded using a 200-ms exposure and a 500-fold magnification. The bacterial cells appearing green were assumed intact, whereas those appearing red were assumed damaged/having ruptured membranes (17).

Results and Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Acknowledgements
  7. References

If one's goal is to develop a general, single-step procedure for making any solid surface bactericidal, then covalent attachment of polymers is probably not a viable option given the paucity of derivatization-amenable functional groups on most common surfaces. Therefore, inspired by the versatility and reliability of oil paints, we decided to explore physical deposition of hydrophobic polycations to hopefully afford the same mechanism of bactericidal action as that exhibited by previously implemented covalently attached coatings (1). We reasoned that, as in the case of oil paints, sufficient hydrophobicity of the deposited polycations could preclude their dissolution in water and also result in their attraction to each other, both factors being conducive to preventing their leaching from the surface into aqueous solution.

For simplicity, we began our investigation with the same moderately hydrophobic polycation that, when covalently immobilized, resulted in highly antibacterial surfaces (5–7). To this end, commercially available, branched, 750-kDa polyethylenimine (PEI), which as depicted in Scheme 1.I has secondary, primary, and tertiary amino groups, was quaternized as shown in Scheme 1.II (n = 6). Namely, PEI was first N-hexylated to introduce hydrophobic groups and to enhance the positive charges. Second, to maximize this process by N-alkylating even those PEI amino groups sterically inaccessible to bromohexane, the N-hexyl-PEI was treated with iodomethane (5–7). Following purification, the resultant N-hexyl,N-methyl-PEI was dissolved in methanol at 50 mg/mL. A glass slide was immersed into that solution for 1 min and then removed, and methanol was allowed to evaporate.

To mimic exposure to aerosolized, airborne bacteria, as previously (2, 4–7) we sprayed a bacterial suspension onto a surface of interest using a laboratory chromatographic sprayer. After a brief drying under air, the slide was overlaid with growth agar gel, placed in a Petri dish, sealed, and incubated at 37 °C overnight, followed by counting the resultant bacterial colonies (2).

When the foregoing procedure, employing the human pathogenic bacterium Staphylococcus aureus, was applied to a standard, noncoated glass slide, typically some 120 bacterial colonies per cm2 were detected (see Figure 1a as an example). However, when the same bacterial suspension was sprayed onto a glass slide coated with N-hexyl,N-methyl-PEI, not a single colony was observed. Therefore, either the coated surface kills the bacteria on contact or the coating's polycations leach from the surface, thus killing the bacteria.

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Figure Figure 1. Photographs of a glass slide (a), of a slide coated with N-copolymer,N-hexyl,N-methyl-PEI (b), and of a leaching test control (c) onto which aqueous suspensions (approximately 5 × 106 cells/mL in a PBS solution) of S. aureus cells were sprayed, followed by drying in air for 2 min, covering with solid growth agar, and incubating at 37 °C overnight. Each white dot corresponds to a bacterial colony grown from a single surviving bacterial cell.

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To test the second possibility, we designed the following control experiment. A polycation-coated glass slide not sprayed with a bacterial suspension was overlaid with the growth agar gel, placed in a Petri dish, sealed, and incubated at 37 °C overnight. Consequently, the slide-deposited N-hexyl,N-methyl-PEI was allowed to leach into the gel slab. Then the same S. aureus suspension as before was sprayed onto a non-coated glass slide, followed by overlaying with the growth agar gel that had been exposed to the polycation-coated slide and a subsequent overnight incubation at 37 °C. We reasoned that if enough of the N-hexyl,N-methyl-PEI had leached into the gel, it would now leach out of it into the covered bacterial cells and kill them. Indeed, no bacterial colonies were observed in this experiment. Thus we were unable to definitively conclude whether the bactericidal action described in the preceding paragraph was due to exposure to the deposited polycations per se, to leaching of the deposited N-hexyl,N-methyl-PEI, or to a combination of the two.

To minimize leaching by creating hydrophobic interactions between the deposited N-hexyl,N-methyl-PEI and the surface, we replaced hydrophilic glass slides with hydrophobic polyethylene ones. A noncoated polyethylene slide was roughly as hospitable to S. aureus bacterium as glass:  typically about 110 colonies per cm2. In contrast, a slide coated with the polycation killed all bacteria sprayed on it, but the same result was also observed in the leaching test control experiment (the penultimate and last lines, middle column, in Table 1), thus again precluding unambiguous attribution of the cause of the bactericidal action.

Table Table 1. Bactericidal Activity against Airborne S. aureus of Glass and Polyethylene Slides Coated with N-Alkyl,N-methyl-PEIa
  bactericidal efficiency,c %
surfacesampleN-hexyl,N-methyl-PEIN-dodecyl,N-methyl-PEIN-octadecyl,N-methyl-PEI
  1. a Bacterial suspensions (5 × 106 cells/mL) in a PBS aqueous solution were sprayed onto a surface of interest, dried in air for 2 min, placed in a Petri dish, covered with 1.5% solid growth agar, sealed, and incubated at 37 °C overnight, and then the colonies were counted.b In this leaching test control, a coated slide surface (no sprayed bacteria) was covered with the solid growth agar gel and incubated at 37 °C overnight. The gel slab was immediately placed on another, non-coated slide following spraying of the bacterial suspension on it. The system was then incubated in a Petri dish at 37 °C overnight, and the colonies were counted.c Bactericidal (killing) efficiency is defined as the number of bacterial colonies/cm2 observed following cultivation on a coated slide divided by that in the case of the corresponding noncoated slide, times 100%. All experiments were carried out at least in duplicate, and the errors indicate the standard deviations.

glasscoated10010059 ± 13
glasscontrolb10000
polyethylenecoated10010045 ± 8
polyethylenecontrolb10000

To eliminate this interpretational ambiguity, we endeavored both to strengthen the adhesion among slide-deposited polycation molecules and to lower even further their solubility in water (and hence, hopefully, prevent leaching) by increasing their hydrophobicity. To this end, instead of bromohexane in Scheme 1.II, we employed bromododecane (i.e., n = 12). The resultant N-dodecyl,N-methyl-PEI was dissolved in butanol and used for coating of glass and polyethylene slides in the otherwise the same manner as its n = 6 predecessor.

As seen in the fourth column of Table 1, both coated slides once again afforded a 100% killing efficiency against S. aureus bacteria; this time, however, unlike with N-hexyl,N-methyl-PEI-coated slides, the leaching test control featured essentially as many bacterial colonies as the noncoated slides. Thus the leaching of the n = 12 polycation (Scheme 1.II) may be deemed negligible in terms of their bactericidal activity. These results indicate that it is the deposited (as opposed to dissolved) N-dodecyl,N-methyl-PEI that kills on contact airborne S. aureus.

To establish the generality of the antibacterial prowess of the N-dodecyl,N-methyl-PEI coating, it was also tested against another, dissimilar human pathogenic bacterium Escherichia coli (which is Gram-negative, unlike S. aureus which is Gram-positive). As seen in Table 2 (the penultimate line), this polycationic coating, whether deposited on a glass (3rd column) or polyethylene (4th column) slide, was 100% lethal to this bacterium as well. Importantly, as with S. aureus, no bactericidal activity was detected in the leaching test control experiments (Table 2). Therefore, N-dodecyl,N-methyl-PEI painted onto a solid surface appears to efficiently kill on contact airborne bacteria.

Table Table 2. Bactericidal Activity against Airborne S. aureus and E. coli of Glass and Polyethylene Slides Coated with N-Dodecyl,N-methyl-PEI and with N-Copolymer,N-hexyl,N-methyl-PEIa
  bactericidal efficiency,c %
  N-dodecyl,N-methyl-PEIN-copolymer,N-hexyl,N-methyl-PEI
bacteriumsampleglasspolyethyleneglasspolyethylene
  1. a-c See corresponding footnotes to Table 1. For E. coli, a 5 × 107 cells/mL bacterial suspension was used.

S. aureuscoated100100100100
S. aureuscontrolb0000
E. colicoated100100100100
E. colicontrolb0000

To verify that this coating is not unique, we explored another hydrophobic polycation where the side chain itself was polymeric. This side chain, as depicted in Scheme 2.II, stemmed from an alkylating agent prepared by copolymerization of styrene, butyl methacrylate, and allyl bromide (1:1:2, w/w/w). The product of this reaction (referred to as the “copolymer-Br”), determined to have an average molecular weight of 8,800 Da, was used to N-alkylate a 750-kDa branched PEI, followed by N-hexylation and N-methylation (Scheme 2.II).

N-Copolymer,N-hexyl,N-methyl-PEI dissolved in methyl ethyl ketone at 100 mg/mL was used to coat a glass slide in the same way as with the previous polycations. When a suspension of S. aureus was sprayed onto this coated slide, no bacterial cells survived (Figure 1b). However, in the leaching test control, the number of colonies grown was virtually the same as with a noncoated glass slide (Figure 1c and 1a, respectively). The same results were obtained with polyethylene slides and with E. coli (Table 2, the last two columns and the last two lines, respectively). These observations indicate that solid surfaces coated with N-copolymer,N-hexyl,N-methyl-PEI (i) kill on contact all airborne bacterial cells reaching them, and (ii) exert this bactericidal action by means other than leaching the hydrophobic polycation from the surface.

The critical remaining question was that of the mechanism of the bactericidal action described above. To elucidate it, as previously with covalently immobilized hydrophobic polycations (7), we employed the Live/Dead two-color fluorescent method to ascertain whether our surface-deposited coatings rupture bacterial membranes. Briefly, this method involves two fluorescent dyes able to bind to nucleic acids, the green stain Calcein-AM and the red stain propidium iodide. The former is membrane permeable and therefore labels all bacterial cells present. In contrast, propidium iodide cannot penetrate into intact bacterial cells and hence labels only those with ruptured membranes. Furthermore, the red propidium iodide stain cancels the green fluorescence of Calcein-AM in the damaged cells by displacing it from complexes with nucleic acids. Consequently, bacteria with intact membranes fluoresce green, whereas those with ruptured membranes fluoresce red (17).

Figure 2, 3, 4 presents the results of the aforementioned Live/Dead analysis with S. aureus (a−c) and E. coli (d−f) cells on glass slides. In both instances, some 98% of bacterial cells adhered to an uncoated slide (a and d) were green after a 2-h incubation in aqueous solution at room temperature, i.e., the population was almost completely intact. In contrast, only 2% and 5%, respectively, of S. aureus (b) and E. coli (e) cells were green, i.e., intact, following adhesion to N-dodecyl,N-methyl-PEI-coated slides. The corresponding percentages in the case of a glass slide coated with N-copolymer,N-hexyl,N-methyl-PEI were 6% (c) and 10% (f). In all instances, no adhered bacterial cells were intact after a longer, 6-h incubation (data not shown).

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Figure Figure 2. Fluorescence microscopy images of adhered S. aureus (a−c) and E. coli (d−f) cells after a 2-h exposure to the surface of untreated glass slides (a and d), slides coated with N-dodecyl,N-methyl-PEI (b and e), and slides coated with N-copolymer,N-hexyl,N-methyl-PEI (c and f). Fifty microliteres of bacterial suspensions (approximately 109 cells/mL) in a PBS aqueous solution was mixed with 50 μL of the Live/Dead cell staining solution (see Methods). A 5-μL aliquot of the mixture was placed on the surfaces, immediately covered with coverslip, and examined by fluorescence microscopy. The bacterial cells appearing green are intact; the red ones have ruptured membranes. See text for details.

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Figure Scheme 1.. (I) Structure of Polyethylenimine (PEI) Used in This Work (Unless Stated Otherwise). (II) Synthesis of N-Alkyl,N-methyl-PEIaa PEI was N-alkylated with 1-bromoalkane (n = 6, 12, or 18, as indicated in the text) and then N-methylated with iodomethane. See text for details.

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Figure Scheme 2.. (I) Synthesis of “Copolymer-Br” by Copolymerization of Styrene, Butyl Methacrylate, and Allyl Bromide (1:1:2, w/w/w). (II) Preparation of N-Copolymer,N-hexyl,N-methyl-PEIaa See text for details.

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These observations indicate that the surface-deposited hydrophobic polycations, like some covalently immobilized ones (7), kill bacteria by rupturing their cell membranes. Presumably, sufficiently long chains of the polycationic molecules stick out even in such noncovalent coatings to reach and damage the bacterial membranes. To verify this conclusion and to gain further mechanistic insights, the following two experiments were conducted.

First, to possess such sufficiently long erect chains, the polycation at least should be large enough itself. In other words, one would expect the killing efficiency to decline with decrease in the size of the polycation. Indeed one can see in Table 3 that while the 750-kDa-PEI-based N-dodecyl,N-methyl-PEI and N-copolymer,N-hexyl,N-methyl-PEI afforded a 100% killing efficiency for both S. aureus and E. coli, the killing efficiencies were slightly lower, 89−96%, in the case of a 25-kDa PEI. Moreover, in the case of a 2-kDa PEI, the killing efficiencies dropped to the 46−60% range (Table 3). Aside from supporting the foregoing membrane rupture conclusion, these data also confirm the view that the bactericidal action is not exerted by leached/dissolved polycations. If it were, there would be no particular reason for the killing efficiency to decrease with the molecular weight of the polycation (Table 3). (Also note in the table that even for smaller PEIs no bactericidal action was observed in the leaching test control experiments.)

Table Table 3. Bactericidal Activity against Airborne S. aureus and E. coli of Glass Slides Coated with N-Dodecyl,N-methyl-PEI and with N-Copolymer,N-hexyl,N-methyl-PEI as a Function of Molecular Weight of the PEIa
  bactericidal efficiency,c%
  N-dodecyl,N-methyl-PEIN-copolymer,N-hexyl,N-methyl-PEI
bacteriumPEI mol wt, kDacoatedcontrolbcoatedcontrolb
  1. a-c See corresponding footnotes to Table 1.

S. aureus75010001000
 2596 ± 101000
 246 ± 2060 ± 40
E. coli75010001000
 2589 ± 3092 ± 20
 247 ± 3051 ± 30

Second, one would expect that, with other things being equal, increasing the hydrophobicity of the polycations should strengthen their intermolecular attraction and hence diminish propensity for their segments to break away from the rest and stick out when in a coating. This prediction was verified by increasing n to 18 in Scheme 1.I, i.e., N-octadecylating PEI (Scheme 1.II) instead of N-dodecylating. As one can see in the last column of Table 1, glass and polyethylene slides coated with N-octadecyl,N-methyl-PEI, unlike the dodecyl analogue, indeed displayed only partial, 59% and 45%, killing efficiencies.

Given the simplicity of the one-step bactericidal painting developed and validating in this work, it should have a greater chance of finding practical applications than its elaborate predecessors.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Acknowledgements
  7. References

This work was financially supported by the U.S. Army through the Institute for Soldier Nanotechnologies under Contract DAAD-19-02-D-0002 with the Army Research Office. The content does not necessarily reflect the position of the U.S. Government, and no official endorsement should be inferred. Daewon Park is grateful for a Korea Research Foundation Grant (KRF-2005-214-D00254) from the Korean Government (MOEHRD, Basic Research Promotion Fund). We thank our colleague Dr. Luis Alvarez for his help with NMR experiments.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Acknowledgements
  7. References