BIOnic liquids: Imidazolium-based ionic liquids with antimicrobial activity

Article abstract of DOI:10.5560/ZNB.2013-3150

We have synthesized twelve new ionic liquids composed of an imidazolium-based cation in combination with an anion that shows antiobiotic or analgesic activity. These BIOnic Liquids have been tested towards their antibiotic activity in a standardized microbiological assay. A surprizingly large number of compounds shows high activity towards a set of bacteria which cannot be explained as simple cumulative effects. The general concept opens up completely new possibilities for the future development of pharmaceutically active compounds.

Full text of DOI:10.5560/ZNB.2013-3150

BIOnic Liquids: Imidazolium-based Ionic Liquids with Antimicrobial
Activity
Frank Postleba, Danuta Stefanikb, Harald Seifertb, and Ralf Giernotha
a
Universität zu Köln, Department für Chemie, Greinstr. 4, 50939 Köln, Germany
Universität zu Köln, Institut für Medizinische Mikrobiologie, Immunologie und Hygiene,
b
Goldenfelsstr. 19 – 21, 50935 Köln, Germany
Reprint requests to Priv.-Doz. Dr. Ralf Giernoth. Fax: +49 221 47-05102.
E-mail: ralf.giernoth@uni-koeln.de
Z. Naturforsch. 2013, 68b, 1123 – 1128 / DOI: 10.5560/ZNB.2013-3150
Received June 7, 2013
We have synthesized twelve new ionic liquids composed of an imidazolium-based cation in combi-
nation with an anion that shows antiobiotic or analgesic activity. These “BIOnic Liquids” have been
tested towards their antibiotic activity in a standardized microbiological assay. A surprizingly large
number of compounds shows high activity towards a set of bacteria which cannot be explained as
simple cumulative effects. The general concept opens up completely new possibilities for the future
development of pharmaceutically active compounds.
Key words: Ionic Liquids, Active Pharmaceutical Ingredients (API), Imidazolium Salts, Antibiotics,
Antimicrobials, Analgesics
Introduction
Task-specific ionic liquids (TSILs) [1] are second-
comprehensive reviews on the topic have appeared in
2005 [4] and in 2010 [5].
The effect of alkyl chain length on the antimicro-
generation ionic liquids (ILs) that are able to per- bial activity of imidazolium salts has been studied by
form a certain task in addition to being “just the sol- Jungnickel et al. [6], as mentioned already earlier. The
vent”. Since Davis’ very first publication on the topic groups of Borowiecki [7, 8] and Yin [9] have focussed
in which he described an IL containing an amine their studies on ionic liquids bearing a hydroxy group
functional group to be able to reversibly chemisorb in the cation. Their results were unsatisfactory; the
CO2 [2], numerous examples of TSILs have appeared OH group seemed to have little effect on the antimi-
in the literature.
crobial activity and the influence of the alkyl chain
Ionic liquids with biological activity which are, length remained dominant. The same result has been
strictly speaking, nothing but TSILs have been termed found by the group of Holzgrabe [10]. They tried to pin
“the third generation of ILs” [3]. It is already well- down the type of interactions responsible for the an-
known that certain ILs, although frequently called timicrobial potential of certain quaternary ammonium
“green”, can be quite toxic [4, 5]. Imidazolium salts salts.
in particular have been studied to a larger extent. It
Gathergood and co-workers have recently studied
was found that the longer the (unbranched) alkyl chain amino acid-functionalized imidazolium salts on their
that is attached to the imidazolium ring, the more toxic activity towards MRSA (methicillin-resistant Staphylo-
the salt [6]. Fortunately, this toxicity depends on the coccus aureus) [11]. Some of the salts were sufficiently
trophic level of the living entity: the higher the species active and additionally showed a reasonable level of
in the food chain, the less harmful the salt becomes [5]. biodegradibility.
Consequently, these salts are much more toxic for bac-
teria than for human beings, which makes them, by lactam antibiotics has been studied by Warner et
definition, antibiotic substances. al. [12]. They reported that in more than 90 % of their
The combination of the [C16mim] cation with β-
Quite a few ionic liquid antibiotics and antimicro- cases the combination outperformed the commercially
bials have already been described in the literature; available antibiotic.
© 2013 Verlag der Zeitschrift für Naturforschung, Tübingen · http://znaturforsch.com
Brought to you by | University of California
Authenticated
Download Date | 6/9/15 9:40 AM

1124
F. Postleb et al. · BIOnic Liquids: Imidazolium-based Ionic Liquids with Antimicrobial Activity
Closely related to our topic, Rogers and co-workers Table 1. Bacterial reference strains used for the determination
of the minimal inhibitory concentration (MIC) of our BIOnic
liquids.
reported the application of pharmaceutically active
ionic liquids that were immobilized onto mesoporous
ATCC no.
Name
Staphylococcus aureus
Methicillin-resistant Staphylococcus aureus (MRSA)
Enterococcus faecalis
Escherichia coli
silica [13]. These solids were very robust and could po-
tentially be used as efficient “device for drug delivery
and in vitro release”.
29213
43300
29212
25922
27853
Results and Discussion
Pseudomonas aeruginosa
Many antibiotics and analgesics currently on the
market are available as (sodium) salts. Therefore, the cyl), since it is already well-known that the length of
active compounds already exist in anionic form. Since the side chain defines for the antimicrobial activity of
the imidazolium cation is (a) an established part of the cation [6]. The compounds are depicted in Fig. 1.
many common ionic liquids and (b) already well- A combination of these resulted in twelve new ionic
known for its antibiotic activity (cf. introduction) we liquids (Table 2).
decided to integrate imidazolium cations into biologi-
The twelve BIOnic liquids have subsequently been
cally active ionic liquids. As the anions we chose chlor- tested for their antibacterial activity in a standardized
amphenicol, fosfomycin and two sulfonamides, and in microbiological assay by determining the minimal in-
addition two common analgesics. In the case of the hibitory concentration (MIC) against five microorgan-
cations we decided for imidazolium with three side isms (Table 1). For comparison we have also tested
chains of different length (butyl, octyl and hexade- the bromide salts of the ionic liquid precursors (“the
O
OH
Cl
O
S
O
O
S
N
N
O
N
O
N
N
O
HN
N
O
Cl
H2N
H2N
O
sulfamethoxazol
sulfadiazin
chloramphenicol
O
O
O
O
P
OH
O
Cl
H
N
O
O
O
O
Cl
fosfomycin
acetylsalicylic acid
diclofenac
N
N+
N
N+
C4mim
C8mim
N
N+
C16mim
Fig. 1. Pharmacologically active anions and cations used in this study for the synthesis of ionic liquids.
Brought to you by | University of California
Authenticated
Download Date | 6/9/15 9:40 AM

F. Postleb et al. · BIOnic Liquids: Imidazolium-based Ionic Liquids with Antimicrobial Activity
1125
Table 2. Minimal inhibitory
concentration (MIC) of the
ionic liquid precursors (i. e.
“cations”), of the neat antibi-
otics (i. e. “anions”) and of our
Compound
Tg
S. aureus MRSA
E. fae-
calis
E. coli P. aerugi-
nosa
(◦C)
[C4mim]Br
[C8mim]Br
[C16mim]Br
Na chloramphenicol
Na sulfadiazin
Na sulfamethoxazol
Na2 fosfomycin
76.0
−38.1
−19.0
n. d.a
n. d.
−
256
0.125
8
−
1024
1
−
128
0.125
4
4
4
−
512
32
4
−
2048
128
256
1024
1024
4
BIOnic liquids in µg mL−1
.
16
A dash (–) denotes no activ-
ity at the highest concentration
tested (2048 µg mL−1).
−
512
−
64
64
2
n. d.
n. d.
−
4
16
32
[C4mim]chloramphenicol
[C4mim]sulfadiazin
[C4mim]sulfamethoxazol
[C4mim]fosfomycin
[C4mim]diclofenac
[C8mim]sulfadiazin
[C8mim]sulfamethoxazol
[C8mim]fosfomycin
[C8mim]acetylacetic acid
[C16mim]sulfadiazin
[C16mim]sulfamethoxazol
[C16mim]fosfomycin
22.9
n. d.
−
n. d.
−
n. d.
16
4
64
512
8
n. d.
64
32
16
−
n. d.
−
−26.0
−30.3
−49.8
n. d.
−
−
2048
16
16
16
512
256
512
n. d.
n. d.
< 0.125
0.5
512
2048
2048
n. d.
n. d.
1
−
3.6
64
32
n. d.
n. d.
8
2048
2048
n. d.
n. d.
128
128
32
−17.3
−44.7
−51.5
10.5
8
n. d.
n. d.
< 0.125
0.125
< 0.125
−27.0
2
1
8
8
30.6
< 0.125
a
n. d.: not determined
Table 3. Exemplary efficiency MIC (average) in µg mL−1 of
[C16mim]fosfomycin in comparison to its key components.
MIC (average) is the sum of the five MICs against our five
bacteria reference strains MIC (total) devided by 5.
cations”) and the neat antimicrobials (“the anions”).
The results are shown in Table 2.
In a common definition, a compound having
antimicrobial activity must show a MIC below
200 µg mL−1 [14]. Table 2 shows that this prerequisite
is already met by some of our neat ionic liquid bro-
mide salts. We can clearly see that the choice of cation
has a strong effect on the antimicrobial activity of the
compounds. For ease of comparison, the activities of
Compound
MIC (total)
MIC (average)
[C16mim]Br
Na2 fosfomycin
[C16mim]fosfomycin
161.25
58
41.25
32.25
11.6
8.25
the neat antimicrobials have also been determined un- each of the components. Table 3 exemplarily shows the
der standardized testing conditions.
average MIC for [C16mim]fosfomycin.
A surprisingly large number of our “BIOnic Liq-
uids” shows a high level of antimicrobial activity Conclusion
(Table 2). Depending on the compound and the mi-
croorganism, there is no general trend in activity ob-
The combination of an antimicrobially active im-
servable. In many cases, the observed MIC resem- idazolium cation with an anionic antimicrobial leads
bles the one of either the corresponding imidazolium to new microbiologically active ionic liquids (“BIOnic
bromide or of the neat antibiotic. But there are also Liquids”). The average efficiency of the BIOnic Liq-
cases in which the BIOnic Liquid is more effec- uids is generally higher than the combined efficiency
tive than each of the individual components (e. g. of their key components.
[C16mim]fosfomycin and [C16mim]sulfadiazin against
This methodology opens up many possibilities for
S. aureus or [C16mim]sulfamethoxazol against E. time- and cost-efficient development of new antimicro-
coli), which can be attributed to efficient cumulative bial agents. By building upon well-known, well-tested
effects. On the other hand, there are cases in which the and (possibly) already approved chemicals in a modu-
BIOnic Liquid is less effective than the key component lar building block concept, it is possible to save valu-
alone (e. g. [C16mim]fosfomycin against E. coli and P. able time for the development and testing of new phar-
aeruginosa).
maceutical drugs. In addition, since the product is po-
Interestingly, the total (average) efficiency of many tentially liquid, the possibility for topical instead of
BIOnic Liquids is higher than the total efficiency of systemical application might prove valuable. Topical
Brought to you by | University of California
Authenticated
Download Date | 6/9/15 9:40 AM

1126
F. Postleb et al. · BIOnic Liquids: Imidazolium-based Ionic Liquids with Antimicrobial Activity
application of active pharmaceutical ingredients can – 1H NMR (300 MHz, [D6]DMSO): δ = 9.21 (s, 1H, 2-H),
7.90 (d, 1H, 19-H), 7.77 (d, 1H, 20-H), 7.66 (d, 1H, 17-H),
7.54 (d, 1H, 18-H), 7.50 (d, 1H, 5-H), 7.30 (d, 1H, 4-H),
6.63 (m, 2H, 7-H), 4.14 (m, 2H, 8-H), 3.85 (s, 3H, 5-H), 2.23
(s, 3H, 6-H), 1.76 (m, 2H, 9-H), 1.24 (b, 8H, 10-H, 11-H,
12-H, 13-H), 0.85 (t, 3H, 14-H). – 13C{1H} NMR (75 MHz,
[D6]DMSO): δ = 169.33 (s, 22-C), 166.31 (s, 24-C), 163.06
(s, 15-C), 150.01 (s, 16-C), 132.13 (s, 2-C), 131.23 (s, 19-C),
129.89 (s, 17-C), 125.60 (s, 18-C), 123.36 (s, 4-C), 121.99
(s, 20-C), 115.78 (s, 5-C), 48.76 (s, 7-C), 35.72 (s, 18-C),
31.18 (s, 8-C), 29.41 (s, 9-C), 28.50 (s, 10-C), 28.36 (s, 11-
C), 25.51 (s, 12-C), 22.08 (s, 13-C), 21.03 (s, 26-C), 13.96
(s, 14-C).
neglect general toxicity issues much more than sys-
temical application in which the drug is distributed
throughout the body.
Experimental Section
Syntheses
[C4mim]Br, [C8mim]Br and [C16mim]Br have been pre-
pared according to established literature procedures [15].
The BIOnic Liquids have subsequently been synthesized by
transforming the corresponding imidazolium bromide into
the hydroxide via ion exchange resin. The hydroxide salt was
then combined with the antibiotic or analgesic to yield the fi-
nal product by elimination of one equivalent of water.
[C4mim]chloramphenicol
Yield: 31 %. – Tg = 22.9 ◦C. – FT-IR (ATR): ν (cm−1) =
623 (m), 700 (m), 750 (m), 826 (w) 851 (w), 1053 (br), 1167
(m), 1344 (s), 1516 (s), 1647 (m), 2874 (w), 2934 (w), 2959
(w), 3080 (w). – 1H NMR (300 MHz, [D6]DMSO): δ = 9.20
(s, 1H, 2-H), 8.19 – 8.16 (d, 2H, 11-H/13-H), 7.78 (s, 1H, 4-
H), 7.72 (s, 1H, 5-H), 7.61 – 7.58 (d, 2H, 16-H/14-H), 5.79
(s, 1H, 25-H), 4.70 (s, 1H, 27-H), 4.16 (t, 2H, 7-H), 3.85 (s,
3H, 6-H), 3.35 (m, 2H, 28-H), 2.71 (m, 1H, 21-H), 1.76 (m,
2H, 8-H), 1.24 (m, 2H, 9-H), 0.89 (t, 3H, 10-H). – 13C{1H}
NMR (75 MHz, [D6]DMSO): δ = 153.10 (s, 15-C), 146.86
(s, 2-C), 146.52 (s, 11-C), 127.87 127.63 (m, 16-C/22-C, 20-
C), 123.91 (s, 4-C), 123.14 (s, 11-C/12-C), 122.56 (s, 5-C),
72.05 (s, 25-C), 63.52 (s, 28-C), 59.12 (s, 21-C), 48.76 (s,
7-C), 36.02 (s, 6-C), 31.66 (s, 8-C), 19.07 (s, 9-C), 13.58 (s,
10-C).
General procedure for the synthesis of microbiologically
active ionic liquids (BIOnic Liquids)
1 eq. of the corresponding imidazolium bromide was dis-
solved in distilled water and sent through an ion exchange
column (Merck ion exchange resin III). To this unstable hy-
droxide salt in water the corresponding antibiotic or anal-
gesic was directly added, and the mixture was stirred for 2 h
at room temperature. The solvent was evaporated under re-
duced pressure. The purity (especially halide residues) was
checked via ion chromatography. Since fosfomycin was only
available as sodium salt, the neat compound was also pro-
duced via ion exchange in water (Dowex 50WX8-100).
[C4mim]diclofenac
[C4mim]sulfadiazin
Yield: 77 %. – FT-IR (ATR): ν (cm−1) = 621 (s), 716 (m),
745 (s), 1167 (m), 1362 (m), 1449 (s), 1506 (m), 1558 (s),
1574 (s), 2874 (w), 2959 (m), 3065 (w), 3144 (w). – 1H
NMR (300 MHz, D2O): δ = 7.15 – 7.08 (s, 3H, 13-H, 15-
H, 11-H), 7.01 – 6.98 (d, 2H, 4-H, 5-H), 6.67 – 6.58 (m, 3H,
21-H, 23-H, 25-H), 6.11 (t, 1H, 24-H), 3.85 (t, 2H, 7-H), 3.65
(s, 3H, 6-H), 3.52 (s, 2H, 26-H), 1.52 (m, 2H, 8-H), 1.04 (m,
Yield: 95 %.
–
Tg = −25.9 ◦C.
– FT-IR (ATR):
ν (cm−1) = 677 (m), 789 (m), 970 (w), 1001 (m), 1072 (m),
1120 (m), 1167 (w), 1225 (br), 1261 (v), 1408 (s), 1502 (w),
1539 (m), 1577 (m), 1597 (m), 2961 (w), 3102 (w), 3148 (w),
3227 (w), 3339 (w). – 1H NMR (300 MHz, [D6]DMSO):
δ = 9.23 (b, 1H, 2-H), 8.07 – 8.05 (d, 2H, 14-H, 16-H),
7.78 – 7.71 (d, 2H, 4-H, 5-H), 7.45 – 7.42 (d, 2H, 25-H, 21-
H), 6.44 – 6.41 (d, 2H, 24-H, 22-H), 6.31 (s, 1H, 15-H), 5.30
(s, 2H, 27-H), 4.18 (t, 2H, 7-H), 3.86 (s, 3H, 6-H), 1.75 (m,
2H, 8-H), 1.24 (m, 2H, 9-H), 0.89 (t, 3H, 10-H). – 13C{1H}
NMR (75 MHz, [D6]DMSO): δ = 212.08 (s, 12-C), 156.91
(s, 14-C, 16-C), 149.63 (s, 23-C), 128.42 (s, 25-C, 21-C),
124.19 (s, 2-C), 123.85 (s, 5-C), 122.26 (s, 4-C), 111.62 (s,
24-C, 22-C), 108.94 (s, 15-C), 48.25 (s, 7-C), 35.46 (s, 6-C),
31.42 (s, 8-C), 18.89 (s, 9-C), 12.93 (s, 10-C).
1
2H, 9-H), 0.69 (t, 3H, 10-H). – 13C{ H} NMR (75 MHz,
D2O): δ = 179.09 (s, 27-C), 142.38 (s, 22-C), 137.45 (s, 14-
C), 130.62 (s, 2-C), 128.90 (s, 21-C, 25-C), 128.50 (s, 23-C,
24-C) 127.04 (s, 16-C), 126.33 (s, 12-C), 123.80 (s, 13-C),
123.27 (s, 15-C), 121.80 (s, 11-C) 121.06 (s, 4-C), 116.13 (s,
5-C), 49.01 (s, 7-C), 42.57 (s, 27-C), 35.45 (s, 6-C), 31.15 (s,
8-C), 18.77 (s, 9-C), 12.72 (s, 10-C).
[C8mim]acetylacetic acid
Yield: 31 %.
–
Tg = −51.5 ◦C.
– FT-IR (ATR):
[C4mim]sulfamethoxazol
ν (cm−1) = 621 (w), 664 (w), 704 (w), 756 (s), 854 (w), 918
(w), 1028 (w), 1085 (w), 1194 (m), 1219 (w), 1248 (m), 1368
Yield: 99 %. – Tg = −30.2 ◦C. – FT-IR (ATR) ν (cm−1) =
(br), 1456 (m), 1483 (m), 1570 (m), 1591 (m), 1707 (m), 673 (s), 739 (s), 939 (s), 1045 (m), 1090 (s), 1120 (s),
1749 (w), 2857 (v), 2926 (m), 2955 (w), 3069 (br), 3148 (w). 1227 (m), 1267 (w), 1404 (m), 1458 (s), 1597 (m), 2961
Brought to you by | University of California
Authenticated
Download Date | 6/9/15 9:40 AM

F. Postleb et al. · BIOnic Liquids: Imidazolium-based Ionic Liquids with Antimicrobial Activity
1127
1
(w), 3221 (w), 3333 (w), 3420 (w). – H NMR (300 MHz, 2H, 15-H, 17-H), 5.74 (s, 1H, 27-H), 5.35 (s, 2H, 7-H), 4.15
[D6]DMSO): δ = 9.20 (s, 1H, 2-H), 7.77 (s, 1H, 5-H), 7.70 (t, 2H, 7-H), 3.85 (s, 3H, 6-H), 2.09 (s, 3H, 31-H), 1.76
(s, 1H, 4-H), 7.31 – 7.28 (d, 2H, 16-H, 14-H), 6.45 – 6.42 (d, (m, 2H, 8-H), 1.24 (b, 10H, 9-H–13-H), 0.85 (t, 3H, 14-
2H, 11-H, 13-H), 5.72 (s, 1H, 23-H), 5.32 (b, 2H, 17-H), 4.16 H). – 13C{1H} NMR (75 MHz, [D6]DMSO): δ = 165.54
(t, 2H, 7-H), 3.85 (s, 3H, 6-H), 2.08 (s, 3H, 27-H), 1.75 (m, (s, 28-C), 149.78 (s, 16-C), 136.60 (s, 2-C), 134.14 (s, 19-
2H, 8-H), 1.26 (m, 2H, 9-H), 0.89 (t, 3H, 10-H). – 13C{1H} C), 127.37 (s, 20-C, 18-C), 123.59 (s, 5-C), 122.25 (s, 4-
NMR (75 MHz, [D6]DMSO): δ = 166.00 (s, 24-C), 164.94 C), 112.23 (s, 15-C, 17-C), 99.04 (s, 26-C), 96.90 (s, 27-C),
(s, 22-C), 149.63 (s, 12-C), 136.61 (s, 2-C), 134.60 (s, 16-C, 48.75 (s, 7-C),35.73 (s, 6-C), 31.17 (s, 8-C), 29.41 (s, 9-C),
14-C), 123.53 (s, 5-C), 122.19 (s, 4-C), 112.22 (s, 11-C, 13- 28.48 (s, 10-C), 28.34 (s, 11-C), 25.50 (s, 12-C), 22.06 (s,
C), 97.07 (s, 23-C), 48.28 (s, 7-C), 35.54 (s, 6-C), 31.39 (s, 13-C), 13.69 (s, 31-C), 12.24 (s, 14-C).
8-C), 18.51 (s, 9-C), 13.30 (s, 27-C), 12.26 (s, 10-C).
[C8mim]fosfomycin
[C4mim]fosfomycin
Yield: 92 %.
–
Tg = −44.7 ◦C.
– FT-IR (ATR):
Yield: 98 %.
–
Tg = −49.8 ◦C.
– FT-IR (ATR):
ν (cm−1) = 627 (m), 716 (m), 851 (s), 889 (s), 1083 (s), 1337
(w), 1456 (m), 1558 (m), 2855 (m), 2924 (m), 3144 (w). – 1H
NMR (300 MHz, D2O): δ = 8.70 (s, 1H, 6-H) 7.47 – 7.43
(d, 2H, 3-H/4-H), 4.19 (s, 2H, 7-H), 3.89 (s, 3H, 6-H), 3.35
(m, 1H, 15-H), 2.98 – 2.93 (m, 1H, 17-H), 1.87 (m, 2H, 8-H),
1.50 (d, 3H, 18-H), 1.30 – 1.27 (b, m, 9-H–13-H), 0.86 (t, 3H,
14-H). – 13C{1H} NMR (75 MHz, D2O): δ = 135.76 (s, 6-
C), 123.43 (s, 4-C), 122.16 (s, 5-C), 54.28 (s, 15-C), 51.89 (s,
17-C), 49.52 (s, 7-C), 35.55 (s, 6-C), 30.91 (s, 8-C), 29.09 (s,
9-C), 28.12 (s, 10-C), 27.92 (s, 11-C), 25.21 (s, 12-C), 21.92
(s, 13-C) 13.33 (s, 14-C, 18-C). – 31P{1H} NMR (121 MHz,
D2O): δ = 11.99 (s, 1-P).
ν (cm−1) = 623 (s), 750 (m), 891 (s), 1038 (s), 1167 (s),
1456 (m), 1558 (m), 2874 (w), 2961 (m), 3096 (w). – 1H
NMR (300 MHz, D2O): δ = 8.66 (s, 1H, 2-H), 7.42 (s, 1H,
5-H), 7.38 (s, 1H, 4-H), 4.14 (t, 2H, 7-H), 3.83 (s, 3H, 6-H),
3.50 – 3.31 (b, 1H, 11-H), 2.96 – 2.86 (b, 1H, 13-H), 1.79 (m,
2H, 8-H), 1.44 (m, 2H, 9-H), 1.21 (m, 3H, 14-H), 0.86 (t,
3H, 10-H). – 13C{1H} NMR (75 MHz, D2O): δ = 136.43 (s,
2-C), 73.63 (s, 5-C), 71.60 (s, 4-C), 67.63 (s, 6-C), 54.27 (s,
11-C), 51.50 (s, 13-C), 49.24 (s, 7-C), 35.61 (s, 14-C), 31.25
(s, 8-C), 18.72 (s, 9-C), 13.36 – 12.62 (b, 10-C). – 31P{1H}
NMR (121 MHz, D2O): δ = 12.20 (s, 1-P).
[C8mim]sulfadiazin
[C16mim]sulfadiazin
Yield: 92 %. – Tg = 3.6 ◦C – FT-IR (ATR): ν (cm−1) =
625 (m), 677 (s), 709 (m), 787 (s), 968 (m), 999 (s), 1074
(s), 1121 (s), 1167 (m), 1227 (m), 1410 (s), 1533 (m), 1578
(s), 2855 (w), 2926 (w), 3096 (w), 3219 (w), 3337 (w). –
1H NMR (300 MHz, [D6]DMSO): δ = 9.28 (s,1H, 2-H),
8.06 – 8.04 (d, 2H, 18-H, 20-H), 7.77 (s, 1H, 5-H), 7.70 (s,
1H, 4-H), 7.44 – 7.42 (d, 2H, 30-H, 26-H), 6.43 – 6.41 (d,
2H, 29-H, 27-H), 6.30 (t, 1H, 19-H), 5.28 (s, 2H, 31-H),
4.16 (t, 2H, 7-H), 3.86 (s, 3H, 6-H), 1.77 (m, 2H, 8-H), 1.24
(b, 10H, 9-H–13-H), 0.85 (s, 3H, 14-H). – 13C{1H} NMR
(75 MHz, [D6]DMSO): δ = 157.44 (s, 20-C, 18-C), 149.97
(s, 28-C), 137.55 (s, 2-C), 137.17 (s, 25-C), 134.59 (s, 30-C,
26-C), 123.97 (s, 5-C), 122.59 (s, 4-C), 112.20 (s, 29-C, 27-
C), 109.18 (s, 19-C), 49.04 (s, 7-C), 36.17 (s, 6-C), 31.61 (s,
8-C), 29.88 (s, 9-C), 28.93 (s, 10-C), 28.79 (s, 11-C), 25.95
(s, 12-C), 22.51 (s, 13-C), 14.41 (s, 14-C).
Yield: 93 %. – Tg = 10.5 ◦C. – FT-IR (ATR): ν (cm−1) =
660 (m), 677 (s), 785 (m), 1001 (m), 1072 (s), 1125 (s), 1174
(m), 1225 (m), 1413 (s), 1500 (w), 1578 (m), 1636 (w), 2851
(m), 2920 (m), 3032 (w), 3215 (w), 3325 (w), 3420 (w). – 1H
NMR (300 MHz, D2O): δ = 9.41 (s, 1H, 2-H), 8.06 – 8.04
(d, 2H, 38-H/36-H), 7.78 (s, 1H, 4-H), 7.71 (s, 1H, 5-H),
7.46 – 7.43 (d, 2H, 28-H/26-H), 6.44 – 6.42 (d, 2H, 23-H/25-
H), 6.33 (t, 1H, 37-H), 5.30 (s, 2H, 29-H) 4.15 (t, 2H, 7-H),
3.87 (s, 3H, 6-H), 1.76 (m, 2H, 8-H), 1.23 (m, 26H, 9-H–
21-H), 0.85 (t, 3H, 22-H). – 13C{1H} NMR (75 MHz, D2O):
δ = 164.27 (s, 34-C), 156.90 (s, 38-C/36-C), 149.67 (s, 24-
C), 136.87 (s, 2-C), 133.75 (s, 27-C), 128.29 (s, 28-C/26-
C), 123.56 (s, 4-C), 122.21 (s, 5-C), 111.77 (s, 23-C/25-C),
108.98 (s, 37-C), 48.70 (s, 7-C), 35.68 (s, 6-C), 31.29 (s, 8-
C), 29.47 (s, 9-C), 29.05 (m, 10-C–18-C), 28.84 (s, 19-C),
25.50 (s, 20-C), 22.09 (s, 21-C), 13.95 (s, 22-C).
[C8mim]sulfamethoxazol
[C16mim]sulfamethoxazol
Yield: 93 %.
–
Tg = −17.3 ◦C.
– FT-IR (ATR):
ν (cm−1) = 671 (s), 743 (s), 795 (m), 833 (m), 937 (s), 1042
Yield: 92 %. – Tg = −27 ◦C. – FT-IR (ATR): ν (cm−1) =
(m), 1090 (s), 1121 (s), 1225 (s), 1267 (m), 1315 (m), 1398 623 (m), 669 (s), 740 (m), 833 (m), 937 (m), 1043 (m),
(m), 1456 (s), 1599 (s), 1649 (m), 2853 (m), 2930 (m), 3117 1092 (s), 1123 (s), 1165 (m), 1231 (m), 1269 (m), 1296 (w),
1
(w), 3230 (m), 3337 (m), 3397 (m). – H NMR (300 MHz, 1400 (m), 1458 (s), 1597 (m), 2852 (m), 2922 (m), 3102 (w),
[D6]DMSO): δ = 9.19 (s, 1H, 2-H), 7.77 (s, 1H, 5-H), 7.70 3148 (w), 3219 (w), 3337 (w). – 1H NMR (300 MHz, D2O):
(s, 1H, 4-H), 7.32 – 7.29 (d, 2H, 20-H, 18-H), 6.45 – 6.42 (d, δ = 9.27 (s, 1H, 2-H), 7.77 (s, 1H, 4-H), 7.70 (s, 1H, 5-H),
Brought to you by | University of California
Authenticated
Download Date | 6/9/15 9:40 AM

1128
F. Postleb et al. · BIOnic Liquids: Imidazolium-based Ionic Liquids with Antimicrobial Activity
7.32 – 7.29 (d, 2H, 26-H/28-H), 6.45 – 6.42 (d, 2H, 23-H/25- (s, 19-C), 22.58 (s, 20-C), 13.79 (s, 26-C), 13.52 (s, 21-C). –
H), 5.73 (s, 1H, 35-H), 5.32 (s, 2H, 29-H), 4.15 (t, 2H, 7-H), 31P{1H} NMR (121 MHz, D2O): δ = 11.91 (s, 1-P).
3.85 (s, 3H, 6-H), 2.09 (s, 3H, 39-H), 1.76 (m, 2H, 8-H), 1.23
Antimicrobial susceptibility testing
(b, 26H, 9-H–21-H), 0.85 (t, 3H, 22-H). – 13C{1H} NMR
Antimicrobial susceptibility testing was performed by
broth micro dilution in cation-adjusted Müller-Hinton broth
according to Clinical Laboratory Standard Institute (CLSI)
guidelines [16]. The inoculum was prepared using a bacterial
suspension of the test strain in 0.9 % NaCl at a final inoculum
concentration of 1×106 cells per mL using a 0.5 McFarland
turbidity standard and subsequent dilution. Inoculation of the
microtiter plates was done by delivering 100 µL of the bac-
terial suspension and 100 µL of the test compound into each
well of the plate. The concentration ranges of the compounds
tested in twofold dilutions were 0.125 – 2048 mg/L. Plates
were incubated in ambient air at 35 ◦C for 16 – 20 h. Plates
were observed for the presence or absence of growth. The
minimal inhibitory concentration (MIC) was determined vi-
sually as the lowest concentration of drug showing no growth
or a significant reduction of growth (> 80 %).
(75 MHz, D2O): δ = 166.46 (s, 34-C), 165.16 (s, 36-C),
149, 65 (s, 24-C), 136.70 (s, 2-C), 134.57 (s, 27-C), 127.28
(s, 28-C/26-C), 123.56 (s, 4-C), 122.23 (s, 5-C), 112.22 (s,
23-C/25-C), 96.95 (s, 35-C), 48.72 (s, 7-C), 35.69 (s, 6-C),
31.29 (s, 8-C), 29.45 (s, 9-C), 29.05 (m, 10-C–18-C), 28.40
(s, 19-C), 25.50 (s, 20-C), 22.09 (s, 21-C), 13.94 (s, 39-C),
12.22 (s, 22-C).
[C16mim]fosfomycin
Yield: 93%. – Tg = 30.6 ◦C. – FT-IR (ATR): ν (cm−1) =
623 (m), 714 (s), 853 (m), 966 (m), 1030 (s), 1150 (s), 1222
(m), 1472 (m), 2311 (w), 2847 (s), 2913 (s), 3096 (w), 3138
(w). – 1H NMR (300 MHz, D2O): δ = 8.91 (s, 1H, 2-H), 7.54
(s, 1H, 4-H), 7.47 (s, 1H, 5-H), 4.21 (m, 2H, 7-H), 3.92 (s,
3H, 6-H), 3.26 (b, 1H, 23-H), 2.90 (d, 1H, 25-H), 1.84 (b, 1H,
29-H), 1.49 (d, 3H, 26-H), 1.25 (m, 26 H, 9-H–20-H), 0.84
(b, 3H, 21-H). – 13C{1H} NMR (75 MHz, D2O): δ = 136.06
(s, 2-C), 123.84 (s, 4-C), 121.95 (s, 5-C), 53.99 (s, 25-C),
Acknowledgement
We acknowledge Deutsche Forschungsgemeinschaft for
51.68 (s, 23-C), 49.37 (s, 7-C), 35.64 (s, 6-C), 31.91 (s, 8-C), funding through the Special Priority Programme 1191 “Ionic
29.85 (s, 9-C), 29.42 (m, 10-C–17-C), 29.11 (s, 18-C), 26.10 Liquids”.
[1] R. Giernoth, Angew. Chem. Int. Ed. 2010, 49, 2834 –
2839.
[10] M. Tischer, G. Pradel, K. Ohlsen, U. Holzgrabe,
ChemMedChem 2011, 7, 22 – 31.
[2] J. H. Davis, Chem. Lett. 2004, 33, 1072 – 1077.
[3] W. L. Hough, M. Smiglak, H. Rodriguez, R. P. Swat-
[11] D. Coleman, M. Špulák, M. T. Garcia, N. Gathergood,
Green Chem. 2012, 14, 1350 – 1356.
loski, S. K. Spear, D. T. Daly, J. Pernak, J. E. Grisel, [12] M. R. Cole, M. Li, B. El-Zahab, M. E. Janes, D. Hayes,
R. D. Carliss, M. D. Soutullo, J. H. Davis, Jr., R. D.
I. M. Warner, Chem. Biol. & Drug Des. 2011, 78,
Rogers, New J. Chem. 2007, 31, 1429 – 1436.
33 – 41.
[4] P. J. Scammells, J. L. Scott, R. D. Singer, Austr. J. [13] K. Bica, H. Rodriguez, G. Gurau, O. Andreea Cojo-
Chem. 2005, 58, 155 – 169.
caru, A. Riisager, R. Fehrmann, R. D. Rogers, Chem.
[5] T. P. T. Pham, C.-W. Cho, Y.-S. Yun, Water Res. 2010,
44, 352 – 372.
Commun. 2012, 48, 5422 – 5424.
[14] U. Gräfe, Biochemie der Antibiotika: Struktur
–
[6] J. Łuczak, C. Jungnickel, I. Ła˛cka, S. Stolte, J. Hupka,
Green Chem. 2010, 12, 593 – 601.
Biosynthese – Wirkmechanismus, Spektrum Verlag,
Heidelberg, 1992.
[7] P. Borowiecki, M. Milner-Krawczyk, D. Brzezin´ska, [15] R. Giernoth, D. Bankmann, Eur. J. Org. Chem. 2008,
M. Wielechowska, J. Plenkiewicz, Eur. J. Org. Chem.
2881 – 2886.
2012, 2013, 712 – 720.
[16] Clinical and Laboratory Standards Institute, Methods
for dilution antimicrobial susceptibility tests for bacte-
ria that grow aerobically. Approved standard M7–A8,
CLSI, Wayne, Pa, 8th edition, 2009.
[8] P. Borowiecki, M. Milner-Krawczyk, J. Plenkiewicz,
Beilstein J. Org. Chem. 2013, 9, 516 – 525.
[9] M. I. Hossain, M. El-Harbawi, N. B. M. Alitheen,
Y. A. Noaman, J.-M. Lévêque, C.-Y. Yin, Ecotox.
Envir. Safety 2013, 87, 65 – 69.
Brought to you by | University of California
Authenticated
Download Date | 6/9/15 9:40 AM