Structural and antimicrobial studies of a new N-phenylamide of monensin A complex with sodium chloride

Article abstract of DOI:10.1016/j.molstruc.2009.01.056

A complex between a new N-phenylamide of monensin A (M-AM1) and sodium chloride has been synthesised and studied by X-ray diffraction and FT-IR spectroscopy. The crystal structure of the complex between M-AM1 and sodium chloride with acetonitrile was exam

Full text of DOI:10.1016/j.molstruc.2009.01.056

Journal of Molecular Structure 923 (2009) 53–59
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Structural and antimicrobial studies of a new N-phenylamide of monensin A
complex with sodium chloride
a
a
a
a
´
Daniel Łowicki , Adam Huczynski , Małgorzata Ratajczak-Sitarz , Andrzej Katrusiak ,
b
a,
c
*
´
Joanna Stefanska , Bogumil Brzezinski , Franz Bartl
a Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland
b Medical University of Warsaw, Department of Pharmaceutical Microbiology, Oczki 3, 02-007 Warsaw, Poland
c Institute of Medical Physics and Biophysics Charité - Universitätsmedizin Berlin Campus Charité Mitte, Ziegelstr. 5/9, 10117 Berlin, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
A complex between a new N-phenylamide of monensin A (M-AM1) and sodium chloride has been syn-
thesised and studied by X-ray diffraction and FT-IR spectroscopy. The crystal structure of the complex
between M-AM1 and sodium chloride with acetonitrile was examined using X-ray diffraction and dis-
cussed in detail. Its structure is stabilised by coordination of the Na+ cation with oxygen atoms. The
Na–O bond lengths are between 2.382(2) and 2.562(2) Å. The chloride anion is involved in a weak inter-
molecular hydrogen bond between different species forming a supramolecule. The ESI-MS spectra indi-
cate that the amide forms stable complexes of exclusively 1:1 stoichiometry with Na+ cations. The FT-IR
spectrum of the crystal is consistent with the results obtained by the X-ray study and provides spectro-
scopic evidence for the complex formation. Due to its specific structural properties N-phenylamide of
monensin A efficiently binds sodium chloride. The result of the PM5 semiempirical calculation is in agree-
ment with the spectroscopic data and allows visualisation of the structure of the M-AM1–Na+ complex.
The new amide of monensin A has been additionally tested in view of its antimicrobial properties. It
Received 23 December 2008
Received in revised form 29 January 2009
Accepted 31 January 2009
Available online 13 February 2009
Keywords:
Ionophores
Monensin A amide
Na+ complex
PM5 calculations
ESI mass spectrometry
shows great activity towards some strains of Gram-positive bacteria (MIC = 6.25–12.5 lg/ml).
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
methyl ester was able to form a proton channel [44]. For several
newly synthesised esters of monensin the antibacterial activity
was observed, especially against Gram-positive bacteria [45,46].
There was also demonstrated that monensin showed antimicrobial
activity against MRSA (methicillin-resistant) and MSSA (methicillin-
susceptible) hospital strains of Staphylococcus aureus at doses
Monensin A, isolated from Streptomyces cinnamonensis is a well-
known representative of polyether ionophore antibiotics [1,2].
Monensin exhibits antibiotic [3–8], coccidiostatic [9–11] and other
important biological properties [12–18]. It forms lipid-soluble
pseudomacrocyclic complexes with monovalent metal cations able
to transport these cations across natural and artificial lipid mem-
branes [19,20].
The structures of monensin A complexes with several metal cat-
ions such as Li+, Na+, K+, Rb+ and Ag+ have been determined by a
combination of X-ray crystallography [21–27], NMR spectroscopy
and molecular modelling [28–30].
MIC = 1–2 lg/ml [46].
As a continuation of these studies, a new complex of N-phenyla-
mide of monensin (M-AM1) with sodium chloride (M-AM1–NaCl)
has been obtained and studied by X-ray, FT-IR, ESI-MS and PM5
methods. The antimicrobial activity of M-AM1–NaCl complex
was also determined.
Up to now various modifications of monensin have been devel-
oped to obtain less toxic derivatives, enabling expansion of their
applications. In the first syntheses, of monensin derivates the three
hydroxyl groups were modified [31–33]. Recently, we synthesised
several new esters of monensin and studied complex formation
with monovalent [34–40] as well as with divalent [41–43] metal
cations by 1H NMR, 13C NMR, FT-IR, electrospray mass spectrome-
try and by semiempirical methods. Surprisingly, the monensin
2. Experimental
2.1. Preparation of monensin N-phenylamide (M-AM1) and its
complex with sodium chloride (M-AM1–NaCl)
The monensin A sodium salt was purchased from Sigma (90–
95%). It was dissolved in dichloromethane and stirred vigorously
with a layer of diluted aqueous sulphuric acid (pH 1.5). The organic
layer containing monensin acid (MONA) was washed with distilled
water. Subsequently dichloromethane was evaporated under re-
duced pressure to dryness.
* Corresponding author. Tel.: +48 618291330.
E-mail address: bbrzez@main.amu.edu.pl (B. Brzezinski).
0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2009.01.056

54
D. Łowicki et al. / Journal of Molecular Structure 923 (2009) 53–59
MONA (1 g, 1.49 mmol), 1,3-dicyclohexylcabodiimide (513 mg,
(3)
OH
2.49 mmol), and aniline (416 mg, 4.47 mmol), dissolved in dichlo-
romethane and 1-hydroxybenzotriazole (331 mg, 2.16 mmol) dis-
solved in tetrahydrofurane were mixed together and stirred at a
temperature below 0 °C for 4 h and subsequently for 24 h at room
temperature. Then the mixture was filtrated to remove the dicyclo-
hexylurea side product. The filtrate was evaporated to dryness un-
der reduced pressure and purified by column chromatography
(Silica gel 60 from Fluka, eluent – CH2Cl2/CH3OH (20/1)) to give
monensin N-phenylamide (M-AM1) (65% yield).
33
27
29
28
Me
Me
Me
Me
(2)
MeO
(1)
O
32
35
30-31
7
23
Me
Et
H
H
(10)
5
25
21
13 16
17 20
12
26
OH
2
3
4
9
1
R
O
(4)
O
(8)
O
(5)
O
(6)
O
(7)
OH
(9)
H
H
H
Me
36
Me
34
N(1)
MONA R=OH
M-AM1 R=
N
4'
1'
H
M-AM1 was dissolved in methanol and an equimolar amount of
sodium chloride dissolved in methanol was added. The solvent was
evaporated to dryness under vacuum to give amorphous powder.
The M-AM1-NaCl complex was dissolved in hot acetonitrile and
left for crystallization for a week. The colourless crystals had melt-
ing point of 135–138 °C.
3'
2'
Scheme 1. The structures and atom numbering of MONA and M-AM1.
graphic Database Centre as a Supplementary Publication No.
CCDC 710817.
Elemental analysis for [C42H67NO10 * NaCl * CH3CN]: Calculated:
C 62.51%; H 8.34%; N 3.31%; Found: C 62.39%; H 8.42%; N 3.28%.
2.3. FT-IR measurements
2.2. X-ray measurements
In the mid infrared region the FT-IR spectra of M-AM1–NaCl
were recorded in nujol/fluorolube mulls. The spectra were taken
with an IFS 113v FT-IR spectrophotometer (Bruker, Karlsruhe)
equipped with a DTGS detector; resolution 2 cmꢀ1, NSS = 64. The
Happ–Genzel apodization function was used.
The crystals which were selected for single-crystal X-ray dif-
fraction measurements formed colourless parallelepipeds with
well-developed faces. They were stable under normal conditions
and the X-ray diffraction measurements were carried out on a
Kuma KM-4 CCD diffractometer at 296 K. The structure was solved
by direct methods and refined by full-matrix least-squares [47].
The positions of all H-atoms were determined on the basis of
molecular geometry (C–H 0.93–0.98, N–H 0.86, O–H 0.82 Å), with
the exception of H(3O) and H(9O), which were located from the
difference Fourier map and refined. Isotropic temperature factors
of H-atoms were related to the thermal vibrations of their carriers
(Uiso = 1.5Ueq for the methyl groups and H(10O), and Uiso = 1.2Ueq
for other H-atoms), except for Uiso of H(3O) and H(9O), which were
refined. The absolute conformation of M-AM1–NaCl in the crystal
was consistent with the chemical information. Selected details
about the crystal structure, experiment structure solution and
refinement are given in Table 1. The crystallographic-informa-
tion-file (CIF) has been deposited at the Cambridge Crystallo-
Table 2
Selected bond lengths (Å) and angles (°) determined from X-ray studies and
calculated by the PM5 semiempirical method.
Parameters
X-ray
PM5
N(1)–C(1)
N(1)–C(37)
O(1)–C(1)
O(2)–C(3)
O(2)–C(35)
O(3)–C(7)
O(3)–Na(1)
O(5)–Na(1)
O(6)–Na(1)
O(7)–Na(1)
O(8)–Na(1)
O(10)–Na(1)
1.368(3)
1.390(3)
1.222(3)
1.419(3)
1.429(3)
1.445(3)
2.4089(18)
2.3816(17)
2.5620(17)
2.4487(17)
2.5374(18)
2.4097(19)
1.37
1.39
1.22
1.42
1.41
1.45
2.42
2.38
2.56
2.45
2.54
2.49
Table 1
C(7)–O(3)–Na(1)
C(9)–O(5)–Na(1)
C(12)–O(5)–Na(1)
C(13)–O(6)–Na(1)
C(16)–O(6)–Na(1)
C(20)–O(7)–Na(1)
C(17)–O(7)–Na(1)
C(25)–O(8)–Na(1)
C(21)–O(8)–Na(1)
C(26)–O(10)–Na(1)
O(1)–C(1)–N(1)
130.72(13)
132.51(12)
115.29(14)
110.81(13)
112.74(12)
116.06(12)
101.14(12)
96.37(12)
99.63(11)
115.51(13)
122.6(3)
129.6
132.5
115.3
111.2
113.8
116.0
101.1
96.4
Crystal data and structure refinement.
Empirical formula
Formula weight
Temperature (K)
Wavelength
Crystal system, space group
Unit cell dimensions
C44H70ClN2NaO10
845.46
293(2)
0.71073 Å
Monoclinic, P21
a = 8.1920(2) Å
b = 25.6679(7) Å
c = 11.2755(4) Å
b = 104.113(3)°
2299.35(12) Å3
2
99.8
110.6
122.6
123.1
74.8
112.6
125.6
115.5
102.1
118.8
178.7
106.7
66.4
64.4
68.5
132.1
98.0
68.5
Volume
Z
Calculated density
Absorption coefficient
F(000)
Crystal size
h range for data collection
Limiting indices
Reflections collected/unique
Completeness to h = 29.85
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
O(1)–C(1)–C(2)
123.1(2)
74.64(6)
O(5)–Na(1)–O(3)
O(5)–Na(1)–O(10)
O(3)–Na(1)–O(10)
O(5)–Na(1)–O(7)
O(3)–Na(1)–O(7)
O(10)–Na(1)–O(7)
O(5)–Na(1)–O(8)
O(3)–Na(1)–O(8)
O(10)–Na(1)–O(8)
O(7)–Na(1)–O(8)
O(5)–Na(1)–O(6)
O(3)–Na(1)–O(6)
O(10)–Na(1)–O(6)
O(7)–Na(1)–O(6)
O(8)–Na(1)–O(6)
N(1A)–C(1A)–C(2A)
1.221 g cmꢀ3
114.20(7)
126.45(8)
115.49(6)
101.91(6)
117.26(7)
178.68(6)
106.66(6)
64.91(6)
64.58(5)
68.20(5)
130.97(7)
98.00(6)
68.64(5)
0.149 mmꢀ1
912
0.30 ꢁ 0.20 ꢁ 0.075 mm
2.45–29.15°
ꢀ11 6 h 6 8, ꢀ33 6 k 6 33, ꢀ14 6 l 6 14
18,318/11,054 Rint = 0.0183
92.7%
Full-matrix least-squares on F2
11,054/1/531
0.964
Final R indices [I > 2
R indices (all data)
r(I)]
R1 = 0.0404, wR2 = 0.0909
R1 = 0.0723, wR2 = 0.1043
0.00(5)
Absolute structure parameter
Largest diff. peak and hole
110.81(6)
178.9(7)
110.8
178.6
0.214 and ꢀ0.249 e Åꢀ3

D. Łowicki et al. / Journal of Molecular Structure 923 (2009) 53–59
55
2.4. ESI-MS studies
The ESI (electrospray ionisation) mass spectrum was recorded
on a Waters/Micromass (Manchester, UK) ZQ mass spectrometer
equipped with a Harvard Apparatus syringe pump. The samples
were prepared in acetonitrile and infused into the ESI source using
a Harvard pump at a flow rate of 20 l
l minꢀ1. The ESI source poten-
tials were: capillary 3 kV, lens 0.5 kV, extractor 4 V. The standard
ESI mass spectra were recorded at the cone voltages: 10, 30, 50,
70, 90, 110 and 130 V. The source temperature was 120 °C and
the dessolvation temperature was 300 °C. Nitrogen was used as
the nebulizing and dessolvation gas at flow-rates of 100 and
300 dm3 hꢀ1, respectively. Mass spectra were acquired in the posi-
tive ion detection mode with unit mass resolution at step size of
1 m/z unit. The mass range for ESI experiments was from m/
z = 300 to m/z = 1000.
2.5. Semiempirical calculations
PM5 semiempirical calculations were performed using the
WinMopac 2003 program. Full geometry optimization of M-
AM1–NaCl was carried out without any symmetry constraints
[48–51].
Fig. 2. Arrangement of complex M-AM1–NaCl in the crystal lattice, projected along
the [100] crystal direction.
Fig. 3. H-donor groups hydrogen-bonded to the Cl1 anion and the oxygen atoms
coordinating the Na cation in the structure of M-AM1–NaCl. The superscript ‘‘i”
refers to the symmetry code in Table 5.
Fig. 1. A perspective view of M-AM1–NaCl (a) in the crystal structure; (b)
calculated by the PM5 semiempirical method.

56
D. Łowicki et al. / Journal of Molecular Structure 923 (2009) 53–59
2.6. Elemental analysis
medium. The results (diameter of the growth inhibition zone) were
read after 18 h of incubation at 35 °C. Compounds with recognised
activity in disc-diffusion tests were examined by the agar dilution
method to determine their MIC – minimal inhibitory concentration
(CLSI) [53]. Concentrations of the agents tested in solid medium
The elemental analysis of [M-AM1 ꢂ NaCl ꢂ CH3CN] was carried
out on Vario ELIII (Elementar, Germany).
2.7. Melting point
ranged from 3.125 to 400 lg/ml. The final inoculum of all studied
organisms was 104 CFU mlꢀ1 (colony forming units per ml), except
the final inoculum for E. hirae ATCC 10541, which was
105 CFU mlꢀ1. Minimal inhibitory concentrations were read after
18 h of incubation at 35 °C.
Corrected melting point was determined on a Mettler FP900.
2.8. Microbiological analysis
Micro-organisms used in this study were as follows: Gram-po-
sitive cocci: Staphylococcus aureus NCTC 4163, Staphylococcus aur-
eus ATCC 25923, Staphylococcus aureus ATCC 6538, Staphylococcus
aureus ATCC 29213, Staphylococcus epidermidis ATCC 12228, Bacil-
lus subtilis ATCC 6633, Bacillus cereus ATCC 11778, Enterococcus hir-
ae ATCC 10541, Micrococcus luteus ATCC 9341, Micrococcus luteus
ATCC 10240; Gram-negative rods: Escherichia coli ATCC 10538,
Escherichia coli ATCC 25922, Escherichia coli NCTC 8196, Proteus vul-
garis NCTC 4635, Pseudomonas aeruginosa ATCC 15442, Pseudomo-
nas aeruginosa NCTC 6749, Pseudomonas aeruginosa ATCC 27853,
Bordetella bronchiseptica ATCC 4617 and yeasts: Candida albicans
ATCC 10231, Candida albicans ATCC 90028, Candida parapsilosis
ATCC 22019. The micro-organisms used were obtained from the
collection of the Department of Pharmaceutical Microbiology,
Medical University of Warsaw, Poland.
3. Results and discussion
The structures of MONA and M-AM1 together with the atom
numbering are shown in Scheme 1.
3.1. Crystal structure of M-AM1–NaCl
In the crystal structure of M-AM1 the oxygen atoms O(3), O(5),
O(6), O(7), O(8) and O(10) coordinate the cation (Table 2). In the
monensin salts [25–27] and esters [34–40] the same oxygen atoms
coordinate the metal cation. The scheme of coordination of Na1
cation is strongly distorted and intermediate between octahedral
and trigonal prism (Figs. 1 and 3). The N-phenylamide of monensin
conformation is additionally stabilised by two intermolecular
hydrogen bonds O(3)Hꢂ ꢂ ꢂClꢀ and O(9)Hꢂ ꢂ ꢂClꢀ (Fig. 1). These hydro-
gen bonds are relatively weak (Table 4) with the donorꢂ ꢂ ꢂacceptor
distances comparable to the sums of van der Waals radii. Further-
more, the Clꢀ anion is involved in the other two intermolecular
hydrogen bonds, O(10)Hꢂ ꢂ ꢂClꢀ and NHꢂ ꢂ ꢂClꢀ. Thus the anion is
‘‘coordinated” tetrahedrally (Fig. 3) by four hydrogen bonds. Addi-
tionally, the Clꢀ anion and Na+ cation are located relatively close in
the molecule, as the distance between them is of 4.80 Å, which is
electrostatically favourable. Thus, this structure demonstrates that
M-AM1 efficiently binds the NaCl salt. The molecular conformation
Antimicrobial activity was examined by the disc-diffusion
method under standard conditions using Mueller-Hinton II agar
medium (Becton Dickinson) for bacteria and RPMI agar with 2%
glucose (Sigma) according to CLSI (previously NCCLS) guidelines
[52].
Sterile filter paper discs (9 mm diameter, Whatman No. 3 chro-
matography paper) were dripped with tested compound solutions
(in MeOH or MeOH/DMSO 1:1) to load 400
lg of a given compound
per disc. Dry discs were placed on the surface of appropriate agar
Fig. 4. ESI-MS spectra of 1:1 mixture of M-AM1 with Na+ at various cone voltages (cv).

D. Łowicki et al. / Journal of Molecular Structure 923 (2009) 53–59
57
can be described by the torsion angles selected in Table 4. It can be
observed that the torsion angles between the molecular rings as-
sume similar values in M-AM1 and monensin salts complexes
[25–27], and that the largest differences in the molecular confor-
mation is in the N-phenylamide region.
The crystal investigated is an inclusion compound with acetoni-
trile (Fig. 2). The acetonitrile molecule interacts via the CHꢂ ꢂ ꢂO and
C„Nꢂ ꢂ ꢂH contacts [54] within the monensin molecules: the short-
est intermolecular contacts are formed between the C(2A)–
H(3A)ꢂ ꢂ ꢂO20 atoms (2.78 Å) and C(1A)„N(1A)ꢂ ꢂ ꢂH(102)00–C(10)00
(2.55 Å) (where symmetry codes are: (0) x + 1, y, z, (00) 2 ꢀ x,
0.5 + y, 1 ꢀ z).
further increase in the cone voltage values the fragmentation of the
complex is observed. The proposed fragmentation pathways start-
ing from the structure A (m/z = 769) are shown in Scheme 2. As
concluded from the m/z peaks in Fig. 4, the first fragmentation step
is the loss of one water molecule as a result of abstraction of the
O(3)H or O(9)H hydroxyl groups yielding the B (m/z = 751) or H
(m/z = 751) cation structures, respectively. Further fragmentation
of cation B is realized in three directions, whereas other types of
complexes [structures C (m/z = 733), D (m/z = 501), E (m/z = 483),
F (m/z = 461), G (m/z = 443), K (m/z = 507) and finally L (m/
z = 479)] can be formed. Cation C is formed from cation B by
abstraction of a second water molecule. The formation of fragmen-
tary complexes D, E and K is achieved by abstraction of the part of
the molecule with the amide group. Cations F and G can be formed
from D and E by abstraction of one C3H4 group. Additionally, cat-
ions E and G can be formed by loss of one water molecule from cat-
ions D and F, respectively. From cation K, after abstraction of one
CO molecule, cation L can be formed. Furthermore, from cations
3.2. Electrospray mass spectrometry (ESI) measurements
The m/z data in the ESI mass spectra of M-AM1–Na complex at
various cone voltage values are shown in Fig. 4. This figure shows
that the M-AM1–Na complex is stable up to at least cv = 90 V. With
O
O
H
O
O
Na+
O
O
O
O
H
I
m/z=733
O
O
O
Na+
H
O
O
O
H
N
-H2O
or
O
O
O
O
H
H
m/z=751
O
H
O
Na+
O
N
O
-H2O
O
J
m/z=733
-H2O
O
H
O
N
O
O
O
O
Na+
O
H
O
O
H
O
O
O
O
H
-H2O
-H2O
O
O
O
O
O
Na+
O
H
Na+
O
O
O
O
A
O
H
m/z=769
H
O
N
C
m/z=733
O
O
B
m/z=751
H
H
O
N
O
N
-H2O
O
O
O
O
O
O
O
O
O
O
O
O
Na+
O
Na+
O
O
Na+
H O
O
H
H
O
H
H
H
O
E
m/z=483
- CO
D
K
m/z=501
m/z=507
-H2O
O
-H2O
O
O
O
O
Na+
O
O
O
O
O
O
O
Na+
O
Na+
O
O
H
H O
O
H
H
O
H
G
m/z=443
F
m/z=461
L
m/z=479
Scheme 2. The proposed fragmentation pathways of M-AM1 complex with sodium cation.

58
D. Łowicki et al. / Journal of Molecular Structure 923 (2009) 53–59
H with abstraction of one water molecule two alternative cations I
and J can be formed, respectively.
data, two OH groups [O(3)H and O(9)–H] as well as one OH and
one N–H groups [O(10)i–H, N(1)i–H] are intra- and inter-molecular
hydrogen-bonded with Clꢀ anion, respectively (Table 5). These
hydrogen bonds are relatively weak but slightly stronger than
the respective ones in the esters of monensin A [34–40].
3.3. FT-IR studies
Fig. 5a presents the FT-IR spectrum of M-AM1–NaCl complex.
The same spectrum on the scale expanded in the ranges of the
In the spectrum of the M-AM1–NaCl complex, the band as-
signed to the m
(C@O) vibrations (amide I) is found at 1697 cmꢀ1
m(OH) and
m(C@O) vibrations is given in Fig. 5b and c, respectively.
and the band assigned to the amide II at 1543 cmꢀ1, indicating that
the carbonyl amide group is not hydrogen-bonded and not en-
gaged in the coordination process of Na+ cation within the complex
structure.
The bands assigned to the
m(OH) and m(NH) vibrations arise broad-
ened in the region 3450–3100 cmꢀ1. This band shows some com-
plex submaxima at 3395, 3320, 3257, 3226, 3190 and 3127 cmꢀ1
appearing as a result of combination of vibrations as well as the
mechanical Fermi resonance. According to our crystallographic
The acetonitrile molecules are incorporated into the crystal
structure of the M-AM1–NaCl complex. This fact is reflected by
the small band assigned to m
(C„N) vibrations at 2252 cmꢀ1. The
position of this band implies that the acetonitrile molecules are
not hydrogen-bonded. Comparable bands assigned to the acetoni-
trile molecules were also observed in the spectra of other inclusion
complexes of monensin A metal salts [25–27].
100
a
3.4. PM5 calculations
2252
50
On the basis of our spectroscopic and X-ray results, the struc-
ture of the inclusion complex of M-AM1–NaCl without acetonitrile
was calculated by the PM5 semiempirical method. This calculated
structure is compared with the X-ray structure given in Fig. 1b.
The interatomic distances between the oxygen atoms of the
monensin N-phenylamide of molecule and the sodium cation as
well as the selected bond lengths and angles are given in Table 3.
The parameters of the hydrogen bonds formed within the structure
are collected in Table 4. The structure implied by the X-ray data is
similar to that obtained by the PM5 calculations. Thus, the PM5
calculations are very effective for visualisation of the probable
structures also in the solid state. The small differences between
the crystallographic data and the respective calculated ones are re-
lated to the fact that the data compared have been obtained for
two different phases: solid and gas and to the neglect of interac-
tions between the acetonitrile and monensin N-phenylamide
molecules.
0
4000
3500
3000
2500
2000
1500
1000
500
100
b
c
3127
50
0
3190
3395
3226
3257
3320
3700
3600
3500
3400
3300
3200
3100
3000
100
50
0
3.5. Antimicrobial activity
Monensin A (MONA) and its amide (M-AM1–NaCl) were tested
in vitro for their antibacterial and antifungal activity. The micro-
organisms used in this study were as follows: Gram-positive bac-
teria, Gram-negative rods as well as yeasts (Table 5). The antimi-
crobial properties of both MONA and M-AM1–NaCl are expressed
by the minimum inhibitory concentration (MIC) and presented in
1543
1697
Table 5. Monensin
Gram-positive bacteria. Monensin A and M-AM1 show comparable
activity against the human pathogenic bacteria (MIC 6.25–12.5
g/
A and M-AM1–NaCl were active against
1800 1750 1700 1650 1600 1550 1500 1450 1400
Wavenumber [cm-1]
l
ml). Both compounds tested are inactive against strains of Candida
(C. albicans and C. parapsilosis). Moreover, as expected, the cell
walls of Gram-negative bacteria do not permit the penetration of
Fig. 5. FT-IR spectra of M-AM1–NaCl: (–) in nujol/fluorolube mulls: (a) 4000–
400 cmꢀ1; (b) 3700–3000 cmꢀ1; (c) 1800–1400 cmꢀ1
.
Table 3
Selected torsion angles (°).
Table 4
Dimensions of the hydrogen bonds (Å and °).
Parameters
X-ray
PM5
97.8
169.5
ꢀ194.9
ꢀ169.3
167.2
61.5
D–Hꢂ ꢂ ꢂA
d(D–H)
d(Hꢂ ꢂ ꢂA)
d(Dꢂ ꢂ ꢂA)
\(DHA)
O(1)–C(1)–C(2)–C(3)
C(1)–C(2)–C(3)–C(4)
C(2)–C(3)–C(4)–C(5)
C(9)–O(4)–C(5)–C(4)
C(3)–C(4)–C(5)–O(4)
O(5)–C(12)–C(13)–O(6)
O(6)–C(16)–C(17)–O(7)
O(7)–C(20)–C(21)–O(8)
O(8)–C(25)–C(26)–O(10)
97.6(3)
169.39(19)
ꢀ164.72(17)
ꢀ169.48(16)
167.32(15)
61.3(3)
X-ray
PM5
O(3)–H(3)ꢂ ꢂ ꢂCl(1)
0.87(4)
0.78(3)
0.82
2.39(4)
2.44(3)
2.39
3.248(2)
3.146(2)
3.128(2)
3.356(2)
170
150
150
173
O(9)–H(9)ꢂ ꢂ ꢂCl(1)
O(10)i–H(10O)iꢂ ꢂ ꢂCl(1)
N(1)i–H(1N)iꢂ ꢂ ꢂCl(1)
0.86
2.50
O(3)–H(3)ꢂ ꢂ ꢂCl(1)
O(9)–H(9)ꢂ ꢂ ꢂCl(1)
0.99
1.00
2.24
2.17
3.23
3.14
170
161
ꢀ70.36(19)
ꢀ70.5
52.8(2)
52.6
ꢀ57.1(2)
ꢀ57.2
Symmetry code: (i): x ꢀ 1, y, z.

D. Łowicki et al. / Journal of Molecular Structure 923 (2009) 53–59
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Table 5
Antimicrobial activity of MONA and M-AM1–NaCl: diameter of the growth inhibition
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l
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Tested strain
MONA
Giz
M-AM1–NaCl
MIC
Giz
MIC
´
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S. aureus NCTC 4163
S. aureus ATCC 25923
S. aureus ATCC 6538
S. aureus ATCC 29213
S. epidermidis ATCC 12228
B. subtilis ATCC 6633
B. cereus ATCC 11778
E. hirae ATCC 10541
M. luteus ATCC 9341
M. luteus ATCC 10240
22
22
20
18
15
22
18
–
2
1
2
1
2
1
2
12.5
4
2
13
11
11
12
–
13
15
–
12.5
12.5
12.5
12.5
12.5
6.25
6.25
>400
6.25
6.25
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