Synthesis, crystal structures, and antibacterial studies of silver(I) complexes with reduced Schiff base amino acid ligands

Article abstract of DOI:10.1007/s11243-016-0060-5

Three Ag(I) complexes of reduced Schiff base amino acid ligands, [Ag₂(Hshis)₂]·3H₂O (1), Ag(Hcgly) (2), and Ag(cala) (3) (H₂shis?=?N-(2-hydroxybenzyl)-l-histidine, H₂cgly?=?N-(2-hydroxy-5-chlorobenzyl)-glycine, Hcala?=?N-(4-chlorobenzyl)-d,l-alanine), have been synthesized and characterized by X-ray crystallography. Complex 1 shows a dimeric structure, while complex 2 shows one-dimensional zigzag chains, which are extended into a two-dimensional supramolecular sheet by hydrogen bonds. Complex 3 exhibits a 2D sheet structure with dangling arms. The antimicrobial activities of the complexes have been investigated.

Full text of DOI:10.1007/s11243-016-0060-5

Transition Met Chem
DOI 10.1007/s11243-016-0060-5
Synthesis, crystal structures, and antibacterial studies
of silver(I) complexes with reduced Schiff base amino acid ligands
Hai-Yan Liu1,2 Qing-Hua Guan3 Jun Tian2 Peng Du1 Hong Chen1
•
•
•
•
Received: 9 March 2016 / Accepted: 9 May 2016
Ó Springer International Publishing Switzerland 2016
Abstract Three Ag(I) complexes of reduced Schiff base
amino acid ligands, [Ag2(Hshis)2]Á3H2O (1), Ag(Hcgly)
(2), and Ag(cala) (3) (H2shis = N-(2-hydroxybenzyl)-L-
Compared to the parent Schiff bases, reduced Schiff bases
are expected to be more stable and can generate more
interesting coordination modes due to the conformational
flexibility of their backbones [10, 11]. Such reduced Schiff
bases generally act as tridentate ligands, coordinating
through the phenolato oxygen, amine nitrogen, and car-
boxylate oxygen. They may also possess potential hydro-
gen-bond donor–acceptor functionalities [12].
histidine,
H2cgly = N-(2-hydroxy-5-chlorobenzyl)-gly-
cine, Hcala = N-(4-chlorobenzyl)-D,L-alanine), have been
synthesized and characterized by X-ray crystallography.
Complex 1 shows a dimeric structure, while complex 2
shows one-dimensional zigzag chains, which are extended
into a two-dimensional supramolecular sheet by hydrogen
bonds. Complex 3 exhibits a 2D sheet structure with dan-
gling arms. The antimicrobial activities of the complexes
have been investigated.
Considerable attention has been devoted to the preparation
and structural characterization of complexes of Cu(II), Co(II),
Ni(II), and Zn(II) with reduced Schiff base amino acid ligands
[13, 14]. However, the crystal structures and biological
properties of silver(I) complexes of such ligands have been
rarely reported [15]. It is widely known that silver(I) ions have
excellent antibacterial properties. In this regard, we expected
that the silver(I) complexes of reduced Schiff base amino
acids could find important applicationsas antibacterial agents.
In this paper, three new reduced Schiff base amino acid
ligands, namely N-(2-hydroxybenzyl)-L-histidine (H2shis), N-
(2-hydroxy-5-chlorobenzyl)-glycine (H2cgly), and N-(4-
chlorobenzyl)-D,L-alanine (Hcala) (Fig. 1), were selected for
assembly with silver(I). Three new silver(I) complexes,
[Ag2(Hshis)2]Á3H2O (1), Ag(Hcgly) (2), and Ag(cala) (3),
have been synthesized and characterized by single-crystal
X-ray diffraction analyses, IR spectroscopy, and elemental
analyses. In addition, the in vitro antimicrobial properties of
the complexes were investigated.
Introduction
In the past decades, transition metal complexes of amino
acid Schiff base ligands have received considerable atten-
tion in chemistry and biology, not only because of their
tremendous structural diversity, but also because of their
marked and various biological properties [1–7]. In partic-
ular, transition metal complexes containing reduced Schiff
base ligands derived from salicylaldehyde or its derivatives
and a-amino acids have been widely studied [8, 9].
& Hai-Yan Liu
67016871@qq.com
1
Department of Chemical Engineering, YingKou Institute of
Technology, Yingkou 115014, People’s Republic of China
Experimental
2
Department of Chemistry and Pharmaceutical Engineering,
Suihua University, Suihua 152061,
People’s Republic of China
Materials and instrumentation
3
Chemicals were purchased from commercial sources and
used without further purification. Elemental analyses were
Animal Science and Technology College, Jilin Agricultural
University, Changchun 130118, People’s Republic of China
123

Transition Met Chem
Fig. 1 Ligands used in this
work
Hcala: Yield, 49 %; mp 269–270 °C; 1H NMR
(d6-DMSO, ppm) d: 7.56 (d, 2H, J = 8.0 Hz, aromatic), 7.45
(d, 2H, J = 8.0 Hz, aromatic), 4.13 (m, 2H, CH2), 3.92 (s,
1H, CH), 1.48 (s, 3H, CH3). Anal. Calcd for C10H12ClNO2
(Mr = 213.66): C, 56.21 %; H, 5.66 %; N, 6.56 %. Found:
C, 56.14 %; H, 5.72 %; N. 6.48 %. FTIR(KBr pellet, cm-1):
3423 m, 1692 v, 1584 s, 1490 m, 1388 s, 1294 s, 1213 s,
1156 s, 1112 s, 1017 s, 827 s, 692 m, 537 s.
obtained with a Carlo Erba 1106 elemental analyzer. FTIR
spectra were recorded from KBr pellets in the range of
4000–400 cm-1 on a Mattson Alpha-Centauri spectrome-
ter. 1H NMR spectra were obtained at room temperature in
DMSO-d6 using a Bruker 400 MHz spectrometer.
Ligand preparations
Synthesis of [Ag2(Hshis)2]Á3H2O (1)
To a solution of the appropriate amino acid (10 mmol) in
water (10 mL) containing KOH (0.56 g, 10 mmol) was
added the appropriate aromatic aldehyde (10 mmol) in
EtOH (10 mL). The yellow solution was stirred for 30 min
at room temperature prior to cooling in an ice bath. The
intermediate Schiff base so obtained was reduced with
excess NaBH4 (0.46 g, 12 mmol). The yellow color slowly
discharged, and after 30 min the solution was acidified
with concentrated HCl to a pH of 4–6. The solvent was
then reduced to half and Et2O was added to precipitate the
product, which was filtered off, washed with ethanol fol-
lowed by diethyl ether, dried, and recrystallized from
water/ethanol (1:1).
A mixture of AgNO3 (0.034 g, 0.2 mmol) and H2shis
(0.052 g, 0.2 mmol) in water (6 mL) plus methanol
(14 mL) was stirred for 20 min at room temperature, and
then filtered. Colorless crystals of complex 1 were obtained
from the filtrate after standing at room temperature for
several days (72 % yield). Anal. Calcd for C26H34Ag2N6O9
(Mr = 790.32): C, 39.51 %; H, 4.33 %; N, 10.63 %.
Found: C, 39.68 %; H, 4.26 %; N, 10.77 %. FTIR(KBr
pellet, cm-1): 3450 m, 3329 s, 3180 m, 1833 s, 1710 s,
1644 s, 1345 m, 1230 s, 1175 m, 1070 w, 980 m, 805 m,
650 m.
H2shis: Yield, 51 %; mp 224–225 °C; 1H NMR
(d6-DMSO, ppm) d: 9.03 (s, 1H, imidazole), 7.49 (s, 1H,
imidazole), 7.39 (d, 1H, J = 12.0 Hz, aromatic), 7.19 (t,
1H, J = 16.0 Hz, aromatic), 6.97 (d, 1H, J = 8.0 Hz,
aromatic), 6.79 (t, 1H, J = 16.0 Hz, aromatic), 4.28 (t, 1H,
J = 12.0 Hz, CH), 4.17 (s, 2H, CH2), 3.49–3.34 (m, 2H,
CH2). Anal. Calcd for C13H15N3O3 (Mr = 261.28): C,
39.51 %; H, 4.34 %; N, 10.63 %. Found: C, 39.44 %; H,
4.42 %; N, 10.57 %. FTIR(KBr pellet, cm-1): 3430 m,
3106 m, 2903 m, 1605 v, 1513 m, 1464 s, 1415 s, 1377 s,
1282 s, 1190 m, 1090 m, 1039 m, 874 s, 826 s, 759 s,
658 m, 630 s.
Synthesis of Ag(Hcgly) (2)
A mixture of AgNO3 (0.034 g, 0.2 mmol), H2cgly
(0.043 g, 0.2 mmol), NaOH (0.004 g, 0.1 mmol), water
(10 mL), and methanol (10 mL) was stirred for several
minutes; then the precipitate was dissolved by dropwise
addition of an aqueous solution of NH3 (14 M). Colorless
block crystals were obtained by evaporation of the solution
for 10 days at room temperature (70 % yield). Anal. Calcd
for C9H9AgClNO3 (322.49): C, 33.52 %; H, 2.81 %; N,
4.34 %. Found: C, 33.51 %; H, 2.69 %; N, 4.29 %.
FTIR(KBr pellet, cm-1): 3370 m, 3289 s, 3145 s, 1878 m,
1690 s, 1536 m, 1370 w, 1310 m, 1156 m, 1080 s, 875 m,
745 m, 630 m.
H2cgly: Yield, 58 %; mp 221–222 °C; 1H NMR
(d6-DMSO, ppm) d: 7.31 (s, 1H, aromatic), 7.20 (d, 1H,
J = 8.0 Hz, aromatic), 6.85 (d, 1H, J = 8.0 Hz, aromatic),
3.92 (s, 2H, CH2), 3.20 (s, 2H, CH2). Anal. Calcd for C9
H10ClNO3 (Mr = 215.63): C, 50.13 %; H, 4.67 %; N,
6.50 %. Found: C, 50.22 %; H, 4.58 %; N, 6.42 %.
FTIR(KBr pellet, cm-1): 3445 w, 3202 m, 2746 m, 1628 s,
1582 v, 1500 s, 1456 s, 1412 s, 1377 s, 1253 s, 1124 s,
1060 m, 850 m, 820 s, 666 s, 548 s.
Synthesis of Ag(cala) (3)
A mixture of AgNO3 (0.034 g, 0.2 mmol), Hcala (0.042 g,
0.2 mmol), NaOH (0.004 g, 0.1 mmol), water (16 mL), and
methanol (4 mL) was stirred for several minutes; then the
precipitate was dissolved by dropwise addition of an aqueous
123

Transition Met Chem
solution of NH3 (14 M). Colorless block crystals were
obtained by evaporation of the solution for 7 days at room
temperature (66 % yield). Anal. Calcd for C10H11AgClNO2
(320.52): C, 37.47 %; H, 3.46 %; N, 4.37 %. Found: C,
37.58 %; H, 3.54 %; N, 4.28 %. FTIR(KBr pellet, cm-1):
3432 s, 3390 m, 3040 s, 1768 m, 1655 s, 1470 m, 1390 m,
1216 m, 1130 s, 970 s, 855 m, 710 m.
determined by a procedure in which 100lL of bacterium
sample with diluted concentration of ca. 5 9 104 to
5 9 105 CFU/mL was spread on a plate full of solid culture
medium. The test sample (5 lL, 4096 lg/mL) was dropped
into a certain area of the culture. The plates were incubated
immediately at 28 °C for 24 h. The antimicrobial activity
of each compound was evaluated by measuring the zone of
growth inhibition against the target microorganisms.
Quantitative antimicrobial assays were carried out by
assaying the minimum inhibitory concentration (MIC) of
each complex against bacterial and yeast strains by means
of the microdilution method. A standardized suspension of
the required test organism (0.2 mL, ca. 5 9 104 to 5 9 105
CFU/mL) and a solution of the test compound at various
concentrations (512, 256, 128, 64, 32, 16, 8, 4, 2, 1, 0.5,
0.25, 0.125, 0.063, 0.031, 0.016, 0.008, 0.004, 0.002,
0.001, and 0.0005 lg/mL) were mixed in a test tube. The
tubes of gram-positive bacteria were incubated at 37 °C for
24 h, while the tubes of gram-negative bacteria and fungus
were incubated at 30 °C for 24 h. The lowest concentration
that produced no visible bacterial growth compared with
the control tubes was observed.
X-ray crystallographic studies
Crystallographic diffraction data for complexes 1–3 were
recorded on an Oxford Diffraction Gemini R CCD with
˚
graphite-monochromated MoKa radiation (k = 0.71073 A)
at 293 K. Absorption corrections were applied using multi-
scan techniques. All three structures were solved by direct
methods within SHELXS-97 and refined by full-matrix
least-square techniques using the SHELXL-97 program [16–
18]. Non-hydrogen atoms were refined with anisotropic
temperature parameters. The detailed crystallographic data
and structure refinement parameters are summarized in
Table 1. Selected bond distances and angles and hydrogen
bonds for the complexes are given in Tables 2–3.
Antimicrobial assays
Results and discussion
Structure of complex 1
The target microbes were Bacillus subtilis (JN-16), My-
cobacterium smegmatis (mc2155), Serratia marcescens
(jn01), and Saccharomyces cerevisiae (jn05).
Qualitative antimicrobial assays were carried out by the
agar-well diffusion method. The bacteriostatic values were
Single-crystal X-ray diffraction analysis reveals that com-
plex 1 crystallizes in the orthorhombic space group
Table 1 Crystal data and
structure refinements for
complexes 1–3
1
2
3
Empirical formula
C26H34Ag2N6O9
790.33
C9H9AgClNO3
322.49
C10H11AgClNO2
320.52
fw
Crystal system
Space group
Orthorhombic
P212121
11.9148(2)
14.0598(3)
17.4528(4)
90
Monoclinic
P21/c
Triclinic
P1
˚
a [A]
10.7663(10)
9.2482(11)
10.2794(12)
90
5.6509(5)
5.6509(5)
9.4274(8)
88.149(7)
85.757(7)
85.002(7)
278.35(4)
1
˚
b [A]
˚
c [A]
a [°]
b [°]
c [°]
90
98.937(10)
90
90
3
˚
Volume [A ]
2923.69(10)
4
1011.08(19)
4
Z
GOF
1.056
1.034
1.063
Reflns collected/unique
18,780/6820
0.0317
4578/2321
0.0285
1879/1563
0.0212
Rint
a
R1 [I [ 2r(I)]
0.0302
0.0357
0.0304
b
wR2 (all data)
0.0653
0.0845
0.0708
a
R1 = R||Fo| - |Fc||/R|Fo|
wR2 = |Rw(|Fo|2 - |Fc|2)|/R|w(F2o)2|1/2
b
123

Transition Met Chem
Table 2 Selected bond lengths
˚
complexes 1–3[a]
Compound 1
[A] and angles [°] for
Ag(1)–N(2)
2.117(2)
2.221(2)
2.511(3)
3.009(3)
167.04(10)
99.50(7)
120.49(9)
74.38(6)
138.42(6)
71.65(6)
Ag(1)–N(5)
Ag(2)–N(1)
Ag(2)–O(4)
2.122(2)
2.224(2)
2.619(3)
Ag(2)–N(4)
Ag(2)–O(1)
Ag(1)–Ag(2)
N(2)–Ag(1)–N(5)
N(5)–Ag(1)–Ag(2)
N(4)–Ag(2)–O(1)
N(4)–Ag(2)–Ag(1)
O(1)–Ag(2)–Ag(1)
O(4)–Ag(2)–N(4)
Compound 2
N(2)–Ag(1)–Ag(2)
N(4)–Ag(2)–N(1)
N(1)–Ag(2)–O(1)
N(1)–Ag(2)–Ag(1)
O(1)–Ag(2)–O(4)
O(4)–Ag(2)–Ag(1)
93.45(7)
156.24(9)
69.23(9)
84.66(6)
93.97(6)
127.17(6)
Ag(1)–N(1)#1
Ag(1)–O(1)
2.206(3)
2.697(2)
2.799(2)
2.133(2)
180.0
Ag(1)–N(1)
2.206(3)
2.697(2)
2.799(2)
2.133(2)
180.00
Ag(1)–O(1)#1
Ag(1)–O(3)
Ag(1)–O(3)#1
Ag(2)–O(2)
Ag(2)–O(2)#2
N(1)#1–Ag(1)–N(1)
O(1)–Ag(1)–O(1)#1
N(1)–Ag(1)–O(1)
Compound 3
O(2)–Ag(2)–O(2)#2
O(3)–Ag(1)–O(3)#1
N(1)–Ag(1)–O(1)#1
180.00
180.00
111.56(11)
68.44(11)
Ag(1)–O(1)
2.150(11)
2.596(5)
176.8(5)
85.8(3)
Ag(1)–N(1)#1
2.170(12)
92.4(3)
Ag(1)–O(2)#2
O(1)–Ag(1)–N(1)#1
N(1)#1–Ag(1)–O(2)#2
O(1)–Ag(1)–O(2)#2
Symmetry codes for 2: #1 -x ? 2, -y, -z ? 1; #2 -x ? 2, -y, -z ? 2. For 3: #1 x ? 1, y-1, z; #2
x ? 1, y, z
Table 3 Hydrogen-bond
geometries for complexes 1 and
2 (A, °)
˚
D–H [A]
˚
˚
D–HÁÁÁA
HÁÁÁA [A]
DÁÁÁA [A]
\D–HÁÁÁA [°]
˚
Compound 1
O(1W)–H(1A)ÁÁÁO(2)
O(6)–H(6B)ÁÁÁO(3W)
O(3)–H(3E)ÁÁÁO(2W)
N(3)–H(3)ÁÁÁO(2)#1
O(1W)–H(1B)ÁÁÁO(5)#2
N(6)–H(6A)ÁÁÁO(1)#3
Compound 2
0.888(10)
0.73(4)
0.73(4)
0.86
2.40(3)
1.91(4)
2.01(5)
2.07
2.772(4)
2.627(6)
2.730(5)
2.795(4)
2.870(5)
2.693(3)
106(3)
167(4)
170(5)
141.4
0.904(10)
0.86
1.968(11)
1.85
176(3)
165.1
N(1)–H(1)ÁÁÁO(2)#3
O(3)–H(3C)ÁÁÁO(1)#4
0.91
2.15
3.004(4)
2.693(4)
156.8
0.71(4)
1.99(4)
170(4)
Symmetry codes for 1: #1 -x - 1/2, -y ? 1, z - 1/2; #2 x - 1, y, z; #3 -x ? 1/2, -y ? 1, z - 1/2. For
2: #3 x, -y - 1/2, z - 1/2; #4 x, 1/2-y, z - 1/2
P212121. This complex possesses a dimeric structure as
shown in Fig. 2a. The asymmetric unit consists of two
kinds of crystallographically unique Ag(I) atoms, two
anionic Hshis ligands, and three free water molecules. Ag1
is coordinated by two imidazole N atoms from two dif-
ferent Hshis ligands with Ag–N distances of 2.117(2) and
donors and two carboxylate O donors. Notably, two Hshis
ligands chelate to the Ag2 atom through their N and O
donor atoms, forming two five-membered rings. The Ag–N
˚
distances are 2.221(2) and 2.224(2) A. The Ag–O bond
˚
lengths are 2.511(3) and 2.619(3) A, which are quite sim-
ilar to the reported values for other complexes [19]. In
˚
addition, the Ag–Ag distance of 3.009(3) A is slightly
˚
2.122(2) A. Ag2 is four-coordinated with a distorted
˚
longer than that in metallic silver (2.88 A) but shorter than
tetrahedral geometry, consisting of two secondary amine N
123

Transition Met Chem
Fig. 2 a ORTEP diagram
showing the coordination
environments of the
Ag(I) atoms in complex 1.
b View of the 2D
supramolecular structure of 1
formed via N–HÁÁÁO and O–
HÁÁÁO hydrogen bonds
˚
the van der Waals contact distance for Ag–Ag of 3.40 A,
indicating that metal–metal interactions exist within the
dimeric unit [20, 21]. As illustrated in Fig. 2b, complex 1
has O–HÁÁÁO and N–HÁÁÁO hydrogen-bonding interactions,
resulting in a 2D supramolecular structure. The geometrical
parameters of the hydrogen bonds are provided in Table 3.
geometry surrounded by two carboxylate O atoms, two
phenolato O atoms, and two N atoms from two Hcgly
ligands. The Ag(1)–O bonds are slightly elongated
˚
(2.697(2) and 2.799(2) A, respectively), although shorter
˚
than the longest Ag–O distance (2.96 A) obtained in a
search of the CSD [22]. The Ag–N bond length is
˚
2.206(3) A, which is quite similar to the reported values for
Structure of complex 2
other complexes. Ag2 is two-coordinated by two car-
boxylate O atoms from two Hcgly ligands (Ag(2)–
˚
O(2) = 2.133(2) A). As shown in Fig. 3b, two Hcgly
Complex 2 crystallizes in the monoclinic space group P21/
c, and the asymmetric unit consists of two Ag(I) atoms and
one Hcgly ligand. As shown in Fig. 3a, both Ag1 and Ag2
localize at a special position with site occupancies of 0.5.
Each Ag1 exhibits a distorted octahedral coordination
ligands chelate one Ag1 to form a neighboring repeating
unit. The repeating units are further connected by Ag2
centers via the second carboxylate oxygen atoms of the
Hcgly ligands, resulting in a 1D zigzag polymeric chain.
123

Transition Met Chem
ligands bridge Ag(I) atoms to generate a 1D chain struc-
ture. Neighboring chains are further linked by N atoms
from the cala ligands to furnish a 2D sheet parallel to the
ab plane. In each layer, the p-chlorobenzene group of the
cala ligand acts as a dangling arm.
Antibacterial activities
A total of four microbial strains, specifically, two gram-
positive bacteria (B. subtilis, M. smegmatis), one gram-
negative bacteria (S. marcescens), and one yeast (S. cere-
visiae), were used for qualitative screening of the
antibacterial and antifungal activities of the complexes and
the corresponding free ligands. The results are summarized
in Table 4. Effectiveness is classified into two categories:
(?) effective and (-) non-effective. Free H2shis and Hcala
showed no inhibition against the selected microorganisms,
while H2cgly was only effective against the gram-negative
bacterium M. smegmatis. However, complexes 1 and 2
were effective against all four microorganisms. Complex 3
was active against both gram-positive and gram-negative
bacteria, but showed no antifungal activity. The antimi-
crobial activities of such silver(I) complexes may result
Fig. 3 a ORTEP diagram showing the coordination environments of
Ag(I) atoms in 2. b View of the 1D polymeric chain structure of 2.
c View of the 2D supramolecular structure of 2
Notably, the Hcgly ligand shows both tridentate chelating
and bidentate bridging coordination modes. In neighboring
chains, there are N–HÁÁÁO hydrogen bonds between sec-
ondary amine groups and carboxylate oxygen atoms
(Fig. 3c; Table 2). These intermolecular hydrogen bonds
link the 1D chains into a 2D supramolecular structure.
Structure of complex 3
Complex 3 crystallizes in the triclinic space group P1 and
consists of one crystallographically independent
Ag(I) atom and one anionic cala ligand (Fig. 4a). Ag1 is
three-coordinated by two O atoms from two cala ligands
and one N atom from one cala ligand in a T-shaped
˚
geometry. The Ag–N distance is 2.170(12) A. The Ag–O
˚
bond lengths are 2.150(11) and 2.596(5) A, respectively,
which are quite similar to previously reported values. As
shown in Fig. 4b, the carboxylate groups of the cala
Fig. 4 a ORTEP diagram showing the coordination environments of
Ag(I) atoms in 3. b 2D layer parallel to the ab plane in 3
123

Transition Met Chem
Table 4 Antimicrobial activities of the free ligands and their
complexes
Supplementary material
CCDC 1429377, 1429378, and 1439621 for 1–3 contain
the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via http://www.
ccdc.cam.ac.uk/data_request/cif or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ,UK [Telephone: ?44-01223-762910:
Fax: ?44-01223-336033; E-mail: deposit@ccdc.cam.
ac.uk].
Strain
H2shis
H2cgly
Hcala
1
2
3
B. subtilis
-
-
-
-
-
?
-
-
-
-
-
-
?
?
?
?
?
?
?
?
?
?
?
-
M. smegmatis
S. marcescens
S. cerevisiae
Table 5 Minimum inhibitory concentrations (MIC in lg mL-1) of
complexes 1–3
Strain
1
2
3
Acknowledgments This work was supported by the National Natural
Science Foundation of China (Grant No. 21201128) and the Science
Research Funds of education department of Liaoning Province
(L2014596).
B. subtilis
0.002
0.031
0.008
8
0.031
1
2
M. smegmatis
S. marcescens
S. cerevisiae
4
0.5
16
4
n.d.
References
n.d. not determined
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ease of ligand replacement appear to be the key factors
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ˇ
In order to obtain quantitative antimicrobial data, we
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the selected bacteria and yeast. Complex 1 proved to be the
most active. This can be explained by the different struc-
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structure, whereas 2 and 3 showed 1D and 2D polymeric
structures, respectively. These differences may affect the
ability of each complex to permeate through the cell
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