Metal complexation induces antibiotic activity in S-ethyl-L-cysteine sulfoxide

Article abstract of DOI:10.1016/j.ica.2018.04.002

Anti-microbial effect is produced when the ligand (L) S-ethyl-L-cysteine sulfoxide (Ethiin) makes coordination complex with metal ‘M’ (M = Cu, Co, Ni), while, ethiin did not show any antimicrobial effect. The synthesized complexes have 1:2 metal to ligand ratio (ML₂). The spectro-chemical analysis revealed that the ligand coordinates with the metals through oxygens of the carboxylate and sulfoxide groups resulting in octahedral geometry around the central metal atom. Techniques like ¹H NMR, thermal analysis, mass spectrometry, UV-Vis spectroscopy, XAFS, FTIR, EPR and magnetic moments were used to elucidate the structure of the ligand and the metal complexes. The expected reasons for the creation of anti-microbial effect are, either the disturbance of the ionic environment within the microbial cytoplasm when the complex enters into it or interaction of the complex with the DNA.

Full text of DOI:10.1016/j.ica.2018.04.002

Accepted Manuscript
Research paper
Metal complexation Induces Antibiotic Activity in S-ethyl-L-cysteine Sulfoxide
Shahbaz Nazir, Jamil Anwar, Munawar Ali Munawar, Javed Iqbal Qazi, Stephen
Peter Best, Michael Cheah, Muhammad Yaseen
PII:
S0020-1693(18)30041-0
https://doi.org/10.1016/j.ica.2018.04.002
ICA 18193
DOI:
Reference:
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
17 January 2018
31 March 2018
2 April 2018
Please cite this article as: S. Nazir, J. Anwar, M.A. Munawar, J.I. Qazi, S.P. Best, M. Cheah, M. Yaseen, Metal
complexation Induces Antibiotic Activity in S-ethyl-L-cysteine Sulfoxide, Inorganica Chimica Acta (2018), doi:
https://doi.org/10.1016/j.ica.2018.04.002
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1
Metal complexation Induces Antibiotic Activity in S-ethyl-L-cysteine
Sulfoxide
a
a
a
b
Shahbaz Nazir* , Jamil Anwar , Munawar Ali Munawar , Javed Iqbal Qazi , Stephen Peter
c
c
d
Best , Michael Cheah , Muhammad Yaseen .
a
Institute of Chemistry, University of the Punjab, Lahore 54590, Pakistan
Department of Zoology, University of the Punjab, Lahore 54590, Pakistan
School of Chemistry, University of Melbourne, Melbourne, Australia..
Department of Chemistry, University of Education, Faisalabad campus, Faisalabad, Pakistan.
b
c
d
Anti-microbial effect is produced when the ligand (L) s-ethyl-L-cysteine sulfoxide (Ethiin) makes
coordination complex with metal ‘M’ (M= Cu, Co, Ni), while, ethiin did not show any
antimicrobial effect. The synthesized complexes have 1:2 metal to ligand ratio (ML ). The
2
spectro-chemical analysis revealed that the ligand coordinates with the metals through oxygens of
the carboxylate and sulfoxide groups resulting in octahedral geometry around the central metal
1
atom. Techniques like H-NMR, thermal analysis, mass spectrometry, UV-Vis spectroscopy,
XAFS, FTIR, EPR and magnetic moments were used to elucidate the structure of the ligand and
the metal complexes. The expected reasons for the creation of anti-microbial effect are, either the
disturbance of the ionic environment within the microbial cytoplasm when the complex enters
into it or interaction of the complex with the DNA.
Keywords: S-ethyl-L-cysteine sulfoxide complexes, antimicrobial effects, sulfoxide coordination
complex, XAFS analysis
1. Introduction
Allium plants (Onion, Garlic, Shive etc.) are rich source of sulphur containing compounds, that
mostly, consist of cysteine derivatives e.g., S-Allyl cysteine, S-Ethyl cysteine, S-Propyl cysteine
and their sulfoxides [1,2]. These compounds have variety of health effects such as
anticarcinogenic,
antibiotic,
anticoagulant,
antiatherogenic,
antihyperlipidaemic,
antihypertensive, immune system protection / stimulant, hepatic system protection, antidiabetic
and antioxidant effects [3, 4-15]. For example, S-propyl cysteine, S-propyl cysteine sulfoxide and
S-methionine sulfoxide reduce the risk of atherosclerosis [16, 17]. The S-alk(en)nyl-L-cysteines
e.g., Methyl cysteine, Allyl cysteine and their sulfoxides show strong antioxidant activity when
tested against lipid hydroperoxide (LOOH) formation in human low density lipoproteins
(LDL)[18].Not only these compounds, but their metal complexes also show promising health
effects. For example, Corbi et al. prepared platinum complex of S-allyl-L-cysteine sulfoxide
(alliin). This complex revealed moderate cytotoxic effect against human cancer cell line HeLa
[19]. Corbi et al. also prepared palladium complex of methionine sulfoxide. This complex
exhibited a high cytotoxic effect against human cancer cell line HeLa [20].
*Corresponding author. Email: shahbaznazir2000@yahoo.com

2
S-ethyl-L-cysteine sulfoxide (Fig. 1) is an important molecule found in Allium plants.
Considering the bioactive potential of cysteine sulfoxides and their metal complexes, we have
prepared the metal complexes of S-ethyl-L-cysteine sulfoxide and studied their biological
activity.
2. Experimental
2.1 Material, Methods and Equipment
Melting points of the ligand and its metal complexes were determined using a Gallenkamp
1
melting point apparatus. H NMR spectrum was taken in D O and recorded at 500 MHz on
2
Varian INOVA-500 instrument. (Abbreviations: s, singlet; d, doublet; t, triplet; m, multiplet).
For 13C NMR spectra, solution of Ethiin in D2O was added with acetone as internal standard.
Mass spectrum was recorded on Jeol MS Route and Waters micromass triple quadrupole quarto II
Electrospray Ionization mass spectrometer. Cone voltages ranging from 5-15 V were used for
best results. IR spectra were recorded on FT-IR Nicolet 6700 of Thermo Scientific Company.
Elemental analysis was performed using CHNS-932 LECO analyzer. UV-Vis spectra were
recorded from 200-800 nm by using Spectro UV-Vis double beam UVD-3500 (Labomed INC.).
o
Magnetic moments were measured at 20 C using Mark 1 instrument from Sherwood scientific
company. Mercury tetrathiocynatocobaltate (II) {Hg[Co(NCS)
4
]} was used as a calibrant. TGA,
DTA were taken by using Universal V4.2E TA instrument-SDT Q600 V8.2 Build 100 and
o
-1
o
analysis were made in Nitrogen environment with heating rate of 10 C min from 25 to 1000 C.
Reagent grade materials were purchased from Aldrich Chemical Co. and used without further
purification.
X-ray absorption spectra were collected from solid samples of copper complexes of S-propyl-L-
cysteine diluted into cellulose powder and finely ground and pressed into 13mm discs by the
application of moderate pressure (10 Tonnes). The composition of the disc was adjusted so as to
achieve a balance between the attenuation of the sample and the transmittance beyond the Cu
absorption edge. For all samples the minimum transmittance was between 10 and 20% through
the edge and XAFS regions.
X-ray fluorescence measurements were made at a temperature of ca. 273K using beamline 20 B
(bending magnet) at the KEK Photon Factory, Tskuba, Japan. A channel-cut Si(1 1 1)
monochromator provided an energy resolution (DE/E) of ca. 2.4_10_4, and higher order
harmonics of the selected wavelength were rejected by detuning the monochromator by a factor
of a half. EXAFS measurements were conducted at the Cu K-edge. Solid samples were measured
in transmission mode using an ion chamber detector. Data reduction of experimental X-ray

3
absorption spectra was performed using the program XFIT [21]. The model structure was refined
using the XFIT software package, which incorporates ab initio FEFF 6.01MS curved wave
calculations [22]. The number of refined variables, Nrv, in the models, including the scale factors
E0 and S0 2 are listed in appendix.
2
.2 Synthesis of S-alkyl-L-cysteine sulfoxide
S-ethyl-L-cysteine sulfoxide was prepared using slightly modified method of Tsuge et al.
[23]. Hence, S-ethyl-L-cysteine (8.25g, 0.1 mole) was dissolved in 500 ml of distilled water and
10 ml of 30% hydrogen per oxide were added to it drop by drop. The resulting solution was
stirred for 2 hours and concentrated under reduced pressure. The product was crystallized from
the solution by the addition of acetone (1000 ml) and recrystallized from ethanol/water system.
Yield 79 %. Anal. Cald. for (C
Found: C, 36.31; H, 6.45; N, 8.58; S, 19.28. m.p. 160-161 C (dec.); IR (cm ): 1588 (ν (COO-)),
5
H
11NO S)( %): C, 36.36; H, 6.66; N, 8.48; S, 19.39.
3
0
-1
+
1
3
180-2865 (ν (NH3+)), 1014 (ν (S=O)). ESI-MS m/z: 166.2 [M +H] ; H NMR ( D
MHz): δ 4.21 (d of t, J= 6.0 and 6.5 Hz, 1H, H at α-Carbon), 3.45 (dd, J=7.5 and 14 Hz, 1H, Ha
on -carbon), 3.18 (dd, J=6.0 and 14 Hz, 1H, Hb on carbon), 2.92 (m, 2H ,CH S on ethyl
O, ppm, 125 MHz): δ 173.0, 51.6, 51.2, 46.9,
2
O,PPM, 500
2
1
3
side), 1.29 (t, J=7.5 Hz, 3H, CH3). CNMR (D
2
6.50.
2
.3 Synthesis of S-Ethyl-L-cysteine sulfoxide (Ethiin) complexes
Ethiin (3.3g, 0.02 mole) was dissolved in 0.02 molar ethanolic solution of sodium
hydroxide. MCl hydrate (M= Cu, Co, Ni) (0.01 mole) was dissolved in minimum amount of
.
2
water and added in the ethiin solution drop by drop and stirred vigorously for an hour. Gel like
precipitates having colour characteristics of respective metal complexes were filtered, washed
o
with ethanol thoroughly and dried in oven at 50 C to obtain solid mass.
2
.3a
Bis(S-Ethyl-L-cysteine sulfoxidato)Cu(II): [Cu(C
Yield 82 %. Anal. Cald.for [ Cu(C S) ]( %) : C, 3.65; H, 5.10; N, 7.15; S, 16.34.
Found: C, 30.31; H, 5.19; N, 7.23; S, 16.28. m.p. Dec.>180 C; FT-IR (cm ): 3288, 3247 (υ
5
H
10NO
3
S)
2
]
5
H
10NO
3
2
o
-1
-
1
(
NH2)), 1596, 1398 (υ (COO-)), 1017(υ (S=O)). UV-Vis (cm ): 15923. μeff (B.M.): 2.12.
2
.3b Bis(S-Ethyl-L-cysteine sulfoxidato)Co(II):[Co(C H NO S) ]
5
10
3
2
Yield 85 %. Anal. Cald. for [Co(C
Found: C, 31.17; H, 5.25; N, 7.35; S, 16.64. m.p. Dec.>180 C; FT-IR (cm ): 3347, 3281 (υ
NH2)), 1592, 1410 (υ (COO-)), 1014 (υ (S=O)). ESI-MS[M+H] : 388.1. UV-Vis (cm ): 37040, 19723.
eff (B.M.): 5.24
5
H
10NO
3
S)
2
]( %) : C, 31.00; H, 5.16; N, 7.23; S, 16.53;
o
-1
+
-1
(
μ
2
.3c
Bis(S-Ethyl-L-cysteine sulfoxidato)Ni(II): [Ni(C
Yield 78 %. Anal. Cald. For[ Ni(C S) ]( %): C, 31.03; H, 5.17; N, 7.24; S, 16.55;
Found: C, 31.18; H, 5.28; N, 7.36; S, 16.65. m.p. Dec.>182 C; FT-IR(cm ): 3346, 3274 (υ (NH2)),
5
H
10NO
3
S)
2
]
5
H
10NO
3
2
o
-1
-
1
+
1584, 1397 (υ (COO-)), 1016 (υ (S=O)). UV-Vis (cm ): 27100, 16077. ESI-MS[M+H] : 387.4. μeff
(B.M.): 3.32

4
3. Results and Discussion
3
.1 FTIR spectroscopy
S-ethyl-L-cysteine sulfoxide ( Fig. 2) can coordinate with metals thorough oxygen,
sulfur and nitrogen atoms (in bold).
Since amino acids exist in zwiter ionic form, so depending on the pH and metal atom
Ethiin can act as monodentate, bidentate and tridentate ligand and can be a bridging or non-
bridging ligands [24, 25, 26].
Literature values for vibrational frequencies of various groups of amino acids, potassium
salt of an amino acid for reference and Ethiin are given in table 3.1.
Table 3.1
Literature values for vibrational frequencies of various groups of amino acids, potassium
-1
salt of amino acids and the ligands. (cm )
+
+
-
–
Amino Acid
ν
α
NH
3
ν
δ
NH
3
.
ν
as COO
ν
s
COO
S=O
Ref.
28
1
1
660-1610
550-1485
1520
3
130-2500
General trend
Alanine
1600-1560
~1410
(
broad-band)
3180-2510
1575
1585
1415
1414
36
29
Methionine
Sulfoxide
3
200-2700
1515
1021
1020
Methionine
sulfoxide
Potassium salt
3600-2750
1587
1596
1410
1398
29
S-ethyl-L-
cysteine
3
210-2666
1506
1014
sulfoxide

5
In solid state, amino acids exist in Zwiter ionic form and hence they show different IR
pattern than the normal amino (NH
characteristic of ionic carboxylate and amine salt. The broad band of NH
asymmetric and symmetric stretches, combination and overtones overlapping with each other
27]. This region becomes wider due to participation of C-H stretching vibrations of the amino
2
) and carboxylic (COOH) group. They show IR pattern
+
3
is composed of
[
+
3
acid. This region become even wider in ionic salts of the amino acids as NH
is deprotonated
here and N-H vibrational frequencies rise due to increase of N-H bond strength. Furthermore
hydrogen bonding involved also contribute in the band widening [28].
Similarly ionized carboxylic group either in zwiter ionic form or in basic salt form e.g.,
-
potassium salt, show absorption band due to asymmetric and symmetric (COO ) stretches around
-
1
1
580 and 1410 cm respectively. The protonated carboxylic group e.g., in hydrochloride salt
-
1
absorb between 1700-1750 cm [27,28].
In case of amino acids containing sulfoxide (S=O) group, IR absorption for sulfoxide
-
1
group appears as strong band around 1020 cm [29].
On coordination of the amino acids to the metal, following changes can be observed in IR
-
absorption frequencies for amino (NH
2
), carboxylic (COO ) and sulfoxide (S=O) groups.
1.
Coordination of amino group is attested by the presence of two well resolved peaks in the
-
1
region 3000-3400 cm . Amino group coordination is also confirmed by the absence of
-
1
band in the region 2050-2150 cm . This band is present in free amino acid and their basic
+
salts and is assigned to non-coordinated NH
in the complex is another proof of NH
2
group [30]. The absence of δas(NH
3
) band
2
coordination. In free ligand this band is present at
-1
1
505 cm [28].
-
2
3
.
.
Coordination of carboxylate (COO ) group to metal causes the asymmetric frequency to
increase and symmetric frequency to decrease. The amount of increase and decrease
depends on the metal involved which in turn depends upon the strength of M-O bond.
The stronger the M-O bond, the more is the increase in asymmetric frequency [28].
For sulfoxide coordination, it is necessary to consider the structures of hybrids of
sulfoxide which are shown in Fig. 3, [28].

6
Sulfoxide group can coordinate either through sulfur atom or through oxygen atom. If
coordination occurs through oxygen atom, it will give rise to partially ionized bond and will make
contribution of structure (I) weaker resulting in weakening of (S=O) bond and hence its
frequency will be shifted to lower value.
On the other hand if coordination occurs through the sulfur atom, the contribution of
structure (II) will decrease resulting in strengthening of (S=O) bond and hence the frequency of
absorption will increase [28].
Another parameter for the metal complexes is ∆ν which is difference of asymmetric and
–
symmetric vibration frequency of carboxylate group of the amino acid, hence ∆ν = νas - ν (COO
s
). When an amino acid coordinates, the asymmetric vibration frequency increases and symmetric
vibration frequency decreases as compared to the free ionic state which in turn depends on the
metal oxygen (M-O) bond strength. The stronger the M-O bond, the more is the shift in
asymmetric and symmetric frequencies. Nakamoto gave the following order of metals for the
increase in the separation of the two frequencies on coordination [28].
Ni(II) < Zn(II) < Cu(II) < Co(III) < Pd(II) ≈ Pt(II) < Cr(III)
The ∆ν not only tells about the strength of the M-O bond but it also tells about the mode
of the coordination of the carboxylate group. Carbxylate group can coordinate either in
monodentate fashion (only one oxygen coordinating) or bidentate fashion (both the oxygen
involved in coordination). The monodentate coordination gives rise to higher ∆ν values while
bidentate coordination gives rise to ∆ν closer to ionic carboxylate group e.g. in potassium salts of
the amino acids [28].
IR frequencies for metal-oxygen and metal-nitrogen bond are also an important proof for
coordination of the ligands with metals. For the metals of first transition series in +2 oxidation
-1
state, the M-N stretching frequency occurs between 400-500 cm and M-O frequency occurs
-
1
between 280-400cm . These frequencies decrease as atomic radius of the metal involved
increases and vice versa [28].
Selected peaks of IR spectrum of the S-ethyl-L-cysteine sulfoxide complexes are given in table
3.2.

7
Table 3.2
IR data of S-ehtyl-L-cysteine sulfoxide complexes
+
–
–
Complex
NH
3
-
/NH
2
ν
as COO
ν
s
COO
∆ν = νas - ν
(COO )
s
S=O
1014
1
-1
-1
–
(cm )
(cm )
(cm )
Ethiin Potassium 3210-2666
salt
1589
1395
194
238
182
189
(
broad band)
3398-3147
broad band)
3365-3181
broad band)
3356-3174
broad band)
Cu ethiin
Co ethiin
Ni ethiin
1631
1592
1594
1393
1410
1405
1002
1004
1006
(
(
(
In all the complexes, a broad band in the region 3400-3100 indicates a non-coordinated
amino group. So coordination of the amino group is ruled out.
The changes in the carboxylate group frequencies prove its coordination to metals. The
∆ν clearly indicates that carboxylate group is coordinated in bidentate fashion. This coordination
is symmetric as both the antisymmetric and symmetric frequency values increase as compared to
cases where anti-symmetric increases and symmetric decreases which indicates unsymmetric
bidentate coordination [31].
In all the complexes a coordination of sulfoxide group through oxygen atom is predicted
as vibrational frequency decreases in complexes as compared to free ligand or its potassium salt.
-
1
Metal ligand vibration frequencies for Ni, Co, Cu can be found at 305, 383, 371 cm respectively
for Metal-oxygen (M-O) bond of the metal coordinated to carboxylate group .
3
.2 Thermogravimetric analysis
Thermogravimetric analysis of the complexes is discussed below.
3.2a Bis(S-ethyl-L-cysteine sulfoxidato)Cu(II): [Cu(C
5
H10NO
S)
3 2
]
In the TGA of copper complex of ethiin, the decomposition proceeds in one step as
o
shown in Fig. 4. Here the entire ligand is removed around 200 C. DTA shows that this one step
is composed of two different heat absorption steps. Hence the two step of decomposition takes

8
place with a difference of very short time. Final residue was CuO. Hence, the molecular formula
was suggested to be Cu(C
5
H10NO
3
S) . No coordinated water was detected.
2
Fig. 4: DTA and DTG of Bis(S-ethyl-L-cysteine sulfoxidato)Cu(II).
3
.2b Bis(S-ethyl-L-cysteine sulfoxidato)Co(II):[Co(C
Decomposition, according to TGA of cobalt ethiin complex, takes place in two distinct
steps as shown in Fig. 5.The first step is the removal of carbon chain including alpha carbon i.e.
CH-CH -S(O)-CH -CH . The second step is removal of the rest of the ligand from the molecule.
DTG and DTA curves also confirm the same pattern. Final residue was CoO so the formula was
supposed to be Co(C S) . No water of coordination was detected in the spectra.
5
H
10NO
3
S)
2
]
–
2
2
3
5
H
10NO
3
2

9
Fig. 5: TGA and DTG of Bis(S-ethyl-L-cysteine sulfoxidato)Co(II).
3
.2c Bis(S-ethyl-L-cysteine sulfoxidato)Ni(II): [Ni(C
TGA of nickel ethiin complex shows single step decomposition around 240 C as shown
Fig.6. All of the ligand is removed in one step. DTG and DTA confirm this observation. Final
5
H
10NO
3
S)
2
]
o
residue was NiO, hence the molecular formula was supposed to be Ni(C
coordinated water was detected.
5
H
10NO
3
S) . No
2

1
0
Fig. 6: TGA and DTG of Bis (S-ethyl-L-cysteine sulfoxidato) Ni(II).
3
.3 ESI-Mass Analysis
+
The important peaks in the ESI-Mass spectrum of all the complexes are [M+H] peaks.
The complexes with proposed molecular formulas and peaks values are as follows,
i)
Bis(S-ethyl-L-cysteine sulfoxidato)Cu(II): Cu(C
Bis(S-ethyl-L-cysteine sulfoxidato)Co(II): Co(C
Bis(S-ethyl-L-cysteine sulfoxidato)Ni(II): Ni(C
These peaks are accompanied with isotopic pattern for the respective metals.
5
H
10NO
3
S)2, = 392.7
ii)
iii)
5
H
10NO
3
S)2, = 388.1
5
H
10NO S)2, = 387.4
3
The other important peaks are of monmeric ligand at 166.1 and dimeric ligand at 331.4. These are
also accompanied with all the isotopic pattern for organosulfur compound. Peaks of the ligand
with S-alkyl group removed are also present.
3
.4 Magnetic Momment
Magnetic moments of copper, cobalt and nickel complexes are given in table 3.3.

1
1
Table 3.3
Magnetic moment of S-ethyl-L-cysteine sulfoxide complexes
Sr. No.
Complex
Limit
Ref.
µ
eff
1
2
3
Bis(S-ethyl-L-cysteine sulfoxidato)Cu(II)
Bis(S-ethyl-L-cysteine sulfoxidato)Co(II)
Bis(S-ethyl-L-cysteine sulfoxidato)Ni(II)
2.12
5.24
3.32
1.7-2.2
4.1-5.2
2.8-4.0
37
37
37
7
8
9
Cobalt, Nickel and copper have d , d , d configuration respectively and here cobalt has
high spin configuration. An octahedral geometry is proposed with the support of UV-Vis data for
these complexes.
3
.5 UV-Vis Spectroscopic Measurements
All of these complexes were soluble in water. Lambda max( λmax ) and extinction
coefficients are given as in table 3.4.
Table 3.4
UV-Vis. Data of S-ethyl-L-cysteine sulfoxide complexes
-
1
-1
Complex
λ
max
ε (l mol cm )
Band assignment
Ref.
nm
2 2
x -y
Bis(S-ethyl-L-cysteine
sulfoxidato) Cu(II)
622
46
d
xy, yz, xz
d
Bis(S-ethyl-L-cysteine
sulfoxidato) Co(II)
4
4
507
22
T
1g
T1g (P)
Bis(S-ethyl-L-cysteine
sulfoxidato) Ni(II)
3
3
3
1
6
3
012
17
18
16
28
A
2g
2g
2g
T
2g
3
A
T
1g
37
3
3
69
A
T
1g (P)
These absorption values are characteristics of octahedral geometry as similar results have
been found for other octahedral systems of related copper, cobalt and nickel complexes. [25,32,
33-34]
3.6 EPR Spectroscopy
Electron paramagnetic resonance spectroscopy is an important tool to study the
distribution of electron density of an orbital around the metal atom like copper. The tetragonal

1
2
distortion of the copper complexes from octahedral geometry due to Jahn-Teller effect is studied
through this technique. The value of the g-factor for copper complex is given in Table 3.5.
Table.3.5
Values of g-factor for the synthesized copper complex
Sr. No.
Complex
g
1
g
2
1
Bis(S-ethyl-L-cysteine sulfoxidato)Cu(II)
2.06
2.20
The g
methionine sulfoxide are 2.05 and 2.21 respectively and for [Cu(H
33]. Similar values have also been reported for the other tetragonally distorted octahedral copper
complexes [35].
1
and g
2
values for the tetragonally distorted complexes e.g. copper complex of
2
O) (HCO ] are 2.06 and 2.31
4
2 2
)
[
So comparison of the above tabulated data with the published literature values indicates a
tetragonally distorted octahedral geometry due to Jahn-Teller effect for the synthesized copper
complex. Hence the copper complex has a tetragonally distorted octahedral geometry.
3
.7 XAFS Analysis
Structural parameters obtained from fitting the XAFS of bis(S-ethyl-L-cysteine
sulfoxidato)Cu(II) are given in table 3.6.

1
3
Table 3.6
Structural parameters obtained from fitting the XAFS of bis(S-ethyl-L-cysteine
sulfoxidato)Cu(II)
Model
Model 1
, L , L
Model 2
Model 3
L
x
y
z
= O
L , L
x y
= O
L , L
x y
= O
L
z
= N
L
z
= S
Cu-L
x
/ Å
1.97 (0.018)
0.0009 (0.0009)
2.71 (0.03)
0.0036 (0.0032)
1.88 (0.02)
0.0035 (0.0033)
0.39 (0.91)
0.88 (0.12)
4.75
1.99 (0.02)
0.0009 (0.0009)
2.71 (0.03)
0.0039 (0.0034)
1.90 (0.02)
0.0033 (0.0031)
0.34 (0.90)
0.92 (0.13)
4.37
1.91 (0.11)
0.0069 (0.0176)
2.05 (0.07)
0.0153 (0.0153)
1.96 (0.06)
0.0025 (0.0021)
-2.81 (3.78)
1.00 (0.09)
7.99
2
2
σ (L
x
)/ Å
/ Å
Cu-L
y
2
2
σ (L
y
)/ Å
Cu-L
z
/ Å
2
2
σ (L
z
)/ Å
E
0
2
0
S
2
χ
R / %
21.1
20.3
27.46
Figures for these fittings are shown 7-9.

1
4
Fig.7: Fitting when all the atoms are oxygen around the copper atom

1
5
Fig. 8: Fitting when four atoms are oxygen and two are nitrogen around copper
Fig. 9: Fitting when four atoms are oxygen and two are sulfur around copper
It is clear from all the above data and figures that the simplicity of the model fails to account for
longer range scattering interactions with atoms in the second coordination sphere. This will show
up in the longer R range and as higher frequency oscillations in the XAFS. While an extension of
the model to include those interactions these additions would increase the number of parameters
required to fit the data. Both in terms of the quality of the data and the questions under
consideration .The extension of the analysis to include those factors is not justified.
Hence there are high frequency oscillations in the residuals and these indicate longer range
scattering interactions not included in the model. This is not at all surprising and is likely to relate
to the backbone of the amino acids.
Conclusion of XAFS analysis
The XAFS analysis strongly suggest a significant axial distortion. While it is likely that the
coordination of the amino acid is through O and N atoms there is little difference between the
statistics of the 4O and 2O, 2N refinements. This is not surprising given the closeness of the
atomic numbers of these atoms. Hence coordination through the oxygens of carboxylate and
oxygen of sulfoxide group is predicted in this complex. These modes of coordination are also
predicted by FTIR spectra of these complexes.

1
6
3
.8 Bioactivity
The complexes were dissolved in distilled water/DMSO to prepare 0.1% W/V solution.
Antimicrobial activity was assessed by employing Staphylococcus aureus, Escherichia coli and
Sacchaomyces cerevisiae as representative of Gram positive, Gram negative and eukaryotic
microorganisms respectively.
A given solution (10µl) was dispensed on autoclaved Whatman filter paper No.1 discs of
6
mm diameter. Growth of overnight incubated culture of a given test microbe in nutrient broth
(10µl) was spread over solidified nutrient agar plate containing (15ml) of medium with the help
of sterilized glass spreader. Five minutes were allowed the surface of the inoculated nutrient agar
to absorb the fluid of inoculum before applying the discs. Then the loaded discs were picked up
with the help of sterilized forceps and placed at least 15mm apart from the edge of the inoculated
nutrient agar plates and 2cm apart from each other along with control discs loaded with 10µl of
respective solvent. Each disc was then gently pressed with the help of blind end of a sterilized
o
steel probe. Plates were then incubated for 18-24hrs at 37 C. After incubation, growth inhibition
zones were measured in millimeters. Photograph of respective zones of growth inhibition were
taken with the help of digital camera.
3
.8.1 Results
Growth inhibition effects of Ethiin and its metal complexes are listed in Table 3.7. Ethiin
alone did not show any bioactivity whereas the tested complexes exerted antimicrobial effects
against the test organisms. However different compounds have different levels of antimicrobial
activity against gram positive, gram negative bacteria and yeast. The results suggest that while
being absorbed in the microbe cell, the complex making ability of ethiin have led ethiin to take
with it, the metal ion, inside the microbe cell which, disturbed the ionic environment of cytoplasm
and hence inhibited the growth of the microbe. Another mechanism can be the interaction of the
complex with the DNA of the microbe resulting in its death. Such type of induction of
antimicrobial activity in a ligand and its mechanism after complexation with metals has also been
reported in literature[36-38]. The complexes reported here can be used as broad spectrum
antibiotic
compounds.

1
7
Table 3.7
Antimicrobial activity of all other complexes
Test Organism
Sr.
Compound
E. coli
S. aureus
S. cerevisae
No.
(
mm)
R
(mm)
R
(mm)
R
1
2
3
4
5
6
H O
2
DMSO
8
R
R
Dioxane:water 1:1
R
R
R
S-ethyl-L-cysteine sulfoxide
Bis(S-ehtyl-L-cysteine sulfoxidato)Co(II)
Bis(S-ethyl-L-cysteine sulfoxidato)Ni(II)
R
R
R
12
12
9
14
16
10
Disc. Diameter = 6.00mm. R= The microbe was resistant to the applied substance.
4
. Conclusion
Based on the spectral and physical data which indicates bidentate symmetrical
carboxylate group coordination and sulfoxide coordination through oxygen atom in all the
complexes, following octahedral structure have been proposed for the complexes of S-ethyl-L-
cysteine sulfoxide shown in Fig. 10. The water solubility of these complexes also indicates their
monomeric nature.

1
8
Such complexes with symmetric bidentate coordination of carboxlate group have already
been reported for amino acids and acetate complexes [31,33,34]. Ethiin did not show any
bioactivity but on complexation, antimicrobial effect is produced.
Acknowledgments
The authors are highly grateful to Higher Education Commission of Pakistan for funding this
project and Mr Peter Wichta of University of Melbourne for helping in carrying out the analysis
work.
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[

21
AppendiX
Input file used for fit for Bis(S-propyl-L-cysteinato)Cu(II): Cu(C
6
H12NO
S)
2 2
#
File generated by the XFIT SAVE command #
theory FEFF601
LEGS
RMAX
PW
=
4
=
4
=
2
CW
E
=
3
=
1.00e+09
PH
= 0
E0(0)
=
=
0
E0i(0)
S02(0)
0
=
0.75
SHELL(0) = Cu
POT(0)
N(0)
x(0)
=
0
=
1
=
0
y(0)
=
=
0
0
z(0)
sigma2(0) =
0
E0(1)
=
=
0
E0i(1)
S02(1)
0
=
0

22
SHELL(1) =
O
POT(1)
N(1)
x(1)
=
1
=
1
=
2.00
y(1)
=
=
0
0
z(1)
sigma2(1) = 0.002
E0(2)
=
=
0
0
E0i(2)
S02(2)
=
0
SHELL(2) =
O
POT(2)
N(2)
x(2)
=
1
=
1
=
-2.04
y(2)
=
=
0
0
z(2)
sigma2(2) = 0.002
E0(3)
=
=
0
0
E0i(3)
S02(3)
=
0
SHELL(3) =
O
POT(3)
N(3)
x(3)
=
2
=
1
=
0
y(3)
=
=
2.6
0
z(3)
sigma2(3) = 0.004
E0(4)
=
0

23
E0i(4)
S02(4)
=
0
=
0
SHELL(4) =
O
POT(4)
N(4)
x(4)
=
2
=
1
=
0
y(4)
=
=
-2.6
0
z(4)
sigma2(4) = 0.002
E0(5)
=
=
0
0
E0i(5)
S02(5)
=
0
SHELL(5) =
O
POT(5)
N(5)
x(5)
=
3
=
1
=
0
y(5)
=
=
0
z(5)
1.90
sigma2(5) = 0.002
E0(6)
=
=
0
0
E0i(6)
S02(6)
=
0
SHELL(6) =
O
POT(6)
N(6)
x(6)
=
3
=
1
=
0
y(6)
=
=
0
z(6)
-2.06

24
sigma2(6) = 0.002
absorber[0] = Cu
edge[0] = K
E0[0]
= 8992
polarisation0[0] = [ 0 , 0 , 0
normal0[0] = [ 0 , 0 , 0
ellipticity0[0] = 0
]
]
O0[0]
= 1
w[0]
kw[0]
N[0]
= 1.00000
= 3.00000
= 1024
rmax[0] = 28.35926
k0[0]
= 2.00000
= 14.25000
= 0.50000
= 0.50000
= cosine
k1[0]
kw0[0]
kw1[0]
ke0[0]
ke1[0]
r0[0]
= cosine
= 1.00000
= 2.75000
= 0.25000
= 0.25000
= cosine
r1[0]
rw0[0]
rw1[0]
re0[0]
re1[0]
= cosine

25
E0(0) > -15 {1}
E0(0) < 0 {1}
S02(0) > 0.5 {0.1}
S02(0) < 1 {0.1}
s1 < 0.02 {0.01}
s3 < 0.02 {0.01}
s5 < 0.02 {0.01}
s1 > 0.001 {0.001}
s3 > 0.001 {0.001}
s5 > 0.001 {0.001}
S1 == S2
S3 == S4
S5 == S6
x2 == -X1
y4 == -y3
z6 == -z5

26