Sonochemical synthesis, characterization, antimicrobial activity and textile dyeing behavior of nano-sized cobalt(III) complexes

Article abstract of DOI:10.1016/j.ultsonch.2016.10.005

Using ultrasonic irradiations, nano-sized cobalt(III) coordination complexes, [Co(NH₃)₆]Cl₃·2H₂O (A), [Co(en)₃]Cl₃·3H₂O (B) (en-ethylenediamine) and [Co(dien)₂]Cl₃·3.5H₂O (C) (dien-diethylenetriamine) were synthesized. These complexes were characterized by spectroscopic studies like IR, UV/Visible and NMR. Morphology of these complexes was determined by SEM and particle size with the help of TEM & Zeta-sizer. The comparative thermal stability along with phase difference between nano structures and their respective bulk complexes has been studied by thermal gravimetric analysis (TGA) and X-ray powder diffraction (XRD) study respectively. The dyeing behavior of nano-sized Co(III) complexes and their respective bulks has also been studied (using both exhaust and pad dyeing methods) on cotton and wool fabrics and results shown rationalized dyeing behavior. All these complexes were further tested for antimicrobial activity (against B. subtilis, E. coli, K. pneumoniae, F. oxysporum and A. alternate) and it was observed that nano sized complexes enhanced the activity further.

Full text of DOI:10.1016/j.ultsonch.2016.10.005

Accepted Manuscript
Sonochemical synthesis, characterization, antimicrobial activity and textile dye-
ing behavior of nano-sized cobalt(III) complexes
Ritu Bala, Jagriti Behal, Varinder Kaur, Subheet Kumar Jain, Riveka Rani,
Rajesh Kumari Manhas, Vinit Prakash
PII:
S1350-4177(16)30344-3
DOI:
http://dx.doi.org/10.1016/j.ultsonch.2016.10.005
ULTSON 3389
Reference:
Ultrasonics Sonochemistry
To appear in:
Received Date:
Revised Date:
Accepted Date:
12 May 2016
6 October 2016
7 October 2016
Please cite this article as: R. Bala, J. Behal, V. Kaur, S. Kumar Jain, R. Rani, R. Kumari Manhas, V. Prakash,
Sonochemical synthesis, characterization, antimicrobial activity and textile dyeing behavior of nano-sized
cobalt(III) complexes, Ultrasonics Sonochemistry (2016), doi: http://dx.doi.org/10.1016/j.ultsonch.2016.10.005
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Sonochemical synthesis, characterization, antimicrobial activity and textile
dyeing behavior of nano-sized cobalt(III) complexes
Ritu Balaa*, Jagriti Behala, Varinder Kaura, Subheet Kumar Jainb, Riveka Ranic,
Rajesh Kumari Manhasc, Vinit Prakashd
aDepartment of Chemistry, UGC Centre for Advanced Studies-1, Guru Nanak Dev
University, Amritsar-143005, Punjab, India
bDepartment of Pharmaceutical Sciences, Guru Nanak Dev University,
Amritsar-143005, Punjab, India
cDepartment of Microbiology, Guru Nanak Dev University Amritsar-143005, Punjab, India
dDepartment of Chemistry, Maharishi Markandeshwar University, Mullana, Ambala -
133207, Haryana, India
Abstract
Using ultrasonic irradiations, nano-sized cobalt(III) coordination complexes, [Co(NH3)6]Cl3.2H2O
(A), [Co(en)3]Cl3.3H2O (B) and [Co(dien)2]Cl3.3.5H2O (C) were synthesized. These complexes were
characterized by spectroscopic studies like IR, UV/Visible and NMR. Morphology of these
complexes was determined by SEM and particle size with the help of TEM & Zeta-sizer. The
comparative thermal stability along with phase difference between nano structures and their
respective bulk complexes has been studied by thermal gravimetric analysis (TGA) and X-ray powder
diffraction (XRD) study respectively. The dyeing behavior of nano-sized Co(III) complexes and their
respective bulks has also been studied (using both exhaust and pad dyeing methods) on cotton and
wool fabrics and results shown rationalized dyeing behavior. All these complexes were further tested
for antimicrobial activity (against B. subtilis, E. coli, K. pneumoniae, F. oxysporum and A. Alternate)
and it was observed that nano sized complexes enhanced the activity further.
Keywords: Antimicrobial activity; Cotton; Fastness properties; Nano-structure of cobalt(III)
complexes; Sonochemical synthesis; Wool; X-ray powder diffraction.
*Corresponding authors. Fax: 0091-183-2258820; Tel: 0091-183-2258802-09(O) Ext: 3197; E-mail
ID:rituhatta@yahoo.com.
1

1. Introduction
In 21st century, nanochemistry is one of the most active research fields in chemistry because
it embraces a number of fields like catalysis [1-2], magnetic [3-4], optical [5-6], biology [7],
medicinal chemistry [8] etc. The diversity of the field is reflected by increased number of
research papers, review articles and monographs published every year. In literature, numbers
of reports are available on nano-sized coordination polymers [9-13] and they have
outstanding properties like magnetic [14], sorption- desorption [15], epoxy resin [16] and
precursors [11]. The coordination complexes, which were known for more than 100 years and
play various important roles (like development of inorganic chemistry [17], medicinal [18-
20], isomerisation [21-22], catalyst [23-26], biology [27-28], optical [29-32], electrical [33]
etc.) but regarding the synthesis of their nanoparticles have sporadic reports [34-36].
Although number of coordination complexes were used as catalysts and precursors for the
synthesis of others nanoparticles [37]. Therefore, we have undertaken an extensive research
programme to explore the synthesis of nanoparticles of (III) coordination complexes
(specially cobalt ammines) using ultrasound irradiations which leads to a significant
reduction of synthetic time. These cobalt(III) complexes are renowned due to their high
stability, long shelf life, use of aqueous solvent, large number of N-H donor groups, high
positive charge (III) and potential applications [38]. This article reports the sonochemical
synthesis and characterization of nano-sized cobalt(III) complexes, [Co(NH3)6]Cl3.2H2O (A),
[Co(en)3]Cl3.3H2O (B) and [Co(dien)2]Cl3.3.5H2O (C) along with antimicrobial activity and
textile dyeing behavior.
2. Experimental
2.1. Materials and Physical Measurements
Analytical grade reagents (Merck) were used without further purification. (Nano material was
synthesized using a probe sonicator (Model PKS-700F, PCi analytics), having 13 mm
2

diameter probe, operating at 20 KHz with 20 % output frequency of 700W at room
temperature. IR spectra (KBr pellet) were recorded using a Varian resolution pro-660 FT/ IR
spectrophotometer in the range 400-4000 cm-). IR spectra (KBr pellet) were recorded using a
Varian resolution pro-660 FT/ IR spectrophotometer in the range 400-4000 cm-1. XRD was
recorded on a Rigaku (Cu- Kα radiation, λ = 0.15418 nm) having angle range 5- 70o.
Elemental analyses were carried out by Flash EA-1112 series CHN analyzer. The electronic
absorption spectra were recorded using Shimadzu Corp uv-1800 spectrophotometer. The
thermal behavior was measured with a NETZSCH STA 449F1 instrument between 20 and
o
700 C in nitrogen. The morphology of samples after gold coating was investigated using a
scanning electron microscope (SEM)-S-3400 N, Hitachi and transmission electron
microscope TEM-Technai, Twin 200KV FEI.
2.2. Method
[Co(NH3)6]Cl3
[39],
[Co(en)3]Cl3.3H2O
[40],
[CoCl(NH3)5]Cl2
[41]
and
[Co(dien)2]Cl3.2.5H2O [42] were prepared according to the method reported in literature.
2.2.1 Preparation of nano-sized [Co(NH3 )6]Cl3.2H2O (A)
An aqueous solution was prepared by dissolving ammonium chloride (6 g), cobalt(II)
chloride hexahydrate (9 g) and charcoal (1g) in 35 ml in water and it was cooled at 0 oC. In
this solution, 30 % hydrogen peroxide (20 mL) was added drop wise with continuous stirring
o
using mechanical stirrer (during stirring temperature should be below 20 C). After that the
above solution was positioned in a high density ultrasonic probe (using probe sonicator) for
twenty minutes and then cooled in ice bath. Yellow coloured precipitates were formed
immediately which were filtered along with charcoal through Buchner funnel. The
precipitates containing charcoal were dissolved in hot acidic water (120 mL water containing
1 mL of concentrated HCl) and filtrated hot to remove charcoal. The filtrate obtained was
again sonicated (using probe sonicator) for 70 minutes and during sonication, concentrated
3

HCl (25mL) was added drop wise which gave orange colour precipitates. The precipitates
were cooled, filtered, washed with acetone and air dried. The yield of the product is 7.98 g
(80%). M. Pt. 492 K (dec.). Anal. Cal (303.5). H, 7.31%, N, 27.69%, O, 10.54% found H,
7.30%, N, 27.63%; O, 10.51%. IR (cm-1), νa 3126 b (NH3); νs 3077 b (NH3); δa 1601 b (NH3);
δs 1322 (HNH); ρr 822 (NH3).
2.2.2 Preparation of nano sized [Co(en)3]Cl3.3H2O (B)
Pink coloured solution was formed after mixing cobalt(II) chloride (3g in 15 mL of H2O) in
ethylenediamine dihydrogen chloride (6.9 g of ethylenediamine in 15 mL water was
dissolved in 5.5 mL of concentrated HCl). In this solution NaOH (4 g) was added with
continuous stirring on mechanical stirrer, the solution tuned bluish and positioned in a high
density ultra sonicator probe (using probe sonicator) for twenty minutes. After sonication 10
mL of 30% of hydrogen peroxide was added drop wise. After the complete addition of H2O2
the solution was diluted with water (25 mL) and further sonicated (using probe sonicator) for
seventy minutes with the formation of orange precipitates. The precipitates were, cooled,
filtered, washed with ethanol and air dried. The overall yield is 3.06 g (70%). M. Pt. 546 K
(dec.). Anal. Cal (399.6). C, 18.03%; H, 7.57%; N, 21.03%; O 12.01% found C,17.99%; H,
7.53%; N, 21.02%; O, 11.09%. IR (cm-1), ν 3494s, 3427s (OH); ν 3208, 3092 (NH); ν
2990vw, 2960vw (CH); δ 1620s (OH); δ 1593m, 1565s (NH2); δ 1463s (CH2); ω 1362m
(CH2); γ 1277w, 1252w (CH2); ω 1156m, 1122m (NH2); ν 1056s, 1005vw (C-N); ρ 898vw
(CH2); ρ 785s,751vw (NH2); ν 579s, 527sh (Co-N).
2.2.3. Preparation of nano-sized [Co(dien)2]Cl3..3.5 H2O (C)
Chloropentaamminecobalt(III) chloride (4.4 g), diethylenetriamine (1.5 g) and charcoal (5 g)
was dissolved in minimum amount of water to obtain slurry and it was positioned in sonicator
bath for seventy minutes. The slurry was diluted with 20 mL water and filtered to separate the
solution from charcoal. The filtrate was positioned in a high-density ultra sonicator probe
4

(using probe sonicator) for sixty minutes. The dark yellowish oily crust was obtained which
was mixed with 50 mL of ethanol (the crust was grinded in ethanol using pestle mortar) to
precipitate the product and it was repeated thrice. The orange coloured precipitates were
filtered off and air dried. Yield is 4.96 (65%). M. Pt. 513 K (dec.). Anal. Cal. (434.7) C ,
22.11%, H, 7.65%, N, 19.33%; O,12.89% found; C, 22.09%, H, 7.63%, N, 19.31%; O,
12.91% IR (cm-1), ν 3412b (OH); ν 3165s (NH2); ν 3065s (NH); ν 2883m (CH2); δ 1553m
(NH2); δ 1478m (CH2); ω 1326m (CH2); γ 1262m (CH2); ω 1120m (NH2) ; C-C 1093m
(en); C-N 1040s (en); ν 519m (Co-N).
2.3. Methodology for Antimicrobial Activity
Antimicrobial activity of metal complexes against various tested organisms such as Gram
positive and Gram negative bacteria, and fungi was performed by agar well diffusion method
[43]. The plates containing Muller-Hinton agar (MHA) and potato dextrose agar (PDA) were
seeded with 100µl of bacterial and fungal suspension, respectively. The wells of 6mm and
9mm for bacteria and fungi, respectively were made by puncturing the seeded plate with
sterile cork borer. For testing the antibacterial activity, 50µl of test compound (0.9mg/ml)
was transferred to well under aseptic conditions. The plates were incubated at 37 oC for 24-48
hrs. For antifungal activity 150µl of the test compound (0.75mg/ml) was used and plates were
incubated for 5 days. Chloramphenicol (0.9mg/ml) and Amphotericin B (0.75mg/ml) were
used as standard antibiotics for antibacterial and antifungal activity. Clear zones around the
wells showed the positive results and zones were measured in millimeters. Various tested
organisms used in the study included Bacillus subtilis (Gram positive bacterium),
Escherichia coli, Klebsiella pneumoniae (Gram negative bacteria) and Fusarium oxysporum
and Alternaria alternata (fungi).
2.4 Fabrics used
Scoured and bleached plain (1/1) cotton having 104.4 GSM (grams per square meter.) and
5

wool twill (2/2) fabric having 145.5 GSM (grams per square meter.) were purchased locally
(Madan textiles, Amritsar).
2.4.1 Preparation of the fabric
The fabrics were treated with a solution containing 5 gL-1 standard soap (SDC, Bradford) at
o
50 C for 30 min. The material to liquor ratio was taken as 1:40. After washing, the fabrics
were thoroughly rinsed in cold water and air dried at room temperature.
2.4.2 Dyeing [44]
Dyeing (1% owf) by exhaust method of the pre-treated samples was performed for 1 h at 100
oC in an open bath beaker dyeing machine at 30:1 liquor to material ratio. The dyed samples
were rinsed in cold water and dried in open air. Alternatively, padded samples (in the
o
presence of 8g/L sodium alginate as a thickener) were steamed for 30 min at 110 C with an
intermediate semidrying. In order to observe the efficiency of pad dyeing and to draw a
o
comparison with exhaust dyeing method, padding mangle was employed at 40 C followed
o
by semidrying and steaming at110 C for 30 min. The dyeing parameters (depth of shade:
o
1.0% owf, steamed at 110 C, 30 min) were selected to illustrate a comparison with the
exhaust dyeing method.
2.4.3 Fastness testing and colourimetric evaluation [45]
Colour fastness to washing was assessed using standard ISO C06 C2S test. ECE reference
detergent (4gL-1) and sodium perborate (1gL-1) at pH 10.5 and steel balls (25) were employed
in the test. A 10 x 4 cm dyed fabric strip stitched through the short end to SDC’s multifibre
test fabric was washed on a Washtec (RBE) at 60 OC for 30 min, the samples was rinsed with
cold water air dried and analyzed for the colour change and staining. Similarly, colour
fastness to rubbing was conducted using IS-766-88 test using a crock meter. The light
fastness was tested on a xenon arc lamp following the test method ISO 105/B02 using blue
wool reference samples.
6

3. Result and Discussion
3.1 Synthesis
Cobalt complexes, [Co(NH3)6]Cl3 [39], [Co(en)3]Cl3.3H2O [40] and [Co(dien)2]Cl3.2.5H2O
[42] were prepared according to the method reported in literature. Their respected nano sized
complexes have been synthesized using same amount of reactants (as given in reported
methods) followed by modified methodology. In this, methodology probe sonicator was used
at two stages, first whenever heating is required and the second, at the time of precipitation.
In solution, the probe causes cavitation which constitutes the main mechanism for sample
processing. In addition, instead of air oxidation of Co(II) to Co(III), hydrogen peroxide was
used as an oxidizing agent in each case. Due to which preparation time was reduced (4 hours
in case of [Co(NH3)6]Cl3 and 3 hour in [Co(en)3]Cl3.3H2O). Moreover, if one can overlook
the oxidation step, still time consumed for the preparation of nano sized complex A, B and C
is reduced i.e., 5 minutes in A, 1.5 hours in B and 2.45 hours in case of C as compared to
their respective reported methods for bulks without sonication. The colour of nano sized
cobalt(III) complex A, B and C (synthesized using probe sonicator) is orange and
indistinguishable from their respective bulks. The elemental analysis of complex B is same
with their respective bulk reported in literature [40]. However, in case of nano-sized complex
A and C are not similar with their reported [39, 42] respective bulks (two additional water
molecules in nano-sized complex A and one addition water molecule in nano sized complex
C). Melting points of bulks as well as nano sized cobalt(III) complexes were determined, the
decomposition points of complex A and B are similar to their respective bulks but in case of
complex C decomposition point is 10 K more as compared to their bulk.
3.2 Spectroscopic characterization
3.2.1 UV/Visible
1
1
For cobalt(III), d6 octahedral low spin complexes, two d-d transitions, A1g →1T1g and A1g
7

→1T2g were reported [46] in aqueous medium around 340 and 470 nm respectively. For nano
size cobalt(III) complexes, these maxima were observed around 338 (ε = 181 M-1cm-1) and
473 (ε = 187 M-1cm-1) for complex A, 336 (ε = 312 M-1cm-1) and 462 (ε = 276 M-1cm-1) for
complex B and 338 (ε = 865 M-1cm-1) and 466 (ε = 834 M-1cm-1) for complex C. The
comparative UV-visible spectra are shown Fig. 1. The absorbance for nano complexes is
more as compared to their respective bulk materials at same concentrations [λmax (ε) for
[Co(NH3)6]Cl3, 338 (ε = 159 M-1cm-1) and 475 (ε = 164 M-1cm-1), [Co(en)3]Cl3.3H2O, 337 (ε
= 256 M-1cm-1) and 464 (ε = 244 M-1cm-1), [Co(dien)2]Cl3.2.5H2O, 338 (ε = 300 M-1cm-1) and
464 (ε = 266 M-1cm-1)]. High absorbance found for nano coordinated cobalt(III) complexes is
may be due to various factors like size, shape etc.
3.2.2 Infrared spectra
The IR spectrum of complex A was obtained and showing indistinguishable pattern with
respect to their bulk material [47] . The band assignments are given in section in 2.2.1 and the
presence of water molecules is not very clear from IR spectrum because of broad bands in the
region 2900-3500 and 1450-1650 cm-1. In case of nano complex B and C, the IR spectra of
both the coordination complexes are indistinguishable with comparison to their respective
bulks [48, 49].
3.3 X-ray powder diffraction
The simulated XRD patterns of complex A, B and C and their respective bulks are given in
Fig. 2. In case of complex A and B, the XRD patterns were similar to their respective bulks.
This indicates that the complexes obtained by sonochemical process have same crystalline
phase with respect their bulk materials. The significant broadening of the peaks reveals that
the particles are of nanometer dimensions. However in complex C, broad peaks were
observed but not fully comparable with their respective bulk because it contain mixture of
three isomers (with a formation ratio of s-fac:u-fac:mer equal to 7:28:65 respectively). This
8

isomeric mixture contains 65 percent of mer-isomer and its peaks dominate in the XRD
pattern and comparable with complex C. The formation of mer-isomer in complex C was
supported by 13C NMR spectroscopy. In 13C NMR spectrum of complex C, three δ values
were observed at 51.0, 47.8 and 46.5 ppm for the unsymmetrical methylene group adjacent to
NH and NH2 respectively.
3.4 SEM/TEM
SEM and TEM images of nano-sized cobalt(III) complexes are shown in Fig. 3. SEM helps
to elucidate the morphology and shape of nanoparticles. The shape of the complex A, B and
C is polygonal, rod and agglomerate respectively (see Fig. 3 d-f). Nano particles in case of
complex A and B are clearly separated and have smooth surfaces however in complex C,
particles form agglomerates. The histogram showing average particle size distribution is
shown in Fig. 4. The average particle size distribution of complex A, B and C is in the range
475-720 nm, 60-90 nm and 475-700 nm respectively (see Fig. 4). TEM images shown in Fig.
3 a-c supported the data of SEM and zeta size analysis.
3.5 TGA Analysis
To examine the thermal stability of the nano-size particles of complex A, B, C and their
O
respective bulks thermal gravimetric analyses (TGA) were carried between 20 and 700 C
under nitrogen flow (Fig. 5). The decomposition of single crystal of complex A occurs as
according to the equation given in literature [50]. But in case of nano complex A, thermal
behavior is quite dissimilar with their respective bulk (see Fig. 5) due to presence of two
o
water molecules. These water molecules were lost in two steps, one at 152 C and other at
o
200 C. The decomposition of bulk material of complex B occurs as according to the
equation given in literature [51]. All the water molecules were lost at 134 oC temperature and
the decomposition steps of complex B and its bulk are similar. In complex C and its bulk
both contains 3.5 and 2.5 water molecules respectively. The loss of all water molecules takes
9

o
o
place at 134 C and 143 C for nano complex C and its bulks. Rest decomposition steps are
similar in both cases.
3.6 Textile
From the results in Table 1 it may be seen that cotton and wool fabrics can be dyed with dye
obtained from cobalt(III) coordination complexes under a variety of conditions. In
comparison to exhaust dyeing, the use of padding technique offers great potential in
industrial processes in terms of reduction in cost, time, and energy. The colours obtained in
the dyeing recorded and are shown in Table 1 along with their K/S values, a good variation in
the colour could be seen when dyeing was conducted using different methods. Further, it has
been observed that using two methods of dyeing i.e., exhaust dyeing as well as pad dyeing,
the wool samples were deeper in depth than cotton as their counterparts (as given by the
higher K/S values of the wool dyeings); however, for the dyeing with nano compounds, it was
found that it did not always result in increased colour strength and depth. The observed
general improvement in fastness to light and washing of the dyeings of the nano extract
secured by Pad dyeing process, together with the effects on the shade of the dyeings, imply
that pad dyeing sequences resulted in the formation of strong dye- fibre interaction in the
presence of sodium alginate
Table 2 shows fastness properties of various samples dyed with fractionated cobal(III)
coordination complexes. The fastness properties are relatively satisfactory for practical
dyeing with many cases, particularly with the steamed samples. Out of the three colour
fastness tests conducted, colour fastness rating of the wash fastness test was most
satisfactory, the colour fastness ratings however were not very good. The colour staining
rating on worsted wool component of the SDC multifibre strip is the highest of all other
components in some cases, may be because of the intrinsic high substantivity and
inaccessibility of the morphology of fibre at the test temperature (60 oC). Light fastness of the
10

dyed samples was moderate to good, whereas rubbing fastness showed variability depending
upon the dyeing method.
The dyeing of cotton and wool using co-ordinate compounds, by which a dye-metal
complex is formed, characteristically imparts improved fastness to light as well as washing
and also the results in a dulling and darkening of the shade in case of steamed method.
However, improvement in the washing fastness of the dyeings with exhast method was not
apparent. The wash and light fastness properties of the dye or pigment on cotton and wool
were determined on 4% owf shade.
Further, it has been observed that using all the two methods of dyeing i.e., exhaust
o
o
dyeing at 100 C as well as padding followed by steaming for fixation conducted at 110 C,
the steamed samples were deeper in depth than their exhaust method as counterparts;
however, for the dyeing followed by steaming, it was found that steaming did not always
result in increased colour strength and depth. The observed general improvement in fastness
to light and washing of the dyeings by exhaust method, together with the effects on the shade
of the dyeings, involve that dyeings resulted in the formation of dye-metal complex. Further,
o
steaming when employed at the near about same temperature as exhaust dyeing (100 C)
furnishes dyeings comparable to exhaust dyeings whilst offering savings in energy.
Cotton is mainly composed of cellulose (99%). Cellulose is a polymer made up of a long
chain of glucose molecules linked by C-1 to C-4 oxygen bridges with elimination of water
(glycoside bonds). The anhydroglucose units are linked together as beta-cellobiose; therefore,
anhydro-beta-cellobiose is the repeating unit of the polymer chain (See figure 6 (a)).
Similarly, wool is composed principally of protein substance and these proteins are poly-
condensation products in which different amino acids are linked together to form the
polypeptide chain as shown in figure 6 (b). In both the cases, hydrogen acceptor groups are
present (like -CH2OH or –OH or >C=O) and they may form strong hydrogen bonding
11

interactions (i.e., O…H-N ) with N-H groups of ligands (like NH3, dien and en) attached to
central metal atom cobalt. This might be the reason of interactions between cobalt(III)
complexes with fibre.
3.7 Antimicrobial Activity
The metal complexes were tested for antimicrobial activity against B. subtilis, E. coli, K.
pneumoniae, F. oxysporum and A. alternata. The antimicrobial activity of the cobalt(III)
complexes was determined by measuring the inhibition zone in millimeters around the well
and is presented in Table 3 and Table 4. All cobalt(III) complexes exhibited antibacterial
activity against B. subtilis (see fig. 7) and antifungal activity against A. alternate. However
no activity was observed by any of the cobalt(III) complex against E.coli, K.pneumoniae and
fungus F. oxysporum. It is also observed that formation of nano sized complexes enhanced
the activity further. Moreover, bulk of nano-complex B and C didn’t show any antifungal
activity but nano complexes B and C exhibited the antifungal activity. In comparison to other
complexes nano-complex A and its bulk showed the potent antibacterial and antifungal
activities. For exploring the antimicrobial activity of cobalt(III) complexes, the following
parameters could be kept in mind like type of ligands (monodentate or chelating), the nature
of the donor ligands (NH3, en or dien),) the nuclearity of the central metal ion, overall
charge, nature of the ion in ionic complex, geometry and size of the complex. In case of
complex A, the complex cation i.e., [Co(NH3)6]3+ is biological mimic of [Mg(H2O)6]2+ [52].
Both complex cation have similar size, similar high charge density and they can form
octahedrally coordinated inner sphere (H2O is a ligand in later case and NH3 in former).
Moreover, complex cation of A can form similar type of outer-sphere H-bonding networks as
[Mg(H2O)6]2+. These similarities permit complex cation of A to bind the sites (as Mg(II)
bind) in bacterial protein and poison them effectively, results antibacterial activity. In case of
complex B and C antimicrobial activity can be explained on the basis of the chelation theory
12

[53] and overtone concept [54]. In complex B and C, ligands are bonded with cobalt(III) in
bidentate (en) and tridentate (dien) fashion respectively i.e., chelation mode. As the N atoms
of these ligands (en or dien) donate its lone pair to empty orbitals of Co(III), the polarity of
the cobalt(III) reduced and lipophilicity enhanced. This enhanced lipophilicity of these
complexes helped them to penetrate in the cell membrane because of Overtone’s concept of
cell permeability. Moreover, due strong tendency of N-H groups of ligand (en or dien) to
form outer-sphere H-bonding networks with bacterial protein restricts the growth of organism
and leads to antibacterial property.
4. Conclusion
It is concluded that nano-sized cobalt(III) coordination complexes, [Co(NH3)6]Cl3.2H2O (A),
[Co(en)3]Cl3.3H2O (B) and [Co(dien)2]Cl3.3.5H2O (C) can be synthesized using ultrasonic
irradiations. In addition to that, there is a significant time reduction for their preparations
particularly in case of B and C as compared to their respective bulks. All these nano-sized
particles are thermally less stable. Moreover, complex A, B and C are antifungal (against B.
Subtilis) and antibacterial (against A. alternata). The dyeing behavior of all nano-sized
cobalt(III) coordination complexes (and their respective bulks obtained) in terms of shade
output as well as fastness properties are rationalized. The results of effective antimicrobial
activity and good fastness properties of nano sized coordination complexes show that these
materials may find potential application in the field of future medical textile.
Acknowledgement
We thank the UGC, New Delhi, India for their financial support under scheme “University
with Potential for Excellence (UPE)” (F. No. 14-2/2012(NS/PE) dated 13.07.2012).
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19

1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
[Co(NH ) ]Cl
3
3
6
[Co(NH ) ]Cl .2H O-Nano
[Co(en) ]Cl .3H O
3
6
3
2
3
3
2
[Co(en) ]Cl .3H O-Nano
3
3
2
[Co(dien) ]Cl .2.5H O
[Co(dien) ]Cl .3.5H O-Nano
2
3
2
2
3
2
200
300
400
500
600
700
Wavelength/nm
Fig. 1. Uv/visible spectra of Cobalt(III) complexes
20

(a)
(b)
(c)
Fig. 2. XRD pattern of cobalt(III) complexes (a) A (b) B (c) C
21

(a)
(d)
(b)
(e)
(c)
(f)
Fig. 3. TEM impage of complex (a) A, b) B, c) C and SEM image of complex (d) A, (e) B,
(f) C
22

(a)
(b)
(c)
Fig. 4. Histrogram of complex (a) A , (b) B and (c) C.
23

Fig. 5. TGA of cobalt(III) complexes
24

O
C
R
O
C
H
N
H
C
H
N
H
N
H
C
C
H
C
O
R
R
(a)
(b)
Fig. 6. Structure of (a) Cotton and (b) Wool fibre.
25

Fig. 7. Photograph showing antibacterial activity of complex A, B, C and their
respective bulks in case of Bacillus subtilis
26

Table 1. Details of cotton and wool samples dyed under different conditions (4% owf).
Sample Fabric
No. used
Compound used
Colours of the dyed
samples after exhaust
dyeing
(100 oC)
Colours of the dyed samples
after Pad dyeing (Steaming
at 110 oC)
Shades obtained
K/S
Shades obtained
K/S
2.065
2.409
3.597
4.029
3.502
8.351
1.
2.
3.
4.
5.
6.
Cotton [Co(NH3)6]Cl3
[Co(NH3)6]Cl3.2H2O
10.927
9.4708
10.689
9.5809
(Nano)
[Co(en)3]Cl3.3H2O
[Co(en)3]Cl3.3H2O
(Nano)
[Co(dien)2]Cl3.2.5H2O
Co(dien)2]Cl3.3.5H2O
(Nano)
3.989
9.5705
19.875
10.689
16.033
15.498
7.
8.
Wool
[Co(NH3)6]Cl3
[Co(NH3)6]Cl3.2H2O
(Nano)
19.481
24.507
19.320
14.498
15.972
16.025
9.
[Co(en)3]Cl3.3H2O
10.
11.
12.
[Co(en)3]Cl3.3H2O
(Nano)
[Co(dien)2]Cl3.2.5H2O
Co(dien)2]Cl3.3.5H2O
(Nano)
20.198
15.389
λmax= 400 nm
27

Table 2. Colour fastness dataa of the dye on cotton and wool samples
Sampleb Colour
fastness
Colour stainingc
Light
fastness
Rubbing fastness
Colour
fastness
Colour
staining
1
2
3
4
5
6
7
8
4
4
2-3
2
3
3
2
3
3
3
2
3
3-4
4
3- 4
2- 3
3- 4
3- 4
3
3- 4
3- 4
3- 4
3
4
4-5
4
4-5
5
4-5 4-5
4
4
4-5
4
4
4
4-5
4
4
4-5
5
4-5
3-4
5
5
5
4-5
5
5
4- 5
4-5
5
4- 5
5
3-4
4- 5
5
4- 5
4
5
4
3-4
4-5 4-5
3
3
4- 5
4-5
5
4
3
3
3
4
3
3
3
4
3
4
4
4
3-4
4
4
4-5
3-4
4-5
5
4-5 4-5 4-5
4-5
4-5
4
4
5
4-5
4
4-5
4
4-5 4-5 4-5 4-5
4-5 4-5
4-5 4-5 4-5
3-4
3-4
5
4-5 4-5
4
5
4-5
3-4 3-4
3-4 4-5
4-5 4-5 4-5
4-5 4-5
4-5 4-5 4-5 4-5 4-5 3-4
4-5 4-5 4-5 4-5 4-5 4-5
4-5 3-4
4
4-5 4-5 4-5 4-5 4-5 4-5
4-5
5
4-5 4-5 4-5 4-5 4-5 4-5
4-5 4-5 4-5
5
5
4-5 4-5
4-5 4-5
9
5
4
3-4
4-5
3-4
4
4
4
4
4
4- 5
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
3-4 4-5
3
4
5
4-5
5
4
4
4-5
4
4
4-5
4
4
3-4
4
4-5 4-5
4
4-5 2-3
4
4
4-5
4-5
5
4
4-5 4-5
5
3-4 4-5
3
3
4
4
4
3
3
5
3- 4
5
4-5
4
4
4
3- 4 3- 4 4-5
4
4-5 4-5 4-5
3-4 3-4
4-5 4-5 3- 4 3-4
3
5
4-5 4-5
5
4-5 4-5 4-5
4-5 4-5 4-5
4-5 4-5
4-5 4-5 4-5
3-4 4-5
5
5
5
5
4-5 4-5
4-5 3-4
4
4
4
4- 5 4- 5
3-4 3- 4 3- 4
4-5
5
5
4
4
5
5
4- 5
4
4
4
3- 4
5
4-5
3-4 4-5 3- 4 4-5
aGrey scale ratings, see Table 1 for dyeing methods Colour staining rating: SCA, secondary
cellulose acetate; BUC, bleached unmercerised cotton; N, nylon 66; P, polyester; A, acrylic; WW,
worsted wool
b
c
28

Table 3. Antibacterial activity of the metal complexes
S. No.
Organisms
Zone of inhibition (mm)
Standard
Bulk Nano
A
Bulk Nano Bulk Nano
C
A
B
B
C
1
2
3
B. subtilis
E. coli
15
16
10
12
-
12
13
-
40
32
26
-
-
-
-
-
-
-
-
K. pneumoniae
-
-
Standard - Chloramphenicol
29