Conjugates of platinum nanoparticles with gallium tetra - (4-Carboxyphenyl) porphyrin and their use in photodynamic antimicrobial chemotherapy when in solution or embedded in electrospun fiber

Article abstract of DOI:10.1016/j.poly.2014.03.050

The conjugation of Pt nanoparticles with ClGa(III) 5,10,15,20-tetrakis-(4- carboxyphenyl) porphyrin (ClGaTCPP) showed greater antimicrobial activity against a gram positive and drug resistant bacteria Staphylococcus aureus, than when the porphyrin was used alone. ClGaTCPP and its conjugate with platinum nanoparticle was successfully electrospun into a polystyrene polymer where the diameter ranged from 10 to 22 μm. The conjugates within the fiber still showed activity towards S. aureus.

Full text of DOI:10.1016/j.poly.2014.03.050

Polyhedron 76 (2014) 94–101
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Conjugates of platinum nanoparticles with gallium
tetra – (4-Carboxyphenyl) porphyrin and their use
in photodynamic antimicrobial chemotherapy
when in solution or embedded in electrospun fiber
⇑
Muthumuni Managa, Edith Antunes, Tebello Nyokong
Department of Chemistry, Rhodes University, Grahamstown 6140, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history:
The conjugation of Pt nanoparticles with ClGa(III) 5,10,15,20-tetrakis-(4-carboxyphenyl) porphyrin
(ClGaTCPP) showed greater antimicrobial activity against a gram positive and drug resistant bacteria
Staphylococcus aureus, than when the porphyrin was used alone. ClGaTCPP and its conjugate with
platinum nanoparticle was successfully electrospun into a polystyrene polymer where the diameter
Received 9 February 2014
Accepted 28 March 2014
Available online 5 April 2014
ranged from 10 to 22
l
m. The conjugates within the fiber still showed activity towards S. aureus.
Keywords:
Platinum nanoparticles
Gallium porphyrin
Ó 2014 Published by Elsevier Ltd.
Staphylococcus aureus
Electrospinning
Photodynamic antimicrobial chemotherapy
1. Introduction
carboxyphenyl) porphyrin (TCPP) which is the ring system
employed in this work [10]. ClGa(III) 5,10,15,20-tetrakis-(4-
carboxyphenyl) porphyrin (ClGaTCPP, Scheme 1) was chosen for
the current studies since metal free (H2TCPP) has been studied in
the presence of NPs [10]. Gallium was chosen as a central metal
due to its size which will enhance intersystem crossing to the trip-
let state, hence improve singlet oxygen (the toxic species for PACT)
production. Even though the syntheses of H2TCPP and other metal
derivatives are known [11,12], the synthesis of the Ga derivative is
reported here for the first time. Conjugation of porphyrins to plat-
inum nanoparticles has not been reported. In this work the conju-
gates of platinum hexagonal nanoparticles and porphyrin will be
used as antimicrobial agents to kill bacteria. The conjugate is rep-
resented as ClGaTCPP–PtNPs. Hexagonal Pt nanoparticles were
chosen since it has been reported [13] that anistropic nanoparticles
have superior long blood circulation time, which is expected to
improve PACT.
Bacterial microorganisms have developed to a stage where they
replicate very rapidly, with their rate of mutation assisting them in
survival even in the presence of an antibiotic (e.g. Staphylococcus
aureus resistance to methicillin) [14–16]. This study reports on
the conjugates of ClGaTCPP with PtNPs for antimicrobial activity
towards a gram positive S. aureus. It is important to place conju-
gates of porpyrins and PtNPs on supports for use in PACT. Electro-
spun fibers are the support of choice in this work. Electrospinning
has been regarded as the most promising approach to produce
Metal nanoparticles (NPs) have become of great interest in
research as they find applications in different fields such as electro-
chemistry, catalysis and biology [1]. Biological applications of
metal NPs include as photosensitizers in photodynamic therapy
(PDT) of cancer and in drug delivery [2]. Metal NPs (such as Ag
or Pt) have also been reported to have antibacterial and antifungal
properties [3]. Metal NPs attach to the cell wall of the fungi or bac-
teria through self-assembly due to their small size, causing cell
death [4,5].
Photodynamic antimicrobial chemotherapy (PACT) is a process
that utilizes a similar concept to PDT [4,6] in that a combination
of light and a photosensitizer produces cytotoxic oxygen specie
that kill bacterial cells. Porphyrins have been employed for
PACT [7,8]. Combining porphyrins (for PACT) with platinum
nanoparticles (PtNPs), may result in a synergistic effect, resulting
in improved antibacterial activity. This is the aim of the current
work.
Metal NPs have been linked to porphyrins for some biological
applications including bio-sensing [9]. In particular, Ag and Au
NPs have been conjugated to metal free 5,10,15,20-tetrakis-(4-
⇑
Corresponding author. Tel.: +27 46 6038260; fax: +27 46 6225109.
E-mail address: t.nyokong@ru.ac.za (T. Nyokong).
http://dx.doi.org/10.1016/j.poly.2014.03.050
0277-5387/Ó 2014 Published by Elsevier Ltd.

M. Managa et al. / Polyhedron 76 (2014) 94–101
95
H
O
The fiber diameters were measured using Cell D software from
Olympus. All plate readings for the antimicrobial studies were
obtained using the LEDETECT 96 for in vitro diagnostic from LAB-
XIM PRODUCTS.
1. acetic acid
H
120 oC, 30 min
N
+
COOH
HOOC
2. pyridine, 1 hr
N
H
COOH
Photo-irradiations for bacterial studies were done using a Gen-
eral electric Quartz line lamp (300 W). A water filter was used to
filter off infrared radiation. Light intensities were measured with
a POWER MAX5100 (Mole electron detector incorporated) power
N
N
H
N
meter and were found to be 9.43 ꢀ 1018 photons sꢁ1 cmꢁ2
.
COOH
HOOC
The singlet oxygen generation was quantified using an ultrasen-
sitive Germanium detector (Edinburgh Instruments, EI-P) com-
bined with a 1000 nm long pass filter (Omega, 3RD 1000 CP) and
a 1270 nm band pass filter (Omega, C1275, BP50) to detect the
intensity of the singlet oxygen phosphorescence band at
1270 nm. These studies were done for ClGaTCPP or ClGaTCPP–
PtNPs in DMF, in the absence and presence of sodium azide (a
physical quencher of singlet oxygen). Details have been provided
before [20].
DMF
GaCl3
100 oC, 15 min
COOH
HOOC
N
Ga
N
N
Cl
N
For the fibers, ADMA, a singlet oxygen chemical quencher in
aqueous media was employed using the absolute method. For
these studies, the modified fibers were suspended in solution and
irradiated using the photolysis system described above.
COOH
Scheme 1. Synthetic pathway of ClGaTCPP.
HOOC
2.3. Synthesis
continuous nanofibers on a large scale. Porphyrins have been
embedded into electrospun fibers for various biological applica-
tions [17,18], but not for PACT. Thus this work reports on PACT
activity of conjugates of ClGaTCPP with PtNPs, embedded in elec-
trospun polystyrene fiber.
2.3.1. Hexagonal Pt NPs
The platinum nanoparticles were synthesized using literature
methods [21,22] with modifications as follows:
Pt(acac)2 (0.21 g, 0.54 mmol), 1,2-hexadecanediol (0.54 g,
2.08 mmol) and diphenyl ether (25 mL) were added into a three
neck flask. Under a nitrogen atmosphere, the mixture was heated
2. Experimental
under reflux for 10 min. Oleic acid (167
lL) and oleylamine
(170 L) were added as stabilizers and the mixture was refluxed
l
2.1. Materials
for 20 min. The reaction was then cooled to room temperature.
Ethanol (60 mL) was added to the solution and immediately a
black precipitate formed. The liquid was removed from the product
by centrifugation. The product was washed with ethanol and then
further dispersed in hexane (60 mL) solution containing stabilizers
Oleic acid and platinum acetylacetonoate (Pt acac)2 were from
Fluka, oleylamine, 1,2-hexadecanediol, acetone, dimethylformam-
ide (DMF), N,N-dicyclohexalcarbodiimide (DCC), sulphonamide,
gallium(II) chloride and anthracene-9,10-bis-methylmalonate
(ADMA) were purchased from Sigma Aldrich. Polystyrene (PS,
Mw = 192,000 g/mol), tetrahydrofuran (THF) and Agar bacteriolog-
ical BBL Mueller Hinton broth (HG000C24.500) and nutrient agar
(HG0000C1.500) were from MERCK Chemical Ltd. S. aureus (ATCC
6538) was purchased from Microbiologics. Column chromatogra-
phy was performed on silica gel 60 (0.04–0.063 mm).
oleic acid (167 lL) and oleylammine (170 lL). The black solution
was then cooled to 37 °C and then sulphonamide (0.4 g,
2.32 mmol) was added as capping agent. The product was dried
overnight in a vacuum.
2.3.2. Synthesis of gallium 5,10,15,20-tetrakis-(4-carboxyphenyl)
porphyrin
The metal free 5,10,15,20-tetrakis-(4-carboxyphenyl) porphyrin
was synthesized according to literature [11]. The synthesis of
ClGa(III)TCPP is as follows: DMF was brought to reflux temperature
in a two necked flask while stirring and then H2TCPP (4 g,
5.1 mmol) was added and temperature brought to 100 °C. Then
gallium chloride (1 g, 5.6 mmol) was added and heating continued
for 15 min. The completion of the reaction was checked using UV/
Vis spectrophotometer. The four bands in the Q band region of the
metal free H2TCPP collapse into two on metalation. The reaction
vessel was then allowed to cool in ice water. Ice cold water
(500 mL) was added onto the resulting partially crystalline precip-
itate, which was then filtered and washed with water then air
dried. The product was purified by column chromatography.
Yield: (31%). IR (KBr, cmꢁ1): 35,443 (O@H), 2938 (C–H), 1732
(C@O), 1443 (C@C), 1365 (CH2), 1037 (C–O). 1H NMR (DMSO-d6):
d, ppm 8.50 (2H, b, Ar–H), 8.31 (1H, s, Ar–H), 8.27–8.12 (5H, b,
Ar–H), 7.95–7.79 (8H, m, Ar–H), 7.51 (2H, m, Ar–H), 7.35–7.25
2.2. Equipment
UV–Vis absorption spectra were recorded at room temperature
using a Shimadzu UV-2550 spectrophotometer. X-ray powder dif-
fraction (XRD) patterns were recorded on a Bruker D8 equipped
0
with a proportional counter, using Cu K
a radiation (k = 1.5405 ÅA,
nickel filter). Details have been provided before [19]. Transmission
electron microscope (TEM) images were recorded using JEOL JEM
1210 at 100 kV acceleration voltages. Samples were prepared in
hexane. Scanning electron microscope (SEM) images of the fiber
alone or in the presence of the porphyrin complex were obtained
using a JOEL JSM 840 scanning electron microscope.
IR spectra were recorded on a Perkin–Elmer Spectrum 100 ATR
FT-IR spectrometer. Fluorescence emission was recorded on a Var-
ian Eclipse spectroflouremeter. Elemental analyses were carried
out on a Vario EL III MicroCube CHNS Analyzer. Mass spectral data
were collected with a Bruker AutoFLEX III Smartbeam TOF/TOF
Mass spectrometer. Details have been provided before [19]. Proton
nuclear magnetic resonance (1H NMR) spectra were recorded using
a Bruker EMX 600 MHz NMR spectrometer.
(4H, b, Ar–H), 7.11 (2H, m, Ar–H). UV–Vis (DMF) kmax nm (log e):
421 (4.50), 587 (3.70), 550 (3.43). Calc. for C48H28N4O8GaCl: C
64.49; H, 3.16; N, 6.26. Found: C, 64.22; H, 3.09; N, 6.12%.
MALDI-TOF-MS m/z calc: 893.914; Found (MꢁH)ꢁ 892.99.

96
M. Managa et al. / Polyhedron 76 (2014) 94–101
2.3.3. Conjugation of gallium 5,10,15,20-tetrakis-(4-carboxyphenyl)
porphyrin to PtNPs
intense band called the Soret or B band at about 400 nm. The Q
bands are observed between 500–600 nm. Fig. 1A shows the spec-
trum of ClGaTCPP with B band at 414 nm, and two Q bands at
589 nm and 549 nm. Fig. 1B showed the emission spectrum of
ClGaTCPP, which is typical of a metallated porphyrin with two
bands differing in intensity at 598 nm and 653 nm [26].
Ga(III)TCPP (0.01 g, 0.01 mmol) was firstly dissolved in DMF
(10 mL), then 0.03 g, 0.145 mmol of DCC was added to convert
the carboxylic group (–COOH) of the porphyrin into an active car-
bodiimide ester group. This mixture was stirred at room tempera-
ture for 24 h. After this time 0.02 g of hexagonal PtNPs were added
and the mixture was allowed to stir for further 24 h. The conjugate
was separated from the un-conjugated nanoparticles using Bio-
Beads S-X1 from Bio-Rad.
3.1.2. PtNPs
Transmission electron microscopy studies (TEM) images, Fig. 2A
show dispersed hexagonal platinum NPs, with the sizes distributed
from 20 to 40 nm. Fig. 2A (insert) shows individual hexagonal
PtNPs more clearly.
2.3.4. Electrospun nanofibres preparation
X-ray diffraction (XRD) pattern for the hexagonal PtNPs, is
shown in Fig. 3a. Comparison with the International Centre for Dif-
fraction Data (ICDD) revealed the platinum NPs pattern fits the
platinum data. The peaks were at 2h of 39.86°, 46.44°, 67.69°,
81.56° and 86.09° with 99.9% match. XRD was employed for crys-
talline size determination, using the Debye Scherrer Eq. (1) [27]:
The electrospinning technique (with or without porpyrin) has
been described before [17,18,23,24]. For this work, the electrospun
fibers were formed by mixing solutions containing 1.5 ꢀ 10ꢁ5 mol
of polystyrene and 1.0 ꢀ 10ꢁ6 mol of ClGaTCPPs (or ClGaTCPP–
PtNPs) in 10 mL DMF/THF (1:1). The resulting solution was then
stirred for 24 h to produce a homogeneous solution. This solution
was then placed in a cylindrical plastic tube which was fitted with
a capillary needle. A potential difference between anode and cath-
ode of 15 kV was applied to provide the charge for the spinning
process. The distance between the cathode (static fiber collection
point) and anode (tip of capillary needle) was 15 cm. The pump
rate was maintained at 0.2 mL/h.
0:9k
bCosh
L ¼
ð1Þ
where k is the wavelength of the X-ray source, (1.5405 Å), b is the
full width at half maximum of the diffraction peak, and h is the
angular position of the peak. The average size of the hexagonal
PtNPs was determined to be 26 nm, which is within the range of
the size determined by TEM.
2.3.5. Antimicrobial activity
S. aureus (ATCC 6538) was grown on nutrient agar plates pre-
pared according to the manufacturer’s specifications to obtain col-
onies. A colony was then inoculated into Luria nutrient broth and
then placed overnight at 37 °C on a rotary shaker (ꢂ200 rpm), to
produce a bacteria culture. The optical density at 600 nm of the bac-
teria culture was adjusted to approximately 0.8 in nutrient broth.
The inactivation of S. aureus was carried out by placing aliquots of
3.1.3. ClGaTCPP–PtNP conjugate
The TEM of ClGaTCPP–PtNPs (Fig. 2B) showed aggregation. The
XRD pattern of ClGaTCPP–PtNPs (Fig. 3b) showed broadening of
the peaks which indicated the amorphous nature of the compound.
The average size (33 nm) of the conjugated was higher than that of
the PtNPs alone (26 nm) due to aggregation.
The UV/Vis spectrum of ClGaTCPP–PtNPs showed a Soret band at
421 nm (Fig. 1) which is slightly red shifted compared to ClGaTCPP
alone at 414 nm. Generally red shifts in porphyrins are a result of
the formation of side-by-side J-aggregates [28]. Aggregation is also
200 lL of the bacteria culture in a 96-well plate containing 50 lL
of ClGaTCPP and ClGaTCPP–PtNPs (concentrations: 0.025, 0.05, 0.1
and 0.25 mg/mL in DMF). The plates were then illuminated with
the setup described above using different times (0, 30, 60 and
90 min). Fluences ranged from 0 to 0.8 J cmꢁ2 at an irradiance of
0.05 W cmꢁ2. Following irradiation, aliquots (50
lL) of the bacteria
culture were taken to determine the colony forming unit (CFU) and
survival fraction was calculated compared to that for the control
containing no photosensitizer. The content of the wells were mixed
before sampling, the aliquots were serially diluted 10-fold in Luria
broth to give dilutions of 10ꢁ1–10ꢁ5 times. The dilution which was
used for survival fraction was 10ꢁ5 as the colonies were not
too numerous to count (TNTC). The sensitizer (ClGaTCPP or
ClGaTCPP–PtNPs) was dissolved in DMF. S. aureus is known to be
resistant to DMF [25]. DMF was employed since the solubility of
the conjugate in water was low. When DMF alone was used without
the photosensitiser, there was no bacterial inactivation.
The antimicrobial activity of the ClGaTCPP, ClGaTCPP–PtNPs
and PtNPs in fibres were studied using agar plates with the modi-
fied fibers embedded. The viable microorganisms were corrected
with controls containing no sensitizer. The optical density of the
bacterial viability was determined at 600 nm. The experiments
were done in duplicates.
3. Results and discussion
3.1. Characterization
3.1.1. ClGaTCPP complex
The complex was characterized by mass, NMR, FTIR and UV–Vis
spectroscopies as well as elemental analyses. The results were con-
sistent with the structure. Porphyrins are characterized by an
Fig. 1. (A) Absorption spectra of ClGaTCPP (dotted line) and ClGaTCPP–hexagonal
conjugate (solid line) and (B) fluorescence emission spectrum of ClGaTCPP.
Solvent = DMF. Insert = expansion of the Q band area.

M. Managa et al. / Polyhedron 76 (2014) 94–101
97
14
(A)
12
10
8
6
4
2
0
20
22
24
26
28
30
32
34
36
38
40
Size distribution (nm)
(B)
Fig. 2. TEM micrographs of dispersed (A) Pt nanohexagons and corresponding histogram, insert = isolated hexagons, and (B) ClGaTCPP conjugates with PtNPs.
PtNPs
ClGaTCPP-PtNPs
160
80
0
40
50
60
70
80
90
100
2θ
Fig. 4. Fourier transform infrared spectroscopy (FTIR) of ClGaTCPP (a) and
ClGaTCPP–hexagonal (b) PtNPs conjugate (A).
Fig. 3. X-ray powder diffraction (XRD) of PtNPs (Red) and ClGaTCPP–PtNPs
conjugate (Black).
clear from the TEM in Fig. 2B. The conjugation of ClGaTCPP to hex-
agonal PtNPs was confirmed using FTIR spectra. The amide bonds
for the hexagonal Pt NPS were visible at 3323 cmꢁ1 due to N-H
stretch and at 1626 cmꢁ1 due to C = O stretch (Fig. 4). These peaks
were not visible on the spectrum of ClGaTCPP but were visible for
ClGaTCPP–PtNPs.
experimental section. Scanning electron microscopic (SEM) was
used to assess the two geometric properties of polymers which is
the fiber morphology and diameter. The diameters of the fibers
were determined using Image J program. The diameter obtained
for polystyrene polymer alone ranged from 1.0 to 2.2 lm, Fig. 5A.
It has been reported that fiber diameter depends allometrically
on solution viscocity [29]. Thus, in the presence of ClGaTCPP the
3.1.4. Electrospun fibers
ClGaTCPP and ClGaTCPP–PtNPs were mixed with polystyrene
and electrospun into nanofibers as was explained in the
fiber diameter increases, ranging from 1.2 to 1.9
the diameter is even larger for the ClGaTCPP–PtNPs ranging from
6 to 14 m Fig. 5B.
lm, Fig. 5C and
l

98
M. Managa et al. / Polyhedron 76 (2014) 94–101
(A)
3
2
1
0
1.0
1.2
1.4
1.6
1.8
2.0
2.2
Diameter μm
(B)
16
14
12
10
8
6
4
2
0
6
7
8
9
10
11
12
13
14
Diameter μm
(C)
8
7
6
5
4
3
2
1
0
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
Diameter μm
Fig. 5. Scanning electron microscopic (SEM) images of (A), polystyrene alone, (B) ClGaTCPP–hexagonal PtNPs conjugate and (C) ClGaTCPP electrospun fiber.
3.2. Singlet oxygen studies
The time resolved phosphorescence decay curve of singlet oxy-
gen at 1270 nm was used to determine singlet oxygen quantum
yield of ClGaTCPP–PtNPs and ClGaTCPPs in DMF using Eq. (2) [30]:
3.2.1. ClGaTCPP in solution
Energy transfer between the triplet state of photosensitizers
and ground state molecular oxygen leads to the production of sin-
glet oxygen. There is a necessity of high efficiency of transfer of
energy between excited triplet state of porphyrin and ground state
of oxygen to generate large amounts of singlet oxygen.
sD
ꢁ
sT
sD
IðtÞ ¼ B
½eꢁt= ꢁ eꢁt=
ꢃ
ð2Þ
sT
sD
where, I(t) is the phosphorescence intensity of 1O2 at time t, sD is
the lifetime of 1O2 phosphorescence decay, sT is the triplet state

M. Managa et al. / Polyhedron 76 (2014) 94–101
99
Table 1
lifetime of the standard or sample and B is a coefficient involved in
sensitizer concentration and 1O2 quantum yield. The singlet oxygen
quantum yield, UD of the complex was then determined in aqueous
media, using Eq. (3):
Singlet oxygen quantum yield values of the ClGaTCPP and ClGaTCPP–PtNPs when in
solution (DMF solvent) or embedded in fibers (water as solvent).
Complex/conjugate
Solvent
(UD)
ClGaTCPP
DMF
DMF
water
water
0.32
0.38
0.21
0.24
B:AStd
UD
¼
USDtd
:
ð3Þ
ClGaTCPP–PtNPs-
ClGaTCPP/fiber
ClGaTCPP–PtNPs-/fiber
BStd:A
where USDtd is the singlet oxygen quantum yield for the standard
ZnTPP USDtd = 0.53 in DMF [31,32]; B and BStd refer to coefficient
Fig. 6. Photodegradation of ADMA in the presence of polystyrene electrospun fibers containing ClGaTCPP Conjugate.
Fig. 7. Logarithmic reduction of S. aureus treated (A) ClGaTCPP and (B) ClGaTCPP–PtNPs conjugate, in liquid broth solution at different concentrations (0.025, 0.05, 0.1,
0.25 mg/mL in DMF) at 0.05 W cmꢁ2
.

100
M. Managa et al. / Polyhedron 76 (2014) 94–101
involved in sensitizer concentration and 1O2 quantum yield for the
sample and standard, respectively; while A and AStd refer to the
absorbances of the sample and standard, respectively at the excita-
tion wavelength. The 1O2 quantum yield was calculated to be 0.38
for ClGaTCPP–PtNPs and 0.32 for ClGaTCPP, Table 1. The increase
for ClGaTCPP–PtNPs is probably due to the heavy atom effect of
PtNPs.
a:A:I
NA
Iabs
¼
ð5Þ
where
a
= 1–10-A(k), A(k) is the absorbance of the sensitizer at the
irradiation wavelength, A is the irradiated area (2.5 cm2), I is the
intensity of light (9.43 ꢀ 1018 photons cmꢁ2 sꢁ1) and NA is Avoga-
dro’s constant. The absorbances used for Eq. (5) are those of the por-
phyrin in the fibers (not in solution) measured by placing the
modified fiber directly on a glass plate. The light intensity measured
refers to the light reaching the spectrophotometer cells, and it is
expected that some of the light may be scattered, hence the UD val-
ues of the porphyrin in the fiber are estimates.
3.2.2. ClGaTCPP or ClGaTCPP–PtNPs on fiber
For ClGaTCPP or ClGaTCPP–PtNPs on fiber, ADMA was employed
as a quencher in aqueous media. The absolute method was
employed instead of time resolved phosphorescence decay due to
lack of standards for the modified fibres. The modified fibre
(5 mg) was suspended in solution in the presence of 9,10-anthra-
cenediyl-bis(methylene)dimalonic acid (ADMA) as the quencher.
The degradation of ADMA was monitored at 380 nm during the
photolysed, Fig. 6.
The singlet oxygen quantum yield (U ) can then be calculated
using Eq. (6):
D
1
1
1
kd
1
¼
þ
ꢄ
ꢄ
ð6Þ
UADMA UD UD ka ½ADMAꢃ
where kd is the decay constant of singlet oxygen in respective sol-
vent and ka is the rate constant of the reaction of ADMA with singlet
The ADMA quantum yields (UADMA) were calculated using Eq.
(4), using the extinction coefficient of AMDA in water, log (
[33].
e) 4.1
1
1
oxygen. The intercept obtained from the plot of
versus
UADMA
½ADMAꢃ
1
gives
UD
ðC0 ꢁ CtÞVR
The U was estimated to be 0.24 for ClGaTCPP–PtNPs and 0.21
D
ð
UADMAÞ ¼
ð4Þ
Iabsꢄt
for ClGaTCPP in the fiber, Table 1. The value is lower in the fibre
(compared to solution) due to two reasons: U values for the fibers
are estimates and the vales in water are always lower than in
organic solvents since water quenches singlet oxygen [34].
D
where C0 and Ct are the ADMA concentrations before and after irra-
diation, respectively; VR is the solution volume; t is the irradiation
time per cycle and Iabs is defined by Eq. (5):
3.3. Antimicrobial activity
3.3.1. Using the photosensitizer in solution
There are two most widely used methods for quantitative deter-
mination of bacterial populations. These methods are the standard
(viable, plate count) and spectrophotometric (turbidimetric) anal-
ysis [35]. The spectrophotometric analysis showed less survival
of bacteria as light exposure time increased Fig. 7A and B.
ClGaTCPP–PtNPs showed less bacterial survival, Fig. 7B, due to
increased singlet oxygen quantum yield. The time interval used
was from 0 to 90 min.
ClGa TCPP
ClGa TCPP - PtNPs
Colony-forming unit (CFU) is an estimate of viable bacterial
number. CFU values may be calculated using Eq. (7) [36,37].
Total colonies ꢀ dilution factor
CFU=mL ¼
ð7Þ
volume plated
Fig. 8. Photoinactivation of S. aureus at different fluences. Survival fraction was
calculated according to [39].
when bacterial colonies are too numerous to count they are called a
lawn where they are recorded as Too Numerous To Count (TNTC)
(A)
(B)
(C)
Illumination
(D)
(E)
Dark
Fig. 9. Images of the antimicrobial inhibition test using (A) polystyrene fiber (used as a control), (B) fibre modified with ClGaTCPP, (C) fibre modified with ClGaTCPP–PtNPs
under illumination. D and E corresponds to B and C, respectively kept in the dark.

M. Managa et al. / Polyhedron 76 (2014) 94–101
101
[38]. Platinum nanoparticles as previously stated in the introduc-
References
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toxicity for ClGaTCPP–PtNPs due to the presence of PtNPs, due to
the toxicity of PtNPs without light and increased singlet oxygen
quantum yield of the porphyrin in the presence of PtNPs. When
comparing with ClGaTCPP alone, the inhibition (survival fraction
[39]) is less for ClGaTCPP–PtNPs at fluence 0.78 Jcm2.
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4. Conclusions
The gallium 5,10,15,20-tetra-(4-carboxyphenyl) porphyrin
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Acknowledgements
This work was supported by the Department of Science and
Technology (DST) and National Research Foundation (NRF) of
South Africa through DST/NRF South African Research Chairs Initia-
tive for Professor of Medicinal Chemistry and Nanotechnology and
Rhodes University.
productPDF_58468.PDF.
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