Formation of disulphide linkages restricts intramolecular motions of a fluorophore: Detection of molecular oxygen in food packaging

Article abstract of DOI:10.1039/c8cc10035g

Reliable and easy detection of oxygen in food packaging without the aid of sophisticated instruments is highly coveted. A tetraphenylethene probe based on oxygen-mediated polymerization via the formation of disulfides causes restricted intramolecular rota

Full text of DOI:10.1039/c8cc10035g

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DOI: 10.1039/C8CC10035G
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Formation of disulphide linkages restricts intramolecular motions
of fluorophore: Detection of molecular oxygen in food package
Sk. Atiur Rahaman, Dipon Kumar Mondal and Subhajit Bandyopadhyay*a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Reliable and easy detection of oxygen in food packaging without packaged dairy product and meat in the presence of oxygen
the aid of sophisticated instruments is highly coveted. efficiently. Therefore products such as cheese and meat are
A
tetraphenylethene probe based on the oxygen mediated specially packaged under nitrogen. Certain moulds can grow on
polymerization via the formation of disulfides causes restricted a variety of food items including nuts, dried fruits, cereals and
intramolecular rotation the TPE phenyls resulting in a >100 fold coffee beans in the presence of oxygen under warm and humid
enhancement of emission and thus detects O2 in food package.
conditions. These fungi can produce naturally occurring toxins
called the mycotoxins which can sometimes be lethal. Small
leakages in the foodstuff packed under vacuum or nitrogen can
sometimes allow oxygen to be present in the package which
might reduce the shelf-life of the food. Each year there are
instances of a number of recalls of the food products because
of the presence of the contaminated strains of bacteria in
packaged food products. Early detection of trace amount of
oxygen in the packaged food can be indicative of the health of
the packed food. Therefore, it is important to device a cheap,
easy-to-use, stench-free, non-toxic and metal-free marker for
the detection of oxygen for food packaging.
Oxygen is one of the most important chemical species for life on
earth. An adult human metabolizes ~200 g of oxygen per day.
Determination of molecular oxygen has important implications
for bio-medicinal,1 industrial, and environmental chemistry.2 As
a consequence, several classes of luminescence-based oxygen
sensors have been developed in the last few year.3‒8 Most of
these probes make use of transition metal complexes
immobilized in polymeric matrices as the active luminescent
species.9‒11 Some luminescent porous coordination polymers
(PCPs) have been recently reported as attractive oxygen-
sensing materials.12‒16 Most of the luminescent based oxygen
sensors function with a turn-off response in the presence of
oxygen. Although, they can be useful for the detection of
molecular oxygen, a turn-on response is perhaps more coveted
as the fluorescence enhancement is more discernable to the
naked eyes.
The shelf-life of a pre-packed food depends on oxygen as it
promotes the growth of fungi and microorganisms. Most
organisms could not survive the powerful oxidative properties
of reactive oxygen species (ROS), highly unstable ions and
molecules derived from partial reduction of oxygen that can
damage virtually any macromolecule or structure with which
they come in contact. Pathogenic bacterial species such as
Salmonella spp., Listeria monocytogenes, Staphylococcus
aureus and enteropathogenic Escherichia coli O157:H7 can pose
high risk to the safety of meat and dairy products for the
consumers. Aerobic strains of Escherichia coli can grow in
Here we report a metal free thiol appended tetraphenylethene
(TPE) based system 1 that detects molecular oxygen with a large
(>100 fold) enhancement of emission intensity. The probe
exploits the simple chemistry where the thiol units readily form
disulfide linkages and results in a restricted intramolecular
rotation of the phenyl rings of the molecule. Moreover, the
scanning electron microscopy (SEM), the advanced Polymer
Chromatography (APC) and the dynamic light scattering (DLS)
measurements were performed to confirm the formation of a
Fig. 1 Formation of a disulphide polymer of 1 upon areal oxidation and restricted
intramolecular rotation of the phenyl rings.
a.Department of Chemical Sciences, Indian Institute of Science Education and
Research (IISER) Kolkata, Mohanpur, Nadia, WB 741246 India
b.Electronic Supplementary Information (ESI) available: Experimental section,
additional figures and tables, SCXRD data. See DOI: 10.1039/x0xx00000x
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DOI: 10.1039/C8CC10035G
Fig. 3 (A) The particle size distribution monitored by DLS studies after the bubbling of O2
to 1 (10 μM) in THF solvent at various time intervals, (B) TCSPC experiments displaying
the decay times of 1 prior to and after bubbling with air (300 min) at 25 oC. (C) APC
analysis of the 1’ polymer (10 μM), (D) SEM image of a dried sample of 1’.
UV-vis spectroscopy and fluorescence spectroscopy in the THF
media.
It is well known that in THF, the free rotation of the phenyl
rings of the propeller-shaped TPE is responsible for the non-
radiative energy dissipation from the excited state. However, in
the presence of water, the hydrophobic TPE molecules
aggregate restricting the rotation of the phenyl rings and also
the nonradiative relaxation channel populating the radiative
excitons, which confers the TPE units a strong emissive
character. This phenomenon is popularly known as the
aggregation induced emission (AIE).26-27 Our thiol appended
Fig. 2 Spectral change upon introduction of O2 from air in THF media (A) Changes in the
UV-vis absorption spectra of compound 1 (10 μM), (B) changes in the emission spectra
of compound 1 (10 μM) (λex: 320 nm, slit: 5/5); Inset: visual change under 366 nm light molecule containing the TPE luminogen shows a faint emission
in THF media at 25 oC. (C) Time dependent changes in the 1H NMR spectra of compound
1 (1 mM) in CDCl3 at 25 oC upon bubbling with air, (D) SCXRD structures of compound 2.
in THF solution. As expected, the emission increases drastically
upon aggregation in the THF/water mixtures with higher
fractions of water. At 95% water content, bright cyan emission
polymer upon introducing of oxygen in the THF solvent. This is
is observed upon exposure under 366 nm UV light (see Fig. S6-
different from the classical mechanism of aggregation-induced
S7, ESI†).
emission (AIE) effect,17-18 where the enhancement in the
However, even in THF in the presence of oxygen, a large
emission signal is a result of the aggregation of the TPE species
enhancement of the fluorescence was observed with the
in an aqueous media, first reported by Tang et al.19 Normally,
tetrathiol 1. The enhancement of the emission in this case was
TPE based supramolecular polymers exhibit higher emissions in
the aggregated state compared to the non-aggregated
monomeric forms due to the restricted rotation of the phenyl
ring in the stacked states in the aqueous media.20 Based on this
principle they have been used as building block units in
luminescent porous materials, such as metal–organic
frameworks (MOFs), covalent organic frameworks (COFs),
supramolecular organic frameworks (SOFs), hydrogen-bonded
organic frameworks (HOFs) and porous polymers. 21-25
way more than that observed for the AIE in the 95 % (v/v) water
in THF. From the UV-vis spectroscopy in a THF solution, it was
found (Fig. 2A) that the absorption of compound
1 at 324 nm
decreased with a 6 nm red shift. The band at 253 nm displayed
a 7 nm red shift upon the introduction of O2 from air. The
emission spectra of the aerated solution of
1 (10M) displayed
a remarkable 112 fold enhancement of the fluorescence
intensity at 485 nm (Fig. 2B) ((0.17) with a 5 nm red shift
compared to the initial band of
1
(0.0012, compared to
Compound
thioacetate
1
was prepared via deacetylation of the TPE
quinine sulfate)). The response of probe
1
at various partial
2
in an inert atmosphere and characterized by
pressures of O2 is shown in figure S11. The LOD of O2 detection
was found to be 30.8 torr (Figure S15). The fluorescence change
spectroscopic and mass spectrometric methods (see Supporting
Information, Experimental details). The single crystal XRD
of compound
the 366 nm UV light as shown in the Fig. 2B (insert)). We
envisaged that the tetrasulfide in the presence of molecular
1 could be clearly observed with naked eyes under
structure of the acetyl protected probe
1, i.e., compound 2 was
obtained (CCDC Number 1879842, See Fig. 2D and ESI†). The
1
photophysical properties of compound
1 were investigated by
oxygen in the presence of the ambient light led to the formation
of the disulphide linkage (Fig. 1). The network of the disulphide
2 | J. Name., 2012, 00, 1-3
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linkages stops the intramolecular rotation of phenyl rings in the
polymeric 1’ and thereby converting it to a highly emissive
species. Since it is known that thiols can be converted to
disulfides with hydrogen peroxide or iodine,28 it was envisaged
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DOI: 10.1039/C8CC10035G
that upon treatment of
species could be generated that would display similar
spectroscopic properties that was observed with in the
presence of oxygen. Thus, compound (10 μM) was treated
with separately with I2 (10 μM) and H2O2 (10 μM) in THF. The
emission spectra of samples of after the treatment with
1 with H2O2 or I2, similar polymeric
1
1
1
iodine, and H2O2 displayed similar emission pattern and
enhancement (see Fig. S8-S9, ESI†). However, the reaction with
H2O2 reached a saturation of the emission intensity in less than
30 min. With I2 the reaction required 2 h, and with O2, the
saturation of the emission intensity required bubbling for 5 h
(see Fig. S9, ESI†).
Fig. 4 Photographs of the cheese samples having two O2-indicator strips, (the probe and
the control) under 366 nm handheld light; (A) and (B) packed under N2 t = 0 and 4 days
respectively (C) and (D) packed under atmospheric air, t = 0 and 2 days respectively.
Note the bright emission from the probe in panel (D).
To verify the mechanism, particle size analysis was
performed by dynamic light scattering experiments. A solution
of compound
1 in THF was found to possess a hydrodynamic
CH2- was observed (Fig. 2C). The decrease in intensity of the
thiol protons were also apparent from the NMR integration
values. The integration of the –CH2- protons were calibrated
against the aromatic protons. The ratio of the newly formed –
radius of 4.7 nm perhaps from the small aggregates of the
organic molecule. After bubbling the solution with gaseous
oxygen for a period of 30 minutes with a bubbling rate of
roughly one bubble per second, the hydrodynamic diameter
was found to increase to 196.0 nm. The size dependence of the
particles with the bubbling time was systematically studied by
DLS in THF media at 25 oC. Upon the bubbling of the
C
H2-S-S- : C
H2SH protons obtained from the 1H-NMR
integrations was 0.85: 1 which is consistent with the expected
structure of 1’ where this ratio is expected to be 0.88:1. There
was also a concomitant decrease in the intensity of the –SH
protons due to formation of 1’. The changes in the signals of the
other protons were small. The shift in the 13C NMR signals (see
Fig. S10, ESI†) were also quite prominent and has been
summarized in Table S1. The decrease in the intensity of the
atmospheric air through a solution of 1, the DLS experiment
revealed that the particle size increased rapidly with time. After
300 minutes of bubbling the particle size displayed a saturation
value with an average diameter of 1362.9 nm of the Z-average
hydrodynamic diameter (Fig. 3A).
thiol protons, the new methylene peaks and the shifts in the 13
C
The fluorescence lifetimes of compound
1 before and after
NMR clearly indicates the crosslinking of a number of the TPE
units through the formation of –S‒S‒ linkages. It is noteworthy
that bubbling molecular oxygen through the NMR tube for > 7
h lead to the formation of an intractable sticky precipitate
presumably due to the formation of larger polymeric structure.
The average molecular weight (Mn) determined from the
advanced polymer chromatographic (APC) studies was 8900 D
with an index of polydispersity value of 1.2 at retention time
with 3.198 min (see Fig. 3C). This clearly indicates the presence
of an average of seventeen TPE units in the cross-linked polymer
which is consistent with the 1H-NMR data.
exposing to oxygen (1’) was studied by TCSPC experiments in
the THF. In both the cases, the decay profile followed a
biexponential decay pattern Fig. 3B. The lifetimes and the
relative amplitudes of the components are provided in Table 1.
The average lifetime of fluorescence increases from 3.7 to 6.34
ns upon polymerization in the presence of oxygen. In addition,
the component with the shorter lifetime (
the polymerization, whereas the component for the longer
lifetime ( 2) increases. From the point of view of the molecular
structure of compound and polymer 1’, it is conceivable that
1) decreases upon

1
the polymer has restricted intramolecular rotation of the phenyl
rings which is responsible for its higher fluorescence lifetime.
The SEM images of a dried sample of compound
1’ from a THF solution were recorded (see Fig. S13, ESI† and Fig.
3D). The compound shows irregular surface with the
1 and polymer
1
Table 1 Fluorescence lifetimes for compound 1 and polymer 1’
aggregated dry samples with an average size of 298 nm. The
polymeric 1’, on the other hand, displayed a rather spherical
shape with an average size of 590 nm.
To check the reversibility of the probe and revalidate the
mechanism, the disulphide 1’ was treated with a reducing
agent, sodium borohydride. Upon systematic treatment of
NaBH4 in THF, the emission intensity of 1’ was found to diminish
Compound
τ1 (ns)
1.41
1.97 (± 0.)
τ2 (ns)
5.659
7.909
<τ> (ns)
3.703
6.362
χ2
1.15
1.13
1
1’
To gain an insight of the changes in the molecular structure
upon the exposure to oxygen, O2 gas was bubbled through a
1
sample of
1
in CDCl3 solvent and the H NMR spectra were
and finally reach a saturation value which was similar to
probe because of the conversion of 1’ to via the reduction
of the –S-S- linkages to –SH (see Fig. S10, ESI†).
the
recorded at various time intervals. With the increase in the
bubbling time, the signal for the doublet methylene protons
next to the –SH group at δ 3.67 decreased gradually and a new
singlet peak at δ 4.03 which can be attributed to the –CH2-S-S-
1
1
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3
4
(a) R. I. Dmitriev and D. B. Papkovsky, Methods AVpiepwl.AFrltiucloerOenslicn.e,
2015, , 034001, (b) S. Sun, B. UnDgeOrI:b1ö0c.1k03a9n/Cd8CTC. 1M00a3y5Gr,
Methods Appl. Fluoresc., 2015, , 034002.
(a) P. W. Zach, O. T. Hofmann, I. Klimant, and S. M. Borisov,
Anal. Chem., 2018, 90, 2741−2748. (b) Z. Sun, C. Cai, F. Guo,
C. Ye, Y. Luo, S. Ye, J. Luo, F. Zhu, and C. Jiang,
Nanotechnology, 2018, 29, 145704.
J. An, C. M. Shade, D. A. Chengelis-Czegan, S. Petoud, and N.
L. Rosi, J. Am. Chem. Soc., 2011, 133, 1220–1223.
M. Eltermann, V. Kiisk, A. Berholts, L. Dolgov, S. Lange, K. Utt,
and R. Jaaniso, Sensors and Actuators B, 2018, 265, 556–564.
Y. Zheng, Y. Jiao, Y. Zhu, Q. Cai, A. Vasileff, L. H. Li, Y. Han, Y.
For practical application of compound
1 as a probe for the
3
detection of the presence of oxygen in sealed food packages,
two samples of cheese (paneer), one packed under nitrogen gas
and the other under atmospheric air were used Indicator labels
were prepared from Whatman 1 filter papers (2 cm x 2 cm)
3
dipped in a solution of 10 mM of 1 in THF and subsequently air
5
6
7
dried. It is to be noted that the paper strips did not have any
malodour of sulphides presumably because of its low
concentration and volatility. For each of the packed cheese, two
indicator labels, one as an oxygen probe (Fig. 4C and 4D, bottom
labels) and the other as a control (Fig 4A and 4B. top labels)
were placed inside the sealed packages. The control labels were
covered with transparent cellulose tape to avoid its exposure to
air; the indicator probe was attached to the inner surface of the
packaging plastic layer with a spot of household PVA glue. After
two days, the indicator packed under air showed bright
emission (Fig. 4D). However the control-indicator label in the
package containing the cheese packed under nitrogen did not
display any significant enhancement of the emission even after
4 days (Fig. 4B). However, lower amount of O2 can be detected
Chen, and S. –Z. Qiao, J. Am. Chem. Soc., 2017, 139
,
3336−3339.
8
9
X. Chen, X. Tian, I. Shin, and J. Yoon, Chem. Soc. Rev., 2011, 40
4783–4804.
,
K. Y. Zhang, P. Gao, G. Sun, T. Zhang, X. Li, S. Liu, Q. Zhao, K.
K.-W. Lo, and W. Huang, J. Am. Chem. Soc., 2018, 140
,
7827−7834.
10 P. Mani, A. Sheelam, S. Das, G. Wang, V. K. Ramani, K.
Ramanujam, S. K. Pati, and S. Mandal, ACS Omega, 2018, 3,
3830−3834.
11 R.-W. Huang, Y.-S. Wei, X.-Y. Dong, X.-H. Wu, C.-X. Du, S.-Q.
Zang, and T. C. W. Mak, Nat. Chem., 2017, 9, 689–697.
12 N. Acha, C. Elosύa, I. R. Matías, and F. J. Arregui, Sensors and
Actuators B, 2017, 248, 836-847.
with the probe
1, if it is exposure to O2 over a longer period of
time. Probe thus offers an economically viable (<$0.05 or <£
1
13 X. Jiang, J. Peng, J. Wang, X. Guo, D. Zhao, and Y. Ma, ACS Appl.
0.04 per indicator label) detection technique for oxygen in food
packages. The probe is metal-free probe and the detection does
not require any sophisticated instrument and is therefore
promising for smart-packaging of vacuum or nitrogen packed
convenient food.
Mater. Interfaces, 2016, 8, 3591−3600.
14 J.-W. Ye, J.-M. Lin, Z.-W. Mo, C.-T. He, H.-L. Zhou, J.-P. Zhang,
and X.-M. Chen, Inorg. Chem., 2017, 56, 4238−4243.
15 F. Lin, F. Li, Z. Lai, Z. Cai, Y. Wang, O. S. Wolfbeis, and X. Chen,
ACS Appl. Mater. Interfaces, 2018, 10, 23335−23343.
16 X.-d. Wang and O. S. Wolfbeis, Chem. Soc. Rev., 2014, 43
3666—3761.
,
Toxicity analysis by the MTT assay was studied with probe
against the mammalian cell line J774A.1. The viability of probe
-treated J774A.1 macrophage reveals that the probe did not
1
17 Y. Wu, H. Hua and Q. Wang, New J. Chem., 2018, 42, 8320-
8324.
1
18 Q. Zhaoa and Y. Liu, Chem. Commun., 2018, 54, 6068—6071.
19 (a) J. Mei, Y. Hong, J. W. Y. Lam, A. Qin, Y. Tang and B. Z. Tang,
Adv. Mater., 2014, 26, 5429. (b) Y. Hong, J. W. Y. Lam and B.
Z. Tang, Chem. Soc. Rev., 2011, 40, 5561-5388. (c) C. Coluccini,
A. K. Sharma, M. Caricato, A. Sironi, E. Cariati, S. Righetto, E.
Tordin, C. Botta, A. Forni, D. Pasini. Phys. Chem. Chem. Phys.,
2013, 15, 1666—1674. (d) A. Nitti, F. V.-Monteleone, A. Pacini,
C. Botta, T. Virgili, A. Forni, E. Cariati, M. Boiocchif, D. Pasini,
Faraday Discuss., 2017, 196, 143–161.
20 J. Mei, N. L. C. Leung, R. T. K. Kwok, J. W. Y. Lam, and B. Z.
Tang, Chem. Rev., 2015, 115, 11718–11940.
21 X.-G. Liu, H. Wang, B. Chen, Y. Zou, Z.-G. Gu, Z. Zhao and L.
Shena, Chem. Commun., 2015, 51, 1677—1680.
have any significant toxicity on the cell viability upto 
(Figure S16).
M
In summary, in this work we have synthesized a tetrathiol
appended TPE system that undergoes a polymerization via an
oxidative transformation of the thiols to disulfides. This
transformation causes a restriction the propeller-like rotation of
the TPE-phenyl rings thereby causing a large enhancement of
the emission of the AIEgen via a less conventional mechanism
that does not involve aggregation of the TPE. The mechanism is
operative in solution and even in paper test strips. Oxygen
detection in packed samples carried out with the test strips
22 N. Baroni, A. Turshatov, M. Adams, E. A. Dolgopolova, S.
Schlisske, G. Hernandez-Sosa, C. Wöll, N. B. Shustova, B. S.
Richards, and I. A. Howard, ACS Appl. Mater. Interfaces, 2018,
10, 25754−25762.
coated with compound
food packaging.
1
demonstrated its potential use for
SB acknowledges DST-SERB for
a
research grant
(EMR/2017/003720) for the financial assistance. SAR is
supported by a doctoral fellowship from IISER Kolkata.
23 Z. Zhou, X. Yan, M. L. Saha, M. Zhang, M. Wang, X. Li, and P. J.
Stang, J. Am. Chem. Soc., 2016, 138, 13131−13134.
24 M. Zhang, G. Feng, Z. Song, Y.-P. Zhou, H.-Y. Chao, D. Yuan, T.
T. Y. Tan, Z. Guo, Z. Hu, B. Z. Tang, B. Liu, and D. Zhao, J. Am.
Chem. Soc., 2014, 136, 7241−7244.
Conflicts of interest
There are no conflicts to declare.
25 N. B. Shustova, T.-C. Ong, A. F. Cozzolino, V. K. Michaelis, R. G.
Griffin, and M. Dinca, J. Am. Chem. Soc., 2012, 134
15061−15070.
,
26 R. Hu, N. L. C. Leungb and B. Z. Tang, Chem. Soc. Rev., 2014,
43, 4494—4562.
27 D. D. La, S. V. Bhosale, L. A. Jones, and S. V. Bhosale, ACS Appl.
Mater. Interfaces, 2018, 10, 12189−12216.
28 M. Kirihara, Y. Asai, S. Ogawa, T. Noguchi, A. Hatano, Y. Hirai,
Synthesis, 2007, 21, 3286-3289.
Notes and references
1
C. Prelnlnger, I. Kllmant, and O. S. Wolfbeis, Anal. Chem.,
1994, 66, 1841-1846.
2
H. Li, J. Li, Z. Ai, F. Jia, and L. Zhang, Angew. Chem. Int. Ed.,
2018, 57, 122 – 138.
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