Biphenyl derivatives containing trimethylsilyl benzyl ether or oxime groups as probes for NO2 detection

Article abstract of DOI:10.1039/c6ra02222g

Four probes based in the use of a biphenyl moiety and functionalized with trimethylsilyl benzyl ether (P1 and P3) and oxime (P2 and P4) groups have been prepared and tested as optical probes for the detection of NO₂. Reaction of NO₂ with acetonitrile solutions of P2-P4 resulted in the formation of aldehydes 7 and 8 with a concomitant redshift of the absorption bands. Probe P2 displayed a bathochromic shift of 45 nm upon reaction with NO₂ and was able to detect this poisonous gas at concentrations as low as 0.02 ppm. P2 was highly selective against NO₂ and other gases (i.e. NO, CO₂, H₂S, SO₂) and vapours of organic solvents (i.e. acetone, hexane, chloroform, acetonitrile or toluene) had no effect in the optical properties of the probe.

Full text of DOI:10.1039/c6ra02222g

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ARTICLE
Biphenyl derivatives containing trimethylsilyl benzyl ether
or oxime groups as probes for NO2 detection
Received 00th January 20xx,
Accepted 00th January 20xx
L. Alberto Juárez,a,b,d Ana M. Costero,a,b,d* Margarita Parra,a,b,d Salvador Gil,a,b,d Javier Ródenas,a,b
Félix Sancenóna,c,d and Ramón Martínez‐Máñeza,c,d
*
Four probes based in the use of a biphenyl moiety and functionalized with trimethylsilyl benzyl ether (P1 and P3) and
oxime (P2 and P4) groups have been prepared and tested as optical probes for the detection of NO2. Reaction of NO2 with
acetonitrile solutions of P2‐P4 resulted in the formation of aldehydes 7 and 8 with a concomitant redshift of the
absorption bands. Probe P2 displayed a bathochromic shift of 45 nm upon reaction with NO2 and was able to detect this
poisonous gas at concentrations as low as 0.02 ppm. P2 was highly selective against NO2 and other gases (i.e. NO, CO2,
H2S, SO2) and vapours of organic solvents (i.e. acetone, hexane, chloroform, acetonitrile or toluene) had no effect in the
optical properties of the probe.
DOI: 10.1039/x0xx00000x
www.rsc.org/
detection is a hot area of research.6 No standards have been
agreed upon for nitrogen oxides in indoor air, moreover
ASHRAE and the US EPA National Ambient Air Quality
Standards list 0.053 ppm as the average 24‐hour limit for NO2
Introduction
Nitrogen oxides (NOx) are formed in large quantities from fuel
combustion in cars, trucks and power plants,1 they are a major
problem in urban areas and are linked to many respiratory
diseases.2 From a chemical point of view NOx mainly refers to
the sum of nitric oxide (NO) and nitrogen dioxide (NO2),
although other nitrogen species can also be included, such as
nitrous and nitric acids. Together with the adverse effects of
direct exposure to NOx on human health, it is also remarkable
its contribution to ground level ozone and fine particle
pollution. Hence, strict regulations regarding levels of nitrogen
oxides are currently applied by governments and the
monitorization of NOx levels based in reliable analytical
methods is of great interest.3
Among NOx species, NO2 causes a range of harmful effects on
lungs such as increased inflammation of the airways, worsened
cough and wheezing, reduced lung function, increased asthma
attacks and increased susceptibility to respiratory infection.4
All these problems are more important for children and older
adults.5 Due to the ubiquitous presence of NO2, the
development of selective and sensitive sensing methods for its
in outdoor air.7 However, NO2 levels in certain cities and at
certain hours can reach even higher values (near 100 ppm).
Laser‐based photoacoustic spectroscopy,8 surface acoustic
wave (SAW),9 transition metal oxide devices,10 carbon
quantum dot‐functionalized aerogels,11 or ozone treated
graphene12 are some reported analytical techniques used to
detect/monitor NO2 levels. However, some of these methods
show certain limitations such as lack of specificity, limited
selectivity, operational complexity, non‐portability, difficulties
in real‐time monitoring and false positive readings. As an
alternative to these instrumental procedures, the
development of molecular chemosensors, constructed under
the chemodosimeter paradigm, has been gaining interest in
recent years. However, the number of publications related
with optical probes for NO2 detection is still relatively scarce.13
OSiR3
D
C. T.
NO2
H
O
A
D
OH
N WA
C. T.
a Instituto Interuniversitario de Reconocimiento Molecular y Desarrollo Tecnológico
(IDM), Unidad Mixta Universidad Politécnica de Valencia‐Universidad de Valencia,
Spain.
NO2
D
b Departamento de Química Orgánica. Universidad de Valencia, Doctor Moliner 50,
46100, Burjassot, Valencia, Spain. E‐mail: ana.costero@uv.es
C. T.
c
Departamento de Química, Universidad Politécnica de Valencia, Camino de Vera
D
s/n, 46022, Valencia, Spain. E‐mail: rmaez@qim.upv.es
d CIBER de Bioingeniería, Biomateriales y Nanomedicina (CIBER‐BBN).
† Footnotes relaꢀng to the ꢀtle and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
Batochromic sifth
Scheme 1. Sensing protocol used for NO2 detection.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1‐3 | 1
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Bearing in mind our interest in the development of chemical
sensors for gas detection,14 we report herein the synthesis and
sensing behavior towards NO2 of four new chemodosimeters
based on the biphenyl chromophore. Among the different
organic reactions involving NO2 we decided to explore the
utility of the generation of aromatic aldehydes from
trimethylsilyl benzyl ethers 15 and oximes16 in order to prepare
suitable chemodosimeters for the detection of this poisonous
and pollutant gas. These are reactions with quantitative yields,
working at room temperature and at ambient pressure. The
synthesized biphenyl probes (vide infra) possess electron
View Article Online
DOI: 10.1039/C6RA02222G
1.4
1.2
1
2
1.8
1.6
1.4
1.2
1
8
P4
P1
7
P2
P3
0.8
0.6
0.4
0.2
0
0.8
0.6
0.4
0.2
0
250
270
290
310
330
350
250
300
350
400
wavelength (nm)
wavelength (nm)
donor groups (such as methoxide electronically connected Figure 1. (Left) UV spectra of probes P1 and P3 (1.0 x 10‐4 M in
with trimethylsilyl) or oxime (weak electron acceptor) acetonitrile) alone and after bubbling 1 ppm of NO2 during 5
moieties. The underlying idea is that, upon NO2 reaction, the min. (Right) UV spectra of probes P2 and P4 (1.0 x 10‐4 M in
formed aldehyde (an electron acceptor moiety) would change acetonitrile) alone and after bubbling 1 ppm of NO2 during 5
the electronic properties of the chemodosimeter with min. The reactions gave aldehydes
subsequent shifts of the absorption bands (see Scheme 1).
7
and
8, respectively.
In a first step, the absorption changes of probes P1
‐
P4 (1.0 x
Results and discussion
10‐4 M in acetonitrile) after bubbling 1 ppm of NO2 during 5
min. (obtained from a commercial cylinder), was tested.
Probes P1
depicted in Scheme 2. Pd(0) catalyzed cross‐coupling reaction centered at 277 nm that was redshifted to 285 nm upon
of the appropriate boronic acids and with 4‐ bubbling air containing 1 ppm of NO2 (see Figure 1).
bromohydroxymethylbenzene ( ) or 4‐bromobenzaldehyde ( Interestingly, the same absorption band centered at 285 nm
yielded the corresponding biphenyl derivatives bearing was observed upon bubbling NO2 into acetonitrile solutions of
hydroxyl ( and ) or aldehyde ( and
) moieties.17 probe P3 (see also Figure 1). The new absorption band, formed
Transformation of the hydroxyl group into the corresponding upon NO2 bubbling, was ascribed to the formation of aldehyde
‐P4 were prepared following the synthetic pathway Acetonitrile solutions of P1 showed an absorption band
(
1
2)
3
4)
5
6
7
8
trimethylsilyl ether (probes P1 and P2) was carried out using
7 as a consequence of the oxidative deprotection of the
hexametildisilazane (HMDS) in dry CH2Cl2,18 whereas the trimethylsilyl ether moiety in P1 and of the rupture of the
probes containing oximes (P3 and P4) were obtained with oxime group in P3. In fact both, the UV and 1H NMR spectra of
hydroxylamine hydrochloride in H2O/MeOH mixed with aldehyde
7
, were fully coincident with that obtained after
sodium carbonate.19 All compounds were characterized by H treatment of probes P1 and P3 with NO2. Optically, the
NMR, 13C NMR and MS (see Supporting Information). transformation of an electron donor (trimethylsilyl ether in P1
Acetonitrile solutions of the four probes (1.0 x 10‐4 M) showed or a weak electron acceptor (oxime in P3) group into an
1
)
intense absorption bands in the 260‐300 nm region with

aldehyde (with a marked ability to attract electronic density)
yielding , resulted in a bathochromic shift of the absorption
values ranging from 6000 to 15000 M‐1 cm‐1.
7
band of P1 and P3. A similar redshifts of the absorption bands
of acetonitrile solutions of P2 and P4 was observed upon
bubbling NO2 (1 ppm in air) (see Figure 1). These changes were
ascribed to the reaction of NO2 with the probes that yielded in
OH
O
Si
OH
3
Br
HMDS
CH2Cl2
5
6
R = H
P1 R = H
P2 R = OCH3
R = OCH3
Pd(PPh3)4
Na2CO3/DMF
HO
OH
both cases aldehyde
UV and H NMR spectra of aldehyde , were fully coincident
8
. Also in this case it was found that the
B
R
1
R
R
8
N
CHO
OH
with that obtained after treatment of probes P2 and P4 with
NO2. The best sensing performance, in terms of a larger shift of
the absorption band, was obtained for probe P2, for which a
redshift of 45 nm (from 264 to 309 nm) was observed upon
bubbling 1 ppm of NO2. For this reason, further detailed
studies with P2 were carried out in order to assess the
sensitivity and selectivity of this probe toward NO2.
CHO
1
2
R = H
R = OCH3
4
NH2OH
Br
P3 R = H
P4 R = OCH3
7
8
R = H
R = OCH3
H2O
MeOH
Pd(PPh3)4
Na2CO3/DMF
R
R
Scheme 2. Synthetic pathways used for the preparation of
probes P1 P4
‐
.
2 | J. Name., 2012, 00, 1‐3
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DOI: 10.1039/C6RA02222G
2.1
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
Competitive studies were also carried out. Thus, Figure 3
shows that the absorption of the band at 309 nm of probe P2
in
the
presence
of
a
complex
gas
mixture
(NO2+NO+CO2+H2S+SO2) was the same than that observed
when NO2 was used alone. This result demonstrated a high
selective response of probe P2 toward NO2 and suggested its
possible use for the detection/monitoring of this poisonous
gas.
Conclusions
Four new biphenyl‐based probes P1‐P4 have been synthesized
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2
- log [NO2]
and used for the selective recognition of NO2. For all four
probes a bathochromic shift of the absorption bands was
observed in the presence of the NO2 and ascribed to the
generation of an aromatic aldehyde upon reaction of NO2 with
Figure 2. Absorbance at 309 nm measured after bubbling
increasing quantities of NO2 into acetonitrile solutions of
probe P2 (1.0 x 10‐4 M).
trimethylsilyl benzyl ether or oxime groups contained in P1
‐P2
and P3 P4, respectively. Among the prepared chemosensors,
‐
P2 showed the higher shift of the absorption band and for this
probe a LOD as low as 0.02 ppm was determined for NO2
detection. Moreover, the response of P2 was highly selective
and no reaction was found in the presence of NO, CO2, H2S,
SO2 or organic vapors of acetone, hexane, chloroform,
acetonitrile or toluene. We believe that these, or similar
probes based in the same chemical reaction, can display a
large potential as optical probes for the selective detection of
NO2.
The limit of detection (LOD) using P2 for NO2 was determined
by UV measurements by bubbling increasing amounts of NO2
into an acetonitrile solution of the probe. As shown in Figure 2,
the absorbance at 309 nm was gradually enhanced when the
concentration of NO2 increases. From the titration profile a
LOD as low as 0.02 ppm was calculated.
In a second step, the selectivity of P2 was assessed. This is an
important issue in the design of probes for pollutant gases in
order to overcome potential interferents or false‐positive
readings produced by other species. Taking this into account,
the potential reactivity of probe P2 with other hazardous gases
(i.e. NO, CO2, H2S, SO2) or organic vapors (i.e. acetone, hexane,
chloroform, acetonitrile, toluene) was tested by bubbling the
selected species into acetonitrile solution of P2 (1.0 x 10‐4 M).
None of the gases tested, at concentrations up to 100 ppm,
induced changes in the UV spectra of probe P2 indicating a
high selective reaction of P2 with NO2 (see Figure 3).
Experimental Section
General remarks: Dichloromethane and acetonitrile were
distilled from P2O5 under Ar prior to use. Silica gel 60 F254
(Merck) plates were used for TLC. Colum chromatography was
performed on silica gel. 1H and 13C NMR spectra were
determined on a Bruker AV 300 spectrometer. Chemical shifts
are reported in parts per million (ppm), calibrated to the
solvent peak set. High‐resolution mass spectra were recorded
in the positive ion mode with
a VG‐AutoSpec mass
2.0
NO2 + NO + CO2 + H2S + SO2
NO2
spectrometer. Absorption and fluorescence spectra were
recorded using a Shimadzu UV‐2600 spectrophotometer.
Synthesis of biphenyl alcohols 5 and 6: In a typical run, the
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
corresponding boronic acid (
1
for the synthesis of
5;
2
for the
(1
preparation of ) (2 mmol) was added, to a solution of
6
3
mmol) in DMF (20 ml) in the presence of sodium carbonate (6
mmol). Afterward, the flask was evacuated and refilled with
argon. Then, tetrakis(triphenylphosphine)palladium(0) was
added and the crude obtained heated at 100 ºC for 30 minutes
with vigorous stirring. The resultant mixture was diluted with
H2O (10 mL) and Et2O (10 mL), followed by extraction twice
with Et2O. The ethereal extract was collected and the solvent
evaporated under vacuum. The final product was isolated by
column chromatography on silica, with hexane/ethyl acetate
(8:2) as eluent, yielding a colourless solid (65%).
NO
organic
vapours
SO2
H2S
CO2
P2
Figure 3. Absorbance at 309 nm of probe P2 alone and in the
presence of selected potential interferents (all compounds at a
concentration of 100 ppm).
1
5: (65%), colourless solid. H NMR (300 MHz, DMSO) δ (ppm):
7.68 ‐ 7.60 (m, 4H), 7.50 ‐ 7.32 (m, 5H), 5.21 (t, J = 5.7 Hz, 1H),
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4.54 (d, J = 5.7 Hz, 2H). 13C NMR (75 MHz, DMSO) δ (ppm): hydrochloride (2.2 mmol) were dissolved in meVtihewanAroticl‐lewOantliener
142.2, 140.5, 138.9, 129.3, 127.6, 127.4, 126.9, 126.7, 62.9.
(1:1, 40 mL). A previously preparedDOsoI:l1u0t.i1o0n39/Co6fRAs0o2d2i2u2mG
1
6: (67%), colourless solid. H NMR (300 MHz, DMSO) δ (ppm): carbonate (2 mmol) in water was slowly added and the
7.50 ‐7.43 (m, 4H), 7.37 (d, J = 8.4 Hz, 2H), 6.91 (d, J = 8.7 Hz, reaction was stirred for 3 h at room temperature. Then,
2H), 5.20 (t, J = 5.7 Hz, 1H), 4.53 (d, J = 5.7 Hz, 2H), 3.79 (s, 3H). methanol was evaporated and the aqueous phase was
13C NMR (75 MHz, DMSO) δ (ppm): 159.1, 132.9, 132.8, 132.7, extracted with ether (4 x 40 mL). The organic phase was
127.9, 127.4, 126.2, 114.7, 63.0, 55.6.
washed with brine (1 x 30 mL) and dried with MgSO4. After
Synthesis of probes P1 and P2: HDMS (40 mmol) was added to evaporation of the solvent probes P3 (99%) and P4 (77%) were
the corresponding alcohol (20 mmol) in dry dichloromethane isolated as white solids.
1
(20 mL). The mixture was stirred at room temperature for 22 h P3: (99%), white crystalline solid, m. p. 142‐145C. H NMR
(full conversion) under argon atmosphere. The solvent was (300 MHz, DMSO‐d6) δ 11.28 (s, 1H), 8.19 (s, 1H), 7.70 (m, 6H),
evaporated and the crude was purified by column 7.48 (m, 2H) 7.40 (m, 1H). 13C NMR (75 MHz, DMSO) δ (ppm):
chromatography on silica using with hexane/ethyl acetate (8:2) 148.1, 141.2, 139.8, 132.6, 129.3, 128.1, 127.3, 127.3, 126.9.
as eluent, to give the probes P1 (90%) or P2 (93%) as white HRMS (EI): m/z calc. for C13H11NO 197.08 [M+1]+ found:
solids.
198.0913. UV‐Vis (acetonitrile) λmax = 282 nm (= 5800 M‐1cm‐
1
P1: (90%), white solid, m. p. 158‐160C. H NMR (300 MHz, 1).
1
DMSO) δ (ppm): 7.50 (m, 4H), 7.27 (m, 5H), 4.56 (s, 2H), 0.00 P4:(77%), white crystalline solid, m. p. 165‐167C. H NMR
(s, 9H). 13C NMR (75 MHz, DMSO) δ (ppm): 140.5, 140.3, 139.2, (300 MHz, Chloroform‐d) δ 8.09 (s, 1H), 7.50 (m, 5H), 6.92 (d, J
129.2, 127.6, 127.3, 126.9, 63.8, ‐0.1. UV‐Vis (acetonitrile) λmax = 8.9 Hz, 2H), 5.23 (s, 1H), 3.79 (s, 3H). 13C NMR (75 MHz,
= 277 nm (= 15300 M‐1cm‐1).
DMSO) δ (ppm): 159.5, 148.2, 140.9, 134.8, 130.5, 128.7,
1
P2: (93%), white solid, m. p. 170‐173C. H NMR (300 MHz, 128.1, 127.0, 114.9, 55.6. HRMS (EI): m/z calc. for C14H13NO2
DMSO) δ (ppm): 7.45 (m, 4H), 7.22 (d, J = 8.4 Hz, 2H), 6.88 (d, J 227.09 [M+1]+ found: 228.1019. UV‐Vis (acetonitrile) λmax
= 8.5 Hz, 2H), 4.55 (s, 2H), 3.66 (s, 3H), 0.00 (s, 9H). 13C NMR 300 nm (= 11800 M‐1cm‐1).
=
(75 MHz, DMSO) δ (ppm): 139.6, 138.8, 132.6, 129.2, 127.9, Limits of detection measurements: Increasing quantities of
127.3, 126.2, 114.6, 63.8, 0.1. UV‐Vis (acetonitrile) λmax = 264 NO2 gas from commercially available NO2 cylinder were
nm (= 8000 M‐1cm‐1).
bubbled for 5 min through a solution of P2 in acetonitrile. The
UV spectra were recorded in 1‐cm path length cells at 25 ºC.
Representation of the wavelength (nm) vs. concentration of
Synthesis of 7 and 8: 4 (1.5 mmol) and
1 or 2 for 7 and 8
respectively (3 mmol) were dissolved in DMF (20 mL). NO2 allowed the limit of detection to be calculated by using
Afterward, sodium carbonate (9 mmol) was added to this the equation (1)
solution. The crude reaction was stirred under inert
atmosphere for 30 min. Then, a catalytic amount of
LOD = 3sb/m (1)
tetrakis(triphenylphosphine)palladium(0) was added and the in which sb is the standard deviation of blank measurements
reaction was stirred at 100 ºC for 10 minutes. After this time and m is the slope of the linear regression plot.
water (10 mL) was added and the mixture was extracted with
ethyl acetate (2 x 20 mL). The organic phase was washed with Acknowledgements
brine (2 x 20 mL), dried with MgSO4 and evaporated to give the We thank the Spanish Government and FEDER founds
product
(MAT2012‐38429‐C04)
and
Generalitat
Valenciana
7
was purified by silica column chromatography with (PROMETEOII/2014/047) for support. SCSIE (Universidad de
hexane/ethyl acetate (9:1) to give a white crystalline solid Valencia) is gratefully acknowledged for all the equipment
1
(82%). H NMR (300 MHz, DMSO‐d6) δ 10.06 (s, 1H), 8.01 (m, employed.
2H), 7.92 (d, J = 8.3 Hz, 2H), 7.78 (m, 2H), 7.50 (m, 3H). 13C
NMR (75 MHz, DMSO‐d6) δ 193.20 , 146.34 , 139.27 , 135.56 , References
130.62 , 129.60 , 129.06 , 127.84 , 127.60 . HRMS (EI): m/z calc. 1. K. Skalska, J.S. Miller, S. Ledakowicz, Sci. Total Environ.
for C13H10O 182.07 [M+1]+ found: 183.0797 UV‐Vis 2010, 408, 3976‐3989.
(acetonitrile) λmax = 289 nm (ε= 9500 M‐1cm‐1).
2. S. C. Barman, N. Kumar, R. Singh, G. C. Kisku, A. H. Khan, M.
was purified by silica column chromatography with M. Kidwai, R. C. Murthy, M. P. S. Negi, P. Pandey, A. K. Verma,
8
hexane/ethyl acetate (8:2) to give a white crystalline solid G. Jain, S. K. Bhargava, J. Environ. Biol. 2010, 31, 913‐920.
1
(75%). H NMR (300 MHz, DMSO‐d6) δ 10.03 (s, 1H), 8.01 – 3. Analytical Techniques for Atmospheric Measurement, Editor D.
7.93 (m, 2H), 7.91 – 7.85 (m, 2H), 7.74 (d, J = 9.0 Hz, 2H), 7.08 Heard, John Wiley & Sons, 2008, pp. 331.
(d, J = 8.9 Hz, 2H), 3.82 (s, 3H).13C NMR (75 MHz, DMSO) δ 4. (a) J. L. Devalia, A. M. Campbell, R. J. Sapsford, C. Rusznak, D.
(ppm): 192.9, 160.2, 145.9, 134.8, 131.3, 130.5, 128.7, 127.0, Quint, P. Godard, J. Bousquet, R. J. Davies, Am J Respir Cell Mol
114.9, 55.6. HRMS (EI): m/z calc. for C14H12O2 212.08 [M+1]+ Biol., 1993, 9, 271‐278. (b) S. M. Horvath, Bull N Y Acad Med. 1980,
found: 213.0901. UV‐Vis (acetonitrile) λmax = 309 nm (
=
56, 835–846.
12700 M‐1cm‐1).
5. (a) W. S. Tunnicliffe, P. S. Burge, J. G. Ayres, Lancet, 1994, 344,
1733‐1736. (b) M. Shima, M. Adachi, Int. J. of E., 2000, 29, 862‐870.
Synthesis of probes P3 and P4: The corresponding aldehyde (
7
and
8 for P3 and P4 respectively, 2 mmol) and hydroxylamine
4 | J. Name., 2012, 00, 1‐3
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DOI: 10.1039/C6RA02222G
New chromogenic biphenyl-based probes for selectively detecting NO2
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