Aqueous polyfluorene probe for the detection and estimation of Fe 3+ and inorganic phosphate in blood serum

Article abstract of DOI:10.1039/c0jm03054f

A novel anionic polyfluorene derivative, poly(9,9-bis(6′-sulfate) hexyl) fluorene-alt-1,4-phenylene sodium salt (P1) is synthesized. P1 exhibits exemplary activity towards the selective detection of Fe³⁺ and phosphates (P_i) under phy

Full text of DOI:10.1039/c0jm03054f

www.rsc.org/materials
Volume 21 | Number 8 | 28 February 2011 | Pages 2389–2752
ISSN 0959-9428
PAPER
Parameswar Krishnan Iyer et al.
Aqueous polyfluorene probe for the detection and estimation
of Fe3+ and inorganic phosphate in blood serum

Dynamic Article Links <
C
Journal of
Materials Chemistry
Cite this: J. Mater. Chem., 2011, 21, 2502
www.rsc.org/materials
PAPER
Aqueous polyfluorene probe for the detection and estimation of Fe3+ and
inorganic phosphate in blood serum†
*
Atul Kumar Dwivedi, Gunin Saikia and Parameswar Krishnan Iyer
Received 11th September 2010, Accepted 6th December 2010
DOI: 10.1039/c0jm03054f
A novel anionic polyfluorene derivative, poly(9,9-bis(60-sulfate)hexyl) fluorene-alt-1,4-phenylene
sodium salt (P1) is synthesized. P1 exhibits exemplary activity towards the selective detection of Fe3+
and phosphates (Pi) under physiological conditions. On binding to Fe3+, exceptional fluorescence
quenching of P1 occurred, demonstrated by a >97% reduction in the fluorescence intensity.
Furthermore, the P1–Fe3+ assay is highly selective for inorganic phosphate (Pi) anions at biological
pH values, observed by complete fluorescence dequenching and confirmed through a >95%
fluorescence enhancement. In order to validate its diagnostic potential, this assay was employed to
monitor the Pi levels in a competing biological environment like blood serum. At pH 7.4 this assay
showed a high specific activity to detect Pi in the bioassay environment, observed by the unique
enhancements in fluorescence intensities for varying and low Pi concentrations. Since this assay
performed Pi detection at very low concentrations we utilized it successfully for the fluorometric
estimation of Pi in blood serum with high accuracy and within short duration. This remarkable
ability of P1 to accomplish in situ monitoring and estimation of indispensable biological targets like
Fe3+ and Pi rapidly and in label-free conditions, corroborates the extension of this assay system for
clinical application.
selective recognition of Fe3+ and phosphates in a competitive
1. Introduction
bioassay environment.
The past decade has witnessed the emergence of water-soluble
conjugated polymers (CPs) for diverse sensor applications.1,2
Polyphenylene vinylene (PPV) based anionic CPs used as dual
sensors were able to achieve up to a million-fold fluorescence
amplification.3 Several such outstanding reports on the sensi-
tivity of CPs that are quenched by oppositely charged or neutral
quenchers in aqueous mediums led to the development of very
versatile systems for the detection of a plethora of chemical and
biological analytes.4 Critical requirements for a superior sensor
system, in addition to aqueous solubility and high sensitivity, is
to have appropriate binding sites, perform more than one task in
label-free conditions and the ability to perform detection and
estimation at physiological pH, particularly for the development
of advanced biosensors. It is highly dubious that such a system
exists. We report here the extraordinary sensing ability of
poly(9,9-bis(60-sulfate)hexyl)fluorene-alt-1,4-phenylene sodium
salt, (P1), a novel anionic polyfluorene derivative, to accomplish
Iron is the most abundant metal in life forms having an
indispensable importance in metabolism. However, excess Fe3+
accumulation leads to kidney, liver and DNA damage, while,
its deficiency causes anemia and breathing problems.5 None-
theless, only meager efforts have been directed towards the
design and development of sensitive and selective Fe3+ detec-
tion systems.6 Likewise, phosphate anions are ubiquitous to
DNA and RNA as their structural framework, all cellular
processes acquire energy in the form of ATP and calcium salts
of phosphates help in bone stiffening. However, detection of
inorganic phosphate (Pi) anions in an aqueous medium is
compounded by the competing solvation effect7 and as
a consequence, reports of Pi detections are scarce.8 A recent
method to detect phosphate in blood serum at physiological
pH highlighted the use of a tripodal ligand embedded onto
a polymer matrix.9 Yet, label-free anionic CPs that are known
for their high sensitivity to small perturbations have not yet
been developed for phosphate detection10 and estimation in
competitive biological environments. Herein, we demonstrate
that P1 fulfils the requirements of detecting indispensable
biological targets like Fe3+ and of estimating Pi in blood serum
at physiological pH, corroborating this system for clinical and
diagnostic validation.
Department of Chemistry, Indian Institute of Technology Guwahati,
Guwahati, 781039, Assam, India. E-mail: pki@iitg.ernet.in; Fax:
+913612582349; Tel: +913612582314
† Electronic supplementary information (ESI) available: Scanned spectra
of monomer 1 and polymers P0 and P1 are presented in this section. See
DOI: 10.1039/c0jm03054f
2502 | J. Mater. Chem., 2011, 21, 2502–2507
This journal is ª The Royal Society of Chemistry 2011

2. Results and discussion
2.1. Synthesis of poly(9,9-bis(60-sulfate)hexyl)fluorene-alt-1,4-
phenylene sodium salt (P1)
This assay technology comprises of a novel anionic CP, poly (9,9-
bis(60-sulfate)hexyl)fluorene-alt-1,4-phenylene sodium salt, P1,
prepared through a Suzuki copolymerization (Scheme 1) of
monomer 1 with benzene-1,4-diboronic acid to obtain polymer
P0. This polymer P0 was stirred with concentrated sulfuric acid
for introducing the unique sulfate groups present in polymer P1
and realizing its water-soluble properties (Experimental section).
Since the synthesis of sulfate terminated CPs is unexplored due to
the inherent synthetic and purification challenges, a new plat-
form for evaluating CP–target molecule interactions is presented
here. This novel polymer P1 could be dissolved in water at room
temperature (100 mg mLꢀ1) and showed maximum absorption at
334 nm and a strong emission wavelength at 411 nm.
2.2. Evaluating the sensing properties of P1
Metal ions alter the optical properties of CPs by associating with
their binding sites, resulting in optical events that can be visu-
alized either by the shift in wavelength or quenching of the
fluorescence intensity.10 P1 was chosen to study the viability of
metal binding since the novel sulfate terminated side chains
would facilitate its association with oppositely charged molecules
by quenching the excited state of the CPs.3 The resulting optical
changes can be conveniently studied by fluorescence spectros-
copy. Salts of Mg2+, Ca2+, Mn2+, Mn3+, Fe2+, Fe3+, Al3+, Co2+,
Ni2+, Cu2+, Zn2+ and Cd2+ (with concentrations of 2.0 ꢁ 10ꢀ6
M
in water) were titrated with P1 (4.0 ꢁ 10ꢀ7 M in water) and
monitored by fluorescence spectroscopy. Metal salts like Co2+,
Al3+ and Cu2+ caused fluorescence quenching of P1 at very high
concentrations whereas all other metal salts had negligible or
virtually no effect on P1 (Fig. 1a). Titrating aqueous solutions of
Fe3+ metal salts (chloride and perchlorate) induced large
quenching in the fluorescence of P1 (Fig. 1b), so much so that
a >97% reduction in fluorescence intensity occurred, clearly
Fig. 1 (a) Bar diagram depicting the effect of various metals on the
fluorescence intensity of P1. (b) PL spectra of P1 (4.0 ꢁ 10ꢀ7 M in water)
with increasing concentration of Fe3+ shows >97% quenching in water.
Inset: Stern–Volmer plot of P1 upon addition of Fe3+ in an aqueous
medium. (c) Images of aqueous P1 and P1–Fe3+ under UV-light.
implying selective association of P1 and Fe3+. Such robust
quenching of P1 by Fe3+ is possibly due to a combination of
factors such as electron transfer, delocalization of excitons and
competent energy migration along the polymer chain.11 The
association occurring between anionic P1 and cationic Fe3+
facilitates the efficient transfer of excited states from polymer P1
to Fe3+, resulting here in high fluorescence quenching.4c The
quenching behavior of P1 was studied using the Fe3+ titration
data. Fig. 1b (Inset) shows a Stern–Volmer plot (KSV), (Io/I vs.
[Q]) where Io is the fluorescence intensity of P1, and I is the
fluorescence intensity of P1 after addition of a given concentra-
tion of quencher [Q], where [Q] ¼ Fe3+. The KSV value was found
to be 1.98 ꢁ 106 Mꢀ1. The absorption maxima (337 nm) of P1
showed a 8 nm shift on titrating with Fe3+ (Fig. 2) confirming the
static quenching mechanism.12 Further, lifetime values of P1
were not modified on titration with Fe3+, signifying the static
quenching mechanism.
Scheme 1 Synthesis of the polymer poly(9,9-bis(60-sulfate)hexyl) fluo-
rene-alt-1,4-phenylene sodium salt, (P1). (a) 2,7-dibromo-9,9-bis(6-bro-
mohexyl)-9H-fluorene, phenol, K2CO3, dry acetone, reflux, 24 h. (b)
Monomer 1, tetrakistriphenylphosphine palladium(0), benzene-1,4-
diboronic acid, 2 M aqueous K2CO3 and THF, reflux, 18 h. (c) Polymer
P0, conc. H2SO4, room temperature, 8 h.
Quenching of P1 is observed to be at its maximum at the
lowest concentration of Fe3+ (2.0 ꢁ 10ꢀ7 M) and >50%
This journal is ª The Royal Society of Chemistry 2011
J. Mater. Chem., 2011, 21, 2502–2507 | 2503

Fig. 2 Changes in the absorption of P1 on addition of an aqueous
solution of Fe3+ metal salts.
quenching occurred at concentrations as low as 6.0 ꢁ 10ꢀ7 M.
The fluorescence of P1 is further quenched on increasing the
concentration of Fe3+ but is less dramatic. This remarkable
ability of P1 as a highly selective and sensitive probe for Fe3+ in
aqueous mediums, irrespective of the Fe3+ salts, opens avenues
for its utility in probing Fe3+ in biological systems, with a broad
range of likely applications that include iron metabolism, anemia
and redox reactions. In recent years, Fe3+ compounds have been
applied as binders of phosphate13 in serum, whole blood and
dietary phosphates, replacing conventional binders like
aluminium,14 lanthanum15 and calcium salts, which have
numerous drawbacks like toxicity, intolerance to patients, cost
and unknown side effects.16 Yet, development of Fe3+ based
phosphate binders, which prevails over all the above drawbacks,
lies dormant and merits investigation. Employing the P1–Fe3+
assay system, we examined the binding of Pi at pH 7.4 by fluo-
Fig. 3 (a) PL spectra of P1–Fe3+ (pH 7.4) with increasing concentration
of Pi shows >95% super-dequenching. (b) Bar diagram depicting the
effect of anions on fluorescence intensity of P1–Fe3+
.
G6P (66%, 8 h), o-phospho-L-serine (45%, 8 h), o-phospho-L-
tyrosine (48%, 8 h), o-phospho-L-threonine (49%, 8 h) and
triethyl phosphate (0%, 8h).
1ꢀ
rescence spectroscopy. Since HPO42ꢀ : H2PO4 exists in 61 : 39
ratio at pH 7.4 we have used the term ‘‘phosphates’’ in this
manuscript.
Fig. 3a depicts the rapid fluorescence dequenching of >95% on
titrating aqueous Pi with the P1–Fe3+ assay. The largest spectral
enhancement is observed at the lowest Pi concentration (3.3 ꢁ
10ꢀ5 M), which gradually levelled off at a concentration of 5.3 ꢁ
10ꢀ4 M. The dequenching of the P1–Fe3+ assay on adding
aqueous Pi to the quenched P1–Fe3+ assay indicates the
displacement of Fe3+ from P1 resulting in high amplification of
the fluorescence. To determine the extent to which this P1–Fe3+
assay would react to other anions, similar titrations were per-
formed with several anions. As observed in Fig. 3b, the fluores-
cence of the P1–Fe3+ assay is barely perturbed on addition of
sulfide, sulfate, chloride, acetate, carbonate, thiosulfate, nitrate,
thiocyanate, cyanate and dicyanamide anions. Similarly,
chelating ligands such as citrate, EDTA and picolinate caused
only 21%, 13% and 5% dequenching respectively. This observa-
tion of ‘‘super-dequenching’’ on adding Pi to the quenched P1–
Fe3+ solution presents a unique, highly sensitive, label-free,
homogenous assay for Pi detection. The interaction of P1–Fe3+
with other phosphates (Fig. 4) showed that fluorescence
dequenching was very slow (2–8 h incubation), incomplete and
incomparable with the rapid fluorescence dequenching with Pi
observed above; e.g. pyrophosphate (87%, 2 h), polyphosphate
(80%, 4 h), ATP (71%, 8 h), ADP (52%, 8 h), AMP (37%, 8 h),
2.3. Evaluating the sensing properties of P1 in blood serum
These results encouraged us to study the detection of Pi in blood
serum to ascertain the practical utility of the P1–Fe3+ assay in
a competitive environment. Three samples of untreated blood
serum, doped with 0.009, 0.018 and 0.03 mg dLꢀ1 (0.0029, 0.0058
and 0.0097 mM Lꢀ1) concentrations of Pi were prepared and
Fig. 4 Fluorescence spectra changes of P1–Fe3+ on addition of various
phosphates (pH 7.4).
2504 | J. Mater. Chem., 2011, 21, 2502–2507
This journal is ª The Royal Society of Chemistry 2011

added carefully to P1–Fe3+ assay at physiological pH. The
fluorescence enhancement responses (Fig. 5) observed on adding
these three blood serum samples were unique and exceptionally
distinguishable even at extremely low concentrations, authenti-
cating this assay for systematic detection and quantification of Pi
in a blood serum environment that consists of competing
proteins, globulins, biophosphates, carboxylate ions and elec-
trolytes. Therefore, even at very low Pi concentrations the
amplification of fluorescence is clearly distinguished, indicating
that the homogenous fluorometric detection of Pi in competitive
bioassays can be practically preformed. Acute renal failure
patients have Pi levels in their blood exceeding 3.5–5.5 mg dLꢀ1
(1.13–1.77 mM Lꢀ1
resulting in hyperphosphatemia and
imbalance of other electrolytes.17
,
)
Since the P1–Fe3+ assay can detect Pi at such low concentra-
tions, we utilized this platform for fluorometric estimation of Pi
in blood serum. A fresh serum sample was deproteinized and the
supernatant was added (4 mL aliquot) to the P1–Fe3+ assay (pH
7.4). The maximum fluorescence enhancement observed was
compared with the standard calibration curve (Fig. 6). The total
Pi present in supernatant was in the range 4.24–4.37 mg dLꢀ1
(1.37–1.41 mM Lꢀ1), estimated by recording six maximum
enhancement readings. To evaluate the precision of these results,
estimation of supernatant Pi was carried out using the literature
method.18 The Pi quantity estimated by this method was 4.46 mg
dLꢀ1 (1.44 mM Lꢀ1), correlating well with the fluorometric esti-
mation results.
Fig. 6 The standard calibration curve for the assay of Pi (4.8 ꢁ 10ꢀ6 M)
and P1–Fe3+. Inset: The recovered fluorescence (a) on adding supernatant
compared to P1–Fe3+(b).
assembly of several chemical and biological entities. P1 demon-
strates the largest quenching and dequenching in a label-free
homogenous environment while performing these detection
tasks. Since P1 can be utilized both as a stand-alone probe as well
as in combination with quenchers, preserving its individual
photo-physical characteristics, a diverse range of sensory plat-
forms, potentially exploiting these collective properties, can be
developed.
This fluorometric estimation method permits analysis of Pi in
serum within a few hours and is accurate, highly sensitive and
easy to perform. Importantly, this assay performs Pi detection
without being encumbered by competing solvent effects and
other ions6 that have hampered development of viable assays for
the detection of Pi. P1–Fe3+ is an exceptional displacement assay
that performs Pi determination in blood serum with a much
higher order of sensitivity compared with clinically permitted
procedures for phosphate estimation.19 Additionally, since the
absorbance (279 nm) and the fluorescence (330 nm) peaks of
serum20 do not overlap or interfere with this assay system, P1 can
be efficiently used for the detection of serum components.
Overall, this unique behavior of P1–Fe3+ displacement assay as
a fluorescence amplification probe for Pi detection under bio-
logical conditions in addition to the very high selectivity and
sensitivity of P1 towards Fe3+, validates this homogenous assay
as a useful platform for understanding the interaction and
3. Experimental
All reagents and solvents were purchased from commercial
sources and were of reagent grade. UV/Visible and PL spectra
were recorded on a Perkin Elmer Lambda-25 spectrophotometer
and a Varian Cary Eclipse Spectrophotometer respectively.
Fluorescence lifetimes were measured with the use of the Jobin
Yon Spex Fluorocube instrument. A IBH 375 nm LED was used
for excitation and emission intensity was recorded using 380 nm
Scotch cut-off filters. The Fluorocube instrument employs
a TBX-04 detector with jitter timing of 250 ps FWHM or better.
The fluorescence decays were analyzed with the reconvolution
method using software provided by IBH. FT-IR spectra were
taken on a Perkin Elmer spectrometer with samples prepared as
KBr pellets. 1H NMR (400 MHz) and 13CNMR (100 MHz)
spectra were obtained with a NMR spectrometer Varian-AS400.
Elemental analysis was performed on Perkin Elmer Series II 2400
elemental analyser. Electro spray ionization mass (ESI-MS)
spectra were recorded on a Waters (Micro mass MS-Technolo-
gies) Q-Tof Premier mass spectrometer. GPC was recorded with
Waters-2414 instrument (Polystyrene calibration). Blood serum
samples from healthy subjects were obtained as gift from the host
institute medical department.
3.1 Synthesis procedure
3.1.1 2,7-Dibromo-9,9-bis(6-phenoxyhexyl)-9H-fluorene. (1).
A mixture of 2,7-dibromo-9,9-bis(6-bromohexyl)-9H-fluorene
(2.0 g, 3.08 mmol), phenol (1.16 g, 12.32 mmol) and K2CO3 (2.12
g, 30.8 mmol) was refluxed in dry acetone for 24 h. Reaction
progress was monitored by TLC. (1 : 9 ethylacetate : hexane)
The mixture was cooled, filtered over a celite pad and the filtrate
Fig. 5 Variation in the PL spectra of P1–Fe3+ (pH 7.4) on adding
varying concentrations of Pi doped blood serum samples.
This journal is ª The Royal Society of Chemistry 2011
J. Mater. Chem., 2011, 21, 2502–2507 | 2505

dried under vacuum. Repeated washing with methanol gave the
1
desired product 1. (1.56 g, 75%). H NMR (400 MHz, CDCl3)
were performed at room temperature and changes monitored
and recorded carefully.
d (ppm): 7.53 (d, J ¼ 8.8Hz, 2H), 7.47 (s, 2H), 7.27 (t, J ¼ 8.4 Hz,
4H), 6.93 (t, J ¼ 7.2 Hz, 2H), 6.85 (d, J ¼ 8.0 Hz, 4H), 3.85 t, J ¼
6.4Hz, 4H), 1.95 (t, J ¼ 8.0 Hz, 4H), 1.62 (q, J ¼ 6.8Hz, 4H), 1.25
(q, J ¼ 7.2Hz, 4H), 1.15 (q, J ¼ 7.2Hz, 4H), 0.64 (q, J ¼ 4.0Hz,
4H). 13C NMR (100 MHz, CDCl3) d (ppm): 159.27, 152.59,
139.33, 130.53, 129.64, 126.38, 121.81, 121.48, 120.707, 114.71,
67.90, 55.87, 40.37, 29.85, 29.40, 25.9, 23.89. Anal. calcd for
C37H40Br2O2: C, 65.69; H, 5.96. Found: C, 65.98; H, 5.72. HR-
MS(ESI) calculated for C37H40Br2O2: 676.5381; found,
679.6098.
3.2.3 Fluorescence titration of P1–Fe3+ with phosphate and
blood serum. Once the solution of P1 was quenched by adding
Fe3+, a solution of sodium dihydrogen phosphate in water was
added in portions of 3.3 ꢁ 10ꢀ5 M and the changes in the fluo-
rescence intensity of P1–Fe3+ were recorded at room tempera-
ture. pH of the solution was adjusted by adding a few drops of
aq. NaOH solution to the P1–Fe3+ assay. Fresh samples of
untreated blood serum from healthy subjects, doped with 0.009,
0.018 and 0.03 mg dLꢀ1 concentrations of phosphate were
prepared and added carefully to the P1–Fe3+ assay at physio-
logical pH. Titration experiments with all other anions and
phosphates with the P1–Fe3+ assay were also performed as
above. Polyphosphate and pyrophosphate salts had to be incu-
bated or shaken for 2–4 h before attaining maximum enhance-
ment, whereas, ATP, ADP, AMP, G6P, o-phospho-L-serine,
o-phospho-L-tyrosine and o-phospho-L-threonine had to be
incubated for approximately 8 h after each addition to observe
dequenching. Triethyl phosphate showed no dequenching even
after prolonged time.
3.1.2 Poly(9,9-bis(6-phenoxyhexyl)fluorene-alt-1,4-phenylene
1 (0.5 g, 0.74 mmol), tetrakis-
(P0).
A
mixture of
triphenylphosphine palladium(0) (0.042 g, 0.03 mmol), benzene-
1,4-bisboronic acid (0.123 g, 0.74 mmol), 5 mL 2 M aqueous
(Milli-Q water) K2CO3 and THF (10 mL) were taken in a flask
fitted with a reflux condenser. The reaction mixture was degassed
thrice by freeze–thaw cycles followed by refluxing for 18 h under
inert atmosphere. Iodo-benzene (0.03 g, 0.147 mmol) was added
to the reaction and refluxed for 3 h. This was followed by addi-
tion of phenyl boronic acid (0.018 g 0.147 mmol) dissolved in 1
mL THF and refluxing for additional 3 h. The reaction mixture
was cooled, poured into methanol and stirred for 30 min. The
precipitates were collected by filtration, followed by washing
with methanol. Soxhlet extraction of the above precipitates by
4. Conclusions
In summary, a novel anionic polyfluorene derivative (P1) having
sulfate as terminal groups was designed and synthesized using
a Suzuki coupling reaction. P1 was utilized for rapid, label-free
detection and estimation of indispensable biological targets like
Fe3+ and Pi in an aqueous medium as well as in competitive
biological environments such as blood serum. These significant
and unique properties of anionic P1 will certainly inspire
fundamental development of sulfate terminated, conjugated
fluorescent polymers that have shown outstanding ability as
amplifying fluorescent polymers in clinical applications. Addi-
tionally, their ability to transport electronic excited states and
inherent film forming properties on desired substrates promises
a bright future for interdisciplinary applications like healthcare,
security, environmental monitoring and optoelectronic devices.
1
acetone for 24 h gave the desired polymer P0 (0.24 g, 55%). H
NMR (400 MHz, CDCl3) d (ppm): 7.75 (b), 7.64 (b), 7.58 (b),
7.47 (b), 7.22 (b), 6.88 (b), 6.82 (b), 3.81 (b), 2.04 (b), 1.59 (b),
1.22 (b), 0.76 (b). 13C NMR (100 MHz, CDCl3) d (ppm): 159.27,
153.21, 151.77, 151.1, 140.43, 130.36, 129.56, 127.70, 126.30,
121.55, 120.62, 114.67, 67.90, 55.67, 40.56, 29.87, 29.32, 25.85,
23.88. MW-30982, PDI-1.81, GPC-Polystyrene standard.
3.1.3 Poly(9,9-bis(6-sulfate)hexyl)fluorene-alt-1,4-phenylene
(P1). Polymer P0 (0.2 g) was stirred with 10 mL conc. H2SO4 for
8 h at room temperature. The reaction mixture was cooled to
0
ꢂC and treated with 20% aqueous NaOH solution carefully
until neutralization. The precipitates obtained were filtered and
washed with cold water. The solid was dissolved in minimum
methanol and added dropwise to acetone to obtain pale yellow
Acknowledgements
1
precipitates of desired P1. (0.13 g, 60%). H NMR (400 MHz,
Financial support from DST, India (SR/S1/PC-02/2009) is
acknowledged. We thank Dr G. Krishnamoorthy (IITG) for
valuable discussions on fluorescence experiments and the IITG
medical section for gifting blood serum samples.
CD3OD) d (ppm): 8.54 (b), 8.35 (b), 7.85 (b), 7.06 (b), 4.02 (b),
2.17 (b), 1.29 (b), 1.09 (b), 0.95 (b). FTIR (nmax, KBr pellet):
3460, 2956, 1645, 1558, 1448, 1415, 1195, 1037, 848, 605 cmꢀ1
.
Notes and references
3.2 UV/Vis and PL titration experiments
1 M. Leclerc, Adv. Mater., 1999, 11, 1491–1498.
2 D. T. McQuade, A. E. Pullen and T. M. Swager, Chem. Rev., 2000,
100, 2537–2574.
3.2.1 UV titration of P1 with Fe3+. To a solution of P1 (2 ꢁ
10ꢀ5 M) a solution of Fe3+ metal salts, up to a concentration of
2 ꢁ 10ꢀ4 M, was carefully titrated. The changes in the absorption
are shown in Fig. 2.
3 (a) L. Chen, D. W. McBranch, H.-L. Wang, R. Helgeson, F. Wudl
and D. G. Whitten, Proc. Natl. Acad. Sci. U. S. A., 1999, 96,
12287–12292; (b) S. J. Dwight, B. S. Gaylord, J. W. Hong and
G. C. Bazan, J. Am. Chem. Soc., 2004, 126, 16850–16859.
4 (a) L. Chen, S. Xu, D. W. McBranch and D. G. Whitten, J. Am.
Chem. Soc., 2000, 122, 9302–9303; (b) J. Wang, D. Wang,
E. K. Miller, D. Moses, G. C. Bazan and A. J. Heeger,
Macromolecules, 2000, 33, 5153–5158; (c) S. W. Thomas III,
G. D. Joly and T. M. Swager, Chem. Rev., 2007, 107, 1339–1386.
3.2.2 Fluorescence titration of P1 with metal salts. An
aqueous solution of P1 (4.0 ꢁ 10ꢀ7 M in water) was placed in the
quartz cell and the fluorescence spectra (345 nm excitation) were
recorded for increasing portions of metal salts. The experiments
2506 | J. Mater. Chem., 2011, 21, 2502–2507
This journal is ª The Royal Society of Chemistry 2011

5 (a) J. B. S. Neilands, Struct. Bonding, 1984, 58, 1–24; (b)
G. Winkelmann, D. van der Helm, J. B. Neilands, Iron Transport in
Microbes, Plants, and Animals, VCH Verlagsgesellschaft mbH, D-
6940, Weinheim, Germany, 1987; (c) B. F. Matzanke,
G. M. Matzanke, K. N. Raymond, Iron Carriers and Iron Proteins,
VCH Publishers, New York, 1989, Vol. 5; (d) C. Brugnara, Clin.
Chem., 2003, 49, 1573.
10 F. Rininsland, W. Xia, S. Wittenburg, X. Shi, C. Stankewicz,
K. Achyuthan, D. W. McBranch and D. G. Whitten, Proc. Natl.
Acad. Sci. U. S. A., 2004, 101, 15295–15300.
11 (a) J.-L. Bredas, J. Cornil, D. Beljonne, D. A. Dos Santos and
Z. Shuai, Acc. Chem. Res., 1999, 32, 267–276; (b) T.-Q. Nguyen,
J. Wu, V. Doan, B. J. Schwartz and S. H. Tolbert, Science,
2000, 288, 652–656; (c) R. M. Jones, T. S. Bergstedt,
D. W. McBranch and D. G. Whitten, J. Am. Chem. Soc., 2001,
123, 6726–6727.
12 (a) J. R. Lakowicz, Principles of Fluorescence Spectroscopy, Kluwer
Academic/Plenum Publishers, New York 1999; (b) Q. Zhou and
T. M. Swager, J. Am. Chem. Soc., 1995, 117, 7017–7018.
13 C. H. Hsu, S. R. Patel and E. W. Young, J. Am. Soc. Nephrol., 1999,
10, 1274–1280.
14 M. R. Wills and J. Savory, Lancet, 1983, 2, 29–34.
15 V. Autisser, S. J. P. Damment and R. A. Henderson, J. Pharm. Sci.,
2007, 96, 2818–2827.
16 (a) E. M. Clarkson, J. B. Eastwood, K. G. Koutsaimanis and H. E. De
Wardener, Kidney Int., 1973, 3, 258–263; (b) E. M. Clarkson,
C. Durrant, M. E. Phillips, P. E. Gower, R. F. Jewkes and H. E. de
Wardener, Clin. Sci., 1970, 39, 693–704.
17 L. C. Plantinga, N. E. Fink, M. E. Melamed, W. A. Briggs,
N. R. Powe and B. G. Jaar, Clin. J. Am. Soc. Nephrol., 2008, 3,
1398–1406.
18 (a) P. P. Van Veldhoven and G. P. Mannaerts, Anal. Biochem., 1987,
161, 45–48; (b) T. Ohno and L. M. Zibilske, Soil Sci. Soc. Am. J.,
1991, 55, 892–895; (c) E. D’Angelo, J. Crutchfield and
M. Vandiviere, J. Environ. Qual., 2001, 30, 2206–2209.
19 M. Kanbay, D. Goldsmith, A. Akcay and A. Covic, Blood Purif.,
2009, 27, 220–230.
€
6 (a) J. L. Bricks, A. Kovalchuk, C. Trieflinger, M. Notz, M. Buschel,
A. I. Tolmachev, J. Daub and K. Rurack, J. Am. Chem. Soc., 2005,
127, 13522–13529; (b) Y. Xiang and A. Tong, Org. Lett., 2006, 8,
1549–1552; (c) C. Qin, Y. Cheng, L. Wang, X. Jing and F. Wang,
Macromolecules, 2008, 41, 7798–7804; (d) C. R. Lohani and K.-
H. Lee, Sens. Actuators, B, 2010, 143, 649–654; (e) B. Ma, S. Wu and
F. Zeng, Sens. Actuators, B, 2010, 145, 451–456; (f) Y. Chen, K.-
Y. Pu, Q.-L. Fan, X.-Y. Qi, Y.-Q. Huang, X.-M. Lu and W. Huang,
J. Polym. Sci., Part A: Polym. Chem., 2009, 47, 5057–5067.
7 (a) A. Bianchi, K. Bowman-James, E. Garcia-Espana, Supramolecular
Chemistry, Wiley-VCH, New York, 1997; (b) E. Fan, D. A. Van
Arman, S. Kincaid and A. D. Hamilton, J. Am. Chem. Soc., 1993,
115, 369–370.
8 (a) M. S. Han and D. H. Kim, Angew. Chem., Int. Ed., 2002, 41, 3809–
3811; (b) S. L. Tobey, B. D. Jones and E. V. Anslyn, J. Am. Chem.
Soc., 2003, 125, 4026–4027; (c) S. L. Tobey and E. V. Anslyn, Org.
Lett., 2003, 5, 2029–2031; (d) C. Li, M. Numata, M. Takeuchi and
S. A. Shinkai, Angew. Chem., Int. Ed., 2005, 44, 6371–6374; (e)
M. Burnworth, S. J. Rowan and C. Weder, Chem.–Eur. J., 2007,
13, 7828–7836; (f) C. Spangler, M. Schaeferling and O. S. Wolfbeis,
Microchim. Acta, 2008, 161, 1–39; (g) M. Comes, M. D. Marcos,
ꢀ~
R. M. Manez, F. Sancenon, J. Soto, L. A. Villaescusaa and
P. Amoros, Chem. Commun., 2008, 3639–3641.
ꢀ
ꢀ
9 G. V. Zyryanov, M. A. Palacios and P. Anzenbacher, Angew. Chem.,
Int. Ed., 2007, 46, 7849–7852.
20 N. Shaklai, R. L. Garlick and H. F. Bunn, J. Biol. Chem., 1984, 259,
3812–3817.
This journal is ª The Royal Society of Chemistry 2011
J. Mater. Chem., 2011, 21, 2502–2507 | 2507