Synthesis and binding properties of a new fluorescent molecular clip based on 2-ethyl cyanoacrylate

Article abstract of DOI:10.3184/030823410X12886279660671

A new fluorescent molecular clip based on 2-ethyl cyanoacrylate has been synthesised and its binding properties investigated by fluorescence spectroscopy to show that it can selectively bind Fe³⁺ with fluorescence quenching.

Full text of DOI:10.3184/030823410X12886279660671

JOURNAL OF CHEMICAL RESEARCH 2010
RESEARCH PAPER 635
NOVEMBER, 635–636
Synthesis and binding properties of a new fluorescent molecular clip
based on 2-ethyl cyanoacrylate
Dehua Zhang*
Department of Chemistry and Environmental Engineering, Hubei Normal University, Huangshi 435002, P. R. China
A new fluorescent molecular clip based on 2-ethyl cyanoacrylate has been synthesised and its binding properties
investigated by fluorescence spectroscopy to show that it can selectively bind Fe3+ with fluorescence quenching.
Keywords: molecular clip, 2-ethyl cyanoacrylate, fluorescence quenching, Fe3+
The design and synthesis of novel receptors with different
molecular cavities is one of the major challenges in hostguest
chemistry. 2-Ethyl cyanoacrylate is useful as an inhibitor of
Pyricularia oryzae, Rhizoctonia solani, Botrytis cinerea and
Gibberella zeae.1 It possesses good symmetry within the aro-
matic walls and shows good binding properties for aromatic
guests, especially, for dihydroxybenzene, by hydrogen bond-
ing, it–it stacking interactions and a so-called cavity-effect.2–4
We have found derivatives of 2-ethyl cyanoacrylate form
new molecular clips. We now report the synthesis of one and
develop its function as a selective fluorescent chemsensor for
Fe3+. We have designed the new molecular clip (4) which has a
large π-system that can be used as the signalling subunit in the
two sidewalls and two carbonyl oxygen atoms of the pyrazole
ring and nitrogen atoms in the cavity be can used as the
potential binding sites. We now report the synthesis of 4 and a
binding study with different metal ions.
The synthesis of the title clip molecule 4 is shown in Scheme
1. The structure and conformation of compound 4 were further
Fig. 1
Changes of the fluorescence properties of 4 (in 1×10−5
M
elucidated by single crystal X-ray diffraction, as shown in
Fig. 1.
DMF) solution caused by 15 equiv. of various metal ions (Co2+,
Cr3+, Sn4+, Cu2+ , Sr2+ , Ag+, Ni2+, Pb2+, Fe3+) were measured
until their emission intensity was constant. The results show
that Fe3+ produced significant quenching of the fluorescent
emission, whereas the other metals ion that were tested
only show a relatively insignificant change (Fig. 2). It can be
concluded that 4 has a high selectivity for the recognition
of Fe3+.
The crystals of 4 were obtained by slow evaporation of its
solution in ethyl acetate/petroleum ether (3:1, v/v) mixtures.
The crystal structure of 4 clearly reveals that it has a well-
defined geometry due to the rigidity that the fused rings confer
on the molecule. The structure shows a planar chlorobenzene
ring (N1, N2, C4, C5, C3) approximately perpendicular to
the pyrazole ring (N1, N2, C4, C5, C3) with a dihedral angle
of 33.3 °, the dihedral angle between the chlorobenzene and
the other pyrazole rings (N5, N6, C21, C22, C23) is 59.9 °,
the dihedral angle between the pyrazole rings is 84.7 °. The
molecular conformation is stabilised by N---H...O hydrogen
bonding. The chlorobenzene ring and pyrazole rings in the
cavity give 4 great potential to bind metal ions.
The sensitivity of the fluorescence emission response of 4
towards Fe3+ was also examined under the same conditions
with various Fe3+ concentrations (Fig. 3). The fluorescence
intensity of 4 decreased continually upon addition of Fe3+.
When the concentration of Fe3+ was increased to 15 equiv, the
fluorescence intensity of 4 was reduced to 80% of the initial
value. From a Stern–Volmer plot (Fig. 3), the quenching
constant was estimated as 5.37×104 M−1.
The binding properties of 4 with various metal ions were
investigated by fluorescent spectroscopy titration experiments.
Scheme 1
* Correspondent. E-mail: zhangdehua200@163.com

636 JOURNAL OF CHEMICAL RESEARCH 2010
and synthesised. It displays high selectivity for Fe3+ revealed
by fluorescence quenching.
Experimental
All reagents, obtained from commercial sources, were of AR grade.
Melting points were determined with an XT4A micro-melting point
apparatus and were uncorrected. 1H NMR spectra were recorded on a
Mercury Plus-400 spectrometer with TMS as internal reference and
CDCl3 as solvent. IR spectra were recorded on a Perkin-Elmer PE-983
IR spectrometer as KBr pellets. MS were obtained with a Finnigan
Trace MS instrument using the EI method. Elemental analyses were
carried out on a Vario EL III instrument. Fluorescence spectra were
determined on a Hitachi F-4500 instrument.
Compounds 1, 2 and 35–6 were prepared by the literature method.
Preparation of 4: To a solution of compound 3 (1.25g, 0.0050 mol)
in CH2Cl2 (18 mL), 4-chloro-3-ethyl-1- methyl-1H-pyrazole-5-car-
bonyl chloride (3.11 g, 0.015 mol) was added. Subsequently, Et3N
(1.52 g, 0.015 mol) was added dropwise into the solution under
stirring. The reaction mixture was heated to reflux, then stirred for
4 h. Subsequently, it was cooled to room temperature. The reaction
solution was filtered off and some white solid was separated. The
organic phase was washed with water and then dried over Na2SO4.
After removal of the solvent, a brown solid was obtained.After column
chromatography using ethylacetate/light petroleum (1:6) as eluent,
compound 4 (1.1g, 37.16%) was obtained as a white solid. M.p.134.2–
134.9 °C (dec.). TLC (CH3COOCH2CH3/petroleum ether, 3:1), Rf
0.51. IR (KBr, cm−1): 2226, 1740, 1728, 1685, 1630, 1645. 1H NMR
δ: 1.25 (t, 6H, CH3, J = 7.5Hz), 1.37 (t, 3H, CO2CH2CH3, J = 7.0 Hz),
2.66 (q, 4H, CH2CH3, J = 7.5 Hz), 3.9 (s, 6H, NCH3), 4.36 (q, 2H,
CO2CH2CH3, J = 7.0 Hz), 7.26–7.45 (m, 4H, ArH). MS (EI): m/z =
593 [M + H]+. Anal. Calcd for C26H25Cl3N604 (591.87): C, 52.75;
H, 4.27; N, 17.98. Found: C, 52.51; H, 4.15; N, 17.67 %.
Fig. 2 Fluorescence emission changes of 4 (1×10−5 M) in DMF
in the presence of 12×10−5 M of various metal ions (excitation at
358 nm). (1) Fe3+, (2) host, (3) Sn4+, (4) Cu2+, (5) Sr2+, (6) Ag+,
(7)Ni2+, (8)Cr3+, (9) Co2+, (10) Pb2+.
X-ray diffraction
A white crystal of 4 was mounted on a glass fibre in a random orien-
tation at 298(2) K. The determination of the unit cell and the data
collection were performed with MoKa radiation (λ = 0.71073 Å) on
a Bruker Smart Apex-CCD diffactometer with a ψ-ω scan mode.
The structure was solved by direct methods with the SHELXS-97 pro-
grams7,8 and expanded by Fourier technique. The non-hydrogen atoms
were refined anisotropically, and the hydrogen atoms were placed at
the calculated positions.
Crystal data for 4: C26H25Cl3N604, M = 591.87, Triclinic, space
group P2(1)/c, a = 10.7277(3)Å, b = 16.1476(5)Å, c = 17.3109(5)Å,
α = 90 °, β = 107.671(2)°, γ = 90°, V = 2857.21(14) Å3, Z = 4, Dc =
1.376 Mg m−3, Reflections collected: 18010, independent reflections:
5600 [Rint = 0.0453], Final R indices [I>2ϭ(I)]: R1 = 0.0646, wR2 =
0.1519. R indices (all data): R1 = 0.1050, wR2= 0.1700.
Fig. 3 Fluorescence emission spectra (excitation at 358nm) of
4 (1×10−5 M) in DMF in the presence of different concentration
of Fe3+. Inset: Stern–Volmer plot of the emission data.
We thank the Scientific Research Foundation of Hubei Normal
University (Grant No. 2008D39) for financial support.
The quenching of the electronically excited state of aromatic
hydrocarbons by Fe3+ chelates is a known phenomenon that
has been the subject of extensive investigations. It has been
suggested that two main pathways can account for the efficient
radiationless deactivation of the singlet excited state, electron
transfer from the excited aromatic chromophore to the metal
and/or energy transfer from the excited aromatic chromophore
to low-lying metal centred energy states. Such processes could
be particularly effective in the complex of 4 with Fe3+, due
probably to the fact that the chelated metal cation is held very
close to two excited aromatic chromophores. In addition,
because the molecular clips 4 has different sidewalls but the
same binding properties compared to previously reported
molecular clips, we may draw the conclusion that the 2-ethyl
cyanoacrylate ring plays a crucial role in the recognition of
Fe3+.
Received 29 July 2010; accepted 26 September 2010
Paper 1000271 doi: 10.3184/030823410X12886279660671
Published online: 24 November 2010
References
1
Huayin Liu. Biorational design, American Chemical Society, 2001,
pp. 226-235.
2
3
H. Toshio, H. Isaburo and H. Hideo, Bull. Chem. Soc. Jpn, 1965, 30, 695.
J.N.H. Reek, A.H. Priem, H. Engelkamp, A.E. Rowan, J.A.A.W. E1emans
and R.J.M. Nolte, J Am. Chem. Soc., 1997, 119, 9956.
J.A.A.W. E1emans, R.R.J. Slangen, A.E. Rowan and R.J.M. Nolte, J Org.
Chem., 2003, 68, 9040.
4
5
6
7
J.N. Phillips and J.L. Huppatz, Z.Naturforsch., 1987, 42C, 684.
J.N. Phillips and J.L. Huppatz, Z.Naturforsch., 1987, 42C, 679.
G.M. Sheldrick. SHEL.XS-97: Program for Crystal Structure Solution.
University of Göttingen: Germany, 1997.
In conclusion, a new clip molecule derived from 2-ethyl
cyanoacrylate as fluorescent chemosensor has been designed
8
G.M. Sheldrick. SHEL.XS-97: Program for Crystal Structure Refinement.
University of Göttingen: Germany, 1997.

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