A new class of functionalized calix[4]arenes as neutral receptors for colorimetric detection of fluoride ions

Article abstract of DOI:10.1039/b800502h

A new class of functionalized calix[4]arenes have been synthesized and evaluated for colorimetric detection of fluoride ions. The molecular receptor 4b selectively recognizes fluoride ions via H-bonds and subsequent deprotonation to elicit a distinct colo

Full text of DOI:10.1039/b800502h

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PAPER
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A new class of functionalized calix[4]arenes as neutral receptors for
colorimetric detection of fluoride ionsw
Har Mohindra Chawla,* Rahul Shrivastava and Satya Narayan Sahu
Received (in Montpellier, France) 21st January 2008, Accepted 23rd April 2008
First published as an Advance Article on the web 15th July 2008
DOI: 10.1039/b800502h
A new class of functionalized calix[4]arenes have been synthesized and evaluated for colorimetric
detection of fluoride ions. The molecular receptor 4b selectively recognizes fluoride ions via
H-bonds and subsequent deprotonation to elicit a distinct colour change from yellow to dark
purple.
(4a–e) with hydrazone functionalities in distal 1,3-positions at
their lower rim for the target purpose. Amongst the synthe-
Introduction
Recognition of fluoride ions is an important target for diverse
applications in chemical and biological processes.1 Real-time
monitoring and accurate detection of fluoride ions using
sized compounds, 4b was found to exhibit selective binding
with fluoride ions via H-bond interactions and elicit a distinct
‘naked eye’ colour change from yellow to dark purple through
convenient colorimetric assay are important aims for practical
efficient deprotonation.
field applications. Amongst several approaches adopted2 for
the development of fluoride ion receptors, the recognition of
fluoride through neutral receptors3 seems to be of utmost
significance. Previous work on colorimetric sensing of fluoride
ions concerns with molecular hosts employing different com-
binations of amide, urea, thiourea and pyrrole units4 which
coordinate and bind the anionic species through N–H–X
hydrogen bonds. The anion interaction triggers a change in
the photophysical response of the chromogen present in the
host molecule to allow fluoride ion sensing through a colour
change.5–7 Due to its small size and high electronegativity,
fluoride ion represents a special case where an ion can form
strong hydrogen bonds at lower concentrations and can act as
a sufficiently strong base at higher concentrations to promote
deprotonation through typical Brønsted acid–base reactions.8
Distinction between these two processes has often been
blurred in the case of fluoride recognition experiments.9 Since
calix[n]arenes10 possess a preorganised molecular architecture
for ionic and molecular recognition,11 we envisaged the use of
these scaffolds for sensing of fluoride ions through host–guest
interactions. The choice of calix[4]arene scaffold was
prompted by our previous work12 on anion recognition as
well as possible use of calixarene cavity for supporting fluoride
entrapment through proper functionalization. Though exam-
ples of calix[4]arene based fluoride receptors utilizing photo-
induced electron transfer (PET) or photoinduced charge
transfer (PCT) have been reported,13 there is a paucity of
colorimetric sensors for selective detection and estimation of
fluoride ions at low concentrations.14 We report herein the
synthesis and evaluation of five new calix[4]arene derivatives
Results and discussion
The synthesis of 4a–e could be achieved through facile
synthetic protocols (Scheme 1). The required starting mate-
rials calix[4]arene 1, bis(bromopropyl)calix[4]arene 2 and
Department of Chemistry, Indian Institute of Technology, Hauz Khas,
New Delhi-110016, India. E-mail: hmchawla@chemistry.iitd.ernet.in;
Fax: +91 11-26591502; Tel: +91 11-26591517
w Electronic supplementary information (ESI) available: UV-visible
spectra, titration plots and binding curves of 4b and 4c upon addition
of TBA-anions, 1H NMR spectra for 4b and 4c and COSY spectra for
4b, and 4b + FÀ and 19F NMR spectra. See DOI: 10.1039/b800502h
Scheme 1 Synthesis of receptors 4a–e. Reagents and conditions: (a)
Br–(CH2)3–Br, K2CO3, CH3CN, reflux, 15 h;12a (b) p-hydroxybenz-
aldehyde or p-hydroxyacetophenone, K2CO3, CH3CN, reflux, 12 h;12a
(c) phenyl hydrazine derivatives, ethanol.
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calix[4]arene derivatives 3a,b in cone conformation were pre-
pared according to previous literature procedures.12a Reaction
of 3a and 3b with phenylhydrazine reagents gave 4a–e in
88–94% yields. The elemental and spectroscopic analysis of
4a–e were consistent with their indicated structures. For
instance 4b showed a pair of doublets at d 3.48 and 4.17 for
axial and equatorial protons, respectively in the 1H NMR
spectrum and a distinct signal at d 30.2 for the methylene
carbons in its 13C NMR spectrum indicated its symmetrical
conformation.15 The singlets of –NH and –OH protons
appeared at d 11.15 and 8.46, respectively which disappeared
on deuteration with D2O. The FT-IR spectrum exhibited a
sharp peak at 1598 cmÀ1 for the 4CQN– absorptions.
The binding of 4a–e with various anions (such as FÀ, ClÀ,
BrÀ, IÀ, H2PO4À, HSO4À, AcOÀ, ClO4À and PF6À, in the form
of their tetrabutylammonium salts) was first monitored
Fig. 2 (a) Absorption spectra of 4b (5 Â 10À5 M)Àupon addition of
FÀ, ClÀ, BrÀ, IÀ, H2PO4À, HSO4À, AcOÀ, ClO4 and PF6 ions
À
(as tetrabutylammonium salts) (1 Â 10À4 M) in DMSO–CH3CN
(0.5 : 9.5 v/v). (b) UV-visible titrations of 4b with 0–8 equiv. of FÀ.
Further addition of fluoride ions to 4b increased the intensity
of the absorption band centered at 549 nm with concurrent
deepening of the purple colour that reached its limiting value
on addition of four equivalents of fluoride ions. Given the fact
that fluoride ion can deprotonate one or more NH protons of
the receptor beyond two equivalents,16 the observed spectro-
photometric titration profile of 4b with fluoride was quite
surprising. Detailed analysis of the UV-visible titration results
indicated that the limiting value in the absorption maxima
centered at 549 nm was attained at four equivalents of FÀ
instead of two equivalents. This can be accounted for by
hypothesizing that the initial addition of one equivalent of
FÀ establishes a hydrogen bond interaction with NH protons
of the receptor (1 : 1 complex) followed by formation of 2 : 1
(FÀ : 4b) hydrogen-bond adduct on addition of a second
equivalent of FÀ ions.14a,17 Further addition of FÀ ions
beyond two equivalents seems to result in the deprotonation
of the NH protons. Experimental observations indicate that
the bathochromic shift observed during the 4b–FÀ interaction
is either due to the formation of hydrogen bonds with the
hydrazone –NH or its deprotonation by fluoride ions which
results in a visual colour change possibly through efficient
charge transfer.18 It was interesting to note that addition of a
few drops of protic solvents (water or methanol) triggered the
disappearance of the observed colour of the 4b–fluoride
complex with immediate regeneration of the original receptor
colour. This suggested that the fluoride–calix[4]arene interac-
tion did not involve any plausible bond formation and that the
complexation of fluoride ion and 4b was reversible in nature.
The binding mode of fluoride ions with receptor 4b was
further investigated by 1H NMR titration experiments in
DMSO-d6. The NMR spectrum of 4b in the presence of
increasing equivalents of tetrabutylammonium fluoride
(Fig. 3) demonstrated that addition of fluoride ions leads to
the broadening of hydrazone –NH signal at d 11.15 which
completely disappears on addition of excess of fluoride. No
effect on the chemical shift of CH and OH protons during this
process indicates that these functions do not participate in the
anion binding process. Detailed analysis of the 1H NMR
titration spectra revealed some interesting aspects about the
mode of fluoride binding with receptor 4b. Gradual addition of
fluoride ion to 4b was found to result in an upfield chemical shift
in the aromatic C–Ha protons of the p-nitrophenyl unit which
continues up to the addition of four equivalents of FÀ while
C–Hb protons are insensitive up to the addition of two equiva-
lents. Addition of fluoride beyond two equivalents was found to
through
visual
and
colorimetric
observations
in
DMSO–CH3CN (0.5 : 9.5 v/v). It was found that the receptor
4b exhibited a prominent and instant colour change from light
yellow to dark purple only with fluoride ions while 4c gave a
marked colour change on interaction with fluoride as well as
with dihydrogen phosphate and acetate anions (Fig. 1).
Receptor 4a did not give any visual response while 4d and
4e gave similar colour changes as observed in the case of 4b
and 4c, respectively on treatment with the tested anions under
similar conditions.
When investigated spectrophotometrically, the interaction
of 4b with fluoride ions exhibited a bathochromic shift (Dlmax
)
of 143 nm in its UV-visible spectrum at 5 Â 10À5 M concen-
tration with the appearance of a new absorption peak at 549
nm whereas no shift in the absorption maxima was observed
with other aÀnionic species (ClÀ, BrÀ, IÀ, H2PO4À, HSO4
,
À
AcOÀ, ClO4 and PF6À) as depicted in Fig. 2(a). It was
observed that gradual addition of a standard solution of
tetrabutylammonium fluoride (TBAF), progressively de-
creased the intensity of the absorption peak at 406 nm with
concurrent increase in the absorption peak centred at 549 nm
in the UV-visible spectrum (Fig. 2). A colour change from
yellow to light purple was observed when the concentration of
fluoride ion approached one equivalent with respect to 4b.
Fig. 1 Selectivity of 4b for fluoride over other anions. Colour changes
of 4b (a) and 4c (b) (50 mM) in DMSO–CH3CN (0.5 : 9.5 v/v) with the
addition of TBA anions (5 Â 10À4 M): A = free receptor, B = FÀ,
C = ClÀ, D = BrÀ, E = IÀ, F = H2PO4À, G = HSO4À, H = AcOÀ,
À
I = ClO4À, J = PF6
.
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Fig. 3) were observed and the saturation point could be
reached on addition of two equivalents of hydroxide ions.
These observations suggested that the deprotonation of 4b
can take place in the presence of two equivalents of hydroxide
ions while the fluoride ion interacts with 4b via hydrogen
bonds up to the addition of two equivalents after which it
leads to deprotonation of NH fragments like that in a typical
base8 and the process gets completed by the addition of four
equivalents of fluoride ion as evidenced by the appearance of a
broad signal at 16 ppm for bifluoride species (HF2À). The
proposed mode of fluoride binding with 4b through sequential
hydrogen bond formation and deprotonation was established
by 19F NMR spectroscopy. When one equivalent of fluoride
ion was added to 4b the fluoride signal shifted from d À106.4
to À143.5 ppm indicating the formation of hydrogen-bonded
fluoride (HF) species. Further addition of fluoride in excess
(8 equiv.) shifted the fluoride signal to d À140.3 ppm which
could be assigned to bifluoride (HF2À) species (see ESIw).
These findings were further confirmed by 2D COSY spectrum
of 4b in the presence of excess fluoride ion and its absence.
Deprotonation of NH fragments was established through
correlation of p-nitrophenyl protons Ha and Hb in the COSY
spectrum (see ESIw). The deprotonated 4b seems to be stabi-
lized by the delocalization of negative charge on the nitrogen
atom over the nitrophenyl group as illustrated in Scheme 2.
Similar experiments with 4c, 4d and 4e gave bathochromic
shifts in the UV-visible spectrum with fluoride ions (Table 1)
while receptors 4c and 4e exhibited shifts of lesser magnitude
in their lmax values on addition of tetrabutylammonium
dihydrogen phosphate and acetate ions (Fig. 4).
Fig. 3 Partial 1H NMR (300 MHz and 298 K) spectra of 4b (10 mM)
upon addition of various equiv. of TBAF (40 mM) in DMSO-d6.
Numbers at the left side indicate the equivalent amounts of FÀ added
(* = ArHa, ꢁ = ArHb).
The additional binding ability of receptors 4c and 4e for
dihydrogen phosphate and acetate ions can possibly be
ascribed to the comparatively less basic nature of the NH
protons due to the presence of two electron withdrawing nitro
substituents.
exhibit an upfield shift in the Hb nuclei which reached its
limiting value on addition of four equivalents of FÀ ions. This
was marked by the appearance of an additional broad signal at
about 16 ppm in the 1H NMR spectrum that could be ascribed
to the formation of a more stable bifluoride [HF2]À species19
with highest calculated hydrogen bond energy (39 kcal molÀ1).20
These observations indicate that the first two equivalents of FÀ
ions are used up to interact through hydrogen bonds with the
NH protons of hydrazone subunits of receptor 4b while addition
beyond two equivalents of fluoride results in the deprotonation
of the NH protons to induce an upfield shift of the Hb proton
due to through-bond propagation of electron density.
The UV-visible titration profile of 4c with FÀ ion have
revealed a progressive decrease of absorption maxima centered
at 389 nm and gradual appearance of a new peak at 485 nm
with a colour change from yellow to purple which reached a
saturation point on addition of four equivalents of fluoride
ions (see ESIw).
À
The titration profiles with AcOÀ and H2PO4 ions reached
their limiting values on addition of one equivalent of the
respective anions (Fig. 5). These observations suggest that
In order to confirm the deprotonation process during the
1
fluoride complexation with 4b, the UV-visible and H NMR
experiments were performed with tetrabutylammonium
hydroxide (TBAOH). The UV-visible titration experiments
of 4b with a standard solution of TBAOH, revealed a similar
spectral pattern as observed in Fig. 2(b) with the difference
that the absorption band centered at 549 nm reached its
limiting value on addition of two equivalents of hydroxide
ions (see ESIw). This can possibly be ascribed to the highly
basic nature of hydroxide ion which instantly deprotonates the
acidic hydrazone NH protons through Brønsted acid–base
type reactions. This was confirmed by the 1H NMR experi-
ments with gradual addition of hydroxide ions to a 10 mM
solution of 4b in DMSO-d6 (see ESIw). A similar pattern of
upfield chemical shifts in Ha and Hb protons (as observed in
Scheme 2 A proposed binding mode and deprotonation of 4b with
fluoride and hydroxide ions.
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Table 1 Shift in absorption peak (lmax) for receptors 4a–e in the
presence of fluoride ion
Receptors (L)
l
max/nm (L)a
l
max/nm (L + FÀ)b
Dlmax/nm
4a
4b
4cc
4d
4ec
a
342
406
389
407
387
351
549
485
548
484
09
143
96
141
97
Scheme 4
Absorption spectra were taken at a concentration of 50 mM in
b
: 9.5 v/v) solution. Tetrabutylammonium
DMSO–CH3CN (0.5
fluoride (1 Â 10À4 M) was added. Concentration was 20 mM.
c
Table 2 Association constants from UV-visible titrations for com-
plexes of receptors 4b–e with anionic guests in DMSO–CH3CN
(0.5 : 9.5 v/v)a
Ka/MÀ1
FÀ
CH3COOÀ
H2PO4
—
À
Receptor
4b
4c
4d
4e
a
9.9 Â 106
1.7 Â 106
7.3 Â 106
3.5 Â 106
—
6.3 Â 105
4.7 Â 105
5.1 Â 105
—
—
6.7 Â 105
The anions were added in the form of their TBA salts.
Fig. 4 Absorption spectra of 4c (2 Â 10À5 M) upon Àaddition of FÀ,
butylammonium salts) (1 Â 10À4 M) in DMSO–CH3CN (0.5 : 9.5 v/v).
ClÀ, BrÀ, IÀ, H2PO4À, HSO4À, AcOÀ, ClO4 and PF6 ions (as tetra-
À
recognition experiments with 5 and 6 at 100 mM concentration
revealed no change in their absorption spectra upon addition of
either tetrabutylammonium salt of acetate or dihydrogen
phosphate while small changes were observed in the absorption
spectra of 5 and 6 upon addition of TBAF. However, it was
noticed that the spectral changes were not as significant as
observed with receptors 4b and 4c within the studied fluoride
concentration range. These observations proved that although
4b, 5 and 4c, 6 have the same type of binding sites, only an
appropriate size of the pseudocavity of 4b and 4c can bind the
anions more effectively.
The receptors 4d and 4e exhibited a similar behavior in the
UV-visible and colorimetric experiments as that of 4b and
4c, respectively thereby suggesting that the azomethine CH
protons (in 4b and 4c) when replaced by a methyl group
(in 4d and 4e) do not affect the binding mode of anions. The
binding constants21 (Ka) for 4b–e with fluoride, acetate
and dihydrogen phosphate ions are summarized in Table 2.
The higher binding constant obtained for fluoride ion is
possibly due to its more basic nature that leads to a stronger
hydrogen bond interaction with the receptor molecules in
comparison to the case of acetate and dihydrogen phosphate
anions.
Fig. 5 ÀUV-visible titrations of 4c with 0–5 equiv. of (a) AcOÀ (b)
H2PO4
.
the binding of FÀ ions with 4c proceedsÀin a similar manner as
that of 4b while the AcOÀ and H2PO4 ions interact with 4c
exclusively through hydrogen bonding (Scheme 3).
To investigate the role of the preorganized structure of calix[4]-
arene, we designed other compounds 5 and 6 (Scheme 4), which
resemble the single binding pod of receptors 4b and 4c. Anion
Conclusion
We conclude that the synthesized new class of neutral calix[4]-
arene receptors with hydrazone functions at their lower rim
(4b–e) exhibit a prominent ‘naked-eye’ colour change and
significant bathochromic shifts when interacted with fluoride
ions. Receptor 4b exhibits a selective binding with fluoride ions
À
via H-bond interactions in prefereÀnce to ClÀ, BrÀ, IÀ, H2PO4
,
À
HSO4À, AcOÀ, ClO4 and PF6 ions and elicits a distinct
colour change from yellow to dark purple through efficient
Scheme 3 A proposed binding mode of 4c with acetate ion.
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deprotonation. These observations pave
a
way for the
Compound 4d. Yield (89%, 1.21 g); mp 167 1C; IR (KBr)
n
max/cmÀ1: 3298, 1596, 1508; 1H NMR (DMSO-d6) d 10.94 (s,
2H, NH), 8.30 (s, 2H, OH), 8.07 (d, J = 8.7 Hz, 4H, ArHNO ),
development of selective colorimetric sensors for fluoride ions.
Further work on this subject is in progress.
2
7.78 (d, J = 8.4 Hz, 4H, ArH), 7.00–7.06 (m, 16H, ArHNO
+
2
ArH + ArHcalix), 6.84 (t, J = 7.2 Hz, 2H, ArHcalix), 6.63
(t, J = 7.2 Hz, 2H, ArHcalix), 4.53 (br s, 4H, OCH2CH2CH2),
4.21 (d, J = 12.8 Hz, 4H, ArCH2Ar), 4.17 (br s, 4H,
CH2CH2CH2O), 3.38 (d, J = 12.8 Hz, 4H, ArCH2Ar), 2.45
(br s, 4H, CH2CH2CH2), 2.29 (s, 6H, CCH3). 13C NMR
(75 MHz, DMSO-d6): d 161.3, 152.1, 151.5, 144.5, 134.4,
129.4, 128.9 128.5, 128.0, 127.71 126.4, 123.1, 119.6, 115.8,
114.6, 73.4, 64.8, 30.42 29.5, 12.3. FAB MS m/z 1047 (M + 1,
calc. 1046). Anal. calc. for C62H58N6O10: C, 71.11; H, 5.58; N,
8.03. Found C, 70.85; H, 5.31; N, 8.15%.
Experimental
Synthesis of starting materials
Compounds 1, 2, 3a and 3b were synthesized by the methods
reported earlier.12a
Synthesis of calix[4]arene-bis(phenylhydrazone) derivative 4a.
A solution of 3a (0.97 g, 1.3 mmol) in 35 ml of acetonitrile–
ethanol (1 : 1 v/v) was treated with 17.0 ml of phenylhydrazine
solution.22 The mixture was heated on a water bath (50 1C)
until crystallization began. Further crystallization was allowed
to continue at room temperature and the product obtained
was filtered off and dried under vacuum to give calix[4]arene-
bis(phenylhydrazone) derivative 4a as an off-white solid, yield
(88%, 1.089 g); mp 185 1C; IR (KBr) nmax/cmÀ1: 3289, 1605;
1H NMR (300 MHz, CDCl3): d 10.49 (s, 2H, NH), 8.05 (s, 2H,
OH), 7.43 (d, 4H, ArH, J = 7.8 Hz), 7.36 (s, 2H, –NQCH),
7.18 (br s, 4H, ArH), 6.97 (m, 10H, ArH), 6.84 (br s, 8H,
ArH), 6.68 (t, J = 7.2 Hz, 2H, ArH), 6.58 (t, J = 7.2 Hz, 2H,
ArH), 4.29 (br s, 4H, OCH2CH2CH2), 4.19 (d, J = 13.2 Hz,
4H, ArCH2Ar), 4.08 (br s, 4H, CH2CH2CH2O), 3.30 (d, J =
13.2 Hz, 4H, ArCH2Ar), 2.33 (br s, 4H, CH2CH2CH2). 13C
NMR (75 MHz, CDCl3): d 157.9, 154.2, 150.2, 147.2, 141.3,
138.2, 133.2, 128.3, 128.2, 127.3, 126.1, 125.4, 124.2, 117.5,
114.2, 111.0, 72.13 63.47 30.4, 28.5. FAB MS m/z 929 (M + 1,
calc. 928). Anal. calc. for C60H56N4O6: C, 77.56; H, 6.08;
N, 6.03. Found C, 77.11; H, 5.98; N, 6.21%.
General procedure for the synthesis of calix[4]arene-bis(2,4-
dinitrophenylhydrazone) derivatives (4c and 4e). A solution of 3a
(0.97 g, 1.3 mmol) and 3b (1.01 g, 1.3 mmol) in 35 ml of
chloroform–ethanol (1
: 2 v/v), 2,4-dinitrophenylhydrazine
(0.63 g, 3.2 mmol) and 2 ml of concentrated sulfuric acid was
added. The mixture was stirred at room temperature for 5 h. After
completion of the reaction (monitored through TLC) the precipi-
tate obtained was filtered off, washed with ethanol (3 Â 20 ml) and
dried under vacuum to give calix[4]arene-bis(2,4-dinitrophenyl-
hydrazone) derivatives 4c and 4e as red solids.
Compound 4c. Yield (93%, 1.33 g); mp 4280 1C (charred);
1
IR (KBr) nmax/cmÀ1: 3287, 1613, 1507; H NMR (300 MHz,
DMSO-d6): d 11.43 (s, 2H, NH), 8.76 (s, 2H, OH), 8.47 (s, 2H,
ArHNO ), 8.46 (s, 2H, –NQCH), 8.26 (d, J = 9.3 Hz, 2H,
ArHNO ), 7.88 (d, J = 9.3 Hz, 2H, ArHNO ), 7.63 (d, J =
2
2
2
8.0 Hz, 4H, ArH), 7.19 (d, J = 7.2 Hz, 4H, ArHcalix), 7.10 (d,
J = 7.2 Hz, 4H, ArHcalix), 7.00 (d, J = 8.04 Hz, 4H, ArH),
6.83 (t, J = 7.5 Hz, 2H, ArHcalix), 6.63 (t, J = 7.5, 2H,
ArHcalix), 4.46 (br s, 4H, OCH2CH2CH2), 4.23 (d, J =
12.8 Hz, 4H, ArCH2Ar), 4.16 (br s, 4H, CH2CH2CH2O),
3.49 (d, J = 12.8 Hz, 4H, ArCH2Ar), 2.43 (br s, 4H, CH2C-
H2CH2). 13C NMR (75 MHz, DMSO-d6): d 160.2, 152.3,
151.3, 148.9, 144.0, 136.5, 133.3, 129.1, 128.7, 128.2, 127.5,
126.1, 125.0, 122.3, 118.8, 116.2, 114.6, 72.6, 64.3, 30.2, 29.2.
FAB MS m/z 1109 (M + 1, calc. 1108). Anal. calc. for
C60H52N8O14: C, 64.98; H, 4.73; N, 10.10. Found C, 64.91;
H, 4.69; N, 10.05%.
General procedure for the synthesis of calix[4]arene-bis-
(4-nitrophenylhydrazone) derivatives (4b and 4d). A solution
of 3a (0.97 g, 1.3 mmol) and 3b (1.01 g, 1.3 mmol) in 35 ml of
chloroform–ethanol mixture (1
: 2 v/v), 4-nitrophenyl-
hydrazine (0.50 g, 3.2 mmol) and 2 ml of glacial acetic acid
was added. The mixture was refluxed for 6 h and then cooled
to room temperature. The whole reaction mixture was evapo-
rated and distilled water was added to it. The precipitate
obtained was filtered off, washed with water (3 Â 25 ml) and
then dried under vacuum to give calix[4]arene-bis(4-nitrophenyl-
hydrazone) derivatives 4b and 4d as yellow solids.
Compound 4e. Yield (94%, 1.38 g); mp 4282 1C (charred);
1
IR (KBr) nmax/cmÀ1: 3307, 1610, 1505; H NMR (300 MHz,
Compound 4b. Yield (91%, 1.20 g); mp 165 1C; IR (KBr)
DMSO-d6) d 10.89 (s, 2H, NH), 8.69 (s, 2H, OH), 8.44 (s, 2H,
ArHNO ), 8.24 (d, J = 9.3 Hz, 2H, ArHNO ), 7.82 (d, J =
n
max/cmÀ1: 3294, 1598, 1501; 1H NMR (300 MHz, DMSO-d6):
2
2
d 11.15 (s, 2H, NH), 8.46 (s, 2H, OH), 8.11 (d, J = 8.9 Hz, 4H,
9.3 Hz, 2H, ArH), 7.76 (d, J = 8.1 Hz, 4H, ArH), 7.13 (d, J =
6.9 Hz, 4H, ArHcalix), 7.05 (d, J = 7.2 Hz, 4H, ArHcalix), 6.96
(d, J = 8.1 Hz, 4H, ArH), 6.80 (t, J = 7.2 Hz, 2H, ArH), 6.59
(t, J = 7.2 Hz, 2H, ArH), 4.35 (br s, 4H, OCH2CH2CH2),
4.16 (d, J = 12.6 Hz, 4H, ArCH2Ar), 4.10 (br s, 4H,
CH2CH2CH2O), 3.51 (d, J = 12.6 Hz, 4H, ArCH2Ar), 2.38
(br s, 4H, CH2CH2CH2), 2.21 (s, 6H, CCH3), 13C NMR
(75 MHz, DMSO-d6): d 160.2, 152.3, 151.3, 144.1, 133.7,
129.9, 128.9, 128.5, 128.0, 127.7, 125.4, 122.7, 119.2, 116.3,
114.2, 73.0, 64.3, 30.4, 29.4, 12.7. FAB MS m/z 1137 (M + 1,
calc. 1136). Anal. calc. for C62H56N8O14: C, 65.48; H, 4.96; N,
9.85. Found C, 65.21; H, 4.79; N, 10.05%.
ArHNO ), 7.98 (s, 2H, –NQCH), 7.68 (d, J = 8.3 Hz, 4H,
ArH), 7.09–7.20 (m, 16H, ArHNO + ArH + ArHcalix), 6.82
2
2
(t, J = 7.2 Hz, 2H, ArHcalix), 6.61 (t, J = 7.2 Hz, 2H,
ArHcalix), 4.52 (br s, 4H, OCH2CH2CH2), 4.17 (m, 8H,
ArCH2Ar + CH2CH2CH2O), 3.48 (d, J = 12.7 Hz, 4H,
ArCH2Ar), 2.41 (br s, 4H, CH2CH2CH2). 13C NMR
(75 MHz, DMSO-d6): d 158.7, 152.0, 150.6, 149.8, 140.5,
137.6, 132.8, 128.1, 127.6, 127.0, 126.8, 125.1, 124.8, 118.5,
113.7, 110.1, 72.1, 63.4, 30.2, 28.8. FAB MS m/z 1019 (M + 1,
calc. 1018). Anal. calc. for C60H54N6O10: C, 70.71; H, 5.34; N,
8.25. Found C, 70.65; H, 5.25; N, 8.05%.
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Synthesis of compound 5. To a solution of benzaldehyde
(1.0 g, 9.3 mmol) in 35 ml of ethanol, 4-nitrophenylhydrazine
(1.73 g, 0.01 mol) and 2 ml of glacial acetic acid was added.
The mixture was refluxed for 3 h and then cooled to room
temperature. The whole reaction mixture was evaporated and
distilled water was added to it. The precipitate obtained was
filtered off, washed with water (3 Â 25 ml) and then dried
under vacuum to give 5 (yield 97%, 2.20 g) as a light yellow
Acknowledgements
The authors gratefully acknowledge the assistance received
from the Sophisticated Analytical Instrument Facility, CDRI,
Lucknow for FAB-MS spectra, DST, DBT, MOEF, MFPI
and MRD, Govt. of India for financial assistance and the
Council of Scientific and Industrial Research, India for senior
research fellowships to S. N. S and R. S.
1
solid; mp 137 1C; IR (KBr) nmax/cmÀ1: 1593, 1501; H NMR
(300 MHz, DMSO-d6): d 11.26 (s, 1H, NH), 8.17 (d, J =
References
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7.9 Hz, 2H, ArH), 7.16 (d, J = 8.4 Hz, 2H, ArHNO ),
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1
1502; H NMR (300 MHz, DMSO-d6): d 11.49 (s, 1H, NH),
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2
8.9 Hz, 1H, ArHNO ), 7.83 (d, J = 8.9 Hz, 1H, ArHNO ), 7.42
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2
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