Triazole-linked anthracenyl-appended calix[4]arene conjugate as receptor for co(II): Synthesis, spectroscopy, microscopy, and computational studies

Article abstract of DOI:10.1021/jo400038x

A new triazole-linked anthracenyl-appended calix[4]arene-1,3-diconjugate (L) has been synthesized and characterized, and its single crystal XRD structure has been established. Binding properties of L toward different biologically relevant metal ions have been studied by fluorescence and absorption spectroscopy in ethanol. L exhibits selective recognition of Co²⁺ and can detect down to a concentration of 55 ppb (0.92 μM). The roles of the calix[4]arene platform as well as the preorganized binding core in L's selective recognition have been demonstrated by studying appropriate control molecules. The mode of binding of L with Co²⁺ has been modeled both by DFT and MD computational calculations. L and its Co²⁺ complex could be differentiated on the basis of the nanostructural features observed in AFM and TEM.

Full text of DOI:10.1021/jo400038x

Article
pubs.acs.org/joc
Triazole-Linked Anthracenyl-Appended Calix[4]arene Conjugate As
Receptor for Co(II): Synthesis, Spectroscopy, Microscopy, and
Computational Studies
V. V. Sreenivasu Mummidivarapu,† Vijaya Kumar Hinge,‡ Khatija Tabbasum,† Rajesh G. Gonnade,§
and Chebrolu P. Rao*,†,‡
‡
†Department of Chemistry and Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Powai,
Mumbai 400 076, India
§Center for Materials Characterization, National Chemical Laboratory, Pune 411 008, India
S
* Supporting Information
ABSTRACT: A new triazole-linked anthracenyl-appended
calix[4]arene-1,3-diconjugate (L) has been synthesized and
characterized, and its single crystal XRD structure has been
established. Binding properties of L toward different bio-
logically relevant metal ions have been studied by fluorescence
and absorption spectroscopy in ethanol. L exhibits selective
recognition of Co2+ and can detect down to a concentration of
55 ppb (0.92 μM). The roles of the calix[4]arene platform as
well as the preorganized binding core in L’s selective
recognition have been demonstrated by studying appropriate
control molecules. The mode of binding of L with Co2+ has
been modeled both by DFT and MD computational
calculations. L and its Co2+ complex could be differentiated
on the basis of the nanostructural features observed in AFM
and TEM.
of L. In turn, the 9-(azidomethyl) anthracene was synthesized
from 9-chloromethyl anthracene. A single strand analogue
devoid of the calix[4]arene platform, L1 has been synthesized
by two steps starting from p-tert-butylphenol instead of p-tert-
butyl-calix[4]arene.7
INTRODUCTION
■
Cobalt is one of the most essential micronutrients and is
present in about 0.3 mg/L concentration in ocean water. The
∼1.5 mg that is present in an adult human body is distributed in
the liver, kidney, and bone.1 Cobalt also plays important role in
the metabolism of iron and thereby in the synthesis of
hemoglobin.2 It is an essential trace element found in the
cobalamin coenzyme (vitamin B12) associated with a number of
enzymes.3 Deficiency of cobalt may cause anemia, retarded
growth, and loss of appetite.1b,4 In large doses, cobalt salts can
be toxic.5 There is an increased interest in studying cobalt in
environmental and biological samples. Thus the development
of synthetic receptors for the selective recognition of cobalt
continues to intrigue researchers. Although there are a few
small molecular chemosensors for Co2+ in the literature, there is
only one in the case of calix[4]arene.6 In this regard, we report
the synthesis, characterization, and metal ion binding studies of
a 1,3-diderivative of calix[4]arene appended to anthracenyl
moiety through a triazole linker and its selectivity toward Co2+.
1
P1, P2, L1, and L were well characterized by H, 13C nuclear
magnetic resonance (NMR), Fourier transform infrared
spectroscopy (FTIR), and high resolution mass spectrometry
(HRMS) (Experimental Section and Supporting Information
1
S1−S4). H NMR spectrum of L supported the presence of
cone conformation as can be noticed from the appearance of
peaks at 2.82 and 3.61 ppm for the bridge -CH2 moiety. The
cone conformation has been further confirmed from the
structure determined on the basis of single crystal X-ray
diffraction (XRD) as reported in this paper. On the other hand,
the two -CH2 groups, viz., the one attached to the anthracenyl
moiety and the other one attached to the lower rim ‘O’ were
identified as 6.46 ppm {cross peak (i)} and 4.80 ppm {cross
peak (ii)} could be differentiated from the heteronuclear single
quantum correlation (HSQC) spectra (Figure 1).
RESULTS AND DISCUSSION
Single Crystal X-ray Structure of the Receptor
Molecule. Single crystals of the receptor were obtained from
■
The receptor molecule L was synthesized in two steps (Scheme
1) starting from p-tert-butylcalix[4]arene, P by reacting with
propargyl bromide to form a dipropargyl, P2. Reaction of P2
with 9-(azidomethyl) anthracene (P1) results in the formation
Received: January 8, 2013
© XXXX American Chemical Society
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a
Scheme 1. Synthesis of L
a
(a) NaN3, DMF; (b) K2CO3, propargyl bromide, dry acetone, 16 h; (c) P1, CuSO4·5H2O, sodium ascorbate, {dichloromethane (5 mL) + tert-
butanol (5 mL) + water (10 mL)}, 24 h. L1 is a control molecule without the calix[4]arene platform.
present between the neighbor anthracene units can be seen
from the packing of molecules in the lattice. The distance
between the centroids of two anthracenyl moieties is 4.18 Å
(Figure 2b). A metal ion binding core of N2O4 is present in L,
and the preorganized binding core can interact with the
incoming metal ion. The stereoview shows that while one of
the anthracenyl moiety is bent inward, the other is bent
outward with respect to the calix[4]arene platform (Supporting
Information, S5).
Fluorescence Titration Studies of L with M2+ in
Ethanol. The ion recognition of L has been studied by
exciting the corresponding solutions at 368 nm and measuring
the emission in the 378−550 nm range. Thus, among Na+, K+,
Mg2+, Ca2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Ag+, and
Hg2+ ions studied, only Co2+ exhibited fluorescence quenching
upon titration with L. As the concentration of Co2+ increases,
the fluorescence intensity of 417 nm band decreases by an
extent of ∼5 1 fold (Figure 3, Supporting Information, S6).
Figure 1. HSQC (1H−13C) spectra for L in DMSO-d6.
The minimum concentration at which L can detect Co2+ was
obtained from a dilution experiment carried out by keeping the
mole ratio of L and Co2+ as 1:1 and was found to be 55 ppb
(0.92 μM) (Supporting Information, S7). The quenching
constant of L by Co2+ has been derived by Stern−Volmer
equation, and the corresponding quenching constant, Kq, was
found to be 476,552 20000 M−1 (Supporting Information,
S8).
slow evaporation of a solution of L dissolved in CHCl3, and
these were found to be triclinic with Pi space group
̅
(Supporting Information, Table S1). The single crystal XRD
structure of L exhibits cone conformation for the calixarene by
retaining two intrarim O−H···O hydrogen bonds with O···O
distance of 2.34 Å at the lower rim (Figure 2a). The distance
between the two phenolic oxygens at the lower rim is 3.29 Å,
and the distance between the centroid of the phenyl to the
centroid of the anthracene moiety is 4.50 Å. The circular
hydrogen bonding stabilizes the L in cone conformation and
Similar fluorescence studies were carried out with the control
molecules such as P1 and L1 and found no significant change in
the emission intensity, suggesting that a preorganized binding
core in L is indeed required for such recognition (Figure 4a).
The formation of a 1:1 complex was confirmed by ESI MS,
1
was confirmed by the H NMR studies. The π···π interactions
Figure 2. (a) Stereoview of the molecular structure of L as obtained from the single crystal XRD. (b) Crystal packing diagram of L.
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Figure 3. Fluorescence studies of L with metal ions: (a) fluorescence spectra obtained during the titration of L with Co2+ in ethanol (λex = 368 nm);
(b) fluorescence intensity as a function of [Co2+]/[L] mole ratio; (c) relative fluorescence intensity of L in the presence of different metal ions.
Figure 4. (a) Relative fluorescence intensity for Co2+ titration of L, L1, and P1. ESI mass spectrum showing the isotopic peak pattern of the
molecular ion peak for the 1:1 complex formed between L and Co2+: (b) experimental and (c) calculated.
Figure 5. Absorption spectra during the titration with Co2+ in ethanol: (a) L, (b) L1, and (c) P1. (d) Plots of absorbance versus mole ratio of
[Co2+]/[L] for different bands.
where the spectrum shows a molecular ion peak at m/z of
1248.6, and the observed isotopic peak pattern supports the
presence of Co2+ (Figure 4b,c).
moiety (Figure 6). Similar titration carried out with L1
exhibited upfield shift as well as broadening in the anthracenyl
-CH2 peak as the metal ion concentration increases
(Supporting Information, Figure S19).
Microscopy Studies. The receptor L comprises spherically
shaped particles that are well spread all over the mica surface as
studied by AFM. However, in the presence of Co2+, these
particles seem to merge to result in aggregation, as noticed by
their increased size. Thus the size of the particles change from
150 30 nm in pure L to 540 80 nm in the presence of Co2+
as a result of the metal ion induced aggregation (Figure 7a and
b).
Absorption Spectral Studies of L and Reference
Molecules with Co2+. In order to confirm the binding of
Co2+ by L, absorption spectral titrations were carried out in
ethanol. The isosbestic points observed at 266 and 303 nm
suggest the complex formation between L and Co2+ (Figure 5,
Supporting Information, S9). On the other hand, the control
molecule, L1, and the precursor molecule, P1, did not show any
significant change in the absorbance when titrated with Co2+,
suggesting that L is sensitive and selective toward Co2+.
1
1H NMR Titration of L with Co2+. During the H NMR
Even TEM reveals the formation of spherically shaped
vesicular particles over the carbon-coated copper grids for L.
These spherical vesicular particles vary in size at 500 100 nm.
In presence of Co2+, these appear to form chainlike structures
as a result of the aggregation promoted by the metal ion
coordination (Supporting Information, S11). Thus, both AFM
and TEM showed clear-cut changes in the nature and size of
titration of L with Co2+, as the metal ion concentration
increases, the anthacenyl -CH2 peak shifts toward upfield and
finally merges with the aromatic proton signals of calix[4]arene.
Changes were also observed in the region of the anthracenyl
moiety. There are no changes observed in the remaining
regions of the spectrum, suggesting that Co2+ interacts in the
region of the calix[4]arene lower rim and the anthracenyl
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Figure 6. 1H NMR spectra measured during the titration of L with Co2+ (in DMSO-d6): (i) 0, (ii) 0.25, (iii) 0.50, (iv) 0.75, (v) 1.0, (vi) 1.5, (vii) 2.0,
(viii) 2.5, and (ix) 3.0 equiv.
Gaussian 03 package8 (Experimental Section) to establish the
complexation features of [CoL]. In order to do that, initially the
crystal structure of L was optimized by DFT. The optimized L
was subjected to the interaction with Co2+, and the
corresponding complex was further optimized (Experimental
Section and Supporting Information, S12). In the optimized
structure of the complex, the Co2+ occupies distorted
octahedral geometry, by bonding through two each of
phoenolate and ether oxygens, and two triazole nitrogens
resulting in an N2O4 binding core (Figure 8). The geometry
optimization of the cobalt complex resulted in conformational
changes at the arms in order to accommodate the metal ion.
This can be gauged from the dihedral angles of the arm and the
distance between the two arms. In the process of optimization
Figure 7. Noncontact mode AFM images of (a) L and (b) {L + Co2+}.
TEM images: (c and d) for L and (e and f) for {L + Co2+}.
of the complex, the anthracenyl moieties were spread out and
the nitrogens of the triazole moieties turned to the interior of
the calixarene to form a phenolate core to bind Co2+. The
highest occupied molecular orbitals (HOMOs) and lowest
unoccupied molecular orbitals (LUMOs) were calculated for
the L, [CoL] (Supporting Information, S13) and demonstrated
the particles formed from L and its Co2+ complex (Figure 7c−
f).
Structural Features of [CoL] by Density Functional
Theory. Computational calculations were carried out using the
Figure 8. DFT optimized structures: (a) [L] and (b) [CoL]. (c) An expanded version of the primary coordination sphere of Co2+. The bond lengths
(Å) and bond angles (deg) in the coordination sphere are O1−Co = 1.891, O2−Co = 1.890, N1−Co = 1.935, N2−Co = 1.936, O3−Co = 2.271,
O4−Co = 2.270; O1−Co−O2 = 85.5, O1−Co−N1 = 91.9, O1−Co−N2 = 165.9, O1−Co−O3 = 83.2, O1−Co−O4 = 88.3, O2−Co−N1 = 165.8,
O2−Co−N2 = 92.0, O2−Co−O3 = 88.2, O2−Co−O4 = 83.2, N1−Co−N2 = 93.6, N1−Co−O3 = 77.6, N1−Co−O4 = 110.5, N2−Co−O3 =
110.5, N2−Co−O4 = 77.6, O3−Co−O4 = 168.5.
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that the phenolate O− and triazole N− core are involved in Co2+
binding.
geometry, by bonding through two phoenolate and two ether
oxygens, and two triazole nitrogens to have a N2O4 binding
core. The hexa-coordination of Co2+ has been further
confirmed from the analysis of the complex species formed
when subjected to the molecular dynamics studies. Thus L can
be used as selective receptor toward Co2+ by fluorescence and
nano structural features.
Conformation of the Arms in Presence of Co2+ by MD
Studies. The conformational aspects of the arms of L upon
binding Co2+ were monitored by analyzing the complex species
formed between L2‑ and Co2+, viz., [LCo] at 0.1-, 1-, and 2-ns
simulations carried out by molecular dynamics (Experimental
section and Supporting Information, S14). Examination of the
cobalt center clearly exhibited six coordinations using the N2O4
core that is evolved through these simulations, though the
geometry does not fit well with a conventional octahedron. The
study clearly showed conformational dynamism of the arms to
accommodate the Co2+ ion at the lower rim. This can be very
well appreciated when the structure of L in [LCo] is compared
with that in the crystal structure. Thus both DFT and MD
studies showed coordination around the Co2+ to be the same.
Time-Dependent Fluorescence Intensity of L When
Titrated with Co2+. As the Co2+-treated L solutions left in air
showed increase in the fluorescence intensity, a systematic
study was carried out to gauge the fluorescence enhancement of
these solutions as a function of time by measuring the intensity
at different time intervals, viz., 0.5, 1, 3, 6, and 10 h. Initially the
fluorescence intensity of L decreases as Co2+ concentration
increases, and when these solutions are left as is, the intensity
once again increases as a function of time and by ∼10 h the
fluorescence intensity is same as that of simple L, suggesting
oxidative detachment of the cobalt ion (Figure 9).
EXPERIMENTAL SECTION
■
General Information and Materials. Single crystal X-ray
diffraction data for L were collected at low temperature (160 K).
NMR spectra were recorded on a 400 MHz spectrometer. FTIR
spectra were recorded from their KBr pellets. HRMS spectra were
recorded by Q-TOF using electrospray ionization method.
Fluorescence and Absorption Titrations. Fluorescence emis-
sion spectra were measured by exciting the samples at 368 nm, and the
emission spectra were recorded in the 378−600 nm range. The bulk
solutions of L and metal ions were prepared in C2H5OH in which 100
μL of CHCl3 was used for dissolving L. Bulk solution concentration of
L and metal ion concentration were maintained at 6 × 10−5 M. All
measurements were made in 1-cm quartz cells, and the effective
cuvette concentration of L was maintained as 5 μM in all of the
titrations. During the titration, the concentration of metal ions was
varied accordingly in order to result in requisite mole ratios of these to
L by taking a fixed volume and varying volumes of the solution of the
metal ions. The total volume of the solution used for the fluorescence
measurements was maintained constant at 3 mL in all the cases by
simply adding the requisite volume of ethanol as the making up
solvent. In the case of absorption titrations the bulk solutions of L and
metal ions were prepared in C2H5OH in which 100 μL of CHCl3 was
used for dissolving L. Bulk solution concentration of L and metal ion
concentration were maintained at 6 × 10−3 M. All measurements were
made in 1-cm quartz cells, and the effective cuvette concentration of L
was maintained as 5 μM in all of the titrations.
Microscopy Studies. The AFM samples of L and [L + Co2+] were
prepared at 6 × 10−5 M concentration in ethanol. The receptor L was
initially dissolved in 100 μL of CHCl3 and then made up with ethanol
to the desired concentration. The stock solutions of these were
sonicated for 15 min. A 50−100 μL aliquot was taken from this stock
solution to spread over a mica sheet using the drop cast method. The
samples were then dried and analyzed by AFM. The TEM samples of
L and [L + Co2+] were prepared at 6 × 10−3 M concentration in
ethanol. The receptor L was initially dissolved in 100 μL of CHCl3 and
then in ethanol. The stock solutions of L and [L + Co2+] were
sonicated for 15 min, after which a 50−100 μL aliquot was taken and
spread over the carbon-coated grid using the drop cast method.
Synthesis and Characterization of P1. A mixture of 9-
(chloromethyl)anthracene (1.0 g, 4.41 mmol) and sodium azide
(0.43 g, 6.62 mmol) was taken in 20 mL of DMF. The resulting
solution was stirred for 12 h at room temperature. After completion of
the reaction, water was added to the reaction mixture and extracted
with EtOAc (3 × 30 mL), and the resulting extract was washed with
water followed by brine solution. A pure product was obtained by
evaporating the organic solvent (yield 0.95gm, 92%). 1H NMR
(CDCl3, 400 MHz, δ ppm) 5.32 (s, 2H, anthracene-CH2), 7.48−7.61
(m, 4H, anthracene-H), 8.04 (d, 2H, J = 8.84, anthracene-H), 8.28 (d,
2H, J = 8.84, Anthracence-H), 8.50 (s, 1H, anthracene-H). 13C NMR
(CDCl3, 100 MHz, δ ppm): 46.5 (anthracene-CH2), 123.7, 125.4,
125.9, 127.0, 129.2, 129.5, 130.9, 131.6 (anthracene-Ar-C) . HRMS:
for C15H11N3: calculated: 233.0953 found: 233.0957 FTIR (KBr,
cm−1): 2096 (ν−N3), 2968 (ν−C−H).
Figure 9. Time-dependent fluorescence intensity of [L + 5 equiv
Co2+].
Conclusions and Correlations. A new triazole-linked
anthracenyl-based 1,3-diconjugate of calix[4]arene (L) and two
control molecules have been synthesized and were well
1
characterized by various techniques. While the H NMR of
the receptor L supports cone confirmation, this has been
proven by establishing the single crystal XRD structure. L
showed selectivity toward Co2+ among 13 biologically and
ecologically relevant metal ions, viz., Na+, K+, Mg2+, Ca2+, Mn2+,
Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Ag+, and Hg2+ as studied by
fluorescence and absorption spectroscopy. L can detect Co2+
down to 55 ppb (0.92 μM), and its fluorescence quenching
constant, Kq, is (4.8
0.2) × 105 M−1. Comparison of the
fluorescence results of L with those of the control, L1, and
precursor, P1, clearly suggests the necessity of the calix[4]arene
platform for the selective detection of Co2+ ion. While the Job’s
plot supported the formation of 1:1 complex between L and
Co2+, the same has been confirmed by ESI-MS. Both the AFM
and TEM showed nanostructural features sufficient enough to
differentiate L from its cobalt complex, particularly based on
the shape and size of the particles. The complexation between
L and Co2+ has been further addressed by computational
modeling wherein the Co2+ occupies distorted octahedral
Synthesis and Characterization of P2. A mixture of potassium
carbonate (5.18 g, 37.34 mmol) and p-tert-butylcalix[4]arene (10.0 g,
15.43 mmol) in acetone (200 mL) was stirred at room temperature for
1 h. Propargyl bromide (6.34 g, 53.08 mmol) was added dropwise into
the stirred mixture over 30 min. The reaction mixture was refluxed for
24 h and then allowed to cool to room temperature. This was then
filtered over Celite to remove insoluble particles and the filtrate was
concentrated by a rota-evaporator. A 100 mL of 2 M HCl was added
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to the concentrated reaction mixture and the product was extracted
with dichloromethane (3 × 100 mL). The combined organic extracts
were successively washed with water and brine (100 mL), dried over
anhydrous Na2SO4, filtered and evaporated to dryness in vacuo. The
crude product was recrystallized from CH2Cl2/CH3OH to afford 2 as
a white solid (Yield, 82%). 1H NMR (CDCl3, 400 MHz, δ ppm): 7.07
(s, 4H, Ar-H), 6.73 (s, 4H, Ar-H), 6.50 (s, 2H, OH), 4.74 (d, J = 2.4
Hz, 4H, OCH2), 4.37 (d, J = 13.4 Hz, 4H, ArCH2Ar), 3.33 (d, J = 13.4
Hz, 4H, ArCH2Ar), 2.54 (t, J = 2.4 Hz, 2H, CCH), 1.30 (s, 18H,
(CH3)3), 0.90 (s, 18H, (CH3)3); 13C NMR (CDCl3, 100 MHz, δ
ppm): 31.1 (-C(CH3)3), 31.9, 32.2 (-C(CH3)3), 34.0, 34.0 (Ar-CH2−
Ar), 63.5 (-O-CH2), 76.5 (-CCH), 78.9 (-CCH), 125.2, 125.7,
128.2, 132.7, 141.8, 147.4, 149.6, 150.5 (Ar-C). HRMS m/z Calcd for
C50H60O4: 725.4570, Found 725.4565 FTIR (KBr, cm−1): 2968
(ν−C−H), 3308 (ν−C−H), 3505 (ν−OH).
and the complex was optimized using B3LYP/6-31G(d,p). The output
obtained at every stage was given as the input for the next higher level
of calculations. In order to make the cobalt complex, [L′(Co)], the
phenolic OH groups were deprotonated and the resulting (L′)2− was
used for further studies. The complex formation was initiated by
placing the Co2+ far away from both arms of (L′)2− in such a way that
the phenolate-O, triazole-N atoms are pointed toward the cobalt
center. The molecular orbital’s (MOs) were generated by using Gauss
view software.
Molecular Dynamics Studies. The DFT optimized structure of L
at B3LYP/-6-31G was used as the starting model. Thus the
interactions present between L and the Co2+ were modeled by
carrying out molecular dynamics (MD) simulations under vacuum
using the GROMOS96 43a1 force field available with the GROMACS
4.0.5 software package.9a,b The force fields were generated for L using
PRODRG server.9c The charges were calculated for using ChelpG9d
method (available with G03) and were added to the topology file that
was generated by PRODRG. The simulations were carried out for 2 ns
with the system where one of the complex, L plus 10 copies of Co2+
were taken in a cubic box. The total contents of the system were
energy minimized for ∼2,000 steps with the Steepest Descent (SD)
method.9e Then the whole cubic box was allowed for simulation under
NVT condition (T = 300 K) with the equation of motion being
integrated by the leapfrog algorithm with a step size of 2 fs. At the time
of carrying out the computations L and the Co2+ were coupled
separately to v-rescale temperature bath. The electrostatic interactions
were calculated using the particle Mesh Ewald summation method.9f
All bond lengths of L were constrained using the LINCS9g algorithm.
NMR Titration. The binding of Co2+ by L was further conformed
Synthesis and Characterization of L. A mixture of calix[4]-
dipropargyl, P2 (0.6 g, 0.4 mmol), and 9-(azidomethyl)anthracene
(0.48 g, 0.9 mmol) were taken in 20 mL of {dichloromethane (5 mL)/
tert-butanol (5 mL)/water (10 mL)}. To this were added
CuSO4·5H2O (0.082 g, 0.016 mmol) and sodium ascorbate (0.130
mg, 0.066 mmol). The resulting reaction mixture was stirred for 12 h
at room temperature. Upon completion of the reaction as monitored
by TLC, the organic layer was separated, and the aqueous layer was
extracted with dichloromethane (2 × 50 mL). The combined organic
layers was washed with brine (2 × 50 mL) and dried over anhydrous
Na2SO4, the mixture was filtered, and the solvent was removed under
vacuum The crude product was purified by column chromatography
using EtOAc/petroleum ether (2:8) (yield 0.55 g, 60%). Pale yellow
1
crystalline solid, mp 285−288 °C. H NMR (CDCl3, 400 MHz, δ
1
by H NMR titration. The receptor L (0.01 M) was dissolved in 0.4
ppm): 0.79 (s, 9H, -C(CH3)), 1.27 (s, 9H, -C(CH3)), 2.81 (d, 4H, Ar-
CH2eq-Ar, J = 12.8), 3.62 (d, 4H, Ar-CH2eq-Ar, J = 12.8), 4.80 (s, 4H,
-O-CH2), 6.30 (s, 4H, anthracene-CH2-triazole), 6.47 (s, 4H, Ar-H),
6.80 (s, 4H, Ar-H), 7.22 (s, 2H, triazole-H), 7.41−7.46 (m, 8H,
anthracenyl-H), 7.92−7.95 (m, 4H, anthracenyl-H), 8.08 − 8.11 (d,
4H, anthracenyl-H, J = 9.2), 8.36 (s, 2H, anthracenyl-H). 13C NMR
(CDCl3, 100 MHz, δ ppm): 30.9, 31.1 (-C(CH3)3), 31.6, 31.9
(-C(CH3)3), 33.9, 33.9 (Ar-CH2-Ar), 47.0 (anthracence-CH2-triazole),
69.6 (Ar-CH2-triazole), 122.8, 123.1, 123.4, 125.0, 125.5, 125.5, 127.4,
127.7, 129.7, 130.2, 130.7, 131.2, 132.2, 141.7, 144.5, 147.3, 149.6,
149.9 (Ar-C). HRMS for C80H83O4N6: calcd 1191.6476, found
1191.6536. FTIR (KBr, cm−1): 3018 (ν‑C‑H), 3428 (ν‑OH).
1
mL of DMSO-d6, and the H NMR spectrum was recorded in the
absence of metal ion. Metal ion titrations were carried out by adding
different volumes of Co(ClO4)2·6H2O (0.1 M) solutions, viz., 5, 10,
20, 30, 40, 60, 80, and 120 μL to the solution of L, which resulted in a
[Co2+]/[L] mole ratio of 0 to 3
ASSOCIATED CONTENT
* Supporting Information
■
S
1H and 13C NMR, mass spectral data of P1, P2, L, and L1;
fluorescence and absorbance spectra of all metal ions; 1H NMR
titration of L1 with Co2+; crystal data for L; DFT and MD data
for L and [CoL]. This material is available free of charge via the
Internet at http://pubs.acs.org.
Synthesis and Characterization of L1. A mixture of the mono
propargyl derivative of p-tert-butylphenol (0.2 g, 1.0 mmol) and 9-
(azidomethyl)anthracene (0.32 g, 1.3 mmol) were taken in 20 mL of
{dichloromethane (5 mL)/tert-butanol (5 mL)/water (10 mL)}. To
this solution were added CuSO4·5H2O (0.054 g, 0.2 mmol) and
sodium ascorbate (0.88 mg, 0.43 mmol). The remainder of the
procedure including purification is the same as that given for L (yield
0.3 g, 66%): a straw yellow crystalline solid with mp 180−185 °C. 1H
NMR (CDCl3, 400 MHz, δ ppm): 1.24 (s, 9H, C(CH3)3), 4.99 (s, 2H,
-OCH2), 6.54 (s, 2H, anthracene-CH2), 6.78 (s, 2H, Ar-H, J = 2.16),
6.80 (s, 2H, Ar-H, J = 2.20), 7.51−7.62 (m, 4H, anthracene-H), 8.07
(d, 2H, anthracene-H, J = 5.2), 8.3 (d, 2H, anthracene-H, J = 5.1), 8.58
(s, 1H, triazole-H). 13C NMR (CDCl3, 100 MHz, δ ppm): 31.6
(-C(CH3)3), 34.2 (-C(CH3)3), 46.7 (triazole-CH2-anthracene), 62.2
(-O-CH2-Ar), 114.3, 122.5, 123.1,123.8, 125.6, 126.3, 127.9, 129.7,
130.1, 130.9, 131.6, 144.0, 144.5, 156.0 (Ar-C). HRMS for
C28H28ON3: calcd 422.2232, found 422.2221, FTIR (KBr, cm−1):
1966 (ν‑CC),3019 (ν‑C−H).
AUTHOR INFORMATION
Corresponding Author
*E-mail: cprao@iitb.ac.in.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
C.P.R. acknowledges financial support from DST, CSIR, and
DAE-BRNS. V.V.S.M. and V.K.H. acknowledge CSIR for SRF,
and K.T. acknowledges UGC for SRF. We thank Ms. Radhika
Anaredy for help obtaining spectra. We also acknowledge FIST
(Physics)-IRCC central SPM facility of IIT Bombay for AFM
studies and CRNTS (SAIF) of IIT Bombay for TEM facility.
Computational Methods. The computational calculations were
carried out to find the mode of complexation of Co2+ with L. As the
formation of 1:1 {LCo} complex species was established by the ESI
MS and were also supported by the other spectroscopic techniques,
the 1:1 L:Co2+ complex species were optimized by using the Gaussian
03 package.8 The initial model for L was taken from the crystal
structure reported in this paper. In order to reduce the computational
times, before optimization, the L′ was made simply by replacing each
of the tert-butyl group of L by a hydrogen. The L′ thus obtained was
optimized by going through PM3 → HF/STO-3G → HF/3-21G →
HF/6-31G → B3LYP/3-21G → B3LYP/6-31G in a cascade manner,
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