Fluorescent but ‘choked’ multipodands: Ag(I) complexation and NMR studies

Article abstract of DOI:10.1007/s00706-020-02715-1

Abstract: A series of fluorescent and non-fluorescent multipodands, substituted with donor S, N, and O heteroatoms, bridged to mesitylene and benzene core at 1, 3-, 1, 3, 5-, and 1, 2, 4, 5-positions have been synthesized and characterized. The liquid–liquid extraction experiment showed that non-fluorescent podands such as mono-, di-, tri-, and tetrapod exhibited excellent complexation abilities towards Ag⁺ ions. The tetrapodand (O, N) shows highest extraction of Ag⁺ (73%) and tetrapodand (S, N) shows the highest Ag⁺/Pb²⁺ selectivity (135). However, for fluorescent dipodands very weak complexation ability towards metal ions were observed likely due to steric crowding. Significantly, these fluorescent dipodands undergoes protonation at very low pH (ca. < 1.0), reminiscent of acid stability—a structural feature of blue copper proteins. The NMR analysis of fluorescent podands showed that amine-appended anthracene moiety(ies) almost fills the podand cavity as lid, shifting most of the protons upfield (~ 0.5?ppm), thus causing acid stability. Graphic abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s00706-020-02715-1

Monatshefte für Chemie - Chemical Monthly (2021) 152:67–76
https://doi.org/10.1007/s00706-020-02715-1
ORIGINAL PAPER
Fluorescent but ‘choked’ multipodands: Ag(I) complexation and NMR
studies
Prabhpreet Singh1
Received: 15 June 2020 / Accepted: 19 November 2020 / Published online: 4 January 2021
© Springer-Verlag GmbH Austria, part of Springer Nature 2021
Abstract
A series of fuorescent and non-fuorescent multipodands, substituted with donor S, N, and O heteroatoms, bridged to mesi-
tylene and benzene core at 1, 3-, 1, 3, 5-, and 1, 2, 4, 5-positions have been synthesized and characterized. The liquid–liquid
extraction experiment showed that non-fuorescent podands such as mono-, di-, tri-, and tetrapod exhibited excellent com-
plexation abilities towards Ag+ ions. The tetrapodand (O, N) shows highest extraction of Ag+ (73%) and tetrapodand (S, N)
shows the highest Ag+/Pb2+ selectivity (135). However, for fuorescent dipodands very weak complexation ability towards
metal ions were observed likely due to steric crowding. Signifcantly, these fuorescent dipodands undergoes protonation
at very low pH (ca.<1.0), reminiscent of acid stability—a structural feature of blue copper proteins. The NMR analysis of
fuorescent podands showed that amine-appended anthracene moiety(ies) almost flls the podand cavity as lid, shifting most
of the protons upfeld (~0.5 ppm), thus causing acid stability.
Graphic abstract
Keywords Transition metal compounds · NMR spectroscopy · Supramolecular chemistry · Fluorescence · Receptors
Introduction
which are by defnition, open chained analogues of crown
compounds and cryptands, now exists in a many structural
variations ranging from single chained basic compounds
to multiarmed dendrimer like molecules and from highly
fexible to rather rigidly preorganized molecular architec-
tures [4–11]. From supramolecular point of view, podands
can be divided into mono, di, tetra, oligo, or multipodands.
These podands (branched oligo and multipodands) possess
anchor group to which the podand segments are attached.
Although in most cases of tripodands, three podand subu-
nits are attached to nitrogen atom, but benzene platform,
1,3,5 triazines, calixarenes, cyclodextrins fused (aromatic)
rings, steroids, or smaller molecules like glycolurils, dis-
plays interesting organization properties. Tetrapodands and
Supramolecular chemistry has continuously progressed
since the Nobel Prize to Cram, Lehn, and Pedersen in 1987
which led to great impetus to the development of new syn-
thetic receptors for molecular recognition [1–9]. Podands,
Supplementary Information The online version contains
supplementary material available at https://doi.org/10.1007/s0070
6-020-02715-1.
* Prabhpreet Singh
prabhpreet.chem@gndu.ac.in
1
Department of Chemistry, UGC Centre for Advanced
Studies, Guru Nanak Dev University, Amritsar 143005,
India
Vol.:(0123456789)
1 3

68
P. Singh
higher polypodal structures could be constructed by con-
sidering these platforms [12–15]. Exploiting the concept
of ‘steric gearing’ hexasubstituted benzene derivative has
seen extensive use. 1,3,5-Trifunctionalised 2,4,6-(trimethyl/
ethyl)benzene derivatives, in their lowest energy conforma-
tion show that the three ethyl/methyl groups and three func-
tional groups are oriented perpendicular to the central ring
in a fully alternated up-down disposition making ababab
type arrangement of these groups [15–18]. Our group and
others have reported benzene scafold which bears difer-
ent recognition units at 1,4- and 1,3,5-positions including
boronic acids, ureas, thioureas, catecholates, guanidinium,
imidazolium, pyrazole, oxazolines, 8-hydroxyquinoline etc.,
for binding of variety of anions and cations [15, 19, 20].
In nature, blue copper proteins play a key role in long
range inter- and intraprotein electron transfer and are char-
acterized by high reduction potentials, rapid transfer rates
and unique spectral features compared to normal tetragonal
copper complexes [21–24]. In rusticyanin the four ligating
atoms (2 N+2 S) are arranged around Cu2+ in a distorted
tetrahedral arrangement but have high acid stability as the
copper binding site is located deep within a hydrophobic
region. Evidently, the potential of mixed ligating sites (S,
N, O or S, N), as prevalent in nature remains more or less
unexploited. The 2-aminothiophenol or 2-aminophenol
which possesses N and S/O donor sites and its derivatives,
have found diferent applications in the feld of medicine,
material and coordination chemistry [25–28]. We have ear-
lier reported 2-aminothiophenol based macrocycles [29,
30] containing para-xylylene, and 9,10-anthracene units for
Cu2+ coordination [31]. The 1,4-placement of ligating sites
does not allow the convergence of all ligating sites towards
one metal ion and these receptors result in formation of
M2L2 or M2L type complexes.
Results and discussion
Synthesis and characterization of fuorescent
multipodands
The S-alkylation of 2-aminothiophenol with
1 - ( b r o m o m e t h y l ) - 2 , 4 , 6 - t r i m e t h y l b e n z e n e ,
1,3-bis(bromomethyl)-2,4,6-trimethylbenzene, and
1,3,5-tris(bromomethyl)-2,4,6-trimethylbenzene, respec-
tively in N,N-dimethylformamide (DMF), NaH (pre-
washed), and tetrabutylammonium hydrogensulfate as a
phase transfer catalyst for 36 h followed by chromato-
graphic (SiO2) purifcation provides monopodand 1, dip-
odand 2, and tripodand 4 in excellent yields (Scheme 1).
These reactions have been performed strictly in N2 atmos-
phere because 2-aminothiophenol leads to the formation
of disulfde bond due to oxidation in air and afects the
overall yield of the reaction. We also found that using
potassium carbonate as base, rather than NaH gives the
comparative yields of the products. These podands showed
characteristics 1H NMR signals of the 2-aminophenylthio
units which includes two doublets and two triplets and
broad singlet of NH2 group.
Monopodand 1 and dipodand 2 showed two singlets for
methyl protons, whereas tripodand 4 showed one singlet
for methyl protons which corresponds well with unsym-
metrical and symmetrical nature of podands around mesi-
tylene core. Similarly, dipodand 3 [26] and tetrapodand
5 were synthesized by reaction of 1,3-bis(bromomethyl)-
benzene and 1,2,4,5-tetrakis(bromomethyl)benzene
with 2-aminothiophenol under similar reaction condi-
tions. To compare the binding ability of S with O, we
also prepared tetrapodand 6 by reaction of 2-nitrophenol
with 1,2,4,5-tetrakis(bromomethyl)benzene in acetoni-
trile using potassium carbonate as base and TBAHSO4 as
phase transfer catalyst in 60% yield, followed by reduc-
tion of NO2 group with NiCl2/NaBH4 complex in metha-
nol [36]. To distinguished between tetrapodands 5 and
In continuation of our interest in multipodal and macro-
cyclic system [32, 33], we envisaged that 1,2- or 1,3-place-
ment of the ligating sites on the benzene platform would
encourage the convergence of these ligating sites towards
one metal cation and these may be able to provide better
receptors. Therefore, based on above discussed features and
keeping in view the possible structural feature of the active
cavity in Cu2+ proteins, and the additional stability provided
by aromatic rings in the case of rusticyanin, we now report
synthesis, complexation and NMR studies of 1,3-, 1,3,5-,
and 1,2,4,5-multipodands based on 2-aminothiophenol and
2-aminophenol bridged to mesitylene (1,3,5-trimethylben-
zene) and benzene platform. The presence of fuorescent
moiety(ies) at one or more than one of these amine nitrogens
would increase hydrophobic character as well as enables
their evaluation through fuorescence spectroscopy.
1
6, characteristic H NMR signals of –CH2 (methylene)
was closely followed. The 1H NMR peak of –CH2 protons
close to S-functionality showed upfeld shift in compare
to O-functionality.
To make fuorescent multipodands, an anthracene or
naphthalene fuorescent bulky group(s) were attached to
the anilinyl NH2 group by reductive amination method
[37]. The presence of bulky group, either at one-, two- and
three-positions as per design, would create hydrophobic
pockets for metal ion complexation. Monopodand 1, dipo-
dand 2, and tripodand 4 on condensation with anthracene-
9-aldehyde in THF-MgSO4 mixture and subsequent reduc-
tion with NaBH4 in the presence of I2 gave fuorescent
1 3

Fluorescent but ‘choked’multipodands: Ag(I) complexation and NMR studies
69
Scheme 1
Scheme 2
S
S
(b,c)
(a,c)
S
NH
HN
H2N
1
7
8
R
R
R
R
R
S
R
S
R
S
R
S
R
S
S
R
S
S
R
R
(b,c)
+
(a,c)
NH
HN
NH2
NH2
NH2
HN
HN
H2N
monopodand 7, mixture of fuorescent dipodand 9 and
11, and fuorescent tripodand 14, respectively (Schemes
2, 3). Similarly, monopodand 1 and tripodand 4 on con-
densation with 2-naphthaldehyde and subsequent reduc-
tion with NaBH4-I2 gave fuorescent monopodand 8 and
fuorescent tripodand 15–17 (Schemes 2, 3). All new com-
pounds were characterized by 1H and 13C NMR, FAB-MS
fuorescent monopodand 7 and 8 shows two singlets due
to methyl groups, a singlet due to SCH2 and doublet due to
CH2NH (converts to singlet on D2O exchange) along with
aromatic protons; fuorescent dipodand 9 exhibits three
singlets due to three methyl groups, two singlets due to
SCH2, one doublet due to NCH2 along with 2-aminophe-
nylthio protons whereas fuorescent dipodand 11 showed
two singlets for methyl protons, one singlet each for SCH2
1
spectra, and elemental analysis. In the H NMR spectra
1 3

70
P. Singh
Scheme 3
S
S
S
S
S
S
NH
NH2
HN
H2N
H2N
15
H2N
14
(a,c)
(b,c)
(b,c)
(b,c)
S
S
S
H2N
NH2
H2N
S
S
4
S
S
S
S
NH
NH
H2N
HN
HN
HN
16
17
and NCH2 (δ=5.18 ppm, 4H) along with NH and aromatic
H signals; fuorescent tripodand 14 exhibit two singlets for
methyl group, two singlets for SCH2 groups, a doublet due
to CH2N along with aromatic protons due to 2-aminophe-
nylthio and anthracene moieties. Benzene based dipodand
3 on condensation with anthracene-9-aldehyde and sub-
sequent reduction with NaBH4-I2 gave 10 (m/z peak at
542) and 12 (m/z peak at 732). Similarly, dipodand 3 on
condensation with 2-naphthaldehyde followed by subse-
quent reduction with NaBH4-I2 gave 13 (m/z peak at 492)
(Scheme 2).
three 2-aminophenylthio groups at 1,3,5-positions (Fig. 1).
These results clearly show that on increasing the number
of aminophenylthio groups, their organization or coopera-
tive binding with Ag+ remarkably increases the extraction of
Ag+ from water. The cooperativity of ligating sites in tripo-
dand 4 is also evident from the increased extraction of even
alkali and alkaline earth metal ions in comparison to that of
dipodand 2. Notably, the dipodand 3 showed poor extraction
(< 2%) of Ag+ and other metal ions (< 0.5%). Therefore,
probably the presence of methyl groups on benzene ring in
dipodand 2 organizes the ligating sites on one plane of the
Complexation studies for Ag(I) ions
As the process of ligand facilitated transport of cations
across apolar membrane has relevance to the development
of separation techniques for the cation, the extraction (com-
plexation) properties of the podands towards Ag+, Pb2+,
Tl+, alkali (Li+, Na+, K+), and alkaline earth (Mg2+, Ca2+,
Sr2+, Ba2+) cations have been determined [38, 39]. Extrac-
tion profles of these podands show that all these podands
extract preferentially Ag+ over alkali, alkaline earth, and
Pb2+ picrates. However, the percentage extraction of the
Ag+ markedly depends on the number of 2-aminophe-
nylthio groups present in the podands and their spatial
positions. Monopodand 1 possessing only one 2-aminophe-
nylthio group extracted only 5% Ag+. The presence of two
2-aminophenylthio groups at 1,3-positions of dipodand
2 increased extraction of Ag+ to 35% which was further
increased to 62% in case of tripodand 4, which possesses
Fig. 1 Extraction (%) profle of picrate salts from water into CHCl3
for podands 1, 2, and 4–6
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Fluorescent but ‘choked’multipodands: Ag(I) complexation and NMR studies
71
benzene ring and results in enhanced extraction of Ag+ in
comparison to dipodand 3 (Table S1).
To investigate further the role of aromatic groups we look
into the energy minimized structures of 9, 14 and 20, 21 (as
control) which shows that the anthracene ring is by and large
placed as a lid to the pseudocavity formed by two 2-ami-
nophenylthio moieties and covers one half of the central
aromatic ring near to it more efciently than the second half
of the central aromatic ring (Fig. S1). This leads to non-
equivalency of SCH2 and CH3 protons. To further investigate
the efect of aromatic group (anthracene) on complexation
due to its over placement on the pseudo cavity, the 1H NMR
spectra of these fuorescent multipodands were analyzed in
detail.
On increasing the number of ligating sites to four in tet-
rapodand 5 in comparison to three ligating sites in tripodand
4, the extraction of Ag+ decreased to 54% and points to the
poor organization of four ligating sites in binding with Ag+.
This can be attributed partially to the larger size of sulfur
atom which does not allow the four-S-linkage on the same
side of phenyl ring. However, on replacing the thioether
linkages with ether linkages in tetrapodand 6, signifcant
increases in extraction of Ag+ to 73% was observed. The
increase in extraction of Ag+ with increasing number of
ligating sites also results in increased selectivity towards
Ag+ over similar sized Pb2+. Monopodand 1 extracts Ag+
only 12.5 times higher than Pb2+ but in dipodand 2 Ag+/Pb2+
selectivity increases to 70 which is further increases to 89 in
tripodand 4. Tetrapodand 5 and 6 exhibit Ag+/Pb2+ selectiv-
ity of the order of 135 and 121, respectively. Amongst all
these podands, 6 shows highest extraction of Ag+ (73%) and
5 shows the highest Ag+/Pb2+ selectivity (135).
1H NMR analysis of multipodands
1
The H NMR spectra of various multipodands show that
the attachment of the anthracene ring to the 10 aromatic
amine causes signifcant changes in chemical shifts of dif-
ferent protons but attachment of the naphthalene ring to
the amine does not cause any change in the chemical shift.
The comparison of 1H NMR spectrum of fuorescent tripo-
dand 14 with that of its parent tripodand 4 shows that in
14, the methyl protons are shifted up feld by ∆δ=0.55 and
∆δ = 0.15 ppm and SCH2 singlets are shifted up feld by
∆δ=0.30 and ∆δ=0.25 ppm. Similarly, the methyl protons
in fuorescent dipodand 9 are shifted up feld by ∆δ=0.58,
0.47, and 0.14 ppm and SCH2 signals are shifted up feld
by ∆δ=0.28 and 0.21 ppm in comparison to chemical shift
in dipodand 2. The presence of two anthracene moieties in
fuorescent dipodand 11, causes enhanced up feld shift of
methyl (∆δ = 0.75 ppm) and SCH2 (∆δ = 0.46 ppm) pro-
tons. Similar up feld shift of SCH2 and methyl protons in
fuorescent monopodand 7, in comparison with those in
monopodand 1 is observed (Fig. 2). However, in case of
naphthyl substituted fuorescent dipodand 13 and tripodand
15, the upfeld shift of <0.10 ppm is observed (Fig. S2). We
also observed that NCH2 signals appeared at 5.18–5.22 ppm
range in all podands where anthracene is attached at amine
nitrogen which attributes that anthracene rings overlap on
the cavity and shield the CH3, SCH2 protons whereas NCH2
protons in these podands are present in the deshielding zone
of the anthracene ring current. We observed that NCH2 sig-
nals appeared upfeld at 4.44–4.50 ppm in all podands where
naphthalene is attached at amine nitrogen which possibly
explains the presence of naphthalene very close to NCH2
rather than CH3 and SCH2 and consequently NCH2 showed
upfeld shift and negligible shift in case of CH3 and SCH2
protons (Table S2).
pH titration
The solution of 9 (50 μM, CH3CN:H2O, 4:1) displayed
absorbance maxima at 385, 366, and 350 nm and on excita-
tion at 366 nm it exhibited fuorescence maxima at 410 nm,
with two shoulders at 390 and 437 nm, typical of anthracene
unit. The fuorescent multipodands 9 and 14, substituted
with aryl/alkyl amine, are non-fuorescent due to efcient
photoinduced electron transfer (PET) process from –NH to
anthracene fuorophore. It was expected that addition of H+
ions will cause the protonation of aryl/alkyl amine unit and
may inhibit the PET process to revive the fuorescence of
anthracene. The pH titration of 9 showed that the fuores-
cence intensity remained unchanged between pH ca. 14–1.0
and on lowering the pH from <1.0, the fuorescence inten-
sity increased progressively at very low pH and it went of
scale. Similarly, fuorescence of 14 remained stable up to
pH 1.0. Probably, in 9 and 14 the hydrophobic environment
created by the aromatic rings makes the protonation more
difcult. In the preliminary fuorescence studies, most of
the transition metal ions, did not modulate the fuorescence
intensity of 9 and 14. Even on addition of excess of Cu2+
ions, no increase in the fuorescence intensity was observed.
This is likely due to intramolecular π–π and π–CH interac-
tions of the anthracene moiety with the rest of the molecule
and as a result although multipodands 9 and 14 seem to have
preorganized structures but ligating sites (N, S) have been
embedded deep into the hydrophobic environment created
by anthracene ring(s). This efect of hydrophobic environ-
ment is clearly manifested into the acid stability of these
multipodands.
We also carried out comparison of 1H NMR spectra of
p-phenylene (1,4-linkage) based-fuorescent dipodands 20
and 21 (Fig. S3) [30] with their parent dipodands 18 and 19
which shows that the presence of anthracene ring shifts most
1 3

72
P. Singh
Fig. 2 The comparison of 1H chemical shifts of 2 with 9 and 11; 4 with 14; 1 with 7
of the protons upfeld. In case of 20, the para-xylene ring
protons become magnetically non-equivalent and are shifted
upfeld by 0.17 and 0.28 ppm and SCH2 signals are shifted
up feld by 0.24 and 0.07 ppm, whereas, in case of 21, SCH2
singlets are shifted up feld by 0.22 and 0.08 ppm; the OMe
singlets are shifted up feld by 0.46 and 0.17 ppm; aromatic
H of 2, 5-dimethoxybenzene ring are shifted upfeld by 0.17
and 0.13 ppm. From these results, we observed that chemical
shifts of the protons are more pronounced in case of 1,3- or
1,3,5-linked podands in compare to 1,4-linked podands.
The aromatic H of 2-aminophenylthio units in podands
7, 9, and 14 is also shifted downfeld by 0.1–0.2 ppm. This
down feld shift of 2-aminophenylthio ArH in comparison to
upfeld shift of SCH2 and methyl protons clearly shows that
SCH2 and central methyl protons remain in shielding zone of
anthracene ring i.e. in its center, whereas 2-aminophenylthio
protons are placed in deshielding zone i.e. away from the
anthracene ring. The 1H NMR spectra on recording between
10–2 and 10–3 M concentrations showed constant chemical
shifts and point to lack of any intramolecular interactions in
aggregated state. Therefore, in 7, 9, 10, and 14, the upfeld
chemical shifts of protons in comparison to those in their
parent amines arise due to intramolecular spatial arrange-
ment of anthracene bulky group.
Conclusion
In conclusion, multipodands possessing 2-aminophenylthio
groups at 1,3-, 1,3,5-, and 1,2,4,5-positions of benzene plat-
form have been synthesized. Tripodand and tetrapodands
showed good extraction of Ag+ and and tetrapodand showed
highest Ag+/Pb2+ selectivity among the other podands. When
anthracene groups were connected to the amine of the 2-ami-
nothiophenol unit on dipodands and tripodands, anthracene
ring(s) organized themselves on to cavity as lid which causes
protonation of amine at low pH due to increased hydrophobic-
ity around the podand. Thus, model structure for blue copper
protein cavity could be achieved but at the loss of compl-
exation ability towards Cu2+ ions. Further refnement in the
model structure by considering stronger coordinating ligands
to achieve both factors (hydrophobicity and copper compl-
exation) simultaneously are currently in progress in our lab.
Experimental
Melting points were determined in open capillaries. For
monitoring the progress of the reaction and for com-
parison with authentic samples, thin layer chromatogra-
phy (tlc) was used. For this purpose, micro slides were
1 3

Fluorescent but ‘choked’multipodands: Ag(I) complexation and NMR studies
73
coated with silica gel ‘G’ containing calcium sulfate as
binder or with the silica gel HF-254 (Qualigens India),
by dipping a pair of slides held back to back in slurry of
adsorbent in chloroform–methanol (80:20). The chromato-
grams were developed in iodine chamber or with UV-254
lamp. Separation of various components was carried out
by column chromatography using silica gel 60–120 mesh
(Qualigens, India) as adsorbent and hexane, ethyl acetate
and their mixtures as eluents. All the fractions collected
from column chromatography were compared with chro-
matograms of the reaction mixture (tlc) for checking their
2-aminothiophenol (5.19 mmol) was added with stirring
under N2 atm at 40 2 °C. The stirring was continued for
20 min. After the hydrogen evolution ceased, TBA HSO4
(25–30 mg) and 500 mg 1-(bromomethyl)-2,4,6-trimeth-
ylbenzene (2.35 mmol) were added and stirring was con-
tinued for additional 24–30 h. During this period reaction
was completed (tlc). The suspended solid was fltered of
and was washed with ethyl acetate. The combined fltrate
was distilled off under vacuum. Recrystallization from
CHCl3–CH3OH (1:1) produce 1.
1
identity and purity. H NMR spectra were recorded on
2‑[(2,4,6‑Trimethylbenzyl)thio]aniline (1, C16H19NS)
JEOL 300 MHz instrument using CDCl3 solutions contain-
ing tetramethylsilane as an internal standard. Abbrevia-
tions used for splitting patterns are s = singlet, bs = broad
singlet, t = triplet, q = quartet, m = multiplet, dd = double
doublet. 13C NMR spectra were recorded at 75 MHz. Mass
spectra were recorded at Central Drug Research Institute,
Lucknow. Elemental analyses (C, H, N, S) of the samples
were performed on a Thermoelectron FLASH EA1112,
CHNS analyzer and their results were found to be in good
agreement ( 0.3%) with the calculated values. Absorp-
tion and emission spectra were obtained respectively on
Shimadzu UV-1601 spectrophotometer and on Shimadzu
RF-1501 spectrofuorophotometers with 1 cm quartz cells.
2-Aminothiophenol, 2-naphthaldehyde, 1, 3, 5-tri-
methylbenzene, 1,2,4,5-tetramethylbenzene, TBAHSO4,
and 9-anthracenealdehyde were procured from Aldrich,
Spectrochem (India), Loba Chemie, and were used
without further purification. 1-(Bromomethyl)-2,4,6-
trimethylbenzene, 1,3-bis(bromomethyl)-2,4,6-tri-
methylbenzene, 1,3,5-tris(bromomethyl)-2,4,6-trimeth-
ylbenzene [34], 1,3-bis(bromomethyl) benzene, and
1,2,4,5-tetrakis(bromomethyl)benzene [35] were prepared
according to the published procedures and their 1H NMR spec-
tra were found to be identical with the ones described in refer-
ences. Moisture-sensitive reactions were performed under N2
atmosphere. CH2Cl2 was freshly distilled from CaH2, THF from
Na/benzophenone, CH3OH from Mg wire, CH3CN from P2O5,
and DMF dried over 4 Å molecular sieves. Other solvents such
as hexane, ethyl acetate, chloroform, and acetone were of LR
grade and were distilled before use. Water was doubly distilled.
Metal salts were of analytical grade. Chloroform and acetoni-
trile used for extraction studies were of AR grade. Compounds
1–4 and 6 have been already published in literature and physi-
cal properties, e.g. 1H and 13C NMR spectra were found to be
identical with the ones described in Refs. [40–43].
1
Yield 0.42 g (70%); thick liquid; H NMR (300 MHz,
CDCl3): δ=7.24 (d, J=7.5 Hz, 1H, ArH), 7.01 (t, J=7.5 Hz,
1H, ArH), 6.74 (s, 2H, ArH), 6.51–6.59 (m, 2H, ArH), 4.22
(s, 2H, NH2, exchanges with D2O), 3.87 (s, 2H, CH2S), 2.23
(s, 6H, 2 CH3), 2.17 (s, 3H, CH3) ppm; 13C NMR (75 MHz,
CDCl3): δ=148.3, 136.7, 136.1, 135.9, 130.7, 129.6, 128.7,
118.1, 117.9, 114.5, 33.8, 20.7, 19.2 ppm; MS (FAB):
m/z=257 (M+).
2,2′,2″,2‴‑[1,2,4,5‑Benzenetetrayltetrakis(methylenethio)]‑
tetraaniline (5, C34H34N4S4)
1
Yield 0.42 g (60%); solid; m.p.: 118–121 °C; H NMR
(300 MHz, CDCl3): δ=7.16 (d, J=7.5 Hz, 4H, ArH), 7.11
(t, J=7.5 Hz, 4H, ArH), 6.68 (d, J=7.5 Hz, 4H, ArH), 6.62 (t,
J=7.5 Hz, 4H, ArH), 6.60 (s, 2H, ArH), 4.23 (bs, 8H, 4 NH2,
exchanges with D2O), 3.78 (s, 8H, 4 CH2S), ppm; 13C NMR
(75 MHz, CDCl3): δ = 148.7, 136.5, 135.1, 132.6, 130.1,
118.5, 117.1, 114.9, 36.1, ppm; MS (FAB): m/z=626 (M+).
General procedure for the synthesis
of multipodands 7, 9–12, 14
The solution of 300 mg 2 (0.760 mmol) and 205 mg anthra-
cenecarbaldehyde (1.0 mmol) in 30 cm3 dry THF containing
suspension of 365 mg dry MgSO4 (3.04 mmol) was stirred
for 48 h at room temperature. MgSO4 was fltered of and
washed with dry THF. The combined fltrate was recol-
lected and to this solution of 68 mg NaBH4 (1.89 mmol)
and 193 mg I2 (0.759 mmol) was added and was stirred at
room temperature for additional 2 h. Then, reaction mix-
ture was refuxed for 36 h. The reaction mixture was cooled;
20 cm3 methanolic KOH (2%) was added and was stirred for
2 h. Then, reaction mixture was diluted with water and was
extracted with CH2Cl2. The solvent was distilled of and the
residue was purifed through column chromatography over
silica using CH2Cl2—hexane as an eluent to get 9 and 11.
Similar reactions of diamines 3, 4, and 1 with anthracen-
ecarbaldehyde gave respective fuoroionophores 10 and 12,
14, and 7.
General procedure for the synthesis of podands 1
and 5
In two neck round bottomed flask, 94 mg pre-washed
NaH (3.95 mmol) was taken in dry DMF and 648 mg
1 3

74
P. Singh
2‑[[3‑[[(2‑Aminophenyl)thio]methyl]‑2,4,6‑trimethylbenzyl] ‑
thio]‑N‑(anthracen‑9‑ylmethyl)aniline (9, C38H36N2S2)
117.3, 117.0, 114.7, 110.0, 40.7, 39.3, 39.1 ppm; MS (FAB):
m/z=542 (M+).
1
Yield 0.13 g (30%); solid; m.p.: 124–125 °C; H NMR
2,2′‑[[1,3‑Phenylenebis(methylene)]bis(sulfanediyl)]bis[N‑
(anthracen‑9‑ylmethyl)aniline] (12, C50H40N2S2)
(300 MHz, CDCl3): δ = 8.50 (s, 1H, ArH), 8.28 (d,
J = 7.5 Hz, 2H, ArH), 8.05 (d, J = 7.5 Hz, 2H, ArH),
7.40–7.53 (m, 6H, ArH), 7.21 (d, J = 7.5 Hz, 1H, ArH),
7.00–7.09 (m, 2H, ArH), 6.73 (t, J = 7.5 Hz, 1H, ArH),
6.58–6.63 (m, 3H, ArH), 5.36 (bs, NH, 1H, exchanges with
D2O), 5.21 (d, J=3.6 Hz, 2H, CH2NH, converts to singlet
on D2O exchange), 4.23 (bs, 2H, NH2, exchanges with
D2O), 3.76 (s, 2H, CH2S), 3.69 (s, 2H, CH2S), 2.16 (s, 3H,
CH3), 1.83 (s, 3H, CH3), 1.75 (s, 3H, CH3) ppm; 13C NMR
(75 MHz, CDCl3): δ = 149.4, 148.4, 136.6, 136.5, 136.1,
136.1, 135.9, 131.7, 131.5, 131.2, 130.7, 130.5, 129.9,
129.8, 129.1, 128.0, 126.5, 125.1, 124.1, 118.5, 118.2,
118.1, 117.1, 114.7, 109.8, 40.6, 34.8, 34.7, 19.6, 19.0,
14.5 ppm; MS (FAB): m/z=585 [ (M+1)+].
1
Yield 0.05 g (8%); solid; m.p.: 177–180 °C; H NMR
(300 MHz, CDCl3): δ = 8.41 (s, 2H, ArH), 8.18 (d,
J = 8.2 Hz, 4H, ArH), 7.96 (d, J = 9.0 Hz, 4H, ArH),
7.38–7.48 (m, 8H, ArH), 7.29 (t, J=7.5 Hz, 2H, ArH), 7.16
(d, J=7.5 Hz, 2H, ArH), 6.93 (d, J=7.5 Hz, 2H, ArH), 6.69
(t, J=7.5 Hz, 2H, ArH), 6.60 (t, J=7.5 Hz, 1H, ArH), 6.55
(d, J=7.5 Hz, 2H, ArH), 6.22 (s, 1H, ArH), 5.12 (bs, 2H, 2
NH, exchanges with D2O), 5.06 (bs, 4H, 2 CH2NH), 3.36 (s,
4H, 2 CH2S) ppm; 13C NMR (75 MHz, CDCl3): δ=149.1,
137.5, 136.4, 131.5, 130.4, 129.1, 128.9, 128.0, 127.1,
126.4, 125.1, 124.0, 117.3, 117.0, 109.9, 40.7, 38.9 ppm;
MS (FAB): m/z=732 (M+).
2,2′‑[[(2,4,6‑Trimethyl‑1,3‑phenylene)bis(methylene)] ‑
bis(sulfanediyl)]bis[N‑(anthracen‑9‑ylmethyl)aniline] (11,
C53H46N2S2)
2,2′‑[[[5‑[[[2‑[(Anthracen‑9‑ylmethyl)amino]phenyl]thio]‑
methyl]‑2,4,6‑trimethyl‑1,3‑phenylene]bis(methylene)] ‑
bis(sulfanediyl)]dianiline (14, C45H43N3S3)
1
1
Yield 0.06 g (10%); solid; m.p.: 230–232 °C; H NMR
Yield 0.09 g (23%); solid; m.p.: 187–190 °C; H NMR
(300 MHz, CDCl3): δ = 8.47 (2H, s, ArH), 8.24 (4H, d,
J=9.0 Hz, ArH), 8.02 (4H, d, J=9.0 Hz, ArH), 7.43–7.50
(m, 8H, ArH), 7.30–7.34 (m, 4H, ArH), 6.98 (d, 2H,
J=7.5 Hz, ArH), 6.69 (t, J=7.5 Hz, 2H, ArH), 6.34 (s, 1H,
ArH), 5.29 (bs, 2H, 2 NH, exchanges with D2O), 5.18 (bs,
4H, 2 CH2NH), 3.51 (s, 4H, 2 CH2S), 1.59 (s, 3H, CH3), 1.58
(s, 6H, 2 CH3) ppm; 13C NMR (75 MHz, CDCl3, 25 °C):
δ=149.3, 136.5, 135.9, 131.5, 131.1, 130.5, 130.5, 129.7,
129.1, 128.0, 126.5, 125.1, 124.1, 118.0, 117.1, 109.7, 40.6,
34.4, 18.9, 14.0 ppm; MS (FAB): m/z=774 (M+).
(300 MHz, CDCl3): δ = 8.50 (s, 1H, ArH), 8.28 (d, J= 7.
5 Hz, 2H, ArH), 8.05 (d, J=7.5 Hz, 2H, ArH), 7.40–7.53
(m, 6H, ArH), 7.21–7.23 (m, 2H, ArH), 7.03–7.10 (m, 3H,
ArH), 6.74 (t, J=7.5 Hz, 1H, ArH), 6.60–6.66 (m, 4H, ArH),
5.35 (bs, 1H, NH, exchanges with D2O), 5.22 (d, J=2.7 Hz,
2H, CH2NH, converts to singlet on D2O exchange), 4.25
(bs, 4H, 2 NH2, exchanges with D2O), 3.77 (s, 4H, 2 CH2S),
3.72 (2H, s, CH2S), 2.24 (s, 3H, CH3), 1.84 (s, 6H, 2 CH3)
ppm; 13C NMR (75 MHz, CDCl3): δ=149.4, 148.4, 136.5,
136.0, 135.8, 135.6, 132.0, 131.5, 130.7, 130.5, 129.8,
129.1, 128.0, 126.5, 125.2, 124.1, 118.6, 118.2, 118.0,
117.2, 114.8, 109.8, 40.6, 35.4, 15.7, 15.1 ppm; MS (FAB):
m/z=721 (M+).
2‑[[3‑[[(2‑Aminophenyl)thio]methyl]benzyl]thio]‑N‑
(anthracen‑9‑ylmethyl)aniline (10, C35H30N2S2)
1
Yield 0.09 g (20%); solid; m.p.: 85–87 °C; H NMR
N‑(Anthracen‑9‑ylmethyl)‑2‑[(2,4,6‑trimethylbenzyl)thio] ‑
aniline (7, C31H29NS)
(300 MHz, CDCl3): δ = 8.51 (s, 1H, ArH), 8.26 (d,
J = 7.5 Hz, 2H, ArH), 8.06 (d, J = 7.5 Hz, 2H, ArH),
7.46–7.54 (m, 4H, ArH), 7.38 (t, J=7.5 Hz, 1H, ArH), 7.25
(d, J = 7.5 Hz, 1H, ArH), 7.14 (d, J = 7.5 Hz, 1H, ArH),
7.04 (d, J=7.5 Hz, 1H, ArH), 7.01 (d, J=7.5 Hz, 1H, ArH),
6.83–6.88 (m, 2H, ArH), 6.66–6.70 (m, 2H, ArH), 6.59 (d,
J=7.5 Hz, 1H, ArH), 6.56 (s, 1H, ArH), 6.55 (t, J=7.5 Hz,
1H, ArH), 6.00 (s, 1H, NH, exchanges with D2O), 5.19 (s,
2H, CH2NH), 3.60 (s, 2H, CH2S), 3.56 (s, 2H, CH2S) ppm;
13C NMR (75 MHz, CDCl3): δ=149.1, 148.4, 138.1, 137.7,
136.7, 136.2, 131.5, 130.6, 130.5, 129.9, 129.1, 128.1,
128.0, 127.3, 127.3, 126.5, 125.1, 124.1, 118.3, 117.3,
1
Yield 0.11 g (22%); solid; m.p.: 147–149 °C; H NMR
(300 MHz, CDCl3): δ = 8.50 (s, 1H, ArH), 8.28 (d,
J = 7.5 Hz, 2H, ArH), 8.05 (d, J = 7.5 Hz, 2H, ArH),
7.40–7.53 (m, 6H, ArH), 7.08 (d, J = 7.5 Hz, 1H, ArH),
6.72 (t, J=7.5 Hz, 1H, ArH), 6.59 (s, 2H, ArH), 5.38 (bt,
J=4.2 Hz, 1H, NH exchanges with D2O), 5.22 (d, J=4.2 Hz,
2H, CH2NH converts to singlet on D2O exchange), 3.69 (s,
2H, CH2S), 2.11 (s, 3H, CH3), 1.79 (s, 6H, 2 CH3) ppm;
13C NMR (75 MHz, CDCl3): δ=149.4, 137.1, 136.6, 136.4,
131.6, 130.6, 130.5, 130.1, 129.1, 128.7, 128.0, 126.5, 125.1,
1 3

Fluorescent but ‘choked’multipodands: Ag(I) complexation and NMR studies
75
124.1, 118.2, 117.1, 109.8, 40.6, 33.9, 20.8, 18.8 ppm; MS
117.2, 114.8, 110.5, 48.2, 35.9, 35.5, 15.8 ppm; MS (FAB):
(FAB): m/z=447 (M+).
m/z=672 [(M+1)+].
General procedure for synthesis of multipodands 8,
13, 15–17
2,2′‑[[[5‑[[(2‑Aminophenyl)thio]methyl]‑2,4,6‑trimethyl‑
1,3‑phenylene]bis(methylene)]bis(sulfanediyl)]bis[N‑
(naphthalen‑2‑ylmethyl)aniline] (16, C52H49N3S3)
The solution of 300 mg compound 3 (0.852 mmol) and
159 mg 2-naphthaldehyde (1.0 mmol) in 30 cm3 dry THF
containing suspension of 271 mg dry MgSO4 (2.25 mmol)
was stirred for 48 h at room temperature. After the comple-
tion of the reaction (tlc), MgSO4 was fltered of and washed
with dry THF. The combined fltrate was recollected and
to this solution of 77 mg NaBH4 (2.12 mmol) and 143 mg
I2 (0.57 mmol) was added and reaction was stirred at room
temperature for 2 h. Then reaction mixture was further
refuxed for 36 h. The reaction mixture was cooled; 20 cm3
methanolic KOH (2%) was added and stirred for additional
2 h. The reaction mixture was diluted with water and was
extracted with CH2Cl2. The solvent was distilled of and the
residue was purifed through column chromatography over
silica using CH2Cl2—hexane as an eluent to get 13. Similar
reaction of diamine 4 and 1 with 2-naphthaldehyde gave
fuorescent multipodand 15–17 and 8.
1
Yield 0.12 g (26%); solid; m.p.: 133–135 °C; H NMR
(300 MHz, CDCl3): δ=7.78–7.83 (m, 8H, ArH) 7.44–7.47
(m, 6H, ArH), 7.36 (d, J = 7.5 Hz, 2H, ArH), 7.23 (d,
J = 7.5 Hz, 1H, ArH), 7.14 (d, J= 7.5 Hz, 1H, ArH), 7.10
(d, J = 7.5 Hz, 1H, ArH), 7.07 (d, J = 7.5 Hz, 1H, ArH),
6.59–6.67 (m, 6H, ArH), 5.58 (t, J = 5.4 Hz, 2H, 2 NH,
exchanges with D2O), 4.47 (d, J = 5.1 Hz, 4H, 2 CH2NH,
converts to singlet on D2O exchange), 4.24 (bs, 2H, NH2,
exchanges with D2O), 3.95 (s, 4H, 2 CH2S), 3.85 (s, 2H,
CH2S), 2.28 (s, 6H, 2 CH3), 2.26 (s, 3H, CH3) ppm; 13C
NMR (75 MHz, CDCl3): δ = 149.3, 148.4, 136.6, 136.4,
136.0, 135.7, 133.4, 132.7, 132.3, 132.2, 130.4, 129.8,
128.4, 127.7, 127.7, 126.2, 125.7, 125.7, 125.5, 118.6,
118.2, 117.9, 117.2, 114.8, 110.5, 103.3, 48.2, 35.8, 35.5,
15.8 ppm; MS (FAB): m/z=811 (M+).
2,2′,2″‑[[(2,4,6‑Trimethylbenzene‑1,3,5‑triyl)tris‑
(methylene)]tris(sulfanediyl)]tris[N‑(naphthalen‑2‑
ylmethyl)aniline] (17, C63H57N3S3)
2‑[[3‑[[(2‑Aminophenyl)thio]methyl]benzyl]thio]‑
N‑(naphthalen‑2‑ylmethyl)aniline (13, C31H28N2S2)
1
1
Yield 0.075 g (18%); thick liquid; H NMR (300 MHz,
Yield 0.11 g (20%); solid; m.p.: 140–142 °C; H NMR
CDCl3): δ = 7.75–7.83 (m, 4H, ArH), 7.42–7.49 (m, 3H,
ArH), 6.89–7.28 (m, 8H, ArH), 6.56–6.66 (m, 4H, ArH),
4.43 (s, 2H, CH2NH), 3.82 (s, 2H, CH2S), 3.76 (s, 2H,
CH2S) ppm; 13C NMR (75 MHz, CDCl3): δ=149.3 148.4,
138.3, 136.7, 136.6, 136.3, 133.4, 132.7, 130.4, 129.9,
129.3, 128.8, 128.3, 127.7, 127.6, 127.5, 127.4, 126.1,
125.7, 125.5, 118.4, 117.4, 117.1, 117.0, 114.8, 110.5, 48.1,
39.8, 39.4 ppm; MS (FAB): m/z=492 (M+).
(300 MHz, CDCl3): δ=7.75–7.80 (m, 12H, ArH), 7.41–7.46
(m, 9H, ArH), 7.31 (d, J = 7.5 Hz, 3H, ArH), 7.12 (t,
J = 7.5 Hz, 3H, ArH), 6.56–6.63 (m, 6H, ArH), 5.54 (bt,
3H, NH, exchanges with D2O), 4.44 (d, J= 4.8 Hz, 6H, 3
CH2NH, converts to singlet on D2O exchange), 3.88 (s, 6H,
3 CH2S), 2.23 (s, 9H, 3 CH3) ppm; 13C NMR (75 MHz,
CDCl3): δ=149.2, 136.6, 136.3, 135.7, 133.4, 132.7, 132.3,
130.3, 128.4, 127.7, 126.2, 125.7, 125.6, 125.4, 117.9,
117.2, 110.5, 48.2, 35.8, 15.8 ppm; MS (FAB): m/z= 952
[(M+1)+].
2,2′‑[[[2,4,6‑Trimethyl‑5‑[[[2‑[(naphthalen‑2‑ylmethyl)‑
amino]phenyl]thio]methyl]‑1,3‑phenylene]bis(methylene)]‑
bis(sulfanediyl)]dianiline (15, C41H41N3S3)
N‑(Naphthalen‑2‑ylmethyl)‑2‑[(2,4,6‑trimethylbenzyl)thio]‑
aniline (8, C27H27NS)
1
Yield 0.095 g (25%); solid; m.p.: 126–128 °C; H NMR
1
(300 MHz, CDCl3): δ=7.81–7.85 (m, 4H, ArH), 7.45–7.48
(m, 3H, ArH), 7.40 (d, J = 7.5 Hz, 1H, ArH), 7.28 (d,
J = 7.5 Hz, 2H, ArH), 7.19 (t, J = 7.5 Hz, 1H, ArH), 7.10
(t, J=7.5 Hz, 2H, ArH), 6.62–6.71 (m, 6H, ArH), 4.55 (bs,
1H, NH, exchanges with D2O), 4.49 (s, 2H, CH2NH), 4.03
(bs, 4H, 2 NH2, exchanges with D2O), 4.01 (s, 2H, CH2S),
3.93 (s, 4H, 2 CH2S), 2.35 (s, 3H, CH3), 2.30 (s, 6H, 2 CH3)
ppm; 13C NMR (75 MHz, CDCl3): δ=149.4, 148.4, 136.6,
136.5, 136.1, 135.8, 133.5, 132.7, 132.3, 130.4, 129.9,
128.4, 127.7, 127.7, 126.2, 125.7,125.6, 118.6, 118.2, 117.9,
Yield 0.14 g (30%); thick liquid; H NMR (300 MHz,
CDCl3): δ = 7.76–7.84 (m, 4H, ArH), 7.36–7.48 (m, 4H,
ArH), 7.14 (t, J = 7.5 Hz, 1H, ArH), 6.76 (s, 2H, ArH),
6.58–6.63 (m, 2H, ArH), 5.62 (t, J = 5.4 Hz, 1H, NH,
exchanges with D2O), 4.45 (d, J=5.4 Hz, 2H, CH2NH con-
verts to singlet on D2O exchange), 3.96 (s, 2H, CH2S), 2.22
(s, 6H, 2 CH3), 2.21 (s, 3H, CH3) ppm; 13C NMR (75 MHz,
CDCl3): δ = 149.4, 136.9, 136.6, 136.5, 133.4, 132.7,
131.0, 130.3, 128.9, 128.3, 127.7, 126.1, 125.7, 125.5,
118.1, 117.1, 110.3, 48.2, 34.5, 20.9, 19.4 ppm; MS (FAB):
m/z=397 (M+).
1 3

76
P. Singh
17. McNicol DD, Wilson DR (1976) J Chem Soc Chem Commun
5:355
Extraction of metal picrates
18. Simaan S, Siegel JS, Biali SE (2003) J Org Chem 68:3699
19. Filby MH, Steed JW (2006) Coord Chem Rev 250:3200
20. Singh P (2006) Design and synthesis of amine and thioether based
acyclic and cyclic receptors. Ph.D. Thesis, Guru Nanak Dev Uni-
versity, Amritsar, India
For the extraction experiments, metal picrate solutions
(0.001 mol dm−3) were prepared in deionised distilled water.
The solutions of receptors (0.001 mol dm−3) were prepared
in chloroform (A.R Grade). An aqueous solution (2 cm3)
of a metal picrate (0.001 mol dm−3) and a chloroform solu-
tion (2 cm3) of a receptor (0.001 mol dm−3) in a cylindrical
tube closed with a septum was shaken for 5 min and kept
at 27 1 °C for 3–4 h. An aliquot of the chloroform layer
(1 cm3) was withdrawn with a syringe and diluted with ace-
tonitrile to 10 cm3. The UV absorption was measured against
CHCl3-CH3CN (1:9) solution at 374 nm. Extraction of the
metal picrate has been calculated as the percentage of the
metal picrate extracted in the chloroform layer and values
are the mean of the three independent measurements which
were within 0.02 error.
21. Romero A, Nar H, Huber R, Messerschmidt A, Kalverda AP, Can-
ters DR, Mathews FS (1994) J Mol Biol 236:1196
22. Hay M, Richards JH, Lu Y (1996) Proc Natl Acad Sci USA 93:461
23. Buning C, Comba P (2000) Eur J Inorg Chem 2000:1267
24. Buning C, Canters GW, Comba P, Dennison C, Jeuken L, Melter
M, Sanders-Loehr J (2000) J Am Chem Soc 122:204
25. Parveen S, Khan MOF, Austin SE, Croft SL, Yardley V, Rock P,
Douglas KT (2005) J Med Chem 48:8087
26. Cross ED, Shehzad UA, Lloy SM, Brown ARC, Mercer TD, Fos-
ter DR, McLellan BL, Murray AR, English MA, Bierenstiel M
(2011) Synthesis 2:303
27. Prabhakaran R, Geetha A, Thilagavathi M, Karvembu R, Krishnan
V, Bertagnolli H, Natarajan K (2004) J Inorg Biochem 98:2131
28. Gok Y, Karabiicek S, Misir MN (1996) Transit Met Chem 21:331
29. Kaur S, Kumar S (2004) Tetrahedron Lett 45:5081
30. Kaur S, Kumar S (2002) J Chem Soc Chem Commun 31:2840
31. Kumar S, Singh P, Kaur S (2007) Tetrahedron 63:11724
32. Singh P, Kumar S (2007) J Incl Phenom Macrocycl Chem 58:89
33. Singh P, Kumar S (2007) J Incl Phenom Macrocycl Chem 59:155
34. Van der Made AW, Van der Made RH (1993) J Org Chem 58:1262
35. Wilhelm W (1952) J Org Chem 17:523
Acknowledgements We thank DST, New Delhi for fnancial assistance
and FIST programme, UGC, New Delhi for CAS programme.
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