Accepted Manuscript

Novel bis-calix[4]arene based molecular probe for ferric iron through colori-metric, ratiometric and fluorescence enhancement response

H.M. Chawla, Tanu Gupta

PII: S0040-4039(14)02144-3DOI: http://dx.doi.org/10.1016/j.tetlet.2014.12.078Reference: TETL 45602

To appear in: Tetrahedron Letters

Received Date: 27 October 2014Revised Date: 12 December 2014Accepted Date: 14 December 2014

Please cite this article as: Chawla, H.M., Gupta, T., Novel bis-calix[4]arene based molecular probe for ferric ironthrough colorimetric, ratiometric and fluorescence enhancement response, Tetrahedron Letters (2014), doi: http://dx.doi.org/10.1016/j.tetlet.2014.12.078

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customerswe are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, andreview of the resulting proof before it is published in its final form. Please note that during the production processerrors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Graphical Abstract

Novel bis-calix[4]arene based molecular

probe for ferric iron through colorimetric,

ratiometric and fluorescence enhancement

response

H.M. Chawla* and Tanu Gupta

Leave this area blank for abstract info.

1

Tetrahedron Letters journal homepage: www.elsevi er .com

Novel bis-calix[4]arene based molecular probe for ferric iron through colorimetric,

ratiometric and fluorescence enhancement response

H.M. Chawla∗ and Tanu Gupta

Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi – 110016, India

———

∗ Corresponding author. Tel.: +91-11-265-91517; fax: +91-11-265-81102; e-mail: hmchawla@chemistry.iitd.ernet.in, hmchawla@chemistry.iitd.ac.in (H.M. Chawla).

Transition metal ions play a very important role in many

fundamental biological processes1-2

. Several attempts have been

made by various research groups to develop chemosensors for

specific metal ion detection by making use of diverse recognition

systems such as fluorescein fluoroinophores3, triazole

derivatives4, crown ethers

5 etc. Amongst transition metal ions,

iron plays an indispensable role6-7

at cellular level, as it enhances

physiological activities and greatly influences gene expression in

prokaryotes. An imbalance of iron concentration is known to

cause severe deleterious effects. For example, an excess

accumulation of iron can cause clinical deterioration and often

death in patients with severe forms of thalassemia. In such cases,

excess iron can be removed from the patient’s body only by

means of iron binding drugs called iron chelators. It is therefore

important to devise novel methods for sensitive resolution of

ferric ion. Calixarenes represent one of the most extensively studied

molecular receptors for recognition of various ions and neutral

molecules8-9

. While most studies in calixarene chemistry have

focused on mono calixarene derivatives, there has been increased

recent interest in the development of multi calixarene

compounds10

. In this connection, bis-calixarenes have attracted

special attention from several research groups as higher order

supramolecular systems which may possess special recognition

abilities. For example, while Rao and coworkers11

have reported

a double calixarene for metal ion sensing, Lhoták and

coworkers12

have reported a bis-calixarene derivative for anion

recognition. The same group has reported another biscalixarene

derivative13

for selective sensing of K+ and Ag

+ ions. Hudrlik and

coworkers14

have also reported their recent attempts to join two

calixarene scaffolds by means of a three-carbon bridge.

Bifunctional reagents can react with calix[4]arene to result in

intermoleculary bridged systems. Although enough efforts have

been devoted to the synthesis and characterization of

biscalixarenes, most of the past work15

has concentrated majorly

on the lower rim- lower rim type of double calixarenes. We

report herein a new bis-calix[4]arene derivative 4, which is

doubly bridged at the upper rims of two calixarene macrocycles

by means of carbohydrazide linkers. To the best of our

knowledge, 4 is the first example of an upper rim- upper rim

double calixarene bridged through a carbohydrazide framework.

Our synthetic strategy was based upon the utilization of the

diformylated calix[4]arene as the pivotal compound that could

allow bridging at the upper rim when reacted with

carbohydrazide. Spectroscopic evaluation of 4 reveals that it

shows a high affinity towards ferric ions. It is significant to note

that only a few chemosensors are available in the literature16

for

Fe3+

and most of them suffer from cross-sensitivity17-18

for

competitive metal ions like Cu2+

, Hg2+

and Cr3+

. Moreover, due

to well known quenching effect of iron on the excited state of

fluorophores by electron transfer processes, the design of turn-on

fluorescent sensors for its detection tends to be much more

challenging19

. A chemosensor that not only detects Fe3+

even in

AR TI C LE IN FO ABS TRAC T

Article history:

Received

Received in revised form

Accepted

Available online

A new bis-calix[4]arene platform (4) formed by upper rim- upper rim linking of two calixarene

units has been obtained by 1: 1 condensation of diformyl calixarene with carbohydrazide. The

synthesized bis-calixarene has been found to selectively sense Fe3+

, without interference from

ferrous or any other metal ion through enhancement in the fluorescence intensity as well as

ratiometric absorption changes accompanied by a color change. The importance of bridged

macro cyclic framework has been further highlighted by comparison with an acyclic reference

compound.

2009 Elsevier Ltd. All rights reserved.

Keywords:

Keyword_1 bis- calix[4]arenes

Keyword_2 ferric iron

Keyword_3 fluorescence enhancement

Keyword_4 ratio metric

Keyword_5 ionic recognition

Tetrahedron 2the presence of high concentrations of Cu

2+ and Cr

3+, but also

exhibits enhancement in emission intensity would be much more

attractive. In this context, chemosensor 4 proves to be highly

advantageous not only for exclusive selectivity towards Fe3+

from

amongst 14 test metal ions but also for a significant enhancement

in fluorescence emission in response to Fe3+

ions.

The reaction of 3 with carbohydrazide in ethanol furnished

compound 4 in 72% yield (Scheme 1). Carbohydrazide was

synthesized as described previously in the literature20

. The

structure21

of bis-calixarene 4 was established by 1H NMR,

13C

NMR and HRMS analysis. The IH NMR spectrum

(Supplementary data, fig. S1) of 4 exhibited deuterium

exchangeable singlets at 10.30 ppm and 7.94 ppm corresponding

to carbohydrazone NH and calixarene phenolic protons

respectively, while calixarene aryl ring protons were obtained at

7.48 and 7.11 ppm. The existence of the synthesized compound

in its cone conformation was further confirmed by 13

C NMR

(Supplementary data, fig. S2) which showed a signal for syn

Ar2CH2 at 30.02 ppm The formation of double calixarene was

further confirmed by HRMS analysis which showed peak at m/z

1659.73 [M+Na]+ corresponding to 4.

H OO H O H OO O HO H

O

O O

O

O O HO H

C H O

O

O

C H O

( i )

( i i)

(i i i )

1 2

3

O H

O

O

O

OO HO H

O

O

O

O

O

O O HO H

O

O4

O

O

O

NN

N H H N

N H H N

N N

OO

S

cheme 1. Synthesis of 4 and 7. Reagents and conditions: (i) Ethyl

bromoacetate, K2CO3, CH3CN, reflux, 24h, yield: 70%; (ii)

hexamethylenetetramine, trifluoroacetic acid, reflux, 48h, yield:

61%; (iii) carbohydrazide, ethanol, reflux, 2h, yield: 72%; (iv)

ethanol, reflux, 2h, yield: 70%.

The selectivity and sensitivity of receptor 4 towards different

metal ions (Mn2+

, Co2+

, Cu2+

, Fe2+

, Fe3+

, Ni2+

, Hg2+

, Ag+, Cd

2+,

Zn2+

, Cr3+

, Na+, Cs

+, Li

+ ) was determined by UV-vis,

fluorescence and 1H NMR spectroscopy. The stock solutions

(1mM) of perchlorate salts of all metal ions were prepared in

HPLC grade DMSO. Absorbance and fluorescence spectra were

recorded by gradual addition of increasing amounts of ions to the

receptor solution (30µM).The absorption spectrum of a DMSO

solution of 4 exhibited characteristic absorption bands at 308 nm

and 321 nm (molar extinction coefficient: 2.22Χ104 M

-1 cm

-1 and

2.20Χ104 M

-1 cm

-1 respectively). The addition of just 0.1 equiv of

Fe3+

to a DMSO solution of 4 (30µM) resulted in the appearance

of a new absorption band around 370 nm, which exhibited

significant absorption enhancement upon further addition of Fe3+

.

The new spectral band at 370 nm, could be attributed to the

complex species formed between 4 and Fe3+

. The change in

absorbance spectrum was accompanied by a color change of

solution from colorless to light yellow. However, addition of

other competitive metal ions to the DMSO solution of 4 did not

alter its absorption spectrum (Supplementary data, fig. S3).

Figure 1 shows the changes in the absorption spectrum as well as

color of a solution of 4 upon gradual addition of Fe3+

from 0 to

7.5 equiv.

Fig.1 Variation in absorption spectrum of 4 (30µM) upon titration

with Fe3+ (0-7.5 equiv) in DMSO. Inset shows color change upon

Fe3+ addition

Such a change in absorbance values at two different

wavelengths offered an interesting opportunity for the ratiometric

determination of the analyte. When absorbance intensity ratios at

370 and 308 nm were plotted as the function of Fe3+

equivalents

added, a typical ratiometric calibration graph was obtained as

shown in figure 2. The absorbance ratio (A370/A308) exhibits

nearly 6- fold enhancement upon addition of Fe3+

(7.5 equiv).

Fig.2 Ratiometric plot of A370/A308 as a function of

equivalents of Fe3+ added.

A Job's Plot was constructed to estimate the binding

stoichiometry of 4 with Fe3+

, which exhibited a 1: 1 metal ligand

complexation. The association constant for 4/Fe3+

was calculated

as 6.0×104 M

-1 (Supplementary data, fig. S4).

from absorption titration data by using Benesi- Hildebrand

equation.22

An acyclic reference compound 7 was synthesized by adopting

adopting a process reported in the literature. 7 was subjected to

similar recognition experiments with Fe3+

. It was determined that

7 showed an absorption maximum at 295 nm along with a

shoulder band at 315 nm. The absorption spectrum of 7 did not

show any obvious changes even on addition of excess (10 equiv)

of Fe3+

ions, thereby confirming the importance of bridged

macrocyclic framework of 4 for Fe3+

sensing. Figure S5,

(Supplementary data), shows the absorption spectrum of 7 upon

addition of excess of Fe3+

.

The selectivity of 4 was also investigated by measuring the

3fluorescence emission spectra against different metal ions in

DMSO. When excited at 320 nm, the fluorescence spectrum of 4

exhibited a maximum at 445 nm. Addition of 2 equiv of Fe3+

to a

DMSO solution of 4 (30µM) resulted in an appreciable

enhancement (~97%) in the fluorescence intensity at 445 nm

(fig.3), while other tested metal ions virtually had no effect on

the fluorescence intensity of 4, indicating that 4 is a reliable,

sensitive and highly selective turn-on fluorescent sensor for Fe3+

.

The increase in the emission intensity could be attributed to the

formation of 4-Fe3+

complex.

Fig.3 Changes in the emission spectrum of 4 (30µM) upon addition

of Fe3+ (0- 2 equiv.) in DMSO.

Supplementary data, fig. S6 depicts the relative increase in

the fluorescence intensity (at λ. 445 nm) of 4 upon addition of

various metal ions. It is quite evident that binding of 4 and Fe3+

is

remarkably selective, while other competing ions (including Fe2+

ions) caused insignificant changes in the emission spectrum of 4.

The selectivity coefficients (kMn+

, Fe3+

= ∆FMn+

/∆FFe3+

)23

measured

for all the tested metal ions (inset, figure S5) showed that the

interaction of other ions with 4 (especially ferrous ions) was

too miniscule to affect the detection of Fe3+

by 4.

The limit of detection24

(LOD) for Fe3+

binding by 4, as

determined from the fluorescence titration data was 3×l0-7

M.

This LOD is lower than the maximum level of Fe3+

(5.4µM)

ions25

permitted in drinking water by the US Environmental

Protection Agency, implying that probe 4 holds a great potential

for use in the development of sensor materials for Fe3+

.

Further, competitive experiments were conducted to know the

effects of coexisting biologically relevant ions on the detection

of Fe3+

(fig 4) by 4 (30µM). Addition of an equimolar amount (2

equiv) of other interfering metal ions to a solution of 4.Fe3+

resulted in negligible effect on the fluorescence intensity of the

complex, indicating that 4 is a reliable, highly selective and

sensitive "turn-on" fluorescence sensor for Fe3+

in DMSO.

Fig.4 Competitive selectivity of 4 for Fe3+ in preference to other

metal ions. Red bar represents the intensity of 4 (30 µM) in presence

of 2 equiv of Fe3+ alone. Green bar denotes intensity of Fe3+/ Mn+

coexisting systems

A plausible binding mode of 4 and Fe3+

was examined by

recording the 1H NMR spectra of DMSO-d6 solution of 4

(5mM), before and after the addition of Fe3+

. As depicted in

figure 5, it was determined that the peak corresponding to

carbohydrazide NH underwent a downfield shift from 10.30 to

10.48 ppm. This shift in the peak of NH protons in the presence

of iron could be attributed to the coordination of carbohydrazide

carbonyl oxygen functionality with ferric ion during

complexation.

Fig. 5 Partial 1H NMR (300 MHz) spectra of (a) 4 in DMSO ; (b) 4 +

0.1 equiv. Fe3+ ; (c) 4 + 0.5 equiv. Fe3+ ; (d) 4 + 1 equiv. Fe3+.

In conclusion, we have realized teh synthesis of a new type of

upper rim linked bis-calixarene platform possessing

carbohydrazide moiety as the bridging unit. It is noteworthy that,

while turn-ON fluorescence sensors for iron are quite sparse, 4

shows a selective enhancement of fluorescence intensity in

response to Fe3+

ions with a quite low detection limit of 3×10-7

M. Furthermore, 4 shows a ratiometric absorption response

towards Fe3+

along with a specific color change which

additionally augments the prospects of 4 to be used as an iron

selective chemosensor.

Acknowledgement. Tanu Gupta thanks CSIR, India for a

research fellowship. Financial assistance from DST(for purchase

of HRMS by Chemistry Department), DBT, MoEF, MoRD and

MoFPI is gratefully acknowledged

References 1. Linder, M. C.; Hazegh- Azam, M. Am. J. Clin. Nutr. 1996, 63, 797S-

811S.

2. Uauy, R.; Olivares, M.; Gonzalez, M. Am. J. Clin. Nutr. 1998, 67,

952S- 959S.

3. (a) Li, T.; Yang, Z.; Li, Y.; Liu, Z.; Qi, G.; Wang, B. Dyes and

Pigments 2011, 88, 103-108; (b) Chawla, H. M.; Shukla, R.; Pandey,

S. Tetrahedron Lett. 2013, 54, 2063-2066.

(a)

(b)

(c)

(d)

λex 320 nm

Tetrahedron 44. (a) Pathak, R. K.; Hinge, V. K.; Mondal, P.; Rao, C. P. Dalton

Trans. 2012, 41, 10652-10660; (b) Park, S. Y.; Yoon, J. H.; Hong, C.

S.; Souane, R.; Kim, J. S.; Matthews, S. E.; Vicens, J. J. Org. Chem.

2008, 73, 8212- 8218.

5. Surowiec, M.; Custelcean, R.; Surowiec, K.; Bartsch, R. A.

Tetrahedron 2009, 66, 7777-7783.

6. (a) Palacios, M. A.; Wang, Z.; Montes, V. A.; Zyryanov, G. V.;

Anzenbacher, P.; Jr. J. Am. Chem. Soc. , 2008, 130 , 10307–10314; (b)

Tolosa, J.; Zucchero, A. J.; Bunz, U. H. F. J. Am. Chem. Soc. 2008,

130 , 6498 – 6506.

7. Youdim, M. B. H. Neurotoxic. Res. 2008, 14 (1), 45 –56.

8. (a) Sahin, O.; Yilmaz, M. Tetrahedron Lett. 2012, 53, 2319- 2234; (b)

Pathak, R. K.; Dessingou, J.; Rao, C. P. Anal. Chem. 2012, 84, 8294-

8300; (c) Nimse, S. B.; Kim, T. Chem. Soc. Rev. 2013, 42, 366-386.

9. (a) Lee, J. W.; Park, S. Y.; Cho, B. K.; Kim, J. S. Tetrahedron Lett.

2007, 48, 2541- 2546; (b) Chawla, H. M.; Sahu, S. N.; Shrivastava, R.;

Kumar, S. Tetrahedron Lett. 2012, 53, 2244- 2247; (c) Chawla, H. M.;

Pant, N.; Kumar, S.; Kumar, N.; Black David St, C. Calixarene-based

materials for chemical sensors In Chemical Sensors Fundamentals of

Sensing Materials; Korotcenkov, G., Ed.; Momentum Press: New

York, 2010; Vol. 3, p 300.

10. (a) Gac, S. L.; Zeng, X.; Reinaud, O.; Jabin, I. J. Org. Chem. 2005, 70,

1204-1210; (b) Tsai, C. –C.; Chang, K. –C.; Ho, I. –T.; Chu, J. –H.;

Cheng, Y. –T.; Shen, L. –C.; Chung, W. –S. Chem. Commun. 2013, 49,

3037-3039.

11. Ali, A.; Joseph, R.; Mahieu, B.; Rao, C. P. Polyhedron 2010, 29, 1035-

1040.

12. Stastny, V.; Lhoták, P.; Michlová, V.; Stibor, I.; Sykora, J.

Tetrahedron, 2002, 58, 7207-7211.

13. Budka, J.; Lhoták, P.; Stibor, I.; Michlová, V.; Sykora, J.; Cisarová, I.

Tetrahedron Lett. 2002, 43, 2857-2861.

14. Hudrlik, P. F.; Hailu, S. T.; Hudrlik, A. M.; Butcher, R. J. J. Mol.

Struct. 2013, 1054-1055, 271-281.

15. (a) Kim, S. K.; Sim, W.; Vicens, J.; Kim, J. S. Tetrahedron Lett. 2003,

44, 805-809; (b) Morales- Sanfrutos, J.; Ortega- Muñoz, M.; Lopez-

Jaramillo, J.; Hernandez- Mateo, F.; Santoyo- Gonzalez, F. J. Org.

Chem. 2008, 73, 7768-7771; (c) Luo, J.; Shen, L. –C.; Chung, W. –S.

J. Org. Chem. 2010, 75, 464-467.

16. (a) Pandya, A.; Sutariya, P. G.; Lodha, A.; Menon, S. K. Nanoscale

2013, 5, 2364-2371; (b) Yang, L.; Yang, W.; Xu, D.; Zhang, Z.; Liu,

A. Dyes and Pigments 2013, 97, 168-174.

17. (a) Liu, J.-M.; Zheng, Q.-Y.; Yang, J.-L.; Chen, C.-F.; Huang, Z.-T.

Tetrahedron Lett. 2002, 43, 9209-9212; (b) Ali, A.; Joseph, R.;

Mahieu, B.; Rao, C. P. Polyhedron 2010, 29, 1035-1040; (c) Wang,

M.; Wang, J.; Xue, W.; Wu, A. Dyes and Pigments 2013, 97, 475-480.

18. (a) Narayanaswamy, N.; Govindaraju, T. Sens. Actuators, B 2012,

161, 304-310; (b) Liu, R.-L.; Lu, H.-Y.; Li, M.; Hu, S.-Z.; Chen, C.-F.

RSC Adv. 2012, 2, 4415-4420.

19. a) Shellaiah, M.; Wu, Y.-H.; Singh, A.; Raju, M. V. R.; Lin, H.-C. J.

Mater. Chem. A 2013, 1, 1310-1318; (b) Bhalla, V.; Sharma, N.;

Kumar, N; Kumar, M. Sens. Actuators, B 2013, 178, 228-232.

20. Li, Z.; Zhu, W.; Yu, J.; Ma, X.; Lu, Z.; Xiao, S. Synth. Commun.

2006, 36, 2613-2619.

21. Analytical data for 4: Yield: 72%; Mp: 194-1960C ; UV (λmax,

DMSO): 308 nm, 321 nm; IR (KBr pellet, cm-1): 3384, 2956, 1610,

1541, 1196; Anal. Calcd: C 68.93, H 6.65, O 17.58; Found: C 68.95,

H 6.66, O 17.55; HRMS (ESI-MS) m/z:calcd 1659.76, found 1659.73;

1H NMR (300 MHz, DMSO, δ in ppm): 10.30 (s, 4H, NH, D2O

exchangeable), 8.24 (s, 4H), 7.94 (s, 4H, OH, D2O exchangeable),

7.48 (s, 8H), 7.11 (s, 8H), 4.82 (s, 8H), 4.42 (d, 8H), 4.32 (q, 8H), 3.60

(d, 8H), 1.32 (t, 12H),1.28 (s, 36H); 13C NMR (75 MHz, DMSO, δ in

ppm) 12.96, 30.02, 32.93, 59.92, 70.94, 116.99, 117.58, 125.04,

126.75, 127.75, 129.02, 131.42, 146.21, 149.50, 151.13, 152.65,

168.01.

22. Benesi, H. A.; Hildebrand, J. H. J. Am. Chem. Soc. 1949, 71, 2703–

2707.

23. Pandey, S.; Azam, A.; Pandey, S.; Chawla, H. M. Org. Biomol. Chem.

2009, 7, 269-279.

24. Ono, A.; Togashi, H. Angew. Chem. Int. Ed. 2004, 43, 4300- 4302.

25. Yi, C.; Tian, W.; Song, B.; Zheng, Y.; Qi, Z.; Qi, Q.; Sun, Y. J.

Lumin. 2013, 141, 15-22.