synthesis of alizarin-crown-6 incorporated calix[4]arene...

CHAPTER-V

Synthesis of alizarin-crown-6 incorporated

calix[4]arene and their interaction with

alkali and alkaline earth metal ions in

aqueous media

CONTENTS

Chapter: V Synthesis of alizarin-crown-6 incorporated calix[4]arene and

their interaction with alkali and alkaline earth metal ions in aqueous media

5.1 Introduction 1

5.2 Experimental section 1

5.2.1. Materials 1

5.2.2. Physical measurement 1

5.2.3. Synthesis of anthraquinone substituted

calix[4]arene-crown-6 ether (I) 2

5.2.4. Determination of selectivity 2

5.2.5. Determination of binding constant by NMR titration 2

5.2.6. Synthesis of metal complexes 3

5.3. Results and discussions 5

5.3.1. Synthesis and characterization of the ionophore (1) 5

5.3.2. Selectivity study 7

5.3.3. NMR titration for determination of binding constant 7

5.3.4. Isolated complexes of the ionophore 1 11

5.4. Conclusions 13

References 14

Chapter-V

1

5.1. Introduction In the earlier chapters, calix[4]arene-crown hybrid ionophores with variation in size of

the crown rings, type of the crown moieties and substituents in the crown/calix moieties

with their competitive complexation property towards alkali and alkaline earth metal

ions have been reported. In this chapter, a calix-crown hybrid ionophore with

anthraquinone moiety attached to the crown ring with its complexation property has

been reported. Anthraquinone is a bulky rigid moiety with keto group, the oxygen atom

of which may interact with the metal ion through axial position and at the same time it

may impose certain steric crowding controlling the selectivity of the ionophore.1-25

It is

therefore interesting to see how this molecule behaves towards complexation with

alkali and alkaline earth metal ions under similar conditions as used for other

ionophores.

In this chapter, synthesis and characterization of the anthraquinone substituted

calix[4]arene-crown-6 ether its selectivity and complexation property has been

reported. Binding constant with strongly interacting metal ions, determined by NMR

titration has also been reported.

5.2. Experimental section

5.2.1.Materials

The compound 1,2-dihydroxy-9,10-anthraquinone was purchased from S.D Fine

chemicals. The other starting materials were purchased from the same source as

described in the earlier Chapters. Starting compounds were also prepared following the

literature procedure as mentioned in the earlier Chapters. The 1, 2-dihydroxy

anthraquinone modified pentaethylene glycol ditosylate was prepared following the

literature procedure.26

5.2.2. Physical measurement

For physical measurements, same instruments as described in Chapters II-IV are used.

Chapter-V

2

5.2.3. Synthesis of anthraquinone substituted calix[4]arene-crown-6 ether (I)

In a typical procedure, calix[4]arene, (0.937 g, 2.2 mmol) and 1,2-dihydroxy

anthraquinone modified pentaethylene glycol ditosylate (1.6 g, 2.2 mmol) and K2CO3

(0.3 g, 2.2 mmol) were taken in 100 mL dry acetonitrile and heated under reflux for 72

h under nitrogen atmosphere. Then the solvent of the reaction mixture was removed

under reduced pressure and the crude product thus obtained was dissolved in 100 mL

dichloromethane and was treated with 100 mL 1N HCl. The organic layer was then

separated and dried with anhydrous Mg(SO)4 and the solution was then evaporated

under reduced pressure. The crude product thus obtained was purified by column

chromatography using 1:2 ethylacetate and hexane. Yield: 40%. Elemental analysis for

C50H44O10, C, 74.76; H, 6.27; Found: C, 74.32; H, 6.52. ES-MS: m/z = 843.64 (100%),

calcd. for [1+K+]

+ 843.92.Selected IR band (KBr pellet, cm

-1) 3387 (OH), 2928-2874

(C=C, aromatic), 1671 (C=O,). 1H NMR (CD3CN) δ: 8.20 (t, J = 6.5 Hz, 2H,

H3H

4 (see Fig.5.2 for naming), 7.96 (d, J = 9.0 Hz, 1H, H

5), 7.82 (t, J = 5.75 Hz, 2H,

H1H

2), 7.83 (s, 2H, ArOH-calix, H

15)7.36 (d, J = 9.0 Hz 1H, H

6), 6.98 (d, J = 6.5 Hz,

2H, ArHp-calix,H17

), 6.94 (t, J = 7.5 Hz, 6H, ArHm-calix, H18

), 6.75 (q, J = 5.0 Hz,

2H, ArHm-calix,H16

), 6.50 (t, J = 7.5 Hz, 2H, ArHp-calix, H19

), 4.43 (t, J = 4.5 Hz, 2H,

anthraquinone-OCH2,H7), 4.40 (t, J = 4.75 Hz, 2H, ArOCH2, H

14), 4.31 (dd, J = 12.16

Hz, 4H, ArCH2Ar,H20

), 4.24 (t, J = 5.0 Hz, 2H, anthraquinone-OCH2,H8), 4.14 (t, J =

4.5 Hz, 2H, anthraquinone-crown, H12

), 4.09 (broad s, 6H, anthraquinone crown,

H9,H

10,H

11), 4.03 (t, J = 4.5 Hz, 2H, ArOCH2,H

13), 3.32 (d, J = 13.0 Hz, 4H, ArCH2Ar,

H21

).

5.2.4. Determination of selectivity

Selectivity of the ionophore 1 was examined with alkali and alkaline earth metal ions in

aqueous media using equimolar mixture of metal ions and various concentrations of

metal ions present in bittern solution following the similar procedure as described in

Chapter IV.

5.2.5. Determination of binding constant by NMR titration

For NMR titration, stock solutions of the picrate salts of the metal ions Na+/ K

+/

Ca2+

were prepared in CD3CN. 1H NMR spectra of the solutions containing 2 mg

of ionophore 1, dissolved in 0.5 mL of the same solvent, was recorded. Into this

Chapter-V

3

solution, required amount of stock solution containing desired metal salt was

added by micro syringe to make the concentrations of the desired concentrations

of the metal ion in the solution and the spectra of the resulting solutions were

recorded. Upon addition of increasing concentration of cations, gradual shift of

certain signals were noted. Using this gradual change in chemical shift, binding

constants were calculated using the literature procedure27,28

5.2.6. Synthesis of metal complexes

The metal complexes were synthesized following a general procedure. In a typical

experiment, a mixture of 0.05 mmol of the ionophore and Na+/ K

+/ Ca

2+ picrate (0.5

mmol, ten-fold excess) was stirred in chloroform at room temperature for 24 h. The

solution was then filtered and the solvent from the filtrate was removed under reduced

pressure. The yellow complex was then purified by dissolving it in dichloromethane,

filtered and removing the solvent. Yield: 80–90 %.

Characterization data

[1.Na+pic

-].H2O.H2O, Elemental analysis for C50H48O12Na, C, 69.52; H, 5.60; Found:

C, 69.13; H, 5.65. ES-MS: m/z = 827.52 (100%), calcd. for [1+Na+]

827.81. Selected IR

band (KBr pellet, cm-1

) 3424 (OH), 2925-2856 (C=C, aromatic), 1671 (C=O),

1633. 1

HNMR (CD3CN) δ: 8.63 (s, 2H, picrate) ,8.23 (d, J = 7.5Hz, 1H, anthraquinone,

H3), 8.20 (d, J = 6.0 Hz, 1H anthraquinone, H

4), 7.96 (d, J = 9.0 Hz, 1H anthraquinone,

H5), 7.91 (s, 2H, ArOH-calix, H

15), 7.88-7.84 (m, 2H, anthraquinone,H

1, H

2), 7.37 (d, J

= 9.0 Hz, 1H anthraquinone,H6), 6.93 (d, J = 7.5 Hz, 2H, ArHp-calix, H

17), 6.86 (t, J =

8.5 Hz, 4H, ArHm-calix, H18


), 6.71 (t, J

=7.5Hz, 2H, ArHm-calix, H16

), 6.34 (t, J =7.5Hz, 2H, ArHp-calix), 4.52 (t, J = 4.25Hz,

2H, anthraquinone-OCH2, H7), 4.38 (t, J = 4.25Hz, 2H, Ar-OCH2,H

14), 4.29

(Overlapped t, J = 6.5Hz, 2H, ArCH2Ar, H20

; 2H, anthraquinone-OCH2, H8; 2H,

anthraquinone-crown, H12

), 4.21(t, J = 4.0 Hz, 2H, anthraquinone-crown, H9), 4.14 (t, J

= 4.25Hz, 2H, anthraquinone-crown, H10

), 4.11(Overlapped t, J = 4.25Hz, 2H,

ArCH2Ar, H20

, 2H, anthraquinone-crown, H11

), 3.94 (t, J = 4.25 Hz, 2H, -


), 3.33 (dd, J = 12.0 Hz, 4H, ArCH2Ar, H21

).

Chapter-V

4

[1.K+pic

-].H2O.H2O, Elemental analysis for C50H48O12K, C, 68.24; H, 5.49; Found: C,

68.05; H, 5.71; ES-MS: m/z = 843.76 (100%), calcd. for [1+K+]

843.92; Selected IR


) 3391 (OH), 2925-2856 (C=C, aromatic), 1671 (C=O),

1632. 1

HNMR (CD3CN) δ: 8.61 (s, 2H, picrate), 8.23 (d, J = 6.0Hz, 1H, anthraquinone,

H3), 8.18 (d, J = 6.0 Hz, 1H anthraquinone, H


H5), 7.90-7.86 (m, 2H, anthraquinone, H

1, H


H6), 7.13 (s, 2H, ArOH-calix,H

15), 6.85 (overlapped t, J = 7.5Hz, 2H, ArHp-calix, H

17;

2H, ArHm-calix, H18


), 6.71 (d, J = 7.0Hz,

4H, ArHm-calix, H18

), 6.64 (t, J =7.5Hz, 1H, ArHm-calix, H16

), 6.31(t, J =7.5Hz, 2H,

ArHp-calix, H19

), 4.60 (t, J = 4.25Hz, 2H, anthraquinone-OCH2, H7), 4.34 (d, J =

3.0Hz, 2H, anthraquinone-OCH2, H14

; 2H, ArOCH2, H8), 4.24 (Overlapped d, J =

7.5Hz, 2H, ArCH2Ar, H20

; 2H, anthraquinone-crown, H9), 4.21(t, J = 2.25Hz, 4H,


,H11

), 4.05 (t, J = 4.25Hz, 2H, anthraquinone crown, H10

),

3.96 (d, J = 13 Hz, 2H, ArCH2Ar, H20

), 3.85 (t, J = 3.75 Hz, 2H, ArOCH2, H13

), 3.38

(d, J = 13.5 Hz, 2H, ArCH2Ar, H21

), 3.27 (d, J = 13.5 Hz, 2H, ArCH2Ar, H21

).

[1.Ca2+

(pic-)2].H2O Elemental analysis for C50H46O11Ca, C, 69.59; H, 5.37; Found: C,

69.12; H, 5.60; ES-MS: m/z = 843.86, calcd. For [1+Ca2+

-H+]

+ 843.89; Selected IR


) 3398 (OH), 2925-2856 (C=C, aromatic), 1671 (C=O);

1HNMR (CD3CN) δ: 8.70 (s, 4H, picrate), 8.18 (d, J = 7.5Hz, 1H, anthraquinone, H

3),

8.15 (d, J = 8.0 Hz, 1H, anthraquinone, H4), 7.98 (d, J = 8.5 Hz, 1H anthraquinone,H

5),

7.87-7.81 (m, 2H, anthraquinone, H1, H

2), 7.73 (s, 2H, ArOH-calix, H

15), 7.32 (d, J =

8.5 Hz, 1H anthraquinone, H6), 7.02 (Overlapped dd, J = 7.0 Hz, 2H, ArHm-calix, H

17,

2H, ArHp-calix, H18

), 6.93 (dd, J = 7.5 Hz, 4H, ArHm-calix, H18

), 6.79-6.73 (m, 2H,

ArHm-calix, H16

), 6.55 (t, J =7.5Hz, 2H, ArHp-calix, H19

4.62 (br s, 2H, anthraquinone-

OCH2,H7), 4.52 (t, J = 3.75Hz, 2H, ArOCH2, H

14), 4.35 (t, J = 3.5Hz, 2H,

anthraquinone-OCH2,H8), 4.32 (t, J = 4.0 Hz, 2H, anthraquinone-crown, H

12), 4.25 (dd,

J = 13.0Hz, 4H, ArCH2Ar, H20

), 4.19 (t, J = 3.75Hz, 2H, -OCH2CH2O-crown, H9), 4.10

(t, J = 4.25Hz, 2H, -OCH2CH2O-crown, H10

), 4.02 (t, J = 4.0Hz, 2H, -OCH2CH2O-

crown,H11

), 4.00 (t, J = 4.25Hz, 2H, Ar-OCH2, H13

), 3.37 (dd, J = 13.0 Hz, 4H,

ArCH2Ar, H21

).

Chapter-V

5

5.3. Results and discussions

5.3.1. Synthesis and characterization of the ionophore (1)

Ionophore 1 has been synthesized by the reaction of 1,2-dihydroxyanthraquinone

modified pentaethylene glycolditosylate and calix[4]arene in the presence of two

equivalents of K2CO3 as a base following the route shown in Scheme 1 and detail

procedure has given in the Experimental Section. Elemental analysis, given in the

Experimental Section, is in excellent agreement with the composition of 1. The ES-MS

spectrum of 1 is shown in Fig.5.1, the m/z value of which (843.64) matched very well

with the calculated value (843.92) for [1+K+]

+. The

1H NMR spectrum of 1 with

assignment of signals is shown in Fig.5.2 and the data are presented in the Experimental

Section. The anthraquinone moiety exhibited signals at δ = 8.20, 7.96, 7.82 and 7.3626

Scheme.1. The route followed for the synthesis of ionophore 1, reagents/solvents: a)

chloroethoxyethanol/acetonitrile/K2CO3/reflux for 72h, b) TsCl/THF/0oC for 24h, c)

1,2-dihydroxy-9,10-anthraquinone modified pentaethylene glycolditosylate/acetonitrile/

reflux for 72h.

Chapter-V

6

m/z150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000

%

0

100

CANT 5 (0.093) 1: TOF MS ES+ 386843.64

242.38

186.30

188.25195.27

827.66623.40607.42

483.35

467.36

288.42243.38

388.34303.24 372.34436.47

484.34

585.43533.56

764.90

624.40

675.50626.42 691.51736.88

765.91

822.78784.66

844.65

845.64

871.73

872.74

873.72875.59

908.80947.77977.83

Fig.5.1. ES-mass spectrum of the ionophore 1, recorded in CD3CN[1+K+]

+

Fig.5.2. 1HNMR spectrum of ionophore 1 recorded in CD3CN

Chapter-V

7

and the phenolic OH of calixarene moiety appeared at δ = 7.83.29,30

The protons for the

methylene bridge of the calixarene moiety appeared at 4.32 (dd, 4H) and 3.32 (d, 4H),

which suggests cone conformation for the calixarene molecule.31

On the basis of these

data the molecular structure assigned for 1 is shown in Scheme 1.

5.3.2. Selectivity study

Selectivity of the ionophore 1 was investigated by two phase extraction method

following the similar procedure described in the earlier Chapters and mentioned in the

Experimental Section. The concentration of metal ions in the extract, determined by

ICP, exhibited K+ = 42, Ca

2+ = 24 , Na

+ % and trace amount of Mg

2+, which indicates

that this ionophore can extract Na+, K

+ and Ca

2+ and not highly selective for any

particular metal ion when mixture of metal ions are present. On the basis of this

information, the binding constants of 1 with all of these three metal ions were

determined by NMR titration.

5.3.3. NMR titration for determination of binding constant

The method followed for NMR titration is described in the Experimental Section and

the 1H NMR spectral change for 1, recorded with incremental addition of picrate salts

of the metal ions (Na+/K

+/Ca

2+) in CD3CN are shown in Figs.5.3-5.5. The spectra for all

the three metal ions exhibited significant changes in chemical shifts for many of the

signals. It may be noted that substantial changes in chemical shifts for all of the metal

ions is observed in the aliphatic region, where signals due to crown moiety appears. It

suggests that the crown moiety is involved in interaction with metal ions, in other

words the metal ions are encapsulated in the calix crown cavity. In the aromatic region,

the signals due to anthraquinone moiety is least affected, which indicates that this

moiety is not involved in making interaction with metal ions. The chemical shift of the

OH proton has shifted most for K+ ion, moderate shift has noted with Ca

2+, whereas no

significant change for Na+ has noted, suggesting that the OH group makes interaction

with the encapsulated K+ and Ca

2+ ions but Na

+ does not interact with the OH group.

Both in the aliphatic and aromatic regions, the signals due to calixarene moiety

exhibited considerable changes, which is maximum for K+. It may be attributed to the

overall conformational change of the ionophore due to complexation with metal ions.

Chapter-V

8

a

b

j

i

h

g

f

e

d

c

3.4 ppm4.24.44.6 ppm6.66.87.07.27.47.67.88.08.28.48.6 ppm

Fig.5.3. 1H NMR spectral change for ionophore 1 upon addition of Na

+Pic

-, 0.06 (a), 0.18 (b),

0.36 (c), 0.60 (d) 0.90 (e), 0.96 (f), 1.44 (g) and 2.04 (h) 2.76 (i) 3.6 (j) 4.56 (k) 5.52 (l) molar

equivalent amounts of Na-picrate.

3.4 ppm4.24.44.6 ppm6.66.87.07.27.47.67.88.08.28.48.6 ppm

a

b

l

k

j

i

h

g

f

e

d

c

Fig.5.4. 1H NMR spectral change for ionophore 1 upon addition of K

+Pic

-, 0.06 (a), 0.18(b),

0.36 (c), 0.60 (d) 0.90 (e), 1.26 (f), 1.70(g)2.40 2.98 (h) 3.61(i) 4.54 (j) 5.78 (k) and 8.09(l)

molar equivalent amounts of K-picrate.

Chapter-V

9

Fig.5.5. 1H NMR spectral changes for ionophore 1 upon addition of Ca(Pic)2 0.06 (a), 0.18 (b),

0.36 (c), 0.60 (d) 0.90 (e), 1.26 (f), 1.74 (g) and 2.34 (h) 4.86 (i) 5.94 (j) molar equivalent

amounts of metal salt.

Binding constants for Na+, K

+ and Ca

2+ ions were determined using the NMR titration

data. Considering the gradual change in chemical shift of a particular signal upon

addition of incremental amount of metal ion, the binding constants were calculated

using the program developed by Hirose32

The non-linear least square fit with Na+, K

+

and Ca2+

are presented in Figs.5.6-5.8, and the binding constants obtained are given in

Table 1. The data suggests that K+ binds strongly followed by Ca

2+ and then Na

+ ion.

Table.1. Binding constants (Ks) for the ionophores 1 with different metal ions.

Ionophore Metal ion Binding constant

(Ks/M-1

)

1 Na+ 1.471x10

2

K+ 1.625x10

3

Ca2+

5.673x102

a

b

j

i

h

g

f

e

d

c

3.4 ppm4.24.44.6 ppm6.87.07.27.47.67.88.08.28.48.6 ppm

k

l

1

Chapter-V

10

Fig.5.6. The non-linear least square fit from 1H NMR titration data for the ionophore 1 with

Na+Pic

- in CD3CN at room temperature.

Fig.5.7. The non-linear least square fit from 1H NMR titration data for the ionophore 1 with

K+Pic

- in CD3CN at room temperature.

Chapter-V

11

Fig.5.8. The non-linear least square fit from 1H NMR titration data for the ionophore 1

with Ca+(Pic

-)2 in CD3CN at room temperature.

5.3.4. Isolated complexes of the ionophore 1

For solid state characterization, Na+, K

+ and Ca

2+ complexes of 1 were synthesized,

detail procedure and characterization data are given in the experimental section.

Elemental analysis is in excellent agreement with the calculated values. The ES-MS

spectra for all the three complexes are shown in Figs.5.9-5.11, the m/z values 827.52,

843.64 and 843.86 for Na+, K

+ and Ca

2+ ions respectively, matched very well with the

calculated values for [1+Na+]

+ (827.81), [1+K

+]

+ (843.10), and [1+Ca

2+-H

+]

+ (843.89),

respectively. The elemental analysis, mass and 1H NMR data, therefore confirmed the

formation of these complexes.

Chapter-V

12

Fig.5.9. ES-mass spectrum of the complex [1+Na+]

+.Pic

- in CH3CN

Fig.5.10. ES-mass spectrum of the complex [1+K+]

+.pic

- in CH3CN

m/z100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

%

0

100

CANT K 3 (0.035) 1: TOF MS ES+ 3.44e3843.77

841.79

306.11142.25 242.43 503.37429.50413.54

573.23 701.88595.59 817.77

844.81

845.82

857.79913.85

1012.11 1037.54 1107.34

m/z100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

%

0

100

C ANT NA 1 13 (0.154) 1: TOF MS ES+ 6.74e3827.52

83.11267.19225.30

139.19 661.77331.37 417.33 491.58535.45 826.88

685.79

828.66

843.71

844.72

845.71

931.73 947.911026.06

Chapter-V

13

Fig.5.11. ES-mass spectrum of the complex [1+Ca2+

].(Pic-)2 in CH3CN

5.4. Conclusions

An anthraquinone substituted calix[4]arene-crown-6 hybrid ionophore has been

synthesised and characterized on the basis of elemental analysis, mass and NMR

spectroscopic data. The selectivity of this ionophore towards alkali and alkaline earth

metal ions in aqueous media has been investigated and it exhibits complexation with

Na+, K

+ and Ca

2+ and not highly selective for any particular metal ion in presence of

mixture of metal ions. The complexation property of this ionophore towards the three

strongly interacting metal ions has also been investigated by 1H NMR titration and the

data has been used to calculate binding constant. The binding constant values suggest

moderate to strong binding of metal ions, in which K+ exhibited highest binding

constant. Metal-complexes of this ionophore with the metal ions Na+, K

+ and Ca

2+ have

been synthesised, isolated in solid state and characterized. Apparently, the bulky and

rigid substituent such as anthraquinone at the crown ring could not provide a

conformational arrangement with controlled steric crowding, which can preferentially

binds a particular metal ion, showing very high selectivity.

m/z100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

%

0

100

CANT CA 1 (0.012) 1: TOF MS ES+ 2.79e3764.16

268.08

86.01 222.04148.07

312.12 718.19400.18 533.38

469.32

566.13702.22

843.54

764.45

765.21

765.54

766.22

843.86

844.59

844.95

845.60

845.961260.33920.14

1072.78 1154.56 1427.15

Chapter-V

14

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