**2. Potentiometric response of tetrapyrrolic macrocyclic compounds liquid membrane electrode towards neutral chloro- and nitrophenols**

The results presented indicate that generally, the membrane incorporating calix[4]pyrrole generated the higher potential changes after stimulation with nitrophenols in comparison to

**Calix[4]phyrin Calix[4]pyrrole** 

*ortho*-nitrophenol -3.0 -3.0 -0,7 ---- -4.3 -6.0 *meta*-nitrophenol -25.9 -24.0 -2,8 ---- -9.7 -9.9 *para*-nitrophenol -25.9 -35.0 -4,1 ---- -14.1 -10.3

**Table 1.** The potentiometric responses of ISEs incorporating of calix[4]pyrrole, calix[4]phyrin,corrole towards of

The potentiometric signal generated by membranes modified with corrole and calix[4]phyrin and stimulated with nitrophenol derivatives are very week and comparable. In spite of

**ΔEMF = EMF0-EMF<sup>f</sup>**

**Calix[4]pyrrole Calix[4]phyrin Corrole pH=4.0 pH=6.0 pH=3.0 pH=6.0 pH=3.0 pH=6.0**

**\***

N NH HN N

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Potentiometry for Study of Supramolecular Recognition Processes Between Uncharged Molecules

H

H

calix[4]phyrin and the corrole-containing membrane.

OC16H33

HN N

OC16H33

 **Corrole Figure 1. The structure of pyrrole hosts.**

NH

N

EMF0 – potential measured in buffer free of analyte

EMFf – potential measured in buffer with analyte at final concentration

**Guests**

**Figure 1.** The structure of pyrrole hosts.

nitrophenols isomers

\*

\*

The calix[4]pyrroles, calix[4]phyrins and corroles are tetrapyrrolic macrocyclic compounds. All of them belong to very large group of porphyrin analogs and they are well known as sensitive and selective receptors for anions [26-32].

The main differences between corroles, calix[4]pyrroles and calix[4]phyrins are the following. The corroles are almost planar, aromatic macrocycles. Imine nitrogen atoms from the corrole cavity can be protonated at low pH [33-36].

This is not expected in the case of calix[4]pyrrole and calix[4]phyrins. The calix[4]phyrins (porphodimethenes) demonstrate partly conjugated character similar to porphyrins and partly the non conjugated character of calix[4]pyrroles. Calix[4]pyrroles possess in their structure the relatively dip cavity [26, 32]. Only the individual pyrroles rings have some aromatic character.

Figure 1 illustrates the structures of calix[4]pyrroles, calix[4]phyrins and corroles being applied for this research.

In Table 1 the values of responses of membrane modified with particular host molecules after stimulation with nitrophenols derivatives are collected.

Potentiometry for Study of Supramolecular Recognition Processes Between Uncharged Molecules http://dx.doi.org/10.5772/52803 497

**Figure 1. The structure of pyrrole hosts. Figure 1.** The structure of pyrrole hosts.

as quaternary ammonium salts [4] and lipophilic polyamines [5, 6] after their stimulation with uncharged phenol derivatives were described the first time. According to authors the mech‐ anism of signal generation by membrane modified with quaternary ammonium salts consist

An Integrated View of the Molecular Recognition and Toxinology - From Analytical Procedures to Biomedical

ation of complexed ArOH and simultaneous ejection of HX to aqueous phase, involving a net

Being inspired by this paper, we have done systematic study on potentiometric signals generated by membranes modified with electrically neutral host molecules and stimulated

As a receptors (host) molecules for recognition of uncharged phenol derivatives, corroles, calix[4]pyrroles, calix[4]phyrins and metalloporphyrines we have applied. Whereas, for recognition of unprotonated aniline derivatives we have used: *p*-*tert*-butylthiacalix[4]arene (BTC[4]ene), tetrabromodialkoxythiacalix[4]arene (BATC[4]ene), tetra-undecylcalix[4]resor‐ cinarene (UDC[4]Rene), tetra-undecyl-tetra-*p*-nitrophenylazocalix[4]resorcinarene (UDAC[4]Rene), tetra-undecyl-tetra-hydroxycalix[4]resorcinarene (UDHC[4]Rene), tetra-

**2. Potentiometric response of tetrapyrrolic macrocyclic compounds liquid**

The calix[4]pyrroles, calix[4]phyrins and corroles are tetrapyrrolic macrocyclic compounds. All of them belong to very large group of porphyrin analogs and they are well known as

The main differences between corroles, calix[4]pyrroles and calix[4]phyrins are the following. The corroles are almost planar, aromatic macrocycles. Imine nitrogen atoms from the corrole

This is not expected in the case of calix[4]pyrrole and calix[4]phyrins. The calix[4]phyrins (porphodimethenes) demonstrate partly conjugated character similar to porphyrins and partly the non conjugated character of calix[4]pyrroles. Calix[4]pyrroles possess in their structure the relatively dip cavity [26, 32]. Only the individual pyrroles rings have some aromatic character.

Figure 1 illustrates the structures of calix[4]pyrroles, calix[4]phyrins and corroles being applied

In Table 1 the values of responses of membrane modified with particular host molecules after

**membrane electrode towards neutral chloro- and nitrophenols**

X-

) from membrane to the aqueous phase [4].

) from the aqueous to the membrane phase. In second step there is proton dissoci‐

leading to a net movement of anionic

of two processes.

movement of cationic species (H+

with uncharged guest molecules [11-25].

species (X-

Applications

496

First is the complexation of extracted ArOH and Q+

undecyl-tetra-bromocalix[4]resorcinarene (UDBC[4]Rene.

sensitive and selective receptors for anions [26-32].

stimulation with nitrophenols derivatives are collected.

cavity can be protonated at low pH [33-36].

for this research.

The results presented indicate that generally, the membrane incorporating calix[4]pyrrole generated the higher potential changes after stimulation with nitrophenols in comparison to calix[4]phyrin and the corrole-containing membrane.


\* EMF0 – potential measured in buffer free of analyte

\* EMFf – potential measured in buffer with analyte at final concentration

**Table 1.** The potentiometric responses of ISEs incorporating of calix[4]pyrrole, calix[4]phyrin,corrole towards of nitrophenols isomers

The potentiometric signal generated by membranes modified with corrole and calix[4]phyrin and stimulated with nitrophenol derivatives are very week and comparable. In spite of significant differences of signal magnitude for each type of membranes, generally all of them displayed the same signal magnitude sequence:

Because the potentiometric signals of calix[4]phyrins and corrole modified membranes were very weak towards nitrophenols, the dinitrophenol isomers as strongest acids were selected

2,4-dinitrophenol -77.1 -4.7 -36.2 -22.8 2,5-dinitrophenol -22.2 -14.9 -7.8 -19.6 2,6-dinitrophenol -54.6 -17.3 -6.1 -13.1

**Table 3.** The potentiometric responses of ISEs incorporating of calix[4]phyrin and corrole towards of dinitrophenol

The sequence of signal magnitude in account of host molecules was as follow:

in account of isomer of dinitrophenol (for calix[4]phyrin host) was as follow:

2.4 –dinitrophenol > 2.6- dinitrophenol > 2.5- dinitrophenol

The responses of both of investigated membranes towards dinitrophenols were stronger than

Again the results obtained support our previous hypothesis that the acidity of target phe‐ nol derivatives is crucial for the potentiometric signals of liquid membrane incorporated with host molecules such as calix[4]pyrrole [19], calix[4]phyrin or corrole [14]. The lipo‐ philicity of analytes is rather a secondary parameter. Similar results were reported for

The nitrophenol guests might interact with calix[4]phyrin, corrole or calix[4]pyrrole via "sinking" into the host cavity with the phenolic OH pointed towards the NH units of macro‐ cycles. This was confirmed by NMR measurements [14]. Taking into account this mechanism of interaction, we can explain the good correlation between the signal magnitude sequences for all type of membranes and steric hindrance around the OH group present in guest molecule.

**3. Elucidation of the mechanism of the potentiometric signal generation of**

The results we have obtained for calix[4]pyrrole [ 16, 17, 19, 20 ], calix[4]phyrin or corrole [14, 15] modified membranes and the results reported for macrocyclic polyamines [5, 6, 38-40] suggest that the intermolecular recognition processes between the ligands investigated and

**calix[4]pyrrole, calix[4]phyrin and corrole –ISEs upon stimulation by**

**Calix[4]phyrin Corrole pH=3.0 pH=6.0 pH=3.0 pH=6.0**

Potentiometry for Study of Supramolecular Recognition Processes Between Uncharged Molecules

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499

as the guest molecules [14].

**Guests**

calix 4 phyrin> corrole

polyamines [5, 6, 38-40].

**undissociated phenol derivatives**

observed for mono – nitrophenols [14].

isomers.

*para* −nitrophenol ≥*meta* −nitrophenol >*ortho* −nitrophenol

This sequence is in good order with the lipophilicity and acidity of the nitrophenolic deriva‐ tives (see Table 2)


**Table 2.** Acidity and lipophilicity of nitrophenol derivatives. Log Poct/water – logarithm of partition coefficient between noctanol and water [36,37] pKa – acidity constants [35,36]

The weak response of the membranes studied towards *ortho-*nitrophenol probably is a consequence of formation of an intramolecular hydrogen bond because of adequate closeness of two functional groups – OH and – NO2 [14,16].

The relationship between the magnitude of the potentiometric response of the polymeric membrane modified with calix[4]pyrrole and the acidity of the undissociated phenolic guests we have although confirmed by the study of isomers of chloro- and fluorophenols [20]. Generally, the sequence of the magnitude of signal generated by discussed phenol derivatives follow their acidity sequence and is as follow:

#### nitrophenols >> chlorophenols >>fluorophenols

Presented results indicate that the acidity of the guest molecules is one of the most important parameters decisive about quality of potentiometric signal generation by membranes modified with ligands under discussion. An increase of the acidity of guest molecules causes an increase of the potentiometric response. The magnitude sequence of the signal generated by the isomeric chlorophenols was the same as in the case of nitrophenols:

#### *para* −chlorophenol >*meta* −chlorophenol > >*ortho* −chlorophenol

Again, the response of *ortho-*chlorophenol was the weakest, because the intermolecular hydrogen bounds formed between –OH and –Cl groups hamper the recognition process of host (calix[4]pyrrole ) molecule and guest (*ortho-*chlorophenol ). In consequence this leads to decrease of membrane potential changes [20].

Because the potentiometric signals of calix[4]phyrins and corrole modified membranes were very weak towards nitrophenols, the dinitrophenol isomers as strongest acids were selected as the guest molecules [14].


**Table 3.** The potentiometric responses of ISEs incorporating of calix[4]phyrin and corrole towards of dinitrophenol isomers.

The responses of both of investigated membranes towards dinitrophenols were stronger than observed for mono – nitrophenols [14].

The sequence of signal magnitude in account of host molecules was as follow:

### calix 4 phyrin> corrole

significant differences of signal magnitude for each type of membranes, generally all of them

An Integrated View of the Molecular Recognition and Toxinology - From Analytical Procedures to Biomedical

This sequence is in good order with the lipophilicity and acidity of the nitrophenolic deriva‐

*Para-nitrophenol* 7.16 1.91 99.99 99.93 93.54 12.63 *Meta-nitrophenol* 8.39 2.00 99.99 99.99 99.6 71.05 *Ortho-nitrophenol* 7.21 1.79 99.99 99.94 94.25 13.95 *2.4-dinitrophenol* 4.11 1.54 99.23 56.31 1.27 0.01 *2.5-dinitrophenol* 5.22 1.75 99.94 94.32 14.24 0.16 *2.6-dinitophenol* 4.15 1.25 99.30 58.54 1.39 0.01

**Table 2.** Acidity and lipophilicity of nitrophenol derivatives. Log Poct/water – logarithm of partition coefficient between n-

The weak response of the membranes studied towards *ortho-*nitrophenol probably is a consequence of formation of an intramolecular hydrogen bond because of adequate closeness

The relationship between the magnitude of the potentiometric response of the polymeric membrane modified with calix[4]pyrrole and the acidity of the undissociated phenolic guests we have although confirmed by the study of isomers of chloro- and fluorophenols [20]. Generally, the sequence of the magnitude of signal generated by discussed phenol derivatives

Presented results indicate that the acidity of the guest molecules is one of the most important parameters decisive about quality of potentiometric signal generation by membranes modified with ligands under discussion. An increase of the acidity of guest molecules causes an increase of the potentiometric response. The magnitude sequence of the signal generated by the

Again, the response of *ortho-*chlorophenol was the weakest, because the intermolecular hydrogen bounds formed between –OH and –Cl groups hamper the recognition process of host (calix[4]pyrrole ) molecule and guest (*ortho-*chlorophenol ). In consequence this leads to

**Neutral form [%] pH = 2.0 pH = 4.0 pH = 6.0 pH = 8.0**

displayed the same signal magnitude sequence:

tives (see Table 2)

Applications

498

**Guest compound pKa Log Poct**

octanol and water [36,37] pKa – acidity constants [35,36]

of two functional groups – OH and – NO2 [14,16].

follow their acidity sequence and is as follow:

nitrophenols >> chlorophenols >>fluorophenols

decrease of membrane potential changes [20].

isomeric chlorophenols was the same as in the case of nitrophenols:

*para* −chlorophenol >*meta* −chlorophenol > >*ortho* −chlorophenol

*para* −nitrophenol ≥*meta* −nitrophenol >*ortho* −nitrophenol

in account of isomer of dinitrophenol (for calix[4]phyrin host) was as follow:

2.4 –dinitrophenol > 2.6- dinitrophenol > 2.5- dinitrophenol

Again the results obtained support our previous hypothesis that the acidity of target phe‐ nol derivatives is crucial for the potentiometric signals of liquid membrane incorporated with host molecules such as calix[4]pyrrole [19], calix[4]phyrin or corrole [14]. The lipo‐ philicity of analytes is rather a secondary parameter. Similar results were reported for polyamines [5, 6, 38-40].

The nitrophenol guests might interact with calix[4]phyrin, corrole or calix[4]pyrrole via "sinking" into the host cavity with the phenolic OH pointed towards the NH units of macro‐ cycles. This was confirmed by NMR measurements [14]. Taking into account this mechanism of interaction, we can explain the good correlation between the signal magnitude sequences for all type of membranes and steric hindrance around the OH group present in guest molecule.
