**5. Potentiometric response of membranes modified with undecylcalix[4] – resorcinarene derivatives towards of unprotonated diaminobenzene isomers**

According to presented mechanism of anionic potentiometric signal generation by membranes modified with nitrogen containing macromolecules as host molecules and stimulated with neutral form of phenol derivatives the crucial phenomenon is transfer of protons from the membrane surface to surface of water phase. From this point of view it was logical and interesting to check if generation of cationic potentiometric signal by membranes modified with macrocycles containing the phenolic group stimulated with unprotonated derivatives of aniline would be possible [25, 52]

There are summarization of systematic research results of the intermolecular recognition processes at the water/polymer membrane border between some derivatives of undecylca‐ lix[4]resorcinarene (Figure 2) and neutral (unprotonated) forms of aniline and its derivatives such as: aminoaniline, chloroaniline, hydroxyaniline, methylaniline, methoxyaniline and nitroaniline obtained with using potentiometry.

**Figure 2.** The structure of host molecules.

In the measuring condition (pH = 5.5), paracetamol molecules exists in undissociated form (pKa =9.5). The formation of the above mentioned complex, according to a combination of mesomeric and inductive effects, causes an increase of the acidity of the phenolic OH function from paracetamol molecule. As a consequence, this leads to a more facile dissociation of the

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This event is responsible for the generation of an anionic response of the polymeric liquid membranes modified with metalloporphyrins after their stimulation with undissociated

The reaction of the metalloporphyrin complex with paracetamol was confirmed by spectro‐ scopic measurements at the border between water and the polymeric membrane. The UV-Vis absorption spectrum of a thin membrane film containing Mn(III)-porphyrin deposited onto glass slides conditioned in 0.01 M phosphate buffer solution (pH = 5.5) exhibited one main band at 470 nm and two weaker bands at 376 and 400 nm. After conditioning in phosphate buffer with an increasing concentration of paracetamol, the absorbance maximum decreased and shifted to shorter wavelength. This blue shift was expected due to the increase in electron density around the Mn(III) centers by the coordinated amide. These data confirm the creation

The electrochemically active Cu(II) dipyrromethene complex immobilized on the surface of gold electrodes previously modified with a dodecanethiol monolayer was successfully applied for voltammetric determination of paracetamol [23]. The interaction of paracetamol with Cu(II) redox centers was a base of analytical signal generation. The presence of human plasma in the measuring solution influence very little on the sensor performance. Its linear dynamic range ( 0.2-3.2 mM) was sufficient for controlling the toxic level of paracetamol in human plasma [23].

**5. Potentiometric response of membranes modified with undecylcalix[4] –**

According to presented mechanism of anionic potentiometric signal generation by membranes modified with nitrogen containing macromolecules as host molecules and stimulated with neutral form of phenol derivatives the crucial phenomenon is transfer of protons from the membrane surface to surface of water phase. From this point of view it was logical and interesting to check if generation of cationic potentiometric signal by membranes modified with macrocycles containing the phenolic group stimulated with unprotonated derivatives of

There are summarization of systematic research results of the intermolecular recognition processes at the water/polymer membrane border between some derivatives of undecylca‐ lix[4]resorcinarene (Figure 2) and neutral (unprotonated) forms of aniline and its derivatives

**resorcinarene derivatives towards of unprotonated diaminobenzene**

of a complex between the Mn(III)-porphyrin and paracetamol [22].

ejection from the interface to the aqueous layer adjacent to the

OH group and finally to H+

organic phase.

Applications

504

paracetamol.

**isomers**

aniline would be possible [25, 52]

In Table 4 the values of potentiometric response of PVC supported liquid membranes incor‐ porated with calixarene host generated in the presence of aniline derivatives are collected. The measurements for all membranes studied were done at pH 7. At this pH investigated aniline derivatives exist in water almost entirely as neutral (unprotonated) compounds (see Table 5).

**Analyte pK1 pK2**

**Table 5.** Percentage of protonated and neutral species at pH 7 [25]

possibility to form intramolecular hydrogen bonds.

the strongest acids between the investigated compounds.

isomer *ortho*, in another meta.

observed phenomena.

 *p*-nitroaniline 1.02 100.0 0.0 *o*-chloroaniline 2.66 100.0 0.0 *m*-chloroaniline 3.52 100.0 0.0 *p*-chloroaniline 3.98 99.9 0.1 *m*-anisidine 4.20 99.8 0.2 *o*-toluidine 4.45 99.7 0.3 *o*-anisidine 4.53 99.7 0.3 *o*-aminoaniline 4.61 1.81 99.6 0.4 *m*-toluidine 4.71 99.5 0.5 aniline 4.87 99.3 0.7 *m*-aminoaniline 5.01 2.56 99.0 1.0 *p*-toluidine 5.08 98.8 1.2 *p*-anisidine 5.36 97.8 2.2 *p*-hydroxyaniline 5.48 97.1 2.9 *p*-aminoaniline 6.22 2.99 85.8 14.2

Potentiometry for Study of Supramolecular Recognition Processes Between Uncharged Molecules

The comparison of the results we have got for all of guest molecules showing the following general tendency: with increase of analyte basicity the response increases. This is truth for all of modified membranes. In most of the cases the isomer *para* generate the highest response. For another isomers is difficult to estimate with one generate higher signal. In some cases it is

Explanation of weak response of membranes after stimulation with *ortho* isomers is the

The correlation between the partition coeffiction of guest (Table 4) and value of potentiometric response is very week. And this suggests that this parameter is rather less important for

The weakest response we have observed for nitro- and chloro- derivatives of aniline. They are

The main differences between the host molecules under study are structure of upper rim. Ligand 1 poses in their upper rim dihydroxybenzene substituents in which the OH groups are in position 1, 3 in relation to each other. Because of this distance the intramolecular hydrogen bounds are very week [43]. Additionally this ligand is substituted in position 2 with azonitro‐ benzene. The presence of this substituent, because of its inductive and rezonance effect causing

**pH 7.0 RNH2 (%) RNH3 + (%)**

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507

As it is seen from results introduced from Table 4, all types of membranes generate cationic response towards aniline derivatives


ΔE[mV] = E0 -E<sup>i</sup> E0 – potential recorded in buffer solution, E<sup>i</sup> – potential record in the presence of analyte at is final concentration

**Table 4.** Potentiometric response of PVC supported liquid membranes incorporated with host undodecylcalix[4] resorcinarene derivatives generated in the presence of aniline derivatives. Log Poct/water – logarithm of partition coefficient between n-octanol and water [36, 37] pKa – acidity constants [35, 36]

Potentiometry for Study of Supramolecular Recognition Processes Between Uncharged Molecules http://dx.doi.org/10.5772/52803 507


**Table 5.** Percentage of protonated and neutral species at pH 7 [25]

In Table 4 the values of potentiometric response of PVC supported liquid membranes incor‐ porated with calixarene host generated in the presence of aniline derivatives are collected. The measurements for all membranes studied were done at pH 7. At this pH investigated aniline derivatives exist in water almost entirely as neutral (unprotonated) compounds (see Table 5).

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As it is seen from results introduced from Table 4, all types of membranes generate cationic

*p*-aminoaniline 6.22 -0.26 148.9 138.4 88,4 86.9 41.5

*p*-anisidine 5.36 1.15 118.6 68.9 53,9 59.4 37.4

*m*-anisidine 4.20 1.32 92.6 62.2 55,1 20.1 28.4

*o*-aminoaniline 4.61 0.37 66.8 57.2 64,2 31.0 31.5

*m-*aminoaniline 5.01 0.03 36.2 42.1 35,8 13.8 7.6

*p*-toluidine 5.08 1.43 92.3 36.2 44.1 27.0 30.2

*p*-chloroaniline 3.98 1.81 31.5 24.2 22,8 -0.6 6.2

*o*-anisidine 4.53 1.65 62.7 20.1 35,7 19.8 7.8

aniline 4.87 1.24 57.7 12.8 34,5 10.7 13.1

*m*-toluidine 4.71 1.59 84.2 9.7 32,9 14.9 22.0

*o*-toluidine 4.45 1.61 75.8 9.4 20,8 10.7 7.7

*p*-nitroaniline 1.02 1.19 4.7 3.0 - - 2.4

*m*-chloroaniline 3.52 1.88 19.8 0.7 2 - 9.2

*o*-chloroaniline 2.66 2.02 8.6 -4.5 1,2 - 1.9

**Table 4.** Potentiometric response of PVC supported liquid membranes incorporated with host undodecylcalix[4] resorcinarene derivatives generated in the presence of aniline derivatives. Log Poct/water – logarithm of partition

E0 – potential recorded in buffer solution, E<sup>i</sup>

coefficient between n-octanol and water [36, 37] pKa – acidity constants [35, 36]

p-hydroxyaniline 5.48 -0.24 27.6 15.5 25,2 -2.1 2.4

**ΔE[mV] Lig 2**

**ΔE[mV] Lig 3**

**ΔE[mV] Lig 4**

– potential record in the presence of analyte at is final

**ΔE[mV] Lig 5**

**ΔE[mV] Lig 1**

response towards aniline derivatives

Applications

506

**Guests pK1 Log Po/w**

ΔE[mV] = E0 -E<sup>i</sup>

concentration

The comparison of the results we have got for all of guest molecules showing the following general tendency: with increase of analyte basicity the response increases. This is truth for all of modified membranes. In most of the cases the isomer *para* generate the highest response. For another isomers is difficult to estimate with one generate higher signal. In some cases it is isomer *ortho*, in another meta.

Explanation of weak response of membranes after stimulation with *ortho* isomers is the possibility to form intramolecular hydrogen bonds.

The correlation between the partition coeffiction of guest (Table 4) and value of potentiometric response is very week. And this suggests that this parameter is rather less important for observed phenomena.

The weakest response we have observed for nitro- and chloro- derivatives of aniline. They are the strongest acids between the investigated compounds.

The main differences between the host molecules under study are structure of upper rim. Ligand 1 poses in their upper rim dihydroxybenzene substituents in which the OH groups are in position 1, 3 in relation to each other. Because of this distance the intramolecular hydrogen bounds are very week [43]. Additionally this ligand is substituted in position 2 with azonitro‐ benzene. The presence of this substituent, because of its inductive and rezonance effect causing

the increase of acidity of phenol groups from upper ring. Ligand 2 contains in its structure dihydroxybenzene with OH groups in positions 1 and 3.

Upon complexation of *para*–diaminobenzene, the absorbance decrease at 214 nm, characteristic for UDC[4]Rene was observed. The absorbance at 239 nm characteristic for *para*–diaminoben‐ zene also decrease and shifted towards red. Additionally, new peak was visible at 267 nm. These absorbance changes clearly indicated that a supramolecular complex UDC[4]Rene-

Potentiometry for Study of Supramolecular Recognition Processes Between Uncharged Molecules

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509

Therefore, it might be concluded that the cationic potentiometric signals observed in the study presented were generated as a result of the supramolecular recognition phenomenon occurring

Based on obtained results and literature data we have proposed the following mechanism of cationic potential signal generation by membranes modified with derivatives of undecylca‐ lix[4]resorcinarene after stimulation with unprotonated derivatives of aminobenzene. In the first step, which is going during the membrane conditioning some of phenolic groups of derivatives of undecylcalix[4]resorcinarene located at the surface of polymeric membranes dissociated and membranes became minus charged. Such type of dissociation of OH groups of upper rim of undecylcalix[4]resorcinarene was described in [53, 54]. In next step, the network of hydrogen bonds between the derivatives of aminobenzene and phenolic groups is formed. In such situation the amino groups are donors of hydrogen atoms and polarity of them are correlated with acidity of phenol groups. The formation of such network is described in [49-51]. As a result of this, the supramolecular complex of undecylcalix[4]resorcinarene – aminobenzene derivatives located at the interface is formed. As a consequence of above complex formation the density of electrons on nitrogen of aminobenzene increases. The measurements were carried out at pH 7. In this condition all of investigated amines exist in solution mostly as unprotonated compounds (Table 5). The increase of the density of electrons at amine nitrogen atoms causing the increase of their basicity. Because of this, they became protonated in spite of pH condition in bulk solution. This protonation is done by means of transfer of proton from surface of water face to surface of organic one. The transfer of proton leading to the increase of plus charge of membrane and we can observe the generation of

The first one concerns dissociation of some phenolic groups from upper rim of investigated

+ H3O<sup>+</sup>

Next step consist of transfer of analyte from bulk solution to the interface and formation of

The consequence of this is the increase of basicity on nitrogen atom from supramolecular



interface + H2O

*para*-diaminobenzene is formed at the membrane surface.

at the organic/aqueous interface.

potentiometric cationic signal.

ligands.

**ii.** HostO-

**iii.** HostO-

complex and its protonation.

Proposed mechanism is based on the three steps:

supramolecular complex ligand –analyte through hydrogen bonds.

interface + NH2-AR <sup>↔</sup> HostO-


**i.** HostOHmembrane+ H2O<sup>↔</sup> HostO-

Next host, number 3, in its upper rim contains the dihydroksybromobenzene. The OH groups are in position 2, 6 in relation to azabenzene substituent. This substituent, because of its inductive and mesomeric effect, increased the acidity of phenols in relation to previous one.

The upper rim of ligand 4 contains the bromo- 2, 5 hydroksybenzene. The close vicinity of OH groups creates the very good conditions for creation of intramolecular network of hydrogen bonds [43]. The last ligand (no 5) posses in upper rim trihydroksybenzene. Similarly as in previous one this system allows to create the intramolecular hydrogen bound network.

Comparison of value of potentiometric response we have got for each ligand showing the general tendency which is as follow:

Ligand 1 > ligand 2 > ligand 3, ligand 4 > ligand 5

This indicates that increase of the acidity of phenols groups in upper rim causing the increase of response value.

The strongest response we have observed for membrane modified with ligand 1 containing in its structure dihydroxybenzene substituted with azonitrobenzene. Acidity of these OH groups is the highest.

Next in this sequence is ligand 2 substituted with dihydroxybenzene. In this case the acidity of OH groups is lower in relation to the previous one, but the accessibility of them for guest is much easier. As consequence the creation of hydrogen bound (H…O…H…N) between host and guest is relatively easy. The next ligand in the discussed sequence, ligand 3 contained in its structure dihydroxybenzene substituted with azobenzene. This causing the increase the acidity of phenolic group in upper rim, but at the same time presence of rather large substituent makes the hindrance in accessibility of OH groups for guest molecules. The value of generated potentiometric signal is the consequence of these two opposite effects.

Membrane modified with host containing the bromo-derivatives of dihydrobenzene in its structure (no 4) is next in sequence of response value. In this case from one side the inductive effect bromine atom causing increase of acidity of phenolic group and from another one large atom of bromine constitute hindrance in accessibility of phenols groups for guest.

The lowest answer we have got for membrane modified with ligand 5, which poses in its structure trihydroksybenzene. In this ligand the network of intramolecular hydrogen bounds is the strongest. And because of this the formation of supramolecular complex with guest is the most difficult between the ligand under study.

The comparison of lipophilicity of investigated guest molecules showing that there is no direct relation between the lipophilicity of amines and values of signal generated by them.

In order to confirm the supramolecular complex formation between undecylcalix[4]resorci‐ narene and aniline derivatives at the border of organic/aqueous interface UV-Vis measure‐ ments were performed according to procedure reported [52].

Upon complexation of *para*–diaminobenzene, the absorbance decrease at 214 nm, characteristic for UDC[4]Rene was observed. The absorbance at 239 nm characteristic for *para*–diaminoben‐ zene also decrease and shifted towards red. Additionally, new peak was visible at 267 nm. These absorbance changes clearly indicated that a supramolecular complex UDC[4]Rene*para*-diaminobenzene is formed at the membrane surface.

Therefore, it might be concluded that the cationic potentiometric signals observed in the study presented were generated as a result of the supramolecular recognition phenomenon occurring at the organic/aqueous interface.

Based on obtained results and literature data we have proposed the following mechanism of cationic potential signal generation by membranes modified with derivatives of undecylca‐ lix[4]resorcinarene after stimulation with unprotonated derivatives of aminobenzene. In the first step, which is going during the membrane conditioning some of phenolic groups of derivatives of undecylcalix[4]resorcinarene located at the surface of polymeric membranes dissociated and membranes became minus charged. Such type of dissociation of OH groups of upper rim of undecylcalix[4]resorcinarene was described in [53, 54]. In next step, the network of hydrogen bonds between the derivatives of aminobenzene and phenolic groups is formed. In such situation the amino groups are donors of hydrogen atoms and polarity of them are correlated with acidity of phenol groups. The formation of such network is described in [49-51]. As a result of this, the supramolecular complex of undecylcalix[4]resorcinarene – aminobenzene derivatives located at the interface is formed. As a consequence of above complex formation the density of electrons on nitrogen of aminobenzene increases. The measurements were carried out at pH 7. In this condition all of investigated amines exist in solution mostly as unprotonated compounds (Table 5). The increase of the density of electrons at amine nitrogen atoms causing the increase of their basicity. Because of this, they became protonated in spite of pH condition in bulk solution. This protonation is done by means of transfer of proton from surface of water face to surface of organic one. The transfer of proton leading to the increase of plus charge of membrane and we can observe the generation of potentiometric cationic signal.

Proposed mechanism is based on the three steps:

the increase of acidity of phenol groups from upper ring. Ligand 2 contains in its structure

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Next host, number 3, in its upper rim contains the dihydroksybromobenzene. The OH groups are in position 2, 6 in relation to azabenzene substituent. This substituent, because of its inductive and mesomeric effect, increased the acidity of phenols in relation to previous one.

The upper rim of ligand 4 contains the bromo- 2, 5 hydroksybenzene. The close vicinity of OH groups creates the very good conditions for creation of intramolecular network of hydrogen bonds [43]. The last ligand (no 5) posses in upper rim trihydroksybenzene. Similarly as in previous one this system allows to create the intramolecular hydrogen bound network.

Comparison of value of potentiometric response we have got for each ligand showing the

This indicates that increase of the acidity of phenols groups in upper rim causing the increase

The strongest response we have observed for membrane modified with ligand 1 containing in its structure dihydroxybenzene substituted with azonitrobenzene. Acidity of these OH groups

Next in this sequence is ligand 2 substituted with dihydroxybenzene. In this case the acidity of OH groups is lower in relation to the previous one, but the accessibility of them for guest is much easier. As consequence the creation of hydrogen bound (H…O…H…N) between host and guest is relatively easy. The next ligand in the discussed sequence, ligand 3 contained in its structure dihydroxybenzene substituted with azobenzene. This causing the increase the acidity of phenolic group in upper rim, but at the same time presence of rather large substituent makes the hindrance in accessibility of OH groups for guest molecules. The value of generated

Membrane modified with host containing the bromo-derivatives of dihydrobenzene in its structure (no 4) is next in sequence of response value. In this case from one side the inductive effect bromine atom causing increase of acidity of phenolic group and from another one large

The lowest answer we have got for membrane modified with ligand 5, which poses in its structure trihydroksybenzene. In this ligand the network of intramolecular hydrogen bounds is the strongest. And because of this the formation of supramolecular complex with guest is

The comparison of lipophilicity of investigated guest molecules showing that there is no direct

In order to confirm the supramolecular complex formation between undecylcalix[4]resorci‐ narene and aniline derivatives at the border of organic/aqueous interface UV-Vis measure‐

relation between the lipophilicity of amines and values of signal generated by them.

atom of bromine constitute hindrance in accessibility of phenols groups for guest.

potentiometric signal is the consequence of these two opposite effects.

dihydroxybenzene with OH groups in positions 1 and 3.

general tendency which is as follow:

of response value.

Applications

508

is the highest.

Ligand 1 > ligand 2 > ligand 3, ligand 4 > ligand 5

the most difficult between the ligand under study.

ments were performed according to procedure reported [52].

The first one concerns dissociation of some phenolic groups from upper rim of investigated ligands.

**i.** HostOHmembrane+ H2O<sup>↔</sup> HostO- + H3O<sup>+</sup>

Next step consist of transfer of analyte from bulk solution to the interface and formation of supramolecular complex ligand –analyte through hydrogen bonds.

$$\begin{array}{cccc} \text{iii} & \text{HostO}^{\cdot}\_{\text{interface}} + & \text{NH}\_{2}\text{-}\text{AR} & \longleftrightarrow & \text{HostO}^{\cdot}\text{---}\text{H}\text{--}\text{NH-}\text{AR}\_{\text{interference}} \\\end{array}$$

The consequence of this is the increase of basicity on nitrogen atom from supramolecular complex and its protonation.

$$\text{iii.} \qquad \text{HostO} \cdot \text{---} \text{H-} \text{-NH-AR}\_{\text{interface}} \text{+H}\_{\text{3}} \text{O}^{\*} \leftarrow \text{HostO} \text{---} \text{H-} \text{-NH}\_{2} \text{-AR}^{\*} \text{}\_{\text{interface}} \text{+H}\_{2} \text{O}^{\*}$$

The formation of such complex at the border we confirmed by means of spectroscopic method. The conformation of first step is based on result we have got for membrane modified with ligand 1 in which the acidity of phenolic groups is the highest.

**•** The sensitivity and selectivity of these processes are governed by the acidity of the target molecules studied as well as the ability of host molecules for creation of hydrogen bonds.

Potentiometry for Study of Supramolecular Recognition Processes Between Uncharged Molecules

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511

The described phenomena open the totally new and very promising field of analytical

Institute of Animal Reproduction and Food Research of Polish Academy of Sciences, Olsz‐

[3] Umezawa Y., "Ion-Selective Electrodes" , in "Encyclopedia of Supramolecular Chem‐

[4] Ito, T., Radecka, H, Tohda, K., Odashima, K., Umezawa,Y. *J. Am. Chem. Soc.* 1998, 120,

[5] Odashima , K., Naganava, R., Radecka, H., Kataoka, M., Kiura, E., Koike, T., Tohda, K., Tange, M., Furta, H., Sessler, J. L.,. Yagi, K., Umezawa, Y. *Supramolecular Chemistry* 1994,

[6] Ito, T., Radecka, H., Umezawa, K., Kiura, T., Yashiro, A., Lin, X., Kataoka, M., Kiura,

[7] M. De Serio H. Mohapatra , R. Zenobi , V. Deckert , Chemical Physics Letters 417 (2006)

[9] Spichiger –Keller U.E., "Chemical Sensors and Biosensors for Medical and Biological

[11] L. Bulgariu, H. Radecka, M. Pietraszkiewicz, O. Pietraszkiewicz, Analytical Letters,

[10] Pretsch, E., Bühlmann, P., Bakker, E., *Chem Rev.,* 1997, 97, 3083; 1998 , 98, 1593.

E., Sessler, J.L., Yagi, K., Umezawa, Y. *Anal. Sciences*. 1998 14, 89.

The lipophilicity of analytes it the secondary parameter.

application of potentiometric method.

and Hanna Radecka

[1] Bakker, E., *Talanta*, 2004 , 63, 21.

\*Address all correspondence to: j.radecki@pan.olsztyn.pl

[2] Gale, P.A., *Coordination Chemistry Reviews* , 2003, 240, 191.

istry", 2004, Marcel Dekker, New York, p.747.

[8] Russell, E., Morris *Nature Chemistry* 2011, 3, 347–348.

Applications" , 1998, Wiley-VCH, Weinheim, Germany.

**Author details**

Jerzy Radecki\*

tyn, Poland

**References**

3049.

4,101.

452–456

2003, 36, 1325-1334.

The results we observed for bromo- and azobenzo- derivatives of investigated undecylca‐ lix[4]resorcinarene showing that the accessibility of phenols groups is very important param‐ eter for intermolecular recognition processes which are going between investigated ligands and analytes.

The weakest response we have observed in case of membranes modified with ligand which has in its structure trihydroxybenzene was explained by possibilities to form the network of intramolecular hydrogen bonds. This is a relatively strong energetic barrier for the described phenomenon.

The second step of proposed mechanism relays on transfer of protons from water phase to organic one. This is supported by fact that independently on the host structure, the strongest signal we have observed for the strongest base between guest compounds under study. The results we have got showed that lipophilicity of analytes it is not crucial parameter.
