Журнал "Макрогетероциклы"

Gulnara A. Gaynanova,^@ Guzalia I. Vagapova, Irina R. Knyazeva, Victoria I. Matveeva, Alexander R. Burilov, and Lucia Ya. Zakharova

A.E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center, Russian Academy of Sciences, 420088 Kazan, Russian Federation

^@Corresponding author E-mail: ggulnara@bk.ru

DOI: 10.6060/mhc151193g

Macroheterocycles 2016 9(1) 23-28

By method of tensiometry it has been shown that calix[4]resorcinol functionalized by phosphonium groups (CR) is able to reduce the surface tension at the water-air interface to 64 mN/m with critical micelle concentration (CMC) equals 0.15 mM. At the concentration of calix[4]resorcinol equal to 0.03 mM a sharp decrease in pH from 7 to 4.3 has been observed. It is probably related to the solubilization and partial ionization of water molecules in CR associates with the formation of free protons. On addition of PEI (C = 0.05 M) the critical aggregation concentration (CAC) of the CR–PEI binary system decreases by two times. According to tensiometry and conductometry data CAC values are equal 0.071 mM and 0.057 mM, respectively. This is due to the fact that the polymer acts as a matrix, which facilitates the process of self-association in solution and leads to a significant reduction in CAC value. The pH values of CR solutions in the presence of PEI (0.05 M) changes slightly with increasing concentration of CR (within the limits of 10.1 – 10.6), indicating a relatively high buffering capacity of the polymer. By method of conductometry it was found that CAC of the CR–PEG system equals 0.12 mM, which is close to the CMC of the CR individual solutions (0.15 mM). Probably, this testifies that a small impact of PEG on the aggregation of this type of amphiphiles or, indirectly, a weak interaction of components occurs. The aggregates with hydrodynamic diameter of 250–300 nm are detected by dynamic light scattering in individual solutions of calix[4]resorcinol. The presence of small aggregates (10 nm) and large aggregates in the system is fixed upon the addition of PEI. Probably, in binary systems the part of aggregates are represented by polymer coils with diameter equal to 10 nm, and the other part by calix[4]resorcinol units peripherally associated with a PEI. Data on the association of calix[4]resorcinol functionalized by phosphonium groups in the absence and presence of polymers were compared with the systems based on cetyltriphenylphosphonium bromide (TPPB-16) to determine the role of the macrocyclic platform. The TPPB-16 self-association in the individual solution and in the presence of PEI and PEG had been investigated earlier in our research group. The individual solutions of CR and TPPB-16 are characterized by approximately the same value of the CMC. Polymer additives have different effects on the value of the CAC. There was no breakpoint refers to CAC at the surface tension isotherm of CR – PEG system. This is probably due to the fact that the value of CAC has shifted to the high concentrations, which in our case could not be prepared. In the case of TPPB-16 – PEG a twofold decrease in the CMC values occurs. The addition of polyethyleneimine which is a weakly charged polycation at pH = 9 leads to a decrease by 2 times in the CAC of the CR–PEI system and three times in the case of TPPB-16 – PEI system. Since PEG is nonionic polymer and PEI has a small positive charge (similar to charge of head group of CR and TPPB -16) the electrostatic interaction cannot play a crucial role in the formation of polymer-colloid complex. Probably, although the number of carbon atoms in the calixarene matrix more than in the hydrocarbon tail of TPPB-16, the linear structure of the hydrophobic fragment of TPPB-16 contributes to a stronger interaction between amphiphilic compound and the polymer matrix, resulting in a larger decrease in the values of CAC in the case of mixed systems TPPB-16 –polymer in comparison with the composition CR – polymer. Thus, by the methods of tensiometry, conductometry and dynamic light scattering it has been shown that calix[4]resorcinol functionalized by phosphonium groups is capable of forming aggregates at the concentration equal to 0.15 mM. Comparative analysis has shown that like triphenylphosphonium surfactant calix[4]resorcinol functionalized by phosphonium groups has a CMC significantly lower than classical surfactants with ammonium head groups and CAC of the binary system in the case of PEI is lower than the CMC. However, unlike phosphonium surfactant a synergistic effect in the binary system CR-PEI is exhibited slightly weaker, and is not appeared at all in the system CR–PEG.

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