Журнал "Макрогетероциклы"

Dinar R. Gabdrakhmanov,^@ Farida G. Valeeva, Vyacheslav E. Semenov, Darya A. Samarkina, Anatoly S. Mikhailov, Vladimir S. Reznik, 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: Nemezc1988@yandex.ru

DOI: 10.6060/mhc151194g

Macroheterocycles 2016 9(1) 29-33

Supramolecular systems based on the novel tetracationic amphiphilic pyrimidinophane, their mixtures with polymer (polyethyleneimine) and lanthanum ions were formed. Using spectrophotometry technique a catalytic activity of these systems was studied on the example of hydrolysis reaction of O-p-nitrophenyl-O-alkylchloromethylphosphonates (alkyl = ethyl (P1) and n-hexyl (P2)). At the first step the catalytic effect of individual solutions of pyrimidinophanes was examined. Pronounced substrate specificity for two different phosphonates was revealed: inhibition of hydrolysis for phosphonate with ethyl residue and catalysis of hydrolysis for phosphonate with n-hexyl moiety. Similar unusual effect for organized systems based on cationic surfactants could be a result of the influence of two opposite factors. On the one hand, pH decrease with the pyrimidinophane concentration was found. It corresponds to reducing of OH^--ions concentration in reaction medium and, therefore inhibition of hydrolysis occurs. On the other hand, aggregation in aqueous solutions of pyrimidinophane induces reactant concentrating in surfactant aggregates that accelerates the reaction. Thereby depending on the domination of the first or the second factor inhibition or catalysis may be observed. Experimental kinetic data allow us to assume that phosphonate P2 because of its higher hydrophobicity and affinity to nonpolar core of micellar pseudophase possesses the higher capability to binding with pyrimidinophane aggregates in comparison with P1. Quantitative treatment of obtained kinetic data in terms of pseudophase model has revealed that binding ability of P2 with pyrimidinophane aggregates is almost 2 times greater than in the case of P1. Moreover, hydrolysis in catalytic complex proceeds more than 5 times faster for substrate with n-hexyl residue. This fact is also due to the high capability of P2 to concentrate within hydrophobic core of pyrimidinophane aggregates. Thus it can be concluded that in the case of P2 the domination of positive contribution over the negative contribution of pH decrease with surfactant concentration is achieved due to high capability of substrate to bind with pyrimidinophane aggregates and high rate of hydrolysis in catalytic complex. It results in catalysis of reaction. At the same time, moderate ability of P1 to bind with aggregates is not enough to compensate pH decrease, which results in inhibition of reaction. Upon the transition from individual solutions of pyrimidinophaneto its binary mixture with polyethyleneimine the difference of kinetic constants between P1 and P2 tends to be preserved. Howeverabsolute values of these constants are much lower than in the case of individual solutions of pyrimidinophane. Probably, it is due to the fact that cooperative aggregation between surfactant and polymer prevents reactant concentration in surfactant/polymer aggregates. However, resulting catalytic effect of binary system for both phosphonates is higher than in the case of individual solutions of pyrimidinophane. It is due to high contribution of general basic catalysis to summary effect with the participation of amino groups of PEI thereby levelling pH decrease. Addition of La³⁺ ions to the surfactant/polymer system allows of inverting catalytic activity from inhibition to catalysis accompanied by significant increase in kinetic constants for P1. Obviously it is due to electrophylic catalysis which involves La³⁺ ion coordination near oxygen atom of phosphoryl group. In the case of P2 expectedincreasein maximum of catalytic activity does not occur. Decrease in OH^--ions concentration during the formation of lanthanum hydroxocomplexes [La(OH)]²⁺ and [La(OH)₂]⁺ due to salt hydrolysis could be the possible reason of this phenomenon. Thereby in the framework of this study supramolecular catalysts for cleavage of organophosphorous substrates were designed on the basis of novel amphiphilic tetracationic pyrimidinophane. Catalytic activity of the system could be controlled by addition of polymer and lanthanum salt. Results obtained could have practical relevance in terms of creation of effective agents for utilization of natural ecotoxicants.

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