Regularities of homo- and heteroassociation of the pinacyanol cation in aqueous solution

Abstract

The ability of the cation of the cyanine dye (pinacyanol) to association in an aqueous solution was studied. The most probable structures of the pinacyanol cation, its dimer, and heteroassociates with anionic forms of several dyes were proposed on the basis of an analysis of the spectral and calculat ed data.Polymethines play a special role among the cyanine dyes. Interest in them is due to the purposeful selection of compounds with the necessary protolytic and spectral luminescence characteristics in true solutions, colloidal systems, and oligomeric media. Great attention is given to pinacyanol (PNC), viz., quinaldine blue. The system atic name of the single charged PNC cation is 1 ethyl 2 [3 (1 ethyl 1H quinolin 2 ylidene)propenyl]quinoli nium. More briefly, although not exactly, in scientific and information literature 1 PNC is called 1,1´ diethyl 2,2´ carbocyanine.Primarily PNC was tested as a standard of the black and white photographic material. 2 The most part of fur ther investigation is related to the study of the properties of PNC in liquid media of various nature. From this point of view, the behavior of PNC was studied in meth anol, 3,4 propanol, 5 glycerol, 3,5 propan 2 ol, 3 and other alcohols, 6 including those containing surfactants. 7 Pina cyanol is prone to manifest aggregation both in solu tions 8,9 and at interfaces (for example, in colloidal silica particles 10 ), which is characteristic of the cyanine dyes. Interactions of PNC with polymers 11 and biopolymers 12 produce thin films, whereas PNC gains optical activity when binding with DNA. 13 In this case, Coulomb forces are the main reason for binding between the cation and the negatively charged phosphate groups of the polymeric acid. 14 Due to the spectrally pronounced interaction with the organized structures, 15,16 PNC was used to de termine the critical micelle concentration of some anionic surfactants. 17, 18 The ability of polymethine cations to interact with organic counterions is also important. This can result in a substantial change in the optical properties of the sys tems due to the formation of ionic associates, aggregates, and molecular ensembles at very low dye concentrations in solutions (~5•10 -7 mol L -1 ). 19 The association of dyes in aqueous systems is of special interest, because water serves as a medium in which the interacting protolytic and aggregative forms exhibit unique spectral lumines cence properties. 20 The associate of a dye (not only poly methine) can act as an analytical reagent, color marker, and bioprobe. This finds use for solving several urgent problems, among which are monitoring of the dimeriza tion and trimerization of nucleic acids, 21 the incorpora tion of photosensitive agents into materials containing cyclodextrins, 22 and search for antibiotics and antitumor drugs. 23, 24 We have earlier 25-28 found a possibility of interaction of the PNC cation (Ct + ) and its structural analogs with a series of organic anions forming ionic associates of different stoichiometric composition in aqueous solu tio...

Heteroassociation of the bromine-containing anions of sulfophthaleins in aqueous solution

“…58 The dimerization of PNC is spectro scopically manifested in a sharp weakening of α band ab sorption and an increase in the β band intensity (see Table 2). …”

Hetero-association of aromatic molecules in aqueous solution

“…NOG-DAU, AO-PF, EB-PI, PF-EB), the structures of hetero-complexes were always antiparallel. If, however, the interacting molecules are non-rigid or contain bulky side chains comparable in their dimension with the aromatic chromophore, the disruption of the compact π-stacking structure may occur as was clearly shown in dye-dye hetero-complexes [219]. It is difficult to ascertain whether in this context the principle of 'structural complementarity' must be supplemented by 'electrostatic complementarity' recently introduced for aromatic interactions [36], as differentiation of their influence on hetero-association is not possible with the data available.…”

“…A number of systems have been studied by NMR under similar solution conditions (0.1 M ionic strength, pH~7.1): the hetero-association of phenanthridine (EB, PI, ethidium mono-and di-azides) [189,[208][209][210][211], acridine (AO, PF) [74,207] and xanthene [212] dyes with the antibiotics DAU, TPT and quinolones; the hetero-association of antitumor antibiotics DAU-NOV [213], DAU-AMD [214,215], DAU-NOR [168], DAU-NOG [167,191], NOV-AMD [214], NOV-NOG [167,191], NOR-NOG [168], NOG-AMD [167,191], DAU-TPT [189], antimalarial drugs [216] and the hetero-association of mutagens: AO-PF [217], EB-PI [218], PF-EB [75,76], dyes [219] and some other aromatic drug molecules [13,220]. These molecules have a planar 3-or 4-ring aromatic chromophore (except the 2-ring NOR molecule) and must potentially be characterised by greater π-stacking interactions than that provided by the derivatives of nucleic acid bases and xanthines.…”

Association of anions of phenolsulfonephthalein and its alkyl-substituted derivatives with single-charged cations of polymethines

“…On the contrary, for PNC the main law of light absorption is fulfilled at low concentrations, because this polymethine is prone to self association in water (the logarithm of dimerization constant of Ct + is equal to 4.79±0.06). 23 The transformation of the monomer into the dimer is manifested as a sharp weakening of the ab sorption of the α band and an increase in the β band in tensity (see Table 1). …”