Self-organization of poly(allylamine)s having hydrophobic groups and its effect on the interaction with small molecules. 2. Fluorescence lifetime and ESR techniques

Abstract

Nanosecond fluorescence lifetime and ESR techniques were used to investigate the interaction of poly(ally1amine)s (PAA) containing long alkyl or benzyl groups with fluorescent probes in an aqueous solution. The fluorescence decay curve was deconvoluted into two components: lifetimes 71 = 14-22 ns and 72 = 3-5 ns are assigned to the probes in the hydrophobic sphere of the amphiphilic polycation and in bulk water, respectively. The rotational correlation times (7R) for the spin probe were also obtained as greater than 10 ns and approximately 0.1 ns, respectively. The compact polymer domain is formed in alow concentration range (approximately lo-' M) and keeps its structure up to the higher concentration range. The values of T I increase with an increase in the chain length and the content of substituent groups. This result suggests that the lower the polarity of the domain, the greater the restriction of the probe located in the domain. The dodecylated PAA has a hard core in the interior of the domain, which loosens with a decrease in pH. On the other hand, the domain structure of the benzylated PAA has better sterical adaptability for probe molecules.The mobility of the probe was estimated to be lower in such a polymer assembly than in micelles formed from small surfactants.

Molecular concepts, self-organisation and properties of polysoaps

“…Notably, the results vary with the probe chosen and the restriction of mobility is not limited to intramolecular aggregation but is seen for intermolecular aggregates as well [298]. The general behaviour is corroborated by measurements of fluorescence life-times of solubilized dyes [152,217,287]. Additional evidence for more restricted mobility in polysoaps in comparison to micelles of low molecular weight surfactants comes from fluorescence quenching and fluorescence depolarisation studies [185].…”

“…This is somewhat surprising as, according to ^-NMR studies, aromatic probes reside at the "micellar interface" [373]. Also, this result contrasts markedly with the increasing polarity in poly soaps based on poly(allylamine) with increasing protonation as sensed by dansyl probes [287]. In the case of poly(undecenoic acid), the I/III values increases strongly around a pH of 8.…”

“…For example azo dyes were used as labels taking advantage of their trans-cis photoisomerization [203,217,260]. More frequently fluorescent labels have been fixed such as dansyl [174,175,177,287], naphthyl [211,259], anthracenyl [183,189] or pyrenyl groups [204,259]. For ESR studies, e.g.…”

“…Studying the motion of the ESR-spin probe, polysoaps Carbon Number C-NMR spectra of polysoap 54: a in D 2 0 (spin-echo); b in bulk (CP-MAS) [357] reduce the mobility of solubilized materials more strongly than micelles of low molecular weight surfactants do [64,74,152,287], thus pointing to a higher microviscosity. Notably, the results vary with the probe chosen and the restriction of mobility is not limited to intramolecular aggregation but is seen for intermolecular aggregates as well [298].…”

“…Additional evidence for more restricted mobility in polysoaps in comparison to micelles of low molecular weight surfactants comes from fluorescence quenching and fluorescence depolarisation studies [185]. There seem to be steric effects of the polymer backbone, too, as the more densely packed dodecylated poly(allylamine) gives rise to stronger mobility restrictions than dodecylated poly(ethyleneamine) [145,287]. Increasing the hydrophobe content and the length of the hydrophobic tails, the mobility of solubilized probes becomes more and more reduced according to both ESR-and fluorescence studies [152,187,189,287].…”