Fluorescence Studies of pH-Responsive Unimolecular Micelles Formed from Amphiphilic Polysulfonates Possessing Long-Chain Alkyl Carboxyl Pendants

Abstract

Reversible pH-induced changes in self-associative behavior in water of random copolymers of 50 mol % sodium 2-(acrylamido)-2-methylpropanesulfonate (NaAMPS) and 50 mol % 6-acrylamidohexanoic acid (AmH), 8-acrylamidooctanoic acid (AmO), or 11-acrylamidoundecanoic acid (AmU) were investigated by various fluorescence techniques with use of fluorescence-labeled polymers. Fluorescence intensities, lifetimes, depolarization, and quenching for the polymers labeled with naphthalene (4 mol %) indicated that all the polymers adopt an open-chain conformation at basic pHs whereas NaAMPS/AmO and NaAMPS/AmU polymers collapsed into a compact conformation upon a decrease in pH to an acidic region. No such pH-induced conformational change was found for NaAMPS/AmH polymers. Nonradiative energy transfer (NRET) for NaAMPS/AmO and NaAMPS/AmU polymers doubly labeled with naphthalene (4 mol %) and pyrene (1 mol %) indicated a strong tendency for intrapolymer hydrophobic self-association, the polymers with pendent octanoic acid and undecanoic acid groups forming unimolecular micelles (unimer micelles) at acidic pHs. The mean aggregation numbers (N agg) of these alkyl carboxylic acid residues in the unimer micelles were determined to be 86 and 74, respectively. These N agg values were fairly close to the numbers of the AmO and AmU units per polymer chain (85 and 69, respectively), indicative of the formation of unimer micelles. The unimer micelles were disrupted into an open-chain conformation when pH was increased to a basic pH, thus exhibiting reversible pH-induced formation and disruption behavior.

Adsorption of bisphenol-A by pH-responsive polymer grafted on porous polyethylene vinyl acetate disk: Effect of the side-chain length of hydrophobic component in polymer on adsorption

“…8 shows the size distribution and average size of the polymer colloids, i.e., unimolecular micelles, formed by poly (NaAMPS-co-NaMmO) and poly(NaAMPS-co-NaMmD) at pH 6. The average size of the polymer colloids observed in this study was 7-12 nm, and was similar to that of the unimolecular micelles reported by Yusa et al [14], although the size distribution was quite wide. Furthermore, the polymer colloids formed by poly (NaAMPS-co-NaMmO) were larger than those formed by poly (NaAMPS-co-NaMmD), although the side chain of NaMmO is shorter than that of NaMmD.…”

“…Poly(NaAMPSco-NaAmO), poly(NaAMPS-co-NaAmU), and poly(NaAMPS-coNaMmD) form unimolecular micelles at pH ranges of 6-7, 7-8, and 9-10, respectively [14,17]. This implies that the pH at which the unimolecular micelles are formed can be controlled by the length of the hydrophobic components, i.e., the number of methylene groups in the pendant hydrophobic group.…”

“…In addition, a few studies recently reported the formation of unimolecular micelles by linear random copolymers in response to solution pH [11][12][13][14][15][16]. These copolymers were composed of sodium 2-(acrylamido)-2-methylpropanesulfonate (NaAMPS) as the hydrophilic component and a pH-sensitive hydrophobic component such as 8-acrylamidooctanoate (NaAmO) or sodium 11-acrylamidoundecanoate (NaAmU), i.e., poly(NaAMPSco-NaAmO) or poly(NaAMPS-co-NaAmU) [14]. It was also reported that a random copolymer of NaAMPS and 12-methacrylamidododecanoate (NaMmD), i.e., poly(NaAMPS-co-NaMmD), exhibited pH-induced formation and disruption of unimolecular micelles [17,18].…”

Thermal, optical, electrochemical properties and conductivity of trans- and cis-poly(1-ethynylpyrene): a comparative investigation

“…For this purpose, we selected poly(1-ethynylpyrene) as model molecule because the pyrene unit is an efficient fluorescent probe, which has been successfully used as a molecular label in the study of many polymers [21][22][23][24][25][26][27][28][29][30]. It is well known that pyrene has a long singlet lifetime and that it readily forms excimers; the relevant photophysical properties of pyrene have recently been reviewed [31].…”

Thermal, Optical, Electrochemical Properties and Conductivity of Pyrene Monomers

“…Furthermore, we have studied the thermal, optical, electrochemical properties and conductivity of polyarylacetylenes bearing condensed aromatic groups in function of the geometry of the polyacetylene backbone and the internal stacking of pendant substituents [13,14]. For this purpose, we selected poly(EP) as model molecule because pyrene is an efficient fluorescent probe, which has been successfully used as a molecular label in the study of a huge variety of polymers [15][16][17][18][19][20][21][22][23][24][25].…”