Regulation of pseudo-Polyrotaxane Formation between α-Cyclodextrins and Azobenzene-Terminated Poly(ethylene glycol)

Abstract

ABSTRACT:Regulation of pseudo-polyrotaxane formation between ix-cyclodextrins (ix-CDs) and azobenzene(Az)-terminated poly(ethylene glycol) (PEG) was studied in terms of the photoisomerization of the terminal Az groups. pseudo-Polyrotaxane formation was analyzed by a change in the transmittance at 550nm in water. It was found that the rate of transmittance change was decreased with an increase in the cis isomer content in Az-PEG. The cis-isomerization effect was quantitatively evaluated, assuming that Az-PEG having two cis-isomerized Az groups does not participate in the pseudo-polyrotaxane formation. From this analysis, it is suggested that pseudo-polyrotaxane formation between ix-CDs and PEG was hindered when the both terminal Az groups were isomerized to cis isomer. The content of Az-PEG in the pseudo-polyrotaxane aggregate and the content of cis-isomerized Az-PEG in the supernatant were measured by 'H NMR and UV-Vis absorption spectrum, respectively, and the obtained results supported our suggestion. It is concluded that the terminal Az groups act as a gate to regulate the pseudo-polyrotaxane formation.KEY WORDS pseudo-Polyrotaxane Formation / Photoisomerization / ix-Cyclodextrin / Poly(ethylene glycol) / Azobenzene / Over the past two decades, new synthetic methods have been investigated in order to design "intelligent" or "smart" materials which exhibit large property change in response to small physical or chemical stimuli. 1 In particular, the progress in supramolecular chemistry has introduced a new fascinating field of nano-organized systems mimicking nanostructures in nature. 2 • 3 The nano-organized systems have been focused on a key technology to realize high-performance smart materials, micromachines and so on. Molecular assemblies organized by their intermolecular forces are believed to be essential for the construction of the nano-organized systems. 4 pseudo-Polyrotaxanes in which many cyclic molecules are threaded onto a linear polymer have been recently studied as a novel molecular assembly. 5 -8 Harada et al. demonstrated pseudo-polyrotaxane formation between cyclodextrins (CDs) and a linear polymer in high yield.It was found that ix-, /3-, or y-CDs were selectively threaded onto various linear polymers. 9 For instance, when ix-CD saturated aqueous solution is mixed with poly(ethylene glycol) (PEG) aqueous solution, the solutions become turbid. 10 This phenomenon is caused by the formation of pseudo-polyrotaxane and its aggregation. Further, when bulky-terminal groups are introduced to the terminals of the polymer, the sterical hindrance for pseudo-polyrotaxane forµiation is changed in relation to the shape of the bulky-terminal groups. For instance, Harada et al. reported that bis(2-naphthylacetyl)-terminated PEG forms a pseudo-polyrotaxane with ix-CD, whereas bis(l-naphthylacetyl)-terminated PEG does not. 11 This report indicates that the pseudo-polyrotaxane formation is affected by the mobility or shape of the terminals of the linear polymer. If stimuli-responsible moieties, which can con...

Synthesis and Characterization of Novel Amphiphilic Azo-Polymers Bearing Well-Defined Oligo(Ethylene Glycol) Spacers

“…Azobenzene and poly(ethylene glycol) have been incorporated into various sophisticated systems such as co-polymers [16,17], nanomaterials [18,19], cellulose derivatives [20,21] and cyclodextrin polymers [22,23], in some cases forming supramolecular complexes with interesting properties [24]. Poly(ethylene glycol) moieties provide flexibility and water solubility to the systems to which they are incorporated.…”

Amphiphilic azo-dyes (RED-PEGM). Part 2: Charge transfer complexes, preparation of Langmuir–Blodgett films and optical properties

“…Aggregation and chromic changes within these systems are described by in-line or J-type aggregation and side-on or H-type aggregation [13]. Azobenzene and poly(ethylene glycol) have been incorporated into more sophisticated systems such as copolymers [14,15], nanomaterials [16,17], cellulose derivatives [18,19] and cyclodextrin polymers [20,21], in some cases forming supramolecular complexes with interesting properties [22].…”

“…The presence of J-aggregates was not observed for this compound, but the presence of head to head J-aggregates was detected in Y-type LB films [24]. In the present work, we studied the formation of intramolecular charge transfer complexes of RED-PEGM-8 and two related azo-dyes: N-methyl-N-{4-[(E )-(4-nitrophenyl)diazenyl] phenyl}-N-(3, 6, 9-trioxadecas-1-yl)amine (RED-PEGM-3) and N-methyl-N-{4-[(E )-(4-nitrophenyl)diazenyl] phenyl}-N- (3,6,9,12,15,18,21,24,27,30)-decaoxauntricontas-1-yl)amine (RED-PEGM-10) in dilute solutions (molecular structures are shown in Fig. 1).…”

“…On the other hand, Z-type LB films of these azo-dyes were prepared and the nonlinear optical properties of RED-PEGM-8 were studied as function of the number of layers. (3, 6, 9, 12, 15, 18, 21, 24-octaoxapentaeicos-1-yl)amine (RED-PEGM-8) and N-methyl-N-{4-[(E )-(4-nitrophenyl)diazenyl] phenyl}-N- (3,6,9,12,15,18,21,24,27,30)-decaoxauntricontas-1-yl)-amine (RED-PEGM-10) were synthesized according to the method previously reported by us [23].…”

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Optical properties of three amphiphilic azo-dyes bearing end-capped oligo] phenyl}-N- (3,6,9,12,15,18,21,24,27,30)-decaoxauntricontas-1-yl)amine (RED-PEGM-10) were studied in Z-type LB films by absorption spectroscopy. RED-PEGM-8 and RED-PEGM-10 formed intramolecular charge transfer complexes in aqueous solution due to coiling of the end-capped poly(ethylene glycol) side-chain around the azobenzene groups.

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