Charge-Induced Microphase Separation in Polyelectrolyte Hydrogels with Associating Hydrophobic Side Chains:  Small-Angle Neutron Scattering Study

Philippova, Olga E.; Andreeva, A. S.; Khokhlov, Alexei R.; Islamov, Akhmed; Куклин, А. И.; Gordeliy, Valentin

doi:10.1021/la034552h

Cited by 35 publications

(28 citation statements)

References 34 publications

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“…The incorporation of hydrophobic substitu ents into chitosan is a very promising approach. These substituents form hydrophobic domains [22][23][24][25][26][27] that may absorb drugs poorly soluble in water; as a result, the application areas of chitosan as a drug carrier become wider. Moreover, hydrophobic substituents may enhance transfection [28][29][30]; therefore, the effi ciency of chitosan as gene delivery vehicle may be improved.…”

Section: Introductionmentioning

confidence: 99%

Chitosan and its hydrophobic derivatives: Preparation and aggregation in dilute aqueous solutions

2012

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This review surveys the main methods of preparing chitosan and its hydrophobic derivatives and their influence on the microstructure of polymers. The experimental data on the aggregation of these poly mers in dilute aqueous solutions are summarized. Basic factors affecting aggregation are analyzed, and its general regularities are revealed. It is shown that, in the case of both chitosan and its hydrophobic derivatives, the formation of aggregates is governed by the competition of attraction of associating groups promoting aggregation and their repulsion arising from the presence of charged units and counterions hindering aggre gation. Various aggregate models that were proposed for chitosan derivatives with different main chain lengths and different contents of associating groups are discussed.

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Section: Introductionmentioning

confidence: 99%

Chitosan and its hydrophobic derivatives: Preparation and aggregation in dilute aqueous solutions

2012

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“…Indeed, in addition to the similarities of rheological properties mentioned earlier, the collapse of hydrophobic clusters also takes place in HM-polyelectrolyte solutions such as hydrophibically modified polyacrylic acid. 29,36,37 In fact, a decrease to low pH in these systems induced phase separation. At this point, the hydrophobic attractions become dominant and the polymer depleted …”

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PFG‐NMR diffusometry: A tool for investigating the structure and dynamics of noncommercial purified pig gastric mucin in a wide range of concentrations

et al. 2007

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For the first time, Pulsed Field Gradient-Nuclear Magnetic Resonance, a powerful noninvasive tool for studying the dynamics and structure of complex gels, has been used to measure diffusion of probe molecules in aqueous solutions/gels of noncommercial purified pig gastric mucin (PGM), in a concentration range up to 5 wt %. Complementary data were obtained from rheology measurements. The combination of techniques revealed a strong pH dependency of the structure of the PGM samples while changes in concentration, ionic strength, and temperature appeared to induce less pronounced alterations. Viscosity was found to vary in a nonmonotonous way with pH, with the more viscous solutions found at intermediate pH. We propose that this finding is due to a reduced charge density at lower pH, which is expected to continuously increase the relative importance of hydrophobic associations. The results suggest a loose network of expanded fully charged PGM molecules with considerable mobility at neutral pH (pH 7.4). At intermediate pH (pH 4), a three-dimensional expanded network is favored. At pH 1, the charge density is low and microphase separation occurs since hydrophobic associations prevail. This leads to the formation of clusters concentrated in PGM molecules separated by regions depleted in PGM. The results obtained increase our knowledge about the gastric mucosal layer, which in vivo contains mucin in the same concentration range as that of the samples investigated here.

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“…The situation is analogous to that seen in polysoaps or comb copolymers where there is experimentally observed and theoretically modeled collapse from a coil to a globular state in solutions of hydrophilic polymers which have been modified with hydrophobic side chains. [27][28][29] In the globular collapse, hydrophobic side chains aggregate to form a core which is enveloped by the hydrophilic polymer backbone, in essence forming a micelle. Backbone segments form loops at the surface of the micelle and may also bridge them.…”

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Supramolecular Microphase Separation in a Hydrogen-Bonded Liquid Crystalline Comb Copolymer in the Melt State

2006

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Hydrogen bonding represents a versatile and convenient route to chemical diversity in natural and synthetic systems. It can be used to join various chemical species to one another to form products ranging from simple dimers to complex supramolecular moieties, some of which may be self-ordering. 1,2 The use of hydrogen bonding to create liquid crystalline materials is an example of using molecular recognition to pursue prescribed molecular or supramolecular architectures for use in functional systems with self-assembled structures. 3,4 Both low molecular weight and polymeric liquid crystals have been realized using hydrogen bonding, starting with the pioneering work of Kato and Frechet 5 and continued by others in different systems. [6][7][8][9][10][11][12][13][14][15] Ruokolainen et al. have used hydrogen bonding and charge transfer to complex aliphatic chains to homopolymers [16][17][18][19][20][21][22][23] and block copolymers. 24 Hydrogen bonding has also been used as a facile method for the preparation of LC block copolymers with novel thermooptic properties 25 and that exhibit orientational switching of the microstructure under electric fields. 26 The current work represents another instance of supramolecular engineering via hydrogen bonding.Poly(acrylic acid) of molecular weight 5.2 kg/mol and polydispersity 1.09 was used as received from Polymer Source. The custom-synthesized mesogen was based on an imidazole headgroup and a rigid biphenyl core, with 10-and 8-carbon aliphatic spacer and tail segments, respectively, as shown in Figure 1.Samples were prepared by codissolving appropriate quantities of PAA and the mesogen in DMF at 2.5 wt % followed by slow solvent removal at 55°C to prevent mesogen crystallization and phase separation. The films produced were dried in a vacuum at room temperature for 72-96 h and used without further treatment. SAXS was performed using a rotating copper anode source (λ ) 1.540 Å) and, primarily, a synchrotron source (λ ) 1.307 Å). DSC was conducted on a Perkin-Elmer DSC7 at a heating rate of 10°C/min. FTIR was performed in reflection on films using a microscope objective for both illumination and collection of reflected radiation on a Nicolet instrument.The mesogen forms a room temperature crystalline solid in the unbound state, with a single, sharp melting transition to a disordered liquid at 97°C. X-ray scattering revealed a layered structure of 35 Å period in the small-angle regime and characteristic peaks on the 3-5 Å range in the wide-angle regime. The layer period was in good agreement with the calculated extended chain length of the molecule, 34 Å.The presence of hydrogen bonding between the imidazole head of the mesogen and the hydroxy group of the acrylic acid repeat units was confirmed by FTIRsthe appearance of a new, broad band centered on 2530 cm -1 was the primary indicator of strong imidazole-carboxylic acid hydrogen bonding. 15 The intensity of the band was found to decrease as samples were heated above room temperature, with recovery of the room temperature ab...

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Charge-Induced Microphase Separation in Polyelectrolyte Hydrogels with Associating Hydrophobic Side Chains: Small-Angle Neutron Scattering Study

Cited by 35 publications

References 34 publications

Chitosan and its hydrophobic derivatives: Preparation and aggregation in dilute aqueous solutions

Chitosan and its hydrophobic derivatives: Preparation and aggregation in dilute aqueous solutions

PFG‐NMR diffusometry: A tool for investigating the structure and dynamics of noncommercial purified pig gastric mucin in a wide range of concentrations

Supramolecular Microphase Separation in a Hydrogen-Bonded Liquid Crystalline Comb Copolymer in the Melt State

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