Reversible addition−fragmentation chain transfer (RAFT) is a versatile, controlled free radical
polymerization technique that operates via a degenerative transfer mechanism in which a thiocarbonylthio
compound acts as a chain transfer agent. The subsequent reduction of the dithioester end groups to thiols
allows the preparation of (co)polymer-modified gold surfaces. Herein we report the immobilization of
poly(sodium 4-styrenesulfonate), poly((ar-vinylbenzyl) trimethylammonium chloride), poly(N,N-dimethylacrylamide), and poly(3-[2-(N-methylacrylamido)-ethyldimethyl ammonio]propane sulfonate-b-N,N-dimethylacrylamide) onto gold films. The presence of the immobilized (co)polymers was confirmed by
atomic force microscopy, attenuated total reflectance Fourier transform infrared spectroscopy, and surface
contact angle measurements. The gold film modified with the block copolymer demonstrated stimuli-responsive behavior as evidenced by its water contact angle being similar to that of poly(N,N-dimethylacrylamide) even though the block based on 3-[2-(N-methylacrylamido)-ethyldimethyl ammonio]
propane sulfonate was expected to be exposed to the aqueous environment.
A series of highly purified galacturonate polysaccharides have been extracted from the Aloe vera plant and analyzed in terms of chemical composition and molecular weight. This Aloe vera polysaccharide (AvP) has been found to exist as a high molecular weight species and possess a unique chemical composition, including a high galacturonic acid (GalA) content and low degree of methyl ester substitution. These factors facilitate gel formation upon exposure to low concentrations of calcium ions, leading to potential application in formulations designed for in situ nasal or subcutaneous protein delivery. Thorough examination of classic dilute solution properties, the [eta]-M(w), and R(g)-M(w) relationships, persistence length (L(p)), and inherent chain stiffness (B parameter), indicate an expanded random coil in aqueous salt solutions. The critical concentration for transition from dilute to concentrated solution, C(e), was determined by measuring both the zero shear viscosity (eta(o)) and fluorescence emission of the probe molecule 1,8-anilino-1-naphthalene sulfonic acid (1,8-ANS) as a function of polymer concentration. Examination of zeta potential and C(e) as a function of ionic strength indicates that the shift in C(e) from 0.60 to 0.30 wt % is related to an increased occurrence of intermolecular interactions at high salt concentrations. Additionally, dynamic rheology data are presented highlighting the ability of AvP to form gels at low polymer and calcium ion concentrations, exemplifying the technological potential of this polysaccharide for in situ drug delivery.
The hydrophobin Sc3 from the fungus Schizophyllum commune assembles from the aqueous phase into ordered structures with substantially different characteristics depending upon experimental conditions. Under the first condition, a vortexing procedure widely reported in the literature, interfacial assembly yields highly ordered, stacked beta-sheets. We have also observed a previously unreported assembly of Sc3 under a second condition, which occurs in a time-dependent manner from quiescent solution. The resulting types of assembled states have been compared utilizing fluorescence techniques, sodium dodecyl sulfate polyacrylamide gel electrophoresis, immunoblotting, density gradient centrifugation, and phase contrast and atomic force microscopy. A model based on this study and previous literature is proposed that suggests three distinct states of Sc3: (1) soluble Sc3 consisting of unimers or multimers in micelle-like association, (2) interfacially assembled I-Sc3 with highly ordered, stacked beta-sheets, presumably formed in a templated manner at the air/water interface of microscopic bubbles generated by vortexing, and (3) solution-assembled S-Sc3, a less-ordered structure formed in a time-dependent manner in the absence of an interface.
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