Functionalizable, Biodegradable, and Protein-Resistant Polymer Fabricated
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solvents. The researchers had previously shown that the extremely high dipole moment of merocyanine results in large dimerization constants (Kdim > 106 M-1) in low-polarity solvents. In addition, the chromophore’s highly polarizable π system provides functionality. While the substituted merocyanine dimers were shown by UV–vis absorption spectra to be stable in low-polarity solvents, even at low dilution levels, the substituted bis(merocyanine) dyes displayed absorption bands associated with three distinct species. In addition to the monomer band, two blue-shifted bands were observed, that is, their blue shift depended on the solvent. The researchers reported that observation of the less blue-shifted band indicated supramolecular polymerization by way of the two receptor sites in each molecule. Furthermore, observation of the bands that were more blue-shifted suggested to the researchers a further aggregation of the polymeric strands, which formed a more stable assembly. As dye concentration increased, a lyotropic mesophase formed, followed by a solventfree film with an unusual liquid-crystalline texture. X-ray diffraction of the film revealed hexagonal columnar order with a lattice constant of 4.34 nm, which was in good agreement with rod size determined in a transmission electron microscope. The researchers conclude that a hierarchical growth process occurs in the structures. As solvent polarity is reduced, each of the two chromophores in the bis(merocyanine) dye dimerizes with another dye in an antiparallel manner. The resulting randomly coiled fibrils fold into helical conformations. Six helices then intertwine to form a densely packed rod with the tridodecyloxybenzyl substituents on the outer, solvent-accessible surface, which is favorable in low-polarity solvents. At higher concentrations, interdigitation of the alkyl substituents leads to a decrease in the rod diameter as mesophases and gels are formed. The researchers said that the tubular structure of their dye aggregates is similar to chlorophyl dye rod elements in the chlorosomes of photosynthetic bacteria. In addition, they envision “fascinating possibilities [that] might arise for merocyanine dye assemblies, especially if their intermolecular arrangement could be changed.” STEVEN TROHALAKI
delivery, and systems for both patterned cell cultures and high-throughout screening of proteins or cells. Poly(ethylene glycol) (PEG) as a main chain polyether has been shown to be a good candidate, except for its functionalization limits and nonbiodegradability. Also, the involvement of carbohydrate moieties in self-assembled monolayers and polymeric materials has shown superior protein resistance. Combining these two merits, Z. Guan, M. Metzke, and J.Z. Bai of the University of California—Irvine designed a sidechain polyether constructed from the
carbohydrate-derived monomers. In addition, this polymer can be degraded by hydrolysis of the ester linkage between the repeating units. The researchers reported their work in the July 2 issue of the Journal of the Ameri
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