Enhanced visualization of polysaccharides from aqueous suspensions

Texture analysis of TEM micrographs of alginate gels for cell microencapsulation

In this work, the morphological characteristics of a calcium alginate gel and a binary (gel) mixture composed of (calcium) alginate and lactose-modified chitosan (chitlac) are evaluated and compared to quantify the differences between the two three-dimensional (3D) structures. A set of textural descriptors based on histogram analysis as well as on gray level co-occurrence matrix and on fractal dimension is extracted from transmission electron microscopy micrographs to describe the morphological differences that the images present. The obtained results reveal significant quantitative morphological differences between the calcium alginate gel and the binary gel mixture that were already inferred from rheological experiments, so as to provide a structural basis for developing new encapsulation systems based on such mixed polymer gels.

Internucleobase-interaction-directed self-assembly of nanofibers from homo- and heteroditopic 1,omega-nucleobase bolaamphiphiles

The complementary 1,omega-thymine, 1,omega-adenine, and 1,omega-(thymine, adenine) bolaamphiphiles, [N,N'-bis[3-(2,4-dihydroxy-5-methylpyrimidine-1-yl)propionyl]1,n-diaminoalkane [T-n-T (n = 10, 11, 12)], N, N'-bis[3-(6-aminopurine-9-yl)propionyl]1,n-diaminoalkane [A-n-A (n = 10, 11, 12)], and N-[3-(2,4-dihydroxy-5-methylpyrimidine-1-yl)propionyl], N'-[3-(6-aminopurine-9-yl)propionyl]1,n-diaminoalkane [T-n-A (n = 10, 11, 12)], respectively] have been synthesized. The spontaneous homo- and heteroassembly of these nucleobase-based bolaamphiphiles has been studied by light microscopy, energy-filtering transmission electron microscopy, FT-IR, and powder X-ray diffraction analyses. The achiral T-10-T bolaamphiphile produced in 10% ethanolic/aqueous solutions unprecedented double-helical ropes of 1-2 microm in widths and several hundred micrometers in length, whereas the complementary homologue A-10-A gave only microcrystalline solids of 1-10 microm in size. In contrast, an equimolar mixture of T-10-T and A-10-A yielded supramolecular fibers of 15-30 nm in width. (1)H NMR, CD, and UV studies of solution photoreactions of T-10-T suggested that under natural light the chiral rope formation is triggered by photodimerization of trace amounts of the thymine moieties in the T-10-T assemblies. Complementary hydrogen bond formation between the thymine-adenine heterobase pairs was found to prevent such a photoreaction and resulted in no chiral rope formation. The heteroditopic T-12-A bolaamphiphile self-assembled to form supramolecular fibers. Multilamellar organization was proposed for the homo- and heteroassemblies made of T-n-T and A-n-A.