Flavin adenine dinucleotide (FAD) undergoes multisite
molecular recognition at the air-water interface
with mixed monolayers that are capable of complementary hydrogen
bonding. Molecular images were
obtained with an atomic force microscope (AFM) for mixed monolayers of
guanidinium (G) and orotate (O)
amphiphiles transferred from pure water and from aqueous FAD. The
AFM image of the G/O mixed
monolayer on FAD showed a periodic oblique pattern composed of two
kinds of methyl peaks with different
heights, whereas that on pure water showed a periodic hexagonal pattern
of only one kind of methyl peak.
The two-dimensional molecular patterning as height difference is
conceivably caused by rearrangement
of monolayer components based on specific recognition by the FAD
template molecule.
In this study, the use of cotton fiber (CF) as a filler in poly(butylene succinate) (PBS) and the effect of silane treatment on the mechanical properties, thermal stability, and biodegradability of PBS/CF composites are investigated. The results showed that the tensile strength of PBS was improved (15%–78%) with the incorporation of CF (10–40 wt%) and was further increased (25%–118%) when CF was treated with a silane coupling agent. Scanning electron microscopy (SEM) observation of the fracture surfaces of PBS/CF composites showed that there was slight improvement in fiber-matrix compatibility. Thermogravimetric (TG) analysis showed that the thermal stability of the composites was lower than that of neat PBS and decreased with increasing filler loading. The biobased carbon content of the composites increased with increasing CF content. The incorporation of CF (with and without silane treatment) in PBS significantly increased the biodegradation rate of the composites
Flavin adenine dinucleotide (FAD) formed a stoichiometric complex at the air-water interface with four molecules of a three-component monolayer that contain guanidinium, diaminotriazine, and orotate head groups. The complementary complexation was confirmed by surface pressure-area isotherm and IR and XPS spectroscopies of the transferred film.
The self-assembly of peptides and proteins into beta-sheet-rich high-order structures has attracted much attention as a result of the characteristic nanostructure of these assemblies and because of their association with neurodegenerative diseases. Here we report the structural and conformational properties of a peptide-conjugated graft copolymer, poly(gamma-methyl-L-glutamate) grafted polyallylamine (1) in a water-2,2,2-trifluoroethanol solution as a simple model for amyloid formation. Atomic force microscopy revealed that the globular peptide 1 self-assembles into nonbranching fibrils that are about 4 nm in height under certain conditions. These fibrils are rich in beta-sheets and, similar to authentic amyloid fibrils, bind the amyloidophilic dye Congo red. The secondary and quaternary structures of the peptide 1 can be controlled by manipulating the pH, solution composition, and salt concentration; this indicates that the three-dimensional packing arrangement of peptide chains is the key factor for such fibril formation. Furthermore, the addition of carboxylic acid-terminated poly(ethylene glycol), which interacts with both of amino groups of 1 and hydrophobic PMLG chains, was found to obviously inhibit the alpha-to-beta structural transition for non-assembled peptide 1 and to partially cause a beta-to-alpha structural transition against the 1-assembly in the beta-sheet form. These findings demonstrate that the amyloid fibril formation is not restricted to specific protein sequences but rather is a generic property of peptides. The ability to control the assembled structure of the peptide should provide useful information not only for understanding the amyloid fibril formation, but also for developing novel peptide-based material with well-defined nanostructures.
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