ABSTRACT
The effect of adding ethylammonium nitrate (EAN), which is an ionic liquid (IL), on the aggregate formation of α-synuclein (α-Syn) in aqueous solution has been investigated. FTIR and Raman spectroscopy were used to investigate changes in the secondary structure of α-Syn and in the states of water molecules and EAN. The results presented here show that the addition of EAN to α-Syn causes the formation of an intermolecular ß-sheet structure in the following manner: native disordered state â polyproline II (PPII)-helix â intermolecular ß-sheet (α-Syn amyloid-like aggregates: α-SynA). Although cations and anions of EAN play roles in masking the charged side chains and PPII-helix-forming ability involved in the formation of α-SynA, water molecules are not directly related to its formation. We conclude that EAN-induced α-Syn amyloid-like aggregates form at hydrophobic associations in the middle of the molecules after masking the charged side chains at the N- and C-terminals of α-Syn.
Subject(s)
Protein Aggregates , Quaternary Ammonium Compounds/chemistry , alpha-Synuclein/chemistry , Amyloid/chemical synthesis , Amyloid/chemistry , Chemical Precipitation/drug effects , Humans , Hydrophobic and Hydrophilic Interactions , Protein Aggregates/drug effects , Protein Conformation, beta-Strand/drug effects , Protein Multimerization/drug effects , Protein Structure, Secondary , Quaternary Ammonium Compounds/pharmacology , Spectroscopy, Fourier Transform Infrared , Spectrum Analysis, Raman , Water/chemistryABSTRACT
SF/polyurethane composite non-woven sheet was fabricated to evaluate the cardiovascular tissue engineering materials in the wet state. The compatibility and microstructure analyses were carried out on the fabricated SF/polyurethane composite non-woven sheet by thermal analysis and solid-state NMR analysis in the wet state. To evaluate the modulus of elasticity, a tensile test was performed and supported with dynamic viscoelasticity and mechanical analysis. Results showed that SF/polyurethane composites form domains within the non-woven sheet and are in a finely dispersed state while maintaining their structures at a scale of several tens of nm. Moreover, an increase of the loss tangent with low elastic modulus proved that a micromolecular interaction occurs between silk fibroin (SF) and polyurethane molecules.
ABSTRACT
Helix-coil transitions of poly α-aspartic acid (PASP) were studied by dc polarography in the presence of Zn(2+) as a marker attached to the polymer. The diffusion current (i(d)) of Zn(2+) declined markedly in the pH range of 3.5-7.4 due to a formation of metal ion-PASP macromolecular complexes. The complex formation also reflects on an increase of the magnitude at ca. 222 nm of CD spectrum, suggesting that PASP forms the helix structure by coordination of Zn(2+) in the corresponding pH region. Helix content, determined by the decrease in i(d) of Zn(2+), corresponds favorably to that by CD measurements. In the lower acidic pH region, the coordination mode of Zn(2+) to PASP is different from that at neutral pH region. The decrease in i(d) of Zn(2+) is independent of the further formation of helix structure. Zn(2+) coordinates with sparsely dissociated carboxylate groups of the helical part of PASP, which bring about an aggregation of polypeptide strands. The diffusion current of the ion attached to the polymer, therefore, is a parameter sensitive to conformational changes of PASP from acidic through neutral pH region.
