Ürenin sulu ortamda bulunan makromoleküller üzerindeki denatürasyon mekanizmasının aydınlatılması

In this thesis, the urea-induced solubility changes of macromolecules in aqueous solutions were investigated by utilizing lower-critical-solution-temperature(LCST) of poly(N-isopropylacrylamide)(PNIPAM) and poly(N,N-diethylacrylamide)(PDEA) as a function of urea concentration upto 6.0 M. Due to the lack of suitable probing methods for collapsed state of interested macromolecules, a temperature-controlled ATR – FTIR spectroscopy based method was developed to explore the interaction between urea and the collapsed state of macromolecule. LCST measurements revealed that the solubility of PDEA increases with increasing urea concentrations, whereas PNIPAM salts-out from the solution monotonically, despite the fact that both polymers have similar molecular structures. Temperature gradient ATR-FTIR measurements were carried out to further investigate this discrepancy. First, no favourable urea accumulation towards the collapsed form of macromolecules was observed upto 6.0 M urea, which puts doubt on the urea clouding mechanism. Moreover, at elevated (>3.0M) urea concentrations, the collapsed form of the PNIPAM and PDEA accumulated towards the cooler parts of temperature gradient in solution, indicating the preferred form of the macromolecule is the soluble (uncollapsed) form. These surprising results indicate that both PNIPAM and PDEA prefers the soluble form at elevated urea concentrations above the LCST. As a molecular mechanism, the urea molecules act as a "glue" between the amide groups of PNIPAM, bringing intra-and inter-molecular parts of the macromolecule into close proximity, and act as a collapsed form of macromolecules. Apparently, such a mechanism isn't valid for PDEA. Our findings shed new light on aqueous phase phenomena, and aggregated (collapsed) phase of macromolecules in aqueous medium.