Browsing by Subject "Macromolecules"
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Item Embargo Ion specificity from small molecules to oligomers and beyond amide-based macromolecules(Bilkent University, 2024-01) Farooq, SobiaPresence of ions in aqueous solution regulate the properties of molecules in the same aqueous environment. Such alteration processes are mainly dependent on the concentration and the identity of ions. In this thesis, two parts of ion specific effects were aimed to be explored. First the synthesis and characterization of PNIPAM oligomers by using both reversible addition-fragmentation chain transfer (RAFT) and radical polymerization methods will be shown. Both of these methods give the control over molecular size of the polymer. Oligomers with charged and neutral end group were synthesized to comparatively investigate ion specific effect. These oligomers were also systematically characterized by using various analytical techniques such as phase transition temperature measurement, 1H-NMR and Gel permeation chromatography (GPC). Such oligomers were employed to investigate the specific ion effects via the salt influence on the Lower Critical solution temperature (LCST). By employing two sodium salts; NaCl (strongly hydrated) and NaSCN (weakly hydrated), it was found that strongly hydrated anions salt-out both charged and neutral oligomers, whereas weakly hydrated anions increase the phase transition temperature with a salting in mechanism. By empirical modeling with a Langmuir-type binding isotherm, a weak binding with a dissociation constant KD = 0.57 M for charged and KD = 1.13 M for neutral oligomers were demonstrated. The second part of this thesis focused on the specific ion effects beyond amide-based macromolecules i.e. hydroxypropyl cellulose (HPC) as a model for sugar-based macromolecules. Eight sodium salts were employed to demonstrate the entire Hofmeister series. Namely; NaSCN, NaI, NaNO3, NaClO4 NaCl, Na2SO4, Na2CO3, NaH2PO4 were measured on the phase transition temperature and 1H-NMR measurements. Salts of weakly hydrated anions; NaSCN, NaI, NaClO4 and NaNO3 showed a salting in mechanism and demonstrate a non-monotonic phase transition behavior. In contrast, salts of strongly hydrated anions; NaCl, Na2SO4, NaH2PO4 and Na2CO3 showed salting out mechanism with a monotonic decrease in the phase transition temperature. Additionally, the site-specific ion-macromolecule interaction was studied by 1H-NMR, and Correlation Spectroscopy (2D-COSY) NMR measurements. Although, the exact binding site cannot be specified, it was concluded that the ion binding site is at the side-chain hydroxypropyl groups and that yields the salting-in effect that was observed for the weakly-hydrated anions.Item Open Access Quantum bistability, structural transformation, and spontaneous persistent currents in mesoscopic aharonov-bohm loops(World Scientific Publishing Co., 2005) Kulik, I. O.Fixed-number-of-electron mesoscopic or macromolecular conducting ring is shown to support persistent currents due to Aharonov-Bohm flux, and the "spontaneous" persistent currents without the flux when structural transformation in the ring is blocked by strong coupling to the externally azimuthal-symmetric environment. In the free-standing macromolecular ring, symmetry breaking removes the azimuthal periodicity which however is further restored at the increasing field. Three-site ring with one or three electrons represent an interesting quantum system which can serve as a qubit (quantum bit of information) and a qugate (quantum logical gate). © 2005 by World Scientific Publishing Co. Pte. Ltd.Item Open Access Sequence-specific self-sorting of the binding sites of a ditopic guest by cucurbituril homologues and subsequent formation of a hetero[4]pseudorotaxane(2009) Celtek, G.; Artar, M.; Scherman, O. A.; Tuncel, D.Ties us together: The selectivity and recognition behavior of cucurbit[n]uril (CB[n]) homologues (n = 6,7,8) towards a ditopic guest containing two distinct binding sites is explored. CB6, CB7, and CB8 recognize and self-sort the binding sites according to their size, shape, and chemical nature. In the presence of both CB6 and CB8 a hetero[4]pseudorotaxane is formed. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA.Item Open Access XPS and water contact angle measurements on aged and corona-treated PP(John Wiley & Sons, Inc., 1999) Süzer, S.; Argun, A.; Vatansever, O.; Aral, O.Effects of corona treatment and aging on commercially produced corona discharged polypropylene (PP) films were followed via surface sensitive roughness analysis by atomic force microscopy (AFM), water contact angle (WCA), and X-ray photoelectron spectroscopic (XPS) measurements. Roughness analysis by AFM gave similar results for both untreated and corona-treated samples. The measured water contact angle decreased after corona treatment but increased with aging. XPS findings revealed that corona treatment caused an increase in the O-containing species on the surface of the films, but the measured O/C atomic ratio decreased with aging. The angle dependence of the observed XPS O/C atomic ratio further revealed that surface modifications by the corona treatment were buried into the polymer away from the surface as a function of aging. This is attributed to a surface rearrangement of the macromolecules in agreement with the findings of Garbassi et al. on oxygen-plasma-treated polypropylene.