https://hdl.handle.net/20.500.12960/9 Vocational Schools 2026-06-04T22:47:37Z https://hdl.handle.net/20.500.12960/1814 Peripheral heterochromatin tethering is required for chromatin-based nuclear mechanical response Attar, Ali Göktuğ; Paturej, Jaroslaw; Sarıyer, Ozan Sabahattin; J Banigan, Edward; Erbaş, Aykut The cell nucleus is a mechanically responsive structure that governs how external forces affect chromosomes. Chromatin, particularly transcriptionally inactive heterochromatin, resists nuclear deformations through its mechanical response. However, chromatin also exhibits liquid-like properties, casting ambiguity on the physical mechanisms of chromatin-based nuclear elasticity. To determine how heterochromatin strengthens nuclear mechanical response, we performed polymer physics simulations of a nucleus model validated by micromechanical measurements and chromosome conformation capture data. The attachment of peripheral heterochromatin to the lamina is required to transmit forces directly to the chromatin and elicit its elastic response. Thus, increases in heterochromatin levels increase nuclear rigidity by increasing the linkages between chromatin and the lamina. Crosslinks within heterochromatin, such as HP1α proteins, can also stiffen nuclei, but only if chromatin is peripherally tethered. In contrast, heterochromatin affinity interactions that may drive liquid-liquid phase separation do not contribute to nuclear rigidity. When the nucleus is stretched, gel-like peripheral heterochromatin can bear stresses and deform, while the more fluid-like interior euchromatin is less perturbed. Thus, heterochromatin's internal structure and stiffness may regulate nuclear mechanics via peripheral attachment to the lamina, while also enabling nuclear mechanosensing of external forces and external measurement of the nucleus' internal architecture. 2025-01-01T00:00:00Z https://hdl.handle.net/20.500.12960/1738 A New Lower Bound for the Number of Conjugacy Classes Çınarcı, Burcu; Keller, Thomas Michael In 2000, Hethelyi and K & uuml;lshammer [Bull. London Math. Soc. 32 (2000), pp. 668-672] proposed that if G is a finite group, p is a prime dividing the group order, and k(G) is the number of conjugacy classes of G, then k(G) >= 2 root p - 1, and they proved this conjecture for solvable G and showed that it is sharp for those primes p for which root p - 1 is an integer. This initiated a flurry of activity, leading to many generalizations and variations of the result; in particular, today the conjecture is known to be true for all finite groups. In this note, we put forward a natural new and stronger conjecture, which is sharp for all primes p, and we prove it for solvable groups, and when p is large, also for arbitrary groups. 2024-01-01T00:00:00Z https://hdl.handle.net/20.500.12960/1713 Chitosan films incorporated with berberine: enhanced mechanical, antioxidant, and antimicrobial properties as potential food packaging material Öztürk, Seray; Kalaycıoğlu, Zeynep; Torlak, Emrah; Akın Evingür, Gülşen; Erim, F. Bedia Conventional food packaging films pose significant environmental hazards. Consequently, there has been a burgeoning interest in biopolymers, leading to numerous studies to develop biodegradable and bioactive films suitable for the food packaging industry. In this study, we present a novel environmentally-friendly chitosan-based film incorporating berberine, a bioactive compound abundant in various plants. Before blending with a chitosan solution, berberine chloride's water solubility was enhanced using 2-hydroxypropyl-beta-cyclodextrin. Fourier transform infrared spectroscopy confirmed the interactions between berberine and chitosan. Scanning electron microscopy and atomic force microscopy analyses demonstrated the even distribution and good compatibility of berberine within the chitosan film. By blending berberine with chitosan, the obtained biopolymer film exhibited improved mechanical properties compared to the control film. Differential scanning calorimetry analysis showed that berberine incorporation reduced the glass transition temperature from 89 degrees C to 68 degrees C. The film also blocked the UV light almost 100%. The addition of berberine decreased the water vapour permeability of the chitosan film while increasing the swelling ratio and water solubility. The berberine-incorporated chitosan film exhibited an antioxidant capacity of 33.7% as measured by the 2,2 diphenyl-1-picrylhydrazyl assay, which was significantly higher than that of the chitosan film, which has 5.92%. The film also demonstrated antimicrobial activity with a reduction in B. cereus and S. typhimurium growth compared to the control. Additionally, the degradation study revealed that the film degraded by 82.5% within ten days under soil. Our findings suggest that the chitosan-berberine film holds promise for applications in the food packaging industry. 2025-01-01T00:00:00Z https://hdl.handle.net/20.500.12960/1695 Cationic dye adsorption on the bioadsorbents based on chitosan and sodium alginate-iron oxide nanoparticles: Kinetic, isotherm and thermodynamic studies Kamacı, Umran Duru; Kamacı, Musa Herein, we fabricated a series of bioadsorbents based on chitosan and sodium alginate-iron oxide nanoparticles for the adsorption of methylene blue. As known, iron nanoparticle-based bioadsorbents have exhibited outstanding adsorption behavior while chitosan has been shown low adsorption due to its low surface area. For this reason, we aimed to increase the chitosan s surface area and dye adsorption behavior by mixing it with sodium alginate and iron nanoparticles. Some characterization techniques such as Fourier Transform-Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Brunauer-Emmett-Teller (BET), and thermogravimetric (TG) analysis were used to confirm the structure of bioadsorbents and to investigate crystalline, surface, and thermal properties. The adsorption of methylene blue onto the bioadsorbents was fitted to pseudo-second order kinetic and Langmuir isotherm models. The maximum methylene blue adsorption capacity was found between 162.77 and 212.77 mg/g. Moreover, thermodynamic parameters such as change in free energy (ΔGo, in the range from −4. 524 to −0.748 kJ/mol), change in enthalpy (ΔHo, in the range from −31.100 to −28.894 kJ/mol), and change in entropy (ΔSo, in the range from −90.963 to −84.454 kJ mol−1 K−1) were calculated with negative values. The findings from the thermodynamic studies indicated that the adsorption process was spontaneous and exothermic. 2025-01-01T00:00:00Z