Researcher:
Akkaş, Tuğçe

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Tuğçe

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Akkaş

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Akkaş, Tuğçe

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20202

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    Characterization of a Jian-like sherd with the optical microscope, confocal Raman, wavelength-dispersive X-ray fluorescence, and portable XRF spectrometers
    (Wiley, 2020) Yıldırım, Sinem; Yılmaz, Suat; Birdevrim, Ahmet Nejat; N/A; Franci, Gülsu Şimşek; Akkaş, Tuğçe; Post Doctorate Student; Post Doctorate Student; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/A; N/A
    The ceramic masterpieces that belong to the private collections and art galleries are rarely studied with analytical instruments to define the authenticity, provenance, and characteristics of the materials because the scientific investigations are required to be solely noninvasive for characterizing the unfractured genuine objects. A monographic program, Blue Print, which was initiated by a German cultural heritage foundation, Art & Science Endowment Trust (ASET) Stiftung, aims at developing on-site research protocols for systematic research investigations on the fragmentary samples, with and without verifiable archeological contexts. For that reason, a combination of analytical techniques was carried out on a Jian-like sherd, which was assumed to be produced either as a genuine artifact between the 11th and late 14th centuries ad or as a Qing Dynasty copy (1644-1911 ad). Before slicing the sherd, confocal Raman microscopy was used to define the red glaze signature and the crystals formed on the glazed surface, whereas portable X-ray fluorescence (XRF) (pXRF) was used to define the composition of the glaze and body. Afterward, the sherd was cut and polished for the characterization with a zoom microscope, wavelength-dispersive XRF (WD-XRF), and Raman. The macroscopic examination revealed the presence of a glassy black colored interface layer, which was detected between the body and red glaze. The composition of the red glaze was determined with XRF and Raman spectrometers, and the presence of cadmium sulfoselenide (CdSxSe1-x, 0 <= x <= 1) with a high amount of zirconium (WD-XRF: 2.20 wt.%, pXRF: 1.55-wt.% ZrO2) was found. Additionally, Raman measurements evidenced the presence of epsilon-hematite crystals formed on the blackened red glazed surface. Unlike the glaze composition, the elemental content of the body is almost the same (Al2O3: 25.7 wt.%, Fe2O3: 8.19 wt.%, K2O: 2.54 wt.%) with the genuine Jian wares already documented by artistic and scientific examinations.
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    PublicationOpen Access
    Cross-linked enzyme lyophilisates (CLELs) of urease: a new method to immobilize ureases
    (Elsevier, 2020) Zakharyuta, Anastasia; Taralp, Alpay; Ow-Yang, Cleva W.; Akkaş, Tuğçe; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM)
    In this study, we presented a new approach for immobilizing JBU (Jack bean urease), by producing urease cross-linked enzyme lyophilisates (CLELs). Through the use of bovine serum albumin (BSA), lyophilisation, cross-linking with dextran polyaldehyde (DPA), and optimizing cross-linker pH, the urease-CLELs produced show an increase in relative catalytic activity that is 1.47 times higher than that of free urease, while remaining stable up to temperatures of 85 degrees C. Urease-CLEL activity increases in direct proportion with the increasing BSA content due to the offered additional lysine (Lys) groups which are potential cross-linking points providing better immobilization and retention of JBU, while lyophilisation also enables stabilization by eliminating solvating water molecules and intra-molecular reactions that may block the cross-linking residues. Two most commonly used cross-linkers that are reacting with the available Lys groups, Le. glutaraldehyde (GA) and bulkier alternative DPA, have been selected for the immobilization of urease. The catalytic activity increase with DPA suggests an improved access to the active site through hindering blockage, while the increase with alkaline pH of the cross-linkers indicates decreased buffer inhibition. The long lifetime (113% residual activity after 4 weeks), recyclability (132% residual activity after 10 cycles) and thermal stability (276% relative activity at 85 degrees C) of these urease-CLELs demonstrate that they are technologically attractive as green biocatalysts, while our immobilization approach offers an alternative to conventional methods for proteins that are difficult to immobilise.