Chemistry / Kimya

Permanent URI for this collectionhttps://hdl.handle.net/11147/4072

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Now showing 1 - 10 of 21
  • Conference Object
    Citation - WoS: 3
    Citation - Scopus: 3
    Halloysite Nanotube Loaded Polyamide Nanocomposites: Structural, Morphological, Mechanical, Thermal and Processing Behaviors
    (American Institute of Physics, 2023) Akar, Alinda Öykü; Yıldız, Ümit Hakan; Tayfun, Ümit
    In this study, the polyamide 6 (PA) matrix was reinforced with the purified, fine ground and amino-silane treated halloysite nanotubes (HNT) at different concentrations. The preparation of composites was carried out using a lab-scale twin-screw micro-compounder with loading ratios at 0.5, 1, 3, and 20% by weight, and the test samples were prepared by the injection-molding process. According to mechanical test results, additions of HNT to the PA matrix caused slight improvements in tensile strength and Youngs' modulus parameters. The optimum concentrations for all of the additives used were estimated by comparison of mechanical test data. The addition of aminosilane-modified HNT resulted in a higher impact performance at high loading levels up to 3% concentrations. Further addition of HNT caused a reduction in the mechanical parameters of composites. Thermal studies revealed that the glass transition temperature of PA shifted to higher values after HNT mineral inclusions. Thermo-mechanical results showed that storage moduli of PA exhibited improvement with an increase in HNT content. The distributions of HNT clay into the PA phase were visualized with SEM images. Based on these observations, a high level of dispersion homogeneity was achieved for lower filling ratios. According to melt-flow and force measurements, composites filled with 20% of HNT displayed a remarkable increase in exerted force during melt-blending. © 2023 Author(s).
  • Conference Object
    Citation - WoS: 1
    Citation - Scopus: 1
    Biomimetic Peptide-Conjugated Membranes for Developing an Artificial Cornea
    (IEEE, 2022) Sunal, Gülşah; Pulat, Günnur; Akgün, İsmail Hakkı; Güven, Sinan; Yıldız, Ümit Hakan; Karaman, Ozan; Horzum, Nesrin
    The corneal endothelium is composed of a single layer of specialized endothelial cells, protecting, and nourishing the inner surface of the cornea. Corneal endothelial cells do not proliferate after birth and their number decrease with age. Trauma, inflammation, or surgical intervention can cause cell loss. When damage is extensive and the density of corneal endothelial cells decreases to a critical level, it results in corneal edema and vision loss. Besides them, when corneal endothelium has irreversible damage, the only treatment way is corneal transplantation. But there are some drawbacks such as finding donors, immune reactions, and the number of patients waiting on the transplantation lists for years. Tissue engineering approaches can provide promising alternatives for the regeneration of corneal endothelium tissue. Peptides can be used to modify and functionalize the scaffolds, allowing for the production of bioactive and biomimetic surfaces. Peptide-modified scaffold surfaces might direct and enhance the behaviors of cells. In this study, the aim was to functionalize the polycaprolactone (PCL) membranes with tissue-specific peptides and to characterize the peptide-conjugated membranes by Fourier-Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and X-ray Photoelectron Spectroscopy (XPS) analysis. The synthesized peptides were successfully conjugated on the PCL biomembranes.
  • Conference Object
    Citation - WoS: 1
    Immunomodulatory Mechanisms of Astragalus Saponins
    (Wiley, 2021) Yakuboğulları, Nilgün; Çağır, Ali; Bedir, Erdal; Sağ, Duygu
  • Conference Object
    Optimization of Mass Spectrometric Ionisation Efficiency Data
    (Springer Verlag, 1997) Özgen, İsmet Tamerkan; Altungöz, Oya; Salih, B.; Vandeginste, B. G. M.
    A new method is developed and tested to find out the excited electronic and vibrational energy levels (fine structure) of molecules from mass spectrometric ionisation efficiency data which were obtained by a conventional mass spectrometer ion source having normal electron energy distribution. Electrons emitted in a conventional mass spectrometer ion source are not monoenergetic, therefore, evaluation of Ionisation Potentials (IF) and Appearance Potentials (AP) from experimental data creates some problems. This is even worse in the evaluation of Fine Structure (excited electronic and vibrational energy levels) from ionisation efficiency data [1]. This is overcome either by using specially designed monoenergetic ion sources which have their own problems (manufacture of special design, difficulty of operation, too much decrease of ion current), or by eliminating disturbing effects in the ionisation efficiency data by some deconvolution techniques [2,4,5,6,7,9]. In this study attempts were made to eliminate the deteriorating effects (mainly arising from electron energy distribution and noise) in the ionisation efficiency data by a deconvolution technique. The technique was applied to the ionisation efficiency data of molecular nitrogen,oxygen and methylammine and its fragment and interesting results were obtained.
  • Conference Object
    Effect of Some Physical, and Chemical Variables on Flocculation and Sediment Behaviour
    (A.A. Balkema Publishers, 2000) Polat, Hürriyet; Polat, Mehmet; İpekoğlu, Üner
    Effect of some chemical and physical variables on the settling rate, final sediment height, sediment viscosity and supernatant turbidity of a clay sample was studied using various polyacrylamide type flocculants. Increasing flocculant concentration significantly increased both the settling rate and sediment viscosity. More importantly, changes in the final sediment, height, hence the packing density, was minimal for all the conditions tested once the sediment was allowed to consolidate. Also, the mode of addition of the polymer, at once or continuous, did not seem to affect any of the parameters measured. Conditioning time seemed to alter the settling rate at low polymer concentrations, but had no effect at high polymer concentrations. However, increasing the conditioning time caused a decrease in the sediment viscosity. Different types of the polyacrylimides generated different settling rates at a given concentration, but the final sediment height was nearly independent of polymer type.
  • Conference Object
    Labeling of Gly-Gly With Technetium-99m and the Assessment of It's Radiopharmaceutical Potential
    (Springer Verlag, 2001) Taner, M.S.; Özdemir, Durmuş; Köseoğlu, K.; Argon, M.; Dirlik, A.; Duman, Y.
    [No abstract available]
  • Conference Object
    Use of Ion Flotation To Remove Copper From Waste Waters
    (2006) Erdoğan, Demet; Polat, Hürriyet; İpekoğlu, Üner
    Flotation studies were carried out to investigate the removal of copper from wastewaters. Various parameters such as pH, surfactant and frother concentrations and airflow rate were tested to determine the optimum flotation conditions. Sodium dodecyl sulfate and Hexadecyltrimethyl ammonium bromide were used as collectors. Recoveries as high as 90% could be to obtained under optimum conditions.
  • Conference Object
    Semi-Synthetic Studies on Astragaloside Vii and Immunomodulatory Activities of the Derivatives
    (Georg Thieme Verlag, 2019) Yakuboğulları, Nilgün; Sağ, Duygu; Çağır, Ali; Bedir, Erdal
    Adjuvants have been used in vaccine sector since 1920s to increase the immunogenicity of antigens, reduce the dosage and minimize frequency of immunizations [1]. The use of saponins as adjuvant in the prophylactic/therapeutic human and veterinary vaccines, and investigation of their immunomodulatory activities have gained importance in recent years [2],[3]. Astragaloside VII (AST VII), a triterpenoid saponin isolated from Astragalus species, stimulates Th1 mediated immune response, antigen-specific antibody response and splenocyte proliferation.
  • Conference Object
    A Novel Inhibitor for Krasg12c Mutant Lung Carcinoma
    (International Association for the Study of Lung Cancer, 2020) Khan, H. Y.; Li, Y.; Aboukameel, A.; Mpilla, G.; Sexton, R.; Kanbur, Tuğçe; Nagasaka, M.; Çetinkaya, Hakkı; Çağır, Ali
    Mutations in KRAS are among the most common aberrations in cancer. However, despite considerable research efforts, KRAS remains a challenging therapeutic target. In recent years, there has been a drive to develop KRAS mutant specific drugs. Among the different known mutations, the KRASG12C (glycine 12 to cysteine) has been considered druggable. Studies have shown that due in part to the close proximity of Cysteine 12 to both the nucleotide pocket and the switch regions, thiol-reactive compounds can bind to the active site covalently and inhibit KRASG12C mutation-driven signaling. The absence of this particular cysteine residue in wild-type KRAS makes such an approach very selective towards cancer cells.
  • Conference Object
    Citation - WoS: 2
    Citation - Scopus: 1
    Determination of Aluminum Oxide Thickness on the Annealed Surface of 8000 Series Aluminum Foil by Fourier Transform Infrared Spectroscopy
    (Springer, 2017) İnanç Uçar, Özlem; Ekin Meşe, Ayten; Birbaşar, Onur; Dündar, Murat; Özdemir, Durmuş
    Aluminum foil produced with prescribed thermomechanical processing route develop oxide film. Alloy chemistry and annealing practices, particularly its duration and exposed temperature, determine the characteristics of the oxide film. The magnitude and characteristics of the oxide film may impair surface features leading to serious problems in some applications, such as coating, printing and in some severe cases failure in formability. Therefore, it is important for the rolling industry to be able to monitor the oxide formation on the foil products and quantify its thickness. Well known methods to measure an oxide thickness that is in the order of nanometer, require meticulous sample preparation techniques, long duration for measurements and sophisticated equipment. However, in this study, a simple and rapid grazing angle attenuated total reflectance infrared (GA-ATR-FTIR) spectroscopic method combined with chemometrics multivariate calibration has been developed for the oxide thickness determination which is validated with x-ray photoelectron spectroscopy (XPS). 3000 and 8000 series aluminum foil materials which were produced by twin roll casting technique were used in this study. Foil samples were annealed at various different temperatures and annealing times in a laboratory scale furnace. Immediately after collecting GA-ATR-FTIR spectra, the 3000 series alloy samples were sent to a laboratory where XPS reference oxide thickness measurements had been performed. Partial Least Squares (PLS) method was used to develop a multivariate calibration model based on FTIR spectra and XPS reference oxide thickness values in order to predict the aluminum oxide thickness. The correlation coefficient of XPS reference oxide thickness values versus grazing angle ATR-FTIR based PLS predicted values was found as 0.9903 the standard error of cross validation (SECV) was found to be 0.29 nm in range of 4.9–14.0 nm for Al2O3. In addition, the standard error of prediction (SEP) for the validation set was 0.24 nm with the model generated with three principal components (PCs). © The Minerals, Metals & Materials Society 2017.