WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/394
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Article Citation - WoS: 11Citation - Scopus: 10UV Light Promoted Dihydrolipoic Acid and Its Alanine Derivative Directed Rapid Synthesis of Stable Gold Nanoparticles and Their Catalytic Activity(Nature Portfolio, 2024-10-21) Temur, Nimet; Dadi, Seyma; Nisari, Mustafa; Ucuncuoglu, Neslihan; Avan, Ilker; Ocsoy, IsmailIn general, colloidal gold nanoparticles (AuNPs) have been synthesized in heated or boiling water containing HAuCl4 precursor with sodium citrate as reducing stabilizing reagent. Although temperature plays a driving for synthesis of AuNPs, elevated temperature in thermal reduction method causes aggregation of the AuNPs. The preferential, rapid and strong binding of dihydro-lipoic acid and its derivatives on surface of AuNPs via thiol - Au chemistry promote the production of very stable AuNPs. In this study, we have developed citric acid (CA), dihydrolipoic acid (DHLA) and DHLA-Alanine (DHLA-Ala) directed rapid synthesis of ultra-stable AuNPs, DHLA@AuNPs and DHLA-Ala@AuNPs, under the UV (311 nm) irradiation at room temperature (RT: 25 degrees C) in around 10 min (min). CA is used as a potential reducing agent to expedite both reduction of Au3+ ion and AuNP formation, DHLA and DHLA-Ala act as stabilizing agents by replacing CA molecules on surface of AuNPs in order to produce quite stable AuNP. It is worthy to mention that reduction of Au3+ ion, formation and surface stabilization of AuNPs are consequently occurred in one step. We also investigated how experimental parameters including reaction time and temperature, pH of reaction solution, affect formation of the AuNPs. The effects of salt concentration and storage temperature were studied to show stability of the AuNPs. The synthesized DHLA@AuNPs and DHLA-Alanine@AuNPs were characterized via UV-Vis spectrophotometer (UV-Vis), scanning transmission electron microscope (STEM), dynamic light scattering (DLS) and Zeta potential (ZT) devices. The reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) was efficiently catalyzed by the AuNPs in the presence of sodium borohydride in aqueous solution.Article Citation - WoS: 13Role of Pretty Nanoflowers as Novel Versatile Analytical Tools for Sensing in Biomedical and Bioanalytical Applications(Wiley, 2024-02) Dadi, Seyma; Ocsoy, IsmailIn recent years, an encouraging breakthrough in the synthesis of immobilized enzymes in flower-shaped called "organic-inorganic hybrid nanoflowers (hNFs)" with greatly enhanced catalytic activity and stability were reported. Although, these hNFs were discovered by accident, the enzymes exhibited highly enhanced catalytic activities and stabilities in the hNFs compared with the free and conventionally immobilized enzymes. Herein, we rationally utilized the catalytic activity of the hNFs for analytical applications. In this comprehensive review, we covered the design and use of the hNFs as novel versatile sensors for electrochemical, colorimetric/optical and immunosensors-based detection strategies in analytical perspective. Formation of nanoflowers and their biosensor function in biomedical and bioanalytical applications. imageArticle Citation - WoS: 10Citation - Scopus: 12Production of Flower-Shaped Nanobiocatalysts From Green Tea and Investigation of Their Peroxidase Mimicking Activity on the Polymerization of Phenol Derivatives(Wiley, 2023-12-13) Kalayci, Berkant; Kaplan, Naime; Dadi, Seyma; Ocsoy, Ismail; Gokturk, ErsenEnzyme catalyzed reactions are known to be environmental friendly and easy method for many applications. However, utilization of enzymes in a variety of reactions is strictly limited due to their high cost, instability in aqueous solutions, denaturation in organic solvents and high temperatures. For this reason, it is important to discover new generation catalyst systems indicating enzyme-like catalytic activity. Here, we report hybrid organic-inorganic flower-shaped green tea-Cu2+ nanobiocatalyst synthesized from green tea extract as an organic component and copper (II) ions (Cu2+) as inorganic component. The effect of the peroxidase-mimicking activity of green tea-Cu2+ nanobiocatalyst was investigated on the polymerization of phenol and derivatives (guaiacol and salicylic acid) through Fenton-like reaction mechanism. Obtained successful outcomes showed that the synthesized nanobiocatalyst showed very high catalytic activity upon polymerization of phenol and guaiacol. The slight solubility of salicylic acid in water limited to achieve its polymerization under-performed reaction conditions. The yields and molecular weights of the obtained polymers were found to be quite high. While free peroxidase enzymes like horseradish peroxidase (HRP) enzyme loses its catalytic activity at 60 degrees C and above temperatures, green tea-Cu2+ nanobiocatalyst exhibited very high catalytic activity upon polymerization reactions even at 60 degrees C reaction temperature. This outcome provides significant advantages in some reactions requiring high temperatures. In order to understand the origin of the catalytic activity of the green tea-Cu2+ nanoflowers, similar biocatalysts were also synthesized from caffeine and catechin alkaloids which are the active components of green tea. Caffeine-Cu2+ and catechine-Cu2+ nanobiocatalysts also exhibited quite high catalytic activity toward polymerization of phenol and derivatives. We suggest that green tea-Cu2+ and similar types of nanobiocatalysts may expand their utilization in polymer chemistry as promising catalytic agents for radicalic polymerizations.Article Citation - WoS: 1Citation - Scopus: 1Investigation of the Free-Radical Polymerization of Vinyl Monomers Using Horseradish Peroxidase (HRP) Nanoflowers(Springer, 2025-01-24) Ozaydin, Gulbahar; Mirioglu, Muge; Dadi, Seyma; Ocsoy, Ismail; Gokturk, ErsenIn this study, we report the production of flower-shaped HRP-Cu2+ hybrid nano biocatalyst (HRP-Cu2+ HNF) from the complexation between horseradish peroxidase (HRP) enzyme and Cu2+ ions, and investigate catalytic activity and stability of the obtained nanoflowers on the polymerization of some vinyl monomers (styrene, methylmethacrylate, acrylamide and N-isopropylacrylamide). Polymerizations of these monomers, except water soluble acrylamide, were accomplished under emulsion conditions using cationic, anionic and non-ionic surfactants in the presence of hydrogen peroxide (H2O2) and 2,4-pentanedione mediator. Optimum polymerizations were achieved under the conditions of non-ionic surfactant (tween 40) used. HRP-Cu2+ HNF mediated polymerizations resulted in very high yields and molecular weights (Mn) of the polymers. Optimum polymerization of styrene with 84% of yield (Mn = 319 kDa) was accomplished at room temperature. However, the highest polymerization yields for acrylamide (96%, Mn = 171 kDa) and N-isopropylacrylamide (85%, Mn = 185 kDa) was achieved at 70 degrees C. Similarly, optimum polymerization of methylmethacrylate was accomplished with 84% of yield (Mn = 190 kDa) at 60 degrees C. While free-HRP loses its catalytic activity at 60 degrees C and above temperatures, HRP-Cu2+ HNF showed very high catalytic activity and stability even at 70 degrees C. Increasing activity and stability of hybrid nanoflowers provide significant advantages for both scientific and industrial applications.Article Citation - WoS: 35Citation - Scopus: 36In Situ Synthesis of Horseradish Peroxidase Nanoflower@Carbon Nanotube Hybrid Nanobiocatalysts With Greatly Enhanced Catalytic Activity(Amer Chemical Soc, 2023-03-21) Dadi, Seyma; Temur, Nimet; Gul, O. Tolga; Yilmaz, Vedat; Ocsoy, IsmailOrganic-inorganic hybrid nanoflowers (NFs) consisting of horseradish peroxidase (HRP) and copper II (Cu2+) are successfully synthesized with the involvement of carbon nanotubes (CNTs) by in situ and post-modification methods. Catalytic activities of in situ synthesized HRP-NF@CNT (HRP-NF@CNT-Is) and post-modification-synthesized HRP-NF@CNTs (HRP-NF@CNT-Pm) are systematically examined. The 30 mg CNTs incorporated HRP-NF@CNT-Is (HRP-NF@ CNT-30Is) exhibits greatly increased catalytic activity and stability toward 3,3 ',5,5 '-tetramethylbenzidine (TMB), thanks to the synergistic effect between HRP-NF and CNTs and the peroxidase-like activity of CNTs in the presence of hydrogen peroxide (H2O2). While HRP-NF@CNT-30Is retains almost 85% of its initial activity even after 10 cycles, HRP-NF (without CNTs) loses half of its initial activity at the same experimental conditions. We study how two experimental parameters, the pH values and temperatures, influence the catalytic activity of HRP-NF@CNT-30Is, in addition to the fact that HRP-NF@CNT-30Is is employed to detect the presence of H2O2 and glutathione (GSH) with colorimetric and spectrophotometric readouts. For instance, HRP-NF@CNT-30Is is used to sensitively detect H2O2 in the range of 20 to 300 mu M with an LOD of 2.26 mu M. The catalytic activity of HRP-NF@CNT-30Is is suppressed in the presence of GSH, and then an obvious color change from blue to nearly colorless is observed. Using this strategy, GSH is also sensitively determined in the range of 20-200 mu M with an LOD of 11.2 mu M. We expect that HRP-NF@CNTs can be used as a promising and novel nanobiocatalyst for various biomedical and industrial applications in the near future.Article Citation - WoS: 2Citation - Scopus: 2Benefiting From Both Ethanol Oxidation and Bidentate Thiol Groups of DHLA Ligands Under Photoirradiation for Synthesis of Au Nanoparticles With Their Catalytic and Peroxidase Like Activity(Amer Chemical Soc, 2025-04-08) Temur, Nimet; Dadi, Seyma; Dogan, Ayse Nur; Nisari, Mustafa; Avan, Ilker; Ocsoy, IsmailIn this work, we rationally synthesized quite stable gold nanoparticles (AuNPs) using dihydrolipoic acid (DHLA) and DHLA-aspartame (DHLA-Asptm) as both reducing and stabilizing agents in a mixture of water/ethanol at RT under photoirradiation in 10 min. The novelty of this work is that benefiting from both the oxidation of ethanol to ethanal and having the bidentate thiol groups of DHLA, stable DHLA@AuNPs and DHLA-Asptm@AuNPs were successfully and rapidly formed without additional reducing reagents. We systematically examined the formation of DHLA@AuNPs and DHLA-Asptm@AuNPs under different pH values and reaction temperatures. Furthermore, the salt tolerance of DHLA@AuNPs and DHLA-Asptm@AuNPs was tested in a series of sodium chloride solutions. We showed the catalytic and peroxidase-like activities of DHLA@AuNPs against 4-nitrophenol and 3,3 ',5,5 '-tetramethylbenzidine. The AuNPs were characterized by UV-vis spectrophotometry, scanning transmission electron microscopy, zeta potential, and dynamic light scattering.