Gallik asit tayini için elektrokimyasal sensör olarak yarıiletken nanokompozit yapılarının geliştirilmesi = Development of semiconductor nanocomposite structures as electrochemical sensors for the determination of gallic acid

Abstract

Free radicals are molecules or atoms with one or more unpaired electrons outside their orbitals. These unpaired electrons are denoted by a dot adjacent to the atom or molecule. Free radicals, in their quest to complete their missing electrons, exhibit high reactivity and a strong tendency to form bonds and compounds. Bond formation necessitates the presence of two electrons with spins oriented in opposite directions. Electron pairs involved in bond formation exhibit structurally stable configurations. Electrons within the human body form compounds and pairs due to the bonds they establish. Upon bond disruption, electrons either disperse to other atoms or remain on a single atom. When electrons remain localized on a single atom, ions are formed, whereas their dispersion to different atoms results in the formation of free radicals. Unpaired electrons possess unexpectedly high energy levels, which can lead to the disruption of paired electrons in other molecules. Antioxidants are substances that inhibit or decelerate undesirable oxidation reactions. They neutralize free radicals, thereby preventing cellular damage induced by oxidative stress. Consequently, due to their role in naturally ameliorating various medical conditions caused by free radicals within the human body, there has been an observed increase in the consumption of antioxidant-rich foods. However, excessive intake of artificially synthesized antioxidants may lead to adverse health conditions, such as cancer. Therefore, antioxidants derived from natural sources are favored. Phenolic compounds are one of the secondary metabolites synthesized during the normal development of plants. These phenolic substances typically possess one or more hydroxyl groups attached to an aromatic ring and can be categorized as metabolic products with varied structures and functions. Phenolic compounds present in foodstuffs are predominantly found in fruits; however, their presence can vary depending on the type of fruit. Even within the same fruit species, the concentration of phenolic compounds can be influenced by multiple factors, including species, growth season, environmental conditions, climatic factors, soil type, geographical location, and ripeness. The term 'oxidative stability' in foods can be modified by phenolics, which can alter attributes such as bitterness, color, taste, pungency, flavor, and aroma. The presence of these compounds significantly impacts the sensory characteristics and shelf life of foods, thereby enhancing consumer acceptance and nutritional value. The hydroxylation pattern around the aromatic ring dictates antioxidant activity. The capacity to act as a hydrogen donor and inhibit oxidation is directly proportional to the number of hydroxyl groups present on the phenolic rings. The fundamental attribute of a molecule or antioxidant system is its ability to maintain equilibrium and, consequently, contribute to the reduction of oxidative stress-induced damage in human metabolism by disrupting or recognizing oxidative propagation chains. Phenolic compounds found in foods, particularly in fruits, have notable health benefits despite lacking direct nutritional functions. Flavonoids and other plant polyphenols are significant antioxidants due to their high redox potentials. Grape seed extract, recognized for its potent antioxidant properties, neutralizes free radicals while exhibiting cytotoxic effects against cancerous cells without harming healthy cells. It has been reported to prevent prostate cancer, and gallic acid (GA) has demonstrated significant effects against leukemia. Additionally, GA possesses protective properties against chronic cardiovascular diseases and cancer. Phenolic compounds in foods, despite lacking nutritional functions, have positive health benefits. Due to their high redox potentials, flavonoids and other plant polyphenols serve as very important antioxidants. The antioxidant effects of phenolic compounds are explained by their ability to bind with metals, form chelates, and inactivate spesifik enzymes. The most common group of naturally occurring phenolic substances is flavonoids. Other phenolic compounds include simple phenols, phenolic acids (such as benzoic and cinnamic acids), coumarins, stilbenes, hydrolyzable and condensed tannins, lignans, and lignins. These diverse phenolic compounds are found across a wide range of plants and thus plant-based foods, providing numerous beneficial effects on human health. Gallic acid (GA), a notable antioxidant present in natural samples, is a member of the polyphenol group and is sometimes referred to as 3,4,5-trihydroxybenzoic acid. Comprising C6H2(OH)3CO2H molecules, gallic acid is a yellow-white crystalline substance. It is highly soluble in water and dissolves in ether, alcohol, and glycerol, but is insoluble in benzene and chloroform. Gallic acid can be found in various fruits such as pomegranate, banana, blackberry, blueberry, avocado, currant, mango, mulberry, and sumac, as well as in plant products like green tea, sumac, walnut, oak, chestnut trees, and certain barks. In recent years, various chromatographic techniques and methods such as chemiluminescence spectrophotometry have been employed for the detection of phenolic compounds. The electrochemical detection of gallic acid occurs due to the release of electrons during its oxidation. Gallic acid is utilized as a standard compound for determining the phenolic content in diverse biological food, juice, and plant samples. In this study, electrochemical sensors for the detection of gallic acid were developed using glassy carbon electrodes (GCE) in conjunction with semiconductors such as zinc oxide (ZnO), zinc sulfide (ZnS), and zinc selenide (ZnSe). Gallic acid detection was performed using these electrochemical sensors with GCE/ZnS, GCE/ZnSe, and GCE/ZnO working electrodes in solutions containing various concentrations of GA in 0.1 M phosphate buffer (PBS) (pH 7.4). The developed GA sensors exhibited a broad linear response range from 10 μM to 1000 μM. The electrochemical sensors developed with GCE/ZnS, GCE/ZnSe, and GCE/ZnO electrodes demonstrated high sensitivity, excellent reproducibility, high selectivity, and long-term stability for GA detection.