Naftokinon tabanlı iyon sensörlerin geliştirilmesi
Naftokinon tabanlı iyon sensörlerin geliştirilmesi
Dosyalar
Tarih
2021
Yazarlar
Mermer, Zeliha
Süreli Yayın başlığı
Süreli Yayın ISSN
Cilt Başlığı
Yayınevi
Lisansüstü Eğitim Enstitüsü
Özet
Cıva (Hg) uçuculuğunun yüksek olması ve sinir sistemine olan etkileri nedeniyle ağır metaller arasından en çok bilinen toksik analittir. Bu yüzden cıvanın oldukça seçici ve hassas tayini için basit ve ileri teknikler geliştirilmesi hem insan sağlığı hem de çevre için bir hayli önem kazanmıştır. Geleneksel metotlar cıva tayini için; atomik absorpsiyon spektroskopisi (AAS), İndüktif olarak eşleştirilmiş plazma kütle spektroskopisi (ICP-MS) ve elektrokimyasal metotları içerir. Bu metotlar oldukça seçici ve hassas olmalarına karşın pahalı ve fazla miktarda numune gerekmektedir. Bu amaç için hazırlanan kimyasal sensörler ucuz, güvenilir ve basit yollarla elde edilebilir olması yönünden birincil önem kazanmaktadır. Bu tez kapsamında öncelikle kolay sentezlenebilen naftokinon tabanlı yeni ve çok kanallı kemosensörler sentezlenmiştir. Kemosensör kullanılarak seçici olarak eser miktarda Hg2+ iyonunun tespit edilmesinde kolorimetrik, florometrik ve voltametrik yöntemler kullanılmıştır. Geliştirilmiş yeni sensörlerin analitik özellikleri detaylı olarak incelenmiştir. Literatürde cıva veya diğer ağır metallere karşı seçici birçok ligant sentezlenmiş ve hassasiyeti UV-Gör ve floresans yöntemleri ile çalışılmıştır. Tez çalışması iki aşamadan oluşmaktadır. Birinci aşamada; 1,4-naftokinon ve anilin bileşiğinin metanol içerisinde substitüsyon reaksiyonu sonucunda hedeflenen Nq-An sensörü literarüre göre elde edilmiştir ve saflaştırılmıştır. FT-IR spektrumunda ve DMSO'da alınan 1H-NMR 13C-NMR spektrumlarında beklenen pikler görülmüştür. MALDI/TOF kütle spektrumu sonucu; bulunan kütle (m/z): 250,259 [M++ H] yapı ile uyum içerisindedir. MeOH içindeki Nq-An çözeltisine Hg(NO3)2.H2O ilave edilerek geri soğutucu altında 1 gece karıştırılıp çözücüsünün buharlaştırılması ve kalan katı ürünün saflaştırılması sonucunda [Hg—(Nq—An)2] cıva kompleksi elde edilmiştir. Kompleksleşme sonucunda FT-IR spektrumunda Nq-An'ye ait piklerin dışında kompleksleşmeye ait 598 (Hg-N), 567 (Hg-C) de beklenen pikler gözlenmiştir. DMSO' da alınan 1H-NMR spektrumu ve DMSO'da alınan 13C-NMR spektrumunda beklenen pikler gözlenmiştir. Civa kompleksinin 13C-NMR spektrumunda, Nq-An'nin C6 atomuna karşılık gelen 102,42 ppm'de gözlenen pik kompleksleşme sonucunda düşük alana kaymıştır. MALDI/TOF kütle spektrumu sonucu; bulunan 699,631 [M++3H] olmuştur. Elementel Analiz sonucunda: yapı ile uyumlu olduğu görülmüştür. 1,4 Naftokinon bileşiğinin piren amin ile olan metanol içerisindeki substitüsyon reaksiyonu sonucunda yeni Nq-Pyr sensörü elde edilmiştir. FT-IR spektrumunda. DMSO' da alınan 1H NMR ve 13C-NMR spektrumu sonucunda beklenen pikler gözlenmiştir. MALDI/TOF kütle spektrumu sonucu; bulunan kütle (m/z), 375,033 [M+] yapı ile uyum içerisindedir. pH 8'de 20 mL DMF/H2O (5:1 v/v) içindeki bir Nq-Pyr' ye Hg(NO3)2.H2O ilave edilerek, oda sıcaklığında 1 gece karıştırılmış ve nihai kalıntı yıkanarak istenilen [Hg— (Nq—Pyr)2] cıva kompleksi elde edilmiştir. Kompleksleşme sonucunda FT-IR spektrumunda beklenen pikler gözlenmiştir. Elementel Analiz sonucu yapı ile uyum içerisindedir. MALDI/TOF Kütle spektrumu sonucu bulunan kütle (m/z), 943,352 [M+] yapıyı doğrulamıştır. Tez çalışmasının ikinci aşamasında naftokinon moleküllerine dayalı eser miktarda Hg2+ iyonunun tayini üç kanallı (UV-Gör, florometrik ve voltametrik) olarak gerçekleştirilmiştir. Bu kapsamda çözücü etkisi, seçicilik, müdahale etme ve pH parametreleri incelenerek Hg2+ nin seçici ve hassas tayini için gerekli optimum koşullar belirlenmiştir. Nq—An ve Nq—Pyr sensörlerinin Hg2+ iyonuna karşı olan tepkisine pH etkisini araştırmak için, çeşitli asitlerin ve tuzlarının 1 ila 10 arasında değişen pH değerlerine sahip bir dizi tampon çözeltileri hazırlanmıştır. Nq—An ve Nq—Pyr'nin çözeltilerinin UV–Gör spektrumları, istenen pH' da (1-10) kaydedilmiştir. Bu reseptörlerin 7-8 pH aralığında Hg2+ katyonunu etkin bir şekilde algıladığı gösterilmiştir. Kolorimetrik olarak yapılan seçicilik çalışmasında problar, ortam sıcaklığında Hg2+ katyonu için turuncu'dan pembe'ye önemli bir renk geçişi gösterirken, rekabetçi katyonların varlığında renkleri değişmemiştir. Nq—An/Nq—Pyr ve bunların Hg2+ komplekslerinin [Hg—(Nq—An)2]/[Hg—(Nq—Pyr)2] elektronik spektrumları sırasıyla DMSO: H2O (1:1 v/v) ve DMF:H2O (5:1 v/v) pH 8' de kaydedilmiştir. Nq-An ve Nq-Pyr' nin Hg2+ ile bağlanma özelliklerini araştırmak için UV-Gör titrasyon çalışmaları da yapılmıştır. Nq—An ve Nq—Pyr tampon çözeltisine artan miktarlarda Hg2+ eklendiğinde, absorbansı 521 ve 506 nm' de izosbestik noktalarla birlikte 475 nm ve 473 nm' deki pikler düzenli olarak azalış, ancak 576 nm ve 571 nm'deki pikler ise artış göstermiştir. İzosbestik noktaların ortaya çıkması, komplekslerin oluşumunu doğrulamıştır. Jobs' un sürekli varyasyon yöntemiyle grafikteki eğrinin çizimi sonucunda 2:1 [Nq—An:Hg2+] oluşumu desteklenmiştir. Ayrıca, 1H-NMR titrasyonunda değişen miktarlarda cıva iyonun ilavesi sonucu 0,5 eşdeğerde beklenen piklerin kaybolması Nq-An'nin Hg2+ katyonu ile 2:1 bağlanmasını göstermiştir. Oransal UV-Gör titrasyon tekniğine dayalı olarak Nq—An ve Nq—Pyr sensörlerinin algılama limitleri, Hg2+ tayini için sırasıyla 1,6×10-6 ve 5,9×10-7 M olarak belirlenmiştir, bu da orta düzeyde Hg2+ algılama hassasiyetine işaret etmiştir. Diğer iyonların beş eşdeğerde bulunduğu Hg2+ varlığında rekabetçi çalışmalar uygulanmıştır. Hg2+, ortamdaki diğer metal iyonlarından etkilenmeyen Nq—An ve Nq—Pyr tarafından başarıyla tanınmış ve Nq—An ve Nq—Pyr sulu çözeltide Hg2+ katyonuna karşı yüksek seçicilik sergilemiştir. Ayrıca sensörlerin tepki süreleri de sırasıyla 10 ve 20 saniye olarak belirlenmiştir ve bu sonuç literatür değerlerine göre oldukça iyidir. Algılama işleminin tersinir olup olmadığını kontrol etmek için, Hg2+ ile inkübe edilen Nq—An ve Nq—Pyr çözeltisi Na2S ile muamele edilmiş ve UV-Gör spektral değişiklikleri kaydedilmiştir. Sonuç olarak her iki reseptörde ortamdan cıvanın uzaklaştırılması sonucu işlemin tersinir olduğu gösterilmiştir. Sensörün florometrik özelliğini ortaya koymak için Hg2+ ve Nq—Pyr etkileşimi floresans spektroskopik analiziyle incelenmiştir. Hg2+ katyonu varlığında, prob 432 nm' de belirgin bir floresans bandı sergilemiş, ancak diğer metal iyonları için herhangi bir özel değişiklik olmamıştır. Hg2+ iyonunun sensörle Hg-C ve Hg-N bağlanması sonucu Metal Şelat Oluşumuna Dayanan Artmış Floresans (MCHEF) mekanizması ortaya koyulmuştur. Florometrik tekniğe dayalı Nq—Pyr sensörünün tayin limiti, Hg2+ iyonu için 7,4×10-8 M olarak belirlenmiştir. Ek bir deney olarak floresans sensörün tepki süresi 75 saniye olarak belirlenmiştir. Kontamine musluk suyunda Hg2+'yi belirlemek için sensörlerin uygulanabilirliği gösterilmiştir. Ayrıca UV-Gör ve floresans için tüm sonuçlar iyi bilinen ICP-MS ve AAS yöntemleriyle karşılaştırılmıştır. Sensörlerimiz LOD açısından ortalama değerlere sahip olmasına rağmen, çok hızlı tepki sürelerinin yanı sıra yüksek doğruluk, kesinlik ve tekrarlanabilirliğe sahiptirler. Her iki sensörün de çok kanallı olması sensörlerin avantajını da arttırmıştır. Voltametrik kısımda ilk olarak Nq—An' nin elektrokimyası, CV ve DPV teknikleri kullanılarak DMSO' daki redoks davranışı ile aydınlatılmıştır. Nq—An' nin elektrokimyasal davranışı, 1,4-naftokinonun(Nq) kine benzerdir ancak, Nq—An ' nin indirgeme potansiyeli, katodik bölgeye kaymıştır. [Hg(Nq-An)2] kompleksinin redoks davranışı incelenmiş ve aynı deney koşullarında Nq—An' nin redoks davranışı ile kıyaslanmıştır. Beklenildiği gibi, [Hg—(Nq—An)2]'nin monoanyon ve dianyonuna karşılık gelen indirgeme potansiyelleri pozitif potansiyel değerlerine kaymıştır. Nq—An ile karşılaştırıldığında [Hg—(Nq—An)2]' nin indirgenme prosesinde akım kaybı gözlemlenmiştir. Kompleksin mono ve dianyon ürünlerine karşılık gelen yarı dalga redoks potansiyeli, sırasıyla hesaplanmıştır. DPV ölçümü, kompleksteki naftokinon çekirdeğine karşılık gelen katodik pik potansiyellerinin iki pike yarıldığını, ve bu da kompleksteki iki naftokinon ünitesinin iki basamak halinde iki elektron indirgeme prosesi ile indirgendiğini göstermiştir. Nq—An reseptörünün tamponlu ortamındaki CV'si de gösterilmiştir. Bu sonuç tamponlu sulu ortamda kinonların genel elektrokimyasal davranışı ile tutarlıdır. Tampon çözeltisindeki Nq-An reseptörüne cıva tuzu eklenerek oluşturulan [Hg—(Nq—An)2] kompleksinin CV' leri gösterilmiştir. Nq-An sensörüne Hg2+ iyonunun eklenmesiyle, nihai voltommogram [Hg—(Nq—An)2] kompleksininkiyle aynıdır. Ayrıca sensörün 0–1x10-5 M konsantrasyonundaki Li+, Na+, K+,Cs+, Be2+, Ca2+, Mg2+, Ba2+, Zn2+, Cu2+, Hg2+, Co2+, Fe2+, Fe3+, Mn2+, Pb2+, Ni2+ iyonları ile kompleks oluşturup oluşturmadığı test edilmiştir. Diğer katyonların varlığında Nq-An'nin sulu çözeltideki voltametrik davranışında bir değişiklik gözlenmemiştir. Hg0/Hg2+ redoks çiftinden kaynaklanan anodik akımın Hg2+ iyon miktarına bağlı olarak 3,5-20,5 ppm konsantrasyonları arasında doğrusal olarak arttığı gözlenmiştir.
Heavy metals are metallic elements that have atomic weights ranging from 63.5 to 200.6 and have higher densities than other atoms. With the rapid development of the industry, metal coatings, mining operations, batteries, the fertilizer industry and the increase in the use of pesticides, heavy metals have spread directly or indirectly to the environment from contaminated wastewater. Heavy metals emitted into the environment aroused great interest because they threaten human life and ecosystems. Many heavy metal ions are known as toxic and carcinogens because they do not biodegrade like organic contaminants and accumulate in living organisms. Known toxic heavy metal ions are as follows: Zn, Cu, Ni, Hg, Cd, Pb and Cr. Mercury (Hg) is the most well-known toxic analyte due to its toxicity to humans and the environment, and it is released into the environment by some industrial processes as well as the combustion of coal and waste. The toxicity of mercury is due to its high volatility and its effects on the nervous system. The intake of mercury into the human body occurs through inhalation, skin contact, and oral route, and WHO stated that the tolerable mercury intake is 2 µg/kg per kilogram of body per day. According to EPA, the maximum allowable concentration of mercury in drinking water is specified as 10 nM. Therefore, the development of simple and advanced techniques for the highly selective and sensitive determination of mercury has gained great importance for both human health and the environment. Traditional methods for the determination of mercury; Atomic absorption spectroscopy (AAS), Inductively coupled plasma mass spectroscopy (ICP-MS) and electrochemical methods. Although these methods are highly selective and sensitive, expensive and large sample sizes are required. Naphthoquinones, which are quinone derivatives, contain two rings. In addition to being obtained as synthetic products, it is quite abundant in nature. Although naphthoquinones can be found in six different structures, the most well-known are 1,2-, 1,4-, 2,6- naphthoquinones. In addition to being obtained synthetically, naphthoquinones compounds found in plants, fungi, and bacteria. Naphthoquinone derivatives play a role in important biological activities such as cellular respiration, photosynthesis, blood coagulation and antioxidants. Chemically, it has pharmacological or natural product synthesis, dye, charge transfer complexes, transition metal coordination with oxygens, oxidizing and electrochemical properties. A major research effort has been concentrated to find inexpensive, reliable, and simple ways of detecting ions in the environment. Thus, finding new selective ion receptor systems, sensor development, environmental remediation, selective separation and extraction of chemical species has become an important goal. Chemical sensors prepared for this purpose gain primary importance as they can be obtained in cheap, reliable and simple ways. In this thesis, first of all, a new and multi-channel chemosensor based on easily synthesized naphthoquinone was synthesized. Colorimetric, fluorometric, and voltammetric methods were used to detect trace amounts of Hg2+ ions selectively using the chemosensors. The analytical properties of the new sensors to be developed have been examined in detail. In the literature, many ligands selective against mercury or other heavy metals have been synthesized and their sensitivity has been studied by UV-Vis and fluorescence methods. The thesis work consists of two stages. In the first stage; by the substitution reaction of 1,4-naphthoquinone and aniline compound in methanol, the targeted Nq-An sensor was obtained and purified according to the literature. MALDI/TOF mass spectrum result; found mass (m/z): 250,259 [M++ H] is in harmony with the structure. [Hg—(Nq—An)2] mercury complex was obtained by adding Hg(NO3)2.H2O to Nq-An solution in MeOH, stirring under reflux for 1 night, evaporation of the solvent and purification of the remaining solid product. As a result of the complexation, in the FT-IR spectrum, apart from the peaks of Nq-An, the expected peaks of 567 cm-1 (Hg-C) and 598 cm-1 (Hg-N), were observed. The expected peaks were observed in the 1H NMR and 13C-NMR spectra taken in DMSO. In the 13C NMR spectrum of the mercury complex, the peak observed at 102.42 ppm, corresponding to the C6 atom of Nq-An, shifted to low area as a result of complexation. MALDI/TOF mass spectrum result shows that the found value 699.631 [M++3H] confirms the structure. As a result of Elemental Analysis, it was found to be compatible with the structure. A new Nq-Pyr sensor was obtained by the substitution reaction of 1,4 naphthoquinone with pyrene amine in methanol. The expected peaks related with the Nq-Pyr were observed ın the FT-IR spectrum. According to the 1H NMR and 13C-NMR spectra taken in DMSO, the expected peaks were observed. MALDI/TOF mass spectrum result; the peak observed at m/z = 375.033 belongs to [M+] of Nq-Pyr. Hg(NO3)2.H2O was added to a Nq-Pyr in 20 mL DMF/H2O (5:1 v/v) at pH 8, stirred at room temperature for 1 night, and the final residue was filtered off, and washed to obtain the desired [Hg— (Nq-Pyr)2] mercury complex. The expected peaks related with the complex were observed in the FT-IR spectrum. Elemental Analysis result is in harmony with the structure. The mass (m/z) found (943.352 for [M+]) from the MALDI/TOF mass spectrum confirmed the structure. In the second part of the thesis, the determination of trace amounts of Hg2+ ions based on naphthoquinone molecules was carried out using spectrophotometric (UV-Vis, fluorometric and voltammetric) methods. In this context, the optimum conditions for the selective and sensitive determination of Hg2+ were determined by examining the solvent effect, selectivity, interference and pH parameters. To investigate the pH effect on the response of Nq—An and Nq—Pyr sensors to the Hg2+ ion, a pH buffer range of 1 to 10 was prepared buffering a 0.2 M solution of acids and their salts. The UV–Vis spectra of the solutions of Nq—An and Nq—Pyr were recorded at the desired pH (1-10). It has been shown that these receptors effectively detect the Hg2+ ion within pH values of 7-8. The colorimetric selectivity study at ambient temperature showed that the probes yielded a notable transition of color from orange to pink where the sample contained Hg2+ ion, while the color of other probes did not change in the presence of competitive cations. This is due to the red shift of the ICT transition band between the nitrogen donors and the electron-deficient naphthoquinone group after complex formation. Electronic spectra of Nq—An/Nq—Pyr and their Hg2+ complexes [Hg—(Nq—An)2]/[Hg—(Nq—Pyr)2] DMSO: H2O (1:1 v/v) and DMF:H2O, respectively (5:1 v/v) recorded at pH 8. The main peaks observed at 475 and 473 nm for Nq—An/Nq—Pyr correspond to the n→π* type ICT transition from nitrogen (donor) to quinone (acceptor). To investigate the binding properties of naphthoquinone probes with Hg2+ ion, UV-Vis titration studies were also carried out. When the amount of Hg2+ was increased in the buffered solutions of the probes, absorbances at 475 nm and 473 nm decreased regularly, along with isosbestic points at 521 and 506 nm, but the peaks at 576 nm and 571 nm increased. The appearance of isosbestic point confirmed the formation of complexes. The formation of 2:1 [Nq—An:Hg2+] was strongly suggested as a result of plotting the curve in the graph with Job's method of continuous variation. Additional to the MALDI/TOF/MS spectra, the absence of expected peaks in 1H NMR titration spectra with 0,5 equivalent of mercuric ion, and elemental analysis also definitely showed 2:1 binding of Nq-An with the Hg2+ cation. Based on the proportional UV-Vis titration technique, the detection limits of the Nq—An and Nq—Pyr sensors are found as 1.6×10-6 and 5.9×10-7 M for the determination of Hg2+, respectively, according to literature, indicating a moderate sensitivity of Hg2+ detection. Mercuric ion, in the presence of five equivalents of other ions, were studied comparatively. The probes are successful in recognizing Hg2+ ion, other metal ions did not disturb the interaction at all, and in aqueous solution, the probes exhibited high selectivity for the mercuric ion. In addition, the sensors had response times of 10 and 20 seconds, respectively, which is considered quite good the response times of the sensors Nq-An and Nq-Pyr were determined as 10 and 20 seconds, respectively, and this result is quite good when the literature values are considered. To find out if the detection was reversible, Nq—An and Nq—Pyr solutions, incubated with Hg2+ ion, were treated with Na2S in a UV-Vis spectral setting. As a result, it has been shown that the process is reversible as a result of removal of mercury from the environment in both receptors. An additional test was conducted for the reversibility, changes in absorbance were determined when mercuric ions or sulfide ions were added. As the amount of sulfur increased in the medium, HgS is formed and the response of the sensor decreased. To reveal the fluorometric property of the sensor, fluorescence spectroscopic analysis showed the interaction of mercuric ion and Nq—Pyr. When Hg2+ cation is present in the medium, the probe showed a distinct band of fluorescence at 432 nm, but other metal ions did not reveal specific changes. When Hg2+ ion binds to the probes by forming Hg-C and Hg-N bonds, the mechanism of Increased Fluorescence Based on Metal Chelate Formation (MCHEF) has been revealed. The detection limit of the Nq—Pyr sensor based on the fluorometric technique was determined as 7.4×10-8 M for the Hg2+ ion. Moreover, the response time of the fluorescent sensor was set at 75 seconds. The applicability of the sensors to detect Hg2+ in contaminated tap water has been demonstrated. In addition, UV-Vis and fluorescence data were compared with popular ICP-MS and AAS data. Our sensors are average in terms of LOD, but they show very short response times, high accuracy, precision, and repeatability. Both sensors are multi-channel, so this increased the advantages of them. In the voltammetric part, the electrochemistry of Nq—An was first elucidated by its redox behavior in DMSO using CV and DPV techniques. Nq—An exhibited a chemically reversible one-electron reduction process to form the semi-quinone radical product: the monoanion Nq—An•–. The more reversible reduction of an electron was observed at more negative potentials; second reduction, dianion Nq—An2–. The electrochemical behavior of Nq—An is similar to that of 1,4-naphthoquinone (Nq), but the reduction potential of Nq—An is shifted to the cathodic region due to the electron donating property of the amino-phenyl group attached to the naphthoquinone core. The redox behavior of the [Hg—(Nq—An)2] complex was investigated and compared with the redox behavior of Nq-An under the same experimental conditions. The reduction potentials corresponding to the monoanion and dianion of [Hg—(Nq—An)2] shifted cathodically as expected. It is because the electron donating ability of the amino-phenyl group decreases when the mercury complex [Hg—(Nq—An)2] is formed. Compared to Nq—An, current loss was observed in the reduction process of its Hg2+ complex. The complex is poorly diffused on the electrode surface. The half-wave redox potentials corresponding to the monoanionic and dianionic products of the complex were calculated. According to DPV measurements, cathodic peak potentials of the naphthoquinone core in the complex were split into two peaks, this is indicative of the fact that the two naphthoquinone units were reduced in two steps. In buffered media, the CV of the Nq—An receptor's CV is also presented. This is harmonious, in buffered aqueous medium, with the general electrochemical behavior of quinones. In the buffered solution, the CVs were obtained for the [Hg-(Nq-An)2] complex formed with a reaction between mercuric salt and Nq-An receptor. When Hg2+ ion is introduced in the solution of the Nq-An sensor, the final voltammogram at hand is the same as what is obtained for [Hg—(Nq—An)2] complex. In addition, the test if the sensor forms complexes with Li+, Na+, K+,Cs+, Be, Ca2+, Mg2+, Ba2+, Zn2+, Cu2+, Hg2+, Co2+, Fe2+, Fe3+, Mn2+, Pb2+, and Ni2+ ions at a concentration range of 0–1x10-5 M. There was not any change observed in the voltammetry of Nq-An in the aqueous solution when other cations are also present in the medium. It was observed that the anodic current resulting from the Hg0/Hg2+ redox couple increased linearly between 3,5-20,5 ppm concentrations depending on the amount of Hg2+ ions.
Heavy metals are metallic elements that have atomic weights ranging from 63.5 to 200.6 and have higher densities than other atoms. With the rapid development of the industry, metal coatings, mining operations, batteries, the fertilizer industry and the increase in the use of pesticides, heavy metals have spread directly or indirectly to the environment from contaminated wastewater. Heavy metals emitted into the environment aroused great interest because they threaten human life and ecosystems. Many heavy metal ions are known as toxic and carcinogens because they do not biodegrade like organic contaminants and accumulate in living organisms. Known toxic heavy metal ions are as follows: Zn, Cu, Ni, Hg, Cd, Pb and Cr. Mercury (Hg) is the most well-known toxic analyte due to its toxicity to humans and the environment, and it is released into the environment by some industrial processes as well as the combustion of coal and waste. The toxicity of mercury is due to its high volatility and its effects on the nervous system. The intake of mercury into the human body occurs through inhalation, skin contact, and oral route, and WHO stated that the tolerable mercury intake is 2 µg/kg per kilogram of body per day. According to EPA, the maximum allowable concentration of mercury in drinking water is specified as 10 nM. Therefore, the development of simple and advanced techniques for the highly selective and sensitive determination of mercury has gained great importance for both human health and the environment. Traditional methods for the determination of mercury; Atomic absorption spectroscopy (AAS), Inductively coupled plasma mass spectroscopy (ICP-MS) and electrochemical methods. Although these methods are highly selective and sensitive, expensive and large sample sizes are required. Naphthoquinones, which are quinone derivatives, contain two rings. In addition to being obtained as synthetic products, it is quite abundant in nature. Although naphthoquinones can be found in six different structures, the most well-known are 1,2-, 1,4-, 2,6- naphthoquinones. In addition to being obtained synthetically, naphthoquinones compounds found in plants, fungi, and bacteria. Naphthoquinone derivatives play a role in important biological activities such as cellular respiration, photosynthesis, blood coagulation and antioxidants. Chemically, it has pharmacological or natural product synthesis, dye, charge transfer complexes, transition metal coordination with oxygens, oxidizing and electrochemical properties. A major research effort has been concentrated to find inexpensive, reliable, and simple ways of detecting ions in the environment. Thus, finding new selective ion receptor systems, sensor development, environmental remediation, selective separation and extraction of chemical species has become an important goal. Chemical sensors prepared for this purpose gain primary importance as they can be obtained in cheap, reliable and simple ways. In this thesis, first of all, a new and multi-channel chemosensor based on easily synthesized naphthoquinone was synthesized. Colorimetric, fluorometric, and voltammetric methods were used to detect trace amounts of Hg2+ ions selectively using the chemosensors. The analytical properties of the new sensors to be developed have been examined in detail. In the literature, many ligands selective against mercury or other heavy metals have been synthesized and their sensitivity has been studied by UV-Vis and fluorescence methods. The thesis work consists of two stages. In the first stage; by the substitution reaction of 1,4-naphthoquinone and aniline compound in methanol, the targeted Nq-An sensor was obtained and purified according to the literature. MALDI/TOF mass spectrum result; found mass (m/z): 250,259 [M++ H] is in harmony with the structure. [Hg—(Nq—An)2] mercury complex was obtained by adding Hg(NO3)2.H2O to Nq-An solution in MeOH, stirring under reflux for 1 night, evaporation of the solvent and purification of the remaining solid product. As a result of the complexation, in the FT-IR spectrum, apart from the peaks of Nq-An, the expected peaks of 567 cm-1 (Hg-C) and 598 cm-1 (Hg-N), were observed. The expected peaks were observed in the 1H NMR and 13C-NMR spectra taken in DMSO. In the 13C NMR spectrum of the mercury complex, the peak observed at 102.42 ppm, corresponding to the C6 atom of Nq-An, shifted to low area as a result of complexation. MALDI/TOF mass spectrum result shows that the found value 699.631 [M++3H] confirms the structure. As a result of Elemental Analysis, it was found to be compatible with the structure. A new Nq-Pyr sensor was obtained by the substitution reaction of 1,4 naphthoquinone with pyrene amine in methanol. The expected peaks related with the Nq-Pyr were observed ın the FT-IR spectrum. According to the 1H NMR and 13C-NMR spectra taken in DMSO, the expected peaks were observed. MALDI/TOF mass spectrum result; the peak observed at m/z = 375.033 belongs to [M+] of Nq-Pyr. Hg(NO3)2.H2O was added to a Nq-Pyr in 20 mL DMF/H2O (5:1 v/v) at pH 8, stirred at room temperature for 1 night, and the final residue was filtered off, and washed to obtain the desired [Hg— (Nq-Pyr)2] mercury complex. The expected peaks related with the complex were observed in the FT-IR spectrum. Elemental Analysis result is in harmony with the structure. The mass (m/z) found (943.352 for [M+]) from the MALDI/TOF mass spectrum confirmed the structure. In the second part of the thesis, the determination of trace amounts of Hg2+ ions based on naphthoquinone molecules was carried out using spectrophotometric (UV-Vis, fluorometric and voltammetric) methods. In this context, the optimum conditions for the selective and sensitive determination of Hg2+ were determined by examining the solvent effect, selectivity, interference and pH parameters. To investigate the pH effect on the response of Nq—An and Nq—Pyr sensors to the Hg2+ ion, a pH buffer range of 1 to 10 was prepared buffering a 0.2 M solution of acids and their salts. The UV–Vis spectra of the solutions of Nq—An and Nq—Pyr were recorded at the desired pH (1-10). It has been shown that these receptors effectively detect the Hg2+ ion within pH values of 7-8. The colorimetric selectivity study at ambient temperature showed that the probes yielded a notable transition of color from orange to pink where the sample contained Hg2+ ion, while the color of other probes did not change in the presence of competitive cations. This is due to the red shift of the ICT transition band between the nitrogen donors and the electron-deficient naphthoquinone group after complex formation. Electronic spectra of Nq—An/Nq—Pyr and their Hg2+ complexes [Hg—(Nq—An)2]/[Hg—(Nq—Pyr)2] DMSO: H2O (1:1 v/v) and DMF:H2O, respectively (5:1 v/v) recorded at pH 8. The main peaks observed at 475 and 473 nm for Nq—An/Nq—Pyr correspond to the n→π* type ICT transition from nitrogen (donor) to quinone (acceptor). To investigate the binding properties of naphthoquinone probes with Hg2+ ion, UV-Vis titration studies were also carried out. When the amount of Hg2+ was increased in the buffered solutions of the probes, absorbances at 475 nm and 473 nm decreased regularly, along with isosbestic points at 521 and 506 nm, but the peaks at 576 nm and 571 nm increased. The appearance of isosbestic point confirmed the formation of complexes. The formation of 2:1 [Nq—An:Hg2+] was strongly suggested as a result of plotting the curve in the graph with Job's method of continuous variation. Additional to the MALDI/TOF/MS spectra, the absence of expected peaks in 1H NMR titration spectra with 0,5 equivalent of mercuric ion, and elemental analysis also definitely showed 2:1 binding of Nq-An with the Hg2+ cation. Based on the proportional UV-Vis titration technique, the detection limits of the Nq—An and Nq—Pyr sensors are found as 1.6×10-6 and 5.9×10-7 M for the determination of Hg2+, respectively, according to literature, indicating a moderate sensitivity of Hg2+ detection. Mercuric ion, in the presence of five equivalents of other ions, were studied comparatively. The probes are successful in recognizing Hg2+ ion, other metal ions did not disturb the interaction at all, and in aqueous solution, the probes exhibited high selectivity for the mercuric ion. In addition, the sensors had response times of 10 and 20 seconds, respectively, which is considered quite good the response times of the sensors Nq-An and Nq-Pyr were determined as 10 and 20 seconds, respectively, and this result is quite good when the literature values are considered. To find out if the detection was reversible, Nq—An and Nq—Pyr solutions, incubated with Hg2+ ion, were treated with Na2S in a UV-Vis spectral setting. As a result, it has been shown that the process is reversible as a result of removal of mercury from the environment in both receptors. An additional test was conducted for the reversibility, changes in absorbance were determined when mercuric ions or sulfide ions were added. As the amount of sulfur increased in the medium, HgS is formed and the response of the sensor decreased. To reveal the fluorometric property of the sensor, fluorescence spectroscopic analysis showed the interaction of mercuric ion and Nq—Pyr. When Hg2+ cation is present in the medium, the probe showed a distinct band of fluorescence at 432 nm, but other metal ions did not reveal specific changes. When Hg2+ ion binds to the probes by forming Hg-C and Hg-N bonds, the mechanism of Increased Fluorescence Based on Metal Chelate Formation (MCHEF) has been revealed. The detection limit of the Nq—Pyr sensor based on the fluorometric technique was determined as 7.4×10-8 M for the Hg2+ ion. Moreover, the response time of the fluorescent sensor was set at 75 seconds. The applicability of the sensors to detect Hg2+ in contaminated tap water has been demonstrated. In addition, UV-Vis and fluorescence data were compared with popular ICP-MS and AAS data. Our sensors are average in terms of LOD, but they show very short response times, high accuracy, precision, and repeatability. Both sensors are multi-channel, so this increased the advantages of them. In the voltammetric part, the electrochemistry of Nq—An was first elucidated by its redox behavior in DMSO using CV and DPV techniques. Nq—An exhibited a chemically reversible one-electron reduction process to form the semi-quinone radical product: the monoanion Nq—An•–. The more reversible reduction of an electron was observed at more negative potentials; second reduction, dianion Nq—An2–. The electrochemical behavior of Nq—An is similar to that of 1,4-naphthoquinone (Nq), but the reduction potential of Nq—An is shifted to the cathodic region due to the electron donating property of the amino-phenyl group attached to the naphthoquinone core. The redox behavior of the [Hg—(Nq—An)2] complex was investigated and compared with the redox behavior of Nq-An under the same experimental conditions. The reduction potentials corresponding to the monoanion and dianion of [Hg—(Nq—An)2] shifted cathodically as expected. It is because the electron donating ability of the amino-phenyl group decreases when the mercury complex [Hg—(Nq—An)2] is formed. Compared to Nq—An, current loss was observed in the reduction process of its Hg2+ complex. The complex is poorly diffused on the electrode surface. The half-wave redox potentials corresponding to the monoanionic and dianionic products of the complex were calculated. According to DPV measurements, cathodic peak potentials of the naphthoquinone core in the complex were split into two peaks, this is indicative of the fact that the two naphthoquinone units were reduced in two steps. In buffered media, the CV of the Nq—An receptor's CV is also presented. This is harmonious, in buffered aqueous medium, with the general electrochemical behavior of quinones. In the buffered solution, the CVs were obtained for the [Hg-(Nq-An)2] complex formed with a reaction between mercuric salt and Nq-An receptor. When Hg2+ ion is introduced in the solution of the Nq-An sensor, the final voltammogram at hand is the same as what is obtained for [Hg—(Nq—An)2] complex. In addition, the test if the sensor forms complexes with Li+, Na+, K+,Cs+, Be, Ca2+, Mg2+, Ba2+, Zn2+, Cu2+, Hg2+, Co2+, Fe2+, Fe3+, Mn2+, Pb2+, and Ni2+ ions at a concentration range of 0–1x10-5 M. There was not any change observed in the voltammetry of Nq-An in the aqueous solution when other cations are also present in the medium. It was observed that the anodic current resulting from the Hg0/Hg2+ redox couple increased linearly between 3,5-20,5 ppm concentrations depending on the amount of Hg2+ ions.
Açıklama
Tez (Doktora) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2021
Anahtar kelimeler
Elektrokimya,
Electrochemistry,
Kimyasal dedektörler,
Chemical detectors