Studies on Prospect of Curcumin As an Analytical Reagent for Aluminum
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STUDIES ON PROSPECT OF CURCUMIN AS AN ANALYTICAL REAGENT FOR ALUMINUM by ZHU QING GONG Thesis submitted in fulfillment of the requirements for the degree of Master of Science UNIVERSITI SAINS MALAYSIA 2009 ACKNOWLEDGEMENT My deepest gratitude goes first and foremost to Associate Professor Sulaiman Ab Ghani, my supervisor, for his constant encouragement and guidance. He has walked me through all the stages of the writing of this thesis. Without his consistent and illuminating instruction, this thesis could not have reached its present form. Second, I would like to express my heartfelt gratitude to Dr. Farook Ahmad and Illyas Md Isa who have instructed and helped me a lot in the past two years. I am also greatly indebted to all the members in our reasarch group, Ali Parsa, Ramin Tehrani, Fariba Bakhtiarzadeh, Zainiharyati Md Zain, Munaratul Aini Yahaya, Khalaf Faris Atia, Zahraa Jarjes. Besides, more thanks are given to all the staffs of School of Chemical Sciences. Last my thanks would go to my beloved family for their loving considerations and great confidence in me all through these years. I also owe my sincere gratitude to my friends who gave me their help and time in listening to me and helping me work out my problems during the difficult course of the thesis. ii TABLE OF CONTENTS Acknowledgement ...…………………………………………………………ii Table of contents ...…………………………………………………………….iii List of tables ..……………………………………………………………….....vi List of figures ..………………………………………………………………...vii List of abbreviations ..………………………………………………………….x Abstrak ...………………………………………………………………………xi Abstract ..…………………………………………………………………...….xii CHAPTER 1 INTRODUCTION 1.1 Aluminum …………………………………………………………… 1 1.1.1 Aluminum properties ……………………………………… 2 1.1.2 Determination of aluminum ……………………………….. 4 1.1.3 Aluminum and health ……………………………………… 5 1.2 Curcumin …………………………………………………………….. 9 1.2.1 Curcumin as a chelating reagent …………………………. 14 1.2.2 Applications ……………………………………………... 17 1.2.2.1 Natural colorant …………………………….. 17 1.2.2.2 Free-radical scavengers …………………….. 19 1.2.3 Determination of curcumin in food products ……………. 21 iii 1.3 Analytical techniques ………………………………………………. 23 1.3.1 Solvent extraction ………………………………………… 23 1.4 Objectives …………………………………………………………... 28 CHAPTER 2 − EXPERIMENTAL 2.1 Reagents ……………………………………………………………. 32 2.2 Equipment ………………………………………………………….. 35 2.3 Extraction procedure ………………………………………………. 36 2.4 Analysis of samples ……………………………………………….. 38 2.4.1 Sample treatment ………………………………………… 38 2.4.2 Sample extraction and standard method …………………. 38 CHAPTER 3 − RESULTS AND DISCUSSION 3.1 Curcumin under various pH conditions ……………………………. 40 3.2 Optimization of operation conditions …………………………….. 43 3.2.1 Effects of other ligands …………………………………... 43 3.2.2 Effect of pH ………………………………………………. 48 3.2.3 Effect of buffer system ………………………………….... 54 3.2.4 Effect of equilibration time ………………………………. 56 3.2.5 Effect of organic solvent/diluent …………………………. 58 3.2.6 Effect of salting-out agent and surfactant ………………. 62 iv 3.2.7 Effect of picric acid concentration ……………………….. 65 3.2.8 Effect of ligand concentration ……………………………. 68 3.2.9 Nature of complex … …………………………………….. 72 3.2.10 Interferences ……………………………………………… 77 3.3 Analysis of aluminum in real samples ……………………………… 79 3.3.1 Deternination of aluminum by curcumin method ………... 79 3.3.2 Determination of aluminum by chrome azurol S method … 80 3.3.3 Comparison of the two methods …………………………. 83 3.3.4 Comparison of the two methods by real sample analyses ... 84 CHAPTER 4 − CONCLUSION AND PROSPECTS REFERENCES v LIST OF TABLES page Table 1.1 The physical properties of aluminum. 2 Table 3.1 Effect of ‘other ligands’ on the absorption peak of 45 -6 Al-Cur at λmax 420 nm after the extraction of 1×10 M Al(III) and 2×10-6 M curcumin in MIBK. Table 3.2 Composition of phosphate buffer solutions. 55 Table 3.3 The absorbance of curcumin and complex in various 60 solvents. Table 3.4 The selected FT-IR absorption bands of picric acid, 76 curcumin and Al-Cur complex. Table 3.5 Comparison of the two methods. 83 Table 3.6 The UV-Visible analysis of aluminum in samples by 86 the proposed and chrome azurol S methods. Table 3.7 Body aluminum content. 88 vi LIST OF FIGURES Page Figure 1.1 The physical look of curcuma longa. 10 Figure 1.2 The major components of curcuminoids. 11 Figure 1.3 The equilibrium of keto-enol formations of 12 curcumin. Figure 1.4 Chemical forms of curcumin in different pH values. 13 Figure 1.5 Structure of rosocyanine in two formulas. 15 Figure 1.6 Structure formulas of rubocurcumin. 16 Figure 1.7 Mechanism of Al-Cur complex in human cycling 29 system. Figure 2.1 Flow diagram of the extraction system. 37 Figure 3.1 Spectrum of curcumin in ethanol at different pH. 41 Figure 3.2 Calibration plot of curcumin in MIBK. 46 Figure 3.3 The UV-Vis spectra of (unless stated otherwise) 47 organic phase (MIBK) of various species. Figure 3.4 Effect of pH on the absorbance of the complex at 49 λmax 378 nm. Figure 3.5 Plot of log D vs. pH of the complex at λmax 378 nm. 53 Figure 3.6 The effect of buffer pH 9.00 systems. 56 vii Figure 3.7 The spectrum of 2×10-6 M curcumin in various 59 solvents. Figure 3.8 The UV-Vis spectrum of the complex in various 62 solvents. Figure 3.9 The effect of salting-out agent and surfactant on the 65 formation of complex at λmax 378 nm. Figure 3.10 The effect of picric acid concentrations in the 67 formation of complex. Figure 3.11 The absorbance at λmax 378 nm of various 69 concentrations of Al(III) and curcumin solutions. Figure 3.12 Absorbance of complex with various Al(Ш) 70 concentration. Figure 3.13 Plot of log D vs. log curcumin of the complex at 71 λmax 378 nm. Figure 3.14 The keto-enolic structural formula of curcumin at 72 pH 9.00. Figure 3.15 Percentage of total aluminum present as a species in 73 various pH. Figure 3.16 The proposed schematic reactions of the extraction 75 system. Figure 3.17 The effect of interference ions in the formation of 78 complex. Figure 3.18 The calibration plot Al-Cur complex. 79 Figure 3.19 Absorption spectra of chrome azurol S and its 81 aluminum complex. viii Figure 3.20 Calibration plot of Al-chrome azurol S. 82 Figure 3.21 Correlation plot of proposed and standard methods. 84 ix LIST OF ABBREVIATIONS AAS Atomic Absorption Spectrophotometer AWWA American Waste Water Association BBB Blood-Brain Barrier DME Dropping Mercury Electrode DMSO Dimethyl sulphoxide FT-IR Fourier Transform Infrared HPLC High Performance Liquid Chromatography THC tetrahydrocurcumin Uv-Vis Ultra violet-visible Spectroscopy MIBK Methyl iso-butyl ketone KD Distribution constant KDR Distribution constant of the reagent KDX Distribution constant of the chelate Kf Overall formation constant Ki Formation constant β Separation factor x KAJIAN KE ATAS PROSPEK KURKUMIN SEBAGAI SATU REAGEN ANALISIS BAGI ALUMINUM ABSTRAK Kajian ini melaporkan kemungkinan menggunakan kurkumin (Cur) sebagai ligan dalam pengekstrakan cecair-cecair aluminum (Al). Pelbagai parameter seperti pelarut, pH, kepekatan ligan, agen penggaraman keluar, zat aktif permukaan dan ligan sekunder telah dikaji menggunakan spectrofotometri ultralembayung- nampak. Kompleks menghasilkan satu puncak penyerapan maksimum yang jelas di 378 nm, dengan adanya asid pikrik. Komposisi molar 1:2 Al:kurkumin telah diperolehi dalam metil iso-butil keton (MIBK) dan penimbal pH 9.00. Spektrum FT-IR membuktikan asid pikrik tidak terlibat dalam pembentukan kompleks. Analisis aluminum dalam sampel terpilih menunjukkan bahawa kaedah yang dicadang adalah setanding dengan kaedah piawai. xi STUDIES ON PROSPECT OF CURCUMIN AS AN ANALYTICAL REAGENT FOR ALUMINUM ABSTRACT This study reported on the possibility of using curcumin (Cur) as ligand in the liquid-liquid extraction of aluminum (Al). Various parameters such as solvent, pH, ligand concentration, salting-out agent, surfactant and secondary ligand were studied by UV-Vis spectrophotometry. The complex had a distinct maximum absorption peak at 378 nm in the presence of picric acid. The 1: 2 Al: curcumin molar composition was obtained in methyl iso-butyl ketone (MIBK) and phosphate buffer pH 9.00. The Fourier transform infrared (FT-IR) spectrum proved that picric acid did not involve in the complex formation. Analyses of aluminum in selected samples had indicated that the proposed method was comparable to the standard method. xii CHAPTER 1 − INTRODUCTION 1.1 Aluminum Aluminum is the third most common element found in the earth’s crust, after oxygen and silicon. It is naturally present in soil, water and air and occurs commonly in the form of hydrated oxides which is known as bauxite ore [1]. Since aluminum is too reactive chemically to occur in nature as the free metal, instead, it is always alloyed with other elements. Aluminum had not been isolated as a metal until the year of 1825 and a further 60 years before a commercial production method was developed. The first major commercial use of aluminum was in cooking ware. With the yield strength of pure aluminum 7-11 MPa, and aluminum alloys yield strength from 200 MPa to 600 MPa, aluminum has about one third the density stiffness of steel. Alloyed with other elements, aluminum is commonly used in the construction of siding, aircrafts, and lightweight utensils because of its good strength and light weight. While aluminum is a reactive metal, and usually occurs bound to other elements or compounds, the naturally occurring forms are stable and do not interact with living organisms [2]. Under acidic conditions, however, aluminum may be released from rocks and soils in a soluble form, which can be absorbed by plants and animals. 1 1.1.1 Aluminum properties Aluminum is located in the main sub group III in the periodic table. It is a silvery white, light metal and a good conductor of heat and electricity.