SYNTHESIS OF SOME POLYAZA-MACROCYCLES AND THEIR APPLICATIONS AS ELECTROCHEMICAL SENSORS

Abstract

Complexes of porphyrins, corrins, and phthalocyanines have been investigated because of their relation to important naturally occurring species containing macrocycles such as heme, cytochromes, or chlorophyll, or because of their potential as dyestuffs or pigments. The vital functions performed by the natural systems can be largely determined by the nature of the metal ion enclosed in it. For example, the catalytic properties ofvitamin B,2 and its coenzyme are due to the ability ofcobalt ion to act as a storehouse for an electron, which can be released (cobalt(II) state) or accepted (cobalt(III) state) as needed. The metal ions are trapped in such a complicated structure that the fundamental properties of the metal ions are still not well understood, which is a real limitation on the pace of advancement of the knowledge in the macrocyclic field. It is, therefore, reasonable to synthesize simple macrocyclic complexes that could be considered as role model compounds. It can be assumed that such an approach will develop the chemistry implied by the functions of metal ions in natural systems and will contribute to the understanding ofbiochemistry as well and will provide much informations in the basic area of metal ion chemistry. Synthetic macrocycles have also been explored as ionophores in electrochemical sensors. Macrocyclic Hgands are noted for their remarkable selectivity towards soft and heavy metal ions. The strong and selective interactions of macrocycles with specific metal ions make these Hgands suitable candidates for use as 11 ionophores in electrochemical sensors. However, all macrocycles are not useful for preparing membrane electrodes. The membrane of a macrocycle is likely to function as a good ion-selective electrode (ISE) provided the macrocycle shows, (i) high complexation or extraction selectivity for a particular metal cation, (ii) enough conformational flexibility for rapid ion-exchange, (iii) high lipophilicity to remain in the membrane and (iv) moderate molecular weight to allow high mobility. Polyazamacrocycles occupy an intermediate position between crown ethers and cryptands, as they are stronger cation binders than crown ethers and more flexible than cryptands. Therefore, they offer great promises in broad areas of metal sensing processes such as ion-selective electrodes. Much of the recent work in this field involves seeking of new ligands that will be specific for particular cation. In the present study an attempt has been made to investigate the abovementioned aspects to add to our existing knowledge on macrocyclic complexes. With this aim in mind, the following studies on the chemistry of macrocycles have been carried out. For the sake of convenience the work embodied in the thesis is presented in the following chapters: The First Chapter of the thesis is general introduction and presents an up-todate survey of literature of macrocyclic compounds and of those metal-selective electrodes that have been prepared. The problem of present research has been posed in the context of the cited work. The Second Chapter of the thesis deals with the basic principles, experimental details, reagent and materials, and theory of ionselective electrodes. Method for the preparation of polyvinyl chloride) and 111 polystyrene based membranes, their functional properties and methods for the determination of selectivity coefficient have been included. The Third Chapter of the thesis deals with the synthesis and characterization of various macrocyclic compounds of some transition metal ions, and macrocyclic ligands used in the preparation of ion-selective electrodes. Four series of macrocyclic complexes were synthesized (via. Template method) and characterized. 15-Membered first macrocyclic series is based on 13,15-dimethyl-l,5,8,12-tatraazacyclopentadeca- 12,15-diene ligand with its Ni(II), Co(II), Cu(II) and Mn(II) metal ion complexes; second series is 13-membered and based on ligand 11,13-dimethyl-l,4,7,10- tetraazacyclotrideca-10,13-diene with its Ni(II), Co(II), Cu(II) and Mg(II) nwtal ion complexes; thirdly, a 14-membered macrocyclic series of Ni(II), Co(II), Cu(II) and Zn(II) metal ions based on ligand 6,7:13,14-dibenzo-2,4,9,ll-tetraphenyl-1,5,8,12- tetraazacyclotetradeca-l,4,8,ll-tetraene and finally, a fourth series based on ligand 14,16-dimethyl-1,4,7,10,13-pentaazacyclohexadeca-13,16-diene macrocyclic ligand with Ni(II), Co(II), Zn(II) and Mn(II) metal ions are reported in this chapter. All the macrocyclic series were prepared by template method. This chapter also includes the synthesis of 3,4:1 l,12-dibenzo-2,5,10,13-tetraoxo-l,6,9,14-tetraazacyclohexadecane; 3,4:12,13-dibenzo-2,5,l l,14-tetraoxo-l,6,10,15-tetraazacyclooctadecane and 4,9- diphenyl-2,ll-dimethyl-l,5,8,12-tetraazacyclotetradeca-l,4,8,ll-tetraenemacrocycl1c ligands. The last three ligands were synthesized by the reported method and were only used in the fabrication of sensors illustrated in chapter four. Electrochemical sensors, incorporating the synthesized polyaza-macrocycles, IV for Cu(II), Co(II), Zn(II), Mn(II), Sr(II), Ni(II) and Cd(II) metal ions are presented in Chapter Four. Cu(II)-selective electrode is based on the ionophore 13,15-dimethyll, 5,8,12-tatraazacyclopentadeca-12,15-diene copper(II) complex and it gave a linear working concentration range of 1.12 x 10"5 - 1.00 x 10"' molL"1 with a Nernstian slope of 29.9 mV/decade of concentration; Co(II)-selective electrode based on the ionophore 11,13-dimethyl-1,4,7,10-tetraazacyclotrideca-10,13-diene cobalt(II) complex exhibited a wide working concentration range of 7.94 x 10"6 - 1.00 x 10" molL'1 and a slope of 29.5 mV/decade of concentration; Zn(II)-selective electrode based on the ionophore 6,7:13,14-dibenzo-2,4,9,ll-tetraphenyl-l,5,8,12-tetraaza cyclotetradeca-1,4,8,11-tetraene zinc(II) complex showed a linear working concentration range of 1.41 x 10"5 - 1.00 x 10"1 molL"1 with a slope of 29.6 mV/decade of concentration; Mn(II)-selective electrode based on the ionophore 14,16 -dimethyl-1,4,7,10,13-pentaazacyclohexadeca-13,16-diene manganese(II) complex exhibited a linear working concentration range of 1.25 x 10"5 - 1.00 x 10" molL" with a slope of 29.5 mV/decade of concentration; Sr(II)- selective electrode was prepared with 4,9-diphenyl-2,l 1-dimethyl-1,5,8,12-tetraazacyclotetradeca-1,4,8,11-tetraene as ionophore and it showed a wide working concentration range of 1.25 x 10' - 1.00 x 10"' molL"1 with a slope of 29.4 mV/decade of concentration; Cd(II)-selective electrode showed a working concentration range of 3.16 x 10" - 1.00 x 10" molL" with slope of 29.8 mV/decade of concentration and was based on 3,4:12,13-dibenzo2,5, ll,14-tetraoxo-l,6,10,15-tetraazacyclooctadecane, where as Ni(II)-selective electrode exhibited a wide working concentration range of3.16 x 10"6 - 1.00 x 10" molL"1 with Nernstian slope of 29.6 mV/decade of concentration was based on 3,4:11,12-dibenzo-2,5,10,13-tetraoxo-1,6,9,14-tetraazacyclohexadecane ionophores. Adetailed study on their working concentration range, slope, response time, lifetime, selectivity and working pH range have been made. All these sensors developed in the laboratory have also been used in partially non-aqueous medium.