Therefore, in the present investigation, the order of stability of the ternary complexes is as follows-. It has been observed that the stability constant of the mixed complex depends on the nature of the metal ions7 and the nature of the ligands8. The study of ternary complexes in solution provides simpler models for more complicated biochemical reactions.17 Biochemical reactions are models of S-21 systems that form ternary complexes.
This led to the study of mutual interaction of two ligands bound to the same metal ion and the effect of the nature of the metal ion on the ternary complex stability. For the same ligand, the stability of the divalent metal ion~ of the I transition series can be arranged as follows. The order of stability of Ni(ll) and CU(Il) complexes depends on whether the ligands create a weak or strong field.
The stabilization factor governing 8logK depends on the coordination number of the mtalion and the denticity of the ligand. So the value of LilogK is affected by the non-statistical factors depending on the nature of the ligands A and L and the structure of the metal ion in some cases20.
ML 2 .t:;: ZMAL
Phenyl Alanine (Ph-ala)
Ethyldiarnine (en)
CHAPTER-2
LITERATURE REVIEW
AIM OF THE PRESENT INVESTIGATION
Most of the transition metals complex with ligand and these metal complexes play very important roles in biological systems. Furthermore, studies of the roles of metal ions in biological systems often involve development of relevant chemistry. Therefore, it is necessary to investigate the action of metal ions with substances of biologically important ligands.
In the present research work we have determined the formation constants of ternary complexes [MAL], where M refers to the metal ion tmnsion e.g. Cn(II), Ni(lI) and Zn(JI), A refers to biologically important ligands such as Aspartic acid (Asp) and 1,10 phenanthroline (1,10 Ph) and L refers to glycine, (I-alanine, phenylalanine , tyrosine, tryptophan, ethylenediamine and oxalic acid Thc protonation constant, binary constant and ternary constant are dd<:nnin<:dpotentiomdical1y using SCOGS (Generalized Stability Constant of Species) computer prograrriI83,184, The formations have been confirmed by .
CHAPTER-3
EXPREMENTAL,RESULTS
DISCUSSION
Potentiometric determination of stability constant
CYCLIC VOLTAMMETRY MEASUREMENT
Cyclic voltammetry (CV) includes a group of electro-analytical methods in which information about the analyte is obtained from the measurement of CUITcnt as a function of applied potential. The cyclic voltammetry cell consists of electrodes immersed in a solution containing the analyte and also an excess of non-reactive electrolyte called the supporting electrolyte, one of the three electrodes is the microelectrode or the working electrode, whose potential is variable. linearly with time. The second electrode is a reference electrode (usually a saturated calomel electrode) whose potential remains constant throughout the experiment.
The third electrode is a counter electrode, which is often a coil of platinum wire or a merkU pool that simply serves to conduct electricity from the signal source through the solution to the microelectrode. The potential of the micro working electrode is varied (slowly scanned) and the resulting current is recorded as a function of the applied potential. Cyclic voltammetry has become an important tool in studying the mechanisms and rates of redox processes, especially in organic and inorganic systems.
Today, this electrochemical technique is used to study coordination chemistry, which is part of inorganic chemistry. Petersen et al.1194 performed part of the research on O2 reduction based on cyclic voltammetry (CV). These voltammograms showed an irreversible oxidation wave at about -IAV and a reversible pair centered at about -Q.SV.
A shift in the half-wave potential of a metal ion in solution in the presence of an added ligand (anion or neutral molecule) is indicative of complex formation. Linganel97 observed that the half-wave potential for the reduction of a metal complex is generally more negative than that for the reduction of the corresponding simple metal ion. Cyclic voltammograms of eu(II), Ni(II) & Zn(lI) complexes were recorded at Pt electrode in aqueous media.
The optimum pH for maximum complex formation was obtained from computer output and species distribution curves. The voltammograms show one oxidation and one reduction peak for all complex compounds and metal perchlorate (copper perchlorate, nickel perchlorate and zinc perchlorate). In the above cases, the anodic potential peak of the complexes, shifted towards a more positive potential than the metal perchlorate peak, indicates the formation of complex compounds. On the other hand, the cathodic peak potential of the formed complexes shifted towards a more negative potential, indicating the decomposition of the formed complexes.
Cyclic Voltammograms
The anodic and cathodic potential gives us information about the relative stability of complexes. The potential required to exhibit an anodic and cathodic peak is called anodic (Epa) and cathodic potentia. Eka). The greater the value of the cathodic and anodic potential, the greater the stability of the complexes will be. The potential difference between EPd and Eea also helps us to determine the relative stability of complexes.
An increase in potential difference between Epn and ECJI indicates the higher stability of the complex compound, i.e. An interesting fact that the study of the cyclic voltammograms of the complexes of [MAj, [MA2], [MAJ], [ML }, [ML2l] and [ML4J types predict that [MA JL2] and [ML4J complexes show the similar Epa and Ee• value in cyclic voltammograms.
CHAPTER-4 SUMMARY
Summary
The stability constants of the ternary complex were determined by performing pH-metric titration in aqueous medium. The protonation constant, binary constant, and ternary constant were determined potentiometrically using the SCOGS software. These values are used as fixed parameters for the optimization of the formation constant of ternary complexes.
It is also reported that for eu(II) ternary complexes, the DologK values are more negative than the corresponding Ni(II) ternary complexes. It is also observed that the value of Mog K becomes more negative with increasing charge on ligand 1. This is due to the electrostatic repulsion between the diionic tridentate ligand Aspertic acid (Asp) and.
It is observed that the DologK value is positive when phenylalanine and tyrosine are coordinated with central metal ion. Another reason for extra stabilization of tyrosine is due to intramolecular interligand hydrogen bonding and stacking interaction between phenylalanine and tyrosine with metal ion. Additional stabilization in the complexes may occur due to the non-covalent hydrophobic interaction between non-coordinated phenyl and hydroxyphenyl side groups of phenylalanine and tyrosine, respectively, with A(Asp, 1.10 ph).
The greater stability of Zn(11) complex compared to that of complexes of Cu(lI) and Ni(ll) is due to the fact that the complex of. More about larger size of Zn(ll) metal is more favorable for the accommodation of ligand easier than Cu(ll) and Ni(II). Thus, in the present investigation the orders of stability of the ternary complexes are as follows-.
CHAPTER-5 REFERENCE
Nakamoto, IR and Raman Spectra of Inorganic and Coordination Compounds, 101m Willy and Sons, New York, 3'd cd, (1978).
![Table - 3.2.5: Stability constant of mixed ligand complexes lNi(Asp)(L)]](https://thumb-ap.123doks.com/thumbv2/filepdfnet/10872574.0/39.817.89.753.172.453/table-stability-constant-mixed-ligand-complexes-lni-asp.webp)
