الفهرس 
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Abstract
The present work comprises a study of the preparation and kinetics of electron transfer reaction of ternary complexes of chromium (Ш) involving Hydrazides and some Amino acids with Periodate.
1- Chapter I: Introduction.
The introduction contains electron transfer, outer- sphere and inner-sphere mechanisms have been discussed.
2- Chapter II: Review of literature.
This chapter contains the nature and properties of chromium (III) and its complexes have been briefly discussed. The nature, chemical behavior and different species in aqueous solutions of periodate have been reported. The literature concerning on the oxidation of organic compounds by periodate are mentioned. Hydrazides as antitumor, antimicrobial, antituberculosis and antimalarial agents have been briefly discussed. Cysteine as a biological thiol exists widely inside and outside of cells has been briefly discussed. Alanine as the major amino acids present in proteins and can be used in the biosynthesis of the amino acids has been briefly discussed also.
3- Chapter III: Materials and methods.
Encompasses chemicals, preparation and characterization of ligands and metal complexes, the experimental procedures, and the technique for the kinetic studies and methods for the data determination.
4- Chapter IV: Results and discussion.
Comprises the layout of the results obtained and their discussions. The Formation and characterization of Hydrazide ligands, The Formation and characterization of chromium complexes and the effect of various parameters on the rate of oxidation reaction also has been discussed. This chapter contains four parts:
1) Part (I):
In this part two main points has been discussed:-
1) Ligands preparation and investigation.
2) Complex [Cr(cys)(HL1)(H2O)3]2+ Formation ,characterization and kinetics of oxidation by Periodate.
Part (I): Ligands preparation and investigation.
Three Ligands prepared [1] N-(2-(ethylperoxy)vinyl)aniline(mp = 56ᵒC),[2] 2-(phenylamino)acetohydrazide(HL1) (mp = 128ᵒC) and [3] (E)-2-(phenylamino)-N’-(pyridin-2-ylmethylene)acetohydrazide (HL2) (mp = 180ᵒC). The structure of the formed Ligands confirmed by elemental analysis, IR spectra, mass spectra, NMR 1H and NMR 13C spectrum. The obtained elemental analysis values of the prepared Ligands are in good agreement with the required for the suggested structure of the prepared Ligands.
The IR spectroscopy is thus used to provide a fingerprint of the Ligands molecule and to identify a newly synthesized compound.
The mass spectrum of compound 2 - (phenylamino) acetohydrazide (HL1) revealed ion peak at m/e = 165.09 (88.60%) which decide that the molecular weight of it is about 165.09 aum. and The mass spectrum of compound (E)-2-(phenylamino)-N’-(pyridin-2-ylmethylene)acetohydrazide revealed ion peak at m/e = 254.12 (59.70%) which decide that the molecular weight is 254.29 amu.
The 1H-NMR spectrum and 13C-NMR spectrum showed a presence of an azomethene proton signals which revealed that the compound 2 Scheme 4 represented the HL2 structure.
Part (I): complex [Cr(cys)(HL1)(H2O)3]2+ Formation ,characterization and kinetics of oxidation by Periodate.
The Formation and characterization of Cr(cys)(HL1)(H2O)3]2+ studied by elemental analysis, IR spectra, Thermal decomposition analysis and Cyclic voltammetry. The dissociation constant of the complex determined by Potentiometric titration to identify whether the complex or its deprotonated form is the reactive species during the oxidation process. The oxidation products examined by HPLC and Uv-visable absorption spectra. The HPLC chromatogram revealed the presence IO3- in product. The Uv-visable absorption spectra revealed the presence of CrVI in oxidation products.
The kinetics of oxidation of Cr(cys)(HL1)(H2O)3]2+ by periodate in aqueous solutions have been studied. The rate of the reaction increases with the increasing of periodate, temperature and pH. The rate of the reaction is independent on the complex concentration and decreases with ionic strength. The oxidation of this complex obeys the following rate law.
d [CrVI] / d t =( k 2 + k 3 / [H+]) [IO4-] [Cr(cys)(HL1)(H2O) 32+]
Where;
kobs.. = (k 2 + k3 / [H+]) [IO4-]
An inner-sphere process accommodated through replacement of coordinate H2O in the one species, by periodate. The enthalpy of activation ∆H* and entropy of activation ∆S* also are calculated.
2) Parts (II), (III), (IV).
The characterization of the complexes [Cr(cys)(HL2)(H2O)2]2+ , [Cr(ala)(HL1)(H2O)3]2+ and [Cr(ala)(HL2)(H2O)2]2+studied by elemental analysis, IR spectra, Thermal decomposition analysis and cyclic voltammetry. The dissociation constants of the three complexes determined by Potentiometric titration.
The kinetics of oxidation of the complexes [Cr(cys)(HL2)(H2O)2]2+ , [Cr(ala)(HL1)(H2O)3]2+ and [Cr(ala)(HL2)(H2O)2]2+ by periodate in aqueous solutions have been studied. The rate of the reaction increases with the increasing of periodate, temperature and pH. The reaction is independent on the complex concentration and decreases with ionic strength. The oxidation of this complexes obeys the general rate law.
d [CrVI] / d t =( k 2 + k 3 / [H+]) [IO4-] [complex].
Where,
kobs.. = (k 2 + k3 / [H+]) [IO4-]
An inner-sphere process accommodated through replacement of coordinate H2O in the one species, by periodate. The enthalpy of activation ∆H* and entropy of activation ∆S* also are calculated.
(2) CONCLUSION.
Four complexes prepared [Cr(cys)(HL1)(H2O)3]2+ , [Cr(cys)(HL2)(H2O)2]2+ , [Cr(ala)(HL1)(H2O)3]2+ and [Cr(ala)(HL2)(H2O)2]2+ where cys= cysteine , ala= alanine , HL1 = 2-(phenylamino)acetohydrazide and HL2 = (E)-2-(phenylamino)-N’-(pyridin-2-ylmethylene)acetohydrazide. The formation and characterization of the four complexes studied by elemental analysis, IR spectrum, Thermal decomposition analysis and cyclic voltammetry. The obtained elemental analysis values of the prepared complexes are in good agreement with the required for the suggested structure of the prepared complexes. The IR band assignments of cysteine and alanine are illustrated in table 51. IR band assignments of the prepared complexes are illustrated in table 52.
The IR spectrum of the prepared complexes brings out the following facts to light: -
1-The spectrum of the solid complexes exhibits broad bands in the 3650-3300 cm-1region, which may be attributed to νOH- of the coordinated water molecule which coordinated with CrIII metal ion.
2- The C=O stretch and the in plane bending of the OH- group associated with carboxylate functionality in the 1390 cm-1 and 1206 cm-1region in cysteine IR spectrum and in the 1400 cm-1 and 1210 cm-1region in alanine IR spectrum completely disappeared and a new carboxylate band νCOO- appeared in the region 1380 to1390 cm-1 in all metal complexes IR spectrum, indicating that the carboxylic group of cysteine or alanine participate in the coordination with the metal ion through deprotonation.
3- The absence of an infrared peak between 450 cm-1 and 490 cm-1 , in [Cr(cys)(HL1)(H2O)3]2+ and [Cr(cys)(HL2)(H2O)2]2+ IR spectrum, which denotes the disulfide bond, indicates that CrIII didn’t oxidize cysteine to form cystine.
4-The shifting of an infrared peaks which denotes the (-CONH) in HL2 or HL1 to a lower wave number value in the spectrum of all solid complexes indicating that the amide group participates in the coordination with CrIII.
Thermal decomposition analysis for complexes shows that the complexes [Cr(cys)(HL1)(H2O)3]2+ and [Cr(ala)(HL1)(H2O)3]2+ have three coordinated water molecules the remaining complexes have two coordinated water molecules. By using the previous analysis from elemental, IR and Thermal decomposition analysis the proposed structure of complexes became clear.
The dissociation constant of the complexes was determined by Potentiometric titration to identify whether the complexes or their deprotonated forms is the reactive species during the oxidation process. After comparing the pH range of reactions and K1 values, the complexes conjugated acid forms are the predominant species and their deprotonated species is not involved in the rate determining step. Table (53) gives the pH of study for each complex and its dissociation constant.
Table (51) IR band assignments of cysteine and alanine (234).
Assignment cysteine alanine
νOH(H2O) 3398 bro. 3408
νNH3+ 3036 bro. 2942
νCH2,CH3 2928 2860
νCH2 2646 w. 2749
νCH2 2618 2607
νSH 2559 --
νCO 1742 1705-1658
δ as NH3+ + νCOO- 1624( δ as NH3+ + νCOO-) 1614( δ as NH3+ + νCOO-)
δ as NH3+ + νCOO- 1573 --
δ as NH3+ 1518 1522
δ CH2,CH3 1422 (δ CH2), 1349 ( δ CH) 1453(δ CH2)
νcoo- 1390(νcoo-) 1400(νcoo-)
νco + δ OH(COOH) 1206 1210
δ SH 991 --
νcc, δ COO- 865 849
νcN + νcc 929
909
Table (52) IR band assignments of complexes.
IR Assignment complex
Cr(cys)(HL1) Cr(cys)(HL2) Cr(ala)(HL1) Cr(ala)(HL2)
νOH(H2O) 3650-3300 3600-3300 3660-3330 3650-3300
νN-H 3232 3217 2960 2925
ν CONH 1635 1650 1600 1649
νNO3 1384 1373 1379 1379
νCr-O 513 565 583 562
νCOOCr 1380 1380 1388 1389
Table (53).The dissociation constant of the complexes
Complex K1 value pK1 Studying pH range
[Cr(cys)(HL1)(H2O)3]2+ 9.95 ×10-7 6.00 1.59-2.60
[Cr(cys)(HL2)(H2O)2]2+ 7.94 × 10-5 4.10 1.59-2.64
[Cr(ala)(HL1)(H2O)3]2+ 1.86×10-5 4.73 1.70 – 2.78
[Cr(ala)(HL2)(H2O)2]2+ 7.76×10-8 7.11 1.60-2.65
The cyclic voltammetry measurements carried out for the four ternary complexes and two binary complexes (CrIIIcys) and (CrIIIala). All ligands cyclic voltammetry measurements also carried out.
The cyclic voltametric values of the ternary complexes revealed that the highest oxidation value of complex [Cr(cys)(HL1)(H2O)3]2+ is 0.69 V , [Cr(cys)(HL2)(H2O)2]2+ is 0.65 V , [Cr(ala)(HL1)(H2O)3]2+ is 0.68 V and [Cr(ala)(HL2)(H2O)2]2+ is 1.30 V. It is proposed that the oxidation process is more difficult for the complexes which have a more positive values of oxidation potential.
The enthalpy of activation, ∆H*, of the oxidation reactions also reflect the more difficult complex in oxidation. Table (54) gives the ∆H*, ∆S* of activation and the complex highest oxidation potential. The dissociation constant of the complexes in the pH range of study don’t reflect the ease or difficult of complexes oxidation by periodate because the complexes conjugated acid forms are the predominant species and their deprotonated species is not involved in the rate determining step.
Table (54). ∆H*, ∆S* of activation and the highest oxidation potential.
Complex ∆H* of activation
(kJ mol-1) ∆S* of activation
(JK-1 mol-1) E
(V)
[Cr(cys)(HL1)(H2O)3]2+ 49.31 -153.12 0.69
[Cr(cys)(HL2)(H2O)2]2+ 27.70 -219.11 0.65
[Cr(ala)(HL1)(H2O)3]2+ 48.38 -148.94 0.68
[Cr(ala)(HL2)(H2O)2]2+ 59.80 -113.50 1.30
The complex [Cr(ala)(HL2)(H2O)2]2+ had the highest ∆H* of activation and the highest oxidation potential cyclic voltametric value while the complex [Cr(cys)(HL2)(H2O)2]2+ had the lower ∆H* of activation and the highest oxidation potential cyclic voltametric value. Also the complex [Cr(ala)(HL2)(H2O)2]2+ had a higher pK1 value than [Cr(cys)(HL2)(H2O)2]2+ . The presence of the –SH group in [Cr(cys)(HL2)(H2O)2]2+ may decreases its stability due to steric effect or may help in the reaction of oxidation.
The ternary complexes oxidation products examined by HPLC and Uv-visable absorption spectra. Examination of the oxidation products by High Performance Liquid chromatography (HPLC) performed to make sure if the complexes dissociated after oxidation or not, also the HPLC performed to identify the oxidation products. Identifying the oxidation products reflect the mechanism of the oxidation process.
The proposed mechanism suggested the complexes dissociation after oxidation and the oxidation products will be IO3- , Amino acid, CrVI and Hydrazide. CrV precursor complex may be also produced as an intermediate or as CrV. CrV is believed to play a role in the genotoxic effects of chromium(III) complexes also may be stabilized by the amino acids.(142)
IO3- and alanine in oxidation products confirmed using HPLC which confirmed the dissociation of the complexes after oxidation. The Uv-Visable spectra of the final product are the same as that of the chromate ion. This provides an evidence that CrVI is an essential product of oxidation of complexes.
A plot of ΔH* versus ΔS* for [Cr(cys)(HL2)(H2O)2]2+ , [Cr(ala)(HL1)(H2O)3]2+ and [Cr(ala)(HL2)(H2O)2]2+ is shown in Figure. 90. An excellent linear relationship is seen; this isokinetic relationship lends support to a common mechanism for the oxidation of chromium (III) complexes, reported here, by periodate.
The parallel and small changes of ΔH* and ΔS* for each reaction series and a common rate-determining step is proposed.
Figure. 90. Isokinetic relationship for the oxidation of [Cr(cys)(HL2)(H2O)2]2+ , [Cr(ala)(HL1)(H2O)3]2+ and [Cr(ala)(HL2)(H2O)2]2