Spectroscopic Studies of Charge Transfer Complexes of Some Amino Acids with Copper (II)

Introduction

Metals are mainly toxic to living room organisms and they tighten to accumulate in their living room tissues. In recent years, there has been has growing public concern and awareness of toilets problems. This is attributed to the great potential human health risks associated with toilets pollution.

Amino acids forming essential shares of human body represent have very interesting class of compounds because of to their utility:

Normal metabolic processes involving all living room organisms and Protection of the organism from toxic effects these metals. The importance of these amino acids is due to their ability to form stable complexes with various metallic cations by chelating reactions[i]^-5.

Many analytical methods use molecular absorption spectrophotometry of co-ordination compounds for the determination of metal ions in solution. This milked study by electronic spectroscopy of the behavior of the aliphatic amino acids with respect to Copper (II) in aqueous solution at 298 K.

The spectroscopic parameter of the association constant,K^AD, Gibbs energy change,

ΔG°, were calculated, as well as molar extinction coefficients, ^AD, by the use of the equation of Benesi-Hildebrand.1. Moreover the energy of absorption (E^CT), as well as the potentials of ionization of the ligands(I^D),will be established in order to better circumscribe the behavior of charge transfer complex of five amino acids with Copper (II)6^-12.

Experimental

General

Copper(II) Nitrate [Cu (No₃)₂,5H₂O] from Merck, amino acids from Fluka (purity 99 %).All the solution was prepared in 100 cm³ in double distilled water.

The UV-visible spectra were measured using Perkin – Elmer lambda 20 and UV-visible Shimadzu 1202 (Shimadzu Europa Gmbh) and a quartz cuvette (1-cm path length). The weightings are carried out in a Sartorius balance CPA124 S.

General procedure  

Electronic spectra of various compounds were recorded between 200 and 1100 nm, in the aqueous solution of variable concentrations of donor and acceptor 10^-2 and 10^-4 mole.l^-1 and maximum wavelength λ _max were characterizing at 298 K.The association constant K^AD, as well as molar extinction coefficients ε^AD, of each complex were calculated using the equation of Benesi-Hildebrand.113.

 

Where:

ABS: absorbance of the charge transfer band,[A₀]: initial concentration of the electron acceptor, [D₀]: initial concentration of the electron donor,K^AD: association constant of charge transfer complex in solution, ε^AD: molar extinction coefficient of charge transfer complex.

The ionization potential of the electron donors were calculated from the position of charge transfer (CT) bands for iodine complexes using the following equations: ^10-17

 

hv_CT: Absorption band energy of charge transfer complex, and h : Plancks constant,

C₁ =5.2 eV,

C₂ =1.5 eV²,

a = 0.67 or 0.87,

b=-1.9 or -3.6.

Where hv_CT is the absorption band energy of the CT complex in e.v., I^D is ionization potential of the electron donor in ev., C₁, C₂, a and b in Equations.2 and 3 are constants and their values for the iodine acceptor in CCl₄are as follows:

Results and Discussion

All the acids amines have the property of absorptive the light ultraviolet. The absorption band of the Copper (II) with various amino acid donors and their charge complex were measured in aqueous solution and are tabulated in Table.1.All complexes exhibit new absorption bands in the visible region their wave lengths are 740,750,750, 750 and 760 nm for the D₁ to D₂ complexes, respectively, wile 810 nm band of the acceptor disappeared.

Table1: Wavelengthλmax(nm)of the Copper complexes Cu (II)with various amino acid donors, in aqueous solution.  Click here to View table

 

The values of association constant K^AD and the coefficients of molar extinction ^AD are deduced by plotting:

 

The comparison of the stability of the complexes [D₄/Cu (II)] and [D₃/Cu (II)] shows a stability appreciably more significant for the complex [D₄ /Cu (II)] because of the grouping methyl substituted for the carbon β which is closer compared to Cα carbon.

The stability compared between the complexes [D₁/Cu (II)] and [D₂/Cu (II)] is clearly in favor of the complex [D₂/Cu (II)]. This is due to the presence of the grouping methyl (inductive donor) substituted for carbon C α.

Moreover, the Gibbs energy changes for the all complex formation reactions calculated from the values of K^AD, are -17,847, -18,119, -17,885, -18,064  and  -18,417 KJ. mole^-1,as shown in Table.3. This shows that the spontaneity of these reactions follows the trend:

[D₁/Cu (II)]> [D₃/Cu (II)] > [D₄/Cu (II)] > [D₂ /Cu (II)] > [D₅/ Cu (II)]

The absorption band energies are calculated by the equation: E_CT =hv_max. (6), the results for each complex are deferred in Table.3.

The values of ionization Potential I^D of the various amino acids,complexing Copper (II) in the aqueous solution calculated by applying equations.4 to 7 whenethe average values of I^D range between 7,686 and  7,897 eV, are reported in  Table.4.^18-21

This study opens new prospects when with the use of these various complexes like catalysts in other reactions of organic chemistry. New studies are undertaken in this direction which aims at correlating the catalytic results obtained with the structure of the organometallic complex. The whole of the results obtained enables us to consider new possibilities in which the amino acids could, through their metal complexes, to constitute good agents extractants in the extractions liquid liquid.

Table3: Values of wavelength, energy of absorption band of the complexes ECT(eV),   Click here to View table

 

Table4: Calculated values of the ionization potentials I D of the different amino acid, in aqueous solution. Click here to View table

 

Conclusion

In this work, the study carried out relates to the behavior complexing of the various aliphatic amino acids with Copper (II) in the aqueous solution with 25 °C, by the means of the electronic spectroscopy.

This study made it possible to release a great number of physical parameters characterizing these complexes:

The spectroscopic results us suggest that the whole of

the complexes are of stoichiometry Ml.

The use of the equation of Benesi-Hildebrand made it possible to establish for the various formed complexes their constants of formation K^AD, molar extinction coefficient ε^AD, as well as the variations of their Gibbs energy change  Δ G°.

The study of the compared values of the various association constants,K^AD for the complexes reflects the greatest stability for that formed with D₅, followed that with the valine. The complex [D₁/Cu (II)] finally proves to be the least stable.

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