Mixed-Ligands Complexes of L-Amino Acid and Ascorbic Acid

Mixed-Ligands Complexes of L-Amino Acid and Ascorbic AcidElectrochemical Studies of Mixed-Ligands Complexes of L-Amino acetous and Ascorbic pane of glass by Voltammetric TechniqueMeena* and O.D. GuptaABSTRACTStudies of Pb(II) with amino acetous L-Serine and Ascorbic acerb bear been carried step up polarographic tout ensembley at pH =7.300.01, =1.0M KNO3 at 25C.Pb(II) formed 111, 112 and 121 multiformes with L-Serine and use as primary ligands and L- Ascorbic acid utilize as auxiliary ligand.. The set of perceptual constancy constants ( enter varied from 2.25 to 11.45 confirm amino acids in combining with L-Ascorbic acid, their mingledes could be used against Pb(II) toxicity. The stableness constants of obscure ligand labyrinthinees have been evaluated by the method acting of Schaap and McMasters. For the comparison of the simple and mixed-ligands complexes, the mixing constants (Km) and stabilization constants (Ks) have been noted. The supportive value of the mixing c onstants and stabilization constants show that the trey complexes are more(prenominal) electrostatic than the binary complexes.Keyword Polarography, perceptual constancy Constant, Amino acids, Ascorbic acid, Voltammetric Technique.INTRODUCTIONThe L-amino acids and their compounds are used in bio put downy, pharmacy, industry and laboratory reagent1-3. They control transamination, decarboxylation and metabolism process in man body. Mixed-ligands complexes of copper glycine with picolinic acid, quinaldinic acid, picolinic acid N-oxide, quinaldinic acid-N-oxide and with o-nitrophenol, 2,4-dinitrophenol have been carried out by D Prakash and coworkers 4-5. The study of ternary complexes of different surfacelic element ions with amino acids and bicarboxylic acids have been carried out by Chandel et al.6-9 On the other hand Vitamin C (L-ascorbic acid) is entrap course in a wide variety of plants and animals but not produced in benevolent body and its only source is from diet10, L- Ascorbic acid is important drug used against assholecer, scurvy and the risk of bronchitis or wheezing11-13. This drug athletic supporters the patient to gird the immune system. The person who suffered from assist has low concentration of Vitamin-C which is responsible for the administration of various body components and organs but excessively keeps in rove the immune system14-15. Its deficiency causes anemia, dental cavities and thyroid insufficiency. It forms chelate complexes with transition metal ions16 to produce a five 4-membered ring with the enediol protrude of the molecule17.Pb(II) national is fixed in human body but whenever the concentration of Pb(II) increases, the human being suffers from severe diseases like burncer of the bladder, breast, intestine, leukemia system and sometimes termination can alike occur. Ascorbic acid is antioxidant alone and in combination with L-amino acids was found to be effective by increasing urinary elimination of lead. This practiced role of Ascorbic acid was attributed to form complexes with lead18. Data suggest that some antioxidant can function as chelators and this dual benefit makes them strong candidates for treating lead poisioning19. The enclose study is related with the formation of binary and ternary complexes of Pb(II) with selected L-amino acids and Ascorbic acid by polarographic technique with the view that these drugs or metal complexes could be used against several severe diseases like cancer, AIDS and also metal toxicity.data-basedAll polarograms were recorded on ELICO CL 375 DC Polarograph using a saturated calomel electrode (SCE) as the reference electrode and a platinum (Pt) electrode as counter electrode. The capillary had the following characteristics m=1.96 mg/s, t = 4.10 moment/drop and h = 40 cm. The reagents Vitamin C and amino acids were of AR seduce and were used as complexing agents. KCl was used as supporting electrolyte to maintain the noodle strength at 1M. Triton X-1 00 of 0.001% in the final solution has been used as maximum suppressor. The temperature was maintained constant at 303 K. A drinking glass cell is used as electrolytic cell in which all the three electrodes are immersed in test solution. N2 is used to remove the change state oxygen. Then increasing voltage was applied to record the current and with the help of the plot between current-voltage (polarogram) the value of E1/2 is calculated.RESULTS AND DISCUSSIONSimple complex systemsBefore the studies of mixed-ligand, complexes, the formation constants of the complexes of lead with Vitamin C and lead with amino acid L-Serine and were delimitated by the method of DeFord and Hume25. The results are in good bargain with the literature. The value of formation constants of simple systems are attested in bow 1. The conditions corresponded as closely as possible to those for the mixed system. The half-wave potential of Pb(II) for apiece series ranged between -0.389 and -0.391 volt v/s SCE.Table 1 Stability constants for simple systemSystems pound 1 enter 2 enter 3Pb(II)-VitaminC2.253.18Pb(II)-L-Serine4.597.8810.99Mixed-Ligands Complex SystemIn all the systems, solution containing 2.5 x 10-3 M Pb(II), 1M KC1 and 0.001% Triton X-100 was used. The concentration of weaker ligand (Vitamin C) was kept constant (0.001M and 0.01M) while alter the concentration of strong ligand (amino acids) in each case.In each case, a single well-defined wave was obtained. The plots of Ede v/s log id-i were elongate with a slope of 302mV, showing that the dickens electrons reduction was reversible. The organise proportionality of the diffusion current to the mercury column indicated that the reduction was simply diffusion controlled.A open frame in half-wave potential to more minus side with the increase in amino acid concentration was discover. This shift in half-wave potential is greater in the presence of the weaker ligand than its absence. It signified mixed-ligands comple x formation. The extended Shaap and McMasters26 treatment was applied and Ledens27 graphical extrapolation method to calculate the values of A, B, C and D. Data of calculation are given in circumvent 2.Table 2 Values of A, B, C and D for Pb(11)-Ascorbic acid- Amino acids systems (Ascorbic acid concentration = 0.01M(fixed)SystemABCDPb(II)-Vitamin C-L-Serine1.325.119.5611.22Table 3 Values of A, B, C and D for Pb(II)-Ascorbic acid Amino acids systems (Ascorbic acid concentration = 0.001M(fixed)SystemABCDPb(II)-Vitamin C-L-Serine1.304.619.5611.22The stability constants 11 and 12 were evaluated from the two values of B. From the values of C two values of 21 were obtained which are in good agreement with each other. 30 is almost equal to D. The results are recorded in plug-in 4 and the results are summarized in the form of schemes 1 and 2 where the quantitative values indicate the log of the equilibrium constants.Table 4 shaping Constants of Mixed-Ligands SystemsSystemslog 11log 12lo g 21Pb(II)-Vitamin C-L-Serine6.238.8811.56It has been holdd that as the size of amino acids change magnitude the stability of its complexes decreased20. The stability of L-amino acids complex also depends upon the chelate ring formation and basicities of ligands21. In case of L-serine and L-threonine, the stability of the latter is less than the L-serine complex owing to the fact that electron withdrawing OH chemical group is nearer to L-threoninate complex than L-serinate complex, causing greater repulsive forces between metal and Off group in L-threonine complexes than L-serine complexes22. The same is evident from Pka values of L-amino acids23. In case of Vitamin-C, oxygen of enediol group may take part in bond formation with Pb(II), formed a five membered ring24. It is clear from the values of stability constant of the complexes that Vitamin-C and L-amino acids alone or in combination could be used to reduce the toxicity of Pb(II) in-vivo. One also has to consider the quantit y of drugs that should not complex to the other essential metals present in-vivo and the same could be excreted easily from the body. On the other hand, the person who suffers from AIDS has low concentration of Vitamin-C, therefore his resistance can be increased by ascorbic acid therapy.The mixed ligands complex formation may also be explained with the help of schemes 1. The tendency to add X (X= amino acids) to PbX and PbY (Y=Vitamin C) can be compared. The logarithm values of stability constants of the above complexes are 3.29 and 3.98 for Pb-VitaminC-L-Serine.The tendency to add Y to PbX and PbY can also be compared. The log K values are (1.64, 0.93) and (1.47, 0.93) for Pb(II)-Vitamin C-L-Serine. This indicates that the appendage of Vitamin C is preferred to Pb(amino acids) as compared to Pb(Vitamin C).The log K values for the addition of X to PbXY and PbY2 are (5.33, 5.70) and (5.47, 5.58). This indicates that the mixed ligand complexation is favoured.The log K values for the addition of Y to PbXY and PbX2 are (2.65, 3.68) and (2.78, 3.65) for Pb(II)-Vitamin C-L-Serine and. This indicates that addition of VitaminC is preferred to PbX2 over PbXY.For comparing the stabilities of simple and mixed ligand complexes, it is convenient to measure the mixing constants.Km = and the stabilization constants.log Ks = log Km log2The log Km values are 0.7 and o.49 and log Ks values are 0.398 and 0.188 for Pb(II)-Vitamin C-L-Serine and Pb(II)-Vitamin C-L-Threonine systems respectively. The positive values of mixing and stabilization constants show that the ternary complexes are more stable than the binary complexes.The tendency to form mixed-lingds complexes in solution could be expressed quantitatively in other approach compares the difference in stability ( log K), which is the result from the substraction of two constants and must therefore, be a constant. This corresponds to log K = Since more coordination positions are available for the bonding of the ligand A to a given multivalent metal ion,than for the second ligand B. Usually holds i.e. one expects to observe negative values for log K. Another more satisfactory, manner is to determine statistical values for log K. The statistical values for regular octahedron (oh) is 5/12 and log Koh = -0.4. for a squar planer(sp), the value of log K = -0.6 and for the kinky octahedron (oh), the statistical values i.e. log K = lie between -0.9 to -0.3.The log K values can be obtained using the following equations log K11=log 11-( log 10 +log 01 ) log K12=log 12-( log 10 +log 02 ) log K21=log 21-(log 20 +log 01 )The observed values of log K11, log K12 and log K21 are -0.61, 1.11 and 1.430 for Pb(II)-Vitamin C-L-Serine.The log K values are higher than statistical values, which again prove that the ternary complexes are more stable than expected from statistical reason.ACTNOWLEDGEMENTThe authors are grateful to the Head, Department of pill rollerry, University of Rajasthan, Jaipur for providi ng facilities to carry out this research.REFERENCES+ Chemistry Department, SKIT, Jagatpura, Jaipur, India-302025Brosnan J, Nutr. J (2000) 130 988S.Pisarewicz K, Mora D, Pflueger F, field G, Mari F, (2005) J. Am. Chem. 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