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Polarographic oxidation of hexacyanoferrate (II) ion in the presence of asparagine,lysine and arginine
SHORT COMMUNICATIONS
147
polarograms of three or more steps should be analysed in accordance with the procedure used in the analysis of three or more waves a. The separation procedure is also valid in the case of the electrode process containing intermediates leading to consecutive chemical reaction 4. Acknowledgement The author is grateful to Dr. Du~an Konrad for helpful discussions. Department of Physical Chemistry, Institute "Ruder Bogkovid", Zagreb, Croatia (Yugoslavia)
Ivica Ru$i6
1 R. BRDI~I(A,Z. Elektrochem., 47 (1941)47. 2 I. Ru~x6ANDM. BRANICA,J. Electroanal. Chem., 22 (1969) 243. 3 I. Ru~Id ANDM. BRANICA,J. Electroanal. Chem., 22 (1969) 422. 4 A. A. VErdi(, Chem. Listy, 50 (1965) 1416, Collection Czech. Chem. Commun., 22 (1957) 1736. Received September 23rd, 1969 J. Electroanal. Chem., 25 (1970) 144-147
Polarographic oxidation of hexacyanoferrate (H) ion in the presence of asparagine, lysine and arginine Introduction The hydrolytic decomposition of hexacyanoferrate(II), A, in the presence of sunlight and the substitution of ammonia, nitro- and nitroso-compounds in the coordination sphere of A have been reported by a number of workers1 - 5. The corresponding reactions with other more basic amino adds, (viz. asparagine, lysine and arginine) have, however, not so far been reported. The reaction between these amino acids and A would be expected to be catalysed by sunlight and substitution to occur through the formation of aquopentacyanoferrate(II). Preliminary experiments have shown that the above reaction does not take place either at low pH or in alkaline medium in the dark. However, a light-brown co.loured soluble product is obtained on exposing an alkaline solution (pH - 10.0) to sunlight. The reaction was followed polarographically. Experimental Reagents and solutions. All solutions were prepared in doubly-distilled water. The solution of potassium hexacyanoferrate(II), (B.D.H.A.R.), was prepared by dissolving a weighed amount in water and was standardized 6 by titrating against standard K M n O 4 solution using diphenylamine as internal indicator. The following buffers were used7 : (i) Sorensen buffer pH 9.7, obtained by mixing 70 ml 0.05 M borax and 30 ml 0.1 M N a O H J. Electroanal. Chem., 25 (1970) 14%150
148
SHORT COMMUNICATIONS
(ii) Naegeli and Tyabji buffer pH 10.85, obtained by mixing 100 ml 0.05 M borax and 99.6 ml 0.1 M NaOH. The pH was measured by an Elico (India) pH meter, model LI-10. The amino acids (B.D.H.) used were in the form of the hydrochloride. The solutions of asparagine and lysine were prepared by dissolving the required amount in Sorensen buffer pH 9.7 and the arginine solution by dissolving a known quantity of the amino acid in Naegeli and Tyabji buffer pH 10.85. The solutions were stored in a refrigerator. Lithium chloride (Merck-pro-analysi) was used as the supporting electrolyte. Methyl red solution, 0.1%, was obtained by dissolving 0.1 g of methyl red (B.D.H.) in hot water using a minimum quantity of sodium hydroxide solution and making the volume up to 100 ml. Apparatus and technique. A Toshniwal (India) polarograph type CLO2A, in conjunction with a Pye Scalamp galvanometer, was used for polarographic measurements. The polarographic cell was immersed in a water thermostat maintained at 25 + 0.1 ° C. A Fischer capillary, with a drop time of 3.0 s (open circuit) and m = 2.07 mg s-1, was used (capillary characteristics, m~ t~ = 1.95 mg~s-½). The mixtures for polarographic analysis were prepared as follows: 1 ml of 1.0 x 10 -2 M K4[Fe(CN)6 ] +increasing amounts, 1-6 ml (x ml), 0.1 M amino acid solution+(7.5-x) ml of buffer of corresponding p H + 1 ml 1 M LiCI+0.5 ml 0.1% methyl red. These mixtures were allowed to stand for 2 h in sunlight and the polarograms were recorded after deaerating them by passing purified hydrogen. V(vs. SCE) 0 -0.1-0.2-0.3-0.4-0.5-0.6
Edrne
0.5 0.4 0.3 0.2 0.1
21-- .
d
l
.
.
.
.
.
.
.
.
.
I
,7,l , / , f . l , f , /
-4r -8
.
_
/ /o/ / / ~/ /
V(vs. SCE) 0 -0.1 - 0 . 2 - 0 . 3 - 0 . 4 - 0 . 5 - 0 . 6
Edme V{vs. SCE) 0 -0.1-0.2-0.3-0.4-0.5-0.6-0.7
Edm e
0.5 0.4 0.3 0.2 Q1 < tO
(9
0
0.4 0.3 0.2 0.1 I
I
,
I
I
,
I
I
I
I
{b)
-2
-2 I
t6 - 4 X
E
¢1
-6 -8
U
d
-10 I
I
I
I
I
I
I
I
I
I
I
-Ioi i
I
I
I
I
I
I
I
Fig. 1. Oxidation waves of 1 x 10 -3 M K4[FeCN)6 ] with and without 0.01-0.06 M amino acid.All curves start at - 0.1 V. (a): (1) K~[Fe(CN)6] ;(2)-(7) + asparagine; pH 9.7. (b): (1) K4[Fe(CN)6 ] ;(2)-(7) + arginine; pH 10.85. (c): (1) K4[Fe(CN)6] ; (2)-(7) +lysine; pH 9.7. J. Eleetroanal. Chem., 25 (1970) 147-150
I
149
SHORT COMMUNICATIONS
Edme/~Vs.
SCE) 0.5 0,4 0.3 0.2 0.1 0 -0.1 -0.2-0.3 -0.4
2
i
i
i
i
I
i
i
i
I
I
I
I
I
I
I
I
.~.~ -2 x
-6
L
~ -10 -12
Fig. 2. Oxidation waves of 1 x 10 -3 M K4[Fe(CN)6 ] in presence of sunlight. (1) after 0, (2) 30, (3) 60, (4) 120 min. All curves start at - 0 . 1 V.
Results and discussion
The polarographic oxidation of hexacyanoferrate(II) in alkaline medium (borax buffers of pH 9.7 and 10.85) gives a diffusion-controlled (confirmed by the linearity of the plots of id vs. M) irreversible anodic wave of E , = + 0.25 V vs. SCE (Figs. la and b, curve 1). On keeping the solution in sunlight a new wave emerges of E l -0.115 V vs. SCE, and the wave height of which increases with time (Fig. 2). This new wave is due to the oxidation of the aquated product 8 of hexacyanoferrate(II) at the DME. TABLE 1 VARIATION IN
E~
Amino acid
OF
K4[Fe(CN)6 ] (1 × 10 -3 M)
WITH
cONCENTRATION
Concn. of amino acid/ M
lOid/pA
E~/V
lOi~/pA
E~/V
Asparagine (pH=9.7)
0.00 0.01 0.02 0.03 0.04 0.05 0.06
4.29 3.95 3.50 3.40 3.50 3.50 3.60
0.250 0.295 0.320 0.340 0.340 0.350 0.335
-0.90 1.58 1.69 1.80 1.80 1.69
-0.125 0.155 0.150 0.150 0.150 0.146
Lysine (pH=9.7)
0.01 0.02 0.03 0.04 0.05 0.06
3.84 3.27 2.71 2.14 1.69 1.35
0.300 0.315 0.325 0.335 0.340 0.340
0.79 1.35 1.92 2.48 3.27 3.60
0.100 0.115 0.125 0.150 0.160 0.165
Arginine
0.00 0.01 0.02 0.03 0.04 0.05 0.06
4.29 3.84 3.50 3.39 2.48 2.26 1.46
0.250 0.310 0.295 0.320 0.330 0.335 0.345
-0.67 0.90 1.35 1.80 2.37 3.05
-0.100 0.115 0.105 0.130 0.155 0.160
(pH = 10.85)
Wave I
OF AMINO ACID
Wave II
J. Electroanal. Chem., 25 (1970) 147-150
150
SHORT COMMUNICATIONS
In the presence of amino acids of more basic character, (viz. asparagine, lysine and arginine) although two waves appear, the height of the second wave is limited and no longer increases with time (Figs. 1, a, b and c). Moreover, the E~ of the second wave is shifted to more positive potentials in the presence of these amino acids {Table 1) showing that the substitution of the amino acid has resulted in the formation of a more difficultly oxidizable species. This indicates that the addition of the more basic amino acids to the hexacyanoferrate(II) solution checks any further tendency to aquation by substituting water and the adjacent cyanogen by the bidentate amino acid molecule. The effect of the amino acid concentration on the wave height of the second wave is also interesting. The height of the second wave in the case of all three amino acids increases with concentration and is constant after a certain concentration is reached (Figs. 1, a, b and c). However, this increase in wave height is notably more for lysine and arginine for which the wave height of the second wave is almost twice the wave height of the corresponding wave for asparagine (36.0 and 30.5/zA for lysine and arginine, respectively, compared to 18.0/IA for asparagine). It may be concluded, therefore, that two-fold substitution takes place in the case of lysine and arginine resulting in the formation of dicyanobis(lysino)ferrate(II) and dicyanobis(arginino)ferrate(II), respectively, as against the formation of a monosubstituted product with asparagine.
Department of Chemistry, University of Roorkee, Roorkee (India) 1 2 3 4 5 6 7 8
Wahid U. Malik M. Aslam
S. ASPERGER, I. MURATI AND O. CUPAHIN, J. Chem. Soc., (1953) 1041. S. ASPERGER, Acta Pharm. Jugoslav., 3 (1953) 20. G. EMSCHWILLER, Compt. Rend., 72 0953) 263. S. ASPERGER, Trans. Faraday Soc., 48 (1952) 617. S. ASPERGERAND D. PAVLOVIC,J. Chem. Soc., (1955) 1449. F. SUTTON, Volumetric Analysis, Butterworths Scientific Pub., London, 13th ed., 1955, p. 331. H. T. S. BRITTON, Hydrogen Ions, Vol. I, D. Van Nostrand, Princeton, N.J., 1964, pp. 355-64. H. M, Ph.D. Thesis, University of Roorkee, Roorkee, 1967.
Received August 25th, 1969
J. Eleetroanal.Chem.,25 (1970) 147-150
147
polarograms of three or more steps should be analysed in accordance with the procedure used in the analysis of three or more waves a. The separation procedure is also valid in the case of the electrode process containing intermediates leading to consecutive chemical reaction 4. Acknowledgement The author is grateful to Dr. Du~an Konrad for helpful discussions. Department of Physical Chemistry, Institute "Ruder Bogkovid", Zagreb, Croatia (Yugoslavia)
Ivica Ru$i6
1 R. BRDI~I(A,Z. Elektrochem., 47 (1941)47. 2 I. Ru~x6ANDM. BRANICA,J. Electroanal. Chem., 22 (1969) 243. 3 I. Ru~Id ANDM. BRANICA,J. Electroanal. Chem., 22 (1969) 422. 4 A. A. VErdi(, Chem. Listy, 50 (1965) 1416, Collection Czech. Chem. Commun., 22 (1957) 1736. Received September 23rd, 1969 J. Electroanal. Chem., 25 (1970) 144-147
Polarographic oxidation of hexacyanoferrate (H) ion in the presence of asparagine, lysine and arginine Introduction The hydrolytic decomposition of hexacyanoferrate(II), A, in the presence of sunlight and the substitution of ammonia, nitro- and nitroso-compounds in the coordination sphere of A have been reported by a number of workers1 - 5. The corresponding reactions with other more basic amino adds, (viz. asparagine, lysine and arginine) have, however, not so far been reported. The reaction between these amino acids and A would be expected to be catalysed by sunlight and substitution to occur through the formation of aquopentacyanoferrate(II). Preliminary experiments have shown that the above reaction does not take place either at low pH or in alkaline medium in the dark. However, a light-brown co.loured soluble product is obtained on exposing an alkaline solution (pH - 10.0) to sunlight. The reaction was followed polarographically. Experimental Reagents and solutions. All solutions were prepared in doubly-distilled water. The solution of potassium hexacyanoferrate(II), (B.D.H.A.R.), was prepared by dissolving a weighed amount in water and was standardized 6 by titrating against standard K M n O 4 solution using diphenylamine as internal indicator. The following buffers were used7 : (i) Sorensen buffer pH 9.7, obtained by mixing 70 ml 0.05 M borax and 30 ml 0.1 M N a O H J. Electroanal. Chem., 25 (1970) 14%150
148
SHORT COMMUNICATIONS
(ii) Naegeli and Tyabji buffer pH 10.85, obtained by mixing 100 ml 0.05 M borax and 99.6 ml 0.1 M NaOH. The pH was measured by an Elico (India) pH meter, model LI-10. The amino acids (B.D.H.) used were in the form of the hydrochloride. The solutions of asparagine and lysine were prepared by dissolving the required amount in Sorensen buffer pH 9.7 and the arginine solution by dissolving a known quantity of the amino acid in Naegeli and Tyabji buffer pH 10.85. The solutions were stored in a refrigerator. Lithium chloride (Merck-pro-analysi) was used as the supporting electrolyte. Methyl red solution, 0.1%, was obtained by dissolving 0.1 g of methyl red (B.D.H.) in hot water using a minimum quantity of sodium hydroxide solution and making the volume up to 100 ml. Apparatus and technique. A Toshniwal (India) polarograph type CLO2A, in conjunction with a Pye Scalamp galvanometer, was used for polarographic measurements. The polarographic cell was immersed in a water thermostat maintained at 25 + 0.1 ° C. A Fischer capillary, with a drop time of 3.0 s (open circuit) and m = 2.07 mg s-1, was used (capillary characteristics, m~ t~ = 1.95 mg~s-½). The mixtures for polarographic analysis were prepared as follows: 1 ml of 1.0 x 10 -2 M K4[Fe(CN)6 ] +increasing amounts, 1-6 ml (x ml), 0.1 M amino acid solution+(7.5-x) ml of buffer of corresponding p H + 1 ml 1 M LiCI+0.5 ml 0.1% methyl red. These mixtures were allowed to stand for 2 h in sunlight and the polarograms were recorded after deaerating them by passing purified hydrogen. V(vs. SCE) 0 -0.1-0.2-0.3-0.4-0.5-0.6
Edrne
0.5 0.4 0.3 0.2 0.1
21-- .
d
l
.
.
.
.
.
.
.
.
.
I
,7,l , / , f . l , f , /
-4r -8
.
_
/ /o/ / / ~/ /
V(vs. SCE) 0 -0.1 - 0 . 2 - 0 . 3 - 0 . 4 - 0 . 5 - 0 . 6
Edme V{vs. SCE) 0 -0.1-0.2-0.3-0.4-0.5-0.6-0.7
Edm e
0.5 0.4 0.3 0.2 Q1 < tO
(9
0
0.4 0.3 0.2 0.1 I
I
,
I
I
,
I
I
I
I
{b)
-2
-2 I
t6 - 4 X
E
¢1
-6 -8
U
d
-10 I
I
I
I
I
I
I
I
I
I
I
-Ioi i
I
I
I
I
I
I
I
Fig. 1. Oxidation waves of 1 x 10 -3 M K4[FeCN)6 ] with and without 0.01-0.06 M amino acid.All curves start at - 0.1 V. (a): (1) K~[Fe(CN)6] ;(2)-(7) + asparagine; pH 9.7. (b): (1) K4[Fe(CN)6 ] ;(2)-(7) + arginine; pH 10.85. (c): (1) K4[Fe(CN)6] ; (2)-(7) +lysine; pH 9.7. J. Eleetroanal. Chem., 25 (1970) 147-150
I
149
SHORT COMMUNICATIONS
Edme/~Vs.
SCE) 0.5 0,4 0.3 0.2 0.1 0 -0.1 -0.2-0.3 -0.4
2
i
i
i
i
I
i
i
i
I
I
I
I
I
I
I
I
.~.~ -2 x
-6
L
~ -10 -12
Fig. 2. Oxidation waves of 1 x 10 -3 M K4[Fe(CN)6 ] in presence of sunlight. (1) after 0, (2) 30, (3) 60, (4) 120 min. All curves start at - 0 . 1 V.
Results and discussion
The polarographic oxidation of hexacyanoferrate(II) in alkaline medium (borax buffers of pH 9.7 and 10.85) gives a diffusion-controlled (confirmed by the linearity of the plots of id vs. M) irreversible anodic wave of E , = + 0.25 V vs. SCE (Figs. la and b, curve 1). On keeping the solution in sunlight a new wave emerges of E l -0.115 V vs. SCE, and the wave height of which increases with time (Fig. 2). This new wave is due to the oxidation of the aquated product 8 of hexacyanoferrate(II) at the DME. TABLE 1 VARIATION IN
E~
Amino acid
OF
K4[Fe(CN)6 ] (1 × 10 -3 M)
WITH
cONCENTRATION
Concn. of amino acid/ M
lOid/pA
E~/V
lOi~/pA
E~/V
Asparagine (pH=9.7)
0.00 0.01 0.02 0.03 0.04 0.05 0.06
4.29 3.95 3.50 3.40 3.50 3.50 3.60
0.250 0.295 0.320 0.340 0.340 0.350 0.335
-0.90 1.58 1.69 1.80 1.80 1.69
-0.125 0.155 0.150 0.150 0.150 0.146
Lysine (pH=9.7)
0.01 0.02 0.03 0.04 0.05 0.06
3.84 3.27 2.71 2.14 1.69 1.35
0.300 0.315 0.325 0.335 0.340 0.340
0.79 1.35 1.92 2.48 3.27 3.60
0.100 0.115 0.125 0.150 0.160 0.165
Arginine
0.00 0.01 0.02 0.03 0.04 0.05 0.06
4.29 3.84 3.50 3.39 2.48 2.26 1.46
0.250 0.310 0.295 0.320 0.330 0.335 0.345
-0.67 0.90 1.35 1.80 2.37 3.05
-0.100 0.115 0.105 0.130 0.155 0.160
(pH = 10.85)
Wave I
OF AMINO ACID
Wave II
J. Electroanal. Chem., 25 (1970) 147-150
150
SHORT COMMUNICATIONS
In the presence of amino acids of more basic character, (viz. asparagine, lysine and arginine) although two waves appear, the height of the second wave is limited and no longer increases with time (Figs. 1, a, b and c). Moreover, the E~ of the second wave is shifted to more positive potentials in the presence of these amino acids {Table 1) showing that the substitution of the amino acid has resulted in the formation of a more difficultly oxidizable species. This indicates that the addition of the more basic amino acids to the hexacyanoferrate(II) solution checks any further tendency to aquation by substituting water and the adjacent cyanogen by the bidentate amino acid molecule. The effect of the amino acid concentration on the wave height of the second wave is also interesting. The height of the second wave in the case of all three amino acids increases with concentration and is constant after a certain concentration is reached (Figs. 1, a, b and c). However, this increase in wave height is notably more for lysine and arginine for which the wave height of the second wave is almost twice the wave height of the corresponding wave for asparagine (36.0 and 30.5/zA for lysine and arginine, respectively, compared to 18.0/IA for asparagine). It may be concluded, therefore, that two-fold substitution takes place in the case of lysine and arginine resulting in the formation of dicyanobis(lysino)ferrate(II) and dicyanobis(arginino)ferrate(II), respectively, as against the formation of a monosubstituted product with asparagine.
Department of Chemistry, University of Roorkee, Roorkee (India) 1 2 3 4 5 6 7 8
Wahid U. Malik M. Aslam
S. ASPERGER, I. MURATI AND O. CUPAHIN, J. Chem. Soc., (1953) 1041. S. ASPERGER, Acta Pharm. Jugoslav., 3 (1953) 20. G. EMSCHWILLER, Compt. Rend., 72 0953) 263. S. ASPERGER, Trans. Faraday Soc., 48 (1952) 617. S. ASPERGERAND D. PAVLOVIC,J. Chem. Soc., (1955) 1449. F. SUTTON, Volumetric Analysis, Butterworths Scientific Pub., London, 13th ed., 1955, p. 331. H. T. S. BRITTON, Hydrogen Ions, Vol. I, D. Van Nostrand, Princeton, N.J., 1964, pp. 355-64. H. M, Ph.D. Thesis, University of Roorkee, Roorkee, 1967.
Received August 25th, 1969
J. Eleetroanal.Chem.,25 (1970) 147-150