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Potentiometric determination of stepwise stability constants of vanadium, molybdenum and tungsten chelates formed with asparagine and glutamine
ANALYTICAL
DATA
POTENTIOMETRIC DETERMINATION OF STEPWISE STABILITY CONSTANTS OF VANADIUM, MOLYBDENUM AND TUNGSTEN CHELATES FORMED WITH ASPARAGINE AND GLUTAMINE (Received 20 June 1972. Accepted 1 August 1972)
The metal chelates of asparagine have been studied earlier by various workers,‘-s but chelates formed with glutamine have not been investigated so extensively. In earlier publications from this laboratory, the stability constants of some aspartate and glutamate chelates6 have been reported. Their formation was studied potentiometrically by Irving and Rossotti’s’ method. This paper gives the results of a similar study of some chelates of vanadium. molybdenum and tungsten formed with asparagine and glutamine. RESULTS
AND
DISCUSSION
The protonation constants are log K2” 8.70, log K,” 2.16 for asparagine and log Ki” 8.91, log Ks” 2.21 for glutamine. The formation curves (ii vs. pL) show that Ti approaches a value of 3 for the asparagine and glutamine chelates of V(IV), Mo(VI) and W(VI). Analysis of the formation curves for the V(IV) chelates show that K, and K2 are very similar, and K, quite different. Since log K1 - log Kt is ~0.5, in these cases. K, and K, cannot be separately computed; instead log K, KZ values were obtained from Albert’s equation’ logK,.K,=logii-log(2-E)-2log[L] Further since K,/K, by the average-value Table 1, Stability
- 103, K, may be regarded as independent method in the range 2 < E < 3.
constants
Metal ion
pH range for ii calculations
V(IV)
3.2-8.0
of vanadium(IV), and glutamine
2.7-8.5
4-8.5
formed with asparagine
Glutamine
Asparagine Method Interpolation at half-n values Albert’s equation
Innreylation
Interpolation values Successive approximation
log K,
at half-n
at half-ii
log Kz
Iog K,
log K,
log Kz
log K,
7.10
4.00
740
7.00
4.00
7.50 log K, 14.50
-
Successive approximation W(VI)
and its value was computed
molybdenum(V1) and tungsten(V1) chelates (Temp. 2S”C, O.lM NaCIO, medium).
Average-value Mo(V1)
of K, and K,,
-
K2
-
4.04
log K, 14.45 800
-
K, -
4.07
6.80
3.35
8.20
7.18
3.45
8.06
7.23
3.45
7.90
6.93
3.35
6.00
500
3.30
5.90
4.35
3.20
5.84
5.11
3.30
5.76
509
3.20
133
134
ANALYTICAL
DATA
For Mo(V1) chelates, K,/K, _ 10 and K,,/K, _ 103’s, whereas for W(VI) chelates K,/K, were obtained by interpolation KzlK3 _ 10”‘. Therefore in these cases estimated stability constants values and these were further refined by successive approximation. Chemical Laboratories University of Allahabad Allahabad. India
- 10 and at half-ii
R. C. TEWARt M. N. SRIVASTAVA
REFERENCES
Biochem. J. 1950. 47, 531. Ci. Tanford and W. S. Shore, J. Am. Chem. Sot., 1953, 75, 816. J. Schubert, ibid., 1954, 76, 3442. D. D. Perrin, J. Chem. Sot., 1958, 3125; 1959, 290. N. C. Li and E. Doody, J. Am. Chem. Sot., 1958, 80, 5901. M. K. Singh and M. N. Srivastava, J. Inorg. Nucl. Chem., 1972, 34, 567, 2067, 19, 699. H. Irving and H. S. Rossotti. J. Chem. Sot., 1953, 3397; 1954, 2904. A. Albert. Biochem. J., 1953, 54, 646.
1. A.
2. 3. 4. 5. 6. 7. 8.
Albert,
2081;
Talanta.
Summary-The metal chelates of V(IV), Mo(VI) and W(VI) formed with asparagine and glutamine have been studied potentiometrically. Stepwise stability constants in O,iM sodium perchlorate at 25°C are reported as follows. Asparagine chelates-log K,KZ 14.50 and log K, 4.04 for V, log K, 8.06, log K, 7.29 and log K, 3.45 for MO, and log K, 5.84, log K2 5.11 and log K, 3.30 for W. Glutamine chelates-log K,K, 14.45, and log K, 4.07 for V, log K, 7.90, log Kz 6.93, and log K, 3.35 for MO. and log K, 5.76, log K2 5.09 and log K, 3.20 for W. Zasammenfassung-Die wurden potentiometrisch O.lM Natriumperchlorat Mit Asparagin. log K,K, log K, 5.84, log K, 5.11, Mit Glutamin. log K,K, fur MO, log K, 5.76, log
Chelate von V(IV), Mo(VI) und W(VI) mit Asparagin und Glutamin untersucht. Es werden folgende stufenweise Stabilitltskonstanten in bei 25°C mitgeteilt: 14.50, log K, 404 fur V, log K, 8.06, log K, 7.29, log K, 3.45 fir MO, log K, 3.30 fur W. 14.45, log K, 4.07 fur V, log K, 790, log K, 6.93, log K, 3.35 K, 5.09. log K, 3.20 fur W.
RkumP-On a etudie potentiometriquement les chelates metalliques de V (IV), MO (VI) et W (VI) form& avec l’asparagine et la glutamine. Les constantes de stabilitt etagees en perchlorate de sodium 0,l M a 25°C sont rapportees comme suit: Chdlates de Pasparagine-log K,K2 14.50 et log K, 4,04 pour V, log K, 8,06, log Kz 7.29 et log K, 3,45 pour MO, et log K, 5.84, log K2 5,ll et log K, 3,30 pour W. 14.45, et log K3 4,07 pour V, log K, 7,90, log Kz 6,93 ChPlates de la glutamine-log K,K, et log K, 3.35 pour MO, et log K, 5,76, log K2 5,09 et log K, 3,20 pour W.
1972.
DATA
POTENTIOMETRIC DETERMINATION OF STEPWISE STABILITY CONSTANTS OF VANADIUM, MOLYBDENUM AND TUNGSTEN CHELATES FORMED WITH ASPARAGINE AND GLUTAMINE (Received 20 June 1972. Accepted 1 August 1972)
The metal chelates of asparagine have been studied earlier by various workers,‘-s but chelates formed with glutamine have not been investigated so extensively. In earlier publications from this laboratory, the stability constants of some aspartate and glutamate chelates6 have been reported. Their formation was studied potentiometrically by Irving and Rossotti’s’ method. This paper gives the results of a similar study of some chelates of vanadium. molybdenum and tungsten formed with asparagine and glutamine. RESULTS
AND
DISCUSSION
The protonation constants are log K2” 8.70, log K,” 2.16 for asparagine and log Ki” 8.91, log Ks” 2.21 for glutamine. The formation curves (ii vs. pL) show that Ti approaches a value of 3 for the asparagine and glutamine chelates of V(IV), Mo(VI) and W(VI). Analysis of the formation curves for the V(IV) chelates show that K, and K2 are very similar, and K, quite different. Since log K1 - log Kt is ~0.5, in these cases. K, and K, cannot be separately computed; instead log K, KZ values were obtained from Albert’s equation’ logK,.K,=logii-log(2-E)-2log[L] Further since K,/K, by the average-value Table 1, Stability
- 103, K, may be regarded as independent method in the range 2 < E < 3.
constants
Metal ion
pH range for ii calculations
V(IV)
3.2-8.0
of vanadium(IV), and glutamine
2.7-8.5
4-8.5
formed with asparagine
Glutamine
Asparagine Method Interpolation at half-n values Albert’s equation
Innreylation
Interpolation values Successive approximation
log K,
at half-n
at half-ii
log Kz
Iog K,
log K,
log Kz
log K,
7.10
4.00
740
7.00
4.00
7.50 log K, 14.50
-
Successive approximation W(VI)
and its value was computed
molybdenum(V1) and tungsten(V1) chelates (Temp. 2S”C, O.lM NaCIO, medium).
Average-value Mo(V1)
of K, and K,,
-
K2
-
4.04
log K, 14.45 800
-
K, -
4.07
6.80
3.35
8.20
7.18
3.45
8.06
7.23
3.45
7.90
6.93
3.35
6.00
500
3.30
5.90
4.35
3.20
5.84
5.11
3.30
5.76
509
3.20
133
134
ANALYTICAL
DATA
For Mo(V1) chelates, K,/K, _ 10 and K,,/K, _ 103’s, whereas for W(VI) chelates K,/K, were obtained by interpolation KzlK3 _ 10”‘. Therefore in these cases estimated stability constants values and these were further refined by successive approximation. Chemical Laboratories University of Allahabad Allahabad. India
- 10 and at half-ii
R. C. TEWARt M. N. SRIVASTAVA
REFERENCES
Biochem. J. 1950. 47, 531. Ci. Tanford and W. S. Shore, J. Am. Chem. Sot., 1953, 75, 816. J. Schubert, ibid., 1954, 76, 3442. D. D. Perrin, J. Chem. Sot., 1958, 3125; 1959, 290. N. C. Li and E. Doody, J. Am. Chem. Sot., 1958, 80, 5901. M. K. Singh and M. N. Srivastava, J. Inorg. Nucl. Chem., 1972, 34, 567, 2067, 19, 699. H. Irving and H. S. Rossotti. J. Chem. Sot., 1953, 3397; 1954, 2904. A. Albert. Biochem. J., 1953, 54, 646.
1. A.
2. 3. 4. 5. 6. 7. 8.
Albert,
2081;
Talanta.
Summary-The metal chelates of V(IV), Mo(VI) and W(VI) formed with asparagine and glutamine have been studied potentiometrically. Stepwise stability constants in O,iM sodium perchlorate at 25°C are reported as follows. Asparagine chelates-log K,KZ 14.50 and log K, 4.04 for V, log K, 8.06, log K, 7.29 and log K, 3.45 for MO, and log K, 5.84, log K2 5.11 and log K, 3.30 for W. Glutamine chelates-log K,K, 14.45, and log K, 4.07 for V, log K, 7.90, log Kz 6.93, and log K, 3.35 for MO. and log K, 5.76, log K2 5.09 and log K, 3.20 for W. Zasammenfassung-Die wurden potentiometrisch O.lM Natriumperchlorat Mit Asparagin. log K,K, log K, 5.84, log K, 5.11, Mit Glutamin. log K,K, fur MO, log K, 5.76, log
Chelate von V(IV), Mo(VI) und W(VI) mit Asparagin und Glutamin untersucht. Es werden folgende stufenweise Stabilitltskonstanten in bei 25°C mitgeteilt: 14.50, log K, 404 fur V, log K, 8.06, log K, 7.29, log K, 3.45 fir MO, log K, 3.30 fur W. 14.45, log K, 4.07 fur V, log K, 790, log K, 6.93, log K, 3.35 K, 5.09. log K, 3.20 fur W.
RkumP-On a etudie potentiometriquement les chelates metalliques de V (IV), MO (VI) et W (VI) form& avec l’asparagine et la glutamine. Les constantes de stabilitt etagees en perchlorate de sodium 0,l M a 25°C sont rapportees comme suit: Chdlates de Pasparagine-log K,K2 14.50 et log K, 4,04 pour V, log K, 8,06, log Kz 7.29 et log K, 3,45 pour MO, et log K, 5.84, log K2 5,ll et log K, 3,30 pour W. 14.45, et log K3 4,07 pour V, log K, 7,90, log Kz 6,93 ChPlates de la glutamine-log K,K, et log K, 3.35 pour MO, et log K, 5,76, log K2 5,09 et log K, 3,20 pour W.
1972.