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Effect of temperature and time on the stability of nitrosyl cobalt complexes with amino acids
INORG. NUCL. CHEM. LETTERS Voi. 16, pp.563-566. Pergamon Press Ltd. J980. Printed in Great Britain.
0020-1650/80/1201-0563502.00/0
EFFECT OF TEMPERATURE AND TIME ON THE STABILITY OF NITROSYL COBALT COMPLEXES WITH AMINO ACIDS B.Jeiowska-Trzebiatowska, Institute
K.Gerega,
G.Formicka-Koz~owska
of Chemistry, University of Wroc~aw, 50-383 vVroc~aw, Poland
Joliot-Curie
14,
(Received 23 March 1980; in revised form l! September 1980)
It is well known that both time and temperature
are factors which
influence considerably the equilibrium of the oxygen binding of cobalt compounds
(I-3). We have now investigated
the effect of these factors
on the effectiveness of nitric oxide binding by similar cobalt complexes with amino acids. In our previous paper (4), the results of studies of the equilibria existing in solution between the active c o b a l t ~ t
com-
plex and the cobalt complex with bonded nitric oxide were presented, and the effect of metal environment was determined.
The equilibria we
are concerned with are as follows:
[Co(II)(Amac)2(H20)n ] + NO=[go~II)(Amac)sN0(H20)n_1 ] + H20 , n:I,2
(I)
[Co(II)(Amam)2(Himid)(H20)]
(2)
+ N0~o(III)(Amam)2(Himid)N0
] + H20
where Amac = amino acid and Himid is imidazole. In the present work the effect of temperature and time on the equilibria (I and 2) existing in aqueous solution is reported. EXPERIMENTAL The synthesis of the cobalt complexes with amino acids with and withour imidazole have been described previously (2,4,5). amino acids were used: glycine (Gly),
alanine (Ala),
The following
ornithine
(Orn),
threonine (Thr)(supplied by E.Merck). The magnetic
susceptibility of the solutions were measured in 2 %
t-butanol in D20 by the method described by Evans (6> at 6,20,40 and 60°C using a JEOL JNM-PS-IO0 nmr spectrometer. the stabilities
The effect of time on
of the nitrosyl cobalt complexes was investigated at
22 + 1°C. Electronic
spectroscopic measurements
in the visible and near infra-
-red range were carried out using a Cary-14 spectrophotometer temperature at cobalt concentrations The magnetic
at room
of 3.8 x I0-2M.
susceptibility of the isolated solid complex was measu-
red by the Gouy method between 80 and 3OO K. Magnetic susceptibilities in the 4 to 60 K range were measured using a Foner magnetometer.
563
564
The Stability of Nitrosyl Cobalt Complexes RESULTS AND DISCUSSION
The results of magnetic susceptibility measurements on solutions containing cobalt, imidazole, amino acid and NO at time intervals from 0 to 48 hours are summarized in Table 1. TABLE I Magnetic Moments and Abundances of Co D 0 and Co ~ I II) Complexes for Solutions with Added Imidazole, in Which the Equilibrium of the NO Binding was Reached (see reaction 2) Measured at Different Times.
Amac
Time
[BM]
Gly pH 8.16
0 lh 24h 48h
3.27 3.32 4.02 4.23
62 63 77 81
38 37 23 19
Ala pH 8.50
0 lh 24h 48h
3.90 3.92 3.83 3.70
74 75 73 70
26 25 27 30
Orn pH 9.07
0 24h 48h
2.03 3.40 3.60
39 65 69
61 35 31
Magnetic susceptibilities for similar systems without imidazole obtained after various time intervals are summarized in Table 2. Our results show that solutions containing alanine, whether with or without added imidazo. le, are stable for up to about 48 hours because the magnetic moments do not show any significant change. On the other hand, a change in temperature from 6 to 60°C increases the magnetic moment of the solution very slightly (Tables 3 and 4). This shows that there is a small shift in the equilibria to the left (equations I and 2) and is entirely consistent with the expected dissociation of the cobalt-NO bond with increase in temperature. At higher temperatures, a pink precipitate is formed and further investigations were not carried out. After about a week at room temperature, the cobalt-NO solution without imldazole decomposes and the same pink precipitate is formed. The solid was diamagnetic and the pink colour suggested a slx-coordinate Co(III) complex. The complex contained no NO and elemental analysis was consistent with the formulation C o ~ l a ) 3"2H20. (Cal&: C, 30.09; N, 11.70; H, 5.05, Found: C, 29.86; N, 11.60; H, 5.13 %).
The Stability of Nitrosyl Cobalt Complexes
565
TABLE 2 ~agnetic Moments and Abundances of Co(ll) and Co(Ill) Complexes for Solutions without Imidazole, in which the Equilibrium of Reaction (I) was Reached
Amac Gly pH 10.00
Time
%~ [BM]
CO (II)
Co(Ill)
0
4.22
80
20
lh
4.51
86
14
24h
4.53
87
13
%
'/o
Ala
O
3.69
70
30
pH 10.64
lh
3.71
71
20
24h
3.82
73
27
0
0
0
100
0.64 1.15
13 22
87 78
1.34
25
75
2.16
41
59
Orn pH 11.20
10 min 30 min 1.5h 24h
Thr pH 11.82
0
100
15 min lh
0
0.98 1.14
0
19 22
81 78
24h
1.60
30
70
In glycine containing solutions, equilibrium was reached much more slowly as judged by the magnetic susceptibility measurements. brium eventually lies more to the left ( C o ~
The equili-
than with alanine conta-
ining solutions whether imidazole was present or not. Even so, a significant amount of the cobalt nitrosyl complex was present at equilibrium about 19 and 13 ~ for the systems with and without added imidazole respectively). Ornithine containing solutions behaved quite differently. They readily absorbed NO and in the system with no added imidazole, equilibrium lies fully to the right ( C o ( I I 0 - N O ) and the solution was diamagnetic. These solutions, however, rapidly decompose, with 22 ~ C o , I )
being formed
within 30 min in solutions without added imidazole. Similar behaviour and instability is found with the threonine system, but the rate of decomposition slows down after 24 hours and suggests an equilibrium substantially to the right.
566
The Stability of Nitrosyl Cobalt Complexes
TABLE 3 Temperature Dependence of Magnetic Moments and Abundances of Co[II) and Co ~ I ~ ~omplexes at pH 8".5 for ~o~II)[Ala)2(Himid)NO] System. Temp
//
Co (If)
Co (III)
Temperature Moments and and qo(II~ for [Co (II~ Temp
TABLE 4 Dependence of Magnetic Abundances of Co(l~ Complexe~ at.pH 10.64 (Ala)2NO[H20)JSystem.
~
Co (II)
°c
IBM]
%
%
°C
IBM]
%
6
4.01 4.20 4.36 4.31
76 80 83 82
24 20 17 18
6 20 40 60
3.71 3.93 4.11 3.99
71 75 78 76
20 40 60
Co (III)
29 25 22 24
In all these cases there is a significant amount of Co ~II)-NO complex is solutions at room temperature varying from as low as 20 W to 100 %. In the case of alanine, the decrease in Co(Ill)-NO complex present as the temperature is raised from 6 to 20°C is very small (about 4 %)and does not decrease much more even up to 60°C. These results show that the Co~II)-NO systems are relatively much more stable than the corresponding systems with oxygen which are particularly unstable above 2°C. ACKNOWLEDGEMENT The authors wish to thank Dr J.B.Raynor (Leicester University, for help during the preparation of this manuscript.
U.K.)
REFERENCES I. M.J.CARTER, D.P.RILLEMA and F.BASOLO, J.Am. Chem.Soc., 96, 392 (1974) 2. B.JEZOW~KA-TRZEBIATOWSKA, A.VOGT, H.KOZLOWSKI and A.JEZIERSKI, Bull.Acad.Polon.Sci.,ser.sci.chim., 20, 187 (1972) 3. R.D. JONES, D.A.SU~ERVILLE and F.BASOLO, Chem.Rev., 79, 139 (1979) 4. B.JEZOWSKA-TRZEBIATOWSKA, K.GEREGA and G.FORMICKA-KOZLOWSKA, Inorg.Chim.Acta, 40, 187 (1980) 5. B. JEZOWSKA-TRZEBIATOWSKA, K.GEREGA and A.VOGT, Inorg.Chim.Acta, 31, 183 (1978) 6. D.F.EVANS, J.Chem. Soc., 2003 (1959)
0020-1650/80/1201-0563502.00/0
EFFECT OF TEMPERATURE AND TIME ON THE STABILITY OF NITROSYL COBALT COMPLEXES WITH AMINO ACIDS B.Jeiowska-Trzebiatowska, Institute
K.Gerega,
G.Formicka-Koz~owska
of Chemistry, University of Wroc~aw, 50-383 vVroc~aw, Poland
Joliot-Curie
14,
(Received 23 March 1980; in revised form l! September 1980)
It is well known that both time and temperature
are factors which
influence considerably the equilibrium of the oxygen binding of cobalt compounds
(I-3). We have now investigated
the effect of these factors
on the effectiveness of nitric oxide binding by similar cobalt complexes with amino acids. In our previous paper (4), the results of studies of the equilibria existing in solution between the active c o b a l t ~ t
com-
plex and the cobalt complex with bonded nitric oxide were presented, and the effect of metal environment was determined.
The equilibria we
are concerned with are as follows:
[Co(II)(Amac)2(H20)n ] + NO=[go~II)(Amac)sN0(H20)n_1 ] + H20 , n:I,2
(I)
[Co(II)(Amam)2(Himid)(H20)]
(2)
+ N0~o(III)(Amam)2(Himid)N0
] + H20
where Amac = amino acid and Himid is imidazole. In the present work the effect of temperature and time on the equilibria (I and 2) existing in aqueous solution is reported. EXPERIMENTAL The synthesis of the cobalt complexes with amino acids with and withour imidazole have been described previously (2,4,5). amino acids were used: glycine (Gly),
alanine (Ala),
The following
ornithine
(Orn),
threonine (Thr)(supplied by E.Merck). The magnetic
susceptibility of the solutions were measured in 2 %
t-butanol in D20 by the method described by Evans (6> at 6,20,40 and 60°C using a JEOL JNM-PS-IO0 nmr spectrometer. the stabilities
The effect of time on
of the nitrosyl cobalt complexes was investigated at
22 + 1°C. Electronic
spectroscopic measurements
in the visible and near infra-
-red range were carried out using a Cary-14 spectrophotometer temperature at cobalt concentrations The magnetic
at room
of 3.8 x I0-2M.
susceptibility of the isolated solid complex was measu-
red by the Gouy method between 80 and 3OO K. Magnetic susceptibilities in the 4 to 60 K range were measured using a Foner magnetometer.
563
564
The Stability of Nitrosyl Cobalt Complexes RESULTS AND DISCUSSION
The results of magnetic susceptibility measurements on solutions containing cobalt, imidazole, amino acid and NO at time intervals from 0 to 48 hours are summarized in Table 1. TABLE I Magnetic Moments and Abundances of Co D 0 and Co ~ I II) Complexes for Solutions with Added Imidazole, in Which the Equilibrium of the NO Binding was Reached (see reaction 2) Measured at Different Times.
Amac
Time
[BM]
Gly pH 8.16
0 lh 24h 48h
3.27 3.32 4.02 4.23
62 63 77 81
38 37 23 19
Ala pH 8.50
0 lh 24h 48h
3.90 3.92 3.83 3.70
74 75 73 70
26 25 27 30
Orn pH 9.07
0 24h 48h
2.03 3.40 3.60
39 65 69
61 35 31
Magnetic susceptibilities for similar systems without imidazole obtained after various time intervals are summarized in Table 2. Our results show that solutions containing alanine, whether with or without added imidazo. le, are stable for up to about 48 hours because the magnetic moments do not show any significant change. On the other hand, a change in temperature from 6 to 60°C increases the magnetic moment of the solution very slightly (Tables 3 and 4). This shows that there is a small shift in the equilibria to the left (equations I and 2) and is entirely consistent with the expected dissociation of the cobalt-NO bond with increase in temperature. At higher temperatures, a pink precipitate is formed and further investigations were not carried out. After about a week at room temperature, the cobalt-NO solution without imldazole decomposes and the same pink precipitate is formed. The solid was diamagnetic and the pink colour suggested a slx-coordinate Co(III) complex. The complex contained no NO and elemental analysis was consistent with the formulation C o ~ l a ) 3"2H20. (Cal&: C, 30.09; N, 11.70; H, 5.05, Found: C, 29.86; N, 11.60; H, 5.13 %).
The Stability of Nitrosyl Cobalt Complexes
565
TABLE 2 ~agnetic Moments and Abundances of Co(ll) and Co(Ill) Complexes for Solutions without Imidazole, in which the Equilibrium of Reaction (I) was Reached
Amac Gly pH 10.00
Time
%~ [BM]
CO (II)
Co(Ill)
0
4.22
80
20
lh
4.51
86
14
24h
4.53
87
13
%
'/o
Ala
O
3.69
70
30
pH 10.64
lh
3.71
71
20
24h
3.82
73
27
0
0
0
100
0.64 1.15
13 22
87 78
1.34
25
75
2.16
41
59
Orn pH 11.20
10 min 30 min 1.5h 24h
Thr pH 11.82
0
100
15 min lh
0
0.98 1.14
0
19 22
81 78
24h
1.60
30
70
In glycine containing solutions, equilibrium was reached much more slowly as judged by the magnetic susceptibility measurements. brium eventually lies more to the left ( C o ~
The equili-
than with alanine conta-
ining solutions whether imidazole was present or not. Even so, a significant amount of the cobalt nitrosyl complex was present at equilibrium about 19 and 13 ~ for the systems with and without added imidazole respectively). Ornithine containing solutions behaved quite differently. They readily absorbed NO and in the system with no added imidazole, equilibrium lies fully to the right ( C o ( I I 0 - N O ) and the solution was diamagnetic. These solutions, however, rapidly decompose, with 22 ~ C o , I )
being formed
within 30 min in solutions without added imidazole. Similar behaviour and instability is found with the threonine system, but the rate of decomposition slows down after 24 hours and suggests an equilibrium substantially to the right.
566
The Stability of Nitrosyl Cobalt Complexes
TABLE 3 Temperature Dependence of Magnetic Moments and Abundances of Co[II) and Co ~ I ~ ~omplexes at pH 8".5 for ~o~II)[Ala)2(Himid)NO] System. Temp
//
Co (If)
Co (III)
Temperature Moments and and qo(II~ for [Co (II~ Temp
TABLE 4 Dependence of Magnetic Abundances of Co(l~ Complexe~ at.pH 10.64 (Ala)2NO[H20)JSystem.
~
Co (II)
°c
IBM]
%
%
°C
IBM]
%
6
4.01 4.20 4.36 4.31
76 80 83 82
24 20 17 18
6 20 40 60
3.71 3.93 4.11 3.99
71 75 78 76
20 40 60
Co (III)
29 25 22 24
In all these cases there is a significant amount of Co ~II)-NO complex is solutions at room temperature varying from as low as 20 W to 100 %. In the case of alanine, the decrease in Co(Ill)-NO complex present as the temperature is raised from 6 to 20°C is very small (about 4 %)and does not decrease much more even up to 60°C. These results show that the Co~II)-NO systems are relatively much more stable than the corresponding systems with oxygen which are particularly unstable above 2°C. ACKNOWLEDGEMENT The authors wish to thank Dr J.B.Raynor (Leicester University, for help during the preparation of this manuscript.
U.K.)
REFERENCES I. M.J.CARTER, D.P.RILLEMA and F.BASOLO, J.Am. Chem.Soc., 96, 392 (1974) 2. B.JEZOW~KA-TRZEBIATOWSKA, A.VOGT, H.KOZLOWSKI and A.JEZIERSKI, Bull.Acad.Polon.Sci.,ser.sci.chim., 20, 187 (1972) 3. R.D. JONES, D.A.SU~ERVILLE and F.BASOLO, Chem.Rev., 79, 139 (1979) 4. B.JEZOWSKA-TRZEBIATOWSKA, K.GEREGA and G.FORMICKA-KOZLOWSKA, Inorg.Chim.Acta, 40, 187 (1980) 5. B. JEZOWSKA-TRZEBIATOWSKA, K.GEREGA and A.VOGT, Inorg.Chim.Acta, 31, 183 (1978) 6. D.F.EVANS, J.Chem. Soc., 2003 (1959)