A thermochemical study of the solid-state coordination reactions of two α-amino acids with copper(II) acetate

Article abstract of DOI:10.1016/S0040-6031(01)00831-0

The two solid-state coordination reactions CuAc₂·H₂O(s) + 2Ala(s) → trans-Cu(Ala)₂(s) + 2HAc(1) + H₂O(1) (1) CuAc₂·H₂O(s) + 2Gly(s) → trans-Cu(Gly)₂·H₂O(s) + 2HAc(1) (2) have been studied by solution calorimetry. The molar dissolution enthalpies of the reactants and the products in some solvents (such as 2 mol 1^-1 HCl or its solutions) of these solid-solid coordination reactions have been measured by an isoperibol solution calorimeter. The standard molar formation enthalpies of [trans-Cu(Ala)₂(s), 298.15 K] and [trans-Cu(Gly)₂(s), 298.15 K] have been determined to be - 1015.42 ± 0.06 and 1252.36 ± 0.05 kJ mol^-1, respectively, from the results of the molar dissolution enthalpies and other auxiliary thermodynamic data.

Full text of DOI:10.1016/S0040-6031(01)00831-0

Thermochimica Acta 387 (2002) 115–119
A thermochemical study of the solid-state coordination reactions
of two a-amino acids with copper(II) acetate
You-Ying Dia,b, Song-Sheng Qua,*, Yi Liua, De-Cai Wena,
Hou-Kuan Tanga, Lin-Wei Lia
aCollege of Chemistry and Molecular Science, Wuhan University, Wuhan 430072, PR China
bDepartment of Applied Chemistry, College of Science, Xi’an Jiaotong University, Xi’an 710049, PR China
Received 20 December 2000; received in revised form 15 October 2001; accepted 24 October 2001
Abstract
The two solid-state coordination reactions
CuAc2 ꢂ H2OðsÞ þ 2AlaðsÞ ! trans-CuðAlaÞ2ðsÞ þ 2HAcðlÞ þ H2OðlÞ
CuAc2 ꢂ H2OðsÞ þ 2GlyðsÞ ! trans-CuðGlyÞ2 ꢂ H2OðsÞ þ 2HAcðlÞ
(1)
(2)
have been studied by solution calorimetry. The molar dissolution enthalpies of the reactants and the products in some solvents
(such as 2 mol lꢀ1 HCl or its solutions) of these solid–solid coordination reactions have been measured by an isoperibol
solution calorimeter. The standard molar formation enthalpies of [trans-Cu(Ala)2(s), 298.15 K] and [trans-Cu(Gly)2(s),
298.15 K] have been determined to be ꢀ1015.42 ꢁ 0.06 and 1252.36 ꢁ 0.05 kJ molꢀ1, respectively, from the results of the
molar dissolution enthalpies and other auxiliary thermodynamic data. # 2002 Elsevier Science B.V. All rights reserved.
Keywords: Copper(II) acetate; Glycine; Alanine; Isoperibol solution calorimetry; Standard molar formation enthalpy
1. Introduction
complex of a-amino acids with copper(II) is one of the
complexes with cis- and trans-geometric isomers,
which has extensive application in food, cosmetics
and medicines as a nutrient.
Solid-state chemical synthesis is an important and
promising method in the field of synthetic chemistry.
The method [1] has been widely used to synthesize
various solid-state coordination compounds of many
metal salts with a-amino acids because it avoids
complicated experimental operations and harsh reac-
tion conditions. It is well-known that a-amino acids
are basic structural units which constitute the proteins
and copper(II) is one of the trace elements necessary
for the human body. It was early established that the
In 1993, Zheng and Xin [2] synthesized a series of
complexes (including trans-Cu(Ala)2(s), trans-
Cu(Gly)2ꢂH2O(s) and others) by means of solid-state
coordination reactions of copper(II) acetate with a-
amino acids at ambient temperature. XRD, IR, DTA
and elemental analysis were employed to characterize
their structures. However, up till now, the enthalpies
of solid-state coordination reactions involved in the
syntheses of these complexes and their respective
standard molar formation enthalpy have not been
reported in literature. The purpose of the present study
* Corresponding author. Fax: þ86-27-876-47617.
E-mail address: ipc@whu.edu.cn (S.-S. Qu).
0040-6031/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 4 0 - 6 0 3 1 ( 0 1 ) 0 0 8 3 1 - 0

116
Y.-Y. Di et al. / Thermochimica Acta 387 (2002) 115–119
is to determine the dissolution enthalpies of the reac-
tants and the products of two solid-state coordination
reactions of copper(II) acetate with a-alanine and
a-glycine, respectively, by isoperibol solution calori-
metry. In addition, the standard molar formation
enthalpies of the products [trans-Cu(Ala)2(s) and
trans-Cu(Gly)2ꢂH2O(s)] of the two solid-state coordi-
nation reactions were derived from the respective
dissolution enthalpies.
and liquid–liquid reactions [3,4]. The volume of the
reaction vessel was 100 cm3. The precisions of con-
trolling and measuring the temperature were ꢁ0.001
and ꢁ0.0001 K, respectively.
The reliability of the calorimeter was confirmed by
measuring the dissolution enthalpies of THAM (NBS
742a, USA) in 0.1 mol lꢀ1 HCl and KCl (calorimetric
primary standard) in twice distilled water at 298.15 K.
The mean dissolution enthalpies are ꢀ29 776 ꢁ
16 J molꢀ1 for THAM and 17 597 ꢁ 17 J molꢀ1 for
KCl, which are well in conformity with the correspond-
ing published data [5,6], ꢀ29 766 ꢁ 31.5 J molꢀ1 for
THAM and 17 536 ꢁ 9 J molꢀ1 for KCl.
2. Experimental
2.1. Chemicals
Copper(II) acetate [Cu(Ac)2ꢂH2O(s)], alanine(s),
glycine(s) and other reagents used in these experi-
ments were of analytical grade and obtained from
Shanghai Reagent Factory. KCl(s) used for calibration
of the isoperibol solution calorimeter was of a purity
greater than 99.99%, and dried in a vacuum oven for
6 h at 135–140 8C prior to use. The water used in
measurements was twice distilled.
3. Results and discussion
3.1. The calorimetric solvent
In these experiments, 2 mol lꢀ1 HCl were chosen as
calorimetric solvents for measurements of the dissolu-
tion enthalpies of the reactants and products in the
reactions of Cu(Ac)2ꢂH2O(s) with alanine and with
glycine.
2.2. Sample preparations and characterization
3.2. The determination of enthalpy change for the
solid-state coordination reaction of Cu(Ac)2ꢂH2O(s)
with alanine
The samples used in the present measurements were
prepared according to the method given in the litera-
ture [1,2], in which 5 mmol Cu(Ac)2ꢂH2O(s) of 80–
100 mesh was mixed and ground with certain amount
of alanine and glycine, respectively, in 1:2 mole ratio.
These were retained for 4 h at ambient temperature. If
subsequent XRD measurement showed that the refrac-
tion peaks of the two reactants in the system of every
solid-state coordination reaction have disappeared, the
reactions have been completed. The products were
washed for three times with absolute ethyl alcohol,
and for once with ethyl ether of analytical grade.
Finally, these were placed in a vacuum desiccator at
ambient temperature to vacuum dry for 4 h. Chemical
and element analyses (model: PE-2400, Perkin-Elmer,
USA) have shown that the purity of the samples
prepared were higher than 99.98 mol%.
Of about 0.31 g sample of Cu(Ac)2(s) and Ala(s)
mixture at mole ratio of n(trans-Cu(Ala)2)/nðAlaÞ ¼
1:2 were dissolved in 100 ml of 2 mol lꢀ1 HCl at
298.15 K.
If ‘s’ ¼ calorimetric solvent of 2 mol lꢀ1 HCl, then,
fCuðAcÞ2 ꢂ H2OðsÞ þ 2AlaðsÞg þ ‘s’ ¼ solution A
The dissolution enthalpies of HAc(aq) [n(HAc)/
nðH2OÞ ¼ 2:1] in 100 ml of 2 mol lꢀ1 HCl were
measured under the same condition
2:1 HAcðaqÞ þ ‘s’ ¼ solution B
The dissolution enthalpies of trans-Cu(Ala)2(s) in
solution B were measured under the same condition
as the above.
2.3. Calorimeter and calibration
trans-CuðAlaÞ2ðsÞ þ solution B ¼ solution A1
The measurement results of dissolution enthalpies for
the reactants and products of reaction (1) are listed in
The isoperibol solution calorimeter used was
adapted for measuring enthalpies of solid–liquid

Y.-Y. Di et al. / Thermochimica Acta 387 (2002) 115–119
117
Table 1
Dissolution enthalpies of [Cu(Ac)2ꢂH2OðsÞ þ 2Ala(s)] and [2:1 HAc(aq)] in 2 mol lꢀ1 HCl and [trans-Cu(Ala)2(s)] in 2:1 HAc(aq) at
298.15 Ka
System
Solvent
Number
m (g)
DEe (mV)
DEs (mV)
Qe (J)
Qs (J)
DSHmY
(kJ molꢀ1
)
DSHmY [Cu(Ac)2ꢂH2O(s) þ 2Ala(s)] ¼ 8.10 ꢁ 0.04 kJ molꢀ1
Cu(Ac)2ꢂH2O(s)
þ 2Ala(s)
2 mol lꢀ1 HCl
1
2
3
4
5
0.3145
0.3141
0.3159
0.3132
0.3122
1.25
1.15
1.14
1.16
1.15
1.60
1.57
1.61
1.57
1.60
5.280
4.840
4.845
4.959
4.862
6.758
8.113
7.955
8.176
8.092
8.181
6.610
6.843
6.712
6.765
DSHmY [2:1 HAc(aq)] ¼ ꢀ 1.36 ꢁ 0.01 kJ molꢀ1
2:1 HAc(aq)
2 mol lꢀ1 HCl
1
2
3
4
5
0.4062
0.4114
0.4063
0.4001
0.4063
1.87
1.68
1.83
1.64
1.73
1.67
1.74
1.76
1.71
1.73
7.732
6.846
7.331
7.057
7.149
ꢀ6.905
ꢀ7.091
ꢀ7.331
ꢀ7.057
ꢀ7.149
ꢀ1.327
ꢀ1.346
ꢀ1.405
ꢀ1.337
ꢀ1.374
DSHmY [trans-Cu(Ala)2(s)] ¼ ꢀ 37.81 ꢁ 0.04 kJ molꢀ1
Trans-Cu(Ala)2(s) 2:1 HAc(aq)
1
2
3
4
5
0.1986
0.1016
0.0981
0.0962
0.0985
6.49
2.55
3.21
3.38
3.36
7.49
3.86
3.68
3.65
3.70
27.168
10.612
14.495
14.167
14.098
ꢀ31.377
ꢀ16.064
ꢀ15.425
ꢀ15.173
ꢀ15.521
ꢀ37.873
ꢀ37.901
ꢀ37.693
ꢀ37.808
ꢀ37.774
þ 2 mol lꢀ1 HCl
a R ¼ 1666:0 O, I ¼ 10:000 mA; m is mass of sample (g); DEe, the voltage change during the electrical calibration (mV); DEs, the voltage
change during the sample dissolution (mV); Qe electrical energy of electrical calibration (J); Qs heat effect (J); DSHmY ¼ ðDEs=DEeÞI2RteðM=mÞ,
where R is the electro-resistance; I, the electrical current; M, the molar mass; te, heating period of electrical calibration.
Table 1. In addition, the enthalpy change of mixing
HAc(l) with H2O(l) in the mole ratio of n(HAc)/
nðH2OÞ ¼ 2:1 can be obtained from literature [7]:
DdHmY ¼ ꢀ3:58 kJ molꢀ1. The enthalpy change of
the solid-state coordination reaction (1) can be calcu-
lated in accordance with a thermochemical cycle and
the experimental results as follows:
not include the enthalpy change of mixing HAc(l) with
H2O(l) in the mole ratio of n(HAc)/nðH2OÞ ¼ 2:1.
The measurement results of dissolution enthalpies
for the reactants and products of the reaction (2) are
listed in Table 2. The enthalpy change of the solid-
state coordination reaction (2) can be also calculated
according to a thermochemical cycle and the experi-
mental results as follows:
DrHmð1Þ ¼ DsHmY½CuðAcÞ2 ꢂ H2OðsÞ þ 2Alaðsފ
ꢀ DsHmY½2:1 HAcðaqފ
DrHmð2Þ ¼ DsHmY½CuðAcÞ2 ꢂ H2OðsÞ þ 2Glyðsފ
ꢀ 2DsHmY½HAcðlފ
ꢀ DsHmY½trans-CuðAlaÞ2ðsފ ꢀ DdHmY
ꢀ DsHmY½trans-CuðGlyÞ2 ꢂ H2Oðsފ
¼ 50:85 ꢁ 0:06 kJ molꢀ1
:
¼ 29:99 ꢁ 0:05 kJ molꢀ1
:
3.3. The determination of enthalpy change of the
solid-state coordination reaction of Cu(Ac)2ꢂH2O(s)
with glycine
3.4. The standard molar formation enthalpies
of trans-Cu(Ala)2(s) and trans-Cu(Gly)2ꢂH2O(s)
The determination of the enthalpy change of the
reaction (2) was similar to that of the reaction (1)
described in Section 3.2 except that [2:1HAcðaqÞþ
‘s’ ¼ solution B] was replaced by [HAcðlÞ þ ‘s’ ¼
solution B]. The enthalpy change of reaction (2) did
The two reaction schemes are used to derive
the standard molar formation enthalpies of trans-
Cu(Ala)2(s) and trans-Cu(Gly)2ꢂH2O(s) are given in
Tables 3 and 4, respectively. The experimental values
of the dissolution enthalpies of the reactants and

118
Y.-Y. Di et al. / Thermochimica Acta 387 (2002) 115–119
Table 2
Dissolution enthalpies of [Cu(Ac)2ꢂH2O(s) þ 2Gly(s)] and [HAc(l)] in 2 mol lꢀ1 HCl and [trans-Cu(Ala)2(s)] in [HAc(l) þ 2 mol lꢀ1 HCl] at
298.15 Ka
System
Solvent
Number
m (g)
DEe (mV)
DEs (mV)
Qe (J)
Qs (J)
DSHmY
(kJ molꢀ1
)
DSHmY [Cu(Ac)2ꢂH2O(s) þ 2Gly(s)] ¼ 13.59 ꢁ 0.03 kJ molꢀ1
Cu(Ac)2ꢂH2O(s)
þ 2Gly (s)
2 mol lꢀ1 HCl
1
0.3269
2.78
2.77
12.804
12.758 13.657
2
3
4
5
0.3303
0.3324
0.3337
0.3289
2.78
2.53
2.76
2.96
2.82
2.77
2.86
2.84
12.726
11.464
12.447
13.298
12.909 13.672
12.552 13.524
12.898 13.518
12.759 13.564
DSHmY [HAc(l)] ¼ ꢀ 0.93 ꢁ 0.03 kJ molꢀ1
HAc(l)
2 mol lꢀ1 HCl
1
2
3
4
5
0.2052
0.3060
0.3064
0.3114
0.3056
1.00
1.19
1.05
1.02
0.96
1.70
1.06
1.06
1.11
1.04
4.508
5.292
4.696
4.541
4.287
ꢀ3.156 ꢀ0.925
ꢀ4.714 ꢀ0.925
ꢀ4.741 ꢀ0.929
ꢀ4.942 ꢀ0.953
ꢀ4.644 ꢀ0.913
DSHmY [trans-Cu(Gly)2ꢂH2O(s)] ¼ ꢀ 14.64 ꢁ 0.02 kJ molꢀ1
trans-Cu(Gly)2ꢂH2O(s)
HAc(l) þ 2 mol lꢀ1 HCl
1
2
3
4
5
0.2194
0.2181
0.2057
0.2069
0.2058
3.13
3.12
2.85
2.84
2.83
3.09
3.07
2.55
2.69
2.82
13.830 ꢀ14.009 ꢀ14.665
13.660 ꢀ13.883 ꢀ14.619
11.736 ꢀ13.117 ꢀ14.646
12.531 ꢀ13.230 ꢀ14.686
13.073 ꢀ13.027 ꢀ14.590
a R ¼ 1666:0 O, I ¼ 10:000 mA.
products in the two solid-state coordination reactions
(1) and (2) were combined with auxiliary thermo-
dynamic data of DfHmY½H2Oðlފ ¼ ꢀ285:83 ꢁ 0:04
kJ molꢀ1 [9], DfHmy ½CuðAcÞ2 ꢂ H2Oðsފ ¼ ꢀ1193:70
kJ molꢀ1 [8], DfHmY½HAcðlފ ¼ ꢀ484:131 kJ molꢀ1
[9], DfHmY½Alaðsފ ¼ ꢀ563:33 ꢁ 0:60 kJ molꢀ1 [10]
and DfHmY½Glyðsފ ¼ ꢀ528:5 ꢁ 0:5 kJ molꢀ1 [10] to
derive the standard molar formation enthalpies of
trans-Cu(Ala)2(s) and trans-Cu(Gly)2ꢂH2O(s)
DfHmY½trans-CuðAlaÞ2 ðsފ
¼ DrHm ð1Þ ꢀ 2DSHmY½HAc ðlފ ꢀ DSHmY½H2O ðlފ
þ DSHmY½CuðAcÞ2 ꢂ H2O ðsފ þ 2DSHY½Ala ðsފ
¼ DH9 ¼ DH1 ꢀ DH2 ꢀ DH3 ꢀ DH4 ꢀm2DH5 ꢀ DH6
þ DH7 þ 2DH8 ¼ ꢀ1015:42 ꢁ 1:20 kJ molꢀ1
:
Table 3
Reaction scheme used to determine the standard molar formation enthalpy of the complex Cu(Ala)2(s) at 298.15 Ka
Number
Reactions
Solution
A
DfHmY or DSHmY ꢁ sÃa (kJ molꢀ1
)
1
2
3
4
5
6
7
8
9
fCuðAcÞ ꢂ H2OðsÞ þ 2AlaðsÞg þ ‘s’
2HAcðlÞ 2þ H2OðlÞ ¼ 2 : 1 HAc(aq)
2:1 HAcðaqÞ þ ‘s’
8.10 ꢁ 0.04
ꢀ3.579b
B
ꢀ1.36 ꢁ 0.01
ꢀ37.81 ꢁ 0.04
ꢀ484.131
Cu(Ala)2ðsÞ þ ‘B’
A1
2H2ðgÞ þ O2ðgÞ þ 2CðsÞ ¼ HAc(l)
H2ðgÞ þ ð1=2ÞO2ðgÞ ¼ H2O(l)
ꢀ285.380 ꢁ 0.042
ꢀ1193.695
CuðsÞ þ 4H2ðgÞ þ ð5=2ÞO2ðgÞ þ 4CðsÞ ¼ Cu(Ac)2ꢂH2O(s)
3CðsÞ þ ð7=2ÞH2ðgÞ þ O2ðgÞ þ ð1=2ÞN2ðgÞ ¼ Ala(s)
CuðsÞ þ N2ðgÞ þ 7H2ðgÞ þ 2O2ðgÞ þ 6CðsÞ ¼ CuðAlaÞ2(s)
ꢀ563.33 ꢁ 0.6
ꢀ1015.421
a The solvent ‘s’ is 2 mol lꢀ1 HCl.
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
P5
measurements; x, the mean value of a set of measurement results.
2
b According to [7] sÃa ¼
i¼1ðxi ꢀ xÞ =nðn ꢀ 1Þ, in which n is the experimental number; xi, a single value in a set of dissolution

Y.-Y. Di et al. / Thermochimica Acta 387 (2002) 115–119
119
Table 4
Reaction scheme used to determine the standard molar formation enthalpy of the complex Cu(Gly)2ꢂH2O(s) at 298.15 Ka
Number
Reactions
Solution
DfHmY or DSHmY ꢁ sÃa (kJ molꢀ1
)
1
2
3
4
5
6
7
fCuðAcÞ ꢂ H2OðsÞ þ 2GlyðsÞg þ ‘s’
A0
B0
A10
13.59 ꢁ 0.03
ꢀ0.93 ꢁ 0.03
ꢀ14.64 ꢁ 0.02
ꢀ484.131
2HAcðlÞ 2þ ‘s’
Cu(Gly)2ꢂH2OðsÞ þ ‘B’
2H2ðgÞ þ O2ðgÞ þ 2CðsÞ ¼ HAc(l)
CuðsÞ þ 4H2ðgÞ þ ð5=2ÞO2ðgÞ þ 4CðsÞ ¼ Cu(Ac)2ꢂH2O(s)
2CðsÞ þ ð5=2ÞH2ðgÞ þ O2ðgÞ þ ð1=2ÞN2ðgÞ ¼ Gly(s)
CuðsÞ þ N2ðgÞ þ 6H2ðgÞ þ ð5=2ÞO2ðgÞ þ 4CðsÞ ¼ trans-Cu(Gly)2ꢂH2O(s)
ꢀ1193.695
ꢀ528.5 ꢁ 0.5
ꢀ1252.363
a The solvent ‘s’ is 2 mol lꢀ1 HCl.
in which DH1 ꢃ DH9 are the enthalpy changes of the
reactions corresponding to the number of reaction in
Table 3.
Acknowledgements
This work was supported by the National Science
Foundation of China.
DfHmY½trans-CuðGlyÞ2 ꢂ H2O ðsފ
References
¼ DrHmð2Þ ꢀ 2DSHmY½HAc ðlފ þ 2DSHmY½Gly ðsފ
þ DSHmY½CuðAcÞ2 ꢂ H2O ðsފ ¼ DH70
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two solid-state coordination reactions can be easily
dissolved in the corresponding solvent. Solution A and
solution A0 are in thermodynamic equivalent states to
solution A1 and solution A01, respectively, which has
been verified by UV spectroscopy and the data of the
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[8] D.R. Frederick, D.W. Donald, H.E. William, et al., Selected
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