The interaction of Cu2 + ions and NaDC micelles.

Article abstract of DOI:10.1016/S1386-1425(01)00601-1

By mixing an aqueous solution of CuCl2 with an NaDC aqueous solution of various concentration and initial molar ratio, seven coordinated samples with distinct appearances and characters were obtained. Their structures and components were investigated by FT-IR spectroscopy, EXAFS (the extended X-ray absorption fine structure), thermal analysis, X-ray diffraction, laser light scattering, TEM (transmission electron micrograph), element analysis and ICP (inductively coupled plasma) analysis. The following conclusions were given: (1) The complexes of Cu2+-NaDC with distinct appearances and properties were synthesized. (2) After Cu(DC)2 dissolved in NaDC aqueous solution, larger micelles (30-90 nm diameter) formed in the supernate, it is a mixed micelle with Cu(DC)2 and NaDC. So these micelles are a new kind of micelle containing two kinds of metal ions. This is a new result using metal ions as bridges to form micelle. (3) According to the different concentration of Cu2+ to NaDC, the complexes formed as gel or poly-crystals. Both the composition of gel complexes and the coordination structure of carboxyl groups with metal ions varied with the initial molar ratio of Cu2+ to Na+. The gel complexes exhibits the non-stoichiometric character. (4) These results are in agreement with physiological condition. All the different states such as gel, precipitate, micelles of various structures are present in bile of gallbladder. We can suggest an ideal model of the interaction between Cu2+ and bile salts in vivo.

Full text of DOI:10.1016/S1386-1425(01)00601-1

Spectrochimica Acta Part A 58 (2002) 1489–1498
www.elsevier.com/locate/saa
The interaction of Cu2+ ions and NaDC micelles
Y. Sun a, Z-L. Yang a, L. Zhang a, T-D. Hu b, R.D. Soloway c, S-F. Weng a,
J-G. Wu a,*
a Department of Chemistry, Peking Uni6ersity, Beijing100871, People’s Republic of China
b Institute of High Energy Physics, Acadenia Sinica, Beijing100089, People’s Republic of China
c Di6ision of Gastroenterology, Department of Internal Medicine, The Uni6ersity of Texas Medical Branch, Gal6eston,
TX 77555-0764, USA
Received 18 June 2001; accepted 30 July 2001
Abstract
By mixing an aqueous solution of CuCl2 with an NaDC aqueous solution of various concentration and initial
molar ratio, seven coordinated samples with distinct appearances and characters were obtained. Their structures and
components were investigated by FT-IR spectroscopy, EXAFS (the extended X-ray absorption fine structure),
thermal analysis, X-ray diffraction, laser light scattering, TEM (transmission electron micrograph), element analysis
and ICP (inductively coupled plasma) analysis. The following conclusions were given: (1) The complexes of
Cu2+ –NaDC with distinct appearances and properties were synthesized. (2) After Cu(DC)2 dissolved in NaDC
aqueous solution, larger micelles (30–90 nm diameter) formed in the supernate, it is a mixed micelle with Cu(DC)2
and NaDC. So these micelles are a new kind of micelle containing two kinds of metal ions. This is a new result using
metal ions as bridges to form micelle. (3) According to the different concentration of Cu2+ to NaDC, the complexes
formed as gel or poly-crystals. Both the composition of gel complexes and the coordination structure of carboxyl
groups with metal ions varied with the initial molar ratio of Cu2+ to Na+. The gel complexes exhibits the
non-stoichiometric character. (4) These results are in agreement with physiological condition. All the different states
such as gel, precipitate, micelles of various structures are present in bile of gallbladder. We can suggest an ideal model
of the interaction between Cu2+ and bile salts in vivo. © 2002 Elsevier Science B.V. All rights reserved.
Keywords: Copper deoxycholate; Sodium deoxycholate; Steroid; Micelle; Gel; FT-IR spectra
1. Introduction
As the predominant ingredients of bile, bile
Abbre6iations: Cu2+, copper ion; NaDC, sodium deoxy-
cholate; Ca(DC)2, calcium deoxycholate; NaC, sodium
cholate; CuC2, copper cholate.
* Corresponding author. Tel.: +86-10-6275-7951; fax: +
86-10-6275-1708.
salts is one of the most important bio-surfactants
in vivo. In gallbladder, bile salts exist mainly as
simple micelles or mixed micelles formed with
phospholipid and cholesterol. Therefore, extensive
studies have been made on the colloid chemical
E-mail address: wjg@chem.pku.edu.cn (J.-G. Wu).
1386-1425/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S1386-1425(01)00601-1

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Y. Sun et al. / Spectrochimica Acta Part A 58 (2002) 1489–1498
properties of bile salts. The aggregation behavior
of bile salts, such as CMC, micelle size, aggrega-
tion number and model, and micelle formation,
have been studied by the methods of crystal struc-
ture [1], conductance [2], viscosity [2], calorimetry
[2,3], surface tension [4], fluorescence [5,6], NMR
[5], time resolved light scattering and neutron
scattering [6–9], small-angle X-ray scattering [10],
micro-calorimetric titration [11], and mutual dif-
fusion measurements [12]. In order to further
understand the physiological function, the mixed
micelle formation of bile salts with phospholipid,
cholesterol and protein has been investigated [13–
15].
them. Vibrational spectroscopy is a sensitive
probe to detect the interaction of metal ions with
bile salts [26–28]. Therefore, in this work, a series
of Cu deoxycholate complexes were prepared by
varying the concentration of reactants. The coor-
dination of Cu with carboxylic group of deoxy-
cholate was investigated using EXAFS and FT-IR
spectroscopic measurements. Furthermore, with
the results of laser light scattering and TEM
(transmission electronic micrograph), the possible
mode of interaction of Cu2+ ion with deoxy-
cholate in aqueous solution was discussed.
The addition of divalent metal ions can effect
the size of simple and mixed micelles and the
transition of mixed micelle to vesicle, in which the
interaction of divalent metal ions with bile salts
plays an important role [16–20]. Copper is a
minor but important component of black-pigment
gallstone, and it has been proposed that copper
bilirubinate acts as a free-radical scavenger in bile,
protecting phospholipids from peroxidation [17].
As one of main metal ions existing in bile, copper
ion involves binding to bile salts or bile salts
micelles [16,19]. So the nature of Cu2+ coordinat-
ing to bile salts or bile salts micelles may play an
important role in the mechanism of black-pigment
gallstone formation. Progress in understanding
how bile salts interact with metal ions in solution
[21–25] depends on knowledge of their coordina-
tion with metal ions. However, few crystal struc-
ture of divalent metal bile salts has been provided
because it is difficult to obtain the single crystal of
2. Experiments
2.1. Materials
Sodium deoxycholate (NaDC) was obtained
from Serve Company and dissolved in ethanol,
filtered, and recrystallized. All other regents used
were of analytical grade.
2.2. Preparation and characterization of Cu
deoxycholate complexes
In our previous work, both of crystalline and
gel state of complexes were obtained by reaction
of Cu2+ ion with Na deoxycholate in aqueous
solution (Table 1). When the concentration of
NaDC was near or below CMC (0.01 M), or the
concentration of NaDC was upon CMC (0.1 M)
and at the same time the concentration of CuCl2
was higher (1 M), the resultant precipitates exhib-
Table 1
Reactants and resultants of deoxycholate complexes synthesis
Synthesis
Final concentration of NaDC
Final concentration of CuCl2
Initial molar ratio
Resultant state
(mol l−1
)
(mol l−1
)
(Cu2+:Na+
)
Sample 1
Sample 2
Sample 3
Sample 4
Sample 5
Sample 6
Sample 7
Sample 8
0.1
0.01
0.1
0.1
0.1
0.1
0.1
0.1
0.5
0.1
0.1
0.1
0.1
0.1
0.1
0.1
1:2
1:2
5:1
2:1
1:1
1:2
1:3
1:4
Crystalline
Crystalline
Gel
Gel
Gel
Gel
Gel
Gel

Y. Sun et al. / Spectrochimica Acta Part A 58 (2002) 1489–1498
1491
ited crystalline-state complexes (Table 1). How-
ever, when the concentration of NaDC was upon
CMC (0.1 M), and simultaneously the concentra-
tion of CuCl2 was lower (0.1 M), the resultant
precipitates exhibited gel-state complexes (Table
1). Moreover, the composition of crystalline-state
complexes was regular, but that of gel-state com-
plexes was varied with initial molar ratio of reac-
tants. In this work, a series of complexes were
prepared by the method of changing the concen-
tration and initial molar ratio of CuCl2 and Na
deoxycholate in aqueous solution. CuCl2 aqueous
solution was added into Na deoxycholate aqueous
solution with the concentration and initial molar
ratios showed in Table 1. The precipitates were
filtered off and washed with distilled water several
times to dissolve the CuCl2 and NaDC absorbed.
Then they were stored over silicon-gel drier to be
desiccated naturally.
was stirred using an electromagnetic stirrer for
48 h, with some precipitate present in the mixture.
Then the precipitate was removed from the solu-
tion by centrifugation at 12 000 rpm for 30 min.
The supernate obtained was identified with an
ICP-AES instrument of Leeman Company, and
was examined by laser light scattering at 25 °C,
with the testing angle 90°. The medium viscosity
was 0.8904 cp and the medium refraction index
was 1.33287. The TEM was observed under a
HITACHI H-800 electron microscope after nega-
tive staining (uranyl acetate, pH 6.0), with Mag-
nification ×33 000.
3. Results
3.1. Binding of Cu2+ to deoxycholate (DC) in
crystalline complex
All the complexes obtained above were iden-
tified by elemental analysis with an Elementar
Vario EL instrument and an ICP-AES instrument
of Leeman Company. The EXAFS was under-
taken in Beijing Synchrotron Radiation Facility
(BSRF) station. The spectra were recorded in
transmission mode on X-ray beam line 4WIB with
a ring energy of 2.2 Gev and ring currents be-
tween 40 and 70 mA. The radiation was
monochromatized with a Si(III) double crystal.
The mid FT-IR spectra were measured on a Nico-
let Magna-IR 750 spectrometer using fluorulube-
mull technique with DTGS detector and 32 scans
at 4 cm−1 resolution. The X-ray powder diffrac-
tion diagrams were recorded on a Rigaku D/Max
2400 diffractometer with CuKa radiation (u=
1.5418 nm) and a LiF monochromator, and the
scanning velocity is 4° min−1 and the scanning
range is 5–40°. The differential thermal and ther-
mogravimetric diagrams were recorded on a DT-
40 thermal analyzer of Shimadzu Corporation
with a-Al2O3 reference substance and Pt simple
The element analysis results indicated that
the component of crystalline Cu deoxycholate
complexes (Sample
1 and Sample 2) were
Cu(DC)2 · 5H2O. Fig. 1 showed the results of dif-
ferential thermal and thermogravimetric analysis,
indicating that the loss of weight was 5.59% corre-
sponding to the loss of three H2O molecules at
cell. The calefactive pace is 10° min−1
.
2.3. Cu(DC)2 was dissol6ed in NaDC aqueous
solution and characterization of the supernate
Cu(DC)2 crystalline complex was added into
0.05 M NaDC aqueous solution, and the mixture
Fig. 1. The results of differential thermal and thermogravimet-
ric analysis of crystalline complex.

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Y. Sun et al. / Spectrochimica Acta Part A 58 (2002) 1489–1498
stretching vibration bands (yas) shifted from 1593
to 1607 cm−1, and the COO− symmetry stretch-
ing vibration bands (ys) of it shifted from 1418 to
1408 cm−1. It provided the evidence that the
complex hydrolyzed one H2O molecule at 210 °C
to produce deoxycholic acid and alkaline copper
deoxycholate. When the temperature further in-
creased to 220 °C, the COO− band disappeared,
and the intensity of COOH and OH bands in-
creased. It indicates that the other H2O molecule
hydrolyzed at 220 °C. These results suggested
that two H2O molecules coordinated to Cu2+ and
involved in H-bonding to two COO− groups. The
change of Cu(DC)2 · 5H2O complex with enhance-
ment of temperature occurred as follows:
Cu(DC)2·5H2O13“0°CCu(DC)2·2H2O21“0°CCu(OH)
(DC)·H2O+HDC22“0°CCu(OH)2+2HDC
Fig. 2. The high-temperature FT-IR spectra of crystalline
complex. (a) Crystalline complex at 25 °C; (b) crystalline
complex at 100 °C; (c) crystalline complex at 210 °C; (d)
crystalline complex at 220 °C; (e) HDC.
Occurrence of hydrolysis or dehydration of a
metal carboxylate complex under high tempera-
ture related to intensity of the binding of H2O
molecule to metal ion and H-bonding of H2O
molecule to COO−. Therefore, the results pro-
posed that only two of five H2O molecules coordi-
nated with Cu2+ and simultaneously involved in
H-bonding with COO− of deoxycholate.
lower than 130 °C. In addition, at 210 and
220 °C the complex absorbed heat but did not
lose weight.
In order to gain further information about
changing of the complex structure with tempera-
ture, the variable temperature FT-IR spectra
showed in Fig. 2 were measured. The results were
listed in Table 2. The FT-IR spectrum of complex
at 130 °C was similar to that at 25 °C. Especially,
the bands corresponding to the asymmetric and
symmetric stretching vibrations of the anion
COO− groups did not change, indicating that
three H2O molecules lost at 130 °C did not coor-
dinate to Cu2+. As the temperature increases to
210 °C, the distinct variation was observed by
comparison with that at 25 °C. Two new bands
of COOH and OH located at 1724 and 3533
cm−1 were observed. The COO− asymmetry
Only one yas COO was observed at 1593 cm−1
−
in FT-IR spectrum of Cu deoxycholate at room
temperature, indicating that two COO− groups in
Cu deoxycholate molecule bound to Cu2+ with
the same mode. The ys COO was at 1418 cm−1
.
−
The Dy was 175 cm−1. Dy of asymmetric and
symmetric stretching vibration (yas−ys) usually
depends on the coordinating mode of COO−
group with metal ion [29]. Dy of monodent mode
is the highest (\200 cm−1), Dy of chelating
mode is the lowest (B100 cm−1), and Dy of the
Table 2
The data of high-temperature FT-IR spectra of copper deoxycholate (cm−1
)
Assignment
COOH
COO−as
CH2
COO−s
Copper deoxycholate at 25 °C
Copper deoxycholate at 130 °C
Copper deoxycholate at 210 °C
Copper deoxycholate at 220 °C
Deoxycholic acid
–
–
1724
1728
1715, 1699
1593
1593
1607
–
1446
1446
1447
1449
1446
1418
1417
1408
–
–
–

Y. Sun et al. / Spectrochimica Acta Part A 58 (2002) 1489–1498
1493
aqueous solution when the concentration of Cu2+
ion was lower and that of NaDC was higher than
its CMC.
Fig. 4 showed a series FT-IR spectra of gel
precipitates (Sample 3–7), and NaDC in solid and
in D2O. Table 3 gave the characteristic frequency
data and their assignments. From Fig. 4, the
FT-IR spectra of gel precipitates varied with the
initial molar ratio of CuCl2 and NaDC, and were
evidently different from that of the crystalline one
showed in Fig. 2.
In OH stretching vibration region (3000–3700
cm−1), the crystalline complex had a series bands
at 3444, 3360, 3338, 3318 cm−1. However, each of
Sample 3–7 had only a broad band at ꢀ3398
cm−1. This suggested that OH group coordinated
with Cu2+ varied.
Fig. 3. (a) The coordination of Na with deoxycholate in NaC
complex; ([30]). (b) The possible coordination of Cu with
deoxycholate in crystalline complex.
In CꢀO stretching vibration region (1400–1800
−
COO
cm−1), crystalline complex has one sharp yas
at 1592 cm−1, and a sharp ys
−
COO
bands at ꢀ1614 and ꢀ1554 cm−1 are observed,
at ꢀ1415
COO−
bridging one is media (100–200 cm−1). Compari-
son with NaC complex (Dy=175 cm−1, and
COO− groups coordinate to Na+ with monodent
mode. Another O atom in COO− group forms
hydrogen band with a H2O molecule, and the O
atom in this H2O molecule coordinates with Na+,
these two COO− groups coordinated with Cu2+
with a mode similar to COO− group in NaC
complex.
cm−1. However, in Sample 3–7 two yas
From the results of EXAFS, it was known that
in the crystalline complex the coordinating num-
ber was 6 and the coordinating atoms were all
oxygen atoms. The shift of OH bands in 3700–
3000 cm−1 region (Fig. 2) suggested that both the
two hydroxyl groups of each deoxycholate anion
bound to Cu2+. However, the two hydroxyl
groups coordinated with the same Cu2+ maybe
come from two different deoxycholate anions.
Based on above results, the possible coordina-
tion of Cu2+ ion with deoxycholate in the crys-
talline complex was suggested as follows (Fig. 3).
3.2. Binding of Cu2+ with the deoxycholate (DC)
in gel complexes
Fig. 4. A series FT-IR spectra of crystalline complex (Sample
1–2), gel precipitates (Sample 3–7), undissolved substance and
NaDC in solid state. (a) Sample 1; (b) Sample 2; (c) Sample 3;
(d) Sample 4; (e) Sample 5; (f) Sample 6; (g) Sample 7; (h)
undissolved substance; (i) NaDC in D2O.
We found that the gel complexes usually ob-
tained by reacting Cu2+ ion with NaDC in

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Y. Sun et al. / Spectrochimica Acta Part A 58 (2002) 1489–1498
Table 3
The characteristic frequency data of FT-IR spectra for gel-like complex and their assignments
OH
CH
COOH
COO−as
COO−s
Sample 1
Sample 2
Sample 3
Sample 4
Sample 5
Sample 6
Sample 7
NaDC (reagent, s)
NaDC (in D2O solution)
3444, 3360, 3378, 3318
3444, 3360, 3378, 3319
2951, 2923, 2855
2951, 2923, 2856
2935, 2863
2936, 2864
2935, 2863
2935, 2863
2934, 2863
2931, 2861
2940, 2868
–
–
1593
1593
1418
1418
1415
1416
1414
1414
1413
1404
1406
3407
3406
3396
3388
3388
3263
3411
1708
1708
1708
1707
1707
–
1613, 1553
1614, 1553
1614, 1554
1614, 1554
1613, 1556
1563
–
1552
and the ys
at ꢀ1415 cm−1 became much
−
COO
broader compared with crystalline complex. From
bands showed
the curve-fitting results of yas
−
COO
in Fig. 5 and Table 4, each of them is composed
of two peaks: one at ꢀ1610 cm−1, the other at
ꢀ1556 cm−1
.
The ICP analysis results of gel complexes given
in Table 5 demonstrated that there was not only
copper but also sodium in gel complex, and with
the increase of CuCl2 to NaDC initial molecular
ratio, the content of copper increased, and that of
sodium decreased. In Fig. 6, the relative intensity
of the peak at ꢀ1610 cm−1 increased with the
increase of the content of copper in gel complex
and that of the peak at ꢀ1556 cm−1 linear
increased with the increase of the content of
sodium. It is suggested that the peak at 1610
cm−1 was corresponded with the yas band of
COO− mainly coordinating with Cu2+, and the
Table 4
The curve-fitting results of yas COO− of gel complexes
Initial
Relative
intensity of
1610 cm−1
band
Relative
intensity of
1556 cm−1
band
molar ratio
(Cu2+:Na+
)
Sample 3
Sample 4
Sample 5
Sample 6
Sample 7
2:1
1:1
1:2
1:3
1:4
0.49
0.46
0.33
0.25
0.23
0.51
0.54
0.67
0.75
0.77
Fig. 5. The curve-fitting results of yas COO− of gel complexes.
(a) Sample 3; (b) Sample 4; (c) Sample 5; (d) Sample 6; (e)
Sample 7.

Y. Sun et al. / Spectrochimica Acta Part A 58 (2002) 1489–1498
1495
Table 5
laser light scattering results which showed that the
diameter of the micelles of the NaDC+Cu2+ was
61.3 nm, while that of NaDC micelle was only
1.2–1.5 nm [6,7]. The addition of Cu2+ strikingly
increased the size of simple NaDC micelles. Cu2+
are attracted to bile salt micelles and change micelle
size through competition and displacement of Na+.
This can be further testified by the TEM. In the
micrograph of NaDC+Cu2+ supernate (Fig. 8),
numerous typical spherical micelles with the diame-
ter of 30–90 nm can be seen. However, in NaDC
aqueous solution, only dot-like micelle with the size
of several nm can be seen. This suggested that Cu2+
can change micelle size by interacting with NaDC
micelle.
ICP analysis results indicated that there was
sodium (Na=1.51%) in the undissolved substance
below the supernate. FT-IR spectra of this dis-
solved substance was similar to that of gel com-
plexes (Fig. 2), and it was demonstrated that
Cu(DC)2–NaDC mixed-micelle settled down to
produce gel complexes.
The ICP analysis results of gel complexes
Initial molar ratio
Cu% Na%
(Cu2+:Na+
)
Sample 1
Sample 2
Sample 3
Sample 4
Sample 5
Sample 6
Sample 7
1:2
1:2
2:1
1:1
1:2
1:3
1:4
7.40
7.40
–
–
4.12 1.58
3.97 1.70
3.57 2.03
3.35 2.27
3.24 2.39
peak at 1556 cm−1 was related to the yas band of
COO− mainly combining with Na+. This was
improved further by the fact that in crystalline
Cu(DC)2 complex COO− yas is at 1592 cm−1 and
in NaDC (in D2O) COO− yas is at 1552 cm−1
.
In CꢁH stretching vibration region (2800–3000
cm−1), the peak shape and position of gel com-
plexes at ꢀ2935 and 2863 cm−1 were much more
similar to that of NaDC in D2O (NaDC exhibits
micelle state in aqueous solution) at 2931 and 2961
cm−1, but more different from that of crystalline
complexes at 2923 and 2855 cm−1. It was suggested
that the deoxycholate in the gel complexes exhibits
NaDC micelle structure.
Based on above results, it was suggested that
Cu2+ reacted with the COO− groups of NaDC
micelles. The DC− micelles connected each other
by ways of Cu2+ bridges to form the gel complexes
with macromolecular structure. All of our experi-
ment results gave supports for the model.
The results of X-ray diffraction analysis showed
in Fig. 7 demonstrated that on comparing with the
crystalline complex, the crystallinity of gel com-
plexes was much lower and the structure of them
varied. The X-ray powder diffraction diagrams of
gel complexes were different from both that of
NaDC and that of Cu(DC)2 crystalline complex.
Comparing NaDC and Cu(DC)2 crystalline com-
plex, they were a new kind of complexes with
distinct structure.
4. Discussion
The present studies have demonstrated the reac-
tion between Cu2+ ions and NaDC that varied
with the concentrations of Cu2+ and NaDC.
We synthesized the complexes of Cu2+ –NaDC
with distinct appearances and properties. Accord-
ing to the different concentration of Cu2+ to
NaDC, the complexes formed as gel or poly-
crystals [1]. When the concentration of NaDC is
below CMC, because NaDC exists as mono-molec-
ular, Cu2+ react with the mono-molecules of
NaDC directly to produce crystalline precipitate.
The component of it is Cu(DC)2 · 5H2O [2]. When
the concentration of NaDC is upon CMC and
the concentration of Cu2+ is higher (at 0.5 or 1 M),
the micelles of NaDC are destroyed completely
by high ionic strength of aqueous solution.
3.3. Analysis of supernate of Cu(DC)2 crystalline
complex dissol6ed in NaDC aqueous solution
The ICP analysis results of the supernate demon-
strated that the concentration of copper and
sodium were 0.0025 and 0.033 mol l−1, respec-
tively. These results gave evidence that Cu2+ could
react with simple NaDC micelles to form mixed
micelles of Cu(DC)2 and NaDC in aqueous solu-
tion. This hypothesis can be further testified by the

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Y. Sun et al. / Spectrochimica Acta Part A 58 (2002) 1489–1498
Fig. 6. (a) The relation of relative intensity of the yas COO− at 1610 cm−1 with the content of copper; (b) the relation of relative
intensity of the yas COO− at 1556 cm−1 with the content of sodium.

Y. Sun et al. / Spectrochimica Acta Part A 58 (2002) 1489–1498
1497
CMC. The component of it is also Cu(DC)2 ·
5H2O. In the two reaction condition above, only
simple Cu(DC)2 · 5H2O complex was formed [3].
When the concentration of NaDC is upon CMC
and the concentration of Cu2+ is lower (at 0.04 M
or more lower), the micelles structure was still
retained. Cu2+ associate with NaDC micelles to
produce gel precipitate. NaDC micelles connect
with each other through the Cu2+ bridges to form
macromolecular structure. Therefore, in this reac-
tion condition, Cu(DC)2–NaDC mixed complexes
formed. In these mixed complexes, the coordina-
tion structure of Na+ varied from that in NaDC
micelle, and the coordination structure of Cu2+
was different from that in Cu(DC)2 crystalline
complex. Furthermore, with the increase of molar
ratio of CuCl2 and NaDC, the copper content
increases and the sodium content decreases in
resultants. So it was a kind of complex with
non-stoichiometric character.
After Cu(DC)2 dissolved in NaDC solution,
large micelles (30–90 nm diameter) formed in the
supernate. These micelles are a new kind of micelle
containing two kinds of metal ions (Cu2+ and
Na+). This is a new result using metal ions as
bridges to form micelles.
Fig. 7. The results of X-ray diffraction analysis. (a) Sodium
deoxycholate; (b) crystalline complex (Sample 1); (c) gel com-
plex (Sample 6).
The concentration of Cu2+ is usually lower than
0.05 M and that of bile salts is upon CMC in
human bile, so the condition in [3] is very similar
to that in human bile. The results in [3] are in
agreement with physiological condition. All the
different states such as gel, precipitate, micelles of
various structures are present in bile of gallblad-
der. We can presume that when the conjugated bile
salts interact with Cu2+, the micelles of them can
also connect with each other through metal ion
bridges to produce mixed micelles with much
bigger size. This can be suggested as an ideal
model of the interaction between divalent metal
ions and bile salts in vivo.
Therefore, Cu2+ react with NaDC molecule to
produce crystalline precipitate, which is similar to
that when the concentration of NaDC is below
Acknowledgements
This work was supported by State Key Project
of Basic Research (G1998061307) and Key Project
(39730160 and 20023005) of National Natural
Science Foundation of China.
Fig. 8. Transmission electron micrograph of the structure of
NaDC–Cu2+ system after negative staining (uranyl acetate,
pH 6.8). Numerous typical mixed-micelles are seen. Magnifica-
tion ×33 000.

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