Crystal structure and chemical oxidation of the palladium(II) cyclam complex within the cavity of cucurbit[8]uril

Article abstract of DOI:10.1016/j.ica.2010.06.031

Inclusion compound of a macrocyclic cavitand cucurbit[8]uril (C ₄₈H₄₈N₃₂O₁₆, CB[8]) with a square-planar palladium(II) complex of a polyamine ligand cyclam, {[Pd(cyclam)]@CB[8]}Cl₂·16H₂O (1), was synthesized and characterized by X-ray crystallography, elemental analysis, IR, and electrospray ionization (ESI) mass spectrometry. The complex [Pd(cyclam)] ²⁺ undergoes chemical oxidation within the CB[8] cavity leading to the formation of the palladium(IV) inclusion compound {trans-[Pd(cyclam)Cl ₂]@CB[8]}Cl₂·14H₂O (2). The Pd(II) and Pd(IV) complexes are completely encapsulated within the CB[8] cavity. The cyclam ring in 1 and 2 adopts the most stable configuration (trans-III (S,S,R,R)).

Full text of DOI:10.1016/j.ica.2010.06.031

Inorganica Chimica Acta 363 (2010) 4387–4391
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Inorganica Chimica Acta
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Crystal structure and chemical oxidation of the palladium(II) cyclam complex
within the cavity of cucurbit[8]uril
*
Tatiana V. Mitkina, Dmitriy Yu. Naumov, Olga A. Gerasko, Vladimir P. Fedin
Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, 3 Akad. Lavrentiev Av., 630090 Novosibirsk, Russian Federation
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 25 June 2010
Inclusion compound of a macrocyclic cavitand cucurbit[8]uril (C48H48N32O16, CB[8]) with a square-planar
palladium(II) complex of a polyamine ligand cyclam, {[Pd(cyclam)]@CB[8]}Cl2Á161 3H2O (1), was synthe-
sized and characterized by X-ray crystallography, elemental analysis, IR, and electrospray ionization
(ESI) mass spectrometry. The complex [Pd(cyclam)]2+ undergoes chemical oxidation within the CB[8] cavity
leading to the formation of the palladium(IV) inclusion compound {trans-[Pd(cyclam)Cl2]@CB[8]}-
Cl2Á14H2O (2). The Pd(II) and Pd(IV) complexes are completely encapsulated within the CB[8] cavity. The
cyclam ring in 1 and 2 adopts the most stable configuration (trans-III (S,S,R,R)).
Dedicated to Prof. A. Müller in recognition of
his creative contributions to Chemistry
Keywords:
Palladium
Cyclam
Ó 2010 Elsevier B.V. All rights reserved.
Cucurbit[n]urils
Host–guest systems
1. Introduction
cavity accessible through two identical carbonyl-fringed portals
(Scheme 1) [14–17]. In contrast to the well-known host–guest
Inclusion compounds of metal complexes into macrocyclic
hosts are known since the investigation of ferrocene encapsulation
into cyclodextrins reported by Breslow in 1975 [1]. The growing
interest to these compounds is essentially caused by the unique
microenvironment provided by the host cavity to a guest metal
complex which is reminiscent of natural enzymes [2,3].
chemistry of cyclodextrins and calixarenes the inclusion chemistry
of metal complexes with CB[n] started to develop in the past decade
since the preparation of larger-cavity cucurbit[n]uril hosts (n > 6).
NMR spectroscopic, calorimetric, and electrochemical data
reveal inclusion compounds of metal complexes into CB[7] and
CB[8] are highly stable [18–22]. Soft-ionization mass spectrometric
techniques are very useful to qualitatively and quantitatively
evaluate host binding selectivity and relative binding constants
of host–guest complexes and it used both to characterize cucur-
bit[n]urils host–guest compounds [23] and to perform their gas-
phase studies [24]. The crystal structures of only few inclusion
compounds have been determined by X-ray diffraction analysis
[19,25–27]. Some interesting and useful properties of host–guest
compounds have been discovered, for example, cucurbit[n]urils
are applied as drug delivery vehicles [4–6,28–31]. The encapsula-
tion of platinum anticancer complexes such as oxaliplatin and mul-
tinuclear amine complexes into CB[7] and CB[8] reduces their high
cytotoxicity in cancer treatment [4–6], and several patents have
been obtained concerning syntheses and antitumor activity of
inclusion compounds of cucurbit[n]urils with platinum, palladium,
and gold complexes [28–31].
Trapping a metal complex inside the cavitand (cyclodextrins,
calixarenes, cucurbiturils) can dramatically alter structural, chem-
ical, and spectroscopic properties of the guest. The reasons for it
are multiple: spatial isolation of guest complex from other species
in solution and in solid state, sterical hindrances caused by partic-
ular shape of the host cavity, different polarity of the cavity in com-
parison with solution polarity, van der Waals, electrostatic and
hydrophobic interactions between the host and the guest etc.
Inclusion of metal complexes into cavitands can stabilize the guest
complex in ‘‘harmful” reaction medium and enhance its solubility
in physiological conditions. There is rapidly developing interest
to the function of macrocyclic host molecules as metal complex
carrier, which is important for drug delivery [4–6]. The other areas,
where inclusion compounds of metal complexes into cavitands can
find or have already found applications, are design of molecular
machines [7,8], enantioselective and size-dependent molecular
separation [9,10], and catalysis [11–13].
Electrochemical studies of inclusion compounds of CB[n] with
some metal complexes (cobaltocene and ferrocene [18,32,33],
copper(II) complex with the tetraazamacrocyclic ligand cyclen
[25], and nickel(II) and cobalt(III) polyamine complexes [34])
demonstrated that electron transfer reactions proceed within
the cavity of the host. It is completely different from the electro-
chemical redox processes of other inclusion compounds (e.g. with
Cucurbit[n]urils (C6nH6nN4nO2n, CB[n]; n = 5–10), macrocyclic
cavitands comprising
n glycoluril units, have a hydrophobic
* Corresponding author. Tel.: +7 (383) 330 9490; fax: +7 (383) 330 9489.
E-mail addresses: cluster@che.nsk.su, cluster@niic.nsc.ru (V.P. Fedin).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.06.031

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T.V. Mitkina et al. / Inorganica Chimica Acta 363 (2010) 4387–4391
(m), 1373 (m), 1317 (m), 1229 (s), 1188 (s), 1153 (w), 1105 (w),
1070 (w), 1026 (w), 968 (m), 829 (m), 806 (s), 758 (m), 671 (m),
629 (w), 443 (w) cmÀ1. Anal. Calc. for C58H104.67Cl2N36O32.33Pd
(2001.08): C, 34.82; H, 5.27; N, 25.20. Found: C, 34.28; H, 5.12;
N, 25.31%. ESI-MS: m/z (%) = 817.3 (100) {[Pd(cyclam)]@CB[8]}2+
.
2.2.2. {trans-[Pd(cyclam)Cl2]@CB[8]}Cl2Á14H2O (2)
The compound 1 (0.030 g, 0.015 mmol) was dissolved in 4 M HCl
(12 mL) upon slight heating. The resulting colorless solution was
cooled, and then NO2 was bubbled through it until the color of
the solution was changed to dark orange-yellow. Slow diffusion of
methanol vapor through the solution within a few days gave yellow
octahedral crystals of 2. They were filtered off, washed with a small
amount of methanol, and dried in air. Yield: 0.015 g (50% based on
Scheme 1.
1). IR (KBr):
m = 3429 (s), 3073 (w), 2959 (w), 2926 (w), 2855 (w),
cyclodextrins) that typically involve free guests escaped from the
cavitands [35,36].
1726 (s), 1647 (w), 1468 (s), 1423 (m), 1373 (m), 1315 (m), 1281
(w), 1228 (s), 1186 (s), 1152 (w), 1124 (m), 1094 (w), 1072 (w),
968 (s), 891 (w), 829 (m), 804 (s), 758 (m), 671 (m), 482 (w), 438
(w) cmÀ1. Anal. Calc. for C58H106Cl4N36O33Pd (2080.55 for n = 17, n
– solvate water molecules): C, 33.45; H, 5.13; N, 24.23; Cl, 6.72.
Found: C, 33.40; H, 5.25; N, 24.20; Cl, 6.76%.
Herein, we report syntheses and crystal structures of new inclu-
sion compounds of the macrocyclic cavitand cucurbit[8]uril with
the palladium(II) and palladium(IV) complexes of the tetraazamac-
rocyclic ligand cyclam, {[Pd(cyclam)]@CB[8]}Cl2Á161 3H2O (1) and
{trans-[Pd(cyclam)Cl2]@CB[8]}Cl2Á14H2O (2). Cyclam (1,4,8,11-tet-
raazacyclotetradecane) is one of the most used macrocyclic poly-
amines and generates continuous interest because of numerous
applications of its complexes in medicine [37]. The reaction of
chemical oxidation of the palladium(II) complex [Pd(cyclam)]2+
encapsulated within the cavity of the CB[8] host to the palla-
dium(IV) complex [Pd(cyclam)Cl2]2+ was realized also. It was
shown that chemical oxidation of the palladium(II) complex
[Pd(cyclam)]2+ to the palladium(IV) complex [Pd(cyclam)Cl2]2+
proceeds within the cavity of the CB[8] host.
2.3. Crystallography
Data collection was performed on a Bruker Nonius X8 Apex dif-
fractometer (Mo Ka, k = 0.71073 Å) equipped with a CCD area
detector (Table 1). The diffraction frames were integrated with
subsequent constrained cell refinement using the SAINT package
and corrected for absorption with SADABS [39]. The structures were
solved by direct methods and refined by full-matrix least-squares
method with SHELXTL packages [39,40]. The positions of hydrogen
atoms of cucurbit[8]uril and cyclam ligand were calculated geo-
metrically and refined using a riding model. The hydrogen atoms
of the water molecules were not located. Water molecules posi-
tions were found by difference electron density and were refined
anisotropically. Chlorine atoms positions were found by the same
way. The atom types were determined from the distance analysis
between them.
2. Experimental
2.1. General
Concentrated aqueous solutions of HCl and NH3 were of com-
mercial quality and used without further purification. Cucur-
bit[8]uril (C48H48N32O16Á20H2O) [17], [Pd(NH3)4]Cl2 [38], and
cyclam@CB[8]Á4HClÁ18H2O [25] were synthesized according to
the procedures published earlier. NO2 was generated by heating
of the mixture of Pb(NO3)2 and some sand at ꢀ220 °C. IR spectra
were recorded using KBr pellets on a Scimitar FTS 2000 spectro-
photometer in the range 4000–400 cmÀ1. Mass spectra (ESI-MS)
were obtained on Quattro LC and QTOF I mass spectrometers
(Micromass, Manchester, UK). Elemental analyses were carried
out by the microanalytical service of the Nikolaev Institute of Inor-
ganic Chemistry SB RAS (Novosibirsk, Russia). The number of water
molecules of crystallization (n) estimated by X-ray diffraction and
elemental analysis can vary for different samples depending on the
experimental conditions and air humidity during storage.
3. Results and discussion
3.1. Synthesis and characterization of
{[Pd(cyclam)]@CB[8]}Cl2Á161 3H2O (1)
Inclusion compound of the palladium(II) complex [Pd(cy-
clam)]2+ into the macrocyclic host cucurbit[8]uril (1) was obtained
according to modified procedure invented by Kim for the synthesis
of similar inclusion compounds of the copper(II) or zinc(II) com-
plexes with cyclen and cyclam [25]. The solution containing the
cucurbit[8]uril inclusion compound of cyclam with the composi-
tion {cyclam@CB[8]}Á4HClÁ18H2O and an excess of [Pd(NH3)4]Cl2
was refluxed during 2 h and subsequently cooled slowly to the
room temperature. Within several days colorless crystals of 1 con-
taminated with orange crystals of trans-[Pd(NH3)2Cl2] were precip-
itated. Aqua complexes of Pd(II) are not appropriate in the
synthesis on account of their hydrolysis upon reflux and precipita-
tion of palladium hydroxides and oxides. The exchange of four NH3
ligands of [Pd(NH3)4]Cl2 for tetradentate cyclam ligand in the first
coordination sphere of the palladium atom is thermodynamically
favorable because of the strong macrocyclic effect of cyclam (bind-
2.2. Syntheses
2.2.1. {[Pd(cyclam)]@CB[8]}Cl2Á161 3H2O (1)
Cyclam@CB[8]Á4HClÁ18H2O (0.100 g, 0.050 mmol) was added to
the solution of [Pd(NH3)4]Cl2 (0.122 g, 0.497 mmol) in water
(24 mL) upon heating; the resulting solution was refluxed on a
sand bath for 2 h, and then cooled slowly. After a few days the col-
orless crystals of
1 contaminated with orange crystals of
[Pd(NH3)2Cl2] were precipitated. The precipitate was filtered off,
washed from [Pd(NH3)2Cl2] with concentrated aqueous NH3 solu-
tion (5 mL), cold water (10 mL), and dried in air. Yield 0.076 g
ing pK are 56.9 and 25.7 for [Pd(cyclam)]2+ and [Pd(NH3)4]2+
,
respectively) [41,42].
Crystals of 1 can be easily purified from trans-[Pd(NH3)2Cl2] con-
taminant by washing with concentrated aqueous solution of NH3,
the yield of the compound 1 is 76%. The attempts to encapsulate
(76% based on cyclam@CB[8]Á4HClÁ18H2O). IR (KBr):
m = 3440 (s),
3119 (w), 3009 (w), 2920 (w), 1722 (s), 1647 (w), 1470 (s), 1425

T.V. Mitkina et al. / Inorganica Chimica Acta 363 (2010) 4387–4391
4389
Table 1
Crystal data and structure refinement details for 1 and 2.
1
2
Formula
C
58H104.67Cl2N36O32.33Pd
C58H100Cl4N36O30Pd
2029.94
Formula weight (g molÀ1
)
2001.08
T (K)
150(2)
150(2)
Crystal system
Space group
a (Å)
Rhombohedral
R3
29.0879(4)
Rhombohedral
R3
38.801(6)
ꢀ
ꢀ
c (Å)
26.4952(9)
19414.3(8)
29.023(6)
37840(11)
V (Å3)
Z
9
18
1.603
Dcalc (mg mÀ3
)
1.540
Crystal size (mm3)
Reflections collected
Independent reflections
Final R indices [I > 2
R indices (all data)
0.40 Â 0.38 Â 0.35
0.35 Â 0.32 Â 0.28
37916
70330
8173 [Rint = 0.0367]
R1 = 0.0639, wR2 = 0.1999
R1 = 0.0757, wR2 = 0.2115
15672 [Rint = 0.0424]
R1 = 0.0612, wR2 = 0.1258
R1 = 0.1209, wR2 = 0.1388
r
(I)]a
a
2
À2
R1
=
R
||Fo| À |Fc||/
R
|Fo|; wR2 = {
R
[w(Fo À Fc2)2]/
R
[w(Fo2)2]}1/2, w = rF
.
the [Pd(cyclam)]2+ complex into the macrocyclic cavitand by a di-
rect synthesis ([Pd(cyclam)]2++CB[8]) give no result apparently be-
cause of the increased conformational rigidity of the complex in
comparison with the free cyclam.
Table 2
Selected bond lengths (Å) and angles (deg) for encapsulated metal complexes in 1 and
2.
[Pd(cyclam)]2+
trans-[Pd(cyclam)Cl2]2+a
According to X-ray crystallographic data, the crystal structure of
1 consists of CB[8] molecules occupied by the [Pd(cyclam)]2+ ions
(Fig. 1). The complex is fully included into the CB[8] with the pal-
ladium atom in the centre of the cavity. It is different from known
platinum anticancer inclusion compounds with only aliphatic or
aromatic ligands encapsulated into the cavity of CB[7] or CB[8]
[4,6]. Palladium atom in 1 has a square planar environment of four
nitrogen atoms of cyclam. The geometrical parameters of the
[Pd(cyclam)]2+ ion (Table 2) somewhat differ from that of the free
M–N
M–Cl
N–C
C–C
2.033(4), 2.037(3)
2.019(5), 2.069(4)
2.3113(13)
1.432(8)–1.554(8)
1.501(9)–1.505(8)
2.065(4), 2.080(5)
2.3028(14)
1.403(8)–1.501(8)
1.513(9)–1.558(9)
86.14(19), 93.86(19)
1.464(6)–1.505(6)
1.503(7)–1.514(7)
N–M–Nb 85.91(14), 94.08(14) 86.9(2), 93.1(2)
N–M–Cl
88.39(14)–91.61(14) 87.35(14)–92.65(14)
a
Data for two symmetrically independent inclusion complexes.
Concerning atoms in cis-positions.
b
complex, {[Ni(cyclam)]@CB[8]}Cl2Á16H2O [46]. The cyclam ring in 1
adopts a configuration in which the hydrogens on the nitrogen do-
nor atoms undergo minimal steric clashes (trans-III (S,S,R,R)). It is
the most stable configuration both for the free, uncomplexed cy-
clam and for cyclam complexes [47–49]. Only one example of sta-
bilization of uncommon high-energy trans-I (R,S,R,S) and trans-II
(R,S,R,R) isomers of the copper(II) cyclam complex as a result of
the encapsulation within the CB[8] cavity has been reported
recently [27].
complex [Pd(cyclam)](ClO4)2 ((M–N)av, 2.051(5) Å; (N–M–N)av
,
83.1(3)°) [43,44] but very close to that in [Pd(cyclam)]Cl2Á2CH3OH
(M–N, 2.029–2.038(4) Å; N–C, 1.475–1.494 Å; C–C, 1.507–1.522 Å;
N–M–N, 84.69–95.18°) [45].
The compound 1 is isostructural to the previously reported by
us inclusion compound of cucurbit[8]uril with the nickel(II) cyclam
The plane built of the palladium atom and four nitrogen atoms
(PdN4) is inclined towards the equatorial plane of the host by the
angle ꢀ68° similar to [Ni(cyclam)]2+ in its CB[8] inclusion com-
pound (ꢀ70°). Encapsulation of the guest causes a moderate ellip-
tical distortion of the CB[8] molecule from the ideal round shape:
the difference between the shortest and longest diameters (mea-
sured between opposite CH carbon atoms, DCH) is 1.10 Å. In the
crystal structure, the inclusion complexes are situated in inversion
centers according to crystallographic positions 9e and the inver-
sion centers form three-layered packing of 2D Kagome lattices.
The arrangement of inclusion complexes leaves channels running
along c axis (approximate opening diameter of 1.8 Å) filled with
water molecules of crystallization and chloride counter ions. A
well-developed network of hydrogen bonds involving solvate
water molecules, chloride anions, and host molecules unites all
structural elements of the crystal.
Oppositely to the inclusion compound of CB[8] with the nicke-
l(II) cyclam complex its palladium(II) analogue is only slightly sol-
uble in water and so NMR characterization of 1 has not been
carried out. Nevertheless the concentration of 1 in aqueous solu-
tion is enough for measurement of electrospray mass spectrum.
ESI-MS reveals only one intense peak at m/z = 817.3 Th that can
be assigned to the molecular ion {[Pd(cyclam)]+CB[8]}2+. This
evidences unequivocally that the metal complex remains encapsu-
lated within CB[8] in aqueous solution.
Fig. 1. Structure of inclusion complex {[Pd(cyclam)]@CB[8]}2+ in 1: (a) top view and
(b) side view (the CB[8] molecule is in gray-wire representation, hydrogen atoms
are omitted for clarity).

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T.V. Mitkina et al. / Inorganica Chimica Acta 363 (2010) 4387–4391
The IR spectrum of 1 is low-informative because of a large num-
ber of intense bands belonging to CB[8] (1800–400 cmÀ1). Stretch-
ing bands in the 3700–2800 cmÀ1 region can be assigned to solvate
water molecules.
3.2. Reaction of Pd(II)/Pd(IV) chemical oxidation and the structure of
{trans-[Pd(cyclam)Cl2]@CB[8]}Cl2Á14H2O (2)
It is well established that a chloride salt of the palladium(II)
complex [Pd(cyclam)]2+ can be oxidized by nitric acid leading to
the formation of the palladium(IV) complex trans-[Pd(cyclam)Cl2]2+
[43]. Thus we were interested to investigate the reactivity of
[Pd(cyclam)]2+ within the cavity of cucurbit[8]uril towards the
reaction of chemical oxidation.
Bubbling NO2 through the colorless solution of the palladium(II)
inclusion compound 1 in 4 M HCl leads to the color change of the
solution to dark yellow-orange. After slow diffusion of methanol
vapor into resulting solution within few days bright yellow crystals
of {trans-[Pd(cyclam)Cl2]@CB[8]}Cl2Á14H2O (2) precipitate. The
crystals are poorly soluble in water. There are no significant IR
spectroscopic differences between 1 and 2 in the investigated
4000–400 cmÀ1 region.
Fig. 3. Crystal packing of the inclusion compound {trans-[Pd(cyclam)Cl2]@CB[8]}-
Cl2Á14H2O (2) (the CB[8] molecules are in gray-wire representation; hydrogen
atoms, chloride counter ions, and water molecules of crystallization are omitted for
clarity).
X-ray crystal packing of compound 2 is built by cucurbit[8]uril
molecules with the palladium(IV) complexes trans-[Pd(cyclam)-
Cl2]2+ encapsulated into their cavities. There are two symmetrically
independent inclusion complexes {trans-[Pd(cyclam)Cl2]@CB[8]}2+
(one of them is shown in Fig. 2) having some differences in
geometrical parameters (Table 2). The palladium atom has an octa-
hedral coordination environment typical of Pd(IV) complexes,
which consists of four nitrogen atoms of cyclam and two trans-
coordinated chloride anions. We believe the next two facts evi-
dence that the chemical oxidation of the Pd(II) complex proceeds
within the cavity: the high stability of the host–guest complex in
aqueous solution and the impossibility of penetration of the
conformational rigid cyclam complex through the CB[8] portals.
The coordination of NO2 to the palladium atom is presumably
hindered because of the lack of free space inside the CB[8] cavity
occupied by bulky [Pd(cyclam)]4+ fragment although the presence
À
of the N-bound NO2 ligand has been suggested for the Pd(IV)
complex prepared by NO2 oxidation of Pd(II) species [50]. The con-
figuration of cyclam in 2 is the same as in 1 (trans-III (S,S,R,R)).
The Pd–Cl distance in 2 (Table 2) is almost identical to that in
the free palladium(IV) complex trans-[Pd(cyclam)Cl2](NO3)2-
ÁHNO3ÁH2O (2.303(1) Å) [43,44]. The palladium atom in 2 is situ-
ated in the centre of the CB[8] cavity similar to that in 1. A slight
increase (in comparison with 1) of the angle between the PdN4
plane and the equatorial plane of CB[8] (ꢀ68° in 1; ꢀ73° and
ꢀ74° in 2) may be caused by the accommodation of two additional
chloride ligands inside the cavity. Also the elliptical distortion
of the host molecule becomes stronger upon the oxidation of the
guest complex (DCH = 1.46 and 1.77 Å for two independent inclu-
sion compounds in 2).
In the crystal structure, the inclusion complexes are situated in
inversion centers according to crystallographic positions 9e and 9d.
Two crystallographically independent inclusion complexes occupy
both type of inversion centers (9d for Pd1 and 9e for Pd2) forming
six-layered packing. The channels (approximate opening diameter
of 4.6 Å) are filled with water molecules of crystallization and
chloride counter ions (Fig. 3). In general, the structure of 2 is a
framework cemented by
a complicated system of hydrogen
bonds between water molecules, chloride counter anions, and host
molecules.
4. Conclusions
We have synthesized new inclusion compounds of the macro-
cyclic host CB[8] with the palladium(II) and palladium(IV) cyclam
complexes. According to X-ray analysis, the complexes are com-
pletely encapsulated within the cavity of CB[8]. The encapsulation
into the cavity does not affect the ability of the palladium(II) com-
plex to chemical oxidation. Being encapsulated in CB[8], the com-
plex [Pd(cyclam)]2+ can be oxidized by nitrogen dioxide with the
formation of the palladium(IV) complex trans-[Pd(cyclam)Cl2]2+
.
To the best of our knowledge, it is the first example of chemical
oxidation of a metal complex proceeding within cucurbiturils.
5. Supplementary material
Fig. 2. Structure of inclusion complex {trans-[Pd(cyclam)Cl2]@CB[8]}2+ in 2: (a) top
view and (b) side view (the CB[8] molecule is in gray-wire representation, hydrogen
atoms are omitted for clarity).
CCDC 723479 and 723480 contains the supplementary crystal-
lographic data for 1 and 2. These data can be obtained free of

T.V. Mitkina et al. / Inorganica Chimica Acta 363 (2010) 4387–4391
4391
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This study was supported by the Russian Foundation for Basic
Research (grant 08-03-00088). A grant of the Russian Academy of
Sciences (program No. 5.6.1) and a grant of the Siberian Branch
of the Russian Academy of Sciences (program No. 107) are grate-
fully acknowledged. We thank Dr. C. Vicent (Universitat Jaume I,
Castellon, Spain) for measurements of ESI-MS.
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