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SUPPLEMENTARY MATERIAL
Calcium and zinc complexes of pyrroglutamate
analogs detected by electrospray ionization mass
spectrometry
Joséphine Beck,1 Laetitia
Marchand-Brynaert1,*
Maton,2
Jean-Louis
Habib
Jiwan2
and
Jacqueline
1
Unité de Chimie Organique et Médicinale, Université catholique de Louvain, Bâtiment
Lavoisier, Place Louis Pasteur 1, B-1348 Louvain-la-Neuve, Belgium
2
Unité de chimie des matériaux, Université catholique de Louvain, Bâtiment Lavoisier, Place
Louis Pasteur 1, B-1348 Louvain-la-Neuve, Belgium
* Corresponding author:
E-mail [email protected];
Phone +32 10 47 27 40;
Fax +32 10 47 41 68.
1. Literature survey of related crystalline complexes
Although the structure of complexes in solution is not necessarily the same in the solid state, possible structures
can be proposed for our complexes based on crystallographic data of complexes known from the literature.
CCDCQuest version 1.9 database was used for this study. Although molecule 1 was already described (Smirnova
et al. 1968), no X-ray structure analysis of this compound has hitherto been reported. No complex between
ligand 1 and calcium or zinc was found in the database; complexes between pyrrolidinone and calcium were not
reported. The research has been expanded to simple structures like ester and amide functions, acetonitrile,
perchlorate and phosphonate groups. In fact, all those functions are complexing motifs toward calcium and zinc.
The structural analysis of [(isonicotinamide)2Ca(H2O)4]Cl2 has been reported (Cole and Holt 1989): calcium is
octahedrally coordinated to six oxygen atoms, four from water molecules and two from the carbonyl oxygen
atom of amide groups of two different isonicotamide molecules. CaI 2(H2O)2 was reacted with ethyl acetate (L) to
lead to the complex [L4Ca(H2O)2]I2 (Fromm et al. 2000). The coordination number around the calcium atom is
six with two water molecules in axial positions and four molecules of ethyl acetate in equatorial positions of a
square tetragonal bipyramid. The calcium cation of [(MeCN) 4Ca(THF)3][Re6S6Cl8] is seven-coordinated and the
complex form is a monocapped trigonal prism (Perruchas et al. 2002). The reaction of dioxazaphosphocane with
calcium perchlorate led to the formation of an oligomeric complex which shows the bridging position of the
calcium ions between four dioxazaphosphocane moieties. The calcium atom is coordinated to six oxygen atoms
-S1-
and involves two oxygens of phosphoryl and two oxygens of carbonyl groups from four dioxazaphosphocane
and two from perchlorate anions (Sutra et al. 2002).
The complex between zinc perchlorate and N,N’-ethylenebis(pyrrolidin-2-one) (ebpyrr) has the following
stoichiometry, i.e. [Zn(ebpyrr)3](ClO4)2.2MeCN, in which zinc atom is coordinated by six oxygen atoms of
ebpyrr ligands (Doyle et al. 1995).In [Zn(CH3CONH2)4.2H2O]2+, zinc cation has a regular octahedral
coordination with four oxygen atoms of four acetamide groups located in the equatorial plane and two oxygen
atoms of water molecules in axial positions (Palkina et al. 1996). Zinc(II) complex of (6-NHCOtBu-2pyridylmethyl)-N(CH2CH2)2S and 1,10-phenantroline has been described: the coordination geometry of the zinc
is distorted octahedral with a weakly coordinated perchlorate counter ion (Rivas et al. 2004). The complex
between tetramethyl ester of EDTA and zinc chloride featured a slightly distorted octahedral geometry
(Buschhaus et al. 2005). The chloride ions and amino atoms of EDTA are coordinated within the equatorial
plane while the axial positions are occupied by carbonyl oxygen atoms of the ester. The reaction of anhydrous
zinc chloride with 18-crown-6 in acetonitrile afforded the unexpected ZnCl2.2CH3CN complex, in which the zinc
atom has a tetrahedral geometry (Bel'skii et al. 1989). In the complex (FcPO3Et2)2.ZnCl2 obtained by reaction of
diethyl ferrocenylphosphonate with zinc chloride (Oms et al. 2004), two chlorine atoms and two oxygen atoms
from the phosphoryl groups define a distorted tetrahedral arrangement around the zinc centre. Complexes
between chiral quadridentate ligands derived from aminoacids and zinc showed a slightly distorted trigonal
bipyramidal coordination environment around zinc atom, with one triflate anion and the tertiary amine nitrogen
atom occupying the axial positions (Niklas et al. 2000). The pyridine and the amide of the aminoacid ligands are
bound in the trigonal plane.
2. Tentative structural assignment of the soluble complexes
From the literature survey, 1-5 complex structures can be proposed. Calcium complexes have generally six and
sometimes seven coordination sites while zinc complexes may have six, five or four coordination sites. For each
ligand, only one complex structure has been drawn.
The structures proposed for complexes [(1)2CaClO4]+ , [(1)2Zn-H]+, [(2)2Ca]2+ and [(2)2Zn]2+ are illustrated in
Scheme S1. The cations are octahedrally coordinated to six oxygen atoms: four from two ester groups of two
different ligands and two from the carbonyl oxygen atom of amide groups of two different ligands.
-S2-
H
N
O
EtO
N
H
O
O
R
M
EtO
OMe
O
OEt
O
O
H
N
O
O
OMe
O 2
MeO
M
OMe
O
MeO
O
OEt
O
O
MeO
M = Ca, R = ClO4 or M = Zn, no R
O
N
H
M = Ca or Zn
Scheme S1. Structures proposed for complexes of 1 and 2.
Possible structures of complexes [(3)2CaClO4]+ , [(3)2Zn-H]+, [(4)2CaClO4]+ and [(4)2Zn-H]+ are depicted in
Scheme S2. The coordination number around the calcium is seven and involves six oxygen atoms of phosphoryl
and carbonyl groups from two ligands and one oxygen atom from perchlorate anion. For the zinc complexes, the
oxygen atoms of ester and phosphoryl groups from ligands are coordinated within the equatorial plane while the
axial positions are occupied by carbonyl oxygen atoms of amide.
O
O
EtO
EtO
N
H
P O
R
M
O
EtO
OEt
O
O P OEt
H
OEt
N
N
EtO
H
P O
EtO
O
EtO
R
M
OEt
O
O P OEt
H
OEt
N
O
O
M = Ca, R = ClO 4 or M = Zn, no R
Scheme S2. Plausible structures of [(L)2CaClO4]+ and [(L)2Zn-H]+.
For ligand 5, the structures of complexes [(5)2CaClO4]+ and [5ZnClO4]+ are represented in Scheme S3. The
calcium has seven coordination sites. The oxygen atoms of phosphonate group and amide group from two
ligands occupy the coordination sphere. Three oxygen atoms from the phosphonate and amide group and one
oxygen atom from perchlorate ion define a distorted tetrahedral arrangement around the zinc centre.
EtO
P O
EtO
ClO3 OEt
O
O
O P OEt
N
H
Ca
H
N
EtO P O
O
EtO
OEt
O P
OEt
O
N
Zn O H
O
P(OEt)2
O Cl O
O P(OEt) 2
O
Scheme S3. Representation of complexes [(5)2CaClO4]+ and [5ZnClO4]+
-S3-
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