Water-soluble silver(i) complexes of (β)-(+)- And (S)-(-)-2pyrrolidone-5-carboxylic acid and their antimicrobial activities. Chiral helical polymer and polymer sheet structures in the solid-state formed by self-assembly of dimeric [Ag(Hpyrrld)]2 cores

Article abstract of DOI:10.1039/b006552h

The synthesis and characterization of two water-soluble silver(i) complexes {[Ag(-R-Hpyrrld)]₂} l and {[Ag2(β-Hpyrrld)(S-Hpyrrld)]} 2 [R- and S-H₂pyrrld = (￡)-(+)- and (5)-(-)-2-pyrrolidone-5-carboxylic acid, respectively] showing wide ranging effective antimicrobial activity are described and their crystal structures determined. Single-crystal X-ray analysis reveals that 1 and 2 in the solid state are a right-handed chiral helical polymer and an achiral polymer sheet, respectively, formed by self-assembly of the Ag2(carboxylato-O,O')₂ units [Ag-Ag 2.899(2) A for 1 and 2.875(2) A for 2; O-Ag-O 160.3(5), 163.2(5)° for 1 and 163.1(2)° for 2J. The helicity of 1 in the solid state was accomplished by connection of only one oxo group in one dimeric core to one of the silver(i) centers of the adjacent dimeric unit. It is elucidated that the chiral helical polymer lisa mirror image of the recently characterized enantiomer {[Ag(S-Hpyrrld)]₂} 3. The bonding modes of 1 and 3 are quite different from those of the achiral polymer sheet 2. Complexes 1 and 2 have been also characterized by elemental analysis, TG/DTA, FT-IR, and solution ('H and I3C) and solid-state I3C NMR spectroscopies. The wide ranging effective antimicrobial activities observed in the complexes suggest that weak silver(i)-oxygen bonding properties play a key role. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b006552h

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Water-soluble silver(I) complexes of (R)-(؉)- and (S)-(؊)-2-
pyrrolidone-5-carboxylic acid and their antimicrobial activities.
Chiral helical polymer and polymer sheet structures in the solid-state
formed by self-assembly of dimeric [Ag(Hpyrrld)] cores
2
Kenji Nomiya,* Satoshi Takahashi and Ryusuke Noguchi
Department of Materials Science, Faculty of Science, Kanagawa University, Hiratsuka,
Kanagawa 259-1293, Japan. E-mail: nomiya@chem.kanagawa-u.ac.jp
Received 10th August 2000, Accepted 26th September 2000
First published as an Advance Article on the web 6th November 2000
The synthesis and characterization of two water-soluble silver() complexes {[Ag(R-Hpyrrld)] } 1 and
2
n
{
[Ag (R-Hpyrrld)(S-Hpyrrld)]} 2 [R- and S-H pyrrld = (R)-(ϩ)- and (S)-(Ϫ)-2-pyrrolidone-5-carboxylic acid,
2
n
2
respectively] showing wide ranging effective antimicrobial activity are described and their crystal structures
determined. Single-crystal X-ray analysis reveals that 1 and 2 in the solid state are a right-handed chiral helical
polymer and an achiral polymer sheet, respectively, formed by self-assembly of the Ag (carboxylato-O,OЈ) units
2
2
[
Ag–Ag 2.899(2) Å for 1 and 2.875(2) Å for 2; O–Ag–O 160.3(5), 163.2(5)Њ for 1 and 163.1(2)Њ for 2]. The helicity
of 1 in the solid state was accomplished by connection of only one oxo group in one dimeric core to one of the
silver() centers of the adjacent dimeric unit. It is elucidated that the chiral helical polymer 1 is a mirror image of
the recently characterized enantiomer {[Ag(S-Hpyrrld)] } 3. The bonding modes of 1 and 3 are quite different
2
n
from those of the achiral polymer sheet 2. Complexes 1 and 2 have been also characterized by elemental analysis,
1
13
13
TG/DTA, FT-IR, and solution ( H and C) and solid-state C NMR spectroscopies. The wide ranging effective
antimicrobial activities observed in the complexes suggest that weak silver()–oxygen bonding properties play a
key role.
In bioinorganic chemistry of coinage metal() complexes,
there have been only a few biological and medicinal studies
of silver() complexes, in contrast with many studies of gold()
acid, respectively, in which the ring NH group in H pyrrld is
replaced with an oxygen atom] have been also prepared.
Complexes 4 and 5 formed by self-assembly of [Ag(othf)]2
cores, but the mode of self-assembly is different from that of
6 and, also, of 3. Such differences have aroused our interest
2
10c
1
1a,b,2
complexes related to their antiarthritic, antitumor,
HIV, and also, recently, antimicrobial activities. The studies
anti-
1a,b
3
4
of silver() complexes have mostly related to their antiethylene
in the mode of self-assembly of such Ag (carboxylato-O,OЈ)2
2
3d–f,5
and antimicrobial activities.
One recently highlighted topic
units. Herein, using enantiomeric (R) and racemic (R,S) forms
in the coordination chemistry of coinage metal() atoms is the
of the S-H pyrrld ligand, the two water-soluble silver() com-
2
10
10
d –d interaction between two closed shell cations, or the
metallophilic interaction, many examples of which have been
plexes {[Ag(R-Hpyrrld)]2}n 1 [R-H pyrrld = (R)-(ϩ)-2-pyrrol-
2
idone-5-carboxylic acid] and {[Ag (R-Hpyrrld)(S-Hpyrrld)]}n
2
6–8
recently reported in gold() and silver() complexes.
The
2 were synthesized and characterized by elemental analysis,
aurophilic interaction, the energy of which is similar to that of
hydrogen bonds, has been rationalized by using relativistic and
thermogravimetric/differential thermal analyses (TG/DTA),
1
13
13
FT-IR, and solution ( H and C) and solid-state C NMR
spectroscopies. Their crystal structures were determined and
their antimicrobial activities were also tested.
6,7a
correlation effects.
with helicity, i.e., properties of helical polymers of d metals,
most of which have been recently observed for silver() com-
A second topic of interest is concerned
9
10
3e,9a,e,10a
plexes with examples including single-stranded helices,
9d
9b,f,10b,c
double helix polymers and chiral helical polymers,
however, only a few helical gold() complexes have been
9g
reported.
Recently,
a
water-soluble silver() complex {[Ag(S-
Hpyrrld)]2}n
3
[S-H pyrrld = (S)-(Ϫ)-2-pyrrolidone-5-carb-
2
oxylic acid] showing wide ranging effective antimicrobial
activity, which shows both a metallophilic interaction and
1
0b
helicity in the solid state, has been synthesized. This com-
pound in the solid state is a left-handed chiral helical polymer
formed by self-assembly of non-centrosymmetric bis-carb-
oxylato-bridged disilver() units with an intramolecular Ag–Ag
interaction [2.9022(7) Å], whereas it is present as a dimeric
Results and discussion
Compositional characterization, and solution and solid-state
NMR spectroscopies
Complexes 1 and 2 were prepared from stoichiometric reactions
of Ag O and H pyrrld in a 1:2 mol ratio. The formulae of {[Ag-
complex [Ag(S-Hpyrrld)] in aqueous solution. The related,
2
2
2
right- and left-handed chiral helical polymers {[Ag(R-othf)]2}n
(R-Hpyrrld)] } 1 and {[Ag (R-Hpyrrld)(S-Hpyrrld)]} 2 were
2
n
2
n
4
and {[Ag(S-othf)]2}n 5, respectively, and the stair-like
consistent with all data (elemental analysis, TG/DTA, FT-IR,
1 13
polymer {[Ag (R-othf)(S-othf)]} 6 [R- and S-Hothf ligands
H and C NMR spectra) shown in the Experimental section.
These complexes were isolated without any solvated molecules.
2
n
are (R)-(Ϫ)- and (S)-(ϩ)-5-oxo-2-tetrahydrofurancarboxylic
DOI: 10.1039/b006552h
J. Chem. Soc., Dalton Trans., 2000, 4369–4373
This journal is © The Royal Society of Chemistry 2000
4369

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Fig. 1 (a) Molecular structure of the local coordination around silver() centers of 1 with 50% probability ellipsoids (symmetry operation i
Ϫx, y ϩ 0.5, Ϫz; ii Ϫx, y Ϫ 0.5, Ϫz). (b) Top view of the main axis showing approximate two-fold helical symmetry of the structure and (c) side view
of the right-handed helical polymer chain extended along the crystallographic b axis with a pitch of 12.740 Å.
Thermal analysis by TG/DTA measurements showed that
decomposition of 1 in the solid-state began around 182 ЊC,
while that of 2 began around 170 ЊC.
The solid-state FT-IR spectra of 1 and 2 showed that the
Ϫ1
multiple vibrational bands in the region 3100–2600 cm
observed in the “free” H pyrrld ligand disappeared, and one
2
Ϫ1
very intense vibrational band around 3400 cm appeared after
complexation. The carbonyl stretching bands of the “free”
Ϫ1
ligand at 1720 and 1648 cm were shifted to 1676 and 1593
Ϫ1
cm after the complexation. These observations suggest that
the peptide –C(O)NH– bond in the ring is likely maintained
in 1 and 2, i.e., the keto form of the ligand participates in the
coordination, and the two carboxyl oxygen atoms accomplish
the formation of the dimeric silver() unit. This feature is also
consistent with the results of X-ray crystallography.
1
The H NMR spectra in D O of 1 and 2 showed signals of
2
Ϫ
the coordinating Hpyrrld ligand as multiplet peaks for the two
methylene groups (H4 and H3) and a double doublet (four
13
lines) of the H5 proton within the ring. The C NMR spectra
in D O of 1 and 2 consisted of five lines arising from signals
2
from C4, C3, C5, C6 and C2, each as a single peak, indicating
Ϫ
that the two Hpyrrld ligands in the dimeric units are equiv-
1
13
alent in solution. Solid-state IR, and solution ( H and C)
NMR spectra of 1 and 2 in D O are very similar to each other,
2
and to those of 3. Complex 3 has been established as a dimer in
aqueous solution by positive-ion electrospray ionization (ESI)
1
13
mass spectrometry, solution ( H and C) NMR and solid-state
13
15
10b
(
C and N) NMR spectroscopies. Complexes 1 and 2 are
also probably present as dimers in aqueous solution.
13
Solid-state C NMR signals of C2, C3 and C6 in 1 were
observed as two peaks each, respectively, reflecting the presence
of two inequivalent Hpyrrld ligands in the solid state, as
Fig. 2 (a) Molecular structure of the local coordination around
silver() centers of 2 with 50% probability ellipsoids (symmetry
operation i Ϫx ϩ 1, Ϫy, Ϫz ϩ 1; ii Ϫx ϩ 0.5, y Ϫ 0.5, Ϫz ϩ 1.5;
iii x ϩ 0.5, Ϫy ϩ 0.5, z Ϫ 0.5). (b) Side view of the polymer sheet
structure.
Ϫ
substantiated by X-ray crystallography. These results are con-
10b
13
sistent with those of 3. On the other hand, the solid-state
C
NMR spectrum of 2 showed single peaks for C4, C3, C5, C6
Ϫ
and C2, suggesting that the two Hpyrrld ligands are equivalent
in the solid state. These results are also supported by X-ray
crystallography.
the carboxylato group acting in a syn–syn bridging mode [C–O
1.26(2), 1.28(2), 1.23(2), 1.24(2) Å; O–C–O 126(2), 130(2)Њ].
This polymer is formed by self-assembly of dimeric units
[
Fig. 1(a)]. The crystal structure consisted of the packing
Crystal and molecular structures
of right-handed 2-fold single helices, with a period along the
crystallographic b axis, i.e., a pitch of 12.740 Å. The helicity of
1 in the solid state was accomplished with a connection of only
one ring carbonyl oxygen (O3) of one dimeric unit to one of the
silver() centers (Ag1 ) of the adjacent dimeric unit [O3–Ag1
2.46(1) Å]. The chiral helical polymer 1, as a mirror image of 3,
Single crystals suitable for single-crystal X-ray analysis were
obtained for 1 and 2. Their molecular structures with the
atom numbering schemes are depicted in Figs. 1 and 2, respec-
tively. Selected bond distances and angles with their estimated
standard deviations are given in Table 1.
i
i
Ϫ
As shown in Fig. 1(b) and (c), the crystal structure of 1 is an
is constructed with the chiral R-Hpyrrld ligand.
unusual single-stranded helical polymer, a 2 helix, composed
The Ag–Ag separation [2.899(2) Å] in the dimeric unit of 1
1
11a
of bis(carboxylato-O,OЈ)-bridged [Ag(R-Hpyrrld)] units, with
[Fig. 1(a)] is close to that of metallic silver (2.88 Å)
and
2
4
370
J. Chem. Soc., Dalton Trans., 2000, 4369–4373

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Table 1 Selected bond distances (Å) and angles (Њ) for 1 and 2
Table 2 Antimicrobial activities of 1–3 evaluated by the minimum
Ϫ1
inhibitory concentration (MIC: µg mL
)
1
2
a
Microbe
1
2
3
i
Ag1–Ag1(a)
Ag1–O1
Ag1–O2(a)
Ag1(a)–O2
Ag1(a)–O1(a)
O1–C6
O2–C6
O3–C2
O1(a)–C6(a)
O2(a)–C6(a)
O3(a)–C2(a)
N1–C2
2.899(2)
2.20(1)
2.19(1)
2.25(1)
2.16(1)
1.26(2)
1.28(2)
1.22(2)
1.23(2)
1.24(2)
1.23(2)
1.33(2)
1.47(2)
1.36(2)
1.46(2)
2.46(1)
Ag1–Ag1
Ag1–O1
Ag1–O2
O1–C6
O2–C6
O3 –C2
N1–C2
N1–C5
Ag1–O3
2.875(2)
2.193(4)
2.200(4)
1.259(7)
1.247(8)
1.239(7)
1.322(8)
1.452(7)
2.476(5)
Escherichia coli
Bacillus subtilis
Staphylococcus aureus
Pseudomonas aeruginosa
15.7
31.3
31.3
15.7
15.7
31.3
31.3
15.7
7.9
31.3
15.7
7.9
ii
Candida albicans
Saccharomyces cerevisiae
7.9
7.9
7.9
7.9
15.7
15.7
Aspergillus niger
Penicillium citrinum
Aspergillus terreus
15.7
15.7
15.7
15.7
500
250
1000
15.7
N1–C5
N1(a)–C2(a)
N1(a)–C5(a)
Rhizopus stolonifer
Chaetomium globosum
Cladosporium cladosporioides
Penicillium islandicum
Aureobasidium pullulans
Fusarium moniliforme
7.9
7.9
15.7
7.9
i
Ag1 –O3
O1–Ag1–O2(a)
O1(a)–Ag1(a)–O2
Ag1–Ag1(a)–O2
Ag1(a)–Ag1–O2(a)
Ag1–Ag1(a)–O1(a)
Ag1(a)–Ag1–O1
Ag1–O1–C6
Ag1(a)–O1(a)–C6(a)
Ag1–O2(a)–C6(a)
Ag1(a)–O2–C6
160.3(5)
163.2(5)
79.5(3)
78.5(3)
83.9(3)
83.5(3)
123(1)
121(1)
127(1)
126(1)
126(2)
130(2)
O1–Ag1–O
O1–Ag1–O3
O1–Ag1–O3
Ag1 –Ag1–O2
Ag1 –Ag1–O1
Ag1 –Ag1–O3
Ag1–O1–C6
Ag1–O2–C6
Ag1 –O3 –C2
O1–C6–O2
163.1(2)
103.5(2)
91.5(2)
84.0(1)
79.2(1)
148.4(1)
128.5(4)
122.2(4)
125.3(5)
126.1(6)
31.3
a
Ref. 10(b).
i
i
i
of centrosymmetric dimers with an Ag–Ag separation of
10c
i
2.781(1) Å [Ag–O 2.178(3), 2.250(3) Å; O–Ag–O 164.8(1)Њ].
Complexes 4–6 also showed a wide ranging effective anti-
ii
ii
10c
microbial activity.
As to the fundamental units of 1–3, the centrosymmetric
dimers formed by two carboxylates and two silver() ions
have been observed in silver()–amino acid complexes such as
O1–C6–O2
O1(a)–C6(a)–O2(a)
12a,b
[
Ag (β-ala) ](NO ) [Ag–Ag 2.855(4) Å, O–Ag–O 161.6(8)Њ]
2 2 3 2
1
2c
and [Ag (Hglygly) ](NO ) (Ag–Ag 2.92 Å, O–Ag–O 160Њ),
2
2
3 2
significantly less than twice the van der Waals radii for silver
and also in several silver() complexes such as [Ag (Et Bet) -
11b
2
3
2
(
3.44 Å), indicating the presence of an intramolecular metal–
8
ϩ
Ϫ
(
NO ) ] [Et Bet = Et N CH CO , Ag–Ag 2.928(1) Å, O–Ag–
3 2 3 3 2 2
12d
metal interaction. The Ag–Ag distances have been recently
found to be significantly influenced by the softness of the
O 160.9(1)Њ], {[Ag (Et Bet) ](ClO ) } [Ag–Ag 2.856(2) Å,
2
1
3
2
4 2 n
2d
O–Ag–O 163.6(1)Њ]
and [Ag (C H NO ) (H O) ]ؒ2H O
10b
2 9 8 3 2 2 2 2
coordinating donor atoms. The two silver() centers with
different coordination numbers, i.e., the non-centrosymmetric
dimeric units of 1 [Ag–O 2.20(1), 2.19(1), 2.25(1), 2.16(1) Å;
O–Ag–O 160.3(5), 163.2(5)Њ] can be compared with those of 3
[
C H NO = N-acetylanthranilato, Ag–Ag 2.831(2) Å, O–Ag–O
9
8
3
12e
1
60.91(1)Њ].
Antimicrobial activities
[
Ag–Ag 2.9022(7); C–O 1.226(8), 1.248(7), 1.252(8), 1.251(8) Å;
Ag–O 2.188(5), 2.217(5), 2.220(4), 2.186(5) Å; O–C–O 126.8(6),
Antimicrobial activities of the silver() complexes 1 and 2,
together with the results of 3 as a comparison, and of the
“free” ligands are listed in Table 2, as estimated by minimum
10b
1
26.4(6)Њ, O–Ag–O 158.7(2), 163.6(2)Њ].
On the other hand, the crystal structure of 2 is a polymer
Ϫ1
sheet [Fig. 2(b)], composed of racemic [Ag (R-Hpyrrld)(S-
inhibitory concentrations (MIC; µg mL ).
2
Hpyrrld)] units, with the carboxylato group acting in the
syn–anti bridging mode [C–O 1.259(7), 1.247(8) Å; O–C–O
Antimicrobial activities of the “free” ligands, R- and S-
H pyrrld, in terms of the minimum inhibitory concentration
2
Ϫ1
Ϫ1
1
26.1(6)Њ]. This polymer sheet is also formed by self-assembly
(MIC; µg mL ) were estimated as >1000 µg mL for bacteria,
ii
iii
of the dimeric units, both ring carbonyl oxygens (O3 and O3 )
yeast and mold, and thus showed no activity. As previously
10a,d
ϩ
of which participate in the coordination to the different silver()
shown,
the Ag ion, as aqueous AgNO , showed remarkable
3
ii
iii
atoms (Ag1 and Ag1 ). This bonding mode is in contrast
activity against Gram-negative bacteria (E. coli, P. aeruginosa),
moderate activity against Gram-positive bacteria (B. subtilis)
and no activity against yeast and mold. Interestingly, 1 and 2
showed a wide range of remarkable and effective activities
against Gram-negative and -positive (B. subtilis and S. aureus)
bacteria and yeast (C. albicans and S. cerevisiae), and even
against two tested molds (A. niger and P. citrinum) (Table 2). In
comparing the antimicrobial activities of 1–3, an anomalous
behavior was observed only in 3; it shows an unusual effect
against some molds (A. niger, P. citrinum and A. terreus).
However, this is likely to be an artifact, because such an unusual
effect has not been found within the closely related silver()
ii
ii
to those of 1 and 3. The O3 –Ag1 distance [2.476(5) Å] in 2
[
Fig. 2(a)] is similar to those in 1 and 3 [2.46(1) and 2.470(4) Å,
respectively]. The Ag–Ag separation [2.875(2) Å] is slightly
shorter than those of 1 and 3. The two silver() centers have the
same coordination number and the dimeric units are centro-
symmetric [Ag–O 2.193(4), 2.200(4) Å; O–Ag–O 163.1(2)Њ].
The chiral helical polymers 1 and 3 can be compared with
related, chiral helical polymers of silver() complexes, {[Ag-
(
R-othf)] } 4 and {[Ag(S-othf)] } 5 with almost the same
2 n 2 n
10c
pitch (5.417 and 5.416 Å, respectively). Both 4 and 5 have
also been formed by self-assembly of non-centrosymmetric
10c
[
Ag(othf)] units and have the same Ag–Ag distance of 2.823(1)
complexes 4–6. Moreover, the silver() complexes with -,
2
Å [Ag–O 2.188(9), 2.220(9), 2.257(8), 2.205(9) Å; O–Ag–O
- and -aspartic acid ligands have shown identical anti-
10f
1
63.8(3), 154.5(3)Њ for 4; and Ag–O 2.179(6), 2.220(6), 2.244(6),
microbial activities. Thus, it should be considered that the
anomalous action of 3 arises from some experimental factors
and, therefore, the antimicrobial actions of 1–3 are similar.
These results indicate that the coordination donor atom to the
silver() center, namely, the weaker silver()–oxygen bonding,
plays a key role in the antimicrobial activities, with replace-
2
.205(6) Å; O–Ag–O 163.9(2), 155.1(2)Њ for 5]. However, the
mode of self-assembly in 4 and 5 is different from that in 1
and 3, being accomplished with a connection of one ring carb-
onyl oxygen and one of the carboxylato oxygens to different
silver() atoms, respectively. Also, the polymer sheet 2 can be
compared with a stair-like polymer {[Ag (R-othf)(S-othf)]} 6
10
ment by biological ligands being possible. These facts are also
2
n
J. Chem. Soc., Dalton Trans., 2000, 4369–4373 4371

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consistent with the results of the three water-soluble Ag–O
bonding complexes 4–6.
2.22; N, 5.89. Calc. for C H NO Ag or [Ag(R-Hpyrrld)] as a
5 6 3
10c
monomer unit: C, 25.45; H, 2.56; N, 5.94%}. TG/DTA data: no
weight loss was observed prior to decomposition. Decomposi-
tion began around 182 ЊC with an exothermic peak at 204 ЊC.
Conclusion
Ϫ1
Prominent IR bands in the 1700–400 cm region (KBr disc):
1
4
2
676vs, 1594vs, 1408s, 1299s, 1154w, 1106w, 1043w, 721m,
Two water-soluble silver() complexes showing wide ranging
remarkable and effective antimicrobial activity {[Ag(R-
Hpyrrld)] } 1 and {[Ag (R-Hpyrrld)(S-Hpyrrld)]} 2 have been
Ϫ1
1
97w cm . H NMR (D O, 25.2 ЊC): δ 1.98–2.07 (H4a, m, 1H),
2
.37–2.41 (H3, t, 2H), 2.45–2.55 (H4b, m, 1H), 4.16–4.20 (H5,
2
n
2
n
13
dd, 1H). C NMR (D O, 25.9 ЊC): δ 28.1 (C4), 32.4 (C3), 61.0
prepared and their crystal structures determined by X-ray
crystallography. The enantiomeric complexes, 1 and 3, in the
solid state were right- and left-handed chiral helical polymers,
respectively, while the racemic complex 2 was a polymer sheet,
all formed by self-assembly of Ag (carboxylato-O,OЈ) units.
2
13
(
C5), 183.0 (C6), 184.5 (C2). Solid-state C NMR (23.8 ЊC):
δ 26.3, 28.3 (C4); 30.2, 33.0 (C3); 59.2 (C5); 177.9, 180.2 (C6);
82.2 (C2).
1
2
2
The mode of self-assembly of the dimeric units has been
compared in 1–3 and, also, in the related complexes 4–6.
The antimicrobial activities observed in 1–3 evidence that the
silver()–oxygen bonding properties, rather than the chiral
helical or achiral polymer structures in the solid state, play a
significant role. Complexes 1–3 are also of interest as a possible
new type of solid-state inorganic polymer.
{[Ag (R-Hpyrrld)(S-Hpyrrld)]} 2. Compound 2 was isolated
2 n
as a powder by similar work-up to 1 using a 1:1 mixture of
R- and S-Hpyrrld. The milk-white powder obtained in 0.41 g
(86.2%) yield was soluble in water, sparingly soluble in DMSO,
but insoluble in most organic solvents. Single crystals of 2
were grown by vapor diffusion of an aqueous solution of 2
with external acetone (Found: C, 25.65; H, 2.20; N, 6.02%). TG/
DTA data: no weight loss was observed prior to decomposition.
Decomposition began around 170 ЊC with an exothermic peak
Ϫ1
Experimental
Materials
at 188 ЊC. Prominent IR bands in the 1700–400 cm region
(
KBr disc): 1676vs, 1593vs, 1408s, 1299s, 1154w, 1106w, 1043w,
Ϫ1
1
1
010w, 721m, 497m cm . H NMR (D O, 20.4 ЊC): δ 2.00–2.08
2
The following were reagent grade and used as received: (R)-
(
H4a, m, 1H), 2.38–2.43 (H3, t, 2H), 2.47–2.56 (H4b, m, 1H),
(
ϩ)- and (S)-(Ϫ)-2-pyrrolidone-5-carboxylic acid (R- and
13
4
.16–4.20 (H5, dd, 1H). C NMR (D O, 20.4 ЊC): δ 28.2
2
S-H pyrrld, respectively) (Aldrich), Ag O, DMSO, acetone
2
2
(C4), 32.5 (C3), 61.1 (C5), 182.8 (C6), 184.3 (C2). Solid-state
(
Wako); D O (99.9 D atom %) (Isotec).
13
2
C NMR (23.9 ЊC): δ 29.1 (C4), 30.2 (C3), 58.0 (C5), 179.8
(
C6), 182.9 (C2).
Instrumentation/analytical procedures
X-Ray crystallography
CHN elemental analyses were performed using a Perkin-Elmer
PE2400 series II CHNS/O Analyzer (Kanagawa University).
Thermogravimetric (TG) and differential thermal analysis
The intensity data for 1 were collected at 296 K on a Rigaku
R-AXIS RAPID imaging-plate diffractometer and those for
2 were collected at 296 K on a Rigaku AFC5S diffractometer.
The structures were solved by direct methods followed by
subsequent difference Fourier calculation and refined by a full-
(
3
DTA) were carried out using a Rigaku TG 8101D and TAS
00 data processing system. TG/DTA measurements were run
Ϫ1
under air with a temperature ramp of 4 ЊC min between 30
and 500 ЊC. Infrared spectra were recorded on a Jasco FT-IR
1
3
matrix least-squares procedure using the TEXSAN package.
3
00 spectrometer in KBr discs at room temperature.
H NMR (399.65 MHz) and C{ H} NMR (100.40 MHz)
1
1
3
1
Crystal data for 1. C H N O Ag , M = 471.95, monoclinic,
1
0
12
2
6
2
spectra in solution were recorded in 5 mm outer diameter tubes
on a JEOL JNM-EX 400 FT-NMR spectrometer with a JEOL
space group P2 (no. 4), a = 5.196(1), b = 12.740(3), c = 9.716(2)
1
3
Ϫ3
Å, β = 94.820(3)Њ, V = 640.9(1) Å , Z = 2, D = 2.446 g cm ,
c
1
13
1
Ϫ1
EX-400 NMR data processing system. H and C{ H} NMR
µ = 30.74 cm , λ(Mo-Kα) = 0.71069 Å, F(000) = 456.0.
spectra of the complexes were measured in D O solution with
Refinement on 1192 data with I ≥ 2.0σ(I) gave R = 0.050,
2
reference to internal DSS. Chemical shifts are reported on the
δ scale and resonances downfield of DSS (δ 0) are recorded as
positive.
R = 0.069 and GOF = 1.22.
w
Crystal data for 2. C H N O Ag , M = 471.95, monoclinic,
10
12
2
6
2
13
Solid-state C NMR (75.58 MHz) spectra were measured
using a JEOL JNM-ECP 300 FT-NMR spectrometer equipped
with a cross-polarization (CP)/magic angle spinning (MAS)
space group P2 /n (no. 14), a = 7.459(1), b = 5.312(5), c =
1
3
15.961(1) Å, β = 92.11(1)Њ, V = 631.9(4) Å , Z = 2, D = 2.480 g
c
Ϫ3
Ϫ1
cm , µ = 31.17 cm , λ(Mo-Kα) = 0.71069 Å, F(000) = 456.0.
Refinement on 875 data with I ≥ 2.0σ(I) gave R = 0.034,
13
accessory. The C NMR chemical shifts were calibrated
indirectly through external hexamethylbenzene [17.3 ppm
relative to TMS (δ 0)]. The experimental errors of the isotropic
R = 0.025 and GOF = 1.23.
w
CCDC reference number 186/2198.
See http://www.rsc.org/suppdata/dt/b0/b006552h/ for crystal-
lographic files in .cif format.
1
3
C NMR chemical shift values were estimated to be about
.5 ppm.
0
Synthesis
[Ag(R-Hpyrrld)] } 1. To a suspension of 0.232 g (1.0 mmol)
Antimicrobial activity
{
Antimicrobial activities of silver() complexes were estimated
2
n
Ϫ1
of Ag O in 10 mL water was added a solution of 0.260 g
by the minimum inhibitory concentration (MIC: µg mL ) as
2
10b,c
(
2.0 mmol) of R-H pyrrld in 10 mL water. During 2 h stirring,
described elsewhere.
2
the black suspension gradually changed to a clear orange
solution. Unreacted black powder of Ag O was filtered off
2
Acknowledgements
through a membrane filter (JV 0.1 µm). Vapor diffusion of
the clear colorless filtrate with external acetone gave colorless
needle crystals, which were collected on a membrane filter
One of us (K. N.) gratefully acknowledges financial support
from JST (Japan Science and Technology Corporation)
Foundation for RSP (Regional Science Promoter) program
at Kanagawa Industrial Technology Research Institute
(Kanagawa Prefecture). We thank Professor Wasuke Mori,
Department of Materials Science, Kanagawa University, for
(
JG 0.2 µm), washed with diethyl ether (100 mL × 2) and dried
in vacuo. Colorless needle crystals of 1 obtained in 0.27 g
57.4%) yield were soluble in water, sparingly soluble in DMSO,
but insoluble in most organic solvents {Found: C, 25.63; H,
(
4
372
J. Chem. Soc., Dalton Trans., 2000, 4369–4373

View Article Online
his assistance in the X-ray measurements using the imaging-
plate diffractometer.
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