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A. Patra et al. / Inorganica Chimica Acta 436 (2015) 195–204
connected to each other involving carboxylate functionality of
amino acid residue and sometime solvent molecule (H2O or OHꢁ)
with Zn—Zn separation ranging from 3.0 to 3.5 Å [18–22]. The
catalytic activity of these zinc containing enzymes is mainly
dependent on the bridging groups that hold the two zinc(II) ions
at a suitable distance giving a fundamental contribution to the sub-
strate orientation and activation.
So, the model studies with simple dinuclear copper(II) and zinc
(II) complexes are becoming more important in understanding the
biological functions of dimetallic cores [23–25]. Generally, in a
dimetallic system, one metal ion is responsible for substrate
binding while the other delivers the activated solvent as
nucleophile for hydrolysis. The dinuclear copper(II) and zinc(II)
complexes, with either one loosely bound apical exogeneous ligand
or coordinatively unsaturated position, have the potential for bind-
ing of biologically important sugar substrates [1,26–28]. In this
regard, the synthetic metallohydrolases catalyzing glycosidic bond
cleavage are useful for promoting biomimetic transformations of
carbohydrates. Recently, Striegler and co-workers [29–32] have
contributed enormously to the field of supramolecular glycosidase
mimics. In this paper, we report the synthesis, structure, spectral
characterization, magnetic properties and glycosidase-like activity
of dinuclear copper(II) and zinc(II) complexes of a new symmetri-
cal dinucleating ligand, H3cpdp.
1,3-diamino-propan-2-ol (1.424 g, 15.00 mmol) in 20 ml methanol.
The yellowish mixture obtained was heated to 60 °C while stirring
for ꢂ4 h. Then the reaction product was cooled in an ice-bath.
Excess NaBH4 (1.500 g, 39.50 mmol) was added in portions to the
cold solution while stirring. The yellow color was slightly dis-
charged. After 30 min 2 ml conc. HCl was added drop wise to
destroy the excess NaBH4. Acidification of the solution to pH ꢂ 5
by further addition of conc. HCl resulted in the precipitation of
white crystalline solid. The white solid was filtered out from
mother liquor and washed with water and methanol, and dried
at ꢂ80 °C. Yield: 4.95 g (87%). The compound was crystallized from
methanol–water solution (1:1; v/v). The product was confirmed by
the elemental analysis as H3cdpꢀH2O. Anal. Calc. for
.
C19H22N2O5 H2O: C, 60.63%; H, 6.43%; N, 7.44%. Found: C, 60.25%;
H, 6.28%; N, 7.33%. 1H NMR for sodium salt of the compound
(400 MHz, D2O, 25 °C, d): 7.46–7.32 (m, 8H), 3.92–3.80 (m, 1H),
2.63 (q, 4H), 2.55 (q, 4H).
2-Picolylchloride hydrochloride (1.640 g, 10.00 mmol) was
added in portions to a solution of N,N0-Bis(2-carboxybenzometh-
yl)-1,3-diaminopropan-2-ol, H3cdp (1.790 g, 5.00 mmol) and
LiOH (0.800 g, 20.00 mmol) in 25 ml of water while stirring.
More LiOH (0.400 g, 10.00 mmol) was added to maintain the
pH ꢂ 11 and the reaction mixture was stirred at room temperature
for ꢂ28 h. The resulting solution was cooled in an ice bath and
acidified with conc. HBr to pH ꢂ 5. The solution was rotary evapo-
rated under reduced pressure to give a reddish brown gummy
product. Then it was extracted in dry methanol and the methanol
extract was rotary evaporated to isolate a pure reddish brown
gummy product. The product was dried in vacuum over P4O10
and obtained as brown waxy material. The product was confirmed
by the elemental and thermogravimetric analyses as
H3cpdpꢀLiClꢀ3LiBrꢀ14H2O. Yield: 4.018 g (77%). Anal. Calc. for
2. Experimental
2.1. Materials and methods
2-Carboxybenzaldehyde,
1,3-diamino-2-propanol,
2-picolylchloride
p-nitrophenyl-
hydrochloride,
-glucopyranoside,
a
-D
p-nitrophenyl-b-D-glucopyranoside and lithium hydroxide were
C
31H32N4O5ꢀLiClꢀ3LiBrꢀ14H2O: C, 33.98%; H, 5.51%; N, 5.11%; Cl,
3.24%; Br, 21.88%. Found: C, 33.88%; H, 5.54%; N, 5.27%; Cl,
2.91%; Br, 21.49%. FTIR (cmꢁ1):
= 3389(b), 2084(b), 1634(s),
purchased from Sigma–Aldrich Chemie GmbH, Germany. Copper
(II) acetate monohydrate, copper(II) chloride dihydrate, zinc(II)
acetate dihydrate and sodium benzoate were purchased from
Merck, India. CAPS buffer was purchased from SRL, India. All other
chemicals and solvents were reagent grade materials and were
used as received without further purification. Microanalyses (C,
H, N) were performed using a Perkin–Elmer 2400 CHNS/O Series
II elemental analyzer. FTIR spectra were obtained on a Perkin–
Elmer L120-000A spectrometer (200–4000 cmꢁ1). UV–Vis spectra
were recorded using a Shimadzu UV 1800 (190–1100 nm; 1 cm
quartz cell) spectrophotometer. 1H and 13C NMR spectra were
obtained on a Bruker AC 400 NMR spectrometer. The ESI mass
spectra were recorded using a Micromass Q-Tof MicroTM (Waters)
mass spectrometer. The potentiometric titration of the ligand
was carried out using a Mettler Toledo Seven Compact S220 digital
Ion/pH meter in aqueous solution. Thermogravimetric (TG) analy-
sis of the ligand was performed on a NETZSCH STA 449F3 thermal
analyzer. The variable temperature magnetic susceptibility data
were collected in the temperature range of 2–300 K under an
applied field of 1 Tesla on powdered microcrystalline sample with
a SQUID magnetometer (MPMS-7, Quantum Design). Experimental
susceptibility data were corrected for the underlying diamagne-
tism using Pascal’s constants [33]. The temperature dependent
magnetic contribution of the holder was experimentally deter-
mined and subtracted from the measured susceptibility data. The
program phi1.9 [34] was used for spin Hamiltonian simulations
of the data.
m
1567(vs), 1441(s), 1399(s), 1298(s), 1154(s), 1094(s), 972(s), 761
(s). 1H NMR (400 MHz, D2O, room temperature, d): 8.47 (d, 2H),
7.81 (t, 2H), 7.64 (d, 2H), 7.39–7.51 (m, 8H), 7.27 (d, 2H), 4.47 (d,
8H), 4.01–4.20 (m, 1H), 3.38 (d, 2H), 3.13 (t, 2H). 13C NMR
(400 MHz, D2O, room temperature, d): 174.65, 149.32, 148.91,
143.99, 141.31, 138.87, 137.23, 133.20, 130.88, 130.44, 125.01,
124.68, 60.47, 60.25, 57.50, 57.11. Mass spectrum (ESI): m/z
565 (100%) (M+ = {H3cpdpꢀH2O + Li}+), 559 (81%) (M+ =
{H3cpdpꢀH2O + H}+). TGA analysis: loss of H2O {136 °C–273 °C:
23.00% (Calculated); 23.35% (Found)}; loss of CO2 {290 °C–367 °C:
8.03% (Calculated); 8.39% (Found)}.
2.3. Synthesis of [Li(H2O)3(CH3OH)]4[Cu2Br4][Cu2(cpdp)(l-
O2CCH3)]4(OH)2 (1)
A methanol solution (10 ml) of [Cu2(O2CCH3)4(H2O)2] (0.184 g,
0.462 mmol) was slowly added to a magnetically stirred methanol
solution (15 ml) of ligand H3cpdp (0.506 g, 0.462 mmol) and NaOH
(0.055 g, 1.386 mmol) at ambient temperature during a period of
10 min. The reaction mixture was stirred for 1 h resulting in a
green solution. The solution was filtered to discard any insoluble
precipitate. The X-ray quality green block shaped single crystals
were obtained by slow ether diffusion into the clear filtrate diluted
by water after 3–4 days. Yield: 0.301 g (70%). Anal. Calc. for
C
136H170N16O46Br4Li4Cu10: C, 43.59; H, 4.57; N, 5.98; Br, 8.53; Cu,
16.96. Found: C, 43.47; H, 4.65; N, 5.89; Br, 8.86; Cu, 16.81. FTIR
(cmꢁ1):
= 3400(b), 1615(s), 1586(s), 1562(s), 1483(s), 1448(s),
1385(s), 1105(s), 1052(s), 872(s), 760(s), 666(s), 614(s). UV–Vis
2.2. Synthesis of N,N0-Bis[2-carboxybenzomethyl]-N,N0-Bis[2-
pyridylmethyl]-1,3-diaminopropan-2-ol (H3cpdp)
m
spectra (H2O): kmax (e
, Mꢁ1 cmꢁ1) = 678 (146), 261 (4229). Mass
A solution of 2-carboxybenzaldehyde (4.643 g, 30.00 mmol) and
NaOH (1.200 g, 30.00 mmol) in 100 ml methanol was added to
spectrum (ESI): m/z 663 (100%) (M+ = {[Cu2(cpdp)]}+), 745 (80%)
(M+ = {[Cu2(cpdp)(O2CCH3)] + Na}+).