of n-butanol–water–acetic acid and using the organic phase. L4H2
was the third product obtained from the column, with such an
eluent mixture. The fractions containing L4H2 were gathered,
the solvent removed under vacuum and 0.01 M aqueous NaOH
was added drop by drop until pH 10 was reached. The product
precipitated as a deliquescent solid, that was further dissolved in
dichloromethane, dried with Na2SO4 and, after solvent removal
on a rotary evaporator, obtained as a whitish waxy solid. Yield
38%. Mass (ESI): m/z 357 (L4H2 + H+). NMR, CDCl3: d = 0.9
(m, 6H; CH3 of the hexyl chains), 1.3 (m, 16H; CH2 of the hexyl
chains), 2.6 (m, 4H; NH–CH2– in the hexyl chains), 2.75 (t, 4H;
NH–CH2–CH2–NHCO), 3.15 (s, 2H; CO–CH2–CO), 3.35 (t, 4H;
CON–CH2), 7.3 (s, 2H; CO–NH–CH2). Elemental analysis calcd
for C19H40N4O2·CH2Cl2·H2O: C 54.17, H 10.00, N 12.63%; found
C 54.14, H 9.98, N 12.60%
bulk solution. At each base addition the pH was recorded and the
emission spectra were recorded in the spectrofluorimeter (kexc
343 nm). Total NaOH addition, at the end of the titrations, did
not exceed 0.8 ml.
=
Coupled pH-spectrophotometric titrations were also carried out
with identical details on solution containing micellized ligand and
Cu2+, in the absence of added pyrene.
Protonation equilibria of micellized ligands were studied in
water containing 6.47 g l−1 of TritonX100, by addition of standard
base (KOH) to a 10−3 M solution of the chosen ligand containing
excess standard nitric acid. Cu2+ complexation equilibria of
micellized ligands were studied under the same conditions, in the
presence of Cu(CF3SO3)2 in equimolar quantity with respect to
the ligand. Solutions were prepared to contain 0.05 M NaNO3 as
the supporting electrolyte, T = 25 ◦C. Potentiometric measure-
ments were carried out automatically, as already described.16 The
titration curves were fitted and the equilibrium constants were cal-
culated by using the nonlinear fitting program HYPERQUAD.10
The titrations (both for protonation and complexation constants)
were repeated at least twice for each compound. The obtained
results were identical within the uncertainty affecting the values.
N,Nꢀ-Bis(2-dihexylaminoethyl)malondiamide (L5H2). 187 mg
(0.99 mmol) of N,Nꢁ-bis(aminoethyl)malondiamide (L0H2) were
dissolved in 40 ml CH3OH. 285 mg (3 mmol) of hexanal, 157 mg
(2.5 mmol) of sodium cyanoborohydride and 204 mg (1.5 mmol)
of zinc chloride were dissolved in 40 ml CH3OH and added to the
solution of L0H2 drop by drop, under a nitrogen atmosphere, at
room temperature. The reaction mixture was further stirred for
8 h under nitrogen, after which time 20 ml of 0.1 M NaOH in
water were added and the solvent removed on a rotary evaporator.
The residue was treated with 50 ml 0.1 M NaOH in water and
extracted with 3 × 50 ml dichloromethane. The organic solvent
was dried on Na2SO4 and removed on a rotary evaporator to give
a yellow oil containing L5H2 and the mono-, di- and tri-hexyl
products as traces. To obtain pure L5H2 the mixture was filtered
on a short SiO2 column, using 1 : 1 v/v n-hexane–ethyl acetate,
with a gradient of CH3COOH from 0.1% to 2%. The fractions
filtered with 2% acetic acid were gathered, the solvent removed on
a rotary evaporator, the residue was redissolved in 10 ml water and
treated drop by drop with 0.1 M NaOH until pH 10 was reached.
L5H2 precipitated as a white solid, that was extracted with 20 ml
dichloromethane, dried with Na2SO4 and obtained as a white pure
solid after solvent removal in vacuum. Yield 40%. Mass (ESI): m/z
525 (L5H2 + H+). NMR, (CD3)2SO, d = 0.9 (m, 12H; CH3– of the
hexyl chains), 1.3 (m, 32H; CH2 in the hexyl chains), 2.6 (m, 8H;
NH–CH2– of the hexyl chains), 2.75 (t, 4H; –HN–CH2–CH2–
NHCO), 3.15 (s, 2H; CO–CH2–CO), 3.35 (t, 4H; CONH–CH2),
7.3 (s, 2H; CO–NH). Elemental analysis calcd for C31H64N4O2·0.5
CH2Cl2: C 66.69, H 11.55, N 9.87%; found C 66.70, H 11.56, N
9.86%.
Instrumentation
Mass spectra were recorded on a Finnigan MAT TSQ 700 instru-
ment, NMR spectra on a Bruker AMX 400. Spectrofluorimetric
measurements were performed with a Perkin Elmer LS 50B
instrument, absorption spectra were taken on a Hewlett-Packard
HP-8453 spectrophotometer. The pH-metric titrations were made
with a Radiometer TitraLab 90 titration system.
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aliquots of concentrated pyrene solutions in tert-butanol, with
a final tert-butanol concentration <0.5% v/v), plus the chosen
ligand in 10−3 M concentration (to observe the effect of protonation
on fluorescence) or the chosen ligand and Cu(CF3SO3)2 both in
10−3 M concentration (to observe the effect of complexation on
fluorescence). Solutions of 25 ml were used under a constant flow
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