Synthesis and characterization of poly [N-acryloyl-(D/L),(+/-)-
phenylalanine-co-(D/L),(-/+)N-methacryloyloxyethyl-
N’-2-hydroxybutyl(urea)] copolymers
77.2 ppm). 2D 1H,1H-COSY (Correlation Spectroscopy)
and 13C,1H-HSQC (Heteronuclear Single Quantum
Coherence) studies were performed using standard
pulse sequences in the version with z-gradients, as
supplied by Bruker with TopSpin 2.1 PL6 operating
software. Fourier Transform infrared (FT-IR) spectra and
UV absorption spectra were recorded on a Bruker Vertex
70 spectrometer and a Specord 200 spectrophotometer
respectively, in DMF. The fluorescent spectra were
recordedusingaPerkin–ElmerLS55spectrophotometer,
at room temperature, in a DMF solution. The average
molecular weights were determined in DMF by gel
permeation chromatography (GPC) measurements
consisting of a model Polymer Laboratory EMD-950
apparatus equipped with an evaporative mass detector
and two PL gel 5 μm columns. The samples were of
2.0 g dL-1 polymer solution in N,N-dimethylformamide
with 0.1 M LiCl and the flow rate of the carrier solvent was
1 mL min-1. The average molecular weight was
calculated on the basis of the molecular weight versus
retention volume curve of monodisperse polystyrene
(PS) standard with a molecular range from 580 to
3150 kD. Thermal transitions were measured through
the Differential Scanning Calorimetry (DSC) in a
nitrogen atmosphere on a STA 449 F1 Jupiter
(Netzsch, Germany) at a heating rate of 10°C min-1.
CD spectra were recorded using a ChirascanTM CD
Spectrometer from Apllied Photophysics. All optical
rotation measurements were carried out in distilled
water (c = 100 μM) at 25.0 ± 0.2°C using quartz cells
with a path length of 2.0 mm. Data were collected at the
wavelengths from 180 to 260 nm in 1.0 nm increments.
Optical activity experiments were performed in a 0.1 N
sodium hydroxide solution (c = 0.01 g cm-3) at 23°C on
an OPTIK Pol 1 polarimeter with the cell path length of
1 dm (λ = 590 nm).
2.3. Polymers synthesis
Synthesis of poly[N-acryloyl-(D/L),(-/+)-phenylalanine-
co-(D/L),(+/-)-N-methacryloyloxyethyl-N’-2-
hydroxybutyl (urea)], A-D-Phe-co-D-MABU and A-L-
Phe-co-L-MABU
Synthesis of A-D/L-Phe-co-D/L-MABU was carried
out through a conventional radical polymerization using
thefollowingprocedure:ineachofthetwopolymerization
ampoules equipped with a magnetic stirrer, 3 g
(13.698 mmol) of A-D/L-Phe was dissolved in 25 mL
of dimethylformamide (DMF). Then, 5.2 mg (1 wt‰) of
azobis(cyclohexanecarbonitrile) (ABCN) was dissolved
in 4 mL of DMF, and this solution was divided equally into
two parts, each being added to the two polymerization
ampoules containing the monomer solution of A-D/L–
Phe. In other two flasks, 0.6 g (2.448 mmol) of either
D-MABU or L-MABU sample was dissolved in 5 mL of
DMF and then, each of them was transferred into the
two polymerization ampoules as follows: the D-MABU
monomer solution was added to the A-D-Phe solution
and the L-MABU solution was added to the A-L-Phe
monomer solution. Both polymerization reactions were
carried out using molar fractions of A-D/L-Phe: D/L-
MABU monomers of 0.76 : 0.24 and 0.64 : 0.36, under
purified nitrogen at a temperature of 80oC for 3 days.
The resulting compounds were precipitated in distilled
water, filtered, and washed several times. Finally, the
formed copolymers were dried under reduced pressure
at 60oC for 24 h. Yield: 2.8 g (80%).
Synthesis
of
poly[N-acryloyl-(D/L),(+/-)-
N’2-
phenylalanine-co-(D/L)-N-methacryloyloxyethyl-
fluoresceinylthiourethane-butyl(urea)], A-D-Phe-co-D-
MABU-F and A-L-Phe-co-L-MABU-F
Functionalization of all the copolymers with
fluorescence units was performed under similar
conditions which were as follows: 1 g of A-L-Phe-co-
L-MABU copolymer was dissolved in 10 mL DMF and
then 0.085 g (0.2185 mmol) of fluorescein isothiocynate
isomer I and a catalytic amount of DBTD were added.
The mixture was stirred at 56oC for 24 h, and the final
product (A-L-Phe-co-L-MABU-F) was precipitated into
diethyl ether, filtered, and dried at 60oC, for 24 h, under
reduced pressure. Yield: 0.6 g (55.3%).
3. Results and discussion
3.1. Synthesis and characterization
Copolymers
with
D/L,(-/+)-phenylalanine
and
D/L,(+/-)-butanol(urea)
moieties
(A-D-Phe-co-D-
MABU and A-L-PheAla-co-L-MABU) in their structures
2.4. Measurements
were synthesized through a conventional free radical
Proton nuclear magnetic resonance spectroscopy polymerization of (D/L),(+/-)-N-methacryloyloxyethyl-
(1H-NMR) spectra were recorded on a Bruker Advance N’-2-hydroxybutyl(urea),
(D/L-MABU)
with
III 400-MHz spectrometer in either CDCl3 or DMSO-d6 N-acryloyl-(D/L),(-/+)-phenylalanine,
(A-D/L-Phe).
at room temperature. H-NMR and 13C-NMR chemical In the first step, the parent monomers, D/L-MABU,
shifts were given in δ units (ppm) as compared to the (Scheme 1a) were obtained through the addition
residual peak of the solvent (1H-NMR: DMSO, 2.51 ppm; reaction of methacryloyloxyethyl-2-isocyanate to D/L,
CDCl3: 7.26 ppm); 13C-NMR: DMSO, 39.47 ppm; CDCl3: (-/+)-2-amino-1-butanol or via a Schotten–Baumann
1
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