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Article
Macromolecules, Vol. 43, No. 6, 2010 2825
spectra were recorded in (CD3)2SO or CDCl3 using TMS as
an internal standard.
Synthesis. 4-(4-(1-(Acryloyloxy)ethyl)-2-methoxy-5-nitro-
phenoxy)butanoic Acid. 4-(4-(1-Hydroxyethyl)-2-methoxy-5-
nitrophenoxy)butanoic acid (4.53 g, 15.1 mmol) and TEA
(8.28 mL, 59.4 mmol) were dissolved in a solution of THF
(50 mL) and cooled to 0 °C. To this solution, a mixture of AC
(2.82 mL, 52.0 mmol) and THF (10 mL) was added dropwise.
The reaction mixture was stirred 24 h and monitored by 1H
NMR. Upon completion, the reaction mixture was poured in
water (1.2 L), stirred at room temperature for 2 h, extracted with
chloroform (5 ꢀ 200 mL), dried over MgSO4, and concentrated
to dryness via rotary evaporation to yield 5.26 g (98%) as a
viscous yellow liquid. 1H NMR (CDCl3, δ): 7.60 (s, Ar-H ortho
to Ar-NO2), 7.02 (s, Ar-H meta to Ar-NO2), 6.55 (m, Ar-
CH(CH3)OCHCH2), 6.42, 5.85 (d, d, Ar-OCHCHCH2), 6.16
(m, Ar-OCHCHCH2), 4.10 (t, Ar-OCH2CH2CH2CO2H), 3.92
(s, Ar-OCH3), 2.58 (t, Ar-OCH2CH2CH2CO2H), 2.23 (m,
Ar-OCH2CH2CH2CO2H), 1.65 (d, Ar-CHCH3).
Figure 1. (a) Negative tone and (b) positive tone are exposed to light
through a photomask. (c) A single hydrogel can be used to create both
raised and pitted features depending on the amount of degradation and
the cross-linking density.
Bis(4-(4-(1-(acryloyloxy)ethyl)-2-methoxy-5-nitrophenoxy)-
butanate)PEG (Mn = 4668) (Photodegradable Macromer).
4-(4-(1-(Acryloyloxy)ethyl)-2-methoxy-5-nitrophenoxy)buta-
noic acid (5.26 g, 14.89 mmol) was reacted with phosphorus
pentachloride (3.26 g, 8.9 mmol) for 30 min at RT. The resultant
phosphorus oxychloride was removed under reduced pressure,
and the residue was dissolved in DCM (40 mL). The solution
was added dropwise to a solution of PEG (14.89 g, 3.7 mmol)
and TEA (2.08 mL, 14.9 mmol) in DCM (50 mL). After stirring
20 h at RT, the reaction was filtered and evaporated via rotary
evaporation. The residue was dissolved in acetone (50 mL),
and the TEA salts were removed by filtration. The product was
collected by precipitation in diethyl ether (750 mL) at -20 °C
and filtration to obtain a very pale-yellow powder (14.20 g,
81.7%). 1H NMR (CDCl3, δ): 7.60 (s, Ar-H ortho to Ar-NO2),
7.02 (s, Ar-H meta to Ar-NO2), 6.55 (m, Ar-CH(CH3)-
OCHCH2), 6.42, 5.85 (d, d, Ar-OCHCHCH2), 6.16 (m,
Ar-OCHCHCH2), 4.25 (t, Ar-OCH2CH2CH2CO2CH2), 4.10
(t, Ar-OCH2CH2CH2CO2R), 3.92 (s, Ar-OCH3), 3.56-3.75
(m, 347-H1), 2.58 (t, Ar OCH2CH2CH2CO2R), 2.17 (m, Ar
OCH2CH2CH2CO2R), 1.65 (d, Ar-CHCH3).
1-(5-Chloro-2,4-dihydroxyphenyl)ethanone. 2,4-Dihydroxy benz-
aldehyde (5.00 g, 36.2 mmol) was dissolved at room temperature in
a solution of sulfuric acid (55 mL) and water (55 mL) and then
cooled to 0 °C. Piperidine (3.60 g, 42.3 mmol) was added dropwise
to a solution of aqueous sodium hypochlorite (55 mL, 41.4 mmol)
at 0 °C and then added dropwise to the aqueous sulfuric acid
mixture and stirred for 20 h. The chlorinated product was collected
by filtration and washed with water to yield 3.75 g (60.0%) as a
yellow powder. The product was a 1:2 mixture of 3- and 5-chloro
isomers and was used without further purification. (Reported yield
represents only 5-chloro-isomer) 1H NMR ((CD3)2SO, δ): 10.89 (s,
Ar-OH), 9.93 (s, Ar-CHO), 7.57 (s, Ar-H ortho to Ar-Cl), 6.54 (s,
Ar-H meta to Ar-Cl).
cross sections orders of magnitude higher (at λ=740 nm, δu=0.4
to 0.7 GM) than o-NBE moieties alone.19 Mechanistic studies of
1-(2-nitrophenyl)ethyl)-caged coumarins show rapid photolysis
and up to an 800 fold increase in fluorescence after uncaging, also
making them ideal candidates for imaging.19
Here we report the lithographic capabilities and limitations of
a biocompatible hydrogel containing o-NBE moieties. Using
single- and two-photon photolysis, we can create well-defined
positive and negative features over multiple length scales
(∼10-7m to 10-2m) in 2D and 3D. We characterize the sensitivity
of this macromer to two-photon photolysis at multiple wave-
lengths (730-872 nm). We also report a new photodegradable
macromer containing a coumarin fluorophore to enhance the
sensitivity of a hydrogel to two-photon photolysis and compare it
with the photodegradable o-NBE macromer.
Experimental Section
Materials. Acryloyl chloride (AC) (Alfa Aesar, 96%), triethyl-
amine (TEA) (Fisher Scientific, 99%), ammonium persulfate
(AP) (J.T. Baker, 98%), tetramethylethylenediamine (TEMED)
(EMD, 99%), tetrahydrofuran (THF) (Fisher Scientific, 99.9%),
chloroform (Fisher Scientific, 99.9%), phosphorus pentachloride
(Alfa Aesar, 98%), sulfuric acid (EMD, 50%), sodium hypo-
chlorite (Fisher Scientific, 6%), piperidine (Spectrum Chemical
MFG. Corp., 99%), malonic acid (Alfa Aesar, 99%), pyridine
(Fisher Scientific, 99.9%), aniline (Sigma Aldrich, 99.5%), etha-
nol (Pharmco-AAPER, 99.5%), 2-hydroxyethyl methacrylate
(Sigma Aldrich, 97%), dichloromethane (DCM) (Fisher Scienti-
fic, 99.9%), acetone (Fisher Scientific, 99.7%), potassium carbo-
nate (Sigma Aldrich, 99%), sodium iodide (EM Science, 99.5%),
magnesium sulfate (Fisher Scientific, 99.6%), 2,4-dihydroxy
benzldehyde (Acros Organics, 98%), N,N-dimethylformamide
(DMF) (Fisher Scientific, 99.8%), poly(ethylene glycol) (PEG)
(Mn=4000 g/mol) (Mallinckrodt Chemicals), and diethyl ether
(Fisher Scientific, 99.9%) were used as received unless otherwise
noted. AC was distilled under vacuum into an airfree flask and
stored under a blanket of Ar at -20 °C in the absence of light.
TEA was distilled under Ar and stored over KOH pellets. THF
was distilled from CaH2 and stored under Ar in a dry, air-free
flask. DCM was distilled and stored under Ar in a dry, airfree
flask. DMF was stored over activated type 4A molecular sieves.
PEG 4000 diacrylate was synthesized according to a modified
literature procedure.20 4-(4-(1-Hydroxyethyl)-2-methoxy-5-nitro-
phenoxy)butanoic acid was synthesized according to a modified
literature procedure.12
6-Chloro-7-hydroxycoumarin-3-carboxylate (Coumarin). 1-(5-
Chloro-2,4-dihydroxyphenyl)ethanone (3.75 g, 21.7 mmol)) was
combined with malonic acid (6.44 g, 65.2 mmol), aniline
(catalytic), and pyridine (25 mL). After stirring for 2 days, the
reaction was quenched in ethanol (80 mL), filtered, and washed
with aqueous hydrochloric acid (0.1 N, 5 ꢀ 50 mL), H2O (3 ꢀ
50 mL) and diethyl ether (2 ꢀ 50 mL). The resultant powder
was dried under vacuum (2.98 g, 57%) (note, no product due
to 3-chloro is detected). 1H NMR ((CD3)2SO, δ): 13.00
(s, -COOH), 11.94 (s, OH), 8.64 (s), 7.98 (s), 6.87 (s).
2-(Methacryloyloxy)ethyl
6-Chloro-7-hydroxycoumarin-3-
carboxylate (Coumarin-HEMA Conjugate). 6-Chloro-7-hydro-
xy-2-oxo-2H-chromene-3-carboxylic acid (coumarin) (0.50 g,
2.1 mmol) was reacted with phosphorus pentachloride (0.45 g,
4.2 mmol) for 30 min at RT. The resultant phosphorus oxy-
chloride was removed under reduced pressure, and the residue
was dissolved in DCM (3 mL). The solution was added dropwise
Techniques. All reactions were performed under a N2 atmo-
sphere using a Schlenk line unless otherwise noted. H NMR
1
spectra (δ) were recorded on a Bruker Biospin Ultrashield
300 MHz NMR spectrometer. Unless otherwise noted, all