Full Paper
ride (1.9 mL, 19.6 mmol; Aldrich 97%) were added dropwise and
the solution was stirred at room temperature for 20 h. The solution
was extracted with a saturated aqueous solution of Na2CO3 (4ꢁ
40 mL). The organic layer was separated, dried over MgSO4, fil-
tered, and the solvent was evaporated at reduced pressure. The
crude product was purified by chromatography (SiO2, hexane/
AcOEt (20:1!10:1)) to obtain 6 as a pale-yellow oil (1.20 g,
persed in THF, and centrifuged again. This process was repeated
three times, followed by drying in a stream of argon to yield dry
nanoparticles NP-1 (1.01 g).
A typical procedure for the preparation of the polymer-grafted
silica nanoparticles through ATRP is described below. Nanoparticles
functionalized with the ATRP initiator (NP-1; 100 mg) were dried
under vacuum at 408C for 10 h. Methacrylate
3 (300 mg,
1
1.01 mmol) and methacrylate 2H+ (365 mg, 1.01 mmol) were
added to NP-1 in methanol/water (3:1). The mixture was degassed
with four freeze-pump-thaw cycles. The flask was placed in a water
bath thermostated at 40.08C for 15 min. CuBr (10 mg) and 2,2-bi-
pyridine (30 mg) were added to the flask in a stream of argon. The
polymerization proceeded for 90 min, and then the flask was re-
moved from the bath and opened to the air. The mixture was di-
luted with MeOH/water (3:1, 4 mL). The nanoparticles were isolat-
ed by centrifugation, separated from the supernatant, washed with
water and methanol, sonicated, and centrifuged again.
3.93 mmol, 84% yield). H NMR (300 MHz, CDCl3): d=1.50 (s, 9H),
1.91 (s, 3H), 2.92 (tr, J=6.9 Hz, 2H), 4.30 (tr, J=6.9 Hz, 2H), 5.53 (s,
1H), 6.07 (s, 1H), 6.52 (brs, 1H), 7.14 (d, J=8.4 Hz, 2H), 7.29 ppm
(d, J=8.4 Hz, 2H); 13C NMR (75 MHz, CDCl3): d=18.3, 28.3, 34.4,
65.2, 80.4, 118.6, 125.5, 129.4, 132.5, 136.2, 136.8, 152.8, 167.3 ppm;
HRMS (ES): m/z calcd for C17H23NO4Na+: 328.1525 [M+Na]+; found:
328.1525.
4-Aminophenethyl methacrylate (7): Trifluoroacetic acid (25 mL)
was added dropwise to 6 (1.20 g, 3.93 mmol) dissolved in anhy-
drous dichloromethane (80 mL), and the solution was stirred at
room temperature for 40 h. The solvent mixture was removed at
reduced pressure, and the residue was dissolved in dichlorome-
thane (50 mL) and washed with a saturated aqueous solution of
Na2CO3 (3ꢁ40 mL). The organic layer was dried over MgSO4, fil-
tered, and the solvent removed at reduced pressure to obtain 7 as
a colorless glassy solid (0.77 g 3.75 mmol, 96% yield). 1H NMR
(300 MHz, CDCl3): d=1.93 (s, 3H), 2.87 (t, J=7.1 Hz, 2H), 3.59 (brs,
2H), 4.29 (t, J=7.1 Hz, 2H), 5.52–5.56 (m, 1H), 6.07–6.10 (m, 1H),
6.64 (d, J=8.4 Hz, 2H), 7.02 ppm (d, J=8.4 Hz, 2H). 13C NMR
The polymerization procedure was repeated several times and the
nanoparticle characterization (TGA, potentiometric titrations, and
SEM) was repeated to confirm the reproducibility of the method.
The nanoparticles employed in the catalytic measurements (i.e.,
HPNP transesterification and cleavage of diribonucleosides) were
from the same polymerization batch to ensure comparable results
were obtained.
Potentiometric titrations
(75 MHz, CDCl3): d=18.3, 34.2, 65.6, 115.3, 125.3, 127.8, 129.7,
+
136.3, 144.7, 167.3 ppm; HRMS (ES): m/z calcd for C12H16NO2
206.1181 [M+H]+; found: 206.1188.
:
Potentiometric titrations were performed by means of an automat-
ic titrator equipped with a combined microglass pH electrode. The
experimental details and the procedure for the electrode calibra-
tion were the same as previously reported.[6] Potentiometric titra-
tions were carried in a nitrogen atmosphere with solutions (3.5–
5.0 mL) of the nanoparticles (10 mg) and 10 mm Me4NClO4 6–9 mg
in 80% DMSO (258C). A solution of 40–60 mm Me4NOH in 80%
DMSO was added to the titration vessel in small increments. Analy-
sis of the titration plots was carried out by using HYPERQUAD
2000.[28]
4-[N,N’-Di(tert-butoxycarbonyl)guanidine]phenethyl methacry-
late (8): Trimethylamine (1 mL) and HgCl2 (680 mg, 2.52 mmol)
were added to a stirred solution of 7 (210 mg, 1.02 mmol) and bis-
Boc-thiourea (670 mg, 2.43 mmol) in dry DMF (20 mL; Aldrich
99.8%) at 08C (cooled with an ice bath). The reaction was
quenched after 2 h by adding AcOEt (30 mL), and the HgS precipi-
tate was filtered. The solvent was removed and the residue was
purified by column chromatography (SiO2, hexane/AcOEt (40:1!
15:1)) to obtain 8 as a white solid (270 mg 0.60 mmol, 59% yield).
1H NMR (300 MHz, CDCl3): d=1.49 (s, 9H), 1.52 (s, 9H), 2.93 (t, J=
6.9 Hz, 2H), 4.31 (tr, J=6.9 Hz, 2H), 5.51–5.54 (m, 1H), 6.05–6.07
(m, 1H), 7.18 (d, J=8.4 Hz, 2H), 7.52 (d, J=8.4 Hz, 2H), 10.31 (brs,
1H), 11.64 ppm (brs, 1H); 13C NMR (75 MHz, CDCl3): d=18.2, 28.00,
28.05, 34.5, 65.0, 79.6, 83.6, 122.2, 125.4, 129.3, 134.4, 135.2, 136.2,
153.4, 167.2 ppm; HRMS (ES): m/z calcd for C23H33N3O6Na+:
470.2267 [M+Na]+; found: 470.2281.
HPNP transesterification
Kinetic measurements of the HPNP cleavage were carried out with
UV/Vis spectrometric analysis by monitoring the para-nitrophenol
liberation at l=400 nm on a double-beam spectrophotometer. Ali-
quots of solutions of Me4NOH (15–100 mm) were added to the re-
action mixture to reach the desired pH value (the measurements
were carried out with a microglass pH electrode calibrated as pre-
viously reported),[6] and the pH value of the solution was also
checked after the kinetic runs. The rate constants were obtained
by using the initial-rate method, and the error limits were on the
order of ꢁ5%, unless otherwise stated in the table. A typical
kinetic run is reported in Figure 5S in the Supporting Information.
4-Guanidinephenethyl methacrylate hydrochloride (2·HCl): A so-
lution of 8 (270 mg, 0.604 mmol) in a mixture of dioxane and 0.5m
hydrochloric acid (1:1, 5 mL was stirred for 2 days at room temper-
ature. Evaporation of the solvent gave 2·HCl as a colorless glassy
solid (210 mg, 0.582 mmol, 91% yield). 1H NMR (300 MHz,
[D4]MeOH): d=1.92 (s, 3H), 3.04 (tr, J=6.6 Hz, 2H), 4.38 (tr, J=
6.6 Hz, 2H), 5.58–5.64 (m, 1H), 6.64–6.09 (m, 1H), 7.25 (d, J=
8.4 Hz, 2H), 7.40 ppm (d, J=8.4 Hz, 2H). 13C NMR (75 MHz,
Cleavage of diribonucleoside monophosphates
[D4]MeOH): d=18.4, 35.5, 66.3, 126.3, 126.7, 131.7, 134.5, 137.7,
The transesterification of 3’,5’-monophosphates NpN’ was moni-
tored by means of HPLC analysis of aliquots of the reaction mix-
ture withdrawn at appropriate time intervals. The reactions were
carried out at pH 9.9 and 50.08C with 0.10 mm NpN’ and
2.0 mgmLꢀ1 solutions of nanoparticles I in 80% DMSO (10 mm
Me4NClO4 was used as an ionic-strength buffer). The pH value of
the solution was measured by using a microglass pH electrode cali-
brated as previously reported.[6] In a typical experiment, a solution
of Me4NOH in 80% DMSO was added to the reaction mixture until
the desired pH value was reached. The mixture was thermostated
+
139.4, 158.1, 168.7 ppm; HRMS (ES): m/z calcd for C13H18N3O2
248.1399 [M+H]+; found: 248.1404.
:
Preparation of hybrid nanoparticles: Trichlorosilane 1 (890 mg,
1.96 mmol) was transferred to a flask containing a suspension of
silica nanoparticles (1.05 g; Aldrich; diameter=20 nm) in anhy-
drous THF (8 mL). The commercially obtained silica nanoparticles
were dried at 1108C for 6 h before dispersion in THF. The reaction
mixture was stirred at room temperature in an argon atmosphere
for 48 h. The nanoparticles were isolated by centrifugation, redis-
Chem. Eur. J. 2015, 21, 1 – 9
7
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ