Sreenivasulu et al.
Supporting Information
for
Controlled Self-assembly of Multiferroic Core-Shell Nanoparticles Exhibiting
Strong Magneto-electric Effects
Gollapudi Sreenivasulu,1 Maksym Popov,1,2 Ferman A. Chavez,3 Sean L. Hamilton,1Piper R.
Lehto,1 and Gopalan Srinivasan1 a)
1
Physics Department, Oakland University, Rochester, MI 48309-4401, USA.
2
Radiophysics Department, Taras Shevchenko National University of Kyiv, Kyiv, 01601,
Ukraine.
3
Chemistry Department, Oakland University, Rochester, MI 48309-4401, USA.
a) email: srinivas@oakland.edu
Sreenivasulu et al.
Experimental
Materials
Trifluoromethanesulfonic anhydride, propargyl alcohol, 3-buten-1-ol, methanesulfonyl chloride,
silica gel (60, 0.0320.063 mm, 230−400 mesh), sodium L-ascorbate were procured from Alfa
Aesar.
Trimethyl citrate and sodium azide were obtained from Sigma-Aldrich. Copper(II)
acetate tetrahydrate, triethylamine, sodium sulfate (anhydrous) were purchased from Acros.
Ethyl acetate, hexanes, and DMSO were obtained from Mallinckrodt. O-propargyltrimethyl
citrate was prepared as described in the literature,1 Tris(3-hydroxypropyltriazolylmethyl)-amine
was prepared by a known method.2 Dichlormethane, THF, DMF, and ether were purified using
an Innovative Technologies, Inc. solvent purification system. Methanol (Fischer) was used as
received. Pyridine (Alfa Aesar) was distilled from CaH2. A Milli-Q water purification system
(Millipore Corporation) was used to generate purified water.
Synthesis
Prop-2-ynyl trifluoromethanesulfonate. This compound was prepared according to a modified
literature method.3 Trifluoromethanesulfonic anhydride (44 mL, 0.262 mol) was dripped slowly
into a stirring solution of dry pyridine (21.1 mL, 0.262 mol) in methylene chloride (600 mL) at
40 °C (acetonitrile/dry ice) under nitrogen. Neat propargyl alcohol (14.7 mL, 0.255 mol) was
added dropwise over a 15 min period. The suspension was allowed to warm and filtered through
a medium sintered glass funnel containing a pad of celite. The dichloromethane was removed in
vacuo and the resultant oil was extracted with pentane (3 x 50 mL). The pentane was filtered
through 1:1 w/w celite:anhydrous sodium sulfate and then removed in vacuo. The product was
Sreenivasulu et al.
isolated by fractional distillation (bath temperature: 40 °C, 60 mmHg). Yield: 18.0 g (26%). The
colorless oil was stored at 70 °C. Spectroscopic characterization matched published values.3
O-propargyl citric acid. 767 mg (2.82 mmol) O-propargyltrimethyl citrate was refluxed in 56
mL 2.4 M HCl for 3 h. The solution was vacuum distilled keeping the solution temperature
below 100 °C. The sample was then placed under high vacuum overnight at 25 °C. Yield: 606.4
mg (93%). Spectroscopic characterization matched published values.1
Functionalization of Nanoparticles. Azide modification was achieved using a procedure similar
to that reported elsewhere.4 The 10-100 nm NFO nanoparticles prepared by co-precipitation and
(vendor supplied) BTO particles were immersed in 3-buten-1-ol and then sealed in a nitrogenfilled quartz cuvette. The cell was mechanically agitated while it was exposed to ultraviolet (UV)
light (254 nm, ∼15 mW/cm2) for 17 h to graft the 3-buten-1-ol molecules to the nanoparticle
surface via the alkene group. The samples were then rinsed sequentially with MeOH, CHCl3,
and iPrOH. The terminal OH groups were converted to methanesulfonyl (mesyl) groups by
immersing the sample in a 10:1 (by volume) CH2Cl2:triethylamine at 0 °C then adding
methanesulfonyl chloride (1 volume) and allowing the mixture to sit for 1 h at 0 °C. After rinsing
with CH2Cl2, MeOH, and iPrOH the mesyl groups were converted to azide groups by immersing
the sample in a solution of supersaturated NaN3 in DMSO for 15 h at 80 ºC. Rinsing with
deionized water for one minute followed by iPrOH resulted in azide-modified nanoparticles.
Successful functionalization was verified using FTIR (KBr pellet) spectroscopy. The appearance
of absorbance bands that are characteristic of azide-bound onto the nanoparticles were not
clearly observed between 13801620 cm1 due to overlap with peaks already present in the
Sreenivasulu et al.
unfunctionalized nanoparticles. A peak at 2036 cm1, however, was clearly observed in the FTIR
spectra in Figure 1(b) and is known to be associated with the azide group.1 Functionalization of
NFO or BTO nanoparticles with O-propargyl citrate groups was accomplished by mixing Opropargylcitric acid1,3 (10 mM in MeOH) with the nanoparticle suspension in methanol. In a
typical reaction, 120 mg of O-propargylcitric acid was dissolved in 60 mL methanol and added to
3 g of BTO. The mixture was ultrasonicated for 1.5 h and then centrifuged using a benchtop
centrifuge. The supernatant was decanted and the pellet was washed with fresh methanol.
Attachment of the O-propargyl citrate groups was verified using FTIR (KBr pellet) spectroscopy.
The appearance of absorbance bands that are characteristic of O-propargyl citrate bound onto the
nanoparticles was observed at 1570 and 1412 cm-1 in the FTIR spectra.1
CuAAC reaction between functionalized nanoparticles. This was carried out as follows: In
one experiment, 75 mg each of alkyne modified BTO (50 nm) and azide modified NFO (10 nm)
along with100 mg of sodium ascorbate were placed in 15 mL of water. To this was added 4.4 mg
of
copper(II)
acetate
tetrahydrate
and
10
mg
of
tris[(1-benzyl-1H-1,2,3-triazol-4-
yl)methyl]amine2 (Cu/TBTA) solution in 10 mL DMSO. This solution was sonicated for 15 min
and allowed to sit at 25 °C for 15 h. The samples were then sequentially rinsed with deionized
water, MeOH, and iPrOH and dried.
Sreenivasulu et al.
References
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2. V. Hong, S. I. Presolski, C. Ma, and M. G. Finn, Angew. Chem. Int. Ed. 2009, 48, 9879.
3. E. Vedejs, D. A. Engler, and M. J. Mullins, J. Org. Chem. 1977, 42, 3109.
4. A. C. Cardiel, M. C. Benson, L. M. Bishop, K. M. Louis, J. C. Yeager, Y. Tan, and R. J.
Hamers, ACS Nano 2012, 6, 310.