Magnetothermia-Induced Catalytic Hollow Nanoreactor for Bioorthogonal Organic Synthesis in Living Cells

Article abstract of DOI:10.1021/acs.nanolett.0c01507

Nanoreactors, in which the reactions are remotely controlled by magnetic fields, are potentially valuable in bioorthogonal chemistry for future applications. Here, we develop a silica-confined magnetothermia-induced nanoreactor (MAG-NER) by selectively gr

Full text of DOI:10.1021/acs.nanolett.0c01507

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Communication
Magnetothermia-Induced Catalytic Hollow Nanoreactor
for Bioorthogonal Organic Synthesis in Living Cells
Jihwan Lee, Sateesh Dubbu, Nitee Kumari, Amit Kumar, Jongwon Lim, Seonock Kim, and In Su Lee
Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.0c01507 • Publication Date (Web): 07 Jul 2020
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Magnetothermia-Induced Catalytic Hollow Nanoreactor for
Bioorthogonal Organic Synthesis in Living Cells
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†
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Jihwan Lee, Sateesh Dubbu, Nitee Kumari, Amit Kumar, Jongwon Lim, Seonock Kim, In Su Lee
†Creative Research Initiative Center for Nanospace-confined Chemical Reactions (NCCR), and
Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang 37673
(South Korea)
§These authors contributed equally to this work.
*To whom correspondence should be addressed
E-mail: insulee97@postech.ac.kr (I. S. L.)
.
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ABSTRACT: Nanoreactors, in which the reactions are remotely controlled by magnetic fields, are
potentially valuable in bioorthogonal chemistry for future applications. Here, we develop a silica-confined
magnetothermia-induced nanoreactor (MAG-NER) by selectively growing Pd nanocrystals on a pre-
installed iron-oxide core inside a hollow silica nanoshell. The growth is achieved by magnetic induction.
The interfacial catalytic site is activated by stimulating localized magnetothermia, and nano-
compartmentalization is realized by the size-selective porous silica. Therefore, MAG-NER can be
conveniently used in complex bio-media, and can even be internalized to living cells, realizing an on-
demand, high-performance intramolecular carbocyclization reaction by remote operation without
compromising the cell viability. This work opens avenues for the design of advanced nanoreactors that
complement and augment the existing bioorthogonal chemical tools.
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KEYWORDS: Nanocatalyst, Hollow nanoreactor, Magnetothermia, Bioorthogonal reactions,
Nanospace confinement
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The hollow vesicular structures of different organelles such as endosomes, exosomes, mitochondria
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and nuclei perform unique sets of biochemistries and establish functional synchronicity. These properties
are mainly conferred by the compartmentalized bio-environment, which maintains the optimum pH,
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molecular transport, and molecular concentrations. Natural organelles and enzymes can only have limited
specific set of biochemical functions; and, their wider applications can suffer from several drawbacks
such as: deactivation under non-native conditions, cumbersome structure-reactivity manipulation, low
scalability, and complex reaction pathways. Advanced organic chemistry offers huge potential for
designing and synthesizing bio-applicable metal-based catalysts for new-to-nature reactions. Such
chemical biology toolkit would enable the highly targeted and on-demand synthesis of bioimaging and
therapeutic molecules, facile protein modification, and regulation of radicals and small biomolecules,
potentially offering great benefits to biomedical science.2-13 Natural compartmentalization has inspired
the development of synthetic hollow and porous nanoshells encapsulating surfactant-free catalytic metal
nanocrystals (NCs). Such hollow nanoreactors can potentially function as artificial catalytic organelles
inside living cells. They provide efficient cellular uptake, high bioorthogonality, easy surface
bioconjugation, and functional customization; moreover, the catalytic surfactant-free NCs are protected
from surface poisoning by unwanted interactions with complex biomolecules. Within the
compartmentalized space, the NCs are free from agglomeration and biotoxicity, and can perform their
catalytic functions undisturbed.14-16 Recently, Destito et al. modified metal NCs within hollow silica
microparticles, and demonstrated their colloidal stability in biological media, but the reaction rates were
compromised by the low reactivity of the catalyst further their large-size limits scope for intracellular
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catalytic reactions. Bioorthogonal reactions have also been regulated by visible/UV light, but visible
light suffers low penetrability and UV light is harmful to biological materials.18,19 Recently we also
reported, remotely stimulated reactions by plasmonic-catalytic hybrids under near-infrared light. However,
controlling the adverse effects of photothermal temperatures and the unwanted light scattering by the bio-
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environment are major bottlenecks.20-23 Among the various energy stimuli, magnetic fields are favored
for biomedical applications owing to their operational convenience, efficacy, controllability and
biocompatibility. Little magnetic energy is transferred to the bio-environment, as has been well proven in
modern magnetic resonance imaging, targeted hyperthermia therapy, on-demand drug delivery, and
magnetic actuation.24,25 Magnetic-field induced heating (MFIH) of hybrid magnetic-catalytic nano-
platforms has been achieved in solution-phase organic synthesis in flow reactors26-28 and closed vessels,29
but as this process generates excessive heat in bulk solution, it is unsuitable for bioorthogonal applications.
Hybrid magnetic-catalytic nanoreactors are a promising alternative, because the MFIH can be remotely
operated and highly localized. Therefore, they can accelerate chemical reactions at nanoconfined catalytic
sites without increasing the macroscopic temperature and hence suitable to perform catalysis in complex
biological media without compromising the catalyst reactivity and stability. However, such nanoreactors
for biorthogonal applications have never been synthesized and utilized. Here, we synthesize a localized
magnetothermia-induced nanoreactor (MAG-NER) by spatioselective growth of catalytic metal NCs at
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magnetic core (Fe
3
O
4
) interface confined inside hollow silica nanospace by applied AMF. The Fe
3
O core
4
of MAG-NER serves as an AMF-nanoheater, directly transferring energy to the intimately synthesized
Pd-site. The heat-activated Pd initiates an efficient intramolecular alkynyl-carbocyclization reaction,
generating fluorescent probes within short reaction times (< 50 min). Meanwhile, the porous silica
enclosure admits only the reactants and products, prohibiting the entrance of large biomolecules that could
poison the metal surface, consequently, preserving the activity of the catalytic NCs. MAG-NERs are
efficiently taken up by living cells, are minimally cytotoxic, and perform efficient intracellular catalytic
reactions only under AMF (Scheme 1).
To synthesize MAG-NER, we first coated iron-oxide nanoparticles (NPs) with amino-silica (forming
Fe
3
O
4
@SiO
2
), then hollowed the SiO
2
shell by hydrolysis at 70℃, the resulting Fe
O
3 4
@h-SiO had an
2
inner diameter of 26 (± 6) nm and an outer diameter of 42 (± 5) nm (Figure 1a, S1). The magnetothermal
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heating efficiency of Fe
SiO
Fe
interior, would lead to the selective growth of Pd NCs on the Fe
mixture of Na PdCl (2 mg/ml) and Fe @h-SiO (1 mg/ml) in ethylene glycol (EG) to AMF (200 G,
255 kHz) for 1h, the bulk solution temperature (T) rose to 25 ℃. The isolated product (Pd/Fe @h-SiO
was characterized by transmission electron microscopy (TEM), which revealed formation of single Pd
NC (7 ± 2 nm) localized at the interface of the Fe -core (Figure 1e). The structure and composition of
Pd/Fe @h-SiO were verified by high-resolution TEM (HRTEM, Figure 1h, 1i), scanning electron
3
O
4
@h-SiO
2
, measured by recording the temperature rise of a colloidal Fe
3
O @h-
4
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solution under applied AMF (Figure 1j). Owing to the highly localized magnetothermal effect of the
-core under AMF induction, we proposed, concentrated temperature gradient within the hollow
-core. We thus exposed a suspension
3
O
4
3
O
4
2
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3
O
4
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)
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microscopy (SEM, Figure 1e inset, S2), X ray diffraction (XRD, Figure S3), scanning tunneling electron
microscopy using a high-angle annular dark-field detector [STEM–HAADF, Figure 1g(i)], STEM-energy
dispersive X-ray spectroscopy [STEM-EDS, Figure 1g(ii–iv), S5] based elemental mapping, and X-ray
photoelectron spectroscopy (XPS) (Figure S6). Average hydrodynamic size of Pd/Fe
Figure S7) was found to be ca. 120 nm (slightly larger than the size measured by TEM (68±7 nm))
through DLS analysis. The SQUID measurement for Pd/Fe @h-SiO , showed a weak ferromagnetism
Figure S8), and slightly lower saturation magnetization (49.5 emu·g ) compared with Fe
O
3 4
@h-SiO
2
in DI
(
O
3 4
2
−1
(
3
4
O (explained
in SI).30,31 This result accords with the unaffected magnetothermal efficiency; the highest macroscopic
temperature of the colloidal suspension was 25℃ at 200 G AMF (Figure 1k).
To understand mechanism for the formation of Pd NCs at the interface of the Fe
Pd/Fe @h-SiO , under AMF exposure, we investigated the time course of the reaction by TEM (Figure
b–e) and XPS (Figure S6) at different time intervals (t). At t = 0 (i), the Pd elements were homogeneously
3
4
O -core in
3
O
4
2
1
2
+
2+
0
distributed throughout the silica shell, and the predominant species was Pd (XPS: Pd /Pd = 80/20), At
t = 10 min (ii), the Pd granules began coalescing into Pd NCs (ca. 4 nm), and the Pd(0) species increased
2+
0
(
XPS: Pd /Pd = 75/25). At t = 30 min (iii), most of the Pd NCs (ca. 5 nm) were near the Fe
3
4
O core, and
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2
+
0
the dominant species was Pd(0) (XPS: Pd /Pd = 40/60). Finally, at t = 60 min (iv), single Pd NCs (ca. 7
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nm) were interfaced at the Fe
3
O core, having Pd /Pd = 20/80. The plausible mechanism deduced from
4
the results has been discussed in SI (Figure S6). Control experiments in ethanol and DI generated only
0
traces of the reduced Pd species, confirming the indispensable role of EG during synthesis (details are
discussed in Figure S9)32-34 In a series of control experiments, we replaced the AMF with conventional
external heating at T = 30, 50 and 70℃, there the Pd NCs were indiscriminately grown on the internal and
external silica-surfaces (Figure 1f, S10), confirming that localized heating by AMF is essential for spatio-
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selective NC growth. In another control experiments, we also proved that the Fe
prerequisitefor the spatio-selective growth of Pd NCs (Table S2). In the experiment (i) with Fe
very few Pd NCs appeared only on the surface of the solid silica shell (Figure S10a), while in (ii) h-SiO
without the Fe
of sf-Fe NCs and h-SiO
S11c). A similar growth pattern was observed in (iv) sf-Fe
mixture of sf-Fe NCs and Fe @h-SiO (v), yielded omnipresent Pd NCs (Figure S11e), but in
control experiment (vi), with a physical mixture of h-SiO and Fe @h-SiO , the Pd NCs were localized
inside the Fe @h-SiO , leaving h-SiO devoid of any Pd NCs (Figure S11f). This series of control
experiments clearly justifies the critical role of the magnetically engineered Fe @h-SiO structure in
directing the synthesis of ligand-free catalytic NCs on pre-installed magnetic-core inside the silica shell,
by exploiting AMF induced highly localized hyperthermia polyol process in synthesis of Pd/Fe @h-
SiO . To check the porosity of Pd/Fe @h-SiO , BET measurements were carried out. The nitrogen
adsorption–desorption isotherms of Pd/Fe @h-SiO showed the type IV isotherm with a hysteresis loop
in the P/P range of 0.5−1.1 revealing characteristics of mesoporous material (Figure S12a). The BET
surface area and pore volume were 559.04 m g and 1.704 m g correspond to the hollow interior of
O
3 4
@h-SiO
2
system is
3
O
4
@SiO
2
,
2
3
O
4
core, the Pd NCs were not formed (Figure S10b). In experiment (iii), a physical mixture
yielded Pd NCs on both the surface of sf-Fe and in bulk solution (Figure
NCs alone (Figure S11d). The physical
3
O
4
2
O
3 4
O
3 4
3
O
4
O
3 4
2
2
3
O
4
2
3
O
4
2
2
3
O
4
2
3
O
4
2
3
O
4
2
3
O
4
2
o
2
−1
3
−1
Pd/Fe
3
O
4
@h-SiO
2
. The Barrett–Joyner–Halenda (BJH) pore size distribution of the hollow nanoparticles
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showed narrow pore size distribution with average d = 3.8 nm (Figure S12b), which can be attributed to
the presence of mesopores in silica shell.
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The synthesized nanoreactors can potentially realize catalytic applications.35-37 The effectiveness of
Pd/Fe
3
O
4
@h-SiO (hereafter called MAG-NER) was first evaluated in the Pd-catalyzed intramolecular
2
carboannulation reaction,38,39 which synthesizes fluorescent 2a from a non-fluorescent procoumarin
substrate 1a (Figure 2a). A typical catalytic reaction was carried out in a vial containing substrate 1a (0.05
mmoles) and MAG-NER ([Pd] = 1 mol%) as the catalyst in a 1:1 mixture of acetonitrile:water (1 mL)
solvent, under AMF exposure (255 kHz, 200 G, Figure 2b, Table S3), after 1h of reaction cyclized product
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a was obtained in ~95% yield (confirmed by NMR). To further study the reaction kinetics, we recorded
the fluorescence spectra (402 nm excitation/ 530 nm emission) corresponding to the product 2a at different
reaction times, and estimated the conversion yields from a calibration plot (Figure S13). In control
reaction, without AMF exposure at 18℃, only 8% of the product 2a was formed after 2 h (Figure 2b).
While, at the physiological temperature (37℃) and no AMF exposure, the yield of 2a was 18%, however,
by externally heating the bulk reaction solution to 55℃, 2a was observed in ~91% (Figure 2b), roughly
matching the yield of the AMF-induced reaction indicating the magnitude of the localized MFIH within
MAG-NER. Notably, in a control experiment using Fe
surface, under AMF and thermal heating (55˚C) conditions, the 2a was only 17% (Figure 2c, S14), and
2 % (Table S5) confirming Pd NCs can’t be sufficiently activated by AMF while present on the silica
shell and not directly interfaced on Fe -core. In another control experiment using Pd@h-SiO (no Fe
under identical reaction conditions, the cyclized product 2a was obtained at 8% (AMF, Figure 2c, S15)
and ca. 60% (thermal heating, Table S5), comparable to the Fe @SiO @Pd catalyst, indicating the
conventional bulk heat-mediated activation of PdNCs in both the cases. The reaction with Fe @Pd
3
O
4
@SiO
2
@Pd with Pd NCs on the outer silica-
6
3
O
4
2
3
4
O )
3
O
4
2
O
3 4
catalyst gave ~ 65% yield of 2a at 55˚C (Table S5), possibly due to the agglomeration of catalyst as
observed in TEM images (Figure S17). All these control experiments have authenticated that MFIH-
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exerting Fe
3
O
4
is necessary for activating the Pd NCs in MAG-NER. Fe
3
O
4
@h-SiO (with no Pd NCs)
2
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resulted almost no reaction (Figure 2c, S18), affirming the [Pd]-mediated carbocyclization mechanism
(plausible mechanism is discussed in SI, page 24). Further to confirm the possibility of Pd (II) to be active
catalyst, we carried out several control experiments. For that purpose, first we synthesize the Fe
3
O @h-
4
SiO containing Pd(II) salt (Fe @h-SiO /Na PdCl ) modified at the interior and exterior silica shell
2
3
O
4
2
2
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and carried out the cyclization reaction using substrate 1a under AMF affording only poor yield (ca. 20%)
of 2a. In another control the cyclization reaction was carried out with catalyst having physical mixture of
Fe
3
O
4
@h-SiO
2
and Na
2
PdCl
4
, where the product yield was 7%, under AMF. While the reaction with the
only Na
2
PdCl
4
did not result in any product formation under AMF condition. Moreover ICP-OES of
supernatant solution of reaction mixture showed absence of any leached Pd (II). We also carried out the
carbocyclization reaction of 1a using this supernatant solution, where formation of 2a was not observed.
All above control experiments suggest that in the presence of AMF, MAG-NERs can catalyze the
carbocyclization reaction by involving Pd(0). Next, we analyzed the influence of the substrate size on
reaction selectivity due to the porous silica-shell in MAG-NER. For this purpose, we synthesized an
alkylnoate substrate with a long alkyl chain (C H19). The bulky substrate 1g was unreactive with MAG-
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NER under AMF and at 55℃. The noticeable non-reactivity of the large substrate is likely attributable to
the restricted approach through the porous silica shell. Unimpeded by the silica shell, substrate 1g was
readily converted by the Fe
3
4
O @Pd, forming the cyclized product within 60 min (yield = 63%) under
AFM (entry 1h in Figure 2e). In order to verify such a reactivity difference in catalysis of 1g by MAG-
NERs, we synthesized a series of substrates having different carbon chain lengths (C1, C5, C7) as shown
in Table S6 and performed carbocylization reaction under AMF exposure using MAG-NERs. In the
reaction with the substrate having C7 carbon chain (entry 3) with almost similar hydrophobicity to C9,
37% of cyclized product was obtained after 80 min of exposure to AMF. While in reaction with substrates
with C5 (entry 2) and methyl-substitution (entry 1) 82% and 92% yield of cyclized products were observed,
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respectively. Such a substrate-size-dependent remarkable difference in chemical reactivity could only be
resulted from a size-selective molecular diffusion through the mesoporous silica-shell in MAG-NERs.
The catalytic efficiency of MAG-NERs for the intramolecular carbocylization reaction under AMF was
replicated on substrates with different aryl substituents (1b1f). As shown in Figure 2e, MAG-NER
efficiently catalyzed carbocyclization of alkynoate substrates bearing electron-donating groups, but
alkynoate substrates bearing electron-withdrawing groups (1e) or alkynamide (1f) were unreactive under
identical conditions. This finding was attributed to the electron-deficient phenyl ring in 1e and the low
electrophilicity of the alkyne group in 1f (Figure S37-45). The recyclability test for MAG-NERs was
performed by isolating them through centrifugation after reaction of substrate 1a (Figure S19). Product
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yield was consistent up to 4 cycle (ca. 90%) while in the 5 cycles, yield was slightly reduced to ca.
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th
however there was loss ca. 33% loss of Pd content after 5 catalytic cycle.
Next, we explored feasibility of MAG-NER to catalyze the carbocyclization reaction in biologically
relevant conditions. For that, we performed the cyclization of substrate 1a to its highly fluorescent
coumarin product 2a. A solution of 1a (in 20% vol. acetonitrile) in phosphate buffered saline (PBS)
solution (pHꢀ=ꢀ7.4) with MAG-NER ([Pd]-1 mol%) provided the cyclized product 2a in ~65% yield
within 1 h of AMF induction (Figure S21). Similarly in bovine serum albumin (BSA, 5 μM), cyclized
product 2a was obtained in ~60% yield after 1 h of AMF induction (Figure 2d, S22). Importantly, the
transformation was efficiently accomplished in complex cell culture media such as Dubelcco’s modified
Eagle’s medium (DMEM), and even in cell lysates, affording 2a at ~70% and ~55% yields (Figure S23,
S24), respectively. Notably, a Fe
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for catalyzing the cyclization reaction in BSA protein solution and DMEM, probably because deactivating
protein corona formation around the Pd NC, as confirmed by the adsorption of fluorescein-labelled BSA
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on to Fe
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BSA on MAG-NER’s silica surface was also characterized by DLS-based hydrodynamic size and zeta
potential measurements data and TEM (Figure S25 and S26).
After evaluating the catalytic activity of MAG-NER in various aqueous solutions, we studied its
intracellular performance in human breast cancer cells (MCF-7 cells). We first tested the cytotoxicity of
MAG-NER by exposing MCF-7 cells (5000 cells per well in a 96-well plate) to different amounts of
MAG-NER (10, 20, 100, 200, 500 μg/mL), and incubating them for 48 h (Figure S27). The cell viability
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(ca. 89%) remained high at MAG-NER concentrations up to 500 µg/mL. In the cellular uptake
experiments, cells treated with MAG-NER for 4 h were washed to remove the excess non-internalized
MAG-NER, and their percentage cellular uptake was estimated as 65% by ICP-OES. Furthermore, the
locations of the MAG-NERs within the cell cytoplasm were affirmed by TEM imaging of fixed and
sectioned MCF-7 cells after NP treatment (Figure 3a). The stable hollow structures of the nanoreactors
were clearly demonstrated in the intracellular environment. For potential biorthogonal applications,
stability of silica in MAG-NERs was tested in different bio-relevant media (PBS and DMEM) and cell
lysate (Figure S28). Localization of MAG-NERs inside cytoplasmic region of living cell (MDA-MB-231
cells) was also analyzed using high resolution confocal laser scanning microscopy (CLSM), indicating
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MAG-NERs to follow endocytosis pathway for internalization (Figure S29, Movie S1). The tolerability
of living cells to MAG-NER under AMF exposure was explored, for that the cells incubated with MAG-
NER were exposed to AMF for different times, and their tolerances were evaluated by cell viability assay.
The results revealed that MAG-NER was minimally toxic (cell viability ca. > 90%) until 30 min of AMF
exposure; in contrast, the cells viability with Fe
3
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O @Pd reduced to < 20% within 30 min of AMF exposure,
demonstrating damaging effect of silica-free magnetic NPs under AMF (Figure 3b). Further, we attempted
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the conversion of procoumarin (1a) to its highly fluorescent coumarin derivative (2a). In a typical
experiment, MCF-7 cells were first incubated with MAG-NER for 4 h, after removing the extra NPs by
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washing, substrate 1a was added in fresh medium. After overnight (or 1 h) incubation, the cells were
washed three times with PBS and labeled with a common nucleus stain NucBlue™ Invitrogen (nuclei
stain). Under AMF application, the intracellular conversion of 1a to 2a was monitored by fluorescence
microscopy and flow cytometry. After exposure to AMF for 30 min, a clear strong fluorescence built
inside the cells, consistent with the formation of the product 2a (Figure 3c, panels ii). In contrast, the
control cells under no magnetic induction showed almost no fluorescence signal (Figure 3d). Also, as
shown in the flow cytometry-based quantitative analysis (Figure 3e), the fluorescence was significantly
higher in the cells exposed to AMF than in the control cells without AMF excitation. In order to confirm
the origin of fluorescence is due to the formation of fluorescent product (2a): in a control experiment,
MCF-7 cells were treated with pre-synthesized 2a as a positive control which resulted the origin of green
fluorescence in the cytoplasm of the cells (Figure S30); whereas incubation with 1a with the cells (in
absence of AMF) did not show characteristic green fluorescence, confirming that the green fluorescence
localized only in the cytoplasmic region is due to the AMF-induced conversion of 1a to 2a with MAG-
NER, not due to some artifacts. We tested the catalytic performance of MAG-NERs for two more cell
lines: MDA-MB-231 (epithelial human breast cancer cells, Figure S31) and MCF-10A (non-cancerous
epithelial cells, Figure S32). Results with both cells were similar to the MCF-7 cells. We estimated the
quantities of internalized Pd by ICP (Figure S33a) and concentrations of the fluorescent product 2a
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(Figure S33b) formed inside different cell lines by fluorescence measurements of different cell lysates.
The estimated number of product molecules formed after intracellular reaction was much higher than Pd
atoms internalized as catalysts inside cell; so, it is reasonable to designate the reaction as catalytic process.
Clearly, the AMF application induced the catalysis in vitro, demonstrating that MAG-NERs are highly
controllable and versatile nanoreactors for bio-applications in complex environments.
In conclusion, we designed and synthesized a new class of magnetically engineered catalytic hollow-
silica-based nanoreactors called MAG-NERs. Under magnetic induction, the growth of catalytic metals
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was guided within the confines of the hollow silica, and was localized at the interface of an in-built Fe
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core. Equipped with highly active, ligand-free Pd NCs at the Fe
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MAG-NER efficiently catalyzes carbocyclization reactions, converting a range of non-fluorescent
substrates to fluorescent products in aqueous and physiologically relevant complex conditions. Besides
maintaining the ambient bulk temperature, MAG-NER can carry out bioorthogonal catalytic reaction in
vitro, under the convenient remote operation of AMF. This work provides new perspectives for
customizing nanoreactors with different catalytic NCs, and augmenting their activity with a bio-friendly,
remotely operable magnetic field. The proposed strategy will greatly benefit biomedical and biological
applications.
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ASSOCIATED CONTENT
Supporting Information. Additional TEM images, XRD patterns, XPS spectra, magnetization curves.
A movie file of CLSM z-stack images. This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
insulee97@postech.ac.kr.
Author Contributions
§contributed equally to this work.
Notes
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The authors declare no competing financial interests.
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ACKNOWLEDGMENT
This work was supported by the Basic Science Research Program through the National Research
Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (MSIP) (Grant
NRF-2016R1A3B1907559) (I.S.L.).
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0. Nadeem, K.; Krenn, H.; Sarwar, W.; Mumtaz, M. Comparison of surface effects in SiO coated
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and uncoated nickel ferrite nanoparticles. Appl. Surf. Sci. 2014, 288, 677–681.
1. Vestal, C. R.; Zhang, Z. J. Effects of surface coordination chemistry on the magnetic properties
of MnFe spinel ferrite nanoparticles. J. Am. Chem. Soc. 2003, 125, 9828–9833.
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2. Favier, I.; Pla, D.; Gꢂmez, M. Palladium nanoparticles in polyols: synthesis, catalytic couplings,
and hydrogenations. Chem. Rev. 2020, 120, 1146–1183.
3. Al-Azri, Z. H. N.; Chen, W.-T.; Chan, A.; Jovic, V.; Ina, T.; Idriss, H.; Waterhouse, G. I. N. The
roles of metal co-catalysts and reaction media in photocatalytic hydrogen production:
performance evaluation of M/TiO
2
photocatalysts (M = Pd, Pt, Au) in different alcohol–water
mixtures. J. Catal. 2015, 329, 355–367.
34. Fiévet, F.; Ammar-Merah, S.; Brayner, R.; Chau, F.; Giraud, M.; Mammeri, F.; Peron, J.;
Piquemal, J.-Y.; Sicarda, L.; Viaub, G. The polyol process: a unique method for easy access to
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metal nanoparticles with tailored sizes, shapes and compositions. Chem. Soc. Rev. 2018, 47,
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35. Qiao, Z.-A.; Zhang, P.; Chai, S.-H.; Chi, M.; Veith, G. M.; Gallego, N. C.; Kidder, M.; Dai, S.
Lab-in-a-shell: encapsulating metal clusters for size sieving catalysis. J. Am. Chem. Soc. 2014,
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36, 11260–11263.
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Chem. Soc. 2013, 135, 15714−15717.
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1. Vidal, C.; Tomás-Gamasa, M.; Destito, P.; López, F.; Mascareñas, J. L. Concurrent and
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orthogonal gold(I) and ruthenium(II) catalysis inside living cells. Nat. Commun. 2018, 9, 1913.
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Scheme 1. Schematics for (a) the synthesis of MAG-NER and (b) its catalytic applications for AMF-
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induced organic catalysis in living cells.
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a
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0 nm
20 nm
Pd
30 nm
20 nm
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0 mins
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20 nm
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0 mins
(
i)
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Fe3O4
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Pd
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Pd
111)
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(iii)
(
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Fe
Si
j 32
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k 32
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10 20 30 40 50 60
30℃
50℃
AMF
External heating
Time (mins)
Time (mins)
Figure 1. (a) TEM images of Fe
showing evolution of Pd NC inside Fe
SEM image of Pd/Fe @h-SiO (inset of e). (f) TEM images of products of Pd-growth reaction with
externally heating at (i) 30℃ and (ii) 50℃, respectively, and (iii) bar diagram displaying the location and
3
O
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@SiO
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(inset) and Fe
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@h-SiO
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. (b-e) Time course TEM images
3
O
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@h-SiO
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, EDS elemental map for Pd at 0 min (inset of b) and
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size of grown Pd NCs under different heating conditions. (g) (i) HAADF-STEM image of Pd/Fe
3
3
O
O
4
4
@h-
@h-
SiO
SiO
2
2
and its EDS elemental maps for (ii) Pd, (iii) Fe and (iv) Si. (h-i) HR-TEM images of Pd/Fe
, showing lattice spacings at Fe
3
O
4
/Pd interface. MFIH data for EG suspensions (10 mg/mL) (j) of
(green) and Fe @h-SiO (blue), measured under AMF at 200 G and 255
@h-SiO at various AMF strengthes.
sf-Fe
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O
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(red), Fe
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O
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@SiO
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O
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kH, and (k) of Pd/Fe
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Figure 2. Catalytic performance of MAG-NERs for intramolecular carbocyclization reaction. (a)
Schematic for [Pd]-catalyzed carbocyclization for tetracyclic flourophore and photos of suspensions
before and after the reaction. (b) A kinetic study on the reaction of MAG-NER under different heating
conditions in CH
fluorescence intensity measurement at λex/em = 402/530 nm. (c) The conversion efficiency of different
catalysts for product 2a formation in CH CN:H O solvent. (d) Carbocyclization yields of 1a into product
a by MAG-NER (blue sticks) and Fe @Pd (grey sticks) in buffer, with additives (BSA) and in
3
CN:H O solvent. The concentration of product 2a formed were calculated from
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biological media (DMEM and cell lysate). MAG-NER effectively catalyzes the cyclization even in
complex biological media. (e) Substrate scope with product yields using MAG-NER.
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Figure 3. (a) Low- and high-mag TEM images of fixed and sectioned MCF-7 cells after treatment with
MAG-NER showing cytosolic internalization of NPs (The difference in size of MAG-NERs between
Figure 1 and Figure 3e is due to the different synthesis batches, which resulted homogeneously different
thicknesses of silica shells). (b) Cell viability results of NPs-treated MCF-7 cells after exposing to
magnetic field for different times. (c-d) Bright field and fluorescence images (green: cytosol, blue: nucleus,
merged) of MCF-7 cells after treatment with MAG-NERs and substrate 1a with and without AMF
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application. (e-g) Flow cytometry analysis showing a population of cells treated with substrate and MAG-
NER with (green) and without (grey) AMF application.
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