Design and synthesis of two novel functional metal-organic microcapsules; An investigation into ligand expansion effects on the metal-organic microcapsules' properties

Article abstract of DOI:10.1039/c6ra23075j

In this study, two novel metal-organic capsules were synthesized based on coordination-directed organization of two new extended tetrazolate ligands (1,4-bis((1H-tetrazol-5-yl)methyl)benzene (btmbenzene), 4,4′-bis((1H-tetrazol-5-yl)methyl)biphenyl (btmbiphenyl)) and Zn²⁺ ions. Furthermore, the function of these capsules in the inclusion of inorganic nanoparticles (Fe₃O₄), dyes (Rhodamine B) and drugs (5-fluorouracil) was investigated. Moreover, the effects of ligand expansion on the size, morphology, loading capacity and other properties of these capsules were studied. In addition, other morphologies of these coordination polymers were fabricated under different conditions. Finally, the obtained microcapsules were utilized for the synthesis of crystalline ZnO hollow spheres via a calcination method.

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DOI: 10.1039/C6RA23075J
Journal Name
ARTICLE
Design and synthesis of two novel functional metal-organic
microcapsules, an investigation on ligand expansion effects on
metal-organic microcapsules' properties
Received 00th January 20xx,
Accepted 00th January 20xx
R. Nouri, S. Abedi, A. Morsali*
DOI: 10.1039/x0xx00000x
In this study, two novel metal-organic capsules were synthesized based on coordination-directed organization of two new
extended tetrazolate ligands (1,4-bis((1H-tetrazol-5-yl)methyl)benzene (btmbenzene), 4,4'-bis((1H-tetrazol-5-
yl)methyl)biphenyl (btmbiphenyl)) and Zn2+ ions. Furthemore, functions of these capsules in inclusion of inorganic
nanoparticles (Fe3O4), dye (Rhodamine B) and drug (5-fluorouracil) were investigated. Moreover, effects of ligand expansion
on the size, morphology, loading capacity and other properties of these capsules were studied. In addition, other
morphologies of these coordination polymers in different conditions were fabricated. Finally, obtained microcapsules were
utilized for synthesis of crystalline ZnO hollow spheres via calcination method.
www.rsc.org/
Introduction
guest molecules.7,8 Afterward in 2010, discus-like nanoscale
coordination polymers comprising a π-conjugated dicarboxylate
Infinite coordination polymers (ICPs) consist of polymerized
metal-ligand networks which can be synthesized by self-
assembly of metal nodes and a polydentate organic ligand, have
recently been regarded as a captivating innovative class of
inorganic–organic materials.1-3 Metal–organic capsules with
capability of adaptive entrapment of various functional species
are new ICP materials which have appealed to researchers in
recent years. Newly, various guest materials as exemplified by
drugs, dyes, small nanoparticles, nucleotides, have been
ligand and lanthanide ions were fabricated by Uvdal et al. which
demonstrated guest inclusion properties. Interestingly, loading
quantity of guest molecules into these ICPs can be regulated by
altering synthesis temperatures.9 Next, Mao and coworkers
could prepare ICP nanoparticles from b-nicotinamide adenine
dinucleotide and terbium ions with encapsulation ability.10 In 2014,
our group revealed synthesis of ICP nanocapsules assembled
from the metal node (Zn2+) and ditopic organic ligand (btb: 1, 3-
bis(tetrazol-5-ylmethyl)benzene) Zn(btb) with spherical
morphology. Accordingly, some core-shell particles could also
be synthesized via calcination of tetrazole-based ICP capsules.11
Recently reported metal-organic capsules with ability of
confining inorganic particles belong to Zhang et al. which were
prepared via photodecomposition of ferrocenedicarboxylic acid
in methanol.12 A dominant challenge in the fabrication of
functional metal-organic capsules is to change chemical
components and increase host-guest interactions without
transforming the fundamental morphology. Expansion is a
regular aspect of metal-organic frameworks (MOFs) fabrication
and directional-bonding synthesis of supramolecular
coordination compounds.13 Generally in this method, ligands
with additional phenyl or ethynyl groups are applied that raise
the length between Lewis basic centers of a polydentate
linker.13 Addition of phenyl or ethynyl spacers leads to
enlargement of the dimension of MOFs cavities and internal
pores of supramolecular coordination compounds without
important influence on the synthesis route. Applying expanded
linkers with a specific secondary building unit (SBU) results in
fabrication of a series of analogous MOFs which have the same
network topology.13 Effects of adding a phenyl group on the size
and other properties of metal-organic capsules have not been
investigated yet.
included
into
self-supported
ICPs
coordination
networks.4,5,7,8,9,10,11 In 2009, Kimizuka et al. reported
preparation of supramolecular networks constructed from
lanthanide ions and nucleotides which exhibited adaptive
encapsulation features. Moreover, ability of these capsules as
contrast enhancing agents for magnetic resonance imaging
(MRI) were proved.5 However, the main drawback of
lanthanide-containing compounds is their toxicity toward the
living systems.6 Concurrently, inorganic-organic empty spheres
consisting of Zn(II) metal ions and 1,4-bis(imidazol-1-ylmethyl)
benzene (bix) were synthesized based on the self-assembly
technology by Maspoch et al..4 Significance of these capsules
was in their magnitude which scope in dimension from about
100 nm to over 1 μm. These capsules are bigger than metal–
organic polyhedra that commonly have sizes of a few
nanometers with narrow ability of inclusion of small numbers of
Department of Chemistry, Faculty of Sciences, Tarbiat Modares University, P.O. Box
14115-4838, Tehran, Iran. E-mail: morsali_a@modares.ac.ir; Fax: +98 21 8009730;
Tel: +98 21 82884416
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
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Fig. 2 a) Fluorescence microscopy image of Zn(btmbenzene)-1 microspheres
deposited onto glass (λex=359–371 nm, λem> 440 nm) b) PL spectrum collected
at λexc=350 nm.
Scheme 1 N-donor-based building blocks for this project.
Fig. 3 Fluorescence optical microscopy images of (a) RhB@Zn(btmbenzene)-1
(λexc=540–552 nm, λem> 590 nm) b) PL spectrum collected at λexc= 350 nm.
Results and Discussion
All ligand syntheses were carried out under an argon atmosphere by
reacting the corresponding 2,2'-(1,4-phenylene)diacetonitrile and
2,2'-(biphenyl-4,4'-diyl)diacetonitrile with sodium azide and
triethylamine hydrochloride in accordance with literature
procedures (ESI).15 To prepare btmbenze ligand, 2,2'-(1,4-
phenylene)diacetonitrile, sodium azide and triethylamine
hydrochloride were refluxed in dry toluene for 72 h under an inert
argon atmosphere. The work up was performed according to
detailed information available in electronic supplementary
information (ESI). The prepared product was characterized by 1H
NMR, 13C NMR spectroscopy (Fig. S2 and Fig. S3 respectively†) and
elemental analysis. All analyses confirmed the formation of
btmbenzene ligand. In an experiment, methanolic solution of
Zn(NO3)2.6H2O was added to the DMF solution of tetrazolate ligand
(btmbenzene, Scheme 1) under stirring and the homogenized
Fig. 1 a) Low-magnification SEM images of the Zn(btmbenzene)-1 spheres. b)
High-magnification SEM image. (c) High-resolution TEM image of an
individual Zn(btmbenzene)-1 sphere.
mixture poured into
a
Teflon-lined stainless steel autoclave.
o
Subsequently, it was heated at 120 C for 12 h and then cooled to
room temperature for 3 h which ended up preparing white powder
named as Zn(btmbenzene)-1. To purify the product, the mixture was
washed with DMF several times and centrifuged. Field-emission
scanning electron microscopy analysis of Zn(btmbenzene)-1 showed
that the product consists of spheres with average diameters of 5 µm
which have smooth surfaces. Fig. 1 (a and b) shows SEM images of
bare Zn(btmbenzene)-1 microspheres. Fig. 1 (c) demonstrates
corresponding high resolution transition electron microscopy
(HRTEM) image of the Zn(btmbenzene)-1 which confirms these
microcapsules are hollow. FT-IR spectrum of the compound
displayed two strong peaks in 1431 and 1657 cm-1 which are
attributed to deprotonation of tetrazole rings and coordination of
ditopic ligands to Zn2+ cations (Fig. S7†). Thermogravimetric analysis
(TGA) of ICPs were performed at a range from 25-800 oC under a flow
of nitrogen gas at a constant rate of 10 oC/min to investigate the
weight loss as a function of temperature and evaluate the thermal
stability.
We supposed that addition of a phenyl group would result in
the larger dimensions of the metal–organic spheres and the
prepared capsules could entrap more amounts of the guest
molecules.13 Moreover, additional phenyl ring in the linker leads
to an increase in the electron density of the structure and
favorable π-π interactions. Hence, such capsules could have a
better interaction with guest molecules.14 Therefore, we aimed
to design two novel metal-organic ICP capsules based on two
new tetrazolate ligands of different length to investigate
expansion effects on these materials (Scheme 1). Moreover,
other morphologies of these coordination polymers were
synthesized in different conditions. We hope that this work can
open a new route for the synthesis of various tetrazole-based
metal-organic microcapsules with novel extended linkers of the
same type and maintaining the original morphology.
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Scheme 2 Synthesis of btmbenzene-based micro- and nano-structures: (a)
MeOH/DMF/solvothermal conditions (b) MeOH/DMF/fast precipitation
method, (c) H2O/DMF/reflux, (d) H2O/DMF/solvothermal.
Fig. 5 a, b) SEM images of Fe3O4@ Zn(btmbenzene)-2 (scale bar a and b =2
and 1 µm respectively) and c, d) HRTEM images of Fe3O4@Zn(btmbenzene)-2
spheres (scale bar c and d =200 and 100 nm respectively)
Fig. 6 Magnetic hysteresis loop of Fe3O4@ Zn(btmbenzene)-2 measured at
room temperature.
Fig.
4 SEM images of (a) Zn(btmbenzene)-2 (scale bar=1 µm), (b)
Zn(btmbenzene)-3 (scale bar =1 µm), (c) Zn(btmbenzene)-4 (scale bar=30 µm)
d) Zn(btmbenzene)-2 after transformation to cubic structures in
H2O/DMF/solvothermal (scale bar=5 µm).
Fluorescence optical microscopy and fluorescence spectroscopy
analyses were carried out to study the dye inclusion talent of these
hollow microspheres. As can be seen in Fig. 3, red emission is
associated with excitation upon 540 nm which indicates inclusion of
This analysis demonstrated that a major loss of weight occurred at
350 oC that ended at about 420 oC (Fig. S11†). X-ray diffraction (XRD)
experiment of the material were carried out to study its structure.
According to XRD analysis of microcapsules, the structure is
amorphous without any crystalline area (Fig. S9†). Elemental analysis
data of the ICPs affirmed [Zn(btmbenzene)]n for Zn(btmbenzene)-1.
dye
RhB@Zn(btmbenzene)-1. Quantity of RhB loading into
Zn(btmbenzene)-1 was also evaluated by UV-vis
molecules
into
Zn(btmbenzene)-1
named
as
spectrophotometer. RhB@Zn(btmbenzene)-1 was dispersed in
deionized water at pH of 5 and stirred for 72 h. Next, the mixture was
centrifuged and absorbency of the supernatant was determined at
554 nm utilizing UV-vis spectrophotometer. According to UV-vis
analysis, loading capacity of Rhodamine B into Zn(btmbenzene)-1
was 20 µmol/g (Table S2 and Fig. S19†). Fig. S20† shows FT-IR spectra
of Zn(btmbenzene)-1 and RhB@Zn(btmbenzene)-1 which are the
same. Moreover, FESEM image of RhB@Zn(btmbenzene)-1 confirms
that the product maintains its spherical morphology after in-situ
encapsulation process (Fig. S21†). Therefore, the guest molecules did
not interfere the overall synthesis of the host polymer during in-situ
encapsulation. Nowadays a common approach for smart drug
delivery to tumor cells is applying microcapsules containing human
therapeutic drugs.20-22 5-Fluorouracil (5-FU) is an anticancer drug
which is broadly applied in clinical chemotherapy for the treatment
of different tumors as exemplified by breast adenocarcinoma and
colon cancer.23-25
Luminescence is
a well-known feature of inorganic-organic
coordination polymers which is due to the presence of aromatic or
conjugated linkers or lanthanide ions in their structures.16
Photoluminescence characteristics of ICPs were studied by
photoluminescence spectroscopy. Excitation of Zn(btmbenzene)-1
microcapsules at 350 nm leaded to emission with peak maximum at
450 nm (Fig. 2b). Fluorescence microscopy images of
Zn(btmbenzene)-1 showed an intensive blue emission for these
microcapsules (Fig. 2a). Inclusion capability of these self-assembled
hollow microspheres was investigated by loading of Rhodamine B
fluorescent dye. Rhodamine B is regularly utilized as a tracer dye,
hydrophilic model drug and widely in biotechnology applications.17-
19Therefore, certain amount of the dye was added to the reaction
mixture to be entrapped inside the polymeric sphere through an in
situ encapsulation process.
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S18†). Moreover, influences of different synthesis strategies and
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solvents on the morphology of this infinite coordination polymer
DOI: 10.1039/C6RA23075J
were studied (Scheme 2). Conventional method reported for
preparation of metal-organic capsules is fast precipitation referring
to addition of a poor solvent to the reaction mixture which leads to
precipitation of polymerized hollow metal-organic capsules.4
Therefore, a solution of Zn(NO3)2·6H2O in methanol was added to
tetrazolate ligand btmbenzene in DMF under vigorous stirring. Fig.
4a displays the SEM images of the product obtained from the
reaction named as Zn(btmbenzene)-2 with the average size of 100
nm. FT-IR spectrum of the sample showed two strong peaks at 1374
and 1667 cm-1 similar to Zn(btmbenzene)-1 related to tetrazole
coordination to Zn2+ ions (Fig. S7†).26,27 XRD analysis showed an
amorphous
phase
for
Zn(btmbenzene)-2
(Fig.
S9†).
Thermogravimetric analysis of the sample exhibited 20 % weight loss
related to DMF and the main weigh loss region is between 320 and
o
420 C (Fig. S12†). Fe3O4 nanoparticles were selected as a model to
investigate the inclusion of the infinite coordination polymers for the
insoluble guest. Fe3O4 nanoparticles were dispersed in the DMF
solution of btmbenzene ligand and methanolic solution of
Zn(NO3)2·6H2O was added to the mixture gradually (ESI). Fig. 5
demonstrates the corresponding FESEM and TEM images of the
product. HRTEM images obviously show Fe3O4 nanoparticles
entrapped inside the polymeric spheres. The magnetic properties of
the obtained Fe3O4@ Zn(btmbenzene)-2 capsules were examined
utilizing a vibrating sample magnetometer. According to the
magnetization curve of the magnetic polymeric nanocapsules, the
saturation magnetizations for Fe3O4@ Zn(btmbenzene)-2 is 10 emu.
g-1 (Fig. 6).
Fig. 7 a) Low-magnification SEM image b) High-magnification SEM images of
the Zn(btmbiphenyl)-1 hollow spheres. (c, d) High-resolution TEM image of
an individual Zn(btmbiphenyl)-1 sphere.
In a practice, aqueous solution of zinc nitrate was added to
btmbenzene ligand solution in DMF and refluxed for 72 h. Next, the
product was separated by centrifuge and characterized by FESEM.
FESEM image of this compound named as Zn(btmbenzene)-3 shows
the morphology of this coordination polymer is rod like structure
(Fig. 4b). XRD analysis of Zn(btmbenzene)-3 rods demonstrated some
sharp peaks indicating a semi-crystalline nature (Fig. S9†). Moreover,
flower-like structures denominated as Zn(btmbenzene)-4 could be
synthesized by reaction of aqueous solution of zinc nitrate and
btmbenzene ligand in DMF at 140 oC in a Teflon-lined stainless steel
autoclave (Fig. 4c). The structure of the material was studied by XRD
analysis which exhibited a crystalline character (Fig. S9†). Elemental
analyses were performed for these four morphologies which
displayed the same percentages on carbon, nitrogen and hydrogen
atoms and approved [Zn(btmbenzene)]n for all these infinite
coordination polymers. As can be seen in Fig. S7, FT-IR spectra of
these three morphologies resemble each other with two distinctive
strong peaks at about 1400 and 1600 cm-1 indicating coordination of
tetrazole groups to Zn2+ ions. These evidences confirm that all five
morphologies of [Zn(btmbenzene)]n have the same constituents. In
addition, transformation of these structures upon changes to
exterior circumstances were studied. Zn(btmbenzene)-2
nanocapsules were separated by centrifuge from the reaction
mixture and washed with DMF and dried, then put into a Teflon-lined
stainless steel autoclave containing DMF and methanol and heated
at 120 oC for 24 h. Remarkably, an important morphological
Fig. 8 PL spectrum of Zn(btmbiphenyl)-1 hollow spheres collected at λexc= 420
nm.
Fig. 9 Fluorescence optical microscopy images of RhB@Zn(btmbiphenyl)-1 (a,
b) λexc= 359 -371 nm and λem>397 nm.
To exhibit the diversity in ability of these hollow spheres for
encapsulation of the molecules, 5-FU was chosen as a guest.
Following alike experimental procedure, Zn(btmbenzene)-1
microspheres which entraped 5-FU were synthesized (ESI). 5-
FU@Zn(btmbenzene)-1 was dispersed in deionized water at pH of 5
and stirred for 72 h.
UV-vis analysis was performed at 260 nm on the supernatant
solution to estimate the quantity of 5-FU loading into 5-
FU@Zn(btmbenzene)-1 microspheres. The quantity of 5-FU
encapsulation in microspheres was 158 µmol/g. (Table S1 and Fig.
transformation
Zn(btmbenzene)-2 turned to
occurred
and
small
nanocapsules
of
spherical microcapsules of
Zn(btmbenzene)-1 (Fig. S15†). In an experiment, nanocapsules of
o
Zn(btmbenzene)-2 were heated at 140 C for 72 h in a Teflon-lined
stainless steel autoclave containing DMF and H2O. FESEM images of
the product showed that these nanocapsules changed to cubic-like
structures (Fig. 4d and S17).
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Scheme 3 Synthesis of btmbiphenyl-based nano- and micro-structures: (a)
MeOH/DMF/solvothermal conditions (b) MeOH/DMF/fast precipitation
method, (c) H2O/DMF/solvothermal.
Fig. 11 FESEM images of ZnO architectures obtained from calcination of the
prepared ICPs after calcination of (a) Zn(btmbenzene)-1 (scale bar=1 µm), (b)
Zn(btmbiphenyl) (scale bar= 20 µm) in air at 550 oC for
3 h, (c)
Zn(btmbenzene)-1 (scale bar =1.5 µm) and (d) Zn(btmbiphenyl)-1 (scale bar
=5 µm), in air at 450 oC for 3 h.
1
The work up procedure is accessible in (ESI). Elemental analysis, H
NMR (Fig. S5†) and 13C NMR (Fig. S6†) spectroscopy proved the
synthesis of btmbiphenyl ligand. Following a similar procedure,
Zn(btmbiphenyl)-1 microcapsules were prepared by solvothermal
reaction of btmbiphenyl ligand in DMF and methanolic solution of
Zn(NO3)2·6H2O salt in 120 oC. The morphology of as-synthesized
product was studied by FESEM analysis. In accordance with the
FESEM images (Fig. 7) particles have spherical morphology with
average size of 20 µm. As anticipated, by employing the extended
linker, the size of the prepared spheres increased obviously.
Moreover, unlike Zn(btmbenzene)-1 microcapsules, the surface of
these expanded ICPs is completely unsmooth. The structure of
Zn(btmbiphenyl)-1 compound was analyzed by HRTEM as well. Fig. 7
exhibits TEM images of the Zn(btmbiphenyl)-1 which validate the
formation of hollow microcapsules. Infrared spectrum of the sample
resembling that of the material Zn(btmbenzene)-1 reveals
frequencies at 1403 and 1604 cm-1 proving polymerization of Zn2+
ions and tetrazole groups (Fig. S8†). Thermogravimetric study of
Zn(btmbiphenyl)-1 exhibited the major weight decline domain
between 310 oC and 430 oC relevant to destruction of ICPs (Fig. S13†).
Powder x-ray diffraction experiment was carried out to investigate
the crystallinity of the sample. Surprisingly, the related XRD pattern
displayed sharp peaks indicating the crystalline structure of these
capsules (Fig. S10†). The elemental composition of these hollow
capsules was examined by elemental analysis. According to
elemental analysis [Zn(btmbiphenyl)]n was offered for
Zn(btmbiphenyl)-1. Emission properties of Zn(btmbiphenyl)-1 was
studied using photoluminescence spectroscopy. When its
microcapsules were excited at 420 nm, the obtained emission
spectrum exhibited a peak with λmax at 660 nm (Fig. 8). PL spectrum
of Zn(btmbiphenyl)-1 showed an obvious red-shift in comparison
with the Zn(btmbenzene)-1. Increasing π-conjugation in the ligand
led to a decrease in the HOMO-LUMO gap which caused ligand to
metal charge transfer became ineffective and consequently, ligand-
based emission occurred and red-shift was observed in the PL
spectrum. To investigate the potential of Zn(btmbiphenyl)-1 for
loading of 5-FU in a similar procedure, it was encapsulated into the
microcapsules (ESI). Amount of 5-FU loaded into the microcapsules
was determined utilizing a UV-vis spectrophotometer (Table S1 and
Fig. 10 SEM images of (a) Zn(btmbiphenyl)-2 (scale bar=2 µm), (b)
Zn(btmbiphenyl)-3 (scale bar =1 µm).
Zinc oxide nanostructures have been considered as significant key
materials due to wide field of applications such as photocatalysts,
gas sensors, antimicrobial activities, electronic and optoelectronic
devices. Various micro and nanostructures of zinc oxide have
been synthesized as exemplified by rods, belts, combs, saws,
spirals, rings and hollow spheres.28-35 Hollow zinc oxide spheres
have been considered as an applicable desired morphology of this
material due to their special advantages such as good surface area
and low density.36-43 We decided to use these hollow metal-
organic microsphere to prepare hollow zinc oxide microspheres
through calcination. Therefore, hollow Zn(btmbenzene)-1
spheres were calcinated at 450 and 550 oC for 3 h in the air to find
the best temperature to prepare ZnO with retaining the spherical
morphology. FESEM images of products show that spheres keep
their spherical morphology after calcination at 450 oC but the
morphology changed under calcination at 550 oC (Fig. 11). The
sample produced at 450 oC was characterized by XRD analysis.
Obtained XRD pattern can be indexed to the wurtzite structure of
zinc oxide (Fig. S14†). It is noteworthy to mention that any other
diffraction peak was not observed confirming the spherical ICPs
entirely changed into the ZnO phase. The diversity and
development of supramolecular coordination compounds
obviously are indebted to the usage of larger extended decorated
bridging ligands.13We chose a longer linker of the same type
(btmbiphenyl) to synthesize an extended network with the
morphology of spherical capsule (Scheme 1). To prepare
btmbiphenyl ligand, 4,4'-bis(bromomethyl)biphenyl was used as
a precursor. The alkyl halide underwent nucleophilic aliphatic
substitution with sodium cyanide in distilled H2O under reflux
condition for 24 h. The obtained dinitrile product was
transformed into tetrazolate ligand through the reaction with
sodium azide and triethylamine hydrochloride under reflux in dry
toluene for 72 h and an inert argon atmosphere.
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Fig. S18†). Outcomes revealed that the 5-FU loading content was 188 microcapsules which could keep the desired holVloieww ArstipclheeOrnilcinael
µmol/g which is interestingly more than Zn(btmbenzene)-1. morphology in both conditions. Therefore, uDsiOnIg: 1Z0n.1(0b3t9m/Cb6ipRhAe2n3y0l7)5-1J
Moreover, encapsulation of Rhodamine B as a guest was performed microspheres also seems a better choice for obtaining hollow zinc
and analyzed through the identical method (Table S2 and Fig. S19†). oxide structures achieving more thermal stability of their
According to UV-vis spectrophotometer analysis, Rhodamine B morphologies.
loading capacity of the RhB@Zn(btmbiphenyl)-1 was 25 µmol/g.
Fluorescence microscopy images of the RhB@Zn(btmbiphenyl)-1
showed intense green emission related to the encapsulated
Conclusions
In brief, we succeeded to report synthesis of two novel self-
assembled hollow spherical metal-organic microcapsules based on
fluorescent dye (Fig. 9). Fig. S22† displays FT-IR spectra of
two new extended tetrazolate ligands of the same type and Zn2+ ions
Zn(btmbiphenyl)-1 and RhB@Zn(btmbiphenyl)-1 which have the
by solvothermal method. Moreover, different morphologies of these
same pattern. In addition, FESEM image of RhB@Zn(btmbiphenyl)-1
ICPs were prepared by changing reaction conditions and solvents
proves that the sample keeps its spherical morphology after in-situ
which include flower-like structures, cubes and rods. In addition,
through an in situ process entrapment of some functional materials
encapsulation process (Fig. S23†). Therefore, our expectations
fulfilled and Zn(btmbiphenyl)-1 microcapsules showed more loading
such as a kind of anticancer drug, fluorescent dye and inorganic
capacity for both 5-FU and Rhodamine B in comparison with
nanoparticles within these coordination networks were examined as
Zn(btmbenzene)-1 which can be attributed to stronger host-guest
a potential application. The loading capacities of these carriers for
interactions due to additional aromatic ring of btmbiphenyl organic
the examined anticancer drug and fluorescent dye were determined
linker (Scheme 1) and larger dimensions of the capsules. Afterward
and compared. Furthermore, these spherical polymeric
we tried to perform encapsulation of Fe3O4 magnetic nanoparticles
microcapsules were applied as precursors for fabrication of hollow
inside the polymeric spheres through an in situ process by
crystalline ZnO spheres via calcination which have been considered
solvothermal method but FESEM analysis of samples did not show
as a favorite morphology of zinc oxide due to their potential
any special structure.
applications in drug delivery carriers and catalysis.
Furthermore, the influences of operating conditions and solvents on
the morphology of these ICPs were also inspected. To study the
conventional method effects on the morphology, methanolic
solution of Zn(NO3)2·6H2O was added to btmbiphenyl ligand in DMF
Acknowledgement
We thank Tarbiat Modares University for supporting of this
investigation appreciatively.
dropwise at RT under stirring. The separated product was entitled as
Zn(btmbiphenyl)-2 and analyzed by FESEM. FESEM images of the
Zn(btmbiphenyl)-2 demonstrated that the flower-like structures
were synthesized (Fig. 10a). XRD analysis of the sample showed some
sharp peaks indicating semi-crystallinity of the compound (Fig. S10†).
In next step, aqueous solution of Zn(NO3)2·6H2O reacted with
btmbiphenyl solution in DMF under solvothermal condition at 140
oC. The morphology of the product named as Zn(btmbiphenyl)-3 was
studied by FESEM analysis. As can be seen in Fig. 10b and Scheme 3c
flower-like structures were obtained which have much ticker
branches in comparison with Zn(btmbiphenyl)-2. The powder was
characterized by XRD analysis and indicated that the compound is
crystalline (Fig. S10†). FT-IR spectra pattern of Zn(btmbiphenyl)-n (n=
2, 3) appeared like Zn(btmbiphenyl)-1 infrared spectrum (Fig. S8†).
According to elemental analyses of Zn(btmbiphenyl)-n (n= 2, 3) these
morphologies have the same formula expressed as
[Zn(btmbiphenyl)]n indicating these three morphologies have the
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