A nano-composite of magnetite and hot-water-soluble starch: A cooperation resulting in an amplified catalytic activity on water

Article abstract of DOI:10.1039/c8nj00718g

Bis-coumarins and xanthenes are privileged compounds with diverse pharmaceutical activities. Hence, we introduce here an efficient synthesis of 3,3′-arylmethylene-bis-(4-hydroxycoumarin-3-yl) and 1,8-dioxooctahydroxanthenes under the soft catalytic activi

Full text of DOI:10.1039/c8nj00718g

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Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Nano-Composite of Magnetite and Hot-Water-Soluble Starch: A
Cooperation Resulting in an Amplified Catalytic Activity on Water
Sanaz Razikazemi,a Kurosh Rad-Moghadam,a,b,* and Saeedeh Toorchi-Roudsari b
Bis-coumarins and xanthenes are privilege compounds with diverse pharmaceutical activities. Hence, we introduce here an
efficient synthesis of 3,3´-arylmethylene-bis-(4-hydroxycoumarin-3-yl) and 1,8-dioxooctahydroxanthenes under soft
catalytic activity of magnetite encapsulated hot-water-soluble starch nanoparticles. The greater catalytic efficiency of the
bio-derived nano-composite in these syntheses over magnetite and hot-water-soluble starch was ascribed to cooperation
of its two components in proton exchange with the reactants. The enhanced proton exchange of the nano-composite was
better interpreted as being conducted by its bioorganic shell through switching between the covalent and the coordination
bonds it forms with the magnetite core. Application of a nontoxic and superparamagnetic bio-consistent catalyst, simple
work-up procedure, and short reaction times are the prominent advantages of the synthetic methods presented here. The
nano-catalyst is stable, as can be recycled in the model reactions at least four times without appreciable decrease in its
catalytic activity.
glucans. Upon these structural characteristics, amylopectin
Introduction
molecules gain more stabilization energy than amylose molecules
on crystallization.6 As a consequence, the hydroxyl groups arranged
along the backbone of amylose molecules are less involved in
crystalline regions by intermolecular hydrogen bonding and are
reactive groups. Owing to these reactive pendant hydroxyl groups
arranged along its polymeric chains, hot-water-soluble starch
In recent decades, application of natural polymers as catalysts has
captivated much attention.1 Interests in this topic lie particularly in
rise of global consciousness about environmental protection and
substitution of the limited resources with those of renewable
natural products. Biopolymers are the best candidates to mimic the
catalytic action of enzymes in designing new catalysts. Despite this
potential advantage, however, a majority of biopolymers are not
available inexpensively, require especial precautions to remain
native in reaction media, or are decomposed easily by molds and
ever-present microorganisms growing on them. Because of these
criteria, much interest was drawn towards applications of cellulose
and chitosan, the most abundant and reasonably robust bio-derived
polymers, which have been applied as backbones or supports in
fabrication of many catalysts.2 However, these bio-polymers are not
available in low molecular weights as easily as starch for production
of nano-catalysts.3 Starch is the most abundant polysaccharide,
after cellulose, being produced by plants for energy storage and
carbon reserve.4 Native starch is a heterogeneous mixture of
amylose and amylopectin, which differ in molecular size and degree
of branching. Flour starch is routinely separated into two fractions
by dispersion in hot water. The soluble fraction largely consists of
amylose and minute amounts of lower amylopectin molecules,
whereas the insoluble ingredient consists entirely of large
amylopectin molecules.5 Indeed, there are structural reasons
behind the solubility differences between these two fractions.
Amylose molecules are small and essentially linear α-1,4-glucans
with tiny amounts of α-1,6-branch linkages. On the other hand,
amylopectin molecules are larger and branched α-1,4- and α-1,6-
(HWSS) provides
a matrix for entrapment and morphological
modification of metal oxides7,8 and is endowed with a potential
catalytic activity.9,10 However, still due to these reactive hydroxyl
groups, HWSS exists as solid aggregates in most organic solvents.
Aggregation of HWSS chains into insoluble solids makes their
recovery feasible, though, with the expense that a majority of their
reactive hydroxyl groups get buried within the hierarchy of the
hydrogen-bonded chains. The ratio of surface hydroxyl groups
relative to those concealed between the H-bonded chains can be
increased by scaling the size of HWSS to nano-dimensions.
However, on the other hand, decreasing the size of solids to nano-
scales will burden their separation from reaction mixtures with the
difficulty of fine-filtering or ultracentrifugation. A practical strategy
to obviate such laborious separation methods is to support HWSS
on magnetic nanoparticles. Typically, nano-magnetic catalysts are
resolved from reaction mixtures by using a simple magnet with
much more efficiency and convenience than filtration or
centrifugation. This makes the so-called magnetic separation
costless and promising for green applications. To date, magnetite
has been the most widely employed material for preparation of
magnetic nanoparticles.11,12 This mixed metal oxide is an excellent
support for preparation of magnetic nano-catalysts due to being an
environmentally compatible compound and possessing a high
superparamagnetic property in nano-sizes. Superparamagnetic
nano-catalysts are strongly attracted to an applied magnetic field
during their magnetic separation from reaction mixtures and gain a
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good dispersion by lose of their magnetism instantly after removal magnetite nanoparticle, its surface iron atoms form less bridging
bonds to other iron atoms of the lattice, so tend to complete their
valence by coordination with the hydroxyl groups of HWSS. Similar
interactions may lead to formation of covalent C-O-Fe bonds and
allow the HWSS to be chemisorbed onto magnetite nanoparticles.
Formation of the hybrid nano-composite HWSS@Fe3O4 is also
rendered by physisorption, mainly through hydrogen bonding, and
coordination of amylose hydroxyl groups with the iron atoms
present on surface of the magnetite nanoparticles. As a result of
these interactions and thinness of the HWSS film sorbed onto Fe3O4
nanoparticle, the extent of hydrogen bonding between HWSS
molecules is considerably reduced by formation of the composite.
Figure 1 is illustrating these facts by comparing the FT-IR spectra of
HWSS and HWSS@Fe3O4. The IR spectrum of the freeze-dried HWSS
displays a very broad O-H stretching band at 3383 cm-1, evidencing
that a wide range of hydrogen bonding exists within the bulk
amylose. In contrast, similar vibrations for HWSS@Fe3O4 appear as
two distinguishable and relatively thinner bands at 3408 cm-1 and
3198 cm-1, arising from the non-coordinated hydroxyl groups of the
nano-composite and those coordinated with the iron atoms of
magnetite, respectively. A similar explanation accounts for the
appearance of two O-H bending bands in the IR spectrum of
HWSS@Fe3O4. Of these, the band at 1520 cm-1 results from a
of the applied field. Magnetite nanoparticle provides a high surface
area ornamented with reactive Fe-OH functionalities, which are
responsible for its intrinsic catalytic activity13-16 and its ability to
form stable composites by physical adsorption or chemical
anchoring of reactive catalysts.17-19 Immobilization of catalysts on
surface of magnetite nanoparticles is
a delicate strategy to
approach homogeneous catalysis by using easily isolable
heterogeneous catalysts.20,21 It was proved that magnetite do not
play just as a support in several of such catalytic composites,22 but
is able to enhance some catalytic activities via polarization of the
supported catalysts 23 or cooperation in the catalysis by its FeII/FeIII
system.24 Direct coordination and chelation with hydroxy ligands
such as carboxylates, phosphates, and catechols again confirm that
magnetite nanoparticle is reactive at its surface.12 In this
background, we introduce here HWSS as a reactive ligand for direct
assembling
a superparamagnetic composite with magnetite
nanoparticles and show that the prepared nano-composite is an
efficient catalyst in the synthesis of 3,3´-(arylmethylene)-bis-(4-
hydroxycoumarin) and 1,8-dioxooctahydroxanthenes on water.
Xanthenes are interesting heterocycles due to their promising member of O-H bonds in the HWSS layer, which have partially lost
their strength on coordination with iron atoms of magnetite, and
the band at 1625 cm-1 relates to bending of the non-coordinated
OH groups.60 Another notable difference between these spectra
occurs in the region of C-O stretching and C-O-H bending at 1154-
1022 cm-1. In this region, the bulk HWSS displays multiple bands
resulting from varied intermolecular interactions between its
molecules and in sharp contrast with HWSS@Fe3O4, which rather
gives only two simple relevant bands at 1121 cm-1 and 1049 cm-1.
Moreover, unlike HWSS, the band characteristic to amorphous
starch at nearly 1022 cm-1 is not seen in the IR spectrum of
HWSS@Fe3O4.61 These findings imply that the magnetite
nanoparticles were coated with thin layers of mostly ordered
amylose chains. Due to its thinness and ordered structure, the
amylose shell of the nano-composite gives also more simple C-H
stretching (2919 cm-1 and 2850 cm-1) and CH2 bending (1422 cm-1
and 1385 cm-1) bands relative to HWSS. It is also worthy to note
that unlike bare magnetite nanoparticles, with different surface and
inner Fe-O bond-strengths and hence two Fe-O stretching bands,62
only one Fe-O band is seen for HWSS@Fe3O4.
antibacterial, antitumor, anticancer, antiviral and antimicrobial
activities.25,26 In addition, these compounds are used as lasing
molecules and pH sensitive fluorescent materials for incarnation of
biomolecules.27,28 However, several routes have so far been
developed for synthesis of xanthenes,29-32 these compounds are
usually synthesized through the reaction of aldehydes with phenols
or cyclic enols by using various catalysts such as p-toluenesulfonic
35
,
acid,33 molecular iodine,34 K5CoW12O40
amberlyst-15,36 cation-
exchange resins,37 silica sulfuric acid,38 sulfamic acid,39 AcOH-
H2SO4,40 CuS quantum dots,41 Sc(OTf)3,42 cyanuric chloride,43
BF3.SiO2,44 Yb(OTf)3,45 In(OTf)3,46 P2O5/Al2O3,47 and ionic liquids.48
Coumarin and its derivatives are widespread in natural products
and in the structures of many synthetic bio-active molecules.49-51
Some bis-coumarin derivatives strongly inhibit tubulin aggregation
and can play essential roles against cancer cells via varied
mechanisms involving anti-angiogenesis and promotion of
apoptosis. These findings tend to classify bis-coumarin derivatives
as privileged drug candidates.52-56 3,3´-Arylmethylene-bis(4-
hydroxycoumarin-3-yl)s are directly synthesized through the
reaction of arylaldehydes and 4-hydroxycoumarin with the aid of
various catalysts.57-59 Although, many of these methods have their
own advantages, it is still worthwhile to develop alternative
expedient and green methods for synthesis of 3,3´-(arylmethylene)-
bis-(4-hydroxycoumarin-3-yl)s and 1,8-dioxooctahydroxanthenes by
using efficient and recyclable catalysts fabricated of bio-compatible
materials.
Results and discussion
A one-pot procedure was set up for the preparation of the
magnetite nanoparticles encapsulated in hot-water-soluble starch
(HWSS). This method delivers the nanoparticles of magnetite
through coprecipitation of FeIII and FeII oxides and disperses them
freshly in the matrix of HWSS. Owing to the finite size of the
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Figure 1. (a) The IR spectrum of HWSS@Fe3O4, (b) The IR spectrum of HWSS
.
showing a monomodal Gaussian distribution with the median of 60-
80 nm and slight drifts to both larger (144 nm) and smaller (32 nm)
sizes. The SEM micrograph substantially differs from that of native
starch, which normally consists of unpacked oval or spherical
granules with smooth surfaces.63
Apparently, the surface and inner Fe-O bonds of the magnetite
nanoparticles achieve comparable strengths as the surface iron
atoms complete their valence by formation of C-O-Fe bonds or
coordination to amylose molecules.
Further insight into the structure of the nano-composite was
obtained from its transmission electron microscopy (TEM) image
(Fig. 3). This image displays the very fine crystallites of magnetite as
dark points dispersed in the grey matrix of nano-sized HWSS
particles. The TEM image illustrates that the nanoparticles seen in
the SEM image (Fig. 2) are indeed the conglomerates of Fe3O4 nano-
crystallites and HWSS in which the magnetite crystallites are
majorly separated by thin layers of HWSS surrounding them. It is
obvious that HWSS have disassembled the agglomerates of
magnetite nanoparticles into smaller sizes and even to their
constituent nano-crystallites, presumably by formation of chemical
bonds with magnetite. The interaction between the two
components is strong enough to overcome the Van der Waals, H-
bonding, and the magnetic attractions between the crystallites. By
reducing the size of the magnetite nanoparticles, they acquire more
and more surface energy which render them to behave as reactive
sorbents. In this way, the magnetite nanoparticles serve as seeds
for formation of the nano-composite HWSS@Fe3O4. The TEM image
also displays that the nano-sized conglomerates partially change
morphology and divide into smaller conglomerates of HWSS@Fe3O4
during dispersion in ethanol used for preparation of the image.
50
Frequency
40
30
20
10
0
40 50 60 70 80 90 100 110 120 130 More
nm
Figure 2. The scanning electron microscopy image of HWSS@Fe3O4
Figure 4. The X-ray diffraction pattern of HWSS@Fe3O4
The X-ray powder diffraction pattern of HWSS@Fe3O4 (Fig. 4) shows
strong and sharp peaks at around 2θ = 30.5o, 35.8o, 43.5o, 54.2o,
57.3o, and 63.0o, corresponding to the Bragg reflections from (2 2
0), (3 1 1), (4 0 0), (4 2 2), (5 1 1) and (4 4 0) Miller planes in the
cubic inverse spinel structure of magnetite, according to the ICDD
card number 19-0629. There are no other resolvable peaks in this
spectrum except the moderate unindexed peak at 2θ= 74.6o, which
previously reported for magnetite64 and very weak peaks at 2θ =
17.4o, 22.9o, and 23.8o attributing to reflections from (3 0 1), (1 2 1),
and (4 1 2) planes of starch.65 The weakness and paucity of the
diffraction peaks relevant to HWSS layer indicate that HWSS@Fe3O4
nano-particles were constructed from thin films of this
polysaccharide. Evidently, the HWSS layer of the nano-composite is
too thin to form nano-crystalline whiskers on surface of the
magnetite nanoparticles. This means that a majority of the hydroxyl
groups pending from the amylose backbone, especially those reside
on surface of the composite, are not stabilized by interchain
hydrogen bonding and remain as very reactive groups. These
reactive hydroxyl groups are expected to enable the nano-
composite to take part efficiently in physical interactions as well as
Figure 3. The transmission electron microscopy image of HWSS@Fe3O4. The
dark points of the magnetite nano-crystallites are shown by the arrows.
Scanning electron microscopy (SEM) was employed to explore the
morphology of HWSS@Fe3O4. As Fig. 2 shows, the SEM image of
this nano-composite displays the spherical morphology and almost
mono-dispersion aspect of its nanoparticles. In this SEM image, the
nanoparticles are seen as tightly packed bright balls. Next to the
SEM image is seen the size distribution histogram of the particles
in chemical reactions with substrates. As
a consequence of
possessing these surface hydroxyl groups, the HWSS@Fe3O4
nanoparticles acquire energetic surfaces which force them to be
tightly packed in dry solid state (Fig. 2).
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liberated from the nano-composite on formation of additional
covalent or coordination bonds between HWSS and magnetite,
seems to be the main event of this degradation step. Removal of
these water molecules from the nano-composite sets the scene for
the amylose chains to adopt a much ordered structure on surface of
the magnetite core by formation of more coordination and covalent
bonds with the iron atoms. Overall, this step seems to be an inverse
gelatinization of amylose, so appears as an exotherm and associates
with early dehydration of HWSS@Fe3O4 at around 40 °C. The DSC
trace is followed instantly by a second exotherm peaking at 329 °C,
which coincides with the midpoint of the main mass-loss in the TGA
curve. Apparently, the main mass-loss step, which initiates at the
onset point of 263 °C, consists of endothermic condensation
between hydroxyl groups of amylose chains and the dominant
exothermic processes such as oxidative degradation of amylose by
magnetite. By the end of this step, totally 13.5% of the mass is lost
at around 400 °C and after that the TGA curve goes down smoothly
with a small mass-loss attributing to disintegration of amylose layer
and the residual char decomposition.66 Based on these analyses, the
average weight of HWSS shell in the nano-composite is estimated to
be ~ 7%.
Figure 5. Magnetization characterization of HWSS@Fe3O4
Owing to the hydrophilic nature of their outermost HWSS layer, the
nanoparticles of HWSS@Fe3O4 are well dispersed in water.
Moreover, the nano-composite is expected to bring the organic
reactants in close vicinity together by adsorbing them on its surface,
where they experience the catalytic effect of the reactive surface
hydroxyl groups especially those having significant acidity due to
coordination with the iron atoms of magnetite. In this viewpoint,
we aimed at exploring the catalytic efficiency of the nano-
composite in the synthesis of 3,3´-arylmethylene-bis-(4-
hydroxycoumarin-3-yl) and 1,8-dioxooctahydroxanthenes. In order
to find an optimum condition, synthesis of 3,3´-(4-
chlorophenyl)methylene-bis-(4-hydroxycoumarin-3-yl)
3,4,6,7-tetrahydro-3,3,6,6-tetramethyl-9-(4-chlorophenyl)-2H-
xanthene-1,8(5H,9H)-dione 5b via the pseudo three-component
reactions of 4-chlorobenzaldehyde with, respectively, 4-
hydroxycoumarin and 5,5-dimethyl-1,3-cyclohexadione
(dimedone) were chosen as the models to be examined in the
presence of various amounts of HWSS@Fe3O4 in different solvents
and at varying temperatures.
4d
and
Figure 6. The TGA and the DSC spectra of HWSS@Fe3O4
1
Magnetic susceptibility measurements for Fe3O4 and HWSS@Fe3O4
at room temperature by using a vibrating sample magnetometer
(VSM) led to the hysteresis loops shown in Fig. 5. Accordingly, the
saturation magnetization of HWSS@Fe3O4 was measured to be 20
emu.g-1, which is significantly higher than that of the pristine Fe3O4
nanoparticles (ca. 3 emu.g-1) it was made from. Disassembly of the
pristine magnetite nanoparticles to smaller nano-crystallites
through interaction with HWSS is the main reason accounting for
the higher magnetic saturation of HWSS@Fe3O4 with respect to
pristine Fe3O4. Upon reduction in size, the multidomain Fe3O4
nanoparticles turn into single-domain magnetic nano-crystallites.
When subjected to an external magnetic field, these particles
develop strong internal magnetization from exchange coupling of
electrons within their single-domain and thus become
superparamagnetic. This observation is indicative of a chemical
separation and dispersion of magnetite nano-crystallites by HWSS
and is better conceived as being driven through formation of
chemical bonds between these two components. Because of
possessing high magnetization susceptibility, HWSS@Fe3O4 shows
significant magnetic responses to separation from reaction mixtures
by using an external permanent magnet. The thermogravimetric
analysis (TGA) of HWSS@Fe3O4 displayed a two-step thermal
degradation trace (Fig. 6). The first step of this thermogram occurs
within the temperature range of 42-239 °C and results in a mass
loss of about 6.4%. This step corresponds to the early exothermic
trace in the differential scanning calorimetry (DSC) curve of the
nano-composite. Evaporation of the water molecules, which are
2
3
According to the results tabulated in Table 1, only moderate yields
of the desired products 4d and 5b are formed in the absence of any
catalyst even after prolong refluxing in water (entry 1). The best
results in terms of yields and reaction times are obtained by
performing the trial reactions in refluxing water and using the bio-
derived nano-composite HWSS@Fe3O4 as catalyst (see also the
electronic supplementary information, ESI). Notably, the same
reaction mixtures give very low yields in volatile and non-hydroxy
solvents (see ESI). Certainly, solvent plays crucial roles in these
synthetic methods such as mass transfer, lowering the energy gap
between reactants and transition states, dispersion of the nano-
composite, and removal of products from surface of the catalyst to
disrobe its catalytic sites. The supremacy of water is particularly
attributed to sorption of this solvent onto HWSS@Fe3O4, leading to
fine dispersion of the nano-catalyst and assisted desorption of the
products from its surface. Upon adsorption of water molecules, the
nano-composite acquires a greater density of fixed surface hydroxyl
groups to carry out its catalytic action. It is noteworthy that HWSS
and Fe3O4 are able to realize the trial syntheses within reasonable
times in refluxing water (entries 12, 13), however, with lower
efficiencies than is met by using the same quantity of their nano-
composite HWSS@Fe3O4.
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After these preliminary evaluations of the nano-catalyst, we set out position react slowly and give slightly lower yields than the
to explore the scope of the method by employing a variety of electron-deficient arylaldehydes. A plausible mechanism for the
arylaldehydes
1
to synthesize 3,3´-arylmethylene-bis-(4- catalytic role of HWSS@Fe3O4 was typically presented in Scheme 1.
hydroxycoumarin-3-yl)s 4 and 2H-xanthene-1,8(5H,9H)-diones 5 Presumably, the reactions are catalyzed via a cascade of proton
under the optimal conditions set forth above. As the results show exchange that the nano-composite makes with the reacting species
(Table 2), this method can inherently tolerate the various functional adsorbed on its surface. The supremacy of HWSS@Fe3O4 over
groups present at different positions of the reacting arylaldehydes. HWSS, magnetite, and the hydroxy solvents (H2O and Et-OH) in
Nevertheless, it is noticeable that electron-rich arylaldehydes and catalysis of the above reactions may be referred to cooperation of
particularly those bearing sterically demanded groups at ortho its bioorganic and inorganic components.
Table 1. Determining the optimized amounts of the catalyst, solvent, and temperature for the trial synthesis of 3,3´-(4-chlorophenyl)methylene-bis-(4-
hydroxycoumarin-3-yl) 4d and 3,4,6,7-tetrahydro-3,3,6,6-tetramethyl-9-(4-chlorophenyl)-2H-xanthene-1,8(5H,9H)-dione 5b
Cl
Cl
5b
3
1
2
4d
O
OH
CHO
OH
O
O
O
OH
O
O
O
O
Cl
O
O
O
Product 4d
Product 5b
Yield (%)a
Entry
Catalysta
Charged
Solvent
Temp (°C)
Time
Yield (%)a
23
Time
1
2
3
4
5
6
7
8
9
--
--
H2O
H2O
H2O
H2O
H2O
90
80
90
90
100
90
r.t.
90
90
90
35 min
35 min
35 min
45 min
35 min
35 min
35 min
35 min
35 min
35 min
30 min
30 min
30 min
40 min
30 min
30 min
30 min
30 min
30 min
30 min
9
HWSS@Fe3O4
HWSS@Fe3O4
HWSS@Fe3O4
HWSS@Fe3O4
HWSS@Fe3O4
HWSS@Fe3O4
HWSS@Fe3O4
HWSS@Fe3O4
HWSS@Fe3O4
15 mg
15 mg
15 mg
15 mg
15 mg
15 mg
15 mg
20 mg
10 mg
84
90
90
88
82
87
87
86
71
--
--
87
63
H2O/EtOH b
H2O
82
trace
trace
90
--
H2O
10
H2O
81
11
12
13
HWSS@Fe3O4
HWSS
5 mg
15 mg
15 mg
H2O
H2O
H2O
90
90
90
35 min
35 min
35 min
64
53
41
30 min
30 min
30 min
28
56
36
Fe3O4
Reaction conditions: 4-hydroxycoumarin (2 mmol) and 4-chlorobenzaldehyde (1 mmol) in distilled water (2 mL). Dimedone (2 mmol) and 4-
chlorobenzaldehyde (1 mmol) in distilled water (2 mL). aYields of the isolated products (± 2%), averaged over three experiments. bAqueous ethanol 50%.
Table 2. The viability of the method by using different substituted arylaldehydesa
M.P. (˚C)
Time
(min)
Product
Ar
Yieldb (%)
92
Ref.
[58]
Observed
229-230
Reported
228 - 230
4a
C6H5
30
4b
4c
4d
4e
4f
4g
4h
5a
5b
5c
5d
5e
5f
4-NO2C6H4
2-ClC6H4
4-ClC6H4
25
50
35
40
43
40
35
35
30
40
35
30
35
40
30
94
79
90
83
80
86
85
88
87
73
84
86
78
76
88
231-235
196-200
256-258
213-218
248-249
264-269
235-240
205-209
223-226
182-186
258-261
227-231
181-185
207-212
220-224
232 - 234
198-199
258 - 259
215-217
249 - 250
269 - 270
238
[58]
[70]
[71]
[72]
[71]
[71]
[57]
[67]
[67]
[68]
[73]
[67]
[54]
[73]
[68]
2-FC6H4
4-CH3OC6H4
4-CH3C6H4
3-CH3OC6H4
C6H5
201-203
231-233
184-186
259-260
224-226
177-180
209–210
230
4-Cl-C6H4
3,4-(MeO)2-C6H3
4-F-C6H4
4-NO2C6H4
3-MeO-C6H4
2-MeO-C6H4
4-CN-C6H4
5g
5h
aReaction conditions: An arylaldehyde (1 mmol), 4-hydroxycoumarin (2 mmol) or dimedone (2 mmol), HWSS@Fe3O4 (15 mg) in distilled water (2 mL) at 90
°C. b Isolated yields (± 2%), averaged over three experiments.
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Journal Name
O
O
O
O
1
2
O
O
2
6
O
H
O
O
H
HO
H
O
H
HO
H
O
O
O
O
OH
OH
O
HO
HO
O
HO
- H2O
O
O
O
4
O
O
O
O
2
HO
O
HO
Fe3O4
Fe3O4
H O
H
H O
H
I
II
I
II
O
O
8
O
O
O
1
3
3
7
O
O
O
O
H
O
O
H
H
O
H
HO
HO
HO
H
O
H
O
H
O
O
O
O
OH
O
OH
OH
HO
HO
HO
HO
O
HO
HO
O
- H2O
O
O
O
O
O
O
O
O
O
O
3
Fe3O4
Fe3O4
O
Fe3O4
I
I
II
II
- H2O
I
II
5
Scheme 1. A proposed push-pull proton donating and accepting mechanism for HWSS@Fe3O4.
deprotonated functional group. Therefore, the net enthalpy of
proton transfers by HWSS@Fe3O4 seems to be determined only by
the reactants and presumably the supremacy of HWSS@Fe3O4 over
HWSS seems to be due to running the concerted proton transfers
between the reactants with less activation energy.
Certainly, the proton exchange is conducted through hydrogen
bonding and its efficiency can be better interpreted as involving
interchanges between the covalent and the coordination bonds
which HWSS forms with the iron atoms of magnetite.74 Upon H-
accepting hydrogen bonding with the nano-composite, the reacting
aldehydes 1 become activated toward nucleophilic addition and the
Fe-coordinated hydroxyl bond I involved in this H-bonding turns
into C-O-Fe covalent bond II. On the other hand, dimedone and 4-
hydroxycoumarin gain an enhanced nucleophilic character upon H-
donating Hydrogen bonding with the nano-composite, leading the
C-O-Fe covalent bond II involved in this hydrogen bonding to switch
into a coordination bond I. A cluster of water molecules are
expected to rely the proton exchange between the proton-donating
I and proton-accepting II sites of the nano-catalyst.75 Similar
concerted proton transfers are conceivable for the Michael
additions of the condensates 6 and 7 with the second molecule of
the enolic nucleophile (2 or 3) and likewise for a Thorpe-Ziegler type
cyclization of the intermediate 8 (Scheme 1). The syntheses go
through nucleophilic addition of 4-hydroxycoumarin 2 or dimedone
100
80
60
40
20
0
90
89
87
89
88
88
86
87
86
86
fresh
1
2
3
4
--5b --4d
Recycle
Figure 7. Reusability tests for the catalyst in the model syntheses: a) 1,8-
3
on the aldehyde
1
followed by dehydration to give the dioxooctahydroxanthene 5b and b) 3,3´-bis-coumarin 4d
and 7, respectively. Nucleophilic
intermediate condensates
6
A beneficial characteristic of the nano-catalyst is the ease with
which it can be separated from the reaction mixtures. Thus, the
recyclability of the nano-catalyst in the model reaction between 4-
hydroxycoumarin and 4-cholorobenzaldehyde was tested. After
completion of the reaction, ethanol was added, while stirring, to
the reaction mixture and the hot solution of the product was
separated from the nano-catalyst by decantation on a permanent
magnet. The separated catalyst was washed once again with hot
ethanol and then dried before being reused in the next cycle of the
same model reaction. As figure 7 shows, the catalytic activity of the
nano-composite was almost not changed even after four times
consecutive recycling in the same model reactions. This finding can
be evidenced to the intact structure of the recycled nano-catalyst,
as is further supported by FT-IR spectroscopy that displays no
addition of 6 with a second molecule of 4-hydroxycoumarin in a
Michael manner gives the product 4. The intermediate 7 similarly
undergoes a Michael addition with the second enolic molecule of
dimedone to give the adduct 8 which cyclocondenses through a
Thorpe-Ziegler type cyclization to deliver the product 5. All of these
step reactions are typically nucleophilic additions in nature, so can
be catalysed by the dual H-donating-accepting functions of
HWSS@Fe3O4. Upon adsorption on surface of this nanocomposite,
the nucleophiles and the electrophiles gain more activities by
proton removing or proton accepting actions of the catalyst,
respectively. In overall, HWSS@Fe3O4 completes the proton
transfer cycle from the nucleophiles to the electrophiles without
undergoing any total structural change. That is, in each H-transfer
cycle, HWSS@Fe3O4 do not acquire any momentary protonated or
6 | J. Name., 2012, 00, 1-3
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ARTICLE
appreciable changes in the pattern of vibrational bands with advantage of working at lower temperatures, they are either
respect to that of the fresh one. Separate experiments showed that sensitive to moisture (entries 4 and 7) or cannot be separated from
HWSS is not leached sensibly from the nano-composite by boiling the reaction mixture and solvent (entries 2 and 3) as easily as
water. Interestingly, addition of iodine to the water boiled with HWSS@Fe3O4. Other methods employ either expensive or non-
HWSS@Fe3O4 did not turn its colour into blue. Alternative tests biocompatible materials (entries 6 and 9).
showed that iodine is nearly completely sorbed from a watery
solution by the suspended nanoparticles of HWSS@Fe3O4. As
Conclusions
another evidence of stability, the nano-composite showed nearly
In summary, encapsulation of magnetite nanoparticles with hot-
the same diffuse reflectance spectra (DRS) before and after a
water-soluble starch provided the bio-derived nano-composite
prolong refluxing in water (Fig. 8). These facts are indicative of
HWSS@Fe3O4. The IR spectrum of this bioorganic-inorganic hybrid
strong binding between magnetite nanoparticles and HWSS and
can be better interpreted as exhibiting strong coordination and
lend support to the postulate of covalent bonds between these two
covalent bonds between its two components. Visual monitoring by
components.
iodine test and an alternative DRS study displayed no sensible
leaching of starch from the magnetic support even after prolong
refluxing of the nano-composite in water. This finding can be
evidenced to formation of covalent and coordination bonds
between HWSS and the iron metals of magnetite core and so
delineates an altered chemical property for the nano-composite
with respect to its components. Indeed, the nano-composite has
shown better catalytic activities than pure HWSS and pristine Fe3O4
nanoparticles in the pseudo three-component syntheses of 3,3´-
arylmethylene-bis-(4-hydroxycoumarin-3-yl)
and
1,8-
dioxooctahydroxanthenes in water. The catalytic activity of
HWSS@Fe3O4 was suggested to be arisen from its prominent
proton-donating and proton-accepting capacity. Certainly, these
proton exchange occur on surface of the HWSS coating and seem to
be amplified by interchanges between the covalent and
coordination bonds which it makes with the iron atoms at surface
of the magnetite core. The nano-catalyst is simply recovered by a
permanent magnet and can be reused several times without
significant decrease in catalytic activity.
Figure 8. The DRS spectra of the iodine-complexed nano-composite before
(a) and after 6 h refluxing (b) in water.
Table 3. A comparative catalytic efficiency of HWSS@Fe3O4 in the synthesis
of the model products 4b and 5b.
Yield
%
Ent
Prd.
Catalyst
Conditions
Time
Ref.
1
2
3
On-water (50 mL)
Piperidine (a few drops)
SDS (20 mol%),
95 o
C
4.5 h
4 h
98
96
98
[76]
[57]
[77]
Experimental
r.t. /EtOH (10
mL)
60 oC / water
3 h
General
4b
Wheat starch and other materials were purchased from Merck and
used without further purification. FT-IR spectra were received in
KBr wafers on a Shimadzu FT-IR 8300 spectrophotometer. X-ray
powder diffraction (XRD) analysis was obtained on a Panalytical
X’Pert Pro X-ray diffractometer using Cu-Kα radiation of wavelength
1.54 Å. Thermogravimetric analysis (TGA) and differential scanning
calorimetry (DSC) data were obtained on a SETARAM thermal
analyzer. The thermal behavior of the specimens was scanned from
40 °C to 600 °C at the rate of 20 °C/min under Helium gas flow. The
surface morphologies and elemental analysis of HWSS@Fe3O4 were
determined by a scanning electron microscope equipped with an
energy dispersive X-ray analyzer (SEM–EDX, VEGA3 TESCAN). The
magnetic properties were measured at room temperature using a
BHV-55 vibrating sample magnetometer. The transmission electron
4
5
6
SiO2Cl (3 g)
40 oC /CH2Cl2
90 oC /H2O
3.5 h
25 min
5 h
85
94
94
[78]
This
work
HWSS@Fe3O4 (15 mg)
Amberlyst-15 (200 mg)
TMSCl (20 mmol)
reflux/ CH3CN
[79]
7
8
reflux/ CH3CN
8 h
5 h
81
94
84
87
[80]
[81]
[82]
Cellulose sulfonic acid
(0.05 g)
110 oC/ solvent-
free
80 oC/ solvent-
free
5b
9
[Hmim]TFA (0.1 g)
5 h
This
work
10
HWSS@Fe3O4 (15 mg)
90 oC/ H2O
30 min
An additional noteworthy observation is that, unlike HWSS, the bio-
derived nano-composite sensibly resists toward
biodegradation by molds.
a short-term
microscopy (TEM) images were taken on
microscope at acceleration voltage of 100 kV. The sample was
catalysts in the synthesis of the model products 4b and 5b are dispersed in deionized water by sonication for 10 min with Misonix-
presented in Table 3. This table is ranking HWSS@Fe3O4 as one of
a Zeiss - EM10C
Comparison of HWSS@Fe3O4 with some previously reported
S3000 ultrasonicator (QSonica, Newtown, CT) before coating on
the most effective catalysts for the pseudo three-component formvar carbon coated grid Cu mesh 300.
syntheses discussed above. It is obvious that the “on water”
synthesis of 4b at 95 oC takes place one order of magnitude slower
than the method of using HWSS@Fe3O4 as catalyst in the same
conditions (compare entries 1 and 5). All the previous methods
based on using the other catalysts of this table similarly give the
products 4b and 5b within catalysts of this table similarly give the
products 4b and 5b within much longer times with respect to the
protocol presented here. Although some of the catalysts have the
Preparation of hot-water-soluble starch (HWSS) for coating of
Fe3O4 nanoparticles.
HWSS was prepared using a modification of a previously reported
method.83 Thus, wheat starch (0.5 g) was wetted with ethanol (95%,
1 mL) in a 100 mL conical flask. Redistilled water (50 mL) was added
to this flask and the slurry heated at 98 °C for 15 min with constant
stirring. For separation of hot-water-insoluble starch (HWIS) from
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ARTICLE
Journal Name
8
9
B. Boury, S. Plumejeau, Green Chem., 2015, 17, 72.
K. Rad-Moghadam, N. Dehghan, J. Mol. Catal. A: Chem.,
2014, 392, 97.
the supernatant solution of the HWSS fraction, the resulting
suspension was centrifuged at 3000 rpm for 5 min. The separated
solution was concentrated under reduced pressure by using a
rotary evaporator operating at 50 °C. Complete dryness of the
extract was accomplished through freeze-drying of the resulting
syrup at -30 °C for 24 hours.
10 F. Buazar, M. H. Baghlani-Nejazd, M. Badri, M. Kashisaz, A.
Khaledi-Nasab, F. Kroushawi, Starch, 2015, DOI:
10.1002/star.201500347.
11 R. K. Sharma, S. Dutta, S. Sharma, R. Zboril, R. S. Varma, M. B.
Gawande, Green Chem., 2016, 18, 3184.
For preparation of HWSS@Fe3O4 nanoparticles,
a mixture of
FeCl2•4H2O (0.5 g) and FeCl3•6H2O (1.3 g) was dissolved in a
solution of HCl (0.33 M, 6.5 mL). To this solution, while stirring
vigorously, was added dropwise a solution of NaOH (3.74 g) in H2O
(62.5 mL). The resulting suspension of Fe3O4 nanoparticles was
sonicated at room temperature for 1 h. This suspension of pristine
Fe3O4 nanoparticles was added to a solution obtained by dissolution
of HWSS (0.03 g) in redistilled water (15 mL) via rapid mechanical
stirring (10 min) at 50 °C. The combined fluid was then refluxed at
12 L. M. Rossi, N. J. S. Costa, F. P. Silva, R. Wojcieszak, Green
Chem., 2014, 16, 2906.
13 M. M. Mojtahedi, M. S. Abaee, A. Rajabi, P. Mahmoodi, S.
Bagherpoor, J. Mol. Catal. A: Chem., 2012, 361–362, 68.
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Angew. Chem., Int. Ed., 2007, 46, 8866.
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Commun., 2012, 26, 231.
16 A. Dhakshinamoorthy, S. Navalon, M. Alvaro, H. Garcia,
60 °C for
6 h. At this end, the resulting nanoparticles of
Chemsuschem, 2012, 5, 46.
17 T. J. Yoon, W. Lee, Y. S. Oh, J. K. Lee, New J. Chem., 2003, 27
227.
HWSS@Fe3O4 were collected on an external magnet, rinsed
thoroughly with distilled water and finally dried in an oven at 50 °C.
,
18 M. Ikenberry, L. Peña, D. Wei, H. Wang, S. H. Bossmann, T.
Wilke, D. Wang, V. R. Komreddy, D. P. Rillema, K. L. Hohn,
Green Chem. 2014, 16, 836.
General procedure for synthesis of 3,3´-arylmethylene-bis-(4-
hydroxycoumarin-3-yl) and 1,8-dioxooctahydroxanthenes.
For the synthesis of 3,3´-(arylmethylene)-bis-(4-hydroxycoumarin-3-
19 Y. Long, K. Liang, J. Niu, X. Tong, B. Yuan, J. Ma, New J. Chem.,
2015, 39, 2988.
yl)s and 1,8-dioxooctahydroxanthenes,
a
mixture of 4-
20 X. Zheng, S. Luo, L. Zhang, J. P. Cheng, Green Chem., 2009,
11, 455.
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23, 44.
22 C. Kamonsatikul, T. Khamnaen, P. Phiriyawirut, S.
Charoenchaidet, E.Somsook, Catal. Commun., 2012, 26, 1.
23 Y. Lee, M. A. Garcia, N. A. Frey Huls, S. Sun, Angew. Chem.,
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hydroxycoumarin/ or dimedone (2 mmol), an aldehyde (1 mmol),
HWSS@Fe3O4 (0.015 g) and H2O (2 mL) was stirred at 90 °C. After
completion of the reaction (as monitored by TLC on silica gel using
ethyl acetate/n-hexane 1/1 as eluent), ethanol (95%, 5 mL) was
added with stirring to the reaction vessel and the supernatant hot
solution of the product was decanted on a magnet (0.7 Tesla).
Washing of the nano-composite, remained in the vessel, was
repeated with another portion of hot ethanol (95%, 3 mL) and the
24 W. Sun, Q. Li, S. Gao, J. K. Shang, Appl. Catal., B, 2012, 125, 1.
combined ethanolic extract was cooled at 4 °C to make the product 25 J. J. Yu, L. M. Wang, J. Q. Liu, F. L. Guo, Y. Liu, N. Jiao, Green
Chem., 2010, 12, 216.
crystalize completely. The solid product was filtered and dried at 50
°C. All the known products gave the physical data consistent with
those reported in the literature and the authentic samples prepared
through previously reported methods. The separated nano-catalyst
was dried at 60 °C before using in the next reaction.
26 (a) G. W. Rewcastle, G. J. Atwell, L. Zhuang, B. C. Baguley, W.
A. Denny, J. Med. Chem., 1991, 34, 217. (b) N. Mulakayala, P.
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Conflicts of interest
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27 C. G. Knight, T. Stephens, Biochem. J., 1989, 258, 683.
,
There are no conflicts of interest to declare.
28 M. Ahmad, T. A. King, D. K. Ko, B. H. Cha, J. Lee, J. Phys. D:
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Acknowledgements
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Authors are grateful to the Research Council of University of Guilan
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New Journal of Chemistry
Page 10 of 10
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DOI: 10.1039/C8NJ00718G
Graphical Abstract
Nano-Composite of Magnetite and Hot-Water-Soluble Starch: A Cooperation Resulting in an Amplified
Catalytic Activity on Water
Sanaz Razi-Kazemi, Kurosh Rad-Moghadam, and Saeedeh Tourchi-Roudsari
The composite of hot-water-soluble starch
and magnetite nanoparticles appeared as an
efficient catalyst for the pseudo three-
component synthesis of bis-coumarins and
xanthenes. The greater catalytic activity of the
nano-composite over magnetite and soluble
starch in these syntheses is attributed to a
cooperation between the two components of
the composite in conducting proton exchanges
with the reactants.
O
O
H
O
H
Amylose
H
O
O
On
HO
Fe3O4
Off
H O
H
H O
H
H O
H