Adamantyl-terminated dendronized molecules: Synthesis and interaction with β-cyclodextrin-functionalized poly(dimethylsiloxane) interface

Article abstract of DOI:10.1039/c3nj00129f

The supramolecular interaction between the host molecule β-cyclodextrin (β-CD) and the guest molecule adamantane is extensively applied in several disciplines. However, recent studies on the applications of this molecular recognition mainly focused on gla

Full text of DOI:10.1039/c3nj00129f

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Adamantyl-terminated dendronized molecules:
synthesis and interaction with b-cyclodextrin-
functionalized poly(dimethylsiloxane) interface†
Cite this: NewJ.Chem., 2013,
37, 2358
Yanrong Zhang,a Qin Tu,a Dong-En Wang,a Yun Chen,a Bingzhang Lu,b
Mao-Sen Yuana and Jinyi Wang*a
The supramolecular interaction between the host molecule b-cyclodextrin (b-CD) and the guest
molecule adamantane is extensively applied in several disciplines. However, recent studies on the
applications of this molecular recognition mainly focused on glass, silicon, and gold substrates. Few
studies have explored the field of poly(dimethylsiloxane) (PDMS), an optically transparent elastomer
widely used in biological microfluidic devices. In the present study, various functional group-modified
adamantyl-terminated dendronized molecules were synthesized via an efficient and facile route. The
binding of adamantyl-terminated dendronized molecules onto b-CD-conjugated PDMS surfaces and
their reversible dissociation from PDMS surfaces through the competitive mechanism of b-CD-N3 were
studied. The results showed that the dissociation is relatively slow compared with the binding, and the
former process can be accelerated through exchanging the original b-CD-N3 solution with a fresh one.
Afterward, more complex multilayer assemblies were constructed on PDMS surfaces using the host–
guest interaction between adamantane and b-CD as well as between biotin and streptavidin. A further
study on the association and dissociation of the established multilayer assemblies showed that the
assembly constructed with a biotinylated monoadamantyl-terminated molecule has a reversible prop-
erty, whereas that with a biotinylated triadamantyl-terminated molecule has an irreversible property.
These results demonstrated that the reversible properties of the fabricated assembly can be easily
modulated on the PDMS surfaces by regulating the valence of the supramolecular interaction between
adamantane and b-CD.
Received (in Montpellier, France)
2nd February 2013,
Accepted 19th April 2013
DOI: 10.1039/c3nj00129f
www.rsc.org/njc
exploited new prospects for the modulation of molecular inter-
actions and the construction of novel functional materials.5
Introduction
In recent years, b-cyclodextrin (b-CD)-based supramolecular
chemistry has been extensively applied in several fields, such
as chromatography,1 controlled drug release,2 and biosensors,3
which stem from the strong combination of b-CD with a variety
of hydrophobic organic molecules through different binding
affinities.4 Compared with the classical methods of covalently
conjugating molecules, the fabrication of a highly ordered
molecular system through supramolecular interaction has
Adamantane, commonly used as a guest molecule of b-CD, can
precisely anchor into the hydrophobic b-CD cavity.6 This supra-
molecular association can also be detached in an b-CD aqueous
solution via a competitive mechanism.7 More importantly,
b-CD has low toxicity, is biodegradable and biocompatible,
and hardly has a negative impact on biological activity.8 More-
over, this binding strength between b-CD and adamantane can
be tuned by varying the valence of the host–guest interaction.
The monovalent association constant of this host–guest inter-
action is approximately 3 ꢀ 104 Mꢁ1 (T = 298 K).6a,9 The
multivalent association of the host–guest interaction involves
simultaneous interactions between multiple functionalities on
one entity and complementary functionalities on another,
which is typically several orders of magnitude stronger than
the monovalent one.7a,10 The application of the multivalent
host–guest interaction makes the formation of a kinetically
a Colleges of Science and Veterinary Medicine, Northwest A&F University, Yangling,
Shaanxi 712100, China. E-mail: jywang@nwsuaf.edu.cn; Fax: +86-298-708-2520;
Tel: +86-298-708-2520
b Department of Chemical Physics, School of Chemistry and Materials Science,
University of Science and Technology of China, Heifei, Anhui 230026, China
† Electronic supplementary information (ESI) available: Photophysical properties
of compound 6, synthesis of compounds 10 and 11, and 1H NMR spectra of all
compounds. See DOI: 10.1039/c3nj00129f
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stable assembly possible. This kind of interaction has gained
Considering the abovementioned analyses, as well as our
increasing interest, particularly in biochemistry, because it previous studies on PDMS surface modification,16,19 an efficient
provides an approach to finely tune the overall interaction and facile route to synthesize various adamantyl-terminated
strengths and has a pivotal role in sundry vital movement.11 dendronized molecules, including fluorescent molecule-,
To date, the supramolecular interaction between b-CD and carbamate nitrophenyl ester-, and biotin-containing adamantane
adamantane has been utilized to build nanometer arrays of derivatives, is described in this study. Meanwhile, the reversible
functional light-harvesting antenna complexes,12 immobilize dissociation of the adamantane derivatives from the pre-prepared
desired proteins,13 control the shape of a peptide-decorated PDMS-PEG-CD surfaces was investigated through the competitive
vesicle,14 detect anti-gliadin autoantibodies in celiac patient mechanism of b-CD-N3. Finally, using the supramolecular inter-
samples or the anthrax biomarker,3a,15 and so on. All of these action between adamantane and b-CD and between biotin and
studies have greatly shown the potential of the host–guest streptavidin (SAv), more complex assemblies were constructed
chemistry in constructing various bioanalytical systems. However, on PDMS surfaces. The reversible property of the constructed
recent studies on the applications of this molecular recognition assembly on the PDMS surfaces was also studied by adjusting
mainly focused on glass, silicon, and gold substrates. Few studies the valence of the supramolecular interaction, that is, using a
have explored the field of poly(dimethylsiloxane) (PDMS), biotinylated triadamantyl-terminated or a monoadamantyl-
an optically transparent elastomer widely used in biological terminated molecule in the assembly.
microfluidic devices because of its prominent advantages, such
as non-toxicity, easy fabrication, practical scalability, and gas
Results and discussion
Synthesis of functionalized adamantyl-terminated dendronized
permeability.16 In addition, previous bioanalytical studies
indicated that occupying the hydrophobic cavity of b-CD with
monovalent supramolecular blocking agent hexa(ethylene glycol)
molecules
mono(adamantyl ether)17 or adding a certain concentration of In this study, methyl gallate was used as the starting material
b-CD in a protein solution18 is always needed in advance to to synthesize various functionalized adamantyl-terminated
suppress nonspecific protein adsorption on b-CD-conjugated dendronized molecules because it has three phenolic hydroxyl
surfaces. In our previous work,19 we presented a strategy for groups at its 3-, 4-, and 5-positions (which can be used to link
the preparation of a dually functionalized PDMS surface (PDMS- three adamantane moieties on its benzene ring) and one
PEG-CD) by conjugating b-CD onto PDMS surfaces via click methyl ester (which can be used to link one desired molecule
chemistry and surface-initiated atom transfer radical polymer- on its benzene ring). The dendritic wedge was synthesized via a
ization of poly(ethylene glycol) (PEG) units. The prepared PDMS- convergent growth strategy (Scheme 1), i.e., starting from the
PEG-CD surface possesses a reversible property; however, it also adamantane periphery and working inward toward what is to
has a good protein-repelling property because of the introduc- be further derived to link another molecule.
tion of PEG units in the b-CD-based supramolecular chemistry
We first synthesized 2-(2-(2-(2-(adamantyl-1-oxy)ethoxy)
system.
ethoxy)ethoxy)ethanol p-toluenesulfonate (Scheme 1, Com-
To realize various biological applications on b-CD-functionalized pound 2) through a two-step reaction.7c The PEG unit in this
interfaces through the supramolecular interaction between b-CD structure has three functions: (1) improves the solubility of the
and adamantane, adamantane must be linked with the desired target molecules in an aqueous solution; (2) effectively prevents
molecules to indirectly anchor them on b-CD-functionalized or decreases nonspecific interaction in a further biological
interfaces. Previous studies used carboxymethyl cellulose as a application because of its well-hydrated nature; and (3) allows
bridge to conjugate adamantane and the desired molecules20 the multiple complexation with b-CD to take place for enough
because it possesses some typical properties of polysaccharides, chain length.5,24 Several reaction conditions were tested to
such as effectively preventing nonspecific protein adsorption, simultaneously link three adamantane moieties onto one
excellent biocompatibility, as well as low toxicity.16b,21 For example, methyl gallate skeleton (Scheme 1, Compound 3). The results
O’Sullivan et al. built a nanostructure using the interfacial self- indicated that the reaction can be completed in 24 h with
assembly of bifunctionalized carboxymethyl cellulose bearing a high yield of 84% under dry potassium carbonate as base,
adamantane unit and an antigenic fragment onto a CD-containing 18-crown-6 as phase transfer catalyst, dry acetone as solvent,
support and realized its applicability in the detection of anti- and the 4 : 1 ratio of compound 2 and methyl gallate. Finally,
gliadin antibodies.3a As a potential alternative to carboxymethyl lithium aluminum hydride (LAH) was used as the reducing
cellulose, PEG also has the same advantages in protein repelling.22 reagent to transform methyl ester to alcoholic hydroxyl group
Reinhoudt et al. used 3,5-dihydroxybenzonitrile as the molecule (Scheme 1, Compound 4), which can further react with several
core and PEG as the linker spacing to prepare the supramolecular other functional groups to covalently link another molecule
patterning of b-CD monolayers on silicon oxide via microcontact onto the benzene ring of the compound 3.
printing and dip-pen nanolithography.23 However, they used
Fluorescence imaging is a powerful and sensitive micro-
Raney cobalt as a catalyst and hydrogen as a reducing reagent scopic technique that allows the study of molecules at the
under relatively harsh conditions to convert the nitrile func- monolayer level and provides the possibility of imaging sites
tionality to an amino group, a prerequisite to further conjugate on a restricted area for the detection of on-surface reaction.25 We
desired molecules.
introduced the fluorescent moiety 3-azido-7-hydroxy coumarin
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Scheme 1 Synthesis of various functionalized triadamantyl-terminated dendronized molecules: (i) Et3N, 180 1C, 24 h; (ii) Et3N, DMAP, CH2Cl2, TsCl, rt; (iii) K2CO3, 18-
crown-6, acetone, reflux, 24 h; (iv) LAH, THF, 50 1C, 6 h. (v) NaH, propargyl bromide, THF, overnight, rt; (vi) CuBr, PMDETA, 3-azido-7-hydroxy coumarin, DMF, rt, 24 h;
(vii) 4-nitrophenyl chloroformate, Et3N, CH2Cl2, rt, 12 h; (viii) DIPEA, n-butylamine, THF, 5 h; (ix) D-biotin, EDC, DMAP, DMF, rt, overnight.
onto the triadamantyl-terminated dendrimeric compound 4 4 using propargyl bromide as the electrophilic reagent; this reaction
(Scheme 1) via fluorogenic click chemistry to visually detect the was smoothly completed overnight with a high yield of
interaction between adamantane and b-CD-anchored PDMS-PEG- 91% (Scheme 1, compound 5). Afterward, 3-azido-7-hydroxy
CD surfaces.26 First, the alkynyl group was introduced to compound coumarin was conjugated onto the alkynyl-ended compound
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5
as the fluorogenic substrate through click chemistry sole amino acid with the side chain of primary amine in all
using CuBr/PMDETA as the catalysis system; we obtained the proteins.31 Under the catalysis of diisopropylethylamine
fluorescent target product as a pale yellow liquid (Scheme 1, (DIPEA), this reaction can be completed in 5 h, accompanied
compound 6). However, when the reaction flask was placed with the appearance of yellow 4-nitrophenol, indicating the
under an ultraviolet lamp (365 nm), only a slight fluorescence success of this reaction (Scheme 1, compound 8). Moreover, this
was observed. The reason for this phenomenon is that Cu(II) reaction can also proceed at room temperature, importantly, in
can quench the fluorescence of the triazole product of fluoro- sodium phosphate buffer and pH 8.0 (verified by thin layer
genic click chemistry.27 Therefore, the organic phase of this chromatography). This condition benefits the real application
reaction was thoroughly washed using the Cu(II)-chelator ethyl- of ligation between the desired proteins and compound 7
enediaminetetraacetic acid (EDTA) aqueous solution (log K = because a common organic solvent is usually destructive and
18.76) until the blue aqueous phase became colorless before can cause the denaturation of proteins.
purification via column chromatography.28
Given that the biotin–SAv affinity couple represents a widely
Thereafter, the photophysical property of compound 6 was used system for various bioconjugations,32 the biotinylated
extensively studied. The results (Fig. S1, S2 and S3, ESI†) triadamantyl-terminated dendronized molecule in the current
demonstrated that this compound has the following photo- study was also prepared. Using compound 4 as a starting
physical properties: (1) a maximum emission at 478 nm with a material and carbodiimide chemistry as the conjugating method,
very large Stokes shift (Dl = 7.81 ꢀ 103 cmꢁ1) in 10 mM b-CD we obtained biotin-functionalized triadamantyl-terminated
solution (Fig. S1, ESI†) that can effectively decrease the inter- dendronized molecule (Scheme 1, compound 9).
ference of excitation light;29 (2) a linear correlation (r = 0.99) in
Study of the reversible interaction between triadamantyl-
terminated dendronized molecule and PDMS-PEG-CD interface
the concentration range of 0.05 to 1.0 mM (Fig. S2, ESI†); and (3)
no obvious photobleaching over a long period (20 min) under
a continuous intensive excitation with a 150 W xenon lamp
(Fig. S3, ESI†). These characteristics proved that compound 6 is
suitable for studying the interaction between the adamantane
and the PDMS-PEG-CD surface using fluorescence imaging.
We also tried to activate the benzyl alcohol group of com-
pound 4 using 4-nitrophenylchloroformate by forming a carbo-
nate group (Scheme 1, compound 7) to conveniently link other
molecules on the triadamantyl-terminated molecule because
the terminal carbonate group reacts with various amino-ended
molecules (e.g., proteins) to form stable urethane linkages.30
As an example, we used n-butylamine as a reactant model
because its similar structure with the side chain of lysine, the
After identifying the photophysical property of compound 6,
the supramolecular interaction between compound 6 and
PDMS-PEG-CD interfaces19 was investigated under a fluores-
cence microscope (Fig. 1, left). The pre-prepared PDMS-PEG-CD
slides (0.5 ꢀ 0.5 cm) were first immersed in 0.2 mM b-CD-
containing aqueous solution (50 mM) of compound 6 for a
certain time in the dark. After washing with deionized water,
the fluorescence images of the post-interaction PDMS-PEG-CD
surfaces were captured, and their fluorescence intensity was
analyzed. Curve i in Fig. 2A shows the relationship between the
incubation time of the PDMS-PEG-CD slides with the fluorescent
compound 6 and the fluorescence intensity of these post-interaction
Fig. 1 Illustration of the reversible supramolecular interaction between PDMS-PEG-CD interface and triadamantyl-terminated dendronized molecules through the
competitive mechanism of b-CD-N3.
c
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intensity was detected after 6 min exposure to the compound 6
solution.
The native PDMS-PEG-CD slides were first incubated with
0.2 mM b-CD-containing aqueous solution of nonfluorescent
compound 4 (50 mM) for 8 min to confirm that this result was
due to the supramolecular interaction between compound 6
and b-CD conjugated on the PDMS surface, not the physical
adsorption of compound 6 on the PDMS-PEG-CD surfaces. After
rinsing with deionized water, the slides were then incubated with
compound 6 for a certain time. After rinsing with deionized water
again, the fluorescence images of the surfaces were also captured
and analyzed following the procedures described earlier (Fig. 1,
right and bottom). Adamantane derivatives form highly stable
inclusion complexes with b-CD;10c thus the adamantane moiety of
compound 4 should occupy the hydrophobic cavity of b-CD
conjugated on PDMS-PEG-CD surfaces and prevent the possible
host–guest interactions between the adamantane moiety of com-
pound 6 and PDMS-PEG-CD surfaces. The result (curve ii in
Fig. 2A) showed that the fluorescence intensity of these surfaces
only had a slight increase with prolonged incubation time,
suggesting that merely a small partial replacement of nonfluor-
escent compound 4 by fluorescent compound 6 occurred, similar
with related studies reported previously.12,17 The results showed
that the immobilization of compound 6 on PDMS-PEG-CD
surfaces was obviously achieved through the specific interaction
between the adamantane moiety of compound 6 and the b-CD
conjugated on the PDMS-PEG-CD surfaces.
The PDMS-PEG-CD surfaces were subsequently immersed in
the aqueous solution of b-CD-N3 (5 mL, 50 mM) with gentle
shaking for a certain time in the dark after reaction with
fluorescent compound 6 to investigate the reversibility and
the kinetic stability of the interaction between compound 6
and PDMS-PEG-CD surface. After rinsing with deionized water,
the fluorescence images of the b-CD-N3-treated PDMS-PEG-CD
surfaces were also captured and analyzed following the procedures
described earlier. Curve i in Fig. 2B shows the relationship between
the incubation time of the compound 6-treated PDMS-PEG-CD
surfaces with the b-CD-N3 aqueous solution and the fluorescence
intensity of these post-reaction surfaces. This curve shows that
the fluorescence intensity of the surfaces decreased with pro-
longed incubation time. However, compared with the associa-
tion process (Curve i in Fig. 2A), this dissociation was very slow
because the fluorescence intensity decreased to approximately
Fig. 2 (A) Effect of incubation time between fluorescent triadamantyl-
terminated molecule (compound 6) and PDMS-PEG-CD surfaces on the surface
fluorescence intensity. The top images are their corresponding fluorescence
images at different time points. (i) No pre-incubation of the PDMS-PEG-CD
surfaces with nonfluorescent triadamantyl-terminated molecule compound 4;
(ii) pre-incubation of the PDMS-PEG-CD interfaces with nonfluorescent triada- 40% of the pristine value after exposure to b-CD-N3 aqueous
mantyl-terminated molecule compound 4. (B) Effect of incubation time between
solution for 30 min and the reduced magnitude of the latter 15
min was slower compared with that of the former 15 min.
These results reflect that a trend to reach a thermodynamic
b-CD-N3 aqueous solution and post-interaction PDMS-PEG-CD surfaces on the
surface fluorescence intensity. The top images are their corresponding fluores-
cence images at different time points. (i) No alteration of the b-CD-N3 solution at
equilibrium between rebinding and dissociation exists.
15 min; (ii) alteration of the b-CD-N3 solution at 15 min. Normalization of the
fluorescence intensity was performed as follows: the fluorescence intensity of We replaced the original b-CD-N3 aqueous solution with a fresh
the nonreacted PDMS-PEG-CD interface was first subtracted from those of
one at 15 min to break this equilibrium to suppress rebinding
and accelerate the dissociation; the fluorescence intensity
rapidly decreased to approximately 97% of the pristine
compound 6 (or b-CD-N3)-treated PDMS-PEG-CD surfaces, and then divided by
the maximum fluorescence intensity obtained in the whole analysis.
value (curve ii in Fig. 2B). We hypothesized that if the replace-
surfaces. This curve indicates that the fluorescence intensity of ment frequency of b-CD-N3 aqueous solution is further
these surfaces increased with prolonged incubation time, and improved, complete dissociation can be achieved in a relatively
the adsorption was fast because no obvious increase in the shorter time.
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Construction of multilayer assembly on the PDMS-PEG-CD
surface via host–guest interaction and biotin–SAv interaction
obtain SAv-functionalized PDMS interface (step ii in Fig. 3). The
SAv-functionalized PDMS slide was further incubated for 30 min
with fluorescent biotin compound 10 to examine whether SAv
was attached on the PDMS surface (step iii in Fig. 3). The
synthesis and characterization of compound 10 are presented
in Scheme S1 and Fig. S4 of the ESI.† The fluorescence images
of the obtained PDMS-PEG-CD surfaces were captured and
analyzed following the procedures described earlier. At the same
time, two negative control experiments were also conducted; one
is that compound 9 was omitted and the other is that SAv was
omitted in the assembly. The results (Fig. 4A) showed that the
fluorescence intensities of the two controls were significantly
lower than that of the unabridged assembly after incubation with
the fluorescent biotin compound 10. These results indicated that
the biotin- and adamantane-bifunctionalized molecule and SAv are
two essential linkers to fabricate this multilayer assembly.
After verifying the reversible assembly on the PDMS-PEG-CD
interface via the host–guest interaction between triadamantyl-
terminated molecule and b-CD conjugated on PDMS-PEG-CD
surfaces, we tried to fabricate a more complex multilayer
assembly on the PDMS surface through two kinds of noncovalent
attachments: the host–guest interaction between b-CD and
adamantane and the biotin–SAv interaction. Previous studies
demonstrated that SAv can attach to the biotin monolayer on a
certain surface through two binding sites of one SAv, and the
remaining two binding sites of SAv can bind to other biotiny-
lated molecules.18,33 Therefore, the biotinylated triadamantyl-
terminated compound 9 (Scheme 1) was synthesized as the
orthogonal linker, in which the adamantane moiety binds it to
the b-CD-functionalized PDMS surface (PDMS-PEG-CD) through
the host–guest interaction and the biotin moiety binds it to SAv
through biotin–SAv interaction. The construction procedure is
illustrated in Fig. 3. PDMS-PEG-CD slide was first incubated with
compound 9 for 8 min to obtain biotinylated PDMS interface
(step i in Fig. 3). After thorough washing, the biotinylated
The fluorescent PDMS surfaces obtained from the inter-
action of compound 10 and the SAv-functionalized PDMS
interfaces were immersed in the aqueous solution of b-CD-N3
(5 mL, 50 mM) with gentle shaking for a certain time in the
dark to test whether such a fabricated multilayer assembly
PDMS interface was then incubated with SAv for 30 min to has stimulus-responsive reversibility under the competitive
Fig. 3 Illustration for fabricating the irreversible multilayer assembly via host–guest interaction and biotin–SAv interaction, using biotinylated triadamantyl-
terminated molecule (compound 9) as linker and fluorescent biotin (compound 10) as indicator (i - ii - iii); and its irreversible property under the competitive
mechanism of b-CD-N3 (iv).
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Fig. 5 Illustration for fabricating the reversible multilayer assembly via host–
guest interaction and biotin–SAv interaction, using biotinylated monoadamantyl-
terminated molecule (compound 11) as linker and fluorescent biotin (compound
10) as indicator (i - ii - iii); and its reversible property under the competitive
mechanism of b-CD-N3 (iv).
Fig. 4 (A) Relationship between the fluorescence intensity of the PDMS surfaces
and the process of the multilayer assembly on the PDMS surfaces. The top images
are the corresponding fluorescence images of these tests: the left for the
unabridged assembly, including biotinylated triadamantyl-terminated molecule
(compound 9), SAv, and fluorescent biotin; the middle for the assembly without
compound 9; the right for the assembly without SAv. (B) Effect of incubation time
between the post-interaction fluorescent PDMS surfaces and b-CD-N3 aqueous
solution on the fluorescence intensity of PDMS surfaces: the top line corresponds
to the multilayer assembly fabricated via biotinylated triadamantyl-terminated
compound 9; the bottom line corresponds to the multilayer assembly fabricated
via biotinylated monoadamantyl-terminated compound 11.
explanation and simultaneously construct a reversible assembly
on the PDMS-PEG-CD surface (Scheme S2, ESI†). The construction
procedure of this reversible assembly using the monoadamantyl-
terminated molecule compound 11 is shown in Fig. 5, which was
different from the construction of the irreversible one (Fig. 3). A
monoadamantyl-terminated molecule was used to construct this
reversible assembly. After the PDMS-PEG-CD slide was incubated
in turn with compound 11, SAv, and fluorescent compound 10, the
obtained PDMS slides were then immersed in the aqueous
solution of b-CD-N3 (5 mL, 50 mM) with gentle shaking for a
certain time in the dark. The results (the bottom curve in Fig. 4B)
mechanism of b-CD-N3. The results (the top curve in Fig. 4B) showed that the fluorescence intensity of these surfaces decreased
showed that the fluorescence intensity of these surfaces had sharply with prolonged incubation time. After 24 min, the fluores-
almost no detectable change with prolonged incubation time, cence intensity of these surfaces decreased to approximately 11%
suggesting that such a multilayer assembly has kinetically stable of the pristine value. In this reversible assembly, two SAv binding
properties.10a,34 These results may be explained as follows. Two SAv sites of one SAv oriented towards biotinylated PDMS-PEG-CD
binding sites of one SAv oriented towards biotinylated PDMS-PEG- surface resulted in no more than bivalent b-CD–adamantane
CD surface resulted in more than trivalent b-CD–adamantane interaction, which is weaker than the multivalent b-CD–
interaction, which reinforced the supramolecular interaction adamantane interaction in the above irreversible assembly
between b-CD and adamantane and made the removal of the and made the removal of this assembly from the PMDS surface
multilayer assembly from PMDS surface impossible.10
easier. This result indirectly verified that the irreversible property
We also synthesized biotinylated monoadamantyl-terminated of the multilayer assembly fabricated through biotinylated
molecule compound 11 to further verify the abovementioned triadamantane-contained molecules (Fig. 3) was caused by the
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more than trivalent b-CD–adamantane interaction. Moreover, recorded on a fluorospectrophotometer (F-4500). The synthesis of
this result implied that the dissociation is directly related to the 3-azido-7-hydroxy coumarin, compound 1, and compound 2 were
valence of the interaction, wherein, the adjustment of the performed according to previous literatures, respectively.7c,35
irreversibility or reversibility of the multilayer assembly can 1H NMR for 3-azido-7-hydroxy coumarin: d 10.55 (s, 1H), 7.61 (s,
be conveniently realized using only a biotinylated triadamantyl- 1H), 7.50 (d, J = 8.50 Hz, 1H), 6.83 (dd, J = 8.50 and 2.00 Hz, 1H),
terminated or a monoadamantyl-terminated molecule.
and 6.78 (d, J = 2.00 Hz, 2H); 1H NMR for compound 1: d 3.72 (t, J =
4.75 Hz, 2H), 3.70 to 3.65 (m, 8H), 3.63 to 3.57 (m, 6H), 2.88 (bs,
1H), 2.14 (s, 3H), 1.75 (s, 6H), and 1.65 to 1.57 (m, 6H); 1H NMR for
compound 2: d 7.80 (d, J = 8.00 Hz, 2H), 7.34 (d, J = 8.00 Hz, 2H),
Conclusion
In this study, starting from the commercially available and 4.16 (t, J = 4.75 Hz, 2H), 3.69 (t, J = 5.00 Hz, 2H), 3.64 to 3.56 (m,
inexpensive material methyl gallate, we successfully synthe- 12H), 2.45 (s, 3H), 2.14 (br, 3H), 1.74 (s, 6H), and 1.65 to 1.56 (m,
sized various functionalized triadamantyl-terminated dendro- 6H); all of which were similar previously reported data.
nized molecules via a convergent growth strategy. Through the
competitive mechanism of b-CD-N3, the reversible association
of adamantyl-terminated molecules onto b-CD-functionalized
PDMS surfaces and subsequent dissociation from the PDMS
Specific procedure for synthesizing triadamantyl-terminated
dendronized molecule compound 4
Compound 4 was synthesized through a two-step reaction
surfaces were realized. Meanwhile, more complex multilayer
assemblies were also successfully constructed on the PDMS (Scheme 1). A suspension of compound 2 (4.90 g, 10 mmol),
surfaces via the b-CD–adamantyl and the biotin–SAv interac- methyl gallate (0.46 g, 2.5 mmol), dry potassium carbonate
tions. Further studies demonstrated that the reversible property (1.66 g, 12 mmol), and 18-crown-6 (0.32 g, 1.2 mmol) in dry
acetone (50 mL) was refluxed for 24 h under nitrogen atmo-
sphere. After the complete disappearance of methyl gallate
monitored through TLC, the solvent was evaporated, and the
residue was partitioned between water (30 mL) and CH2Cl2
(60 mL). The aqueous layer was extracted with CH2Cl2 (3 ꢀ 30 mL)
of the fabricated multilayer assembly on PDMS interfaces can
be controlled by adjusting only the valence of biotinylated
adamantane. Many biomolecules or molecules can be easily
biotinylated, thus, they can be conveniently conjugated onto
PDMS surfaces through the method developed in this study,
which paves the route for further study on the construction of and the combined organic layer was dried over anhydrous
various functionalized PDMS surfaces via b-CD-based supra- Na2SO4. The solvent was evaporated and the residue was
molecular chemistry, and for further exploring the wide-ranging purified by column chromatography (eluent: CH2Cl2/MeOH,
50 : 1, v/v) to afford compound 3 as a colorless liquid (2.34 g,
84%). MS (ESI): [M+Na]+ calculated for C62H98O17Na, 1137.68,
found 1137.62; 1H NMR (500 MHz, CDCl3): d 7.29 (s, 2H), 4.23–
4.18 (m, 6H), 3.89 to 3.85 (m, 7H), 3.80 (t, J = 4.75 Hz, 2H), 3.72
to 3.70 (m, 6H), 3.68 to 3.62 (m, 18H), 3.60 to 3.57 (m, 12H),
2.15 (br, 9H), 1.74 (br, 18H), and 1.65 to 1.57 (m, 18H); 13C NMR
applications of these surfaces in PDMS microfluidic device-based
biomedical fields.
Experimental
Materials and physical methods
1-Bromoadamantane, p-nitrophenyl chloroformate, and 18-crown-6 (125 MHz, CDCl3): 166.59, 152.29, 142.57, 124.96, 109.05, 72.42,
were purchased from Alfa Aesar (Lancaster, England). Cuprous 72.27, 71.29, 70.82, 70.66, 70.57, 69.62, 68.86, 41.48, 36.47,
bromide (CuBr), methyl gallate, N,N-dimethylpyridine-4-amine and 30.52.
(DMAP), N,N,N0,N0 0,N00-pentamethyldiethylene-triamine (PMDETA),
Under nitrogen atmosphere, LAH (76 mg, 2 mmol) was
n-butylamine, tetraethylene glycol, D-biotin, Streptavidin (SAv), and added in portions at 0 1C to the solution of compound 3
ethyl diisopropyl amine (DIPEA) were purchased from Aladdin (1.12 g, 1 mmol) in dry THF (20 mL). The resulting mixture
(Shanghai, China). 2,4-Dihydroxy benzaldehyde, N-acetylglycine, was stirred for 1 h at this temperature, gradually warmed to
and anhydrous sodium acetate were purchased from Ouhe room temperature, and then stirred for another 6 h at 50 1C.
Technology Co. Ltd (Beijing, China). 1-Ethyl-3-(3-(dimethyl- The reaction was quenched by sequential drop-wise addition of
amino) propyl) carbodiimide (EDC) was purchased from GL water (5 mL), 10% NaOH (10 mL), and water (5 mL). The
Biochem Ltd. (Shanghai, China). Solvents were purified by resulting precipitate was filtered off, and THF was evaporated.
standard procedures. All other materials were purchased from The residue was dissolved in CH2Cl2 (40 mL), and then washed
local commercial suppliers and were of analytical reagent grade, with brine solution. After drying over Na2SO4, the residue was
unless otherwise stated. The preparation of PDMS-PEG-CD purified by column chromatography (eluent: CH2Cl2/MeOH,
surfaces followed the method reported by ourselves.19 All reac- 30 : 1, v/v) to obtain compound 4 as a colorless liquid (956.3
tions were monitored by thin-layer chromatography (TLC) with mg, 88%). MS (ESI): [M+Na]+ calculated for C61H98O16Na,
1
1
detection by UV or by iodine. H and 13C NMR spectra of the 1109.69, found 1109.78; H NMR (500 MHz, CDCl3): d 6.64 (s,
products were recorded on a Bruker 500 MHz NMR spectrometer 2H), 4.57 (s, 2H), 4.17 (t, J = 4.75 Hz, 4H), 4.13 (t, J = 4.50 Hz,
in CDCl3 solution using tetramethylsilane (TMS) as the internal 2H), 3.83 (t, J = 4.50 Hz, 4H), 3.78 (t, J = 4.50 Hz, 2H), 3.72 to 3.68
standard (chemical shifts in ppm). Mass spectra (MS) were (m, 6H), 3.68 to 3.60 (m, 18H), 3.59 to 3.55 (m, 12H), 2.13
recorded on a Bruker instrument using standard conditions (br, 9H), 1.74 (br, 18H), and 1.65 to 1.57 (m, 18H); 13C NMR
(electron spray ionization, ESI). The fluorescence spectra were (125 MHz, CDCl3): 152.68, 137.85, 136.84, 106.80, 72.34, 72.27,
c
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71.27, 70.79, 70.69, 70.58, 70.50, 69.84, 68.90, 65.13, 59.26, example, the synthesis of compound 8 was as follows: first,
41.48, 36.47, and 30.52.
under nitrogen atmosphere, p-nitrophenyl chloroformate
(0.402 g, 2 mmol) and compound 4 (1.09 g, 1 mmol) were
dissolved in 20 mL of dry dichloromethane, and then triethyl-
amine (2 mmol, 280 mL) was added drop-wise. The reaction
Specific procedure for synthesizing fluorescent triadamantyl-
terminated molecule compound 6
Compound 6 was obtained through a two-step reaction (Scheme 1). mixture was stirred at room temperature for 12 h until the
First, a solution of compound 4 (1.63 g, 1.5 mmol) in THF (20 mL) disappearance of compound 4, which was confirmed via TLC.
was added drop-wise to the THF suspension of NaH (0.12 g, 60% Dichloromethane was evaporated, and the residue was purified
suspension in oil, 3.0 mmol, 2.0 equiv.) at 0 1C under nitrogen through column chromatography (eluent: CH2Cl2/MeOH, 50 : 1,
atmosphere. The reaction mixture was gradually warmed to room v/v) to obtain compound 7 as a pale yellow liquid (1.09 g, 87%).
temperature for 2 h, and propargyl bromide (0.28 g, 2.3 mmol, MS (ESI): [M+Na]+ calculated for C68H101NO20Na, 1274.69,
1.5 equiv.) was subsequently added drop-wise. The resulting mixture found 1274.27; 1H NMR (500 MHz, CDCl3): 8.28 (d, J =
was stirred at room temperature for 12 h, and then cooled to 0 1C. 9.00 Hz, 2H), 7.40 (d, J = 9.00 Hz, 2H), 6.68 (s, 2H), 5.18
Saturated NH4Cl solution was slowly added to the reaction mixture (s, 2H), 4.17 (t, J = 5.00 Hz, 6H), 3.86 (t, J = 4.50 Hz, 4H), 3.79
to terminate the reaction. After THF was evaporated under vacuum, (t, J = 4.50 Hz, 2H), 3.74 to 3.69 (m, 6H), 3.68 to 3.60 (m, 18H),
the residue was extracted with CH2Cl2 three times. The organic 3.62 to 3.55 (m, 12H), 2.13 (br, 9H), 1.74 (br, 18H), and 1.65 to
phase was washed with saturated NaCl solution and dried over 1.55 (m, 18H); 13C NMR (125 MHz, CDCl3): 155.52, 152.83,
anhydrous Na2SO4. The crude product was purified through column 152.34, 145.38, 139.14, 129.41, 125.26, 121.76, 108.54, 72.17,
chromatography (eluent: CH2Cl2/MeOH, 50 : 1, v/v) to obtain alkynyl- 71.26, 70.82, 70.64, 70.57, 70.51, 69.69, 68.99, 59.24, 41.47,
contained molecule compound 5 as a colorless liquid (1.13 g, 91%). 36.45, and 30.48.
MS (ESI): [M+Na]+ calculated for C64H100O16Na, 1147.70, found
The corresponding carbamate nitrophenyl ester compound
1
1147.68; H NMR (500 MHz, CDCl3): d 6.59 (s, 2H), 4.49 (s, 2H), 7 (125.1 mg, 0.1 mmol) was dissolved in 5 mL of dry THF, to
4.20 to 4.10 (m, 8H), 3.83 (t, J = 5.00 Hz, 4H), 3.78 (t, J = 5.00 Hz, 2H), which, n-butylamine (20 mL, 0.2 mmol) and DIPEA (35 mL,
3.73 to 3.68 (m, 6H), 3.68 to 3.60 (m, 18H), 3.59 to 3.55 (m, 12H), 0.2 mmol) were sequentially added drop-wise. The resulting
2.54 (t, J = 2.50 Hz, 1H), 2.13 (br, 9H), 1.74 (br, 18H), and 1.65 to 1.57 mixture was stirred for 5 h at room temperature. The solvent
(m, 18H); 13C NMR (125 MHz, CDCl3): 152.63, 138.07, 132.71, was evaporated under vacuum and the residue was purified
107.60, 79.55, 74.82, 72.27, 72.18, 70.79, 70.69, 70.58, 70.50, 69.84, through column chromatography (eluent: CH2Cl2/MeOH, 40 : 1,
68.90, 65.13, 59.23, 56.97, 41.45, 36.44, and 30.47.
v/v) to obtain compound 8 as a colourless liquid (98.4 mg,
Compound 5 (0.26 g, 0.23 mmol), 3-azido-7-hydroxy coumarin 83%). MS (ESI): [M+NH4]+ calculated for C66H111N2O17, 1203.75,
(60 mg, 0.29 mmol), PMDETA (5 mL, 0.023 mmol), and dried found 1204.34; 1H NMR (500 MHz, CDCl3): 6.59 (s, 2H), 4.97
DMF (10 mL) were added to a Schlenk tube equipped with a (s, 2H), 4.16 to 4.13 (m, 6H), 3.84 (t, J = 5.00 Hz, 4H), 3.78 (t, J =
magnetic stirring bar. The resulting mixture was degassed via 5.00 Hz, 2H), 3.73 to 3.70 (m, 6H), 3.68 to 3.62 (m, 18H), 3.60 to
three freeze-thaw cycles, and CuBr (3.3 mg, 0.023 mmol) was 3.55 (m, 12H), 3.19 (q, J = 6.50 Hz, 2H), 2.13 (br, 9H), 1.74 (br,
added under a nitrogen atmosphere. After stirring the mixture at 18H), 1.65 to 1.55 (m, 18H), 1.51 to 1.47 (m, 2H), 1.37 to 1.30
room temperature for 24 h, DMF was removed under vacuum. (m, 2H), and 0.92 (t, J = 7.00 Hz, 3H); 13C NMR (125 MHz,
The residue was dissolved in 30 mL of CH2Cl2, the organic phase CDCl3): 152.59, 132.14, 125.99, 115.81, 107.73, 72.32, 59.22,
was washed with EDTA [1% (w/v), 2 ꢀ 15 mL] and water 41.44, 36.44, and 30.48.
successively, and then dried over anhydrous Na2SO4. The crude
product was purified through column chromatography (eluent:
CH2Cl2/MeOH, 25 : 1, v/v) to obtain compound 6 as a yellow
Specific procedure for synthesizing biotinylated triadamantyl-
terminated molecule compound 9
liquid (253.5 mg, 83%). MS (ESI): [M+Na]+ calculated for A solution of 4-DMAP (25.0 mg, 0.2 mmol) in 2 mL of DMF was
C73H105N3O19Na, 1350.73, found 1350.54; 1H NMR (500 MHz, first added drop-wise to an ice-cooled mixture solution of
CDCl3): 8.47 (s, 1H), 8.43 (s, 1H), 7.48 (d, J = 9.00 Hz, 1H), 6.97 compound 4 (217.5 mg, 0.2 mmol) and D-biotin (48.9 mg,
(br, 2H), 6.55 (s, 2H), 5.30 (s, 2H), 4.74 (s, 2H), 4.13 (t, J = 5.00 Hz, 0.2 mmol) in 10 mL of DMF. After stirring for 5 min at room
4H), 4.09 (t, J = 5.00 Hz, 2H), 3.83 (t, J = 5.00 Hz, 4H), 3.74 (t, J = temperature, EDC (46 mg, 0.24 mmol) was sequentially added
5.00 Hz, 2H), 3.74 to 3.65 (m, 6H), 3.67 to 3.62 (m, 18H), 3.60 to upon stirring the reaction mixture. The reaction mixture was
3.55 (m, 12H), 2.12 (br, 9H), 1.73 (br, 18H), and 1.65 to 1.55(m, kept in an ice-water bath for another 10 min, and then stirred
18H); 13C NMR (125 MHz, CDCl3): 162.58, 156.44, 154.85, 154.79, overnight at room temperature. DMF was removed under
152.47, 134.69, 133.66, 130.24, 124.00, 115.30, 115.20, 110.61, vacuum and the residue was resolved in CH2Cl2 and washed
107.16, 103.29, 103.24, 72.67, 71.27, 71.20, 70.66, 70.57, 70.51, with 1 M HCl to remove 4-DMAP. After drying over anhydrous
70.35, 69.66, 68.58, 59.27, 41.44, 36.42, and 30.51.
Na2SO4, the organic layer was purified through silica gel
column chromatography (eluent: CH2Cl2/MeOH, 15 : 1, v/v) to
afford compound 9 as a colourless liquid (264.8 mg, 91%). MS
General procedure for linking amino-ended molecule with
triadamantyl-terminated molecule
(ESI): [M+Na]+ calculated for C81H134N2O18SNa, 1477.94, found
1
A two-step reaction is required to link an amino-ended mole- 1477.86; H NMR (500 MHz, CDCl3): 6.45 (s, 1H), 6.19 (s, 1H),
cule with triadamantyl-terminated molecule (Scheme 1). For 5.77 (s, 1H), 4.84 (s, 2H), 4.30 (br, 1H), 4.10 (br, 1H), 4.00
c
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NJC
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(br, 6H), 3.70 (br, 6H), 3.57 (t, J = 2.80 Hz, 3H), 3.60 to 3.40 (m,
36H), 2.96 (br, 1H), 2.68 (br, 1H), 2.57 to 2.50 (m, 1H), 2.23 (t, J =
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Acknowledgements
This work was supported by the Natural Science Foundation of 11 M. Mammen, S. K. Choi and G. M. Whitesides, Angew.
Shaanxi (2011JQ2006), the National Natural Science Foundation of Chem., Int. Ed., 1998, 37, 2754.
China (20975082 and 21175107), the Ministry of Education of the 12 M. Escalante, Y.-P. Zhao, M. J. W. Ludden, R. Vermeij,
People’s Republic of China (NCET-08-0464), the Scientific Research
Foundation for the Returned Overseas Chinese Scholars, the State
Education Ministry, and the Northwest A&F University.
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