Enhancement of affinity in molecular recognition via hydrogen bonds by POSS-core dendrimer and its application for selective complex formation between guanosine triphosphate and 1,8-naphthyridine derivatives

Article abstract of DOI:10.1039/c1ob06630g

We report that a polyhedral oligomeric silsesquioxane (POSS) core in a dendrimer can enhance the affinity of the molecular recognition via hydrogen bonds between 1,8-naphthyridine and guanosine nucleotides. The complexation of the naphthyridine ligands with a series of guanosine nucleotides was investigated, and it is shown that the POSS core should play a significant role in the stabilization of the complexes via hydrogen bonds. Finally, we demonstrate that the 1,8-naphthyridine ligand can selectively recognize guanosine triphosphate by assisting with the POSS-core dendrimer.

Full text of DOI:10.1039/c1ob06630g

View Article Online / Journal Homepage / Table of Contents for this issue
Organic &
Biomolecular
Chemistry
Dynamic Article Links
Cite this: Org. Biomol. Chem., 2012, 10, 90
www.rsc.org/obc
PAPER
Enhancement of affinity in molecular recognition via hydrogen bonds by
POSS-core dendrimer and its application for selective complex formation
between guanosine triphosphate and 1,8-naphthyridine derivatives†
Kazuo Tanaka, Masahiro Murakami, Jong-Hwan Jeon and Yoshiki Chujo*
Received 24th September 2011, Accepted 12th October 2011
DOI: 10.1039/c1ob06630g
We report that a polyhedral oligomeric silsesquioxane (POSS) core in a dendrimer can enhance the
affinity of the molecular recognition via hydrogen bonds between 1,8-naphthyridine and guanosine
nucleotides. The complexation of the naphthyridine ligands with a series of guanosine nucleotides was
investigated, and it is shown that the POSS core should play a significant role in the stabilization of the
complexes via hydrogen bonds. Finally, we demonstrate that the 1,8-naphthyridine ligand can
selectively recognize guanosine triphosphate by assisting with the POSS-core dendrimer.
the dendrimers are feasible for site- and time-selective delivery.
Introduction
We have recently reported the retention ability of water-soluble
Hydrogen-bond-mediated molecular recognition in water is a
dendrimers composed of polyhedral oligomeric silsesquioxane
(POSS).9 In polar solvents, the POSS-core dendrimers could
form globular conformations even at lower generations and could
create a distinct hydrophobic space around the POSS core.10,11
Consequently, larger amounts of the hydrophobic guest molecules
can be sustained inside the dendrimers than inside those of the
same generation of the polyamidoamine (PAMAM, Scheme S1†)
dendrimer which has similar dendrons.10 Our interest next focused
on realizing selective capturing of biomolecules using the distinct
hydrophobic spaces inside the POSS-core dendrimers.
Herein, we describe the influence on the binding affinity with
the naphthyridine ligand and guanosine derivatives by the POSS-
core dendrimer. The binding constants were evaluated from
the fluorescence quenching by adding a series of guanosine
nucleotides. In addition, from the investigation of the recognition
mechanism with the dendrimer PAMAM and various kinds of
naphthyridine derivatives (Scheme 1), it was suggested that the
POSS core should offer a hydrophobic space where the strength of
the hydrogen bonds should be enhanced. This is the first example,
to the best of our knowledge, not only of using the amphiphilicity
of the dendrimer to enhance molecular recognition via hydrogen
bonding in the aqueous phase but also of capture of biomolecules
by a dendrimer.
topic with high relevance to biological systems. To realize stable
complexation between the receptor and the target, some elabo-
ration to maintain the binding affinity should be necessary to
compensate for the inhibition of bond formation by hydration.1
A familiar examples can be seen in the RNA polymerases. In
the active pocket, recognition with the nucleoside triphosphates
based on hydrogen-bond patterns can be accomplished along the
template sequences with high fidelity in the gene transcription.2 In
contrast, complexation with the complementary nucleosides can
scarcely be observed in water without enzymes.
1,8-Naphthyridine derivatives can work as a receptor for
guanosine nucleotides.3 Nakatani et al. have presented a series of
1,8-naphthyridine derivatives for the highly-sensitive recognition
of nucleobases.4 Cooperative interaction plays a significant role
in the enhancement of affinity, leading to the specific recognition
of guanine-involving mismatch sites in DNA.5 Cywinski et al.
have reported cyclic GMP (cGMP)-selective recognition using
modified polymer particles with naphthyridine derivatives.6 The
cooperativity between the zeta potential of the particles and the
recognition properties of the naphthyridine receptor can result in
molecular recognition ability for cGMP with high specificity.
Hydrophilic polymeric materials which can retain guest
molecules are a versatile platform as biosensors or vessels for drug
delivery systems.7 In particular, because of the uniform structures,
the characteristics of the dendrimers can be readily modulated by
the size tuning and peripheral modification.8 These advantages of
Experimentals
Materials
1H NMR and 13C NMR spectra were measured with a JEOL EX–
Department of Polymer Chemistry, Graduate School of Engineer-
ing, Kyoto University, Katsura, Nishikyo-ku, Kyoto, 615-8510, Japan.
E-mail: chujo@chujo.synchem.kyoto-u.ac.jp; Fax: (+81) 75-383-2605;
Tel: (+81) 75-383-2604
† Electronic supplementary information (ESI) available: Experimental
details. See DOI: 10.1039/c1ob06630g
1
400 (400 MHz for H and 100 MHz for 13C) spectrometer. 29Si
NMR spectra were measured with a JEOL JNM–A400 (80 MHz)
spectrometer. Coupling constants (J values) are reported in
hertz. The chemical shifts are expressed in ppm downfield from
90 | Org. Biomol. Chem., 2012, 10, 90–95
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
Scheme 1 Synthetic scheme for the naphthyridine derivatives. Reagents and conditions: (a) Malic acid, 95% H2SO4, 110 ◦C, 3 h, 92%; (b) POCl3, reflux,
4 h, 33%; (c) ethynylbenzene, PdCl2(PPh3)2, CuI, triethylamine, THF, r.t., 16 h, 30%; (d) acetic anhydride, chloroform, r.t., 3 h, 80%.
tetramethylsilane, using residual dimethyl sulfoxide (d = 2.50 in 1H
NMR, d = 39.5 in 13C NMR) as an internal standard. Emission
from the samples was monitored using a Perkin Elmer LS50B at
25 ◦C using 1 cm path length cell. Mass spectra were obtained on
a JEOL JMS–SX102A. The synthetic schemes for compound 312
and the G2 POSS-core dendrimer are shown in Schemes S2 and
S3 in the Supporting Information.† The G2 PAMAM dendrimer
was purchased from Aldrich as a methanol solution and directly
used for the analyses.
gradient of methanol in chloroform (chloroform/methanol from
20 : 1 to 10 : 1) yielded 41 mg of pure compound 2 (30%) as a
1
white powder. H NMR (CDCl3) d 7.92 (d, 1H, J = 8.0 Hz),
7.85 (d, 1H, J = 8.8 Hz), 7.62 (m, 2H), 7.41 (d, 1H, J = 8.4 Hz),
7.37 (m, 3H), 6.77 (d, 1H, J = 8.8 Hz), 5.05 (br,1H). 13C NMR
(CDCl3) d 159.97, 155.80, 145.35, 137.59, 136.26, 132.18, 129.07,
128.34, 122.13, 121.68, 116.77, 133.70, 90.57, 89.32. LRMS (NBA)
[(M+H)+] calcd. 246, found 246: LRMS (NBA) [(M+H)+] calcd.
246.1031, found 246.1021.
Compound 113
Compound 412
In a 25 mL round-bottom flask, 30 mg of 2 (0.122 mmol) and 5 mL
of acetic anhydride were stirred in 10 mL of chloroform at room
temperature for 3 h. After evaporation, compound 1 (28 mg, 80%)
was purified as a white powder from column chromatography in
silica gel with ethyl acetate. 1H NMR (CDCl3) d 9.04 (br,1H), 8.55
(d, 1H, J = 8.8 Hz), 8.18 (d, 1H, J = 8.8 Hz), 8.11 (d, 1H, J = 8.4
Hz), 7.65 (m, 2H), 7.60 (d, 1H, J = 8.4 Hz), 7.41 (m, 3H), 2.31 (s,
3H). 13C NMR (CDCl3) d 170.27, 154.74, 154.64, 146.78, 138.94,
136.58, 132.27, 129.42, 128.47, 124.02, 121.90, 119.70, 115.97,
91.39, 89.13, 25.08. LRMS (NBA) [(M+H)+] calcd. 288, found
288: LRMS (NBA) [(M+H)+] calcd. 288.1137, found 288.1125.
A reaction mixture containing 9.07 g of malic acid (67.6 mmol)
and 6.67 g of 2,6-diaminopyridine (61.1 mmol) was slowly added
to 40 mL of 95% H2SO4 at 0 ◦C. After stirring at 110 ◦C for 3 h,
the solution was neutralized with NH4OH, and the product was
obtained as a precipitate. Compound 4 was separated by filtration
1
as a white powder (9.05 g, 92%). H NMR (DMSO-d6) d 11.85
(br, 2H), 7.64 (d, 1H, J = 9.6 Hz), 7.63 (d, 1H, J = 9.2 Hz), 6.32 (d,
1H, J = 9.2 Hz), 6.01 (d, 1H, J = 8.9 Hz). LRMS (NBA) [(M+H)+]
calcd. 162, found 162.
Compound 512
The hydroxyl compound 4 (1.0 g, 6.21 mmol) was refluxed with
50 mL of POCl3 for 4 h. After cooling, the reaction solution
was neutralized with NH4OH, and extracted with chloroform.
Evaporation of the chloroform extract gave the crude product
which was recrystallized from toluene giving 370 mg of the pure
product 5 as a yellow powder (33%). 1H NMR (DMSO-d6) d 7.86
(d, 1H, J = 8.0 Hz), 7.82 (d, 1H, J = 8.8 Hz), 7.17 (d, 1H, J =
8.0 Hz), 6.75 (d, 1H, J = 6.8 Hz), 5.33 (bs, 2H). LRMS (NBA)
[(M+H)+] calcd. 180, found 180.
Complexation with the dendrimers
The general procedure for retention of the guest molecules by
the dendrimers is described here. Stock solutions (¥10) of the
guest molecules and G2 POSS-core dendrimer were mixed at room
temperature, and then 500 mL of the samples were prepared by
adding solvents.
Evaluation of the amount of retained ligand in the G2 POSS-core
dendrimer
Compound 213
The sample solutions were stored under ambient conditions for
2 days and filtered through Nanosep 3 K centrifugal devices
(Pall Life Sciences) by centrifugation (2000g, 30 min, 25 ◦C). The
concentration of ligand 1 was determined from the fluorescence
emission of the filtrates. The amount of retention was evaluated
by comparing to the intensities of the filtrates at 0 day (I0) and 2
days (I2d). The results are shown in Fig. 2.
In a 25 mL round-bottom flask, 100 mg of 2-amino-7-chloro-
1,8-naphthyridine (5) (0.557 mmol), 10 mg of PdCl2(PPh3)2 (cat.)
and 3 mg of CuI (cat.) were stirred in 5 mL of dry THF under
argon. To the solution, 0.6 mL of triethylamine was slowly added
through a syringe. The mixture was stirred at room temperature
for 30 min and then 0.1 mL of ethynylbenzene (0.980 mmol) was
added. The reaction was stirred at room temperature overnight.
Upon removal of the volatiles under reduced pressure, the residue
was dissolved in dichloromethane, passed through a plug of Celite
and then washed with ethyl acetate. The product was dried under
vacuum. Column chromatography in silica gel with an increasing
Fluorescence measurements of the complexes
The fluorescence emission of the ligand solution (10 mM) in the
presence and absence of the dendrimers (100 mM, pH = 5.0) with
or without guanosine derivatives under excitation at 330 nm was
This journal is
The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 90–95 | 91
©

View Article Online
Results and discussion
We designed the ligand 1 as shown in Fig. 1. We expected
that the POSS core could provide hydrophobic spaces inside the
dendrimer, leading to the enhancement of hydrogen bonding.
The 1,8-naphthyridine moiety can form a complex with the
guanine skeleton via hydrogen bonds.3 In particular, as applied
for fluorescence sensors for guanosine nucleotides in the previous
work,3 the fluorescence emission can be quenched via electron
transfer through the hydrogen bonds.6 In other words, a decrease
in emission represents complex formation of the naphthyridine
ligand with guanosine nucleotides. Thereby, the binding constants
can be evaluated with the Stern–Volmer equation in the case of
the non-emissive complex model according to eqn (2).14 These
optical properties of the naphthyridine can make it possible
to quantitatively assess the stability of the complexes of the
naphthyridine moiety with guanosine nucleotides. The benzene
ring is expected to play a role in the adsorption of the ligand on
the surface of the POSS core via the hydrophobic interaction and to
be engaged into the internal space of the POSS-core dendrimers.
The terminal amino groups are expected to bind the guanosine
nucleotides by the electrostatic interaction with the phosphate
groups.
Fig. 1 Chemical structures of G2 POSS-core dendrimer and the com-
plexes of ligand 1 and the guanosine nucleotides used in this study.
Initially, 1-amino-7-chloronaphthyridine was prepared accord-
ing to the previous reports.12 The ligand 1 was obtained via
Sonogashira–Hagihara cross coupling reaction, following acetyla-
tion at the amino group on the 7 position. The second generation
of the POSS-core dendrimer (G2 POSS-core dendrimer) was
prepared according to the literature.9,15 Complexation of the
G2 POSS-core dendrimer with the naphthyridine ligand was
performed by mixing. To confirm the retention in the dendrimer,
we investigated the fluorescence emission of the filtrate passed
through the size-exclusion filter.11 If the naphthyridine ligand
forms aggregates or adsorbs onto the vessel walls, the filtrate
shows significant low emission intensity. On the other hand, if
the naphthyridine ligand can be retained in the dendrimers, the
adsorption should be inhibited. Thereby, the fluorescence can be
observed from the filtrate. In addition, the emission intensity of
the filtrate can represent the amount of retention. We prepared
solutions with various concentrations of G2 POSS-core dendrimer
and investigated the intensity changes of the filtrate after 2 days
from the ligand 1 (Fig. 2). The filtrate in the absence of G2
POSS-core dendrimer provided subtle emission from the ligand
1. In contrast, fluorescence emission from the filtrate was mostly
maintained in the presence of G2 POSS-core dendrimer. These
results suggest that 10 mM of the ligand 1 should be retained
in the dendrimer (100 mM). Moreover, it was found that the
naphthyridine ligand retained in the G2 POSS-core dendrimer can
maintain a good dispersion state without non-specific aggregation
or adsorption on the vessel wall for at least two days. This is long
enough to do further experiments.
Fig. 2 The emission changes of the filtrates after 2 days. Solutions
containing 10 mM 1 and variable concentrations of the G2 POSS-core
dendrimer were stored under ambient conditions for 2 days and then
passed through a size-exclusion filter membrane by centrifugation. Emis-
sion spectra were obtained with excitation light at 330 nm at 25 ◦C.
monitored using a Perkin Elmer LS50B at 25 ◦C with a 1 cm path
length cell. The excitation bandwidth was 1 nm. The emission
bandwidth was 1 nm. The quantum yields were determined as an
absolute value with an integral sphere.
Stern–Volmer plots14
The data were analyzed in terms of the Stern–Volmer equation
[eqn (1)]:
I
0 =1+KSV[Q]
(1)
I
The emission intensity was plotted according to a Stern–Volmer
equation, reporting I0/I versus the concentrations of guanosine
derivatives [Q], where I0 is the intensity in the absence of quencher
and I is the intensity in the presence of quencher. KSV is the Stern–
Volmer quenching constant. A plot of I0/I versus [Q] yields an
intercept of one and a slope equal to KSV
.
Binding constants calculation14
We investigated the changes in fluorescence intensity from the
ligand 1 by adding a series of guanosine nucleotides (Table 1).
The emission spectra were obtained from the aqueous solutions
containing 10 mM ligand 1 and 100 mM G2 POSS-core dendrimer
with excitation light at 330 nm (Fig. 3). The strong fluorescence
emission with the peak around 380 nm was observed from the
ligand 1 in the aqueous solution. The addition of guanosine
triphosphate (GTP) caused the significant quenching of the
If non-emissive complex formation between the naphthyridine
ligand and guanosine nucleotides occurs, the binding constant
(KA) can be calculated with the number of the binding molecules
(n) from eqn (2):
I0 −I
(2)
log
=logKA +nlog[Q]
I
92 | Org. Biomol. Chem., 2012, 10, 90–95
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
Table 1 Optical properties and the binding constants of the ligand 1a
changed (Fig. S2). This result suggests that the triphosphate group
has less influence on the emission properties of the naphthyridine
derivatives.
Nucleotidesb
Uc
KSV [¥103 mol L-1]d
ne
KA [M-1]e
We prepared Stern–Volmer plots with guanosine nucleotides
as quencher (Fig. 4). Based on the formation of a non-emissive
complex model, the binding constants were calculated (Fig. 5). All
plots obtained from the titration of GTP and cGMP were fitted
on the line, and the binding constants could be determined. It
was found that POSS can enhance the binding affinity with GTP
approximately 10 times more than that with cGMP. These results
suggest that the ligand 1 can selectively recognize GTP in the G2
POSS-core dendrimer.
None
rG
GMP
cGMP
GTP
0.39
0.39
0.39
0.34
0.30
n.d.f
n.d.f
n.d.f
1.14
2.83
n.d.f
n.d.f
n.d.f
0.95
1.10
n.d.f
n.d.f
n.d.f
670
7500
a Procedures and conditions are described in the Experimental section
in the Supporting Information.† b 100 mM solutions. c Determined as an
absolute value. d Quenching constants were determined from the slopes of
the fitting line in the Stern–Volmer plots. e Calculated according to ref. 14
f n.d. = not determined because of too weak an interaction.
Fig. 4 Stern–Volmer plots with a solution containing 10 mM 1 by adding
various kinds of guanosine derivatives.
Fig. 3 Emission changes of 10 mM 1 in the presence and absence
of 100 mM G2 POSS-core dendrimers by adding 100 mM guanosine
nucleotides in water at 25 ◦C. Excitation wavelength was 330 nm.
emission from the ligand 1 (Fig. 3a). Complex formation with
GTP was suggested. In the presence of cGMP, the emission was
also quenched (Fig. 3b). Corresponding to the results reported
by Cywinski et al., complex formation via hydrogen bonds should
occur between the ligand 1 and cGMP.6 A slight effect on emission
intensity was observed by adding rG and GMP to the solution.
These results suggest that the interaction particularly between
GTP and the ligand 1 can be enhanced by the G2 POSS-core
dendrimer.
To evaluate the role of the POSS core, we performed fluorescence
measurements using the same procedure using the G2 PAMAM
dendrimer which possesses an ethylene diamine core instead of
POSS. On addition of guanosine nucleotides including GTP, the
emission from the ligand 1 was less affected (Fig. S1†). These
results clearly indicate that the POSS core is responsible for
enhancing the complex formation between ligand 1 and GTP.
The hydrophobic space around the POSS core could reduce the
hydration of the naphthyridine ligand, resulting in enhancement
of the affinity of the complex via hydrogen bonds. Moreover,
fluorescence measurements were also carried out with adenosine
triphosphate (ATP), and it was found that the emission was hardly
Fig. 5 Plots for determining binding constants between the ligand 1
and guanosine nucleotides according to eqn (2). The slopes represent the
number of binding guanosine nucleotides. The y-intercepts represent the
logKA values. The lines are prepared with the least-squares method. R2 is
the determination coefficient.
In order to investigate the influence of the substituents at the
naphthyridine ligand on the recognition, the emission spectra were
measured with the various kinds of naphthyridine derivatives12
listed in Fig. 6. The retention of these derivatives in the G2
POSS-core dendrimer in the same manner as above, and the
emission changes, were examined. Significant quenching was
hardly observed on addition of guanosine nucleotides to the series
of naphthyridine ligands. These results mean that all substituents
on the ligand 1 are necessary to maintain the recognition ability.
The hydrogen bonds and the hydrophobic interaction with the
surface of the POSS core might cooperatively contribute to the
selective recognition of ligand 1 with GTP in the G2 POSS-core
dendrimer.
This journal is
The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 90–95 | 93
©

View Article Online
Fig. 8 Emission spectra of solutions containing 10 mM 1 in 50 mM
sodium phosphate buffer (pH = 7.0) and 0.1 N HCl at 25 ◦C. Excitation
wavelength was 330 nm.
Fig. 6 Chemical structures and emission spectra of 10 mM (a) 2 and (b)
3 in the presence and absence of 100 mM G2 POSS-core dendrimers by
adding 100 mM GTP in water at 25 ◦C. Excitation wavelength was 330 nm.
dendrimer. Although the affinity is lower than those of the
aptamers16 as previously reported, our system is applicable over a
wide pH range and salt concentration. Our data indicate that the
dendrimer complex with the naphthyridine ligand can selectively
recognize and capture GTP. Furthermore, in this system, the
POSS-core dendrimer and the ligand molecules interact only via
non-covalent bonds. Therefore, it can be expected that the target
guest molecules can be tuned by replacing the ligand units. This
might be applicable not only to development of new tools for
biosensing but also for modulating the concentrations of targets
in the cells.
To elaborate the influence of the charge on the surface of the
dendrimer, the emission intensity of the complex was compared
in solutions of various pH (Fig. 7). Under alkaline conditions,
the degree of fluorescence quenching was reduced, while the
quenching ability can be maintained under acidic conditions.
These results indicate that the terminal-ammonium groups should
contribute to binding GTP via electrostatic interaction. Under
the extremely acidic conditions in 0.1 N hydrochloric acid, the
fluorescence emission was largely suppressed (Fig. 8, U = 0.13),
and a new peak appeared in the longer wavelength region.
Therefore, the protonation of the naphthyridine moiety induced
by the triphosphate moiety of GTP should hardly be responsible
for the quenching. From the series of data, a recognition model for
guanosine nucleotides by the dendrimer complex can be proposed.
The naphthyridine ligand and G2 POSS-core dendrimer form a
stable complex in which guanosine nucleotides can enter and leave.
GTP should be retained in the complex for a relatively longer time
because of the cooperative interaction via hydrogen bonds with
the naphthyridine ligand and the stronger electrostatic attraction.
Thus, selective capturing of GTP by the dendrimer complex could
be observed.
Notes and references
1 T. Sawada, M. Yoshizawa, S. Sato and M. Fujita, Nat. Chem., 2009, 1,
53.
2 K. D. Westover, D. A. Bushnell and R. D. Kornberg, Cell, 2004, 119,
481.
3 J. H. Liao, C. T. Chen, H. C. Chou, C. C. Cheng, P. T. Chou, J. M. Fang,
Z. Slanina and T. J. Chow, Org. Lett., 2002, 4, 3107; J. M. Fang, S. Selvi,
J. H. Liao, Z. Slanina, C. T. Chen and P. T. Chou, J. Am. Chem. Soc.,
2004, 126, 3559; Z. Xu, K. Morita, Y. Sato, Q. Dai, S. Nishizawa and
N. Teramae, Chem. Commun., 2009, 6445; Y. Sato, S. Nishizawa, K.
Yoshimoto, T. Seino, T. Ichizawa, K. Morita and N. Teramae, Nucleic
Acids Res., 2009, 37, 1411.
4 K. Nakatani, S. Hagihara, Y. Goto, A. Kobori, M. Hagihara, G.
Hayashi, M. Kyo, M. Nomura, M. Mishima and C. Kojima, Nat. Chem.
Biol., 2005, 1, 39.
5 K. Nakatani, S. Sando and I. Saito, Nat. Biotechnol., 2001, 19, 51; K.
Nakatani, S. Sando, H. Kumasawa, J. Kikuchi and I. Saito, J. Am.
Chem. Soc., 2001, 123, 12650; T. Peng, C. Dohno and K. Nakatani,
Angew. Chem., Int. Ed., 2006, 45, 5623.
6 P. J. Cywinski, A. J. Moro, T. Ritschel, N. Hildebrandt and H. G.
Lo¨hmannsro¨ben, Anal. Bioanal. Chem., 2011, 399, 1215.
7 S. Matsumoto, S. Yamaguchi, S. Ueno, H. Komatsu, M. Ikeda, K.
Ishizuka, Y. Iko, K. V. Tabata, H. Aoki, S. Ito, H. Noji and I. Hamachi,
Chem.–Eur. J., 2008, 14, 3977; S. Matsumoto, S. Yamaguchi, A. Wada,
T. Matsui, M. Ikeda and I. Hamachi, Chem. Commun., 2008, 1545;
H. Komatsu, S. Matsumoto, S. Tamaru, K. Kaneko, M. Ikeda and I.
Hamachi, J. Am. Chem. Soc., 2009, 131, 5580; J. Boekhoven, A. M.
Brizard, K. N. K. Kowlgi, G. J. M. Koper, R. Eelkema and J. H. van
Esch, Angew. Chem., Int. Ed., 2010, 49, 4825.
8 N. Morimoto, N. Ogino, T. Narita and K. Akiyoshi, J. Biotechnol.,
2009, 140, 246; A. Morimoto, X.-P. Qiu, F. M. Winnik and K. Akiyoshi,
Macromolecules, 2008, 41, 5985; N. Morimoto, T. Ohki, K. Kurita and
K. Akiyoshi, Macromol. Rapid Commun., 2008, 29, 672.
9 P.-A. Jaffre´s and R. E. Morris, J. Chem. Soc., Dalton Trans., 1998,
2767; F. J. Feher and K. D. Wyndham, Chem. Commun., 1998, 323; F.
J. Feher, K. D. Wyndham, D. Soulivong and F. Nguyen, J. Chem. Soc.,
Dalton Trans., 1999, 1491; X. Zhang, K. J. Haxton, L. Ropartz, D. J.
Cole-Hamilton and R. E. Morris, J. Chem. Soc., Dalton Trans., 2001,
3261.
Fig. 7 The influence of pH on the quantum yield of emission from
solutions containing 10 mM 1, 100 mM G2 POSS-core dendrimer, and
100 mM GTP in 50 mM sodium phosphate buffer at 25 ◦C. Excitation
wavelength was 330 nm.
Conclusions
In conclusion, we present that the binding affinity of the naph-
thyridine ligand with GTP can be enhanced by the POSS-core
94 | Org. Biomol. Chem., 2012, 10, 90–95
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
13 The 1H NMR spectrum is shown in the Supporting Information.
10 K. Tanaka, K. Inafuku, K. Naka and Y. Chujo, Org. Biomol. Chem.,
2008, 6, 3899; K. Tanaka, K. Inafuku and Y. Chujo, Chem. Commun.,
2010, 46, 4378; K. Tanaka, K. Inafuku, S. Adachi and Y. Chujo,
Macromolecules, 2009, 42, 3489.
11 K. Tanaka, W. Ohashi, N. Kitamura and Y. Chujo, Bull. Chem. Soc.
Jpn., 2011, 84, 612.
14 Y. Sun, S. Bi, D. Song, C. Qiao, D. Mu and H. Zhang, Sens. Actuators,
B, 2008, 129, 799.
15 M. C. Gravel, C. Zhang, M. Dinderman and R. M. Laine, Appl.
Organomet. Chem., 1999, 13, 329; F. J. Feher and K. D. Wyndham,
Chem. Commun., 1998, 323.
12 R. G. Newkome, J. S. Garbis, K. V. Majestic, R. F. Fronczek and G.
Chiari, J. Org. Chem., 1981, 46, 833.
16 J. H. Davis and J. W. Szostak, Proc. Natl. Acad. Sci. U. S. A., 2002, 99,
11616.
This journal is
The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 90–95 | 95
©