Multipodal dynamic coordination involving cation-π interactions to control the structure of helical polymers

Article abstract of DOI:10.1039/c7cc04220e

A precise tuning of the four possible states of a helix (P/M helical sense and stretched/compressed helical backbone) is attained by controlling the complexation between Li⁺ and a poly(phenylacetylene) that bears amide, ester and phenyl ring functionalities at the pendant group. Depending on the MeOH ratio that is present as a cosolvent, different coordination sites are involved in interactions leading to complexes I-III, each one with a characteristic structure (tri-, bi-, and unipodal) and an associated helical state. This dynamic coordination allows the selective modification of the helical sense or the stretching/compression backbone of a helical polymer.

Full text of DOI:10.1039/c7cc04220e

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Multipodal dynamic coordination involving cation-π interactions
to control the structure of helical polymers
Mohammad Alzubi,‡ Sandra Arias,‡ Iria Louzao, Emilio Quiñoá, Ricardo Riguera * and Félix Freire*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
A precise tuning of the four possible states of a helix (P/M helical pendant in two different ways, each one promoting one helical
sense and stretched/compressed helical backbone) is attained by sense in the backbone.9 From the structural point of view, this
controlling
the
complexation
between
Li+
and
a
change in complexation/helical sense involves the control of
interaction.
poly(phenylacetylene) that bears amide, ester and phenyl ring the formation and cleavage of a cation-
π
functionalities at the pendant group. Depending on the MeOH Herein, we describe a more sophisticated system where tuning
ratio that is present as cosolvent, different coordination sites are the complexation of the metal ion with different groups in the
involved leading to complexes I-III, each one with a characteristic pendants allows not only the control on the helical sense of the
structure (tri-, bi-, unipodal) and associated helical state. This polymer but also on the elongation of the chain.
dynamic coordination allows the selective modification of the To this end, we devised
a pendant comprising three
helical sense or the stretching/compression backbone of a helical complexation sites with different coordinating ability and
polymer.
located at adequate distance for chelation: two carbonyl
groups and an aromatic ring for metal cation−π interaction).
This pendant should be able to complex the metal ion in
different ways, generating complexes whose different
structures and interactions with the vicinal pendants will
determine a given helix for each one (Scheme 1).
The control of the helical sense and elongation of helical
polymers,1 by the action of external stimuli,1-4 has attracted the
attention of the scientific community due to the potential
interest of those materials in applications as sensors,2
molecular devices,3 chiro-optical switches,4 memory elements
and chiral catalysts.5 Poly(phenylacetylene)s6 are a family of
helical polymers especially suited for those applications due the
wide range of substituents available and above all, their
dynamic behaviour that allows a helical PPA to invert or amplify
its helical sense, and even to modulate its elongation by the
action of an external stimuli.7
2
Li+
3
1
R
Co-solvent
Li+
Chelation to
1
2 and 3
2
Li+
R
In
poly(phenylacetylene) bearing the anilide of the (R)-
methoxy- -phenylacetic acid as pendant [poly-(R)- ], (null CD,
our
group
we
recently
described
that
a
3
3
1
α
-
1
2
1
2
3
NH-C=O
MeO-C=O
Ph
R
α
1
axially racemic due to the 1:1 sp/ap conformational ratio),8 can
be specifically shifted to adopt either the P or the M helical
sense by addition —in CHCl3 solution— of a small amount of a
monovalent metal ion (Na+ or Ag+) that, depending on the
amount of a crucial donor cosolvent (i.e., MeOH), chelates the
Chelation to
1 and 2
coordinating groups
R = Non coordinating group
Co-solvent
Li+
Co-solvent
3
R
2
3
1
1
R
Li+
2
Chelation to
1
and 3
Chelation to
2 and 3
Co-solvent
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In this paper, we demonstrate this successful idea using as
π interaction with the aryl ring of the amino acid (Figure 2b).
pendants the benzamides of (S)-phenylglycine methyl ester [m- During the formation of this complex, a helical inversion is
(S)- ], where observed from helix I to helix II, due to the conformational
],10 and (S)-phenylalanine methyl ester [m-(S)-
2
3
their amide, ester and phenyl ring functions act as complexing change produced at the pendant moiety, which places the
sites (Figure 1). We will show also that selective conversion of bulkiest group in the opposite direction.
the PPA into its complexes allows the preparation of the four Next, complex I was titrated with different amounts of MeOH
different helical states, represented by the P and M helical to study the dynamic coordination chemistry of the poly-(S)-(
2
senses and compressed/stretched skeleton.
or 3
)/Li+ system.
Thus, 4-ethynylbenzamide of L-phenylglycine methyl ester and
L-phenylalanine methyl ester were prepared and polymerized
using [{Rh(nbd)Cl}2] as catalyst (nbd= 2,5-norbornadiene) that
gave the poly-(S)-
93% respectively) and with
2
and poly-(S)-
3
PPAs in good yield (90 % and
high content of the cis
a
configuration of the double bonds (see SI for details).
CD studies of poly-(S)- and poly-(S)- in chloroform (0.3
mg/mL) show preferred helical structure —helix I—
associated to the presence of preponderant anti-
2
3
a
a
conformation (the two carbonyls oppositely oriented in the
pendant group, Figure 2).10
Next, lithium perchlorate in MeOH (10 mg/mL) was added to a
chloroform solution of poly-(S)-(
poly-(S)-
/Li+/MeOH in a 1.0/0.5/133 mole ratio and poly-(S)-
/Li+/MeOH in a 1.0/0.5/130 mole ratio.11 In these conditions
[i.e., poly-(S)-( or
)/Li+/MeOH= 1.0/0.5/<135], complex I—
2 or 3) (0.3 mg/mL) to prepare
2
3
2
3
where the metal ion coordinates both carbonyl groups (amide
and ester) as inferred from IR studies— is formed (Figure 2).
Moreover, 7Li NMR studies show a strong shielding of the 7Li
peak once poly-(S)-
5.89 ppm, typical for a cation-
were obtained for the Li NMR of poly-
2
is present in the solution, resonating at -
interaction12 (similar results
/Li+ complex I). This
π
3
chemical shift also indicates that Li+ ion interacts with a single
phenyl ring.13 Thus, in complex I, the Li+ ion chelate the two
carbonyls in a syn orientation, establishing also an extra cation-
2 | J. Name., 2012, 00, 1-3
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conformation at the pendant group, induced by the chelation
of the two carbonyl groups with the monovalent metal ion and
without cation-
Interestingly, it was found that when the amount of MeOH Ulterior additions of MeOH produce the inversion of the helical
added to the poly-(S)-( or sense directly forming helix IV (Figure 3). Contrary to what was
)/Li+ complex is in a poly-(S)-
(mru)/MeOH ratio of 1/ (278-326) (mol/mol), and in a poly-(S)- observed in poly-(S)-( or ), the presence of helix III was not
(mru)/MeOH ratio of 1/ (226-277) (mol/mol), a new helical detected. This is related to the absence in poly-(S)- , of the
π interaction (Figure 3).
2
3
2
2
3
3
4
inversion was produced associated to the evolution of complex cation−π bonding, necessary to stabilize the complex leading to
7
I to a new complex II (Figure 2c). In complex II, the metal ion helix III (see complex II in Figure 2). Moreover, Li NMR [δ(7Li) ≈
remains coordinated to the amide group —inferred from IR -2 ppm] confirmed the absence of any cation−π interaction in
studies—, and to the
analysis:
(7Li)= -5.96 ppm for poly-
poly-
/Li+—13 but the linkage with the ester group has
π
system —determined by 7Li NMR all the poly-(4)/Li+ complexes.
δ
2
/Li+ and -6.04 ppm for
a)
b)
3
50
0
No aryl
ring
O
N
disappeared (Figure 2). Thus, in complex II the metal ion has
only two points for chelation and the complex adopts the anti-
conformation producing a helical structure with the same
helical sense as helix I. In fact, this second inversion clearly
shows a hypsochromic shift observed both at the CD and UV
spectra (Figure 2 and SI). Thus, complex II is structurally
represented by a helix with the same sense as helix I, but a
more compressed scaffold (Figure 2 and SI).
O
N
-50
-100
H
O
Me
poly-4
poly-3
H
O
Me
poly-(S)-2
poly-(S)-2
poly-2
O
poly-4
O
250
300
350
400
450
P
P
Wavelength (nm)
Helix I
50
0
IR
O
CO1: 1646 cm-1
CO2: 1738 cm-1
OMe:1053 cm-1
1
N
H
O
O
Me
Finally, the addition of a larger amount of methanol —poly-(S)-
poly-4 (sp1)
2
-50
P
(2
)/Li+/MeOH in a 1.0/0.5/>380 (mol/mol/mol) ratio, and poly-
250
300
350
400
450
Helix
Li+
Wavelength [nm]
Poly-4 Li+ MeOH
(mol) (mol) (mol)
(S)-(3
)/Li+/MeOH in a 1.0/0.5/>330 (mol/mol/mol) ratio—,
IR
Inversion
ꢀν CO1= +12
ꢀν CO2= +10
ꢀν OMe= -42
1
0.0
0
produced another structural change in the complex formed
between the Li+ ion and the pendant group. In this new mode
of complexation (i.e., complex III), the metal ion “jumps” from
the amide to the ester group, without altering the anti
conformation at the pendant moiety, and therefore no helical
inversion is observed (Figure 2d). On the other hand,
examination of the CD and UV spectra indicate the stretching of
the helix once complex III is formed (see Figure 2d and SI for
details). This elongation is explained by the presence of a
Li+
c)
7Li NMR
O
50
0
O
O
Helix 2
δ= -2.7
N
H
Helix II
Li MeOH-d5
δ= 0.75
complex I
M
-50
poly-4 /Li+ /MeOH
/ 0.2 / <300
250
300
Wavelength [nm]
Poly-4 Li+
MeOH
(mol)
1
1
350
400
450
1
NO cation-π
(mol) (mol)
0.0
0.2
00
52
IR
Helix
Inversion
MeOH
cation-
π interaction [δ 2 or 3
(7Li)≈ -6.2 ppm for poly-( )/Li+]
ꢀν CO1: +4 cm-1
ꢀν CO2: +6 cm-1
ꢀν OMe: -46 cm-1
d)
50
0
between vicinal amino acid groups (Figure 2d). In this way, the
anti conformation will remain unaltered, while the constraint
originated by the placement of the metal ions between
neighbouring pendants is released via elongation of the
polyene chain.
O
1
7Li NMR
N
H
Helix 2
δ= -2.7
O
Me
O
2
Helix 4
δ= -2.5
-50
Helix IV
complex III
250
300
350
400
450
P
Li+
Wavelength [nm]
poly-4 /Li+ /MeOH
/ 0.2 / >300
Poly-4
(mol)
1
1
Li+ MeOH
(mol) (mol)
In order to demonstrate the generality of this sequential
modification of a helix and the role of the different groups, we
perform the same studies using a different PPA. In this case, we
1
0.2
0.2
52
240
NO cation-π
chose poly-(S)-4, bearing the benzamide of L-alanine methyl
ester as pendant group that differs from the previously studied
ones in the replacement of the Ph ring found in poly-(S)-2 by a
methyl group (Figure 3).
CD spectra of poly-(S)-
practically identical CD trace to the one adopted by poly-(S)-(2-
) (Figure 3a) indicating that the three polymers adopt the
4 in CHCl3 (0.3 mg/mL) shows a
In conclusion, it has been demonstrated that addition of low
amounts of Li+ salt to a polyphenylacetylene with pendants
containing amide, ester and phenyl ring functions at precise
distances, allows the sequential formation of three different
complexes (complexes I-III) each one involving different
coordination sites (amide, ester and cation-π) and structures
(tri-, bi-, unipodal) that modify the helical sense or the
stretching/compression of the original helix. The dynamic
character of the complexation allows its manipulation by
3
same helical structure (helix 1).
Addition of LiClO4 in MeOH (10 mg/mL) to the chloroform
solution of poly-(S)-4 (0.3 mg/mL) where poly-(S)-4
/Li+ is in a
1.0/0.5 (mol/mol) ratio, produced a helical inversion with
formation of a complex I, in a similar manner as that observed
for poly-(S)-(
ratio (Figure 2). In this case, the helix inversion observed in
complex-I of poly-(S)- is due to the adoption of a syn
2 or 3
)/Li+/MeOH in a 1.0/0.5/<135 (mol/mol/mol)
4
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Memory, in Polymeric Chiral Catalyst Design and Chiral
controlled addition of MeOH that debilitates some
coordinations and favours others.
Polymer Synthesis, ed. Itsuno, S., John Wiley
Hoboken, NJ, USA, 2011, ch. 7, p 201.
(a) F. Freire, E. Quiñoá and R. Riguera, Chem. Rev., 2016, 116,
& Sons,
In this way, a single helical polymer can be forced to adopt any
6
of the four forms of
a
helix (P/M sense and
1242; (b) E. Yashima, N. Ousaka, D. Taura, K. Shimomura, T.
Ikai and K. Maeda, Chem. Rev., 2016, 116, 13752; (c) J. G.
Rudick, V. Percec, Acc. Chem. Res., 2008, 41, 1641; (d) E.
Yashima and K. Maeda, Macromolecules, 2008, 41, 3; (e) E.
Yashima and K. Maeda, Helically Folding Polymers in
stretched/compressed backbone) by selection of the
complexing state (uncomplexed polymer and complexes I-III).
We think that this approach can be extended to other dynamic
helical polymers, where adequate selection of the pendant
groups and metal ion could generate multiple helical structures
via dynamic coordination chemistry.
Foldamers: Structure Properties
Hecht, I. Huc, WILEY- VCH, Weiheim, 2007, pp 331; (f) K.
Maeda and E. Yashima, Top. Curr. Chem., 2006, 265, 47; (g)
ꢀand Applications; Eds: S.
ꢀ
H. Nakako, R. Nomura, M. Tabata and T. Masuda,
Macromolecules, 1999, 32, 2861.
(a) S. Arias, M. Núñez-Martínez, E. Quiñoá, R. Riguera and F.
Freire, Small, 2017, 13, 1602398; (b) S. Arias, F. Freire, E.
We thank Ministerio de Economía y Competitividad [CTQ2015-
70519-P, CTQ2014-61470-EXP], Erasmus Mundus (M. Alzubi),
Fundación Gil Dávila (S. Arias), Xunta de Galicia (Centro singular
de investigación de Galicia accreditation 2016-2019,
GRC2014/040) and European Union (European Regional
Development Fund - ERDF) for financial support.
7
Quiñoá and R. Riguera, Angew. Chem. Int. Ed., 2014, 53
,
13720; (c) F. Freire, J. M. Seco, E. Quiñoá and R. Riguera, J.
Am. Chem. Soc., 2012, 134, 19374; (d) J. Bergueiro, F. Freire,
E. P. Wendler, J. M. Seco, E. Quiñoá and R. Riguera, Chem.
Sci., 2014,
(a) R. Rodríguez, J. Ignés-Mullol, F. Sagués, E. Quiñoá, R.
Riguera and F. Freire, Nanoscale, 2016, , 3362; (b) F. Freire,
5, 2170.
8
9
8
J. M. Seco, E. Quiñoá and R. Riguera, Angew. Chem. Int. Ed.,
2011, 50, 11692.
(a) S. Arias, J. Bergueiro, F. Freire, E. Quiñoá and R. Riguera,
Small. 2016, 12, 238; (b) S. Arias, F. Freire, E. Quiñoá and R.
Riguera, Polym. Chem, 2015, 6, 4725.
Notes and references
1
(a) E. Yashima, K. Maeda and Y. Furusho, Acc. Chem. Res.,
2008, 41, 1166; (b) E. Yashima, K. Maeda, H. Iida, Y. Furusho
and K. Nagai, Chem. Rev., 2009, 109, 6102; (c) J. Liu, J. W. Y.
Lam and B. Z. Tang, Chem. Rev., 2009, 109, 5799; (d) B. M.
Rosen, C. J. Wilson, D. A. Wilson, M. Peterca, M. R. Imam and
V. Percec, Chem. Rev., 2009, 109, 6275; (e) E. Schwartz, M.
Koepf, H. J. Kitto, R. J. M. Nolte and A. E. Rowan, Polym.
10 I. Louzao, J. M. Seco, E. Quiñoá and R. Riguera, Angew.
Chem., Int. Ed., 2010, 49, 1430.
11 The use of MeOH is necessary to dissolve the lithium
perchlorate salt, but at this point the amount added can be
considered negligible to affect the poly (S)-(2-3)/Li+ complex.
As far as other metal ions is concerned, Na+ gave no inversion
and Ag+ gave just helices II and IV, with less MeOH needed to
cause the changes.
Chem, 2011, 2, 33.
(a) E. Anger, H. Iida, T. Yamaguchi, K. Hayashi, D. Kumano, D.
2
Crassous, N. Vanthuyne, C. Rousselc and E. Yashima, Polym.
Chem., 2014, 5, 4909; (b) H. Iida, M. Miki, S. Iwahana and E.
12 (a) L. Liu, T. Namikoshi, Y. Zang, T. Aoki, S. Hadano, Y. Abe, I.
Wasuzu, T. Tsutsuba, M. Teraguchi and T. Kaneko, J. Am.
Chem. Soc., 2013, 135, 602; (b) T. Aoki, T. Kaneko, N.
Maruyama, A. Sumi, M. Takahashi, T. Sato and M. Teraguchi,
J. Am. Chem. Soc., 2003, 125, 6346; (c) M. Tabata, Y. Tanaka,
Y. Sadahiro, T. Sone, Yokota and K. I. Miura, Macromolecules,
1997, 30, 5200; (d) C. I. Simionescu, V. Percec and S.
Dumitrescu, J. Polym. Sci. Polym. Chem. Ed., 1977, 15, 2497.
13 (a) V. Ya Lee, R. Kato, M. Ichinhe and A. Sekiguchi, J. Am.
Chem. Soc., 2005, 127, 13142; (b) J. W. Caldwell and P. A.
Kollman, J. Am. Chem. Soc., 1995, 117, 4177; (c) A. Sekiguchi,
Y. Sugai, K. Ebata, C. Kabuto and H. Sakurai, J. Am. Chem. Soc.,
1993, 115, 1144; (d) R. A. Kumpf and D. A. Dougherty,
Science, 1993, 261, 1708.
Yashima, Chem. Eur. J. 2014, 20, 4257; (c) S. Leiras, F. Freire,
J. M. Seco, E. Quiñoá and R. Riguera, Chem. Sci., 2013, 4,
2735.
(a) P. Thodupunuri, S. Katukuri, K. V. Ramakrishna, G. Sharma,
A. C. Kunwar, A. Sarma and H. Hofmann. J. Org. Chem., 2017,
82, 2018; (a) B. L. Feringa, Acc. Chem. Res., 2001, 34, 504.
(a) S. Sakurai, K. Okoshi, J. Kumaki and E. Yashima, J. Am.
Chem. Soc., 2006, 128, 5650; (b) K. Okoshi, S. Sakurai, J. K.
3
4
Ohsawa and E. Yashima, Angew. Chem., Int. Ed., 2006, 45
,
8173; (c) D. Pijper, M. G. M. Jongejan, A. Meetsma and B. L.
Feringa, J. Am. Chem.Soc., 2008, 130, 4541.
(a) M. Burgess, J. S. Moore and J. R. López, Acc. Chem. Res.,
2016, 49, 2649; (b) X. Liu, L. Lin and X. Feng, Acc. Chem. Res.,
2011, 44, 574; (c) H. Iida and E. Yashima, Synthesis and
Application of Helical Polymers with Macromolecular Helicity
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TOC
Dynamic coordination, by means of multipodal metal complexes
and cation- interactions, controls the structure of helical polymers
π
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