Host-guest-driven color change in water: Influence of cyclodextrin on the structure of a copper complex of poly((4-hydroxy-3-(pyridin-3-yldiazenyl)phenethyl)methacrylamide-codimethylacrylamide)

Article abstract of DOI:10.3762/bjoc.10.259

In the present work we report the synthesis of poly((4-hydroxy-3-(pyridin-3-yldiazenyl)phenethyl)methacrylamide-co-dimethylacrylamide) and its reversible optical and complex-forming properties due to copper and cyclodextrin (CD) interactions. Color changing effects are characterized by UV-vis spectroscopy and the supramolecular behavior is investigated by dynamic light scattering experiments.

Full text of DOI:10.3762/bjoc.10.259

Host–guest-driven color change in water: influence of
cyclodextrin on the structure of a copper complex of poly((4-
hydroxy-3-(pyridin-3-yldiazenyl)phenethyl)methacrylamide-co-
dimethylacrylamide)
Nils Retzmann, Gero Maatz and Helmut Ritter*
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2014, 10, 2480–2483.
Institute of Organic Chemistry and Macromolecular Chemistry,
Heinrich-Heine-University Duesseldorf, Universitaetsstraße 1,
D-40225 Duesseldorf, Germany
doi:10.3762/bjoc.10.259
Received: 02 April 2014
Accepted: 25 September 2014
Published: 24 October 2014
Email:
Helmut Ritter* - h.ritter@uni-duesseldorf.de
This article is part of the Thematic Series "Superstructures with
cyclodextrins: Chemistry and applications II".
* Corresponding author
Keywords:
Guest Editor: G. Wenz
cyclodextrin; copolymer; copper(II) sulfate; supramolecular; water
complex
© 2014 Retzmann et al; licensee Beilstein-Institut.
License and terms: see end of document.
Abstract
In the present work we report the synthesis of poly((4-hydroxy-3-(pyridin-3-yldiazenyl)phenethyl)methacrylamide-co-dimethy-
lacrylamide) and its reversible optical and complex-forming properties due to copper and cyclodextrin (CD) interactions. Color
changing effects are characterized by UV–vis spectroscopy and the supramolecular behavior is investigated by dynamic light scat-
tering experiments.
Introduction
In recent years, the interest in stimuli-responsive polymers In this connection, also the interactions of suitable polymers
increased exponentially [1]. Many polymers have been with cyclodextrin (CD) have been studied extensively, causing
described, showing sensitivity towards e.g. light, pH and heat for example a blue to red color transition of polydiacetylenes
[2-4].
(PDAS) due to the formation of inclusion complexes [6,7].
Accordingly, polymer-based fluorescent and colorimetric Azo dyes, with their remarkable ability to form stable azo–met-
chemosensors have attracted great attention due to several al chelate complexes with outstanding thermal and optical prop-
important advantages such as their simplicity of use, or their erties have been studied widely and led to an increased usage of
versatile structural designs [5].
dyes in the field of optical recording media [8,9].
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Beilstein J. Org. Chem. 2014, 10, 2480–2483.
However, up to now, only little is known about the interactions The resulting copolymer 7 is orange colored. The color-
of azo–metal chelate complexes in supramolecular structures changing effects of 7 upon addition of CuSO4 alone and in the
with CD as a modulator for macromolecular effects. Few presence of γ-CD were investigated and representative images
reports dealt with the reversibility of CD–dye hydrogels by ad- are shown in Figure 1.
dition of metal ions, as well as the sensing of copper ions using
cyclodextrin–dye rotaxane [10,11].
The addition of CuSO4 to polymer 7 in a water/methanol mix-
ture caused a color change from orange to red, which could be
Herewith we thus wish to describe our recent results about the
synthesis of a water-soluble polymer bearing a novel azo dye
and the presumed formation of complexes with Cu ions and CD
in aqueous media under respect of color change.
Findings
The aim of this work was to synthesize the polymerizable azo
dye N-(4-hydroxy-3-(pyridin-3-yldiazenyl)phenethyl)meth-
acrylamide (5) which should potentially be able to form stable
azo–metal complexes in aqueous solutions. Therefore tyramine
(1) was selectively methacrylated at room temperature fol-
lowed by a diazotation coupling with 3-aminopyridine (4)
leading to N-(4-hydroxy-3-(pyridin-3-yldiazenyl)phen-
ethyl)methacrylamide (5). Subsequently, the azo dye containing
polymer 7 was synthesized through free radical copolymeriza-
tion of 5 with N,N-dimethylacrylamide (6) using 2,2’-
azobis(2,4-dimethyl)valeronitril (V-65) as an initiator
(Scheme 1).
Figure 1: Color-changing effects of polymer 7 upon addition of A)
CuSO4 and B) CuSO4 and γ-CD in a 50:50 vol % in methanol/water
solution.
Scheme 1: Synthesis of N-(4-hydroxy-3-(pyridin-3-yldiazenyl)phenethyl) methacrylamide (5) and preparation of its water-soluble copolymer 7.
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Beilstein J. Org. Chem. 2014, 10, 2480–2483.
reversed by subsequent addition of γ-CD (Figure 1). Thus, we
can anticipate a donor–acceptor-type bonding of the electron-
rich azo dye with copper ions, that can be displaced by the addi-
tion of γ-CD [12].
Subsequent UV–vis spectroscopy allowed us to characterize the
above mentioned color changes in the diluted state (Figure 2).
Figure 3: Number average particle size distribution of 7 obtained by
DLS experiments.
Supporting Information
Supporting Information File 1
Experimental.
[http://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-10-259-S1.pdf]
Figure 2: UV–vis absorption spectra of (orange) the solved copolymer
7 with the induced shifts by addition of (red) copper(II) sulfate and
(blue) γ-CD in an aqueous methanol medium.
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