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Dynamic Chemistry-based Sensing: A Molecular System for Detection of Saccharide, Formaldehyde and Silver Ion Xingmao Chang, Zhaolong Wang, Yanyu Qi, Rui Kang, Xinwen Cui, Congdi Shang, Kaiqiang Liu, and Yu Fang Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.7b02170 • Publication Date (Web): 24 Jul 2017 Downloaded from http://pubs.acs.org on July 26, 2017
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Analytical Chemistry
Dynamic Chemistry-based Sensing: A Molecular System for Detection of Saccharide, Formaldehyde and Silver Ion Xingmao Chang1,2, Zhaolong Wang1,3, Yanyu Qi1,3, Rui Kang1,3, Xinwen Cui1,3, Congdi Shang1,3, Kaiqiang Liu1,3, and Yu Fang1,3* 1
Key Laboratory of Applied Surface and Colloid Chemistry (Ministry of Education), 2School of Materials Science and Engineering, 3
School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi'an, 710119, P. R. China *Correspondence to
[email protected] Abstract: Development of artificial complex molecular systems is of great importance in understanding complexity in natural processes and for achieving new functionalities. One of the strategies is to create them via optimized utilization of noncovalent interactions and dynamic covalent bonds. We report here on a new complex molecular system, which was constructed by integrating the multiple interactions containing dynamic covalent interaction between 1,2-diol and boronic acid, coordination interaction between silver ion and pyridyl, and an easy accessible reaction between secondary amine and formaldehyde. By employing the three dynamic interactions, a pyrene (Py), a well-known fluorophore, labeled compound, PPB, was designed and synthesized. The compound reacts with fructose (F), a monosaccharide, in aqueous phase and produces a fluorescent adduct, PPB-F, which can be further used as a sensing platform for formaldehyde (FA) and silver ion. The respective dynamic interactions are companied with color changes due to the reversible switching between Py monomer emission and excimer emission. The respective experimental detection limits (DLs) for the three analytes are much lower than 0.2 mM, 0.1 mM and 2.5 µM, respectively. Presence of relevant compounds or ions shows little effect upon the sensing. No doubt, the stuff as presented shows that integration of supramolecular interactions including dynamic covalent bonds can be employed as a general strategy to develop new functional molecular systems or materials. Keywords: complex molecular systems, supramolecular interaction, dynamic covalent bonds, fluorescence sensing
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INTRODUCTION In nature, abundance of substructures could self-assemble into fibers, rods, ribbons, networks or other wellorganized aggregates with different morphologies through van der Waals force, hydrogen bonding, π-π stacking, dipole-dipole interaction, ion association or other noncovalent interactions.1 These self-assembling behaviors often lead to formation of different functional systems, which are the basis of most biological processes. Because of the multiple, integrated and synergetic interactions behind, complexity has been recognized as one of the key features of natural systems by chemists in the long time.2 Therefore, construction of artificial complex molecular systems and study of their properties have become one of the powerful approaches to understand life and to develop new functional systems (materials). Inspired by nature, chemists are trying to imitate biological processes by constructing favorable dynamic systems from mono-interaction-based simple to multiple-interaction, including dynamic covalent interaction, based complex ones.3 Different from conventional non-reversible covalent interactions, dynamic noncovalent and covalent interactions used in constructing complex molecular systems impart reversible, self-repairing and degradable characteristics to the systems due to their reversible nature. It is the dynamic nature and structure/ composition designability of complex molecular systems that make them have the potential to be employed as a general principle to develop smart materials with multiple functions.4-7 In this paper, we report on a new complex molecular system which could be used for the determination of saccharide, formaldehyde (FA), and silver ion in aqueous phase. The system was constructed through synthesis of a pyrene (Py) labelled compound, PPB, which contains, in an appropriate way, several different but carefully chosen dynamic interaction sites. To be soluble and functioning in aqueous phase, all the structural units, with exception of Py, contained in the compound are compatible with water. Specifically, pyridine, phenylboronic acid and secondary amine moieties were chosen to combine silver ion,8 saccharides9 and FA,10 respectively. The expected solution behavior of PPB and its interactions with the analytes can be described by Scheme 1. From the scheme, it is seen that, (1) PPB may exist in aggregated state, showing Py excimer emission (green), in its aqueous solution possibly due to multiple inter-molecular dynamic interactions; (2) The PPB aggregates as formed may be de-aggregated if the solution is heated and the green emission should be changed into Py monomer emission (blue); (3) The disassembly of the PPB aggregates could be also achieved by introducing fructose (F), a sample mono-saccharide, into the system due to combination of the phenylboronic acid moiety of PPB with the 1,2-diol structure of the saccharide, F, resulting 2 / 17
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Analytical Chemistry
in a product of PPB-F, which should be also a process accompanied with a fluorescence color change from green to blue; (4) PPB-F could be further cross-linked by either silver ion or FA due to their interactions with pyridyl residue or secondary amine structure of PPB, resulting in dimerization or polymerization of the PPB structure and fluorescence color change from blue to green again. In this way, the PPB-based complex molecular system could be used for the determination of F, FA and silver ion. To have a better understanding to the molecular system, two reference compounds, PP and PB, were also designed and synthesized, of which PP and PB are both pyrenyl derivatives, but the former contains a pyridyl uint, and the later a phenylboronic acid residue, respectively. As stated, Py was specially introduced to report the aggregation, dimerization or polymerization and the reversed processes of the respective compounds. The details of the synthesis and characterization of the three pyrenyl derivatives are provided in the supporting information (Figure S1).
Scheme 1 The structures of PPB, PB, and PP, as well as the schematic representation of the formation and transformation of PPB-based dynamic aggregates. Note: the relevant states of the dynamic molecular system are specially denoted.
RESULTS AND DISSCUSSION Solution Behavior of PPB, PP and PB Concentration effect Considering the fact that interaction between boronic acid and 1,2-diol in aqueous phase occurs generally at basic condition, the fluorescence emission spectra of the three pyrenyl derivatives were recorded in carbonate buffer (pH~9.0) at different concentrations. The results are depicted in Figs. 1a-1b, S2.
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With reference to the figures, it is seen that the profiles of the fluorescence emission spectra of them at low concentrations (
