Solvatochromic isocyanonaphthalene dyes as ligands for silver(I) complexes, their applicability in silver(I) detection and background reduction in biolabelling

doi:10.1016/j.snb.2017.09.061

Sensors and Actuators B: Chemical

Volume 255, Part 3, February 2018, Pages 2555-2567

https://doi.org/10.1016/j.snb.2017.09.061 Get rights and content

Highlights

•
Silver-isocyanide complexes with solvatochromic fluorescent dyes as ligand were prepared.
•
The complexation of the dyes can be used for the quantification of silver(I) ions.
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The PL switch-off in the case of MICAN yields a significant contrast enhancement in biolabeling.
•
Cell staining applications of the complex(es) is shown on fixated HaCat cells.

Abstract

The complexation behavior of reactive and nonreactive N-substituted 1-amino-5-isocyanonaphthalene (ICAN) derivatives was studied in the presence of Ag(I) ions by UV–vis, steady-state and time resolved fluorescence measurements. The effect of ligand, solvent and counterion is covered. The equilibrium constants were found to be K_AgL ∼ 10⁶ M⁻¹ in dioxane and water. Complex formation results a significant, solvent dependent (30–59 nm) batochromic shift of the emission maximum. This shift is accompanied by a switch-off effect in the case of the unreactive ligands, while in the case of the acrylated derivative (ACAIN) significant intensity enhancement was detected. Based on spectroscopic results only 1:1 AgL complex could be detected in solution at low concentrations c_AgL <10⁻⁴ M, while at higher concentrations pure 1:2 AgL₂ formed which was characterized by ESI–MS, IR and NMR methods The structure and optical behavior of the complexes are discussed based on high-level quantum chemical calculations. It is shown that the complexation of ACAIN can be used for the selective detection and quantification of silver(I) ions from aqueous media. In addition, the fluorescene switch-off in the case of MICAN yields a significant contrast enhancement in biolabeling applications as is shown on fixated HaCat cells.s

Graphical abstract

The exclusive presence of highly stable, fluorescent 1:1 AgL complex was detected and supported by DFT calculations upon the complexation of solvatochromic, reactive and nonreactive N-substituted ICANs with Ag(I) ions. 30–59 nm batochromic shift of λ_em,max was observed, accompanied by a ligand dependent switch-off or switch-on effect, which was used for quantification of Ag(I) ions and contrast enhancement during the staining of HaCat cells.

Introduction

Isonitriles are excellent ligands in organometallic chemistry because of their polar and easily variable π-accepting character. Although the first isonitrile complex Ag(NCR)(CN) was prepared as early as 1869 by Gautierin, metal-isonitrile complexes have always been overshaded by other alternatives. The chemistry of isonitriles has undiscovered resources, the reactive C single bond N bond can serve as a versatile base for many organic reactions, such as the Ugi reaction [1], heterocyclic ring formation and other insertion reactions which are particularly useful in drug synthesis [2], as well as different multicomponent reactions [3]. Isonitriles easily form complexes with transition metal ions and are stronger σ-donors compared to their isoelectronic CO counterparts [2]. While gold(I)-isonitrile complexes are well studied, having a number of applications (e.g. deposition of gold films, preparation of liquid crystalline phases) [4], [5], the related isonitrile complexes of silver(I) are much less studied, in spite of interesting properties such as liquid crystalline behaviour [6], [7], or luminescence both in liquid and solid phase [8].

The structure of the silver(I)-isonitrile complexes is an interesting issue. They are more flexible than the rigid rod-like gold(I) complexes with strictly two-coordinate metal centers, which serve a good basis for the construction of supramolecular frameworks and mesogenic phases. The silver(I) centers can become three- or four-coordinate by interactions with the ligands or the counterions [9]. Most of them has a composition of 1:2, 1:3 or 1:4 Ag:Ligand ratio with ligands, such as p-tolyl isonitrile [10], [11], 2,4-di-t-butyl-6-methylphenyl, 2,4,6-tri-t-butylphenyl, 2,6-dimethylphenyl and t-butyl isocyanides [12], methyl and cyclohexy1 isocyanide [13]. Only a few examples can be found in the literature for the 1:1 complexes, and most of them are dimers. In most of the above mentioned cases the Ag:Ligand ratio of the complex depends on the ratio of the reagents used for the synthesis, and it can also show dependence on the counterion. Therefore, 1:1 Ag:Ligand complexes can also form from p-tolyl and cyclohexyl isonitrile using chloride counterion instead of perchlorate or nitrate [14]. Usually these complexes are more stable than the silver(I)-containing parent compounds, however the solubility of the 1:1 complexes are significantly worse than the 1:2 ones. In most cases the latter are practically insoluble.

A unique advantage of these complexes in addition to their high thermal stability is that if a luminescent ligand is used, the organic-inorganic coordination between the metal ion and the ligand can affect the luminescent properties of the ligand, therefore allows a novel versatile route to construct various types of light-emitting materials, which can be used as LEDs [15]. In the literature dicyanide [16] and diisocyanide [17] based polymeric materials can be found above all of such type of luminescent materials. The spectral changes caused by the complexation can be explained by metal-ligand charge transfer (MLCT) in most cases [18]. In addition, the application of luminescent ligands (probes) opens the way for the detection of ions and biomacromolecules and for cellular and in vivo imaging or even for the detection of viruses such as influenza [19], [20], [21].

However, there are several examples for silver(I)-isonitrile complexes, even with luminescent ligands in the literature, to our best knowledge, no one has ever used solvatochromic isonitrile ligands in combination with silver(I). For ligands in this study we used our recently developed 1-amino-5-isocyanonaphthalene (ICAN) derivatives (Scheme 1) to investigate the optical changes accompanied their complexation with Ag(I). The ligands were selected in a way that mono and dialkylated derivatives with reactive and unreactive substituents are also included.

Since these ligands are solvatochromic dyes, their luminescent properties will no longer be dependent upon solvent polarity only, but metal-ligand interactions will also have to be taken into consideration. These new interactions are supposed to favorably alter the fluorescent properties and practical applicability of the dyes. Based on our ongoing in vitro biological experiments a few of our ICAN derivatives can be used as vital cell stains. Since these dyes are well tolarated by living cells, their silver(I) complexes may also be suitable for enhanced biolabeling.

Section snippets

Results and discussion

The formation of Ag–isonitrile complexes were investigated by UV–vis and steady-state fluorescence methods in different solvents by adding portions of AgTFA solutions (in the range of 0.1–2 M eq.) to ICAN (c ∼ 10⁻⁵ M–10⁻⁶ M) dissolved in the proper solvent. In chloroform, dichloromethane, dioxane, methanol, tetrahydrofuran and acetonitrile a batochromic shift in both the absorption and emission spectra is clearly visible as is presented for THF and CHCl₃ in Fig. 1. The spectra recorded in other

Conclusions

The complex formation of novel, solvatochromic 1-amino-5-isocyanonaphthalene (ICAN) derivatives was studied in the presence of Ag(I) ions. UV–vis and steady-state fluorescence spectroscopic results revealed the exclusive presence of 1:1 complexes in solutions in concentrations below 10 mM. By increasing the concentration, independently of the ratio of the Ag(I) and ligand the formation of a solid yellow precipitate was observed, which was identified as the 1:2 AgL₂ complex. The 1:2 complex can

Materials

Acetonitrile (MeCN), tetrahydrofuran (THF), methanol (MeOH), dimethyl-sulfoxide (DMSO), chloroform, ethyl-acetate (EtOAc), 1,4-dioxane (reagent grade, Reanal, Hungary), silver-trifluoroacetate (AgTFA, Sigma-Aldrich), silver-tetrafluoroborate (AgBF₄) and silver-perchlorate (AgClO₄) (Alfa Aesar GmbH) were used without further purification.

TbCl₃, MnCl₂, ZnCl₂, Pb(NO₃)₂, NiCl₂, NdCl₃, GdCl₃, MgCl₂, CuCl₂, AlCl₃, CoCl₂, CeCl₃, DyCl₃, CaCl₂, LuCl₃, EuCl₃, YCl₃, Ga(NO₃)₂, Bi(ClO₄)₃, Fe(NO₃)₃ aqueous

Synthesis

The synthesis of the ligands: 1-amino-5-isocyanonaphthalene (ICAN), 1-N-methylamino-5-isocyanonaphthalene (MICAN) 1-N,N-dimethylamino-5-isocyanonaphthalene (diMICAN) 1-N,N-diallylamino-5-isocyanonaphthalene (diAllylICAN) and 1-(2-acryloyloxy-3-chloro-prop-1-yl)-amino-5-isocyanonaphthalene (ACAIN) are given in Refs. [22], [33], [34].

NMR

¹H spectra were recorded in DMSO-d6 at 25 °C on a Bruker AM 360 spectrometer at 360 MHz with tetramethylsilane as the internal standard.

Electrospray quadrupole time-of-flight MS/MS (ESI-Q-TOF)

The ESI–MS measurements were carried out by a MicroTOF-Q type Qq-TOF MS instrument (Bruker Daltonik, Bremen, Germany). The spray voltage was 4 kV and N₂ was used as nebulizer and drying gas (temperature: 200 °C, flow rate: 4.0 l/min). The samples were solved in methanol in the concentration of 0.01 mg/ml and injected directly to the mass spectrometer with a syringe

Acknowledgments

This work was financially supported by the grants K-116465 and GINOP-2.3.2-15-2016-00041 given by NFKI (National Research, Development and Innovation Office, Hungary). Furthermore, this paper was also supported by the János Bolyai Research Scholarship of the Hungarian Academy of Sciences (Miklós Nagy). The research was supported through the NEW NATIONAL EXCELLENCE PROGRAM of the Ministry of Human Capacities of Hungary (J. Kalmár).

Miklós Nagy is an assistant professor at the Department of Applied Chemistry, University of Debrecen. His research interest focuses on the development of novel fluorescent smart materials among all solvatochromic dyes for analytical and biological applications.

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Isocyanonaphthalenes as extremely low molecular weight, selective, ratiometric fluorescent probes for Mercury(II)
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On the other hand, isonitriles also easily form complexes with transition metal ions [19]. Recently, we developed a novel amino-isocyanonaphthalene (ICAN) based solvatochromic fluorophore family [20] (Scheme 1), which in addition to its easy preparation and being nontoxic supravital stain [21,22], can be utilized in silver analytics as isocyanide ligands and their silver complexes turned out to enhance the contrast during cell staining applications [23]. Since the complexation of ICAN by Ag(I) is accompanied by a bathochromic shift of the emission maximum and the reduction of the NC group by Hg(II) terminates the dipolar nature of the molecule resulting in a considerable hypsochromic shift.
The specially designed chemical structure of our recently developed solvatochromic amino-isocyanonaphthalene (ICAN) dye family enables the selective detection of Hg²⁺ and at the same time is able to indicate the presence of Ag⁺. In addition to its easy preparation and nontoxic nature, ICAN is the lowest molecular weight dye reported for ratiometric fluorescent Hg²⁺ detection in water, so far. The basis of this double selectivity is the reduction of the isonitrile moiety to amine by a chemical reaction with Hg²⁺ resulting in a greater than 100 nm hypsochromic shift (and switch on of fluorescence) of the emission maximum relative to ICAN, whereas the complexation of Ag⁺ with the NC group yields an approximately 20 nm bathochromic shift (and quenching). In contrast, other common ions have little effect on the position of the emission maximum in aqueous medium. In completely aqueous medium at pH = 6, the limit of quantification was found to be lower than 17 nM and the limit of detection lower than 6 nM for Hg²⁺. The practical applicability of the method was demonstrated on dental amalgam.
Nano-molar to milli-molar level Ag (I) determination using absorption of light by ZnS QDs without organic ligand
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Fluorescence emission was detected with a band-pass filter at 530 ± 30 nm and with a long-pass filter above 650 nm, respectively. Meanwhile, IR-TLS and toxicology tests were performed to prove that HaCaT cells tolerated much higher MICAN concentration (5 μg/ml) as well (Nagy et al., 2018). The scope of the current work was to investigate MICAN, the N-methylamino derivative of fluorophore 1-amino-5-isocyanonaphthalene (ICAN).
Fluorescence time-lapse microscopy is in connection with the invasive properties of fluorochrome applied, and with the toxicity of the excitation energy and wavelength of the dye itself. Experiments with the newly synthesized fluorescent dye 1-N-methylamino-5-isocyanonaphthalene (MICAN) served to test its cytotoxicity on human HaCaT keratinocyte cell cultures. Experiments related to staining capability were performed with paraformaldehyde (PFA) fixed cells and observed with fluorescence microscope. It was assumed that the fluorophore 1-amino-5-isocyanonaphthalene (ICAN) and especially its N-methylamino derivative MICAN, containing condensed aromatic rings could serve as a nonselective fluorescent dye capable to stain cellular structures of fixed, living, damaged and dead cells. This notion was confirmed by the MICAN staining of cytoplasmic proteins primarily rough endoplasmic reticulum (RER), smooth endoplasmic reticulum (SEM) and less efficiently nuclear proteins suggesting the involvement of staining of subcellular structures involved in protein synthesis. MICAN was not only well tolerated by living cells but turned out to be a strong heterochromatin and RER staining agent. This led to the development of a MICAN staining protocol for native and living samples. Relative to other fluorescent dyes, MICAN is not only useful but also cost-effective. Toxicology tests were performed using 30, 10, 5, 0.5 μg/ml MICAN concentrations. Time-lapse videomicroscopy at near-infrared (NIR) illumination has been used for the examination of MICAN effect on cell division. It was found that MICAN as a vital stain had no significant harmful effect on HaCaT cells. MICAN turned out to be a non-toxic, highly quantum-efficient vital stain with minimal, or no photobleaching, and can be applied to co-stain with propidium-iodide due the strong spectral separation.
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Dávid Rácz received his PhD in macromolecular chemistry (2015) from the University of Debrecen. He is now an assistant professor at the Department of Applied Chemistry. His research interests focus on the design and synthesis of novel solvatochromic fluorescent dyes and light emitting polymers.

Zsolt László Nagy received his MSc degree (2015) in pharmaceutics from the University of Debrecen. He is currently working on the synthesis of solvatochromic dyes as a PhD student at the Department of Applied Chemistry, University of Debrecen.

Péter Pál Fehér received his MSc degree in Chemistry from the same university. He is a PhD student at the Department of Physical Chemistry. He is researching into reaction mechanism and spectrum simulations by quantum chemical calculations.

Alexandra Kiss received her BSc degree (2017) in Biochemical Engineering from the University of Debrecen. She is doing her MSc in Biotechnology at the same university. Her research area is cell biology.

István Fábián is currently a full professor and the head of the Department of Inorganic and Analytical Chemistry at the University of Debrecen, Hungary. His broad research interest is focused on the kinetics and mechanism of redox ractions, as well as, various aspects of analytical chemistry.

József Kalmár received his PhD degree in physical chemistry in 2013 from the University of Debrecen, Hungary. He is currently an assistant professor at the same university, and his research focuses on photophysics and materials science.

Miklós Zsuga is an emeritus professor, the former head of the Department of Applied Chemistry. His reearch area covers natural and synthetic macromolecules, mass spectrometry and chemical technology.

Sándor Kéki is currently a full professor and the head of the Department of Applied Chemistry at the University of Debrecen. His broad research interest is focused on the kinetics and mechanism of polymerization reactions, mass spectrometry and the development of polymeric and small molecule smart systems.

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Solvatochromic isocyanonaphthalene dyes as ligands for silver(I) complexes, their applicability in silver(I) detection and background reduction in biolabelling

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Results and discussion

Conclusions

Materials

Synthesis

NMR

Electrospray quadrupole time-of-flight MS/MS (ESI-Q-TOF)

Acknowledgments

Surf. Sci.

Sens. Actuators B: Chem.

Angew. Chem. Int. Ed.

Dyes Pigm.

J. Photochem. Photobiol. A

Dyes Pigm.

J. Photochem. Photobiol. A

Chem. Phys. Lett.

THEOCHEM

Eur. J. Org. Chem.

Adv. Synth. Catal.

Chem. Rev.

J. Am. Chem. Soc.

J. Mater. Chem.

Cryst. Growth Des.

Can. J. Chem.

Z. Naturforsch.

Chem. Ber.

J. Am. Chem. Soc.

Inorg. Chim. Acta

J. Chem. Soc. Dalton Trans.

Inorg. Chem.

Chem. Rev.