Solvatochromic shift and estimation of dipole moment of synthesized coumarin derivative: Application as sensor for fluorogenic recognition of Fe3 + and Cu2 + ions in aqueous solution

doi:10.1016/j.molliq.2016.07.047

Journal of Molecular Liquids

Volume 222, October 2016, Pages 253-262

https://doi.org/10.1016/j.molliq.2016.07.047 Get rights and content

Highlights

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Characterization and detailed spectroscopic properties of a newly synthesized coumarin derivative are reported.
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High value of dipole moment has been observed of the excited state compared to ground state.
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Sensor behavior of the compound to metal ions has also been examined.
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The DFT based theoretical studies support the experimental observations.

Abstract

(S)-4-((4-((3-amino-2-oxo-4-phenylbutoxy)methyl)-1H-1,2,3-triazol-1-yl)methyl)-7 hydroxy-2H-chromen-2-one hydrochloride was synthesized and characterized by detailed spectroscopic studies such as ¹H, ¹³C NMR and HRMS. Excited state dipole moment of synthesized compound was obtained using different solvatochromic shift methods. High value of dipole moment is observed for excited state as compared to ground state value and this is attributed to more polar excited state of molecule. Also, fluorescence emission peak undergoes a bathochromic shift with increase in the polarity of the solvent, confirming π → π* transition. The potential sensor behavior of the compound to metal ions has also been examined. Chemosensor shows the sensitivity for Fe^3 + and Cu^2 + over other metal cations in aqueous solution. The detection limits of Fe^3 + and Cu^2 + were calculated to be 143 nM and 71.31 μM, respectively. The LC–mass analysis indicated that 1:1 complex was formed between Fe^3 + (or) Cu^2 + and compound. Binding energy values for the complexation of the compound with metal ions are theoretically computed at M06/6–31 + G(d,p) level. The DFT based binding energy values show good correlation with the experimental observations.

Graphical abstract

Introduction

Coumarin derivatives are biologically active substances with numerous metabolites, and are widespread in nature [1]. These compounds are known to exert antitumor effects and can cause significant changes in the regulation of immune responses, cell growth [2] and play a significant role in pharmacological activity such as antibacterial, anti-HIV and anticancer activities [3]. Coumarins are organic fluorescent chromophores and widely used in synthesizing laser dyes, fluorescent whiteners and organic nonlinear optical materials [4].

When a compound is dissolved in different solvents, the effect of solvent on the absorption and fluorescence spectra has been a subject of interesting investigation [5]. Therefore, the systematic analysis on solvent effect provides beneficial information in studying the excited states behavior of the molecule. A change in solvent is accompanied by a change in polarity, dielectric constant or change in polarizability of the surrounding medium. Therefore, a change in solvent affects the ground and excited states differently.

The knowledge of dipole moments of electronically excited species is often useful in the design of non-linear optical materials [6] and elucidation of the nature of excited states. Excitation of a molecule gives rise to redistribution of charges and electron densities leading to conformational changes in the excited state. Thus, dipole moment of the excited state can increase and/or decrease as compared to ground state. The ground and excited state dipole moments of some coumarin derivatives were previously determined experimentally by using different methods [7].

Solvatochromic method does not use any external field [8], it is experimentally much simpler and widely accepted. It is based on a linear correlation between the wavenumbers of the absorption and emission maxima and solvent polarity function which involves relative permittivity (ε_r), and refractive index (n), of the medium [9].

There is an enormous demand for chemical sensors for many areas and disciplines. High sensitivity and ease of operation are two main issues for sensor development. Fluorescence techniques can easily fulfill these requirements and therefore fluorescent-based sensors appear as one of the most promising candidates for sensing. Metal ions are of great significance to the environment and biological system, resulting in the appearance of numerous sensory reports with diverse mechanisms for different metal ions [10]. Iron and copper are respectively the first and third largest amount of transition elements exist in our human body. As one of the most necessary trace metal nutrients in our body to maintain human health order, copper is involved in many vital processes in organisms [11]. However, the accumulation of excessive copper is highly toxic and even causes Wilson's disease in humans [12]. Most of the copper-selective sensors already suffer from the interfering effect of other cations, such as Zn^2 +, Hg^2 +, Pb^2 + and Ag⁺. Similarly iron is essential ion in the human body which is involved with the oxygen-transport mechanism and acts as a cofactor in many enzymatic processes [13]. However excess of iron in body is also responsible for diseases, such as Parkinson's and Alzheimer's [14]. Therefore selective and sensitive determination of iron and copper in biological and environmental systems is very essential. However, there are only limited fluorescence chemosensors [15] available for detection of Cu^2 + and Fe^3 + ions in various systems with their own merits and demerits as low selectivity or sensitivity, poor water-solubility and small Stokes shift. Thus there is a need to develop a simple and selective fluorescence chemosensor for detection of metal ions in various systems.

1,2,3-Triazole linked coumarin derivatives are important biomolecules [16] and act as chromophores, dyes, sensors [17] and photostabilizers [18]. Therefore, we focused on 1,2,3-triazole for designing of chemosensor and have attempted to determine the ground state (μ_g) and excited state (μ_e) dipole moments of Cl⁻ N⁺ H₃-L-Phe-triazole-7-OH-coumarin by using Bilot–Kawski [19], Lippert–Mataga [20], Bakhshiev [21], Kawski–Chamma–Viallet [22] and Reichardt [23] solvatochromic methods and studied the fluorescence properties of the chemosensor upon addition of various metal cations in aqueous solution. The compound was found to be fluorescent chemosensor for Cu^2 + and Fe^3 + in aqueous solution. The DFT based computations put some new shades on the relative stability of the particular system after the attachment of metal ions at different active sites.

Section snippets

Material

All the solvents used were of HPLC grade or AR (purchased from Alfa Aesar). All chemicals were obtained from commercial suppliers and used without further purification.

Procedure for the synthesis of (S)-(1-((7-hydroxy-2-oxo-2H-chromen-4-yl)methyl)-1H-1,2,3-triazol-4-yl)methyl 2-((tert-butoxycarbonyl)amino)-3-phenylpropanoate (3)

To a solution of 4-azidomethyl-7-hydroxycoumarin (1) (0.800 g, 3.6 mmol), in ethanol:H₂O (1:1), was added boc protected l-phenylalanyl acyl O-propargyl ester (2) (1.10 g, 3.6 mmol1), followed by the addition of CuSO₄ (0.008 g, 0.03 mmol) and sodium ascorbate (0.071 g, 0.36 mmol). The reaction mixture was stirred at room temperature for 12

Computational details

Density Functional Theory (DFT) [25], [26] based calculations are performed to test some of the experimental observations. Entire theoretical calculations are done using Gaussian 09 program suit [27]. All the molecular structures of the compound along with its metal-complexed analogues are optimized at M06 [28]/6–31 + G(d,p) level of theory without imposing any constrain. The solvent effect is considered through self-consistent reaction field (SCRF) [29] method using integral equation formalism

Results and discussion

(S)-4-((4-((3-amino-2-oxo-4-phenylbutoxy)methyl)-1H-1,2,3-triazol-1-yl)methyl)-7-hydroxy-2H-chromen-2-one hydrochloride (4) used in the present study was synthesized as shown in Scheme 1.

We have studied the ground and excited state dipole moments of the synthesized novel coumarin–triazole based fluorescent molecule, using Bilot–Kawski [19], Lippert–Mataga [20], Bakhshiev [21], Kawski–Chamma–Viallet [22] and Reichardt [23] methods. Effects of various common metal ions on fluorescence spectra of

Conclusions

We have calculated ground state and exited state dipole moments of newly synthesized (S)-4-((4-((3-amino-2-oxo-4-phenylbutoxy)methyl)-1H-1,2,3-triazol-1-yl)methyl)-7hydroxy-2H-chromen-2-one hydrochloride. The excited (μ_e) state dipole moment was estimated from the different solvatochromic shift methods. We observed large variation of the dipole moment value between the ground state and the excited state, which suggests that fluorescence originates from highly polar excited state. In the excited

Acknowledgements

We acknowledge Department of Science and Technology, New Delhi, for major research project. SK is thankful to UGC for SRF. We greatly acknowledge the reviewer for providing the opportunity to improve the quality of our manuscript.

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Solvatochromic shift and estimation of dipole moment of synthesized coumarin derivative: Application as sensor for fluorogenic recognition of Fe3 + and Cu2 + ions in aqueous solution

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Material

Procedure for the synthesis of (S)-(1-((7-hydroxy-2-oxo-2H-chromen-4-yl)methyl)-1H-1,2,3-triazol-4-yl)methyl 2-((tert-butoxycarbonyl)amino)-3-phenylpropanoate (3)

Computational details

Results and discussion

Conclusions

Acknowledgements

Tetrahedron Lett.

Am. J. Clin. Nutr.

Biochemistry

J. Fluoresc.

Spectrochim. Acta A

Sensors Actuators B Chem.

Tetrahedron

Sensors Actuators B Chem.

J. Lumin.

J. Phys. Chem. A

Molecules

Theor. Chem. Accounts

Chem. Phys.

Chem. Phys.

J. Chem. Phys.

Theor. Chem. Accounts

Phys. Chem. Chem. Phys.

Curr. Pharm. Des.

Curr. Pharm. Des.

J. Pharm. Biomed. Anal.

Bioorg. Med. Chem.

Non-Linear Optical Properties of Organic Molecules and Crystals

Solvatochromic shift and estimation of dipole moment of synthesized coumarin derivative: Application as sensor for fluorogenic recognition of Fe^3 + and Cu^2 + ions in aqueous solution