NIR Fluorophores in Practical Analytical Chemistry

Swamy, Anand R.; George, Abraham; Tarazi, Leila; Patonay, Gábor; Strękowski, Lucjan

doi:10.1007/978-94-011-5102-3_9

Near-Infrared Dyes for High Technology Applications 1998

DOI: 10.1007/978-94-011-5102-3_9

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NIR Fluorophores in Practical Analytical Chemistry

Anand R. Swamy

Abraham George

Leila Tarazi

et al.

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2004

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“…The direct spectral measurements are possible because few natural products show absorption above 650 nm and, as a result, any biological medium is extensively penetrated by near-infrared radiation [3]. Recently, covalent and non-covalent labeling of biological macromolecules with a near-infrared chromophore has become a firmly established trend in bioanalytical research [3][4][5][6].Due to their limited solubility, the two pH-sensitive dye systems mentioned above have found little application. In continuation of our research we now report for the first time the synthesis of a series of ketone/cyanine compounds that are water soluble.…”

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Water‐soluble pH‐sensitive 2,6‐bis(substituted ethylidene)‐cyclohexanone/hydroxy cyanine dyes that absorb in the visible/near‐infrared regions

Strękowski

Mason

Say

et al. 2004

Journal of Heterocyclic Chem

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Three methods were used to synthesize a series of the title compounds. The ketones absorb in the visible region, and upon protonation (pH<6) they are converted to hydroxy-substituted heptamethine cyanines that show an intense absorption in the near-infrared region (>700 nm). The conversion is reversible and depends solely on pH conditions. J. Heterocyclic Chem., 41, 227 (2004).A decade ago we reported for the first time a novel pHsensitive dye system 1=O/1-OH shown in equation 1 [1]. Ketone 1=O exhibits absorption in the visible region (λ max = 535 nm), and upon protonation it is transformed into hydroxy cyanine 1-OH with an intense absorption in the n e a r-infrared region (λ m a x = 709 nm). This change is reversible and depends solely on pH conditions. A related dye (not shown) has been described by us more recently [2]. The search for new pH-sensitive dyes that absorb in the near-infrared region of the electromagnetic spectrum (>650 nm) has been stimulated by potential application of such indicators in bioanalytical chemistry. When complexed or covalently attached to a protein, the pH-sensitive label can act as a pH-dependent reporter molecule in a complex biological material by using non-invasive spectroscopic detection. The direct spectral measurements are possible because few natural products show absorption above 650 nm and, as a result, any biological medium is extensively penetrated by near-infrared radiation [3]. Recently, covalent and non-covalent labeling of biological macromolecules with a near-infrared chromophore has become a firmly established trend in bioanalytical research [3][4][5][6].Due to their limited solubility, the two pH-sensitive dye systems mentioned above have found little application. In continuation of our research we now report for the first time the synthesis of a series of ketone/cyanine compounds that are water soluble. The previous chemistry [1,2] is evaluated, and an improved synthetic methodology is presented.The structures of new pH-sensitive compounds are given in Scheme 1. For the sake of clarity of presentation, only the cyanine forms (9-OH -12-OH, 15-OH) are shown. As can be seen, all these dyes are N-substituted with hydrophilic sulfoalkyl groups, additional two sulfo groups are attached to the aromatic subunits of 1 0 -O H, and an additional carboxylic acid function is present in 15-OH. Chloro cyanines 9-Cl -13-Cl served as precursors to the final products. The cyanines 9-Cl -13-Cl were efficiently synthesized by condensation of indolium derivatives 2-6 with Vilsmeier-Haack reagents 7 or 8. This is a classical preparation that is conveniently conducted in ethanol in the presence of sodium acetate as a base [7]. The conversion of substrates 9-Cl -13-Cl to the corresponding pH-sensitive dyes is summarized in Table 1 and discussed as follows.The Sodium-Acetate Method.

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Water‐soluble pH‐sensitive 2,6‐bis(substituted ethylidene)‐cyclohexanone/hydroxy cyanine dyes that absorb in the visible/near‐infrared regions

Strękowski

Mason

Say

et al. 2004

Journal of Heterocyclic Chem

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NIR Fluorophores in Practical Analytical Chemistry

Cited by 1 publication

References 10 publications

Water‐soluble pH‐sensitive 2,6‐bis(substituted ethylidene)‐cyclohexanone/hydroxy cyanine dyes that absorb in the visible/near‐infrared regions

Water‐soluble pH‐sensitive 2,6‐bis(substituted ethylidene)‐cyclohexanone/hydroxy cyanine dyes that absorb in the visible/near‐infrared regions

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