A Cyanuric Acid Platform Based Tripodal Bis-heteroleptic Ru(II) Complex of Click Generated Ligand for Selective Sensing of Phosphates via C–H···Anion Interaction

A new bis-heteroleptic trinuclear Ru­(II) complex (<b>1</b>[PF₆]₆) has been synthesized from electron deficient cyanuric acid platform based copper-catalyzed azide–alkyne cycloaddition, i.e., CuAAC click generated ligand, 1,3,5-tris [(2-aminoethyl-1H-1,2,3-triazol-4-yl)-pyridine]-1,3,5-triazinane-2,4,6-trione (<b>L1)</b>. Complex <b>1</b>[PF₆]₆ displays weak luminescence (ϕ_f = 0.002) at room temperature with a short lifetime of ∼5 ns in acetonitrile. It shows selective sensing of hydrogen pyrophosphate (HP₂O₇^3–) through 20-fold enhanced emission intensity (ϕ_f = 0.039) with a 15 nm red shift in emission maxima even in the presence of a large excess of various competitive anions like F^–, Cl^–, AcO^–, BzO^–, NO₃^–, HCO₃^–, HSO₄^–, HO^–, and H₂PO₄^– in acetonitrile. Selective change in the decay profile as well as in the lifetime of <b>1</b>[PF₆]₆ in the presence of HP₂O₇^3– (108 ns) further supports its selectivity toward HP₂O₇^3–. UV–vis and photoluminescence titration profiles and corresponding Job’s plot analyses suggest 1:3 host–guest stoichiometric binding between <b>1</b>[PF₆]₆ and HP₂O₇^3–. High emission enhancement of <b>1</b>[PF₆]₆ in the presence of HP₂O₇^3– has resulted in the detection limit of the anion being as low as 0.02 μM. However, <b>1</b>[PF₆]₆ shows selectivity toward higher analogues of phosphates (e.g., ATP, ADP, and AMP) over HP₂O₇^3–/H₂PO₄^– in 10% Tris HCl buffer (10 mM)/acetonitrile medium. Downfield shifting of the triazole C–H in a ¹H NMR titration study confirms that the binding of HP₂O₇^3–/H₂PO₄^– is occurring via C–H···anion interaction. The single crystal X-ray structure of complex <b>1</b> having NO₃^– counteranion, <b>1</b>[NO₃]₆ shows binding of NO₃^– with complex <b>1</b> via C–H···NO₃^– interactions

Bis-Heteroleptic Ruthenium(II) Complex of a Triazole Ligand as a Selective Probe for Phosphates

A new bis-heteroleptic ruthenium­(II) complex (<b>1</b>) of 2-(1-methyl-1<i>H</i>-1,2,3-triazol-4-yl) pyridine (<b>L</b>) ligand was extensively explored for anion sensing studies. <b>1</b>[PF₆]₂ shows selective sensing of dihydrogen phosphate (H₂PO₄^–)/hydrogen pyrophosphate (HP₂O₇^3–) among halides, HCO₃^–, AcO^–, NO₃^–, ClO₄^–, HSO₄^–, OH^–, BzO^–, H₂PO₄^–, and HP₂O₇^3– in acetonitrile. Enhancement of emission intensity of <b>1</b>[PF₆]₂ along with a 10 nm red shift of the emission maximum is observed in the presence of H₂PO₄^–/HP₂O₇^3– selectively. The photoluminescence (PL) titration experiment of <b>1</b>[PF₆]₂ results in binding constants (<i>K</i>_a) of 5.28 × 10⁴ M^–1 and 4.67 × 10⁴ M^–1 for H₂PO₄^– and HP₂O₇^3–, respectively, which is in good agreement with the <i>K</i>_a values obtained from UV–vis titration experiments (2.97 × 10⁴ M^–1 and 2.45 × 10⁴ M^–1 for H₂PO₄^– and HP₂O₇^3–, respectively). High selectivity of <b>1</b>[PF₆]₂ toward these two anions in acetonitrile is further confirmed by PL intensity measurement of <b>1</b>[PF₆]₂ upon addition of these two anions in the presence of a large excess of other competitive anions. Further, considerable changes in the lifetime (τ) as well as in the decay pattern of <b>1</b>[PF₆]₂ in the presence of H₂PO₄^–/HP₂O₇^3– among all tested anions support the selective binding property of <b>1</b>[PF₆]₂ toward these two anions. Significant downfield shift of the triazole −CH proton of <b>1</b>[PF₆]₂ with 1 equiv of H₂PO₄^– (Δδ = 0.26 ppm) and HP₂O₇^3– (Δδ = 0.23 ppm) in deuterated dimethyl sulfoxide proclaim binding mechanism via C–H···anion interaction in solution state. Finally, single-crystal X-ray structural analysis confirms the first example of dihydrogen pyrophosphate (H₂P₂O₇^2–) recognition via solitary C–H···anion interactions

Ruthenium(II) Complex-Based Luminescent Bifunctional Probe for Ag⁺ and Phosphate Ions: Ag⁺‑Assisted Detection and Imaging of rRNA

A new <i>bis</i>-heteroleptic Ru­(II) complex (<b>1</b>) of benzimidazole-substituted 1,2,3-triazole pyridine ligand has been designed and constructed for the photoluminescent detection of cationic and anionic analytes, Ag⁺ and phosphate ions. Compound, <b>1­[PF</b>_<b>6</b><b>]</b>_<b>2</b> was fully characterized by various spectroscopic techniques and the solid-state structure was determined via single-crystal X-ray diffraction. The cation and anion sensing properties in 50% aqueous buffer (pH 9.2) and pure acetonitrile were carefully examined in photoluminescence (PL) spectroscopy. The <b>1­[PF</b>_<b>6</b><b>]</b>_<b>2</b> was found to be highly selective to pyrophosphate; PPi/HP₂O₇^3– and H₂PO₄^– ions in CH₃CN. It showed ∼10-fold PL intensity enhancement at 583 nm in the presence of only 1 and 2 equiv of PPi and H₂PO₄^– ions, respectively. The PL titrations of <b>1­[PF</b>_<b>6</b><b>]</b>_<b>2</b> with PPi and H₂PO₄^– in CH₃CN furnished the association constant (<i>K</i>_a = 3.3 × 10³ M^–1 and 6.8 × 10³ M^–1) and the detection limit was as low as 5.73 and 5.19 ppb, respectively. The <b>1­[PF</b>_<b>6</b><b>]</b>_<b>2</b> also selectively detected Ag⁺ over other competitive cations through the luminescence light up in 50% aqueous buffer (pH 9.2) media. The PL titration of <b>1­[PF</b>_<b>6</b><b>]</b>_<b>2</b> with Ag⁺ showed ∼8-fold luminescence enhancement at 591 nm and yielded association constant, <i>K</i>_a = 3.5 × 10⁴ M^–1 and the detection limit was determined to be 5.05 ppb. A new cation sensing mechanism has been established where the Ag⁺ ion is detected in photoluminescence spectroscopy through the <i>unique</i> cyclometalated Ag⁺-triazolide complex formation. The high selectivity of <b>1­[PF</b>_<b>6</b><b>]</b>_<b>2</b> for phosphates and Ag⁺ was established by PL in the presence of various competing ions. Finally, for biological application, the cytotoxicity study was performed. The probe showed low cytotoxicity and was suitable for intracellular Ag⁺ imaging. The cell imaging and <i>in vitro</i> photoluminescence study revealed that the probe stained the cell nucleoli and specifically bind with ribosomal RNA (rRNA) and, therefore, it can also serve as a luminescent probe for rRNA in the presence of Ag⁺

Regioselective synthesis of functionalized [1,6]-naphthyridines by KF/basic alumina as a recyclable catalyst and a brief study of their photophysical properties

<p>An efficient, one-pot, solvent-free, regioselective synthesis of functionalized [1,6]-naphthyridines was explored by a heterogeneous catalyst via a three-component multicomponent reaction (MCR). KF/basic alumina–catalyzed double heteroannulation of aryl alkyl ketones, malononitrile, and alkyl amines generates the compounds with high appendage diversity combinatorially via Knoevenagel condensation followed by Michael addition and cyclization pathway. Short reaction time, high yield, simple reaction technique, and recoverability and reusability of the catalyst without compromising the yield and purity of the compounds are the salient features of this methodology. Additionally, these compounds exhibit promising photophysical properties.</p

Aggregation-Induced Emission-Active Ruthenium(II) Complex of 4,7-Dichloro Phenanthroline for Selective Luminescent Detection and Ribosomal RNA Imaging

The development of red emissive aggregation-induced emission (AIE) active probes for organelle-specific imaging is of great importance. Construction of metal complex-based AIE-active materials with metal-to-ligand charge transfer (MLCT), ligand-to-meal charge transfer (LMCT) emission together with the ligand-centered and intraligand (LC/ILCT) emission is a challenging task. We developed a red emissive ruthenium­(II) complex, <b>1­[PF</b>_<b>6</b><b>]</b>_<b>2</b>, and its perchlorate analogues of the 4,7-dichloro phenanthroline ligand. <b>1­[PF</b>_<b>6</b><b>]</b>_<b>2</b> has been characterized by spectroscopic and single-crystal X-ray diffraction. Complex <b>1</b> showed AIE enhancement in water, highly dense polyethylene glycol media, and also in the solid state. The possible reason behind the AIE property may be the weak supramolecular π···π, C–H···π, and C–Cl···H interactions between neighboring phen ligands as well as C–Cl···O halogen bonding (XB). The crystal structures of the two perchlorate analogues revealed C–Cl···O distances shorter than the sum of the van der Waals radii, which confirmed the XB interaction. The AIE property was supported by scanning electron microscopy, transmission electron microscopy, dynamic light scattering, and atomic force microscopy studies. Most importantly, the probe was found to be low cytotoxicity and to efficiently permeate the cell membrane. The cell-imaging experiments revealed rapid staining of the nucleolus in HeLa cells via the interaction with nucleolar ribosomal ribonucleic acid (rRNA). It is expected that the supramolecular interactions as well as C–Cl···O XB interaction with rRNA is the origin of aggregation and possible photoluminescence enhancement. To the best of our knowledge, this is the first report of red emissive ruthenium­(II) complex-based probes with AIE characteristics for selective rRNA detection and nucleolar imaging

Aggregation-Induced Emission-Active Ruthenium(II) Complex of 4,7-Dichloro Phenanthroline for Selective Luminescent Detection and Ribosomal RNA Imaging

The development of red emissive aggregation-induced emission (AIE) active probes for organelle-specific imaging is of great importance. Construction of metal complex-based AIE-active materials with metal-to-ligand charge transfer (MLCT), ligand-to-meal charge transfer (LMCT) emission together with the ligand-centered and intraligand (LC/ILCT) emission is a challenging task. We developed a red emissive ruthenium­(II) complex, <b>1­[PF</b>_<b>6</b><b>]</b>_<b>2</b>, and its perchlorate analogues of the 4,7-dichloro phenanthroline ligand. <b>1­[PF</b>_<b>6</b><b>]</b>_<b>2</b> has been characterized by spectroscopic and single-crystal X-ray diffraction. Complex <b>1</b> showed AIE enhancement in water, highly dense polyethylene glycol media, and also in the solid state. The possible reason behind the AIE property may be the weak supramolecular π···π, C–H···π, and C–Cl···H interactions between neighboring phen ligands as well as C–Cl···O halogen bonding (XB). The crystal structures of the two perchlorate analogues revealed C–Cl···O distances shorter than the sum of the van der Waals radii, which confirmed the XB interaction. The AIE property was supported by scanning electron microscopy, transmission electron microscopy, dynamic light scattering, and atomic force microscopy studies. Most importantly, the probe was found to be low cytotoxicity and to efficiently permeate the cell membrane. The cell-imaging experiments revealed rapid staining of the nucleolus in HeLa cells via the interaction with nucleolar ribosomal ribonucleic acid (rRNA). It is expected that the supramolecular interactions as well as C–Cl···O XB interaction with rRNA is the origin of aggregation and possible photoluminescence enhancement. To the best of our knowledge, this is the first report of red emissive ruthenium­(II) complex-based probes with AIE characteristics for selective rRNA detection and nucleolar imaging

Aggregation-Induced Emission-Active Ruthenium(II) Complex of 4,7-Dichloro Phenanthroline for Selective Luminescent Detection and Ribosomal RNA Imaging

The development of red emissive aggregation-induced emission (AIE) active probes for organelle-specific imaging is of great importance. Construction of metal complex-based AIE-active materials with metal-to-ligand charge transfer (MLCT), ligand-to-meal charge transfer (LMCT) emission together with the ligand-centered and intraligand (LC/ILCT) emission is a challenging task. We developed a red emissive ruthenium­(II) complex, <b>1­[PF</b>_<b>6</b><b>]</b>_<b>2</b>, and its perchlorate analogues of the 4,7-dichloro phenanthroline ligand. <b>1­[PF</b>_<b>6</b><b>]</b>_<b>2</b> has been characterized by spectroscopic and single-crystal X-ray diffraction. Complex <b>1</b> showed AIE enhancement in water, highly dense polyethylene glycol media, and also in the solid state. The possible reason behind the AIE property may be the weak supramolecular π···π, C–H···π, and C–Cl···H interactions between neighboring phen ligands as well as C–Cl···O halogen bonding (XB). The crystal structures of the two perchlorate analogues revealed C–Cl···O distances shorter than the sum of the van der Waals radii, which confirmed the XB interaction. The AIE property was supported by scanning electron microscopy, transmission electron microscopy, dynamic light scattering, and atomic force microscopy studies. Most importantly, the probe was found to be low cytotoxicity and to efficiently permeate the cell membrane. The cell-imaging experiments revealed rapid staining of the nucleolus in HeLa cells via the interaction with nucleolar ribosomal ribonucleic acid (rRNA). It is expected that the supramolecular interactions as well as C–Cl···O XB interaction with rRNA is the origin of aggregation and possible photoluminescence enhancement. To the best of our knowledge, this is the first report of red emissive ruthenium­(II) complex-based probes with AIE characteristics for selective rRNA detection and nucleolar imaging

Highly Sensitive Bifunctional Probe for Colorimetric Cyanide and Fluorometric H₂S Detection and Bioimaging: Spontaneous Resolution, Aggregation, and Multicolor Fluorescence of Bisulfide Adduct

A 4-methylbenzothiazole linked maleimide-based single molecular bifunctional probe <b>1</b> has been synthesized for the colorimetric and fluorometric detection of highly competitive H₂S and cyanide ion in aqueous DMSO media. The probe <b>1</b> selectively detected CN^– under the UV–vis spectroscopy through the rapid appearance of deep pink color. The bright pink color developed due to ICT in the moderately stable cyano substituted enolate intermediate. The absorbance titration of <b>1</b> with CN^– revealed a new band at 540 nm and the nonlinear curve fitting analysis showed good fit with 1:1 model. In fluorescence channel, <b>1</b> was found to be highly selective to H₂S in 50% aqueous buffer (pH 7). It exhibited ∼16-fold fluorescence intensity enhancement at 435 nm after reaction with 1 equiv of H₂S due to the inhibition of PET. The <b>1-SH</b> adduct showed TICT phenomenon and behaved like molecular rotor. It further displayed aggregation behavior at higher concentration and excitation wavelength dependent multicolor emission properties. Most interestingly, the spontaneous resolution of chiral <i>S</i>-isomer of the 1-SH adduct occurred during crystallization. The cell imaging study revealed the staining of the cell and multicolor emission in the presence of H₂S

Highly Sensitive Bifunctional Probe for Colorimetric Cyanide and Fluorometric H₂S Detection and Bioimaging: Spontaneous Resolution, Aggregation, and Multicolor Fluorescence of Bisulfide Adduct

A 4-methylbenzothiazole linked maleimide-based single molecular bifunctional probe <b>1</b> has been synthesized for the colorimetric and fluorometric detection of highly competitive H₂S and cyanide ion in aqueous DMSO media. The probe <b>1</b> selectively detected CN^– under the UV–vis spectroscopy through the rapid appearance of deep pink color. The bright pink color developed due to ICT in the moderately stable cyano substituted enolate intermediate. The absorbance titration of <b>1</b> with CN^– revealed a new band at 540 nm and the nonlinear curve fitting analysis showed good fit with 1:1 model. In fluorescence channel, <b>1</b> was found to be highly selective to H₂S in 50% aqueous buffer (pH 7). It exhibited ∼16-fold fluorescence intensity enhancement at 435 nm after reaction with 1 equiv of H₂S due to the inhibition of PET. The <b>1-SH</b> adduct showed TICT phenomenon and behaved like molecular rotor. It further displayed aggregation behavior at higher concentration and excitation wavelength dependent multicolor emission properties. Most interestingly, the spontaneous resolution of chiral <i>S</i>-isomer of the 1-SH adduct occurred during crystallization. The cell imaging study revealed the staining of the cell and multicolor emission in the presence of H₂S