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Two new transition metal complexes of a dipyrazinylpyridine (dppy) ligand 3,4-diethoxyphenyl-2,6-di(pyrazine-2-yl)pyridine L, {[CuL2]Cl2 (1) and [ZnL2]Cl2 (2)}, have been synthesized and characterized using NMR (for L and 2), UV-vis spectroscopy, ESR (for 1), HRMS, elemental analysis and DFT study. Upon interaction with bovine serum albumin (BSA), complexes 1 and 2 demonstrated varying binding capabilities, with 1 displaying superior binding (binding constant 4.5 x 104 M-1) towards BSA than 2 (binding constant 1.2 x 104 M-1). Similarly, with calf-thymus DNA (ct-DNA), 1 showed better binding affinity (1.1 x 106 M-1) than 2 (8.5 x 105 M-1) as observed from UV-visible spectroscopy. The mechanism that leads to the quenching of BSA fluorescence by 1 and 2 is attributed to static quenching. The complexes demonstrated an intercalative binding mode with ct-DNA, and molecular docking has been employed to elucidate the biomolecular interactions with the complexes. Circular dichroism spectra have been utilized to confirm the binding and assessment of the interactions with the biomolecules. Furthermore, studies of the anticancer potentials of 1-2 were evaluated using the Dalton's lymphoma (DL) cancer cell line. Following 48 hours of treatment, the IC50 values for 1 and 2 were identified as 24 mM and 28 mM, respectively, indicating their potency in inhibiting cancer cell growth. [ABSTRACT FROM AUTHOR]

[Display omitted] • Selective copper hydrogel formation using terpyridine ligand L in dilute acidic medium. • Hydrogel is sensitive to S2− and I− ions. • Anion sensing study confirms the sensitivity of the copper complex towards S2− and I− ions with low LOD values. • DFT calculations were studied for non-covalent interactions and anion sensing study. 2,2′:6′,2″-Terpyridines (tpy) are well known for their ability to form a gel in the presence of transition metals. Due to the strong binding affinities towards transition metal ions aided by non-covalent interactions, tpy tends to form hydrogel with more than one metal ion. Interestingly, a simple chloro substituted 2,2′:6′,2″-terpyridine ligand L selectively forms a gel with only Cu(II) ion in a mild acidic medium. The hydrogel has a fibrous structure and is sensitive to S2− and I− anions, which is confirmed by both morphological analysis and rheological study. The copper complex was characterized using a variety of techniques, including HRMS, ESR, FTIR, elemental analysis, and DFT calculations. Further, DFT calculations were used to study the non-covalent interactions within the complex and to understand why the hydrogel responds to specific anions. The free energies of the CuI and CuS precipitate formation were calculated to get an idea of the feasibility of the process. Notably, UV–visible absorption spectroscopic study shows that the copper(II) complex CuCl 2 L selectively detected S2− and I− anions in aqueous acetonitrile with LOD of 2.63 and 2.08 μM, respectively. [ABSTRACT FROM AUTHOR]

• Selective Hg(II) triggered hydrogelation of ligand 4′-(pyridin-2-yl)-2,2′:6′,2″-terpyridine L in dilute nitric acid. • Hg(II)-hydrogel showed non-uniform, fibrous, and well-developed cross-linked gel morphology. • Optimized structure of HgCl 2 L. We report the addition of aqueous solution of different divalent transition metal ions M2+ (M = Mn, Fe, Co, Ni, Cu, Zn, Cd, Hg) to a dilute acidic solution of 4′-(pyridin-2-yl)-2,2′:6′,2″-terpyridine (L). An irreversible, translucent, and thixotropic hydrogel was selectively produced in the case of Hg(II). FESEM and HR-TEM images of Hg(II)-hydrogel showed non-uniform, fibrous, and cross-linked gel morphology. Further, the hydrogel was treated with sodium salts of different anions (F−, I−, Br−, Cl− , SO 4 2−, NO 3 −, HCO 3 −, SO 3 2−) in water. The iodide ion showed unusual behavior by forming a yellow precipitate of the hydrogel with a plate-like structure, as observed from FESEM images. DFT study has also been conducted to understand the aggregation behavior in Hg(II) based hydrogel. We also synthesized the mercury complex HgCl 2 L and characterized it by 1H NMR, elemental analysis, and mass spectrometry. Selective hydrogelation behavior of pyridinyl substituted terpyridine ligand 4′-(pyridin-2-yl)-2,2′:6′,2″-terpyridine L in dilute acidic medium in the presence of Hg(II) is reported and analyzed by FESEM and HRTEM techniques. The influence of anions on the gel morphologies have also been explored. In addition, DFT study has also been conducted to explore the possible interaction in mercury induced hydrogel. [Display omitted] [ABSTRACT FROM AUTHOR]

The hydrogelation behavior of 4′-(4-methoxyphenyl)-2,2′:6′,2′'-terpyridine in the presence of Cu(II), Zn(II), Cd(II), and Hg(II) has been reported, and the morphology has been analyzed using FESEM technique. Blue fluorescence exhibited by the Zn(II), Cd(II), and Hg(II) metallogels when exposed to UV light (365 nm). [Display omitted] We reported the hydrogel formation ability of 4′-(4-methoxyphenyl)-2,2′:6′,2′'-terpyridine L with different transition metal ions in a mild acidic medium. Irreversible, thixotropic and translucent hydrogel was achieved in case of divalent Cu2+, Zn2+, Cd2+ and Hg2+ ions. FESEM images of the hydrogels showed that Cu2+ hydrogel exhibited a fibrous network, while Zn2+ based hydrogel comprised a non-uniform fibrous structure. On the other hand, Cd2+ and Hg2+ hydrogels showed unusual flake-like structures. Further, Zn2+, Cd2+ and Hg2+ hydrogels exhibited blue fluorescence upon exposure to UV light (365 nm). [ABSTRACT FROM AUTHOR]

• Copper(II) and Cadmium(II) triggered hydrogelation of ligand 4′-(3,4,5-trimethoxyphenyl)-2,2′:6′,2′'-terpyridine l in an aqueous medium. • Cu(II) hydrogel is non-fluorescent, while Cd(II) hydrogel shows green fluorescence. • Single crystal analysis of Cd(II) hydrogel. We report the hydrogelation behavior of methoxy‑terpyridine ligand 4′-(3,4,5-trimethoxyphenyl)-2,2′:6′,2′'-terpyridine L in water in the presence of Cu(II) and Cd(II) metal ions. The Cd(II) mediated hydrogel exhibits green fluorescence upon UV light exposure (365 nm). The gel morphologies were studied with the help of SEM. Crystal structure of CdCl 2 L and the influence of anions on the gel morphologies were also explored. Hydrogelation behavior of methoxy‑terpyridine ligand 4′-(3,4,5-trimethoxyphenyl)-2,2′:6′,2′'-terpyridine in water in the presence of Cu(II) and Cd(II) is reported and analyzed by SEM. The Cd(II) mediated hydrogel exhibits green fluorescence upon UV light exposure (365 nm). Crystal structure of the CdCl 2 L and the influence of anions on the gel morphologies were also explored. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Synthesis and characterization of Cu(II) complex of dppy ligand L. • Selective recognition of l -Cysteine and l -Histidine by Cu-dppy complex. • Validation of amino acid detection studies by theoretical investigation. Developing simple and effective receptors for instantaneous detection of l -amino acids is vital for the recognition of life-threatening diseases in their early stage. Here, we report the synthesis and characterization of 2,6-di(pyrazin-2-yl)pyridine (dppy) based ligand L (L = 2,2′-(4-(3,4-diethoxyphenyl)pyridine-2,6-diyl)dipyrazine) and its copper (II) complex, [Cu(NO 3) 2 L]. The in-situ prepared [Cu(H 2 O) 2 L](NO 3) 2 receptor in aqueous acetonitrile (4:1 v / v, 10 mM HEPES buffer, pH 7.4) medium displayed instantaneous response s towards biologically important bio-thiol l -Cysteine (Cys) and essential amino acid l -Histidine (His) over other l -amino acids through UV–Visible absorption spectral studies. Additionally, the competitive experiments confirmed that in-situ prepared [Cu(H 2 O) 2 L](NO 3) 2 receptor selectively detects Cys (1 equivalent) in the presence of other l -amino acids. The detection limits of Cys and His were calculated to be 8.23 × 10−7 M and 2.55 × 10−6 M, respectively. The density functional theory (DFT) calculation shows that selectivity of [Cu(H 2 O) 2 L](NO 3) 2 towards Cys is due to the reduction of Cu(II) to Cu(I) in the presence of Cys, while Cys is oxidized to cystine (Cys-Cys). For His, selectivity observed due to the formation of [Cu(His) 2 ] moiety between Cu(II) ion with one His via N , O coordination mode and another His via N,N,O -coordination mode. [ABSTRACT FROM AUTHOR]

The binding of HSA with two new Cu(II) and Zn(II) complexes of a dipyrazinyl pyridine ligand has been studied, and their drug displacement activity has been investigated. [Display omitted] • Syntheses of novel copper and zinc complexes of a dipyrazinyl pyridine ligand and their characterization by 1H NMR, ESR, and HRMS. • The interaction of HSA with metal complexes has been studied. • A drug displacement study has been done using ibuprofen, warfarin, and bilirubin. • A theoretical analysis by DFT and molecular docking has been done. A one-pot method was employed for the preparation of zinc and copper complexes of 4-methoxyphenyl-2,6-di(pyrazine-2-yl)pyridine ligand (L). The complexes were designed to acknowledge their potential as selective binders with serum albumins. The reaction of the metal chlorides with an excess of ligand L yielded mononuclear [Cu L 2 ]Cl 2 (1) and [Zn L 2 ]Cl 2 (2) complexes. 1H NMR, UV–Vis spectroscopy, ESR, HRMS, XRD, and elemental analysis were carried out to characterize the complexes. The interactions of the synthesized complexes with Human Serum Albumin (HSA) and their drug displacement properties using ibuprofen and warfarin were investigated with the help of spectroscopic as well as molecular modeling techniques. Complex 1 exhibited better binding capability, indicated by its binding constant value (31.2 × 104 M−1) towards HSA, than complex 2 (5.6 × 104 M−1), as depicted from UV–Visible and fluorescence spectroscopic studies. Moreover, the complexes showed better binding affinity towards HSA than the corresponding free ligand (0.2 × 104 M−1). The mechanism through which fluorescence quenching of HSA takes place (when metal complexes 1 – 2 were added to it) is static in nature. The Stern-Volmer (SV) equation was utilized to deduce the binding constants (K b) through a fluorescence titration method. Moreover, structure optimization of the synthesized complexes and theoretical studies using density functional theory (DFT) has been carried out to determine the nature of the interaction of the complexes with the biomolecules. [ABSTRACT FROM AUTHOR]