Mn^II- and Co^II-Catalyzed Transformation of 2‑Cyanopyrimidine to Methylimidate by Sodium Azide: Isolation, Structural Characterization, and Magnetic Studies on 2D Mn^II- and Cu^II-Complexes

The Mn^II-mediated transformation of 2-cyanopyrimidine to methylimidate in the presence of inorganic azide is proven through isolation and structural characterization of a metal complex. Though the reaction conditions are favorable for a “click” reaction leading to the formation of tetrazole, as evidenced from recent studies, we are astonished to see the formation of methylimidate in MeOH instead of tetrazole, which is supposed to form only in the presence of catalytic amount of corresponding alkoxide ion as base. The catalytic nature of this transformation reaction was confirmed by performing these experiments under catalytic conditions and analyzing the products using liquid chromatography–mass spectrometry techniques, which clearly showed ∼96% and ∼60% selectivity of methylimidate along with almost 100% conversion in the presence of Mn^II and Co^II as catalysts, respectively. In absence or presence of other metal ions like Cu^II, Ni^II, Fe^II, Zn^II, etc. only tetrazole formation takes place. So the present findings extended the formation of methylimidate catalyzed by metal ions in the presence of azide ion in alcoholic medium. Importantly, a probable mechanism for this unexpected transformation was framed based on the structural analysis and high-resolution mass spectrometry (electrospray ionization MS⁺) studies. The magnetic studies were also performed on complexes [Mn­(L)­(N₃)₂]_<i>n</i> (<b>1</b>) and [Cu (L²)₂]_<i>n</i> (<b>2a</b>), showing anti-ferromagnetic character for compound <b>1</b> and negligible coupling for the copper complex <b>2a</b>

A rhodamine hydrazide–<i>4-nitroindole-3-carboxaldehyde</i> based turn on Hg²⁺ chemosensor: cytoplasmic live cell imaging, logic gate and memory device applications and computational studies

<p>A new, highly sensitive probe <b>L²</b> for the selective detection of Hg²⁺ in organo-aqueous (H₂O:CH₃CN, 1:1, v/v, HEPES buffer, pH 7.2) medium has been synthesized from rhodamine 6G-hydrazide and <i>4-nitroindole-3-carboxaldehyde</i>. It was thoroughly characterized by physicochemical techniques including single crystal X-ray diffraction studies. The reaction of <b>L²</b> with Hg²⁺ gives a 1:1 stoichiometry resulting in a 146 fold fluorescence enhancement and a binding constant (<i>K</i>_f) of 3 × 10⁴ M⁻¹. The spirolactam form of the probe is non-fluorescent; however, it shows dual channel (absorbance and fluorescence) recognition of Hg²⁺ via CHEF effect through the opening of the spirolactam ring. The quantum yields of <b>L²</b> (0.00045) and <b>L²</b>-Hg²⁺ (0.29) show the higher stability of complex in the excited state over the free ligand. The 44.5 nM LOD value demonstrates the detection of Hg²⁺ at a very low concentration range. Cell imaging studies show the cytoplasmic recognition of Hg²⁺ by <b>L²</b>. Experimental results are comparable with theoretical values obtained by DFT studies. The fluorescence emission of the complex was completely quenched by I^- and from the reversibility studies an advance level INHIBIT logic gate and memory device can be framed.</p

Morphology-Directing Synthesis of Rhodamine-Based Fluorophore Microstructures and Application toward Extra- and Intracellular Detection of Hg²⁺

A new, easily synthesizable rhodamine-based chemosensor with potential N₂O₂ donor atoms, <b>L</b>^<b>3</b>, has been characterized by single-crystal X-ray diffraction together with ¹H NMR and high-resolution mass spectrometry (HRMS) studies. <b>L</b>^<b>3</b> was found to bind selectively and reversibly to the highly toxic Hg²⁺ ion. The binding stoichiometry and formation constant of the sensor toward Hg²⁺ were determined by various techniques, including UV–vis, fluorescence, and Job’s studies, and substantiated by HRMS methods. None of the biologically relevant and toxic heavy metal ions interfered with the detection of Hg²⁺ ion. The limit of detection of Hg²⁺calculated by the 3σ method was 1.62 nM. The biocompatibility of <b>L</b>^<b>3</b> with respect to its good solubility in mixed organic/aqueous media (MeCN/H₂O) and cell permeability with no or negligible cytotoxicity provides good opportunities for in vitro/in vivo cell imaging studies. As the probe is poorly soluble in pure water, an attempt was made to frame nano/microstructures in the absence and in the presence of sodium dodecyl sulfate (SDS) as a soft template, which was found to be very useful in synthesizing morphologically interesting <b>L</b>^<b>3</b> microcrystals. In pure water, micro-organization of <b>L</b>^<b>3</b> indeed occurred with block-shaped morphology very similar to that in the presence of SDS as a template. However, when we added Hg²⁺ to the solution of <b>L</b>^<b>3</b> under the above two conditions, the morphologies of the microstructures were slightly different; in the first case, a flowerlike structure was observed, and in second case, a simple well-defined spherical microstructure was obtained. Optical microscopy revealed a dotlike microstructure for <b>L</b>^<b>3</b>–SDS assemblies, which changed to a panicle microstructure in the presence of Hg²⁺. UV–vis absorption and steady-state and time-resolved fluorescence studies were also carried out in the absence and presence of Hg²⁺, and also the SDS concentration was varied at fixed concentrations of the receptor and guest. The results revealed that the fluorescence intensity increased steadily with [SDS] until it became saturated at ∼7 mM SDS, indicating that the extent of perturbation to the emissive species increases with the increase in [SDS] until it becomes thermodynamically stable. There was also an increase in anisotropy with increasing SDS concentration, which clearly manifests the restriction of movement of the probe in the presence of SDS

Water-Stable Manganese(IV) Complex of a N₂O₄‑Donor Non-Schiff-Base Ligand: Synthesis, Structure, and Multifrequency High-Field Electron Paramagnetic Resonance Studies

A novel water-stable (<i>t</i>_1/2 ∼ 6.8 days) mononuclear manganese­(IV) complex of a hexacoordinating non-Schiff-base ligand (H₄L) with N₂O₄-donor atoms has been synthesized and characterized crystallographically. High-frequency electron paramagnetic resonance experiments performed on a single crystal reveal a manganese­(IV) ion with an <i>S</i> = ³/₂ ground spin state that displays a large single-ion anisotropy, setting the record of mononuclear manganese­(IV) complexes reported so far. In addition, spin–echo experiments reveal a spin–spin relaxation time <i>T</i>₂ ∼ 500 ns

Domain-Specific Association of a Phenanthrene–Pyrene-Based Synthetic Fluorescent Probe with Bovine Serum Albumin: Spectroscopic and Molecular Docking Analysis

In this report, the interaction between a phenanthrene–pyrene-based fluorescent probe (PPI) and bovine serum albumin (BSA), a transport protein, has been explored by steady-state emission spectroscopy, fluorescence anisotropy, far-ultraviolet circular dichroism (CD), time-resolved spectral measurements, and molecular docking simulation study. The blue shift along with emission enhancement indicates the interaction between PPI and BSA. The binding of the probe causes quenching of BSA fluorescence through both static and dynamic quenching mechanisms, revealing a 1:1 interaction, as delineated from Benesi–Hildebrand plot, with a binding constant of ∼10⁵ M^–1, which is in excellent agreement with the binding constant extracted from fluorescence anisotropy measurements. The thermodynamic parameters, Δ<i>H</i>°, Δ<i>S</i>°, and Δ<i>G</i>°, as determined from van’t Hoff relationship indicate the predominance of van der Waals/extensive hydrogen-bonding interactions for the binding phenomenon. The molecular docking and site-selective binding studies reveal the predominant binding of PPI in subdomain IIA of BSA. From the fluorescence resonance energy transfer study, the average distance between tryptophan 213 of the BSA donor and the PPI acceptor is found to be 3.04 nm. CD study demonstrates the reduction of α-helical content of BSA protein on binding with PPI, clearly indicating the change of conformation of BSA

Water-Stable Manganese(IV) Complex of a N₂O₄‑Donor Non-Schiff-Base Ligand: Synthesis, Structure, and Multifrequency High-Field Electron Paramagnetic Resonance Studies

A novel water-stable (<i>t</i>_1/2 ∼ 6.8 days) mononuclear manganese­(IV) complex of a hexacoordinating non-Schiff-base ligand (H₄L) with N₂O₄-donor atoms has been synthesized and characterized crystallographically. High-frequency electron paramagnetic resonance experiments performed on a single crystal reveal a manganese­(IV) ion with an <i>S</i> = ³/₂ ground spin state that displays a large single-ion anisotropy, setting the record of mononuclear manganese­(IV) complexes reported so far. In addition, spin–echo experiments reveal a spin–spin relaxation time <i>T</i>₂ ∼ 500 ns

CO₂ Fixation by Dimeric Tb(III) Complexes: Synthesis, Structure, and Magnetism

Two dinuclear complexes, [Tb2(L1)2(piv)2(NO3)2]·H2O (1) and [Tb2(L2)2(CF3CO2)2(H2O)4].2NO3 (2), have been prepared and characterized by single-crystal X-ray diffraction, where each metal ion is doubly phenoxido-bridged by the two phenolato oxygen atoms of the tetradentate Schiff-base ligand. Previous magnetic studies of 1 show that it is not a single-molecule magnet (SMM), while AC magnetic measurements of 2 show that it relaxes quite fast with μSQUID measurements revealing the presence of an interaction operating between the Tb ions. Through DC, μSQUID, and CASSCF calculations, the strength of the interaction in 2 can be quantified, which is of dipolar origin. Both complexes showed efficient catalytic activity toward the carbon dioxide insertion reaction into epoxides for the formation of organic cyclic carbonates. Catalytic synthesis of organic cyclic carbonates smoothly occurred at 60 °C under1 bar carbon dioxide pressure and neat conditions. Exocyclic as well as endocyclic epoxides produced a respective cyclic carbonate product with moderate to high yield (43–100%). Moreover, a high turnover number (7300–10000) along with a high turnover frequency (537.5–5000 h–1) are found in this catalytic reaction