Solid-to-Solid Oxidation of a Vanadium(IV) to a Vanadium(V) Compound: Chemisty of a Sulfur-Containing Siderophore

Visible light facilitates a solid-to-solid photochemical aerobic oxidation of a hunter-green microcrystalline oxidovanadium­(IV) compound (<b>1</b>) to form a black powder of <i>cis</i>-dioxidovanadium­(V) (<b>2</b>) at ambient temperature. The siderophore ligand pyridine-2,6-bis­(thiocarboxylic acid), H₂L, is secreted by a microorganism from the <i>Pseudomonas</i> genus. This irreversible transformation of a metal monooxo to a metal dioxo complex in the solid state in the absence of solvent is unprecedented. It serves as a proof-of-concept reaction for green chemistry occurring in solid matrixes

Solid-to-Solid Oxidation of a Vanadium(IV) to a Vanadium(V) Compound: Chemisty of a Sulfur-Containing Siderophore

Visible light facilitates a solid-to-solid photochemical aerobic oxidation of a hunter-green microcrystalline oxidovanadium­(IV) compound (<b>1</b>) to form a black powder of <i>cis</i>-dioxidovanadium­(V) (<b>2</b>) at ambient temperature. The siderophore ligand pyridine-2,6-bis­(thiocarboxylic acid), H₂L, is secreted by a microorganism from the <i>Pseudomonas</i> genus. This irreversible transformation of a metal monooxo to a metal dioxo complex in the solid state in the absence of solvent is unprecedented. It serves as a proof-of-concept reaction for green chemistry occurring in solid matrixes

Fabrication of a Cu(II)-Selective Electrode in the Polyvinyl Chloride Matrix Utilizing Mechanochemically Synthesized Rhodamine 6g as an Ionophore

A Cu­(II)-selective electrode has been fabricated by utilizing a mechanochemically synthesized copper-specific ionophore “L” embedded in a poly­(vinyl chloride) membrane. 2-Nitrophenyloctylether and sodium tetraphenylborate have been used as a plasticizer and as a solvent mediator, respectively, and found to be enhancing the sensitivity of the fabricated ion-selective electrode (ISE). A range of membranes (S1–S7) with varying compositions were casted and investigated in ISE. Results revealed an excellent Nernstian response of 29.38 ± 0.55 mV/dec for the ISE S6. The fabricated ISE operates well in the pH window 4.0–7.5, and the limit of detection was found to be 5 μM (0.3 ppm). Quick response time (15 s), long shelf-life, and selectivity (on the order of 10–4 and 10–5) over a number of interfering cations enabled S6 promising for real off laboratory sample analysis and can be employed to detect copper ion in various industrial as well as biological and environmental samples. To demonstrate the practical application of these ISE, the Cu concentration in the digested printed circuit board has been estimated using the standard calibration plot. The fabricated ISE has been regenerated through extracting copper by chelating with ethylenediaminetetraacetic acid

Mechanistic Insight of Sensing Hydrogen Phosphate in Aqueous Medium by Using Lanthanide(III)-Based Luminescent Probes

The development of synthetic lanthanide luminescent probes for selective sensing or binding anions in aqueous medium requires an understanding of how these anions interact with synthetic lanthanide probes. Synthetic lanthanide probes designed to differentiate anions in aqueous medium could underpin exciting new sensing tools for biomedical research and drug discovery. In this direction, we present three mononuclear lanthanide-based complexes, EuLCl3 (1), SmLCl3 (2), and TbLCl3 (3), incorporating a hexadentate aminomethylpiperidine-based nitrogen-rich heterocyclic ligand L for sensing anion and establishing mechanistic insight on their binding activities in aqueous medium. All these complexes are meticulously studied for their preferential selectivities towards different anions such as HPO42&minus;, SO42&minus;, CH3COO&minus;, I&minus;, Br&minus;, Cl&minus;, F&minus;, NO3&minus;, CO32&minus;/HCO3&minus;, and HSO4&minus; at pH 7.4 in aqueous HEPES (2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanesulfonic acid) buffer. Among the anions scanned, HPO42&minus; showed an excellent luminescence change with all three complexes. Job&rsquo;s plot and ESI-MS support the 1:2 association between the receptors and HPO42&minus;. Systematic spectrophotometric titrations of 1&ndash;3 against HPO42&minus; demonstrates that the emission intensities of 1 and 2 were enhanced slightly upon the addition of HPO42&minus; in the range 0.01&ndash;1 equiv and 0.01&ndash;2 equiv., respectively. Among the three complexes, complex 3 showed a steady quenching of luminescence throughout the titration of hydrogen phosphate. The lower and higher detection limits of HPO42&minus; by complexes 1 and 2 were determined as 0.1&ndash;4 mM and 0.4&ndash;3.2 mM, respectively, while complex 3 covered 0.2&ndash;100 &mu;M. This concludes that all complexes demonstrated a high degree of sensitivity and selectivity towards HPO42&minus;

NMR Crystallography for Structural Characterization of Oxovanadium(V) Complexes: Deriving Coordination Geometry and Detecting Weakly Coordinated Ligands at Atomic Resolution in the Solid State

NMR crystallography is an emerging method for atomic-resolution structural analysis of ubiquitous vanadium­(V) sites in inorganic and bioinorganic complexes as well as vanadium-containing proteins. NMR crystallography allows for characterization of vanadium­(V) containing solids, based on the simultaneous measurement of ⁵¹V–¹⁵N internuclear distances and anisotropic spin interactions, described by ¹³C, ¹⁵N, and ⁵¹V chemical shift anisotropy and ⁵¹V electric field gradient tensors. We show that the experimental ⁵¹V, ¹³C, and ¹⁵N NMR parameters are essential for inferring correct coordination numbers and deriving correct geometries in density functional theory (DFT) calculations, particularly in the absence of single-crystal X-ray structures. We first validate this approach on a structurally known vanadium­(V) complex, (¹⁵N-salicylideneglycinate)-(benzhydroxamate)­oxovanadium­(V), VO¹⁵NGlySalbz. We then apply this approach to derive the three-dimensional structure of (methoxo)­(¹⁵N-salicylidene-glycinato)­oxovanadium­(V) with solvated methanol, [VO­(¹⁵NGlySal)­(OCH₃)]­·(CH₃OH). This is a representative complex with potentially variable coordination geometry depending on the solvation level of the solid. The solid material containing molecules of CH₃OH, formally expressed as [VO­(¹⁵NGlySal)­(OCH₃)]­·(CH₃OH), is found to have one molecule of CH₃OH weakly coordinated to the vanadium. The material is therefore best described as [VO­(¹⁵NGlySal)­(OCH₃)­(CH₃OH)] as deduced by the combination of multinuclear solid-state NMR experiments and DFT calculations. The approach reported here can be used for structural analysis of systems that are not amenable to single-crystal X-ray diffraction characterization and which can contain weakly associated solvents

Switching Off Electron Transfer Reactions in Confined Media: Reduction of [Co(dipic)₂]⁻ and [Co(edta)]⁻ by Hexacyanoferrate(II)

The kinetics of reduction of two cobalt­(III) complexes with similar redox potentials by hexacyanoferrate­(II) were investigated in water and in reverse micelle (RM) microemulsions. The RMs were composed of water, surfactant [(sodium­(bis­(2-ethylhexylsulfosuccinate)), NaAOT], and isooctane. Compared to the reaction in water, the reduction rates of (ethylenediaminetetraacetato)­cobaltate­(III) by hexacyanoferrate­(II) were dramatically suppressed in RM microemulsions whereas a slight rate increase was observed for reduction of bis-(2,6-dipicolinato)­cobaltate­(III). For example, the ferrocyanide reduction of [Co­(dipic)₂]⁻ increased from 55 M^–1 s^–1in aqueous media to 85 M^–1 s^–1 in a <i>w</i>_o = 20 RM. The one-dimensional (1-D) and two-dimensional (2-D) ¹H NMR and FT-IR studies are consistent with the reduction rate constants of these two complexes being affected by their location within the RM. Since reduction of [Co­(edta)]⁻ is switched off, in contrast to [Co­(dipic)₂]⁻, these observations are attributed to the penetration of the [Co­(edta)]⁻ into the interfacial region of the RM whereas [Co­(dipic)₂]⁻ is in a region highly accessible to the water pool and thus hexacyanoferrate­(II). These results demonstrated that compartmentalization completely turns off a redox reaction in a dynamic microemulsion system by either reactant separation or alteration of the redox potentials of the reactants