Understanding of [RuL(ONO)]n+ acting as nitric oxide precursor, a theoretical study of ruthenium complexes of 1,4,8,11-tetraazacyclo- tetradecane having different substituents: How spin multiplicity influences bond angle and bond lengths (Ru-O-NO) in releasing of NO

Generation of nitric oxide has been a great interest in cell biology as it involves a wide range of physiological functions including the blood pressure control; thus the exploitation of ruthenium chemistry has been motivated in biochemical and clinical points of view. Herein, the structural and electronic properties of ruthenium(II) complexes of 1,4,8,11-tetraazacyclotetradecane containing pyridyl, imidazole and benzimidazole (L¹, L², L³) were analyzed theoretically in the context of how spin multiplicity plays a crucial role influencing the NO release from the LRu-ONO moiety. The results show that β-cleavage of nitrito in the complex motivates the release of NO as it depends highly on total spin multiplicity of metal ion altering significantly the geometrical parameters; particularly, a decrease of bond length of Ru-ONO is highly associated with an increase of RuO-NO bond distance that correlates with the decrease of the Ru-O-NO bond angle ultimately leading to the release of NO; apparently, the bending nature of Ru-O-NO defines its release from the complex. This is consistent with orbital energy (d_x²-_y²) where the stabilization of axial Ru-O bond in the complex was observed, and proved by molecular orbital studies. In the excitation of the complex (singlet to triplet or singlet to quintet), the NO release has been facilitated, agreeing with the Gibbs free energy data where a lower energy for NO release was obtained compared to other types of excitations. In the calculated electronic spectra, a visible broad band with relatively high intensity for [RuL¹ONO]⁺ was observed, agreeing approximately with reported experimental results.

Na3[Ru2(µ-CO3)4] as a Homogeneous Catalyst for Water Oxidation; HCO3− as a Co-Catalyst

In neutral medium (pH 7.0) [RuIIIRuII(µ-CO3)4(OH)]4− undergoes one electron oxidation to form [RuIIIRuIII(µ-CO3)4(OH)2]4− at an E1/2 of 0.85 V vs. NHE followed by electro-catalytic water oxidation at a potential ≥1.5 V. When the same electrochemical measurements are performed in bicarbonate medium (pH 8.3), the complex first undergoes one electron oxidation at an Epa of 0.86 V to form [RuIIIRuIII(µ-CO3)4(OH)2]4−. This complex further undergoes two step one electron oxidations to form RuIVRuIII and RuIVRuIV species at potentials (Epa) 1.18 and 1.35 V, respectively. The RuIVRuIII and RuIVRuIV species in bicarbonate solutions are [RuIVRuIII(µ-CO3)4(OH)(CO3)]4− and [RuIVRuIV(µ-CO3)4(O)(CO3)]4− based on density functional theory (DFT) calculations. The formation of HCO4− in the course of the oxidation has been demonstrated by DFT. The catalyst acts as homogeneous water oxidation catalyst, and after long term chronoamperometry, the absorption spectra does not change significantly. Each step has been found to follow a proton coupled electron transfer process (PCET) as obtained from the pH dependent studies. The catalytic current is found to follow linear relation with the concentration of the catalyst and bicarbonate. Thus, bicarbonate is involved in the catalytic process that is also evident from the generation of higher oxidation peaks in cyclic voltammetry. The detailed mechanism has been derived by DFT. A catalyst with no organic ligands has the advantage of long-time stability.

Exploration of highly selective fluorogenic 'on-off' chemosensor for H2 PO4 - ions: ICT-based sensing and ATPase activity profiling

In this study, the recognition contour of Chemosensor 1 was investigated using semiaqueous methanol (X_H , mole fraction = 0.31) for a range of anions and bioactive species. Host-receptor signalling based on the internal charge transfer mechanism for Chemosensor 1 was explored and reported. Structure of Chemosensor 1 and its plausible anion coordination based on hydrogen bonding is complemented with density functional theory. Consequently, we investigated the applicability of the synthesized probe in blood plasma, urine, tap water samples, and for monitoring of ATP in lysosomes by apyrase enzyme.

A smart chemosensor: Discriminative multidetection and various logic operations in aqueous solution at biological pH

A novel rhodamine-pyrazole based molecular probe was designed and easily synthesized. The probe could to detect several analytes in aqueous solution at biological pH (HEPES, pH = 7.2). Several heavy metal cations, including Cu²⁺, Fe³⁺, Al³⁺, Hg²⁺ and Ni²⁺ were detected discriminately by the probe. Also, the novel compound exhibited a good sensory selectivity towards S₂O₅^2- by both absorption and emission spectra. Moreover, probe/Cu²⁺ complex could to detect several anions, including F^-, CN^-, S^2-, CH₃COO^-, CO₃^2- and NO₂^-. Furthermore, the probe exhibited a high potential to work as a molecular system able to perform a number of logical operations such as AND, NAND, NOR and INHIBIT logic gates.

Two macrocycle-based sensors for anions sensing

Two macrocyclic bis-benzimidazolium salts 2 and 4 (23-membered for 2 and 25-membered for 4) were prepared, and their structures were confirmed by X-ray crystallography, 1H NMR and 13C NMR spectroscopy. The research of anion recognitions using 2 or 4 as hosts were carried out with the methods of fluorescence and ultraviolet spectroscopy, 1H NMR titrations, MS and IR spectra. The experiment results show that 2 can detect acetate anion and 4 can detect nitrate anion with favorable selectivity and sensitivity.

Novel thiophene-based colorimetric and fluorescent turn-on sensor for highly sensitive and selective simultaneous detection of Al3+ and Zn2+ in water and food samples and its application in bioimaging

A novel bifunctional thiophene-based Schiff base TS as a colorimetric and fluorescent turn-on sensor for rapid and simultaneous detection of Al³⁺ and Zn²⁺ ions with high selectivity and sensitivity has been developed. The sensor shows remarkable fluorescence enhancement response for Al³⁺ and Zn²⁺ over a broad pH range with good anti-interference capability, which accompanied with an obvious color change easily detected by naked eyes. Sensor TS can detect as low as 3.7 × 10^-9 M for Al³⁺ and 3.0 × 10^-8 M for Zn²⁺, whereas respective association constants are 1.16 × 10⁴ M^-1 and 2.08 × 10⁴ M^-1. With the help of fluorescence titration and Job's plot, the stoichiometric ratio of TS with Al³⁺/Zn²⁺ was determined to be 1:1. The sensing mechanism of sensor TS with Al³⁺/Zn²⁺ based on the chelation-enhanced fluorescence (CHEF) was analyzed in detail through ¹H NMR titration, FTIR, HRMS and DFT studies. Moreover, sensor TS has been applied to the detection of Al³⁺ and Zn²⁺ in real environmental water and food samples as well as the filter paper-based test strips. Furthermore, sensor TS has good cell-permeability and can be used to selectively sense intracellular Al³⁺ and Zn²⁺ by bioimaging.