Tuning the recognition properties of urea based receptor towards cyanide in aqueous medium: Effect of fluorine substitution on strength and selectivity of the anion receptor

Miniaturized dual-wavelength β-correction spectrophotometric probe for sensitive detection of cyanide in water via formation of cyano dithizone adduct

Cyanide toxicity in water significantly threatens public health and the environment. To address this, a miniaturized simple, low-cost, selective and sensitive direct dual wave β-correction spectrophotometric probe has been established for cyanide detection in water. The dual-wavelength β-correction spectrophotometry enhances the selectivity and sensitivity of the probe in the presence of interfering species. The assay relies a highly selective nucleophilic addition of cyanide ions to dithizone (H2Dz) as chromogenic reagent in aqueous media of pH 6.8-7.2, forming a red-colored cyano H2Dz adduct. The electronic spectrum of the formed adduct displays a sharp absorption peak at λmax = 480 nm, enabling precise colorimetric detection. The molar absorptivity and Sandell's sensitivity index for the cyano H2Dz adduct with and without β-correction spectrophotometry were 5.62 × 103, and 1.79 × 103 L mol-1 cm-1, and 0.002 and 0.0033 µg cm-2, respectively. Beer's law and Ringbom's plots are valid in the range 0.01-5.0 and 0.06-2.0 µg mL-1 CN- concentration, respectively. The limits of detection (LOD) and quantification (LOQ) improved from 1.03 × 10-1 and 3.13 × 10-1 μg/mL using ordinary spectrophotometry to 2.8 × 10-2 and 8.7 × 10-2 μg mL-1 employing β-correction spectrophotometry. The probe offers rapid response, good anti-interference ability, reproducibility, and cost-effectiveness. The probe was successfully applied for detection of trace levels of cyanide ions in water with good repeatability. It has been also validated in water samples with good recoveries (99.2 ± 5.02 %). The experimental Student t test (texp = 1.2-1.5) was lower than the critical (texp = 2.78) at 95 % probability (n = 5). The stoichiometry and mechanism of formation of the cyano adduct were assigned and addressed.

The strength and selectivity of perfluorinated nano-hoops and buckybowls for anion binding and the nature of anion-π interactions

Perfluorinated cycloparaphenylenes (F-[n]CPP, n = 5-8), boron nitride nanohoop (F-[5]BNNH), and buckybowls (F-BBs) were proposed as anion receptors via anion-π interactions with halide anions (Cl^- , Br^- and I^- ), and remarkable binding strengths up to -294.8 kJ/mol were computationally verified. The energy decomposition approach based on the block-localized wavefunction method, which combines the computational efficiency of molecular orbital theory and the chemical intuition of ab initio valence bond theory, was applied to the above anion-π complexes, in order to elucidate the nature and selectivity of these interactions. The overall attraction is mainly governed by the frozen energy component, in which the electrostatic interaction is included. Remarkable binding strengths with F-[n]CPPs can be attributed to the accumulated anion-π interactions between the anion and each conjugated ring on the hoop, while for F-BBs, additional stability results from the curved frameworks, which distribute electron densities unequally on π-faces. Interestingly, the strongest host was proved to be the F-[5]BNNH, which exhibits the most significant anisotropy of the electrostatic potential surface due to the difference in the electronegativities of nitrogen and boron. The selectivity of each host for anions was explored and the importance of the often-overlooked Pauli exchange repulsion was illustrated. Chloride anion turns out to be the most favorable anion for all receptors, due to the smallest ionic radius and the weakest destabilizing Pauli exchange repulsion.

A molecular phototropic system for cyanide: Detection and sunlight driven harvesting of cyanide with molecular sunflower

We are reporting a simple, easy to prepare, and conformation switchable first molecular phototropic system L, "(E)-2-(2,4-dinitrophenyl)-1-((pyren-8-yl)methylene)hydrazine, for cyanide harvesting. This molecular phototropic system behaves as a molecular sunflower in which the conformation of this molecular sunflower can be altered in response to the sunlight. This molecular flower can sense and bind the cyanide anion colorimetrically through its transition state. Further, upon exposure of this transition state cyanide complex 1, under sunlight, this system is capable to release the bound cyanide via -C=N- free rotation to reach its lower energy stable conformation. Similar behaviors were observed for acetate and fluoride with L. The strength of the phototropic system L towards cyanide, acetate and fluoride is found to be 4.5 × 10⁵, 1.53 × 10² and 6.09 × 10² M^-1.

Hydrogen bonding elements, π - hole functional moieties and C3v tripodal scaffold controlled turn-on cyanide and turn-off azide selective receptors

Here in, we are reporting electron deficient amide and sulfonamide based tripodal receptors L, L¹, L² and L³. Systematic studies show a strong selectivity towards cyanide and azide anions. Detailed UV-Visible and fluorescent spectrometric investigation shows the amide based tripodal receptors L and L³ acts as a colorimetric and turn-on fluorescent chemo-sensor for cyanide, and the sulfonamide based tripodal receptors L¹ and L² acts as a colorimetric and turn-off fluorescent chemo-sensor for azide. At the end we have successfully prepared tripodal receptors for a particular anion with judicious choice of recognition elements such as hydrogen bonding amide/sulfonamide moiety, electron deficient pentafluorophenyl functionality for anion-π interaction and the well defined C₃v symmetric tripodal backbone for perfect recognition.