A highly selective chemiluminescent probe for the detection of chromium(VI)

Immobilization of diphenylcarbazide on paper-based analytical devices for the pre-concentration and detection of chromium VI in water samples

A novel approach using a smartphone for the detection of Cr (VI) has been developed. In this context, two different platforms were designed for the detection of Cr (VI). The first one was synthesized via a crosslinking reaction of chitosan with 1,5-Diphenylcarbazide (DPC-CS). The obtained material was integrated into a paper to develop a new paper-based analytical device (DPC-CS-PAD). The DPC-CS-PAD exhibited high specificity toward Cr (VI). The second platform (DPC-Nylon PAD) was prepared by covalent immobilization of DPC onto a Nylon paper and then its analytical performances regarding Cr (VI) extraction and detection were evaluated. DPC-CS-PAD presented a linear range of 0.1-5 ppm with detection and quantification limits of about 0.04 and 0.12 ppm, respectively. The DPC-Nylon-PAD exhibited a linear response of 0.1-2.5 ppm with detection and quantification limits of 0.06 and 0.2 ppm, respectively. Furthermore, the developed platforms were effectively applied for testing the effect of the loading solution volume for trace Cr (IV) detection. For the DPC-CS material, a volume of 20 mL allowed the detection of 4 ppb of Cr (VI). In the case of DPC-Nylon-PAD, the loading volume of 1 mL permitted the detection of the critical concentration of Cr (VI) in water.

A novel liquid crystal resonance Rayleigh scattering spectral probe for determination of trace Cr6

Hexavalent chromium (Cr⁶⁺) has strong oxidizing property and toxicity. It has been identified as a carcinogen with obvious carcinogenic effect by the International Anti-cancer Research Center. Therefore, it has a great significance to establish a simple and sensitive method for Cr⁶⁺. In the solution, liquid crystal (LC) trans, trans-4-(3,4-difluorophenyl)-4'-n-pentylbicyclohexyl (DP) exhibits strong resonance Rayleigh scattering (RRS) effect due to formation DP nanoparticles. It was used firstly as nanoprobe, to establish a simple and sensitive RRS energy transfer (RRS-ET) method for the determination of trace Cr⁶⁺ in water samples. The Cr⁶⁺ reacts with diphenylcarbazide (DCB) to produce purple complex. It is adsorbed on the nanoprobe surface, the purple complex as energy receptor and DP as energy donor to produce RRS-ET phenomenon, to make the RRS signal of 370 nm decreasing. In the range of 3-30 nmol/L Cr⁶⁺, with the increase of concentration, the RRS signal decreased linearly at 370 nm, with a detection limit of 0.49 nmol/L. This new RRS-ET method was applied to the determination of Cr⁶⁺ in water samples, with recovery of 96.0-104.7% and the relative standard deviation (RSD) of 4.44-9.98%.

Different Schiff Bases-Structure, Importance and Classification

Schiff bases are a vast group of compounds characterized by the presence of a double bond linking carbon and nitrogen atoms, the versatility of which is generated in the many ways to combine a variety of alkyl or aryl substituents. Compounds of this type are both found in nature and synthesized in the laboratory. For years, Schiff bases have been greatly inspiring to many chemists and biochemists. In this article, we attempt to present a new take on this group of compounds, underlining of the importance of various types of Schiff bases. Among the different types of compounds that can be classified as Schiff bases, we chose hydrazides, dihydrazides, hydrazones and mixed derivatives such as hydrazide-hydrazones. For these compounds, we presented the elements of their structure that allow them to be classified as Schiff bases. While hydrazones are typical examples of Schiff bases, including hydrazides among them may be surprising for some. In their case, this is possible due to the amide-iminol tautomerism. The carbon-nitrogen double bond present in the iminol tautomer is a typical element found in Schiff bases. In addition to the characteristics of the structure of these selected derivatives, and sometimes their classification, we presented selected literature items which, in our opinion, represent their importance in various fields well.

Colorimetric detection of chromium (VI) ion using poly(N-phenylglycine) nanoparticles acting as a peroxidase mimetic catalyst

This paper reports on enzyme-like catalytic properties of polyethylene glycol-functionalized poly(N-phenylglycine) (PNPG-PEG) nanoparticles, which have not been explored to date. The developed nanoparticles have the ability to display great inherent peroxidase-like activity at very low concentrations, and are able to catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) substrate in presence of hydrogen peroxide (H₂O₂). The oxidized product of TMB has a deep blue color with a maximum absorbance at ~655 nm. The PNPG-PEG nanoparticles exhibit K_m values of 0.2828 for TMB and 0.0799 for H₂O₂, indicating that TMB oxidation takes place at lower concentration of H₂O₂ in comparison to other nanozymes. Based on the known mechanism of H₂O₂ oxidation by hexavalent chromium [Cr(VI)] ions to generate hydroxyl radicals (^•OH), these nanoparticles were successfully applied for the colorimetric sensing of Cr(VI) ions. The sensor achieved good performance for Cr(VI) sensing with detection limits of 0.012 μM (0.01-0.1 μM linear range) and 0.52 μM (0.05-12.5 μM linear range). The detection scheme was highly selective, and successfully applied for the detection of Cr(VI) in real water samples.

Ln-CPs constructed from unsymmetrical tetracarboxylic acid ligand: Tunable white-light emission and highly sensitive detection of CrO42-, Cr2O72-, MnO4- in water

A series of isostructural lanthanide coordination polymers (Ln-CPs), [Ln(Hbptc)(H₂O)₄]·H₂O [Ln = Er (1), Pr (2), Dy (3), Sm (4), Gd (5), Nd (6) and Tb(7); H₄bptc = 2,3,3',4'-biphenyl tetracarboxylic acid] have been isolated based on an unsymmetrical tetracarboxylic acid. Single-crystal X-ray diffraction analysis reveals that all CPs featured a two dimensional (2D) layer with (6, 6, 6)-connected 6³ topology. Luminescent spectra demonstrate that CPs 1-7 exhibit impressive UV-visible luminescence in the solid state at room temperature. More significantly, a single-component white-light material with International Commission on Illumination (CIE) coordinates of (0.335, 0.334) for 4 (Sm-CP), very closing to the pure white-light of (0.333, 0.333) was obtained by finely tuning of the excitation wavelength. In addition, the luminescent detection for anions of 7 is investigated. Fluorescence measurements show that 7 can detect oxoanion pollutants Cr₂O₇^2-, CrO₄^2-, and MnO₄^- anions in aqueous solutions with high selectivity and sensitivity, which suggests that the Tb-CP is a promising functional luminescence probe for toxic oxoanions. The possible mechanisms of the quenching effect were also discussed in detail.

Development of a New Kinetic Spectrophotometric Method for the Determination of Chromium with an Optical Probe

The aim of this work is the development, optimization, and validation of a new spectrophotometric kinetic method for the determination of dissolved chromium species in water samples with the use of the polymethine dye Astra Phloxine FF. The progress of the chemical reaction was simple, effective, and precisely monitored from the start of the reaction using an optical probe. The method is based on the impact of Cr(VI) concentration on the rate of decrease in the Astra Phloxine FF concentration. The experimental data were evaluated using four experimental data analysis methods, namely with the initial rate method, the average rate method, the fixed time method, and the absorption peak volume change method. Under the optimal reaction conditions, the best results were achieved using the method of the average rate constant for evaluating the experimental data. Using this data evaluation method for the determination of Cr(VI), the LoD was found to be 1.87 µg L^-1 and RSD ( n = 6; 0.2 mg L^-1 Cr) 3.59%. The presented work was used for the determination of chromium in model samples-CRM material and tap and waste water-and with the calibration line method and the standard additions method.

Novel selective and sensitive optical chemosensor based on phenylfluorone derivative for detection of Ge(IV) ion in aqueous solution

A water soluble chemosensor for Ge⁴⁺ ion based on fluorone derivative containing 3,4-bis(2-(diethylamino)-2-oxoethoxy)phenyl (R8) has been synthesized. The binding abilities between R8 and 10 equiv. of Na⁺, K⁺, Ca²⁺, Fe²⁺, Cu²⁺, Cd²⁺, Hg²⁺, Pb²⁺, Al³⁺, Cr³⁺, Fe³⁺ and Ge⁴⁺ ions in 1% v/v EtOH-water (tris-buffer pH 7.0) were studied using UV-vis and fluorescence spectrophotometry. When observed by naked-eyes, the color of R8 changed from yellow-orange to pink and the fluorescent color changed from green to non-fluorescence when complexed with Ge⁴⁺ ion. The spectral analysis showed that UV-vis absorption and fluorescence emission intensity of R8 decreased dramatically when Ge⁴⁺ ion was added comparing with other ions. To explain this behavior, the quantum calculation was performed using the hybrid density functional at B3LYP /LanL2DZ level of theory. The calculated orbital energies indicated that the decreasing of UV-vis absorption and the quenching of fluorescence were due to the complexation induced metal to ligand charge transfer. The association constants (K_a) of R8-Ge⁴⁺ complexes calculated from Benesi-Hildebrand equation was 6.21 × 10⁵ M^-1. The UV-vis detection limit for Ge⁴⁺ was 4.40 × 10^-7 M which was three orders of magnitude lower than those of Al³⁺, Cd²⁺, Cu²⁺ and Na⁺ ion.