Lithium Selective Chromogenic Azocrown Ethers

Novel chromogenic crown ethers having an intraannular azo and phenolic hydroxy subunits have been used as complexing reagents for alkali metal cations. The complex formation was studied by visible spectroscopy and formation constants were calculated. The most pronounced spectral changes were observed for lithium ion.     

A New Ultrasensitive Chromogenic Chelating Reagent for use in the Chromatographic Separation and Detection of Metal Ions

JPC – Journal of Planar Chromatography – Modern TLC - The heavy metal ions Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Bi3+, and Ag+ can be visualized as violet, black, green, yellow-green,...     

Novel Chromogenic 21-Membered Azocrown Ether Lithium Selective Reagent

Abstract

Novel chromogenic 21-membered crown ether having an intraannular azo and hydroxy subunits has been used as a complexing reagent for alkali metal cations. The complex formation was detected by visible spectroscopy and formation constants were calculated. The most pronounced spectral changes were observed for lithium ion.     

A Chromogenic Probe for the Selective Recognition of Sarin and Soman Mimic DFP

The synthesis, characterization and sensing features of a novel probe 1 for the selective chromogenic recognition of diisopropylfluorophosphate (DFP), a sarin and soman mimic, in 99:1 (v/v) water/acetonitrile and in the gas phase is reported. Colour modulation is based on the combined reaction of phosphorylation of 1 and fluoride-induced hydrolysis of a silyl ether moiety. As fluoride is a specific reaction product of the reaction between DFP and the −OH group, the probe shows a selective colour modulation in the presence of this chemical. Other nerve agent simulants, certain anions, oxidant species and other organophosphorous compounds were unable to induce colour changes in 1. This is one of the very few examples of a selective detection, in solution and in the gas phase, of a sarin and soman simulant versus other reactive derivatives such as the tabun mimic diethylcyanophosphate (DCNP).     

Copper‐Chelating Azides for Efficient Click Conjugation Reactions in Complex Media

The concept of chelation‐assisted copper catalysis was employed for the development of new azides that display unprecedented reactivity in the copper(I)‐catalyzed azide–alkyne [3+2] cycloaddition (CuAAC) reaction. Azides that bear strong copper‐chelating moieties were synthesized; these functional groups allow the formation of azide copper complexes that react almost instantaneously with alkynes under diluted conditions. Efficient ligation occurred at low concentration and in complex media with only one equivalent of copper, which improves the biocompatibility of the CuAAC reaction. Furthermore, such a click reaction allowed the localization of a bioactive compound inside living cells by fluorescence measurements.     

Sulfonephthalein dyes: Part VII. Chromogenic Reactions of Semi-Glycicethymol Blue

The chromogenic reactions of semi-glycinethymol blue have been studied spectrophotometrically and by complementary tristimulus colorimetry. The separation of the dye from a commercial product of glycinethymol blue is described. The five dissociation constants were determined; the means of the pK_a (H_iI) values for i= 5, 4, 3, etc. are —1.5, 0.3, 1.5, 7.5, and 12.7, respectively. Colour reactions with some metal ions are reported; the reaction with copper(II) is suggested for the determination of the composition of commercial samples of glycinethymol blue.     

N-2-Pyridinylmethyl-N'-arylmethyl-diaminomaleonitriles: New Highly Selective Chromogenic Chemodosimeters for Copper(II)

Copper chemodosimeters: The copper(II)-promoted air oxidation of 1-3 to form 4-6 permits the highly selective colorimetric detection of Cu(2+) ions. The formation of copper(II) complexes of 4-6 proceeds rapidly, and the chemodosimeters 1-3 are viable at physiological pH.     

Selective Reactions with Organoaluminum Compounds

With the aid of selected examples an overview is given of the development trends in highly discriminative reactions using organoaluminum compounds. (1) Isomerization of substituted oxiranes into allyl alcohols has been effected both stereo- and regioselectively by means of a new organoaluminum reagent, diethylaluminum 2,2,6,6-tetramethylpiperidide (DATMP); this reaction which provides a new route for the regiospecific transformation of allyl alcohols into 1,3-dienes. (2) A novel nonenzymic heterolysis of allylic phosphates of terpenoids has been effected by organoaluminum compounds and has enabled development of a new method for the selective synthesis of cyclic terpenes. (3) The reductive condensation of α-haloketones with carbonyl compounds in the presence of diethylaluminum chloride and zinc affords β-hydroxy-carbonyl derivatives in good yields with exclusion of undesired self-condensations products.     

Nanostructured Vanadium Oxide Model Catalysts for Selective Oxidation Reactions

Controlled synthesis based on spectroscopic characterization, structure, and catalytic performance of mesoporous silica SBA‐15‐supported vanadium oxide model catalysts (see TEM image) are reviewed. The effect of water on the structure and dispersion of highly dispersed vanadium oxide is discussed in the light of recent results in multiple in situ spectroscopy.

     

Selective Phase Transfer Reagents (OxP-crowns) for Chromogenic Detection of Nitrates Especially Ammonium Nitrate

Nitrogen and phosphorus-containing ions such as ammonium, nitrates and phosphates are anthropogenic pollutants while ammonium nitrate may be diverted for nefarious purposes in improvised explosive devices. Crown ether-oxoporphyrinogen conjugates ( OxP -crowns) are used to selectively detect nitrates, especially their ion pairs with K⁺ and NH₄⁺, based on ion pair complexation of OxP -crowns under phase transfer conditions. The presence of phosphate and carbonate lead to deprotonation of OxP -crowns. OxP-1N18C6 is capable of extracting ion pairs with nitrate from aqueous phase leading to a selective chromogenic response. Deprotonation of the OxP moiety leads to [ OxP ⁻] -1N18C6 [K⁺] and is promoted by crown ether selective cation binding coupled with hydration of basic oxoanions, which are constrained to remain in the aqueous phase. This work illustrates the utility of molecular design to exploit partitioning and ion hydration effects establishing the selectivity of the chromogenic response.     

A Selective HIV‐Protease Assay Based on a Chromogenic Amino Acid

(2S,3S)‐2‐Amino‐3‐hydroxy‐5‐(4‐nitrophenoxy)pentanoic acid ( 5 ) was prepared stereoselectively as the N‐Fmoc, O‐(tert‐butyl)‐protected derivative 5a in eleven steps from ethyl (E)‐4‐benzyloxypent‐2‐enoate ( 6 ). This protected amino acid was used for the solid‐phase peptide synthesis of oligopeptides, which serve as sequence‐specific chromogenic protease substrates when used in the presence of NaIO₄ and bovine serum albumin. The peptide 1 (KRAVNle 5  EANleNH₂ (Nle=norleucine)) allows detection of HIV‐protease activity spectrophotometrically at 405 nm.     

Chromogenic oxazines for cyanide detection

[reaction: see text] We have designed two heterocyclic compounds for the colorimetric detection of cyanide. The skeleton of both molecules fuses a benzooxazine ring to an indoline fragment and can be assembled efficiently in three synthetic steps starting from commercial precursors. The two compounds differ in the nature of the substituent on the carbon atom at the junction of the fused heterocycles, which can be either a methyl or a phenyl group. In the presence of cyanide, both molecules are converted quantitatively into cyanoamines with the concomitant appearance of an intense band in the visible region of the absorption spectrum. The developing absorption is a result of the opening of the benzooxazine ring with the formation of a 4-nitrophenylazophenolate chromophore. Nuclear magnetic resonance spectroscopy and X-ray crystallographic analyses demonstrate that the covalent attachment of a cyanide anion to the indoline fragment is responsible for these transformations. The chromogenic process is particularly fast for the methyl-substituted oxazine and can be exploited to detect micromolar concentrations of cyanide in water. Furthermore, the colorimetric response of this compound to cyanide does not suffer the interference of the halide anions, which instead are known to complicate the detection of cyanide in conventional sensing protocols. Thus, our mechanism and compounds for the colorimetric identification of cyanide can lead to the development of practical strategies for the convenient determination of this toxic anion in aqueous environments.     

Radiation Chemical Studies of Protein Reactions: Effect of Chelating Agents on Optical Rotation

Abstract

1,2-Diamine and 1,2-dihydroxy derivatives such as ethylene-diamine, ethylenediaminetetraacetic acid and propylene glycol were found to protect against changes in the internal relationships of the atoms in the protein molecule from radiation damage. The optical rotation behavior closely resembles that found with amino acid as shown by a similar dependence on the concentration.     

Determination of Chelating Properties of Detergent Builders with the Calcium Selective Ion Electrode

Abstract

A liquid membrane calcium selective ion electrode was used to measure the free calcium content in equilibrium with calcium chelates. The chelating value, chelating curves, formation constants and equivalent weights of several detergent builders were calculated from these measurements.     

Carboxy Group as a Remote and Selective Chelating Group for C−H Activation of Arenes

The first example of carboxy group assisted, remote‐selective C(sp²)?H activation with a Pd^II catalyst has been developed and proceeds through a possible κ² coordination of the carboxy group, thus suppressing the ortho‐C?H activation through κ¹ coordination. Besides meta‐C?H olefination, direct meta‐arylation of hydrocinnamic acid derivatives with low‐cost aryl iodides has been achieved for the first time. These findings may motivate the exploration of novel reactivities of the carboxy assisted C?H activation reactions with intriguing selectivities.     

Well-Defined,Versatile and Recyclable Half-Sandwich Nickelacarborane Catalyst for Selective Carbene-Transfer Reactions

Catalytic carbene-transfer reactions constitute a class of highly useful transformations in organic synthesis. Although catalysts based on a range of transition-metals have been reported, the readily accessible nickel(II)-based complexes have been rarely used. Herein, an air-stable nickel(II)-carborane complex is reported as a well-defined, versatile and recyclable catalyst for selective carbene transfer reactions with low catalyst loading under mild conditions. This catalyst is effective for several types of reactions including diastereoselective cyclopropanation, epoxidation, selective X−H insertions (X = C, N, O, S, Si), particularly for the unprotected substrates. This represents a rare example of carborane ligands in base metal catalysis.