Sharp Color Change Research Articles

Study on Cyclometalated Palladium‐azo Complexes as Colorimetric Probes for Hazardous Gas in Water

AbstractA synthesized cyclometalated palladium‐azo complex was explored as a multifunctional probe for visual detection of SO2, H2S and NH3 in water. In acidic aqueous environment, the sensing solution underwent a sharp color change from poor violet to deep blue when titrated with Na2SO3 standard solution. But the color changed from poor violet to bright yellow when titrated with Na2S standard solution. In basic environment, the sensing solution rapidly changed to magenta when titrated by NH4Cl‐NH3 standard buffer solution at high concentration. However, the color of sensing solution changed to blue when titrated by NH4Cl‐NH3 standard buffer solution at low concentration although the pH was kept constant during the titration. Different species of these hazardous gases at environmentally relevant concentration levels were differentiated by independent optical signal outputs, and the interference from other inorganic ions commonly existing in water was very small.

Synthesis of hydrophilic Fischer carbene complexes as organometallic marker and PEGylating agent for proteins

Syntheses of Fischer carbene complexes with various hydrophilic tethers ( 4, 6a, 6b, 6c, 8a, 8b, 14a, 14b, 15 and 19) are described. The water-soluble carbene complex, 14b, was used to label and pegylate bovine serum albumin (BSA) without affecting its conformation. The red complex, 19, underwent a sharp color change to yellow on reaction with BSA, a feature that is potentially useful for developing assay methods.

Assembling an ignimbrite: Compositionally defined eruptive packages in the 1912 Valley of Ten Thousand Smokes ignimbrite, Alaska

The 1912 Valley of Ten Thousand Smokes (VTTS) ignimbrite was constructed from 9 compositionally distinct, sequentially emplaced packages, each with distinct proportions of rhyolite (R), dacite (D), and andesite (A) pumices that permit us to map package boundaries and flow paths from vent to distal extents. Changing pumice proportions and interbedding relationships link ignimbrite formation to coeval fall deposition during the first ∼16 h (Episode I) of the eruption. Pumice compositional proportions in the ignimbrite were estimated by counts on ≥100 lapilli at multiple levels in vertical sections wherever accessible and more widely over most of the ignimbrite surface in the VTTS. The initial, 100% rhyolite ignimbrite package (equivalent to regional fall Layer A and occupying ∼3.5 h) was followed by packages with increasing proportions of andesite, then dacite, emplaced over ∼12.5 h and equivalent to regional fall Layers B 1 -B 3 . Coeval fall deposits are locally intercalated with the ignimbrite and show parallel changes in R:D (rhyolite:dacite) proportions, but lack significant amounts of andesite. Andesite was thus dominantly a low-fountaining component in the eruption column and is preferentially represented in packages filling the VTTS north of the vent. The most extensive packages (3 and 4) occur in B 1 and early B 2 times where flow mobility and volume were optimized; earlier all-rhyolite flows (Package 1) were highly energetic but less voluminous, while later packages (5-9) were both less voluminous and emplaced at lower velocities. Package boundaries are expressed as one or more of the following: sharp color changes corresponding to compositional variations; persistent finer-grained basal parts of flow units; compaction swales filled by later packages; erosional channels cut by the flows that fill them; lobate accumulations of one package; and (mostly south of the vent) intercalated fall deposit layers. Clear flow-unit boundaries are best developed between ignimbrite of non-successive packages, indicating time breaks of tens of minutes to hours. Less well-defined stratification may represent rapidly emplaced successive flow units but often changes over short distances and indicates variations in localized depositional conditions.

A sleeping host awoken by its guest: recognition and sensing of imidazole-containing molecules based on double Cu2+ translocation inside a polyaza macrocycle.

pH-driven double Cu2+ ion translocation occurs inside an heteroditopic macrocycle. The movement opens and closes the system allowing or preventing it to function as receptor for bidentate anions. When imidazole is added to a solution buffered at an appropriate pH value, opening of the system and substrate binding can be induced by the substrate itself, which results in a sharp color change (see picture).

A chromogenic penta-aza scorpionand for nickel(II) and copper(II) ions

The nickel(II) and copper(II) complexes of a new scorpionand in which the side chain has been functionalized with the powerful chromophore 4-amino-7-nitro-benzo-2-oxa-1,3-diazole have been prepared. The pendant arm of the new ligand undergoes pH-dependent complexation/decomplexation to the metal centre, with simultaneous deprotonation of the aniline nitrogen atom of the pendant arm, thus inducing drastic modifications of the spectral features of the chromophore and a sharp colour change. The p K a values observed for both complexes change according to the metal promoting the deprotonation, being lower for the Ni complex than for the Cu species, because of the different coordination geometries adopted by the two ions.

Natural Dyes as Neutralization Indicators — A Short Review

AbstractFor Abstract see ChemInform Abstract in Full Text.

A new visualization technique for the study of solute dispersion in model porous media

A new technique of high resolution is developed to perform visualization experiments of the hydrodynamic dispersion of pollutants in transparent glass-etched pore networks, which are regarded as representative models of natural porous media and single fractures. The technique is based on the continuous detection of the sharp colour changes caused on an aqueous solution, as the solute concentration varies, because of the strong sensitivity of a system of indicators to pH. Image analysis is used for the transformation of the spatial distribution of colour intensity to solute concentration profiles. Unidirectional miscible displacement and single source-solute transport experiments are used to identify and quantify the transient and steady-state solute dispersion regimes in a pore network, and estimate the longitudinal and transverse dispersion coefficients as functions of Peclet number. The dispersion coefficients are estimated by fitting the spatial/temporal distribution of solute concentration over various regions of the network to analytic solutions of the convection–dispersion equation, obtained by using a flux-type boundary condition at solute sources. The experimental technique and the method of analysis of its results may be proved very useful for model validation, sensitivity analysis of dispersion coefficients with respect to pore space parameters, and identification of liquid pollutant dispersion regimes in underground aquifers.

Thermal studies of copper(II) squarate complexes of diamines in the solid state

CuL2C4O4 [L=ethane-1,2-diamine (en)], CuL2C4O4⋅2H2O [L=N-methylethane-1,2-diamine (meen), N-ethylethane-1,2-diamine (eten),N-propylethane-1,2-diamine (pren), N-methyl-N’-ethylethane- 1,2-diamine (meeten) andpropane-1,2-diamine (pn)], CuL2C4O4⋅0.5H2O [L=N,N’-dimethylethane- 1,2-diamine (dmeen)], CuL2C4O4⋅4H2O [L=propane-1,2-diamine (pn)]and CuL2C4O4⋅H2O[L=2-methylpropane-1,2-diamine (ibn)] have been synthesized by the addition of respective diamine to finely powdered CuC4O4⋅2H2O and their thermal studies have been carried out in the solid state. Cu(en)2C4O4 upon heating loses one molecule of diamine with shar pcolour change yielding Cu(en)C4O4 which upon further heating transforms to unidentified products. All aquated-bis-diamine species [CuL2C4O4⋅2H2O, CuL2C4O4⋅0.5H2O and CuL2C4O4⋅H2O] upon heating undergo deaquation–anation reaction in the solid state showing thermochromism and transform to CuL2C4O4, which revert on exposure to humid atmosphere (RH ∼90%). All the squarato bis-diamine species, CuL2C4O4, on further heating transform to unidentified products through the formation of CuLC4O4 as intermediates. The mono diamine species, have been isolated pyrolytically in the solid state and can be stored in a desiccator as well as in open atmosphere. They are proposed to be polymeric.

Thermal studies on solid complexes of saccharin with divalent transition metal ions

The thermal decompositions of Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes of saccharin were studied in static air atmosphere. All of the complexes contain four molecules of coordination water and two molecules of crystallization water. The water molecules were removed in a single stage, except from the Zn(II) complex, which exhibited two endothermic effects. The dehydration process was usually accompanied by a sharp colour change. The anhydrous complexes exhibited a phase transition and the decomposition or combustion of saccharin occurred in the second and subsequent stages. The final decomposition products were identified by XRPD as the respective metal oxides. The kinetic parameters, such as the order of reaction and energy of activation for the dehydration stage, were evaluated and the thermal stabilities of the complexes are discussed.

Thermally induced electron-transfer reactions of heterometallic dinuclear complexes in the solid state

Thermally induced electron-transfer reactions of dinuclear complexes of the composition [L2MnII(H2O)2][L2MnII(CN)2FeIII(CN)4]2·6H2O, where L = 1,10-phenanthroline 1 or 2,2′-bipyridyl 2, have been carried out. Both the complexes have been synthesized and characterized by elemental analysis, IR, electronic, EPR, Mössbauer spectra and thermal analysis. Heating in an inert atmosphere at 210°C for complex 1 and at 190°C for complex 2 caused conversion to [MnII(Phen)2(H2O)2][(Phen)2MnIII(CN)2 FeII(CN)4]2 la and [MnII(bipy)2(H2O)2][(bipy)2MnII(CN)2FeII(CN)4]2 2a with a sharp colour change from yellow to reddish brown in each case. Thermal investigation of complexes 1 and 2 under non-isothermal conditions in a dynamic inert atmosphere showed endothermic peaks in DTA curves at 210 and 190°C, respectively, whereas no mass loss in the corresponding TGA curves was observed. The rate constant of the electron transfer has been evaluated from DTA curves at different temperatures. Activation energy and enthalpy change were also evaluated. This process is irreversible as no peak appeared in the DTA curve on cooling. X-ray powder diffraction patterns were recorded and showed that 1, la and 2, 2a are almost identical. We were not able to synthesize single crystals of the complexes 1 and 1a, 2 and 2a due to the lack of solubility in most of the solvents.

Thermally induced electron transfer reaction of heterometallic dinuclear complex in the solid state

Solid state thermal investigation and electron transfer reaction of a dinuclear complex [(phen) 2Mn II(CN) 2Fe III(CN) 3(NH 3)]·3H 2O ( 1) has been carried out. Compound 1 was synthesized and characterized by elemental analysis, IR spectra, electronic spectra, magnetic moment and thermal analysis. Heating in an inert atmosphere at 180°C compound ( 1) converted to [(phen) 2Mn II(CN) 2Fe II(CN) 3(NH 3)] ( 3) with a sharp colour change from light yellow to reddish brown. This reaction was also observed in by DTA an endotherm with no associated mass loss (by TGA) curve was observed. The rate constant of the transformation was evaluated from DTA results at different temperatures. Activation energy and enthalpy change were also evaluated. The reaction process is irreversible X-Ray powder diffraction patterns were recorded for ( 1) and ( 2) which are almost identical. We were unable to synthesize a single crystal of either compound ( 1) or ( 2) for lack of solubility in most of the solvents.

Electrical conductivity of polydiacetylene, poly[5,7-dodecadiyn-1,12-diol-bis(n-butoxy carbonylmethyl urethane)] gel: 1. Sol-gel transition and conduction mechanism

Electrical conductivity, colour change and sol—gel transition behaviour were studied for a polydiacetylene, poly[5,7-dodecadiyn-1,12-diol-bis(n-butoxy carbonylmethyl urethane)] abbreviated as P(4BCMU), in toluene gels. For P(4BCMU)-28 with weight average molecular weight of 280 000, the sol—gel transition temperature was determined to be around 348 K varying slightly depending on the methods employed for the determination. The alternating current (a.c.) and direct current (d.c.) conductivities of P(4BCMU)-28 gels exhibited a broad maximum at ∼336 K. Upon heating the gels, the colour changed from red to yellow at ∼348 K, while upon cooling a sharp colour change was observed at ∼340 K indicating the supercooling of the sol phase. These characteristic temperatures increased with increasing molecular weight. The a.c. and d.c. conductivities were enhanced approximately 20 times by adding a dopant iodine to the gels. We also observed a weak photoconductivity similar to the bulk P(4BCMU). These results suggest that the conduction mechanism of the gels is due predominantly to electronic origins through the gel networks rather than ionic ones in the toluene medium.

Determination of organotrithiocarbonates with o-diacetoxyiodobenzoate and N-chlorosuccinimide in aqueous and non-aqueous media

The determination of organotrithiocarbonates with o-diacetoxyiodobenzoate and N-chlorosuccinimide in aqueous and non-aqueous media using visual and potentiometric methods is described. The visual end-point is indicated by a sharp colour change from straw yellow to deep yellow caused by the first drop of oxidant solution in excess. Potentiometric titrations were performed with antimony or modified calomel reference electrodes and a bright platinum wire as the indicator electrode. The proposed method is simple, rapid, requires the minimum of apparatus and is also applicable to the determination of β-carboxythiols, 1-thioglycerol and carbon disulphide.

A geochemical investigation of reduction haloes developed under turbidites in brown clay

The sediments of the Nares Abyssal Plain contain olive or grey silt/clay turbidites interbedded within brown pelagic clays. Three examples of a pale brown/orange horizon, located immediately under turbidite units, have been investigated. These horizons, which are up to 22 cm thick, have sharp colour changes at their upper and lower boundaries. They are interpreted as reduction haloes within pelagic clay units, developed as a result of the nearcomplete removal of Mn(IV) oxyhydroxides from these regions following the deposition of the overlying turbidites. This has resulted in “bleaching” of the dark brown pelagic sediment. This is believed to be caused by bacterially mediated oxidation of the labile organic carbon of the pelagic surface buried beneath the turbidite by Mn and Fe oxyhydroxides in post-oxic conditions. In addition, a further displacement of Mn(IV) by Fe(II) occurs in this region. As a concomitant of the contemporaneous oxidation of the organic carbon of the overlying turbidite unit by a progressive oxidation front, much of the Mn(II) remobilised from the halo has been concentrated in the lower reaches of this unit by reprecipitation with oxygen. Clear associations are evident, of Co and Ni with Mn, and of P and As with Fe. Copper and Pb have also been affected, but the controls on these elements are uncertain. The current distributions of the redox sensitive elements are therefore much changed since deposition because of this early diagenetic effect, and exhibit subtle detail of distribution. In contrast, the haloes themselves appear featureless because evidence of bioturbation detail has been largely destroyed by bleaching.

A colorimetric method for the enzymatic analysis of gases: The determination of ethanol and formaldehyde vapors using solid alcohol oxidase

A novel enzymatic approach to the direct determination of ethanol vapors in the gas phase is described. The system is composed of alcohol oxidase, peroxidase, and the color indicator 2,6-dichloroindophenol dispersed on microcrystalline cellulose (avicel). Simple devices are developed for the semiquantitative determination of ethanol in the breath. The devices are optimized to produce a sharp color change at a set time of 1 min for ethanol concentrations above the legal limit for driving (kinetic method) or a stable final color after 5 min (equilibrium method). Such color changes are detectable by simple visual observation. Using TLC plastic sheets and a transmittance densitometer, the system can also be used as a quantitative method for the determination of ethanol or formaldehyde vapors. Dehydrated enzymes may be useful for the analysis of hazardous gases.

An evaluation of the use of a pH indicator for the detection of β-lactamase in enzyme immunoassay

The use of a mixed pH indicator containing bromocresol purple and bromothymol blue was evaluated for the detection of β-lactamase activity in enzyme immunoassays (EIA) based on this enzyme. The EIA was found to correlate well with a bioassay for antibodies to tetanus toxoid in sheep sera. Results could be read spectrophotometrically at 450 nm or visually as a colour change from dark blue to yellow. The mixed pH indicator was found to have a number of desirable features including good stability, ease of preparation and a sharp colour change which makes the system suitable for visual determination of titration end points.

EDTA titration of zinc with 1-(2-pyridylazo)-2-naphthol indicator in the presence of a surface-active agent as a solubilization agent

1-(2-Pyridylazo)-2-naphthol (PAN) reacts with zinc in an aqueous solution in the presence of a non-ionic surfactant, Brij 35, to form a soluble complex. The optimum condition for the EDTA titration of zinc with PAN indicator were studied. The formation constants of zinc-PAN chelate, and the acid dissociation constants of PAN in the presence of surface-active agent were investigated at 0.1 mo1/l (NaClO4) ionic strength and at 30 °C. The observed pH range to obtain sharp color change was decreased by pH 0.5 from calculated value by using the formation constants of zinc-EDTA chelate in the aqueous solution. The proposed procedure is as follows :To a sample solution containing of zinc (654 μg), add 20 ml of acetic acid-sodium acetate buffer (pH 6.3), 1 ml of Brij 35(0.1 g/ml) solution and 0.2 ml of PAN(10-3 mol/l), and then titrate with EDTA (10-2 mol/1).

Physicochemical Studies on Some Phenolic Polymer-Transition Metal Complexes in Nonaqueous Media

Abstract The formation of complexes between phenolic oligomer/polymer with some transition metal ions has been studied by conductance and emf measurements. Sharp changes in color, conductance, and potential at definite stoichiometric quantities of ligand and metal ions have been attributed to polymer-metal chelation. Interpretations of the results have been sought in terms of the length of the polymer chain and the nature of the transition metal ions.

Improved nonradioactive method for routine clinical analysis for long- and medium-chain stool lipids.

We describe a simple, practical method for routine clinical determination of long- and medium-chain stool lipids. Stool lipids were extracted into a hot mixture of benzene/ethanol/water (12/59/29, by vol), saponified in 30 min without formation of ethyl esters, and titrated in a clear, one-phase medium to a sharp color change. CVs for the titration were 2, 1, and 1% for 0.05, 0.25, and 0.5 mmol of fatty acids, respectively. Interference of stool short-chain acids other than fatty acids was not statistically significant. The precision of sampling of stool homogenate was improved by analysis of two aliquots, one from the top and one from the bottom of the suspension. This method of sampling is a practical alternative to the unpleasant homogenization with a blender or to the addition of large quantities of bile salts. The accuracy of the method may be increased, in special cases, by removing potential interferants.

Study of the development of mass transport paths via an electrochemical flow visualization technique

AbstractMass transport patterns in natural convection generated in non‐flow cells at horizontal electrodes have been studied by an electrochemical visualization technique. Sharp colour changes in the thymbol‐blue indicator during electrolysis, due to local pH‐variations occurring in the cathodic boundary layer allow direct tracing of the propagation of flow filaments into the electrolyte bulk. The results provide direct evidence for the enhancing effect of magnetic fields on electrolytic mass transport rates and for the existence of horizontal velocity components of appreciable size at the convective surfaces.