Sharp Color Change Research Articles

Indole-based distinctive chemosensors for ‘naked-eye’ detection of CN and HSO4−, associated with hydrogen-bonded complex and their DFT study

AbstractColorimetric detection of anions (HSO4− and CN−) was achieved via analyte triggered colour changing of the dipodal and tripodal sensors in CH3CN–H2O (1:1). The sensors exhibited very sharp visual colour changes and fluorescence quenching–enhancing effect upon addition of the HSO4− and CN−. The large downfield shift of the NH proton signals in 1H-NMR complexation studies and quantum chemical DFT calculations proved the formation of hydrogen-bonded complexes where no proton transfer mechanism was found.

Highly sensitive colorimetric and fluorometric anion sensors based on mono and di-calix[4]pyrrole substituted diketopyrrolopyrroles

Four novel deeply coloured and highly fluorescent anion sensors have been developed by coupling calix[4]pyrrole with two different diketopyrrolopyrroles. The sensors showed both colorimetric and fluorometric sensitization by selective anions. Complexation properties of the receptors with anions like halides, acetate, phosphate, sulphate, hydrogen sulphate, perchlorate and cyanide were investigated by UV–vis spectroscopy and fluorescence spectroscopy. Sharp visual colour changes as well as complete fluorescence quenching was observed in the presence of selective anions like fluoride, acetate, phosphate and cyanide. Visual detection of sensing properties was achievable up to anion concentration of 1.15ppm for detection in visible light and 0.025ppm under UV light. One of the sensor, namely S1, showed a dramatic colour change in the presence of CN− ion. Furthermore, a cheap and highly efficient procedure for bulk scale synthesis of monoiodo-octamethylcalix[4]pyrrole, which is one of the main building blocks for the design of calix[4]pyrrole based sensors has been developed.

Is colour change a good measure of a water penetration front?

GARField nuclear magnetic resonance (NMR) profiling is used to demonstrate that the sharp colour change boundary commonly used to locate the water front in cement and concrete capillary absorption tests is a poor indicator of the true depth of water penetration. Across a range of mortars and concretes, NMR invariably shows a smooth and often near-zero gradient in the degree of saturation at this boundary. Any sharp front that does exist, as might arise from a strong dependence of the effective diffusivity on concentration and a multi-modal pore size distribution on the nanoscale, is always far beyond the colour change line.

GREEN CHEMISTRY: STUDY OF ACID-BASE INDICATOR PROPERTY OF GOLDEN BEET ROOT

In acid- base titrations, indicators are used to show a sharp color changes at interval of pH.Natural pigments in plants are highly colored substances and may show color changes withvariation of pH. An attempt has been made to investigate the indicator activity of root extract of golden beet root and to replace the synthetic indicators as they have certain disadvantages like chemical pollution, availability problems and high cost. A study has been done to investigate the indicator activity of aqueous extract of root pigments and compared with that of already existing synthetic indicators. Pigments were extracted using hot water and a definite volume was added which gave accurate and reliable results for all the four different types of neutralization titrations - strong acid against strong base, strong acid against a weak base, weak acid against strong base and weak acid against weak base. The work proved to be acceptable in introducing root pigments as a substitute to the synthetic acid-base indicators.

Stimuli-Responsive Matrix-Assisted Colorimetric Water Indicator of Polydiacetylene Nanofibers.

An alternative signal transduction mechanism of polydiacetylene (PDA) sensors is devised by combining stimuli-responsive polymer hydrogel as a matrix and PDA sensory materials as a signal-generating component. We hypothesized that volumetric expansion of the polymer hydrogel matrix by means of external stimuli can impose stress on the imbedded PDA materials, generating a sensory signal. PDA assembly as a sensory component was ionically linked with the alginate hydrogel in order to transfer the volumetric expansion force of alginate hydrogel efficiently to the sensory PDA molecules. Under the same swelling ratio of alginate hydrogel, alginate gel having embedded 1-dimensional thin PDA nanofibers (∼20 nm diameter) presented a sharp color change while 0-dimensional PDA liposome did not give any sensory signal when it was integrated in alginate gel. The results implied that dimensionality is an important design factor to realize stimuli-responsive matrix-driven colorimetric PDA sensory systems; more effective contact points between 1-dimensional PDA nanofibers and the alginate matrix much more effectively transfer the external stress exerted by the volumetric expansion force, and thin PDA nanofibers respond more sensitively to the stress.

Asymmetric Donor–π‐Acceptor‐Type Benzo‐Fused Aza‐BODIPYs: Facile Synthesis and Colorimetric Properties

AbstractNovel aza‐diisoindolylmethene and their BF2‐chelating complexes (benzo‐fused aza‐BODIPYs) were synthesized on a large scale and in a facile manner from phthalonitrile in tBuOK‐DMF solution. The unique asymmetric donor–π‐acceptor structure facilitates BN bond detachment in the presence of trifluoroacetic acid (TFA) in dichloromethane, resulting in sharp color change from red to colorless, with over 250 nm hypsochromic shift in the absorption maximum. This colorimetric process can be reversed by adding a very small amount of proton‐accepting solvents or compounds. A 1H and 11B NMR spectroscopy study and also density functional theory (DFT) calculations suggest that TFA‐induced BN bond cleavage may disrupt the whole π‐conjugation of the BODIPY molecule, resulting in significant colorimetric behavior.

Asymmetric Donor-π-Acceptor-Type Benzo-Fused Aza-BODIPYs: Facile Synthesis and Colorimetric Properties.

Novel aza-diisoindolylmethene and their BF2 -chelating complexes (benzo-fused aza-BODIPYs) were synthesized on a large scale and in a facile manner from phthalonitrile in tBuOK-DMF solution. The unique asymmetric donor-π-acceptor structure facilitates B-N bond detachment in the presence of trifluoroacetic acid (TFA) in dichloromethane, resulting in sharp color change from red to colorless, with over 250 nm hypsochromic shift in the absorption maximum. This colorimetric process can be reversed by adding a very small amount of proton-accepting solvents or compounds. A (1) H and (11) B NMR spectroscopy study and also density functional theory (DFT) calculations suggest that TFA-induced B-N bond cleavage may disrupt the whole π-conjugation of the BODIPY molecule, resulting in significant colorimetric behavior.

Synthesis, Characterization, and Theoretical Investigation of Two-Coordinate Palladium(0) and Platinum(0) Complexes Utilizing π-Accepting Carbenes.

An elegant general synthesis route for the preparation of two coordinate palladium(0) and platinum(0) complexes was developed by reacting commercially available tetrakis(triphenylphosphine)palladium/platinum with π-accepting cyclic alkyl(amino) carbenes (cAACs). The complexes are characterized by NMR spectroscopy, mass spectrometry, and single-crystal X-ray diffraction. The palladium complexes exhibit sharp color changes (crystallochromism) from dark maroon to bright green if the C-Pd-C bond angle is sharpened by approximately 6°, which is chemically feasible by elimination of one lattice THF solvent molecule. The analogous dark orange-colored platinum complexes are more rigid and thus do not show this phenomenon. Additionally, [(cAAC)2 Pd/Pt] complexes can be quasi-reversibly oxidized to their corresponding [(cAAC)2 Pd/Pt](+) cations, as evidenced by cyclic voltammetry measurements. The bonding and stability are studied by theoretical calculations.

Natural Dyes as Acid-Base Indicators fromBeta vulgaris

In acid-base titrations, indicator are used to show a sharp color changes at end point which are mostly organic dyes. Due to environmental pollution, availability and cost, the search for natural acid-base indicator was started. In the present study the extract of Beta vulgaris was used to replace the synthetic indicators due to the disadvantage of less availability and high cost of synthetic dye. Extract of Beta vulgaris gives sharp and intense color changes as compared to synthetic indicator. The extracts were evaluated by using strong acid-strong base, strong acid-weak base, weak acid-strong base and weak acid-weak base. In all these titrations the extract was found to be very useful and accurate for indicating the neutralization point. Methanolic extract of Beta vulgaris was found to be a very useful, economical, simple and accurate for titration. The proposed herbal indicators can be used as a substitute to synthetic indicators.

Silver nanoparticle based highly selective and sensitive solvatochromatic sensor for colorimetric detection of 1,4-dioxane in aqueous media.

A citrate stabilised silver nanoparticle (Ci-AgNP) based solvatochromic sensor, which functions as a highly selective and sensitive colorimetric probe for 1,4-dioxane in aqueous media is reported. The surfaces of the AgNPs generate reactive oxygen species, which promote the degradation of 1,4-dioxane assembled in the vicinity of the nanoparticle surfaces through charge transfer interactions. During this process, Ag(0) is oxidised to Ag(+) and the yellow colour of the solution turns to colourless. The sensor was used for the estimation of 1,4-dioxane in ground water and also 1,4-dioxane vapour diffused in aqueous media.

Ion pair charge-transfer thiogermanate salts [MV]2Ge4S10·xSol: solvent induced crystal transformation and photocurrent responsive properties

As most of the chalcogenidometalate anions are well-known electron-rich systems, design and preparation of ion pair compounds, by integrating an organic acceptor (A) with an inorganic chalcogenidometalate donor (D), are an attractive strategy to obtain new functional materials. We report herein the single-crystal structures and properties of three new ion pair charge-transfer (IPCT) compounds by incorporating thiogermanates with methylviologen (MV(2+), N,N'-dimethyl-4,4'-bipyridinium dication), [MV]2Ge4S10·xSol (Sol = solvent). Sharp and fast solvent-induced color changes and switchable fluorescence emission are observed for the compounds. The weak interactions that relate to the solvent and ions in the structures are likely the key points to modulate the cation-anion charge-transfer. A photocurrent response is observed for the photoelectric system of the IPCT compound upon repetitive switching of light on and off.

Colorimetric detection of Cu2+ and Pb2+ ions using calix[4]arene functionalized gold nanoparticles

Calixarene functionalized gold nanoparticles (CFAuNPs) have been prepared and characterized by spectroscopic and microscopic (TEM) techniques. To use this material as potential colorimetric sensor, the binding property of this new material has been investigated with a large number of metal ions. It exhibited sharp colour change from dark brown to green and blue, detectable by naked-eye, in the presence of Cu2+ and Pb2+ ions, respectively. It has also triggered substantial change in surface plasmon resonance (SPR) band of the functionalized gold nanoparticles, which in case of Pb(II) is due to the inter particle plasmon coupling arising from the metal-induced aggregation of the nanoparticles and for Cu(II), it is because of the formation of AuCu alloy due to anti-galvanic exchange. The size and aggregation of the nanoparticles are confirmed from HRTEM images, elemental analysis and the line profiling for both the metal ions have been done by STEM-EDX analysis.

Colorimetric detection of mercury(II) in aqueous media with high selectivity using calixarene functionalized gold nanoparticles

A facile strategy for the preparation of water soluble gold nanoparticles functionalized by dithiocarbamate derivative of calixarene and application of this material as colorimetric sensor for metal ions in aqueous media is reported. This material selectively detects Hg2+ in aqueous media in presence of a large number of metal ions with a sharp colour change, detectable by naked eyes. No significant interference from other metal ions used in this study is noted. The stability of the functionalized nanoparticles in water is examined with variation in pH and found that it is highly stable in the pH range of 4.4–7.8. At the optimum conditions, it exhibited a dynamic response for Hg2+ in the concentration range of 0.2μM to 100μM of metal ion with the detection limit of 40ppb. Detail spectroscopic and microscopic studies revealed that the visual colour change from red to violet and the shifting of SPR band is due to assembly of gold nanoparticles into arrays through the bare surfaces by dipole–dipole interaction. The bare surfaces of gold nanoparticles were generated by the displacement of calixarene derivative from the surface of the functionalized gold nanoparticles due to strong complexation between Hg2+ and calixarene derivative. The HRTEM images, UV–vis spectral study and results of DLS measurements are consistent to support this conclusion. For practical application, this new material is successfully tested for detection of Hg2+ in drinking water as real sample.

Pterin-based highly selective, ratiometric, and sensitive ‘naked-eye’ sensor for acetate

The design and synthesis of a new pterin-based ratiometric and sensitive ‘naked-eye’ sensor R for highly selective recognition of acetate are reported. The acidic lactam NH and the NH of 2-N-pivaloyl group of receptor R along with 2,4-dinitrophenyl hydrazone group having the other acidic NH moiety lead to the binding of acetate anion in a 1:2 ratio by change of spectroscopic behavior on complexation (UV–vis and 1H NMR studies) which is also proven by Job plot. The sharp color change from light yellow to violet promises R to be a useful chromogenic ratiometric sensor for acetate amongst other common anions.

Use of Argyreia cuneata Flower Extract as a Natural Indicator in Acid Base Titration

Indicators help to determine the equivalence point in acid – base titrations (neutralization titrations). They show sharp color change with respect to change in pH. Commonly used indicators for neutralization titrations are synthetic in nature. They are found to posses hazardous effects in human body. The highly colored pigments obtained from plants are found to exhibit color changes with change in pH. In the present work, acid base titration has been performed by using natural indicators. The natural indicator is prepared from the ethanolic extract of Argyreia cuneata. Two acids (H2SO4 and CH3COOH) and two bases (KOH and NH4OH) were selected for acid base titration. 0.1N, 0.5N, 1N and 5N strength of these acids and bases were prepared. The end points obtained by the flower extract coincide with the end points obtained by standard indicators. Therefore, use of ethanolic extract of flower as an indicator is more economical and having the same accuracy of result as that given by synthetic indicator.

Gold nanoparticles for designing of smart colorimetric logic gates operations and scavengers for mercury ions in water

A smart colorimetric AND logic gate based on citrate stabilized gold nanoparticles using DM and H2PO4− as inputs, which operates in aqueous media with low concentration, is reported. A mechanistic study revealed that the catechol groups of DM interact with the surface of the gold nanoparticles and the amino group of DM cross-linked to H2PO4− through hydrogen bonds leading to the aggregation of AuNPs showing a distinct colour change, which is supported by UV-vis study and TEM images. The purple coloured aggregated gold nanoparticles with DM and H2PO4− exhibit sharp colour change in the presence of Hg2+. On the basis of this observation, a nonimplication logic gate system is demonstrated with Hg2+ and (DM + H2PO4−) as the inputs. In this system, the Hg2+ ion is reduced to form Au–Hg amalgam with the aid of citrate anions as the reducing agent and exhibited a colour change from purple to reddish-brown, which is supported by XRD data, TEM images and UV-visible study. An AND logic gate thus developed was used for the quantitative analysis of Hg2+ in lake water at low concentration as a test sample, satisfactory results were obtained.

Effects of topography and land use on soil characteristics along the toposequence of Ele watershed in southern Ethiopia

Information on soil properties and distribution is critical for making decisions with regard to crop production and mitigating land degradations. A reasonable way of deriving the information is using proxy environmental characteristics that have demonstrated relationships with soil properties. A field study was conducted to evaluate the relationship between topography, land use and soil properties. Three slope classes were considered and a total of three pedons, one on each slope class, were opened and described at the Ele watershed in southern Ethiopia. Soil samples collected from identified horizons of each pedon were analyzed for physicochemical properties. Additionally, random soil samples were collected from adjacent cultivated, grassland and forest soils; and three composites were made for each land use type within the three slope classes. All three pedons showed remarkable variability in physical, chemical, and morphological characteristics of the soils. The field as well as laboratory textural class determinations revealed the dominance of clay fraction in the soils. The existence of buried horizons with abrupt textural as well as sharp changes in color both in dry and in moist showed the occurrence of lithological discontinuity. Both soil pH and EC were low for steep slope and highest for the middle slope class, whereas the organic carbon (OC), total N (TN) and available P decreased down the slope. Gentle and moderate slope classes had the highest exchangeable bases, while the steep slope had the lowest owing to the removal and deposition of exchangeable bases by water erosion. The chemical properties of the soils were also significantly affected by land use. The highest values of both pH and EC were obtained in cultivated land, whereas grassland had relatively more OC, exchangeable Ca, Mg, K and available micronutrients than the other land use types.

Highly stable water dispersible calix[4]pyrrole octa-hydrazide protected gold nanoparticles as colorimetric and fluorometric chemosensors for selective signaling of Co(II) ions

Water dispersible stable gold nanoparticles (AuNps) have been synthesized by using calix[4]pyrrole octa-hydrazide (CPOH) as a reducing as well as stabilizing agent. CPOH-AuNps have been characterized by surface plasmon resonance, particle size analyzer and transmission electron microscopy. CPOH-AuNps are water dispersible, highly stable for more than 150days at neutral pH with a size of less than 10nm and zeta potential of 15±2MeV. Ion sensing property of CPOH-AuNps has been investigated for various metal ions Pb(II), Cd(II), Mn(II), Fe(III), Ni(II), Zn(II), Hg(II), Co(II) and Cu(II) by colorimetry and spectrofluorimetry. Among all the metal ions investigated, only Co(II) ions gives sharp colour change from ruby red to blue and is easily detectable by naked-eye. CPOH-AuNps being fluorescent in nature also shows great sensitivity and selectivity for Co(II) ions. Co(II) ions can be selectively detected at very low concentration level of 1nM in a facile way of fluorescence quenching.

Evaluation Studies of Flower Extract of Butea monosperma as Herbal Indicator

The stability study of flower extract of Butea monosperma (FEBM) was evaluated by studying the effect of different pH (1 to 14) on the color of FEBM as well as comparing the absorbance pattern. The FEBM was also evaluated for its indicator property using titrimetric analyses involving various acid-base titrations. The results showed good stability of FEBM at acidic and neutral pH but not in alkaline pH. The titrimetric analysis with FEBM showed sharp and intense color change at the end point which may be due to the presence of flavonoids, and it can be used as an alternative to routine synthetic indicators.

Boerhavia Erecta Linn. Stem Bark Extract A Natural Acid-Base Indicator

Synthetic indicators have been tried as indicators in acid-base titrations but due to environmental pollution, availability and cost, natural compounds are best alternate. Natural pigments in plants are highly colored substances and may show sharp color changes with variation in pH .An attempt has been made to extract natural indicator by maceration from stem bark of Boerhavia erecta Linn. The equivalence points obtained by the BEI strong acid-strong base, strong acid-weak base, weak acid-strong base and weak acid weak base titrations were coincident with the equivalence points obtained by synthetic indicators. Thus natural indicator was found to be eco-friendly, economical, simple and accurate for all acid-base titrations. Phytochemical analysis and spectral studies confirmed presence of anthocyanins and flavonoids in BEI responsible for accurate and sharp colour change at equivalence point. The present study reports the use of this natural indicator in different acid base titrations.