Induced Color Change Research Articles

Effect of the incorporation of antimicrobial/antioxidant proteins on the properties of potato starch films

Glycerol plasticized potato starch films containing bioactive proteins (lactoferrin (LF) and/or lysozyme (LZ), at 0.1 and 0.2 ratio with respect to starch) were obtained by casting method and characterized as to their microstructural, thermal and physical (water content, mechanical, water and oxygen barrier, optical) properties. The bioactive properties, named antioxidant and antimicrobial, of the proteins and the films were also characterized. The incorporation of proteins affected the structural and physical properties of potato starch films, while modifying their thermal behavior and increasing the glass transition temperature. Both proteins showed a certain degree of compatibility with starch chains through the bond formations (increase in Tg), while a part is separated and migrates to the film surface. Their incorporation, especially that of lactoferrin, greatly increased the film's brittleness, regardless of the films water content, although they enhance the water vapor and oxygen barrier properties, whatever the age of the film. Protein also reduced the film's transparency and gloss, while lactoferrin induced color changes. The thermal degradation of blend films and isolated proteins occurred at temperatures of over 250°C, which means that blend starch films can be thermoprocessed, according to their thermoplastic properties and following the usual practices of the plastics industries. A synergistic antimicrobial action against Escherichia coli and coliforms was observed when both LZ and LF were simultaneously applied. Both of these exhibited antioxidant capacity.

Investigating the Validity of Microfading Spectroscopy to Predict Photochemically Induced Color Change at Lower Light Levels

Two investigations of the validity of microfading spectroscopy to predict the fading behavior of a diversity of colorants at lower light levels is discussed. The specific research question being: what is the probability that a particular sample being tested with micro-fading will alter significantly differently from the same luxhours light exposure at ambient light intensities? In one experiment two ISO Blue Wool Standards and 15 dyed papers were tested. Accelerated light aging at four illuminance levels stepping from 250 lux to one tenth of the microfading irradiance of 12.5 Mlux was conducted over different time periods using either standard fadometer lightfastness testing apparatus or a microfadometer. Samples received similar lux-hours exposure. In a second experiment a 2.2 Mlux illuminance from a microfadometer was compared to that of a QUV Weatherometer light aging chamber (with UV filtration). Ten different dyes were each faded for 10 minutes using the microfadometer and then for 21 hours using a QUV Weatherometer (with UV filtration). Samples again received the same lux-hours exposure. Results from both experiments illustrate a positive correlation between the compared light sensitivity testing methods, leading to the conclusion that fugitive colorants can be reliably highlighted by the microfading technique. In both experiments a lower value of induced color difference was observed when using microfading compared to standard lightfastness testing apparatus (light box aging) indicating that the quantative prediction of color change from real illumination in lower illuminance conditions is not secure. A short discussion of the origins of error in the technique follows.

Photochromism based on reversible proton transfer

Abstract Photochromism based on reversible proton transfer between metastable-state photoacids and acidochromic dyes is studied. Metastable-state photoacids reversibly produce a large proton concentration under moderate irradiation, protonate the acidochromic dyes and induce color change. This mechanism is different from that of conventional photochromic materials based on photoinduced structural change. The color change and the stimulating wavelength can be controlled by choosing different acidochromic dyes and photoacids. Reversible changes of various colors under sunshine or visible lights of different wavelengths were demonstrated in both solutions and polymer matrix.

Mechanically induced color change based on the chromophores of anthracene and rhodamine 6G

We report herein the mechanically induced luminescent color change of a molecule with two anthracene moieties and a rhodamine 6G unit at both sides of a branched amidoamine spacer. Different emission properties of this compound are due to the π–π overlap of anthracene moieties and the ring-opening reaction of rhodamine 6G.

X-ray induced color change on dense yttria samples obtained by spark plasma sintering

This work focuses on a particular behavior of dense yttria samples fabricated by spark plasma sintering, which display a reddish coloration when subjected to X-ray irradiation. The reddish coloration appears exclusively in sintered material. Optical measurements, X-ray photoelectron spectroscopy and chemical methods have been used to investigate the properties of consolidated yttria. The results obtained suggest that the sintered material exhibits a relatively high concentration of oxygen vacancies. Thermoluminescence measurements indicate that they act as electronic trapping sites. A generalized-order kinetic analysis suggests that at least five different shallow traps can be identified.

A novel phenol-based BODIPY chemosensor for selective detection Fe3+ with colorimetric and fluorometric dual-mode

A novel BODIPY-based colorimetric fluorescent chemosensor (L) with phenol as binding site for Fe3+ has been developed. L is capable of showing high selectivity and sensitivity toward Fe3+ with little interference from Al3+/Cr3+. In presence of Fe3+, L shows a significant blue-shift in the absorption spectra from 571 to 502nm and an increase of the ratio of the absorbance at 502 and 571nm (A502/A571) over 268-fold, which induces color changes from pink to yellow. Upon excitation at 502nm, L upon interaction with Fe3+ ions displays a 40-fold fluorescence enhancement and blue-shifts from 604 to 530nm, resulting in emission color change from orange to green. The binding mode of L with Fe3+ has been investigated by Job's plot, MALDI-TOF-MS and FT-IR experiments. In addition, the cell imaging experiments demonstrate that L can be successfully applied as a bioimaging agent for monitoring Fe3+ in cells.

Influence of opacity on the color stability of a nanocomposite.

The aim of this study was to evaluate the color stability in relation to the opacity of the nanocomposite Filtek Ultimate (3M ESPE), by immersing the specimens in different types of natural and artificial staining solutions. Eighty disks of the shades A1 body (A1B), A1 dentine (A1D), A1 enamel (A1E), and white enamel (WE) (n = 4) of the nanocomposite Filtek Ultimate (3M ESPE) were immersed in staining solutions Orange II, Amaranth, coffee, tea, and artificial saliva. Color coordinates Commission Internationale de l'éclairage (CIE) L*a*b* were collected before and after immersion at 4, 6, 12, 24 h and 7 days. Two-way repeated measurements ANOVA was used in order to assess the effect of immersion time, staining solutions, and materials on CIE L*a*b* parameters, translucency parameter (TP), and color difference (ΔE*). For comparisons between staining solutions and materials, pairwise contrasts adjusted by Bonferroni method were used. The color difference (ΔE*) after 7 days of immersing in staining solution ranged between 0.9 and 15.8. The highest ΔE* after 7 days was obtained for WE, followed by A1E, A1B, and A1D (for all of the immersion solutions, except coffee). There were differences among staining solutions regarding the induced color changes. Coffee induced the most pronounced color differences. However, Orange II, Amaranth, and artificial saliva generated similar behavior in time, for all tested materials. No statistically significant differences were found among various opacities of Filtek Ultimate regarding the ΔE*, TP, ΔL*, and Δb* overtime. In contrast, Δa* was significantly affected by the type of material. The purpose of this study was to predict the color change of different layers of composites, in cases of complex stratified dental restorations.

Photochemical Transformations in Fullerene and Molybdenum Oxide Affect the Stability of Bilayer Organic Solar Cells

Thin films of fullerene C60 and molybdenum oxide (MoO3) are ubiquitously used as the electron acceptor material and hole extraction interfacial layer for the fabrication of organic photovoltaic (OPV) cells. It is well known that light exposure induces color changes in MoO3 (photochromism) and the formation of intermolecular bonds between C60 molecules (photopolymerization). The influence of these photoinduced reactions on the long‐term stability of OPV cells, however, has not previously been studied in detail. Here, a study and discussion of the early (<5 days) aging mechanisms occurring in illuminated ITO/MoO3/organic cyanine dye/C60/Alq3/Ag bilayer solar cells under nitrogen atmosphere is presented. A degradation process at the organic heterojunction is identified and the formation of Mo5+ species during illumination is found to adversely affect cell behavior. For these widely used materials, the results suggest that light processing is a first necessary step before OPV characteristics can be meaningfully rated.

High pressure–low temperature processing of beef: Effects on survival of internalized E. coli O157:H7 and quality characteristics

Abstract High pressure–low temperature (HPLT) processing was investigated to achieve Escherichia coli O157:H7 inactivation in non-intact, whole muscle beef while maintaining acceptable quality characteristics. Beef semitendinosus was internally inoculated with a four strain E. coli O157:H7 cocktail and frozen to − 35 °C, then subjected to 551 MPa for 4 min (HPLT). Compared to frozen, untreated control (F), HPLT reduced microbial population by 1.7 log colony forming units (CFU)/g on selective media and 1.4 log on non-selective media. High pressure without freezing (551 MPa/4 min/3 °C) increased pH and lightness while decreasing redness, cook yield, tenderness, and protein solubility. Aside from a 4% decrease in cook yield, HPLT, had no significant effects on quality parameters. It was demonstrated that HPLT treatment reduces internalized E. coli O157:H7 with minimal effect on quality factors, meaning it may have a potential role in reducing the risk associated with non-intact red meat. Industrial relevance In the current work, high pressure (551 MPa, 4 min) was applied to beef semitendinosus while it was at subfreezing temperatures ( E. coli O157:H7 reductions of 1.4–1.7 log colony forming units (CFU)/g, which, while lower than conventional high pressure processing (HPP), may be sufficient to eliminate O157 populations typical of non-intact, whole muscle beef. Various quality factors, including color, purge losses and cooked tenderness, were unaffected by HPLT, while an equivalent HPP process at nonfreezing temperatures (551 MPa, 3 °C) induced color change (loss of redness), increased cook losses and decreased cooked tenderness compared to the control and HPLT beef. Producers of non-intact, whole muscle (blade tenderized or brine injected) meat, especially those that ship and sell frozen products, may look to HPLT processes to improve food safety.

A rhodamine-based fluorescent probe for Hg2+ and its application for biological visualization

A new visible light excitable fluorescent probe (1) is synthesized by appending a hydroxymethyl-pyridine to rhodamine B hydrazide. The probe displays very specific Hg2+-induced colour change and fluorescent enhancement in the aqueous systems. The “turn-on” response of fluorescence is based on a binding-induced ring-opening process from the spirolactam (nonfluorescent) to acyclic xanthene (fluorescent) in rhodamine B. The coordinating atoms O–N–N–O from the hydroxymethyl-pyridine and rhodamine B hydrazide play dominant role in the formation of a complex with 1:1 stoichiometry of Hg2+ to 1. It exhibits a linear response in the range of 0.1–5μM with the limit of detection (LOD) of 15.7nM (3σ/slope), while the calculated value of the association constant of Hg2+/1 is 0.70×105M−1. Furthermore, confocal microscopy imaging experiment demonstrates the probe 1 can be applied as a fluorescent probe for visualization of Hg2+ in living HeLa cells.

A new simple and reliable Hg2+ detection system based on anti-aggregation of unmodified gold nanoparticles in the presence of O-phenylenediamine

A simple and reliable colorimetric detection system based on anti-aggregation of gold nanoparticles (AuNPs) is proposed for rapid detection of Hg2+ with high selectivity and sensitivity. O-phenylenediamine (OPD) can cause the aggregation of AuNPs due to formation of the strong covalent NHAu bond, and then induce color change of the AuNPs solution from red to blue. However, in the presence of Hg2+, OPD prefers to combine with Hg2+ rather than AuNPs resulting in inhibition of the color change. Based on the anti-aggregation mechanism, Hg2+ can be detected by observing the color change of AuNPs solution containing OPD. After optimization, the selectivity of this Hg2+ detection system by the naked eyes and UV–vis spectra is excellent comparing with other ions. The limit of the detection (LOD) is 0.1μM by the naked eyes and 5.0nM by UV–vis spectroscopy, which is lower than the mercury toxic level (10nM) defined by US Environmental Protection Agency. It's a good linear relationship between A520/A680 and Hg2+ concentration from 0.01μM to 2.0μM, which is used for the quantitative assay of Hg2+. The applicability of our detection system is also verified by analysis of Hg2+ in tap water and lake water.

Synthesis, characterization, structural analysis of metal(II) complexes of N′-[(E)-3-Bromo-5-Chloro-2-hydroxybenzidene]-4-hydroxybenzohydrazide—Multisubstituted Schiff base as a F− and Cu2+ ions selective chemosensor

New colorimetric chemosensor, N′-[(E)-3-Bromo-5-Chloro-2-hydroxybenzidene]-4-hydroxybenzohydrazide, containing OH and NH groups as binding sites have been synthesized and characterized by spectral UV, IR, NMR and ESR. The molecular structure of ligand is determined by X-ray crystallography and it has the monoclinic space group P21/c with cell parameters a=15.1058(6), b=14.3433(6), c=17.5800(8)Å and Z=8. The electronic spectral measurements show that Co2+, Ni2+ and Zn2+ complexes have tetrahedral geometry, while Cu2+ complex has square planar geometry. Magnetic measurements show that Cu2+, Co2+ and Ni2+ complexes have paramagnetic behavior and Zn2+ complex has diamagnetic behavior. Anion binding studies carried out using 1H NMR and UV–visible spectrophotometric titrations revealed that these receptors exhibit selective recognition towards F− over other halide anions. The selectivity for F− among the halides is attributed mainly to the hydrogen-bond interaction of the receptor with F−. Receptor (5×10−5M) shows color change from colorless to yellow in the presence of tetrabutylammonium fluoride (TBAF, 1.5×10−3M). Moreover, F−-induced color changes remain the same even in the presence of large excess of Cl−, Br− and I−. The binding constant is found to be higher towards F− ion and this may be due to presence of OH group, which offers extra binding site. Chromogenic receptor undergoes distinct color changes from colorless to green on gradual addition of Cu2+ can be used as colorimetric probes for spectrophotometric and visual analysis of Cu2+ in the presence of other transition metal ions such as Co2+, Ni2+ and Zn2+.

Geometric Change of a Thiacalix[4]arene Supramolecular Gel with Volatile Gases and Its Chromogenic Detection for Rapid Analysis

A coordination polymer gel that is self-assembled to form a network structure between a thiacalix[4]arene derivative (L) and Co(2+) has been prepared. This gel is capable of selectively changing color in the presence of gases that yield hydrogen chloride upon hydrolysis. The UV-vis absorption spectrum of a coordination polymer gel derived from Co(NO3)2 exhibits an absorption band at 527 nm and is colored red, indicating the formation of an octahedral Co(2+) complex. Treatment with a small amount of volatile gases containing a chlorine atom (VGCl) causes a red shift of ∼150 nm, resulting in a new strong band with a maximum at 670 nm and a color change to blue. In addition, the red color of the filter paper coated with a Co(NO3)2 coordination polymer gel changed to blue upon exposure to VGCl, reflecting a change in the coordination geometry. Red and blue colors of single crystals of Co(2+) complexes were obtained from a basic solution. From X-ray crystallographic analysis, the red Co(2+) complex corresponds to an octahedral structure, while the blue Co(2+) complex reflects the presence of a tetrahedral structure. Thus, the induced color change of Co(2+) gel from red to blue upon exposure to VGCl is due to the coordination geometry. The quantitative concentration of VGCl was calculated by employing the RGB histogram available in a smartphone application.

Environmentally induced colour change during natural degradation of selected polymers

The aim of this study was to examine the simultaneous effect of multiple degradation agents on selected polymer materials in natural environments, and the relative effect of atmospheric pollutants compared to other environmental parameters (heat, humidity and light). A complex exposure experiment was set up to investigate the colour change of 17 different types of polymers (cellulose carboxylate, polyamide, poly(vinyl chloride), polystyrene, polyethylene, polypropylene, polycarbonate, polyurethane, and melamine formaldehyde and phenol formaldehyde resins) in real time in different environmental conditions over a 2-year period at 11 sites across Europe and North Africa, sheltered from UV light and precipitation. Suitable environmental monitoring equipment, such as data loggers and gas samplers, and analytical methods to characterize sample degradation, specifically non-destructive spectrocolorimetry, were used, as colour is one of the most important properties of polymers in art and heritage contexts. A methodology based on multivariate data analysis was used for data interpretation. The results of this study suggested that light and concentration of NO2 are the most important environmental variables leading to colour change in polymer materials, and to a lesser extent the concentration of O3, while other factors such as heat, relative humidity and the concentration of SO2 were less significant. Based on the assessment of the relative contributions of light and traffic-generated pollutants to the natural ageing processes of synthetic polymers, this study enables prioritisation of environmental degradation factors in environmental management of collections and in historic material degradation studies.

A novel BODIPY-based colorimetric and fluorometric dual-mode chemosensor for Hg2+ and Cu2+

A novel BODIPY-based colorimetric fluorescent sensor with bis[2-(phenylseleno)ethyl]amine as binding site (Se-1) for Hg2+ and Cu2+ has been developed. Se-1 shows high selectivity and sensitivity toward Hg2+ and Cu2+ over alkali and transition metal ions. Se-1shows a significant red-shift in the absorption spectra from 525 to 571nm for Hg2+ and 590nm for Cu2+, which induces color changes from pink to purple and blue. Upon excitation at 570nm, Se-1 upon interaction with Hg2+ ions displays a 5-fold fluorescence enhancement with a 2nm blue-shift, while Se-1 with Cu2+ exhibits a 13-fold fluorescence enhancement and red-shifts from 595 to 610nm. The binding mode of Se-1 with Hg2+ or Cu2+ has been investigated by Job's plot, ESI and 1H NMR experiments. The absorption and fluorescence of the Se-1–Hg2+ complex can be reversibly restored to that of the uncomplexed ligand by using EDTA or cysteine, however, the sensing processing of Se-1 in response to Cu2+ ions cannot.

The mechanically induced color change from UV to visible region

The branched amidoamine molecule 1 with different chromophores of a rhodamine B and two pyrenyl moieties at each side was synthesized. The luminescent properties of 1 with the color change from bright blue (UV region) to reddish (visible region) under mechanical stimulus were observed, which was attributed to the emission of pyrene excimer II, with a sandwich packing mode, and the chemical reaction of rhodamine B from a spirolactam to a ring opened amide.

Gold nanoflowers based colorimetric detection of Hg2+ and Pb2+ ions

An optical detection method based on the interaction of gold nanoflowers with Hg2+ and Pb2+ has been described. After interaction, gold nanoflowers change the color from violet to wine red. The nanoflowers are capable of determining Hg2+ and Pb2+ over a dynamic range of 1.0×10−6 and 1.0×10−5M, respectively. The response time of nanoflowers depends on the concentration of ions. The presence of both Hg2+ and Pb2+ ions in the mixture having Au nanoflowers induced color changes of the solution within several seconds even at 1.0×10−6M. Common metal ions were chosen to investigate their interference in Hg2+ and Pb2+ detection, and the concentration of each metal ion studied was 1.0×10−5M. Other metallic ions could not induce color change even at 1.0×10−5M. The feasibility of our method to detect Hg2+ and Pb2+ ions at high concentration in real water samples was verified. Water samples were from our own laboratory and no pretreatment was made. As the particles are stable they can be used for more than 3months without observing any major deviation.

Modeling of vacuum puffing characteristics and color change of liquid honey

Vacuum puffing of liquid honey, mixed with drying ingredients, was carried out in a vacuum dryer in order to model the puffing characteristics and color change of the mix. The drying ingredients i.e., maltodextrin (0.6kg/kg dry honey solid), glycerol monosteareate (0.02kg/kg dry honey solid) and tricalcium phosphate (0.02kg/kg dry honey solid) were mixed with the liquid honey. The puffing characteristics of the honey mix were carried out at various sample thickness (0.002, 0.003 and 0.004m) and vacuum chamber plate temperature (65, 70 and 75°C). Among the five drying models fitted to the puffing data, Page model was observed to predict the moisture content and puffing time data well at all experimental conditions with a relative deviation percentage value of less than 10%. Effective moisture diffusivity varied between 8.875×10−10m2s−1 and 4.132×10−9m2s−1. The effective moisture diffusivity was found to increase with increase in thickness of the honey mix and puffing temperature. Increase in temperature enhanced the temperature induced color change of the honey powder. Increase in thickness increased the total puffing time.

Electrically Induced Color Changes in Polymer‐Stabilized Cholesteric Liquid Crystals

Electrically Induced Color Changes in Polymer‐Stabilized Cholesteric Liquid Crystals

Characterization of Trilayer Antimicrobial Diffusion Films (ADFs) Based on Methylcellulose–Polycaprolactone Composites

Novel trilayer antimicrobial diffusion films (ADFs) were developed for food applications. ADFs were composed of two external layers of polycaprolactone and one internal layer of nanocrystalline cellulose (NCC)-reinforced methylcellulose (MC) matrix. Two antimicrobial mixtures (formulations A and B) were incorporated in the MC layer and compared via the evaluation of film properties. Resulting ADFs were inserted as diffusion devices into vegetable packages, and samples were stored at 4 °C for 14 days. Microbiological diffusion assays in the presence of ADFs were performed on pathogenic bacteria. From this, the study focused on characterizing the structural, physicochemical properties and total phenols (TP) release from ADFs. This TP release was determined by Folin-Ciocalteu's method and by FTIR analysis. Results indicated a controlled release of antimicrobials into the headspace (16.5% for formulation A and 13.4% for formulation B). Good correlations (≥90%) between both methods allowed validating an innovative, accurate, rapid FTIR procedure to quantify the diffusion of TP. SEM micrographs showed fibrillar structure due to NCC and a more compact network due to antimicrobials. Encapsulated antimicrobial formulations induced color changes without affecting visual attributes of films. ADFs containing formulation B exhibited the highest tensile strength (17.3 MPa) over storage.