Colour Change Research Articles

Colorimetric-based detection of enteric bacterial pathogens using chromogens-functionalized iron oxide-gold nanocomposites biosynthesized by Bacillus subtilis

Bio-functionalized nanomaterial has emerged as a promising technique for colorimetric detection of foodborne pathogens to promote food safety and quality. For this study, we evaluated the performance of novel chromogen-functionalized iron oxide-gold nanocomposites (Fe3O4-AuNCs) for colorimetric detection of enteric bacteria. Iron oxide nanoparticles (Fe3O4-NPs) and gold nanoparticles (AuNPs) biosynthesized by Bacillus subtilis (B. subtilis) were monitored and characterized with UV–Vis spectroscopy, Fourier transform infrared (FTIR), scanning electron microscope (SEM), energy dispersive x-ray (EDX) and x-ray diffractometer (XRD). Fe3O4-AuNCs were formed using ethylenediaminetetraacetic acid-capped Fe3O4-NPs and polyethyleneimine (PEI)/polyethylene glycol (PEG)-immobilized AuNPs. Different functionalized-Fe3O4-AuNCs were derived from chromogens such as 2-Nitrophenyl-alpha-D-glucopyranoside (2-NPGP), urea, and 2,3,5,-triphenyl tetrazolium chloride (TTC). The performances of the developed chromogens-functionalized Fe3O4-AuNCs were evaluated on Staphylococcus aureus (S. aureus), Escherichia coli (E. coli), and Salmonella typhimurium (S. typhi). Biosynthesized Fe3O4-NPs and AuNPs revealed 261 and 548 nm absorbance spectra with mean sizes of 72 and 118 nm, respectively. The EDX spectra revealed an increased percentage of elemental gold in Fe3O4-AuNCs linked by PEI than in Fe3O4-AuNCs linked by PEG (75.56%;61.40%). However, a reduced percentage of iron was observed in Fe3O4-AuNCs linked by PEI than in Fe3O4-AuNCs linked by PEG (7.40%;20.00%). The 2-NPGP-functionalized Fe3O4-AuNCs linked by PEI showed a light pale colour with S. aureus and a limit of detection (LOD) of 104 CFU/mL. Urea-functionalized Fe3O4-AuNCs linked by PEI/PEG had no colour change with the test pathogens. TTC-functionalized Fe3O4-AuNCs linked by PEI revealed an intense red colour with S. typhi and E. coli within 2 and 6 h, respectively, and a 108 CFU/mL LOD. This study showed that TTC-functionalized Fe3O4-AuNC linked by PEI is promising for detecting S. typhi and E. coli.

An aqueous, paper, and gel-based method by using eco-friendly synthesised silver nanoparticles towards rapid colorimetric sensing of palladium ion

ABSTRACT In this study, developments were made for silver nanoparticles (AgNPs) synthesis as a colorimetric sensor that is rapid and selective using a bio-reductant of lemongrass extract. The synthesised AgNPs were designed to detect Pd2+ using aqueous, paper, and gel methods. AgNPs were characterised by UV-Vis, FTIR (Fourier Transform Infrared), TEM (Transmission Electron Microscopy), and XRD spectroscopic analysis (X-Ray Diffraction). These AgNPs aqueous colorimetric sensors showed a good selectivity towards Pd metal ions, which was characterised by AgNPs SPR (Surface Plasmon Resonance) tape shifts at 430 nm wavelengths, with the colour change from dark yellow to clear greyish within 5 seconds. The colour changed from yellow to white for AgNPs paper and dark yellow to bright yellow for the gel colorimetric sensor after 5 seconds interaction with Pd2+. The limit of detection for aqueous, paper, and gel were 48.635 ppb, 5 ppm and 5 ppm, respectively. Method validation has been conducted, and these AgNPs sensors were applied for monitoring the Lake Sasak, South Tangerang, water samples and the accuracy and precision of the sensor were tested. This sensor is expected to establish an alternative technique for in situ Pd2+ detection and lake water monitoring.

Quality of Sous Vide-Cooked Pork Loin Stored in Refrigerated Conditions

The sous vide cooking method offers advantage in preparing meat dishes in advance. This study aimed to evaluate the effect of refrigerated storage on the quality attributes of pork loin sous vide cooked under selected, optimised temperature and time parameters. Pork loin was cooked at varying temperatures (57–63 °C) and times (3.5–5.5 h), followed by refrigerated storage for up to 7 days. Analytical methods, including TBARS index for lipid oxidation, instrumental colour measurement, texture analysis, and volatile compound profiling, were used to assess changes in meat quality over time. The results indicated that heat treatment and storage time significantly influenced lipid oxidation, colour, and texture. The highest TBARS values were observed at higher cooking temperatures (61 °C and 63 °C), reflecting increased lipid oxidation. Colour changes were also temperature- and time-dependent, with a decrease in redness (a*) and an increase in lightness (L*) and yellowness (b*). Sensory evaluation revealed that juiciness, aroma intensity, tenderness, and flavour acceptability were strongly correlated with overall acceptability, while physical characteristics like colour and texture had a lesser impact. The study highlights the impact of sous vide cooking parameters on the quality and sensory attributes of pork loin, suggesting that optimised heat treatment can help preserve desirable meat characteristics during refrigerated storage.

The Pleistocene Witch Ground Ice Stream in the central North Sea

AbstractThe North Sea Basin has been covered by ice sheets originating from both the British Isles and Scandinavia at multiple times during the Pleistocene. The Witch Ground Basin (WGB) in the central northern North Sea is a critical location in terms of interpreting Late Pleistocene glacial to glacimarine history of the North Sea since it was the location of the Witch Ground Ice Stream that was active on multiple occasions during the Mid to Late Pleistocene. We map five mega‐scale glacial lineation flowsets corresponding to the changing ice flow direction of the Witch Ground Ice Stream and investigate the sedimentological fingerprint and corresponding subglacial depositional processes of this palaeo‐ice stream. We show that sorted sand layers within a subglacial traction till represent periodic hydraulic jacking and ice–bed decoupling at the base of the Witch Ground Ice Stream. In contrast to previous studies that have described glacitectonites deposited below the most recent grounded ice in the WGB, we present analysis of sediment cores that recovered primarily massive diamictons without any obvious deformation structures. The most recent ice cover in the WGB (~18–16 ka) was thought to have been sourced from a localized ice cap over Orkney and Shetland. The presence of chalk clasts sourced from NW of the WGB described in this study from the stratigraphically youngest till confirms this interpretation. The transition from subglacial to glacimarine deposition, while acoustically well defined (from opaque to laminated acoustic units), appears surprisingly uniform in the recovered sediment cores, but can be differentiated based on a change in colour including mottling and banding, presence of whole intact shells, and the increased number of silt and sand lenses. 14C dating of glacimarine muds indicate high sedimentation rates of between 80 and 260 cm ka−1. The transition from glacimarine to marine deposition is represented by a comparative decrease in sedimentation rate and deposition of Holocene age sandy mud. This study demonstrates a highly dynamic Witch Ground Ice Stream in the northern North Sea during the Late Pleistocene with evolving subglacial hydrology and depositional processes at the ice stream bed that left a distinct geomorphological and sedimentological fingerprint within the WGB.

Weathering Resistance of Wood Following Thermal Modification in Closed Process Under Pressure in Nitrogen

The wood of Scots pine (Pinus sylvestris), silver birch (Betula pendula), and European aspen (Populus tremula) was thermally modified in nitrogen under pressure. Three commercial linseed oil-based coatings without or with brown and grey pigments were applied to the specimens. Specimens were placed outside, and weathering stability was assessed for 3 months. The test measured total surface colour change (ΔE) and colonization by wood dicolouring fungi. Following the test, all uncoated specimens demonstrated poor colour fastness and resistance to fungal growth. All tested coatings were unsuitable for protecting untreated wood from dicolouring fungi. The transparent coating was inefficient since it did not significantly prevent untreated or TM wood from fading, and fungal resistance was increased only for a few TM regimes. The colour fastness of specimens with pigmented coatings was enhanced. Specimens with a grey coating exhibited the lowest ΔE and remained consistent throughout the test period. TM specimens with coloured surfaces exhibited greater fungal resistance. However, not all TM aspen and birch regimes had a sufficient growth mark (rating 0 or 1). TM aspen was less resistant to fungi, whereas TM pine displayed very strong fungal resistance across all TM regimes.

Changes in optical properties of aesthetic paediatric restorative materials following exposure to beverages: In-vitro study.

Optical properties of recent aesthetic restorative materials must maintain an acceptable appearance throughout their functional lifetime. This study aimed to assess the changes in translucency and colour of recent resin-based restorative materials after exposure to beverages commonly consumed by children. An experimental in-vitro study on 48 discs specimens prepared from; Group I: Filtek Z250 XT (Nanohybrid), Group II: Cention N (Alkasite bulkfill), and Group III: SDR flow Plus (Flowable bulkfill). The prepared disc specimens were randomly assigned into 4 subgroups (n = 12) according to the immersion solution: Subgroup A (control): distilled water, B: Coca-Cola, C: chocolate milk, and D: Orange juice. Translucency and colour measurements were done before immersion (baseline) and on day 30 of exposure. Statistical analysis involved Two Way Repeated Measures ANOVA and Kruskal-Wallis test. The statistical analysis revealed that the restorative material, immersion time, and immersion solution had a significant effect on the change in translucency (p < 0.0001*, p < 0.0001*, p = 0.001*, respectively). Regarding colour changes, different immersion solutions had a statistically significant effect on Filtek Z250 XT and Cention N (p < 0.0001*). Distilled water and Coca-Cola were found to have a significant effect on colour change for all restorative materials investigated (p < 0.0001*, p = 0.003*). the optical properties of resin-based restorative materials used in paediatric dentistry were notably affected by prolonged exposure to beverages commonly consumed by children.

Antifungal, toxicological, and colorimetric properties of Origanum vulgare, Moringa oleifera, and Cinnamomum verum essential oils mixture against Egyptian Prince Yusuf Palace deteriorative fungi

The increasing demand for sustainable alternatives to conventional antifungal agents has prompted extensive research into the antifungal properties of plant essential oils (EOs). This study investigates the use of EOs mixture (Origanum vulgare, Moringa oleifera, and Cinnamomum verum) for controlling fungal deterioration in wall paintings at the archaeological Youssef Kamal Palace in Nag Hammadi, Egypt. Fungal isolates were collected from deteriorated wall paintings and identified using phenotypic and genotypic analyses. Aspergillus sp. was found to be the predominant species (50%), followed by Penicillium sp. (16.7%), Fusarium sp. (16.7%), and others. They were genetically identified to be Aspergillus oryzae, Aspergillus niger, Penicillium chrysogenum, Fusarium solani, Alternaria alternata, Botrytis cinerea, and Trichoderma viride. The antifungal activity of three individual oils (oregano, moringa and cinnamon) was evaluated against the most predominant A. niger strain. Out of the three oils, oregano oil showed the strongest antifungal effect with an inhibition zone diameter (IZD) of 4.5 cm followed by moringa (3.5 cm) and cinnamon (3.2 cm). A mixture design approach optimized the EOs combination, with the most effective composition being (44% oregano, 46% moringa, 10% cinnamon), yielding an IZD of 6.5 cm. The optimized EOs mixture demonstrated complete inhibition against all tested fungal strains. The minimal inhibitory concentration tests showed varying efficacies against different fungal strains, with MIC values ranging from 125 to 500 µg/mL. GC-MS analysis identified the major bioactive compounds: carvacrol (83.25%) in oregano, trans-13-octadecenoic acid (22.62%) in moringa, and cinnamaldehyde (24.42%) in cinnamon. Cytotoxicity testing on human skin fibroblasts (HSF) showed minimal toxicity of EOs mixture with 87.64% cell viability at 100 µg/ml. Colorimetric measurements revealed some colour changes in experimental painting samples, particularly with cinnamon oil on white pigment (ΔE = 9.64) and moringa oil on a yellow pigment (ΔE = 16.31). However, oregano oil consistently showed the least impact across all pigments. These findings demonstrate the potential of the EOs combination as an effective, eco-friendly approach to mitigating fungal deterioration in wall paintings, contributing to sustainable conservation strategies for cultural heritage preservation.

PlomBOX: a low cost bioassay for the sensitive detection of lead in drinking water

This paper reports the design of a biosensor for sensitive, low-cost measurement of lead in drinking water. The biosensor uses a genetically-modified strain of Escherichia coli, which serves as both signal amplifier and reporter of lead in water, measured via colour change. We developed the PlomBOX measurement platform to image this colour change and we demonstrate its capability to detect concentrations as low as the World Health Organisation upper limit for drinking water of 10 ppb. Our approach does not require expensive infrastructure or expert operators, and its automated sensing, detection and result visualisation platform is user-friendly and robust compared to existing lead biosensors—critical features to enable measurement by non-experts at the point of use.

Evaluation of the antibacterial and antibiofilm effect of mycosynthesized silver and selenium nanoparticles and their synergistic effect with antibiotics on nosocomial bacteria

BackgroundThe healthcare sector faces a growing threat from the rise of highly resistant microorganisms, particularly Methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant Pseudomonas aeruginosa (MDR P. aeruginosa). Facing the challenge of antibiotic resistance, nanoparticles have surfaced as promising substitutes for antimicrobial therapy. Recent studies showcase the effectiveness of various fungi species in nanoparticle synthesis. Mycosynthesized silver nanoparticles (AgNPs) and selenium nanoparticles (SeNPs) using Aspergillus carneus MAK 259 has been investigated and demonstrate antibacterial, antibiofilm and synergistic activities against (MRSA) and (MDR P. aeruginosa).ResultsIn the current research, silver nanoparticles (AgNPs) and selenium nanoparticles (SeNPs) were produced extracellularly using A. carneus MAK 259 culture supernatants. Colour change, an initial evaluation of the production of AgNPs and SeNPs. Then, UV absorption peaks at 410 nm and 260 nm confirmed the production of AgNPs and SeNPs, respectively. AgNPs and SeNPs were dispersed consistently between 5‒26 nm and 20–77 nm in size, respectively using TEM. FT-IR analysis was used for assessing proteins bound to the produced nanoparticles. The crystallinity and stability of AgNPs and SeNPs was confirmed using X-ray diffraction analysis and zeta potential measurements, respectively. Antibacterial, antibiofilm and synergistic effects of both (NPs) with antibiotics against MRSA and MDR P. aeruginosa were tested by Agar well diffusion, tissue culture plate and disc diffusion method respectively. Both (NPs) inhibited the growth of P. aeruginosa more than S. aureus. But, SeNPs was stronger. AgNPs had stronger antibiofilm effect especially on biofilms producing S. aureus. as regard synergestic effects, Both (NPs) had higher synergestic effects in combination with cell wall inhibiting antibiotics against P. aeuroginosa While, on S. aureus with antibiotics that inhibit protein synthesis and affect metabolic pathways.ConclusionsOur study demonstrated that the mycosynthesized SeNPs had remarkable antibacterial effect while, mycosynthesized AgNPs exhibited a considerable antibiofilm effect. Both NPs exhibited higher synergistic effect with antibiotics with different modes of action. This approach could potentially enhance the efficacy of existing antibiotics, providing a new weapon against drug-resistant bacteria where the described silver and selenium nanoparticles play a pivotal role in revolutionizing healthcare practices, offering innovative solutions to combat antibiotic resistance, and contributing to the development of advanced medical technologies.

The colour stability of nanofilled composite resin after immersion in pomegranate juice: a laboratory experimental study

Introduction: Composite resin is highly valued for its aesthetic appeal, as its colour closely resembles that of natural teeth. Nanofilled composite resins, in particular, offer impressive colour stability. However, restorative materials can undergo colour changes due to intrinsic and extrinsic factors. One such extrinsic factor is fruit pigments, like those found in pomegranates. This study aims to analyze the colour stability of nanofilled composite resin after immersion in pomegranate juice. Methods: This laboratory experiment utilized a pre-test and post-test control group design. A total sample of forty nanofilled composite resins (Filtek Z350 XT), each with a diameter of 10 mm and a thickness of 2 mm, was divided into four groups. Each sample in the two treatment groups was immersed in 10 mL of commercial pomegranate juice for one day and seven days, respectively. Meanwhile, each sample in the two control groups was immersed in 10 mL of distilled water for the same duration. Colour measurements were carried out before and after immersion using a spectrophotometer. The data were statistically analyzed using the Shapiro-Wilk normality test to assess distribution. For normally distributed data, a one-way ANOVA was conducted, followed by the Tukey HSD post-hoc test for significant differences. For non-normally distributed data, the Kruskal-Wallis test was applied, followed by the Mann-Whitney post-hoc test if significant differences were observed. Results: The one-way ANOVA test for the L parameter yielded a p-value of 0.067 (p&gt;0.05), indicating no significant changes after immersion in both pomegranate juice and distilled water. The Kruskal-Wallis test yielded p-values of 0.000 for E, 0.001 for C, and 0.000 for H (p&lt;0.05), demonstrating substantial differences after immersion in both pomegranate juice and distilled water. Conclusion: The nanofilled composite resin exhibited minimal discolouration after immersion in pomegranate juice, as evidenced by changes in E, C, and H. No significant change was observed in L.

Thermochromic paint with three‐stage colour transition effect based on thermochromic microcapsules and its crosslinking modification

AbstractTo expand the colour change range of thermochromic materials, two types of thermochromic microcapsules (TCMs) with different colour change temperatures and effects were utilised to prepare a TCMs blending system exhibiting a three‐stage colour transition at temperatures ranging from 10 to 60°C. Thermochromic paints were then prepared based on this TCMs blending system using a modified waterborne polyurethane (WPU). The thermochromic properties of the TCMs blending system and the impact of crosslinking modification on the coating properties were investigated. The findings revealed that the ratio of TCMs influences the colour change effect and temperature of the blending system. With temperature variations, the colour of the TCMs blending system can reversibly transition between blue, green and yellow, offering a more vibrant thermochromic effect compared with conventional thermochromic materials. The modified WPU enabled the preparation of paint from the blending system, which was applied to fabric surfaces to create multistage thermochromic fabrics. The mechanical properties, water resistance and adhesion of the modified coating were enhanced, and the colour fastness to washing of the fabrics improved by two grades. This study has practical significance for the application of TCMs and the development of colour‐changing textiles.

Assessment of the effect of experimental gel of pregabalin associated with 35% hydrogen peroxide bleaching on bovine dental enamel: an in vitro study.

To assess the effect of bleaching with gel of pregabalin associated with 35% hydrogen peroxide on the mechanical and chemical properties and ultramorphology of dental enamel. Thirty-six (36) specimens of bovine dental incisors were obtained and divided into three groups (n = 12), namely: CG = bleaching with 35% hydrogen peroxide; KFG = bleaching with 5% potassium nitrate and 2% sodium fluoride gel + 35% hydrogen peroxide; and PGG = bleaching with experimental gel of pregabalin + 35% hydrogen peroxide. The specimens were assessed with respect to Knoop microhardness, surface roughness, and colour change, before and after bleaching. They were also assessed using scanning electron microscopy and energy-dispersive spectroscopy after treatments. All groups exhibited an increase in surface roughness and a reduction in Knoop microhardness after the protocols. There was colour change in all groups, with no difference between them. In addition, there were changes in enamel morphology and non-significant loss of calcium and phosphorus. The experimental gel of pregabalin did not influence the action of 35% hydrogen peroxide, yielding results similar to those of the other groups assessed in all the parameters. Therefore, the gel of pregabalin can be an alternative for topical application on the surfaces of the teeth in association with bleaching treatments.

Spectral unmixing of hyperspectral images revealed pine wilt disease sensitive endmembers.

Throughout the entire cycle of leaf phenological events, leaf colour undergoes changes that are influenced by either abiotic stress or biotic infection. These changes in colouration are closely linked to the quantity and quality of photosynthetic pigments, which directly impact the primary productivity of plants. Therefore, monitoring and quantifying leaf colouration changes are crucial for distinguishing damage caused by pine wilt nematodes from natural tree senescence. In this study, a hyperspectral camera sensor was employed for the non-invasive and non-destructive evaluation of needle colour changes in coniferous trees grown in field tests. Three distinct needle colour variations of six coniferous tree species were selected and monitored using a hyperspectral sensor: those displaying seasonal autumn colours, undergoing nematode-infected necrosis processes, and experiencing natural death. To mitigate the inherently mixed spectral properties of hyperspectral data, endmembers were extracted from individual images using the Purity Pixel Index algorithm under the assumption of linear mixing of endmembers. From a total of 1,321 endmembers extracted from 378 hyperspectral images of six pine species, eight endmembers were ultimately chosen to reconstruct hyperspectral images and generate abundance maps. Among these eight endmembers, four represent varying levels of photosynthetic pigment contents-ranging from very low to high. Consequently, these coniferous endmembers hold promise for assessing seasonal leaf phenology and the extent of damage in pine trees infected by pine wilt nematodes. This comprehensive approach underscores the effectiveness of spectral unmixing of hyperspectral images in advancing precision forestry through meticulous coniferous needle trait analysis.

New 8-hydroxyquinoline-based azo dyes as highly sensitive colorimetric chemosensors for nickel cation.

A new series of sensitive 8-hydroxyquinoline azo-compounds (S1-S8) as sensors was synthesized by diazotization and diazo-coupling, and these compounds were characterized through UV, FTIR, 1H-NMR, 13C-NMR and ESI-MS investigations. The UV-visible spectral data revealed that Ni2+ was sensed by compounds S2, S3, S4, and S6, producing colour changes ranging from violet to orange, and exhibited bathochromism of +8, +67, +63, and +85 nm, respectively. Optimized conditions included a mixture of ethanol/water (4 : 1) solvent system; pH 4 for compounds S3, S4, and S6, and pH 8 for compound S2; reaction time of 2 min; and a stoichiometric ratio of 3 : 1. The limits of detection for the Ni2+ cation demonstrated by the dyes were in the range of 0.012-0.038 μM using UV-visible spectroscopy, which is lower than the permissible value of Ni2+ (1.2 μM) in drinking water specified by the United States Environmental Protection Agency. Intra-day and inter-day accuracies of the Ni2+ cation spiked in tap and underground water (in terms of relative errors) were less than 5%, while precisions were less than 4.0% (RSD). The accuracy and precision of chemosensor-based analyses were comparable to those of the inductively coupled plasma mass spectrometry (ICP-MS) method. Colour changes of paper strips with sensors S2, S3, S4, and S6 ranged from orange to violet in the presence of nickel. Infrared analysis confirmed that sensors interacted with Ni2+ through nitrogen and hydroxyl moieties of quinoline. Thus, an easy-to-use, highly sensitive, and low-cost method for analyzing nickel in water samples was established.

Comparative evaluation of changes in colour (L*, a* and b*) and sensory characteristics of freeze-dried shrimp (Metapenaeus affinis) in different packaging materials

Comparative evaluation of changes in colour (L*, a* and b*) and sensory characteristics of freeze-dried shrimp (Metapenaeus affinis) in different packaging materials

Fluoride binding-modulated supramolecular chirality of urea-containing triarylamine and its photo-manifestation.

In recent years, the regulation of anion-mediated chiral assemblies has gained significant interest. This study investigated the modulation of supramolecular chiroptical signals and chiral assembled structures in a triarylamine system containing a urea moiety through fluoride ion-urea bond interactions, aiming to understand the chiral sense amplification in supramolecular assemblies. Chiral triarylamine derivatives containing urea or amide units were synthesized and the self-assemblies were examined in the absence and presence of fluoride ions. The results revealed that the addition of F- led to an increase in the circular dichroism (CD) intensity for the triarylamine compounds containing urea, accompanied by a transformation of the nanofiber structure into chiral twists. Comparative studies with other anions confirmed the selective specificity for F-. Additionally, the combination of photo-induced triarylamine anion radicals allowed the F- in the system to be visualized through photoirradiation, resulting in distinct colour changes that were detectable by the naked eye. The research demonstrates that F- can selectively amplify supramolecular chirality through urea-F- interactions, which may have promising applications in the fields of sensing and chiroptical devices.

Synthesis of nonaromatic [16]thiatriphyrin(2.2.1)s.

[16]Thiatriphyrin(2.2.1)s containing one thiophene and two pyrroles connected via five meso-carbons were synthesized by condensing a new precursor, meso-fused thiatripyrrane, with an appropriate aryl aldehyde in CH2Cl2 under acid-catalyzed inert conditions followed by open air oxidation with DDQ. These are the first examples in a new series of stable triphyrin(2.2.1)s and both experimental and theoretical studies indicated the nonaromatic nature of the macrocycles. The macrocycles showed strong absorptions in the UV-visible region and exhibited easier oxidations and difficult reductions. The protonated derivatives generated by the addition of TFA to the macrocycles in CHCl3 showed distinct colour changes with significant bathochromic shifts in absorption bands. DFT optimized structures of one of the [16]thiatriphyrins and its protonated derivative revealed that the thiophene ring was almost perpendicular whereas the two pyrrole rings were almost in plane with the mean plane defined by the five meso-carbons and TD-DFT studies were in agreement with the experimental observations.

Laser-induced optical and structural modification in AgI thin films loaded with silver nanoparticles.

Silver-silver iodide (Ag-AgI) films are photosensitive materials in the visible light region. In this work, the colour change in Ag-AgI films under low-power monochromatic laser irradiation is shown, which is due to the size variation of silver nanoparticles (AgNPs) on the AgI thin films. This colour variation depends on the wavelength of the laser beam. In contrast, it is independent of the silver iodide thickness. Laser irradiation is employed not only for the colouration of Ag-AgI films but also for promoting the crystallinity of Ag and AgI in these films. At room temperature and atmospheric pressure, the β-phase and the γ-phase of AgI crystals are formed. The optical and structural changes of the Ag-AgI films with two different thicknesses of silver iodide, before and after laser irradiation, are characterized by synchrotron X-ray diffraction, UV-vis spectrophotometry, and X-ray photoelectron spectroscopy. The growth of silver crystals after laser irradiation is significant, especially in the sample with a thinner AgI film under the irradiation of green and blue laser beams with an energy higher than the bandgap energy. However, in the sample with a thicker film of AgI, the size of the β-phase and the γ-phase of AgI crystals increases faster than that of silver crystals after laser irradiation. This study demonstrated that Ag-AgI films have antibacterial and photocatalytic activities.

Shape-responsive host-guest chemistry: metal-free tetracationic porphyrin nonplanarity promoted by clay mineral interactions assessed by theoretical simulations.

Distortions in the porphyrin core from planarity can trigger a unique structure-property relationship, imparting its basicity, chemical stability, redox potential, and excited-state energetics, among other properties. The colour change promoted by such distortion is signed by red shifts in its electronic absorption spectra. The adsorption of guest meso-substituted free-base porphyrin species onto inorganic hosts, such as clay minerals (layered aluminium or magnesium silicates), is known to further promote colour changes. However, the origin of these changes remains a subject of debate without a clear consensus. In this work, an extensive theoretical study was conducted using density functional theory (DFT) to model the interactions between tetracationic porphyrins, specifically meso-substituted groups N-methyl-4-pyridyl (p-TMPyP) and N-methyl-3-pyridyl (m-TMPyP), and montmorillonite (MMT) with the ideal formula [(Al1.67Mg0.33)Si4O10(OH)2]-0.33. The following conditions were evaluated: (i) adsorption or intercalation of p-TMPyP into MMT host structure, (ii) intercalation of m-TMPyP into MMT, and (iii) the influence of water on the intercalation process. The electrostatic interactions between the porphyrins and the MMT siloxane surface induced conformational changes in p-TMPyP, characterized by rotation of the substituent groups at the macrocycle periphery and a twist of the porphyrin plane. The nonplanarity of the intercalated p-TMPyP guest produced robust Brønsted basic sites capable of abstracting H+ ions from intercalated water molecules, resulting in the formation of a dication. The macrocycle distortion was found to decrease π-conjugation, thereby enhancing the localisation of the lone pair on the imine nitrogen atom. On the other hand, m-TMPyP exhibited slight core macrocycle deformations and minor changes in the dihedral angles of its meso-substituent groups compared to its isomer, with no observed protonation reaction upon intercalation. These findings highlight the clay microenvironment as a promising strategy for inducing conformational alterations in porphyrins, promoting nonplanarity, and exemplifying a shape-responsive system within the framework of guest-host chemistry.

Dynamic colour change in zebrafish (Danio rerio) across multiple contexts.

Many animals are capable of rapid dynamic colour change, which is particularly well represented in fishes. The proximate mechanisms of dynamic colour change in fishes are well understood; however, less attention has been given to understanding its ecological relevance. In this study, we investigate dynamic colour change in zebrafish (Danio rerio) across multiple contexts, using a protocol to image the colouration of live fish without anaesthesia under standardized conditions. We show that zebrafish respond to different visual environments by darkening their overall colouration in a dark environment and lightening in a light environment. This is consistent with crypsis through background matching as a function of dynamic colour change. Additionally, we find that zebrafish use dynamic colour change to increase the internal contrast of their striped patterning in the presence of conspecifics. We speculate that this may function in social signalling and/or dazzle colouration. We find no effect of a predator stimulus on dynamic colour change. Finally, we discuss the potential for zebrafish to use multiple colouration strategies simultaneously as distance-dependent effects, considering the typical viewing distances of zebrafish and their predators.