Sharp Color Change Research Articles

‘Turn-on’ fluorescence sensing of Al(III) ions in water using a simple N-hydroxy-4-amino-1,8-naphthalimide chemosensor

A simple fluorophore, N-hydroxy-4-amino-1,8-naphthalimide (Nap-OH), has been designed and used as a fluorescent “turn-on” chemosensor for sensing metal cations in water. Nap-OH exhibited solvent-dependent photophysics in different solvents and displayed high selectivity and reversible sensing ability for Al(III) ions with femtomolar (10−15 M) sensitivity. The initial emission intensity of Nap-OH was drastically enhanced upon the addition of Al(III) ions and the calculated Stern-Volmer binding constant (KSV) is 4.70 × 104 M−1. The selective sensing of Al(III) was also reflected by sharp visual color changes and further demonstrated the use of Nap-OH for sensing Al(III) in real-water samples.

Intramolecular charge transfer-induced fluorochromic covalent organic frameworks for high speed on-line monitoring of volatile amines

Direct and visual evaluation of volatile amine molecules, a group of hazardous gases and indicators, remains challenge in the fields of chemical industry, environmental detection and food safety. Herein, a convenient and reversible intramolecular charge transfer (ICT)-induced fluorescence-colorimetric approach is proposed for on-line, visual and quantitative monitoring on volatile amines at molecular level through skeletal constructing of cationic pyridinium sites in a carbon-conjugated covalent organic framework (COF). In the presence of volatile amine molecules, the deprotonation of pyridinium sites causes a strong fluorescence enhancement (fluorescence quantum yield > 13 %) and a sharp color change. Specifically, with the reversable pyridinium sites, the COFs-based sensor first exhibits an ultrafast response time (τrise) of 0.65 s to ammonia gas (51.8 ppm), which outperforms reported nanostructure-based ammonia sensors. Meanwhile, through studying the relationship between the total volatile basic nitrogen (TVB-N) and Red/Green/Blue (RGB) outputs of home-made COFs membrane on the food spoilage (fish meat: R2 > 0.9987, shrimp meat: R2 > 0.9917), the protonated TPCH-mOBPy COF is fully verified to work as an on-line fluorochromic probe for visually, AI-intelligently and quantitatively monitoring the generation of volatile amines.

Use of Ipomoea involucrata B. flower as metallochromic indicator for complexometric titrations

The present work highlights the use of Ipomoea involucrate B. flower extract as a complexometric indicator in complex formation between the EDTA and the following metal solutions (Cu2,+ Ba2,+ Hg2+, Fe3+, and Bi3+). Ipomoea involucrate is a species of the Ipomoea genus, belonging to the family Convolvulaceae. This natural indicator was extracted in 2M HCl at 100 0C for 30-40 minutes, cooled and the extract filtered and extracted with ethyl acetate and the pigment extracted with amyl alcohol which was separated and concentrated over a water bath. The flower extract was screened for its use as an metallochromic indicator at different pHs in metal solutions of Cu2,+ Ba2,+ Hg2+, Fe3+, and Bi3+.This natural indicator from the results obtained gave sharp intense color change at the equivalence point of complex formation between the metals and the EDTA at both acidic and alkaline pHs in the metal solution of Cu2+ and Fe3+ and that with different amount of EDTA used in the titration, which increased as the pH value increased, while the ipomoea indicator gave sharp intense color change at the equivalence point of complex formation between the metals and the EDTA at alkaline pHs in the metal solution of Ba2+, Hg2+ and Bi3+ at pH > 10. Natural flower indicators could take the place of the synthetic metallochromic indicators currently used in conventional laboratories because these flower extracts have excellent performance with sharp and intense color change in end points during the complexometric titrations and simple, cost-effective and environmentally friendly extraction methods.

A COVID19-selective pH-paper test: Ultrafast and highly accurate antibody-free viral detection in native saliva

COVID-19 is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). SARS-CoV-2 has led to high mortality worldwide, with social and financial effects expected to persist for years to come. Since asymptomatic individuals cause a large portion of transmission, actions taken to curb the COVID-19 pandemic mostly rely on procedures aimed at detecting viral-related molecules in infected carriers. Currently, leading available detection methods fall short in reliability or point-of-care mass screening applicability.Here, we present an unprecedented antibody-free smart pH paper-based seconds-long detection platform against the virus-related enzyme 3CLpro as a saliva biomarker of SARS-CoV-2 infection. The selective proteolytic activity of 3CLpro is directly detected from native saliva using a peptide substrate-embedded pH-paper platform. 3CLpro presence in infected individuals leads to an ultrafast pH-drop in the paper matrix, thus leading to a sharp color change as direct means of detection.Ultrafast detection, simplicity, no requirement of surface chemistry by sensitive biomolecules, long-term stability, and point-of-care compatibility for COVID-19 mass screening were demonstrated. Forty-two subjects were tested, exhibiting highly sensitive and specific detection of SARS-CoV-2 infection. Finally, we foresee that this universal approach could be implemented for the multiplexed detection of other viral infections by detecting specific viral proteases.Importantly, since our approach does not require immune-specific antibodies for specific detection, the overall platform is extremely cost-efficient, less than 2 USD cents per assay, and suitable for the worldwide mass screening of viral infections, particularly in remote and developing world locations. Moreover, we propose an extremely easy-to-use and produce practical test strip design.

New dual-responsive fluorescent sensor for hypochlorite and cyanide sensing and its imaging application in live cells and zebrafish

Excessive levels of cyanide (CN−) and hypochlorite (ClO−) anions are the significant threats to the human health and the environment. Thus, great efforts have been to design and synthesize molecular sensors for the simple, instantaneous and efficient detecting environmentally and biologically important anions. Currently, developing a single molecular sensor for multi-analyte sensing is still a challenging task. In our present work, we developed a new molecular sensor (3TM) based on oligothiophene and Meldrum's acid units for detecting cyanide and hypochlorite anions in biological, environmental and food samples. The detecting ability of 3TM has been examined to various testing substances containing amino acids, reactive oxygen species, cations and anions, showing its high selectivity, excellent sensitivity, short response time (ClO−: 30 s, CN−: 100 s), and broad pH working range (4–10). The detection limits were calculated as 4.2 nM for ClO− in DMSO/H2O (1/8, v/v) solution and 6.5 nM for CN− in DMSO/H2O (1/99, v/v) solution. Sensor 3TM displayed sharp turn-on fluorescence increasement (555 nm, 435 nm) and sensitive fluorescence color changes caused by CN−/ClO−, which is ascribed to the nucleophilic addition and oxidation of ethylenic linkage by cyanide and hypochlorite, respectively. Moreover, sensor 3TM was applied for hypochlorite and cyanide detecting in real-world water, food samples and bio-imaging in live cells and zebrafish. To our knowledge, the developed 3TM sensor is the seventh single-molecular sensor for simultaneous and discriminative detecting hypochlorite and cyanide in food, biological and aqueous environments using two distinct sensing modes.

Ultra-trace level colorimetric composite sensor based on novel DH-1,6-NAPY-8-CN-AgNPs for the detection of Clonazepam in aqueous and human plasma samples

It’s crucial to develop cost-effective, rapid & reliable detection methods of specific analytes through sensors useful in the analytical and medicinal chemistry. We report a highly sensitive and selective colorimetric method for the detection of clonazepam by the new composite sensor DH-1,6-NAPY-8-CN-AgNPs containing 5-amino-7-(4-benzylpiperazin-1-yl)-2,4-bis(4-bromophenyl)-2-methyl-1,3-dihydro-1,6-naphthyridine-8-carbonitrile capped silver nanoparticles (AgNPs). The detection mechanism is based on the H-bonding interactions between clonazepam and the sensor, that caused the aggregation of NPs that initiated a sharp color change from yellow to red. The linear relationship between the adjacent absorbance values (ΔA) vs. clonazepam concentration (range = 0.05–75 µM) showed a correlation coefficient of 0.9927. The limit of detection (LOD) was 3 nM, that is very significant achievement over the existing reports. The proposed sensor is highly selective, with no interference from many other possible interfering substances. The sensor was successfully applied to the aqueous and human plasma samples, therefore DH-1,6-NAPY-8-CN-AgNPs demonstrated great potential for the on-site and real-time screening of Clonazepam.

N-aryl-4-amino-1,8-naphthalimide Tröger's bases-based internal charge transfer (ICT) fluorescence ‘turn-on’ chemosensors for volatile organic amines

The design of reliable sensor systems for quick sensing and monitoring the trace concentrations of volatile organic compounds (VOCs) has been a topical area of research in recent years due to their serious menace to living systems and environmental hazardousness. In this article, we report two unique ‘cleft-shaped’ N-aryl-4-amino-1,8-naphthalimide derived Tröger's bases (TBNap-Ph and TBNap-Es) as efficient, fast fluorescence sensors for discriminative sensing of volatile organic amines (VOAs). The fluorescence titration studies using TBNap-Ph and TBNap-Es demonstrated discriminative fluorescence sensing responses for VOAs with high selectivity for benzylamine detection. The initial emission intensity of TBNap-Ph and TBNap-Es was enhanced drastically upon the addition of benzylamine. However, similar titration studies using other VOAs such as n-propylamine, n-butylamine, diethylamine, isopropylamine, 3-dimethylamino-1-propylamine, triethylamine, and ethanolamine elicited poor to negligible changes in the fluorescence emission intensity. The selective ‘turn-on’ fluorescence sensing of benzylamine was also reflected by sharp color changes and these sensors can be used to detect benzylamine at the parts-per-millions (ppm) level of sensitivity. Furthermore, the experimentally observed discriminative fluorescence sensing property of TBNap-Ph and TBNap-Es towards VOAs was supported by computational calculations.

PH-sensitive green tea-derived carbon quantum dots for real-time monitoring of shrimp freshness

Green-emitting carbon dots (CDs) were synthesized via a one-step hydrothermal approach using green tea leaf powder (GLP) as a single precursor. The stability and effectiveness of the synthesized GLP-CDs were verified by zeta potential, optical, and luminescence analyses. The prepared CD has excellent pH-responsive properties, providing exciting possibilities for pH-induced intelligent monitoring of packaged foods. GLP-CD was useful for determining liquid ammonia in the linear range of 1–100 μM with the lowest detection limit of 0.4 μM. Additionally, the paper indicator coated with GLP-CDs exhibits a sharp color change from yellow to brown, indicating its ability to detect ammonia vapor. The efficacy of the GLP-CDs-based paper indicator was evaluated as a real-time freshness indicator of shrimp packaging by determining total volatile basic nitrogen. The paper indicator based on GLP-CD has proven to be a simple and cost-effective system for visually monitoring shrimp freshness in the field for suppliers and consumers.

Green Indicators-An Ecofriendly Endpoint

Although acid-base titrations can be done using numerous indicators which are either synthetic or semi-synthetic, the investigation was started for natural compounds as the former ones result in polluting the habitat despite their limited availability, complicated method of preparation, and expensiveness. Equivalence point determination is the point of interest in neutralization titrations. With the change in pH, the indicators which are natural, usually end up giving a sharp color change. Plant-derived pigments that are of various shades and tints generally vary in their dyeing nature by altering pH. An indicator is a substance that exhibits the property of interchangeable color of the reaction mixture when reaching the vicinity of point with the change in pH. Acid-base titration indicators are normally weak acids or bases. Hibiscus rosa-sinensis, Ipomoea biloba, Dahlia pinnata, etc. are among the typical neutralization indicators that are extracted from plants. These natural Indicators are easily available and economical. In this review, we are discussing an overview of plant extracts, and natural pH indicators, and their significance in correspondence to analytical chemistry is illustrated.

Synthesis, Structure, and Optical Properties of a Bis-Macrocycle Derived from a Highly Emissive 1,3,6,8-Tetra(1H-pyrrol-2-yl)pyrene.

A tetra-functionalized pyrene precursor 4b is prepared using the Suzuki-Miyaura coupling of 1,3,6,8-tetrabromopyrene with N-Boc-2-pyrroleboronic acid. 4b displayed a blue emission with a high quantum yield (ϕF = 0.89). 4b is subjected to [3 + 2] Lewis acid-catalyzed condensation with 2,2'-bithiophene-dialcohol 5, affording a planar bis-N2S2 internally linked with pyrene. The single-crystal X-ray structure of bis-N2S2 revealed a planar conformation with all of the pyrrolic nitrogens and thiophenic sulfurs pointing toward the macrocyclic core. Further, the reduction of bis-N2S2 was attempted in the presence of Zn/NH4Cl at room temperature in CHCl3. A sharp color change from pink to brown was observed presumably due to the formation of its reduced congener bis-N2S2-2H. However, the reduced species was found to revert back to its oxidized form over a period of 25 min in CHCl3. Density functional theory (DFT) studies reveal that the two monocyclic halves of bis-N2S2-2H exhibit differences in aromaticity depending on amino and imino pyrroles present inside each individual core. Such a conversion was also monitored by ultraviolet-visible (UV-vis) absorption spectral studies, and the exact composition of bis-N2S2-2H was confirmed by High-resolution/mass spectrometry (HR/MS) analysis. Experimental and theoretical studies reveal a weak aromatic character of bis-N2S2 due to the absence of global conjugation.

Selective Recognition and Reversible “Turn-Off” Fluorescence Sensing of Acetate (CH3COO−) Anion at Ppb Level Using a Simple Quinizarin Fluorescent Dye

A simple and cost-effective optical sensing system based on quinizarin fluorescent dye (QZ) for the selective and reversible sensing of CH3COO− anions is reported. The anion binding affinity of QZ towards different anions was monitored using electronic absorption and fluorescence emission titration studies in DMSO. The UV-visible absorption spectrum of QZ showed a decrease in the intensity of the characteristic absorption peaks at λ = 280, 323, and 475 nm, while a new peak appeared at λ = 586 nm after the addition of CH3COO− anions. Similarly, the initial strong emission intensity of QZ was attenuated following titration with CH3COO− anions. Notably, similar titration using other anions, such as F−, Cl−, I−, NO3−, NO2−, and H2PO4-, caused no observable changes in both absorption and emission spectra. The selective sensing of CH3COO− anions was also reflected by a sharp visual color change from bright green to faint green under room light. Further, the binding was found to be reversible, and this makes QZ a potential optical and colorimetric sensor for selective, reversible, and ppb-level detection of CH3COO− anions in a DMSO medium.

Acid-Base Indicator Properties of Synthesized Phenylhydrazones: 4-(2-(2,4-Dinitrophenyl) Hydrazono) Methyl)-2 Methoxy Phenol and 4-(2-(2,4-Dinitrophenylhydrazono) Methyl) Benzene-1,3-diol

4-(2-(2,4-Dinitrophenyl) hydrazone) methyl)-2 methoxy phenol (IND-X) and 4-(2-(2, 4-dinitrophenylhydrazono) methyl) benzene-1,3-diol (IND-Y) were synthesised by condensation reactions with 2,4-dinitrinophenylhydrazine and were observed to possess acid-base indicator properties. The study was conducted to explore and verify their use in different analytical situations and, consequently, validate them. Analysis of their use in acid-base titrations between strong acids/strong bases and weak acids/strong bases as well as pharmaceutical applications in the assay of ibuprofen pure powder and batch of ibuprofen tablets (400 mg) using standard methods in the British Pharmacopoeia (2020) was all considered. The validations were performed by the International Conference on Harmonisation of Technical Requirements for the registration of Pharmaceuticals for Humans Q2 (R1) guidelines. The outcomes were statistically compared with existing conventional analytical approaches. Titrimetric data obtained were analyzed statistically by Student’s t-test and one-way ANOVA at a 95% confidence level. IND-X and IND-Y were shown to be similar in behaviour to phenolphthalein, methyl orange, and methyl red as visual indicators after preliminary evidence of sharp colour changes in acid, alkaline, and neutral pH solutions. The use of the two indicators in the assay of ibuprofen powder and tablets has also been established. The validation parameters considered were found to be consistent with respective acceptance criteria for analytical purposes. IND-X and IND-Y are therefore proposed as alternative acid-base indicators to methyl red, methyl orange, and phenolphthalein for routine volumetric analysis in students’ laboratory experiments. They also serve as alternative indicators to phenolphthalein for the titrimetric analysis of ibuprofen-based samples and products.

A Naked-Eye Visual Reverse Transcription Loop-Mediated Isothermal Amplification with Sharp Color Changes for Potential Pen-Side Test of Foot-and-Mouth Disease Virus.

Visual loop-mediated isothermal amplification (LAMP) is qualified to be applied in the field to detect pathogens due to its simplicity, rapidity and cost saving. However, the color changes in currently reported visual reverse transcription LAMP (RT-LAMP) for foot-and-mouth disease virus (FMDV) detection are not so obvious to the naked eye, so interpretation of results is troublesome. In this study, a new naked-eye visual RT-LAMP to detect all seven distinct serotypes of FMDV was established based on the 3D genes by using pH-sensitive neutral red as the indicator, rendering a sharp contrast of color changes between the negative (light orange) and the positive (pink). Analytical sensitivity tests showed that the detection limit of the visual RT-LAMP was 104 copies/µL while those were 103 and 104 copies/µL for the RT-qPCR and conventional RT-PCR methods, respectively. Specificity tests proved that the established visual RT-LAMP assay had no cross-reactivity with other common livestock viruses. Furthermore, the analysis of 59 clinical samples showed 98.31% and 100% concordance with the RT-qPCR and the RT-PCR, respectively. The pan-serotypic FMD visual RT-LAMP assay could be suitable for a pen-side test of all seven serotypes of FMDV because the results could be easily distinguished by the naked eye without the requirement of complicated instruments and professional technicians. Hence, the novel method may have a promising prospect in field tests which exert an important role in monitoring, preventing, and controlling FMD, especially in regions with no PCR or qPCR instrument available.

Ag and Au Nanoparticles as Color Indicators for Monomer/Micelle-Nanoparticle Interactions.

Ag and Au nanoparticles (NPs) were used as color indicators to determine the monomer/micelle adsorption on the NP surface. A simple methodology based on the color change of Ag/Au NPs upon interacting with surface-active molecules was developed. A contrasting color change occurred when NPs interact with the monomer/micelle. This was demonstrated by monitoring the adsorption behavior of a series of Gemini surfactants. UV-visible measurements showed a large change in the intensity and wavelength of Ag/Au NP absorbance upon the surface adsorption of the monomer/micelle of Gemini surfactants. The mechanism of surface adsorption and molecular orientation on the solid-liquid interface of NPs was determined by performing the FT-IR and XPS measurements. Results demonstrated that sharp color changes from yellow to red for Ag NPs and red to purple for Au NPs happened when the Gemini surfactant monomer/micelle adsorbs on the NP surface. This colorimeter-based methodology highlighted the applicability of Ag/Au NPs in complex media where such NPs frequently encounter surface-active molecules.

3D Printing of Metal-Organic Framework-Based Ionogels: Wearable Sensors with Colorimetric and Mechanical Responses.

Soft ionotronics are emerging materials as wearable sensors for monitoring physiological signals, sensing environmental hazards, and bridging the human-machine interface. However, the next generation of wearable sensors requires multiple sensing capabilities, mechanical toughness, and 3D printability. In this study, a metal-organic framework (MOF) and three-dimensional (3D) printing were integrated for the synthesis of a tough MOF-based ionogel (MIG) for colorimetric and mechanical sensing. The ink for 3D printing contained deep eutectic solvents (DESs), cellulose nanocrystals (CNCs), MOF crystals, and acrylamide. After printing, further photopolymerization resulted in a second covalently cross-linked poly(acrylamide) network and solidification of MIG. As a porphyrinic Zr-based MOF, MOF-525 served as a functional filler to provide sharp color changes when exposed to acidic compounds. Notably, MOF-525 crystals also provided another design space to tune the printability and mechanical strength of MIG. In addition, the printed MIG exhibited high stability in the air because of the low volatility of DESs. Thereafter, wearable auxetic materials comprising MIG with negative Poisson's ratios were prepared by 3D printing for the detection of mechanical deformation. The resulting auxetic sensor exhibited high sensitivity via the change in resistance upon mechanical deformation and a conformal contact with skins to monitor various human body movements. These results demonstrate a facile strategy for the construction of multifunctional sensors and the shaping of MOF-based composite materials.

Tunable Thermofluorochromic Sensors Based on Conjugated Polymers

AbstractEven though thermofluorochromic materials are eternal candidates for their use in multiple applications, they are still limited as they require complex synthetic strategies to accomplish tunable optical properties and/or provide optical changes only over a very wide temperature range. By taking advantage of the high sensitivity of the optical properties of conjugated polymers and oligomers to the external environment, herein phase change material (PCM)‐based thermofluorochromic mixtures are created, where the solid‐to‐liquid transition of the PCM host triggers a sharp fluorescence color change of the dispersed polymers/oligomers. Fluorophore conjugation length, concentration, and PCM nature can be used to vary the spectral properties of the resulting materials along the visible region, covering a large part of the CIE 1931 color space. For the preparation of functional devices, this behavior can be directly transferred to the solid state by soaking or printing cellulose papers with the obtained thermofluorochromic mixtures as well as by structuring them into solid lipid particles that can be dispersed within polymer matrices. The resulting materials show very promising features as thermal sensors and anticounterfeiting labels.

Discriminative fluorescent sensing of nitro-antibiotics at ppb level using N-phenyl-amino-1,8-naphthalimides chemosensors

The design of suitable fluorescent chemosensors for the trace detection of emerging organic pollutants attracted great research interest because of their serious menace to the environment and health hazards. Herein, we report two 1,8-naphthalimide-based fluorescent chemosensors, N-phenyl-4-amino-1,8-naphthalimide (Nap-1) and N-phenyl-3-amino-1,8-naphthalimide (Nap-2), for the discriminative fluorescent sensing of nitro-containing antibiotics. Nap-1 and Nap-2 have been synthesized in two steps from their respective nitro-1,8-naphthalic anhydride precursors and they were fully characterized using standard spectroscopic techniques such as FT-IR, and NMR (1H, and 13C), and HRMS. Both Nap-1 and Nap-2 are highly emissive due to internal-charge transfer (ICT) transition and exhibited a positive solvatochromism in different solvent mediums. The fluorescence titration studies of Nap-1 and Nap-2 with various antibiotics showed high selectivity and strong binding affinity for nitro-containing antibiotics with a parts-per-billions (ppb) level of sensitivity. The initial fluorescence emission intensity of Nap-1 and Nap-2 was quenched upon the addition of nitro-antibiotics such as Nitrofurazone (NFZ) and Dimetridazole (DMZ). Notably, the co-existence of other competing antibiotics showed negligible to moderate fluorescence quenching. The observed discriminative fluorescence sensing was also reflected by sharp visual colour changes. The Stern-Volmer quenching constants (KSV) were calculated to be in the order of 104 M−1. These studies suggest that Nap-1 and Nap-2 can be used as potential “turn-off” fluorescent chemosensors for the selective, sensitive, and fast detection of nitro-antibiotics.

Electrochemistry Under Microscope: Measuring the Thickness of Diffusion Layer in Thin Layer Electrochemical Cells with Optical Microscope

Electrochemical reactions are heterogeneous in nature, and an electrochemical reaction involves mass transfer from the bulk solution to the electrode surface, heterogeneous electron transfer at the electrode surface, and mass transfer back to the bulk solution. There are three modes of mass transport to the working electrode surface: diffusion, migration, and convection. Among these modes, diffusion is the one that involved in all electrochemical processes and sometimes is the sole mode of mass transfer. Thus, the key concept underpinning electrochemical science are that of the diffusion and diffusing layer, the region in the vicinity of an electrode layer that affected by electrode reaction. The thickness of diffusion layer is an important parameter in understanding chronoamperometry, cyclic and hydrodynamic voltammetry. The thickness of this zone can be measured either by simulation or analysis of the electrochemical responses. But interpretation of the concentration profiles and related current time responses require understanding the Fick’s law and its related mathematical representations. Although these basic are crucial in understanding electrochemistry but their mathematical representation is challenging specially for the students or scientists who are new to the field. The thickness of diffusion layer for a typical electroanalytical experiment varies between 20 to 200 micrometers, depends on the time of experiment. The size is not visible to the human eye easily but doesn’t required expensive research-grade microscopes and can be seen using even kids grade microscopes with 100 times magnification. Here we have developed a thin-layer electrochemical cell compatible with low-cost microscopes to demonstrate a microscopy activity in which students measure the thickness of micrometer-sized diffusion layer. The electrode processes involve the reactions of redox indicators with sharp color changes or acid base indicators with sharp color change in response to electrochemically generated proton or hydroxide, from water electrolysis. This Imaging tools advance electrochemistry education by enabling students to see the electrode processes that are not visible to the human eye without any research grade instrumentation. This device also aids in the explicit visualization and interpretation of a typical concentration profiles near the working electrode surface for chronoamperometry, cyclic and hydrodynamic (e.g., rotated disk) voltammetry experiments.

Redox of Viologen for Powering and Coloring.

Viologen is among the most attractive and easiest-to-use organic redox active group in many functional molecular assemblies. It plays crucial roles as an electron transfer mediator in the artificial photo-energy conversion systems and electron-transfer protein assemblies and as a building block of supramolecules. Its features include electrochemically reversible redox activity and stability. Strong blue color and tendency to dimerization of the one-electron reduced form, viologen mono-radical mono-cation, are remarkable. In this Account, we describe the use of viologen to give a powered movement of small molecules and motion of millimetre-sized macroscopic soft-matters and the use of viologen ionic liquid as electrochromic materials. Attractivities of the use of viologen units for powering and coloring are demonstrated and discussed. In particular, we highlight driving of mechanical movements by π-π stacking dimerization, incorporation in a hydrogel to attain highly deformable material, induction of 2D phase transformation, and sharp color change of very thin ionic liquid layer in a compartment-less electrochromic display.

Green synthesis of silver nanoparticles using Omani pomegranate peel extract and two polyphenolic natural products: characterization and comparison of their antioxidant, antibacterial, and cytotoxic activities

BackgroundGreen synthesis of silver nanoparticles (AgNPs) has gained popularity due to the economical and eco-friendly approach associated with it. The aim of the study was to biosynthesize silver nanoparticles using pomegranate peel extract (PPE), quercetin (Q), and gallic acid (GA) and to evaluate their antioxidant, antimicrobial, and cytotoxic activities.ResultsA sharp color change from yellow to brown, appearance of a peak in a UV spectrum around 413–425 nm, and four intense peaks in XRD spectra matching with the reference silver crystal confirmed the formation of AgNPs. SEM and TEM analysis revealed particles to be mostly spherical with few aggregates. Average particle size distribution and zeta potential was found to be 43.6 nm and −18.01mV, 31.6 nm and −21.5 mV, and 21.7 nm and −27.9 mV for Q-AgNPs, P-AgNPs, and GA-AgNPs, respectively. P-AgNPs showed excellent in vitro antioxidant activity (84.85–89.20%) and cytotoxic activity (100% mortality). P-AgNPs and GA-AgNPs exhibited good antimicrobial activity against the four bacterial strains comparable to the reference antibiotics but Q-AgNPs failed to inhibit the growth of P. vulgaris.ConclusionsOmani pomegranate peel extract seems to be a potential and alternative source for the simple, one pot, eco-friendly green synthesis of extracellular stable AgNPs. The synthesized nanoparticles have the potential to be developed as possible antimicrobial agents and antioxidants.Graphical abstract