Showing papers on "Titration published in 2023"

A new single-armed salamo-based sensor with aggregation-induced emission characteristic for selective sensing of aluminium ions

Abstract: A single-armed salamo-based fluorescence sensor QANS was designed and synthesized. QANS exhibited aggregation-induced emission (AIE) property in a binary solvent mixture (DMF/H2O) as the water content increased, and the QANS powder showed strong orange-yellow emission in solid state. In addition to the intriguing AIE characteristic, QANS demonstrated high selectivity and sensitivity for Al3+ over various metal ions through a “turn-on” fluorescence response. A plausible mechanism for the interaction of sensor QANS with Al3+ was proposed according to the ESI-MS, Job’s plot, 1H NMR titration analysis and DFT calculations. Furthermore, the sensor QANS was applied in monitoring Al3+ in actual water samples. To further determine its applicability, the convenient paper strips of QANS were applied for selective monitoring of Al3+ ions.

An Automated Microfluidic Analyzer for In Situ Monitoring of Total Alkalinity.

Abstract: We have designed, built, tested, and deployed an autonomous in situ analyzer for seawater total alkalinity. Such analyzers are required to understand the ocean carbon cycle, including anthropogenic carbon dioxide (CO2) uptake and for mitigation efforts via monitoring, reporting, and verification of carbon dioxide removal through ocean alkalinity enhancement. The microfluidic nature of our instrument makes it relatively lightweight, reagent efficient, and amenable for use on platforms that would carry it on long-term deployments. Our analyzer performs a series of onboard closed-cell titrations with three independent stepper-motor driven syringe pumps, providing highly accurate mixing ratios that can be systematically swept through a range of pH values. Temperature effects are characterized over the range 5-25 °C allowing for field use in most ocean environments. Each titration point requires approximately 170 μL of titrant, 830 μL of sample, 460 J of energy, and a total of 105 s for pumping and optical measurement. The analyzer performance is demonstrated through field data acquired at two sites, representing a cumulative 25 days of operation, and is evaluated against laboratory measurements of discrete water samples. Once calibrated against onboard certified reference material, the analyzer showed an accuracy of -0.17 ± 24 μmol kg-1. We further report a precision of 16 μmol kg-1, evaluated on repeated in situ measurements of the aforementioned certified reference material. The total alkalinity analyzer presented here will allow measurements to take place in remote areas over extended periods of time, facilitating affordable observations of a key parameter of the ocean carbon system with high spatial and temporal resolution.

Economically viable multi-responsive probes for fluorimetric detection of trace levels of Ga3+, Al3+ and PPi in near aqueous medium

Abstract: Gallium compounds are commonly used in cancer treatment and are known to be compounds with minimal toxicity. On the other hand, aluminium has procured extensive significance in modern lifestyle as well as industrial applications. Both these Group III metal ions, irrespective of their amicable properties and applications, in their excesses harm human and ecological health. We report in this work two tailor-made reversible chemosensors c towards the end of achieving recognition of these relevant metal ions. H3L1 was sensitive to both Ga3+ and Al3+ while H4L2 was highly selective towards Ga3+. They exhibited sensing of these ions via a turn-on strategy. Both these ligands sequentially detected pyrophosphate ion in an off-on-off manner. Very low detection levels were achieved for all the targeted analytes in near-aqueous medium. Fluorescence experiments, HR-MS data, NMR titrations were used to speculate the binding mode of the probes and the prevalent mechanisms. Both the probes could detect P2O74− in a sequential, manner. Apart from paper strip tests, cytotoxic studies and bio-imaging of Ga3+ and Al3+ were conducted in Vero cells in an effort to explore the practical applications of probes.

Beyond Karl Fischer titration: a monolithic quantum cascade sensor for monitoring residual water concentration in solvents

Abstract: Quality control of liquids is an important part of analytical chemistry. The gold standard for measuring residual water in organic solvents and pharmaceutical applications is Karl Fischer titration. It has a high sensitivity, selectivity and accuracy. The downsides are a time-consuming offline analysis, together with the need for toxic reagents producing waste, and it suffers from poor inter-laboratory reproducibility. In this work, we present a high-performance lab-on-a-chip sensor exploiting mid-IR spectroscopy for liquid sensing. It is operating at 6.1 μm wavelength and is suitable for robust and flexible real-time in situ analysis of the residual water concentration in isopropyl alcohol. This is demonstrated in two experiments. A custom-made 60 μL flow cell is employed to measure only minute amounts of analyte in an inline configuration. In a second approach, the whole sensor is immersed into the analyte to demonstrate sensitive and rapid in situ operation on the millisecond time scale. This is confirmed by the ability for time resolved single water-droplet monitoring, while they are mixed into the liquid sample. We obtain a limit of detection between 120 ppm and 150 ppm with a concentration coverage spanning three orders of magnitude from 1.2 × 10−2%vol to 25%vol for the flow cell and 1.5 × 10−2%vol to 19%vol in the in situ configuration, respectively.

Rapid determination of solid-state diffusion coefficients in Li-based batteries via intermittent current interruption method

Abstract: Abstract The galvanostatic intermittent titration technique (GITT) is considered the go-to method for determining the Li + diffusion coefficients in insertion electrode materials. However, GITT-based methods are either time-consuming, prone to analysis pitfalls or require sophisticated interpretation models. Here, we propose the intermittent current interruption (ICI) method as a reliable, accurate and faster alternative to GITT-based methods. Using Fick’s laws, we prove that the ICI method renders the same information as the GITT within a certain duration of time since the current interruption. Via experimental measurements, we also demonstrate that the results from ICI and GITT methods match where the assumption of semi-infinite diffusion applies. Moreover, the benefit of the non-disruptive ICI method to operando materials characterization is exhibited by correlating the continuously monitored diffusion coefficient of Li + in a LiNi 0.8 Mn 0.1 Co 0.1 O 2 -based electrode to its structural changes captured by operando X-ray diffraction measurements.

Imidazole-derived new colorimetric/fluorometric chemosensor for the sensitive recognition of CN− ions: Real-time application in food samples and fluorescence bio-imaging

Abstract: On account of the supreme toxicity of CN− ions in the physiological systems, it is essential to develop a sensitive chemosensor to detect cyanide ions. Herein, we designed a new 5-(3-(4,5-diphenyl-1H-imidazol-2-yl)-2-hydroxybenzylidene)-2,2-dimethyl-1,3-dioxane-4,6-dione (BMA) sensor, which exhibits tremendous colorimetric as well as fluorometric behaviour towards CN− ions. This could be due to the nucleophilic attack of CN− ions on the dione-vinyl site, which induces intramolecular charge transfer (ICT) capabilities. The cyanide recognition mechanism of BMA was verified by optical experiments such as UV–visible and fluorescence spectroscopy, NMR, and mass analysis. Moreover, the structural characterization was done by 1H NMR titration and HRMS analysis, and the molecular orbital interactions were studied by TDDFT calculations. The sensor BMA exhibited a rapid response towards CN− ions (10 sec) with low detection limit (7.87 nM), great pH stability in the physiologically applicable pH range (6–12) and had good sensitivity and selectivity towards CN− ions. Encouraged by these detection properties, we successfully used sensor BMA to determine CN− ions in real water and food samples. To validate the colorimetric behavior of the sensor BMA, test paper strip experiments were carried out in the laboratory. We also extensively studied the effect of the sensor in Escherichia coli (E.coli) bacterial cells.

Design, Synthesis and Evaluation of a Series of Zinc(II) Complexes of Anthracene-Affixed Multifunctional Organic Assembly as Potential Antibacterial and Antibiofilm Agents against Methicillin-Resistant Staphylococcus aureus.

Abstract: A novel class of zinc(II)-based metal complexes, i.e., [Zn2(acdp)(μ-Cl)]·2H2O (1), [Zn2(acdp)(μ-NO3)]·2H2O (2), and [Zn2(acdp)(μ-O2CCF3)]·2H2O (3) (Cl- = chloride; NO3- = nitrate; CF3CO2- = trifluoroacetate) of anthracene-affixed multifunctional organic assembly, H3acdp (H3acdp = N,N'-bis[anthracene-2-ylmethyl]-N,N'-bis[carboxymethyl]-1,3-diaminopropan-2-ol), have emerged as promising antibacterial and antibiofilm agents in the domain of medicinal chemistry. Accordingly, complexes 1-3 were synthesized by utilizing H3acdp in combination with ZnCl2, Zn(NO3)2·6H2O, and Zn(CF3CO2)2·H2O respectively, in the presence of NaOH at ambient temperature. The complexation between H3acdp and Zn2+ was delineated by a combined approach of spectrophotometric and spectrofluorometric titration studies. The stoichiometry of acdp3-/Zn2+ in all three complexes is observed to be 1:2, as confirmed by spectrophotometric/spectrofluorometric titration data. Elemental analysis (C, H, N, Zn), molar conductance, FTIR, UV-vis, and thermoanalytical (TGA/DTA) data were effectively used to characterize these complexes. Besides, the structures of 1-3 were established by density functional theory (DFT) calculation using B3LYP/6-311G, specifying a self-assembled compact geometry with average Zn···Zn separation of 3.4629 Å. All three zinc complexes exhibited significantly high antibacterial and antibiofilm activity against methicillin-resistant Staphylococcus aureus (MRSA BAA1717). However, complex 1 showed a more recognizable activity than 2 and 3, with minimum inhibitory concentration (MIC) values of 200, 350, and 450 μg/mL, respectively. The antimicrobial activity was tested by employing the minimum inhibitory concentration (MIC) and time-kill assay. The crystal violet (CV) assay and microscopic study were performed to examine the antibiofilm activity. As observed, complexes 1-3 had an effect on the production of extracellular polymeric substance (EPS), biofilm cell-viability, and other virulence factors such as staphyloxanthin and hemolysin production, autoaggregation ability, and microbial cell-surface hydrophobicity. Reactive oxygen species (ROS) generated due to inhibition of staphyloxanthin production in response to 1-3 were also analyzed. Moreover, complexes 1-3 showed an ability to damage the bacterial cell membrane due to accumulation of ROS resulting in DNA leakage. In addition, complexes 1-3 displayed a synergistic/additive activity with a commercially available antibiotic drug, vancomycin, with enhanced antibacterial activity. On the whole, our investigation disclosed that complex 1 could be a promising drug lead and attract much attention to medicinal chemists compared to 2 and 3 from therapeutic aspects.

Visual and Rapid Detection of Nerve Agent Mimics in Gas and Solution Phase by a Simple Fluorescent Probe.

Abstract: Chemical nerve agents are highly toxic organophosphorus compounds that are easy to obtain and can be utilized by terrorists to threaten homeland security and human safety. Those organophosphorus nerve agents contain nucleophilic ability that can react with acetylcholinesterase leading to muscular paralysis and human death. Therefore, there is great importance to explore a reliable and simple method to detect chemical nerve agents. Herein, the o-phenylenediamine-linked dansyl chloride as a colorimetric and fluorescent probe has been prepared to detect specific chemical nerve agent stimulants in the solution and vapor phase. The o-phenylenediamine unit serves as a detection site that can react with diethyl chlorophosphate (DCP) in a rapid response within 2 min. A satisfied relationship line was obtained between fluorescent intensity and the concentration of DCP in the range of 0-90 μM. In the optimized conditions, we conducted the fluorescent titration to measure the limits of detection (0.082 μM) with the fluorescent enhancement up to 18-fold. Fluorescence titration and NMR studies were also conducted to explore the detection mechanism, indicating that the formation of phosphate ester causes the intensity of fluorescent change during the PET process. Finally, probe 1 coated with the paper test is utilized to detect DCP vapor and solution by the naked eye. We expect that this probe may give some admiration to design the small molecule organic probe and applied in the selectivity detection of chemical nerve agents.

Structure and Site Evolution of Framework Ni Species in MIL-127 MOFs for Propylene Oligomerization Catalysis.

Abstract: A mixed-valence oxotrimer metal-organic framework (MOF), Ni-MIL-127, with a fully coordinated nickel atom and two iron atoms in the inorganic node, generates a missing linker defect upon thermal treatment in helium (>473 K) to engender an open coordination site on nickel which catalyzes propylene oligomerization devoid of any cocatalysts or initiators. This catalyst is stable for ∼20 h on stream at 500 kPa and 473 K, unprecedented for this chemistry. The number of missing linkers on synthesized and activated Ni-MIL-127 MOFs is quantified using temperature-programmed oxidation, 1H nuclear magnetic resonance spectroscopy, and X-ray absorption spectroscopy to be ∼0.7 missing linkers per nickel; thus, a majority of Ni species in the MOF framework catalyze propylene oligomerization. In situ NO titrations under reaction conditions enumerate ∼62% of the nickel atoms as catalytically relevant to validate the defect density upon thermal treatment. Propylene oligomerization rates on Ni-MIL-127 measured at steady state have activation energies of 55-67 kJ mol-1 from 448 to 493 K and are first-order in propylene pressures from 5 to 550 kPa. Density functional theory calculations on cluster models of Ni-MIL-127 are employed to validate the plausibility of the missing linker defect and the Cossee-Arlman mechanism for propylene oligomerization through comparisons between apparent activation energies from steady-state kinetics and computation. This study illustrates how MOF precatalysts engender defective Ni species which exhibit reactivity and stability characteristics that are distinct and can be engineered to improve catalytic activity for olefin oligomerization.

Effects of Chitosan Molecular Weight and Degree of Deacetylation on Chitosan−Cellulose Nanocrystal Complexes and Their Formation

Abstract: This study was conducted to determine the effects of chitosan molecular weight and degree of deacetylation (DD) on chitosan–cellulose nanocrystal (CNC) polyelectrolyte–macroion complexes (PMCs) and their formation. Chitosan samples with three different molecular weights (81, 3 · 103, 6 · 103 kDa) and four different DDs (77, 80, 85, 89%) were used. The effects on PMC formation were determined by turbidimetric titration. An effect of the molecular weight of chitosan was not observed in turbidimetric titrations. Turbidity levels were higher for CNCs with lower sulfate group density and larger hydrodynamic diameter than for CNCs with higher sulfate group density and smaller hydrodynamic diameter. Conversely, turbidity levels were higher for chitosans with higher DD (higher charge density) than for chitosans with lower DD (lower charge density). PMC particles from chitosans with different molecular weights were characterized by scanning electron microscopy, laser Doppler electrophoresis, and dynamic light scattering. PMCs from high-molecular-weight chitosan were more spherical and those from medium-molecular-weight chitosan had a slightly larger hydrodynamic diameter than PMCs from the respective other two chitosans. The molecular weight of the chitosan was concluded to have no effect on the formation of chitosan–CNC PMC particles and only a minor effect on the shape and size of the particles. The higher turbidity levels for CNCs with lower sulfate group density and larger hydrodynamic diameter and for chitosans with higher DD were attributed to a larger number of CNCs being required for charge compensation.

Molecular Influences on the Quantification of Lewis Acidity with Phosphine Oxide Probes.

Abstract: Gutmann-Beckett-type measurements with phosphine oxide probes can be used to estimate effective Lewis acidity with 31P nuclear magnetic resonance spectroscopy, but the influence of the molecular structure of a given probe on the quantification of Lewis acidity remains poorly documented in experimental work. Here, a quantitative comparison of triethyl (E), trioctyl (O), and triphenyl (P) phosphine oxides as molecular probes of Lewis acidity has been carried out via titration studies in MeCN with a test set of six mono- and divalent metal triflate salts. In comparison to E, the bulkier O displays a similar range of chemical shift values and binding affinities for the various test metal ions. Spectral linewidths and speciation properties vary for individual cation-to-probe ratios, however, confirming probe-specific properties that can impact the data quality. Importantly, P displays a consistently narrower dynamic range than both E and O, illustrating how electronic changes at phosphorus can influence the NMR response. Comparative parametrizations of the effective Lewis acidities of a broader range of metal ions, including the trivalent rare earth ions Y3+, Lu3+, and Sc3+ as well as the uranyl ion (UO22+), can be understood in light of these results, providing insight into the fundamental chemical processes underlying the useful approach of single-point measurements for quantification of effective Lewis acidity. Together with a study of counteranion effects reported here, these data clarify the diverse ensemble of factors that can influence the measurement of Lewis acid/base interactions.

Zinc binding of a Cys2His2-type zinc finger protein is enhanced by the interaction with DNA

Abstract: Abstract Zinc finger proteins specifically recognize DNA sequences and, therefore, play a crucial role in living organisms. In this study the Zn(II)-, and DNA-binding of 1MEY#, an artificial zinc finger protein consisting of three finger units was characterized by multiple methods. Fluorimetric, circular dichroism and isothermal calorimetric titrations were applied to determine the accurate stability constant of a zinc finger protein. Assuming that all three zinc finger subunits behave identically, the obtained thermodynamic data for the Zn(II) binding were ΔH binding site = − (23.5 − 28.0) kcal/mol (depending on the applied protonation state of the cysteines) and log β ’ pH 7.4 = 12.2 ± 0.1, being similar to those of the CP1 consensus zinc finger peptide. The specific DNA binding of the protein can be characterized by log β ’ pH 7.4 = 8.20 ± 0.08, which is comparable to the affinity of the natural zinc finger proteins (Sp1, WT1, TFIIIA) toward DNA. This value is ~ 1.9 log β ’ unit higher than those determined for semi- or nonspecific DNA binding. Competitive circular dichroism and electrophoretic mobility shift measurements revealed that the conditional stability constant characteristic for Zn(II) binding of 1MEY# protein increased by 3.4 orders of magnitude in the presence of its target DNA sequence. Graphical abstract

Rapid Detection of Cd2+ Ions in the Aqueous Medium Using a Highly Sensitive and Selective Turn-On Fluorescent Chemosensor

Abstract: Herein, a novel optical chemosensor, (CM1 = 2, 6-di((E)-benzylidene)-4-methylcyclohexan-1-one), was designed/synthesized and characterized by 1H-NMR and FT-IR spectroscopy. The experimental observations indicated that CM1 is an efficient and selective chemosensor towards Cd2+, even in the presence of other metal ions, such as Mn2+, Cu2+, Co2+, Ce3+, K+, Hg2+,, and Zn2+ in the aqueous medium. The newly synthesized chemosensor, CM1, showed a significant change in the fluorescence emission spectrum upon coordination with Cd2+. The formation of the Cd2+ complex with CM1 was confirmed from the fluorometric response. The 1:2 combination of Cd2+ with CM1 was found optimum for the desired optical properties, which was confirmed through fluorescent titration, Job’s plot, and DFT calculation. Moreover, CM1 showed high sensitivity towards Cd2+ with a very low detection limit (19.25 nM). Additionally, the CM1 was recovered and recycled by the addition of EDTA solution that combines with Cd2+ ion and, hence, frees up the chemosensor.

Fluorenone Appended Colorimetric Sensor for Cascade Detection of Fluoride and Calcium Gluconate with Applications in Solid State and Logic Gate Systems

Abstract: A novel fluorenone derived Schiff base chemosensor (1) has been synthesized as a colorimetric sensor for fluoride (F−) ions in CH3CN and characterized by various analytical techniques. The chemosensor 1 perceived high selectivity for F− ion detection in the presence of other anions along with naked eye color change from yellow to orange-red with quantitative detection limit of 900 nM. The UV-vis changes, density functional theoretical (DFT) calculations and 1H NMR titration studies pointed to F− ion induced deprotonation of −OH of sensor 1 that has been proposed to be responsible for the observed absorption as well as color changes. The sensor 1 has also been efficiently applied for the solid state concentration dependent naked eye detection of F− ions in the form of filter paper strips and smartphone applications. The in-situ generated 1-F− complex was further utilized for cascade recognition of calcium gluconate (CG). The reversible and reproducible changes produced by the addition of F− ions and CG enabled 1 to be used as “INHIBIT” molecular logic system and “SET/RESET” memorized device at the molecular level.

Production of Activated Carbons from Food/Storage Waste

Abstract: This paper deals with the adsorption of organic and inorganic pollutants on the surface of carbonaceous adsorbents prepared via the chemical activation of expired or broken food products—the solid residue of the “cola-type” drink as well as spoilt grains of white rice and buckwheat groats. The activation process was conducted in the microwave furnace with the use of two activating agents of different chemical nature—potassium carbonate and orthophosphoric acid. The activated carbons were characterized based on the results of elemental analysis, low-temperature nitrogen adsorption/desorption, Boehm titration, thermal analysis, and scanning electron microscopy. Additionally, the suitability of the materials prepared as the adsorbents of methylene blue and iodine from the aqueous solutions was estimated. The materials obtained via chemical activation with H3PO4 turned out to be much more effective in terms of both model pollutant adsorptions. The maximum sorption capacity toward iodine (1180 mg/g) was found for the white-rice-based activated carbon, whereas the most effective in the methylene blue removal (221.3 mg/g) was the sample obtained from the solid residue of the expired “cola-type” drink. For all carbonaceous materials, a better fit for the experimental adsorption data was obtained with the Langmuir isotherm model than the Freundlich one.

AIE-active phenothiazine based Schiff-base for the selective sensing of the explosive picric acid in real water samples and paper-based device

Abstract: A highly selective and sensitive AIE fluorescent chemosensor based on phenothiazine and ethylene diamine was synthesized (DPTZ-SB) for the exclusive detection of picric acid (PA). Interestingly, DPTZ-SB can sense PA exclusively over five other competitive explosives, due to the specific complexation ability of DPTZ-SB towards PA. For the better mechanistic understanding, Stern-Volmer, Modified Stern-Volmer and Job’s plot were employed, which showed the limit of detection and binding constant to be 0.2 ppb and 4.05 × 1010 M−1, respectively, and the stoichiometric ratio of DPTZ-SB:PA as 1:2. The values are promising as compared to the AIE fluorophores reported for PA sensing recently. The sensing mechanism was elucidated using DFT studies and 1H NMR titration experiment, which revealed the active involvement of the imine groups of the Schiff base in the complexation process. Furthermore, in order to broaden the applicability, the probe DPTZ-SB was applied in real water samples obtained from the local river, lake and tap water. Interestingly, a paper based fluorescent sensor was devised by embedding DPTZ-SB on the filter paper and was analyzed by a handheld UV lamp. Under UV light illumination, the paper-based sensor exhibited prominent fluorescence quenching in the presence of PA, which can be conveniently visualized. Moreover, the color-scanning application available in smart phones was coupled with the paper-based sensor to quantitate the scanometric assays. On a parallel note, DPTZ-SB showed excellent aggregation induced enhanced emission (AIEE) property. In fact, a 9.4-times enhancement in the photoluminescence (PL) intensity was noted for a 90:10 H2O:DMF of DPTZ-SB as compared to that in pure DMF. Therefore, the multifaceted applicability of the Schiff base has been explored, particularly in the fields of PA explosive detection device in real life samples and AIEE.

Dacryodes edulis leaf derived biochar for methylene blue biosorption

Abstract: Carbonized Dacryodes edulis leaf (CDEL) which was obtained at 250 °C, was used for the biosorption of methylene blue (MB) dye from aqueous solutions. The biosorbent was characterised using Boehm titration, pH of zero point charge (pHzpc), FTIR, SEM, XRD and ED-XRF. Mineral compositions of CDEL revealed good amounts of Fe, Ca and K which are of nutritional importance. The pH at zero point of charge (pHzpc) and specific surface area (SSA) of CDEL were found to be 7.5 and 0.983 m2/g respectively. Freundlich isotherm gave good fit to equilibrium biosorption data. Elovich kinetic model gave the best fit to kinetic data which is consistent with chemisorption. Scanning electron microscopy (SEM) and infrared spectroscopy (FTIR) revealed effective biosorption processes. Calculated thermodynamic parameters revealed spontaneous and exothermic biosorption of MB onto CDEL. Highest amount of MB was removed at pH 4 and the percentage removal was about 93%; hence, CDEL is a good biosorbent for MB from aqueous solutions. Generally, CDEL exhibited > 70% MB removal after three adsorption-desorption cycles, showing that it is re-usable and a promising biosorbent for the treatment of MB dye contaminated water.

Charge Regulation of Poly(acrylic acid) in Solutions of Non-Charged Polymer and Colloids

Abstract: Weak polyelectrolytes (WPEs) are responsive materials used as active charge regulators in a variety of applications, including controlled release and drug delivery in crowded bio-related and synthetic environments. In these environments, high concentrations of solvated molecules, nanostructures, and molecular assemblies are ubiquitous. Here, we investigated the effect of high concentrations of non-adsorbing, short chains of poly(vinyl alcohol), PVA, and colloids dispersed by the very same polymers on charge regulation (CR) of poly(acrylic acid), PAA. PVA does not interact with PAA (throughout the full pH range) and thus can be used to examine the role of non-specific (entropic) interactions in polymer-rich environments. Titration experiments of PAA (mainly 100 kDa in dilute solutions, no added salt) were carried out in high concentrations of PVA (13–23 kDa, 5–15 wt%) and dispersions of carbon black (CB) decorated by the same PVA (CB-PVA, 0.2–1 wt%). The calculated equilibrium constant (and pKa) was up-shifted in PVA solutions by up to ~0.9 units and down-shifted in CB-PVA dispersions by ~0.4 units. Thus, while solvated PVA chains increase the charging of the PAA chains, as compared to PAA in water, CB-PVA particles reduce PAA charging. To investigate the origins of the effect, we analyzed the mixtures using small-angle X-ray scattering (SAXS) and cryo-TEM imaging. The scattering experiments revealed re-organization of the PAA chains in the presence of the solvated PVA but not in the CB-PVA dispersions. These observations clearly indicate that the acid–base equilibrium and the degree of ionization of PAA in crowded liquid environments is affected by the concentration, size, and geometry of seemingly non-interacting additives, probably due to depletion and excluded volume interactions. Thus, entropic effects that do not depend on specific interactions should be taken into consideration when designing functional materials in complex fluid environments.

AIEE Active Azomethine-Based Rhodamine Derivative For Ultrasensitive Multichannel Detection of Au3+ Through a Fluorimetrically, Electrochemically, and RGB-Based Sensing Assay.

Abstract: In this study, a novel rhodamine-based optically and electrochemically active chemosensor, integrated with a p-DMAC moiety, demonstrated extremely selective identification of Au3+ ions relative to other metal species, including (Li+, Na+, K+, Ba2+, Ca2+, Mg2+, Co2+, Mn2+, Zn2+, Pb2+, Ni2+, Fe2+, Hg2+, Fe3+, Cd2+, Pd2+, Al3+, Cr3+, Cu2+, and nitrate salt of Ag+). These compounds demonstrated a novel and outstanding aggregation-induced emission enhancement (AIEE) behavior by aggregating in DMF/H2O medium. Furthermore, the degree of quenching was varying linearly with a Au3+ concentration from 0 to 40 nM, with a lower detection limit by RH-DMAC nanoaggregates of 118.79 picomolar (40.35 ppm). The Stern-Volmer plots, Job's plot, Benesi-Hildebrand plot, 1H NMR titrations, ESI-mass, and FTIR all revealed significant interactions between the sensor and Au3+. Moreover, the proposed electrochemical sensor afforded a linear correlation before the peak current and concentration of Au3+ in the range of 0-40 nM, with a detection limit of 483.73 pM or 164.36 ppt (by cyclic voltammetry method) and 298.0 pM or 101.24 ppt (by the Differential Pulse Voltammetry method). Furthermore, the proposed sensing assay was used to measure Au3+ ion in spiked water samples (tap, drinking, waste, and river water), achieving acceptable accuracy and precision with high recovery rates. Furthermore, RH-DMAC-coated fluorescence paper test strips were designed for on-site Au3+ detection. Apart from this, the use of smartphone-based RGB (Red Green Blue) color analysis shortened the operating process, accelerated the detection technique, and provided a novel methodology for the instantaneous, real-time examination of Au3+ in real water samples.