HEPES Buffer Research Articles

Manipulating Intramolecular Charge Transfer in Terpyridine Derivatives Towards "Turn-On" Fluorescence Chemosensors for Zn2.

A series of donor-acceptor (D-A) terpyridine derivatives with various intramolecular charge transfer interactions have been successfully synthesized bearing phenyl, methoxyphenyl, N-butyldiphenylamine (DPA), and triphenylamine (TPA) as electron-donors and terpyridine (TPY), 2,6-di(pyrazin-2-yl)pyridine (PYDPZ), and N,N-dimethylated PYDPZ (PYDPZ-2CH3) as electron acceptors. Upon the introduction of pyrazine rings instead of pyridine ones and further selective N,N'-dimethylation, the intramolecular D-A interactions are significantly enhanced, resulting in the remarkable reduced intramolecular charge transfer (ICT) transitions and quenched PL emissions in CH2Cl2 solution. However, their ICT emissions are clearly recovered upon adding Zn2+. Especially, for double positively charged compound 12, the Zn2+-induced "turn-on" green emission (λmax, em=518 nm, Φ=0.24) with excellent sensitivity (I/I0=77) and selectivity (IZn/ICd=23) is detected. Under the optimized experimental condition (EtOH-H2O (9 : 1, v/v), containing 0.05 M HEPES buffer (pH=7.4)), this probe is used to quantitative determination of Zn2+ in a water sample with an average recovery of 97.5 %. Furthermore, the probe is applied to imaging of Zn2+ ions in HeLa cells and its mechanism is confirmed by the molecular dynamics simulation, in which lower coulomb potential for membrane surface adsorption and energy barrier for membrane translocation can be found.

Interference of metal ions on the bioluminescent signal of firefly, Renilla, and NanoLuc luciferases in high-throughput screening assays

Bioluminescent high-throughput screening (HTS) assays, based largely on the activity of firefly (FLuc), Renilla (RLuc), and/or NanoLuc (NLuc) luciferases, are widely utilised in research and drug discovery. In this study, we quantify the luciferase-based real-life HTS assay interference from biologically and environmentally relevant metal ions ubiquitously present in buffers, environmental and biological matrices, and as contaminants in plastics and compound libraries. We also provide insights into the cross-effects of metal ions and other key experimental and biological reagents (e.g., buffer types, EDTA, and glutathione) to inform HTS assay design, validation, and data interpretation. A total of 21 ions were screened in three robust HTS assays (“SC” assays) based on the luminescence of FLuc, RLuc, and NLuc luciferases. Three newly optimised HEPES buffer variants (“H” assays) were developed for direct luciferase comparison. Interference in bioluminescent signal generation was quantified by calculating the IC50 values from concentration-dependent experiments for selected highly active and relevant metal ions. Metal ion inhibition mechanisms were probed by variations in specific reagents, EDTA, GSH, and the sequence of addition and buffer composition. In this study, we revealed a significant impact of metal ions’ salts on luciferase-mediated bioluminescence, even at biologically and environmentally relevant concentrations. The extent of signal interference largely aligned with the Irving–Williams series of metal ion–ligand affinities (Cu > Zn > Fe > Mn > Ca > Mg), supporting previous reports on metal ion-dependent FLuc inhibition. However, the absolute magnitude and relative extent of signal reduction by metal ions’ salts differed between SC and H assays and between luciferases, suggesting a complex network of metal ions’ interactions with enzymes, substrates, reactants, and buffer elements. The diversity of the tested conditions and variability of responses provided insights into potential interference mechanisms and synergies that may exacerbate or alleviate interference. The beneficial influence of EDTA and the impact of glutathione, present natively in cells, on bioluminescence readout were pinpointed. Given the ubiquity of metal ions in analysed samples, the causative role in false-positive generation in drug discovery, and the wide breadth of luciferase-based assays used in screening, awareness and quantification of metal influence are crucial for developing assay validation protocols and ensuring reliable screening data, ultimately increasing the critical robustness of bioluminescence-based HTS assays.

Towards Optimal Automated 68Ga-Radiolabeling Conditions of the DOTA-Bisphosphonate BPAMD Without Pre-Purification of the Generator Eluate.

DOTA-functionalized bisphosphonates can be useful tools for PET imaging of bone metastases when radiolabeled with 68Ga. Moreover, the versatility of DOTA allows the complexation of radiometals with therapeutic applications (e.g., 177Lu), positioning these bisphosphonates as attractive theranostic agents. Among these molecules, BPAMD is a compound whose radiolabeling with 68Ga has already been described, but only through manual methods. Thus, a fully automated protocol for 68Ga radiolabeling of BPAMD on the GAIA® ± LUNA® synthesis module was designed, and a thorough study of the radiolabeling conditions was undertaken. [68Ga]Ga-BPAMD was produced in good radiochemical purity (> 93%) and high radiochemical yield (> 91%) using 0.3 M HEPES buffer. The nature of the reaction vessel showed no significant effect on the radiolabeling outcome. Similarly, addition of an antiradiolysis compound to the reaction medium did not significantly improve the already excellent stability of [68Ga]Ga-BPAMD over time. The radiolabeled product obtained by automated synthesis was evaluated invivo in healthy mice and confirmed high accumulation in the joints and along the backbone.

Long-Term Stability of Nicotinamide Cofactors in Common Aqueous Buffers: Implications for Cell-Free Biocatalysis.

The use of nicotinamide cofactors in cell-free biocatalytic systems is necessitated by the high specificity that these enzymes show for their natural redox mediators. Unfortunately, isolation and use of natural cofactors is costly, which suggests that enhancing their stability is key to enabling their use in industrial processes. This study details NAD+ and NADH stability in three buffer systems (sodium phosphate, HEPES, and Tris) at 19 °C and 25 °C and for up to 43 d. In Tris, both NADH and NAD+ were found to be highly stable. NADH degradation rates of 4 μM/d (19 °C) and 11 μM/d (25 °C) were observed in Tris buffer, corresponding to >90% and 75% remaining after 43 d, respectively. Higher degradation rates (up to 34 μM/d) were observed when sodium phosphate or HEPES buffers were used. The effect of a mild increase in temperature was determined to be significant for long-term stability, and it was shown that degradation under these conditions can be easily monitored via UV-Vis, because the degradation proceeds via the oxidation/de-aromatization of the dihydropyridine ring. Overall, this work emphasizes that the choice of buffer system is consequential for bioreactor systems employing natural nicotinamide cofactors for extended periods of time.

Design, Synthesis and Crystal Structure of a Novel Fluorescence Probe for Zn2+ Based on Pyrano[3,2-c] Carbazole.

Zinc is a trace element, which plays an important role in many biological processes. The deficiency of zinc will lead to many diseases. Thus, it is of great significance to develop fast and efficient quantitative detection technology for zinc ions. In this study, a novel fluorescence probe FP2 was designed for Zn2+ quantification based on pyrano[3,2-c] carbazole. The structure of FP2 was characterized by 1HNMR, 13CNMR, HRMS, and X-ray diffraction. In the HEPES buffer solution, FP2 is responsive to Zn2+ and greatly enhanced. The pH value and reaction time were investigated, and the optimum reaction conditions were determined as follows: the pH was 7~9 and the reaction time was longer than 24 min. Under the optimized conditions, the concentration of FP2 and Zn2+ showed a good linear relationship in the range of 0~10 μM, and the LOD was 0.0065 μmol/L. In addition, through the 1H NMR titration experiment, density functional theory calculation, and the job plot of FP2 with Zn2+ in the HEPES buffer solution, the binding mode of FP2 and Zn2+ was explained. Finally, the method of flame atomic absorption spectrometry (FAAS) and FP2 were used to detect the content of Zn2+ in the water extract of tea. The results showed that the FP2 method is more accurate than the FAAS method, which shows that the method described in this work could be used to detect the content of Zn2+ in practical samples and verify the practicability of this method.

4,4'-Sulfonyldianiline Derived Aggregation-Induced Emission Luminogen for the Detection of Ofloxacin.

The excessive use of antibiotic ofloxacin (Oflx) can cause serious detrimental effects to human health. Therefore, the utmost research priority is required to develop facile methods to detect Oflx. Herein, a V-shaped aggregation-induced emission (AIE) active Schiff base SDANA was introduced for the fluorescent turn-on detection of Oflx. The Schiff base SDANA was synthesized by condensing 4,4'-sulfonyldianiline with two equivalents of 2-hydroxy-1-naphthaldehyde. The nearly non-fluorescent SDANA in DMSO showed strong orange emission with the increase in HEPES buffer (H2O, 10 mM, pH 7.4) fractions in DMSO from 70 %-95 % due to the combined effects of AIE and ESIPT. The DLS and SEM analyses were performed to complement the formation of self-aggregates of SDANA. With the addition of Oflx, the fluorescence emission of AIE luminogen (AIEgen) SDANA (λem=575 nm, λex=400 nm) was blue-shifted and enhanced at 530 nm. The interactions of Oflx over the surface of SDANA aggregates disrupted the intramolecular charge transfer and aggregation morphology of SDANA, which gave a distinct fluorescence response to detect Oflx. The detection limit for Oflx was estimated as 0.81 μM, and the developed probe AIEgen SDANA was applied for the quantification of Oflx in human blood serum.

Selective separation of dyes and tetracycline hydrochloride in polymer‐nucleotide coacervate droplets

AbstractThis paper reports the formation of coacervates by the electrostatic interaction of poly (diallyldimethylammonium chloride) (PDDA) and adenosine triphosphate (ATP) in aqueous solution, examining its formation conditions, stability, and efficiency in separation. The ideal concentration for creating coacervate droplets in pure water, HEPES buffer, and NaCl solution was determined to be 20 mM of PDDA and ATP. Enhancing the stability of coacervates was achieved by incorporating phospholipid vesicles on their surface, presenting a novel strategy for building cell models. Ostwald Ripening was employed to comprehend the growth mechanism of the coacervates, while the Hofmeister Ion Series and Schulze‐Hardy's rule were utilized to elucidate the stability differences in solutions containing NaCl, Na2SO4, and MgCl2. These coacervates were stable at concentrations below 90 mM NaCl, 200 mM Na2SO4, and 30 mM MgCl2, respectively. We also explored the specific separation of dyes and tetracycline hydrochloride (TC) in the coacervates. Separation efficiencies of 92.98% for methylene blue (MB), 94.19% for methyl orange (MO), and 85.94% for TC, were achieved by the coacervates, which can be attributed to the synergistic effects of hydrophobicity, electrostatic forces, and π‐π interactions. The proposed coacervates have great potential in cell mimicry and water treatment.

A simple Cu(II)-dppy complex for selective detection of hazardous sulfide anion in water and its application in DNA and BSA binding

The traditional hazardous sulfide species (S2–, HS–, and H2S) are widely dispersed throughout the environment and have widespread applications in various industrial processes. Despite numerous applications, excessive exposure to sulfide species can lead to several chronic diseases. In light of the importance of sulfide detection in water, we have reported a novel water-soluble 1:2 copper complex ([CuL2]Cl2) of 2,2′-(4-(3,4-dimethoxyphenyl)pyridine-2,6-diyl)dipyrazine ligand L. The [CuL2]Cl2 receptor has been utilized for the sulfide detection in the vicinity of other anions of higher concentration (ten equivalents of F−, I−, Br−, Cl−, H2PO4−, NO3− HCO3−, OH−, CH3CO2−, SO42−, CO32−, P2O74- (PPi), SO32−, HPO42−, S2O32− (10 mM)) in water at physiological pH 7.4 (10 mM HEPES buffer) with the help of absorption spectral studies and colorimetric study. The detection limit of sulfide is calculated to be 1.13 µM. DFT calculations suggested that the most exergonic free energy (-31.99 kcal/mol) is associated with sulfide, leading to the displacement of Cu(II) ion from the [CuL2]Cl2 receptor, which well supported the experimental absorption spectral data. In addition, [CuL2]Cl2 receptor also demonstrated noteworthy interactions with Calf-Thymus DNA (CT-DNA) and bovine serum albumin (BSA).

Synthesis and Evaluation of 68Ga- and 177Lu-Labeled [Pro14]bombesin(8-14) Derivatives for Detection and Radioligand Therapy of Gastrin-Releasing Peptide Receptor-Expressing Cancer.

The gastrin-releasing peptide receptor (GRPR) is overexpressed in a variety of cancers and represents a promising target for diagnosis and therapy. However, the extremely high accumulation in the pancreas observed for most of the clinically evaluated GRPR-targeted radiopharmaceuticals could limit their applications. In this study, we synthesized one GRPR antagonist (ProBOMB5) and two GRPR agonists (LW02056 and LW02057) by replacing the 4-thiazolidinecarboxylic acid (Thz14) residue in our previously reported GRPR-targeted tracers with Pro14. The 68Ga and 177Lu labeling were conducted in HEPES (2 M, pH 5.0) buffer and acetate (0.1 M, pH 4.5) buffer, respectively, and the radiolabeled products were obtained in a 24-57% decay-corrected radiochemical yield and >92% radiochemical purity. The binding affinities (Ki) of Ga-ProBOMB5, Ga-LW02056, Ga-LW02057, and Lu-ProBOMB5 were measured via in vitro competition binding assays and were 12.2 ± 1.89, 14.7 ± 4.81, 13.8 ± 2.24, and 13.6 ± 0.25 nM, respectively. The PET imaging and ex vivo biodistribution studies were conducted in PC-3 tumor-bearing mice at 1 h post injection. [68Ga]Ga-ProBOMB5, [68Ga]Ga-LW02056, and [68Ga]Ga-LW02057 enabled clear tumor visualization in PET images. The tumor uptake values of [68Ga]Ga-ProBOMB5, [68Ga]Ga-LW02056, and [68Ga]Ga-LW02057 were 12.4 ± 1.35, 8.93 ± 1.96, and 7.64 ± 0.55%ID/g, respectively, and their average pancreas uptake values were minimal (0.60-1.37%ID/g). Longitudinal SPECT imaging and ex vivo biodistribution studies were also conducted for [177Lu]Lu-ProBOMB5 and clinically validated [177Lu]Lu-RM2. Despite comparable tumor uptake at 1 h post injection ([177Lu]Lu-ProBOMB5:8.09 ± 1.70%ID/g; [177Lu]Lu-RM2:7.73 ± 0.96%ID/g), a faster clearance from PC-3 tumor xenografts was observed for [177Lu]Lu-ProBOMB5, leading to a lower radiation-absorbed dose delivered to tumors. Our data demonstrate that [68Ga]Ga-ProBOMB5 is a promising tracer for clinical translation for detecting GRPR-expressing tumor lesions. However, further optimizations are needed for [177Lu]Lu-ProBOMB5 to prolong tumor retention for therapeutic applications.

Sensitive detection of α-amylase based on host–guest inclusion system of γ-cyclodextrin and dansyl-derived diphenylalanine

A highly sensitive detection system for α-amylase was developed via host–guest complexation between γ-cyclodextrin and dansyl-modified diphenylalanine (FF-Dns). The host–guest inclusion of FF-Dns into the cavity of γ-CD in a HEPES buffer solution (10 mM, pH 7.4) significantly enhanced the fluorescence intensity, and the emission wavelength gradually shifted from 558 to 535 nm. The hydrolysis of γ-CD by the addition of α-amylase released FF-Dns, leading to the recovery of the fluorescence emission characteristics. Therefore, the FF-Dns/γ-CD host–guest complexation system can serve as a platform for the sensitive detection of α-amylase with good selectivity against potential interference. The limit of detection (LOD) of the system was 0.004 U/mL, with a linear working range of 0–6 U/mL. The detection assay was successfully applied in 0.1 % serum, achieving an LOD of 0.017 U/mL and a linear working range of 0–10 U/mL.

A-043 A Fast, Novel and Analytically Sensitive Clinical Research Method for the Analysis of Free Testosterone using UPLC-MS/MS

Abstract Background The aim of this work was to develop an analytically sensitive, rapid clinical research method for the analysis of free testosterone in serum using a small sample volume. Laboratories have found this difficult, partly due to the inherent low concentrations (less than 3% of total testosterone is free), technical challenges and variability in results have been noted with equilibrium dialysis, which is considered the gold standard. Methods Testosterone certified reference material (Merck, UK) was used to create calibrators in 52.75 mM HEPES buffer adjusted to pH 7.4 to mimic the ionic environment of serum. Precision was evaluated using in-house QC materials prepared in serum (Golden West Biologicals, USA and BioIVT, UK). 200 µL serum was incubated at 37°C with 400 µL pH-adjusted 52.75 mM HEPES buffer for 2 hours, mixing at 800 r.p.m. with Rapid Equilibrium Analysis (RED) inserts and plates (Thermo Scientific™, UK). Testosterone-13C3 (Merck, UK) was spiked into resultant diasylate, then liquid-liquid extraction (LLE) was used to concentrate and clean the sample. The ACQUITY™ UPLC™ I-Class System with the Waters™ ACQUITY UPLC BEH C18, 1.7µm, 2.1 x 100 mm Column using a water/methanol/ammonium fluoride gradient and the Waters Xevo™ TQ Absolute Mass Spectrometer were used for quantification. An accelerated protocol for equilibrium dialysis, using a 2-hour incubation and fast mixing step was used (4 hours or longer is more typical historically) though it is essential to control the pH of the dialysis buffer and, particularly, the temperature of the chamber. Results No significant carryover or matrix effects were demonstrated with linearity from 0.5-650 pg/mL. Addition of high concentrations of endogenous substances (albumin, bilirubin, creatinine, cholesterol, triglycerides and uric acid) did not affect quantification. Analytical sensitivity investigations indicated the analytical sensitivity would allow precise quantification (≤20%CV and ≤15% bias) at 0.50 pg/mL. Coefficients of variation (CV) for total precision and repeatability on 5 analytical runs for low, mid and high QCs at approximately 2.79, 8.80 and 134 pg/mL respectively were all ≤ 8.4% (n=25). Accuracy was assessed by analyzing 45 male external quality assurance samples (NEQAS, UK) ranging in concentration from 50.1-268.6 pg/mL and the Bland-Altman agreement showed a small negative bias of -7.6% compared with the all-laboratory trimmed mean (ALTM), though excellent agreement overall. When LC-MS/MS determined concentrations were processed against Vermeulen equation determined concentrations (total testosterone and SHBG concentrations were provided by the scheme, a concentration of 45 g/L albumin was assumed), again good agreement was shown by the Bland-Altman bias of -7.7%. Conclusions A novel clinical research method using a fast equilibrium dialysis procedure with LLE and LC-MS/MS analysis with only 200 µL of serum has been demonstrated for clinical research use. Sub pg/mL analytical sensitivity, excellent linearity and precision, with minimal matrix effects and a strong agreement with an EQA scheme were established.

Enzymatically Triggered Drug Release from Microgels Controlled by Glucose Concentration.

This study aims to design microgels for controlled drug release via enzymatically generated pH changes in the presence of glucose. Modern medicine is focused on developing smart delivery systems with controlled release capabilities. In response to this demand, we present the synthesis, characterization, and enzymatically triggered drug release behavior of microgels based on poly(acrylic acid) modified with glucose oxidase (GOx) (p(AA-BIS)-GOx). TEM images revealed that the sizes of air-dried p(AA-BIS)-GOx microgels were approximately 130 nm. DLS measurements showed glucose-triggered microgel size changes upon glucose addition, which depended on buffer concentration. Enzymatically triggered drug release experiments using doxorubicin-loaded microgels with immobilized GOx demonstrated that drug release is strongly dependent on glucose and buffer concentration. The highest differences in release triggered by 5 and 25 mM glucose were observed in HEPES buffer at concentrations of 3 and 9 mM. Under these conditions, 80 and 52% of DOX were released with 25 mM glucose, while 47 and 28% of DOX were released with 5 mM glucose. The interstitial glucose concentration in a tumor ranges from ∼15 to 50 mM. Normal fasting blood glucose levels are about 5.5 mM, and postprandial (2 h after a meal) glucose levels should be less than 7.8 mM. The obtained results highlight the microgel's potential for drug delivery using the enhanced permeability and retention (EPR) effect, where drug release is controlled by enzymatically generated pH changes in response to elevated glucose concentrations.

3‐Hydroxy‐2‐naphthohydrazide: A Commercially Available Compound for Fluorescence Sensing of Ortho‐Vanillin and Vanillin

ABSTRACTVanillin and ortho‐vanillin are the most important flavoring additives used in the food industry at a large scale. Herein, the aggregation‐induced emission (AIE) behavior of commercially available 3‐hydroxy‐2‐naphthohydrazide (3HN) was explored and applied for the detection of vanillin and ortho‐vanillin. The weakly fluorescent 3HN in DMSO showed fluorescence enhancement at 500 nm with the increase in HEPES or PBS buffer (pH 7.4) fractions in DMSO. The 3HN in DMSO containing 30% HEPES buffer is used as Probe 1 for the selective detection of ortho‐vanillin. Probe 1 showed a new fluorescence emission at 415 nm for ortho‐vanillin without altering the probe emission at 500 nm. With high specificity, Probe 1 can detect ortho‐vanillin down to 0.3 μM. In contrast, 3HN in DMSO containing 20% PBS buffer is used as Probe 2 for the selective turn‐off detection of vanillin. The green fluorescence emission of Probe 2 at 500 nm is selectively quenched by vanillin with a detection limit of 0.8 μM. Finally, the analytical novelty of the developed probes was examined by quantifying ortho‐vanillin and vanillin in spiked food samples with good recovery percentages.

A lanthanide luminescent sensor doped polymer dots for ratiometric fluorescence detection of hydrogen sulfide

As one of the indexes of food freshness, hydrogen sulfide content is closely related to food spoilage. A dual-emission sensor for H2S detection was reported in this paper. Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] Polymer dots (MEH-PPV-Pdots) were prepared by copolymer of poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] and styrene-maleic anhydride. The sensor was obtained by embedding purple MEH-PPV-Pdots in a green MOF. The accommodated MEH-PPV-Pdots were considered as the reference signal, while copper ions on the host skeleton served as accessible reaction sites, allowing MEH-PPV-Pdots/Tb0.99Cu0.01-MOF to selectively sense H2S. The sensor exhibited reduced green fluorescence and proportional response to H2S. Because H2S can transfer charge on copper ions and thus affect the green light emitted by rare earth ions. The results showed that the sensor had good stability to H2S in HEPES buffer, fast response, obvious color change, high selectivity and sensitivity. The sensor has been applied to the detection of aquatic products, showing good visualization effect.

Development of a new rhodamine 6G based probe and its application as an optical sensor of Cu2+ and Fe3+ ions: A comprehensive experimental and Theoretical studies

A new rhodamine appended probe 3-allyl salicylaldehyde rhodamine hydrazone (RGAL) has been synthesized and thoroughly characterized using various spectroscopic techniques, as well as single crystal XRD. The optical properties of RGAL were investigated in 10 mM HEPES buffer in H2O:CH3CN (2:8, v/v, pH=7.2) in the presence of various cations. RGAL showed selectivity and sensitivity towards Cu2+ during absorption process and “turn on” behavior towards Fe3+ during emission study owing to the opening of a spirolactum ring. The detection limits for Cu2+ and Fe3+ ions using RGAL were determined to be 6.15 ppm and 4.75 ppm, respectively. The binding constant of RGAL with Cu2+ and Fe3+ ions was found to be 1.20 × 104 M−1 and 1.71 × 104 M−1, respectively. Hirshfeld surface and fingerprint analysis of RGAL provides the in-depth analysis of pairwise interaction between two atoms. Furthermore, the topological analysis of RGAL is performed using NCI, AIM, ELF and LOL analysis. The analysis provides information about O78-H79…N71 and C40-H41…O77 hydrogen bonding interactions in themonomer of RGAL whereas various inter- and intra- molecular interactions give strength to the dimer pattern of RGAL.

Self‐Assembly of UiO‐66 on Conjugated Polyelectrolytes: Toward Enhanced Photophysical Properties

AbstractIn this study, the synthesis and characterization of the fluorescent metal–organic framework (MOF)‐polymer composites is reported based on zirconium‐based MOFs (UiO‐66 and UiO‐66(OH)₂) and a conjugated polyelectrolyte, poly(phenylene ethynylene) carboxylate (PPE‐CO₂‐108). The defect‐rich nature of these Zr‐MOFs facilitates strong interactions between the polyelectrolyte's carboxylic acid moieties and the open metal sites on the Zr clusters within the MOF nanoparticles. The composites are prepared by a simple impregnation approach, where MOF nanocrystals suspended in HEPES buffer are added to the polymeric solution under sonication for 10 min. The obtained MOF composites (i.e., UiO‐66‐CPE and UiO‐66 (OH)2‐CPE) are characterized using powder X‐ray diffraction (PXRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Brunauer‐Emmett‐Teller (BET) surface area, zeta potential measurements, and UV–vis spectroscopy. The characterization confirmed the homogeneous distribution of the MOF nanocrystals on the polymer as seen in the SEM images, and the interaction with PPE‐CO₂‐108 is confirmed by the decrease in the surface areas from 1050 to 590 m2 g−1 for UiO‐66‐CPE and from 500 to 137 m2 g−1, for UiO‐66(OH)2‐CPE. Fluorescence microscopy revealed strong fluorescence in the microparticles, confirming robust polymer‐MOF interaction. The composites also exhibit improved photostability of the conjugated polyelectrolyte, suggesting their potential for applications in biomedical imaging and other areas requiring stable and bright fluorescent systems.

Nanomolar Hg2+ detection via phenothiazine fluorogenic chemosensor: Applications in water analysis and intracellular imaging

A Knoevenagel condensation reaction paved the way for the development of the PTZ-BCN probe namely (z)-2-(1H-benzo[d]imidazole-2-yl)-3-(10-ethyl-10H-phenothiazin-3-yl) acrylonitrile. PTZ-BCN’s spectral characteristics were verified through the application of IR, 1H NMR, 13C NMR, and HRMS techniques. The PTZ-BCN probe showed a high selectivity and sensitivity toward Hg2+ ions over other interfering competing metal ions in CH3CN: HEPES buffer (9:1, v/v) system. The addition of Hg2+ results in a notable redshift and fluorescence quenching of the PTZ-BCN probe. An examination of the interaction between the PTZ-BCN probe and Hg2+ involved recoding 1H NMR titration spectra, HRMS, DFT analysis, and Job’s plot respectively. Quantification of the lowest detectable Hg2+ concentration at 2.3 nM, exhibiting a correlation coefficient of R2 = 0.9985. PTZ-BCN probe has proven effective in quantitatively determining the existence of Hg2+ in real-time water samples, test strips, solid state, and Hela living cells.

An eugenol-sulfonyl based fluorescent probe for recognition of Al3+ in real sample analysis and biological application

The present work describes an eugenol-sulfonyl based fluorescence chemosensor, H4L [H4L=6,6′-((1E,1′E)-((sulfonylbis(6-hydroxy-3,1- phenylene))bis(azanylylidene))bis(methanylylidene))bis(4-allyl-2-methoxyphenol)], which shows maximum emission intensity towards Al3+ ion in presence of other competing metal ions. Upon excitation at 440 nm H4L exhibits a significant rise in fluorescence at 547 nm upon gradual addition of Al3+ ion in the HEPES buffer at pH=7.4 (MeOH:H2O, 4:1, (v/v)). The increasing value of fluorescence is mainly due to chelation enhanced fluorescence effect (CHEF). Complete characterization of the probe (H4L) and metal bound complex (1) have been determined using a range of methods including UV–Vis absorption titration, fluorescence titration, NMR, ESI-mass, etc. Thus 1:2 binding stoichiometry between H4L and metal ion has been also proved. Another important aspect: regeneration and reversibility of H4L are investigated in presence of Na2EDTA. H4L exhibits ∼ 10−6 M order detection limit and significant binding constant (∼106 M−1) for the Al3+ ion, suggesting its potential use in bio-imaging studies. The probe was effectively used in real samples as well as paper strip to locate the Al3+ ion.

Experimental and theoretical studies for instantaneous detection of l-cysteine and l-histidine using a simple Cu(II)-dppy complex

Developing simple and effective receptors for instantaneous detection of l-amino acids is vital for the recognition of life-threatening diseases in their early stage. Here, we report the synthesis and characterization of 2,6-di(pyrazin-2-yl)pyridine (dppy) based ligand L (L = 2,2′-(4-(3,4-diethoxyphenyl)pyridine-2,6-diyl)dipyrazine) and its copper (II) complex, [Cu(NO3)2L]. The in-situ prepared [Cu(H2O)2L](NO3)2 receptor in aqueous acetonitrile (4:1 v/v, 10 mM HEPES buffer, pH 7.4) medium displayed instantaneous responses towards biologically important bio-thiol l-Cysteine (Cys) and essential amino acid l-Histidine (His) over other l-amino acids through UV–Visible absorption spectral studies. Additionally, the competitive experiments confirmed that in-situ prepared [Cu(H2O)2L](NO3)2 receptor selectively detects Cys (1 equivalent) in the presence of other l-amino acids. The detection limits of Cys and His were calculated to be 8.23 × 10−7 M and 2.55 × 10−6 M, respectively. The density functional theory (DFT) calculation shows that selectivity of [Cu(H2O)2L](NO3)2 towards Cys is due to the reduction of Cu(II) to Cu(I) in the presence of Cys, while Cys is oxidized to cystine (Cys-Cys). For His, selectivity observed due to the formation of [Cu(His)2] moiety between Cu(II) ion with one His via N,O coordination mode and another His via N,N,O-coordination mode.

A metal–organic framework composite loaded with coumarin guests as a turn-on luminescent sensor for detection of cysteine in aqueous solution

In this work, a composite material (ACE@UiO-66-NH2) has been synthesized conveniently by loading a cysteine-responsive molecular probe Acrylic acid 3-acetyl-2-oxo-2H-chromen-7-yl ester (ACE) on a UiO-type zirconium-based metal–organic framework (UiO-66-NH2). Furthermore, the resulting ACE@UiO-66-NH2 demonstrated to be a fluorescent turn-on probe for selective recognition of Cys from other amino acids in aqueous HEPES buffer systems. Additionally, the proposed recognition mechanism has been confirmed by 1H NMR and TLC. The study provided a promising approach to rationally design MOF-based fluorescent sensor for Cys in aqueous system.