1H NMR Titration Research Articles

Selective chromogenic nanomolar level sensing of arsenite anions in food samples using dual binding site probes

In the present study, two chromogenic probes, N7R2 and N7R3, each containing two binding sites, were designed and synthesized for the selective detection of arsenite in DMSO/H2O (1:1, v/v). The probes exhibited stability across a pH range spanning from 5 to 12. The lower detection limits of 2.01 ppb (18.86 nM) for N7R2 and 1.79 ppb (16.75 nM) for N7R3, which are much lower than the WHO recommended permissible limit of arsenite, confirmed the superior efficiency of the probes in detecting arsenite. The detection mechanism for arsenite was proposed through UV and 1H NMR titrations, electrochemical studies, and DFT calculations. Practical applications were demonstrated through the fabrication of test strips and molecular logic gates. The probes efficiently recognized arsenite in real water, honey, milk samples, and fruit/vegetable juices. Both N7R2 and N7R3 exhibited excellent recovery rates in the analysis of food samples, demonstrating the probes' usefulness in real sample analysis.

Selective cyanide ion detection using hydrazine carbothioamide probe: A fluorescence turn-on approach

This study reports the synthesis of various hydrazine carbothioamide derivatives through a Schiff base reaction, confirmed by FT-IR, NMR (1H and 13C), and HRMS spectroscopic methods. Among the synthesized derivatives, probe L ((4-fluorobenzylidene)-2-(1-phenylethylidene)hydrazine-1-carbothioamide) was identified as a highly selective fluorometric chemosensor based on its absorbance and emission spectra. Probe L showed a CN− ion-specific turn-on fluorescence response, with very little interference from other anions. Job's method established a 1:1 binding stoichiometry among probe L and the cyanide ion. The detection limits (LOD) and quantification (LOQ) were observed to be 0.639 µM and 2.116 µM, respectively. With the use of FT-IR spectroscopy, 1H NMR titration, 13C NMR and HRMS, the binding mechanism was clarified. Moreover, probe L was employed effectively for detecting CN− ions in water and food samples, highlighting its potential as a practical sensor for cyanide detection.

A novel thiourea‐based fluorescent turn‐on sensor for rapidly detecting hypochlorite through a desulfurization reaction

AbstractExcess hypochlorite (ClO−) is harmful to living organisms and can cause various oxidative diseases in the human body. Owing to the toxicity of ClO−, the development of efficient fluorescence sensors to track ClO− is necessary. In this work, we report a novel thiourea‐based fluorescent turn‐on sensor 1‐(9‐ethyl‐9H‐carbazol‐3‐yl)‐3‐(naphthalen‐1‐yl)thiourea (ECNT) for recognizing ClO−. ECNT can detect ClO− with high selectivity, relatively low interference with other analytes, and a significantly fast response time (<1 s) through a desulfurization reaction. The detection limit of ECNT for ClO− is calculated as 5.59 μM. Of note, ECNT is a chemosensor that reacts the fastest with ClO− among the reported thiourea‐based fluorescence turn‐on sensors for detecting ClO−. The response mechanism of ECNT to ClO− is demonstrated through 1H NMR titration, ESI mass, and density functional theory calculations.

Fluorenone-naphthyl encapsulated dual sensor for recognition of F− and Hg2+: Syngenetic effect with drug sobisis and molecular docking studies

A novel fluorenone-naphthyl pendant sensor (FTU) possessing thiourea functionality has been synthesized via a simple condensation method and utilized for the recognition of F− and Hg2+ ions in the solution of CH3CN. The addition of F− and Hg2+ ions to the FTU solution led to the appearance of red-shifted absorption bands at 340 and 315 nm, respectively. On the other hand, in the fluorescence spectrum, the two-fold decrease in fluorescence intensity of probe FTU was observed with F− ions; while complete quenching of the fluorescence intensity was noticed with Hg2+ ions at 423 nm. The limit of detection values of F− and Hg2+ ions were found to be 1.02 & 29.1 nM, respectively, measured by UV–vis studies and 0.0185 & 0.81 nM, respectively, measured by fluorescence studies, which are less than recommended by WHO. DFT computational assessments and 1H NMR titration experiments pointed to F− induced deprotonation of thiourea NH signals. However, the chelation-enhanced quenching effect (CHEQ) was held responsible for fluorescence quenching with Hg2+ addition. Moreover, the in-situ formed FTU + F− complex was utilized for secondary sensing of drug sobisis. Furthermore, the real-world applicability of sensor FTU has been successfully scrutinized for the recognition of F− ions in the toothpaste samples. In addition, molecular docking studies revealed that FTU exhibited excellent antibacterial potency towards different gram-positive as well as negative strains.

A simple and efficient chemodosimeter for colorimetric and “turn-on” fluorescent detection of sulphite in aqueous solution

Described in this article the design and synthesis of a simple fluorogenic and chromogenic chemodosimeter C for sensitive and selective detection of sulphite via the 1,4-Michael addition reaction. This chemodosimeter demonstrated high SO32− selectivity over other twenty-three competitive analytes in ∼100 % aqueous solution. Chemodosimeter C revealed a 35-fold “turn-on” fluorescence enhancement towards sulphite ions, as well as fluorometric color change from colorless to cyan. The chemodosimeters’ detection limit for sulphite ions was determined to be 0.782 µM. The sensing mechanism was established using 1H NMR titration, HRMS, and theoretical calculations. Additionally, convenient chemodosimeter C-based test strips and C-treated silica gel were developed for rapid on-site visual detection of sulphite ions.

A turn-on anthraquinone-derived colorimetric and fluorometric dual-mode probe for highly selective Hg2+ determination and bioimaging in living organisms

Mercury ion (Hg2+) is considered a harmful neurotoxin, and real-time monitoring of Hg2+ concentrations in environmental and biological samples is critical. Fluorescent probes are a rapidly emerging visualization tool owing to their simple design and good selectivity. Herein, a novel fluorescence (FL) probe 2-(4-((6-((quinolin-8-yloxy)methyl)pyridin-2-yl)methyl)piperazin-1-yl)anthracene-9,10-dione (QPPA) is designed using piperazine as a linker between the anthraquinone group, which serves as a fluorophore, and N4O as the Hg2+ ligand. The probe exhibits FL “turn-on” sensing of Hg2+ because the complex inhibits the photo-induced electron transfer (PET) process. Moreover, QPPA can overcome the invasion by other possible cations, resulting in a clear color change from orange to colorless with the addition Hg2+. The chelation of QPPA with Hg2+ in a 1:1 ratio. Subsequently, the theoretically determined binding sites of the ligand to Hg2+ are validated through 1H NMR titration. The in situQPPA–Hg2+ complex can be subjected to Hg2+ extraction following the introduction of S2− owing to its robust binding capacity. The exceptional limit of detection values for Hg2+ and S2− are obtained as 63.0 and 79.1 nM (S/N = 3), respectively. Moreover, QPPA can display bright red FL in the presence of Hg2+ in different biological specimens such as HeLa cells, zebrafish, onion root tip tissues, and water flea Daphnia carinata, further providing an effective strategy for environmental monitoring and bioimaging of Hg2+ in living organisms.

Six-Cyclic Crown Ether-Type Pillar[5]Arene: Enhanced Binding Ability to Bispyridinium Derivatives.

A six-cyclic crown ether-type pillar[5]arene was synthesized, and the five ethylene oxide loops were located outside the cavity and not affected by temperature changes which was confirmed by variable-temperature NMR experiment in DMSO-d6 and CDCl3 and 2D 1H-1H NOESY experiment in CDCl3. The six-cyclic pillar[5]-crown also showed greater binding ability of host-guest with bis(pyridinium) derivatives than conventional alkoxy pillar[5]arenes that illustrated through 1H NMR titration spectroscopic experiment in acetone-d6/CDCl3 (1 : 1) and UV-vis titration experiments in CHCl3 at room temperature. The five benzocrown ethers at the periphery were able to bind metal cations by 1H NMR titration spectroscopic experiment in CD2Cl2/methanol-d4(9 : 1).

Colorimetric sensors for discriminatory detection of arsenite ions: Application in milk, honey and water samples and molecular logic gates

Millions of people are exposed to dangerous arsenic levels in drinking water, highlighting the urgent need for affordable, continuous on-site arsenic monitoring methods. It is crucial to specifically detect arsenite among inorganic arsenic anions because it is more poisonous than arsenate. Addressing these concerns, the present study developed 5-(4-nitrophenyl)-2-furaldehyde based two colorimetric chemosensors, N5R3 and N5R4, with different signaling groups for the selective detection of arsenite anions over arsenate in DMSO/H2O (6:4, v/v). The red-shift in the UV–Vis absorption spectra supported the distinct color changes of sensors N5R3 and N5R4 displayed upon binding with arsenite. Sensors demonstrated stability over a pH range of 6 to 12 and exhibited stability over a considerable time period. Among the chemosensors, N5R3 exhibited the lowest detection limit of 7.41 ppb with a high binding constant of 2.9976 × 106 M−1 for arsenite. The 1:1 binding interactions between the chemosensors and arsenite were confirmed using B-H plot and Job’s plot analysis. The intramolecular charge transfer (ICT) mechanism for detecting arsenite was proposed through UV and 1H NMR titrations, electrochemical studies, mass spectral analysis and DFT calculations. The interactions between the sensor and arsenite anions were further analyzed using global reactivity parameters (GRPs). Practical applications were demonstrated through the utilization of test strips and molecular logic gates. Both chemosensors efficiently recognized arsenite in real water, honey, and milk samples.

Development of a novel isophorone-derived near-infrared fluorescent probe for specific and visual detection of Pb2+: Theoretical, practical and bioimaging investigations

The development of specific and visually detectable fluorophores for the accurate and rapid Pb2+ recognization is crucial. In this study, we introduced a novel isophorone-derived fluorescent probe, (E)-2-(3-(3-formyl-4-hydroxystyryl)-5,5-dimethylcyclohex-2-en-1-ylidene)malononitrile (YSQ), rationally designed for prompt and high-quality Pb2+ detection. YSQ demonstrated noticeable red emitting fluorescence enhancement upon Pb2+ interactions (upon binding, τavg 16.7 ns, Φ 12 %) with visible color changes discernible to the naked eye in MeOH/H2O (v/v 9/1, pH 7.4, 0.2 mM). The probe YSQ achieved a quite low detection limit (LOD) of 18 nM and a high association constant of 2.93 × 105 M−1 towards Pb2+ using fluorescence titration. We proposed a binding mechanism of YSQ with Pb2+ ions, supported by the density functional theory (DFT/TD-DFT), 1H NMR titration experiments, IR and HRMS analysis. In addition, a simple and affordable smartphone-supported specific Pb2+ detection technique was developed with visible color changes. Furthermore, this NIR emissive properties of YSQ offered broad potential applications in actual water sample and solid analysis, bio-imaging and test strips.

DGA-grafting pyridine for ultra-selective and prior extraction of 99TcO4− from simulated spent nuclear fuel

Selective and prior extraction of 99TcO4− ahead of uranium and plutonium separation is a beneficial strategy for the modern nuclear fuel cycle. Herein, a novel DGA-grafting pyridine ligand BisDODGA-DAPy (L1) was tailored for the efficient separation of TcO4− from simulated spent nuclear fuel based on the selectivity of pyridine and synergistic effect of diglycolamide (DGA) group. Compared to the ligands BisDOSCA-DAPy (L2) and BisDODGA-MPDA (L3) with similar structure, BisDODGA-DAPy (L1) demonstrated the better separation performance including good extraction efficiency, reusability, and high loading capacity for TcO4− under high acidic medium. The interactions of the ligands with Tc(VII)/Re(VII) have been investigated in detail using FT-IR, 1H NMR titration, UV-Vis spectrophotometric titration, ESI-HRMS and DFT simulations. The extraction mechanism affected by the protonation of ligand was elucidated under different acidity. BisDODGA-DAPy (L1) demonstrated the ultra-selective extraction ability for TcO4− from simulated spent nuclear fuel. The maximum SFTc/U and SFTc/Pu values were up to 1.29 × 104 and 5.08 × 103, respectively. In the presence of 9 × 104-fold excess of NO3−, the extraction of TcO4− was almost unaffected. Moreover, the good radiolytic stability further highlights the promising potential of this ligand for 99Tc separation. DFT calculation revealed the dominant role of DAPy and DODGA in TcO4− extraction, providing the theoretical evidence for BisDODGA-DAPy (L1) to selectively bind TcO4− over NO3−.

A coumarin containing hemicyanine-based probe for dual channel detection of cyanide ion

Cyanide(CN−) is known as one of the most toxic inorganic anions and is harmful to the environment and human health. Its wide use and severe toxicity have led to the development of highly selective cyanide detection, and quantification is desirable. A coumarin-containing hemicyanine-based probe has been developed for highly selective colorimetric and fluorometric detection of cyanide in acetonitrile and aqueous medium. The probe was characterized by 1D NMR (1H and 13C) and HRMS Spectroscopy, and the sensing properties have been studied in colorimetric and fluorometric methods. The high selectivity of the probe for CN− was established by UV–vis and fluorescence spectroscopy in the presence of other competing anions. The probe can detect cyanide as low as 0.7 μM within 90 s. A remarkable change in spectroscopic properties has been observed upon adding cyanide ion. The weakly luminescent probe emitted strongly upon the reaction with CN− which is due to the inhibition of internal charge transfer (ICT) from coumarin to indolinium moiety. Furthermore, the colour change from yellow to colourless and the appearance of a blue luminescence, which can be observed by the naked eye, provides a simple real-time method for cyanide detection, also supported by 1H NMR titration and theoretical study. Furthermore, a paper strip kit loaded with probe has been constructed for a real-time application of CN detection without any interference from other competitive analytes.

Preparation of tetra-imidazolium salt and sensing for fluoride anion

One tetra-imidazolium salt (2) based on quinoxaline was prepared and characterized, and the detection of anions by compound 2 as a chemosensor was researched through fluorescence spectra, UV/Vis spectra, 1H NMR titrations, MS and IR spectra. The experimental results displayed that sensor 2 can selectively recognize F− through the instrument or the naked eyes (the color changed from colorless to brown in visible light). The high K value (6.4 × 104 M−1) for 2 F− indicated that 2 had strong bonding force to F−. The low detection limit (1.84 × 10−7 mol/L) indicated that the detection of F− by 2 was sensitive.

Pyrrole-based acyclic hexapodal aldehyde for anion recognition

A novel acyclic hexapodal host (4a) featuring with multiple formyl groups, pyrrole cores, and ester linkages has been prepared and characterized through 1H NMR, 13C NMR, high-resolution mass spectrometry and single-crystal X-ray diffraction techniques. This versatile host molecule exhibits robust anion recognition for CN−, F−, SO42−, HSO4−, H2PO4−, and HP2O73− with the binding constants spanning 0.18 × 105 M−1 to 7.72 × 105 M−1. Interactions with these anions were elucidated through UV–visible and 1H NMR titrations, complemented by DFT calculations. At low guest concentrations (5- to 100-fold excess), a 1:1 complexation is predominant. However, at high concentrations (1000-fold excess), the host's flexibility promotes the assembly of other host-guest complexes. Comparative studies with related pyrrole-based hexapodal ester 4b and tetrapodal aldehyde 4c highlight the importance of peripheral formyl groups, pyrrolic NH groups, the number of pendant arms, and conformational adaptability in anion recognition. These insights underscore the potential of acyclic multipodal hosts in advancing supramolecular chemistry and anion recognition.

N-Confused strapped calix[4]pyrrole: the missing member of calix[4]pyrrole chemistry.

The first example of N-confused strapped calix[4]pyrrole 5 is presented. The structural integrity of 5 and its regular isomer 4 was unambiguously confirmed by single crystal X-ray diffraction analysis. Anion binding studies using 1H NMR titration carried out in CDCl3 revealed a small but detectable tendency of 5 to interact with an anion. Conversely, the isomeric regular strapped calix[4]pyrrole 4 displayed high selectivity for fluoride anions under similar experimental conditions. The high fluoride selectivity of 4 and unexpectedly low anion affinity of 5 were ascribed to the presence of intramolecular hydrogen bonds within strapping subunits.

Fluorescent and colorimetric dual-mode chemosensor for easy detection of Cu2+: Practical and smartphone-based application to test strip and water sample

A fluorescent and colorimetric dual-mode chemosensor HNHQ, based on the julolidine and naphthol moieties, was synthesized. Compound HNHQ exhibited unique photophysical properties of an intense fluorescence with a high quantum yield (Φ = 0.363) and a light yellow color through the ICT mechanism. HNHQ could detect Cu2+ through both a fluorescence turn-off and a colorimetry variation of light yellow to yellowish brown. HNHQ reacted with Cu2+ with a binding ratio of 1:1. The detection limit for Cu2+ was analyzed to be 1.60 μM for fluorescence and 1.32 μM for UV–vis, considerably below the safe value of 31.5 μM established by the World Health Organization (WHO). HNHQ analyzed Cu2+ in the pH range of 6–8 and reversibly identified Cu2+ by using ethylenediaminetetraacetic acid (EDTA). Moreover, HNHQ could effectively detect Cu2+ in mineral and tap water samples, in addition to test strips through fluorescent and colorimetric changes. As a portable probe, HNHQ was successfully applied to a smartphone-based RGB analysis for the quantitative examination of Cu2+. The detection mechanism of HNHQ for Cu2+ was illustrated by 1H NMR titration, ESI-MS analysis, and density functional theory (DFT) calculations.

A highly sensitive and colorimetric fluorescent probe for visualizing hydroxylamine in immune cells

BackgroundHydroxylamine (HA) is vital industrial raw material and pharmaceutical intermediate. In addition, HA is an important cellular metabolite, which is intermediate in the formation of nitric oxide and nitroxide. However, excessive amounts of HA are toxic to both animals and plants. Conventional methods for the detection of HA are cumbersome and complicated. The detection of HA with fluorescent probes is convenient and sensitive. There are few probes available for the detection of hydroxylamine. Therefore, a fluorescent probe for the sensitive and selective detection of HA was developed in this work. ResultsA coumarin derivative SWJT-22 was synthesized as a colorimetric fluorescent probe to detect hydroxylamine (HA), with high sensitivity and selectivity. The detection limit of the probe to HA was 0.15 μM, which was lower than most probes of HA. Upon the addition of HA to aqueous solution containing SWJT-22, the color of the solution changed from orange to yellow, and the fluorescence color also changed from orange to green. The reaction mechanism of SWJT-22 to HA was confirmed by 1H NMR titrations, mass spectrometry and round bottom flask experiments. Moreover, SWJT-22 had been fabricated into portable test strips for the detection of HA. SWJT-22 had been successfully used in cellular imaging and could detect both endogenous and exogenous HA in HeLa cells and RAW 264.7 cells. SignificanceDue to the physiological role of hydroxylamine in organisms, it is crucial to detect hydroxylamine selectively and sensitively. This work provided a convenient tool for the detection of hydroxylamine, not only to detect endogenous and exogenous HA in cells, but also made into portable test strips. The HA fluorescent probe SWJT-22 is expected to promote the study of HA in physiological processes.

A highly selective and sensitive quinoline-based fluorescent turn-off chemosensor for the detection of picric acid

A simple turn-off quinoline-based fluorescent chemosensor, 1-(6-amino-2-methyl-4-phenylquinolin-3-yl)ethan-1-one (QN) has been developed, synthesized, and characterized by various spectroscopic methods. This probe is selective for the sequential recognition of picric acid (PA), using a fluorescent turn-off method. QN exhibits a broad emission band at 504 nm, but fluorescence quenching occurs upon the addition of picric acid over other nitro compounds. The binding stoichiometric ratio between QN and picric acid was calculated to be 1:1 through Job's plot analysis, and the binding constant was determined. The limit of detection towards picric acid was found to be 9.33 µM. Further, the mechanistic approach for binding has been investigated by spectroscopic methods like 1H NMR titration, FT-IR studies, and density functional theory (DFT) studies.

Active Hydrogen Free, Z-Isomer Selective Isatin Derived "Turn on" Fluorescent Dual Anions Sensor.

An efficient and anions fluorescence "on-off" sensor of 1-(prop-2-yn-1-yl)-3-(quinolin-3-ylimino)indolin-2-one (PQI) has been developed for the selective sensing of dual anions of F- and NO3- ions in aqueous medium. Active hydrogen and Lewis acidic binding sites free, Z- isomer of isatin based π-conjugated quinoline exhibited excellent sensing activity against F- and NO3- ions in UV light. The fluorescence turns on the process accomplished via the PET "on-off" mechanism. The interaction between probe molecule and anions is thought to be a non-covalent interaction of the low electron density covalently bonded N-methylene moiety of propargyl isatin (-N-CH2-) of probe molecule with F- ion and the terminal acidic proton of propargyl group of isatin (-C≡C-H) with NO3- ions. The modes of anions binding with PQI and plausible mechanisms are proposed by 1H and 13C NMR titrations. The selectivity of anions sensing may be offered by the bucked structure of the Z-isomer. The calculated association constant values for PQI and F- and NO3- are ions 2.5 × 104M-1 and 2.2 × 103M-1, respectively, indicating strong binding interaction between the PQI and anions. The association nature of anions and probes was analyzed by a Jobs plot and the finding indicates both F- and NO3- ions are in 1:1 complexation with PQI. The limit of detection (LOD) of the probe with F- and NO3- ions is calculated and is to be 6.91 × 10-7M and 9.93 × 10-7M, respectively. The proposed PQI fluorophore possesses a low limit of detection (LOD) for both F- and NO3- ions which is within the WHO prescribed detection limit.

Dual detection of tryptophan and S2O82− by a simple yet rapid fluorometric half-salamo-based chemodosimeter in actual water samples

Tryptophan (Trp) and persulfate (S2O82−) are attracting extensive attention because they have significant influence on biological reactions and the natural environment. Thus, developing a novel method for simultaneous detection of Trp and S2O82− is significant and challenging. Herein, a new type of fluorescent chemodosimeter HL based on a half-salamo was synthesized, which has specific recognition for Trp and S2O82−. The chemodosimeter HL showed high selectivity and rapid detection for Trp and S2O82− over various interfering analytes, and the limits of detection of the HL for Trp and S2O82− were 1.2 × 10−7 and 9.8 × 10−7 M, respectively. The response mechanism of HL for Trp and S2O82− was confirmed by ESI-MS, Job′s plot, 1H NMR titration & DFT calculations. Additionally, the applicability of HL for the detection of Trp and S2O82− was investigated in actual water samples, indicating its potential for usefulness.

Pyrene‐based ratiometric fluorescent chemosensor for sensitive detection of hypochlorite in a perfect aqueous solution

AbstractWe synthesized a pyrene‐based sensitive fluorescent chemosensor, TPA‐Cl ((E)‐N,N,N‐trimethyl‐2‐oxo‐2‐(2‐(pyren‐1‐ylmethylene)hydrazinyl)ethan‐1‐aminium chloride), to detect hypochlorite in a perfect aqueous solution. TPA‐Cl showed high selectivity for hypochlorite through fluorescence color change from sky blue to blue. The detection limit for hypochlorite was calculated as 0.27 μM, which is a quite low value. Moreover, the presence of other anions or ROS hardly hindered the sensing of hypochlorite by TPA‐Cl. Furthermore, TPA‐Cl could be applied successfully as a test kit for the simple recognition of hypochlorite. Surprisingly, TPA‐Cl is the first pyrene‐based fluorescent chemosensor that can detect ClO− by using the TPA‐Cl‐coated test kit. Moreover, TPA‐Cl could achieve the quantification of ClO− in various environmental water samples. The hydrolytic cleavage and oxidation mechanism of TPA‐Cl by hypochlorite was elucidated through UV–vis and fluorescent spectroscopy, 1H NMR titration, ESI‐MS analysis and DFT calculation.