The highly selective rhodol-based putrescine probe and visual sensors for on-site detection of putrescine in food spoilage

Putrescine (Butane-1,4-diamine) has been regarded as a vital marker of spoiling protein-rich foods, especially meat and seafood. The detection of putrescine in food is considered a convenient and powerful method for evaluating the degree of spoilage of protein-rich foods. Herein, a novel rhodol-based fluorescent probe RSMA (formyl-rhodol Schiff base with methoxyaniline) was developed to detect putrescine. RSMA exhibited excellent linearity (R2 = 0.9912) in the concentration range of 0-45 μM of putrescine with a detection limit as low as 0.45 μM. Although RSMA had moderate responses to some aliphatic diamines, the selectivity of RSMA for putrescine was one of the best reported in the literature so far. Moreover, RSMA was successfully fabricated to solid-state sensors for on-site detection of putrescine in shrimp, that demonstrated its application in monitoring food spoilage.

A Chromo-fluorogenic Probe for Selective Detection of Picric Acid Alongside Its Recovery by Aliphatic Amines and Construction of Molecular Logic Gates

Nitroaromatic compounds are illicit explosive chemicals. For environmental security and homeland safety, selective and sensitive identification of these secondary-class explosives has been a reason for the exhaustive research arena of chemists for about a decade. We introduced a sensitive optical sensor with desalted neutral red (NR) dye. After ingressing picric acid (PA) in acetonitrile, the probe becomes non-fluorescent, displaying a colorimetric change from yellow to pink. The quenched phenomena and the changed color were re-established with aliphatic amine, trimethylamine (TEA). The reversibility is produced cyclically, both in fluorimetrically and spectrophotometrically. The detection limit for PA with our probe comes out as 0.639 µM; this value is significantly lower than many chemosensors available in the literature. Also, NR-stained filter paper strips-based test kit analysis has been deployed as a displayable photonic device for in-situ detection of PA. Furthermore, the whole system was conceptualized to produce single input, single output, and double input single output logic gates, which can be applied to digital devices. The chronological input manner as NTP (NR- TEA-PA) pushed us to configure a molecular keypad lock system, the basis of digital locking devices. The repeatable & reversible detection system exhibits "Write read- Erase-read Write-read' type memory devices.

Recent Advances in Chemodosimeters Designed for Amines

The analysis of amines has long been a very important task in science, industry, and healthcare. To date, this task has been accomplished by using expensive and time-consuming methods. Colorimetric and fluorescent chemodosimeters enable the fast, accurate, and sensitive analysis of various species with inexpensive instruments or the naked eye. Accordingly, the studies on these probes have gained great momentum in the last 20 years. In this review, amine chemodosimeters developed in the last 10 years were investigated. The investigated chemodosimeters are metal-free structures based on small organic compounds. The strategies for the detection, differentiation, and quantification of amines were discussed by considering the reaction types.

A New Compound for Sequential Sensing of Picric Acid and Aliphatic Amines: Physicochemical Details and Construction of Molecular Logic Gates

Picric acid (PA) at low concentration is a serious water pollutant. Alongside, aliphatic amines (AAs) add to the queue to pollute surface water. Plenty of reports are available to sense PA with an ultralow limit of detection (LOD). However, only a handful of works are testified to detect AAs. A new fluorescent donor-acceptor compound has been synthesized with inherent intramolecular charge transfer (ICT) character that enables selective and sensitive colorimetric quantitative detection of PA and AAs with low LODs in non-aqueous as well as aqueous solutions. The synthesized compound is based on a hemicyanine skeleton containing two pyridenylmethylamino groups at the donor and a benzothiazole moiety at the acceptor ends. The detailed mechanisms and reaction dynamics are explained spectroscopically along with computational support. The fluorescence property of the detecting compound changes due to protonation of its pyridinyl centers by PA leading to quenching of fluorescence and subsequently de-protonation by AAs to revive the signal. We have further designed logic circuits from the acquired optical responses by sequential interactions.

A reaction-based sensing scheme for volatile organic amine reagents with the chromophoric-fluorogenic dual mode

In this study, we present the classical Michael's addition reaction-based sensing scheme for volatile organic amine reagents such as ethylenediamine, N, N-dimethylethylenediamine and diethylenetriamine using a near-infrared fluorescent dye TCF1. Obvious spectral changes in the UV-vis absorption and fluorescence spectra of TCF1 were observed upon addition of these amine reagents with an effective catalyst DBU, resulting in significant and fast color changes detectable by the naked-eye. TCF1 showed an efficient response to these amine reagents with a low detection limit, especially for diethylenetriamine. NMR and MS spectral analysis proved that the mechanism of the detection was based on the classical Michael addition, which was also verified by the theoretical calculations. In addition, a portable test paper incorporated with TCF1 had also successfully realized the detection of a low concentration of these amine reagents.

Detection of organic amines using a ratiometric chromophoric fluorescent probe with a significant emission shift

Taking advantages of both the well-known α,β-unsaturated structure and the special nucleophilicity of organic amines toward its acceptor moieties, intramolecular charge transfer as a signaling mechanism is used to design and synthesize a new ratiometric chromophoric fluorescent probe (BI-CA-ID) with large emission shifts toward organic amines. This probe is employed for the detection of organic amines with high selectivity and sensitivity and a “naked-eye” color change (from red to colorless). Ultraviolet–visible and fluorescence spectrometric measurements are used to determine detection limits as low as 0.024 and 0.43 μM. Furthermore, nucleophilic addition of the amine on the α,β-unsaturated of BI-CA-ID indicated that the sensing mechanism occurs via interruption of the π-conjugation.

A very sensitive and highly selective organic selector in CNTs composite chemiresistive for efficient differentiation of organic amine vapours

With the call for the IoE (Internet of Everything), stable and efficient electric noses/tongues have become the most critical part of the sensor network. Identifying target gases efficiently and rapidly at ambient air becomes a focus on sensor research. We designed a chemiresistive sensor based on a composite of a specific selector and single-walled carbon nanotubes (SWNTs) for the detection and differentiation of organic amine vapours in air (25 ℃, 55% RH). The synergetic combination of F4-TCNQ (2,3,5,6-Tetrafluoro-7,7',8,8'-tetracyanoquinodimethane) and SWCNTs could modulate the electrical properties of sensor leading to the enhancement of response up to ppb-level for primary amine vapor detection. Different from traditional chemiresistive sensor, this sensing materials exhibit unique differences in response to different types of amines thought different mechanisms. We have proven the practical possibilities through the detection of the simulated complexed environmental atmosphere in industrial production. Furthermore, we explored the working mechanism of high-performance sensors, which could provide theoretical guidance for sensor design for more commercial applications. This study provided a simple, convenient, and highly efficient practical method for organic amine detection at ambient air for real-life applications.

Dual-mode recognition of biogenic amine tryptamine and fluoride ions by a naphthyl hydrazone platform: application in fluorescence imaging of HeLa cells and zebrafish embryos

A new type of selective and sensitive naphthyl hydrazone anchored Schiff base derivative (PYNA) was synthesized and applied to the fluorogenic and chromogenic recognition of both tryptamine (TryptA) and F⁻ions, further it has good cell permeability and biocompatibility in zebrafish embryos and HeLa cells.

Macroscopic helical chirality and self-motion of hierarchical self-assemblies induced by enantiomeric small molecules

Transfer of molecular chirality to supramolecular chirality at nanoscale and microscale by chemical self-assembly has been studied intensively for years. However, how such molecular chirality further transfers to the macroscale along the same path remains elusive. Here we reveal how the chirality from molecular level transfers to macroscopic level via self-assembly. We assemble a macrostripe using enantiomeric camphorsulfonic acid (CSA)-doped polyaniline with hierarchical order. The stripe can twist into a single-handed helical ribbon via helical self-motion. A multi-scale chemo-mechanical model is used to elucidate the mechanism underlying its chirality transfer and induction. The molecular origin of this macroscopic helical chirality is verified. Results provide a comprehensive understanding of hierarchical chirality transfer and helical motion in self-assembled materials and even their natural analogues. The stripe exhibits disparate actuation behaviour under stimuli of enantiomeric amines and integrating such chiral perception with helical self-motion may motivate chiral biomimetic studies of smart materials.

Chirality transfer by chemical self-assembly has been studied intensively for years but chirality transfers along the same path remains elusive. Here the authors use a multiscale chemo-mechanical model to elucidate the mechanism underlying the chirality transfer via self-assembly in hierarchical camphorsulfonic acid doped polyaniline.

Fluorescent β-ketothiolester boron complex: substitution based “turn-off” or “ratiometric” sensor for diamine

Boron diketonate 3 provides a choice of turn-off or ratiometric detection of diamine with respect to substitution on the boron-chelating ring. Detection of the diamine involves a substitution reaction by elimination of a methylsulfanyl group, favouring selective detection of diamine.

Enantioselective Fluorescent Recognition of Amino Acids by Amide Formation: An Unusual Concentration Effect

A BINOL-based perfluoroalkyl ketone shows a highly enantioselective fluorescence enhancement in the presence of various amino acid-TBA salts and can be used to determine the enantiomeric composition of these compounds. It was found that the amino acid-TBA salts can act as nucleophiles to cleave the perfluoroalkyl group off of the ketones to form the corresponding amides at room temperature in DMSO. This is the first example of an enantioselective fluorescent sensor for the recognition of amino acids by forming amide bonds under very mild conditions. This study has also revealed an unusual concentration effect leading to an "off-on-off" fluorescence response of the sensor toward one enantiomer of the amino acids.

Developing a sensor layer for the optical detection of amines during food spoilage

A colourimetric sensor layer has been developed for ammonia and biogenic amines. Amine exposure induces a traffic light colour change from green to red. Recognition is performed by a pH indicator dye, covalently immobilised onto cellulose microparticles. The sensor microparticles are embedded into food-grade silicone. Selectivity of the pH indicator dye towards gaseous amine is obtained by complete embedding of the sensor particles within the ion-impermeable silicone. A response time of 1.5h has been achieved, with a reverse response occurring after 20h. This time frame is considered sufficient for spoilage processes. Cytotoxicity studies confirm the layers are non-toxic.

Amino acid recognition by fine tuning the association constants: tailored naphthalimides in pillar[5]arene-based indicator displacement assays

Three naphthalimide derivatives were synthesized with different anchoring groups to adjust the supramolecular interactions with carboxylato-pillar[5]arene. The complexes were used as indicator displacement assays for basic amino acids and diamines.

Colorimetric and fluorescence probe for the detection of nano-molar lysine in aqueous medium

A new BODIPY based lysine selective probe,THBPY, is synthesized and detects nano-molar lysine in aqueous medium, exhibiting both a visible change in color from yellow-green to orange and a change in the fluorescence profile.

Reversible and “fingerprint” fluorescence differentiation of organic amine vapours using a single conjugated polymer probe

By embedding multiple reactive groups onto one polymer, an ultrasensitive and reversible fluorescent probe for different organic amines vapour has been reported.

Fluorescence quenching of carbazole by 2-chloro-3,5-dinitrobenzotrifluoride-ethylamines intermolecular charge-transfer complex

The interaction between carbazole and 2-chloro-3,5-dinitrobenzotrifluoride-ethylamines, (mono-, di-, and triethylamine) charge-transfer complex in DMSO was studied using fluorescence spectroscopy. The positive deviation from linearity has been observed in the Stern-Volmer plots. The experimental results showed that the fluorescence of carbazole was quenched by 2-chloro-3,5-dinitrobenzotrifluoride-ethylamines charge-transfer complex through a combined quenching procedure. The Stern-Volmer quenching constants, K(SV), have been determined and found to be greater quenching efficiency of ethylamine. Carbazole/2-chloro-3,5-dinitrobenzotrifluoride loaded PMMA film was exposed to ethylamine vapor, where the resulting absorption and emission changing properties were clearly monitored.

Sensitive fluorescent detection and Lewis basicity of aliphatic amines

In this contribution is reported the sensitive properties of the Zn(II) Schiff base complex, 1, in dichloromethane with respect a series of primary, secondary, and tertiary aliphatic amines through the study of fluorescence enhancement upon amine coordination to the Lewis acidic Zn(II) metal center with formation of 1:1 adducts. It is found that complex 1 exhibits selectivity and nanomolar sensitivity for primary and alicyclic amines. A distinct selectivity is also observed along the series of secondary or tertiary amines, paralleling the increasing steric hindrance at the nitrogen atom. The binding interaction can be related to the Lewis basicity of the coordinating amine; thus, complex 1 represents a suitable reference Lewis acid, and estimated binding constants within the investigated amine series can be related to their relative Lewis basicity. A relative order of the Lewis basicity can be established for acyclic amines, primary > secondary > tertiary, while an inverted order, tertiary > secondary ≈ primary (acyclic), is found in the case of alicyclic amines. The present approach represents a simple, suitable method to ranking the relative Lewis basicity of aliphatic amines in low-polarity, nonprotogenic solvents.

Dynamic multi-component covalent assembly for the reversible binding of secondary alcohols and chirality sensing

Reversible covalent bonding is often employed for the creation of novel supramolecular structures, multi-component assemblies, and sensing ensembles. In spite of remarkable success of dynamic covalent systems, the reversible binding of a mono-alcohol with high strength is challenging. Here we show that a strategy of carbonyl activation and hemiaminal ether stabilization can be embodied in a four-component reversible assembly that creates a tetradentate ligand and incorporates secondary alcohols with exceptionally high affinity. Evidence is presented that the intermediate leading to binding and exchange of alcohols is an iminium ion. Further, to demonstrate the use of this assembly process we explored chirality sensing and enantiomeric excess determinations. An induced twist in the ligand by a chiral mono-ol results in large Cotton effects in the circular dichroism spectra indicative of the alcohol’s handedness. The strategy revealed in this study should prove broadly applicable for the incorporation of alcohols into supramolecular architecture construction.

A molecular probe for the optical detection of biogenic amines

A coumarin derivative was employed for the detection of biogenic amines in buffered aqueous solution by UV-Vis or fluorescence spectroscopy. Incorporated in a polymeric matrix, the dye can also be used for the optical detection of gaseous amines.

Molecular recognition of organic ammonium ions in solution using synthetic receptors

Ammonium ions are ubiquitous in chemistry and molecular biology. Considerable efforts have been undertaken to develop synthetic receptors for their selective molecular recognition. The type of host compounds for organic ammonium ion binding span a wide range from crown ethers to calixarenes to metal complexes. Typical intermolecular interactions are hydrogen bonds, electrostatic and cation-π interactions, hydrophobic interactions or reversible covalent bond formation. In this review we discuss the different classes of synthetic receptors for organic ammonium ion recognition and illustrate the scope and limitations of each class with selected examples from the recent literature. The molecular recognition of ammonium ions in amino acids is included and the enantioselective binding of chiral ammonium ions by synthetic receptors is also covered. In our conclusion we compare the strengths and weaknesses of the different types of ammonium ion receptors which may help to select the best approach for specific applications.