Search

The synthesis and characterisation of two novel self‐assembled amphiphiles (SSAs) SQS‐1 and SQS‐2 are reported. Both compounds, based on the squaramide motif, were fully soluble in a range of solvents and were shown to undergo self‐assembly through a range of physical techniques. Self‐assembly was shown to favour the formation of crystalline domains on the nanoscale but also fibrillar film formation, as suggested by SEM analysis. Moreover, both SQS‐1 and SQS‐2 were capable of anion recognition in DMSO solution as demonstrated using 1H NMR and UV/Vis absorption spectroscopy, but displayed lower binding affinities for various anions when compared against other squaramide based receptors. In more competitive solvent mixtures SQS‐1 gave rise to a colourimetric response in the presence of HPO4 2− that was clearly visible to the naked eye. We anticipate that the observed response is due to the basic nature of the HPO4 2− anion when compared against other biologically relevant anions., Sticky squaramides: Two squaramide‐based self‐assembled amphiphiles (SSAs) are reported that are capable of colorimetric anion recognition in both organic and aqueous solution. Although these SSAs displayed lower binding affinities for anions than other squaramide‐based receptors, in competitive aqueous mixtures, they are fully soluble and capable of selective recognition of HPO4 2− in comparison with other biologically relevant anions.

With this research we set out to develop a number of coumarin-based ‘AND’ logic fluorescence probes that were capable of detecting a chosen analyte in the presence of HCys. Probe JEG-CAB was constructed by attaching the ONOO� reactive unit, benzyl boronate ester, to a HCys/Cys reactive fluorescent probe, CAH. Similarly, the core unit CAH was functionalised with the nitroreductase (NTR) reactive p-nitrobenzyl unit to produce probe JEG-CAN. Both, JEG-CAB and JEG-CAN exhibited a significant fluorescence increase when exposed to either HCys and ONOO� (JEG-CAB) or HCys and NTR (JEG-CAN) thus demonstrating their effectiveness to function as AND logic gates for HCys and a chosen analyte.

Owing to their easy accessibility and high degree of structural and functional diversity, many multicomponent reactions (MCRs) have been a rich source of conjugate π-systems, functionalised chromophores (or fluorophore) and redox active molecules. Despite their high explorative potential and practical benefits, only a few MCR products have been so far investigated for their metal sensing abilities. In the present report, two furopyrimidinones (FPys) based molecular systems have been synthesized by [4 + 1] cycloaddition based MCR sequence. Designed chemosensors displayed optic (absorption spectra) as well as electroanalytical (ion selective electrode) response toward Cu2 + ion in solution and membrane phase respectively (dual channel sensing). Different aspects of both the sensing phenomena such as selectivity, association constants, detection limit, membrane composition etc. were studied in detail using UV–Vis spectroscopy, NMR titration and cell assembly. Both the compounds showed excellent performance characteristics such as high selectivity, acceptable affinity and low detection limits (10− 7 M) in both sensing assays with potential utility in the area of sample monitoring.

A new sensing functionalized chemosensor 3-hydroxy-2-(1H-indol-3-yl)-4H-chromen-4-one ( M1) was readily prepared in facile reaction conditions and explored its sensing nature response towards metal ions in semi-aqueous medium. The chemosensor M1 exhibited high selective and sensitive fluorescence turn “off-on” response for Al 3+ and Zn 2+ ions in the existence of several metal ions and the changes are enabled for naked-eye detection. These high selectivity expressed by high binding constants 2.62 × 10 4 (Al 3+ ) and 1.92 × 10 4 M −1 (Zn 2+ ) calculated by the Benesi-Hildebrand equation based on the emission studies. The binding strategy was also supported by 1 H NMR titration.

Despite the fact that a large number of chemical sensors for Cu 2+ have been proposed by different groups in recent past, most of them fall into very few classes of molecular framework with similar utilities and limitations. In order to broaden the scope and to overcome the limitation of present day chemical sensors, design, synthesis and testing of molecular systems based on novel fluoro/chromophore is a research goal of significant interest. In the present report, two novel furan-2-yl substituted imidazoazine based optic chemosensors ( IA-1 and IA-2 ) for Cu 2+ have been disclosed for the first time. Proposed sensors were found to have high association constants (10 4 M −1 ), acceptable detection limits (10 −7 M), high selectivity and reversibility/reusability. Different aspects of this sensing phenomenon were studied using fluorescence spectroscopy and NMR based titrations. Designed probe have shown potential applications in the area of sample monitoring, photo-printing and membrane sensing.

With this research we set out to develop a coumarin-based novel fluorescent probe NTR-AHC for the detection of biological thiols and nitroreductase (NTR). Probe NTR-AHC was constructed by attaching the NTR trigger moiety (p-nitrobenzyl) and biothiol acceptor (maleic acid monoamide), to the core fluorophore AHC. In the presence of both glutathione (GSH) and NTR, probe NTR-AHC produced a >8-fold increase in fluorescence intensity at 463 nm.

New antipyrine Schiff bases 2,3-dimethyl-4-(3-oxo-1,3-diphenylpropylideneamino)-1-phenyl-1,2-dihydropyrazol-5-one ( AP1 ) and 2,3-dimethyl-4-(2-oxo-1,2-diphenylethylideneamino)-1-phenyl-1,2-dihydropyrazol-5-one ( AP2 ) have been synthesized by simple condensation method and investigated their metal recognition abilities. Different aspects of metal sensing phenomena were extensively studied and results indicated that Schiff base AP1 and AP2 exhibited selective colorimetric and fluorescent sensing behavior towards Al 3+ and Cr 3+ in methanol with high binding nature, which could be directly detected by the naked-eye. Stoichiometry of metal-ligand complexes were determined by job's plots titrations and further verified with HRMS data. Both sensors exhibited excellent fluorescent sensing behavior in acidic and neutral pH with low detection limits 0.49, 0.96 μM for AP1 + Al 3+ , AP1 + Cr 3+ and 0.73, 1.21 μM for AP2 + Al 3+ and AP2 + Cr 3+ , respectively.

A new rhodamine-derived Schiff base RH was synthesized and its sensing behavior toward various metal ions was investigated by UV–vis and fluorescence spectroscopic techniques. The sensor exhibited highly selective and sensitive colorimetric response to Cu2+ and Al3+, and “off–on” fluorescence response toward Fe3+ in semi-aqueous media. The spectral changes obtained are large enough in the visible region of the spectrum and thus enable naked-eye detection. Experimentally proved that the formation of RH–Al3+ complex is fully reversible and can sense to AcO−/F− via break the complex. The results revealed that the sensor offers the sequential detection of Al3+ and AcO−/F−.

Two furochromenone based molecular systems (FC1 and FC2) were synthesized by a microwave assisted three component reaction and investigated for their metal sensing abilities. Reported chemosensors displayed a selective turn off fluorescence response in the presence of Cu2+ in solution phase with high association constants [1.27×104 M–1 (FC1) and 1.05×104 M–1 (FC2)] and low detection limits [2.88 × 10−7 M (FC1) and 2.87 × 10−7 M (FC2)]. Both the molecular systems were also selective for cupric ion in voltammetric and membrane base studies.

This review covers recent advances in the use of the squaramide moiety in chemical research. We focus on the varied applications of squaramides under the broad headings of self-assembly, organocatalysis, molecular recognition, medicinal chemistry, and bioconjugation and highlight several examples of each application.

The present report highlights the role of comprehensive structure property relationships (SPRs) in the discovery of a new and more effective molecular system for sensing purposes. From an extensive survey of different classes of amino substituted annulated furanones, it was realized that with some exceptions, these functionalized furanones could sense Cu2+ ions in the semi-aqueous phase irrespective of the nature of substituents; furthermore the same scaffolds could also detect Al3+, if the aldehydic position is specifically filled by a 3-indoyl group. As a result, amino substituted annulated furanones with 3-indoyl groups could detect both metal ions, response time of which mainly depends on the overall molecular framework. After replacing different furanone frameworks, a dual metal ion sensor (for Cu2+ and Al3+) with short response time and high selectivity and association constant was identified. The proposed bifunctional sensor displayed a distinct but observable response (turn off colorimetric for Cu2+ and turn on fluorescence for Al3+) to both metal ions with potential applications in the area of real sample analysis and membrane sensing.

Two new highly selective colorimetric and fluoregenic aminopyridine Schiff bases (L1 and L2) were synthesized by simple refluxing method and characterised via standard NMR and HRMS techniques. Its excellent metal sensing abilities explored on absorbance and fluorescence spectroscopy. The recognition colorimertric sensing behavior of probes L1 and L2 towards Ni(II), Zn(II), Fe(III) and UO2(II) ions were carefully investigated with different aspects of sensing behavior such as sensitivity, binding constant, stoichiometry, pH range and interference effect. Moreover, L1 and L2 also displayed excellent “off-on” fluoregenic selectivity with Zn(II). The results revealed that the sensors provided colorimetric and fluoregenic sensing excellent response with low limit of detection, under neutral conditions.

Furans are an important class of compounds and exhibit a diverse range of activities and properties. As such, improved synthetic access to furans is an important research goal. In the present report, a solvent- and catalyst-free reaction between 5,5-dimethyl-1,3-cyclohexanedione (dimedone), an aryl aldehyde and an isocyanide under microwave irradiation is presented. This method is significantly improved from previously described protocols in terms of applicability of wide ranging aryl aldehydes, better yields, shorter reaction times, facile work up and essentially no need of column chromatography. The photophysical properties of this series of compounds were studied for their possible applicability in the field of metal ion sensors. In solution, two compounds, 2-(cyclohexylamino)-3-(1H-indol-3-yl)-6,6-dimethyl-6,7-dihydrobenzofuran-4(5H)-one (1 i) and 2-(tert-butylamino)-3-(1H-indol-3-yl)-6,6-dimethyl-6,7-dihydrobenzofuran-4(5H)-one (1 j), underwent an observable color change from yellow to colorless in the presence of aluminum(III) ions. Further studies to investigate the UV absorption and luminescence behavior of these compounds revealed their utility as "naked-eye sensors" for aluminum detection.

Phthalocyanine tetrasulfonic acid (PCTS) performed as a optical probe for selective detection of Cu2+ in DMSO solution over other metal ions used. The complexation behavior of chemodosimeter toward various metal ions has been studied via UV–vis absorption and fluorescence emission spectra. Induced changes were found to be observable from naked eye. The association constant (Ka) and low limit of detection were found to be 8.80 × 105 M−1 and 5.53 × 10−7 M, respectively. The optode showed excellent selectivity behavior in the environmental pH range.

In this research, multiwalled carbon nanotubes (MWCNTs) was oxidized and chemically modified through reaction with 3-(trimethoxysilyl)propan-1-amine (TMSPA) and their subsequent reaction with 2-hydroxy-3-methoxy benzaldehyde. Subsequently, this material was metalized by reaction with copper acetate that lead to formation and impergeation of 2-methoxy-6-((3-(trimethoxysilyl)propylimino)methyl)phenol MMSPIMPMWCNT-Cu. This novel material was identified with different techniques such as SEM and FT-IR analysis. In this work, the reported material are exhibited high accurate and repeatable monitoring of iodide due to its high surface area with various reactive centre. It exhibited selectivity for iodide over the wide linear dynamic range between 1.8×10−6 and 1.15×10−1 M, with a Nernstian slope of −59.12±0.7 mV per decade of activity and detection limit of 1.8×10−6 M. Copper sulfide nanoparticles were prepared and their effect on the electrode response was investigated. The results were improved in the presence of nanoparticles with fast and stable response, good reproducibility, long-term stability, high selectivity over the presence of common organic and inorganic anions, high detection limit and dynamic range. The proposed sensor has been applied as potentiometric determination of some iodine species over a pH range of 2.5–10.

A new azo compound, 1-(2-pyridylazo)-2-naphthol, has been prepared and characterized. The synthesized compound shows a very high affinity for aluminium. The complexation reaction of aluminium has been explored by Colorimetry, FT-IR, 1 H NMR, HRMS and fluorescence spectroscopy. The detection limit has been found to be 1.81 × 10 −8 M estimated by the titration method. The turn-on fluorescence behaviour of aluminium interaction with ligand has been found to be so fast (

A simple 4-Methyl-7-hydroxy-8-formyl Coumarin (CS) serves as a selective chemosensor for Mg 2+ in the presence of alkali and alkaline earth metal ions. It showed a significant fluorescence enhancement towards Mg 2+ . The receptor CS exhibited a good binding constant and lowest detection limit for Mg 2+ . The variation of emission signal exists via of reversible chelation enhanced fluorescence (CHEF) with this inherent quenching metal ion.

Two molecular probes based on the furoquinolinol (FQ) framework have been rationally designed for the rapid detection and trace level quantification of Cu2+ in organic and semi-aqueous mediums. Synthesized FQs were extensively examined for their Cu2+ sensing abilities by UV-vis/fluorescence experiments, NMR titrations and DFT based calculations. Higher binding constant [2.11 × 104 M−1 (FQ1) and 1.87 × 104 M−1 (FQ2)], low detection limit [1.52 × 10−7 M (FQ1) and 2.13 × 10−7 M (FQ2)], high selectivity, fast response, wide operational pH range, and repeated usability are some of the salient features of the reported sensors. Furthermore, these compounds (FQs) retained their metal detection abilities in thin PVC membranes.

Antipyrine schiff bases 4-(4-hydroxy-3-methoxybenzylideneamino)-2,3-dimethyl-1-phenyl-1,2-dihydropyrazol-5-one (L1) was successfully synthesized and characterized. The complexation behavior of chemosensor with different metal ions including Zn2+ ions in methanolic solution was studied on UV–vis absorption spectra and Photofluorescent spectra. Results showed that the chemosensor (L1) exhibited 55 fold enhancements in fluorescence at 533 nm after adding Zn2+ ions. Such fluorescent responses could be detected by naked eye under UV-lamp. The limit of detection was calculated to be 10−7 M by titration method. The chemosensor (L1) showed excellent selectivity fluorescent behavior in acidic pH range. The complex solution (L1-Zn2+) exhibited reversibility with EDTA.

Thiazole Schiff bases 2-(4-phenyl-1,3-thiazol-2-yliminomethyl)phenol (L 1 ) and 1-(4-phenyl-1,3-thiazol-2-yliminomethyl)naphthalen-2-ol (L 2 ) have synthesized and characterized. The interaction of Schiff bases with different metal ions has been studied over UV–vis absorption spectra and photofluorescent spectra. The results are indicated that Schiff base L 1 and L 2 exhibited turn-on fluorescent behavior with Al 3+ ions in methanol, which could be directly detected by the naked-eye under the UV-lamp. The limits of detection were calculated for L 1 and L 2 since 1.0 × 10 −6 and 7.5 × 10 −7 by the titration method. Both sensors exhibited excellent fluorescent behavior in 5.0–13.5 pH range. The fluorescent behavior of legends-aluminum complex solution goes to turn-off in the presence of Ni 2+ and EDTA.

A new gadolinium(III) selective electrode has been developed from poly vinyl chloride (PVC) matrix membrane which is based on synthesized neutral carrier [L1] 2-(2-aminothiazol-4-yl)phenol and [L2] 2-(4-phenyl-1,3-thiazol-2-yliminomethyl)phenol as ionophores. The membrane having a composition of ionophore (L2):PVC:plasticizer (acetophenone):additive (sodium tetraphenylborate) in the ratio of 5:33:60:2 exhibited calibration performance over a wide range of concentration of gadolinium (9.38 × 10−7 to 1.0 × 10−2 M) and exhibited a Nernst slope of 19.5 ± 0.5 mV per decade of Gd(III) activity. It exhibited a quick response time of 8 s and its potential response was independent of pH across the pH range of 3.5–8.5. The membrane can be used with a good reproducibility over a period of 3 months. Membrane sensor was used as a indicator electrode for determination of end point in potentiometric titration of Gd (III) ion with EDTA. The proposed membrane electrodes were successfully applied for the determination of the concentration of gadolinium (III) ion in a mineral sample.

Owing to their easy accessibility and high degree of structural and functional diversity, many multicomponent reactions (MCRs) have been a rich source of conjugate π-systems, functionalised chromophores (or fluorophore) and redox active molecules. Despite their high explorative potential and practical benefits, only a few MCR products have been so far investigated for their metal sensing abilities. In the present report, two furopyrimidinones (FPys) based molecular systems have been synthesized by [4+1] cycloaddition based MCR sequence. Designed chemosensors displayed optic (absorption spectra) as well as electroanalytical (ion selective electrode) response toward Cu

Furans are an important class of compounds and exhibit a diverse range of activities and properties. As such, improved synthetic access to furans is an important research goal. In the present report, a solvent- and catalyst-free reaction between 5,5-dimethyl-1,3-cyclohexanedione (dimedone), an aryl aldehyde and an isocyanide under microwave irradiation is presented. This method is significantly improved from previously described protocols in terms of applicability of wide ranging aryl aldehydes, better yields, shorter reaction times, facile work up and essentially no need of column chromatography. The photophysical properties of this series of compounds were studied for their possible applicability in the field of metal ion sensors. In solution, two compounds, 2-(cyclohexylamino)-3-(1H-indol-3-yl)-6,6-dimethyl-6,7-dihydrobenzofuran-4(5H)-one (1 i) and 2-(tert-butylamino)-3-(1H-indol-3-yl)-6,6-dimethyl-6,7-dihydrobenzofuran-4(5H)-one (1 j), underwent an observable color change from yellow to colorless in the presence of aluminum(III) ions. Further studies to investigate the UV absorption and luminescence behavior of these compounds revealed their utility as "naked-eye sensors" for aluminum detection.

A new rhodamine functionalized fluorogenic Schiff base CS was synthesized and its colorimetric and fluorescence responses toward various metal ions were explored. The sensor exhibited highly selective and sensitive colorimetric and "off-on" fluorescence response towards Al(3+) in the presence of other competing metal ions. These spectral changes are large enough in the visible region of the spectrum and thus enable naked-eye detection. Studies proved that the formation of CS-Al(3+) complex is fully reversible and can sense to AcO(-)/F(-) via dissociation. The results revealed that the sensor provides fluorescence "off-on-off" strategy for the sequential detection of Al(3+) and AcO(-)/F(-).