Fluorimetric Response Research Articles

Pyrazole appended Schiff base based sensor for Al3+ detection: Spectroscopic investigation, real sample analysis and cell imaging studies

Herein, we are reporting a new pyrazole derived chemosensor named H2QPC [(E)-N’-((2-hydroxyquinolin-3-yl)methylene)-3-methyl-1H-pyrazole-5-carbohydrazide] exhibiting selective “off–on” fluorimetric response towards Al3+ ion in different solvents. The probe exhibited a submicromolar detection level (LOD = 0.37 μM) for the Al3+. The density functional theory (DFT) and time dependent DFT (TD-DFT) of the probe and corresponding Al3+-complex revealed that a change of structural conformation of probe H2QPC upon complexation. The pyrazole unit creates a specific cavity to tether Al3+, and consequently H2QPC shows as a promising molecule for Al3+ detection. Further, the probe has been used successfully for qualitative determination of Al3+ using filter paper strips. The in situ Al3+ ion cell imaging in HCT116 cells discloses the cellular penetrability of the sensor, and holds pronounced promise for application in biological and environment sciences.

Reactivity-based detection of nitrite ion: Rapid colorimetric and fluorometric response down to nM level

Recent developments in our lab provided significant insight into the structure–reactivity relationship between electronic properties and the detection of nitrite ions. By fine-tuning electron-withdrawing and electron-donating power, the sulfonamide group on aniline moiety was found to be the fastest nitrite probe among the first generation of probe molecules. Based on our understanding of the detection mechanism, our attention was moved to additional modification by installing stronger electron-donating groups on the azo-coupling partner. Accordingly, the bis methoxy group version of the probe molecule was prepared. It showed clean conversion from the probe to the benzo[c]cinnoline product and excellent linear response to very low levels of nitrite ions. Proton NMR and high-resolution mass spectrometer captured the reaction between the probe molecule and nitrite ions. As the reaction with nitrite ion triggers diazonium intermediate formation followed by intramolecular cyclization, both absorption and emission property changes were monitored as the signal readout to assay nitrite ion. In this report, our design principle of a probe molecule and its performance in colorimetric and fluorimetric responses will be discussed. In addition, the low detection limit achieved by leveraging chromatographic separation and assaying by the mass detector will be discussed.

Distinctive Nucleic Acid Recognition by Lysine-Embedded Phenanthridine Peptides.

Three new phenanthridine peptide derivatives (19, 22, and 23) were synthesized to explore their potential as spectrophotometric probes for DNA and RNA. UV/Vis and circular dichroism (CD) spectra, mass spectroscopy, and computational analysis confirmed the presence of intramolecular interactions in all three compounds. Computational analysis revealed that compounds alternate between bent and open conformations, highlighting the latter's crucial influence on successful polynucleotide recognition. Substituting one glycine with lysine in two regioisomers (22, 23) resulted in stronger binding interactions with DNA and RNA than for a compound containing two glycines (19), thus emphasizing the importance of lysine. The regioisomer with lysine closer to the phenanthridine ring (23) exhibited a dual and selective fluorimetric response with non-alternating AT and ATT polynucleotides and induction of triplex formation from the AT duplex. The best binding constant (K) with a value of 2.5 × 107 M-1 was obtained for the interaction with AT and ATT polynucleotides. Furthermore, apart from distinguishing between different types of ds-DNA and ds-RNA, the same compound could recognize GC-rich DNA through distinct induced CD signals.

An ESIPT-active orange-emissive 2-(2'-hydroxyphenyl)imidazo[1,2-a]pyridine-derived chemodosimeter for turn-on detection of fluoride ions via desilylation.

Fluoride is an essential element for oral health with an optimum concentration of 0.7-1.2 ppm in drinking water, but it is detrimental at higher concentrations, causing fluorosis, acute gastric ulcer, urolithiasis, and kidney infection, which adds immense significance to its detection in water sources. In the current study, a new chemodosimeter (HIPS-Br) is designed by protecting a 2-(2'-hydroxyphenyl)imidazo[1,2-a]pyridine derivative (HIP-Br) with a fluoride recognizable tert-butyldiphenylsilane moiety and utilized for the selective detection of F- ions by an excited-state intramolecular proton transfer (ESIPT)-based fluorimetric response. The probe HIPS-Br exhibits blue fluorescence in solution, and upon the incremental addition of F- ions, it exhibits a turn-on response, exhibiting a strong orange emission at 598 nm by spontaneous cleavage of the tert-butyldiphenylsilane group to release fluorescent HIP-Br in the working solution. HIPS-Br displayed no or insignificant response towards numerous common anions, cations and small molecules, affirming its selectivity to F- ions and offered a low limit of detection (LOD) of 1.2 ppb (6.6 × 10-8 M). The real sample analysis by spiking fluorides in water and toothpaste samples showed excellent percent recoveries. The chemodosimeter was successfully utilized in the solid-phase detection of F- ions on silica-coated TLC plates and analyzed by ImageJ analysis, marking its utility in on-site quantitation purposes.

Tetracationic bis-triarylborane tetraynes as dual fluorescence and SERS sensors for DNA, RNA and proteins

We report herein two new dual luminescent and Raman (SERS)-active probes, able to sense submicromolar concentrations of DNA and protein in aqueous samples. Both analogues, characterized by a tetrayne linker connecting two triarylborane fluorophores, show high binding affinities and strong fluorescent and SERS responses to ds-DNA, ds-RNA, and protein (BSA). Detailed studies revealed that both the neutral and tetracationic analogue bind to ds-DNA/RNA grooves and protein (BSA) with similar affinities, at variance to previous non-charged triarylboranes, which interacted only with BSA. The fluorimetric response upon binding to BSA was different to that observed for previous analogues; the tetracationic analogue emission was enhanced and the neutral analogue emission quenched, this selectivity being attributed to the difference in solvatochromism of the triarylborane fluorophore (charged vs neutral). The neutral dye did not show any SERS signal due to the lack of interaction with negatively charged Ag nanoparticles, stressing the importance of positive charge for the application of SERS sensing. The SERS signal of the tetrayne linker of the tetracationic analogue was shifted by −81 cm−1 compared to that of the previously studied diyne analogue. The SERS signal intensity change was proportional to dye binding to ds-DNA, and completely quenched by nanomolar concentrations of BSA, such a specific response being attributed to the complete immersion of the dye within BSA.

Triarylborane-"Click" Fluorescent Tag for Orthogonal Amino Acid Labelling, Interactions with DNA, Protein, and Cyclodextrins.

The innovative design of a triarylborane (TB)-dye with one NMe2-alkylated (propargylated) group and one NMe2 group yielded a system that is both an NMe2 π-donor and an inductive NMe2-alkyl cationic acceptor. Consequently, the new TB-dye was highly sensitive to a "click" reaction with an azide-substituted lysine side chain (yielding TB-lysine), resulting in a bathochromic shift of emission of 100 nm. In addition, fluorene attached to the lysine C-terminus showed FRET with the TB-chromophore, also sensitive to interactions with targets. Both the TB-dye and TB-lysine showed high affinities towards both DNA and proteins, reporting binding by an opposite fluorimetric response for DNA/RNA (quenching) vs. BSA (increase). Thus, the novel TB-dye is an ideal fluorimetric probe for orthogonal incorporation into bio-targets by "click" reactions due to fluorescence reporting of the progress of the "click" reaction and further sensing of the binding site composition. The TB-dye is moderately toxic to human cell lines after 2-3 days of exposure, but efficiently enters cells in 90 min, being non-toxic at short exposure. The most important product of the "click" reaction, TB-lysine, was non-toxic to cells and showed equal distribution between mitochondria and lysosomes. Further studies would focus particularly on the very convenient monitoring of the progress of "click" conjugation of the TB-dye with biorelevant targets inside living cells by confocal microscopy.

Boron-Doped Carbon Nanodots as a Theranostic Agent for Colon Cancer Stem Cells.

Carbon nanodots have drawn a great deal of attention due to their green and expedient opportunities in biological and chemical sciences. Their high fluorescence capabilities and low toxicity for living cells and tissues make them excellent imaging agents. In addition, they have a fluorimetric response against inorganic and organic species. Boron-doped carbon nanodots (B-CDs) with high fluorescence yield were produced from phenylboronic acid and glutamine as boron and carbon sources, respectively, by a hydrothermal method. First, the effects of the temperature on their fluorescence yield and the structural characteristics of B-CDs were investigated. Second, their cytotoxicity and cell death and proliferation behaviors were examined. The cytotoxicity was evaluated by the MTT assay. The cellular properties were evaluated with the distribution of caspase 3, Ki67, lamin B1, P16, and cytochrome c after the indirect immunoperoxidase technique. After the MTT assay, 1:1 dilution of all applicants for 24 h was used in the study. After immunohistochemical analyses, the application of B-CDs synthesized at 230 °C did not change control cell (Vero) proliferation, and also apoptosis was not triggered. Colo 320 CD133+ and CD133- cell-triggered apoptosis and cellular senescence were found to be synthesis temperature dependent. In addition, Colo 320 CD133- cells were affected relatively more than CD133+ cells from B-CDs. While B-CDs did not affect the control cells, the colon cancer stem cells (Colo 320 CD133+) were affected in a time-dependent manner. Therefore, the use of the synthesized B-CD product may be an alternative method for controlling or eliminating cancer stem cells in the tumor tissue.

The Nature of the (Oligo/Hetero)Arene Linker Connecting Two Triarylborane Cations Controls Fluorimetric and Circular Dichroism Sensing of Various ds-DNAs and ds-RNAs.

A series of tetracationic bis-triarylborane dyes, differing in the aromatic linker connecting two dicationic triarylborane moieties, showed very high submicromolar affinities toward ds-DNA and ds-RNA. The linker strongly influenced the emissive properties of triarylborane cations and controlled the fluorimetric response of dyes. The fluorene-analog shows the most selective fluorescence response between AT-DNA, GC-DNA, and AU-RNA, the pyrene-analog's emission is non-selectively enhanced by all DNA/RNA, and the dithienyl-diketopyrrolopyrrole analog's emission is strongly quenched upon DNA/RNA binding. The emission properties of the biphenyl-analog were not applicable, but the compound showed specific induced circular dichroism (ICD) signals only for AT-sequence-containing ds-DNAs, whereas the pyrene-analog ICD signals were specific for AT-DNA with respect to GC-DNA, and also recognized AU-RNA by giving a different ICD pattern from that observed upon interaction with AT-DNA. The fluorene- and dithienyl-diketopyrrolopyrrole analogs were ICD-signal silent. Thus, fine-tuning of the aromatic linker properties connecting two triarylborane dications can be used for the dual sensing (fluorimetric and CD) of various ds-DNA/RNA secondary structures, depending on the steric properties of the DNA/RNA grooves.

Selective Fluorimetric Detection of Pyrimidine Nucleotides in Neutral Aqueous Solution with a Styrylpyridine-Based Cyclophane

A styrylpyridine-containing cyclophane with diethylenetriamine linkers is presented as a host system whose association with representative nucleotides was examined with photometric and fluorimetric titrations. The spectrometric titrations revealed the formation of 1:1 complexes with log Kb values in the range of 2.3–3.2 for pyrimidine nucleotides TMP (thymidine monophosphate), TTP (thymidine triphosphate) and CMP (cytidine monophosphate) and 3.8–5.0 for purine nucleotides AMP (adenosine monophosphate), ATP (adenosine triphosphate), and dGMP (deoxyguanosine monophosphate). Notably, in a neutral buffer solution, the fluorimetric response to the complex formation depends on the type of nucleotide. Hence, quenching of the already weak fluorescence was observed with the purine bases, whereas the association of the cyclophane with pyrimidine bases TMP, TTP, and CMP resulted in a significant fluorescence light-up effect. Thus, it was demonstrated that the styrylpyridine unit is a useful and complementary fluorophore for the development of selective nucleotide-targeting fluorescent probes based on alkylamine-linked cyclophanes.

Chemoselective detection based on experimental and theoretical calculations of Cu2+ ions via deprotonation of chromone derived probe and its application

A new Schiff base chemosensor 2-Ethoxy-3-(((2‑hydroxy-4-nitrophenyl)imino)methyl)-2H-chromen-4-ol (CANP) was synthesized and characterized by 1HNMR , FT-IR, HRMS, FE-SEM spectral techniques for the detection of cupric ions through colorimetric and fluorimetric response in THF. Colorimetric change from yellow to orange and fluorescence turn-off behavior was observed for chemosensor in presence of cupric ions over the rest of metal ions. This turn-off behavior was observed due to the paramagnetic nature of cupric ions. Job's plot indicated that complex formed in 2:1 (CANP:Cu2+) ratio and binding stoichiometry was confirmed by HRMS spectral technique. The binding constant was obtained as 2.84 × 104 M − 1 and 1.71 × 104 M − 1 via absorbance and fluorimetric titrations respectively. The LOD values were obtained as 4.93 × 10−6 M and 2.06 × 10−6 M via absorbance and fluorimetric titrations respectively. Selectivity of chemosensor towards cupric ions was observed in pH range 6–11. The reversibility effect was observed on the addition of sodium salt of EDTA. No interference from other competitive metal ions confirmed the selectivity of chemosensor for cupric ions. The probe and its cupric ion complex was found to be stable over a span time period. Theoretical calculations based on DFT were performed for a better understanding of the optical character of CANP and the effect of cupric ions titration; moreover, these results validated the experimental data. Time decay data illustrated that complex of chemosensor formed with cupric ions was stable. FESEM analysis of chemosensor CANP and its complex confirmed the formation of complex as morphology changed after complex formation. Additionally, this chemosensor was successfully used for the detection of cupric ions in environmental water samples. Also, it was applied to recognize cupric ions in human blood serum with micromolar detection limits.

Rhodamine functionalized cellulose for mercury detection and removal: A strategy for providing in situ fluorimetric and colorimetric responses

A new cellulose-based material as adsorbent was prepared for Hg (II) detection and removal from aqueous solution. Rhodamine moiety was conjugated with cellulose as an efficient sensor, enabling the material to exhibit excellent optical signals on the contact with Hg (II). Fourier transform infrared spectra, elemental analysis, thermogravimetry, differential thermal analysis, scanning electron microscope analysis, Brunauer-Emmett-Teller surface area, pore volume and pore size were employed to verify the modification of cellulose. A 7-fold enhancement of fluorescence intensity afforded the adsorbent “off–on” fluorimetric response exclusively towards Hg (II) without the interference of more than ten other kinds of metal ions. The detection limit reached as low as 9.18 × 10-7 M. Besides, the adsorbent also showed an obvious color change during the adsorption to realize “naked-eye” recognition with Hg (II) in the range of 1–400 ppm. Thus, a colorimetric card was prepared to evaluate the concentration of Hg (II) in a convenient and rapid manner. In addition, the adsorption properties of the material including the effect of initial concentration, pH, and contact time were systematically investigated by batch adsorptions. The adsorption process was found to fit well with Langmuir adsorption model and pseudo-second-order kinetics. The mercury triggered spirolactam ring-opening reaction was responsible for the sensitive and selective fluormetric sensing and confirmed by the Job’s plot (1:1 binding stoichiometry) and X-ray photoelectron spectroscopy. Furthermore, density functional theory studies also indicated the energetically favorable Hg (II) induced ring-opening process. The highly sensitive and selective performance in tap water further demonstrated the tremendous potential of as-prepared adsorbent for practical application.

Real time sensor for Fe3+, Al3+, Cu2+ & PPi through quadruple mechanistic pathways using a novel dipodal quinoline-based molecular probe

A quinoline-based small molecular probe, H2L was designed, synthesized and characterized by different spectroscopic methods. It was utilized as a multi-responsive probe for the detection of Fe3+, Al3+, Cu2+ and PPi. It showed very selective instant turn-on fluorimetric response towards Fe3+and Al3+ with a detection limit in nanomolar range. Solutions of H2L containing Fe3+ or Al3+ could sequentially sense PPi by a turn-off mechanism. Also, H2L could determine the presence of Cu2+ very selectively among a series of other metal ions by a sharp change in colour. Detection of Cu2+ through colorimetry was further investigated by systematic UV–Vis studies and the potential of H2L to act as a potential colorimetric sensor for Cu2+ was suitably established. Filter-paper strip experiments were conducted to demonstrate the practical utility of the proposed sensor. Potential applications of H2L as a sensor for pH in the acidic range has also been explored.

Novel tetra-arm chemosensor supply “collaboration effect” for highly sensitive fluorescent and colorimetric sensing of L-Arg

Due to the crucial role of l-Arginine (L-Arg) in human metabolism, efficient sensing L-Arg is very important. Herein, to improve the selectivity and sensitivity for recognition L-Arg, we rationally introduced the “collaboration effect” into the design of chemosensor to enhance the host-guest interactions. For this purpose, a novel tetra-arm chemosensor FINH was designed and synthesized. The FINH has four pyridylhydrazone functionalized arms and two hydroxyl groups. Based on the collaboration of these groups, the FINH could high sensitively and selectively detect L-Arg through colorimetric and fluorimetric dual-channel response. The possible recognition mechanism was investigated by experiments and theoretical calculations. The results showed that the FINH could specificity binding L-Arg via the collaboration of the tetra-pyridylhydrazone and two hydroxyl groups through multiple intermolecular hydrogen bonding and electrostatic attractions, the lowest detection limit (LODs) of FINH toward L-Arg is 3.25 × 10−8 M. Furthermore, a convenient L-Arg test tool based on the FINH was prepared, which could efficiently sense L-Arg.

Selective, pH-Dependent Colorimetric and Fluorimetric Detection of Quadruplex DNA with 4-Dimethylamino(phenyl)-Substituted Berberine Derivatives.

The 9‐ and 12‐dimethylaminophenyl‐substituted berberine derivatives 3 a and 3 b were readily synthesized by Suzuki‐Miyaura reactions and shown to be useful fluorescent probes for the optical detection of quadruplex DNA (G4‐DNA). Their association with the nucleic acids was investigated by spectrometric titrations, CD and LD spectroscopy, and with DNA‐melting analysis. Both ligands bind to duplex DNA by intercalation and to G4‐DNA by terminal π stacking. At neutral conditions, they bind with higher affinity (K b=105−106 M−1) to representative quadruplex forming oligonucleotides 22AG, c‐myc, c‐kit, and a2, than to duplex calf thymus (ct) DNA (K b=5‐7×104 M−1). At pH 5, however, the affinity of 3 a towards G4‐DNA 22AG is higher (K b=1.2×106 M−1), whereas the binding constant towards ct DNA is lower (K b=3.9×103 M−1) than under neutral conditions. Notably, the association of the ligand with DNA results in characteristic changes of the absorption and emission properties under specific conditions, which may be used for optical DNA detection. Other than the parent berberine, the ligands do not show a noticeable increase of their very low intrinsic emission intensity upon association with DNA at neutral conditions. In contrast, a fluorescence light‐up effect was observed upon association to duplex (Φ fl=0.01) and quadruplex DNA (Φ fl=0.04) at pH 5. This fluorimetric response to G4‐DNA association in combination with the distinct, red‐shifted absorption under these conditions provides a simple and conclusive optical detection of G4‐DNA at lower pH.

Berberrubine Phosphate: A Selective Fluorescent Probe for Quadruplex DNA.

A phosphate-substituted, zwitterionic berberine derivative was synthesized and its binding properties with duplex DNA and G4-DNA were studied using photometric, fluorimetric and polarimetric titrations and thermal DNA denaturation experiments. The ligand binds with high affinity toward both DNA forms (Kb = 2–7 × 105 M−1) and induces a slight stabilization of G4-DNA toward thermally induced unfolding, mostly pronounced for the telomeric quadruplex 22AG. The ligand likely binds by aggregation and intercalation with ct DNA and by terminal stacking with G4-DNA. Thus, this compound represents one of the rare examples of phosphate-substituted DNA binders. In an aqueous solution, the title compound has a very weak fluorescence intensity (Φfl < 0.01) that increases significantly upon binding to G4-DNA (Φfl = 0.01). In contrast, the association with duplex DNA was not accompanied by such a strong fluorescence light-up effect (Φfl < 0.01). These different fluorimetric responses upon binding to particular DNA forms are proposed to be caused by the different binding modes and may be used for the selective fluorimetric detection of G4-DNA.

Zeolitic imidazolate framework-derived porous carbon enhances methanogenesis by facilitating interspecies electron transfer: Understanding fluorimetric and electrochemical responses of multi-layered extracellular polymeric substances.

Modulating microbial electron transfer during anaerobic digestion can significantly improve syntrophic interactions for enhanced biogas production. As a carbonaceous conductive material, zeolite imidazolate framework-67 (ZIF-67)-derived porous carbon (PC) was hypothesized to act as a microbial electron transfer highway and assessed with respect to understanding the fluorimetric and electrochemical responses of multilayered extracellular polymeric substances (EPS). The highest biomethane yield (614.0 mL/g) from ethanol was achieved in the presence of 100 mg/L PC prepared at a carbonization temperature of 800 °C (PC-800), which was 28.2% higher than that without PC addition. Electrochemical analysis revealed that both the redox peak currents and conductivity of the methanogenic sludge increased, while the free charge transfer resistance decreased with PC-800 addition. The conductive PC-800 potentially functioned as an abiotic electron conduit to promote direct interspecies electron transfer, thereby resulting in decreased expression of functional genes associated with electrically conductive pili (e-pili) and hemeproteins. Additionally, PC-800 stimulated the secretion of redox-active humic substances (HSs), and excitation emission matrix spectra analysis indicated that the largest increase in percent fluorescence response of HSs occurred in the tightly bound EPS (TB-EPS) with addition of PC-800. This was attributed to the strong complexation ability of PC-800 particles to hydroxyl/carboxylic/phenolic moieties of HSs contained in the TB-EPS. Microbial analysis revealed that syntrophic/exoelectrogenic bacteria such as Pelotomaculum and Syntrophomonas, as well as hydrogenotrophic/electrotrophic methanogens such as Methanoculleus and Methanobacterium, were enriched in methanogenic sludge with adding PC-800. This study provided comprehensive insights for understanding the interactions among ZIF-derived PC, methanogenic microorganisms and their multilayered EPS.

An aroylhydrazone-containing diarylethene derivative derived chemosensor for colorimetric and fluorimetric dual sensing Cu2+

A diarylethene derivative with an aroylhydrazone unit was designed and synthesized as a colorimetric and fluorimetric dual responsive sensor for Cu2+ with high selectivity and rapid response. Connecting 7-diethylamino-3-hydrazide-coumarin moiety and 2-pyridyl-containg diarylethene provided an intramolecular charge transfer (ICT) system with affluent binding site (N^N^O), which was developed for the selective and sensitive detection of Cu2+ by dual colorimetric and fluorimetric responses. A clear Cu2+-induced ratiometric colorimetric sensor with color change from light yellow to orange red and on-off fluorescence with fluorescence color change from bright cyan to deep teal was constructed. At the same time, colorimetric and fluorimetric responses to Cu2+ were both achieved at the photostationary state. Based on the obvious color change, the sensor was used for the fabrication of test strips that can be used as the standard cards for detecting Cu2+. This study is expected to facilitate and broaden the application of diarylethene derivative in tracing Cu2+ in future work.

On the swelling behavior of poly(N-Isopropylacrylamide) hydrogels exposed to perfluoroalkyl acids.

Per- and polyfluoroalkyl substances (PFAS) have rapidly accumulated in the environment due to their widespread use prior to commercial discussion in the early 21st century, and their slow degradation has magnified concerns of their potential toxicity. Monitoring their distribution is, therefore, necessary to evaluate and control their impact on the health of exposed populations. This investigation evaluates the capability of a simple polymeric detection scheme for PFAS based on crosslinked, thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) hydrogels. Surveying swelling perturbations induced by several hydrotropes and comparable hydrocarbon analogs, tetraethylammonium perfluorooctane sulfonate (TPFOS) showed a significantly higher swelling ratio on a mass basis (65.5 ± 8.8 at 15°C) than any of the other analytes tested. Combining swelling with the fluorimetric response of a solvachromatic dye, nile red, revealed the fluorosurfactant to initiate observable aggregation (i.e., its critical aggregation concentration) at 0.05 mM and reach saturation (i.e., its charge neutralization concentration) at 0.5 mM. The fluorosurfactant was found to homogeneously distribute throughout the polymer matrix with energy dispersive X-ray spectroscopy, marking the swelling response as a peculiar nexus of fluorinated interfacial positioning and delocalized electrostatic repulsion. Results from the current study hold promise for exploiting the physiochemical response of PNIPAM to assess TPFOS's concentration.

Naphthalene diimide-amino acid conjugates as novel fluorimetric and CD probes for differentiation between ds-DNA and ds-RNA.

Two novel unnatural amino acids, prepared by linking a dicationic purple-coloured and fluorescent naphthalene diimide (NDI) at core position to amino acid side chains of variable length, strongly interacted with ds-DNA/RNA by threading intercalation. Different from a reference NDI dye with identical visible range absorbance (520–540 nm) and Stokes shifts in emission (+60 nm, quantum yield > 0.2), only these amino acid–NDI conjugates showed selective fluorimetric response for GC-DNA in respect to AT(U)-polynucleotides. The DNA/RNA binding-induced circular dichroism (ICD) response of NDI at 450–550 nm strongly depended on the length and rigidity of the linker to the amino acid unit, which controls the orientation of the NDI unit inside within the intercalative binding site. The ICD selectivity also depends on the type of polynucleotide, thus the studied NDI dyes act as dual fluorimetric/ICD probes for sensing the difference between here used GC-DNA, AT-DNA and AU-RNA.

Thiosemicarbazone-based bifunctional chemosensors for simultaneous detection of inorganic cations and fluoride anion

Two thiosemicarbazone-based bifunctional chemosensors (L1 and L2) have been synthesized and characterized by various spectroscopic techniques. Sensing behavior of the chemosensors were initially tested by colorimetric signalling, followed by absorption, emission, NMR and CV techniques, and found to behave as bifunctional molecules. These bifunctional chemosensors recognize selected cations (Mn2+, Co2+, Ni2+, Cu2+ and Zn2+) and F¯ anion among the studied cations (Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Ag+, Hg2+ and Pb2+) and anions (F¯, Cl¯, Br¯, I¯ and HSO4¯). Both the sensor molecules displayed remarkable colorimetric and fluorimetric responses in the presence of cations and fluoride anion with a rapid response through color change of the solution. Nitrogen and thione donors of the receptor molecules are liable for cation binding, whereas –NH protons of thiosemicarbazone moiety was found to be responsible for selective fluoride ion sensing. Binding ability of the chemosensors toward cations and F¯ anion were determined with spectrophotometric data by calibration plot, and the binding stoichiometry of the complexes was studied by Job’s plot. Electrochemical measurements showed that the addition of anion to the chemosensors pretreated with cations resulted in greater changes in reduction potentials compared to the addition of anion to the receptors in the absence of cations. Computational studies using density functional theory were also carried out, whereupon comparison of the interactions of copper cation and fluoride anion with the chemosensors explains the selective detection towards respective ions.