Fluorimetric Response Research Articles

A fluorescent coumarin-thiophene hybrid as a ratiometric chemosensor for anions: Synthesis, photophysics, anion sensing and orbital interactions

A colorimetric and fluorimetric fluorescent chemosensor (CT-2), having a coumarin ring as a signaling unit and an acetamido thiophene ring as an H-donor receptor, has been synthesized from amino derivative (CT-1) of CT-2 for the purpose of recognition of anions in DMSO. The absorption and emission maxima were both determined for the fluorescent dye in different solvents. Both hypsochromic shift at the absorption maximum, and quenching of fluorescence after interactions between the anions and the receptoric part, were observed. This phenomenon was explained using orbital interactions based on quantum chemical calculations. The selectivity and sensitivity of CT-2 for F−, Cl−, Br−, I−, AcO−, CN−, H2PO4−, HSO4− and ClO4− anions were determined with spectrophotometric, fluorimetric and 1H NMR titration techniques and it was found that CT-2 be utilized for the detection of CN−, F− and AcO− in the presence of other ions as competitors. Color and fluorescence changes visible to the naked eye and under UV (365 nm) were observed upon addition of CN−, F− and AcO− to the solution of chemosensor (CT-2) in DMSO. The sensor showed no colorimetric and fluorimetric response for the anions such as Cl−, Br−, I−, H2PO4−, HSO4−, and ClO4−. However, 1H NMR titration shows that the chemosensor was more sensitive to CN−, than F− and AcO− at the stochiometric ratio of 1:2.5 respectively. Additionally, the compounds CT-1 and CT-2 showed good thermal stability for practical applications.

A simple Schiff base as ‘naked eye’ and fluorescent ‘on–off’ sensor for detecting cyanide in mixed aqueous solution

A simple Schiff base sensor (L1) derived from N-(1-naphthyl) ethylenediamine dihydrochloride was designed and synthesised by simple chemistry procedures. The sensor exhibited a visible colour change observed by both colorimetric and fluorimetric responses for cyanide ion in aqueous solution. The detection of cyanide was performed via the nucleophilic attack of cyanide anion on the imine group of the sensor with a 1 : 1 binding stoichiometry. Moreover, test strips based on the sensor were fabricated, which served as convenient and efficient CN− test kits and the sensor L1 is a good way to detect hydrogen cyanide in aqueous extracts of sprouting potatoes.

Discriminating detection of multiple analytes (F− and CN−) by a single probe through colorimetric and fluorescent dual channels

Two novel Schiff base type receptors containing phenol hydroxyl group (1) or methoxy group (2) were designed and synthesized. The receptor 1 with phenol hydroxyl group exhibited different colorimetric and fluorimetric responses to fluoride and cyanide ions. In the colorimetric channel, the colorless solution turned to yellow towards F−, but red in the presence of CN−. In the fluorimetric channel, the nonluminous solution showed different “turn-on” response to F− and CN−, respectively. The distinguishing responses of receptor 1 to the two anions in dual channels were attributed to the disparate interaction mechanisms. F− was detected through the formation of hydrogen bonds and the subsequent deprotonation process. CN− initially formed hydrogen bonds and then it attacked the receptor via a nucleophilic addition reaction. In contrast, the receptor 2 with methoxy group only showed remarkable color change from colorless to yellow towards F−. These results proved that the phenol hydroxyl group played an important role in the discriminating detection of F− and CN−.

Aggregation-Induced Emission Active Metal-Free Chemosensing Platform for Highly Selective Turn-On Sensing and Bioimaging of Pyrophosphate Anion.

We report the synthesis of a metal-free chemosensor for highly selective sensing of pyrophosphate (PPi) anion in physiological medium. The novel phenylbenzimidazole functionalized imine containing chemosensor (L; [2,6-bis(((4-(1H-benzo[d]imidazol-2-yl)phenyl)imino) methyl)-4 methyl phenol]) could sense PPi anion through "turn-on" colorimetric and fluorimetric responses in a very competitive environment. The overall sensing mechanism is based on the aggregation-induced emission (AIE) phenomenon. Moreover, a real time in-field device application was demonstrated by sensing PPi in paper strips coated with L. Interestingly, detection of intracellular PPi ions in model human cells could also be possible by fluorescence microscopic studies without any toxicity to these cells.

Colorimetric and fluorimetric response of Schiff base molecules towards fluoride anion, solution test kit fabrication, logical interpretations and DFT-D3 study.

Two newly synthesized Schiff base molecules are herein reported as anion sensors. -NO2 substituted receptor (P1) is comparatively more acidic and can sense F(-), OAc(-) and H2PO4(-), whereas -CN substituted receptor (P2) is less acidic and is selective for F(-) only. Reversible UV-Vis response for both receptors with F(-) can mimic multiple logic gate functions, and several complex electronic circuits based on XNOR, XOR, OR, AND, NOT and NOR logic operations with 'Write-Read-Erase-Read' options have been executed. Interesting 'turn on and off' fluorescence responses were noticed for the receptors with F(-). Intracellular F(-) detection as a diagnosis of non-skeletal fluorosis was successful using a fluorescence microscope with Candida albicans (prokaryotic cell, a diploid fungus) and pollen grains of Tecoma stans (eukaryotic cell) incubated in 10(-6) M fluoride-contaminated hand-pump water collected from Bankura, West Bengal, India. Furthermore, a solution test kit was fabricated for easy and selective detection of F(-) in an aqueous solvent.

β-Cyclodextrin decorated nanocellulose: a smart approach towards the selective fluorimetric determination of danofloxacin in milk samples.

An innovative and versatile strategy of Solid Phase Microextraction (SPME) is shown by using a new type of β-cyclodextrin-modified nanocellulose (CD-NC) as a sorbent material. β-cyclodextrin (used as an inclusion-type selector) was covalently bonded to amine-modified nanocellulose by an amidation reaction. Such novel nanocavities were successfully applied to the selective recognition of danofloxacin (DAN), an antibiotic used to treat animal diseases, via supramolecular host-guest interactions. The SPME methodology, using a platform based on β-cyclodextrin-"decorated" nanocellulose as a sorbent material, showed a wide linear fluorimetric response against DAN from 8 to 800 μg L(-1) and a detection limit of 2.5 μg L(-1). The specific recognition of DAN has been proven to be highly selective and efficient against this metabolite and other fluoroquinolones. The reusability and the high efficiency in the extraction and preconcentration of DAN in milk samples allow recoveries of 94%.

A rapid selective colorimetric and ‘On–Off’ fluorimetric sensor for detecting Cu2+ ions in aqueous media based on a simple bis-schiff-base derivative

A simple colorimetric and fluorimetric ‘On–Off’ sensor L (3,3′-dimethyl -[1,1′-biphenyl]-4,4′-diyl)bis(azanylylidene)bis(methanylylidene)bis(naphthalen-2-ol) for Cu2+ ions bearing o-tolidine substituents has been designed and synthesised, and exhibits significant fluorimetric and colorimetric response for Cu2+ in DMSO/H2O (8:2, v/v) HEPES buffer (pH 7.2) solution. The detection limit of the sensor towards Cu2+ is 7.25 × 10− 8 M and the association constant Ka of 9.86 × 104 M− 1 was determined. Furthermore, other anions, including Fe3+, Hg2+, Ag+, Ca2+, Co2+, Ni2+, Cd2+, Pb2+, Zn2+, Cr3+ and Mg2+ have almost no influence on the probe's behaviour. Test strips based on the sensor L were fabricated, which could act as convenient and efficient Cu2+ test kits.

The Interaction of Fluoride with Fluorogenic Ureas: An ON1–OFF–ON2 Response

The anion binding tendencies of the two fluorogenic ureas L(1)H and L(2)H, containing the 2-anthracenyl and 1-pyrenyl moieties as signaling units, respectively, have been investigated in MeCN and DMSO by absorption, emission, and (1)H NMR spectroscopies. The formation of stable 1:1 receptor:anion H-bond complexes has been confirmed by structural studies on the crystalline [Bu4N][L(1)···Cl] and [Bu4N][L(2)H···CH3COO] salts. Complexation induces significant variations of the emission properties of L(1)H and L(2)H according to a multifaceted behavior, which depends upon the fluorogenic substituent, the solvent, and the basicity of the anion. Poorly basic anions (Cl(-), Br(-)) cause a red shift of the emission band(s). Carboxylates (CH3COO(-), C6H5COO(-)) induce fluorescence quenching due to the occurrence of an electron-transfer process taking place in the locally excited complex [*L-H···X](-). However, this excited complex may undergo an intracomplex proton transfer from one urea N-H fragment to the anion, to give the tautomeric excited complex [L···H-X](-)*, which emits at higher wavelength. F(-) displays a unique behavior: It forms with L(1)H a stable [L-H···F](-) complex which in the excited state undergoes intracomplex proton transfer, to give the poorly emissive excited tautomer [L···H-F](-)*. With L(2)H, on moderate addition of F(-), the 1:1 H-bond complex forms, and the blue fluorescence of pyrene is quenched. Large excess addition of F(-) promotes deprotonation of the ground-state complex, according to the equilibrium [L(2)H···F](-) + F(-) ⇆ [L(2)](-) + HF2(-). The deprotonated receptor [L(2)](-) is distinctly emissive (yellow fluorescence), which generates the fluorimetric response ON(1)-OFF-ON(2) of receptor L(2)H with respect to F(-).

An analytical solution to the characterization of antigen–antibody interactions by kinetic exclusion assay

A simpler derivation of the basic expression for the dependence of fluorimetric response ratio (RAg/Ro) on free antigen concentration has demonstrated the universal invalidity of the analysis that is incorporated into the manufacturer’s software for determining immunoaffinities by kinetic exclusion assay, and traced the error to inadequate allowance for antibody bivalence in the solution phase of the assay. An analytical solution to the quantitative characterization of antigen–antibody interactions from the dependence of RAg/Ro on total antigen concentration is also described, thereby eliminating the necessity for the extensive simulative procedures employed in current determinations of dissociation constants by kinetic exclusion assay. In the illustrative application of this analytical approach to published results on the interaction between a metal chelate (cadmium–ethylenediaminetetraacetic acid, Cd–EDTA) and an elicited monoclonal antibody, the analytical processing of the data has been performed on a calculator. However, there is no need to replace the more sophisticated procedure that is incorporated into the Sapidyne software provided that programming changes are made to rectify the erroneous equation on which the simulative analysis is based.

Selective recognition of fluoride ions through fluorimetric and colorimetric response of a first mesitylene based dipodal sensor 15employing thiosemicarbazones

A new dipodal chromo-fluorogenic anion sensor (2Z,2′Z)-2,2′-(((((2,4,6-trimethyl-1,3-phenylene)bis-(methyl-ene))bis-(oxy))bis(2,1-phenylene))bis(methanylylidene))bis(N-methylhydrazinecarbothio-amide) has been synthesized and characterized for the detection of F− ion in DMSO. The sensor has proven to be highly selective and sensitive to F− ion, moreover it can act as naked eye chromogenic sensor. The mechanism involved in the detection of fluoride ion is the deprotonation of the –NH groups, which was confirmed by using TBAOH. The pre-organization of the dipodal receptor provides chelating H-bonds with the spherical F− ion. These strong H-bonding interactions result in fast deprotonation of the sensor, producing an optical response. Employing only a weak fluorescence capability of the imine groups, 1 behaves as a fluorogenic sensor by exhibiting fluorescence enhancement at λex 438nm upon addition of F− ions.

Asymmetric Distyrylpyridinium Dyes as Red‐Emitting Fluorescent Probes for Quadruplex DNA

The interactions of three cationic distyryl dyes, namely 2,4-bis(4-dimethylaminostyryl)-1-methylpyridinium (1a), its derivative with a quaternary aminoalkyl chain (1b), and the symmetric 2,6-bis(4-dimethylaminostyryl)-1-methylpyridinium (2a), with several quadruplex and duplex nucleic acids were studied with the aim to establish the influence of the geometry of the dyes on their DNA-binding and DNA-probing properties. The results from spectrofluorimetric titrations and thermal denaturation experiments provide evidence that asymmetric (2,4-disubstituted) dyes 1a and 1b bind to quadruplex DNA structures with a near-micromolar affinity and a fair selectivity with respect to double-stranded (ds) DNA [K(a)(G4)/K(a)(ds)=2.5-8.4]. At the same time, the fluorescence of both dyes is selectively increased in the presence of quadruplex DNAs (more than 80-100-fold in the case of human telomeric quadruplex), even in the presence of an excess of competing double-stranded DNA. This optical selectivity allows these dyes to be used as quadruplex-DNA-selective probes in solution and stains in polyacrylamide gels. In contrast, the symmetric analogue 2a displays a strong binding preference for double-stranded DNA [K(a) (ds)/K(a) (G4)=40-100), presumably due to binding in the minor groove. In addition, 2a is not able to discriminate between quadruplex and duplex DNA, as its fluorescence is increased equally well (20-50-fold) in the presence of both structures. This study emphasizes and rationalizes the strong impact of subtle structural variations on both DNA-recognition properties and fluorimetric response of organic dyes.

Dual channel chromo/fluorogenic chemosensors for cyanide and fluoride ions – an example of in situ acid catalysis of the Strecker reaction for cyanide ion chemodosimetry

Two mesitylene based probes, having catechol/phenol units in conjunction to the Schiff base have been synthesized. The probe with a catechol unit can be used to sense and discriminate between F(-) and CN(-) through different colorimetric and fluorimetric responses using DMSO as solvent. However in DMSO:water (2:1) solution it responds selectively to CN(-) ion. The probe with a phenol unit is highly selective and sensitive for CN(-) and can be used for naked eye, semiquantitative sensing of CN(-) ion in DMSO:water (2:1) solution. The chemodosimetry has been attributed to the acid catalyzed Strecker's reaction of an imine bond and is being reported for the first time in a Schiff's base.

The bis-phenanthridinium system flexibility and position of covalently bound uracil finely tunes the interaction with polynucleotides

A series of structurally similar bis-phenanthridinium derivatives, some with uracil at different positions, revealed different interactions with various polynucleotides. The uniform binding of mononucleotides to all studied compounds by "cyclobisintercaland" binding type indicated that compound-polynucleotide interaction selectivity was the consequence of polynucleotide secondary structure and not direct nucleobase recognition. Although affinity and fluorimetric response of all studied compounds toward ds-DNA/RNA was similar, the thermal denaturation and ICD signal-based sensing was highly sensitive to polynucleotide basepair composition and secondary structure. In particular, for the specific poly rAH(+)-poly rAH(+) double helix MD parameters are newly developed and used for analysis of its complexes. The highly sensitive orientation of phenanthridinium as well as the role of the uracil substituent, both binding interactions finely tuned by the steric and binding properties of the DNA/RNA-ligand interaction site, offer novel structural information about binding and steric properties of particular DNA-RNA systems.

Enzyme Substrates Protective Encapsulation within Polymeric Microspheres

Determination of enzymes activity is an important task of analytical and biomedical oriented fluorimetry. Despite of a long track record of application, there is still some room for improvements in this field. In the case of hydrolases, spontaneous decomposition of substrate leads to substantial errors in determination of enzyme activity. An innovative and effective approach is proposed allowing protection of enzyme substrate within the lipophilic moiety of polyacrylate microspheres. It is shown that the introduction of substrate into microspheres is not only an effective method of prevention of unwanted spontaneous process, but also does not disturb the availability of substrate for enzymatic hydrolysis. The effect of presence of proteins in the sample on fluorimetric responses was studied. In contrary to previous studies related to application of lipophilic polymers in biomedical analysis, it is shown that the presence of bovine serum albumins enhances the sensitivity of fluorimetric determination. It is shown that this surprising effect is related to adsorption of proteins on the microspheres surface and change of surface charge of polymer.

Quick accessible dual mode turn-on red fluorescent chemosensor for Cu(ii) and its applicability in live cell imaging

A novel fluorescent chemosensor 9,10-Diphenyl-7H-benzo[d,e]imidazo[2,1-a]isoquinolin-7-one (BIDQ-1), which exhibits rapid colorimetric and fluorimetric response for copper ions over other competitive metal ions under mild conditions has been synthesized easily by a simple one pot condensation method. On addition of Cu(II), BIDQ-1 shows a distinct color change from yellow to green, thus permitting the probe to be used for naked eye detection of Cu(II). The new fluorescent probe exhibits a turn-on fluorescence response towards Cu2+ under physiological conditions with high sensitivity and selectivity. The turn-on fluorescence behaviour of BIDQ-1 with Cu(II) was found to be via an intramolecular charge transfer (ICT) mechanism, by TD-DFT calculations. The probe was found to be applicable for imaging intracellular Cu2+ in living cells.

Spectral response of a methylimidazolium-functionalized polythiophene to phosphates

We report on the colorimetric and fluorimetric responses of the cationic water-soluble polythiophene derivative poly[3-(2-(N-(N′-methylimidazole))ethoxy)-4-methylthiophene] in presence of different phosphates with a focus on ATP. UV/Vis absorbance and fluorescence measurements show that ATP concentrations can be determined in aqueous solutions with a sufficient selectivity to other phosphates. Measurements of circular dichroism reveal that the polymer forms a random coil structure that exhibits no signal in the CD spectrum. Upon addition of ATP the conformation changes to a helix, yielding in strong CD peaks. These experimental data suggest that this polymer is an attractive, simple and versatile colorimetric and fluorimetric probe for nucleoside triphosphates such as ATP.

Dye-functional mesoporous silica material for fluorimetric detection of Cr(III) in aqueous solution and biological imaging in living systems

A dye-functionalized silica nanomaterial, SBA-RT was prepared by the immobilization of the Rhodamine-based chemosensor R6G-TETA within the channels of SBA-15. SBA-RT exhibits several different properties compared to the free R6G-TETA, such as higher selectivity, blue-shift of the UV–vis spectra due to special spatial environment in the channels of the mesoporous material. It presents Cr(III)-selective fluorimetric and colorimetric responses in aqueous solution. The fluorescence responses are reversible by treating with EDTA and do not vary over a broad pH range suitable for Cr(III) bioimaging application. Through isolating of the metal ions within the mesopores of the silica, SBA-RT can extract Cr(III) from the solution with only trace amounts remaining. The fluorescence images experiment demonstrated the possibility of further application in monitoring Cr(III) in living cells and organisms.

Guanidiniocarbonyl-pyrrole-aryl conjugates as nucleic acid sensors: switch of binding mode and spectroscopic responses by introducing additional binding sites into the linker

Two novel guanidiniocarbonyl pyrrole-pyrene conjugates 3 and 4 as spectroscopic probes for ds-polynucleotides were synthesized and their interaction with different ds-DNAs/RNAs studied. Compared to a previously reported first set of conjugates (1 and 2) the significant extension and increased rigidity of the central part of the structure resulted in a switch of DNA binding mode from intercalative (previously studied derivatives 1 and 2 with a nonbinding and flexible linker) to minor groove binding of the two novel guanidiniocarbonyl-pyrrole-pyrene conjugates 3 and 4. These two compounds interact strongly with ds-DNAs, but only weakly with ds-RNA. The newly incorporated heterocyclic moieties within the central part of the structure of 3 and 4 were able to control by steric and hydrogen-bonding effects the alignment of the molecules within various, structurally different forms of DNA minor grooves, whereby even small differences in the position of the attached pyrene within the groove were reflected in different fluorimetric responses. In addition, 3 and 4 revealed intriguing in vitro selectivity among various human tumour cell lines.

The phenanthridine biguanides efficiently differentiate between dGdC, dAdT and rArU sequences by two independent, sensitive spectroscopic methods

At submicromolar concentrations two novel phenanthridine biguanides exhibit distinctly different spectroscopic signals for dGdC and dAdT sequences, respectively, by opposite fluorimetric changes (quenching for dGdC and increase for dAdT) and especially the bis-biguanide derivative gives an opposite ICD response (negative ICD for dGC and strong positive for dAdT). This specific signalling was explained by the ability of compounds to switch the binding mode from intercalation into dGdC to minor groove binding into dAdT sequences. Both compounds bind to rArU by intercalation, yielding different fluorimetric and CD response in comparison to any of aforementioned ds-DNA. Moreover, both compounds revealed significantly higher affinity toward ds-polynucleotides in comparison to previously studied alkylamine- and urea-analogues. Furthermore, DNA/RNA binding properties of novel compounds could be controlled by pH, due to the protonation of heterocyclic nitrogen. Low in vitro cytotoxicity of both compounds against human cell lines makes them interesting spectrophotometric probes.

Blockade of calcium entry in smooth muscle cells by the antidepressant imipramine

The present study was designed to evaluate the effects of antidepressants on smooth muscle contractile activity. In rat aortic rings, the antidepressants imipramine, mianserin and sertraline provoked concentration-dependent inhibitions of the mechanical responses evoked by K + (30 mM) depolarization. These myorelaxant effects were not modified by the presence of glibenclamide or 80 mM K + in the bathing medium. Moreover, the vasodilator properties of imipramine were not affected by atropine, phentolamine and pyrilamine. Radioisotopic experiments indicated that imipramine failed to enhance 86 Rb outflow from prelabelled and perifused aortic rings whilst counteracting the increase in 45 Ca outflow provoked by a rise in the extracellular K + concentration. Simultaneous measurements of contractile activity and fura-2 fluorescence revealed that, in aortic rings, imipramine reduced the mechanical and fluorimetric response to K + challenge. In A7r5 smooth muscle cells, whole cell recordings further demonstrated that imipramine inhibited the inward Ca 2+ current. Under different experimental conditions, the ionic and relaxation responses to the antidepressants were reminiscent of those mediated by the Ca 2+ entry blocker verapamil. Lastly, it should be pointed out that imipramine exhibited a myorelaxant effect of similar amplitude on rat aorta and on rat distal colon. All together, these findings suggest that the myorelaxant properties of imipramine, and probably also setraline and mianserin, could result from their capacity to inhibit the voltage-sensitive Ca 2+ channels.