A Chemosensing Ensemble for the Detection of Cysteine Based on the Inner Filter Effect Using a Rhodamine B Spirolactam

A fluorescent chemosensing ensemble for the detection of cysteine is designed based on the fluorescence inner filter effect. The method employs the coordination of Cu²⁺ ion with salicylaldehyde rhodamine B hydrazone (I), a colorless and non-fluorescent rhodamine B spirolactam derivative to form I-Cu(II), a pink color but weakly fluorescent complex. When rhodamine B was introduced to the I-Cu(II) complex solution, the fluorescence signal of rhodamine B is dramatically decreased because of the fluorescence inner filter effect (IFE). Upon adding cysteine to the above solution, it can complex preferentially to Cu²⁺ compared to I, and the I-Cu(II) complex dissociates, which thus decreases the fluorescence IFE of the solution, and in turn leading to the fluorescence increase of the chemosensing system. Based on the above mechanism, a fluorescent chemosensing ensemble for cysteine is developed. The fluorescence increase is linearly with cysteine concentration up to 10.0 μ mol L⁻¹, with a detection limit of 1.4 × 10⁻⁷ mol L⁻¹ (3σ). The optimal conditions of the proposed method were studied and the selectivity of the proposed method was investigated in this paper.     

Fluorescence Study of the Relaxation Process in Excited Hetarylthiazole Cations

The absorption and fluorescence spectra of five cations protonated at the quinolyl nitrogen atom (IH⁺–VH⁺) and one ethylated (IEt⁺) cation were investigated. For these compounds (except VH⁺) both an anomalously large fluorescence Stokes shift (up to 238 nm) and a large short-wavelength fluorescence shift (up to 145 nm) at decreasing temperatures (down to 77 K) were observed. This is not the case for unprotonated molecules. The ground-state conjugation between quinolyl and another molecular fragment was found for II, IH⁺, IIH⁺, and IEt⁺. The relaxation process of excited cations is medium viscosity and temperature dependent. The experimental results are explained in terms of excited-state structural relaxation.     

Fluorescence Properties and Dipole Moments of Novel Fused Thienobenzofurans. Solvent and Structural Effects

The electronic absorption, fluorescence excitation and emission spectra, and fluorescence quantum yields of novel fused thienobenzofurans, including thieno[3,2-b][1]benzofuran (1), [1]benzothieno[3,2-b]furan (2), and [1]benzothieno[3,2-b][1]benzofuran (3), were recorded in fourteen solvents of different polarities at room temperature. Compound 2 was not fluorescent. Experimental ground-state dipole moments of compounds 1–3 were measured in benzene at 298 K and compared with the corresponding theoretical dipole moment values. The solvent effects on the electronic absorption and fluorescence spectra of these thienobenzofurans were quantitatively investigated by means of solvatochromic correlations based on the Kawski-Chamma-Viallet and McRae equations. A weak negative solvatochromic behavior was found for these compounds, showing that their dipole moments are slightly lower in the excited singlet-state than in the ground-state. Kamlet-Abboud-Taft multiparameter relationships were also established for electronic absorption and fluorescence wavenumbers, and fluorescence quantum yields in most solvents, demonstrating the occurrence of specific solute-solvent interactions.     

Quenching of Pyrene Fluorescence by Calix[4]arene and Calix[4]resorcinarenes

Interactions involving calixarene and its derivatives are of major importance due to their widespread applications as unique hosts. Fluorescence from a common probe pyrene is used to study interactions involving calix[4]resorcinarene [1a] and its tetra-morpholine derivative [1b] in 1 M aqueous NaOH. These compounds efficiently quench the pyrene fluorescence. A comparison with the fluorescence quenching behavior of N-methylmorpholine clearly indicates the presence of long-range interactions involving 1a and 1b; the interactions are specific to the calixarene molecular framework. This is not the case for a tetra-nitro-substituted calix[4]arene [2b], an electron/charge acceptor quencher, as p-nitrophenol also shows similar interactions with pyrene. Effectiveness of cesium as the quencher of pyrene fluorescence is reduced in the presence of electron/charge donating 1b; fluorescence enhancement is observed upon addition of cesium as the concentration of 1b is increased in the solution. The role of calixarene framework in interactions involving such compounds is established.     

Spectroscopic and photophysical investigations on the nature of localization of rhodamine-123 and its dibromo derivative in different cell lines

Steady-state and time-resolved spectroscopic properties of rhodamine-123 (rh123) and 4,5-dibromorhodamine methyl ester (dbr123) bound to different cell lines are evaluated. Studies are also performed on the dye bound to extracted mitochondria. Results are compared with those obtained in homogeneous and microheterogeneous media. Results suggest that these dyes can specifically bind only with cell mitochondria. As a result of binding, excitation and emission spectra are red shifted by 10 to 12 nm. The fluorescence decay of these dyes bound to mitochondria shows two lifetimes. Values are about 4.0 and 2.0 ns forrh123 and about 1.9 and 0.5 ns fordbr123. Detailed global analysis of emission wavelength and dye concentration dependences of the fluorescence decay is performed. Results indicate that these dyes are bound to two different binding sites at mitochondria. The decay-associated fluorescence spectrum for the species corresponding to each binding site is recovered. Species1, corresponding to the longer lifetime, is found to be more red shifted compared to species2. The fluorescence of species2 is heavily quenched. The origin of this quenching is explained in terms of resonance energy transfer between donor species2 and acceptor species1. The possible nature of the two binding sites is also discussed.     

Luminescence and Reversible Luminescence Thermochromism of Bulk and Microcrystals of Dibenzoylmethanatoboron Difluoride

Essential differences in the luminescence properties of dibenzoylmethanatoboron difluoride (1) bulk and microcrystals were detected. Analysis of the spectral data showed that in every case the fluorescence spectrum of 1 consisted of three components: monomer fluorescence, excimer fluorescence, and fluorescence related with interdimer interaction. Evolution of luminescence spectra observed with decrease of the crystal size are bound with decrease of monomer fluorescence intensity and considerable growth of intensity of fluorescence related to interdimer interaction. The presence of reversible luminescence thermochromism was discovered for 1: lowering the temperature from 300 to 77 K resulted in essential hypsochromic shift of the luminescence band maximum (∼60 nm) connected with considerable decrease of the distances between the planes of the neighboring molecules (∼0.1 Å) that lead to the weakening of interdimer interaction and intensification of monomer luminescence.     

Relation between proteins tertiary structure, tryptophan fluorescence lifetimes and tryptophan S(o)→(1)L(b) and S(o)→(1)L(a) transitions. Studies on α1-acid glycoprotein and β-lactoglobulin

We measured fluorescence lifetimes and fluorescence spectra (excitation and emission) of tryptophan residues of α₁-acid glycoprotein (three Trp residues) and β-lactoglobulin (two Trp residues) in absence and presence of 450 μM progesterone. Progesterone binds only to α₁-acid glycoprotein. In absence of progesterone, each of the two proteins displays three fluorescence lifetimes. Addition of progesterone induces a partial inhibition of the S _o → ¹ L _a transition without affecting fluorescence lifetimes. The same experiments performed in presence of denatured proteins in 6 M guanidine show that addition of progesterone inhibits partially the S _o → ¹ L _a transition and its peak is 15 nm shifted to the red compared to that obtained for native proteins. However, the S _o → ¹ L _b transition position peak is not affected by protein denaturation. Thus, the tertiary structure of the protein plays an important role by modulating the tryptophan electronic transitions. Fluorescence emission decay recorded in absence and presence of progesterone yields three fluorescence lifetimes whether proteins are denatured or not. Thus, protein tertiary structure is not responsible for the presence of three fluorescence lifetimes. These characterize tryptophan substructures reached at the excited states and which population (pre-exponential values) depend on the tryptophan residues interaction with their microenvironment(s) and thus on the global conformation of the protein.     

Spectrophotometric Characteristics of New Pyridylindolizine Derivatives Solutions

Three new pyridylindolizine derivatives, 1, 2, 3-tricarbometoxi-7-(4-pyridyl)-pyrrolo[1, 2-a]pyridine (I), 1,2-dicarboethoxy-3-(4-bromobenzoyl)-7-(4-pyridyl)-pyrrolo[1,2-a]pyridine (II) and its isomer 1,2-dicarboethoxy-3- (4-bromobenzoyl) -5- (2-pyridyl) -pyrrolo[1, 2-a]pyridine (III) have been investigated in different solutions by UV-VIS absorption, steady-state, and time-resolved fluorescence methods. The effects of the substituent and solvent on the spectroscopic properties have been demonstrated. The fluorescence decay data could be fitted to a single-exponential function. The lifetime values are higher in protic polar than in aprotic apolar solvents for compound I. In the case of compounds II and III the fluorescence intensities and lifetimes are very low, with the exception of III in aprotic solvents. The absorption and fluorescence properties of the compounds showed a solvent dependence.     

Fluorescence of N,N-di(2-carboxyethyl)-<Emphasis Type="Italic">p</Emphasis>-anisidine in solution and crystalline states

The fluorescence properties of N,N-di(2-carboxyethyl)-p-anisidine (I) in solvents of various nature and in the crystalline state have been studied at room temperature (273 K) and at the boiling point of liquid nitrogen (77 K). Fluorescence in aqueous solutions of I with protonated (λ _ex /λ _fl ^max = 225/290 nm) and unprotonated (λ _ex /λ _fl ^max = 270/380 nm) amino nitrogen has been detected. On going from aqueous solutions to nonaqueous, the fluorescence band of unprotonated I experiences a blue shift and its intensity rises. The fluorescence intensity of the band in aprotic polar solvents is higher than that in protic solvents. A linear dependence of the fluorescence intensity of deprotonated I on Cu(II) concentration (ranging from 1.0 to 5.0 mg/dm³) in aqueous solution has been found. The fluorescence intensity of I in aqueous solutions at 77 K and pH 1–6 has been shown to increase in the presence of Zn(II) (1–170 mg/dm³) and Cd(II) (2–330 mg/dm³) although a similar dependence is not observed at 293 K.     

A Multifunctional Fluorescence Probe for the Detection of Cations in Aqueous Solution: the Versatility of Probes Based on Peptides

We synthesized a tetra-functional fluorescence probe based on dansyl and peptide motif, dansyl-Gly-Trp (DGT, 1), that efficiently bound several metal ions and showed distinguishing optical properties. The probe 1 could respond to Hg²⁺ with enhanced and blue-shifted fluorescence emission but to Cu²⁺ with obvious fluorescence quenching. In addition, 1 was sensitive to pH ranging from 2.0 to 5.0 and precipitated in the presence of Pb²⁺ at neutral conditions. The combination of these intrinsic properties with the selective responses to different chemical inputs allows this system to be implemented as an ionic switch. Furthermore, 1 could penetrate the cell membrane and accumulated well in intracellular region. The underlying mechanisms of the probe to different kind of metal ion were explored successfully by using either ¹H NMR, NOESY, electron paramagnetic resonance (EPR) or FT-IR spectra. In addition, to investigate the binding model of 1/Hg²⁺ and 1/Cu²⁺, simulations were also performed by using density functional theory (DFT) and reasonable binding configurations were achieved for these two complexes.     

Fluorescence of Crowned Butadienyl Dye and Its Metal Complexes

The absorption and fluorescence spectra of complexes of butadienyl dye (1) with lithium, sodium, magnesium, and calcium cations in MeCN were investigated. The addition of Li, Na, Mg, and Ca perchlorates to the solution of dye 1 in acetonitrile results in a significant (up to 5900-cm^–1) short-wavelength shift of the absorption spectrum and a small (about 200-cm^–1) short-wavelength shift of the fluorescence spectrum. The recoordination reaction in metal complexes of 1 takes place by intramolecular mechanism. The fluorescence quantum yield of 1Li⁺, 1Na⁺, and 1Ca²⁺ is approximately two times higher than that for 1. It was supposed that Li⁺ cation coordinates predominantly with oxygen atoms of macrocycle and, hence, influences weakly macrocycle nitrogen atoms conjugated with a molecule -system.     

A Fluorescence Study of Novel Styrylindoles in Homogenous and Microhetrogeneous Media

In this paper are presented absorption and fluorescence emission properties of 3-styrylindoles viz. 3-(2-phenylethenyl-E)-NH-indole (1), 3-[2-(4-nitrophenyl)ethenyl-E)-NH-indole (2), 3-[2-(4-cyanophenyl)ethenyl-E]-N-ethylindole (3) and 3-[2-(4-cyanophenyl)ethenyl-E]-NH-indole (4) in organic solvents, 1,4-dioxane-water binary mixtures and micelles (SDS, CTAB and Triton-X-100). The fluorescence properties of 2-4 have been utilized to probe the microenvironment (binding constant, CMC, micropolarity and solubilization site) of the micelles.     

A New Fluorescent Squaraine Probe for the Measurement of Membrane Polarity

The present study was undertaken to evaluate the sensitivity of newly synthesized squaraine dye 1 to the changes in lipid bilayer physical properties and compared it with the well-known dye 2. Partitioning of the dye 1 into lipid bilayer was found to be followed by significant increase of its fluorescence intensity and red-shift of emission maximum, while intensity of the dye 2 fluorescence increased only slightly on going from aqueous to lipidic environment. This suggests that dye 1 is more sensitive to the changes in membrane properties as compared to dye 2. Partition coefficients of the dye 1 have been determined for the model membranes composed of zwitterionic phospholipid phosphatidylcholine (PC) and its mixtures with positively charged detergent cetyltrimethylammonium bromide (CTAB), anionic phospholipid cardiolipin (CL), and sterol (Chol). The spectral responses of the dye 1 in different liposome media proved to correlate with the increase of bilayer polarity induced by Chol and CL or its decrease caused by CTAB. It was concluded that dye 1 can be used as fluorescent probe for examining membrane-related processes.     

Enhanced Fluorimetric Determination of Samarium with Dibenzoylmethane and Diphenylguanidine by Gadolinium

Abstract

The fluorescence of Sm-dibenzoylmethane (DBM)-diphenylguanidine (DPG) system was enhanced by about two to three orders of magnitude when it was excited in the presence of Gd in ethanol-water solution. The excitation and emission wavelegths were 390 nm and 652 nm, respectively. The fluorescence intensity was a linear function of the concentration of Sm in the range of 1.0 × 10^?9–2.0 × 10^?6 M. The fluorescence mechanism of the system is discussed.     

The Anthracen-9-ylmethyloxy Unit: An Underperforming Motif Within the Fluorescent PET (Photoinduced Electron Transfer) Sensing Framework

Compound 2, which was designed to act as a fluorescent sensor for calcium according to the PET (Photoinduced Electron Transfer) principle, shows a relatively small Ca²⁺-induced fluorescence enhancement factor (FE) of 1.8 whereas its close relative 1 is known to display a far higher FE value of 16. Though designed as fluorescent PET sensors for solvent polarity, compounds 5 and 6 also show negligible fluorescence enhancement as their environments are made progressively less polar even though their relatives 3 and 4 show limiting FE values of 53 and 3, respectively. Indeed, 3 and 4 are useful since they are fluorescent sensors for solvent polarity without being affected by Bronsted acidity. The poor sensory performance of 2, 5, and 6 relative to their cousins is attributed to the presence of an oxygen proximal to the 9-position of an anthracene unit, which opens up a CT (charge transfer) channel. Normal PET sensing service is resumed when the offending oxygen is deleted.     

Stilbene-Like Molecules as Fluorescent Probes Applied for Monitoring of Polymerization Process

2-(p-N,N-dimethylaminostyryl)benzoxazole (OS), 2-(p-N,N-dimethylaminostyryl)-benzothiazole (SS) and 2-(p-N,N-dimethylaminostyryl)naphtiazole (PS) were prepared and their absorption and fluorescence spectra were measured in various solvents at room temperature. On the basis of the solvatochromic behavior the ground state (μ_g) and excited state (μ_e) dipole moments of these pN,N-dimethylaminostyryl derivatives were evaluated. The dipole moments (μ_g and μ_e) were estimated from solvatochromic shifts of absorption and fluorescence spectra as function of the dielectric constant (ɛ) and refractive index (n) of applied solvents. The absorption spectra only slightly are affected by the solvent polarity in contrast to the fluorescence spectra that are highly solvatochromic and display a large Stokes shift. The analysis of the solvatochromic behavior of the fluorescence spectra as function of Δf (ɛ, n) revealed that the emission occurs from a high polarity excited state. The large dipole moment change along with the strongly red-shifted fluorescence, as the solvent polarity is increased, demonstrate the formation of an intramolecular charge transfer state (ICT). Compounds under the study were used as fluorescence probes for monitoring the kinetics of polymerization. The study on the changes in fluorescence intensity and spectroscopic shifts of studied compounds were carried out during thermally initiated polymerization of methyl methacrylate (MMA) and during photoinitiated polymerization of 2-ethyl-2-(hydroxymethyl)propane-1,3-diol triacrylate (TMPTA).     

Investigation of the Interaction Between Rutin and Trypsin in Solution by Multi-Spectroscopic Method

ABSTRACT

The interactions between rutin and trypsin were investigated by UV-Vis absorption, CD, fluorescence, resonance light-scattering spectra, synchronous fluorescence, and three-dimensional fluorescence spectra techniques under physiological pH 7.40. Rutin effectively quenched the intrinsic fluorescence of trypsin via static quenching. The enthalpy change and entropy change were estimated to be ?8.23 kJ·mol^?1 and 53.66 J·mol^?1·K^?1 according to the van't Hoff equation. The process of binding rutin to trypsin was a spontaneous molecular interaction procedure. This result indicates that hydrophobic and electrostatic interactions played a major role in stabilizing the complex. The conformation of trypsin was discussed by CD, synchronous, and three-dimensional fluorescence techniques.     

A Novel Chemosensor Based on Rhodamine Derivative for Colorimetric and Fluorometric Detection of Cu<Superscript>2+</Superscript> in Aqueous Solution

A new rhodamine-based reversible chemosensor (2) was synthesized, which exhibits high sensitivity and selectivity for Cu²⁺ but no significant response toward other competitive metal ions in aqueous solution. Upon the addition of Cu²⁺, the spirolactam ring of 2 was opened and the solution color changed from colorless to red. Strangely, an unexpected fluorescence quenching was observed, which is contrary to the fluorescence turn-on of the most rhodamine-based chemosensors. The likely novel sensing mechanism has been proposed.     

Synthesis and Chiral Recognition Properties of Novel Fluorescent Chemosensors for Amino Acid

The charge neutral chiral optical sensors 1a∼d containing thiourea and amide groups were synthesized by simple steps in good yields and their structures were characterized by IR, ¹H NMR, ¹³C NMR, MS spectra and elemental analysis. The enantioselective recognition for α-phenylglycine and phenylglycinol was examined by fluorescence emission and UV-vis spectra. The fluorescence and UV-vis spectra changes of 1a were obvious when the enantiomers of α-phenylglycine anion were added, which exhibited that 1a has good enantioselective recognition ability towards α-phenylglycine. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A Pyrene-based Highly Selective Turn-on Fluorescent Sensor for Copper(II) Ion and its Application in Live Cell Imaging

A new pyrene derivative (chemosensor 1) containing a picolinohydrazide moiety exhibits high selectivity for Cu²⁺ ion detection in mixed aqueous media (CH₃OH:H₂O = 7:3). Significant fluorescence enhancement was observed with chemosensor 1 in the presence of Cu²⁺. However, the metal ions Ag⁺, Ca²⁺, Cd²⁺, Co²⁺, Cu²⁺, Fe²⁺, Fe³⁺, Hg²⁺, K⁺, Mg²⁺, Mn²⁺, Ni²⁺, Pb²⁺, and Zn²⁺ produced only minor changes in fluorescence for the system. The apparent association constant (K _a) of Cu²⁺ binding in chemosensor 1 was found to be 2.75*10³ M⁻¹. The maximum fluorescence enhancement caused by Cu²⁺ binding in chemosensor 1 was observed over the pH range 5–8. Moreover, by means of fluorescence microscopy experiments, it is demonstrated that 1 can be used as a fluorescent probe for detecting Cu²⁺ in living cells.