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New emissive dopamine derivatives as fluorescent chemosensors for metal ions: A CHEF effect for Al(III) interaction
Abstract
Three new Schiff-base ligands 1–3 derivatives from neurotransmitter dopamine, bearing an indazole (1), methylimidazole (2) or hydroxynaphthaldehyde (3) units were successfully synthesized and characterized by elemental analysis, 1H NMR, 13C NMR, IR (infrared), ESI-TOF (electrospray ionization-time of flight-mass), UV–Vis absorption and emission spectroscopy. The interaction with the metal ions Li+, Na+, Mg2+, Ca2+, Zn2+, Cd2+, Cu2+, Ni2+, Ag+, Fe3+ and Al3+ has been explored by absorption and fluorescence emission spectroscopy. Compound 3 shows to be the most emissive one, with a quantum yield of 0.022, followed by compound 2 (ϕ = 0.009) and 1 (ϕ = 0.001). Compound 1 reveals quite selective for Al3+, generating an emissive complex formed by three units of 1 per metal ion. On the other hand compound 3, shows a ratiometric effect with Al3+ appearing as a new emission band centred at 530 nm. With the other transition and post-transition metal ions, a quenching in the emission was observed, being 3 the most sensitive one, being quenched by 0.34 ppm of Zn2+ and Cu2+, 0.48 ppm of Ni2+, 0.061 ppm of Fe3+ and 0.047 ppm of Al3+. In most cases a stoichiometry of three ligands by one metal ion was postulated. In order to study the fluorescence properties in the solid state, the Al3+ metal complexes of 1 (4) and 3 (5) were synthesized as new emissive materials. In both cases a very strong emissive systems were obtained, with a quantum yield of 0.01 and 0.04 for 4 and 5.
... 相比于其他检测方法, 荧光法由于具有 灵敏度高、选择性好等优点而受到广泛关注 [2] . [22,23] . ...
... 荧光探针检测的 研究: 萘类 [3~7] 、氟硼二吡咯(BODIPY)类 [8~10] 、香豆 素类 [11~14] 及罗丹明类 [15~19] , 其中萘类荧光探针合成较 为简单, 然而, 其通常荧光寿命短、发射波长较短[20,21] ; 提供络合位点, Al 3+ 与C=N双键上的N原子络合后会抑 制分子异构化, 同时增加分子平面刚性[22,23] , 引起颜色 及光谱变化, 实现对Al 3+ 的检测, 为拓展其在传感器研 制方面的应用奠定基础. ...
... In addition, poly(dopamine) surface coatings have found use in a number of applications, including biotechnology and biomedicine, and water treatment membranes [5,6]. Oliver et al. (2012) investigated the chemosensory properties of new dopamine-containing Schiff bases against some metal ions (Li, Na, Mg, Ca, Cd, Zn, Cu, Ni, Ag, Fe, and Al) and observed the best chemosensory property against Al 3+ ion [7]. Kareem et al. (2021) synthesized bidentate complexes using dopamine Schiff bases and metal salts of Ni (II), Pd (II), and Pt (IV) and investigated the antioxidant activity of the compounds. ...
... The Chelation Enhanced Fluorescence (CHEF) is due to the enhanced emission intensity that takes place when Al 3+ ion complexes with receptor1 termed as turn off-on fluorescence. The receptor1 and Al 3+ ion complex is regid because the freely rotatable C-N bond between thiazole and imine is arrested due to binding [52,53]. During the chelation process -C=N isomerization is blocked, which eventually enhances the emission intensity [54]. ...
The thiazole based Schiff base 2-hydroxy-1-naphthaldehyde-2-amino thiazole (receptor1) was synthesized through a single step process and characterized by spectroscopic and analytical techniques. The cation detecting ability of the receptor1 was explored by fluorescent spectroscopic methods. The receptor1 has recognized Al3+ ions by a turn-on process over a panel of other potentially competing metal ions. The binding constant of receptor1 with Al3+ was found to be 8.27 × 103 M−1. Computational studies Density Functional Theory (DFT) and Time-dependent Density Functional Theory (TD-DFT) were performed to provide detailed information on electronic states and photophysical property of receptor1 and receptor1-Al3+ ions. MTT (3-(4,5-dimethyl thiazole-2-yl)-2,5-diphenyl tetrazolium bromide) assay and bioimaging applications were made on breast carcinoma cells in humans.
... Many of them operate according to the "on-off" principle regarding the formation of a fluorescent signal and its registration [26][27][28][29]. In recent years, a number of similar fluorescent probes have been developed, including those for the detection of Al 3+ in living cells and biosamples [30][31][32][33]. The importance of developing sensors for monitoring Al 3+ in real conditions was noted, also [34]. ...
The conditions for the formation of metal complexes (aluminium, radionuclides) in solutions are considered. The properties of solid extractants (TVEX) and their application for the selective extraction of metals and radionuclides are discussed. The extraction of 90Sr, 90Y, 137Cs and U(VI) radionuclides from aqueous TVEX solutions impregnated with calixarenes C45 and CIP67 has been studied. The use of surfactants in combination with OAR (PA) is a typical example of the fact that the analytical capabilities of even well-known reagents are far from exhausted, and the use of functionalized reagents can significantly improve the basic analytical characteristics of metal detection.
... Currently, Schiff bases compounds are vastly recognized as fluorescence probes for metal ions with the high sensitivity, good selectivity, and high excitation coefficients, but a lot of them displayed fluorescence "on-off" behavior [24][25][26], which is a disadvantage for the visualization study. In recent years, a few "off-on" fluorescence probes have been developed, but the probes applied to detect Al 3+ in living cells and real samples were scarce [27][28][29][30]. Hence, it is very meaningful to develop "off-on" probes for Al 3+ monitoring in real application [31]. ...
An excess of Al3+ will lead to biological disorders and even many diseases. Therefore, detecting the levels of Al3+ in the human body has drawn great attention for health monitoring. The fluorescence method has been broadly applied because of high sensitivity, real-time detection, and intracellular imaging. In this work, a new probe with “turn-on” fluorescence based on Schiff base derivative, 3,6-imine-triphenylamine-(9-ethyl) carbazole (ITEC), has been successfully synthesized and studied. The high selectivity and sensitivity of ITEC to Al3+ were verified by fluorescence spectra and the detection limit was 2.19 nmol/L. A 1:2 stoichiometry of ITEC-Al3+ was obtained by the 1H NMR spectra and Job’s plot. Furthermore, ITEC was successfully applied to the detection of Al3+ with different concentrations in living HeLa cells. The analog experiments about nature contamination of Al3+ in cells and real samples were finished.
... [6][7][8][9][10][11] To overcome these problems, some serious efforts have been made for the development of aluminium sensing fluorescent probes such as BINOL, 12 BODIPY, 13 8-hydroxyquinoline, 14 anthraquinone, 15 coumarin, 9 and Schiff base molecules. [16][17][18][19] The majority of these probes have provided moderate success because of their difficult synthetic methodologies, 13 limited solubility, poor selectivity and interfering sensitivity towards other d-block cations like Fe 3+ and Zn 2+ . Hence, the invention of a new superior effective probe for Al 3+ detection is still in demand. ...
High absorption coefficient, fluorescence quantum yield, photo stability and relatively long wavelengths of rhodamine dye expand its applicability as a promising fluorescent probe. In the present investigation, two dyes namely rhodamine and azobenzene have been conjugated for the detection of Al3+ in aqueous ethanol. The turn on fluorescence response of chemosensor L towards Al3+ is attributed to the inhibited PET (photoinduced electron transfer) and CHEF (chelation enhanced fluorescence) process along with spirolactam (non-fluorescent) to ring-opened amide (fluorescent) process. The presence of PET and CHEF process was corroborated by time-resolved photoluminescence study and the spirolactam ring opening was confirmed by 13C NMR and infrared spectroscopy. In presence of Al3+, the opened spirolactam ring forms a 1:1 binding complex with metal which is supported by its high binding constant (Ka = 7.033×103 M-1). Limit of detection (LOD) and limit of quantification (LOQ) value are found to be 1.1×10-7 M and 3.6×10-7 M, respectively. The reversible recognition of Al3+ was also proved in presence of Na2EDTA by both UV-Vis and fluorometric titration. The sensing behaviour of chemosensor towards Al3+ was supported by DFT/TDDFT calculations.
... In particular, selective and sensitive detection of the fluorescence emission of metal ions like aluminum is extremely important due to the well known neurotoxicity of aluminum. In addition, compound derivatives from aluminum are widely used in water treatment and in food additives (Oliveira, Santos, Capelo, & Lodeiro, 2012). ...
A new sensitive fluorimetry method for the simple and rapid measurement of aluminum in some food samples, which used 3',6'-bis(diethylamino)-2-{[(1E)-(4-ethoxyphenyl) methylene] amino}spiro[isoindole-1,9'-xanthen]-3(2H)-one (DEMAX) for Al(III) chelation is described herein. The fluorescence intensity of the aluminum-DEMAX complex remains unaltered for over 24 h at room temperature and is a linear function of the concentration of aluminum in the 0–1000 mg/L range with a detection limit (LOD, defined as 3s/b) of 3.02 µg L⁻¹ and quantification limit (LOQ, defined as 10Sb/m) of 30 µg L⁻¹. The relative standard deviation (RSD) was 0.1% for a 1 µg L⁻¹ aluminum level. The influences of the analytical parameters such as pH, waiting time of aluminum-DEMAX complex, amount of reagent, effect of temperature etc. were investigated. The developed method was successfully used for assaying aluminum in some food samples and dialysis solution, measured by the new home-made fluorimetric system. The results of analysis of the certified reference material (INCT-TL-1) are in good agreement with the certified value.
... In comparison with d-block ions, the chemists reported a fewer fluorescent chemosensors for Al(III). Although the poor complex ability of aluminum, the researchers studied sensors is still investigated to the selective-sensitive fluorescent chemosensors for Al (III) ion [24][25][26][27][28][29][30][31][32][33] . ...
A novel triazole-linked Bodipy-Anthraquinone (Bodipy-A) was easily prepared through one step click chemistry. Bodipy-A displayed a remarkable increasing in fluorescence intensity in the presence of trace amounts of Al (III). These changes could be attributed to the intramolecular charge transfer (ICT), which showed also high selectivity over a series of other metal ions in methanol/water (9/1). The result performed by absorption spectroscopy titration (Job plot) suggested a 2:1 ligand-to-metal complex which was further demonstrated by FT-IR spectroscopy. The binding constant K of the target complex was then calculated by using the Benesi-Hildebrand equation. All fluorescence experiments have shown that compound Bodipy-A has a good selectivity with Al (III) ion. The results show that this system could be used in semi-aqueous system.
... Oliveira et al. 109 have reported three new Schiff base ligands from neurotransmitter dopamine, bearing an imidazole, methylimidazole or hydroxyl naphthaldehyde (NAP10) units. ...
Developments in the field of fluorescent chemosensors for trace level determination of Al3+ have been described. Design, synthesis and applications of Al3+ selective fluorescent sensors have attracted a great deal of attention due to their versatile and emerging biological implications. A systematic description of different fluorescent probes based on their fluorophore skeleton has been made. The sensing mechanism of each fluorescent probe has been briefly discussed. Special emphasis has been given to consideration of the greenness of the methods, particularly, the use of greener solvents like water. The review covers published work on fluorescence sensing of Al3+ worldwide together with our own contribution in this field.
... However, unregulated amounts of aluminum in the human body may lead to central nervous system malfunction, Parkinson's disease, and Alzheimer's disease [6]. For these reasons, much effort has been devoted to the design of various chemosensors specific for Cr 3+ and Al 3+ detection [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. In particular, it is valuable to screen samples for multiple targets with a single probe because it would lead to faster analytical processing and potential cost reductions. ...
... The design of new bio-inspired compounds (Lodeiro et al. 2010; Pazos et al. 2009) containing amino acid units (Costa et al. 2008; Oliveira et al. 2012a), peptides (Oliveira et al. 2011a, b), neurotransmitters (Oliveira et al. 2012b) or other biological molecules as receptors, and bearing fluorescent dyes is up to now an area of great development due to their huge potential applications in biological and environmental fields. A bio-inspired chemosensor has a similar structure to a classical chemosensor, but in this case, the receptor is formed by an amino acid (natural or synthetic) or by a peptide chain (Lodeiro et al. 2010). ...
Two new bio-inspired non-proteinogenic compounds L1 and L2, containing coumarin and/or acridine chromophores and bearing as spacer an alanine amino acid were successfully synthesized and fully characterized by elemental analysis, (1)H and (13)C NMR, infrared spectroscopy (KBr discs), melting point, ESI-TOF (electrospray ionization-time of flight-mass), UV-vis absorption and emission spectroscopy, fluorescence quantum yields and lifetime measurements. A relative fluorescence quantum yield of 0.02 was determined for both compounds. In L2 the presence of an intramolecular energy transfer from the coumarin to the acridine unit was observed. L1 and L2 are quite sensitive to the basicity of the environment. At alkaline values both compounds show a strong quenching in the fluorescence emission, attributed to the photoinduced electron transfer (PET). However, both deprotonated forms recover the emission with the addition of Zn(2+), Cd(2+) and Al(3+) metal ions. As multifunctional emissive probes, the titration of L1 and L2 with lanthanides (III), Eu(3+) and Tb(3+) was also explored as new visible bio-probes in the absence and in the presence of liposomes. In a liposomal environment a lower energy transfer was observed.
A simple fluorescence chemosensor of FHS-OH based on salicylaldehyde Schiff base was developed via a one-step reaction, which achieved a fast and highly selective response for Al(iii). Mechanism studies showed that when FHS-OH was exposed to Al(iii) with 1 : 2 binding stoichiometry in an aqueous solution at neutral pH, C 00000000 00000000 00000000 00000000 11111111 00000000 11111111 00000000 00000000 00000000 N isomerization and PET processes were limited, resulting in a ‘turn-on’ fluorescence response with a low detection limit of 63 nmol L⁻¹ and a satisfying linear range of 0.0–20.0 μmol L⁻¹. Compared to traditional detection methods for Al(iii), fluorometry using FHS-OH has several advantages, including simplicity, quick response, and capability of real-time detection. More importantly, the detection of Al(iii) on a solid matrix (test paper) was successfully achieved. After the addition of Al(iii), a significant emission colour change from green to bright blue was observed by the naked eye owing to the intrinsic aggregation-induced emission (AIE) characteristic of FHS-OH.
The polyfluorene copolymers with different pyrimidine content has been synthesized and characterized by 1HNMR, 13CNMR and FT-IR spectrum. The aggregation, acidochromicity, and metallochromicity of copolymers has been investigated. The pyrimidine content of polymer has great affect in acidochromic properties for methanesulfonic acid (MSA) and selectivity for Al3+. The colour change of copolymer/Al3+ complexes can be detected by the naked eye. The copolymers are found to be good linearly proportional to the concentration of Al3+ ions in a range from 1.0×10-6 to 1.0×10-3 M with a detection limit of 1.895×10-8 M. The binding constant of the copolymer/Al3+ complexes was calculated using Benesi-Hildebrand equation and was found to be 8.95×105 M-1. The XPS spectroscopy, SEM micrograph and the EDS analysis reveal that the metal ion coordination occurs on the pyrimidine ring in the copolymers. This copolymer will be widely used for detection of protons and metals as fluorescent sensors.
Synthesis and chelation induced fluorescence emission from two imidazo[1,2-a]pyridine derivatives are described. The nonfluorescent molecule 1 containing N and O donor atoms, achieves coplanarity upon interactions with trivalent cations Al3+, Fe3+ and Cr3+, that favors fluorescence emission. Molecule 2 containing two N donor atoms attains coplanarity upon interaction with the only Zn2+ and becomes fluorescent. Both molecules 1 and 2 form a 1:1 complex with interacting metal ions. Other trivalent metal ions (including Bi3+ and In3+) and common divalent metal ions (including Hg2+ and Cd2+) fail to form any complex with 1 or 2, and they do not interfere in the detection of Zn2+, Al3+, Fe3+ or Cr3+ ions. Noninterference of other metal ions renders 1 and 2 suitable for the detection of fungal cells contaminated with Zn2+, Al3+, Fe3+ or Cr3+ ions.
A sensitive fluorescent analytical method for the detection of dopamine (DA) was developed based on surface-enhanced Tb(III)/La(III) co-luminescence using silver nanoflowers (AgNFs). Anisotropic AgNFs show strong surface-enhanced fluorescence effect owing to the abundant sharp tips. Tb(III)/La(III)-DA complexes mainly bind to the sharp tips of AgNFs and thus shorten the distance between the complexes. The shortened distance gives rise to obvious surface-enhanced Tb(III)/La(III) co-luminescence effect. In this work, AgNFs offer many superior properties, such as enhanced intrinsic green fluorescence of Tb(III) (λex/λem = 310/546 nm), increased fluorescence lifetime, and improved energy transfer efficiency. Under the optimum conditions, the fluorescence intensity is linearly correlated with the concentration of DA in the range of 0.80–10 nM (R2 = 0.9970), and the detection limit is 0.34 nM (S/N = 3). The fluorescent nanoprobe was successfully applied to the determination of DA in human serum samples with recoveries ranging from 99.1 to 102.6%.
Graphical abstract
In this work, a new rhodamine chemosensor (P) with excellent photochromic properties upon vis irradiation was designed and synthesized. The fabricated chemosensor P could detect Al³⁺ via the opening of the spirolactam ring of the rhodamine unit with high selectivity and sensitivity. The spirolactam ring opening was confirmed by NMR and infrared spectroscopy. Upon binding with Al³⁺, the generated 1 : 1 P-Al³⁺ complex, confirmed by Job's plot titrations and mass spectrometry analysis, could exhibit a remarkable fluorescence enhancement with a limit of detection (LOD) of 0.16 μM. Furthermore, the sensing of P to Al³⁺ in vivo was also studied quantitatively and qualitatively in detail, and the results showed that the coordination between P with Al³⁺ was reversible in living cells.
Antipyrine and naphthoic acid based hybrid molecular architect has been synthesized and further investigated their photophysical behavior towards various cations and anions. The probe 1 has been used for selective estimation of Al3+ ions and signalled the binding event through formation of new absorption band at 405 nm and ‘turn-on’ fluorescence band at 505 nm via CHEF effect and restricting PET phenomenon with lowest detection limit of 28 nM. The probe 1 showed selective estimation of CN- and OH- ions among all other anions by forming new absorption band at 400 nm and fluorescence ‘turn-on’ at 520 nm with lowest detection limit of 77 nM. Aluminium concentration was also detected by probe 1 in sewage water upto 7.4-8.6 ppm. All the results were correlated by 1H NMR titrations and theoretical studies.
A novel fluorescent probe was designed and synthesized. The probe exhibited much higher selectivity and sensitivity for detecting aluminum(III) compared with other metal ions, anions, and amino acids in C2H5OH/H2O media through a fluorescence enhancement. The mechanism was proposed to form a kind of 2:1-type complex between probe and aluminum(III) with a detection limit of 0.17 μM.
An efficient fluorescein based probe (H2L) for the dual sensing of Al³⁺ and Cu²⁺ has been synthesized and characterized. H2L was highly selective toward these two ions with different fluorescence signals and binding modes in two different media. In EtOH-H2O (3:2, v/v; pH 4.0), H2L selectively binds Al³⁺ to form a 1:1 ligand/metal complex, giving rise to a visible pale pink-to-yellow color change and fluorescence enhancement at 440 nm, while in CH3CN-H2O (2:3, v/v; pH 7.2), H2L and Cu²⁺ form a 1:2 ratio complex, resulting in a color change from pink to orange-yellow and a significant fluorescence enhancement at 520 nm. The binding modes were confirmed by fluorescence, absorption, IR, ESI-MS and ¹H NMR titrations. The detection limits were calculated to be 7.32 × 10⁻⁸M and 1.47′10⁻⁸M for Al³⁺ and Cu²⁺, respectively. Cell imaging studies demonstrate that this sensor is capable of sensing Al³⁺ and Cu²⁺ in living cells.
The electromagnetic spectrum covers a wide long range of light that surrounds us every day. However, our eyes are sensitive to a minor part of the light. From all regions of the electromagnetic spectrum such as microwaves, infrared light, visible light, ultraviolet light, x-rays and gamma-rays, the ultraviolet and visible ones are the most appealing to us, since here are located the optical chemosensors (fluorimetric and colorimetric) which can be sensitive and selective to several relevant analytes. Herein, we will focus in distinguishing optical probes containing invisible and visible excitable chromophores and in their chemoresponsive towards several targets in solution and also in the solid state. Probes containing chromophores as coumarin, anthracene, benzoxazole, pyrene, crown ethers (benzo)imidazole-based, anthraquinones, indolylmethanes, fluorescein, cresyl violet, rhodamine, corrole, porphyrine, as well as, boron, palladium and platinium complexes are addressed. Concerning this area, the latest advances in our group will be emphasized, such as the way to the construction of more robust and efficient systems (76 references).
A coumarin-quinoline based fluorescence resonance energy transfer (FRET) system (TCQ) has been synthesized and employed as a ratiometric fluorescence probe. The selective fluorescent response of the probe TCQ toward Al3+ was devised by employing a quinoline moiety as a FRET energy donor with a coumarin moiety as an energy acceptor. The quinoline emission at 390 nm decreased and the coumarin emission at 480 nm increased concurrently on addition of Al3+ under excitation wavelength at 253 nm. The TCQ probe exhibited high selectivity for Al3+ as compared to other tested metal ions and the ratiometric sensing of Al3+ was determined by plotting the fluorescence intensity ratio at 480 nm and 390 nm versus Al3+ ion concentration. Moreover, test strips based on TCQ were fabricated, which were found to act as a convenient and efficient Al3+ ion detection kit. Furthermore, this system has been used for imaging of Al3+ in living cells.
A new chemosensor L based on the naphthalimide moiety was synthesized and characterized. L exhibited the high selectivity and sensitivity for Al3 + in CH3OH, along with colorimetric and fluorometric dual-signaling responses based on the joint contribution of the ICT and CHEF processes. A1:1 stoichiometry for the L-Al3 + complex was formed with an association constant of 7.6 × 104 M− 1, and the limit of detection for Al3 + was determined as 6.9 μM. In addition, L was successfully applied to the determination of Al3 + in real water samples.
A new simple Schiff-base ligand 2-Hydroxy-1-naphthaldehyde-(2-pyridyl) hydrazone (HL) was synthesized and characterized as a fluorescent probe. In aqueous solution containing 10% ethanol (Hexamethylenetetramine-HCl buffer, pH5.3), HL selectively binds Al3+to form a 1:1 ligand/metal complex, resulting in a color change from colorless to yellow-green and a significant fluorescence enhancement at 454 nm. The addition of EDTA quenches fluorescence of the HL·Al3+ complex, indicating that HL serves as a reversible chemosensor for Al3+. Under the optimum conditions, the dynamic range of the system was found to be linear up to 4.0 × 10-6 M Al3+ ions with a limit of detection of 36.6 nM. The probe is very effective for detection of intracellular Al3+ through fluorescence microscopic imaging.
A simple probe (compound 1) sensing Al3+ or Fe3+ by suppression of photoinduced electron/energy transfer (PET) process and chelation-enhanced fluorescence is described. Compound 1 was prepared from 2-(bromomethyl)benzo[d]thiazole and pyridine-2,6-diamine. Compound 1 showed a much stronger fluorescence response to Al(III) than to Fe(III). The best fluorescence response of 1 to Al3+ was found to be at pH near 7. The results indicated that 1 could be a promising fluorescent turn-on chemosensor for Al3+ or Fe3+. Ratiometric sensing of 1 to Al3+ or Fe3+ was accomplished by plotting the absorbance ratio at 338 to 310 nm versus Al3+ or Fe3+ concentration. The fluorescent turn-on response of 1 to Al3+ or Fe3+ can be attributed to suppression of PET process and chelation-enhanced fluorescence upon binding with Al3+ or Fe3+. The binding mode of 1-Al3+ or 1-Fe3+ was found to be a 1:1 complex based on Job’s plot, electrospray ionization (ESI) mass spectroscopy (MS) data, and density functional theory (DFT) calculation results.
A simple and selective spectrofluorimetric method for the determination of trace levels of aluminium has been developed using Alizarin Complexone (AC). Exhibiting absorption and fluorescence changes in the presence of Al3+ in EtOH–H2O solution at pH 4.6, AC could be used as a colorimetric and fluorescent chemosensor for the detection of Al3+. In the presence of Al3+ ions, AC undergoes fluorescence quenching at 487 nm and shows the formation of a new red-shifted band at 558 nm. A good linear relationship could be obtained between the fluorescence intensity ratio (I487/I558) and the concentration of Al3+ ions in the range of 0.3–4.5 ×10−5 M (R2 = 0.9825). The intensity changes allow a ratiometric detection of Al3+ in acid semi-aqueous solution with the detection limit of 5.2 × 10−7 M. Moreover, the colorimetric and fluorescent response of AC to Al3+ can be conveniently detected by the naked eye, which provides a facile method for visual detection of Al3+. The optimized ground state geometry and corresponding UV-Vis absorption spectral characteristics of AC and AC•Al3+ complex have also been calculated using Density Functional Theory (DFT) with CEP-31G basis sets.
In this study, a turn-on coumarin-based fluorescent probe, 7-hydroxy-6-[(2-hydroxy-naphthalen-1-ylmethylene)-amino]-4-methyl-chroman-2-one (CN), was developed for detecting Al(3+) in aqueous systems. The binding ratio of CN-Al(3+) complexes was determined from the Job plot and ESI-MS data to be 1 : 1. The binding constant (Ka) of Al(3+) binding to CN was calculated to be 9.55 × 10(4) M(-1) from a Benesi-Hildebrand plot and the detection limit was evaluated to be as low as 0.10 μM (LOD = 3σ/slope). CN could be used as an effective fluorescent probe for detecting Al(3+) in living HeLa cells. Moreover, CN could also be applied in the in vivo detection of Al(3+) in zebrafish.
A new ligand 1-(pyridin-2-ylmethyl)-2-(3-(1-(pyridin-2-ylmethyl)benzimidazol-2-yl) propyl) benzimidazole (L) and its Cu(II) complex (1) have been synthesized and characterized spectroscopically and structurally. The Cu(II) ion is coordinated by two nitrogen atoms of benzimidazole groups, two oxygen atoms of the nitrate anions and one oxygen atom of a water molecule forming distorted trigonal bipyramidal geometry. The ligand and its complex have been utilized as a fluorescent sensor for 4-(2-aminoethyl)benzene-1,2-diol. A plot of F0/F − F0 vs 1/Conc (4-(2-aminoethyl)benzene-1,2-diol) at a selected wavelength of 306 nm with (L) that shows a straight line behavior, supports the validity of the assumption of 1:1 complex formation and the association constant of (L) with 4-(2-aminoethyl)benzene-1,2-diol is calculated to be 9868 M− 1. Sensor (L) is found to be selective for 4-(2-aminoethyl)benzene-1,2-diol over aromatic amines, phenols, amino catechol (L-3,4-dihydroxyphenylalanine) and 4,6-ditertiarybutyl benzene-1,2-diol.
A new reactive and highly selective fluorescent chemosensor (1) based on thiazole was synthesized for the quantification of aluminum ions in ethanol. The mechanism of fluorescence was based on the aluminum-promoted hydrolysis of the ester moiety and subsequent complexation.
An efficient Al(3+) receptor, 6-(2-hydroxybenzylideneamino)-2H-chromen-2-one (), has been synthesized by condensing salicylaldehyde with 6-aminocoumarin. The molecular structure of has been determined by a single crystal X-ray analysis. It was established that in the presence of Al(3+), shows 25 fold enhancement of fluorescence intensity which might be attributed to the chelation-enhanced fluorescence (CHEF) process. binds Al(NO3)3 in a 1 : 1 stoichiometry with a binding constant (K) of 7.9 × 10(4) M(-1). Fe(3+) and Mn(2+) quench the emission intensity of the [ + Al(3+)] system to an insignificant extent at a concentration 10 times higher compared to that of Al(3+). is highly efficient in the detection of intracellular Al(3+) under a fluorescence microscope.
A new compound soluble in water derived from vitamin B6 was successfully synthesized and characterized. The complex Al(3+) is a turn-on selective fluorescent probe for histidine in HEPES buffer, with detection and quantification limits of 0.3 μM and 0.6 μM, respectively. The application of the complex Al(3+) in real urine samples is reported.
A novel and simple Schiff base based on 2-pyridine formaldehyde and 4-aminoantipyrine was synthesized and characterized as a fluorescent probe. In the presence of Al(3+), the fluorescent intensity has a dramatic enhancement over other examined metal ions in aqueous solution. The method of Job's plot indicated the formation of 1:1 complex between probe and Al(3+), and the possible binding mode of the system was also proposed. Moreover, other examined metal ions had no effect on the detection of Al(3+).
A new ligand N-(5,6-dihydro-4H-1,3-thiazin-2-yl)indazole (InTz) and its metal complexes [Co(NO3)2(InTz)2] and [Cd(NO3)2(InTz)2] have been prepared and characterized by a variety of physico-chemical techniques. Likewise, the structures have been determined by X-ray diffraction. Metal complexes have C2 symmetry. The environment around the cobalt atom may be described as a distorted octahedral geometry with the metallic atom coordinated to two oxygen atoms from two monodentate nitrate groups, two thiazine nitrogen atoms and two indazole nitrogen atoms. The cadmium complex consists of molecules in which the cadmium atom is eight coordinated, with two bidentate nitrate groups and two bidentate InTz ligands, each of the latter having one thiazine and one indazole nitrogen atom involved in coordination. The geometry around the cadmium atom is adequately described as a distorted dodecahedron.
Efficient sensors for metal ions can be made by assembling an appropriate receptor with a fluorescent fragment. The occurrence of the receptor/cation interaction is signalled through a sharp change of the fluorescence emission. The situation is especially favourable in the case of transition metal ions, which are typically redox active and provide an electron release to the excited fluorophore (or uptake therefrom), causing fluorescence quenching. Thus, the supramolecular design of fluorescent sensors should consider a ligating subunit able to promote the redox activity of the envisaged metal ion. An identical approach can be used for the synthesis of moleculer redox switches, i.e. systems in which the distinctive property of a given subunit (e.g. fluorescence) is controlled by an adjacent control subunit, sensitive to the variation of the redox potential. Couples involving metal centres can be conveniently used to switch on/off the fluorescence of the proximate fluorophore through the variation of the redox potential.
A new fluorescent probe (5-[(4-diethylamino-2-hydroxy-benzylidene)-amino]-1H-pyrimidine-2, 4-dione) (Receptor 1) has been synthesized by the Schiff base condensation of 5-aminouracil with 4-(diethylamino)salicylaldehyde. The receptor 1 exhibits high selectively for Al(3+) in DMSO as well as in aqueous solution even in the presence of biologically relevant cations such as Na(+), K(+), Ca(2+), Mg(2+), Pb(2+) and several transition metal ions. The lowest detection limit for the receptor 1 was found to be 1.62 × 10(-10) M with its linear response towards Al(3+) in the concentration range of 1.75 × 10(-9) to 3.3 × 10(-8) M in DMSO. Receptor 1 is the first ever example where a single molecular probe is able to show imine (C=N) isomerization inhibition along with twisted intramolecular charge transfer (TICT) in combinatorial fashion.
To investigate the effect of aluminum and silica in drinking water on the risk of dementia and Alzheimer's disease, the authors analyzed data from a large prospective cohort (Paquid), including 3,777 subjects aged 65 years and over living at home in 75 civil parishes in Gironde and Dordogne in southwestern France in 1988-1989. The subjects were followed for up for 8 years with an active search for incident cases of dementia or Alzheimer's disease. Mean exposure to aluminum and silica in drinking water was estimated in each area. The sample studied included 2,698 nondemented subjects at baseline, for whom components of drinking water and covariates were available. A total of 253 incident cases of dementia (with 17 exposed to high levels of aluminum), including 182 Alzheimer's disease (with 13 exposed to high aluminum levels), were identified. The relative risk of dementia adjusted for age, gender, educational level, place of residence, and wine consumption was 1.99 (95 percent CI: 1.20, 3.28) for subjects exposed to an aluminum concentration greater than 0.1 mg/liter. This result was confirmed for Alzheimer's disease (adjusted relative risk = 2.14, 95 percent CI: 1.21, 3.80). However, no dose-response relation was found. Inversely, the adjusted relative risk of dementia for subjects exposed to silica (> or = 11.25 mg/liter) was 0.74 (95 percent CI: 0.58, 0.96). These findings support the hypothesis that a high concentration of aluminum in drinking water may be a risk factor for Alzheimer's disease.
Naphthalenic compounds are a rich resource for designers of fluorescent sensing/switching/logic systems. The degree of internal charge transfer (ICT) character in the fluorophore excited states can vary from negligible to substantial. Naphthalene-1,8;4,5-diimides (11–13), 1,8-naphthalimides (16) and 4-chloro-1,8-naphthalimides (15) are of the former type. The latter type is represented by the 4-alkylamino-1,8-naphthalimides (1). Whether ICT-based or not, these serve as the fluorophore in 'fluorophore-spacer-receptor' switching systems where PET holds sway until the receptor is bound to H +. On the other hand, 4-dialkylamino-1,8-naphthalimides (3–4) show modest H +-induced fluorescence switching unless the 4-dialkylamino group is a part of a small ring (5). Electrostatic destabilization of a non-emissive twisted internal charge transfer (ICT) excited state is the origin of this behaviour. An evolution to the non-emissive twisted ICT excited state is responsible for the weak emission of the model compound 6 (and related structures 7 and 8) across the pH range. Twisted ICT excited states are also implicated in the switch 9 and its model compound 10, which are based on the 6-dialkylamino-3H-benzimidazo[2,1-a]-benz[d,e]isoquinolin-3-one fluorophore.
Long-range radiationless energy transfer from the triplet states of aromatic hydrocarbons to the singlet states of fluorescent dyes (10—3M) is used to measure the efficiencies of energy dissipation (&phgr;F, &phgr;IS, &phgr;P) for triphenylene, phenanthrene, p-terphenyl, chrysene, naphthalene, and/or their deuterated counterparts. Rhodamine B, rhodamine 6G, acriflavin, and fluorescein were found to be suitable acceptors. By measuring phosphorescence efficiencies directly, reliable estimates of T↠S radiative rate constants can be obtained.
To design a new metal sensory system, calix[4]arene bearing pyrene (as a fluorophore) and nitrobenzene (as a quencher) near the ionophoric cavity is synthesized: in response to the metal-binding event the fluorescence intensity is dramatically enhanced.
The number and relative energies of nitrate combination frequencies in the 1700–1800 cm−1 region of the infrared spectrum may be used as an aid to distinguish the various coordination modes of the nitrate group. The data also provide an excellent probe for the strength of the metal–nitrate interaction.
Inorganic chemistry plays a central role in the workings of the human body, in sickness and in health. The elements of Groups 3 and 13 of the Periodic Table, including the lanthanides and actinides, illustrate this theme in respect of essential elements and toxicity, and of the varied applications of inorganic species in the diagnosis of disease and subsequent therapy.
Coordination of the neurotransmitter dopamine (DA) and the metal-binding component of neuromelanin 5,6-dihydroxyindole (DHI) with ferric iron has been studied in aqueous solution in the presence of ancillary ligands containing amine nitrogen and carboxylate oxygen donor sites. With nitrilotriacetic acid (nta) and ethylenediamine diacetic acid (edda) coligands, coordination of the catecholate ligands DA and DHI is observed to be complete at physiological pH. The resulting complexes of DA have the characteristic two-component electronic spectrum observed characteristically for L4Fe(Cat) complexes. The spectrum obtained with DHI consists of a single broad absorption in the visible region. Both DA and DHI are able to coordinate with Fe3+ in the presence of edta, displacing carboxylate oxygen donors at pH values just above physiological pH. These results demonstrate the strong affinity of DA and DHI for Fe3+, pointing to in vivo complex formation in neuronal mixtures at physiological pH.
A series of benzofused heterocycles was examined to replace the metabolically unstable benzyl alcohol P2/P2′ groups of DMP 323 (1). Extremely potent inhibitors of HIV protease (Ki < 0.01 nM) and excellent antiviral activity (IC90 = 8 nM) were found. An X-ray crystal structure of benzimidazolone 5a bound to HIV protease showed H-bonds to Asp30 and a bridging water molecule to Gly48.
A coumarin Shiff-base derivative, 7-hydroxy-3-(2-hydroxybenzylideneamino)-2H-chromen-2-one (CSB), was obtained by simple two-step organic synthesis from cheap and commercially available starting materials. CSB has nearly no fluorescence in CH3CN solution. However, in the presence of Zn(II) ion, a “turn-on” fluorescence was observed. Other metal ions in CSB solution show very little emission or do not show any emission. CSB can also be used as a colorimetric chemosensor for Zn(II), which is easily observed from colorless to yellow by the naked eye. The absorption maximum of CSB shows a large red shift from 374 to 452nm upon addition of Zn(II).
An examination of the infra-red spectra of the TBP solvates M(NO3)3·3TBP, M(NO3)4·2TBP and MO2(NO3)2·2TBP has been made, and compared with the infra-red spectra of the corresponding hydrates. It is observed that a considerable decrease in symmetry of the nitrate group has occurred in going from the hydrates to the TBP solvates.
From the Publisher:This volume presents the results of approximately 15 years of work from researchers around the world on the use of fuzzy set theory to represent imprecision in databases. The maturity of the research in the discipline and the recent developments in commercial/industrial fuzzy databases provided an opportunity to produce this survey. Fuzzy Databases: Principles and Applications is self-contained providing background material on fuzzy sets and database theory. It is comprehensive covering all of the major approaches and models of fuzzy databases that have been developed including coverage of commercial/industrial systems and applications. Background and introductory material are provided in the first two chapters. The major approaches in fuzzy databases comprise the second part of the volume. This includes the use of similarity and proximity measures as the fuzzy techniques used to extend the relational data modeling and the use of possibility theory approaches in the relational model. Coverage includes extensions to the data model, querying approaches, functional dependencies and other topics including implementation issues, information measures, database security, alternative fuzzy data models, the IFO model, and the network data models. A number of object-oriented extensions are also discussed. The use of fuzzy data modeling in geographical information systems (GIS) and use of rough sets in rough and fuzzy rough relational data models are presented. Major emphasis has been given to applications and commercialization of fuzzy databases. Several specific industrial/commercial products and applications are described. These include approaches to developing fuzzy front-end systems and special-purpose systems incorporating fuzziness.
This review describes some developments on the coordination chemistry of chemosensors based on polyamines and related compounds, with particular emphasis on their photochemical properties. The reported systems are essentially based on the work developed by the authors since 2000. Some inter- esting properties beyond sensing molecules and/or atoms by fluorescence or colorimetry can arise from these systems. In particular pH and light can be used as external stimuli to carry out functions, like molec- ular movements, jumping of metal ions inside-outside polyaza cavities, photocatalytic effects, energy and electron transfer.
The preparations of compounds of the types Ni(en)2(NO3)2 and [Ni(Cn)2NO3]ClO4 (en = ethylenediamine) and analogs with other diamines and with some cyclic tetramines are described. The infrared spectra of the nitrate ion for the two types of compound can be distinguished from each other, and from ionic nitrate, and are taken to indicate monodentate and bidentate nitrato groups, respectively. For Ni(dien)( NO3)2 (dien = diethylenetriamine) nitrato groups of both types are present while for one of the cyclic tetraminenickel(II) dinitrates, bidentate and ionic nitrates are present. The reflectance spectra of the dinitrato compounds are indicative of trans structures, while those of the mononitrato compounds resemble those of the known cis compounds [Ni2(Cn)4Cl2]Cl2 and Ni(tren)(NCS)2 (t.en = 2,2′,2″-triaminotriethylamine). The magnetic susceptibilities, all μeff ∼ 3.1 B.M., are reported.
A chemosensor 1, based on the Schiff base, is easily prepared by reacting tryptophan and 2-hydroxy-1-naphthaldehyde in methanol. The optical properties of 1 are investigated in buffered aqueous solution, which displays specific recognition to Zn2+, and especially avoids the interference of Cd2+ when 1 is tested against a range of physiological and environmentally relevant metal ions. Such a novel fluorescent probe can also be used to detect Zn2+ in live cells.
The stoichiometry and stability constant of metal complexes with 4-(3-methoxy-salicylideneamino)-5-hydroxynaphthalene-2,7-disulfonic
acid monosodium salt (H2L) and 4-(3-methoxysalicylideneamino)-5-hydroxy-6-(2,5-dichlorophenylazo)-2,7-naphthalene disulfonic acid monosodium salt
(H2L1) were studied by potentiometric titration. The stability constants of H2L and H2L1 Schiff bases have been investigated by potentiometric titration and u.v.–vis spectroscopy in aqueous media. The dissociation
constants of the ligand and the stability constants of the metal complexes were calculated pH-metrically at 25°C and 0.1m KCl ionic strength. The dissociation constants for H2L were obtained as 3.007, 7.620 and 9.564 and for H2L1, 4.000, 6.525, 9.473 and 10.423, respectively. The complexes were found to have the formulae [M(L)2] for M=Co(II), Ni(II), Zn(II) and Cu(II). The stability of the complexes follows the sequence: Zn(II) < Co(II) < Cu(II)
< Ni(II). The high stability of H2L1 towards Cu(II) and Ni(II) over the other ions is remarkable, in particular over Cu(II), and may be of technological interest.
Concentration distribution diagram of various species formed in solution was evaluated for ligands and complexes. The formation
of the hydrogen bonds may cause this increased stability of ligands. The pH-metric data were used to find the stoichiometry,
deprotonation and stability constants via the SUPERQUAD computer program.
The synthesis of a new oxaaza macrocyclic ligand, L, derived from O-1,O-7-bis(2-formylphenyl)-1,4,7-trioxaheptane and tren containing an amine terminal pendant arm, and its metal complexation with alkaline earth (M = Ca2+, Sr2+, Ba2+), transition (M = Co2+, Ni2+, Cu2+, Zn2+, Cd2+), post-transition (M = Pb2+), and Y3+ and lanthanide (M = La3+, Er3+) metal ions are reported. Crystal structures of [H2L](ClO4)(2).3H(2)O, [PbL](ClO4)(2), and [ZnLCl](ClO4).H2O are also reported. In the [PbL] complex, the metal ion is located inside the macrocyclic cavity coordinated by all N4O3 donor atoms while, in the [ZnLCI] complex, the metal ion is encapsulated only by the nitrogen atoms present in the ligand. pi-pi interactions in the [H2L](ClO4)(2).3H(2)O and [PbL](ClO4)(2) structures are observed. Protonation and Zn2+, Cd2+, and Cu2+ complexation were studied by means of potentiometric, UV-vis, and fluorescent emission measurements. The 10-fold fluorescence emission increase observed in the pH range 7-9 in the presence of Zn2+ leads to L as a good sensor for this biological metal in water solution.
The main classes of fluorescent molecular sensors for cation recognition are presented: they differ by the nature of the cation-controlled photoinduced processes: photoinduced electron transfer, photoinduced charge transfer, excimer formation or disappearance. In each class, distinction is made according to the structure of the complexing moiety: chelators, podands, coronands (crown ethers), cryptands, calixarenes. The most representative examples are presented in each subclass with special attention given to selectivity.
A new family of compounds able to promote host–guest interactions with specific molecules (e.g., cyanuric and parabanic acids) and to coordinate metal ions, namely Zn(II) and Cu(II), has been synthesized and fully characterized. The new probes derive from the attachment of two methylaminopyrene units to the carbonyl precursor 2,6-bis(2-formylphenoxymethyl)pyridine.Its signalling properties result from the fluorescence emission properties, which reveal the existence of intramolecular excimer formation. The compounds have showed to be highly sensitive to the solvent and hydrogen ion concentration of the medium. Depending on these, different monomer-to-excimer fluorescence ratio is displayed by the two probes. The compound with a single pyrene unit revealed absence of excimer formation and was used as model compound. The overall results are discussed on the basis of the studied probes as potentially revealing molecular movements, off–on–off fluorescent photoinduced electron transfer (PET), host–guest interactions with specific compounds and of sensing metal ions.
Three new compounds bearing furyl, aryl, or thienyl moieties linked to an imidazo-crown ether system (1, 2, and 3) were synthesized and fully characterized by elemental analysis, infrared, UV-vis absorption, and emission spectroscopy, X-ray crystal diffraction, and MALDI-TOF-MS spectrometry. The interaction toward metal ions (Ca(2+), Cu(2+), Ni(2+), and Hg(2+)) and F(-) has been explored in solution by absorption and fluorescence spectroscopy. Mononuclear and binuclear metal complexes using Cu(2+) or Hg(2+) as metal centers have been synthesized and characterized. Compounds 2 and 3 show a noticeable enhancement of the fluorescence intensity in the presence of Ca(2+) and Cu(2+) ions. Moreover compound 3 presents a dual sensory detection way by modification of the fluorimetric and colorimetric properties in the presence of Cu(2+) or Hg(2+). EPR studies in frozen solution and in microcrystalline state of the dinuclear Cu(II)3 complex revealed the presence of an unique Cu(2+) type.
This critical review describes some developments on the chemistry of fluorescent and colorimetric molecular probes or chemosensors, based on polyamines and associated compounds having oxygen and/or sulfur as donor atoms. The reported systems are essentially based on some selected published work in this field in the last five years, and in the work developed by the authors from 2000 onwards. Some interesting properties beyond sensing molecules, ions or/and cations by fluorescence, colorimetry as well as by MALDI-TOF MS spectrometry can arise from these systems. A short brief on different examples activated by PET (photoinduced electron transfer), ICT (internal charge transfer) and EET (electronic energy transfer) phenomena will be provided. Finally the introduction of bio-inspired compounds derived from emissive amino acid or short peptide systems and nanoparticle devices to detect metal ions will be reviewed (202 references).
A new suite of 10 programs concerned with equilibrium constants and solution equilibria is described. The suite includes data preparation programs, pretreatment programs, equilibrium constant refinement and post-run analysis. Data preparation is facilitated by a customized data editor. The pretreatment programs include manual trial and error data fitting, speciation diagrams, end-point determination, absorbance error determination, spectral baseline corrections, factor analysis and determination of molar absorbance spectra. Equilibrium constants can be determined from potentiometric data and/or spectrophotometric data. A new data structure is also described in which information on the model and on experimental measurements are kept in separate files.
In view of the effects of chronic manganese poisoning on cerebral dopamine, appropriate measurements were initiated which, for the moment, have shown the following: Adult mice consuming diets containing massive amounts of manganese developed statistically significant elevations of cerebral dopamine. The experiments have not yet been carried on long enough to determine whether this increase is followed by the decrease characteristic of chronic manganese poisoning. The normally occurring postnatal increase in cerebral manganese was accompanied by an increase in cerebral dopamine, the extent of which seems thus far susceptible to acceleration or deceleration by manipulating the manganese intake of lactating mothers. The functional consequences of interfering with the dopaminergic apparatus by dietary means remain to be defined.
Manganese is an essential trace element for human metabolism, but at higher concentrations it is a potent neurotoxin that presents clinical symptoms similar to those of Parkinson's disease. Since the toxicity of manganese may be related to its ability to accelerate the oxidation of catecholamines, we have examined the effect of aqueous Mn2+ on the formation and decay of the dopamine semiquinone radical ion. ESR spectroscopy was used to measure the kinetics of the disappearance of the semiquinone radical spectrum and the simultaneous appearance of the six-line spectrum of aqueous Mn2+ in Tris buffer. From the proposed mechanism for the autoxidation of dopamine to the quinone, the rate expression for semiquinone radical disappearance has the functional form -rate = k'[D(OH)2][Mn2+] at constant pH and molecular oxygen concentration, while the pH dependence is given by -log(rate) = log(constant) + (2 x pH), in agreement with the experimental results. The autoxidation of dopamine is catalyzed by manganese through the formation of a highly reactive complex. The effect of manganese is due to the fact that it can participate in a redox cycle which involves intramolecular electron transfer between manganese and the dopamine ligand.
The mechanisms that lead to degeneration of melanized dopaminergic neurons in the brain stem, and particularly in the substantia nigra (SN) in patients with Parkinson's disease (PD) are still unknown. Demonstration of increased iron (Fe) in SN of PD brain has suggested that Fe-melanin interaction may contribute to oxidative neuronal damage. Energy dispersive X-ray electron microscopic analysis of the cellular distribution of trace elements revealed significant Fe peaks, similar to those of a synthetic melanin-Fe3+ complex, in intraneuronal electron-dense neuromelanin granules of the SN zona compacta, with highest levels in a case of PD and Alzheimer's disease (AD). No Fe increase was found in Lewy bodies or in SN neurons of control specimens. The relevance of the in vitro chemical reactions of dopamine (DA), 5-hydroxydopamine (5-OHDA), and 6-hydroxydopamine (6-OHDA) with Fe3+ and with dioxygens for the pathogenesis of PD was investigated. An initiating mechanism for a chain reaction is suggested by which excessive Fe3+ arises. Melanin can act as an efficient antioxidant and in the presence of Fe can promote the formation of cytotoxic hydroxyl free radicals (.OH) which, in turn, initiate lipid peroxidation and consequent cell damage. While in vitro studies indicate that DA oxidation leading to melanin formation is independent of metal ions, saturation of melanin with large amounts of Fe3+ causes a significant generation of free .OH radicals. The relevance of the events induced by the melanin-Fe complex for the degeneration of dopaminergic neurons in PD is discussed. Free redox-active metal ions in the cytoplasm may cause site-specific peroxidation and thus exert neurotoxic effects. Excessive hydrogen peroxide in post mortem frontal cortex of a patient with PD and AD could be shown by confocal fluorescence microscopy, and this observation may be a direct indicator of oxidative stress.
Real-time and real-space analysis of heavy and transition metal ions employing fluorescent sensor molecules has received much attention over the past few years. Since many of these cations possess intrinsic properties that usually quench the fluorescence of organic dye molecules, a lot of research has lately been devoted to designing fluorescent probes that show complexation-induced fluorescence enhancement. Such an analytical reaction would be highly desirable in terms of increased sensitivity and selectivity. However, in this particular field of sensor research, the photophysical and photochemical mechanisms involved as well as the chemical constitutions of the sensor molecules employed are rather diverse and up to now, very few attempts have been made to establish some general concepts for rational probe design. By analyzing various systems published by other researchers as well as own work, this contribution aims at an elucidation of some of the underlying principles of heavy and transition metal ion-enhanced emission.
Most synthetic sensors are designed with covalent attachment between a receptor and a reporter moiety. In this report, we describe the current progress of our use of noncovalently attached indicators to signal binding of analytes. With these systems, analyte binding leads to indicator displacement from the binding cavity, which in turn yields an optical signal modulation. We include previous examples, the strategies involved in our development, and the advantages as well as disadvantages of this method. Finally, our latest research in this field is briefly presented.
Conjugated polymers (CPs)-based sensors are reviewed to illustrate the many configurations by which a CP can be harnessed to give a transducible response to analytes. The review emphasizes that CPs represent one of the most useful chemical platforms for the design of chemical sensors.
The reaction of [Cu(dien)NO(3)]NO(3) with 2-amino-5-methylthiazole (2A5MT), 2-amino-2-thiazoline (2A-2Tzn), imidazole (im), N,N'-thiocarbonyldiimidazole (Tcdim), 2-aminothiazole (2AT) and 2-ethylimidazole (2Etim), gave a new series of mixed-ligand compounds of the general formula [Cu(dien)(B)NO(3))]NO(3); (dien, diethylenetriamine; B, 2A5MT, 2A-2Tzn, im, Tcdim, 2AT and 2Etim). The complexes have been characterised by elemental analysis, molar conductivity and magnetic measurements, as well as by electronic and IR spectral studies. According to the above measurements the possible structure of the compounds is the square pyramidal in the solid state and the square planar in aqueous solution. We tested all complexes for antiproliferative (cytostatic and cytotoxic) activity against a panel of cell lines (HeLa, L929, HT-29 and T47D). All [(dien)Cu(B)NO(3))](NO(3)) complexes had an activity against colon cancer cells (HT-29), inducing G2/M cell cycle arrest, an effect that for most of the complexes could be attributed to p34cdc2 inhibition by tyrosine-phosphorylation and/or to induction of (cyclin-dependent kinase inhibitor) p21(WAF1). Other cell lines were resistant to the majority of the complexes, except [Cu(dien)(2A5MT)NO(3))](NO(3)), that had showed the highest anti-proliferative activity against HT-29 cells also. The predilection for colon cancer cells and the relatively low toxicity against normal (L929) cells justify further investigation of this group of compounds.
One of the key interests in the recent development of fluorescent molecular sensors and switches is the realization of systems that show strong signal changes as a response to the chemical trigger. Aiming at rational probe design, this article compiles and compares different promising strategies to extract those supramolecular and photophysical features that allow the construction of molecular devices suitable for efficient signaling. The examples comprise fluorescence 'OFF'-'ON' as well as 'ON'-'OFF' operative systems and the mechanisms, properties, and limitations of the different design concepts are discussed.
Chronic exposure to manganese (Mn) positively correlates with the occurrence of Parkinsonism but little is known about mechanisms of its neurotoxicity. In the present study, we determined the clearance of Mn from rat substantia nigra after its nigral injection and correlated it with the establishment of apomorphine-induced rotational behaviour and loss of striatal tyrosine hydroxylase (TH) immunoreactivity. Our results suggest that Mn is slowly cleared from the substantia nigra, following a first-order kinetics with a t(1/2) of 3 days. Appearance of apomorphine-induced rotational behaviour and loss of TH immunoreactivity within the striatum follows metal clearance were both detected 24 hours after intra-nigral Mn microinjection and maximal 72 hours after injection. The present data suggest that the cellular mechanisms induced by Mn and leading to dopaminergic cell death, occurred shortly after its injection and that the metal concentration needs to reach a threshold value to induce neurotoxic effects. This would indicate that nigral damages are a direct consequence of Mn accumulation.
Boron dipyrromethene (BODIPY) is known to have a high quantum yield (phi) of fluorescence in aqueous solution but has not been utilized much for biological applications, compared to fluorescein. We developed 8-(3,4-diaminophenyl)-2,6-bis(2-carboxyethyl)-4,4-difluoro-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (DAMBO-P(H)), based on the BODIPY chromophore, as a highly sensitive fluorescence probe for nitric oxide (NO). DAMBO-P(H) had a low phi value of 0.002, whereas its triazole derivative (DAMBO-P(H)-T), the product of the reaction of DAMBO-P(H) with NO, fluoresced strongly (phi = 0.74). The change of the fluorescence intensity was found to be controlled by an intramolecular photoinduced electron transfer (PeT) mechanism. The strategy for development of DAMBO-P(H) was as follows: (1) in order to design a highly sensitive probe of NO, the reactivity of o-phenylenediamine derivatives as NO-reactive moieties was examined using 4,5-diaminofluorescein (DAF-2, a widely used NO fluorescence probe), (2) in order to avoid pH-dependency of the fluorescence intensity, the PeT process was controlled by modulating the spectroscopic and electrochemical properties of BODIPY chromophores according to the Rehm-Weller equation based on measurement of excitation energies of chromophores, ground-state reduction potentials of PeT acceptors (BODIPYs), and calculation of the HOMO energy level of the PeT donor (o-phenylenediamine moiety) at the B3LYP/6-31G level, (3) in order to avoid quenching of fluorescence by stacking of the probes and to obtain probes suitable for biological applications, hydrophilic functional groups were introduced. This strategy should be applicable for the rational design of other novel and potentially useful bioimaging fluorescence probes.
Several triazenoindazoles and triazenopyrazoles were prepared transforming the appropriate aminoindazoles and aminopyrazoles in the corresponding diazonium salts which were reacted with dimethylamine, diethylamine and pyrrolidine. All the triazenes were tested for their antiproliferative activity against K562, HL60, L1210 and MCF7 cell lines. The biological data showed that the benzocondensation plays a positive role on the antiproliferative activity. The (1)H-NMR spectra showed that the rotational barrier around the N(2)-N(3) bond in the triazene group can be influenced both by the position of this group in the indazole nucleus and by the substitution pattern in the benzene moiety.
For Abstract see ChemInform Abstract in Full Text.
Three new fluorescent devices for protons and metal ions have been synthesized and characterized, and their photophysical properties have been explored; these are the macrocycles 7-(9-anthracenylmethyl)-3,11-dithia-7,17-diazabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L1) and 7-(10-methyl-9-anthracenylmethyl)-3,11-dithia-7,17-diazabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L2) and the bis macrocycle 7,7'-[9,10-anthracenediylbis(methylene)]bis-3,11-dithia-7,17-diazabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L3). All these systems have a pyridil-thioether-containing macrocycles as a binding site and an anthracene moiety as a signaling agent. The coordination properties of these ligands toward Cu(II), Co(II), Ni(II), Zn(II), and Pd(II) have been studied in solution and in the solid state. The addition of these metal ions to dichloromethane solutions of L1, L2, and L3 produce strong changes in the absorption and emission spectra of these ligands. The stoichiometry of the species, formed at 298 K, have been determined from absorption and fluorescence titrations. The Co(II) and Cu(II) complexes of L1 have been studied by EPR spectroscopy. This last complex and its free ligand have also been characterized by X-ray crystallography.
[reaction: see text] A new sensing mechanism based on C=N isomerization, which shows a very significant fluorescence enhancement to the metal cations in a simple and efficient way, is demonstrated. A coumarin derivative (L) containing a C=N group was designed as an example for illustration. The free ligand L is almost nonfluorescent due to the isomerization of C=N double bond in the excited state. However, the solution of ligand shows about a 200-fold increase of fluorescence quantum yield (about 30%) upon addition of Zn(ClO4)2.
The unexpected effects of Ca(2+) on the free-radical chain reactions of dopamine, norepinephrine, isoproterenol, and pyrocatechol oxidation are studied using oxygen consumption measurements, EPR-spectroscopy, UV/VIS spectrophotometry, and by potentiometric titration. It is found that the formation of Ca(2+)-catecholate complexes is accompanied by an increase in the dissociation constants (K(ai) ) of their phenolic hydroxyls. At pH>pK(ai) and in the presence of alkaline-earth metal cations, the rate of catecholate oxidation increases (Ca(2+), Mg(2+)> Sr(2+), Ba(2+)), whereas on addition of Zn ions the rate decreases. The effects of Group II metal cations on catecholate autoxidation are concomitant with a transient increase of the EPR signal for metal-semiquinonate complexes. Therefore, the effects of Ca(2+) and other alkaline-earth metal cations on catecholate autoxidation can be defined as 1) additional deprotonation of catechol OH-groups involved in the formation of M(2+)-catecholate complexes, the latter exceeding catechols in the susceptibility to dioxygen-induced oxidation and 2) formation of relatively stable free-radical intermediates responsible for chain propagation.
Compound 1, a new fluorescent chemosensor signaling via significantly enhanced fluorescence when bound with cation analytes, was synthesized and characterized. This fluorescent chemosensor exhibits its selectivity to Cd2+ among a series of cations in HEPES buffer solution. Its in vitro sensitivity to Cd2+ was demonstrated in the HK-2 cell line with use of confocal microscopy. The mechanistic selectivity and sensitivity of compound 1 to Cd2+ was discussed on the basis of fluorescence, 1H NMR, and mass spectroscopic results.
Two different coumarin derivatives have been connected via an imine linkage to obtain a new fluorescence signaling system. This compound itself does not show any emission due to rapid isomerization around the C[double bond]N bond. However, in the presence of a Mg(II) ion, this isomerization is stopped because of bonding to the metal ion resulting in high-intensity (approximately 550-fold) emission. Other metal ions like Li(I), Ca(II), and Zn(II) show very little emission, while biologically relevant transition-metal ions do not show any emission. In this way, the Mg(II) ion can be detected in the presence of these ions.
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