Cation Binding Properties Research Articles

A coumarin based Schiff base probe for selective fluorescence detection of Al3 + and its application in live cell imaging

A new coumarin based Schiff base compound, CSB-1 has been synthesized to detect metal ion based on the chelation enhanced fluorescence (CHEF). The cation binding properties of CSB-1 was thoroughly examined in UV–vis and fluorescence spectroscopy. In fluorescence spectroscopy the compound showed high selectivity toward Al3+ ion and the Al3+ can be quantified in mixed aqueous buffer solution (MeOH: 0.01M HEPES Buffer; 9:1; v/v) at pH7.4 as well as in BSA media. The fluorescence intensity of CSB-1 was enhanced by ~24 fold after addition of only five equivalents of Al3+. The fluorescence titration of CSB-1 with Al3+ in mixed aqueous buffer afforded a binding constant, Ka=(1.06±0.2)×104M−1. The colour change from light yellow to colourless and the appearance of blue fluorescence, which can be observed by the naked eye, provides a real-time method for Al3+ sensing. Further the live cell imaging study indicated that the detection of intracellular Al3+ ions are also readily possible in living cell.

Dual Sensing By Simple Heteroditopic Salt Receptors Containing an Anthraquinone Unit

We synthesized simple ion pair receptors consisting of a crown ether cation binding site and an anthraquinone supported thiourea anion binding domain and studied their anion, cation and salt binding properties using spectroscopic, spectrophotometric and electrochemical measurements in acetonitrille solution. Apart from carboxylate anions, which cause deprotonation all the anions tested were found to associate with receptors more strongly in the presence of sodium cations, whereas in the presence of potassium or ammonium cation the anion binding strength was greatly diminished. A homotopic anion receptor lacking a crown ether unit, was unable to bind sodium salt more strongly than tetrabutylammonium salts. Solution and solid state X-ray measurements revealed that strong sodium coordination with the cation binding domain is responsible for the salt binding enhancement. Electrochemical measurements showed that the addition of anions to the ditopic ion pair receptors pretreated with sodium cations resulted in greater changes in reduction potentials compared to the addition of anions to receptors in the absence of Na+. Karbarz, M.; Romanski, J. Inorg. Chem. 2016, 55, 3616-3623. Figure 1

Anthracene excimer-based “turn on” fluorescent sensor for Cr3+ and Fe3+ ions: Its application to living cells

A novel anthracene based fluorescent probe containing benzothiazole group (BFA) was designed and synthesized. The cation binding properties of BFA were studied in the presence of various cations. Both UV–vis and fluorescence spectroscopic studies indicated that BFA was highly sensitive and selective toward trivalent cations (Cr3+ and Fe3+), while there was no response to monovalent, divalent cations and also Al3+ ion. The interaction of BFA with Cr3+ and Fe3+ caused a significant enhancement in emission intensity due to the combination of a unique anthracenyl static excimer formation, the restricted C=N isomerization and the suppression of highly efficient photoinduced electron transfer (PET) process. The detection limits of BFA for Cr3+ and Fe3+ were 0.46 and 0.45µM, which presented a pronounced sensitivity toward Cr3+ and Fe3+, respectively. Also, possible utilization of BFA as bio-imaging fluorescent probe to detect Cr3+ and Fe3+ in human prostate cancer cell lines was observed by confocal fluorescence microscopy.

A highly selective fluorescent sensor based on calix[4]arene appended benzothiazole units for Cu2+, S2− and HSO4− ions in aqueous solution

A novel calix[4]arene receptor containing benzothiazole units in 1,3-alternate conformation (L) was synthesized and characterized by 1H, 13C, APT, COSY NMR, FTIR, elemental analysis, and UV–vis spectral data. The cation and anion binding properties of L were investigated in the presence of various cations and anions. L showed “on–off” type fluorescence response towards Cu2+ with high selectivity in aqueous solution (CH3CN/H2O, 4/1, v/v). Once binding with Cu2+, L-Cu2+ complex displayed high selectivity for sulfide. Among the various anions, only sulfide anion induced the revival of fluorescence of L, resulting in “off–on” type sensing of sulfide anion. Furthermore, L served exclusive response towards HSO4− ion via hydrolysis process with 10-fold fluorescence enhancement at 542nm.

Synthesis and properties of new N,N′-phenyltetrazole podand

AbstractThe synthesis of a new chromogenic N,N′-phenyltetrazole receptor is reported here. The cationbinding properties of this receptor in solution were investigated by naked-eye colour change, electrochemical methods and UV-Vis spectroscopy in various solvents (CH

Calcium intolerance of fen mosses: Physiological evidence, effects of nutrient availability and successional drivers

Species composition of peatlands is determined by the dominance of either Sphagnum or non-sphagnaceous (brown) mosses. Sphagnum species are more or less intolerant to alkaline waters rich in calcium bicarbonate, but the physiological background of this intolerance is poorly understood. Recently, sphagna have been widening their realized niches, expanding to alkaline brown-moss fens and altering their functioning. One possible reason is increased nutrient availability, but existing evidence is equivocal. We approached this problem by a series of laboratory experiments with 15 fen moss species cultivated submerged in solutions corresponding to natural poor- to rich-fen waters. We tested basic ecophysiological mechanisms of calcium tolerance (ion compartmentalization, cell-wall cation-binding properties, phosphorus and iron uptake), the breadth of fundamental pH/calcium niches for protonemata and adult plants, interspecific competition, and relationships between nutrient availability and pH/calcium tolerance. Our results suggest that calcium toxicity in calcifugous bryophytes is caused by insufficient control over the balance of intracellular Ca2+ uptake/efflux. Cell-wall cation-exchange sites of living mosses remain unsaturated with Ca2+ even in calcareous solutions, contradicting the proposed inhibitory effect of Ca2+-oversaturation on cell-wall expansion and monovalent cation uptake. Growth and biomass accumulation of brown mosses was highest in alkaline fen waters, but they could also survive and germinate in poor-fen waters. Calcium-tolerant sphagna survived along the entire poor–rich gradient, but their growth was inhibited by calcium bicarbonate. The three most obviously expanding sphagna produced protonemata even under calcareous conditions. Flowing but not stagnant alkaline fen waters were toxic for calcifugous sphagna, the strongest competitors in poor-fen waters. Increased potassium availability facilitated the survival of calcifugous sphagna in alkaline fens, corroborating field observations that potassium facilitates sphagnum expansion. Surprisingly, the rare and declining moss Hamatocaulis vernicosus was supported by nitrogen and phosphorus more than its competitors. Our comparison of fundamental and realized niches suggests that the dominance of particular moss functional groups in fens is governed by a competitive hierarchy altered by different calcium levels. The expansion of calcium-tolerant sphagna into brown-moss fens therefore requires perturbation that weakens competition. Additionally, expansion of calcifugous sphagna to alkaline environments may be stimulated by potassium availability.

Coumarin phthalonitriles: Synthesis and cation binding properties

Coumarin possess a number of biological activities like anticoagulant, antimicrobial, anti-inflammatory, analgesic,antioxidant, anticancer, antiviral, antimalarial etc. Coumarin belongs to a group as benzopyrones, which consists of a benzene ring joined to a pyrone nucleus. In this work, new coumarin phtalonitriles derivatives were synthesized and characterized via spectroscopic techniques IR, 1H NMR, 13C NMR, mass spectra and elemental analysis.The synthesis of coumarin phtalonitriles resulting from a nucleophilic aromatic substitution reaction between 4-nitrophtalonitrile and coumarins derivatives. The complexing properties of the coumarin derivatives toward alkali metal, alkaline earth metal, some transition metals and some heavy metal cations have been investigated in acetonitrile by means of UV spectrophotometry absorption and conductivity methods. Thus, the stoichiometry of the complexes formed and their stability constants were determined

FRET study of G-quadruplex forming fluorescent oligonucleotide probes at the lipid monolayer interface

Spectral properties and G-quadruplex folding ability of fluorescent oligonucleotide probes at the cationic dioctadecyldimethylammonium bromide (DODAB) monolayer interface are reported. Two oligonucleotides, a 19-mer bearing thrombin binding aptamer sequence and a 21-mer with human telomeric sequence, were end-labeled with fluorescent groups (FAM and TAMRA) to give FRET probes F19T and F21T, respectively. The probes exhibited abilities to fold into a quadruplex structure and to bind metal cations (Na+ and K+). Fluorescence spectra of G-quadruplex FRET probes at the monolayer interface are reported for the first time. Investigations included film balance measurements (π-A isotherms) and fluorescence spectra recording using a fiber optic accessory interfaced with a spectrofluorimeter. The effect of the presence of DODAB monolayer, metal cations and the surface pressure of monolayer on spectral behavior of FRET probes were examined. Adsorption of probe at the cationic monolayer interface resulted in the FRET signal enhancement even in the absence of metal cations. Variation in the monolayer surface pressure exerted rather modest effect on the spectral properties of probes. The fluorescence energy transfer efficiency of monolayer adsorbed probes increased significantly in the presence of sodium or potassium ion in subphase, which indicated that the probes retained their cation binding properties when adsorbed at the monolayer interface.

Tree species affect cation exchange capacity (CEC) and cation binding properties of organic matter in acid forest soils

Soil organic matter (SOM) in forest soil is of major importance for cation binding and acid buffering, but its characteristics may differ among soils under different tree species. We investigated acidity, cation exchange properties and Al bonding to SOM in stands of Scots pine, pedunculate oak, Norway spruce, European beech and common hornbeam in southern Poland. The content of total carbon (Ct) was by far the major contributor to total cation exchange capacity (CECt) even in loamy soils and a strong relationship between Ct and CECt was found. The slope of the regression of CECt to Ct increased in the order hornbeam≈oak<beech<spruce≈pine, suggesting that the number of negatively charged sites of SOM at any value in the acid pH range was smallest for hornbeam and oak, and largest for spruce and pine soils. This was supported by the apparent dissociation constant (pKapp) values of SOM, which were largest in soils under oak. The maximum values of Al saturation were similar between the stands. However, maximum Al bonding to SOM occurred at higher pH values in soils under pine and spruce than under oak. Therefore, at any value in the acid pH range, the SOM in pine soil has less Al complexed and more adsorbed H+ than SOM from oak soils. Such differences in Al and H bonding are not only important for pH buffering and metal solubility controls, but also for stabilization of SOM via saturation of functional groups by Al and H.

Coumarin derivatives: Synthesis and cation binding properties

Coumarin derivatives were easily prepared starting from 7-hydroxy 4-methyl-2H-chromen-2-one with 40% formaldehyde and suitable secondary amines in 95% ethanol in rather good yield. The structures of all compounds were confirmed via spectroscopic techniques IR, 1H NMR, 13C NMR, mass spectra and elemental analysis. The complexing properties of the coumarin derivatives toward alkali metal, alkaline earth metal, some transition metals and some heavy metal cations have been investigated in methanol by means of UV spectrophotometry absorption and conductivity methods. Thus, the stoichiometry of the complexes formed and their stability constants were determined.

Effect of Cholesterol Anchoring Group on the Properties of G-Quadruplex-Based FRET Probes for Potassium Ion

In this study we report on the spectral properties and G-quadruplex folding ability of fluorescent oligonucleotide probes modified by the attachment of a cholesterol moiety. These probes were designed and studied in order to verify their potential as potassium-sensing devices that can be incorporated into the cellular membrane. The 19-meric guanine-rich deoxyoligonucleotide was labeled with reporter fluorescent FRET groups (FAM and TAMRA) and a cholesterol anchor was attached using different approaches. The probes exhibited abilities to fold into a quadruplex structure and to bind metal cations (Na+ and K+). In an unbound state, both termini of the oligonucleotide are separated, thus fluorophores do not interact with each other and the probe exhibits an unperturbed fluorescence spectrum. In the presence of K+, the quadruplex structure is developed such that it enables fluorophores to be arranged in close proximity, causing generation of a different fluorescence spectrum (FRET signal). Folding properties of probes and their spectral behavior were examined by recording the UV-Vis, fluorescence emission, and excitation spectra (FRET efficiency), and the temperature stability of G-quadruplex structures adopted by probes (melting profiles). Fluorescence energy transfer efficiency increased with increases in sodium or potassium ion concentrations in an aqueous solution, which indicated that the probes retained their cation-binding properties and could be promising candidates for potassium sensing at the cell membrane interface.

Experimental and theoretical study of the cation binding properties of macrocyclic dehydrodibenzopyrido[15]annulenes

The UV/Vis titration measurements, vibrational and NMR spectroscopy of isomeric dehydrodibenzopyrido[15]annulenes (DBPA) 1 and 2 clearly show that under proper conditions these macrocycles can achieve fast, quantitative and unselective binding of metal ions. The macrocycle 1 is an example of a hindered amine 2,6-bis(R)pyridine and its isomer 2 of a non-hindered amine 3,5-bis(R)pyridine. The protonation stoichiometry for both 1 and 2 was assumed to be DBPA:H+=1:1 and the formation constants logK=4.77±0.02 for 1, and logK=6.78±0.08 for 2 were obtained that well agree with those obtained under similar conditions for a macrocycle containing bipyridine units. The protonation of 2 gave the estimated stoichiometry of 2:H+=1:1 while the stoichiometric protonation of macrocycle 1 could not be achieved and the lower stability of the ion pair containing 1H+ is most likely due to the inaccessibility of the nitrogen atom of 1 to the counterions and solvent molecules. The structures and electronic absorption spectra of 1 and 2, as well as the structures and spectra of 1H+ and 2H+, i.e. the species formed by protonation of the pyridine nitrogen, were calculated with the time-dependent DFT method with a B3LYP functional and a 6-31+G(d) basis set. The solvent effects were incorporated by means of the polarizable continuum model (PCM). The agreement of the calculated absorption data for the parent and protonated species with the observed spectra is rather satisfactory. Vibrational IR and Raman spectra of 1, 2, 1H+ and 2H+ in vacuo were calculated at the B3LYP/cc-pVTZ level of theory. Macrocycles 1 and 2, and their products protonated by trifluoromethanesulfonic acid (1HOTf and 2HOTf) were also characterized by temperature-dependent FTIR technique known as two dimensional IR correlation analysis. Quite large difference in degradation temperature between macrocycle 1 and 2 and their protonated complexes was measured, indicating that inclusion of proton leads to significant thermal stabilization of dehydroannulene ring.

Isolated cell walls exhibit cation binding properties distinct from those of plant roots

Aims The principal contributor to the cation binding properties of roots is currently considered to be the cell wall or, alternatively, the plasma membrane. The aim of this study was to highlight their respective contributions in the binding properties.

Cation-induced switching on–off luminescence in an imidazole 4,5-dicarboxylate-bridged RuIIOsII bipyridine complex: A combined experimental and DFT/TD-DFT investigation

A heterobimetallic complex of the composition [(bpy)2Ru(Imdc)Os(bpy)2](ClO4), where Imdc3−=imidazole-4,5-dicarboxylate(3−) ion and bpy=2,2′-bipyridine, was synthesized and characterized using standard analytical and spectroscopic techniques, including X-ray crystallography. Steady state and time resolved luminescence data at room temperature showed that an efficient intramolecular electronic energy transfer takes place from the Ru center to the Os based component in the dyad. The cation binding properties of the complex were thoroughly investigated in solution using UV–Vis absorption, steady state and time-resolved emission spectroscopic techniques. It is interesting to note that the luminescence intensity, quantum yield as well as the lifetime of the complex were enhanced substantially in the presence of selective cations, showing cation-induced molecular switching behavior. The effect of different cations on the rate of photoinduced intramolecular energy transfer in the dyad was also explored. Density functional theory (DFT) and time-dependent DFT (TD-DFT) studies were utilized to investigate the structural and electronic properties of the dyad. The optimized geometrical parameters for the dyad, computed both in the gas phase and in solution, are reported and compared with the single crystal X-ray data. Computational (TD-DFT) studies also provide insight into the nature of the ground and excited states, with detailed assignments of the orbitals involved in the absorption and emission transitions. In particular, the blue-shifts of the absorption and emission bands in the presence of selective cations are reproduced by our calculations.

Narrow-Rim Functionalization of Calix[4]arene through Ugi-4CR: Synthesis of a Series of Calix[4]arene Peptoids

Adaptation of Ugi-4CR for the narrow-rim modification of calix[4]arene toward the synthesis of a series of tripeptoid and tetrapeptoid calix[4]arenes is described. The metal ion/organic cation binding properties of the newly synthesized peptoid calix[4]arenes were also investigated.

Synthesis, Structure and Cation-Binding Properties of Some [4 + 4] Metallocyclic MO22+ (M = Mo or W) Derivatives of 9-Phenyl-2,3,7-trihydroxyfluor-6-one

The trianion Z(3-) obtained from 9-phenyl 2,3,7-trihydroxyfluor-6-one, ZH3, affords dioxomolybdenum and dioxotungsten derivatives which contain [4 + 4] metallocycles of composition [(MO2)4Z4](4-) (M = Mo, W) in combination with a variety of counter cations. The syntheses, structures and ESMS of the following compounds are presented: compound 1, (MePPh3)3(NBu4)[(MoO2)4Z4]; compound 2, (MePPh3)3(NBu4)[(WO2)4Z4]; compound 3, (MePPh3)4[(WO2)4Z4]; compound 4, (PPh4)2(NBu4)2[(MoO2)4Z4]; compound 5, (AsPh4)3(NBu4)[(MoO2)4Z4]; compound 6, (AsPh4)2(NBu4)2[(WO2)4Z4]; compound 7, (Ph3PNPPh3)(NBu4)3[(MoO2)4Z4]; compound 8, (Ph3PNPPh3)(NBu4)3[(WO2)4Z4]; compound 9, (NEt4)(NBu4)3[(MoO2)4Z4]. The metallocycles in all of these compounds have similar structures, with the four metal centers located at the corners of a square slightly distorted, to varying degrees, toward a rhombus and also toward a tetrahedron. Various cations are bound inside the anionic metallocycles. ESI mass spectrometry shows that the metallocycles remain intact in the gas phase, forming [(MO2)4Z4](4-), {X-[(MO2)4Z4]}(3-) and in some cases {X2-[(MO2)4Z4]}(2-) where X(+) is an organic cation.

The Molecular Basis for the Pharmacokinetics and Pharmacodynamics of Curcumin and Its Metabolites in Relation to Cancer

This review addresses the oncopharmacological properties of curcumin at the molecular level. First, the interactions between curcumin and its molecular targets are addressed on the basis of curcumin's distinct chemical properties, which include H-bond donating and accepting capacity of the β-dicarbonyl moiety and the phenylic hydroxyl groups, H-bond accepting capacity of the methoxy ethers, multivalent metal and nonmetal cation binding properties, high partition coefficient, rotamerization around multiple C-C bonds, and the ability to act as a Michael acceptor. Next, the in vitro chemical stability of curcumin is elaborated in the context of its susceptibility to photochemical and chemical modification and degradation (e.g., alkaline hydrolysis). Specific modification and degradatory pathways are provided, which mainly entail radical-based intermediates, and the in vitro catabolites are identified. The implications of curcumin's (photo)chemical instability are addressed in light of pharmaceutical curcumin preparations, the use of curcumin analogues, and implementation of nanoparticulate drug delivery systems. Furthermore, the pharmacokinetics of curcumin and its most important degradation products are detailed in light of curcumin's poor bioavailability. Particular emphasis is placed on xenobiotic phase I and II metabolism as well as excretion of curcumin in the intestines (first pass), the liver (second pass), and other organs in addition to the pharmacokinetics of curcumin metabolites and their systemic clearance. Lastly, a summary is provided of the clinical pharmacodynamics of curcumin followed by a detailed account of curcumin's direct molecular targets, whereby the phenotypical/biological changes induced in cancer cells upon completion of the curcumin-triggered signaling cascade(s) are addressed in the framework of the hallmarks of cancer. The direct molecular targets include the ErbB family of receptors, protein kinase C, enzymes involved in prostaglandin synthesis, vitamin D receptor, and DNA.

Novel Naphthalene Based Lariat-Type Crown Ethers Using Direct Single Electron Transfer Photochemical Strategy

This study explored a direct SET-photochemical strategy to construct a new family of thioene conjugatednaphthalamide fluorophore based lariat-crown ethers which show strong binding properties towards heavy metal ions. Irradiations of designed nitrogen branched (trimethylsilyl)methylthio-terminated polyethylenoxytethered naphthalimides in acidic methanol solutions have led to highly efficient photocyclization reactions to generate naphthalamide based lariat type thiadiazacrown ethers directly in chemo- and regio-selective manners which undergo very facile secondary dehydration reactions during separation processes to produce their corresponding amidoenethio ether cyclic products tethered with electron donating diethyleneoxy- and diethyenethio-side arm chains. Fluorescence and metal cation binding properties of the lariat type enamidothio products were examined. The photocyclized amidoenethio products, thioene conjugated naphthalamide fluorophore containing lariat-thiadiazacrowns exhibited strong fluorescence emissions in region of 330-450 nm along with intramolecular exciplex emissions in region of 450-560 nm with their maxima at 508 nm. Divalent cation Hg 2+ and Pb 2+ showed strong binding to sulfur atom(s) in side arm chain and atoms in enethiadiazacrown ether rings which led to significant enhancement of fluorescence from its chromophore singlet excited state and concomitant quenching of exciplex emission. The dual fluorescence emission responses towards divalent cations might provide a new guide for design and development of fluorescence sensors for detecting those metals.

Synthesis, structural characterization, and multichannel anion and cation sensing studies of a bifunctional Ru(ii) polypyridyl–imidazole based receptor

A mixed-ligand monometallic ruthenium(ii) complex of composition [(bipy)2Ru(tpy-Hbzim-dipy)](ClO4)2 (), where tpy-Hbzim-dipy = 4'-[4-(4,5-di-pyridin-2-yl-1H-imidazol-2-yl)-phenyl]-[2,2';6',2'']terpyridine and bipy = 2,2'-bipyridine has been synthesized and characterized using standard analytical and spectroscopic techniques including X-ray crystallography. The complex displays very intense, ligand centered absorption bands in the UV and moderately intense MLCT bands in the visible region. On excitation at the MLCT bands, the complex exhibits strong luminescence at room temperature with lifetimes in the range of 116-257 ns, depending upon the nature of the solvents. The complex is found to undergo one reversible oxidation in the positive potential window (0 to +1.8 V) and two successive quasi-reversible reductions in the negative potential window (0 to -2.0 V). Both anion and cation binding properties of the receptor were thoroughly investigated in acetonitrile solution using (1)H NMR, absorption, steady state and time-resolved emission spectral studies and by cyclic voltammetry. The anion sensing studies revealed that the receptor acts as a "turn on" luminescence sensor for H2PO4(-) and HSO4(-) ions, and as a "turn off" sensor for F(-) and AcO(-) ions. It is evident that in the presence of excess F(-) and AcO(-) ions, deprotonation of the imidazole N-H fragment of the receptor occurs, an event which is signaled by the change of color from orange yellow to red visible to the naked eye. On the other hand, the probable mode of interaction of the receptors with H2PO4(-) and HSO4(-) ions is through hydrogen bonding interaction. The cation-sensing properties showed that the receptor was found to exhibit a colorimetric sensing ability that was highly selective for Fe(2+), as evidenced by the distinct color change from yellow orange to deep red-violet to the naked eye over the other cations studied (Mn(2+), Fe(3+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), and Hg(2+)).

Theoretical study on conformational features and cation-binding properties of a diquinone calix[4]arene

Theoretical studies of a diquinone calix[4]arene and its interactions with the cations Li+, Na+, K+ and Ag+ have been performed. Conformational features and cation-binding properties were evaluated with the restricted hybrid Becke three-parameter exchange functional method using the 6-31G(d) basis set and its relativistic effective core potentials. To model the effect of medium, the polarisable continuum model was also used. Four typical conformations of the parent diquinone calix[4]arene were studied. The calculated results show that the most stable conformers are 1,3-alternate and partial cone in the gas phase and in CH2Cl2 solution, respectively. The optimised geometric structures were used to perform natural bond orbital analysis. The two main types of driving force metal–ligand and cation–π interactions are investigated. The calculated binding energy for cations (Li+, Na+, K+ and Ag+) is discussed. The calculated results indicate that cone complexes are the most stable.