Aqueous HEPES Buffer Research Articles

Affinity Directed Surface Functionalization of Two Different Metal Nanoparticles by a Natural Ionophore: Probing and Removal of Hg2+ and Al3+ Ions from Aqueous Solutions

In this work, we report affinity controlled surface modifications of two different metal nanoparticles (MNPs) using a hydrophilic natural ionophore (microbial chelator) aeruginic acid (abbreviated as H2L) that possesses two different types of binding pockets viz. O/O from carboxylic acid group and N/O from a phenol-thiazole moiety. Preferred binding of the former donor set (i.e., O/O) on to the surface of silver nanoparticles (AgNPs) has resulted in a colorimetric nanomaterial HL@AgNPs, which showed naked eye observable easy detection of Hg2+ in aqueous HEPES buffer at pH 7.4, even in the presence of other metal ions. On the other hand, excellent affinity of the phenol-thiazole moiety (i.e., N/O) for iron nanosurfaces (FeNPs) develops a fluorogenic nanomaterial HL@FeNPs. Brilliant emission behavior of this nanomaterial enabled it to be useful for highly selective recognition of Al3+ under identical experimental conditions. Remarkable fluorescence enhancement (122-folds) of HL@FeNPs upon addition of Al3+ remain unchanged even in the presence of other competing metal ions. The nanomaterials HL@AgNPs and HL@FeNPs could even detect the target analytes instantly offering lower detection limits of 2 and 80 nM, respectively. Presence of toxic metal ions as environmental pollutant demands for dual-functional materials capable of performing the task of probing cum removal. Surface functionalizations of the nanomaterials of silver and iron with H2L have also resulted two removal agents that can efficiently and easily extract Hg2+ and Al3+ ions from contaminated water, respectively. We are not aware of any work that highlights the manifold utilization of a microbial chelator (i.e., natural ionophore) in the facile construction of different metal nanoparticles for environmental applications such as detection cum removal of toxic metal ions from aqueous solutions.

A novel OFF-ON-OFF fluorescence probe based on coumarin for Al3+ and F- detection and bioimaging in living cells.

A novel fluorescence probe L2 based on coumarin has been designed and synthesized. The probe L2 can be used for relay recognition of metal ions Al3+ and anion F- in the aqueous HEPES buffer (0.05 M, pH = 7.4), and build a OFF-ON-OFF detection system. The probe showed high selectivity and sensitivity to target ions in the process of relay recognition, and the corresponding detection limit could be as low as 0.014 μM (Al3+) and 0.03 μM (F-). Besides, the geometry optimizations of probe L2 and [L2 + Al3+] complex were carried out using the Gaussian 16 program based on DFT, and the identification mechanism of the probe was also discussed by the mass spectrometry and theoretical calculations. Moreover, the probe has also been successfully applied to detection of target ions in living cells.

Synthesis and characterization of a new diimine Schiff base and its Cu2+ and Fe3+ complexes: Investigation of their photoluminescence, conductance, spectrophotometric and sensor behaviors

The newly synthesized Schiff base (HL2) and its binary [ML2] type of Cu(II) and Fe(III) complexes were characterized by various spectroscopic methods. The photoluminescence property of [CuL22] and [FeL22](NO3) complexes, and HL2 was studied in the absence and presence of Cu2+/Fe3+ ions in DMF: aqueous HEPES buffer (v: v, 1: 1, pH = 6.8). The conductance behaviors of compounds were investigated. The complexation reaction of the receptor with these ions, and the formation constants were determined in solution by spectrophotometric and conductometric method. The sensing ability of HL2 against Cr3+, Fe3+, Ni2+, Zn2+, Cu2+, Co2+, Pb2+, Ba2+ and Ag+ ions were also evaluated in DMF: HEPES. High sensitivity and selectivity was achieved for Cu2+ and Fe3+ by UV–vis spectra in the presence of other ions, and it showed reversibility with EDTA. Job's method confirmed 2: 1 structure between HL2 and Cu2+ and Fe3+. Receptor was applied for the ppm level detection of Fe3+ ion. Also, it sensed pH by “naked eye”. Upon the addition of acid and base, its color instantly changed from yellow to colorless, corresponding to a blue shifting and disappearance in the absorption bands for acid and to orange for base.

Benzoquinone based chemodosimeters for selective and sensitive colorimetric and turn-on fluorescent sensing of cyanide in water

Dibromobenzoquinone-indole ensembles containing different substituents (OMe, Me, H, Br, and NO2) have been designed, synthesized and characterized using spectral techniques. These chemodosimeters selectively sense cyanide ion colorimetrically with turn-on fluorescence in aqueous HEPES buffer. Absorption and emission spectral studies suggest that the interaction between the receptors and cyanide is strong (binding constant in the order of 104M−1) with 1:1 stoichiometry. The detection limit for these receptors to sense cyanide is found to be in the nano molar range which is far below the permissible limit recommended by WHO for cyanide ion in drinking water. 1H and 13C NMR titration results indicate that the mechanism of sensing of cyanide by these receptors is through nucleophilic addition of cyanide to the CC bond of the indole ring. The electro-reduction potentials for the quinone moiety before and after the addition of cyanide substantiate the proposed mechanism. Mulliken charges computed, using DFT method, suggest that these receptors possess an electropositive C-atom for the addition reaction to occur, while such charge polarization is not there in similar compounds containing benzoquinone or naphthoquinone. The effect of substituents on the λICT, binding constant and δNH of indole has been explained using Hammett's substituents constants (σp).

A highly sensitive turn-on fluorescent chemosensor for recognition of Zn2 + and Hg2 + and applications

A fluorescence probe has been designed and synthesized, and applied with a combined theoretical and experimental study. Research suggests that the probe can be used to sense Zn2+ and Hg2+ through selective turn-on fluorescence responses in the aqueous HEPES buffer (0.05M, pH=7.4). The limit of detection (LOD) were determined as 1.46×10−7M (Zn2+) and 2.50×10−7M (Hg2+). Moreover, based on DFT, the geometry optimizations of probe 1, [1-Hg2+] complex and [1-Zn2+] complex were carried out using the Gaussian 09 program, in which the B3LYP function was used. The electronic properties of free probe 1 and the metal complexes were studied based on the Natural Bond Orbital (NBO) analyses. The probe 1 has also been successfully applied to detection of Zn2+ and Hg2+ in living cells.

Coumarine–imino–C2-glucosyl conjugate as receptor for Cu2+ in blood serum milieu, on silica gel sheet and in Hep G2 cells and the characterization of the species of recognition

A coumarine–imino–C2-glucosyl conjugate (L) was synthesized and characterized. The conjugate L is found to recognize Cu2+ in aqueous HEPES buffer by exhibiting a 95% fluorescence quenching in pH range 7–10 even in the presence of several biologically and ecologically relevant metal ions. Fluorescence on–off behavior has been clearly demonstrated on the basis of the binding variability of Cu2+ to L. The binding has been elicited through the changes observed in fluorescence, absorption, ESI-MS and 1H NMR titrations. All the other thirteen metal ions studied did not show any change in the fluorescence emission. These ions do not interfere with the recognition of Cu2+ by L. The structural features of [CuL]2 complex in both the isomeric forms were established by DFT computational calculations. The utility of L has been demonstrated by showing its sensitivity toward Cu2+ on a thin layer of silica gel. The L gives sensitive fluorescence signals for Cu2+ even in blood serum and exhibits appropriate fluorescence responses in living cells.

Real-time fluorescence assays of alkaline phosphatase and ATP sulfurylase activities based on a novel PPi fluorescent probe

An anthracene-armed tetraaza macrocyclic fluorescent probe 3-(9-anthrylmethyl)-3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene(l) for detecting Zn2+ in aqueous medium was synthesized. L–Zn2+ complex, showed selectivity toward pyrophosphate ion (PPi) by quenching the fluorescence in aqueous HEPES buffer (pH 7.4). Furthermore, L–Zn2+ was also used to set up a real-time fluorescence assay for monitoring enzyme activities of alkaline phosphatase (ALP) and adenosine triphosphate sulfurylase (ATPS). In the presence of ALP inhibitor Na3VO4 and ATPS inhibitor chlorate, two enzymes activities decreased obviously, respectively.

Unique fluorogenic ratiometric fluorescent chemodosimeter for rapid sensing of CN(-) in water.

A new benzimidazole-spiropyran conjugate chemosensor molecule (BISP) has been synthesized and characterized by (1)H NMR spectroscopy, mass spectrometry (ESI-MS), and elemental analysis. The two isomeric forms (BISP↔BIMC) were shown to be highly selective and sensitive to CN(-) among the ten anions studied in aqueous HEPES buffer, as shown by fluorescence and absorption spectroscopy and even by visual color changes, with a detection limit of 1.7 μM for BIMC. The reaction of CN(-) with BIMC was monitored by (1)H NMR spectroscopy, high-resolution mass spectrometry (HRMS), UV/Vis measurements, and fluorescence spectroscopy in HEPES buffer of pH 7.4. TDDFT calculations were performed in order to correlate the electronic properties of the chemosensor with its cyanide complex. Further, titration against thiophilic metal ions like Au(3+), Cu(2+), Ag(+), and Hg(2+) with [BIMC-CN] in situ showed that it acts as a secondary recognition ensemble toward Au(3+) and Cu(2+) by switch-on fluorescence. In addition, a reversible logic-gate property of BIMC has been demonstrated through a feedback loop in the presence of CN(-) and Au(3+) ions, respectively. Furthermore, the use of BIMC to detect CN(-) in live cells by fluorescence imaging has also been demonstrated. Notably, test strips based on BIMC were fabricated, which could serve as convenient and efficient CN(-) test kits.

Azobenzene chemosensor based on nitrogen chelator for the detection of Cu (II) ion in aqueous medium

Abstract A bis-pyridine unit containing azobenzene chemosensor for Cu2 + ion is designed and synthesized with good yield. The structure of the receptor I is determined by FT-IR, 1H NMR, 13C NMR, ESI-MS and single crystal XRD. The receptor I is constructed on the basis of internal charge transfer (ICT) mechanism with bis-pyridine unit acting as the binding part for Cu2 + ion. In solution, the proposed receptor I produces a cation induced 120 nm blue shift for Cu2 + ion from 457 nm to 337 nm with remarkable colour change from red to colourless. Whereas no significant colour change is observed upon addition of other metal ions in aqueous HEPES buffer (pH 7.0). Moreover, spectroscopic studies confirm the formation of 1: 1 stoichiometry between the receptor I and Cu2 + ion with an association constant of ca. 1.45 × 106 M− 1. The receptor I is highly specific to Cu2 + ions in aqueous solution attributed to the rational design of the molecular structure.

Carbazole substituted 2-aminobenzamide compounds: synthesis, fluorescence ON–OFF–ON sensing of Zn(ii) and PPi ions, assay for alkaline phosphatase, and computational study

A new mononuclear Zn(II) complex based receptor for PPi sensing and alkaline phosphatase assay was fabricated using 2-aminobenzamide as a scaffold, appended with N,N-bis(2-pyridylmethyl) ethylenediamine (BPEA) and amide as a chelator and carbazole as a fluorophore. Based on an “ON–OFF–ON” molecular switch with zinc ion and PPi inputs, two highly efficient fluorescent chemosensors (4- and 5-isoACBA) were developed, which show a large binding affinity (Ka ≈ 2.5 × 1010 M−2) and high selectivity for PPi (43–48 fold fluorescent enhancement) over a wide range of anions including Pi, AMP, ADP and ATP in an aqueous HEPES buffer (pH 7.4). The binding mode of isoACBA–Zn(II) in the absence or presence of PPi was thoroughly investigated by UV and fluorescence titrations, ESI-HRMS analysis, and DFT studies. The results reveal that the synergistic effects of metal coordination and hydrogen bonding interactions in the structures of the isoACBAs should contribute to the remarkable binding affinity and high sensing selectivity for PPi.

A selective and sensitive fluorescence probe for imaging endogenous zinc in living cells

A carboxamidoquinoline-based fluorescent Zn2+ probe 1 containing N/S/S heteroatoms as a receptor was designed and readily synthesized, which was featured by the Zn2+-induced red-shift of emission (45 nm) based on internal charge transfer (ICT) in an aqueous HEPES buffer (pH=7.4). Moreover, spectroscopic studies indicated that the composition of the complex 1-Zn2+ was 1:1, which was also confirmed by X-ray crystallography. In addition, 1H NMR titration experiment suggested that probe 1 transformed from the amide tautomer to imidic acid tautomer after binding with Zn2+. The binding of zinc with 1 was easily reversed by addition of N,N,N′,N′-tetrakis(2-picolyl)ethylenediamine (TPEN) or EDTA. Furthermore, probe 1 was successfully applied to image both exogenous and endogenous zinc in living HeLa cells.

Zinc(II) and PPi Selective Fluorescence OFF–ON–OFF Functionality of a Chemosensor in Physiological Conditions

A fluorescent chemosensor based on a quinoline derivative, L(2) (OFF state), selectively senses Zn(2+) by effective chelate-enhanced fluorescence (ON state), which further shows selectivity toward PPi over competing anions like Pi, AMP, and ATP via fluorescence quenching (OFF state) in a 100% aqueous HEPES buffer (pH 7.4). A plausible mode for the selective binding of PPi to 1 has been demonstrated by quantum mechanical density functional theory calculations and high-resolution mass spectrometry analysis.

An integrated system of pyrene and rhodamine-6G for selective colorimetric and fluorometric sensing of mercury(II)

A pyrene and rhodamine-6G functionalized simple chemosensor L is studied toward sensing of metal ions in solution extensively. L shows selective color change from colorless to pink in the presence of Hg 2+ in acetonitrile and the UV–Vis study shows peak at 525 nm with a ε value of 5.2 × 10 4 M −1 cm −1 due to selective ring opening of rhodamine spirolactam moiety. The selective sensing of Hg 2+ by L in the presence of other metal ions and reversible nature of “OFF–ON–OFF” functionality of L by Hg 2+ and EDTA, respectively, are also established. The fluorescence study of L in the presence of Hg 2+ shows emission at 550 nm when excited at 525 nm (ring opened rhodamine wavelength) or 340 nm (pyrene wavelength) in dry CH 3CN. Thus L acts as a selective colorimetric and fluorometric probe (dual probe) for the Hg 2+ in solution. Metal ion sensing ability of L is also carried out in water as well as in aqueous Hepes buffer. These studies suggest that the fluorescence output of L in presence of Hg 2+ in aqueous environment is apparently due to the generation of acid upon addition of Hg 2+ salt in water.

Synthesis of 3-hydroxyflavone fluorescent probes and study of their fluorescence properties

Direct measurement of dipole potential in biological membranes has been impossible and 3-hydroxyflavones (3HFs) have allowed detection of changes in dipole potential in biological systems. In the present study, sixteen derivatives of 3HF with aliphatic hydrocarbon chains of different lengths at 4′-position and 6-position were synthesized. The basic fluorescence properties of 3HFs are maintained in all the probes in terms of strong blue shift in maximum fluorescence emission wavelength and >100 fold increase in quantum yield in organic solvents and in dioleoylphosphatidylcholine (DOPC) small unilamellar vesicles (SUV) in comparison to in aqueous Hepes buffer (15 mmol/L, pH 7.4). More importantly, the ability of the new compounds to report dipole potential changes in biological systems are also maintained, since all the new probes showed spectrum properties that are similar to yet different from that of F4N1, which potentially may allow more sensitive measurement of the dipole potential change in membranes.

Multivalent Macrocyclic Hosts: Histone Surface Recognition, Guest Binding, and Delivery by Cyclophane-Based Resorcinarene Oligomers

As a new class of host for both specific proteins and hydrophobic molecular guests, cyclophane-based resorcinarene oligomers were designed on the basis of a molecular design that allows the assembly of four or 12 anionic resorcinarenes on a cyclophane skeleton. We prepared a cyclophane-based resorcinarene tetramer (4), constructed with a tetraaza[6.1.6.1]-paracyclophane skeleton and four resorcinarenes bearing heptacarboxylic acid residues that connect to the macrocycle through amide linkages. In addition, we prepared an extended analogical dodecamer (12), which was constructed with a pentakis(cyclophane) skeleton and 12 resorcinarenes. The cyclophane-based resorcinarene oligomers exhibited potent recognition capabilities toward histone, a small basic protein of eukaryotic chromatins. The binding constants (K) of cyclophane-based resorcinarene tetramer 4 and dodecamer 12 with histone were determined to be 1.3x107 and 8.4x107 M-1, respectively, by means of surface plasmon resonance measurements. The K values of 4 and 12 with histone were 31- and 200-fold larger than that of an untethered reference resorcinarene, reflecting the multivalency effects in resorcinarenes. In addition to that, cyclophane-based resorcinarene tetramer 4 and dodecamer 12 captured hydrophobic guests such as 6-p-toluidinonaphthalene-2-sulfonate, with respective binding constants of 2.4x103 and 2.5x104 M-1 in an aqueous HEPES buffer as evaluated by fluorescence spectroscopy. Furthermore, the resorcinarene oligomers were also found to act as guest carriers from the bulk aqueous phase to histone surfaces, as confirmed by fluorescence spectroscopy.

119Sn Mössbauer studies of bis[cysteinato(1−)‐S]‐ and bis[penicillaminato(1−)‐S]‐diorganotin(IV) species in the crystalline state and in frozen aqueous solution

AbstractThe bonding and the configuration of the tin environment in the title compounds {R2Sn[SCH2CH(NH3+)COO−]2 and R2Sn[SC(CH3)2CH(NH3+)COO−]2, indicated in the following as R2Sn(cysH)2 and R2Sn(penH)2 respectively} has been investigated through the determination of the Mössbauer‐Zeeman spectra of Ph2Sn(cysH)2 and Ph2Sn(penH)2 in the solid state, and through conventional Mössbauer spectroscopy of Me2Sn(penH)2 in the solid state as well as of Me2Sn(cysH)2 and Me2Sn(penH)2 in aqueous solution (frozen). The treatment of the data by the pointcharge model approach suggested the general occurrence of a tetrahedral C2SnS2 core. In aqueous Hepes buffer, a tertiary amino nitrogen atom has been observed to coordinate tin in Me2Sn(cysH)2 and Me2Sn(penH)2, with formation of trigonal bipyramidal tin environments. The latter solutions undergo slow decomposition reactions at room temperature. From (Me2SnS)3 occurs, as well as formation of soluble complex species in the presence of glycylglycine; Me2Sn(penH)2 appears to undergo a slow desulfuration reaction.

Ionophore-mediated cation translocation in artificial systems: I. A23187-mediated calcium translocation

The inophore A23187 stimulates the translocation of calcium from an aqueous Hepes buffer into an organic immiscible phase. At saturating calcium concentrations, 2 molecules of ionophore seem to complex each atom of calcium. Consistent with such a stoichiometric behaviour, the apparent ratio of calcium-ionophore association to dissociation rate constants increases as the concentration of ionophore is raised. As a result, at low calcium concentrations, the amount of translocated calcium increases as a power function of A23187 concentration. When allowance is made for such a phenomenon, the relation between calcium translocation and concentration is characterized by usual substrate-receptor binding kinetics.