HEPES Buffer Medium Research Articles

Adsorption and desorption of hydroxychloroquine onto sulphur doped graphene powders as a potential drug for COVID-19: physicochemical investigation, surface chemistry and in vitro cytotoxicity evaluation

Hydroxychloroquine (HCQ) is a very substantial drug active substance that was approved for emergency use by the FDA during the peak of the COVID-19 pandemic due to its potent antiviral properties. In this study, adsorption and desorption of hydroxychloroquine on sulfur (S)-doped graphene powders were investigated. While the adsorption experiments were carried out in the environment of distilled water (pH 5.0-6.0), HEPES buffer (pH 7.6), and Tris.HCl buffer (pH 8.0) the desorption studies were performed in distilled water. The HCQ adsorbed S-doped graphene powders were characterized by UV-Vis, FT-IR, XRD, BET and TEM techniques. According to UV-Vis measurements, the adsorption efficiency in the HEPES buffer medium at pH 7.6 was the highest (68.72% for H3 (HCQ adsorption with SGr3 graphene in HEPES medium)). FT-IR and XRD analyses confirmed the presence of HCQ on the graphene powders’ surface. While morphological changes on the surfaces of graphene powders were imaged by TEM, BET surface area changes proved the HCQ adsorption. The in vitro toxicity of the developed H3 was found to be lower than that of HCQ alone on the L929 cell line. These fundamental findings of the surface interaction between HCQ and graphene are precious for the design and optimization of a targeted drug based on this molecule and material. The adsorption/desorption features of HCQ onto graphene-based carrier systems which in particular doped with sulfur from functional metals have been investigated for the first time.

Nitroquinolone Fused Salicyl and Naphthyl Hydrazone Fluorescent Probes for the Detection of Fe3+and Pb2+ Ions.

The application of quinolones stretches over a large umbrella of medicinal field as well as chemosensor due to the presence of privileged heterocyclic aromatic rig system. Salicyl and Naphthyl Hydrazide motifs are also established fluorophore groups. Therefore in this work, we have designed and synthesized Salicyl hydrazide (3a-c) and naphthyl hydrazide fused nitroquinolones (5a-c) investigated for their fluorescent behaviour. Preliminary UV- absorption studies were carried out and the metal selectivity were examined with various metal ion. Among them, it was found that compound 3a was selective towards Fe3+ ions (λex = 330nm, 1:1 DMF:H2O at pH = 7.4 in HEPES Buffer medium). 3a shows decrease emission intensity in presence of Fe3+ ions. Compound 5a shows enhancement in fluorescence intensity upon addition of Pb2+ ion (λex = 280nm, 1:1 DMF:H2O at pH = 7.4 in HEPES Buffer medium). Further, the concentration dependence, competitive binding and EDTA reversibility were studied for selected compounds towards the respective cations selectivity. Jobs plot analysis indicate that 1:1 binding of 3a with Fe3+ ion (Ka = 3.17 x104M-1 and Limit Of Detection (LOD) = 5.1 × 10-7 M) whereas 5a showed 1:2 binding mode with Pb2+ ions (Ka = 2.14 × 106M-1 and Limit Of Detection (LOD) = 2.613 × 10-9M). Density Function Theoretical studies were performed as support for the experimental results.

MOF-Fabric Composites Based on a Multi-Functional MOF as Luminescent Sensors for a Neurotransmitter and an Anti-Cancer Drug.

A biocompatible, reliable, fast, and nanomolar-level dual-functional sensor for a neurotransmitter (e.g., adrenaline) and an anti-cancer drug (e.g., 6-mercaptopurine (6-MP)) is still far away from the hand of modern-day researchers. To address this issue, we synthesized an aqua-stable, bio-friendly, thiourea-functionalized Zr(IV) metal-organic framework (MOF) for selective, rapid sensing of adrenaline and 6-MP with ultra-low limit of detection (LOD for adrenaline = 1.9 nM and LOD for 6-MP = 28 pM). This is the first MOF-based fluorescent sensor of both the targeted analytes. The sensor not only can detect adrenaline in HEPES buffer medium but also in different bio-fluids (e.g., human urine and blood serum) and pH media. It also exhibited 6-MP sensing ability in aqueous medium and in various wastewater specimens and pH solutions. For the quick and on-site detection of this neuro-messenger (adrenaline) and the drug (6-MP), cost-effective sensor-coated cotton fabric composites were fabricated. The MOF@cotton fabric composite is capable of detecting both the analytes up to the nanomolar level by the naked eye under UV light. The sensor can be recycled up to five times without significantly losing its efficiency. The Förster resonance energy transfer in the presence of adrenaline and inner-filter effect in the presence of 6-MP are the most likely reasons behind the quenching of the MOF's fluorescence intensity, which were proved with the help of appropriate instrumental techniques.

Aza-Crown-Based Macrocyclic Probe Design for "PET-off" Multi-Cu2+ Responsive and "CHEF-on" Multi-Zn2+ Sensor: Application in Biological Cell Imaging and Theoretical Studies.

The work represents a rare example of an aza-crown-based macrocyclic chemosensor, H2DTC (H2DTC = 1,16-dihydroxy-tetraaza-30-crown-8) for the selective detection of both Zn2+ and Cu2+ in HEPES buffer medium (pH 7.4). H2DTC exhibits a fluorescence response for both Zn2+ and Cu2+ ions. The reversibility of the chemosensor in its binding with Zn2+ and Cu2+ ions is also examined using a Na2EDTA solution. H2DTC exhibits a chelation-enhanced fluorescence (CHEF) effect in the presence of Zn2+ ions and a quenching effect (CHEQ) in the presence of paramagnetic Cu2+ ions. Furthermore, the geometry and spectral properties of H2DTC and the chemosensor bound to Zn2+ have been studied by DFT and TDDFT calculations. The limit of detection (LOD) values are 0.11 × 10-9 and 0.27 × 10-9 M for Cu2+ and Zn2+, respectively. The formation constants for the Zn2+ and Cu2+ complexes have been measured by pH-potentiometry in 0.15 M NaCl in 70:30 (v:v) water:ethanol at 298.1 K. UV-vis absorption and fluorometric spectral data and pH-potentiometric titrations indicate 1:1 and 2:1 metal:chemosensor species. In the solid state H2DTC is able to accommodate up to four metal ions, as proved by the crystal structures of the complexes [Zn4(DTC)(OH)2(NO3)4] (1) and {[Cu4(DTC)(OCH3)2(NO3)4]·H2O}n (2). H2DTC can be used as a potential chemosensor for monitoring Zn2+ and Cu2+ ions in biological and environmental media with outstanding accuracy and precision. The propensity of H2DTC to detect intracellular Cu2+ and Zn2+ ions in the triple negative human breast cancer cell line MDA-MB-468 and in HeLa cells has been determined by fluorescence cell imaging.

Active Bromoaniline-Aldehyde Conjugate Systems and Their Complexes as Versatile Sensors of Multiple Cations with Logic Formulation and Efficient DNA/HSA-Binding Efficacy: Combined Experimental and Theoretical Approach.

Two fluorescence active bromoaniline-based Schiff base chemosensors, namely, (E)-4-bromo-2-(((4-bromophenyl)imino)methyl)phenol (HL1) and (E)-2-(((4-bromophenyl)imino)methyl)phenol (HL2), have been employed for the selective and notable detection of Cu2+ and Zn2+ ions, respectively, with the simultaneous formation of two new metal complexes [Cu(L1)2] (1) and [Zn(L2)2] (2). X-ray single crystal analyses indicate that complexes 1 and 2 are tetra-coordinated systems with substantial CH...π/π...π stacking interactions in the solid-state crystal structures. These two complexes are exploited for the next step detection of Al3+ and Hg2+ where complex 2 exhibits impressive results via turn-off fluorescence quenching in (DMSO/H2O) HEPES buffer medium. The sensing phenomena are optimized by UV–vis spectral analyses as well as theoretical calculations (density functional theory and time-dependent density functional theory). The combined detection phenomena of the ligand (HL2) and complex 2 are exclusively utilized for the first time to construct a molecular memory device, intensifying their multisensoric properties. Furthermore, the DNA- and human serum albumin (HSA)-binding efficacies of these two complexes are examined by adopting electronic and fluorometric titration methods. Complex 2 shows a higher DNA-binding ability in comparison with complex 1, whereas in the case of HSA, the reverse situation is observed. Finally, the binding modes of both the complexes with DNA and HSA have been investigated through molecular docking studies, suggesting good agreement with the experimental results.

Fluorescent chemosensor for lethal cesium detection using thin film membrane

ABSTRACTTwo new simple fluoroionophores viz. L1 and L2 were synthesized and characterized. These two fluoroionophores were shown to be sensitive and selective for Cs+ among the 12 metal ions in organic HEPES buffer medium by absorption and fluorescence. An attractive glowing green and blue color emission were observed in the presence of Cs+ for L1 and L2.The fluoroionophores were found to be as an effective fluorescence chemosensors for Cs+ ions with the detection limit of 0.03 ppm and 0.49 ppm, respectively. In order to evaluate the chemosensor activity in organo-aqueous medium, organic thin films (OTFs) and TLC kits of fluoroionophores viz. L1 and L2 were formed using physical coating method.

2-hydroxy-5-methylisophthalaldehyde based fluorescent-colorimetric chemosensor for dual detection of Zn2+ and Cu2+ with high sensitivity and application in live cell imaging

A 2-hydroxy-5-methylisophthalaldehyde (HMP) based Schiff-base ligand (HL) was successfully developed as a fluorescent and colorimetric chemosensor for dual detection of Zn2+and Cu2+ions in HEPES buffer medium (H2O:Methanol = 9:1 (v/v), pH= 7.4). Interestingly, in presence of Zn2+ around 16 times increment in fluorescence intensity and in presence of Cu2+ ~ 174 times decrease in fluorescence intensity has been observed. The 1:2 binding modes for both HL-Zn2+/Cu2+complexes are proved by fluorescence measurements, ESI-MS analysis and DFT-Calculations. The reversibility and regeneration process of HL are also established using Na2EDTA. It has been observed that Chemosensor HL exhibits a rapid change in fluorescence intensity within pH range 6–8 against Zn2+and Cu2+ions. Low detection limit was found to be 1.059 × 10-9(M) and 3.53 × 10-9 (M) for Zn2+ and Cu2+ ions respectively. These values also suggest that the chemosensor HL has great potential to detect Zn2+ and Cu2+ ions in environmental and biological studies.

A quinoline appended naphthalene derivative based AIE active “turn–on” fluorescent probe for the selective recognition of Al3+ and colourimetric sensor for Cu2+: Experimental and computational studies

A naphthalene quinoline based sensor L is being designed with hydrazine moeity acting as a bridge capable of displaying aggregation induced emission (AIE) properties. L can detect Cu2+ in CH3OH/aqueous HEPES buffer medium through sharp colorimetric responses. The ligand (L) shows an excellent selectivity toward Al3+ ion among the other fourteen metal ions studied. The addition of the metal Al3+ to the solution of L generates a noticeable fluorescence enhancement accompanied with obvious colour change detected by the naked eye under UV light with high binding constant of 6.22 × 106M−1.The sensitivity of the fluorescent based sensor L (3.10 μM) for Al3+ is far below the limit in the World Health Organization (WHO) guidelines for drinking water (7.41 μM). The binding of the ligand L with Al3+ was investigated through ESI-Mass and Job’s plot analysis. The Density Functional Theory and TDDFT calculations were performed in order to demonstrate the structure of ligand and complexes and its electronic properties. Moreover the ligand response towards Al3+ ion remains convincing through the solid phase study carried out by mortar pestle. Therefore, sensor L could be useful for detection of Al3+ as a laboratory indicator in real sample.

Carbazole-driven ratiometric fluorescence turn on for dual ion recognition of Zn2+ and Hg2+ by thiophene-pyridyl conjugate in HEPES buffer medium: spectroscopy, computational, microscopy and cellular studies

Carbazole-based thiophene-pyridyl conjugate (L) was synthesised and characterised. The complexation between L with Zn2+ and Hg2+ was studied in HEPES buffer medium by fluorescence, absorption and visual colour change with the detection limit of ~3.7 and ~4.8 μM, respectively. The L detects Zn2+ by bringing ratiometric change in the fluorescence signals at 418 and 515 nm, but in the case of Hg2+, the signals are observed at 418 and 365 nm, while no new band is observed at 515 nm. The structure of L has been established by single-crystal XRD and that of complexes [ZnL] and [HgL] by density functional theory calculations. TDDFT calculations were performed in order to demonstrate the electronic properties of receptors and their zinc and mercury complexes. The isolated fluorescent complexes [ZnL] and [HgL] were found to be sensitive and selective towards phosphate-bearing ions and sulfide ions, respectively, among the other anions studied. The nanostructural features such as shape and size obtained using atomic force microscopy distinguish L from its complexes formed between L and Zn2+ from that formed with Hg2+. Moreover, the utility of the conjugate L in showing the zinc recognition in live cells has also been demonstrated using RAW cells as monitored by fluorescence imaging.

Highly Selective Ratiometric Fluorescent Probes for Detection of Perborate Based on Excited‐State Intramolecular Proton Transfer (ESIPT) in Environmental Samples and Living Cells

AbstractBenzthiazole‐based ratiometric fluorescent probes acetylphenylbenzthiazole (APBT) and acetylnaphthylbenzthiazole (ANBT), were synthesized and characterized. These two excited‐state intramolecular proton transfer (ESIPT)‐based first ratiometric fluorescent probes were shown to be selective and sensitive for perborate (BO3–) among the 15 anions studied in HEPES buffer medium by fluorescence, absorption, and visual emission color change. Upon treatment with perborate in aqueous HEPES buffer solution, the acetyl protective group of probes APBT and ANBT was removed readily and ESIPT of the probes was switched on, which resulted in remarkable photo‐physical changes. Time dependent‐ density functional theory (TD‐DFT) calculations were performed in order to demonstrate the electronic properties of APBT and ANBT and their anion. An easy‐to‐prepare test paper, obtained by dipping the paper into the solution of APBT, was able to detect BO3– in practical samples. Moreover, the utility of the APBT and ANBT probes in perborate recognition has also been demonstrated in Vero cells using Confocal imaging.

Differentially selective chemosensor with fluorescence off-on responses on Cu(2+) and Zn(2+) ions in aqueous media and applications in pyrophosphate sensing, live cell imaging, and cytotoxicity.

A new benzoyl hydrazone based chemosensor R is synthesized by Schiff base condensation of 2,6-diformyl-4-methylphenol and phenyl carbohydrazide and acts as a highly selective fluorescence sensor for Cu(2+) and Zn(2+) ions in aqueous media. The reaction of R with CuCl2 or ZnCl2 forms the corresponding dimeric dicopper(II) [Cu2(R)(CH3O)(NO3)]2(CH3O)2 (R-Cu(2+)) and dizinc(II) [Zn2(R)2](NO3)2 (R-Zn(2+)) complexes, which are characterized, as R, by conventional techniques including single-crystal X-ray analysis. Electronic absorption and fluorescence titration studies of R with different metal cations in a CH3CN/0.02 M HEPES buffer medium (pH = 7.3) show a highly selective binding affinity only toward Cu(2+)and Zn(2+) ions even in the presence of other commonly coexisting ions such as Na(+), K(+), Mg(2+), Ca(2+), Mn(2+), Fe(2+), Fe(3+), Co(2+), Ni(2+), Cd(2+), and Hg(2+). Quantification of the fluorescence titration analysis shows that the chemosensor R can indicate the presence of Cu(2+)and Zn(2+) even at very low concentrations of 17.3 and 16.5 ppb, respectively. R-Zn(2+) acts as a selective metal-based fluorescent sensor for inorganic pyrophosphate ion (PPi) even in the presence of other common anions such as F(-), Cl(-), Br(-), I(-), CH3COO(-), CO3(2-), HCO3(-), N3(-), SO4(2-), PPi, AMP, ADP, and ATP in an aqueous medium. The propensity of R as a bioimaging fluorescent probe to detect Cu(2+) and Zn(2+) ions in human cervical HeLa cancer cell lines and their cytotoxicity against human cervical (HeLa), breast cancer (MCF7), and noncancer breast epithelial (MCF10a) cells have also been investigated. R-Cu(2+) shows better cytotoxicity and sensitivity toward cancer cells over noncancer cells than R and R-Zn(2+) under identical conditions, with the appearance of apoptotic bodies.

Pyrophosphate Sensing by a Fluorescent Zn2+Bound Triazole Linked Imino-Thiophenyl Conjugate of Calix[4]arene in HEPES Buffer Medium: Spectroscopy, Microscopy, and Cellular Studies

An in situ prepared Zn(2+) complex of triazole linked imino-thiophenyl conjugate of calix[4]arene, [ZnL], was demonstrated to be highly fluorescent in HEPES buffer solution. [ZnL] has been used as a chemo-sensing ensemble for the recognition of phosphates in general and pyrophosphates in particular among the eighteen different anions studied. The chemo-sensing behavior of the [ZnL] has been demonstrated through fluorescence, absorption, visual fluorescent color changes, ESI MS, and (1)H NMR titrations. Variations in the microstructural features of L, its zinc complex and the complex upon addition of PPi have been demonstrated through atomic force microscopy and transmission electron microscopy. Such studies have been extended to see the permeability of the conjugate into the HeLa cells by fluorescence microscopy. In accession, a reversible "write-read-erase-read" logic gate property of L has been demonstrated through a feedback loop in the presence of Zn(2+) and PPi.

Imino–Phenolic–Pyridyl Conjugates of Calix[4]arene (L1 and L2) as Primary Fluorescence Switch-on Sensors for Zn2+ in Solution and in HeLa Cells and the Recognition of Pyrophosphate and ATP by [ZnL2

Pyridyl-based triazole-linked calix[4]arene conjugates, viz. L(1) and L(2), were synthesized and characterized. These two conjugates were shown to be selective and sensitive for Zn(2+) among the 12 metal ions studied in HEPES buffer medium by fluorescence, absorption, and visual color change with the detection limit of ~31 and ~112 ppb, respectively, by L(1) and L(2). Moreover, the utility of the conjugates L(1) and L(2) in showing the zinc recognition in live cells has also been demonstrated using HeLa cells as monitored by fluorescence imaging. The zinc complexes of L(1) and L(2) were isolated, and the structure of [ZnL(1)] has been established by single-crystal XRD and that of [ZnL(2)] by DFT calculations. TDDFT calculations were performed in order to demonstrate the electronic properties of receptors and their zinc complexes. The isolated zinc complexes, viz. [ZnL(1)] and [ZnL(2)], have been used as molecular tools for the recognition of anions on the basis of their binding affinities toward Zn(2+). [ZnL(2)] was found to be sensitive and selective toward phosphate-bearing ions and molecules and in particular to pyrophosphate (PPi) and ATP among the other 18 anions studied; however, [ZnL(1)] was not sensitive toward any of the anions studied. The selectivity has been shown on the basis of the changes observed in the emission and absorption spectral studies through the removal of Zn(2+) from [ZnL(2)] by PPi. Thus, [ZnL(2)] has been shown to detect PPi up to 278 ± 10 ppb at pH 7.4 in aqueous methanolic (1/2 v/v) HEPES buffer.

Spontaneous Changes in Mitochondrial Membrane Potential in Single Isolated Brain Mitochondria

In this study we measured ΔΨm in single isolated brain mitochondria using rhodamine 123. Mitochondria were attached to coverslips and superfused with K +-based HEPES-buffer medium supplemented with malate and glutamate. In ∼70% of energized mitochondria we observed large amplitude spontaneous fluctuations in ΔΨm with a time course comparable to that observed previously in mitochondria of intact cells. The other 30% of mitochondria maintained a stable ΔΨm. Some of the “stable” mitochondria began to fluctuate spontaneously during the recording period. However, none of the initially fluctuating mitochondria became stable. Upon the removal of substrates from the medium or application of small amounts of Ca 2+, rhodamine 123 fluorescence rapidly dropped to background values in fluctuating mitochondria, while nonfluctuating mitochondria depolarized with a delay and often began to fluctuate before complete depolarization. The changes in ΔΨm were not connected to oxidant production since reducing illumination or the addition of antioxidants had no effect on ΔΨm. Fluctuating mitochondria did not lose calcein, nor was there any effect of cyclosporin A on ΔΨm, which ruled out a contribution of permeability transition. We conclude that the fluctuations in ΔΨm reflect an intermediate, unstable state of mitochondria that may lead to or reflect mitochondrial dysfunction.

Thermally reversible VPBA–NIPAM copolymer gels for nucleotide adsorption

A thermosensitive gel matrix was prepared by free radical copolymerization of Nisopropylacrylamide (NIPAM) with a boronic acid-carrying monomer (i.e. 4-vinylphenylboronic acid, VPBA). The synthesis of the gel was performed at 70°C in an alcohol-water mixture, using azobisisobutyronitrile and methylenebisacrylamide as the initiator and the crosslinker, respectively. Toproduce thermosensitive gels with a higher diol-binding affinity, an amino-containing comonomer, N-[3-(dimethylamino)propyl]methacrylamide (DMAPM) was included in the gel formation recipe. Thermally reversible VPBA-NIPAM and VPBA-DMAPM-NIPAM gels with different swelling properties were obtained by changing the feed concentrations of VPBA and DMAPM. To test the usability of the produced gels as sorbents in nucleotide adsorption, β-nicotinamide adenine dinucleotide (β-NAD) was selected as a model biomolecule. Then the adsorption isotherm for β-NAD was obtained at +4°C in HEPES buffer medium with a pH of 8.5. The support material was in a highly swollen form under these conditions, due to its thermosensitive character. This property was then used to enhance β-NAD adsorption onto the gel matrix. Equilibrium adsorption capacities up to 70 mg β-NAD/g dry gel could be achieved with the thermosensitive support prepared with the 12.9 mol% VPBA feed. The gels produced with higher VPBA and DMAPM feed concentrations exhibited higher equilibrium adsorption capacities for β-NAD.