Physiological pH Values Research Articles

Human Serum Albumin Protein Corona in Prussian Blue Nanoparticles.

Prussian Blue nanoparticles (PBnps) are now popular in nanomedicine thanks to the FDA approval of PB. Despite the numerous papers suggesting or describing the in vivo use of PBnps, no studies have been carried out on the formation of a protein corona on the PBnp surface and its stabilizing role. In this paper, we studied qualitatively and quantitatively the corona formed by the most abundant protein of blood, human serum albumin (HSA). Cubic PBnps (41 nm side), prepared in citric acid solution at PB concentration 5 × 10-4 M, readily form a protein corona by redissolving ultracentrifuged PBnp pellets in HSA solutions, with CHSA ranging from 0.025 to 7.0 mg/mL. The basic decomposition of PBnp@HSA was studied in phosphate buffer at the physiological pH value of 7.4. Increased stability with respect to uncoated PBnps was observed at all concentrations, but a minimum CHSA value of 3.0 mg/mL was determined to obtain stability identical to that observed at serum-like HSA concentrations (35-50 mg/mL). Using a modified Lowry protocol, the quantity of firmly bound HSA in the protein corona (hard corona) was determined for all the CHSA used in the PBnp@HSA synthesis, finding increasing quantities with increasing CHSA. In particular, an HSA/PBnp number in the 1500-2300 range was found for CHSA 3.0-7.0 mg/mL, largely exceeding the 180 HSA/PBnp value calculated for an HSA monolayer on a PBnp. Finally, the stabilization brought by the HSA corona allowed us to carry out pH-spectrophotometric titrations on PBnp@HSA in the 3.5-9-0 pH range, revealing a pKa value of 6.68 for the water molecules bound to the Fe3+ centers on the PBnp surface, whose deprotonation is responsible for the blue-shift of the PBnp band from 706 nm (acidic solution) to 685 nm (basic solution).

Printing amphotericin B on microneedles using matrix-assisted pulsed laser evaporation.

Transdermal delivery of amphotericin B, a pharmacological agent with activity against fungi and parasitic protozoa, is a challenge since amphotericin B exhibits poor solubility in aqueous solutions at physiologic pH values. In this study, we have used a laser-based printing approach known as matrix-assisted pulsed laser evaporation to print amphotericin B on the surfaces of polyglycolic acid microneedles that were prepared using a combination of injection molding and drawing lithography. In a modified agar disk diffusion assay, the amphotericin B-loaded microneedles showed concentration-dependent activity against the yeast Candida albicans. The results of this study suggest that matrix-assisted pulsed laser evaporation may be used to print amphotericin B and other drugs that have complex solubility issues on the surfaces of microneedles.

Isothiocyanate-Corticosteroid Conjugates against asthma: Unity makes strength

Asthma is a major noncommunicable disease, affecting both children and adults, and represents one of the major causes leading to high health care costs due to the need for chronic pharmacological treatments. The standard gold therapy of inflammation in asthmatic patients involves the use of glucocorticoids even if their chronic use is often related to serious adverse effects. Growing evidence suggests the biological relevance of hydrogen sulfide (H2S) in the pathogenesis of airway diseases. Hence, aiming to associate the beneficial effects of steroidal anti-inflammatory drugs (SAIDs) to H2S biological activity, we designed and synthesized novel multi-target molecules by chemically combining a group of glucocorticoids, usually employed in asthma treatment, with an isothiocyanate moiety, well-known for its H2S releasing properties. Firstly, the synthesized compounds have been screened for their H2S-releasing profile using an amperometric approach and for their in vitro effects on the degranulation process, using RBL-2H3 cell line. The physicochemical profile, in terms of solubility, chemical and enzymatic stability of the newly hybrid molecules, has been assessed at different physiological pH values and in esterase-rich medium (bovine serum albumin, BSA). The selected compound 5c, through both its corticosteroid and H2S releasing component, has been evaluated in vivo in experimental model of asthma. The compound 5c inhibited in vivo all asthma features with a significative effect on the restoration of pulmonary structure and reduction of lung inflammation.

Synthesis, characterization, and biological study of new synthetic opioid hemorphin-4 peptides containing sterically restricted nonnatural amino acids.

Some new hemorphin-4 analogs with structures of Xxx-Pro-Trp-Thr-NH2 and Tyr-Yyy-Trp-Thr-NH2, where Xxx is 2-amino-3-(4-hydroxy-2,6-dimethylphenyl)propanoic acid or 2-amino-3-(4-dibenzylamino-2,6-dimethylphenyl)propanoic acid, and Yyy is (2S,4S)-4-amino-pyrrolidine-2-carboxylic acid, were synthesized and characterized by electrochemical and spectral analyses. In vivo anticonvulsant and antinociceptive activities of peptide derivatives were studied after intracerebroventricular injection in mice. The therapeutic effects of the modified peptides on seizures and pain in mice were evaluated to provide valuable insights into the potential applications of the novel compounds. Electrochemical characterization showed that the compounds behave as weak protolytes and that they are in a soluble, stable molecular form at physiological pH values. The antioxidant activityof the peptides was evaluated with voltammetric analyses, which were confirmed by applying the 2,2-Diphenyl-1-picrylhydrazyl method. The compounds showed satisfactory results regarding their structural stability, reaching the desired centers for the manifestation of biological activity without hydrolysis processes at 37°C and physiological pH. Dm-H4 and H4-P1 exhibited 100% and 83% potency to suppress the psychomotor seizures in the 6-Hz test compared to 67% activity of H4. Notably, only the H4-P1 had efficacy in blocking the tonic component in the maximal electroshock test with a potency comparable to H4. All investigated peptides containing unnatural conformationally restricted amino acids showed antinociceptive effects. The analogs Db-H4 and H4-P1 showed the most pronounced and long-lasting effect in both experimental models of pain induced by thermal and chemical stimuli. Dm-H4 produced a dose-dependent thermal antinociception and H4-P2 inhibited only formalin-induced pain behavior.

Strategic Structural Control of Polyserotonin Nanoparticles and Their Application as pH-Responsive Nanomotors.

Serotonin-based nanomaterials have been positioned as promising contenders for constructing multifunctional biomedical nanoplatforms due to notable biocompatibility, advantageous charge properties, and chemical adaptability. The elaborately designed structure and morphology are significant for their applications as functional carriers. In this study, we fabricated anisotropic bowl-like mesoporous polyserotonin (PST) nanoparticles with a diameter of approximately 170 nm through nano-emulsion polymerization, employing P123/F127 as a dual-soft template and 1,3,5-trimethylbenzene (TMB) as both pore expander and emulsion template. Their formation can be attributed to the synchronized assembly of P123/F127/TMB, along with the concurrent manifestation of anisotropic nucleation and growth on the TMB emulsion droplet surface. Meanwhile, the morphology of PST nanoparticles can be regulated from sphere- to bowl-like, with a particle size distribution ranging from 432 nm to 100 nm, experiencing a transformation from a dendritic, cylindrical open mesoporous structure to an approximately non-porous structure by altering the reaction parameters. The well-defined mesopores, intrinsic asymmetry, and pH-dependent charge reversal characteristics enable the as-prepared mesoporous bowl-like PST nanoparticles' potential for constructing responsive biomedical nanomotors through incorporating some catalytic functional materials, 3.5 nm CeO2 nanoenzymes, as a demonstration. The constructed nanomotors demonstrate remarkable autonomous movement capabilities under physiological H2O2 concentrations, even at an extremely low concentration of 0.05 mM, showcasing the 51.58 body length/s velocity. Furthermore, they can also respond to physiological pH values ranging from 4.4 to 7.4, exhibiting reduced mobility with increasing pH. This charge reversal-based responsive nanomotor design utilizing PST nanoparticles holds great promise for advancing the application of nanomotors within complex biological systems.

Polyamines (PAs) but not small peptides with closely spaced positively charged groups interact with DNA and RNA, but they do not represent a relevant buffer system at physiological pH values.

Polyamines (PAs) including putrescine (PUT), spermidine (SPD) and spermine (SPM) are small, versatile molecules with two or more positively charged amino groups. Despite their importance for almost all forms of life, their specific roles in molecular and cellular biology remain partly unknown. The molecular structures of PAs suggest two presumable biological functions: (i) as potential buffer systems and (ii) as interactants with poly-negatively charged molecules like nucleic acids. The present report focuses on the question, whether the molecular structures of PAs are essential for such functions, or whether other simple molecules like small peptides with closely spaced positively charged side chains might be suitable as well. Consequently, we created titration curves for PUT, SPD, and SPM, as well as for oligolysines like tri-, tetra-, and penta-lysine. None of the molecules provided substantial buffering capacity at physiological intracellular pH values. Apparently, the most important mechanism for intracellular pH homeostasis in neurons is not a buffer system but is provided by the actions of the sodium-hydrogen and the bicarbonate-chloride antiporters. In a similar approach we investigated the interaction with DNA by following the extinction at 260 nm when titrating DNA with the above molecules. Again, PUT and tri-lysine were not able to interact with herring sperm DNA, while SPD and SPM were. Obviously, the presence of several positively charged groups on its own is not sufficient for the interaction with nucleic acids. Instead, the precise spacing of these groups is necessary for biological activity.

PH responsive curcumin released from urea-amine group functionalized mesoporous organosilica nanoparticles.

Studies on natural products with anticancer properties have gained more importance in recent years in order to not damage healthy tissues during cancer treatments or to perform the treatment causing the least damage. Curcumin is a common natural product with anticancer properties, but its low solubility, instability, and bioavailability have limited its use in clinical applications in cancer research. As a proposed solution to this problem, a new mesoporous organosilica nanocarrier (MON-A) functionalized with a 1,2-diphenylethane-1,2-diamine structure capable of pH-controlled release was prepared in this study. MON-A was characterized by TGA, BET, XRD, FT-IR, and SEM-EDS analyses. Dispersion of MON-A into curcumin stock solution in ethanol afforded a curcumin-loaded MON-A-Cur system. Elevated loading capacity and pH-controlled release were provided by the Schiff base reaction that occurred during loading of curcumin with 1,2-diphenylethane-1,2-diamine placed on the silica wall of the nanocarrier system. The encapsulation efficiency was 25% for MON-A-Cur. In in vitro release experiments, curcumin release from the MON-A-Cur system was 0.5% at physiological and endosomal pH values. The resulting low release percentage indicates the presence of very strong interactions between the nanocarrier MON-A and curcumin. This strong interaction showed that MON-A nanocarrier could carry 99.5% of the curcumin without leakage under physiological and endosomal pH conditions without using pore capping agents. At a lower acidic pH value (pH 4.5), 26.3% curcumin release was obtained. These findings showed that the cumulative release of curcumin from the MON-A-Cur system can be achieved in a long-term and pH-controlled manner.

Easy-to-prepare graphene-based inkjet-printed electrodes for diclofenac electrochemical sensing

Inkjet-printed electrodes (IPEs) from flexible Kapton® as substrate and easy to prepare graphene oxide (GO)-based inks (K/GO) were prepared using a standard desktop printer. Subsequently, they were submitted to a post-processing thermal treatment (K/GO_TR400) and assessed as disposable working electrodes (WEs) for diclofenac (DCF) indirect electrochemical detection at pH 7.0 (close to physiological pH value). DCF monitoring is attracting much interest, due to its classification as contaminant of emerging concern in water sources. The performance of the printed active sensor material was compared to that of thermally reduced (at 400 °C) graphene oxide (TRGO-400, in a powder form), which has been successfully used as glassy carbon electrode (GCE) modifier for the detection of DCF. This electrode worked linearly within the concentration range between 5 and 25 μM with an LOD value of 2.25 μM. Moreover, the morphology and chemical composition of the obtained IPEs were characterized by means of scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) and compared with GCE/TRGO-400. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) measurements using a miniaturized 3-electrode cell of the post-processed IPEs showed a promising electrochemical performance for DCF sensing. Thus, this study demonstrated the effective partial recovery of the valuable properties of graphene on the IPEs after the thermal treatment and the successful production of flexible and disposable electrodes for target analyte detection. Therefore, this is a promising alternative to conventional modified GCEs, as it offers a facile approach for the fabrication of cutting edge graphene-based electrodes and widens the available portfolio of electrochemical sensors towards detection of water contaminants of emerging concern.

Kinetics of Flavonoid Degradation and Controlled Release from Functionalized Magnetic Nanoparticles.

Flavonoids are naturally occurring antioxidants that have been shown to protect cell membranes from oxidative stress and have a potential use in photodynamic cancer treatment. However, they degrade at physiological pH values, which is often neglected in drug release studies. Kinetic study of flavonoid oxidation can help to understand the mechanism of degradation and to correctly analyze flavonoid release data. Additionally, the incorporation of flavonoids into magnetic nanocarriers can be utilized to mitigate degradation and overcome their low solubility, while the release can be controlled using magnetic fields (MFs). An approach that combines alternating least squares (ALS) and multilinear regression to consider flavonoid autoxidation in release studies is presented. This approach can be used in general cases to account for the degradation of unstable drugs released from nanoparticles. The oxidation of quercetin, myricetin (MCE), and myricitrin (MCI) was studied in PBS buffer (pH = 7.4) using UV-vis spectrophotometry. ALS was used to determine the kinetic profiles and characteristic spectra, which were used to analyze UV-vis data of release from functionalized magnetic nanoparticles (MNPs). MNPs were selected for their unique magnetic properties, which can be exploited for both targeted drug delivery and control over the drug release. MNPs were prepared and characterized by X-ray diffraction, infrared spectroscopy, scanning electron microscopy, superconducting quantum interference device magnetometer, and electrophoretic mobility measurements. Autoxidation of all three flavonoids follows a two-step first-order kinetic model. MCE showed the fastest degradation, while the oxidation of MCI was the slowest. The flavonoids were successfully loaded into the prepared MNPs, and the drug release was described by the first-order and Korsmeyer-Peppas models. External MFs were utilized to control the release mechanism and the cumulative mass of the flavonoids released.

Molecular Interactions between a Flavonoid and Lysozyme: A Spectroscopic, Thermodynamic, and Computational Study

AbstractTransferulic acid has therapeutic importance hence it is very crucial to understand how this molecule interacts with lysozyme proteins for the purpose of drug design, and evaluation. The study is very helpful for drug pharmacology and the thermodynamic parameters of the polyphenolic compound and this protein interaction which is important for disease encounter and prevention. Here the spectroscopic, thermodynamic, and computational study has been reported as experiments. The CD study of the binding of lysozyme and trans ferulic acid found significant structural stability of the protein. Spectroscopically the UV‐Vis & fluorescence study has shown a substantial shift of absorption spectra in the binding of these two molecules, to confirm the interaction. An ITC experimental study found an affinity of the molecule to protein with a binding constant of Ka having a significant value. The Molecular Dynamics study found details of the geometric posture and main force of binding of TFA molecule upon binding with lysozyme site in PBS buffer at physiological pH value. The complex of lysozyme and trans ferulic acid also proved as a stable conformation by Molecular Dynamics study. In the DSC study, stable interaction of lysozyme and trans ferulic acid is shown upon changing the melting enthalpies and temperatures.

Interaction of Hoechst 33342 with POPC Membranes at Different pH Values.

Hoechst 33342 (H33342) is a fluorescent probe that is commonly used to stain the DNA of living cells. To do so, it needs to interact with and permeate through cell membranes, despite its high overall charge at physiological pH values. In this work, we address the effect of pH in the association of H33342 with lipid bilayers using a combined experimental and computational approach. The partition of H33342 to 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid membranes was experimentally quantified using fluorescence spectroscopy and isothermal titration calorimetry (ITC) measurements. Quantum chemical calculations were performed to select the most stable isomer of H33342 for the overall charges 0, +1, and +2, expected to predominate across the 5 < pH < 10 range. The interaction of these isomers with POPC bilayers was then studied by both unrestrained and umbrella sampling molecular dynamics (MD) simulations. Both experimental results and computational free energy profiles indicate that the partition coefficient of H33342 displays a small variation over a wide pH range, not exceeding one order of magnitude. The enthalpy variation upon partition to the membrane suggests efficient hydrogen bonding between the probe and the lipid, namely, for the protonated +2 form, which was confirmed in the MD simulation studies. The relatively high lipophilicity obtained for the charged species contrasts with the decrease in their general hydrophobicity as estimated from octanol/water partition. This highlights the distinction between lipophilicity and hydrophobicity, as well as the importance of considering the association with lipid bilayers when predicting the affinity for biomembranes.

Study of magnesium-sodium double phosphates ceramic for bone treatment

Ceramics based on magnesium-sodium double phosphate MgNaPO4 and magnesium-sodium double orthophosphate Mg4Na(PO4)3 were synthesized. The most suitable calcination temperatures were found as 800 °C for MgNaPO4 and 900 °C for Mg4Na(PO4)3. At higher sintering temperatures, crack formation was observed, which can be explained by the presence of polymorphic transformations and thermal decomposition of MgNaPO4. The crystal structures and lattice parameters for magnesium-sodium double phosphates were refined by using powder X-ray diffraction method. Obtained ceramic samples based on MgNaPO4 and Mg4Na(PO4)3 are characterized by pH values in aqueous solutions of 7.1 and 8.2, respectively, which are close values to physiological pH values. They also undergo resorption in a model environment, and may be promising in regenerative surgery.

Ex situ and in situ functionalized Yb/Fe nanoparticles obtained by scanning pulsed laser ablation in liquids: A route to obtain biofunctionalized multiplatform contrast agents for MRI and CT imaging

Two distinct strategies were used to improve the colloidal properties of hybrid Yb/Fe oxide NPs previously prepared by the pulsed liquid laser ablation process for use as a contrast agent in medical imaging.First, an exhaustive optimization process of the laser ablation synthesis parameters was carried out to reduce the hydrodynamic diameters of the Yb/Fe NPs. The hydrodynamic size was successfully reduced to <200 nm, thereby decreasing the polydispertivity index.Second, ex situ and in situ functionalization processes using glutathione, cysteamine, or polyethylenimine as capping agents have been developed to increase their colloidal stability at physiological pH values. Transmission electron microscopy, dynamic light scattering, Z-potential measurements, and Fourier Transform Infrared spectroscopy were used to examine the structure, morphology, colloidal and surface properties of Yb/Fe NPs.Colloidal stability of the Yb/Fe NPs as well as the linkage mechanism of functionalization have been studied extensively. This last parameter provides a critical information for subsequently bioconjugations in biomedical applications. Additionally, the biocompatibility of the Yb/Fe NPs was evaluated by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) experiments. These results indicate more appropriate colloidal characteristics and higher biocompatibility for ex situ-functionalized Yb/Fe NPs, especially when the capping agent is glutathione. Additionally, these Yb/Fe NPs show good magnetic resonance imaging and X-ray computerized tomography imaging abilities, thereby indicating promising potential as dual contrast agents.

Highly Sensitive Physiological Sensor Based on Tapered Fiber-Optic Interferometer for Sweat pH Detection

The pH value of human sweat correlates with metabolic activities and diseases. Precise sweat pH sensing can serve as a health-profiling strategy. This study demonstrates a compact fiber-optic sweat pH sensor that contains an optimized conical structure coated with polyelectrolyte membrane as the pH sensitive layer. To functionalize the tapered sensing area for pH monitoring, chitosan/polyacrylic acid (PAA) polyelectrolytes are deposited as pH-sensitive membranes. As the swelling degree of the sensing film depends on the pH value, the tapered fiber-optic sensor based on the Mach-Zehnder interferometer (MZI) demonstrates the corresponding wavelength shift to various pH values in sweat. The fiber-optic sensor presents a high pH sensitivity of -27.06nm/pH in the physiological sweat pH value ranging from 5.0 to 7.5 with a low temperature cross-sensitivity of 0.012 nm/°C in the normal physiological range of 25-45°C. Further, the pH sensing range can be extended to pH 10 in aqueous solutions, and the sensitivity is 28.44nm/pH. Considering the advantages including wide sensing range, simple fabrication technique, and high sensitivity, the sensor can be potentially applied in many other liquid physiological detections for healthcare monitoring.

Physicochemical and Anti-fungal Studies of the Pharmaceutical Co-crystal/Salt of Fluconazole.

Crystal engineering is one green alternative to organic synthesis that can be used to manipulate molecular behavior promptly and economically. We report the preparation and characterization of the pharmaceutical organic salt (FLC-C) of fluconazole (FLC) and organosulfonate (NDSA-2H), based on the sulfonate-pyridinium supramolecular synthon. Structural studies validate the crystallization of the two-component stoichiometric crystal with two molecules of water in the triclinic P1̅ space group. The anticipated proton transfer between the crystal forms leads to ionic interactions, augmenting the organic salt's thermal stability. Hirshfeld studies of FLC-C help to understand the role and significance of different types of intermolecular interactions responsible for crystal packing. The structural and theoretical studies indicate the absence of π-π interactions in FLC-C, which account for the incipience of solid-state emission in the product. The solubility studies establish augmented aqueous solubility of FLC-C over pristine FLC at physiological pH values of 2 and 7. Interestingly, in in vitro studies, FLC-C appears to serve as a potential alternative to FLC, displaying a wide spectrum of antifungal activity. FLC-C is active against several human pathogenic yeast strains, including the leading and emerging Candida strains (Candida albicans and Candida auris, respectively), at comparable and/or lower drug concentrations without showing any enhanced host cell toxicity. Interestingly, the pharmaceutical co-crystal also displays fluorescence properties inside the Candida cells.

Optogenetic cytosol acidification of mammalian cells using an inward proton-pumping rhodopsin

Ion gradients are a universal form of energy, information storage and conversion in living cells. Advances in optogenetics inspire the development of novel tools towards control of different cellular processes with light. Rhodopsins are perspective tools for optogenetic manipulation of ion gradients in cells and subcellular compartments, controlling pH of the cytosol and intracellular organelles. The key step of the development of new optogenetic tools is evaluation of their efficiency. Here, we used a high-throughput quantitative method for comparing efficiency of proton-pumping rhodopsins in Escherichia coli cells. This approach allowed us to show that an inward proton pump xenorhodopsin from Nanosalina sp. (NsXeR) is a powerful tool for optogenetic control of pH of mammalian subcellular compartments. Further, we demonstrate that NsXeR can be used for fast optogenetic acidification of the cytosol of mammalian cells. This is the first evidence of optogenetic cytosol acidification by an inward proton pump at physiological pH values. Our approach offers unique opportunities to study cellular metabolism at normal and pathological conditions and might help to understand the role of pH dysregulation in cellular dysfunctions.

Features of complex formation of native and polymeric β-cyclodextrins with sulfasalazine

The work is devoted to the study of the complex formation of sulfasalazine with native and polymeric β-cyclodextrins in buffer solutions with a physiological pH value using isothermal saturation and 1H NMR methods. It was established that sulfasalazine forms two types of complexes when interacting with the cyclodextrins under consideration, but only the process of formation of inclusion complexes determines the observed increase in drug solubility, which is more pronounced in the presence of polymeric β-cyclodextrin. It was determined that complexation with β-cyclodextrin and its polymeric derivative leads to a decrease in the permeability coefficients of sulfasalazine through the model membrane, which is determined by both the stability constant of the complexes and their ability to pass through the membrane.

CH vs. HC-Promiscuous Metal Sponges in Antimicrobial Peptides and Metallophores.

Histidine and cysteine residues, with their imidazole and thiol moieties that deprotonate at approximately physiological pH values, are primary binding sites for Zn(II), Ni(II) and Fe(II) ions and are thus ubiquitous both in peptidic metallophores and in antimicrobial peptides that may use nutritional immunity as a way to limit pathogenicity during infection. We focus on metal complex solution equilibria of model sequences encompassing Cys-His and His-Cys motifs, showing that the position of histidine and cysteine residues in the sequence has a crucial impact on its coordination properties. CH and HC motifs occur as many as 411 times in the antimicrobial peptide database, while similar CC and HH regions are found 348 and 94 times, respectively. Complex stabilities increase in the series Fe(II) < Ni(II) < Zn(II), with Zn(II) complexes dominating at physiological pH, and Ni(II) ones-above pH 9. The stabilities of Zn(II) complexes with Ac-ACHA-NH2 and Ac-AHCA-NH2 are comparable, and a similar tendency is observed for Fe(II), while in the case of Ni(II), the order of Cys and His does matter-complexes in which the metal is anchored on the third Cys (Ac-AHCA-NH2) are thermodynamically stronger than those where Cys is in position two (Ac-ACHA-NH2) at basic pH, at which point amides start to take part in the binding. Cysteine residues are much better Zn(II)-anchoring sites than histidines; Zn(II) clearly prefers the Cys-Cys type of ligands to Cys-His and His-Cys ones. In the case of His- and Cys-containing peptides, non-binding residues may have an impact on the stability of Ni(II) complexes, most likely protecting the central Ni(II) atom from interacting with solvent molecules.

Electrochemical evaluation and determination of antiretroviral drug ganciclovir based on Fe-Cu/TiO2/ multi-walled carbon nanotubes sensor

Cyclic voltammetry, differential pulse voltammetry (DPV), and chronoamperometry were employed in this study to examine the ganciclovir’s electrochemical behavior on the surface of the modified electrode Fe-Cu/TiO2/multi-walled carbon nanotubes/carbon paste (Fe-Cu/TiO2/MWCNTs/CPE). As such, our proposed sensor proved to be stable while presenting a high sensitivity for the analysis of GCV under the physiological pH value (pH 7.4). Meanwhile, the calibration plots remained linear in the concentration, whose ranges were 25 nM to 40 µM (R2 = 0.996, n = 21) by DPV technique and 0.1 nM to 40 nM (R2 = 0.991, n = 9) through the hydrodynamic amperometry in stirred solutions under optimized conditions. A detection limit of 0.02 nM was obtained while the RSD prove to be 2.3% for six replicate detections of 10 μM GCV. To conclude, the recommended sensor ended up with great sensitivity and selectivity to determine GCV in real samples.

PH-dependent redox properties of epigallocatechin gallate (EGCG) and its effect on respiration, photosynthesis and cell death in pea

The redox properties of the green tea component epigallocatechin gallate (EGCG) in vitro were studied and its effect on plant (pea) cells was tested. EGCG exhibited both pro- and antioxidant properties. In solutions, EGCG was oxidized by oxygen at physiological (slightly alkaline) pH values. Lowering the pH slowed down this process. Oxidation of EGCG was accompanied by the formation of O2-• and H2O2. In addition, EGCG functioned as an electron donor for peroxidase and, in combination with it, utilized H2O2. Exposure of EGCG to pea cells (leaf cuts or epidermis) suppressed respiration, reduced the transmembrane electric potential difference (Δψ) in mitochondria, and inhibited electron transfer in the photosynthetic electron transfer chain. Among the sites of the photosynthetic redox chain, Photosystem II was the least sensitive to the action of EGCG. EGCG reduced the rate of formation of reactive oxygen species in the epidermis, which was induced by NADH treatment and was registered using 2′,7′-dichlorofluorescine diacetate. In vivo, EGCG at concentrations from 10 µM to 1 mM suppressed KCN-induced death of guard cells in the epidermis, which was determined from the destruction of cell nuclei. EGCG at a concentration of 10 mM disrupted the barrier function of the guard cell plasma membrane, increasing its permeability to propidium iodide.