Membrane potential is a fundamental property of biological cells. Changes in membrane potential characterize a vast number of vital biological processes, such as the activity of neurons and ...cardiomyocytes, tumorogenesis, cell-cycle progression, etc. A common strategy to record membrane potential changes that occur in the process of interest is to utilize organic dyes or genetically-encoded voltage indicators with voltage-dependent fluorescence. Sensors are introduced into target cells, and alterations of fluorescence intensity are recorded with optical methods. Techniques that allow recording relative changes of membrane potential and do not take into account fluorescence alterations due to factors other than membrane voltage are already widely used in modern biological and biomedical studies. Such techniques have been reviewed previously in many works. However, in order to investigate a number of processes, especially long-term processes, the measured signal must be corrected to exclude the contribution from voltage-independent factors or even absolute values of cell membrane potential have to be evaluated. Techniques that enable such measurements are the subject of this review.
Controlling oxygen content in the primary circuit of nuclear reactors is one of the key tasks needed to ensure the safe operation of nuclear power plants where lead-bismuth eutectic alloy (LBE) is ...used as a coolant. If the oxygen concentration is low, active corrosion of structural materials takes place; upon increase in oxygen content, slag accumulates due to the formation of lead oxide. The generally accepted method of measuring the oxygen content in LBE is currently potentiometry. The sensors for measuring oxygen activity (electrochemical oxygen sensors) are galvanic cells with two electrodes (lead-bismuth coolant serves as working electrode) separated by a solid electrolyte. Control of corrosion and slag accumulation processes in circuits exploring LBE as a coolant is also based on data obtained by electrochemical oxygen sensors. The disadvantages of this approach are the low efficiency and low sensitivity of control. The alternative, Impedance Spectroscopy (EIS) Sensors, are proposed for Real-Time Corrosion Monitoring in LBE system. Currently their applicability in static LBE at temperatures up to 600 °C is shown.
Quantum mechanics/molecular mechanics (QM/MM) models are a widely used tool to obtain detailed insight into the properties and functioning of proteins. The outcome of QM/MM studies heavily depends on ...the quality of the applied QM/MM model. Prediction and right placement of internal water molecules in protein cavities is one of the critical parts of any QM/MM model construction. Herein, we performed a systematic study of four protein hydration algorithms. We tested these algorithms for their ability to predict X-ray-resolved water molecules for a set of membrane photosensitive rhodopsin proteins, as well as the influence of the applied water placement algorithms on the QM/MM calculated absorption maxima (
λ
max
) of these proteins. We used 49 rhodopsins and their intermediates with available X-ray structures as the test set. We found that a proper choice of hydration algorithms and setups is needed to predict functionally important water molecules in the chromophore-binding cavity of rhodopsins, such as the water cluster in the N-H region of bacteriorhodopsin or two water molecules in the binding pocket of bovine visual rhodopsin. The QM/MM calculated
λ
max
of rhodopsins is also quite sensitive to the applied protein hydration protocols. The best methodology allows obtaining an 18.0 nm average value for the absolute deviation of the calculated
λ
max
from the experimental
λ
max
. Although the major effect of water molecules on
λ
max
originates from the water molecules located in the binding pocket, the water molecules outside the binding pocket also affect the calculated
λ
max
mainly by causing a reorganization of the protein structure. The results reported in this study can be used for the evaluation and further development of hydration methodologies, in general, and rhodopsin QM/MM models, in particular.
Accurate prediction of water molecules in protein cavities is an important factor for obtaining high-quality rhodopsin QM/MM models.
In this work, three series of micro-sized heterometallic europium-containing terephthalate MOFs, (Eu1-xLnx)2bdc3·nH2O (Ln = La, Gd, Lu), are synthesized via an ultrasound-assisted method in an ...aqueous medium. La3+ and Gd3+-doped terephthalates are isostructural to Eu2bdc3·4H2O. Lu3+-doped compounds are isostructural to Eu2bdc3·4H2O with Lu contents lower than 95 at.%. The compounds that are isostructural to Lu2bdc3·2.5H2O are formed at higher Lu3+ concentrations for the (Eu1-xLux)2bdc3·nH2O series. All materials consist of micrometer-sized particles. The particle shape is determined by the crystalline phase. All the synthesized samples demonstrate an “antenna” effect: a bright-red emission corresponding to the 5D0-7FJ transitions of Eu3+ ions is observed upon 310 nm excitation into the singlet electronic excited state of terephthalate ions. The fine structure of the emission spectra is determined by the crystalline phase due to the different local symmetries of the Eu3+ ions in the different kinds of crystalline structures. The photoluminescence quantum yield and 5D0 excited state lifetime of Eu3+ are equal to 11 ± 2% and 0.44 ± 0.01 ms, respectively, for the Ln2bdc3·4H2O structures. For the (Eu1-xLux)2bdc3·2.5H2O compounds, significant increases in the photoluminescence quantum yield and 5D0 excited state lifetime of Eu3+ are observed, reaching 23% and 1.62 ms, respectively.
In this work, we proposed a rapid single-stage laser-induced fabrication of bimetallic micropatterns on the oxide glass surface using deep eutectic solvents (DESs) consisting of choline chloride, ...citric acid along with nickel, copper and cobalt acetates as metallization solutions. The resulting bimetallic micropatterns were tested as working electrodes for non-enzymatic determination of dopamine. The linear range for dopamine detection was found to be 1–500 µM, with sensitivity of 340.4 µA mM
− 1
and 615.2 µA mM
− 1
and detection limit of 0.36 µM and 0.51 µM for Ni-Cu and Ni-Co sensor, respectively. For the first time, bimetallic Ni-Cu and Ni-Co structures have been obtained from DESs for high-performance dopamine detection with great potential for further application in non-enzymatic sensing and biosensing.
The conversion of metal-organic frameworks (MOFs) into advanced functional materials offers a promising route for producing unique nanomaterials. MOF-derived systems have the potential to overcome ...the drawbacks of MOFs, such as low electrical conductivity and poor structural stability, which have hindered their real-world applications in certain cases. In this study, laser scribing was used for pyrolysis of a Cu-based MOF (Cu4{1,4-C6H4(COO)2}3(4,4′-bipy)2n) to synthesize a Cu-CuO@C composite on the surface of a screen-printed electrode (SPE). Scanning electron microscopy, X-ray diffractometry, and Energy-dispersive X-ray spectroscopy were used for the investigation of the morphology and composition of the fabricated electrodes. The electrochemical properties of Cu-CuO@C/SPE were studied by cyclic voltammetry and differential pulse voltammetry. The proposed flexible electrochemical Cu-CuO@C/SPE sensor for the simultaneous detection of hydroquinone and catechol exhibited good sensitivity, broad linear range (1–500 μM), and low limits of detection (0.39 μM for HQ and 0.056 μM for CT).
Azobenzene/tetraethyl ammonium photochromic ligands (ATPLs) are photoactive compounds with a large variety of photopharmacological applications such as nociception control or vision restoration. ...Absorption band maximum and lifetime of the less stable isomer are important characteristics that determine the applicability of ATPLs. Substituents allow to adjust these characteristics in a range limited by the azobenzene/tetraethyl ammonium scaffold. The aim of the current study is to find the scope and limitations for the design of ATPLs with specific spectral and kinetic properties by introducing para substituents with different electronic effects. To perform this task we synthesized ATPLs with various electron acceptor and electron donor functional groups and studied their spectral and kinetic properties using flash photolysis and conventional spectroscopy techniques as well as quantum chemical modeling. As a result, we obtained diagrams that describe correlations between spectral and kinetic properties of ATPLs (absorption maxima of
and
isomers of ATPLs, the thermal lifetime of their
form) and both the electronic effect of substituents described by Hammett constants and structural parameters obtained from quantum chemical calculations. The provided results can be used for the design of ATPLs with properties that are optimal for photopharmacological applications.
A new series of luminescent heterometallic europium(III)–lutetium(III) terephthalate metal–organic frameworks, namely (EuxLu1−x)2bdc3·nH2O, was synthesized using a direct reaction in a water ...solution. At the Eu3+ concentration of 1–40 at %, the MOFs were formed as a binary mixture of the (EuxLu1−x)2bdc3 and (EuxLu1−x)2bdc3·4H2O crystalline phases, where the Ln2bdc3·4H2O crystalline phase was enriched by europium(III) ions. At an Eu3+ concentration of more than 40 at %, only one crystalline phase was formed: (EuxLu1−x)2bdc3·4H2O. All MOFs containing Eu3+ exhibited sensitization of bright Eu3+-centered luminescence upon the 280 nm excitation into a 1ππ* excited state of the terephthalate ion. The fine structure of the emission spectra of Eu3+ 5D0-7FJ (J = 0–4) significantly depended on the Eu3+ concentration. The luminescence quantum yield of Eu3+ was significantly larger for Eu-Lu terephthalates containing a low concentration of Eu3+ due to the absence of Eu-Eu energy migration and the presence of the Ln2bdc3 crystalline phase with a significantly smaller nonradiative decay rate compared to the Ln2bdc3·4H2O.
Luminescent, heterometallic terbium(III)–lutetium(III) terephthalate metal-organic frameworks (MOFs) were synthesized via direct reaction between aqueous solutions of disodium terephthalate and ...nitrates of corresponding lanthanides by using two methods: synthesis from diluted and concentrated solutions. For (TbxLu1−x)2bdc3·nH2O MOFs (bdc = 1,4-benzenedicarboxylate) containing more than 30 at. % of Tb3+, only one crystalline phase was formed: Ln2bdc3·4H2O. At lower Tb3+ concentrations, MOFs crystallized as the mixture of Ln2bdc3·4H2O and Ln2bdc3·10H2O (diluted solutions) or Ln2bdc3 (concentrated solutions). All synthesized samples that contained Tb3+ ions demonstrated bright green luminescence upon excitation into the 1ππ* excited state of terephthalate ions. The photoluminescence quantum yields (PLQY) of the compounds corresponding to the Ln2bdc3 crystalline phase were significantly larger than for Ln2bdc3·4H2O and Ln2bdc3·10H2O phases due to absence of quenching from water molecules possessing high-energy O-H vibrational modes. One of the synthesized materials, namely, (Tb0.1Lu0.9)2bdc3·1.4H2O, had one of the highest PLQY among Tb-based MOFs, 95%.
The synthesis of conductive gold and copper-gold microstructures with high developed surface based on the method of laser-induced metal deposition from solution was developed. The topology and ...crystallization phase of these structures were observed by means of scanning electron microscopy and X-ray diffraction, respectively. The electrochemical properties of the synthesized materials were investigated using cyclic voltamperometry and amperometry. According to the obtained results, it was found out that copper-gold microstructures demonstrate a linear dependence of Faraday current vs. concentration from 0.025 to 5µM for D-glucose and from 0.025 to 10µM for hydrogen peroxide. In turn, gold deposit exhibits a linear dependence of Faraday current vs. concentration from 0.025 to 50µM for D-glucose and from 0.025 to 1µM for hydrogen peroxide. Moreover, the synthesized materials reveal low detection limits (0.025µM) with respect to the aforementioned analytes, which is quite promising for their potential application in design and fabrication of new non-enzymatic biosensors.
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•The method for synthesis of copper-gold and gold microelectrodes was proposed.•The produced conductive metal structures have highly developed surface area.•These structures reveal high selectivity towards D-glucose and hydrogen peroxide.•Copper-gold and gold electrodes exhibit rather good reproducibility and stability.
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