The coupled photocycle of phenyl-p-benzoquinone and Light-Harvesting Complex II (LHCII) within the biohybrid system.

The combination of trimeric form of the light-harvesting complex II (LHCII3), a porous graphite electrode (GE), and the application of phenyl-p-benzoquinone (PPBQ), the quinone derivative, allow the construction of a new type of biohybrid photoactive system. The Chl fluorescence decay and voltammetric analyzes revealed that PPBQ impacts LHCII3 proportionally to accessible quenching sites and that PPBQ forms redox complexes with Chl in both ground and excited states. As a result, photocurrent generation is directly dependent on PPBQ-induced quenching of Chl fluorescence. Since PPBQ also undergoes photoactivation, the action of GE-LHCII3-PPBQ depends on the mutual coupling of LHCII3 and PPBQ photocycles. The GE-LHCII3-PPBQ generates a photocurrent of up to 4.5 µA and exhibits considerable stability during operation. The three-dimensional arrangement of graphite scraps in GE builds an active electrode surface and stabilizes LHCII3 in its native form in low-density multilayers. The results indicate the future usability of such designed photoactive device.

Recommendation on an updated standardization of serum magnesium reference ranges.

PURPOSE: Serum magnesium is the most frequently used laboratory test for evaluating clinical magnesium status. Hypomagnesemia (low magnesium status), which is associated with many chronic diseases, is diagnosed using the serum magnesium reference range. Currently, no international consensus for a magnesemia normal range exists. Two independent groups designated 0.85 mmol/L (2.07 mg/dL; 1.7 mEq/L) as the low cut-off point defining hypomagnesemia. MaGNet discussions revealed differences in serum magnesium reference ranges used by members' hospitals and laboratories, presenting an urgent need for standardization. METHODS: We gathered and compared serum magnesium reference range values from our institutions, hospitals, and colleagues worldwide. RESULTS: Serum magnesium levels designating "hypomagnesemia" differ widely. Of 43 collected values, only 2 met 0.85 mmol/L as the low cut-off point to define hypomagnesemia. The remainder had lower cut-off values, which may underestimate hypomagnesemia diagnosis in hospital, clinical, and research assessments. Current serum magnesium reference ranges stem from "normal" populations, which unknowingly include persons with chronic latent magnesium deficit (CLMD). Serum magnesium levels of patients with CLMD fall within widely used "normal" ranges, but their magnesium status is too low for long-term health. The lower serum magnesium reference (0.85 mmol/L) proposed specifically prevents the inclusion of patients with CLMD. CONCLUSIONS: Widely varying serum magnesium reference ranges render our use of this important medical tool imprecise, minimizing impacts of low magnesium status or hypomagnesemia as a marker of disease risk. To appropriately diagnose, increase awareness of, and manage magnesium status, it is critical to standardize lower reference values for serum magnesium at 0.85 mmol/L (2.07 mg/dL; 1.7 mEq/L).

Magnesium Deficiency Alters Expression of Genes Critical for Muscle Magnesium Homeostasis and Physiology in Mice.

Chronic Mg2+ deficiency is the underlying cause of a broad range of health dysfunctions. As 25% of body Mg2+ is located in the skeletal muscle, Mg2+ transport and homeostasis systems (MgTHs) in the muscle are critical for whole-body Mg2+ homeostasis. In the present study, we assessed whether Mg2+ deficiency alters muscle fiber characteristics and major pathways regulating muscle physiology. C57BL/6J mice received either a control, mildly, or severely Mg2+-deficient diet (0.1%; 0.01%; and 0.003% Mg2+ wt/wt, respectively) for 14 days. Mg2+ deficiency slightly decreased body weight gain and muscle Mg2+ concentrations but was not associated with detectable variations in gastrocnemius muscle weight, fiber morphometry, and capillarization. Nonetheless, muscles exhibited decreased expression of several MgTHs (MagT1, CNNM2, CNNM4, and TRPM6). Moreover, TaqMan low-density array (TLDA) analyses further revealed that, before the emergence of major muscle dysfunctions, even a mild Mg2+ deficiency was sufficient to alter the expression of genes critical for muscle physiology, including energy metabolism, muscle regeneration, proteostasis, mitochondrial dynamics, and excitation-contraction coupling.

Electrochemical characterization of LHCII on graphite electrodes - Potential-dependent photoactivation and arrangement of complexes.

Light-dependent electrochemical properties of the light harvesting complexes of Photosystem II (LHCII) and the corresponding interactions with screen-printed graphite electrodes (GEs) are determined. No exogenous soluble redox mediators are used. LHCII isolated from spinach leaves are immobilized on GE by physical adsorption and through interactions with glutaraldehyde. Importantly, the insertion of LHCII into the pores of a GE is achieved by subjecting the electrode to specific potentials. Both trimeric and aggregated forms of LHCII located within the graphite layer retain their native structures. Voltammetric current peaks centred at ca. -230 and + 50 mV vs. Ag/AgCl (+94 and + 374 mV vs. NHE) limit the investigation of the reduction and oxidation processes of immobilized LHCII. An anodic photocurrent is generated in the LHCII-GE proportional to light intensity and can reach a value of 150 nA/cm2. Light-dependent charge separation in LHCII followed by electron transfer to the GE occurs only at potentials of above -200 mV vs. Ag/AgCl (+124 mV vs. NHE). Our results illustrate the importance of the structural proximity of LHCII and GE for photocurrent generation.

Ionized magnesium in plasma and erythrocytes for the assessment of low magnesium status in alcohol dependent patients.

BACKGROUND: Studies on the homeostasis of magnesium in alcohol-dependent patients have often been characterized by low hypomagnesemia detection rates. This may be due to the fact that the content of magnesium in blood serum constitutes only 1% of the average magnesium level within the human body. However, the concentration of ionized magnesium is more physiologically important and makes up 67% of the total magnesium within a human organism. There are no data concerning the determination of the ionized fraction of magnesium in patients addicted to alcohol and its influence on mental health status. METHODS: This study included 100 alcohol-dependent patients and 50 healthy subjects. The free magnesium fraction was determined using the potentiometric method by means of using ion-selective electrodes. The total magnesium level was determined by using a biochemical Indiko Plus analyzer. In this study, different psychometric scales were applied. RESULTS: Our results confirm the usefulness of ionized magnesium concentrations in erythrocytes and plasma as a diagnostic parameter of low magnesium status in alcohol-dependent patients. CONCLUSIONS: The lower the concentration of ionized magnesium, the worse the quality of life an alcohol-dependent person might experience. In the case of total magnesium, no such correlation was determined.

Supercoiled and linear plasmid DNAs interactions with methylene blue.

Slow accumulation of plasmids from their diluted, pg/mL solutions (pH 4.7) on a well defined glassy carbon (GC) electrode surface allowed for the formation of stable electrode layers consisting of two types of plasmid DNAs - pUC19 and pGEX-4T-2, in two forms - supercoiled circular (sc) and linear (lin). In the presence of methylene blue (MB), a typical redox indicator, the oxidation signals of nucleic acid bases are significantly enhanced. The interactions of the plasmids with MB are tested and used to distinguish between various types of plasmids. Instead of an MB reduction signal at ca. -0.2V vs. SCE, typically used to study MB interactions with DNAs, we have used the corresponding oxidation signal at ca. -0.2V, MB(I), as well as another oxidation signal at 1.05 V, MB(III). On a bare GC electrode, the MB(III) and MB(I) signals are proportional to each other, while in the presence of the plasmid DNAs the relations between MB(III) and MB(I) depend on the type of plasmid. The plots: MB(III)/MB(I) vs. [MB] and MB(I) potential shift vs. [MB] are used to distinguish between the supercoiled and linear forms of the pUC19 and pGEX-4T-2 plasmids.

Selectivity coefficients of ion-selective magnesium electrodes used for simultaneous determination of magnesium and calcium ions.

Membrane ion-selective magnesium electrodes are commonly used to determine ionized magnesium concentration in blood serum and intracellular fluid by potentiometric clinical analyzers. The selectivity of these electrodes against calcium ion is typically insufficient to avoid calcium interference in blood serum analysis. For this reason the selectivity coefficient for calcium ion has to be studied to make possible any mathematical corrections for calcium ion influence. Existing methods relate to the thermodynamic concept of ISE response which suggest a single constant value of the selectivity coefficient and slope that are stable over the concentration ranges of calcium and magnesium ions in the samples. Unfortunately, this rarely happens, and we rather observe dependences on solution and membrane composition, readout time, matrices (anticoagulant, vial coats) that justify usage of apparent selectivities and slopes. To get the practical insight into the response of magnesium ion-selective electrodes a novel method for estimating the selectivity coefficients and the slope of the electrode characteristics is proposed. This method is an effective starting point for selecting electrodes and designing transient signal software in a potentiometric clinical analyzer. The method allows obtaining the ionized magnesium concentration in blood serum with minimal possible error by addressing the assessed targets, i.e. apparent selectivity and slope. The method is based on computer simulation and on the Nicolsky-Eisenman equation. Usually only a few iterations are needed to obtain stable congruent results. The method presented is particularly useful in conditions where is not possible to obtain calibration curve, which is typical for clinical analyzer where at most three point calibration is performed.

Biomimetic study of the Ca(2+)-Mg2+ and K(+)-Li+ antagonism on biologically active sites: new methodology to study potential dependent ion exchange.

Competitive divalent (magnesium and calcium) or monovalent (potassium, lithium and sodium) ion exchange and its influence on a membrane potential formation was studied at biological ligands (BL) such as adenosine triphosphate (ATP), asparagine (Asn) and glutamine (Gln) sites. The sites are dispersed electrochemically in membranes made of the conducting polymers (CPs)--poly(N-methylpyrrole) (PMPy) and poly(pyrrole) (PPy). The membranes are made sensitive to calcium and magnesium or to potassium, sodium and lithium by optimized electrodeposition and soaking procedures supported by the study of membrane topography and morphology. Distinctively different electrochemical responses, i.e. electrical potential transients or currents, are observed in the case of "antagonistic" calcium and magnesium or potassium and sodium/lithium ion pairs. Dissimilarity in the responses is ascribed to a difference between on site vs. bulk concentrations of ions, and is dictated by different transport properties of the ions, as shown by using the Nernst-Planck-Poisson (NPP) model and the diffusion-layer model (DLM). The method described allows inspecting potential-dependent competitive ion-exchange processes at the biologically active sites. It is suggested that this approach could be used as an auxiliary tool in study of potential dependent block in realistic membrane channels, such as Mg block in the N-methyl D-aspartate receptor channel (NMDA).

Time-dependent phenomena in the potential response of ion-selective electrodes treated by the Nernst-Planck-Poisson model. 1. Intramembrane processes and selectivity.

The variability of selectivity coefficients, resulting from potential changes over time and the concentration ratio of primary to interfering ions, impedes many practical applications of ion-selective electrodes (ISEs). Existing theoretical interpretations of ISE selectivity are restricted by severe assumptions, such as steady state and electroneutrality, which hinder theorizing on this problem. For this reason, for the first time, the Nernst-Planck-Poisson equations are used to predict and visualize the selectivity variability over time and the concentration ratio. Special emphasis is placed on the non-Nernstian response in the measurements with liquid-ion-exchanger- and neutral-carrier-based ISEs. The conditions under which measured selectivity coefficients are true (unbiased) are demonstrated.

Ion-selective electrode for measuring low Ca2+ concentrations in the presence of high K+, Na+ and Mg2+ background.

In this work, ion-selective electrodes for calcium ion were investigated. Two ionophores were used in the membranes: ETH 1001 and ETH 129. An internal filling solution buffered for primary ion was used that allowed the lower detection limit to be decreased down to 10(-8.8) M. Theoretical and experimental electrode characteristics pertaining to both primary and interfering ions are discussed. Better behavior was obtained with the electrode prepared with ETH 129 in the membrane. This electrode would be the most likely candidate for obtaining a low Ca(2+) detection limit in measurements performed with high K(+), Na(+), Mg(2+) background, which is found inside the cells of living organisms, for example. The potentiometric response of the electrode in solutions containing main and interfering ions is in good agreement with simulated curves obtained using the Nernst-Planck-Poisson (NPP) model.

DNA-based electrochemical biosensors for monitoring of bis-indoles as potential antitumoral agents, chemistry, X-ray crystallography.

Facile and practical electrochemical DNA bioassay, X-ray diffraction analysis, synthesis and 1H and 13C NMR data of the 5,5'-disubstituted-3,3'-methanediyl-bis-indoles are reported. On the basis of electrochemical measurements we have hypothesized that the analyzed bis-indoles have an effect on human tumor cells due to DNA binding at adenine-thymidine deoxynucleotides rich region in a concentration/substituent dependent manner. Interesting N-H...pi and hydrogen-bonding intermolecular interactions were observed which may differentiate their biological features. The 5,5'-dimethoxy-3,3'-methanediyl-bis-indole (2) was found to reduce considerably the growth of cancer cell lines HOP-92 (lung), A498 (renal) and MDA-MB-231/1TCC (breast). The results indicate that title compounds could be interesting as potential antitumoral chemotherapeutics.

Factors affecting the potentiometric response of all-solid-state solvent polymeric membrane calcium-selective electrode for low-level measurements.

An all-solid-state calcium-selective electrode was constructed with poly(pyrrole) solid-contact doped with calcium complexing ligand Tiron. The potentiometric response of this sensor can have a linear range down to 10(-)(9) M with a slope close to Nernstian and detection limit equal to 10(-)(9.6). The effects of pH and the activity of the interfering ion in the conditioning solution on the potentiometric behavior of the constructed sensors were examined. Potential stability, reproducibility, and impedance studies were performed. The selectivity of the constructed electrode is better than that of the conventional calcium-selective electrode with internal filling solution of 10(-)(2) M CaCl(2) and comparable to that of the best liquid-contact electrodes.

Ionized magnesium in erythrocytes--the best magnesium parameter to observe hypo- or hypermagnesemia.

BACKGROUND: Almost 99% of the body magnesium is inside cells. The concentration of intracellular ionized magnesium (iMg) is physiologically relevant. iMg in erythrocytes is a new parameter that can help to establish reliable information on the functional magnesium status. METHODS: iMg concentration in erythrocytes and serum was measured by ion-selective electrode, in clinical analyzer Microlyte (KONE). Total magnesium (tMg) concentration was measured by atomic absorption spectrometry (AAS). Albumin and total protein concentration were measured colorimetrically. RESULTS: In critically ill postoperative patients, the mean of albumin, protein and hematocrit concentration was significantly lower compared to healthy individuals. Hypomagnesemia was found in 15.9% patients as tMgs, at 22.2% as iMgs and 36.5% as iMge. Significant correlations are between iMgs and tMgs or iMge and iMgs/tMgs. In dialyzed patients, the mean of hematocrit was significantly lower, iMge was significantly higher compared with healthy individuals. Significant negative correlations are between iMgs and tMge or iMge/tMge and tMge. CONCLUSIONS: iMge is the best magnesium parameter to observe hypo- or hypermagnesemia for both groups of patients. The function of magnesium is mainly intracellular and intracellular magnesium concentrations can be the method to evaluate the magnesium status.

Improving the detection limit of anion-selective electrodes: an iodide-selective membrane with a nanomolar detection limit.

The lower detection limit and the selectivity behavior of anion-selective electrodes (ISEs) are improved by using optimized inner solutions and membrane compositions. With a membrane based on the recently described ionophore [9]mercuracarborand-3, a detection limit of 2 x 10(-9) M has been achieved for iodide. Nevertheless, the improvements are less pronounced than in the case of cation ISEs. This is mainly due to the fact that so far no anion ISE is known with the extremely high selectivities of cation ISEs. If the membrane does not contain an ionophore, leaching of the ion exchanger from the membrane into the sample is also a relevant limiting factor except for ion exchangers of very high lipophilicity.

All-solid-state calcium solvent polymeric membrane electrode for low-level concentration measurements.

An all-solid-state calcium-selective electrode with a plastic membrane phase containing a calcium ionophore ETH-1001 placed on poly(3-methylthiophene) ion-to-electron transducting layer functionalized to bind calcium cations has been constructed. The obtained potentiometric sensors were characterized with a calibration line of slope close to Nernstian within the activity from 10(-5) to 0.1 M. For Ca2+ activity lower than 10(-5) M, super-Nernstian behavior was observed. The super-Nernstian response that is observed for electrodes with an internal solution strongly binding primary ions was in this case attributed to incorporation of calcium ions in the modified solid-contact phase. With this arrangement, the evaluation of selectivity coefficients much closer to those that depend on the properties of the ion-selective membrane itself was possible.

Carbonate ion-selective electrode with reduced interference from salicylate.

A carbonate ion-selective electrode for determination of total carbon dioxide species such as carbon dioxide, bicarbonate and carbonate with reduced interference from salicylate is described. Derivatives of trifluoroacetophenone were used as neutral carriers for carbonate. A polymer-free liquid carbonate-selective membrane with a cellophane outer membrane was found to give a carbonate-selective electrode with a negligible response to salicylate. The electrical contact was obtained by insertion of a silver/silver chloride electrode directly into the liquid membrane. The electrode does not require any aqueous filling solution and is therefore maintenance-free. The response to carbon dioxide species was found to be highly reproducible with a response time of 1-2 min at total carbon dioxide concentrations in the range from 5 to 50 mM. The lifetime of the electrode was at least 3 months. The electrode is regarded as very promising for clinical analysis of carbon dioxide species in body fluids such as plasma and serum.

Comparison of the potentiometric, (31)P NMR, and zero-point titration methods of determining ionized magnesium in erythrocytes.

A simple and rapid method of determining ionized magnesium in erythrocytes using a potentiometric clinical analyzer, Microlyte 6 (Kone, Finland), was investigated. The erythrocyte cell membranes were destroyed using ultrasound. The results were compared with those obtained with the (31)P nuclear magnetic resonance spectroscopy method and the zero-point titration method using atomic absorption spectrometry. The results obtained from potentiometry and from the other methods did not differ significantly (Student t test, alpha = 0.01). Total magnesium concentration was determined using atomic absorption spectrometry.