Convenient Agarose Preparation with Hydrogen Peroxide and Desulfation Process Analysis

Agarose is a natural seaweed polysaccharide and widely used in the medicine, food, and biological fields because of its high gel strength, non-toxicity, and electrical neutrality. The sulfate group is one of the main charged groups that affect the performance of agarose. In the present study, a simple, eco-friendly, and efficient method was explored for agarose preparation. After desulfation with hydrogen peroxide (H2O2), the sulfate content of agar reached 0.21%. Together with gel strength, electroendosmosis, gelling and melting temperature, the indicators of desulfated agar met the standards of commercially available agarose. Notably, the desulfated agar can be used as an agarose gel electrophoresis medium to separate DNA molecules, and the separation effect is as good as that of commercially available agarose. Further, the H2O2 desulfation process was analyzed. The addition of a hydroxyl radical (HO•) scavenger remarkably decreased the H2O2 desulfation rate, indicating that HO• has a certain role in agar desulfation. Sulfate content detection indicated that sulfur was removed from agar molecules in the form of sulfate ions (SO42−) and metal sulfate. The band absence at 850 cm−1 indicated that the sulfate groups at C-4 of D-galactose in sulfated galactan were eliminated.

The application of logarithmic charts when evaluating the equilibrium concentrations of all particles in acid-base systems

Until recently, due to the absence of other suitable approaches, equilibrium concentrations in acid-base systems have been studied exclusively by measuring the pH of a solution. However, this method can not be used for organic (non-aqueous) solvent solutions. It is known that the ionic strength of a solution, which is a fundamental component in assessing the activity coefficient and the thermodynamic dissociation constant of an electrolyte, is influenced by the ions present in the system. The concentration of these ions is variable during interactions in aqueous and more complex non-aqueous solutions, which differ significantly in their physicochemical properties (boiling temperature, structure, permittivity, autoprotolysis constant, solvating ability, dipole moment, viscosity, etc.). Meanwhile, in order to obtain more objective and valid estimates of acid-base interactions, in addition to the activity of hydrogen ions, appropriate account should be taken of the equilibrium concentrations of all particles in the solution, which affect its ionic strength. In this article, on the basis of the law of mass action and equations describing equilibrium processes, the ionic product of a solvent, electrical neutrality and material balance in a solution, the corresponding equations were derived and a method was proposed for considering the effect of the concentrations of all particles in the system (not only hydrogen ions – pH), significantly affecting the properties of acid-base equilibrium systems. The proposed method can also be used to obtain the dependence of the equilibrium concentrations of all process substances on the state of the medium (test solution), determined by various chemical and instrumental methods in logarithmic coordinates, which makes it pos-sible to directly assess the equilibrium concentra- tions of all particles present in the system.

Intracellular pH Regulation and the Acid Delusion

The concentration H+ ([H+]) in intracellular fluid (ICF) must be maintained in a narrow range in all species for normal protein functions. Thus, mechanisms regulating ICF are of fundamental biological importance. Studies on the regulation of ICF [H+] have been hampered by use of pH notation,failure to consider the roles played by differences in the concentration of strong ions ( SID), the conservation of mass, the principle of electrical neutrality and that [H+] and [HCO3-] are dependent variables. This argument is based on the late Peter Stewart’s physical- chemical analysis of [H+] regulation reported in this journal nearly forty years ago. We start by outlining the principles of Stewart’s analysis and then provide a general understanding of its significance for regulation of ICF [H+]. The system may initially appear complex, but it becomes evident that changes in SID dominanate regulation of [H+]. The primary strong ions are Na+, K+ and Cl-, and a few organic strong anions. The second independent variable, PCO2, can easily be assessed. The third independent variable, the activity of intracellular weak acids ([Atot]), is much more complex but largely plays a modifying role. Attention to these principles potentially will provide new insights into ICF pH regulation.

Synthesis, crystal structure determination of a novel phosphate Ag1.64Zn1.64Fe1.36(PO4)3 with an alluaudite-like structure

Single crystals of Ag1.64Zn1.64Fe1.36(PO4)3 [silver zinc iron phosphate (1.64/1.64/1.36/3)] have been synthesized by a conventional solid-state reaction and structurally characterized by single-crystal X-ray diffraction. The title compound crystallizes with an alluaudite-like structure. All atoms of the structure are in general positions except for four, which reside on special positions of the space group, C2/c. The Ag+ cations reside at full occupancy on inversion centre sites and at partial occupancy (64%) on a twofold rotation axis. In this structure, the unique Fe3+ ion with one of the two Zn2+ cations are substitutionally disordered on the same general position (Wyckoff site 8f), with a respective ratio of 0.68/0.32 (occupancies were fixed so as to ensure electrical neutrality for the whole structure). The remaining O and P atoms are located in general positions. The three-dimensional framework of this structure consists of kinked chains of edge-sharing octahedra stacked parallel to [10\overline{1}]. These chains are built up by a succession of [MO6] (M = Zn/Fe or Zn) units. Adjacent chains are connected by the PO4 anions, forming sheets oriented perpendicular to [010]. These interconnected sheets generate two types of channels parallel to the c axis, in which the Ag+ cations are located. The validity and adequacy of the proposed structural model of Ag1.64Zn1.64Fe1.36(PO4)3 was established by means of bond-valence-sum (BVS) and charge-distribution (CHARDI) analysis tools.

Electronic Structure Calculations in Electrolyte Solutions: Methods for Neutralization of Extended Charged Interfaces

Density functional theory (DFT) is often used for simulating extended materials such as infinite crystals or surfaces, under periodic boundary conditions (PBCs). In such calculations, when the simulation cell has non-zero charge, electrical neutrality has to be imposed and this is often done via a uniform background charge of opposite sign (`jellium'). This artificial neutralization does not occur in reality, where a different mechanism is followed as in the example of a charged electrode in electrolyte solution, where surrounding electrolyte screens the local charge at the interface. The neutralizing effect of surrounding electrolyte can be incorporated within a hybrid quantum-continuum model based on a modified Poisson-Boltzmann equation, where the concentrations of electrolyte ions are modified to achieve electroneutrality. Among the infinite possible ways of modifying the electrolyte charge, we propose here a physically optimal solution which minimizes the deviation of concentrations of electrolyte ions from those in open boundary conditions (OBCs). This principle of correspondence of PBCs with OBCs leads to the correct concentration profiles of electrolyte ions and electroneutrality within the simulation cell and in the bulk electrolyte is maintained simultaneously, as observed in experiments. This approach, which we call the Neutralization by Electrolyte Concentration Shift (NECS), is implemented in our electrolyte model in the ONETEP linear-scaling DFT code which makes use of a bespoke highly parallel Poisson-Boltzmann solver, DL_MG. We further propose another neutralization scheme (`accessible jellium') which is a simplification of NECS. We demonstrate and compare the different neutralization schemes on several examples.

Electronic Structure Calculations in Electrolyte Solutions: Methods for Neutralization of Extended Charged Interfaces

Density functional theory (DFT) is often used for simulating extended materials such as infinite crystals or surfaces, under periodic boundary conditions (PBCs). In such calculations, when the simulation cell has non-zero charge, electrical neutrality has to be imposed and this is often done via a uniform background charge of opposite sign (`jellium'). This artificial neutralization does not occur in reality, where a different mechanism is followed as in the example of a charged electrode in electrolyte solution, where surrounding electrolyte screens the local charge at the interface. The neutralizing effect of surrounding electrolyte can be incorporated within a hybrid quantum-continuum model based on a modified Poisson-Boltzmann equation, where the concentrations of electrolyte ions are modified to achieve electroneutrality. Among the infinite possible ways of modifying the electrolyte charge, we propose here a physically optimal solution which minimizes the deviation of concentrations of electrolyte ions from those in open boundary conditions (OBCs). This principle of correspondence of PBCs with OBCs leads to the correct concentration profiles of electrolyte ions and electroneutrality within the simulation cell and in the bulk electrolyte is maintained simultaneously, as observed in experiments. This approach, which we call the Neutralization by Electrolyte Concentration Shift (NECS), is implemented in our electrolyte model in the ONETEP linear-scaling DFT code which makes use of a bespoke highly parallel Poisson-Boltzmann solver, DL_MG. We further propose another neutralization scheme (`accessible jellium') which is a simplification of NECS. We demonstrate and compare the different neutralization schemes on several examples.

Structural Variations Induced by Temperature Changes in Rotavirus VP6 Protein Immersed in an Electric Field and Their Effects on Epitopes of The Region 300-396

Rotavirus diarrhea is an infectious intestinal disease that causes about 215 thousand deaths annually in infants under five years old. This virus is formed by three layers of concentric proteins that envelop its genome, from which VP6 structural protein is the most conserved among rotavirus serotypes and an excellent vaccine candidate. Recent studies have shown that structural proteins are susceptible to losing their biological function when their conformation is modified by moderate temperature increments, and in the case of VP6, its antigen efficiency decreases. We performed an in silicoanalysis to identify the structural variations in the epitopes 301-315, 357-366, and 376-384 of the rotavirus VP6 protein -in a hydrated medium- when the temperature is increased from 310 K to 322 K. In the latter state, we applied an electric field equivalent to a low energy laser pulse and calculated the fluctuations per amino acid residue. We identified that the region 301-315 has greater flexibility and density of negative electrical charge; nevertheless, at 322 K it experiences a sudden change of secondary structure that could decrease its efficiency as an antigenic determinant. The applied electric field induces electrical neutrality in the region 357-366, whereas in 376-384 inverts the charge, implying that temperature changes in the range 310 K-322 K are a factor that promotes thermoelectric effects in the VP6 protein epitopes in the region 300-396.

Nonionic Low-Osmolar Monomeric Iodinated Contrast Material: Some Aspects of use for Computed Tomography in Children

Iodine containing contrast media are used much frequently now-a-days for computed tomography examinations in children. The group of non-ionic monomers occupies a special place among modern contrast agents. Low osmolarity and viscosity, electrical neutrality and the highest iodine content of these contrast materials provide the best diagnostic efficacy with minimum risk of adverse reactions. However, characteristic anatomic and physiological aspects of a growing child’s body require additional attention and care during diagnostic procedures with use of such contrast agents. This article presents concise literature review of recent years highlighting practical aspects of nonionic lowosmolar iodinated contrast material use for computed tomography assisted diagnostic examinations in child population.

Heliospheric modulation of cosmic rays: model and observation

This paper presents the basic model of cosmic ray modulation in the heliosphere, developed in Yu.G. Shafer Institute of Cosmophysical Research and Aeronomy of the Siberian Branch of RAS. The model has only one free modulation parameter: the ratio of the regular magnetic field to the turbulent one. It may also be applied to the description of cosmic ray intensity variations in a wide energy range from 100 MeV to 100 GeV. Possible mechanisms of generation of the mentioned turbulence field are considered. The primary assumption about the electrical neutrality of the heliosphere appears to be wrong, and the zero potential needed to match the model with observations in the plane of the solar equator can be achieved if the frontal point of the heliosphere, which is flowed around by interstellar gas, lies near the mentioned plane. We have revealed that the abnormal rise of cosmic ray intensity at the end of solar cycle 23 is related to the residual modulation produced by the subsonic solar wind behind the front of a standing shock wave. The model is used to describe features of cosmic ray intensity variations in several solar activity cycles.