Possible conformational change within the desolvated and cationized sBBI/trypsin non-covalent complex during the collision-induced dissociation process

Electrospray ionization mass spectrometry (ESI-MS) has become an analytical technique widely used for the investigation of non-covalent protein-protein and protein-ligand complexes due to the soft desolvation conditions that preserve the stoichiometry of the interacting partners. Dissociation studies of solvated or desolvated complexes (in the source and in the collision cell, respectively) allow access to information on protein conformation and localization of the metal ions involved in protein structure stabilization and biological activity. The complex of bovine trypsin and small soybean Bowman-Birk inhibitor (sBBI) was studied by ESI-MS to determine changes occurring within the complex during its transfer from droplets to the gas phase independently of the ion polarity. Under collision-induced dissociation (CID) conditions, unexpected binding of the Ca(2+) ion (cofactor of native trypsin) to the inhibitor molecule was observed within the desolvated sBBI/trypsin/Ca(2+) complex (with a 1:1:1 stoichiometry). This formal gas-phase migration of the calcium ion from trypsin to the inhibitor may be related to conformational rearrangements in the solvent-free and likely collapsed complex. However, under conditions leading to the increase in complex charge state, the appearance of the cationized trypsin molecule was detected during complex dissociation, thus reflecting different pathways of the evolution of complex conformation.     

Thermochemical characterization of chicken litter and peat as a source for energy recovery

The shortage of raw materials and the environmental problems due to pollution require development of new green technologies utilizing some wastes and transforming them to secondary raw materials. The aim of this work is to study the properties of poultry waste to propose possibilities to minimizing the released emissions and avoiding the risk for human health and the environment. At the same time, two types of low grade peats with different origin are studied as components for the production of soil conditioners. During the studies, we applied the inductively coupled plasma (ICP) and chemical analysis, powder X-ray diffraction, thermal analysis, IR spectroscopy, and scanning electron microscopy for determining the composition, crystal phase, the shape and size of particles, and thermal stability of the investigated samples. The chemical and the phase compositions of the studied samples confirmed that the content of nutrient compounds and of the carbon substances is suitable as an effective secondary raw material for soil conditioners. It is found that the poultry wastes and peat samples have a similar phase and chemical composition and contain an organic mass in the form of carbon components with amorphous, fibrous, and skeleton-like structure, suitable to be combined with other nutrient-containing compounds. During the thermal treatment, the carbon compounds are oxidized releasing heat. Based on that the materials under study are considered as environmentally friendly fuels, releasing relatively low emissions.     

Thermodynamics of oxygen in CaMnO3 − δ

The experimental data for equilibrium oxygen content were used in order to extract increments of partial molar thermodynamic functions of oxygen with changes of oxygen stoichiometry in calcium manganite CaMnO_3???δ . It is shown that along with the oxygen exchange reaction, thermal excitation of Mn⁴⁺ cations plays an important role in equilibration of charged manganese species that appear in response to the loss of oxygen at heating. The interrelation of partial molar enthalpy and entropy of oxygen with electron and ion defect formation parameters is obtained in approximation of the point defect model. The nearly linear changes of oxygen partial molar enthalpy are shown to directly reflect thermally driven changes in concentration of Mn³⁺ cations.     

Electron transport in CaMnO3 − δ at elevated temperatures: a mobility analysis

The drift mobility of electron charge carriers in oxygen non-stoichiometric manganite CaMnO_3???δ was calculated by combining the total electrical conductivity and oxygen non-stoichiometry data at 700–950 °С and oxygen partial pressure varying between 10^?6 and 1 atm. The carrier concentration changes with pressure and temperature were obtained with the help of the earlier-developed defect model involving reactions of oxygen exchange and thermal excitation of manganese sites. The activation energy for mobility is found to increase with oxygen non-stoichiometry. High-temperature electron transport properties of the manganite CaMnO_3???δ can be explained in terms of activated jumps of n-type small polarons in adiabatic regime. The relatively small mobility of charge carriers is explained by strong localization of polarons on manganese sites.     

Studies on the Structure and Properties of Membrane Phospholipase A1 Inclusion Bodies Formed at Low Growth Temperatures Using GFP Fusion Strategy

The effect of cultivation temperatures (37, 26, and 18 °C) on the conformational quality of Yersinia pseudotuberculosis phospholipase A₁ (PldA) in inclusion bodies (IBs) was studied using green fluorescent protein (GFP) as a folding reporter. GFP was fused to the C-terminus of PldA to form the PldA-GFP chimeric protein. It was found that the maximum level of fluorescence and expression of the chimeric protein is observed in cells grown at 18 °C, while at 37 °C no formation of fluorescently active forms of PldA-GFP occurs. The size, stability in denaturant solutions, and enzymatic and biological activity of PldA-GFP IBs expressed at 18 °C, as well as the secondary structure and arrangement of protein molecules inside the IBs, were studied. Solubilization of the chimeric protein from IBs in urea and SDS is accompanied by its denaturation. The obtained data show the structural heterogeneity of PldA-GFP IBs. It can be assumed that compactly packed, properly folded, proteolytic resistant, and structurally less organized, susceptible to proteolysis polypeptides can coexist in PldA-GFP IBs. The use of GFP as a fusion partner improves the conformational quality of PldA, but negatively affects its enzymatic activity. The PldA-GFP IBs are not toxic to eukaryotic cells and have the property to penetrate neuroblastoma cells. Data presented in the work show that the GFP-marker can be useful not only as target protein folding indicator, but also as a tool for studying the molecular organization of IBs, their morphology, and localization in E. coli, as well as for visualization of IBs interactions with eukaryotic cells.     

Dramatic Effect of A Ring Size of Alicyclic α-Dioximate Ligand Synthons on Kinetics of the Template Synthesis and of the Acidic Decomposition of the Methylboron-Capped Iron(II) Clathrochelates

Kinetics and thermodynamics of the template synthesis and of the acidic decomposition of the methylboron-capped iron(II) tris-1,2-dioximates—the clathrochelate derivatives of six (nioxime)- and eight (octoxime)-membered alicyclic ligand synthons—were compared. In the case of a macrobicyclic iron(II) tris-nioximate, the plausible pathway of its formation contains a rate-determining stage and includes a reversible formation of an almost trigonal-antiprismatic (TAP) protonated tris-complex, followed by its monodeprotonation and addition of CH₃B(OH)₂. Thus, the formed TAP intermediate undergoes a multistep rate-determining stage of double cyclization with the elimination of two water molecules accompanied by a structural rearrangement, thus giving an almost trigonal-prismatic (TP) iron(FII) semiclathrochelate. It easily undergoes a cross-linking with CH₃B(OH)₂, resulting in the elimination of H⁺ ion and in the formation of a macrobicyclic structure. In contrast, the analogous scheme for its macrobicyclic tris-octoximate analog was found to contain up to three initial stages affecting the overall synthesis reaction rate. The rates of acidic decomposition of the above clathrochelates were found to be also affected by the nature of their ribbed substituents. Therefore, the single crystal XRD experiments were performed in order to explain these results. The difference in the kinetic schemes of a formation of the boron-capped iron(II) tris-nioximates and tris-octoximates is explained by necessity of the substantial changes in a geometry of the latter ligand synthon, caused by its coordination to the iron(II) ion, due to both the higher distortion of the FeN₆-coordination polyhedra, and the intramolecular sterical clashes in the molecules of the macrobicyclic iron(II) tris-octoximates.     

Chlorine dioxide oxidation of dihydronicotinamide adenine dinucleotide (NADH)

The oxidation of dihydronicotinamide adenine dinucleotide (NADH) by chlorine dioxide in phosphate buffered solutions (pH 6-8) is very rapid with a second-order rate constant of 3.9 x 10(6) M(-1) s(-1) at 24.6 degrees C. The overall reaction stoichiometry is 2ClO2(*) per NADH. In contrast to many oxidants where NADH reacts by hydride transfer, the proposed mechanism is a rate-limiting transfer of an electron from NADH to ClO2(*). Subsequent sequential fast reactions with H(+) transfer to H2O and transfer of an electron to a second ClO2(*) give 2ClO2(-), H3O(+), and NAD(+) as products. The electrode potential of 0.936 V for the ClO2(*)/ClO2(-) couple is so large that even 0.1 M of added ClO2(-) (a 10(3) excess over the initial ClO2(*) concentration) fails to suppress the reaction rate.     

Simultaneous separation of inorganic anions and metal-citrate complexes on a zwitterionic stationary phase with on-column complexation

The retention and separation selectivity of inorganic anions and on-column derivatised negatively charged citrate or oxalate metal complexes on reversed-phase stationary phases dynamically coated with N-(dodecyl-N,N-dimethylammonio)undecanoate (DDMAU) has been investigated. The retention mechanism for the metal-citrate complexes was predominantly anion exchange, although the amphoteric/zwitterionic nature of the stationary phase coating undoubtedly also contributed to the unusual separation selectivity shown. A mixture of 10 inorganic anions and metal cations was achieved using a 20 cm monolithic DDMAU modified column and a 1 mM citrate eluent, pH 4.0, flow rate equal to 0.8 mL/min. Selectivity was found to be strongly pH dependent, allowing additional scope for manipulation of solute retention, and thus application to complex samples. This is illustrated with the analysis of an acidic mine drainage sample with a range of inorganic anions and transition metal cations, varying significantly in their concentrations levels.     

Selectivity of solid-contact Ag potentiometric sensors based on thiacalix[4]arene derivatives

Potentiometric sensors based on glassy carbon electrode covered with polyaniline and thiacalix[4]arenes containing amidopyridine, morpholide, pyrrolidide and hydrazide functional groups in cone, partial cone and 1,3-alternate conformations have been developed and applied for determination of Ag(+) ions in the range from 1.0 x 10(-2) to 4.0 x 10(-7)M and limits of detection from 1 x 10(-7) to 3.5 x 10(-8)M. The sensitivity of Ag(+) detection decreases in the following range of thiacalix[4]arene substituents: morpholide>pyrrolidide>amidopyridine>hydrazide. Potentiometric selectivity coefficients predominantly showed binding of Ag(+), Hg(II) and Fe(III) ions over other transient and alkali metals. The influence of functional groups and conformation of receptor on the selectivity of the sensor response was investigated. As shown, selectivity and sensitivity of Ag(+) determination depends on the steric accessibility of the binding site and flexibility of the receptor structure. For Fe(III) ions, changes of the sensor potential are also determined by their implementation in redox reactions of polyaniline.