Role of the linker region in the expression of <Emphasis Type="Italic">Rhizopus oryzae</Emphasis> glucoamylase

Background  

Rhizopus oryzaeglucoamylase (RoGA) consists of three domains: an amino (N)-terminal raw starch-binding domain (SBD), a glycosylated linker domain, and a carboxy (C)-terminal catalytic domain. The 36-amino-acid linker region (residues 132–167) connects the two functional domains, but its structural and functional roles are unclear.     

Solvation effect in the thermal decomposition of 2,2′‐azoisobutyronitrile in the three‐component system

The thermal decomposition rate constant (k_d ) of 2,2′‐azoisobutyronitrile in acrylonitrile (AN; monomer A)–methyl methacrylate (MM; monomer B) comonomer mixtures in N,N‐dimethylformamide (DMF) as a function of the comonomer mixture composition and its concentration in the solvent at 60 °C was studied. The dependences k_d = f(x_A ,C) [x_A (mole fraction of A in the comonomer mixture) = A/(A + B) = A/C, where C is the comonomer mixture concentration] have a different course as a function of C: from a curve k_d = f(x_A ) approaching the straight line (C = 2 mol · dm⁻³) to a convex curve possessing a maximum at a point x_A = 0.7 (C = 4 mol · dm⁻³) to a curve with a flattened wide maximum within the range of x_A = 0.2–0.8 (C = 7 mol · dm⁻³) to a curve with the shape of a lying s (C = 9 mol · dm⁻³). All the courses of the experimental dependences k_d = f(x_A ,C) can be explained with a hypothesis of initiator solvation by the comonomers AN and MM and the solvent DMF. The existing solvated forms, their relative stability constants, the thermal decomposition rate constants, and the relative contents in the system were determined. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2156–2166, 2000     

Effect of the Structure of Pyridine Ligands and the Substituent in the Carboxylate Anion on the Geometry of Transition Metal Complexes [M<Subscript>2</Subscript>(O<Subscript>2</Subscript>CR)<Subscript>4</Subscript>L<Subscript>2</Subscript>]

A series of binuclear tetracarboxylate-linked Mn(II), Fe(II), Co(II), Ni(II), and Cu(II) complexes with 1,2-substituted pyridine, viz., 2,3-cyclododecenopyridine (L), were prepared. Study of the crystal structures of isolated compounds (CIF file CCDC nos. 1575855–1575859) revealed a distortion of the {Ni₂(O₂CR)₄L₂} binuclear moiety, manifested as a change in the NiNiN angle (151.67°), in the bridging function of two out of the four carboxylate groups (from μ_2- to (κ²,μ_2-)), and in the coordination environment of the metal ion (NiO₅N). The results were analyzed in comparison with known data. The magnetic properties of copper(II) and nickel(II) complexes were studied. The copper(II) complex is diamagnetic as a result of strong exchange interactions between the unpaired electrons; in the nickel(II) complex antiferromagnetic exchange interactions were detected (J_Ni–Ni =–25 cm^–1).     

Chalcone epoxide inter­mediates in the syntheses of lignin‐related phenyl­coumarans

Compounds (2R*,3S*)‐1‐(3,4‐dimethoxy­phen­yl)‐3‐{3‐meth­oxy‐2‐[(2R*)‐tetra­hydro­pyran‐2‐yl­oxy]phen­yl}‐2,3‐ep­oxy‐1‐propanone, C₂₃H₂₆O₇, (I), and trans‐1‐(3,4‐dimethoxy­phen­yl)‐3‐[3‐meth­oxy‐2‐(methoxy­methoxy)­phen­yl]‐2,3‐ep­oxy‐1‐propanone, C₂₀H₂₂O₇, (II), were obtained on epoxidation of chalcones. The stereochemistries of (I) and (II) were elucidated. In both compounds, the substituents on the oxirane ring are trans‐oriented. Compound (I) was obtained together with a diastereometric form that differs from (I) with respect to the configuration of the asymmetric C atom in the tetra­hydro­pyran group. The geometries of the substituted oxirane rings of (I) and (II) are very similar. The hydrogen‐bonding patterns, mediated via weak C—H⋯O inter­actions, differ considerably. The crystal structures of (I) and (II) are compared with those of related chalcone epoxides. The conversion of (I) and (II) into lignin‐related phenyl­coumarans is discussed.     

Determination of Cobalt in the Form of an Ion Associate in Vitamin B<Subscript>12</Subscript>

The possibility of application of the ion-associated complex formed between the anionic chelate cobalt(II)-4-(2-thiazolylazo) resorcinol (TAR) with the cation of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) for extraction-spectrophotometric determination of cobalt in the form of an ion associate in Vitamin B₁₂ was studied. The liquid–liquid extraction system Co(II)-TAR-MTT-H₂O-CHCl₃ was applied. This system was chosen by our previous research of the ion associates of the cobalt by spectrophotometric investigation of fourteen different liquid–liquid extraction systems, containing azo derivatives of resorcinol (TAR or 4-(2-pyridylazo) resorcinol (PAR)) and mono or ditetrazolium salts. Based on the obtained results, a sensitive, relatively simple, convenient and inexpensive method for determination of cobalt in the form of an ion associate in Vitamin B₁₂ was developed. The proposed method can be implemented for biological, medical and pharmaceutical samples containing cobalamin (Vitamin B₁₂).     

Three‐body molecular states of the system in the Born–Oppenheimer approximation

In this work, we present a quantum mechanical treatment of the three‐body molecular system in the Born–Oppenheimer (BO) approximation, were the nuclei dynamics is evaluated over the potential energy surfaces (PES) induced by the electronic states. The PES corresponding to the two lowest electronic levels are the ones described by Martinazzo et al. (Chem. Phys. 2003, 287, 335), and are used to write the three‐body Schrdinger equation of the three atomic system. We use the generalized Sturmian functions method to expand the wave functions in each (distinguishable) pair of relative coordinates or Jacobi pairs, and analyze the convergence differences between the series. A partial‐wave decomposition of the potential is proposed to simplify the Hamiltonian matrix element calculation. Bound states are considered for the ground and first excited electronic PES, the spreading of energies after sudden electronic transitions studied, and the break‐up probability induced by the sudden change of the PES evidenced.     

Study of the thermal evolution of the cyclic‐oligomer formation in a cyclic‐oligomer‐free PET

A low percentage of cyclic oligomers can be found in poly(ethylene terephthalate) (PET) from its synthesis onward. In this article, a cyclic‐oligomer‐free PET (COFP) obtained by solvent extraction was used to study the thermodynamics of the re‐formation of cyclics from the melt. The cyclic‐oligomer content re‐increased into molten COFP, finally reaching an equilibrium. An analysis of the fraction of the re‐formed cyclic oligomers showed that a majority of cyclic trimer (60–70%) was found at the equilibrium. Before the establishment of the equilibrium, an unusual behavior was observed in the relative proportion of cyclic trimer and tetramer during the first steps of their formation that was probably due to a competition between kinetic and thermodynamic products. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 416–422, 2000     

Effect of Thiourea on the Kinetics of the Hydrogen Evolution Reaction at Iron and the Transport of Hydrogen through a Steel Membrane in Solutions of C<Subscript>2</Subscript>H<Subscript>4</Subscript>(OH)<Subscript>2</Subscript>-H<Subscript>2</Subscript>O-HCl

The effect of thiourea (0.5–10 mM) on the kinetics of the hydrogen evolution reaction (HER) at iron and the hydrogen transport through a steel membrane out of ethylene glycol (containing 2 and 10 wt % H₂O) and aqueous solutions containing HCl (0.1–0.99 M) with a constant ionic strength equal to unity is studied in parallel experiments. The presence of 0.5 mM of thiourea in the solutions raises the overvoltage of hydrogen evolution, while a subsequent increase in its concentration does not effect the HER kinetics. The dependence of the flux of hydrogen diffusion through the membrane on the thiourea content passes through a maximum.     

Optimization of signal-to-noise ratio in the <Emphasis Type="Italic">in vivo</Emphasis><Superscript>31</Superscript>P magnetic resonance spectra of the human brain

The main problem in ³¹P magnetic resonance spectroscopy is a low signal-to-noise ratio (SNR) of spectra acquired with clinical magnetic resonance imaging (MRI) scanners. Using spin-spin phosphorus-proton (³¹P-¹H) decoupling and heteronuclear Overhauser effect and taking into account the effect of the longitudinal relaxation time T₁ on the SNR, the method for localization and excitation of the region of interest (Image Selected in vivo Spectroscopy pulse sequence) was optimized to increase the SNR in the ³¹P magnetic resonance spectra of the human brain to ~50% without increasing signal acquisition time.     

Cytotoxic Terpenes from the Stems of <i>Dipterocarpus obtusifolius</i> Collected in Cambodia

From the stems of Dipterocarpus obtusifolius, five new triterpenes, 3-oxo-20-hydroxy-30α-methyl,17(29)α-epoxy-28-norlupane (1), 3-oxo-20-hydroxy-30β-methyl-17(29)α-epoxy-28-norlupane (2), 3,20-dioxo-28,29-norlupan-17α-ol (3), 27-demethyl-20(S)-dammar-23-ene-20-ol-3,25-dione (4), and 3-epi-cecropic acid (5) together with 13 known compounds including diterpene, sesquiterpenes and triterpenes were isolated and characterized. All isolates were tested for their cytotoxicities against a small panel of human cancer cell lines. Of the tested compounds, compounds 4-11 were found to be cytotoxic against one or more human cancer cell lines.     

Reactivity of oil shale ashes in the binding of SO<Subscript>2</Subscript>

The extensive use of fossil fuels in energy production causes serious pollution of atmosphere with SO₂, CO₂, NO_x, etc. In Estonia the electricity production is based mainly on the pulverized firing (PF) of low-grade local fuel – Estonian oil shale (EOS) which is characterized by a low calorific value (~9 MJ kg^–1) and a high content of mineral matter (65–70%) from which approximately 50% are carbonates. Since 2004, also two boilers based on circulating fluidized bed combustion (CFBC) of EOS are in exploitation. The present study is focused on the comparative investigation of the efficiency of different ashes collected from different technological points of CFB and PF boilers as sorbents for SO₂. The influence of experimental temperature on the SO₂-binding characteristics of ashes as well as the possibilities of activation of ashes (grinding, hydration) were investigated. It was shown that the SO₂-binding capacity of initial ashes at 700°C and p(SO₂)=190 mm Hg was for CFBC ashes 24–30 mg and for PF ashes 10–23 mg SO₂ per 100 mg sample, the best binding capacities belonging to economizer ash (ECOA) and electrostatic precipitator ash from the 1st field (PESPA1f), respectively. However, during initial stage of binding the best results were obtained with air pre-heater ash (PHAA) and ESPA1f (both CFBC ashes). Grinding improved the SO₂-binding ability, being the most effective in the case of bottom ash (BA) from CFBC and cyclone ash (PCA) from PF – increase in binding capacity 2 and 2.3 times, respectively. As compared to initial CFBC ashes, the binding characteristics of PF ashes remained lower even after grinding. Hydration and previous calcination improved the binding characteristics only of PF ashes. Hereby, the SO₂-binding ability of CFBC ashes is better than of PF ashes and they are more promising sorbents for acidic gases, for example, for sulphur dioxide.     

Dislocation of the <Superscript>137</Superscript>Cs and <Superscript>40</Superscript>K radionuclides in the podsol profiles of the Tatra Mountain soils (South Poland)

Summary The amount and dislocation of the gamma-radionuclides (artificial cesium and natural potassium) in the Haplic podsol profiles of the Tatra Mountains have been described. These soils belong to the group of penetrable formations what is a result of their texture. They provide a good example of percolation and sorption possibilities of the radionuclides within the soil profile. The highest concentration of radionuclides has been detected in raw humus and spodic (illuvial humus-iron) layers, at the surface.     

Factors That Affect the Nature of the Final Oxidation Products in “Peroxo‐Shunt” Reactions of Iron–Porphyrin Complexes

The present study focuses on the oxidation of the water‐soluble and water‐insoluble iron(III)–porphyrin complexes [Fe^III(TMPS)] and [Fe^III(TMP)] (TMPS=meso‐tetrakis(2,4,6‐trimethyl‐3‐sulfonatophenyl)porphyrinato, TMP=meso‐tetrakis(2,4,6‐trimethylphenyl)porphyrinato), respectively, by meta‐chloroperoxybenzoic acid (m‐CPBA) in aqueous methanol and aqueous acetonitrile solutions of varying acidity. With the application of a low‐temperature rapid‐scan UV/Vis spectroscopic technique, the complete spectral changes that accompany the formation and decomposition of the primary product of O? O bond cleavage in the acylperoxoiron(III)–porphyrin intermediate [(P)Fe^III? OOX] (P=porphyrin) were successfully recorded and characterized. The results clearly indicate that the O? O bond in m‐CPBA is heterolytically cleaved by the studied iron(III)–porphyrin complexes independent of the acidity of the reaction medium. The existence of two different oxidation products under acidic and basic conditions is suggested not to be the result of a mechanistic changeover in the mode of O? O bond cleavage on going from low to high pH values, but rather the effect of environmental changes on the actual product of the O? O bond cleavage in [(P)Fe^III? OOX]. The oxoiron(IV)–porphyrin cation radical formed as a primary oxidation product over the entire pH range can undergo a one‐ or two‐electron reduction depending on the selected reaction conditions. The present study provides valuable information for the interpretation and improved understanding of results obtained in product‐analysis experiments.     

On the photodissociation of ozone in the range of 5–9 eV

The photoabsorption spectrum of ozone in the UV range (5–9 eV) is calculated from a short-time wave packet propagation using six potential energy surfaces obtained from ab initio electronic structure calculations. It is shown that the (unnamed) band around 7 eV, which is immediately adjacent to the intense Hartley band, is primarily due to excitation of three electronic states: 5 ¹A′ (3 ¹A₁), 6 ¹A′ (4 ¹A₁), and 4 ¹A″ (2 ¹B₁). Excitation of the state 8 ¹A′ (¹B₂) leads to a broad and intense band starting around 8 eV with a maximum near 9.1 eV. In full accord with the recent experimental study of Brouard et al. [M. Brouard, R. Cireasa, A.P. Clark, G.C. Groenenboom, G. Hancock, S.J. Horrocks, F. Quadrini, G.A.D. Ritchie, C. Vallance, J. Chem. Phys. 125 (2006) 133308], the excitation at 193 nm (6.42 eV) involves at least two states (5 ¹A′ and 4 ¹A″) different from the state excited in the Hartley band (3 ¹A′). The dynamics along the dissociation path is discussed in terms of one-dimensional potential curves. Several avoided crossings among the excited ¹A′ as well as the ¹A″ states point to a complicated fragmentation process. Although a quantitative analysis of branching ratios is not possible on the basis of the present calculations, we surmise, that in addition to and O(¹D) + O₂(¹Δ_g), the next higher spin-allowed channel, , also is likely to be a major product channel, in agreement with experimental observations.     

HILIC LC‐MS for the determination of 2′‐C‐methyl‐cytidine‐triphosphate in rat liver

A very accurate and selective LC‐MS/MS method was developed and validated for the quantification of 2′‐C‐modified nucleoside triphosphate in liver tissue samples. An efficient pretreatment procedure of liver tissue samples was developed, using a fully automated SPE procedure with 96‐well SPE plate (weak anion exchange sorbent, 30 mg). Nucleotide hydrophilic interaction chromatography has been performed on an aminopropyl column (100 mm×2.0 mm, 3 μm) using a gradient mixture of ACN and ACN/water (5:95 v/v) with 20 mM ammonium acetate at pH 9.45 as mobile phase at 300 μL/min flow rate. The 2′‐C‐modified nucleoside triphosphate was detected in the negative ESI mode in multiple reaction monitoring (MRM) mode. Calibration curve was linear over the 0.05–50 μM concentration range. Satisfying results, confirming the high reliability of the established LC‐MS/MS method, were obtained for intraday precision (CV = 2.5–9.1%) and accuracy (92.6–94.8%) and interday precision (CV = 9.6–11.5%) and accuracy (94.4–102.4%) as well as for recovery (82.0–112.6%) and selectivity. The method has been successfully applied for pharmacokinetic studies of 2′‐C‐methyl‐cytidine‐triphosphate in liver tissue samples.     

Conductivity and thermal expansion of the Ce<Subscript>0.8</Subscript>Gd<Subscript>0.2</Subscript>O<Subscript>1.9</Subscript> solid electrolyte in the oxidizing and reducing atmospheres

Highly compact (99%) solid electrolyte Ce_0.8Gd_0.2O_1.9 with submicron (0.3 μm) grains is synthesized. The dilatometric (20–850°C) and conductivity (180–350°C) measurements are performed on the electrolyte in air and as a function of the partial oxygen pressure \(p_{O_2 } \) (0.21?1×10^?25 atm) at 600, 700, and 800°C. An inflection is found in the temperature dependences of the thermal coefficient of linear expansion and conductivity (impedance measurements) at ～230°C, which is the evidence for a phase transition. The activation energies for conduction in the grain bulk and boundaries differ only slightly, indicating that the grain boundaries’ resistance is caused not by the precipitation of the second phase at the boundaries, but most probably by the presence of intergranular nanopores. The dilatometric measurements confirm a significant increase in the linear dimensions of Ce_0.8Gd_0.2O_1.9 in the reducing atmospheres with a parallel increase in its electron conductivity. The electron conductivity and specific elongation increase proportionally to \(p_{O_2 }^{ - 1/4} \) at all temperatures. The \(p_{O_2 } \) values, at which the transport numbers of ions t _i = 0.5, are determined. They are 10^?22.5, 10^?20, and 10^?18 atm at 600, 700, and 800°C, respectively.     

Features of propane conversion in the presence of SmVO<Subscript>3</Subscript> and SmVO<Subscript>4</Subscript>

Features of propane conversion in the presence of samarium vanadite and samarium vanadate, both produced via solid-phase synthesis, are studied. It is shown that SmVO₃ catalyzes mainly the propane cracking process to form methane and ethylene, while SmVO₄ equally accelerates both cracking and the dehydrogenation of propane. Based on the results from catalytic experiments, energies of activation are calculated for the thermal cracking of propane (104 kJ/mol) and the conversion of propane in the presence of SmVO₃ (39 kJ/mol) and SmVO₄ (42 kJ/mol). The thermal stability of SmVO₄ in a hydrogen atmosphere is studied via temperature-programmed reduction, while SmVO₃ stability in an oxidizing environment is studied by DTA. Energies of activation for the reduction of SmVO₄ (75 kJ/mol) and the oxidation of SmVO₃ (244 kJ/mol) are calculated using the Kissinger method.     

Study of the oxidation of some catechols in the presence of 4‐amino‐3‐thio‐1,2,4‐triazole by digital simulation of cyclic voltammograms

Electrochemical oxidation of catechol and its derivatives ( 1a–d ) has been studied in the presence of 4‐amino‐3‐thio‐1,2,4‐triazole ( 3 ) at various pHs. Some electrochemical techniques such as cyclic voltammetry using the diagnostic criteria derived by Nicholson and Shain for various electrode mechanisms and controlled‐potential coulometry were used. Results indicate the participation of catechols ( 1a–d ) with 3 in an intramolecular cyclization reaction to form the corresponding 1,2,4‐triazino[5,4‐b]‐1,3,4‐thiadiazine derivatives. In various scan rates, based on an electron transfer–chemical reaction–electron transfer–chemical reaction mechanism, the observed homogeneous rate constants (k_obs) for Michael addition reaction were estimated by comparing the experimental cyclic voltammetric responses with the digital simulated results. The oxidation reaction mechanism of catechols ( 1a–d ) in the presence of 4‐amino‐3‐thio‐1,2,4‐triazole ( 3 ) was also studied. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 340–345, 2007     

Features of the valence electron charge distribution in LiB<Superscript>II</Superscript>X<Superscript>V</Superscript> crystals

Total, difference, and deformation electron densities are calculated from the first principles using the density functional theory and the sublattice method for LiBX (B = Mg, Ca, Zn; X = N, P, As) crystals with the sphalerite structure. The nature and formation features of the chemical bonding caused by a change in the chemical composition are revealed. A weak bond between Li⁺ ions with X anions enables their displacements in the space between crystal-forming tetrahedral (BX)^– groups. It is found that Ca–X bonds are mainly ionic and in a series of crystals the ionic covalent Li–B bond is traced.     

Calculation of <Superscript>15</Superscript>N NMR chemical shifts of amines in the framework of the density functional theory

The ¹⁵N NMR magnetic shielding constants (followed by recalculation into chemical shifts) in a representative series of amines were calculated in the framework of the density functional theory. The results were compared with experiment. The accuracy factors of this calculation (functional, basis set, solvent effects, and multistandard) were studied. Taking into account all the above factors leads to a noticeable decrease in the average absolute error in the calculation of the ¹⁵N NMR chemical shifts (from 13 to 4 ppm) in a range of their changing in the studies series of compounds of ～60 ppm (which is 6—7% in relative units).