Fermentation Performance and Structure Characteristics of Xanthan Produced by <Emphasis Type="Italic">Xanthomonas campestris</Emphasis> with a Glucose/Xylose Mixture

The ability of Xanthomonas campestris to convert glucose and xylose to xanthan and the structure of xanthan derived from the glucose/xylose mixture media are important when the lignocelluloses hydrolysate was used in xanthan production. In this paper, the features related to xanthan fermentation in the glucose/xylose mixture media and the structures of xanthan derived from the mixture media were studied. Glucose was the preferred carbon source to produce xanthan while xylose was also utilized with a very low consumption rate. When the fraction of glucose decreased from 100% to 25%, the glucose consumption rate and xanthan production rate reduced from 0.44 g L⁻¹ h⁻¹ to 0.25 g L⁻¹ h⁻¹ and 0.21 g L⁻¹ h⁻¹ to 0.04 g L⁻¹ h⁻¹ respectively while xylose was consumed at a very stable rate (0.053–0.060 g L⁻¹ h⁻¹). On the other hand, when the xylose fraction increased from 0% to 50%, pyruvate and acetate content of xanthan increased from 2.43% to 3.78% and 2.55% to 7.05%. The existence of xylose also led to higher average molecular weight. Therefore, it could be concluded that xylose was not efficiently utilized by X. campestris to produce xanthan. The concentration of glucose rather than the total sugar was the main factor to determine the xanthan production. But xylose was helpful to improve the quality of xanthan.     

Radiation effects in plutonium and carbonate co-doped calcium hydroxy apatite: An EPR study

Electron paramagnetic resonance studies were conducted on synthetic calcium hydroxy apatite samples co-doped with ²³⁹Pu and carbonate ion. These investigations were carried out to assess the self-irradiation effects in bone and teeth on exposure to plutonium, as calcium hydroxy apatite is the major constituent of bone and teeth. On self-irradiation, in addition to the signal from O^- ion arising from the radiolysis of hydroxide ion, EPR signals due to CO₂ ^-, PO₂ ^2- and another signal assigned to surface O^- ions were observed in the samples. In freshly quenched gamma irradiated samples, signals from CO₃ ^-, O^- , PO₂ ^2- and O₂ ^- ions were observed. The EPR signal of O₂ ^- ion shows a doublet splitting suggesting that O₂ ^- ion gets preferentially stabilized close to Pu⁴⁺. The radiation damage due to Pu⁴⁺ at Ca²⁺ sites, in the sample appears to be lower as compared to that due to external gamma-irradiation. Moreover, the alpha-dose in ²³⁹Pu doped samples has self-annealing effects. These are attributed to localized radiation damage due to alpha-particles compared to evenly distributed radical ions produced due to gamma-irradiation.     

Selenosulfonation of allenes

Se-Phenyl p-tolueneselenosulfonate (1a) undergoes highly regioselective, photoinitiated, free-radical addition to allenes (R₁CHCCR₂R₃) to afford the regioisomer R₁CH(SePh)C(SO₂Ar)CR₂R₃ (13) arising from addition of the p-tolylsulfonyl group to the central carbon of the allene and transfer of the phenylseleno group to the less highly substituted of the two terminal carbons. This regioselectivity, which contrasts with that observed in the majority of radical additions to allenes, can be explained by reference to concepts proposed by Heiba as being important in determining the orientation in different radical additions to allenes. Oxidation of the PhSe group in 13 to PhSe(O) gives allylic selenoxides that undergo a reaction sequence of facile, concerted, [2,3]-sigmatropic rearrangement followed by hydrolysis of the resulting selenenate to afford β-tolylsulfonyl-substituted allylic alcohols, R₁CHC(SO₂Ar)C(OH)R₂R₃ (14) in 70–98% yield. Photoaddition of 1a to allenes, followed by the conversion of 13 to 14 thus provides a simple, high-yield route to a wide variety of 14, a class of compounds that would seem to have a number of interesting possible uses in synthesis.     

High-resolution HeI and HeII photoelectron spectra of the Zn 3d and Cd 4d orbitals in the zinc and cadmium dihalides: Ligand field splittings and intensity variations

We have recorded the high-resolution HeI and HeII photoelectron spectra of the Zn 3d and Cd 4d levels in gas-phase MX₂ molecules (M = Zn, Cd; X = Cl, Br, I). The d level spectra split into five peaks due to the combined effect of spin-orbit splitting and ligand field splitting on the d⁹ hole state, and the spectra have been fitted to a crystal field hamiltonian involving the cubic (C₄⁰) and non-cubic (C₂⁰) parts of the field from the halide ligands. Additional peaks in some spectra are due to vibrational splitting and configuration interaction. The ¦C₂⁰¦ value increases substantially from the chloride to the iodide for both Zn and Cd. Calculations of both the crystal field (C_{2 CF}⁰) and valence (C_{2 val}⁰) parts of C₂⁰ show that the increase in observed C₂⁰ is due to the C_{2 val}⁰ term attributed to the increase in covalency from the chlorides to the iodides. Shifts in the peak position due to the 2Σ_{$\text{1}\text{2 g}$} and 1Π_{$\text{3}\text{2 g}$} states from those expected on the ligand field basis. are attributed to slight bonding effects. These effecs cause a large discrepancy between calculated and observed C₄⁰ values. The intensities of the five Zn 3d peaks change markedly from HeI- to HeII-excited spectra. The Xα SW method has been used to calculate the intensities of the σ, π and δ 3d orbitals as a function of photon energy. These calculations show dramatic changes in intensity due. for example. to shape resonances. There is usually qualitative agreement between calculated and observed intensities.     

Allylic lithiation of methylenecyclobutanes

Methylenecyclobutanes undergo a lithiation reaction in the presence of n-BuLi or n-BuLi/KO^tBu from −78 °C to room temperature or to 40 °C in THF within 3 h and then quenching with a variety of electrophiles to give the corresponding addition products (alcohols) in moderate to good yields within 2 h. The alcohols can be easily oxidized to the ketones, which can be transformed to the substituted cyclopentenes in the presence of AlCl₃ within short reaction time.     

A new approach to determine soil microbial biomass by calorimetry

A method to determine soil microbial biomass (SMB) by isothermal calorimetry is reported. Soil samples ranging in pH from 6.2 to 9.4 and different textures were used to develop the method. Soil at 60% of its field capacity humidity was amended with a previously determined amount of glucose as to give the maximal response of CO₂ evolution. Then, an aliquot was weighed in the calorimeter ampoule and specific thermal power (p)–time (t) curves were obtained at 25 °C. After 1–2 h, a vial containing a 0.5 M NaOH solution was introduced to determine the specific thermal power due to CO₂ evolution, pCO₂ during 1–2 h. Then, the vial was removed and the experiment continued for 1–2 h. Specific thermal power due to CO₂ evolution was converted to rate (CO₂-C/mm³ g⁻¹ h⁻¹) by using the heat of reaction of CO₂ with NaOH and the molar volume. This value was further converted into SMB/μg g⁻¹ by using a conversion factor of 32.4. A guide to perform the calculations is given. Values of log SMB were linearly related with values of log p giving a similar relation to a previously reported where SMB was determined by conventional methods.     

The thermal properties of poly(pivalolactone)

Quantitative thermal analysis was carried out for poly-(pivalolactone) (PPVL), including heat capacity determinations from 140 to 550 K. The experimental C_p below the glass transition temperature was fitted to an approximate vibrational spectrum and the ATHAS computation scheme was used to compute the “vibration only” heat capacities from 0.1 to 1000 K. The liquid C_p was derived from an empirical addition scheme and found to agree with the experimental C_p with an RMS of ±2.8% from 240 K to 550 K. A glass transition, T_g, could be detected at 260 K, and the change in heat capacity for 100% amorphous PPVL was calculated to be 38.8 J/(K mol). Above T_g, semicrystalline samples seem to show a rigid amorphous fraction that does not contribute to the increase in heat capacity at T_g. Using the ATHAS recommended heat capacities, the various thermodynamic functions (enthalpy, entropy, and Gibbs function) were derived. The residual entropy at 0 K for the amorphous PPVL was calculated to be 5.2 J/(K mol) per mobile bead, and was comparable to that obtained for a series of linear, aliphatic polyesters analyzed earlier.     

Thermodynamic perturbation theory of simple liquids: Monte Carlo simulation of a hard sphere system and the Helmholtz free energy of SW fluids

The Monte Carlo method is used to simulate similar sized hard sphere systems in a wide range of densities (from η 0.005 to 0.530 with a step of η = 0.005). The models are used to calculate the coefficients of the thermodynamic perturbation theory series for SW fluids up to the fourth order. The width of the attraction zone of the SW potential λ is varied from 1 to 2.5 sphere diameters. The analytical expressions approximating the obtained coefficients by polynomials with respect to the variables η and λ are determined. The absolute accuracy of the approximation is estimated to be better than ±0.001. All the necessary data for the calculation of the Helmholtz free energy of SW fluids up to the fourth-order perturbation theory are given.     

SO2− and sodium perfluoroalkanesulfinate initiated addition of perfluoroalkyl iodide to olefin

The sulfinatodeiodination reagent Ce⁴⁺ ?NaHSO₃ was shown to be able to initiate the addition of perfluoroalkyl iodides to olefins at 50—70°C to give the corresponding adducts in good yield. Similarly, SO₂^? generated from Fe³⁺?NaHSO₃ system can also initiate the same addition although the reagent is not able to cause sulfinatodeiodination. Furthermore it was shown that sodium perfluoroalkanesulfinate is able to initiate the same addition and there is no exchange between the perfluoroalkyl groups of R'_FSO₂Na and R_FI.     

Dilatometric studies of Y2W3O12 with added Al2O3

Y₂W₃O₁₂ exhibits negative thermal expansion along the three crystallographic directions due to the transverse thermal vibrations perpendicular to the Y-O-W linkage. It is highly hygroscopic and forms a trihydrate structure at room temperature. Dilatometric studies of Y₂W₃O₁₂ show large thermal expansion hysteresis due to large grain size and a large initial positive thermal expansion due to the removal of water molecules. Al₂O₃ has been added to Y₂W₃O₁₂ upto 10 wt% in an attempt to overcome the hygroscopicity and reduce the particle size and thereby the thermal expansion hysteresis. Thermo gravimetric, dilatometric and electron microscopic studies are presented to support these observations. Dedicated to Professor C N R Rao on his 70th birthday     

Elemental composition and fatty acid profile of the edible fruits of Amatungula (Carissa macrocarpa) and impact of soil quality on chemical characteristics

The Amatungula fruit, from Carissa macrocarpa, is commonly consumed by the local people of KwaZulu-Natal (KZN), South Africa. Levels of elements in the fruit were determined to assess if they conform to recommended dietary allowances (RDAs) and to assess for potential toxicities. Soils and fruit samples from nine sites in eastern KZN were investigated. Concentrations of elements in the fruit were found to be in the order of Ca > Mg > Fe > Mn ≈ Cu ≈ Pb > Se > Cr > Ni > Zn. For the elements in focus, except for Pb, all of the elements found in the fruit contribute significantly towards the RDAs. Lipid profiling was also done to determine the fruits potential as a source of essential fatty acids. The fruit was rich in monounsaturated and essential fatty acids with the linoleic acid to α-linolenic acid ratio conforming to the recommended range for cardiac health. Concentrations of elements in soil had no significant effect on plant concentrations, but competition between elements in soil influenced their availability. Total soil concentrations of most metals studied have significantly correlated Pb availability, indicating the impact of these metals on Pb availability. The Amatungula fruit showed tendency to accumulate Pb, with Pb levels in fruit at all sites being toxic to human health. Site location had a major effect on plant concentrations however uptake and distribution was primarily dependent on the plants inherent controls, as evidenced by the accumulation and exclusion of elements, to meet its physiological requirements.     

Natural radioactivity of spring water used as spas in Spain

Spring waters used as spas may contain significant amounts of natural radionuclides, so, in some circunstances, a radiation protection issue can arise for the population and/or the spas workers. EU has identified some groups of employees to be exposed to natural radiation in the 1996 Euratom Directive. Among these are workers of thermal spas who may be exposed to high radiation doses due to high radon concentrations in indoor air. In order to evaluate the potencial risk of the spring waters used as spas, gross-α and gross-β activity, ²²⁶Ra and ²²²Rn concentration levels were measured in 82 spas all over the country. Gross-alpha and gross-beta concentrations ranged from LLD to 17 Bq·l⁻¹ and from LLD to 60 Bq·l⁻¹, respectively. ²²⁶Ra concentrations ranged from <4 to 3,660 mBq·l⁻¹. ²²²Rn concentrations ranged from <4 to 1868 Bq·l⁻¹. Correlations between ²²⁶Ra concentrations and gross-α activity were obtained.     

Enzyme assay for chitinase catalyzed hydrolysis of tetra-N-acetylchitotetraose by isothermal titration calorimetry

Isothermal titration calorimetry (ITC) has been used to observe the chitinase-catalyzed hydrolysis of tetra-N-acetylchitotetraose. Enzymatic hydrolysis of tetra-N-acetylchitotetraose by chitinase B from Serratia marcescens produces exclusively two molecules of di-N-acetylchitobiose allowing for the determination of a single glycosidic bond hydrolysis heat that was used to monitor the rate of the enzymatic reaction. The change in heat rate with respect to time (dQ/dt) was translated to the reaction rate, and the total heat produced was related to substrate concentration throughout the reaction. Reaction rates versus substrates concentration were fit to Michaelis-Menten plots, yielding a k_cat of 40.9 ± 0.5 s⁻¹ and a K_m of 54 ± 2 μM.     

Correlation of optical properties and temperature-induced irreversible phase transitions in europium-doped yttrium carbonate nanoparticles

Nanophase europium-doped yttrium carbonate precursors are subjected to heat treatments, ranging from 300 °C to 1100 °C for dwell times of 5 min, 30 min, and 180 min. XRD, TEM, FT-IR, fluorescence, fluorescence excitation, and fluorescence lifetime measurements are used to characterize the materials. Upon heating, the material transitions through several amorphous stages until it reaches the crystalline cubic Y₂O₃ phase. DSC measurements show an exothermic transition at 665.7 °C, indicating the formation of crystalline Y₂O₃. The grain size development is fitted by the relaxation equation and yields an activation energy of 50.3 kJ/mol. The amorphous phases are characterized by inhomogenously broadened optical spectra. Heating up to 700 °C leads to an increased fluorescence lifetime (from about 1 ms to 2.4 ms). As the material is heated to higher temperatures and completes the formation of the crystalline cubic Y₂O₃ phase, the optical spectra become narrower and the fluorescence lifetime decreases to about 1.2 ms.     

Differential pulse polarographic study of thiamine (vitamin B1) in neutral and acidic aqueous solutions

The differential pulse (dp) polarograms of thiamine in neutral aqueous solutions exhibited six peaks at low depolarizer concentration (⋦10⁻⁴ mol dm⁻³) and only three peaks at concentrations ≥10⁻³ mol dm⁻³. Only one of these was found to correspond to the diffusion-controlled reduction of this compound at the dme and this was shown to be an irreversible two-electron process. The kinetic parameters derived from the dp polarograms were found to be in good agreement with those calculated from classical polarograms and were:E _1/2=−1·261 Vvs SCE,an _a=0·54 andD≈3·5×10⁻⁶ cm² sec⁻¹ for 10⁻³ mol dm⁻³ thiamine in 0·1 mol dm⁻³ acetate buffer (pH 6·5). The reduction product has been identified as dihydrothiamine. The effect of pH on the dpp of thiamine was studied in the pH range 0–7. In the pH region 5·5 to 7·0 only one peak attributable to the B₁ ⁺ form of thiamine is present. In the pH region 3·5–5·5 another dpp peak attributable to the protonated form (B₁H²⁺) of thiamine was also observed. At pHs less than 3 only one peak was observed which could be attributed to the doubly protonated form (B₁ H₂ ³⁺) of thiamine. Surfactants like triton-X-100 and CTABr were found to inhibit the electroreduction of thiamine due to the strong adsorption of these compounds on the dme. Thiamine itself was found to have an inhibitory effect on its own electroreduction, although to a smaller extent.     

Structural Relationships and Theoretical Study of Electron Transfer Properties of 1,3,2-Dithiazolyl Radicals with Fullerenes in Nanostructure [1,3,2-DTA(s)]@Cn Supramolecular Complexes

Various empty carbon fullerenes with different carbon atoms have been obtained and investigated. The dithiazolyl radicals have shown important electron-transfer properties. Topological indices are digital values that are assigned based on chemical composition. These values are purported to correlate chemical structures with various chemical and physical properties. They have been successfully used to construct effective and useful mathematical methods to establish clear relationships between structural data and the physical properties of these materials. In this study, the number of carbon atoms in the fullerenes was used as an index to establish a relationship between the structures of 2,3-naphthalene-1,3,2-dithiazolyl (NDTA), 2,3-quinoxaline-1,3,2-dithiazolyl (QDTA), and 1,2,5-thiazolo[3,4-b]-1,3,2-dithiazolo[3,4-b]pyridazin-2-yl (TDP-DTA), radicals, 1–3 as molecular conductor radicals and fullerenes C_n (n = 60, 70, 76, 82, and 86), which create [1,3,2-DTA(s)]@C_n, A-1 to A-5 (NDTA]@C_n), B-1 to B-5 ([QDTA]@C_n), and C-1 to C-5 ([TDP-DTA]@C_n). The relationship between the number of carbon atoms and the free energies of electron transfer (ΔG_et(1) to ΔG_et(4) ) are assessed using the Rehm–Weller equation for A-1 to A-5, B1 to B-5, and C-1 to C-5 supramolecular [1,3,2-DTA(s)]@C_n complexes. Calculations are presented for the four reduction potentials ( ^Red.E₁ to ^Red.E₄ ) of fullerenes C_n . The results were used to calculate the four free energies of electron transfer (ΔG_et(1) to ΔG_et(4) ) of supramolecular complexes A-1 to A-18, B-1 to B-18, and C-1 to C-18 (5–60) for fullerenes C₆₀ to C₃₀₀.     

Effects of γ-radiation on the thermal stability of cobalt oxides

Pure cobaltic oxide, prepared by thermal decomposition of pure basic cobalt carbonate in air at 500°C, was subjected to different doses of γ-radiation varying between 5 and 50 M rad. The influence of γ-radiation on the thermal decomposition of cobaltic oxide to cobaltous oxide and the re-oxidation of CoO to Co₃O₄ was studied using DTA, with a controlled rate of heating and cooling. The effects of γ-radiation on the specific surface area (S_BET) and oxidation character of Co₃O₄ were also investigated.The DTA investigation revealed that γ-radiation effectively decreased the thermal stability of cobaltic oxide to an extent proportional to the dose employed. The maximum decrease in the thermal stability of 60% was attained by exposing Co₃O₄ solid to 30 M rad. γ-Irradiation, however, exerted no detectable effect on the re-oxidation of CoO by O₂ to Co₃O₄.The S_BET measurements showed that the small dose (5 M rad) of γ-radiation effected a decrease of 15% in the surface area of Co₃O₄, the higher doses (10–50 M rad) caused a further slight decrease of 18% in its surface area.γ-Irradiation was found to decrease the oxidation character of Co₃O₄ to an extent proportional to the dose employed.The decrease in the thermal stability of Co₃O₄ due to radiation is explained in terms of the decrease in the oxidation character of cobaltic oxide observed after subjecting the solid to γ-radiation.     

Degradation of chlorpyrifos by ionizing radiation

Summary A survey was carried out to determine radioactivity concentrations and associated dose rates from the naturally occurring nuclides ²³² Th, ²³⁸U and ⁴⁰K in various surface soil formations of Alhkraje city. Samples were collected from different areas of the study, sieved through a fine mesh, sealed in 0.5-liter plastic Marinelli beaker, and measured in the laboratory for 24 hours each. From the measured g-ray spectra, radioactivity concentrations were determined for ²³² Th ranging from 5.32±2.59 to 16.40±2.04 Bq ^. kg^-1, ²³⁸U (2.87±0.18 to 18.83±0.81 Bq ^. kg^-1), ⁴⁰K (211.33±55.04 to 378.97±36.46 Bq ^. kg^-1) and ¹³⁷Cs (0 to 3.19±1.02 Bq ^. kg^-1). Absorbed dose rates in air doors were calculated to be in the range of 15.29±2.65 to 30.00±3.24 nGy ^. h^-1, the corresponding effective dose rates per person outdoors were estimated to be between 21.00±0.95 to 36.83±2.11 mSν^. y^-1, assuming a 20% occupancy factor.     

Structure and donor–acceptor properties of Au<Subscript>12</Subscript>M (M = Hf,Ta, W,Re, and Os) intermetallic clusters

Evolution of three-dimensional configurations, electronic properties, and energies of attachment of donor and acceptor ligands to Au₁₂M (M = Hf, Ta, W, Re, and Os) intermetallic clusters were studied by quantum-chemical methods. The attachment of F to clusters Au₁₂Re and Au₁₂Os and the attachment of H to clusters Au₁₂Ta and Au₁₂Hf are found to give rise to more symmetric structures. The energies of attachment of F to >18-electron Au₁₂M clusters and the energies of attachment of H to <18-electron clusters exceed the energies of attachment of the same atoms to 18-electron cluster Au₁₂W and to cluster Au₁₂.