Stability of Rare-Earth Oxychloride Phases: Bond Valence Study

The crystal structures of the tetragonal rare earth (RE) oxychlorides, REOCl (RE=La-Nd, Sm-Ho, and Y) were studied by X-ray powder diffraction measurements, Rietveld analyses, and bond valence calculations. The tetragonal structure (space group P4/nmm, No. 129, Z=2) is stable for all but Er-Lu oxychlorides, which possess a hexagonal structure. The tetragonal structure consists of alternating layers of (REO)_nⁿ⁺ complex cations and Xⁿ⁻ anions, where the rare earth is coordinated to four oxygens and four plus one chlorines in a monocapped tetragonal antiprism arrangement. The Rietveld analyses yielded a coherent series of structural parameters. Preferred orientation and microabsorption effects were found significant. The evolution of interatomic distances and bond angles indicated that the reason for the preferred structure changing from tetragonal to hexagonal is the strain in the chlorine layer. The bond valence parameter B for the RE-O bonds had to be recalculated due to the covalent nature of the (REO)_nⁿ⁺ unit. The results obtained with the new parameter confirmed the strains in the chlorine layer to be the cause for the phase transition.     

Structural,torsional, vibrational and response electric properties of 2,2′-bitellurophene rotamers. An ab initio and density functional theory investigation

The molecular structure, conformational behaviour, vibrational spectra and electronic (hyper)polarizabilities of tellurophene and 2,2′-bitellurophene rotamers were determined in gas by correlated ab initio and density functional theory calculations. The torsional potential for the rotation around the C²–C^2′ inter-ring bond shows two minima corresponding to anti-gauche and syn-gauche structures and three maxima to planar anti and syn forms and to perpendicular conformation. The potential energy curve is rather flat over the entire 0°–180° twisting range and free rotation cannot be excluded. The IR and Raman spectra of the gauche structures are rather similar to each other, vibrational transitions being scarcely helpful for an unambiguous identification of the rotamers. The dipole moment and the first-order hyperpolarizability increase on passing from the anti-gauche to the syn-gauche conformation by a factor of five and four, respectively. The second harmonic generation nonlinear optical process can be useful to identify the 2,2′-bitellurophene rotamers. On the other hand, the electronic polarizabilities of these structures are much more closer to each other, being predicted to be within 2–13 %.     

Molecular energy parameters by solution thermodynamics

The relationships between statistical thermodynamics and equilibrium constants, either cumulative, stepwise or specific site constants are investigated. In order to show the link between equilibrium constants and statistical thermodynamic microscopic properties, a distinction has been introduced between non-reacting and reacting systems. The non-reacting systems are those for which continuous statistical distributions of enthalpies can be assumed. The distribution function can be obtained as an integral of the interparticle potential extended to the whole ensemble. Molecular partition functions ζ_A, are used to describe the properties of the ensembles. The reacting ensemble is represented by distinct distributions of enthalpies, each distribution being grouped around a mean value. Each level is representative of one species. Around each mean level the distribution is continuous as in non-reacting ensembles. The reacting ensemble of particles is described by a grand canonical molar partition function Z_M=(1+kγ(i)[A])^t where k is the specific site constant, γ(i) is the cooperativity function, [A] is the concentration of free ligand, and the power t indicates the maximum number of i sites in one class. The specific site constant k is proportional to the affinity of binding and is related to the depth of the minimum of the potential function. The factor γ_i is the cooperativity factor given by the value of the cooperativity function γ(i) at the ith level and indicates how the depth of the potential function is affected by previous binding of a ligand. The values of the stability constant and cooperativity factor can be optimized by a computer program. The derivatives of the partition function Z_M with respect to ln[A] correspond to the formation function 〈n〉 (first derivative) and to the buffer capacity B_C (second derivative). The derivatives of the partition function Z_M with respect to temperature are reaction enthalpy ΔH (first derivative with −(1/T)) and apparent heat capacity ΔC_p,app (second derivative with ln T). The denaturation heat obtained by integration of ΔC_p,app dT for many proteins explains why the denaturation enthalpy depends linearly upon T.     

Theoretical studies on selectivities in the Staudinger reaction of vicinal diimines and ketenes

The selectivities,including peri-,regio-,and diastereoselectivities,in the Staudinger reaction involving vicinal diimines and ketenes were investigated theoretically via the density functional theory(DFT) calculation.The results indicate that vicinal diimines prefer stepwise [2+2] cycloaddition rather than [2+4] cycloaddition to generate cis-4-imino-β-lactams.The diimines attack the less sterically hindered exo-side of ketenes to generate zwitterionic intermediates,which directly undergo a conrotatory ring closure to produce cis-4-imino-β-lactams whatever diimines with less or more bulky N-substituents.For unsymmetric vicinal ketoaldehyde-derived diimines,their ketimines attack the exo-side of ketenes and undergo a conrotatory ring closure to produce cis-4-aldimino-β-lactams due to less steric effect.The current theoretical studies provide very important information for in-depth understanding of the selective formation of mono-cis-β-lactams from vicinal diimines and ketenes.     

Far infrared spectrum and conformational potential function of n-butane

The far i.r. spectrum of gaseous n-butane obtained at 0.06 cm⁻¹ resolution is reported between 80 and 230 cm⁻¹. Several transitions for the asymmetric torsion of the trans conformer have been identified. Utilizing these data along with the previously reported asymmetric torsional transitions of the gauche conformer from Raman spectroscopic data, the potential function for the conformational change has been obtained. The determined potential parameters were found to be: V₁ = 181, V₂ = 148, V₃ = 1154 and V₆ = −33 cm⁻¹. The s-trans to gauche, gauche to gauche, and gauche to s-trans barriers in cm⁻¹ were found to be: 1315 (3.76 kcal/mol), 1090 (3.12 kcal/mol) and 1070 (3.06 kcal/mol), respectively. The potential functions obtained from these spectroscopic data are consistent with the trans to gauche energy difference, but not with the high trans/cis potential barrier suggested by recent ab initio calculations.     

An improved model of the fringing fields of a quadrupole mass filter

The fringing field region of a quadrupole mass filter is modelled using an iterative finite difference technique to solve Laplace's equation for the electrostatic potential. The results are used to formulate an expression f(z) such that the electrostatic potential of the fringing field, F(x, y, z, t) may be written in the form F(x, y, z, t) = f(z) φ(x, y, t), where φ(x, y, t) is the hyperbolic field of the quadrupole. The function f(z) is expressed in the form f(z) = 1 - exp {- az - bz²}), where a and b are constants and z is in units of r_O, where 2r_O is the spacing of the quadrupole rods. The effect of the distance from the quandrupole rods to the end plate of the quadrupole mass filter, d on f(z) is investigated and the results presented show that for d < 0.125 r_O the function f(z) does not alter significantly.     

The Isolation and Characterization of Antagonist Trichoderma spp. from the Soil of Abha,Saudi Arabia

Background: The genus Trichoderma is widely spread in the environment, mainly in soils. Trichoderma are filamentous fungi and are used in a wide range of fields to manage plant patho-genic fungi. They have proven to be effective biocontrol agents due to their high reproducibility, adaptability, efficient nutrient mobilization, ability to colonize the rhizosphere, significant inhibitory effects against phytopathogenic fungi, and efficacy in promoting plant growth. In the present study, the antagonist Trichoderma isolates were characterized from the soil of Abha region, Saudi Arabia. Methodology: Soil samples were collected from six locations of Abha, Saudi Arabia to isolate Trichoderma having the antagonistic potential against plant pathogenic fungi. The soil dilution plate method was used to isolate Trichoderma (Trichoderma Specific Medium (TSM)). Isolated Trichoderma were evaluated for their antagonistic potential against Fusarium oxysporum, Alternaria alternata and Helminthosporium rostratum. The antagonist activity was assessed by dual culture assay, and the effect of volatile metabolites and culture filtrate of Trichoderma. In addition, the effect of different temperature and salt concentrations on the growth of Trichoderma isolates were also evaluated. Results: The most potent Trichoderma species were identified by using ITS4 and ITS 5 primers. Total 48 Trichoderma isolates were isolated on (TSM) from the soil samples out of those six isolates were found to have antagonist potential against the tested plant pathogenic fungi. In general, Trichoderma strains A (1) 2.1 T, A (3) 3.1 T and A (6) 2.2 T were found to be highly effective in reducing the growth of tested plant pathogenic fungi. Trichoderma A (1) 2.1 T was highly effective against F. oxysporum (82%), whereas Trichoderma A (6) 2.2 T prevented the maximal growth of H. rostratum (77%) according to the dual culture data. Furthermore, Trichoderma A (1) 2.1 T volatile metabolites hindered F. oxysporum growth. The volatile metabolite of Trichoderma A (6) 2.2 T, on the other hand, had the strongest activity against A. alternata (45%). The Trichoderma A (1) 2.1 T culture filtrate was proven to be effective in suppressing the growth of H. rostratum (47%). The temperature range of 26 °C to 30 °C was observed to be optimum for Trichoderma growth. Trichoderma isolates grew well at salt concentrations (NaCl) of 2%, and with the increasing salt concentration the growth of isolates decreased. The molecular analysis of potent fungi by ITS4 and ITS5 primers confirmed that the Trichoderma isolates A (1) 2.1 T, A (3) 3.1 and A (6) 2.2 T were T. harzianum, T. brevicompactum, and T. velutinum, respectively. Conclusions: The study concludes that the soil of the Abha region contains a large population of diverse fungi including Trichoderma, which can be explored further to be used as biocontrol agents.     

Para-selectivity of SAPO-5 and mordenite catalysts in the alkylation of cumene with 2-propanol

Alkylation of cumene with 2-propanol was studied on SAPO-5 and mordenite catalysts. The primary products of the alkylation on every catalyst examined here were p- and m-diisopropylbenzene (DIPB) in a ratio of 75:25. The p-DIPB fraction in DIPB isomers (para-selectivity) decreased with increasing yield of DIPB, due to the secondary reaction of p-DIPB to m-DIPB. On SAPO-5, mordenite and silica-alumina, this secondary reaction proceeds through dealkylation of p-DIPB to cumene, followed by re-alkylation of the resultant cumene to m-DIPB. The dealkylation of p-DIPB would occur preferentially over that of m-DIPB. This was due to the higher reactivity of p-DIPB and probably to the reactant molecular shape selectivity of SAPO-5 and mordenite. The para-selectivity was improved by supporting boron oxide on SAPO-5 and mordenite; this improvement was caused by suppression of the secondary dealkylation of p-DIPB.     

Stereoselective synthesis of 3a,7a-dihydro-3H,4H-furo[3,4-c]pyran-1-ones via intramolecular hetero-Diels-Alder reaction

The synthesis of 3a,7a-dihydro-3H,4H-furo[3,4-c]pyran-1-ones via an intramolecular hetero-Diels-Alder reaction of easily accessible α,β-unsaturated γ-ketoesters was investigated. The reaction was found to proceed in a highly stereoselective way leading to single, cis-configured product isomers. The same diastereomer is formed, independently of the configuration of the enone double bond of the precursor. The respective E- and Z-isomers react either through an endo-E-syn or an exo-Z-syn transition state.     

Structural,magnetic and transport properties of S doping in Sr2FeMoO6 compound

The polycrystalline Sr₂FeMoO_6-xS_x (0.0 ≤ x ≤ 0.4) series were synthesized. The structure of Sr₂FeMoO_6-xS_x is assigned to tetragonal system with space group I4/mmm. The cell volume decreases with x from 0.0 to 0.3, then, increases with x from 0.3 to 0.4. S doping leads the oxygen/sulfur at 4e and 8h positions to movement away from Fe and to displacement toward Mo, respectively. The M_S at room temperature increases with degree of order of Fe and Mo ions. The electrical resistivity for studied samples exhibits a semiconductor-like behavior. The resistivity decreases with S doping. The electrical transport behavior is mainly dominated by electron-electron interactions except x = 0.4 in 0.0 magnetic field.     

The structure of low temperature triplet energy traps in organic solids from pmdr spectroscopy 11. 1,3,5-Trichloro and hexachlorobenzenes

The new technique of polarized microwave PMDR spectroscopy is used to determine the structure of the low temperature (1.6 – 4.2°K) triplet energy traps. The structure of 1.3,5-trichlorobenzene (Tri-CB) and hexachlorobenzene (HCB) molecules in hexamethylbenzene (HMB) host as well as in their own neat crystals (present as x-traps) is determined from the linear polarization characteristics of their optically detected microwave zerofield (zf) transitions as well as from the analysis of their phosphorescence emission. The former technique gives the direction of the principal magnetic axes of these trap molecules in the crystal as well as the relative order of their zf levels.ln HMB host, deviation from trigonal symmetry is found to be only slight for HCB and absent for Tri-CB. ln the neat crystals, large deviations from trigonal symmetry are observed for the traps of both HCB and Tri-CB. In HCB x- traps, the HCB molecule is found to be slightly contracted along the CCl axis near parallel to the c′ crystal axes. Deviation From planarity is also strongly suggested by the large value of the zf parameter D. ln addition, the principal magnetic axis of the 2|E| moment for HCB x-traps is found to lie only 5° off the molecular N axis. The |D| + |E| and |D| — |E| moments, however, are 15° away from the A and B molecular axis, respectively.In Tri-CB neat crystal. two traps are observed optically with their phosphorescence origins 10 cm^?1 apart. The zf parameter E is found to have a non-zero value and is opposite in sign for the two traps. If the distortion is to be blamed on pseudo-Jahn-Teller forces, the results lead to the conclusion that the x-(shallow) trap is contracted while the y- (deep) trap is expanded along an in-plane axis going through the CCl bonds near parallel to the a axis of the Tri-CB crystal. The plane containing the |D| + |E| and |D| — |E| moments of the x-trap suffers a rotation around the N-molecular axis, which is almost parallel to the 2|E| moment. Th |D| + |E| moment is 10° off the A axis and the |D| — |E| moment is 10° off the B axis. The 2|E| transition moment of the y-trap lies off the molecular N axis and the plane containing the |D| + |E| and |D| — |E| moments moves upward from theThe results of these and other studies suggest that low temperature trapping in neat crystals of this type results from crystal induced geometrical and orientational changes in the molecules at point defects. The observed traps are those molecules for which the crystal field induced deformation leads to a lowering in their singlet-triplet transition energy as compared with that for the host lattice.     

Interfacial change on morphological transitions in styrene-isoprene diblock copolymer

The specific interfacial area (S/V) and interfacial thickness in each microstructure of styrene-isoprene diblock copolymer were estimated by analyzing the deviations from Porod’s law. The thermally induced phase transitions proceeded from lamellae (L) to hexagonally ordered cylinder (HEX), via hexagonally perforated layer (HPL) and gyroid (G). The S/V ratio increased stepwise at the order-order transition (OOT) from L to HEX, via HPL and G. The S/V data can be utilized for OOT determination.     

Solubilities of terephthalaldehydic,p-toluic,benzoic, terephthalic and isophthalic acids in N,N-dimethylformamide from 294.75 to 370.45 K

Using a laser monitoring observation technique, solubilities of terephthalaldehydic, p-toluic, benzoic, terephthalic and isophthalic acids in N,N-dimethylformamide have been measured as a function of temperature in the temperature range 294.75–370.45 K. The experimental data are correlated with the λh equation. The calculated results show good agreement with the experimental solubilities. The molar mixing enthalpy of solution H^E is estimated from the h parameter to discuss the properties of solution. In the terephthalic acid-N,N-dimethylformamide system a repulsive interaction exists between solute and solvent, which leads to an endothermic effect during dissolution. The strongest attractive interaction exists in the p-toluic acid-N,N-dimethylformamide system, causing a significant exothermic effect.     

Semiclassical variational study of size effects in neutral and charged jellium droplets

An analytic expression for the total energy of metallic clusters composed ofN identical atoms of valencev and with net chargeQ is obtained by means of a variational solution of the Thomas-Fermi-Weizsäcker energy density functional within the spherical jellium model. The minimum energy is given as an expansion in decreasing powers of the cluster radiusR=r _s Z ^1/3, withZ=vN andr _s the radius per electron of the bulk metal. The coefficients are obtained as functions ofr _s . Terms of volume (R ³), surface (R ²), curvature (R), constant (R ⁰), (1/R) and (1/R ²) are clearly separated in the formula, as well as the different contributions (kinetic, coulombic and exchange-correlation) to each of them. The asymptotic values (R→∞) for the work functions,W(r _s ), and surface energies σ(r _s ), are compared to analogous semiclassical and Kohn-Sham calculations of jellium-like surfaces and to the experimental values. The size dependent behaviour of chemical potentials, μ(R), electron affinities,AF(R), and ionization potentials,IP(R), are easily obtained for any kind of metallic clusters. In particular we discuss the Coulomb and quantum corrections to the coefficients β, δ in the asymptotic formulae:IP?W+β/R andAF?W+δ/R.     

Offline and online capillary electrophoresis enzyme assays of β-N-acetylhexosaminidase

Enzyme assays of β-N-acetylhexosaminidase from Aspergillus oryzae using capillary electrophoresis in the offline and online setup have been developed. The pH value and concentration of the borate-based background electrolyte were optimized in order to achieve baseline separation of N,N′,N″-triacetylchitotriose, N,N′-diacetylchitobiose, and N-acetyl-d-glucosamine. The optimized method using 25 mM tetraborate buffer, pH 10.0, was evaluated in terms of repeatability, limits of detection, quantification, and linearity. The method was successfully applied to the offline enzyme assay of β-N-acetylhexosaminidase, which was demonstrated by monitoring the hydrolysis of N,N′,N″-triacetylchitotriose. The presented method was also utilized to study the pH dependence of enzyme activity. An online assay with N,N′-diacetylchitobiose as a substrate was developed using the Transverse Diffusion of Laminar Flow Profiles model to optimize the injection sequence and in-capillary mixing of substrate and enzyme plugs. The experimental results were in good agreement with predictions of the model. The online assay was successfully used to observe the inhibition effect of N,N′-dimethylformamide on the activity of β-N-acetylhexosaminidase with nanoliter volumes of reagents used per run and a high degree of automation. After adjustment of background electrolyte pH, an online assay with N,N′,N″-triacetylchitotriose as a substrate was also performed.

Bioremediation of Hydrocarbons Contaminating Sewage Effluent Using Man-made Biofilms: Effects of Some Variables

Biofilm samples were established on glass slides by submerging them in oil-free and oil-containing sewage effluent for a month. In batch cultures, such biofilms were effective in removing crude oil, pure n-hexadecane, and pure phenanthrene contaminating sewage effluent. The amounts of the removed hydrocarbons increased with increasing biofilm surface area exposed to the effluent. On the other hand, addition of the reducing agent thioglycollate dramatically inhibited the hydrocarbon bioremediation potential of the biofilms. The same biofilm samples removed contaminating hydrocarbons effectively in three successive batch bioremediation cycles but started to become less effective in the cycles thereafter, apparently due to mechanical biofilm loss during successive transfers. As major hydrocarbonoclastic bacteria, the biofilms harbored species belonging to the genera Pseudomonas, Microvirga, Zavarzinia, Mycobacterium, Microbacterium, Stenotrophomonas, Gordonia, Bosea, Sphingobium, Brachybacterium, and others. The nitrogen fixer Azospirillum brasilense and the microalga Ochromonas distigma were also present; they seemed to enrich the biofilms, with nitrogenous compounds and molecular oxygen, respectively, which are known to enhance microbiological hydrocarbon degradation. It was concluded that man-made biofilms based upon sewage microflora are promising tools for bioremediation of hydrocarbons contaminating sewage effluent.     

Hyperfine structure in the configurations4f 4 6s 2 and4f 4 5d 6s of Nd I

The high resolution laser-atomic-beam technique was used to investigate the hyperfine structure in Nd I 4f ⁴6s ^{2 5} I,⁵ F,⁵ S and 4f ⁴5d6s ⁷ L,⁷ K,⁷ I,⁷ H. The metastable states were populated by an arc discharge burning in the atomic beam. The measured hyperfine constantsA andB of the levels of 4f ⁴6s ² and 4f ⁴5d6s allow a parametric analysis to be performed using the effective tensor operator formalism. The experimental radial integrals of the 4f and 5d electrons fit with those of the other lanthanides. The 4f radial integrals are in agreement with values of optimized Hartree-Fock-Slater calculations. The spectroscopic quadrupole moments of¹⁴³Nd and¹⁴⁵Nd are deduced from the 4f parameters:Q _I =?0.610(21) b and ?0.314(12) b, respectively. TheQ _I resulting from the 5d parameter are in satisfactory agreement with these values. The hyperfine anomaly due to thes electron in 4f ⁴5d 6s amounts to about 1%.     

Vibrational analysis of n-butyl, n-pentyl,and n-hexyl fluorides

Infrared spectra were obtained for n-butyl, n-pentyl, and n-hexyl fluorides in the liquid and solid states, and liquid-state Raman spectra were obtained for the first two of these. Normal coordinate calculations were carried out and twenty force constants of the C-CH₂F group were refined to provide the best fit for the 114 assigned frequencies of trans-n-propyl, gauche-n-propyl, TT-n-butyl, and TG-n-butyl fluorides. The resulting force constants were used to calculate the frequencies of the GT- and GG conformations of n-butyl fluoride and the two conformations for each of n-pentyl and n-hexyl fluoride that have coplanar carbon chains. The presence of all four conformers of n-butyl fluoride in the liquid state is indicated, but only the TG-conformer is present in the solid. The existence of the two conformations of n-pentyl and n-hexyl fluorides for which calculations were made is supported by comparison of the observed and calculated frequencies. Additional conformations seem to be present. The simplest solid-state spectrum is due only to the conformer that has a coplanar chain of carbons and the fluorine atom in the gauche position. Previous tentative conclusions about the relation between C-F stretching frequency and configuration have been revised.     

Interspecific Variation between the American Quercus virginiana and Mediterranean Quercus Species in Terms of Seed Nutritional Composition,Phytochemical Content,and Antioxidant Activity

This study aimed to evaluate a complete nutritional composition in the seeds Quercus virginiana to compare this nutritional composition with three Mediterranean Quercus species. We analyzed the seed morphometry, proximate composition, phytochemicals, and antioxidant capacity. The seed of Q. virginiana presented the smaller seed size and weight, while Q. suber presented the highest values. Moreover, Q. virginiana seeds showed the highest amounts of sugar and total lipids, digestibility, energy, palmitic acid, and stearic acid. On the other hand, Q. virginiana seeds showed the lowest values of linoleic acid. Moreover, Q. coccifera seeds presented the highest total phenolics and flavonoids contents and antioxidant activity. The clustering analysis revealed a significant similarity in seed morphometry and nutritional composition between the Mediterranean Q. ilex and Q. suber, grouping with the American Q. virginiana, but to a considerable distance; by contrast, the Mediterranean Q. coccifera was the most distant in the clustering analysis. The content of phenolics and flavonoids and digestibility value were the variables that contributed to the separation to a greater extent in the clustering of the four species. The nutritional and biological activity assessment of plant seed may be considered as an essential mission to find new sustainable sources and novel chemical agents. In this sense, Quercus seeds may be an alternative and a competitive food source for the agri-food industry.