Mössbauer spectroscopic studies of the magnetic hyperfine interaction in the ferric hexaquo complex in frozen aqueous solution

The ferric hexaquo complex, [Fe(H₂O)₆]³⁺, in aqueous solution frozen to a homogeneous glass, has been investigated by Mössbauer spectroscopy, using magnetically dilute samples. Spectra with a well resolved magnetic hyperfine structure were obtained at 4.5 and 78 K with various applied magnetic fields up to 12kG. A consistent interpretation within the spin Hamiltonian formalism is possible if the crystal field parameters are admitted some random variation from one iron ion to another in the glass matrix. The results are given in terms of a crystal field spin Hamiltonian ($\text{S =}\text{5}\text{2}$) with quadratic terms, D = 0.10cm^?1, λ = 0.20, as well as a quartic, cubic term, a = 0.017 cm^?1 (the parameters quoted are the average values). Reliable results can be obtained only after a careful determination of the saturation hyperfine field (H_O = 585 kG). The value found for the cubic splitting factor a is of the same order as that found previously by EPR in the diluted (crystalline) iron alums, which also contain the ferric hexaquo complex.     

Dynamics of a model of a railway wheelset

In this paper we continue a numerical study of the dynamical behavior of a model of a suspended railway wheelset. We investigate the effect of speed and suspension and flange stiffnesses on the dynamics. Numerical bifurcation analysis is applied and one- and two-dimensional bifurcation diagrams are constructed. The onset of chaos as a function of speed, spring stiffness, and flange forces is investigated through the calculation of Lyapunov exponents with adiabatically varying parameters. The different transitions to chaos in the system are discussed and analyzed using symbolic dynamics. Finally, we discuss the change in orbit structure as stochastic perturbations are taken into account.     

Effect of solvent composition on the association behavior of pectin in methanol-water mixtures

Turbidity, small-angle neutron scattering (SANS), and dynamic light scattering measurements have been carried out on semidilute systems of pectin in methanol-water media of various composition ratios. Structural and dynamical properties of pectin dissolved in water-methanol mixtures (case I) are compared with the corresponding conditions when pectin was dissolved in water before the prescribed amounts of methanol were added (case II). The turbidity rises as the percentage of methanol in the mixture increases and this trend is much stronger when the first procedure is used to dissolve pectin. The wavelength dependence of the turbidity indicates that larger association complexes are formed for the samples prepared according to case I. These findings indicate that at a given methanol-water composition, the preparation procedure in case I gives rise to poorer thermodynamic conditions of the system. Local structures probed by SANS experiments do not reveal any significant differences between the systems prepared by the two different procedures. The dynamic light scattering (DLS) results show that increasing methanol concentration in the mixture promotes the formation of association complexes and the disengagement relaxation time of individual chains or clusters is longer at higher percentage of methanol for case II. This can be attributed to stronger entanglement effects in case II. The features from DLS can be rationalized in the framework of the coupling model for constrained and interconnecting systems.     

The adsorption structure of NO on Pd(111) at high pressures studied by STM and DFT

Using a combination of scanning tunneling microscopy (STM) and density functional theory (DFT) calculations, we study the adsorption structure of NO on Pd(111) at pressures of up to 720 Torr. From atomically resolved STM images, we identify, at high pressures, only the (2 x 2)-3NO structure, which is identical with the highest NO-coverage structure found at low pressure and low temperature. DFT calculations confirm that the (2 x 2)-3NO structure is indeed the most stable adsorption structure at high pressures. Contrary to recent suggestions in the literature, we therefore conclude that we find no evidence for a (3 x 3)-7NO structure on Pd(111) at high NO pressure.     

Action and Ion Mobility Spectroscopy of a Shortened Retinal Derivative

The development of tandem ion mobility spectroscopy (IMS) known as IMS-IMS has led to extensive research into isomerizations of isolated molecules. Many recent works have focused on the retinal chromophore which is the optical switch used in animal vision. Here, we study a shortened derivative of the chromophore, which exhibits a rich IM spectrum allowing for a detailed analysis of its isomerization pathways, and show that the longer the chromophore is, the lower the barrier energies for isomerization are.

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Graphical Abstract

     

Interfacial and molecular properties of high-pressure-treated beta-lactoglobulin B

Interfacial properties of beta-lactoglobulin B subjected to hydrostatic pressures up to 400 MPa were studied by measuring surface pressure at the air/water interface and the elastic interfacial shear modulus at the oil/water interface. The surface hydrophobicity of pressurized beta-lactoglobulin was determined by an 1-anilino-naphthalene-8-sulfonate assay and exposure of free thiol groups using the Ellman assay. The molar mass of pressure-induced oligomers was measured using a combination of size exclusion chromatography, light scattering, and refractive index measurements. High-pressure treatment of beta-lactoglobulin increased the surface pressure growth rate and its final level at the air/water interface. After high-pressure treatment, the maximum interfacial elasticity at the oil/water interface increased, and the time lag before growth of the interfacial elasticity decreased. Up to 200 MPa, large amounts of monomeric beta-lactoglobulin were formed with increased exposure of thiol groups and increased surface hydrophobicity compared to unpressurized beta-lactoglobulin. At a pressure higher than 200 MPa, surface hydrophobicity continued to increase, while exposure of thiol groups decreased, the latter due to the formation of covalently linked oligomers. We have shown that surface hydrophobicity rather than thiol exposure is important for the pressure-induced increase in growth rate and the final level of surface pressure at the air/water interface and in interfacial elasticity at the oil/water interface.     

Cloning of a new allelic variant of aSaccharomyces diastaticus glucoamylase gene and its introduction into industrial yeasts

A new allelic variant of theSTA2 gene, designated asSTA2 ^K, coding for a secreted glucoamylase, was cloned. Differences were revealed both in the structural gene and in the promoter region, as compared to otherSTA genes. The most peculiar structural features ofSTA2 ^K are 1. a 1.1-kb natural deletion in its promoter located 189 nucleotides upstream of the translation start codon; and2. an Asn→ Asp single amino acid change within the putative active site of the encoded glucoamylase. Neither the presence of glucose in the medium nor the host cell's mating type constellation affected the expression level ofSTA2 ^K inS. cerevisiae. Self-replicating yeast plasmids containingSTA2 ^K were constructed and used to transform a laboratory yeast strain and various brewing strains. Pilot brewing tests with glucoamylase-secreting transformants of a brewing strain produced superattenuated beers at accelerated fermentation rates.     

Physical properties of aqueous solutions of a thermo-responsive neutral copolymer and an anionic surfactant: turbidity and small-angle neutron scattering studies

Aqueous mixtures of the anionic sodium dodecyl sulfate (SDS) surfactant and thermo-responsive poly(N-vinylcaprolactam) chains grafted with omega-methoxy poly(ethylene oxide) undecyl alpha-methacrylate (PVCL-g-C11EO42) have been characterized using turbidimetry and small-angle neutron scattering (SANS). Turbidity measurements show that the addition of SDS to a dilute aqueous copolymer solution (1.0 wt %) induces an increase of the cloud point (CP) value and a decrease of the turbidity at high temperatures. In parallel, SANS results show a decrease of both the average distance between chains and the global size of the objects in solution at high temperatures as the SDS concentration is increased. Combination of these findings reveals that the presence of SDS in the PVCL-g-C11EO42 solutions (1.0 wt %) promotes the formation of smaller aggregates and, consequently, leads to a more homogeneous distribution of the chains in solution upon heating of the mixtures. Moreover, the SANS data results show that the internal structure of the formed aggregates becomes more swollen as the SDS concentration increases. On the other hand, the addition of moderate amounts of SDS (up to 4 mm) to a semidilute copolymer solution (5.0 wt %) gives rise to a more pronounced aggregation as the temperature rises; turbidity and SANS studies reveal in this case a decrease of the CP value and an increase of the scattered intensity at low q. The overall picture that emerges from this study is that the degree of aggregation can be accurately tuned by varying parameters such as the temperature, level of surfactant addition, and polymer concentration.