Extraction of Co-Products from Biomass: Example of Thermal Degradation of Silymarin Compounds in Subcritical Water

In an effort to increase revenues from a given feedstock, valuable co-products could be extracted prior to biochemical or thermochemical conversion with subcritical water. Although subcritical water shows significant promise in replacing organic solvents as an extraction solvent, compound degradation has been observed at elevated extraction temperatures. First order thermal degradation kinetics from a model system, silymarin extracted from Silybum marianum, in water at pH 5.1 and 100, 120, 140, and 160 °C were investigated. Water pressure was maintained slightly above its vapor pressure. Silymarin is a mixture of taxifolin, silichristin, silidianin, silibinin, and isosilibinin. The degradation rate constants ranged from 0.0104 min⁻¹ at 100 °C for silichristin to a maximum of 0.0840 min⁻¹ at 160 °C for silybin B. Half-lives, calculated from the rate constants, ranged from a low of 6.2 min at 160 °C to a high of 58.3 min at 100 °C, both for silichristin. The respective activation energies for the compounds ranged from 37.2 kJ/gmole for silidianin to 45.2 kJ/gmole for silichristin. In extracting the silymarin with pure ethanol at 140 °C, no degradation was observed. However, when extracting with ethanol/water mixtures at and 140 °C, degradation increased exponentially as the concentration of water increased. An erratum to this article can be found at     

Analysis of triacetone triperoxide by gas chromatography/mass spectrometry and gas chromatography/tandem mass spectrometry by electron and chemical ionization

The explosive triacetone triperoxide (TATP) has been analyzed by gas chromatography/mass spectrometry (GC/MS) and sub-nanogram detection limits are reported by ammonia positive ion chemical ionization (PICI), electron ionization (EI) and methane negative ion chemical ionization (NICI). Analysis by methane PICI and ammonia NICI gave detection limits in the low nanogram range. Analyses were carried out on (linear) quadrupole and ion trap instruments. Analysis of TATP by PICI using ammonia reagent gas is the preferred analytical method, producing low limits of detection as well as an abundant (greater than 60% of base peak) diagnostic adduct ion at m/z 240 corresponding to [TATP + NH4]+. Isolation of the [TATP + NH4]+ ion with subsequent collision-induced dissociation (CID) produces extremely low abundance product ions at m/z values greater than 60, and the m/z 223 ion corresponding to [TATP + H]+ was not observed. Density functional theory (DFT) calculations at the B88LYP/DVZP level indicate that dissociation of the complex to form NH4+ and TATP occurs at energies lower than peroxide bond dissociation, while protonation of TATP leads to cleavage of the ring structure. These results provide a method for pico-gram detection levels of TATP using commercial instrumentation commonly available in forensic laboratories. As a point of comparison, a detection limit of 15 ng was obtained by flame ionization detection.     

The diamagnetic susceptibility of hydrogenic donor in two-dimensional semiconductors with anisotropic effective mass of carriers

In this study, the effects of quantum confinement and effective mass anisotropy parameter on the diamagnetic susceptibility of a hydrogenic donor placed in GaAs, Si, and Ge quantum wells with infinite confinement potential are investigated in the effective mass and parabolic band approximations by using two and one parameter trial wave functions. It is observed that the diamagnetic susceptibility of a hydrogenic donor in anisotropic quantum wells is essentially equal to the transverse diamagnetic susceptibility part when well widths are larger than L > 100 Å, and the impurity is located at center. Moreover, a two parameter trial wave function model gives higher values of diamagnetic susceptibility, except for χ_z (GaAs).     

Rigid orthogonal bis-TEMPO biradicals with improved solubility for dynamic nuclear polarization

The synthesis and characterization of oxidized bis-thioketal-trispiro dinitroxide biradicals that orient the nitroxides in a rigid, approximately orthogonal geometry are reported. The biradicals show better performance as polarizing agents in dynamic nuclear polarization (DNP) NMR experiments as compared to biradicals lacking the constrained geometry. In addition, the biradicals display improved solubility in aqueous media due to the presence of polar sulfoxides. The results suggest that the orientation of the radicals is not dramatically affected by the oxidation state of the sulfur atoms in the biradical, and we conclude that a biradical polarizing agent containing a mixture of oxidation states can be used for improved solubility without a loss in performance.     

Stress–strain behaviour of aluminium alloys at a wide range of strain rates

The stress–strain behaviour of extruded AA6xxx and AA7xxx aluminium alloys in T6 temper was studied at a wide range of strain rates. Tensile tests at low to medium strain rates were performed in a standard tensile test machine, while a split-Hopkinson tension bar was used to carry out tests at high rates of strain. Extruded aluminium alloys have anisotropic mechanical properties, and tests were therefore done in three directions with respect to the extrusion direction. It is found that the AA6xxx alloys exhibit no significant rate sensitivity in the stress–strain behaviour, while moderate rate sensitivity was found for the AA7xxx alloys. There seems to be no significant difference between the rate sensitivity in the three tensile directions. The experimental data were used to identify the parameters of a thermo-viscoplastic constitutive relation for the extruded alloys, which includes the effects of strain hardening, strain-rate hardening, thermal softening and plastic anisotropy.     

Galilean invariance in the lattice-Boltzmann method and its effect on the calculation of rheological properties in suspensions

The lattice-Boltzmann method (LBM) provides an efficient simulation technique for the study of particle suspensions. These simulations provide an important tool in elucidating the effect of suspended particles on the rheology of suspensions. The most common solid–fluid boundary condition used in the LBM is the bounce-back operation, and as such, the errors introduced by this operation to the dynamics of the particles and the calculation of relevant rheological quantities must be quantified. This paper derives the Galilean invariant term in the standard bounce-back operation and shows the effect of this error on the calculation of particle dynamics and stresslet. In particular, an error is found in the calculation of normal stresses that may be significant in magnitude compared with typical values found in suspensions of rigid spherical particles. A correction is proposed, and simulation results are shown that verify the original assessment and show the reduction of error when using the proposed correction.     

Chemoenzymatic synthesis of sialylated glycopeptides derived from mucins and T-cell stimulating peptides.

The Tn, T, sialyl-Tn, and 2,3-sialyl-T antigens are tumor-associated carbohydrate antigens expressed on mucins in epithelial cancers, such as those affecting the breast, ovary, stomach, and colon. Glycopeptides carrying these antigens are of interest for development of cancer vaccines and a short, chemoenzymatic strategy for their synthesis is reported. Building blocks corresponding to the Tn (GalNAc alpha-Ser/Thr) and T [Gal beta(1-->3)GalNAc alpha-Ser/Thr] antigens, which are relatively easy to obtain by chemical synthesis, were prepared and then used in the synthesis of glycopeptides on the solid phase. Introduction of sialic acid to give the sialyl-Tn [Neu5Ac alpha(2-->6)GalNAc alpha-Ser/Thr] and 2,3-sialyl-T [Neu5Ac alpha(2-->3)Gal beta(1-->3)GalNAc alpha-Ser/Thr] antigens is difficult when performed chemically at the building block level. Sialylation was therefore carried out with recombinant sialyltransferases in solution after cleavage of the Tn and T glycopeptides from the solid phase. In the same manner, the core 2 trisaccharide [Gal beta 1-->3(GlcNAc beta 1-->6)GalNAc] was incorporated in glycopeptides containing the T antigen by using a recombinant N-acetylglucosaminyltransferase. The outlined chemoenzymatic approach was applied to glycopeptides from the tandem repeat domain of the mucin MUC1, as well as to neoglycosylated derivatives of a T cell stimulating viral peptide.     

Polypeptide N-acetylgalactosaminyltransferase-Associated Phenotypes in Mammals

Mucin-type O-glycosylation involves the attachment of glycans to an initial O-linked N-acetylgalactosamine (GalNAc) on serine and threonine residues on proteins. This process in mammals is initiated and regulated by a large family of 20 UDP-GalNAc: polypeptide N-acetylgalactosaminyltransferases (GalNAc-Ts) (EC 2.4.1.41). The enzymes are encoded by a large gene family (GALNTs). Two of these genes, GALNT2 and GALNT3, are known as monogenic autosomal recessive inherited disease genes with well characterized phenotypes, whereas a broad spectrum of phenotypes is associated with the remaining 18 genes. Until recently, the overlapping functionality of the 20 members of the enzyme family has hindered characterizing the specific biological roles of individual enzymes. However, recent evidence suggests that these enzymes do not have full functional redundancy and may serve specific purposes that are found in the different phenotypes described. Here, we summarize the current knowledge of GALNT and associated phenotypes.     

Delamination of compressed thin layers at corners

An analysis of delamination for a thin elastic layer under compression, attached to a substrate at a corner is carried out. The analysis is performed by combining results from interface fracture mechanics and the theory of thin shells. In contrast with earlier results for delamination on a flat substrate, the present problem is not a bifurcation problem. Crack closure at sufficiently high stress levels are shown to occur. Results show a very strong dependency on fracture mechanical parameters of the angle of the corner including the range of parameters where crack closure occurs. Analytical results for the fracture mechanical properties have been obtained, and these are applied in a study of the effect of contacting crack faces. Special attention has been given to analyse conditions under which steady state propagation of buckling driven delamination takes place.