Adsorption of humic acid on goethite: isotherms, charge adjustments, and potential profiles

The adsorption of natural organic matter (NOM) on mineral (hydr)oxide plays an important role in the evaluation of the speciation of toxic metal ions in the environment. Because both NOM and mineral oxide have variable charges that adjust upon adsorption, a good understanding of proton binding is required before the binding of metal ions can be understood. In this study, the adsorption of purified Aldrich humic acid (PAHA) on goethite was examined as a function of the environmental conditions (pH, salt concentration, and free concentration of PAHA) together with the proton adsorption to PAHA, goethite, and their mixtures. The induced charges on both components were separated on the basis of the difference between the charge/pH curves of the mixture and those of the single components. The electrostatic potential profile across the adsorbed layer was obtained as a numerical solution of the Poisson-Boltzmann equation using the charge density of the adsorbed PAHA and the goethite surface. From the quantitative evaluation of the induced charge on both components, it is revealed that the degree of the charge adjustment is related to the electrostatic affinity between the PAHA segments and the goethite surface, the electrostatic repulsion between the PAHA segments, and the electrostatic shielding by salt ions. Considering the charge distribution of the adsorbed PAHA at the goethite surface, it is concluded that the change of the charge adjustment is sensitive to that of the conformation of the adsorbed PAHA. From the detailed inspection of the assumptions made and the comparison with the reported theoretical calculations, the obtained potential profiles are considered to broadly reflect the true potential profiles. Because a charge adjustment is not frequently considered in detail in relation to the NOM adsorption on metal (hydr)oxides, the obtained results can form the basis for the further development of modeling of the adsorption of NOM on (hydr)oxide surfaces.     

Optimization of azeotropic protein separations in gradient and isocratic ion-exchange simulated moving bed chromatography

The separation of dilute binary mixtures of proteins by salt aided ion-exchange simulated moving bed (SMB) chromatography is optimized with respect to throughput, desorbent consumption and salt consumption. The optimal flow-rate ratios are analytically determined via an adopted "triangle theory". Azeotropic phenomena are included in this procedure. The salt concentrations in the feed and recycled liquid are subsequently determined by numerical optimization. The azeotropic separation of bovine serum albumin and a yeast protein is used to illustrate the procedure. Gradient operation of the SMB is generally preferred over isocratic operation. A feed of azeotropic salt concentration can only be separated in a gradient SMB. Desorbent and salt consumption are always lower in gradient than in isocratic SMB chromatography.     

Luminescence Properties of Terbium-, Cerium-, or Europium-Doped α-Sialon Materials

New interesting luminescent α-sialon (M_(m/val+)^val+ Si_12-(m+n) Al_(m+n)OnN_(16−n)) (M=Ca, Y) materials doped with Ce, Tb, or Eu have been prepared and their luminescence properties studied. These show that Tb and Ce are in the 3+ and Eu in the 2+ state. Low-energy 4f↔5d transitions are observed as compared to the luminescence of these ions doped in oxidic host-lattices. This is partially explained by the nitrogen-rich coordination of the rare-earth ion and partially by the narrow size of the lattice site. The latter gives rise to a strong crystal-field splitting of the 5d band and a rather large Stokes shift for Ce³⁺ and Eu²⁺ (6500-7500 and 7000-8000 cm⁻¹, respectively). For (Y,Tb)-α-sialon the Tb³⁺ 4f→5d excitation band (∼260 nm) is in the low-energy host-lattice absorption band (?290 nm), giving rise to a strong absorption for 254-nm excitation, but a low quantum efficiency. The latter is due to photoionization processes or selective excitation of Tb³⁺ at the defect-rich surface, resulting in radiationless transitions. Ce- and Eu-doped Ca-α-sialon show bright long-wavelength luminescence (maxima at 515-540 and 560-580 nm for Ce and Eu, respectively) with a high quantum efficiency and high absorption for 365- and 254-nm excitation. The Eu²⁺ emission intensity and absorption increases for increasing m, which is explained by the Eu²⁺ richer α-sialon composition. The position of the Eu^2α emission does not shift with changing composition of the host-lattice (m, n values), indicating that the local coordination of the Eu²⁺ ion is hardly dependent on the matrix composition.     

Mixed IR/Vis Two‐Dimensional Spectroscopy: Chemical Exchange beyond the Vibrational Lifetime and Sub‐ensemble Selective Photochemistry

Two‐dimensional exchange spectroscopy (2D EXSY) is a powerful method to study the interconversion (chemical exchange) of molecular species in equilibrium. This method has recently been realized in femtosecond 2D‐IR spectroscopy, dramatically increasing the time resolution. However, current implementations allow the EXSY signal (and therefore the chemical process of interest) only to be tracked during the lifetime (T₁) of the observed spectroscopic transition. This is a severe limitation, as typical vibrational T₁ are only a few ps. An IR/Vis pulse sequence is presented that overcomes this limit and makes the EXSY signal independent of T₁. The same pulse sequence allows to collect time‐resolved IR spectra after electronic excitation of a particular chemical species in a mixture of species with strongly overlapping UV/Vis spectra. Different photoreaction pathways and dynamics of coexisting isomers or of species involved in different intermolecular interactions can thus be revealed, even if the species cannot be isolated because they are in rapid equilibrium.     

Biotransformation-mediated synthesis of (1S)-1-(2,6-dichloro-3-fluorophenyl)ethanol in enantiomerically pure form

An efficient four-step biotransformation-mediated synthesis of (1S)-1-(2,6-dichloro-3-fluorophenyl)ethanol in enantiomerically pure form is described. This compound is a key intermediate required for the preparation of PF-2341066, a potent inhibitor of c-Met/ALK that is currently in clinical development. The described synthesis was used to manufacture 6 kg of the title compound and can also be employed to produce the corresponding (1R)-enantiomer.     

Lattice fermions in euclidean space-time

A very short proof of a no-go theorem for putting fermions on a lattice is given using the Poincaré-Hopf theorem. The no-go theorem forbids the lattice formulation of theories with handed fermions without species doubling. Examples of such theories are chiral invariant QCD and the Weinberg-Salam-Glashow model. We give arguments why it could be possible to circumvent the no-go theorem by relaxing one of the assumptions, viz. bilinearity of the action in the fermion fields.     

Cross-linked aggregates of (R)-oxynitrilase: a stable, recyclable biocatalyst for enantioselective hydrocyanation

[Reaction: see text] The (R)-oxynitrilase from almonds was immobilized as a cross-linked enzyme aggregate (CLEA) via precipitation with 1,2-dimethoxyethane and subsequent cross-linking using glutaraldehyde. The resulting preparation was a highly effective hydrocyanation catalyst under microaqueous conditions, which suppress the nonenzymatic background reaction. The beneficial effect of these latter conditions on the hydrocyanation of slow-reacting aldehydes is demonstrated. The oxynitrilase CLEA was recycled 10 times without loss of activity.