GUESSmix-guided optimization of elution–extrusion counter-current separations

Rational strategies for the optimization of separations are vital to any chromatographic technique. In counter-current separations (CS), once a suitable solvent system is selected for a given separation, the operator is faced with the task of optimizing the separation through the manipulation of those adjustable operation parameters allowed for by the current CS technology. This study employed a mixture of 21 natural products of varying polarity, molecular mass, and functionality, termed the GUESSmix, as a tool to assess the effectiveness of optimization strategies. The behavior of the GUESSmix was observed in the hexane/ethyl acetate/methanol/water 4:6:4:6 (HEMWat +3) solvent system. The effect of operation parameters on both the elution and extrusion stages of a recently introduced CS methodology, termed elution–extrusion counter-current chromatography (EECCC), was investigated. The resulting chromatograms were plotted with K-based reciprocal symmetry plots (ReS and ReSS), which allow comparison of the K values of significant peaks and assessment of resolution of eluting compounds in the interval 0 ≤ K ≤ ∞. The operation parameters studied were: (1) the effect of temperature controlled water circulation around the centrifuge; (2) the combination of flow rate and revolution speed; (3) sample loading capacity; (4) the direction of rotation either agreeing with or opposing the direction of coil winding; (5) injection before equilibration, a practice that saves operator time and reduces solvent consumption. The GUESSmix was found to be a highly useful reference mixture to compare and contrast stationary phase retention volume ratios, resolution, K-values, peak shapes, and extrusion characteristics between CS experiments. EECCC is shown to be a robust technique that may be enhanced with appropriate temperature, rpm, flow rate, sample loading, direction of rotation, and injection timing. Plotting ReS[S] chromatograms enables systematic study of CS parameters, which are not reproducibly represented in retention time or volume plots.     

Graphene on Ru(0001): a 25 x 25 supercell

The structure of a single layer of graphene on Ru(0001) has been studied using surface x-ray diffraction. A surprising superstructure containing 1250 carbon atoms has been determined, whereby 25 x 25 graphene unit cells lie on 23 x 23 unit cells of Ru. Each supercell contains 2 x 2 crystallographically inequivalent subcells caused by corrugation. Strong intensity oscillations in the superstructure rods demonstrate that the Ru substrate is also significantly corrugated down to several monolayers and that the bonding between graphene and Ru is strong and cannot be caused by van der Waals bonds. Charge transfer from the Ru substrate to the graphene expands and weakens the C-C bonds, which helps accommodate the in-plane tensile stress. The elucidation of this superstructure provides important information in the potential application of graphene as a template for nanocluster arrays.     

SCON—a Short Conditional intrON for conditional knockout with one-step zygote injection

The generation of conditional alleles using CRISPR technology is still challenging. Here, we introduce a Short Conditional intrON (SCON, 189 bp) that enables the rapid generation of conditional alleles via one-step zygote injection. In this study, a total of 13 SCON mouse lines were successfully generated by 2 different laboratories. SCON has conditional intronic functions in various vertebrate species, and its target insertion is as simple as CRISPR/Cas9-mediated gene tagging.Subject terms: Genetic engineering, Gene targeting, Genetic models     

Spectrally optimal illuminations for diabetic retinopathy detection in retinal imaging

Optical Review - Retinal photography is a standard method for recording retinal diseases for subsequent analysis and diagnosis. However, the currently used white light or red-free retinal imaging...     

Suzuki's scaling limit and the theory of statistical fluctuations in nuclear fission

Statistical fluctuations near dynamically instable points require a special theoretical treatment. The saddle point in fission is such a point. A method developed by Suzuki (“scaling limit”) is applied to this problem. It is shown that large differences exist between the variances of the kinetic energy distribution, or of the momentum distribution, of the fission variable takenat a fixed time, and the variances of these quantities evaluatedat a given position of the fission variable. This fact is of considerable importance for the calculation of the width of the kinetic energy distribution of fission products. It is probably relevant also for the evaluation of statistical fluctuations in heav-ion reactions.     

A microscopic,but not self-consistent approach to nuclear binding and deformation energies

Using various versions of the Skyrme force and Negele's interaction, we calculate deformation energies of nuclei by evaluating the expectation value of the many-body Hamiltonian in wave functions taken to be antisymmetrized products of single-particle functions. These single-particle functions are eigenfunctions of a phenomenological potential, here taken to be a deformed Woods-Saxon well. The method can be thought of as an extension of the Strutinsky shell-correction method, to make the connection with the two-body interaction. The method employed here is checked by comparison with Hartree-Fock (HF) results; our method is, however, much faster than the HF method, and, therefore, suitable for a wide range of problems where one tests the sensitivity of results to changes in the two-body interaction. A fairly good agreement with the HF method is obtained for ground-state energies, radii and deformations, as well as for deformations of shape isomers. The main discrepancy is that our energies tend to increase slightly too rapidly with deformation, indicating that we may not have chosen the best phenomenological well. Two-dimensional energy surfaces, which agree quite well with those from the Strutinsky method, are found for ²⁴⁰Pu.     

Comparative EPR study of copper(II) complexes with threonine derivatives

Summary In order to get better insight into the structural reasons for different properties of copper(II) complexes withL-threonine,L-allo-threonine,L-N,N-dimethyl-threonine, andL-N,N-dimethyl-allo-threonine, their EPR spectra were studied as a function ofpH and temperature. AtpD9.4, in all complexes a change in the copper(II) coordination sphere from the glycine to the hydroxy type was observed. Inbis(L-threoninato)copper(II), the hydroxy type formed atpD9.4 was found to be stablized by increasing the temperature of the solution from 280 to 320 K. In all other copper(II) complexes, the conformational change is accompanied by the disruption of the Cu-N bond of one chelate ring.

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Vergleichende EPR-Untersuchungen von Kupfer(II)-Threonin-Komplexen

Zuzammenfassung Um einen besseren Einblick in die Beziehungen zwischen Struktur und Eigenschaften von Kupfer(II)-Komplexen mitL-Threonin,L-allo-Threonin,L-N,N-Dimethyl-Threonin undL-N,N-Dimethyl-allo-Threonin zu gewinnen, wurden ihre EPR-Spektren in Abhängigkeit vompH-Wert und von der Temperatur untersucht. Bei einempH-Wert von 9.4 (in deuterierter Lösung) wurde eine Veränderung in der Kupfer (II)-Koordinationssphäre festgestellt, die von einer Glycin-ähnlichen Konformation in eine vermutlich Hydroxy-ähnliche Konformation übergeht. Derbis(L-Threoninato)-Kupfer (II)-Hydroxy-Komplex wird durch eine Temperaturerhöhung von 280 auf 320K stabilisiert. Die Veränderung der Koordination vom Glycin-Typ wird von einem Bruch der Cu-N-Bindung eines Chelatrings begleitet.

     

Redox-induced coordination isomerization of a phosphoniobenzophospholide

1-Triphenylphosphoniobenzo[c]phospholide 1 reacts with [M(CO)(5)Br] (M = Mn, Re) and [Mn(CO)(3)(naphthalene)][BF(4)] to give complexes cis-[M(CO)(4)(1)Br] (5 a,b) and [Mn(CO)(3)(1)][BF(4)] (6 a[BF(4)]), respectively, featuring eta(1)(P)- and eta(5)(pi)-coordination of the phosphole ring. The corresponding reactions with [M(2)(CO)(10)] proceed with conservation of the metal-metal bond and yield, depending on the reaction temperature, dinuclear complexes [M(2)(CO)(8)(1)] (M=Mn, 7 a) or [M(2)(CO)(6)(1)(2)] (M=Mn, Re, 8 a,b) with mu(2)-bridging eta(1)(P):eta(2)(Pdbond;C) coordination of the phosphole moiety. All complexes formed were characterized by spectroscopic data; 5 b, 6 a[BF(4)], and 8 a,b were characterized by X-ray diffraction studies as well. The structural and (31)P NMR data of the dinuclear manganese complex 8 a suggest that the interaction between the metal atoms and the eta(2)-bound Pdbond;C double bond moieties is dominated by the L-->M charge-transfer contribution; this hints at a very low back-donation ability of the central M(2)(CO)(6) fragment. Investigation of the reactions of the Mn complexes 6 a and 8 a with Mg or ferrocenium hexafluorophosphate ([Fc][PF(6)]), respectively, revealed that the chemically reversible mutual interconversion between both species was feasible. Likewise, oxidation of the rhenium complex 8 b with [Fc][PF(6)] gave spectroscopic evidence for the formation of a Re analogue of 6 a. Electrochemical studies suggested that the oxidation 8 a-->2 6 a involves two consecutive single-electron-transfer steps, the first of which is electrochemically reversible and produces a metastable radical cation that is detectable by ESR spectroscopy. The mutual interconversion between 6 a and 8 a represents the first case of a reversible coordination isomerization of a phosphaarene that is triggered by a redox process and might stimulate further studies directed at the use of dinuclear phosphaarene complexes in redox-catalysis.     

27Al NMR Study of Al-Speciation in Aqueous Alumina-Sols

A new method of preparing concentrated alumo-sols, the hydrolysis of Al-tri-sec-butylate in acidic aqueous media at 85°C, was studied in detail by varying the H₂O/Al- and NO₃ ⁻/Al-ratios in wide ranges. The components of the sols were characterized by ²⁷Al NMR spectroscopy. The pH-value depends on both the chosen H₂O/Al- and NO₃ ⁻/Al-ratio and on the aging time of the sols and reflects the composition of the sols. Al₁₃ polycations were detected in sols with a pH-value between 3.0 and 3.7. As a new result its presence was shown by NMR below 3.4. The Al₁₃ content of the sols increased with pH and the maximum fraction of Al₁₃ polycations was detected in the sol with the highest pH (3.7). Nearly 65% of the entire aluminium content of this solution is bound in the Al₁₃ polycations. Hence, a new synthetic method for the preparation of Al₁₃ ions containing sols was developed. Aging studies of the sols showed, that the Al₁₃ polycations were more stable in solutions with higher pH-value. Al₁₃ polycations were detected after an aging time of four months only in sols with a pH-value of 3.7. Tempering the aged sols at 40° to 80°C caused formation of Al₁₃ and also of Al₃₀ polycations.