Micro-X-ray fluorescence as a general high-throughput screening method for catalyst discovery and small molecule recognition

A powerful high-throughput screening technique is described for the rapid screening of bead-based libraries for catalyst discovery and molecular recognition. Micro-X-ray fluorescence (MXRF) screens materials for elemental composition with mesoscale analysis. This method is nondestructive and requires minimal sample preparation and no special tags for analysis, and the screening time is dependent on the desired sensitivity. The speed, sensitivity, and simplicity of MXRF as a high-throughput screening technique were applied to screen bead-based libraries of oligopeptides for phosphate hydrolysis catalysts and molecular recognition of selective receptors for the degradation products and analogues of chemical warfare agents. This paper demonstrates the analytical or HTS capability of MXRF for combinatorial screening. It is meant only to show the capabilities of MXRF and is not meant as an exhaustive study of the catalyst and molecular recognition systems presented.     

Carbon phases on nickel surfaces

The conditions of the formation of different carbon surface phases on nickel substrates by the example of a planar Ni( 110) surface and a stepped Ni(771 ) surface similar in structure were determined. The structure of the phases was investigated by means of scanning tunneling microscopy (STM), and the influence of carbon on the structure of the nickel surface was demonstrated. The process of graphene synthesis by propylene cracking is described. A method for forming graphene islands on nickel is proposed. A variety of phase transitions between the carbon surface phases (e.g., surface carbide, graphene, and graphene islands) and the reasons for their irreversibility are discussed. The relation between the structures of the surface carbide phases and the crystal structures of the initial surfaces for two different substrates is shown.     

Counter-current chromatography of lipoproteins with a polymer phase system using the cross-axis synchronous coil planet centrifuge.

Lipoproteins were separated by counter-current chromatography using the type-XLL coil planet centrifuge. The separation was performed with a polymer phase system composed of 16% (w/w) polyethylene glycol 1000 and 12.5% (w/w) dibasic potassium phosphate by eluting the lower phase at a flow-rate of 0.5 ml/min. About 5 ml of the sample solution containing approximately 150 mg of a lipoprotein mixture were loaded. High- and low-density lipoproteins were resolved within 12 h. Each component was detected by gel electrophoresis with oil red staining.     

Angle-resolved photoelectron spectroscopy of geometrically nonuniform surfaces

The formation of angle-resolved photoelectron spectra for crystal surfaces with a complex geometric relief is considered. A simple model of a thin corrugated single-crystal film is proposed which illustrates the main specific features of this process. It is shown that photoelectron spectra of these surfaces exhibit features that, rather than reflecting the true electronic structure of the system, result from its superposition with the geometric structure. The validity of the model is demonstrated with the use of a physical system based on Ni(771) and Ni(755) stepped surfaces with periodic steps. It is revealed that, as a graphite coating grows to a monolayer thickness, these surfaces become faceted to form a geometrically nonuniform surface relief. The photoelectron spectra obtained for such a surface can be used to derive a quantitative characteristic of both the electronic structure of the surface and its geometric properties. The surface topography of the system is determined independently using scanning tunneling microscopy.     

Photoemission from stepped W(110): initial or final state effect?

The electronic structure of the (110)-oriented terraces of stepped W(331) and W(551) is compared to the one of flat W(110) using angle-resolved photoemission. We identify a surface-localized state which develops perpendicular to the steps into a repeated band structure with the periodicity of the step superlattices. It is shown that a final-state diffraction process rather than an initial-state superlattice effect is the origin of the observed behavior and why it does not affect the entire band structure.     

Preparation and Reactivity of 4,4′-diaminostilbene-2,2′disulphonate

The precursor compound 4,4′-diaminostilbene-2,2′disulphonic acid DAS-(SO₃H)₂ was successfully deprotonated through reactions with (n-Bu₄N)(OH) and NaOH to produce the corresponding salts sodium 4,4′-diaminostilbene-2,2′disulphonate Na₂(DAS-(SO₃)₂) (1) and tetrabutylammonium 4,4′-diaminostilbene-2,2′disulphonate (n-Bu₄N)₂(DAS-(SO₃)₂) (2). The structure of (n-Bu₄N)₂(DAS-(SO₃)₂) (2) was confirmed through the use of single crystal X-ray diffraction. Compound (2) crystallizes in the monoclinic space group P2₁/n with the lattice parameters of a = 10.0645(6), b = 14.2573(9), c = 17.6053(11), and β = 94.3160(10). The reaction of Cu²⁺(aq) with (n-Bu₄N)₂(DAS-(SO₃)₂) resulted in the crystallization of the molecular organocopper cluster, [CuDAS-(SO₃)₂]₂·3H₂O (3), that resembles a molecular parallelogram as revealed by single crystal X-ray diffraction. Compound (3) crystallizes in the monoclinic space group P2₁/n with the lattice parameters of a = 8.8647(6), b = 10.5247(7), c = 21.2265(14), and β = 93.1730(10). Within the structure of (3) each [DAS-(SO₃)₂]²⁻ ligand is shown to bind two copper atoms through interactions with three of the five available metal binding sites.

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Graphical abstract Preparation and Reactivity of 4,4′-diaminostilbene-2,2′disulphonate Natalie C. Rader, Heather A. Nees, Paul S. Szalay*, Matthias Zeller and Allen D. Hunter The preparation of 4,4′-diaminostilbene-2,2′disulphonic and its reactivity with copper(II) are described.

     

Primary constituents of blue cohosh: quantification in dietary supplements and potential for toxicity

Dietary supplements containing dried roots or extracts of the roots and/or rhizomes of blue cohosh (Caulophyllum thalictroides) are widely available. This botanical has a long history of use by Native Americans and its use continues to the present day. The primary constituents of blue cohosh are its alkaloids and saponins. The structures of the alkaloids magnoflorine, baptifoline, anagyrine, and N-methylcytisine have been known for many years. The last 10 years have seen a great increase in isolation and identification of the large number of saponins present in blue cohosh. Important developments in nuclear magnetic resonance techniques have contributed substantially to the increase in elucidation of the structures of the complex saponins. Several authors have described quantitative methods for both the alkaloids and saponins in blue cohosh. Such methods have made it possible to quantify these constituents in dietary supplements containing this botanical ingredient. Concentrations of both alkaloids and saponins vary substantially in dietary supplements of blue cohosh. The nicotinic alkaloid, N-methylcytisine, a potent toxicant, has been found in all dietary supplements of blue cohosh analyzed. The teratogenic alkaloid anagyrine has been found in some but not all dietary supplements.     

Sweeteners from plants—with emphasis on Stevia rebaudiana (Bertoni) and Siraitia grosvenorii (Swingle)

In addition to their widely recognized use as dietary supplement ingredients, plant-derived compounds are increasingly used as natural sweeteners. The search for nonnutritive sweeteners has been stimulated over the last 20–30 years by concern over demonstrated or suspected relationships between consumption of sucrose and high-fructose corn syrups and a variety of health-related conditions. In the USA, there is increased use of plant extracts known to contain highly sweet terpenoids. Purified extracts of Stevia rebaudiana (Bertoni) containing the diterpene glycosides stevioside and rebaudioside A are popular as sweeteners and are also used as dietary supplements, and soft drinks and nutritional and energy shakes incorporating extracts of Siraitia grosvenorii (Swingle) fruits containing sweet triterpene glycosides such as mogroside V are also on the market. Here, we review recent studies on these two important sources of noncaloric natural sweeteners, including analytical methods used to identify and quantify specific constituents and structural features relating to their sweetness. We also review the generally recognized as safe status of specific components and their status with respect to review by the Joint FAO/WHO Expert Committee on Food Additives.