Ethylene oxide-bridged bipyridine oligomers that function as selective host molecules for the encapsulation of small alkali cation guests

Two novel ethylene oxide-bridged bipyridine oligomers were synthesized that contain host pockets with four (1) or six (2) oxygen donor atoms and a pyridyl nitrogen donor. The alkali picrate extracting ability and selectivity of these free ligands was investigated using a liquid–liquid dichloromethane–water extraction study. Both open-chain oligomer frameworks display unexpectedly high extraction efficiency (EE) values for specific guest ions (EE = 57% Na⁺ extracted by 1, and EE = 39% Cs⁺ extracted by 2). These extraction values are comparable to macrocyclic analogues and their ion selectivities follow the ‘same-fit’ concept that has been extensively reported for fixed pocket systems. The shorter chain oligomer (1) binds ions in the series (Na⁺ > K⁺ > Cs⁺), while the larger oligomer (2) binds ions in the reverse order (Cs⁺ > K⁺ > Na⁺). Formation of the host–guest ligand–ion complexes were verified by ¹H NMR spectroscopy and MALDI-TOF mass spectrometry experiments. A Job’s plot analysis based on UV spectral data also supported the 1:1 (oligomer to ion) complexation observed in the MALDI mass spectra.     

Scope and mechanism for lewis acid-catalyzed cycloadditions of aldehydes and donor-acceptor cyclopropanes: evidence for a stereospecific intimate ion pair pathway

In this work, the one-step diastereoselective synthesis of cis-2,5-disubstituted tetrahydrofurans via Lewis acid catalyzed [3 + 2] cycloadditions of donor-acceptor (D-A) cyclopropanes and aldehydes is described. The scope and limitations with respect to both reaction partners are provided. A detailed examination of the mechanism has been performed, including stereochemical analysis and electronic profiling of both reactants. Experimental evidence supports an unusual stereospecific intimate ion pair mechanism wherein the aldehyde functions as a nucleophile and malonate acts as the nucleofuge. The reaction proceeds with inversion at the cyclopropane donor site and allows absolute stereochemical information to be transferred to the products with high fidelity. The mechanism facilitates the stereospecific synthesis of a range of optically active tetrahydrofuran derivatives from enantioenriched D-A cyclopropanes.     

The ultimate veal calf reference experiment: hormone residue analysis data obtained by gas and liquid chromatography tandem mass spectrometry

A lifetime controlled reference experiment has been performed using 42 veal calves, 21 males and 21 females which were fed and housed according to European regulations and common veterinary practice. During the experiment feed, water, urine and hair were sampled and feed intake and growth were monitored. Thus for the first time residue analysis data were obtained from guaranteed lifetime-untreated animals. The analysis was focused on the natural hormones estradiol and testosterone and their metabolites, on 17beta- and 17alpha-nortestosterone, on 17beta- and 17alpha-boldenone and androsta-1,4-diene-3,17-dione (ADD), and carried out by gas chromatography tandem mass spectrometry (GC/MS/MS), an estrogen bioassay and liquid chromatography (LC) MS/MS. Feed, water and hair samples were negative for the residues tested. Female calf urines showed occasionally low levels of 17alpha-estradiol and 17alpha-testosterone. On one particular sampling day male veal calf urines showed very high levels of 17alpha-testosterone (up to 1000 ng mL(-1)), accompanied by lower levels of estrone and 17beta-testosterone. Despite these extreme levels of natural testosterone, 17beta-boldenone was never detected in the same urine samples; even 17alpha-boldenone and ADD were only occasionally beyond CCalpha (maximum levels 2.7 ng mL(-1)). The data from this unique experiment provide a set of reference values for steroid hormones in calf urine and demonstrate that 17beta-boldenone is not a naturally occurring compound in urine samples.     

Competition between receptors in dynamic combinatorial libraries: amplification of the fittest?

Dynamic combinatorial chemistry is a powerful tool for the discovery of strong binders (synthetic receptors or ligands) because binding causes a shift in the equilibrium of library members toward those that bind well. Ideally, the best binders are selectively amplified. However, theoretical studies predict this is not always the case. This paper describes the first quantitative experimental evidence proving that, under special circumstances, the preferential amplification of suboptimal synthetic receptors can indeed occur. Our results also demonstrate that reducing the amount of guest in the library can rectify such undesirable behavior and ensures selective amplification of the fittest receptor.     

Elucidation of tautomer structures of 2-acetyltetrahydropyridine using gas chromatography/mass spectrometry and gas chromatography/infrared spectroscopy

2-Acetyltetrahydropyridine is an important flavor component in heated corn products such as popcorn and corn chips. The compound exists as a mixture of two tautomers that have different flavor/aroma characteristics. The tautomers also exhibit different chromatographic behaviors and are distinguishable spectroscopically. Though their electron ionization mass spectra are different, structure assignment based on low-resolution mass spectra alone has been subject to error. A combination of high resolution exact mass measurement and vapor phase infrared measurement of the separated tautomers was used to unambiguously assign the tautomer structures.     

Efficient classical simulation of continuous variable quantum information processes

We obtain sufficient conditions for the efficient simulation of a continuous variable quantum algorithm or process on a classical computer. The resulting theorem is an extension of the Gottesman-Knill theorem to continuous variable quantum information. For a collection of harmonic oscillators, any quantum process that begins with unentangled Gaussian states, performs only transformations generated by Hamiltonians that are quadratic in the canonical operators, and involves only measurements of canonical operators (including finite losses) and suitable operations conditioned on these measurements can be simulated efficiently on a classical computer.