Evidence for dynamics on a 100 ns time scale from single- and double-quantum nitrogen-14 NMR in solid peptides

The indirect detection of 14N spectra via protons in the manner of heteronuclear multiple-quantum correlation (HMQC) allows one to obtain single- (SQ) and double-quantum (DQ) 14N spectra in solids. A comparison of the SQ and DQ line widths as a function of temperature with simulations reveals motions in the tripeptide AAG with rates on the order of 107 s(-1) at 49 degrees C.     

Carbene-alkene complexes between a nucleophilic carbene and electron-poor alkenes

Spirooxadiazoline 5 is a clean thermal source of tricyclo[6.2.1.0 (2,7)]undec-9-en-11-ylidene (7), a typical foiled carbene. Species 7 can be trapped efficiently at 165 degrees C by electron-deficient alkenes like acrylonitrile and fumaronitrile whereby the anti addition products are obtained exclusively. Higher temperatures, however, favor intramolecular reactions. Density functional theory (DFT) calculations predict the formation of a strong complex between both reactants which actually is a minimum on the free energy scale. These results confirm the nucleophilic character of foiled carbenes and the presence of a significant barrier toward rearrangement.     

Cost Effective Electrochemical Sensor for L-Methionine Based on Graphitic Carbon Nitride Sheets Modified Electrode

L-methionine (L−Me) deficiency in human body leads to several complications. In the present work, graphitic carbon nitride nanosheets (GCN−S) modified glassy carbon electrode (GC/GCN−S) was developed as a cost effective electrochemical sensor for L−Me. The oxidation of L−Me at bare GC electrode shows an ill-defined peak and it was unstable whereas a well-defined stable oxidation peak was obtained at GC/GCN−S electrode. While increasing L−Me concentration from 100 nM to 0.2 mM, the amperometric current increases linearly with R²=0.9901 and LOD was found to be 0.32 nM (S/N=3). Finally, GC/GCN−S electrode was used to determine L−Me in blood serum samples.     

Droplet microfluidics

Droplet-based microfluidic systems have been shown to be compatible with many chemical and biological reagents and capable of performing a variety of "digital fluidic" operations that can be rendered programmable and reconfigurable. This platform has dimensional scaling benefits that have enabled controlled and rapid mixing of fluids in the droplet reactors, resulting in decreased reaction times. This, coupled with the precise generation and repeatability of droplet operations, has made the droplet-based microfluidic system a potent high throughput platform for biomedical research and applications. In addition to being used as microreactors ranging from the nano- to femtoliter range; droplet-based systems have also been used to directly synthesize particles and encapsulate many biological entities for biomedicine and biotechnology applications. This review will focus on the various droplet operations, as well as the numerous applications of the system. Due to advantages unique to droplet-based systems, this technology has the potential to provide novel solutions to today's biomedical engineering challenges for advanced diagnostics and therapeutics.     

Asymmetric synthesis of vicinal amino alcohols: xestoaminol C, sphinganine and sphingosine

The highly diastereoselective anti-aminohydroxylation of alpha,beta-unsaturated esters, via conjugate addition of lithium (S)-N-benzyl-N-(alpha-methylbenzyl)amide and subsequent in situ enolate oxidation with (+)-(camphorsulfonyl)oxaziridine, has been used as the key step in the asymmetric synthesis of N,O-diacetyl xestoaminol C (41% yield over 8 steps), N,O,O-triacetyl sphinganine (30% yield over 8 steps) and N,O,O-triacetyl sphingosine (30% yield over 7 steps).     

Unconventional metal organic frameworks: porous cross-linked phosphonates

The past decade has witnessed an exponential growth of metal organic framework compounds (MOFs). The defining character of these compounds is their porosity. However, in many cases no effort was made to show evidence that a stable porous structure has been achieved and that the pores may be accessed. In the present paper we describe recent work on porous pillared zirconium diphosphonates, and the newer and in many respects different characteristics of tin(iv) phosphonates. The Sn(IV) monophosphonates form spherical globules that exhibit very high surface areas. The surface area arises from their nano-sized particles that pack in a "house of cards" arrangement. Also, it is shown that the 1,4-monophenyldiphosphonic acid forms highly porous (250-400 m2 g(-1)) materials with Sn(IV) when prepared in alcohol-water media. This is not the case with analogous Zr(IV) compounds. The many variations in the syntheses of both the zirconium and tin aryl- and alkyldiphosphonate pillars and their combinations with spacers such as methyl- and monophenylphosphonic acid have created a variety of highly porous materials that are stable to 400 degrees C in air, highly stable in acid media, do not collapse when de-solvated, and can be post and presynthesis altered to include functional groups. Several new directions taken by other researchers are also described. However, it is emphasized in this presentation that the cross-linked compounds form particles that precipitate rapidly into nanoparticles that exhibit only short range order. Therefore, they differ from the more conventional MOFs in that they are not amenable to structure solution by X-ray or neutron diffraction techniques. Rather, they must be understood on the basis of modeling and indirect data from EM, NMR, and additional spectroscopic and textural studies.