Strong enantioselective self-recognition of a small chiral molecule

In the present report, we have crystallized a single enantiomer and the racemate of N-3,5-dinitrobenzoyl (DNB) leucine. In both cases, the X-ray structures show clear evidence of homochiral dimerization in the solid state. Moreover, only homochiral dimers were observed in the unit cell of the racemate, a result of solid-state enantioselective complexation. The crystal structures support a chiral recognition mechanism involving two hydrogen bonds and an offset pi-pi interaction between the DNB rings.     

Hierarchical nanomanufacturing: from shaped zeolite nanoparticles to high-performance separation membranes

Despite more than a decade of intense research on the high-resolution selectivity of thin zeolite films as alternatives to energy-intensive industrial separations, membranes consisting of intergrown, oriented zeolite crystals have fallen short of gaining wide commercial application. Factors including poor performance, high cost, and difficulties in scale up have contributed to this, and have also stunted their application in other niche markets. Until recently, rational design of these materials was limited because of the elusive mechanism of zeolite growth, and forced more empirical approaches. New understanding of zeolite growth along with recent advances in the molecular engineering of crystal microstructure and morphology, assembly of crystal monolayers, and synthesis of ordered films constitute a strong foundation for meeting stringent industrial demands in the future. Together with new processing capabilities, such a foundation should make it possible to synthesize commercially viable zeolite membranes through hierarchical approaches. Such advances open exciting prospects beyond the realm of separations for assembly of novel and complex functional materials including molecular sensors, mechanically stable dielectrics, and novel reaction-diffusion devices.     

Biocatalytic microcontact printing

Immobilized biocatalytic lithography is presented as an application of soft lithography. In traditional microcontact printing, diffusion limits resolution of pattern transfer. By using an immobilized catalyst, the lateral resolution of microcontact printing would depend only on the length and flexibility of the tether (<2 nm) as opposed to diffusion (>100 nm). In the work, exonuclease reversibly immobilized on a relief-patterned stamp is used to ablate ssDNA monolayers Percent of ablation was determined via confocal fluorescence microscopy to be approximately 70%.     

Defect‐Controlled Electronic Properties in AZn2Sb2 Zintl Phases

Experimentally, AZn₂Sb₂ samples (A=Ca, Sr, Eu, Yb) are found to have large charge carrier concentrations that increase with increasing electronegativity of A. Using density functional theory (DFT) calculations, we show that this trend can be explained by stable cation vacancies and the corresponding finite phase width in A_1?xZn₂Sb₂ compounds.     

Pyrone Diels–Alder Routes to Indolines and Hydroindolines: Syntheses of Gracilamine,Mesembrine, and Δ7‐Mesembrenone

Although the Diels–Alder reaction has long been utilized for the preparation of numerous heterocycles, opportunities to extend its power remain. Herein, we detail a simple, modular, and robust approach that combines various amines regioselectively with 4,6‐dichloropyrone to create substrates which, under appropriate conditions, can directly deliver varied indolines and hydroindolines through [4+2] cycloadditions with substitution patterns difficult to access otherwise. As an initial demonstration of the power of the strategy, several different natural products have been obtained either formally or by direct total synthesis, with efforts toward one of these—the complex amaryllidaceae alkaloid gracilamine—affording the shortest route to date in terms of linear step count.     

Characterization of fulvic acids by liquid chromatography-quadrupole time-of-flight mass spectrometry

Fulvic acid standards from Suwannee River, Pony Lake, Elliot Soil, Waskish Peat, and Nordic Reservoir were characterized by liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) operating in negative electrospray ionization mode. The method employed a commercially available stationary phase that resulted in a distinctive chromatographic peak for each of the fulvic acid samples that differed in width and retention time at peak maximum. The QTOF-MS, operating in TOF mode, revealed that the unique chromatographic peak shapes were the result of the relative fraction of hydrogen and oxygen contained in various fulvic acid components. Those species that contained larger amount of hydrogen displayed a larger mass defect and were retained longer on the LC column, indicating reduced polarity. This is supported by a reduction in the degree of fragmentation related to polar functional groups as the mass defect and retention time increased. Lastly, the analysis of even and odd mass (at m/z 1 greater) ion intensity ratios revealed a correlation to the percent nitrogen of the various standards.