Case of enantiomer impurity identification by normal-phase chiral high-performance liquid chromatography with optical rotation and mass spectrometric detection

An impurity produced in the synthesis of compound I is separated and identified as its enantiomer II using normal-phase chiral high-performance liquid chromatography (HPLC) with UV absorbance, optical rotation (OR) and mass spectrometric (MS) detection. The results show that the impurity II and compound I have equal and opposite specific rotations, identical MS spectra and the same MS-MS fragmentation pattern, as required for enantiomers. The procedures presented demonstrate a novel combination of methods for enantiomer identification and characterization that do not require the preparation of individual enantiomer markers or even the racemic mixture, thus reducing the need for additional synthetic work.     

Adsorption of a diverse set of organic vapors on the bulk water surface

The bulk water surface is of fundamental interest to physical as well as environmental chemistry. As there is a lack of wide-ranging adsorption data from the air to the bulk water surface, a large and diverse data set of adsorption coefficients of nonionic, organic compounds has been produced with inverse gas chromatography. The 61 compounds were chosen to cover a large range of properties, considering the intermolecular interactions between the compounds and the bulk water surface, i.e., van der Waals and electron-donor/acceptor interactions. The data set gained in this work was interpreted with a linear free energy relationship (LFER) based on these intermolecular interactions. From this LFER, a general adsorption model is derived, including compound (i) and surface (surf) properties: log K(i surf/air)(m(3)/m(2)) = 0.135(+/-0.003) log K(i hexadecane/air)(gamma(surf)(vdW))(0.5) + 5.11(+/-0.15)Sigma beta(i2)(H)EA(surf) + 3.60(+/-0.28)Sigma alpha(i2)(H)ED(surf) - 8.47. This adsorption model can be used for the characterization of adsorption to any other surface. The adsorption model for bulk water surface adsorption as well as the general adsorption model can be used as prediction tools in natural or technical systems.     

A numerical/experimental study of the dynamic structure of a buoyant jet diffusion flame

An overview of a joint numerical/experimental investigation of the dynamic structure of a low-speed buoyant jet diffusion flame is presented. The dynamic interactions between the flame surface and the surrounding fluid mechanical structures are studied by means of a direct numerical simulation closely coordinated with experiments. The numerical simulation employs the full compressible axisymmetric Navier-Stokes equations coupled with a flame sheet model. Counterrotating vortex structures both internal and external to the flame surface are seen to move upward along with flame sheet bulges. These buoyancy-driven dynamic features compare well with those observed experimentally by means of phase-locked flow visualizations over entire flame-flickering cycles. The flicker frequencies measured both computationally and experimentally also compare well. Other aspects of this investigation which are discussed include sudden jumps in flicker frequency with increasing coflow velocity and the utilization of background pressure changes to simulate gravitational force variations experimentally.     

Calculated strain response of vibrational modes for H-containing point defects in diamond

The low mass of hydrogen leads to highly localised, high-frequency vibrational modes associated with H-containing defects in crystalline materials. In addition to vibrational spectroscopy, the presence of hydrogen in diamond has been identified from several experimental techniques. In particular, paramagnetic resonance shows that H is often associated with lattice vacancies, but in many cases the microscopic structure of the defects remains to be determined. We present the results of first-principles density-functional modelling of selected H-containing point defects, reporting both the calculated frequencies and the change in frequencies with applied strain. We show that more constrained environments lead to significantly larger strain-related shifts in frequency than more open environments, such as where the H is associated with lattice vacancies.     

The saponins: polar isoprenoids with important and diverse biological activities

Saponins are polar molecules that consist of a triterpene or steroid aglycone with one or more sugar chains. They are one of the most numerous and diverse groups of plant natural products. These molecules have important ecological and agronomic functions, contributing to pest and pathogen resistance and to food quality in crop plants. They also have a wide range of commercial applications in the food, cosmetics and pharmaceutical sectors. Although primarily found in plants, saponins are produced by certain other organisms, including starfish and sea cucumbers. The under explored biodiversity of this class of natural products is likely to prove to be a vital resource for discovery of high-value compounds. This review will focus on the biological activity of some of the best-studied examples of saponins, on the relationship between structure and function, and on prospects for synthesis of ‘‘designer’’ saponins.     

Holographic flow visualization as a tool for studying three-dimensional coherent structures and instabilities

Holography is capable of three-dimensional (3D) representation of spatial objects such as fluid interfaces and particle ensembles. Based on this, we adapt it into a 3D flow visualization tool called Holographic Flow Visualization (HFV). This technique provides a novel means of studying spatially and temporally evolving complex fluid flow structures marked by a disperse phase or interfaces of different fluids. This paper demonstrates that HFV is a straightforward technique, especially when the In-line Recording Off-axis Viewing (IROV) configuration is used. The technique can be applied either as a stand-alone experimental tool for studying scalar-based coherent structures, flow instabilities, interactions of different fluids driven by fluid dynamics, interfacial phenomena, or as a precursor to volumetric 3D velocity vector field measurement of complex transient flow dynamics. Experimental results in several complex fluid flows and flames demonstrate the effectiveness of HFV. Different methods are used to mark flow structures undergoing different instabilities: 1) a vortex ring grown out of a drop of polymer suspension falling in water, 2) cascade of a bag-shaped drop of milk in water, and 3) internal flow structures of a jet diffusion flame.