Spiroborates derived from catecholborane and ephedrine type aminoalcohols - model compounds for the study of intramolecular N→B coordination by dynamic 1H-, 11B- and 13C-NMR.

A convenient synthesis of the title compounds is reported. These serve as models to study intramolecular N→B coordination by means of dynamic NMR spectroscopy (¹H, ¹¹B, ¹³C). Steric interactions between substituents at the boroxazolidine ring (C(5)Ph, C(4)Me, NMe) determine the stability of the N→B bond and the nitrogen configuration.     

Nonpolar organic compounds in fine particles: quantification by thermal desorption–GC/MS and evidence for their significant oxidation in ambient aerosols in Hong Kong

Nonpolar organic compounds (NPOCs) in ambient particulate matter (PM) commonly include n-alkanes, branched alkanes, hopanes and steranes, and polycyclic aromatic hydrocarbons (PAHs). The recent development of thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) has greatly reduced time and labor in their quantification by eliminating the laborious solvent extraction and sample concentration steps in the traditional approach that relies on solvent extraction. The simplicity of the TD-GCMS methods has afforded us concentration data of NPOCs in more than 90 aerosol samples in two aerosol field studies and 20 vehicular emissions-dominated source samples in Hong Kong over the past few years. In this work, we examine the interspecies relationships between select NPOCs and their concentration ratios to elemental carbon (EC) among the ambient samples and among the source samples. Our analysis indicates that hopanes were mainly from vehicular emissions and they were significantly oxidized in ambient PM. The hopane/EC ratio in ambient samples was on average less than half of the ratio in vehicular emissions-dominated source samples. This highlights the necessity in considering oxidation loss in applying organic tracer data in source apportionment studies. Select PAH/EC ratio–ratio plots reveal that PAHs had diverse sources and vehicular emissions were unlikely a dominant source for PAHs in Hong Kong. Biomass burning and other regional sources likely dominated ambient PAHs in Hong Kong.     

An unusual conformational similarity of two peptide folds featuring sulfonamide and carboxamide on the backbone

Two folded peptides featuring carboxamide and sulfonamide at the core of the peptide fold have been shown to possess almost similar conformational features, despite the well-known fact that carboxamides and sulfonamides have strikingly different hydrogen-bonding and geometrical preferences.     

In‐line Particle Size Measurement for Control of Jet Milling

Jet milling is suitable for the production of very fine powders with a well‐defined particle size distribution (PSD). The major disadvantage of the process is the poor energy efficiency. In practice jet mills have to be operated below their maximum capacity in order to avoid the production of off‐specification material, due to operation disturbances. Therefore, it is important to automate operation with a real‐time PSD instrument for quality control. In this paper, a study for in‐line particle size measurement using laser diffraction is presented to improve operation control. This measurement system uses a novel CMOS pixel array, which has a robust and flexible feature for the application. It also includes an in‐line cell system, where direct measurement is implemented in the product particle stream coming from the mill and an air purge for the cell window allows continued operation. Experiments were conducted on a 10‐inch spiral jet mill pilot plant with alpha‐Al₂O₃ as test material. The milling process is investigated by varying the operational conditions. The measurement results are useful to build a grinding model for control purpose.