Development of a Mild and Versatile Directed Cycloaddition Approach to Pyridines

The aza‐Diels–Alder cycloaddition of 1,2,4‐triazines with alkynes offers a rapid and convenient method for the synthesis of highly substituted pyridines, but often requires harsh conditions and long reaction times. The present study offers a solution to these limitations by use of a temporary tether established by a Lewis acid–base complexation of in situ generated alkynylboranes and triazines bearing a Lewis basic donor. The cycloaddition reactions take place within 20 min at 40 °C and provide direct access to a broad range of pyridines with complete and predictable regiocontrol. The carbon?boron bond can be further functionalised by cross‐coupling allowing further functionality to be introduced after cycloaddition.     

In vivo brain imaging using a portable 3.9 gram two-photon fluorescence microendoscope

We introduce a compact two-photon fluorescence microendoscope based on a compound gradient refractive index endoscope probe, a DC micromotor for remote adjustment of the image plane, and a flexible photonic bandgap fiber for near distortion-free delivery of ultrashort excitation pulses. The imaging head has a mass of only 3.9 g and provides micrometer-scale resolution. We used portable two-photon microendoscopy to visualize hippocampal blood vessels in the brains of live mice.     

Determination of methylamines and trimethylamine-N-oxide in particulate matter by non-suppressed ion chromatography

An ion chromatography method with non-suppressed conductivity detection was developed for the simultaneous determination of methylamines (methylamine, dimethylamine, trimethylamine) and trimethylamine-N-oxide in particulate matter air samples. The analytes were well separated by means of cation-exchange chromatography using a 3 mM nitric acid/3.5% acetonitrile (v/v) eluent solution and a Metrosep C 2 250 (250 mm × 4 mm i.d.) separation column. The effects of the different chromatographic parameters on the separation were also investigated. Detection limits of methylamine, dimethylamine, trimethylamine, and trimethylamine-N-oxide were 43, 46, 76 and 72 μg/L, respectively. The relative standard deviations of the retention times were between 0.42% and 1.14% while the recoveries were between 78.8% and 88.3%. The method is suitable for determining if methylamines and trimethylamine-N-oxide are a significant component of organic nitrogen aerosol in areas with high concentration of these species.     

Furan tetracarboxylic acid

Furan tetracarboxylic acid is a surprisingly strong acid. It forms well defined salts with a variety of bases. Its structure, and that of an intermediate in its preparation, is discussed in relation to its ultra-violet and infra-red spectra.     

Enantiomeric separation of R,S-naproxen by conventional and nano-liquid chromatography with methyl-beta-cyclodextrin as a mobile phase additive

Chiral separations of R,S-naproxen mixtures were obtained on an achiral column (ODS) with methyl-beta-cyclodextrin as a mobile phase additive using conventional and nano-LC. The optimised mobile phase composition was 20 mmol l(-1) methyl-beta-cyclodextrin, 20% (v/v) acetonitrile, and 50 mmol l(-1) sodium acetate buffer at pH 3 using hydrochloric acid for pH adjustment. In addition to UV detection at 232 nm, amperometric detection was also investigated. Without using any internal standard, the reproducibility of amperometric detection (+1.05 V vs. Ag/AgCl) over a long analysis cycle in LC was greatly improved by choosing the peak area ratio between R- and S-naproxen as the analytical readout (the relative standard deviation was 2.11%) and enantiomeric purity could be assessed directly. This method was successfully employed for enantiomeric purity assessment in commercial naproxen tablets. Finally, successful transfer from conventional LC to nano-LC was realised, resulting in over 1000-fold reduction in reagent consumption.     

Stereochemical relationships in the eudesmane (selinane) group of sesquiterpenes

The stereochemical correlations in the eudesmane¹ group of sesquiterpenes are highly ramified. In this article we attempt to summarise the evidence on which the correlations are founded. Most of the classical chemistry of the group of compounds has been reviewed, and some of the more recent developments have been described by Barton and de Mayo.     

On-line analysis of diesel engine exhaust gases by selected ion flow tube mass spectrometry

Selected ion flow tube mass spectrometry (SIFT-MS) has been used to analyse on-line and in real time the exhaust gas emissions from a Caterpillar 3304 diesel engine under different conditions of load (idle and 50% of rated load) and speed (910, 1500 and 2200 rpm) using three types of fuel: an ultra-low-sulphur diesel, a rapeseed methyl ester and gas oil. SIFT-MS analyses of the alkanes, alkenes and aromatic hydrocarbons in the headspace of these fuels were also performed, but the headspace of the rapeseed methyl ester consists mainly of methanol and a compound with the molecular formula C4H8O. The exhaust gases were analysed for NO and NO2 using O2+* reagent ions and for HNO2 using H3O+ reagent ions. The following aldehydes and ketones in the exhaust gases were quantified by using the combination of H3O+ and NO+ reagent ions: formaldehyde, acetaldehyde, propenal, propanal, acetone, butanal, pentanal, butanone and pentanone. Formaldehyde, acetaldehyde and pentenal, all known respiratory irritants associated with sensitisation to asthma of workers exposed to diesel exhaust, are variously present within the range 100-2000 ppb. Hydrocarbons in the exhaust gases accessible to SIFT-MS analyses were also quantified as total concentrations of the various isomers of C3H4, C3H6, C4H6, C5H8, C5H10, C6H8, C6H10, C7H14, C6H6, C7H8, C8H10 and C9H12.