Comparison of digestion procedures for the determination of mercury in soils by cold-vapour atomic absorption spectrometry

Five digestion procedures were investigated for the determination of mercury in soils by cold-vapour atomic absorption spectrometry. These methods included three acid leaching procedures in open systems and two acid digestion procedures in closed decomposition vessels. The closed vessels were heated in a conventional laboratory oven or a laboratory microwave oven. In the open systems, digestion with concentrated acids at elevated temperatures led to considerable losses of (organo) mercury compounds, while digestion at ambient temperature gave incomplete oxidation of the sample matrix. To prevent any losses of mercury and to obtain complete oxidation, the use of a closed decomposition system at elevated temperatures appeared to be necessary. The results obtained with these closed systems were in good agreement with those obtained by neutron activation analysis. Heating in a microwave oven appeared to be a considerable improvement over conventional thermal heating.     

Zirconium-catalysed N-acylation of lactams using unactivated carboxylic acids

A large number of chemicals including surfactants, nootropic drugs and pesticides contain an N-acylated lactam moiety in their molecular structure. In this work, the direct, catalytic N-acylation of a number of lactams with various unactivated carboxylic acids is reported. Several Lewis acid catalysts were evaluated for their activity in the N-acylation of pyroglutamic acid methyl ester with palmitic acid; the highest activities were observed for zirconium-based catalysts. Yields of up to 97% were obtained utilising 10?mol% Zr(propoxide)₄ in mesitylene at reflux temperature, but ZrOCl₂·8H₂O was determined as the most stable catalyst. The substrate scope was investigated and a number of lactam-carboxylic acid combinations were successfully converted into the desired products in 57–97% yield. This method provides an alternative synthetic pathway towards the drug aniracetam, which can be produced in 84% yield. A plausible catalytic mechanism is presented based on kinetic experiments.     

Preparation of 4′-Spirocyclobutyl Nucleoside Analogues as Novel and Versatile Adenosine Scaffolds

Despite the large variety of modified nucleosides that have been reported, the preparation of constrained 4′-spirocyclic adenosine analogues has received very little attention. We discovered that the [2+2]-cycloaddition of dichloroketene on readily available 4′-exo-methylene furanose sugars efficiently results in the diastereoselective formation of novel 4′-spirocyclobutanones. The reaction mechanism was investigated via density functional theory (DFT) and found to proceed either via a non-synchronous or stepwise reaction sequence, controlled by the stereochemistry at the 3′-position of the sugar substrate. The obtained dichlorocyclobutanones were converted into nucleoside analogues, providing access to a novel class of chiral 4′-spirocyclobutyl adenosine mimetics in eight steps from commercially available sugars. Assessment of the biological activity of designed 4′-spirocyclic adenosine analogues identified potent inhibitors for protein methyltransferase target PRMT5.     

Photoinduced rearrangements in transition metal compounds

In this contribution a range of photoinduced ligand rearrangements observed for the 1st and 2nd row transition metal and organometallic compounds are discussed. The processes discussed include photoinduced ligand exchange, linkage isomerisation and changes occurring within the coordination sphere of the compounds such as cis–trans and fac–mer isomerisations. The relevance of these processes for photocatalytic cycles or their application as synthetic tools is discussed where appropriate.     

Catalytic hydrogen production at cobalt centres

The catalytic properties of a wide range of cobalt complexes with respect to proton reduction are discussed. Electrocatalytic as well as photocatalytic systems are addressed and to allow comparison between the different systems reported considerable attention is paid to the reaction conditions used. For the photocatalytic proton reduction a range of ruthenium, iridium and rhenium complexes are discussed as potential photosensitizers. The photocatalytic systems are discussed in detail and issues such as the nature of the sacrificial agent and the solvents used. Both intermolecular and intramolecular photocatalysis are considered. The results obtained are considered with respect to the need to the development of sustainable energy sources.     

The Use of Second‐Harmonic Generation to Study Diffusion through Films under a Liquid Phase

Knowledge of the diffusion of chemicals through buried films is important for a wide variety of systems—from sensing to drug delivery. Herein, we show that second‐harmonic generation (SHG) can be used to follow the diffusion through a thin film buried under a liquid in situ. More specifically, the diffusion of 4‐(4‐diethylaminostyryl)‐1‐methylpyridinium iodide through zeolite precursor films of different thickness is followed. The diffusion coefficients are calculated according to Fick’s law.     

Filter paper saturated by urine sample in metabolic disorders detection by proton magnetic resonance spectroscopy

NMR spectroscopy of urine samples is able to diagnose many inborn errors of metabolism (IEM). However, urinary metabolites have a poor stability, requiring special care for routine analysis (storage of urine at −20 or −80 °C, fast transport). The aim of our study was to investigate the reliability of dried urine filter paper for urine storage and transport and to evaluate the ability of NMR to detect several IEM using this method. Urine samples from five healthy subjects were analyzed by ¹H NMR following different storage conditions (−20 vs 4 °C vs dried on filter paper) and at different time points (24 h, 48 h, 96 h, and 7 days). Urine pattern of fresh urine was considered as a reference. We analyzed the conservation of some amino acids and organic acids using Bland and Altman plot with intraclass correlation coefficient determination. Then, we evaluated the use of filter paper to detect four different IEM (methylmalonic and isovaleric acidurias, ornithine transcarbamylase deficiency, and cystinuria). Analysis of urine samples from healthy subjects revealed a high stability of studied molecules (ICC > 0.8) even after 7 days of storage on filter paper. Moreover, an excellent preservation of metabolites specifically accumulated in IEM was observed when analysis of dried urine filter paper was compared to fresh urine (coefficient of variation < 15%). This preliminary study demonstrates that storage of dried urine on filter paper is reliable for ¹H NMR spectroscopy analysis. Preservation of urine molecules over time using that method is convenient for routine clinical practice.