Singlet molecular oxygen: Düsseldorf - São Paulo, the Brazilian connection.

Inspired by Helmut Sies we continue the development of suitable chemical generators of (1)O2 based on the thermodissociation of naphthalene endoperoxide derivatives. The present manuscript focuses on how the use of [(18)O]-labeled endoperoxides and hydroperoxides can be applied to study mechanistic aspects related to the generation of singlet molecular oxygen and its reactions in biological systems. The peroxidation reactions of the main cellular targets including unsaturated lipids, proteins and nucleic acids have received major attention during the last three decades. Emphasis is placed in this manuscript on the description of the synthesis and the main use of [(18)O]-labeled compounds, and especially of peroxides and (1)O2, for tracer elucidation of reaction mechanisms.

Revealing the ammonia oxidation process and shortcut nitrification performance using nitrogen and oxygen isotope fractionation effect.

Natural abundance isotope fractionation properties have become the most effective way to explore nitrogen transformations of biological nitrogen removal from wastewater. The migration and transformation characteristics of N and O elements in the shortcut nitrification were analyzed using the N and O dual isotopic fractionation technique. The effects of dissolved oxygen (DO) and temperature changes on the performance of shortcut nitrification and isotopic fractionation were investigated. The fractionation characteristics of N and O elements during shortcut nitrification were explored by adjusting DO concentration (0.2-0.4, 1-1.2 and 3-4 mg/L) and temperature (33 ± 1 °C, 25 ± 1 °C and 18 ± 1 °C). Both δ15NNO2 and δ18ONO2 showed a gradually increasing trend with the accumulation of NO2--N, and the fractionation effects induced by temperature were significantly higher than those by DO. The higher the temperature, the more significant the increase in δ15NNO2; the higher the DO, the more remarkable the increase in δ18ONO2, while δ15NNO2: δ18ONO2 was maintained at 0.77-6.45. The 18O-labeled H2O was successfully transferred to NO2--N, and the replacement of O element was as high as 100 %, indicating that DO and H2O simultaneously participated in the shortcut nitrification process. The dynamic changes in isotope fractionation effects can be successfully applied to reveal the performance and mechanism of shortcut nitrification.

A general and efficient approach to synthesize the phosphoramidites of 5'-18O labeled purine nucleosides.

5'-18O labeled RNA oligos are important probes to investigate the mechanism of 2'-O-transphosphorylation reactions. Here we describe a general and efficient synthetic approach to the phosphoramidite derivatives of 5'-18O labeled nucleosides starting from the corresponding commercially available 5'-O-DMT protected nucleosides. Using this method, we prepared 5'-18O-guanosine phosphoramidite in 8 steps (13.2% overall yield), 5'-18O-adenosine phosphoramidite in 9 steps (10.1% overall yield) and 5'-18O-2'-deoxyguanosine phosphoramidite in 6 steps (12.8% overall yield). These 5'-18O labeled phosphoramidites can be incorporated into RNA oligos by solid phase synthesis for determination of heavy atom isotope effects in RNA 2'-O-transphosphorylation reactions.

Structural characteristics of carrageenans of red alga Mastocarpus pacificus from sea of Japan.

The sulfated polysaccharide from sterile alga Mastocarpus pacificus was investigated. Partial reductive hydrolysis and NMR spectroscopy showed that the extracted polysaccharides were only carrageenans. According to FT-IR- and NMR spectroscopy this polysaccharide was a hybrid kappa/iota-carrageenan with a predominance of kappa-type units. According to MALDI-TOFMS, oligosaccharide fragments obtained by mild acid hydrolysis had a polymerization degree of 1-9, while chains built up of galactose residues were up to 3. Tandem ESI mass spectrometry together with innovative 18O-labelling method showed that the polymer chain of the carrageenan included kappa-carrabiose, kappa-carratetraose, iota-carrabiose, hybrid kappa/iota oligosaccharide units and contained minor insertions of mu-carrageenan (the precursor of kappa-carrageenan). Parallel artificial membrane permeability assay shown that the studied carrageenan inhibited bile salts permeation through an artificial membrane imitating the gastrointestinal barrier by 50 % on average compared to negative control independent of incubation time. However, its action was less pronounced than the hindering ability of cholestyramine.

Alkaline hydrolysis pathway of 2,4-dinitroanisole verified by 18O tracer experiment.

The environmental fate of insensitive munitions compounds, such as 2,4-dinitroanisole (DNAN), has drawn increasing attention because of their growing use in military activities. One of the main attenuation mechanisms of DNAN degradation in aqueous environments is alkaline hydrolysis. We investigated the pathway for alkaline hydrolysis of DNAN at pH 12 by a combined approach of experiment and theory. An experiment using 18O-labeled water was performed to verify the reaction pathway. Calculated free energies for two putative reaction pathways by density-functional theory optimized at the SMD(Pauling)/M06-2X/6-311++G(2d,2p) level including explicit solvation of DNAN by 10 H2O molecules and one OH- ion gave a prediction in agreement with the experimental result. The verified reaction pathway for alkaline hydrolysis of DNAN is a SN2Ar nucleophilic aromatic substitution with a methoxy leaving group (OCH3) at the C1 site.