Unsymmetrical dimethylhydrazine transformation products: A review.

Unsymmetrical dimethylhydrazine (UDMH) is a widely used rocket propellant, which oxidizes to different compounds. The determination of UDMH transformation products in the environment is of great importance since many of them are highly toxic. Along with well-known transformation products, researchers report new compounds, and establishing their structures is difficult and may be unreliable, and data on their properties, such as toxicity, are often not available. Moreover, the available information on the existence of various UDMH transformation products is quite scattered, many compounds are mentioned in the literature only once and/or without satisfactory confirmation of the structure, and labeled as assumed compounds. All this complicates the identification of new UDMH transformation products and obfuscates the search for already known compounds. This review aimed to summarize and systematize the UDMH oxidation pathways and its transformation products. The attention was paid to in which environmental compartment or only in the laboratory study UDMH transformation products were detected, as well as their formation under conditions of combustion and generating by engines. Schemes for the transformation of confirmed UDMH products were summarized; required conditions for the relevant chemical reactions were described. A group of assumed UDMH transformation products - those substances found in contaminated compartments, but without full structure confirmation - is shown in a separate table. Data on the UDMH and its transformation products acute toxicity are presented. Predicting the transformation products properties, including acute toxicity, cannot be the primary determination method, as the results obtained often do not reflect real values and, when dealing with unknown substances, may lead to using false results. Improved understanding of the UDMH transformation pathways in environmental compartments potentially can lead to more accurate identification of new transformation products with future use in developing approaches to reduce the toxic effects of UDMH and its transformation products.

1-Methyl-1H-1,2,4-triazole as the main marker of 1,1-dimethylhydrazine exposure in plants.

With their wide application in chemical industry, human health and environmental toxic effects of hydrazines arise extensive concerns. Although hydrazine exposure is known to lead to inhibition of seed germination and seedling growth in plants, there are few reports about the mechanism of oxidation or transformation ways of hydrazines in plant tissue. In this research, garden cress (Lepidium sativum L.) and zucchini (Cucurbita pepo L.) were used as model plant objects to study 1,1-dimethylhydrazine exposure in vitro using the GC-MS system. The seed germination and plant growth experiments were carried out in Petri dishes using an aqueous media. Among the detected 1,1-dimethylhydrazine transformation products in plant tissues, 1-methyl-1H-1,2,4-triazole had the highest intensity and reproducibility. In our research, 1-methyl-1H-1,2,4-triazole formed at all contaminant concentrations in an extremely short period. This preliminary study determined 1,1-dimethylhydrazine environment contamination by detecting 1-methyl-1H-1,2,4-triazole in combination with other transformation products.

A peculiar chromatographic selectivity of porous graphitic carbon during the separation of dileucine isomers.

Porous graphitic carbon is a versatile stationary phase for high-performance liquid chromatography which performs especially well for isomeric separations. Shape-sensitivity of the stationary phase is caused by a steric effect when a molecule interacts with a flat carbon surface. It follows that branched, non-flat molecules are eluted much earlier than flat or linear molecules. In this short communication we show that if a molecule has a highly ionizable group, the "shape" of a molecule part which is farther from the ionizable group affects retention much more than the "shape" of a molecule part which is closer to the ionizable group. Dipeptides which consist of tert-leucine and norleucine were used as an example. Basic and acidic eluents were used. Retention strongly depends on whether a norleucine or tert-leucine residual is located near the non-ionized side in an eluent for both basic and acidic eluents. A residual located on the opposite side is less important. To investigate the possible causes of this peculiar retention behavior we compared the retention behavior of these dipeptides for porous graphitic carbon with the behavior for other types of stationary phases and with the calculated physicochemical properties. Strong and complex dependence of elution order on a mobile phase composition is demonstrated. The separation of other dileucine isomers is also considered. The applicability of porous graphitic carbon for the separation of complex mixtures of isomeric peptides is discussed.

Isomeric derivatives of triazoles as new toxic decomposition products of 1,1-dimethylhydrazine.

Unsymmetrical dimethylhydrazine (UDMH) is a rocket propellant for carrier rockets and missiles. UDMH is environmentally hostile compound, which easily forms a variety of toxic products of oxidative transformation. The liquidation of unused UDMH from retired launch sites is performed by the complete burning of UDMH-containing wastes. Due cyclicity of the burning equipment the UDMH-containing wastes are subject of prolonged storage in contact with atmospheric oxygen and thus contains a complicated mixture of UDMH degradation products. High performance liquid chromatography (HPLC), high resolution mass spectrometry (HRMS) and NMR were used for the isolation on characterization of new highly polar and potentially toxic UDMH transformation products in the mixture. Two series of unreported isomers with high ionization cross section in electrospray ionization were isolated by repeated preparative HPLC. The structures of the isomers were established by tandem HRMS and NMR. The cytotoxicity of the isolated compounds has been preliminarily studied and found to be similar to UDMH or higher.