Journal of Analytical Chemistry

Characteristics of tryptic peptides that provide the detection and identification of these compounds and corresponding proteins by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry with α-cyano-4-hydroxycinnamic acid as a matrix are determined and discussed. Twenty-five proteins are identified; the features of reliably identified peptides are compared to those of the compounds that might be produced by trypsinolysis but were not detected. Two key factors enhancing a possibility of the detection of tryptic peptides are determined. One refers to the basicity of peptides in the gas phase, which is the highest for peptides with the C-terminal arginine residue; this reason for the emergence of significant analytical signals is well known. Another factor contributing to the ionization of peptides in study under MALDI conditions is their hydrophilicity. This result did not correlate with the most conclusions of earlier relevant studies discussed in the article.

The interaction of aliphatic alcohols ROH with phosphorus trichloride in the absence of bases leads to the formation of exclusively dialkyl phosphonates (RO)₂PHO. To obtain trialkyl phosphites (RO)₃P, insufficiently described to date, the pH of the reaction mixtures was adjusted by adding N,N-dimethylaniline (pK_a 5.1 ± 0.1). The identification of trialkyl phosphites directly in reaction mixtures without preparative isolation implies a joint consideration of their mass spectra and gas chromatographic retention indices, provided that all other components of such mixtures are identified. The need to comply with this condition has led to the identification of several homologues of a previously uncharacterized series of 2-alkoxy-1,3,2-dioxaphospholanes, formed from a random admixture of ethylene glycol. The use of such combined mass spectrometric parameters as homologous increments of retention indices helps to distinguish trialkyl phosphites from isobaric dialkyl phosphonates; the compounds of both series belong to the homologous group of y = 12, y ≡ M(mod14). Despite the absence of molecular ion signals in the electron ionization (EI) mass spectra, the molecular weights of trialkyl phosphites can be estimated. In addition, a comparison of the homologous increments of retention indices shows that, compared with dialkyl phosphonates, trialkyl phosphites are significantly less polar.

The H₃O⁺(H₂O)_n reagent ion is widely used in ion mobility spectrometry and atmospheric pressure chemical ionization mass spectrometry. In this work, calculated data on the structure and properties of the H₃O⁺(H₂O)_n (n = 0–4) reagent ion are obtained. They are of interest for the study of the regularities of chemical ionization and the prediction and interpretation of ion mobility spectra and mass spectra. Using quantum chemical methods, we calculated the structures and refined the isomeric composition of the H₃O⁺(H₂O)_n ions. It was found that ions with n = 2, 3, and 4 have 2, 5, and 15 isomers, respectively. The most stable isomers, which possess branched non-cyclic structures with the H₃O⁺ core, were determined. The thermodynamic parameters of hydration reactions of the most stable isomers of H₃O⁺(H₂O)_n (n = 0–3) ions and the equilibrium composition of the reagent ion in a wide range of temperatures and concentrations of water vapor are computed. The obtained results agree with the available experimental and calculated data. Using the computed structural data and data on the composition of the reagent ion, its mobility was calculated by the trajectory method. The error of calculations is close to the experimental one.

A procedure for the determination of phosphonylated tyrosine, a marker of exposure to organophosphorus nerve agents, in dried blood plasma spot (DBS) samples by means of liquid chromatography/tandem high-resolution mass spectrometry was developed. The DBS samples on Protein Saver 903 Card substrates were shown to be stable for two months on storage at 22 and 40°C. It was found that the temperature of storage has a high impact on the stability of the DBS samples: the analyte concentration in the samples stored at 40°C was about three times lower than that in the samples stored at room temperature. It was shown that the special Protein Saver 903 Card substrates could be replaced by an ordinary blue ribbon filter paper. In the latter case, the tyrosine adducts of nerve agents were reliably determined in the DBS samples stored for a month at room temperature (22°C). However, for storage at elevated temperatures (40°C), the use of filter paper substrates is not recommended. The proposed approach to storage of blood samples allows one to take and easily transport large series of samples and automate their analysis.

Mass spectrometry was applied to identify metabolites and estimate the efficiency of phenanthrene biodegradation and transformation by rhizosphere bacteria Pseudomonas aureofaciens BS1393. Strains P. aureofaciens BS1393(pOV17) and P. aureofaciens BS1393(NPL-41) bearing various naphthalene biodegradation plasmids were used in the work. The strain BS1393(pOV17) contains the pOV17 wild type naphthalene biodegradation plasmid that determines the oxidation of naphthalene to Krebs cycle metabolites. The strain BS1393(NPL-41) contains the mutant plasmid NPL-41 governing the initial stages of naphthalene oxidation into salicylic acid. The limiting stages of phenanthrene biodegradation in bacteria with various plasmids have been identified according to the accumulation of intermediates. When bacteria were grown on phenanthrene, the main metabolites were as follows: (a) 2-hydroxy-2H-benzo[h]chromene-2-carboxylic acid/trans-4-(1-hydroxynaph-2-yl)-2-oxobut-3-enoic acid, (b) 1-hydroxy-2-naphthoic acid, and (c) salicylic acid. In the strain BS1393(pOV17), metabolite (а) was observed during 1–14 days of cultivation. Unlike it, in the strain BS1393(NPL-41), an insignificant amount of this metabolite was found after only 14 days. The availability of metabolite (b) in the growth of both strains was an evidence of the limited rate of its further decarboxylation. Metabolite (c) as a final product was found in the growth of the strain BS1393(NPL-41). Contrastingly, in the strain BS1393(pOV17), this metabolite was not found, which indicates the complete oxidation of phenanthrene.