Effects of geometric isomerism in electron ionization mass spectra of dialkyl 1,4-cyclohexanedicarboxylates.

RATIONALE: 1,4-Cyclohexanedicarboxylic acid and its esters are widely used as building blocks in the production of polymers and copolymers. The properties of such compounds directly depend on the ratio of cis- and trans-isomers in the starting materials. The identification of such stereoisomers by mass spectrometry can be used for the analysis of complex reactions and pyrolysis mixtures. METHODS: 1,4-Cyclohexanedicarboxylic acid propyl, isopropyl, butyl, 2-butyl, pentyl, 2-pentyl, 4-methylpentyl, heptyl, octyl, and nonyl esters were synthesized and analyzed by gas chromatography-electron ionization mass spectrometry. The general fragmentation patterns of the synthesized compounds in electron ionization conditions were determined using high-resolution mass spectrometry. The relative response factors for the isomers were established on the basis of NMR and GC-MS data. RESULTS: Regardless of the structure of the alkyl groups, the EI mass spectra of cis- and trans-dialkyl 1,4-cyclohexanedicarboxylates differ very sharply. The stereoselectivity of fragmentation processes is due to the steric proximity of the substituents in the case of cis-isomers. Elemental composition of all ions appearing in the mass spectra of the analytes under study was confirmed by high-resolution mass spectrometry. Despite the perceptible differences in the EI mass spectra of the isomers their ionization efficiencies are close. CONCLUSIONS: The possibility of the unambiguous identification of stereoisomeric dialkyl cis and trans 1,4-cyclohexanedicarboxylates on the basis of their EI mass spectra was shown. The differences in mass spectra of the isomers are due to the conformational rigidity of the considered monocyclic molecules, which ensures the unique stereoselectivity of the elimination of neutral molecules owing to the 1,3-cis-diaxial proximity effect.

Coding smell patterns of crude oil by the electronic nose: A soil pollution case.

In our study, we leveraged an electronic nose to detect the patterns of crude oils and their mixtures, sourced from the oil fields from neighboring regions in pursuit of the task of environmental impact evaluation. The temporal dynamics of oil-related patterns acquired by an electronic nose was tracked to identify the influence of high or low emissions of volatiles that depend on the oil composition. Analyzing the oils by Fourier-transform IR-spectroscopy and GC×GC-MS, we confirmed the correlation between sensor responses and the oil compositions, significantly dependent on the ratio of aromatic compounds/alkanes. Using pattern recognition techniques, Random Forest classifier enabled good accuracy of classification of oil samples and contaminated soils underscoring a high-resolution distinction between the response data. Applying these principles to determine the oil origin, we observed that the studied oil samples and contaminated soil samples corroborate with the dynamic changes in odor patterns based only on volatile and semivolatile compounds. Crude oils from the border of two oil fields facilitate a change in the odor pattern to remain one of the fields depending on the weathering time. These proposed intelligent multisensor systems show great promise as a tool for estimating oil-contaminated soils, thereby potentially enhancing environmental monitoring practices.

The Copper Reduction Potential Determines the Reductive Cytotoxicity: Relevance to the Design of Metal-Organic Antitumor Drugs.

Copper-organic compounds have gained momentum as potent antitumor drug candidates largely due to their ability to generate an oxidative burst upon the transition of Cu2+ to Cu1+ triggered by the exogenous-reducing agents. We have reported the differential potencies of a series of Cu(II)-organic complexes that produce reactive oxygen species (ROS) and cell death after incubation with N-acetylcysteine (NAC). To get insight into the structural prerequisites for optimization of the organic ligands, we herein investigated the electrochemical properties and the cytotoxicity of Cu(II) complexes with pyridylmethylenethiohydantoins, pyridylbenzothiazole, pyridylbenzimidazole, thiosemicarbazones and porphyrins. We demonstrate that the ability of the complexes to kill cells in combination with NAC is determined by the potential of the Cu+2 → Cu+1 redox transition rather than by the spatial structure of the organic ligand. For cell sensitization to the copper-organic complex, the electrochemical potential of the metal reduction should be lower than the oxidation potential of the reducing agent. Generally, the structural optimization of copper-organic complexes for combinations with the reducing agents should include uncharged organic ligands that carry hard electronegative inorganic moieties.

Reactive Matrices for Analytical Matrix-Assisted Laser Desorption/Ionization (MALDI) Mass Spectrometry.

In recent years, a special focus is placed on the usage of reactive matrices for analytical matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS). Since 2003, when the term "reactive matrices" was suggested and the dignity of compounds, possessing dualistic properties as matrices and derivatization agents was demonstrated, corresponding approach has found application in various fields and, in particular, in bioanalysis (metabolomics, lipidomics, etc.). The main advantage of this methodology is that it reduces sample treatment time, simplifies the procedure of sample handling, improves the sensitivity of analysis, enhances the molecular identification and profiling. Within the framework of this review, the main attention is paid to "true" reactive matrices that interact with analyte molecules through an exchange or addition reactions. A special section discusses practical application of reactive matrices in the determination of the distribution of targeted and non-targeted organic substances on the surface of biological tissue sections by MALDI-MS imaging. In this critical review, a controversial proposal is made to consider protonating and deprotonating matrices as reactive, because they can undergo a chemical reaction such as proton transfer that occurs in both target solution and MALDI plume. In this respect, special attention is paid to "proton sponge" matrices that have found a wide application in the analysis of various acidic compounds by MALDI-MS in the negative mode. Historical data on the formation of ions and the fate of matrices in MALDI are considered at the beginning of this article.

A simple soft ionization approach for GC-MS assisted by capillary array.

Electron ionization (EI) is the most widely used ionization method in gas chromatography/mass spectrometry (GC-MS). This method possesses a lot of advantages including versatility for various classes of volatile and semi volatile organic compounds, high sensitivity, structure informativity and reproducibility, production of database searchable mass spectra. On the other hand there are a number of compounds, which molecular ions are not stable enough to produce corresponding peaks in EI mass spectra, making it difficult to determine structures of compounds not presented in databases. A new approach allowing easy implementation of EI in a molecular beam formed by a capillary assembly is proposed for discussion in this communication. Primary experimental results achieved using this approach demonstrate its possibility to produce suitable for database search mass spectra with increased intensity of molecular ion peak.

Derivatization to increase the detectability of small peptides in blood serum in the analysis by ESI and MALDI high resolution mass spectrometric methods.

This work highlights the efficient approach to highly sensitive determination of dipeptides that can present in biological liquids at very low and trace quantities. The approach involves preliminary derivatization of peptides with tris(2,4,6-trimethoxyphenyl)-methyl carbenium hexafluoroborate followed by ESI and MALDI high-resolution mass spectrometry. Using model dipeptides with various amino acid compositions and sequences, it was shown that the derivatization reaction proceeded smoothly in mild conditions and gave rise to pink-red colored salt derivatives. Ready cations of interest for the analysis are easily desorbed from the salt-derivatives providing strong signals in ESI and MALDI mass spectra and this ensures high sensitivity of the analysis. Another positive aspect is the removal of the target signal from the region of a matrix noise, since the introduced fragment possesses a large mass increment (359 Da). High resolution mass spectrometry, which provides the determination of accurate weights and elemental compositions of ions, was used to reliably detect model dipeptides added to artificial urine and blood serum. A number of these dipeptides was shown to be present in real blood serum collected from volunteers. Collision induced dissociation of precursor cations composed of derivatizing reagent and dipeptide moieties gives rise to characteristic and simple fragmentation mass spectra. A comparison of limits of detection (LOD) measured for non-modified and derivatized dipeptides showed that the latter derivatives provide the highest sensitivity when LOD is determined by using multiple reaction monitoring (MRM) transitions. The suggested derivatization approach was shown to be useful for unambiguous identification of special dipeptides in artificial media and dietary supplements.

Phosphazene-Containing Epoxy Resins Based on Bisphenol F with Enhanced Heat Resistance and Mechanical Properties: Synthesis and Properties.

Organophosphazenes are of interest due to the combination of increased mechanical and thermal properties of polymer materials obtained with their use, however, they are characterized by a complex multi-stage synthesis. Moreover, the high viscosity of phosphazene-containing epoxy resins (PhER) makes their processing difficult. To simplify the synthesis of PhER, a one-step method was developed, and bisphenol F was chosen, which also provided a decrease in viscosity. In the current study, PhER were formed by a one-stage interaction of hexachlorocyclotriphosphazene (HCP) with bisphenol F isomers and epichlorohydrin in the presence of alkali, which was a mixture of epoxycyclophosphazenes (ECPh) with a functionality from 1 to 4 according to the results of MALDI-TOF analysis. Conventional epoxy resins based on bisphenol F, also formed during the process, showed high mechanical properties and glass transition temperature, and the reactivity of the obtained resins is similar to the base epoxy resins based on bisphenols A and F. Cured PhER had higher or the same mechanical properties compared to base epoxy resins based on bisphenol A and F, and a glass transition temperature comparable to base epoxy resins based on bisphenol F: glass transition temperature (Tg) up to 174.5 °C, tensile strength up to 74.5 MPa, tensile modulus up to 2050 MPa, tensile elongation at break up to 6.22%, flexural strength up to 146.6 MPa, flexural modulus up to 3630 MPa, flexural elongation at break up to 9.15%, and Izod impact strength up to 4.01 kJ/m2. Analysis of the composition of the obtained PhER was carried out by 1H and 31P NMR spectroscopy, MALDI-TOF mass spectrometry, X-ray fluorescence elemental analysis, and contained up to 3.9% phosphorus and from 1.3% to 4.2% chlorine. The temperature profile of the viscosity of the resulting epoxy resins was determined, and the viscosity at 25 °C ranged from 20,000 to 450,000 Pa·s, depending on the ratio of reagents. The resins studied in this work can be cured with conventional curing agents and, with a low content of the phosphazene fraction, can act as modifiers for traditional epoxy resins, being compatible with them, to increase impact strength and elasticity while maintaining the rest of the main mechanical and processing properties, and can be used as a resin component for composite materials, adhesives, and paints.

Copper coordination compounds with (5Z,5Z')-2,2'-(alkane-α,ω-diyldiselenyl)-bis-5-(2-pyridylmethylene)-3,5-dihydro-4H-imidazol-4-ones. Comparison with sulfur analogue.

A series of new organic ligands (5Z,5Z')-2,2'-(alkane-α,ω-diyldiselenyl)-bis-5-(2-pyridylmethylene)-3,5-dihydro-4H-imidazol-4-ones (L) consisting of two 5-(2-pyridylmethylene)-3,5-dihydro-4H-imidazol-4-one units linked with polymethylene chains of various lengths (n = 2-10, where n is the number of CH2 units) have been synthesized. The reactions of these ligands with CuCl2·2H2O and CuClO4·6H2O gave Cu2+ or Cu1+ containing mono- and binuclear complexes with Cu2LCl x (x = 2-4) or CuL(ClO4) y (y = 1, 2) composition. It was shown that the agents reducing Cu2+ to Cu1+ in the course of complex formation can be both a ligand and an organic solvent in which the reaction is carried out. This fundamentally distinguishes the selenium-containing ligands L from their previously described sulfur analogs, which by themselves are not capable of reducing Cu2+ during complexation under the same conditions. A higher cytotoxicity and reasonable selectivity to cancer cell lines for synthesized complexes of selenium-containing ligands was shown; unlike sulfur analogs, ligands L themselves demonstrate a high cytotoxicity, comparable in some cases to the toxicity of copper-containing complexes.

Options of the Main Derivatization Approaches for Analytical ESI and MALDI Mass Spectrometry.

The inclusion of preliminary chemical labeling (derivatization) in the analysis process by such powerful and widespread methods as electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) is a popular and widely used methodological approach. This is due to the need to remove some fundamental limitations inherent in these powerful analytic methods. Although a number of special reviews has been published discussing the utilization of derivatization approaches, the purpose of the present critical review is to comprehensively summarize, characterize and evaluate most of the previously developed and practically applied, as well as recently proposed representative derivatization reagents for ESI-MS and MALDI-MS platforms in their mostly sensitive positive ion mode and frequently hyphenated with separation techniques. The review is focused on the use of preliminary chemical labeling to facilitate the detection, identification, structure elucidation, quantification, profiling or MS imaging of compounds within complex matrices. Two main derivatization approaches, namely the introduction of permanent charge-fixed or highly proton affinitive residues into analytes are critically evaluated. In situ charge-generation, charge-switch and charge-transfer derivatizations are considered separately. The potential of using reactive matrices in MALDI-MS and chemical labeling in MS-based omics sciences is given.

Tandem Synthesis of Ultra-High Molecular Weight Drag Reducing Poly-α-Olefins for Low-Temperature Pipeline Transportation.

Ultra-high molecular weight poly-α-olefins are widely used as drag reducing agents (DRAs) for pipeline transportation of oil and refined petroleum products. The synthesis of polyolefin DRAs is based on low-temperature Ziegler-Natta (ZN) polymerization of higher α-olefins. 1-Hexene based DRAs, the most effective at room temperature, typically lose DR activity at low temperatures. The use of 1-hexene copolymers with C8-C12 linear α-olefins appears to offer a solution to the problem of low-temperature drag reducing. The present work aims to develop two-stage synthesis of polyolefin DRAs that is based on selective oligomerization of ethylene in the presence of efficient chromium/aminodiphosphine catalysts (Cr-PNP), followed by polymerization of the olefin mixtures, formed at oligomerization stage, using efficient titanium-magnesium ZN catalyst. We have shown that oligomerization of ethylene in α-olefin reaction media proceeds faster than in saturated hydrocarbons, providing the formation of 1-hexene, 1-octene, and branched C10 and C12 olefins; the composition and the ratio of the reaction products depended on the nature of PNP ligand. Oligomerizates were used in ZN polymerization 'as is', without additional treatment. Due to branched character of C10+ hydrocarbons, formed during oligomerization of ethylene, resulting polyolefins demonstrate higher low-temperature DR efficiency at low polymer concentrations (~1 ppm) in comparison with benchmark polymers prepared from the mixtures of linear α-olefins and from pure 1-hexene. We assume that faster solubility and more efficient solvation of the polyolefins, prepared using 'tandem' ethylene-based process, represent an advantage of these type polymers over conventional poly(1-hexene) and linear α-olefin-based polymers when used as 'winter' DRAs.

Homobivalent Lamellarin-Like Schiff Bases: In Vitro Evaluation of Their Cancer Cell Cytotoxicity and Multitargeting Anti-Alzheimer's Disease Potential.

Marine alkaloids belonging to the lamellarins family, which incorporate a 5,6-dihydro-1-phenylpyrrolo[2,1-a]isoquinoline (DHPPIQ) moiety, possess various biological activities, spanning from antiviral and antibiotic activities to cytotoxicity against tumor cells and the reversal of multidrug resistance. Expanding a series of previously reported imino adducts of DHPPIQ 2-carbaldehyde, novel aliphatic and aromatic Schiff bases were synthesized and evaluated herein for their cytotoxicity in five diverse tumor cell lines. Most of the newly synthesized compounds were found noncytotoxic in the low micromolar range (<30 µM). Based on a Multi-fingerprint Similarity Search aLgorithm (MuSSeL), mainly conceived for making protein drug target prediction, some DHPPIQ derivatives, especially bis-DHPPIQ Schiff bases linked by a phenylene bridge, were prioritized as potential hits addressing Alzheimer's disease-related target proteins, such as cholinesterases (ChEs) and monoamine oxidases (MAOs). In agreement with MuSSeL predictions, homobivalent para-phenylene DHPPIQ Schiff base 14 exhibited a noncompetitive/mixed inhibition of human acetylcholinesterase (AChE) with Ki in the low micromolar range (4.69 µM). Interestingly, besides a certain inhibition of MAO A (50% inhibition of the cell population growth (IC50) = 12 µM), the bis-DHPPIQ 14 showed a good inhibitory activity on self-induced ß-amyloid (Aß)1-40 aggregation (IC50 = 13 µM), which resulted 3.5-fold stronger than the respective mono-DHPPIQ Schiff base 9.

New suitable deprotonating matrices for the analysis of carboxylic acids and some acidic compounds by matrix-assisted laser desorption/ionization mass spectrometry in negative ion mode.

RATIONALE: Direct non-derivatization analysis of organic acids and acidic compounds by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) in positive ion mode is not always possible due to the low ionization efficiency of analytes. Some new efficient deprotonating matrices were suggested that allowed the production of negative ions from acidic compounds during MALDI-MS experiments. METHODS: Various tested carboxyl-containing compounds as well as compounds with acidic properties were mixed with the suggested deprotonating matrices [4-dimethylaminobenzaldehyde (DMABA), N,N-dimethylamino-p-phenylenediamine or 3-aminoquinoline] and applied on a standard MALDI target followed by recording MALDI mass spectra in negative ion mode. RESULTS: All the tested acidic compounds mixed with the suggested deprotonating matrices produced abundant [M - H]- ions under MALDI conditions. DMABA produced the strongest signals reflecting greater sensitivity of analysis. CONCLUSIONS: The suggested deprotonating matrices are commercially available compounds and are good alternatives to well-known matrices of this kind and, in particular, the often used 9-aminoacridine. DMABA is the best of the tested potential matrices and is suitable for the detection of low molecular weight carboxyl-containing compounds, substituted phenols, and mixtures of naphthenic acids by (-)MALDI-MS.

Synthesis of Bisphenol A Based Phosphazene-Containing Epoxy Resin with Reduced Viscosity.

Phosphazene-containing epoxy oligomers (PEO) were synthesized by the interaction of hexachlorocyclotriphosphazene (HCP), phenol, and bisphenol A in a medium of excess of epichlorohydrin using potassium carbonate and hydroxide as HCl acceptors with the aim of obtaining a product with lower viscosity and higher phosphazene content. PEOs are mixtures of epoxycyclophosphazene (ECP) and a conventional organic epoxy resin based on bisphenol A in an amount controlled by the ratio of the initial mono- and diphenol. According to 31P NMR spectroscopy, pentasubstituted aryloxycyclotrophosphazene compounds predominate in the ECP composition. The relative content in the ECP radicals of mono- and diphenol was determined by the MALDI-TOF mass spectrometry method. The organic epoxy fraction, according to gas chromatograpy-mass spectrometry (GC-MS), contains 50-70 wt % diglycidyl ether of bisphenol A. PEO resins obtained in the present work have reduced viscosity when compared to other known phosphazene-containging epoxy resins while phosphazene content is still about 50 wt %. Resins with an epoxy number within 12-17 wt %, are cured by conventional curing agents to form compositions with flame-retardant properties, while other characteristics of these compositions are at the level of conventional epoxy materials.

Suitable in-situ derivatization of alcohols by reaction with basic amines in Direct Analysis in Real Time mass spectrometry.

This work highlights the discovered in-situ analytical reaction between primary/secondary alcohols and nitrogenous bases (pyridine, quinoline) that involves the substitution of hydroxyl groups for nitrogen-containing charged species and proceeds in an ionization region of Direct Analysis in Real Time mass spectrometry (DART-MS) instrument at gas stream temperature of 150-450 °C. Resulted cations provide strong signals in mass spectra and this ensures high sensitivity of the analysis. Collision induced dissociation of such precursor ions gives rise to characteristic and simple fragmentation mass spectra revealing mainly protonated nitrogenous bases and carbonium cations resulting from the elimination of neutral nitrogen-containing bases. The dependence of signal response on gas stream temperature was elucidated. It was also found that, independently of gas stream temperature, high volatility low-molecular weight alcohols did not demonstrate characteristic DART spectra owing to a high rate of desorption/evaporation which does not provide sufficient probability of the reaction. To the best of our knowledge, this type of specific reactions in a plasma-based source of DART mass spectrometer is reported for the first time. It represents a new and interesting derivatization approach providing a rapid and sensitive complement method for the detection and identification of individual monools of various origin, profiling plant sterols and other steroid alcohols in different matrices.

Synthesis of Resorcinol-Based Phosphazene-Containing Epoxy Oligomers.

Phosphazene-containing epoxy-resorcinol oligomers (PERO) are synthesized in one stage with the direct interaction of hexachlorocyclotriphosphazene (HCP), resorcinol, and epichlorohydrin in the presence of solid NaOH. Depending on the initial ratio of HCP:resorcinol, PERO contains from 20 to 50 wt.% phosphazene component (2.0⁻4.8% of phosphorus) and have an epoxy group content up to 30 %. Products are characterized using ¹H and 31P NMR spectroscopy, MALDI-TOF mass spectrometry, and elemental analysis. According to mass spectrometry, the phosphazene fractions of PERO include up to 30 individual compounds with a predominance of cyclotriphosphazenes with one unsubstituted chlorine atom and four or five glycidyl groups. PERO has a lower viscosity in comparison with similar resins based on bisphenol A, which can simplify their use as a binder for polymer composites, adhesives, and paints.

Synthesis, molecular docking, and biological activity of 2-vinyl chromones: Toward selective butyrylcholinesterase inhibitors for potential Alzheimer's disease therapeutics.

We investigated the biological activity of a series of substituted chromeno[3,2-c]pyridines, including compounds previously synthesized by our group and novel compounds whose syntheses are reported here. Tandem transformation of their tetrahydropyridine ring under the action of activated alkynes yielding 2-vinylsubstituted chromones was used to prepare nitrogen-containing derivatives of a biologically active chromone system. The inhibitory activity of these chromone derivatives against acetylcholinesterase (AChE), butyrylcholinesterase (BChE) and carboxylesterase (CaE) was investigated using the methods of enzyme kinetics and molecular docking. Antioxidant (antiradical) activity of the compounds was assessed in the ABTS assay. The results demonstrated that a subset of the studied chromone derivatives selectively inhibit BChE but do not exhibit antiradical activity. In addition, the results of molecular docking effectively explained the observed features in the efficacy, selectivity, and mechanism of BChE inhibition by the chromone derivatives.

Regio-isomeric effects in tandem mass spectra of sulfonium cations generated from thiacyclane based sulfonium salts under soft ionization conditions.

The influence of regio-isomerism of even-electron sulfonium ions on tandem electrospray and matrix-assisted laser desorption/ionization mass spectra recorded by using collision-induced dissociation was investigated. The initial organic sulfides belonged to isomeric thiabicyclane series (substituted 7- and 8-thiabicyclo[4.3.0]nonanes, 2- and 3-thiabicyclo[4.4.0]decanes) and phenylthiolanes. To investigate by the abovementioned mass spectrometry methods, the sulfides were preliminary S-alkylated by methyl, ethyl iodides, their deuterated analogs and trialkoxonium tetrafluoroborates to form corresponding sulfonium salts. The latter salts readily gave off corresponding sulfonium cations under abovementioned desorption/ionization conditions and these cations were precursor ions in collision-induced dissociation experiments. The main quantitative and frequently qualitative differences between collision-induced dissociation spectra of isomers were manifested in mass numbers and relative intensities of the ions Alk-S+ = CHR (formal structure) that originated from the destruction of sulfur-containing ring. Corresponding peaks are particularly abundant for cations Alk-S+ = CH2 and their intensities are usually greater than for other C-substituted homologues. Qualitative difference between fragmentation features of 2- and 3-phenylthiolanium cations is that only the latter can eliminate neutral C2H4S molecule.

Letter: α,ω,N,N-Dimethylaminoalkylamines as possible derivatization agents for the analysis of small carbonyl compounds by low energy mass spectrometry.

Reaction with α,ω-N,N-dimethylaminoalkylamines (2-dimethylaminoethylamine, 3- dimethylaminopropylamine, 4-dimethylaminobutylamine) to form Schiff bases followed by quaternization of the N,N-dimethylamino group by alkyl (deuteroalkyl) halides to generate fixed-charge fragments is suggested for the characterization of carbonyl compounds by matrix-assisted laser desorption ionization (MALDI) mass spectrometry. As model objects, some aliphatic aldehydes and alicyclic and steroid ketones were involved in the modification. Using gas chromatography mass spectrometry, the first modification stage proved to be quantitative. Not only the MALDI conditions but also the nanostructurized target provided spectra that revealed peaks for the cationic parts of derivatives. It was shown that the use of deuterated alkyl halides allows one to prepare deuterium-labeled standards for possible quantitative analysis.

Reactive matrices for matrix-assisted laser desorption/ionization mass spectrometry of primary amines.

Some aromatic carbonyl compounds [2,4-dihydroxybenzaldehyde (2,4-DHBA), 2,5- dihydroxyacetophenone (DHAP), 2,3,5-trihydroxybenzaldehyde and 2,4-dinitrobenzaldehyde] were examined as potential reactive matrices for the analysis of mono-, di-, and polyamines by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS). Although all the above compounds readily and quantitatively react with primary amines to form Schiff bases (the completeness of the reactions was proved by gas chromatography MS of derivatized aliphatic amines), only DHBA and DHAP provide efficient desorption/ionization under MALDI conditions. This means that two these aromatic carbonyl compounds can simultaneously exhibit properties of both derivatization agents and efficient matrices for MALDI-MS analysis. The use of such reactive matrices eliminates the need to perform additional derivatization experiments. With the aid of DHBA and DHAP, it was confirmed that each individual oligomer of polypropylene glycols and co- polyethylene/propylene glycols contained two terminal amino groups. To calculate the number of NH2 groups, mass increments of the introduced groups and a difference in the masses of cations attached to the initial and derivatized amines were used. The suggested approach, involving the application of the same reactive matrices, was applied to the determination of a number of NH(2) groups in individual oligomers of branched polyethyleneimines (PEIs) by MALDI-MS. In this case, DHAP appeared to be the best reactive matrix. The dependence of the number of NH(2) groups on the quantity of monomeric units and branching of each individual PEI oligomer is shown.

Simple approach to derivatization of alcohols and phenols for the analysis by matrix(surface)-assisted laser desorption/ionization time-of-flight mass spectrometry.

RATIONALE: Direct analysis of hydroxyl-containing compounds by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) methods is not always possible due to the neutral character of analytes. The suggested fixed-charge derivatization may increase the ionization efficiency for various alcohols and phenols in specific matrix- and surface-activated LDI conditions. METHODS: Aliphatic and steroid alcohols, as well as chlorophenols, were converted into various ammonioacetyl derivatives, containing a covalently bonded charged group, by reaction with bromoacetyl chloride and amine-type compounds such as triethylamine, pyridine or quinoline. The derivatives are suitable for MALDI-time-of-flight (TOF)MS analysis. RESULTS: Triethylammoniumacetyl, pyridyliumacetyl and quinoliniumacetyl derivatives were prepared from aliphatic alcohols, some sterols and chlorinated phenols in one stage with quantitative yields. The derivatives produced characteristic MALDI and SALDI mass spectra. CONCLUSIONS: The suggested derivatization approach for the modification of alcohols is simple and does not require any expensive reagents. The derivatives include a fixed charge and produce intense signals in MALDI (preferentially non-acidic matrices) and matrix-free SALDI (nanostructured target) conditions. Corresponding mass spectra are suitable for the determination of molecular mass and profiling of alcohols.