1,1′,2,2′,6,6′-Hexaphenyl-4,4′-bipyridinium cation radical

Aniline reacts with 2,2,6,6-tetraphenyl-4,4-bipyrilium perchlorate to form 1,1,2,2,6,6-hexaphenyl-4,4-bipyridine perchlorate. A relatively stable cation radical is formed in the first stage of electrochemical reduction of this compound, which has been examined by ESR, where there are splittings from two nitrogen nuclei and the four protons in the 3,3,5,5 positions: a_N=0.38; a_H=0.14 mT.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, No. 1, pp. 61–64, January–February 1992.     

Electrochromic Detection of Latent Fingermarks on Metal Surface Using 1,1′-Dibenzyl-4,4′-bipyridinium Dichloride

The electrochromic detection of latent fingermarks on polished or unpolished, flat or curved metal surfaces is described using electrochromic material, 1,1’-dibenzyl-4,4’-bipyridinium dichloride. The surface area covered by fingermarks acts as an insulating mask, causing 1,1’-dibenzyl-4,4’-bipyridinium dichloride to change color and produce inversed images of the fingermark. By changing the applied potential, the optical properties of 1,1’-dibenzyl-4,4’-bipyridinium dichloride can be continuously and reversibly adjusted to optimize the visual contrast of fingermarks, so as to realize the detection of latent fingermarks on stainless steel surface. It is demonstrated that the fabricated electrochromic devices can detect the fingermarks on these types of surfaces within twenty seconds at −1.0∼−2.0 V. This work can qualify as a tangible improvement in fingermark detection of the natural fingermarks on the never-cleaned (more than 3 years) and curved surfaces of daily-used container, e. g. cup, and the handle of cleaning tool, mop.     

Complex Formation of Hematoporphyrin with Cyclodextrins and 1,1′-Diheptyl-4,4′-bipyridinium Dibromide in Aqueous Solutions

At around 5×10^-6?mol?dm^-3 of hematoporphyrin (HP), an HP dimer exists as well as an HP monomer. The equilibrium constant for the dimerization of HP in pH 10.0 buffer has been evaluated to be 1.70×10⁵?mol^-1?dm³ from the HP concentration dependence of the absorption spectrum. In aqueous solution, HP forms 1:1 inclusion complexes with β-cyclodextrin (β-CD), γ-cyclodextrin (γ-CD), and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (TM-β-CD). The fluorescence of HP is significantly enhanced by the addition of CDs. From simulations of the fluorescence intensity changes, the equilibrium constants for the formation of the CD–HP inclusion complexes have been estimated to be 200, 95.7, and 938?mol^-1?dm³ for β-CD, γ-CD, and TM-β-CD, respectively. HP forms a 1:1 complex with 1,1′-diheptyl-4,4′-bipyridinium dibromide (DHB) in aqueous solution. In contrast to the addition of CDs, the HP fluorescence is significantly quenched by the addition of DHB. The equilibrium constant for the formation of the HP–DHB complex has been evaluated to be 1.98×10⁵?mol^-1?dm³ from the fluorescence intensity change of HP. The addition of DHB to an HP solution containing β-CD induces a circular dichroism signal of negative sign, indicating the formation of a ternary inclusion complex involving β-CD, HP, and DHB. In contrast, there is no evidence for the formation of a ternary inclusion complex of HP with DHB and TM-β-CD.     

Differentiation of 2′-O- and 3′-O-methylated Ribonucleosides by tandem mass spectrometry

Recent studies revealed that the 3'-terminal nucleotides in plant microRNAs were methylated on the ribose at the 2' or 3' hydroxyl groups. Here we examined the fragmentation of the electrospray-produced [M + H]+ and [M - H]- ions of 2'- and 3'-O-methylated ribonucleosides. It turned out that the predominant fragmentation pathway for the [M + H]+ ions of ribose-methylated nucleosides was the neutral loss of the methylated ribose, which made it impossible to distinguish 2'-O-methylation from 3'-O-methylation by positive-ion MS/MS. However, characteristic fragment ions, resulting from the cleavage through the ribose rings, were produced for the [M - H]- ions of each pair of ribose-methylated nucleosides. In this respect, the neutral loss of a 90-Da fragment (C3H6O3) was observed for 2'-O-methylated cytidine, guanosine and adenosine, but not for their 3'-O-methylated counterparts. On the other hand, the neutral loss of a 60-Da fragment (C2H4O2) was found for 3'-O-methyluridine, but not for 2'-O-methyluridine.     

Determination of arsenic by inductively coupled plasma mass spectrometry – comparison of sample introduction techniques

A comparison is made of four sample introduction techniques for the determination of As by inductively coupled plasma mass spectrometry. The techniques studied were 1) flow injection with pneumatic nebulization (FIA-PN), 2) direct electrothermal vaporization (ETV), 3) continuous hydride generation (HG) and 4) hydride generation with in situ trapping followed by electrothermal vaporization (HG-ETV). It was found that FIA-PN and ETV gave similar detection limits in concentration units (about 20 pg mL^–1), although ETV had a much lower absolute detection limit (0.2 pg). Sample introduction by hydride generation gave an inferior detection limit (100–200 pg mL^–1), also in combination with in situ trapping and ETV, owing to the blank signal from traces of As in NaBH₄ which is difficult to eliminate. The results indicate that the more elaborate sample introduction techniques based on ETV and HG may not offer significant advantages compared to normal solution nebulization for the determination of As in simple sample matrices such as natural fresh waters, where matrix removal is not required.     

Studies of electronic structures of 1,1′-disubstituted silaoxacyclohexa-3,5-dienes

Spatial and electronic structures of 1,1-disubstituted silaoxacyclohexa-3,5-dienes have been calculated using the AMPAC and HYPERCHEM 3.0 program packages. Interatomic distances, bond angles, torsion angles, atomic charges, electron densities, bond orders, parameters of localized molecular Orbitals,etc. have been determined. Based on data obtained, it has been concluded that the -R'SiO-fragment in these molecules is a saturated structural linkage, which exhibits an inductive effect on the diene system; however, the linkage does not interact with the diene system by the mesomeric (resonance) mechanism.Translated fromIzvestiya Akademii Nauk. Setiya Khimicheskaya, No. 10, pp. 1917–1920, October, 1995.     

Preparation of chiral C2-symmetrical 1,1′-disubstituted ferrocenes

A biocatalytic procedure for the resolution and concurrent desymmetrization of tetraacetoxyferrocene (±, meso)-2 is described. Enantiomerically pure (R,R)- and (S,S)-forms have been converted into the corresponding epoxide 6, a useful starting material for the preparation of polyfunctional C₂-symmetric ferrocenes.     

Identification of polyethanolamines by chromatography–mass spectrometry

Presumable structures of polyethanolamines, synthesized by the catalytic β-hydroxyethylation of ammonia with an excess of ethylene oxide are determined by gas chromatography–electron ionization mass spectrometry and tandem mass spectrometry qualitatively, following fragmentation ways and also taking into account retention data. The preferable paths of consecutive reactions of the synthesis of polyethanolamines in a homologous series of isomers are found.     

Investigation of protein–protein interactions in living cells by chemical crosslinking and mass spectrometry

The identification of protein–protein interactions within their physiological environment is the key to understanding biological processes at the molecular level. However, the artificial nature of in vitro experiments, with their lack of other cellular components, may obstruct observations of specific cellular processes. In vivo analyses can provide information on the processes within a cell that might not be observed in vitro. Chemical crosslinking combined with mass spectrometric analysis of the covalently connected binding partners allows us to identify interacting proteins and to map their interface regions directly in the cell. In this paper, different in vivo crosslinking strategies for deriving information on protein–protein interactions in their physiological environment are described.     

Comparative study of extraction techniques for determination of garlic flavor components by gas chromatography–mass spectrometry

Several sampling techniques based on steam distillation (SD), simultaneous distillation and solvent extraction (SDE), solid-phase trapping solvent extraction (SPTE), and headspace solid-phase microextraction (HS-SPME) have been compared for the determination of Korean garlic flavor components by gas chromatography–mass spectrometry (GC–MS). Diallyl disulfide (57.88%), allyl sulfide (23.59%), and diallyl trisulfide (11.40%) were found to be the predominant flavor components of garlic samples extracted by SDE whereas these components were at levels of 89.77%, 2.43%, and 3.89% when the same sample was extracted by SD, 97.77%, 0.17%, and 0.10% by SPTE, and 97.85%, 0.01%, and 0.01% by HS-SPME using the 50/30-m divinyl benzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fiber. Thermal degradation of components such as allyl methyl sulfide, dimethyl disulfide, and thiirane were observed for SDE and SD but not for SPTE or HS-SPME. HS-SPME had several advantages compared with SD, SDE, and SPTE—rapid solvent-free extraction, no apparent thermal degradation, less laborious manipulation, and less sample requirement. Five different fiber coatings were evaluated to select a suitable fiber for HS-SPME of garlic flavor components. DVB/CAR/PDMS was most efficient among the five types of fiber investigated.     

Investigation of genetic variants of α-1 acid glycoprotein by ultra-performance liquid chromatography–mass spectrometry

Genetic variants of human plasma alpha-1 acid glycoprotein (AGP) have been studied in cancer, compared with a group of healthy control. AGP has four genetic variants: AGP F1, F2, and S variants correspond to the ORM1 gene whereas AGP A corresponds to the ORM2 gene. The proportion of ORM1 and ORM2 variants were studied in plasma using a novel UPLC–MS method. Plasma total AGP level was 0.5 ± 0.2 g L⁻¹ and the proportions of the ORM1 and ORM2 variants were 76.3 ± 8.2% and 23.7 ± 8.2%, respectively. In cancer plasma AGP levels increased fourfold and the proportion of ORM1 variants increased to 88.7 ± 6.8%. Changes in the proportion of genetic variants due to cancer were clearly significant, as shown by statistical analysis. Three different cancer types have been studied, lymphoma, melanoma, and ovarian cancer. The results did not show any difference depending on cancer type. The results indicate that, in accordance with prior expectations, the ORM1 variant is predominantly responsible for the acute-phase property of AGP.     

Study of archaeological artifact by chromatography–mass spectrometry

An archaeological artifact, representing a compound piece of the Bronze Age, the outer surface of which is encrusted with seeds, has been investigated. The chemical composition of the organic binder was determined by gas chromatography and mass spectrometry; X-ray fluorescence analysis was used to determine the nature of the inorganic base of the artifact.     

Investigation of ligand interactions with human RXRα by hydrogen/deuterium exchange and mass spectrometry

Several different agonists of the retinoic X receptor alpha (hRXRalpha) were examined for their effects on the amide H/D exchange kinetics of the homodimeric protein using mass spectrometry. Some agonists, LG 100268, SR11246, and DHA, bind such that slower deuterium exchange-in occurs compared with 9-cis-retinoic acid (9-cis-RA), whereas others, fenretinide and methoprenic acid, result in poorer protection during binding and hence faster exchange-in. Protection against H/D exchange by different agonists and the inhibition of H/D exchange kinetics relative to 9-cis-RA varies markedly in different regions of the protein. Agonists LG 100268, SR11246, and DHA generally inhibit faster exchange processes in the ligand binding regions of hRXRalpha than does the native ligand 9-cis-RA. In at least half of these regions, the level of protection by 9-cis-RA lags behind the agonists even after 60 min. Methoprenic acid did not significantly protect hRXRalpha against amide hydrogen exchange. An efficient method is described for comparing the effects of different agonists on the protein structure of the agonist-RXRalpha complex.     

Novel aspects of quantitation of immunogenic wheat gluten peptides by liquid chromatography–mass spectrometry/mass spectrometry

A novel, specific and sensitive non-immunological liquid chromatography–mass spectrometry (LC–MS) based assay has been developed to detect and quantify trace levels of wheat gluten in food and consumer products. Detection and quantification of dietary gluten is important, because gluten is a principle trigger of a variety of immune diseases including food allergies and intolerances. One such disease, celiac sprue, can cause intestinal inflammation and enteropathy in patients who are exposed to dietary gluten. At present, immunochemistry is the leading analytical method for gluten detection in food. Consequently, enzyme-linked immunosorbent assays (ELISAs), such as the sandwich or competitive type assays, are the only commercially available methods to ensure that food and consumer products are accurately labeled as gluten-free. The availability of a comprehensive, fast and economic alternative to the immunological ELISA may also facilitate research towards the development of new drugs, therapies and food processing technologies to aid patients with gluten intolerances and for gluten-free labeling and certification purposes. LC–MS is an effective and efficient analytical technique for the study of cereal grain proteins and to quantify trace levels of targeted dietary gluten peptides in complex matrices. Initial efforts in this area afforded the unambiguous identification and structural characterization of six unique physiologically relevant wheat gluten peptides. This paper describes the development and optimization of an LC–MS/MS method that attempts to provide the best possible accuracy and sensitivity for the quantitative detection of trace levels of these six peptides in various food and consumer products. The overall performance of this method was evaluated using native cereal grains. Experimental results demonstrated that this method is capable of detecting and quantifying select target peptides in food over a range from 10 pg/mg to 100 ng/mg (corresponding to approximately 0.01–100 ppm). Limits of detection (LOD) and quantification (LOQ) for the six target peptides were determined to range from 1 to 30 pg/mg and 10–100 pg/mg respectively. Reproducibility of the assay was demonstrated by evaluation of calibration data as well as data collected from the analysis of quality control standards over a period of four consecutive days. The average coefficient of determination (R²) for each peptide was consistently found to be >0.995 with residuals ranging from approximately 80% to 110%. Spike recovery data for each peptide in various matrices was evaluated at a concentration level near the approximate LOQ for each, as well as at higher concentration levels (30 and 60 ng/mg). The average range of accuracy of detection for all peptides at the lower concentration level was determined to be 90% (±11), while accuracy at the 30 and 60 ng/mg levels was 98% (±5%) and 98% (±3%), respectively. The usefulness and capabilities of this method are presented in a practical application to prospectively screen a variety of common commercially available (native and processed) gluten-containing and gluten-free foods and products.     

Simultaneous determination of 1,1-dimethylhydrazine and products of its oxidative transformations by liquid chromatography–tandem mass spectrometry

A liquid chromatography–tandem mass spectrometry method is proposed for the simultaneous determination of 1,1-dimethylhydrazine, methylhydrazine, N,N-dimethylformamide, 1-methyl-1H-1,2,4-triazole, dimethylguanidine, N-nitrosodimethylamine and 1,1,4,4-tetramethyltetrazene, important rocket fuel pollutants of soils. Chromatographic separation was conducted according to previously published results in an isocratic mode on an analytical column with a Nucleosil-100–5SA sulfo-cation-exchanger. The mobile phase composition was optimised in order to achieve effective separation of all analytes and provide high sensitivity of mass spectrometric detection – an ammonium acetate buffer solution (50 mM, pH 5.4) containing methanol (25%) was used. Detection was performed in the positive electrospray ionisation mode with multiple reaction monitoring (MRM). The parameters of ion source, ion optics, the inlet potentials of the quadrupoles and the collision energy for the detection of the found product ions were optimised. Calibration dependences for all compounds are linear in wide concentration ranges, covering 3–4 orders of magnitude. The detection limits vary from 40 pg mL^?1 for dimethylguanidine to 18 ng mL^?1 for methylhydrazine. No significant matrix effects were observed in the analysis of acid peaty soil extracts. The method was validated and successfully used to analyse a real soil sample collected at the place of impact of the first stage of a carrier rocket.     

Highly sensitive determination of 1,1-dimethylhydrazine by high-performance liquid chromatography–tandem mass spectrometry with precolumn derivatization by phenylglyoxal

A new highly sensitive and rapid approach to the determination of 1,1-dimethylhydrazine in natural water is developed (determination range is 0.03–1 μg/L). It is based on the use of high-performance liquid chromatography–tandem mass spectrometry with precolumn derivatization by phenylglyoxal and does not require any preconcentration. Derivatization, chromatographic separation conditions, and tandem mass spectrometry detection parameters are chosen. Intra-day precision of the results of measurements of 1,1- dimethylhydrazine in natural water is 12–16%, and inter-day precision is 16–22%. The lowest limit of detection and the lowest limit of quantification are 0.010 μg/L and 0.030 μg/L, respectively.     

Enantioselective alkylation of benzaldehyde with diethylzinc catalyzed by 1,1′- and 1,2-disubstituted ferrocenyl amino alcohols

Optically active 1,1′- and 1,2-disubstituted ferrocenyl amino alcohols have been synthesized from 1,1′- and 1,2-ferrocene dicarboxaldehyde. They have been used as chiral catalysts in the asymmetric addition of diethylzinc to benzaldehyde. 1-Phenylpropanol has been obtained in up to 83% enantiomeric excess.     

Synthesis and properties of 2,2′-dipyridyl and 4,4′-dipyridyl complexes with thulium salts

Summary New complexes of 2,2-dipyridyl and 4,4-dipyridyl with thulium salts TmX ₃ (whereX=Cl^–, Br^–, NO ₃ ^– , NCS^–, and ClO ₄ ^– ) have been prepared and their solubilities in water at 21 °C were determined. The IR spectra of these compounds are discussed. The conditions of thermal decomposition of the complexes were also studied.

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Synthese und Eigenschaften von 2,2-Dipyridyl- und 4,4-Dipyridylkomplexen mit Thuliumsalzen

Zusammenfassung Es wurden neue 2,2-Dipyridyl- und 4,4-Dipyridyl-Komplexen mit Thuliumsalzen TmX ₃ (X=Cl^–, Br^– No ₃ ^– , NCS^–, ClO ₄ ^– ) dargestellt und ihre Wasserlöslihkeit bei 21 °C bestimmt. Die IR-Spektren werden diskutiert. Das thermische Verhalten der erhaltenen Komplexe wurde untersucht.

     

Liquid chromatography–electrospray tandem mass spectrometry investigations of fragmentation pathways of biliary 4,4′-methylenedianiline conjugates produced in rats

4,4′-methylenedianiline (DAPM) is the main building block for production of 4,4′-methylenediphenyldiisocyanate that has been widely used in the manufacturing of polyurethane materials including medical devices. Although it was revealed that damage to biliary epithelial cells of the liver and common bile duct occurred upon acute exposure to DAPM, the exact mechanism of DAPM toxicity is not fully understood. Both phase I and II biotransformations of DAPM, some of which generate reactive intermediates, are characterized in detail by liquid chromatography electrospray tandem mass spectrometry. The two most prominent metabolites found in rat bile (M2 and M7) implicated glutathione, glucuronic acid, and glycine conjugations (phase II) following hydroxylation, and N-oxidation (phase I). Their decomposition pathways, as evidenced by MS ⁿ experiments, have been elucidated in detail. Figure Proposed fragmentation pathways of a DAPM metabolite