Structural characterization and differentiation of isomeric omega-bromoalkoxy derivatives of (E)-chalcone by means of mass spectrometry

Mass spectrometry with electron ionization and electrospray ionization have been applied to characterize and differentiate the isomeric ortho-, meta- or para-(E)-bromoalkyloxychalcones 1-15. The difference in the values of micro1-micro5 (i.e. the ratio of abundances of the selected fragment ions to those of the molecular ions) in the series of isomeric chalcones studied and the so-called "in-source" fragmentation induced by increasing cone voltage have been found to be important and reliable indicators differentiating the isomers studied.     

Optimized derivatization of acidic herbicides with trimethylsilyldiazomethane for GC analysis

In the present study, the preparation of methyl esters of chlorophenoxy acids with trimethylsilyldiazomethane (TMSD) is reported. TMSD is a mild and safe alternative to the highly toxic, thermally labile, and explosive diazomethane. Due to the novelty of this method, the characteristics of the reaction were investigated and the derivatization procedure was screened for statistically significant factors. The parameters identified as influential are the amount of methanol as well as reaction time and temperature. A careful optimization by a complete factorial response surface design was carried out to generate optimal reaction conditions with respect to maximum recovery and reaction yield. Special emphasis has been given to an accurate validation of the derivatization procedure. LODs were determined between 4.1 and 8.1 ng/mL for the enriched sample and linearity was proofed for more than five orders of magnitude. The applicability of the method was demonstrated by the analyses of quality control material including sample preparation with SPE. Polar herbicides investigated in the study belong to acetic acid (2,4-D, MCPA, and 2,4,5-T), butanoic acid (MCPB), and propanoic acid (mecoprop). An efficient, fast, and high-throughput method for the determination of polar herbicides including the potential for automation is proposed.     

2,2′-Dithiobispyrazine: about the disulfide bond

X-ray diffraction studies reveal that pyrazine-2-thiol undergoes condensation to 2,2′-dithiobispyrazine [systematic name: 2-(pyrazin-2-yldisulfanyl)pyrazine], C₈H₆N₄S₂ ( I ), under aerial conditions. In the molecule of I , the pyrazine rings are arranged in an almost perpendicular manner, with an absolute value of the C—S—S—C torsion angle of −91.45 (6)°. A search in the Cambridge Structural Database confirmed that such a conformation is typical for disulfide compounds. Three different rotamers of disulfide I were studied using quantum theoretical studies. The rotamer of lowest energy was observed in the crystalline state in the structure stabilized by hydrogen-bond, chalcogen-bond and stacking interactions. Further quantum chemical computations confirm that 2,2′-dithiobispyrazine can react according to the S_N2 mechanism.     

Application of high-performance liquid chromatography with amperometric and coulometric detection to the analysis of SZ1677, a new neuromuscular blocking agent, and its two derivatives

A HPLC method with amperometric and coulometric detection for the determination of SZ1677 and its two derivatives SZ1676 and SZ1823 has been developed. This active substance is under development (clinical trial) and there are no analytical methods published for the determination of SZ1677 thus far. The limit of quantitation for SZ1677 was 25 and 100ngml(-1) by the coulometric and amperometric detection, respectively. The elaborate method for the simultaneous analysis of SZ1677 and its two derivatives proved to be fast, precise, accurate and sensitive.     

Addition of dimethyl phosphite to N,N'-dialkyl- and -diaryl terephthalaldimines and its stereochemistry contrary to behavior of other analogues

The addition of dimethyl phosphite to N,N'-terephthalylidene-alkyl- (or aryl-) amines resulted in new tetramethyl 1,4-phenylene-bis-(N-alkylaminomethyl)-phosphonates in moderate yields. The stereochemical behavior of these reactions was studied by NMR, demonstrating that the reactions lead to the formation of both possible diastereomeric forms from 1:1 to 1:2 ratios. This was unexpected considering that previously investigated additions of diethyl, dibenzyl, and diphenyl phosphites to terephthalaldimines were diastereoselective up to 100%. Attempts were made to find reasonable explanation for the phenomenon using semi-empirical and DFT calculations.     

A Singular Behaviour of a Set-Valued Approximate Orthogonal Additivity

We show that unlikely to the single-valued case, the set-valued orthogonally additive equation is unstable. After presenting an example showing this phenomenon, we provide some special cases where a set-valued approximately orthogonally additive function can be approximated by the one which satisfies the equation of orthogonal additivity exactly.     

Selective adsorption of modified nucleoside cancer biomarkers by hybrid molecularly imprinted adsorbents

Modified adenosine nucleosides have been proposed to be potential DNA‐based biomarkers for early diagnosis of tumor and a promising tool for the development of noninvasive prediction systems. However, the low concentration of modified adenosine nucleosides in physiological fluids makes them challenging for both quantitative and qualitative determination. Therefore, materials, which are potentially useful for selective adsorption of nucleobase‐containing compounds, were obtained. To obtain the adsorbents, the silica gel particles were coated layer‐by‐layer with films of the polymers with different combinations of polymers containing thymine groups. Next, the microspheres were irradiated with UV light in the presence of 2’‐deoxyadenosine or 5’‐deoxy‐5’‐(methylthio)adenosine, as template molecules, which resulted in the photodimerization of thymine moieties and molecular imprinting of adsorbed modified adenosine compounds. The selectivity of the adsorption was significantly enhanced by the photoimprinting process. Eventually, the imprinted particles have shown an improved ability to recognize mainly 2’‐deoxyadenosine and 5’‐deoxy‐5’‐(methylthio)adenosine molecules. The best performing adsorbent was obtained using modified natural polysaccharides. The studied materials could serve as promising adsorbents of biomarkers for tumor diagnostics.     

Source of Cooperativity in Halogen‐Bonded Haloamine Tetramers

Inspired by the isostructural motif in α‐bromoacetophenone oxime crystals, we investigated halogen–halogen bonding in haloamine quartets. Our Kohn–Sham molecular orbital and energy decomposition analysis reveal a synergy that can be traced to a charge‐transfer interaction in the halogen‐bonded tetramers. The halogen lone‐pair orbital on one monomer donates electrons into the unoccupied σ*_N?X orbital on the perpendicular N?X bond of the neighboring monomer. This interaction has local σ symmetry. Interestingly, we discovered a second, somewhat weaker donor–acceptor interaction of local π symmetry, which partially counteracts the aforementioned regular σ‐symmetric halogen‐bonding orbital interaction. The halogen–halogen interaction in haloamines is the first known example of a halogen bond in which back donation takes place. We also find that this cooperativity in halogen bonds results from the reduction of the donor–acceptor orbital‐energy gap that occurs every time a monomer is added to the aggregate.     

From a theorem of R. Ger and T. Kochanek to marginal joints of means

We answer in the negative a problem posed in Daróczy (Report on 52nd International Symposium on Functional Equations. Aequat. Math., 2015) by the first author, in connection with a result of Ger and Kochanek (Colloq Math 115:87–99, 2009), and its generalization formulated in Daróczy et al. (Report on 52nd International Symposium on Functional Equations. Aequat. Math., 2015). A further generalization is posed as an open problem. Elaborating an idea of the construction of means presented in Examples 1.2 and 1.4 we come to the notion of marginal joints of means. It provides a pretty wide class of means extending two given means on adjacent intervals.     

The Annealing of Acetylated Potato Starch with Various Substitution Degrees

This study aimed to determine the effect of “annealing” acetylated potato starch with a homogenous granule size and various degrees of substitution on the thermal pasting characteristics (DSC), resistance to amylases, rheology of the prepared pastes, swelling power and dynamics of drug release. A fraction of large granules was separated from native starch with the sedimentation method and acetylated with various doses of acetic anhydride (6.5, 13.0 or 26.0 26 cm³/100 g starch). The starch acetates were then annealed at slightly lower temperatures than their pasting temperatures. The annealing process caused an almost twofold increase in the resistance to amylolysis and a threefold increase in the swelling power of the modified starch preparations. The heat of phase transition decreased almost two times and the range of starch pasting temperatures over two times, but the pasting temperature itself increased by ca. 10 °C. The 40 g/100 g addition of the modified starch preparation decreased the rate of drug release from a hydrogel by ca. one-fourth compared to the control sample.