Acetyl Exchange between Pyridine N-Oxides in Acetonitrile Solutions: An Attempt to Apply the Marcus Equation to Acetyl Transfer

Forty-three (including eight identical) reactions of acetyl transfer from N-acetyloxypyridinium salts to pyridine N-oxides in acetonitrile solutions were studied. The rate constants k ₂ vary in the range 10⁷-10^{- 1} l mol^{- 1} s^{- 1}; the equilibrium constants K, in the range 10⁷-10^{- 7}; the activation enthalpy H , in the range 17-30 kJ mol^{- 1}; the activation entropy -S , in the range 60-85 J mol^{- 1} K^{- 1}; and the heat of reaction -H ⁰, within ±50 kJ mol^{- 1}. All reactions occur in a single stage by the concerted SN2 mechanism with a low degree of bond cleavage in the transition state. The rate and equilibrium of the acetyl exchange are satisfactorily described by the Brönsted equation. The quality of predicting the reactivity is substantially improved by introducing into the correlation equation a second parameter, the rates of identical reactions.     

Silicon polypodands: powerful metal cation complexing agents and solid-liquid phase-transfer catalysts of new generation

Silicon polypodands 5-7 are found to be powerful complexing agents of alkali metal salts in low polarity solvents and very efficient catalysts in anion-promoted reactions under solid-liquid PTC conditions. The catalytic activity is comparable with that of the cyclic polyether PHDB18C6 8.     

Kinetics and mechanism of the silane decomposition

The homogeneous gas-phase decomposition kinetics of silane has been investigated using the single-pulse shock tube comparative rate technique (T = 1035–1184?K, P_total ≈? 4000 Torr). The initial reaction of the decomposition SiH₄ \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm SiH}_{\rm 4} \mathop \to \limits^1 {\rm SiH}_{\rm 2} + {\rm H}_{\rm 2} $\end{document} SiH₂ + H₂ is a unimolecular process in its pressure fall-off regime with experimental Arrhenius parameters of logk₁ (sec^?1) = 13.33 ± 0.28–52,700 ± 1400/2.303RT. The decomposition has also been studied at lower temperatures by conventional methods. The results confirm the total pressure effect, indicate a small but not negligible extent of induced reaction, and show that the decomposition is first order in silane at constant total pressures. RRKM-pressure fall-off calculations for four different transition-state models are reported, and good agreement with all the data is obtained with a model whose high-pressure parameters are logA₁ (sec^?1) = 15.5, E_1(∞) = 56.9 kcal, and ΔE^0±₀(1) = 55.9 kcal. The mechanism of the decomposition is discussed, and it is concluded that hydrogen atoms are not involved. It is further suggested that silylene in the pure silane pyrolysis ultimately reacts with itself to give hydrogen: 2SiH₂ → (Si₂H₄)* → (SiH₃SiH)* → Si₂H₂ + H₂. The mechanism of H ? D exchange absorbed in the pyrolysis of SiD₄-hydrocarbon systems is also discussed.     

Kinetics of the transfer of the dimethyl-carbamoyl group from N- and O-acylonium salts to azines and their N-oxides

The rate constants and activation energies were determined for a series of reactions involving the transfer of a dimethylcarbamoyl group from the N,N-dimethylcarbamoylonium salts of a series of nitrogen heterocycles and their N-oxides to nucleophiles (azines and their N-oxides) in acetonitrile. The measured values were compared with the structural, reaction, and equilibrium characteristics. L. M. Litvinenko Institute of Physical Organic Chemistry and Coal Chemistry, National Academy of Sciences of Ukraine, Donetsk. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 3, pp. 143–148, May–June, 1997.     

Adhesion and Anti-Adhesion Abilities of Potentially Probiotic Lactic Acid Bacteria and Biofilm Eradication of Honeybee (Apis mellifera L.) Pathogens

Lactic acid bacteria (LAB) naturally inhabits the organisms of honeybees and can exhibit adhesive properties that protect these insects against various pathogenic microorganisms. Thus, cell surface (auto-aggregation, co-aggregation, hydrophobicity) and adhesive properties of LAB to two abiotic (polystyrene and glass) and four biotic (collagen, gelatin, mucus, and intestinal Caco-2 cells) surfaces were investigated. Additionally, anti-adhesion activity and the eradication of honeybee pathogen biofilms by LAB metabolites (culture supernatants) were determined. The highest hydrophobicity was demonstrated by Pediococcus pentosaceus 19/1 (63.16%) and auto-aggregation by Lactiplantibacillus plantarum 18/1 (71.91%). All LAB showed a broad spectrum of adhesion to the tested surfaces. The strongest adhesion was noted for glass. The ability to co-aggregate with pathogens was tested for the three most potently adherent LAB strains. All showed various levels of co-aggregation depending on the pathogen. The eradication of mature pathogen biofilms by LAB metabolites appeared to be weaker than their anti-adhesive properties against pathogens. The most potent anti-adhesion activity was observed for L. plantarum 18/1 (98.80%) against Paenibacillus apiarius DSM 5582, while the strongest biofilm eradication was demonstrated by the same LAB strain against Melissococcus plutonius DSM 29964 (19.87%). The adhesive and anti-adhesive activity demonstrated by LAB can contribute to increasing the viability of honeybee colonies and improving the conditions in apiaries.     

Effects of Insecticides and Microbiological Contaminants on Apis mellifera Health

Over the past two decades, there has been an alarming decline in the number of honey bee colonies. This phenomenon is called Colony Collapse Disorder (CCD). Bee products play a significant role in human life and have a huge impact on agriculture, therefore bees are an economically important species. Honey has found its healing application in various sectors of human life, as well as other bee products such as royal jelly, propolis, and bee pollen. There are many putative factors of CCD, such as air pollution, GMO, viruses, or predators (such as wasps and hornets). It is, however, believed that pesticides and microorganisms play a huge role in the mass extinction of bee colonies. Insecticides are chemicals that are dangerous to both humans and the environment. They can cause enormous damage to bees’ nervous system and permanently weaken their immune system, making them vulnerable to other factors. Some of the insecticides that negatively affect bees are, for example, neonicotinoids, coumaphos, and chlorpyrifos. Microorganisms can cause various diseases in bees, weakening the health of the colony and often resulting in its extinction. Infection with microorganisms may result in the need to dispose of the entire hive to prevent the spread of pathogens to other hives. Many aspects of the impact of pesticides and microorganisms on bees are still unclear. The need to deepen knowledge in this matter is crucial, bearing in mind how important these animals are for human life.     

On the existence of one-sided designs

A collection of subsets (called blocks) of a fixed vertex set (possibly with repetition) is called a (t _n , t _n –1, ..., t ₁; a _m , a _m –1, ..., a ₁)-design if it satisfies certain regularity conditions on the number of blocks which contain subsets of the vertex set of certain size, and other regularity conditions on the size of the intersections of certain numbers of the blocks. (For example, a BIBD (or (b, v, r, k, )-configuration) is a (1, 2; 1)-design, and a t-design is a (t, t–1, ..., 1; 1)-design.) A design has design-type (t _n , ..., t ₁; a _m , ..., a ₁) if it satisfies only those conditions. A one-sided design is a design with design-type (t _n , ..., t ₁;) or (;a _m , ..., a ₁). In this paper we show, by construction, that any one-sided design-type is possible.