Sigmatropic rearrangements in 5-allyloxytetrazoles

Mechanisms of thermal isomerization of allyl tetrazolyl ethers derived from the carbocyclic allylic alcohols cyclohex-2-enol and 3-methylcyclohex-2-enol and from the natural terpene alcohol nerol were investigated. In the process of the syntheses of the three 1-aryl-5-allyloxytetrazoles, their rapid isomerization to the corresponding 1-aryl-4-allyltetrazol-5-ones occurred. The experiments showed that the imidates rearrange exclusively through a [3,3']-sigmatropic migration of the allylic system from O to N, with inversion. Mechanistic proposals are based on product analysis and extensive quantum chemical calculations at the DFT(B3LYP) and MP2 levels, on O-allyl and N-allyl isomers and on putative transition state structures for [1,3']- and [3,3']-sigmatropic migrations. The experimental observations could be only explained on the basis of the MP2/6-31G(d,p) calculations that favoured the [3,3']-sigmatropic migrations, yielding lower energies both for the transition states and for the final isomerization products.     

Chemical oxidative polymerization of m-phenylenediamine and its derivatives using aluminium triflate as a co-catalyst

Aromatic diamine monomers, including m-phenylenediamine (mPD), 2-methyl-m-phenylenediamine (2Me-mPD), 4-methyl-m-phenylenediamine (4Me-mPD) and trimethyl-m-phenylenediamine (tMe-mPD), were polymerized by chemical oxidation using ammonium persulfate as an oxidant. Aluminium triflate (Al(OTf)₃) was also used for the first time as a co-catalyst under various polymerization conditions. The polymerization yield was improved when Al(OTf)₃ was introduced to the polymerization reaction for most polymers. The poly(2-methyl-m-phenylenediamine) (P(2Me-mPD)), poly(4-methyl-m-phenylenediamine) (P(4Me-mPD)) and poly(trimethyl-m-phenylenediamine) (P(tMe-mPD)) polymers exhibited better solubility than poly(m-phenylenediamine) (P(mPD)) polymers in most common solvents. The homopolymers obtained were characterized by FT-IR, ¹H and ¹³C NMR, WAXD and TGA. The results showed that the yield, solubility and structure of the polymers are significantly dependent on the polymerization conditions. TGA measurements indicated that the polymers have good thermal stability and decompose above 400 °C in nitrogen.     

Sequential single pion production explaining the dibaryon "d*(2380)" peak

In this study, we investigate the two step sequential one pion production mechanism, that is, \begin{document}$ np(I=0)\to $\end{document}\begin{document}$ \pi^-pp $\end{document} followed by the fusion reaction \begin{document}$ pp\to \pi^+d $\end{document}, to describe the \begin{document}$ np\to \pi^+\pi^-d $\end{document} reaction with \begin{document}$ \pi^+\pi^- $\end{document} in state \begin{document}$ I=0 $\end{document}. In this reaction, a narrow peak identified with a "\begin{document}$ d(2380) $\end{document}" dibaryon has been previously observed. We discover that the second reaction step \begin{document}$ pp\to \pi^+d $\end{document} is driven by a triangle singularity that determines the position of the peak of the reaction and the high strength of the cross section. The combined cross section of these two mechanisms produces a narrow peak with a position, width, and strength, that are compatible with experimental observations within the applied approximations made. This novel interpretation of the peak accomplished without invoking a dibaryon explains why this peak has remained undetected in other reactions.     

Multi-solutions with specific geometrical wave structures to a nonlinear evolution equation in the presence of the linear superposition principle

Lump solutions are one of the most common solutions for nonlinear evolution equations.This study aspires to investigate the generalized Hietarintatype equation.We auspiciously provide multiple M-lump waves.On the other hand,collision phenomena to multiple M-lump waves with soliton wave solutions are also provided.During the collision,the amplitude of the lump will change significantly over the processes,whereas the amplitude of the soliton will just minimally alter.As it is of paramount importan...     

The synthesis of substituted pyrido[1′,2′:1,5]pyrazolo[3,4-d]pyrimidines

A convenient synthesis of derivatives of the pyrido[1′,2′:1,5]pyrazolo[3,4-d]pyrimidine ring system from readily available 2-amino-3-cyano-5,7-diphenylpyrazolo[1,5-a]pyridine I and carbon disulfide, aryl isothiocyanates or nitriles is described. Derivatives of compound I undergo cyclization to the titled ring system by action of dimethylformamide dimethylacetal or hydrogen sulfide followed by treatment with triethylamine.     

Rapid determination of fungicides in fruit juices by micellar electrokinetic chromatography: use of organic modifiers to enhance selectivity and on-column high-salt stacking to improve sensitivity

A rapid, reliable method for the multiresidue analysis of eight commonly used fungicides by micellar electrokinetic chromatography (MEKC) was developed. Excellent separation of the eight fungicides (carbendazim, metalaxyl, captan, procymidone, folpet, captafol, vinclozolin and iprodione) is achieved within about 10 min by using optimized electrophoretic conditions that include the addition of a mixture of organic modifiers to the running buffer for improved resolution. The sensitivity of the method is enhanced by using an enrichment step that involves on-column high-salt stacking. Limits of detection in the microgram-per-liter region and relative standard deviations from 2.1 to 5.9% are thus obtained for the fungicides without detracting from peak resolution. These results reveal that the high-salt stacking method provides highly improved sensitivity and enables highly flexible adjustment of the selectivity of the separation method. Also, the method surpasses other stacking alternatives used in MEKC and affords routine analyses of fruit juice containing fungicides at trace levels following a straightforward sample treatment. The robustness of the high-salt stacking method as demonstrated in this work makes MEKC methods involving stacking procedures an attractive choice for routine analyses.     

A transferable ab initio based force field for aqueous ions

We present a new polarizable force field for aqueous ions (Li(+), Na(+), K(+), Rb(+), Cs(+), Mg(2 +), Ca(2 +), Sr(2 +), and Cl(-)) derived from condensed phase ab initio calculations. We use maximally localized Wannier functions together with a generalized force and dipole-matching procedure to determine the whole set of parameters. Experimental data are then used only for validation purposes and a good agreement is obtained for structural, dynamic, and thermodynamic properties. The same procedure applied to crystalline phases allows to parametrize the interaction between cations and the chloride anion. Finally, we illustrate the good transferability of the force field to other thermodynamic conditions by investigating concentrated solutions.     

Combined study of anion recognition by a carbazole-based neutral tripodal receptor in a competitive environment

Anion recognition studies have been carried out on a series of neutral synthetic receptors in which carbazole-2-carboxamide has been used as building block. Different ligands which include one to three carbazole units in their structure have been prepared. Binding experiments have been performed under competitive conditions in DMSO and DMSO-water solutions. The tripodal receptor offered a better host-guest association due to the synergistic effect of a well arranged set of hydrogen bonds. A selective response towards the biologically important pyrophosphate anion has been achieved. This selectivity is enhanced when studies are carried out with an increasing water content, which gets as high as 20% (v/v) in NMR experiments. The significance of this result lies in the use of a neutral receptor which exclusively interacts with the anionic guest through hydrogen bonding. The influence of multiple equilibria in the studied system has been analysed. Several techniques ((1)H NMR, (31)P NMR, mass spectrometry, diffusion-NMR, ITC, absorption and emission spectroscopy) have been employed to get a better understanding of the different processes taking place in solution for the evaluated receptors.     

Reaction of 3-hetero-substituted 2-phenyl-4-thioxo-3,4-dihydro-quinazolines with acyl chlorides and phenacyl bromides

Some 2, 5-disubstituted 1, 3, 4-thiadiazoles 5 were obtained by reaction of 3-amino-2-phenyl-4-thioxo-3, 4-dihydroquinazoline ( 1 ) with acyl chlorides. Reaction of 3-hydroxy-2-phenyl-3, 4-dihydroquinazoline ( 3 ) with phenacyl bromides was carried out either in dry acetonitrile or dimethylformamide to give 2-phenyl-4-phenacylthio-3-quinazolinium N-oxides 7 or 2-phenyl-4-phenacylidene-1H-3-quinazolinium N-oxides' 8 , respectively.