Synthesis of highly stable unusual charge-separated pyridinium-, isoquinolinium-, quinolinium-, and N-methylimidazolium-tetronic acid zwitterions

A unique strategy for the synthesis of highly stable unusual charge-separated pyridinium-, isoquinolinium-, quinolinium-, and N-methylimidazolium-tetronic acid zwitterions from the reaction of pyridine, isoquinoline, quinoline, and N-methylimidazole with dialkyl acetylenedicarboxylates and 3-chlorotetronic acid in EtOH at room temperature is described.     

Two significantly different conformations in crystal: formation of a molecular dimer governed by cation-π interactions

Two significantly different conformations were observed in crystal of 1, which form an unsymmetrical molecular dimer governed by cation-π interactions between a pyridinium cation and a phenyl ring, whereas compound 2 forms a head-to-tail type of dimer.     

Zwitterionic Salts from the Reaction of Symmetrical and Unsymmetrical (thio)Barbituric Acids with 2‐Pyridinecarbaldehyde under Solvent‐free Condition

A simple and efficient synthesis for the preparation of unusual charge‐separated pyridinium (thio)barbiturate zwitterion derivatives was achieved via a one‐pot reaction of (thio)barbituric acid derivatives and 2‐pyridinecarbaldehyde under solvent‐free condition and also in methanol under refluxing. The structure of the compounds was confirmed by ¹H NMR, ¹³C NMR, FT‐IR, mass and X‐ray analysis. The mechanism of the formation is discussed. Instead, no related pyridinium zwitterion was afforded from the reaction between dimedone and 2‐pyridinecarbaldehyde under the same conditions and its xanthene derivative was obtained.     

Novel Protein Binding Capacity and Selectivity of Immobilized Pyridinium Pseudo-Affinity Gels: Applications in Immunoglobulin G Purification and Quantitative Determination

Abstract

A series of novel pseudo-affinity gels using synthetic, immobilized pyridinium ligands have been prepared. These gels exhibit extraordinarily high protein binding capacity and selectivity. Initial applications of these gels were directed toward the purification and quantitative, rapid determination of immunoglobulins. The results showed that these pseudo-affinity gels functionally mimic, to a high degree of similarity, the behavior of immobilized Protein A or G for immunoglobulins purification. In contrast to the labile nature of protein-based affinity gels, these immobilized pyridinium gels can withstand harsher treatments, such as prolonged exposure of the gels to proteolytic enzymes, organic solvents, acid or base and high temperatures.     

UV/Vis-LED激发的香豆素吡啶鎓盐光引发剂的合成及性能

设计合成了3种基于香豆素骨架的紫外-可见发光二极管(UV/Vis-LED)可激发的新型吡啶鎓盐光引发剂, 并研究了这3种香豆素吡啶鎓盐的构效关系及其作为单组分自由基光引发剂在丙烯酸酯体系中的光引发活性. 紫外-可见吸收光谱分析表明, 这3种香豆素吡啶鎓盐在300~400 nm区域有较强吸收. 在LED@365 nm和LED@405 nm光源辐照下, 研究了3种光引发剂的稳态光解和光聚合动力学. 研究表明, 这3种香豆素吡啶鎓盐光引发剂在相应光辐照下都具有较好的光解速率. 此外, 3种光引发剂对丙烯酸酯都具有较好的引发活性. 构效关系研究表明, 吡啶环4号位引入推电子的甲氧基会使其引发丙烯酸酯单体聚合的活性降低; 而引入吸电子的乙酰基会使其引发丙烯酸酯单体聚合的活性增加. 差示扫描量热(DSC)实验表明, 此类吡啶鎓盐光引发剂具有较好的热稳定性. 当3种光引发剂与丙烯酸单体混合时可提升体系的热稳定性; 通过电子自旋共振(ESR)证明了活性物种的产生, 并对该类引发剂的引发机理进行了探讨.     

1,3-Dipolar cycloaddition reaction of bipyridinium ylides with the propynamido-β-cyclodextrin. A regiospecific synthesis of a new class of fluorescent β-cyclodextrins

The 1,3-dipolar cycloaddition reaction of bipyridinium ylides with the electron deficient propynamido-β-cyclodextrin was studied. This reaction resulted in the regiospecific formation of a new class of fluorescent β-cyclodextrins. The new fluorophore systems were characterized spectroscopically by their absorption and emission maxima and their quantum yields.     

1,5‐Dipolar Electrocyclizations of Thiocarbonyl Ylides Bearing CN Groups: Reactions of N‐[(Dimethylamino)methylene]thiobenzamide and 2‐(Dimethylhydrazono)‐1‐phenylethane‐1‐thione with Diazo Compounds

The reactions of thiobenzamide 8 with diazo compounds proceeded via reactive thiocarbonyl ylides as intermediates, which underwent either a 1,5‐dipolar electrocyclization to give the corresponding five membered heterocycles, i.e., 4‐amino‐4,5‐dihydro‐1,3‐thiazole derivatives (i.e., 10a, 10b, 10c , cis‐ 10d , and trans‐ 10d ) or a 1,3‐dipolar electrocyclization to give the corresponding thiiranes as intermediates, which underwent a S_Ni′‐like ring opening and subsequent 5‐exo‐trig cyclization to yield the isomeric 2‐amino‐2,5‐dihydro‐1,3‐thiazole derivatives (i.e., 11a, 11b, 11c , cis‐ 11d , and trans‐ 11d ). In general, isomer 10 was formed in higher yield than isomer 11 . In the case of the reaction of 8 with diazo(phenyl)methane ( 3d ), a mixture of two pairs of diastereoisomers was formed, of which two, namely cis‐ 10d and trans‐ 10d , could be isolated as pure compounds. The isomers cis‐ 11d and trans‐ 11d remained as a mixture. In the reactions of the thioxohydrazone 9 with diazo compounds 3b and 3d , the main products were the alkenes 18 and 23 , respectively. Their formation was rationalized by a 1,3‐dipolar electrocyclization of the corresponding thiocarbonyl ylide and subsequent desulfurization of the intermediate thiiran. As minor products, 2,5‐dihydro‐1,3‐thiazol‐5‐amines 21 and 24 were obtained, which have been formed by 1,5‐dipolar electrocyclization of the thiocarbonyl ylide, followed by a 1,3‐shift of the dimethylamino group.     

Dithionite adducts of pyridinium salts: regioselectivity of formation and mechanisms of decomposition

¹H and ¹³C NMR spectroscopy has been used to detect and to characterize the adducts formed, in alkaline solutions, by the attack of dithionite anion on 3-carbamoyl or 3-cyano substituted pyridinium salts. In all studied cases, only 1,4-dihydropyridine-4-sulfinates, formed by attack of dithionite oxyanion on the carbon 4 of pyridinium ring, were found. This absolute regioselectivity seems to suggest a very specific interaction between the pyridinium cation and the dithionite through the formation of a rigidly oriented ion pair, determining the position of attack. In weak alkaline solution, the adducts decompose according to two mechanisms S_Ni and S_Ni′: the S_Ni path is operative in all studied cases and preserves the 1,4-dihydro structure yielding the corresponding 1,4-dihydropyridines, whereas the S_Ni′ path involves the shift of 2,3 or 5,6 double bonds yielding 1,2- or 1,6-dihydropyridines, respectively. The formation of 1,2- or 1,6-dihydropyridines, in addition to 1,4-dihydro isomers, depends on their respective thermodynamic stabilities.     

Study of the reactions of pyridinium poly(hydrogen fluoride) with some ternary oxides

The products of the reaction of pyridinium poly(hydrogen fluoride), PPHF, with KIO₃, Na₂SnO₃, NaBiO₃, K₂CrO₄, Na₂MoO₄ and Na₂WO₄ were KIO₂F₂; Na₂SnF₆; NaHF₂, BiF₃; K₃CrF₆, KHF₂, (PyH)₃CrF₆; NaHF₂, (PyH)₂MoO₂F₄·2NaHF₂; and (PyH)₂WO₂F₄·2NaHF₂, respectively, while KClO₃, KBrO₃ and KIO₄ react with complete decomposition to form KHF₂ as the fluorinated product. This differential reactivity and mode of reaction has been discussed in terms of the oxidation state of the central atom, the nature and strength of the bonds and the complex behaviour of the formed intermediate or fluorinated products that undergo complexation or solvation with pyridine and/or hydrogen fluoride.     

One-pot synthesis of ω-bromoesters from aromatic aldehydes and diols using pyridinium hydrobromide perbromide

A simple and efficient one-pot procedure has been developed for the synthesis of ω-bromoesters from aromatic aldehydes and diols in the presence of pyridinium hydrobromide perbromide (PHPB) and triethoxymethane in which aldehyde reacts first with diol and the product, cyclic acetal, reacts with PHPB to give the final product, ω-bromoesters.