A study of the aromaticity of heteroannelated cyclooctatetraene derivatives

The aromaticity of the rings of thiophene, pyrrole, furan, and benzene annelated cyclooctatetraene (COT) derivatives and of their double charged ions was studied using the graph-theoretical theory of aromaticity. On the basis of topological resonance energy, it was found that the global aromaticity is dependent upon on the arrangement of heteroatoms in the given molecule. Relative stability of these molecules when in different charged states can been explained in terms of the topological charge stabilization rule. We expect that fusing the COT ring with an increasing number of aromatic rings will lead to an increase in the aromaticity of the molecule. According to the bond resonance energy (BRE) and circuit resonance energy (CRE) indices, local antiaromaticity of the COT ring is weakened as the number of fused rings increases, and these changes play a significant role in the global aromaticity of the molecule. For some compounds, our BRE and CRE indices do not predict the same order of magnitude of the local aromatic character of certain rings that the nucleus independent chemical shift (NICS(0) and (NICS(1)) methods predict. Finally, for the available compounds, correlations between the diatropic and paratropic chemical shifts of the protons and our ring current results were analyzed and good agreement was found.     

A deep-red xanthene-based highly sensitive fluorescent probe for detection of hypochlorite

As an oxidant, deodorant and bleaching agent, the hypochlorous acid (HClO) and hypochlorite (ClO⁻) are widely used in corrosion inhibitors, textile dyes, pharmaceutical intermediates and in our daily lives. However, excess usage or aberrant accumulation of ClO⁻ leads to tissue damage or some diseases and even cancer. Therefore, it is necessary to develop a fluorescent probe that specifically identifies ClO⁻. In this article, we synthesized a deep-red xanthene-based fluorescent probe (XA-CN). The strong electron deficient group dicyano endows the probe XA-CN deep-red fluorescent emission with high solubility, selectivity and sensitivity for ClO⁻ detection. Studies showed that the probe demonstrated turn-off fluorescence (643 nm) at the presence of ClO⁻ in dimethylsulfoxide/phosphate-buffered saline 1:1 (pH 9) solution with a limit of detection of 1.64 μM. Detection mechanism investigation revealed that the electron deficient group -CN and the hydroxyl group was oxidized into aldehyde or carbonyl groups at the presence of ClO⁻, resulting ultraviolet-visible absorption of the probe blue shifted and turned-off fluorescence. Furthermore, XA-CN was successfully used for the detection of ClO⁻ in tap water samples.     

Aromaticity and kinetic stability of fullerene C36 isomers and their molecular ions

The aromatic character of fullerene C₃₆ isomers was examined by the Hess-Schaad resonance energy (HSRE), topological resonance energy (TRE) and the percentage topological resonance energy (%TRE) models. According to the nucleus-independent chemical shift (NICS) at the cage center, C₃₆ fullerene isomers must be highly aromatic with negative values. However, they are predicted to be antiaromatic with negative HSREs and negative TREs. The TRE method revealed that they all are aromatized by acquiring two or more electrons. NICSs at the cage center and the 2(N + 1)² rule cannot be used as an indicator of the aromatic stabilization for C₃₆ isomers and their molecular ions. We utilized the bond resonance energy (BRE) model to estimate the kinetic stability of C₃₆ isomers and their molecular ions. C₃₆ isomers are only stabilized kinetically in penta- and hexavalent molecular anions. All the results indicate that aromaticity and kinetic stability are closely related to the cyclic motion of π electrons.     

红褐斑腿蝗的食物消耗与利用及其对温度的依赖性

昆虫是变温动物 ,外界温度的波动会影响昆虫的体温 ,这也必然会影响昆虫的新陈代谢 ,从而引起一系列生理生化反应。红褐斑腿蝗 [Ｃａｔａｎｔｏｐｓｐｉｎ ｇｕｉｓ(Ｓｔａｌ) ]是浙江农田常见的蝗类害虫 ,分布广 ,数量多 ,常为害玉米 (Ｚｅａｍａｙｓ)、豆类 (Ｇｌｙｃｉｎｅｍａｘ)及茶树 (Ｃａｍｌｌｉａｓｉｎｅｎｓｉｓ)。据作者观察 ,该种蝗虫常以成虫越冬 ,而浙江省冬季最冷的 1月份平均气温为 2 5～ 7 5℃ ,极端低温多年平均在 - 8℃以下。文献研究表明 ,红褐斑腿蝗的过冷却点可达 - 2 0℃以下 (有关结果拟另文发表 ) ,显示其具…     

A comparative study of the aromaticity of pyrrole, furan, thiophene, and their aza-derivatives

The relative aromaticity of pyrrole, furan, thiophene, and their aza-derivatives has been examined using TRE (topological resonance energy), MRE (magnetic resonance energy), ring current (RC), and ring current diamagnetic susceptibility (χ_G) methods. The results obtained were compared with results obtained by others who used the energetic method ASE (aromatic stabilization energy), the geometric method HOMA (harmonic oscillator model of aromaticity), and the magnetic method NICS(1) (nucleus-independent chemical shift). The impact of nitrogen atoms on the aromaticity of the aza-derivatives of pyrrole, furan, and thiophene is discussed. An excellent correlation was found between the energetic (TRE, MRE) and magnetic (RC and χ_G) criteria of aromaticity for all compounds. It was expected that inclusion of a heteroatom would decrease the aromaticity relative to the cyclopentadienyl anion. Our results show that the type of the first heteroatom, which donates two electrons to the system, as well as the number of nitrogen atoms and their positions in the molecule have a strong effect on aromaticity. In general, aromaticity is enhanced when the nitrogen atom is adjacent to the first heteroatom. The magnitude of aromaticity is related closely with the uniformity of distribution of π-electrons in the molecule.