Synthesis and mesomorphic properties of chiral nematic liquid crystals based on cholesterol

A new series of mesogenic compounds having a cholesteryl moiety has been synthesised by condensing p-amino benzoate of cholesterol and methoxy substituted 4-n-alkoxy cinnamoyl chlorides and their liquid crystalline properties has been studied. All the members of the series are enantiotropic and exhibit chiral nematic (N*) mesophase. The plot of transition temperatures versus number of carbon atoms in the alkoxy chain exhibits odd–even effect and falling tendency for N*–isotropic transition temperatures. The compounds exhibit oily streak textures that on slight disturbance change to the plane textures and show iridescent colours. High anisotropy, linearity and intermolecular hydrogen bonding confer rich mesomorphic properties on the system. Intermolecular hydrogen bonding arising from amide linkage can lead to supramolecular motifs.     

T-shaped non-symmetrical twin liquid crystalline compounds

New unconventional T-shaped non-symmetrical dimeric liquid crystalline compounds have been synthesised and their thermotropic properties studied on the hot-stage of a polarising microscope. These compounds consist of an azo-ester mesogenic unit with a range of terminal substituents (–CH₃, –OCH₃, –NO₂ or –Cl) at one end, interconnected by a flexible spacer (n?=?4, 5 or 10) via ether and ester linking units to a biphenyl moiety at the lateral hydroxyl position of the azo-ester. All the compounds were characterised using a combination of elemental analysis and standard spectroscopic methods. The compounds were found to exhibit enantiotropic nematic and smectic mesophases. The effect of different terminal substituents on mesomorphism is discussed.     

Mesophase behaviour of laterally di-fluoro-substituted four-ring compounds

Four new groups of the di-fluoro-substituted 4-(2′-(or 3′)-fluoro phenylazo)-2-(or 3-) fluoro phenyl-4″-alkoxyphenylazo benzoates (In–IVn) were prepared and investigated for their mesophase behaviour. An alkoxy group of variable chain length (n = 6, 10 and 14 carbons) is attached to the terminal phenylazo benzoate moiety, and two lateral fluoro substituents are attached individually with different orientations to the other two adjacent rings. The molecular structures of the prepared compounds were confirmed by Fourier transform infrared spectroscopy and ¹H NMR spectroscopy. The study aims to investigate the steric effect of the spatial orientation and relative positions of the two lateral fluorine atoms on the mesomorphic properties in their pure states. The mesophase behaviour was investigated via differential scanning calorimetry and mesophases were identified by polarised light microscopy. The investigation shows that these compounds exhibit high enantiotropic mesophases (SmC and N) and broad mesophase temperature range. The type and stability of the mesophase depends on the length of the terminal alkoxy chain and the position the two fluoro substituents. A comparison between these investigated compounds with their corresponding three-ring analogues was discussed.     

CONJUGATE ADDITION OF AMINES TO SUGAR DERIVED OLEFINIC ESTERS: SYNTHESIS OF GLYCOSYLATED AMINO ESTERS AS DNA TOPOISOMERASE-II INHIBITORS

Conjugate addition of amines to olefinic esters derived from sugars leading to formation of glycosylated amino esters in a stereoselective manner is described. Some of the synthesized compounds possess DNA topoisomerase-II enzyme inhibitory activities at low concentrations.     

Asymmetric Michael addition of 2-alkoxyphenyl α-substituted nitroacetates to non-prochiral α,β-unsaturated carbonyl compounds catalyzed by podand-type alkali metal 2′-substituted 1,1′-binaphthalen-2-oxides

The asymmetric Michael addition of 2-alkoxyphenyl α-substituted nitroacetates to non-prochiral α,β-unsaturated carbonyl compounds catalyzed by 10 mol % of sodium 2′-[2-(2-methoxyethoxy)ethoxy]-1,1′-binaphthalen-2-oxide gave the desired adducts in high yields with up to 95% ee.     

An appraisal of the Suzuki cross-coupling reaction for the synthesis of novel fluorescent coumarin derivatives

We report the chemical design and development of 3-aryl-substituted 7-alkoxy-4-methylcoumarins with enhanced fluorogenic properties. The 3-aryl substituents are installed via an optimized Suzuki–Miyaura cross-coupling (SMC) reaction between a 7-alkoxy-3-bromo-4-methylcoumarin and aryl boronic MIDA esters using Pd(OAc)₂/XPhos in a catalytic system with K₂CO₃ in aqueous THF. Under these conditions, an exocyclic ester functionality is found to be unaffected. Subsequent saponification revealed a carboxylic acid functionality that is suitable for conjugation reactions. Evaluation of their fluorescence properties indicated that the installed 3-heteroaryl substituent, particularly benzofuran-2-yl, resulted in a significant red shift of both the excitation and emission wavelengths.     

Octyl 1‐(5‐tert‐butyl‐1H‐pyrazol‐3‐yl)‐2‐(4‐chlorophenyl)‐1H‐benzimidazole‐5‐carboxylate: complex sheets built from N—H...N,C—H...N and C—H...O hydrogen bonds

In the title compound, C₂₉H₃₅ClN₄O₂, the bond lengths provide evidence for aromatic delocalization in the pyrazole ring but bond fixation in the fused imidazole ring, and the octyl chain is folded, rather than adopting an all‐trans chain‐extended conformation. A combination of N—H...N, C—H...N and C—H...O hydrogen bonds links the molecules into sheets, in which the hydrogen bonds occupy the central layer with the tert‐butyl and octyl groups arranged on either side, such that the closest contacts between adjacent sheets involve only the octyl groups. Comparisons are made with the supramolecular assembly in some simpler analogues.     

三唑环修饰的苯并菲二羧酸酯和酰亚胺: 合成、液晶及凝胶性

在盘状液晶分子外围柔性链中引入功能不同的基团, 是设计和合成具有良好液晶性能化合物的常用策略. 本工作从苯并菲2,3-二甲酸和酸酐出发, 通过亲核取代和点击反应, 分别合成了两类三唑环修饰的苯并菲二羧酸酯和苯并菲酰亚胺化合物. 热重分析仪(TGA)测试表明, 新制备的主要中间产物与目标化合物失重为5%时的温度在274~389 ℃之间, 均表现出良好的热稳定性. 我们通过差示扫描量热法(DSC)、偏光显微镜(POM)和变温X射线衍射(XRD)实验对这些化合物的热力学行为和介晶性进行了研究. 除三唑环修饰的酯3a和3b无液晶性外, 主要中间产物(2和5)与三唑环修饰的酰亚胺产物(6a和6b)均有一个六方柱状液晶相. 此外, 制备的以三唑为桥联基团的酰亚胺二聚体10为室温液晶, 具有173 ℃的液晶范围. XRD证实了该二聚体中存在有序度不同的两种柱状液晶相(Col_h1和Col_h2). 另外, 由于三唑环的引入, 三唑环修饰的酯类和酰亚胺两类化合物在某些有机溶剂中都能形成有机凝胶. 其中, 二聚体10在1,2-二氯乙烷和1,4-二氧六环中表现出优异的凝胶能力, 其临界凝胶浓度(CGC)可低至1 mg/mL. 相比之下, 不含三唑环的中间产物2和5则不能形成凝胶, 表明三唑环之间的偶极-偶极作用和液晶刚性核π-π堆积的协同作用对于超分子凝胶的形成起着重要的作用. 因此, 同时表现出液晶和凝胶性质的三唑环修饰的苯并菲2,3-二酰亚胺分子具有成为一种多功能材料的潜在应用价值.     

肉豆蔻酸单萜醇酯对布南色林经皮透过的影响

本文以环状单萜醇α-萜品醇、L-薄荷醇及链状单萜醇香叶醇、香茅醇为先导化合物,采用酰氯酯化法合成肉豆蔻酸α-萜品醇酯(TER-C14)、肉豆蔻酸-L-薄荷醇酯(MEN-C14)、肉豆蔻酸香叶醇酯(GER-C14)和肉豆蔻酸香茅醇酯(CIT-C14),并考察单萜醇及其肉豆蔻酯作为促透剂对布南色林(Blo)的促透效果。通过体外经皮渗透实验、体外释放实验和分子模拟技术初步探究单萜醇及其肉豆蔻酯的促透机制。结果显示,当GER-C14或CIT-C14为促透剂时,均有显著的促透效果(P<0.05),并且24h经皮累积透过量是空白组的4.84倍和4.45倍。促透机制为肉豆蔻酸单萜醇酯破坏药物与神经酰胺之间的氢键相互作用,增加脂质迁移率和药物的自由能,从而促进药物的渗透。肉豆蔻酸单萜醇酯有望作为新型促透剂在经皮给药系统中广泛应用。     

大概念引领下的真实情境结构化教学实践*——羧酸及其衍生物

以高中化学“羧酸”一节为例,以大概念“化学源自生活,结构决定性质”为引领,结合系列真实情境,将乙酸的性质、羧酸的性质、羧酸衍生物的性质结构化地整合在一起,螺旋上升式地实施教学,顺应学生学习心理,促进学生学科知识结构化和认知结构化的建立,凸显教学中学生的主体地位,厚植学生的化学学科核心素养,也促进教师的二次成长,达到教学相长。