Field-induced phase transitions in chiral smectic liquid crystals studied by the constant current method

In ferroelectric liquid crystals, phase transitions can be induced by an electric field. The current constant method allows these transition to be quickly localized and thus the(E, T) phase diagram of the studied product can be obtained.In this work, we make a slight modification to the measurement principles based on this method. This modification allows the characteristic parameters of ferroelectric liquid crystal to be quantitatively measured. The use of a current square signal highlights a phenomenon of ferroelectric hysteresis with remnant polarization at null field, which points out an effect of memory in this compound.     

Recent observations of negative longitudinal magnetoresistance in semimetal

The discovery of Dirac semimetal and Weyl semimetal has motivated a growing passion for investigating the unique magneto-transport properties in the topological materials.A Weyl semimetal can host Weyl fermions as its low-energy quasi-particle excitations,and therefore perform exotic features analogous to those in high-energy physics,such as the violation of the chiral charge conservation known as the chiral anomaly.One of the electrical transport signatures of the chiral anomaly is the Adler-Bell-Jackiw(ABJ) anomaly which presents as a negative magnetoresistance when the magnetic field and the current are parallel.Very recently,numerous experiments reported negative longitudinal magnetoresistance(NLMR) in topological materials,but the details of the measurement results are various.Here the materials and the corresponding experiment results are briefly reviewed.Besides the plausible explanation of the ABJ anomaly,some other origins of the NLMR are also discussed.     

新型Rh_2(esp)_2配体手性类似物的合成

以(R)-叔丁基亚磺酰胺为手性助剂,与1,3-苯二甲醛经缩合反应制得关键中间体——(Rs,Rs)-双叔丁基亚磺酰亚胺(7);锂化的羧酸酯与7经不对称加成反应合成了两个新型的Rh_2(esp)_2配体类似物——(Rs,Rs',R,R')-β-胺基羧酸酯和(Rs,Rs',R,R',R,R')-α,β-氮杂环丙烷羧酸酯,产率分别为96%和65%,非对映选择性均大于20∶1。化合物的结构经1H NMR和13C NMR表征。     

硅胶负载手性氨基醇聚合物的合成及其应用

以L-亮氨酸(L-Leu)为手性源,经酯化、格氏化、酰胺化等步骤制备手性单体(L-NALAA),以该单体为手性识别基团,在引发剂偶氮二异丁腈和交联剂乙二醇二甲基丙烯酸酯(EDMA)的作用下,与烯化功能硅胶发生自由基共聚反应,制备了新型键合硅胶手性固定相,其结构经FT-IR、TGA、EA表征。以4种对映异构体为模型药物对手性材料手性固定相的手性拆分性能进行研究,结果表明,手性材料手性固定相对奥美拉唑和兰索拉唑的拆分效果较好。     

Chiral,pH responsive hydrogels constructed by N‐Acryloyl‐alanine and PEGDA/α‐CD inclusion complex: preparation and chiral release ability

Chiral, pH‐responsive hydrogels are constructed by poly(ethylene glycol) diacrylate/α‐cyclodextrin (PEGDA/α‐CD) inclusion complex and L‐N‐acryloyl‐alanine or D‐N‐acryloyl‐alanine (L‐NAA or D‐NAA) by an effective free radical polymerization approach. PEGDA containing two C=C end groups was used simultaneously to introduce α‐CD units in the resulting hydrogels and to serve as a cross‐linking agent, by which forming the designed hydrogels in quantitative yield. Hydrophilic α‐CD moieties acted as pore‐forming agent, while the L(D)‐NAA‐based polymer chains bearing –COOH groups enabled the hydrogels to display remarkable swelling–deswelling behavior in response to pH variation. The chiral NAA monomer‐derived polymer chains rendered the hydrogels with intriguing optical activity, according to circular dichroism spectra. Scanning electron microscopy revealed the uniformly porous microstructures of hydrogels. More remarkably, the L‐NAA‐based hydrogels preferentially adsorbed trans‐4‐hydroxy‐d ‐proline and preferentially released trans‐4‐hydroxy‐l ‐proline, while D‐NAA‐based hydrogels provided opposite results. The hydrogels also demonstrated remarkable enantioselective release ability towards chiral drug ibuprofen. Copyright © 2015 John Wiley & Sons, Ltd.     

Structures and Properties of Three Solvent‐Dependent Chiral Compounds Based on N‐Benzoyl‐L‐glutamic Acid

Three solvent‐dependent chiral copper(II) compounds, {[Cu₂(bzgluO)₂(H₂O)₂]·4H₂O}_n ( 1 ), {[Cu₂(bzgluO)₂(DMSO)₂]·H₂O}_n ( 2 ) and [Cu₂(bzgluO)₂(DMF)₂]_n ( 3 ) (H₂bzgluO=N‐benzoyl‐L‐glutamic acid) have been synthesized under ambient temperature conditions and characterized by elemental analysis, IR spectra, UV spectra, thermogravimetric analysis, powder X‐ray diffraction (PXRD) and single‐crystal X‐ray diffraction. Compounds 1 and 2 both crystallize in the orthorhombic space group P2₁2₁2₁. Compound 3 crystallizes in the tetragonal space group P4₃. Compound 1 exhibits a ladder‐like 1D chain structure, which is extended by hydrogen‐bonding interactions to form a 3D supramolecular network. Compounds 2 and 3 both give a diamond‐like 3D structure. Besides, there are hydrogen‐bonding interactions in 2 . The structural difference indicates that the solvent system plays a crucial role in modulating structures of coordination compounds. Circular dichroism (CD) and the magnetic properties of the compounds have also been investigated.     

Crystal Structure Analysis of Betti Base 1-((2-hydroxynaphthalen-1-yl)(2-hydroxyphenyl)methyl)urea•2DMF Solvate

A novel Betti base compound, 1-((2-hydroxynaphthalen-1-yl)(2-hydroxyphenyl)methyl)urea, UBB, was synthesized and characterized by spectral, structural and thermal studies. Single crystal X-ray diffraction studies reveal that the racemic mixture of the compound, when crystallized from DMF, yields R-isomer preferentially (prismatic crystals), whereas, when crystallized from 5:1 (v/v) mixture of DMF-THF, it yields S-isomer (rectangular shaped crystals) with two molecules of DMF, included in both the cases. The crystal structure is discussed in terms of supramolecular interactions and molecular modeling. Both R and S enantiomeric DMF solvate crystals are in their chiral triclinic P1 space group.     

Trigonometrical sums connected with the chiral Potts model,Verlinde dimension formula,two-dimensional resistor network,and number theory

We have recently developed methods for obtaining exact two-point resistance of the complete graph minus N$N$ edges. We use these methods to obtain closed formulas of certain trigonometrical sums that arise in connection with one-dimensional lattice, in proving Scott’s conjecture on permanent of Cauchy matrix, and in the perturbative chiral Potts model. The generalized trigonometrical sums of the chiral Potts model are shown to satisfy recursion formulas that are transparent and direct, and differ from those of Gervois and Mehta. By making a change of variables in these recursion formulas, the dimension of the space of conformal blocks of SU(2)$SU\left(2\right)$ and SO(3)$SO\left(3\right)$ WZW models may be computed recursively. Our methods are then extended to compute the corner-to-corner resistance, and the Kirchhoff index of the first non-trivial two-dimensional resistor network, 2×N$2\times N$. Finally, we obtain new closed formulas for variant of trigonometrical sums, some of which appear in connection with number theory.     

Stress‐dependent correlations for resonant Raman bands in graphite with defects

We have studied the Raman features characteristics of defects generated in graphite under high stress conditions. Defects are generated in pristine highly oriented pyrolytic graphite by squeezing the samples in a high‐pressure anvil cell and monitored in situ by Raman spectroscopy. On the basis of our Raman measurements and existing literature correlations, we conclude that vacancies and grain boundaries are generated during compression–decompression cycles, being the defects mostly generated during the decompression stage. Our results demonstrate that the relative intensities of the D, D′, and (D + D′) bands are strongly correlated. Which is important for practical application of Raman spectroscopy in the characterization of carbon materials is that such correlations are essentially constant over the whole stress range covered in the experiments (~7 GPa). An additional interesting result concerns the relative intensities of the denoted 2D₁ and 2D₂ contributions, which are correlated with the intensity of the G band; the intensity ratio between both features is modified by stress indicating that the stress affects the stacking order of pristine graphite. Finally, we find that the decrease in intensity of the 2D₂ band with decreasing crystallite size found in existing studies on unstrained graphite remains under stress conditions. Copyright © 2014 John Wiley & Sons, Ltd.     

Enhanced complete photonic band gap in the optimized planar diamond structure

The diamond photonic crystal with dielectric rods has been modified to enlarge the fundamental band gap. By planarizing the diamond structure and reducing the thickness of the hexagonal meshes, the band gap can be increased substantially. The band gap is 29% for a refractive index contrast of 3.6. The modified structure is amenable to fabrication at optical and infrared wavelengths using state-of-the-art silicon-processing methods. Transfer matrix calculations demonstrate a large attenuation within the band gap.