Liquid crystalline polymers V. Thermotropic liquid crystalline poly(azomethine-ether)s containing a cycloalkanone moiety in the polymer backbone

A new homologous series of thermotropic liquid crystalline poly(azomethine-ether)s was synthesized by solution polycondensation of various diformyl-alpha,omega-diphenoxyalkanes, I-VIII with 2,5-bis(m-aminobenzylidene)cyclopentanone, XI and 2,6-bis(m-aminobenzylidene)cyclohexanone, XII. The inherent viscosities of the polymers were in the range 0.34-0.75 dI g^-1. The mesomorphic properties were studied as a function of the diphenoxyalkane spacer length. Analyses by DSC and optical polarized microscopy demonstrated that the poly(azomethine-ether)s form nematic mesophases over wide temperature ranges. The poly(azomethine-ether)s based on the cyclohexanone moiety had better thermal stabilities than the corresponding poly(azomethine-ether)s based on cyclopentanone.     

Apolar 2‐alkoxyalkoxy‐substituted nematic liquid crystals

The synthesis is reported of a series of apolar nematic liquid crystals incorporating an alkoxyalkoxy chain attached in a terminal position to the molecular core. The dependence of the mesomorphism and phase transition temperatures on the nature of the terminal chain with one, two or three oxygen atoms was studied. Some compounds with a completely alicyclic molecular core and a terminal 2‐methoxyethoxy chain exhibit a nematic phase with a low melting point, birefringence and viscosity and a relatively high clearing point in the absence of smectic phases. They do not to absorb light in the near UV and may be useful as components of UV‐stable nematic mixtures for use in photoluminescent liquid crystal displays. The presence of the methoxyethoxy chain leads to a relatively large dipole moment perpendicular to the molecular long axis.     

New symmetric azomethinic dimer: the influence of structural heterogeneity on the liquid crystalline behaviour

The paper deals with the study of the thermotropic liquid crystalline properties of a new azomethinic symmetric dimer and some of its structural heterogeneous mixtures with one of its reagents. Their thermotropic behaviour was monitored by polarised light microscopy, differential scanning microscopy and variable temperature X-ray diffraction measurements. The influence of the structural heterogeneity on the mesomorphic behaviour was established and some similarities with the mesomorphic behaviour of the polydisperse polymers were underlined.     

A comprehensive conformational analysis of tryptophan,its ionic and dimeric forms

Tryptophan is an essential amino acid, and understanding the conformational preferences of monomer and dimer is a subject of outstanding relevance in biological systems. An exhaustive first principles investigation of tryptophan ( W ) and its ionized counterparts cations (WC) , anions (WA) , and zwitterions (WZ) has been carried out. A comprehensive and systematic study of tryptophan dimer (WD) conformations resulted in about 62 distinct minima on the potential energy surface. The hydrogen bonds and a variety of noncovalent interactions such as OH‐π, NH‐π, CH‐π, CH‐O, and π‐π interactions stabilized different forms of tryptophan and its dimers. Over all in monomeric conformers which have NH‐O, hydrogen bonds showed higher stability than other conformers. A cursory analysis reveal that the most stable dimers stabilized by hydrogen bonding interactions while the less stable dimers showed aromatic side chain interactions. Protein Data Bank analysis of tryptophan dimers reveals that at a larger distance greater than 5 Å, T‐shaped orientations (CH‐π interactions) are more prevalent, while stacked orientations (π‐π interactions) are predominant at a smaller distance. © 2013 Wiley Periodicals, Inc.     

Antimicrobial Metabolites against Methicillin-Resistant Staphylococcus aureus from the Endophytic Fungus Neofusicoccum australe

Antimicrobial bioassay-guided fractionation of the endophytic fungi Neofusicoccum australe led to the isolation of a new unsymmetrical naphthoquinone dimer, neofusnaphthoquinone B (1), along with four known natural products (2–5). Structure elucidation was conducted by nuclear magnetic resonance (NMR) spectroscopic methods, and the antimicrobial activity of all the natural products was investigated, revealing 1 to be moderately active towards methicillin-resistant Staphylococcus aureus (MRSA) with a minimum inhibitory concentration (MIC) of 16 µg/mL.     

Hydrolysis of HNSO2: A potential route for atmospheric production of H2SO4 and NH3

The hydrolysis of sulfonylamine (HNSO₂) results in the formation of sulfuric acid along with ammonia, and is of significant interest due to their negative impact on environment and life on Earth. The formation of H₂SO₄ through the reaction of HNSO₂ with (H₂O)_2-4 has been studied using high level electronic structure calculations. This hydrolysis reaction is a step-wise process, in the first step a H-atom from H₂O is transferred to the N-atom of HNSO₂ which results in the formation of NH₂, and in the next step, H₂SO₄, NH₃ and water molecule(s) are formed. The results show that the energy barrier associated with the formation of intermediates and product complexes is reduced by 7 to 10 kcal/mol when the number of water molecules is increased from 2 to 4. The rate constant was calculated using canonical variational transition state theory with small curvature tunneling correction over the temperature range of 200 to 1000 K. At 298 K, the calculated rate constant for the formation of intermediate in the first step is 2.24 × 10⁻¹⁶, 1.03 × 10⁻¹², and 2.10 × 10⁻¹¹ cm³ mol⁻¹ s⁻¹, respectively, for the reaction with water dimer, trimer and tetramer. The calculated enthalpy and free energy show that the reaction corresponding to the formation of H₂SO₄ is highly exothermic and exoergic in nature.     

Microporotriol,a new cadinane-type sesquiterpenoid from the cultures of the wood-decay fungus Microporus affinis HFG829

Abstract

A new cadinane-type sesquiterpenoid, microporotriol (1), together with four known compound, 5-methylresorcinol (2), (22E,24R)-ergosta-4,6,8(14),22-tetraen-3-one (3), (22E,24R)-ergosta-5,7,22-trien-3β-ol (4), (22E,24R)-5α,8α-epidioxy-ergosta-6,22-dien-3β-ol (5), were isolated from the fermentation broth of the wood decaying fungus Microporus affinis HFG829. The structures of the compounds were established by extensive spectroscopic methods, including 1D & 2D NMR, along with HRMS spectroscopic analysis. The relative configuration of 1 was confirmed by NMR calculation. Compound 1 was evaluated for the cytotoxicity against five human cancer cell lines.     

Effect of Bulky Functional Groups on Donor and Acceptor Interactions and their Photoluminescence Properties

Material designs that use donor and acceptor units are often found in organic optoelectronic devices. Molecular level insight into the interactions between donors and acceptors are crucial for understanding how such interactions can modify the optical properties of the organic optoelectronic materials. In this paper, tris(4-(tert-butyl)phenyl)amine (pTPA) was synthesized as a donor in order to compare with unmodified triphenylamine (TPA) in a donor–acceptor system by having 2,4,6-triphenyl-1,3,5-triazine (TRZ) as an acceptor. Dimerization of donors and acceptors occurred in solvent when the concentration of solute is high. At 0 K, using a polarizable continuum model, the nitrogen atom of TPA is found to stack on top of the center of triazine of TRZ, whereas such alignment is offset in pTPA and TRZ. We attributed such alignment in TPA-TRZ as the result of attractive interactions between partial localization of 2p_z electrons at the nitrogen atom of TPA and the π deficiency of triazine in TPA-TRZ. By taking into account random motions of the solvent effect at 300 K in quantum molecular dynamics and classical molecular dynamics simulations to interpret the marked difference in emission spectra between TPA-TRZ and pTPA-TRZ, it was revealed that the attractive interaction between pTPA and TRZ in toluene is weaker than TPA and TRZ. Because of the weaker attractive interaction between pTPA and TRZ in toluene, the dimers adopted numerous ground state conformations resulting in broad emission bands superimposed with multiple small Gaussian peaks. This is in contrast to TPA-TRZ which has only one dominant dimer conformation. This study demonstrates that the strength of intermolecular interactions between donors and acceptors should be taken into consideration in designing supramolecular structures.     

手性金属配合物Δ,Λ-[Ru(IP)_2dppz]~(2 )对含G:T错配的环丁烷嘧啶二聚体识别和部分构型修复的分子力学研究

环丁烷嘧啶二聚体(CyclobutanePyrimidineDimer,CPD)是紫外线对DNA损伤导致皮肤癌的首要环节,XPC-hHR23B是最早作为对CPD的损伤识别剂的,但其识别效率很低.本文首次采用分子力学方法模拟了一种新的手性金属配合物?,Λ-[Ru(IP)2dppz]2 对含G:T错配的CPD双螺旋DNA的识别作用.模拟结果显示:金属配合物[Ru(IP)2dppz]2 的两个手性异构体都对含G:T错配的CPD双螺旋DNA具有识别作用,识别的过程体现了很强的手性选择性、沟选择性和位点特异性.同时,我们发现:在Λ-[Ru(IP)2dppz]2 插入到CPD后,形成CPD的两个T碱基由原来的敞口形状部分地转为近平行状,使其在构型上得到初步的修复.