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161.
162.
M. D. Ossowska-Chruściel 《Liquid crystals》2013,40(8):1159-1165
A secondary chiral (R)-(?)-2-alcohol underwent the Mitsunobu reaction with triphenylphosphine, diethyl azodicarboxylate and ethyl 4-hydroxybiphenylcarboxylate, resulting in the desired (S)-(+)-product with high enantiomeric purity (>99% ee), with the chiral branched chain attached to the biphenyl. This method is operationally simple and provides the very important chiral precursor in good yields (62% in dry THF and 72% in dry Et2O). The condensation of the (S)-(+)-acid chloride from this material and a suitable 4-n-alkylthiophenol in toluene in the presence of pyridine or triethylamine furnishes the chiral (S)-(+)-thiobenzoate liquid crystals in good yields (80–83% in pyridine and 65–68% in Et3N). (S)-(+)-4-(1-Methylheptyloxy)biphenyl 4-alkylthiobenzoates are abbreviated (S)-MHOBSn , where n varies from 4 to 10 and denotes the number of carbon atoms in the alkyl chain. DSC, polarizing microscopy and X-ray diffraction showed that the (S)-MHOBSn series possesses a rich phase polymorphism: two highly ordered tilted phases CrG* and SmI*, as well as the ferroelectric smectic C (SmC*) and chiral nematic (N*) phase. In this series, the seldom observed transition between the chiral phases SmI*–SmC* is seen. All the compounds possess stable enantiotropic SmC* and N* phases. The existence of weak intermolecular hydrogen-bonding in (S)-MHOBSn was confirmed by FTIR spectroscopy. 相似文献
163.
164.
Dr. Noam Shemesh Dr. Jean‐Nicolas Dumez Prof. Lucio Frydman 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(39):13002-13008
Nuclear magnetic resonance spectroscopy is governed by longitudinal (T1) relaxation. For protein and nucleic acid experiments in solutions, it is well established that apparent T1 values can be enhanced by selective excitation of targeted resonances. The present study explores such longitudinal relaxation enhancement (LRE) effects for molecules residing in biological tissues. The longitudinal relaxation recovery of tissue resonances positioned both down‐ and upfield of the water peak were measured by spectrally selective excitation/refocusing pulses, and compared with conventional water‐suppressed, broadband‐excited counterparts at 9.4 T. Marked LRE effects with up to threefold reductions in apparent T1 values were observed as expected for resonances in the 6–9 ppm region; remarkably, statistically significant LRE effects were also found for several non‐exchanging metabolite resonances in the 1–4 ppm region, encompassing 30–50 % decreases in apparent T1 values. These LRE effects suggest a novel means of increasing the sensitivity of tissue‐oriented experiments, and open new vistas to investigate the nature of interactions among metabolites, water and macromolecules at a molecular level. 相似文献
165.
Linear {NiII–LnIII–NiII} Complexes Containing Twisted Planar Ni(μ‐phenolate)2Ln Fragments: Synthesis,Structure, and Magnetothermal Properties 下载免费PDF全文
Sourav Das Atanu Dey Subrata Kundu Sourav Biswas Prof. Dr. A. J. Mota Prof. Dr. Enrique Colacio Prof. Dr. Vadapalli Chandrasekhar 《化学:亚洲杂志》2014,9(7):1876-1887
Sequential reaction of a multisite LH4 ligand {2‐[2‐hydroxy‐3‐(hydroxymethyl)‐5‐methylbenzylideneamino]‐2‐methylpropane‐1,3‐diol} with appropriate lanthanide salts followed by the addition of Ni(NO3)2 ? 6 H2O in a 4:1:2 stoichiometric ratio in the presence of triethylamine afforded four heterobimetallic trinuclear complexes [Ni2Gd(LH3)4] ? 3 NO3 ? 3 MeOH ? H2O ? CH3CN ( 1 ), [Ni2Tb(LH3)4] ? 3 NO3 ? 3 MeOH ? CH3CN ( 2 ), [Ni2Dy(LH3)4] ? 3 NO3 ? 3 MeOH ? H2O ? CH3CN ( 3 ), and [Ni2Ho(LH3)4] ? 3 NO3 ? 3 MeOH ? H2O ? CH3CN ( 4 ). Complexes 1 – 4 possess linear trimetallic cores with a central lanthanide ion. Magnetic studies revealed a predominant ferromagnetic interaction between the Ni and Ln centers. Alternating current susceptibility measurements of complex 3 showed a small frequency dependence of the out‐of‐phase signal, χ′′M , under zero direct current field, but without achieving a net maximum above 2 K. Magnetic studies on 1 revealed that it has a significant magnetocaloric effect. 相似文献
166.
Chunhui Liu Dr. Chengyi Xiao Chengcheng Xie Qinglian Zhu Dr. Qiaomei Chen Prof. Wei Ma Prof. Weiwei Li 《Chemphyschem》2022,23(2):e202100725
Adding insulating polymers to conjugated polymers is an efficient strategy to tailor their mechanical properties for flexible organic electronics. In this work, we selected two insulating polymers as additives for high-performance photoactive layers and investigated the mechanical and photovoltaic properties in organic solar cells (OSCs). The insulating polymers were found to reduce the electron mobilities in the photoactive layers, and hence the power conversion efficiencies were significantly decreased. More importantly, we found that the insulating polymers exhibited negative effect on the mechanical properties of the photoactive layers, with reduced Young's modulus and low crack onset strains. Further studies revealed that the insulating polymers had poor miscibility with the photoactive layers, providing large domains and more cavities in blend thin films, which act as negative effect for the tensile test. The studies indicate that rational selection of insulating polymers, especially enhancing the non-covalent interaction with the photoactive layers, will be critically important for the stretchable OSCs. 相似文献
167.
Besides human red blood cells (RBC), a standard model used in AFM-single cell force spectroscopy (SCFS), little is known about apparent Young’s modulus (Ea) or adhesion of animal RBCs displaying distinct cellular features. To close this knowledge gap, we probed chicken, horse, camel, and human fetal RBCs and compared data with human adults serving as a repository for future studies. Additionally, we assessed how measurements are affected under physiological conditions (species-specific temperature in autologous plasma vs. 25 °C in aqueous NaCl solution). In all RBC types, Ea decreased with increasing temperature irrespective of the suspension medium. In mammalian RBCs, adhesion increased with elevated temperatures and scaled with reported membrane sialic acid concentrations. In chicken only adhesion decreased with higher temperature, which we attribute to the lower AE-1 concentration allowing more membrane undulations. Ea decreased further in plasma at every test temperature, and adhesion was completely abolished, pointing to functional cell enlargement by adsorption of plasma components. This halo elevated RBC size by several hundreds of nanometers, blunted the thermal input, and will affect the coupling of RBCs with the flowing plasma. The study evidences the presence of a RBC surface layer and discusses the tremendous effects when RBCs are probed at physiological conditions. 相似文献
168.
Oleg B. Shchekin Peter J. Schmidt Fahong Jin Nate Lawrence Kenneth J. Vampola Helmut Bechtel Danielle R. Chamberlin Gerd O. Mueller 《固体物理学:研究快报》2016,10(4):310-314
Droop, the decrease of efficiency with increased power density, became a major topic with InGaN LEDs, after its introduction in 2007. This paper provides insight into droop in localized center luminescence phosphors, exemplified here by Eu2+ doped materials. This topic is of increasing importance, as high brightness blue LEDs have reached outputs >1 W/mm2. The nonlinearities in phosphor quantum efficiency result in drive‐dependent color point shift and reduction of overall efficiency of phosphor converted white LEDs which utilize Eu2+ activated phosphors. The efficiency quenching can be traced back to two processes, well‐known in laser physics, excited state absorption or/and cross relaxation by Foerster/Dexter transfer. Both processes lead to reduction in phosphor efficiency, but they can be differentiated. Understanding the root cause of efficiency quenching opens ways to minimize the practical consequences. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
169.
Efficient cross polarization with simultaneous adiabatic frequency sweep on the source and target channels 总被引:2,自引:2,他引:0
In this work, we propose a new and efficient heteronuclear cross polarization scheme, in which adiabatic frequency sweeps from far off-resonance toward on-resonance are applied simultaneously on both the source and target spins. This technique, which we call as Simultaneous ADIabatic Spin-locking Cross Polarization (SADIS CP), is capable of efficiently locking both the source and target spins with moderate power even in the presence of large spectral distribution and fast relaxation. It is shown that by keeping the time-dependent Hartmann-Hahn mismatch minimal throughout the mixing period, polarization transfer can be accelerated. Experiments are demonstrated in a powder sample of L-alanine. 相似文献
170.
Laredo E Prutsky N Bello A Grimau M Castillo RV Müller AJ Dubois P 《The European physical journal. E, Soft matter》2007,23(3):295-303
Thermally stimulated depolarization currents, TSDC, wide-angle X-ray scattering, WAXS, differential scanning calorimetry,
DSC, and polarized light optical microscopy, PLOM, have been used to examine poly(L-lactide)-b -poly(
-caprolactone) diblock copolymers in a wide composition range. Both components are crystallizable and the miscibility in
the amorphous phase has been determined from the behavior of the primary relaxations which are the dielectric manifestation
of the glass transition, and also from the superstructural morphology revealed by PLOM and the compositional dependence of
the melting points as determined by DSC. Distinct segmental mobilities in the amorphous phase which can be well resolved by
TSDC are present; the
mode of the slower component shifts to lower temperatures as the PCL content increases while the glass transition of neat
PCL is present for all compositions. A relaxation times bimodal distribution is apparent for PCL-rich copolymers. The composition
dependence of the multiple glass transitions detected in these weakly segregated copolymers are predicted by the self-concentration
model for a miscible blend made of components with a large Tg contrast. 相似文献