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141.
Yeon‐Ju Lee Dong‐Geun Lee Hyun Soo Rho Vladimir B. Krasokhin Hee Jae Shin Jong Seok Lee Hyi‐Seung Lee 《Journal of heterocyclic chemistry》2013,50(6):1400-1404
Three new 5‐hydroxyindole alkaloids ( 1 , 2 , 3 ) along with seven known analogs ( 4 , 5 , 6 , 7 , 8 , 9 , 10 ) were isolated from a Dokdo marine sponge Scalarispongia sp. The elucidation of the structures of the new compounds by spectroscopic analyses indicated that these compounds were an indole glyoxylate ( 1 ), a mono‐indole analog of hyrtinadine A ( 2 ), and a symmetrical bis‐indole with pyridine linker ( 3 ). The comparison of IC50 values for obtained compounds against a human leukemia cell line revealed that the bis‐indole structure is a requirement for cytotoxicity. 相似文献
142.
143.
Chong-Kwang Lee Corresponding author Soon-Sik Kwon Tae-Sung Kim E-Joon Choi Sung-Tae Shin Wang-Cheol Zin 《Liquid crystals》2013,40(12):1401-1406
New chiral bent-core mesogens, derivatives of 1,3-phenylene bis[4-(alkanyloxyphenyliminomethyl)benzoate], were synthesized with variation of a substituent (X=F, Cl); their antiferroelectric properties are described. The mesomorphic and switching properties were characterized by differential scanning calorimetry, polarizing optical microscopy, triangular wave method, and X-ray diffractometry in the small and wide angle regions. The presence of chiral tails at the terminals of side wings in the bent-core molecules induced a decrease in transition temperature and formation of the switchable SmC* phase in the melt. In addition, the introduction of a lateral halogen substituent in the Schiff's base moiety prevented the regular stacking of the molecules, resulting in the formation of very complex optical textures. The smectic phase with F-substituted PBFDOB and Cl-substituted PBCDOB showed layer spacings of 39 and 38.5?Å, respectively, corresponding to the end-to-end distance of molecules with a bent conformation. Significantly, the smectic phases of PBFDOB and PBCDOB exhibited a period of 179.5 and 131?Å, respectively, compatible with a helical structure with periodicity about 4.6 and 3.4 times the layer spacings. 相似文献
144.
Glenn Mangelinckx Jeroen Beeckman Olga Chojnowska Jungsoon Shin James D.K. Kim Roman Dąbrowski 《Liquid crystals》2013,40(11):1553-1558
This paper describes a novel implementation of a dual-frequency liquid crystal optical shutter of the guest–host type. The transmissive state of the filter is obtained by applying a low-frequency electric field that brings the dichroic dye in a homeotropic orientation. The light-absorbing state is realised by a twisted planar configuration for which the absorption is quasi-independent of the polarisation. Switching between the two states occurs in about 1 ms and the devices show no scattering for wavelengths inside or outside the absorption band of the dichroic dye. Simulations and experiments reveal how a twisted state is obtained through the backflow phenomenon. 相似文献
145.
Chong-Kwang Lee Soon-Sik Kwon Seung-Tae Shin E-Joon Choi Soonnam Lee Liang-Chy Chien 《Liquid crystals》2013,40(8):1007-1013
Banana-shaped achiral compounds, the 1,3-phenylene bis[4-(alkenyloxyphenyliminomethyl)benzoate]s, were synthesized with varying length of the alkenyl group; their ferroelectric properties are described. The smectic mesophases, including a switchable chiral smectic C (SmC*) phase, were characterized by differential scanning calorimetry, polarizing optical microscopy and the triangular wave method. The presence of vinyl groups at the ends of the linear side-wings in the banana-shaped achiral molecules, containing a Schiff's base mesogen, induced a decrease in melting temperature and formation of the switchable SmC* phase in the melt. The compound having the octenyloxy group exhibited a spontaneous polarization of 120 nC cm?2 on reversal of an applied electric field. 相似文献
146.
Highly α‐selective sialylation of sialic acid N‐phenyltrifluoroacetimidate with various galactose and lactose acceptors has been achieved by introducing the C‐5 N‐phthalyl group on the donor. The “fixed dipole effect” of the N‐phthalyl group was proposed to explain the high reactivity and α‐selectivity. The microfluidic system was applied to the present α‐sialylation, which is amenable to large‐scale synthesis. The N‐phthalyl group was removed by treatment with methylhydrazine acetate, for which protocol can be readily applied to the synthesis of a variety of sialic acid‐containing oligosaccharides. 相似文献
147.
Dr. Bishnu Prasad Bastakoti Prof. Kevin C.‐W. Wu Dr. Masamichi Inoue Prof. Shin‐ichi Yusa Prof. Kenichi Nakashima Prof. Yusuke Yamauchi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(15):4812-4817
We have developed core‐shell‐corona‐type polymeric micelles that can integrate multiple functions in one system, including the capability of accommodating hydrophobic dyes into core and hydrophilic drug into the shell, as well as pH‐triggered drug‐release. The neutral and hydrophilic corona sterically stabilizes the multifunctional polymeric micelles in aqueous solution. The mineralization of calcium phosphate (CaP) on the PAA domain not only enhances the diagnostic efficacy of organic dyes, but also works as a diffusion barrier for the controlled release. 相似文献
148.
149.
Christopher M. Lee Ashutosh Mittal Anna L. Barnette Kabindra Kafle Yong Bum Park Heenae Shin David K. Johnson Sunkyu Park Seong H. Kim 《Cellulose (London, England)》2013,20(3):991-1000
Sum-frequency-generation (SFG) vibration spectroscopy is a technique only sensitive to functional groups arranged without centrosymmetry. For crystalline cellulose, SFG can detect the C6H2 and intra-chain hydrogen-bonded OH groups in the crystal. The geometries of these groups are sensitive to the hydrogen bonding network that stabilizes each cellulose polymorph. Therefore, SFG can distinguish cellulose polymorphs (Iβ, II, IIII and IIIII) which have different conformations of the exocyclic hydroxymethylene group or directionalities of glucan chains. The C6H2 asymmetric stretching peaks at 2,944 cm?1 for cellulose Iβ and 2,960 cm?1 for cellulose II, IIII and IIIII corresponds to the trans-gauche (tg) and gauche-trans (gt) conformation, respectively. The SFG intensity of the stretch peak of intra-chain hydrogen-bonded O–H group implies that the chain arrangement in cellulose crystal is parallel in Iβ and IIII, and antiparallel in II and IIIII. 相似文献
150.
The (132R)-methoxycarbonyl group of methyl pheophorbide a, one of the chlorophyll-a derivatives, was converted to a methyl group through methylation at the C132 position followed by removal of the methoxycarbonyl group. The methylation of the C132 carboanion gave a 4:1 mixture of methyl 132-methyl-pheophorbide a and its 132-epimer. The successive pyrolysis of the major methylated product afforded methyl (132R)-methyl-pyropheophorbide a with a small amount of its (132S)-epimer. The substitution effects at the C132 position including stereochemistry were discussed on the basis of 1D/2D NMR, UV–vis absorption, and circular dichroism spectroscopic analyses as well as molecular modeling simulation. 相似文献