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1.
Homologous series of 2-alkoxycarbonyl-4-(4-ethoxyphenylazo)phenyl 4-methoxybenzoates (L) and their orthopalladated μ-chloro dimers (Pd2Cl2L2) have been synthesized and their thermotropic phase transition behaviour has been characterized. The ligands, L, are three-ring nematogens with their central rings substituted in the 2-position by n-alkyl chains of varied length. The thermal stability of the nematic phases decreases rapidly with increasing side chain length and then levels off as the series is ascended. In every case the mesomorphic phase appears only over a small temperature range (less than 20° C). The orthopalladated species also proved to be nematogenic. Melting and clearing points rise on the average by 87° C and 126° C, respectively, and thus the temperature ranges of the nematic phases are enlarged considerably upon metallation. In relation to the observed stabilization of the nematic phases, particularly of higher homologues, a lath-like molecular structure, in which the side chains of the ligands fill up the clefts of the core part, has been deduced for a Pd2Cl2L2 homologue from its solution 1H-NMR spectrum. 相似文献
2.
Alexander Aster Christopher Rumble Anna-Bea Bornhof Hsin-Hua Huang Naomi Sakai Tom olomek Stefan Matile Eric Vauthey 《Chemical science》2021,12(13):4908
1,4,5,8-Naphthalenediimides (NDIs) are widely used motifs to design multichromophoric architectures due to their ease of functionalisation, their high oxidative power and the stability of their radical anion. The NDI building block can be incorporated in supramolecular systems by either core or imide functionalization. We report on the charge-transfer dynamics of a series of electron donor–acceptor dyads consisting of a NDI chromophore with one or two donors linked at the axial, imide position. Photo-population of the core-centred π–π* state is followed by ultrafast electron transfer from the electron donor to the NDI. Due to a solvent dependent singlet–triplet equilibrium inherent to the NDI core, both singlet and triplet charge-separated states are populated. We demonstrate that long-lived charge separation in the triplet state can be achieved by controlling the mutual orientation of the donor–acceptor sub-units. By extending this study to a supramolecular NDI-based cage, we also show that the triplet charge-separation yield can be increased by tuning the environment.Ultrafast electron transfer from singlet and triplet excited states in equilibrium results in the population of both singlet and triplet charge-separated states. 相似文献
3.
Rahimipour S Litichever-Coslovsky N Alaluf M Freeman D Ehrenberg B Weiner L Mazur Y Fridkin M Koch Y 《Photochemistry and photobiology》2005,81(2):250-258
A combination of light, oxygen and a photosensitizer is used to induce death of cancer cells by photodynamic therapy. In this study, we have synthesized several new methyl helianthrone derivatives and compared their phototoxicity with that of hypericin. In contrast to hypericin, methyl helianthrones are soluble in aqueous solutions and have a broad range of light absorbance, which allows the use of polychromatic light. Structural modifications of methyl helianthrone demonstrated that substitution of hydrogen atoms of methyl helianthrone at Positions 2 and 5 with Br atoms or methylation of its phenolic hydroxyls, significantly increases the corresponding singlet oxygen quantum yield and their phototoxicity toward alphaT3-1, M2R and LNCaP cells. The phototoxicity of some of these compounds was similar to that of hypericin. Methyl helianthrones, like hypericin, accumulated mainly in the perinuclear region as evident by confocal microscopy. Irradiation of cells pretreated with methyl helianthrone derivatives generates intracellular reactive oxygen species and lipid free radicals, as shown by a fluorescentic probe and electron paramagnetic resonance methods, respectively. The phototoxicity of these methyl helianthrones as well as their ability to oxidize membrane lipids were significantly decreased on addition of specific Type-II inhibitors, suggesting the involvement of singlet oxygen as the main oxidant. 相似文献
4.
Berman Abraham Shaked-Monderer Naomi 《Central European Journal of Operations Research》2022,30(3):1093-1099
Central European Journal of Operations Research - Completely positive matrices are matrices that can be decomposed as $$BB^T$$ , where B is an entrywise nonnegative matrix. These matrices have many... 相似文献
5.
Ikuta A Mizuta N Kitahata S Murata T Usui T Koizumi K Tanimoto T 《Chemical & pharmaceutical bulletin》2004,52(1):51-56
Six novel branched beta-cyclodextrins (betaCDs) having beta-D-galactose residues on the non-reducing terminal of the sugar side chains, namely 6(1),6(4)-di-O-(beta-D-galactosyl)-betaCD (10), 6-O-(beta-D-galactosyl)-betaCD (11), 6(1),6(4)-di-O-(beta-lactosyl)-betaCD (14), 6-O-(beta-lactosyl)-betaCD (15), 6(1),6(4)-di-O-(4'-O-beta-D-galactosyl-beta-lactosyl)-betaCD (18), and 6-O-(4'-O-beta-D-galactosyl-beta-lactosyl)-betaCD (19), were chemically synthesized using the trichloroacetimidate method. The reaction products were separated by HPLC on an amino column into dibranched and monobranched betaCDs. Their structures were confirmed by mass spectrometry (MS) and two-dimensional (2D) NMR spectroscopic analysis. To study the length of the sugar side chains attached to the CD ring, which leads to differences in the functions of the branched CDs, interactions of these compounds with peanut (Arachis hypogaea) agglutinin (PNA) were investigated using an optical biosensor and an inhibition assay based on hemagglutination. The results showed that all branched betaCDs interacted with PNA, and the binding affinity was 18>14>10 and 19>15>11 when the derivatives were compared on the basis of side chain length. 相似文献
6.
Naomi Masuda Yatsuhisa Nagano T. Kimura 《Journal of Thermal Analysis and Calorimetry》2005,81(3):533-535
Summary The standard molar enthalpy of formation of methyl methylthiomethyl sulfoxide, CH3(CH3SCH2)SO, at T=298.15 K in the liquid state was determined to be -199.4±1.5 kJ mol-1 by means of oxygen rotating-bomb combustion calorimetry. 相似文献
7.
Yuji Hanzawa Kei-ichi Kawagoe Naomi Tanahashi Yoshiro Kobayashi 《Tetrahedron letters》1984,25(42):4749-4752
The hydrometallation of trifluoromethylated propargyl alcohol derivatives with metal hydride reagents proceeds smoothly to give cis- and trans-olefins on H2O quenching. The halodemetallation of intermediate formed in the reaction process was also examined. 相似文献
8.
N-[5-(10,20-Diphenylporphinato)zinc(II)]-N'-(octyl)pyromellitic diimide (PZn-PI), a meso-pyromellitimide-substituted (porphinato)zinc(II) compound, has been fabricated from the reaction of (5-amino-10,20-diphenylporphinato)zinc(II) with pyromellitic dianhydride in the presence of octylamine. Interrogation of the photoinduced charge separation (CS) and thermal charge recombination (CR) electron-transfer (ET) dynamics for PZn-PI in CH(2)Cl(2) via pump-probe transient absorption spectroscopic methods shows that tau(CS) and tau(CR) are 770 and 5200 fs, respectively. These ET dynamics differ from those elucidated previously for closely related 5-quinonyl-substituted (porphinato)metal compounds, and derive from the fact that the low-lying excited states for PZn-PI are porphyrin-localized, possessing little charge-transfer character. The synthesis of N-(5-[15-(2-(triisopropylsilyl)ethynyl)-10,20-diphenylporphinato]zinc(II))-N'-(octyl)pyromellitic diimide demonstrates that PZn-PI can be halogenated at its 15-meso-position and used subsequently as a substrate in metal-catalyzed cross-coupling reactions; the reactivity of PZn-PI is unusual with respect to many directly linked donor-acceptor compounds in that it is stable to these oxidizing and reducing reaction conditions. 相似文献
9.
Michelle Hampson Naomi Driesen Jennifer K. Roth John C. Gore R. Todd Constable 《Magnetic resonance imaging》2010
Functional brain imaging studies have identified a set of brain areas typically activated during cognitive tasks (task-positive brain areas) and another set of brain areas typically deactivated during cognitive tasks (task-negative brain areas). Negative correlations, or anticorrelations, between task-positive and task-negative brain areas have been reported at rest. Furthermore, the strength of these anticorrelations appears to be related to cognitive function. However, studies examining anticorrelations have typically employed global regression or similar analysis steps that force anticorrelated relationships to exist between brain areas. Therefore the validity of these findings has been questioned. Here we examine anticorrelations between a task-negative region in the medial frontal gyrus/anterior cingulate cortex and dorsolateral prefrontal cortex, a classic task-positive area, using an analysis that does not include global regression. Instead, we control for whole-brain correlations in the group-level analysis. Using this approach, we demonstrate that the strength of the functional connection between the medial frontal cortex and the dorsolateral prefrontal cortex is related to cognitive function and that this relationship is not an artifact of global regression. 相似文献
10.