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61.
A Supramolecular Chiral Auxiliary Approach: “Remote Control” of Stereochemistry at a Hierarchically Assembled Dimeric Helicate
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David Van Craen Prof. Dr. Markus Albrecht Prof. Dr. Gerhard Raabe Fangfang Pan Prof. Dr. Kari Rissanen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(10):3255-3258
Dimeric hierarchically‐assembled titanium(IV) helicates are in solvent‐dependent equilibrium with the corresponding monomers. Statistically formed mixtures of such complexes bearing chiral stereocontrolling ligands and achiral diene‐substituted ligands show high diastereoselectivity and reasonable enantioselectivity in the Diels–Alder reaction with maleimides if the reaction proceeds with the dimer but not with the monomer. Thus, solvent dependent switching between the monomer and dimer enables on/off switching of the enantioselectivity. 相似文献
62.
Tommi Kaplas Kari Laitinen Tuula Moilanen Yrj? Tolonen Kristoffer Albrecht Raimo Silvennoinen 《Optical Review》2010,17(3):252-256
Traditional Japanese woodblock printing is a centuries old art form. This time-honoured form of art is at risk of extinction
as a consequence of the increasing lack of availability of wild cherry trees, which are a traditionally used woodblock material.
Solutions for this material problem have been investigated for several years, but none of the tested materials has been sufficient
when compared with the watercolour print quality imprinted by wild cherry woodblocks. To contribute to overcoming this material
problem, we have investigated the physical properties of heat-treated woodblock materials made from different wood species.
The International Commission on Illumination (CIE) tristimulus values, the CIELAB coordinates, the total reflectance, and
the gloss, as well as, the water contact angle from the woodblock surface is observed to have a strong relation to the surface
treatment of a woodblock. The surface treatment of a woodblock, in turn, relates to its water delivery, which is the basis
for watercolour printing. 相似文献
63.
64.
α-Methylstyrene/isobutene, α-methylstyrene/diisobutene, cyclopentadiene/isobutene, and cyclopentadiene/α-methylstyrene were copolymerized by cationic polymerization techniques. Several properties of the copolymers such as softening ranges and oxidation stability depend on their constitutional composition, and were controlled by variation of the conditions of their synthesis. 相似文献
65.
An intramolecular, organocatalyzed Michael addition has been developed to obtain biologically important 2,3‐disubstituted cis‐2,3‐dihydrobenzofurans. By using mandelic acid salts of primary aminocatalysts, derived from cinchona alkaloids, the intramolecular cyclization reaction has been developed to proceed in high yield, with moderate to good diastereoselectivity, and up to 99 % ee. Based on the absolute configuration of the formed 2,3‐disubstituted‐cis‐2,3‐dihydrobenzofurans and by considering the observed substrate scope restrictions, a mechanistic rationalization has been presented. 相似文献
66.
Krzysztof Kaczmarek Barbara Pacholczyk-Sienicka ukasz Albrecht Janusz Zabrocki Ronald J. Nachman 《Molecules (Basel, Switzerland)》2021,26(11)
A facile solid-phase synthetic method for incorporating the imidazoline ring motif, a surrogate for a trans peptide bond, into bioactive peptides is reported. The example described is the synthesis of an imidazoline peptidomimetic analog of an insect pyrokinin neuropeptide via a cyclization reaction of an iminium salt generated from the preceding amino acid and 2,4-diaminopropanoic acid (Dap). 相似文献
67.
The stable isotopic composition (delta(2)H and delta(18)O) of short-term (daily) precipitation collected from October 2002 to September 2003 at two stations in a coastal, karstic area in south-western Slovenia was investigated. In addition, monthly composite samples were collected and analysed for comparison with amount-weighted monthly means. The delta(2)H and delta(18)O values obtained show a wide range and reflect seasonal climatic variations. Deuterium excess and local meteoric water lines (LMWLs) were determined and cumulative frequency analysis and coincidence tests were performed. The statistical coincidence test showed that the LMWLs calculated from monthly data for Portoroz and Kozina are coincident, but the LMWLs calculated from daily precipitation events are not. This difference could be explained by the greater variance of the isotopic composition of daily precipitation in comparison to monthly composite samples and also to the influence of evaporation during events below<1 mm at Portoroz during the extremely dry and warm spring-summer season of 2003. Finally, synoptic maps and backward trajectories of a selected precipitation event showed that changes of isotopic composition are related to mixing of air masses originating from the continent and Mediterranean cyclogenesis. 相似文献
68.
Metalation of CH2OH-substituted triazolium salts with CoCl2 under basic conditions affords C,O-bidentate chelating carbene Co(III) complexes ( 3a , 3b ), while analogous phenyl-substituted triazolium salts produce monodentate carbene Co(II) complexes ( 3c , 3d ). The distinct substituent-induced properties of the metal centers were demonstrated by electrochemical measurements and catalytic activities in two specific processes. The complexes showed appreciable activity in the reduction of C=O bonds through hydrosilylation, with methoxybenzene-functionalized triazolylidene Co(III) complex 3a achieving a high selectivity towards aldehydes vs. ketones with turnover frequencies (TOFs) up to 200 h−1. The C,O-chelate systems were also active catalysts in the Biginelli process, a one-step three-component reaction for efficient dihydropyrimidinone synthesis. Optimization of reaction conditions provides high activity with complex 3a , reaching TOFs of 800 h−1, the highest activity known for cobalt NHC complexes to date. 相似文献
69.
Matthias Krumb Dr. Maximilian Jäger Alice Voss Loreen Immig Dr. Karin Peters Danuta Kowalczyk Prof. Dr. Albrecht Bufe Prof. Dr. Till Opatz Prof. Dr. Otto Holst Prof. Dr. Christian Vogel Dr. Marcus Peters 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(3):928-933
Arabinogalactan, a microheterogeneous polysaccharide occurring in plants, is known for its allergy-protective activity, which could potentially be used for preventive allergy treatment. New treatment options are highly desirable, especially in a preventive manner, due to the constant rise of atopic diseases worldwide. The structural origin of the allergy-protective activity of arabinogalactan is, however, still unclear and isolation of the polysaccharide is not feasible for pharmaceutical applications due to a variation of the activity of the natural product and contaminations with endotoxins. Therefore, a pentasaccharide partial structure was selected for total synthesis and subsequently coupled to a carrier protein to form a neoglycoconjugate. The allergy-protective activity of arabinogalactan could be reproduced with the partial structure in subsequent in vivo experiments. This is the first example of a successful simplification of arabinogalactan with a single partial structure while retaining its allergy-preventive potential. 相似文献
70.
Sensing of Phosphates by Using Luminescent EuIII and TbIII Complexes: Application to the Microalgal Cell Chlorella vulgaris
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Sandeep Nadella Jashobanta Sahoo Dr. Palani S. Subramanian Abhishek Sahu Dr. Sandhya Mishra Prof. Dr. Markus Albrecht 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(20):6047-6053
Phenanthroline‐based chiral ligands L1 and L2 as well as the corresponding EuIII and TbIII complexes were synthesized and characterized. The coordination compounds show red and green emission, which was explored for the sensing of a series of anions such as F?, Cl?, Br?, I?, NO3?, NO2?, HPO42?, HSO4?, CH3COO?, and HCO3?. Among the anions, HPO42? exhibited a strong response in the emission property of both europium(III) and terbium(III) complexes. The complexes showed interactions with the nucleoside phosphates adenosine triphosphate (ATP), adenosine diphosphate (ADP), and adenosine monophosphate (AMP). Owing to this recognition, these complexes have been applied as staining agents in the microalgal cell Chlorella vulgaris. The stained microalgal cells were monitored through fluorescence microscopy and scanning electron microscopy. Initially, the complexes bind to the outer cell wall and then enter the cell wall through holes in which they probably bind to phospholipids. This leads to a quenching of the luminescence properties. 相似文献