The first total synthesis and structural elucidation of cryptomoscatone D1, and a novel synthetic approach for cryptomoscatone D2 were achieved in 30% and 29% overall yield, respectively. The synthesis relied on the use of a key Mukaiyama aldol reaction followed by a diastereoselective carbonyl reduction that allowed the preparation of four cryptomoscatone isomers in a stereochemically divergent manner. Comparison of NMR data and CD curves of the synthetic stereoisomers and natural products confirmed the stereochemical nature of cryptomoscatone D2, and led to establishing the absolute configuration of cryptomoscatone D1. 相似文献
Various one‐, two‐ and three‐dimensional Group 14 (C, Si, Ge, Sn, and Pb) element structures at P=1 atm are studied in this work. As expected, coordination number (CN)—not an unambiguous concept for extended structures—plays an important part in the stability of structures. Carbon not only favors four‐coordination, but also is quite happy with π‐bonding, allowing three‐ and even two‐coordination to compete. Highly coordinated (CN>4) discrete carbon molecules are rare; that “saturation of valence” is reflected in the instability of C extended structures with CN>4. Si and Ge are quite similar to each other in their preferences. They are less biased in their coordination than C, allowing (as their molecular structures do) CN=5 and 6, but tending towards four‐coordination. Sn and Pb 3D structures are very flexible in their bonding, so that in these elements four‐ to twelve‐coordinate structures are close in energy. This lack of discrimination among ordered structures also points to an approach to the liquid state, consistent with the low melting point of Sn and Pb. The Group 14 liquid structures we simulate in molecular dynamics calculations show the expected, effective, first coordination number increase from 5.1 for Si to 10.4 for Pb. A special point of interest emerging from our study is the instability of potential multilayer graphene structures down Group 14. Only for C will these be stable; for all the other Group 14 elements pristine, unprotected, bi‐ and multilayer graphenes should collapse, forming “vertical” bonds as short as the in‐plane ones. 相似文献
This article represents two types of entanglements, [Co2(bibp)(BTB)2][Co(bibp)2(H2O)2] (1) and [Co3(bibp)2(H2O)2(BTB)2]·2H2O·2DMF (2) (bibp = 4,4′-bis(1-imidazolyl)biphenyl and H3BTB = 1,3,5-tris(4-carboxyphenyl)benzene), which are 2-D→3-D polycatenated frameworks formed by parallel catenation of 1-D+2-D→2-D polythreaded motifs based on the double-layered sheet penetrated by ribbons of rings (1) and a 2-D→3-D mutual polythreading of three double-layered sheets with dangling arms (2), which is assembled by the same initial materials by simply changing the volume ratio of water/DMF medium. 相似文献
We demonstrate an innovative technique to achieve organic 2D and 3D waveguides with peculiar shapes from an acicular, stimuli-responsive molecular crystal, (2Z,2′Z)-3,3′-(anthracene-9,10-diyl)bis(2-(3,5-bis(trifluoromethyl)phenylacrylonitrile), Ant-CF3. The greenish-yellow fluorescent (FL) Ant-CF3 molecular crystals exhibit laser power-dependent permanent mechanical bending in 2D and 3D. Investigation of a single-crystal using spatially-resolved Raman/FL/electron microscopy, and theoretical calculations revealed photothermal (Z,E)/(E,E) isomerization-assisted transition from crystalline to amorphous phase at the laser-exposed regions. This phenomenon facilitates the dimension engineering of a 1D crystal waveguide into 2D waveguide on a substrate or a 3D waveguide in free space. The bends can be used as interconnection points to couple different optical elements. The presented technique has broader implications in organic photonics and other crystal-related photonic technologies. 相似文献
The synthesis and characterization of novel optically-active macrocycles, obtained by esterification reaction from a binaphthyl-containing diol and phthalic or terephthalic acids, and possessing overall D2 or D3 symmetry, is described. 相似文献
The inherent ability of peptides to self-assemble with directional and rationally predictable interactions has fostered a plethora of synthetic two-dimensional (2D) supramolecular biomaterials. However, the design of peptides with hierarchical assembly in different dimensions across mesoscopic lengths remains a challenging task. We here describe the structural exploration of a d /l -alternating cyclic octapeptide capable of assembling one-dimensional (1D) nanotubes in water, which subsequently pack laterally to form giant 2D nanosheets up to 500 μm long with a constant 3.2 nm thickness. Specific amino acid mutations allowed the mapping of structure–assembly relationships that determine 2D self-assembly. Nine peptide modifications were studied, revealing key features in the peptide sequence that nanosheets tolerated, while a total of three peptide variants included modifications that compromised their 2D arrangement. These lessons will serve as guide and inspiration for new 2D supramolecular peptide designs. 相似文献
Superhydrophobic dandelion‐like 3D microstructures self‐assembled from 1D nanofibers of PANI were prepared by a self‐assembly process in the presence of perfluorosebacic acid (PFSEA) as a dopant. The dandelion‐like microspheres (about 5 µm) are composed of uniform Y‐shaped junction nanofibers of about 210 nm average diameter and several micrometers in length, as measured by SEM. The dandelion‐like microstructure is coreless with a hollow cavity, and the shell thickness is about one third of the sphere diameter, as measured by TEM. Since PFESA dopant has a low surface energy perfluorinated carbon chain and two hydrophilic COOH end groups, it has dopant, is a “soft‐template” and brings about superhydrophobic functions at the same time. Moreover, it is proposed that the self‐assembly of PANI 1D nanofibers, driven by a combined interaction of hydrogen bonding, π‐π stacking and hydrophobic interactions, leads to the formation of the 3D microstructures.
The total synthesis of luminacin D (1) is reported on the basis of two aldol reactions to form the carbohydrate sector, aldehyde 30. Reaction of aldehyde 30 with the aryllithium intermediate derived from aryl iodide 38, cleavage of the silyl ether, and oxidation led to keto aldehyde 41. This advanced intermediate could be converted to luminacin 1 and its 6',8'-epimer. 相似文献
Short tandem repeat (STR) automatic typing technology is extensively used in forensic laboratories with commercial kits, in rare cases genotyping misinterpretations or mislabeling may occur due to unexpected rare alleles. This study refers to the investigation of several rare alleles observed from routine cases. Besides cross-kit verification with Goldeneye 25A (Beijing PeopleSpot Inc, China) and Huaxia platinum (Thermo Fisher Scientific, USA) kits, the next-generation sequencing technology by MiSeq FGx System (Illumina, USA) was applied to further validation. To solve the inconsistent outcomes reached by the above mentioned approaches at D2S441 locus, single gene amplification, gene cloning, and genetic sequencing was also performed. As a result, five rare alleles were detected. Two novel alleles of allele 3 at the D13S317 locus and allele 5 at the D2S441 locus were found; three previously reported alleles of allele 9 at D1S1656 locus, allele 19 at Penta D locus, and allele 28 at D12S391 locus in STRBase were initially supplemented with sequence information. We, therefore, propose that such uncommon observations with rare events should be carefully investigated and interpreted. 相似文献
The total synthesis of furano-epothilone D by a convergent route is reported. The key fragments are available on a large scale to provide sufficient material for biological evaluation. The approach involves a palladium-catalyzed coupling that generates a highly functionalized aldehyde which is connected in a stereoselective aldol reaction to yield the framework of furano-epothilone D. Finally, a macrolactonization provides furano-epothilone D. 相似文献
In the field of oriented‐attachment crystal growth, one‐dimensional nanocrystals are frequently employed as building blocks to synthesize two‐dimensional or large‐aspect‐ratio one‐dimensional nanocrystals. Despite recent extensive experimental advances, the underlying inter‐particle interaction in the synthesis still remains elusive. In this report, using Ag as a platform, we investigate the van der Waals interactions associated with the side‐by‐side and end‐to‐end assemblies of one‐dimensional nanorods. The size, aspect ratio, and inter‐particle separation of the Ag precursor nanorods are found to have dramatically different impacts on the van der Waals interactions in the two types of assemblies. Our work facilitates the fundamental understanding of the oriented‐attachment assembling mechanism based on one‐dimensional nanocrystals. 相似文献
The structural characteristics, energies, and spectroscopic properties of 1D linear chains and 2D planar sheets of (meso-meso, β-β, β-β)-linked magnesium porphines have been calculated by the density functional theory B3LYP method. The trends in the changes in the ionization potential, electron affinity, relative multiplet energies, and electron and spin density characteristics have been scrutinized as a function of the oligomer size and n in the range 0–8. 相似文献