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21.
[reaction: see text] The gas-phase thermal isomerization of cis,anti,cis-tricyclo[6.3.0.0(2,7)]undec-3-ene (1) to endo-tricyclo[5.2.2.0(2,6)]undec-8-ene (2) at 315 degrees C occurs cleanly through a symmetry-forbidden [1,3] suprafacial,retention (sr) pathway. 相似文献
22.
Four-component equilibria in substituted 1,3-dioxanes were applied to the determination of conformational energies not accessible by conventional equilibration, with the following conclusions: 1. The difference in free energy between the chair and twist forms of 2,2,trans - 4,6 - tetramethyl - 1,3 -dioxane is 7·4 kcal/mol. 2. Equatorial Me substituents at C-4,6 exert a palpable buttressing effect on the corresponding axial substituents. 3. Equatorial substituents at C-2 exert a similar buttressing effect on the geminal axial substituent. 4. The effect of equatorial t-Bu substitution or gem-dimethyl substitution at C-5 on conformational energy seems to be of minor importance. The more complex effects of equatorial 4-t-Bu substitution are discussed. 相似文献
23.
Petrassi HM Johnson SM Purkey HE Chiang KP Walkup T Jiang X Powers ET Kelly JW 《Journal of the American Chemical Society》2005,127(18):6662-6671
Transthyretin (TTR) amyloidogenesis requires rate-limiting tetramer dissociation and partial monomer denaturation to produce a misassembly competent species. This process has been followed by turbidity to identify transthyretin amyloidogenesis inhibitors including dibenzofuran-4,6-dicarboxylic acid (1). An X-ray cocrystal structure of TTR.1(2) reveals that it only utilizes the outer portion of the two thyroxine binding pockets to bind to and inhibit TTR amyloidogenesis. Herein, structure-based design was employed to append aryl substituents at C1 of the dibenzofuran ring to complement the unused inner portion of the thyroxine binding pockets. Twenty-eight amyloidogenesis inhibitors of increased potency and dramatically increased plasma TTR binding selectivity resulted. These function by imposing kinetic stabilization on the native tetrameric structure of TTR, creating a barrier that is insurmountable under physiological conditions. Since kinetic stabilization of the TTR native state by interallelic trans suppression is known to ameliorate disease, there is reason to be optimistic that the dibenzofuran-based inhibitors will do the same. Preventing the onset of amyloidogenesis is the most conservative strategy to intervene clinically, as it remains unclear which of the TTR misassembly intermediates results in toxicity. The exceptional binding selectivity enables these inhibitors to occupy the thyroxine binding site(s) in a complex biological fluid such as blood plasma, required for inhibition of amyloidogenesis in humans. It is now established that the dibenzofuran-based amyloidogenesis inhibitors have high selectivity, affinity, and efficacy and are thus excellent candidates for further pharmacologic evaluation. 相似文献
24.
The chiral separation of halogenated amino acids by ligand-exchange CE is described. Halogenated amino acids attracted increasing interest in recent years because of their physiological activities. Different chiral selectors, as there are L-4-hydroxyproline, L-histidine, and N-alkyl derivatives of L-4-hydroxyproline in form of their copper(II) complexes, are compared for their chiral recognition ability for halogenated amino acids. The influence of various parameters, such as selector concentration, pH, organic modifier, and field strength, on the resolution was investigated. All halogenated amino acids investigated were baseline-separated under optimized conditions. 相似文献
25.
The New Data for the Reaction of Arylenedioxy Trihalogenophosphoranes with Alkyl- and Arylacetylenes
Vladimir F. Mironov Alfiya A. Shtyrlina Ravil R. Petrov Tamara A. Baronova Fedor F. Alekseev Elena N. Varaksina 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6-7):1381-1385
The new data concerning the reaction between substituted arylenedioxy trihalogenophosphoranes and monoalkyl- or arylacetylenes are summarized. The reaction leads to formation of six-membered heterocycles-2-oxo-4-R-benzo[ e ]-1,2-oxaphosphorin-3-enes. The substituent effects in the phosphorane and acetylene molecules on the ipso -substitution and halogenation regiochemistry are discussed. The ipso -substitution of tert -butyl group on chlorine and the exchange of bromine on chlorine and iodine on hydrogen have been observed, along with formation of benzophosphorines. The interaction of tetrachloro- ortho -benzoquinone with phosphorus trichloride and arylacetylenes is proposed as a new modification of the reaction leading to the formation of benzo[ e ]-1,2-oxaphosphorines. The structures of some benzo[ e ]-1,2-oxaphosphorines are determined by the single crystal X-ray diffraction. 相似文献
26.
Alexander P. Filippov Elena V. Belyaeva Tamara K. Meleshko Alexander V. Yakimansky 《Journal of Polymer Science.Polymer Physics》2014,52(23):1539-1546
A polyimide‐graft‐polystyrene (PI‐g‐PS) copolymer with a polyimide backbone and polystyrene side chains was synthesized by the “grafting from” method using styrene polymerization on a polyimide multicenter macroinitiator via ATRP mechanism. The side chain grafting density z = 0.86 of PI‐g‐PS is rather high for graft‐copolymers synthesized by the ATRP method. Molecular characteristics and solution behavior of PI‐g‐PS were studied in selective solvents using light scattering and viscometry methods. In all solvents, the backbone tends to avoid contact with a poor solvent. To describe the conformation and hydrodynamic properties of PI‐g‐PS macromolecules in thermodynamically good solvents for side chains and PI‐g‐PS, the wormlike spherocylinder model is used. Macromolecules of the studied graft‐copolymer are characterized by high equilibrium rigidities (Kuhn segment length >20 nm). In Θ‐conditions, PI‐g‐PS macromolecules may be modeled by a rigid prolate ellipsoid of revolution with a low asymmetry form and a collapsed backbone as the ellipsoid core. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1539–1546 相似文献
27.
Prof. Dr. Steven Stevenson Amanda J. Rothgeb Katelyn R. Tepper Prof. Dr. James Duchamp Prof. Dr. Harry C. Dorn Xian B. Powers Mrittika Roy Prof. Dr. Marilyn M. Olmstead Prof. Dr. Alan L. Balch 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(54):12545-12551
Purified samples of Ho3N@C2(22010)-C78 and Tb3N@C2(22010)-C78 have been isolated by two distinct processes from the rich array of fullerenes and endohedral fullerenes present in carbon soot from graphite rods doped with Ho2O3 or Tb4O7. Crystallographic analysis of the endohedral fullerenes as cocrystals with Ni(OEP) (in which OEP is the dianion of octaethylporphyrin) shows that both molecules contain the chiral C2(22010)-C78 cage. This cage does not obey the isolated pentagon rule (IPR) but has two sites where two pentagons share a common C−C bond. These pentalene units bind two of the metal ions, whereas the third metal resides near a hexagon of the cage. Inside the cages, the Ho3N or Tb3N unit is planar. Ho3N@C2(22010)-C78 and Tb3N@C2(22010)-C78 use the same cage previously found for Gd3N@C2(22010)-C78 rather than the IPR-obeying cage found in Sc3N@D3h-C78. 相似文献
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Spartak S. Khutsishvili Marina V. Lesnichaya Tamara I. Vakul’skaya Gania Dolmaa Galina P. Aleksandrova Aleksandr L. Rakevich 《光谱学快报》2018,51(4):169-173
Structural peculiarities and supramolecular organization of medicinally promising nanocomposites, synthesized from humic substances, which essentially differ depending on decomposition degree, have been studied using electron spin resonance, transmission electron, and confocal laser scanning microscopy techniques and some other modern physical–chemical methods. It is shown that stable zero-valent gold nanoparticle of about 10–17?nm in size are formed in a natural macromolecular matrix. The nanocomposites obtained turn out to be stable in aggregative state for a long time and preserve their properties that are extremely important for prospective medicinal substances. 相似文献