Total synthesis of (+/-)-chartelline C

The first total synthesis of (+/-)-chartelline C in a concise 10-step sequence is reported. Highlights of the completion of this decades-old puzzle include (1) chemo- and position-selective installation of the heteroaromatic halogens, (2) halogen-sparing monoreduction of an alkyne linker, (3) a simple strategy for placement of the sensitive beta-chloroenamide, (4) an unusually facile thermolysis of a vinyl carboxylic acid, and (5) a powerful ring contraction whose potential utility in heterocyclic chemistry merits further investigation.     

Gold-catalyzed hydrosilyloxylation driving tandem aldol and mannich reactions

The chemoselective formation of an enolate from alkyne in the presence of a carbonyl and imine group was realized, which constructed a variety of structural motifs under exceedingly mild reaction conditions in a tandem process. Reaction driving tandem hydrosilyloxylation/aldol reactions was achieved through the formation of enol silyl ethers catalytically generated in situ from readily available alkynes. These reactions were expanded to obtain β-amino enol silyl ethers in good yields via the tandem hydrosilyloxylation/isomerization/Mannich reaction.     

A new reagent for direct difluoromethylation

Molecular scaffolds containing alkylfluorine substituents are desired in many areas of chemical research from materials to pharmaceuticals. Herein, we report the invention of a new reagent (Zn(SO(2)CF(2)H)(2), DFMS) for the innate difluoromethylation of organic substrates via a radical process. This mild, operationally simple, chemoselective, and scalable difluoromethylation method is compatible with a range of nitrogen-containing heteroarene substrates of varying complexity as well as select classes of conjugated π-systems and thiols. Regiochemical comparisons suggest that the CF(2)H radical generated from the new reagent possesses nucleophilic character.     

The role of rebound spikes in the maintenance of self-sustained neural spiking activity

Nonlinear Dynamics - In general, the mechanisms that maintain the activity of neural systems after a triggering stimulus has been removed are not well understood. Different mechanisms involving at...     

Protective Effects of Traditional Polyherbs on Cisplatin-Induced Acute Kidney Injury Cell Model by Inhibiting Oxidative Stress and MAPK Signaling Pathway

Acute kidney injury (AKI) is a disease caused by sudden renal dysfunction, which is an important risk factor for chronic renal failure. However, there is no effective treatment for renal impairment. Although some traditional polyherbs are commercially available for renal diseases, their effectiveness has not been reported. Therefore, we examined the nephroprotective effects of polyherbs and their relevant mechanisms in a cisplatin-induced cell injury model. Rat NRK-52E and human HK-2 subjected to cisplatin-induced AKI were treated with four polyherbs, Injinhotang (IJ), Ucha-Shinki-Hwan (US), Yukmijihwang-tang (YJ), and Urofen^TM (Uro) similar with Yondansagan-tang, for three days. All polyherbs showed strong free radical scavenging activities, and the treatments prevented cisplatin-induced cell death in both models, especially at 1.2 mg/mL. The protective effects involved antioxidant effects by reducing reactive oxygen species and increasing the activities of superoxide dismutase and catalase. The polyherbs also reduced the number of annexin V-positive apoptotic cells and the expression of cleaved caspase-3, along with inhibited expression of mitogen-activated protein kinase-related proteins. These findings provide evidence for promoting the development of herbal formulas as an alternative therapy for treating AKI.     

Transitive Limit Closures of Convex Dynamical Systems

Convex dynamical systems are iterated set-valued maps with convex graphs. The closed union of all finite powers of a given convex relation will be called its limit closure. We address the question of transitivity of limit closures and establish a sufficient condition for such transitivity (limit transitivity). We also present examples showing that the limit closure of a general compact convex system is not necessarily transitive. limit closure can be intransitive as well. It is also shown that the restriction of a linear single-valued map to a convex set containing an open neighborhood of the origin is always limit transitive.     

Embeddings in the Strong Reducibilities Between 1 and npm

We consider the strongest (most restricted) forms of enumeration reducibility, those that occur between 1- and npm-reducibility inclusive. By defining two new reducibilities (which we call n1- and ni-reducibility) which are counterparts to 1- and i-reducibility, respectively, in the same way that nm- and npm-reducibility are counterparts to m- and pm-reducibility, respectively, we bring out the structure (under the natural relation on reducibilities strong with respect to') of the strong reducibilities. By further restricting n1- and nm-reducibility we are able to define infinite families of reducibilities which isomorphically embed the r. e. Turing degrees. Thus the many well-known results in the theory of the r. e. Turing degrees have counterparts in the theory of strong reducibilities. We are also able to positively answer the question of whether there exist distinct reducibilities ≤_y and ≤_a between ≤_e and ≤_m such that there exists a non-trivial ≤_y-contiguous ≤_z degree.     

PIV analysis of in-cylinder flow structures over a range of realistic engine speeds

In-cylinder PIV measurements have been performed in a four-valve single cylinder optical gasoline direct injection engine, motored at speeds of 750, 2,000 and 3,500 rpm. Mean vector flow fields have been produced during the latter half of the intake stroke in the symmetry plane between the valve pairs. The flow fields show the development of the in-cylinder flow structures at 1.6, 2.4 and 3.2° crank angle steps for a time period of approximately 5 ms at each of the three engine speeds, respectively. Tumble ratios have been calculated for the available field of view showing a change in the flow structure between 2,000 and 3,500 rpm. This is believed to be caused by an increase in the flow of air traveling underneath the recirculation vortex at the higher engine speed. This translates the vortex position upwards and further to the right when compared to the lower engine speeds.