Reactive diene for synthesis of substituted catechols

(2R,3R)-2,3-Dimethoxy-2,3-dimethyl-5,6-dimethylene-1,4-dioxane has been synthesized and is a highly efficient diene in Diels-Alder reactions. Reaction with acetylenic dienophiles provides a simple route to substituted catechols. Reactions with some ethylenic dienophiles are also reported.     

The relationships between oxidase and synthase activities of flavin dependent thymidylate synthase (FDTS)

New findings lead to a revised understanding of the substrates' binding order, the role of the substrate as an activator, and the observed lag phase in the FDTS catalyzed reaction.     

Intramolecular hydride addition to pyridinium salts: new routes to enantiopure dihydropyridones

The transformation of a simple disubstituted pyridine into a pyridinium ion bearing an exocyclic hydroxyl group, protected as a silane, enabled an intramolecular hydride transfer reaction to take place when fluoride was used as a nucleophile. The addition was both regio- and stereoselective and enabled the formation of enantiopure dihydropyridones when enantiopure pyridine derivatives were used in this sequence. The heterocyclic products contain ample functionality for further elaboration reactions and subsequent derivatization.     

多光子过程中相位退相干时两原子布局数反转

利用全量子理论的方法,研究了存在相位退相干时多光子T-C模型中两个二能级原子与二项式光场相互作用系统中两原子的布居数反转。讨论了相位退相干系数、二项式光场系数、最大光子数、跃迁光子数对原子布居数反转的影响。结果表明：相位退相干减少了原子布居数反转的振幅、破坏了原子的量子特性。改变跃迁光子数,可以改变原子间布居数反转演化周期及演化强度。当二项式光场的最大光子数增大时,原子布居差的崩塌-回复现象就会逐渐消失。相位退相干因子不变时, 二项式光场从相干态过渡到数态过程中,原子布居的振荡频率由大变小,周期性的崩塌与回复现象逐渐消失。     

The vitamin D debate: translating controlled experiments into reality for human sun exposure times

Exposure to sunlight, specifically the ultraviolet radiation, has both positive and negative health effects. Maximizing the benefits (vitamin D synthesis) while minimizing the damage is a multifaceted problem in which many of the elements are poorly quantified. Here we show how rigorously conducted large sample size laboratory studies of the effect of ultraviolet radiation dose on vitamin D status can be applied to real-life situations. This was achieved by modeling the radiation incident on different surfaces for different solar locations, and equating with the controlled exposures in the laboratory studies. Results from both model and experimental data show that relatively short exposures of a modest amount of unprotected skin to summer sunlight in northern climes, on a regular basis during lunchtime hours, increases vitamin D to sufficiency status (≥20 ng mL(-1) ) in the white Caucasian population. While both sun exposure conditions and human skin responses are variable in real life, these quantitative findings provide a guide for authorities devising sunlight exposure recommendations.     

The First Principles Investigations of the Thermoelectric Properties of GaN with p- and n-Type Doping

We investigate the thermoelectric properties of GaN with p-and n-type doping by the first principles calculation and the semi-classical Boltzmann theory. We find that the power factors (S2σof p-type GaN (-3500 W/mK2) is about twice that of the n-type (-1750 W/mK2), which indicates the thermoelectric properties of p-type GaN would be better. Thermal conductivity of GaN crystal decreases rapidly as the temperature increases, but it is still too large for thermoelectric applications. The figure of merit (ZT) estimated at 1500 K is 0.134 for p-type GaN crystal and 0.062 for the n-type.     

44-Methylgambierone,a new gambierone analogue isolated from Gambierdiscus australes

A new analogue of gambierone, 44-methylgambierone, was isolated from the benthic dinoflagellate Gambierdiscus australes collected from Raoul Island (Rangitahua/Kermadec Islands). This molecule has been previously reported as maitotoxin-3. The structure of 44-methylgambierone was elucidated using 1D- and 2D-nuclear magnetic resonance spectroscopy and mass spectrometry techniques. The nine-ring polyether backbone (A–I) and functional groups (carbonyl, terminal diol, 1,3-diene and monosulphate) are the same for both compounds with the addition of an olefinic methyl group being the only modification in 44-methylgambierone.