Defensive and other secretions of the australian cocktail ant, iridomyrmex nitidiceps

Iridodial and isovaleric acid were characterized as major components of the total extract, and of the anal gland secretion, of Iridomyrmex nitidiceps. Minor constituents identified from the total extract included iridolactones, dihydronepetalactones, actinidine, 2- and 3-pentenoic acid, and fatty acids.Behaviour experiments demonstrated isovaleric acid to be primarily an alarm substance, developing repellency only at high concentration. Iridodial was deduced to be the basic repellant. Together the two served a defensive function. Their combination as products of one pair of glands showed a high level of social development.     

Optimal packaging of dispersion-compensating fibers for matched nonlinear compensation and reduced optical noise

A method of packaging dispersion-compensating fibers (DCFs) is discussed that achieves optimal nonlinearity compensation and a good signal-to-noise ratio simultaneously. An optimally packaged dispersion-compensating module (DCM) may consist of portions of DCFs with higher and lower loss coefficients. Such optimized DCMs may be paired with transmission fibers to form scaled translation-symmetric lines that could effectively compensate for signal distortions due to dispersion and nonlinearity, with or without optical phase conjugation.     

Efficient source of single photons: a single quantum dot in a micropost microcavity

We have demonstrated efficient production of triggered single photons by coupling a single semiconductor quantum dot to a three-dimensionally confined optical mode in a micropost microcavity. The efficiency of emitting single photons into a single-mode traveling wave is approximately 38%, which is nearly 2 orders of magnitude higher than for a quantum dot in bulk semiconductor material. At the same time, the probability of having more than one photon in a given pulse is reduced by a factor of 7 as compared to light with Poissonian photon statistics.     

Two New Tetranortriterpenoids from Amoora dasyclada

Two new tetranortriterpenoids 3-oxo-24, 25, 26, 27-tetranortirucall-7-ene-23(21)-lactone,3α-hydroxy-24, 25, 26, 27-tetranortirucall-7-ene-23(21)-lactone were isolated from Amoora dasyclada. Their structures were elucidated by spectroscopic evidences.     

离子交换法提取D-核糖的研究

采用离子交换法提取D-葡萄糖发酵液中的D-核糖，其中Ca^2 型阳离子交换树脂具有良好的选择性，最佳吸附条件为25℃，以0．5BV／h的流速进行吸附，最佳解吸条件为80℃下，以0．5BV／h的流速进行解吸．解吸液浓缩后加入四倍量乙醇，可得到结晶D-核糖．     

TRANSPOSITION INHIBITION OF Tn5 IN Rhizobium leguminosarum

A recombinant transposon Tn5-GmSp, produced by replacing the central BglⅡ fragmentwith a BamHⅠ one of R1033, was utilized to detect Tn5 transposition inhibition in Rhizo-bium leguminosarum. Two types of suicide plasmids (pXS102 and pCW3/pCW30) were con-structed for Tn5-GmSp transposition. The frequency of transposition in both constructs wasgreatly reduced in the Rhizobium strains where a resident Tn5 was already present. WhenpXS102 was transferred into a Tn5-containing Rhizobium strain, the transconjugants retainedthe deleted forms of pXS102, indicating that the failure of transposition was due to the lossof the unstable prophage Mu element. In the case of pCW3/pCW30, vectors were not ob-served in the transconjugants although most of them retained the antibiotic resistant markers.This result suggested the integration of Tn5-GmSp into the rhizobial host genome throughrecombination.     

MECHANISM OF CONCENTRATION QUENCHING OF A XANTHENE DYE ENCAPSULATED IN PHOSPHOLIPID VESICLES

Encapsulating a xanthene dye in phospholipid vesicles produces vesicle solutions that contain dye at very high microscopic concentrations, but have a low overall optical density, thereby eliminating reabsorption. Using this system, we have studied the effects of concentration on the fluorescence lifetime of one such dye, sulforhodamine 101. We have observed that the lifetime decreases as a function of encapsulated dye concentration, which is indicative of collisional quenching. The lifetime decreases from 4.5 nsec for sulforhodamine in dilute aqueous solution to 0.69 ns at an encapsulated concentration of 33 m M . The bimolecular rate constant for this event is 2.6 10¹⁰ M ^-1 s^-1, consistent with a diffusion controlled event. However, the quenching constant calculated from changes in intensity is 2.2 10¹¹ M ^-1 s^-1. Thus, collisional quenching is not the predominant mechanism of quenching. The absorption spectra of dye in vesicles indicate an important contribution from static complex formation. Förster distance calculations indicate that energy transfer can also occur to a significant extent, with a predicted efficiency of transfer of 34% at a dye concentration of only 1 m M     

The participation of alkynylboronates in inverse electron demand [4 + 2] cycloadditions: a mechanistic study

The participation of alkynylboronates in [4 + 2] cycloadditions has been investigated using both kinetic and DFT studies. Kinetic studies of the cycloaddition of tetrazine 1 with alkynylboronate 2 strongly suggest that a concerted cycloaddition mechanism is in operation. This mechanism has been confirmed by DFT calculations; moreover, a highly synchronous transition state appears to operate in this process. The experimentally observed poor reactivity of electron-rich dienes with alkynylboronates has also been confirmed by theoretical studies by analyzing the transition states of the cycloadditions with bis-2,5-trimethylsilyloxyfuran. The surprising conclusion has been made that alkynylboronates are relatively electron rich and have a cycloaddition reactivity that resembles that of acetylene. In contrast, the related dichloroalkynylborane cycloaddition reactivity resembles that of dimethylacetylene dicarboxylate.     

Paradoxical activation of Raf by a novel Raf inhibitor.

BACKGROUND: Raf is a proto-oncogene that is activated in response to growth factors or phorbol esters, and is thought to activate MAP kinase kinase-1 (MKK1) and hence the classical MAP kinase (MAPK) cascade. RESULTS: The compound ZM 336372 is identified as a potent and specific inhibitor of Raf isoforms in vitro. Paradoxically, exposure of cells to ZM 336372 induces > 100-fold activation of c-Raf (measured in the absence of compound), but without triggering any activation of MKK1 or p42 MAPK/ERK2. The ZM 336372-induced activation of c-Raf occurs without any increase in the GTP-loading of Ras and is not prevented by inhibition of the MAPK cascade, protein kinase C or phosphatidylinositide 3-kinase. ZM 336372 does not prevent growth factor or phorbol ester induced activation of MKK1 or p42 MAPK/ERK2, or reverse the phenotype of Ras- or Raf-transformed cell lines. The only other protein kinase inhibited by ZM 336372 out of 20 tested was SAPK2/p38. Although ZM 336372 is structurally unrelated to SB 203580, a potent inhibitor of SAPK2/p38, the mutation of Thr106-->Met made SAPK2/p38 insensitive to ZM 336372 as well as to SB 203580. CONCLUSIONS: Raf appears to suppress its own activation by a novel feedback loop, such that inhibition is always counterbalanced by reactivation. These observations imply that some agonists reported to trigger the cellular activation of c-Raf might actually be inhibitors of this enzyme, and that compounds which inhibit the kinase activity of Raf might not be useful as anticancer drugs. The binding sites for ZM 336372 and SB 203580 on Raf and SAPK2/p38 are likely to overlap.     

A new monoterpenoid indole alkaloid from Rauvolfia yunnanensis

One new monoterpenoid indole alkaloid, 11-methoxyburnamine-17-O-3′,4′,5′-trimethoxybenzoate (1), was isolated from Rauvolfia yunnanensis Tsiang. Its structure was identified by spectroscopic evidences.