2 + 2] photocycloadditions in the synthesis of chiral molecules

A strategy for the synthesis of chiral molecules that receives growing popularity among organic chemists employs the photochemically mediated [2 + 2] cycloaddition reaction. These reactions can be performed on a multigram scale and often proceed with high yield and with stereocontrol. These features, in combination with the useful properties of the four-membered ring photoproducts in subsequent chemical transformations, make them attractive options in the early stage of a synthesis design. Various combinations of unsaturated functional groups can participate in this reaction process. Accordingly, these chemical reactions can be economical solutions to problems relating to the synthesis of a variety of target molecules.     

Über die Wirkung von Maisgärfutter auf Milchertrag und Milchqualität1

• 1 Es wurden Fütterungsversuche mit einer niedrigen (10 kg) und einer höheren (20 kg) Gabe von Maisgärfutter zu Milchkühen durchgeführt.
• 2 Die Fütterungsversuche wurden als Periodenversuche wie folgt durchgeführt: 1. Grundfutterversuch — Fütterungsversuch mit 10 kg Maisgärfutter —, 2. Grundfutterversuch. Es folgte 2. Grundfutterversuch — Fütterungsversuch mit 20 kg Maisgärfutter —, 3. Grundfutterversuch.
• 3 Jeder der 5 Versuche dauerte 28 Tage. Ein Versuch umfaßte die 14tägige Vorperiode und die 14tägige Hauptperiode. Die Milchmenge und der Fettgehalt wurden täglich während der ganzen Versuchsdauer ermittelt; zur Auswertung gelangte jedoch nur die Hauptperiode.
• 4 Die niedrige (10 kg) Gabe an Maisgärfutter wirkte erhohend auf die Milchmenge, beeinflußte jedoch den Fettgehalt der Milch nicht.
• 5 Die höhere (20 kg) Gabe von Maisgärfutter verdoppelte die Milchmenge der 10 kg Gabe, zeigte jedoch ebenfalls keinen Einfluß auf den Fettgehalt.
• 6 Das Maisgärfutter erhöht somit eindeutig die Milchmenge bei gleichbleibendem Fettgehalt der Milch.

     

Effect of Oil Overlay on Inhibition Potential of Roscovitine in Sheep Cumulus‐Oocyte Complexes

Inhibitors of cyclin‐dependent kinases, as roscovitine, have been used to prevent the spontaneous resumption of meiosis in vitro and to improve the oocyte developmental competence. In this study, the interference of oil overlay on the reversible arrest capacity of roscovitine in sheep oocytes as well as its effects on cumulus expansion was evaluated. For this, cumulus‐oocyte complexes (COCs) were cultured for 20 h in TCM 199 with 10% foetal bovine serum (Control) containing 75 μm roscovitine (Rosco). Subsequently, they were in vitro matured (IVM) for further 18 h in inhibitor‐free medium with LH and FSH. The culture was performed in Petri dishes under mineral oil (+) or in 96 well plates without oil overlay (?) at 38.5°C and 5% CO₂. At 20 and 38 h, the cumulus expansion and nuclear maturation were evaluated under stereomicroscope and by Hoechst 33342 staining, respectively. No group presented cumulus expansion at 20 h. After additional culture with gonadotrophins, a significant rate of COCs from both Control groups (+/?) exhibited total expansion while in both Rosco groups (+/?) the partial expansion prevailed. Among the oocytes treated with roscovitine, 65.2% were kept at GV in the absence of oil overlay while 40.6% of them reached MII under oil cover (p < 0.05). This meiotic arrest was reversible, and proper meiosis progression also occurred in the Control groups (+/?). So, the culture system without oil overlay improved the meiotic inhibition promoted by roscovitine without affecting the cumulus expansion rate or the subsequent meiosis progression.     

Status of the Pelecanidae

The recent history, current status and prospects in the immediate future of the seven species of the Pelecanidae are reviewed. As a consequence of pesticide poisoning, Pelecanus occidentalis suffered severe population declines in the 1950s and 1960s in portions of its range in the United States. However, since the ban on use of DDT in 1972 the species is again laying eggs of near normal thickness, reproductive success appears to be normal and populations are stable or increasing. Similarly, available data indicate that the world populations of P. rufescens, P. conspicillatus, and P. erythrorynchos remain stable, although local population fluctuations do occur. Data for P. onocrotalus show a stable population in Africa but a decline in Asia and Europe, both in numbers of birds and breeding colonies. More seriously, only very small populations of P. crispus and P. philippensis exist. Fewer than 1000 pairs of P. crispus next in 19 colonies in eastern Europe and Asia. Fewer than 1200 pairs of P. philippensis nest in four colonies in eastern/southern India and 23 colonies in Sri Lanka. The populations of both species have declined considerably in the past few decades. The causes for the declines are not documented but are thought to result from a combination of human disturbance in nesting colonies; destruction of nesting and roosting-loafing areas; declines in fish availability; and pesticide contamination. Only immediate action and concerted efforts at stabilizing the populations in the wild, in conjunction with the establishment of captive breeding populations, will preserve these two species from extinction.     

Pesticide toxicity using protozoans as test organisms

Summary A toxicity test using protozoa as test organisms was devised for pesticides. Two different methods were used, the most probable number method and the absorbance method (based on measurement of protozoa growth through absorbance). The ciliates Colpoda cucullus and Blepharisma undulans and the flagellate Oikomonas termo were isolated from different biological starter cultures and tested with the herbicides Chlorex, MCPA, dichlorprop and Matrigon, the fungicide Benlate, and the insecticide Sumicidin. The protozoans showed quite different sensitivities to the pesticides, using 9-h lethal concentrations (LC₅₀ and LC₁₀) as criteria. The 9-h LC₅₀ (concentration at which 50% of the protozeon population has died after 9 h of incubation) ranged from 0.7 ppm for Benlate to 40000 ppm for Chlorex. The usual soil application rates of Chlorex, MCPA, and Benlate were toxic to some of the organisms.     

Interferon-gamma: the major mediator of resistance against Toxoplasma gondii

Mice were injected with a monoclonal antibody to interferon-gamma to examine the importance of endogenous production of this lymphokine in resistance against infection with the sporozoan parasite Toxoplasma gondii. Mice with intraperitoneal infections of T. gondii that received no antibody survived and developed chronic T. gondii infection, whereas the infected mice that received the monoclonal antibody died of toxoplasmosis. The activation of macrophages, which kill T. gondii in vivo, was inhibited by administration of the monoclonal antibody, but the production of antibodies to T. gondii was not suppressed. The fact that an antibody to interferon-gamma can eliminate resistance to acute Toxoplasma infection in mice suggests that this lymphokine is an important mediator of host resistance to this parasite.     

Conservation management of calcareous grasslands. Changes in plant species composition and response of functional traits during 25 years

Five management treatments have been applied to a calcareous grassland since 1974 to study their efficiency in maintaining high diversity of grassland species. The treatments were: continuing sheep grazing, mowing, mulching, burning and leaving fallow (unmanaged). After 25 years of management, the treatments mowing and mulching resulted in a species composition similar to that from grazing by sheep. Thus, mowing and mulching can be useful management alternatives to grazing. In contrast, both burning and leaving fallow considerably changed the species composition. The changes were similar in both treatments and neither can be recommended for management purposes. We also evaluated eight traits with assumed sensitivity to the treatments (life form, life cycle, growth form, runners, lateral spread, fecundity, seed mass, germination season). In 1999, all traits except life cycle were found to respond to the different treatments. Trait response is discussed in detail.     

Effects of accelerators on mobility of 14C-2,4-dichlorophenoxy butyric acid in plant cuticles depends on type and concentration of accelerator

Effects of diethyl suberate (DESU), diethyl sebacate (DES), dibutyl suberate (DBSU), dibutyl sebacate (DBS), and tributyl phosphate (TBP) on diffusion of 14C-2,4-dichlorophenoxy butyric acid (2,4-DB) across cuticular membranes (CM) was studied. Astomatous CM were isolated enzymatically from Stephanotis floribunda Brongn. leaves, and diffusion was measured at 20 degrees C. The alkyl-substituted dicarboxylic acids constitute a homologous series with carbon numbers increasing from C12 to C18. Molecular weights increased only moderately from 230.0 (DESU) to 314.5 (DBS), while partition coefficients varied over orders of magnitude from 92 (DESU), to 1213 (DES), to 15,988 (DBSU), to 210,762 (DBS). All the above compounds turned out to be accelerators as they increased 2,4-DB mobility by up to 40-fold with accelerator concentrations in the CM ranging from only 9.2 to 105 g kg(-1). Efficacy (2,4-DB mobility in the presence/mobility in the absence of accelerators) increased with increasing concentrations of accelerators in CM or in reconstituted cuticular waxes. Plotting efficacy vs accelerator concentration in the CM resulted in straight lines, and their slopes increased in the order DBS (0.14), DBSU (0.31), DES (0.51), and DESU (0.85). Hence, DESU was the most powerful accelerator in this series as it increased 2,4-DB mobility in the CM about 6 times more than DBSU. Waxes constitute the major barrier in plant cuticles, and plots of efficacy vs accelerator concentration in Stephanotis wax were also linear, but compared to CM slopes were steeper by factors of 3.20 (DBS), 2.97 (DBSU), 2.70 (DES), and 1.62 (DESU). TBP was similarly effective as DESU, but plots of efficacy vs concentration were not linear, and curves approached a plateau at 60-80 g kg(-1). These data are discussed with regard to suitability of these accelerators for formulating systemic pesticides.     

The relationship between cavity-nesting birds and snags on clearcuts in western Oregon

Relationships between cavity-nesting birds (CNB) and density and characteristics of snags were investigated on 13 clearcuts in central coastal Oregon. Species richness and density of CNB were positively (P<0.05) related to snag density and were still increasing at the maximum snag density evaluated. Cavity-nesting birds selected (P<0.05) snags taller than 6.4 m and greater than 78–102 cm in diameter, and avoided (P<0.05) snags less than 28 cm in diameter. Snags of intermediate decay stages were used for nesting more (P<0.05) than snags of early and advanced stages of decay. Cavity-nesting birds selected snags with more (P<0.05) bark cover (greater than 11%) than the average cover found on available snags. Individual CNB species exhibited significantly different (P<0.05) selections for snag height, diameter, hardness and bark cover. To optimize density and richness of CNB, forest managers should provide ≥ 14 snags ha⁻¹ between 28 and 128 cm diameter at breast height (dbh), between 6.4 and 25 m tall, with at least 10% bark cover, and with a majority in hardness stages 3 and 4.