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Binary solar system objects are common and range from satellite systems with very large mass ratios $M_1/M_2$ to mass ratios very close to unity. A well-known example of a binary is the Pluto-Charon system. With Charon only eight times less massive than Pluto the question arises as for many other systems, why the mass-ratio is still close to unity. There is much evidence that (binary) planet(esimal) formation happened early, when the protoplanetary gas disk was still around. It is likely that (some of) these binaries grew up together subject to pebble accretion. Here we focus on the question of how the mass arriving in the gravitational influence zone of the binary during pebble accretion, is distributed over the binary components. Does the accretion through time lead to a converging mass ratio, or to a diverging mass ratio? We numerically integrate pebble paths in the same well-known fashion as for a single mass subject to pebble accretion and track what the efficiency of accretion is for the two separate binary components, compared to a single body with the same mass. These numerical simulations are done for a range of binary mass-ratios, mutual separations, Stokes numbers and two orbital distances, 2.5 and 39 au. We find that in the limit where pebbles start to spiral around the primary (this holds for relatively large pebbles), the pebble preferentially collides with the secondary, causing the mass ratio to converge towards unity on Myr timescales. In this regime the total sweep-up efficiency can lower to half that of a pebble-accreting single body because pebbles that are thrown out of the system, after close encounters with the system. The results show that systems such as Pluto-Charon and other larger equal mass binaries could well have co-accreted by means of pebble accretion in the disk phase without producing binaries with highly diverging mass-ratios., 10 pages, 8 figures, submitted to Astronomy and Astrophysics

The (2 + 2)- and (4 + 2)-cycloaddition of triplet xanthenethione to phenyl-, methoxy-tert-butoxy-, (methylthio)-, (tert-butylthio)- and 1,1-dimethyl-allene gives rise to thietanes 3 and 4, and to thiopyran derivative 5, respectively. The mechanism of the reaction is discussed. In the case of thietane 3 (X = Ph), prototropy to the stable thiete 6 has been observed.

α,β-Unsaturated thioamides and vinylogous thioamides have been prepared by thermal addition of trithiocarbonates RS-C(S)SR1 to 1-(diethylamino)propyne. Aromatic dithio esters Ar-C(S)SR only gave the α,β-unsaturated thioamides. The dithio ester Me2CH-C(S)SMe adds as acidic enethiol tautomer Me2CC(SH)SMe to 1-(diethylamino)propyne. Reaction mechanisms and the stereochemistry of the adducts are discussed.

A modified synthetic route to 1,2,3-butatrienyl ethers 3 is presented. It involves hydroxyalkylation of 2-propynyl ethers with an aldehyde or a ketone, followed by trimethylsilylation of the hydroxy ether 1 and 1,4-elimination of Me3SiOH from 2 with ethyllithium.

Condensates and naphtha are petroleum samples with largely gasoline-range components (C5–C10). Metal organic complexes are source inherited components of oils which are associated with the polar components and asphaltenes of oils. Because of the very low levels of biomarkers such as hopanes and steranes in condensates, they present a special correlation problem. Geochemically significant metals, such as V and Ni, can be measured in some condensates using conventional Meinhardt–Scott chamber inductively coupled plasma mass spectrometry (ICP-MS). In order to increase the sensitivity and the range of condensates which can be analysed, the Cetac U-6000 AT Ultrasonic nebuliser–desolvation system was tested. The Cetac system improved the sensitivity for V and Ni by a factor of about 40. Valuable information for relating these difficult samples to each other and to heavier oils in a basin can thus be supplied to exploration geochemists. The influence of organic matrix on the analytical signal was investigated. Matrix effects are more pronounced for the Cetac system than for the conventional ICP-MS system. For both systems, the use of an In internal standard was found to be necessary for compensating for differences in nebulisation and combustion behaviour caused by variations in the nature of the sample. The use of ICP-MS for the analysis of toxic metals such as Hg and Pb in condensates and naphthas is also discussed. The results are compared with those obtained using electrothermal atomic absorption spectrometry and cold vapour atomic absorption spectrometry in an interlaboratory study of naphthas. Conventional Meinhardt–Scott chamber ICP-MS provided good accuracy and precision of analysis compared with the other techniques during this study. Volatile species such as Et4Pb and Me2Hg were lost in the desolvation unit when using the Cetac system. Volatilisation effects were not observed when using the conventional Meinhardt–Scott chamber ICP-MS system.

Using cDNA-AFLP RNA fingerprinting throughout potato tuber development, we have isolated a transcript-derived fragment (TDF511) with strong homology to plant steroid dehydrogenases. During in vitro tuberization, the abundance profile of the TDF shows close correlation to the process of tuber formation. However, when tuberization is inhibited by the addition of gibberellins (GAs) to the growth medium, the appearance of TDF511 in the fingerprint is delayed, then steadily increases in intensity during later stages of development. TDF511 was used to isolate the corresponding cDNA (CB12). The DNA and deduced amino-acid sequences of the cDNA show high homology to a fruit-ripening gene from tomato, a series of steroid dehydrogenases, and the maize Ts2 gene. A section of the cDNA was cloned in antisense orientation behind a 35S CaMV promoter and transformed into potato. Transgenic plants expressing the antisense gene showed significantly earlier emergence, an increase in height, and longer tuber shape. In vitro tuberization experiments reveal extended stolon lengths in comparison to the controls. The analysis of endogenous GA levels showed that the transgenic antisense plants have elevated levels of biologically active GAs and their respective precursors. We propose that this gene plays a role in the metabolism of plant-growth substances important for tuber life cycle and plant development.

Using the cDNA-AFLP method, we have isolated a transcript-derived fragment (TDF) which shows a differential expression pattern during tuber organogenesis of Solanum tuberosum L. The TDF was used to isolate a cDNA clone carrying a 1.5 kb insert and potentially coding for a 32.5 kDa peptide which, by homology, represents a potato homologue of an alpha-snap gene and has been designated Stsnap. Northern analysis showed that the Stsnap gene is expressed in actively dividing tissues throughout the potato plant. Analysis of genomic DNA from potato revealed that the Stsnap gene is likely to be a single-copy gene. The expression of antisense Stsnap cDNA under the control of the CaMV 35S promoter results in plants with an altered morphology such as curled leaves. Several of these transgenic lines also display cellular and developmental abnormalities with distinct changes in assimilate transport including accumulation of starch and soluble sugars in source leaves. We argue that these findings are consistent with the hypothetical function of the StSNAP gene product in vesicle targeting and fusion during plant development.

Silencing of genes is mostly studied in diploid, homozygous, self-fertile and sexually propagated species. However, conclusions drawn for these species are not always applicable to crops like potato, which is an autotetraploid, highly heterozygous, vegetatively propagated species. Factors influencing the level of silencing in potato are discussed, with emphasis on inhibition of the granule-bound starch synthase I (GBSSI) gene. Type of construct, number of integrated T-DNA copies, structural arrangement of the T-DNA locus, integration site, target tissue and genetic background are important factors for all plant species. Ploidy level and multiple allelism are factors deserving special attention when the efficiency of silencing of endogenous genes is studied in polyploid, heterozygous species such as potato.

An electron microprobe interdiffusion study was made in single crystals between 1200° and 1331°C over the solid-solution compositional range 0 to 20 mol% YF3 in CaF2. At constant temperature, the value of δ, the interdiffusion coefficient, increased approximately exponentially with increasing YF3 content. As YF3 content increased, the temperature dependence of δ decreased. Extrapolation of δ to 0% YF3 combined with consideration of the defect formation mechanism at mite dilution allowed estimation of the impurity diffusion coefficient for Y in essentially pure CaF2.

Tertiary acetylenic alcohols have been transformed into the O-trimethylsilyl derivatives with trimethylsilyl chloride and triethylamine, using catalytic amounts of dimethyl sulfoxide, hexamethylphosphoric triamide, imidazole, or 1,5-diazabicyclo[5.4.0]undec-5-ene. Saturated tertiary alcohols can be trimethylsilylated in the same way.

A modified synthetic route to 1,2,3-butatrienyl ethers 3 is presented. It involves hydroxyalkylation of 2-propynyl ethers with an aldehyde or a ketone, followed by trimethylsilylation of the hydroxy ether 1 and 1,4-elimination of Me3SiOH from 2 with ethyllithium.

The (2 + 2)- and (4 + 2)-cycloaddition of triplet xanthenethione to phenyl-, methoxy-tert-butoxy-, (methylthio)-, (tert-butylthio)- and 1,1-dimethyl-allene gives rise to thietanes 3 and 4, and to thiopyran derivative 5, respectively. The mechanism of the reaction is discussed. In the case of thietane 3 (X = Ph), prototropy to the stable thiete 6 has been observed.

α,β-Unsaturated thioamides and vinylogous thioamides have been prepared by thermal addition of trithiocarbonates RS-C(S)SR1 to 1-(diethylamino)propyne. Aromatic dithio esters Ar-C(S)SR only gave the α,β-unsaturated thioamides. The dithio ester Me2CH-C(S)SMe adds as acidic enethiol tautomer Me2CC(SH)SMe to 1-(diethylamino)propyne. Reaction mechanisms and the stereochemistry of the adducts are discussed.

Tertiary acetylenic alcohols have been transformed into the O-trimethylsilyl derivatives with trimethylsilyl chloride and triethylamine, using catalytic amounts of dimethyl sulfoxide, hexamethylphosphoric triamide, imidazole, or 1,5-diazabicyclo[5.4.0]undec-5-ene. Saturated tertiary alcohols can be trimethylsilylated in the same way.