A study of comparability in amplified fragment length polymorphism profiling using a simple model system

A simple amplified fragment length polymorphism (AFLP) model, using the bacteriophage lambda genome, was developed to test the reproducibility of this technique in an international comparative study. Using either non-selective or selective primers, nine fragments or subsets of two or three fragments, respectively, were predicted using in silico software. Under optimized conditions, all predicted fragments were experimentally generated. The reproducibility of the AFLP model was tested by submitting both "unknown" DNA template that had been restricted and ligated with AFLP linkers (R/L mixture) and corresponding primer pairs to nine laboratories participating in the study. Participants completed the final PCR step and then used either slab gel electrophoresis or CE to detect the AFLP fragments. The predicted fragments were identified by the majority of participants with size estimates consistently up to 3 base pair (bp) larger for slab gel electrophoresis than for CE. Shadow fragments, 3 bp larger than the predicted fragments, were often observed by study participants and organizers. The nine AFLP fragments exhibited relative intensities ranging from less than 3% to 22% and, apart from the two weakest fragments, with a % CV of 16 to 25. Fragments containing the highest guanine-cytosine (GC) content of 50-56% showed the greatest stability in the AFLP profiles.     

Addressing the role of working memory in mathematical word-problem solving when designing intervention for struggling learners

ZDM – Mathematics Education - The focus of this article is the well documented association between low working memory capacity and difficulty with mathematical word-problem solving. We begin...     

Volatile Constituents of Achillea ligustica All. by HS-SPME/GC/GC-MS. Comparison with Essential Oils Obtained by Hydrodistillation from Corsica and Sardinia

The volatile components extracted from the headspace (HS) of Achillea ligustica All. samples and their separated organs using solid phase microextraction (SPME) were investigated by gas chromatography and gas chromatography-mass spectrometry. Fiftyseven compounds were identified, the main components were camphor (14.2–29.8%), artemisia ketone (0.3–26.7%), santolina alcohol (0.5–9.4%), camphene (3.0–9.0%) and trans-sabinyl acetate (1.6–5.5%). Moreover, the chemical composition of Corsican and Sardinian A. ligustica oils obtained from flowers and leafy stems harvested in four regions of both islands, were investigated. Two collective oils of A. ligustica were also investigated, comparison between both oils as well as from data literature were reported. A comparison of hydrodistillation and HS-SPME extraction of volatile components in term of isolation time, plant-consuming and chemical composition was discussed. HS-SPME technique was clearly fast in contrast to hydrodistillation (90 min/300 min). HS extraction was performed with a much smaller amount of plant than hydrodistillation. Although the aromatic profiles of HS-fractions and oils showed several quantitative differences HS-SPME can be applied to routine control analysis of aromatic and medicinal plants.

     

A novel cacalolide from Psacalium decompositum

A new cacalolide sesquiterpenoid, named as Romo-A, was isolated from the roots of Psacalium decompositum, Asteraceae, a Mexican medicinal shrub with antidiabetic properties. Its structure was elucidated by NMR, MS, IR, UV, and confirmed by X-ray diffraction studies.     

Improvement of a low pH antigen-antibody dissociation procedure for ELISA measurement of circulating anti-Aβ antibodies

Background  

Prior work from our group found that acid dissociation (pH 2.5 incubation) of serum from APP transgenic mice vaccinated against Aβ increased the apparent anti-Aβ titers, suggesting antibody masking by antigen in the ELISA assay. Subsequently, we found that pH 2.5 incubation of serum from unvaccinated non-transgenic mice showed antibody binding to Aβ1–42, but no increase when other proteins, including shorter Aβ peptides, coated the ELISA plate. To investigate further the effects of low pH incubation on apparent anti-Aβ1–42 signals, we examined normal sera from nonTg unvaccinated mice, nonTg mice vaccinated with Aβ peptide (to produce authentic anti-Aβ antibodies) or a monoclonal antibody against Aβ (6E10) using competitive-inhibition ELISA and Aβ epitope mapping assays. In addition, we examined use of a less stringent low pH procedure at pH 3.5, to ascertain if it had the same effects as the pH 2.5 procedure.     

Phospha-Michael additions to activated internal alkenes: steric and electronic effects

The addition of P(O)-H bonds to internal alkenes has been accomplished under solvent-free conditions without the addition of a catalyst or radical initiator. Using a prototypical secondary phosphine oxide, a range of substrates including cinnamates, crotonates, coumarins, sulfones, and chalcones were successfully functionalized. Highly activated acceptors such as isopropylidenemalononitrile and ethyl 2-cyano-3-methyl-2-butenoate underwent the phospha-Michael reaction upon simple trituration of the reagents at room temperature, whereas less activated substrates such as ethyl cinnamate and methyl crotonate required heating (>150 °C) in a microwave reactor to achieve significant consumption of the starting alkenes. For the latter alkenes, a competing reaction involving disproportionation of the ditolylphosphine oxide into ditolylphosphinic acid and ditolylphosphine was observed at the high temperatures needed to promote the addition reaction.