Synthetic studies pertaining to a novel class of structurally related glycosidic 14-membered macrolides of marine origin are reported. The evolution of a versatile aldol-based strategy that culminated in the total syntheses of callipeltoside A and aurisides A and B is detailed. Using a combination of biogenetic considerations and conformational analysis, a revised stereochemical assignment for the related polyketide dolastatin 19 was proposed and validated by total synthesis.
A sensor network key distribution scheme for hierarchical sensor networks was recently proposed by Cheng and Agrawal. A feature of their scheme is that pairwise keys exist between any pair of high-level nodes (which are called cluster heads) and between any (low-level) sensor node and the nearest cluster head. We present two attacks on their scheme. The first attack can be applied for certain parameter sets. If it is applicable, then this attack can result in the compromise of most if not all of the sensor node keys after a small number of cluster heads are compromised. The second attack can always be applied, though it is weaker.
The dissolution mechanisms of model protein gels (made from a single protein, ß- lactoglobulin) in alkali were studied at different NaOH concentrations and temperatures. A recent study has shown that the free volume within the swollen gel is a key parameter that determines the dissolution rate (Food Hydrocolloids (2007) 21:1275). This suggests that proteins diffuse in the swollen gel next to the solution before they are dissolved. We extend this hypothesis here by showing that only small oligomers (trimers and smaller), such as those formed after the cleavage of large aggregates, are likely to diffuse throughout the gel. Large aggregates (> 200 kDa) are considered to disentangle at the gel/solvent interface. Size exclusion chromatography has been used to determine the size distributions of the aggregates released from the gel matrix, and to follow the breakdown kinetics of soluble aggregates in alkaline conditions. Analysis of the dissolution process at different temperatures reveals that at low NaOH concentrations (< 0.1 M), the breakdown of large aggregates in alkali exhibits a temperature dependency different from that of the overall dissolution process. At high NaOH concentrations (> 0.3 M), where swelling is inhibited, the increase in the dissolution rate seems to be related to the destruction of cross-linked aggregates, in particular via the beta-elimination of intermolecular disulfide bonds. A previously unobserved type of dissolution behavior at 0.87 M NaOH and at high temperatures is reported.
Surface tension is an important property of milk concentrates because it affects atomisation in spray drying. A Krüss tensiometer and Wilhelmy plate were used to measure surface tension. Skim milk and whole milk were tested at a range of solids concentrations and were compared with the surface tension of standard and reconstituted milks. It was found that surface tension was affected more by temperature than by fat content or solids concentration. The surface tensions for concentrates correspond to published values for standard milks below 60°C, but above 60°C, the surface tension increases markedly, which can be attributed to changes in the milk chemistry. The difficulty associated with using the Wilhelmy plate method is the time taken to perform each measurement, which allows a skin to form and reduces the accuracy of the measurements.
Background: Cerebrospinal fluid (CSF) amyloid β1-42 (Aβ1-42), total tau (T-tau) and phosphorylated tau181 (P-tau) are finding increasing utility as biomarkers of Alzheimer’s disease (AD). The purpose of this study was to determine whether measured CSF biomarker concentrations were affected by aliquot storage volume and whether addition of detergent-containing buffer mitigates any observed effects.
Methods: AD and control CSF was distributed into polypropylene tubes in aliquots of different volumes (50–1500 μL). Aβ1-42, T-tau and P-tau were measured with and without addition of Tween 20 (0.05%).
Results: Measured concentrations of Aβ1-42 increased two-fold with aliquot storage volume. A volume increase of 10 µL caused an Aβ1-42 increase of 0.95 pg/mL [95% confidence interval (CI) 0.36–1.50, p=0.02] in controls, and 0.60 pg/mL (CI 0.23–0.98 pg/mL, p=0.003) in AD samples. Following addition of Tween 20, the positive relationship between Aβ1-42 and aliquot volume disappeared. T-tau and P-tau were not significantly affected.
Conclusions: CSF aliquot storage volume has a significant impact on the measured concentration of Aβ1-42. The introduction of a buffer detergent at the initial aliquoting stage may be an effective solution to this problem.
The ~151 Ma Guadalupe Igneous Complex (GIC) is a tilted, bi-modal intrusion that provides a rare view into the deeper, mantle-derived portions of a granitic pluton. Major oxide relationships show that GIC granitic rocks formed by in situ differentiation. Assimilation of sedimentary country rock is precluded, as GIC alumina saturation indices (ASI) are too low by comparison, while TiO2 and P2O5 contents disallow partial melting of metavolcanic lower/middle crust. In contrast, Rb-Sr systematics support in situ magmatic differentiation, as unaltered GIC whole rock samples fall on a single 151 Ma isochron (initial 87Sr/86Sr = 0.7036) matching zircon age dates (Saleeby et al. 1989).
Crystal/liquid segregation, though, was not continuous: mafic and felsic samples form discordant compositional trends, with a gap between 60-66% SiO2. We posit that crystal/liquid segregation is continuous between 50-60% SiO2, and leads to the genesis of intermediate composition liquids that are then too viscous to allow further continuous liquid segregation. Further crystal/liquid separation thereafter occurs discontinuously (at F ≈ 45-50%), to yield a mafic crystalline (52-59% SiO2) residue and a silicic (70-75% SiO2) liquid (Bachmann and Bergantz 2004), which are, respectively, preserved in the Meladiorite and Granite/Granophyre units of the GIC. Outcrops in the gabbroic section support this view, where mafic crystalline layers feed directly into granitic dikes, and intermediate compositions are absent; mass balance calculations at the outcrop scale also support this model. It is unclear, though, to what extent this model applies to larger Sierran plutons; the smaller GIC may represent an end-member process, where rapid cooling limits mixing, due to rapid increases in mafic/felsic melt viscosity contrasts.
In situ spatially resolved X-ray absorption near edge structure (m-XANES) spectra are obtained for natural Cu-In-bearing sphalerite. Copper K-edge spectral data show that, in Cu-In-bearing sphalerite, in which an excellent correlation between the Cu and In contents is noted, Cu is present in the Cu+ state. This offers indirect proof for the coupled substitution 2 Zn2+ ↔ Cu+ + In3+, which allows indium to enter the sphalerite structure. The study clearly demonstrates the utility of synchrotron radiation to accurately determine oxidation state in small volumes of mineral in which the concentration of the element of interest is low or very low. The study also demonstrates that good quality μ-XANES spectra can be collected on TEM foils prepared in situ at a chosen position on the surface of a polished sample using the focused ion beam-scanning electron microscope method.