ALBERT

Description: Tropical South America is one of the three main centres of the global, zonal overturning circulation of the equatorial atmosphere (generally termed the 'Walker' circulation1). Although this area plays a key role in global climate cycles, little is known about South American climate history. Here we describe sediment cores and down-hole logging results of deep drilling in the Salar de Uyuni, on the Bolivian Altiplano, located in the tropical Andes. We demonstrate that during the past 50,000 years the Altiplano underwent important changes in effective moisture at both orbital (20,000-year) and millennial timescales. Long-duration wet periods, such as the Last Glacial Maximum—marked in the drill core by continuous deposition of lacustrine sediments—appear to have occurred in phase with summer insolation maxima produced by the Earth's precessional cycle. Short-duration, millennial events correlate well with North Atlantic cold events, including Heinrich events 1 and 2, as well as the Younger Dryas episode. At both millennial and orbital timescales, cold sea surface temperatures in the high-latitude North Atlantic were coeval with wet conditions in tropical South America, suggesting a common forcing.

Description: The valuable nutraceutical γ-linolenic acid (GLA, (6Z,9Z,12Z)-octadecatrienoic acid) is biosynthesized by a series of regio- and stereoselective dehydrogenation reactions that are catalyzed by a set of enzymes known as fatty acid desaturases. As part of ongoing research into the mechanism of these remarkable catalysts, we have examined the cryptoregiochemistry (site of initial oxidation) of Δ6 desaturation as it occurs in the protozoan Tetrahymena thermophila. Two complementary approaches that address this issue are described. In the first set of experiments, we measured the individual primary deuterium kinetic isotope effects associated with the C−H bond cleavages at C-6 and C-7. Competition experiments using appropriately deuterium-labeled 4-thiasubstrates revealed that a large KIE (kH/kD = 7.1 ± 0.5) was observed for the C−H bond-breaking step at C-6, whereas the C−H bond cleavage at C-7 was insensitive to deuterium substitution (kH/kD = 1.04 ± 0.05). These results point to C-6 as the site of initial oxidation in Δ6 desaturation since the first chemical step in this type of reaction is rupture of a strong, unactivated C−H bond, an energetically difficult process that typically exhibits a large KIE. This conclusion was supported by the results of our second approach, which involved locating the position of the putative diiron oxo oxidant with respect to substrate by monitoring the efficiency of oxo transfer to a series of thia fatty acid probes. Thus only a 6-thia-analogue is converted to significant amounts of the corresponding sulfoxide (9% yield). The absolute configuration of this product was determined to be S using (S)-MPAA as a chiral shift reagent. Taken together, these results point to the abstraction of the C-6 pro S hydrogen as the initial event in Δ6 desaturation as it occurs in T. thermophila.

Description: One way of accounting for lowered atmospheric carbon dioxide concentrations during Pleistocene glacial periods is by invoking the Antarctic stratification hypothesis, which links the reduction in CO2 to greater stratification of ocean surface waters around Antarctica1, 2. As discussed by Sigman and Boyle3, this hypothesis assumes that increased stratification in the Antarctic zone (Fig. 1) was associated with reduced upwelling of deep waters around Antarctica, thereby allowing CO2 outgassing to be suppressed by biological production while also allowing biological production to decline, which is consistent with Antarctic sediment records4. We point out here, however, that the response of ocean eddies to increased Antarctic stratification can be expected to increase, rather than reduce, the upwelling rate of deep waters around Antarctica. The stratification hypothesis may have difficulty in accommodating eddy feedbacks on upwelling within the constraints imposed by reconstructions of winds and Antarctic-zone productivity in glacial periods.

Description: From the aerial parts of Putoria calabrica, two new flavonol triglycosides were isolated and their structures were elucidated as quercetin-3-O-[α-l-rhamnopyranosyl-(1→2)-α-l-arabinopyranoside]-7-O-β-d-glucopyranoside (1, calabricoside A) and quercetin-3-O-[4‘ ‘‘-O-caffeoyl-α-l-rhamnopyranosyl-(1→2)-α-l-arabinopyranoside]-7-O-β-d-glucopyranoside (2, calabricoside B). Additionally, seven iridoid and three lignan glycosides were isolated and characterized. Radical scavenging activities of all compounds were determined by quantifying their effects on luminol-enhanced chemiluminescence in formyl-methionyl-leucyl-phenylalanine (FMLP) stimulated human polymorphonuclear neutrophils (PMNs). Calabricoside A and B showed strong radical scavenging activity with IC50 values of 0.25 and 0.3 μM, respectively.

Description: To what extent was the Arctic Ocean glaciated in the past? Heavily, according to data, gathered by a submarine, which show considerable ice-scouring of topography in parts of the ocean basin