The Cameroon Line revisited: petrogenesis of continental basalts from lithospheric and asthenospheric mantle sources.

The volcanic activity of Mts Bambouto and Oku (Western Highlands) and of the Ngaoundere Plateau, in the continental sector of the Cameroon Volcanic Line, Equatorial West Africa, ranges in age from Oligocene to Recent. It is characterized by basanitic, alkali basaltic and transitional basaltic series. Mineral chemistry, major and trace element bulk-rock compositions, and geochemical modelling suggest that the magmatic series evolved mainly at low pressure (2–4 kbar) through fractional crystallization of clinopyroxene and olivine ± magnetite, at moderately hydrated (H2O = 0·5–1 wt %) and QFM (quartz–fayalite–magnetite) to QFM + 1 fO2 conditions. Basalts from Ngaoundere (Miocene to Quaternary) and from the early activity (31–14 Ma) of the Western Highlands have incompatible trace element and Sr–Nd isotopic compositions similar to those of oceanic Cameroon Line basalts, pointing to a similar asthenospheric mantle source. By contrast, the late (15–4 Ma) Western Highlands basanites and alkali basalts have anomalously high concentrations of Sr, Ba and P, and low concentrations of Zr, which are exclusive features of continental Cameroon basalts. The genesis of these latter magmas is consistent with derivation from an incompatible element enriched, amphibole-bearing lithospheric mantle source. Western Highlands basalts show a continuous spectrum from high to low Sr–Ba–P compositions, and may result from variable amounts of mixing between melts derived from an anhydrous lherzolite source (asthenospheric component) and melts from an amphibole-bearing peridotite source (lithospheric HSr component). New 40Ar/39Ar ages for Mts Oku and Bambouto basalts, combined with previous 40Ar/39Ar and K/Ar ages of basaltic and silicic volcanics, and with volcanic stratigraphy, suggest a NE–SW younging of the peak magmatic activity in the Western Highlands. This SW younging trend, extending from the Oligocene volcanism in northern Cameroon (e.g. Mt Oku) to the still active Mt Cameroon, suggests that the African plate is moving above a deep-seated mantle thermal anomaly. However, the age and location of the Ngaoundere volcanism does not conform to the NE–SW younging trend, implying that the continental sector of the Cameroon Volcanic Line cannot be easily interpreted as the surface expression of a single hotspot system

Synthesis of Structurally Simplified Analogues of Pancratistatin: Truncation of the Cyclitol Ring

Pancratistatin is a phenanthridone-type natural product isolated from several plants of the Amaryllidaceae family. Its potent antiproliferative, antivascular, antiviral, and antiparasitic properties have attracted the attention of synthetic, biological, and medicinal chemists. Pancratistatin’s low natural availability and complex structure have steered many of these research projects toward the preparation of its simplified synthetic analogues with useful levels of activity. In this work we have developed synthetic chemistry aimed at the preparation of pancratistatin analogues with a truncated cyclitol portion of the molecule. The described synthetic pathways are based on a highly anti-diastereoselective arylcuprate conjugate addition to γ-alkoxy-α,β-enoates and syn-selective azidation at the α-position of ester enolates. Analogues with the formally cleaved C3−C4 bond, and thus containing an open ring C, as well as a compound containing a truncated lactol moiety in lieu of the cyclitol, were prepared. Several of the analogues exhibited weak antiproliferative activity, with the highest potency observed in the case of the lactol analogue. From these results implications for the design of future pancratistatin analogues are discussed. Furthermore, the synthetic pathways can be used to construct pancratistatin-mimetic libraries, in which the cyclitol moiety is replaced by other cyclic motifs

Development of Enhanced Nanocomposite Preformed Particle Gels for Conformance Control in High-Temperature and High-Salinity Oil Reservoirs

In this paper, we describe the synthesis, characterization and evaluation of nanocomposite preformed particle gels (PPGs) for use as conformance control agents in high-temperature and high-salinity oil reservoirs. The chemical stability of conventional acrylamide (AM)-homopolymer-based PPGs was improved by incorporating an optimized ratio of new functional groups into their structure to withstand harsh reservoir conditions. The modified PPGs were synthesized via free radical crosslinking polymerization at room temperature using AM, vinylpyrrolidone (VP) and 2-acrylamido-2-methylpropane sulfonic sodium salt (AMPSNa) monomers and an N,N-methylenebis (acrylamide) (MBA) crosslinker. The mechanical properties of the PPGs were enhanced by adding a dispersion of modified bentonite (MB) to the formulation. The chemical and mechanical stabilities of the synthesized PPGs were evaluated at a high temperature (130 °C) and under high-salinity conditions using production water (with a TDS of 83 942.63 p.p.m.) and connate water (with a TDS of 254 873.09 p.p.m.), both of which were collected from an oil reservoir. The experimental results showed that PPGs prepared with 30 wt.% of a 1:1:1 molar mass ratio of AM, VP and AMPS monomers with 0.5 wt.% MBA and 2 wt.% MB exhibited the highest stability of the investigated PPGs under oil reservoir conditions