Simón Bolívar University

About: Simón Bolívar University is a education organization based out in Caracas, Venezuela. It is known for research contribution in the topics: Population & Crystallization. The organization has 5912 authors who have published 8294 publications receiving 126152 citations.

(Pentamethylcyclopentadienyl)iridium-PTA (PTA = 1,3,5-Triaza-7-phosphaadamantane) Complexes and Their Application in Catalytic Water Phase Carbon Dioxide Hydrogenation

Abstract: The water-soluble iridium(III) complexes [Cp*Ir(PTA)Cl2] (1) and [Cp*Ir(PTA)2Cl]Cl (2) (PTA = 1,3,5-triaza-7-phosphaadamantane) have been synthesised and characterised by spectroscopy and X-ray crystallography. The complexes were evaluated as catalyst precursors for the hydrogenation of CO2 and hydrogen carbonate in aqueous solutions, in the absence of amines or other additives, under relatively mild conditions. Complex 1 performed poorly while 2 catalyses the hydrogenation with moderate activity. The catalytically active monohydride [Cp*Ir(PTA)2H]+ was identified by multinuclear NMR spectroscopy and its nature confirmed by independent synthesis.

Reproductive Biology of the Gregarious Mediterranean Vermetid Gastropod Dendropoma Petraeum

Abstract: The reproductive biology of the gregarious Mediterranean vermetid gastropod Dendropoma petraeum (Mollusca: Gastropoda) has been studied in the south-eastern coast of Spain. It apparently is a gonochorisric species with the sex ratio biased toward females (71%). A broad peak of more intense reproductive activity occurs in spring months and an inactive reproductive period during winter. The gonad of the males develops about two months before those of females, and storage of sperm by females has been observed. Internal fertilization takes place after the capture of pelagic spermatophores.The egg capsules lie free within the female mantle cavity, and females brood up to 86 capsules simultaneously (the highest number reported for any vermetid gastropod). The size of the capsules is somewhat variable and increases slightly from those containing first stages of development (mean = 678×579 μm) to those containing late stages (mean = 996×693 μm). Each egg capsule usually contains a single large egg or embryo, but sometimes two (8.2% of the capsules) or rarely three (0.24%). Production of egg capsules by females seems to be continuous throughout the reproductive period (from March to October).The unsegmented eggs measure from 440 to 507 μm in diameter (mean = 482) and are the largest reported for any vermetid gastropod. Nurse eggs are not present, and therefore most of the intracapsular nutrition comes from the internal yolk of the embryo.Development is lecithotrophic without a pelagic larval phase. The late intracapsular veliger stage metamorphoses within the capsule and hatching occurs at a crawling juvenile stage.

Sex ratio at birth deviations in modern Venezuela: The Trivers‐Willard effect

Abstract: This study evaluates the impact of the Trivers‐Willard (T‐W) effect on human populations, using demographic data collected from vital registration data in Venezuela. The evaluation of the sex ratio at birth (SRB) and of fetal and infant deaths supports the existence of T‐W effect in the Venezuelan population in extreme conditions. This T‐W effect was observable in the SRB but not at later ages and is related to the marital status of the mother. The results indicate that the investment in females associated with environmental adversity is greater than the investment in males associated with good environmental conditions.