It has been speculated that lead poisoning may have played a role in the fall of the Roman Empire: it is thought to have been caused by the concentration of grape juice in lead containers.
Though the introduction of lead-free gasoline has reduced damage to the environment, the annual production of lead continues to increase worldwide because lead is still used in batteries, glass, and electronic components. However, there has thus far been little research into what, at a molecular level, causes the toxic effects of lead. French researchers have now applied quantum chemistry to very simple enzyme models and gained new insights. As they have reported in Angewandte Chemie, it seems that the lead¡¯s ¡°electron shield¡± is the main culprit.
Lead does the most damage to the nervous system, kidneys, liver, brain, and blood. These kinds of damage are especially severe for children as they can be irreversible. Complexation agents that grab onto the metal cations are used as antidotes. However, these agents are not lead-specific, meaning that they also remove other important metal cations from the body.
C. Gourlaouen and O. Parisel (Laboratoire de Chimie Th¨¦orique, Universit¨¦ Paris 6) took a closer look at two proteins to which lead likes to bind. Calmodulin, a calcium-binding protein, plays an important role in regulating and transporting the calcium cation in the human body. A calcium ion binds to seven ligands at the active centers of the enzyme. If one of the four possible calcium ions of calmodulin is replaced by lead, the lead ion remains roughly heptacoordinated, but this active center becomes distorted and inefficient; the three remaining sites get a reduced efficiency.
¦Ä-Aminolevulinic acid dehydratase is essential for the biosynthesis of hemoglobin. Inhibition of this enzyme disrupts the formation of blood to the point of anemia. At the active center, a zinc ion binds to four ligands, three of which involve a sulfur atom. When lead replaces zinc, it only binds to the three sulfur atoms. The reason for this is the emerging free electron pair of the lead cation. It acts as an electronic shield on one side, pushing away the fourth ligand. Such a dramatic geometrical distortion at the active center could explain why lead inhibits this enzyme.
The different behavior of lead in these two enzymes demonstrates that it can enter into complexes in which the metal¨Cligand bonds can either point in all directions, or into only one hemisphere, while the other hemisphere is filled by the free electron pair. This observation may help in the design of future lead-specific antidotes.
Author: Olivier Parisel, Universit¨¦ Pierre et Marie Curie, Paris VI (France), http://www.lct.jussieu.fr/rubrique13.html
Title: Is an Electronic Shield at the Molecular Origin of Lead Poisoning? A Computational Modeling Experiment
Angewandte Chemie International Edition 2007, 46, No. 4, 553¨C556, doi: 10.1002/anie.200603037
Funding of Collaborative Research Center developing nanomaterials for cancer immunotherapy extended
28.06.2017 | Johannes Gutenberg-Universität Mainz
Zeolite catalysts pave the road to decentral chemical processes Confined space increases reactivity
28.06.2017 | Technische Universität München
An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.
Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...
Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.
Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...
Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.
As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...
Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.
With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...
Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine
Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...
19.06.2017 | Event News
13.06.2017 | Event News
13.06.2017 | Event News
28.06.2017 | Physics and Astronomy
28.06.2017 | Physics and Astronomy
28.06.2017 | Health and Medicine