Middle Ordovician astrochronology decouples asteroid breakup from glacially-induced biotic radiations

Meso-Cenozoic evidence suggests links between changes in the expression of orbital changes and millennia-scale climatic- and biotic variations, but proof for such shifts in orbital cyclicity farther back in geological time is lacking. Here, we report a 469-million-year-old Palaeozoic energy transfer from precession to 405 kyr eccentricity cycles that coincides with the start of the Great Ordovician Biodiversification Event (GOBE). Based on an early Middle Ordovician astronomically calibrated cyclostratigraphic framework we find this orbital change to succeed the onset of icehouse conditions by 200,000 years, suggesting a climatic origin. Recently, this icehouse was postulated to be facilitated by extra-terrestrial dust associated with an asteroid breakup. Our timescale, however, shows the meteor bombardment to post-date the icehouse by 800,000 years, instead pausing the GOBE 600,000 years after its initiation. Resolving Milankovitch cyclicity in deep time thus suggests universal orbital control in modulating climate, and maybe even biodiversity accumulation, through geological time.

Supplemental Material: Orbital control of Pleistocene euxinia in Lake Magadi, Kenya

Comparison of Lake Magadi euxinia with global paleoclimate and orbital parameters, photography of selected core intervals, geochemical data, and statistical analyses.<br>

Supplemental Material: Orbital control of Pleistocene euxinia in Lake Magadi, Kenya

Comparison of Lake Magadi euxinia with global paleoclimate and orbital parameters, photography of selected core intervals, geochemical data, and statistical analyses.<br>

Catalysis by the JmjC histone demethylase KDM4A integrates substrate dynamics, correlated motions and molecular orbital control

The second sphere residues and regions of the protein in histone demethylase enzymes that makes correlated motion with the active site contribute to efficient catalysis.

Quantum-chemical simulation of the interaction of 2-methyl-5,7-dinitrobenzo[d]oxazole with tetrahydride borate ion by DFT method

The aim of the work was quantum chemical modeling by the theory of the functional density functional of the interaction of 2-methyl-5,7-dinitrobenzo[d]oxazole with tetrahydride borate ion. For this, geometric optimization and calculation of the total energies of the 2-methyl-5,7-dinitrobenzo[d]oxazole molecule in the gas phase and water were carried out using the DFT/B3LYP/aug-cc-pVDZ method. To determine the likely reaction centers for a nucleophile attack, atomic charges according to Mulliken and NBO charges in the molecule of the initial substrate were established. The largest positive charges according to Mulliken in the studied molecule, both in the gas phase and in water, are concentrated on the carbon atoms C4 and C6, whereas in the case of NBO analysis, such is the carbon atom C2. Analysis of nucleophilic atomic frontal electron densities on the atoms of the substrate showed that from the point of view of orbital control, the attachment of a nucleophile is most likely to the carbon atom in the 4 position. The data obtained are consistent with previous experimental studies in which a rigid base – methoxide ion is attached to a carbon atom C2, which is a rigid acid reaction center, and a reaction with a soft base – tetrahydride borate ion proceeds along softer acid centers – carbon atoms C4 and C6 of the benzene ring. The calculation of the total energies of the proposed -adducts allowed us to establish that the most thermodynamically stable structure when one hydride ion is attached to the 2-methyl-5,7-dinitrobenzo[d]oxazole molecule is the product of nucleophile addition to the C4 carbon atom, and in the case of two hydride ions – at positions 4 and 6 of the annelated benzene ring activated by nitro groups. Thus, the calculation of the Mulliken charges, as well as the values of the nucleophilic atomic frontal electron densities at the atoms of the substrate, best reflects the course of the reaction under conditions of orbital control with a tetrahydroborate ion, and NBO charges are better suited to describe the course of the reaction under conditions of charge control.