ENERGY OF THE INITIATION REACTION OF CATIONIC POLYMERIZATION OF 2-METHYLPENTENE-1 IN THE PRESENCE OF AQUACOMPLEX OF ETHYLALUMINUM CHLORIDE AND HEPTANE

The ab initio 3.21G method was used to study the initiation mechanism of 2-methylpentene-1 under the action of a complex catalyst AlClCH - HO in heptane of stoichiometric composition 1:1:1:1. The energetics of this reaction is estimated, the values of its energy barrier and enthalpy are obtained.

A QM/MM Study on the Initiation Reaction of Firefly Bioluminescence—Enzymatic Oxidation of Luciferin

Among all bioluminescent organisms, the firefly is the most famous, with a high luminescent efficiency of 41%, which is widely used in the fields of biotechnology, biomedicine and so on. The entire bioluminescence (BL) process involves a series of complicated in-vivo chemical reactions. The BL is initiated by the enzymatic oxidation of luciferin (LH2). However, the mechanism of the efficient spin-forbidden oxygenation is far from being totally understood. Via MD simulation and QM/MM calculations, this article describes the complete process of oxygenation in real protein. The oxygenation of luciferin is initiated by a single electron transfer from the trivalent anionic LH2 (L3−) to O2 to form 1[L•2−…O2•−]; the entire reaction is carried out along the ground-state potential energy surface to produce the dioxetanone (FDO−) via three transition states and two intermediates. The low energy barriers of the oxygenation reaction and biradical annihilation involved in the reaction explain this spin-forbidden reaction with high efficiency. This study is helpful for understanding the BL initiation of fireflies and the other oxygen-dependent bioluminescent organisms.

On Criticality for a Generalized Couette Flow of a Branch-Chain Thermal Reactive Third-Grade Fluid with Reynold’s Viscosity Model

This research considers the third-grade liquid flow and criticality branched-chain of a thermal reaction in a Couette generalized medium with a nonlinear viscosity model. A dimensionless transformation of the system momentum and heat equations are carried out. Compared with the diffusion coefficient, the flow is stimulated by initiation reaction rate, reaction branch-chain order, non-Newtonian term, thermal Grashof number, and pressure gradient. The reactive fluid is fully exothermic with consumption of the material, and the heat exchange in the system is greater than the exchange of heat with the ambient. A semianalytical collocation weighted residual scheme is employed for the branch-chain slice bifurcation, dimensionless energy, and momentum solutions. The results show that exponential decreases in the thermal fluid viscosity can help in controlling the boundless heat produced by the Frank-Kamenetskii term and initiation reaction rate. Therefore, the results will help in stimulating positive combustion processes.

Kinetic study of HTPB (Hydroxyl Terminated Polybutadiene) Synthesis Using Infrared Spectroscopy

A kinetic study of HTPB synthesis by radical polymerization of butadiene with hydrogen peroxide initiator was conducted using infrared spectroscopy. HTPB conversion was determined based on the conjunction termination rate constant, and all polymerization kinetics were evaluated to identify the constant. All polymerization steps (decomposition, initiation, propagation, conjunction, and proportional termination) can be evaluated based on polymer conversion and functionality from data provided by infrared spectroscopy. The investigation variables included the initial molar ratio of initiator to monomer (H2O2/butadiene) and the reaction temperature. These steps were assumed as the first-order reactions, giving constant reaction rates of kd, ka, kp, kt, ktc, and ktd. The reaction rates obtained for these constants were 4.2 × 10–5 sec–1, 8.9 × 10–4, 7.7 × 103, 8.5 × 107, 3.2 × 107 and 5.3 × 107 L mol–1 sec–1, respectively, with activation energy of 7608, 14188, 2247, 105, 87 and 135 kJ mol–1, respectively. The determining step of the reaction rate was identified as the initiation reaction. HTPB conversion can be measured if all polymerization kinetics constants have been evaluated.

Long-range interdomain communications in eIF5B regulate GTP hydrolysis and translation initiation

Translation initiation controls protein synthesis by regulating the delivery of the first aminoacyl-tRNA to messenger RNAs (mRNAs). In eukaryotes, initiation is sophisticated, requiring dozens of protein factors and 2 GTP-regulated steps. The GTPase eIF5B gates progression to elongation during the second GTP-regulated step. Using electron cryomicroscopy (cryo-EM), we imaged an in vitro initiation reaction which is set up with purified yeast components and designed to stall with eIF5B and a nonhydrolyzable GTP analog. A high-resolution reconstruction of a “dead-end” intermediate at 3.6 Å allowed us to visualize eIF5B in its ribosome-bound conformation. We identified a stretch of residues in eIF5B, located close to the γ-phosphate of GTP and centered around the universally conserved tyrosine 837 (Saccharomyces cerevisiae numbering), that contacts the catalytic histidine of eIF5B (H480). Site-directed mutagenesis confirmed the essential role that these residues play in regulating ribosome binding, GTP hydrolysis, and translation initiation both in vitro and in vivo. Our results illustrate how eIF5B transmits the presence of a properly delivered initiator aminoacyl-tRNA at the P site to the distant GTPase center through interdomain communications and underscore the importance of the multidomain architecture in translation factors to sense and communicate ribosomal states.