Visual Interpretation of the Meaning of kcat/KM in Enzyme Kinetics

kcat and kcat/KM are the two fundamental kinetic parameters in enzyme kinetics. kcat is the first-order rate constant that determines the reaction rate when the enzyme is fully occupied at a saturating concentration of the substrate. kcat/KM is the second-order rate constant that determines the reaction rate when the enzyme is mostly free at a very low concentration of the substrate. Both parameters provide critical information on how the enzyme lowers the energy barriers along the reaction pathway for catalysis. However, it is surprising how often kcat/KM is used inappropriately as a composite parameter derived by dividing kcat with KM to assess both catalytic power and affinity to the substrate of the enzyme. The main challenge in explaining the true meaning of kcat/KM is the difficulty to demonstrate how the reaction energetics of enzyme catalysis determines kcat/KM in a simple way. Here, I report a step-by-step demonstration on how to visualize the meaning of kcat/KM on the reaction energy diagram. By using the reciprocal form of the expression of kcat/KM with the elementary rate constants in kinetic models, I show that kcat/KM is a harmonic sum of several kinetic terms that correspond to the heights of the transition states relative to the free enzyme. Then, I demonstrate that the height of the highest transition state has the dominant influence on kcat/KM, i. e. the step with the highest transition state is the limiting step for kcat/KM. The visualization of the meaning of kcat/KM on the reaction energy diagram offers an intuitive way to understand all the known properties of kcat/KM, including the Haldane relationship.

Effect of contact barrier height on performances of BaSi2 heterojunction and homojunction solar cells

The effects of contact barrier height on performances of Si/BaSi2 p–n heterojunction, BaSi2 p–n homojunction and Si/BaSi2/Si p–i–n heterojunction were numerical calculated. Band energy diagram, built-in electric field, carrier generation and carrier transportation distributed in the devices are comprehensively investigated. BaSi2 p–n homojunction solar cells are very sensitive to front contact barrier height due to the high light absorption coefficient of front p-BaSi2 layer. Si/BaSi2 p–n heterojunction and BaSi2 p–n homojunction solar cells with donor concentration [Formula: see text] less than [Formula: see text] are apparently affected by back contact barrier height. The ideal [Formula: see text]-Si/BaSi2/[Formula: see text]-Si p–n solar cell achieves a high [Formula: see text] of 1.131 V, suggesting a promising and alternative structure to gain excellent BaSi2-based solar cells once the Urbach tail states and defects can be effectively eliminated. The results help to fundamentally understand operation mechanism and provide intuitive guidance for achieving high-efficiency BaSi2 solar cells.

Tetrahydroxydiboron-Initiated Atom-Transfer Radical Cyclization

In this work, the first diboron reagent initiated atom-transfer radical cyclization was reported, in which the boryl radicals were generated by the homolytic cleavage of a B-B single bond weakened by the coordination of Lewis base. To clarify the role of carbonate and DMF in the cleavage of B-B bond, we calculated the free energy diagram of two pathways by density functional theory (DFT) investigations. The DFT calculation showed that the presence of carbonate facilitates the B-B bond cleavage to form boron radicals which can be further stabilized by DMF. Subsequent atom transfer cyclization initiated by stabilized dihydroxyboron radical are also energetically favored.

Development of ultraviolet-B long-lived persistent phosphors in Pr3+-doped garnets

A series of Pr3+-doped garnet-based UVB persistent phosphors have been designed and developed by combining conduction band engineering, the vacuum referred binding energy diagram and persistent energy transfer control.

CH4 dissociation on the Pd/Cu(111) surface alloy: A DFT study

The periodic four-layered model of the pure Cu(111) surface has been considered, and the effect of doping with palladium on CH4 dissociation has been investigated. The most stable adsorption geometries of CHx species (x = 1–4) and H atom on the PdCu(111) and pure Cu(111) surfaces have been obtained. Their computed adsorption energy results on the pure Cu(111) surface have been compared with the previously reported studies. Then, transition state geometries of CH4 dehydrogenation steps on both surfaces were calculated by the climbing image nudged elastic band method. Finally, the relative energy diagram for CH4 complete dehydrogenation has been represented. The results show that the PdCu(111) surface is more favorable than the Cu(111) surface in terms of the activation energies. The addition of Pd atoms to the Cu(111) surface significantly improves the catalytic activity. This knowledge can enable an efficient catalyst design at a lower cost using different strategies.

The order analysis for the two loop corrections to lepton MDM

The experimental data of the magnetic dipole moment(MDM) of lepton(e, $$\mu $$ μ ) is very exact. The deviation between the experimental data and the standard model prediction maybe come from new physics contribution. In the supersymmetric models, there are very many two loop diagrams contributing to the lepton MDM. In supersymmetric models, we suppose two mass scales $$M_{SH}$$ M SH and M with $$M_{SH}\gg M$$ M SH ≫ M for supersymmetric particles. Squarks belong to $$M_{SH}$$ M SH and the other supersymmetric particles belong to M. We analyze the order of the contributions from the two loop diagrams. The two loop triangle diagrams corresponding to the two loop self-energy diagram satisfy Ward-identity, and their contributions possess particular factors. This work can help to distinguish the important two loop diagrams giving corrections to lepton MDM.