tsüklimehhanisme

Tsüklimehhanisme, or cycle mechanism, refers to a mechanism in which a process proceeds through a repeating sequence of steps that returns the system to a starting state after each turnover. In such mechanisms, an active species is regenerated at the end of the cycle, allowing continuous operation under suitable conditions. The concept is used across chemistry, catalysis, and biochemistry to describe how complex transformations occur in a series of linked events.

In chemistry, catalytic cycles describe how a catalyst participates in a substrate transformation and is regenerated to begin another turn of the cycle. A cycle typically involves distinct steps such as substrate binding, chemical transformation to a reactive intermediate, release of product, and regeneration of the active catalyst. Common themes include the handling of intermediates, the balance of thermodynamics and kinetics, and the identification of the rate-determining step. Examples include metal-catalyzed cross-coupling and hydrogenation cycles, where steps such as oxidative addition, migratory insertion, and reductive elimination (or their equivalents) describe the flow of matter around the cycle.

In biochemistry, cyclic pathways such as the citric acid (Krebs) cycle exemplify tsüklimehhanisme. Acetyl-CoA enters a fixed sequence of enzymatic transformations, producing energy-rich molecules (NADH, FADH2, GTP) while regenerating oxaloacetate to continue the cycle. The efficiency and regulation of such cycles are central to cellular metabolism, energy production, and biosynthesis.

Studying tsüklimehhanmehanisme involves identifying intermediates, determining kinetic steps, and assessing thermodynamic feasibility, often using labeling, spectroscopy, and computational methods.