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In chemistry, quenching refers to any process which decreases the fluorescent intensity of a given substance. A variety of processes can result in quenching, such as excited state reactions, energy transfer, complex-formation and collisions. As a consequence, quenching is often heavily dependent on pressure and temperature.
Instead of a mechanical stopping system, the reaction is halted by quenching, where the products are immediately stopped by freezing, chemical denaturation, or exposure to a denaturing light source. Similar to the continuous-flow method, the time between mixing and quenching can be adjusted by varying the length of the reaction tube.
Relaxation from an excited state can also occur through collisional quenching, a process where a molecule (the quencher) collides with the fluorescent molecule during its excited state lifetime. Molecular oxygen (O 2 ) is an extremely efficient quencher of fluorescence because of its unusual triplet ground state.
For diffusion-limited quenching (i.e., quenching in which the time for quencher particles to diffuse toward and collide with excited particles is the limiting factor, and almost all such collisions are effective), the quenching rate coefficient is given by = /, where is the ideal gas constant, is temperature in kelvins and is the viscosity of ...
The Dexter energy transfer rate, , is indicated by the formula: = ′ [] where is the separation of the donor from the acceptor, is the sum of the Van der Waals radii of the donor and the acceptor, and ′ is the normalized spectral overlap integral, where normalized means that both emission intensity and extinction coefficient have been adjusted to unit area.
YFP fluorescence is sensitive to various small anions with relative potencies iodine > nitrate > chloride > bromide > formate > acetate. [2] YFP sensitivity to these small anions results from ground-state binding near the chromophore , [ 3 ] which apparently alters the chromophore ionization constant and hence the fluorescence emission.
Photobleaching is an important parameter to account for in real-time single-molecule fluorescence imaging in biophysics. At light intensities used in single-molecule fluorescence imaging (0.1-1 kW/cm 2 in typical experimental setups), even most robust fluorophores continue to emit for up to 10 seconds before photobleaching in a single step. For ...
In materials science, quenching is the rapid cooling of a workpiece in water, gas, oil, polymer, air, or other fluids to obtain certain material properties. A type of heat treating , quenching prevents undesired low-temperature processes, such as phase transformations, from occurring.