Stopped flow
Encyclopedia
A stopped flow instrument is a rapid mixing device used to study the chemical kinetics
of a reaction in solution. After two or more solutions containing the reagent
s are mixed, they are studied by whatever experimental methods are deemed suitable. Different forms of spectroscopy
and scattering
of radiation are common methods used. The dead time is the time between the end of mixing the two solutions and the beginning of observation of the kinetics of the reaction. The usual dead time of a stopped flow apparatus is 1-2 milliseconds but some new devices have been developed that have dead times of 0.3-0.6 ms.
A stopped flow instrument coupled to either a circular dichroism
spectrometer or a fluorescence spectrometer
is often used in the field of protein folding
, to observe rapid unfolding and/or refolding of proteins.
In a quenched flow instrument, the reaction is stopped after a certain amount of time has passed after mixing. The stopping of the reaction is called quenching and it can be achieved by various means, for example by mixing with another solution, which stops the reaction (chemical quenching), quickly lowering the temperature (freeze quenching) or even by exposing the sample to light of a certain wavelength (optical quenching).
Chemical kinetics
Chemical kinetics, also known as reaction kinetics, is the study of rates of chemical processes. Chemical kinetics includes investigations of how different experimental conditions can influence the speed of a chemical reaction and yield information about the reaction's mechanism and transition...
of a reaction in solution. After two or more solutions containing the reagent
Reagent
A reagent is a "substance or compound that is added to a system in order to bring about a chemical reaction, or added to see if a reaction occurs." Although the terms reactant and reagent are often used interchangeably, a reactant is less specifically a "substance that is consumed in the course of...
s are mixed, they are studied by whatever experimental methods are deemed suitable. Different forms of spectroscopy
Spectroscopy
Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...
and scattering
Scattering
Scattering is a general physical process where some forms of radiation, such as light, sound, or moving particles, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which they pass. In conventional use, this also includes deviation of...
of radiation are common methods used. The dead time is the time between the end of mixing the two solutions and the beginning of observation of the kinetics of the reaction. The usual dead time of a stopped flow apparatus is 1-2 milliseconds but some new devices have been developed that have dead times of 0.3-0.6 ms.
A stopped flow instrument coupled to either a circular dichroism
Circular dichroism
Circular dichroism refers to the differential absorption of left and right circularly polarized light. This phenomenon was discovered by Jean-Baptiste Biot, Augustin Fresnel, and Aimé Cotton in the first half of the 19th century. It is exhibited in the absorption bands of optically active chiral...
spectrometer or a fluorescence spectrometer
Fluorescence spectroscopy
Fluorescence spectroscopy aka fluorometry or spectrofluorometry, is a type of electromagnetic spectroscopy which analyzes fluorescence from a sample. It involves using a beam of light, usually ultraviolet light, that excites the electrons in molecules of certain compounds and causes them to emit...
is often used in the field of protein folding
Protein folding
Protein folding is the process by which a protein structure assumes its functional shape or conformation. It is the physical process by which a polypeptide folds into its characteristic and functional three-dimensional structure from random coil....
, to observe rapid unfolding and/or refolding of proteins.
In a quenched flow instrument, the reaction is stopped after a certain amount of time has passed after mixing. The stopping of the reaction is called quenching and it can be achieved by various means, for example by mixing with another solution, which stops the reaction (chemical quenching), quickly lowering the temperature (freeze quenching) or even by exposing the sample to light of a certain wavelength (optical quenching).