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..Dialysis is an important means by which small molecules can pass through, while large molecules cannot be separated by the principle of semi-permeable membranes. It is common practice to put a mixture of small molecules and large molecules into
dialysis bags made of semi-
and sink in large amounts of water. The small molecules in the bag continue to enter the external solvent through the membrane until the balance is achieved. If the solvent of the tylow water dialysis or constantly changing the dialysis bag can make the mixture in the bag almost free of small molecules. The speed of dialysis is influenced by a number of factors. These factors are discussed roughly below., membrane
1, material fire cotton glue is the most commonly used dialysis bag material. Various specifications of fire cotton plastic bags have been made into merchandise for sale. You can also use colored paper instead of fire cotton glue.2, prepare a proper size and length of dialysis tube in alkaline
EDTA
solution boiling for 30 minutes to avoid the loss of activity of the molecules to be dialysis. Then, wash the dialysis tube with distilled water. At one end of the ligation tube, fill the material under study with a dialysis tube (bag) and then lid the top. Dialysis is best carried out in newly prepared tubes, as wet dialysis bags are highly susceptible to micro-biological infections. If the dialysis bag must be kept, trace amounts of benzoic acid should be added to the solution.
3, the permeability of the dialysis bag varies depending on the size of the bag and the method of pre-treatment. However, when dialysis is overnight, the semidialysis membrane can generally allow the relative molecular mass (Mr) of less than 30,000
compounds
pass. In fact, there are no strict boundaries, and slightly larger molecules pass through the membrane when dialysis time is extended. There is a range of commodity materials with higher dialysis speeds and finer permeable ranges for fine separation.
. Second, solvent 1, aqueous solution generally speaking, dialysis speed in distilled water is the largest, although usually requires a specific pH and ion strength of the water solution to stabilize the molecules studied.
2, large molecule solution dialysis water will enter the dialysis bag, so the dialysis bag should be filled to avoid dialysis material too diluted. If an inactive polymer compound such as polyethylene alcohol 6000 is used instead of the usual aqueous solution as a solvent, water will seep out of the dialysis bag during dialysis, which can be used overnight to concentrate the 200mL solution to a few mL., physical conditions
1, temperature dialysis speed is also affected by temperature, the higher the temperature, the faster the dialysis speed. As the temperature is increased, the viscosity of the solvent decreases and the diffusion speed increases. In addition, many large molecules are sensitive to temperature, so dialysis
such as
proteins and proteins is usually performed at low temperatures.2, pressure molecules and small molecules are also affected by the pressure gradient as they pass through the membrane. The dialysis bag can be placed in a vacuum (not in the solution) and opened at one end of the dialysis bag, at which point water and small molecules seep out of the dialysis bag to form a sofiltration
solution, while the large molecules left in the dialysis bag are concentrated. This process is called ultrafiltration.
. Fourth, Donnan membrane balancedue to the presence of large molecule electrolytes, so that the general electrolyte is not equally distributed on both sides of the semi-permeable membrane average state, called membrane balance.
the permeable pressure of the protein solution is related to the pH of the solution. Under acidic pH, proteins are present in cations with a positive charge, while under alkaline pH, they are present in anions with a negative charge.
When the protein salt solution dialysis, the charged protein molecules can not pass through the semi-permeable membrane, and the opposite anions or cations in the solution will be through the semi-permeable membrane to balance the charge, which leads to uneven distribution on both sides of the ion membrane, at the same time related to pH changes. This phenomenon is called the Dongnan effect, also known as distribution, and produces pH changes at the same time.
this phenomenon is called the Dongnan effect, also known as dongnan balance. Such as negatively charged protein salt solution to hydrodialysis, the protein can not pass through the dialysis bag, and its anti-ions can pass, resulting in excessive cations in the environmental medium. In order to remain neutral, the water breaks down the hydrogen ions and moves them into the dialysis bag, and the pH of the protein part decreases and the pH of the water part rises.
, if the protein is positively charged, the pH changes the opposite. The Dongnan effect can lead to protein precipitation or denaturation and is therefore undesirable. In order to reduce the Dongnan effect, dialysis is usually performed on salt solutions with appropriate concentrations.
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