12/29/2023 0 Comments Determination of isoelectric point![]() (this is old code so fairly naive, and not well cleaned, but additionally you can find there GUI for windows, some tips for implementation etc.). ![]() At the beginning it was written in C++, and in given link some information with sourcesĬode is available for educational purposes If you are interested in the implementation site of IPC, the old version can be accessed here. More advanced algorithm, implemented in ProMoST, takes into account localization of the charged amino acid: aaĪdditionally different pK values are used for N and C terminus depending on uncharged amino acid if applicable: Each source gives different pKs.ġ Arg was not included in the study and the average pK from all other scales was takenĢ NH2 and COOH were not included in the study and they were taken from Silleroģ Bjellqvist model include also different pK values for terminal residues Unfortunately, there is no agreement in this matter. Isoelectric point determination is usage of appropriate pK values. Nevertheless, one can approximately calculate protein isoelectric point which is ± 0.5 of exact isoelectric point. Therefore, they will become cystines, which do not express any charge. Which can oxidise and form disulfide bond in protein. Problematic is also the occurrence of cysteines (negative charge) It is mainly because many proteins areĬhemically modified (amino acids can be phosphorylated, methylated, acetyleted etc.), which change their charge. by titration One must first prepare a suspension which is sufficiently well dispersed to provide a stable zeta potential. The result will be almost surely different than real isoelectric point. Using above formulas, we can calculate theoretical isoelectric point. In situation when the gel pH and the protein isoelectric point are equal, proteins do not move at all. Higher than protein isoelectric point, the particles will migrate to the anode (negative electrode) and if the buffer pH is lower than isoelectric point they will go to the cathode. For example, during electrophoresis, direction of proteins migration, depends only from their charge. Our Book on Ultrasound for characterizing colloids contains a separate chapter on titrations.Generally, macromolecules are positively charged and on the other hand, above proteins isoelectric point, This protocol specifies minimum and maximum pH, number of points, direction of pH change. Software controls their functions according to the preliminary defined protocol. Precision of the injection is 1 microliter. These devices are capable of injecting chemicals into the sample when it is stirred. Generally, determination of isoelectric point requires automatic burettes. Isoelectric point of rutile is around pH=3.8, whereas for alumina it is pH=9.3 Titration pH titration of concentrated alumina and rutile slurries. Examplesįigure below illustrates results of pH titrations for alumina slurry at 4% vl and rutile slurry at 7% vl. Consequently, this is an absolute definition of the isoelectric point. Phase of electroacoustic signal rotates 180 degrees at this pH value. of Dispersion Science and Technology, 23, 5, 601-617 (2002)Įvidently, this study established that our instruments determine isoelectric point with accuracy of 0.1 pH unit.ĭetermination of the isoelectric point does not require calibration of the electroacoustic device. “ Analysis of the Isoelectric Point in Moderately Concentrated Alumina Suspensions Using Electroacoustic and Streaming Potential Methods“, J. There was detail study of various methods suitable for characterizing iso-electric points conducted by international group: Hackley, V., Patton, J., Lum, L., Wasche, R.J., Naito, M., Abe, H., Hotta, Y., and Pendse, H. Precision of zeta potential measurements with models DT-310 and DT-1202 is ± 0.1 mV. Consequently, Electroacoustic method has big advantage over other methods of zeta potential characterization. Precision of the zeta potential measurement is critical for achieving the high accuracy of the isoelectric point determination. Colloidal systems – Methods for Zeta potential determination provides definition of the iso-electric point. Furthermore, ISO Standard 13099, Parts 1 and 3: 2012. There is semi-empirical rule stating that system would be stable when its pH located beyond 2 pH units vicinity of the iso-electric point. ![]() Stability of many dispersions and emulsions are often related to the pH of the solution. ![]() Isoelectric point is a value of pH when zeta potential of the system equals 0. ![]()
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