isoelectric point

(noun)

The pH at which a particular molecule or surface carries no net electrical charge

Related Terms

  • anode
  • cathode

Examples of isoelectric point in the following topics:

  • The Effect of pH on Solubility

    • The pH at which the net charge is neutral is called the isoelectric point, or pI (sometimes abbreviated to IEP).
    • Proteins can therefore be separated according to their isoelectric point.
    • In a method called isoelectric focusing, proteins are run through a gel that has a pH gradient.
    • For example, a protein that is in a pH region below its isoelectric point will be positively charged and so will migrate towards the cathode (negative charge).
    • At this point, it has no net charge, and so it stops moving in the gel.
  • α-Amino Acids

    • All three compounds are soluble in organic solvents (e.g. ether) and have relatively low melting points.
    • These differences all point to internal salt formation by a proton transfer from the acidic carboxyl function to the basic amino group.
    • At intermediate pH's the zwitterion concentration increases, and at a characteristic pH, called the isoelectric point (pI), the negatively and positively charged molecular species are present in equal concentration.
    • The isoelectric points range from 5.5 to 6.2.
    • As defined above, the isoelectric point, pI, is the pH of an aqueous solution of an amino acid (or peptide) at which the molecules on average have no net charge.
  • Peptides & Proteins

    • As expected, the free amine and carboxylic acid functions on a peptide chain form a zwitterionic structure at their isoelectric pH.
  • Wilson's Fourteen Points

  • Point-Slope Equations

    • The point-slope equation is another way to represent a line; to use the point-slope equation, only the slope and a single point are needed.
    • The point-slope form is great if you have the slope and only one point, or if you have two points and do not know what the $y$-intercept is.
    • Then plug this point into the point-slope equation and solve for $y$ to get:
    • Write an equation of a line in Point-Slope Form (given two points)  Convert to Slope-Intercept Form
    • Plug this point and the calculated slope into the point-slope equation to get: $y-6=-2[x-(-3)]$.
  • Electric Field from a Point Charge

    • A point charge creates an electric field that can be calculated using Coulomb's law.
    • The electric field of a point charge is, like any electric field, a vector field that represents the effect that the point charge has on other charges around it.
    • If the charge is positive, field lines point radially away from it; if the charge is negative, field lines point radially towards it .
    • The electric field of a point charge is defined in radial coordinates.
    • The positive r direction points away from the origin, and the negative r direction points toward the origin.
  • Linear Perspective

    • A drawing has one-point perspective when it contains only one vanishing point on the horizon line.
    • These parallel lines converge at the vanishing point.
    • A drawing has two-point perspective when it contains two vanishing points on the horizon line .
    • This third vanishing point will be below the ground.
    • Four-point perspective, also called infinite-point perspective, is the curvilinear variant of two-point perspective.
  • Boiling Point Elevation

    • The boiling point of a solvent is elevated in the presence of solutes.
    • This is referred to as boiling point elevation.
    • The extent of the boiling point elevation can be calculated.
    • In this equation, $\Delta T_b$ is the boiling point elevation, $K_b$ is the boiling point elevation constant, and m is the molality of the solution.
    • The boiling point of a pure liquid.
  • Stress and Strain

    • A point charge creates an electric field that can be calculated using Coulomb's Law.
    • The electric field of a point charge is, like any electric field, a vector field that represents the effect that the point charge has on other charges around it.
    • If the charge is positive, field lines point radially away from it; if the charge is negative, field lines point radially towards it.
    • The electric field of a point charge is defined in radial coordinates.
    • The positive r direction points away from the origin, and the negative r direction points toward the origin.
  • Maximum and Minimum Values

    • The second partial derivative test is a method used to determine whether a critical point is a local minimum, maximum, or saddle point.
    • The second partial derivative test is a method in multivariable calculus used to determine whether a critical point $(a,b, \cdots )$ of a function $f(x,y, \cdots )$ is a local minimum, maximum, or saddle point.
    • For example, if a bounded differentiable function $f$ defined on a closed interval in the real line has a single critical point, which is a local minimum, then it is also a global minimum (use the intermediate value theorem and Rolle's theorem).
    • Its only critical point is at $(0,0)$, which is a local minimum with $f(0,0) = 0$.
    • Apply the second partial derivative test to determine whether a critical point is a local minimum, maximum, or saddle point
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