isoelectric point

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