Buffers

Amphipathic molecules are biological molecules such as proteins, certain vitamins, steroids, and phospholipids that are polar and nonpolar.

Fahrenheit formula to convert celsius into F is 1.8 x C +32

Henderson-Hasselbach Equation: pH and pKa. pH = -log [H+]

Buffers are aqueous systems that resist changes in pH when small amounts of acid or base are added. Isoelectric point is the point at which, for example, the concentration of acetic acid and acetate ions are equal. At that point there is no net charge since the pH is equal to the pKa. Buffers have both an intensive and extensive properties. The intensive property is a function of the pKa value of the buffer acid or base. The extensive property is known as buffer capacity which is dependent on the concentration of buffer solution. A buffer capaciy of 1 is when 1 mol of acid or alkali is added to 1 liter of buffer and pH changes by 1 unit. The buffer capacity of mixed weak acid-base buffer is much greater when the individual pKa values are in close proximity with each other. Buffer capacity of a mixture of buffers is additive.

Buffers must meet a certain criteria in order for them to be useful.

  • Their pka should be between 6-8

  • Should be ± 1 of the pka of the the drug that is used

  • Exhibit high water solubility and minimal solubility in organic solvents. Needs to be that way so that buffers can dissolve in what the body is made most of, %70 water.

  • Should NOT permeate cell membranes

  • Should NOT exhibit toxicity towards cells

  • Should NOT interfere with any biological process

  • Salt effect should be minimal, they interfere the electrolasticity of the bonds due to their charges associated.

  • Ionic composition of the medium and temp should have a minimal effect of buffering capacity. Check the pH’s temperature.

  • Should be stable and resistant to enzymatic degredation

  • Should NOT absorb either in the visible or in the UV region. If visible or UV is used, if a buffer has aromatic then it will interfere with the visible or UV spectroscopy.

pKa is the concentration at which it is half ionized. You dont want pKa to close to the physiological pH as a drug will only ionize to 50%. Ideally we want a drug to be 99% or 100% ionized so that it can reach the drug target.

When studying calcium related drugs, phosphate buffers should not be used since phosphate breaks down calcium bonds.

When choosing a buffer, take these things into consideration - Purity and costs