Day 2: Acids/Bases and Acid/base Disorders Flashcards
Bronstead-Lowry definition of acid/base
Acid = proton donor
Base = Proton Acceptor
What are strong acids?
Essentially 100% dissociated (increase H+ significantly) HCl
What are strong bases
essentially 100% dissociated (increase in OH- significantly) NaOH
What are conjugate pairs?
Drugs have weak acids or bases and a drug that has both acidic and basic forms are the conjugate pairs
What is the pKa value?
The tendencu of the donor form of the pair to donate a proton.
is derived from the Ka and the Ka is the equilibrium constant that quantitates teh tendency of the donor form to donate its proton
What causes there to be a higher vs low Ka value?
If drug molecules are weak acids then they will have a low numerical value. (unlikely to donate a proton; base)
If a drug has a strong tendency to donate a protein the Ka will be higher and the log value will be lower. (donate a protein; acid)
What kind of molecules willl have a low pKa
Acids will have a lower pKa
Explain how the example of HQ has its conjugate base and how the pKa value determines the strength of its conjugate base
Q- (potential proton acceptor) is the conjugate base of HQ.
The strength of Q- as a proteon acceptor is inversely related to the strength of its conjugate acid.
EX: if the pKa is 4 it means its a stronger base (higher means higher base) than if the pKa was 2.
What is a major consideration for drug delivery ?
Whether or from where a drug will be absorbed from the digestive tract. This requires the ability of a molecule to pass thro lipophilic (hydrophobic) bio membranes
This is less likely to occur if the molecule is ionized. this makes it important to know the degree of ionization (charge) of the drug molecule within the body
Equation to find the pH
pH= -log[H+]
Equation for the pKa
pKa = -log_[H+][Q-]_/[HQ]
Equation to find pH using the pKa
pH= pKa+log[Q-]/[HQ]
How can you think about amines and carboxylic acids in terms if acids and bases
amines = bases
carboxylic acids = acids
What are the two forms of an amine and what are the charges of them
The acidic form (donor form, protonated form) is charged
the basic form (acceptor form, deprotonated form) is neutral
What is the forms of carboxylic acids and their charge?
Acidic form (donor form, protonayed form) is neutral
basic form (acceptor form, deprotonated form) is charged
Generally what are true for donors, or protonated forms?
- present at low pH
- on the left side of an equilibrium
- in the denominator of the Henderson-hasselbalch equation
What is the normal pH of arterial blood ?
7.40 with a reference range of 7.36-7.44)
What are the three major mechanisms that maintain pH?
- chemical buffering
- action of the lungs (respiratory regulation)
- action of the kidney (renal regulation)
What does the body do in order to prevent drastic changes in pH
It uses “buffering” by the action of weak acids and their conjugate bases that act to neutralize incoming H+ or incoming OH-
Explain how the body handles this in buffering its pH
If HA is a weak acid, it can donate a proton to water to yeild the conjugate acid and the weak base A-. If a strong acid is added to the system the rxn will move to the left (reducing the effect of excess H+)
If a base is added it will drive the rxn to the right
What is the bicarbonate buffer system?
Most important extracellular buffering system and the one generally considered cliniclally.
Carbonic acid (H2CO3) exists in very low concentrations in the body. For this reason CO2 is considered to be the weak acid in the system