Buffers II - Kevin Ahern's BB 450 Lecture #2 - 2016
1. Contact - [email protected] 2. Kevin's lectures with The Great Courses - https://www.thegreatcoursesplus.com/b... 3. Kevin's Lecturio videos for medical students - https://www.lecturio.com/medical-cour... 4. Course materials at https://kevingahern.com/biochemistry-... 5. Course video channel at • Introduction - Kevin Ahern's BB 450 Lectur... 6. Metabolic Melodies at https://teeheetime.com/category/lyric... 7. Kevin's Free Biochemistry books - https://kevingahern.com/biochemistry-... 8. Kevin's Pre-med Audio course on Listenable - https://listenable.io/web/courses/143... Highlights Buffers 1. Students should know the basic structures from organic chemistry. 2. Single carbon bonds are oriented in a tetrahedral shape. 3. Electronegativity is a measure of the "pull" a nucleus has for electons. 4. Unequal sharing of electrons gives rise to partial positive and partial negative charges. 5. Reduction is the gain of electrons by a substance. Oxidation is the loss of electrons by a substance. 6. Gibbs free energy allows us to determine the direction of a reaction. 7. Bonds between oxygen and hydrogen involve unequal sharing of electrons and thus partial positive and negative charges. These partial positive and negative charges attract each other. If hydrogen is involved, the resulting bond is called a hydrogen bond. Water is full of hydrogen bonds. 8. The term hydrophobic describes non-polar compounds that don't form hydrogen bonds with water and are insoluble in it. Hydrophilic compounds form hydrogen bonds with water and dissolve in it. 9. Amphiphilic compounds have part(s) that are hydrophobic and part(s) that are hydrophilic. 10. Amphiphilic compounds include glycerophospholipids and sphingolipids 11. Soaps form micelles in water. Glycerophospholipids and sphingolipids form lipid bilayers in water. 12. Proteins fold in water partly as a function of their hydrophobic and hydrophilic regions - hydrophilic amino acids tend to be on the outside and hydrophobic amino acids tend to be on the inside for proteins in aqueous environments. 13. Hydrogen bonds occur between many different structures - hydrogen of water and carbonyl group; hydrogen of an amine group and oxygen of water; hydrogen of alcohol and oxygen of water. 14. Hydrogen bonding allows water to dissolve ionic compounds. 15. Hydrogen bonds are much weaker bonds that are also important in biological molecules. H-bonds are weaker than covalent bonds, but are VERY important in stabilizing protein and DNA structures. 16. Covalent bonds are VERY strong bonds that hold atoms/molecules togethe - much stronger than hydrogen bondsr. Covalent bonds are the 'glue' that holds together biomolecules. 17. pH is a measure of the proton concentration in a solution. The pH is the negative log of the hydrogen ion concentration. The lower the pH, the higher the hydrogen ion concentration and the stronger the acid. pH + pOH = 14. The pOH is the negative log of the hydroxide ion concentration. The pKa is, therefore, the negative log of the Ka. The lower the pKa for an acid system (such as the acetic acid system discussed in class), the stronger the acid is. 18. Acid here refers to the molecule containing the most protons and salt refers to the acid which has lost a proton. 19. Acetic acid (HAc above) is a weak acid because it doesn't completely dissolve in water. HCl is a strong acid because it completely dissociates in water. 20. Addition of protons (from HCl, for example) to the HAc GOES TO H+ + Ac- system will drive the reaction to the left due to Le Chatelier's principle. This will INCREASE the amount of HAc and DECREASE the amount of Ac-. The total amount of HAc and Ac- will remain the same in a system (unless, of course one adds additional HAC or Ac- ) 21. Addition of NaOH (strong base) the same system will drive the reaction to the right, causing there to be LESS HAc and MORE Ac- 22. When protons are removed from the system by NaOH, HAc releases protons to make up the difference. 23. A buffer system will be at maximum capacity when the concentration of HAc equals that of Ac- (Weak Acid = Salt). 24. For a system in its buffering range (+/- 1 pH unit of pKa), addition of each HCl molecule will cause one mole/molecule salt to convert to one mole/molecule weak acid. Addition of each NaOH molecule will cause one mole/molecule weak acid to convert to one mole/molecule salt. 25. The Henderson Hassselbalch equation is pH = pKa + log ([Salt]/[Acid]). 26. Buffers are maximally effective (strongest) when the pH = pKa. Within one pH unit on either side of the pKa, a buffer is reasonably effective.
