1. Chapter Two Water: The Solvent for Biochemical Reactions
Paul D. Adams University of Arkansas

2. What makes water polar? What is a polar bond:
• Electrons are unequally shared, more negative charge found closer to one atom.
• Due to difference in _________________________of atoms involved in bond.

3. Electronegativity
__________________: a measure of the force of an atom’s attraction for electrons it shares in a chemical bond with another atom
Oxygen and Nitrogen, ____________ electronegative than carbon and hydrogen
_______________ is most electronegative (4)

4. Polar Bonds & Molecules
Molecules such as CO2 have polar __________ but, given their geometry, are nonpolar _______; that is, they have a __________ dipole moments

5. Solvent Properties of H2O
_________ compounds (e.g.,KCl) and low-molecular- weight ________ covalent compounds (e.g., C2H5OH and CH3COCH3) tend to dissolve in ______________
The underlying principle is electrostatic ________ of _____________ charges; the positive dipole of water for the negative dipole of another molecule, etc.
____________ interaction: e.g., KCl dissolved in H2O
____________ interactions: e.g., ethanol or acetone dissolved in H2O
____________ interactions: weak and generally do not lead to solubility in water

6. Hydration Shells Surrounding Ions in Water

7. Ion-dipole and Dipole-dipole Interactions
• ____________ and ____________ interactions help ionic and polar compounds dissolve in water

8. Solvent Properties of H2O
____________ : water-loving
tend to dissolve in water
____________ : water-fearing
tend not to dissolve in water
____________ : characteristics of both properties
molecules that contain one or more ____________ and one or more ____________ regions, e.g., sodium palmitate

9. Amphipathic molecules
• both ____________ and ____________ character
Interaction between ____________ molecules is very weak, called van der Waals interactions

10. Micelle formation by amphipathic molecules
Micelle: a ____________ arrangement of organic molecules in ___________ solution clustered so that
their ____________ parts are buried inside the sphere
their ____________ parts are on the surface of the sphere and in contact with the water environment
formation depends on the attraction between ____________ ____________ ____________

11. Examples of Hydrophobic and Hydrophilic Substances

12. Hydrogen Bonds
Hydrogen bond: the attractive interaction between dipoles when:
positive end of one dipole is a hydrogen atom bonded to an atom of high electronegativity, most commonly O or N, and
the negative end of the other dipole is an atom with a lone pair of electrons, most commonly O or N
Hydrogen bond is ______________________

13. Interesting and Unique Properties of Water
• Each water molecule can be involved in ___ hydrogen bonds: ___ as donor, and ___ as acceptor
• Due to the ____________ arrangement of the water molecule (Refer to Figure 2.1).

14. Hydrogen Bonding
Even though hydrogen bonds are ___________ than covalent bonds, they have a significant effect on the physical properties of hydrogen-bonded compounds

15. Other Biologically Important Hydrogen bonds
• Hydrogen bonding is important in _______________ of 3-D structures of biological molecules such as: DNA, RNA, proteins.

16. Acids, Bases and pH
Acid: a molecule that behaves as a ____________ ____________
Strong base: a molecule that behaves as a ____________ ____________

17. Acid Strength
One can derive a numerical value for the strength of an acid (amount of hydrogen ion released when a given amount of acid is dissolved in water).
Describe by Ka:
Written correctly,

18. Ionization of H2O and pH
Lets quantitatively examine the dissociation of water:
• Molar concentration of water (55M)
• Kw is called the ion product constant for water.
• Must define a quantity to express hydrogen ion concentrations…pH

19. Henderson-Hasselbalch
Equation to connect Ka to pH of solution containing both acid and base.
We can calculate the ratio of weak acid, HA, to its conjugate base, A-, in the following way

20. Henderson-Hasselbalch (Cont’d)
Henderson-Hasselbalch equation
From this equation, we see that
when the concentrations of weak acid and its conjugate base are equal, the pH of the solution equals the pKa of the weak acid
when pH < pKa, the weak acid predominates
when pH > pKa, the conjugate base predominates

21. Titration Curves a monoprotic acid releases one H+ per mole
________________ : an experiment in which measured amounts of acid (or base) are added to measured amounts of base (or acid)
_______________________ : the point in an acid-base titration at which enough acid has been added to exactly neutralize the base (or vice versa)
a monoprotic acid releases one H+ per mole
a diprotic acid releases two H+ per mole
a triprotic acid releases three H+ per mole

22. Buffers
buffer: a solution whose ________ resists change upon addition of either more acid or more base
consists of a weak acid and its conjugate base
Examples of acid-base buffers are solutions containing
CH3COOH and CH3COONa
H2CO3 and NaHCO3
NaH2PO4 and Na2HPO4

23. Buffer Range
A buffer is effective in a range of about +/- 1 pH unit of the pKa of the weak acid

24. Buffer Capacity
Buffer capacity is related to the ____________ of the weak acid and its conjugate base
the greater the concentration of the weak acid and its conjugate base, the greater the buffer capacity

25. Naturally Occurring Buffers
____________ is the principal buffer in cells
____________ is an important (but not the only) buffer in blood
____________ can result in increased blood pH
____________ can result in decreased blood pH
(Biochemical Connections p. 60)

26. Selecting a Buffer The following are typical criteria suitable pKa
no interference with the reaction or detection of the assay
suitable ionic strength
suitable solubility
its non-biological nature

27. Laboratory Buffers