Lecture 2 : Water and Biological Buffers Flashcards
What is the shape, hybrid orbital orientation. and degree of a water molecule?
How many H-bonds can form per water?
4 bonds
2 on Hydrogen - 2 on electron pairs
How much strength is required to break a hydrogen bond?
20 kJ/mol
When water freezes what is the organized form?
Hexagonal, contains maximal hydrogen bonds/ water molecules, forcing the water molecules into equidistant arrangement
Is waters dielectric constant high or low and why does it matter?
Waters high dielectric constant reduces attraction between oppositely charged ions in salt crystals; almost not attraction at large ( >40 nm) distances.
What is the equation for strength of ionic interaction
F = (Q1 * Q2)/ (ε * r2)
Does the mixture of an ionic compound and water lower or increase entropy?
Strong electrostatic interactions between the solvated ions and water molecules lower the total energy of the system.
Entropy increases
What are the two components of van der Waals interaction
- Attractive force (London dispersion, which depends on the polarizability
- Repulsive force (steric repulsion) which depends on the size of atom
When do attractive forces and repulsive forces dominate for van der Waals?
Attraction dominates at longer distances, typically .4 - .7 nm
Repulsion dominates at very short distances
Why are van der Walls interactions important?
- Determines steric complementarity
- Stabilizes biological macromolecules (stacking in DNA)
- Facilitates binding of polarizable ligands
What is the hydrophobic effect?
refers to the association or interaction of nonpolar molecules or components of molecules in the aqueous solution
Why is the hydrophobic effect important?
Protein folding
Protein-protein association
formation of lipid micelles
Binding of steroid hormones to their receptors
Does the hydrophobic effect occur because of a direct attraction?
No, results from the system’s achieving the greatest thermodynamic stability by minimizing the number of ordered water molecules required to surround hydrophobic portions of the solute molecule.
Why are nonpolar molecules poorly soluble in water?
The movement of molecules from the disordered gas phase into the aqueous phase decrease entropy
Why do nonpolar portions of an amphipathic molecule aggregate?
So that fewer water molecules are ordered and entropy increases
What is a micelle
With high enough concentration of amphipathic molecules, they completely aggregates into micelles
How does the hydrophobic effect favor ligand binding?
- Binding site in enzymes and receptors are often hydrophobic
- Such sites can bind hydrophobic substrates and ligands such as steroid hormones
What are colligative properties?
are properties that depend upon the concentration of solute molecules or ions, but not upon the identity of the solute. Colligative properties include vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure.
What is osmotic pressure?
Water moves from areas of high water concentration to areas of low water concentration. Osmotic pressure is the force necessary to resist the movement.
Water ionizes, is it a good electrical conductor and where does the equilibrium lay?
- very low electrical conductivity
- Is strongly to the left
What is solvation?
Solvation is the interaction of a solvent with the dissolved solute—in the case of water, solvation is often referred to as hydration
What is the Kw of water?
Kw = Keq [H2O] = [H+][OH-] = 1 x 10-14
