Lecture 3 Flashcards
What are electrostatic interactions?
transient electrostatic interactions between opposite charges
(sometimes called salt bridge)
e.g. side chains with charges (+ and -) may form electrostatic interactions
How to increase electrostatic interaction?
Increase magnitude of charges, decrease distance between charges, decrease dielectric constant
What are van der Waal forces?
include all intermolecular forces that act between electrically neutral molecules (so technically they include H-bonds)
exist because every atom has an electron cloud that fluctuates, yielding a transient electric dipole – the dipoles of one atom can influence the electron distribution in another, inducing a transient dipole in that atom
Describe london dispersion forces
Nonpolar groups polarize electrons in neighbouring group; very weak & transient, fall off with distance
e.g. Ch3 - H3C
Describe dipole-induced dipole interaction
a molecule w/permanent dipole inducing dipole in neighbouring group
e.g. C=O - H3C
Describe permanent dipoles
polar molecules interacting with another polar molecule
C=O - C=O
Describe hydrophobic interactions
Consequence of nrg needed to insert a non polar molecule into water (H-bonds in water must be broken to insert non polar molecule)
What bonds do non polar molecules form in water and with what?
van der Waal interactions with other non polar molecules
What are clathrates
cage-like structure water molecules form around non polar molecules
are clathrates thermodynamically favourable?
no
when non polar molecules spontaneously aggregate in aq sln, is that favourable?
yes reduces # of water molecules in ordered clatherate structures inc entropy of system
Is folded protein thermodynamically favourable
yes, less ordered req for water molecules to solubilize protein
Is Keq fixed at constant temperature or concentrations?
Keq fixed at constant temps
What is the keq of water?
keq= [H+][OH-]/[H20] [H+] = 10-7 M [OH-] = 10-7 M [H2O] is 55.5 M Keq = 1.8 x 10-16 M
Kw of water?
10^-14 M^2
When does Kw change?
NEVER
What is the henderson-hasselbalch eqn?
pH = pka + log[A-]/[HA]
What is the titration midpoint?
Buffer zone, where pH = pKa
Characteristics of covalent bonds
- strong and short
- most stable
- formed by sharing of electrons between atoms
- holds atoms together in molecule (intramolecular)
Characteristics of non-covalent bonds? Examples
- weaker, reversible bonds
- distances between atoms are greater than in covalent bonds
- intramolecular and intermolecular
- examples include hydrogen bonds, electrostatic interactions, van der Waal interaction (dipoles, dispersion forces), hydrophobic interaction
How do hydrogen bonds form? Characteristics?
- between H atom covalently attached to an electronegative atom (donor) and lone pair of 2nd electronegative atom (acceptor)
- strongest of weak non-covalent bonds
- has directional property (won’t form if not properly oriented)
- “partially covalent bond:
Why does water have a very high melting point, boiling point & heat of vaporization compared to other solvents?
Due to hydrogen bonding, which holds the molecules together & requires significant energy to break
Why is water a good solvent
Water hydrates ions by electrostatic interactions
- its partial negatively charged oxygen interacts with positively charged ions, its partial positively charged hydrogens interact with negatively charged ions
- forms hydration spheres around ions, proteins, macromolecules
Ability of water to surround ions in electrostatic interactions and diminish their attraction to one another is a measure of?
The dielectric constant
- the greater the dielectric constant of a solvent, the lower the force between 2 charges in that solvent
