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26 Cards in this Set

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What is a hydrogen bond?
an electrostatic attration an electronegative molecule and an electropositive hydrogen.
Hydrogen bonds are stronger/weaker than covalent bonds?
weaker (20 kJ/mol vs. 348 kJ/mol)
What is the hydrogen bond acceptor?
The electronegative atom participating in the bond
What is the hydrogen bond donor?
The electropositive hydrogen
Why does butanol have a very high boiling point compared to butane?
Because hydrocarbon H's do not participate in H-bonds
What types of compounds form H-bonds w/H20 and tend to be water soluble?
alcohols, ketones, and compounds w/N-H bonds (uncharged, polar molecules)
In what orientation are H-bonds strongest?
When the H-bond acceptor is "in-line" with the covalent bond of the H-bond donor (H)
What are electrostatic interactions?
a property of charged particles
What do most charged groups arise from in biological molecules?
derivates of carboxylic acids (COO-) amines (-NH3+), phosporic acid, and sulfuric acid
What do alternative bonding partners do to ionic interactions?
Weaken them
What is a salt bridge?
The association of two ionic protein groups of opposite charge
Give an example
carboxyl group of Glu
ammonium group of Lys
Free ions in aqeous solution are highly _______?
solvated
What is the result of this?
There is no difference in free energy between the ionic and solvated form.

Thus, they contribute little to the stability of the protein
Why do polar molecules dissolve readily in H20?
Because they can replace water-water interactions with water-solute interactions (move favorable)
CO2, N2, 02, are polar/nonpolar?
non-polar
What is a hydrophobic interaction?
The forces that cause non-polar molecules to minimize contact w/polar solvents
Why is water effective at screening electrostatic interactions between molecules?
Because of it's high di-electric constant (E) - # of dipoles present in a solvent
What formula gives the strength of the ionic interaction btw. molecules?
F=(Q1*Q2)/Er^2
Hydrophobic solutes in a polar solvent cause a _____ in enthalpy and _____ in entropy
small increase in enthalpy
decrease in entropy
Why is the decrease in entropy present?
because water molecules must form a cage-like shell around the non-polar solute, decreasing the number of highly ordered H20 molecules
What is a micelle?
an amphipathic molecule in solution (polar faces out, non-polar away from H20)
ex. of hydrophobic interaction
What is the driving force behind a substrate binding to enzyme in a polar solvent
The increase in enthalpy caused by disrupting the structures around the substrate and enzyme
What are the 3 types of Van der Waals interactions?
1.dipole-dipole
2.dipole-induced dipole
3.induced dipole-induced dipole
What is the Van der Waals radius
a measure of how close 2 atoms can approach each other (measure of maximum attrative force)
What is referred to as Van der Waals contact
1. When the attractive forces balance repulsive force
2. Equal to Van der Waals radius