MCDB 310: CHAPTER 2
42 Cards in this Set
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What are the properties of water?
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bent molecule; tetrahedral geometry
hydrogen partially positively charged
oxygen partially negatively charged
-two lone pairs of electrons water- makes water have a dipole moment
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Electrostatic interaction is quantiatively measured by
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Coulumb's Law
F = qz*q2/ 4 π *ε0*εr *r^2
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What are the types of electrostatic interactions?
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H-bond
Ionic Interaction
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An H-bond is
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____ is an electrostatic interactions involving partial charges
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An ionic interaction is
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____ is an electrostatic interaction between full charges
(ions, Na+ or Cl-, full charges)
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Hydrogen bond characteristics (requirements, components, strength)
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Three atoms in a line (directional)
Two flanking atoms must be electronegative
Requires a free electron pair on a electronegative proton acceptor, and a proton bonded to a electronegative atom
Atom covalently bonded to H is the H bond donor
Atom non covalently bonded to H is H bond …
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Will there be hydrogen bonding if the H is bonded to a C? Why/why not
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No,
we don't think of carbon as an electronegative atom
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What if the three atoms in an H bond are not co-linear/ directional? Why?
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Can't have h-bonding, not directional, can never be a straight line
•BothBoth atoms are partially negative, Want to keep charges far apart from eachother because they will repel one another, need to be in a straight line
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Importance of Hydrogen Bonds
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Essential for the acid-base properties of aqueous solutions
Essential for the structure and function of polypeptides (e.g. structural proteins, enzymes, several hormones)
Essential for the structure and function of DNA
mRNA-tRNA H-bonds are essential for protein synthesis by the riboso…
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What is crystalline structure of ice due to? Why is water a liquid, has high bp & heat capacity?
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H-bonding
•Every H molecule surrounded by 4 oxygen molecules
•Perfect H bonding comes at expense of lower packing density
•Breaking hydrogen bonds when you heat water
•Break about 15% of bonds broken when heating
•Make and break different hydrogen molecules between eachother, increa…
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What is solubility?
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Ability of a solvent to interact more strongly w/ solute particles than the solute particles interact w/ eachotehr
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How does H-bonding help solubilize polar molecules?
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H-bonds help dissolve polar, uncharged compounds
they are hydrophilic because they like to dissolve in water
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Is hydrogen bonding enthalpy or entropy driven?
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Entropy driven
-If it dissolves you increase the entropy driven, entropy drives glucose to dissolve in water
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Ionic interactions strength vs H bonds
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Ionic interactions are very strong compared to H bonds
NaCl lattice energy ~800 kj/mol h bond ~20 kj/mol
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What does water do in electrostatic interactions? Why?
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•Water ‘shields’ (i.e. reduces) electrostatic interactions
•Water reduces attraction between opposite charges
•Water reduces repulsion between like charges
Water has VERY large dialectric constant, high dialectric constant = lower electrostatic force
dipoles of water arrange around …
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The dialectric constant of water allows it to ____ How?
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The _____ of water allows it to dissolve salts
Chloride ions surrounded by water molecules
delta positive on H helps interact w/ chloride
Water binds to each of them and seperates them, reduces interactions between Sodium and Chloride
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Is solubility of salts enthalpy driven or entropy driven?
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Entropy driven, now replacing ionic bonds
more entities --> more randomness --> more entropy
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Ionic compounds are hydrophilic or hydrophoboic?
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hydrophilic
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Properties & examples of hydrophobic compounds
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Insoluble in water
Non-polar in nature
Soluble in non-polar solvents (e.g. benzene, hexane)
Examples:
Non-polar gases (e.g. O2 or CO2)
Organic compounds with long aliphatic chains (e.g. fatty acids), phenyl groups etc.
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What happens when you put a hydrophobic compound in water?
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Bulk water constantly makes an breaks H-bonds
Water surrounding compound is very ordered, makes cage
Solubiliation of water compound is thermodynamiocally unfavorable
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Hydrophobic interaction in aqueous solutions
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Hydrophobic molecules tend to cluster together in aqueous solutions
-phase separation
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What do systems tend to do
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Tend to minimize free energy so that ΔG <0
maximize entropy
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How do systems maximize entropy?
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minimize # of ordered water molecules
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What is the way hydrophic molecules are arranged? Why?
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Hydrophic molecules cluster in linear formation that minimize number of ordered hydrophic molecules, so straight and compacked next to eachother NOT haphazardly clustered
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Amphiphathic compounds
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contain both polar/ionic (hdrophilic_ and non-polar (hydrophobic) regions (e.g. in biology; lipids)
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Formation of micelles
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Surrounding water molecules forced to remain ordered
hydrophobic regions are no longer exposed to water
hydrophobic groups are sequestered from water, ordered shell of H2O moecules is minimzed and entropy s further increased
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Biological membrane bilayer
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section of a spherical membrane surrounded & filled w/ water
there will be no hydrophobic (yellow) section exposed to water in an
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How do distinguish between hydrophobic and hydrophilic
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Hydrophobic (blue) Hydrophilic (yellow)
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Van der waals interactions (what are they, strength, radius)
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attractive forces between small electric dipoles induced on uncharged atoms , usually between non-polar molecules very weak, ~0.3 kj/mol
radius: half of the internuclear seperation of two non-bonded atoms of the same element on their closest possible approach
• • Although very weak, ca…
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Cumulative Effect of Weak Interactions
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• Most ia have a short distance, i.e. surfaces have to match to achieve optimal stability!
• also negative interactions are important to determine specificity (repulsion, too close distance,…)
crucuial for structure of molecules, molecular recognition
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Equilibrium constant equation
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Keq = e^(-ΔG/RT)
More negative ΔG is --> larger Keq
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Dissociation constant of an acid: Ka
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Defines strength of an acid
The stronger the acid à the more of the acid is dissociated into protons à the higher is Ka à lower the pKa
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Protonated vs. De-protonated
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Free acid = protonoated
Conjugated base = de-protonated
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What happens at pH > pKa
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Acid is deprotonated
[deprotonated] > [protonated]
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What happens at pH < pKa
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Acid is protonated
[protonated] > [deprotonated]
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CO2/ bicarbonate buffer system
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1)In the alveoli of the lung, CO2 is transferred from the gas phase into liquid phase; CO2(d) is also produced by metabolism
2)Hydration of CO2 is unfavorable (1:300 Keq!) and slow -> catalysis by carbonic anhydrase
3)Carbonic acid is acid in equilib with bicarbonate
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Alternates mechanisms for buffer in blood
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•Elimination of H+ by respiration
HCO3- + H+ CO2 + H2O
• Production of H+ via secretion of bicarbonate by kidneys
(urine)
H2CO3 HCO3- + H+
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If blood becomes too acidic
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Want to remove protons, remove the acid from blood (carbon dioxide), hyperventilate “breath heavily” breath out a lot of carbon dioxide, removing acid from blood
also can remove ammonium via urine
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If blood becomes too basic
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Increase protons, increase acidity, remove the base so more free protons. Bicarbonate is a salt so it can be excreted via urine
or hypoventilate, breath lesss, keep CO2 in blood (acidity)
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Metabolic acidosis (what is it, symptoms, treatment)
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• Severe diarrhea (loss of HCO3-)
• Symptoms: patients show often rapid and deep breathing (“blowing off CO2”)
• treatment: bicarbonate
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Respiratory Acidosis
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• Impaired pulmonary function (hypoventilation)
• Symptoms: often kidneys compensate by excreting more H+ in the form of NH4+
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Respiratory vs. metabolic changes
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respiratory changes fast, metablolic changes slow
if respiratory alteration for pH adjustment, body adjusts fast
if use kidneyalteration for pH, body adjsuts slow
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MCDB 310: CHAPTER 2