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Week 10 in Perspective

• Chemistry and Thermodynamics of Water
• Amphilicity from the perspective of solvent

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Coarse Breakdown of Adsorption Mechanisms
Not an EITHER OR PROPOSITION!!!
Some of both can occur simultaneously, esp.
w/complex multifunctional macromolecules
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Adsorption Mechanisms

1. Ion exchange
2. Ion pairing
3. Hydrogen bonding
4. Polarization of aromatic rings
5. Dispersion forces
6. Hydrophobic bonding

From M. J. Rosen, "Surfactants and Interfacial
Phenomena," Wiley, New York, 1978, pp 34-35.
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Adsorption Mechanisms

1. Ion exchange
2. Ion pairing
3. Hydrogen bonding
4. Polarization of aromatic rings
5. Dispersion forces
6. Hydrophobic bonding

All of these solute-surface reactions occur in
competition with solvent-surface reactions
From M. J. Rosen, "Surfactants and Interfacial
Phenomena," Wiley, New York, 1978, pp 34-35.
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? -
HOH
?
? -
0.25 nm
Water is approximately the size of atomic oxygen
a very small molecule.
?
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Review some important thermodynamic properties of
water
Interpreted in terms of biological consequences
Discuss molecular origin of waters special
properties
Interpreted in terms of self association
Explore mechanismS of surface hydration
Interpreted in terms of biomaterial properties
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Supporting Literature

• E. A. Vogler, in Water in Biomaterials Surface
  Science, M. Morra, ed., John Wiley Sons From
  Vogler Web Site
• Chapter 1 Biological Properties of Water
• Chapter 6 On the Origins of Water Wetting
  Terminology
• Chapter 10 How Water Wets Biomaterials

and many, many citations therein.
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Where
Does
Water
Come
From???
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Water is Ubiquitous in the Cosmos
Huge water factories in space
ITHACA, N.Y. -- A team of U.S. astronomers, led
by Cornell University astrophysicist Martin
Harwit, has discovered a massive concentration of
water vapor within a cloud of interstellar gas
close to the Orion nebula. The amount of water
measured is so high -- enough to fill the Earth's
oceans 60 times a day -- that the researchers
believe it provides an important clue to the
origin of water in the solar system. Cernicharo,
J., J. R. Pardo, et al. (1999). Observations of
Water in Orion. Astrophys. J. Lett. 520
L131-L134.
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Water from Space????
as it approached the Sun
Images from the
Estimated to carry 3.6 million tons of water!
http//www.gsfc.nasa.gov/GSFC/SpaceSci/origins/lin
earwater/linearwater.htm
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Fire and Ice Sizzling Comets Around a Dying Star
Evidence for Extra-Solar System Water
The Submillimeter Wave Astronomy Satellite(SWAS)
detects water vapor near an expanding star as it
vaporizes local icy comets
http//sao-www.harvard.edu/swas/pr010711.html
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From Space
to
Your Home
Liberally mix O and H atoms, heat to gt 90 oC and
voilà
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Q How long has water been on Earth?
A Nearly as long as Earth has existed.
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Oceans that cover 75 of the Earths surface have
existed for 4 billion years
with constant volume for the last 500 million
years.
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Water on Earth

• Powers atmospheric cycling and processes solar
  radiation
• Mediates diurnal and seasonal temperature
  swings
• Geological chisel
• Biological solvent system, mobile transport
  medium, physiologic mediator

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Large amount of heat must be absorbed by water
for a unit increase in temperature
If water had a low Cp then
Environmental temperature swings would be
unfavorable life would boil over without a high
heat-capacity solvent system to dissipate
metabolic heat r r?exp(-E?/kT)
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Large amount of heat is required to covert solid
ice to liquid water (melt) and liquid water to
water vapor (boil)
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Remarkable Water Thermal Properties
Graphic taken from K. S. Davis, and J. A. Day,
"Water The Mirror of Science," Doubleday Co.,
Garden City, NY, 1961.
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Large amount of heat is required to covert solid
ice to liquid water (melt) and liquid water to
vapor (boil)
If water had a low heat of fusion then
Heat from the sun or metabolism would induce
phase transitions melting, boiling
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Large amount of heat is required to covert solid
ice to liquid water (melt) and liquid water to
vapor (boil)
If water had a low heat of vaporization then
water on Earth would exist predominately as vapor
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Large amount of heat is required to covert solid
ice to liquid water (melt) and liquid water to
vapor (boil)
If water had a low heat of vaporization then
perspiration would not effectively control body T
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Space occupied by water molecules expands and
contracts with temperature
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3
o
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Water is Strange Stuff
If density of ice gt liquid water then
Ice would sink, inexorably leading to an
inhospitable world frozen at the bottom and hot
at the top
Space occupied by water molecules expands and
contracts with temperature
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Parable of Count Rumfords Bucket

• Born Benjamin Thompson in Woburn, Massachusetts
• Loyalist politics forced Rumford to leave
  (hurriedly) in 1776.
• Employee of the Bavarian government
• Investigator into the nature of heat
• Inventor of the Rumford fireplace

Count Rumford of the Holy Roman Empire 1753 -
1814
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Parable of Count Rumfords Bucket
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Parable of Count Rumfords Bucket
Even in a container as shallow as Rumfords
bucket, the artificial circumstance of sunken ice
creates a heat transfer problem that would not be
resolvable in deep containers such as
terrestrial lakes, oceans, and streams that are
heated from the top
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The Environmental Calamity of Rumfords Bucket
Snowball Earth

• Seasonal ice would accumulate
• reflection of sunlight (albedo) from the
  undoubtedly expanded poles would cause the
  climate to chill further
• inexorably the world would freeze solid.

All the world we know hinges on a 0.08 g/cc
density differential between ice and water
Graphic taken from R. A. Kerr "An Appealing
Snowball Earth That's Still Hard to Swallow,"
Science, 287, 1734-1736 (2000).
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If water had low interfacial tension then
The driving force for adsorption and adhesion
would be small
Large cohesive interaction energy
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Abstraction of the Adsorption/Adhesion Event
Surface Dehydration
P
P
Surface
Surface
Water
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P particle, protein, or surfactant S solid
surface L liquid phase
Work of adhesion or adsorption
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High work of cohesion favors adhesion and
adsorption from water
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Review some important thermodynamic properties of
water
?
Interpreted in terms of biological consequences
Discuss molecular origin of waters special
properties
Interpreted in terms of self association
Explore mechanismS of surface hydration
Interpreted in terms of biomaterial properties
36
Water is a self associating molecule
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Water Long and Controversial Subject of Intense
Research
Recurring theme of water structure
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Water Long and Controversial Subject of Intense
Research
Complexes of fundamental gas molecules, solid
particles of water, heavy water molecules,
water molecule aggregates, ice molecules
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Water Long and Controversial Subject of Intense
Research
one will soon find even in the textbooks that
while ice is trihydrol, and steam monohydrol,
liquid water is mostly dihydrol with some
trihydrol in it near the freezing point and a
little monohydrol near the boiling
point. James Walker, 1910
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CONTRIBUTION FROM THE CHEMICAL LABORATORY OF THE
UNIVERSITY OF CALIFORNIA. POLARITY AND
IONIZATION FROM THE STANDPOINT OF THE LEWIS
THEORY OF VALENCE. BY WENDELL M. LATIMER AND
WORTH H. RODEBUSH. Received April 26, 1920.    
Some years ago Abegg and Bodlander1 discussed the
general facts concerning strong and weak
electrolytes, the solubility of salts and the
formation of complex ions in solution. They
showed that these facts may be coordinated and
explained to a surprising extent by attributing
to each element or radical, in greater or less
degree, a property which they called
electro-affinity. This property has been more
commonly designated as electropositive or
electronegative character, and its relation to
position in the periodic table is clearly
recognized.
Then, in terms of the Lewis theory, a free pair
of electrons on one water molecule might be able
to exert sufficient force on a hydrogen held by a
pair of electrons on another water molecule to
bind the two molecules together.
J. Am. Chem. Soc., 42, 1419-1433 (1920).
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Water Long and Controversial Subject of Intense
Research
Then, in terms of the Lewis theory, a free pair
of electrons on one water molecule might be able
to exert sufficient force on a hydrogen held by a
pair of electrons on another water molecule to
bind the two molecules together. Latimer and
Rodebush, 1920
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Water Long and Controversial Subject of Intense
Research
A significant review article by Richards and
Chadwell only mentions Latimer Rodebushs
hydrogen bond idea in passing to focus more on
the hot idea of water polymers
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Missing the biggest idea in chemistry since
Lewiss notions of chemical bonding.
For years H. E. Armstrong in England has chided
the physical chemists for considering water only
as water, whereas it is a complex and variable
mixture... Everybody admits that water is a
polymerized liquid and that the degree of
polymerization may change on the addition of
electrolytes. Harris Marshall Chadwell, 1927
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Basics of water chemistry not understood until
the 1960s
There is little doubt that liquid water
consists of water molecules joined together to a
considerable extent by hydrogen bonds. The
complexes are not stable and rigid, but are
labile. 1959
Linus Carl Pauling 1901 - 1994
Recognized the importance of hydrogen bonding
concept and the effect on water properties.
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The Chemistry Behind Waters Unusual Physical
Properties
Is a 3D Network
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Water is a self associating molecule
Pauling was among the first to fully appreciate
that hydrogen bonding was partly covalent in
naturenot just an electrostatic effect
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Water Long and Controversial Subject of Intense
Research
but the exact nature of hydrogen bonding remains
a topic of continued research.
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Hydrogen Bonding in Water Physics or Chemistry?
Physics
Electrostatic interaction
Partial charge sharing in molecular orbitals
Chemistry
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Hydrogen Bonding in Water Physics or Chemistry?
Physics
Force-over-distance following r-2 (center to
center) relationship.
Electrostatic interaction
Chemistry
Partial charge sharing in molecular orbitals
Multivalent bonding with complex
force-over-distance and angular dependence.
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Hydrogen Bonding in Water Physics or Chemistry?
Physics
Electrostatic interaction
Hydrogen bond (HB) strength greater than dipole
interaction by an order-of-magnitude
Partial charge sharing in molecular orbitals
Chemistry
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Bulk water is in a transient self associated
network of molecules interconnected by
flickering (picosecond) hydrogen bonds (HB)
75 of water molecules are interconnected by 3
and 4 HBs HBs may be characterized as Lewis
acid-base type, 3-5 kcal/mole
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Water Long and Controversial Subject of Intense
Research
A drop of liquid is thus regarded as a single
large molecule. In fact, the whole earth,
including the oceans, but excluding the
atmosphere, may be looked upon as a single
molecule. Irving Langmuir, 1916
Did not fully appreciate the transient nature of
self association at this early stage of
understanding chemical bonding.
Irving Langmuir 1881-1957
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History of Chemistry of Water
which was not used by Latimer and Rodebush in
the context of water chemistry until 1920
G. N. Lewis had not published his theory of
bonding until 1916
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Adapted from G. Nemethy, and H. A. Scheraga
"Structure of Water and Hydrophobic Bonding in
Proteins. I . A Model for the Thermodynamic
Properties of Liquid Water," J. Chem. Phys., 36,
3382-3400 (1962).
Breaking HBs and replacing with dipolar
interactions increases molecular energy because
HB strength is greater by order-of-magnitude
lowest energy state corresponds to 4 HBs,
increasing energy with decreasing self
association.
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hence HOH is strongly self associatedhas a very
high interfacial tension reflecting strong
molecular cohesion.
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hence HOH is strongly self associatedhas high
latent heats of fusion and vaporization as well
as heat capacity.
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HOH density (mole/vol.) is relatively high (low
partial molar volume, vol./mole) because HOH is a
very small molecule that packs efficiently by H
bonding
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however, HBs take up space and density of
crystalline ice (fully H-bonded) has a lower
density (higher partial molar volume) than liquid
HOH.
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as ice melts, HBs are lost leading to a rapid
increase in density (decrease in partial molar
volume), achieving a density maximum at 3.98
oCdensity rolls off smoothly with temperature
thereafter.
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• Structure ( density) and reactivity (
  unmatched HBs) of water is controlled by the
  extent of self association
• Less associated network ? more dense ? more
  (available HBs) reactive ? more powerful solvent
  with more H-bonding opportunities
• More associated network ? less dense ? less
  (available HBs) reactive ? less powerful solvent

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H-Bonding, Structure, and Thermodynamic
Properties of HOH
The idea that water should be regarded as a
mixture has over the years been attractive to
chemists and, since 1933, repugnant to
physicistsit has been very difficult for
chemical physicists to see how one molecule in
liquid water could avoid being subject to the
same strong forces as acted on every other
molecule. This has made the concept of an
"unbonded" molecule unpalatable to most chemical
physicists and has inclined them toward what have
been referred to as "uniformist models, in which
all molecules must be regarded as
equivalent. Henry S. Frank, 1970
Mixture Model HOH flickering clusters exist is
a sea of less associated water.
Uniformist Model HOH is everywhere subjected to
the same bonding environment.
largely superseded by computerized molecular
dynamics models.
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Convergence of Experiment and Theory in Modern
Water Research

• Bulk water is in a transient self associated
  network of molecules interconnected by
  flickering (picosecond) hydrogen bonds (HB)
• 75 of water molecules are interconnected by 3
  and 4 HBs
• HBs may be characterized as Lewis acid-base type,
  3-5 kcal/mole
• Structure ( density) and reactivity (
  unmatched HBs) of water is controlled by the
  extent of self association
• Less associated network ? more dense ? more
  (available HBs) reactive ? more powerful solvent
• More associated network ? less dense ? less
  (available HBs) reactive ? less powerful solvent

63
Review some important thermodynamic properties of
water
?
Interpreted in terms of biological consequences
Discuss molecular origin of waters special
properties
?
Interpreted in terms of self association
Explore mechanismS of surface hydration
Interpreted in terms of biomaterial properties