ZeroG and StickyNano Property #1&2:

All things stick to each other at the nanoscale.

Gravity can be completely ignored. Forget Gravity.

Objects tend to stick Objects

don’t fall. No gravity

Why no Gravity??All objects in the universe are subject to gravitational force

The Gravitational force is proportional to mass.

The masses of atoms,molecules and other nano objects are vanishingly small.

Why no Gravity??

An individual water molecule weighs

18 amu or 18 g/mol.

18 g/mol / (6*1023 atoms/mol) = 3 * 10 -23 g

Or 7* 10-26 pounds

0.00000000000000000000000007 lbs.

This weight is billions of times lower than the other forces acting on the water molecule.

H20 Weight = 3*10-22 N

Van der Waals Forces : 10-12 – 10-10 N

Covalent Bonds: ~10-9 N

Gravitational Force Between two carbon atoms ~10-42N

Why no Gravity??

An individual water molecule weighs

18 amu or 18 g/mol.

What is this weight in grams?

In pounds ?

Gr. weak, Stickiness Strong

Forces between atoms and molecules dominate.

Electrostatic and “Steric” in origin.

Electrostatic Forces

Opposite Charges Attract

Like Charges Repel.

Electric Charges: Positive and Negative + _

+ +

+ _

Atoms

Bohr Model

Electrons electrical charge= -e

Protons electrical charge= +e

Neutrons

How sticky is it?Our intuition based on our macroscopic world fails us here. In general objects don’t stick in our daily lives.

Its Very Sticky down there

Stickiness = BondingMany types of bonding

Two main categories:

Chemical and Physical

Chemical Bonds are very strong (intra-molecular)

Physical Bonds are much weaker (inter-molecular)

Chemical BondsAtoms interact chemically to form molecules

Atom 1 Atom 2

Molecule

“Molecule”A group of atoms connected by chemical bonds

They share / trade electrons

Chemical BondsWater

Protein

Carbon nanotubes

Gold nanocluster

Chemical BondsDifferent Types of Chemical Bonds

• Covalent Bonds

• Ionic Bonds

• Metallic Bonds

Chemical Bonds 1: Covalent Bonds

Atoms SHARE electrons

strc.herts.ac.uk/bio/markr/ biology/day1.htm

Electronic Orbitals: The wave mechanical model

of atoms

S-Orbital

P-Orbital

D-Orbital F-Orbital

S-Orbital

P-Orbital

D-Orbital F-Orbital

Chemical Bonds 2:Ionic Bonds

Atoms TRADE electrons

Ionic BondsAtoms TRADE electrons

WEAK in WATER

Chemical Bonds 3: Metallic Bonds

Atoms DONATE MOBILE electrons

Atom

electron

Physical or Intermolecular BondsInteractions between molecules

Molecules interact but remain independent. No “sharing” of electrons.

Physical BondsDifferent Types of Physical Bonds

• Van der Waals

• Hydrogen Bonds

• Hydrophobic Interactions

Physical Bonds are Electrostatic in origin

Nano Object

Neutral Charge: equal positive and negative charge

An object of neutral charge can be polarized. +-

Van der Waals forces : Polarizability 1

Polarized Object

Polarized Object

Dipole- Dipole interaction. Attractive. Sticky

Van der Waals forces : Polarizability 2

Polarized Object

Polarizable Object

Dipole-Induced Dipole InteractionAttractive. Sticky.

Van der Waals forces : Polarizability 3

Polarizable Object Polarizable Object

Induced Dipole- Induced Dipole Interaction. Attractive. Sticky.

Van der Waals BondingDifferent Types of Physical Bonds

• dipole - dipole

• dipole - induced dipole

• induced dipole – induced dipole

Hydrogen Bonding

WaterO

H H

_

+ +

Hydrogens have a slight positive charge

Oxygen has a slight negative charge

Hydrogen Bonding

O

H

H

_

+

+ O

H

H

_

++

O

H

_

+

Hydrogen Bond

Hydrogen Bonding: DNA

Base Pairing

Hydrophobic Bonding

Micelles/Detergents/Fatty AcidsHydrophillic

Hydrophobic

water

water

water

water

water

water

Micelles/Detergents/Fatty Acids

water

water

water

water

water

Micelles/Detergents/Fatty Acids

water

water

water

water

water

Micelles/Detergents/Fatty AcidsHydrophillic

Hydrophobic

water

water

water

water

water

water

oil

Micelles/Detergents/Fatty Acids

oil

water

water

water

water

water

Bond EnergiesBond Energies kJ/mol* eV/bond E/kBT

Covalent/Ionic Bonds 200-500 2-5 100-200

Van der Waals Bonds ~1 0.01 0.4

Hydrogen Bonds 10-40 0.1-0.4 5-15

Hydrophobic Bonds ~10 0.1 5

Avidin Biotin ~80-100 1 40

* 1kJ/mol = 0.24 kcal/mol

How strong are these bonds force-wise?It depends but roughly speaking…

Covalent ~ 1000pN Non-Covalent 50-200pN

Pot

enti

al E

nerg

y

xEb

x

0

Bond EnergiesBond Energies kJ/mol* eV/bond E/kBT

Covalent/Ionic Bonds 200-500 2-5 100-200

Van der Waals Bonds ~1 0.01 0.4

Hydrogen Bonds 10-40 0.1-0.4 5-15

Hydrophobic Bonds ~10 0.1 5

Avidin Biotin ~80-100 1 40

* 1kJ/mol = 0.24 kcal/mol

How strong are these bonds force-wise?It depends but roughly speaking…

Covalent ~ 1000pN Non-Covalent 50-200pN

Why no Gravity??

An individual water molecule weighs

18 amu or 18 g/mol.

18 g/mol / (6*1023 atoms/mol) = 3 * 10 -23 g

Or 7* 10-26 pounds

0.00000000000000000000000007 lbs.

This weight is a hundred trillion times smaller than the bond force of an individual hydrogen bond.

H20 Weight = 3*10-25 N

Van der Waals Forces : 10-12 – 10-10 N

Covalent Bonds: ~10-9 N

How does bond energy relate to the rupture force of a bond?

Pot

enti

al E

nerg

y

xEb

x

0

It Depends . . .

Effects of thermal energy on Bond StrengthP

oten

tial

Ene

rgy

xEb

kBT

Thermal Energy affects the Dissociation Constant and Bond Strength.

Thermal Energy aids the dissociation of a bond.

0

Bond Strength: Boltzman FactorWhat is the probability that a bond will spontaneously dissociate????

P=e-Eb/kTkT at room temperature = 0.025 meV

The rate of dissociation

rde-Eb/kBT

Attempt frequencyVibrational frequency of bond orinverse relaxation time

Probability per attempt

Rate of dissociation