Transcript What is Vesicles? - Complex Systems and Statistical Physics Lab

Applications of Polymerized Vesicles
Seung-Woo Son,
Complex System and Statistical Physics Lab.
Motivation : Nature and Membranes
What is a membrane structure ?
Simply lipid bilayers or vesicles !
Introduction : Glossaries of Soft Matters
• What is Vesicles?
– Spherical closed bilayer structures
– Surfactants comprising two alkyl chains and a cationic polar
head (ammonium, phosphate or zwitterion)
cf.) micelles, microemulsions, bilayers
• Liposomes ( a special case of vesicles )
– Vesicles formed from naturally occurring lipid molecules.
• Lipid : 비극성 유기용매의 추출에 의해 세포나 조직으로부터 분리되는 자연계에 존재하
는 유기분자 ( 종류 : 지방, 왁스, 콜레스테롤, 스테로이드 )
* Other useful expression…
– In vivo : 생체에서…
– In vitro : 시험관에서…
Physics of Soft Matters
• Micelles, bilayers, vesicles and biological membranes
– Self-assembly of certain amphiphilic molecules
– Association colloids or complex fluids
– Soft, flexible (fluid-like) unlike solid particles, rigid
macromolecules(ex.DNA)
– Van der Waals force, hydrophobic, hydrogen-bond, screened
electrostatic interactions etc.(not covalent bond or ionic bond)
– Solution conditions(electrolyte concentration, pH, temperature,
etc.) change the size and shape of molecule aggregates.
•
Ref. Jacob N. Israelachvili, “Intermolecular and Surface Forces” Ch 16, 17
Special Character of Vesicles
• Diameter ~ 10nm, thickness 4~5nm spherical water-filled pockets
• Several weeks lifetime
– Great kinetic stability
– Lower surfactant exchange rate
– Higher number of surfactant molecules
Spherical micelles
Microemulsions
Vesicles
Mean molecular
weight
1-3  104
105 - 106
> 107
Aggregation
number
20 -100
103
104 - 105
Diameter ( Å )
30 - 60
50 - 500
300 - 5000
Monomer
exchange rate (s)
10-5
10-5
>1
Aggregate lifetime
10-3 – 1 s
Very long
Week, month
Dilution in water
Destroyed
Altered
Stable
Polymerization of Vesicles
• The aim of polymerization is to fix the structure
–
–
–
–
To observe the shape of vesicle, to measure the size
Control the size, rigidity, permeability
Actually unlimited lifetime(several month) : greater stability
To clarify the mechanism of vesicle fusion
Polymerization Strategies
Applications of Polymerized Vesicles (1) : DDS
• Active molecule transport
– Pharmacology : selectively carry a compound
to a preselected site in the organism.
– pH, temperature, photochemical isomerisation,
enzymes, etc.
Applications of Polymerized Vesicles (2) : catalysts
• Ideal medium for the formation of small and uniform colloidal
particles of metals or oxides.
– Potassium tetrachloroplatinatr ( K2PtCl4 ) + polymerisable
surfactants : extremely efficient colloidal platinum catalyst.
• Artificial photosynthesis
– Photochemical solar-energy conversion using colloidal
semiconductor
– Decomposing water
Summaries
• Vesicles의 모양와 성질에 대해서
• Polymerization을 연구해야 하는 이유
• Polymerization 방법들
• Polymerized vesicles의 응용
Motivation :
Applications of Polymerized Vesicles (2) : photosynthesis