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 !

• What is Vesicles?– Spherical closed bilayer structures– Surfactants comprising two alkyl chains and a cationic polar head (a

mmonium, 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

존재하는 유기분자 ( 종류 : 지방 , 왁스 , 콜레스테롤 , 스테로이드 )

* Other useful expression…– In vivo : 생체에서…

– In vitro : 시험관에서…

Introduction : Glossaries of Soft Matters

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 electro

static 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 surfactan

ts : extremely efficient colloidal platinum catalyst.

• Artificial photosynthesis– Photochemical solar-energy conversion using colloidal semiconducto

r– Decomposing water

Summaries

• Vesicles 의 모양와 성질에 대해서

• Polymerization 을 연구해야 하는 이유

• Polymerization 방법들

• Polymerized vesicles 의 응용

Motivation :

Applications of Polymerized Vesicles (2) : photosynthesis