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Synthesis of a model lipid and observation of behaviour of model liposomes by electrophoresis Song, Xu Chun
Abstract
A model lipid consisting of a cholesterol base, tetraethoxy— spacer and glucuronic acid head group was synthesized. First, the head group was prepared by acetylation and esterification of glucuronolactone to produce methyl (1, 2,3,4-tetra-O— acetyl——D—glucopyran)uronate (j.) which was then brominated to produce methyl (2,3,4—tri-O—acetyl—--D—glucopyranosyl bromide)uronate (Z). The combination of the cholesterol part and tetra— ethoxy chain was made by reacting cholesteryl—p—toluenesulfonate and tetraethylene glycol, to produce 3—O—(i1-hydroxy—3, 6, 9—trioxaundecyl)cholest —5-ene (tetra-EC) (3). The above steps were carried out with methods reported previously. The coupling of the head group and tetra-EC employed a different method, which had been used by others in the coupling reaction of the same head group and cholesterol, by using silver oxide as the catalyst instead of silver carbonate. Methyl t3—O--(3,6,9—trioxaundecyl) cholest—5—en—3-yl—2,3, 4—tri—O—acetyl——D—glucopyranosid3uronate () was produced from the coupling reaction with a yield estimated to be — 50’!., higher than that of the reaction with silver carbonate as the catalyst. The final step was to remove the methyl group and the acetyl protecting groups on the head group by using excess MaCH in a specific solvent system and acidifying with HC1, to obtain crude 3—O—(3,6,9—trioxundecyl) cholest—5—en—3—yl——D—glucopyranosiduronic acid (). The crude acid product was primarily purified by adjusting the pH of the suspension of the acid in warn ethanol and water and the salt form was obtained. The salt product, (i), was precipitated pure from chloroform solution by addition of mixed ethyl acetate arid hexane. The product (tetra—ECG), which has a negative charge on the head group, was used with other lipids to prepare liposomes. The liposomes, which vary in poly(ethylene glycol) (PEG) chain density and charge location were made for the purpose of mimicking the glycocalyx region in actual biomembranes. Particle electrophoresis was used to measure the mobilities of the liposomes in the solutions with variation of pH (1.8—9.9), ionic strength (O.OO1M—O.1H) and PEG chain density (O-60’A by molar ratio). The classical theory for particle electrophoresis was applied to calculate the mobility and the apparent charge density of the liposoznes. The pKa of tetra—ECG was determined with a plot of the mobility of the tetra—ECG—containing liposome against pH on the surface of the particle. A numerical model, which has been developed as a computational program, was used to interpret the results of electrophoresis as a function of ionic strength, in terms of several parameters which describe the surface properties of the liposomes.
Item Metadata
Title |
Synthesis of a model lipid and observation of behaviour of model liposomes by electrophoresis
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1994
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Description |
A model lipid consisting of a cholesterol base, tetraethoxy— spacer
and glucuronic acid head group was synthesized. First, the head group was
prepared by acetylation and esterification of glucuronolactone to produce
methyl (1, 2,3,4-tetra-O— acetyl——D—glucopyran)uronate (j.) which was then
brominated to produce methyl (2,3,4—tri-O—acetyl—--D—glucopyranosyl
bromide)uronate (Z). The combination of the cholesterol part and tetra—
ethoxy chain was made by reacting cholesteryl—p—toluenesulfonate and
tetraethylene glycol, to produce 3—O—(i1-hydroxy—3, 6, 9—trioxaundecyl)cholest
—5-ene (tetra-EC) (3). The above steps were carried out with methods
reported previously. The coupling of the head group and tetra-EC employed
a different method, which had been used by others in the coupling reaction
of the same head group and cholesterol, by using silver oxide as the
catalyst instead of silver carbonate. Methyl t3—O--(3,6,9—trioxaundecyl)
cholest—5—en—3-yl—2,3, 4—tri—O—acetyl——D—glucopyranosid3uronate () was
produced from the coupling reaction with a yield estimated to be — 50’!.,
higher than that of the reaction with silver carbonate as the catalyst.
The final step was to remove the methyl group and the acetyl protecting
groups on the head group by using excess MaCH in a specific solvent
system and acidifying with HC1, to obtain crude 3—O—(3,6,9—trioxundecyl)
cholest—5—en—3—yl——D—glucopyranosiduronic acid (). The crude acid
product was primarily purified by adjusting the pH of the suspension of the
acid in warn ethanol and water and the salt form was obtained. The salt
product, (i), was precipitated pure from chloroform solution by addition of
mixed ethyl acetate arid hexane. The product (tetra—ECG), which has a negative charge on the head
group, was used with other lipids to prepare liposomes. The liposomes,
which vary in poly(ethylene glycol) (PEG) chain density and charge location
were made for the purpose of mimicking the glycocalyx region in actual
biomembranes. Particle electrophoresis was used to measure the mobilities
of the liposomes in the solutions with variation of pH (1.8—9.9), ionic
strength (O.OO1M—O.1H) and PEG chain density (O-60’A by molar ratio). The
classical theory for particle electrophoresis was applied to calculate the
mobility and the apparent charge density of the liposoznes. The pKa of
tetra—ECG was determined with a plot of the mobility of the tetra—ECG—containing
liposome against pH on the surface of the particle. A numerical
model, which has been developed as a computational program, was used to
interpret the results of electrophoresis as a function of ionic strength,
in terms of several parameters which describe the surface properties of the
liposomes.
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Extent |
1477536 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-02-26
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0059587
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1994-05
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.