Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The combination of natural and synthetic polymers allow for the synthesis of advanced
hybrid copolymers. These hybrid copolymers have applications in biomedical areas, one
such area being in drug delivery systems (DDS). In this study, a modular approach was
used to prepare amphiphilic block copolymers with the ability to self-assemble into three
dimensional structures.
Reversible addition-fragmentation chain transfer (RAFT) was the synthetic tool used to
mediate the polymerization of N-vinylpyrrolidone. RAFT is a versatile method to prepare
polymers with control over molecular weight and dispersity. A xanthate chain transfer
agent (CTA) was used to obtain the hydrophilic poly(N-vinylpyrrolidone) (PVP) block. An
aldehyde functionality could be introduced due to the lability of the xanthate moiety, the
procedure of which was effectively optimized to produce quantitative conversion. A dixanthate
CTA was synthesized to produce a PVP chain which after the modification
reaction, resulted in a α,ω-telechelic polymer.
A polypeptide was synthesized via the ring-opening polymerization of Ncarboxyanhydrides
(ROP NCA). The living and controllable ROP of NCAs is a method
which results in polypeptides, but without a well-defined amino acid order. Poly(γ-
benzyl-L-glutamate) (PBLG) was synthesized with a narrow dispersity (Đ = 1.10 – 1.15)
using conditions that promote the retention of a terminal primary amine. A protected
cysteine functionality was introduced via the terminal amine PBLG chain-end, using
peptide synthesis techniques. This resulted in the conjugation of the aldehyde functional
PVP and the cysteine terminal PBLG using a covalent, non-reducible thiazolidine
linkage.
The deprotection of the cysteine, more specifically the deprotection of the thiol was a
non-trivial procedure. The thiol protecting acetamidomethyl (Acm) group could not be
cleaved using traditional methods, but instead a modified procedure was developed to
effectively remove the Acm group while inhibiting hydrolysis of the benzyl esters. It was determined that the conjugation reaction could effectively proceed in N,Ndimethylformamide
(DMF) at a slightly elevated temperature and so continued to
prepare the amphiphilic hybrid block copolymers, PVP-b-PBLG. A structurally different
PBLG chain, namely PBLG-b-Cys was conjugated to the ω-aldehyde PVP and the
conjugation efficiency was compared to our PBLG-Cys block. In the case of PBLG-b-
Cys the in situ deprotection and conjugation as well as a two-step deprotection and
conjugation reaction with PVP resulted in very low conjugation efficiency. The cysteine
end-functional PBLG resulted in near quantitative conjugation with PVP.
The critical micelle concentration (CMC) for PVP90-b-PBLG54 was determined to be
6 μg/mL, using fluorescence spectroscopy. Particle sizes were determined with TEM
and DLS and found to range from 25 nm to 120 nm depending on the polymer block
lengths as well as hydrophobic/hydrophilic block length ratios. Furthermore, when the
micelles were subjected to an increased acidic environment, the labile benzyl ester
bonds were hydrolyzed. This was observed with TEM where the particle sizes increased
10-fold to form vesicular structures. Hydrolysis was further confirmed with ATR-FTIR
and 1H-NMR spectroscopy.
Cytotoxicity tests confirmed that the copolymer micelles had good cell compatibility at
high concentrations such as 0.9 mg/mL. Investigation into drug loading using a pyrene
probe confirmed the viability of using PVP-b-PBLG as a responsive DDS. / AFRIKAANSE OPSOMMING: Die kombinasie van natuurlike en sintetiese polimere maak dit moontlik vir die sintese
van gevorderde hibried kopolimere. Hierdie kopolimere het aanwending in biomediese
gebiede, een so 'n gebied is in medisinale vervoer sisteme (MVS). 'n Modulêre
benadering is in hierdie studie gebruik om amfifiliese blok kopolimere te berei.
Omkeerbare addisie-fragmentasie kettingoordrag (OAFO) is gebruik as die sintetiese
tegniek vir die polimerisasie van N-vinielpirolidoon (NVP). OAFO is 'n veelsydige metode
om polimere te berei met beheer oor molekulêre gewig en dispersiteit (Đ). 'n Xantaat
kettingoordrag agent (KOA) is gebruik om die hidrofiliese poli(N-vinielpirolidoon) (PVP)
blok te sintetiseer. ‘n Aldehied endgroep was deur die terminale xantaat funksionaliteit
berei, ‘n proses wat geoptimiseer is tot kwantitatiewe omsetting. 'n Di-xantaat KOA is
gesintetiseer om, na modifikasie, 'n α, ω-telecheliese polimeer te produseer.
Die polipeptied was gesintetiseer deur middel van ’n ringopening polimerisasie van Nkarboksianhidriede
(ROP NKA). Die lewende en beheerbare ROP van NKAe is 'n
metode wat lei tot polipeptiede sonder ’n gedefinieerde aminosuur volgorde. Poli(γ-
benzyl-L-glutamaat) met 'n lae dispersiteit (Đ = 1.10 – 1.15), is gesintetiseer deur
gebruik te maak van kondisies wat die behoud van 'n terminale primêre amien bevorder.
'n Beskermde sistien-funksionaliteit is ingebou via die terminale amien met behulp van
peptiedsintese tegnieke.
Die tiol beskerming van die asetamidometiel (Asm) groep kon nie gekleef word deur
gebruik te maak van tradisionele metodes nie, maar ‘n nuwe proses is ontwikkel om die
Asm groep te kleef sowel as om die hidrolise van die bensiel esters te inhibeer.
Die koppelings reaksie het effektief verloop in DMF by 'n effens verhoogde temperatuur
en sodoende is die amfifiliese hibried blok-kopolimere, PVP-b-PBLG berei. Twee
verskillende PBLG kettings is gekoppel aan die ω-aldehied PVP en die koppeling
doeltreffendheid is vergelyk. Daar is bevind dat net die sistien end-funksionele PBLG tot
kwantitatiewe konjugasie kon lei. Die kritiese misel konsentrasie is bepaal vir PVP90-b-PBLG54 as 6 μg/mL met behulp van
fluoressensie spektroskopie. Die deeltjie-groottes is bepaal met TEM en DLS en wissel
van 25 nm tot 120 nm, afhangende van die polimeer bloklengtes sowel as hidrofobiese /
hidrofiliese blok lengte verhoudings. Die miselle is blootgestel aan 'n verhoogde suur
omgewing, wat tot die hidrolise van die bensiel ester groepe gelei het. TEM het getoon
dat die deeltjie-groottes met 10-voud vergroot het tot vesikulêre strukture. Hidrolise is
verder bevestig met ATR-FTIR en 1H-KMR spektroskopie.
Sitotoksiese toetse het bevestig dat die miselle geen of min toksisiteit toon teenoor
eukariotiese selle nie, selfs teen 'n hoë konsentrasies soos 0.9 mg/ml. Die medisinale
behoud vermoë is met behulp van pireen bevestig en dus ook die potensiaal van PVP-b-PBLG as ‘n moontlike MVS.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/20369 |
| Date | 03 1900 |
| Creators | Jacobs, Jaco |
| Contributors | Klumperman, Bert, Pound-Lana, Gwenaelle, Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Format | 118 p. : ill. (some col.) |
| Rights | Stellenbosch University |
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