magistrska naloga
Povzetek
Liotropni tekoči kristali so kot nosilni sistemi zdravilnih učinkovin za dermalno,
parenteralno in oralno dostavo v današnjem času pogost predmet znanstvenega raziskovanja.
Nastajajo spontano z dodajanjem topila (voda/olje) amfifilnim molekulam. Mezofaze, ki jih
tvorijo, ločimo glede na razporeditev molekul v topilu in jih delimo na heksagonalne,
kubične in lamelarne faze. Vsaka faza ima značilne fizikalno-kemijske lastnosti, ki jih
proučujemo z različnimi analiznimi metodami. Najpogosteje se uporablja kombinacija več
različnih tehnik, katerih rezultati se med seboj dopolnjujejo in so zato bolj zanesljivi.
V okviru magistrske naloge smo proučevali supramolekularno strukturo tekočih kristalov,
sestavljenih iz emulgatorske zmesi lecitina in Tweena 80®, oljne faze izopropilmiristata in
vode, z metodo elektronske paramagnetne resonance. V sisteme smo vgradili različne
spinske označevalce, ki poročajo o dogajanju v specifičnem lokalnem okolju
supramolekularnih struktur v katerem se nahajajo. Spektre vzorcev smo posneli pri
temperaturah v območju med 22 °C in 62 °C. Ugotovili smo, da so v lipidnem dvosloju
območja alkilnih verig blizu polarnih glav bolj urejena, so zelo viskozna in dajejo izrazito
anizotropne spektre, medtem ko so območja v notranjosti supramolekularnih struktur bolj
fluidna, gibljivost molekul je večja. Urejenost lipidne faze se je manjšala tako s povečanjem
deleža vode kot tudi z naraščanjem temperature. Razlike v urejenosti lokalnega okolja med
posameznimi sistemi tekočih kristalov pa so se z višanjem temperature manjšale. Glede na
delež vodne komponente se sistem z najmanjšim deležem vode izoblikuje v heksagonalno
fazo, sistem z najvišjim deležem vode predstavlja prehodno stanje med lamelarno in micelno
fazo, vmesni sistemi pa so urejeni v lamelarne faze z možnostjo obstoja paličastih micelov.
Ti rezultati so v skladu z rezultati, ki so jih pridobili z drugimi analiznimi metodami na istih
sistemih. S simulacijami EPR spektrov smo ugotovili, da je vsak spekter sestavljen iz treh
spektralnih komponent, ki ponazarjajo določen tip domene z zanjo značilnimi fizikalnokemijskimi
lastnostmi. Pri višjih temperaturah smo opazili združevanje domen. S počasnim
segrevanjem vzorcev faznih prehodov nismo odkrili, kar pa je zaželeno v primeru tekočih
kristalov, z namenom uporabe kot nosilnih sistemov za različne načine dostave.
Ključne besede
liotropni tekoči kristali;elektronska paramagnetna resonanca;spinski označevalec;lamelarna faza;ureditveni parameter;
Podatki
Jezik: |
Slovenski jezik |
Leto izida: |
2017 |
Tipologija: |
2.09 - Magistrsko delo |
Organizacija: |
UL FFA - Fakulteta za farmacijo |
Založnik: |
[S. Islamović] |
UDK: |
615.8:549(043.3) |
COBISS: |
4324465
|
Št. ogledov: |
339 |
Št. prenosov: |
73 |
Ocena: |
0 (0 glasov) |
Metapodatki: |
|
Ostali podatki
Sekundarni jezik: |
Angleški jezik |
Sekundarni naslov: |
Structural evaluation of lyotropic liquid crystals using electron paramagnetic resonance |
Sekundarni povzetek: |
Lyotropic liquid crystals are extensively studied as drug delivery systems for dermal and
parental applications and for applications in oral cavity. They are formed spontaneously, by
addition of the solvent (water/oil) to amphiphilic molecules. Various mesophases formed
can be divided by their arrangement in the solvents to hexagonal, cubic and lamellar phases.
Each phase has its unique physio-chemical features. Various analytical methods are used for
their investigation, however in many cases a combination of techniques is used in order to
obtain complementary and more reliable data.
In the thesis, the supramolecular structure of liquid crystals based on lecithin and Tween 80®
as surfactant mixture, oil phase isopropyl myristate and water was evaluated using electron
paramagnetic resonance. Different spin probes, which report about actions in a specific local
environment of supramolecular structures in which they are located, were built into the
systems. Samples spectra were recorded at temperatures between 22 °C and 62 °C. Regions
near water-lipid layer have a high order parameter, are very viscous and give anisotropic
spectra, while the areas in the inner part of the membrane are highly fluid; mobility of the
molecules is high. Order of phases was lowered by enlargement of water content as well as
with higher temperatures. On the other hand, minimal differences between samples were
observed with increasing temperature. Based on the water component content, the system
with the lowest water content had hexagonal structure, the system with the highest water
content was identified as phase transition system between lamellar and micellar phase, while
the systems in between had lamellar structure with the possibility of presence of rod-like
micelles. Similar conclusions have been made for these systems based on other analytical
techniques as well. Composition of each spectrum from three different components,
representing a defined type of domain with its distinguished physio-chemical properties, was
shown with EPR spectra simulations. Association of domains was observed at higher
temperatures. We were keen to investigate the potential of phase transition between different
phases as well. This phenomenon was evaluated by slowly heating the samples and was not
observed for liquid crystals systems tested. The phase transition is not a desired property of
liquid crystals, which are used as carriers for various routs of applications. |
Sekundarne ključne besede: |
lyotropic liquid crystals
electron paramagnetic resonance (EPR)
spin label
lamellar phase
order parameter; |
Vrsta dela (COBISS): |
Magistrsko delo/naloga |
Komentar na gradivo: |
Univ. Ljubljana, Fak. za farmacijo |
Strani: |
VI, 55 f. |
ID: |
12044618 |