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Vrednotenje strukture liotropnih tekočih kristalov z elektronsko paramagnetno resonanco : magistrska naloga
Islamovič, Sara (Author), Mravljak, Janez (Mentor) More about this mentor... This link opens in a new window, Gosenca Matjaž, Mirjam (Co-mentor)

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Abstract
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.

Language:Slovenian
Keywords:liotropni tekoči kristali elektronska paramagnetna resonanca spinski označevalec lamelarna faza ureditveni parameter
Work type:Master's thesis/paper (mb22)
Tipology:2.09 - Master's Thesis
Organization:FFA - Faculty of Pharmacy
Year:2017
Publisher:[S. Islamović]
Number of pages:VI, 55 f.
UDC:615.8:549(043.3)
COBISS.SI-ID:4324465 This link opens in a new window
Views:201
Downloads:57
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Secondary language

Language:English
Title:Structural evaluation of lyotropic liquid crystals using electron paramagnetic resonance
Abstract:
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.

Keywords:lyotropic liquid crystals electron paramagnetic resonance (EPR) spin label lamellar phase order parameter

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