Photoregulation of molecular assembly in thin surface films

Ličen, Matjaž (author), Drevenšek Olenik, Irena (mentor)

The versatility and many appealing properties of DNA nucleobase derivatives have made them the target of investigations for use in a wide range of possible applications: from medicine to novel materials for nanotechnology and biocompatible electronics. By modifying a nucleobase with a photoactive moiety, one is able to control the binding between nucleobases by irradiating the molecules with light of specific wavelengths. In this doctoral thesis, I present the results of the studies of the behaviour of three azo-functionalised guanosine derivatives in thin surface films at the air-water interface and after transfer to solid substrates by using the Langmuir-Blodgett method. Even though the studied molecules did not possess a typical amphiphilic structure, we found that all of them formed sufficiently stable films at the air-water interface. Furthermore, optical irradiation induced changes in the measured properties of the films, and could be used to reversibly switch the films from one state to the other using two different wavelengths of light. Finally, a phenomenological model was developed to describe the time dependence of surface pressure in a Langmuir film during irradiation with actinic light. Using this model, we were able to show that the behaviour of a mixed guanosine–cytidine film during irradiation was consistent with photoinduced inhibition of hydrogen bonds.

• Language: English
• Keywords: DNA nucleotides, photoisomerization, azobenzene, Langmuir films, Langmuir-Blodgett films, hydrogen bonding
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: FMF - Faculty of Mathematics and Physics
• Year: 2020
• PID: 20.500.12556/RUL-117099
• COBISS.SI-ID: 23962627
• Publication date in RUL: 24.06.2020

Secondary language

• Language: Slovenian
• Title: Fotoregulacija urejanja molekul v tankih površinskih slojih

Abstract

Derivati nukleobaz so zaradi svoje vsestranskosti predmet raziskav na mnogih področjih, kot so medicina, biologija, znanost materialov, biokompatibilna elektronika ipd. Modifikacija nukleobaz s fotoaktivnimi skupinami omogoča optično regulacijo vodikovih vezi, ki se tvorijo med nukleobazami, kar pomeni, da lahko lastnosti takih materialov preklapljamo, tako da jih osvetlimo s svetlobo primerne valovne dolžine. V tem doktorskem delu so predstavljeni rezultati študij obnašanja treh azo-funkcionaliziranih derivatov gvanozina v tankih površinskih slojih, tako na vodni površini kot po prenosu na trdne substrate s tehniko Langmuir-Blodgett. Kljub temu, da preučevane molekule nimajo tipične amfifilne strukture, se je izkazalo, da so molekulski filmi, ki jih te molekule tvorijo na vodni površini, dovolj stabilni, da je mogoče preučevati vpliv svetlobe na njihove lastnosti. Tako smo lahko izmerili reverzibilno spreminjanje lastnosti filmov, tako na vodni površini kot na trdnih substratih, pri osvetljevanju z UV in vidno svetlobo. Za opis spreminjanja površinskega tlaka pri osvetljevanju z UV svetlobo smo razvili matematični model na osnovi 2D Van der Waalsove enačbe stanja. Razviti model se ujema z izmerjenimi fotoinduciranimi spremembami površinskega tlaka v filmih sestavljenih iz mešanice derivatov dveh nukleobaz, analiza izmerjenih podatkov preko tega modela pa nakazuje, da pri optičnem osvetljevanju filma iz derivatov gvanozina in citidina pride do reverzibilnega razdiranja vodikovih vezi med nukleobazami.

• Keywords: nukleotidi, fotoizomerizacija, azobenzen, Langmuirjevi sloji, sloji Langmuir-Blodgett, vodikova vez