Utjecaj temperature i izotopne supstitucije na UV-Vis spektar askorbata

master's thesis

• Title (english): Effect of temperature and solvent isotopic composition on the UV-spectrum of ascorbate
• Author: Silvia Osmak
• Mentor: Viktor Pilepić (mentor)
• Committee member: Viktor Pilepić (predsjednik povjerenstva)
• Committee member: Monika Barbarić (član povjerenstva)
• Committee member: Sandra Jurić (član povjerenstva)
• Granter: University of Zagreb; Faculty of Pharmacy and Biochemistry; (Department of physical chemistry); Zagreb
• Defense date and country: 2017-05-29, Croatia
• Scientific / art field, discipline and subdiscipline: BIOMEDICINE AND HEALTHCARE; Pharmacy; Pharmacy

Abstract

U ovom diplomskom radu istraživan je učinak temperature i izotopne supstitucije zbog otapala na položaj apsorpcijskog
maksimuma i širinu apsorpcijske vrpce UV-Vis spektra askorbata, reaktivnog oblika vitamina C u fiziološkim uvjetima. UVVis
spektri otopine askorbata koncentracije 5∙10-5 mol/dm3 izmjereni su u vodi i u teškoj vodi u temperaturnom intervalu od
1 ºC do 55 ºC pomoću tri različita spektofotometra kojima su prethodno utvrđene mjerne karakteristike. Mjerenjem UV
spektra pri koncentraciji askorbata u rasponu od 5∙10-5 mol/dm3 do 5∙10-3 mol/dm3 utvrđeno je da položaj apsorpcijskog
maksimuma ne ovisi o koncentraciji askorbata. Iz dobivenih UV-spektara askorbata u lakoj i teškoj vodi pokazano je da s
povećanjem temperature dolazi do povećanja širine apsorpcijske vrpce i pomaka apsorpcijskog maksimuma prema većim
valnim duljinama. Ove promjene u temperaturnom rasponu od 50 °C iznose 1,2 nm za širinu apsorpcijske vrpce i 1,1 nm za
položaj apsorpcijskog maksimuma. Utvrđene su i razlike u UV-Vis spektru između otopina askorbata u lakoj i teškoj vodi.
Položaj apsorpcijskog maksimuma u UV-Vis spektru otopine askorbata u teškoj vodi pomaknut je za 0,7 nm prema nižim
valnim duljinama, a širina apsorpcijske vrpce manja je za 0,8 nm u odnosu na UV-Vis spektar otopine askorbata u lakoj vodi
na istoj temperaturi. Spinsko-okolinska relaksacijska vremena (T1) izmjerena pomoću NMR spektrometra za 1H jezgre
askorbata u otapalu 10 % D2O + 90 % H2O kraća su za oko tri puta u odnosu na T1 istih 1H jezgri u 99 % D2O.
Dobiveni rezultati protumačeni su promjenom solvatacije, odnosno promjenom vibracijske i elektronske energije askorbata
kao posljedice usporavanja reorganizacije vodikovih veza otapala i askorbata u otopini do koje dolazi radi snižavanja
temperature ili izotopne supstitucije. Obzirom da je u ove promjene uključena π orbitala koja sudjeluje i u reakcijama
prijenosa naboja, te promjene mogu se dovesti u vezu s reaktivnosti askorbata što može biti od koristi u istraživanjima
reakcija prijenosa naboja u kojima sudjeluje askorbat u složenim procesima koji se odvijaju u biološkim sustavima.

Abstract (english)

The effect of temperature and solvent isotopic composition on the position of absorption maximum and width of
the absorption band in UV-Vis spectrum of ascorbate, predominant reactive form of vitamin C in physiological
conditions, has been studied in this diploma thesis. The UV-Vis spectra of 5∙10-5 mol/dm3 ascorbate solutions in
H2O and D2O in the temperature range from 1 to 55 ºC have been measured by using three different
spectrophotometers with previously determined measuring characteristics. By measuring the UV spectrum of
ascorbate solution ranging from 5∙10-3 to 5∙10-5 mol/dm3, it was found that the position of the absorption band
maximum is not dependent on the concentration of ascorbate. From the UV spectra obtained in H2O and D2O, it
has been shown that increasing the temperature increases the absorption band width and shifts the absorption
maximum to higher wavelenghts. These changes are 1.2 nm for the of absorption band width and 1.1 nm for the
absorption maximum position in the temperature range of 50 ºC. Differences in the UV-Vis spectra of the
ascorbate solution in H2O and in D2O were also found. The absorption maximum position in UV-Vis spectrum
of the ascorbate solution in D2O was shifted by 0.7 nm at lower wavelenghts, and the width of the absorption
band was 0.8 nm less than the UV-Vis spectrum of ascorbate solution in H2O at the same temperature. The spinlattice
relaxation times (T1) measured by NMR spectrometer for 1H ascorbate nuclei in 10 % D2O + 90 % H2O
solvent are about the three times shorter than the corresponding T1 for 1H nuclei in 99 % D2O. The obtained
results has been interpreted by solvation changes, or by the ascorbate vibrational and electronic states energy
changes resulted as a consequence of slowing down the solvent and ascorbate hydrogen bonds reorganization in
a solution caused by lowering the temperature or isotopic substitution. Since these changes include the π orbital
involved also in charge transfer reactions, these changes may be related also to the ascorbate reactivity what
could be useful in research of charge transfer reactions involving ascorbate in complex processes which take
place in biological systems.

• Keywords: askorbinska kiselina; promjena spektra; izotopna supstitucija; UV-Vis spektroskopija; T1 relaksacijsko vrijeme
• Keywords (english): ascorbic acid; change of spectrum; isotopic substitution; UV-Vis spectrofotometry; T1 relaxation time
• Language: croatian
• URN:NBN: urn:nbn:hr:163:779337
• Study programme: Title: Pharmacy; Study programme type: university; Study level: integrated undergraduate and graduate; Academic / professional title: magistar/magistra farmacije (magistar/magistra farmacije)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2018-12-17 12:55:14