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Resolution of ultrafast excited state kinetics of bilirubin in chloroform and bound to human serum albumin
Umeå University, Faculty of Science and Technology, Department of Chemistry.
2004 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 6, no 19, 4535-4537 p.Article in journal (Refereed) Published
Abstract [en]

The Z–E-isomerisation of bilirubin upon excitation with visible light is a fundamental step in phototherapy of newborns with neonatal jaundice. Here we report results of an ultrafast optical spectroscopy study of bilirubin in CHCl3 as well as bound to human serum albumin. The data show that the initially excited singlet state has sub-ps decay times with major amplitude. Transient absorption measurements reveal that the ultrafast decay of the emission is accompanied by the formation of a transient intermediate which decays on the 15–20 ps timescale. The initial photoprocesses are thus considerably faster than the previously reported fastest lifetimes for bilirubin and this is, to our knowledge, the first time that the earliest processes in excited bilirubin have been resolved.

Place, publisher, year, edition, pages
2004. Vol. 6, no 19, 4535-4537 p.
Keyword [en]
nuclear magnetic-resonance; quantum yield; neonatal jaundice; wavelength dependence; dimethyl ester; isomerization; phototherapy; photochemistry; photoproducts; spectroscopy
National Category
Chemical Sciences Physical Sciences
Identifiers
URN: urn:nbn:se:umu:diva-4915DOI: 10.1039/b409840dOAI: oai:DiVA.org:umu-4915DiVA: diva2:144196
Available from: 2006-01-12 Created: 2006-01-12 Last updated: 2011-10-11Bibliographically approved
In thesis
1. An Ultrafast Spectroscopic and Quantum-Chemical Study of the Photochemistry of Bilirubin: Initial Processes in the Phototherapy for Neonatal Jaundice
Open this publication in new window or tab >>An Ultrafast Spectroscopic and Quantum-Chemical Study of the Photochemistry of Bilirubin: Initial Processes in the Phototherapy for Neonatal Jaundice
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Bilirubin is a degradation product of haem, which is constantly formed in all

mammals. Increased levels of bilirubin in humans lead to jaundice, a condition

that is very common during the first days after birth. This neonatal

jaundice can routinely be treated by phototherapy without any serious side

effects. During this treatment, bilirubin undergoes a photoreaction to isomers

that can be excreted. The most efficient photoreaction is the isomerisation

around a double bond (Z-E-isomerisation), which results in more soluble

photoproducts.

The work presented in this thesis shows results of a femtosecond optical

spectroscopy study, combined with quantum-mechanical investigations, of

the mechanism of isomerisation of bilirubin. The spectroscopic research was

conducted with bilirubin in organic solvents, and in buffer complexed by

human serum albumin. This albumin complex is present in the blood, and

has thus medical importance. Quantum-chemical calculations (CASSCF) on

a bilirubin model were used to explain experimental results.

The fluorescence decay observed with femtosecond spectroscopy shows an

ultrafast component (~120 fs), which is explained by exciton localisation,

followed by processes with a lifetime of about 1-3 ps. These are interpreted

as the formation of a twisted intermediate, which decays with a lifetime of

10-15 ps back to the ground state, as observed by absorption spectroscopy.

CASSCF calculations, in combination with the experimental results, suggest

the ca. 1-3 ps components to be relaxation to the twisted S1 minimum, followed

by the crossing of a barrier, from where further relaxation takes place

through a conical intersection back to the ground state.

Time-dependent DFT calculations were utilised to analyse the absorption

spectrum of bilirubin. Good agreement with the measured spectrum was

achieved, and low-lying states were observed, that need further investigation.

The theoretically obtained CD spectrum provides direct evidence that

bilirubin preferentially binds to human serum albumin in the enantiomeric

P-form at neutral pH.

Abstract [sv]

Bilirubin är en nedbrytningsprodukt av hem som ständigt bildas hos alla

däggdjur. En förhöjd bilirubinkoncentration i den mänskliga kroppen kan

leda till gulsot, något som är mycket vanligt under de första dagarna efter

födelsen (neonatal gulsot). Fototerapi används rutinmässigt som säker behandlingsmetod,

under vilken bilirubin genomgår en fotoreaktion till en

isomer som kan utsöndras. Den mest effektiva fotoreaktionen är en Z-Eisomerisation,

vilken leder till lösligare fotoprodukter.

Arbetet som presenteras i denna avhandling visar resultaten av en kombinerad

femtosekund optisk-spektroskopisk och kvantmekanisk undersökning

av mekanismen bakom bilirubins isomerisation. Den spektroskopiska

studien genomfördes med bilirubin, löst i organiska lösningsmedel och i

buffert i komplex med humant serumalbumin. Detta albuminkomplex finns i

blodet, och är därför av medicinskt intresse. Kvantmekanistiska CASSCFberäkningar

på en bilirubinmodell användes för att förklara de experimentella

resultaten.

Det uppmätta fluorescence sönderfallet visar ultrasnabba komponenter

(~120 fs). Dessa tolkas som excitonlokalisering, som följs av bildandet av

ett vridet intermediat med en hastighetskonstant på ca. 1 ps-1(beroende på

lösningsmedlet). Absorptionsmätningar visar att detta intermediat sönderfaller

tillbaka till grundtillståndet med en livstid på 10-15 ps.

CASSCF beräkningar, i kombination med de experimentella resultaten, tyder

på att sönderfallet med livslängden på ca. 1 ps är en relaxation till det

vridna S1-tillståndet. Reaktionsvägen därifrån antas passera en barriär till en

konisk genomskärning, som möjliggör snabb relaxation till grundtillståndet.

Tidsberoende DFT-beräkningar användes för att analysera bilirubins absorptionsspektrum,

vilket gav bra överensstämmelse med uppmätta data. Dessutom

hittades ett tillstånd med låg excitationsenergi, som kräver ytterligare

studier. Med hjälp av det beräknade CD-spectret kunde det visas att bilirubin

binder till albumin i P-formen vid neutralt pH.

Place, publisher, year, edition, pages
Umeå: Kemi, 2006. 61 p.
Keyword
Bilirubin, Phototherapy, Neonatal Jaundice, Femtosecond Spectroscopy, CASSCF, TD-DFT, Isomerisation Dynamics
National Category
Physical Chemistry
Identifiers
urn:nbn:se:umu:diva-672 (URN)91-7264-010-3 (ISBN)
Public defence
2006-01-27, KB3A9, KBC-huset, Umeå Universitet, Umeå, 13:00
Opponent
Supervisors
Available from: 2006-01-12 Created: 2006-01-12Bibliographically approved

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