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Effects of Charge Location on the Absorption by and Lifetimes of Protonated Tyrosine Peptides <i>in Vacuo</i>
MedLine Citation:
PMID:  22268622     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
Nearby charges affect the electronic energy levels of chromophores, with the extent of the effect being determined by the magnitude of the charge and degree of charge-chromophore separation. The molecular configuration dictates the charge-chromophore distance. Hence, in this study we aim to assess how the location of the charge influences the absorption of a set of model protonated and diprotonated peptide ions, and whether spectral differences are large enough to be identified. The studied ions were the dipeptide YK, the tripeptide KYK (Y = tyrosine, K = lysine) and their complexes with 18-crown-6-ether (CE). The CE targets the ammonium group by forming internal ionic hydrogen bonds and limits the folding of the peptide. In the tripeptide, the distance between the chromophore and the backbone ammonium is enlarged relative to that in the dipeptide. Experiments were performed in an electrostatic ion storage ring using a tunable laser system, and action spectra based on lifetime measurements were obtained in the range from 210 nm to 310 nm. The spectra are all quite similar though there seems to be some changes in the absorption band between 210 nm and 250 nm, while in the lower energy band all ions had a maximum absorption at ~275 nm. Lifetimes after photoexcitation were found to shorten upon protonation and lengthen upon CE complexation, in accordance with the increased number of degrees of freedom and an increase in activation energies for dissociation as the mobile proton model is no longer operative.
Authors:
Orla Kelly; Chris R Calvert; Jason B Greenwood; Henning Zettergren; Steen Brøndsted Nielsen; Jean Ann Wyer
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-1-23
Journal Detail:
Title:  The journal of physical chemistry. A     Volume:  -     ISSN:  1520-5215     ISO Abbreviation:  -     Publication Date:  2012 Jan 
Date Detail:
Created Date:  2012-1-24     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9890903     Medline TA:  J Phys Chem A     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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