Biomedical Engineering Reference
In-Depth Information
Chapter 10
Soft X-ray Interaction with Organic Molecules
of Biological Interest
P. Bolognesi, P. O'Keeffe, and L. Avaldi
Abstract
Molecular fragmentation following absorption of X-ray radiation is one
of the effects of radiation damage. To investigate this process in a class of organic
molecules of biological interest the inner shell excitation, ionisation, electron
decay and fragmentation of the pyrimidine molecule have been fully characterised
by electron and ion spectroscopy techniques and theoretical calculations. These
techniques have allowed us to observe site-selective molecular fragmentation of the
N and C (1 s) core excited states and to explain that it is governed by the final singly
charged ion state reached by resonant Auger electron decay.
10.1
Inner shell mechanisms for radiation damage
It has long been known that soft and hard X-ray exposure causes dramatic effects
on living organisms, producing both reparable and irreparable damage, which lead
to alterations, malfunctioning and even mutations and cellular death. There is
nowadays substantial evidence that macroscopic damage may be initiated at the
microscopic scale of the DNA chain contained in living cells [
1
]. These DNA
alterations are due to significant energy deposition either in the DNA constituents
or in its neighbouring molecules, causing direct and indirect effects respectively.
On the other hand, the same pathogenic effects of X-ray radiation are proficiently
used in radiotherapy for cancer treatment. In this respect, the harmful action of
ionising radiation on tumour cells can be further enhanced via the use of properly
designed radiosensitisers [
2
], aiming at a more selective and amplified damage of the
tumour rather than healthy cells. Pyrimidine and halogenated pyrimidines play an
important role in this context. The former is the building block of cytosine, thymine
and uracil DNA/RNA bases, while the latter group of molecules, which mimic the
