Electron Transmission through Molecular Layers

Naaman, Ron; Haran, A.; Nitzan, Abraham; Evans, Deborah G.; Galperin, Michael

doi:10.1021/jp980427g

Cited by 56 publications

(38 citation statements)

References 60 publications

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“…2), photoelectrons are ejected from the gold substrate on which the molecules are adsorbed (19). The sample is held in an ultra-high-vacuum chamber [10 Ϫ9 torr (1 torr ϭ 133 Pa)].…”

Section: Methodsmentioning

confidence: 99%

On the capturing of low-energy electrons by DNA

Ray

Daube

Naaman

2004

Proc. Natl. Acad. Sci. U.S.A.

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142

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Many of the mutagenic or lethal effects of ionization radiation can be attributed to damage caused to the DNA by low-energy electrons. To gain insight on the parameters affecting this process, we measured the low-energy electron (<2 eV) transmission yield through self-assembled monolayers of short DNA oligomers. The electrons that are not transmitted are captured by the layer. Hence, the transmission reflects the capturing efficiency of the electrons by the layer. The dependence of the capturing probability on the base sequence was studied, as was the state of the captured electrons. It is found that the capturing probability scales with the number of G bases in the single-stranded oligomers and depends on their clustering level. Using two-photon photoelectron spectroscopy, we find that, once captured, the electrons do not reside on the bases. Rather, the state of the captured electrons is insensitive to the sequence of the oligomer. Double-stranded DNA does not capture electrons as efficiently as single-stranded oligomers; however, once captured, the electrons are bound more strongly than to the single strands.monolayer ͉ radiation damage ͉ guanine ͉ photoemission M any of the mutagenic or lethal effects of ionization radiation can be attributed to secondary electrons that are created within 10 Ϫ15 sec along radiation tracks and spurs and have kinetic energies Ͻ20 eV (1, 2). Experimental (3) and theoretical (4-6) studies indicate that electrons with subionization energies play an important role in inducing damage in DNA (7). Our goal in the present work is to determine the structural and chemical elements in the DNA that are governing the electron-capturing process by studying electron transmission through organized adsorbed layers of DNA.The detailed mechanism for electron-DNA interaction is difficult to address experimentally in vivo, where many parameters affect the electron-DNA interaction and the electron energy is not well defined. Therefore, we investigated the interaction of electrons possessing well defined energy, with monolayers of single-stranded (ss) and double-stranded (ds) DNA oligomers adsorbed on a gold surface. By methodically varying the bases in the oligomers, the effect of each base on the interaction with electrons could be determined, as could the difference between single and double strands. Furthermore, the binding energy of the captured electrons could be determined.Past findings hint that G bases act as ''DNA protectors.'' For example, G-rich telomeres found at the ends of chromosomes (8) were shown recently to increase the resistance of DNA to ionizing radiation (9). It is also well accepted that G is the most easily oxidized nucleotide (10,11). It has been demonstrated also that positive charges can transport over long distances in DNA through multistep hopping between G bases (12, 13). The putative role of G bases as protectors of the genome from electrons with kinetic energies greater than the ionization energy of the bases seems to result from their ability to easily form cations...

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“…2), photoelectrons are ejected from the gold substrate on which the molecules are adsorbed (19). The sample is held in an ultra-high-vacuum chamber [10 Ϫ9 torr (1 torr ϭ 133 Pa)].…”

Section: Methodsmentioning

confidence: 99%

On the capturing of low-energy electrons by DNA

Ray

Daube

Naaman

2004

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

142

162

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“…[12][13][14] Recent interest in molecular electronics has brought the basic science in this field closer to modern technology than ever before. [8][9][10][11] Here we present, for the first time, the phenomenon of molecular orientation dependent electron-molecule interaction. Specifically, by tuning of the oxygen coverage on ruthenium, the orientation of methyl bromide could be controlled bromine down or methyl down on O/Ru(001).…”

Section: Introductionmentioning

confidence: 99%

Steric Effect in Electron−Molecule Interaction

Lilach

Asscher

2004

J. Phys. Chem. B

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A steric effect has been identified and measured in the interaction of electrons with oriented molecules, for the first time. Photoelectron mediated reactivity has been determined, with a cross section of σ ) (3.0 ( 0.4) × 10 -19 cm 2 (methyl down) for an adsorbed CD 3 Br on O/Ru(001). A three times smaller cross section was obtained for the bromine down configuration, controlled by oxygen precoverage. A qualitatively similar molecular orientation dependent effect was measured by direct bombardment with 10 eV electrons, however, at much larger cross sections. The significance of the steric effect reported here for electron-transfer processes in general is discussed.

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“…The transmission probability for disorderd layers is considerably less structured, and the dip associated with the bandgap is shallower [11]. The band structure in the ordered film is found to develop as the film thickness is increased [10]. At a six layer thickness the observed transmission dip is already very close to its bulk value, indicating that the band structure is very well developed.…”

Section: Introductionmentioning

confidence: 90%

“…Simulations of transmission probability through four and six crystalline layers of argon indicate the existence of a band structure above the vacuum level, as evident by the drop of the transmission probability for electrons above 4 eV [10]. The transmission probability for disorderd layers is considerably less structured, and the dip associated with the bandgap is shallower [11].…”

Section: Introductionmentioning

confidence: 91%