[seminar] Podsjetnik na DANAŠNJI seminar na IF-u 15:00h - Aleš Omerzu: DNA as a 1D Electronic System

[Osor Barisic]

Poštovani, podsjećamo na današnji seminar na IF-u u 15h. 



15. prosinca 2014. (ponedjeljak) u 15:00 sati 

Institut za fiziku, Bijenička cesta 46, predavaonica u III krilu 





Aleš Omerzu 




Jozef Stefan Institute, Ljubljana 




DNA as a 1D Electronic System 





With the advent of nanoscience and nanotechnology in the late 1990’s a research activity on DNA electronic properties sharply increased. It was mainly due to the unique properties of DNA single strands - complementarity and recombination ability. They enable formation of complex nanostructures by self-assembly which could be utilized in nanoelectronics. Early two-contact measurements of conductivity on single molecules or bundles of few DNA molecules gave discrepant results which spanned the whole spectrum of conductivities from insulating and semiconducting to conducting [1]. However, it was shown lately that DNA is a very poor conductor of electricity at distances longer than ~10 nm [2]. The reason for that lies in DNA electronic structure. Similarly to quasi 1D organic conductors, DNA consist of planar stacks of heterocyclic aromatic molecules with intrastack distances of ~ 3Å, where the π -π overlap of molecular HOMO and LUMO orbitals forms the valence and the conduction band, respectively. But in contrast to 1D organic conductors, DNA lacks counterions which would partially fill a conduction band of the 1D stack. Apparently, to improve conducting properties of DNA one should add either additional electrons in the conducting band or additional holes in the valence band. A possibility of electron doping of DNA emerged with discovery of M-DNA [3], a complex which DNA spontaneously forms with transition metal cations, Co2+, Ni2+ and Zn2+. Fluorescence quenching and electrochemical measurements in solution have shown a strong increase in electron transfer rates upon formation of the M-DNA complex. Measurements of M-DNA electric conductivity in the solid state have shown significant differences between a semiconducting behaviour in DNA and a metallic-like in M-DNA. Still, the mechanism of improved conductivity of M-DNA was not clear. In order to detect free charge carriers in M-DNA we performed ESR measurements on a dry Zn-DNA complex [4]. Additional electrons in Zn-DNA result in a strong, broad and asymmetric ESR signal. The shape and position of the ESR line suggest that unpaired electrons could be delocalized thus explaining the metallic nature of M-DNA. Later measurements of temperature dependence of the ESR parameters – line-width, resonant field and ESR intensity, as well the microwave absorption, have confirmed that the additional electrons introduced into the LUMO levels in M-DNA form a strongly correlated 1D system of delocalized electrons. 





[1] R. G. Endres, D. L. Cox, R. R. P. Singh, Rev. Mod. Phys. 76, 195 (2004). 
[2] A. J. Storm, J. van Noort, S de Vries, C. Dekker, Appl. Phys. Lett. 79, 3881 (2001) 
[3] P. Aich et al., J. Mol. Biol. 294, 477 (1999). 
[4] A. Omerzu et al., Phys. Rev. Lett. 104, 156804 (2010). 






Voditelji seminara IF-a: Nikša Krstulović i Osor Barišić 
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