By a reverse process of photosynthesis occurring in our mitochondria, the plant-product carbohydrate provide us with the energy we need to live. DNA is a double helix molecule formed by two intertwining strands of deoxyribonucleic acid, nucleic acid bases are stacked in pairs one on top of the other with a slight twist reminiscent of a spiral staircase.
The single stacking and overlapping order of the outer n- and p -electron of DNA bases may provide a preferred path for electron transfer. Similarly, the exceptional closeness of the stacked bases may have important consequences for charge motion in DNA duplexes. From a health perspective, both radiation and natural cellular process damage DNA and create reduced and oxidized ET products.
However in some instances this is not the case, and tumors or cancer result. Radiation damage to DNA involves primary ionization steps as well as migration of charges to trap sites where irreversible chemical reactions occur.
At this model a steady-state quenching of the donor D excited state is performed by the acceptor A molecules, both linearly intercalated to DNA. Such arrangement make it possible to use a model to investigate the distance r 0 dependence of this process between donor and acceptor. The model to be used is commonly applied to an sphere distribution, where the acceptor molecules are randomly distributed surrounding the donor, which is in the center of the sphere.
We consider that radius r 0 of this sphere is the own DNA duplexes whereon donor and acceptor are intercalated. At the present example the quenching is due the electron transfer process and r 0 is the critical distance for the electron transfer to occur.
Working with a small donor concentration, it may be considered that the quenching of donor excited state only happens with its nearest neighbor. Naming p 1 r the probability of the donor finding the first nearest acceptor molecule in a distance r and normalizing this probability, one has. It also means that the rate of decay is unique and a function of the distance r , i. So, the distribution p w dw becomes p 1 r 4 p r 2 dr. The equation 3 is rearranged giving.
Absorption measurements at the UV region, and nm determined the degree of contamination of the DNA by proteins. The ionic strength of the solution was 0. Aqueous solutions of ethidium bromide D and methyl viologen A purchased from Sigma, were prepared by dissolution of the substances under the conditions as before.
The fluorescence cuvette was filled with 1 ml of the ethidium bromide stock solution. Excitation wavelength was set to nm, the excitation and emission slits to 5 nm. The emission maximum was determined by a slow scan of the emission wavelength from to nm, and the measurements were obtained in this particular wavelength. A gaussian fitting was used to determine the fluorescence intensity with its center fixed at nm.
Fluorescence measurements of ethidium binding to DNA are well known. In recent paper Beratan 13 discussed the earliest studies of electron-transfer proteins and its application to DNA, emphasizing the contribution of the p -electron system of the DNA base pairs.
The following results do not confirm exactly the migration path of the electron using the p -electron system of the DNA base pairs but confirm the existence of such reaction.
The data of Figure 1 were obtained with the ethidium D at a concentration of 1. The fluorescence intensity increment was expected in face of the intercalative binding of ethidium to DNA. The DNA addition stopped when no modification in intensity was observed confirming that all intercalant disposable in bulk solution was bound.
The second step was the addition of methyl viologen A a quenching promoter, so the fluorescence intensity was expected to decrease see Figure 2. Addition of Methyl Viologen solution was continued until no modification on fluorescence intensity was detected, which may be understood by considering that all Methyl Viologen added was anchored to DNA surface.
The absence of free D and A molecules at the bulk solution avoided the quenching process occurring by random collision, what should restrain the use of the Perrin model and confirmed that the distribution of donor and acceptor molecules happened along the DNA matrix. A linear regression fit of these data gave a result of Deep-hole transfer leads to ultrafast charge migration in DNA hairpins. N2 - Charge transport through the DNA double helix is of fundamental interest in chemistry and biochemistry, but also has potential technological applications such as for DNA-based nanoelectronics.
AB - Charge transport through the DNA double helix is of fundamental interest in chemistry and biochemistry, but also has potential technological applications such as for DNA-based nanoelectronics. Abstract Charge transport through the DNA double helix is of fundamental interest in chemistry and biochemistry, but also has potential technological applications such as for DNA-based nanoelectronics.
Fingerprint Charge transfer. Charge injection. Electronic states.
The significance of proton migration during hole hopping through DNA. Patty K. Fluorescence measurements of ethidium binding to DNA are well known. Scattering matrix approach to electronic dephasing in long-range electron transfer. Recebido em In this case, the surfaces are further modified using 2-ME to prevent any possible nonspecific interactions during hybridization. If you do not receive an email within 10 minutes, your email address may not be registered, and you may need to create a new Wiley Online Library account.
Electron energy levels. Grozema, F. Nature chemistry , 8 11 , Renaud, Nicolas ; Harris, Michelle A. In: Nature chemistry. In: Nature chemistry , Vol.