[Show abstract][Hide abstract] ABSTRACT: We have characterized ultraviolet (UV) photon-induced DNA strand break processes by determination of absolute cross sections for photoabsorption and for sequence-specific DNA single strand breakage induced by photons in an energy range from 6.50 eV to 8.94 eV. These represent the lowest-energy photons able to induce DNA strand breaks. Oligonucleotide targets are immobilized on a UV transparent substrate in controlled quantities through attachment to DNA origami templates. Photon-induced dissociation of single DNA strands is visualized and quantified using atomic force microscopy (AFM). The obtained quantum yields for strand breakage vary between 0.06 and 0.5 indicating highly efficient DNA strand breakage by UV photons, which is clearly dependent on the photon energy. Above the ionization threshold strand breakage becomes clearly the dominant form of DNA radiation damage, which is then also dependent on the nucleotide sequence.
[Show abstract][Hide abstract] ABSTRACT: The electronic structure of DNA is determined by its nucleotide sequence, which is for instance exploited in molecular electronics. Here we demonstrate that also the DNA strand breakage induced by low-energy electrons (18 eV) depends on the nucleotide sequence. To determine the absolute cross sections for electron induced single strand breaks in specific 13 mer oligonucleotides we used atomic force microscopy analysis of DNA origami based DNA nanoarrays. We investigated the DNA sequences 5′-TT(XYX)3TT with X = A, G, C and Y = T, BrU 5-bromouracil and found absolute strand break cross sections between 2.66 · 10−14 cm2 and 7.06 · 10−14 cm2. The highest cross section was found for 5′-TT(ATA)3TT and 5′-TT(ABrUA)3TT, respectively. BrU is a radiosensitizer, which was discussed to be used in cancer radiation therapy. The replacement of T by BrU into the investigated DNA sequences leads to a slight increase of the absolute strand break cross sections resulting in sequence-dependent enhancement factors between 1.14 and 1.66. Nevertheless, the variation of strand break cross sections due to the specific nucleotide sequence is considerably higher. Thus, the present results suggest the development of targeted radiosensitizers for cancer radiation therapy.
[Show abstract][Hide abstract] ABSTRACT: DNA nanotechnology holds great promise for the
fabrication of novel plasmonic nanostructures and the potential to
carry out single-molecule measurements using optical spectroscopy.
Here, we demonstrate for the first time that DNA origami
nanostructures can be exploited as substrates for surface-enhanced
Raman scattering (SERS). Gold nanoparticles (AuNPs) have been
arranged into dimers to create intense Raman scattering hot spots in
the interparticle gaps. AuNPs (15 nm) covered with TAMRA-modified
DNA have been placed at a nominal distance of 25 nm to demonstrate
the formation of Raman hot spots. To control the plasmonic coupling
between the nanoparticles and thus the field enhancement in the hot
spot, the size of AuNPs has been varied from 5 to 28 nm by electroless
Au deposition. By the precise positioning of a specific number of
TAMRA molecules in these hot spots, SERS with the highest sensitivity down to the few-molecule level is obtained.
[Show abstract][Hide abstract] ABSTRACT: The combination of the Ugi four-component reaction (Ugi-4CR) with acyclic diene metathesis (ADMET) or thiol-ene polymerization led to the formation of poly-1-(alkylcarbamoyl) carboxamides, a new class of substituted polyamides with amide moieties in the polymer backbone, as well as its side chains. 10-Undecenoic acid, obtained by pyrolysis of ricinoleic acid, the main fatty acid of castor oil, was used as the key renewable building block. The use of different primary amines, as well as isonitriles (isocyanides) for the described Ugi reactions provided monomers with high structural diversity. Furthermore, the possibility of versatile post-modification of functional groups in the side chains of the corresponding polymers should be of considerable interest in materials science. The obtained monomers were polymerized by ADMET, as well as thiol-ene, chemistry and all polymers were fully characterized. Finally, ortho-nitrobenzylamide-containing polyamides obtained by this route were shown to be photoresponsive and exhibited a dramatic change of their properties upon irradiation with light.
Chemistry - A European Journal 04/2012; 18(18):5767-76. DOI:10.1002/chem.201103341 · 5.73 Impact Factor