6 research outputs found
DNA Based Carbon Nanotube Porphyrin Nanohybrids Molecular Recognization and Regeneration
In the search to improve solar cells, scientists are exploring new materials that will provide better current transfer. One material that has emerged as a strong contender is the single walled carbon nanotube (SWNT). Current DNA-SWNT based films combined with chromophores have poor operational lifetimes compared to commercial solar cells. Once exposed to light the chromophore begins to degrade, eventually rendering the solar cell unusable. To solve this problem, we used a method involving multiple steps. First we found which DNA sequences formed structures around the SWNT that could hold the most chromophores by using a spectrophotometer to test the concentration of chromophores on each film. Secondly we determined which chromophores generated the strongest current when exposed to light by testing the photocurrent of each film. Finally we searched for a chemical, or solution, that would remove damaged chromophores without damaging or removing the DNA or SWNTs from the film. Currently it has been found that DNA sequences high in guanine, which form G-quadruplexes, are ideal for holding chromophores. Through testing, we found that zinc porphyrin created the strongest current of the chromophores tried. Research still needs to be done to find an ideal solution for removing damaged chromophores, but progress has been made into making organic solar cells viable. Eventually automating this process, a solar cell could be repeatedly refunctionalized, thus extending the life of the solar cells indefinitely
Understanding the Mechanical Properties of DNA Origami Tiles and Controlling the Kinetics of Their Folding and Unfolding Reconfiguration
DNA origami represents a class of highly programmable macromolecules that can go through conformational changes in response to external signals. Here we show that a two-dimensional origami rectangle can be effectively folded into a short, cylindrical tube by connecting the two opposite edges through the hybridization of linker strands and that this process can be efficiently reversed via toehold-mediated strand displacement. The reconfiguration kinetics was experimentally studied as a function of incubation temperature, initial origami concentration, missing staples, and origami geometry. A kinetic model was developed by introducing the j factor to describe the reaction rates in the cyclization process. We found that the cyclization efficiency (j factor) increases sharply with temperature and depends strongly on the structural flexibility and geometry. A simple mechanical model was used to correlate the observed cyclization efficiency with origami structure details. The mechanical analysis suggests two sources of the energy barrier for DNA origami folding: overcoming global twisting and bending the structure into a circular conformation. It also provides the first semiquantitative estimation of the rigidity of DNA interhelix crossovers, an essential element in structural DNA nanotechnology. This work demonstrates efficient DNA origami reconfiguration, advances our understanding of the dynamics and mechanical properties of self-assembled DNA structures, and should be valuable to the field of DNA nanotechnology
Understanding the Mechanical Properties of DNA Origami Tiles and Controlling the Kinetics of Their Folding and Unfolding Reconfiguration
DNA origami represents
a class of highly programmable macromolecules
that can go through conformational changes in response to external
signals. Here we show that a two-dimensional origami rectangle can
be effectively folded into a short, cylindrical tube by connecting
the two opposite edges through the hybridization of linker strands
and that this process can be efficiently reversed via toehold-mediated
strand displacement. The reconfiguration kinetics was experimentally
studied as a function of incubation temperature, initial origami concentration,
missing staples, and origami geometry. A kinetic model was developed
by introducing the <i>j</i> factor to describe the reaction
rates in the cyclization process. We found that the cyclization efficiency
(<i>j</i> factor) increases sharply with temperature and
depends strongly on the structural flexibility and geometry. A simple
mechanical model was used to correlate the observed cyclization efficiency
with origami structure details. The mechanical analysis suggests two
sources of the energy barrier for DNA origami folding: overcoming
global twisting and bending the structure into a circular conformation.
It also provides the first semiquantitative estimation of the rigidity
of DNA interhelix crossovers, an essential element in structural DNA
nanotechnology. This work demonstrates efficient DNA origami reconfiguration,
advances our understanding of the dynamics and mechanical properties
of self-assembled DNA structures, and should be valuable to the field
of DNA nanotechnology
Regeneration of Light-Harvesting Complexes via Dynamic Replacement of Photodegraded Chromophores
All-synthetic
molecular donor–acceptor complexes are designed,
which are capable of counteracting the effect of photoinduced degradation
of donor chromophores. Anionic gallium protoporphyrin IX (GaPP) and
semiconducting carbon nanotube (CNT) are used as a model donor–acceptor
complex, which is assembled using DNA oligonucleotides. The GaPP-DNA-CNT
complex produces an anodic photocurrent in a photoelectrochemical
cell, which steadily decays due to photo-oxidation. By modulating
the chemical environment, we showed that the photodegraded chromophores
may be dissociated from the complex, whereas the DNA-coated carbon
nanotube acceptors are kept intact. Reassociation with fresh porphyrins
leads to the full recovery of GaPP absorption and photocurrents. This
strategy could form a basis for improving the light-harvesting performance
of molecular donor–acceptor complexes and extending their operation
lifetime