3 research outputs found
Tracking Hole Transport in DNA Hairpins Using a Phenylethynylguanine Nucleobase
The
hole transport dynamics of DNA hairpins possessing a stilbene
electron acceptor and donor along with a modified guanine (G) nucleobase,
specifically 8-(4′-phenylethynyl)Âdeoxyguanosine, or EG, have
been investigated. The nearly indistinguishable oxidation potentials
of EG and G and unique spectroscopic characteristics of EG<sup>+•</sup> make it well-suited for directly observing transient hole occupation
during charge transport between a stilbene electron donor and acceptor.
In contrast to the cation radical G<sup>+•</sup>, EG<sup>+•</sup> possesses a strong absorption near 460 nm and has a distinct Raman-active
ethynyl stretch. Both spectroscopic characteristics are easily distinguished
from those of the stilbene donor/acceptor radical ion chromophores.
Employing EG, we observe its role as a shallow hole trap, or as an
intermediate hole transport site when a deeper trap state is present.
Using a combination of ultrafast absorption and stimulated Raman spectroscopies,
the hole-transport dynamics are observed to be similar in systems
having EG vs G bases, with small perturbations to the charge transport
rates and yields. These results show EG can be deployed at specified
locations throughout the sequence to report on hole occupancy, thereby
enabling detailed monitoring of the hole transport dynamics with base-site
specificity
Charge Transport across DNA-Based Three-Way Junctions
DNA-based molecular electronics will
require charges to be transported
from one site within a 2D or 3D architecture to another. While this
has been shown previously in linear, π-stacked DNA sequences,
the dynamics and efficiency of charge transport across DNA three-way
junction (3WJ) have yet to be determined. Here, we present an investigation
of hole transport and trapping across a DNA-based three-way junction
systems by a combination of femtosecond transient absorption spectroscopy
and molecular dynamics simulations. Hole transport across the junction
is proposed to be gated by conformational fluctuations in the ground
state which bring the transiently populated hole carrier nucleobases
into better aligned geometries on the nanosecond time scale, thus
modulating the π–π electronic coupling along the
base pair sequence
Conformationally Gated Charge Transfer in DNA Three-Way Junctions
Molecular structures that direct
charge transport in two or three
dimensions possess some of the essential functionality of electrical
switches and gates. We use theory, modeling, and simulation to explore
the conformational dynamics of DNA three-way junctions (TWJs) that
may control the flow of charge through these structures. Molecular
dynamics simulations and quantum calculations indicate that DNA TWJs
undergo dynamic interconversion among “well stacked”
conformations on the time scale of nanoseconds, a feature that makes
the junctions very different from linear DNA duplexes. The studies
further indicate that this conformational gating would control charge
flow through these TWJs, distinguishing them from conventional (larger
size scale) gated devices. Simulations also find that structures with
polyethylene glycol linking groups (“extenders”) lock
conformations that favor CT for 25 ns or more. The simulations explain
the kinetics observed experimentally in TWJs and rationalize their
transport properties compared with double-stranded DNA