46 research outputs found
Genome-Wide Identification of Transcriptional Start Sites in the Plant Pathogen Pseudomonas syringae pv. tomato str. DC3000
RNA-Seq has provided valuable insights into global gene expression in a wide variety of organisms. Using a modified RNA-Seq approach and Illumina's high-throughput sequencing technology, we globally identified 5′-ends of transcripts for the plant pathogen Pseudomonas syringae pv. tomato str. DC3000. A substantial fraction of 5′-ends obtained by this method were consistent with results obtained using global RNA-Seq and 5′RACE. As expected, many 5′-ends were positioned a short distance upstream of annotated genes. We also captured 5′-ends within intergenic regions, providing evidence for the expression of un-annotated genes and non-coding RNAs, and detected numerous examples of antisense transcription, suggesting additional levels of complexity in gene regulation in DC3000. Importantly, targeted searches for sequence patterns in the vicinity of 5′-ends revealed over 1200 putative promoters and other regulatory motifs, establishing a broad foundation for future investigations of regulation at the genomic and single gene levels
Probing Intermolecular Electron Delocalization in Dimer Radical Anions by Vibrational Spectroscopy
Delocalization of
charges is one of the factors controlling charge
transport in conjugated molecules. It is considered to play an important
role in the performance of a wide range of molecular technologies,
including organic solar cells and organic electronics. Dimerization
reactions are well-suited as a model to investigate intermolecular
spatial delocalization of charges. While dimerization reactions of
radical cations are well investigated, studies on radical anions are
still scarce. Upon dimerization of radical anions with neutral counterparts,
an electron is considered to delocalize over the two molecules. Here,
by using time-resolved infrared (TRIR) detection coupled with pulse
radiolysis, we show that radical anions of 4-<i>n</i>-hexyl-4′-cyanobiphenyl
(<b>6CB</b>) undergo such dimerization reactions, with an electron
equally delocalized over the two molecules. We have recently demonstrated
that nitrile νÂ(Cî—ĽN) vibrations respond to the degree
of electron localization of nitrile-substituted anions: we can quantify
the changes in the electronic charges from the neutral to the anion
states in the nitriles by monitoring the νÂ(Cî—ĽN) IR shifts.
In the first part of this article, we show that the sensitivity of
the νÂ(Cî—ĽN) IR shifts does not depend on solvent polarity.
In the second part, we describe how probing the shifts of the nitrile
IR vibrational band unambiguously confirms the formation of dimer
radical anions, with <i>K</i><sub>dim</sub> = 3 × 10<sup>4</sup> M<sup>–1</sup>. IR findings are corroborated by electronic
absorption spectroscopy and electronic structure calculations. We
find that the presence of a hexyl chain and the formation of π–π
interactions are both crucial for dimerization of radical anions of <b>6CB</b> with neutral <b>6CB</b>. The present study provides
clear evidence of spatial delocalization of electrons over two molecular
fragments
Experimental Insight into the Thermodynamics of the Dissolution of Electrolytes in Room-Temperature Ionic Liquids: From the Mass Action Law to the Absolute Standard Chemical Potential of a Proton
Room-temperature ionic liquids (ILs)
are a class of nonaqueous
solvents that have expanded the realm of modern chemistry, drawing
increasing interest over the last few decades, not only in terms of
their own unique physical chemistry but also in many applications
including organic synthesis, electrochemistry, and biological systems,
wherein charged solutes (i.e., electrolytes) often play vital roles.
However, our fundamental understanding of the dissolution of an electrolyte
in an IL is still rather limited. For example, the activity of a charged
species has frequently been assumed to be unity without a clear experimental
basis. In this study, we have discussed a standard component-based
scheme for the dissolution of an electrolyte in an IL, supported by
our observation of ideal Nernstian responses for the reduction of
silver and ferrocenium salts in a representative IL, 1-ethyl-3-methylimidazolium
bisÂ(trifluoromethanesulfonyl)Âimide ([emim<sup>+</sup>]Â[NTf<sub>2</sub><sup>–</sup>] or [emim<sup>+</sup>]Â[TFSI<sup>–</sup>]). Using this scheme, which was also supported by temperature-dependent
measurements with ILs having longer alkyl chains in the imidazolium
ring, and the solubility of the IL in water, we established the concept
of Gibbs transfer energies of “pseudo-single ions” from
the IL to conventional neutral molecular solvents (water, acetonitrile,
and methanol). This concept, which bridges component- and constituent-based
energetics, utilizes an extrathermodynamic assumption, which itself
was justified by experimental observations. These energies enable
us to eliminate inner potential differences between the IL and molecular
solvents (solvent–solvent interactions), that is, on a practical
level, conditional liquid junction potential differences, so that
we can discuss ion–solvent interactions independently. Specifically,
we have examined the standard electrode potential of the ferrocenium/ferrocene
redox couple, Fc<sup>+</sup>/Fc, and the absolute intrinsic standard
chemical potential of a proton in [emim<sup>+</sup>]Â[NTf<sub>2</sub><sup>–</sup>], finding that the proton is more acidic in the
IL than in water by 6.5 ± 0.6 units on the unified pH scale.
These results strengthen the progress on the physical chemistry of
ions in IL solvent systems on the basis of their activities, providing
a rigorous thermodynamic framework
Thermodynamic Aspects of Electrocatalytic CO<sub>2</sub> Reduction in Acetonitrile and with an Ionic Liquid as Solvent or Electrolyte
Thermodynamic Aspects of Electrocatalytic CO<sub>2</sub> Reduction in Acetonitrile and with an Ionic Liquid as Solvent or
Electrolyt
Vibrational Stark Effects To Identify Ion Pairing and Determine Reduction Potentials in Electrolyte-Free Environments
A recently developed instrument for
time-resolved infrared detection
following pulse radiolysis has been used to measure the νÂ(Cî—ĽN)
IR band of the radical anion of a CN-substituted fluorene in tetrahydrofuran.
Specific vibrational frequencies can exhibit distinct frequency shifts
due to ion pairing, which can be explained in the framework of the
vibrational Stark effect. Measurements of the ratio of free ions and
ion pairs in different electrolyte concentrations allowed us to obtain
an association constant and free energy change for ion pairing. This
new method has the potential to probe the geometry of ion pairing
and allows the reduction potentials of molecules to be determined
in the absence of electrolyte in an environment of low dielectric
constant
Identification of Ion-Pair Structures in Solution by Vibrational Stark Effects
Ion
pairing is a fundamental consideration in many areas of chemistry
and has implications in a wide range of sciences and technologies
that include batteries and organic photovoltaics. Ions in solution
are known to inhabit multiple possible states, including free ions
(FI), contact ion pairs (CIP), and solvent-separated ion pairs (SSIP).
However, in solutions of organic radicals and nonmetal electrolytes,
it is often difficult to distinguish between these states. In the
first part of this work, we report evidence for the formation of SSIPs
in low-polarity solvents and distinct measurements of CIP, SSIP, and
FI, by using the νÂ(Cî—ĽN) infrared (IR) band of a nitrile-substituted
fluorene radical anion. Use of time-resolved IR detection following
pulse radiolysis allowed us to unambiguously assign the peak of the
FI. In the presence of nonmetal electrolytes, two distinct red-shifted
peaks were observed and assigned to the CIP and SSIP. The assignments
are interpreted in the framework of the vibrational Stark effect (VSE)
and are supported by (1) the solvent dependence of ion-pair populations,
(2) the observation of a cryptand-separated sodium ion pair that mimics
the formation of SSIPs, and (3) electronic structure calculations.
In the second part of this work, we show that a blue-shift of the
νÂ(Cî—ĽN) IR band due to the VSE can be induced in a nitrile-substituted
fluorene radical anion by covalently tethering it to a metal-chelating
ligand that forms an intramolecular ion pair upon reduction and complexation
with sodium ion. This adds support to the conclusion that the shift
in IR absorptions by ion pairing originates from the VSE. These results
combined show that we can identify ion-pair structures by using the
VSE, including the existence of SSIPs in a low-polarity solvent