26 research outputs found
Acetohydrazone: A Transient Directing Group for Arylation of Unactivated C(sp<sup>3</sup>)–H Bonds
A straightforward
and efficient method has been developed for the
synthesis of 2-benzylbenzaldehyde derivatives from 2-methylbenzaldehyde
and iodobenzene via a CÂ(sp<sup>3</sup>)–H activation process.
In the course of the activation reaction, acetohydrazone is formed
between 2-benzylbenzaldehyde and acetohydrazine as a transient directing
group. As a new kind of transient directing group, acetohydrazone
exhibits a remarkable directing effect to give corresponding products
in good to excellent yields
Ultrasensitive Detection of Transcription Factors Using Transcription-Mediated Isothermally Exponential Amplification-Induced Chemiluminescence
Transcription factors (TFs) are important
cellular components that
modulate gene expression, and the malregulation of transcription will
lead to a variety of diseases such as cancer and developmental syndromes.
However, the conventional methods for transcription factor assay are
generally cumbersome and costly with low sensitivity. Here, we develop
a label-free strategy for ultrasensitive detection of transcription
factors using a cascade signal amplification of RNA transcription,
dual isothermally exponential amplification reaction (EXPAR), and
G-quadruplex DNAzyme-driven chemiluminescence. Briefly, the specific
binding of TF with the detecting probe prevents the cleavage of the
detecting probe by exonuclease and subsequently facilitates the conversion
of TF signal to abundant RNA triggers in the presence of T7 RNA polymerase.
The obtained RNA triggers can initiate the strand displacement amplification
to yield abundant DNAzymes and DNA triggers, and the released DNA
triggers can further initiate the next rounds of EXPAR reaction. The
synergistic operation of dual EXPAR reaction can produce large amounts
of DNAzymes, which subsequently catalyze the oxidation of luminol
by H<sub>2</sub>O<sub>2</sub> to yield an enhanced chemiluminescence
signal with the assistance of cofactor hemin. Conversely, in the absence
of target TF, the naked detecting probes will be completely digested
by exonucleases, leading to neither the transcription-mediated EXPAR
nor the DNAzyme-driven chemiluminescence signal. This method has a
low detection limit of as low as 6.03 × 10<sup>–15</sup> M and a broad dynamic range from 10 fM to 1 nM and can even measure
the NF-κB p50 of crude cell nuclear extracts. Moreover, this
method can be used to measure a variety of DNA-binding proteins by
simply substituting the target-specific binding sequence in the detecting
probes
Application of Nano Fe<sup>III</sup>–Tannic Acid Complexes in Modifying Aqueous Acrylic Latex for Controlled-Release Coated Urea
Acrylic
latexes are valuable waterborne materials used in controlled-release
fertilizers. Controlled-release urea coated with these latexes releases
a large amount of nutrients, making it difficult to meet the requirement
of plants. Herein, Fe<sup>III</sup>–tannic acid (TA) complexes
were blended with acrylic latex and subsequently reassembled on a
surface of polyacrylate particles. These complexes remarkably retarded
the release of urea (the preliminary solubility was decreased from
22.3 to 0.8%) via decreasing the coating tackiness (<i>T</i><sub>g</sub> was increased from 4.17 to 6.42 °C), increasing
the coating strength (tensile stress was improved from 3.88 to 4.45
MPa), and promoting the formation of denser structures (surface tension
was decreased from 37.37 to 35.94 mN/m). Overall, our findings showed
that a simple blending of Fe<sup>III</sup>–TA complexes with
acrylic latex produces excellent coatings that delay the release of
urea, which demonstrates great potential for use in controlled-release
fertilizers coated with waterborne polymers
Base-Excision-Repair-Induced Construction of a Single Quantum-Dot-Based Sensor for Sensitive Detection of DNA Glycosylase Activity
DNA
glycosylase is an initiating enzyme of cellular base excision
repair pathway which is responsible for the repair of various DNA
lesions and the maintenance of genomic stability, and the dysregulation
of DNA glycosylase activity is associated with a variety of human
pathology. Accurate detection of DNA glycosylase activity is critical
to both clinical diagnosis and therapeutics, but conventional methods
for the DNA glycosylase assay are usually time-consuming with poor
sensitivity. Here, we demonstrate the base-excision-repair-induced
construction of a single quantum dot (QD)-based sensor for highly
sensitive measurement of DNA glycosylase activity. We use human 8-oxoguanine-DNA
glycosylase 1 (hOGG1), which is responsible for specifically repairing
the damaged 8-hydroxyguanine (8-oxoG, one of the most abundant and
widely studied DNA damage products), as a model DNA glycosylase. In
the presence of biotin-labeled DNA substrate, the hOGG1 may catalyze
the removal of 8-oxo G from 8-oxoG·C base pairs to generate an
apurinic/apyrimidinic (AP) site. With the assistance of apurinic/apyrimidinic
endonuclease (APE1), the cleavage of the AP site results in the generation
of a single-nucleotide gap. Subsequently, DNA polymerase β incorporates
a Cy5-labeled dGTP into the DNA substrate to fill the gap. With the
addition of streptavidin-coated QDs, a QD-DNA-Cy5 nanostructure is
formed via specific biotin–streptavidin binding, inducing the
occurrence of fluorescence resonance energy transfer (FRET) from the
QD to Cy5. The resulting Cy5 signal can be simply monitored by total
internal reflection fluorescence (TIRF) imaging. The proposed method
enables highly sensitive measurement of hOGG1 activity with a detection
limit of 1.8 × 10<sup>–6</sup> U/μL. Moreover, it
can be used to measure the enzyme kinetic parameters and detect the
hOGG1 activity in crude cell extracts, offering a powerful tool for
biomedical research and clinical diagnosis
Supplementary Material from Photoprotection through ultrafast charge recombination in photochemical reaction centres under oxidizing conditions
Materials and Methods; Figures S1-S10
Intensity-Modulated Scanning Kelvin Probe Microscopy for Probing Recombination in Organic Photovoltaics
We study surface photovoltage decays on sub-millisecond time scales in organic solar cells using intensity-modulated scanning Kelvin probe microscopy (SKPM). Using polymer/fullerene (poly[<i>N</i>-9″-heptadecanyl-2,7-carbazole-<i>alt</i>-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]/[6,6]-phenyl C<sub>71</sub>-butyric acid methyl ester, PCDTBT/PC<sub>71</sub>BM) bulk heterojunction devices as a test case, we show that the decay lifetimes measured by SKPM depend on the intensity of the background illumination. We propose that this intensity dependence is related to the well-known carrier-density-dependent recombination kinetics in organic bulk heterojunction materials. We perform transient photovoltage (TPV) and charge extraction (CE) measurements on the PCDTBT/PC<sub>71</sub>BM blends to extract the carrier-density dependence of the recombination lifetime in our samples, and we find that the device TPV and CE data are in good agreement with the intensity and frequency dependence observed <i>via</i> SKPM. Finally, we demonstrate the capability of intensity-modulated SKPM to probe local recombination rates due to buried interfaces in organic photovoltaics (OPVs). We measure the differences in photovoltage decay lifetimes over regions of an OPV cell fabricated on an indium tin oxide electrode patterned with two different phosphonic acid monolayers known to affect carrier lifetime
Controllable Mismatched Ligation for Bioluminescence Screening of Known and Unknown Mutations
Single-nucleotide
polymorphisms (SNPs) are closely related to human
diseases and individual drug responses, and the accurate detection
of SNPs is crucial to both clinical diagnosis and development of personalized
medicine. Among various SNPs detection methods, ligase detection reaction
(LDR) has shown great potential due to its low detection limit and
excellent specificity. However, frequent involvement of expensive
labels increases the experimental cost and compromises the assay efficiency,
and the requirement of careful predesigned probes limits it to only
known SNPs assays. In this research, we develop a controllable mismatched
ligation for bioluminescence screening of both known and unknown mutations.
Especially, the ligation specificity of <i>E. coli</i> ligase
is tunable under different experimental conditions. The mismatches
locating on the 3′-side of the nick cannot be ligated efficiently
by <i>E. coli</i> ligase, whereas all mismatches locating
on the 5′-side of the nick can be ligated efficiently by <i>E. coli</i> ligase. We design a 3′-discriminating probe
(3′-probe) for the discrimination of known mutation and introduce
a T7 Endo I for the detection of unknown mutation. With the integration
of bioluminescence monitoring of ligation byproduct adenosine 5'-monophosphate
(AMP), both known and unknown SNPs can be easily detected without
the involvement of any expensive labels and labor-intensive separation.
This method is simple, homogeneous, label-free, and cost-effective
and may provide a valuable complement to current sequencing technologies
for disease diagnostics, personalized medicine, and biomedical research
Vibronic Coherence in the Charge Separation Process of the <i>Rhodobacter sphaeroides</i> Reaction Center
Two-dimensional
electronic spectroscopy was applied to a variant
of the reaction center (RC) of purple bacterium <i>Rhodobacter
sphaeroides</i> lacking the primary acceptor ubiquinone in order
to understand the ultrafast separation and transfer of charge between
the bacteriochlorin cofactors. For the first time, characteristic
2D spectra were obtained for the participating excited and charge-transfer
states, and the electron-transfer cascade (including two different
channels, the P* and B* channels) was fully mapped. By analyzing quantum
beats using 2D frequency maps, excited-state vibrational modes at
153 and 33 cm<sup>–1</sup> were identified. We speculate that
these modes couple to the charge separation (CS) process and collectively
optimize the CS and are responsible for the superhigh efficiency
Direct Observation of Energy Detrapping in LH1-RC Complex by Two-Dimensional Electronic Spectroscopy
The purple bacterial
core light harvesting antenna-reaction center
(LH1-RC) complex is the simplest system able to achieve the entire
primary function of photosynthesis. During the past decade, a variety
of photosynthetic proteins were studied by a powerful technique, two-dimensional
electronic spectroscopy (2DES). However, little attention has been
paid to LH1-RC, although its reversible uphill energy transfer, trapping,
and backward detrapping processes, represent a crucial step in the
early photosynthetic reaction dynamics. Thus, in this work, we employed
2DES to study two LH1-RC complexes of Thermochromatium (Tch.) tepidum. By direct observation of detrapping, the complex reversible process
was clearly identified and an overall scheme of the excitation evolution
in LH1-RC was obtained
Excitonic and Vibrational Coherence in the Excitation Relaxation Process of Two LH1 Complexes as Revealed by Two-Dimensional Electronic Spectroscopy
Ultrafast
excitation relaxation within a manifold exciton state
and long-lived vibrational coherence are two universal characteristics
of photosynthetic antenna complexes. In this work, we studied the
two-dimensional electronic spectra of two core light-harvesting (LH1)
complexes of <i>Thermochromatium</i> (<i>Tch.</i>) <i>tepidum</i>, native Ca<sup>2+</sup>-LH1 and modified
Ba<sup>2+</sup>-LH1. The role of the vibrational coherence in the
exciton relaxation was revealed by comparing the two LH1 with similar
structures but different electronic properties and by the evolution
of the exciton and vibrational coherence as a function of temperature