Two water-soluble near-infrared luminescent probes, which possess both conventional intense Stokes fluorescence and unique single-photon frequency upconversion luminescence (FUCL), were developed for sensitive and selective detection of pH changes in live cells. The water solubility and biocompatibility of these probes were achieved by introducing mannose residues through 2,2′-(ethylenedioxy)diethylamine tethered spacers to a near-infrared conventional fluorescence (CF) and FUCL organic fluorophore. At a pH higher than 7.4, the probes have ring-closed spirocyclic lactam structures, thus are colorless and nonfluorescent. Nevertheless, they sensitively respond to acidic pH values, with a drastic structural change to ring-opened spirocyclic lactam forms, which cause significant absorbance increases at 714 nm. Correspondingly, their near-infrared CF and FUCL intensities at 740 nm are also significantly enhanced when excited by 690 and 808 nm, respectively. The probes hold a variety of advantages such as high sensitivity, excellent reversibility and selectivity to pH over metal ions, low cellular autofluorescence background interference, good cell membrane permeability and photostability, as well as low cytotoxicity. Our results have successfully proven that these probes can visualize intracellular lysosomal pH changes in live cells by monitoring both near-infrared CF and FUCL changes.
N-heterocyclic
carbene (NHC) organocatalysis is widely employed
for the umpolung of aldehydes and recently to the umpolung of Michael
acceptors and aldimines. Described herein is the NHC-organocatalyzed
umpolung of aldimines for the enantioselective synthesis of nitrogen
heterocycles. The bisimines generated from the condensation of 1,2-phenylenediamines
and salicylaldehydes undergo intramolecular cyclization in the presence
of a chiral NHC catalyst, resulting in the formation of dihydroquinoxalines
in moderate to good yields and er values. Detailed DFT studies shed
light on the role of −OH groups in stabilizing the initially
generated aza-Breslow intermediates via intramolecular hydrogen bonds.
Preliminary photophysical studies on the synthesized dihydroquinoxalines
revealed that these molecules can be used for the sensing of various
acids and bases.
Efficient detection of arsenate (AsO43-) from contaminated drinking water extracted from underground becomes a matter of utmost necessity as well as exquisite challenge owing to on growing public health damage...
Exploring a covalent organic framework
(COF) material as an efficient
metal-free photocatalyst and as an adsorbent for the removal of pollutants
from contaminated water is very challenging in the context of sustainable
chemistry. Herein, we report a new porous crystalline COF, C6-TRZ-TPA COF, via segregation of donor–acceptor moieties through
the extended Schiff base condensation between tris(4-formylphenyl)amine
and 4,4′,4″-(1,3,5-triazine-2,4,6-triyl)trianiline.
This COF displayed a Brunauer–Emmett–Teller (BET) surface
area of 1058 m2 g–1 with a pore volume
of 0.73 cc g–1. Again, extended π-conjugation,
the presence of heteroatoms throughout the framework, and a narrow
band gap of 2.2 eV, all these features collectively work for the environmental
remediation in two different perspectives: it could harness solar
energy for environmental clean-up, where the COF has been explored
as a robust metal-free photocatalyst for wastewater treatment and
as an adsorbent for iodine capture. In our endeavor of wastewater
treatment, we have conducted the photodegradation of rose bengal (RB)
and methylene blue (MB) as model pollutants since these are extremely
toxic, are health hazard, and bioaccumulative in nature. The catalyst
C6-TRZ-TPA COF showed a very high catalytic efficiency
of 99% towards the degradation of 250 parts per million (ppm) of RB
solution in 80 min under visible light irradiation with the rate constant
of 0.05 min–1. Further, C6-TRZ-TPA COF
is found to be an excellent adsorbent as it efficiently adsorbed radioactive
iodine from its solution as well as from the vapor phase. The material
exhibits a very rapid iodine capturing tendency with an outstanding
iodine vapor uptake capacity of 4832 mg g–1.
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