2 research outputs found
Copper-Catalyzed Ring-Expansion Cascade of Azirines with Alkynes: Synthesis of Multisubstituted Pyridines at Room Temperature
The
first intermolecular ring-expansion cascade of azirines with
alkynes for the synthesis of pyridines, enabled by a copper/triethylamine
catalytic system via simultaneous generation and utilization of yne-enamine
and skipped-yne-imine intermediates, is reported. Experimental as
well as computational mechanistic studies revealed that the role of
triethylamine is crucial in deciding the reaction pathway toward the
pyridine products. This process offers a novel, one-step, direct,
and practical strategy for the rapid construction of highly substituted
pyridines under exceedingly mild conditions, and an installed alkyne
functionality
Cytotoxicity Induced by Engineered Silver Nanocrystallites Is Dependent on Surface Coatings and Cell Types
Due to their unique antimicrobial properties silver nanocrystallites
have garnered substantial attention and are used extensively for biomedical
applications as an additive to wound dressings, surgical instruments
and bone substitute materials. They are also released into unintended
locations such as the environment or biosphere. Therefore it is imperative
to understand the potential interactions, fate and transport of nanoparticles
with environmental biotic systems. Numerous factors including the
composition, size, shape, surface charge, and capping molecule of
nanoparticles are known to influence cell cytotoxicity. Our results
demonstrate that the physical/chemical properties of the silver nanoparticles
including surface charge, differential binding and aggregation potential,
which are influenced by the surface coatings, are a major determining
factor in eliciting cytotoxicity and in dictating potential cellular
interactions. In the present investigation, silver nanocrystallites
with nearly uniform size and shape distribution but with different
surface coatings, imparting overall high negativity to high positivity,
were synthesized. These nanoparticles included polyÂ(diallyldimethylammonium)
chloride-Ag, biogenic-Ag, colloidal-Ag (uncoated), and oleate-Ag with
zeta potentials +45 ± 5, −12 ± 2, −42 ±
5, and −45 ± 5 mV, respectively; the particles were purified
and thoroughly characterized so as to avoid false cytotoxicity interpretations.
A systematic investigation on the cytotoxic effects, cellular response,
and membrane damage caused by these four different silver nanoparticles
was carried out using multiple toxicity measurements on mouse macrophage
(RAW-264.7) and lung epithelial (C-10) cell lines. Our results clearly
indicate that the cytotoxicity was dependent on various factors such
as surface charge and coating materials used in the synthesis, particle
aggregation, and the cell-type for the different silver nanoparticles
that were investigated. PolyÂ(diallyldimethylammonium)-coated Ag nanoparticles
were found to be the most toxic, followed by biogenic-Ag and oleate-Ag
nanoparticles, whereas uncoated or colloidal silver nanoparticles
were found to be the least toxic to both macrophage and lung epithelial
cells. Also, based on our cytotoxicity interpretations, lung epithelial
cells were found to be more resistant to the silver nanoparticles
than the macrophage cells, regardless of the surface coating