5 research outputs found
Rare Example of TICT Based Optical Responses for the Specific Recognition of Cr<sup>3+</sup> by a 2,2ā²:6ā²,2ā³-Terpyridine Derivative and Demonstration of Multiple Logic Operations
Chemosensor <b>L</b> showed a <i>nonlinear
fluorescence</i> response on specific binding to Cr<sup>3+</sup> ion in the presence
of various alkali, alkaline-earth, transition, and lanthanide metal
ions. A luminescence band with maxima at 512 nm for <b>L</b> was observed (Ī»<sub>ext</sub> = 330 nm) for a twisted intramolecular
charge transfer (TICT) transition following antienergy gap law behavior.
However, normal energy gap law behavior prevailed on formation of
a new nonluminescent charge transfer complex, M<sup><i>n</i>+</sup>Ā·<b>L</b>. For paramagnetic metal ions, paramagnetism
induced luminescence quenching could have also contributed to this.
A new <i>switched on</i> fluorescence response at Ī»<sub>ems</sub> of 356 nm (Ī»<sub>ext</sub> of 330 nm) was observed
due to FranckāCondon charge transfer (FC-CT) transition only
on the formation of a complex, (Cr<sup>3+</sup>)<sub>2</sub>Ā·<b>L</b>. Spectral studies revealed a unique dynamic coordination
behavior and migration of Cr<sup>3+</sup> from the terpyridyl fragment
to the N<sub>NMe<sub>2</sub></sub> center of <b>L</b> as a function
of the varying concentration of another ion (Zn<sup>2+</sup>) and
the subtle difference in the binding affinities of the terpyridyl
moiety toward Cr<sup>3+</sup> and Zn<sup>2+</sup>. Further, spectral
responses of <b>L</b> toward Zn<sup>2+</sup>, different concentration
of Cr<sup>3+</sup>, H<sup>+</sup> and on subsequent addition of F<sup>ā</sup> as different ionic inputs could be correlated well
for demonstrating various basic and combinatorial circuits
A Taco Complex Derived from a Bis-Crown Ether Capable of Executing Molecular Logic Operation through Reversible Complexation
As learned from natural systems, self-assembly and self-sorting
help in interconnecting different molecular logic gates and thus achieve
high-level logic functions. In this context, demonstration of important
logic operations using changes in optical responses due to the formation
of molecular assemblies is even more desirable for the construction
of a molecular computer. Synthesis of an appropriate divalent as well
as a luminescent crown ether based host <b>1</b> and paraquat
derivatives, <b>2</b>(PF<sub>6</sub>)<sub>2</sub> and <b>3</b>(PF<sub>6</sub>)<sub>2</sub>, as guests helped in demonstrating
a reversible [3]Ā(taco complex) (<b>1</b>Ā·{<b>2</b>(PF<sub>6</sub>)<sub>2</sub>}<sub>2</sub> or <b>1</b>Ā·{<b>3</b>(PF<sub>6</sub>)<sub>2</sub>}<sub>2</sub>) formation in nonpolar
solvent. Detailed <sup>1</sup>H NMR studies revealed that two paraquat
units were bound cooperatively by the two crown units in <b>1</b>. Because of preorganization, the flexible host molecule <b>1</b> adopts a folded conformation, where each of two paraquat units remain
sandwiched between the two aromatic units of each folded crown ether
moiety in <b>1</b>. Disassembly of the ātacoā
complex in the presence of KPF<sub>6</sub> and reassembly on subsequent
addition of DB18C6 was initially demonstrated by <sup>1</sup>H NMR
spectral studies, which were subsequently corroborated through luminescence
spectral studies. Further, luminescence spectral responses as output
signals with appropriate and two independent molecular inputs could
be correlated to demonstrate basic logic operation like OR and YES
gates, while the results of the three molecular inputs could be utilized
to demonstrate important logic operation like an INHIBIT gate
Recognition of Hg<sup>2+</sup> and Cr<sup>3+</sup> in Physiological Conditions by a Rhodamine Derivative and Its Application as a Reagent for Cell-Imaging Studies
A new rhodamine-based receptor, derivatized with an additional
fluorophore (quinoline), was synthesized for selective recognition
of Hg<sup>2+</sup> and Cr<sup>3+</sup> in an acetonitrile/HEPES buffer
medium of pH 7.3. This reagent could be used as a dual probe and allowed
detection of these two ions by monitoring changes in absorption and
the fluorescence spectral pattern. In both instances, the extent of
the changes was significant enough to allow visual detection. More
importantly, the receptor molecule could be used as an imaging reagent
for detection of Hg<sup>2+</sup> and Cr<sup>3+</sup> uptake in live
human cancer cells (MCF7) using laser confocal microscopic studies.
Unlike HgĀ(ClO<sub>4</sub>)<sub>2</sub> or HgĀ(NO<sub>3</sub>)<sub>2</sub> salts, HgCl<sub>2</sub> or HgI<sub>2</sub> failed to induce any
visually detectable change in color or fluorescence upon interaction
with <b>L</b><sub><b>1</b></sub> under identical experimental
conditions. Presumably, the higher covalent nature of Hg<sup>II</sup> in HgCl<sub>2</sub> or HgI<sub>2</sub> accounts for its lower acidity
and its inability to open up the spirolactam ring of the reagent <b>L</b><sub><b>1</b></sub>. The issue has been addressed on
the basis of the single-crystal X-ray structures of <b>L</b><sub><b>1</b></sub>Ā·HgX<sub>2</sub> (X<sup>ā</sup> = Cl<sup>ā</sup> or I<sup>ā</sup>) and results from
other spectral studies
Recognition of Hg<sup>2+</sup> and Cr<sup>3+</sup> in Physiological Conditions by a Rhodamine Derivative and Its Application as a Reagent for Cell-Imaging Studies
A new rhodamine-based receptor, derivatized with an additional
fluorophore (quinoline), was synthesized for selective recognition
of Hg<sup>2+</sup> and Cr<sup>3+</sup> in an acetonitrile/HEPES buffer
medium of pH 7.3. This reagent could be used as a dual probe and allowed
detection of these two ions by monitoring changes in absorption and
the fluorescence spectral pattern. In both instances, the extent of
the changes was significant enough to allow visual detection. More
importantly, the receptor molecule could be used as an imaging reagent
for detection of Hg<sup>2+</sup> and Cr<sup>3+</sup> uptake in live
human cancer cells (MCF7) using laser confocal microscopic studies.
Unlike HgĀ(ClO<sub>4</sub>)<sub>2</sub> or HgĀ(NO<sub>3</sub>)<sub>2</sub> salts, HgCl<sub>2</sub> or HgI<sub>2</sub> failed to induce any
visually detectable change in color or fluorescence upon interaction
with <b>L</b><sub><b>1</b></sub> under identical experimental
conditions. Presumably, the higher covalent nature of Hg<sup>II</sup> in HgCl<sub>2</sub> or HgI<sub>2</sub> accounts for its lower acidity
and its inability to open up the spirolactam ring of the reagent <b>L</b><sub><b>1</b></sub>. The issue has been addressed on
the basis of the single-crystal X-ray structures of <b>L</b><sub><b>1</b></sub>Ā·HgX<sub>2</sub> (X<sup>ā</sup> = Cl<sup>ā</sup> or I<sup>ā</sup>) and results from
other spectral studies
Ratiometric Detection of Cr<sup>3+</sup> and Hg<sup>2+</sup> by a Naphthalimide-Rhodamine Based Fluorescent Probe
Newly synthesized rhodamine derivatives, <b>L</b><sub><b>1</b></sub> and <b>L</b><sub><b>2</b></sub>, are found
to bind specifically to Hg<sup>2+</sup> or Cr<sup>3+</sup> in presence
of large excess of other competing ions with associated changes in
their optical and fluorescence spectral behavior. These spectral changes
are significant enough in the visible region of the spectrum and thus,
allow the visual detection. For <b>L</b><sub><b>1</b></sub>, the detection limit is even lower than the permissible [Cr<sup>3+</sup>] or [Hg<sup>2+</sup>] in drinking water as per standard
U.S. EPA norms; while the receptor, <b>L2</b> could be used
as a ratiometric sensor for detection of Cr<sup>3+</sup> and Hg<sup>2+</sup> based on the resonance energy transfer (RET) process involving
the donor naphthalimide and the acceptor Cr<sup>3+</sup>/Hg<sup>2+</sup>-bound xanthene fragment. Studies reveal that these two reagents
could be used for recognition and sensing of Hg<sup>2+</sup>/Cr<sup>3+</sup>. Further, confocal laser microscopic studies confirmed that
the reagent <b>L</b><sub><b>2</b></sub> could also be
used as an imaging probe for detection of uptake of these ions in
A431 cells