A smart
molecule, QT490, containing thiosemicarbazide moiety acts
as a highly selective turn-on in vitro NO sensor through the unprecedented
NO-induced transformation of thiosemicarbazide moiety to 1,3,4-oxadiazole
heterocycle with the concomitant release of HSNO, thereby eliminating
any interference from various endogenous biomolecules including dehydroascorbic
acid, ascorbic acid, etc. The kinetic studies of the reactions between
QT490 and NO provide a mechanistic insight into formation
of HSNO/RSNO from the reaction between H2S/RSH and NO in
the biological system. This novel probe is non-cytotoxic, cell permeable,
water-soluble, and appropriate for intracellular cytoplasmic NO sensing
with the possibilities of in vivo applications.
In this report, the
interaction between a phenanthrene–pyrene-based
fluorescent probe (PPI) and bovine serum albumin (BSA), a transport
protein, has been explored by steady-state emission spectroscopy,
fluorescence anisotropy, far-ultraviolet circular dichroism (CD),
time-resolved spectral measurements, and molecular docking simulation
study. The blue shift along with emission enhancement indicates the
interaction between PPI and BSA. The binding of the probe causes quenching
of BSA fluorescence through both static and dynamic quenching mechanisms,
revealing a 1:1 interaction, as delineated from Benesi–Hildebrand
plot, with a binding constant of ∼10
5
M
–1
, which is in excellent agreement with the binding constant extracted
from fluorescence anisotropy measurements. The thermodynamic parameters,
Δ
H
°, Δ
S
°,
and Δ
G
°, as determined from van’t
Hoff relationship indicate the predominance of van der Waals/extensive
hydrogen-bonding interactions for the binding phenomenon. The molecular
docking and site-selective binding studies reveal the predominant
binding of PPI in subdomain IIA of BSA. From the fluorescence resonance
energy transfer study, the average distance between tryptophan 213
of the BSA donor and the PPI acceptor is found to be 3.04 nm. CD study
demonstrates the reduction of α-helical content of BSA protein
on binding with PPI, clearly indicating the change of conformation
of BSA.
A novel sensor (HL5) recognizes sensitively and selectively trivalent metal ions M3+ (M = Al, Fe and Cr) with prominent enhancement in emission intensities with logic gate circuits and memory devices with living cell imaging application.
A novel H3SAL-NH probe exhibits ESIPT from the phenolic OH group to the azomethine N atom in the excited state. This is blocked in the presence of Zn2+ and Al3+ giving turn on fluorescence which is useful for imaging in live HepG2 cells.
A new, easily synthesizable rhodamine-based chemosensor with potential N2O2 donor atoms, L(3), has been characterized by single-crystal X-ray diffraction together with (1)H NMR and high-resolution mass spectrometry (HRMS) studies. L(3) was found to bind selectively and reversibly to the highly toxic Hg(2+) ion. The binding stoichiometry and formation constant of the sensor toward Hg(2+) were determined by various techniques, including UV-vis, fluorescence, and Job's studies, and substantiated by HRMS methods. None of the biologically relevant and toxic heavy metal ions interfered with the detection of Hg(2+) ion. The limit of detection of Hg(2+)calculated by the 3σ method was 1.62 nM. The biocompatibility of L(3) with respect to its good solubility in mixed organic/aqueous media (MeCN/H2O) and cell permeability with no or negligible cytotoxicity provides good opportunities for in vitro/in vivo cell imaging studies. As the probe is poorly soluble in pure water, an attempt was made to frame nano/microstructures in the absence and in the presence of sodium dodecyl sulfate (SDS) as a soft template, which was found to be very useful in synthesizing morphologically interesting L(3) microcrystals. In pure water, micro-organization of L(3) indeed occurred with block-shaped morphology very similar to that in the presence of SDS as a template. However, when we added Hg(2+) to the solution of L(3) under the above two conditions, the morphologies of the microstructures were slightly different; in the first case, a flowerlike structure was observed, and in second case, a simple well-defined spherical microstructure was obtained. Optical microscopy revealed a dotlike microstructure for L(3)-SDS assemblies, which changed to a panicle microstructure in the presence of Hg(2+). UV-vis absorption and steady-state and time-resolved fluorescence studies were also carried out in the absence and presence of Hg(2+), and also the SDS concentration was varied at fixed concentrations of the receptor and guest. The results revealed that the fluorescence intensity increased steadily with [SDS] until it became saturated at ∼7 mM SDS, indicating that the extent of perturbation to the emissive species increases with the increase in [SDS] until it becomes thermodynamically stable. There was also an increase in anisotropy with increasing SDS concentration, which clearly manifests the restriction of movement of the probe in the presence of SDS.
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