10 research outputs found
Molecular Recognition Controlled Delivery of a Small Molecule from a Nanocarrier to Natural DNA
Controlled and targeted release of
an active small molecule at
the site of demand is very crucial in pharmaceutical applications.
In the present article, we have reported a very simple yet unique
chemical system which can be used for the controlled and quantitative
transfer of a small molecule from a nanocarrier to natural DNA using
an external stimulus. Due to the high sensitivity of emission intensity
toward its microenvironments, an ultrafast molecular rotor has been
used as a spectroscopic probe. SDS micelle has been used as a nanocarrier
and the cyclodextrin molecules are used as an external stimulus. The
molecular recognition property of the stimulus toward the hydrophobic
chain of the surfactant molecules has been utilized for controlled
transfer of the small molecule from the nanocarrier to DNA. Through
detailed steady state and time-resolved spectroscopic studies, it
has been demonstrated that quantitative transfer of the small molecules
from nanocarrier to the natural DNA molecules could be achieved. The
present chemical system might be very promising in the field of controlled
and targeted drug delivery
Supramolecular Dye Aggregate Assembly Enables Ratiometric Detection and Discrimination of Lysine and Arginine in Aqueous Solution
Constructing
sensor systems for rapid and selective detection of
small biomolecules such as amino acids is a major area of focus in
bioanalytical chemistry. Considering the biological relevance of arginine
and lysine, significant efforts have been directed to develop fluorescent
sensors for their detection. However, these developed sensors suffer
from certain disadvantages such as poor aqueous solubility, technically
demanding and time-consuming synthetic protocols, and more importantly,
most of them operate through single wavelength measurements, making
their performance prone to small variations in experimental conditions.
Herein, we report a ratiometric sensor that operates through lysine-
and arginine-induced dissociation of a supramolecular assembly consisting
of emissive H-aggregates of a molecular rotor dye, thioflavin-T (ThT),
on the surface of a polyanionic supramolecular host, sulfated β-cyclodextrin.
This disassembly brings out the modulation of monomer–aggregate
equilibrium in the system which acts as an ideal scheme for the ratiometric
detection of lysine and arginine in the aqueous solution. Besides
facile framework of our sensor system, it employs a commercially available
inexpensive probe molecule, ThT, which provides an added advantage
over other sensor systems that employ synthetically demanding probe
molecules. Importantly, the distinctive feature of the ratiometric
detection of arginine and lysine provides an inherent advantage of
increased accuracy in quantitative analysis. Interestingly, we have
also demonstrated that arginine displays a multiwavelength distinctive
recognition pattern which distinguishes it from lysine, using a single
supramolecular ensemble. Furthermore, our sensor system also shows
response in heterogeneous, biologically complex media of serum samples,
thus extending its possible use in real-life applications
Emissive H‑Aggregates of an Ultrafast Molecular Rotor: A Promising Platform for Sensing Heparin
Constructing “turn
on” fluorescent probes for heparin, a most widely used anticoagulant
in clinics, from commercially available materials is of great importance,
but remains challenging. Here, we report the formation of a rarely
observed emissive H-aggregate of an ultrafast molecular rotor dye,
Thioflavin-T, in the presence of heparin, which provides an excellent
platform for simple, economic and rapid fluorescence turn-on sensing
of heparin. Generally, H-aggregates are considered as serious problem
in the field of biomolecular sensing, owing to their poorly emissive
nature resulting from excitonic interaction. To the best of our knowledge,
this is the first report, where contrastingly, the turn-on emission
from the H-aggregates has been utilized in the biomolecule sensing
scheme, and enables a very efficient and selective detection of a
vital biomolecule and a drug with its extensive medical applications,
i.e., heparin. Our sensor system offers several advantages including,
emission in the biologically advantageous red-region, dual sensing,
i.e., both by fluorimetry and colorimetry, and most importantly constructed
from in-expensive commercially available dye molecule, which is expected
to impart a large impact on the sensing field of heparin. Our system
displays good performance in complex biological media of serum samples.
The novel Thioflavin-T aggregate emission could be also used to probe
the interaction of heparin with its only clinically approved antidote,
Protamine
Excited-State Proton Transfer on the Surface of a Therapeutic Protein, Protamine
Proton
transfer reactions on biosurfaces play an important role
in a myriad of biological processes. Herein, the excited-state proton
transfer reaction of 8-hydroxypyrene-1,3,6-trisulfonate (HPTS) has
been investigated in the presence of an important therapeutic protein,
Protamine (PrS), using ground-state absorption, steady-state, and
detailed time-resolved emission measurements. HPTS forms a 1:1 complex
with Protamine with a high association constant of 2.6 × 10<sup>4</sup> M<sup>–1</sup>. The binding of HPTS with Protamine
leads to a significant modulation in the ground-state prototropic
equilibrium causing a downward shift of 1.1 unit in the acidity constant
(p<i>K</i><sub>a</sub>). In contrast to a large number of
reports of slow proton transfer of HPTS on biosurfaces, interestingly,
HPTS registers a faster proton transfer event in the presence of Protamine
as compared to that of even the bulk aqueous buffer medium. Furthermore,
the dimensionality
of the proton diffusion process is also significantly reduced on the
surface of Protamine that is in contrast to the behavior of HPTS in
the bulk aqueous buffer medium, where the proton diffusion process
is three-dimensional. The effect of ionic strength on the binding
of HPTS toward PrS suggests a predominant role of electrostatic interaction
between anionic HPTS and cationic Protamine, which is further supported
by molecular docking simulations which predict that the most preferable
binding site for HPTS on the surface of Protamine is surrounded by
multiple cationic arginine residues
Stimulus-Responsive Supramolecular Aggregate Assembly of Auramine O Templated by Sulfated Cyclodextrin
Self-aggregation
of organic molecules is rarely seen with macrocyclic
hosts like β-cyclodextrin, as they preferentially involve the
formation of inclusion complexes with the guest molecule. In this
contribution, we report the self-aggregation of a guest molecule induced
by negatively charged sulfated β-cyclodextrin (SCD) to yield
highly emissive aggregates of a recently projected amyloid marker
dye, Auramine O (AuO). The SCD templated AuO aggregates display very
different photophysics when compared to its reported behavior in a
wide range of various chemical and biological environment but show
a remarkable similarity with the recently reported photophysical behavior
of AuO in human insulin fibrillar media, thus providing important
insights into the molecular form of AuO responsible for its amyloid
sensing ability. The self-assembled AuO aggregates formed in the presence
of SCD display a significantly long excited-state lifetime, suggesting
the retardation of the torsional relaxation of dye in the aggregated
state, which otherwise leads to a very short excited-state lifetime
for the monomeric form of the dye in the isolated form. Detailed time-resolved
emission spectra (TRES) measurements show a dynamic Stokes shift suggesting
excitonic migration within the AuO aggregates. The supramolecular
aggregate assembly displays remarkable sensitivity to important external
stimuli like temperature or ionic strength of the medium, pitching
for its possible application in designing stimuli-responsive sensing
schemes for important analytes
Controlled Sequestration of DNA Intercalated Drug by Polymer–Surfactant Supramolecular Assemblies
Triblock
copolymer and surfactant based supramolecular assemblies
have been used for the controlled sequestration of the DNA intercalator.
The triblock copolymer micelles do not affect the molecules that are
intercalated in the DNA. However, on addition of charged surfactant
to the triblock copolymer micellar solution, sequestration of the
intercalated molecules from DNA to the polymer–surfactant supramolecular
assemblies takes place. Such sequestration of the intercalated molecules
in the polymer–surfactant supramolecular assemblies has been
explained on the basis of the charged surface formed in the polymer
micelles due to the addition of surfactants. Sequestration of the
intercalated molecules from the DNA to the polymer–surfactant
supramolecular assemblies has been monitored through the ground state
absorption, steady state, and time-resolved emission measurements.
It is shown that the extent of sequestration of the intercalated molecules
can be finely tuned by tuning the concentration of the surfactant
in the triblock copolymer solution. Quantitative sequestration of
the intercalated molecules by the supramolecular assemblies has been
achieved. Such controlled sequestration of the DNA intercalated molecules
by polymer–surfactant supramolecular assemblies can be used
to study the binding of drug with DNA and may be useful in applications
like detoxification in the case of drug overdose
Ultrafast Torsional Relaxation of Thioflavin‑T in Tris(pentafluoroethyl)trifluorophosphate (FAP) Anion-Based Ionic Liquids
Ultrafast
spectroscopy on solutes, whose dynamics is very sensitive
to the friction in its local environment, has strong potential to
report on the microenvironment existing in complex fluids such as
ionic liquids. In this work, the torsional relaxation dynamics of
Thioflavin-T (ThT), an ultrafast molecular rotor, is investigated
in two fluoroalkylphosphate ([FAP])-based ionic liquids, namely, 1-ethyl-3-methylimidazolium
tris(pentafluoroethyl)trifluorophosphate ([EMIM][FAP]) and 1-(2-hydroxyethyl)-3-methylimidazolium
tris(pentafluoroethyl)trifluorophosphate ([OHEMIM][FAP]), using ultrafast
fluorescence up-conversion spectroscopy. The emission quantum yield
and the excited-state fluorescence lifetime measurement suggest that
the torsional relaxation of Thioflavin-T, in this class of ionic liquids,
is guided by the viscosity of the medium. The temporal profile of
the dynamic Stokes’ shift of ThT, measured from time-resolved
emission spectrum (TRES), displays a multiexponential behavior in
both ionic liquids. The long time dynamics of the Stokes’ shift
is reasonably slower for the hydroxyethyl derivative as compared to
the ethyl derivative, which is in accordance with their measured shear
viscosity. However, the short time dynamics of Stokes’ shift
is very similar in both the ionic liquids, and seems to be independent
of the measured shear viscosity of the ionic liquid. We rationalize
these observations in terms of different locations of ThT in these
ionic liquids. These results suggest that despite having a higher
bulk viscosity in the ionic liquid, they can provide unique microenvironment
in their complex structure, where the reaction can be faster than
expected from their measured shear viscosity
Differential Hydration of Tricyanomethanide Observed by Time Resolved Vibrational Spectroscopy
The degenerate transition corresponding to asymmetric stretches of the <i>D</i><sub>3<i>h</i></sub> tricyanomethanide anion, C(CN)<sub>3</sub><sup>–</sup>, in aqueous solution was investigated by linear FTIR spectroscopy, femtosecond pump–probe spectroscopy, and 2D IR spectroscopy. Time resolved vibrational spectroscopy shows that water induces vibrational energy transfer between the degenerate asymmetric stretch modes of tricyanomethanide. The frequency–frequency correlation function and the vibrational energy transfer show two significantly different ultrafast time scales. The system is modeled with molecular dynamics simulations and ab initio calculations. A new model for theoretically describing the vibrational dynamics of a degenerate transition is presented. Microscopic models, where water interacts axially and radially with the ion, are suggested for the transition dipole reorientation mechanism
Evaluation of an Ultrafast Molecular Rotor, Auramine O, as a Fluorescent Amyloid Marker
Recently,
Auramine O (AuO) has been projected as a fluorescent
fibril sensor, and it has been claimed that AuO has an advantage over
the most extensively utilized fibril marker, Thioflavin-T (ThT), owing
to the presence of an additional large red-shifted emission band for
AuO, which was observed exclusively for AuO in the presence of fibrillar
media and not in protein or buffer media. As fibrils are very rich
in β-sheet structure, a fibril sensor should be more specific
toward the β-sheet structure so as to produce a large contrast
between the fibril form and native protein form, for efficient detection
and in vitro mechanistic studies of fibrillation. However, in this
report, we show that AuO interacts significantly with the native form
of bovine serum albumin (BSA), which is an all-α-helical protein
and lacks the β-sheet structure, which are the hallmarks of
a fibrillar structure. This strong interaction of AuO with the native
form of BSA leads to a large emission enhancement of AuO for the native
protein itself, and leads to a low contrast between the BSA protein
and its fibrils. More importantly, the large red-shifted emission
band of AuO, reported in the presence of human insulin fibrils, and
which was projected as its major advantage over ThT, is not observed
in the presence of BSA fibrils as well as fibrils from other proteins,
such as lysozyme, human serum albumin, and β-lactoglobulin.
Thus, our results provide information on the
universal applicability of the distinctive and claimed-to-be-advantageous
photophysical features reported for AuO in human insulin fibrils towards
fibrils from other proteins. Time-resolved fluorescence measurements
also support the proposition of a strong interaction of AuO with native
BSA. Additionally, tryptophan emission of the protein has been explored
to further elucidate the binding mechanism of AuO with native BSA.
Evaluation of thermodynamic parameters revealed that the binding of
AuO with native BSA involved positive enthalpy and entropy changes,
suggesting dominant contributions from hydrophobic and electrostatic
interactions toward the association of AuO with native BSA. Molecular
docking calculations have been performed to identify the principal
binding location of AuO in native BSA
On the Molecular Form of Amyloid Marker, Auramine O, in Human Insulin Fibrils
Designing extrinsic fluorescence
sensors for amyloid fibrils is
a very active and important area of research. Recently, an ultrafast
molecule rotor dye, Auramine O (AuO), has been projected as a fluorescent
amyloid marker. It has been claimed that AuO scores better than the
most extensively utilized gold-standard amyloid probe, Thioflavin-T
(ThT). This advantage arises from the fact that AuO, in addition to
its usual emission band (∼500 nm), also displays a large red-shifted
emission band (∼560 nm), exclusively in the presence of human
insulin fibril medium
and not in the native protein or buffer media. On the contrary, for
ThT, the emission maximum (∼490 nm) largely remains unchanged
while going from protein to fibril. This otherwise unknown large red-shifted
emission band of AuO, observed in the presence of human insulin fibrils,
was tentatively attributed to a species formed upon fast proton dissociation
from excited AuO. It was proposed that because of the long excited-state
lifetime (∼1.8 ns) of AuO upon association with human insulin
fibrils, this fast proton dissociation from excited AuO could be observed,
which is otherwise not observed in buffer or native protein media,
owing to its very short excited-state lifetime (∼1 ps). Herein,
we show that despite the long excited-state lifetime of AuO in other
fibrillar media (human serum albumin and lysozyme), the new red-shifted
emission band at 560 nm is not observed, thus possibly suggesting
a different origin of the red-shifted emission band of AuO in human
insulin fibril medium. We convincingly show that this red-shifted
band of AuO (∼560 nm) could be observed under conditions that
promote dye aggregation, such as a premicellar concentration of surfactants
and polyelectrolytes. These AuO aggregates display strong emission
wavelength dependence of transient decay traces, similar to that for
AuO in human insulin fibril medium. Detailed time-resolved emission
spectral (TRES) measurements suggest that the AuO/premicellar surfactant
and AuO/human insulin fibril system share similar features, such as
a dynamic red-shift in TRES and an isoemissive point in the time-resolved
area-normalized emission spectra, suggesting that the characteristic
red-shifted emission band of AuO in human insulin fibril medium may
arise from AuO aggregates