Pulsed laser excitation of phosphate stabilised silver nanoparticles

Laser flash photolysis studies were carried out on two types of silver nanoparticles prepared by γ-radiolysis of Ag+ solutions in the presence of polyphosphate as the stabiliser. Type I silver nanoparticles displayed a surface plasmon band at 390 nm. Type II silver nanoparticles showed a 390 nm surface plasmon band with a shoulder at 550 nm. On photoexcitation in the surface plasmon band region, using 35 picosecond laser pulses at 355 nm and 532 nm, the type II solutions showed transient bleaching and absorption signals in the 450-900 nm region, which did not decay appreciably up to 5 nanoseconds. These transient changes were found to get annealed in the intervalt where 5ns < t < 100 ns. Extended photolysis of the nanoparticle solutions with repetitive laser pulses resulted in a decrease in the values of the average particle size which were measured by employing the dynamic light scattering technique

Supramolecular assembly of coumarin 7 with sulfobutylether-β-cyclodextrin for biomolecular applications

Coumarins, in general, exhibit a wide range of photophysical characteristics and are highly sensitive to their microenvironment, and, therefore, their fluorescence characteristics have attracted immense attention as sensors in chemical and biological systems. In the present study, the supramolecular interaction of a bichromophoric coumarin dye, namely, Coumarin 7 (C7) with sulfobutylether-β-cyclodextrin (SBE7βCD) macrocyclic host at different pH conditions has been investigated by using optical spectroscopic techniques such as absorption, steady-state and time-resolved emissions, and circular dichroism measurements and compared with that of βCD. Considerable enhancement in the fluorescence intensity and lifetime of C7 on complexation with SBE7βCD proposes that non-radiative processes like TICT behavior are strictly hindered due to the confinement in the host cavity experienced by the C7 dye. The increase in the rotational correlation time evaluated from the fluorescence anisotropy decay kinetics further confirms the formation of tightly bound inclusion complexes. The binding constant values reveal that the monocationic form of dye at pH 3 shows ∼3 times stronger interaction with SBE7βCD than the neutral form of dye at pH 7 due to strong electrostatic cation-anion interaction. SBE7βCD:C7 exhibits an improved photostability and an upward pKa shift of 0.4 unit compared to the contrasting downward pKa shift of 0.5 with the βCD. The enhanced fluorescence yield and increased photostability have been exploited for bioimaging applications, and better images were captured by staining the Drosophila fly gut with the SBE7βCD:C7 complex. The enhancement in the binding interaction and the emission intensity were found to be responsive to external stimuli such as small competitive binders or metal ions and nearly quantitative dissociation of the complex was demonstrated to release the dye and would find stimuli-responsive applications

Taming fluorescent dyes with cucurbituril

Abstract. The potential of the supramolecular host molecule cucurbi

<em>p</em>H-Responsive supramolecular assemblies of Hoechst‑33258 with cucurbiturils: Modulation in the photophysical properties

241-253Stimuli-responsive molecular assemblies of potential drug/guest molecules through non-covalent host-guest interaction have been found very attractive in transporting and releasing the desired form on demand. In this review article, the supramolecular interaction of a biologically important dye Hoechst-33258 (H33258) has been investigated in aqueous solutions at two different pHs (~4.5 and ~7), in the presence of macrocyclic hosts, namely, cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8). The pH-dependent emission behaviour of H33258 is inherently connected with its protolytic equilibria which allows the dye to exist in different geometrical conformations. This pH-dependent structural orientation is greatly affected by the complexation with cucurbiturils. The strong ion-dipole interactions provided by the carbonyl portals of the CB7 host adequately stabilizes the CB7-H33258 complex, both in 1:1 and 2:1 stoichiometries at both the pH conditions. The non-covalently stabilized assembly brings out large enhancement in the fluorescence emission due to the unique structural orientation attained by H33258 partly within the CB7 cavity, which reduces the non-radiative relaxation pathways. The pH-dependent structural conformations of H33258 are found to be decisive in determining the stoichiometry and geometry of the supramolecular assembly. Interaction of H33258 with larger macrocycle, CB8, at pH 7 is found to be very strong. The non-covalently stabilized assembly with 2:1 (CB8: H33258) stoichiometry brings out ~26 fold enhancement in the emission yield. On the other hand, the strong ion-dipole interactions provided by the dicationic H33258 at pH 4.5 allows the CB8 to uptake two dicationic dyes in its cavity in a 1:2 stoichiometry, resulting in a quenching in the fluorescence emission. The distinct pH-mediated stoichiometric switching of CB8-H33258 complexes and the demonstrated contrasting fluorescence properties are expected to find application in the field of biomolecular imaging and exchange of included guests for a selective drug transport/release

Supramolecular approach to devolve emissive soft material in aqueous solution

by Palash Jana, Nilotpal Barooah, Jyotirmayee Mohanty and Sriram Kanva

The face mask: A tale from protection to pollution and demanding sustainable solution

The usage of face masks in various sectors of healthcare facilities dates back to years ago. However, the utilization of facial coverings experienced a rapid surge as a result of the escalating rate of COVID-19 infections witnessed across the entire globe. This culminated in an unparalleled inundation of disposed facial coverings within the surrounding ecosystem. This transforms the face mask from a potent protectant into a massive emerging solid plastic waste pollutant with long-term adverse effects on the environment and human health. The utilization of facial coverings on a worldwide scale escalated to an immensely significant 129 billion per month at the onset of the pandemic. Nanomaterial-based technologies have been integrated into mask manufacturing chains to increase performance and provide antiviral characteristics. Nanotechnology encompasses multidisciplinary aspects including artificial intelligence, chemistry, biology, material science, physical science, and medicine. Abridgment of this review aims to make discarded face masks into a sustainable solution to many environmental pollution. In addition, it culminates collaborative and well-conducted trials, done for generating sustainable greener solutions for disposed face masks with the intention that usage of face masks in an environment-friendly manner. Given the preceding, the purpose of this review is to discuss the evolution of discarded face masks from sentinel pathogens to emerging environmental pollutants over time, as well as to comprehend the effect of discarded face masks on the biosphere, human health, and the food chain, by developing scientifically validated strategies to treat discarded face masks for a sustainable future

pH-Mediated Stoichiometric Switching of Cucurbit[8]uril–Hoechst-33258 Complexes

Stimuli-responsive molecular assemblies of potential drug/guest molecules through noncovalent host–guest interaction have been found very attractive in transporting and releasing the desired form on demand. In this article, the host–guest interaction of a drug, Hoechst-33258 (H33258), has been investigated in aqueous solutions in the presence of a macrocyclic host, namely, cucurbit[8]­uril (CB8). The pH dependent structural conformations of H33258 are found to be decisive in determining the stoichiometry and geometry of the supramolecular assembly. Interaction of CB8 with the monocationic H33258 at pH 7.2 is very strong with an overall binding constant of the order of 10¹¹ M^–2. The noncovalently stabilized assembly with 2:1 (CB8:H33258) stoichiometry brings out ∼26-fold enhancement in the emission yield. On the other hand, the strong ion–dipole interactions provided by the dicationic dye at pH 4.5 support the CB8 to uptake two dicationic H33258 dyes in its cavity in a 1:2 stoichiometry (<i>K</i>_(pH 4.5) = (3.2 ± 0.2) × 10¹¹ M^–2). In this case, the fluorescence displayed a quenching with a decrease in the emission yield from 0.4 to 0.2. The distinct pH-mediated stoichiometric switching of CB8–H33258 complexes and the contrasting fluorescence properties demonstrated here would find application in the field of biomolecular imaging and exchange of included guests for a selective drug transport/release