Separating Convective from Diffusive Mass Transport Mechanisms in Ionic Liquids by Redox Pro-fluorescence Microscopy.

The study of electrochemical reactivity requires analytical techniques capable of probing the diffusion of reactants and products to and from electrified interfaces. Information on diffusion coefficients is often obtained indirectly by modeling current transients and cyclic voltammetry data, but such measurements lack spatial resolution and are accurate only if mass transport by convection is negligible. Detecting and accounting for adventitious convection in viscous and wet solvents, such as ionic liquids, is technically challenging. We have developed a direct, spatiotemporally resolved optical tracking of diffusion fronts which can detect and resolve convective disturbances to linear diffusion. By tracking the movement of an electrode-generated fluorophore, we demonstrate that parasitic gas evolving reactions lead to 10-fold overestimates of macroscopic diffusion coefficients. A hypothesis is put forward linking large barriers to inner-sphere redox reactions, such as hydrogen gas evolution, to the formation of cation-rich overscreening and crowding double layer structures in imidazolium-based ionic liquids.

Luciferase-free Luciferin Electrochemiluminescence.

Luciferin is one of Nature's most widespread luminophores, and enzymes that catalyze luciferin luminescence are the basis of successful commercial "glow" assays for gene expression and metabolic ATP formation. Herein we report an electrochemical method to promote firefly's luciferin luminescence in the absence of its natural biocatalyst-luciferase. We have gained experimental and computational insights on the mechanism of the enzyme-free luciferin electrochemiluminescence, demonstrated its spectral tuning from green to red by means of electrolyte engineering, proven that the colour change does not require, as still debated, a keto/enol isomerization of the light emitter, and gained evidence of the electrostatic-assisted stabilization of the charge-transfer excited state by double layer electric fields. Luciferin's electrochemiluminescence, as well as the in situ generation of fluorescent oxyluciferin, are applied towards an optical measurement of diffusion coefficients.

Tailoring Spectral and Photochemical Properties of Bioinspired Retinal Mimics by in Silico Engineering.

Controlling the spectral tunability and isomerization activity is currently one of the hot topics in the design of photoreversible molecular switches for application in optoelectronic devices. The present work demonstrates how to manipulate the absorption of the retinal protonated Schiff base (rPSB) chromophore over the entire visible range by targeted functionalization of the retinal backbone. Moreover, a correlation between the vertical excitation energy and the profile of the potential energy surface of the bright excited state responsible for the photoreactivity of rPSB is established. This correlation was exploited to rank the functionalized rPSBs into different classes with characteristic photoisomerization activity. Eventually, the synergic effects of functionalization and of external electric fields in the range of a few MV cm-1 were applied to achieve reversable and regioselective control of the photoisomerization propensity of selected rPBS derivatives.

Microwave-assisted supramolecular double crosslinked chitosan-based molecularly imprinted polymer for synergistic recognition and selective recovery of Cd(II) and As(V) from water: Performance and mechanistic insights.

A novel model of the sustainable double crosslinked molecularly imprinted polymer (D-Crosslinked MIP) represented as a supramolecular imprinted polymer was synthesized via the bulk polymerization method. The primary crosslinking was fabricated using biomacromolecule chitosan as a functional monomer and glutaraldehyde as a crosslinker. The primary crosslinked was subjected to dynamic interactions in a secondary crosslinking by binding Al2O3-NPs and TiO2-NPs, forming the supramolecular D-Crosslinked-MIP. The dually crosslinked formed from combining three distinct crosslinkers in one system for the interaction with As(V) and Cd(II). A microwave was employed to evaluate the performance of the designed material in selectivity and extraction of metal ions from water. The FT-IR, XRD, TG/DTA, SEM-EDX, TEM, and XPS were used to verify the characteristics of (D-nano-Al2O3@Crosslinked Chitosan@D-nano-TiO2). The type of solvents, selectivity, interferences, microwave-contact time, pH, temperatures, concentrations, and regeneration were investigated. By using the D-Crosslinked-MIP, at 15 s, Cd(II) revealed a recovery capacity of 99.03 %, Qmax 862.07 mg/g, while As(V) demonstrated a recovery capacity of 99.06 %, Qmax 850.75 mg/g. The D-Crosslinked-MIP exhibited BETs of 69.01 m2/g with a pore volume of 0.2340 cm3/g owing to polymeric crosslinking by metal oxide NPs. The kinetics, isotherm models, and mechanisms of dually crosslinking and extraction of toxic metals were discussed.

In-lab synthesized turn-off fluorescence sensor for estimation of Gemigliptin and Rosuvastatin polypill appraised by Spider diagram, AGREE and whiteness metrics.

Gemigliptin-Rosuvastatin single-pill combination is a promising therapeutic tool in the effective control of hyperglycemia and hypercholesterolemia. Organic sensors with high quantum yields have profoundly significant applications in the pharmaceutical industry, such as routine quality control of marketed formulations. Herein, the fluorescence sensor, 2-Morpholino-4,6-dimethyl nicotinonitrile 3, (λex; 226 nm, λem; 406 nm), was synthesized with a fluorescence quantum yield of 56.86% and fully characterized in our laboratory. This sensor showed high efficiency for the determination of Gemigliptin (GEM) and Rosuvastatin (RSV) traces through their stoichiometric interactions and simultaneously fractionated by selective solvation. The interaction between the stated analytes and sensor 3 was a quenching effect. Various experimental parameters and the turn-off mechanism were addressed. The adopted approach fulfilled the ICH validation criteria and showed linear satisfactory ranges, 0.2-2 and 0.1-1 µg/mL for GEM and RSV, respectively with nano-limits of detection less than 30 ng/mL for both analytes. The synthesized sensor has been successfully applied for GEM and RSV co-assessment in their synthetic polypill with excellent % recoveries of 98.83 ± 0.86 and 100.19 ± 0.64, respectively. No statistically significant difference between the results of the proposed and reported spectrophotometric methods in terms of the F- and t-tests. Ecological and whiteness appraisals of the proposed study were conducted via three novel approaches: the Greenness Index via Spider Diagram, the Analytical Greenness Metric, and the Red-Green-Blue 12 model. The aforementioned metrics proved the superiority of the adopted approach over the previously published one regarding eco-friendliness and sustainability. Our devised fluorimetric turn-off sensing method showed high sensitivity, selectivity, feasibility, and rapidity with minimal cost and environmental burden over other sophisticated techniques, making it reliable in quality control labs.

Relationship between Excited State Lifetime and Isomerization Quantum Yield in Animal Rhodopsins: Beyond the One-Dimensional Landau-Zener Model.

We show that the speed of the chromophore photoisomerization of animal rhodopsins is not a relevant control knob for their light sensitivity. This result is at odds with the momentum-driven tunnelling rationale (i.e., assuming a one-dimensional Landau-Zener model for the decay: Zener, C. Non-Adiabatic Crossing of Energy Levels. Proc. R. Soc. London, Ser. A 1932, 137 (833), 696-702) holding that a faster nuclear motion through the conical intersection translates into a higher quantum yield and, thus, light sensitivity. Instead, a model based on the phase-matching of specific excited state vibrational modes should be considered. Using extensive semiclassical hybrid quantum mechanics/molecular mechanics trajectory computations to simulate the photoisomerization of three animal rhodopsin models (visual rhodopsin, squid rhodopsin and human melanopsin), we also demonstrate that phase-matching between three different modes (the reactive carbon and hydrogen twisting coordinates and the bond length alternation mode) is required to achieve high quantum yields. In fact, such "phase-matching" mechanism explains the computational results and provides a tool for the prediction of the photoisomerization outcome in retinal proteins.

Photoelectrochromism in the Retinal Protonated Schiff Base Chromophore: Photoisomerization Speed and Selectivity under a Homogeneous Electric Field at Different Operational Regimes.

The spectral tunability, photoisomerization efficiency and selectivity, of the native all-trans retinal protonated Shiff base (PSB) chromophore driven by a homogeneous electric field is systematically investigated. By analyzing the absorption wavelength dependence, charge distribution, and PES profiles along selected torsional angles, as well as the electronic structure, energetics, and topography of the CI seam in the presence of strong positive and negative electric fields, we recognize the existence of qualitatively/fundamentally different photophysics and photochemistry with respect to the unperturbed (i.e., absence of an electric field) chromophore. We rationalize the findings within the scope of molecular orbital theory and deliver a unified picture of the photophysics of the retinal PSB chromophore over a wide, even beyond the usually observed, spectral regime, ranging from the near-infrared to the ultraviolet absorption energies. This work has a 3-fold impact: a) it accounts for, and extends, previous theoretical studies on the subject; b) it delivers a rationale for the ES lifetimes observed in retinal proteins, both archeal and visual rhodopsins, as well as in solvent; and c) the transferability of the discovered trends on PSB mimics is demonstrated.