Polar Media Research Articles

Relative Stability and Basicity of Enamines from Aminocatalysts

The relative thermodynamic stability of two series of enamines has been examined using DFT (mainly M06‐2X), MP2, and CCSD(T) calculations, supplemented by 1H NMR spectroscopy in some cases. The basicity of enamines derived from pyrrolidine and various carbonyl compounds has been computationally compared in the gas phase and in water; the results indicate which enamines or iminium ions may predominate in nonpolar and polar acidic media when pyrrolidine and two or more carbonyl groups or carbonyl compounds are present in the reaction flask. The relative basicity of a second series of enamines, from propanal and chiral pyrrolidines or imidazolidin‐4‐ones, has also been investigated; this sheds light on the main intermediates to be expected when two or more secondary amines are present in acid‐catalyzed aldehyde reactions. Non‐covalent interactions explain the stability of folded side‐chain conformers of O‐silylated prolinol enamines, according to M06‐2X, wB97X‐D, and B3LYP‐D3 (but not B3LYP) predictions. The significant stability of iminium ions containing appropriate electron‐donating atoms or groups accounts for the basicity of the corresponding enamines. These findings pave the way for the future development of dual aminocatalytic processes.

A New Proton Transfer Complex Between 3,4-Diaminopyridine Drug and 2,6-Dichloro-4-nitrophenol: Synthesis, Spectroscopic Characterization, DFT Studies, DNA Binding Analysis, and Antitumor Activity.

The proton transfer (PT) complexation reaction between 3,4-diaminopyridine (3,4-DAP), an important drug, and 2,6-dichloro-4-nitrphenole (DCNP) was investigated experimentally and theoretically. The experimental results indicated a chemical reaction occurred because of a hydrogen bonding, followed by proton transfer from the DCNP to the 3,4-DAP in different polar media. The Benesi-Hildebrand equation was used to estimate the formation constant (Kf), molar absorptivity (εPT), and other physical parameters. The formed PT complex was characterized using FTIR, 1H, and 13C NMR spectra. In addition, the nanocrystalline structure, particle sizes, and surface morphology of the complex were investigated by XRD and SEM-EDX. The structure of the 1:1 PT complex was calculated theoretically in the gas phase and the presence of solvent effects. Using TD-DFT calculations, the band observed at 406 nm (Calc. 379.5 nm) and 275 nm (Calc. 272.3 nm) could be assigned to the HOMO→LUMO transition (99%), and HOMO→L+3 transition (87%), respectively. The DNA binding ability of the PT complex was investigated, revealing an intercalative binding mechanism with a binding constant Kb of 4.6 × 104 M-1. Based on the results of the Ct-DNA binding study, the binding free energy of the PT complex with the receptor of human DNA (PDB ID:1BNA) is found to be -7.2 kcal/mol. The cytotoxic effects of the PT complex were evaluated on selected cancer cell lines, demonstrating significant antitumor activity against A-549 and MCF-7 cancer cell lines.

Effect of locally excited state on fluorescence transition dipole moment in quadrupolar molecules subjected to symmetry breaking charge transfer.

In excited centrosymmetric donor-acceptor triads of type A-D-A or D-A-D, symmetry breaking charge transfer (SBCT) in polar media has been explored for a few decades. SBCT is accompanied by significant reorganization of the electronic structure of the molecule, which leads to a change in the fluorescence transition dipole moment (TDM). Previously, experiments revealed a 20%-30% reduction in TDM, which occurs on the timescale of SBCT. Simple SBCT models explain this reduction. Here, the effect of the interaction of a locally excited state with zwitterionic states on TDM is investigated. This interaction is shown to have a drastic impact on the TDM and its dependence on the solvent polarity. The magnitude of TDM can decrease monotonically, increase monotonically, and also pass through a maximum with an increase in the SBCT degree due to the locally excited state effect. The scale of changes in TDM in the course of SBCT increases greatly. The conditions for the implementation of a particular scenario have been determined. This work clearly demonstrates the observable influence of upper excited states on the photochemistry and photophysics of molecules. Methods for controlling the fluorescent characteristics of quadrupolar molecules are proposed.

Preferential Formation of Three-layered Host-Guest Complexes of a Planar Dinuclear Metallohost with Alkali Metal Ions.

We synthesized a planar macrocyclic dinuclear nickel(II) metallohost from the corresponding macrocyclic imine ligand containing two N2O2chelate coordination sites and an O6cation binding site like 18-crown-6 as well as peripheral hexyl groups. Due to the lipophilic nature of the hexyl groups, the metallohost was soluble in less polar media where its interaction with alkali metal ions was enhanced. The binding studies by NMR spectroscopy clearly showed its strong tendency to form multi-layered structures. The metallohost formed 2:1 and 1:1 (host/guest) complexes with Na+with the two-step binding constants of logK1= 6.6 and logK2= 3.0. In contrast, its complexation with larger alkali metal ions (K+, Rb+, Cs+) preferentially gave 3:2 (host/guest) complexes when 2/3 equiv of the guest was present. The three-layered structures of these 3:2 complexes were well characterized by mass spectrometry and 2D COSY/ROESY experiments as well as DFT calculations, elucidating their unique structural feature with three chemically different environments due to the oppositely curved two [Ni(saloph)] moieties of the metallohost. Therefore, the three-layered structures were preferentially formed when larger alkali metal ions (K+, Rb+, Cs+) were complexed with the metallohost.

Effect of branching in the alkyl chain of diglycolamide on the sequestration of tetravalent actinides: solvent extraction and theoretical studies.

DGA (diglycolamide) ligands show a different extraction behavior of trivalent metal ions by changing the branching alkyl chain length as well as the branching at the methylene position. There are no studies of these factors on the extraction efficiency of these DGA derivatives for the extraction of tetravalent actinides. We have evaluated four different DGA derivatives for the extraction of Np, Pu, and Th from molecular diluents. The n-butyl derivative shows enhanced extraction efficiency and branching gives rise to a reduction in the extraction efficiency of tetravalent ions. The distribution ratios are higher in pure octanol than in a mixture of 30% octanol and 70% n-dodecane. This behavior is in marked difference to that of the extraction of trivalent ions where the addition of an alcohol generally decreases the distribution ratio of trivalent ions due to the ligand-modifier intercation, poor aggregation or micelle formation tendency of DGAs in polar solvents. This suggests that micelle-mediated extraction may not be the dominating factor for the extraction of tetravalent metal ions. Slope analysis suggests the involvement of only two DGA molecules in the extracted species suggesting no/poor possibility of micelle formation in the present system. The higher extraction in pure octanol may be due to a better solubility of the extracted complexes in this polar medium compared to the mixture of octanol and n-dodecane. The water and acid uptake, the back extraction, and the radiation stability of the solvent systems were also investigated. DFT studies were performed to get a better insight into the extraction and complexation of the different DGA solvent systems.

A Theoretical Perspective on the Stereochemistry of Benzoanellated Aroyl‐X,N‐Ketene Acetal Derivatives

ABSTRACTKetene 1,3‐oxazoles and their derivatives present intriguing structures for the study of rotational barriers due to their pseudo–double‐bond character stemming from resonance in the ketene moiety. A diverse range of compounds featuring this motif underwent quantum‐chemical investigation to elucidate the nature of the stereochemical singularity observed in numerous cases. Because rotational barriers in most instances are too high to permit rapid interconversion, the findings are ascribed to thermodynamic rather than kinetic factors in the gas phase and within an implicit polar medium. The stabilities are attributed to internal hydrogen bonding where feasible. However, in cases where this is not possible, chalcogen bonding rather than steric effects governs the stereochemical preferences, particularly when S and Se comprise the heterocycle of these compounds. These findings hold promise for guiding the design of compounds whose properties hinge on stereochemistry and resonant structures, such as dyes.

Colloidal dispersions of cobalt ferrite nanoparticles in EMIM TFSI, propylene carbonate and their mixtures

Liquid thermocells are promising devices for the recovery of low-grade waste heat and its conversion into electricity. The present study proposes dispersing charged magnetic nanoparticles in liquids to improve thermoelectric conversion, due to their thermodiffusive and magnetic properties. Core@shell cobalt ferrite@maghemite nanoparticles (NPs) of various sizes with three different kinds of coatings are tested for dispersion in EMIM TFSI (ethyl-methylimidazolium bistriflimide), an ionic liquid (IL) of high electrical conductivity. Among the tested ligands, PAC6MIM±Br− (1-(6-hexylphosphonate) 3-methyl imidazolium bromide) emerges as the most efficient due to its phosphonic group. This ligand leads to dispersions of clusters of a few dozen NPs in water and a few NPs in EMIM TFSI. For improving both the viscosity and the electrical conductivity, dispersions in binary mixtures of propylene carbonate (PC), a polar medium, and EMIM-TFSI are further investigated with the sample based on NPs of ∼ 9 nm diameter. Through a pumping and heating procedure, stable dispersions are obtained with a subsequent reduction of the size of the NP clusters, down to 1 to 2 NPs in EMIM TFSI and a few NPs in PC and their binary mixtures. The mixture with an IL mole fraction ∼0.2–0.3 and maximal electrical conductivity is a promising candidate for further thermoelectric investigations.

Wormlike Micellar Glycerol Solutions Formed from a Double-Tailed Surfactant with Two Quaternary Ammonium Head Groups.

Herein, a quaternary ammonium surfactant with dual heads and tails, N1,N1,N1,N3,N3-pentamethyl-N3-(3-(2-tetradecylhexadecanamido)propyl)propane-1,3-diaminium dibromide, abbreviated as Di-C14-N2, was synthesized. For the first time, clear observation of aggregate structures formed by surfactants in pure glycerol systems was achieved using cryogenic transmission electron microscopy (cryo-TEM). The system's rheological properties were analyzed using both steady-state shear and oscillatory rheological measurements. The lubricating efficiency of the Di-C14-N2 glycerol solution was assessed for its tribological properties using a tribological wear tester, white light interferometer, and scanning electron microscope. In glycerol, Di-C14-N2 formed long wormlike micelles, which resulted in a glycerol solution with the zero-shear viscosity of 1013 Pa·s at 90 mM, which is the most viscous glycerol system up to now. The system displayed distinct rheological properties from the aqueous system, as evidenced by two intersections in the loss and storage moduli. The formed wormlike micelles in glycerol lead to a significant alteration in the viscoelasticity of the system, thus endowing the Di-C14-N2 glycerol solution with potential as an eco-friendly lubricant. The friction coefficient of the system was found to be 23% lower and the wear rate was 83% lower than that of pure glycerol after the addition of Di-C14-N2. This demonstrates that the addition of Di-C14-N2 greatly improves the frictional properties of pure glycerol. This study offers the possibility of directly observing the aggregate structures formed by surfactants in pure glycerol systems. It contributes to the exploration of the self-assembly behavior of surfactants in nonaqueous polar media, thereby aiding in a deeper understanding of the correlation between molecular structure, mesoscale structure, and macroscopic properties.

CsPbBr3@PbSO4 nanocomposites with near-unity photoluminescence and ultrastability via in-water in situ embedding synthesis strategy

Perovskite quantum dots (PQDs) are emerging as promising nanomaterials for optoelectronic applications. However, developing a cost-effective green synthesis process that simultaneously possesses satisfactory photoluminescence quantum yield (PLQY) and stability remains a severe challenge. Here, CsPbBr3@PbSO4 nanocomposites with a near-unity PLQY of 99.8 % and robust ambient stability are synthesized in situ in water via 4-Bromobenzenesulfonic acid and ditetradecylamine ligands. Notably, these nanocomposites show no decline in PLQY even after being immersed in water for over 250 days, and also exhibit superior stability against heating, ultrasonication, UV irradiation, anion exchange, and erosion by polar solvents. First-principles calculations reveal that CsPbBr3@PbSO4 nanocomposites can form a natural quantum well structure, which effectively promotes the radiative recombination of carriers in CsPbBr3 QDs. Meanwhile, the remarkable stability is attributed to the ultrahigh decomposition enthalpy of PbSO4 that serves as a strong barrier preventing the invasion of anions and polar media into the embedded CsPbBr3 QDs. Finally, besides the convenient application of green fluorescent paper, a fingerprint recognition is demonstrated by fabricating a bright-green LED integrated with the CsPbBr3@PbSO4 nanocomposites powder and a commercial UV chip. This work provides a new strategy for green synthesis and practical application of high-efficient and ultrastable PQDs.

The Role of Alkylammonium Bromides on the Surface Passivation of Stable Alcohol‐Dispersed CsPbX3 Nanocrystals and on the Stability Enhancement in Light‐Emitting Applications

AbstractThe ligand passivation is considered an attractive strategy to prepare high‐quality perovskite nanocrystals (PNCs) with improved photophysical features in polar media. However, the long‐term stabilization of PNCs in these environments is still challenging, being pivotal to understanding the protection mechanism given by prominent surface ligands and avoiding material deterioration in polar solvents. In this work, how the nature of diverse alkylammonium bromides used during surface passivation influences the photophysical properties and quality of CsPbX3 PNCs fully dispersed in alcohol environments, exhibiting stability up to 10 months are investigated. By adding didodecyldimethylammonium benzyldodecyldimethylammonium and tetrabutylammonium bromides (DDAB, BDAB, and TBAB, respectively), DDAB and BDAB promote a suitable and partial surface coverage are observed, respectively, suppressing defect sites in the nanocrystals. Conversely, TBAB shows poor surface protection, decreasing the PL features of PNCs. The presence of DDAB and BDAB favors the fabrication of color converters, and efficient light‐emitting diodes (LEDs) with external quantum efficiencies (EQE) of ≈23%. Interestingly, significant device stability with BDAB capping shows an LED half‐life of 20‐fold longer than for DDAB. This contribution offers a promising approach for preparing highly luminescent and stable alcohol‐dispersed PNCs, useful for fabricating efficient optoelectronic devices.

Periodic Trends in Intra-ionic Excited State Quenching by Halide.

The preassociation of reactants in a photoinitiated redox reaction through the use of noncovalent interactions can have a significant impact on excited state reactivity. As these noncovalent interactions render some stabilization to the associated species, they impact the kinetics and thermodynamics of photoinitiated electron transfer. Reported herein is a novel iridium(III) photocatalyst, equipped with an anion-sensitive, amide-substituted bipyridine ligand, and its reactivity with the halides (X = I-, Br-, Cl-) in acetonitrile and dichloromethane. A noteworthy periodic trend was observed, where the size and electron affinity dramatically altered the observed photoredox behavior. The binding affinity for the halides increased with decreasing ionic radius (Keq ∼103 to >106) in a polar medium but association was stoichiometric for each halide in a nonpolar medium. Evidence for the static quenching of iodide and bromide is presented while dynamic quenching was observed with all halides. These results highlight how the photophysics of halide adducts and the thermodynamics of intra-ionic photo-oxidation are impacted as a consequence of preassociation of a quencher through hydrogen bonding.

Surface Modification of Calcined Kaolinite for Enhanced Solvent Dispersion and Mechanical Properties in Polybutylene Adipate/Terephthalate Composites.

In order to regulate the surface properties of calcined kaolinite for the purpose of achieving uniform distribution within various polar dispersion media, 3-aminopropyltriethoxysilane and phenyl glycidyl ether were employed to chemically modify calcined kaolinite. The grafting rate, surface properties, and dispersion properties of calcined kaolinite particles in different polar organic media were changed by varying the dosage of the modifiers. FT-IR analysis confirmed successful surface modification, while thermogravimetric analysis indicated a maximum graft coverage of 18.44 μmol/m2 for the modified particles. Contact angle measurements and particle size distribution analyses demonstrated the effective adjustment of surface characteristics by the modifiers. Specifically, at a mass ratio of 1.0 of modifier to kaolinite particles, the modified particles exhibited a contact angle of around 125°, achieving uniform dispersion in different polarity media. Particle size distribution ranged from 1600 nm to 2100 nm in cyclohexane and petroleum ether, and from 900 nm to 1200 nm in dioxane, ethyl acetate, and DMF, showcasing a significant improvement in dispersion performance compared to unmodified particles. Concurrently, to improve the mechanical properties of PBAT, modified particles were incorporated into the PBAT matrix, and the effect of modified particle addition on the tensile strength and fracture tensile rate of the composites was investigated. The optimal amount of modified particles is 6 wt.%~8 wt.%. This article aims at synthesizing modifier molecules containing different hydrophilic and hydrophobic groups to chemically graft onto the surface of calcined kaolinite. The hydrophilic and hydrophobic groups on the modified particles can adapt to dispersed systems of different polarities and achieve good distribution within them. The modified particles are added to PBAT to achieve good compatibility and enhance the mechanical properties of the composite material.

Tunable Intracavity Coherent Up-Conversion with Giant Nonlinearity in a Polar Fluidic Medium.

The study has demonstrated a novel microcavity-based flexible photon up-conversion system using second harmonic generation (SHG) from a polar nematic fluidic medium doped with a laser dye. The idea is based on coherent light generation via stimulated emission (lasing) and simultaneous frequency doubling inside a microcavity. The polar nematic fluid equips very high even-order optical nonlinearity due to its polar symmetry and large dipole moment along the molecular long axis. At the same time, its inherent fluidic nature allows to easily functionalize the media just by doping, in the present case, with an emissive laser dye. The demonstrated system exhibits a giant nonlinear optical response to input light, while enabling spectral narrowing and multiple-signal output of up-converted light, which is not attainable through the simple SH-conversion of input light. Furthermore, the susceptibility of the liquid crystal offers dynamic modulation capabilities by an external stimulus, such as signal switching by the application of electric field or wavelength tuning through temperature variation. Such a brand-new type of simple coherent flexible up-conversion system must be promising as a new principle for easily accessible and down-scalable wavelength conversion devices.

Correlation of relaxation processes by BDS: Calorimetric, spectral findings and molecular dynamics of active side chain amino acids in hydrated medium

The dielectric dispersion behavior of amino acids (L-arginine and L-glutamic acid) was studied in the aqueous state by Broadband Dielectric Spectroscopy (BDS). The complex permittivity spectra of the solutions were recorded for the frequency regime 10 MHz – 50 GHz at a temperature range of 283 K to 303 K for various mole fractions. The interaction of polarized side chains of the solute (positive in L-arginine and negative in L-glutamic acid) with hydrated polar media is the significance of the work. The hydration effect of the amino acid modifies the dielectric and physicochemical properties of the solution. The study of Differential Scanning Calorimetry (DSC) analysis and thermal parameters specifies that the L-glutamic acid has super strong nature than L-arginine. The formation of hydrogen bond, nature and strength of the interaction through side chain are confirmed by spectral analysis (FT-Raman, FT-IR and NMR). The geometrical properties were computed with DFT/B3LYP −6-31G(d,p) basis set. The obtained spectral signals were compared with experimental data. The experimental and quantum mechanical calculations are used to identify the hydrodynamic coupling of the solution. The present study correlate the dielectric, thermal parameters, spectral inferences with molecular structure, dynamics is a novel approach which confirms the nature and strength of the complex formation.

Is lecanoric acid a good antioxidant?

Lecanoric acid (LA), an abundant chemical found in lichens, has demonstrated a wide range of biological activities, including anti-cancer cytotoxic, antibiotic, antimycobacterial, antiviral, and anti-hepatocarcinoma properties. The antioxidant capacity of this molecule, while inferred from certain experimental findings, is doubtful based on structural characteristics and therefore remains to be established. DFT calculations are used in this work to conduct a comprehensive evaluation of the mechanism and kinetics governing the antiradical activity of LA in lipidic and aqueous solvent environments. Although the DPPH/ABTS+ assays revealed good antioxidant activity in vitro, the modeling yielded mixed results. The data suggests that LA is an efficient scavenger of the HO radical with rate constants of 2.01 × 1010 and 2.80 × 108 M−1 s−1 in polar and lipid media, respectively, by the FHT and RAF mechanisms. However, the data also suggests that LA exhibits only weak activity against the HOO radical in all physiological environments. This is consistent with structural features that predict low activity.

Augmenting the effect of solvents on optical nonlinearity by spectroscopic, DFT, solvatochromism and z-scan studies of push-pull chalcone: (2E)-1-(4-ethoxyphenyl)-3-(4-methoxyphenyl)prop-2-en-1-one

In this article, the structural and nonlinear optical behaviour of a chalcone derivative, (2E)-1-(4-ethoxyphenyl)-3-(4-methoxyphenyl)prop-2-en-1-one have been studied. FT-IR, FT-Raman, and NMR spectroscopy were analyzed to validate the molecular structure. To predict the nonlinear optical characteristics of the chalcone, the DFT approach was used and the experimental results were corroborated by the computations. The bathochromic shift is obtained in linear absorbance spectra and is validated using TD-DFT. Also, the broad emission in the blue region demonstrates the blue light emission property of the sample. Using the finite-field method, the dipole moments, polarizability, first-order and second-order hyperpolarizability parameters have been computed. Ground and excited state dipole moments were quantified by solvatochromism. The third-order nonlinear optical characteristics of chalcone in polar and non-polar solvent media were examined using the open/closed-aperture z-scan technique. The chalcone displayed considerable two-photon absorption with a positive nonlinear absorption coefficient and a positive index of refraction due to the self-focussing effect. Furthermore, the optical limiting study manifests that the investigated chalcone might well be favourable for NLO applications.

Antibody‐Targeted Phytohormone Delivery Using Foliar Sprayed Silk Fibroin Pickering Emulsions

AbstractEfficient delivery systems based on biopolymers offer new solutions to enhance food security by boosting crop yield and quality while decreasing agrochemical input and mitigating environmental impact. Herein, a novel Pickering emulsion fabrication method that utilizes antibody‐functionalized silk fibroin to enhance foliar adhesion upon application for efficient agrochemicals delivery is reported. Silk fibroin microparticles (SFMPs) stabilize both nonpolar and polar oil‐in‐water Pickering emulsions, revealing the cooperative function of both oil phase polarity and aqueous media pH in stabilization, where phytohormones addition influenced the stability and oil‐water contact angle. Phytohormone‐containing Pickering emulsions are functionalized with anti‐pectic polysaccharide (alpha‐1,5‐arabinan) antibody labeled SFMPs through adsorption, to enhance droplet adhesion to leaf cuticle surface. As a proof‐of‐concept, Pickering emulsion containing 0.1 mM jasmonic acid (JA) is applied to Arabidopsis thaliana via foliar spraying. Following washing, treatment with antibody‐functionalized Pickering emulsion increased trichome numbers on young leaves by 20% and 3%, when compared to nonencapsulated JA and nonfunctionalized emulsions, respectively. The functionalized Pickering emulsion stabilized by SFMPs exhibited no plant toxicity and biodegraded 50 wt.% in 7 days, catalyzed by Streptomyces griseus protease. Results highlight the potential of SFMP‐stabilized oleic acid‐in‐water Pickering emulsion as a sustainable and biodegradable solution to precisely deliver agrochemicals through foliar spray.

Unveiling the inherent properties and impact of ultrafine nanobubbles in polar and alcoholic media through unsupervised machine learning and atomic insight

The presence of dissolved gas in the host medium in various industrial processes, such as the presence of oxygen and hydrogen during water splitting or carbon dioxide in fuel cells, or the dissolution of nitrogen for industrial applications, increases the probability of the formation of bubbles at nano-scale. Nanobubbles (NBs), spanning tens to hundreds of nanometres, display exceptional attributes, including remarkable stability, enduring longevity, and an impressive surface-to-volume ratio. These qualities firmly position NBs as pivotal entities with applications that extend across diverse industries, encompassing fields such as energy and chemistry. Therefore, it is crucial to have a comprehensive understanding of their inherent properties and behaviour right from the nucleation stage to grasp their distinctive traits fully. This paper focuses on the combination of data-driven and molecular dynamics simulation to provide a clear understanding of the mechanisms behind NBs nucleation and behaviour in liquids and identify their characteristics. The nucleation process of four gases in two potential liquids for hosting NBs, namely water and methanol, was investigated through scattering nitrogen, oxygen, carbon dioxide, and hydrogen in host liquids using molecular dynamics simulations. Then, high-throughput screening based on the DBSCA (density-based spatial clustering of applications with noise) algorithm was used to screen the formed NB clusters through dissolved gases in the host liquids to determine the size of formed NBs, their density, and motion over time. The findings offer unique insights, indicating that the density of the surrounding liquids is altered and decreased by formed nanobubbles, influenced by the establishment of a nanolayer. The lowest density was recorded for hydrogen and nitrogen nanobubbled methanol samples at 0.61673 and 0.68918 g/ml, respectively, and for hydrogen and nitrogen nanobubbled water samples at 0.93797 and 0.93722 g/ml, respectively. Additionally, the highest density among the scattered gases was observed in non-nanobubbled carbon dioxide methanol and water samples at 0.77724 and 0.99588 g/ml, respectively. Furthermore, the viscosity of the host liquids is influenced, particularly in the presence of high-density nanobubbles, as the highest viscosity was observed for nitrogen nanobubbled water samples at 0.00103 Pa.s.

Characterization of Excited-State Electronic Structure in Diblock π-Conjugated Oligomers with Adjustable Linker Electronic Coupling.

Diblock conjugated oligomers are π-conjugated molecules that contain two segments having distinct frontier orbital energies and HOMO-LUMO gap offsets. These oligomers are of fundamental interest to understand how the distinct π-conjugated segments interact and modify their excited state properties. The current paper reports a study of two series of diblock oligomers that contain oligothiophene (Tn) and 4,7-bis(2-thienyl)-2,1,3-benzothiadiazole (TBT) segments that are coupled by either ethynyl (-C≡C-) or trans-(-C≡C-)2Pt(II)(PBu3)2 acetylide linkers. In these structures, the Tn segment is electron rich (donor), and the TBT is electron poor (acceptor). The diblock oligomers are characterized by steady-state and time-resolved spectroscopy, including UV-visible absorption, fluorescence, fluorescence lifetimes, and ultrafast transient absorption spectroscopy. Studies are compared in several solvents of different polarity and with different excitation wavelengths. The results reveal that the (-C≡C-) linked oligomers feature a delocalized excited state that takes on a charge transfer (CT) character in more polar media. In the (-C≡C-)2Pt(II)(PBu3)2-linked oligomers, there is weak coupling between the Tn and TBT segments. Consequently, short wavelength excitation selectively excites the Tn segment, which then undergoes ultrafast energy transfer (~1 ps) to afford a TBT-localized excited state.

Comprehensive kinetic investigation of antiradical activity of urolithins and their potential inhibitory effect on Xanthine Dehydrogenase

This work aimed to explore the antiradical activity of various ellagitannin metabolites, including Urolithin A (UroA), Urolithin B (UroB), Urolithin C (UroC), and Urolithin D (UroD), in a non-polar (benzene) and polar (water) medium. The antiradical effect of the investigated compounds against reactive oxygen species HO• was evaluated in water (physiological conditions) and benzene, while against CH3OO• and CCl3OO• it was assessed solely in benzene, using the Quantum Mechanics-based Test for Overall Free-radical Scavenging Activity (QM-ORSA) methodology. In non-polar media, compounds UroA, UroC, and UroD exhibit antiradical capabilities against the HO• through Proton-coupled electron transfer (PCET) and Radical Adduct Formation (RAF) processes. Conversely, UroB predominantly exhibits inhibitory activity on HO• through the RAF pathway. On the other hand, the reaction with CH3OO• and CCl3OO• only occurs through the Hydrogen Atom Transfer (HAT). Under physiological conditions, all investigated compounds show antiradical capacity against the HO•, primarily via the SPLET and RCF mechanisms. The reactivity of radical species in both solvents decreases in the following order: HO• > CCl3OO• > CH3OO•. The thermodynamic and kinetic parameters in both solvents indicate that the investigated compounds’ reactivity follows a decreasing order of UroD > UroA > UroC > UroB. Furthermore, newly formed radical species of urolithin exhibit lower reactivity towards the fatty acid model in comparison to investigated reactive radical species, potentially preventing lipid peroxidation initiation. The investigated compounds can regenerate glutathione (GSH) by providing a hydrogen atom to the glutathione radical (GS•), which forms during interaction with highly reactive radical species. In water, tested compounds also regenerate GSH by donating H atoms to GS•, as well as by transferring electrons from dominant acid-base species to GS•, followed by protonation of the resulting GS¯. Urolithins showed similar inhibitory effects as the conventional inhibitors Y-700, FYX-051, and Febuxostat on Xanthine Dehydrogenase (XDH). Reactivity towards XDH enzyme decreases in the following order UroC > UroB > UroD > UroA.