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      Exploring the photoexcited electron transfer dynamics in artificial sunscreen PBSA-coupled biocompatible ZnO quantum dots

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          Abstract

          Frequent exposure to ultraviolet (UV) radiation without any protection turns out to be a fatal threat leading to skin cancer, necessitating the use of sunscreen cosmetic product with enhanced efficiency to dissipate the UV absorbed energy.

          Abstract

          Frequent exposure to ultraviolet (UV) radiation without any protection turns out to be a fatal threat leading to skin cancer. This can be forestalled by the direct application of sunscreen cosmetic products. The efficiency of UV absorbed energy dissipation by sunscreen can be enhanced if it contains a charge and/or energy acceptor species. 2-Phenylbenzimidazole-5-sulfonic acid (PBSA) is an artificial sunscreen component that acts as an electron donor in alliance with biocompatible and environment-friendly ZnO quantum dot (QD) acceptors. Functionalized ZnO QDs are synthesized by the colloidal method using mercaptoacetic acid (MAA), mercaptopropionic acid (MPA), l-cysteine (LC), ethylene glycol (EG), β-alanine (BA), and citric acid (CA) ligands that help to develop an interaction with the PBSA. Steady-state photoluminescence (SSPL) and time-resolved photoluminescence (TRPL) analysis were employed to study the efficiency and rate of the electron transfer (ET) process. Our findings reveal that the electron transfer rate strongly depends on the size and the nature of the functionalizing ligands. The highest ET efficiency for the PBSA-ZnO QD dyad is noticed in the case of MAA (87.9%) and the lowest with the CA (33.8%) ligand. This indicates that MAA-functionalized ZnO QDs are the best electron acceptor amongst the other aforementioned functionalizing ligands as evidenced by the cyclic voltammetry (CV) measurements of PBSA- and MAA-functionalized ZnO QDs. These findings suggest that in the case of the PBSA-ZnO QD dyad, small-sized thiol functionalizing ligands like MAA, MPA and LC facilitate the electron transfer process more than large-sized ligands containing hydroxyl and amine functionalities, such as EG, BA, and CA.

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          Most cited references43

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          Effects of crystallization and dopant concentration on the emission behavior of TiO2:Eu nanophosphors

          Uniform, spherical-shaped TiO2:Eu nanoparticles with different doping concentrations have been synthesized through controlled hydrolysis of titanium tetrabutoxide under appropriate pH and temperature in the presence of EuCl3·6H2O. Through air annealing at 500°C for 2 h, the amorphous, as-grown nanoparticles could be converted to a pure anatase phase. The morphology, structural, and optical properties of the annealed nanostructures were studied using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy [EDS], and UV-Visible diffuse reflectance spectroscopy techniques. Optoelectronic behaviors of the nanostructures were studied using micro-Raman and photoluminescence [PL] spectroscopies at room temperature. EDS results confirmed a systematic increase of Eu content in the as-prepared samples with the increase of nominal europium content in the reaction solution. With the increasing dopant concentration, crystallinity and crystallite size of the titania particles decreased gradually. Incorporation of europium in the titania particles induced a structural deformation and a blueshift of their absorption edge. While the room-temperature PL emission of the as-grown samples is dominated by the 5D0 - 7F j transition of Eu+3 ions, the emission intensity reduced drastically after thermal annealing due to outwards segregation of dopant ions.
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            The Advancing of Zinc Oxide Nanoparticles for Biomedical Applications

            Zinc oxide nanoparticles (ZnO NPs) are used in an increasing number of industrial products such as rubber, paint, coating, and cosmetics. In the past two decades, ZnO NPs have become one of the most popular metal oxide nanoparticles in biological applications due to their excellent biocompatibility, economic, and low toxicity. ZnO NPs have emerged a promising potential in biomedicine, especially in the fields of anticancer and antibacterial fields, which are involved with their potent ability to trigger excess reactive oxygen species (ROS) production, release zinc ions, and induce cell apoptosis. In addition, zinc is well known to keep the structural integrity of insulin. So, ZnO NPs also have been effectively developed for antidiabetic treatment. Moreover, ZnO NPs show excellent luminescent properties and have turned them into one of the main candidates for bioimaging. Here, we summarize the synthesis and recent advances of ZnO NPs in the biomedical fields, which will be helpful for facilitating their future research progress and focusing on biomedical fields.
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              Understanding hydrogen atom transfer: from bond strengths to Marcus theory.

              Hydrogen atom transfer (HAT), a key step in many chemical, environmental, and biological processes, is one of the fundamental chemical reactions: A-H + B → A + H-B. Traditional HAT involves p-block radicals such as tert-BuO(•) abstracting H(•) from organic molecules. More recently, the recognition that transition metal species undergo HAT has led to a broader perspective, with HAT viewed as a type of proton-coupled electron transfer (PCET). When transition metal complexes oxidize substrates by removing H(•) (e(-) + H(+)), typically the electron transfers to the metal and the proton to a ligand. Examples with iron-imidazolinate, vanadium-oxo, and many other complexes are discussed. Although these complexes may not "look like" main group radicals, they have the same pattern of reactivity. For instance, their HAT rate constants parallel the A-H bond strengths within a series of similar reactions. Like main group radicals, they abstract H(•) much faster from O-H bonds than from C-H bonds of the same strength, showing that driving force is not the only determinant of reactivity. This Account describes our development of a conceptual framework for HAT with a Marcus theory approach. In the simplest model, the cross relation uses the self-exchange rate constants (k(AH/A) for AH + A) and the equilibrium constant to predict the rate constant for AH + B: k(AH/B) = (k(AH/A)k(BH/B)K(eq)f)(1/2). For a variety of transition metal oxidants, k(AH/B) is predicted within one or two orders of magnitude with only a few exceptions. For 36 organic reactions of oxyl radicals, k(AH/B) is predicted with an average deviation of a factor of 3.8, and within a factor of 5 for all but six of the reactions. These reactions involve both O-H or C-H bonds, occur in either water or organic solvents, and occur over a range of 10(28) in K(eq) and 10(13) in k(AH/B). The treatment of organic reactions includes the well-established kinetic solvent effect on HAT reactions. This is one of a number of secondary effects that the simple cross relation does not include, such as hydrogen tunneling and the involvement of precursor and successor complexes. This Account includes a number of case studies to illustrate these and various other issues. The success of the cross relation, despite its simplicity, shows that the Marcus approach based on free energies and intrinsic barriers captures much of the essential chemistry of HAT reactions. Among the insights derived from the analysis is that reactions correlate with free energies, not with bond enthalpies. Moreover, the radical character or spin state of an oxidant is not a primary determinant of HAT abstracting ability. The intrinsic barriers for HAT reactions can be understood, at least in part, as Marcus-type inner-sphere reorganization energies. The intrinsic barriers for diverse cross reactions are accurately obtained from the HAT self-exchange rate constants, a remarkable and unprecedented result for any type of chemical reaction other than electron transfer. The Marcus cross relation thus provides a valuable new framework for understanding and predicting HAT reactivity.
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                Author and article information

                Contributors
                (View ORCID Profile)
                (View ORCID Profile)
                (View ORCID Profile)
                Journal
                NJCHE5
                New Journal of Chemistry
                New J. Chem.
                Royal Society of Chemistry (RSC)
                1144-0546
                1369-9261
                May 23 2022
                2022
                : 46
                : 20
                : 9526-9533
                Affiliations
                [1 ]Department of chemistry, Quaid-I-Azam University, Islamabad-45320, Pakistan
                [2 ]Core Research Facilities, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia
                Article
                10.1039/D2NJ01153K
                5ccd5ae6-3a97-4aec-ae75-3bfb3c635614
                © 2022

                http://rsc.li/journals-terms-of-use

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