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Phenomenological modeling of electron-hole recombination in promising photo-catalytic magnetic materials
No full textRecent experiments have demonstrated impressive photo-catalytic performances in spin-polarized materials. The existence of spin-dependent recombination between spin split bands has been suggested as the cause for at least part of the improved photo-catalysis. To test the efficacy of this mechanism, we develop a set of rate equations for carrier charge and spin to shed light on recent experiments with metal-defected or doped oxides, magnetically decorated metal-organic frameworks, and magnetically-doped perovskites. Our results show that recombination will be dependent on the band spin polarization and the lengthening of decay times can be optimized by engineering the electronic structure
Deoxytrifluoromethylation/Aromatization of Cyclohexan(en)ones to Access Highly Substituted Trifluoromethyl Arenes
No full textTrifluoromethyl arenes (Ar–CF3) are amongst the commonly encountered fluorinated substructures in pharmaceutical, agrochemical, and material sciences. However, predominant methods to access Ar–CF3 possess several limitations, including harsh conditions, lack of availability of substrates, and poor regioselectivity, which combined restrict access to desirable highly functionalized Ar–CF3-containing compounds. To expand the scope of accessible Ar–CF3-based molecules, we present an innovative and orthogonal deoxyfluoroalkylation/aromatization approach that exploits readily accessible and programable cyclohexan(en)one substrates, which undergo a reliable 1,2-addition reaction with the Ruppert-Prakash reagent (TMSCF3) followed by aromatization to deliver highly functionalized Ar–CF3 compounds in a one/two-pot sequence. This general strategy enables access to highly substituted Ar–CF3-containing molecules that are difficult, expensive, and/or impossible to access by current synthetic methods
Sugar characteristics of honey from Abu Dhabi (United Arab Emirates) market
No full textHoney is a natural sweetening agent having concentrated solution of sugars. The sugar composition and percentage ratio are valuable quality parameters as some of the physiochemical properties like hygroscopicity, granulation, viscosity is influenced by the composition of sugars. Honey samples from the retail markets in the Emirate of Abu Dhabi were utilized to determine fructose, glucose, and sucrose values due to their dominance in the nectars having profound impact in determining the honey quality. The sum of reducing sugar content was in the range of 27% to 87% while sucrose content was between 5 to 37%. About 33% of the samples failed to comply with standard threshold of glucose and fructose. The samples having higher sucrose content exhibited decreased glucose and fructose levels. In conclusion, the commercially available honey samples require rigorous scrutiny and monitoring due to higher levels of quality non-compliance in accordance with local standards
Selective depolymerization of polyolefin plastics into olefin monomers on electrified tungsten filament
No full textPolyolefin plastics account for ~60% of global plastic waste, and thus depolymerizing large quantities of waste polyolefin plastics into olefin monomers is attractive for both recycling plastics in a circular economy and providing sustainable raw materials for the chemical industry. However, the selectivity of olefin monomers is limited even with catalysts. Here we report an electrified tungsten filament method for depolymerizing polyolefin plastics into olefin monomers with competitive selectivities. In this system, a high temperature zone exceeding 1000 °C enables plastic depolymerization within 1 s, while the flow field transfers the products to a zone near room temperature, preventing nonselective further conversion. For depolymerizing polyethylene to ethylene, this method achieves a selectivity of 48%, substantially improved compared with that of traditional methods, such as catalytic pyrolysis (typically <20%). Moreover, polyethylene and polypropylene of various molecular weights and their mixtures have been depolymerized with monomer selectivities of 45–58% without the formation of tars and chars. This strategy offers rich possibilities for advancing a circular economy based on waste plastics
Hypothesis of Concerted Reactivity of Singlet Non-Covalent Radical Dimers
No full textThis work explores the intriguing domain of Frustrated Radical Pairs (FRPs) and their potential to form non-covalent dimers, termed Entangled Radical Pairs (ERPs), which exhibit unique singlet ground states and potential concerted reactivity, differing from traditional stepwise reactions. A few recent publications showed that in certain cases when two radicals cannot form a covalent bond, they unexpectedly form a non-covalent dimer with a singlet ground state. This potentially opens a new elusive route of FRPs’ reactivity, in which both radicals react simultaneously as one molecule. Here, we review several published articles, in which such reactivity probably took place, but was overlooked. The idea presented in this proposal suggests a path towards many interesting reactions, such as low-temperature metal-free dehydrogenation of aliphatic hydrocarbons and others. Additionally, an alternative mechanism for the reactivity of Frustrated Lewis Pairs (FLPs) based on the ERP framework is proposed. Lastly, the implications of the ERP model on the general theory of chemical bond formation are contemplated, suggesting a revision of the traditional views on hybridization and electron entanglement. The manuscript calls for further experimental and theoretical investigations to substantiate the presented hypotheses, aiming to unlock new pathways in radical chemistry and beyond
Principled Approach for Computing Free Energy on Perturbation Graphs with Cycles
No full textA common approach for computing free energy differences among multiple states is to build a perturbation graph connecting the states and compute free energy differences on all edges of the graph. Such perturbation graphs are often designed to have cycles. Because free energy is a function of states, the free energy around any cycle is zero, which we refer to as the cycle consistency condition. Since the cycle consistency condition relates free energy differences on edges of a cycle, it could be used to improve the accuracy of free energy estimates. Here we propose a Bayesian method called coupled Bayesian multistate Bennett acceptance ratio (CBayesMBAR) that can properly couple the calculations of free energy differences on edges of cycles in a principled way. We apply CBayesMBAR to compute free energy differences among harmonic oscillators and relative protein-ligand binding free energies. In both cases, CBayesMBAR provides more accurate results compared to methods that do not consider the cycle consistency condition. Additionally, it outperforms the cycle closure correction method that also uses cycle consistency conditions
(Pyridyl)-Aminotriazoles as Versatile Synthetic Synthons: Amido Complexes, “Normal” Triazole-Based Imines and Metallo Mesoionic Imines
No full textMesoionic compounds are currently hugely popular in several fields such as organic chemistry, organometallic chemistry and homogeneous catalysis. A new class of mesoionic compounds are the mesoionic imines (MIIs). For MIIs based on a 1,2,3-triazole core, the synthetic strategy involves alkylation/arylation of the triazole-N3 atom and subsequent deprotonation to de-liver MIIs. We present here 5-amino-4-pyridyl-1,2,3-triazole as an alternative and versatile synthon for generating metallo-MIIs. In this approach, we make use of metallation at the N-pyridyl/N3-traizole chelating pocket (instead of quarternisation of N3-triazole) and subsequent deprotonation to generate highly versatile and tunable metallo-MIIs. These unprecedented metallo-MIIs contain a highly nucleophilic N-donor site, and a tunable electrophilic metal site within the same platform. Apart from displaying strong and directed H-bonding interactions like their “classical” MII analogues, the metallo-MIIs engage in aromatic C-F activation as well as meta-C-H activation reactions. Facile synthesis of homo and heterodincuelar complexes which contain a mixed coordinative saturation/unsaturation with these metallo-MICs is presented. Apart from the metallo-MICs we have also used 5-amino-4-pyridyl-1,2,3-triazole as a viable precursor to generate the first examples of amido-1,2,3-triazole complexes and the first example of a “normal” (and not mesoionic) 1,2,3-triazole based imine. Apart from a combination of synthetic chemistry, multinuclear NMR spectroscopy and single crystal X-ray diffraction, (TD)DFT calculations were also used to shed light on the electronic structure and the frontier orbital situation of these compounds. Our results thus establish metallo-MIIs as a versatile new class of mesoionic compounds that combine the modularity of click reactions, with the functionality of metal fragments to generate electronically ambivalent compounds with a huge potential in synthetic chemistry, catalysis and beyond
Applying Marcus Theory to Describe Photoluminescent Intermittency and Temperature Dependent Emission in CdTe Nanoplatelets
No full textPhotoluminescence (PL) intermittency (also known as blinking) is a critical aspect of the optical properties of molecules and nanomaterials. Considerable work has expounded on the mechanism of blinking in nanocrystals, with the canonical model arguing that intermittently trapped charges serve to quench emission via charge-exciton Auger recombination. The dynamics of the emission trace are analyzed by fitting a histogram of on- and off- times to power-law distributions. These histograms in turn, reveal non-exponential kinetics, arguing for a distribution of electron or hole traps. What is not revealed is the origin of these distributed states, whether they arise from various trap energetic depths, long-range electron or hole tunneling, or any other process which gives rise to distributions of rates. We explore a model which invokes both a distribution of trap energies, combined with the chemical intuition of charge transfer via Marcus theory. We find that a self-consistent Marcus theory model can explain different power-law slopes for on- and off- times, and the observed changes in intensity as a function of temperature in films of CdTe nanoplatelets (NPLs). We believe this provides a self-consistent model to describe blinking behavior that leads to unusually low PL quantum yield (QY) in CdTe, and argues that improved passivation will be critical to achieving higher QY
Diffusion-programmed catalysis in nanoporous material
No full textIn the realm of heterogeneous catalysis, the diffusion of reactants into catalytically active sites stands as a pivotal determinant influencing both turnover frequency and geometric selectivity in product formation. While accelerated reactants diffusion can elevate reaction rates, it often entails a compromise in geometric selectivity. Porous catalysts, including metal-organic and covalent organic frameworks, confront formidable obstacles in regulating reactant diffusion rates. Consequently, the chemical functionality of the catalysts typically governs turnover frequency and selectivity. This study presents an approach harnessing diffusion length to achieve improved selectivity and manipulation of reactant residence time at active sites to augment reaction kinetics. Through the deployment of a thin film composed of a porous metal-organic framework catalyst, we illustrate that how programing reactant diffusion within a cross-flow microfluidic catalytic reactor can concurrently amplify turnover frequency (exceeding 1000-fold) and enhance geometric selectivity (~2-fold) relative to conventional nano/microcrystals of catalyst in one-pot reactor. This diffusion-programed strategy represents a robust solution to surmount the constraints imposed by bulk nano/microcrystals of catalysts, marking an evolution in the design of porous catalyst-driven organic reactions
Imaging and quantifying the biological uptake and distribution of nanoplastics using a dual-functional model material
No full textNanoplastics (NPs) are invisible to human eyes yet pose significant concerns to human health due to their wide environmental presence and high potential for biological uptake, transport, and accumulation. Conventional analytical methods suffer from low accuracy and precision in NP detection due to their limited reliability and quantitative ability. To address these challenges, we developed a dual-functional model NP that allows for in-situ imaging by surface-enhanced Raman spectroscopy (SERS) and ex-situ quantification by inductively coupled plasma-mass spectrometry (ICP-MS). In this study, the model NP has a core-shell structure with Raman reporter-functionalized gold nanoparticles as the core and a layer of plastic as the shell. The gold core can enhance the Raman reporter signals and make model PS detectable, which can be used to visualize the uptake of the model NP in plant tissue by SERS. Meanwhile, the model NP particle numbers in the collected plants can be quantified by ICP-MS based on the presence of gold in the core. The model PS demonstrated stability in structure, size, and surface charges over one year, with no indication of chemical leaching. In this study, garlic plants were used as our experimental matrix to evaluate the potential of the dual-functional model PS for application in living organisms. Our aim was to determine whether the model PS in the garlic plants could be effectively quantified and qualified by SERS and ICP-MS. Garlic plants were grown in various concentrations of model NP suspensions for a 30-day period. The results showed that the NP uptake was concentration-dependent with higher concentrations of model NP leading to higher uptake by the garlic roots. The study also investigated the changes in NP uptake over time, showing that longer NP exposure resulted in more NP uptake in garlic roots. The study also demonstrated the effective coordination between SERS and ICP-MS. In cases where SERS had limitations in detecting the presence of model PS, ICP-MS proved capable of facilitating detection in garlic tissue. This study demonstrates the potential use of this dual-functional model NP for studying NP behavior with SERS and ICP-MS in living organisms, which holds significant implications for better understanding their impact on crops for future studies