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Understanding Catalytic Enantioselective C-H Bond Oxidation at Nonactivated Methylenes Through Predictive Statistical Modeling Analysis
No full textEnantioselective C(sp3)‒H bond oxidation is a powerful strategy for installing functionality in C(sp3)‒H rich molecules. Site- and enantioselective oxidation of strong C‒H bonds in monosubstituted cyclohexanes with hydrogen peroxide catalyzed by aminopyridine manganese catalysts in combination with alkanoic acids has been recently described. Mechanistic uncertainties and nonobvious enantioselectivity trends challenge development of the full potential of this reaction as a powerful synthetic tool. Herein, we apply predictive statistical analysis to identify mechanistically informative correlations that provide valuable reaction understanding and will guide the development and optimization of new enantioselective C‒H oxidation reactions
Weighted distribution of relaxation time analysis of battery impedance spectra using Gaussian process regression for noise estimation
No full textElectrochemical impedance spectroscopy (EIS) is one of the most widely deployed methods to characterise electrochemical systems such as batteries, fuel cells or electrolyzers. The distribution of relaxation times (DRT) represents a technique to simplify EIS data by deconvolution with a suitable kernel, while with equivalent circuit modelling (ECM) a user-selected function is fitted to characterize the investigated system. Ideally, the residuals of a DRT fit should represent random white noise without systematic residuals, hence no useful data is lost by this analysis step. Thereby DRT can provide the number of distinguishable features based solely on the EIS data, without a priori knowledge of the response of the investigated system. It is demonstrated that such a \u27lossless\u27 DRT inversion is possible if the local noise amplitude is considered, which requires a weighted DRT procedure and a method to estimate the frequency dependent noise amplitude. A noise estimate to determine the necessary weights was obtained using multiple EIS acquisitions of the same battery at identical state-of-charge. Alternatively, it is shown that Gaussian process regression (GPR) is capable of estimating an equivalent weighting matrix from a single data set as a prerequisite for automatized weighted DRT inversion without user intervention. The obtained DRT spectrum is then used for the selection of an equivalent circuit model, its initial parametrization, and setting of constraints. The robustness and reliability of this technique is tested numerically using a simple digital twin model. Eventually, by means of the investigated battery it is discussed that using a combination of DRT and ECM, a more physically relevant description of processes in an electrochemical system can be achieved
Enhanced Sampling with Sub-optimal Collective Variables: Reconciling Accuracy and Convergence Speed
No full textWe introduce an enhanced sampling algorithm to obtain converged free energy landscapes of molecular rare events, even when the collective variable (CV) used for biasing is not optimal. Our approach is a combination of the On-the-fly probability enhanced sampling (OPES) and its exploratory variant, OPES Explore (OPESe). We demonstrate the successful application of this combined algorithm on the two-dimensional Wolfe-Quapp potential, ligand-receptor binding in trypsin-benzamidine complex, and folding-unfolding of chignolin. Apart from computing accurate free energy profiles, we can discover additional metastable configurations not distinguished by the sub-optimal CV space. Moreover, we can control the trade-off between accuracy and convergence speed by varying the ratio of the barrier parameters in OPES and OPESe components. The improved efficiency and accuracy of free energy calculation, and the possibility of using generic and intuitive collective variables, make our proposed algorithm particularly promising for the simulation of complex molecular systems
Chemiluminescence signature arrays coupling with machine learning for Alzheimer’s disease serum diagnosis
No full textTremendous efforts have been made to directly identify serum components using traditional omics approaches. However, several unmet medical needs persist, particularly for chronic diseases that lack reliable biomarkers. The subtle physicochemical abnormality of serum has been widely overlooked and currently lacks detection methods. Inspired by the bat echolocation mechanism, we proposed a chemiluminescence “echoes” approach to depict the disease-specific signatures in biofluids. Specifically, Alzheimer’s disease (AD) serums were used for proof-of-concept study. We first demonstrated the discrepancy in physicochemical properties between AD and healthy control (HC) serums. On this basis, we developed a simple, fast and versatile UNICODE (UNiversal Interaction of Chemiluminescence echOes for Disease Evaluation) array for AD diagnosis. By employing a "bat" probe (ADLumin-1), which generates chemiluminescence autonomously, and combined with a panel of “flag” molecules that enable “echo” formation, we were able to create distinct signatures for various serum components and subtle physicochemical environments. To develop an AD-specific UNICODE diagnosis, we screened a library of over 1000 small molecules, and identified 12 “flag” molecules (top-12) that optimally depict the differences between AD and HC serums. Finally, we used the top-12 array for AD diagnosis. By modeling the UNICODE signatures with seven machine learning methods, we successfully differentiated AD (n = 31) and HC (n = 37) serums, and our best model of random forest provided accuracy = 85.48%, precision = 85.00%, recall = 88.60%, f1 = 85.63%, and AUC = 90.24%. Our strategy could provide new insights into biofluid abnormality and prototype tools for developing liquid biopsy diagnoses for AD and other diseases
2D TiNBr as photocatalyst for overall water splitting
No full textTwo-dimensional (2D) Janus materials gain increasing attention as water splitting photocatalysts for hydrogen production. We use first-principles calculations to predict a stable 2D Janus -TiNBr structure, with strong near-ultraviolet sunlight absorption and band edges that align favorably with the water redox potentials for oxygen and hydrogen evolution. We show that the optical and electronic properties of -TiNBr can be modulated to a certain extend by applying external uniaxial strain. Explicit calculations of the redox reactions reveal that solar-driven water splitting is viable at the N-side of -TiNBr, while the Br-side requires modifications such as vacancy creation, the application of an external potential, or adjustment of the pH conditions
The Role of Phosphorous in the Solid Electrolyte Interphase of Argyrodite Solid Electrolytes
No full textThe solid electrolyte interphase that forms on Li6PS5Cl argyrodite solid electrolytes has been reported to continually grow through a diffusion-controlled process, yet this process is not fully understood. Here, we use a combination of electrochemical and X-ray photoelectron spectroscopy techniques to elucidate the role of phosphorus in this growth mechanism. We uncover how Li6PS5Cl can decompose at a potential well above the full reduction to Li3P, forming partially lithiated phosphorus species LixP. We provide evidence of a gradient of LixP species throughout the SEI thickness, leading to a diffusion-limited growth. We predict continuous SEI growth as long as lithium metal is present
Selective Ni-Catalyzed Cross-Electrophile Coupling of Heteroaryl Chlorides and Aryl Bromides at 1:1 Substrate Ratio
No full textNickel-catalyzed cross-electrophile coupling (XEC) reactions of (hetero)aryl electrophiles represent appealing alternatives to palladium-catalyzed methods for biaryl synthesis, but they often generate significant quantities of homocoupling and/or proto-dehalogenation side products. In this study, an informer library of heteroaryl chloride and aryl bromide coupling partners is used to identify Ni-catalyzed XEC conditions that access high selectivity for the cross-product when using equimolar quantities of the two substrates. Two different catalyst systems are identified that show complementary scope and broad functional-group tolerance, and time-course data suggest the two methods follow different mechanisms. A NiBr2/terpyridine catalyst system with Zn as the reductant converts the aryl bromide into an aryl-zinc intermediate that undergoes in situ coupling with 2-chloropyridines, while a NiBr2/bipyridine catalyst system with tetrakis(dimethylamino)ethylene as the reductant uses FeBr2 and NaI as additives to achieve selective cross-coupling
Bifunctional photocatalysts display proximity-enhanced catalytic activity in metallaphotoredox C–O coupling
No full textDual catalytic reactions may be made more effective through an improved integration of the catalytic cycles achieved using bifunctional catalysts. Herein we describe new bifunctional photocatalysts consisting of a photoactive donor-acceptor cyanoarene unit linked to a bipyridine ligand moiety that can bind transition metals. The bifunctional photocatalysts were synthesized in 3-5 steps form commercially available compounds and fully characterized in terms of photophysical properties, which are strongly affected by the type of linkage used (C vs. O) to connect the cyanoarene core to the ligand. Catalytic tests carried out in the Nicatalyzed C-O cross-coupling of alcohols to aryl bromides promoted by visible light have shown that the bifunctional systems are more active than the corresponding ‘dual catalytic systems’ (i.e., not covalently bound), taking advantage of the proximity between the two catalytic moieties (Ni-complex and photocatalyst). The best bifunctional dyes were tested with several alcohols and aryl halides, giving good yields at low catalytic loading (0.5-2 mol%)
Molecular photothermal activation assisted synthesis, and orthogonal assembly of metal-organic-framework
No full textTemperature is a fundamental parameter in any chemical process, affecting reaction rates, selectivity, and more. Typically, chemists think of temperature as a homogeneous property, remaining unchanged throughout the reaction in space and time. Recently, photothermal materials have been emerging as an exciting tool opening new paths for innovative research, challenging the viewpoint described above. Herein, we develop a synthesis and in-situ assembly technique for metal-organic frameworks (MOFs) based on the distinct heterogeneous heating of photothermal materials under visible light. Notably, a simple cobalt chloride molecular complex was utilized as an efficient and stable light-to-heat converter for initial MOF formation. A thorough investigation of the assembly mechanism revealed the key role photothermal activation had in the formation of the superstructures. Finally, palladium nanoparticles (NP) were utilized as competing photothermal agents shedding light on the dynamics between different heat sources within a reaction and resulting in MOF-NP composites. This work highlights the versatility of the photothermal approach in the synthesis of advanced materials introducing a promising route to the micro/nano assembly of different materials
A Practical, Large Scale Preparation of Ni(tmeda)(o-tol)Cl
No full textA convenient, inexpensive synthesis of the previously reported and well-defined complex Ni(tmeda)(o-tol)Cl is described. This protocol enables rapid and safe access to Ni(tmeda)(o-tol)Cl, obviating the use of the hazardous reagent AlMe3 or the air-sensitive Ni(COD)2. Ni(tmeda)(o-tol) is prepared, from the commercially available and easily synthesized precursor, Ni(acac)2 at room temperature and the product can be isolated at gram scale in air via simple filtration. We expect this simple method to be attractive to chemical industry and academia given the types of solvents, reaction temperature and reagents used