Absolute Determination Research Articles

Stable Axially Chiral Cyclohexylidenes from Catalytic Asymmetric Knoevenagel Condensation.

Axially chiral cycloalkylidenes are interesting but less developedaxially chiral molecules. Here, a bispidine-based chiral amine catalytic system was developed to promote efficiently the asymmetric Knoevenagel condensation ofN-protected oxindoles and benzofuranones with 4-substituted cyclohexanones. A variety of alkylidenecycloalkanes with stable axial chirality were obtained in good yields with high er. Based on the absolute configuration determination of product and DFT calculations, a possible mechanism of stereoselective induction was proposed.

Effects of phantom microstructure on their optical properties.

Developing stable, robust, and affordable tissue-mimicking phantoms is a prerequisite for any new clinical application within biomedical optics. To this end, a thorough understanding of the phantom structure and optical properties is paramount. We characterized the structural and optical properties of PlatSil SiliGlass phantoms using experimental and numerical approaches to examine the effects of phantom microstructure on their overall optical properties. We employed scanning electron microscope (SEM), hyperspectral imaging (HSI), and spectroscopy in combination with Mie theory modeling and inverse Monte Carlo to investigate the relationship between phantom constituent and overall phantom optical properties. SEM revealed that microspheres had a broad range of sizes with average and were also aggregated, which may affect overall optical properties and warrants careful preparation to minimize these effects. Spectroscopy was used to measure pigment and SiliGlass absorption coefficient in the VIS-NIR range. Size distribution was used to calculate scattering coefficients and observe the impact of phantom microstructure on scattering properties. The results were surmised in an inverse problem solution that enabled absolute determination of component volume fractions that agree with values obtained during preparation and explained experimentally observed spectral features. HSI microscopy revealed pronounced single-scattering effects that agree with single-scattering events. We show that knowledge of phantom microstructure enables absolute measurements of phantom constitution without prior calibration. Further, we show a connection across different length scales where knowledge of precise phantom component constitution can help understand macroscopically observable optical properties.

Absolute frequency measurement of the 5s5p 1P1 - 5s5d 1D2 transition in strontium

We report on the absolute frequency determination of the 5s5p 1P1 - 5s5d 1D2 transition in atomic strontium, achieved through frequency comb-referenced laser-induced-fluorescence (LIF) spectroscopy. We excite the 5s21S0 - 5s5p 1P1 transition using an on-resonance laser at ≈461 nm, and then measure the variation in the LIF signal while scanning the laser at ≈767 nm across the 5s5p 1P1 - 5s5d 1D2 transition. We determine the absolute frequency of 390599571.7±0.4 MHz, with an accuracy that surpasses the previous most accurate measurement by two orders of magnitude. This measurement technique can be readily applied for precision spectroscopy of high-lying states not only in strontium, but also in other atomic species.

Hobbes, Locke, and the Christian Commonwealth

Abstract Locke refrained from engaging explicitly with Hobbes in any of his writings. Locke’s policy of non-engagement should be interpreted, we argue, neither as evidence of his lack of interest in (or ignorance of) Hobbes’s arguments, nor as an attempt to conceal from the uninitiated Locke’s covert Hobbesian commitments. Locke’s silence reveals rather than conceals. What it reveals is an absolute determination to “distinguish between the business of civil government and that of religion, and to mark the true bounds between them”. Approached in this way, precisely because Locke’s account of the “business of civil government” says nothing about ecclesiastical government, the second of Two Treatises can be read, in its entirety, as a powerful critical response to Hobbes. To see why, it is necessary to grasp that Part iii of Leviathan (“Of a Christian Common-wealth”) is integral to Hobbes’s positive argumentative purposes in the work.

Absolute structure determination of Berkecoumarin by X-ray and electron diffraction.

X-ray and electron diffraction methods independently identify the S-enantiomer of Berkecoumarin [systematic name: (S)-8-hydroxy-3-(2-hydroxypropyl)-6-methoxy-2H-chromen-2-one]. Isolated from Berkeley Pit Lake Penicillium sp., Berkecoumarin is a natural product with a light-atom composition (C13H14O5) that challenges in-house absolute structure determination by anomalous scattering. This study further demonstrates the utility of dynamical refinement of electron-diffraction data for absolute structure determination.

[Quantitative 31P-NMR for Purity Determination of Organophosphorus Compounds (Pharmaceuticals)].

Quantitative NMR (qNMR), particularly 1H-qNMR, is useful for determining the absolute purity of organic molecules. However, identifying the target signal(s) for quantification is difficult, because of the overlap and complexity of organic molecules. Therefore, we focused on the 31P nucleus, owing to the simplicity of its signals, and investigated the 31P-qNMR absolute determination method by using organophosphorus drugs, water-soluble cyclophosphamide hydrate (CP), and water-insoluble sofosbuvir (SOF). The optimized and reproducible 31P-qNMR conditions, such as qNMR sample preparation [i.e., selecting suitable deuterated solvents and a reference standard (RS) for 31P-qNMR], hygroscopicity and solution stability of the analyte and RS, and qNMR measurements-such as acquisition time, relaxation delay time, and spectral width-were examined. The CP purities determined using 31P-qNMR agreed well with those for the established 1H-qNMR method in D2O. In contrast, the SOF purity determined using 31P-qNMR was 1.6% higher than that for 1H-qNMR in the protic solvent CD3OD. Therefore, using a protic solvent, such as CD3OD, was not suitable for 31P-qNMR; the deuterium exchange with the RS for 31P-qNMR (i.e., phosphonoacetic acid) resulted in a small integrated intensity. Consequently, the aprotic solvent DMSO-d6 was employed to determine the SOF purity. The data revealed that the SOF purities determined using 31P-qNMR agreed well with the established 1H-qNMR values, indicating that the absolute quantification of SOF using both 31P-qNMR and 1H-qNMR is possible in DMSO-d6. Thus, we established an optimized and reproducible 31P-qNMR method in validation study across multiple laboratories.

Absolute and non-invasive determination of the electron bunch length in a free electron laser using a bunch compressor monitor

In a linac driven Free Electron Laser (FEL), the shot-to-shot and non-invasive monitoring of the electron bunch length is normally ensured by Bunch Compressor Monitors (BCMs). The bunch-length dependent signal of a BCM results from the detection and integration—over a given frequency band—of the temporal coherent enhancement of the radiation spectral energy emitted by the electron beam while experiencing a longitudinal compression. In this work, we present a method that permits to express the relative variation of the bunch length as a function of the relative statistical fluctuations of the BCM and charge signals. Furthermore, in the case of a BCM equipped with two detectors simultaneously operating in two distinct wavelength bands, the method permits an absolute determination of the electron bunch length. The proposed method is beneficial to a FEL. Thanks to it, the machine compression feedback can be tuned against the absolute measurement of the bunch length rather than a bunch-length dependent signal. In a CW-superconducting-linac driven FEL, it can offer the precious opportunity to implement a fully non-invasive and absolute diagnostics of the bunch length.

Dislocation Does Not Seem To Be an Absolute Factor Effecting the Short- to Medium-Term Poor Prognosis of Patients with Acetabular Posterior Wall Fracture.

Dislocation is a complication of acetabular fractures involving the posterior wall, but whether dislocation is an absolute factor impacting the short- to medium-term prognosis of the hip joint remains controversial. This study aimed to compare the short- to medium-term clinical and radiological results among patients diagnosed with an acetabular fracture involving the posterior wall, with or without dislocation.Seventy-nine patients diagnosed with an acetabular fracture involving the posterior wall were retrospectively divided into posterior dislocation and non-dislocation groups. All fractures were open reduction + internal fixation with a plate screw combination through the single Kocher-Langenbeck approach. The short- to medium-term radiographic outcomes of follow-up were evaluated using the Matta radiologic grading system, while the clinical outcomes were evaluated using the modified Merle d'Aubigné-Postel evaluation system.The mean follow-up duration for all patients was 43.90 (range 24-75) months. Both groups achieved similar short- to medium-term clinical and radiographic results. There seems to be no significant differences between the two groups regarding the short- to medium-term assessment of clinical and radiographic results and the occurrence of postoperative complications (p>0.05).In patients with acetabular fractures involving the posterior wall, hip dislocation is probably not an absolute determinant of a poor outcome. Even with early reduction, the short- to medium-term prognosis results appear similar to those of patients without dislocation.

Prediction of Cumulative Biomethane Yield Using Artificial Neural Network - Case Study of an Industrial Biogas Plant

There are many facets to the applications of Artificial Intelligence (AI) in the energy sector however, this research focuses on the utilization of Artificial Neural Networks (ANN) as parts of AI technique to simulate and model the operating performance of an industrial biogas plant data set. In this study, eight (8) model network architectures were developed using the ANN tool of MATLAB 2016a version and it was found that the best result was obtained based on the model performance evaluation metrics used such as Root Mean Square Error (RMSE), Mean Absolute Percentage Error (MAPE), Mean Absolute Deviation (MAD) and Determination Coefficient (R2) was as a result of the combination of two activation functions namely: tansig and logsig. The model, that produced the best result was a result of the architecture that contains 2 hidden neurons and the training algorithm of Scaled Conjugate Gradient (SCG). It was also observed that the ANN-predicted network diagram is better than the observed.

Two New Compounds Isolated from the Itea omeiensis and Their Anti-oxidant Activities.

Two new compounds (1-2) together with ten known compounds (3-12) were isolated for the first time from the 95 % EtOH extract of aerial parts of Itea omeiensis. Their structures were elucidated based on extensive spectroscopic analyses and comparison with published data. The structure of 1 was further confirmed through single-crystal X-ray diffraction analysis, and circular dichroism (CD) spectrum in combination with acid hydrolysis was employed for the absolute configuration determination of 2. Compound 1 was the first 2-arylbenzo[b]furan with an extra six-membered lactone ring from Itea plants. Anti-oxidant assays indicated that compound 1 possessed significant radical scavenging effects on 1,1-Diphenyl-2-picrylhydrazyl (DPPH) and 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS⋅+ ) with IC50 values of 0.14 and 0.06 mg/mL, respectively, which were comparable to the positive control of ascorbic acid. However, no obvious anti-hepatocellular carcinoma activity was observed for compounds 1 and 2.

Quantitative 31P-NMR for the Purity Determination of the Organophosphorus Compound Brigatinib and Its Method Validation.

The spectrum of 31P-NMR is fundamentally simpler than that of 1H-NMR; consequently identifying the target signal(s) for quantitation is simpler using quantitative 31P-NMR (31P-qNMR) than using quantitative 1H-NMR (1H-qNMR), which has been already established as an absolute determination method. We have previously reported a 31P-qNMR method for the absolute determination of cyclophosphamide hydrate and sofosbuvir as water-soluble and water-insoluble organophosphorus compounds, respectively. This study introduces the purity determination of brigatinib (BR), an organophosphorus compound with limited water solubility, using 31P-qNMR at multiple laboratories. Phosphonoacetic acid (PAA) and 1,4-BTMSB-d4 were selected as the reference standards (RSs) for 31P-qNMR and 1H-qNMR, respectively. The qNMR solvents were chosen based on the solubilities of BR and the RSs for qNMR. CD3OH was selected as the solvent for 31P-qNMR measurements to prevent the influence of deuterium exchange caused by the presence of exchangeable intramolecular protons of BR and PAA on the quantitative values, while CD3OD was the solvent of choice for the 1H-qNMR measurements to prevent the influence of water signals and the exchangeable intramolecular protons of BR and PAA. The mean purity of BR determined by 31P-qNMR was 97.94 ± 0.69%, which was in agreement with that determined by 1H-qNMR (97.26 ± 0.71%), thus indicating the feasibility of purity determination of BR by 31P-qNMR. Therefore, the findings of this study may provide an effective method that is simpler than conventional 1H-qNMR for the determination of organophosphorus compounds.

Predicting band gaps of ABN3 perovskites: an account from machine learning and first-principle DFT studies.

The present paper is primarily focused on predicting the band gaps of nitride perovskites from machine learning (ML) models. The ML models have been framed from the feature descriptors and band gap values of 1563 inorganic nitride perovskites having formation energies <-0.026 eV and band gaps ranging from ∼1.0 to 3.1 eV. Four supervised ML models such as multi-layer perceptron (MLP), gradient boosted decision tree (GBDT), support vector regression (SVR) and random forest regression (RFR) have been considered to predict the band gaps of the said systems. The accuracy of each model has been tested from mean absolute error, root-mean-square error and determination coefficient R2 values. The bivariate plots between the predicted and input band gaps of the compounds for both the training and test datasets have also been estimated. Additionally, two ABN3-type nitride perovskites CeBN3 (B = Mo, W) have been selected and their electronic band structures and optoelectronic properties have been studied from density functional theory (DFT) calculations. The band gap values of the said compounds have been estimated from DFT calculations at PBE, HSE06, G0W0@PBE, G0W0@HSE06 level of theories. The present study will be helpful in exploring the ML models in predicting the band gaps of nitride perovskites which in turn may bear potential applications in photovoltaic cells and optical luminescent devices.

Total Synthesis of the Sesquiterpene (-)-Merrillianin.

The first total synthesis of (-)-merrillianin (1), which is a natural sesquiterpene with a tricyclic structure having a cyclopentane ring and five- and seven-membered lactone parts, is demonstrated. This asymmetric total synthesis enabled the absolute stereostructure determination of naturally occurring (-)-1.

Stratigraphy of Late Mid‐Pleistocene in Lithuania: the current status and issues

The principal aim of this paper is to present a critical overview of the stratigraphical subdivision and correlation of the Late Mid‐Pleistocene (LMP) sediments in Lithuania. In recent decades, a number of studies of LMP sediments have been carried out, allowing clarification of the stratigraphical position of individual sedimentary sections. Particular efforts have been made to determine the age of sediments using a variety of absolute age determination methods. However, there are still several outstanding questions. It is still unclear how many warm periods occurred during the Saalian in Lithuania and of what magnitude. The least problematic issue is identification of the Butėnai (Holsteinian) Interglacial as it correlates well biostratigraphically with the contemporaneous sections of adjacent areas. The most controversial unit is the Snaigupėlė Interglacial, the age of which continues to be a subject of debate. Recently, more evidence has emerged that the sediments considered to be of the Snaigupėlė Interglacial are contemporaneous with the Merkinė (Eemian) Interglacial. The chronological placement of these sediments closely hinges on the unresolved stratigraphical classification of the Medininkai deposits (MIS 6 or MIS 8?) and the Žemaitija tills (MIS 8 or MIS 10?). The debate is centred on whether these two tills were formed during two entirely different glaciations or represent different phases of a single major glaciation event. Traditionally, these two tills were attributed to distinct glaciation events separated by the Snaigupėlė Interglacial. However, no sedimentary sections have been discovered that contain both these tills and the interglacial sediments that separate them. Given the similar lithological, geochemical and petrographic composition of the Medininkai and Žemaitija tills some research has supported their possible stadial rank. The clarification of these stratigraphical issues in the future may be facilitated by the application of new proxies and re‐examination of the existing LMP key sections.

Synthesis, crystal structure, DFT calculation and confirmation of absolute configuration of empagliflozin

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disorder characterized by long-term disruptions in metabolism. In the course of drug development over the past decades, sodium-glucose cotransporter 2 (SGLT2) has emerged as a novel therapeutic target for treating T2DM. Empagliflozin, a significant pharmacologically active aryl glycoside, functions as a sodium-glucose cotransporter 2 (SGLT2) inhibitor and has been extensively used for blood glucose control in patients with both T2DM and diagnosed cardiovascular disease (CVD). In this study, empagliflozin was synthesized through a six-step reaction and subjected to single-crystal growth, with its structure analyzed via X-ray diffraction. Subsequently, comprehensive computational predictions of empagliflozin's structural properties were carried out using DFT theory, encompassing infrared, nuclear magnetic resonance, Raman spectra, and ECD measurements. The results were subjected to a combined analysis with experimental data, bearing significant implications for the spectral analysis and absolute configuration determination of empagliflozin. In order to gain insights into the reasons behind the formation of empagliflozin crystals, a single crystal structure analysis was performed. Additionally, DFT calculations were employed to investigate various physicochemical properties of empagliflozin, including RDG, ELF, FMOs, MEP, etc. This study aimed to provide insights into the physicochemical properties of empagliflozin and its various non-covalent interactions. The findings are anticipated to provide valuable insights for subsequent structure optimization and drug discovery endeavors.

Evaluating the enantioselective capability of a cellulose tris(3,5‐dimethylphenyl carbamate)‐based stationary phase towards 5,7,2'‐trihydroxyflavanone

AbstractIn this study, an evaluation of the enantioselective of a chiral flavanone with 2'‐OH substitution (5,7,2'‐trihydroxyflavanone) on ring C was studied by high performance liquid chromatography using the cellulose tris(3,5‐dimethylphenyl carbamate)‐based stationary phase with n‐hexane and iso‐propanol doped with 0.1% (v/v) trifluoroacetic acid as a mobile phase. Column temperature and mobile phase composition were investigated in the assessment of the chiral separation by considering the enantiomeric resolution factor (Rs). Also, the absolute configurations of single enantiomers were determined by measuring CD spectra based on the exciton‐coupling method. The results pointed out that the 2'‐hydroxy group was capable of advancing the enantioselective of flavanones on the cellulose tris(3,5‐dimethylphenyl carbamate)‐based stationary phase when the column temperature was higher than 30 oC and the mobile phase was of 10% iso‐propanol doped with 0.1% (v/v) TFA in n‐hexane. The absolute configuration determination showed that the enantiomer with the 2S configuration was the first eluted and, consequently, the elution order of the enantiomers of 5,7,2'‐trihydroxyflavanone at optimal conditions was in contrast to 5,7,4'‐trihydroxyflavanone and 5,7‐dihydroxyflavanone. The 2'‐OH substitution on the phenyl moiety appears to be capable of inducing or altering the strength of inter‐and intramolecular interactions when the chiral selectors are immobilized on the silica stationary phase.

210Pb-based dating of recent sediments with χ-mapping versions of the CFCS, CIC, CF and TERESA models

The 210Pb-based method allows for absolute age determination in recent sediments on the centennial scale. The most common sedimentary scenarios involve ideal deposition without any further redistribution. The conventional models apply to such conditions by adding specific assumptions that allow analytical formulations: constant flux (CF), constant initial concentration (CIC), and constant flux with constant sedimentation (CFCS). The χ-mapping models are presented as a novel methodological approach. They generate a large number (105 to 106) of potential solvers, consisting of sets of n (the number of slices in the core) values of initial activity concentrations, A0, and sedimentation rates, w. Empirical data serve to attract the solver that minimizes a χ function after encountering the best sorting along the core of the A0 and w values. The specific assumptions of the above models are reformulated in terms of the statistical distributions of A0 and w. The performance of the χ-mapping versions is demonstrated with a set of cores from the literature with independent chronologies. The main advantages compared to known analytical formulations are: i) χ-mapping provides a more robust fitting method. ii) It overcomes the problem of age reversals often found in the CIC model. iii) The CF model successfully applies to cores with unsteady and/or incomplete inventories. iv) The TERESA model (time estimates from random entries of sediments and activities), without analytical counterpart, is the only model that can manage continuous trends of change in the fluxes of unsupported 210Pb. The work discusses the conditions for compensating model errors in the chronologies, and the use of the palaeorecords of fluxes, A0 and w. The methodology can be extended to other assumptions (models) and provides novel and insightful views on the 210Pb-based dating of recent sediments.

Evaluation of the Relative Phase Comparison Method at Its Limits Used for Absolute Phase Determination of an AC Cage Current Shunt Group.

AC current shunts are used for precise current measurements. The application of AC current shunts requires that their amplitude phase characteristics are known. A group of three geometrically identical current shunts and a reference shunt are observed in this paper. The phase characteristics of the reference shunt have been previously obtained. A relative phase comparison has been made between the three geometrically identical shunts, and phase displacement values for each have been obtained. After this, the results are verified with the reference shunt. The relative method is most suitable for shunts, where their respective RC and L/R values are small (compared with 1/ω) and of the same order. The ratios of the nominal resistance values of the shunts used in this paper are at the limit of the given statement. The conclusion is that the method applied at the mentioned limits, in terms of the metrology-grade phase angle determination of current shunts, is not to be considered reliable at frequencies higher than 1 kHz.

Determination of the handedness of urea inclusion compounds.

Since the discovery of urea inclusion compounds (UICs) in 1940, the handedness of this chiral helical system has not been established experimentally. By studying three UIC systems containing light-atoms only, the optical rotations were first measured, and the absolute structures of the enantiomorphic domains of three UICs were determined via single crystal X-ray diffraction (SCXRD). The correlation between the optical rotation and the absolute configuration of the UICs was finally established, showcasing the power of absolute structure determination via SCXRD, which is essential in structural chemistry and pharmaceutical research.

Comparison of Swarm-based Metaheuristic and Gradient Descent-based Algorithms in Artificial Neural Network Training

This paper aims to compare the gradient descent-based algorithms under classical training model and swarm-based metaheuristic algorithms in feed forward backpropagation artificial neural network training. Batch weight and bias rule, Bayesian regularization, cyclical weight and bias rule and Levenberg-Marquardt algorithms are used as the classical gradient descent-based algorithms. In terms of the swarm-based metaheuristic algorithms, hunger games search, gray wolf optimizer, Archimedes optimization, and the Aquila optimizer are adopted. The Iris data set is used in this paper for the training. Mean square error, mean absolute error and determination coefficient are used as statistical measurement techniques to determine the effect of the network architecture and the adopted training algorithm. The metaheuristic algorithms are shown to have superior capability over the gradient descent-based algorithms in terms of artificial neural network training. In addition to their success in error rates, the classification capabilities of the metaheuristic algorithms are also observed to be in the range of 94%-97%. The hunger games search algorithm is also observed for its specific advantages amongst the metaheuristic algorithms as it maintains good performance in terms of classification ability and other statistical measurements.