Synthesis Spectra Research Articles

Photooxidation of Toluene Derivatives under HAT and ROS Synergy.

The valorization of toluene offers a dual solution by addressing its environmental impact while also facilitating the synthesis of a diverse array of valuable fine chemicals and pharmaceutical intermediates, thus ensuring both ecological sustainability and economic viability. We report herein a synergistic approach that harmonizes hydrogen atom transfer (HAT) process with the generation of reactive oxygen species (ROS) under mild condition and low catalyst loading, which enables the efficient synthesis of a broad spectrum of esteemed benzoic acid derivatives and aryl ketones through the photocatalytic oxidation of toluene derivatives. Mechanistic elucidation reveals that the HAT reagent anthraquinone has both the capabilities to abstract hydrogen atoms and the ability to generate singlet oxygen 1O2 during energy transfer with triplet oxygen 3O2, and the combination of these two potencies significantly improves the catalytic efficiency of the reaction. This study not only introduces the amalgamation of HAT with ROS generation but also delineates a systematic approach for the selection of HAT reagents with energy transfer proficiency for ROS generation in catalytic oxidation reactions.

Rapid and General Access to α‐Halogenated Carbonyl Compounds Using Amidine Halide Salts as Halogen Sources under Mild Conditions

Rapid and efficient construction of α‐haloketones with diazo compounds and amidine·HX (X = Cl, Br, I) salts as halogen sources has been recognized as a simple and practical strategy. The reaction exhibits a broad scope and scalability, thereby enabling synthesis of a broad spectrum of functionally orchestrated α‐haloketones under mild and metal‐free conditions in a short time. Control experiments established the involvement of triffate 11 in the mechanism

Determination of the Abundance of Mercury from the Hg ii Line at 5677.10 Å in Late B-type Stars. VII. HD 141556 (χ Lupi)

The weak line of Hg ii located at 5677.10 Å is used to measure the mercury abundance in the most massive component of the double-lined spectroscopic binary HgMn star HD 141556 (χ Lupi). This line is detected at 3σ above the noise in the adjacent continuum. The synthesis of this line confirms a large overabundance of mercury, about +5.30 dex, which is about twice the excess derived from the 3983.93 Å line in earlier studies. Spectrum synthesis yields estimates of the abundance deficiencies/excesses for fourteen other elements which agree well with previous measurements.

Three-Dimensional Nonlocal Thermodynamic Equilibrium Abundance Analyses of Late-Type Stars

The chemical compositions of stars encode the history of the universe and are thus fundamental for advancing our knowledge of astrophysics and cosmology. However, measurements of elemental abundance ratios, and our interpretations of them, strongly depend on the physical assumptions that dictate the generation of synthetic stellar spectra. Three-dimensional radiation-hydrodynamic (3D RHD) box-in-a-star simulations of stellar atmospheres offer a more realistic representation of surface convection occurring in late-type stars than do traditional one-dimensional (1D) hydrostatic models. As evident from a multitude of observational tests, the coupling of 3D RHD models with line formation in nonlocal thermodynamic equilibrium (non-LTE) today provides a solid foundation for abundance analysis for many elements. This review describes the ongoing and transformational work to advance the state of the art and replace 1D LTE spectrum synthesis with its 3D non-LTE counterpart. In summary: ▪3D and non-LTE effects are intricately coupled, and consistent modeling thereof is necessary for high-precision abundances; such modeling is currently feasible for individual elements in large surveys. Mean 3D (〈3D〉) models are not adequate as substitutes.▪The solar abundance debate is presently dominated by choices and systematic uncertainties that are not specific to 3D non-LTE modeling.▪3D non-LTE abundance corrections have a profound impact on our understanding of FGK-type stars, exoplanets, and the nucleosynthetic origins of the elements.

Photoredox Catalyzed Conia-Ene-Type Cyclization/Smiles Rearrangement Cascade Reactions to Access Substituted Methylenecarbocycles.

We report a novel visible-light-driven photoredox-catalyzed cascade reaction involving Conia-ene-type cyclization and Smiles rearrangement initiated from alkyne-tethered α-sulfonyl esters. This methodology not only facilitates the rapid synthesis of a broad spectrum of highly substituted methylenecarbocycles but also introduces a new mechanistic pathway with aryl group migration, surpassing the conventional 1,5-hydrogen shift typically observed in Conia-ene reactions.

Generating Sonic Phantoms with Quadratic Difference Tone Spectrum Synthesis

Abstract Quadratic difference tones belong to a family of perceptual phenomena that arise from the neuromechanics of the auditory system in response to particular physical properties of sound. Long deployed as “ghost” or “phantom” tones by sound artists, improvisers, and computer musicians, in this article we address an entirely new topic: How to create a quadratic difference tone spectrum (QDTS) in which a target fundamental and harmonic overtone series are specified and in which the complex tone necessary to evoke it is synthesized. We propose a numerical algorithm that solves the problem of how to synthesize a QDTS for a target distribution of amplitudes. The algorithm aims to find a solution that matches the desired spectrum as closely as possible for an arbitrary number of target harmonics. Results from experiments using different parameter settings and target distributions show that the algorithm is effective in the majority of cases, with at least 99% of the cases being solvable in real time. An external object for the visual programming language Max is described. We discuss musical and perceptual considerations for using the external, and we describe a range of audio examples that demonstrate the synthesis of QDTSs across different cases. As we show, the method makes possible the matching of QDTSs to particular instrumental timbres with surprising efficiency. Also included is a discussion of a musical work by composer Marcin Pietruszewski that makes use of QDTS synthesis.

Primordial Lithium from Globular Cluster Turnoff Stars: M13 and M71

During Big Bang nucleosynthesis (BBN) in the first 15 minutes of the Universe, some 7Li was created along with isotopes of H and He. The determination of that primordial value of Li can help constrain the conditions at that time. The oldest stars with known ages can be found in globular clusters which have well-determined ages through stellar evolution models. High-resolution spectra of Li have been obtained with the Keck I Telescope and HIRES in several unevolved stars in the clusters M13 and M71 with V magnitudes of 17.6–17.9. Abundances of Li have been determined with spectrum synthesis techniques and show a range of a factor of 4. We attribute that spread to differences in initial angular momentum resulting in different amounts of spin-down, related mixing, and destruction of Li. Our results are compared with similar results for main-sequence and turnoff stars in other globular clusters. The range in age of these clusters is 11.2–14.2 Gyr for an age span of 3 Gyr. These clusters range in [Fe/H] from −0.75 to −2.24 corresponding to a factor of 30 in metallicity. The maximum in the Li abundance for these unevolved stars in all eight clusters is the same corresponding to Li/H = 3.16 × 10−10, while the predicted Li abundance, based on the deuterium abundance and the BBN predictions, is 5.24 × 10−10.

A Modular Three-Component Approach for Site-selective Tandem Arene Thiophosphorylation.

Thiophosphates serve as pivotal reagents within the realms of both organic and inorganic synthesis, with their most notable applications observed in agricultural chemistry. This manuscript delineates a modular three-component synthetic strategy for site-selective arene C-H thiophosphorylation with thianthrenium salt, 1,4-diazabicyclo[2.2.2]octane-sulfur dioxide (DABSO), and diarylphosphine oxides as substrates. This approach facilitates the metal-free and green synthesis of a diverse spectrum of S-aryl phosphorothioates through C-H functionalization and late-stage modification showcasing practicality and broad applicability.

Li Evolution among Stars of Low/Intermediate Mass: the Metal-deficient Open Cluster NGC 2204

We have analyzed high-dispersion spectra in the Li 6708 Å region for 167 stars within the anticenter cluster NGC 2204. From 105 probable members, abundance analysis of 45 evolved stars produces [Fe/H] = −0.40 ± 0.12, [Si/Fe] = 0.14 ± 0.12, [Ca/Fe] = 0.29 ± 0.07, and [Ni/Fe] = −0.12 ± 0.10, where quoted errors are standard deviations. With E(B − V) = 0.07 and (m − M)0 = 13.12, appropriate isochrones provide an excellent match from the main sequence through the tip of the giant branch for an age of 1.85 ± 0.05 Gyr. Li spectrum synthesis produces A(Li) below 1.4 at the base of the red giant branch to a detectable value of −0.4 at the tip. Six probable asymptotic giant branch stars and all but one red clump star have only Li upper limits. A rapidly rotating red giant is identified as a possible Li-rich giant, assuming it is a red clump star. Main-sequence turnoff stars have a well-defined A(Li) = 2.83 ± 0.03 (sem) down to the Li-dip wall at the predicted mass of 1.29 M ☉. Despite having the same isochronal age as the more metal-rich NGC 2506, the luminosity distribution of red giants reflects a younger morphology similar to NGC 7789, possibly indicating a deeper impact of metallicity on stellar structure and A(Li) than previously assumed. As in NGC 2506 and NGC 7789, the NGC 2204 turnoff exhibits a broad range of rotation speeds, making abundance estimation impossible for some stars. The place of the cluster within Galactic A(Li) evolution is discussed.

Decarbonylative and Dehydrogenative Cascade Annulation of N‐(o‐Cyanobiaryl)acrylamides with Aldehydes

AbstractDecarbonylative and dehydrogenative cascade annulation of aldehydes with N‐(o‐cyanobiaryl)acrylamides was developed for the synthesis of a broad spectrum of alkyl‐ and carbonyl‐substituted pyrido[4,3,2‐gh]phenanthridines. Secondary and tertiary aldehydes can undergo the decarbonylative cascade under DTBP/malonic acid conditions, while aryl, primary, and secondary aldehydes can undergo dehydrogenative reaction under TBHP system. Such transformations were triggered by alkyl and acyl radicals, and the annulations were accomplished through intramolecular additions of carbon‐centered radical to nitrile group and iminyl radical to aromatic ring.

Ortho-Halobenzyl Halides as Precursors for the Synthesis of Five- to Nine-Membered Ring Structures Employing Transition Metals as Catalysts

AbstractThis review highlights the multifaceted usefulness of o-halobenzyl halides as pivotal substrates for the construction of five- to nine-membered cyclic structures with the aid of transition metals as catalysts. These privileged entities engage dual active sites, enabling the combination of both intermolecular benzylation and intramolecular arylation strategies that directs the formation of a diverse repository of cyclic structures. The introduction of transition-metal catalysis in cross-coupling transformations sparked a revolution in forging aryl–heteroatom bonds, culminating in the evolution of more potent methodologies for the synthesis of a wide spectrum of valuable compounds. Furthermore, the associated pharmaceutical and biological attributes of these cyclic structures augment their significance in medicinal chemistry research. This review aims to showcase the importance of this synthetic methodology and its far-reaching applications in synthesis.1 Introduction2 Synthesis of Five-Membered Rings3 Synthesis of Six-Membered Rings4 Synthesis of Seven-Membered Rings5 Synthesis of Eight- and Nine-Membered Rings6 Conclusion

M3DIS - A grid of 3D radiation-hydrodynamics stellar atmosphere models for stellar surveys. I. Procedure, validation, and the Sun

Large-scale stellar surveys, such as SDSS-V, 4MOST, WEAVE, and PLATO, require accurate atmospheric models and synthetic spectra of stars for accurate analyses of fundamental stellar parameters and chemical abundances. The primary goal of our work is to develop a new approach to solve radiation-hydrodynamics (RHD) and generate model stellar spectra in a self-consistent and highly efficient framework. We build upon the Copenhagen legacy RHD code, the MULTI3D non-local thermodynamic equilibrium (NLTE) code, and the DISPATCH high-performance framework. The new approach allows us to calculate 3D RHD models of stellar atmospheres on timescales of a few thousand CPU hours and to perform subsequent spectrum synthesis in local thermodynamic equilibrium (LTE) or NLTE for the desired physical conditions within the parameter space of FGK-type stars. We compare the 3D RHD solar model with other available models and validate its performance against solar observations, including the centre-to-limb variation of intensities and key solar diagnostic lines of H and Fe. We show that the performance of the new code allows to overcome the main bottleneck in 3D NLTE spectroscopy and enables calculations of multi-dimensional grids of synthetic stellar observables for comparison with modern astronomical observations.

Photodecarboxylative Radical Cascade Involving N-(Acyloxy)phthalimides for the Synthesis of Pyrazolones.

We disclose N'-arylidene-N-acryloyltosylhydrazides as novel skeletons for the synthesis of biologically relevant alkylated pyrazolones through a photoinduced radical cascade with N-(acyloxy)pthalimides as readily available alkyl surrogates. The reaction proceeds through the formation of a photoactivated electron donor-acceptor (EDA) complex between alkyl N-(acyloxy)phthalimide (NHPI) esters and LiI/PPh3 as a commercially available donor system. The reaction exhibits a broad scope and scalability, thereby enabling synthesis of a broad spectrum of functionally orchestrated alkylated pyrazolones under mild and transition-metal-free conditions.

Key Role of Water in Copper‐ and Base‐free Sonogashira Coupling in Ethanol with [{Pd(µ‐OH)Cl(IPr)}2] as a Highly Effective Precatalyst

Aryl bromides and 4‐chlorotoluene as an example aryl chloride in the presence of N‐heterocyclic carbene (NHC) palladium hydroxo dimers of the type [{Pd(µ‐OH)Cl(NHC)}2] (where NHC = IPr, SIPr, IMes, SIMes) undergo an efficient and selective Sonogashira cross‐coupling with (hetero)arylacetylenes. The procedure allows the high‐throughput and selective synthesis of a broad spectrum of 1,2‐diarylacetylenes using 10 ppm of [{Pd(OH)Cl(IPr)}2] as precatalyst. For the coupling of 4‐chlorotoluene with phenylacetylene, TON = 560000 was achieved. Hydrogen chloride was observed as a product of the Sonogashira cross‐coupling reaction. The formation of the active Pd(0) from the Pd(II) complex was found to proceed via ethanol oxidation. Mechanistic studies showed that water plays a key role in the reaction.

Combustion Synthesis of Ag Nanoparticles and Their Performance During NaBH4 Hydrolysis

Due to their tremendous industrial, environmental, and biological applications, research focusing on the synthesis and applications of silver nanoparticles (Ag NPs) has attracted increased interest from researchers over the past two decades. Their structural as well as textural properties can be easily tuned depending on the synthesis protocol utilized. Combustion synthesis has received increased attention as a one-pot route for the synthesis of a wide spectrum of nanomaterials. In this study, we present the results of synthesizing Ag NPs employing urea as a combustion fuel. The effect of the temperature of calcination on the formation and structural features of Ag NPs has been checked over the 400–700 °C temperature range. The characterization of the synthesized Ag NPs has been performed using XRD, SEM, TEM, and XPS techniques. It was found that Ag NPs, with a crystallite size of 40 nm, start to form at around 400 °C. Conducting the calcination at the 500–700 °C range results in the persistence of the obtained Ag NPs. Moreover, the obtained nanomaterials are characterized by a membrane-like morphology. The activity performance of the synthesized Ag NPs was examined for the hydrolysis of sodium borohydride (NaBH4) over a temperature range of 35–50 °C. Increasing the calcination temperature has led to a decrease in the activity of the Ag NPs during the NaBH4 hydrolysis.Graphical

Revisiting El-Sayed Synthesis: Bayesian Optimization for Revealing New Insights during the Growth of Gold Nanorods.

In diverse fields, machine learning (ML) has sparked transformative changes, primarily driven by the wealth of big data. However, an alternative approach seeks to mine insights from "precious data", offering the possibility to reveal missed knowledge and escape potential knowledge traps. In this context, Bayesian optimization (BO) protocols have emerged as crucial tools for optimizing the synthesis and discovery of a broad spectrum of compounds including nanoparticles. In our work, we aimed to go beyond the commonly explored experimental conditions and showcase a workflow capable of unearthing fresh insights, even in well-studied research domains. The growth of AuNRs is a nonequilibrium process that remains poorly understood despite the presence of well-established seeded growth protocols. Traditional research aimed at understanding the mechanism of AuNR growth has primarily relied on altering one reaction condition at a time. While these studies are undeniably valuable, they often fail to capture the synergies between different reaction conditions, thus constraining the depth of insights they can offer. In the present study, we exploit BO, to identify diverse experimental conditions yielding AuNRs with similar spectroscopic characteristics. Notably, we identify viable and accelerated synthesis conditions involving elevated temperatures (36-40 °C) as well as high ascorbic acid concentrations. More importantly, we note that ascorbic acid and temperature can modulate each other's undesirable influences on the growth of AuNRs. Finally, by harnessing the power of interpretable ML algorithms, complemented by our deep chemical understanding, we revisited the established hierarchical relationships among reaction conditions that impact the El-Sayed-based growth of AuNRs.

Improving 2-D Resolution in Geosynchronous SAR via Spatial Spectrum Synthesis: Method and Verification

Improving 2-D Resolution in Geosynchronous SAR via Spatial Spectrum Synthesis: Method and Verification

Large-scale RCI calculation of energy levels in W9+

The Flexible Atomic Code (FAC) is developed to extend the computational scale based on the Relativistic Configuration Interaction (RCI) in the theoretical study of W9+ atomic structure. The results of the lowest 144 energy levels are consistent with the GRASP calculations, with a mean deviation of 2.11 %. The reference configuration selections for central potential optimization in the RCI calculations at different computational scales are studied. The contributions of the inner core 4d to the energy levels of the RCI calculations are also investigated. The mean deviation of the theoretical wavelengths of five M1 transitions of W9+ from the experimental results is within 0.86 %. This work demonstrates the feasibility of improving the accuracy of RCI calculations of complex atomic systems through large-scale computation based on FAC, which is helpful for experimental spectral line identifications and spectrum synthesis in many fields of plasma spectroscopy.

Unique distant classical Cepheid OGLE GD-CEP-1353 with anomalously high abundances of s- and r-process elements

Aims. While looking for recently discovered distant Cepheids with an interesting chemical composition, we noticed one star (OGLE GD-CEP-1353) with extremely large equivalent widths of spectral lines of heavy elements. The aim of this work is to perform an abundance analysis, and to find a possible explanation for the found chemical anomaly. Methods. Quantitative analysis of the equivalent widths and synthetic spectrum synthesis were used to derive abundances in this star. Both local and nonlocal thermodynamic equilibrium (LTE and NLTE) approximations were used in our analysis. Results. Abundances of 28 chemical elements from carbon to thorium were derived. While light and iron peak elements show abundances typical for distant Cepheids (located in the outer disk), the s-process elements are overabundant about one dex. r-process elements are slightly less overabundant. This makes the star a unique Cepheid of our Galaxy.

Excitation Threshold Reduction Techniques for Organic Semiconductor Lasers: A Review

Organic semiconductor lasers have shown great application potential in various fields, such as low-cost sensing, high-performance lighting and display, and lab-on-a-chip devices. Since the introduction of organic lasers in the 1960s, research on semiconductor laser devices has expanded to include various materials and structures. The organic laser has attracted much attention due to its wide range of emission spectrum and simple synthesis and processing. Researchers constantly pursue the goal of using organic semiconductors to fabricate low-threshold thin-film organic laser devices while retaining the characteristics of a wide luminescence spectrum of organic materials, simple and portable structure, and low cost. However, organic semiconductor lasers face challenges due to material stability under optical pumping and large optical losses under electrical pumping, making commercialization difficult. Many scholars have put great efforts into enhancing the performance of materials and optimizing the structure to minimize the threshold of organic semiconductor lasers. Herein, based on the basic principles of organic lasers, the main factors affecting the excitation threshold are summarized. A comprehensive analysis of the relevant factors and threshold conditions is performed, considering both positive and negative aspects of modal gain and modal loss that need to be addressed. We expect to provide a wide range of ideas for reducing the threshold of organic lasers and offer theoretical guidance for the practical industrial production of organic lasers.