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In this study, the effects of chlorine substitution on the valence orbitals and electronic states of 3-chloropyridine (3-CP) were investigated utilizing high-resolution vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy and computational methods. High-quality vibrational spectra were obtained from the VUV-MATI spectra of 3-CP isotopomers (35Cl and 37Cl), revealing high-quality vibrational spectra for the lowest cationic states. The adiabatic ionization energies (AIEs) of these isotopomers were accurately determined, providing detailed information about the electronic structure and ionization dynamics. Intense spectra peaks were linked with the D1 excited state of the 3-CP cation, with vibronic transitions in this state closely matching those predicted by Franck–Condon simulations. This provided insights into the cationic structure and the roles of the highest occupied molecular orbital (HOMO) and the HOMO-1. The HOMO was primarily a π orbital of the pyridine ring, while the HOMO-1 consisted of nonbonding orbitals. The AIEs suggested that meta-chlorine substitution stabilizes nonbonding orbitals less effectively than ortho substitution, indicating closely spaced electronic states in the 3-CP cation. Minor discrepancies in vibrational frequencies and intensities, particularly above 800 cm−1, suggested the presence of vibronic coupling, warranting further investigation. Overall, this study provided a comprehensive understanding of the vibronic and ionization properties of 3-CP, emphasizing the influence of the position of the chlorine substitution on molecular orbitals and the value of advanced theoretical and experimental approaches for analyzing the vibrational spectra of complex molecules. [ABSTRACT FROM AUTHOR]

The ultrafast proton transfer and the following dynamics for aromatic Schiff bases N,N′-bis(salicylidene)ethylenediamine (salen) and N,N′-bis(salicylidene)-1,4-butylenediamine (salbn) were investigated with experimental and theoretical methods. A dual emission property with a large Stokes shift in salen and salbn indicates that excited state intramolecular proton transfer occurs with photoexcitation. An efficient single proton transfer was confirmed within 200 fs for both molecules. Subsequently, a fast twisted motion of the keto moiety carries cis-keto to a relaxed stable geometry in the S1 state. Following the twisted motion, the phenol ring at keto moiety further rotates to a conical intersection with the ground state and a cis–trans isomerization occurs. The isomerization rate is high, which dominates the competition with the radiative transition, resulting in weak emission intensity. It is confirmed that the length of alkyl chain affects the direction of phenol ring twisting and rotation during the whole subsequent relaxation of excited cis-keto tautomer. Compared with polar solvent acetonitrile, the barrier of isomerization is higher and the hydrogen bond on keto moiety is stronger in nonpolar solvent toluene. It makes fluorescence radiation channels competing with isomerism more likely to occur, contributing to the observed difference of enol/keto emission ratios of salen and salbn in toluene and acetonitrile. [ABSTRACT FROM AUTHOR]

The unusual d-l-l-d-d-l-l pattern of stereochemistry in residues 1-7 of the peptide antibiotic teixobactin is critical to its extraordinary antibiotic activity, creating an unusual amphiphilic β-sheetlike structure that is essential to its mechanism of action. The current study sought to replace the three d-amino acids in the tail with l-amino acids while maintaining amphiphilicity. We find that swapping residues d-Gln4 and d-allo-Ile5 in O-acyl isopeptide prodrugs of teixobactin permits the introduction of l-stereochemistry with retention of antibiotic activity. Nevertheless, modifying the N-terminal stereochemistry results in a loss of antibiotic activity.

Modern life is essentially homochiral, containing D-sugars in nucleic acid backbones and L-amino acids in proteins. Since coded proteins are theorized to have developed from a prebiotic RNA World, the homochirality of L-amino acids observed in all known life presumably resulted from chiral transfer from a homochiral D-RNA World. This transfer would have been mediated by aminoacyl-RNAs defining the genetic code. Previous work on aminoacyl transfer using tRNA mimics has suggested that aminoacylation using D-RNA may be inherently biased toward reactivity with L-amino acids, implying a deterministic path from a D-RNA World to L-proteins. Using a model system of self-aminoacylating D-ribozymes and epimerizable activated amino acid analogs, we test the chiral selectivity of 15 ribozymes derived from an exhaustive search of sequence space. All of the ribozymes exhibit detectable selectivity, and a substantial fraction react preferentially to produce the D-enantiomer of the product. Furthermore, chiral preference is conserved within sequence families. These results are consistent with the transfer of chiral information from RNA to proteins but do not support an intrinsic bias of D-RNA for L-amino acids. Different aminoacylation structures result in different directions of chiral selectivity, such that L-proteins need not emerge from a D-RNA World.

Our laboratory reported the chemical synthesis and stereochemical assignment of the recently discovered peptide antibiotic clovibactin. The current paper reports an improved, gram-scale synthesis of the amino acid building block Fmoc-(2R,3R)-3-hydroxyasparagine-OH that enables structure-activity relationship studies of clovibactin. An alanine scan reveals that residues Phe1, d-Leu2, Ser4, Leu7, and Leu8 are important for antibiotic activity. The side-chain amide group of the rare d-Hyn5 residue is not essential to activity and can be replaced with a methyl group with a moderate loss of activity. An acyclic clovibactin analogue reveals that the macrolactone ring is essential to antibiotic activity. The enantiomer of clovibactin is active, albeit somewhat less so than clovibactin. A conformationally constrained clovibactin analogue retains moderate antibiotic activity, while a backbone N-methylated analogue is almost completely inactive. X-ray crystallography of these two analogues reveals that the macrolactone ring adopts a crown-like conformation that binds anions.

Herein, we report concise total syntheses of diterpene natural products (-)-crinipellins A and B with a tetraquinane skeleton, three adjacent all-carbon quaternary centers, and multiple oxygenated and labile functional groups. Our synthesis features a convergent Kozikowski β-alkylation to unite two readily available building blocks with all the required carbon atoms, an intramolecular photochemical [2 + 2] cycloaddition to install three challenging and adjacent all-carbon quaternary centers and a 5-6-4-5 tetracyclic skeleton, and a controlled Cargill rearrangement to rearrange the 5-6-4-5 tetracyclic skeleton to the desired tetraquinane skeleton. These strategically enabling transformations allowed us to complete total syntheses of (-)-crinipellins A and B in 12 and 13 steps, respectively. The results of quantum chemical computations revealed that the Bronsted acid-catalyzed Cargill rearrangements likely involve stepwise paths to products and the AlR3-catalyzed Cargill rearrangements likely involve a concerted path with asynchronous alkyl shifting events to form the desired product.

A simple empirical method is described that allows the assignment of absolute configurations of natural products containing chiral vicinal bromochloro (VBC) units, including the bromochloro substituted isoprenyl units present in the structures of antiproliferative halomon (1a) and its halogen-swapped isomer iso-halomon (1b) from the red alga, Portieria hornemannii, and callophycols A (3) and B (4) from Callophycus serratus. The relative configurations of 3 and 4, published in 2007, were incomplete: C-16 was left unassigned. It is now shown that the additivity of molar rotations, [M]D (herein, abbreviated [M])─a consequence of vant Hoffs principle of optical superposition─could be used to deconvolute rotatory contributions, designated as [MX] and [MY] of the two remotely spaced chiral substructures within 3 and 4 using simple arithmetic. Input of proxy values, [M Y1] and [MY2], for the two different VBC units in two equations for [MX] and application of a conditional test returns the same value for [MX] only when a proxy with the correct configuration is included. It is revealed that 3 and 4 have opposite configurations at the C-16 stereocenter: 16S and 16R, respectively. Two important implications lie in these findings: 3 and 4 appear to qualify as paired-regioisomers, coupled through a putative dyotropic rearrangement (DR), and the biosyntheses of other Callophycus secondary metabolites, now numbering over 50, are tightly controlled by stereoelectronic considerations including neighboring group interactions of the DR. It now appears, counter to earlier suggestions, that the chirality of Callophycus secondary metabolites, despite their high chemodiversity, are surprisingly highly conserved. Enantiofacial halogenation additions to the C═C double bonds of precursor alkenes appear to direct the formation of the remaining stereocenters at both the halogenated benzoate-decalin core and the distal VBC of 3 and 4. A consistent hypothesis is proposed to account for macrolactonizations in other Callophycus natural products including bromophycolides A and B. The conditional test of molar rotations was applied in a different context to understand the chiroptical properties and trends observed in the highly iodinated meroditerpenes, iodocallophycols A-E, also from Callophycus sp., resulting in the revision of the configuration of callophycol E from (10R,14R) to (10S,14S).

Halogenated phenazine meroterpenoids are a structurally unusual family of marine actinobacterial natural products that exhibit antibiotic, antibiofilm, and cytotoxic bioactivities. Despite a lack of established phenazine halogenation biochemistry, genomic analysis of Streptomyces sp. CNZ-289, a prolific lavanducyanin and C2-halogenated derivative producer, suggested the involvement of vanadium-dependent haloperoxidases. We subsequently discovered lavanducyanin halogenase (LvcH), characterized it in vitro as a regioselective vanadium-dependent chloroperoxidase, and applied it in late-stage chemoenzymatic synthesis.

Catalysis with engineered enzymes has provided more efficient routes for the production of active pharmaceutical agents. However, the potential of biocatalysis to assist in early-stage drug discovery campaigns remains largely untapped. In this study, we have developed a biocatalytic strategy for the construction of sp3-rich polycyclic compounds via the intramolecular cyclopropanation of benzothiophenes and related heterocycles. Two carbene transferases with complementary regioisomer selectivity were evolved to catalyse the stereoselective cyclization of benzothiophene substrates bearing diazo ester groups at the C2 or C3 position of the heterocycle. The detailed mechanisms of these reactions were elucidated by a combination of crystallographic and computational analyses. Leveraging these insights, the substrate scope of one of the biocatalysts could be expanded to include previously unreactive substrates, highlighting the value of integrating evolutionary and rational strategies to develop enzymes for new-to-nature transformations. The molecular scaffolds accessed here feature a combination of three-dimensional and stereochemical complexity with rule-of-three properties, which should make them highly valuable for fragment-based drug discovery campaigns.

Isomerized amino acid residues have been identified in many peptides extracted from tissues or excretions of humans and animals. These isomerized residues can play key roles by affecting biological activity or by exerting an influence on the process of aging. Isomerization occurs spontaneously and does not result in a mass shift. Thus, identifying and localizing isomerized residues in biological samples is challenging. Herein, we introduce a fast and efficient method using tandem mass spectrometry (MS) to locate isomerized residues in peptides. Although MS2 spectra are useful for identifying peptides that contain an isomerized residue, they cannot reliably localize isomerization sites. We show that this limitation can be overcome by utilizing MS3 experiments to further evaluate each fragment ion from the MS2 stage. Comparison at the MS3 level, utilizing statistical analyses, reveals which MS2 fragments differ between samples and, therefore, must contain the isomerized sites. The approach is similar to previous work relying on ion mobility to discriminate MS2 product ions by collision cross-section. The MS3 approach can be implemented using either ion-trap or beam-type collisional activation and is compatible with the quantification of isomer mixtures when coupled to a calibration curve. The method can also be implemented in combination with liquid chromatography in a targeted approach. Enabling the identification and localization of isomerized residues in peptides with an MS-only methodology will expand accessibility to this important information.

Methods to access chiral sulfur(VI) pharmacophores are of interest in medicinal and synthetic chemistry. We report the desymmetrization of unprotected sulfonimidamides via asymmetric acylation with a cinchona-phosphinate catalyst. The desired products are formed in excellent yield and enantioselectivity with no observed bis-acylation. A data-science-driven approach to substrate scope evaluation was coupled to high throughput experimentation (HTE) to facilitate statistical modeling in order to inform mechanistic studies. Reaction kinetics, catalyst structural studies, and density functional theory (DFT) transition state analysis elucidated the turnover-limiting step to be the collapse of the tetrahedral intermediate and provided key insights into the catalyst-substrate structure-activity relationships responsible for the origin of the enantioselectivity. This study offers a reliable method for accessing enantioenriched sulfonimidamides to propel their application as pharmacophores and serves as an example of the mechanistic insight that can be gleaned from integrating data science and traditional physical organic techniques.

Repurposing the intrinsic properties of natural enzymes can offer a viable solution to current synthetic challenges through the development of novel biocatalytic processes. Although amino acid racemases are ubiquitous in living organisms, an amine racemase (AR) has not yet been discovered despite its synthetic potential for producing chiral amines. Here, we report the creation of an AR based on the serendipitous discovery that amine transaminases (ATAs) can perform stereoinversion of 2-aminobutane. Kinetic modeling revealed that the unexpected off-pathway activity results from stereochemically promiscuous futile cycles due to incomplete stereoselectivity for 2-aminobutane. This finding motivated us to engineer an S-selective ATA through in silico alanine scanning and empirical combinatorial mutations, creating an AR with broad substrate specificity. The resulting AR, carrying double point mutations, enables the racemization of both enantiomers of diverse chiral amines in the presence of a cognate ketone. This strategy may be generally applicable to a wide range of transaminases, paving the way for the development of new-to-nature racemases.

Chirality at the metal center is a well‐established concept, exemplified by numerous four‐ and six‐coordinated complexes. Here, a pioneering example of linear chirality‐at‐metal is described: [Ag(NHC)2]+ (NHC=N‐heterocyclic carbene). In solution, stabilizing π‐π interactions preserve the chiral information of the solid state. Consequently, a novel class of atropisomers is identified, whose stereogenicity arises from hindered rotation around a C−Ag−C axis, instead of a typical C−C bond. [ABSTRACT FROM AUTHOR]

The transformation of biobased alkanediols over heterogeneous catalysts is a major object. Here, a series of catalysts were prepared for 2,4‐pentanediol dehydration to 3‐penten‐2‐ol. Ceria‐based catalysts had a unique property of showing high efficiency. More importantly, a stereocatalytic effect was observed for CeO2, yielding trans‐3‐penten‐2‐ol with a high selectivity. Raman, XPS, TPD, and TPR were carried out to clarify the catalyst structure, and the relationship between the catalyst structure and catalytic performance were studied. The amount of Lewis acid sites can hardly be correlated with the total concentrations of the oxygen vacancies. It was suggested that the geometry structure of the active sites played a crucial role in trans‐3‐penten‐2‐ol production. The oxygen vacancies originating from CeO2 consisted of active sites with a geometrical structure, which were different from those created by Pr doping CeO2. In addition, the Pr doping enhanced the oxygen migration, which resulted in side reactions, consequently, giving a lower selectivity to trans‐3‐penten‐2‐ol. [ABSTRACT FROM AUTHOR]

The increasing interest in axially chiral biaryl moieties, which are prevalent in chiral ligands, organocatalysts, and bioactive molecules, has raised the need for developing novel efficient synthetic methods for these types of molecules. In addition to the currently available methods, such as kinetic resolution, desymmetrization and enantio‐ and diastereo‐selective biaryl coupling, we herein report a lipase‐catalyzed dynamic kinetic resolution (DKR) of racemic 2‐hydroxybiaryls through enantioselective O‐acylation. This method features the production of enantiomerically enriched atropisomers (89 %–98 % ee) in 91 %–99 % yields from eleven racemates. Notably, the DKR proceeds without any racemization catalyst since in situ‐racemization was achieved by easy rotation about the biaryl axis of the substrates. The enzymatic O‐acylation then furnished conformationally stable biaryl‐containing esters, in which the increased steric bulkiness of the O‐acyl moiety suppresses the rotation, i. e., racemization, under the reaction conditions of 35–50 °C. This experimental study was accompanied by a computational determination of the rotational barrier of substrates and products. The choice of suitable substrates with a significant difference in their rotational barrier compared to that of their products turned out to be the key to an efficient implementation of this method. [ABSTRACT FROM AUTHOR]

The present microreview focuses on different typologies of isomerism documented along the years for metal carbonyl clusters (MCCs), and outlines their analogies to other classes of ligand‐protected molecular clusters and nanoclusters. Isomerism in molecular MCCs is discussed within two main categories, that is, surface isomerism and core isomerism. The first Section presents some representative examples of surface isomerism involving inorganic (carbonyls and hydrides) and organic ligands, as well as isomerism due to ML fragments decorating the cluster surface. The second Section focuses on three major categories of core isomerism, that is: (1) isomers that mainly differ on M–M distances; (2) isomers displaying different structures of the metal kernels; (3) isomers possessing almost identical metal kernels and ligand shells, but differing for the positions of different types of metal atoms within the metal kernel. The third Section briefly discusses two related and very rare cases of isomerism, that is, polymerisation and coordination isomerism. General conclusions are outlined in the final Section. [ABSTRACT FROM AUTHOR]

Conformational isomerism of organic photovoltaic materials has a profound impact on their molecular packing and therefore performance of polymer solar cells (PSCs). However, the conformations of oligomeric acceptors (OAs) are mostly predicted by simulations rather than experimental determinations. Herein, the stereochemical S‐shaped structure of two dimeric‐type acceptor molecules, V‐DYIC and V‐DYIC‐4F, is first confirmed with different end groups (IC for V‐DYIC and IC‐2F for V‐DYIC‐4F), incorporating vinylene linkage for connecting the distinct state‐of‐the‐art small molecule acceptor Y‐segments. Through the synthetic control of fluorination sites adjacent to the vinyl‐linker, S‐shaped the conformation by NMR experiments is validated. Compared to the O‐shaped dimer, S‐shaped conformation results in enhanced lamellar order and reduced nonradiative recombination losses. The optimal acceptor, V‐DYIC‐4F, achieved a champion efficiency of 18.10% with the lowest energy loss of 0.556 eV in its devices paired with PM6 due to their efficient carrier transport, and suppressed recombination compared to other devices, being attributed to the synergistic effect of conformation and end group fluorination. The insights gained in this work contribute valuable knowledge of both synthetic control and structural determination of OAs, providing strategic design guidelines for the future development of dimeric acceptors toward high‐efficiency PSCs. [ABSTRACT FROM AUTHOR]

Dinuclear Re(I) complexes have proportionally been much less studied than mononuclear analogues. In particular, very little information is available about their solid-state emission properties. In this work, two structural isomers of dinuclear complexes (Bi-Re-metaPhe and Bi-Re-paraPhe), which differ by the relative position of the coordination spheres on a central phenyl ring, were synthesized and compared with each other and with the parent mononuclear compound (Mono-Re-Phe), from a theoretical and experimental point of view. In solution, the electronic, electrochemical and spectroscopic properties of the dinuclear complexes were almost identical, and rather close to those of the monomer. In the solid state, the photoluminescence (PL) efficiency of dimers was not higher than that of the monomer, but a clear mechanoresponsive luminescence (MRL) effect appeared only for the former ones. The positional isomerism influenced the amplitude of this effect, as well as the aggregation-induced emission (AIE) properties in a water-acetonitrile mixture. This study reveals the importance of positional isomerism to modulate the emission properties in the solid state. It also shows the advantage of dinuclear structures to access new MRL-active materials. [ABSTRACT FROM AUTHOR]

Achieving amorphous polymers with ultralong room‐temperature phosphorescence (RTP), tunable organic afterglow, and reversible photoactivation behavior is highly desirable for practical applications but challenging. Herein, simple positional isomers with three carboxyl groups located in the ortho, meta, and para positions of the triphenylamine skeleton are designed and synthesized. By physically blending with the poly(vinyl alcohol) matrix, these isomers show ultralong RTP properties, among which the meta‐isomer has the longest RTP lifetime (620.1 ms). Theoretical calculations reveal that the more efficient intersystem crossing, the slower radiative decay rate of the lowest triplet excitons, and stronger intermolecular hydrogen‐bonding interactions should be responsible for the superior RTP property of meta‐isomer. Furthermore, the tunable organic afterglow is readily realized via a triplet‐to‐singlet energy transfer process. More impressively, the meta and para isomers exhibit reversible photoactivated ultralong RTP properties after embedding into the rigid poly(methyl methacrylate) matrix. Finally, amorphous and flexible polymer films prepared from these positional isomers show potential applications in advanced anti‐counterfeiting and multilevel encryption through subtly combining ultralong RTP lifetime, tunable organic afterglow, and reversible photoactivation behavior. [ABSTRACT FROM AUTHOR]

ABSTRACT Aims Methods Results Conclusion In addition to well‐documented tachycardias involving twin atrioventricular (AV) nodes, tachycardias involving a single node have been clinically experienced in right atrial isomerism (RAI). This study aimed to characterize the AV node involvement patterns and evaluate the outcome of ablation therapy in RAI patients with tachycardias.We retrospectively analyzed the medical records of 16 RAI patients who underwent catheter ablation of tachycardias involving twin or single AV nodes at our center between April 2006 and March 2020.A total of 22 ablation procedures were performed in 16 patients. The median age and body weight were 2 years (range 20 months–31 years) and 11.2 kg (range 7.4–42 kg), respectively. Two QRS complexes were confirmed in 11/16 patients, and a single QRS complex in 5/16. The dominant AV node was anterior in 7/16. Four patterns of tachycardias were identified: tachycardias reciprocating between two AV nodes with retrograde conduction through the anterior AV node (3/16) or through the posterior AV node (4/16); and reentrant tachycardias involving the anterior AV node only (3/16) or posterior AV node only (6/16). Ablation successfully eliminated the tachycardias in 15/16 patients (93.8%). Recurrence was reported in 7/16 (44%) during a median follow‐up period of 96.5 months. Five of those 7 patients underwent additional ablation, and the tachycardias were eliminated in 3/5 patients. None of the patients developed ventricular asynchrony after ablation.Transcatheter ablation was effective in RAI patients with tachycardias involving twin or single AV nodes, and deterioration of the cardiac function was rare. [ABSTRACT FROM AUTHOR]

The tunable molecular scaffold of organic moieties in metallopolymers generates variation in their properties, but what could be the minimal change that can produce variation in the properties of these macromolecules is still untouched. This research has meticulously explored the trivial change in the molecular scaffold of the ligand capable of making a mammoth difference in the nonvolatile memory and coordination pattern in two metallopolymers. The significance of this research lies in the fact that it demonstrates how a slight change in the organic building block can significantly alter the memristive and fluorescence properties of iron(II) metallopolymers, opening up new possibilities for their design and synthesis. Two novel positional isomeric ligands and their corresponding iron(II)-polymers were synthesized and thoroughly characterized using NMR, XRD, ATR-IR, FESEM, AFM and other techniques. Bright orange solid and solution state fluorescence was observed both in the solid and solution states for ligand L2 (3,3′-bis((E)-(pyridin-3-ylimino)methyl)-[1,1′-biphenyl]-4,4′-diol), while ligand L1 (3,3′-bis((E)-(pyridin-2-ylimino)methyl)-[1,1′-biphenyl]-4,4′-diol) showed blue fluorescence in the solution state only. A robust memristive property for Fe(II)-L1-poly with a high current ON/OFF ratio of 104, remarkable random access behaviour, and a long retention time greater than 35 000 seconds was observed while its counterpart was entirely silent. Both polymers showed solution-state electrochromism. These synthesised metallopolymers also showed good specific capacitance in the range of 50–60 F g−1 with a remarkable retention of 98% of the initial value even after 5000 charge–discharge cycles. The AFM and FESEM micrographs revealed the formation of long polymer nano-rods, which correlates with the NMR, ATR-IR, and XRD results. The difference in the properties of polymers generated by such a slight change in the organic building block forces different coordination patterns of these two ligands around the same central metal ion, and this is also evident in all the characterization methods. [ABSTRACT FROM AUTHOR]

Bioactive dimeric (pre‐)anthraquinones are ubiquitous in nature and are found in bacteria, fungi, insects, and plants. Their biosynthesis via oxidative phenol coupling (OPC) is catalyzed by cytochrome P450 enzymes, peroxidases, or laccases. While the biocatalysis of OPC in molds (Ascomycota) is well‐known, the respective enzymes in mushroom‐forming fungi (Basidiomycota) are unknown. Here, we report on the biosynthesis of the atropisomers phlegmacin A1 and B1 of the mushroom Cortinarius odorifer. The biosynthesis of these unsymmetrically 7,10'‐homo‐coupled dihydroanthracenones was heterologously reconstituted in the mold Aspergillus niger. Methylation of the parental monomer atrochrysone to its 6‐O‐methyl ether torosachrysone by the O‐methyltransferase CoOMT1 precedes the regioselective homocoupling to phlegmacin, catalyzed by the enzyme CoUPO1 annotated as an "unspecific peroxygenase" (UPO). Our results reveal an unprecedented UPO reaction, thereby expanding the biocatalytic portfolio of oxidative phenol coupling beyond the commonly reported enzymes. The results show that Basidiomycota use peroxygenases to selectively couple aryls independently of and convergently to any other group of organisms, emphasizing the central role of OPC in natural processes. [ABSTRACT FROM AUTHOR]

Structurally flexible organic porous molecular arrays are promising for the development of vapochromic materials with superior detection performance. Exploring the photophysical control of vapochromic materials using these molecular arrays is important for the design of new vapochromic materials. However, difficulties arise in the formation and control of organic porous molecular arrays owing to weak and less‐oriented noncovalent forces and their tendency to arrange into energetically preferred high‐density configurations. Herein, an efficient strategy is presented to control molecular arrays by manipulating the shapes of donor–acceptor–donor system‐based molecular building blocks using positional isomerism and report on the correlation between controlled molecular arrays and vapochromic behavior. Depending on their shape (Z‐shaped, quasi‐Z‐shaped, or linear shape), the building blocks formed different molecular arrays that controlled the intermolecular interactions and void volumes. This led to differences in the final microstructural morphologies. Consequently, they exhibited different vapochromic behaviors, and an in‐depth understanding of the correlation between the molecular arrays and vapochromism/vapofluorochromism is obtained. [ABSTRACT FROM AUTHOR]

Racemisation without Consequence: MOM deprotection during a routine synthesis of phosphoric acid 1 promoted partial racemisation of the product BINOL 5. Surprisingly, however, after phosphorylation of the partially racemised BINOL, enantiopure acid 1 was isolated. Further inspection revealed that during phosphorylation, unhydrolysed racemic phosphorochloridate 6 precipitated, thus restoring homochirality in the product phosphoric acid 1. Moreover, MOM deprotection partial racemisation was avoided by conducting reactions at lower temperatures for no longer than the required deprotection time, and/or by application of other deprotection conditions from the literature. [ABSTRACT FROM AUTHOR]

Atropisomeric compounds have been discovered in pharmaceuticals and materials science, and their enantioselective syntheses have gained tremendous attention. Among strategies for catalytic atroposelective synthesis, desymmetrization provides robust and straightforward approaches to axially chiral biaryls. Due to the relative ease of substrate design compared to other atroposelective strategies, desymmetrization has emerged as a pivotal stage for converting fascinating chemistry into its atroposelective counterpart, despite challenges such as the formation of achiral products by subsequent catalytic reactions and the long distance between the reaction site and the stereogenic axis. This review offers a comprehensive overview of recent advancements in atroposelective desymmetrization using chiral organo‐ and metal catalysts, addressing challenges and solutions, and aims to provide insights into future developments in this field. [ABSTRACT FROM AUTHOR]

Cardiovascular disease (CVD) is a leading cause of global mortality, with dyslipidemia being a significant modifiable risk factor. Dyslipidemia refers to all abnormalities in blood lipid levels. It plays a fundamental role in the development and progression of atherosclerosis. The reduction of low‐density lipoprotein (LDL) cholesterol has been shown to decrease cardiovascular risk. Cholesteryl ester transfer protein (CETP) plays a role in LDL metabolism, and its inhibition results in lower LDL levels. This study synthesizes and evaluates novel benzene sulfonamide derivatives as CETP inhibitors. Twenty compounds were synthesized and tested for their inhibitory activity using an in vitro bioassay. The results revealed that para‐methylated derivatives exhibited higher inhibitory activity compared to meta‐methylated derivatives, where compound 6n has an IC50 of 24.4 µM. Furthermore, electron withdrawing groups such as chlorine and nitro substitutions on the sulfanamido‐phenyl rings demonstrated superior inhibitory effects compared to electron donating groups. Positional isomerism of the substitutions also influenced inhibitory activity, with para substitutions being more effective. Nitro‐substituted compounds showed greater inhibition than chlorine‐substituted compounds, where compound 6t has an IC50 of 18.3 µM. Overall, this study provides valuable insights into the SAR of CETP inhibitors and identifies promising compounds for further investigation as potential therapeutics for CVD. [ABSTRACT FROM AUTHOR]

Photoreduction of CO2 into the chemical feedstocks of fuels provides a green way to help solve both the energy crisis and carbon emission issues. Nevertheless, undesirable charge separation and migration, as well as rapid reverse charge recombination results in the unsatisfactory photocatalytic activity of most conjugated microporous polymers (CMPs). Herein, a pair of donor–acceptor (D-A) CMPs for CO2 photoconversion was developed through position isomerism by altering linkage sites. The results show that Py-D27F with 2,7-site linkage exhibits a completely conjugated structure and a large molecular dipole moment, thus significantly accelerating charge separation and transfer. As a result, Py-D27F achieves a higher yield of 320.9 μmol g−1 h−1 for CO2-to-CO photoreduction (without the addition of any photosensitizers and precious metals), which is about three-fold greater than that of Py-D36F (3,6-site linkage). This study provides a valuable idea for exploring outstanding CMP photocatalysts for the efficient processing of photocatalysis. [ABSTRACT FROM AUTHOR]

Methods are lacking that can prepare deuterium-enriched building blocks, in the full range of deuterium substitution patterns at the isotopic purity levels demanded by pharmaceutical use. To that end, this work explores the regio- and stereoselective deuteration of tetrahydropyridine (THP), which is an attractive target for study due to the wide prevalence of piperidines in drugs. A series of d0–d8 tetrahydropyridine isotopomers were synthesized by the stepwise treatment of a tungsten-complexed pyridinium salt with H−/D− and H+/D+. The resulting decomplexed THP isotopomers and isotopologues were analyzed via molecular rotational resonance (MRR) spectroscopy, a highly sensitive technique that distinguishes isotopomers and isotopologues by their unique moments of inertia. In order to demonstrate the medicinal relevance of this approach, eight unique deuterated isotopologues of erythro-methylphenidate were also prepared. Deuteration of active pharmaceutical ingredients is increasingly applied as the isosteric and isotopic replacement can modulate the pharmacokinetic profile, without necessarily having to alter the overall synthetic strategy toward the compound of interest. Here, the authors show manifold deuterations of piperidines and apply molecular rotational resonance (MRR) spectroscopy as a methodology to distinguish isotopomers within a distribution of products. [ABSTRACT FROM AUTHOR]

Thermoplastic polyimide (PI) matrixes, including PI-a (cc-34ODA) and PI-b (ct-34ODA) were prepared via the hot-pressing procedures of the resins derived from the 3,4′-oxydianiline (34ODA) and two alicyclic dianhydrides of 1S,2R,4S,5R-hydrogenated pyromellitic dianhydride (ccHPMDA) and 1R,2S,4S,5R-hydrogenated pyromellitic dianhydride (ctHPMDA), respectively. The resins exhibited thermoplastic features with good formability at higher temperatures. The afforded semi-alicyclic PI sheets exhibited enhanced properties in comparison to commercially available, wholly aromatic thermoplastic PIs, such as PI-ref1, which are derived from 3,3′,4,4′-oxydiphthalic anhydride (ODPA) and 4,4′-oxydianiline (44ODA), as well as PI-ref2, which is based on pyromellitic dianhydride (PMDA) and 4,4′-bis(3-aminophenoxy)biphenyl (mBAPB). In addition, the developed PI sheets exhibited high heat deflection temperatures (HDT) of 267.4 °C for PI-a and 268.6 °C for PI-b. There values were significantly higher when compared with those of PI-ref1 (Ratem® YS20, HDT: 239.0 °C), PI-ref2 (Aurum® PL450C, HDT: 238.0 °C), PI-ref3 (Ultem® 1000, HDT: 206.0 °C), PI-ref4 (Therplim® TO65, HDT: 180.0 °C), and PI-ref5 based on phthalic anhydride-terminated fluorinated PIs (HDT: 215.0 °C). In terms of mechanical properties, the current PI sheets showed superior flexural properties among the polymers with the flexural strength of 189.0 ± 11.7 MPa (PI-a) and 200.5 ± 4.2 MPa (PI-b), respectively. In addition, the PI sheets exhibited comparable compression properties, inferior impact strength, and tensile properties compared with the referenced PI counterparts. Basically, the PI-b sheet showed better comprehensive properties than those of the stereoisomeric PI-a analog. [ABSTRACT FROM AUTHOR]

The first total synthesis of the Australian marine tunicate fungus-derived cyclic peptide talarolide A (1) has confirmed the structure previously proposed on the basis of spectroscopic and chemical analyses and re-affirmed the importance of the unique hydroxamate H-bond bridge in ring conformer stabilization. The unexpected co-synthesis of atrop-talarolide A (8) revealed, for the first time, that hydroxamate H-bond bridging in the talarolide framework invokes non-canonical atropisomerism and that talarolides A (1), C (3), and D (4) all exist naturally as atropisomers. These discoveries raise the intriguing prospect that comparable functionalisation of other cyclic peptides, including those with commercial value, could provide ready access to new "unnatural atropisomeric" chemical space, with new and/or improved chemical and biological properties. [ABSTRACT FROM AUTHOR]

Structures at serine‐proline sites in proteins were analyzed using a combination of peptide synthesis with structural methods and bioinformatics analysis of the PDB. Dipeptides were synthesized with the proline derivative (2S,4S)‐(4‐iodophenyl)hydroxyproline [hyp(4‐I‐Ph)]. The crystal structure of Boc‐Ser‐hyp(4‐I‐Ph)‐OMe had two molecules in the unit cell. One molecule exhibited cis‐proline and a type VIa2 β‐turn (BcisD). The cis‐proline conformation was stabilized by a C–H/O interaction between Pro C–Hα and the Ser side‐chain oxygen. NMR data were consistent with stabilization of cis‐proline by a C–H/O interaction in solution. The other crystallographically observed molecule had trans‐Pro and both residues in the PPII conformation. Two conformations were observed in the crystal structure of Ac‐Ser‐hyp(4‐I‐Ph)‐OMe, with Ser adopting PPII in one and the β conformation in the other, each with Pro in the δ conformation and trans‐Pro. Structures at Ser‐Pro sequences were further examined via bioinformatics analysis of the PDB and via DFT calculations. Ser‐Pro versus Ala–Pro sequences were compared to identify bases for Ser stabilization of local structures. C–H/O interactions between the Ser side‐chain Oγ and Pro C–Hα were observed in 45% of structures with Ser‐cis‐Pro in the PDB, with nearly all Ser‐cis‐Pro structures adopting a type VI β‐turn. 53% of Ser‐trans‐Pro sequences exhibited main‐chain COi•••HNi+3 or COi•••HNi+4 hydrogen bonds, with Ser as the i residue and Pro as the i + 1 residue. These structures were overwhelmingly either type I β‐turns or N‐terminal capping motifs on α‐helices or 310‐helices. These results indicate that Ser‐Pro sequences are particularly potent in favoring these structures. In each, Ser is in either the PPII or β conformation, with the Ser Oγ capable of engaging in a hydrogen bond with the amide N–H of the i + 2 (type I β‐turn or 310‐helix; Ser χ1t) or i + 3 (α‐helix; Ser χ1g+) residue. Non‐proline cis amide bonds can also be stabilized by C–H/O interactions. [ABSTRACT FROM AUTHOR]

The pavilion is a time-honored architectural form in the Chinese silhouette with strong regional characteristics. Its appearance and technical means are often adaptively combined according to the characteristics of local architecture. The "kiln–house isomorphism" is a unique construction technology of the Shanxi construction type in China. Therefore, the "kiln–house isomorphism" is generally adopted for the construction of pavilions in Shanxi. This study focuses on Xiaonanzhuang Village, Yuci District, Jinzhong City, Shanxi Province. Taking the Xiang-ming Pavilion, the core building of the village, as an example, we analyze the architectural characteristics of the "kiln–house isomorphism" in the pavilion in this area, describe the general construction rules of the region, and conduct a deep investigation of the five "cultural isomerism" factors of the pavilions in the region, namely, geomancy, etiquette and music, beliefs, clans, and cultivation and study. The results of this research will enrich the regional knowledge of such pavilions and add new objects for the protection of local architectural heritage, providing a theoretical basis for the contemporary adaptive reuse of pavilions in the Yuci area from a cultural perspective. [ABSTRACT FROM AUTHOR]

Axially chiral diaryl ethers represent a distinct class of atropisomers, characterized by a unique dual C─O axes system, which have been found in a variety of natural products, pharmaceuticals, and ligands. However, the catalytic enantioselective synthesis of these atropoisomers poses significant challenges, due to the difficulty in controlling both chiral C─O axes, and their more flexible conformations. Herein, an efficient protocol for catalytic enantioselective synthesis of axially chiral diaryl ethers is presented using organocatalyzed asymmetric Povarov reaction‐enabled desymmetrization, followed by aromatizations. This method yields a wide range of novel quinoline‐based diaryl ether atropoisomers in good yields and high enantioselectivities. Notably, various aromatization protocols are developed, resulting in a diverse set of polysubstituted quinoline‐containing diaryl ether atropisomers. Thermal racemization studies suggested excellent configurational stabilities for these novel diaryl ether atropisomers (with racemization barriers up to 38.1 kcal mol−1). Moreover, this research demonstrates for the first time that diaryl ether atropisomers lacking the bulky t‐Bu group can still maintain a stable configuration, challenging the prior knowledge in the field. The fruitful derivatizations of the functional group‐rich chiral products further underscore the value of this method. [ABSTRACT FROM AUTHOR]

This paper proposes a molecular model of covalent grafting of azobenzene derivatives with graphite-like carbon nitride based on hydrogen bond regulation to improve the azobenzene photothermal energy storage density. The enthalpy of isomerization (Δ H) of azobenzene molecular cis - trans isomers is calculated using density functional theory, and the magnitude of Δ H is used to evaluate the photothermal storage performance of the azobenzene graphite-like carbon nitride model. The results showed that the molecular Δ H value increased by 0.105–0.243 eV after the azobenzene derivatives were covalently grafted to the graphitic carbon nitride template. In addition, when the donator group replaced the active benzene ring ortho-site of azobenzene, its value was 0.069–0.295 eV higher than that of the electron-withdrawing groups. Moreover, intramolecular hydrogen bonds can stabilize cis - trans isomers and increase the energy of azobenzene. Compared with unsubstituted azobenzene, the energy of azobenzene Δ H containing one intramolecular hydrogen bond increased by 0.295 eV, while the energy of azobenzene Δ H containing multiple intramolecular hydrogen bonds increased by 0.775 eV. [Display omitted] • A molecular model for covalent grafting of azobenzene onto g-C 3 N 4 with hydrogen bond was developed. • The energy conversion density of azobenzene synthetic was determined using density functional theory. • The grafting effect was evaluated by considering intramolecular hydrogen bond, substitution location, and electron group. [ABSTRACT FROM AUTHOR]

A desymmetrizing 1,2‐addition of silicon nucleophiles to biaryl derivatives containing an 2,6‐dicarbaldehyde‐1‐yl unit is reported. The reaction is catalyzed by copper with a triazolium‐ion‐derived N‐heterocyclic carbene as the chiral ligand and makes use of an Si–B reagent as the silicon pronucleophile. The practical methodology furnishes axially chiral aromatic carbaldehydes decorated with a centrally chiral α‐hydroxysilane moiety in moderate to good yields and with high enantio‐ as well as excellent diastereoselectivities. The silicon nucleophile always attacks at the diastereotopic face of either carbonyl group away from the ortho substituent on the phenyl ring at C1 of the 2,6‐dicarbaldehyde‐1‐yl fragment. The resulting axially and centrally chiral products can be further converted into valuable biaryl compounds with hardly any erosion of the enantiomeric excess. [ABSTRACT FROM AUTHOR]

Covalent triazine frameworks (CTFs) involving a donor‐π bridge‐acceptor (D‐π‐A) structure are considered one of the most promising photocatalytic materials, in which the π bridge is known to play an important role in influencing the photocatalytic performance. So far, much effort has been directed at the designing of the different π bridge structure to facilitate the photo‐induced charge separation. However, the orientation of the π bridge units (configurational isomerism) has not been considered. In this paper, a pair of pyridine‐bridged D‐π‐A type CTFs, named TFA‐P1‐CTF and TFA‐P2‐CTF, were designed to investigate how the orientation of the π bridge would influence their performance in the photocatalytic oxidation of olefins into carbonyl compounds. Interestingly, due to the superior charge separation capability, TFA‐P2‐CTF was found to be able to catalyze the reaction more efficiently than TFA‐P1‐CTF. Our study eventually provided a guide for the design of D‐π‐A type CTFs as high‐performance photocatalytic materials via tuning the configurational isomerism of the π bridge unit for use in chemical transformations. [ABSTRACT FROM AUTHOR]

Multiple resonance thermally activated delayed fluorescence (MR‐TADF) emitters are promising for high‐definition organic light‐emitting diodes (OLEDs) due to their high exciton utilization and color purity. However, strong interchromophore interactions cause most MR‐TADF emitters with planar structures to aggregate at high doping concentrations, leading to degraded efficiencies. Herein, using benzenesulfonyl‐functionalized dibenzothiophene sulfoximine with steric effects, three MR‐TADF emitters (2SBN, 3SBN, and 4SBN) are synthesized by coupling the classic DtBuCzB skeleton at different sites. Three emitters exhibit green or blue‐green emission with full width at half maximum (FWHM) values less than 29 nm and photoluminescence quantum yields exceeding 90%. OLEDs based on 2SBN, 3SBN, and 4SBN achieve high maximum external quantum efficiency (EQEmax) values of 30.1%, 27%, and 33.8%, respectively, at a 5 wt.% doping concentration. Notably, due to the distorted conformation of 4SBN and suppressed intermolecular interaction, the OLED remains high EQEmax of 28.9% at a doping concentration of 20 wt.%. These results demonstrate the feasibility of molecular design to modulate spatial conformations via positional isomerism to develop MR‐TADF emitters with reduced concentration quenching. [ABSTRACT FROM AUTHOR]

Modulating the assembly pathway is an indispensable strategy for optimizing the performance of optical materials. However, implementing this strategy is nontrivial for metal nanocluster building blocks, due to the limited functional modification of nanoclusters and complexity of their emission mechanism. In this report, we demonstrate that a gold nanocluster modified by 4,6‐diamino‐2‐pyrimidinethiol (DPT‐AuNCs) self‐assembles into two distinct aggregation structures in methanol (MeOH)/water mixed solvent, thus exhibiting pathway complexity. Kinetic studies show that DPT‐AuNCs firstly assembles into non‐luminescent nanofibers (kinetically controlled), which further transforms into strongly luminescent microflowers (thermodynamically controlled). In‐depth analysis of the assembly mechanism reveals that the transformation of aggregation structures involves the disassembly of nanofibers and a subsequent nucleation‐growth process. Temperature‐dependent photoluminescence (PL) spectroscopy and infrared (IR) measurements reveal that inter‐cluster hydrogen bonding bridged by solvent molecules and C−H⋅⋅⋅π interaction are the key factors for emission enhancement. The photoluminescent property of DPT‐AuNCs can be controlled by varying the cosolvent in water, enabling DPT‐AuNCs to distinguish different kind of alcohols, particularly the isomerism n‐propanol (NPA) and isopropanol (IPA). Additionally, the addition of seeds effectively regulate the assembly kinetics of DPT‐AuNCs. This study advances our understanding of assembly pathways and improves the luminescent performance of nanoclusters (NCs). [ABSTRACT FROM AUTHOR]

Two series of unsymmetric α-cyanostilbene-based tetracatenars containing three hexadecyl chains at one end and one alkyl chain with varying lengths at the other end were prepared by using Suzuki coupling and Knoevenagel reactions. These tetracatenars with the terminal three hexadecyl chains, which are adjacent to the cyano group are non-mesogens, whereas the isomers with one alkyl chain, which is adjacent to the cyano group display transition from non-mesogens to monotropic hexagonal columnar liquid crystal upon elongation of the alkyl chain. This transition could be attributed to that the three hexadecyl chains which are adjacent to the cyano group decrease the interactions between π-conjugated rigid cores, hindering the formation of mesophase. In addition, weak slovatochromism implies weak ICT in both series tetracatenars. Both series isomers exhibit distinct AIE characteristics attributing to the presence of α-cyanostilbene, which could induce stereoisomerism and restricted intermolecular rotation in the aggregated state. Different mechanochromism behaviors could be achieved due to the positional isomerism of terminal alkyl chains. Therefore, tuning the position of terminal alkyl chains could give rise to distinct changes in the molecular aggregate, which provides a scheme to build multifunctional materials with diverse potentials. [ABSTRACT FROM AUTHOR]

The reaction of [RuNO(Py)2Cl2OH] with bipyridine in water–ethanol media results in trans-(NO, OH)-[RuNO(Py)(Bpy)ClOH]+ with an acceptable yield (60–70%) as hexafluorophosphate salt. Further treatment of the hydroxy-complex with concentrated HF quantitatively leads to trans-(NO, F)-[RuNO(Py)(Bpy)ClF]+. Despite the chirality of both coordination spheres, the hexafluorophosphate salts crystallized as racemates. A NO-linkage isomerism study of the obtained complexes was performed at 80 K with different excitation wavelengths (405, 450, 488 nm). The most favorable wavelengths for the MS1 isomer (Ru-ON) formation were 405 and 450 nm, where the linkage isomer populations were 17% and 1% for [RuNO(Py)(Bpy)ClOH]PF6 and [RuNO(Py)(Bpy)ClF]PF6. The shift of the excitation wavelength to the green (488 nm) sharply decreased the MS1 population. The IR-spectral signatures of MS1 were registered. Reverse-transformation Ru-ON (MS1)-Ru-NO (GS) was investigated for [RuNO(Py)(Bpy)ClOH]PF6 using IR and DSC techniques that made it possible to determine the kinetic parameters (Ea and k0) and decay temperature. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Chiral BINAM‐derived selenide/achiral acid co‐catalyzed atroposelective electrophilic sulfenylation of pyrrole derivatives has been realized for the first time. A variety of C—N axially chiral sulfur‐containing pyrrole derivatives were readily obtained in moderate to good yields with moderate to excellent enantioselectivities. This catalytic system involves sequential desymmetrization and kinetic resolution. [ABSTRACT FROM AUTHOR]

Atropisomerism, an expression of axial chirality caused by limited bond rotation, is a prominent aspect within the field of medicinal chemistry. It has been shown that atropisomers of a wide range of compounds, including established FDA‐approved drugs and experimental molecules, display markedly different biological activities. The time‐dependent reversal of chirality in atropisomers poses complexity and obstacles in the process of drug discovery and development. Nonetheless, recent progress in understanding atropisomerism and enhanced characterization methods have greatly assisted medicinal chemists in the effective development of atropisomeric drug molecules. This article provides a comprehensive review of their special design thoughts, synthetic routes, and biological activities, serving as a reference for the synthesis and biological evaluation of bioactive atropisomers in the future. [ABSTRACT FROM AUTHOR]

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In the field of energetic materials, traditional materials with high toxicity or other disadvantages are mostly used. There is an urgent need for trinitrotoluene replacements (TNT), which itself is toxic and its production is problematic due to red wastewater. New materials should be safe to handle, have good performance, and be inexpensive to synthesize. Nitratoalkylazoles are known to have low melting points and good energetic properties compared to TNT. In this paper, seven energetic compounds are synthesized starting from 5-methyltetrazole, 5-hydroxymethyltetrazole and 4,5-bishydroxymethyltriazole. The nitrates are characterized in terms of their physical, chemical, and energetic properties. Of those seven compounds, five are solid, melting between 27 °C and 110 °C, and two are liquid. Methylation and hydroxyalkylation were performed and discussed extensively. The organic nitrate is introduced in the last step so that the synthesis remains safe and scalable. Correlations between the molecular geometry and the melting points are explained. Calculations indicate detonation velocities that are 6%–11% higher than those of TNT. A discussion of the effect of isomerism on the properties leads to surprising insights and should help focus and accelerate research on the replacement of TNT.

The RET (REarranged during Transfection) gene, which encodes for a transmembrane receptor tyrosine kinase, is an established oncogene associated with the etiology and progression of multiple types of cancer. Oncogenic RET mutations and rearrangements resulting in gene fusions have been identified in many adult cancers, including medullary and papillary thyroid cancers, lung adenocarcinomas, colon and breast cancers, and many others. While genetic RET aberrations are much less common in pediatric solid tumors, increased RET expression has been shown to be associated with poor prognosis in children with solid tumors such as neuroblastoma, prompting an interest in RET inhibition as a form of therapy for these children. A number of kinase inhibitors currently in use for patients with cancer have RET inhibitory activity, but these inhibitors also display activity against other kinases, resulting in unwanted side effects and limiting their safety and efficacy. Recent efforts have been focused on developing more specific RET inhibitors, but due to high levels of conservation between kinase binding pockets, specificity remains a drug design challenge. Here, we review the background of RET as a potential therapeutic target in neuroblastoma tumors and the results of recent preclinical studies and clinical trials evaluating the safety and efficacy of RET inhibition in adults and children. We also present a novel approach to drug discovery leveraging the chemical phenomenon of atropisomerism to develop specific RET inhibitors and present preliminary data demonstrating the efficacy of a novel RET inhibitor against neuroblastoma tumor cells.

Rationale: 1,4‐Cyclohexanedicarboxylic acid and its esters are widely used as building blocks in the production of polymers and copolymers. The properties of such compounds directly depend on the ratio of cis‐ and trans‐isomers in the starting materials. The identification of such stereoisomers by mass spectrometry can be used for the analysis of complex reactions and pyrolysis mixtures. Methods: 1,4‐Cyclohexanedicarboxylic acid propyl, isopropyl, butyl, 2‐butyl, pentyl, 2‐pentyl, 4‐methylpentyl, heptyl, octyl, and nonyl esters were synthesized and analyzed by gas chromatography‐electron ionization mass spectrometry. The general fragmentation patterns of the synthesized compounds in electron ionization conditions were determined using high‐resolution mass spectrometry. The relative response factors for the isomers were established on the basis of NMR and GC–MS data. Results: Regardless of the structure of the alkyl groups, the EI mass spectra of cis‐ and trans‐dialkyl 1,4‐cyclohexanedicarboxylates differ very sharply. The stereoselectivity of fragmentation processes is due to the steric proximity of the substituents in the case of cis‐isomers. Elemental composition of all ions appearing in the mass spectra of the analytes under study was confirmed by high‐resolution mass spectrometry. Despite the perceptible differences in the EI mass spectra of the isomers their ionization efficiencies are close. Conclusions: The possibility of the unambiguous identification of stereoisomeric dialkyl cis and trans 1,4‐cyclohexanedicarboxylates on the basis of their EI mass spectra was shown. The differences in mass spectra of the isomers are due to the conformational rigidity of the considered monocyclic molecules, which ensures the unique stereoselectivity of the elimination of neutral molecules owing to the 1,3‐cis‐diaxial proximity effect. [ABSTRACT FROM AUTHOR]

The anti‐emulsification property of lubricating oil is an important index to measure the quality of oil. In this paper, the behaviour of surfactants such as lubricating oil additives at the oil–water interface and the influence of the position of ethylene oxide (EO) and propylene oxide (PO) in the block polyether demulsifier on the demulsification effect were investigated by molecular simulation and experimental verification. The properties of seven lubricating oil additives with different functions and two pairs of isomers were investigated by molecular simulation, and their demulsification effects were verified by experiments. Some simulation results such as interface thickness and density distribution can accurately predict the experimental demulsification effect. Moreover, it was found that the position isomerism of surfactants affected the demulsification performance by changing the lipophilic balance and interface properties. The demulsification performance of sequenced copolymers is generally better than that of anti‐sequenced copolymers. The accurate prediction of molecular dynamics simulation makes the selection of lubricating oil demulsifier more extensive and has practical application value. [ABSTRACT FROM AUTHOR]

Introduction. The structure of dihydroquercetin (DHQ) is characterized by two chiral centers at positions 2 and 3 of the benzopyran cycle, resulting in possible diastereomers: trans- and cis-isomers. Therefore, the development of methods for qualitative and quantitative control of DHQ diastereomers in analyzed samples is essential for patient safety management. Nuclear magnetic resonance (NMR) spectroscopy is one of the physicochemical methods that can be used for this purpose.Aim. The study objective was to accumulate the analytical and structural characteristics of cis-DHQ by NMR spectroscopy of the spheroidal form of this flavonoid (DHQs).Materials and Methods. 1D 1H, 1H,1H-COSY, 1H,1H-NOESY, and 1H,13C-HSQC NMR spectra were acquired at 298 K on an 800 MHz NMR spectrometer equipped with a TXI triple resonance probe. The number of scans was 32. The mixing time in the NOESY experiment was 400 ms. The 1H and 13C were analyzed using CcpNmr software. The dihedral angles were calculated by applying the Karplus equation.Results and discussion. In trans-DHQ, the chemical shift values for H2 and H3 are 4.93 ppm and 4.52 ppm, respectively, and in cis-DHQ they are 5.31 ppm and 4.20 ppm, respectively. The spin-spin coupling constants between H2 and H3 of trans- and cis-DHQ are 12.00 Hz and 2.40 Hz, respectively. Thus, the dihedral angles for the trans- and cis-isomers are 154° and 64°, respectively. We found that DHQs contains 12.5 % of the cis-isomer.Conclusion. Our experiments confirmed that NMR spectroscopy can discriminate between trans- and cis-DHQ based on the chemical shift values for the cross-peaks of H2 and H3. The second major finding was that this method can be considered as a more selective quantitative analysis than HPLC with UV detection without reference. One of the most important results of this study for drug development is the updated information on the structural parameters of DHQ diastereomers in the liquid phase.

Stretchable conjugated polymers with conjugation break spacers (CBSs) synthesized via random terpolymerization have gained considerable attention because of their efficacy in modulating mobility and stretchability. This study incorporates a series of dianhydrohexitol diastereomers of isosorbide (ISB) and isomannide (IMN) units into the diketopyrrolopyrrole‐based backbone as CBSs. It is found that the distorted CBS (IMN) improves the mobility–stretchability properties of the polymer with a highly coplanar backbone, whereas the extended CBS (ISB) enhances those of the polymer with a noncoplanar backbone. Additionally, the different configurations of ISB and IMN sufficiently affect the solid‐state packing, aggregation capabilities, crystallographic parameters, and mobility–stretchability properties of the polymer. The IMN‐based polymers exhibit the highest mobility of 1.69 cm2 V−1 s−1 and crystallinity retentions of (85.7, 78.6)% under 20% and 60% strains, outperforming their ISB‐based or unmodified counterparts. The improvement is correlated with a robust aggregation capability. Furthermore, the CBS content affects aggregation behavior, notably affecting mobility. This result indicates that incorporating CBSs into the polymer can enhance backbone flexibility via movement and rotation of the CBS without affecting the crystalline regions. [ABSTRACT FROM AUTHOR]