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Infrared (IR) action spectroscopy is utilized to characterize carbon-centered hydroperoxy-cyclohexyl radicals (·QOOH) transiently formed in cyclohexane oxidation. The oxidation pathway leads to three nearly degenerate ·QOOH isomers, β-, γ-, and δ-QOOH, which are generated in the laboratory by H-atom abstraction from the corresponding ring sites of the cyclohexyl hydroperoxide (CHHP) precursor. The IR spectral features of jet-cooled and stabilized ·QOOH radicals are observed from 3590 to 7010 cm−1 (∼10–20 kcal mol−1) at energies in the vicinity of the transition state (TS) barrier leading to OH radicals that are detected by ultraviolet laser-induced fluorescence. The experimental approach affords selective detection of β-QOOH, arising from its significantly lower TS barrier to OH products compared to γ and δ isomers, which results in rapid unimolecular decay and near unity branching to OH products. The observed IR spectrum of β-QOOH includes fundamental and overtone OH stretch transitions, overtone CH stretch transitions, and combination bands involving OH or CH stretch with lower frequency modes. The assignment of β-QOOH spectral features is guided by anharmonic frequencies and intensities computed using second-order vibrational perturbation theory. The overtone OH stretch (2νOH) of β-QOOH is shifted only a few wavenumbers from that observed for the CHHP precursor, yet they are readily distinguished by their prompt vs slow dissociation rates to OH products. [ABSTRACT FROM AUTHOR]

The A ̃ 1A″ ← X ̃ 1A′ absorption spectra of HONO and DONO were simulated by a full six-dimensional quantum mechanical method based on the newly constructed potential energy surfaces for the ground and excited electronic states, which were represented by the neural network method utilizing over 36 000 ab initio energy points calculated at the multireference configuration interaction level with Davidson correction. The absorption spectrum of HONO/DONO comprises a superposition of the spectra from two isomers, namely, trans- and cis-HONO/DONO, due to their coexistence in the ground X ̃ 1A′ state. Our calculated spectra of both HONO and DONO were found to be in fairly good agreement with the experiment, including the energy positions and widths of the peaks. The dominant progression was assigned to the N=O stretch mode ( 2 0 n ) associated with trans-HONO/DONO, which can be attributed to the promotion of an electron to the π* orbital of N=O. Specifically, the resonances with higher vibrational quanta were found to be in the domain of the Feshbach-type resonances. The assignments of the spectra and mode specificity therein are discussed. [ABSTRACT FROM AUTHOR]

A number of internal rotation codes can deal with the combination of one or two internal rotors with one 14N quadrupole nucleus, but once it comes to two 14N nuclei, no such code is available even for the case of one internal rotor. We present here the extension of our internal rotor program called BELGI-2N using the rho-axis method global approach to deal with compounds containing one methyl rotor and two weakly coupling 14N nuclei. To test our new code, we applied it to the microwave data recorded for N-methylimidazole, 2-methylimidazole, 4-methylimidazole, and 5-methylimidazole using a chirped-pulse Fourier transform microwave spectrometer in the 7.0–18.5 GHz frequency range. Compared to the previously published study, BELGI-2N was able to (i) significantly increase the number of assigned and fitted lines, (ii) fit the complete datasets considering both the internal rotation and the 14N nuclear quadrupole coupling effects simultaneously, and (iii) achieve standard deviations within the measurement accuracy for all methylimidazole isomers. [ABSTRACT FROM AUTHOR]

Superfluid helium nanodroplets are unique nanomatrices for the isolation and study of transient molecular species, such as radicals, carbenes, and ions. In this work, isomers of C3H4+ were produced upon electron ionization of propyne and allene molecules and interrogated via infrared spectroscopy inside He nanodroplet matrices. It was found that the spectrum of C3H4+ has at least three distinct groups of bands. The relative intensities of the bands depend on the precursor employed and its pickup pressure, which indicates the presence of at least three different isomers. Two isomers were identified as allene and propyne radical cations. The third isomer, which has several new bands in the range of 3100–3200 cm−1, may be the elusive vinylmethylene H2C=CH–CH+ radical cation. The observed bands for the allene and propyne cations are in good agreement with the results of density functional theory calculations. However, there is only moderate agreement between the new bands and the theoretically calculated vinylmethylene spectrum, which indicates more work is necessary to unambiguously assign it. [ABSTRACT FROM AUTHOR]

Chromones are a class of naturally occurring compounds, renowned for their diverse biological activities with significant relevance in medicine and biochemistry. This study marks the first analysis of rotational spectra of both the chromone monomer and its monohydrate through Fourier transform microwave spectroscopy. The observation of nine mono-substituted 13C isotopologues facilitated a semi-experimental determination of the equilibrium structure of the chromone monomer. In the case of chromone monohydrate, two distinct isomers were identified, each characterized by a combination of O–H⋯O and C–H⋯O hydrogen bonds involving the chromone's carbonyl group. This study further delved into intermolecular non-covalent interactions, employing different theoretical approaches. The relative population ratio of the two identified isomers was estimated to be about 2:1 within the supersonic jet. [ABSTRACT FROM AUTHOR]

Monolayer protected metal clusters comprise a rich class of molecular systems and are promising candidate materials for a variety of applications. While a growing number of protected nanoclusters have been synthesized and characterized in crystalline forms, their dynamical behavior in solution, including prenucleation cluster formation, is not well understood due to limitations both in characterization and first-principles modeling techniques. Recent advancements in machine-learned interatomic potentials are rapidly enabling the study of complex interactions such as dynamical behavior and reactivity on the nanoscale. Here, we develop an Au-S-C-H atomic cluster expansion (ACE) interatomic potential for efficient and accurate molecular dynamics simulations of thiolate-protected gold nanoclusters (Aun(SCH3)m). Trained on more than 30,000 density functional theory calculations of gold nanoclusters, the interatomic potential exhibits ab initio level accuracy in energies and forces and replicates nanocluster dynamics including thermal vibration and chiral inversion. Long dynamics simulations (up to 0.1 μs time scale) reveal a mechanism explaining the thermal instability of neutral Au25(SR)18 clusters. Specifically, we observe multiple stages of isomerization of the Au25(SR)18 cluster, including a chiral isomer. Additionally, we simulate coalescence of two Au25(SR)18 clusters and observe series of clusters where the formation mechanisms are critically mediated by ligand exchange in the form of [Au-S]n rings.

In search of the cause behind the similarities often seen in the fragmentation of PANHs, vacuum ultraviolet (VUV) photodissociation of two pairs of isomers quinoline–isoquinoline and 2-naphthylamine-3-methyl-quinoline are studied using the velocity map imaging technique. The internal energy dependence of all primary fragmentation channels is obtained for all four target molecules. The decay dynamics of the four molecules is studied by comparing their various experimental signatures. The dominant channel for the first pair of isomers is found to be hydrogen cyanide (HCN) neutral loss, while the second pair of isomers lose HCNH neutral as its dominant channel. Despite this difference in their primary decay products and the differences in the structures of the four targets, various similarities in their experimental signatures are found, which could be explained by isomerization mechanisms to common structures. The fundamental role of these isomerization in controlling different dissociative channels is explored via a detailed analysis of the experimental photoelectron–photoion coincidences and the investigation of the theoretical potential energy surface. These results add to the notion of a universal PANH fragmentation mechanism and suggests the seven member isomerization as a key candidate for this universal mechanism. The balance between isomerization, dissociation, and other key mechanistic processes in the reaction pathways, such as hydrogen migrations, is also highlighted for the four molecules. [ABSTRACT FROM AUTHOR]

The growth mechanism of thiolate-protected gold nanoclusters (AuNCs) has been advanced, but precise crystal structure information is lacking. Recent mass spectrometry and nuclear magnetic resonance analysis experiments traced the Au24(SR)18 cluster as a non-negligible byproduct intermediate during the reaction between [Au25(SR)18]−, the flagship cluster of the remarkable nanocluster ship, and Au25(SR)19, a cluster with 25 Au atoms but featuring a completely different structure than the [Au25(SR)18]− cluster. However, the precise structure of the Au24(SR)18 cluster is unknown. In this study, a total of seven Au24(SR)18 isomers were constructed using the grand unified model. Density functional theory calculations demonstrated that two of them could be considered quasi-degenerate suggesting that both might coexist in experiments. Geometrical features, electronic structures, and absorption spectra were calculated for potential future comparisons. This work contributes to fully interpreting the growth mechanism of AuNCs. [ABSTRACT FROM AUTHOR]

The Chemical Communications journal, published by The Royal Society of Chemistry, features a variety of research articles on topics such as luminescent lanthanide metallopeptides, CO2 electrolysis, and supramolecular palladium complexes for cancer therapy. The journal covers a range of scientific discoveries in the field of chemistry, including studies on high-entropy alloy nanomaterials, asymmetric radical reactions, and novel nitrogen-doped porous carbon nanospheres for supercapacitors. The articles provide valuable insights into cutting-edge research in the chemical sciences, showcasing innovative approaches and applications in the field. [Extracted from the article]

A fluorescence method has been successfully constructed to accurately measure the D / L -Arb configuration content in optical isomers, and its application in ion detection has been expanded, which has greater sensitivity and universality than the circular dichroism (CD) method. It also promotes the study of the emission mechanism of nonconventional luminogens. [ABSTRACT FROM AUTHOR]

The subtle structural variations among carbohydrate isomers pose significant challenges for their identification and quantification. Here, we propose a strategy for rapid identification and quantification of isomeric disaccharides via derivatization with 4-(3-methyl-5-oxo-pyrazolin-1-yl) benzoic acid (CPMP) and analysing by ion mobility spectrometry (IMS). After derivatization, the ionization efficiency of disaccharides was significantly improved. The disaccharide isomers were distinguished by determining the different ion mobilities of CPMP-labelled disaccharides. Among them, [M + 2CPMP + H]+ was separated with a resolution of 1.484, almost achieving baseline separation. Subsequently, [M + CPMP + Na]+ was used for the relative quantification of lactose and maltose, showing a good linear relationship with R2 > 0.990. Finally, the method was successfully applied to the identification of lactose and maltose in beer and milk. The method is fast, accurate and effective for the identification of disaccharide isomers in complex samples. [ABSTRACT FROM AUTHOR]

The aim of this study was to develop and validate a High-Performance Thin Layer Chromatographic (HPTLC) method for simultaneous determination of ceftriaxone and ceftriaxone e-isomer in powder for injection formulation. Ceftriaxone sodium injection is an antibiotic that used globally. It has Z/E geometrical conformation, in which ceftriaxone sodium and 3 ene-isomer have Z- conformation while (E)-isomer has E- conformation and the potential toxicity of ceftriaxone (E)-isomer has been reported. Thus, to safeguard the public health, a simple and easy to use, rapid and reliable method was developed for qualitative and quantitative determination of ceftriaxone sodium and its (E)–isomer. Samples were applied on HPTLC glass plates precoated with silica gel 60F254 by using Linomat semi-auto sampler. Separation was carried out using acetone, triethyl amine, water, chloroform and ethyl acetate as a mobile phase in different ratios. The Rf values of separated compounds were 0.51 ± 0.01 and 0.62 ± 0.01 for ceftriaxone sodium and ceftriaxone (E)-isomer respectively. The method was validated by studying Specificity, Linearity, Accuracy, Precision, Robustness, Limit of Detection (LOD) and Limit of Quantification (LOQ) and Solution stability. The developed method was successfully, sensitive, simple, precise, accurate, robust and applicable for the simultaneous determination of ceftriaxone sodium and ceftriaxone (E)-isomer in powder for injection formulation. [ABSTRACT FROM AUTHOR]

Atmospheric traces of radioactive xenon can be a strong indicator for underground nuclear fission reactions. 131mXe, 133Xe, 133mXe and 135Xe are the primary gaseous isotopes/isomers currently used to identify and classify nuclear events. During decay, each of these radioactive species produces a unique beta-gamma energy spectra, which can be measured using beta-gamma coincidence counting. Current operational Xe beta-gamma spectrum analysis software relies on Region of Interest (ROI) counting (Bowyer et al. in J Environ Radioact 59(2):139–151, 2002). This algorithm occasionally produces mismeasurements, especially when quantifying meta-stable isomers, due to overlapping ROIs and shifts in detector calibration in fielded systems over time (Ringbom and Axelsson in Appl Radiat Isot 156:108950, 2020). In an attempt to better de-convolve overlapping isotope spectra we have developed a technique that applies a supervised neural-network implemented in TensorFlow with Keras to classify and quantify the isotopes and mixtures of isomers based on their beta-gamma spectra—similar to image recognition. From this, we have improved upon the false-positive rate for classification and regression models, however challenges remain with dealing with differing detector energy calibrations and with estimating measurement uncertainty. [ABSTRACT FROM AUTHOR]

The relative stabilities of the syn‐ and anti‐conformers of 72 molecules belonging to the XC(W)ZY type, with X, Y = F, Cl, Br and W, Z = O, S, Se, have been computed using the B3LYP/aug‐cc‐pVDZ approximation. The conformational preferences, represented by the energy differences between the two rotamers, exhibit a systematic trend in relation to both the halogen atoms and the chalcogen atoms. These computational predictions are in agreement with available experimental results. The NBO formalism was employed to assess the influence of both the conjugative and anomeric interactions on the relative energy of the conformers. It has been determined that the conjugative interaction provides a satisfactory explanation for the energy differences between rotamers. In contrast, the anomeric interactions favors the syn‐conformation in all cases. The relative stabilities between XC(W)ZY/YC(W)ZX and XC(W)ZY/XC(Z)WY constitutional isomers have also been computed and correlated with the experimental data. [ABSTRACT FROM AUTHOR]

Recently B←N organic frameworks (BNFs) have gained substantial attention owing to their unique dative bond energy, which imparts them with specialized functionalities across a broad spectrum of applications. Despite previous reports on BNFs with permanent porosity, research endeavors towards three‐dimensional (3D) BNFs with similar properties are scarce, with no report of robust 3D BNFs featuring permanent porosity to date. Herein, electrostatic complementary strategy is proposed to construct the first example of 3D robust and microporous BNF, BNF‐100, featuring a reo topology with 8‐connected sandwich nodes assembled via dative B←N bonds. The activated form BNF‐100 a exhibits excellent chemical stability and permanent porosity with Langmuir surface area of 645.9 m2 g−1 and pore volume of 0.23 cm3 g−1. BNF‐100 a can efficiently separate hexane isomers through sieving mechanisms, as confirmed by vapor adsorption experiments and dynamic breakthrough tests, surpassing the performance of most MOF materials. Finally, we achieved the purification of different branched hexane isomers using a single breakthrough column in a combined breakthrough and purging experiment, which is the first reported instance in the literature on hexane isomer separation. [ABSTRACT FROM AUTHOR]

We report a synthesis of the trans and cis isomers of 1,4‐di‐tert‐butyl‐2,2,3,3,5,5,6,6‐octamethyl‐1,4‐diphenylcyclohexasilane (3), together with the solid‐state structure of cis‐3. Both isomers were characterized using multinuclear NMR and UV spectroscopies and were compared based on these data, together with DFT calculations. Remarkably, we found that both isomers of 3 showcase redshifted UV maxima when compared with other known cyclosilanes. To explain this, the theoretical calculations show that the transitions involved in the excited states of trans‐3 and cis‐3 have, in addition to the expected σ conjugation component of the Si6 ring, significant π contributions of phenyl substituents. The results presented herein show the effect of the substituent's electronic properties regarding reactivity of intermediates, reaction yield, identity, and electronic properties of novel silicon‐containing molecules. [ABSTRACT FROM AUTHOR]

We present the design of an anthracenyl–naphthyl (ANT‐NAPH) dyad and its application as a luminescent 4‐stage photo switch. Both segments can individually react with singlet oxygen to switch off an optical response. In their initial form the larger ANT component reacts significantly faster and thus an ANTO2‐NAPH stage is turned on, observed by optical response of the remaining NAPH. To reduce its reactivity, ANT is substituted with two pyridine rings. This concept is first investigated and quantified on ANT and NAPH as separated molecules. Upon protonation the reaction of ANT becomes significantly slower. For the three possible pyridyl isomers this effect increases along the order meta

A unique direct asymmetric synthesis of α‐aminoimines is realized, through rapid and exclusive mono‐allylation of chiral bis‐N‐sulfinylimines using allylboronic acids. The highly selective allylation was possible as electrophilic imine functional group in the product α‐aminoimines remained unreactive towards allyl boronic acid nucleophiles. Notably, by varying the geometry and chiral auxiliary, all four isomers of the α‐aminoimines were accessed from readily available precursors. A range of allyl nucleophiles, which are tricky to generate by other means possessing highly reactive functional groups also took part in this reaction, expanding the scope further. The applicability of the products α‐aminoimines were further demonstrated by accessing a range of structurally diverse chiral cyclic and acyclic 1,2‐diamines bearing adjacent stereocenters through addition of a second nucleophile or Prins‐type cyclization by exploiting the nucleophilicity of the tethered alkene moiety. Moreover, the leaving group aptitude of sulfinyl auxiliary attached to imine, was exploited to access valuable chiral α‐aminonitriles under thermal conditions without employing any reagents. Detailed DFT calculation revealed a chair‐like transition state, arising from corresponding allylboroxine species, likely operating for the allylboration reaction across imine. [ABSTRACT FROM AUTHOR]

We previously showed that the anticancer drug imatinib mesylate (IMT, trade name: Gleevec) and a chemically distinct compound, DV2-103 (a kinase-inactive derivative of the potent Abl and Src kinase inhibitor, PD173955) lower Aβ levels at low micromolar concentrations primarily through a lysosome-dependent mechanism that renders APP less susceptible to proteolysis by BACE1 without directly inhibiting BACE1 enzymatic activity, or broadly inhibiting the processing of other BACE1 substrates. Additionally, IMT indirectly inhibits γ-secretase and stimulates autophagy, and thus may decrease Aβ levels through multiple pathways. In two recent studies we demonstrated similar effects on APP metabolism caused by derivatives of IMT and DV2-103. In the present study, we synthesized and tested radically altered IMT isomers (IMTi's) that possess medium structural similarity to IMT. Independent of structural similarity, these isomers manifest widely differing potencies in altering APP metabolism. These will enable us to choose the most potent isomers for further derivatization. [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]

A Pd‐catalyzed asymmetric isomerization‐hydroamidocarbonylation of amide‐containing alkenes was developed, affording a variety of chiral α‐alkyl succinimides in moderate to good yields with high enantioselectivities. The key to success was introducing bulky 1‐adamentyl P‐substitution and 2,3,5,6‐tetramethoxyphenyl group into the rigid P‐chirogenic bisphosphine ligand to create stronger steric hinderance and deeper catalytic pocket. By this approach, regio‐ or stereo‐convergent synthesis of enantiomeric succinimides from the mixture of olefin isomers was achieved. [ABSTRACT FROM AUTHOR]

[Cp*Ir(R‐pica)Cl] (Cp*=pentamethylcyclopentadienyl anion, pica=2‐picolineamidate) complexes bearing carbohydrate substituents on the amide nitrogen atom (R=methyl‐β‐D‐gluco‐pyranosid‐2‐yl, 1; methyl‐3,4,6‐tri‐O‐acetyl‐β‐D‐glucopyranosid‐2‐yl, 2) were tested as catalysts for formic acid dehydrogenation in water. TOFMAX values over 12000 h−1 and 50000 h−1 were achieved at 333 K for 1 and 2, respectively, with TON values over 35000 for both catalysts. Comparison with the simpler cyclohexyl‐substituted analogue (3) indicated that glucosyl‐based complexes are much better performing under the same experimental conditions (TOFMAX=5144 h−1, TON=5000 at pH 2.5 for 3) owing to a lower tendency to isomerize to the less active k2‐N,O isomer upon protonation. The 5‐fold increase in TOFMAX observed for 2 with respect to 1 is reasonably due to an optimal steric protection by the acetyl substituent, which may prevent unproductive inner‐sphere reactivity. These results showcase a powerful strategy for the inhibition of the common deactivation pathways of [Cp*Ir(R‐pica)X] catalysts for FA dehydrogenation, paving the way for the development of better performing hydrogen storage systems. [ABSTRACT FROM AUTHOR]

Metallacyclobutadienes (MCBDs) are key intermediates of alkyne metathesis reactions. There are in principle two isomerization pathway from kinetic to thermodynamic MCBDs, intermolecular and intramolecular. However, systems that simultaneously isolate two kinds of MCBD isomers have not been achieved, thus restricting the mechanistic studies of the isomerization. Here the reactivity of a metallapentalyne that contains an M≡C bond within the aromatic ring, with alkynes to afford a series of MCBD‐fused metallapentalenes is studied. In some cases, both kinetic and thermodynamic products are isolated in the same system, which has never been observed in previous MCBD reactions. Furthermore, the isomerization of MCBD‐fused metallapentalenes is investigated both experimentally and theoretically, indicating that it is an intramolecular process involving a metallatetrahedrane (MTd) intermediate. This research provides experimental evidence demonstrating that one MCBD can undergo intramolecular rearrangement to transform into another. [ABSTRACT FROM AUTHOR]

Thermodynamic characteristics are calculated for new products of the transformation of N,N‑dimethylhydrazine, the values of which can be used to reliably identify these compounds and predict their periods of retention. For the first time, the ideal gas–rigid rotator–harmonic oscillator approximation is used to predict entropies in the gas phase, and the Feller–Peterson–Dixon approach is used to obtain reliable enthalpies of formation in the gas phase for the considered compounds. Retention of the considered isomeric triazole derivatives under conditions of reverse phase high-performance liquid chromatography correlates well with the obtained values of thermodynamic characteristics. [ABSTRACT FROM AUTHOR]

Omeprazole (OME) is a CYP2C19 phenotyping probe, marketed as a racemic (S)/(R) mixture or as an S‐enantiomer. Both CYP2C19 and CYP3A4 enzymes mediate (R)‐OME hydroxylation to (R)‐5‐hydroxyomeprazole, while (S)‐OME is exclusively hydroxylated via CYP2C19. This study investigates OME and its 5‐hydroxymetabolite enantiomers' pharmacokinetics using data from two studies involving healthy volunteers. In Study A, volunteers received OME alone in Session 1, OME combined with voriconazole and fluvoxamine in Session 2 and finally OME with rifampicin in Session 3. In Study B, volunteers received OME alone in Session 1, OME combined with voriconazole in Session 2 and finally OME with fluvoxamine in Session 3. Despite low metabolic ratio values of (S)‐OME, detectable modulation of CYP2C19 activity suggests both (R)‐ and (S)‐OME isomers could effectively assess CYP2C19 activity. Further research is needed for precise cut‐offs in different phenotype groups. [ABSTRACT FROM AUTHOR]

Zigzag-shaped [6]phenacene isomers with fused thiophene rings, fulmineno[2,1-b:10,9-b′]dithiophene (FuDT-α) and fulmineno[1,2-b:9,10-b′]dithiophene (FuDT-β), were syntheized and their p-type organic semicondutor properties were studied. Small effective masses of holes were estimated from the crystal structures of both isomers, which was particularly demonstrated by the hole mobility of 10.5 cm2 V−1 s−1 for FuDT-α single crystals. [ABSTRACT FROM AUTHOR]

A domino sequence consisting of a rhodium‐catalyzed Doyle‐Kirmse rearrangement followed by a Claisen‐thioimidate rearrangement has been developed. This type of thio‐Claisen rearrangement represents the first example reported in the homoallenylsulfenyl series. The sequence involves 2‐propargylsulfenyl benzazoles and diazoesters, affording N‐butadienyl substituted benzazole‐2‐thiones as a mixture of Z and E isomers, in yields ranging from 12% to quantitative (32 examples). The method provides a rapid access to a new family of highly substituted polyfunctionalized 2‐aminobuta‐1,3‐dienes with potential synthetic applications. [ABSTRACT FROM AUTHOR]

The problem of whether and how the captodative aromatic systems with the donor and acceptor substituents at the same carbon atom of the C=C bond can be more stable than the π‐conjugated push‐pull counterparts with the two substituents in the vicinal position is analyzed for cyclopentadienyl derivatives possessing an aromatic cyclopentadienyl ring. The analysis of electronic, magnetic, and structural criteria of aromaticity showed that among typical organic donors, such as amines NR3, ethers R2O, guanidine (NH2)2C=NH, siloxane O(SiH3)2, silatrane, the captodative isomers [cyclopentadienylium]−C(X+) = CH2 can be more stable than their push‐pull isomeric counterparts [cyclopentadienylium]−—CH=CH—X+. The largest energy difference in favor of the former was found to be ca. 13 kcal/mol for X = NH=C(NH2)2. [ABSTRACT FROM AUTHOR]

We report the design, synthesis, photoswitching and computational studies of N-methyl arylazo-3,5-(di-2-pyridyl)pyrazole and its N-alkyl pyridinium derivatives with an ionic center proximally located to the azo group. Besides achieving excellent photoswitching characteristics, particularly at longer wavelengths, and tuning Z isomer stability due to the effects of counter ions and pH, the utility of neutral and ionic photoswitches for pH modulation by light was achieved. [ABSTRACT FROM AUTHOR]

To replace traditional phthalate plasticizers, our previous research revealed that trioctyl citrate (CA) with an alkyl chain containing 8 carbon atoms (C8) exhibited excellent plasticizing properties. In order to delve deeper into the plasticization effects of CA isomers, CA with different side‐chain structures (C8‐Line, C8‐Branch, and C8‐Star) were synthesized by esterification reactions, and various CA/polyvinyl chloride (PVC) composite films with different CA contents were prepared using a solution casting method. The plasticization mechanisms of these isomers were systematically explored through experimental and molecular dynamics simulations. The results indicate that C8‐Branch demonstrates the optimal plasticizing effect, followed by C8‐Line, while C8‐Star exhibits poorer performance. The C8‐Branch/PVC composite system displays the best plasticizing effect, attributed to the strong interaction forces between the Cl atoms of PVC and the COO groups of CA. On the contrary, the formation of stable dipole pairs between C8‐Star and PVC is impeded by steric hindrance effects. The interaction between the two is predominantly dependent on the intertwining of the alkyl chains in C8‐Star with the PVC chains, also elucidating the observed higher migration rate in the C8‐Star/PVC system. This study provides technical guidance and theoretical basis for the optimized design of high‐performance CA/PVC composites. [ABSTRACT FROM AUTHOR]

Context: 1,1- and 1,2-ethenedithiol are elusive systems that could potentially exist in interstellar space, similar to analogous diols. In this paper, we investigate the structure, stability, and bonding characteristics of these compounds as well as the ions produced by protonation, deprotonation, or simple ionization processes. 1,2-ethenedithiol has two isomers, Z and E, with the most stable conformer being syn-anti for the Z isomer and anti-anti for the E isomer. However, the energy gaps between the different conformers are never larger than 6 kJ·mol−1. For 1,1-ethenedithiol, the global minimum is the syn-anti conformer. The vertical and adiabatic ionization processes as well as the intrinsic basicities and acidities of these families of compounds were analyzed and compared with those of the corresponding diols previously reported in the literature. This comparison revealed not only the numerical differences in these thermodynamic properties but also distinct trends between the two families of compounds. Methods: State-of-the-art G4 ab initio calculations were employed to calculate the structures and total energies of the systems under investigation. The QTAIM, ELF, and NBO approaches were used to analyze the electron density of all the neutral and charged systems included in our study. Van der Waals contributions, when relevant, were analyzed by locating regions of low reduced density gradient(s) using the NCIPLOT approach. [ABSTRACT FROM AUTHOR]

This study employs a high‐dimensional consensus mass spectral (HDCMS) similarity scoring technique to discriminate isomers collected using an electron ionization mass spectrometer. The HDCMS method was previously introduced and applied to the discrimination of mass spectra of constitutional isomers, methamphetamine and phentermine, collected with direct analysis real‐time mass spectrometry (DART‐MS). The method formulates the problem of discriminating mass spectra in a mathematical Hilbert space and is hence called "high dimensional." It requires replicate mass spectra to build a Gaussian model and evaluate the inner products between these functions. The resulting measurement variability is used as a signature by which to discriminate spectra. In this work, HDCMS is tested on electron impact ionization (EI) mass spectra of 7 terpene and terpene‐related (C10H16 and C10H14) isomers with experimental retention indices that differ by less than 30 and with traditional cosine similarity scores greater than 0.9, on a scale of 0 to 1, when compared with at least one other compound in the test set. Using identical instrument parameters, 15 replicate gas chromatography–electron ionization–mass spectrometry (GC‐EI‐MS) spectra of each isomer were collected and separated into distinct library and query sets. The HDCMS algorithm discriminated each isomer, indicating the method's potential. Because the method requires replicate measurements, observations from a simple heuristic study of the number of replicates required to discriminate these isomers is presented. The paper concludes with a discussion of compound discrimination using HDCMS and the benefits and drawbacks of applying the method to EI‐MS data. [ABSTRACT FROM AUTHOR]

The possibility of refinement upon the energy of the 8.36-eV Th nuclear isomer, which is the most probable candidate for a nuclear reference value for frequency, by means of resonance optical pumping is discussed. Attention is given primarily to the problem of broadening the resonance with the aim of reducing the time of scanning. The proposed two-photon method uses a sharp broadening of the isomer line owing to mixing with an electron transition. In contrast to internal-conversion-induced resonance broadening or a deliberate extra-broadening of the pumping-laser spectral line, this method is not adversely affected by the reduction of cross section. In the case being considered, it is two orders of magnitude more efficient and is applicable both to ionized and to neutral thorium atoms. The implementation of the method entails the excitation of both the nucleus involved and the electron shell in the final state. [ABSTRACT FROM AUTHOR]

Benzene is one of the most ubiquitous structural motifs in chemistry. The valence isomers of benzene have also attracted synthetic chemists' attention due to their unique structures, bonding, and reactivity. We have been investigating boron‐nitrogen‐containing benzene valence isomers via photoisomerization of 1,2‐azaborines. In this contribution, we summarize recent developments of these highly strained BN‐heterocyclic compounds including their synthesis, characterization, proposed mechanism of formation, and their potential applications. [ABSTRACT FROM AUTHOR]

This paper describes the synthesis of a cerium(IV)‐based molecular gear composed of a thioether functionalized phthalocyanine anchoring ligand, and a helical naphthalocyanine rotating cogwheel functionalized with four carbazoles. The naphthalocyanine ligand 9 was obtained after eleven steps (overall yield of 0.2 %) as a mixture of three geometrical isomers, two of which are chiral and exhibit high levels of steric hindrance, as shown by DFT calculations. Their attributions have been made using 1H‐NMR based on their different symmetry groups. The ratio of isomers was also determined and the prochiral C4h naphthalocyanine shown to be the major compound (55 %). Its heteroleptic complexation with cerium (IV) and the anchoring phthalocyanine ligand 10 gave the targeted molecular gear in a 16 % yield. [ABSTRACT FROM AUTHOR]

Carbohydrate recognition is essential for numerous biological processes and is governed by various factors within the supramolecular environment of the cell. Photoswitchable glycoconjugates have proven as valuable tools for the investigation and modulation of carbohydrate recognition as they allow to control the relative orientation of sugar ligands by light. In order to advance the possibilities of such an "optoglycomics" approach for the glycosciences, we have synthesized a biantennary glycocluster in which two glycoazobenzene antennas are conjugated to the 3‐ and 6‐position of a scaffold glycoside. Orthogonal isomerization of the photoswitchable units was made possible by the different conjugation of the azobenzene moieties via an oxygen and a sulfur atom, respectively, and the ortho‐fluorination of one of the azobenzene units. This design enabled a switching cycle comprising the EE, EZ and the ZZ isomer. This is the first example of an orthogonally photoswitchable glycocluster. The full analysis of its photochromic properties included the investigation of the isolated glycoazobenzene antennas allowing the comparison of the intra‐ versus the intermolecular orthogonal photoswitching. The kinetics of the thermal relaxation were analyzed in detail. A molecular dynamics study shows that indeed, the relative orientation of the glycoantennas and the distances between the terminal sugar ligands significantly vary depending on the isomeric state, as intended. [ABSTRACT FROM AUTHOR]

A commercially scalable five-step synthetic process starting from cis/trans (7:3) mixture of dimethyl 1,4-cyclohexanedicarboxylate is devised for preparation of tranexamic acid with more than 99.5% purity. All impurities are controlled as per monograph. 47% overall yield over five steps has been achieved based on recovery. Epimerization of a cis-predominant isomeric mixture to trans predominant isomeric mixture under mild conditions followed by exploiting the difference in solubility to obtain trans isomer in very high purity is the key feature of the synthesis. In addition to this, use of readily available and cost efficient raw materials/reagents, recycling of cis isomer, explicit design of downstream processing enabling the retention of the trans-stereochemistry until final API are some of the highlights of this synthesis. This process also circumvents the use of hazardous chemicals and harsh reaction conditions making it greener and safer compared to the previous reports." [ABSTRACT FROM AUTHOR]

α-Hydroxy-benzylphosphonates obtained by the Pudovik reaction of substituted benzaldehydes and dialkyl phosphites were added to the triple bond of dialkyl acetylenedicarboxylates. Optimum conditions involved a 24 hours stirring in the presence of 10% diazabicycloundecene in dichloromethane to afford the adducts as a mixture of predominant E - and a minor Z -isomers in 75–90% yields after flash chromatography. The structures of the geometrical isomers were confirmed by NOE- and ROE-measurements. Catalytic hydrogenation of the olefinic moiety of the adducts led to the diastereoisomers of corresponding saturated derivatives. [ABSTRACT FROM AUTHOR]

Relative populations of the four energy-lowest IPR (isolated-pentagon-rule) isomers of Er@C82 under the high-temperature synthetic conditions are computed using the Gibbs energy based on characteristics from the density functional theory calculations (B3LYP/6-31+G*∼SDD energetics, B3LYP/6-31G*∼SDD entropy). Two leading isomers are predicted - Er@ C 2 v (9) -C82 and Er@ C s (6) -C82. The calculated equilibrium isomeric relative populations agree with available observations. As Er@C82 is one of the metallofullerenes recently used as dopants for improvement of efficiency and stability of perovskite solar cells, the calculations should help in finding rules for further selections of fullerene endohedrals for such new applications in photovoltaics. [ABSTRACT FROM AUTHOR]

Three new organic–inorganic hybrid phosphites salts, namely, (enH2)[M(H2O)6](HPO3)2, with [M = Co (1), Ni (2) and Mg (3), and "en" refers to ethylenediamine C2N2H8] have been synthesized at room temperature by the slow evaporation method. The solid-state structures were solved from single crystal X-ray diffraction data. These compounds are isostructural, all crystallizing in the orthorhombic system, space group, Pbca (no 61). The FTIR spectroscopy shows the expected bands of ethylenediamine (en), water molecules, and hydrogen-phosphite oxoanion groups. The thermal stability until 100 °C of the three compounds was confirmed using combined analyses (TGA/DTA, powder X-ray diffraction and Raman spectroscopy). Two catalytic activity performances were investigated: the catalytic efficiency on the water decontamination of the three compounds by the reduction of three nitrophenol isomers and the Hydrogen Evolution Reaction (HER) in an alkaline environment. The three hybrid compounds turned out to be very efficient new catalysts for reducing the three nitrophenol isomers. The fastest electron transport and the most favorable HER reaction kinetics are displayed by (enH2)[Ni(H2O)6](HPO3)2, while the highest current density with the lowest overpotential was obtained for (enH2)[Co(H2O)6](HPO3)2. [ABSTRACT FROM AUTHOR]

Benezediols are widely used in different areas of industry, thus identification and quantification of benzenediols is of utmost importance due to their toxicity and high environmental abundance. In this work, benzenediol isomers (pyrocatechol, resorcinol, and hydroquinone) were investigated by using the Bray–Liebhafsky (BL) oscillatory reaction. All three isomers exhibit different behavior in the BL reaction, which renders the BL system applicable as a chemosensor. The period between the fifth and sixth oscillation, the amplitude of the sixth oscillation and in the case of hydroquinone, the emergence of a new oscillation in the BL reaction were selected as the parameters used for the identification and quantification of these isomers. Furthermore, electron paramagnetic resonance spectroscopy and DFT calculations were performed in order to provide insights into the mechanism of benzenediols reactions with the BL system. [ABSTRACT FROM AUTHOR]

Background: Specialised anti-herbivory metabolites are abundant in the solanaceous genus Nicotiana. These metabolites include the large family of 17-hydroxygeranyllinalool diterpene glycosides (HGL-DTGs). Many HGL-DTGs occur exclusively within the Nicotiana genus, but information from the molecular model species N. tabacum, N. benthamiana, and the tree tobacco N. glauca is limited. Objectives: We studied HGL-DTG occurrence and complexity in these species with the aim of providing in-depth reference annotations and comprehensive HGL-DTG inventories. Methods: We analysed polar metabolite extracts in comparison to the previously investigated wild reference species N. attenuata using positive ESI(+) and negative ESI(-) mode electrospray ionisation LC-MS and MS/MS. Results: We provide annotations of 66 HGL-DTGs with in-source and MS/MS fragmentation spectra for selected HGL-DTGs with exemplary fragment interpretations of ESI(+) as well as less studied ESI(-) spectra. We assemble a potential biosynthesis pathway comparing the presence of HGL-DTGs in N. tabacum, N. glauca, and N. benthamiana to N. attenuata. Approximately one-third of HGL-DTGs are chromatographically resolved isomers of hexose, deoxyhexose, or malonate conjugates. The number of isomers is especially high for conjugates with low numbers of deoxyhexose moieties. Conclusions: We extend the number of known HGL-DTGs with a focus on Nicotiana model species and demonstrate that the HGL-DTG family of N. tabacum plants can be surprisingly complex. Our study provides an improved basis with detailed references to previous studies of wild Nicotiana species and enables inference of HGL-DTG pathways with required enzymes for the biosynthesis of this important family of specialised defence metabolites. [ABSTRACT FROM AUTHOR]

Dalbavancin is the second‐generation approved semisynthetic lipoglycopeptide by the United States Food and Drug Administration (USFDA) for the treatment of acute bacterial skin and skin‐structure infections. Unlike other lipoglycopeptides, the stability behavior of Dalbavancin was least explored, which is a prerequisite. The current study endeavors to elucidate the oxidative and hydrolytic stability behavior of Dalbavancin by exposing the drug to oxidative, acidic, and basic stress conditions. A simple liquid chromatography (LC) method was developed, where significant resolution between Dalbavancin, its homologs, and the generated degradation products was achieved. Seven degradation products were identified under acidic, basic, and oxidative stress conditions. Using liquid chromatography and high‐resolution mass spectrometry (LC‐HRMS), MS/MS studies, the generated degradation products were identified and characterized. Formation of isomeric degradation products was identified especially upon exposure to basic stress conditions. The mechanistic fragmentation pathway for the seven degradation products was established, and the chemical structure for the identified degradation products was elucidated. The results strongly suggest that Dalbavancin is highly susceptible to degradation under oxidative and hydrolytic stress conditions. This study provides insights into the hydrolytic and oxidative stability of Dalbavancin, which can be employed during drug development and discovery in synthesizing relatively stable analogs. [ABSTRACT FROM AUTHOR]

Relative populations of the four energy-lowest IPR (isolated-pentagon-rule) isomers of Er@C82 under the high-temperature synthetic conditions are computed using the Gibbs energy based on characteristics from the density functional theory calculations (B3LYP/6-31+G*∼SDD energetics, B3LYP/6-31G*∼SDD entropy). Two leading isomers are predicted - Er@ C 2 v (9) -C82 and Er@ C s (6) -C82. The calculated equilibrium isomeric relative populations agree with available observations. As Er@C82 is one of the metallofullerenes recently used as dopants for improvement of efficiency and stability of perovskite solar cells, the calculations should help in finding rules for further selections of fullerene endohedrals for such new applications in photovoltaics. [ABSTRACT FROM AUTHOR]

Five coordination polymers constructed from Co(II) salts, N,N'-bis(3-pyridylmethyl)oxalamide (L) and 4,4'-methylenedibenzoic acid (H2MBA), {[Co(L)(MBA)(H2O)]·H2O}n, 1, {[Co(L)(MBA)]·4H2O}n, 2, {[Co(L) (MBA)]·0.25H2O}n, 3, [Co(L)(MBA)(H2O)2]n, 4, and {[Co(L)0.5(MBA)(H2O)2]·CH3OH}n, 5, are reported, which have been structurally characterized by using single crystal X-ray crystallography. Complexes 1 and 4 have the same formula, but differ in the number of coordinated and cocrystallized water molecules, whereas 2 and 3 form a pair of supramolecular isomers with different numbers of cocrystallized water molecules. Complexes 1 and 4 show interdigitated 2D layers with a (64·8·10)(6)-2,4L3 topology, which differ in the ligand conformations of L and bonding modes of MBA2-. Complex 2 shows 2-fold interpenetrated 2D layers with a (64·8·10)(6)-2,4L3 topology and 3 displays a 2-fold interpenetrated 3D framework with a (4·6²) (4·66·8³)-fet topology, whereas 5 is a 1D ladder with a (6²·10)(6)-2,3C1 topology, indicating that the coordination and/or cocrystallization of solvent molecules are important in determining their structural diversity. The structural transformations of 1-4 are also evaluated. [ABSTRACT FROM AUTHOR]

Multiple stimuli-responsive molecular crystals have gained significant attention recently owing to their wide-range of applications in diverse fields such as optical switches, storage devices, and mechanical actuators. In this study, a nitropentaammine cobalt(III) complex stabilized by 4-nitro cinnamate (C-1) was synthesized and characterized using various spectroscopic and analytical techniques, including singlecrystal X-ray diffraction (SCXRD) study. The complex C-1 exhibits dual-responsive behaviour under UV light (365 nm) and heat, showing bending, cracking, splitting, and displacement. These photo-/thermomechanical responses are attributed to nitro-to-nitrito linkage isomerization within the crystalline phase. The energy optimization of C-1 and its corresponding nitrito isomer through density functional theory (DFT) study reveals that the nitro isomer is energetically more stable than nitrito by 24 kcal mol-1. This indicates that upon irradiation of UV light/heat, the nitro compound gains energy and is converted to the nitrito isomer. The photo-/thermo-mechanical behaviour of C-1 was successfully transferred to a polymer composite, which was fabricated via a solution casting method using C-1 and agarose (1 : 1 weight ratio) and shows actuating behaviour, with the extent of actuation varying for both the external stimuli. [ABSTRACT FROM AUTHOR]

Detailed experimental and computational studies of the nitrone 3,3‐dimethyl‐6‐phenyl‐2,3‐dihydro‐1,2,4‐triazin‐4‐oxide (2), which is a cyclized product of an open‐chain isomer 2‐phenyl‐2‐(propan‐2‐ylidenehydrazono)acetaldehyde oxime (1), are reported. The isolated compound 2 was characterized by elemental analysis, powder X‐ray diffraction, IR and UV‐vis spectroscopy, and spectrofluorometry. Electronic properties of 1 and 2 were elucidated by the DFT‐based calculations in water, which revealed that both compounds are pronounced electrophiles. The ADMET properties of the oxime 1 and nitrone 2 were predicted using the SwissADME, which includes the BOILED‐Egg method, and ProTox‐II online tools. Using a molecular docking approach, the discussed compounds were also predicted to actively interact with all the studied herein SARS‐CoV‐2 proteins. The most pronounced activity for both discussed compounds was established with Nonstructural protein 14 (Nsp14_N7‐MTase). Complex Nsp14_N7‐MTase‐1 is characterized by the calculated ligand efficiency scores being close for a Hit. [ABSTRACT FROM AUTHOR]

A synergetic interaction between two or more photochromic chromophores has a potential to achieve advanced photochemical properties beyond conventional photochromic molecules and to realize photochemical control of complex systems using only a single molecule. Herein, we report a hybrid photochromic molecule consisting of hexaarylbiimidazole (HABI) and terarylene that exhibits multi‐state photochromism. The biphotochrome hybrid shows four‐state photochromic reaction involving sequentially proceeding photoreactions. The UV or visible light irradiation to the biphotochrome leads to the C−N bond breaking reaction of the HABI in preference to the ring‐closing reaction of the 6π‐electron system in the terarylene unit, leading to two terarylene radical molecules. The photogenerated terarylene radical further exhibits the 6π‐electrocyclization reaction by UV irradiation. The delocalized π‐radical on the closed‐ring form of the terarylene is efficient to enhance the photosensitivity to the NIR−I and ‐II region. Furthermore, a recombination reaction of radicals between the open‐ and closed‐ring isomers of terarylene affords an unprecedented photochromic dimer as a structural isomer of the initial molecule. This is a consequence of the sequential hybrid photochromic system involving the HABI and terarylene units. [ABSTRACT FROM AUTHOR]

Formation of molecular complexes and subsequent heterolytic halogen‐halogen bond splitting upon reactions of molecular Cl2 with nitrogen‐containing Lewis bases (LB) are computationally studied at M06‐2X/def2‐TZVPD and for selected compounds at CCSD(T)/aug‐cc‐pvtz//CCSD/aug‐cc‐pvtz levels of theory. Obtained results are compared with data for ICl and I2 molecules. Reaction pathways indicate, that in case of Cl2∙LB complexes the activation energies for the heterolytic Cl‐Cl bond splitting are lower than the activation energies of the homolytic splitting of Cl2 molecule into chlorine radicals. The heterolytic halogen splitting of molecular complexes of X2∙Py with formation of [XPy2]+…X3−$$ {\mathrm{X}}_3^{-} $$ contact ion pairs in the gas phase is slightly endothermic in case of Cl2 and I2, but slightly exothermic in the case of ICl. Formation of {[ClPy2]+…Cl3−$$ {\mathrm{Cl}}_3^{-} $$}2 dimers makes the overall process exothermic. Taking into account that polar solvents favor ionic species, generation of donor‐stabilized Cl+ in the presence of the Lewis bases is expected to be favorable. Thus, in polar solvents the oxidation pathway via donor‐stabilized Cl+ species is viable alternative to the homolytic Cl‐Cl bond breaking. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of specific cis- and trans-isomers of a cobalt(II) bis-nalidixate complex with a pyridine-based urea, 1-(4-chlorophenyl)-3-(pyridin-4-ylmethyl)urea (L), ligand are reported. The two isomers, cis-[Co(L)2(NALD)2]·0.5DMF·H2O and trans-[Co(L)2(NALD)2]·2DMF·2H2O (the nalidixate anion is abbreviated to NALD) were prepared by anion-guided synthesis. When cobalt(II) chloride was used as one of the reactants, the reaction yielded the trans-isomer under ambient reaction conditions. Whereas a reaction using cobalt(II) nitrate provided only the cis-isomer when the reaction was continued for a prolonged time. On the other hand, the cis-isomer was converted to the trans-isomer in solution upon treatment with chloride ions. The chloride-assisted formation of the trans-isomer was investigated by a UV-visible study, and it passed through a bond reorganization by forming a tetrahedral intermediate complex. A DFT calculation was carried out to show the difference in energy between the isomers as well as the energy of a plausible tetrahedral cobalt complex. The aggregation behavior of the cis-isomer in different solvents was investigated, and solvent-dependent aggregation and a solvent-dependent Cotton effect were observed. [ABSTRACT FROM AUTHOR]