Search

Isomerisation reactions provide streamlined routes to organic compounds which are otherwise hard to directly synthesise. The most common forms are positional, geometrical or stereochemical isomerisations which involve the relocation of a double bond or a change in relative location of groups in space. In contrast, far fewer examples of structural (or constitutional) isomerisation exist where the connectivity between atoms is altered. The development of platforms capable of such rearrangement poses a unique set of challenges because chemical bonds must be selectively cleaved, and new ones formed without overall addition or removal of atoms. Here, we show that a dual catalytic system can enable the structural isomerisation of readily available allylic alcohols into more challenging‐to‐synthesise α‐arylated ketones via a H‐atom transfer initiated semi‐pinacol rearrangement. Key to our strategy is the combination of a cobalt catalyst and photocatalyst under reductive, protic conditions which allows intermediates to propagate catalytic turnover. By providing an unusual disconnection to structural motifs which are difficult to access through direct arylation, we anticipate inspiring other advanced catalytic isomerisation strategies that will further retrosynthetic logic for complex molecule synthesis. [ABSTRACT FROM AUTHOR]

In this contribution we report on a novel approach towards luminescent light‐responsive ligands. To this end, cyanostilbene‐ guanidiniocarbonyl‐pyrrole hybrids were designed and investigated. Merging of a luminophore with a supramolecular bioactive ligand bears numerous advantages by overcoming the typical drawbacks of drug‐labelling, influencing the overall performance of the active species by attachment of a large luminophore. Here we were able to establish a simple and easily accessible synthesis route to different cyanostyryl‐guanidininiocarbonyl‐pyrrole (CGCP) derivatives. These compounds were investigated regarding their light‐responsive double bond isomerisation, their molecular structures in single crystals by means of X‐ray diffractometry, their emission properties by state of the art photophysical characterisation as well as bioimaging and assessment of cell toxicity. [ABSTRACT FROM AUTHOR]

The silica functionalized with propylsulfonic acid (SFS) was found to be an efficient solid acid catalyst for the solvent-free isomerization of longifolene giving complete conversion into iso-longifolene with ~ 100% selectivity in 40 min. at 180 ºC. The as-synthesized SFS contained strongly bound water molecules with sulfonic acid (–SO3H) groups, which greatly lowered the strength of Brønsted acidic sites (of –SO3H groups) and exhibited reduced catalytic activity for the isomerization of longifolene. These bound water molecules could be removed by heating the SFS at a high temperature (225 ºC), which strengthened the acidity of –SO3H groups and enhanced the activity giving faster conversion of longifolene (within 20 min.) at a lower reaction temperature (160 ºC). The SFS catalyst heated at 225 ºC (activated SFS) was found to be stable and reusable without any treatment for regeneration. The activated SFS being a metal free solid acid catalyst can provide a cost-effective and environmentally benign process for the synthesis of iso-longifolene. [ABSTRACT FROM AUTHOR]

Herein, we report the skeletal isomerisation and cracking of 1-dodecene over a zeolite catalyst, viz. H–MCM-22 loaded with a group VIII metal species (i.e. Ru). Fourier-transform infrared spectroscopy and powder X-ray diffraction studies confirmed the presence of the MWW framework and successful loading of Ru. The good dispersion of Ru particles on the surface of the H–MCM-22 framework was confirmed by scanning electron microscopy. Furthermore, transmission electron microscopic observations indicated that the size of Ru particles loaded on H–MCM-22 was 5–6 nm. X-ray photoelectron spectroscopy confirmed the formation of metallic Ru from ruthenium oxide dispersed on the H–MCM-22 surface under reducing conditions. The enhanced acidity and acidic strength distribution of the Ru-loaded catalyst were confirmed through NH3 desorption studies. The vapour-phase isomerisation of 1-dodecene over the developed Ru-loaded H–MCM-22 catalyst was studied at 300 ℃ with a weight hourly space velocity (WHSV) of 1.78 h−1 using nitrogen as the carrier gas. The strong interaction between metallic Ru and surface acidic sites of H–MCM-22 improved the catalytic activity of the materials, resulting in conversion rates exceeding 90%. Remarkably, the catalytic activity of Ru-loaded H–MCM-22 was stable over 8 h of time-on-stream, and the Ru particles on H–MCM-22 enhanced the product selectivity compared with that obtained using the parent H–MCM-22 as the catalyst. Ru–H–MCM-22 showed complete conversion of 1-dodecene with exclusive formation of cracked products at 340 οC in vapour phase conditions. [ABSTRACT FROM AUTHOR]

The search for the chemical structures that account for diffuse interstellar bands remains the main challenge in astrochemistry. It relies on experimental verification of structures obtained from stable isomers in laboratory conditions. The actual interstellar medium, however, is exposed to much harsher conditions. Herein we demonstrate the isomerisation of small, doubly charged polyaromatic hydrocarbon phenanthrene obtained by electron ionisation at relatively high electron energies. We performed electronic and vibrational tagging photodissociation spectroscopy measurements. Our results show that phenanthrene dication has a broad visible spectrum, making it unsuitable for DIB search. We also detected another C14H102+ isomer, originating from the isomerisation of phenanthrene dication during the ionisation process. Hole-burning spectroscopy experiments provided the IR spectrum of an isomer which could be assigned based on DFT calculations as a fully conjugated system representing the global minimum on the C14H102+ potential energy surface. [ABSTRACT FROM AUTHOR]

The Diels–Alder reaction of three chiral dihydro‐2H‐[2,3‐a]oxazolopyridines with N‐methylmaleimide afforded the corresponding chiral cycloadducts as diastereomeric mixtures. In the presence of a solvent, some of the originally formed adducts underwent isomerisation to new isoquinuclidines. [ABSTRACT FROM AUTHOR]

Amide groups are pervasive across the chemical space continuum, where their structural and pharmacological importance, juxtaposed with the hydrolytic vulnerabilities, continues to fuel bioisostere development. Alkenyl fluorides have a venerable history as effective mimics (Ψ[CF=CH]) owing to the planarity of the motif and intrinsic polarity of the C(sp2)−F bond. However, emulating the s‐cis to the s‐trans isomerisation of a peptide bond with fluoro‐alkene surrogates remains challenging, and current synthetic solutions only enable access to a single configuration. Through the design of an ambiphilic linchpin based on a fluorinated β‐borylacrylate, it has been possible to leverage energy transfer catalysis to affect this unprecedented isomerisation process: this provides geometrically‐programmable building blocks that can be functionalised at either terminus. Irradiation at λmax=402 nm with inexpensive thioxanthone as a photocatalyst enables rapid, effective isomerisation of tri‐ and tetra‐substituted species (up to E/Z 98 : 2 in 1 h), providing a stereodivergent platform for small molecule amide and polyene isostere discovery. Application of the methodology in target synthesis and initial laser spectroscopic studies are disclosed together with crystallographic analyses of representative products. [ABSTRACT FROM AUTHOR]

Aromatic amides can be used to construct light‐harvesting materials with valuable optical properties. The amide bond is formed using well‐known coupling agents in near quantitative yield, as illustrated here through the synthesis of two boron dipyrromethene derivatives bearing an amide linkage. The primary concern with acyl amides is rotation around the C−N bond, leading to cis and trans isomers. Using NMR spectroscopy, quantum chemical calculations and critical comparison to simpler benzamides, the stereochemistry of the target compounds has been addressed. The N‐cyclohexyl derivative gave diffraction quality crystals that established a trans geometry for the amide bond. Quantum chemical calculations support the trans geometry as being the lowest‐energy structure in solution but indicate that inversion of the aryl ring is an important structural feature. Indeed, rotation around the C(sp2)−C(aryl) bond has a strong influence on the solution‐phase NMR spectra. The amide connection has minimal effect on the photophysical properties. [ABSTRACT FROM AUTHOR]

There is increasing interest in kinetic models of catalytic refining processes, because of their importance in developing and improving these processes. In fact, the models can be used to predict process performance parameters and to determine the optimum operating conditions. In this work, a detailed reaction kinetic model was developed to describe light naphtha isomerisation reactions over different Pt/zeolite catalysts (Pt/mordenite, Pt/ZSM5, and Pt/BETA). The proposed kinetic model included 66 isomerisation, 28 ring opening, 1 olefin saturation, 22 dehydrogenation, and 90 hydrocracking reactions for 52 real light naphtha components graded from methane to n-octane. A power law reaction kinetics was assumed for all reactions, and 414 kinetic parameters were fine-tuned by comparing the predictions of the model with the results of light naphtha isomerisation experiments at six different temperatures (290, 310, 330, 350, 370, and 390 °C). The Matlab software (version 2015a) was used to perform all the calculations in the current study, and the optimum set of kinetic parameters was estimated using genetic algorithm optimisation. The mean absolute errors for all component compositions at different temperatures were found to be 0.003608, 0.004841, and 0.004757 for the Pt/mordenite, Pt/ZSM5, and Pt/BETA catalysts, respectively. The values of the mean absolute errors estimated from the comparison between the experimental and predicted results showed a very good agreement between the model predictions and the experimental data.

There is increasing interest in kinetic models of catalytic refining processes, because of their importance in developing and improving these processes. In fact, the models can be used to predict process performance parameters and to determine the optimum operating conditions. In this work, a detailed reaction kinetic model was developed to describe light naphtha isomerisation reactions over different Pt/zeolite catalysts (Pt/mordenite, Pt/ZSM5, and Pt/BETA). The proposed kinetic model included 66 isomerisation, 28 ring opening, 1 olefin saturation, 22 dehydrogenation, and 90 hydrocracking reactions for 52 real light naphtha components graded from methane to n -octane. A power law reaction kinetics was assumed for all reactions, and 414 kinetic parameters were fine-tuned by comparing the predictions of the model with the results of light naphtha isomerisation experiments at six different temperatures (290, 310, 330, 350, 370, and 390 °C). The Matlab software (version 2015a) was used to perform all the calculations in the current study, and the optimum set of kinetic parameters was estimated using genetic algorithm optimisation. The mean absolute errors for all component compositions at different temperatures were found to be 0.003608, 0.004841, and 0.004757 for the Pt/mordenite, Pt/ZSM5, and Pt/BETA catalysts, respectively. The values of the mean absolute errors estimated from the comparison between the experimental and predicted results showed a very good agreement between the model predictions and the experimental data. [ABSTRACT FROM AUTHOR]

A combined three-step flow cascade conversion of n-butanol to propene is demonstrated. Zeolite H-ZSM-5 gives high conversion in the initial n-butanol dehydration step (98%). Subsequent isomerisation of terminal butenes to internal butenes over zeolite H-Fer takes place with good conversion (87%). Finally, cross-metathesis with ethene over a tungsten on acid-washed SiO2/Al2O3 catalyst affords propene with good selectivity (65%). Coupling these three steps into a single flow sheet gives an overall yield of 64% propene from n-BuOH. Ethene cross-metathesis catalyst performance was probed using 2-pentene as a model co-substrate giving good conversion (~90%) and moderate selectivity to butenes (67%).

This paper, a tribute to Mike Spencer's research contribution to zeolite technology, details work carried out with ICI proprietary (and other) zeolites during the late 70's to mid- 80's. The projects were stimulated by the 1970's oil crises, and Mobil Oil's publications on ZSM-5 technology, and involved a collaborative partnership between ICI Agricultural and Petrochemicals Divisions, with Mike a major participant. The work described covers zeolite synthesis, xylenes isomerisation, toluene methylation, the methylamines process and methanol to gasoline. Much of the work discussed is unpublished or in the patent literature. Significant progress was made in this area of technology, enabling the licensing of two zeolite catalysed processes. [ABSTRACT FROM AUTHOR]

Acyl derivatives of aziridine-2-carboxylic acid have been synthesized and tested as PDIA1 inhibitors. Calculations of charge value and distribution in aziridine ring system and some alkylating agents were performed. For the first time was found that acyl derivatives of aziridine-2-carboxylic acid are weak to moderately active PDIA1 inhibitors. [ABSTRACT FROM AUTHOR]

Racemic cloprostenol methyl ester was converted via cyclic 9,11‐phenylboronate esters to 9α,11α‐dihydroxy‐15α‐siloxy (OTBDPS, OTBDMS) derivatives. TES‐Morf selectively reacts with last compounds to exclusively give 11‐TES derivative. In the course of further transformations, the J‐type PG was obtained. The optimal conditions for the 13,14‐double bond shift in the latter were determined and ▵12 derivatives were obtained. 15‐TBDMS derivative PGJ2 was converted to the target ω‐aryloxy derivatives ▵12‐PGJ2, its 13Z isomer, and ▵12,14‐PGJ2 by hydrolysis of the TBDMS protective group. The anticancer activity of some of the synthesized compounds was studied. [ABSTRACT FROM AUTHOR]

Aminotroponiminate (ATI) ligands are a versatile class of redox‐active and potentially cooperative ligands with a rich coordination chemistry that have consequently found a wide range of applications in synthesis and catalysis. While backbone substitution of these ligands has been investigated in some detail, the impact of electron‐withdrawing groups on the coordination chemistry and reactivity of ATIs has been little investigated. We report here Li, Na, and K salts of an ATI ligand with a nitro‐substituent in the backbone. It is demonstrated that the NO2 group actively contributes to the coordination chemistry of these complexes, effectively competing with the N,N‐binding pocket as a coordination site. This results in an unprecedented E/Z isomerisation of an ATI imino group and culminates in the isolation of the first "naked" (i. e. without directional bonding to a metal atom) ATI anion. Reactions of sodium ATIs with silver(I) and tritylium salts gave the first N,N‐coordinated silver ATI complexes and unprecedented backbone substitution reactions. Analytical techniques applied in this work include multinuclear (VT‐)NMR spectroscopy, single‐crystal X‐ray diffraction analysis, and DFT calculations. [ABSTRACT FROM AUTHOR]

Summary: Allulose, also known as rare sugar, is a very reactive monosaccharide in browning reactions. In this study, the caramelisation of allulose was investigated for the first time. To study caramelisation, sugar solutions (glucose, fructose and allulose) were prepared with distilled water and buffer solutions at pH 7, 10, 12 and were freeze‐dried afterwards. To let caramelisation occur, samples were incubated at 55% relative humidity (RH) and 50 °C. Results showed that samples prepared with pH 10 and pH 12 buffer solutions resulted in a higher browning rate than samples prepared with distilled water (DW) and pH 7 buffer solution. Moreover, according to HPLC and total reducing sugar content results, allulose (Allu) samples had the lowest remaining reducing sugar (RRS) amount, indicating that Allu samples depleted more in the reaction. Overall, the approach followed in this study can be considered as a novel strategy to obtain allulose‐containing caramel‐like products more efficiently than conventional methods. [ABSTRACT FROM AUTHOR]

Oxywater(H 2 OO) is an intermediate in the oxidation of hydrogen peroxide (HOOH), and along with its relatives H 2 SS and H 2 SeSe, plays an important role in atmospheric and biochemical processes. In this research, we study the isomerisation of H 2 XY species to HXYH (X, Y = O, S, Se) using ab initio methods. Geometries and harmonic frequencies were obtained using both a scalar relativistic X2C-1e-CCSD(T) approach and non-relativistic CCSD(T) using an effective core potential on Se. A focal point approach was used to extrapolate electronic energies at CCSD(T)/aug-cc-pVTZ geometries to a CCSDT(Q)/CBS level of theory. The isomerisation reactions of H 2 XX to HXXH have barriers of 6.6, 20.6, and 14.1 kcal mol − 1 and exothermicities of 45.8, 27.2, and 28.3 kcal mol − 1 for X=O, S, and Se, respectively. The isomerisation reactions of H 2 OS and H 2 SO to HOSH have barriers of 15.4 and 44.2 kcal mol − 1 and exothermicities of 36.2 and 17.7 kcal mol − 1 . The isomerisation reactions of H 2 OSe and H 2 SeO to HOSeH have barriers of 10.1 and 36.2 kcal mol − 1 and exothermicities of 33.5 and 31.7 kcal mol − 1 . The isomerisation reactions of H 2 SSe and H 2 SeS to HSSeH have barriers of 16.2 and 18.1 kcal mol − 1 and exothermicities of 23.3 and 32.1 kcal mol − 1 . [ABSTRACT FROM AUTHOR]

This study clarifies the mechanism behind the isomerization of cresol, focusing on a shaped cerium-modified Beta zeolite. The catalysts were characterized using a series of characterization techniques, including XRD, Py-IR, XPS, and TGA. The results emphasize the pivotal role of cerium, particularly at a 5 % modification concentration, in improving catalyst acidity. The mechanism of isomerization is revealed through kinetic calculation of reversible monomolecular systems, emphasizing the significance of acid sites. TGA analysis of catalyst deactivation reveals distinctive carbon deposition patterns, with the cerium-modified zeolite displaying enhanced resistance to pore blockage through Type II carbon deposition. XPS analysis post-deactivation indicates an increased proportion of Ce3+, suggesting elevated oxygen vacancies and unsaturated chemical bonds, influencing the catalytic activity negatively. In summary, an appropriate cerium modification, especially at the 5 % concentration, strikes a balance between enhanced acidity and resistance to carbon deposition, providing valuable insights for tailoring zeolite catalysts in cresol isomerization. [Display omitted] • Discovered a catalyst for cresol isomerization and determined the optimal metal Ce modification concentration. • It was determined that Brønsted acid played a positive role in the reaction. • According to the kinetic calculation results, the basic process of the isomerization reaction was verified. [ABSTRACT FROM AUTHOR]

Modular β‐borylacrylates have been validated as programmable, ambiphilic C3‐synthons in the cascade annulation of 2‐halo‐phenol derivatives to generate structurally and electronically diverse coumarins. Key to this [3+3] disconnection is the BPin unit which serves a dual purpose as both a traceless linker for C(sp2)–C(sp2) coupling, and as a chromophore extension to enable inversion of the alkene geometry via selective energy transfer catalysis. Mild isomerisation is a pre‐condition to access 3‐substituted coumarins and provides a handle for divergence. The method is showcased in the synthesis of representative natural products that contain this venerable chemotype. Facile entry into π‐expanded estrone derivatives modified at the A‐ring is disclosed to demonstrate the potential of the method in bioassay development or in drug repurposing. [ABSTRACT FROM AUTHOR]

Quantum mechanical studies of the Z/E (syn/anti) acetoin oxime interconversion have been conducted using both density functional theory (DFT) and ab initio post-Hartree–Fock methods in order to understand the thermodynamic properties of the syn/anti isomerisation of the aliphatic α-hydroxyoxime 5,8-diethyl-7-hydroxydodecan-6-oxime. The anti isomer of this molecule is the active component in LIX63, a commercial reagent used in hydrometallurgical solvent extraction (SX). The effect of different sized alkyl (R) groups on both kinetic and thermodynamic properties of the equilibrium between syn and anti isomers of aliphatic α-hydroxyoxime has been studied. Theoretically, it has been shown that using R = C3H8 on both ends of the oxime is the minimum substituent size required to obtain good agreement for the thermodynamics in comparison to experimental data for LIX63. Further increases in the size of the R group do not have any significant effect on the final distribution between syn and anti isomers of LIX63 hydroxyoxime. Inversion was determined to be the most energetically favourable hydroxyoxime isomerisation mechanism, with the energy barrier lowered when isomerisation is considered between syn and anti isomers with larger R groups. [ABSTRACT FROM AUTHOR]

A novel N,N'‐allyl‐bridged bisimidazolium salt and a novel dinuclear Ag(I) and a Au(I) NHC complex are reported. Both metallacyclic complexes have a twisted structural shape due to the rigid allylic system and form two different isomers relating to the position of the double bonds. The allyl‐group shows photoisomerisation, but no reactivity towards bases for the additional coordination of Pd(II). [ABSTRACT FROM AUTHOR]

While the use of visible light in conjunction with transition metal catalysis offers powerful opportunities to switch between on/‐off states of catalytic activity, the next frontier would be the ability to switch the actual function of the catalyst and resulting products. Here we report such an example of multi‐dimensional catalysis. Featuring an easily prepared, bench‐stable cobalt(I) hydride complex in conjunction with pinacolborane, we can switch the reaction outcome between two widely employed transformations, olefin migration and hydroboration, with visible light as the trigger. [ABSTRACT FROM AUTHOR]

Despite the enormous biological significance, the structure-stability relationship in S-Nitrosothiols (RSNOs) that govern their activity in vivo is not well understood. We provide useful structural properties (bond length, vibrational frequency, dissociation energy, and interconversion barrier) of the -SNO group in RSNOs ( R = H and CH 3 ) using the recently suggested computationally cost-ffective multireference ab initio method which includes electron correlation effects by means of the perturbation theory using a multiconfigurational zero-order wave function. A sizable rotation barrier of cis-trans RSNO interconversion imply a partial S-N double-bond like nature. The low stretching frequency, elongated length, and small dissociation energy indicate that this bond is relatively weak and labile. Although the study of S– bond in RSNOs is a challenging case even for the current generation computational approaches, IVO-SSMRPT method (having several appealing features) employed here is competent to reproduce the structure and stability of RSNO isomers in close agreement with the reference high-level estimates. [ABSTRACT FROM AUTHOR]

Cyanine dyes, as used in super‐resolution fluorescence microscopy, undergo light‐induced "blinking", enabling localization of fluorophores with spatial resolution beyond the optical diffraction limit. Despite a plethora of studies, the molecular origins of this blinking are not well understood. Here, we examine the photophysical properties of a bio‐conjugate cyanine dye (AF‐647), used extensively in dSTORM imaging. In the absence of a potent sacrificial reductant, light‐induced electron transfer and intermediates formed via the metastable, triplet excited state are considered unlikely to play a significant role in the blinking events. Instead, it is found that, under conditions appropriate to dSTORM microscopy, AF‐647 undergoes reversible photo‐induced isomerization to at least two long‐lived dark species. These photo‐isomers are characterized spectroscopically and their interconversion probed by computational means. The first‐formed isomer is light sensitive and transforms to a longer‐lived species in modest yield that could be involved in dSTORM related blinking. Permanent photobleaching of AF‐647 occurs with very low quantum yield and is partially suppressed by the anaerobic redox buffer. [ABSTRACT FROM AUTHOR]

Strategies to achieve spatiotemporal regulation of pre‐existing alkenes via external stimuli are essential given the ubiquity of feedstock olefins in chemistry and their downstream applications. Mirroring the 1‐0 switch that underpins mammalian vision through selective geometric isomerisation in retinal, strategies to manipulate 2D space by both geometric and positional isomerisation of alkenes via chemical, thermal and light‐driven processes are being intensively pursued. This minireview highlights the current state of the art in activating and achieving directionality in these fundamental chemical transformations. [ABSTRACT FROM AUTHOR]

Summary: L‐Ascorbic acid (AA) is an essential component for organisms and is responsible for various functions in the human body. Its structure is in a way that suffering significant structural changes during storage. Herein, the stability of L‐ascorbic acid aqueous solution at various thermal (25 and 90 °C ± 2) and atmospheric oxygen or argon was monitored by optical rotation changes as a function of time intervals. Under oxygen, specific optical rotation [α] of the solution was decreased from + 22.0 to + 2.0 after 32 days and under argon + 11.5 after 9 months at 25 °C. The loss of [α] increased at 90 °C under both oxygen and argon atmospheres. Subsequently, the obtained reaction mixtures were evaporated to dryness and analysed by FT‐IR, 1H‐NMR and GC‐MS techniques. Results of these analyses indicate that AA was decomposed to a complex mixture of reaction products. [ABSTRACT FROM AUTHOR]

We present a theoretical study of the ground electronic state potential of the Ca+Ar2 complex and of its photoabsorption spectra, simulated at temperatures ranging between 20 and 220 K. These calculations exploit a Monte-Carlo (MC) method, based on a one-electron pseudo-potential approach. A pairwise additive potential fitted to coupled cluster ab initio points, is used to model the Ca+Ar2 complex. Our study shows that the most stable form of Ca+Ar2 is a bent C2v structure, whereas the linear isomer is located at around 90 ± 10 cm−1 above in energy. The analysis of the photoabsorption spectra establishes that a structural transition from bent Ca+Ar2 to linear ArCa+Ar occurs at T∼100 K. Trends in binding energies of both isomers, bond lengths and bond angles are also discussed. Molecular orbital overlaps provide an explanation for the order of stability between the bent and linear structures. [ABSTRACT FROM AUTHOR]

Arylazopyrazoles show significant potential as next‐generation photoswitches, in particular because of the high thermal stability of their Z‐isomers. Herein we investigate the potential to perform Z−E isomer chemical switching of arylazopyrazoles using acid. We show that acid‐accelerated isomerisation allows for robust Z−E switching using mild acids and opens up the possibility to use light‐acid cycles to near quantitatively and reversibly switch the arylazopyrazoles at room temperature. We attribute the chemical switching to azonium formation, facilitated by mesomeric stabilisation by the pyrazole ring. Coupled with their exceptionally long Z‐isomer half‐lives, we believe our study may open up a wider array of functional opportunities for the arylazopyrazoles. [ABSTRACT FROM AUTHOR]

Highlights • Accurate quantitation of vitamin D 3 requires resolution of vitamin D and previtamin D • Columns that can resolve the four vitamin D forms identified • Equivalent thermal isomerisation of vitamin D 2 and vitamin D 3 to their previtamin forms confirms use of vitamin D 2 as an internal standard. Abstract Conventional methods using HPLC with UV detection have used vitamin D 2 as an internal standard with the expectation that this fully compensates for the heat-dependent equilibrium of vitamin D 3 with its previtamin. Previtamin D has a different spectral absorptivity from vitamin D and may be present in different proportions in samples and standards. Therefore, vitamin D 2 and vitamin D 3 and their previtamin forms must be chromatographically resolved to achieve accurate quantitation of total vitamin D. This study identified four chromatographic columns (ACE C 18 , ACE C 18 AR, Vydac 201 TP C 18 and Polaris C 18 -Ether) with adequate selectivity that should be applied for food testing and further confirmed that both parent vitamins isomerise at the same rate under thermal conditions. [ABSTRACT FROM AUTHOR]

In order to examine competitive photoisomerization, a series of novel photochromic PtII molecules that contain both dithienylethene (DTE) and B(ppy)Mes2 units (ppy=2‐phenylpyridine, Mes=mesityl) were successfully synthesized and fully structurally characterized. Their photochromic properties were examined by UV/Vis, emission and NMR spectroscopy. It was found that the DTE unit in all three compounds is the preferred photoisomerization site, exhibiting reversible photochromism with irradiation. The B(ppy)Mes2 unit does not undergo photoisomerization in these molecules, but likely enhances the photoisomerization quantum efficiency of the DTE moiety through the antenna effect. Extended irradiation with UV light leads to the rearrangement of the ring‐closed isomers of DTE. TD‐DFT computational studies indicate that the DTE photocyclization proceeds via a triplet pathway through an efficient energy transfer process. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract An enzymatic alternative to the chemical synthesis of chiral gem -difluorinated alcohols has been developed. The method is highly effective and stereoselective, feasible at laboratory temperature, avoiding the use of toxic heavy metal catalysts which is an important benefit in medicinal chemistry including the synthesis of drugs and drug precursors. Candida antarctica lipases A and B were applied for the enantioselective resolution of side-chain modified gem -difluorinated alcohols, (R)- and (S)-3-benzyloxy-1,1-difluoropropan-2-ols (1a and 1b), compounds serving as chiral building blocks in the synthesis of various bioactive molecules bearing a gem- difluorinated grouping. The catalytic activity of these lipases was investigated for the chiral acetylation of 1a and 1b in non-polar solvents using vinyl acetate as an acetyl donor. The dependence of the reaction course on various substrate and enzyme concentrations, reaction time, and temperature was monitored by chiral capillary electrophoresis (CE) using sulfobutyl ether β-cyclodextrin as a stereoselective additive of the aqueous background electrolyte. The application of CE, NMR, and MS methods has proved that the complex enzyme effect of Candida antarctica lipase B leads to the thermodynamically stable (S)-enantiomer 1b instead of the expected acetylated derivatives. In contrast, the enantioselective acetylation of racemic alcohol 1 was observed as a kinetically controlled process, where (R)-enantiomer 1a was formed as the main product. This process was followed by enzymatic hydrolysis and chiral isomerisation. Finally, single pure enantiomers 1a and 1b were isolated and their absolute configurations were assigned from NMR analysis after esterification with Mosher's acids. [ABSTRACT FROM AUTHOR]

Sample preparation techniques for the analysis of vitamin D3 in food matrices typically utilise a saponification step, either at room temperature or at elevated temperatures. A calciferol (vitamin D2 or isotope labelled vitamin D3) is generally chosen as the internal standard to compensate for changes of previtamin D3–vitamin D3 isomerisation during analysis, as well as to correct for analyte loss through complex sample preparation steps. Manufacturing practices and processing parameters contribute to previtamin D formation in food products. A significant proportion (5.6–8.3%) of the total vitamin D3 in premixes was found as previtamin D3, indicating that it is likely, depending upon storage temperature and the time since manufacture, that a vitamin D3-fortified food product will contain a similar proportion of previtamin D3 prior to analysis. Conversely, freshly prepared internal standard solutions have low previtamin D levels (< 1%). In lieu of direct measurement, this discrepancy in previtamin D content between the internal standard and analyte forms of vitamin D will lead to analytical bias. To mitigate this as a source of potential error, it is recommended that sample pretreatment steps are appropriately set and controlled. Based on this work, saponification times greater than 300, 120, or 60 min for temperatures of 60, 70, or 80 °C respectively should be employed and that saponification at room temperature be avoided. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Chiral allenes were synthesized from MBH adduct of isatins via Claisen rearrangement for the first time. • The chiral 1,3-substituted allene entity was achieved using (R)-but-3-yn-2-ol. • In adjacent positions three asymmetric centres containing compounds were synthesized. • Four diastereomers due to two asymmetric carbons and one asymmetric chiral allene. • 1,3-Proton shift and Claisen rearrangement were achieved as a one pot condition. Abstract Chiral allenes are synthesized from Morita–Baylis–Hillman adduct of isatin derivatives via Claisen rearrangement for the first time. The chiral 1,3-substituted allene entity is achieved using (R)-but-3-yn-2-ol. The details of the work are elaborately discussed in this letter. [ABSTRACT FROM AUTHOR]

The performance of the extended multi-state (XMS)-complete active space second-order perturbation theory (CASPT2) method has been assessed for the benchmark of a truncated retinal model, the penta-2,4-dieniminium cation (PSB3). This benchmark presents a challenge for multireference electronic structure methods because the wave function character is changing considerably. The assessment comprises ground and excited state pathways of the isomerisation, including transition states and conical intersection (CI) points. It also includes circular paths centred around different CIs, and 2D potential energy scans located in the branching planes. In this work, we compare the performance of the previous formulations of CASPT2, the single-state and the multi-state, with the recently developed XMS-CASPT2. Besides, we have also tested two variants of internal contraction in XMS-CASPT2, namely, the single-state single reference (SS-SR) and multi-state multireference (MS-MR) schemes. In our study, we find that XMS-CASPT2 corrects the artefacts and discontinuities present in other CASPT2 variants. The investigation of a circular loop and 2D potential energy surfaces around the surface crossing point shows that XMS-CASPT2 exhibits a smooth topology at the CI with the correct degeneracy. It also agrees better with the reference method MRCISD+Q in regions of the potential energy surfaces further away from CIs. Another observation is the close agreement between the results from the SS-SR contraction scheme and the more demanding MS-MR scheme. [ABSTRACT FROM AUTHOR]

Conversion of food and beverage (F&B) waste into high fructose syrup (HFS) was proposed in this study. Hydrolysate obtained from saccharification of mixed F&B waste is rich in glucose (260.3 ± 7.8 g L−1) and fructose (54.1 ± 1.6 g L−1) but also contains trace preservatives, caffeine, colourants, ions and soluble proteins. Over 99% of these impurities were removed by adsorption and ion exchange chromatography, followed by enzymatic isomerisation where glucose was converted to reach 50% of fructose content. Pilot scale downstream processing was successfully conducted with more than 89% of sugars recovered from the hydrolysate. Mass balance analysis indicated an overall conversion yield of 0.08 kg HFS per kg of mixed F&B waste and meanwhile the HFS also conforms to industrial standards. This proposed process is believed to promote the development of a circular economy by recycling F&B waste as a renewable resource for HFS production. [ABSTRACT FROM AUTHOR]

Mordenite zeolites with diffusion-restricted access to the acid sites located in mono-dimensional 12-ring channels and 8-ring side pockets have found broad applications as catalysts for hydroisomerisation of linear C 5 and C 6 alkanes and other highly relevant acid-catalysed processes. The accessibility of the porous structure of mordenite (MOR) zeolite is traditionally enhanced by dealumination, but this is invariably connected with a dramatic reduction in the aluminium content and corresponding concentration of the acid sites in the zeolites. Here we describe the preparation of MOR zeolite with high micropore volume, three-dimensional supermicropores (d ∼ 7.5 Å) and good acid site accessibility by concurrent extraction of Si and Al using postsynthesis fluorination-alkaline-acid treatment. The concurrent extraction of Si and Al enables formation of more developed supermicroporous structure and preservation of the molecular Si/Al. The procedure yields MOR with a crystalline structure in which the Si/Al ratio and the micropore volume can be tailored (Si/Al from ∼ 6, V MI up to 0.25 cm 3 .g −1 ) by the chemical conditions of the treatment. The Al-rich 3D supermicroporous structure with accessible Brønsted and Lewis active sites provides strongly enhanced activity, selectivity and long-term catalytic stability in the transformation of n -hexane into the corresponding branched isomers. [ABSTRACT FROM AUTHOR]

Biomolecular homochirality refers to the assumption that amino acids in all living organisms were believed to be of the l -configuration. However, free d -amino acids are present in a wide variety of organisms and d -amino acid residues are also found in various peptides and proteins, being generated by enzymatic or non-enzymatic isomerization. In mammals, peptides and proteins containing d -amino acids have been linked to various diseases, and they act as novel disease biomarkers. Analytical methods capable of precisely detecting and quantifying d -amino acids in peptides and proteins are therefore important and useful, albeit their difficulty and complexity. Herein, we reviewed conventional analytical methods, especially 0 h extrapolating method, and the problems of this method. For the solution of these problems, we furthermore described our recently developed, sensitive method, deuterium-hydrogen exchange method, to detect innate d -amino acid residues in peptides and proteins, and its applications to sample ovalbumin. This article is part of a Special Issue entitled: d -Amino acids: biology in the mirror, edited by Dr. Loredano Pollegioni, Dr. Jean-Pierre Mothet and Dr. Molla Gianluca. [ABSTRACT FROM AUTHOR]

Abstract: In this article we show that the catalytic isomerization of isohexide sugar alcohols as well as their respective ethers can occur by a hydride‐based mechanism rather than a dehydrogenation/re‐hydrogenation. C−H bonds in α‐position to hydroxy and ether groups are activated using Ru/C as solid catalyst at temperatures as high as 160 °C and above. Hydrogen isotope exchange experiments proved that a full hydride exchange and isomerization is possible for isohexides but unexpectedly also for their methyl ethers. This is of great importance as it proves the co‐existence of the both mechanisms for reactions that were so far assumed to occur solely by a dehydrogenation/re‐hydrogenation. Hence, this co‐existence should be taken into account for kinetic investigations of such reaction systems especially in the conversion of biomass‐based chemicals under hydrogenation conditions. [ABSTRACT FROM AUTHOR]

Abstract: Molecules comprised of three covalently linked bi‐stable switches can exist in states described by a combination of binary numbers, one for each individual switch: ⟨000⟩, ⟨001⟩, etc. Here we have linked three photo‐/thermoswitches together in a rigid macrocyclic structure, one azobenzene (bit no 1) and two dihydroazulenes (DHAs; bits no 2 and 3) and demonstrate how electronic interactions and unfavorable strain in some states can be used to control the speed by which a certain state is reached. More specifically, upon irradiation of state ⟨000⟩, the AZB isomerizes from trans to cis and the two DHAs to vinylheptafulvenes (VHFs), generating ⟨111⟩. The thermal VHF‐to‐DHA back‐reactions from this state also occur stepwise and can be accelerated by photo‐induced AZB cis‐to‐trans conversion, proceeding via ⟨011⟩ to ultimately furnish ⟨000⟩. Overall, the accessibility to a specific state of one bit was found to depend on the states of its neighboring bits. [ABSTRACT FROM AUTHOR]

[Display omitted] • H 4 SiW 12 O 40 , WO 3 , TiO 2 and SnO 2 /SiO 2 catalysts were tested in the dehydration of isobutanol. • The catalytic activity was related to the Brønsted acidity and not the Lewis one. • Selectivity to butenes close to 100% was obtained for weak and moderate Brønsted type catalysts. • Linear butenes were mostly obtained through the equilibrium between carbocations. H 4 SiW 12 O 40 heteropolyanions, WO 3 , TiO 2 and SnO 2 were supported over SiO 2 at high loading by wet impregnation or grafting methods and evaluated in the dehydration of isobutanol to butenes. Their structural and textural properties were determined by different techniques such as XRD, TEM, IR, XPS and N 2 liquid physisorption respectively. Most of the prepared compounds contained amorphous oxide clusters of few nanometers lying over SiO 2 and were mesoporous. Their acidic properties (nature, density and strength) were investigated by pyridine and CO adsorption followed by FTIR. H 4 SiW 12 O 40 /SiO 2 contained strong Brønsted acid sites while mostly moderate Lewis acid sites were present on TiO 2 /SiO 2 and SnO 2 /SiO 2. WO 3 /SiO 2 had a mixed character with both moderate Brønsted and Lewis acid sites. The catalytic activity was related to the Brønsted acidity and the best selectivity to butenes close to 100% were obtained for the catalysts containing moderate and weak sites (WO 3 /SiO 2 and TiO 2 /SiO 2). Except for SnO 2 /SiO 2 catalysts, which were unstable and unselective to dehydration products, a significant selectivity to linear butenes (ca 30%) was obtained with all the catalysts. It is proposed that this isomerisation activity is mainly related to the equilibrium between carbocations formed after E 1 elimination of water. Its slight increase for H 4 SiW 12 O 40 /SiO 2 (and to a lesser extent WO 3 /SiO 2) was attributed to strong Brønsted acid sites able to catalyse the isomerization of isobutene to linear butenes. [ABSTRACT FROM AUTHOR]

The impact of desilication on the performance of a series of alkali-treated NaY zeolites impregnated with 5 wt.% of magnesium for glucose isomerisation into fructose has been studied. Desilication at different NaOH concentrations increases the mesoporous volume and external surface area, without compromising microporosity and crystallinity. The observed reduction of the microporous volume due to magnesium impregnation was found to decrease for the alkali-treated zeolites. Higher density and strength of basic sites and stronger magnesium-support interaction were also achieved with the treatment. These improved properties resulted in a significant increase of both glucose conversion and fructose yield on the magnesium-doped desilicated zeolites. Glucose conversion continuously increases with desilication (28–51%), whereas fructose yield passes through a maximum (35%) at low desilication levels. Among the prepared desilicated samples, low-severity alkali-treated zeolites also show lower deactivation in consecutive reaction runs, as well as superior regeneration behaviour. Thus, hierarchical NaY zeolites impregnated with magnesium could be favourably used for glucose isomerisation into fructose if suitable alkaline treatment conditions are selected, with low-severity treated NaY zeolites being the best choice. Higher fructose productivities were achieved for the low-severity desilicated zeolites than for higher magnesium content NaY zeolites reported previously, leading to a lower Mg requirement. [ABSTRACT FROM AUTHOR]

Abstract: A range of cyclopropyl‐fused N‐tosyl piperidines have been synthesised and shown to undergo ring‐opening isomerisation on treatment with platinum(II) catalysts. The products can have either an endo‐cyclic or exo‐cyclic double bond. The selectivity is influenced by reaction temperature, solvent and, most significantly, the catalyst. A mechanism involving C−C bond activation and β‐hydride elimination is proposed. When β‐hydride elimination is blocked, a stereospecific platinum‐driven Wagner–Meerwein shift is observed. [ABSTRACT FROM AUTHOR]

The studies presented in this work offer an insight into xylene isomerization process, followed by 2D COS analysis, in the terms of different acidity of microporous zeolites ZSM-5. The isomerisation reaction proceeded effectively over zeolites ZSM-5 of Si/Al equal of 12 and 32. Among them, the Al-poorer zeolite (Si/Al = 32) was found to offer the highest conversion and selectivity to p -xylene with the lowest number of disproportionation products, both in ortho - and meta -xylene transformation. Further reduction of Brønsted acidity facilitated the disproportionation path (zeolites of Si/Al = 48 and 750). The formation of intermediate species induced by the diffusion constraints for m -xylene in 10-ring channels was rationalized in the terms of the methylbenzenium ions formation inside the rigid micropore environment. Finally, both microporous character of zeolite and the optimised acidity were found to be crucial for high selectivity to the most desired product i.e. p -xylene. The analysis of asynchronous maps allowed for concluding on the order of the appearance of the respective products on the zeolite surface. [ABSTRACT FROM AUTHOR]