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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 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]

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]

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]

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]

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]

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]

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]

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]

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]

Hopanoids are pentacyclic triterpenoids produced by a wide range of bacteria. Within modern settings, hopanoids mostly occur in the biological 17β,21β(H) configuration. However, in some modern peatlands, the C 31 hopane is present as the ‘thermally-mature’ 17α,21β(H) stereoisomer. This has traditionally been ascribed to isomerisation at the C-17 position catalysed by the acidic environment. However, recent work has argued that temperature and/or hydrology also exert a control upon hopane isomerisation. Such findings complicate the application of geohopanoids as palaeoenvironmental proxies. However, due to the small number of peats that have been studied, as well as the lack of peatland diversity sampled, the environmental controls regulating geohopanoid isomerisation remain poorly constrained. Here, we undertake a global approach to investigate the occurrence, distribution and diagenesis of geohopanoids within peat, combining previously published and newly generated data (n = 395) from peatlands with a wide temperature (−1 to 27 °C) and pH (3–8) range. Our results indicate that peats are characterised by a wide range of geohopanoids. However, the C 31 hopane and C 32 hopanoic acid (and occasionally the C 32 hopanol) typically dominate. C 32 hopanoic acids occur as αβ- and ββ-stereoisomers, with the ββ-isomer typically dominating. In contrast, C 31 hopanes occur predominantly as the αβ-stereoisomer. These two observations collectively suggest that isomerisation is not inherited from an original biological precursor (i.e. biohopanoids). Using geohopanoid ββ/(αβ + ββ) indices, we demonstrate that the abundance of αβ-hopanoids is strongly influenced by the acidic environment, and we observe a significant positive correlation between C 31 hopane isomerisation and pH ( n  = 94, r 2  = 0.64, p < 0.001). Crucially, there is no correlation between C 31 hopane isomerisation and temperature. We therefore conclude that within peats, αβ-hopanoids are acid-catalysed diagenetic products and their occurrence at shallow depths indicates that this isomerisation is rapid. This shows that geohopanoid ββ/(αβ + ββ) indices can be used to reconstruct pH within modern and ancient peat-forming environments. However, we only recommend using ββ/(αβ + ββ) indices to interrogate large amplitude (>1 pH unit) and longer-term (>1 kyr) variation. Overall, our findings demonstrate the potential of geohopanoids to provide unique new insights into understanding depositional environments and interpreting terrestrial organic matter sources in the geological record. [ABSTRACT FROM AUTHOR]

• Thermal isomerisation of pyrethrin I and II occurs in the injector and on-column. • Elevated injector T leads to greater production of isopyrethrin I and II isomers. • Above an oven T of about 200 °C, on-column isomerisation occurs. • GC×GC provides a valuable means for interpretation of the isomerisation process. • Natural pyrethrin retention index data on various column phases are investigated. This study aims to assess and qualitatively compare the visual presentation of chromatographic data from the isomerisation of natural pyrethrins – a group of pesticides derived from Chrysanthemum flowers – using one-dimensional gas chromatography (1DGC) and comprehensive two-dimensional gas chromatography (GC×GC). Molecular structural changes, such as thermal isomerisation in this case, occur during gas chromatography injection and separation, to provide characteristic patterns which may not be routinely recognised on the 1D chromatogram. To demonstrate the influence of analytical method parameters on isomerisation processes, variations in oven temperature (isothermal vs. temperature programmed analysis), inlet mode (split vs. splitless), inlet temperature, and carrier gas flow rate were investigated. Increasing oven temperature was the most significant factor affecting isomerisation. Splitless injection mode and increasing inlet temperature promoted isopyrethrin formation, while the effect of inlet temperature appeared minimal with a split injection technique, most likely due to the short residence time in the inlet. Increased carrier gas flow rates in a temperature programmed analysis reduced retention time and minimised isomerisation. The unique presentation of isopyrethrin peaks on a GC×GC contour plot allows for facile recognition of isomerisation especially at low concentrations, simplifies chromatogram interpretation, and aids in analyte identification. It also confirms that the isomerisation process is irreversible since the pyrethrin I and II compounds are absent throughout the bridge formation. These benefits support the use of GC×GC over 1DGC to study isomerisation. Additionally, due to limited data in the literature, Kováts retention indices and linear retention indices of the natural pyrethrins, including isopyrethrins, were experimentally determined on four columns: DB-5 ms UI, Rxi-17Sil MS, SLB-IL60i, and SLB-IL111i. [ABSTRACT FROM AUTHOR]

Magnesium-impregnated NaY, NaMOR, NaBEA, NaZSM-5 and NaFER zeolites have been prepared and investigated for glucose isomerisation into fructose. It was shown that better magnesium dispersion and smaller reduction of textural properties were obtained with three-dimensional rather than with mono- and two-dimensional zeolites. MgO particle size was also observed to be dependent on the zeolite structure. Various contributions were found to affect the final catalyst performances: availability of MgO, the strength of basic sites, location where the reaction takes place, and the extent of homogeneous reaction due to Na and Mg leaching. Higher glucose conversions were achieved over the MOR, BEA and ZSM-5 zeolites (37–39%), while Y and FER zeolites presented a relatively moderate performance (28 and 27%). In general, lower fructose selectivities were reached for the most active samples, except for the ZSM-5 zeolite. For this catalyst, the reaction appeared to take place mostly on the external surface due to the smaller pore size. Among the various structures investigated, 5%MgNaY zeolite revealed the most resistance to MgO particle size agglomeration during consecutive reaction runs. In addition, 5%MgNaY was found to be the only catalyst capable of recovering its initial activity when regenerated at high temperature. Thus, the type of zeolite structure selected as support for MgO appears to have a significant effect on the catalyst performance for the glucose isomerisation into fructose, with Y zeolite being the most attractive choice for this application. [ABSTRACT FROM AUTHOR]

Isomerisation of n -hexane was studied in the presence of acid and bifunctional metal-acid catalysts based on Keggin-type heteropoly acids (HPA), in particular focusing on Cs 2.5 H 0.5 PW 12 O 40 (CsPW) and Pt/CsPW as the catalysts, using a fixed-bed microreactor under differential conditions ( n -hexane conversion ≤ 10%) at 180–220 °C, ambient pressure and a ratio of n -hexane and H 2 partial pressures of 0.06–0.24. The turnover rate of HPA-catalysed isomerisation was found to correlate with the acid strength of HPA (initial enthalpy of ammonia adsorption). Bifunctional Pt-HPA catalysts were more efficient than monofunctional HPA catalysts. In the isomerisation over Pt/CsPW bifunctional catalyst, n -hexane dehydrogenation step was found to equilibrate at a molar ratio of Pt and H + surface sites Pt s /H +  ≥ 0.8, corresponding to a Pt loading ≥6%. Bimetallic PtAu/CsPW catalyst showed higher activity in n -hexane isomerisation than Pt/CsPW, although the Au alone without Pt was inert. In the presence of Au, the turnover rate at Pt sites increased more than twofold. The effect of Au is attributed to PtAu alloying. Scanning transmission electron microscopy–energy dispersive X-ray spectroscopy (STEM-EDX) and X-ray diffraction (XRD) analyses of PtAu/CsPW indicated the presence of bimetallic PtAu nanoparticles with a wide range of Pt/Au atomic ratios. [ABSTRACT FROM AUTHOR]

An effective method of dehydrating 9_-hydroxyandrost-4-ene-3,17-dione by mineral acids in organic solvents, producing essentially quantitative formation of androsta-4,9(11)-diene-3,17-dione is proposed. Quantitative isomerization of the side product androsta-4,8(9)-diene-3,17-dione to target product was shown to be pssible. [ABSTRACT FROM AUTHOR]

BACKGROUND Lactulose, a bioactive lactose derivative, has been widely used in food and pharmaceutical industries. Isomerisation of lactose to lactulose by cellobiose 2-epimerase ( CE) has recently attracted increasing attention, since CE produces lactulose with high yield from lactose as a single substrate. In this study, a new lactulose-producing CE from Caldicellulosiruptor obsidiansis was extensively characterised. RESULTS The recombinant enzyme exhibited maximal activity at pH 7.5 and 70 °C. It displayed high thermostability with Tm of 86.7 °C. The half-life was calculated to be 8.1, 2.8 and 0.6 h at 75, 80, and 85 °C, respectively. When lactose was used as substrate, epilactose was rapidly produced in a short period, and afterwards both epilactose and lactose were steadily isomerised to lactulose, with a final ratio of 35:11:54 for lactose:epilactose:lactulose. When the reverse reaction was investigated using lactulose as substrate, both lactose and epilactose appeared to be steadily produced from the start. CONCLUSION The recombinant CE showed both epimerisation and isomerisation activities against lactose, making it an alternative promising biocatalyst candidate for lactulose production. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The performance of magnesium-impregnated NaY zeolite catalysts for the glucose isomerisation into fructose at 100 °C has been evaluated. Although crystallinity and textural properties of the zeolites are reduced through Mg addition, glucose conversion improves (6–49%) by increasing magnesium content (0–15 wt.%) due to an increase of the number of basic sites. Conversely, selectivity to fructose drops (96–66%). Nevertheless, good fructose yields were still reached with 10 and 15 wt.% of magnesium (about 32%), being similar or even higher than those found for a commercial hydrotalcite and a pure magnesium oxide. Catalysts lose performance through carbon retention and cations leaching. Deactivation of magnesium-based zeolites was further investigated by consecutive reaction runs. If no regeneration of the catalyst is performed, the activity of the zeolites decreases mainly as a result of cations leaching, the effect reducing with the number of runs. Regeneration allows the catalyst to recover almost totally its initial activity. Interestingly, used samples show higher fructose selectivity due to the additional pore opening resulting from cations leaching and/or carbon removal. Cations leaching results in a homogeneous catalytic reaction which is most significant for the highest magnesium content. Magnesium-based NaY zeolites are revealed as potential catalysts for glucose isomerisation into fructose with high fructose productivities and good performance in consecutive reactions combined with intermediate regeneration. [ABSTRACT FROM AUTHOR]

We report the role of hydrogen spillover in n-hexane isomerisation over carbon nanotubes or SiC mixed with hierarchical zeolite beta. Here we infer that: (1) hydrogen spillover is a necessary step; (2) spilled-over H hydrogenates isomerised olefin at Brønsted acid sites only; and (3) closeness between acid and metal sites at the nanoscale enhances the rate of reaction, though this is not a requirement for this reaction to proceed. The economic advantage of the spillover phenomenon (necessitating less Pt on the catalyst) has been highlighted. [ABSTRACT FROM AUTHOR]

Pt-promoted S2O82-/ZrO2-Al2O3 (SZA) catalysts were successfully prepared by the microemulsion (Pt-SZA-M) and impregnation (Pt-SZA-I) methods. The effects of the preparation parameters (surfactant-to-oil ratio, surfactant-to-cosurfactant ratio, types of cosurfactant and oil phase, etc.) on the catalytic activity of Pt-SZA-M catalysts in the isomerisation of n-pentane were investigated. The results showed that the optimal catalyst preparation conditions were: a cetyltrimethylammonium bromide (CTAB)/n-butanol mass ratio of 4:6, a (CTAB + n-butanol)/cyclohexane mass ratio of 3:7, a content of H2PtCl6 solution in microemulsion of 3.6 wt% and a N2H5OH/H2PtCl6 molar ratio of 25:1. A comparison of the isopentane yield for Pt-SZA-M with that for Pt-SZA-I was also performed. The results showed that the microemulsion method led to smaller and more uniform Pt particles (4.5 nm) on the SZA. In comparison with Pt-SZA-I, the isopentane yield for Pt-SZA-M was increased by 13.5% at 180 °C, showing the catalytic performance of Pt-SZA-M at lower temperature was improved significantly. At a reaction temperature of 230 °C, a pressure of 2.0 MPa, a hydrogen/n-pentane molar ratio of 4:1 and a weight hourly space velocity of 1.0 h-1, the yield of isopentane for Pt-SZA-M reached 60.8%. [ABSTRACT FROM AUTHOR]

Bifunctional Ni-S2O82-/ZrO2-Al2O3 (Ni-SSZA) solid superacid catalysts were prepared by microemulsion (Ni-SSZA-M) and impregnation (Ni-SSZA-I) methods and their performance for n-pentane isomerisation was studied. The catalysts were characterised by BET, XPS, XRD, FTIR, Py-FTIR, TPR, TEM and CO uptake. The results show that, compared with the Ni-SSZA-I catalyst, the Ni-SSZA-M catalyst shows smaller and more uniform Ni particles, higher surface area, smaller crystallite size of tetragonal ZrO2, more metal active sites and stronger acidity. The activity test indicated that loading Ni by the microemulsion method can significantly improve the isomerisation activity of the catalyst at lower reaction temperatures. In comparison with the Ni-SSZA-I catalyst, the isopentane yield for Ni-SSZA-M was improved by 11.6% and the optimum temperature was decreased by 60 °C. [ABSTRACT FROM AUTHOR]

Large zeolite crystals of ferrierite have been used to study the deactivation, at the single particle level, of the alkyl isomerisation catalysis of oleic acid and elaidic acid by a combination of visible micro-spectroscopy and fluorescence microscopy (both polarised wide-field and confocal modes). The large crystals did show the desired activity, albeit only traces of the isomerisation product were obtained and low conversions were achieved compared to commercial ferrierite powders. This limited activity is in line with their lower external non-basal surface area, supporting the hypothesis of pore mouth catalysis. Further evidence for the latter comes from visible micro-spectroscopy, which shows that the accumulation of aromatic species is limited to the crystal edges, while fluorescence microscopy strongly suggests the presence of polyenylic carbocations. Light polarisation associated with the spatial resolution of fluorescence microscopy reveals that these carbonaceous deposits are aligned only in the larger 10-MR channels of ferrierite at all crystal edges. The reaction is hence further limited to these specific pore mouths. [ABSTRACT FROM AUTHOR]

Quantitative 1 H selective saturation transfer NMR spectroscopy ( 1 H SST qNMR) was used to fully describe the milieu dependent dynamics of the isomeric system of d -erythrose. Thermodynamic activation parameters are calculated for acidic as well as for basic catalysis combining McConnell's modified Bloch equations for the chemical exchange solved for the constraint of saturating the non-hydrated acyclic isomer, the Eyring equation and Hudson's equation for pH dependent catalysis. A detailed mathematical examination describing the milieu dependent dynamics of sugar isomerisation is provided. Thermodynamic data show evidence that photo-catalysed sugar isomerisation as well as degradation has to be considered. Approximations describing the pH and temperature dependence of thermodynamic activation parameters are derived that indicate the possibility of photo-affecting equilibrium constants. Moreover, the results show that isomerisation dynamics are closely related to degradation kinetics and that sugars' reactivities are altered by the concentration of acyclic carbonyl isomer and the sum of its ring closing rate constants. Additionally, it is concluded that sugar solutions show a limited self-stabilising behaviour. [ABSTRACT FROM AUTHOR]

At 300–500 °C, three C-thiolated closo -dicarbadodecaborane isomers 1-(HS)-1,2-C 2 B 10 H 11 ( 1- o ), 1-(HS)-1,7-C 2 B 10 H 11 ( 1- m ), and 1-(HS)-1,12-C 2 B 10 H 11 ( 1- p ), and two B-thiolated isomers 9-(HS)-1,7-C 2 B 10 H 11 ( 9- m ) and 9-(HS)-1,2-C 2 B 10 H 11 ( 9- o ) show two types of reaction: first, removal of an SH group from the closo -dicarbadodecaborane skeleton, and second, skeletal isomerizations from ortho to meta to para that lead to new isomers. A previously unreported SH skip from carbon-to-boron is also observed. The effect of the thiol group on the skeletal rearrangement is discussed. The isomerisation products are assigned on the basis of correlation of their computationally obtained dipole moments with their gas-chromatographic retention times. Computational results on molecular energies for the mono-thiolated species show good agreement between the calculated relative stabilities and the incidence and relative quantities of the isomerization products. Two of the starting B-thiolated isomers, 9- o and 9- m , were characterized using single-crystal X-ray diffraction analyses and their crystallographic packings as well as some selected structural parameters are discussed. All starting compounds were characterized using multinuclear NMR spectroscopy. [ABSTRACT FROM AUTHOR]

The isomerisation of β-pinene oxide was studied over supported ionic liquid catalysts (SILCAs) consisting of Lewis acids in immobilized ionic liquid. SILCAs were demonstrated as efficient catalysts for the transformation of β-pinene oxide to myrtanal with the product distribution and activity being dependent on the nature of the ionic liquid and Lewis acid strength of catalytic species. With the catalyst ZnCl 2 /[N(3-OH-Pr)Py][NTf 2 ]/ACC, the highest myrtanal molar yield obtained was 68%. [ABSTRACT FROM AUTHOR]

We report the structures and analytical data for several highly branched isoprenoid (HBI) mono- and di-unsaturated alkenes (monoenes and dienes). This has been achieved by isolating several well characterised HBI dienes from diatom cultures and sediments, and transforming these to structurally related monoenes and other dienes using partial hydrogenation and clay-catalysed, or diphenyl disulphide induced, isomerisation reactions. HBI double bond (DB) positions have been determined through analysis of a combination of GC–MS and NMR data, along with RuO 4 oxidation of HBI monoenes that produce characteristic ketones. Our structural identifications have also enabled the assignments of a number of previously reported HBI monoenes and dienes to be confirmed or corrected. Monoenes and dienes undergo clay-catalysed isomerisation in the laboratory, which likely has implications for the sedimentary occurrences of such biomarkers. Under our conditions, alkenes with C6/17 DBs are particularly sensitive to isomerisation, yielding isomers with C5/6, C6/7, C7/8 and C7/20 DBs. Isomers with C5/6 and C7/20 DBs also isomerise with each other and to isomers with C6/7 and C7/8 DBs, but not to ones with a C6/17 DB. In contrast, we see no evidence for isomerisation of the Arctic sea ice biomarker IP 25 which has a DB at C23/24. These observations may have implications for the use of certain monoenes (e.g. IP 25 ) and dienes for paleo sea ice reconstruction. A scheme to summarise the (monoene) isomerisation reactions is proposed. On the basis of the usual DB positions in HBIs obtained from diatom cultures, the outcomes from our isomerisation reactions, and of previous sedimentary reports, we discuss the potential origins (biogenic versus sedimentary transformation) of HBIs with different DB positions. However, confirmation of such assignments will require further investigation. [ABSTRACT FROM AUTHOR]

The subject of our investigation was the intensity of the fluorescence of 1,4,5,8-naphtalisoimides subjected to gamma radiation (the absorbed doses were 242 Gy, 1 kGy and 2.242 kGy). Dynamic changes of fluorescence intensity have been observed; the greatest relative increase of fluorescence intensity (and simultaneously, the least durable increase) occurs as a result of structural isomerisation. [ABSTRACT FROM AUTHOR]

The lycopene content in food may be increased by thermal and mechanical processing. Food processing is beneficial because it disrupts food matrices facilitating the release and solubilisation of lycopene resulting in increased carotenoid bioavailability for the formation of cis-isomers. A lycopene-rich and β-carotene oil-based system was used in this study. High-performance liquid chromatography (HPLC) and colour coordinates analyses were employed to analyse lycopene, its cis-isomers and β-carotene stability of the following sample set after 28 days of storage: fridge temperature at 1 ± 1°C in absence of light (FT dark), ambient temperature at 20 ± 1°C in natural light with different day and night illumination (AT light), ambient temperature at 20 ± 1°C in absence of light (AT dark), thermostatically controlled temperature at 37 ± 1°C in absence of light (TT dark) and thermostatically controlled temperature at 37 ± 1°C in UV irradiation (TT UV). The control sample in our study was lycopene enriched oil stored in the dark at 1 ± 1°C on day zero (0). The aim of this study was to create lycopene-enriched oil from tomato to investigate its stability and to prepare the recommendations to consumers for the storage conditions of this functional food. The results indicated that the trans-lycopene amount changed from 76.6% to 61.0% at ambient temperature (AT light and AT dark sample), and from 76.6% to 46.8% (TT dark) and 44.4% (TT UV) at 37 ± 1°C. According to our investigation, the highest percentage of 5-cis-lycopene isomer in all samples was found after 28 days of storage. The TT UV samples had the most colour changes. Vegetable oil enriched with lycopene from tomatoes is a high quality food product that can supplement daily diet and enhance absorption of lycopene from the intestine. [ABSTRACT FROM AUTHOR]

The photophysics, photochemistry and thermal stability of four 1-aryl-2-( N -methyl-2-benzothiazolium) ethene iodides (aryl: phenyl, 1-naphthyl, 9-phenanthryl and 9-anthryl) were studied. Although the absorption spectra are found to be hypsochromic-shifted, fluorescence spectra are bathochromic-shifted. The dipole moment in the relaxed excited state was found to be larger than that in the ground state. To investigate effects of N -methylation and the aryl-ring size, a detailed comparison was made between those in the present work (of charged compounds) and previous studies of their neutral analogues, with computed electron affinity and ionisation potentials serving to rationalise the experimentally observed bathochromic shifts in absorption and emission spectra. The kinetics of thermal isomerisation depend strongly on the nature of the aryl moiety and solvent; the larger the aryl ring, the slower the rate of isomerisation. The fastest isomerisation process was found to take place in MeOH. The anthryl derivative did not isomerize either by light- or heat-exposure, due to high energy barriers of rotation around the ethenic bond. Based on the significant blue-shift of the Z -isomer absorption maximum relative to that of the E -isomer, and the high percentage of Z -isomers in the photostationary state, these compounds may serve as potential promising candidates for optical data-storage applications. [ABSTRACT FROM AUTHOR]

The isomerisation of α-pinene oxide has been intensively investigated for selective preparation of campholenic aldehyde, a compound used in the synthesis of fragrances. Selective preparation of another product of α-pinene oxide rearrangement, trans -carveol, still remains a challenging task. Trans -carveol is a highly valuable compound used in perfume bases, food flavour compositions and as an active pharmaceutical substance in chemoprevention of mammary carcinogenesis. In the present work zeolite beta with different SiO 2 /Al 2 O 3 molar ratios was modified by iron, characterised and tested per se and in the modified form for trans -carveol preparation from α-pinene oxide. The isomerisation reaction was carried out in a polar basic solvent N , N -dimethylacetamide at 140 °C. The activities and selectivities of the catalysts were correlated with their acid properties and with the iron content. [ABSTRACT FROM AUTHOR]

The [Ru(CO)H(PNN)] pincer complex based on a dearomatised PNN ligand (PNN: 2-di- tert-butylphosphinomethyl-6-diethylaminomethylpyridine) was examined for its ability to isomerise alkenes. The isomerisation reaction proceeded under mild conditions after activation of the complex with alcohols. Variable-temperature (VT) NMR experiments to investigate the role of the alcohol in the mechanism lend credence to the hypothesis that the first step involves the formation of a rearomatised alkoxide complex. In this complex, the hemilabile diethylamino side-arm can dissociate, allowing alkene binding cis to the hydride, enabling insertion of the alkene into the metal-hydride bond, whereas in the parent complex only trans binding is possible. During this study, a new uncommon Ru0 coordination complex was also characterised. The scope of the alkene isomerisation reaction was examined. [ABSTRACT FROM AUTHOR]

Linear isomers of C6N radical differ in the position of the nitrogen atom in the carbon chain of C6N. Reaction routes, involving intramolecular nitrogen atom insertion at varying position in the carbon chain of C6N, are analyzed for the isomerisation between linear isomers of C6N. Through an automated and systematic search performed with global reaction route mapping of the potential energy surface, thermal isomerisation pathways for C6N radical are proposed based on the computations carried out at CASSCF/aug-cc-pVTZ, and CCSD(T)/6-311++G(d,p)//B3LYP/6-311++G(d,p) levels of the theory. Notably, a high lying linear isomer, centrosymmetric with respect to the nitrogen atom, is observed to be stabilized by a unique crossover three center-four electron π long bond between the carbon atoms that are spatially separated by a nitrogen atom in a natural bond orbital. This long bond is concluded to be responsible for the predicted thermal isomerisation to be more feasible than the dissociation during the isomerisation pathway of a linear isomer of C6N. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

This review examines recent studies of the spectroscopy, dynamics, reactivity and electronic structure of iso-halocarbons, which are isomers of organic halogens that are critically important reactive intermediates in the chemistry of these species. We approach this review from the viewpoint of isomerisation as electron transfer, in as much as the dominant resonance structure of the isomer is an ion pair of halocarbenium ion and halide anion. We show that this perspective is important in understanding the spectroscopy, dynamics and chemical reactivity of the iso-halocarbons. We examine experimental methods for study of the isomer, focusing on the complementary nature of steady state matrix isolation experiments and time-resolved studies, typically carried out in solution. We review experimental data concerning the solvent dependence of the isomer lifetime in solution, examine SN1 style nucleophilic reactions of the isomer with water and related solvents, discuss the role of the isomer as methylene transfer agent in cyclopropanation reactions and probe the possible role of the isomer in photoinduced halogen exchange. We then discuss the role of the isomer in the gas-phase chemistry and photochemistry of halocarbons, where isomerisation is demonstrated as a path to molecular elimination. Moving beyond the polyhalomethanes, we describe the existence of proton-coupled electron-transfer pathways involving the isomer in the gem-dihaloethanes, examine the potential importance of spin-orbit coupling and the role of triplet states and briefly discuss the potential importance of similar isomeric structures in other organic molecules. We conclude with future perspectives and research on this intriguing class of intermediates. [ABSTRACT FROM PUBLISHER]