Isomerization Process Research Articles

Beyond Photochromism: Alternative Stimuli to Trigger Diarylethenes Switching.

Diarylethenes (DAEs) are typical photochemically reversible type (P-type) photochromic materials with excellent thermal stability and high fatigue resistance and are widely exploited as photo-switches for various applications in molecular devices, data storage, photoresponsive materials, and bioimaging, etc. In recent years, there is an increasing number of reports using heat, acid, electrochemistry, etc. to drive the isomerization reaction of DAEs. The response to two or more different stimuli enables multi-functionality within a single DAE molecule, which would facilitate complex logic-gate operations, multimode data storage, and increased information density. Herein, the recent advances in DAE systems utilizing stimuli "beyond photo" to trigger the isomerization processes from three perspectives: acidochromism, thermochromism, and electrochromism are reviewed. Emphasis is placed on the molecule design strategies and the underlying mechanisms for cyclization and cycloreversion processes addressed by the alternative stimulus. Then the noticeable applications made in multi-stimuli responsive DAE systems are summarized. Additionally, the challenges and opportunities of DAE switches driven by stimuli "beyond photo" in the future are also discussed.

Magnetic‐induced isomerization of paramagnetic bridged azobenzene derivatives with conjugated alkyl chains

AbstractInducing a reversible structural transformation in organic photochromophores under the effect of a magnetic field is challenging owing to their poor magnetic properties. Compared with common azobenzene materials, bridged azobenzene materials exhibit a considerable potential for rapid trans‐cis isomerization induced by an external magnetic field because of the restricted torsion of N=N bonds during the transformation. Herein, we designed and synthesized pentenyl‐grafted bridged azobenzene (BA‐X5), hexenyl‐grafted bridged azobenzene (BA‐X6), and pentynyl‐grafted bridged azobenzene (BA‐Q5). Density functional theory calculations indicate that the activation energy for the trans‐cis transition of BA‐X5 and BA‐X6 is ~18.0 kcal/mol, which is 8.2% lower than that of BA‐Q5 (19.6 kcal/mol). The results obtained using EPR and a superconducting quantum interference device demonstrate that during the isomerization process, a net spin reduction of bridged azobenzene occurred because of the aggregation of the electron cloud toward the C−N bond, leading to a reduction in the paramagnetism of the materials. BA‐X5 and BA‐X6 exhibit a clear and rapid magnetically induced trans‐cis isomerization with short half‐lives, which are 10.4% and 16.9%, respectively, lower than those obtained under dark conditions. In contrast, the isomerization of BA‐Q5 under the effect of the same magnetic field does not change. Magnetically induced isomerization might be attributed to the combined effect of the magnetothermal effect, changes in the net spin density of the electron cloud, and regularity of molecular arrangement under the effect of the magnetic field. These results provide a basis for exploring the design and research of magnetically controlled azobenzene derivatives.

Evolution of Chemistry in the envelope of HOt CorinoS (ECHOS). II. The puzzling chemistry of isomers as revealed by the HNCS/HSCN ratio

The observational detection of some metastable isomers in the interstellar medium with abundances comparable to those of the most stable isomer, or even when the stable isomer is not detected, highlights the importance of non-equilibrium chemistry. This challenges our understanding of the interstellar chemistry and shows the need to study isomeric forms of molecular species to constrain chemical processes occurring in the interstellar medium. Our goal is to study the chemistry of isomers through the sulphur isomer pair HNCS and HSCN, since HSCN has been observed in regions where its stable isomer has not been detected, and the observed HNCS/HSCN ratio seems to significantly vary from cold to warm regions. We used the Nautilus time-dependent gas-grain chemical code to model the formation and destruction paths of HNCS and HSCN in different astrochemical scenarios, as well as the time evolution of the HNCS/HSCN ratio. We also analysed the influence of the environmental conditions on their chemical abundances. We present an observational detection of the metastable isomer HSCN in the Class I object B1-a ($N$=(1.1pm 0.6)times 1012 cm$^ $), but not of the stable isomer HNCS, despite HNCS lying 3200 K lower in energy than HSCN. Our theoretical results show an HNCS/HSCN ratio sensitive to the gas temperature and the evolutionary time, with the highest values obtained at early stages ($t$lesssim 10$^4$ yr) and low ($T_ g $lesssim 20 K) temperatures. A more detailed analysis also shows that the main mechanism forming HNCS in young ($t$$<$10$^5$ yr) and cold ($T_ g $$=$10 K) objects at moderate-low densities ($n$$_ H $leq 10$^5$ cm$^ $) is a grain surface reaction (the chemical desorption reaction N$_ solid $+HCS$_ solid $rightarrow HNCS), unlike previous predictions that suggest only gas-phase chemistry for its formation. However, for the formation of its metastable isomer HSCN, over the same time range and physical conditions, we find that both surface and gas-phase reactions (through the ion H$_2$NCS$^+$) play important roles. In warmer ($T_ g $geq 50 K) regions, the formation of this isomer pair is only dominated by gas-phase chemistry through the ions H$_2$NCS$^+$ (mainly at low densities) and HNCSH$^+$ (mainly at high densities). The results suggest a different efficiency of the isomerisation processes depending on the source temperature. The progressive decrease of HNCS/HSCN with gas temperature at early evolutionary times derived from our theoretical results indicates that this ratio may be used as a tracer of cold young objects. This work also demonstrates the key role of grain surface chemistry in the formation of the isomer pair HNCS and HSCN in cold regions, as well as the importance of the ions H$_2$NCS$^+$ and HNCSH$^+$ in warm/hot regions. Since most of the interstellar regions where HSCN is detected are cold regions (starless cores, Class 0/I objects), a larger sample including sources characterised by high temperatures (e.g. hot cores) are needed to corroborate the theoretical results.

Synthesis of the cis‐ and trans‐3‐Fluoro Analogues of Febrifugine and Halofuginone

The novel synthesis of racemic cis‐ and trans‐3‐fluorofebrifugine and halofuginone is described. This straight‐forward seven‐step process relies on an electrophilic fluorination‐allylation sequence generating a mixture of N‐Cbz protected, diastereomeric 2‐allyl‐3‐fluoropiperidines. On separation, a Wacker oxidation‐methyl functionalisation sequence enabled introduction of the required quinazolinone portion. Finally, removal of the N‐Cbz protecting group lead to isolation of the 3‐fluorofebrifugine dihydrobromide analogues that are of potentially pharmacological use. Analysis of the NMR spectra for each stereoisomer provides information concerning the preferred conformers of the different diastereomers. Evidence indicates that the cis‐diastereomer favours a conformation where the F‐atom occupies an axial orientation. In contrast, for its trans‐stereoisomeric counterpart, the 2‐substituent overrides any F‐atom effect and it preferentially occupies a conformer where both substituents occupy equatorial positions. Finally, interconversion between the cis‐ and trans‐diastereomers was studied. In DMSO‐d6 and as their free‐bases, isomerisation of each diastereomer gave a common 65:35 ratio of trans‐ to cis‐3‐fluorofebrifugine. Determination of the reaction rate constants for the isomerisation process at different temperatures enabled calculation of the activation energy barriers, for each process, using an Arrhenius plot. The activation energy barrier for the isomerisation of the trans‐isomer was 94.3 kJ mol‐1, whereas for the cis‐isomer it was 84.5 kJ mol‐1

A visible light-activated azo-fluorescent switch for imaging-guided and light-controlled release of antimycotics

Azo switches are widely employed as essential components in light-responsive systems. Here, we develop an azo-fluorescent switch that is visible light-responsive and its light-responsive processes can be monitored using fluorescence imaging. Visible light irradiation promotes isomerization, accompanied by changes in fluorescence that enable the process to be monitored through fluorescence imaging. Furthermore, we document that the nanocavity size of liposome encapsulated nanoparticles containing azo changes in the isomerization process and show that this change enables construction of a light-responsive nanoplatform for optically controlled release of antimycotics. Also, natural light activation of nanoparticles of the switch loaded with an antimycotic agent causes death of Rhizoctonia solani. The results show that these nanoparticles can double the holding period in comparison to small molecule antimycotics. The strategy used to design the imaging-guided light-controlled nano-antimycotic release system can be applicable to protocols for controlled delivery of a wide variety of drugs.

Visualization of azobenzene mesogens trans-cis isomerization through structural color of photonic crystal

Azobenzene, a representative photoresponsive liquid crystal, has extensive applications in fields such as bionic robotics, actuators, artificial muscles, motors, and various functional devices. Photoisomerization (trans-cis isomerization) is the most important mechanism for its photoresponse. Currently, the isomerization of azobenzene mesogens can be measured through UV–vis absorption spectra, NMR techniques or transient grating methods. Visualization of the trans-cis isomerization of azobenzene mesogens still remains a challenge. In this study, a linear relationship is observed between the absorption intensity of azobenzene mesogens and the stopband shift of azobenzene inverse opals (AZOIOs) films during the isomerization process. This phenomenon can be used to determine the isomerization degree of azobenzene mesogens through the switching of the stopband of the AZOIOs film, enabling the visualization of the azobenzene mesogens’s configuration transition. The results of this study are highly significant for the design and fabrication of novel azobenzene devices.

Nitrate Enhanced Sulfamethoxazole Degradation by 222 nm Far-UVC Irradiation: Role of Reactive Nitrogen Species.

The application of 222 nm far-UVC irradiation for degrading organic micropollutants in water shows promise. Nitrate (NO3-), found in nearly all water bodies, can significantly impact the performance of 222 nm far-UVC-driven systems. This work was the first to investigate the effect of NO3- on sulfamethoxazole (SMX) photodegradation at 222 nm, finding that NO3- significantly enhances SMX degradation in different dissociated forms. Besides the hydroxyl radical (•OH), reactive nitrogen species (RNS) also played important roles in SMX degradation. With increasing NO3- concentration, the RNS contribution to SMX degradation decreased from 25.7 to 8.6% at pH 3 but increased from 1.5 to 24.7% at pH 7, since the deprotonated SMX with electron-rich groups reacted more easily with RNS. The transformation mechanisms of SMX involving isomerization, bond cleavage, hydroxylation, nitrosation, and nitration processes were proposed. 15N isotope labeling experiments showed that the RNS-induced nitrated products even became the major products of SMX in the 222 nm far-UVC/NO3- system at pH 7 and exhibited a higher toxicity than SMX itself. Further research is necessary to avoid or eliminate these toxic byproducts. This study provides valuable insights for guiding the utilization of 222 nm far-UVC for treating antibiotics in NO3--containing water.

Electro-activation for efficient lactulose production: The impact of operational parameters, electrolyte types, and environmental conditions

The electro-activation (EA) process has been employed to convert lactose into lactulose, a potent prebiotic with numerous health benefits. The study identified optimal conditions for lactulose production, including a specific current density, the use of calcium chloride as an efficient electrolyte, and the superiority of a steel cathode over a graphite cathode. The formation of intermediates other than lactulose increased as the temperature increased. The changes in pH and oxidation-reduction potential during the isomerization process were observed, highlighting their vital role in the formation of an ideal alkaline environment for lactulose production. The resultant solution produced by the EA process has significant antioxidant characteristics, likely due to the formation of Maillard Reaction Products during lactulose production. In conclusion, the EA system, with optimal operating conditions, is an energy-efficient, reagent-free, and environmentally friendly alternative for lactulose production.

Monoterpenoids isomerization and cyclization processes in Gewürztraminer wines: A kinetic investigation at different pH and temperatures

The evolution of volatile compounds in wine comprises several acid-catalyzed reactions, such as glycosides precursors’ hydrolysis and rearrangements, and significantly contributes to its sensory qualities, even after prolonged aging. The aim of this work was to use a well-defined experimental design and to examine how terpenoids in Gewürztraminer wine change over time when subjected to different temperatures and pH levels over two weeks. A theoretically-based approach was used, involving the definition of a complete system of ordinary differential equations (ODE) with well-established boundary conditions (initial concentration of reactants/products), using Kinetiscope, a kinetic simulation software. The calculated optimal rate constants, based on the experimental curves, produced a comprehensive data set describing the evolution of the terpenoid profile, highlighting the reversible and irreversible interconversion processes. Finding revealed that higher pH and lower temperature conditions are crucial for preserving the important terpenoid compounds that characterize the typicality and exemplarity of Gewürztraminer aroma profile.

No Switching Cooperativity between Coordinated Azo Ligands on Complexes Having {MII(phosphane-κ2P)}2+ (M = Pd, Pt) Scaffolds.

A series of square-planar palladium and platinum compounds with cis-blocking phosphanes and terminal azobenzene ligands [M(dppp)(azo)2](OTf)2 (azo = CN(C6H4)-N═N-(C6H4)CN (iso-cyano), CN(C6H4)-N═N-(C6H5) (iso-Ph)) and [{M2(tpbz)}(azo)4](OTf)4 (azo = CN(C6H4)-N═N-(C6H5) (iso-Ph)) have been synthesized and fully characterized. Similarly to the uncoordinated ligands, the new coordination compounds have shown to be photochemically active with respect to their trans-to-cis isomerization process. Their cis-to-trans back spontaneous reaction have been studied as a function of solvent, temperature and pressure and the corresponding activation parameters determined in order to investigate the mechanism of these transformations. The results obtained are indicative of the operation of a rotational mechanism with no cooperativity between the azo ligands attached to the same metal. Density functional theory calculations have been carried out in order to estimate the relative energies of the different photoisomers for the theoretical interpretation of the experimental data.

Optimized energy efficient reactive distillation for octane upgrading with economic and environmental considerations

Advancing fuel efficiency and production technologies can significantly reduce “Well to Wheels” and “Octane on Demand” emissions. This has been accomplished by integrating intensified technologies in fuel refineries. However, maintaining low energy consumption and high octane number while considering the impact of operating conditions under uncertainty on the process feasibility remains a challenge. Therefore, this article proposes a novel absorption heat pump reactive distillation (AHPRD). Aiming to maximize the economic potential of the AHPRD, an optimization framework that considers operating conditions under uncertainty (i.e. temperature (T), pressure (P), reflux ratio (RR), and feed stage (FS)) is developed. The optimization framework synchronizes Monte Carlo simulation and particle swarm optimization (PSO) to maximize the net present value (NPV). The framework used a hybrid Python-DWSim interface platform. The AHPRD was further investigated and compared against existing processes, namely, a conventional process refinery (CP) and reactive distillation (RD), to improve energy saving, increase financial return, and cut CO2 emissions. Attractively, the AHPRD outperforms existing processes, both economically and environmentally, doubling profit values and avoiding 52.2% − 77.4% of CO2 emissions. This study believes that the future direction will be to build an artificial intelligence model for process optimization and economic prediction.

Ru-Catalyzed Asymmetric Hydrogenation of α,β-Unsaturated γ-Lactams.

A highly efficient Ru-catalyzed asymmetric hydrogenation of α,β-unsaturated γ-lactams has been developed by using a C2-symmetric ruthenocenyl phosphine-oxazoline as the chiral ligand. This method achieves the enantioselective synthesis of chiral β-substituted γ-lactams in high yields and with excellent enantioselectivities (up to 99% yield with 99% ee). Mechanistic studies based on detailed control experiments and computational investigation revealed that the cationic Ru-complex acts as the active catalytic species; the protonation process of the oxa-π-allyl-Ru complex, which is formed by the migratory insertion of the C=C double bond to the Ru-H bond (the stereocontrolling step) followed by an isomerization process, is the rate-determining step, and the existence of PPh3 is crucial for the highly efficient catalytic behavior. The protocol provides a straightforward and practical pathway for the synthesis of key intermediates for several chiral drugs and bioactive compounds, particularly for the 150 kg-scale industrial production of Brivaracetam, an antiepileptic drug that shows 13-fold more potent binding to the synaptic vesicle protein 2A compared with the well-known Levetiracetam.

Synthesis of Linoleic Acid of Conjugated Isomers from Sesame (Sesamum Indicum) Seed Oil: Its Use and Effect in a Microstructured Product Type Oil-in-Water Emulsion

The development of functional foods is an area of great interest and innovation in the food industry. The use of conjugated linoleic acid (CLA) in food formulations has been growing in recent years due to its multiple health benefits. In this study, conjugated linoleic acid was obtained from sesame oil, and its use in the formulation of oil-in-water food emulsions was evaluated. Conjugated linoleic acid (CLA) was synthesized from the linoleic acid present in sesame oil using the alkaline isomerization method using proplyeneglycol as a solvent. The effect of alkali concentration (NaOH) and reaction time on the conversion of linoleic acid to CLA was evaluated. A 96.6% conversion of CLA was obtained with a NaOH concentration of 7% and a reaction time of 2 h. Emulsions were prepared using CLA as oil phase and soy lecithin, tween 80, carboxymethylcellulose as emulsifying agents. Emulsions with mixtures of carboxymethylcellulose and tween 80 were stable, presenting a non-Newtonian fluid behavior of pseudoplastic type (n<1). The Ostwald-de-Waele model shows an optimal fit to the experimental data of apparent viscosity (R2>0.99 ), and its microstructural characterization shows a homogeneous particle distribution. These results show that the alkaline isomerization process using propylene glycol as a solvent is an excellent alternative for the synthesis of CLA from vegetable oils such as sesame oil and its application in the development of microstructured products such as functional emulsions, and their subsequent application in the development of new food products with beneficial health characteristics.

An AIE-active Schiff base derivative with reversible thermochromism based on two-step isomerization in the solid state

Thermoresponsive aggregation-induced emission (AIE) luminogens, especially in the solid state, have attracted extensive attention due to their potential applications as smart materials. Herein, we report an AIE-active tetraphenylethene (TPE)-based Schiff base derivative (TPENOMe-I) that exhibits rapid and reversible thermochromism along with luminescence in the solid state. The excited-state intramolecular proton transfer-induced AIE and efficient thermochromism (rather than photochromism) are facilitated by the relatively compact crystal packing and polymorphism of TPENOMe-I, which effectively suppress cis-to-trans isomerization. Theoretical calculations demonstrated that the two-step isomerization process between the enol isomer and the cis- and twisted cis-keto isomers is responsible for the thermochromic behavior of solid-state TPENOMe-I. The chromic transitions may result from the reversible interconversion between various twisted cis-keto forms during the thermal isomerization process. Three composites containing TPENOMe-I that were simply prepared with low cost excited reversible thermochromism and were successfully demonstrated in thermochromic patterns. The findings suggest that these TPENOMe-I composites have promising applications for use in warning labels, thermochromic textiles, and thermal printing.

Efficient Capture and Low Energy Release of NH3 by Azophenol Decorated Photoresponsive Covalent Organic Frameworks.

In NH3 capture technologies, the desorption process is usually driven by high temperature and low pressure (such as 150-200 °C under vacuum), which accounts for intensive energy consumption and CO2 emission. Developing light responsive adsorbent is promising in this regard but remains a great challenge. Here, we for the first time designed and synthesized a light responsive azophenol-containing covalent organic framework (COF), COF-HNU38, to address this challenge. We found that at 25 °C and 1.0 bar, the cis -COF exhibited a NH3 uptake capacity of 7.7 mmol g-1 and a NH3/N2 selectivity of 158. In the adsorbed NH3, about 29.0 % could be removed by vis-light irradiated cis-trans isomerization at 25 °C, and the remaining NH3 might be released at 25 °C under vacuum. Almost no decrease in adsorption capacity was observed after eight adsorption-desorption cycles. As such, an efficient NH3 capture and low energy release strategy was established thanks to the multiple hydrogen bond interactions (which are strong in total but weak in individuals) between NH3 and the smart COF, as well as the increased polarity and number of hydrogen bond sites after the trans-cis isomerization.

Exploring formation of turanose in honey via stable isotope labelling and high-resolution mass spectrometry analysis

Turanose, an isomer of sucrose, naturally exists in honey. Previous study indicated that turanose content increased gradually in acacia honey as honeybees brewed honey in the hive. However, it is unclear how turanose is generated in honey. We hypothesised that turanose was produced by enzymes from honeybees and performed a series of simulation experiments to prove this hypothesis. We found turanose in honey was produced by honeybees processing sucrose. Furthermore, we determined that sugar composition of simulated nectar influenced the turanose concentration in honey: when sucrose concentration was below 5%, turanose was difficult to form, whereas high concentration of fructose and limited glucose were beneficial in producing turanose. Using 13C-labelled sucrose tests combined with proteomics analysis, we identified that α-glucosidase converted sucrose to turanose through an intermolecular isomerisation process. This study reveals the formation mechanism of turanose in honey and assists in the scientific control and improvement of honey quality.

Ultrafast Hot Exciton Nonadiabatic Excited-State Dynamics in Green Fluorescent Protein Chromophore Analogue.

The ultrafast high-energy nonadiabatic excited-state dynamics of the benzylidenedimethylimidazolinone chromophore dimer has been investigated using an electronic structure method coupled with on-the-fly quantitative wave function analysis to gain insight into the photophysics of hot excitons in biological systems. The dynamical simulation provides a rationalization of the behavior of the exciton in a dimer after the photoabsorption of light to higher-energy states. The results suggest that hot exciton localization within the manifold of excited states is caused by the hindrance of torsional rotation due to imidazolinone (I) or phenolate (P) bonds i.e., ΦI- or ΦP-dihedral rotation, in the monomeric units of a dimer. This hindrance arises due to weak π-π stacking interaction in the dimer, resulting in an energetically uphill excited-state barrier for ΦI- and ΦP-twisted rotation, impeding the isomerization process in the chromophore. Thus, this study highlights the potential impact of the weak π-π interaction in regulating the photodynamics of the green fluorescent protein chromophore derivatives.

Monitoring cis-to-trans isomerization of azobenzene using Brillouin microscopy

Brillouin spectroscopy is commonly used to study the acoustic properties of materials. Here we explored its feasibility in studying the photoinduced isomerization of azobenzene. The isomerization of azobenzene changes the solution elastic modulus, and Brillouin scattering is sensitive to these changes. In this study, we experimentally demonstrated the photoswitching of azobenzene in DMSO using our home-made virtually imaged phased array-based high-resolution optical Brillouin spectrometer, and confirmed the results by ultraviolet–visible spectrophotometry. Remarkable Brillouin frequency shift variations were quantitatively recorded upon irradiation, and it was found that this method can indeed be used to monitor the isomerization process in situ. Importantly, our strategy also allows us to provide the relationship between the fraction of trans- and cis- azobenzene and the Brillouin frequency shift. This shows that Brillouin spectroscopy has broad prospects for the characterization of azobenzene isomerization and other photoresponsive materials.

Optimization of Liquid Fructose Sugar Production from Cassava Peel Waste using the Isomerization Process

Optimization of Liquid Fructose Sugar Production from Cassava Peel Waste using the Isomerization Process

Thermal isomerization of astaxanthin esters in the green alga Haematococcus lacustris without any chemicals

Recent evidence indicates that carotenoid Z-isomers have higher oral bioavailability and biological activity than the all-E-isomers. Therefore, many researchers have investigated the development of efficient carotenoid isomerization techniques, primarily thermal treatment. However, most of them studied the free form of carotenoids. In this study, the thermal isomerization characteristics of astaxanthin esters derived from the food-grade Haematococcus alga were investigated. For practical applications, edible oils were used as the medium in the isomerization process, and organic solvents or other chemicals were not used. Furthermore, a continuous heated flow isomerization system was installed. The optimal heating conditions increased the total Z-isomer ratio of astaxanthin esters to approximately 60% while inhibiting astaxanthin decomposition. The resulting Z-isomer-rich astaxanthin esters displayed excellent storage stability. The stability was shown to be potentially higher than that of the free form. This superior stability of the Z-structure of ester forms was demonstrated by density-functional theory. The observations of this study would contribute to the practical applications of Z-isomer-rich astaxanthin materials.