Fast Isomerization Research Articles

Conformational transformations of N-[arylsulfonylimino(methyl)methyl]-1,4-benzoquinonemonoimines

In solutions of N-[arylsulfonylimino(methyl)methyl]-1,4-benzoquinonemonoimines, several Z,E-isomerization processes occur simultaneously: a fast inversion isomerization process (topomerization) relative to the C=N1 quinoneimine bond; a slow inversion isomerization process relative to the C=N2 exocyclic bond; and a process of inhibited rotation around the =N1–С= bond that connects two imine fragments. In the 1H NMR spectra, isomerization with respect to the C=N2 exocyclic bond was only detected. The theoretical values of the isomerization barriers for the C=N1 and C=N2 bonds, as well as for the inhibited rotation around the =N1–C= bond were determined, along with the experimental Z,E-isomerization barriers for to the C=N2 bond. It was established that in the 1H NMR spectra for N-[arylsulfonylimino(methyl)methyl]-1,4-benzoquinonemonoimines, only Z, E-isomerization relative to the C=N2 bond can be observed.

Dynamic surface gratings for optical encryption: A simple approach based on azobenzene photoisomerization and solvent engineering

Dynamic diffraction gratings are optical devices that allow for non-mechanical, non-contact and remote on-demand control, and have garnered significant interest in optical encryption. Azobenzene materials are ideal materials for developing dynamic gratings owing to the advantages of fast photo isomerization and good reversibility. It is still challenging to precisely fabricate ordered periodic gratings on the surfaces of azobenzene materials. Here, controllable dynamic grating patterns were successfully fabricated by mask exposure and solvent engineering on azobenzene polyamide acid (PAA-Azo)-solvent system. The movement and mass migration of polymer chains can be regulated by modulating the intermolecular hydrogen bonding and free volume based on different solvents and solvent contents within the system, resulting in the formation of surface gratings with customizable morphology and light-splitting ability. Finally, by regulating the periodicity and amplitude of gratings, colorful dynamic patterns were obtained to monitor the expiration of light-sensitive and short shelf-life products, based on the azobenzene polyamide acid (PAA-Azo)-solvent system. This work provides a new and simple approach for controllable preparation of high-regularity and high-performance dynamic gratings.

Light-Triggered Reversible Swelling of Azobenzene-Containing Block Copolymer Worms via Confined Deformation Prepared by Polymerization-Induced Self-Assembly.

Stimuli-responsive block copolymer nanoparticles (NPs) have received close attention in recent years owing to their tremendous application potential in smart materials. Azobenzene-containing NPs are widely studied due to the advantages of light as a stimulus and fast reversible trans-cis isomerization of azobenzene chromophores. However, the inefficient preparation process and difficult reversible transformation of morphologies limit their development. Herein it is demonstrated that the light-triggered reversible swelling behavior of wormlike NPs with high azobenzene content could be realized via confined deformation. These worms are prepared in large quantities via polymerization-induced self-assembly based on the copolymerization of 11-(4-(4-butylphenylazo)phenoxy)undecyl methacrylate (MAAz) and N-(methacryloxy)succinimide (NMAS) monomers. Upon UV/visible light irradiation, the reversible deformation of worms is achieved when the feed molar ratio of NMAS/MAAz is relatively high or via crosslinking using diamines, which leads to the reduction of the photoisomerization efficiency. The diameter variation of the worms is influenced by the amount and types of crosslinkers. Moreover, the scalability of this strategy is further proved by the fabrication of photo- and reductant-responsive crosslinked worms. It is expected that this study not only provides a new route to affording reversible photoresponsive NPs but also offers a unique insight into the reversible photodeformation mechanism of azobenzene-containing NPs.

Molecular design of a solvent-free spiropyran-containing DNA material with triple external stimuli-responsive behavior

External stimuli-responsive behavior allows smart materials to gain controllable physicochemical changes. Compared to single stimulus response, the multiple stimuli-responsive behavior makes materials suitable for accommodating different environments, which is highly desired but appreciably more difficult to be addressed. In this study, a spiropyran-containing ammonium surfactant SPA is designed and synthesized for the electrostatic complexation with DNA, affording the ionic biomaterial DNA-SPA with a triple stimuli-responsive behavior. The treatments of UV irradiation and heating can promote fast ring-opening isomerization of DNA-SPA by giving distinct orange-to-purple color change. These properties make DNA-SPA a good candidate biomaterial for information recording and temperature indication. DNA-SPA also responds to humidity by showing linear fit between absorption intensity and relative humidity, providing the potential use as a hygrometer. The half-life of the ring-opening isomer of DNA-SPA favors the stable indications of UV irradition, temperature and humidity, and the sensitivity of ring-opening isomer to Vis light promotes the recyclable use of such biomaterial. This study provides a designing strategy for the fabrication of multiple external stimuli-responsive functional materials, opening a new pathway for gaining smart biomaterials capable of working in various fields.

A Molecular Modeling Study into Brønsted and Lewis Acid Catalyzed Conversion of CBD into Other Cannabinoids

A Molecular Modeling Study into Brønsted and Lewis Acid Catalyzed Conversion of CBD into Other Cannabinoids

Regioselective Hydroxylation of Unsymmetrical Ketones Using Cu, H2O2, and Imine Directing Groups via Formation of an Electrophilic Cupric Hydroperoxide Core.

Herein, we describe the regioselective functionalization of unsymmetrical ketones using imine directing groups, Cu, and H2O2. The C-H hydroxylation of the substrate-ligands derived from 2-substituted benzophenones occurred exclusively at the γ-position of the unsubstituted ring due to the formation of only one imine stereoisomer. Conversely, the imines derived from 4-substituted benzophenones produced E/Z mixtures that upon reacting with Cu and H2O2 led to two γ-C-H hydroxylation products. Contrary to our initial hypothesis, the ratio of the hydroxylation products did not depend on the ratio of the E/Z isomers but on the electrophilicity of the reactive [LCuOOH]1+. A detailed mechanistic analysis suggests a fast isomerization of the imine substrate-ligand binding the CuOOH core before the rate-determining electrophilic aromatic hydroxylation. Varying the benzophenone substituents and/or introducing electron-donating and electron-withdrawing groups on the 4-position of pyridine of the directing group allowed for fine-tuning of the electrophilicity of the mononuclear [LCuOOH]1+ to reach remarkable regioselectivities (up to 91:9 favoring the hydroxylation of the electron-rich arene ring). Lastly, we performed the C-H hydroxylation of alkyl aryl ketones, and like in the unsymmetrical benzophenones, the regioselectivity of the transformations (sp3 vs sp2) could be controlled by varying the electronics of the substrate and/or the directing group.

In silico investigation of the photoisomerization mechanism of push-push azoderivatives

The design of novel chromophores showing specific photophysical traits is nowadays crucial for the development of new dyes and optical devices. Azobenzene derivatives comprise the largest fraction of industrial dyes and remain one of the main functions to be employed in the design of general-purpose photoactivated switches. In this context, we have investigated the optical and photoisomerization properties of two push-push azo derivatives, from a purely theoretical perspective, to outline a mechanistic landscape that can contribute to setting the grounds for the future goal of formulating dyes with specific photophysical properties. Both derivatives show downhill excited-state potential energy surfaces, hinting at fast photoactivated isomerization. In addition, both the trans and cis forms show nearly complementary absorption spectra leading to discriminatory color and differential excitation possibilities. Additionally, the reverse cis to trans ground state thermal isomerization reactions show higher energy barriers than the parent azobenzene molecule, supporting their potential use in different technological applications.

Efficient and selective dual-pathway polyolefin hydro-conversion over unexpectedly bifunctional M/TiO2-anatase catalysts

The huge scale of plastic waste generation and its environmental consequences drive the demands for catalytic plastic upcycling processes. Here, we report efficient polypropylene (PP) hydro-conversion over Ru and Ni supported on a sol-gel anatase TiO2 (TiO2-A-SG). A small number of Brønsted acid sites on TiO2-A-SG enables hydrocracking, improving efficiency, steering the selectivity towards high-valued C4–20, and allowing more isomerization, compared to Ru-based monofunctional hydrogenolysis catalysts. The relative contribution of hydrocracking increases with lower hydrogen partial pressure, more branched substrates, and lower Ru loading. Ni/TiO2-A-SG exhibits superior hydrocracking activity and selectivity to Ni on conventional Brønsted-acidic supports, particularly zeolites. Mechanistic studies shows fast isomerization and sequential β-scissions caused by strong polymer-catalyst interaction and fast cracking with abundant 3C. This favors C4–12 formation and prevents secondary reactions. This work demonstrated a novel, highly efficient noble-metal-free catalyst for plastic waste upcycling, while advancing the mechanistic understanding of polyolefin hydro-conversion.

Fast Isomerization Before Isomerization‐Hydroformylation: Probing the Neglected Period with A Novel Microfluidic Device

AbstractBy combining the concept of flash chemistry and radial synthesis, a novel microreactor (Flashstop reactor) was designed to study isomerization process of hydroformylation by a Rh/tetraphosphite catalyst in a time scale of seconds. It was found that in the initial 313 seconds, 60–99 % of 1‐octene was isomerized to 2‐ and 3‐octenes before the formation of aldehydes. Within this period, two different types of isomerization reactions were observed. It was proposed that a monohydride complex without CO ligand accounts for the ultrafast isomerization in the initial 30 seconds. The isomerization rate with such monohydride species was calculated much faster than that with the well‐known H(CO)Rh(P−P) species. Both experimental and DFT computational studies were carried out to support this assumption. Fast transformations early on in catalytic cycles have been rarely studied due to the lack of proper tools. We believe that the Flashstop reactor is a powerful tool for analysis of kinetics in gas‐liquid biphasic reactions within a time scale of seconds to minutes.

Fast Isomerization Before Isomerization-Hydroformylation: Probing the Neglected Period with A Novel Microfluidic Device.

By combining the concept of flash chemistry and radial synthesis, a novel microreactor (Flashstop reactor) was designed to study isomerization process of hydroformylation by a Rh/tetraphosphite catalyst in a time scale of seconds. It was found that in the initial 313 seconds, 60~99% of 1-octene was isomerized to 2- and 3-octenes before the formation of aldehydes. Within this period, two different types of isomerization reactions were observed. It was proposed that a monohydride complex without CO ligand accounts for the ultrafast isomerization in the initial 30 seconds. The isomerization rate with such monohydride species was calculated much faster than that with the well-known H(CO)Rh(P-P) species. Both experimental and DFT computational studies were carried out to support this assumption. Fast transformations early on in catalytic cycles have been rarely studied due to the lack of proper tools. We believe that the Flashstop reactor is a powerful tool for analysis of kinetics in gas-liquid biphasic reactions within a time scale of seconds to minutes.

Large Gas-Phase Source of Esters and Other Accretion Products in the Atmosphere.

Dimeric accretion products have been observed both in atmospheric aerosol particles and in the gas phase. With their low volatilities, they are key contributors to the formation of new aerosol particles, acting as seeds for more volatile organic vapors to partition onto. Many particle-phase accretion products have been identified as esters. Various gas- and particle-phase formation pathways have been suggested for them, yet evidence remains inconclusive. In contrast, peroxide accretion products have been shown to form via gas-phase peroxy radical (RO2) cross reactions. Here, we show that these reactions can also be a major source of esters and other types of accretion products. We studied α-pinene ozonolysis using state-of-the-art chemical ionization mass spectrometry together with different isotopic labeling approaches and quantum chemical calculations, finding strong evidence for fast radical isomerization before accretion. Specifically, this isomerization seems to happen within the intermediate complex of two alkoxy (RO) radicals, which generally determines the branching of all RO2-RO2 reactions. Accretion products are formed when the radicals in the complex recombine. We found that RO with suitable structures can undergo extremely rapid C-C β scissions before recombination, often resulting in ester products. We also found evidence of this previously overlooked RO2-RO2 reaction pathway forming alkyl accretion products and speculate that some earlier peroxide identifications may in fact be hemiacetals or ethers. Our findings help answer several outstanding questions on the sources of accretion products in organic aerosol and bridge our knowledge of the gas phase formation and particle phase detection of accretion products. As esters are inherently more stable than peroxides, this also impacts their further reactivity in the aerosol.

ESIPT‐Inspired Dual‐Mode Photoswitches with Fast Molecular Isomerization in the Solid State

AbstractPhotoswitchable materials have attracted considerable attention in various fields. Developing excellent solid‐state dual‐mode photoswitches is an important but challenging task. Herein, we propose a new strategy to construct an excited‐state intramolecular proton transfer (ESIPT) inspired photoswitch (DiAH‐pht) that possesses aggregation‐induced emission (AIE) features and displays a fast molecular isomerization process characterized by dual‐mode behavior in the solid state. Mechanistic studies indicate that introduction of a bulky group can create a folded molecular conformation that provides adequate volume to facilitate photoisomerization and the enhanced ESIPT effect can boost the isomerization process. The feasibility of our strategy was further demonstrated by the activated photoisomerization performance of the Schiff base derivatives. Furthermore,DiAH‐phtshows good performance in the fields of dual‐mode information encryption and high‐density data storage.

ESIPT-Inspired Dual-Mode Photoswitches with Fast Molecular Isomerization in the Solid State.

Photoswitchable materials have attracted considerable attention in various fields. Developing excellent solid-state dual-mode photoswitches is an important but challenging task. Herein, we propose a new strategy to construct an excited-state intramolecular proton transfer (ESIPT) inspired photoswitch (DiAH-pht) that possesses aggregation-induced emission (AIE) features and displays a fast molecular isomerization process characterized by dual-mode behavior in the solid state. Mechanistic studies indicate that introduction of a bulky group can create a folded molecular conformation that provides adequate volume to facilitate photoisomerization and the enhanced ESIPT effect can boost the isomerization process. The feasibility of our strategy was further demonstrated by the activated photoisomerization performance of the Schiff base derivatives. Furthermore, DiAH-pht shows good performance in the fields of dual-mode information encryption and high-density data storage.

Physicochemical characterization of green sodium oleate-based formulations. Part 3. Molecular and collective dynamics in rodlike and wormlike micelles by proton nuclear magnetic resonance relaxation

HypothesisSodium oleate (NaOL) self-aggregates in water forming rodlike micelles with different length depending on NaOL concentration; when KCl is added wormlike micelles form, which entangle giving rise to a viscoelastic dispersion. It is expected that aggregates with different size and shape exhibit different internal and overall molecular motions and collective dynamics. ExperimentsTwo low viscosity NaOL/water and two viscoelastic NaOL/KCl/water formulations with different NaOL concentration (0.23 and 0.43 M) were investigated by 1H fast field cycling NMR relaxometry over broad temperature and Larmor frequency ranges, after a first screening by 1H and 13C NMR spectroscopy at high frequency. FindingsThe analysis of the collected data indicated that fast conformational isomerization and rotation of NaOL about its long molecular axis and lateral diffusion of NaOL around the axis of the cylindrical aggregates are slightly affected by the aggregate shape and length. On the other hand, fluctuations of the local order director are quite different in the fluid and viscoelastic systems, reflecting the shape and size of the aggregates. Quantitative information was obtained on activation energy for fast internal and overall motions, correlation times and activation energy for lateral diffusion, and coherence length for collective order fluctuations.

Confinement-Driven Photophysics in Hydrazone-Based Hierarchical Materials.

Confinement-imposed photophysics was probed for novel stimuli-responsive hydrazone-based compounds demonstrating a conceptual difference in their behavior within 2D versus 3D porous matrices for the first time. The challenges associated with photoswitch isomerization arising from host interactions with photochromic compounds in 2D scaffolds could be overcome in 3D materials. Solution-like photoisomerization rate constants were realized for sterically demanding hydrazone derivatives in the solid state through their coordinative immobilization in 3D scaffolds. According to steady-state and time-resolved photophysical measurements and theoretical modeling, this approach provides access to hydrazone-based materials with fast photoisomerization kinetics in the solid state. Fast isomerization of integrated hydrazone derivatives allows for probing and tailoring resonance energy transfer (ET) processes as a function of excitation wavelength, providing a novel pathway for ET modulation.

Confinement‐Driven Photophysics in Hydrazone‐Based Hierarchical Materials

AbstractConfinement‐imposed photophysics was probed for novel stimuli‐responsive hydrazone‐based compounds demonstrating a conceptual difference in their behavior within 2D versus 3D porous matrices for the first time. The challenges associated with photoswitch isomerization arising from host interactions with photochromic compounds in 2D scaffolds could be overcome in 3D materials. Solution‐like photoisomerization rate constants were realized for sterically demanding hydrazone derivatives in the solid state through their coordinative immobilization in 3D scaffolds. According to steady‐state and time‐resolved photophysical measurements and theoretical modeling, this approach provides access to hydrazone‐based materials with fast photoisomerization kinetics in the solid state. Fast isomerization of integrated hydrazone derivatives allows for probing and tailoring resonance energy transfer (ET) processes as a function of excitation wavelength, providing a novel pathway for ET modulation.

DFT Insights into the Variety in the Coordination Modes of the Equatorial Halides in [Au13 Ag12 (PR3 )10 X8 ]+ (X=Cl/Br) Clusters.

The bonding character within metal nanoclusters represents an intriguing topic, shedding light on the inherent driving force for the packing preference in nanomaterials. Herein, density functional theory (DFT) calculations were conducted to investigate the correlation of the series of isomeric [Au13 Ag12 (PR3 )10 X8 ]+ (X=Cl/Br) clusters, which are mainly differentiated by the coordination mode of the equatorial halides (μ2 -, μ3 - and μ4 -) in the rod-like, bi-icosahedral framework. The theoretical simulation corroborates the variety in the configuration of the Au13 Ag12 clusters and elucidates the fast isomerization kinetics among the different configurations. The easy tautomerization and the variety in chloride binding modes correspond to a fluxionality character of the equatorial halides and are verified by the potential energy curve analysis. The structural flexibility of the central Au3 Ag10 block is the main driving force, while the relatively stronger Ag-X bonding interaction (compared to that of Au-X), and a sufficient number of halides are also requisite for the associating Ag-X tautomerizations.

Pre-steady-state kinetics and solvent isotope effects support the "billiard-type" transport mechanism in Na+ -translocating pyrophosphatase.

Membrane‐bound pyrophosphatase (mPPase) found in microbes and plants is a membrane H+ pump that transports the H+ ion generated in coupled pyrophosphate hydrolysis out of the cytoplasm. Certain bacterial and archaeal mPPases can in parallel transport Na+ via a hypothetical “billiard‐type” mechanism, also involving the hydrolysis‐generated proton. Here, we present the functional evidence supporting this coupling mechanism. Rapid‐quench and pulse‐chase measurements with [32P]pyrophosphate indicated that the chemical step (pyrophosphate hydrolysis) is rate‐limiting in mPPase catalysis and is preceded by a fast isomerization of the enzyme‐substrate complex. Na+, whose binding is a prerequisite for the hydrolysis step, is not required for substrate binding. Replacement of H2O with D2O decreased the rates of pyrophosphate hydrolysis by both Na+‐ and H+‐transporting bacterial mPPases, the effect being more significant than with a non‐transporting soluble pyrophosphatase. We also show that the Na+‐pumping mPPase of Thermotoga maritima resembles other dimeric mPPases in demonstrating negative kinetic cooperativity and the requirement for general acid catalysis. The findings point to a crucial role for the hydrolysis‐generated proton both in H+‐pumping and Na+‐pumping by mPPases.

Liquid and Photoliquefiable Azobenzene Derivatives for Solvent-free Molecular Solar Thermal Fuels.

A series of liquid and photoliquefiable azobenzene (Azo) derivatives (Azo-Cn-Br) have been synthesized for molecular solar thermal fuels. Each of the liquid and photoliquefiable azo derivatives shows a high degree of isomerization, a fast isomerization rate, a long half-life, an appropriate energy storage density, and a solvent-free "charging" and "discharging" process. The photoliquefied azo derivatives can isomerize upon UV light irradiation at low temperatures to give the "UV-charged" azo ones. Therefore, the phase transition enthalpy is stored simultaneously along with the isomerization enthalpy. The "UV-charged" azo derivatives are capable of releasing heat under the manipulation of blue light.

E-Selective Manganese-Catalyzed Semihydrogenation of Alkynes with H2 Directly Employed or In Situ-Generated.

Selective semihydrogenation of alkynes with the Mn(I) alkyl catalyst fac-[Mn(dippe)(CO)3(CH2CH2CH3)] (dippe = 1,2-bis(di-iso-propylphosphino)ethane) as a precatalyst is described. The required hydrogen gas is either directly employed or in situ-generated upon alcoholysis of KBH4 with methanol. A series of aryl-aryl, aryl-alkyl, alkyl-alkyl, and terminal alkynes was readily hydrogenated to yield E-alkenes in good to excellent isolated yields. The reaction proceeds at 60 °C for directly employed hydrogen or at 60–90 °C with in situ-generated hydrogen and catalyst loadings of 0.5–2 mol %. The implemented protocol tolerates a variety of electron-donating and electron-withdrawing functional groups, including halides, phenols, nitriles, unprotected amines, and heterocycles. The reaction can be upscaled to the gram scale. Mechanistic investigations, including deuterium-labeling studies and density functional theory (DFT) calculations, were undertaken to provide a reasonable reaction mechanism, showing that initially formed Z-isomer undergoes fast isomerization to afford the thermodynamically more stable E-isomer.