Isomerization Reactions Research Articles

Enhancing optical absorbance and accelerating rotational speed in molecular motors through oriented external electric fields

Accelerating the rotational speed of light-driven molecular motors is among the foremost concerns in molecular machine research, as this speed directly influences the performance of a motor. Controlling the motor’s rotation is crucial for practical applications, and using an oriented external electric field (OEEF) represents a feasible method to achieve this objective. We have investigated the impact of an OEEF on the optical and kinetic properties of a novel π-donor/acceptor di-substituted molecular motor, R2,3-(NH2, CHO). We employed density functional theory (DFT) and time-dependent DFT methods to analyze the electronic excitation and thermal isomerization behavior. Our results demonstrate that the absorption wavelength, absorption efficiency of the motor, and rate constant of the thermal isomerization reaction can be adjusted by applying OEEFs, which are predictable based on the dipole moment and polarizability of the molecules under consideration. In particular, we observed a shift in the absorption wavelength toward longer ranges, an enhancement in light absorption intensity, and an acceleration in the rotation rate when applying a weak positive directional external electric field to the R2,3-(NH2, CHO) motor. In summary, this theoretical study highlights the potential of OEEFs for improving the performance of molecular motors.

Moderating acidity of ZSM-50 by Fe-substitution for n-Heptane isomerization

Effective regulation of acid sites is essential to strengthen the reaction performance and to modulate product distribution of an isomerization reaction. In this study, ZSM-50 (Al-EUO) and Fe-substituted ZSM-50 zeolites, namely FeAl-EUO-n (n = 0.25, 0.50 and 0.75) and Fe-EUO, are synthesized by a seed-assisted hydrothermal method. The study has shown that Fe has effectively entered the Al-EUO framework as a tetrahedrally-coordinated species. More importantly, the Fe-substitution has resulted in a significant increase in the amount of surface weak- and medium-strength Brönsted acids and a reduction in the strength of strong acids of FeAl-EUO-n. This study also evaluates the catalytic performance of Pt/FeAl-EUO-n catalysts in n-heptane hydroisomerization. It shows that the introduction of Fe in ZSM-50 greatly enhances the isomer yield, achieving a maximum yield of 66.1 % at 320 °C over Pt/FeAl-EUO-0.50 compared to 16.4 % at 300°C over Pt/Al-EUO. At the same time, the fraction of multi-branched iso-heptane also increases noticeably in the reaction product.

Development of a Detailed Chemical Kinetic Model for 1-Methylnaphthalene

1-Methylnaphthalene is a critical component for constructing fuel surrogates of diesel and aviation kerosene. However, the reaction pathways of 1-methylnaphthalene included in existing detailed chemical kinetic models vary from each other, leading to discrepancies in the simulation of ignition and oxidation processes. In the present study, reaction classes and pathways involved in the combustion of 1-methylnaphthalene were analyzed, and effects of rate constants of reactions related to 1-methylnaphthalene and its significant intermediates on ignition delay times and species concentration profiles were discussed, involving hydrogen abstraction and substitution reactions of 1-methylnaphthalene, oxidation, isomerization, and addition reactions of 1-naphthylmethyl, hydrogen abstraction and oxidation reactions of indene, as well as the oxidation of indenyl and naphthalene. On this basis, a new detailed chemical kinetic model for 1-methylnaphthalene was developed, which includes 1389 species and 7185 reactions. The validation of this mechanism shows that it can predict accurately the available experimental ignition delay times, species concentration profiles, and laminar flame speeds of 1-methylnaphthalene. Finally, reaction paths and sensitivity analysis of ignition delay times were performed using the proposed reaction mechanism, and the result shows that the conversion of 1-methylnaphthalene to 1-naphthaldehyde plays an important role in its ignition.

Rhodium‐Catalyzed Reductive Hydroformylation of Polyunsaturated Vegetable Oils Assisted by Triethylamine/N‐methylimidazole Ligands Combination

AbstractIn this work, the reductive hydroformylation of linseed and sesame oils was carried out successfully by using a rhodium catalyst precursor associated to triethylamine/N‐methylimidazole ligands combination. Interestingly, in the presence of triethylamine and N‐methylimidazole at a precise ratio with respect to rhodium, the isomerization reaction can be inhibited and control experiments realized on methyl linoleate and methyl linolenate have clearly shown that no conjugated products were formed. This new catalytic system is full of interest since the yields in alcohols, after 24 h, are equal to 21% and 15% for Rh/triethylamine combination, whereas equal to 58% and 63% for Rh/triethylamine/N‐methylimidazole combination, for linseed and sesame oils, respectively.

Influence of ionic liquid film thickness and flow rate on macrocyclization efficiency and selectivity in supported ionic liquid-liquid phase catalysis.

Supported ionic-liquid phase (SILP) technology in a biphasic setting with n-heptane as the transport phase was applied to the Ru-alkylidene-N-heterocyclic carbene (NHC) catalyzed macrocyclization of α,ω-dienes to elucidate the effect of ionic liquid (IL)-film thickness, flow rate as well as substrate and product concentration on macrocyclization efficiency, and Z-selectivity. To understand the molecular-level behavior of the substrates and products at the n-heptane/IL interphase, atomistic molecular dynamics simulations were conducted and correlated with experimental observations. The thickness of the IL layer strongly influences the Z/E ratio of the products in that a thin IL layer favors higher Z/E ratios by confining the catalyst between the pore wall and the liquid-liquid interphase whereas a thick IL layer favors formation of the E-product and Ru-hydride catalyzed isomerization reactions. Also, macrocyclization efficiency, expressed by the ratio of oligomers/macromonocycle (O/MMC), is influenced both by the flow rate and the thickness of the IL layer.

The Role of Kinetic Asymmetry in Chemical and Thermodynamic Coupling

AbstractThe input of energy can shift an isomerization reaction A⇌B away from equilibrium, but which way, in favor of A or in favor of B? The answer to this question lies in understanding kinetic asymmetry, a concept first discussed in the context of how energy from an oscillating or fluctuating perturbation can act in concert with a catalyst to drive a reaction away from equilibrium. The key theoretical result is the non‐equilibrium pumping equality that generalizes the idea of the equilibrium constant to the non‐equilibrium steady‐state.

Promotion of Metal‐Free Catalytic Coupling of Fluorinated Halogenated Hydrocarbons By a Base for the Synthesis of Difluoromethyl Heterocyclic Amines

The selective functionalization of difluoromethyl groups (‐CF2) is a promising approach and an attractive synthetic route for accessing fluorine‐containing moieties with medicinal benefits. Here, we report a case of a C‒N coupling reaction between bromodifluoropropene with heterocyclic amines, such as indole, pyrrole, and imidazole, promoted by an alkali without the use of transition metal catalysis. This reaction differs from existing methods in that it does not undergo a difluoromethylation isomerization reaction but directly retains the structure of the terminal olefin. This chemical conversion process has a wide substrate range, good functional group tolerance, and an ideal reaction conversion rate, making it an effective new method for the difluoropropenation of heterocyclic amines.

Aromatics Alkylated with Olefins Utilizing Zeolites as Heterogeneous Catalysts: A Review

The alkylation reaction of aromatic compounds gains considerable attention because of its wide application in bulk and fine chemical production. Aromatics alkylated with olefins is a well-known process, particularly for linear alkylbenzene, phenyloctanes, and heptyltoluene production. As octane boosters and precursors for various petrochemical and bulk chemical products, a wide range of alkylated compounds are in high demand. Numerous unique structures have been proposed in addition to the usual zeolites (Y and beta) utilized in alkylation procedures. The inevitable deactivation of industrial catalysts over time on stream, which is followed by a decrease in catalytic activity and product selectivity, is one of their disadvantages. Therefore, careful consideration of catalyst deactivation regarding the setup and functioning of the process of catalysis is necessary. Although a lot of work has been carried out to date to prevent coke and increase catalyst lifespan, deactivation of the catalyst is still unavoidable. Coke deposition can lead to catalyst deactivation in industrial catalytic processes by obstructing pores and/or covering acid sites. It is very desirable to regenerate inactive catalysts in order to remove the coke and restore catalytic activity at the same time. Depending on the kind of catalyst, the deactivation processes, and the regeneration settings, each regeneration approach has pros and cons. In this comprehensive study, the focus was on discussing the reaction mechanism of 1-octene isomerization and toluene alkylation as an example of isomerization and alkylation reactions that occur simultaneously, shedding light in detail on the catalysts used for this type of complex reaction, taking into account the challenges facing the catalyst deactivation and reactivation procedures.

Development of an eco-fractionation process for Ricinodendron heudelotii oil to obtain α-eleostearic acid and β-eleostearic acid

Abstract The present article studies the transformations and fractionation of the reserve lipids of Ricinodendron heudelotii. The native triglycerides of this oil are composed mainly of conjugated polyunsaturated fatty acids, in particular α-eleostearic acid C18:3 n– 5 (9c, 11t, 13t) at 60%. This particular fatty acid of CLnA family exerts many activities potentially beneficial for health: anti-inflammatory, anti-leukemic, anti-microbial, anti-tumor, anti-ulcer and anti-diabetic. A process for transforming this acid into its isomers β-eleostearic acid and catalpic acid was explored with the aim of obtaining fractions enriched in β-eleostearic acid C18:3 n– 5 (9t, 11t, 13t). The β-eleostearic acid is a fatty acid of great interest because it is even more reactive and more efficient as antioxidant than α-eleostearic acid due to its higher trans content. Isomerization reaction of α-eleostearic acid in oil was carried out using artificial solar radiation treatment. The enrichment of concentrates in β-eleostearic acid was therefore tested using an eco-fractionation process. This process was carried out in two stages. The first step was the Candida rugosa lipase-catalyzed hydrolysis of triglycerides from native or isomerized Ricinodendron heudelotii oil. The second step was fractionation of the reaction medium obtained after hydrolysis. Triglyceride hydrolysis was complete, with a yield of free fatty acids of over 95% after 2 h of reaction. Treatment of the reaction media yielded 3 lipid concentrates with new chemical compositions of polyunsaturated fatty acids: a first concentrate, derived from hydrolysis of the native oil, composed of 60% α-eleostearic acid and 22% linoleic acid, and two other concentrates derived from fractionation of the hydrolysate of the oil isomerized by radiation. One was composed of 34% linoleic acid, 21% β-eleostearic acid, 11% α-eleostearic acid and 6% catalpic acid, and the last concentrate was composed of over 80% β-eleostearic acid. In addition to offering nutritional benefits similar to those of α-eleostearic acid, β-eleostearic acid also offers an interesting physical property: a very high melting point of 72 °C. Such a polyunsaturated fatty acid, which is solid at room temperature, could prove to be a raw material of choice, particularly in the world of food formulation, where manufacturers are looking for replacements with physical properties close to those of palm oil (the melting point of palmitic acid is 62 °C). Ricinodendron heudelotii oil has thus demonstrated its major role as a source of the triptych of α-eleostearic, β-eleostearic and linoleic fatty acids.

Substrate specificity and kinetic mechanism of 3β-hydroxy-[formula omitted]5-C27-steroid oxidoreductase

Cholesterol is a key sterol whose homeostasis is primarily maintained through bile acid metabolism. Proper bile acid formation is vital for nutrient and fat-soluble vitamin absorption and emulsification of lipids. Synthesis of bile acids occurs through two main pathways, both of which rely on 3-hydroxy-5-C27 steroid oxidoreductase (HSD3B7) to begin epimerization of the 3β hydroxyl of cholesterol into its active 3α conformation. In this sequence HSD3B7 catalyzes the dehydrogenation of the 3β-hydroxy group followed by isomerization of the Δ5-cholestene-3-one. These reactions are some of the many steps that transform cholesterol for either storage or secretion. HSD3B7 has distinct activity from other 3β-HSD family members leaving significant gaps in our understanding of its mode of catalysis and substrate specificity. Additionally, the role of HSD3B7 in health and disease positions it as a metabolic vulnerability that could be harnessed as a therapeutic target. To this end, we evaluated the mechanism of HSD3B7 catalysis and reveal that HSD3B7 displays activity towards diverse 7α-hydroxylated oxysterols. HSD3B7 retains its catalytic efficiency towards these substrates, suggesting that its substrate binding pocket can withstand changes in polarity upon alterations to this hydrocarbon tail. Experiments aimed at determining substrate order are consistent with HSD3B7 catalyzing a sequential ordered bi bi reaction mechanism with the binding of NAD+ followed by 7α-hydroxycholesterol to form a central complex. HSD3B7 bifunctional activity is dependent on membrane localization through a putative membrane-associated helix giving insight into potential regulation of enzyme activity. We found strong binding of the NADH product thought to activate the isomerization reaction. Homology models of HSD3B7 reveal a potential substrate pocket that allows for oxysterol binding and mutagenesis was utilized to support this model. Together these studies offer an understanding of substrate specificity and kinetic mechanism of HSD3B7 which can be exploited for future drug development.

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.

Theoretical and modeling studies on the kinetics of diethylamine dehydrogenation and subsequent isomerization and decomposition reactions

Small-molecule nitrogen-containing contaminants can be produced by the pyrolysis of diethylamine (DEA) alone or in conjunction with other molecules. To investigate the theoretical chemistry of the combustion of DEA, the CBS method determines the potential energy surface and the rate constants are calculated based on a combination of RRKM and TST theories. The H-abstraction reactions by H radicals are more kinetically advantageous. Site α has the most difficult H-abstraction procedure, but site γ has the competitive capacity to form subsequent products. The H-abstraction by NO2 radical produces trans-HONO, cis-HONO, and HNO2. For the reaction channels of DEA radicals, decomposition reactions have more kinetic advantages than isomerization. Kinetic parameters were obtained and the model was modified based on the fitted rate constants. The modified model has better predictive ability at low temperatures. This work provides extensive data to improve the modeling of DEA combustion at low and medium temperatures.

Ultrafast Photochemical Reaction of Exiguobacterium sibiricum Rhodopsin (ESR) at Alkaline pH

Rhodopsin from the eubacterium Exiguobacterium sibiricum (ESR) performs the function of light-dependent proton transport. The operation of ESR is based on the ultrafast photochemical reaction of isomerization of the retinal chromophore, which triggers dark processes closed in the photocycle. Many parameters of the photocycle are determined by the degree of protonation of Asp85 – the primary counterion of the chromophore group and the proton acceptor. ESR in detergent micelles pumps protons most efficiently at pH 9, when Asp85 is almost completely deprotonated. In this work, the photochemical reaction of ESR at pH 9.5 was studied by femtosecond laser absorption spectroscopy. It was shown that photoisomerization of the chromophore group occurs in 0.51 ps, and the contribution of the reactive excited state is about 80%. A comparison with the data we obtained at pH 7.4 showed that at pH 9.5 the reaction proceeds much faster and more efficiently. The data obtained confirm the important role of the chromophore group counterion in the photoactivated processes of rhodopsins.

Cavity-modified local and non-local electronic interactions in molecular ensembles under vibrational strong coupling.

Resonant vibrational strong coupling (VSC) between molecular vibrations and quantized field modes of low-frequency optical cavities constitutes the conceptual cornerstone of vibro-polaritonic chemistry. In this work, we theoretically investigate the role of complementary nonresonant electron-photon interactions in the cavity Born-Oppenheimer (CBO) approximation. In particular, we study cavity-induced modifications of local and non-local electronic interactions in dipole-coupled molecular ensembles under VSC. Methodologically, we combine CBO perturbation theory (CBO-PT) [E. W. Fischer and P. Saalfrank, J. Chem. Theory Comput. 19, 7215 (2023)] with non-perturbative CBO Hartree-Fock (HF) and coupled cluster (CC) theories. In a first step, we derive up to second-order CBO-PT cavity potential energy surfaces, which reveal non-trivial intra- and inter-molecular corrections induced by the cavity. We then introduce the concept of a cavity reaction potential (CRP), minimizing the electronic energy in the cavity subspace to discuss vibro-polaritonic reaction mechanisms. We present reformulations of CBO-HF and CBO-CC approaches for CRPs and derive second-order approximate CRPs from CBO-PT for unimolecular and bimolecular scenarios. In the unimolecular case, we find small local modifications of molecular potential energy surfaces for selected isomerization reactions dominantly captured by the first-order dipole fluctuation correction. Excellent agreement between CBO-PT and non-perturbative wave function results indicates minor VSC-induced state relaxation effects in the single-molecule limit. In the bimolecular scenario, CBO-PT reveals an explicit coupling of interacting dimers to cavity modes besides cavity-polarization dependent dipole-induced dipole and van der Waals interactions with enhanced long-range character. An illustrative CBO-coupled cluster theory with singles and doubles-based numerical analysis of selected molecular dimer models provides a complementary non-perturbative perspective on cavity-modified intermolecular interactions under VSC.

Unveiling the low‐temperature oxidation chemistry of dipropyl carbonate

AbstractDialkyl carbonates (DACs) own an environmentally friendly synthesis route, making them potential candidates as alternative fuels. However, for DACs to be widely accepted as an alternative fuel, a comprehensive understanding of their combustion behavior is essential. Dipropyl carbonate (DPrC) represents a transition from short‐chain to mid‐chain carbonates, understanding its combustion behaviors holds significance in unraveling the combustion chemistry of carbonates. In this study, the oxidation of DPrC was investigated with the initial fuel mole fraction of 0.5% at three equivalence ratios of 0.5, 1.0, and 2.0 within a temperature range of 550–1100 K in a jet‐stirred reactor for the first time. Gas chromatography was utilized for the quantitative detection of reactants, intermediates, and products. A detailed DPrC mechanism was first developed, and good agreements between measurements and simulations were obtained. A notable negative temperature coefficient (NTC) behavior was first observed in the oxidation of DACs. Such NTC phenomenon occurred at fuel‐lean conditions in the temperature range of 620–660 K, while only a weak low‐temperature consumption was observed at the stoichiometric condition. Kinetic modeling studies showed that this unique low‐temperature chemistry of DPrC can be attributed to the differences in the RO2 isomerization reactions between DPrC and short‐chain DACs. The RO2 isomerization via a six‐member ring transition state could happen in DPrC oxidation but not in dimethyl carbonate and diethyl carbonate oxidation, due to the different fuel molecular structure. Therefore, the subsequent reaction pathways via QOOH → O2QOOH → HO2Q = O + OH → OQ = O + OH were promoted and two OH radicals were released in this process. Moreover, it is conceivable that mid or long‐chain DACs could also exhibit an NTC phenomenon due to the increased potential for RO2 isomerization via a six‐ or seven‐member ring transition state, thereby increasing the likelihood of RO2 isomerization occurrence.

Synthesis of gold nanoparticles using soybean byproducts: applications in catalysis

AbstractThis study demonstrates the feasibility of extracting lecithin from oil industry byproducts in an eco‐friendly manner, with minimal use of water and without harmful chemicals. Liposomes can be generated directly from this extracted lecithin, enhancing the value of these byproducts and enabling the production of catalytic gold nanoparticles (AuNPs). Thin‐layer chromatography of the extracted lecithin revealed a phospholipid composition primarily consisting of phosphatidylethanolamine and phosphatidylcholine, and surface tension studies demonstrated similar behavior between the extracted and commercial lecithin. Liposome formation using sustainable lecithin (LPn) resulted in structures that were stable for at least 10 days, exhibiting a low polydispersity index (0.395) and uniform size (approximately 214 ± 7 nm). Gold nanoparticles were synthesized successfully in LPn loaded with [HAuCl4] by using different photoreduction methods: ultraviolet (UV) lamp, pulsed laser 355 nm, and sunlight irradiation. The AuNPs exhibited characteristic sizes (ranging from 5.03 to 6.78 nm) and optical properties typical of nanoparticles, including a distinct surface plasmon resonance. As a proof of concept, we also demonstrated that the synthesized AuNPs exhibited catalytic activity in UV‐induced cis‐trans isomerization reactions. Overall, the study highlights the potential of sustainable soy lecithin extraction for diverse applications, including nanoparticle synthesis and catalysis.

The unexpected and important role of alcohol stabilizer in thermal cis-trans isomerization of push-pull dyes in chloroform solution

The study demonstrates the influence of ethanol as a stabilizer in chloroform on the thermal cis-trans isomerization kinetics of photochromic compounds based on azobenzene and azopyridine derivatives. The significance of the addition of ethanol as a stabilizer in chloroform-based solutions on the isomerization reaction of the hydroxy- and the 6-hydroxylalkoxy-substituted azo compounds was investigated. The results have revealed that the presence of a polar stabilizer in a solvent can significantly reduce the reaction rate constant of the dark cis-trans isomerization due to the formation of hydrogen bonds at both ends of the azo-chromophore, thereby inhibiting the isomerization. Furthermore, a stabilizer can facilitate the reversion of azo-hydrazone tautomers of azophenols to their azobenzene form, resulting in a decrease in the reaction rate constant. The research presented in this paper can be essential for scientists who study the kinetics of the trans-cis and the cis-trans isomerization reactions of azo-chromophores. The results show that the use of solvents with polar stabilizers should be rather avoided, as their usage without information about stabilizers can lead to different experimental data. The authors should ensure that detailed information about stabilizers used in unstable solvents is included in the experimental section of their works (a detail currently often omitted in the literature).

Picoplatin (II)-loaded chitosan nanocomposites as effective drug delivery systems: Preparation, mechanistic investigation of BSA/5-GMP/GSH binding and biological evaluations

The goal of the current study is to improve the characteristics and bioavailability of the drug picoplatin (PPt) by encapsulating it in chitosan nanoparticles (CS NPs) which allows for the targeted delivery of cytotoxic cargo to cancerous tissue, reducing toxic side effects and raising the therapeutic index. When picoplatin was delivered into the CS, it was able to produce a complex with CS (PPt@CS NPs) that had an appropriate particle size of 275 ± 10 nm, a reasonably low PDI of 0.15 ± 0.05, and high stability (ζ = −22.1 ± 0.3 mV). Since almost all pharmaceuticals work by binding to specific proteins or DNA, the in vitro binding mechanism and affinity of bovine serum albumin (BSA), low molecular building units of nucleic acids (5−GMP), and Glutathione (GSH) (considering that cisplatin resistance could be due to a reaction between cisplatin and GSH) to PPt and PPt@CS NPs were examined using stopped-flow and other spectroscopic approaches. Through two reversible processes, a rapid second-order binding followed by a slower first-order isomerization reaction, and a static quenching mechanism, PPt and PPt@CS NPs bind to BSA with relative reactivity of around (PPt)/(PPt@CS NPs) = 1/2.5. The 5−GMP interaction studies demonstrated that, in addition to changing the binding mechanism, PPt's encapsulation in CS increases its rate of reaction through coordination affinity. PPt interacted with 5-GMP via two reversible processes, a rapid second-order binding to phosphate followed by a slower first−order migration to the N7 of pyrimidine moiety. PPt@CS NPs showed weaker binding to GSH compared to PPt and hence PPt@CS NPs exhibits a lower resistance factor. It was also found that the in vitro drug release of PPt@CS NPs in PBS at pH 7.4 was steady, releasing 30 % of the PPt in just 5 h. Nonetheless, 75 % of the release in a pH 5.4 solution containing 10 mM GSH—a solution that mimics the tumor microenvironment—shows that the PPt@CS NPs system is sensitive to GSH and specifically targets malignant tissue. The encapsulation of PPt in CS complex maintained its anticancer activity, as shown by an in vitro cell-survival assay on HepG2 cancer cell lines and also cleavage efficiency toward the minor groove of pBR322 DNA via the hydrolytic way. These findings collectively suggested that inclusion PPt in CS would be an effective strategy to formulate a novel picoplatin formulation intended for use as targeted anticancer treatment.

Study of the potential energy surface of reactions in a system containing <i>i</i>-propyl and <i>n</i>-propyl radicals

The energy pathways of possible decomposition and isomerization reactions of iso-propyl (i-C3H7) and n-propyl (n-C3H7) radicals have been studied by computational methods of quantum chemistry. B3LYP, M062X, MP2, and CBS-QB3 methods are used to localize stationary points on the potential energy surface of a system containing propyl radicals. A number of intermediate compounds formed during the isomerization and decomposition of propyl radicals have been identified, and information has been obtained on their structure and thermochemical parameters. Based on the results of the research, a diagram of the energy levels of the system under consideration was constructed.

Reversible Photochromic Reactions of Bacteriorhodopsin from Halobacterium salinarum at Femto- and Picosecond Times

The operation of bacteriorhodopsin (BR) from the archaeon Halobacterium salinarum is based on the photochromic reaction of isomerization of the chromophore group (the retinal protonated Schiff base, RPSB) from the all-trans to the 13-cis form. The ultrafast dynamics of the reverse 13-cis → all-trans photoreaction was studied using femtosecond transient absorption spectroscopy in comparison with the forward photoreaction. The forward photoreaction was initiated by photoexcitation of BR by pulse I (540 nm). The reverse photoreaction was initiated by photoexcitation of the product K590 at an early stage of its formation (5 ps) by pulse II (660 nm). The conversion of the excited K590 to the ground state proceeds at times of 0.19, 1.1, and 16 ps with the relative contributions of ~20/60/20, respectively. All these decay channels lead to the formation of the initial state of BR as a product with a quantum yield of ~1. This state is preceded by vibrationally excited intermediates, the relaxation of which occurs in the 16 ps time range. Likely, the heterogeneity of the excited state of K590 is determined by the heterogeneity of its chromophore center. The forward photoreaction includes two components—0.52 and 3.5 ps, with the relative contributions of 91/9, respectively. The reverse photoreaction initiated from K590 proceeds more efficiently in the conical intersection (CI) region but on the whole at a lower rate compared to the forward photoreaction, due to significant heterogeneity of the potential energy surface.