Classical Reaction Research Articles

General Regio- and Diastereoselective Allylic C-H Oxygenation of Internal Alkenes.

Branched allylic esters and carboxylates are fundamental motifs prevalent in natural products and drug molecules. The direct allylic C-H oxygenation of internal alkenes represents one of the most straightforward approaches, bypassing the requirement for an allylic leaving group as in the classical Tsuji-Trost reaction. However, current methods suffer from limited scope─often accompanied by selectivity issues─thus hampering further development. Herein we report a photocatalytic platform as a general solution to these problems, enabling the coupling of diverse internal alkenes with carboxylic acids, alcohols, and other O-nucleophiles, typically in a highly regio- and diastereoselective manner.

Beyond the Zincke reaction: Modern advancements in the synthesis and applications of N-aryl pyridinium salts

In this review, we highlight recent advances in the synthesis of N-aryl pyridinium salts, which have moved beyond the classical Zincke SNAr reaction to focus on strategies reliant on C–N bond formation using an ever expanding array of reaction manifolds. This expansion to include C–N bond forming approaches, as well as enabling an unprecedented breadth of both arene and N-heterocyclic coupling partners, has led to a shift in perception of N-aryl pyrdinium salts to now serving as a platform for aryl amine synthesis. As a result, new synthetic applications of these salts have begun to emerge, both utilizing classic (nucleophilic additions, radical reactions, cycloadditions, etc) and emergent transformations such as deaminative transformations, isotopic labeling, and molecular editing. This review provides a timely synopsis of novel N-aryl pyridinium salt syntheses from the last 10 years (2013 to present). These strategies are separated into the two main classes, radical cation and non-radical cation methods. Highlights of recent transformations and applications of the resultant N-aryl pyridinium salts are also discussed to demonstrate the untapped synthetic potential of these scaffolds and highlight areas of continued interest.

Exploring the first-stage ignition and model optimization in the comprehensive study of n-dodecane oxidation

n-Dodecane is commonly employed as a surrogate for investigating the combustion characteristics of jet and diesel fuels. Enhancing comprehension of its combustion behavior and developing accurate chemical kinetics models for simulating combustion is of paramount importance in engine development. This study focuses on a detailed exploration of n-dodecane oxidation kinetics under low-temperature conditions and presents a novel dataset concerning the first-stage ignition delay time. A broad spectrum of experimental conditions is investigated, encompassing a range of temperature (600 ∼ 1350 K), pressure (5 ∼ 20 atm), equivalence ratios (0.5 ∼ 1.0), and dilution gases (N2 and Ar). Additionally, combustion experiments in a pure oxygen environment are performed, contributing valuable data to existing research. To enhance the precision of the chemical reaction kinetics model of n-dodecane, this study integrates updated rate coefficients obtained from the latest theoretical calculations for specific reaction classes. The improved rate rule provides a more accurate reference for the construction of the chemical reaction kinetics model of long straight alkane. The resulting improved model excels in accurately predicting both the first-stage ignition delay time and the total ignition delay time under a wide range of operational conditions. Additionally, the model performance is rigorously evaluated through a comprehensive assessment against a diverse array of datasets gathered from various literature references. The results show that, in contrast to the previously proposed model, this enhanced model provides highly reliable predictions over a broad range of parameters.

Frontal Polymerization for the Rapid Obtainment of Polymer Composites.

Among the different polymerization techniques, frontal polymerization (FP) has gained high interest from the scientific community because of its peculiar characteristics: in particular, compared to classic polymerization reactions, FP allows for a better exploitation of the heat of polymerization involved, without requiring any external energy input apart from an initial photo or thermal ignition that triggers the reaction. The latter usually propagates in a few tenths of seconds or (at most) minutes through a hot self-sustaining polymerization front, giving rise to the formation of fully cured thermosetting networks or thermoplastic polymers. Furthermore, different polymerization mechanisms can be involved in FP reactions, comprising cationic or anionic, ring-opening metathesis, and free-radical polymerization, among others. Further, it is possible to run FP reactions in bulk, in solution, or even using solid monomers if they are melted at the temperature of the front, notwithstanding the possibility of using reactive systems containing fillers or fiber/fabric reinforcements. In this context, the use of FP is becoming very important also for the design and production of advanced (nano)composite materials, saving processing time and achieving the completeness of the curing reaction, even in the presence of high filler/reinforcement loadings. Therefore, this mini-review aims to provide the reader with the basics of FP and its main peculiarities, even in the context of preparing high-performing composites. In this respect, some recent case studies witnessing the potentialities of frontal polymerization for the design of advanced (nano)composite systems will be elucidated. Finally, some perspectives about possible future developments will be proposed.

Emergence of non-trivial solutions from trivial solutions in reaction–diffusion equations for pattern formation

Reaction–diffusion equations serve as fundamental tools in describing pattern formation in biology. In these models, nonuniform steady states often represent stationary spatial patterns. Notably, these steady states are not unique, and unveiling them mathematically presents challenges. In this paper, we introduce a framework based on bifurcation theory to address pattern formation problems, specifically examining whether nonuniform steady states can bifurcate from trivial ones. Furthermore, we employ linear stability analysis to investigate the stability of the trivial steady-state solutions. We apply the method to two classic reaction–diffusion models: the Schnakenberg model and the Gray–Scott model. For both models, our approach effectively reveals many nonuniform steady states and assesses the stability of the trivial solution. Numerical computations are also presented to validate the solution structures for these models.

Highly pathogenic avian influenza H5N8 and H5N1 outbreaks in Algerian avian livestock production

Avian Alpha-influenza-virus (AIV) massively affects poultry, targeting mainly the respiratory tract for virus replication. Recently, two major H5N8 and H5N1 outbreaks caused tremendous losses in Algerian poultry. The clinical symptoms that had not been seen in the past didn’t prompt a rapid reaction to control the epidemics. We report here the characteristics of these outbreaks and the epidemiological status of AIV in Algeria. Following autopsy observation samples from target organs were taken and analyzed by the classical real-time reverse transcription polymerase chain reaction (RRT-PCR). Specific PCR HA and NA identification was used for subtyping H5 and N1/N8 genes. Systemic damage was observed in the upper-respiratory tracts with hemorrhagic and congestive tracheas, lungs, proventriculus, gut, and cecal tonsils were bloody. Out of 77 positive cases 13 were H5N8, 8 H5N1, and 10 H5Nx strains. These findings raise questions about the strain’s pathotype considering severe organ damage and high mortality.

Iron‐Catalyzed C−C and C−N Bond‐Forming Tandem Amidation Offering Access to 3‐Amino‐3‐Aminomethyl‐2‐Oxindole Frameworks

AbstractAn iron‐catalyzed protocol for the synthesis of 3‐amino‐3‐aminomethyl‐2‐oxindole heterocyclic structures is disclosed employing isatins and non‐nucleophilic N‐methoxybenzamides. This reaction class is associated with broad scope and tolerates numerous functionalities, such as fluoro, chloro, bromo, iodo, trifluoromethyl, nitrile, ester, ether, and alkenyl, including heteroaryl – thiophene, benzothiophene, carbazolyl, indolyl, eugenol, and polycyclic cholesterol moieties. Detailed mechanistic investigations reveal that the reaction proceeds via iron‐catalyzed N−O bond cleavage in N‐methoxybenzamides, generating formaldehyde and benzamide, and through the intermediacy of isatin‐ketimines and N‐(hydroxymethyl)benzamides. Overall, this amidation reaction involves one C−C and two C−N bond‐forming tandem processes, providing a range of β‐amino‐aminomethyl‐oxindoles (45 examples) in up to 88% yields.

Selective Hydrosilylation and Hydroboration of Allenes Catalyzed by Cobalt‐Pincer Complexes

AbstractAchieving precise control over regioselectivity and stereoselectivity in the hydroelementation of terminal allenes presents a formidable challenge. Despite the existence of various catalytic methods for their functionalization, this entire class of reactions remains significantly underdeveloped and demands extensive research. Here, we report a method for the hydroelementation of allenes using inexpensive PN5P pincer cobalt complexes built on a triazine backbone. Depending on the substituent at the ring, the method enables the selective synthesis of E‐alkenylsilane or Z‐allylborane derivatives. In the presented approach, silanes and pinacoloboranes play a dualistic role of simultaneous activator and substrate excluding the need for the addition of external bases. Finally, the application potential of the obtained compounds was demonstrated by performing further functionalizations of the obtained compounds.

Click Chemistry: Reaction Rates and Their Suitability for Biomedical Applications.

Click chemistry has become a commonly used synthetic method due to the simplicity, efficiency, and high selectivity of this class of chemical reactions. Since their initial discovery, further click chemistry methods have been identified and added to the toolbox of click chemistry reactions for biomedical applications. However, selecting the most suitable reaction for a specific application is often challenging, as multiple factors must be considered, including selectivity, reactivity, biocompatibility, and stability. Thus, this review provides an overview of the benefits and limitations of well-established click chemistry reactions with a particular focus on the importance of considering reaction rates, an often overlooked criterion with little available guidance. The importance of understanding each click chemistry reaction beyond simply the reaction speed is discussed comprehensively with reference to recent biomedical research which utilized click chemistry. This review aims to provide a practical resource for researchers to guide the selection of click chemistry classes for different biomedical applications.

Toehold Strand Displacement-Mediated Exponential HCR for Highly Sensitive and Specific Analysis of miRNA in Living Cells.

As an important disease biomarker, the development of sensitive detection strategies for miRNA, especially intracellular miRNA imaging strategies, is helpful for early diagnosis of diseases, pathological research, and drug development. Hybridization chain reaction (HCR) is widely used for miRNA imaging analysis because of its high specificity and lack of biological enzymes. However, the classic HCR reaction exhibits linear amplification with low efficiency, limiting its use for the rapid analysis of trace miRNA in living cells. To address this problem, we proposed a toehold-mediated exponential HCR (TEHCR) to achieve highly sensitive and efficient imaging of miRNA in living cells using β-FeOOH nanoparticles as transfection vectors. The detection limit of TEHCR was as low as 92.7 fM, which was 8.8 × 103 times lower compared to traditional HCR, and it can effectively distinguish single-base mismatch with high specificity. The TEHCR can also effectively distinguish the different expression levels of miRNA in cancer cells and normal cells. Furthermore, TEHCR can be used to construct OR logic gates for dual miRNA analysis without the need for additional probes, demonstrating high flexibility. This method is expected to play an important role in clinical miRNA-related disease diagnosis and drug development as well as to promote the development of logic gates.

Facile access to benzofuran-based bis-stilbene for organic laser dyes

A concise and efficient synthetic protocol for the synthesis of furan-based bis-stilbene derivatives (BPBFCz1) was described, which is a very promising organic laser dye. Starting with 4,4’-diethynylbiphenyl, BPBFCz1 was prepared with a total yield of 40% through a three-step classical reaction of Sonogashira Coupling, intramolecular cyclization of 2-alkynyl phenol, and Buchwald Hartwig cross-coupling. The crystal structure of BPBFCz1 was presented for the first time. The synthesis strategy was applied to the synthesis of other three materials with similar structure and the yields of 28.6–36.6% were obtained.

Discrimination of chiral amino acid enantiomers through photoelectrochemical sensing platform

Chirality plays fundamental functions in the activity of biological molecules and broad classes of chemical reactions, but its recognition and detection still remain a great challenge. Herein, inspired by the stereo-control characteristics of chiral amino acids adjacent to the active sites of natural enzymes, a photoelectrochemical (PEC) chiral sensor was constructed by encapsulating Au nanoparticles with the recognition unit l-Cysteine into mesoporous BiVO4 skeleton. The chiral sensor exhibits a high sensitivity and selectivity discrimination of 3,4-dihydroxyphenylalanine (DOPA) enantiomers. The possible mechanism of enantioselectivity was proposed with the guidance of DFT calculations, suggesting that the origin of chiral selectivity lies in the different hydrogen bonds forms between l-Cys and DOPA. This work provides a powerful strategy for constructing PEC chiral sensing device with excellent chiral recognition performance.

Polymers of intrinsic microporosity with alkaline pyrrolidine and piperidine functional groups for high-temperature proton exchange membranes

Recently, the polymers of intrinsic microporosity (PIMs) exhibit good potential in high-temperature proton exchange membrane fuel cells (HT-PEMFCs) due to their tunable microporosity and functionality. In this paper, alkaline pyrrolidine and piperidine functional groups were introduced onto PIM-1 via the classical Mannich reaction obtaining PIM-1/PIM-Py-50 and PIM-1/PIM-MePi-50. It was found that, compared with commercial Meta-polybenzimidazole (m-PBI) membrane, PIMs membranes showed superior retention of phosphoric acid (PA) and conductivity due to their grafting alkaline groups and rich micropores. After equilibration under 80 °C/40 % relative humidity (RH) for 150 h, the PA retention of PA doped PIM-1/PIM-Py-50 (PIM-1/PIM-Py-50/PA) and PA doped PIM-1/PIM-MePi-50 (PIM-1/PIM-MePi-50/PA) membranes were 74.13 % and 68.52 %, respectively, much higher than PA doped m-PBI (m-PBI/PA) (45.73 %). PIMs membranes maintain excellent dimensional and conductivity stability at 160 °C operating conditions, e.g. PIM-1/PIM-Py-50/PA membrane showed area swelling retention and volume swelling retention of 84.69 % and 82.19 % after 230 h at 160 °C. In addition, with the similar PA uptake, PIMs membranes displayed higher conductivity and peak power density (PPD) at 160 °C. In the accelerated stress test (AST) the PPD of the fuel cell (FC) with the PIM-1/PIM-Py-50/PA membrane remained 81.25 % after 200 aggressive start-up/shut-down cycles at 80 °C. Therefore, PIM-based membranes alkaline groups exhibit a wider temperature operating window, providing theoretical guidance for the design and study of the next generation of high-temperature proton exchange membranes (HT-PEMs).

Unexpected rearrangement of phenoxypicramide to 1,3-dinitro-10H-phenoxazine

The attempt to obtain phenoxypicramide from a classical nucleophilic substitution reaction using as reagents phenoxyamine and picryl chloride unexpectedly led to the formation of 1,3-dinitro-10H-phenoxazine. The possible mechanisms of formation, involving a molecular rearrangement with expelling of a nitro group, are discussed.

Kinetic Computation of Cyclization Reactions of Large Keto-Hydroperoxide Radicals in Low Temperature Combustion.

The cyclization reactions of keto-hydroperoxide (KHP) radicals leading to the formation of keto cyclic ethers and OH radicals play an important role in low temperature combustion for hydrocarbon fuels or oxygenated hydrocarbon fuels. However, due to the lack of kinetic data of cyclization reactions of KHP radicals, researchers often derive high-pressure-limit rate constants of cyclization reactions of KHP radicals from analogous cyclization reactions of hydroperoxyl alkyl radicals during construction of the combustion mechanism. This study aims to systematically investigate the kinetics of cyclization reactions of KHP radicals involving short-to-large-sized radicals. The studied reactions are divided into 7 reaction classes, according to the size of the cyclic transition state, the conjugative effect (whether KHP radicals are resonance-stabilized or not), and the position of the carbonyl group (whether the carbonyl group is inside or outside of the reaction center). The isodesmic reaction method, in conjunction with transition state theory, is utilized for each reaction class to compute the energy barriers and high-pressure-limit rate constants at the DFT level. The study revealed that energy barriers calculated at the DFT level with correction by the isodesmic reaction method are close to the results from the benchmark CCSD(T) method. To develop more accurate rate rules, these reaction classes are further divided into subclasses based on the relative site of the OOH group with the carbonyl group, the type of carbon atoms where the OOH group is located, and the type of carbon atoms where the radical site is located. For each subclass, high-pressure-limit rate rules are derived by averaging the rate constants of reactions in the subclass, and it is found that the maximum absolute deviation of the energy barrier and the ratio of the largest rate constant to the smallest rate constant among reactions in each subclass are within chemical accuracy limits, indicating acceptable use of the developed rate rules. A comparison of the rate constants for cyclization reactions of KHP radicals with the values of analogous cyclization reactions of hydroperoxyalkyl radicals as provided in reported mechanisms is made. Additionally, a comparison is drawn between our developed rate rules for subclasses of the cyclization reactions of KHP radicals and the rate rules for analogous subclasses of cyclization reactions of hydroperoxyl alkyl radicals. These comparisons demonstrate significant differences and highlight the necessity for improved rate rules for cyclization reactions of KHP radicals to enhance the automatically generated combustion mechanisms for hydrocarbon and oxygenated hydrocarbon fuels.

Semantic and Syntactic Predictions in Reading Aloud: Are Good Predictors Good Statistical Learners?

Recent research suggests that becoming a fluent reader may partially rely on a domain-general statistical learning (SL) mechanism that allows a person to automatically extract predictable patterns from the sensory input. The goal of the present study was to investigate a potential link between SL and the ability to make linguistic predictions. All previous studies investigated quite general levels of reading ability rather than the dynamic process of making linguistic predictions. We thus used a recently developed predictive reading task, which consisted of having participants read aloud words that were preceded by either semantically or syntactically predictive contexts. To measure the componential nature of SL, we used a visual and an auditory SL task (VSL, ASL) and the classic serial reaction time task (SRT). General reading ability was assessed with a reading speed/comprehension test. The study was conducted online on a sample of 120 participants to make it possible to explore interindividual differences. The results showed only weak and sometimes even negative correlations between the various SL measures. ASL correlated positively and predicted general reading ability but neither semantic nor syntactic prediction effects. Similarly, one of the SRT measures was significantly associated with reading level and reading speed but not with linguistic prediction effects. In sum, there is little evidence that domain-general SL is a good predictor of people's ability to make domain-specific linguistic predictions. In contrast, SL shows a weak but significant association with general reading ability.

Wide Voltage Swing Potentiostat with Dynamic Analog Ground to Expand Electrochemical Potential Windows in Integrated Microsystems.

Electrochemical measurements are vital to a wide range of applications such as air quality monitoring, biological testing, food industry, and more. Integrated circuits have been used to implement miniaturized and low-power electrochemical potentiostats that are suitable for wearable devices. However, employing modern integrated circuit technologies with low supply voltage precludes the utilization of electrochemical reactions that require a higher potential window. In this paper, we present a novel circuit architecture that utilizes dynamic voltage at the working electrode of an electrochemical cell to effectively enhance the supported voltage range compared to traditional designs, increasing the cell voltage range by 46% and 88% for positive and negative cell voltages, respectively. In return, this facilitates a wider range of bias voltages in an electrochemical cell, and, therefore, opens integrated microsystems to a broader class of electrochemical reactions. The circuit was implemented in 180 nm technology and consumes 2.047 mW of power. It supports a bias potential range of 1.1 V to -2.12 V and cell potential range of 2.41 V to -3.11 V that is nearly double the range in conventional designs.

A high-performance organic fluorescent probe with aggregation-induced emission properties for long-term tumor monitoring

Near-infrared organic fluorescent probes have great need in biological sciences and medicine but most of them are still largely unable to meet demand. In this work, a delicate multipurpose organic fluorescent probe (DPPM-TPA) with aggregation-induced emission performances is designed and prepared by facile method to reflect fluorescence labeling, two-photon imaging, and long-term fluorescent tracking. Specifically, DPPM-TPA NPs was constructed from 4-(diphenylamino)phenylboronic acid and DPPM-Br by classical Suzuki coupling reaction and then coated with F127. Such nanoprobe possessed high stability in diverse medium under ambient temperatures, low cytotoxicity, and brilliant fluorescence performance. More importantly, DPPM-TPA NPs showed excellent two-photon imaging and extraordinary long-term fluorescence tracing capacity to malignant tumor, and it can last up to 9 days. These results indicated that DPPM-TPA NPs is expected to serve as a fluorescent probe for photodiagnostic and providing a new idea for the development of long-term fluorescent tracker.

An experimental and chemical kinetic modeling study of octane isomer oxidation. Part 1: 2,3,4-trimethyl pentane

2,3,4-trimethyl pentane (234-TMP) is an isomer of octane with the same number of methyl branching groups as 2,2,4-trimethyl pentane (iso-octane). However, there are very few studies of this fuel available in the literature. In this work, a detailed chemical kinetic model is developed to describe the oxidation of 234-TMP using NUIGMech1.3 as the core mechanism. The rate constants for some important reaction classes are updated following a review of literature rate constants. Additionally, the impact of each rate constant on simulated ignition delay times for 234-TMP compared to 2,2,3-trimethyl pentane and 2,2,4-trimethyl pentane (iso-octane) is discussed. The thermodynamic data of the alkanes (RH), alkyl (Ṙ), alkyl peroxy (RȮ2), hydroperoxy-alkyl Q˙OOH, and peroxy hydroperoxyalkyl (Ȯ2QOOH) radicals are newly estimated based on recently updated group values in the literature. Moreover, this study presents the first set of data available for the oxidation of 234-TMP at higher pressures (15 and 30 atm), in the temperature range 600–1600 K, and at fuel/‘air’ equivalence ratios (φ) of 0.5, 1.0 and 2.0. The chemical kinetic model shows general good agreement with the experimental measurements. In addition, flux and sensitivity analyses are conducted to identify the important pathways and reactions controlling fuel oxidation at different temperatures. Furthermore, the reactivity of 234-TMP is compared to that of iso-octane, indicating that 234-TMP is slower to react as it has more tertiary carbon sites compared to iso--octane.

Global attractivity for reaction–diffusion equations with periodic coefficients and time delays

In this paper, we provide sharp criteria of global attraction for a class of non-autonomous reaction–diffusion equations with delay and Neumann conditions. Our methodology is based on a subtle combination of some dynamical system tools and the maximum principle for parabolic equations. It is worth mentioning that our results are achieved under very weak and verifiable conditions. We apply our results to a wide variety of classical models, including the non-autonomous variants of Nicholson’s equation or the Mackey–Glass model. In some cases, our technique gives the optimal conditions for the global attraction.