Mechanistic Insights into Statistical Co-Assembly of Metal Complexes

Statistical copolymerization plays a key role in many biological and technological processes; however, mechanistic understanding of the formation of analogous supramolecular counterparts remains limited. Herein, we report detailed insights into the supramolecular co-assembly of two π-conjugated Pd^II and Pt^II complexes, which in isolation self-assemble into flexible fibers and nanodisks, respectively. An efficient single-step co-assembly into only one type of nanostructure (fibers or nanodisks) takes place if any of the components is in excess. In contrast, equimolar mixtures lead to Pd^II-rich fiber-like co-assemblies by a statistical co-nucleation event along with a residual amount of self-sorted nanodisks in a stepwise manner.     

Mechanistic Insights into Cu-Catalyzed Asymmetric Aldol Reactions: Chemical and Spectroscopic Evidence for a Metalloenolate Intermediate

In situ IR spectroscopy and transmetalation experiments confirm a postulated catalytic cycle. The metalloenolate 1 describes the active intermediate in the aldol reaction catalyzed by [CuF₂{(S)-tol-binap}] (see reaction scheme). (S)-tol-binap=(S)-(−)-2,2′-bis(di-p-tolylphosphanyl)-1,1′-binaphthyl.     

Mechanistic Insights into the Luminescent Sensing of Organophosphorus Chemical Warfare Agents and Simulants Using Trivalent Lanthanide Complexes

Organophosphorus chemical warfare agents (OP CWAs) are potent acetylcholinesterase inhibitors that can cause incapacitation and death within minutes of exposure, and furthermore are largely undetectable by the human senses. Fast, efficient, sensitive and selective detection of these compounds is therefore critical to minimise exposure. Traditional molecular‐based sensing approaches have exploited the chemical reactivity of the OP CWAs, whereas more recently supramolecular‐based approaches using non‐covalent interactions have gained momentum. This is due, in part, to the potential development of sensors with second‐generation properties, such as reversibility and multifunction capabilities. Supramolecular sensors also offer opportunities for incorporation of metal ions allowing for the exploitation of their unique properties. In particular, trivalent lanthanide ions are being increasingly used in the OP CWA sensing event and their use in supramolecular sensors is discussed in this Minireview. We focus on the fundamental interactions of simple lanthanide systems with OP CWAs and simulants, along with the development of more elaborate and complex systems including those containing nanotubes, polymers and gold nanoparticles. Whilst literature investigations into lanthanide‐based OP CWA detection systems are relatively scarce, their unique and versatile properties provide a promising platform for the development of more efficient and complex sensing systems into the future.     

Mechanistic Insights into the Triplet Sensitized Photochromism of Diarylethenes

Operating photoswitchable molecules repetitively and reliably is crucial for most of their applications, in particular in (opto)electronic devices, and related to reversibility and fatigue resistance, which both critically depend on the photoisomerization mechanism defined by the substitution pattern. Two diarylethene photoswitches bearing biacetyl triplet sensitizers either at the periphery or at the core were investigated using both stationary as well as transient UV/Vis absorption spectroscopy ranging from the femtosecond to the microsecond time scale. The diarylethene with two biacetyl moieties at the periphery is switching predominantly from the triplet excited state, giving rise to an enhanced fatigue resistance. In contrast, the diarylethene bearing one diketone at the photoreactive inner carbon atom cyclizes from the singlet excited state and shows significantly higher quantum yields for both cyclization and cycloreversion.     

Mechanistic Insights into the Formation of Lithium Fluoride Nanotubes

Born–Oppenheimer molecular dynamics (BOMD) and periodic density functional theory (DFT) calculations have been applied for describing the mechanism of formation of lithium fluoride (LiF) nanotubes with cubic, hexagonal, octagonal, decagonal, dodecagonal, and tetradecagonal cross-sections. It has been shown that high energy structures, such as nanowires, nanorings, nanosheets, and nanopolyhedra are transient species for the formation of stable nanotubes. Unprecedented (LiF)_n clusters (n≤12) were also identified, some of them lying less than 10 kcal mol^−[1] above their respective global minima. Such findings indicate that stochastic synthetic techniques, such as laser ablation and chemical vapor deposition, should be combined with a template-driven procedure in order to generate the nanotubes with adequate efficiency. Apart from the stepwise growth of LiF units, the formation of nanotubes was also studied by rolling up a planar square sheet monolayer, which could be hypothetically produced from the exfoliation of the FCC crystal structure. It was shown that both pathways could lead to the formation of alkali halide nanotubes, a still unprecedented set of one-dimensional materials.     

Mechanistic Insights into a Sustainable Mechanochemical Synthesis of Ettringite

Mechanochemistry offers an environmentally benign and facile synthesis method for a variety of cement paste constituents. In addition, these methods can be used to selectively tune the properties of cement components. The mineral ettringite is an important component of cementitious materials and has additional technological potential due to its ion exchange properties. Synthesis of ettringite via mechanochemistry is an environmentally friendly alternative to conventional wet-chemical synthesis established in industry. This contribution explores the mechanism of a two-step mechanochemical synthesis of ettringite, which was previously found to greatly improve the reaction conversion as compared with one-pot synthesis. The crystallinity of Al(OH)₃ was found to decrease during the first stage of this mechanochemical synthesis. This was correlated to a significant decrease in the particle size of Al(OH)₃ in this stage. No other significant changes were found for the other components, suggesting that mechanochemical activation of Al(OH)₃ is responsible for the enhanced formation of ettringite by the two-step approach. The environmentally friendly approach developed for ettringite synthesis offers a versatile synthetic strategy, which can be applied to synthesise further cementitious materials.     

Gold Nanoparticle Ensembles Allow Mechanistic Insights into Electrochemical Processes

Gold‐nanoparticle‐modified electrodes find wide and diverse applications in the area of electrochemistry. We demonstrate for the first time that gold‐nanoparticle‐modified electrodes can provide mechanistic information and we exemplify this with the electrochemical deposition of arsenic(III). Our approach of using nanoparticle ensembles is a facile and economical methodology that provides an alternative to using expensive gold single‐crystal electrodes that require careful surface preparation before each measurement.     

Mechanistic Insights into the Photophysics of Ortho-hydroxyl GFP Core Chromophores

Herein we have employed the MS-CASPT2//CASSCF method to study the S₁ excited-state intramolecular proton transfers (ESIPTs) of recently synthesized ortho-hydroxyl GFP core chromophores, i.e. OHIM, CHBDI, and MHBID, and their excited-state relaxation pathways. We have found that in OHIM and CHBDI, the ESIPT process is associated with small barriers of 3.4 and 4.2 kcal/mol; while, in MHBDI, it becomes essentially barrierless. Moreover, we have found two main S₁ excited-state radiationless channels. In the first one, the enol S₁ species decays to the S₀ state via the enol S₁/S₀ conical intersection after overcoming considerable barriers of 7.0 and 7.7 kcal/mol in OHIM and CHBDI (however, in MHBDI, it is nearly barrierless). In the second one, the keto S₁ species is first generated through the ESIPT event; then, it is de-excited into the S₀ state in the vicinity of the keto S₁/S₀ conical intersection. These energetically allowed excited-state decay channels rationalize experimentally observed ultralow fluorescence quantum yields. The insights gained from the present work may help to guide the design of new ortho-hydroxyl GFP core chromophores with improved fluorescence emission and brightness.     

Mechanistic Insights into the Synthesis of Fully Condensed Polyhedral Octaphenylsilsesquioxane

A comprehensive study on the efficient one‐pot synthesis of polyhedral octaphenylsilsesquioxane (OPS) is reported via the hydrolytic condensation of phenyltrimethoxysilane (PTMS) in the presence of basic catalyst to investigate the specific synthesis mechanism. The synthetic reactions are monitored with real time infrared (RTIR) spectroscopy. Then RTIR coupled with ²⁹Si nuclear magnetic resonance spectroscopy (NMR) and matrix‐assisted laser desorption/ionization time of flight mass spectrometry (MALDI‐TOF‐MS) are used to monitor the reactions and identify the intermediary species during the reaction. The rapid hydrolysis of PTMS is detected by RTIR. Contrary to previous reports, the ladder‐like structured species are identified as intermediates during the reaction process. It is suggested that formation of caged T₈ OPS is realized through the chain break and rearrangement of the ladder‐like phenyltrimethoxysilanes. Accordingly, a scheme from hydrolysis of the PTMS to formation of the OPS is provided.     

Conventional Molecular and Novel Structural Mechanistic Insights into Orderly Organelle Interactions

The orderly organelle interaction network is prerequisite for normal life activity of cell, ensuring a balance between communication and uniqueness of organelles. Disorder organelle interaction is implicated in the occurrence and development of many diseases. An in-depth understanding of mechanisms of orderly organelle interaction helps to reveal the pathogenesis of related diseases. Chemical and genetic tools have identified the roles of specific proteins in orderly organelle interaction; however, little is known about the modes, functions and mechanisms of orderly interaction between organelles. With rapid development of imaging tools, deep-going insights into the structure feature of cell membranes have substantially improved our understanding of the mechanisms of ordered organelle interactions. This review summarizes the conventional molecular mechanism of orderly organelle interactions, and highlights the new progress regarding membrane structure and the novel structural mechanism of orderly organelle transport.     

Mechanistic Insights into RNA Transphosphorylation from Kinetic Isotope Effects and Linear Free Energy Relationships of Model Reactions

Phosphoryl transfer reactions are ubiquitous in biology and the understanding of the mechanisms whereby these reactions are catalyzed by protein and RNA enzymes is central to reveal design principles for new therapeutics. Two of the most powerful experimental probes of chemical mechanism involve the analysis of linear free energy relations (LFERs) and the measurement of kinetic isotope effects (KIEs). These experimental data report directly on differences in bonding between the ground state and the rate‐controlling transition state, which is the most critical point along the reaction free energy pathway. However, interpretation of LFER and KIE data in terms of transition‐state structure and bonding optimally requires the use of theoretical models. In this work, we apply density‐functional calculations to determine KIEs for a series of phosphoryl transfer reactions of direct relevance to the 2′‐O‐transphosphorylation that leads to cleavage of the phosphodiester backbone of RNA. We first examine a well‐studied series of phosphate and phosphorothioate mono‐, di‐ and triesters that are useful as mechanistic probes and for which KIEs have been measured. Close agreement is demonstrated between the calculated and measured KIEs, establishing the reliability of our quantum model calculations. Next, we examine a series of RNA transesterification model reactions with a wide range of leaving groups in order to provide a direct connection between observed Brønsted coefficients and KIEs with the structure and bonding in the transition state. These relations can be used for prediction or to aid in the interpretation of experimental data for similar non‐enzymatic and enzymatic reactions. Finally, we apply these relations to RNA phosphoryl transfer catalyzed by ribonuclease A, and demonstrate the reaction coordinate–KIE correlation is reasonably preserved. A prediction of the secondary deuterium KIE in this reaction is also provided. These results demonstrate the utility of building up knowledge of mechanism through the systematic study of model systems to provide insight into more complex biological systems such as phosphoryl transfer enzymes and ribozymes.     

Computational Insights into the Role of External and Local Electric Fields in Macrocyclic Chemical and Biological Systems

The investigation of the role of the electric field in systems of widespread interest employing computational techniques is an emerging area of research. The outcome of applying an oriented external electric field (OEEF) on the geometric and electronic properties of the chemically unique π-conjugated cyclic carbon ring compounds has been explored with density functional theory (DFT). Distinct changes in the structural and electronic features of such ring compounds are observed upon the application of OEEFs. Importantly, the calculations indicate that a mixed aliphatic-aromatic conjugated ring converts from a singlet to a triplet after the application of an OEEF, suggesting potential applications in optoelectronics for such molecules, without the need for photochemically induced change in the spin state. Furthermore, the influence of built-in local electric fields (LEFs) present in naturally occurring macrocyclic systems such as valinomycin has also been explored. Static and ab initio molecular dynamics (AIMD) calculations indicate that LEFs are the primary driving factor in determining the energetically favoured position of counter anions such as chloride (Cl⁻) in the potassium (K⁺) and sodium (Na⁺) coordinated valinomycin macrocycle structures: they exist inside the cage in the case of K⁺ sequestration by valinomycin and outside for Na⁺. This divergence has been proposed to be the determining factor for the selectivity of the valinomycin macrocycle for binding a K⁺ cation over Na⁺.     

Mechanistic Insights into the Self-Assembly of an Acid-Sensitive Photoresponsive Supramolecular Polymer

The supramolecular polymerization of an acid-sensitive pyridyl-based ligand ( L₁ ) bearing a photoresponsive azobenzene moiety was elucidated by mechanistic studies. Addition of trifluoroacetic acid (TFA) led to the transformation of the antiparallel H-bonded fibers of L₁ in methylcyclohexane into superhelical braid-like fibers stabilized by H-bonding of parallel-stacked monomer units. Interestingly, L₁ dimers held together by unconventional pyridine–TFA N⋅⋅⋅H⋅⋅⋅O bridges represent the main structural elements of the assembly. UV-light irradiation caused a strain-driven disassembly and subsequent aggregate reconstruction, which ultimately led to short fibers. The results allowed to understand the mechanism of mutual influence of acid and light stimuli on supramolecular polymerization processes, thus opening up new possibilities to design advanced stimuli-triggered supramolecular systems.     

Mechanistic Insights into Rhenium-Catalyzed Regioselective C-Alkenylation of Phenols with Internal Alkynes

A (μ-aryloxo)rhenium complex was isolated and confirmed as a key precatalyst for rhenium-catalyzed ortho-alkenylation (C-alkenylation) of unprotected phenols with alkynes. The reaction exclusively provided ortho-alkenylphenols; the formation of para or multiply alkenylated phenols and hydrophenoxylation (O-alkenylation) products was not observed. Several mechanistic experiments excluded a classical Friedel–Crafts-type mechanism, leading to the proposed phenolic hydroxyl group assisted electrophilic alkenylation as the most plausible reaction mechanism. For this purpose, the use of rhenium, a metal between the early and late transition metals in the periodic table, was key for the activation of both the soft carbon–carbon triple bond of the alkyne and the hard oxygen atom of the phenol, at the same time. ortho-Selective alkenylation with allenes also provided the corresponding adducts with a substitution pattern different from that obtained by the addition reaction with alkynes.     

Structural and Mechanistic Insights into CO2 Activation by Nitrogenase Iron Protein

The Fe protein of nitrogenase catalyzes the ambient reduction of CO₂ when its cluster is present in the all-ferrous, [Fe₄S₄]⁰ oxidation state. Here, we report a combined structural and theoretical study that probes the unique reactivity of the all-ferrous Fe protein toward CO₂. Structural comparisons of the Azotobacter vinelandii Fe protein in the [Fe₄S₄]⁰ and [Fe₄S₄]⁺ states point to a possible asymmetric functionality of a highly conserved Arg pair in CO₂ binding and reduction. Density functional theory (DFT) calculations provide further support for the asymmetric coordination of O by the “proximal” Arg and binding of C to a unique Fe atom of the all-ferrous cluster, followed by donation of protons by the proximate guanidinium group of Arg that eventually results in the scission of a C−O bond. These results provide important mechanistic and structural insights into CO₂ activation by a surface-exposed, scaffold-held [Fe₄S₄] cluster.     

Mechanistic Insights into Polycycle Formation by Reductive Cyclization in Ikarugamycin Biosynthesis

Ikarugamycin is a member of the polycyclic tetramate macrolactams (PTMs) family of natural products with diverse biological activities. The biochemical mechanisms for the formation of polycyclic ring systems in PTMs remain elusive. The enzymatic mechanism of constructing an inner five‐membered ring in ikarugamycin is reported. A three‐gene‐cassette ikaABC from the marine‐derived Streptomyces sp. ZJ306 is sufficient for conferring ikarugamycin production in a heterologous host. IkaC catalyzes a reductive cyclization reaction to form the inner five‐membered ring by a Michael addition‐like reaction. This study provides the first biochemical evidence for polycycle formation in PTMs and suggests a reductive cyclization strategy which may be potentially applicable in general to the corresponding ring formation in other PTMs.     

Novel Chemical and Biological Insights of Inositol Derivatives in Mediterranean Plants

Inositols (Ins) are natural compounds largely widespread in plants and animals. Bio-sinthetically they derive from sugars, possessing a molecular structure very similar to the simple sugars, and this aspect concurs to define them as primary metabolites, even though it is much more correct to place them at the boundary between primary and secondary metabolites. This dichotomy is well represented by the fact that as primary metabolites they are essential cellular components in the form of phospholipid derivatives, while as secondary metabolites they are involved in a plethora of signaling pathways playing an important role in the surviving of living organisms. myo-Inositol is the most important and widespread compound of this family, it derives directly from d-glucose, and all known inositols, including stereoisomers and derivatives, are the results of metabolic processes on this unique molecule. In this review, we report the new insights of these compounds and their derivatives concerning their occurrence in Nature with a particular emphasis on the plant of the Mediterranean area, as well as the new developments about their biological effectiveness.     

理解量子效应的新视角

以一维势箱中的粒子为例,从直观的视角对量子效应及其之间的关联做了阐明。作为讨论一维势箱量子效应的补充材料,有助于学生进一步理解微观粒子基本特征。     

Mechanistic Insights into the Fluorescence Quenching of Rhodamine 6G by Graphene Oxide

The fluorescence quenching of Rhodamine 6G (R6G) by graphene oxide (GO) was interrogated by R6G fluorescence measurements using a set of controlled GO samples with varied C/O ratios as the quencher.The carbonyl groups on the GO nanosheet turned to play a dominant role in quenching the R6G fluorescence.The quenching in the static regime can be described by the "sphere of action" model.The significant absorption of the R6G fluorescence by the ground-state complex formed between R6G and GO was identified to be responsible for the static quenching.This work offers helpful insights into the fluorescence quenching mechanisms in the R6G/GO system.