Chemical composition and reaction analysis of single aerosol particles

In situ measurements of gas-liquid surface reactions of single aerosol microdroplets are presented. By means of optical levitation in combination with elastic (Mie) and inelastic (Raman) light scattering it is possible to get information on the chemistry of e.g. acid/base reactions as well as the physical behavior of single microparticles.     

Auto‐Tandem Catalysis: A Single Catalyst Activating Mechanistically Distinct Reactions in a Single Reactor

Domino reactions have received great attention as efficient synthetic methodologies for the construction of structurally complex molecules from simple materials in a single operation. Catalysts in domino reactions have also been well studied. In these reactions, a catalyst activates the substrate(s) only once, and the structure of the product is delineated at that time. Recently, the new concept of “tandem catalysis” in domino reactions, in which catalyst(s) sequentially activate more than two mechanistically distinct reactions, has been proposed. Tandem catalysis is categorized into three subclasses: orthogonal‐, auto‐, and assisted‐tandem catalyses. Auto‐tandem catalysis is defined as a process in which one catalyst promotes more than two fundamentally different reactions in a single reactor. An overview of recent and significant achievements in auto‐tandem catalysis is presented in this paper.     

Low-temperature chemistry in helium droplets: reactions of aluminum atoms with O2 and H2O

The doping of He droplets by Al atoms and their reactions with H(2)O and O(2) at T = 0.37 K was investigated. It was found that at high doping concentrations, the incorporated Al atoms do not aggregate to form clusters. They rather remain as separated atoms inside of the He droplets. Mass spectrometry and the recently developed depletion method have been applied to study the reactions. It was found that single Al atoms react with single O(2) molecules. The dominant product of this reaction occurring inside of the He droplets is AlO(2). The reaction between Al and O(2) clusters has also been detected. The Al clusters react with single H(2)O molecules or clusters. While single Al atoms react with H(2)O clusters, no reaction of single Al atoms with a single water molecule was found.     

Microwave-assisted regioselective addition of P(O)-H bonds to alkenes without added solvent or catalyst

The addition of P(O)-H bonds to alkenes has been accomplished using microwave irradiation in the absence of added solvent and catalyst. In addition to single addition reactions, tandem hydrophosphinylation reactions with alkynes afforded unsymmetrical species such as phosphine oxide-phosphinates. [reaction: see text]     

Visible‐Light‐Induced Organic Photochemical Reactions through Energy‐Transfer Pathways

Visible‐light photocatalysis is a rapidly developing and powerful strategy to initiate organic transformations, as it closely adheres to the tenants of green and sustainable chemistry. Generally, most visible‐light‐induced photochemical reactions occur through single‐electron transfer (SET) pathways. Recently, visible‐light‐induced energy‐transfer (EnT) reactions have received considerable attentions from the synthetic community as this strategy provides a distinct reaction pathway, and remarkable achievements have been made in this field. In this Review, we highlight the most recent advances in visible‐light‐induced EnT reactions.     

Kinetic determinations of reactants utilizing uncatalyzed reactions

Kinetic-based determinations of reactants utilizing uncatalyzed chemical reactions do not match the polularity of catalytic methods for the determination of catalysts (particularly transition metal ions) or reactants (e.g., in enzymatic reactions) and this reflects on the scarcity of reviews on the topic. In some cases, however, advances in instrumentation and data manipulation provide competitive alternatives to nonkinetic-based methods for single as well as multispecies determinations. Such advances are reviewed here and applications illustrated.     

Electron‐Transfer and Hydride‐Transfer Pathways in the Stoltz–Grubbs Reducing System (KOtBu/Et3SiH)

Recent studies by Stoltz, Grubbs et al. have shown that triethylsilane and potassium tert ‐butoxide react to form a highly attractive and versatile system that shows (reversible) silylation of arenes and heteroarenes as well as reductive cleavage of C−O bonds in aryl ethers and C−S bonds in aryl thioethers. Their extensive mechanistic studies indicate a complex network of reactions with a number of possible intermediates and mechanisms, but their reactions likely feature silyl radicals undergoing addition reactions and S_H2 reactions. This paper focuses on the same system, but through computational and experimental studies, reports complementary facets of its chemistry based on a) single‐electron transfer (SET), and b) hydride delivery reactions to arenes.     

Recent advances in polyoxometalates acid-catalyzed organic reactions

Polyoxometalates (POMs) have conducive properties such as controlled Brønsted and Lewis acidity, high thermal stability, nontoxic nature, tunable solubility, and less corrosiveness. POMs have been extensively applied in catalytic organic reactions and have an exciting prospect for industrial applications. This review summarized recent progress in the application of POMs as acid catalysts for various organic reactions including CC bond formation, CN bond formation, CO bond formation, heterocyclic synthesis reactions, cyanosilylation and hydrolysis reactions. Various POMs catalysts including heteropoly acids (HPAs) and cationic functionalized HPAs with Brønsted acidity, HPAs supported on non-precious metal support with Brønsted acidity (or both Brønsted and Lewis acidity), transition metal substituted POMs with Lewis acidity were applied in above reactions. This review attempts to provide up-to-date information about POMs acid-catalyzed organic reactions and propose future prospects.     

Titanocene and zirconocene σ-alkynyl complexes in C---C single bond coupling and cleavage reactions

Group 4 metallocene mono- and bis-σ-alkynyl complexes of the type L₂M(σ-CCR) and L₂M(σ-CCR)₂ with M=titanium and zirconium in the oxidation states +3 and +4 and L=Cp (η⁵-cyclopentadienyl) and Cp^* (η⁵-pentamethylcyclopentadienyl) are important compounds for stoichiometric and catalytic C---C single bond coupling and cleavage reactions. Detailed investigations show five-membered metallacyclocumulenes L₂M(η⁴-1,2,3,4-RC₄R) as the key intermediates in both reactions of a C---C single bond cleavage of different 1,4-substituted 1,3-butadiynes RCC---CCR to alkynyl groups and the opposite reaction of C---C single bond formation starting from alkynyl groups under the formation of 1,4-substituted 1,3-butadiynes. Depending on different metals M and ligands L, coupling or cleavage is favoured. Combination of both reactions offered the first C---C single bond metathesis in homogeneous solution, which is photocatalyzed and titanocene-mediated. It proceeds via titanocene–mono-alkynyl complexes, which are interesting species also for other stoichiometric and catalytic C---C coupling reactions. Some similarities regarding the σ-to-π conversion exist between the coupling of the alkynyl groups at titano- and zirconocenes to complexed 1,3-butadiynes on one side and the coupling of phenyl groups at chromium to complexed diphenyl on the other side.     

Carbocations and Electrophilic Reactions

The general concept of carbocations encompasses all cations of carbon containing compounds which can be differentiated into two distinct classes: trivalent (“classical”) carbenium ions and pentacoordinated (“nonclassical”) carbonium ions. In this paper the preparation and structural study (by NMR, IR, Raman and ESCA spectroscopy) of stable carbenium ions and carbonium ions are discussed. As is well known, trivalent carbenium ions play an important role in electrophilic reactions of π- and n-donor systems. Similarly, pentacoordinated carbonium ions are the key to electrophilic reactions of σ-donor systems (single bonds). The ability of single bonds to act as σ-donor lies in their ability to form carbonium ions via triangular two electron, three-center bond formation. Consequently there seems to be no principle difference between the electrophilic reactions of π- and σ-bonds except that the former react more easily, even with weak electrophiles, whereas the latter necessitate more severe conditions. The role of carbocations in electrophilic reactions of π- and σ-donor systems is discussed.     

Multiplex digital PCR: breaking the one target per color barrier of quantitative PCR

Quantitative polymerase chain reactions (qPCR) based on real-time PCR constitute a powerful and sensitive method for the analysis of nucleic acids. However, in qPCR, the ability to multiplex targets using differently colored fluorescent probes is typically limited to 4-fold by the spectral overlap of the fluorophores. Furthermore, multiplexing qPCR assays requires expensive instrumentation and most often lengthy assay development cycles. Digital PCR (dPCR), which is based on the amplification of single target DNA molecules in many separate reactions, is an attractive alternative to qPCR. Here we report a novel and easy method for multiplexing dPCR in picolitre droplets within emulsions-generated and read out in microfluidic devices-that takes advantage of both the very high numbers of reactions possible within emulsions (>10(6)) as well as the high likelihood that the amplification of only a single target DNA molecule will initiate within each droplet. By varying the concentration of different fluorogenic probes of the same color, it is possible to identify the different probes on the basis of fluorescence intensity. Adding multiple colors increases the number of possible reactions geometrically, rather than linearly as with qPCR. Accurate and precise copy numbers of up to sixteen per cell were measured using a model system. A 5-plex assay for spinal muscular atrophy was demonstrated with just two fluorophores to simultaneously measure the copy number of two genes (SMN1 and SMN2) and to genotype a single nucleotide polymorphism (c.815A>G, SMN1). Results of a pilot study with SMA patients are presented.     

Difunctionalization of Alkenes and Alkynes via Intermolecular Radical and Nucleophilic Additions

Popular and readily available alkenes and alkynes are good substrates for the preparation of functionalized molecules through radical and/or ionic addition reactions. Difunctionalization is a topic of current interest due to its high efficiency, substrate versatility, and operational simplicity. Presented in this article are radical addition followed by oxidation and nucleophilic addition reactions for difunctionalization of alkenes or alkynes. The difunctionalization could be accomplished through 1,2-addition (vicinal) and 1,n-addition (distal or remote) if H-atom or group-transfer is involved in the reaction process. A wide range of moieties, such as alkyl (R), perfluoroalkyl (R_f), aryl (Ar), hydroxy (OH), alkoxy (OR), acetatic (O₂CR), halogenic (X), amino (NR₂), azido (N₃), cyano (CN), as well as sulfur- and phosphorous-containing groups can be incorporated through the difunctionalization reactions. Radicals generated from peroxides or single electron transfer (SET) agents, under photoredox or electrochemical reactions are employed for the reactions.     

First-Principles Study of Pd Single-Atom Catalysis to Hydrogen Desorption Reactions on MgH2(110) Surface

MgH₂ is a promising and popular hydrogen storage material. In this work, the hydrogen desorption reactions of a single Pd atom adsorbed MgH₂(110) surface are investigated by using first-principles density functional theory calculations. We find that a single Pd atom adsorbed on the MgH₂(110) surface can signi cantly lower the energy barrier of the hydrogen desorption reactions from 1.802 eV for pure MgH₂(110) surface to 1.154 eV for Pd adsorbed MgH₂(110) surface, indicating a strong Pd single-atom catalytic effect on the hydrogen desorption reactions. Furthermore, the Pd single-atom catalysis significantly reduces the hydrogen desorption temperature from 573 K to 367 K, which makes the hydrogen desorption reactions occur more easily and quickly on the MgH₂(110) surface. We also discuss the microscopic process of the hydrogen desorption reactions through the reverse process of hydrogen spillover mechanism on the MgH₂(110) surface. This study shows that Pd/MgH₂ thin films can be used as good hydrogen storage materials in future experiments.     

Stereoselective synthesis of N-protected pyrrolidines via Pd-catalyzed reactions of γ-(N-acylamino) alkenes and γ-(N-Boc-amino) alkenes with aryl bromides

The stereoselective synthesis of N-acyl- and N-Boc-protected pyrrolidines via Pd-catalyzed reactions of γ-(N-acylamino) alkenes and γ-(N-Boc-amino) alkenes with aryl bromides is described. These reactions effect formation of two bonds in a single operation and proceed with generally high levels of diastereoselectivity. In contrast to previously described reactions of γ-(N-arylamino) alkenes, these transformations proceed in high yield and high regioselectivity with both electron-rich and electron-deficient aryl bromides as well as vinyl bromide substrates.     

Poly(propylene sulfide)–borane: convenient and versatile reagent for organic synthesis

Poly(trimethylene sulfide)–borane adduct has been used as an efficient borane reagent in hydroboration reactions to produce various organoboranes, which have then been used without isolation in further reactions that involve single, double and triple migrations of alkyl groups. The presence of the polymer causes no problems, but there are practical advantages associated with its use, including lack of odour and easy recoverability.     

Nanoplasmonic Photoluminescence Spectroscopy at Single‐Particle Level: Sensing for Ethanol Oxidation

Surface plasmon resonances of metal nanoparticles have shown significant promise for the use of solar energy to drive catalytic chemical reactions. More importantly, understanding and monitoring such catalytic reactions at single‐nanoparticle level is crucial for the study of local reaction processes. Herein, using plasmonic photoluminescence (PL) spectroscopy, we describe a novel sensing method for catalytic ethanol oxidation reactions at the single‐nanoparticle level. The Au nanorod monitors the interfacial interaction with ethanol during the catalytic reaction through the PL intensity changes in the single‐particle PL spectra. The analysis of energy relaxation of excited electron–hole pairs indicates the relationship between the PL quenching and ethanol oxidation reaction on the single Au nanorod.     

Kinetic analysis of simple irreversible non-homogeneous reactions

Simple non-homogeneous irreversible reactions between a mobile reactant A, and immobile reactive groups R, in a solid yielding immobile product B, are considered. The possibilities are discussed of analysing such reactions when they are partially rate-controlled by the diffusion of A. It is shown that the effect of diffusion can be approximately described by a single parameter (“kinetic modulus”) up to a fairly marked degree of diffusion control; so that methods of kinetic analysis analogous to those used for reactions where the solid acts merely as a catalyst can be applied. The “effective reaction constant” previously defined for use as a kinetic modulus (analogous to the “Thiele modulus” of heterogeneous catalytic reactions) is considered further here. An improved, experimentally measurable kinetic modulus, based on the distribution of B across the solid, is also defined and studied.     

Exploring Te–Te Bond Cleavage with Palladium(II): Synthesis,X‐ray Structural Characterization,and Optical Features of Tellurolate and Telluro‐Ether Complexes of Palladium(II)

The focus of this study was to explore reactions of (RTe)₂ with palladium(II) salts. These reactions led to Te–Te bond cleavage and the formation of three tellurolate‐bridged dinuclear complexes and a mononuclear telluro‐ether palladium(II) complex. The methodologies used yielded single source precursors for interesting materials. UV/vis spectroscopy results supported the measured optical bandgap for the complexes in the solid state. A study on the structure of all complexes in the solid state was carried out using single‐crystal X‐ray diffraction. Other analytical methodologies, such as elemental analysis and infrared spectroscopy, were also used for the characterization of the complexes.     

An efficient approach to the synthesis of 3-vinylidene tetrahydropyrans via Prins-type cyclization

Lewis acid-catalyzed intramolecular reactions of oxocarbenium ions with propargylsilanes are described. The results obtained indicate that trimethylsilyl trifluoromethanesulfonate (TMSOTf) efficiently catalyses cyclization leading to the corresponding 3-vinylidene tetrahydropyrans in high yield as single isomers.