Monomer size effect in inelastic collisional dynamics of non-equilibrium soot nucleation.

Molecular dynamics (MD) simulations of the collisional dynamics of the coronene-acepyrene and coronene radical-acepyrene pairs have been carried out to investigate the size effect of monomers of polycyclic aromatic hydrocarbons (PAH) on their non-equilibrium dimerization. The results compared to the previous MD simulations of the smaller pyrene-acepyrene and pyrenyl-acepyrene systems corroborate the non-equilibrium hypothesis of crosslinking PAH dimerization enhanced by physical interaction between the monomers. The phenomenon of inelastic collisional dynamics responsible for non-equilibrium van der Waals dimerization, which fosters a covalent bond formation between the monomers, amplifies with increasing PAH size.

Low-temperature gas-phase formation of cyclopentadiene and its role in the formation of aromatics in the interstellar medium.

The cyclopentadiene (CH) molecule has emerged as a molecular building block of nonplanar polycyclic aromatic hydrocarbons (PAHs) and carbonaceous nanostructures such as corannulene (CH), nanobowls (CH), and fullerenes (C) in deep space. However, the underlying elementary gas-phase processes synthesizing cyclopentadiene from acyclic hydrocarbon precursors have remained elusive. Here, by merging crossed molecular beam experiments with rate coefficient calculations and comprehensive astrochemical modeling, we afford persuasive testimony on an unconventional low-temperature cyclization pathway to cyclopentadiene from acyclic precursors through the reaction of the simplest diatomic organic radical-methylidyne (CH)-with 1,3-butadiene (CH) representing main route to cyclopentadiene observed in TaurusMolecular Cloud.

Experimental and theoretical study of the Sn-O bond formation between atomic tin and molecular oxygen.

The merging of the electronic structure calculations and crossed beam experiments expose the reaction dynamics in the tin (Sn, P) - molecular oxygen (O, XΣ-g) system yielding tin monoxide (SnO, XΣ) along with ground state atomic oxygen O(P). The reaction can be initiated on the triplet and singlet surfaces addition of tin to the oxygen atom leading to linear, bent, and/or triangular reaction intermediates. On both the triplet and singlet surfaces, formation of the tin dioxide structure is required prior to unimolecular decomposition to SnO(XΣ) and O(P).

Interstellar Formation of Nitrogen Heteroaromatics [Indole, CHN; Pyrrole, CHN; Aniline, CHNH]: Key Precursors to Amino Acids and Nucleobases.

Nitrogen-substituted polycyclic aromatic hydrocarbons (NPAHs) are not only fundamental building blocks in the prebiotic synthesis of vital biomolecules such as amino acids and nucleobases of DNA and RNA but also a potential source of the prominent unidentified 6.2 μm interstellar absorption band. Although NPAHs have been detected in meteorites and are believed to be ubiquitous in the universe, their formation mechanisms in deep space have remained largely elusive.

Gas-Phase Structures of Fucosylated Oligosaccharides: Alkali Metal and Halogen Influences.

Fucosylated carbohydrate antigens play critical roles in physiology and pathology with function linked to their structural details. However, the separation and structural characterization of isomeric fucosylated epitopes remain challenging analytically. Here, we report for the first time the influence of alkali metal cations (Li, Na, K, Rb, and Cs) and halogen anions (Cl, Br, and I) on the gas-phase conformational landscapes of common fucosylated trisaccharides (Lewis A, X, and H types 1 and 2) and tetrasaccharides (Lewis B and Y) using trapped ion mobility spectrometry coupled to mass spectrometry and theoretical calculations.

Fulvenallenyl Radical (CH)-Mediated Gas-Phase Synthesis of Bicyclic Aromatic CH Isomers: Can Fulvenallenyl Efficiently React with Closed-Shell Hydrocarbons?

To understand the reactivity of resonantly stabilized radicals, often found in relevant concentrations in gaseous environments, it is important to determine their main reaction pathways. Here, it is investigated whether the fulvenallenyl radical (CH) reacts preferentially with closed-shell molecules or radicals. Electronic structure calculations on the CH potential energy surface accessed by the reactions of CH with methylacetylene (CHCCH) and allene (HCCCH) were combined with RRKM-ME calculations of temperature- and pressure-dependent rate constants using the automated EStokTP software suite and kinetic modeling to assess the reactivity of CH with closed-shell unsaturated hydrocarbons.

Exploring the chemical dynamics of phenanthrene (CH) formation the bimolecular gas-phase reaction of the phenylethynyl radical (CHCC) with benzene (CH).

The exploration of the fundamental formation mechanisms of polycyclic aromatic hydrocarbons (PAHs) is crucial for the understanding of molecular mass growth processes leading to two- and three-dimensional carbonaceous nanostructures (nanosheets, graphenes, nanotubes, buckyballs) in extraterrestrial environments (circumstellar envelopes, planetary nebulae, molecular clouds) and combustion systems. While key studies have been conducted exploiting traditional, high-temperature mechanisms such as the hydrogen abstraction-acetylene addition (HACA) and phenyl addition-dehydrocyclization (PAC) pathways, the complexity of extreme environments highlights the necessity of investigating chemically diverse mass growth reaction mechanisms leading to PAHs. Employing the crossed molecular beams technique coupled with electronic structure calculations, we report on the gas-phase synthesis of phenanthrene (CH)-a three-ring, 14π benzenoid PAH- a phenylethynyl addition-cyclization-aromatization mechanism, featuring bimolecular reactions of the phenylethynyl radical (CHCC, XA) with benzene (CH) under single collision conditions.

Differentiating Structurally Similar Fentanyl Analogs by Comparing Density Functional Theory (DFT) Calculations and Surface-Enhanced Raman Spectroscopy (SERS) Results.

Fentanyl and fentanyl analogs are the main cause of recent overdose deaths in the United States. The presence of fentanyl analogs in illicit drugs makes it difficult to estimate their potencies. This makes the detection and differentiation of fentanyl analogs critically significant.

Methanetriol─Formation of an Impossible Molecule.

Orthocarboxylic acids─organic molecules carrying three hydroxyl groups at the same carbon atom─have been distinguished as vital reactive intermediates by the atmospheric science and physical (organic) chemistry communities as transients in the atmospheric aerosol cycle. Predicted short lifetimes and their tendency to dehydrate to a carboxylic acid, free orthocarboxylic acids, signify one of the most elusive classes of organic reactive intermediates, with even the simplest representative methanetriol (CH(OH))─historically known as orthoformic acid─not previously been detected experimentally. Here, we report the first synthesis of the previously elusive methanetriol molecule in low-temperature mixed methanol (CHOH) and molecular oxygen (O) ices subjected to energetic irradiation.

Phenalenyl growth reactions and implications for prenucleation chemistry of aromatics in flames.

The energetics and kinetics of phenalene and phenalenyl growth reactions were studied theoretically. Rate constants of phenalene and phenalenyl H-abstraction and CH addition to the formed radicals were evaluated through quantum-chemical and rate-theory calculations. The obtained values, assigned to all π radicals, were tested in deterministic and kinetic Monte Carlo simulations of aromatics growth under conditions of laminar premixed flames.

Transformation of Mercurous [Hg(I)] Species during Laboratory Standard Preparation and Analysis: Implication for Environmental Analysis.

Hg(I) may control Hg redox kinetics; however, its metastable nature hinders analysis. Herein, the stability of Hg(I) during standard preparation and analysis was studied. Gravimetric analysis showed that Hg(I) was stable in its stock solution (1000 mg L), yet completely disproportionated when its dilute solution (10 μg L) was analyzed using liquid chromatography (LC)-ICPMS.

Elucidating the chemical dynamics of the elementary reactions of the 1-propynyl radical (CHCC; XA) with 2-methylpropene ((CH)CCH; XA).

Exploiting the crossed molecular beam technique, we studied the reaction of the 1-propynyl radical (CHCC; XA) with 2-methylpropene (isobutylene; (CH)CCH; XA) at a collision energy of 38 ± 3 kJ mol. The experimental results along with and statistical calculations revealed that the reaction has no entrance barrier and proceeds indirect scattering dynamics involving CH intermediates with lifetimes longer than their rotation period(s). The reaction is initiated by the addition of the 1-propynyl radical with its radical center to the π-electron density at the C1 and/or C2 position in 2-methylpropene.

Plasmon-mediated dehydrogenation of the aromatic methyl group and benzyl radical formation.

Plasmonic molecular junctions can harvest visible light and effectively catalyze chemical reactions. The strong light field concentrated in the plasmonic junction also enables the application of surface enhanced Raman spectroscopy (SERS) to probe the catalyzed chemical reactions and in real time down to single-molecule resolution. The benzyl radical produced from the aromatic methyl group through the dehydrogenation reaction is an important precursor for a large variety of reactions.

One Collision-Two Substituents: Gas-Phase Preparation of Xylenes under Single-Collision Conditions.

The fundamental reaction pathways to the simplest dialkylsubstituted aromatics-xylenes (C H (CH ) )-in high-temperature combustion flames and in low-temperature extraterrestrial environments are still unknown, but critical to understand the chemistry and molecular mass growth processes in these extreme environments. Exploiting crossed molecular beam experiments augmented by state-of-the-art electronic structure and statistical calculations, this study uncovers a previously elusive, facile gas-phase synthesis of xylenes through an isomer-selective reaction of 1-propynyl (methylethynyl, CH CC) with 2-methyl-1,3-butadiene (isoprene, C H ). The reaction dynamics are driven by a barrierless addition of the radical to the diene moiety of 2-methyl-1,3-butadiene followed by extensive isomerization (hydrogen shifts, cyclization) prior to unimolecular decomposition accompanied by aromatization via atomic hydrogen loss.

6-azido and 6-azidomethyl uracil nucleosides.

Azido nucleosides have been utilized for click reactions, metabolic incorporation into cellular DNA, and fluorescent imaging of live cells. Two classes of 6-azido modified uracil nucleosides; one with azido group directly attached to uracil ring and second with azido group attached methylene linker are described. The 6-azido-2'-deoxyuridine (6-AdU) was prepared in 55% overall yield by lithiation-based regioselective C6-iodination of silyl protected 2'-deoxyuridine followed by treatment with sodium azide and deprotection with TBAF.

Gas-phase preparation of azulene (CH) and naphthalene (CH) the reaction of the resonantly stabilized fulvenallenyl and propargyl radicals.

Synthetic routes to the 10π Hückel aromatic azulene (CH) molecule, the simplest polycyclic aromatic hydrocarbon carrying an adjacent five- and seven-membered ring, have been of fundamental importance due to the role of azulene - a structural isomer of naphthalene - as an essential molecular building block of saddle-shaped carbonaceous nanostructures such as curved nanographenes and nanoribbons. Here, we report on the very first gas phase preparation of azulene by probing the gas-phase reaction between two resonantly stabilized radicals, fulvenallenyl and propargyl , in a molecular beam through isomer-resolved vacuum ultraviolet photoionization mass spectrometry. Augmented by electronic structure calculations, the novel Fulvenallenyl Addition Cyclization Aromatization (FACA) reaction mechanism affords a versatile concept for introducing the azulene moiety into polycyclic aromatic systems thus facilitating an understanding of barrierless molecular mass growth processes of saddle-shaped aromatics and eventually carbonaceous nanoparticles (soot, interstellar grains) in our universe.

Gas-phase formation of the resonantly stabilized 1-indenyl (CH) radical in the interstellar medium.

The 1-indenyl (CH) radical, a prototype aromatic and resonantly stabilized free radical carrying a six- and a five-membered ring, has emerged as a fundamental molecular building block of nonplanar polycyclic aromatic hydrocarbons (PAHs) and carbonaceous nanostructures in deep space and combustion systems. However, the underlying formation mechanisms have remained elusive. Here, we reveal an unconventional low-temperature gas-phase formation of 1-indenyl via barrierless ring annulation involving reactions of atomic carbon [C(P)] with styrene (CHCH) and propargyl (CH) with phenyl (CH).

Gas-Phase Synthesis of Coronene through Stepwise Directed Ring Annulation.

Molecular beam experiments together with electronic structure calculations provide the first evidence of a complex network of elementary gas-phase reactions culminating in the bottom-up preparation of the 24π aromatic coronene (CH) molecule─a representative peri-fused polycyclic aromatic hydrocarbon (PAH) central to the complex chemistry of combustion systems and circumstellar envelopes of carbon stars. The gas-phase synthesis of coronene proceeds via aryl radical-mediated ring annulations through benzo[]pyrene (CH) and benzo[]perylene (CH) involving armchair-, zigzag-, and arm-zig-edged aromatic intermediates, highlighting the chemical diversity of molecular mass growth processes to polycyclic aromatic hydrocarbons. The isomer-selective identification of five- to six-ringed aromatics culminating with the detection of coronene is accomplished through photoionization and is based upon photoionization efficiency curves along with photoion mass-selected threshold photoelectron spectra, providing a versatile concept of molecular mass growth processes via aromatic and resonantly stabilized free radical intermediates to two-dimensional carbonaceous nanostructures.

Exploring the Chemical Dynamics of Phenylethynyl Radical (CHCC; XA) Reactions with Allene (HCCCH; XA) and Methylacetylene (CHCCH; XA).

The bimolecular gas-phase reactions of the phenylethynyl radical (CHCC, XA) with allene (HCCCH), allene- (DCCCD), and methylacetylene (CHCCH) were studied under single-collision conditions utilizing the crossed molecular beams technique and merged with electronic structure and statistical calculations. The phenylethynyl radical was found to add without an entrance barrier to the C1 carbon of the allene and methylacetylene reactants, resulting in doublet CH collision complexes with lifetimes longer than their rotational periods. These intermediates underwent unimolecular decomposition via atomic hydrogen loss through tight exit transition states in facile radical addition─hydrogen atom elimination mechanisms forming predominantly 3,4-pentadien-1-yn-1-ylbenzene (CHCCCHCCH) and 1-phenyl-1,3-pentadiyne (CHCCCCCH) in overall exoergic reactions (-110 kJ mol and -130 kJ mol) for the phenylethynyl-allene and phenylethynyl-methylacetylene systems, respectively.

Quantum Tunneling Mediated Low-Temperature Synthesis of Interstellar Hemiacetals.

Sugars and sugar-related molecules are ubiquitous in carbonaceous meteorites and in star-forming regions, but the underlying mechanisms of their formation have remained largely elusive. Herein, we report an unconventional synthesis of the hemiacetal, (/)-1-methoxyethanol (CHOCH(OH)CH), through quantum tunneling mediated reactions in low-temperature interstellar model ices composed of acetaldehyde (CHCHO) and methanol (CHOH). The detection of racemic 1-methoxyethanol through a bottom-up synthesis from simple, abundant precursor molecules within interstellar ices represents a vital starting point to the formation of complex interstellar hemiacetals.

Synthesis of interstellar propen-2-ol (CHC(OH)CH) - the simplest enol tautomer of a ketone.

Enols - tautomers of ketones or aldehydes - are anticipated to be ubiquitous in the interstellar medium and play a key role in the formation of complex organic molecules in deep space, but their fundamental formation mechanisms have remained largely elusive as of now. Here we present a combined experimental and computational study demonstrating the first preparation of propen-2-ol (CHC(OH)CH) and its isomer methyl vinyl ether (CHOCHCH) in low-temperature acetone (CHCOCH) ices upon exposure to energetic electrons. Propen-2-ol is the simplest enol tautomer of a ketone.

Unconventional gas-phase preparation of the prototype polycyclic aromatic hydrocarbon naphthalene (CH) the reaction of benzyl (CH) and propargyl (CH) radicals coupled with hydrogen-atom assisted isomerization.

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the interstellar medium and in meteorites such as Murchison and Allende and signify the missing link between resonantly stabilized free radicals and carbonaceous nanoparticles (soot particles, interstellar grains). However, the predicted lifetime of interstellar PAHs of some 10 years imply that PAHs should not exist in extraterrestrial environments suggesting that key mechanisms of their formation are elusive. Exploiting a microchemical reactor and coupling these data with computational fluid dynamics (CFD) simulations and kinetic modeling, we reveal through an isomer selective product detection that the reaction of the resonantly stabilized benzyl and the propargyl radicals synthesizes the simplest representative of PAHs - the 10π Hückel aromatic naphthalene (CH) molecule - the novel Propargyl Addition-BenzAnnulation (PABA) mechanism.

Anticancer Drug Doxorubicin Spontaneously Reacts with GTP and dGTP.

Here, we reported a spontaneous reaction between anticancer drug doxorubicin and GTP or dGTP. Incubation of doxorubicin with GTP or dGTP at 37 °C or above yields a covalent product: the doxorubicin-GTP or -dGTP conjugate where a covalent bond is formed between the C14 position of doxorubicin and the 2-amino group of guanine. Density functional theory calculations show the feasibility of this spontaneous reaction.

Gas phase synthesis of the C40 nano bowl CH.

Nanobowls represent vital molecular building blocks of end-capped nanotubes and fullerenes detected in combustion systems and in deep space such as toward the planetary nebula TC-1, but their fundamental formation mechanisms have remained elusive. By merging molecular beam experiments with electronic structure calculations, we reveal a complex chain of reactions initiated through the gas-phase preparation of benzocorannulene (CH) via ring annulation of the corannulenyl radical (CH) by vinylacetylene (CH) as identified isomer-selectively in situ via photoionization efficiency curves and photoion mass-selected threshold photoelectron spectra. In silico studies provided compelling evidence that the benzannulation mechanism can be expanded to pentabenzocorannulene (CH) followed by successive cyclodehydrogenation to the C40 nanobowl (CH) - a fundamental building block of buckminsterfullerene (C).

Radical-Radical Reactions in Molecular Weight Growth: The Phenyl + Propargyl Reaction.

The mechanism for hydrocarbon ring growth in sooting environments is still the subject of considerable debate. The reaction of phenyl radical (CH) with propargyl radical (HCCCH) provides an important prototype for radical-radical ring-growth pathways. We studied this reaction experimentally over the temperature range of 300-1000 K and pressure range of 4-10 Torr using time-resolved multiplexed photoionization mass spectrometry.