February 2025
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3 Reads
The Journal of Physical Chemistry A
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February 2025
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3 Reads
The Journal of Physical Chemistry A
February 2025
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20 Reads
ACS Central Science
January 2025
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33 Reads
The Journal of Physical Chemistry Letters
December 2024
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10 Reads
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. The increase in the size of the colliding monomers enhances the non-equilibrium effects as the growing pool of low-frequency modes provides a larger sink for the energy of the colliding PAH monomers. Based on the direct count of the crosslinking reaction events observed in the MD simulations, the forward rate constant for the coronene radical–acepyrene association is estimated at ∼10⁻¹¹ cm³ molecule⁻¹ s⁻¹, showing a 15-fold increase with respect to the value from the statistical Rice–Ramsperger–Kassel–Marcus calculations. A comparison with the eightfold increase reported previously for the pyrenyl–acepyrene system shows that the statistical (equilibrium-based) calculations increasingly underestimate the reaction rate with the increasing size of the interacting PAHs from pyrene to coronene. The total increase of the MD-assessed rate constant for the coronene radical–acepyrene dimerization reaction as compared to pyrenyl–acepyrene is a factor of 2.4, with the overall collision efficiency to produce dimerized products growing by 30%.
December 2024
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63 Reads
Proceedings of the National Academy of Sciences
The cyclopentadiene (C 5 H 6 ) molecule has emerged as a molecular building block of nonplanar polycyclic aromatic hydrocarbons (PAHs) and carbonaceous nanostructures such as corannulene (C 20 H 10 ), nanobowls (C 40 H 10 ), and fullerenes (C 60 ) 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 (C 4 H 6 ) representing main route to cyclopentadiene observed in TaurusMolecular Cloud. This facile route provides potential solution for the incorporation of the cyclopentadiene moiety in complex aromatic systems via bottom–up molecular mass growth processes and offers an entry point to the low-temperature chemistry in deep space leading eventually to nonplanar PAHs in our carbonaceous Universe.
October 2024
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8 Reads
Physical Chemistry Chemical Physics
The merging of the electronic structure calculations and crossed beam experiments expose the reaction dynamics in the tin (Sn, ³ P j ) − molecular oxygen (O 2 , X ³ Σ g ⁻ ) system yielding tin monoxide (SnO,...
October 2024
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105 Reads
Journal of the American Chemical Society
September 2024
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11 Reads
The Journal of Physical Chemistry B
July 2024
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57 Reads
The Journal of Physical Chemistry A
June 2024
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118 Reads
Aromatic molecules represent fundamental building blocks in prebiotic chemistry and are contemplated as vital precursors to DNA and RNA nitrogen bases. However, despite the identification of some 300 molecules in extraterrestrial environments, the pathways to pyridine (C5H5N), pyridinyl (C5H4N), and (iso)quinoline (C9H7N) the simplest representative of mono and bicyclic aromatic molecule carrying nitrogen are elusive. Here, we afford compelling evidence on the gas phase formation of methylene amidogen (H2CN) and cyanomethyl (H2CCN) radicals via molecular beam studies and electronic structure calculations. The modeling of the chemistries of Taurus Molecular Cloud (TMC 1) and Titans atmosphere contemplates a complex chain of reactions synthesizing pyridine, pyridinyl, and (iso)quinoline from H2CN and H2CCN at levels of up to 75%. This study affords unique entry points to precursors of DNA and RNA nitrogen bases in hydrocarbon rich extraterrestrial environments thus changing the way we think about the origin of prebiotic molecules in our Galaxy.
... Since the HAVA mechanism generally involves only submerged barriers, it can operate at low temperatures like those in dense molecular clouds. Recently, the reaction between the phenylethynyl radical (C 6 H 5 CC • ) and benzene has been proposed as another viable bottom-up mechanism to form phenanthrene at low temperature 40 . However, vinylacetylene addition to the 4-phenanthrenyl radical is not expected to form pyrene 41 . ...
May 2024
Faraday Discussions
... A previous study revealed that the potency of fentanyl analogues varies based on molecular variations at para, ortho, and meta positions. 23 These results confirm this concept reflected in the data presented as specific levels of BChE inhibition occurred when exposed to different fentanyl analogues, which is highlighted in the inhibitory patterns represented in Figure 8. ...
April 2024
Applied Spectroscopy
... The same applies when Hg 0 (aq) is removed from the solution, e.g., by a gas stream. Hg 2 2+ can be a major speciation component in heavily polluted waters (Fang et al., 2024), but is insignificant in the atmosphere. ...
April 2024
Environmental Science and Technology
... One of the main stages of the synthesis and destruction of PAHs is the sequential addition of acetylene molecules, atomic or molecular hydrogen or various hydrocarbon radicals to PAH molecules, usually consisting of several five-and six-member ring fragments [5][6][7][8][9][10][11][12][13][14]. Fusion reactions of two or more hydrocarbon fragments into a single complex are also one of possible growth mechanism of soot particles [15][16][17]. ...
April 2024
Physical Chemistry Chemical Physics
... Besides the intensively investigated reactions discussed above, a diverse range of other plasmon-driven bondcleaving reactions, including but not limited to N-H bond cleavage in mercaptopyridine [177] and hypoxanthine [178], C-B bond cleavage in mercaptophenylboronic acid [179], C-N bond cleavage in para-nitrothiophenol [180], azo bond cleavage in 4,4 ′ -dimercaptoazobenzene [181], O-O bond cleavage in hydrogen peroxide [182], [183], C-I bond cleavage in diaryliodonium salts [184], [185], C-H bond cleavage in aromatic methyl groups [186], and C-O bond cleavage in 1-phenoxy-2-phenylethane [187], allyl phenyl ether [188], and alkoxyamines [189], have also been reported in the literature. The experimental observations reported so far suggest that these reactions are primarily driven by either injection of hot carriers into the molecular adsorbates or plasmon-enhanced intramolecular electronic excitations. ...
Reference:
Plasmon-driven molecular scission
November 2023
... This radiosensitization enhancement is believed to be attributed to the generation of nitrogen centered radicals (NCRs) such as the oxidizing neutral, π-type aminyl radical (RNH•) [25][26][27][28] and their subsequent reactions [29][30][31] known to play an important role in peptide cellular signaling [32][33][34] and conjugation [35]. Employing a combination of electron spin resonance (ESR) spectroscopy at low temperature, pulse radiolysis at ambient temperature and theoretical calculations, we previously showed that azidosubstituted nucleosides and sugars form NCRs specifically at the site of the azide group via dissociative electron attachment (DEA) [25][26][27][28][36][37][38]. Thus, addition of an electron to the azido group in 5-AmdU forms the highly unstable azide anion radical (RN 3 •‾) which following facile N 2 loss forms the highly basic nitrene anion radical (RN•‾). ...
October 2023
Nucleosides Nucleotides & Nucleic Acids
... Finally, the T(θ) function exhibits a forwardbackward symmetry with sideway scattering and hence a distribution maximum at 90 o . These results propose indirect scattering dynamics via the formation of long-lived C2NH3 intermediates 33 . ...
September 2023
Science Advances
... The experiments were conducted at the VUV beamline (BL03U) at the National Synchrotron Radiation Laboratory (NSRL) in Hefei, China [9]. Details of the experimental setup are documented in previous publications [10]. Briefly, the reactor consists of a 40 mm long silicon carbide (SiC) tube located in a high vacuum chamber (~10 -6 Torr). ...
September 2023
... Second, 7, 18, and 19 form via barrierless radical-radical recombination via reactions [5][6][7]. These reactions are exoergic by 334 kJ mol −1 to 420 kJ mol −1 48,49 . ...
August 2023
Chem
... Pyrazole, as an aromatic heterocycle with π-electron excess, displays distinct reactivity patterns in organic chemistry. Nucleophilic attacks are favored at positions 3 and 5, while electrophilic substitution reactions preferentially take place at position 4 [10] ( Figure 2). Unsubstituted pyrazole can be represented in three distinct tautomeric forms, as illustrated in Figure 3. ...
July 2023
Crystals