Exotic Reaction Research Articles

Diamond formation kinetics in shock-compressed C─H─O samples recorded by small-angle x-ray scattering and x-ray diffraction.

Extreme conditions inside ice giants such as Uranus and Neptune can result in peculiar chemistry and structural transitions, e.g., the precipitation of diamonds or superionic water, as so far experimentally observed only for pure C─H and H2O systems, respectively. Here, we investigate a stoichiometric mixture of C and H2O by shock-compressing polyethylene terephthalate (PET) plastics and performing in situ x-ray probing. We observe diamond formation at pressures between 72 ± 7 and 125 ± 13 GPa at temperatures ranging from ~3500 to ~6000 K. Combining x-ray diffraction and small-angle x-ray scattering, we access the kinetics of this exotic reaction. The observed demixing of C and H2O suggests that diamond precipitation inside the ice giants is enhanced by oxygen, which can lead to isolated water and thus the formation of superionic structures relevant to the planets' magnetic fields. Moreover, our measurements indicate a way of producing nanodiamonds by simple laser-driven shock compression of cheap PET plastics.

Gas-Phase Preparation of Silyl Cyanide (SiH3CN) via a Radical Substitution Mechanism.

The silyl cyanide (SiH3CN) molecule, the simplest representative of a fully saturated silacyanide, was prepared in the gas phase under single-collision conditions via a radical substitution mechanism. The chemical dynamics were direct and revealed a pronounced backward scattering as a consequence of a transition state with a pentacoordinated silicon atom and almost colinear geometry of the attacking cyano radical and leaving hydrogen. Compared to the isovalent cyano (CN)-methane (CH4) system, the CN-SiH4 system dramatically reduces the energy of the transition state to silyl cyanide by nearly 100 kJ mol-1, which reveals a profound effect on the chemical bonding and reaction mechanism. In extreme high-temperature environments including circumstellar envelopes of IRC +10216, this versatile radical substitution mechanism may synthesize organosilicon molecules via reactions of silane with doublet radicals. Overall, this study provides rare insights into the exotic reaction mechanisms of main-group XIV elements in extreme environments and affords deeper insights into fundamental molecular mass growth processes involving silicon in our universe.

Stem Cell Transplantation: A Promising Therapy for Spinal Cord Injury

Spinal Cord Injury (SCI) causes irreversible functional loss of the affected population. The incidence of SCI keeps increasing, resulting in huge burden on the society. The pathogenesis of SCI involves neuron death and exotic reaction, which could impede neuron regeneration. In clinic, the limited regenerative capacity of endogenous cells after SCI is a major problem. Recent studies have demonstrated that a variety of stem cells such as induced Pluripotent Stem Cells (iPSCs), Embryonic Stem Cells (ESCs), Mesenchymal Stem Cells (MSCs) and Neural Progenitor Cells (NPCs) /Neural Stem Cells (NSCs) have therapeutic potential for SCI. However, the efficacy and safety of these stem cellbased therapy for SCI remain controversial. In this review, we introduce the pathogenesis of SCI, summarize the current status of the application of these stem cells in SCI repair, and discuss possible mechanisms responsible for functional recovery of SCI after stem cell transplantation. Finally, we highlight several areas for further exploitation of stem cells as a promising regenerative therapy of SCI.

Direct dioxygen evolution in collisions of carbon dioxide with surfaces

The intramolecular conversion of CO2 to molecular oxygen is an exotic reaction, rarely observed even with extreme optical or electronic excitation means. Here we show that this reaction occurs readily when CO2 ions scatter from solid surfaces in a two-step sequential collision process at hyperthermal incidence energies. The produced O2 is preferentially ionized by charge transfer from the surface over the predominant atomic oxygen product, leading to direct detection of both O2+ and O2−. First-principles simulations of the collisional dynamics reveal that O2 production proceeds via strongly-bent CO2 configurations, without visiting other intermediates. Bent CO2 provides dynamic access to the symmetric dissociation of CO2 to C+O2 with a calculated yield of 1 to 2% depending on molecular orientation. This unexpected collision-induced transformation of individual CO2 molecules provides an accessible pathway for generating O2 in astrophysical environments and may inspire plasma-driven electro- and photo-catalytic strategies for terrestrial CO2 reduction.

Gas‐Phase Synthesis of the Elusive Cyclooctatetraenyl Radical (C8H7) via Triplet Aromatic Cyclooctatetraene (C8H8) and Non‐Aromatic Cyclooctatriene (C8H8) Intermediates

AbstractThe 1,2,4,7‐cyclooctatetraenyl radical (C8H7) has been synthesized for the very first time via the bimolecular gas‐phase reaction of ground‐state carbon atoms with 1,3,5‐cycloheptatriene (C7H8) on the triplet surface under single‐collision conditions. The barrier‐less route to the cyclic 1,2,4,7‐cyclooctatetraenyl radical accesses exotic reaction intermediates on the triplet surface, which cannot be synthesized via classical organic chemistry methods: the triplet non‐aromatic 2,4,6‐cyclooctatriene (C8H8) and the triplet aromatic 1,3,5,7‐cyclooctatetraene (C8H8). Our approach provides a clean gas‐phase synthesis of this hitherto elusive cyclic radical species 1,2,4,7‐cyclooctatetraenyl via a single‐collision event and opens up a versatile, unconventional path to access this previously largely obscure class of cyclooctatetraenyl radicals, which have been impossible to access through classical synthetic methods.

Gas-Phase Synthesis of the Elusive Cyclooctatetraenyl Radical (C8 H7 ) via Triplet Aromatic Cyclooctatetraene (C8 H8 ) and Non-Aromatic Cyclooctatriene (C8 H8 ) Intermediates.

The 1,2,4,7-cyclooctatetraenyl radical (C8 H7 ) has been synthesized for the very first time via the bimolecular gas-phase reaction of ground-state carbon atoms with 1,3,5-cycloheptatriene (C7 H8 ) on the triplet surface under single-collision conditions. The barrier-less route to the cyclic 1,2,4,7-cyclooctatetraenyl radical accesses exotic reaction intermediates on the triplet surface, which cannot be synthesized via classical organic chemistry methods: the triplet non-aromatic 2,4,6-cyclooctatriene (C8 H8 ) and the triplet aromatic 1,3,5,7-cyclooctatetraene (C8 H8 ). Our approach provides a clean gas-phase synthesis of this hitherto elusive cyclic radical species 1,2,4,7-cyclooctatetraenyl via a single-collision event and opens up a versatile, unconventional path to access this previously largely obscure class of cyclooctatetraenyl radicals, which have been impossible to access through classical synthetic methods.

Electrospray ion mobility mass spectrometry of positively and negatively charged (1R,2S)-dodecyl(2-hydroxy-1-methyl-2-phenylethyl)dimethylammonium bromide aggregates.

Self-assembling processes of surfactants in the gas phase constitute a developing research field of interest since they allow information to be gained on the peculiar structural organization of these aggregates, on their ability to incorporate from small molecules up to proteins and on their possible use as carriers of drugs in the gas phase or as cleaning agents and exotic reaction media. The mass spectra of charged aggregates of the chiral surfactant (1R,2S)-dodecyl(2-hydroxy-1-methyl-2-phenylethyl)dimethylammonium bromide (DMEB) in the gas phase have been recorded using a Synapt G2-Si mass spectrometer in the positive and negative ion mode. For comparison purposes, the mass spectra of sodium bis(2-ethylhexyl)sulfosuccinate and sodium octane sulfonate aggregates have also been recorded under the same experimental conditions. The collisional cross sections of positively and negatively charged DMEB aggregates were obtained through an appropriate calibration of the measured drift times. For all the surfactants investigated, it has been found that there is a lowest and a highest limit of the aggregation number at each charge state: no aggregates are found outside this range. Moreover, the occurrence at each aggregation number and extra charge of a unique value of drift time points toward aggregates whose conformations do not show discernible shape change in the experiment time scale. The analysis of the collisional cross sections emphasizes that the DMEB aggregates are nearly spherical clusters somewhat affected by the charge state and constituted by interlaced polar and apolar domains. The analysis of all the experimental findings indicates that in the gas phase DMEB forms supramolecular aggregates characterized by an internal organization whose stability is triggered by the charge state. The comparison of the behavior of DMEB aggregates with that of sodium bis(2-ethylhexyl)sulfosuccinate and sodium octane sulfonate aggregates allows us to highlight the effects on the aggregate organization in gas phase due to nature of the head group and alkyl chain steric hindrance.

Exotic reaction front migration and stage structure in lithiated silicon nanowires.

Nanostructured silicon anodes, which possess extremely high energy density and accommodate large strain without pulverization, have been developed rapidly for high-power lithium ion batteries. Here, using in situ transmission electron microscopy, the lithiation behavior of silicon nanowires with diameters smaller than 60 nm was investigated. The study demonstrated a direct dependence of the self-limiting lithiation on the pristine diameter. A "punch-through" lithiation process at the core of nanowires with pristine diameters slightly larger than the self-limiting threshold is suggested to occur with the consequent formation of a stage structure. Our work demonstrates the crucial role of mechanical stress and local defects in determining the migration and geometry of the reaction front at the mesoscopic scale. This intriguing finding holds critical significance for the application of silicon nanostructures in high-power lithium ion batteries.

ChemInform Abstract: Transition Metal Mediated Cleavage and Activation of C—C Single Bonds

AbstractReview: ca. 200 refs.

Transition‐Metal‐Mediated Cleavage and Activation of C–C Single Bonds

AbstractThe activation and cleavage of C–C single bonds mediated by transition metal complexes is one of the most challenging reactions, both practically and in terms of understanding, in the field of metal organic chemistry. In this review the fundamental reactions – oxidative addition, β‐carbon elimination, retro‐allylation, and radical cleavage – so far successfully applied for this transformation are discussed in terms of their mechanisms, their intrinsic problems, and their published examples, which are still fairly rare. Decarbonylation, as another fundamental reaction, is only touched briefly. This group of reactions is today poised to set aside its shadow existence as an exotic reaction class. Meanwhile the number of catalytic and even enantioselective processes involvingC–C single bond cleavage is slowly increasing, although the substrates used in these reactions are still limited to quite special connection patterns. The basic challenges for the future and the paradigms concerning this reaction are presented.

R-matrix calculation of negative muon capture by helium ions

Negative muon ({mu}{sup -}) capture by helium ions (He{sup +}), i.e., {mu}{sup -}+He{sup +}{yields}{mu}{sup -}He{sup 2+}+e, is investigated by carrying out a rigorous R-matrix quantum-mechanical calculation. The present exotic reaction exhibits a Rydberg series of resonances, which are described as an electron attached to an ion core {mu}{sup -}He{sup 2+}, or in other words as a Feshbach type originating from the product channel {mu}{sup -}He{sup 2+}+e. The series limit of the resonances is the excited-state energy of {mu}{sup -}He{sup 2+}. The {mu}{sup -} capture cross sections (or collision strengths) and their energy-averaged quantities are calculated at collision energies up to 7 eV. At a rough guess, a resonance bunch belonging to each Rydberg state appears in the form of two humps. The final-state distribution of the product ions {mu}{sup -}He{sup 2+} is also presented. The highest energetically possible states are mostly occupied by {mu}{sup -}He{sup 2+} at all the energies. However, the angular momentum distribution of {mu}{sup -}He{sup 2+} becomes quite different in individual cases of resonances.

Dissociative recombination of antiprotonic helium ions:e+p¯He2+→p¯+He+

Rearrangement reaction in electron scattering from antiprotonic helium ions $(\overline{p}{\text{He}}^{2+})$ in highly excited states, i.e., $e+\overline{p}{\text{He}}^{2+}\ensuremath{\rightarrow}\overline{p}+{\text{He}}^{+}$, is theoretically investigated by using the $R$-matrix method. This type of reaction can be identified as dissociative recombination (DR) which is well known in molecular physics. If the concept of the adiabatic Born-Oppenheimer separation is applied, the present exotic reaction has a similarity to the DR of ${\text{HeH}}^{+}$ molecules in the sense that the system has no crossings of the adiabatic potential curves. The present exotic DR reaction shows a variety of resonances, which can be described as a Rydberg electron attached to a $\overline{p}{\text{He}}^{2+}$ ion excited to an energetically forbidden state. The cross sections and rate coefficients for the present DR are calculated. As the bound motion of $\overline{p}{\text{-He}}^{2+}$ is closer to a circular orbit, the DR reaction, which leads to the destruction of $\overline{p}{\text{He}}^{2+}$, occurs less frequently. For the antiprotonic ion $\overline{p}{\text{He}}^{2+}$, it turns out that the circular states are the most stable against electron impacts.

Transfer, sequential decay, and quasi-free reactions induced by 18-MeV 6He beam on 6Li, 7Li, and 12C

The He-6 + Li-6,Li-7 and He-6 + C-12 scattering and reactions have been studied using an 18-MeV He-6 beam. Experimental results for the elastic scattering on all three targets are in fair agreement with optical model predictions, using the potentials found in the analysis of the Li-6 scattering on the same targets and at close beam energies. Several two-body exit channels show clear signatures of a direct reaction mechanism allowing extraction of spectroscopic information. The measured angular distribution for the He-6 + Li-6 --> alpha + Li-8 reaction indicated close similarity between the alpha + 2n configuration in He-6 and the alpha + d configuration in Li-6. The obtained results for alpha-particle pickup from both Li-6 and Li-7 give large values of a spectroscopic factors for some Be-10 states, indicating their well-developed alpha + He-6 cluster structure. The exotic two-proton pickup reaction (He-6, Be-8) was studied, as well as two-neutron and triton transfer reactions. Quasi-free scattering of He-6 on deuteron and a particle in Li-6 was also observed. The sequential decay reactions He-6 + Li-6 --> He-6 + alpha + d, He-6 + Li-6 --> 2 alpha + t + n, He-6 + Li-7 --> He-6 + alpha + t, and He-6 + C-12 --> Be-10 + 2 alpha were clearly seen, and alpha clustering of some states in Li-6,Li-7, Be8-10, and C-14 was thus studied. Several new spectroscopic results obtained for some Be-10 states support the existence of a molecule-like rotational band in Be-10 with a very large moment of inertia.

An exotic osteoclastic reaction to breast implant that mimicked breast carcinoma

An exotic osteoclastic reaction to breast implant that mimicked breast carcinoma

Nitride Chemistry of the s‐Block Elements

AbstractFor Abstract see ChemInform Abstract in Full Text.

Exotic reaction fronts in the steady state

Simulations of the steady-state reaction-diffusion front formed by opposing currents of species A and B are carried out. For reaction schemes of the form mA + nB → 0, and for symmetrized reaction schemes of the form A + nB → 0/ nA + B → 0, the reaction rate profile is described by a single length scale. The scaling properties, including upper critical dimension and scaling exponents, of this length are in good agreement with theoretical predictions.

The exotic transfer reaction (18O, 17F) on 198Pt: existence and mass of 199Ir

Abstract A Q -value of −8.240 ± 0.041 MeV has been determined for the exotic transfer reaction: 198 Pt( 18 O, 17 F) 199 Ir. This result yields a value of −24.425 ± 0.041 MeV for the mass excess of the previously-unmeasured nucleus, 199 Ir. Excited states in this nucleus are indicated in the region of 160 and 240 keV. The new result for the mass excess, together with existing ones, has been used to investigate systematic trends in the n-p interaction strength across the Z = 82 and N = 126 shell closures.

Spatial temperature oscillations during hydrogen oxidation on a nickel foil

Temperature waves were observed on the surface of a nickel disk on which oxidation was carried out. The temperature front moved at a velocity of about 1 cm/s and had a width of about 1 cm. Complex dynamic local temperatures of overall reaction rate may be due to interaction among temperature waves triggered at different positions rather than an exotic reaction mechanism.

Sum rules for the inclusive μ−e conversion exotic reaction

Microscopic non-energy weighted sum-rules for the total rates of the neutrinoless μ−e conversion process are constructed in the frame of the shell model for closed shell nuclei. For non-closed shell nuclei the relevant rates were obtained by interpolation. Also the contribution of the coherent process to the total μ−e conversion rate is calculated and discussed.

Application of feedback-induced bifurcation for evaluating steady-state and transient heterogeneous catalysis kinetic models

Experimental study of bifurcations to steady-state multiplicity and oscillatory dynamics provides a systematic and sensitive data base for evaluating kinetic models. Previously limited to exotic reaction systems which exhibit such behavior naturally, bifurcations can be induced in tame systems using an external feedback loop to manipulate reaction conditions. This strategy has been applied to ethylene hydrogenation over Pt/Al 2O 3 in a catalytic CSTR by manipulating the ethylene and hydrogen feed rates as functions of the ethylene concentration in the reactor effluent. Pitchfork bifurcations to steady-state multiplicity have been experimentally observed for 0.5% Pt/Al 2O 3 (30 °C, 1 atm) as functions of ethylene feedback gain, given several different hydrogen gains. The data demonstrate the general result that small discrepencies between the actual and the chosen reference steady state give rise to imperfect, cusp-like bifurcations. These phenomena are well described by a kinetic model proposed by Mullins and Saltsburg. Steady-state rate data were used to find two parameter sets for the model; however, only one of these sets adequately approximates the bifurcation data. Examples of Hopf bifurcation to limit cycles are also presented and compared with results for Hopf bifurcation on 0.05% Pt/Al 2O 3. Hopf and step-response transient experiments for the 0.5% Pt/Al 2O 3 catalyst are well described by the model containing only two surface time constants while three or more are required for the low-loaded catalyst. Hydrogen spillover is suggested as the source of this difference.