Ab Initio Chemical Kinetics for the Thermal Decomposition of SiH4 + Ion and Related Reverse Ion–Molecule Reactions of Interest to PECVD of a-Si:H Films

Plasma Chemistry and Plasma Processing - The thermal unimolecular decomposition of SiH4 + ion and its related reverse reactions, SiH3 + + H and SiH2 + + H2, have...     

Spatial location of indomethacin associated with unimeric amphiphilic carrier macromolecules as determined by nuclear magnetic resonance spectroscopy

A combination of nuclear magnetic resonance (NMR) techniques including, proton NMR, relaxation analysis, two‐dimensional nuclear Overhauser effect spectroscopy, and diffusion‐ordered spectroscopy, has been used to demonstrate the spatial location of indomethacin within a unimolecular micelle. Understanding the location of drugs within carrier molecules using such NMR techniques can facilitate rational carrier design. In addition, this information provides insight to encapsulation efficiency of different drugs to determine the most efficient system for a particular bioactive. This study demonstrates that drugs loaded by the unimolecular amphiphile under investigation are not necessarily encapsulated but reside or localize to the periphery or interfacial region of the carrier molecule. The results have further implications as to the features of the unimolecular carrier that contribute to drug loading. In addition, evidence of drug retention associated with the unimolecular surfactant is possible in organic media, as well as in an aqueous environment. Such findings have implications for rational carrier design to correlate the carrier features to the drug of interest and indicate the strong retention capabilities of the unimolecular micelle for delivery applications. Copyright © 2016 John Wiley & Sons, Ltd.     

Dynamics of ethyl radical decomposition. II. Applicability of classical mechanics to large-molecule unimolecular reaction dynamics

The classical trajectory method is used to investigate the unimolecular dynamics of ethyl radical dissociation. It is found that chaotic trajectories need not be backward integrable to yield accurate lifetime, and product energy and angular momenta distributions. This allows the use of large numerical integration step sizes in trajectory calculations. The product energy and angular momenta distributions are independent of the ethyl radical lifetime, and are obtained after only 50 dissociation events. Differences between classical and quantal unimolecular dynamics are discussed, and a prognosis for future trajectory studies of large-molecule unimolecular decompositions is given.     

Emission enhancement of conjugated polymers through self-assembly of unimolecular micelles to multi-micelle aggregates

By using a cosolvent self-assembly approach, the emission of multi-micelle aggregates from star copolymer unimolecular micelles is enhanced greatly through restriction of concentration self-quenching and intermolecular aggregation of a conjugated polymer core, due to the existence of a PEG shell of HCP-star-PEG unimolecular micelles.     

Kinetics of Nitroxide Mediated Radical Polymerization of Styrene with Unimolecular Initiators

Summary: This study examined the kinetics of nitroxide-mediated radical polymerization of styrene with unimolecular (alkoxyamine) initiators. Control of polymerization rate and polymer molecular weight in unimolecular nitroxide-mediated radical polymerization was studied by looking at the effects of the three main factors: initiator concentration, temperature, and initiator molecular weight on polymerization rate, molecular weight and polydispersity. In addition, the behavior of the unimolecular initiating systems was compared to that of the corresponding bimolecular system. The effective TEMPO concentration and degree of self-initiation of styrene were proved to be significant in dictating magnitudes of molecular weight averages and widths of molecular weight distribution.     

Comparison of Hyperbranched and Linear Polyglycidol Unimolecular Reverse Micelles as Nanoreactors and Nanocapsules

Summary: Amphiphilic‐hyperbranched polyglycidols and a linear analogue were tested for their ability to act as nanoreactors for the unimolecular elimination (E1) reactions of tert‐alkyl iodides. Their encapsulation properties were also compared. The linear polymer was found to have very good “unimolecular reverse micellar” characteristics as well, even though the results showed the advantages of a hyperbranched nature over a linear one. Our results stress the need for a direct comparison of branched and linear polymers for any application.

Amphiphilic polyglycidol unimolecular reverse micelles.     

“Close loop” mechanistic schemes for hydrocarbon polymer oxidation

Mechanistic schemes of radical oxidation of hydrocarbon polymers in which initiation is only due to unimolecular or bimolecular hydroperoxide decomposition have been studied. The results of their kinetic analysis have been compared with literature data relative to the thermal oxidation of polypropylene in solid state (60-160°C). These data are in remarkably good agreement with the “unimolecular” scheme whose main characteristics are: (1) the quasi-independence of the kinetic behavior with initial conditions (for low initial content of thermolabile structures), and (2) the fact that an arbitrarily defined induction period depends only on the rate constant of unimolecular hydroperoxide decomposition. © 1995 John Wiley & Sons, Inc.     

Enthalpy considerations applied to the relatively slow unimolecular reactions of a series of homologous CnH2n radical cations

The concept that the slow, unimolecular reactions of the homologous series of radical cations are largely determined by the relative energetics of the possible product combinations is discussed. The concept is shown to provide a reasonably consistent rationalization of the known metastable dissociations of and correctly predicts the reactions undergone by . The concept may be useful in discussing the unimolecular chemistry of isomers.     

Energy transfer in unimolecular reactions at high temperatures

The application of modern theories of energy transfer to unimolecular reactions taking place at very high temperatures is discussed. It is shown that the efficiency of energy transfer for both reactant–reactant and reactant–inert diluent collisions may be substantially smaller than the values determined experimentally at lower temperatures. Consequently at high temperatures unimolecular falloff effects, particularly in some shock-tube measurements, may be greater than has been believed hitherto. The application of these calculations to the unimolecular reactions of cyclopropane, cyclobutane, and cyclohexene at temperatures around 1300°K is discussed, and it is shown that under shock-tube conditions the apparent first-order rate coefficient may be at least ten times less than the high-pressure limiting value.     

THE QUEST FOR UNIMOLECULAR RECTIFICATION FROM OXFORD TO WALTHAM TO EXETER TO TUSCALOOSA

A unimolecular electronic device should perform active electronic functions by exploiting the energy levels, or conformations, of a singlemolecule, or a very few molecules, and should be addressable electrically by macroscopic electrodes. We found unimolecular rectification in a molecule, γ-hexadecylquinolinium tricyanoquinomethanide, 4, in which the ground state is Zwitterionic: D⁺-π-A^?, while the first excited state is undissociated: D⁰-π-A⁰. This 2.3 nm long unimolecular device, measured three years ago between Al electrodes and now between Au electrodes, confirms a 1974 proposal by Aviram and Ratner.     

Temperature- and pH-responsive unimolecular micelles with a hydrophobic hyperbranched core

The dendritic unimolecular polymeric micelles with a hydrophobic dendritic polyester (Boltorn H40) as the core and the grafted biocompatible poly(N, N-diethylacrylamide)-b-poly(2-(dimethylamino)ethyl methacrylate) (PDEAAM-b-PDMAEMA) as the shell were synthesized by successive reversible addition–fragmentation transfer (RAFT) polymerization of N, N-diethylacrylamide (DEAAM) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) monomers. Laser light scattering studies indicated that the resulting unimolecular polymeric micelles H40–PDEAAM–PDMAEMA with double stimuli-responsive shells exhibited a reversible two-stage phase transition behavior. The effect of varying the block length of PDMAEMA on the thermosensitivity of unimolecular polymeric micelles was studied. With an increase in the outer corona length of PDMAEMA, the temperature range of phase transition for the inner shell PDEAAM would become broad. As pH decreased to 2, the high hydrophilic PDMAEMA blocks with high protonation were independent of temperature, and the size of unimolecular polymeric micelles increased due to the extended-chain conformation of outer layer. The internal core cavities of the unimolecular polymeric micelles exhibited a great potential of loading guest molecules according to the analysis of pyrene probe fluorescence spectra.     

Metastable transitions in n-butane and n-butane-d7

Metastable ions have been investigated for n-butane d₇ molecular ions using a tandem mass spectrometer which samples unimolecular decay processes occuring during the time interval of c.2 μs to 4 ms after ion formation. Some 37% of ions formed by 70 eV electron impact decay on this time scale. The competing unimolecular processes observed, in order of relative importance, are methance, methyl radical and hydrogen atom elimination. The slow metastables sample the threshold energy regime of unimolecular reactions responsible for forming the ordinary mass spectrum of butance and very large isotope effect are noted for the deuterated molecule.     

CF2HCI在金属钨表面上的反应动力学

The unimolecular reaction of CF_2HCl on W filament has been studied. This reaction shows zero order at rather high pressure. The temperature threshold is about 440 ℃. The apparent activation energy of this reaction is 119.7 kJ mol~(-1) which is about a half of the activation energy for homogeneous unimolecular reaction of CF_2HCl, 233.5 kJ mol~(-1).     

脲和盐酸胍诱导的牛碳酸酐酶B的去折叠

采用非变性聚丙烯酰胺凝胶电泳、十二烷基硫酸钠-聚丙烯酰胺凝胶电泳、高效凝胶排阻色谱和激光光散射光谱研究了脲和盐酸胍诱导的牛碳酸酐酶B的去折叠.实验结果表明,在脲和盐酸胍诱导的牛碳酸酐酶B的去折叠过程中,溶液中只含有单分子牛碳酸酐酶B和二分子牛碳酸酐酶B集聚体;二分子牛碳酸酐酶B集聚体是通过单分子牛碳酸酐酶B之间的疏水和...     

单分子微正则系综反应速率常数的理论研究──曲率校准和转动选态速率常数的计算

研究了微正则系综下单分子反应速率常数的理论计算公式,并将曲率因子Ａ引入含振动和转动的隧道几率表达式中,进而得到了反应速率常数表达式。应用该式研究了Ｆ─Ｃ≡Ｃ─Ｈ反应的氢迁移过程的转动选态及曲率因子对反应速率常数的影响。结果表明：在隧道效应区域内,曲率因子对速率常数的影响比较显著,它将引起速率常数的增加;转动选态对速率的影响不太明显。     

Synthesis and Characterization of a Unimolecular Capsule

There is more than one way to assemble the two halves of a tethered, urea-substituted calix[4]arene dimer (shown schematically): formation of unimolecular capsules (far left), dimers, or oligomers. By combination of NMR spectroscopy and electrospray mass spectrometry, a hexamethylene spacer was shown to be exactly right to permit the preferential formation of a unimolecular capsule under inclusion of solvent or other guest molecules.     

Controlled syntheses of polythiophene nanoparticles with plain and hollow nanostructures templated from unimolecular micelles

Polythiophene nanoparticles (PTNs), as one of the typical conjugated polymer nanoparticles (CPNs) with novel optical and electronic properties have won extensive attentions, especially their applications in electronics and bioimaging. However, PTNs obtained with traditional methods are usually nonuniform or unstable. Herein, we developed a novel method to prepare uniform and stable PTNs templated from star‐like unimolecular micelles. Cyclodextrin‐cored unimolecular micelles with tailored components were prepared through atom transfer radical polymerization, and PTNs with plain or hollow nanostructures can be obtained via crosslinking the suspended thiophene units in designed domain of unimolecular micelles. The unimolecular micelles and PTNs were characterized via nuclear magnetic resonance, Fourier transform infrared, transmission electron microscopy, atomic force microscopy, dynamic light scattering, ultraviolet–visible, and photoluminescence, indicating that the PTNs exhibit uniform size, controllable surface chemistry, and well‐defined nanostructures. The obtained PTNs have potential applications in optics, electronics, and bioimaging. Also, this provides a new way to synthesize CPNs with tailored sizes, nanostructures, and surface chemistry. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1550–1555     

VLPP unimolecular rate theory

The exact theory is derived for the thermal unimolecular decomposition of gas-phase molecules activated and deactivated exclusively through heterogeneous collisions with the walls of a spherical vessel. This theory is appropriate for the treatment of very-low-pressure pyrolysis (VLPP) experiments and other experiments carried out at very low pressures. It is shown, however, that the exact theory is closely approximated by ordinary gas-phase unimolecular rate theory and that for practical application to experiments the results of both theories are indistinguishable.     

Doubly hydrophilic multiarm hyperbranched polymers with acylhydrazone linkages as acid-sensitive drug carriers

A novel type of drug carrier capable of controlled drug release is proposed. It consists of an acid-sensitive doubly hydrophilic multiarm hyperbranched copolymer with a hyperbranched polyamidoamine core and many linear poly(ethylene glycol) arms. Using pH-sensitive acylhydrazone linkages, the polymer forms unimolecular micelles that can encapsulate hydrophobic drugs. Due to their amphiphilicity, the drug-loaded unimolecular micelles can self-assemble into multimolecular micelles that show acid-triggered intracellular delivery of the hydrophobic drugs.     

Atomistic-scale simulations of the initial chemical events in the thermal initiation of triacetonetriperoxide

To study the initial chemical events related to the detonation of triacetonetriperoxide (TATP), we have performed a series of molecular dynamics (MD) simulations. In these simulations we used the ReaxFF reactive force field, which we have extended to reproduce the quantum mechanics (QM)-derived relative energies of the reactants, products, intermediates, and transition states related to the TATP unimolecular decomposition. We find excellent agreement between the QM-predicted reaction products and those observed from 100 independent ReaxFF unimolecular MD cookoff simulations. Furthermore, the primary reaction products and average initiation temperature observed in these 100 independent unimolecular cookoff simulations match closely with those observed from a TATP condensed-phase cookoff simulation, indicating that unimolecular decomposition dominates the thermal initiation of the TATP condensed phase. Our simulations demonstrate that thermal initiation of condensed-phase TATP is entropy-driven (rather than enthalpy-driven), since the initial reaction (which mainly leads to the formation of acetone, O(2), and several unstable C(3)H(6)O(2) isomers) is almost energy-neutral. The O(2) generated in the initiation steps is subsequently utilized in exothermic secondary reactions, leading finally to formation of water and a wide range of small hydrocarbons, acids, aldehydes, ketones, ethers, and alcohols.