Reactions of gas phase amino acids with the prevailing radicals in biomass thermal treatments

Amino acids, N-containing compounds, hold a significant importance in various field. Within the biomass energy sector, amino acids constitute a large fraction of the biomass's nitrogen content. As such, it is essential to comprehend their combustion chemistry; most specifically their biomolecular interactions with governing radicals in the pyrolytic and combustion media that prevail during thermal utilization of biomass. Herein, we have employed quantum chemical calculations and reaction rate theory to investigate reactions of a selected set of amino acids with H, CH₃, NH₂, OH, HO₂, and HS radicals. Thermo-kinetic calculations have been performed to determine the rates of hydrogen abstraction by these six radicals across all possible reaction channels for three specific amino acids: alanine, cysteine, and methionine. The investigation of other amino acids like glycine, threonine, and other models have been carried out for α-C positions as the most probable abstractable sites. The study also examines the individual effects of different substituents (COOH, NH₂, HS, and CH₂) and uncovers significant insights. Notably, the presence of the COOH group introduces polar effects that counterintuitively deactivate the thermodynamically favored α-abstraction pathway. Presented thermo-kinetic values are anticipated to complement existing biomass kinetic models and to improve current understanding of chemical events that participate in the complex nitrogen transformation reactions in biomass.     

Kinetics for the hydrogen‐abstraction of CH4 with NO2

The detailed mechanism of the NO₂+CH₄ reaction has been computationally investigated at the M06‐2X/MG3S, B3LYP/6‐311G(2d,d,p), and MP2/6‐311+G(2df,p) levels. The direct dynamics calculations were preformed using canonical transition state theory with tunneling correction and scaled generalized normal‐mode frequencies including anharmonic torsion. The calculated results indicate that the NO₂+CH₄ reaction proceeds by three distinct channels simultaneously, leading to the formation of trans‐HONO (1a), cis‐HONO (1b), and HNO₂ (1c), and each channel involves the formation of intermediate having lower energy than the final product. The anti‐Hammond behavior observed in channel 1a is well analyzed. Proper treatment of anharmonic torsions about the C···H···O (or N) axis in the transition structures greatly improves the accuracy of kinetics predictions. The activation energy for each channel increases substantially with temperature, but is not strictly a linear function of temperature. Therefore, the thermal rate constants are fitted to the four‐parameter expression recommended for this case over the wide temperature range 400–4000 K. © 2012 Wiley Periodicals, Inc.     

Theoretical studies on the hydrogen abstraction reactions of methyl esters with HO2 radical and the following β‐scission reactions

Unsaturated fatty acid methyl esters are ubiquitous in biodiesel fuels. The C = C double bond greatly affects the combustion characteristics of biodiesel, especially its ignition behavior at low temperatures. In this work, we report detailed theoretical study on the mechanism and kinetics of the hydrogen abstraction reactions of linear unsaturated C6 methyl esters with hydroperoxy radical (HO₂), which play a critical role in the low‐temperature combustion of biodiesel. Reaction profiles are obtained via intrinsic reaction coordinate (IRC) analysis including the formation of reactant complexes and product complexes at the entrance and exit channels, respectively. The potential energy surfaces are explored at the CBS‐QB3 level. The following β‐scission reactions of the forming radicals are also investigated at the same level of theory. The high‐pressure limit rate constants for all the reactions in the temperature range from 500 to 2000 K are calculated via conventional transition‐state theory with quantum tunneling effect and fitted to the modified Arrhenius expression.     

Visualization of network structure by the application of hypernodes

In the literature several authors describe methods to construct simplified models of networks. These methods are motivated by the need to gain insight into the main properties of medium sized or large networks. The present paper contributes to this research by setting focus on weighted networks, the geographical component of networks and introducing a class of functions to model how the weights propagate from one level of abstraction to the next. Hierarchies of network models can be constructed from reordering of the adjacency matrix of the network; this is how “hypernodes” are derived in the present paper. The hypernode algorithm is explored and it is shown how it can be formulated to handle weighted networks. Weighted networks enable handling the uncertainty or the strength of the components which make up the network. The hypernode algorithm can be run in an iterative manner so that a hierarchy of simplified models of the network can be derived. Some case studies demonstrate the hypernode algorithm. In the first case the algorithm is compared with a similar implementation described in the literature. In the second case an airline dataset is analysed. This study shows that when networks are embedded in the geographical space hypernodes may relate to clusters in the spatial domain. The selection of the visual variables to illustrate the strength of the edges and nodes in a weighted network is discussed.     

Hydrogen‐Atom Abstraction Reactions by Manganese(V)– and Manganese(IV)–Oxo Porphyrin Complexes in Aqueous Solution

High‐valent manganese(IV or V)–oxo porphyrins are considered as reactive intermediates in the oxidation of organic substrates by manganese porphyrin catalysts. We have generated Mn^V– and Mn^IV–oxo porphyrins in basic aqueous solution and investigated their reactivities in C? H bond activation of hydrocarbons. We now report that Mn^V– and Mn^IV–oxo porphyrins are capable of activating C? H bonds of alkylaromatics, with the reactivity order of Mn^V–oxo>Mn^IV–oxo; the reactivity of a Mn^V–oxo complex is 150 times greater than that of a Mn^IV–oxo complex in the oxidation of xanthene. The C? H bond activation of alkylaromatics by the Mn^V– and Mn^IV–oxo porphyrins is proposed to occur through a hydrogen‐atom abstraction, based on the observations of a good linear correlation between the reaction rates and the C? H bond dissociation energy (BDE) of substrates and high kinetic isotope effect (KIE) values in the oxidation of xanthene and dihydroanthracene (DHA). We have demonstrated that the disproportionation of Mn^IV–oxo porphyrins to Mn^V–oxo and Mn^III porphyrins is not a feasible pathway in basic aqueous solution and that Mn^IV–oxo porphyrins are able to abstract hydrogen atoms from alkylaromatics. The C? H bond activation of alkylaromatics by Mn^V– and Mn^IV–oxo species proceeds through a one‐electron process, in which a Mn^IV–‐oxo porphyrin is formed as a product in the C? H bond activation by a Mn^V–oxo porphyrin, followed by a further reaction of the Mn^IV–oxo porphyrin with substrates that results in the formation of a Mn^III porphyrin complex. This result is in contrast to the oxidation of sulfides by the Mn^V–oxo porphyrin, in which the oxidation of thioanisole by the Mn^V–oxo complex produces the starting Mn^III porphyrin and thioanisole oxide. This result indicates that the oxidation of sulfides by the Mn^V–oxo species occurs by means of a two‐electron oxidation process. In contrast, a Mn^IV–oxo porphyrin complex is not capable of oxidizing sulfides due to a low oxidizing power in basic aqueous solution.     

Finitistic dimension and Igusa–Todorov algebras

The notion of Igusa–Todorov algebras is introduced in connection with the (little) finitistic dimension conjecture, and the conjecture is proved for those algebras. Such algebras contain many known classes of algebras over which the finitistic dimension conjecture holds, e.g., algebras with the representation dimension at most 3, algebras with radical cube zero, monomial algebras and left serial algebras, etc. It is an open question whether all artin algebras are Igusa–Todorov. We provide some methods to construct many new classes of (2-)Igusa–Todorov algebras and thus obtain many algebras such that the finitistic dimension conjecture holds. In particular, we show that the class of 2-Igusa–Todorov algebras is closed under taking endomorphism algebras of projective modules. Hence, if all quasi-hereditary algebras are 2-Igusa–Todorov, then all artin algebras are 2-Igusa–Todorov by [V. Dlab, C.M. Ringel, Every semiprimary ring is the endomorphism ring of a projective module over a quasihereditary ring, Proc. Amer. Math. Soc. 107 (1) (1989) 1–5] and have finite finitistic dimension.     

饱和烃促进渣油热反应初期生焦的考察

研究了石油渣油饱和烃的热裂化夺氢化学对渣油热反应体系生焦的影响,对由饱和烃－供氢探针、饱和烃－沥青质组成的二元模型反应体系,以及由饱和烃－供氢探针－沥青质组成的三元模型反应体系,分别进行高压热反应;然后关联二元反应体系和三元反应体系中饱和烃夺氢能力及供氢探针的供氢量和沥青质生焦率。结果表明饱和烃夺氢能力可促进沥青质生焦;并且饱和烃的热裂化夺氢反应性能与饱和烃的物理沉积性能相比较,前者更能促进沥青质形成凝聚相而生焦。进而测定四种减压渣油的热反应生焦趋势,发现渣油饱和分的夺氢量与渣油热反应被期的生焦趋势密切相关,而较苛刻的条件下的生焦趋势主要是由原料渣油残炭值所决定。     

Understanding halogen‐substituent assistance in H‐atom abstraction‐based reactions of CHCl•− with CH4 − nXn (X = H,F, Cl; n = 0–3)

The effect of halogen‐substituent on hydrogen abstraction mechanisms was studied by applying density functional theory functional calculations to the gas‐phase reactions between CHCl^?? and CH_{4 ? n}X_n (X = H, F, Cl; n = 0–3), and it is found that a heavier X substituent in the substrate results in a greater stabilization of corresponding complex, a lower activation energy, a faster H‐abstraction reaction, and greater exothermicity. However, CH₄– reaction is more reactive than CH₃F– reaction under the same condition because of dominant π‐donation from the electronegative F atom. We also explored the reactivity difference for the seven reactions in terms of factors derived from bond order, second‐order perturbative energy, and activation strain model analysis. The rate constants are evaluated over a wide temperature range of 298–1000 K by the conventional transition state theory. Copyright © 2014 John Wiley & Sons, Ltd.     

Melt grafting of polymethyl methacrylate onto poly(ethylene‐co‐1‐octene) by reactive extrusion: Model compound approach

The grafting of poly(methylmethacrylate) onto poly(ethylene‐co‐1‐octene) by in situ radical polymerization of methyl methacrylate is a process where the side reactions are difficult to characterize. To increase the understanding of both the nature and the extent of such reactions, products resulting from the same chemical system, where polymer is replaced by squalane and/or pentadecane, are analyzed. The influence of the temperature, the nature of peroxides (used as radicals generators) and the monomer concentration are investigated toward the chain length of the grafts. The resulting grafted PMMA and PMMA homopolymer are qualitatively analyzed by MALDI‐TOF spectroscopy and size exclusion chromatography. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5215–5226, 2007