Structure-dependence in Initial Decomposition of trans-1,2-Dimethylcyclohexyl Isomers: Kinetic Exploration and Conformational Analysis

Cyclohexyl radicals are crucial primary intermediates in combustion of fossil and alternative fuels. They would present the inherent conformation feature, i.e. diverse conformers retained in inversion-topomerization pathways, jointly controlled by the varying radical site and specific spatial positions of alkyl side chains on “easy-distortion” cyclic ring. These conformers for one radical have different energies and thermodynamics, and are highly expected to influence their subsequent decomposition reactions in terms of energetics and kinetics. To reveal such impact, all conformational structures and their interconversion mechanisms for trans-1,2-dimethylcyclohexyl isomers were explored by employing quantum chemical calculations coupled with transition state theory. Originated from distinct conformers, all accessible transition states were explicitly identified in different reaction paths for each type of intramolecular H-transfer or β-scission, and then were carefully used in computing rate coefficients. The kinetic predictions demonstrate that the fairly speedy equilibrium among conformers would be established for one isomer via conformation before they proceed the initial decomposition over 300-2500 K. This allows thoroughly evaluating the contribution of various conformers to the kinetics for multiple paths in one reaction regarding to their thermodynamic properties. Moreover, conformational analysis elucidates that H-transfers exhibit strong structure dependence. Note that the most favorable 1,5 H-transfer is only feasible for one twist-boat with radical site in axial side chain accompanied by one isoclinal methyl group. The results for β-scissions are affected by steric energies and substituent effects remained in conformational structures. These findings facilitate to finally suggest the proper kinetic parameters for each decomposition reaction with the aim of their potential implication in kinetic modelling.

Jihad Digital: Pembingkaian Narasi Kontra Radikalisasi NU Online di Dunia Maya

The development of digitalization has shifted the institutionalization values patterns from conventional to cyberspace, it is containing radical values through the website which also developed along with the development of digitalization. Radicalization in cyberspace requires the counter-sites which committed to religious moderation. NU Online is one of this counter-site. This study uses qualitative methods with data analysis framing techniques. NU Online distinguishes the radicalization and intolerance narratives in cyberspace is a source of the uproar of the national ideology and disharmony in the interfaith relations. In its prognosis strategy, NU Online develops the narratives such as Islam is very compatible with Pancasila. While in its motivational strategy, NU Online invites all elements of the nation to maintain the integration of the nation by publishing the headline such as “four reasons for rejecting the <em>Khilafah</em>”. This counter-radicalization framing is different from that carried out by panjimas.com as a representation of the radical site

Structure-activity relationships for unimolecular reactions of peroxy radicals, RO2, at atmospheric temperatures

&lt;p&gt;The oxidation of most organic matter emitted to the atmosphere proceeds by radical reaction steps, where peroxy radicals, ROO&lt;sup&gt;&amp;#8226;&lt;/sup&gt;, are critical intermediates formed by addition of O&lt;sub&gt;2&lt;/sub&gt; molecules to carbon-based radicals. The chemistry of these RO&lt;sub&gt;2&lt;/sub&gt; radicals in high-NOx conditions is well-known, forming alkoxy radicals and NO&lt;sub&gt;2&lt;/sub&gt;. In low-NOx and pristine conditions, the RO&lt;sub&gt;2&lt;/sub&gt; radicals react with HO&lt;sub&gt;2&lt;/sub&gt; and other R'O&lt;sub&gt;2&lt;/sub&gt; radicals, but can have a sufficiently long lifetime to also undergo unimolecular reactions. Hydrogen atom migration, forming a hydroperoxide (-OOH) and a new peroxy radical site after addition of an additional O&lt;sub&gt;2&lt;/sub&gt; on the newly formed radical site, has been studied extensively in some compounds, such as isoprene where it was shown to be the a critical step in OH radical regeneration. RO&lt;sub&gt;2&lt;/sub&gt; ring closure reactions have likewise been studied, where for &amp;#946;-pinene it has been shown to be a critical step governing the yield of the decomposition products such as acetone and nopinone.&lt;/p&gt;&lt;p&gt;Despite the interest in RO&lt;sub&gt;2&lt;/sub&gt; unimolecular reactions, and the potential impact on atmospheric chemistry, no widely applicable structure-activity relationships (SARs) have been proposed to allow systematic incorporation of such unimolecular reactions in gas phase atmospheric kinetic models. In this work, we present a series of systematic theoretical predictions on the site-specific rate coefficients for such reactions for a wide range of molecular substitutions. Combined with extensive literature data this allows for the formulation of a SAR for RO&lt;sub&gt;2&lt;/sub&gt; unimolecular reactions, covering aliphatic, branched, and unsaturated RO&lt;sub&gt;2&lt;/sub&gt; with oxo, hydroxy, hydroperoxy, nitrate, carboxylic acid, and ether substitutions.&lt;/p&gt;&lt;p&gt;The predictions are compared to experimental and theoretical data, including multi-functionalized species. Though some molecular classes are well represented in the training set (e.g. aliphatic RO&lt;sub&gt;2&lt;/sub&gt;), other classes have little data available and additional work is needed to enhance and validate the reliability of the SAR. Direct experimental data is scarce for all RO&lt;sub&gt;2&lt;/sub&gt; classes. The fastest H-migrations are found to be for unsaturated RO&lt;sub&gt;2&lt;/sub&gt;, with the double bond outside the H-migration TS ring. Ring closure of unsaturated RO&lt;sub&gt;2&lt;/sub&gt; are likewise fast if the product radical carbon is exocyclic to the newly formed peroxide ring.&lt;/p&gt;

Exploration of doubtful cases of leucine and isoleucine discrimination in mass spectrometric peptide sequencing by electron-transfer and higher-energy collision dissociation-based method

Electron-transfer dissociation (ETD) and electron-transfer and higher-energy collision dissociation (EThcD) spectra of short tryptic peptides with leucine/isoleucine residues in neighboring positions demonstrate intensive w-ions. On the contrary, u-ions possess very low intensities (if present at all). Therefore radical site migration is negligible in the applied conditions while ETD (EThcD) spectra allow for the reliable discrimination of the isomeric residues in the sequencing process. The presence of a fragment ion 43.055 mass units lower than z2-ion of peptides with IK sequence at their C-termini was shown to be a result of alternative fragmentation starting from the loss of propylammonium ion from the doubly protonated peptide molecule and formation of an oxazole fragment ion.

Flavonoids as reductants of ferryl hemoglobin.

The ferryl derivatives of hemoglobin are products of the reactions of oxy- and methemoglobin with hydrogen peroxide. Ferryl hemoglobins, either with or without a radical site on the protein moiety, are oxidizing species. Plant polyphenols, flavonoids, have been shown to act as antioxidants in vivo and in vitro. Reactions of met- and oxyhemoglobin with hydrogen peroxide in the presence of catechin, quercetin and rutin were studied. These flavonoids accelerated reduction of ferryl hemoglobin to methemoglobin. The rate constants of the reactions of ferryl hemoglobin with catechin, quercetin and rutin were in the order of 10(2) M(-1) s(-1), i.e. similar to the rate constants of ferryl hemoglobin with intracellular reducing compounds like urate or ascorbate. The beneficial effect of flavonoids against oxidative damage of hemoglobin caused by hydroperoxides, reported in the literature, is probably, at least in part, connected with the ability of flavonoids to scavenge ferryl hemoglobin.

Cu(II)-Catalyzed Reactions in Ternary [Cu(AA)(AA – H)]+ Complexes (AA = Gly, Ala, Val, Leu, Ile, t-Leu, Phe)

The unimolecular chemistry of [Cu(II)AA(AA – H)]+ complexes, composed of an intact and a deprotonated amino acid (AA) ligand, have been probed in the gas phase by tandem and multistage mass spectrometry in an electrospray ionization quadrupole ion trap mass spectrometer. The amino acids examined include Gly, Ala, Val, Leu, Ile, t-Leu and Phe. Upon collisionally-activated dissociation (CAD), the [Cu(II)AA(AA – H)]+ complexes undergo decarboxylation with simultaneous reduction of Cu(II) to Cu(I); during this process, a radical site is created at the α-carbon of the decarboxylated ligand (H2N1 – •CαH – CβH2 – R; R = side chain substituent). The radical site is able to move along the backbone of the decarboxylated amino acid to form two new radicals (HN1• – CαH2 – CβH2–R and H2N1 – CαH2 – •CβH – R). From the complexes of Gly and t-Leu, only Cα and N1 radicals can be formed. The whole radical ligand can be lost to form [Cu(I)AA]+ from these three isomeric radicals. Alternatively, further radical induced dissociations can take place along the backbone of the decarboxylated amino acid ligand to yield [Cu(II)AA(AA – 2H – CO2)]+, [Cu(I)AA(•NH2)]+, [Cu(I)AA(HN = CαH2)]+, or [Cu(I)AA(H2N – CαH = CβH – R′]+ (R′ = partial side chain substituent). The sodiated copper complexes, [Cu(II)(AA – H + Na)(AA – H)]+, show the same fragmentation patterns as their non-sodiated counterparts; sodium ion is retained on the intact amino acid ligand and is not involved in the CAD pathways. The amino groups of both AA units, the carbonyl group of the intact amino acid, and the deprotonated hydroxyl oxygen coordinate Cu(II) in square-planar fashion. Ab initio calculations indicate that the metal ion facilitates hydrogen atom shuttling between the N1, Cα and Cβ atoms of the decarboxylated amino acid ligand. The dissociations of the decarboxylated radical ions unveil important insight about the so far largely unknown intrinsic chemistry of α-amino acid and peptide radicals, which are implicated as intermediates in numerous pathogenic biological processes.